Asphaltene Deposit Removal Long-Lasting Treatment With a CO-SOLVENT

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S

Society of PetroIeun ngineers

SPE 21 38

Asphaltene Deposit Removal: Long Lasting Treatment With

a Co Solvent

M.G. Trbovich, WelChem Inc., and G.E. King, * Amoco Production O

SP Member

Copyright

1991,

Society of Petroleum Engineers, Inc.

This paper was prepared for presentation at the SPE International Symposium on Oilfield Chemistry held in Anaheim, California, February 20-22,

1991.

This paper was selected for presentation by an SPE Program Committee following review of information contained

in

an abstract submitted by the author s . Contents of the paper,

as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author s . The material, as presented, does not necessarily reflect

any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subjectto publication review by Editorial Committees of the Society

of Petroleum Engineers. Permission to copy is restricted to an abstract of not more than

300

words. Illustrations may not be copied. The abstract should contain conspicuous acknowledg

ment of where and by whom the paper is presented. Write Publications Manager, SPE, P O Box

833836,

Richardson, TX

75083-3836

U.S.A. Telex,

730989

SPEDAL.

ntrodu tion

Asphaltene

problems

ar e increasing on a wide

scale

in th e

petroleum

industry. The

deposition

of these

materials

has been increasingly not.ed in production

wells of O

2

floods and in miscible drive floods, after

acid

st.imulations

in

a spha lt ic c rude oil formations, and as

pressures

in older fields near

th e

deplet.ion point.

Many reservoirs produce

wit.hout

evidence

of

asphaltenes

until

th e

oi l stability

is

disturbed.

After the

ini tial problems wit.h a spha lt enes , even t ho se cau sed by

a

single use,

catalytic

behaving stimulus

such

as

an

acid

job,

many

wells con ti nue t o exh ib it problems

long

after

opel at.ions return to

normal.

NumenHis n ~ m e d i e s

to remove asphalt.ic

deposits

and stabi lizat ion met.hods t o

control th e

deposit.ion

have

influences

are

removed,

th e

asphaltic

particles

coalesce

into larger

groups, called flocs, that separate and, with

a

density of

1.2

g/cc,

precipitate from th e

oil.

7

Asphal

t en e con tent s may range from 0 to over 60 .8

Resin

volume-to-asphaltene ratio is on the order of 1:1 to 20:1

in oils that

are

s tab le t o

less than

1:1 in oils that ar e

characterized by rapid

precipitation

of

asphaltenes.

7

•

9

•

10

Asphaltene content usually i nc re as es w ith

decreasing

API

gravityll

but instances of asphaltene precipi tat ion in

light

oi l

and even wet ga s streams are known, though

the occurrence

is

rare.

The

treatment

of

the asphaltene deposition problem

should begin with a discussion

of

th e factors

involved

in

inducing precipitation.

Destabilization Forces



2

ASPHALTENE DEPOSIT REMOVAL - LONG LASTING TREATMENT WITH A

COSOLVENT SPE

21038

2

3.

4

5.

Rich Gas - Flooding with ric h gas destabilizes th e

asphaltene complex by lower ing th e carbon-to-hy

drogen ratio.1

6

Stripping gas from

th e

oil

ha s

been

shown to improve

th e

solubility of

asphaltenes.

17

.

18

The

straight

chain hydrocarbons

have

less affinity

for

the asphaltic

ring structures

that oils that have a

higher carbon-to-hydrogen

ratio. The negative effect of

rich

gas

is

at

a

maximum near

th e

bubble point 1O 12 18 -

20 and

may

decline

afte r th e

bubble point is

reached.1

8

This

behavior

near

th e bubble point

in

more

pro

nounced

with

th e

r ich gas

than

with CO

2

12

pH shift

- This

may

be

caused

by CO

2

,

mineral

acid, or natural ly occurring or bacterial produced

organic acid.

A

shi ft i n well operating

conditions

may alter th e

equilibrium

under

which th e

crude

exists in

th e

reservoir and l iberate more

natural

acids, surfactants, or

other reactants

or products.

Mixing of

crude

streams - Thi s i nc ludes

local

instabilities that may not even

occur

under

more

complete

mixing.1

8

Most likely causes

ar e a

shift

of

pH by a natural organic

acid in an

incoming

crude, and CO

2

outgassing or physical

shear

or

other

d is rupt ion caused

by cavitation in some

pumps

or mixing

manifolds

or chambers.1

8

Prob

lems

of this type can

sometimes

be prevented

by

more complete mix ing

of

th e crude s tr eams unde r

r educed shear .

One

sou rce r epor ted

that a

deposit of as pha lt ic mate ri al was resolubilized

after

mixing

procedure was

changed.

18

This mixing

problem also cover s the a spha lt ic upsets caused

by

ho t

oiling.

Incompatible

organic

chemicals - Isopropyl alcohol,

methyl

alcohol, acetone, and even some

glycol,

alcohol, or

surfactant

based mutua l solvents

that

do no t have an aromatic component ca n

selec

tively

wet or

attract

th e mal tene s and res in s and

drop th e

asphaltenes.

9

10.

temperature

reduction may cause an

area

of

instability, or asphaltene deposition envelope as

described by Leon Taritis,

o

Strict

pressure

f luctua tion can a lso cause precipi ta tion as

shown

by Akbar and

Saleh.1

9

It shou ld

be noted that

these

tests show

the behavior of

specific crude-oil

samples.

Other oils will

vary

in

behavior accord

ing

t o a roma ti c/ asphal tene conten t, mal tene and

r es in con tent, a nd

specific

asphaltene

structure.

Perhaps one of

th e

largest effects on behavior

is

th e

production treatment.

In general, if

asphal

tene

precipitation problems

occur

at one

set of

operating conditions, a

shift

i n wel l head pressure

or

other operating condition

may

change th e ra te

of deposition.

Turbulence

may

increase

th e

amount of asphaltenes precipitated

I9

or improved

mixing of crude streams may

prevent

precipitation.1

8

Streaming potential - Streaming potential through

porous

media ha s

been

identified

as

a cause of

aspha ltene precipi ta tion and mar. be associated

w it h p re ss ur e drop

or

charge.

I

4

Only limi ted

operational

data is

available at this

time.

Temperature drop - This

factor

may have more to

do with ind irec t destabilization by

upsetting

th e

stabilizing

forces

than by having a direct

effect

on

th e asphaltenes.1

3

Temperature may

affect

th e

solubility of

the maltenes

and

resins

or

a temper

ature

drop may

create

a

paraffin

precipitation

that traps

some a sph al te nes as it solidifies. CO

2

also contributes to the oI ganic precipitation

problem

by cooling th e wellbore

during

i ts expan

sion. Temperature readings

during

logging runs

in

producing

wells

with very severe

CO

2

break

through have

been reported as

40°F

below

th e

static

bottom hole

temperature

of

95°F in one

Texas panhandle

location. Other

operators

have

reported

no

significant temperature change.

6.

Stimulation - Very severe asphaltic upsets can

follow

acidizing

and other

forms

of

chemical

treating.

7

16 20 Acidizing involves

a

violent shif t in

local

chemical

equilibrium, pH, and

CO

2

gas

lib

eration.

also sharply elevates concentrat ion of

some

ions, such as iron,21 that may hav e a direct

or symbiotic

relationship

with formation of

11.

Charged, bare

metal surfaces

- This condi tion may

be

a

combination

of

th e

problems

o f s hea r and

pressure drop and

is

one of t he l ea st unde rs tood

of th e destabilizing forces.

3

21 22 has

been not ed

in h igh veloc ity flow streams near liner slots. a nd

may assoc ia ted with

outgassing.



SPE

21038

M

G TRBOVICH

AND G E.

KING

3

tene content

are

noted

in

th e

literature.

These h ighe r

asphaltene

values ar e

typical of low gravity, high pour

point

crudes.

A high asphaltic

content does

not, how-

ever,

result

in precipitation problems

if

th e resin com-

ponent is also high.1°

Over

a

period

of

severa l years

of

operation

of CO

2

floods and miscible floods, asphaltenes

from several

parts

of th e

country

have been

collected

and

analyzed

for

general solubility.

Most of th e

deposits

ar e

mixed with

paraffins,

scales , and

other foreign material. An analysis

w as made

of a

group

of

samples

from th e Bairoil field

in

Wyoming (under

CO

2

flood). In

this

set of

samples,

with

al l

having

th e same black, viscous appearance, asphaltic

conten ts var ied from 0 to

92 .

The

wide

variety in

composi ti on was

typical

for asphaltene samples col-

lected

ove r th e past t en year s.

Asphaltene deposi tion

in

th e

formation has been

known for an exte nd ed period of time, but has been

described by relatively few authors.

4

•

24

Most in

situ

deposition of

asphaltenes probably occurs as a result

of

th e oi l

mixing

with incompatible solvents, acids, and

other hydrocarbon fluids. These addi tives

or

fluids may

include

drilling, workover, stimulation or packer fluids,

or extraneous liquids

from casing

or tubing

leaks. Once

th e deposit is formed

in

the

formation,

clean up is

often

slow.

Experimental

Results

Of the numerous a sphaltene samples that were

obtained

for

study,

th e solubility in th e primary solvent

xylene was amazingly similar. Approximately 8 to

10 grams of the asph altic m aterial pe r hundred

cc's

of

xylene approached the

solubility

limit. Very

slow

rate

of

removal

as

th e solubility limit is

neared

leads to

speculation that

th e

l im it may be only that quantity

of

asphaltene that can be quickly pulled into

solution.

Additional

material may

be

softened and go into solution

with

time.

Once

in

th e

solution,

the materi al s remained

stable.

Additional

material may

also be

dispersed.

Asphaltene solvents o th er t han

xylene

have

been

t ri ed , bot h

in

th e literature

and

in

th e work for this

study 5 2 27 The per fo rmance o f t he se

additives

is usually

dependent

on

th e specific conditions, reaction is influ-

enced by many

factors.

benefit

in a 1) water

wet s ys tem

or in a

2)

water

external emulsion or sludge that is stabilized by asphal

tenes.

By combining th e xylene

with non adsorbing,

field

proven, water penetrating solvents, a series of cosolvents

were formulated that could outperform

th e

straight

xylene in

asphaltene stabilization tests and some removal

comparisons.

The

cosolvent mix tu re s

ar e

not

an

improvement

on xylene in dissolving capacity;

because

they

are

only

partly

xylene,

actual

solubility is less.

These

cosolvents offer a broader application to asphaltic

removal problems that may inc lude s ludges , emuls ions

and some hard deposits.

These

deposits were found to

be

bound with or

wetted by water in many field

samples.

The

information

gathered through experimental

and

isolated

field tests was taken to th e field

and

tests

on

chemical removal

and stabilization

was started. In many

of t he se t es ts , blends of

sol vent s, b ot h a roma tic

and

linear,

were tried

in

an a tt empt

to

establish

a

balance

of

solubility and wett ing

character.

Field

Resul ts o f

Cosolvent

Treatment

Thirty-one random ly

selected

wells ranging

geographically

from Alaska,

Alberta,

Wyoming , Colo-

rado,

New

Mexico,

Nebraska,

Michigan, Kansas, and

Texas were squeezed treated with t he su rfa cta nt free,

cosolvent

aromatic blends to remove

both suspected and

proved asphaltene damage. The

candidate

wells

from

these areas

were

s el ec ted based on

identification

of low

productivity

from

aspha lt ene and

heavy

tar

deposition,

combination aspha lt ene and paraffin accumulation, and

emulsion formation .

Specific

combinations of w ells

within a field with

common p robl ems were sel ec ted for

comparison with

other

chemical

and

mechanical treat

ments.

The

key areas

of

comparison were:

1)

removal

of damage with a sma ll volume o f t re at ing fluid, and

2) maintenance of the product ivi ty

increase.

In

general,

mechanical scraping was one of the

worst

techniques, with

most operations ei ther failing

to

increase product ion

or

actually decreas ing production.

Single

solvent t reatments

of

xylene were

successful

in

mos t cases

in

restoring

production,

but failed to achieve

long lasting productivity increase. The best overall

damage removal

approach

was

th e use of the cosolvents

that

could

both

dissolve and

disperse

asphaltene

deposits

and

actually

water

wet

th e surf ac es

in vo lved i n

th e



ASPHALTENE DEPOSIT REMOVAL -

LONG

LASTING TREATMENT WITH A

COSOLVENT SPE 21038

wett ing propert ies

made pos si ble by

th e

us e of moderate

length carbon chain length alcohols. Performance

results

on tests following

th e

recovery of initial load

fluid

ar e shown in Figure 2

for

a dozen

wells from

Canada

to

Nebraska.

Immediate

post treatment

production was charac

terized by a spike of peak production,

followed

by a

slight to

moderate decline,

then a stabilized

rate

with a

slow

decline

last ing several months.

Longevity

effect of

th e

treatment

under

asphaltic

conditions

lasted up to

35 mon th s w it h an

average

improved response of

6

to

8 months . T he r es ult s

from

two of

these

t reatmen ts a re

r ef lect ed in F igures 3 and 4. In this

dat a, t he

peak pro

duction tapers

off

slowly.

Single

component. a roma tic a nd

mechanical c1ean

outs y ie lded lower treatment

peak

production rates, as

well

as

a

shorter duration of

increased productivity.

A

comparison of t he se t re atmen t

results

wit h th os e of a

cosolvent. are

s hown in F igure 5 for

wells

in a

common

field. The mechani ca l

scraping

results in this figure

show poo r

response.

The overa ll success of

th e

scraping

seemed to depend on th e lo cati on of

th e

asphalt . ic prob

lem.

A deposit. in t.he tubing

could

be

removed

by

scraping,19

but s cr ap ing o f a

deposit

near th e

per fs cou ld

introduce

th e

sol ids i nto

th e

perfs. The

xylene

jobs

were

t.ried on th e

higher

rat.e

wells

and p robabl y had

less

ini

t.ial damage

to remove.

The after

treatment

results

of

Product A

showing

over 100 improvement

is

a

typical

response.

On e

of

th e most graphic

illust.rations of

th e

cosolvent's

ability

to providing

long

last ing response is

shown

in

Figure

6. In

t hi s t es t,

a small soak

treatment

with xyl ene r ai sed p roduct ion briefly

bu t declined

rap

idly

to pret.reatment levels. Treatment with Product

B

produced a sharp i nc rease in product ion accompanied by

an equally sharp dec line to pre tr ea tmen t. levels in

less

than

two weeks .

Subsequent

treatment

with

Product A

produced

a

stable

increase

that has lasted

several

months.

Injection well treatment with other solvents, Fig

ures 7 an d 8, shows ver y good r esponse with

pressures

lowered substantially or inject.ion rate improved at con

stant p re ssur e. Longevi ty in these jobs was considered

Payout

Chemical treating payouts of approximate ly one

week wer e

common,

an d al l th e s uc ce ss es were b etween

3 and

30

days.

Th e

extreme short payou t was

possible

by

th e

immediate

spike production, sustained high

levels

of

production and

minimal

mechani ca l app li ca ti on

expense

involved.

Level

o f T r ea tmen t

Success

The treatments using products A, B, an d C were

successful in

27

of

31

treatments with succe ss defined

a s abi li ty to both payout

th e

job in

30

days or less an d

provide longer l as ting result.s t han o th er

alternatives.

The typical initial production

increase

was one

hundred percent .

Th e amount

of

sustained

production

increases varied

with

the t reatmen t.

The c aus es of the four

failures

were varied.

One

of

the failures was a

well

treated with 1 gallft that

res po nd ed v ery

slowly

and required over

30

days'

c le an up to s how an improved rat.e. The delayed response

was

thought

to

be

attribut.ed to below minimal

treat

ment

volumes.

The second

failure

was th e treatment. of an uncon

solidated sand with a

perf

wash tool. The well sanded

up

following

injection. Previous treatments in

these

unconsolidated sands wer e squeezed

down

th e backside.

Two

failures

offered

no

significant explanation to

explain their lack of response. One exh ib it ed a large

incremental response, bu t

declined

to pretreatment

levels.

The fourth

well failed

to respond

and

was

t.hought to be

a problem in placement. The

well

is

heavily

naturally fractured.

Conclusions

The

aromat.ic-containing

cosol vent sys tem

offers

advantages

t o

th e

us e of st l'a ight aromat ic

solvent

in

three areas.

1. The success o f t he cosolvents

of

over

80

in

pro

viding production Increases was very high for



SPE 21038

M. G. TRBOVICH N

G.

E. KING

5

Nature of

SPE

16713,

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

Dubey, S. T., Wa) man, M. H., Asphaltene

Adsorpt ion and Desorp ti on

From

Mineral

Sur

faces, SPE 18462, 1989, pp. 51-62.

Witherspoon,

P. A., Ray,

B. R. Grim,

R. E.:

A

Study of th e

Colloidal

Characteristic of Petroleum

Using

an Ultracentrafuge,

J.

Phys.

Chern, 61,

1957, 1296-1302.

Newberry,

M.

E

Barker,

K. M.,

Formation

Damage Prevent ion Through th e Control of

Paramn and Asphaltene Deposition, SPE

13796,

1985, pp. 53-61.

Bunger, James

W.,

Chemistry of Asphaltenes

Summary of Symposium, Salt Lake

City,

1979,

pp. 1028-1031.

Sachanen, A.

N.,

T he Chemical Constituents of

Petroleum, Reinhold Publishing

Corp. (1945).

Leontaritis, Kosta

J. and Mansoo ri, G. Ali,

Asphaltene Deposition:

A

Survey of

Field Expe

riences and Research

A(lproaches,,, Journal

of

Petroleum Sc ien ce and Eng in eering, Volume

1

(1988), pp. 229-239.

Newberry,

M. E.,

Crude

Oil

Production and

Flowline Pressure Problems, SPE 11561, 1983,

151-164.

o n ~ e r T. G.,

Trujillo,

D. E., Organic

Deposition

Durmg CO

2

and Rich-Gas Flooding, SPE 18063,

pp. 63-73.

Monger,

T. G., Fu, J. C.,

The

CO

2

-Induced Organic Deposition,

1987,

pp_

147-159.

Fuhr, B.

J. , Klein,

L.

L.,

Komishke, B.

D., Reic

hert,

C., and Ridley, R. K.,

Effects

of

Diluents

and Ca rbon

Dioxide on

Asphaltene Flocculation

in Heavy Oil Solutions, Fourth

Unitar/UNDP

Conference on Heavy Crude and Tar Sands,

<Paper No. 75 pp. 75-1 -

75-12_

Kawanaka,

S.,

Park,

S.

J ., Mansoori ,

G. A.,

The

Role

of Asphaltene

Deposition in EOR

Gas

Flooding: A

Predictive

Technique,

SPE/

DOE

17376, pp. 617-627.

Mansoori,

G. A.,

Jiang,

T. S.,

Asphaltene

Deposi

17.

18.

19_

20.

21.

22.

23.

24.

25.

26.

27.

28.

Von Albrecht, C., Diaz , B., Salathiel, W. M., Nier

ode,

D. E.,

Stimulation of

Asphal tic Deep Wells

and Shallow Wells in

Lake Maracaibo,

Venezuela, pp. 55-62.

Thaver,

R., Nicoll, D. C.,

Dick,

G.,

Asphaltene

Deposi tion in

Production Facilities,

SPE 18473,

pp. 137-146.

Akbar, S. H., Saleh, A. A., A Comprehensive

App ro ach To Solve Asphaltene Deposi tion Prob

lem

in Some

Deep

Wells, SPE 17965, pp. 377-384.

Addison, G. E.,

Identification

and Treating of

Downhole Organic Deposits, SPE

18894, 1989,

pp. 627-632.

Claassen,

E.

J ., I ron

Sulfide

as

a

Water-Deposited

Scale

in Sour Gas Wells, Paper 191,

Corrosion

1988,

St. Louis ,

March

21-25, pp. 191-1 - 191-14.

Tuttle, Robert N., High-Pour-Point and Asphaltic

C rude Oils and Condensates ,

Journal

of Petro

leum Technology, 1983, pp. 1192-1196.

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Pierre M.,

Asphaltene

Deposition

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-

Usage of Asphaltenes

in

Emulsion

Stability, Oil

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1977, pp. 609-624.

Collins, S. H.,

Melrose,

J. C.,

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of

Asphaltenes an d Wate r

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Rock

Min

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11800, 1983, pp. 249-256.

Dean, Kim

Renea and McAtee,

James

L.

Jr.,

Aspha lt ene and Water

Adsorption

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Waco,

Texas, SPE

13403, pp. 1-20.

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A., DeJong, L. N.

J . , Schipper,

A.,

Meijers,

J. G.:

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P. L.,

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3687, 1971, pp. 1-12.

Douglass, B. C., King, G. E., A Comparis on of

Solvent/

Acid Workovers in Embar Completions



Table

Desc ript ions o f

cosolvents used

in

the w ell

tes ts

Product

Description

A romatic and

straight

chain solvents

with

small amount of hydrophylic solvent

B romatic solvent

with

small amount of

hydrophylic

solvent

C Hydrophylic solvent and small amount of

aromatic solvent



S 2

8

PRODUCTION

RESPONSE

AFTER

LOAD RECOVERY OF

SEVERAL WELLS TO TREATMENT W T PRODUCT

A

FIGURE 2

14

Cl

12

j

J

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_ BOPD BEFORE TREAT

BOPD AFTER TREAT

l

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8

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6

U

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<

W

ll

LONGEVITY

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FIGURE

3

LONGEVITY OF PRODUCTION

RESPONSE FOLLOWING

TREATMENT

W T

PRODUCT

A SUNSHINE BASIN

WYOMING

FIGURE 4

I

I I

Legend

_ PRE TRE TMENT BOPD

AFTER TREATMENT BOPD

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o

3 6 9 5 8 4 7 3

MONTHS AFTER TREATMENT

3

5

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MONTHS AFTER TREATMENT

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ASPHALTIC

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FIGURE 6

C O ~ P R I S O N OF

ASPHALTENE

REMOVAL

METHODS

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PRODUCTIO)J, NEBRASKA

WELLS

FIGURE 5

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00

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C

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OF AN

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MEDICINE HAT, ALBERTA

FIGURE 7

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AN

INJECTION

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MEDICINE HAT,

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Legend

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BOPD

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BOPD AFTER TREAT. a

SCRAPE XYLENE XYLENE SCRAPE A AA

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Legend

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KPA

INJECTION RATES M3

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6000

6000

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5000

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Documents

Asphaltene Deposit Removal Long-Lasting Treatment With a CO-SOLVENT