Geothermal Well Casing Buckling

v

c ' ! b d b i A REPORT SAND82-0863

Unlimited Release UC-66c

Printed February 1983

Euler Buckling of Geothermal Well Casing

SAND--82-0863 DE83 010292

Robert P. Rechard, Karl W. Schuler

Prepared by Sandia National Laboratories Albuquerque, New Mexico 87 185 and Llvermore, California 94550 for the United States Department of Energy under Contract DE-AC04-76DP00789

DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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h u e d by Sandin National Laboratories, operated for the United States Department of Energy by Sandia Corporation. NOTICE: This report was repared as an account of work sponsored by an agency of the United States 8overnment. Neither the United States Govemment nor any agency thereof, nor MY of theu em loyees, nor MY of theu contractors,subeontraetora. or their employees,d e s any warranty, express or im lied,or assumes any al liability or responsibility for the accuTBcy, any information,apparatus, product, or procomppeteness,or use*= ceaa Wd, or represents that its use would not infringe privately owned rights. Reference herein to any rpecifk commercial product, proceaa, or trade m e , trademark, manufacturer, or othe-, does not y constitute or imply its endorsement,recommendation,or favoring by the United States Gwernment, any n y q thereof or MY of their contractors or subcontractors. The views an opmions expressed herein do not necessarily state or reflect thcae of the United States Government, any agency thereof or any of their contractors or subcontractom.

3

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NTIS ricecodes Print2 copy A04 Microfiche copy A01

UC-66~

SAND82-0863 EULER BUCKLING OF GEOTHERMAL WELL C A S I N G

R. K.

P.

Rechard

W. S c h u l e r

A p p l i e d Mechanics D i v i s i o n Sandia N a t i o n a l L a b o r a t o r i e s A l b u q u e r q u e , New M e x i c o 87185 HOTICE PORTIONS OF THIS REPQRT ARE ILLEGIELE.

tt has been rcprosfuced from the best available copy to permit the broadest possible avatfability, - . -. _ . . - - . ABSTRACT Geothermal w e l l o p e r a t o r s have expressed concern over t h e v u l n e r a b i l i t y of u n s u p p o r t e d c a s i n g t o b u c k l i n g f r o m t h e r m a l I n t h i s r e p o r t , we p r e s e n t p r e l i m i n a r y n u m e r i c a l elongation. and t h e o r e t i c a l c a l c u l a t i o n s , which i n d i c a t e t h e b u c k l i n g phenomenon s h o u l d n o t b e s e r i o u s i n N-80 c a s i n g i f t h e s t r i n g i s t e n s i o n preloaded. B u c k l i n g w o u l d b e d e t r i m e n t a l f o r ' K-55 casing. The e f f e c t o f w a l l c o n t a c t was f o u n d t o b e b e n e f i c i a l f o r c l o s e l y c o n f i n e d p i p e s t r i n g s and o f n o d e t r i m e n t when h o l e gaps a r e l a r g e . The weakness o f A P I s c r e w j o i n t s i n b e n d i n g appears t o be t h e s t r u c t u r a l l i m i t a t i o n . The a n a l y s i s assumed s t r e s s e s above y i e l d c o n s t i t u t e d f a i l u r e , t h a t t h e r m a l e x p a n s i o n was s t r a i n c o n t r o l l e d , and t h a t t h e c a s i n g was continuous. E x c e s s i v e i n t e r n a l p r e s s u r e i n s t a b i l i t y was ignored. The t e m p e r a t u r e v a r i a t i o n c o n s i d e r e d was b e t w e e n c e m e n t i n g c o n d i t i o n s o f 100-200°F (40-95°C) and s h u t - i n c o n d i t i o n s o f 425-450°F ( 2 2 0 - 2 3 0 ° C )

.

"

CONTENTS

Page

................. . Geothermal Well C o n s t r u c t i o n . . . ...... Well Casing Design. . . . . . . . . . . . . Temperature Environment . . . . . . . . . . . . Casing I n s t a b i l i t y . . . . . . . . .... ANALYSIS. . . .. .. .. . .. . . .. . T h e o r e t i c a l Model . . . . N u m e r i c a l Model . . . . . . Addition o f Constant Stress . . . .. A n a l y t i c Summary. . . . . . . . . . . . . . . . RESULT IMPLICATIONS . . . . . . . . . . . . . . . T h e r m a l l y Induced E u l e r Buckling. . . . . . . . Joint Behavior.,. . . . . . . . . . . . . . . SUMMARY AND CONCLUSIONS . . . . . . . . . . . . REFERENCES. . . . . . . . . . . . . . . . . . . . APPENDIX A - Nomenclature . . . . . . . . . . . . . APPENDIX B - Derivation o f Equations. . .. INTRODUCTION.

1 1 5 6 11 17 17

30 33 33 35 35 37 39 41

43 45

iii

I L L U STR AT IO NS Figure 1. 2. 3. 4.

Page T y p i c a l G e o t h e r m a l W e l l C o n s t r u c t i o n and Casing Temperature P r o f i l e .

........... I d e a l i z e d C o n d i t i o n s Causing Casing B u c k l i n g w i t h Temperature Excursion. . . . . . . . . . . . P r e l i m i n a r y GEOTEMP C a l c u l a t i o n s o f Temperature C o n d i t i o n s D u r i n g Cementing . . . . . P o s t u l a t e d B u c k l i n g F a i l u r e Modes: a) Local, P l a s t i c Deformation, b) E u l e r b u c k l i n g , c ) E u l e r B u c k l i n g w i t h Subsequent Wall Contact, and d ) H e l i c a l B u c k l i n g

.............

5. 6.

7.

Q u a l i t a t i v e P l o t o f T e m p e r a t u r e Change V e r s u s Unsupported Length D e p i c t i n g B u c k l i n g Regions D e f i n i t i o n o f Terms: b ) F r e e Body Diagram.

9.

10.

12

..............

19

a ) L i n e S k e t c h and

Locus D e l i n e a t i n g E u l e r B u c k l i n g R e g i o n : ?lot o f T e m p e r a t u r e Change ( A T ) V e r s u s N o r m a l i z e d Unsupported Length (L/D). Maximum S t r e s s ( u ) V e r s u s T e m p e r a t u r e Change ( A T ) f o r 1 3 - 3 / 8 i n c h 54.5 p p f C a s i n g Assuming U n s u p p o r t e d L e n g t h s ( L / D ) o f 50, 100, and 200

.

21

25

Maximum D e f l e c t i o n V e r s u s T e m p e r a t u r e Change ( A T ) for 1 3 - 3 / 8 i n c h 54.5 p p f C a s i n g Assuming U n s u p p o r t e d L e n g t h s ( L / D ) o f 50, 100, and 200

26

D e f o r m e d C a s i n g Shapes w i t h W a l l C o n s t r a i n t P r e d i c t e d b y MARC and T h e o r e t i c a l M o d e l s ,at a ) A T = 80'F, b ) MARC R e s u l t s a t A T = 300 F, a n d c ) A n a l y t i c R e s u l t s a t AT = 300°F

27

Maximum S t r e s s ( u ) V e r s u s A T f o r 1 3 - 3 / 8 i n c h 54.5 p p f C a s i n g f o r U n s u p p o r t e d L e n g t h ( L / D ) o f 100 w i t h Wall Contact: a ) A n a l y t i c Model, b ) MARC Computer Code, and c ) C o n s t a n t S t r e s s Addition.

29

....................

i v

9

14

......

11.

7

.

............

8.

3

c P

. INTRODUCTION

D r S l l i n g f o r g e o t h e r m a l e n e r g y b e g a n as e a r l y as t h e 1 9 2 0 ' s i n t h e Geysers f i e l d i n n o r t h e r n C a l i f o r n i a , b u t a s e r i o u s e f f o r t t o h a r n e s s g e o t h e r m a l e n e r g y f o r power g e n e r a t i o n was n o t begun i n t h e U n i t e d S t a t e s u n t i l t h e 1 9 7 0 ' s . scale,

On a n a t i o n a l

t h e r e i s t h e g e o l o g i c p o t e n t i a l t o d e v e l o p 20,000

e l e c t r i c a l energy.

MW o f

The g e o t h e r m a l e n e r g y i n d u s t r y p e r f o r m a n c e

i n t h e l a s t 1 0 y e a r s and t h e g e o l o g i c p r o s p e c t s i n d i c a t e t h e i n d u s t r y has t h e p o t e n t i a l f o r g r o w t h and can make a c o n t r i b u t i o n i n s u p p l y i n g t h e e n e r g y needs o f t h e n a t i o n . T h e r e a r e numerous s i m i l a r i t i e s b e t w e e n c o n v e n t i o n a l o i l and gas w e l l s and g e o t h e r m a l w e l l s i n c o n s t r u c t i o n and operation. However, i m p o r t a n t d i f f e r e n c e s do e x i s t ( w h e t h e r f r o m d r y steam, d r y h o t r o c k , h o t w a t e r , o r g e o p r e s s u r i t e d f l u i d reservoirs). F l u i d f l o w r a t e s a r e an o r d e r o f m a g n i t u d e l a r g e r than i n the petroleum industry. The h i g h t e m p e r a t u r e s e n c o u n t e r e d a f f e c t t h e d r i l l b i t , d r i l l i n g mud and t h e cement performance. R e s e r v o i r c a l c u l a t i o n s m u s t i n c l u d e an e n e r g y b a l a n c e as w e l l as a mass b a l a n c e . F i n a l l y , d i f f i c u l t geology, c o r r o s i v e e n v i r o n m e n t s , and t h e r m a l s t r e s s e s i n d u c e d i n t h e w e l l c a s i n g p r e s e n t t h e c a s i n g d e s i g n e r w i t h a new s e t o f f a i l u r e modes t o c o n s i d e r . Geothermal W e l l C o n s t r u c t i o n This introduction i s intended t o provide the reader u n f a m i l i a r w i t h g e o t h e r m a l w e l l c a s i n g d e s i g n and c o n s t r u c t i o n necessary background i n f o r m a t i o n .

However, i t a l s o s e r v e s t o

r e m i n d t h e r e a d e r t h a t a l t h o u g h t h e c a s i n g s e l e c t i o n i s based on t h e w o r s t case d e s i g n c r i t e r i a f r o m b u r s t , c o l l a p s e , tension,

etc.,

s t r e s s e s f r o m many d i f f e r e n t l o a d s c a n b e

p r e s e n t s i m u l t a n e o u s l y -and c o n t r i b u t e t o c a s i n g f a i l u r e .

More

comprehensive d i s c u s s i o n s o f t h e v a r i o u s f a c t s o f Geothermal w e l l s a r e a v a i l a b l e (e.g.

Edwards e t a l . ,

1982).

F i g u r e 1 shows a s c h e m a t i c o f a g e o t h e r m a l w e l l w h i c h w i l l be used f o r d i s c u s s i o n .

T e m p e r a t u r e p r o f i l e s o f t h e c a s i n g and

u n d i s t u r b e d f o r m a t i o n a r e a l s o shown.

Figure 1 contains well

f e a t u r e s f r o m s e v e r a l t y p e s o f g e o t h e r m a l f i e l d s and t h u s c a n n o t t r u l y b e c l a s s i f i e d as l l t y p i c a l . l l The w e l l i s shown v e r t i c a l , are d i r e c t i o n a l l y d r i l l e d . difficult

b u t f r e q u e n t l y geothermal w e l l s

Appropriate d r i l l s i t e s are

t o l o c a t e i n t h e r o u g h t e r r a i n o f t e n f o u n d above

geothermal f i e l d s .

I t i s a l s o d e s i r a b l e t o d r i l l a t an a n g l e

t o i n t e r s e c t more f r a c t u r e s

.

Geothermal r e s e r v o i r s f r e q u e n t l y

o c c u r i n f r a c t u r e d r e s e r v o i r s b e l o w 3000 f t ( 9 0 0 m ) ;

hence

fractures are primarily vertical. Most g e o t h e r m a l r e s e r v o i r s a r e b e l o w t h e d r i l l mud h y d r o s t a t i c p r e s s u r e which causes l o s t c i r c u l a t i o n problems d u r i n g d r i l l i n g and c e m e n t i n g . Also, low geothermal r e s e r v o i r p r e s s u r e s make d e t e c t i o n o f s t e a m fractures d i f f i c u l t .

or h o t w a t e r b e a r i n g

The u s e o f a i r r e d u c e s t h e d r P l l f l u i d

d e n s i t y and g r e a t l y s p e e d s u p d r i l l i n g .

However, t h e d r i l l b i t

l i f e i s g r e a t l y reduced because o f t h e h i g h t e m p e r a t u r e s encountered.

The n e a r s o n i c v e l o c i t i e s p r o d u c e d w h i l e c a r r y i n g

t h e c u t t i n g s up t h e o u t s i d e o f t h e d r i l l p i p e a l s o causes excessive erosion o f t h e d r i l l pipe. The s t a n d a r d c o m p o n e n t s o f t h e w e l l c a s i n g p r o g r a m a r e conductor pipe, s u r f a c e casing, production casing.

i n t e r m e d i a t e c a s i n g and

The p r o d u c t i o n c a s i n g i s o f t e n s e t as a

production l i n e r with a tieback.

P r o d u c t i o n c a s i n g and

p r o d u c t i o n l i n e r s a r e d e s i g n e d w i t h t h e same c r i t e r i o n as i n t e r m e d i a t e c a s i n g and d r i l l i n g l i n e r s e x c e p t t h a t c o n s i d e r a t i o n o f d r i l l i n g wear i s n o t r e q u i r e d .

The w e l l

construction d i f f e r s s l i g h t l y from conventional o i l wells i n t h a t each c a s i n g i s cemented t o t h e s u r f a c e . Conductor p i p e i s t h e f i r s t s t r i n g o f p i p e t o be installed.

2

I t a i d s i n p r e v e n t i n g washouts around t h e d r i l l

GEOTHERMAL WELL SCHEMATIC AND CASING TEMPERATURE

-

Q526'F

50°F

350°F-

I

100

I

200c THE SURFACE TEMPERATURE PROFILES

INTERMEDIATE

0 -UNDISTURBED

13-3/8 INCH

FORMATION

I'

-CEMENT-SET TEMPERATURE

BUTTRESS JOINTS

0 -0PERATINa

CASING TEMPERATURE

-SHUT-IN CASING TEMPERATURE

5001

8001

J F i g u r e 1.

L 100

200

300

400

Ll

500

TEMPERATUREOF

T y p i c a l G e o t h e r m a l We1 1 C o n s t r u c t Temperature P r o f i l e .

on and C a s i n g

3

. r i g s , provides a conduit f o r d r i l l i n g f l u i d s t o surface p i t s , and h e l p s s u p p o r t w e l l h e a d e q u i p m e n t . Conductor p i p e i s s e t s h a l l o w and i s n o t u s u a l l y c o n s i d e r e d a p r e s s u r e s t r i n g . The s u r f a c e c a s i n g i s t h e f i r s t t r u e c a s i n g s t r i n g .

As a

p r i m a r y s t r u c t u r a l member i t p r o v i d e s s u p p o r t f o r s u b s e q u e n t casing strings.

To a v o i d b u c k l i n g p r o b l e m s f r o m t h e

compressive loads applied,

i t i s o f t e n cemented t o t h e s u r f a c e

even i n c o n v e n t i o n a l w e l l s . sufficient hole stability,

S u r f a c e c a s i n g must a l s o p r o v i d e protection to aquifers,

support f o r t h e r e s e r v o i r pressure,

solid

and p r e s s u r e i n t e g r i t y i n

t h e e v e n t o f a b r u p t p r e s s u r e i n c r e a s e s ( b l o w o u t s and k i c k s ) . S u r f a c e c a s i n g i s s u b j e c t e d t o d r i l l i n g wear w h i c h r e q u i r e s heavy casing.

Common s e t t i n g d e p t h s a r e b e t w e e n 1000 a n d 2500

f t ( 3 0 0 t o 760 m).

I n a c o n v e n t i o n a l w e l l , i n t e r m e d i a t e c a s i n g can be exposed t o h i g h bottom h o l e pressures which r e q u i r e s s u b s t a n t i a l b u r s t resistance.

High c o l l a p s e r e s i s t a n c e i s a l s o r e q u i r e d f o r t h e

deeper casing.

Heavy muds and cement s l u r r i e s r e q u i r e d f o r

deep d r i l l i n g can c r e a t e h i g h c o l l a p s e l o a d s s h o u l d l o s t c i r c u l a t i o n zones empty t h e p i p e . heavy casing.

These c o n d i t i o n s d i c t a t e

As w i t h s u r f a c e s t r i n g s ,

i n t e r m e d i a t e c a s i n g and

d r illi n g 1 i n e r s a r e s u b j e c t e d t o m e c h a n i c a l damage f r o m d r i l l i n g wear. T h e c a s i n g s i z e s shown i n F i g u r e 1 a r e commonly s e l e c t e d v a l u e s i n many g e o t h e r m a l f i e l d s .

However,

a standard casing

program i n t h e p r o m i n e n t Geysers geothermal f i e l d c o n s i s t s o f

26 a n d / o r 20 i n c h ( 6 6 0 o r 508 mm) d i a m e t e r c o n d u c t o r p i p e , 13-3/8

i n c h ( 3 4 0 mm) s u r f a c e c a s i n g ,

and 9 - 5 / 8

i n c h ( 2 4 4 mm)

i n t e r m e d i a t e c a s i n g or l i n e r ( w i t h o r w i t h o u t a t i e b a c k s t r i n g

of e i t h e r 9-5/8 (Capuano,

o r 10-3/4

1979).

i n c h ( 2 4 4 o r 273 mm) c a s i n g )

Because s u p e r h e a t e d s t e a m i s p r o d u c e d ,

p r o d u c t i o n c a s i n g i s n o t needed. i s usually stable.

4

a

An open h o l e i n t h e r e s e r v o i r

z

Well C --a s i n g Des& The p r o p e r s e l e c t i o n o f t h e t y p e ,

size,

and s e t t i n g d e p t h

o f t h e w e l l c a s i n g i s b a s e d on t h e e x p e c t e d w e l l o p e r a t i o n c o n d i t i o n s and t h e d r i l l i n g s i t e g e o l o g y .

The u s u a l p r a c t i c e

i s t o c o n s i d e r t h e w o r s t c a s e o r maximum l o a d i n d e t e r m i n i n g the required casing configuration. nesting are usually ignored. i n c l u d e s (Snyder, *Metal failure:

C o m p l i c a t i o n s due t o c a s i n g

A l i s t o f c a s i n g f a i l u r e modes

1979): burst,

collapse, tension,

or corrosion,

* M e c h a n i c a l damage: d r i l l p i p e wear, w e l d i n g p r o b l e m s , t h r e a t damage, o r l e a k a g e and p e r f o r a t i o n , .Casing i n s t a b i l i t y : l a t e r a l deflection (buckling) from e x c e s s i v e c o m p r e s s i v e l o a d s (e.g t h e r m a l e x p a n s i o n ) o r i n t e r n a l pressure, *Cement f a i l u r e s : v o i d s f r o m l o s t c i r c u l a t i o n zones' o r cement t o o l p r o b l e m s , cement d i s s o l u t i o n and c o r r o s i o n p e r m i t t i n g f l u i d movement b e t w e e n c a s i n g and f o r m a t i o n , poor high-temperature s l u r r y behavior,

or

*Thermal s t r e s s f a i l u r e s : compression and/or t e n s i o n f a i l u r e s ( t e l e s c o p i n g ) , leakage i n couplings from c y c l i c l o a d i n g , e x c e s s i v e b e n d i n g l o a d s i n dog l e g s , s t r a i n b e y o n d ultimate. T h i s t a b u l a t i o n p r e s e n t s p o s s i b l e f a i l u r e modes. U n f o r t u n a t e l y l i t t l e d e t a i l e d p u b l i c i n f o r m a t i o n e x i s t s on geothermal w e l l c a s i n g f a i l u r e s .

The a n a l y s t can o n l y

p o s t u l a t e t y p e s and f a i l u r e mechanisms and t h u s t h e d a n g e r e x i s t s t h a t an i m p o r t a n t o r more l i k e l y f a i l u r e mechanism has been o v e r l o o k e d . I t s h o u l d b e n o t e d t h a t t h e f a i l u r e modes l i s t e d a r e n o t

independent.

For--example,

a cement f a i l u r e c o u l d c a u s e

i n s u f f i c i e n t l a t e r a l s u p p o r t and r e s u l t i n c a s i n g i n s t a b i l i t y when h i g h i n t e r n a l p r e s s u r e s o c c u r r e d .

The r e s u l t i n g l a t e r a l

d e f l e c t i o n c o u l d i n t u r n r e s u l t i n e x c e s s i v e d r i l l p i p e wear d u r i n g t h e d r i l l i n g o p e r a t i o n and s u b s e q u e n t b u r s t o f t h e casing during the production operation.

5

I n o i l o r gas w e l l c a s i n g d e s i g n ,

t h e major concern

addressed i s metal f a i l u r e from b u r s t , However,

collapse,

or tension.

t h e presence o f thermal loads i n geothermal w e l l

casing g r e a t l y increases the opportunity f o r casing instability.

C a s i n g s t a b i l i t y can b e i m p r o v e d by:

1) cementing t h e e n t i r e s t r i n g t o p r o v i d e l a t e r a l support o r 2 ) a p p l y i n g a t e n s i o n l o a d i n t h e uncemented s e c t i o n s .

Fully

cementing t h e casing s t r i n g i s t h e usual choice. Unfortunately,

poor formation c o n d i t i o n s f r e q u e n t l y e x i s t i n

geothermal areas.

The r e s e r v o i r i s u s u a l l y b e l o w h y d r o s t a t i c

p r e s s u r e a n d can b e h i g h l y f r a c t u r e d .

Consequently,

lost

c i r c u l a t i o n w h i l e d r i l l i n g w i t h mud o r c e m e n t i n g c a s i n g i s common.

I t i s t h u s i m p o s s i b l e t o e n s u r e a c o m p l e t e cement j o b

i n many i n s t a n c e s .

F a i l u r e o f stage cementing t o o l s i n

g e o t h e r m a l w e l l s i s f r e q u e n t and a l s o c r e a t e s u n s u p p o r t e d t u b u l a r s e c t i o n s ( S n y d e r , 1979). Buckling failures o f the c a s i n g f r o m t h e r m a l e x p a n s i o n w h e r e cement f a i l u r e s h a v e occurred i s the subject o f t h i s r e p o r t (Figure 2 ) . TemDerature Environment The t e m p e r a t u r e e n v i r o n m e n t i s i m p o r t a n t i n f o r m a t i o n f o r the thermal analysis.

f i g u r e 1 presents a hypothetical

temperature environment.

The s u r f a c e and b o t t o m h o l e

t e m p e r a t u r e s a r e as s u r m i s e d b y t h e w e l l o p e r a t o r s i n The G e y s e r s f i e l d (Pye,

1980;

J e n k i n s and S n y d e r ,

1979),

but the

a c t u a l t e m p e r a t u r e p r o f i l e s t h r o u g h o u t t h e s t r a t i g r a p h y and c a s i n g a r e unknown.

I n F i g u r e 1 casing temperatures are

assumed t o v a r y l i n e a r l y . shown w i t h one e l b o w .

The u n d i s t u r b e d f o r m a t i o n p r o f i l e i s

A f e w p r o f i l e s a v a i l a b l e f r o m The

Geysers f i e l d c o n t a i n two k i n k s :

t h e second elbow o c c u r s

w i t h i n t h e f i r s t 500 f t ( 1 5 0 m ) . For w e l l s completed i n low-pressure hot-water

o r steam

r e s e r v o i r s , t h e c a s i n g s a r e t h o u g h t t o b e cemented a t a t e m p e r a t u r e b e t w e e n 100-2OO'F

6

(40-95°C).

T h i s assumes t h e

i

.

HOT WATER, STEAM CEMENT SHEATH

ENLARGED HOL

PIPE DIAMETER Fig ure 2 .

I d e a l i z e d Conditions Causing Casing Buck, l i n g with Temperature Excursion.

7

c a s i n g i s n o t p u r p o s e l y a l l o w e d t o h e a t up b e f o r e cementing. Upon c o m p l e t i o n ,

t h e w e l l i s t e m p e r a t u r e c y c l e d between

p r o d u c i n g c o n d i t i o n s o f a p p r o x i m a t e l y 325-400°F s h u t i n c o n d i t i o n s o f 425-450°F

(220-235°C).

(160-205°C)

and

The c y c l i n g i s

due t o a i r p o l l u t i o n s t a n d a r d s w h i c h l i m i t t h e v e n t i n g o f geothermal w e l l s .

C y c l i n g c a n o c c u r 2 t o 3 t i m e s p e r week i f

t h e s t e a m c o n t a i n s a p o l l u t a n t s u c h as h y d r o g e n s u l f i d e ( H 2 S ) . When t h e w e l l r e q u i r e s r e m e d i a l w o r k ,

t h e casing temperature i s

r e d u c e d t o a r o u n d 100°F ( 4 0 ° C ) w i t h c o o l w a t e r .

These a r e

approximate values only. A temperature p r o f i l e i s very useful i n v i s u a l i z i n g t h e

t e m p e r a t u r e change t o w h i c h each t y p e o f c a s i n g i s s u b j e c t e d . Accurate i n f o r m a t i o n o f t h i s t y p e would g r e a t l y a i d t h e design and a n a l y s i s o f t h e c a s i n g i n t e g r i t y .

As seen i n F i g u r e 1, t h e

c a s i n g can b e s u b j e c t e d t o l a r g e t e m p e r a t u r e changes. C o n s e q u e n t l y l a r g e t h e r m a l s t r e s s e s must be a n t i c i p a t e d .

It i s

seen t h a t t h e more s e v e r e t e m p e r a t u r e changes o c c u r n e a r t h e s u r f a c e d u r i n g t h e c y c l i n g b e t w e e n p r o d u c t i o n and s h u t - i n . However, t h e w h o l e c a s i n g s t r i n g can b e s u b j e c t e d t o l a r g e t e m p e r a t u r e changes a f t e r c e m e n t i n g and whenever t h e w e l l m u s t b e quenched. An a c c u r a t e c e m e n t - s e t

temperature i s essential t o t h e

t h e r m a l s t r e s s a n a l y s i s because t h i s i s t h e t e m p e r a t u r e t h e c a s i n g becomes c o n s t r a i n e d . (Wooley,

1980; M i t c h e l l ,

The GEOTEMP c o m p u t e r p r o g r a m

1982) b e i n g developed under c o n t r a c t

t o S a n d i a w i l l be h e l p f u l i n more c a r e f u l l y d e f i n i n g t h e temperature regime o f t h e w e l l casing.

P r e l i m i n a r y GEOTEMP

t e m p e r a t u r e c a l c u l a t i o n s a r e shown i n F i g u r e 3. t e m p e r a t u r e s a t 200 f t

Radial

( 6 0 m) depth under t h r e e geothermal

f l u i d flow c o n d i t i o n s are depicted f o r a Geysers w e l l . c e m e n t i n g c o n d i t i o n s a r e l o w e r t h a n g e n e r a l l y assumed b y operators.

V e r i f i c a t i o n o f t h e GEOTEMP p r o g r a m i s n o t

c o m p l e t e , b u t t h e t e m p e r a t u r e d i f f e r e n c e shown c o u l d b e s i g n i f i c a n t and needs t o b e more c a r e f u l l y e x a m i n e d .

The

c

*

PROFILES TAKEN FROM GEOTEMP ANALYSIS 100 1

I

I

t

I

20 INCH 13 3/8 INCH B 5/8 INCH

n

5

Y

90

u

-

t

A

n 10'

06 h INJECTION COOLING 250 gal/rnin 0 3 h SHUT IN AFTER INJECTION

-

A 5 h CONDITIONING 400 gal/rnin 2 h CEMENTING I

I

I

I

r (FEET) RADIAL TEMPERATURES AT 200 FOOT DEPTH

Figure 3 .

Preliminary GEOTEMP C a l c u l a t i o n s o f Temperature Conditions During Cementing.

9

. c a s i n g i s n o t p u r p o s e l y a l l o w e d t o h e a t up b e f o r e cementing. Upon c o m p l e t i o n ,

t h e w e l l i s t e m p e r a t u r e c y c l e d between

p r o d u c i n g c o n d i t i o n s o f a p p r o x i m a t e l y 325-400°F s h u t i n c o n d i t i o n s o f 425-450°F

(220-235°C).

(160-205°C)

and

The c y c l i n g i s

due t o a i r p o l l u t i o n s t a n d a r d s w h i c h l i m i t t h e v e n t i n g o f geothermal wells.

C y c l i n g c a n o c c u r 2 t o 3 t i m e s p e r week i f

t h e s t e a m c o n t a i n s a p o l l u t a n t s u c h as h y d r o g e n s u l f i d e (H2S). When t h e w e l l r e q u i r e s r e m e d i a l w o r k , r e d u c e d t o a r o u n d 100°F (40'C)

the casing temperature i s

with cool water.

These a r e

approximate values only. A temperature p r o f i l e i s very useful i n v i s u a l i z i n g the t e m p e r a t u r e change t o w h i c h each t y p e o f c a s i n g i s s u b j e c t e d . Accurate i n f o r m a t i o n o f t h i s type would g r e a t l y a i d t h e design and a n a l y s i s o f t h e c a s i n g i n t e g r i t y .

As seen i n F i g u r e 1,

c a s i n g can be s u b j e c t e d t o l a r g e t e m p e r a t u r e changes. C o n s e q u e n t l y l a r g e t h e r m a l s t r e s s e s must be a n t i c i p a t e d .

the

It i s

seen t h a t t h e m o r e s e v e r e t e m p e r a t u r e c h a n g e s o c c u r n e a r t h e s u r f a c e d u r i n g t h e c y c l i n g b e t w e e n p r o d u c t i o n and s h u t - i n . However, t h e w h o l e c a s i n g s t r i n g c a n b e s u b j e c t e d t o l a r g e t e m p e r a t u r e c h a n g e s a f t e r c e m e n t i n g and whenever t h e w e l l m u s t b e quenched. An a c c u r a t e c e m e n t - s e t

temperature i s essential t o the

t h e r m a l s t r e s s a n a l y s i s because t h i s i s t h e t e m p e r a t u r e t h e c a s i n g becomes c o n s t r a i n e d . (Wooley,

1980; M i t c h e l l ,

The GEOTEMP c o m p u t e r p r o g r a m

1982) b e i n g developed under c o n t r a c t

t o S a n d i a w i l l b e h e l p f u l i n more c a r e f u l l y d e f i n i n g t h e temperature regime o f t h e w e l l casing.

P r e l i m i n a r y GEOTEMP

t e m p e r a t u r e c a l c u l a t i o n s a r e shown i n F i g u r e 3.

Radial

(60 m ) depth under t h r e e geothermal f l u i d f l o w c o n d i t i o n s are d e p i c t e d f o r a Geysers w e l l . The c e m e n t i n g c o n d i t i o n s a r e l o w e r t h a n g e n e r a l l y assumed b y operators. V e r i f i c a t i o n o f t h e GEOTEMP p r o g r a m i s n o t c o m p l e t e , b u t t h e t e m p e r a t u r e d i f f e r e n c e shown c o u l d b e s i g n i f i c a n t a n d n e e d s t o b e more c a r e f u l l y e x a m i n e d . t e m p e r a t u r e s a t 200 f t .

10

W h i l e f a i l u r e s i n cemented s t r i n g s s u c h as c o m p r e s s i o n a n d / o r t e n s i o n f a i l u r e s and c o n n e c t i o n f a i l u r e s a r e o f c o n c e r n , o p e r a t o r s have expressed g r e a t e r concern over c a s i n g buck1 i n g i n p a r t i a l l y cemented s t r i n g s (Pye, Snyder,

1979).

1980; Kumataka,

1981,

As r e g a r d s p a r t i a l l y c e m e n t e d s t r i n g s , w o r k i n

t h e a r c t i c o i l f i e l d s h a s shown t h a t t h e cement a n d l o r f o r m a t i o n s u p p o r t needed t o a v o i d b u c k l i n g f r o m s u b s i d e n c e i s q u i t e s m a l l ( W i l s o n e t al.,

1980).

( B o t h s u b s ' i d e n c e and

thermal stress loads are s t r a i n c o n t r o l l e d . ) ,

Because l i t t l e

l a t e r a l s u p p o r t i s necessary, b u c k l i n g i s l i m i t e d t o areas where f o r m a t i o n c o n d i t i o n s cause e n l a r g e d h o l e s t o f o r m w i t h s u b s e q u e n t v o i d s i n t h e cement s h e a t h s u c h t h a t a c o m p l e t e l y unsupported s e c t i o n occurs ( F i g u r e 2). Casing i n s t a b i l i t y f a i l u r e s from a thermal l o a d i n p a r t i a l l y c e m e n t e d s t r i n g s can b e d i v i d e d i n t o f o u r categories.

The f a i l u r e t y p e i s d e p e n d e n t on t h e u n s u p p o r t e d

c a s i n g l e n g t h and i n t e r n a l - e x t e r n a l ( F i g u r e 4).

pressure i n t e r a c t i o n

The c a t e g o r i e s a r e : %

.Local

p l a s t i c deformation,

~ E u l e rb u c k 1 i n g , C o n s t r a i n e d E u l e r b u c k l i n g f o l l o w e d by plas.tic deformation o r c o l l a p s e due t o o v a l a t i o n , ' .

*He1 i c a l b u c k l i n g . I t i s i m p o r t a n t t o emphasize t h e d i f f e r e n c e between

s t a n d a r d c o l u m n b u c k l i n g u n d e r an a p p l i e d . l o a d a b u c k l i n g f r o m t h e r m a l f a r c e s where s u p p o r t o f - a f o l l o w e r a x i a l load i s not required.

Rather than c a t a s t r o p h i c f a i l u v e from a .

5

c r i t i c a l t e m p e r a t u r e change, t h e c a s i n g s l o w l y d e f o r m s e l a s t i c a l l y i n t o t h e d e f o r m e d shape f o r l a r g e + u n s u p p o r t e d lengths.

Thus c o l u m n " b e n d i n g " i s a more a p p r o p r i a t e

d e s c r i p t i o n o f t h e phenomenon.

The p i p e s t r i n g i n s t a b i l i t y

m a n i f e s t s i t s e l f as a l a t e r a l d e f l e c t i o n . 11

I

7 SHORT

LONG UNSUPPORTED LENGTH

UNSUPPORTED

a) LOCAL, PLASTIC DEFORMATION

b) EULER BUCKLING

H

c) EULER BUCKLING WITH SUBSEQUENT WALL CONTACT (PLASTIC DEFORMATION OR COLLAPSE DUE TO OVALATION POSSIBLE)

Figure 4 .

12

d) HELICAL BUCKLING

Postulated Buckling F a i l u r e Modes: a ) Local, P l a s t i c Deformation, b ) Euler Buckling, c ) Euler Buckling with Subsequent Wall Contact, a n d d ) H e l i c a l Buckling.

.

c

The r e s u l t i n g d e f o r m a t i o n may n o t impede o p e r a t i o n s i f t h e deformation i s slight.

The l a r g e s t t h e r m a l s t r e s s e s a r e

introduced during shut-in

a f t e r t h e w e l l i s completed,

thus the

d a n g e r o f e x c e s s i v e p i p e wear d u r i n g d r i l l i n g h a s p a s s e d . However, e v e n s l i g h t b e n d i n g a t c o n n e c t i o n s can r e s u l t i n j o i n t f a f l u r e because s t a n d a r d American P e t r o l e u m I n s t i t u t e ( A P I ) j o i n t s a r e n o t designed t o w i t h s t a n d bending stresses. F i g u r e 5 q u a l i t a t i v e l y i n d i c a t e s where v a r i o u s buck1 i n g modes o c c u r .

It i s important t o note t h a t internal-external

p r e s s u r e i n t e r a c t i o n has been i g n o r e d .

Only unsupported l e n g t h

a n d t e m p e r a t u r e was c o n s i d e r e d . For s h o r t unsupported l e n g t h s o n l y l o c a l i z e d p l a s t i c d e f o r m a t i o n a n d / o r c o l l a p s e would be expected.

A t longer

unsupported lengths, Euler b u c k l i n g would occur. With c o n t i n u e d t e m p e r a t u r e i n c r e a s e , t h e c a s i n g c o u l d d e f l e c t enough t o contact the d r i l l hole sides.

P l a s t i c deformation or pipe

c o l l a p s e f r o m t h e weakening e f f e c t s o f c r o s s - s e c t i o n o v a l a t i o n could follow. H e l i c a l b u c k l i n g occurs i n l o n g unsupported lengths. the o i l well industry,

t h e c o r k s c r e w i n g i s due p r i m a r i l y t o

excessive, destabilizing, 1962).

In

i n t e r n a l p r e s s u r e s ( L u b i n s k i e t a1

.,

F r e q u e n t l y , t h e d e f o r m a t i o n i s n o t s e v e r e enough t o

c a u s e p e r m a n e n t d e f o r m a t i o n ( T e x t e r , 1955).. Because l o n g u n s u p p o r t e d l e n g t h s a r e much l e s s l i k e l y and t h e u l t i m a t e f a i l u r e mechanism i s s i m i l a r t o t h a t e n c o u n t e r e d w i t h s i n g l e order Euler buckling, t h i s region i s o f less interest. Two b a s i c s u b j e c t a r e a s need t o b e i n v e s t i g a t e d c o n c e r n i n g t h e r m a l b u c k l i n g and l o c a l i z e d p l a s t i c d e f o r m a t i o n o f geothermal casing.

First, analysis of the Euler buckling

r e g i m e assuming b u i l t - i n

ends and s u b s e q u e n t e l a s t i c - p l a s t i c

b e n d i n g needs t o be examined.

Analysis o f nested casing

b e h a v i o r when c o n s t r a i n e d b y cement a n d / o r f o r m a t i o n s c o u l d a l s o be i n v e s t i g a t e d more t h o r o u g h l y . I

Second,

analysis of

l o c a l i z e d p l a s t i c d e f o r m a t i o n s s u c h as s y m m e t r i c a l b u c k l i n g and w r i n k l i n g i n s t a b i l i t i e s needs t o b e e x a m i n e d .

Small s c a l e 13

QUALITATIVE DESCRIPTION OF VARIOUS BUCKLING MODES 1 I-