Risk Assessment of Underbalanced and Managed Pressure Drilling Operations Mari Oma Engevik May 31, 2007 1
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Risk Assessment of Underbalanced and Managed PressureDrilling Operations
Mari Oma Engevik
May 31, 2007
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Date 2007-01-04
Our reference MAR/LMS
Faculty of Engineering Science and Technology Department of Production and Quality Engineering
MASTER THESIS Spring 2007
for stud. techn. Mari Oma Engevik
RISK ASSESSMENT OF UNDERBALANCED AND MANAGED PRESSURE DRILLING OPERATIONS (Risikovurdering av underbalansert boring og boring med styrt trykk (”managed pressure drilling”)) In recent years, underbalanced drilling (UBD) and managed pressure drilling (MPD) have been developed as alternatives to the traditional overbalanced drilling technique. The new techniques have several advantages, but the blowout risk is yet not fully understood. The main objective of the current master thesis is to develop a blowout risk model for UBD and MPD that is compatible with the blowout frequency assessment model (BlowFAM) that has been developed by Scandpower. As part of this thesis, the candidate shall:
1. Give a detailed presentation of the technology and procedures that are used for UBD and MPD. The presentation shall be based on a detailed literature survey and contacts with drilling operators and their consultants.
2. Identify, describe and document hazardous events during the various steps of a UBD and an
MPD operation. The hazard identification shall be carried out by using analytical tools and supplemented by interviews with relevant personnel and analyses of available field performance data.
3. Extract descriptions of relevant well control incidents from available data and identify and
describe root causes and causal distributions.
4. Establish formulas for relations between the causes in para. 3 and formation characteristics.
5. Establish a generic blowout frequency model that is compatible with BlowFAM. Following agreement with the supervisor, the various items may be given different weights.
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Master Thesis Spring 2007 for
stud. techn. Mari Oma Engevik
Date 2007-01-04
Our reference MAR/LMS
Within three weeks after the date of the task handout, a pre-study report shall be prepared. The report shall cover the following:
• An analysis of the work task's content with specific emphasis of the areas where new knowledge has to be gained.
• A description of the work packages that shall be performed. This description shall lead to a
clear definition of the scope and extent of the total task to be performed.
• A time schedule for the project. The plan shall comprise a Gantt diagram with specification of the individual work packages, their scheduled start and end dates and a specification of project milestones.
The pre-study report is a part of the total task reporting. It shall be included in the final report. Progress reports made during the project period shall also be included in the final report. The report should be edited as a research report with a summary, table of contents, conclusion, list of reference, list of literature etc. The text should be clear and concise, and include the necessary references to figures, tables, and diagrams. It is also important that exact references are given to any external source used in the text. Equipment and software developed during the project is a part of the fulfilment of the task. Unless outside parties have exclusive property rights or the equipment is physically non-moveable, it should be handed in along with the final report. Suitable documentation for the correct use of such material is also required as part of the final report. The student must cover travel expenses, telecommunication, and copying unless otherwise agreed. If the candidate encounters unforeseen difficulties in the work, and if these difficulties warrant a reformulation of the task, these problems should immediately be addressed to the Department. Two bound copies of the final report and one electronic version are required.
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Master Thesis Spring 2007 for
stud. techn. Mari Oma Engevik
Date 2007-01-04
Our reference MAR/LMS
Responsible professor/supervisor at NTNU Professor Marvin Rausand Telephone: 73 59 25 42 E-mail: [email protected] Local supervisor at Scandpower Risk Aexander Solberg, senior consultant Management AS offices will be Scandpower Risk Management AS
P.O.Box 3 NO 2027 Kjeller Telephone: 64 84 45 43 E-mail: [email protected]
DEPARTMENT OF PRODUCTION AND QUALITY ENGINEERING
Asbjørn Rolstadås Professor/Head of Department
Marvin Rausand
Responsible Professor
Preface
This master thesis was has been written during the spring semester 2007, at the Norwegian Uni-versity of Science and Technology, NTNU.
The main objective of the master project was to developed a generic blowout frequency modelfor underbalanced and managed pressure drilling operations. The work was performed in co-operation with Scandpower, and the model developed was supposed to be compatible with theirblowout frequency assessment model for conventional overbalanced drilling operations. Accord-ing to the consulted companies, only two blowouts during MPD operations have occurred. Be-cause of lack of data, it was not possible to develop a blowout frequency model. The focus of thethesis was therefore shifted toward a description of underbalanced and managed pressure drillingtechnology, and various risk assessment methods and their use during these operations.
It is assumed that the readers of this report have basic knowledge in drilling technology.I would like to thank my supervisors Professor Marvin Rausand at NTNU and Senior Consul-
tant Alexander Solberg at Scandpower for their assistance during the preparation of this report. Iwould also like to thank Michael Golan, Dave Samuelson, Per Holand, Arild Rødland, Alf Breivik,Harald Tveit, Johan Eck-Olsen for their contributions to this thesis.
Mari Oma EngevikTrondheim June 8, 2007
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Management summary
25% to 33% of all remaining undeveloped oil and gas reasources can not be utilized by means ofconventional overbalanced drilling. In addition, there are wells still containing oil and gas whichcould have produced more if alternative technologies to overbalanced drilling technology whereutilized.Since 1990 underbalanced and managed pressure drilling has become increasingly usedalternative technologies to conventional overbalanced drilling technology. With proper use thesetechnologies may; eliminate or minimize formation damage, minimize costs related to the well,and increase safety during the drilling operations. However, the risk during these operations areyet not known.
During overbalanced drilling operations fluid from the reservoir is prevented from flowing intothe well by a static mud pressure. This pressure is a result of the mud which is used during adrilling operation to carry cuttings from the formation to the surface. The pressure at surface isat atmospheric pressure. In underbalanced and managed pressure drilling, a lighter drill fluidcan be used because a surface pressure is imposed. The main difference between overbalanceddrilling and the alternative drilling technologies, is the use of a surface pressure during the drillingoperation.
Numerous accidents have been documented with use of overbalanced drilling technology. Byevaluating earlier accidents and their cause, the risk these operations exposed to human, environ-ment and assets, are fairly well known. In order to learn more about the risk during underbalancedand managed pressure drilling operations, earlier incidents should be collected and analyzed in aproper way.
To collect data of well incidents during underbalanced and managed pressure drilling opera-tions, authorities and companies in th U.S., Canada, and Norway were contacted. Only two in-cidents have occurred, both with use of managed pressure drilling technology. No reports werefound on the well incidents.
A hazard analysis was performed on a managed pressure drilling operation. This operation isat the moment performed on Kvitebjørn. Kvitebjørn is a field operated by Staoil, located in theNorth-Sea. The purpose was to identify hazards, and evaluate the most risk contributing factorsduring the operation. The analysis was made on a procedure the personnel follows during theconnections of pipes operation. Connections of pipes are made in order to drill to further depths.With new technology it is important to train personnel involved in the operation, and make surethat the level of competence is high. During the operation, external managed pressure drillingpersonnel will be involved. The communication will be in English. The internal personnel usuallycommunicates in Norwegian. Extra focus on the communication is needed. In addition, it is im-portant that the personnel, the internal as well as the external, have clear responsibilities and thatthe procedures they follow are sufficient.
In order to state causes leading to incidents, and prevent future accidents from occurring dur-ing drilling operations, a numerous of accident investigation methods has been developed. Fourdifferent methods were evaluated on behalf of their; scope, user friendliness, and resource need.
One of the methods were utilized on an accident to evaluate the course of events, and to de-velop a set of precautions to prevent similar accident form occurring. The accident occurred ona well drilled overbalanced. During the drilling operation, the pressure of the mud column be-came lower than the pressure from an unexpected gas containing pocket in the formation, andunwanted gas flowed into the well. The crew managed to regain and maintain control over thewell the following days. The accident may have been prevented if; better equipment were utilizedto detect gas pockets in the formation, analysis of the formation had been better, or if alternative
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drilling technologies were utilized.In overbalanced drilling operations, the probability of having an uncontrolled release of for-
mation fluid is known. This is not the case for underbalanced and managed pressure drilling oper-ations. By gathering information of the fluids flow rate through critical equipment during under-balanced and managed pressure drilling operations, the probability of release of formation fluidscan be calculated. An uncontrolled release of formation fluids may occur if more than one of thewell safety equipment should fail to function properly. The probability of uncontrolled release offormation fluid, can be calculated by combining the critical equipments probability.
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Part 1 Introduction
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Introduction
During the last 17 years underbalanced drilling, UBD, and managed pressure drilling, MPD, havebecome increasingly used alternatives to conventional overbalanced drilling, OBD, technology.The new techniques provide several advantages, but the blowout risk during these operations isyet not fully understood.
Since the rotary drilling technology was introduced early in the last century, it has been themost used drilling technology in the oil and gas industry [2, 5]. The technique is well-established,and a number of well incidents have been documented. This has made the risk picture during OBDoperations fairly well known. As for UBD and MPD operations the well incident data is limited, andthe risk picture is not complete.
Scandpower has developed a blowout frequency assessment model, BlowFAM. The model is adata tool for qualitative and quantitative safety evaluation of blowouts during OBD and well oper-ations. BlowFAM reflects the actual elements; the technical, the operational and the organisationalas well as reservoir conditions, that play an important role for the blowout risk. The program doesnot include UBD and MPD operations, and it is of interest to implement these techniques into theprogram.
Few well incidents have occurred during UBD and MPD operations. Hazard analysis and riskevaluations of well projects that utilize these technologies have been performed, but there has notbeen developed any worldwide accident investigation to state causal distributions and blowoutstatistics. Because there has been an increasingly use of UBD and MPD technology world wide, itis important to understand the risk during these operations.
On the Norwegian continental shelf one UBD operation , and five MPD operations have beenperformed. In 2004, Statoil successfully performed an UBD operation on Gullfaks well C-05. OneMPD operation was made by British Petroleum (BP) in the late 90’s by use of coiled tubing. Cono-coPhillips used MPD on Tommeliten, and Statoil has performed 3 operations on Gullfaks and isat the moment using the technology on Kvitebjørn. All of the wells were drilled successfully. Inaddition, Statoil is planning to use MPD on Kristin [4].
In order to collect well incident data during UBD and MPD operations, different people werecontacted, working for; Minerals Management Service (MMS), Canadian Association of OilwellDrilling Contractors (CAODC), British Columbia Oil and Gas Commission (OGC), WeatherfordCanada, ENFORM – the petroleum industry’s commitment to training and safety, Alberta energy &utilities board (EUB), and Exprosoft.
Two well incidents with use of MPD were revealed in Alberta.The objectives of this paper is to; learn and describe technology and procedures used for UBD
and MPD operations, identify and describe hazardous events during various steps of UBD andMPD operations, perform accident investigations of relevant well control incidents, and estab-lish formulas between incident causes and formation characteristics. The lack of data limited thepossibility to develop a causal distribution and relations between causes and formation character-istics. In addition, no detailed UBD or MPD well incident was found. The accident investigationperformed is on a well incident during an OBD operation.
Deviations from the master thesis main objectives, has been settled in co-operation with su-pervisor, Marvin Rausand.
This report consists of four parts; 1) Introduction to the master thesis, 2) An article on riskassessment of UBD and MPD operations, 3) Description of the data gathering, and a quantita-tive approach of blowout frequencies during UBD and MPD operations, and 4) Conclusion andrecommendations for further work. The preparatory report and progress report can be found in
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appendix..... The main objectives of the article in part two, are to a) give a technical descriptionof UBD and MPD operations, b) identify hazardous events during a MPD operation, and c) per-form an accident investigation with use of Haddon’s matrix and the 10 strategies on an OBD wellincident.
A literature study has been carried out covered by relevant books, articles, Internet cites and byattending a MPD course held by Statoil. Data collection has mainly been gathered by contactingrelevant companies, authorities and persons. In addition to this, searches on the Intrenet has beenmade.
The master thesis has been performed over a period of 20 weeks. The main limitations duringthis thesis has been; the availability of relevant data, and finding relevant literature.
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Part 2 Hazard identification and SAFOP analysis of a MPD connection
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Risk Assessment of Underbalanced and Managed PressureDrilling Operations
Mari Oma Engevik
May 31, 2007
1 Abstract
Since 1990 underbalanced and managed pressure drilling have become increasingly used alternativesto conventional overbalanced drilling. The new techniques provide several advantages, but the blowoutrisk during these operations is yet not fully understood. The main objective of this article is to evaluatethe risk during underbalanced and managed pressure drilling operations.
With use of a continuous circulation system during a managed pressure drilling connection, the safeoperability analysis revealed the blind ram as the most critical component. The continuous circulationsystem is a fairly new, and the operation requires special personnel. Communication, clear respon-sibilities, and good procedures are of great importance in order to prevent unwanted situations or tomitigate the consequences.
Haddon’s matrix in combination with Haddon’s ten strategies, gives a detailed accident descriptionand provides risk reducing measures to prevent future accidents. The method covers all socio-technicalaspects, and does not require hands-on experience. In formations containing potential gas pockets;detailed pre-hazard analysis of the geotechnical properties of the specific area should be performed,equipment capable of detecting the gas pockets as early as possible should be utilized, and alternativedrilling technologies should be considered.
2 Introduction
According to studies made by the American Petroleum Institute (API) and the Minerals ManagementService (MMS), 25% to 33% of all remaining undeveloped reservoirs are not drillable using conventionaloverbalanced drilling, OBD, methods. This is due to increased likelihood of well control problems suchas differential sticking, lost circulation, kicks, and blowouts [3]. In addition, many depleted wells whichstill contain petroleum reserves could be utilized with alternative technologies to OBD.
The challenge to the industry is to seek an efficient method to drill and develop these reservoirs in amanner that is no less safe than the overbalanced drilling method.
With the right use, UBD and MPD may [14];
• eliminate or minimize formation damage
• minimize well costs by;
- increasing the rate of penetration
- extending the bit life
- drilling in formations with small drilling windows
- avoiding fluid loss
- minimizing differential sticking
- reducing the drill time
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• increase safety during drilling operations
The Underbalanced Drilling Sub-Committee [9] did in 1994 define UBD; "When the hydrostatichead of a drilling fluid is intentionally designed to be lower than the pressure of the formation beingdrilled, the operation will be considered underbalanced drilling. The hydrostatic head of the drillingfluid may be naturally less than the formation pressure or it can be induced. The induced state may becreated by adding natural gas, nitrogen, or air to the liquid phase of the drilling fluid. Whether inducedor natural, this may result in an influx of formation fluids which must be circulated from the well andcontrolled at surface." [13]
The International Association of Drilling Contractors, IADC, subcommittee define managed pres-sure drilling, MPD, as; "An adaptive drilling process used to precisely control the annular pressure pro-file throughout the wellbore. The objectives are to ascertain the downhole pressure environment limitsand to manage the annular hydraulic pressure profile accordingly" [27, 22].
UBD and MPD are used globally to drill new wells and to deepen or side-track from existing wellbores [44]. UBD is as much a completion technology as it is a drilling technology [13].
During UBD and MPD the bottom hole pressure is lower than during OBD. In conventional OBD,well control is performed by controlling the density of the drill-fluid. Because of the significant dif-ference in friction and static pressure during OBD operations, friction pressure does not specificallyinfluence the bottom hole pressure. The pressure at the top of the mud columns is at atmospheric pres-sure and does not contribute to regulate the bottom hole pressure. As opposed to conventional rotarydrilling, UBD and MPD utilize surface pressure during the operations. The bottom hole pressure is con-trolled by a back-pressure choke which allows the use of lighter drill fluids. In UBD and MPD there arethree ways to control the bottom hole pressure. It is done by controlling; the top pressure, the frictionpressure (when fluid is circulated), and the static mud weight pressure.
UBD and MPD utilize relatively light fluids with low static pressure and the circulated flow frictionwill have a greater impact during these operations.
The two main differences between UBD and MPD operations are the bottomhole pressure and theinflux of formation fluid. In UBD operations, the bottomhole pressure is below the reservoir pore pres-sure as in contrast to MPD operations where the bottom hole pressure is slightly above or equal to thereservoir pore pressure. Because the bottom hole pressure during UBD operations are lower than thepore pressure, influx of formation fluid is induced into the wellbore. In MPD operations influx of for-mation fluid is an unwanted situation.
It is important to understand the risk during operations and be aware of potential dangers in or-der to prevent unwanted events from occurring and mitigate potential consequences. UBD and MPDtechnologies are utilized on a world wide basis. This makes it important to understand the risk theseoperations contribute to human, environment, and assets.
Safe operability, SAFOP, analysis evaluates procedures and operational sequences in order to iden-tify hazards and causes of existing or planned operations. The method has its origin in the hazard andoperability, HAZOP, analysis developed in 1963. SAFOP is suitable for detailed assessment and pre-liminary assessment. During examination of the operation, the operation procedures are divided intovarious steps. Relevant guide-words are further applied to the steps in order to reveal deviations fromthe design intent. The result of the analysis is usually a list of preventive actions in order to improveoperations and procedures.
By analyzing accidents that have occurred during UBD and MPD operations, the risk during theseoperations can be better understood and precautions can be taken.
The main objective of this article is to evaluate the risk during UBD and MPD operations. This isaccomplished by collecting possible accident data during UBD and MPD operations, identify hazardsrelated to a MPD operation, and by performing an accident investigation based on an accident investi-gation report of a well incident.
The hazard analysis is made on a connection with use of MPD. The method used is a SAFOP analysis.The system consists of a continuous circulation system, CCS. The main focus of the analysis has beenon the pressure chamber utilized during the operation.
To collect information of accidents related to UBD and MPD operations, authorities in the U.S.,Norway, and Canada were contacted. Two accidents has been revealed related to MPD operations, but
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no reports of the accidents were found. The accident investigation is performed on a well drilled withuse of OBD technology.
This paper consists of three different parts. The first gives a technical description of UBD and MPDoperations. In the second part a SAFOP is performed on a MPD connection operation, performed withuse of CCS. The last part concerns accident investigation methods of UBD and MPD operations. Anaccident investigation is performed on a well incident during an OBD operation. The accident investi-gation is performed with use of Haddon’s matrix and Haddon’s 10 strategies to prevent harmful energyof getting in contact with individuals or objects.
3 Underbalanced Drilling
Figure 1 illustrates the different bottom hole pressures with use of a low or high density drill fluid, andwith use of a low density drill fluid with top side pressure. We note that the top side pressure makes itpossible to use light density drill fluids to achieve the wanted bottom hole pressure. By utilizing lighterdensity fluids, it is possible to drill sections with narrower drilling windows.
Figure 1: Illustration of bottom hole pressure during OBD and UBD operations
During OBD operations, the bottom hole pressure should be below the formations fracture pressureand above the pore pressure, see figure 2. If the pressure exceeds the fracture pressure the formation willstart cracking and drill fluid will be lost to the formation. In a worst case scenario the loss of drill fluidcan lead to a kick or even a blowout. If the pressure goes below the pore pressure, influx of formationfluid to the wellbore will occur. In UBD operations the bottom hole pressure is below the pore pressureand influx of formation fluid is a normal situation. However if the bottom hole pressure drops too muchthe invasion of formation fluid may exceed the platforms capacity to handle it, or the hole may evencollapse, see figure 2. Because the bottom hole pressure in UBD operations is below the pore pressurethe probability of exceeding the fracture pressure is of a lower probability than in an OBD operation. InUBD operations influx of formation fluid is a normal situations and kicks are therefor defined differentfor OBD and UBD operations. According to the American Petroleum Institute (API) a kick during UBDoperations are defined when the system is designed in a manner where it is not capable of handlingthe formation pressure or flow rate that is experienced. This can be a result of engineering errors, poorchoke control or formation characteristics [6].
There are basically 4 different methods to drill UB related to the drill fluids used [21];
1. Drilling mud (flow drilling); uses liquid mud where no gas is added. The mud can either be waterbased mud or oil based mud. It is a homogeneous liquid and incompressible with constant den-
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Figure 2: Pressure margins in OBD and UBD operations adapted from [21]
sity. The liquid may however become compressible if it is mixed with formation hydrocarbon inthe annulus of the well. With use of drilling mud, mud is pumped through the drill string as inconventional drilling. This kind of technology is limited to few particular cases of high formationpressure. It is used in formation where the pressure is rather high and the liquid is light enoughto provide the desired UB conditions [21].
2. Gaseated fluid; can either consist of a mixture of liquid and gas, or gas with liquid mist.
- Mixture of liquid and gas. Gas is entrained in liquid mud which makes it lighter. The gasused can be; nitrogen, natural gas, air, and exhaust gas. The liquid can be water or oil based.Gasified mud can be introduced in two manners; surface mixing (introduced into the topof the drill string) or downhole mixing (introduced through parasite pipe string or parasitecasing). This technology is used to drill in formations with low hydrostatic pressure.
- Gas with liquid mist (wet gas). Basically gas drilling with injection of very small quantitiesof liquid in the gas stream. Typical mist systems have <2,5% liquid content. Mist flow isinjected in the drill string and runs down the drill pipe and up the annulus. Liquid mistis introduced to assist in; cleaning the face of the drill bit, and lift very small and poweredparticles, like cutting surrounding the bit, through the annulus.
3. Stable foam; uses a homogeneous emulsion generated by mixing liquid gas and surfactant, anemulsifying agent. The gas used in this process is normally nitrogen, but other gases might alsobe utilized. Typical foams systems range from 55% to 97,5% gas. With use of stable foam, foam isgenerated at the surface and introduced to the top of the drill string.
4. Gas-air drilling system; uses dry gas. The use of air and natural gas for drilling in tight sandstonebegan over 30 years ago in the Arkoma Basin of western Arkansas and eastern Oklahoma [23]. Inan gas-air drilling system dry gas is used as a medium. The gas utilized might be air, nitrogen, nat-ural gas, and exhaust gas. When drilling with air or gas, the gas is compressed downhole throughthe drill string. When formation fluids are mixed with the dry gas at the bottom of the well gasreturns through annulus as a mist flow where small liquid droplets are suspended in the gas likea spry. Gas drilling is probably the most used UBD method world wide [21].
The introduction and circulation of light fluids during an UBD operation can be done in three dif-ferent ways;
• Drill string injection; the medium is run through the drill string and up the annulus.
• Parasite pipe string; during casing a separate injection string is implemented in the cement. Inthese cases the drill fluid is introduced through the parasite string and flows up the annulus.
• Parasite casing (only in vertical wells); separate "‘injection-annulus"’ which makes is possible toinsert fluid into the annulus while drilling. The fluid runs down the "‘injection-annulus"’ and upthe annulus.
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3.1 UBD Equipment
UBD operation can be conducted using a conventional drilling rig, or as a rig-less operation [21].UBD operations may vary in equipment, fluid, procedures and purpose. Common for all UBD oper-
ations are; the drilling operations are performed with an UB pressure ratio, the wellbore at the top of thewell is sealed around the drill string while drilling and tripping, and the surface equipment is designedto remove formation fluid from the well and working area.
UBD equipment systems are composed of all systems required to safely allow drilling ahead in ge-ological formations with pressure at surface and under varying rig and well conditions. These systemsinclude: the rig circulating equipment, the drill string, drill string non return valves, surface blowoutpreventer (BOP), control devices (rotating or non-rotating) independent of the BOP, choke and kill lines,UBD flow lines, choke manifolds, hydraulic control systems, UBD separators, flare lines, flare stacks andflare pits and other auxiliary equipment. The primary functions of these systems are to contain well flu-ids and pressures within a design envelope in a closed loop system, provide means to add fluid to thewellbore, and allow controlled volumes to be withdrawn from the wellbore [44].
There are different layouts and equipment used depending of fluid in use and the drilling site. Figure3 an example of a UBD systems flow loop is given. The system can be divided into a well system and asurface separation package system.
Figure 3: Illustration of a UBD system
The surface separation package includes separators, pumps, mud processing area and rig pits. Theamount of separators may vary some. In this example the system is designed with one 1st stage anda 2nd stage separator, able to handle four phase fluid. In the 1st stage separator high pressure gas isseparated. Low pressure gas is extracted in the 2nd stage separator. From the 2nd stage separator oiland gas goes to a test separator where they are separated. The mud and solid is separated in the mudprocessing area. Mud returns to the mud pit, before it once again is circulated into the well.
In the well system drill fluid is introduced either through the drill string, a parasite string or a par-asite casing. Drill fluid is mixed with formation fluid and flows back through the BOP stack to the ESDvalve, the flow spool, the choke manifold before it enters the SSP system.
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In UBD operations the top of the well is continuously pressurized and the drillstring has to rotateand move axially through the seal at the top of the well. A rotating diverter is used as a seal elementin the annulus to allow rotation and movement of the drillstring. The rotating diverter is basically anannular BOP where the seal element is in constant contact with the rotating drill string and rotatestogether with the string [21, 36, 44]. There are basically two different rotating diverters [21, 36];
• Rotating Control Head, RCH; uses the elasticity of the rubber element with added energy fromthe well pressure, to maintain the seal around the drill string. It is a low pressure diverter, designedto rotate with drill pipe and used mainly in air drilling.
• Rotating Blowout Preventer, RBOP; rotating annular preventer designed to rotate with pipe andseal on both pipe and kelly while allowing upward and downward movement of the pipe. It isenergized by hydraulic pressure.
Emergency Shutdown Valve refers to a remotely controlled, full opening valve that is installed onthe flow line usually as near the BOP stack as possible [44].
3.1.1 UBD surface equipment
The surface equipment during UBD operations may vary from use of simple rotating control devicewith a combination of all or some of the UBD equipment listed below [15, 23, 10, 14];
• Rotating Control Device – RCD; maintains a dynamic seal on the annulus enabling chokes tocontrol the annular pressure at the surface while drilling proceeds.
• Downstream choke-manifold system; choke and choke manifold
• Atmospheric or pressurized separation system including downstream fluid-separation package –3-phase or 4-phase separation system
• Geological sampler
• Emergency shutdown system
• Alarm system
• Chemical injection unit; added to the circulation system. May include corrosion inhibitors, hy-drate suppressors, foam inhibitors, emulsion breakers, inhibitors of H2S embitterment [21]
• Evacuation of gas, oil, water and mud cuttings
• Pressure relief systems and unloading, and hydrocarbon disposal facilities in cases of emergency
• Mud pits in order to re-use mud
• Mud pumps
• Metering devices
• Flowlines
The surface part of the circulation system treats the evacuated fluid, separate and disposes the drillcuttings, separate the produced formation fluids and drilling fluids, and pumps the drilling fluid to thetop of the injection system and into the well.
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3.1.2 UBD subsurface equipment
As mentioned earlier in section 3, there are three ways to inject fluid during UBD operations; throughthe drill string, a parasite string or a parasite casing.
The downhole equipment in UBD consists of the following elements [21];
• Drill string
• Bottom hole assembly of the drill string
• String and wellbore isolation valves particular to the UB operations
Drill string There exist two categories of UBD drill strings which are;
• A conventional jointed drill string which has a full drilling rig scale, or
• A small sized drill string or coiled tubing which respectively is methods for slim hole drilling andthrough tubing drilling.
Bottom hole assembly The bottomhole assembly with use of liquid based drilling mud is the same asin OBD, consisting of; drill bit, steer-able motors in cases with direction drilling, measure while dillingand logging while drilling packages. With use of other medium in the drill fluid special logging and mea-suring equipment needs to be used because of difficulties transmitting information as incompressiblemud pulses through the drill string. A possible solution to this problem is to use low frequency electro-magnetic signals which runs through the geological formations.
String and wellbore isolation valves particular to UB operations String and wellbore isolation valvesparticular to UB operations are;
• Downhole check valves in the drill string prevent backflow into the drill string, enable light fluidsto be pumped through the drill string, and prevents gas from blowing back to the drill floor whenpipe connections are made.
• Formation Isolation valves are designed to allow tripping in and tripping out of the wellbore. Thewellbore is isolated from the formation pressure, and there is no pressure at the top of the string.
• Lower Kelly cock is a manually operated quick closing block valve. It is normally used at the Kellyor below the top drive.
3.2 UBD Barriers
According to NORSOK standard D-010, which regulates the minimum requirements to safety barriersduring drilling and well operations on the Norwegian continental shelf, there should be two well barri-ers available during all well activities and operations [5].
This is a specialized drilling technique used where conditions are well known, predictable and riskscan be managed. In UBD, the primary well control function of the mud column, is replaced by a com-bination of flow and pressure control. Bottom-hole pressure and return well flow are continuouslymeasured and controlled by means of respectively, pressure while drilling (PWD) measurements anda closed-loop system. The complete UBD system comprises of the DP circulating system, a rotatingcontrol device (RCD), a UBD choke manifold (not the rig’s well control choke manifold), a four-phaseseparator and a flare stack or flare pit. In addition, non-return valves (NRV’s) are installed in the BHAand drill string to prevent flow up the DP. The rig’s BOP’s are still considered secondary well controlequipment and contingency plans to return to an overbalanced condition must be in place under cer-tain predefined conditions or operational problems. Automated systems are also available that allow afairly constant bottom hole pressure to be maintained while drilling and making up connections [44].
During conventional drilling the primary barrier is the mud column, and the secondary barrier isthe BOP . In UBD operations the hydrostatic pressure is lower than the formation pressure, and thus not
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working as a barrier. The primary barrier during UBD operations is made by a combination of flow andpressure control [5, 37]. The flow control system consists of; rotating control device, choke manifold,flowline, emergency shutdown valve (ESDV), and the surface separation system. In addition to thisnon-return valves (NRV) are installed in the bottom hole assembly and drill string to prevent flow upthe drill pipe when a work string is run UB [5]. The secondary barrier during UBD operations is madeby the BOP consisting of the wellhead connector and drilling BOP with kill/choke line valves.
3.3 Pro and Cons with use of UBD technology
Reservoir criteria which favor an UBD process:
• Easily damaged reservoirs
• Fractured reservoirs
• Pressure Depleted reservoirs
• Poorly understood complex geological formations
• Prone to damage [14]
• Hard rock [14]
Drilling criteria which favor an UBD process:
• Loss circulation potential.
• Severe pressure depletion.
• Poor ROP.
• Mechanical drilling problems.
• Potential for fluid trapping.
• Known fluid sensitivity issues.
Contra-indications to an UBD process:
• Technical issues.
• Safety issues.
• Logistics.
• Depth/Location constraints.
• Borehole stability issues.
UBD provides advantages as to reduced formation damage, reduced lost circulation, increased rateof penetration, reduced drilling time, reduced differential sticking, extended bit life, get a rapid indica-tion of productive reservoir zones, and it has the potential for dynamic flow testing while drilling whichmight make it a safer operation [35, 20, 41, 33, 14, 2].
Under balanced drilling is however not appropriate in all formations e.g. in a lot of shale formations,salt formations, shattered coal sections, unconsolidated sections, in wellbore that are not stable or inwellbores with risk of high levels of sour gas on surface [4, 14, 2].
Potential downsides and damage mechanisms associated with UBD are increased cost and safetyconcerns, mechanically induced wellbore damage, and difficulties in maintaining a continuously UBcondition Bennion et al., 1998 cited in [20]
8
4 Managed Pressure Drilling
MPD has evolved since the mid-sixties [22], and is according to IADC subcommittee defined as; "adap-tive drilling process used to precisely control the annular pressure profile throughout the wellbore. Theobjectives are to ascertain the downhole pressure environment limits and to manage the annular hy-draulic pressure profile accordingly".[27, 22]
The primary difference between conventional drilling and MPD is that in general MPD relies upona closed circulating system whereby flow and pressure in the wellbore can be controlled [44].
The level of planning and actual equipment requirements for MPD depends on the specific tech-nique, whether the application of the technology is for drilling enabling, reservoir damage reductionor reservoir characterization; whether hydrocarbons are present in the section being drilled, and in thecase of drilling in the reservoir section, whether the intent is to produce hydrocarbons or not, the com-plexity and risk level associated with the section being drilled and finally, whether the well is onshore oroffshore and deepwater or shallow water [44].
MPD is a form of drilling which allows greater and more precise wellbore pressure control thanconventional drilling. The technology is suitable for wells with narrow margins. [7, 22, 15] The fluidsused are non-compressible and as opposed to UBD, MPD does not invite influx of hydrocarbons. Thetechnology exploits the opportunity to drill in a effective overbalanced state and makes it possible tojoin pipes without interrupting circulation. [15, 34] The mud weight used will be lower than for theconventional mud weight and a secondary choke or frictional pressure will be applied on surface tocreate a combined annular pressure profile withing the well. [18]
Compared with UBD MPD is better suited for drilling operations in severely depleted reservoirswhere there is a small margin between formation fracture and hole stability. [18]
MPD provides advantages as to [22, 18, 14];
• Deeper open holes
• Deeper, fewer, or smaller casings
• Fewer Mud Density Changes to TD
• Less NPT
• Enhanced control of the well
• Control of formation gas flow rates
• Improved well control procedures
• Minimized risk of circulation losses and stuck pipe
• Increased ROP
• Avoid fluid invasion and fraction
• Reduced drilling time
• Has potential to be a more reliable operation
• No influx of formation fluids
• Reduced chances of hydrate plugs forming at seabed
• Extended bit life
9
4.1 MPD Technology
There two categories of MPD;
1. Reactive when MPD technology is used on a well with conventional casing set points and fluidprograms.
2. Proactive the well is special designed for the MPD operation. Casing, fluids and open-hole pro-gram takes fully advantage of the MPD opportunities
In addition to these two categories there exist variations of the MPD technology. In Marine environ-ments there are said to be four main variations of MPD. The four variants each containing several undergroups representing some differences e.g. variations in equipment [15, 22, 27];
• Constant Bottomhole Hole Pressure
- e.g.Continuous circulation system (CCS), dynamic annular pressure control (DAPC), low densitydrilling fluid (with choke valve for back pressure control), and Secondary annulus circulation us-ing a mud with varying density.
• Pressurized Mud Cap Drilling (PMCD)
- e.g. Low riser return system (LRRS), and
• Dual Gradient (DG)
- e.g. Gas lift in riser (GLIR), equivalent circulating density reduction tool (ECDRT), and secondaryannulus circulation.
• HSE or Returns Flow Control
Where constant bottom hole pressure, PMCD and HSE are the most commonly applied methods.The dual gradient drilling (DGD) technique used in deepwater drilling is the result of a joint indus-
try project’s effort to develop a practical solution to the problems associated with dynamic overpressureon the formations due to the long column of mud in the riser between seafloor and rig floor. In a con-ventional offshore drilling operation, mud is circulated down the drill string, through the bit and backup to the rig floor through a riser. The exposed formations see an equivalent circulating pressure thatincludes frictional pressure and the hydrostatic pressure equal to the entire mud column from bit tosurface. In a normally pressured formation, its pore pressure is generally equal to a column of seawaterand therefore, the pressure it sees during drilling operations is the difference between the hydrostaticpressure of the mud column and a column of seawater. While this may not be a problem in shallowwater, it is a real concern in deep water and often prevents reaching target reservoirs. The use of DGDmay enable reaching targeted TD with fewer, larger-diameter casing strings. The equipment requiredto create a dual-gradient condition is a pump with intake for the mud at the seabed and discharges itto the rig’s mud handling system at surface. The pump mechanically isolates the mud return line fromthe intake line (wellbore annulus) and maintains the annulus pressure equal to the seawater’s hydro-static pressure, thereby creating the dual (seawater/mud) pressure gradient on the annulus side of thewell. Note: the technique can be applied with or without a riser [44]. Mud Cap Drilling This is a drillingtechnique that can be applied when a well is experiencing total dynamic mud losses to a thief zone ator near the bottom of a section and it is not safe and/or practical to drill completely blind. However, noreservoir fluid flow to surface is intended. Drilling fluid (usually water), is pumped down the drill pipe.A higher density fluid is also pumped down the annulus at a controlled rate to overcome hydrocarbonmigration. All of the pumped fluid, produced fluid and the cuttings are pumped into the fractures. Itis the safest method for drilling sour reservoirs with a loss zone above, because there are no returns tosurface. There are two types of mud cap drilling techniques: Floating mud cap - Annular fluid densityis high enough to force fluid and cuttings into loss zone. This requires large volume of mud materialsand is generally used in an open system, when a rotating control device is not available. Pressurizedmud cap - Utilizes annular pressure and fluid column, to divert drill fluid and drilled cuttings into the
10
loss zone. This allows lower density annular fluid (nitrogen gas can also be used in highly depleted sourgas zones) to be used and annular injection rate to be optimized. Annular pressure provides direct in-dication of what is happening down-hole; therefore, less fluid is lost to formation. Viscosifiers can beadded to slow gas migration up the annulus. A rotating control device is a minimum requirement forpressurized mud cap drilling. Continuous Circulation Systems The fluid circulation system is designedsuch that the dynamic pressure profile in the wellbore is maintained during the drilling phase, includingconnections. Low Head Drilling The low head drilling (LHD) technique is where the hydrostatic headof the wellbore fluid column is reduced to be either in balance or slightly greater than the formationpressure thus not planning to induce hydrocarbons or formation fluids into the wellbore. This can beaccomplished using either a non-weighted low-density fluid or a gasified fluid. In addition, techniques(manual and automatic) are also available that allow drilling with an UB equivalent mud weight whilemaintaining balance or predetermined overbalance by use of flow control devices. [44]
4.2 MPD Equipment
The surface equipment used in MPD operations may vary from just a rotating control device tied intothe flowlines, to include one or more of the equipment mentioned below;
• Choke which controls the back-pressure during the drilling operation, may be manually or auto-matically controlled
• Surface separation package able to handle unwanted influx
The Rotating Control Device – RCD; maintains a dynamic seal on the annulus enabling chokes to con-trol the annular pressure at the surface while drilling proceeds [10]. There exist three types of RCDsystems [37];
1. Passive systems; depends on the friction fit between the drill pipe and the rotating pack-off andwell bore pressure to affect the seal
2. Active systems; uses a hydraulic system to seal around the drill pipe
3. Hybrid system; uses a combination of passive elements and active elements and hydraulic closingsystem.
RCD usually consist of three components [15];
- Body with flow line outlet flange
- Bearing assembly with a Stripper Rubber able to stripping drill pipe and tool joints
- Clamp or latch in order to connect and secure the bearing assembly and stripper rubber assemblyto the bowl
In addition to this the MPD system consists of auxiliary components as ESD system, pumps, datasystems etc.
4.3 MPD Safety
Because of MPD uses a closed pressure-controlled system it has a more sensitive kick detection and isbetter suited to control kicks [7, 14, 37].
The pressure differential across the RCD’s Bearing and Stripper Rubber Assembly are modest mak-ing MPD operations with use of RCD an operation with good reliability. [22]
• training
• seal failures
• mud in system
11
• ballooning effects
• Access to chromium
[27]Should have a technological control device during MPD in HPHT it is not a demand, but for a human
to be intensed focus for several days is hard.MPD will likely improve the well control capabilities, combined with predictive modeling.MPD will probably require a smaller team and be done more quickly and to a lower cost than an
UBD operation [27].Mud cannot be considered as a barrier during MPD operations [27].On installations consisting of subsea BOP with marine riser and telescoping slip-joints, the slip-joint
with typically be the weakest link in the riser system relative to pressure containment [15].Better prepared for invasion of influx than conventional drilling technology. [15]
If the the riser and choke system in a "closed loop" MPD operation is filled with gas, a fast andefficient down hole response is challenging. This problem is handled by CMC MPD operations [18]
5 Managed Pressure Drilling
MPD has evolved since the mid-sixties [22], and is according to IADC subcommittee defined as; "adap-tive drilling process used to precisely control the annular pressure profile throughout the wellbore. Theobjectives are to ascertain the downhole pressure environment limits and to manage the annular hy-draulic pressure profile accordingly".[27, 22]
MPD is a form of drilling which allows greater and more precise wellbore pressure control thanconventional drilling. The technology is suitable for wells with narrow margins. [7, 22, 15] The fluidsused are non-compressible and as opposed to UBD, MPD does not invite influx of hydrocarbons. Thetechnology exploits the opportunity to drill in a effective overbalanced state and makes it possible tojoin pipes without interrupting circulation. [15, 34] The mud weight used will be lower than for theconventional mud weight and a secondary choke or frictional pressure will be applied on surface tocreate a combined annular pressure profile withing the well. [18]
Compared with UBD MPD is better suited for drilling operations in severely depleted reservoirswhere there is a small margin between formation fracture and hole stability. [18]
MPD provides advantages as to [22, 18, 14];
• Deeper open holes
• Deeper, fewer, or smaller casings
• Fewer Mud Density Changes to TD
• Less NPT
• Enhanced control of the well
• Control of formation gas flow rates
• Improved well control procedures
• Minimized risk of circulation losses and stuck pipe
• Increased ROP
• Avoid fluid invasion and fraction
• Reduced drilling time
• Has potential to be a more reliable operation
12
• No influx of formation fluids
• Reduced chances of hydrate plugs forming at seabed
• Extended bit life
5.1 MPD Technology
There two categories of MPD;
1. Reactive when MPD technology is used on a well with conventional casing set points and fluidprograms.
2. Proactive the well is special designed for the MPD operation. Casing, fluids and open-hole pro-gram takes fully advantage of the MPD opportunities
In addition to these two categories there exist variations of the MPD technology. In Marine environ-ments there are said to be four main variations of MPD. The four variants each containing several undergroups representing some differences e.g. variations in equipment [15, 22, 27];
• Constant Bottomhole Hole Pressure
- e.g.Continuous circulation system (CCS), dynamic annular pressure control (DAPC), low densitydrilling fluid (with choke valve for back pressure control), and Secondary annulus circulation us-ing a mud with varying density.
• Pressurized Mud Cap Drilling (PMCD)
- e.g. Low riser return system (LRRS), and
• Dual Gradient (DG)
- e.g. Gas lift in riser (GLIR), equivalent circulating density reduction tool (ECDRT), and secondaryannulus circulation.
• HSE or Returns Flow Control
Where constant bottom hole, PMCD and HSE are the most commonly applied methods.
5.2 MPD Equipment
The surface equipment used in MPD operations may vary from just a rotating control device tied intothe flowlines, to include one or more of the equipment mentioned below;
• Choke which controls the back-pressure during the drilling operation, may be manually or auto-matically controlled
• Surface separation package able to handle unwanted influx
The Rotating Control Device – RCD; maintains a dynamic seal on the annulus enabling chokes to con-trol the annular pressure at the surface while drilling proceeds [10]. There exist three types of RCDsystems [37];
1. Passive systems; depends on the friction fit between the drill pipe and the rotating pack-off andwell bore pressure to affect the seal
2. Active systems; uses a hydraulic system to seal around the drill pipe
3. Hybrid system; uses a combination of passive elements and active elements and hydraulic closingsystem.
13
Table 1: Different MPD technologies with areas of application and characteristics adapted from [15, 22]
MPD technology Area of Application Characteristics
CBHP Narrow pressure Pipe connections made withenvironments surface pressure
Not exceed fracture gradientduring drilling
PMCD Lost circulation Process where heavy fluid isissues added. The amount of lostZones capable of fluid is replaced with sea-consume drilling water, increasing ROPfluids and cuttingsWells with grosslydepleted zones
DG Deepwater drilling two different annulus fluidthere. There exist gradientslong section of mudin the riser betweenseafloor and rig floor
HSE Typically on HPHT Closed mud return system onwells the rig floorDrilling on plat-forms where simul-tanious productionis ongoing
RCD usually consist of three components [15];
- Body with flow line outlet flange
- Bearing assembly with a Stripper Rubber able to stripping drill pipe and tool joints
- Clamp or latch in order to connect and secure the bearing assembly and stripper rubber assemblyto the bowl
In addition to this the MPD system consists of auxiliary components as ESD system, pumps, datasystems etc.
5.3 MPD Safety
Because of MPD uses a closed pressure-controlled system it has a more sensitive kick detection and isbetter suited to control kicks [7, 14, 37].
The pressure differential across the RCD’s Bearing and Stripper Rubber Assembly are modest mak-ing MPD operations with use of RCD an operation with good reliability. [22]
• training
• seal failures
• mud in system
• ballooning effects
• Access to chromium
14
[27]Should have a technological control device during MPD in HPHT it is not a demand, but for a human
to be intensed focus for several days is hard.MPD will likely improve the well control capabilities, combined with predictive modeling.MPD will probably require a smaller team and be done more quickly and to a lower cost than an
UBD operation [27].Mud cannot be considered as a barrier during MPD operations [27].On installations consisting of subsea BOP with marine riser and telescoping slip-joints, the slip-joint
with typically be the weakest link in the riser system relative to pressure containment [15].Better prepared for invasion of influx than conventional drilling technology. [15]
If the the riser and choke system in a "closed loop" MPD operation is filled with gas, a fast andefficient down hole response is challenging. This problem is handled by CMC MPD operations [18]
6 Comparison of UB, OB and MP drilling technologies
MPD vs UBD [14];
1. Because MPD operates with bottom hole pressure equal to or slightly higher than the pore pres-sure, the potential of hole collapse during UBD operations are greater.
2. Both UBD and MPD can reduce drilling-induced formation damage, but unlike MPD UBD hasthe potential to eliminate the formation damage.
3. Reduced equipment is usually required during MPD operations, e.g. need for separators capableof handling great amounts of mud, cuttings and formation fluids.
4. The production maximizing is greater for UBD operations than MPD operations because the for-mation damages are usually greater in MPD operations than in UBD operations.
5. Because UBD operations invite influx while drilling, formation characteristics can be fully evalu-ated during the operation. MPD use measurement tools as MWD (measure while drilling) etc. toevaluate formation characteristics.
The scores represented under are made on a general basis of each drilling technology.OBD MPD UBD
investment cost + + + -safety + + + +equipment + + + -ROP - + + +Drill long sections - + +Lost circulation - + + +Cope with kicks - - + + +Formation damage - + +Deep water wells - +shallow water wells + -Well control + + + +Riser margin + + + -
7 Safe operability analysis of connection during MPD
Kvitebjørn is a HPHT well located in the North Sea. The reservoir consists of sandstones in the MiddleJurassic Brent group, and lies at approximately 4 000 meters depth [11]. There are a total of 11 wellswhere 7-8 at the moment is drilled.
15
Production in the Kvitebjørn field has lead to lower fracture and pore pressure in the formation.Some places high pore-pressure zones are in the formation, leading to a narrow and difficult drillingwindow to predict and drill [1]. For further development it will not be economical favorable, or in somecases even possible, to drill conventional. In order to cope with the difficult conditions at Kvitebjørn,MPD technology with use of a continuous circulation system, CCS, is planned.
CCS utilizes a circulation system in order to join drill pipes to the drill string without interruptingthe drilling process [29, 40].
The potential benefits with use of CCS are [29, 31];
• Elimination of surges during start and stop of circulation
• Continuous movement of cuttings in the annulus, no rig downtime to clean the bottom hole as-sembly
• Reduced total connection time
• Reduced chance of stuck pipe during a connection
• No downtime in HPHT wells to circulate out connection gas
• Improved hole conditions
• Improved control of equivalent circulation density
• Elimination of ballooning effects
• Elimination of kicks while making connections
CCS technology might benefit from OBD connection technology, but there might also be potentialdownsides. For Kvitebjørn this operation has never been performed before. With use of new technol-ogy there will always be a certain risk. In order to identify hazardous events, a SAFOP analysis was per-formed on a connection with use of a continuous circulation system. The SAFOP analysis is describedin appendix A.
In the following section a description of connection with CCS is made. During the analysis only onlyexamination and documentation will be performed, see 8 in appendix A. The examination will be per-formed by first identifying the various steps in the procedure before relevant guide words are applied toone step of the procedure at a time. The guide words used in this section is listed and described in ap-pendix A along with the procedure that was used during this SAFOP performance. The documentationof the SAFOP results will be listed in work sheets in appendix B.
7.1 Connections with use of Continuous Circulation Systems
7.2 CCS connection description
The CCS consists of a pressure chamber containing two pipe and a blind ram which is placed in betweenthe two pipe rams. During a connection the chamber is filled with mud equalizing the pressure insideand outside the drill string. Pipe rams will later on close around the drill pipe. After this is done thepipes are disconnected and the blind ram is closed. The upper part of the chamber is bled of, and thepipe removed. The circulation of mud is now made through the lower part of the pressure chamber anddown the drill pipe, see figure 4. New stands of pipes are prepared and inserted in the upper chamber.The pipe ram is closed around the new pipe stand, and the chamber is pressurized. Mud is circulatedthrough the new joint of pipes, the blind ram is opened, and the drill pipes are connected.
7.3 CCS connection procedure
1. Lift the pipes
2. Activate the pipe rams and the pipe slips
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Table 2: Description of equipment in CCS system adapted from [29]
Equipment Description
Pipe guide Guides the pipes in right positionSnubber It’s object is to control movement of drill pipes into and out of the
coupler. Operates with vertical and rotational forces and is connectedto the coupler by four hydraulic rams. Uses hydraulic motors to spinthe pipes into/out of connections and the hydraulic rams to apply makeup or break out torque.
Coupler A pressure chamber located on the rig floor over the rotary table.It seals around the drill pipe pin and box during the connectionprocess. It consists of three pressure chambers; the upper with piperams, the middle with blind rams, and the lower with inverted piperams.
Pipe slips Holds the pipe in position.Flow paths Two are drain lines from the upper and lower coupler chamber and one
is fill line into the lower chamber connected to the mud divertermanifold.
Mud diverter Switches mud flow between the top drive and the coupler during drillmanifold pipe connections. It is connected into the discharge line between the
mud pumps and the standpipe manifold.
(a) Activate the pipe rams
(b) Activate the pipe slips
3. Pressurize the chamber
4. Connect the snubbing unit
5. Disconnect the pipes
6. Lift the upper pipe
7. Close the blind ram
8. depressurize the upper chamber
(a) Seal the standpipe
(b) Open the drain valve to the upper chamber
(c) Bleed off the standpipe
9. Disconnect the snubbing unit and the upper pipe ram
(a) Disconnect the snubbing unit
(b) Open the upper pipe ram
10. Remove the pipe, and add new the pipe joint
(a) Remove the pipe
(b) Add new pipe joint
11. Close the pipe ram, and connect the snubbing unit
(a) Close the pipe ram
(b) Connect the snubbing unit
17
Figure 4: The upper chamber is fully depressurized (Step 8 in the procedure)
12. Close the drain valve to the upper chamber
13. Pressurize the upper chamber
14. Open the blind ram
15. Connect the pipe joint and the drillstring
(a) Lower the pipe joint
(b) Connect the pipe joint to the drillstring
16. Close the valve to the lower chamber
17. Bleed off the chamber
18. Close the drain valve
19. Disconnect the snubbing unit
20. Disconnect the pipe slips
21. Open the pipe rams
7.4 SAFOP of connection with use of CCS
The SAFOP work sheets can be found in appendix B. The consequences related to each step, is given ascore according to safety and operability considerations. The scores that are given;
• L = low, and was given the value 1
• M = medium, and was given the value 2
• H = high, and was given the value 3
The main focus of this project is on safety and the rating of each procedure will therefor be regardingthe safety contributing factors. In order to find the procedures with the strongest influence on the safety,the average value of each procedure was calculated by using the score values. The results from theanalysis can be found in figure 5
18
Figure 5: SAFOP results for each step in the procedure
7.5 SAFOP conclusion
The steps that are most critical to the safety, are listed in figure 6;The blind ram is of great importance in the procedure. This component seals and separates the
two chambers from each other. For instance will the blind ram play an important role when the upperchamber is drained. By separating the chamber into two separate chambers, the upper chamber can bedepressurized, and new pipe joints can be added. If the blind ram does not seal the lower chamber fromthe upper chamber, the pressure will decrease. If this is not detected before the bottom hole pressurebecomes lower than the pore pressure, influx from the formation will occur. A kick will occur. In alloperations listed in figure 6, the pressure inside the chamber plays an important role. The pressureinside the chamber should be easy to monitor and adjust when needed. Since it is the first time MPDoperations are performed on Kvitebjørn, it is important to train personnel and makes sure that thelevel of competence is high. During the operation there will be MPD personnel involved in the drillingoperations. Because the communication will be in English, and not Norwegian as usual, extra focus onthe communication is needed. The personnel should be consistent when communicating, have clearresponsibilities, and have good procedures to;
• prevent unwanted situations from occurring
• handle unwanted situations in a controlled and good way to reduce the consequences.
19
Figure 6: Most risk contributing steps
8 Accident Investigation
There exist various descriptions of the accident investigation process, depending on the author.The U.S. department of energy (DOE) divides the investigation process into three phases [12];
1. Evidence and fact collection
2. Analysis of the collected facts
3. Conclusion, development of needs, and the report writing
This paper will focus on different methods to analyse data.There exist a great number of accident investigation methods, or techniques. Various methods are
listed in table 3.
Table 3: Accident investigation methods adapted from [17, 12]
Accident Anatomy Method Events and Causal Factors Charting and AnalysisAction Error Analysis Barrier AnalysisAccident Evolution and Barrier Analysis Change AnalysisChange Evaluation/Analysis Fault Tree AnalysisCause-Effect Logic Diagram Managed Oversight and Risk TreeCausal Tree Method Project Evaluation Tree AnalysisFault Tree Analysis Time Loss AnalysisHazard and Operability Study Human Factors AnalysisHuman Performance Enhancement System Integrated Accident Event MatrixHuman Reliability Analysis Event Tree Failure Modes and Effects AnalysisMultiple-Cause, System-Oriented Incident Software Hazards AnalysisInvestigation Common Cause Failure AnalysisMultilinear Events Sequencing Sneak Circuit AnalysisManagement Oversight Risk Tree Materials and Structural AnalysisSystematic Cause Analysis Techniques Design Criteria AnalysisSequentially Timed Events Plotting Accident ReconstructionTapRootT M Incident Investigation System Scientific ModelingTechnique of Operations ReviewWork Safety Analysis
The selection of accident investigation method, depends on the nature of the accident being inves-tigated, the object of the investigation, and the amount of available information [25]. The purpose ofthe analysis may vary from company to company, and are either to [42, 16];
• identify and describe the true course of the events (what, where, and when)
• identify the direct and root causes/contribution factors of the accident (why)
• identify risk reducing measures to prevent future, comparable accidents (learning)
20
• investigate and evaluate the basis for potential criminal prosecution (blame)
• evaluate the question of guilt in order to assess the liability for compensation (pay)
Usually, major accidents are the result of multiple interrelated causal factors. Actors or decisionmakers influencing the normal work process might also affect accident scenarios directly or indirectly.According to the DOE, the causal factors in an accident, can be divided into three different types [12];
• Direct cause; an immediate event or condition that caused the accident
• Contributing cause; an event or condition that together with other causes increase the likelihoodof an accident but which individually did not cause the accident
• Root cause; the casual factor(s) that, if corrected, would prevent the recurrence of the accident
The various methods scope, can be related to the socio-technical system involved in risk manage-ment. The different socio-technical levels are [42];
1. the work and technological system
2. the staff level
3. the management level
4. the company level
5. the regulators and associations level
6. the Government level
In appendix C, a presentation of the following four accident investigation methods is given;
• Events and causal factors charting (ECFC)
• Sequentially timed events plotting (STEP)
• Man-Technology-Organisation analysis(MTO-analysis)
• Haddon’s matrix
The MTO-analysis and Haddon’s matrix are not listed in table 3. MTO is a commonly used methodin several European countries. The method is utilized in different industries [42]. Haddon’s matrix hasits origin in accident investigations of traffic accidents, but is adapted in other industries.
8.1 Comparison of accident investigation methods
The aim of accident investigations should be to identify the event sequence and all causal factors in-fluencing the accident scenario in order to suggest risk reducing measures which may prevent futureaccidents.
ECFC, STEP and MTO are all primary methods, which means that they are techniques fully capableof standing alone. In addition, the methods give graphical illustrations of the accident scenario illus-trating the total accident scenario [42].
Haddon’s matrix is a method to sequential list multiple causes leading to an accident. By combiningthe method with Haddon’s 10 strategies to prevent harmful energy from getting in contact with individ-uals or objects, the method is capable of standing alone, as a primary method.
All the methods are process models.ECFC, STEP and Haddon’s matrix are all methods that do not demand hands-on experience. As
opposed to the MTO analysis, which require an experienced person or a specialist, the methods arefairly easy to use.
ECFC and the MTO-analysis, cover level one to four on the socio-technical levels. STEP and Had-don’s matrix, cover level one to six.
In the following section an accident investigation is carried out. The investigation is performed withuse of Haddon’s matrix and his 10 strategies. The choice of method was based on;
21
• the methods scope
• no-hands on experience is needed
• required resources
8.2 Accident investigation of well no. 6 at South Tambier block
The main objective is to convert an accident investigation into Haddon’s matrix and his 10 strategies.The result is dependent on the analysts understanding of the documented accident.
The analysis of the collected facts seeks to find out what happened, when and where it happened,and why it happened. Haddon’s 10 strategies will give a list of actions that could have prevented theaccident from occurring, or mitigated the consequences.
The data collection was based on a prepared public accident report made by the MMS.During the first of December 2005, a loss of well control occurred in the conductor hole section
on the South Timbalier Block Well No. 6 located on in the Gulf of Mexico. While drilling ahead beneathdrive pipe in open water at a depth of 1,027 ft, there was observed a background gas reading of 224 unitswith corresponding mud weight loss from 9.8 pounds per gallon to 9.6 pounds per gallon. Mud wasweighted up to 10.2 pounds per gallon, and drilling continued. The prescribed mud weight up schedulewas followed. At a depth of 1,318 ft in the conductor hole section, the well became unstable and releaseda pocket of gas. Personnel on the rig floor experienced that the gumbo box was overflowing. The drillerimmediately stopped the operation to undertake a flow check. Within minutes of this action, mud wasseen flowing out of the rotary table. The well was placed on the diverter system. At the rig floor, itoccurred flow from both of the diverter lines. One of the diverter valves placed at the rig floor, wasclosed because of the wind direction. Kill weight mud was circulated into the well. The well continuedto "burp" gas over the next five days. Heavy weighted mud was circulated, while washing to bottom andback-reaming to prevent stuck pipe [47].
In Figure 7, the accident is analyzed by use of Haddon’s matrix. Figure 7, gives a description of failurecauses according to the accidental time axis.
The main causes of loss of well control, was the low margin of overbalance at a shallow depth withstructural overpressure coupled with an inadequate and an ill-defined pre-hazard study of the geotech-nical properties of the area.
The 10 strategies should have been applied separately for each causal event revealed in Haddon’smatrix. In this paper a set of strategies is developed on a general level. The different events have notbeen analyzed one by one.
Because the well was successfully put on a diverter and controlled, Haddon’s 10 strategies is onlymade on the preventive strategies.
Haddon’s 10 strategies;
1. Perform a proper analysis of the formation. Make sure that the formation data is based on actualwell geological and geophysical data. Look at earlier well incident cases in the South TimbalierBlock. There had been two well incidents in the early 70’s, which had experienced similar prob-lems with shallow gas. Use a drilling manager that has experiences within the South Timbaliertrench. Use better seismic equipment which most likely would discover present gas pockets.
2. Utilize a separator capable of handling influx from the formation.
3. Locate the measuring equipment as closed to the bit as possible. Gas pockets can be revealed,before potential incidents occur.
4. Make sure the drive pipe is driven deep enough into the formation. This will give a better isolationof shallow gas. Stop drilling when the background gas noted in the mud returns exceeds 200 units.Have the operator set a casing at this point. Perform a casing operation before drilling into thesand lens below 1,000 feet. Make sure that the mud weight is sufficient, and that the drilling isperformed in an overbalanced manner. Utilize a choke with back-pressure to controll the bottomhole pressure.
22
Figure 7: Accident investigation with use of Haddon’s matrix
5. Develop better routines and utilize equipment capable of detecting deviations. Earlier reactionscould have reduced the flow of fluids. Mud with at higher weight should have been pumped intothe well at a earlier point in time to reduce the unwanted flow of fluids.
9 Conclusions and further work
Only two accidents have been revealed, both with use of MPD technology. The collection of data toevaluate risk during UBD and MPD operations were concluded.
SAFOP is a tool made to identify hazards to prevent unwanted events from occurring, or to mitigatethe consequences. Because the risk during UBD and MPD operations are not fully known, pre-hazardanalysis is important to evaluate risk contributing factors during the drilling operations. The SAFOPmethod is performed by a team of experts, and is applicable for both UBD and MPD operations. Ac-cording to the SAFOP analysis made on the connection with CCS, the blind ram is the most importantrisk contributor. It is the first time this operation is performed by Statoil, and specialized MPD oper-ators are included in the drilling operation. To perform a safe operation it is important to have goodcommunication, well functioning procedures, and clear areas of responsibilities.
ECFC, STEP, and MTO are primary methods with graphical illustrations. Haddon’s matrix with useof Haddon’s ten strategies is capable of standing alone as a accident investigation method. All the mod-els are process models. MTO is the only method that requires hands-on experience. Haddon’s matrixcombined with Haddon’s ten strategies, along with the STEP, covers all the socio-technical levels as op-posed to ECFC and MTO. Haddon’s techniques are fairly easy to use. As opposed to the STEP method,Haddon’s techniques do no require a lot of available data. The techniques are suitable for accident
23
investigation of UBD and MPD operations.In formations containing potential gas pockets; detailed pre-hazard analysis of the geothechniqal
properties of the specific area should be performed, equipment capable of detecting the gas pocketsas early as possible should be utilized, and alternative drilling technologies should be considered. Forinstance with use of UBD technology, separators capable of handling shallow gas, and formation flu-ids are utilized. The shallow gas would most likely not have caused any problems if this was an UBDoperation.
Recommendations to further work would be to; collect data on a world wide basis, and include anUBD and MPD profile in the SINTEF blowout database.
10 Acknowledgment
I would like to thank my supervisors Professor Marvin Rausand at NTNU and Senior Consultant Alexan-der Solberg at Scandpower for their assistance during the preparation of this paper. I would also like tothank Michael Golan, Dave Samuelson Per Holand, Arild Rødland, Alf Breivik, Harald Tveit, Johan Eck-Olsen.
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27
A Safe operability analysis
A.1 Safe operability analysis history
SAFOP or procedure HAZOP is developed from the hazard and operability, HAZOP, analysis. HAZOPhad its origin in 1963, developed by the Imperial Chemical Industries (ICI). The beginning of todaysHAZOP was developed for use in assessing the hazards involved in the processes of chemical plants[30]. The process was based upon review of system piping and instrumentation diagrams (P&IDs). Themethod further developed to review the safety and operability of more complex activities [46].
Different needs and industries has lead to various HAZOP approaches;
• Process HAZOP; technique originally developed to assess plants and process systems.
• Human HAZOP; focuses on the human aspect and risk contribution rather than the technicalfailures.
• Software HAZOP; Identifies possible errors in the development of software.
• Procedure HAZOP or SAFOP (SAFe Operation Study); Evaluates procedures and operational se-quences.
The HAZOP analysis is usually performed on a process or operation in an early phase in order toinfluence the design. However it is also applicable on existing operations or processes to identify modi-fications that should be implemented in order to reduce risk and operability problems. It is a systematicand qualitative method based on guide words to identify deviations from the design intent [28]. Theanalysis is performed during a set of meetings by a HAZOP group consisting of; a leader, a secretary,and 4-6 technical experts [39, 38, 45].
In the traditional HAZOP analysis the guide words; NO, NOT, DON’T, MORE, LESS, OTHER THAN,PART OF and REVERSE are used. In addition there are guide words related to sequences as; EARLY, LATEBEFORE, and AFTER. These guide words may not be as applicable for all variations of HAZOP analysis,and alternative guide words recommended by the HAZOP team can be used.
A.2 Safe operability analysis description
SAFOP is an examination of an existing or planned operation procedure to identify hazards and causesof operational problems, quality problems, and delays [38].
The methodology used during a SAFOP analysis is the same as for a HAZOP analysis. The maindifferences between the two methods are; variation in use of guide words, and SAFOPs consideration ofhuman errors in addition to technical failures.
SAFOP is best suitable for detailed assessment, but can also be used for coarse preliminary assess-ment. The result of such an analysis is usually a list of preventive actions in order to improve operationsand procedures [38, 8].
According to IEC 61882 there are four sequential steps in HAZOP, see figure 8. In this report the mainfocus will be on step 3, see figure 8, which deals with the examination of the procedure. There will alsobe a documentation of the results, see step 4 figure 8, but no follow up will be performed.
During the examination of the operation the procedure is divided into various sequences and fur-ther into operational steps. Deviation from the design intent are revealed by applying relevant guidewords to the various steps. For each step, potential human and technical failures are stated, and theconsequences of these failures are described. The examination of the various steps can be done eitherby applying relevant guide words to one step at a time, or by applying one guide word to the relevantsteps. Figure 9 illustrates the first examination method, which will be use further in this report.
A set of guide words adapted from [8] is used during the case studies later in this report [46];Documentation during the analysis is listed in SAFOP work sheets, see appendix B.The different columns are;
28
Figure 8: HAZOPs four basic sequential steps according to IEC 61882, adapted from [28]
29
Figure 9: Flow chart of a SAFOP analysis adapted from [28]
30
Table 4: Guide words in SAFOP et al B. Kirwan adapted from [38]Guide word Description
Unclear Procedure is written in a hard way to understand andmight be confusing
Step in wrong place The procedure does not imply the correct sequence ofactions that should be made.
Wrong action The action presented in the procedure is incorrectIncorrect Information that are checked prior to actions areinformation incorrectly specified.Step omitted Step not performedStep unsuccessful The step is performed incorrectlyInterference effects The procedure performance is affected by otherfrom others personnel carrying out simultaneous tasks
Table 5: Work sheet explanationColumn Explanation
No. The SAFOP reference numbers.Work step The studied step in the procedure.Guide word Guide words applied to the various steps.Deviation Deviation from the desired output of the step.Possible cause The event causing the deviation.Consequences Possible consequences from the deviation.Action required Pre-actions to prevent the deviation from
occurring.
A.2.1 Pros
Positive aspects of SAFOP analysis [39, 38, 45, 46, 28, 8];
• Provides creative thinking. Specialists are gathered to review the system and identify failure modes
• Includes both technical and human errors
• The method gives a systematic examination
• It is applicable in all phases on the facility
• Identifies potential hazards before they are introduced to the system
• Gives the different persons participating in the process, or procedure, insight to other areas of thework process.
• Provides flexibility in choice of guide-words
A.2.2 Cons
Negative aspects of SAFOP analysis [39, 38, 45, 46, 28, 8];
• The results of the analysis depends on the knowledge, interaction and experience of the personsinvolved
• It is defendant on the availability and the detail description of the procedures
• It is time consuming
31
• The study generates extensive information
• The analysis is dependent on the extent of the investigation
• Some team members may dominate more than others
• It is not and "in-depth" review of causes and consequences
• Does not consider common cause failures
32
B SAFOP of connection with use of a continuous circulation system
33
Sheet:
Date
Meeting date
No. Step Guideword Deviation Possible causes Consequences Action required # S O1 Unclear Pipes are in wrong position
The pipes are not liftedEquipment and pipes are damaged
The position is written in a confusing way. Wrong equipment is used because of unclearance in the procedure.Wrong force is applied, or pipes are moved too fast due to a confusing procedure.
1 The operation is delayed2 There are damage on the pipes3 Equipment is damaged4 Surges might occur
Find the position, speed, and tools that should be used during the lifting of the pipes, and make sure the procedure is clear and easy to understand.
1234
LM M H
MMHH
2 Wrong action Pipes are left in wrong position.Pipes are lost to the bottom of the hole.
The wrong force is specified, either the force given is too high or too low. The wrong equipment is specified.
1 Bit is damaged 2 Equipment is damaged3 Pipes are damaged. 4 Surges might occur
Have a person check the procedures to make sure that the action stated in the procedure is correct.
1234
LMLH
MHMH
3 Incorrect information The pipes are lost, damaged or in wrong position.
Wrong force might be applied, or the wrong positions are given. The equipment used does not the needed strength to lift the pipes in right position.
1 Bit is damaged 2 Pipe rams are damaged3 Pipes are damaged4 Operation is delayed
Review procedures and make sure right equipment, pressure and position is given.
1234
LMLH
MHMH
4 Step omitted Pipes are left in wrong position.
The pipes are not lifted because the operation to lift the pipes is not performed, or left out in the procedure.
1 Bit is damaged 2 Pipe rams are damaged3 Pipes are damaged
Train personnel and review procedure to make sure all the steps in the operation are included.
123
LML
MHM
5 Step unsuccessful Pipes are left in wrong position. Pipes are lost downhole.
Wrong action is performed by the personnel.
1 Bit is damaged 2 Pipes are damaged3 Equipment is damaged
Train personnel and make sure that the work environment is good.
123
LMM
MMH
6 Interference effects from others
Pipes are left in wrong position. The pipes are lost downhole.
Operator is distracted, and fails to make the right action.
1 Bit is damaged 2 Pipes are damaged3 Equipment is damaged
Train personnel and review the work environment.
123
LMM
MMH
1. L
ift p
ipes
Con
sequ
ence
#Sa
fety
O
pera
bilit
y
Part considered Instruction step
Study title:
Revision No:
Team composition
Procedure title:
No. Step Guideword Deviation Possible causes Consequences Action required # S O7 Unclear The pipe rams are not
closed, or in wrong position. The right terms are not used in the procedure. The correct pressure is not specified in a clear manner.
1 Pipes are damaged2 Equipment is damaged 3 Pipe rams does not support the pipes 4 The chamber is not sealed, which might lead to mud spill
Find right pressure, and speed that should be applied, and make sure they are clearly stated in the procedure.
1234
LMLL
MHHM
8 Step in wrong place Pipe rams are not closed, or they are closed before the pipes are lifted.
The steps are in wrong sequnece in the procedure.
1 Pipes are not supported 2 Pipes are damaged3 Equipment is damaged4 The chamber is not sealed, which might lead to mud spill
Review procedure to make sure that the steps are in right order.
1234
LLML
HMHM
9 Wrong action Pipe rams are not closed, or closed too fast, too hard, or too loose.
Wrong action is given. The correct pressure is not specified, or the right terms are not used.
1 Pipes are damaged2 Pipe rams are damaged. 3 Pipe rams does not support the pipes4 Chamber is not sealed, which might lead to mud spill
Find the right pressure, and speed that should be used, and make sure they are applied to the procedure.
1234
LMLL
MHHM
10 Incorrect information Pipe rams are in wrong position
Wrong pressure and positions are given.
1 Pipe rams are damaged 2 Pipes are damaged.3 Pressure chamber is not sealed, which might lead to mud spill
Review procedure before starting the operation.
123
MLL
HMH
11 Step omitted Pipe rams are not activated Operator does not activate the pipe rams, or it is not documented in the procedure.
1 Pipes are not supported. 2 The chamber is not sealed, which might lead to mud spill
Review the procedure and train the operator.
12
LL
HH
2 a)
Act
ivat
e pi
pe ra
ms
No. Step Guideword Deviation Possible causes Consequences Action required # S O12 Step unsuccessful Pipe rams are not activated,
or they are in wrong positionOperator fails to perform the right action. The wrong amount of pressure is applied or the operator fails to leav the pipe rams in the right positions.
1 Pipes are damaged 2 Pipe rams are damaged3 Chamber is not sealed, which may lead to mud spill.If the chamber leaks it might lead to;4 mud loss5 Kicks if pressure inside and outside the drillpipe is not equalized before disconnection is made
Train personnel, and have an extra person to make sure the operation is performed correctly.
12345
LMLMH
MHH LH
13 Interference effects from others
Pipe rams are left in the wrong position
The operator fails to take the right action because of distractions from co-workers.
1 Pipe rams are damaged 2 Pipes are damaged.3 Pressure chamber is not sealed, which might lead to mud spill
Review the procedure before performing the operation.
123
MLL
HMH
2 a)
Act
ivat
e pi
pe ra
ms
No. Step Guideword Deviation Possible causes Consequences Action required # S O14 Unclear Pipe slips are not closed, or
they are in wrong position.The terms used are unclear. The pressure is given in a confusing way.
1 Operation is delayed.2 Pipes are damaged.3 Equipment is damaged.4 Pipe slips does not support the pipes.5 The chamber is not sealed.
Find the right pressure and speed, and apply the information to the procedures.
12345
LLMMH
MMHHH
15 Wrong action Pipe slips are not closed, or they are in wrong position.
The wrong action is given. Correct pressure is not specified. The right terms are not used.
1 Operation is delayed. 2 Pipes are damaged.3 Pipe rams are damaged. 4 Pipe rams does not support the pipes.5 The chamber is not sealed.
The procedure should be reviewed before the operation is started.
12345
LLMMH
MMHHH
16 Incorrect information The pipe slips are in wrong position.
Wrong speed and pressure is specified in the procedure.
1 Equipment is exposed to unnecessary wear. 2 Equipment is damaged. 3 Pipe is damaged4 Pipes are not supported
Review procedure before starting on the operation.
1234
LMLM
MHMH
17 Step omitted Pipe slips are not activated. Step is omitted in the procedure or by the operator .
1 Pipes are not supported. 2 Pipes might be lost downhole or damaged when disconnected.
Review procedure before starting on the operation, and train personnel.
12
MM
HH
2 b)
Act
ivat
e pi
pe s
lips
No. Step Guideword Deviation Possible causes Consequences Action required # S O18 Step unsuccessful Pipe slips are not in right
positionIncorrect action is taken. Operator does not supply the right amount of pressure, or the pipe slips are left in wrong position.
1 Pipes are damaged2 Equipment is damaged. 3 Pipe might be lost downhole when disconnection is made
Train personnel and have an extra person check on the operation.
123
LMM
MHH
19 Interference effects from others
Pipe slips are not in right position
Operator fails to take the right action due to distractions
1 Pipes are damaged2 Equipment is damaged. 3 Pipes are not supproted, and might be lost downhole when disconnection is made
Train personnel, and look at the work environment
123
LMM
MHH
2 b)
Act
ivat
e pi
pe s
lips
No. Step Guideword Deviation Possible causes Consequences Action required # S O20 Unclear The valve to lower chamber
is not opened, or there is too much or too little flow .
The valve is not properly named, or the correct pressure is not specified.
1 The chamber might burst if the pressure becomes too high.2 Operation is delayed.3 Mud can be lost4 Equipment is damaged.5 Kicks might occur during disconnection if the chamber is not properly pressurized.
Control procedures before starting the operation.
12345
HLMMH
HHLHH
21 Step in wrong place Valve is opened before the pipe rams are closed.
The sequence of operations is wrong in the procedure
1 Mud spill Review procedure before action is taken.
1 L M
22 Wrong action Chamber is not pressurized, not fully pressurized, or over pressurized.
The wrong valve is specified to open in the procedure. The flow rate given in the procedure is either too high, too low, or the wrong end pressure is given.
The perssure is not equal on the inside and on the outside og the drillstring.1 Chamber might burst. 2 Operation is delayed. Pressure might be too high or too low which can lead to; 3 Mud loss.4 Damage on equipment. 5 Kicks during disconnection.
Review procedures before starting the operation, and have an extra person cheking it.
12345
HLMMH
HHLHH
3 Pr
essu
rize
cham
ber
No. Step Guideword Deviation Possible causes Consequences Action required # S O23 Incorrect information Chamber is not fully
pressurized, or it is pressurized too much.
The wrong instruction and information is given in the procedure.
The perssure is not equal on the inside and on the outside og the drillstring.1 Chamber might burst. 2 Operation is delayed. Pressure might be too high or too low which can lead to; 3 Mud loss.4 Damage on equipment. 5 Kicks during disconnection.
Make sure the pressure inside the drillstring is given and review the pressures before action is taken.
12345
HLMMH
HHLHH
24 Step omitted The chamber is not pressurized.
Step is omitted in the procedure or by the operator
The pressure outside and inside the drillstring is not equalized. 1 Equipment is damaged. 2 Kicks might occur.3 Operation is delayed.
Review procedure, and control the pressure inside the chamber. Have an extra person checking.
123
MHL
HHM
25 Step unsuccessful Chamber is not fully pressurized, or it is pressurized too much.
The chamber is not pressurized correctly by the operator.
1 Chamber might burst. Pressure outside and inside the drillstring is not equal, which might lead to;2 Mud spill3 Mud loss or even 4 Kicks.
Train operator, and have a second person looking over the operation. Make sure there is good communication between the involved personnel
1234
HLMH
HML H
26 Interference effects from others
Chamber is not fully pressurized, or it is pressurized too much.
Operator fails to take the right action due to distractions from co-workers
1 Chamber might burst. Pressure outside and inside the drillstring is not equal, which might lead to;2 Mud spill3 Mud loss or even 4 Kicks.
Train personnel, monitor the pressure constantly, and review the work environment
1234
HLMH
HML H
3 Pr
essu
rize
cham
ber
No. Step Guideword Deviation Possible causes Consequences Action required # S O27 Unclear Snubbing unit is not
connecte, or connected in the right way.
Procedures are confusing and misleading.
1 Operation is delayed 2 Snubbing unit is damaged 3 Pipes are damaged
Review procedures before the operations is started.
123
LLL
MHM
28 Wrong action Snubbing unit is incorrectly connected.
Wrong instructions are given in the procedure.
1 Delay2 Damaged pipes3 Damaged equipment
Have an experienced person checking the procedure.
123
LLM
MMH
29 Incorrect information Snubbing unit is incorrectly connected
Wrong torque is applied, either it is used too much or too little.
1 Equipment is damaged2 Pipes might be damaged
Make sure that the specifications given on pipe dimensions and torque are right before the operation is started.
12
ML
HM
30 Step omitted Snubbing unit is not connected.
Step is omitted in the procedure or by the operator.
1 Operation is delayed Review procedure 1 L M
31 Step unsuccessful Snubbing unit is not connected the right way.
Wrong action is performed by the operator.
1 Equipment is damaged. 2 Pipe is damaged.3 Operation is delayed because it is not possible to disconnect the pipes.
Train personnel and double check the operation.
123
MLL
HMM
32 Interference effects from others
Snubbing unit is incorrectly connected.
The operator is distracted, and fails take the right action.
1 Equipment is damaged. 2 Pipe is damaged3 Operation is delayed because it is not possible to disconnect the pipes.
Train personnel and make sure that the work environment is good.
123
MLL
HMM
4 C
onne
ct s
nubb
ing
unit
No. Step Guideword Deviation Possible causes Consequences Action required # S O33 Unclear The pipes are not
disconnected, or they are damaged
Procedures are insufficient as to what torque that should be applied. Pipes might be screwed in the wrong direction.
1 Pipes are damaged. 2 Equipment is damaged. 3 Operation is delayed
Review procedures before starting on the operation, and make sure the pressure outside the drillstring is equal to the one inside the drillstring.
123
LML
MHM
34 Step in wrong place Disconnection is made before the chamber is pressurized.
The wrong sequence given in the procedure.
1 Pipes are damaged2 Equipment is damaged3 Mud loss4 Kicks
Review procedure before starting on the operation.
1234
LMMH
MHLH
35 Wrong action The pipes are not disconnected. Equipment and pipes are damaged.
The wrong torque is specified in the procedure.
1 Pipes are damaged 2 Equipment is damaged3 Operation is delayed
Check procedure before the operation is started.
123
LML
MHM
36 Incorrect information The pipes are not disconnected. Equipment and pipes are damaged.
Too much or too little torque is applied, or the pipes might be screwed in the wrong direction due to incorrect information in the procedure.
1 Pipes are damaged 2 Equipment is damaged. 3 Mud might be lost4 Kicks may occur.
Make sure that the pressure outside and inside the drillstring is equal, and that the right amount of torque is given before action is taken.
1234
LMMH
MHLH
37 Step omitted The pipes are not disconnected.
Step is omitted in the procedure or by the operator
1 Operation is delayed because the pipes are not disconnected.2 Pipes are damaged3 Equipment is damaged if lifting is performed and the pipes are not disconnected.
Review procedure and have a second person making sure the pipes are disconnected.
123
LLM
MMH
38 Step unsuccessful The pipes are not disconnected, or they are damaged
The operator fails to take the right action.
1 Pipes are damaged. 2 Equipment is damaged.
Train personnel. 12
LM
MH
39 Interference effects from others
The pipes are not disconnected, or they are damaged
Operator is distracted during the operation, and fails to take the right action.
1 Pipes are damaged. 2 Equipment is damaged.
Train personnel, and evaluate at the work environment.
12
LM
MH
5 D
isco
nnec
tion
of p
ipes
No. Step Guideword Deviation Possible causes Consequences Action required # S O40 Unclear Pipes are in wrong position.
Equipment is damaged.Equipment that should have been activated is not clearly specified. The end position of the pipes and the speed used to move the pipes with are not clearly defined.
1 Equipment is damaged. 2 Pipes are damaged. 3 Operation is delayed.
Review procedures before starting on the operation.
123
MLL
HMM
41 Step in wrong place The pipes are lifted before pipe ram is disconnected.
Wrong sequence is given in the procedure.
1 Equipment is damaged2 Pipes are damaged
Review procedure before action is taken.
12
ML
HM
42 Wrong action Pipes are in wrong position. Wrong position is given in the procedure.
1 Operation is delayed. 2 Equipment is damaged 3 Pipes are damaged
Review procedures before starting on the operation.
123
LML
MHM
43 Incorrect information Pipes are in wrong position.Equipment and pipes are damaged.
Wrong position is given in the procedure.
1 Equipment is damaged2 Pipes are damaged
Review procedure before starting on the operation.
12
ML
HM
44 Step omitted Pipes are not lifted. Step is omitted in the procedure or by the operator.
1 Pipes are damaged if the blind ram is closed. Lost control of the pressure downhole. The pressure might exceed/undergo the drilling window which might lead to;2 Mud loss3 Kicks
Review procedure, and have an extra person to check on the operation.
123
LMH
MLH
45 Step unsuccessful Upper pipes are in wrong position.
Operator fails to take the right action.
1 Pipes are damaged 2 Equipment is damaged
Train personnel 12
LM
MH
46 Interference effects from others
Upper pipes are in wrong position.
Operator is distracted, and fails to make the right action.
1 Pipes are damaged 2 Equipment is damaged
Train personnel, and evaluate the work environment
12
LM
MH
6 Li
ft up
per p
ipes
No. Step Guideword Deviation Possible causes Consequences Action required # S O47 Unclear Blind ram is not closed, or it
is in the wrong position.The terms used are unclear. The correct pressure that should have been applied is given in a confusing way.
1 Blind ram is damaged Blind ram does not seal between the upper and lower chamber which might lead to;2 Mud loss3 Kicks
Find the right pressure and speed that should have been applied, and make sure that this is stated in a clear manner in the procedure.
123
MMH
HLH
48 Step in wrong place Blind ram is closed before the pipes are connected.
The wrong sequnece is given in the procedure.
1 Equipment is damaged2 Pipes are damaged
Review procedure before action is taken.
12
ML
MH
49 Wrong action Blind ram is not closed, or it is in wrong position.
Wrong action or position is given in the procedure.
1 Blind ram is damaged Chamber is not fully divided and sealed in two separate parts which might lead to;2 Mud loss, or even3 Kicks
Make sure the right positions are given before starting on the operation
123
MMH
HLH
50 Incorrect information Blind ram is in wrong position, or the blind ram is damaged.
Wrong position and closure pressure is given.
1 Blind ram is damaged.The chamber is not divided in two parts, and the blind ram does not seal between the two separate parts. This can create wrong pressure downhole, which might lead to;2 Mud loss or even 3 Kicks
Make sure that the right position and closure pressure is given before starting on the operation.
123
MMH
HLH
* Operation is not delayed for a long time. The valves are rather easy to open and close leading to a lower operation cost than for e.g. the snubbing unit displacement
7 C
lose
blin
d ra
m *
No. Step Guideword Deviation Possible causes Consequences Action required # S O51 Step omitted Blind ram is open. The step is omitted in the
procedure or by the operator The chamber is not divided into two separate parts. This might lead to wrong pressure downhole and further to;1 Mud loss, or even2 Kicks
Review procedure, and have an extra person to check the operation.
12
MH
LH
52 Step unsuccessful Blind ram is not fully closed, or it is damaged.
The operator fails to leave blind ram in right position.
Chamber is not divided into two separate parts. The blind ram does not seal the chambers, which might lead to the wrong pressure downhole and further to;1 Mud loss or even2 Kicks
Train personnel and have a second part to control the operation.
12
MH
LH
53 Interference effects from others
Blind ram is not fully closed, or it is damaged.
Operator fails to take the right action because of distractions.
Chamber is not divided into two separate parts. The blind ram does not seal the chambers, which might lead to the wrong pressure downhole and further to;1 Mud loss or even2 Kicks
Train personnel, and evaluate the work environment
12
MH
LH
* Operation is not delayed for a long time. The valves are rather easy to open and close leading to a lower operation cost than for e.g. the snubbing unit displacement
7 C
lose
blin
d ra
m *
No. Step Guideword Deviation Possible causes Consequences Action required # S O54 Unclear Valve is not closed, or it is
not fully closed.Description of the operation or marking of the valve is insufficient in the procedure.
1 Operation is delayed. *Mud continues flowing through the standpipe and into the chamber. Too much pressure might lead to; 2 Leak through blind ram.3 Leak of mud.4 **Upper chamber might burst.
Review procedures before starting on the operation.
1234
LMLH
LHMH
55 Wrong action Valve is not closed, or it is not fully closed.
The valve is marked wrong in the procedure. The wrong closure pressure is given in the procedure.
1 Operation is delayed. *Mud continues flowing through the standpipe and into the chamber. Too much pressure may lead to; 2 Leak throgh blind ram. 3 Leak of mud.4 Upper chamber might burst **.
Review procedures before starting on the operation.
1234
LMLH
LMMH
56 Incorrect information Standpipe is not sealed Wrong pressure is given 1 Operation is delayed. *Mud continues flowing through the standpipe and into the chamber. Too much pressure may lead to; 2 Leak in the blind ram 3 Leak of mud
Review closing pressure before action is taken
123
LML
LMM
* Operation is not delayed for a long time. The valves are rather easy to open and close leading to a lower operation cost than for e.g. the snubbing unit displacement** Because of the amount of mud and pressure inside the chamber the consequences will be severe
8 a)
Sea
l sta
ndpi
pe
No. Step Guideword Deviation Possible causes Consequences Action required # S O57 Step omitted The standpipe is not sealed. The valve is not closed due to
missing step in the procedure or because the step is omitted by the operator.
1 Operation is delayed. *Mud continues flowing through the standpipe and into the chamber. Too much pressure might lead to; 2 Leak in blind ram. 3 Mud leak.4 Upper chamber might burst. **
Review procedure, train operator, and have an extra person to check the operation.
1234
LMLH
LMMH
58 Step unsuccessful The valve is not fully closed. Wrong action is taken by the operator. The person fails to close the valve completely.
1 Leak of mud.2 Leak in blind ram.
Train personnel. 12
LM
MM
59 Interference effects from others
The valve is not fully closed. Wrong action is taken by the operator. The operator fails to fully close the valve because of distractions
1 Leak of mud.2 Leak in blind ram.
Train personnel, and evaluate the work environment.
12
LM
MM
8 a)
Sea
l sta
ndpi
pe
* Operation is not delayed for a long time. The valves are rather easy to open and close leading to a lower operation cost than for e.g. the snubbing unit displacement** Because of the amount of mud and pressure inside the chamber the consequences will be severe
No. Step Guideword Deviation Possible causes Consequences Action required # S O60 Unclear The chamber is not
depressurized, or not fully depressurized. The drain line is damaged.There is too much flow through the drain valve.
The drain valve in the procedure is marked in a confusing way. Flow rate is not specified clearly in the procedure.
1 Operation is delayedPressure is build up. Too much pressure may lead to;2 Leak of mud through the blind ram 3 Mud spill4 Damage on equipment
Make sure that the valve is marked in the same manner in the procdure, and on the control panel. Review procedure and specifications before action is taken.
1234
LMLM
LMMH
61 Step in wrong place The pressure is not bled of before pipe ram is opened.
Wrong sequence is given in the procedure.
1 Operation is delayed2 Mud is spilled
Review procedures before starting on the operation.
12
LM
MM
62 Wrong action The chamber is not depressurized. There is too much flow through the drain valve.
The valve is marked wrong. The flow rate is specified wrong.
1 Operation is delayed. 2 Damage on equipment3 Mud spill
Review procedure and make sure that the valve is marked correctly, and make sure that the right flow rate is given, before starting on the operation.
123
LML
LHM
8 b)
Ope
n dr
ain
valv
e to
the
uppe
r cha
mbe
r
No. Step Guideword Deviation Possible causes Consequences Action required # S O63 Incorrect information The chamber is not
depressurized.The valve is not fully opened. The wrong amount of mud that is supposed to be drained is given.
1 Operation is delayed2 Mud is spilled
Review procedure before starting the operation.
12
LL
LM
64 Step omitted The valve is in a closed position.
The valve is not opened due to missing step in the procedure, or because the step is omitted by the operator.
1 Operation is delayedPressure is build up. Too much pressure may lead to;2 Leak of mud through the blind ram 3 Mud spill4 Damage on equipment
Review the procedure, and have a second person to check that the valve is in right position.
1234
LMLM
LMMH
65 Step unsuccessful The chamber is not depressurized, or there is too much flow through the drain valve.
Operator fails to leave the valve in right position.
1 Operation is delayed. 2 Damage on equipment3 Mud spill
Train the operator. 123
LML
LHM
66 Interference effects from others
The chamber is not depressurized.
Operator is distracted during the operation
1 Operation is delayed2 Mud is spilled
Review the work environment, and train personnel.
12
LL
LM
8 b)
Ope
n dr
ain
valv
e to
the
uppe
r cha
mbe
r
No. Step Guideword Deviation Possible causes Consequences Action required # S O67 Unclear There is mud in the
standpipe.The standpipe is not bleed of properly because the procedure does not give a clear description on how to perform the operation.
1 Mud is in the standpipe. This might lead to mud spill.
Review procedures before starting on the operation.
1 L M
68 Step in wrong place Standpipe is bled of before the drain valve is opened.
Wrong sequence is given in the procedure.
Chamber is not pressurized properly, which might lead to; 1 Chamber bursting 2 Operation is delayed
Review procedure before the operation is started.
12
HL
HH
69 Wrong action There is mud in the standpipe.
The amount of mud in standpipe, and the dimensions of the standpipe given in the procedure is wrong.
1 There is mud in the standpipe. This might lead to mud spill.
Make sure the right measures are made before starting on the operation.
1 L M
70 Incorrect information There is mud in the standpipe.
The wrong amount of mud is given in the procedure.
1 There is mud in the standpipe. This might lead to mud spill.
Make sure the right measures are given and applied to the procedure, before action is taken.
1 L M
71 Step omitted The standpipe is not bled off.
Step is omitted in the procedure, or by the operator
1 There is mud in the standpipe. This might lead to mud spill.
Review procedure and calculations before taking action. Make sure that the pressure is fully bled off.
1 M M
72 Step unsuccessful There is mud in the standpipe.
Operator fails to take the right action.
1 There is mud in the standpipe. This might lead to mud spill.
Train personnel. 1 L M
73 Interference effects from others
There is mud in the standpipe.
Operator fails to take the right action, because he is distracted.
1 There is mud in the standpipe. This might lead to mud spill.
Train personnel, and review the work environment.
1 L M
8 c)
Ble
ed o
f sta
ndpi
pe
No. Step Guideword Deviation Possible causes Consequences Action required # S O74 Unclear Snubbing unit is not
disconnected, or it is disconnected wrong.
The operation is not clearly specified in the procedure.
1 Operation is delayed2 Equipment is damaged 3 Pipes are damaged
Check procedures and clarify the steps before starting on the operation.
123
L ML
MHM
75 Wrong action Snubbing unit is not disconnected correctly.
The step specified in the procedure is wrong.
1 Pipes are damaged 2 Equipment is damaged
Check the procedure and make sure the steps are right before action is taken.
12
LM
MH
76 Incorrect information Snubbing unit is not disconnected correctly.
Incorrect information as to the pressure and operation is given in the procedure.
1 Damaged pipes 2 Damaged equipment
Check procedure before starting on the operation.
12
LM
MH
77 Step omitted Snubbing unit is not disconnected.
Step is omitted in the procedure, or by the operator
1 Operation is delayedIf the pipes are removed before the snubbing unit is removed, there will be;1 Damage on pipes 2 Damage on equipment
Review procedure and check, and make sure that the equipment is properly disconnected.
123
LLM
MMH
78 Step unsuccessful Snubbing unit is not disconnected correctly.
The wrong action is taken. 1 Damaged pipes 2 Damaged equipment
Train personnel, and double check the operation.
12
LM
MH
79 Interference effects from others
Snubbing unit is not disconnected correctly.
Operator is distracted during the operation.
1 Damaged pipes 2 Damaged equipment
Train personnel, and review at the work environment.
12
LM
MH
9 a)
Dis
conn
ect s
nubb
ing
unit
No. Step Guideword Deviation Possible causes Consequences Action required # S O80 Unclear Upper pipe ram is not
opened. Not opened fully Not clearly specified in the procedure. Wrong ram is opened. Pressure given in an confusing way
Not cleared from the pipe, or in wrong position, might lead to damage on;1 Pipe2 Equipment
Check procedures and clarify the steps and pressures before starting operation
12
LM
MH
81 Step in wrong place Pipe ram is opened before the chamber is depressurized
Wrong sequence in the procedure
1 Mud spill 1 H H
82 Wrong action Upper pipe ram is not opened. Not opened fully
The wrong pipe ram is given in the procedure or the wrong position is given.
Not cleared from the pipe, or in wrong position, might lead to damage on;1 Pipe2 Equipment
Review procedure before starting operation
12
LM
MH
83 Incorrect information Upper pipe ram is tightened. Not opened fully
Pressure and position is incorrect specified
Not cleared from the pipe, or in wrong position, might lead to damage on;1 Pipe2 Equipment
Review information given in procedure, and make sure they are right before action is taken.
12
LM
MH
84 Step omitted Upper pipe ram is closed Step is omitted in the procedure or by the operator
Not cleared from the pipe, might lead to damage on;1 Pipe2 Equipment
Review procedure and make check that the right position is achieved.
12
LM
MH
85 Step unsuccessful Upper pipe ram in wrong position
Operator fails to take the right action.
1 Pipe is damaged2 Pipe ram is damaged
Train personnel, and double check the positions.
12
LM
MH
86 Interference effects from others
Pipe ram is not closed, or in wrong position
Distraction leads to wrong pipe ram is opened, or pipe ram is placed in wrong position
Not cleared from the pipe, or placed in wrong position might lead to damage on;1 Pipe2 Equipment
12
LM
MH
* If the pipe ram is damaged without being detected, kicks might occur. This is due to difficulties to maintain the right pressure inside the chamber.
9 b)
Ope
n up
per p
ipe
ram
87 Unclear Not in right position Not clearly described in procedure
1 Equipment is damaged 2 Pipe is damaged3 Operation is delayed
Check procedures and clarify the steps and positions before starting operation
123
MLL
HMM
88 Wrong action Pipes in wrong position Wrong position is given. 1 Equipment is damaged 2 Pipe is damaged3 Operation is delayed
Make sure the right positions is given before starting operation
123
MLL
HMM
89 Incorrect information Pipes in wrong position Wrong positions are given 1 Equipment is damaged 2 Pipe is damaged3 Operation is delayed
Review procedure information before action is taken
123
MLL
HMM
90 Step omitted Pipe is not removed Step is omitted in the procedure or by the operator
1 Operation is delayed. Train personnel 1 L L
91 Step unsuccessful Pipes in wrong position Operator fails to take the right action.
1 Equipment is damaged 2 Pipe is damaged3 Operation is delayed
Train personnel 123
MLL
HMM
92 Interference effects from others
Pipes in wrong position Distraction leads the operator to get pipes out of position
1 Equipment is damaged 2 Pipe is damaged3 Operation is delayed
Make sure there is a good work environment and train personnel
123
MLL
HMM
93 Unclear Wrong pipes. Not in correct position
What kind of pipes not clarified in the procedure. Not clearly described in the procedure
1 Equipment is damaged 2 Pipe is damaged3 Operation is delayed
Check procedures and clarify the steps, equipment and positions before starting operation
123
MLL
HMM
94 Wrong action Wrong pipes are added. Pipes in wrong position
Wrong pipes are listed in the procedure. Wrong position and dimensions are given in the procedure
1 Equipment is damaged 2 Pipe is damaged3 Operation is delayed
Review procedure and make sure the right pipes and positions is given before starting operation
123
MLL
HMM
95 Incorrect information Wrong pipes are added. Pipes in wrong position
Wrong pipes are listed in the procedure
1 Equipment is damaged 2 Pipe is damaged3 Operation is delayed
Review procedure 123
MLL
HMM
96 Step omitted New pipe joints are not added
Step is omitted in the procedure or by the operator
Operation is delayed Train personnel 1 L L
97 Step unsuccessful Wrong pipes are added. Pipes in wrong position
Wrong actions are made 1 Equipment is damaged 2 Pipe is damaged3 Operation is delayed
Train personnel, and make sure the communication is good
123
MLL
HMM
10 b
) Add
new
pip
e jo
ints
10 a
) Rem
ove
pipe
98 Interference effects from others
Pipes in wrong positionWrong pipes are added
Distraction leads the operator to get pipes out of position or fails to add the right pipes
1 Equipment is damaged 2 Pipe is damaged3 Operation is delayed
Make sure there is a good work environment and train personnel
123
MLL
HMM
99 Unclear Ram is not closedRam is not in right positionEquipment is damagedPipe is damaged
The terms used are unclear. Correct pressure is given in a confusing way.
1 Operation is delayed. 2 Pipes are damaged3 Pipe rams are damaged4 Pipe rams does not support the pipes, equipment is damaged5 Chamber leaks if pressurized, leading tomud spill
Find right pressure, and speed that should be applied, and apply to the procedures
12345
LLMML
MMHHM
100 Step in wrong place Closed before pipes are in positionClosed after the connection of snubbing unit
Step is listed in the procedure in the wrong sequence
1 Damage on pipes2 Equipment is damaged
Review procedure 12
LM
MH
101 Wrong action Pipe rams are not closed. Closed too fast, too hard, or too loose.
Wrong action is given. Correct pressure is not specified. The right terms are not used
1 Operation is delayed. 2 Pipes are damaged3 Pipe rams are damaged4 Pipe rams does not support the pipes, equipment is damaged5 Chamber leaks if pressurized, leading to mud spill
Find right pressure, and speed that should be applied, and apply to the procedures
12345
LLMML
MMHHM
102 Incorrect information Pipe ram in wrong position Wrong pressure and positions are given
1 Pipe rams are damaged 2 Pipes are damaged. 3 Does not support the pipes, equipment is damaged4 Pressure chamber is not sealed (may lead to mud spill)
Review procedures before starting the operation.
1234
LMML
MHHM
11 a
) Clo
se p
ipe
ram
103 Step omitted Pipe ram is not activated Operator does not activate the pipe ram or it is not documented in the procedure
1 Pipes are not supported, equipment is damaged 2 The chamber is not sealed which may lead to mud spill
Review procedure and train operator. Have an extra person checking.
12
ML
HM
104 Step unsuccessful Pipe ram is not fully closed Operator fails to leave pipe ram in right position.
1 Pipe rams are damaged 2 Pipes are damaged. 3 Does not support the pipes, equipment is damaged4 Pressure chamber is not sealed (may lead to mud spill)
Train personnel 1234
LMML
MHHM
105 Interference effects from others
Pipe ram in wrong position Distraction from other operators leads to wrong action.
1 Pipe rams are damaged 2 Pipes are damaged. 3 Does not support the pipes, equipment is damaged4 Pressure chamber is not sealed (may lead to mud spill)
Train personnel. View work environment.
1234
LMML
MHHM
106 Unclear Snubbing unit is not connected. Not connected the right way.
Procedures are confusing 1 Operation is delayed. 2 Damage on equipment 3 Pipes are damaged
Review procedures before starting the operation
123
LMM
MHM
107 Step in wrong place Snubbing unit is not connected when the chamber is pressurized
Step in wrong place in the procedure
1 Damaged pipes 2 Damaged equipment3 Mud spill
Review procedure and have an extra person looking over it before operation is started.
123
MML
MHM
108 Wrong action Snubbing unit is connected wrong
Wrong instructions 1 Damage on equipment 2 Pipes are damaged
Have an experienced person checking the procedure
12
MM
HM
unit
109 Incorrect information Snubbing unit is not correctly connected
Wrong torque is applied, too much or too little.
1 Damage on equipment 2 Pipes are damaged
Have an experienced person checking the procedure
12
MM
HM
110 Step omitted Snubbing unit is not connected
Step is omitted in the procedure or by the operator
1 Operation is delayed If this is not detected before the chamber is pressurized this might lead to;2 Equipment is damaged 3 Pipes are damaged4 Mud spill
Review procedure 1234
LMML
MMHM
111 Step unsuccessful Snubbing unit is not correctly connected
Wrong torque is applied, too much or too little.
1 Damage on equipment 2 Pipes are damaged
Have an experienced person checking the procedure
12
MM
HM
112 Interference effects from others
Snubbing unit is not correctly connected
Distraction from other operators leads to wrong action
1 Damage on equipment 2 Pipes are damaged
Train personnel and look at the work environment
12
MM
HM
113 Unclear Valve is not closedValve is not fully closed
Procedures are confusing. Valve marked in a confusing way
1 Delay because the drain valve is open or leaks
Review procedures before starting the operation. Check pressure inside the chamber
1 L L
114 Step in wrong place Valve is open when the chamber is pressurized
Wrong sequence in the procedure
Operation is delayed Review procedure 1 L L
115 Wrong action Valve is not closedValve is not fully closed
Wrong thermology is used. Wrong position is given
1 Delay because the drain valve is open or leaks
Review terminology and closing pressure before starting the operation. Check pressure inside the chamber
1 L L
116 Incorrect information Valve is not fully closed. The wrong positions and closuring pressures are given
1 Delay because the drain valve leaks
Review procedure, and check pressure inside the chamber
1 L L
11 b
) Con
nect
snu
bbin
g u
ain
valv
e to
upp
er c
ham
ber
117 Step omitted Valve is not closed Step is omitted in the procedure or by the operator
1 Delay because the drain valve is open
Review procedure, and check pressure inside the chamber
1 L L
118 Step unsuccessful Valve is not fully closed. Operator fails to leave the valve in right position.
1 Delay because the drain valve leaks
Have a second person checking the position of the valve
1 L L
119 Interference effects from others
Valve is not fully closed. Valve is open
Operator is distracted, and fails to make the right action
1 Delay because the drain valve is open or leaks
Look at the work environment
1 L L
120 Unclear Valve in standpipe not openedToo much flowToo little flowNot the right pressure
Valve not properly named. Correct pressure is not specified. Procedures are insufficient with respect to the correct pressure. Can not verify the right pressure
1 The chamber might burst 2 Operation is delayed. Pressure may be too high or too low which during connection might lead to;3 Mud loss 4 Damage on equipment 5 Kicks
Review procedures before starting the operation.
12345
HLMMH
HMLHH
121 Step in wrong place Chamber is not pressurized when blind ram is opened
1 Mud loss 2 Damage on equipment 3 Kicks
Review procedure 123
MMH
LHH
122 Wrong action Chamber is not depressurized. Not fully depressurized, or over pressurized
Right valve is not specified to open. Flow rate is too high or too low. Wrong end pressure is given.
1 The chamber might burst 2 Operation is delayed. Pressure may be too high or too low which during connection might lead to;3 Mud loss 4 Damage on equipment 5 Kicks
Review procedures before starting the operation, and have an extra person checking pressure in the upper chamber
12345
HLMMH
HMLHH
per c
ham
ber
12 C
lose
dra
123 Incorrect information Chamber is not fully pressurized, or pressurized too much
The wrong instruction and information is given in the procedure
1 The chamber might burst Pressure may be too high or too low which during connection might lead to;2 Mud loss 3 Damage on equipment 4 Kicks
Make sure the right pressure is given and review the pressures before action is taken
1234
HMMH
HLHH
124 Step omitted Chamber is not pressurized Step is omitted in the procedure or by the operator
1 Operation is delayedIf the blind ram is opened before detection of the omitted step, this will lead to;2 Mud loss 3 Damage on equipment 4 Kicks
Review procedure. Control the pressure inside the chamber. Have an extra person checking.
1234
LMMH
MLHH
125 Step unsuccessful Chamber is not correctly pressurized
Operator fails to make the wrong action. The chamber is not correctly pressurized.
1 Mud loss 2 Damage on equipment 3 Kicks
Train operator and have a second part checking the operation
123
MMH
LHH
126 Interference effects from others
Chamber is not correctly pressurized
The operator is distracted, and fails to pressurize the chamber correctly
1 Mud loss 2 Damage on equipment 3 Kicks
Have a second part checking the operation, and look at the work environment
123
MMH
LHH
127 Unclear Lower and upper chamber not connected, or not connected in the right way
Blind ram is not opened. Not fully opened. Not clearly specified in the procedure. Pressure given in an confusing way
1 Operation is delayedChamber is still in an upper and lower part. Not connected in the right way, which might lead to; 2 Damage equipment3 Damage on pipe
Check procedures and clarify the steps and pressures before starting operation
123
LMM
LHM
128 Step in wrong place Blind ram is opened before the chamber is pressurized
Wrong sequence in the procedure
1 Mud loss 2 Damage on equipment 3 Kicks
Review procedure 123
MMH
LHH
13 P
ress
uriz
e up
p
129 Wrong action Blind ram is not opened. Upper and lower chamber is not connected the right way
Wrong action or information is given in the procedure.
1 Operation is delayedChamber is still in an upper and lower part. Not connected in the right way, which might lead to; 2 Damage equipment3 Damage on pipe
Control procedures before starting the operation.
123
LMM
LHM
130 Incorrect information Blind ram is in wrong position. Blind ram is damaged
Wrong pressure and position is given in the procedure
1 Operation is delayedChamber is still in an upper and lower part. Not connected in the right way, which might lead to; 2 Damage equipment3 Damage on pipe
Control procedures before starting the operation.
123
LMM
LHM
131 Step omitted Blind ram is not opened. Step is omitted in the procedure or by the operator
1 Operation is delayedChamber is still in an upper and lower part, which might lead to; 2 Damage equipment3 Damage on pipe
Review procedure, train operator
123
LMM
LHM
132 Step unsuccessful Blind ram in wrong position Operator fails to leave the blind ram in right position
1 Operation is delayedChamber is still in an upper and lower part, which might lead to; 2 Damage equipment3 Damage on pipe
Train personnel 123
LMM
LHM
133 Interference effects from others
Blind ram in wrong position Operator is distracted, and fails to make the right action
1 Operation is delayedChamber is still in an upper and lower part. Not connected in the right way, which might lead to; 2 Damage equipment3 Damage on pipe
Train personnel and look at the work environment
123
LMM
LHM
14 O
pen
blin
d ra
m
134 Unclear Pipes are in wrong position. Pipes are moved too fast
Equipment that should be activated are not specified. Position and speed is not clearly defined.
1 Operation is delayed2 Equipment is damaged3 Pipe is damaged
Review procedures before starting the operation.
123
LMM
MHM
135 Step in wrong place Lowered before the blind ram is closed
Wrong sequence in the procedure
1 Pipe is damaged2 Equipment is damaged
12
MM
MH
136 Wrong action Pipes in wrong position. Pipes are moved too fast
Wrong position is given in the procedure. Wrong speed and force is given.
1 Operation is delayed2 Equipment is damaged3 Pipe is damaged
Review procedures before starting the operation.
123
LMM
MHM
137 Incorrect information Pipes in wrong position. Wrong position is given in the procedure. Wrong speed and force is given.
1 Operation is delayed2 Equipment is damaged3 Pipe is damaged
Review procedures before starting the operation.
123
LMM
MHM
138 Step omitted Pipes are not lowered Step is omitted in the procedure or by the operator
1 Operation is delayed Review procedure, train operator
1 L L
139 Step unsuccessful Pipes in wrong position. Operator fails to make the right action.
1 Operation is delayed2 Equipment is damaged3 Pipe is damaged
Train operator 123
LMM
MHM
140 Interference effects from others
Pipes in wrong position Operator is distracted, and fails to make the right action
1 Operation is delayed2 Equipment is damaged3 Pipe is damaged
Train operator, and look at the work environment
123
LMM
MHM
141 Unclear Pipes are not connected properly.
Procedures are insufficient as to torque that should be applied. Too much or too little torque is applied.
1 Pipes leak2 Pipes are damaged. 3 Equipment is damaged. 4 Operation is delayed
Review procedures before starting the operation.
1234
MMML
LMHL
142 Step in wrong place Pipes are not connected before the drain valve is opened
Wrong sequence in the procedure
1 Pressure decrease, and kicks might occur.
Review procedure before starting the operation
1 H H
143 Wrong action Pipes are not properly connected.
Wrong torque is given in the procedure, too much or too little. Wrong rotation way is given
1 Pipes leak2 Pipes are damaged. 3 Equipment is damaged. 4 Operation is delayed
Review the procedure before the operation is performed
1234
MMML
LMHL
144 Incorrect information Pipes are damaged Wrong force is specified. 1 Pipes leak2 Pipes are damaged. 3 Equipment is damaged. 4 Operation is delayed
Review the procedure before the operation is performed
1234
MMML
LMHL
15 a
) Low
er th
e pi
pe jo
int
ct p
ipe
join
ts
145 Step omitted Pipes are not connected Step is omitted in the procedure or by the operator
1 Operation is delayed. 2 Pressure downhole may increase and mud be lost. 3 If lower drain valve is opened, the pressure will decrease and kicks might occur.
Review procedure, train operator
123
LMH
LLH
146 Step unsuccessful Pipes are not properly connected.
Operator fails to make the right action.
1 Pipes leak2 Pipes are damaged. 3 Equipment is damaged. 4 Operation is delayed
Train personnel, and have a second person checking
1234
MMML
LMHL
147 Interference effects from others
Pipes are not properly connected.
Wrong sequence in the procedure
1 Pipes leak2 Pipes are damaged. 3 Equipment is damaged. 4 Operation is delayed
Train personnel, and look at the work environment
1234
MMML
LMHL
148 Unclear Valve is not closedValve is not fully closed
Insufficient procedures and marking of valves.
Flow of mud continues. May lead to a higher pressure than wanted;1 Mud spill 2 Chamber might burst
Review procedures before starting the operation. Keep an extra eye on the pressure inside the chamber
12
LH
MH
149 Step in wrong place Valve to lower chamber is closed before blind ram is opened
Wrong sequence in the procedure
Problems controlling the BHP leading to kicks
Review procedure 1 H H
150 Wrong action Valve is not fully closed Wrong position is given Flow of mud continues. May lead to a higher pressure than wanted;1 Mud spill 2 Chamber might burst
Review procedures before starting the operation. Keep an extra eye on the pressure inside the chamber
12
LH
MH
151 Incorrect information Valve is not fully closed. The closuring pressure or position is not correctly given in the procedure
Flow of mud continues. May lead to a higher pressure than wanted;1 Mud spill 2 Chamber might burst
Review procedures before starting the operation. Keep an extra eye on the pressure inside the chamber
12
LH
MH
15 b
) Con
nelv
e to
low
er c
ham
ber
152 Step omitted Valve is not closed Step is omitted in the procedure or by the operator
Flow of mud continues. May lead to a higher pressure than wanted;1 Mud spill 2 Chamber might burst
Review procedures before starting the operation. Keep an extra eye on the pressure inside the chamber. Train personnel
12
LH
MH
153 Step unsuccessful Valve is not fully closed. Operator fails to make the right action.
Flow of mud continues. May lead to a higher pressure than wanted;1 Mud spill 2 Chamber might burst
Train operator, and always keep an eye on the pressure inside the chamber
12
LH
MH
154 Interference effects from others
Valve is not fully closed. Operator is distracted, and fails to make the right action
Flow of mud continues. May lead to a higher pressure than wanted;1 Mud spill 2 Chamber might burst
Train operator, look at the work environment, and always keep an eye on the pressure inside the chamber
12
LH
MH
155 Unclear Chamber is not depressurized. Not fully depressurized. Drain line is damaged. Too much flow
Valve in procedure is marked in a confusing way. Flow rate is not specified, opening in valve not specified
1 Operation is delayedPressure build up. Too much pressure may lead to;2 Leak of mud through the blind ram 3 Mud spill4 Damage on equipment
Check marking and review procedure and specifications before operation is started
1234
LMLM
LMMH
156 Step in wrong place Depressurize of the chamber starts before the connection is made
Wrong procedure sequence 2 Kicks Review procedure before the operation is started.
1 H H
157 Wrong action Chamber is not depressurized. Too much flow
Valve is not correctly marked. Flow rate specified wrong, diameter opening in valve is too small or too wide in the procedure
1 Operation is delayed. 2 Damage on equipment3 Mud spill
Review procedure and make sure valve is marked in the right way in the procedure, and right pressure for the drain line and opening of the valve is given before starting operation.
123
LML
LHM
ed o
f cha
mbe
r16
Clo
se v
al
158 Incorrect information Chamber is not depressurized
Valve is not fully opened. Wrong amount of mud is given
1 Operation is delayed2 Mud is spilled
Review procedure before starting operation
12
LL
LM
159 Step omitted Valve is not opened The valve is not opened due to missing step in the procedure or omitted step by the operator
1 Operation is delayedPressure build up. Too much pressure may lead to;2 Leak of mud through the blind ram 3 Mud spill4 Damage on equipment
Review procedure and have a second person checking.
1234
LMLM
LMMH
160 Step unsuccessful Chamber is not depressurized. Too much flow
Operator fails to leave the valve in right position.
1 Operation is delayed. 2 Damage on equipment3 Mud spill
Train operator 123
LML
LHM
161 Interference effects from others
Chamber is not depressurized
Operator is distracted during the operation
1 Operation is delayed2 Mud is spilled
View the work environment and train personnel
12
LL
LM
162
18 C
lose
dra
in v
alve Step in wrong place Drain valve is closed before
the chamber is depressurized.
Wrong sequence in the procedure
Pressure builds up. Too much pressure may lead to;2 Leak of mud through the blind ram 3 Mud spill4 Damage on equipment
Review procedure before starting the operation
123
MLM
MMH
163 Unclear Snubbing unit is not disconnected, or not disconnected right
Not clearly specified in the procedure.
1 Operation is delayed2 Damage on equipment3 Damage on pipes
Check procedures and clarify the steps before starting operation
123
L ML
MHM
164 Wrong action Snubbing unit is not disconnected correctly
The steps are wrong 1 Damaged pipes 2 Damaged equipment
Check procedure and make sure the steps are right before action is taken
12
LM
MH
165 Incorrect information Snubbing unit is incorrectly disconnected
Incorrect information of pressure and procedure
1 Damaged pipes 2 Damaged equipment
Check procedure before starting the operation.
12
LM
MH
17 B
lee
t snu
bbin
g un
it
166 Step omitted Snubbing unit is not disconnected.
Step is omitted in the procedure or by the operator
1 Operation is delayedIf the pipes are removed before snubbing unit is removed, it will be2 Damage on pipes 3 Damage on equipment
Review procedure and check that the equipment is disconnected.
123
LLM
MMH
167 Step unsuccessful Snubbing unit is not disconnected correctly
Wrong action is taken. 1 Damaged pipes 2 Damaged equipment
Train personnel, double check operation.
12
LM
MH
168 Interference effects from others
Snubbing unit is not disconnected correctly
Operator is distracted during the operation
1 Damaged pipes 2 Damaged equipment
Train personnel, and look at the work environment
12
LM
MH
169 Unclear Pipe slips are not disconnected, or not disconnected right
Not clearly specified in the procedure.
1 Operation is delayed2 Damage on equipment3 Damage on pipes
Check procedures and clarify the steps before starting operation
123
L ML
MHM
170 Wrong action Pipe slips are not disconnected correctly
The steps are wrong 1 Damaged pipes 2 Damaged equipment
Check procedure and make sure the steps are right before action is taken
12
LM
MH
171 Incorrect information Pipe slips are incorrectly disconnected
Incorrect information of pressure and procedure
1 Damaged pipes 2 Damaged equipment
Check procedure before starting the operation.
12
LM
MH
172 Step omitted Pipe slips are not disconnected.
Step is omitted in the procedure or by the operator
1 Operation is delayedIf the pipes are removed before pipe slips are removed, it will become;2 Damage on pipes 3 Damage on equipment
Review procedure and check that the equipment is disconnected.
123
LLM
MMH
173 Step unsuccessful Pipe slips are not disconnected correctly
Wrong action is taken. 1 Damaged pipes 2 Damaged equipment
Train personnel, double check operation.
12
LM
MH
174 Interference effects from others
Pipe slips are not disconnected correctly
Operator is distracted during the operation
1 Damaged pipes 2 Damaged equipment
Train personnel, and look at the work environment
12
LM
MH
175 Unclear Pipe rams are not opened. Not opened fully
Not clearly specified in the procedure. Pressure given in an confusing way
1 Damaged pipes 2 Damaged equipment
Check procedures and clarify the steps and pressures before starting operation
12
LM
MH
19 D
isco
nnec
t20
Dis
conn
ect p
ipe
slip
s
176 Step in wrong place Not opened before the procedure continues. Opened before the pressure is bled off
Wrong sequence in the procedure
1 Damaged pipes 2 Damaged equipment3 Mud spill
Review procedure and monitor the pressure inside the chamber
123
LMM
MHM
177 Wrong action Pipe rams are not opened. Not opened fully
Wrong position is given in the procedure.
1 Damaged pipes 2 Damaged equipment
Review procedure before starting operation
12
LM
MH
178 Incorrect information Pipe rams are tightened. Not opened fully
Pressure and position is incorrect specified
1 Damaged pipes 2 Damaged equipment
Review information given in procedure, and make sure they are right before action is taken.
12
LM
MH
179 Step omitted Pipe rams are closed Step is omitted in the procedure or by the operator
1 Damaged pipes 2 Damaged equipment
Review procedure and make check that the right position is achieved.
12
LM
MH
180 Step unsuccessful Pipe rams in wrong position Operator fails to make the right action.
1 Damaged pipes 2 Damaged equipment
Train personnel 12
LM
MH
181 Interference effects from others
Pipe rams in wrong position Operator fails to make the right action, because of disturbing factors
1 Damaged pipes 2 Damaged equipment
Train personnel and look at the work environment
12
LM
MH
21 O
pen
pipe
ram
s
C Description of various accident investigation methods
C.1 Events and causal factors charting
Events and causal factors charting (ECFC) is a method to identify multiple failure causes. It gives agraphical illustration of event sequences necessary and sufficient for an accident to occur.
The method is used to determine causal factors by identifying events and conditions that lead to theaccident.
Figure 10 presents symbols and guidelines used to prepare the events and causal factors chart. Anillustration of the chart is given in figure 11. The elements used in this illustration, are explained infigure 10. The graphing is a dynamical process to ensure that the investigation is done in a best pos-sible manner, and that the investigators have a clear representation of accident chronology for use inevidence collection and witness interviewing [12].
Figure 10: Guidelines and symbols for preparing an events and causal factors chart, adapted from [12]
Figure 11: Illustration of events and causal factors chart, adapted from [12]
34
C.2 Sequentially timed events plotting
STEP was developed in 1987 by Hendrick and Benner. The method is a multi-linear method, with par-allel time bases. Different activities, performed by different actors, can take place at the same time. Anactor is a person or an item that directly influence the flow of events leading to an accident. The inves-tigation follows a process view and consists of a STEP-worksheet illustrating different events that occurand the time they take place, see figure 12 [42].
Figure 12: Illustration of a STEP-worksheet, adapted from [42]
Arrows combine the different event relations in the accident chain. The arrow gives an overview ofthe events leading to an accident.
The STEP-method also includes the following truth-testing procedures [42];
1. The row test, which makes sure each actor is broken down sufficiently and that all the events areincluded.
2. The column test, which makes sure the sequences of events are paired with the relevant actions ofother actors. The event is checked by making sure that it is placed right on the time scale relativeto the other events.
3. The necessary-and-sufficient test, which looks at the events leading to next action. It makes surethe relations between events are right. That the event studied is a result of one or more of earlierevents, and which ones.
STEP focuses on actions that leads to the accident rather than the causes [43]. The method is suitedfor systematization of incidents contributing to an accident with respect to time and persons involved[25].
The STEP methodology also includes a recommended method for identification of safety problemsand development of safety recommendations. STEP event set approach is a method which might beused to identify safety problems inherent in the accident process. The analyst follows the chain andmarks on the time line where safety problems occur, and safety recommendations are created [42].
C.3 Man-technology-organisation-analysis
The MTO approach was developed for the Swedish nuclear power industry. The method focuses ontechnical, human and organisational factors.
The method consists of the following elements [26, 42];
1. Description of the chain of events in a block diagram
2. Identification of what caused the accident
3. Identification of barriers that were meant to reveal abnormal situations, but failed to. The barrierscan be technical, human or organisational.
4. Deviation description
35
The first two elements listed above, results in an event and cause chart, the third is a barrier analysisand the fourth is a change analysis. For further explanation of barrier and change analysis see [42].
The method starts by identifying the chain of events and illustrate these in a block diagram. Furtherthe analyst should identify possible technical and human causes for each event and dedicate thesevertically to the relevant events in the diagram, see figure 13. After this is done a barrier analysis oftechnical, human and organisational barriers that have failed, or were not present, should be listed.These are illustrated and placed on the bottom of the worksheet, see figure 13. Deviation description isthe last step that is performed. The deviations and the normal situation is illustrated at top of the eventand cause chart [42].
Figure 13: Illustration of a MTO-worksheet, adapted from [42]
The MTO-analysis includes a checklist to identify failure causes. The checklist contains the follow-ing factors [42];
1. organisation
2. work organisation
3. work practice
4. management of work
5. change procedures
6. ergonomic / deficiencies in the technology
7. communication
8. instructions / procedures
9. education /competence
10. work environment
For each failure cause, there exists a detailed checklist for basic or fundamental causes e.g. deviationfrom work instruction, poor preparation or planning, lack of self inspection, use of wrong equipment,or wrong use of equipment [42].
In the end of the MTO-analysis, recommendations are given. These can be either technical, humanor organisational [42].
36
C.4 Haddon’s Matrix
Haddon’s matrix was developed by W. Haddon in the 1970’s, and is a process method. Accidents aredescribed as a chronological sequence of events [43]. The method was developed for traffic accidents,where the accident was revealed as a result of system failure between driver (human), vehicle (machine),and road and surroundings (environment). The method evaluates the system failures according to anaccidental time axis. This axis is divided into; before, during, and after the event occurred [32]. Haddon’smatrix consist of columns representing the three different system failures, and the rows represent theaccidental time axis [43, 19]. The method is used mainly to map the accident. By combining the matrixwith Haddon’s accident prevention strategies the method can be used for both preventive precautionand minimization of possible consequences if an accident should occur [32].
The accident prevention strategies are based on the "energy - barrier model". The model is a strategyto prevent harmful energy getting in contact with individuals or objects. The 10 strategies are listedbelow, copied from [24];
1. Prevent the build-up of energy
2. Modify the characteristics of the energy
3. Limit the amount of energy
4. Prevent the uncontrolled release of energy
5. Modify the rate and concentration of the energy
6. Separate the source of energy and the potential victim in time or space
7. Separate by means of physical barriers
8. Improve the target’s ability to endure an energy flow
9. Limit the development of injury/damage
10. Stabilize, repair, and rehabilitate
The five first stages are related to the energy source, the sixth and seventh to the barriers, while thelast three are related to the target [24]. The method states in a more detailed manner why the accidenthappened, and is used to reveal precautions that could have prevented the accident from occurring ormitigated the consequences.
37
Part 3 Data collection and a quantitative approach of blowout frequen-cies during UBD and MPD operations
9
1 Data collection
To collect well incident data during UBD and MPD operations, authorities and companies in theU.S., Canada, and Norway, were contacted. To develop a frequency assessment model for UBDand MPD operations, collection of well incidents during these operations were of interest. By an-alyzing accident reports, accident contributing factors along with reservoir characteristics couldhave been identified. A model could have been developed on behalf of these facts, which wouldhave contributed to a better risk understanding of UBD and MPD operations.
In table 1 a list of persons that have contributed information to this paper is given.
Table 1: List of contacts
Contact person E-mail address Company
Per Holand [email protected] ExprosoftDave Samuelson [email protected] EUBDon Buckland [email protected] OGCMelinda Mayes [email protected] MMSMildered Williams [email protected] MMSMurray P. Sunstrum [email protected] Enform
Per Holand, at Exprosoft, is responsible of frequently updating a blowout database owned bySINTEF. This database documents blowouts and well releases world wide. According to him, noblowouts are recorded in the database during UBD or MPD operations. Accident investigationreports from 2003 until present were examined, but no well incidents with use of UBD or MPDtechnology was found.
No blowouts during UBD operations has been revealed. Dave Samuelson from EUB stated thatthere have occurred two well incidents with use of MPD.
In Canada, far more wells have been drilled with use of UBD and MPD technology than on theNorwegian continental shelf. On the Norwegian continental shelf, the use of UBD and MPD havebeen in cases that are not technologically possible to drill OB. This is not necessary the case inCanada. The risk is greater in UBD and MPD operations performed on the Norwegian continentalshelf. Regardless of this, data from Canada was evaluated during this project.
Well incidents that has occurred in Canada with use of MPD technology;
1. One incident occurred in 2002, and was the result of the bottom hole assembly separatingfrom the drill string during tripping. The rig crew was unaware of this when they becamepipe light with 3 joints left. The string hydraulicked out of the hole.
2. The other incident occurred in 2003, also while tripping. This incident was caused by thecrew shutting in the well with the rotating blowout preventer. The rotating blowout pre-venter failed due to excessive pressure build up. Well control was regained almost immedi-ately by closure of the annular preventer. The accident was classified as a ’blow’, and not ablowout.
EUB have not got a record how many UBD and MPD applications that have taken place inAlberta. It was not until September 2003, EUB revised their well licensing process to include aquestion where the applicant would indicate if UBD operations were planned for the well. Thishas still not been done for MPD operations. Since the question was added, and up to December
10
2006, only 175 applicants indicated they would be conducting UBD operations. The actual numberis expected to be much higher due to rate of penetration application, and air drilling for barefootcompletions. Barefoot completions are open hole completions, which are very common for theCanadian sweet shallow gas targets.
In a period from 2001-2006, the total amount of wells drilled in Alberta were 106 600 accordingto the Canadian Association of Petroleum Producers (CAPP) [6]. EUB’s official number for the sameperiod is 103 163. The number of wells drilled in this period, does not correspond to the CAPP’snumber due to a variety of reasons such as; reentries, resumption of drilling, spud timing (a wellmight be spudded one year, while the rig is released the following year) etc., but they are reasonablyclose. The number of spuds EUB have for 2002 and 2003 is respectively 13 193, and 17 108. It wasnot stated how many of these that were drilled with use of MPD.
2 A quantitative approach of blowout frequencies during UBD and MPDoperations
An other way to quantify the blowout risk during UBD and MPD operations is to look at uncer-tainties related to the fluid flow rate. Fluid flows through a variety of equipment. A blowout mightoccur if critical equipment in the process is incapable of handling the fluid rate. The probability ofa blowout can be calculated by establishing the probability of exceeding critical equipments fluidrate capacity. For instance may the separators flow rate capacity be exceeded. Figure 1 illustratesthe fluid flow from the well into the separator.It is possible to look at reservoirs containing oil, gasand water. To simplify, this discussion will only consider a reservoir containing a low compressiblefluid.
Figure 1: Pressures and flow during UBD operations
The fluid rate running through the separator is given by [3];
11
q = J (pR −pw ) = J∆p (1)
pR is the reservoir pressure, pw is the bottom hole pressure in the well, and J is the productivityindex. The productivity index for oil is given in equation 2. To account for a mixture of liquids, theproductivity index must be modified.
Jo = 2πkh
µoBo(l n rerw
− 34 )
(2)
k is the permeability, h is the formation thickness, µo is the oil viscosity, Bo is the oil formationvolume factor (oil shrinks on the way up), re is the external drainage radius of the well, and rw isthe wellbore radius. It is assumed pseudo steady state, which is applicable for the beginning phaseof the production [3].
The maximum rate a specific separator can handle, qmax , is known. This gives the maximumpressure drawdown, ∆pmax ;
∆pmax = qmax
J(3)
It is assumed that ∆pmax does not exceed the pressure difference between the hole collapsepressure and the pore pressure. If this had been the case, the hole would have collapsed before theseparator capacity was exceeded.
There are uncertainties related to the bottom hole pressure in the wellbore and in the formationpressure. These might be a result of for instance inaccuracies in the measuring equipment and inthe geological estimation of the pore pressure. The uncertainty related to the permeability, k, inequation 2, is disregarded in this paper. The productivity index is assumed constant.
Because there are uncertainties related to the reservoir pressure and the bottom hole pressure,they both have a probability distribution. To determine the pressure drawdown uncertainty, theuncertainties related to the reservoir pressure and the bottom hole pressure needs to be combined.
The reservoir pressures and the bottom hole pressure are independent of each other. If X andY are independent stochastic variables, the variance of aX +bY will be;
V ar (aX +bY ) = a2V ar (X )+b2V ar (Y ) (4)
The variance in the pressure drawdown ∆p, see 1, is;
V ar (∆P ) =V ar (PR )+V ar (Pw ) (5)
The separator can burst if the pressure drawdown,∆p, exceeds the allowed pressure drawdown∆pmax , see equation 3. The probability of a exceeding the separators capacity is;
Pr (∆P >∆pmax ) (6)
In MPD operations ∆pmax equals zero.In MPD operations where the drilling window often is narrow, formation fracture can be a
problem. If the bottomhole pressure exceeds the fracture pressure, the formation will start crack-ing. This might in an extended view, lead to a blowout. Uncertainties are related to the bottom holepressure and the analyzed fracture pressure. The variance of the distribution is found by equation4. The probability of exceeding the fracture pressure is;
12
Pr ((P f −Pw ) < or = 0) (7)
In addition to the flow rate, equipment might have constraints to fluid pressures. The maxi-mum pressure, pmax , equipment can handle, is known. The top pressure is given in equation 8.
pt = pw −ρg h − 1
2fρ
dv2 (8)
pt is the top pressure, ρ is the mud density, g is the gravity force, f is the friction force, and dis a combination of the well diameter and the annulus diameter [1].
Where the velocity, v , is given by;
v = q
A= 2q
πd 2 (9)
A is the areal in the annulus.Equation 8 and 9 gives;
pt = pw −ρg h − 1
2f
ρ
d 5π2 q2h (10)
A blowout might occur if the top pressure exceeds the max pressure of critical equipment. Theprobability of exceeding the max pressure of the equipment is;
Pr(Pt > pmax ) (11)
The same equations 8 - 10 will apply for equipment that is not placed on top of the well. Theonly difference will be the value of the hight, h. The probability calculation in these cases, will bemore complicated.
For a blowout to occur a set of barriers that prevents unwanted situations from happening,must fail. The barriers can be configured in a serial or parallel structure. In figure 2, a fictitiousbarrier example is illustrated.
Figure 2: Barrier diagram
The blowout probability will be in this case will be;
Pr (bl owout ) = (qA +qB −qA qB )qC (12)
By combining the barrier diagram for an actual UBD or MPD operation, with the probabilitiesof exceeding equipments capacity related to fluid flow and pressures, the blowout probability of aUBD or MPD operation can be found.
13
Table 2: Data
Reservoir properties Value SI value
Permeability, k 1000 mD 1E-12 m2
Oil viscosity, µo 0.5 cp 5E-4 N s/m2
Oil formation volume factor, µo 1.4 m3/Sm3 1.4 m3/Sm3
Well bore radius, rw 7 i n 0.1764 mExternal drainage radius, re 3000 f t 914.4 mSeparator flow rate capacity, qmax 1000 Sm3/d 1.1547E-3 Sm3/sFormation thickness, h 100 f t 30.48 m
Table 3: Probability data
Reservoir pressure, mean value 300 barReservoir pressure, standard deviation 1 barBottom hole pressure, mean value 299 barBottom hole pressure, standard deviation 0.5 bar
2.1 Example; probability of exceeding the separators capacity
To illustrate the quantitative approach , an example of the probability of exceeding the separatorcapacity during an UBD operation is given.
Data presented in table 2 and table 3, are normal reservoirs values in the North-Sea. The sepa-rators flow rate capacity value, is assumed.
The probability of exceeding the separator capacity is 0.02. The drawdown probability distri-bution plot is given in figure 3.
Figure 3: Probability plot
14
Table 4: Calculations
Drawdown, mean value 1 barDrawdown, standard deviation 1.12 barProductivity index, Jo 3.506E-3 m/sbarMaximum drawdown, ∆pmax 3.3 barProbability of exceeding the separator capacity 0.02
3 Conclusion and further work
Recommendations to further work on the quantitative approach of blowout frequencies duringUBD and MPD operations, are to;
1. gather uncertainty data.
2. include multiphase flow in the model.
3. develop blowout probabilities for fluid pressure.
4. develop a blowout model for UBD and MPD operations.
References
[1] H. A. Asheim. Brønnproduktivitet – strømning i produksjonsrøyr.http://www.ipt.ntnu.no/ãsheim/info.html, 29.05.2007.
[2] E. Framnes. Plattformtyper og boreutstyr, 4th edition. 2000.
[3] M. Golan and C. H. Whitson. Well Performance, Second Edition. 1996.
[4] Johnny Gundersen. [email protected]. Works in Petroleum Safety Authority Norway,07.05.2007.
[5] F. Jahn, M. Cook, and M. Graham. Hydrocarbon Exploration and Production. 1998.
[6] The Canadian Association of Petroleum Producers (CAPP). Statistical handbook. The Cana-dian Association of Petroleum Producers (CAPP), Calgery, Canada, May 2007.
15
Preparatory study
Master Thesis
Risk Assessment of Underbalanced and Managed Pressure Drilling Operations
Stud.techn. Mari Oma Engevik
2
Preface This report was carried out as a preparation plan for the Master thesis the final year of the Master degree program at NTNU (Norwegian University of Science and Technology). The study was a required task, made to support the work methodology during the projects development. The projects title is; “Risk Assessment of Underbalanced and Managed Pressure Drilling Operations” and was carried out in co-operation with NTNU and Scandpower. Prime and secondary teaching supervisor Marvin Rausand, NTNU, and Alexander Solberg, Scandpower, will be available during the period this project is ongoing.
3
Table of contents 1 Introduction ........................................................................................................................ 4
1.1 Background ................................................................................................................ 4 1.2 Main Goal................................................................................................................... 4 1.3 Approach .................................................................................................................... 4 1.4 Success criteria ........................................................................................................... 4
2 Project planning and control .............................................................................................. 5 2.1 Activity plan – Work Breakdown Structure............................................................... 5 2.2 Work Load.................................................................................................................. 5 2.3 Work Task Analysis ................................................................................................... 5 2.4 Project plan – Gantt diagram...................................................................................... 5
Appendix 1 Work Breakdown Structure................................................................................. i Appendix 2 Work Task Analysis ........................................................................................... ii Appendix 3 Gantt diagram.................................................................................................... xi
4
1 Introduction During the 5th year of master study at NTNU, a Master Thesis will be carried out. In the following report a plan on how the project will be performed is presented.
1.1 Background In recent years, underbalanced drilling (UBD) and managed pressure drilling (MPD) have been developed as alternatives to the traditional overbalanced drilling technique. The techniques have many advantages compared to overbalanced drilling, but the blowout risk during these operations has not fully been understood
1.2 Main Goal The main object of this thesis is to establish a risk evaluation model for UBD and MPD operations compatible with BlowFAM.
1.3 Approach In order to achieve the main goal there will be performed literature studies on UBD and MPD in conformity with incident investigation during these operations. In order to create a generic blowout frequency model compatible with BlowFAM, it is necessary to understand how the program is operates, and the way it works. Because of the scope, not all variants of UBD and MPD operations will be covered in this thesis.
1.4 Success criteria Success criteria related to the project is based on my understanding of technical systems, analytical abilities, and the availability of data and relevant literature.
5
2 Project planning and control
2.1 Activity plan – Work Breakdown Structure Work Breakdown Structure, WBS, gives a segmentation of the different work tasks involved in the project and explains how the project is built up. Appendix 1 contains WBS for this project.
2.2 Work Load The duration of this project is 20 weeks with an estimated consumption of 37, 5 hour each week. According to this the total amount of workload will be 750 hours. A preparatory plan is not a final statement. The project actual performance may vary some from the plan.
2.3 Work Task Analysis Appendix 2 gives a work task description of the activities in WBS.
2.4 Project plan – Gantt diagram A Gantt diagram is a useful tool in order to plan resources and distribute the time available and purposed each project task. The diagram is presented in appendix 3.
i
Appendix 1 Work Breakdown Structure
Figure 1 WBS diagram
ii
Appendix 2 Work Task Analysis Note that in this section the literature study, activity 3, also is included in the duration of activities number 4, 5, 6, 7 and 8.
Activity
1 Preparatory Study Problem: Perform a preparatory study of the project in order to analyse problems and give a description of work that has to be done in order to produce a good result. The study will contain the project tasks and when they are due in time. Purpose:
• Create an overview of the workload • Define each activities goals • Distribute each activities time consume and the amount of work that needs to be done • Create a plan for further following-up
Content: Preparatory Study with problems to be addressed, goals and demarcations Literature:
• Rolstadås, A, Praktisk Prosjektstyring, 2001 • Various literature
Method of work: • Create a plan on how the project will be completed • Give a problem description • Create WBS, CTR and Gantt-diagram
Challenges: • Create a functioning preparatory study where the work amount for each activity is
properly managed. Results:
• Plan on how to perform the project • Definition of problems and work load for each activity
Duration: Hours Start Finish 22,5 22.01.07 24.01.07
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Activity
2 Progress Report
Problem: Prepare a report considering the projects progress, time consumes and modifications compared with the preparation plan. Purpose:
• View the projects progress, consider derogations and prepare corrections Content:
• Status report; gives an overview of the projects progress. • The report will also show variances that might have occurred regarding the paper and
project goals.|| Literature:
• Rolstadås, A, Praktisk Prosjektstyring, 2001 • Various literature
Method of work: • Compare the preparation report with the projects actual progress
Challenges: • Create good solutions as for how to solve possible derogations.
Result: • A report considering the projects progress along with possible derogations compared
to the preparation plan. If derogation, these will be explained, and correction plans will be stated.
Duration: Hours Start Finish 7,5 16.03.07 16.03.07
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Activity
3 Literature Study
Problem: Gather and seek literature for use in the project Purpose:
• Find and present relevant literature Content:
• Gather information from different sources. The literature should be of high quality and create a good foundation in the project.
Literature: Method of work:
• Seek information from Internet • Seek information on BIBSYS • Communicate with competent persons • Technical and Scientific literature • Gather information from reports
Challenges: • Gather the literature of high quality • Sort and select relevant and good literature
Result: • Create a technical and professional basis for the project
Duration Hours Start Finish 352,5 15.01.07 11.05.07
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Activity
4 Describe UBD and MPD
Problem: Learn and describe, on a theoretical level, technology and procedures that are used for UBD and MPD. Purpose:
• Look at different methods and technologies used in offshore industry • Get provided with information on how things work and how they are performed
Content: • Description of UBD and MPD technology and procedures
Literature: • Research papers • Various literature regarding the subject • Persons with competence
Method of work: • Read relevant literature and meet with competent experts. • Get an overview of the technology and different methods and equipment that is need. • Get familiar with UBD and MPD procedures
Challenges: • Understand the various technologies and technical terms • Get an overview of the different UBD and MPD operations • Find relevant literature
Results: • An overview of different methods and technologies that exist on UBD and MPD. • Describe procedures during these operations
Duration: Hours Start Finish 127,5 15.01.07 09.02.07
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Activity
5 Hazardous events during UBD and MPD
Problem: Identify and describe hazardous events during various steps of a UBD and MPD operation. Purpose:
• To create a risk picture of UBD and MPD operations. • Establish hazardous events
Content: • Hazard identification by use of an analytical tool
Literature: • Various literature on risk analysis method • Communication with experts • Available field performance data
Method of work: • Choose an analytical method suitable for hazard identification • Perform a hazard identification and description by using the analytical tool, interview
relevant persons, and analyse available field performance data Challenges:
• Evaluate which method that is best suited • Perform a good hazard identification
Results: • Identification and description of hazardous events during UBD and MPD operations • Create a basis for activity 8
Duration: Hours Start Finish 187,5 12.02.07 15.03.07
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Activity
6 Description of relevant well control incidents
Problem: Investigate different well control incidents related to UBD and MPD operations, and describe the root-causes and causal distributions Purpose: Get a better risk picture of UBD and MPD operations and establish which events that are most risk contributing. Content:
• Incidents during UBD and MPD operations • Root-causes and causal distributions related to these incidents • Outline the most important risk contributors
Literature: • Various literature • Incident documentations • Communicate with experts and competent persons
Method of work: • Range different incidents according to size and consequences • Identify root causes and causal distributions • Establish the most important risk contributors
Challenges: • The scope of the analysis • Find data • Find relevant incidents and arrange them into different groups • Create a realistic risk picture in UBD and MPD operations
Result: • What causes well control incidents during UBD and MPD • Causal distributions • Ranking of risk contributing events
Duration: Hours Start Finish 105 19.03.07 13.04.07
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Activity
7 Establish formulas between causes and formation characteristics
Problem: Establish formulas for relations between the causes of well control incident, in activity 6, and formation characteristics. Purpose: Create a plant specific risk picture of UBD and MPD operations Content:
• Formulas reflection relations between incident causes, in activity 6, and formation characteristics
Literature: • Various literature • Competent persons
Method of work: • Look at relation between consequences of well control incidents related to the
formation characteristics • Use a regression program to create a formula reflecting these relations
Challenges: • Get enough data
Results: • Formula reflecting relations between causes of well control incidents and formation
characteristics Duration: Hours Start Finish 75 16.04.07 27.04.07
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Activity
8 Establish generic blowout frequency models compatible with BlowFAM
Problem: Create a blowout frequency model for UBD and MPD which is compatible with BlowFAM Purpose: Further development of BlowFAM in order to include UBD and MPD operations Content:
• Blowout frequencies during UBD and MPD operations • Question list in order to identify plant specific performance • Weighting of different plant specific aspects
Literature: • BlowFAM • Various literature • Literature from activity 5,6 and 7 • Competent persons
Method of work: • Learn how BlowFAM operates • Use results from activity 5, 6 and 7 • Create question lists and weight different outcome
Challenges: • Establish the right questions and give each the right weight
Results: • Blowout frequency model for UBD and MPD operations in BlowFAM
Duration: Hours Start Finish 187,5 30.04.07 01.06.07
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Activity
9 Collocation and printing of project thesis
Problem: Complete and hand in the project thesis and make sure the report is consistent Purpose: Make sure the report is consistent, and it is well written Content:
• Collocation of the report • Print and hand in the project
Literature: Method of work:
• Examine the report and make sure it is consistent and grammatically correct. Challenges:
• Make sure there is none mistakes or defects in the report Results:
• Hand in a well written report within the time limit. Duration: Hours Start Finish 37,5 04.06.07 11.06.07
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Appendix 3 Gantt diagram
Figure 2 Gantt diagram
Progress Report
Master Thesis
Risk Assessment of Underbalanced and Managed Pressure Drilling Operations
Stud.techn, Mari Oma Engevik
Progress According to the preparation study report the following activities should have been completed;
• Activity 1; Preparation study • Activity 2; Progress report • Activity 4; Describe UBD and MPD • Activity 5; Hazardous events during UBD and MPD • Activity 6; Description of relevant well control incidents
At the present moment only activity 1, 2 and is finished. According to the preparatory study the progress report should have been carried out 16/03-07, but the activity was not performed until 16/04-07. Activity 4 and 5 is mainly finished, but some final writing still has to be done. The activities progress is shown in Table 1 below.
Task name Duration[hrs]
% Work Planned Completed
Planned WorkProgress [hrs]
% Work Completed
Actual Work Progress [hrs]
Master Thesis 750,0 65 490,3 62 464,1 Preparatory study 22,5 100 22,5 100 22,5 Preparatory studty hand in 0,0 100 0,0 100 0,0 Progress report 7,5 100 7,5 100 7,5 Progress report hand in 0,0 100 0,0 100 0,0 Literature study 352,5 68 239,7 55 193,9 Report writing and analysis 330,0 55 181,5 40 132,0 Final Report commissioning 37,5 0 0,0 0 0,0 Final report hand in 0,0 0 0,0 0 0,0 Table 1 Work progress (19/04-07) As you cans see from Table 1 the progress has not been as good as planned, but instead of making a new plan I will stick to the original one and try to catch up the undone work.
Deviation The reason the activities are not completed is that the amount of time needed to complete the various tasks has been greater than first assumed. The reason for this is mainly because it has been hard finding relevant literature and getting access to data and procedures.
Figure 1 Gantt-diagram of work progress (19/04-07)
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