Solvent Stimulation of Viscous Crude Oil Production

8/9/2019 Solvent Stimulation of Viscous Crude Oil Production

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SOCIETY OF PETROLEUM ENGINEERS OF AIME

6200 North Central Expressway

Dallas, Texas

75206

PAPER

NUM RPE 3680

~HIS IS A PREPRINT --= SUBJECT TO CORRECTION

Sol vent Stimul ati on of Vi scous

Crude-Oi l Producti on

By

G. L. Gates, Member AIME, and W. H. Caraway, USBM

This paper was prepared for the 42nd Annual California Regional Meeting of the Society of

Petroleum Engineers of AIME, to be held in Los Angeles, Calif., Nov. 4-5, 1971.

Permission to copy

is restricted to any abstract of not more than 300 words.

Illustrations may not be copied.

The

abstract should contain conspicuous acknowledgment of where and by whom the paper is presented.

Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF

PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the p p r q n i t e t ou r n i

provided agreement to give proper credit is made.

Discussion of this paper is invited.

Three copies of any discussion should be sent to the

Society of Petroieum Engineers office.

Such discussion may be presented at the above meeting and,

with the paper,

may be considered for publication in one of the two SPE magazines.

ABSTRACT.

To improve both the rate and volume of pro-

duction of viscous crude oils, the USBM made a

study of solvents to stimulate production.

Five

laboratory methods were used to evaluate the

effectiveness of several solvents in the stim-

ulation of viscous oil production.

These meth-

ods were (1) viscosity reduction, (2) gravity

drainage production from sand columns, (3) dis-

placement from capillary tubes, (4) effect of

organic acids on crude oil viscosity and (5)

oils.

Previous USBM studies showed that over”

100 billion bbl of viscous crude oil are pre-

sent in over 2,000 petroleum reservoirs.1 2

California has the largest resource of viscous

crude oil

-- about 75 percent of the oil clas-

sified as most favorable for recovery by

stimulative methods. Exploration costs for

viscous oils are almost nonexistent because the

large reserves are in known fields where many

producing facilities already exist.

Interest

in the viscous crude oil resource has been en-

hanced further by the development of high-yield


2/11

2

SOLVENT STIMULATION OF VISCOUS CRUDE-OIL PRODUCTION

SPE 3680

Bursell, Taggart and Demirjian5 reported

that steam displacement tests in a pilot area

in the Kern River field recovered over 35 per-

cent of the oil in place in 3 years.

Primary

production methods in the previous 66 years

produced about 10 percent of the oil in place.

In 1970, 138,000 B/D of California produc-

tion were attributed to thermal stimulation.6

Review of other methods for stimulation of

crude oil production showed that miscible flood-

ing using propane is a means of increasing

appreciably (to 51 per cent of oil in place)

recovery of some crude oils.7 However, this

method may not be feasible for highly viscous

oils. Propane is known to precipitate asphal-

tenes from viscous asphaltic crude oils.

Solvents have been used successfully in

California to aid in the production of viscous

crude oils. In the Oxnard field, California,

pumping of viscous crude oil from wells in the

Vaca tar sands is facilitated by pumping a

solvent down hollow sucker rods and out ports a

8 By this method,

hort distance above the pump.

the viscous crude oil can be pumped and, at the

end of the steam production cycle, the pump and

rods can be pulled.

In the San Ardo field, California, solvent

is added to crude oil in the wells to aid in

shipping the viscous crude oil from the field to

the refinery.

Solvents have been used in well clean-out

operations for many years.

However,

adding a

solvent into the formation and back some dis-

FUNCTIONS OF SOLVENTS

The solvent added to a petroleum reservoir

containing viscous crude oil has four primary

functions in stimulating production.

Those

functions are (1) reduction of viscosity of

crude oil, (2) breaking of emulsions, (3) re-

moval of organic deposits -- asphaltenes and

paraffins and (4) removal of insoluble solids

-- clays, siits and sand.

Reduction of Viscositv

Although the importance of viscosity reduc

tion in production has been known for a long

time, the advent of steam stimulation was the

first large-scale successful use of this con-

cept.ll Owens and Suter12 showed by field data

that the rate of production of high viscosity

oils was inversely proportional to the viscosit

of the oil, which is to be expected from

consideration of Darcy’s equation.

Liquid mixtures are believed to be viscous

because large molecules or associated clusters

of molecules cannot move freely over one anothe

As explained by Harris and Prausnitz,13 devia-

tions from ideal behavior in liquid mixtures ca

be interpreted in terms of intermolecular force

.—--.L...-....L,..-L..— —.......-

operazlng wlznln me mlxzure.

n-.--_l--_——-,..—-

Druauly speafixng

it is convenient to distinguish between strong

attractive (chemical) forces leading to forma-

tion of chemical species and weak attractive

(physical) forces, frequently called van der

Waals forces. Accordingly, the traditional

theory of liquid solutions has followed two

distinct paths. One path interprets solution

nonideality in terms of chemical forces, neglec


3/11

SPE 3680

G. L. GATES and W. H. CARAWAY

3

greater than the viscosity of the crude oil.

Emulsion viscosities as large as 46.5 times

that of clean oil have been reported.14

Solvents generally break emulsions and

therefore decrease the viscosity of the mixture

of oil and water flowing from the well, thus

enhancing well productivity.

Reduction of

emulsions in production after solvent intro-

duction was reported.g

Removal of Organic Solids--

Asphaltenes and Paraffins

Black asphaltene deposits have diminished

flow from many California wells by plugging

screens, liners, gravel packs, and probably

the formations surrounding wellbores. Highly

aromatic oils have been used successfully to

wash wells to remove these deposits.

Good sol-

vents have improved the production and lowered

the asphaltene contents of the produced oil, as

has bee; reported by Jeffries-Harris and

Coppel.

Teberg15 credits wellbore cleanup as the

most important contribution, at least in the

first cycle, 02 steam stimulation in the

Wilmington field.

This conclusion was reached

when it was observed that well productivity

remained high after the temperatures of the oil

decreased to the normal reservoir temperature.

Removal of Insoluble Solids--

Clavs. Silts and Sand

Both laboratory and field tests have shown

that injection and backflush of solvents

able for the process:

(1) the producing sand

contains a high oil saturation and occurs at a

shallow depth, (2) an inexpensive and efficient

solvent is readily available, (3) the solvent

Penetrates the oil ----s..

----.A--.L1 m , 4.—

sana LU a UmDLUCLaU.. -..–

tance from the well and mixes with the oil, (4)

most of the solvent is recovered with the pro-

duced oil and (5) the cost of the solvent is

minimized,

either by being recovered in a top-

ping plant in the field or by increasing the

selling price of the oil-solvent mixture.

Laboratory tests were made to provide some

of the information needed to make feasibility

studies of solvent injection in fields contain-

ing viscous oils. These tests were designed to

provide answers to such questions as (1) how

much more will an expensive solvent such as

toluen4 reduce viscosity when compared to a

less expensive solvent such as a light fraction

from a nearby refinery, (2) how much additional

production can be expected by flushing the pro-

ducing sand with various solvents and (3) can

the results of the laboratory tests be gener-

.–.L..—-s A-——- L-

aiized n oroaa terms bu SaY, fOY e~arlp~e,t~~t

aromatic solvents will provide sufficient

additional oil to pay the additional cost of

solvent stimulation?

In order to provide answers to these and

other questions, five series of laboratory tests

were made: (1) reduction of viscosity obtained

by mixing crude oils with various solvents, (2)

additional oil recovery obtained by gravity

drainage from sand-packed columns containing

crude oil and irreducible water saturation by

the addition of solvent to the top of the colunu

(3) the time required to displace crude oil frou


4/11

A

SOLVENT STIMULATION OF VISCOUS CRUDE-OIL PRODUCTION

SPE 3680

solvent mixtures having a viscosity greater than

about 50 cp were measured with a Brookfield

viscometer,

using standard procedures, while

those of lower viscosities were measured with

the Zeitfuch viscometer. Viscosities were

measured at 100°, 111°, 125° and 150° F. The

crude oils contained less than about 2 percent

water.

A rather wide range was found in the effec-

tiveness of the different solvents in reducing

the viscosity of crude oil, as shown in Table 4.

The addition of only a few percent of the more

effective solvents resulted in a large reduction

in the viscosity of the San Ardo crude oil. A

typical example (Kern River crude oil and

toluene) is shown in Fig. 2.

Molecular Weight

The molecular weights of the solvents were

determined with a vapor-pressure osmometer. An

approximate correlation between solvent molecu-

lar weight and viscosity reduction effective-

ness was found. The solvents with low

molecular weight generally were most effective

in viscosity reduction, as shown in Table 5.

Sand-Column Production by Gravity Drainage

Solvents were evaluated also by observing

their effectiveness in increasing recovery

volume and rate of recovery of viscous crude oil

from sand-packed columns by gravity drainage.

Monterey beach sand was packed in glass columns

about 30 cm long. Pore space in the column was

filled first with water and then the water was

partially displaced by the viscous crude oil.

for the Kern River crude oil and toluene.

Toluene recovered more oil in less time than

Mobil solvent,

as shown in Fig. 3.

AS shown in Figs. 3 and 4, both the rate

and volume of oil produced were increased by

addition of the solvent.

Although the unstim-

ulated production curve may appear eventually

to cross the stimulated production curve at

some long extrapolated time, observed production

for very long times indicated that the curves do

not cross. Both curves asymptoticallyapproach

different final values.

A series of tests were made in which the

effluent from a sand column was carefully mon-

itored.

The composition of the effluent from

the column was analyzed for solvent (toluene),

using a gas chromatographythat was modified for

use with viscous crude oils.

A glass tube was

used in the chromatographyinjector so that the

residue of the material not vaporized in the

glass tube could be removed periodically.

With

this equipment, the movement of toluene through

the sand during gravity drainage of oil from the

column could be determined by quantitatively

measuring the toiuene content of the effluent

produced from the column.

As shown in Figs. 3 and 4, production from

the columns increased above the unstimulated

rate in about 2 to 4 hours.

When the acceler-

ated rate was observed, the solvent added to the

top of the column visibly had moved down only

about 2 cm from the top of the column. At this

time, analysis of the column effluent showed

that measured quantities of toluene were in the

column effluent.

How did the toluene reach the


5/11

SPE 3680

G. L. CL4TESand W. H. CARAWAY

5

moved viscous crude oil from small glass capil-

lary tubes was observed.

In this series of

tests,

capillary glass tubing, 0.4 mm ID and 1.5

in. long, was filled with heated viscous crude

and, after cooling, immersed in the solvent.

The time required for the solvent to remove the

crude oil from the tubing was visually observed

and recorded.

Tests were made with the capil-

lary tube placed horizontally and vertically.

Tubes placed vertically had a displacing force

resulting from the difference in density of the

crude oil and solvent.

The results shown in Table 6 indicate that

the solvents containing large quantities of

aromatic hydrocarbons removed the viscous crude

faster than paraffinic-naphthenic solvents. The

longest removal time was required for n-decane.

The shortest time was recorded when the tubes

were immersed in toluene.

Study by USBE Laramie Energy

Researcn

-- .._l-

Center of the properties of asphalts indicated

that the addition of monofunctional group com-

pounds caused a decrease in viscosity of the

asphaltic mixtures.

In contrast,

the addition

of difunctional group compounds caused an in-

crease in the viscosity of asphaltic mixtures.

Consideration of the reported presence of

many organic acids in a California viscous crude

oii17 suggested that additiomil E.t-udy-imitihi

made of the effect of these compounds on viscous

crude oils. Stearic acid (monofunctional) was

added to Oxnard viscous crude oil in the San

aromatic solvents of low molecular weight great-

.

Ly increas’eci ttle Feeot”ery d Crtde Gil

r-. ....

-m =~nd

columns by gravity drainage.

Small quantities

of effective solvents greatly increased both the

rate of production and the volume of crude oil

produced.

For example, drainage from the column

was about 20 percent of one crude oil without

stimulation.

However, the addition of 10 percen’

of an effective solvent to the top of the sand

column increased the production to about 65

percent of the crude oil in 50 hours. Quantitie:

of solvent as low as 2 percent increased the

production rate.

Small quantities of effective solvents

caused large reduction of crude oi% viscosity.

For example, 5 percent toluene lowered Oxnard

crude oil viscosity from 64,4ii0to

Y, fuu cp at

...

100° F.

Effective solvents generally required less

the te rerlev?Vie.cxxus

~r.uden 1 a f~~~= ~~p~~~~r~

“.-.

tubes immersed in the solvent. Toluene was very

effective and n-decane ineffective in removing

viscous crude oilS froinea~i~l=ry t“@XS. Tb,e

effectiveness of toluene and contrasting in-

effectiveness of n-decane correlates with the

ability of the solvents to dissolve asphaltenes.

However,

it does not correlate with the effec-

tiveness of these solvents in viscosity reductiol

and production of viscous crude oil from the sant

columns.

An effective solvent for lowering the vis-

-----.._= ....-e-.,- .l.fi,,lAa ~~p~~~~ Qf

GuaLL?y UL VAVLUUV CxWfe Gzl .’.”--- J.J-

disassociating aggregates or complexes into

smaller and simpler molecules which can move

freely at low viscosity.

This disassociation


6/11

6

SOLVENT STIMULATION OF V S OUS CRUDE-OIL PRODUCTION

SPE 3680

porous reservoir rock containing the viscous

crude oil and water.

Successful field stimulation by solvents is

dependent upon proper selection of an effective

solvent and the most desirable fields.

Solvent

stimulation can be an effective method for

greatly increasing the rate and volume of pro-

duction of viscous crude oils heretofore avail-

able only at slow rates near the economic limit.

AcKNOWLElX3tElTi’S

Grateful acknowledgment is made to Getty

Oil Co., Mobil Oil Corp., Standard Oil Co. of

California, Atlantic Richfield Co. and Champlin

Petroleum Co. for their helpful cooperation in

supplying samples and data. @articular thanks

are due to personnel of the USBM Iaramine EnerG

Research Center for the hydrocarbon analysis of

two of the solvents.

REFERENCES

1.

2*

3.

4.

“Heavy Crude Oil Resource, Reserve, and

Potential Production in the United States”,

IC S352, USBM (1967).

Dietzman, W. D., Carrales, M., Jr. and

Jirik, C. J.: “Heavy Crude Oil Reservoirs

in the United States:

A Survey”, IC 8263

USBM (1965).

Burns, James:

“A Review of Steam Soak

Operations in California”, J. Pet. Tech.

(Jan., 1969) 25-34.

“Ann&l Review of California Oil and Gas

Production, Los Angeles, Calif.”, Conser-

vation Committee of California Oil

Producers (1970) Table XXIII-A.

6.

7.

8.

9.

10.

11

12.

13.

14.

15.

16.

“Annual Review of California Oil and Gas

Production, Los Angeles, ~lif.”,

Conservation Committee of California Oil

Producers (1970) 30.

flA”

Block, W, E. and ‘Ilnovaii,R. ~.: -.

Economically Successful Miscible Phase

Displacement Project”, J. Pet. Tech.

(Jan., 1961) 35-51.

Dosch, M. W.:

“Pliocene Tar Sands in

Oxnard Oil Field”, Summary of Oil Opera-

tions, California Oil Fields (1965) 73.

Jeffries-Harris, Michael J. and Coppel,

Claude P.:

“Solvent Stimulation in Low

Gravity Oil Reservoirs”, J. Pet. Tech.

(Feb., 1969) 167-175.

Gidley, John L.:

“Stimulation of Sandstone

Formations with the Acid-Mutual Solvent

Method”,

J. Pet. Tech. (May, 1971) 551-558.

Lewis. J. O.:

“Methods for Increasing the

,--

Recovery From Oil Sands”, Bull. 148, USBM

(1917) 13.

w-en, w. B.

a=d SLLter,%~e E.:

“Steam

Stimulation for Secondary Recovery”, Drill.

and Prod. Prac., API (1965) 162. —

Harris, H. G. and Prausnitz, J. M. :

‘ t’hermodynamicsf Solutions With Physical

and Chemical Interactions”, Ind. &Eng.

Chem. Fundamentals (WY, 1969) 180-188

Woelflin, William:

“The Viscosity of Crude

Oil Emulsions”,

Drill. and Prod. Prac., API

(1942) 148-153.

Teberg, J. A.:

“Wilmington Field Steam

Operations”. Paper SPE 1494 presented at

41st Annual SPE Fall Meeting, Dallas,

Oct. 2-5, 1966.

Krueger, R. F., Vogel, L. C. and Fisher,

P*

w.:

“Effect of Pressure Drawdown on

Clean-Up of Clay- or Silt-Blocked


7/11

TABLE 1 -

VISCOSITY OF MIXTURES OF MOBIL SOLVENT

Source of crude

SanArdo . . . . . . .

Kern Ri ver . . . . .

Mdway Sunset . .

Oxnard . . . . . . . . .

W lmngton . . . . .

South Bel ri dge .

Bart l ett (Kansas)

AND CRUDE OILS AT 100°F, CP

o

31, 500

1,760

1,500

64, 400

645

765

4,100

Sol vent

Toluene . . . . . . . . . . . . .

Mobi l sol vent . . . . . . .

San Ardo cutter . . . . .

Oxnard cutter . . . . . . .

No. 3 whi te oi l . . . . .

n-decane . . . . . . . . . . . .

n-pentane . . . . . . . . . . .

n- hexadecane . . . . . . . .

Tetrahydrofuran

2, 2, 4- tr i methyl - ” ““””

2

84~

54, 400

Sol vent,

5

8,800

675

505

21, 600

291

265

673

rcent

10

1,930

292

291

6,000

182

164

406

-—

TABLE 2 - SOLVENTPROPERTIES

Sp gr

60/ 60° F

0.869

. 870

. 871

. 910

. 869

. 734

. 630

. 777

. 892

OAPI

60° F

31

: :

24

31

61

93

51

27

Mol ecul ar

wei ght

1::

235

294

330

142

72

226

72

20

490

102

96

661

65

1 i E

30

129

40

257

30

4;

Domnant

hydrocarbon

type

aromati c

aromati c

not determned

aromati c

- mh hanie

llapllbllllmb

paraff i ni c

paraf f i ni c

paraff i ni c

oxygen ri ng


8/11

TABLE 4 -

VISCOSITYOF MIXTURES OF SAN ARDO CRUDE

OIL AND SOLVENTSAT 100°F, CP

Sol vent, percent

Sol vent

o

2

Tol uene . . . . . . . 31, 500 -

n-decane . . . . . . 31,500

Mobi l sol vent. .

31, 500

:

San Ardo cutt er

31, 500 17,500

Oxnard cut ter . 31,500

-

n-pentane

. . . . .

31, 500

-

n-hexadecane. . .

31, 500

-

No. 3whi te oi l

31, 500

2, 2, 4 tri methyl -

pentane. . . . . .

31, 500

-

Tetrahydrofuran 31, 500 -

5 10 20 50

I I

I

4,950

4, 4G0

8,800

10, 140

11, 000

1,320

875

1,930

4,550

3,550

61. 2

2,4b(J

5,980

206

~6~

490

1,275

1,360

I

-

8

2,350

- -

1,340 - -

100

0. 49

, 70

1. 33

3. 20

5. 60

TABLE 5 -

RELATION OF VISCOSITYREDUCTION TO

TO SOLVENTMOLECULARWEIGHT

Vi scosi ty of 10 percent sol vent-


9/11

TABiE

6 - TIME FOR DISPLACEMENTOF VISCOUS CRUDE OILS

FROM CAPILLARYTUBES BY SOLVENTS,HOURS

SAN ARDO CRUDE

OIL VISCOSITY

>100, 000 CP,

73° F

Cap: : ; : ry

Mobi l

San Ardo Oxnard

Tol uene sol vent cut ter stock cut ter stock

n-decane

posi ti on

3

17

72

144 >720

vert i cai

WLMNGTON TAR ZONE CRUDE OIL VISCOSITY 2 100 CP 73° F

Mobi l

90 aromati c, Li ght coker

Tol uene

sol vent U.P.

oi l , U.P.

n-decane

6.5

I

21

I

46

I

22

I

>

Capi l l ary

tube

posi ti on

hori zontal

TABLE

7 -

EFFECT OF COMPOUNDSHAVING MONO ANE DIFUNCTIONAL

GROUPS ON VISCOSITYOF OXNARD CRUDE OIL AT 100°F

,

Vi scosi ty, cp

Aci d added

Aci d added, percent

o

0.5

1.0

2.0

3.0

Monofunct i onal

st ear i c aci d . . . . 97 000

77 900 72 100 59 100 57 000

Di functi onal


10/11

I

I

I

I

/

/

1

sowd +u- ‘AIISOXIA

—

—

—

d


11/11

4

10 Percent Toluene

{

/=;

/=

/ 10 Percent Mobil solvent

/

without

/

/“

/

.~~

0

40

60

80

TIME.

hours

/’

/“

solvent

100

Figs 3 . Effect of toulene and Mobil solvent on Tecov?ry Of

viscous Kern River crude oil from sand columns.

‘o

—1

2b

Percent’ Toluene ‘

/’”-

{

ys5=-

//

Percenlt To uene

/ 2 Percent Toluene

/Y

1)

Without solvent

(b

/

\

/

<

~—~

o

20

40

60

810

100

1

TIME,

hours

Fig. 4 - Relation of viscous oil recovery to quantity of toluene used in

stimulation of production of Kern River crude oil f’r~msand ~O~umn~.

I

Documents

Solvent Stimulation of Viscous Crude Oil Production