Chapter 18
Oil Recovery with Multiple Micellar Slugs 1
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Downloaded by COLUMBIA UNIV on February 26, 2013 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch018
S. Thomas, S. B. Supon, and S. M . Farouq Ali
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1Department of Mining, Metallurgical and Petroleum Engineering, The University of Alberta, Edmonton, Alberta T6G 2G6, Canada Petroleum and Natural Gas Engineering, Pennsylvania State University, University Park, PA 16802
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Micellar flooding process has been shown to be an effective tertiary o i l recovery technique for watered-out light o i l reservoirs, based upon many f i e l d tests. However, under the present o i l prices i t has not been economic in most cases. In other instances, recovery methods such as carbon dioxide flooding may be more attractive. The present research was aimed at improving the efficiency of the micellar flooding process through the use of multiple micellar slugs. The slugs were selected on the basis of the phase behaviour of various ternary systems (crude, water, surfactant). Equilibrium micellar phases chosen from the single phase region or, micellar compositions formed along the dilution path of a suitable micellar slug in the single phase region were used to form the composite slugs. O i l - r i c h and water-rich slugs were compared for their effectiveness to recover tertiary oil. Multiplicity of slugs on recovery efficiency was examined by injecting portions of o i l - r i c h and water-rich slugs alternately until the desired slug volume was reached. The use of graded composite slugs - starting with an o i l - r i c h slug and ending with a water-rich slug - was successful in improving process efficiency. (Process efficiency, in this work, is defined as the tertiary recovery per unit volume of slug injected). For example, process efficiency increased five fold when a single slug was replaced by a graded composite slug of equivalent size. 0097-6156/89/0396-0345$06.00/0 e 1989 American Chemical Society In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Downloaded by COLUMBIA UNIV on February 26, 2013 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch018
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OIL-FIELD CHEMISTRY
The works o f v a r i o u s i n v e s t i g a t o r s s u c h as G o g a r t y and T o s c h (1), H e a l y and Reed ( 2 ) , and D a v i s and Jones Q), have shown t h a t t h e m i c e l l a r f l o o d i n g p r o c e s s can be u s e d e f f e c t i v e l y t o m o b i l i z e r e s i d u a l o i l i n watered-out l i g h t o i l reservoirs. Many f i e l d t e s t s c o n d u c t e d i n t h e U.S. have f u r t h e r p r o v e d i t s e f f e c t i v e n e s s . However, t h e economics of the p r o c e s s remain u n a t t r a c t i v e f o r implementing the process f o r t e r t i a r y o i l recovery. Recent works by Holm ( A ) , Pope (H), Sayyouh and F a r o u q A l i (£), Enedy and F a r o u q A l i (2) made s i g n i f i c a n t c o n t r i b u t i o n s towards i m p r o v i n g t h e e f f i c i e n c y o f t h e process. The p r i m a r y o b j e c t i v e o f t h i s r e s e a r c h was t o devise a m i c e l l a r flooding process that i s economically as w e l l as t e c h n i c a l l y a t t r a c t i v e t o t h e i n d u s t r y , t h r o u g h t h e use o f m u l t i p l e m i c e l l a r s l u g s . Process
Description
P r o c e s s e f f i c i e n c y , i n t h i s s t u d y , i s d e f i n e d as t h e t e r t i a r y o i l r e c o v e r y p e r u n i t volume o f t h e s l u g injected. T h i s r e f e r s t o t h e e f f i c i e n c y o f an o i l - r i c h slug. Economic r e c o v e r y e f f i c i e n c y v a r i e s from s l u g t o s l u g due t o v a r i a t i o n s i n t h e s u r f a c t a n t c o n t e n t . It s h o u l d be n o t e d t h a t t h e m i c e l l a r s l u g s were f o r m u l a t e d w i t h an e f f o r t t o keep t h e c o s t a minimum. Basic Process. H y d r o c a r b o n , w a t e r / b r i n e and surfactant a r e t h e b a s i c components o f a m i c e l l a r s o l u t i o n . A small amount o f a l c o h o l i s u s u a l l y added t o improve t h e s o l u t i o n s t a b i l i t y , t o a d j u s t t h e v i s c o s i t y , and t o r e d u c e t h e s u r f a c t a n t l o s s due t o a d s o r p t i o n on t h e r e s e r v o i r rock. A s u i t a b l y formulated m i c e l l a r slug m i s c i b l y d i s p l a c e s the r e s i d u a l o i l , l e a d i n g t o a very small f i n a l o i l saturation. F o r economic r e a s o n s , a s m a l l p o r e volume (2-5%) m i c e l l a r s l u g i s i n j e c t e d , and i t i s e f f e c t i v e l y p r o p a g a t e d t h r o u g h t h e r e s e r v o i r by t h e mobility buffer. The m o b i l i t y b u f f e r p r o t e c t s t h e s l u g f r o m d i l u t i o n by t h e d r i v e water t o o e a r l y i n t h e process. The e f f i c i e n c y o f t h e p r o c e s s can be augmented by u s i n g a s u i t a b l e c o m p o s i t e s l u g c o n f i g u r a t i o n . A c o m p o s i t e s l u g c o n s i s t s o f o i l - r i c h and w a t e r - r i c h slugs, i n j e c t e d a l t e r n a t e l y i n two o r more s t e p s , u n t i l t h e d e s i r e d p o r e volume i s r e a c h e d . The economics o f t h e p r o c e s s can be f u r t h e r enhanced by u s i n g a g r a d e d composite s l u g . Such s l u g s can r e d u c e the s u r f a c t a n t r e q u i r e m e n t t o a minimum, and maximize t h e t e r t i a r y recovery e f f i c i e n c y . Phase B e h a v i o u r S t u d i e s and
Slug
Formulation
The e f f i c i e n c y o f a m i c e l l a r s l u g t o r e c o v e r t e r t i a r y o i l i s l a r g e l y dependent on i t s a b i l i t y t o r e m a i n a s i n g l e phase d u r i n g t h e f l o o d i n g p r o c e s s so t h a t t h e o i l may be d i s p l a c e d " m i s c i b l y " and hence, c o m p l e t e l y . However,
In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Downloaded by COLUMBIA UNIV on February 26, 2013 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch018
18.
THOMAS ETAL.
Multiple Micellar Slugs
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v a r i o u s f a c t o r s such as s l u g d i l u t i o n by r e s e r v o i r f l u i d s , s u r f a c t a n t l o s s t o t h e r e s e r v o i r rock, r e s e r v o i r s a l i n i t y e t c . i n f l u e n c e t h e phase b e h a v i o u r a d v e r s e l y . Once s l u g breakdown o c c u r s , t h e d i s p l a c e m e n t becomes i m m i s c i b l e a n d some o f t h e r e s i d e n t o i l c a n be l e f t trapped i n the pores. T e r t i a r y r e c o v e r y c a n be s u b s t a n t i a l l y improved i f t h e s l u g c o m p o s i t i o n h a s a minimal multiphase r e g i o n t o p r o l o n g the m i s c i b l e d i s p l a c e m e n t regime, and a low i n t e r f a c i a l t e n s i o n i n t h e m u l t i p h a s e r e g i o n t o enhance t h e i m m i s c i b l e d i s p l a c e m e n t . Another f a c t o r c o n t r i b u t i n g t o o i l displacement i s t h e r e l a t i v e l y l a r g e r o l e i c phase volume a t s l u g breakdown. W i t h t h e s e ends i n view, a number o f phase b e h a v i o u r s t u d i e s were made t o f o r m u l a t e e f f i c i e n t m i c e l l a r s l u g s f o r t h e t e r t i a r y r e c o v e r y o f t h r e e l i g h t o i l s - Bonnie G l e n , P r o v o s t , and B r a d f o r d c r u d e s . Phase B e h a v i o u r C h a r a c t e r i s t i c s . Studies of ternary systems, r e p r e s e n t i n g c r u d e o i l , w a t e r / b r i n e a n d s u r f a c t a n t systems were c o m p l e t e d p r i o r t o t h e s e l e c t i o n of m i c e l l a r s l u g s . The b r i n e u s e d i n t h i s s t u d y was 2 % ( w t . / v o l . ) sodium c h l o r i d e i n d i s t i l l e d w a t e r . I t was f o u n d t h a t t h e phase b o u n d a r i e s depend, t o a g r e a t e x t e n t , on t h e w a t e r / o i l r a t i o i n t h e i n i t i a l system. Because o f t h e multicomponent n a t u r e o f t h e m i c e l l a r s o l u t i o n s , t h e phase b e h a v i o u r o f t h e system i s much more complex t h a n a s i m p l e t h r e e component system. Therefore, a p s e u d o t e r n a r y system c o u l d o n l y be u s e d t o q u a l i t a t i v e l y c o r r e l a t e t h e o b s e r v a t i o n s on t h e phase behaviour o f the m i c e l l a r s o l u t i o n s . Due t o economic reasons and v i s c o s i t y requirements, t h e s u r f a c t a n t and o i l c o n c e n t r a t i o n s were l i m i t e d t o 5-15% a n d
