Final Seminar Report - Nikhil

of 25

Seminar report on

Drill String Design

Submitted to

University of Pune

In partial fulfilment of ME-II curriculum

Submitted by:

Nikhil G Barshettiwar

ME-II (Fourth semester)

Maharashtra Institute of Technology, Pune

of 25

Certificate

This is to certify that, seminar report entitled Drill string Design submitted by Mr. Nikhil

Barshettiwar, Exam Seat number:5086, ME-II Petroleum Engineering, is a record of bonafide

work carried out by him /her under my supervision, in partial fulfilment for ME Second Year

Course requirement of University of Pune, Pune

Prof Dr. P. B. Jadhav, Prof. Sanjay Joshi

Head, Date: 23 May, 2015

Department of Petroleum Engineering, Seminar Supervisor

MAEERs Maharashtra Institute of Technology,

124, Paud Road, Pune -411038

of 25

Acknowledgement

First and foremost would like to first thank Prof. Sanjay Joshi for guiding me through my

Masters. It is through his patience and teaching that I could reach here to present a seminar on

Drill String Design.

I am extremely grateful to entire Petroleum Engineering faculty for their excellence in guidance.

I firmly believe that they have battered me as petroleum engineer and I will carry with me the

skills that they have given in future work.

Last but not least I would like to thank my parents for encouragement at important junctures of

studies.

Submitted By:

Nikhil G. Barshettiwar

ME-II (Semester IV)

Maharashtra Institute of Technology, Pune

of 25

Contents

SUMMARY .................................................................................................................................... 5

INTRODUCTION .......................................................................................................................... 6

CHAPTER-1 ................................................................................................................................... 7

DRILLSTRING COMPONENTS .................................................................................................. 7

CHAPTER -2 ................................................................................................................................ 14

BOTTOM HOLE ASSEMBLY (BHA) DESIGN ........................................................................ 14

CHAPTER 3 ................................................................................................................................. 17

DRILLPIPE DESIGN ................................................................................................................... 17

CHAPTER 4 ................................................................................................................................. 19

STABILIZER & JAR PLACEMENT .......................................................................................... 19

CHAPTER 5 ................................................................................................................................. 20

CASE STUDY-STRING DESIGN & BHA ANALYSIS ............................................................ 20

REFERENCES ............................................................................................................................. 25

of 25

SUMMARY

This study is mainly focused on Drill String design using most widely used industry based

software LANDMARK (Well Plan). BHA module in Well Plan is three-dimensional analysis of

static BHA subjected to geometry of the wellbore according to inclinations and directions. It uses

finite element analysis to predict the forces generated between the components of BHA and

given wellbore trajectory. The directional tendencies for predicting left or right hand walk rate

also can be determined.

Here in this report, one case study undertaken to do all above mentioned analysis of BHA.

of 25

INTRODUCTION

Effective drill String design is key parameter to complete holes successfully. Improper design of

drill String can lead to catastrophic events while drilling. It consumes more time as well as

money. Following considerations should be made while designing optimum drill string. Well

engineer should keep two important points in mind during designing i.e. maximum stress in drill

string should always be less than yield strength of the components in the string, select

components and configure assemblies to retard fatigue as much as economically practical and if

H2S is expected consider it while designing.

Design procedure includes:

Selection of drill collar diameter, length, grade and connections.

Selection of drill pipe according to sections.

Selection of BHA

Stabilizer and jar placement

Burst pressure

Collapse pressure

Stability forces and drill pipe buckling

Slip crushing

Estimation of allowable load, margin of over-pull

Each of the above parameter is discussed in detail in this report.

of 25

CHAPTER-1

DRILLSTRING COMPONENTS

Heavy wall drill pipe:

Heavy weight drill pipe also called as Heavy weight drill pipe. It is abbreviated to HWDP. It is

an intermediate weight string member. It has heavy wall tubes at the middle called as center wear

joint. At end long tool joints double than tool joints of drill pipe.

Uses:

In case of slim hole drilling where clearance is less HWDP are preferred over Drill

Collars. It reduces chances to become differentially stuck.

In high angle hole because comparatively it is less rigid than DC. Additional

advantage is it has less contact area.

As a transition medium between DP and DC for gradual crossover.

It permits high speed drilling with less torque which ultimately reduces wear and tear

and aids for better directional control.

Since it has easy handling compare to DCs, tripping is comparatively faster.

Figure 1 Heavy weight Drill Pipe

of 25

Stabilizers:

Stabilizers are components in drill string with blades coming out from body. It used in BHA for

directional control. Generally it has same diameter as of the diameter of bit.

When it comes to connection both types of stabilizers are used in string i.e. box-box connection

and pin-box connection. Generally near-bit stabilizers have box-box connection in order to

accommodate pin connection of the bit.

Uses of stabilizers:

Directional control using at different position to get fulcrum, packed hole and

pendulum effect. Fulcrum effect builds an angle. Packed hole (very less distance

between two stabilizers) maintains constant hole angle. Pendulum effect drops the

angle.

It prevents buckling of BHAs in vertical long holes.

Since stabilizer is continuous in contact with wellbore wall, it produces more torque

and drag. Hence it recommended using maximum four stabilizers in BHA.

Stabilization may reduce vibration in BHAs but under certain circumstances.

In deviated wells, there is always one stabilizer on top of the DC in order to prevent

the string being pulled into a key seat and getting stuck.

of 25

Subs:

Cross-over subs

Cross-over subs are short sections of DC material (around 2 ft long) which acts as cross-overs

between different diameters and types of threaded connection. They are available in different

combinations i.e. Pin/pin, pin/box, box/box and box/pin.

Float sub

Float sub is unidirectional valve use above the bit in order to prevent back-flow. Another reason

is to prevent blow-out from the string.

of 25

Dart sub

Dart sub acts as platform or landing sub for a pump down and drop in pressure valves. It is use to

prevent kick through drill-string. The landing sub is installed near the drill collars. Valve is

pumped in dart sub prior to pulling out.

Circulating sub

This sub is optional. This sub can be incorporated in drill-string and in case if required, can be

operated while drilling to provide a large opening to circulate through. When drilling with

directional BHA with mud motor, it is directly run above the MWD sub. In case of rotary drilling

it is directly run above the bit sub.

Generally main principle reasons to use circulating subs are:

o If loss circulation situation is encountered during drilling, loss circulation material is

pumped through the string to cure that zone. Loss circulation material generally has

larger sizes so that they can bridge the zone. Its not possible to pump this material

through bit nozzles as their sizes are small. It can plug the nozzle. In such case circulating

sub can be use to pump coarse material.

o It allows higher flowrate. Higher flow rates are required prior to pulling out of hole for

hole cleaning.

of 25

Bent sub

Bent subs are use in directional assemblies. Bent sub can be supplied with angles of 1-3 degree

with increment of half-degree. Generally bent sub is part of non-rotating directional BHA. Bent

sub also includes a mule shoe sleeve with an alignment key to orient the mule shoe survey barrel.

The mule shoe sleeve is installed inside the bent sub. Sleeve is lined in direction of toolface

orientation. Once survey tools run inside the hole, mule shoe assembly will lock place inside the

mule shoe sleeve.

of 25

Jars and Accelerators:

Bumper sub

Bumper sub has similar OD as DC. It has length around 2 m. The sub is manufactured in two

parts which slides inside each other. The inner mandrel slides w.r.t. outer body. Mandrel striking

with knocker creates impact force.

These subs are generally use for fishing operations where only up jar and up accelerator installed

in the string. Inclusion of bumper sub allows both sides striking on string.

Jars

Jars have same dimensions as of drill collars. They use to create great impact force for freeing

stuck pipes.

Two main sections in jar operation are firing and knocking. A jar is fired by applying an axial

force to it, then waiting for jar latch to release. Cocking is action of resetting the latch. Jars can

give both up and down blows; others can simple give up blows.

Jars are basically categorized as drilling jar or fishing jar. Drilling jars incorporated into string

during normal drilling operations. Thus it is immediately available for freeing of stuck pipe.

Fishing jars are use to for fishing operation to remove left string inside the hole.

of 25

Mechanical Jar

Hydraulic-Mechanical Jar

Double Acting Hydraulic Jar

of 25

CHAPTER -2

BOTTOM HOLE ASSEMBLY (BHA) DESIGN

While designing BHA one should consider performance characteristics of previous BHAs use in

particular area of operations. In case of directional drilling, directional operator can provide the

best performed BHAs. The length of BHAs should be short as possible.

While choosing BHA components generally care should be taken to maintain uniform cross

sectional area though downhole conditions may not allow it. Changes in cross-sectional area of

component parts can result in concentration of bending stresses around the weaker component

which can result in pre-mature fatigue failure. If bending strength ratio is maintained in given

limit then failure can be prevented.

Selecting Drill Collars

Drill collars are most dominant component of any BHA. Selection of DCs depends upon its

weight, shape, diameter and connection. Both slick and spiral DCs are used as BHA component.

Where chances of stuck pipe are high, spiral DCs are preferred.

Recommendations to choose size of DCs:

Hole section (inches) Recommended DC ODs

36 9 + 8

26 9 +8

17 9 +8

12 8

8 6

6 4

Following factors need to be considered for selection of DCs:

Size of Drill Collar:

Size of Drill Collar depends upon the type of formation. Unless differential sticking problem, the

largest diameter DCs consistent with other needs are generally best. Increase in diameter gives

more directional stability. Large OD also decreases buckling stress and the rate of connection

fatigue (As clearance is less).

Bending strength ratio:

BSR is a ratio of relative stiffness of Box to the pin for a given connection type. If the connection

is not properly balanced, weaker component may lead to fatigue. Traditional value of BSR is

around 2.5 which gained from field experience. Actually in theory, higher the value of BSR,

there is higher the risk of pin failure. Lesser the value of BSR, there is higher the risk of box

failure.

of 25

Where, D= outside diameter of box

d= inside diameter of bore

b= thread root diameter of box threads at end of pin

R= thread root diameter of pin threads from shoulder of pin

Recommended value of BSR:

Drill collar OD Traditional BSR range Suggested BSR range

Less than 6 2.25-2.75 1.8-2.5

6-8 2.25-2.75 2.25-2.75

8 and up 2.25-2.75 2.5-3.2

During designing connection between drill collar and heavy weight drill pipe is most overlooked

connection. To maintain proper BSR, bottleneck sub is recommended.

Length of BHA:

Determining length of drill collar section depends mainly of required weight on bit (WOB).

According to shell standard, three types of BHA configuration and design is given below;

Type A: This configuration uses heavy weight drillpipe above the section of drill collars

(DCs). Use of HWDP is only for smooth transition.

Type B: This configuration has only enough DCs for

directional control along with above heavy weight drill pipes. Weight of bit applied by

both DCs and HWDPs. It reduces chance of differential sticking and drill string

failures.

Type C: This configuration has more than one size of

drill collar but weight on bit is applied by drill collar and Heavy weight DPs.

of 25

Design factor is applied is ensure that the neutral point stays in the BHA.

BHA Connection Thread form:

Thread forms should be use which has full root radii in all BHA connections in order to

maximize fatigue resistance. Few such thread forms are API regular, NC and 5 Full Hole

connections meet this requirement. API NC is comparatively superior to the others.

BHA Connection Torsional Strength:

Torque is transmitted from top to bottom of the string. BHA connections are usually subjected to

lower torsional loads compare to connections at the top in the string. But in case of stick/slip

condition, where BHA is stuck at the bottom, torsional strength need to be checked specially if

BHA is running on PAC connections.

Value of f is taken from following table:

DC Type DC OD

6 7/8

PAC f = 0.795 Not available

H-90 f = 0.511 f = 0.562

Other f = 0.568 f = 0.625

of 25

CHAPTER 3

DRILLPIPE DESIGN

Drill pipe design should be carried out for all the wells to be drilled. This design will based on

most expected severe conditions. The selection of basis of various grades to make a string is

always to maintain desired margin of over pull (MOP) at all the points in the string. When doing

this, lowest grade pipe will come above the BHA and higher grades working upwards. Highest

grade should be at the top as it carries whole string weight. Top joint carries weight of BHA plus

remaining drill pipes. When working load of pipe reached, the grade should be upgraded.

Definitions in drill pipe design:

Minimum yield strength

It is a tensile strength of pipe required to produce total elongation of 0.5 % of the gauge length.

Design factor

Design factor use to de-rate the tensile load capacity of the pipe.

Allowable load

Allowable load is de-rated load of the pipe by design factor.

Working load

It is maximum expected load during the operations.

Load calculations:

Tensile loading

In general operations drill pipes are in tension hence they are designed for tension loading. Load

at any point in the string can be calculated as follows;

+Ldp*Wdp+ ......)*BF

In inclined wellbore multiply right hand side with the factor COS (I) where I is inclination of

wellbore.

To prevent permanent deformation of drill pipe, safety factor 90 percent of tabulated tension

value is considered for calculation.

Basically MOP is difference between calculated load and maximum tensile load. MOP is the

margin beyond which extra pull can part the string. General value of MOP is assumed to be

1,00000-1,50000 lb in case of stuck up.

of 25

And safety factor is ratio of allowable load to actual working load.

From above all equations,

Or

As per discussion above, if drill string consist more than one size, pipe having lowest capacity

should be placed just above the BHA. As soon as working load is reached for this grade, it must

be upgraded to higher grade.

Collapse loading

During well testing operations, drillpipe subjected to an external pressure which is greater than

internal pressure resulting in collapse.

Net collapse pressure is as mentioned below,

Burst loading

In general, use of drillpipe in high internal pressure operations should be avoided if gas is source

of the high pressure. General use design factor for burst loading is 1.1.

Combined loading

Combined loading takes effect of axial load on burst and collapse rating of pipe. Tension on pipe

causes stretching of drill pipe, which leads to reduction in its wall thickness. Reduction in

thickness, reduce the collapse strength of pipe. Although there is no effect tension on burst rating

of the drill pipe.

Torsional loading

Torsional loading of drill pipe is critical in deviated holes, deep holes or in case of stuck pipe.

Torque applied to tool joint should not exceed actual tool joint make up torque.

of 25

CHAPTER 4

STABILIZER & JAR PLACEMENT

Stabilizers:

Stabilizer placement often depends on directional requirements. But not only directional hole in

vertical hole also it matters in order to prevent buckling. Stabilizers reduce connection stress by

restricting freedom of lateral drill collar movement. In fact, it helps to increase life of the

connection.

Problem of differential sticking can prevented using large stabilizers as it keeps away the drill

collars from wellbore wall. At the same time, it increases the chances of mechanical sticking as

there is very less clearance, even small caving can pack-off the assembly.

Stabilizer placing plays vital role when it comes to drill collar and wellbore contact. Below

mentioned tables give recommended spacing of stabilizers;

Wellbore inclination between 0-3 degrees:

Hole size (inch) Stabilizer spacing (ft)

120 ft 90 ft 60 ft 30 ft

17 Possible No No No

12 Yes Possible Possible No

8 Yes Yes Possible No

5 Yes Yes Yes Possible

Wellbore inclination between 30-50 degrees:

Hole size (inch) Stabilizer spacing (ft)

120 ft 90 ft 60 ft 30 ft

17 Yes No No No

12 Yes Yes Possible No

8 Yes Yes Yes No

5 Yes Yes Yes Yes

Jar Placement:

According BG drill string design guidelines, it is recommended that drilling jar must be run in all

the assemblies below the surface casing. Long stroke, dual action and hydraulic jars are preferred

design.

In order to get optimized jar performance, jar positioning in BHA matters a lot. Jar should be

run in tension wherever possible. This is compulsory for mechanical jars. Even though hydraulic

jars can be run in compression but it is not preferred to do so. It is bad practice to drill with a

neutral point in jar because jars are comparatively more prone to fatigue failure than drill collars.

of 25

Guidelines for placement of Jar:

Place a jar in BHA such way that neutral point is at least 30 ft below the jar.

Running few drill collars above jar allows jarring upward and downward.

CHAPTER 5

CASE STUDY-STRING DESIGN & BHA ANALYSIS

Statement: Design of drill-string for gas well with depth of 3000 m TVD.

Data Input:

Hole section (inch) Casing shoe

depth (m)

Pore pressure

(ppg)

Mud weight

(ppg)

Fracture Pressure

(ppg)

26 550 m 9 ppg 9.8 ppg 12 ppg

17 1400 m 11.5 ppg 12.3 ppg 14 ppg

12 2400 m 15 ppg 15.8 ppg 18.8 ppg

8 3000 m 15.6 ppg 16.0 ppg 18.8 ppg

String design: According to general rule of thumb required weight on bit (WOB) assumed to be

40,000 lb for string design.

Step 1: Find out buoyancy factor

Step 2: Design BHA which includes selecting number of drill collars, number of heavy water,

Stabilizer and Jar placement.

Step 3: Design of drill pipe

Input data required for BHA design:

1. Find buoyancy factor

Mud weight in use = 16.0 ppg

Buoyancy factor = 0.756

2. Weight on Bit

WOB = 40,000 lb

3. Selection of drill-collars (DC) and HWDP

Since generally shorter the BHA length, easier the handling. Length is restricted to 220 m.

Two equations and two unknowns, we can get the Ldc and Lhwdp.

of 25

Assuming the length of one DC = 9.4 m and one HWDP= 9.14 m (30 ft), lets find out number of

DC and HWDP joints.

- 18 DCs

- 6 HWDP

4. BHA formulation

Tri-Cone Bit

Near Bit stabilizer

Bit Sub

DC*1

IBS

DC*1

IBS

DC*16

Hydraulic Jar

DC*2

HWDP*5

Note: Additional two DCs are added to make sure neutral point stays below Jar.

5. Selecting Drill Pipe

Since of the operators in India preferred using S-135 & G-105 Grade, here S grade is

assumed for string.

Maximum length of S-135 can be used: 23,047 ft

Length to be run to reach TD: 9107 ft

Cumulative string weight in air: 272,516 lb

Cumulative string weight in mud: 205, 886 lb

Hydrostatic pressure at the bottom: 7,556 psi

Maximum length: 12, 054 ft

of 25

REFERENCES

Landmark: Well Plan Manual 2003.1

Shell Well Engineering Design Part- II Distance Learning Module, 1996

BG Drill String Design Manual, 2002

ONGC Drilling Operations Manual

---------------------------------------------------END--------------------------------------------------

Final Seminar Report - Nikhil

Documents

Transcript of Final Seminar Report - Nikhil