Phase Equilibria and Fluid Properties in the Chemical Industry

13 Oil Recovery by C O Injection 2

RALPH SIMON

Downloaded by NANYANG TECHNOLOGICAL UNIV on June 10, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0060.ch013

Chevron Oil Field Research Co., LaHabra, CA 90631

In the U.S. ( e x c l u d i n g Alaskan North Slope) =420 b i l l i o n b a r r e l s of o i l have been d i s c o v e r e d ( F i g u r e 1 ) . Of t h i s amount 110 b i l l i o n have a l r e a d y been produced and an a d d i t i o n a l 30 b i l l i o n can be economically recovered a t present p r i c e s as primary o r secondary p r o d u c t i o n . Of the ^280 b i l l i o n unrecoverable by primary and secondary methods o n l y a f r a c t i o n can be recovered. P u b l i s h e d s t u d i e s suggest t h a t CO2 might recover 5 t o 10 b i l l i o n b a r r e l s . T h i s amount depends on economic parameters, t h e primary one being t h e p r i c e of crude o i l . The s u i t a b i l i t y of a s p e c i f i c r e s e r v o i r f o r CO2 i n j e c t i o n can be estimated from phase behavior measurements, p h y s i c a l p r o p e r t y c a l c u l a t i o n s , and displacement t e s t s i n v a r i o u s porous media. R e s e r v o i r s t h a t a r e candidates f o r CO2 i n j e c t i o n g e n e r a l l y have pressures exceeding 1500 p s i a (100 atmospheres) and crude o i l s w i t h s p e c i f i c g r a v i t y 30° A P I ) . In 1976 t h e r e a r e 6 commercial CO2 i n j e c t i o n p r o j e c t s ( 1 ) , and more a r e planned. I t ' s d o u b t f u l t h a t enough g o o d - q u a l i t y n a t u r a l l y o c c u r r i n g CO2 can be found f o r a l l of them. Displacement

Mechanisms i n C O 2 — R e s e r v o i r O i l Systems

The p h y s i c a l phenomena t h a t occur d u r i n g CO2 i n j e c t i o n can be e x p l a i n e d w i t h t h e a i d of a s e r i e s of s i m p l i f i e d network model drawings o f a porous medium. F i g u r e 2 r e p r e s e n t s a v i r g i n r e s e r v o i r c o n t a i n i n g o i l as t h e continuous phase and connate water i n i s o l a t e d c l u s t e r s of pores. F i g u r e 3 shows the r e s e r v o i r a f t e r a w a t e r f l o o d , i n d i c a t i n g the r e s i d u a l o i l not d i s p l a c e d by the water and the continuous water phase r e a c h i n g from i n l e t t o o u t l e t . F i g u r e 4 i l l u s t r a t e s the i n v a s i o n of CO2 f o l l o w i n g the w a t e r f l o o d . The advancing CO2 d i s s o l v e s i n the r e s i d u a l r e s e r v o i r o i l , causing i t t o s w e l l , decreasing i t s v i s c o s i t y , and v a p o r i z i n g the more v o l a t i l e components i n the o i l . The advancing vapor phase i s a l s o a b l e t o enter and d i s p l a c e pores c o n t a i n i n g r e s i d u a l o i l 241

Storvick and Sandler; Phase Equilibria and Fluid Properties in the Chemical Industry ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

242

P H A S E EQUILIBRIA

A N D F L U I D PROPERTIES

IN C H E M I C A L INDUSTRY

BILLION BARRELS US DISCOVERIES*

420

PRODUCED TO DATE

110


PRODUCIBLE WITH EXISTING PROCESSES AND ECONOMICS

30

FROM COn

5-10

EXCLUDING ALASKAN NORTH SLOPE

Figure 1

0

WATER

•

OIL

•

INJECTED WATER

ED c o

Figure 2.

(INTERSTITIAL)

2

Oil (continuous) with connate water



13.

SIMON

Oil Recovery by C0

2

243

Injection

0

WATER (INTERSTITIAL)

•

OIL

•

INJECTED WATER

•

Figure 3.

co

2

Oil after waterflood

0

WATER (INTERSTITIAL)

•

OIL

•

INJECTED WATER

E3 c o

Figure 4.

2

Oil with C0 injection 2


244

P H A S E EQUILIBRIA A N D

F L U I D PROPERTIES IN

CHEMICAL

INDUSTRY

because of low i n t e r f a c i a l t e n s i o n between the advancing gas and r e s i d u a l l i q u i d . The combination of these phenomena enables CO2 to d i s p l a c e o i l i n e i t h e r secondary or t e r t i a r y c o n d i t i o n s .


Phase and Flow Behavior C h a r a c t e r i s t i c s of C02 — R e s e r v o i r O i l Systems The mechanisms described i n the previous s e c t i o n are expressed q u a n t i t a t i v e l y i n Figures 5 through 10. Figure 5 shows CO2 s o l u b i l i t y i n o i l as a f u n c t i o n of pressure and temperature. Note that at t y p i c a l r e s e r v o i r c o n d i t i o n s e.g. 2,000 p s i a (135 atmospheres), and 170°F (77°C) the s o l u t i o n cont a i n s 65 mol percent CO2. At these c o n d i t i o n s the d e n s i t y of the

TEMPERATURE

Figure 5.

C0

2

solubility in oil



13.

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Oil Recovery by C0

2

Injection

245

CO2 and some r e s e r v o i r o i l s a r e n e a r l y equal, thus m i n i m i z i n g CO2 gravity override. F i g u r e 6 shows o i l phase v o l u m e t r i c expansion. With 65 mol percent CO2 i n s o l u t i o n the s w e l l i n g can be 25 percent. As the o i l s w e l l s i t d i s p l a c e s adjacent o i l toward the producing w e l l s . F i g u r e 7 d i s p l a y s the v i s c o s i t y of C02~crude o i l m i x t u r e s . The data show that d i s s o l v e d CO2 can reduce v i s c o s i t y as much as 100 f o l d . This improves the m o b i l i t y r a t i o and decreases the tendency of CO2 to f i n g e r i n the h i g h p e r m e a b i l i t y paths. A comp l e t e d i s c u s s i o n of F i g u r e s 5, 6, and 7 and r e l a t e d measurements i s i n Reference 2. F i g u r e 8 shows the two phase boundary and c r i t i c a l p o i n t f o r a C 0 2 - r e s e r v o i r o i l system and notes t h a t a s o l i d p r e c i p i t a t e d a t

1.40

-

0

.20

X co

40

.60

2

Figure 6. Swelling factor vs. mol fraction C0

2

*vol @ safn press, ir temp vol @ 1 atm ir temp


246


A N D F L U I D PROPERTIES IN C H E M I C A L INDUSTRY


1.0 | -

0

1000

2000

SATURATION PRESSURE, PSIA

Figure 7.

Viscosity of C0 -crude oil mixtures at 120°F 2


SIMON

Oil Recovery

by CO

$

Injection


13.

Figure 8.

Pressure-composition diagram at 130°F: Oil A

American Chemical Society Library 1155 16th St., N.W. Storvick and Sandler; Phase Equilibria and Fluid Properties in the Chemical Industry Washington, D.C. 20036 ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

247

248

PHASE

EQUILIBRIA A N D F L U I D

PROPERTIES IN C H E M I C A L

INDUSTRY

CO2 c o n c e n t r a t i o n s >60 mol percent. C r i t i c a l p o i n t s of systems s t u d i e d ranged from 60 mol percent CO2 and 2570 p s i a (175 atmospheres) to 75 mol percent and 4890 p s i a (330 atmospheres). F i g u r e 9 p r o v i d e s "K" data f o r one C T ^ - r e s e r v o i r o i l system at one p r e s s u r e . For systems near the c r i t i c a l p o i n t , the K s approach 1.0 and a s i g n i f i c a n t amount o f o i l v a p o r i z e s . F i g u r e 10 i n d i c a t e s how i n t e r f a c i a l t e n s i o n between gas and l i q u i d phases v a r i e s w i t h CO2 c o n c e n t r a t i o n and p r e s s u r e , approaching zero near the c r i t i c a l p o i n t . The flow behavior of C 0 2 ~ r e s e r v o i r o i l systems i n porous media i s s t u d i e d by performing displacement t e s t s i n both bead-packed s l i m tubes (length/diameter >100) and c o n s o l i d a t e d sandstone and


f

Figure 9.

KP vs. F plot for 55 mol % C0 , oil at 130°F 2

45 mol % reservoir


SIMON

Oil Recovery by C0

2

249

Injection


13.

δ s ο «s to to

S o to ©ι Ο

υ s S

Ι

to v. ce

ο

Ί to H to to .g

to Ο ο »-< to κ.


250




limestone cores. The tubes are used to determine the optimum pressure f o r o i l displacement (Figure 11 ( 3 ) ) ; the cores to measure o i l recovery versus pore volumes i n j e c t e d . F i g u r e 12 i n d i c a t e s the p o t e n t i a l o f CO2 to recover o i l from a p r e v i o u s l y waterflooded reservoir.


Calculations The phase and flow behavior data d e s c r i b e d above are the b a s i s f o r c a l c u l a t i o n s used to evaluate new p r o j e c t s , design approved ones, and operate them e f f i c i e n t l y . These c a l c u l a t i o n s a r e done p r i n c i p a l l y w i t h a Compositional S i m u l a t o r . The main c a l c u l a t i o n

1001-

O AT71°F 80

AT C0 BREAKTHROUGH 2

Q LU CC LU >

60

o o

40

20 -

0 1200

1600 2000 FLOOD PRESSURE (PSIG)

Figure 11. Oil recovered from C0

2

2400

floods of 48-ft long sand pack


Storvick and Sandler; Phase Equilibria and Fluid Properties in the Chemical Industry ACS Symposium Series; American Chemical Society: Washington, DC, 1977. Figure 12. Oil recovery vs. HCPVI


to ox

A N D FLUID PROPERTIES






13.

SIMON

Oil Recovery by C0

2

Injection

253

i s a performance p r e d i c t i o n t h a t shows recovery versus time f o r a s p e c i f i e d number and l o c a t i o n o f w e l l s , i n j e c t i o n r a t e , r e s e r v o i r pressure and temperature, e t c . Compositional S i m u l a t o r c a l c u l a t i o n s a r e a l s o used to h e l p understand the e f f e c t s o f mass t r a n s f e r as CO2 advances through the r e s e r v o i r and d i s p l a c e s o i l . Two examples: F i g u r e 13 shows the C2+ i n the gas phase versus time and d i s tance. Note how the gas phase e n r i c h e d w i t h 20 mol percent C2+ moves through the r e s e r v o i r . F i g u r e 14 d i s p l a y s i n t e r f a c i a l t e n s i o n versus time and d i s tance. Here a low ( e s s e n t i a l l y zero) i n t e r f a c i a l t e n s i o n f r o n t i s shown moving through the r e s e r v o i r . Under these c o n d i t i o n s CO2 provides a m i s c i b l e displacement. Research In recent years there have been s i g n i f i c a n t advances i n o b t a i n ing data on C 0 2 - r e s e r v o i r o i l systems. However, more data a r e needed i n order to e v a l u a t e , design, and operate i n d i v i d u a l CO2 i n j e c t i o n p r o j e c t s w i t h o u t f i r s t making e x t e n s i v e , c o s t l y , and time-consuming experimental s t u d i e s . A d d i t i o n a l i n f o r m a t i o n i s needed p r i m a r i l y i n two c a t e g o r i e s : 1. P r e d i c t i n g the p r o p e r t i e s o f two-phase m i x t u r e s — s p e c i f i c a l l y , more r e l i a b l e K c o r r e l a t i o n s and i n t e r f a c i a l t e n s i o n equations. 2. Understanding mass t r a n s f e r and p r e d i c t i n g i t s e f f e c t versus time and d i s t a n c e as a CO2 f r o n t moves through the r e s e r v o i r .

Abstract Various authors have estimated that five to ten billion barrels of U.S. crude oil (excluding Alaskan North Slope) may be potentially recoverable by CO injection. This recovery will result when CO dissolves in the oil, swellsit,reduces its viscosity and lowers interfacial tension between the injected gas and the residual oil thus enhancing oil displacement. Also CO vaporizes the volatile part of the oil, carrying it from the reservoir in the gas phase. Physical property correlations and displacement tests with CO -reservoir oil systems are needed to calculate the effect of CO injection. The calculations are used in evaluating new projects, designing approved ones, and operating them efficiently. Research is needed to improve the reliability of present calculation methods, particularly for predicting the properties of two-phase mixtures. 2

2

2

2

2

Literature Cited (1)

O i l & Gas Journal, April 5 (1976).






254

to to ΰ ."co

to

I CO

•2 "co

s to

to to S

8


13.

SIMON

Oil Recovery by C0

2

Injection


(2) Simon, R., and Graue, D. J., J. Pet. Tech., (1965). (3) Holm, L. W., and Josendahl, V. Α., J. Pet. Tech., (1974).


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Phase Equilibria and Fluid Properties in the Chemical Industry

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