Using True Real-Time Data Interpretation to Facilitate Deepwater Drilling

Copyright 2001 AADE National Drilling Technical Conference

This paper was prepared for presentation at the AADE 2001 National Drilling Conference, “Drilling Technology- The Next 100 years”, held at the Omni Houston Westside in Houston, Texas, March 27 - 29,2001. This conference was hosted by the Houston Chapter of the American Association of Drilling Engineers. The information presented in this paper does not reflect any position, claim or endorsementmade or implied by the American Association of Drilling Engineers, their officers or members. Questions concerning the content of this paper should be directed to the individuals listed as author/s of thiswork.

AbstractSignificant challenges in deepwater drilling operations

are exacerbated by narrow operating windows, especiallywhen running synthetic-based muds in the cold-temperature environment. As such, downhole pressuremeasurements provided by PWD (pressure while drilling)have become virtually indispensable. Unfortunately, certaininherent characteristics of PWD technology can restrict oreven prevent its application during critical operations. Anadvanced, real-time hydraulics system (RTHS) has beendeveloped to complement and, in special cases, substitutefor PWD. The RTHS, which has been used successfully inover seven exploratory wells in deepwater to 8,000 ft, is thesubject of this paper.

The RTHS calculates downhole pressure, temperature,and hole-cleaning profiles in true real time based onsurface-measured inputs. Calculated ECDs typically havebeen within 0.1 lb/gal of PWD values during normal drillingoperations. In one case, a well-control situation waspreceded by noticeable differences between measured andcalculated downhole ECDs. In other cases, the RTHS hashelped guide critical casing liner jobs in low-fracture-gradient environments. With no PWD tool installed, theRTHS was uniquely available to provide the instantfeedback needed to minimize potentially serious problems.

The primary focus of this paper is RTHS deepwatercase histories. Some discussion is included regardingbasic modeling, hardware and software descriptions.

IntroductionThe causes and severe consequences of hydraulics-

related problems in deepwater drilling are well known.1,2

Perhaps the most critical problems are associated withnarrow operating windows, created at shallower depths byultra-low fracture gradients and at deeper depths byconvergence of formation pore and fracture pressures.Navigation through these narrow windows is exacerbatedby the dramatic effects of low temperatures on mud densityand rheological properties during drilling and especiallywhen running casing.

Fig. 1 shows low-temperature PVT (pressure-volume-temperature) data taken on a Huxley-Bertram unit for anIO1618 fluid commonly used to formulate deepwater,synthetic-based muds (SBM). Originally built as a HTHP

viscometer, the Huxley-Bertram design incorporates afloating piston mechanism that makes the device ideallysuited for generating PVT data on base fluids and wholemuds. Fig. 2 presents temperature and pressure effectson basic rheological parameters of a 16.0-lb/gal IO1618SBM as measured on a Fann Model 75 viscometer. Bothtest protocols call for circulating anti-freeze solutionrather than water through the respective pressure cellsfor tests run colder than ambient temperature. Theimpact of cold temperatures experienced in deepwater isclearly demonstrated in the two figures. Oneconsequence is that mud weights must be associatedwith the temperature at which they are measured.Another is that rheology on deepwater rigs is nowroutinely measured at three or more differenttemperatures and synchronized with Fann Model 70/75tests run periodically in the lab.

Downhole conditions in deepwater wells (especiallytemperature) acting on the drilling fluid (especiallySBMs) help create complex hydraulic situations andcontribute to recurring drilling problems. Recentadvancements in downhole hydraulics simulation3

certainly have helped. Understandably, the application ofPWD (pressure while drilling) to measure downholepressures has become widespread and an essential partof ECD management in deepwater drilling. However,there are some inherent, indisputable limitations tocurrent PWD technology.

PWD limitations have been targeted by a unique,first-generation computer system4 developed specificallyto complement (but not replace) PWD technology. Thereal-time hydraulics system (RTHS) leverages advancedhydraulics modeling and low-cost, high-powered com-puters. It can provide accurate ECD predictions that areof particular value when a PWD tool is not installed orhas failed, or when measured data are not received atthe surface in real time. If both data are availableconcurrently, such as during conventional drilling, well-site engineers can compare the PWD “what-is” and theRTHS “what-should-be” scenarios in order to makeinformed decisions and identify/prevent problems. Also,the RTHS generates surface-to-TD pressure profiles thataugment the single-position data from the PWD tool andimprove ECD predictions at the casing shoe.

AADE 01-NC-HO-09

Using True Real-Time Data Interpretation to Facilitate Deepwater DrillingMario Zamora and Sanjit Roy, M-I L.L.C.

2 M. Zamora and S. Roy AADE 2001

True real-time hydraulics interpretation is applicable toall types of critical drilling projects4,5, but is of particularbenefit in the high-cost, technically challenging deepwaterenvironment. The RTHS has been used successfully onone land and twelve offshore wells drilled in the US GulfCoast, Norwegian sector of the North Sea, and the Nigeriancontinental shelf. Seven of these wells were drilled indeepwater from 2,100 to 8,000 ft, one by a floater and theother six by the same drillship. The primary goal of thispaper is to present selected case history data from threedeepwater Gulf of Mexico wells. The two wells drilled offNigeria remain tight holes. Some discussion is devoted toRTHS basic modeling, hardware, and software concepts.

RTHS DescriptionThe RTHS is a computer system that uses surface-

measured input data to simulate in true real time thedownhole hydraulics environment of water, oil, andsynthetic-based fluids under extreme pressures andtemperatures (low and high). “True” real time is achieved ifresults can be provided fast enough to actually affectchanges in dynamic processes before their completion.While the acceptable time response for normal drilling canbe minutes or even hours, drillstring connections andcasing jobs require solutions in a matter of seconds forsuitable action to be taken based on the results.

The software consists of two key parts - the underlyingdata acquisition/management system and the engineeringmodeling. The internal data management system is basedon an event-driven, multi-threaded architecture that makesextensive use of low-level Windows API calls. Individualmodules run concurrently and exchange informationthrough shared global memory.

The comprehensive models used by the RTHS havepreviously been validated for offline use in various drillingapplications.3 Key considerations include, among others:

• temperature and pressure effects on downhole muddensity based on a library of PVT data taken oncommonly used base fluids,

• temperature and pressure effects on mud rheologicalproperties based on Fann 35A and Fann 70/75measurements,

• semi-steady-state and transient temperature profilesthat consider complex geothermal profiles,

• multiple rheological models including Herschel-Bulkley, power law, Bingham plastic, and others,

• effect of constricted tool joints on frictional pressures,• transient surge/swab pressures when running casing

and tripping pipe,• flow through special cement fill equipment for liner

jobs, and• fuzzy-logic, hole-cleaning analysis including effects of

inclination, annular velocity, flow regime, mud type,mud properties, well geometry, eccentricity, piperotation, cuttings characteristics, transient cuttingsconcentration, and other parameters.

Considerations for transient behavior are required toadapt and update the models for use in real-timeapplications. If sensors are available to continuouslymeasure inlet mud weight and temperature, thedownhole density of each barrel of mud entering the holecan be dynamically tracked as it circulates throughoutthe well. This clearly is complicated by pipe movementand circulating off bottom. Realistic ESD and ECD(equivalent static and circulating densities, respectively)are then calculated based on transient temperatureeffects on density and rheological properties. The firstcirculation after the mud has been static for a period oftime in deepwater is particularly critical.

The RTHS relies on a continuous stream of qualitysurface data (preferably at 1 Hz or faster) and periodicmanual entries for data not measured by sensors. Ifavailable, some downhole measurements are alsouseful. For example, temperature measurements fromPWD tools or from sensors installed on subsea stackscan be used to calibrate temperature simulations. PWDand subsea-stack pressures are helpful for comparisonand interpretation, but are neither used nor required bythe current calculation module.

Discrete RTHS results can be continually transmittedback into the rig’s data pool within seconds afterreceiving input data. This allows results to be displayedat the driller’s workstation as if they were measured,rather than calculated. ESD and ECD determined at thelast casing shoe, total depth, and PWD-tool location arethe most prominent results provided. The RTHS screenconcurrently displays these and other measured,calculated, and interpreted parameters in graphicswindows configured for drilling, tripping, and otheroperations. Four of these screens are illustrated in Fig.3. Additional screens can easily be customized forspecial applications.

RTHS InstallationThe RTHS uses a conventional Windows NT/2000

computer that typically is installed in the rig’s mud lab ormud-logging unit. Fig. 4 shows schematically how theRTHS can be added to an existing rig data-acquisitionset up using the mud-logging unit as the central datasource. On deepwater rigs, multiple data suppliers arerequired to continuously synchronize, share, and archivethe high volume of measured and calculated data.Target data rate when the RTHS is involved is 1 Hz, butslightly slower speeds are acceptable in certainsituations. For the deepwater wells on which the RTHShas been used, the most difficulties were encounteredwith initial setup and connectivity, including both hard-line connection and data-transfer synchronization.

Connectivity on the floater involved the mud-loggingunit’s proprietary data-transfer protocol using TCP/IPover an Ethernet LAN (local-area network). Thisapproach was superior in terms of simplicity, efficiency,and performance. However, considerable effort was

3 Using True Real-Time Data Interpretation to Facilitate Deepwater Drilling AADE 2001

required to work with the data company (mud logging andPWD) to pre-install and validate their proprietary protocolon the RTHS computer.

The industry standard WITS6 protocol was used on thedrillship. Although a LAN was available, the mud logger atthat time was unable to send WITS over TCP/IP. Instead,communications with the mud-logging unit were conductedserially over fiber-optic cable. Despite the thousands of feetof cable strung throughout the brand-new rig, initially therewas no connection between the RTHS (in the mud lab) andthe mud-logging unit. Running the fiber-optic cable provedto be particularly frustrating, primarily because of thecircuitous path illustrated in Fig. 5, the rig crew’s high workload during the initial rig shakedown, and numerousproblems with connectors and cable integrity. The finalcable connection covered several decks and much of thedrillship’s length.

In a typical installation, calculated RTHS results wouldbe returned to the data source for updating rig-floor andother wellsite workstations. However, a shortage of serialports made it more practical to send ESD and ECD valuesto the PWD unit over TCP/IP for subsequent distribution.

During the time the drillship was operating in the Gulf ofMexico, satellite communications allowed data exchangebetween the rig’s RTHS computer and computers in theoperator’s office on land. Inexpensive, commercial com-munication software was used to transmit the RTHS screendirectly onto an office computer every 2-3 sec. Thisinformation could have been accessed from any computeraround the world that could login behind the operator’sfirewall. Also, the office computer could take control of theRTHS to remotely enter data, fix problems, update files,and conduct other conventional computer operations.

Most of the conventional rig sensors proved adequate.Pipe velocity and acceleration values, calculated from bitdepth, and required for surge/swab pressures while runningcasing were suitable, with few data anomalies. The data-transfer rate can be critical if velocity and accelerationcalculations are not made at or close to the bit depthsensor. Accurate density sensors were only available onone well to measure real-time mud weight in and out.Periodic manual entry of inlet mud weight was required onall other jobs. Clearly, sensitivity was much greater withaccurate sensors, but real-time modeling results withsimulated mud weight “in” values still were quite reasonableoverall. Mud rheology (at multiple temperatures, andatmospheric and high pressures) also had to be enteredmanually, since practical inline viscometers are not yetavailable.

On occasion, problems were encountered with bit depth,one of the two critical variables used to synchronize datafrom different providers (the other is time). Accurate valueswere required for surge/swab calculations. Also, bit depthfrom one vendor was not consistently provided whilemaking connections. During these short periods, it wasimpossible to calculate surge/swab pressures.

Case HistoriesThe seven exploratory deepwater wells on which the

RTHS has been used are summarized chronologically inTable 1. The first well was drilled from a floater in theGulf of Mexico and the final six wells were drilled by thesame deepwater drillship for three different operators.

Overall, calculated ECDs during drilling operationswere typically within 0.1 lb/gal of PWD measurementswhen they were available. Calculated values substitutedwell for PWD when tools were not available orinoperable. Also, the RTHS helped guide several linerruns in narrow pressure-margin environments withminimal or controlled losses.

Case history data presented here are taken fromthree of the Gulf of Mexico wells – labeled C, D, and E inTable 1. Unfortunately, no information can be releasedat this time on the Nigerian wells drilled in Blocks 217and 218. Examples are provided to illustrate (a) how wellRTHS predictions compared to PWD measurements, (b)calculated surge pressures while running casing, (c) useof RTHS to substitute for a failed PWD tool, and (d)transient hole cleaning and its effects on ECD. Figs. 6-10 were drawn from Well D data; Figs. 11-12 from WellE; and Fig. 13 from Well C. Mud-weight and rheologicalproperties are given in Table 2 with reference to thefigure number used in this paper. Note that all the mudswere the same IO SBM that stayed with the drillship.

The following are general comments that apply toFigs. 6-13:

• PWD data (when shown on a graph) isunprocessed and does not include data that isstored but not transmitted to the surface in realtime. These instances, easily recognized asstraight, horizontal lines on the graphs, are usuallyunder no-flow conditions.

• Much of the connection data during drillingsequences do not include surge/swab effectsbecause instantaneous bit depths were notprovided. However, the relatively “flat” lines duringthese periods reflect the calculated, real-time ESDplus cuttings. The associated PWD values shouldbe ignored (see previous comment).

• RTHS ECD is calculated at the PWD tool locationwhen both are provided on the same graph.Otherwise, the ECD is calculated at the last casingshoe depth.

Figs. 6-7, originally presented in a previous paper4,are included here for comparison purposes and tocorrect certain details. The figures summarize operationsin Well D to drill below 20-in. casing and run the 16-in.casing liner to 11,376 ft. The 20-in. casing shoe at10,203 ft initially was tested to 9.65-lb/gal equivalent,and was subsequently retested to 10.0 lb/gal. The planwas to use PWD for ECD management while drilling theinterval with a 20-in. bi-center bit and 9.0-lb/gal @ 58°F

4 M. Zamora and S. Roy AADE 2001

SBM. Unfortunately, the tool was inoperable before startingto drill. Rather than trip in order to repair/replace the tool,the operator decided to rely on RTHS interpretations. Fig. 6is a plot of calculated ECDs at the shoe, penetration rates,and flow rates for a 10-hr portion of that interval. Becauseof ultra-low fracture gradients and indications from theRTHS of steadily increasing cuttings loading, penetrationrates were controlled to reduce ECDs starting at the 3-hrmark on the figure. The noticeably uneven calculated ECDvalues reflect the transient hole-cleaning analysis(illustrated for a different well later in Fig. 13). Beyond theinterval shown in the graph, lost circulation wasencountered while circulating 9.6-lb/gal mud after a shorttrip, at which time it was decided to run casing.

Fig. 7 shows a 16-hr period of running the 16-in. casingliner in Well D. Between the 8 and 12-hr marks on thegraph, casing was run at a gross average speed of 1,050ft/hr with closed preventers and an open line to isolate weakzones downhole while saving running time. Surgepressures during this period, while artificial, still reflect theimpact on the shoe that would have occurred with openpreventers. Below the stack, the casing running speed wasreduced to about 640 ft/hr to minimize losses, although theywere still considerable.

Figs. 8-9 illustrate drilling the 143/4-in. interval andrunning 117/8-in. casing on Well D. The interval shown inFig. 8 from 11,956 to 13,096 ft was drilled at 200-300 ft/hrwith 9.6-lb/gal SBM circulating at about 1,200 gal/min.Correlation between calculated ECD and PWD was verygood. The maximum calculated ECD was 10.09 lb/gal;maximum measured PWD was 10.14 lb/gal. The averagecalculated ESD plus cuttings was 9.93 lb/gal. No holeproblems were encountered until 14,857 ft where circulationwas lost after weighting up to 10.2 lb/gal @52°F. Nearly1,000 bbl of mud were lost cumulatively before runningcasing to 14,814 ft. Fig. 9 is the surge/swab graph for theinterval of 1,583 to 13,422 ft. Mud losses averaged 20 bbl/jt,but the casing was successfully run and cemented.

Fig. 10 presents results from drilling in Well D the 121/4-in. section with a bi-center bit. Penetration rates were about100 ft/hr for the 17,361 to 17,991 ft interval shown on thegraph. Agreement between calculated ECD and PWDmeasurements was excellent, ranging over the interval from10.80 to 10.87 lb/gal and 10.81 to 10.90 lb/gal, respectively.The previous shoe was tested to 11.4 lb/gal. The completeinterval was drilled with no problems.

Fig. 11 compares PWD and RTHS results while drillingthe 17-in. interval in Well E with a bi-center bit. The intervalon the graph is from 12,189 to 12,854 ft. A 16-in. casingliner had been set at 11,565 ft. No drilling problems wereencountered in this hole interval. Average mud weight forthe SBM was 9.9 lb/gal @ 61°F; maximum ECDs at thePWD-tool location were measured at 10.4 lb/gal andcalculated at 10.36 lb/gal. The ESD plus cuttings averagedjust below 10.2 lb/gal.

Fig. 12 data were generated while drilling the 143/4-in.interval in Well E. Agreement was excellent between PWD

and RTHS results for the first 4 hr on the graph.Penetration rates ranged from 100 to 200 ft/hr. Thecalculated increase in annular pressure averaged 0.29lb/gal while circulating the 11.0-lb/gal @60°F SBM atabout 1,100 gal/min. The swivel packing was replacedduring the 4 and 5.5-hr time interval on Fig. 12. Drillingresumed until the well was shut-in on a gas kick at14,523 ft, close to the 9-hr time mark. Note the variancebetween calculated and measured ECDs immediatelypreceding the kick. Unfortunately, this was not picked upat the time, despite the concurrence of otherconventional kick-detection parameters.

Fig. 13 demonstrates how the RTHS softwarehandles transient hole cleaning and illustrates the impacton the ECD profile. The series of graphs represent a 2-hr 13-min time sequence from Well C just below 10,000ft. A 17-in. bi-center bit was used to drill out an 81/2-in.pilot hole. Penetration rate was about 150 ft/hr; flow ratewas 1,100 gal/min. The hole was fairly clean prior tostart of the sequence after conducting coring operations.

Hole-cleaning performance is indicated by a fuzzylogic index where values to the left represent very goodcleaning and values to the extreme right represent verypoor cleaning. In this vertical interval, the hole-cleaningindex was closely related to the cuttings concentration inthe annulus. The ECD scale is 9.5 to 9.8 lb/gal. Notehow newly generated cuttings were circulated up thewell and somewhat redistributed by the drilling process.The impact on the ECD profile also is evident. The slightlateral shifts in ECD curves were caused by changingannular temperature profiles.

Conclusions1. True real-time interpretation of downhole hydraulics

has been successfully applied in seven exploratorywells in deepwater to 8,000 ft in the Gulf of Mexicoand Nigeria continental shelf.

2. This first-generation technology has helped facilitatedeepwater drilling by complementing PWD, andeven substituting for PWD when data were neitheravailable nor transmitted to surface in real time.

3. Downhole ECDs were consistently calculated in realtime to within 0.1 lb/gal of measured values duringnormal drilling operations.

4. Real-time, surge-pressure calculations wereuniquely available to guide casing operations,because no other tools were available to determinethe combined effects of transient downholehydraulics and pipe dynamics.

5. While most conventional rig sensors provedadequate, hydraulics interpretation was improved onone well by the use of an inline sensor to measurereal-time mud weight (in and out).

6. Greatest difficulties with the new computer systemhave been encountered with initial setup andconnectivity, including both hard-line connection anddata-transfer synchronization.

5 Using True Real-Time Data Interpretation to Facilitate Deepwater Drilling AADE 2001

AcknowledgementsThe authors thank M-I L.L.C. for supporting this effort and

giving permission to publish this paper. They also thank theM-I field engineers, data-unit personnel, and rig crews thatdevoted time and effort to this project, and Mary Dimatarisfor helping prepare the manuscript.

References1. Zamora, M., et al.: “The Top 10 Mud-Related Concerns in

Deepwater Drilling,” SPE 59019, SPE International PetroleumConf, Villahermosa, Tabasco, Mexico, 1-3 Feb 2000.

2. Zamora, M. and Roy, S.: “The Top 10 Reasons to RethinkHydraulics and Rheology,” IADC/SPE 62731, IADC/SPE AsiaPacific Drilling Tech Conf, Kuala Lumpur, Malaysia, 11-13Sept 2000.

3. Zamora, M.: “Virtual Rheology and Hydraulics ImproveUse of Oil and Synthetic-Based Muds,” Oil & Gas Journal(3 Mar 1997) 43.

4. Zamora, M., et al.: “Major Advancements in True Real-Time Hydraulics,” SPE 62960, Annual Conf, Dallas, 1-4Oct 2000.

5. Thorsrud, A.K., et al.: “Application of Novel DownholeHydraulics Software to Drill Safely and Economically aNorth Sea High-Temperature/High-Pressure ExplorationWell,” IADC/SPE 59189, IADC/SPE Asia Pacific DrillingTech Conf, Kuala Lumpur, Malaysia, 11-13 Sept 2000.

6. WITS - Wellsite Information Transfer SystemImplementation Guideline, API Publication 3855, version1.1 (July 1991).

Table 1RTHS Deepwater Case Histories

Well ID Location Water Depth (ft) Rig TypeA Gulf of Mexico 2,100 FloaterB Gulf of Mexico 6,663 DrillshipC Gulf of Mexico 7,212 DrillshipD Gulf of Mexico 8,000 DrillshipE Gulf of Mexico 6,286 DrillshipF Nigeria CS 4,793 DrillshipG Nigeria CS 4,200 Drillship

Table 2- Mud Type/Weight and Fann 35A Rheological Properties by Figure Number

Parameter Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig. 11 Fig. 12 Fig. 13Mud Type IO SBM IO SBM IO SBM IO SBM IO SBM IO SBM IO SBM IO SBMS/W Ratio 69/31 72/28 69/31 67/33 70/30 72/28 69/31 73/27Density (lb/gal) 9.0 9.6 9.6 10.2 10.4 9.9 11.0 9.45Density Temp (°F) 58 78 53 54 60 61 60 50Rheology Temp (°F) 150 150 150 150 150 150 150 150R600 46 52 55 52 50 52 57 42R300 31 33 39 34 33 34 38 27R200 25 26 32 27 26 24 30 22R100 18 17 24 18 19 16 25 17R6 11 10 14 14 8 10 19 11R3 10 9 13 12 7 9 17 1010s Gel 12 9 14 14 16 14 24 610m Gel 17 12 19 16 21 18 28 11

6 M. Zamora and S. Roy AADE 2001

0.76

0.77

0.78

0.79

0.80

0.81

0.82

0.83

0 1000 2000 3000 4000 5000 6000

Pressure (psi)

Sp

ecif

ic G

ravi

ty (g

/cm

3 )

33°F

41°F

51°F

75°F

122°F

144°F

Low-Temperature PVT Data for an IO1618 Synthetic Fluid

Fig. 1 - Low-temperature PVT data for an IO1618 synthetic fluid run on a Huxley-Bertram HTHPviscometer.

0

20

40

60

80

100

120

30 40 50 60 70 80 90 100

Temperature (°F)

Pla

stic

Vis

cosi

ty (

cps)

, Yie

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oin

t (l

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4,000 psi

2,000 psi

0 psi

4,000 psi

2,000 psi

0 psi

Temperature and Pressure Effects on 16-ppg IO1618 SBM Rheology

Plastic Viscosity

Yield Point

Fig. 2 – Low-temperature and pressure effects on PV and YP of a 16-lb/gal, 85/15 SWR IO1618synthetic-based mud.

7 Using True Real-Time Data Interpretation to Facilitate Deepwater Drilling AADE 2001

Do

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Fig. 3 - Example RTHS display screens for different operations.

WITS or proprietary protocolSerial or Ethernet connectivity

Driller

PWD Unit

Sensors

Sensors

Sensors

Mud Logger

CompanyManDriller

PWD Unit

Sensors

Sensors

Sensors

Mud Logger

CompanyMan

RTHSRTHSRTHS

Fig. 4 - Typical RTHS installation on deepwater projects.

8 M. Zamora and S. Roy AADE 2001

Fig. 5 - Complex fiber-optic cable connection from RTHS in mud lab to mud-logger data source.

8.9

9.0

9.1

9.2

9.3

9.4

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)

0

1000

2000

3000

4000

5000

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ate

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), R

OP

(ft/

hr*

10)

Calculated ECD @Shoe (10,203 ft)

Measured Flow Rate

Measured ROP*10Calc ECD

ROP

Flow

Fig. 6 - Calculated ECDs at the casing shoe, penetration rates, and flow rates while drilling onWell D.

9 Using True Real-Time Data Interpretation to Facilitate Deepwater Drilling AADE 2001

9.4

9.6

9.8

10.0

10.2

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)

0

500

1000

1500

2000

2500

Flo

w R

ate

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)

Measured PWDFlow RateCalculated PWD

Calc ECD

PWD

Flow

Fig. 8 - Well D RTHS and PWD comparison while drilling 143/4-in. interval from 11,956 to 13,096 ft.

9.0

9.5

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Time (hr)

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)

0

3

6

9

12

Dep

th (

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ft)

Calculated ECD @Shoe (10,203 ft)

Depth (1,500 - 9,835 ft)

Calc ECD

Depth

Fig. 7 - RTHS-calculated surge ECDs for a 16-hr segment while running a casing liner in Well D.

10 M. Zamora and S. Roy AADE 2001

10.2

10.3

10.4

10.5

0 2 4 6 8 10 12 14 16 18

Time (hr)

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ng

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sity

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0

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10

15

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th (

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Depth

Fig. 9 - Well D surge/swab pressures while running 117/8-in. casing from1,583 to 13,422 ft.

10.0

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1250

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Calc ECD

PWD

Flow

Fig. 10 - Drilling 121/4-in. interval 17,361 ft to 17,991 ft on Well D.

11 Using True Real-Time Data Interpretation to Facilitate Deepwater Drilling AADE 2001

9.5

9.7

9.9

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Calc ECD

PWD

Flow

Fig. 11 - Drilling 17-in. interval on Well E from 12,189 to 12,854 ft.

11.0

11.2

11.4

11.6

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0

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Calc ECD

PWD

Flow

Fig. 12 - Drilling 143/4-in. section on Well E from 13,847 to 14,523 ft immediately before kick.

12 M. Zamora and S. Roy AADE 2001

0 0.5 1 0 0.5 1 0 0.5 1 0 0.5 1 0 0.5 1 0 0.5 1 0 0.5 1 0 0.5 1 0 0.5 1

0:46 0:51 1:00 1:11 1:18 1:42 1:58 2:05 2:13

0 0.5 1 0 0.5 1 0 0.5 1 0 0.5 1 0 0.5 1 0 0.5 1 0 0.5 1

0:09 0:14 0:20 0:25 0:28 0:35 0:41

0 0.5 1

0:04

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HCI

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Fig. 13 - 2:13 hr sequence of ECD and hole-cleaning index profiles for Well C in 17-in. hole drilledthrough an 81/2-in. pilot hole.