Note: Descriptions are shown in the official language in which they were submitted.
11'~'7~3~
F-0731 -1-
OIL RECOVERY EMPLOYING AN ALCOHOL AND AN_ETHER-LINKED
SULFATE OR SULFONATE
This invention relates to the recovery of oil ~rom
subterranean oil reservoirs and more partlcularly to imPraved
water-floodinq oPerations involvin~q the ln~ection of an oll slug
containing a preferentially oil-soluble alcohol and a
preferentially oil-soluble ether-linked anionic surfactant.
In the recovery of oil from oil-bearing reservoirs, it
usually is Possible to recover only minor portions of the
oriqinal oil in Place by the so-called primary recovery methods
which utilize only the natural forces~Present in the reservoir.
Thus, a variety of suDplemental recovery techniques has been
emPloyed in order to increase the recovery of oil from
subterranean reservoirs. The most widely used supDlementa
recovery techniaue is waterflooain~, which involves the
injection of water into the reservoir. 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 recoqnized that factors such as the
interfacial tension between the injected water and the reservoir
oil, the relative mobilities of the reservoir oil and injectea
water, and the wettability characteristics of the rock surfaces
within the reservoir are factors which influence the amount of
oil recovered by waterfloodinq. Thus, it has been proposed to
add surfactants to the flood water in order to lower the
oil-water interfacial tension and/or to alter the wettaDility
characteristics of the reservoir rock. Also, it has been
pro~Posed to add viscosifiers such as Polymeric 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 imProvin~q the sweeP efficiency of
the waterflood.
q~
,
11~7'i~36
F-0731 -2-
Processes which involve the injection of aqueous
surfactant solutions are commonly referred to as surfactant
waterflooding or as low tension waterflooding, the latter term
having reference to the mechanism involvlng the reduction of tne
oil-water interfacial tension. Thus far, many such
waterflooding applications have emPloyed anionic surfactants.
For example, a paPer by W. R. Foster entitlea "A Low-Tension
Waterflooding Process", Journal of Petroleum Technology, Vol.
25, Feb. 1973, PP. 205-210, describes a promising technique
involving the injection of an aqueous solution of petroleum
sulfonates within designated e~uivalent weight ranges and under
controlled conditions of salinity. The Petroleum sulfonate slug
is followed by a thickened water slug which contains a
viscosifier such as water-soluble bioPolymer in a graded
concentration in order to provide a maximum viscosity greater
than the viscosity of the reservoir oil and a terminal viscosity
near that of water. This thickened water slug is then followed
by a driving fluid such as a field brine which is injected as
necessary to carry the process to conclusion.
One problem encountered in waterflooding with certain
of the anionic surfactants such as the sulfonates is the lack of
stability of these surfactants in a so-called "high ~rine"
j environment. These surfactants tend to precipitate from
solution in the presence of monovalent salts such as sodium
chloride in concentrations in excess of about 2 to 3 weight
percent and in the presence of much lower concentrations of
divalent metal ions such as calcium and magnesium ions.
Typically, divalent metal ion concentrations of about 50 to 100
ppm and above cause Precipitation of the petroleum sulfonates.
Various surfactant formulations which contain anionic
sulfonates that tolerate high salinities and/or high aivalent
metal concentrations have been proposed for use in high ùrine
':.;
--- li'7'7~36
F-0731 -3-
environments. Thus, U. S. Patent No. 3,827,497 and U. S. Patent
No. 3,890,239 disclose a surfactant composition comprisinq a
mixture of an orqanic sulfonate and a sulfated or sulfonatea
oxyalkylated alcohol and a polyalkylene qlycol alkyl ether. The
sulfonate is exemplified by the formula
C12-C150(CH2CH20)mS03-Na+,
where m is an averaqe of 3.
Another surfactant waterflooding process employing an
ether-linked anionic surfactant in high salinity environments is
disclosed in U. S. Patent No. 3,977,471. This Patent discloses
the use of an Rl hydrocarbyl ether-linked R2 hydrocarbyl
sulfonate. The Rl lipophilic base is provided by a benzene,
toluene, or xylene radical having an alkyl substituent
containinq 6-24 carbon atoms and the R2 grouP linking the
sulfonate grouP with the alkoxy ether grouP is a Cl-C8
alkyl, cycloalkyl, alkene or aryl radical. The R2 hydrocar~yl
group may be substituted with a hydroxy grouD or a Cl-C8
aliphatic grouP. Dodecyl, dimethyl benzene ether propane
sulfonate is specifically disclosed by patentees. The Patent
process is said to be Particularly useful in reservoirs having
high salinity brines, i.e. salinities of 2% or more, and the
dodecyl, dimethyl benzene ether proPane sulfonate is said to be
stable in saline solutions containing from 7-14 weight percent
sodium chloride. U. S. Patent No. 4,161,983 discloses the use
ot` similar sulfonates. In addition to the use of the
ether-linked surfactants in aqueous surfactant solutions,
3,977,471 discloses that the surfactants may be used in liquid
hydrocarbon solvents or in microemulsions. The microemulsion
contains a refined or crude oil, an aqueous medium, and the
'7~ 6
F-0731 -4-
previously described ether-linked surfactant. In addition, the
microemulsion may contain a co-surfactant. Partlcularly
effective co-surfactants are said to lnclude alcohols,
ethoxylated alcohols, sulfated ethoxylated alcohols, sulfonate~
ethoxylated alcohols, ethoxylated phenols, sulfated ethoxylate~
Phenols and synthetic sulfonates. Alcohols disclosed in the
Patent for use as microemulsion co-surfactants include
C3-C20 aliphatic alcohols such as isoproDanol~ isobutanol,
tertiary butanol, amyl alcohols, hexanols, octanols, and
dodecanols. The patentees sPecifically disclose flooding with
microemulsion systems containing 91~ to 93% water containing 6~
sodium chloride, 5~ oil, 1% to 3% dodecyl dimethylbenzene ether
proPane sulfonate, and 1% butyl alcohol.
Yet another surfactant waterflooding process involving
the use of an anionic ether-linked surfactant is disclosed in
U.S. Patent No. 4,018,278. The ether-linked surfactants
employed include sulfonated polyethoxylated aliPhatic alcohols
and sulfonated polyethoxylated alkyl phenols. The patentee
discloses the use of the ether-linked sulfonates alone or as a
co-surfactant with anionic surfactants such as petroleum
sulfonates and in high brine environments, e.g., in a solution
having a salinity of 183,000 ppm and a total hardness of 9400
ppm. The surfactant system is said to be particularly useful at
temperatures in excess of 120F. Also, U. S. Patent No.
4,217,957 discloses an aqueous mixture of an alkylbenzene
ethoxylated proPylene sulfonate and the dialkylbenzene
derivative, useful in waterflooding.
In accordance with the Present invention, there is
Provided a new and imProved waterflooding process emPloying an
alcohol and an ether-linked surfactant which exhibit oil
solubility preferences. In carrying out the invention, at least
a portion of the fluid introduced into the oil reservoir via a
suitable injection system is oil slug li~uid containing a
~,,
. .
1177tj36
F-0731 -5~
preferentially oil-soluble alcohol of ~imited water solu~ility
and a Preferentially oil-soluble anionic surfactant comprising a
hydrocarbyl ether-linked sulfonate or sulfate wherein the
hydrocarbyl groUP provides a liPoPhilic surfactant base and
wherein the ether linkage is provided by an alkoxy linkage
having a ratio of carbon atoms to oxygen atoms within the range
of 2 to 3. In a Preferred embodiment of the invention, the
Preferentially oil-solu~le alcohol is an aliPhatic alcohol
containing from 5 to 7 carbon atoms. The alcohol is employed in
a concentration such that the weight ratio of the alcohol to the
preferentially oil-soluble surfactant is within the range of
about 0.2 to 1Ø Preferred ether-linked surfactants for use in
the invention are sulfonated polyethoxylated aliphatic phenols
having 1 to 20 ethylene oxide units, preferably from about 3 to
about 10, and in which the phenyl nucleus has attached thereto
at least 2 linear or branched-chain aliphatic groups containing
from 8 to 12 carbon atoms. The multiple groups are chosen so
that together they total at least 16 carbon atoms.
Ether-linked anionic surfactants are old and well known
in the detergent art. For example, Schwartz et al., SURFAOE
ACTIVE AGENTS AND DETERGENTS, Vol. II, 1958, Interscience
Publishers, Inc., New York, disclose ether-linked sulfonates
under the headings "Sulfonates with Intermediate Linkages" at
Pa9es 71-78 and "Alkylarylsulfonates with Intermediate Linkages"
at pages 91-93. As noted previously, the aforementioned patents
disclose the use of anionic ether-linked sulfates in surfactant
waterflooding Processes or the use of ether-linked sulfonates in
such Processes. Applicant's invention involves surfactant
waterflooding in which such anionic ether-linked sulfonates are
employed in conjunction with alcohols under conditions such that
the surfactant and alcohol exhibit oil solubility preferences.
More sPecifically, the alcohol which is both water and
oil-soluble is Preferentially oil soluble. That is, with equal
11~7'7~ 6
F-0731 -6-
'. .
amounts of oil and water, a greater amount of the alcohol will
dissolve in the oil than in the water or stated otherwise, if
the alcohol is exPosed to both oil and water phases, the alcohol
will tend to partition between the two with a greater
concentration in the oil phase. The preferred alcohols may be
characterized as having a water solubility at the reservair
temperature of less than 3.0 weight percent and preferably less
than 1.0 weight percent and as being substantially oil
miscible. The anionic ether-linked sulfonate or sulfate
employed in conjunction with the alcohol is preferentially oil
soluble also.
The sulfonate or sulfate anionic group may be linked to
any suitable hydrocarbon grouP which Provides a lipophilic base
of the surfactant as disclosed in the aforementioned patents.
Thus, the lipoPhilic base of the anionic ether-linked sulfonates
or sulfates employed in the Present invention may be provided
Preferably by dialiphatic substituted aryl grouPs~ Where the
lipophilic base is provided by a dialiPhatic substituted aryl
group, the aryl component may be mononuclear (benzyl) or
dinuclear (naphthyl). Preferably the aryl component will be
mononuclear in view of the Practical consideration of economy
and Product availability. The aryl grouP is substituted with at
least 2 linear or branched-chain aliPhatic grouPs~ each having
at least 8 carbon atoms, with the total number of aliPhatic
carbon atoms being within the range of 16 to 24.
The ether linkage of the anionic ether-linked sulfates
or sulfonates emPloyed in carrying out the Present invention
preferably is provided by an alkoxylated grouP having a ratio of
carbon atoms to oxygen atoms within the range of 2 to 3. Stated
otherwise, the ether linkage is derived from ethylene oxide or
Propylene oxide or mixtures of ethylene oxide and propylene
oxide. The number of alkoxy groups in the ether linkage will
vary dependinq uPon such factors as the character of the
',','
.:
' .
,
..
:
`` 1 1'~'7 ~ ~ 6
F-07~1 -7-
lipophilic surfactant base and the salinity of the aqueous
surfactant solution, but normally the ether lin~age will contain
from l to 20 alkylene oxide units.
A Preferred ether-linked sulfonate ~or use in carrylng
out the present invention is characterized by the formula
(Rl)a Ar O(CnH2nO)x R2 S03M
wherein Rl is a linear or branched-chain aliphatic grouP
containing from 8 to 12 carbon atoms, and wherein Rl may be
the same or different,
n is 2 or 3,
q is at least 2,
x is a number within the range of l to 20,
Ar is Phenyl or naphthyl,
R2 is a Cl to C4 alkylene group,
R3 is a hydrogen, a hydroxy grouP or a methyl group,
and
M is an alkali metal, ammonium, or substituted ammonium
ion,
and wherein the Rl grouPs provide a total of at least 16
carbon atoms.
The useful sulfates may be characterized by the formula:
(Rl)q Ar-0 (CnH2n)x - 503M
wherein Rl n, q, x, Ar, and M have the same meaning as above.
Where M is an alkali metal ion, it usually will take
the form of sodium or potassium. Substituted ammonium ions
which may be emPloyed include mono-, di-,
.
'7f~36
F-0731 -8-
or tri-substituted alkylammonium or alkanolammonium ions.
Examples of alkylammonium ions include methylammonium,
ethylammonium, and normal or isoproPylammonium ions and examPles
of alkanolammonium ions include monoethanolammonium and
triethanolammonium ions.
Preferably the ether linkage is provided by one or more
ethylene oxide grouPs. Thus, in a Preferred form of surfactant
characterized by formula (1), n is 2 and x is a number within
the range of 3 to 8. In the case where the lipophilic grouP
Rl is a dialiPhatic substituted aryl group, the aliPhatic
substituents Preferably Provide at least 18 carbon atoms. In
this instance, as noted previously, it is desira~le that a
mononuclear aryl radical such as Phenyl be emPloyed. As
indicated by the formulae, the alkyl grouP connecting the
sulfonate grouP with the ether linkage is provided by a Cl to
C4 alkylene group which may be unsubstituted or which may be
substituted by a hydroxy grouP or a methyl grouP. Preferably,
however, the alkylene linkage is Provided by an ethylene or
Propylene grouP which is unsubstituted or substituted by a
hydroxy grouP. That is, preferably R2 contains 2 or 3 carbon
atoms and R3 is a hydrogen atom or hydroxy group.
The results of laboratory oil disPlaCement tests
carried out with regard to an aromatic crude oil are set forth
in Table I. The oil displacement tests were carried out
employing 5-foot long flow tubes having an inside diameter of
about 1/4 inch. In each tube run, the tube was packed with
unconsolidated Berea sand and then saturated with saline water.
The crude oil was then flooded into the tube until the effluent
from the tube contained no water, with the total amount of water
being displaced from the tube during this operation being
measured to determine the initial oil saturation. Each tube was
then subjected to a simulated waterflood by injecting a brine in
an amount as necessary until the effluent was free of oil. The
' '
' ~. ' -
- ' ~ .
""
~ t
- 117'~3fi
- F-0731 -9-
amount of oil Pro~uced during th~s oPeration was measure~ in
order to determine the residual oil saturation after waterflood
of the tube. A simulated surfactant waterflood was then carried
out bV injecting an oil slug surfactant slug ~surfactant plus
alcohol dissolved in West Ranch crude) followed by the lnJection
of a driving aqueous fluid until the effluent from the tube was
free of oil. The drivinq fluid was water containing 6.6~ TDS,
includinq 0.15X by wt. of Ca++ and Mg++ (total) and O.lX by
wt. of "Kelzan". This is the anionic polysaccharide B-1459
produced bV fermentation of glucose with the bacterium
Xanthomonas campestrls (NRRL B-1459 USOA), which is available
from the Kelco Company as '!KelZan *- The amount of oil recovered
during this oPeration was measured in order to arrive at the
final residual oil saturation and the amount of tertiary oil
recovered.
The surfactant was
CgHlg)2 ~ (C2H40)6.8 C3H6S3
TABLE 1
Surfactant X
Run No. PV X Wt. Alcohol Alcohol X WFRO X SOR
1 0.093 7.7 none none 76.5 5.0
2 0.093 7.7 nC50H 2.0 85.6 3.2
3 0.093 7.7 nC50H 4.0 88.5 2.5
4 0.093 7.7 nC60H 2.0 89.0 2.3
0.093 7.7 nC60H 4.0 99.0 0.3
6 0.055 7.7 nC60H 4.0 80.9 4.2
7 0.055 7.7 nC60H 6.0 66.5 7.2
B * Trad~k
1~ 6
F-0731 -10-
The present invention may be carried out utilizing
injection and production systems as defined by any suitable
arrangement of wells. One well arrangement commonly used in
waterflooding oPerations and suitable for use in carrylng out
the present invention is an integrated five-spot pattern of the
type illustrated in U. 5. Patent No. 3,927,716 to aurdyn et al.
Other well arrangements may be used in carrying out the present
invention, examples of which are set fortn in the Burdyn et al.
patent. By the term ~Pore volume" as used herein is meant that
volume of the portion of the formation underlying the well
pattern employed, as described in greater detail in the Burdyn
et al. Patent~
The present invention may be carried out in conjunction
with the use of a thickening agent added for mobility control
purPoses. As indicated by the previously described displacement
tests, the thickening agent may be added to the aqueous solution
of alcohol and surfactant or it may be injected in a seParate
mobility control slug. Where a separate mo~ility control slug
is employed, it normally will be injected immediately after the
slug containing the surfactant. The thickening agent may be
added in concentrations so as to Provide a graded viscosity at
the trailing edge of the mobility control slug as disclosed in
the aforementioned paper by Foster or graded viscosities at both
the leading and trailing edges of the mobility control slug as
disclosed in U. S. Patent No. 4,018,281 to Chang.
Alternatively, the thickening agent concentration may be
relatively constant throughout. Normally, the viscosity of at
least a portion of the mobility control slug should be at least
as great as that of the reservoir oil and tyPically it will be
within the range of about 1 to 4 times the viscosity of the
reservoir oil. Various thickening agents which may be emPloyed
for mobility control Purposes are well known to those skilled in
.
.
- --` 11'7'7~ 6
F-0731 -11-
the art and include such polymers as the bioPolymer "Kelzan",
Previously identified, and the various partially hydrolyzed
polyacrylamiaes availaole from the Oow Chemical Company under
the trademark "Pusher" chemicals.
The ether-linked surfactant may be PreSent in any
suitable concentration depending upon the characteristics of the
Particular reservoir involved and such factors as surfactant
consumption, e.g., by adsorPtion, and disPersion of the
surfactant into the reservoir water. The surfactant
concentration may ranqe from û.Ol to 15 weight percent although
in most aPplications the surfactant will be employed in a
concentration within the range of about 1 to about 10 weight
Percent. The alcohol concentration will, of course, depend upon
the concentration of the surfactant and the desire~ ratio of
alcohol to surfactant. The oil slug containing the alcohol and
ether-linked surfactant may be injected in amounts ranging from
about 0.01 to aDout 0.1 Pore volumes with the larger pore volume
amounts being used with the lower surfactant Goncentrations.
Usually it will be desired to inject the alcohol-surfactant slug
in an amount within the range of about 0.01 to about 0.0~ pore
volumes.
~':
B
.
