International Drilling-Solid Buildup Project Report

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