Note: Descriptions are shown in the official language in which they were submitted.
~-75596
9452 Back round of the In~ention
This invention relates to the reco~ery of oil
from subterranean ~il reservoirs and more particularly to
improved waterflooding operations involving the injection
` 5 of a hydrocarbon solvent followed by the injection of a
thickened aqueous surfactant slug.
In the recovery of oil from oil-bearing reservoirs,
it is usually pos~ible to recover only minor portions of the
original oil in place by the so-called primary recovery
methods which utilize only the natural forces presen~ iff
the reservoir. Thus a variety of supplemental recovery
techniques has been employed in order to increase the
recovery of oil from subterranean reservoirs. The most
widely used ~upplemental recovery technique is waterflooding
which involves the injection of water into an oil-bearing
reservoirO As the water moves through the reservoir, it
acts to displace oil therein to a production system composed
of one or more wells through which the oil is recovered.
; It has long been recognized that factors uch a6
the interfacial tension between the lnjec~ed water and the
- reservoir oil, the relative mobilitie~ of the reservoir oil
and in~ected water, and the wettability characteristics of
the rock surfaces within the reservoir are factors which
influence the amou~t of oil recovered by waterflooding.
Thus it has keen proposed to add surfactants to the injected
water in order to lower the oil-water interfacial tension
and/or to alter the wettability characteristics of the
- '
~6
107S596
9452 reservoir rock. Also, it has been proposed to add thickening
agents- to all or part of the injected water in order to
increase the viscosity thereof, thus decreasing the mobility
ratio between the injected water and oil and ~mproving the
sweep efficiency of the waterflood.
Processes which involve the injection of aqueous
surfactant solutions in order to reduce the oil-water
interfacial tension are commonly referred to as low tensi~n
waterflood ng techniques. To date one Qf the more promising
low tension waterflooding techniques involves the injection
of aqueous solutions of petroleum sulfonates within a
designated equivalent weigkt range and under c~ntrolled
conditions of salinity. For example, in a paper by W. R. Foster
entitled "A Low-Tension Waterflooding Process", Journal of
Petroleum Teehnology, ~ol. 25, Feb. 1973, pp. 205-210, ~here
is disclosed a procedure which involves the~sequential
injection of a protective slug, a surfactant slug~ and a
mobility control 81ug.
The surfactant slug comprises an aqueous solution
-20 of petroleum sulfonates having an average molecular weight
within the range of 350-500 in concen~rations ranging fr~m
about 1.0-3.0 ~eight percent. The 6urfactant slug contains
sodium chloride in a concentration, typically about 1.0 to
2.0 weight percent, which will promote the desired low
inter~acial tension between the injected water and the
reservoir oil. m e subsequently injected thickened water
slug contains a viscosifier such aæ a water-soluble biopolymer
. ' - . ~
1075596
.
9451 in a graded concentration in order to provide an initial
viscosity greater than the viscosity of the re~ervoir oil
and a terminal viscosi~y near that of water. This mobility
control slug has a lower sodium chloride concentra~ion ~han
S the surfactant slug. This somewhat lower salini~y functions
to increase the desorption of the previously adsorbed
surfactant to move the surfactant through the reservoir by
a chromatographic-desorption process.
Various modifications of, or alternatives to,
surfactant waterflooding involve the injection of a surfactant
and a hydrocarbon 81ug or the injection of surfactants in both
a hydrocarbonaceous solution and an aqueous solut~on. For
example, U.S. Patent No. 3,468,377 to Dunlap et al. discloses
the injection of an aqueous solution of petroleum sulfonates
having a median molecular weight within the range of about
375 to about 430. The aqueous surfactant solution may be
- preceded by a hydrocarbonaceous solution of surfac~ants in
a ~olume of about one-tenth of to about equal to the volume
- of the aqueous solution with the total volume of the
hydrocarbonaceous and aqueous solution being from about
0.01 to about 0.2 pore volume. U.S. Patent No. 3,491,834
to Ahearn et al. discloses the in~ection of a nonpolar
(hydrocarbon) slug containing a preferentially oil-soluble
sulfonate surfactant followed by a polar (aqueous) slug
containing a somewhat lower molecular weight sulfonate
which is preferentially water-soluble. The size of the
nonpolar slug is said to be between 0.5 percent and
--4--
'
~ `": ~
1075596
9452 20 percent of the reserv~ir pore volume and preferably
between 2 percent and 10 percent. The polar slug varies
from 0.5 percent to 100 percent of ~he pore volume,
prefierably from 25 percent to 75 percent, and may contain
S a thickening agent.
U.S. Patent No. 3,865,187 to Carlin et al.
discloses an oil recovery process which involves an
; emulsification mechanism resulting from the injection of a
hydrocarbon solvent containing a mono-unsaturated secondary
alcohol followed by an aqueous solution containing a sulfate
salt of a fatty alcsho~. Each of the respective slugs varies
in size from about 5 percent to about 50 percen~ reservoir
pore volume with the alcohol present in a concentration
within the range of 0.1-10 percent by weight and the alcohol
L5 sulfate being present in amo~nts from abo~t 0.1 to about
` 2.0 percent by weight. The aqueous slug may be ollowed
by water containing a thickening agent in an amount from
about 0.01 to 0.5 weight percent. Another process disclosed
in U.S. Patent ~o. 2,669,306 to Teter et al. involves the
injection of a liquefied normally gaseous hydrocarbon such
as propane, followed by the injection of drive water. The
patentees disclose that recovery of hydrocarbons may be
impro~ed by * e addition of surface-acti~e agents selected
so as to avoid emulsification difficultles.
~anadia~ Patent Application No. 284,548 discloses
an i~prcved waterflooding process involv~ng the sequential
' "
-5-
.
1075596
9452 injection of a relati~ely low viscosity hy~rocarbon slu~,
a surfactant slug, and a mobility control slug. The
hydrocarbon is in~ected in an amount withi~ the range of
0.01-0.04 pore volume followed by the surfactant slug in
an amount within the range of 0.0~-0.3 pore ~olume and
which contains a surfactant in-an amount within the range
of 0.5-4.0 weight percent. The surfactant slug is followed
by an aqueous mobility control slug, at ~east a portion of
which has a viscosity at least as great as the viscosity
of the hydrocar~on slug.
. Canadia~ Patent Applic~tion No. 278312 (corresponding rO ~.S.
Patent No. 4~042030) discloses an improved waterflooding process --
in which at least a portion of the injected water is
thickened by employing an alkylaryl sulfonate surfactant
having an average molecular weight within the range of
350-500 in combination with a water-soluble C4-C6 aliphatic
alcohol ha~ing a hydrocarbon chain link of at least 3 carbon
atoms. The thickened aqueous liquid exhibits a monovalent
salt sali~ity and a surfactant concentration within the
ranges of 0.5-3.0 ~eight percent and~0.5-4.0 weight percent,
respecti~ely, and more specifically9 within the range of
0.8-2.5 and 0.5-3.0 weight percent, respectively. m e
; aliphatic alcohol is present in concentration such that
the ratio o~ the sulfonate surfactant to the sum of the
amount of sulfonate surfactant and alcohol is within the
range of 0.3-0.8.
, . , '
--6--
1075596
452 . Another waterflooding process involving the
~- injec~ion of a thickened ~urfactant ~olution is discl~sed
. in our co-p ~ lng Ca~dlz~ P~e~t Appl~cat~n ~0. 29~,930 f~led ~ current~y
~th ehe pre~ t appl~cation, ~ to~ ~o~ep~ Geor~e Sa~ , Jcrr~
S Wai~e, and Ralph F. Burdyn, entitled WATERFL~OD~NG
EMPLOYING MIXIURES OF SULFONATE SURF~CIANTS~
This application
discloses the in3ection of a vi~cous susfactant ~lug
. oontaining a petroleum sulfonate having a relatively .
. 10 broad lecular weight distribution and a synthetic sulfonate .
having a relatively narrow m~lecular weight distr~but~on
-' which interact synergistically to thicken ~he aqueous liquid
. for mobility control purposes. This multicomponent surfactant
: ~ system may optionally contain a water-soluble C3-C6 aliphatic
. 15 alcohol.
` SummarY of the Invention
- In accordance with ~he present invention, there i8
provided a new and impro~ed waterflooding process which
involves the ~eque~tial injection of a hydrocarbon slug and
.j ., .
- 20 a thickened surfactant slug. In carrying out the ~nvention,
a hydrocarbon having a ~iscos~ty less than that of the
.. .
resexvo~r oil iB injected into the seservoir vi- a ~uitable
injection system in an Emcunt of at least 0.02 pore volume.
. i Subse~uent to the i~ection of the hydrocarbon ~lug, a
2~ thickened aqueous surfactant slug is inj ected. me surfactant
slug contains a surfactant system comprising an organic
sulfonate surfactant which functions to incxease the viscosity
- -7-
~ .
1~75S96
of the aqueous liquid to a value at least as great as the
viscosity of the reservoir oil while decreasing the
interfacial tension between the aqueous liquid and the
reservoir oil. Subsequent to the injection of the thickened
aqueous surfactant slug, an aqueous flooding medium is
injected into the reservoir in order to displace reservoir
oil to a spaced production system from which the oil is
recovered
Description of Specific Embodiments
The aforementioned Canadian Patent No. 1,053,11~7
discloses that the injection of a low viscosity hydrocarbon
slug in conjunction with the injection of a surfactant slug
and subsequent mobility control slug decreases the surfactant
utilization necessary to achieve satisfactory oil recovery
and lessens the maximum water viscosity needed for effective
mobility control. ~n accordance with the present invention,
roughly equivalent oil recovery without excessive surfactant
utilization can be achieved through the injection of a
hydrocarbon solvent followed by a thickened surfactant slug
but without the need for a separate mobility control slug.
The initially injected hydrocarbon slug may take
the form of any suitable hydrocarbon which exhibits a
viscosity under reservoir conditions which is less than -
the viscosity of the reservoir oil. Suitable hydrocarbons
are disclosed in the aforementioned Waite et al. Canadian appli- :
cation and include low to intermediate molecular weight alkanes
such as propane, hexane, and decane as well as relatively
--8--
- 1075S96
low viscosity crude oils and hydrocarbon mixtures such as
found in liquefied petroleum gas (LPG). The hydrocarbon
slug is injected in an amount of at least 0.02 pore volume.
It usually will be desirable to limit the hydrocarbon slug
to a maximum size of 0.2 pore volume for reasons of economy.
The thickened surfactant slug may contain any
suitable surfactant system which includes an organic
sulfonate and which functions to increase the viscosity of
the injected aqueous liquid to a value equal to or greater
than the viscosity of the reservoir oil. While the
relationship between oil-water interfacial tension and oil
displacement is not well defined, a pronounced reduction
in oil-water interfacial tension, normally to a value of
less than 0.1 dyne per centimeter, is usually required for
significant oil recovery. Preferably the surfactant system
is one which will reduce the oil-water interfacial tension
to a value of .005 dyne per centimeter or less although
,
interfacial tensions of up to .04 dyne per centimeter can
produce 100 percent oil recovery.
One type of surfactant system which may be employed
in carrying out the present invention comprises a mixture of
an organic sulfonate surfactant and a water-soluble aliphatic
alcohol which interact synergistically to produce a thickening
effect. Preferred surfactant systems of this type are
disclosed in Canadian Patent No. 1,053,147.
The sulfonate surfactant is an alkylaryl sulfonate having
an average molecular weight within the range of 350-500.
107559~;
The alkylaryl sulfonates may be synthetic sulfonates such
as those derived from sulfonation of products such as
keryl benzenes or they may be petroleum sulfonates derived
from sulfonation of petroleum oils or petroleum oil fractions.
The aliphatic alcohols employed in conjunction with the
alkylaryl su~fonate contain from 4 to 6 carbon atoms and
have a hydrocarbon chain link (the chain link of the
hydrocarbon portion of the alcohol molecule exclusive of
the carbinol group) of at least 3 carbon atoms. The
sulfonate and alcohol components are employed in relative
amounts such that, the ratio a of the amount of the
sulfonate surfaclt'an~ `to'`'thé-'~sum--~ofithe~'sù'lfonate'surfactant
a~d ~t~'e7 alc'oho'l'~c$om~onen-'t is within the range of 0.3-0.8.
The sulfonate surfactant is employed in a
concentration within the range of 0.5 4.0 weight percent
in an aqueous liquid having a monovalent salt salinity
within the range of 0.5-3.0 weight percent as explained
in greater detail in the aforementioned Canadian Patent No.
1,053,147. Examples of alkylaryl sulfonates which may be
employed include the petroleum sulfonates "TRS 10-80"*
available from the Witco Chemical Company and "Stepan 107"**
available from the Stepan Chemical Company. Synthetic
alky1aryl sulfonates useful in carrying out this embodiment
of the invention include the monoethanolamine alkylaryl
sulfonate available from the Exxon Chemical Company under the
trademark "FA 400" and the sodium alkyl orthoxylene sulfonate
available under the trademark
~Trademark
**Trademark
: :
--10-- -
1075596
"Synacto 426" from Esso Chemie France, an affiliate of the
Exxon Chemical Company. Exemplary of the alcohols which
may be employed in combination with the alkylaryl sulfonates
includes isobutyl alcohol, n-butyl alcohol, and the amyl
and hexyl alcohols such as n-pentanol and n-hexanol.
Normally the greatest thickening effect is achieved through
the use of the but~13,alcohols, particularly n_butyl alcohol.
As disclosed in Canadian Patent No. 1,053,147, the
thickening action of the surfactant-alcohol system is time
and temperature dependent in the sense that ~t occurs upon
aging of the system in aqueous solution and further in the
fact that the thickening process may be accelerated by the
application of heat. The thickening effect is also
salinity dependent in the sense that the viscosi~y of the
surfactant-alcohol system may be increased or decreased
; by varying the salinity within the range of 0.5-3.0 weight
percent. Changes in viscosity may also be effective by
varying the ratio 0 within the range of 0.3-0.8 For a
more detailed description of these thickened surfactant
slugs, reference is made to U.S. Patent No. 4,042,030, issued
May 24, 1976.
Another surfactant system which is preferred for
use in carrying out the present in~ention comprises a
'~ mixture of a petroleum sulfonate and a synthetic alkyl
or alkylaryl sulfonate as disclosed in the aforementioned
Canadian application Serial No. 298,930. The petroleum
sulfonate has a
--11_
10~5596
relatively broad molecular weight distribution and the
synthetic alkyl or alkylaryl sulfonate has a moaecular
weight distribution which is narrower than that of the
petroleum sulfonate. These sulfonates are employed in
concentration such that the ratio of the petroleum
sulfonate to the synthetic sulfonate is within the range
of 1: a-l 1 . Preferably the petroleum sulfonates and the
synthetic alkyl or alkylaryl sulfonates have average
molecular weights within the range of 350-500. Suitable
synthetic sulfonates include the alkylaryl sulfonate
Synacto 426, previously identified, and a sodium polybutene
sulfonate available from Amoco Chemicals Corporation under
the trade mark "Amoco Sulfonate 151". "Amoco Sulfonate 151"
has an average hydrocarbon chain length of about C21-C23
and an average molecular weight of about 400 to 420.
Suitable petroleum sulfonates include "TRS 10-80", pre~ ously
identified, and "Petrostep 420"-:~ available from the Stepan
Chemical Company. "Petrostep 420" is a sodium petroleum
sulfonate derived by sulfona-tion of a gas oil fraction.
It has an average molecular weight of about 420 and a
molecular weight distribution ranging from about 200 or
less to about 600 or more. The petroleum sulfonate-synthetic
sulfonate system may optionally contain a water-soluble
aliphatic alcohol containing from 3 to 6 carbon atoms as
disclosed in Canadian application Serial No. 298,930.
The alcohol is not an essential component
since the synergistic thickening effect is achieved through
*Trademark
,
IO~SS96
the use of the petroleum sulfonate and synthetic sulfonate
in the relative concentrations described previously. However,
the alcohol is useful in attaining maximum oil displacement
particularly where the surfactant ratio approaches the upper
end of the range 1:3_1:1 or where the surfactant solution
is ont at optimum salinity. It is preferred to employ the
alcohol in an amount to provide a surfactant-alcohol ratio 0
within the range of 0.3-0.8 as described in Canadian Patent
No. 1,053,147.
The petroleum sulfonate and synthetic alkylaryl
sulfonates are employed in any suitable concentrations
provided that the ratio of the petroleum sulfonate and
- the synthetic sulfonate is maintained within the range
previously described. Normally, the total surfactant
concentration will be within the range of 1.0_5.0 weight
percent and preferably within the range of 1-2 weight
; percent. In order to obtain good oil displacement without
excessive surfactant utilization the petroleum sulfonate~
synthetlc sulfonate surfactant system~ 7 S employed in an
aqueous liquid exhibiting a monovalent salt salinity within
the range of 1.5-4.0 weight percent. Where the salinity is
~~ near the upper end of this range, it is desirable to use a
i?
~ relatively concentrated surfactant solution of about 3 to
' 5 weight percent in order to attain adequate thickening
of the water for good mobility control. Preferably the
salinity of the surfactant solution is within the range
of 1.5-3.0 weight percent, particularly where somewhat
:
i' :
-13_
075596
lower surfactant concentrations of 1.0-2.0 weight percent
are employed. For a further description of the use of
petroleum sulfonate-synthetic sulfonate mixtures in
formulating the thickened surfactant slug, reference is
made to the aforementioned Canadian application Serial No.
298,930 of Savins et al.
Surfactant systems other than the preferred
systems described above can be employed in formulating
the thickened surfactant slug. For example, the petroleum
sulfonate, "Petrostep 420", and the synthetic alkylaryl
sulfonate, "Synacto 426', exhibit a viscosifying effect
when used alone, even in the absence of an alcohol, under
certain carefully controlled conditions of salinity and
surfactant concentration. Tables I and II present a
summary,of the viscosity and interfacial tension characteristics
for "Petrostep 420" and "Synacto 426", respectively, at different
surfactant concentrations and salinities. In each of
Tables I and II, the first column indicates the salinity
; 20 of the surfactant solution and the remaining columns
indicate the viscosities, , in centipoises and the
interfacial tensions, , in millidynes per centimeter as
measured for solutions containing surfactant concentrations
of 1.0, 1.5, 2.0, and 4.0 weight percent. The legend "dd"
in Table II indicates that the interfacial tension
measurements were not obtained because the oil drop dispersed
or disappeared and the legend "T" in Table I indicates that
the surfactant solution was too turbld to see the oil drop
and thus obtain an interfacial tension measurement. The
viscosity measurements set forth in Tables I and II were
obtained at 1~.7~sec~
-14-
.
~075596
9452
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-15 - -
1075S96
9452 Fro~ an examination of the data presented in
Tables I and II, it can be seen that the use of the petroleum
sulfonate or the synthetic alkylaryl sulfonate can produce
significant thickening within narrow regions of surfactant
concentration and salini~y. For exæmp~e, the Petrostep 420
in a solution of 1.5 weight percent sodium chloride showed
viscosities of 8.8, 4.4, and lO centipoises at concentration~
of 1, 1.5, znd 2.0 weight percent, respectively. Howe~er,
at a surfactant concentration of 4.0 weight percent a
~ignificant increase in viscosity occurred in the 1.5 weight
percent sodium chloride solution. Even higher viscosities
were obser~ed at salinities of 2.0 and 2.5 weigh~ percent.
Similar viscosity increases within narrowly defined ranges
of salinity and surfactant concentration were observed for
the synthetic alkylaryl sulfonate, Synacto 426. For
example, a significant viscosifying effect was observed
for a surfactant concentration of 1.5 weight percent in a
2.5 weight percent sodium chloride solution and at a
surfactant concentration of 2.0 weight percent in a 1.5
weight percent sodium chloride solution. For the more
concentrated 4 percent surfactant solution, signif;cant
viscosity yields were observed within the range of 1.0-2.0
weight percent. In many cases the single component
surfactant systems produced interfacial ~ensions which
were somewhat marginal in terms of optimum oil
displacement. However, it is probable that the systems
where the interfacial tension measurement could no~ be
-16-
- 107SS96
obtained because the oil drop dispersed or disappeared
actually produced interfacial tensions which were low
enough for maximum oil displacement.
The results achieved by the present invention
in terms of oil displacement and surfactant requirements
are illustrated by laboratory oil displacement tes~s-c~rried
out on a crude oil for which the displacement efficiency by
conventional surfactant flooding was relatively poor. This
crude oil is the same as that employed in the tests
summarized in Table I of the previously identified Canadian
application No. 284,548 and thus the results of the displacement
tests described hereiln may be compared with those described
; in Canadian application No. 284,548. The crude oil was
employed in two forms, one a "stock tank oil" having very
little dissolved gases therein and the other a "separator
oil!' recovered from an oil gas separator and thus containin~
light hydrocarbons. The stock tank oil exhibited a pour
point of approximately 22 C. and viscosities at 25 C.,
38 C., and 54 C., and 60C. of about 80, 12, 7, and 6
centipoises, respectively. The viscosity of the separator
oil was not measured but its viscosity characteristics
appeared to be similar to those of the stock tank oil. The
surfactants employed in these displacement tests were the
petroleum sulfonates "TRS 10-80" and "Petrostep 420", and the
synthetic alkylaryl sulfonate "Synacto 426". Alcohols used
were isobutyl alcohol, n-butyl alcohol, and hexanol. The
hydrocarbon banks employed in the displacement experiments
were formulated from propane or hexane. The test parameters
and results for these oil displacement experiments are set
forth in Table III. ~ -
-17-
; 11D75596
. 9452
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-18 -
1075596
9452 The displacement experiments were performed in
plastic or glass tubes having inside di2meters of about
1/4 to 5/16 inch. The tubes were 3 feet long except in
the case of Run 12 where the tube had a length of 6 feet.
In each tube run, the tube was packed with unconsolidated
Berea sand and then saturated with water containing 2.0
weight percent sodium chloride. The crude oil was then
flooded into the tube until ~he effluent from the tube
contained no ~ater in order to arrive at an initial oil
saturation. A waterflood ~hen was simulated by injecting
water until no more oil was produced from ~he tube in
order to arrive at a waterflood residual oil saturation.
Run No. 2 was not preceded by a separate simulated
waterflood, as explained hereinafter.
After injection of the initial water, displacement
experiments were carried out employing a thickenéd surfactant
; 81ug with and without the injection of a prior hydrocar~on
61ug. In Runs 1-4, the displacement experiments were
carried out at a temperature of 60 C. and in the remaining
runs at a temperature of 35 C. In Run 1, the thickened
surfactant slug comprised 3 weight percent TRS 10-80 and
3 weight percent isob~tyl alcohol. In Runs 2, 3, and 4,
the s~rfactant slug contained 4.0 weight percent TRS 10-80
and 2.0 weight percent isobutyl alcohol~ In the remaining
runs, Runs 5~12, the surfactant system employed was composed
of Petrostep 420 and Synacto 426, each in a concentration
of 0.75 weight percent to provide a total surfactant
-19-
-
1075596
9452 concentration of 1.5 weight percent and n-butyl alcohol
in an amount of 0.75 weight percent.
In Table III, ~he second and third columns
set forth the salinity and pore volume amount, respectively,
of the water injected immediately ahead of the hydrocarbon
slug or, where no hydrocarbon slug was employed, ahead
of the surfactant slug. In Runs 1, 3, and 4, the
- pre-surfactant waterflood involved the injection of about
2-l/2 pore volumes of 1.2 weig~t percent sodium chloride `
solution (not shown in Table III) which was followed by
an aqueous solution of 0.8 weight percent sodium chloride,
0.6 weight percent sodium carbonate and 0.2 weight percent
sodium tripolyphosphate in the pore volume amounts indicated
in the third column. Run 2 was carried out at the completion
of Run 1 in the same tube. Thus, at the completion of Run 1,
0,12 pore volume of an aqueous solution of 0.8 weight percent
sodium chloride, 0.6 weight percent sodium carbonate, and
0.2 weight percent tripolyphosphate was injected followed by
injection of the thickened sur~actant slug. With respect to
Runs 5-12, the pore volume amount and salinity of the
pre-surfaetant waterflood are as shown in Table III. In
Run 5, the simulated waterflood contained 1.6 weight percent
sodium chloride, and O.l weight percent esch of sodium
carbonate and sodium tripolyphosphate. In the remaining
uns, Runs 6-12, the simNlated waterflood contained 2.0
weight percent sodium chloride and 0.1 weight percent each
of sodium carbonate and sodium tripolyphosphate The
.
-20-
.. .
. .
1075596
; 9452 fourth column sets forth the pore volume amount of the
hydrocarbon slug employed. In Run S, the hydrocarbon slug
was composed of propane and in the remaining runs, Runs 6-12,
- the hydrocarbon slug was hexane. Columns 5, 69 and 7
characterize the thickened surfactant slug in terms of pore
volume amount, æalinity, and viscosity, respectively. In
Run 4, the aqueou~ surfactant solutions containing the TRS 10-80
and isobutanol were injected in two parts. The first exhibi~ed
a viscosity of 170 centipoises and was injected in an amount
of 0.18 pore volume. This was followed by 0.32 pore volume
of thickened surfactant solution having a viscosity of
320 centipoi&es. In Runs 1-4, the surfactant slug con~ained
; 0.6 and~0.2 weight percent of sodium carbonate and sodium
tripolyphosphate, respectively, plus 0.8 weight percent
sodium chloride to provide a tot~l salini~y of 1.6 weight
percent. In Runs 5-12, the surfactant 31ug contained 0.2
weight percent each of sodium carbonate and sodium
tripolyphosphate plus sufficient sodium chloride to provide
the total salinity indicated in column 6.
Run 3 involved the continuous injection ~f a
thickened surfactant slug in a total pore volu~e amount of
1.38. The remaining runs involved the injection of a
limited pore volume ~mount of thickened surfac~ant which was
then followed by a drive water injected in such amounts as
necessary to carry the run to a concluding point at which
'
- no fur~her oil was recovered. The sodium chloride
concentration of the driving fluid is set forth in column 8
,. . .. .
-21-
~ .
107S596
9452 With the exception of Runs 5 and li, the driving fluid contained
no other additives. In Run 11, the first 0.1 pore volume of
the drive water contained 0 7~ weight percent n-butyl alcohol
and, in Run 5, 0.75 weight percent n-butyl alcohol was
present ~hroughout the drive water.
Column 9 of Table III presents the percent oil
recovery, R, at the conclusion of the displacement run and
column 10 sets forth the remaining residual oil saturation~
The percent oil recovery is calculared as the percentage
of waterflood residual oil recovered and thus is repreæentative
of tertiary oil recovery. Column 11 in Table III sets forth
the amount, ST, of surfactant employed in terms ~f milligrams
of surfactant per gram of sand. The last column pre~ents
the amount of surfactant employed in milligrams per græm
as normalized to reflect 100 percent oil recovary. This
normalized amount, Sr, is derived at by dividing the amount
of surfactant, ST, in milligrams of surfactant per gram of
sand by the decimal equivalent of the percent oil recovery.
- From an examin~tion of the data set forth in
Table III it ca~ be seen that the injection of the thickened
~surfactant slug in fractional pore volume amounts resulted
in rela~ively low oil recoverieæ. Run No. 1 which involved
the injection of 0.13 pore volume of surfactant slug
achieved an oil recovery of only 28 percent. Run 4 which
involved the injection of a total amount of thicklened
surfactant slug of 0.5 pore volume resulted in a recovery
of 60 percen~. Only in the case of ~un 3 which involved
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9452 the continuous injection of a thickened surfactant solution
was 100 percent oil recovery achieved.
The displacement Runs 5-12 simulating the practice
of the present invention generally produced significantly
higher oil recoveries and required much lower surfactant
utilization and lower viscosi~y for effective mobility
control. Further, only a relatively small pore volume amount
of the surfactant slug is required to accomplish both
microscopic and macroscopic oil displacement. In RNn 5,
100 percent oil recovery was achieved employing only
0.08 pore volume of the thickened surfactant slug. However,
the slug was displaced by water containing ~utanol throughout
and this probably acted by desorption of previously adsorbed
surfactant to produce a somewhat larger pore volume amount
of thickened aqueous solution wit~in the sand pack. I~
; will be noted in this regard that Run 6 which involved the
in~ec~ion of 0.09 pore volume of surfac~ant slug resulted
in a tertiary oil recovery of 43 percent. While recovery
here was probably limited by ~he amount of surfactant
available, as well as by the sizè of the thickened surfactant
slug, the data indicates that the ~hickened surfactant slug
should be employed ~n an amount of at least 0.1 pore volume
unless relatively high surfactant concentrations on the order
of 4 or 5 percent are employed. Preferably, the thickened
sur~actant slug is employed in an amount of at least 0.2
pore volume and not more than 0.5 pore volume. As noted
previously~ the thickened surfactant slug has a viscosity
1075596
at least as great as that of the reservoir oil. In mo~t
cases the surfactant slug viscosity will be within the
range of 1 to 4 times the viscosity of the reservoir oil.
The driving fluid injected immediately after
the surfactant slug preferably exhibits a relatively low
salinity of one-half or less than that of the surfactant
slug in order to enhance the chromatographic movement of
the surfactant components through~the formation. This
low salinity drive water may be injected in an amount
within the range of 0.5 to 1.5 pore volume and may
contain an aliphatic alcohol of the type employed in
formulating the thickened surfactant slug as described
previously. The low salinity water-is followed by any
water which is lcoally available and not incompatible
w~rth the formation. This driving fluid is injected in
such amounts as is necessary to carry the process to
conclusion.
The present invention may be carried out utilizing
injection and production systems as defined by any- suitab~e
arrangement- of wells. One well arrangement commonly used
in waterflooding operations and suitable for use in carrying
out the present invention is an integrated five-spot pattern
of the type illustrated in the aforementioned Canadian
' Patent No. 1,053,147. Other well arrangements
may be used in carrying out the invention examples of
which are set forth in sa~d Canadian Patent No. 1,053,147.
By the term "pore volume" as used herein is meant the pore
volume
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~075596
of that portion of the formation underlying the well patt~rn
employed as described in greater detail in Canadian Patent
No. 1,053,147.
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