Institut für Erdöl- und Erdgastechnik Abteilung Erdöl-, Erdgasgewinnung und Erdgasversorgung
Project Assignment
By
International Drillers
Huzaif Memon,
Gohul Dhanarasu,
Faissal Boulakhrif
Roy Radido Okech,
And Muhammad Shahzad,
Stuck Drill Pipe Phenomenon – Solid Buildup
Prof. Dr. Catalin Teodoriu Advanced Drilling Technology – WS 2012/2013
Institute of Petroleum Engineering
Clausthal University of Technology
28/01/2013
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1 Table of Contents
2 INTRODUCTION 3
2.1 PROBLEM DESCRIPTION 3 2.2 OBJECTIVES 3
3 LITERATURE REVIEW 4
3.1 PIPE STICKING 4 3.1.1 COMMON STUCK PIPE SCENARIOS 4 3.2 MECHANICAL PIPE STICKING 6 3.2.1 DRILLED CUTTINGS 6
4 PROJECT OVERVIEW 9
4.1 CUTTINGS TRANSPORT IN DEVIATED WELLS. 9 4.1.1 EFFECT OF MAJOR DRILLING PARAMETERS ON CUTTING TRANSPORT 9 4.2 PROJECT COMPONENTS 10 4.2.1 DIMENSIONS AND SPECIFICATIONS 10 4.2.2 DRAWING AND DESIGN 11 4.2.3 CONSTRUCTION 15 4.1 PRINCIPLE OF OPERATION 19 4.2 SAFETY MEASURES 22
5 DISCUSSION 23
5.1 THE CAUSES OF INADEQUATE CLEANING OF CUTTINGS FROM THE HOLE 23 5.2 THE MAJOR WARNING SIGNS AND INDICATIONS OF CUTTINGS SETTLING 23
6 CONCLUSIONS AND RECOMMENDATIONS 24
6.1 PREVENTIVE MEASURES TO MINIMIZE THE POSSIBILITY OF SETTLED CUTTINGS 24 6.2 RECOMMENDATIONS 24
7 REFERENCES 25
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2 Introduction
2.1 Problem Description
It is almost certain that problems will occur while drilling a well, even in very carefully
planned wells. For example, in areas in which similar drilling practices are used, hole
problems may have been reported where no such problems existed previously because
formations are non-homogeneous. Therefore, two wells close to each other may have totally
different geological conditions.
In well planning, the key to achieving objectives successfully is to design drilling programs
on the basis of anticipation of potential hole problems rather than on caution and
containment. Drilling problems can be very costly. The most prevalent drilling problems
include pipe sticking, lost circulation, hole deviation, pipe failures, borehole instability, mud
contamination, formation damage, hole cleaning, H2S-bearing formation and shallow gas,
and, equipment and personnel-related problems.
Understanding and anticipating drilling problems, understanding their causes, and planning
solutions are necessary for overall-well-cost control and for successfully reaching the target
zone. This project addresses the problem of drilling pipe differential sticking, due to solid
buildups in the wellbore, possible solutions, and preventive measures.
2.2 Objectives
• To design and construct a model wellbore and drilling system.
• To demonstrate the solid buildup phenomenon using the model wellbore system.
• To discuss possible solutions and preventive measures.
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3 Literature Review
3.1 Pipe Sticking
During drilling operations, a pipe is considered stuck if it cannot be freed and pulled out of
the hole without damaging the pipe and without exceeding the drilling rig’s maximum
allowed hook load.
Stuck pipe is one of the more common and serious drilling problems. It can range in severity
from minor inconvenience, which can increase costs slightly, to major complications, which
can have significantly negative results, such as loss of the drill string or complete loss of the
well. A large percentage of stuck pipe instances eventually result in having to sidetrack
around the stuck pipe called a fish and re-drill the interval. Stuck pipe prevention and remedy
are dependent on the cause of the problem. Therefore, to avoid stuck pipe and correct it
efficiently, it is important to understand the various causes and symptoms so that proper
preventive measures and treatments can be taken.
If the pipe becomes stuck, every effort should be made to free it quickly. The probability of
freeing stuck pipe successfully diminishes rapidly with time. Early identification of the most
likely cause of a sticking problem is crucial, since each cause must be remedied with
different measures. An improper reaction to a sticking problem could easily make it worse.
An evaluation of the events leading up to the stuck pipe occurrence frequently indicates the
most probable cause and can lead to the proper corrective measures.
3.1.1 Common Stuck Pipe Scenarios
Stuck pipe can often be freed. However, it is critical first to determine why the pipe is stuck.
Some of the most common stuck pipe situations, with the most common ways to free it, are
as follows:
1. Pipe sticks while tripping into the hole before the bit reaches the casing shoe.
• If it is possible to circulate, the casing probably has collapsed.
• If it is not possible to circulate, and the mud is cement-contaminated or contains a
high lime concentration, the pipe is probably stuck in cement or contaminated mud.
2. Pipe sticks while tripping into the hole (pipe moving) with the bit and BHA below the
casing shoe. It is impossible to rotate the pipe.
• If stuck off bottom, and the BHA has been lengthened or stiffened, the string probably
has been wedged into a dogleg. Circulation should be possible, but may be restricted.
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• If the pipe is stuck close to bottom, it may be jammed into an undergauge hole or
dogleg.
Circulation should be possible, but may be restricted.
• If it is not possible to circulate, pipe is stuck in fill or if the mud has been
contaminated with cement, the mud or cement probably has set up.
3. If the pipe sticks while making a connection or taking a survey.
• If the pipe can be rotated with restricted circulation, it is an indication of rocks,
cement blocks or junk in the hole.
• If the pipe cannot be rotated with full circulation, it is probably differentially stuck.
4. The pipe sticks when circulating kill mud during a well-control operation while the pipe
was not being worked or rotated. It is probably differentially stuck.
5. The pipe sticks while picking up or tripping, and it is still possible to rotate, circulate and
move the pipe a limited amount. It is probably junk in the hole.
6. The pipe sticks suddenly while pulling out of the hole on a trip and cannot be worked up or
down, with full circulation, and usually can be rotated. It is probably key seated.
In general, pipe becomes stuck either mechanically or differentially. Differential
pressure pipe sticking and mechanical pipe sticking are addressed below.
Mechanical sticking is caused by a physical obstruction or restriction. Differential sticking is
caused by differential pressure forces from an overbalanced mud column acting on the drill
string against a filter cake deposited on a permeable formation. Mechanical sticking usually
occurs when the drill string is moving. It also is indicated by obstructed circulation.
Occasionally, however, a limited amount of up/down mobility or rotary freedom is evident,
even when the pipe is mechanically stuck. Differential sticking usually occurs while the pipe
is stationary, such as when connections are being made or when a survey is being taken. It is
indicated by full circulation and no up/down mobility or rotary freedom other than pipe
stretch and torque.
Mechanically stuck pipe can be grouped into two major categories:
1. Hole pack-off and bridges.
2. Wellbore geometry interferences.
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Pack-offs and bridges are caused by:
• Settled cuttings
• Shale instability
• Unconsolidated formations
• Cement or junk in the hole
Wellbore geometry interferences are caused by:
• Key seats
• Undergauge hole
• Stiff drilling assembly
• Mobile formations
• Ledges and doglegs
• Casing failures
3.2 Mechanical Pipe Sticking
The causes of mechanical pipe sticking are inadequate removal of drilled cuttings from the
annulus; borehole instabilities, such as hole caving, sloughing, or collapse; plastic shale or
salt sections squeezing (creeping); and key seating.
3.2.1 Drilled Cuttings
Excessive drilled-cuttings accumulation in the annular space caused by improper cleaning of
the hole can cause mechanical pipe sticking, particularly in directional-well drilling. The
settling of a large amount of suspended cuttings to the bottom when the pump is shut down or
the downward sliding of a stationary-formed cuttings bed on the low side of a directional well
can pack a bottom hole assembly (BHA), which causes pipe sticking. In directional-well
drilling, a stationary cuttings bed may form on the low side of the borehole. If this condition
exists while tripping out, it is very likely that pipe sticking will occur. This is why it is a
common field practice to circulate bottom up several times with the drill bit off bottom to
flush out any cuttings bed that may be present before making a trip. Increases in torque/drag
and sometimes in circulating drill pipe pressure are indications of large accumulations of
cuttings in the annulus and of potential pipe-sticking problems.
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Settled cuttings If cuttings are not removed from the borehole, they accumulate in the well, eventually
causing the hole to pack off, often around the Bottom-Hole Assembly (BHA) and sticking the
drill string. This problem is encountered often in over gauge sections, where annular
velocities are reduced as shown by the calculations below:
Calculation of Velocity of cuttings through the wellbore:
Area between well bore and Drill collar = π / 4 (well bore ID 2 – Drill collar OD 2)
= π / 4 (0.188 2 – 0.18 2)
A = 2.3 x 10 -3 m 2
Area between well bore and Drill pipe = π / 4 (well bore ID 2 – Drill pipe OD 2)
= π / 4 (0.188 2 – 0.05 2)
A = 0.025 m 2
Velocity through drill collar and well bore = Q = VA
1.27 x 10-3 m3/sec = V x 2.3 x 10 -3 m 2
V = 0.55 m/s
Velocity through drill pipe and well bore = Q = VA
1.27 x 10-3 m3/sec = V x 0.025 m 2
V = 0.0508 m/s
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In deviated wells, cuttings will build up on the low side of the hole and may eventually slump
down the hole, causing pack off.
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4 Project Overview
4.1 Cuttings Transport in deviated Wells.
A comprehensive cuttings transport model should allow a complete analysis for the entire
well, from surface to the bit. The different mechanisms which dominate within different
ranges of wellbore angle should be used to predict:
• Cuttings bed heights and annular cuttings concentrations as functions of operating
parameters (flow rate and penetration rate)
• Wellbore configuration (depth, hole angle, hole size or casing ID, and pipe size)
• Fluid properties (density and rheology)
• Cuttings characteristics (density, size, bed porosity, and angle of repose)
• Pipe eccentricity
• Rotary speed
4.1.1 Effect of Major Drilling Parameters on cutting transport
The influence of major drilling parameters on cuttings transport in deviated and horizontal
wells, are presented as follows:
• Mud flow rate – significant positive effect
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• Mud rheology – moderate positive or negative effect depending on cuttings size, pipe
rotation, hole inclination, and annular eccentricity
• Hole angle – significant negative impact with increase in inclination
• Mud weight – small positive impact to moderate positive effect
• Mud type
• Hole size – small to no effect for the same annular fluid velocity
• Rotation Speed – Significant positive effect
• Eccentricity - significant negative effect
• ROP – moderate negative effect
• Drill bit type – unknown influence due to the regrinding of cuttings after they have
been generated
• Cutting size – small negative or positive impact depending on several conditions
In this project, the only variable is the hole angle. All other parameters are kept constant.
4.2 Project Components
4.2.1 Dimensions and Specifications
• Wellbore ID: 18.8 cm = 0.188 m
Wellbore OD: 20 cm = 0.2 m
Length of well bore: 150 cm = 1.5 m
• Drill collar OD: 18 cm = 0.18 m
Length of Drill collar: 50 cm = 0.5 m
• Drill Pipe OD = 5 cm = 0.05 m
• Maximum H: 45m
Maximum Flow rate: 4600 litre/hour = 1.27 x 10-3 m3/sec
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4.2.2 Drawing and Design
3D Model
Wellbore
Drill pipe
Drill collar
Mud pump
Inclined plate
Mud inflow line
Mud tank
Mud outflow line
Annulus
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Cross-sectional Model
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2D Model
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Isometric Model
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4.2.3 Construction
Completed Model Wellbore System
Mud inflow line
Mud pump
Cuttings samples
Drill collar
Drill pipe
Annulus
Mud outflow line
Mud tank
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Wellbore and Drill Pipe
Mud Tank
Mud inflow line
Out flow line
Drill Pipe
Drill Collar
Inclined lever
Pump
Inclined base
Wellbore
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‘Mud’ Tank
Pump
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Lever System
Cuttings Sample
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4.1 Principle of Operation
When the pump is turned on, the mud (water in our case), is pumped inside the
wellbore from bottom, at a rate of 1.27 x 10-3 m3/sec. The mud lifts the cuttings up the
wellbore at a velocity of 0.55 m/s between the well bore and drill collar, and at 0.0508
m/s between the well bore and drill pipe.
This abrupt decrease in velocity causes the cuttings to settle down on the top and sides
of the drill collar. This phenomenon would cause the drill string to stick in the wellbore
during drilling.
Mud circulating the cuttings
The mud attempts to remove the cuttings which are settled on the top and sides of the drill collar.
Drill Pipe
Mud Flow
Mud inflow pipe
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Cuttings Settling-Solid Buildup
Drill collar Top
Cuttings settling on top of the drill collar
Settled cuttings
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Drill String being pulled off bottom to remove stuck cuttings
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4.2 Safety Measures
• Do not attempt to disassemble the electric equipment (pump).
• Equipment must not leak; avoid any fluid spillages on the pump motor.
• Keep your fingers away from the pump during operation.
• Do not operate the pump with wet hands.
• Operate the inclined lever with utmost care.
• Avoid putting your fingers and hands below the inclined plate.
• Do not block the pump motor’s air vents.
• Handle the cart with care while moving from one place to another knocks and bumps.
• It is recommended to use hand gloves while operating the apparatus.
• Eating and drinking is prohibited while operating the apparatus.
• Keep fire extinguishers close during operation, in case of an electrical fire.
• Keep a first aid box close in case of any emergency injuries during operation.
• Do not siphon fluid from the apparatus by use of mouth, use appropriate pipetting tools.
• Ensure the apparatus are kept clean at all times.
• Many other operations normally carried out in the workshop are potentially dangerous.
The greatest care should be taken at all times to ensure your safety and that of others in the
workshop.
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5 Discussion
5.1 The causes of inadequate cleaning of cuttings from the hole
• Drilling at excessive Rates Of Penetration (ROP) for a given circulation rate. This
generates cuttings faster than they can be circulated mechanically from the annulus.
• Inadequate annular hydraulics.
• Failure to suspend and carry cuttings to the surface with adequate mud rheology.
• Highly deviated well paths. High angle wells are more difficult to clean, since the
drilled solids tend to fall to the low side of the hole. Beds of cuttings will form, which
are not easily removed.
• Formation sloughing and packing off around the drill string.
• Not circulating enough to clean the hole before tripping out or making connections.
When circulation is interrupted, cuttings may settle around the BHA and pack off,
sticking the pipe.
• Drilling blind (without mud returns) and not adequately sweeping the hole
periodically with a viscous mud.
• Unintentionally drilling without circulation.
5.2 The major warning signs and indications of cuttings settling
• Fill on bottom after connections and tripping.
• Few cuttings returning at the shakers relative to the drill rate and hole size.
• Increase in torque, drag and pump pressure.
• Over pull on connections and while tripping out.
• Increase in Low-Gravity Solids (LGS) and possible mud weight and/or viscosity
increases.
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6 Conclusions and Recommendations
6.1 Preventive measures to minimize the possibility of settled cuttings
• Maintain proper mud rheology in accordance with hole size, ROP and hole
inclination.
• In near-vertical wells, sweep the hole with high-viscosity mud. In highly deviated
wells, sweep with low-viscosity/high-viscosity pills. Always circulate until the
sweeps have returned to the surface and the shakers are clean.
• Use optimized hydraulics compatible with the respective hole size, inclination and
ROP. Higher circulation rates always provide improved hole cleaning.
• Control drilling in high ROP or marginal hole-cleaning situations.
• Use aggressive drill string rotation for improved hole cleaning.
• Make a wiper trip after all long motor runs.
• Use drill string motion (rotate and reciprocate), while circulating at the maximum rate
to disturb cuttings beds and reincorporate them into the flow stream.
• Inadequate hole cleaning causes overloading of the annulus. In highly deviated or
horizontal wells, this results in the formation of a cuttings bed on the low side of the
borehole.
If the annulus becomes overloaded, attempts to establish circulation must be attempted. In
addition, a downward force should be applied gradually until circulation begins. Once
circulation is established, the drill string should be rotated to further disturb the cuttings. In
low angle holes, a weighted high viscous pill should be used to “float out” the cuttings. In
high angle holes, a low viscous pill should be used to disturb the cuttings bed, followed by
weighted pills to carry the cuttings out of the hole.
6.2 Recommendation
• The project can be modified to include a variable mud pump system, in order to monitor the influence of pump rate on solid buildup.
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7 References
• Petroleum Engineering Handbook, Volume II ( Larry W. Lake)
• MI Swaco Hand books and Manual
• PetroWiki
• petroleumsupport.com
• sereneenergy.org