EFFECT OF TOOL JOINTS ON CONTACT FORCE AND AXIAL

FORCE TRANSFER IN HORIZONTAL WELLBORES

(PROPOSAL)

RESEARCHER : Ozgur Bulent DUMAN Petroleum Engineer graduated from Istanbul Technical University, Petroleum and Natural gas Engineering Department, Turkey, in 1997. He had a scholarship from Turkish Petroleum Corporation (TPAO) and joined Tulsa University Drilling Research project (TUDRP) in Spring 99. SPONSOR : TPAO AND TUDRP OBJECTIVES Developments of pipe body-wellbore contact and post-buckling configuration will be observed. Contact forces between tool joints and wellbore will be measured. Axial force transfer through the pipe will be measured. Analytical model will be developed to calculate contact force at tool joints and axial force at the bottom. APPROACH Conduct an extensive review of related literature. Analytical and experimental study of the influence of tool joints on the contact force and axial force transfer. Comparison between the experimental results and analytical models. DELIVERABLES Experimental results and comparison between the analytical model. Development of a computer program to evaluate contact forces, axial forces and critical buckling forces by considering tool joints effect. Semiannual and Final Reports. EXPECTED COMPLETION DATE December 2000

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CONTENTS

INTRODUCTION .............................................................................3

PROBLEM STATEMENT................................................................3

PRELIMINARY LITERATURE REVIEW......................................4

RESEARCH AT TUDRP ..................................................................7

EXPERIMENTAL FACILITY..........................................................7

SCOPE ...............................................................................................7

FIGURES...........................................................................................8

NOMENCLATURE ..........................................................................10

REFERENCES ..................................................................................10

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INTRODUCTION

One of the most important problems in drilling horizontal wells is transmitting the axial

load to the bit. Frictional drag in horizontal wells is bigger than that of vertical or nearly

vertical wells. Frictional forces make it difficult to transfer axial load from the surface to

the bit. Low weight on bit (WOB) decreases rate of penetration (ROP) and results in loss

of money. If the string is buckled helically, the load transmission becomes even more

difficult. Large lateral forces cause excessive drill pipe and tool joint wear. In addition,

helical buckling results in early fatigue and failure of the drillstring and change of bit

angle.

Critical buckling load is very sensitive to the radial clearance. Presence of tool joints will

decrease the radial clearance, consequently, increase the critical buckling load.

Interestingly, this problem has not been paid enough attention.

The oil industry needs an experimentally verified analytical expression for the critical

buckling force and lateral contact force of tool jointed pipe. The first step should be

experimental evaluation of pipe with connectors under the axial compressive load. This

evaluation will provide basis for making improvements in the future.

STATEMENT OF THE PROBLEM

Because of the gravitational forces, pipe lies on the lower side of the hole in horizontal

wells. If coiled tubing is used, pipe contacts the wellbore thorough the horizontal section

of the well (Fig-1). However, if drill pipe is used, pipe contacts the wellbore at tool joints

(Fig-2). Fig-3 illustrates that the deflection of pipe increases with the increase of axial

compression load. The contact point between drillpipe body and wellbore is shown in

Fig-4. Further increase in axial compression load may result in a wrap contact between

pipe body and wellbore (Fig-5).

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Nevertheless, depending on the critical buckling force, wrap contact and even point

contact may not occur. If the critical (sinusoidal) buckling force is low enough, pipe may

buckle laterally (snaking) before the point contact and/or wrap contact occurs.

The sinusoidal buckling force of pipe in horizontal wells is given by Dawson and Paslay1.

rAgSinEIFcrit

2= ............................................................ (1)

is equal to 90 o in horizontal wells.

If the axial force keeps increasing, the deflection will increase, and finally pipe will

buckle into helix. The helical buckling load for long pipes in horizontal wells is given by

Wu and Juwkam-Wold2.

( ) 2121222 = rEIWF ehel ............................................(2)

However, it is unknown whether the aforementioned equations can be applicable to tool

jointed pipe or not. They need to be verified experimentally.

PRELIMINARY LITERATURE REVIEW

Euler3 (1744) found the critical load, depending on the end conditions, for an originally

perfectly straight elastic column.

Lubinski4 (1950) was the first person who introduced a mathematical model of buckling

in the oil and gas well operations. His solution for the critical load of buckling gave

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precise results for short strings. However, his solution didnt give correct results for long

strings.

In 1962, Lubinskis4 classical paper was published. In this paper, he expressed the well-

known force/pitch relationship for helical buckling.

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28p

EIF = ...........................................................................(3)

Lubinskis papers led many authors to develop analytical models of buckling for many

cases.

Cheatham and Pattillo6 (1982) showed that Lubinskis solution could be applicable

during the loading (compression is increasing) whereas their solution is valid during

unloading (compression is decreasing).

2

2

2

2 84p

EIFp

EI ............................................................(4)

There is a factor of two between two cases.

Dawson and Paslay1 (1984) simplified Paslay and Bogys7 result to find the critical

compressive load in inclined holes (eq.1). They stated that the presence of tool joints

would reduce the radial clearance and increase the critical buckling loads. Nevertheless,

no experimental results have been reported to prove this. Schuh8 (1991) presented

equations for curved wellbore and he stated that the Paslay-Dawson1 equation is the best

representation of the buckling phenomenon. Mitchell9 (1996) presented a practical

solution for deviated wells. He expressed some criteria for lateral and helical buckling to

occur in deviated wells.

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Miska and Cunha10-11 (1995) derived new equations to find the critical buckling force.

They included rotary torque effect and concluded that the effect of torque can be

disregarded except at high torque conditions.

Chen12 et al (1990) developed new equations for helical buckling of pipe in horizontal

wellbores.

2

1* 22

=

rEIwF ................................................................(5)

Wu and Juwkam-Wold1,13 proved that the equation developed by Chen12 et al (1990) is

actually the average axial load during the helical buckling process.

Chen and Cheatham14 (1990) investigated wall contact forces on helically buckled

tubulars in inclined wells. Mitchell15 (1988) expressed the most general relationship for

contact forces.

EIrFWn 4

2

= ...............................................................................(6)

Sadiq and Juwkam-Wold16 (1995) derived a lateral contact force equation by using

Lubinskis5 pitch-force equation and verified this with experimental results. They didnt

use tool-jointed pipe in their experiment.

The only study in the literature discussing tool joints effect was presented by Mitchell17

(1999). He derived new equations for calculating the contact force between the tool joints

and wellbore. He suggested that connector radial clearance should be used in lateral

buckling stability criteria, as Dawson and Paslay1 suggested, instead of the pipe body

radial clearance.

No experimental results have been reported to support this theory.

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It can be understood from the analysis of related literature that the effect of tool joints has

not been taken into account yet.

RESEARCH AT TUDRP

An M.Sc. study is currently being conducted to investigate axial force transfer and lateral

contact force through coiled tubing. This study will be extended by including tool joints.

EXPERIMENTAL FACILITY

Tulsa University Drilling Research Project (TUDRP) has an experimental facility (Fig-6)

that will be used for this study. The facility will allow us to measure the axial force

transfer capacity of the pipe and contact forces.

SCOPE

Effect of tool joint on contact force and axial force transfer will be studied. Post-buckling configuration of tool jointed pipe in horizontal wells will be

investigated.

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Lc

fFt Fb

Lc

Ft Fb

f

Fig-2 Drillpipe in a horizontal well

Fig-3 Drillpipe goes under compression in a horizontal well

Ft Fbf

Lc

Fig-1 Coiled tubing in a horizontal well

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Ft Fb

Lc

f

Fig-4 Point Contact between pipe body and wellbore

Ft Fb

Lc

f

Fig-5 Wrap contact between pipe body and wellbore

LoadCell

Lc

F

LoadCell

F

Pump

oo

Fig 6) TUDRP Experimental Facility

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NOMENCLATURE

A=Cross sectional area of pipe, in2. [cm2], E= Youngs modulus, psi [kPa], f=Frictional forces, lbf [N], F= Axial compressive force, lbf [N], F*, Fhel = Helical buckling force, lbf [N], Fcrit = Critical (Sinusoidal) buckling force, lbf [N], g= Gravitational force, lbf [N], I= Moment of inertia, in4 [cm4], Lc= Lateral contact force at tool joints, lbf [N], P= Helical pitch of buckled pipe, in [cm], r= Radial clearance between pipe and hole, in [cm], w= Weight per unit pipe length, lbm/in [kg/cm], Wn= Tubing/Casing contact load per length, lbf/in [N/m], We=Effective weight of pipe per unit length in wellbore, lbf/in [N/m], = Weight per cubic inch, lbm [kg],

REFERENCES

1. Dawson, Rapier and Paslay, P.R., Drillpipe Buckling in inclined Holes, JPT

(October 84).

2. Wu, J., and Juwkam-Wold, H.C., Study of Helical Buckling of Pipes in Horizontal

Wells, paper (SPE 25503) presented at Production Operations Symposium held in

Oklahoma City, Ok, March 21-23,1993.

3. Love, A. E., A treatise on the Mathematical Theory of Elasticity, Dover

Publications Inc., New York City, pp. 3, 405, 414-419,425-426

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4. Lubinski, A., Developments in Petroleum Engineering-Collected works of Arthur

Lubinski, Edited by Stefan Miska, Gulf Publishing Company, 1987.

5. Salies, J.B., Experimental Study and Mathematical Modeling of Helical Buckling of

Tubulars in Inclined Wellbores, Ph.D. Dissertation, Tulsa University Drilling

Research Projects, 1994.

6. Cheatham, J.B., and Pattillo, P.D., Helical Postbuckling Configuration of a

Weightless Column Under the Action of an Axial Load, SPEJ (Aug.1984) 467-72

7. Paslay, P.R., and Bogy, D.B, The Stability of a Circular Rod Laterally Constrained

to Be in Contact with an Inclined Circular Cylinder, Journal of Applied Mechanics

December, 1964 (605-610)

8. Schuh, F.J., The Critical Buckling Force and Stresses for Pipe in Inclined Curved

Bore holes, SPE/IADC Paper No: 21942, presented at the 1991 SPE/IADC Drilling

Conference held in Amsterdam, 11-14 March 1991

9. Mitchell, R.F., Buckling Analysis in Deviated Wells: A Practical Method, SPE

Paper No: 3761, presented at the 1996 SPE Annual Technical Conference and

Exhibition held in Denver, Colorado, 6-9 October 1996.

10. Miska, S. and Cunha, J.C., Helical Buckling of Long Weightless String Subjected to

Axial and Torsional Loads, paper presented at the Drilling Symposium of the

ASME Energy & Environmental EXPO 95, Houston, TX, January 19-February 1,

1995.

11. Miska, S. and Cunha, J.C., An Analysis of Helical Buckling of Tubulars Subjected

to Axial and Torsional Loading in Inclined Wellbore, paper presented at the

Production and Operation Symposium held in Oklahoma city, OK, 2-4 April, 1995.

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12. Chen, Yu-Che, Lin, Yu-Hsu, and Cheatham, John B., Tubing and Casing Buckling

in Horizontal Wells, JPT (February 90).

13. Wu, J., and Juwkam-Wold, H.C. and Lu, R., Helical Buckling of Pipes in Extended

Reach and Horizontal Wells-Part 1: Preventing Helical buckling,, Journal of Energy

Recourses Technology (September 1993), 190-195.

14. Chen, Yu-Che, and Cheatham, John B., Wall Contact Forces on Helically Buckled

Tubulars in Inclined wells, Journal of Energy Resources Technology V112, number

2, pp. 142-144, June 1990.

15. Mitchell, R.F., New Consepts for Helical Buckling, SPEDE (September 1988),

303-310.

16. Sadiq, T. and Juwkam-Wold, H.C., Lateral Contact Force in Horizontal Wells: An

Experimental Study, CADE/CAODC Spring Drilling Conference, Calgary, Canada,

April 1995.

17. Mitchell, R.F., Helical Buckling of Pipe with connectors, SPE/IADC Paper No:

52847, presented at the 1999 SPE/IADC Drilling Conference held in Amsterdam, 9-

11 March 1999