CA1081442A - Waterflood oil recovery process employing divalent ion tolerant surfactant systems - Google Patents

Abstract

WATERFLOOD OIL RECOVERY PROCESS EMPLOYING
DIVALENT ION TOLERANT SURFACTANT SYSTEMS

Abstract of the Disclosure Waterflooding technique for the recovery of oil from subterranean oil reservoirs in which an ether-linked methane sulfonate is employed as a surfactant in at least a portion of the water injected into the oil reservoir.
The ether-linked methane sulfonate is compatible with relatively high concentrations of divalent metal ions. It may be employed as a co-surfactant to stabilize hydrocarbon sulfonate surfactants to relatively high divalent metal ion concentrations.

Description

9074 Background of the Invention This invention relates to the recovery of oil from subterranean oil reservoirs and more particularly to ~mproved waterflooding operations involving the use of an ether-linked metha~e sulfonate surfactant system which is compatible with divalent metal ions.
In the recovery of oil from oil-bearing reservoirs, it usually is possible to recover only minor portions of the original oil in place by the so-called primary recovery methods which utilize only the natural forces present in the reservoir. Thus a variety of supplemental recovery techni~ues have been employed in order to increase the recovery of oil from subterranean reservoirs. The most widely used supple-mental recover~ technique is waterflooding which involves the in3ection of water into the reservoir. As the water moves through the reservoir, it acts to displace oil therei.n to a production system composed of one or more wells through which the oil is recovered.
It has long been recogni~ed that factors such as the interfacial tension between th~ injected water and the reservoir oil, the relative mobilities of the reservoir oil and in~ected water, and the wettability characteristics of the rock surfaces within the reservoir are factors which influence the amount of oil recovered by waterflooding.
Thus it has been proposed to add surfactants to the ~lood water in order to lower the oil-wàter interfacial tension and/or to alter the wettability characteristics of the .

, . .

:

g074 reservoir rock. Also, it has been:proposed 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 S and oil and improving 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 tension waterflooding.
Thus far, most low tension waterfl:ooding applications have employed anionic surfac.tants. For example, a paper by W. P.
~oster entitled-"A Low-Tension Waterflooding Process", Jou;-nal o Petroleum Technology, Vol. 25, Feb. 1973, pp. 205-210, describes a promising technique i~..volving the injection of an aqueous solution of petroleum sulfonates within designated equivalent weight ranges and under controlled conditions or salinity. The petroleum sulfonate slug is followed by a thickened water slug which contains a viscosifier such as a water-soluble biopolymer in a graded.concentration in orde~ to .
provide a m~ximum viscosity greate.r than the viscosity of the ~ . 20 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 in~ected as necessary to carry the process to conclusion.
One limitation encounteled in waterflooding with anionic surfactants such'as petroleum sulfonates is the tendency of the surfactants to precipitate from solution in the presence of even moderate concentrations of divalent . ....

.

9074 metai ions such as calcium and ma~nesium ions. Typically, divalent metal-ion concentrations of about 50-100 ppm and above cause precipitation of the petroleum sulfonates. Thus, as taught for example in the Foster paper, the surfactant slùg may be preceded by a protective slug which functions to displace reservoir waters containing unacceptable amounts of divalent ions ahead o the subsequently injected surfactant slug. Another limitation imposed upon the use of anionic surface-active agents resides in the fact that desired low interfacial tensions can seldom be achieved, even in the absence of divalent metal ions, at salinities significantly in excéss of 2 or 3 weight percent. Thus, the protective slug as well as the surfactant slug normally will be of a relatively low salinity.
A number of recent patents are directed to low tension waterflooding employing surfactant systems which - will tolerate relatively high salinities and/or divalent metal ion concentrations. For exsmple, U.S. ~atent No.
3,811,504 to Flournoy et al. is directed to a low tension waterflood process for use in environments exhibiting a polyvalent ion concentration of about 1500 to about 12,000 parts per million and which employs a three-component surfactant system containing two anionic surfactants and one nonionic surfactant. One of the anionic surfactants is an alkyl or alkylaryl sulfonate and the other anionic surfactant is an alkyl polyethoxy sulfate containing from 1 to 10 ethoxy groups and from 7 ~o 20 carbon atoms in the 1081~Z

9074 alkyi group. The nonionic surfactant may be a polyethoxylated alkyl phenol or a polyethoxylated aliphatic alcohol.
U.S. Pate~t No. 3,508,612 to Reisberg et al. is directed to a low tension waterflooding process employing 21 calcium-compatible anionic-anionic surfactant system which can be employed in saline solutio~s containing from 0.01 t~
S molar NaCl and from about 0 to 0.1 molar CaC12. One of the anionic surfactants employed in the Reisberg et al. process is an organic sulfonate such as a petroleum sulfonate having ; 10 an average molecular weight within the range of 430-470 an the o~her surfactant is a sulfated ethoxylated alcohol. A
preferred sulfated alcohol is one containing a C12-C15 ~lkyl group and three ethylene oxide groups.
Another technique involving the use of calcium-compatible surfactant systems in low tension waterflooding is disclosed in U.S. Patent No. 3,827,497 to Dycus et al.
In this process, a three-component or two-component surfac~ant ;~ system may be employed. The three-component system comprises an organic sulfonate surfactant such as a petroleum sulfonate, a polyalkylene glycol alkyl ether, and a salt of a sulfonated or sulfated oxyalkylated alcohol. The two-component system , ~ .
comprises an organic sulfonate surfactan~ and a salt of a sulfonated oxyalkylated alcohol. These surfactant systems may be employed in a brine solution which, as noted in col~unn 3, will usually contain about 0.5-8 percent sodium chloride and will often contain 50-5,000 ppm polyvalent metal ions such as calcium and/or magnesium ions. The sulfated or sulfonated . ~ .

: ~ _ 5 _ .;
. . - : . . . . .. .
'' : .. . .
.
.. , , - , . ~

108~44Z
oxyaikylated alcohols may be derived from aliphatic alcohols of 8-20 carbon atoms or from alkyl phenols containing 5-20 carbon atoms per alkyl group. The oxyalkyl moiety in this surfactant will usually be derived from ethylene oxide -although other lower alkylene oxides containing 2-6 carbon atoms or mixtures thereof may be employed.
Summary of the Invention In accordance wqth the ~resent invention, there is provided a new and improved low tension waterflooding proc~ss employ:ng an anionic surfactant w~ich is particularly suita~12 for use in reservoirs in which connate waters exhib~t a high divalent metal ion concentration or which may be employed in ~aterfloods in which the available Lnjection waters exhibit a relatively high divalent io~
conce~tra~ion. In carrying out the invention, at least a portio~ of the injected fluid comprises an aqueous liquid containing a water-soluble-aliphatic or aliphatic-substitu~ed aryl ethex-linked methane sulfonate. The ether linkage Ln this surfactant is provided by a polyalkylene oxide containing from 2 to 4 carbon atoms in each alkylene oxide unit and preferably 2 or 3 carbon atoms in each alkylene oxide unit.
The aliphatic or aliphatic-substituted aryl portion of said ether-linked methane sulfonate provides a lipophilic base.
The above-mentioned water-soluble aliphatic or aliphatic-substituted aryl ether-linked methans sulfonate is employed in combination with a hydrocarbon sulfonate surfactant such as a petroleum sulfonate which normally precipitates in the presence of even moderate concentrations of divalent ion. The ether-lined methane sulfonate functions to stabilize the hydrocarbon D
.

--`` 1081442 9074 sulfonate surfactant in the presence of relatively high divalent ion concentrations.
More specifically, in carrying out the invention, a preferred form o the ether-linked methane sulfonate is characterized by the formula R-~OCH2CH2~n OCH2S03- M;
wherein R is an aliphatic group or an aliphatic-substitute aryl group, n is at least 3, and M is an alkali metal, ammonium, or substituted ammonium ion.
DescriDtion of Specific Embodiments -This invention relates to certain ether-linked sulfonates and their use in low tension waterflooding. These ether-linked sulfonates may be emFloyed either alone or as co-surfactants in combination wit~ hydrocarbon sulfona~es of the type heretofore employed as waterflood surfactants. These hydrocarb~n sulfonates, which nor~ally take the form of petroleum sulfonates or in some cases synthetic alkylaryl sulfonates~ function to decrease interfacial tension between the injected flooding water and the reservoir oil and thus increase the microscopic displacement efficiency of the oil by the water. While theoretically any decrease in oil-water interfacial tension results in better microscopic displacement efficiency, this phenomenon ordinarily does not become significant until the oil-water interfacial tension is reduced to a value significantly less than 0.1 dyne per centimeter.

:: ~ . . .. ., . . .-~081442 9074 Preferably the oil-water interfacial tension is reduced to a value of 0.005 dyne per centimeter or less in order to reach an optimum microscopic displaceme~t efficiency.
As noted previously, one difficulty with the use of hydrocarbon sulfonates resides in the fact that even small amounts of divalent ions wi~l cause their precipitation, thus greatly reducing their effectiveness. When such hydrocarbon sulfonates are employed in the absence of a stabilizing co-surfactant, the divalent metal ion concentration normally should be less than 50 p~;m and if it exceeds 300-'iO0 ppm the use of such hydrocarbon sulfonates alone is usually inefective.
' Ether-linked sulfonates are well known in the art.
For example, Schwartz et al., SUF~CE ACTIVE AGENTS AND
DETERGENTS, Interscience Publishe~s, Inc., New York, Vol. LI, at pages 74 and 75, disclose sulfonated polyethoxylated all;yl phenols and their method of preparation by reaction o~ an ethoxylated alkyl phenol with sodium ethanol sulfonate. In sddition? Schwartz et al. disclose that ether-linked sulfonates ` 20 may be prepared by the addition re~ction of butane sultone with an alkyl phenol. As noted previously, the aforementioned patent to Dycus et al. discloses the use of ether-linked - sulfonates in low tension waterflooding operations. Dycus ; et al. suggest that the ether-lin~ed sulfonate may be ~ormed by sulfatil-g an oxyalkylated alcohol and then reacting the ; sulfate with sodium sulfite to produce t~e corresponding sulfonated oxyalkylated alcohol.

.
.

.

.. .. . .

1081~42 9074 As distinguished from the sulfonated oxyalkylated surfactants described above, the ether-linked sulfonates of the present invention are characterized by a methane bridge between the alkoxy oligomer linked to the oleophilic portion of the molecule. The lipophilic base of the methane sulfonates employed in the preseni- invention is provided by aliphatic groups or aliphatic-substituted aryl groups. The aliphatic groups or aliphatic substituents may contain from about 6 to 30 carbon atoms depending upon the nature of the oxyal~yl oligomer which links the lipophilic base to the methan~ sulfonate. Where the lipophilic base is provided by an zliphatic-substituted aryl group, the aryl component may be mononuclear or polynuclear (containing up to 3 rings) and contains one or more aliphatic substituents. Preferably, the aryl component will be mononuclear in view of the practical considerations of economy and product availability.
The aliphatic group or aliphatic substituent may be unsaturated and/or contain branched chains but usually wilL
take ~the form of normal alkyls.
20 ~ The ether linkage is a polyalkoxy oligomer derived from low molecular weight alkylene oxides or mixtures thereo~
containing from 2 to 4 carbon atoms. Preferably, however, the polyalkoxy ether linkage is derived from ethylene oxide ; or propylene oxide or mixtures of ethylene oxide and propylene oxide. Stated other~wise, the ether linkage takes the fonm of an alkoxy oligomer containing 2 or 3 carbon atoms in each -alkylene oxide monomer unit.

. .. ~ . .. . .

10814~Z

9074 In a preferred embodiment of the present invention, the ether-linked methane sulfonate is an aliphatic or aliphatic-substituted aryl polyethoxy methylene sulfonate characterized by the formula:
R~~CH2CH2~n 0CH2S3 M (1) wherein R is an aliphatic or aliphatic-substituted aryl group as described previously, n is a number equal to or greater than 3, and M iB an alkali metal, ammonium, or substituted ammonium ion.
Where M is an a~kali metal ion, it usually will take the form of sodium or potassium. Substituted ammonium ions which may ; be employed include methylammonium, ethylammonium, and normal-or iso-propylammonium ions. The substituted am~onium ions may also take the form of mono-, di-, or tri-substituted alka ~olammonium ions such as monoethanolammonium or triethanol~mmonium ions.
In the case where R is an aliphatic-substituted 1, .
aryl group, the aliphatic substitu~nt normally will contain 1 20 from 8 to 25 carbon atoms. Preferably, the lipophilic base will take the form o a mono-substituted aryl group in which the aliphatic substituent contains 9 to 12 carbon atoms.
`I Where the lipophilic base does not include an aromatic nucleus, the aliphatic group normally will contain from 10 to 30 carbon atoms, with a chain link of 12 to 15 carbon atoms being preferred. The ether linkage, as indicated, should contain at least 3 ethylene oxide groups and may -10- `

, .. - : . . . ' ' : .: .' : , .

~ 081442 :
74 range up to 30 ethylene oxide groups depending upon the - character of the aliphatic or aliphatic-substituted aryl group. Normally, the number of ethylene oxide units will increase with the number of carbon atoms in the aliphatic groùp ar substitutent. In most cases it will be preferred to provide from 3 to 12 ethylene oxide units in the ether ., .
linkage.
As indicated by the exp~rimental data presented hereinafter, the ether-linked methane sulfonates of the prese2t il~vention are stable even at high temperatures in the presence of high salinities and high divalent ion conce~-rations. In addition they function to stabilize ~! hydrocarbon sulfonates such as the petroleum sulfonates normall~ employed in low tension waterflooding in the .~, prese~ce of high salinities and high concentrations of divalent metal ions. Thus in the present ..;
'~ inve~tion, the ether-linked methane sulfonates are employecl as co-surfactants in combination ~ith hydrocarbon sulfonates.
~-1 The hydrôcarbon sulfonates employed in carrying i. .
out this invention may be of any suitable type such as those conventionally employed in Low tension waterflooding. Many hydrocarbon sulfonate surfactants are ~;
~ known in the detergent art and have been proposed for use :' 1 ~ in such waterflooding applications. Preferably an alkyl . ~ . .
'l25 aryl sulfonate having an average molecular weight within .,, the range of 350 to 500 will be employed in combination with the ether-linked methane sulfonates. T~hile the ':

:: - 1 1 -:'' 74 selection of a particular hydrocarbon sulfonate is somewhat ~, specific with regard to the reservoir oil-injection water system involved, normally the use of alkyl aryl sulfonates , within this molecular weight range will lead to the desired low interfacial tension, normally 0.005 dyne/cm or less.
The sulfonate molecular weights referred to herein are calculated as equivalent weights for the sodium form assu~'ng 100 percent monosulfonation. The alkyl aryl sulfonates ma,7 be the so-called synthetic sulfonates such as those derive~l from sulfonation of products such-as keryl benzenes or the-y m2y be petroleum sulforates derived from sulfonation of petroleum oils or petroleum oil fractions. Normally it will , be preferred to employ petroleum sulfonates in this embodiIIent , of the invention since they are more economical than the ,;, 15 synthetic sulfonates and since they usually provide a mixture ', of hydrocarbon sulfonates having a fairly wide molecular weight distribution which is helpful Ln arriving at the . . .
,;' desired low interfacial tension.
t ' ~he relative amounts of the ether-linked methane ~20 sulonate and the hydrocarbon sulfonate employed in this ,,, invention may vary depending upon the '~' reservoir conditions and particularly the salinity and 'i divalent ion concentration of the reservoir water ~nd of ' the water employed for injection purposes. Normally, the weight ratio of the ether-linked methane sulfonate to the hydrocarbon sulfonate will be within the ranOe of 0.1 to 3.
In most instances it will be preferred to provide a weight, , .

.. . . .
: . . .
~' , .

-. : .

9074 ratio of the ether-linked methane sulfonate to the hydrocarbon sulfonate within the range of 0.2 to 1.
The ether-linked methane sulfonates of the presel~t invention may be prepared by a base-cataly~ed condensation 5 reaction between a halogenated methane sulfonate and the :. .
appropriate ethoxylated precursor... The reaction proceeds in the presence of a base to convert the alkanol functional group to the corresponding alkylate. The halomethane sulfonate reacts with the alkylate to produce the ether-linked methane sulfonate with a halide being produced as a byprodllct.
The halomethane.sulfonate normally will take the form of the .- bromo or chloro derivatives with chloromethane sulfonate being preferred~ Chloromethane sulfonate may be prepared in a f suitable ~orm as the sodium salt by reaction of sodium sul~ite ;~ 15 and methylene chloride as disclosed., for example, in '! ' Smith et al., "Acid-Base Equilibri.a and Glacial Acetic Acid", I Journal of the American Chemical Society, Vol. 75, page 356 -~ : (1953).
¦~ The following examples i:llustrate the preparation ", ~ .
I : 20 Of the preferred polyethoxy methane sulfonates characterized by formula (1) above.
~! ~
i ~ Example 1 ,~ In the preparation of a C12-Cls alkyl polyethoxy methane s~lfonate, five grams of codium hydride were ,~ ~ 25 dispersed in 500 milliliters of N;N-dimethyl formamide (D~) :.' :. contained in a two-neclc flask. A solution of 34 grams ` (about 0.1 mole) of a polyethoxylated C12-C15 aliphatic ., i ' :~ -13-.:
., -, ,. ~ :
., . , . . , :

1081~4Z
;
:' .
9074 alcohol containing an average of 3 ethylene oxide groups alld available from Shell Chemical Company under the trade mark 1'Neodol 25-3" in 150 milliliters of DMF was then added to the flask. The mixture of these tS~o solutions was attended by the evolution of hydrogen gas. After gas evolution had ceased, a solution of 15.5 grams ~about 0.1 mole) of sodiu~
. chloromethane monosulfonate in 100 milliliters of DMF was added to the flask and the mixture was then heated under reflug conditions until an aliquot, when dissolved in water, gave a neutral reaction on pH paper. The sodium chloride formed as a byproduct ~as filtered from the solution and !,~ dimethvl formamide was then evaporated in vacuo to provide i~
r a yield o~ 41 grams of the sodium C12-Cl5 polyethoxy methal~e sulfonate.
tl 15 Example 2 ~
!'i, Another methane sulfonate surfactant was prepared employing the procedure and amounts of Example 1 except that in this case the starting material employed was an ;~ ethoxylated C12-Cl5 primary alcohol containing an average of 7.2 ethylene oxide units and available from the Shell Chemical ;~ Company under the trade mark "Neo~.ol 25-7'1. The "Neodol 25-7"
was added to the DMF dispersion of soaium hydride as described previously in an amount of 52 grams (0.1 mole) in 150 milliliters of DMF. Sodium chloromethane sul~fonate was then added in accordance with the previous example and the ether-linked methane sulfonate was recovered in an amount o~ 55 ~rams.

: ~ .
~, . .
... .
A

~081442 9074 Example_3 This example illustrates the preparation of alkyl aryl polyethoxy methane sulfonates of the present invention.
In this case the procedure and amounts of Example 1 were employed except that the starting material was a polyethoxylated ; nonyl phenol available from the GhF Corporation under the ~rade mark "Igepal C0-520". "Igepal C0-520" contains an average of about 5.4 ethylene oxide units per molecule. The "Igepal C0-5 0" was ; added in an amount of 46 grams (0.1 mole) in 150 milliliters of D~F to 500 milliliters of DMF containing 5 grams of sodium hydride as described in Example 1. Sodium chloromethane sulfonate was then added in the same amounts as employed in Example 1 to provide a yield of sodium nonyl phenol polyet~oxy ! methane sulfonate in an amount of 52 grams.
The aforementioned examples illustrate the preparation i o~ ether-linked methane monosulfon~tes which are the preferred ~ . .
æurfactants employed in carrying out the present invention.
;J;. However, the present invention also contemplates the use oi ,, .
ether-linked methane disulfonates ~nd it will be recognizec by those skilled in the art that these disulfonates can be prepared by procedures analogous to those set forth in Examples 1-3 above. In this case a halomethane disulfonate , . ~
such as sodium chloromethane disulfonate would be employed as the sulfonating reactant.
; 25 To demonstrate the effect of salinity (total dissolved solids content) and divalent metal ion concentrations on the ether-linked methane sulfonates of . . .
. .
,,, ~
,:,;. .
... .
.. -15-.:~;' ' - ' .
'~` ~' ' , `

,:
9074 the present invention, brine stability experLments were carried out for the ether-linked methane sulfonates alone and in co~bination with a hydrocarbon sulfonate. The ether-linked methane sulfonates employed in these experiments were the linear alkyl polyethoxymethane monosulfonates prepared in accordance with Exampies 1 and 2 above and the alkyl aryl polyethoxy methane monosulfonate of Example 3.
The hydrocarbon sulfonate employed was a petroleum sulfona~e , available from the Witco Chemical Company under the trade mark "TRS 10-f~O". "TRS 10-~0" has an average molecular weight of about 420 and a molecular weight distribution of about ;~ 335 to 460. "TRS 10-fsO" is about P~O percent active a~d the concentrations of this product set forth herein are expresced in a weight percent active basis which excludes the impurities ~;l 15 (o~l, water, and inorganic salts) which are contained in the ~ . .
commercial product. The brine solutions employed in these ;'~ tests and also in the oil displace~ent tests described herei~after were prepared from a stock mixed brine solution containi~g 19.3 weight percent sodium chloride, 7.7 weight percent calcium chloride, and 3.0 ~eight percent magnesium i~ chloride for a total salinity of 30 weight percent. The ;`~ stock solution was mixed with distillèd water to form the brine solutions of the indicated salinities.
In carrying out the salinity tolerance experiments, the surfactant systems tested were dissolved in brine ;
solutions and then aged for periods of several weeks, both ` at room temperature and at an elevated temperature of about ''';
. .
. .

. ; .

. . .
;. ,, ~ , 9074 150 F. Under these experimental conditions, the linear alkyl polyethylene methane monosulfonates prepared in accordance with Examples 1 and 2 above were found to tolerate salin~ties in excess of 15 percent and about S 18,000 parts per million of divalent metal ions without precipitation. The alkyl aryl polyethylene monosulfonate prepared in accordance with Examp]e 3 above was found to tolerate a total salinity of about 10 percent and a divalent metal ion concentration of 12,000 parts per million withou~
precipitation. In each instance, the ether-linked methane sulfonate was added to the brine solution in a concentration of 2.0 weight percent.
Another set of experimerts illustrates the effectiveness of the ether-linked methane sulfonates of the present invention as co-surfa~tants in stabilizing hydrocarbon sulfonates. Aqueous olutions of 1.25 weight percent TRS 10-80 and 1.25 weight percent of the alkyl polyethoxy methane monosulfonate cf Example l in a lO weight percent mixed brine solution (cont;aining about 12,000 parts .
per million c~lcium and magnesium ion) were aged for periods of about 3 weeks, at room temperature and at 150~ F. In both instances, there was no sign of precipitation of either the ether-linked methane sulfonate or the hydrocarbon sulfonate. A similar procedure was carried out employing 1.75 weight percent TRS 10-80 and 0.8 weight percent of the l - alkyl polyethoxy methane monosulfonate prepared in -, accordance with Example 2 in a solution exhibiting a total ' :, , ~ , . .

, ' .

. : - . , , . . . ..
. . . . .. : ... . . .
. .

10814~Z

9074 salinity of about 6 weight percent and a divalent metal ion concentration of about 7000 parts per million. Again, neither the hydrocarbon sulfonate nor the ether-linked methane sulfonate showed signs of precipitation at room ~ 5 temperature or at 150 F.
; Laboratory displacement experiments were carried - out in order to demonstrate the efficacy of the ether-linked methane sulfonates of the present invention when employed - alone and when employed as co-suriactants in combination with 8 hy~rocarbon sulfonate. me laboratory tests involv d linea- displacement tests performed in 3-foot long glass tubes having an inside diameter o` 11/32 inch.
In each tube run, the glass tube was packed with uncon~olidated Berea sand and then saturated with brine of the same salinity as employed for oil displacement. The tube was then flooded with a crude oil having a viscosity at room temperature of about 4 centiyoises until the effluent from the tube contained no water in order to achieve a j state of initial oil saturation. The tube was then subjected `~ 20 to a simulated conventional waterflood by the injection of a brine of the same salinity as employed in formulating the surfactant slug until no further oil was displaced, leaving the t~be with a waterflood residual oil saturation. Thereafter the tube was subjected to a surfaetant flood employing the alkyl polyethoxy methane monosulfonate produced by the , . . .
procedure of Example 1 above either alone or in combination h with the petroleum sulfonate TRS 10-80, described previously The surfactant slug was then followed by the injection of ,; .
. .

.
.

, '' .

9074 brine as a driving fluid until no further oil was recovered.
Each of the displacement tests described herein was carried ` out using brines of a salinity of 3 weight percent or 6 weight percent for ini.tial water saturation and for oil displacement.
The brines were formulated from the stock mixed brine solution described above. The 3 percent brine contained about 3500 parts per million divalent metal ions and the 6 percent brine about 7000 parts per million divalent metal ions.
The results of these displacement tests are summarize~l in Table I. In Table I the second column indic;ltes ' r the surfactant ormulation and concentration in weight per~ent in the surfactant slug with the petroleum sulfonate TRS 10-80 designated by the code letters PS and the alkyl polyethoxy . methane s~lfonate designated by the code letters M~. The third column indicates the salinity of the brine employed for initial water saturation and ~or oil displacement .- including the simulated waterflood, the surfactant slug, !~ and the drive fluid. The ourth column indicates the resi(lual oil in milliliters remaining ater the initial waterfloodir:g procedure and the fifth column indicates the size of the surfac.tant slug in milliliters. In each of Runs 1 through 6, the surfactant slug was injected in an amount of about 0.3 pore volume and in Run 7 the sur~actant slug was injec~ed in an amount of about 0.6 pore volume. The sixth column indicates the tertiary oil in milliliters recovered as a ~ result of the suractant 100d and the seventh column indicates ,~ the tertiary oil recovery as a percent of the water100d : residual oil. The last column in Table I indicates the quantity i~ ~
in milliliiters of brine injected as a driving fluid after the 3~ surfa~tant slug.

. ~

. . . . . . . . . . . . . . ..
. -108144;~

- ,, ~,_ rl ~ O ~ O t~ ~ O ~D
~ ~ 00 ~ tf~

.

~ t~ tr) ; . JJ 0-- ~ ~ O ~D O u~ tr~
~ t~ ~ ~ o oo o ~ oo ,_, , ~
,` 'o ., ~,~ ,_ C`l ~ ~o o ~ o ~ O ~ ~ I~ ~ I~
1~ Po ~, J~
~, W Ei ~, _ o Cd O~
H ~I t~l . . . . .
1. ~ U~ U~

_I_ o ~:
~ . : ~

~1 ~ ~ 3 ~.0 d .~ . ~ .

. "
~ 0 .

:~ -O . . . . . ;
~ c~l _1 0 ~ ~0 ~

. . .

;' :
` ' ' ' '' , .

-2 0-. . .
., .
. ' '' ' .
, ~ .
:,, .: . . ~ .
. . ~ ~

9074 From an examination of the data presented in Table I
it can be seen that the use of the ether-linked methane sulfonate alone resulted in the recovery of additional oil over that recovered by the initial waterflood. Where the ether-linked methane sulfonate was employed as a co-surfactant in combination with the hydrocarbcn sulfonate, even greater oil recoveries were achieved. In two instances (Runs 3 and 5), all o~ the waterflood residual oil was recovered by the - tertiary surfactant flood. The remaining runs employing the - 10 ether-linked methane sulfonate in combination with tne petroleum sulfonate resulted in tertiary oil recoveries ranging from about 85 to 95 percer.t of the waterflood residual oil.
The present invention m.~y be carried out in conjuncti~n with the use of a thi~kening agent added for } mobility control purposes. The tllickening agent may be added to the aqueous surfactant slug containing the ether-linked methane sulfonate or it may be in~ected in a separate ~- mobility control slug. Normally, the thickening agent will be employed in a separate mobility control slug injected immediately after the slug containing the surfactant. The thickening agent may be added in concentrations so as to ¦ provide graded viscosity at the trailing edge of the mobility control slug or graded viscosities at both the leading and :j trailing edges of the mobility control slug. Alternatively, the thickening agent concentration may be relatively constant throughou~. Normally, the viscosity of at least a portion of .. .

'` ' , .
., .
''' ' ' .

.. : : ~
.

~08144Z

9074 the mobility con~rol slug should be at least as great as that of the reservoir oil and typically it will be within ~he range of about 1 to 4 times the viscosity of the reservoir : oil. Various thickening agents which may be employed for S mobility control purposes are well known to those skilled in the art and include such polymers as Polysaccharide B-1459 available from the Kelco Ccmpany under the trade mark "Kelzan" and the various partially hydrolyzed polyacrylamides available from the Dow Chemical Company 0 under the trade mark "Pusher Chemicals".
In view of the compatibility of the ether-linked methane sulfonates of the present invention with divalent metal ions, a preferred application of the present invention is in reservoirs in which the connate water contains significant divalent ion concentrctions and in situations where the available flooding medi~.m contains divalent metal ions inconsistent with the convent.ional use of ~ydrocarbon sulfonate surfactants. Thus a preferred application of the present invention is in those situations in which the reservoir waters and/or the waters employed in formulating the flooding medium exhibit a divalent metal ion concentration .: ~ within the range of 500 to 20,000 par.ts per million.
.~ Ether-linked methane sulfonates may be employed in accordance with the present inven~ion in any suitable concentration depending upon t~e characteristics of the particular reservoir involved and such factors as surfactant consumption, e.g. by adsorption, and dispersion of the .~ .

:~08144Z

9074 surfactant into the reservoir wa~ers. In most cases, it will ~e preferred to employ the ether-linked methane sulfonate in a concentration withi..n the range of 0.1 to 2.5 weight percent. I~ere the eth.er-linked methane sulfonate is employed as a co-suractant in combination with a hydrocarbon sulfona~e, the hydrocarbon sulfonate will be employed in a concentration sufficient to provide the desired co-surfactant-surfactant ratio as described previously.
While the aqueous solut:ion of ether-linked methane sulfo~ate, either alone or as a co-surfactant in combinatiDn with a hydrocarbon sulfonate, may be employed as the sole displacing 1uid, it will usually be injected as a discrete slug and then followed by a driving fluid. Preferably, the aqueous surfactant solution is injected in an amount of at 1 least 0.05 pore volume. Typically the size of the surfactant .
! slug will be within the range of 0 05 to 0.6 pore volume.
Where a relatively viscous mobility control fluid is employed, : as described previously, it normally will be injected in a~
amount within a range of 0.05 to 0.2 pore volume. Thereafter a driving fluid is injected in order to displace the . previously injected fluids through the formation. The driving fluid typically may be an~ water which is locally available and is not incompatible with the formation. The driving fluid is injected in such amount as necessary to carry the recovery process to its:conclusion.

.;` , ~

.1 .
,. .

9074 The present invention may be carried ou~ 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 carrying out the present invention is an integrated five-spot pattern , .
of the type illustrated in U.S. Patent No. 3,927,716 to Burdyn et al. Other well arrangements may be used in carrying out the present invention, examples of which are ; set orth in the Burdyn et al. pat:ent. By the term "pore volume" as used herein, it is meant that volume of the .
j portion of the formation underlying the well pattern employed, as described in greater detail in the Burdyn et al. patent.
' .1 . .

: ..

.,, ~- .
. j ., ~ .
., ~ . .
.. . .

., .

.~ , .
.~ , ~ -24-. 1 . . .

.;
. ~, !

.. .
., .

Claims (15)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for the recovery of oil from a subterranean oil reservoir penetrated by spaced injection and production systems in which an aqueous fluid is introduced into said reservoir via said injection system to displace oil to said production system, the improvement comprising employing as at least a portion of the fluid introduced into said injection system an aqueous solution of a hydrocarbon sulfonate surfactant and a water-soluble aliphatic or aliphatic-substituted aryl ether-linked methane sulfonate surfactant wherein the ether linkage is provided by a polyalkylene oxide containing from 2 to 4 carbon atoms in each alkylene oxide unit and the aliphatic or aliphatic-substituted aryl portion of said ether-linked methane sulfonate provides a lipophilic base.

2. The method of claim 1 wherein the weight ratio of said ether-linked methane sulfonate to said hydrocarbon sulfonate surfactant is within the range of 0.1 to 3Ø

3. The method of claim 1 wherein the ether linkage of said ether-linked methane sulfonate is provided by a polyalkylene oxide containing 2 or 3 carbon atoms in each alkylene oxide unit.

4. The method of claim 3 wherein said hydrocarbon sulfonate surfactant comprises a petroleum sulfonate having an average molecular weight within the range of 350 to 500.

5. The method of claim 4 wherein the weight ratio of said ether-linked methane sulfonate to said petroleum sulfonate is within the range of 0.2 to 1Ø

6. The method of claim 1 wherein said subterranean oil reservoir contains water having a divalent metal ion con-centration within the range of 500 to 20,000 parts per million.

7. The method of claim 1 wherein said aqueous liquid has a divalent metal ion concentration within the range of 500 to 20,000 parts per million.

8. In a method for the recovery of oil from a sub-terranean oil reservoir penetrated by spaced injection and production systems in which an aqueous fluid is introduced into said reservoir via said injection system to displace oil to said production system, the improvement comprising employing as at least a portion of the fluid introduced into said injec-tion system an aqueous solution of a hydrocarbon sulfonate surfactant and a water-soluble ether-linked surfactant characterized by the formula R (OCH2CH2)n OCH2SO3-M+
wherein R is an aliphatic hydrocarbyl group or an aliphatic hydrocarbyl-substituted aryl group providing a lipophilic base, n is at least 3, and M is an alkali metal, ammonium, or substituted ammonium ion.

9. The method of claim 8 wherein R is an aliphatic-substituted aryl group having an aliphatic substituent containing from 8 to 25 carbon atoms.

10. The method of claim 9 wherein R is an aliphatic-substituted aryl group having an aliphatic substituent containing from 9 to 12 carbon atoms.

11. The method of claim 8 wherein R is an aliphatic group containing from 10 to 30 carbon atoms.

12. The method of claim 11 wherein R is an aliphatic group containing from 12 to 15 carbon atoms.

13. The method of claim 8 wherein said hydrocarbon sulfonate surfactant comprises a petroleum sulfonate having an average molecular weight within the range of 350 to 500.

14. The method of claim 8 wherein said subterranean oil reservoir contains water having a divalent metal ion concentration within the range of 500 to 20,000 parts per million.

15. The method of claim 8 wherein said aqueous liquid has a divalent metal ion concentration within the range of 500 to 20,000 parts per million.