Surfactant-Based Mobility Control - American Chemical Society

Chapter 19

Carbon Dioxide—Foam Mobility Measurements at High Pressure

Downloaded by CORNELL UNIV on August 10, 2016 | http://pubs.acs.org Publication Date: July 20, 1988 | doi: 10.1021/bk-1988-0373.ch019

Hae Ok Lee and John P. Heller New Mexico Petroleum Recovery Research Center, New Mexico Institute of Mining and Technology, Socorro, N M 87801

Mobility control of high pressure CO floods by use of foam is a promising technique of enhanced oil recovery. Critical information for the use of CO foam as a thickened displacement fluid is the ratio of combinedCO and surfactant solution flow rate to pressure drop in the swept region. In this work, foam mobility measurements have been carried out on a laboratory scale. A high pressure apparatus has been designed and carefully calibrated to measure pressure drop across a core sample. The measured steady-state data are used to evaluate the mobility of foam. These measurements are made during simultaneous flow of the dense CO and surfactant solution through core samples. Dependences of the mobility of CO -foam on aqueous surfactant concentration andCO volume fraction have been investigated. 2

2

2

2

2

2

The a d d i t i o n o f s u r f a c t a n t t o t h e f l o w i n g water d u r i n g t h e f l o o d r e d u c e s CO2 m o b i l i t y and s h o u l d improve b o t h a r e a l and v e r t i c a l sweep e f f i c i e n c i e s by s t a b i l i z i n g v i s c o u s f i n g e r i n g and f l o w t h r o u g h t h e more permeable zones ( 1 - 3 ) . Numerous l a b o r a t o r y s t u d i e s have demonstrated t h a t , i f c o n t a c t i s made w i t h t h e o i l , dense s u p e r c r i t i c a l CO2 c a n d e v e l o p m u l t i c o n t a c t m i s c i b i l i t y w i t h many c r u d e s ( 4 , 5 ) . Most o f t h e t i m e , though, o i l r e c o v e r i e s w i t h CO2 have been much h i g h e r i n t h e l a b o r a t o r y t h a n i n t h e f i e l d because t h e f i e l d c o n d i t i o n s a r e more s e v e r e f o r a l l o i l r e c o v e r y p r o c e s s e s , p e r m i t t i n g much more n o n - u n i f o r m f l o w . CC^-foam p r e s e n t s an i m m e d i a t e l y a v a i l a b l e , and p e r h a p s a more e f f i c i e n t way o f a t t a i n i n g u n i f o r m d i s p l a c e m e n t i n t h e r e s e r v o i r because a foam c o n s i s t s o f a t l e a s t 80% CO2, and because the c o s t o f needed s u r f a c t a n t p r o m i s e s t o be minor. Furthermore, foam p o s s e s s e s p r o p e r t i e s t h a t a r e f a v o r a b l e f o r o i l r e c o v e r y ,

0

0097-6156/88/0373-0375$06.00/0 1988 American Chemical Society

Smith; Surfactant-Based Mobility Control ACS Symposium Series; American Chemical Society: Washington, DC, 1988.


376

SURFACTANT-BASED MOBILITY C O N T R O L

e s p e c i a l l y by CO2 f l o o d i n g . The a p p a r e n t v i s c o s i t y o f foam i n porous r o c k i s g r e a t e r t h a n t h e a c t u a l v i s c o s i t i e s o f i t s comp o n e n t s , and i n c r e a s e s w i t h t h e r o c k p e r m e a b i l i t y . A l s o , foam l a m e l l a e i n c r e a s e t r a p p e d gas s a t u r a t i o n . As gas s a t u r a t i o n increases, o i l s a t u r a t i o n decreases. U s u a l l y , a h i g h - t r a p p e d gas s a t u r a t i o n r e d u c e s gas m o b i l i t y . Foam f l o o d i n g i s a method t h a t m o d i f i e s t h e f l o w mechanism by changing t h e s t r u c t u r e o f t h e d i s p l a c i n g f l u i d a t t h e pore l e v e l . A c r i t i c a l l i t e r a t u r e r e v i e w on foam r h e o l o g y i s g i v e n e l s e w h e r e (6). The i n j e c t i o n o f f o a m - l i k e d i s p e r s i o n s o r CC^-foams i s a u s e f u l method i n enhanced o i l r e c o v e r y ( 7 ) . T h i s method o f d e c r e a s i n g t h e m o b i l i t y o f a l o w - v i s c o s i t y f l u i d i n a porous r o c k r e q u i r e s t h e use o f a s u r f a c t a n t t o s t a b i l i z e a p o p u l a t i o n o f bubble f i l m s o r l a m e l l a e w i t h i n t h e p o r e s p a c e o f t h e r o c k ( 8 ) . The degree o f t h i c k e n i n g a c h i e v e d a p p a r e n t l y depends t o some e x t e n t on the p r o p e r t i e s o f t h e rock i t s e l f . These p r o p e r t i e s p r o b a b l y i n c l u d e b o t h t h e d i s t a n c e s c a l e o f t h e p o r e space and t h e w e t t a b i l i t y , and so can be e x p e c t e d t o d i f f e r from r e s e r v o i r t o r e s e r v o i r , as w e l l as t o some e x t e n t w i t h i n a g i v e n f i e l d ( 9 , 1 0 ) . In t h e c a s e o f CO2 f l o o d s , a p a r t i a l l y compensating f e a t u r e has been r e p o r t e d (_11). U n e x p e c t e d l y low m o b i l i t i e s have been o b s e r v e d d u r i n g CO2 i n j e c t i o n i n b o t h f i e l d and l a b o r a t o r y e x p e r i m e n t s , and some a u t h o r s have c o n c l u d e d t h i s e f f e c t i s caused by " m i x e d - w e t t a b i l i t y " o f t h e r o c k . The d e c r e a s e d m o b i l i t y a l s o might p o s s i b l y be c o n n e c t e d w i t h t h e h i g h s o l u b i l i t y o f CO2 i n c r u d e o i l , which adds t o t h e e f f e c t i v e n e s s o f t r a n s v e r s e d i s p e r s i o n i n t e n d i n g t o d i s s i p a t e a t l e a s t t h e c l o s e l y spaced fingers. D e s p i t e t h e s e m i t i g a t i n g f e a t u r e s , most CO2 f l o o d s do show e a r l y b r e a k t h r o u g h , i n d i c a t i n g h i g h e r f l o w r a t e i n a CO2 f i n g e r o r c h a n n e l c o n n e c t i n g t h e i n j e c t i o n and p r o d u c t i o n w e l l s . So l o n g as t h i s f i n g e r expands l a t e r a l l y , t h e r e b y e n t r a i n i n g enough a d d i t i o n a l o i l t o make c o n t i n u a n c e o f t h e f l o o d economic, t h e produced CO2 can be r e i n j e c t e d . The c o s t s o f g a t h e r i n g , p r o c e s s i n g and r e c o m p r e s s i o n a r e an a d d i t i o n a l o p e r a t i n g expense t h a t must n e c e s s a r i l y h a s t e n t h e day o f abandonment. Because o f t h i s t h e o v e r a l l r e c o v e r y e f f i c i e n c y i s reduced - a l o s s of o i l t h a t can be c o n s i d e r e d a r e s u l t o f t h e u n f a v o r a b l e m o b i l i t y r a t i o . R e s e a r c h e r s have i n v e s t i g a t e d t h e n a t u r e o f t h e foam f l o w by examining t h e mechanisms o f foam g e n e r a t i o n (1^2). An e x t e n s i v e s t u d y (1JO, t h a t i s q u i t e r e l e v a n t t o t h e mechanism o f foam f l o w i n p o r o u s media, has shown t h a t t h e a p p a r e n t v i s c o s i t y o f foam i n a c a p i l l a r y tube d e c r e a s e s r a p i d l y as t h e r a t i o o f b u b b l e r a d i u s to-tube radius i s increased. B e s i d e t h e i n v e s t i g a t i o n on foam f l o w mechanisms, r e s e a r c h e r s have endeavored t o f i n d good foaming a g e n t s , e s p e c i a l l y a p p l i c a b l e t o enhanced o i l r e c o v e r y ( 1 4 ) . F u r t h e r m o r e , due t o t h e h a r s h r e s e r v o i r c o n d i t i o n s , s t u d i e s on t h e c o m p a t i b i l i t y o f t h e s u r f a c t a n t w i t h o i l f i e l d b r i n e s a t r e s e r v o i r temperatures and p r e s s u r e s have been made ( 1 5 ) . A l t h o u g h t h e r e has been c o n s i d e r a b l e e f f o r t t o c a l c u l a t e t h e m o b i l i t y o f foam i n porous media from f i r s t p r i n c i p l e s , u t i l i z i n g u s u a l l y measured r o c k p r o p e r t i e s (16), a d i f f e r e n t approach i s used h e r e . I n t h i s r e s e a r c h , major emphasis has been on measurement o f t h e m o b i l i t y o f CC^-foam i n r o c k c o r e samples. The


19. L E E AND HELLER

C0 -Foam Mobility Measurements 2

377

work on t h i s method o f t h i c k e n i n g has a l s o i n c l u d e d t h e t e s t i n g o f several features of surfactant s u i t a b i l i t y . The work r e p o r t e d d e s c r i b e s t h e development o f a p p a r a t u s and e x p e r i m e n t a l methods and p r e s e n t s a v a i l a b l e r e s u l t s .


Experimental D e s c r i p t i o n o f t h e Foam M o b i l i t y Measurement A p p a r a t u s . A s c h e m a t i c o f t h e CO2 foam m o b i l i t y measurement a p p a r a t u s i s g i v e n i n F i g u r e 1. The Ruska pump p r e s s u r i z e s t h e l i q u i d CO2, m a i n t a i n e d a t a c o n s t a n t t e m p e r a t u r e by c i r c u l a t i n g a n t i f r e e z e i n s i d e t h e j a c k e t e d pump. The CO2 f l o w s t h r o u g h t h e c a p i l l a r y tube; t h e p r e s s u r e drop a c r o s s t h e t u b e i s measured by a V a l i d y n e d i f f e r e n t i a l pressure transducer. An I s c o pump i s used t o p r e s s u r i z e t h e b r i n e s u r f a c t a n t s o l u t i o n , which a l s o flows through t h e foam g e n e r a t o r and t h e c o r e . As a m a t t e r o f p r o c e d u r e , t h e core i s i n i t i a l l y saturated f u l l y with b r i n e - s u r f a c t a n t s o l u t i o n . The foams a r e g e n e r a t e d i n s i d e t h e s h o r t c o r e used as a foam g e n e r a t o r , where t h e m i x i n g between CO2 and s u r f a c t a n t s o l u t i o n occurs. The mixed CC^-foam f l o w s t h r o u g h t h e c o r e . The p r e s s u r e drop a c r o s s t h e c o r e i s r e c o r d e d by a second V a l i d y n e d i f f e r e n t i a l pressure transducer. The arrangement o f z e r o i n g v a l v e s a t each o f these t r a n s d u c e r s i s important t o p o i n t out. I n a d d i t i o n t o t h e d i g i t a l r e a d o u t o f t h e v a l u e s o f APcap and APcore, a two-pen r e c o r d e r i s used t o r e c o r d t h e s i m u l t a n e o u s measurements. The n e e d l e v a l v e i s o p e r a t e d by t h e e l e c t r o n i c f l o w r e g u l a t o r system. To m a i n t a i n t h e m a c r o s c o p i c s t e a d y - s t a t e c o n d i t i o n o f t h e f l o w o f dense CO2 t h r o u g h t h e c a p i l l a r y t u b e , s e v e r a l t e s t s have been made i n t h e development o f an optimum f l o w d e v i c e . Two f i n e t a p e r e d n e e d l e v a l v e s i n s e r i e s a r e used t o r e g u l a t e t h e f l o w r a t e o f t h e CO2 a t h i g h p r e s s u r e . A f i n e adjustment d i a l on one o f t h e v a l v e s p e r m i t s r e p e a t a b l e manual s e t t i n g s . Steady-state i s a c c o m p l i s h e d m a n u a l l y by s e t t i n g t h e d i a l t o g i v e a d e s i r e d p r e s s u r e drop a c r o s s t h e c a l c u l a t e d c a p i l l a r y t h a t c a r r i e s dense CO2 from t h e pump. To a c c o m p l i s h t h i s a u t o m a t i c a l l y , a c o n t r o l l e r s e t p o i n t t h a t c o r r e s p o n d s t o t h e d e s i r e d p r e s s u r e drop a c r o s s t h e c a p i l l a r y i s chosen. A f t e r opening t h e manual n e e d l e v a l v e t o an a p p r o x i m a t e l y d e s i r e d v a l u e , t h e a p p r o p r i a t e PID g a i n s ( p r o p o r t i o n a l , i n t e g r a l , d i f f e r e n t i a l ) a r e o p t i m i z e d t o open o r c l o s e the motorized needle valve e l e c t r o n i c a l l y , according t o the s e t p o i n t . A l l c a l c u l a t i o n s were p e r f o r m e d w i t h s t e a d y - s t a t e d a t a w h i c h were averaged over a p e r i o d o f t i m e . I n t e r p r e t a t i o n o f the Experimental Data. In t h i s experiment, t h e measured v a r i a b l e s a r e APcap and APcore. Besides these v a r i a b l e s , o t h e r d a t a , such as t h e Ruska pump f l o w r a t e , I s c o pump f l o w r a t e , i n l e t p r e s s u r e o f CO2, and t h e t e m p e r a t u r e o f t h e CO2 a t t h e i n l e t are recorded. Knowing t h e APcap, t h e f l o w r a t e o f p u r e CO2 i n t o t h e c o r e i s computed by u s i n g t h e c a l i b r a t i o n c o n s t a n t o b t a i n e d earlier. The I s c o pump f l o w r a t e g i v e s t h e f l o w r a t e o f t h e aqueous s u r f a c t a n t s o l u t i o n , and t h e t o t a l f l o w r a t e i s s i m p l y t h e sum o f t h e s e two f l o w r a t e s . From t h e t o t a l f l o w r a t e and t h e APcore, t h e m o b i l i t y c a n be e v a l u a t e d from:



C0

2

F i g u r e 1.

RATE SET AT

WATER-JACKETED RUSKA PUMP

2

L

-

SET — POINT

CAPILLARY TUBE

CAP

(

ISCO

_

A P

CORE

OUT

1

NEEDLE f VALVE

-0

! I

S-E

measurement

ELECTRONIC FLOW REGULATOR SYSTEM

-FOAM GENERATOR

RECORDER

CHECK / VALVE

[ θ is "quality" or flowing fraction of CO2]

°1 brine = (^^)q,CO~ surf \ Q / t

SURFACTANT SOLUTION RATE SET AT

r

ΔΡ

Schematic o f t h e C02 foam m o b i l i t y apparatus.

CQ

(^)

co

q

r


Η

Ο Ο

S Ο w

•

5!

00

19.

L E E AND HELLER


λ =

where

Q A L APcore

is is is is

the the the the

379

(1)

t o t a l flow r a t e c r o s s - s e c t i o n a l a r e a o f t h e r o c k sample l e n g t h o f t h e r o c k sample p r e s s u r e drop a c r o s s the r o c k sample.


C02-Foam M o b i l i t y Measurements E f f e c t of Surfactant Concentrations. The e f f e c t o f t h e s u r f a c t a n t c o n c e n t r a t i o n on foam m o b i l i t y has been s t u d i e d e x t e n s i v e l y . The s u r f a c t a n t under i n v e s t i g a t i o n f o r t h i s e f f e c t was V a r i o n CAS, a z w i t t e r i o n i c s u r f a c t a n t from Sherex. The r o c k under s t u d y was B e r e a s a n d s t o n e which has a p e r m e a b i l i t y o f 308 ± 9 md measured by u s i n g 1% b r i n e s o l u t i o n . The p e r m e a b i l i t y u s i n g N2 gas a t a t m o s p h e r i c p r e s s u r e was 1000 ± 6.2 md. The e f f e c t o f c o n c e n t r a t i o n o f t h e V a r i o n CAS was s t u d i e d . The i n i t i a l c o n c e n t r a t i o n (0.001 wt% a c t i v e ) was s e l e c t e d from t h e measurement o f s u r f a c e and i n t e r f a c i a l t e n s i o n s . I t l i e s i n the range o f CMC v a l u e f o r t h e s e measurements, which were p e r f o r m e d by u s i n g t h e Wilhelmy p l a t e method i n a Rosano s u r f a c e t e n s i o m e t e r . The s t a n d a r d p r o c e d u r e d e s c r i b e d i n t h e manual was c a r e f u l l y followed. S u r f a c e t e n s i o n was measured a g a i n s t t h e a i r , whereas t h e i n t e r f a c i a l t e n s i o n was measured a g a i n s t i s o o c t a n e , w h i c h was used t o s i m u l a t e dense CO2. I t i s w e l l known f a c t t h a t good foamers a r e most e f f e c t i v e w e l l above t h e CMC range and i n subsequent t e s t s t h e c o n c e n t r a t i o n s were i n c r e a s e d w e l l above t h a t range. Two s i g n i f i c a n t c o n c l u s i o n s can be drawn from t h i s e x p e r i m e n t . F i g u r e 2 shows t h e measurements o f m o b i l i t y o f CO2foam, a t v a r i o u s l e v e l s o f s u r f a c t a n t c o n c e n t r a t i o n i n N a C l + CaClC2 b r i n e . The m o b i l i t y g e n e r a l l y d e c r e a s e s w i t h t h e i n c r e a s e of the s u r f a c t a n t concentration. The second c o n c l u s i o n i s t h a t t h e r e e x i s t s a c r i t i c a l c o n c e n t r a t i o n above which f u r t h e r i n c r e a s e i n c o n c e n t r a t i o n causes no s i g n i f i c a n t r e d u c t i o n i n t h e magnitude o f t h e foam m o b i l i t y . Because i t i s d i f f i c u l t t o r e a d a l l o f t h e d a t a a t the h i g h e r c o n c e n t r a t i o n s on t h i s c u r v e , t h e y a r e a l l given i n Table I. In a d d i t i o n , t h e p o i n t s measured a t d i f f e r e n t v e l o c i t i e s and t h e same c o n c e n t r a t i o n have been a v e r a g e d , and t h e s e a v e r a g e m o b i l i t i e s p l o t t e d i n F i g u r e 3 on a l o g - l o g s c a l e , a g a i n s t the c o n c e n t r a t i o n s . The g e n e r a l form o f t h e e f f e c t o f c o n c e n t r a t i o n i s e a s i e r t o see i n t h i s p l o t . The l i n e e x t r a p o l a t e d towards t h e l e f t i s based on one a d d i t i o n a l m o b i l i t y measurement made d u r i n g s i m u l t a n e o u s f l o w o f dense CO2 and b r i n e c o n t a i n i n g no s u r f a c t a n t a t a l l . The remainder o f t h e l i n e drawn t h r o u g h t h e f i v e p o i n t s , and e x t r a p o l a t e d t o h i g h e r c o n c e n t r a t i o n s , might be c o n s i d e r e d more s p e c u l a t i v e . But s u c h a lower l i m i t o f a t t a i n a b l e m o b i l i t y , as i s shown on t h e F i g u r e , has a l s o been o b s e r v e d w i t h one o t h e r s u r f a c t a n t . If i t p r o v e s t o be a g e n e r a l f e a t u r e o f a l l s u r f a c t a n t s t h a t a r e e f f e c t i v e i n s t a b i l i z i n g CO2 foams, i t w i l l be o f g r e a t economic i n t e r e s t , s i n c e i t w i l l f i x t h e maximum c o n c e n t r a t i o n s o f p a r t i c u l a r s u r f a c t a n t s t h a t c o u l d be u s e f u l i n t h e f i e l d .


380

SURFACTANT-BASED MOBILITY CONTROL


Bereo Sandstone (k •> .308 md)

Vorion CAS ( Ζ ) Concentration, wt %

ρ L U

+ 0.0010 X 0.010 • 0.030 Ο 0.050 Δ 0.50

0.

1

2

, | 6

5

p

s

i

a

Τ = 25 0 ° C

x

3

4

5

Velocity F i g u r e 2.

. 2-'

6

7

8

9

10

(ft/day)

E f f e c t of surfactant

concentrations.


19. L E E AND HELLER

381


Table I. C 0 - F o a m Mobility Measurements 2

E f f e c t of Surfactant Concentrations V a r i o n CAS ( Z ) i n 1% B r i n e *

Rock t y p e : B e r e a Sandstone Permeability of the rock: 308 ± 9 md I n l e t p r e s s u r e o f t h e pumps: 1615 ± 5 p s i a Temperature o f t h e C 0 i n Ruska pump: 25.0 ± 0.2°C


2

Concentration (wt% a c t i v e )

v

(ft/day)

λ

r (cp" ) x

(md/cp)

1

c o

2 (quality,**

%)

0.,0010

3.60 A.86 8.10

39.4 37.8 44.5

0.128 0.123 0.144

82.7 80.8 81.5 81.7 ± 1.0

0.,010

2.84 5.76 6.14 6.86

10.5 13.2 14.2 17.5

0.0340 0.0428 0.0461 0.0568

78.1 78.4 81.7 82.2 80.1 + 2.1

0.,030

1.73 2.97 3.60

0.953 1.64 1.28

0.00309 0.00531 0.00414

81.2 83.2 82.7 82.4 ± 1.0

0,.050

2.46 3.54 3.74 3.82 3.88 4.53 4.85 5.16

0.520 0.643 0.582 0.755 0.662 0.762 0.927 0.854

0.00169 0.00209 0.00189 0.00245 0.00215 0.00247 0.00301 0.00277

79.7 82.4 83.3 83.7 83.9 83.5 83.3 83.1 82.9 ± 1.4

0,.50

2.37 4.14 4.80 6.36

0.743 0.549 0.648 0.753

0.00241 0.00178 0.00210 0.00244

81.0 81.9 81.8 80.7 81.4 ± 0.6

'«Standard b r i n e s o l u t i o n i s made o f 0.5% N a C l and 0.5% C a C l . * * Q u a l i t y i s t h e volume f r a c t i o n o f t h e C 0 . 2

2



382


Some o b s e r v a t i o n s were r e c o r d e d d u r i n g t h e e x p e r i m e n t . Through t h e t r a n s p a r e n t , low p r e s s u r e o u t l e t t u b i n g , no foam l a m e l l a e have been o b s e r v e d when t h e c o r e was f l u s h e d w i t h c o n c e n t r a t i o n s o f 0.001 wt% and 0.01 wt% a c t i v e s . F u r t h e r m o r e , d u r i n g t h e s i m u l t a n e o u s f l o w o f dense CO2 and t h e s e c o n c e n t r a t i o n s of s u r f a c t a n t s o l u t i o n , the bubbles e x i t i n g the o u t l e t t u b i n g d i d n o t have much e l a s t i c i t y , e i t h e r . I t seemed as i f i n s u f f i c i e n t s u r f a c t a n t m o l e c u l e s were p r e s e n t t o g e n e r a t e d u r a b l e foam l a m e l l a e t o p a s s c o n t i n u o u s l y t h r o u g h t h e r o c k t o have an a p p r e c i a b l e e f f e c t on t h e f l o w r e s i s t a n c e i n t h e c o r e . W i t h 0.03 wt% a c t i v e and up, w e l l - f o r m e d foam l a m e l l a e were o b s e r v e d i n t h e o u t p u t t u b e as t h e c o r e was washed w i t h each new c o n c e n t r a t i o n b e f o r e t h e a c t u a l e x p e r i m e n t w i t h dense CO2. With simultaneous r u n o f dense CO2, e l a s t i c b u b b l e s were seen t h r o u g h t h e o u t l e t tubing. As t h e c o n c e n t r a t i o n s were i n c r e a s e d from 0.001 wt% and up t o 0.05 wt%, t h e measured p r e s s u r e d r o p s a c r o s s t h e c o r e increased s i g n i f i c a n t l y . However, from 0.05% and up, t h e p r e s s u r e a c r o s s t h e c o r e was f a i r l y c o n s t a n t . T h i s i s an i n d i c a t i o n t h a t s u f f i c i e n t s u r f a c t a n t m o l e c u l e s a r e p r e s e n t and f u r t h e r i n c r e a s e i n c o n c e n t r a t i o n seems t o have f u r t h e r no e f f e c t on g e n e r a t i n g more foam l a m e l l a e . T h i s phenomenon i s a n a l o g o u s t o t h e c r i t i c a l m i c e l l e c o n c e n t r a t i o n (CMC) where f u r t h e r i n c r e a s e i n s u r f a c t a n t c o n c e n t r a t i o n does n o t lower t h e v a l u e o f t h e s u r f a c e t e n s i o n . Whenever t h e c o n c e n t r a t i o n was i n c r e a s e d , s u f f i c i e n t p o r e volumes were u s e d t o wash t h e c o r e t h o r o u g h l y . Some o f t h e d a t a were r e p e a t e d i n o r d e r t o a s s e s s t h e r e l i a b i l i t y o f t h e a p p a r a t u s . The o r d e r o f magnitude o f t h e m o b i l i t y was t h e same f o r a l l measurements a t each p a r t i c u l a r c o n c e n t r a t i o n , i n d e p e n d e n t o f t o t a l f l o w r a t e . T h i s i n d e e d d e m o n s t r a t e s t h e s e n s i t i v i t y and v i a b i l i t y o f t h i s foam m o b i l i t y m e a s u r i n g a p p a r a t u s . V a r i o n CAS foams w e l l but t h e foam a l s o d i e s out r a t h e r quickly. I t must be a f a s t d r a i n i n g foam. I n g e n e r a l , t h e c r i t i c a l c o n c e n t r a t i o n (above w h i c h no f u r t h e r m o b i l i t y r e d u c t i o n t a k e s p l a c e ) i s w e l l above t h e CMC range o f t h e s u r f a c t a n t solution. The E f f e c t o f COo F r a c t i o n . The e f f e c t o f CO2 f r a c t i o n (sometimes termed " q u a l i t y " ) on foam m o b i l i t y measurements has a l s o been studied. The s u r f a c t a n t under t h e i n v e s t i g a t i o n i n t h i s c a s e was t h e a n i o n i c E n o r d e t X2001 from S h e l l . F o u r d i f f e r e n t CO2 f r a c t i o n s were t e s t e d a t c o n s t a n t s u r f a c t a n t c o n c e n t r a t i o n o f 0.05 wt% active. A g a i n , t h e c o n c e n t r a t i o n o f 0.05% was chosen from t h e measurements o f s u r f a c e and i n t e r f a c i a l t e n s i o n s . The r o c k sample used f o r t h e t e s t was B e r e a s a n d s t o n e w i t h k = 302 ± 16 md. The v a r i a t i o n o f foam m o b i l i t y w i t h d i f f e r e n t v a l u e s o f CO2 fraction i s c l e a r l y s e e n i n F i g u r e 4, where t h e m o b i l i t i e s a r e p l o t t e d a g a i n s t t o t a l f l o w r a t e . The c o r r e s p o n d i n g n u m e r i c a l d a t a a r e p r e s e n t e d i n T a b l e I I . I n F i g u r e A, t h e e f f e c t o f CO2 f r a c t i o n i s q u i t e d e f i n i t e . As has been e x p e c t e d , t h e foam m o b i l i t y d e c r e a s e s w i t h d e c r e a s i n g CO2 f r a c t i o n : g r e a t e r p r e s s u r e drop i s o b s e r v e d across the core with the i n c r e a s e of s u r f a c t a n t f r a c t i o n . This v e r i f i e s t h e f a c t , l o n g known i n t h e l i t e r a t u r e , t h a t t h e p r e s e n c e o f s u r f a c t a n t s o l u t i o n a l o n g w i t h CO2 lowers t h e m o b i l i t y .


19.

383

C0 -Foam Mobility Measurements

LEE AND HELLER

2


Varion CAS in Bereo Sandstone

1.0E-4

1.0E-3

1.0E-2

Figure

3.

Effect

1.0ΕΟ

1.0E-1

Surfactant Concentration,

%

of surfactant concentration

on foam m o b i l i t y .

Bereo Sandstone (k = 302 md) D.057. Encrdet X2001 (A)

C0 .i T = 25.0 C

P

ft

2

s

1

6

1

5

p

s

i

0

e

C0 Δ

ο

0.

2

FOAM 89.710.6

•

6 8 . I i 1.4

V

5 8 . 6 1 0.4

1

2

3

4

5

Velocity F i g u r e 4.

Effect

6

7

8

9

10

11

(ft/day) of C0

2

fraction.


384


Table

II

C0 -Foam M o b i l i t y Measurements 2

E f f e c t of C0 Foam F r a c t i o n E n o r d e t X2001 (A) i n 1% Brines2

0.05%

Rock Type: B e r e a Sandstone P e r m e a b i l i t y o f the r o c k : 302 ± 16 md I n l e t p r e s s u r e o f t h e pumps: 1615 ± 5 p s i a Temperature o f t h e C 0 i n Ruska pump: 25.0 ± 0.2°C 2

C0 ( Q u a l i t y , * * %)


2

ν (ft/day)

λ (md/cp)

A χ

r

(10~

3

58.6

± 0.4

4.86 7.17

0.785 0.791

2.60 2.62

68.1

± 1.4

3.57 3.91 4.02 4.05 6.12 7.86 8.04 8.10

1.05 1.10 0.998 1.13 1.11 1.05 1.13 1.18

3.48 3.64 3.31 3.75 3.67 3.47 3.73 3.91

81.1

± 1.0

3.20 3.92 4.75 5.57 6.17 7.03 7.36 8.23 9.04

1.62 1.35 1.54 1.91 1.56 1.95 1.96 1.91 1.69

5.37 4.48 5.10 6.32 5.16 6.46 6.49 6.32 5.60

89.7

± 0.6

3.12 3.27 4.88 5.79 7.36

2.07 2.24 2.47 2.68 2.85

6.85 7.42 8.18 8.87 9.44

^ S t a n d a r d b r i n e s o l u t i o n i s made o f 0.5% N a C l and * * Q u a l i t y i s t h e volume f r a c t i o n o f t h e C0 .

0.5%

1

cp" )

CaCl .

2


2

19.

L E E AND HELLER

C0 -Foam Mobility Measurements

385

2

I t i s a l s o i n t e r e s t i n g to observe t h a t the s l o p e of the f i t t e d l i n e s ( t h a t i s , t h e dependence o f m o b i l i t y on o v e r a l l f l o w r a t e ) d e c r e a s e s as t h e s u r f a c t a n t f r a c t i o n i n c r e a s e s . A p o s s i b l e e x p l a n a t i o n i s t h a t t h e l a m e l l a e formed i n t h e p o r e space between the C0 and s u r f a c t a n t m i x t u r e become more d u r a b l e as t h e aqueous f r a c t i o n i s i n c r e a s e d . From a m a c r o s c o p i c v i e w p o i n t , more u n i f o r m d i s p l a c e m e n t would be e x p e c t e d as a r e s u l t o f t h e d e c r e a s e d mobility. Furthermore, g r e a t e r s c a t t e r i n g of data i s observed f o r the C 0 f r a c t i o n o f 81.1 ± 1.0%. It i s possible that this p a r t i c u l a r m i x t u r e may be more t h e r m o d y n a m i c a l l y u n s t a b l e t h a n "foams" o f d i f f e r e n t q u a l i t y . 2


2

T h i s v a r i a t i o n o f m o b i l i t y w i t h CO2 f r a c t i o n has a l s o been o b s e r v e d w i t h o t h e r s u r f a c t a n t s , such as V a r i o n CAS and Chembetaine BC-50. A l t h o u g h t h o s e d a t a a r e n o t p r e s e n t e d h e r e , s i m i l a r b e h a v i o r c o n s i s t e n t w i t h such a s i g n i f i c a n t d e c r e a s e i n m o b i l i t y w i t h i n c r e a s e i n s u r f a c t a n t f r a c t i o n was o b s e r v e d . The r e s u l t s o f an e x t e n s i v e s t u d y w i t h E n o r d e t X2001 have s u p p o r t e d the p r e v i o u s o b s e r v a t i o n s . To v e r i f y t h e r e p r o d u c i b i l i t y o f a l l t h e s e e x p e r i m e n t a l p o i n t s , some o f t h e measurements were p u r p o s e l y r e p e a t e d . A t y p i c a l d a t a s e t , such as t h o s e w i t h a C 0 f r a c t i o n o f 81.1 ± 1.0% of 0.05% E n o r d e t X2001 was used t o do some s t a n d a r d e r r o r analysis. The r e l a t i v e e r r o r on t h e m o b i l i t y measurement, i t s e l f , was a p p r o x i m a t e l y 4%. The e r r o r was j u d g e d t o a r i s e p r i m a r i l y from t h e u n c e r t a i n t i e s i n t h e t o t a l f l o w r a t e due t o t h e d i f f i c u l t y o f m a i n t a i n i n g " i d e a l " s t e a d y - s t a t e because C 0 is a compressible f l u i d . A l s o , t h e f l o w r a t e i s measured by u s i n g a V a l i d y n e d i f f e r e n t i a l p r e s s u r e t r a n s d u c e r which a l s o p r o d u c e s some u n c e r t a i n t y even though i t has been c a l i b r a t e d a g a i n s t a deadw e i g h t t e s t e r , and i t s z e r o i s f r e q u e n t l y checked d u r i n g t h e experiment. I n a d d i t i o n t o t h e s e , i n a c c u r a c y o c c u r s as a r e s u l t of t h e h e t e r o g e n e i t i e s o f t h e r o c k . 2

2

In our l a b o r a t o r y , we have s c r e e n e d a number o f s u r f a c t a n t s . The s t a n d a r d s u r f a c t a n t s c r e e n i n g t e s t i n c l u d e d foam h e i g h t measurement, t h e r m a l a g i n g t e s t , and pH e v a l u a t i o n . V a r i o n CAS and E n o r d e t X2001 performed v e r y w e l l on t h e foam h e i g h t measurement. B o t h a l s o showed v e r y p r o m i s i n g r e s u l t s on t h e t h e r m a l a g i n g t e s t , even though t h e i r r e s u l t s a r e n o t p r e s e n t e d here. Conclusions From t h e r e s e a r c h on C 0 - f o a m m o b i l i t y measurements, a few s i g n i f i c a n t c o n c l u s i o n s on foam f l o o d i n g have been drawn. The e f f e c t o f c o n c e n t r a t i o n on foam m o b i l i t y has been c l e a r l y seen w i t h t h e V a r i o n CAS. W i t h t h i s s u r f a c t a n t an i n c r e a s e beyond 0.05% o f i t s c o n c e n t r a t i o n seemed t o s e c u r e no f u r t h e r d e c r e a s e i n mobility. The same g e n e r a l p a t t e r n o f v a r i a t i o n was o b s e r v e d w i t h o t h e r s u r f a c t a n t s . The e f f e c t o f C 0 f r a c t i o n was measured i n a comprehensive s t u d y u s i n g E n o r d e t X2001. A g a i n , t h e same t r e n d was o b s e r v e d w i t h o t h e r s u r f a c t a n t s , such as Chembetaine BC-50 and V a r i o n CAS, a l t h o u g h t h e d a t a were n o t p r e s e n t e d h e r e . The m o b i l i t y i s d e f i n i t e l y lowered by i n c r e a s i n g t h e s u r f a c t a n t f r a c t i o n i n t h e foam. I t seems c l e a r t h a t , i n t h e p r e s e n c e o f 2

2


386



s u r f a c t a n t s o l u t i o n s , dense CO2 forms foam l a m e l l a e , i n t h e p o r e s p a c e , and t h a t t h i s i s t h e r e s p o n s i b l e mechanism o f m o b i l i t y reduction. A t s u r f a c t a n t c o n c e n t r a t i o n s lower t h a n t h e CMC, l a m e l l a e a r e so r a r e as t o have no i n f l u e n c e on t h e f l o w . A l t h o u g h n o t p o i n t e d o u t i n t h e t e s t , i t may be o b s e r v e d from t h e d a t a t h a t t h e r e i s some e f f e c t on m o b i l i t y o f v e l o c i t y o r t o t a l f l o w r a t e . Some s h e a r t h i n n i n g o r p s e u d o p l a s t i c b e h a v i o r has been o b s e r v e d under c e r t a i n c o n d i t i o n s . T h i s i s , o f c o u r s e , t h e more f a v o r a b l e o f p o s s i b l e non-Newtonian b e h a v i o r s f o r foam m o b i l i t y c o n t r o l , s i n c e i t would mean t h a t l e s s t h i c k e n i n g o c c u r r e d i n t h e v i c i n i t y o f t h e i n j e c t i o n w e l l , than f u r t h e r out i n t h e formation.

Literature Cited 1. Bernard, G.G.; Holm, L.W.; Harvey, C.P. Soc. Pet. Eng. J. 1980, 20, 281-92. 2. Wang, G.C., presented at the SPE/DOE Fourth Symposium on Enhanced Oil Recovery, Tulsa, OK, April 1984. 3. Wellington, S.L.; Vinegar, R.J. Soc. Pet. Eng. J. 1987, 27, 885-98. 4. Hydrocarbon Displacement by Carbon Dioxide Dispersion, Technical Note, U.S. Department of Energy, March 1986. 5. Holm, L.W.; Josendal, V.A. J. Pet. Tech. 1974, 26, 1427-37. 6. Heller, J.P.; Kuntamukkula, M.S. Ind. Eng. Chem. Res. 1987, 26, 318-25. 7. Heller, J.P.; Lien, C.L.; Kuntamukkula, M.S. Soc. Pet. Eng. J. 1985, 25, 603-13. 8. Radke, C.J.; Ransohoff, T.C., presented in part at the 61st SPE Annual Technical Conference and Exhibition, New Orleans, LA, Oct. 1986. 9. Heller, J.P., presented at the SPE/DOE Fourth Symposium on Enhanced Oil Recovery, Tulsa, OK, April 1984. 10. Heller, J.P.; Boone, D.A.; Watts, R.J., presented at the 60th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, Las Vegas, NV, Sept. 1985. 11. Patel, P.D.; Christman, P.G.; Gardner, J.W., presented at the 60th SPE Annual Technical Conference and Exhibition, Las Vegas, NV, Sept. 1985. 12. Falls, A.H. et al., presented at the DOE/SPE Fifth Symposium on Enhanced Oil Recovery, April 1986. 13. Hirasaki, G.J.; Lawson, J.B. Soc. Pet. Eng. J. 1985, 25, 17690. 14. Borchardt, J.K. presented at the SPE International Symposium on Oilfield Chemistry, San Antonio, TX, Feb. 1987. 15. Maini, B.B., Ma, V. J. Can. Pet. Tech. 1986, 25, 65-9. 16. Khatib, Z.I., Hirasaki, G.J., and Falls, A.H., presented at the 61st SPE Annual Technical Conference and Exhibition, New Orleans, LA, Oct. 1986. RECEIVED January 5, 1988


Surfactant-Based Mobility Control - American Chemical Society

Recommend Documents