CA1086046A

CA1086046A - Oil recovery by waterflooding employing an anionic- nonionic surfactant system

Info

Publication number: CA1086046A
Application number: CA285,383A
Authority: CA
Inventors: Stamoulis Stournas
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1976-11-26
Filing date: 1977-08-24
Publication date: 1980-09-23
Also published as: US4340492A

Abstract

OIL RECOVERY BY SURFACTANT WATERFLOODING

Abstract of the Disclosure Process for the recovery of oil from a subterranean oil reservoir involving injection into the reservoir of a substantially oil-free aqueous liquid containing a surfactant having a nonionic polyalkylene oxide hydrophilic group and an anionic sulfonate hydrophilic group molecularly linked to a common lipophilic base. The invention is applicable to reservoirs in which the connate waters have relatively high concentrations of divalent ions and in situations in which the water available for injection purposes contains relatively high amounts of divalent ions. Specifically disclosed surfactants include aliphatic aryl polyalkoxyol sulfonates in which the polyalkoxyol group contains at least three alkylene oxide units and is derived from ethylene oxide or propylene oxide or mixtures thereof.
The aliphatic groups may be substituted directly on the aryl nucleus or indirectly as through an intermediate succinimido group.

Description

~ 6~ ~ 6 -:. ~
9192 Background of the Invention This invention relates to the recovery of oil from ,, subterranean oil reservoirs and more particularly to improved : waterflooding operations involving the injection of surfactants containing both anionic and nonionic polar groups moleculaxly linked to a common lipophilic base.
In the recovery of oil from oil-bearing reservoirs, it usually is possible ~o recover only minor portions of the original oil in place by the so-called primary recovery methods which utilize only the natural orces present i~ the reservoir. Thus a variety of supplemental recovery techniques ,~ have been employed in oxder to increase the recovery of oil from subterranean reservoirs. The most widely used .; . . .
,' supplemental recovery technique is waterflooding which -,.~ - 15 involves the introduction of water into the reservoir through - an injection system comprised of one or more wells.- As the water moves through the reservoir, it acts to displace ~
therein to a productio~ system composed o one or more wells through which the oil is recovered.
It has long been recognized that factors such as the interacial tension between the injected water and the - reservoir oil, the relatlve mobilities of the reservoir ,, oil and injected water, and the wettability characteristics o~ the rock surfaces within the rese,rvoir are actors which ~S in1uence the amount o~ oil recovered by waterflooding.
Thus it has been proposed to add sur~actants to the fl~od water in order to lower the oil~water interfacial tension ~ -2- ~
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9192 and/or ~o alter the wettability characteriskics of the reservoir rock. Also, it has been proposed to add 1.
viscosifiers such as polymeric thickening agents to all or part of the injected wa~er in order to increase the viscosity ~, - 5 thereo~, thus decreasing the mobility ratio between the injected water and oil and improving the sweep e~ficiency of the waterflood. ;
Processes which involve the injection of aqueous surfactan~ solutions in order to reduce the oil-water interacial tension are commonly re~erred to as low tensio~
waterflood;ng techniques. Thus far, most low tension waterflooding applications have employed anionic` surfacta~ts.
For example, a p~per by W. R. Foster entitled "A Low-Tension Waterflooding Process", Journal of Petroleum Technology~
Vol. 25, Feb. 1973~ pp. 205-21, describes a promising technique involving the injectlon o an aqueous solution ,, . . :
o~ petroleum sulfonates within designated equivalent -; . weight ranges and under con~rolled conditions o salinity.
., ~ . , , . , . .- ; The petroleum sulfonate slug is follow~d by a thickened wa~er slug which contains a viscosifier such as a water-solu~le biopolymer ln a graded concentration in order to provide a , maximum viscosity g~eater than the viscosity o the reservoir ; o~l and a terminal ~iscosity near that of water. This th~ckened ~a~er slug is then followed by a driving fluid such as a ield brine which is injected as necessary to '~" carry the process to conclusion.
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~ ' One limitation encountered in waterfloodinz with ',' certain anionic surfactanLs such as the petroleum sulfonates is the tendency of the surfactants to pre~ipitate from solution in the presence of even moderate concentrations of '; divalent metal ions such as calcium and m~gnesium ions. , '-Another limitation imposed upon the us~ of such 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 '~0 in excess of 2 or 3 weight percent~
In view of these limitations, it has ~een proposed to carry out waterflooding empioying mixtures of anionic -surPactants which will tolerate relatively high salinities and concentrations of divalent metal ions. U.S. Patent No. 3,50~,612 to Reisberg et al. is directed to a low tension waterf,l~oding process employing a mixture ~f anio~ic surfactants which can be employed in saline solutions ' containing from 0.01 to 5 molar ~aCl and from about 0 to 0.1 molar CaCl2. One of the anionic surfactants employed 0 in the Reisberg et al. process is an organic sulfonate such `' as a petroleum sulfonate having an average molecular weight wi~h~n the range o 430-470 and the other surfactan~ is a sulated ethoxylated alcohol. A preferred sulfated alcohol ' is one containing a C12- C15 alkyl group and three ethylene ,j!S oxide groups.
Another technique involving the use of a calcium-compatible mixture of anionic surfactants in low tension ` ~ ', ' ,, -: i 136~46 -. i 9192 waterflooding is disclosed in U.S. Patent No. 3,827,497 to Dycus et al. In this process, a three-component or two-component surfactant system may be employed. The three-component system cornprises an organic sulfonate surfactant S such as a petroleum sulfonate, a polyalkylene glycol alkyl ether, and a salt o~ a sulfonated or sulfated oxyalkylated alcohol. The two-component system comprises an organic sulfonate surfactant and a salt of a sulfonated oxyalkylated alcohol. These sur~actant sys~ems may be employed in a brine solution which, as noted in column 3, will usually contain about 0.5~8 percen~ sodium chloride and will often contain 50-5,000 ppm polyvalent metal ions such as calcium and/or magnesium ions. The sulfated or sulfonated oxyalkylated alcohols may be derived from aliphatic alcohols - 15 of ~-20 carbon atoms or from alkyl phenols containing 5-~0 ; carbon atoms pe-; alkyl group. The oxyalk~l moiety in this surfactant will usually be derived ~rom ethylene oxide - ¦
. -although other lower alk~lene oxides containing 2-6 carbon - - atoms or mixtures thereo may be employed~
A number of recent patents are directed to the use o~ mixtures of anionic and nonionic s-lrfactants in low tension water~loods carried out in the presence of high divalent me~al ;~ ~on concentrations. For example, U.S. Patent No. 3,811~SOS to Flournoy et al. discloses a mixture o~ anionic and nonionic surfactants for use in formations containing water having concentrations of divalent ions such as calcium and inagnesium within a range o~ about 500 to about 9,000 parts pe~ million.
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9~92 - The nonionic surfactants employed in the Flournoy et al, process include polyethoxylated alkyl phenols in which the alkyl grou~
has from S-20 carbon atoms and polyethoxylated alipha~ic alcohols having from 5-20 carbon atoms. These surfactants are said to contain from 6-20 ethylene oxide groups. The anionic surfactants employed include alkyl sul~onates and phosphates having fxom 5-25 caxbon atoms and alkylaryl sulfonates and phosphates having from 5-25 carbon atoms in - - the alkyl groups. Both the anionic and nonionic surfactants may be employed in concentrations within the range of 0.05 to S.0 percent with the ratio of anionic surfactant to nonionic surfactant being about 0.1 to about 10.
U.S. Patent No. 3,811,504, also to Flournoy et al., is directed to a low tension waterflood process for . ., ~.
use in en~ironments exhibiting a polyvalent ion concentration of about 1,500 to about 12,000 parts per million and which . ~ - . .
employs a three-component surfactant system con~aining ~wo an~onic sur~actan~s and one nonionic surfactant. One o~
the anionic sùr~actants is an alkyl or al~ylaryl sulfonate and the other anionic surfactant is an alkyl polyethoxy , sula~e. The nonionic surfactant may be a polyethoxylated alkyl phenol or a polyethoxylated ali.phatic alcohol as disclosed in the previously men~ioned Flournoy et al. p~tent or i~ may take the ~orm of a fatty acid dialkanolamid~ or a ~atty acid monoalkanolamide in which the fa~ty acid contains ~rom S 20 carbon atoms. In this process as in the previously described Flournoy et al. patent, a .

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thickening agent such as a polyacrylamide or polysaccharide may be added to the surfactant slug or to a subsequently injected slug. In addition the surfactant slug may be preceded by a sacrificial agent such as sodium polyphosphate or sodium carbonate.
Summary of the Invention In accordance with the present invention, there is provided a new and improved waterflooding process ` employing a water-soluble anionic-nonionic surfactant and which is particularly suitable in reservoirs in which the connate waters exhibit a relatively high salt content, including divalent metal salts, or which may be employed in waterfloods in which the available injection waters exhibit a relatively high salt content. In carrying out the invention, at least a portion of the fluid injected `~ into the reservoir comprises a substantially oil-free aqueous liquid containing a surfactant which has a terminal nonionic polyalkylene oxide hydrophilic group and a terminal anionic sulfonate hydrophilic grou~p both of which are separately molecularly linked to a common lipophilic base.
In a more specific aspect of the invention, the anionic-, nonionic surfactant comprises an aliphatic aryl polyalkoxyol sulfonate wherein the polyalkoxyol chain contains at least 3 alkylene oxide units having 2 or 3 carbon atoms therein.
preferred aliphatic aryl polyalkoxyol sulfonate for use in the present invention is characterised by the formula:

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, (Ao )n -- Ar (1) (S03~1)n 1 wherein R is an aliphatic group, an aliphatic-substituted succinimido group, or the corresponding succinamic acid derivative of said aliphatic-substituted succinimido group, Ar is a mononuclear or condensed ring dinuclear aryl group, Ao is a polyalkylene oxide having a terminal hydroxyl group and containing at least 3 alkylene oxide units having 2 or 3.carbon .
atoms ~herein, n is 1 or 2, M is an alkali metal, ammonium, or substituted a~monium ion, and nl is 1 or 2. .

Brief Description of the Drawin~
FIGS. 1, 2, and 3 are graphs illustrating sur~ace tensions measured for various mixed brine -solutions o~ anionic-nonionic sur~actants o the present invention.
~ IG. 4 is a graph illustrating inter~acial tensions observed against an oil for mix~d brine solutions containing an anionic-nonionic surfactant of the present invention.

~ 6 ~ ~ 6 9192 Description o Speci~ic Embodlmen~s As recognized b~ those skilled in the art, many of the chemical additives employed in water~looding procedures are subject to adsorption onto the reservoir rock surfaces.
Such additives thus move through the reservoir by a chromatographic adsorption-desorption process in which the adsorbing solute moves at a rate lower than the aqueous liquid in ~hich it is dissolved. The rate at which a given solute is chromatographically transported through the reser~voir depends upon the adsorption characteristics of the solute in the liquid-solid systemr Thus a strongly adsorbing solute is chromatographically transported through the reservoir at a rate lower than that of a solute which is less adsorbing. ~ -In view of the foregoing consi.deratio~s, it can be seen that the several surfactant co~ponents of a surfactant mlxture are subject to chromatographic separation as the surfactant slug is moved through the reservoir. A
number of actors can influence the degree of adsorption and thus the chromatographic transport rate of such surac~an~
components. For example, species of dif~erent molecular weights or water solubilities will eæhibit dif~erent adsorp~ion characteristics in a given liquid-solute system.
Thus ~or a mixture o different molecular weight petroleum sulonates, the higher molecular weight petroleum sul*onates can be expected to adsorb at a greater rate than the lower moleculaF weight petroleum sulronates and thus move ~hrough _ g _ 9192 the reservoir at a lower transpor~ rate. The surface characteristics of the adsorbing substrate can also be expected to in~luence ~he surfactant adsorpkion. Most petroleum reservoirs contain clay surfaces having negatively and positively charged sites with the negatively charged sites usually predominating. In a mixture'of anionic and nonionic surfactants such as disclosed in the aforementioned patents to Flournoy et al., the negativeLy charged sites tend to retard adsorption of the anionic surfactant while presenting adsorption sites to the nonionic sur~actant.
The nonionic surfactant thus adsor~s preferentially with respect to the anionic surfactant resulting ultimately in chromatographic separation of the surfactant components.
The present invention offers a means o~ achieving tolerance to monovaLent and'divalent salt-~ exhibited ~
mixtures of a~ionic and nonionic sur~actants while ~t the .
same time of avoiding the limitations im~osed by chromatographic separation o~ the components of such ''' surfactan~ mixtures. This is accomplished by employing '~
a sur~actant having a nonionic polyalkylene oxide hydrophilic group linked to a lipophilic base and also an anionic ' sul~onate' hydrophilic group also linked ~o the same ' ' l:lpoph~llc base. By linking the anionic and nonionic `-groups to the same structure, ~he chromatographic separation ~5 attendant to the use of surfactant mixtures is a~oided.
~t the same time as indicated by the laboratory data presented hereinafter, the polyfunctional surfacta~ts of -,1,0 ~
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' 36~6 9192 this invention exhibit surace-active characteristics in the presence of high salt concentra~ions and are not subiect to salting out in these environments.
The anionic-nonionic surfacta~ts are employed in S accordance with the present in~ention in a "substantially oil-free aqueous liquid". The quoted expression is used herein to distinguish the present invention which involves an application of low tension waterflooding from those procedures which involve the injection of oil-water-surfactant - co-surfactant systems characterized i.n the prior art as '~microemulsions", "transpaxent emulsions", or ''micellar solutions". r~hus U.S. Patent No. 3,885,628 to Reed et al. is directed to oil recovery by the injection of microemulsions and discloses the use of sulfonated lS ethoxylated phenols as co-surfactants. The microemulsions .
o Reed et al. :nclude substantial quantities o oi'. Ln contras~ the aqueous surfactant solutions of the present invention are free of oil or contain only minor amounts o~ ¦
oil, i.e. less than one percent, such as may be present as an impurity. .
A suitable class of anionic-noni~nic sur~actan~s use~ul in the practice of the invention may be characterized as aliphatic aryl polyalkoxyol sulfonates. The term "polyalkoxyol" is employed herein to designate the nonionic ~S ~llkylene oxide chain as a terminal functional group as distin~uished from polyalkoxylated sulfonates of the type disclosed, for example, in the aforementioned patent to ~11- ' :

a6 9192 Dycus. As will be recognized by those skilled in the art, sur~actants of this type are anionic only, with the polyalkylene oxide chain providing an ether linkage between the sulfonate group and the lipophilic base. The polyalkoxyol group in the anionic-nonionic surfactants o the present invention contains at least 3 alkylene oxide units and is derived from ethylene oxide or propylene oxide or mixtures of ethylene and propylene oxide. Stated otherwise, each alkylene o~ide unit in the polyalkoxyol chain has 2 or 3 carbon atoms therein.
The lipophilic base of the anionic-nonionic `
suractants is provided by an aliphatic substituted aryl group in which the aryl component is mononuclear or polynuclear and contains l or more aliphatic substituents.
The aliphatic substituents may be unsaturated and/or contain branched chains but usually will take the form - o normal alkyl groupsO The aliphatic groups may be 8ubstituted directly on the aryl nucleu~ or may contaIn an intermedia~e linkage as in the case of the alkyl succinimido aryl polyalkoxyol sulfonates described hereina~er~
- In a preferred embodimen~ of the invention, the-anLonic-nonionic surfactant employed in the injected aqueous liquid contains a mononuclear or condensed ring dinuclear aryl group, e.g. benzene or naphthalene, which is substitued ~5 with 1 or 2 polyalko~yol grQups and 1 or 2 sulfonate groups.
The lipophilic base is completed with an aliphatic group substituted on the aryl group directly or by means o an , 1.
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B61)46 intermediate linkage provided by a succinimido group or -the corresponding succinamic acid derivative of the succinimido group. These aliphatic aryl polyalkoxyol sulfonates may be characterized by the formula:
(Ao)n R - Ar (1) (SO M)nl wherein R is an aliphatic group, an aliphatic-substituted succinimido group, or the corresponding succinamic acid derivative of said aliphatic-substituted succinimido group, Ar is a mononuclear or condensed ring dinuclear aryl group, Ao is a polyalkylene oxide having a terminal hydroxyl group and containing at least 3 alkylene oxide units having 2 or 3 carbon atoms therein, n is 1 or 2, M is an alkali metal, ammonium, or substituted ammonium ion, and nl is 1 or 2. ;~
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-, or tri-substituted alkyl ammonium or alkanol ammonium ions. Examples oE alkyl ammonium ions include methyl ammonium, ethyl ; ammonium, and normal- or iso-propyl ammonium ions. Examples o alkanol ammonium ions include monoethanol ammonium and triethanol ammonium ions.

, ,, , ' ` ~1(~1511~04~6 In the case where R is an aliphatic group directly substituted on the aryl nucleus, the aliphatic substituent normally will contain from 8-30 carbon atoms. Where an intermediate linkage between the aliphatic group and the aryl nucleus is provided by a succlnimido group, or its corresponding succinamic acid derivative, the aliphatic group normally will contain from 8-25 carbon atoms.
The aliphatic aryl polyalkoxyol sulfonates with an intermediate succinimido linkage in accordance with the present invention may be characterized by the formula:

O
~ (Ao)n Rl ~ N Ar (2) ~ ~03M)nl wherein Rl is an aliphatic group and Ar, Ao, n, M, and nl are as defined previously.
The succinimido group is subject to hydrolysis at a pH within the alkaline range and/or at elevated temperatures to form the corresponding succinamic acid derivative which may be characterized by the formula:

~ H (Ao)n Rl ~ Ar ~ (S3M)nl - 10'8G046 9192 wherein Rl, Ar, ~o, n, M, and nl are as described previously and M' is the same as M or is hydrogen. At room temperature and at a pH on the order of 9, about one-half of the succinimido linked surfactant characterized by ormu1a (2) will be converted to its corresponding succinamic acid derivative charac ~rized by formula (33 in a matter of several days. At elevated temperatures on the order of 200 F., the rate of hydrolysis is accelerated so that most of the succin~mido aryl surfactant is con~erted to its corresponding succinamic acid derivative in a matter of several hours. Even at the neutral or near neutral pH `
conditions encoun~ered in most subterranean oil reservoirs, the h~drolysis ~eaction can be expected to take place - although a~ a significantly lower ra~e ~ccordingly, injection of the succinimido surfactant characterized .
by formula (2) will result, because o~ hydrolysis in the reservoir, in a mixture of the surfactants characterized by ~ormulas ~2) and (3). It may be noted here, however, that the polyalkoxyol and sulfonate groups will still be linked to a common molecular structure so that chromato~aph~c separation~of the anionic and nonionic groups will not occur.
In a preferred embodiment o~ the invention, the an~onic-nonionic surfactant injected into the subterranean oil reservoir is a sulfonated ethoxylated aliphatic phenol characterized by the ormula:

R2~_o(C2~f) ~15-108G~46 9192 wherein R2 is an aliphatic group containing rom 8-30 carbon atoms, n2 is a number within the range of 3-20, and M is an alkali metal, ammonium, or substituted ammonium ionO As indicated by formula (43, the polyethylene oxlde group is in the para position with respect to the aliphatic group.
The sulfonate group may be either or~ho or meta with respec~
. to the aliphatic group.
- The aliphatic aryl polyalkoxyol sulfonates emplo-yed.
in the present invention may be prepared by sul~onating ~he corresponding alkoxylated compound after first esteriying the end of the polyalkylene oxide group to remove the terminal hydroxy as a sulfation site. Esterification may - be accomplished by any suitable technique such as by reaction .
o~ the alkoxylated precursor with acetic anhydride. Thereafter, a suitable sulfonating agent such as sulfuric acid may be .
used to sulfonate the a~yl nucleus. The resulting product may then be neutralized with a suitable base such as sodium hydroxide -ln orde~ to neutralize the sul~onic acid group to ~he correspond~ng salt and ~o hydrolyze the acetic anhydride es~er to provide a terminal hydroxyl group on tha polyalkylene oxide chain. .
.
- The ~ollowing examples illustrate the preparation oE khe pre~erred aliphatic aryl polyalko~yol sulfonates charac~erized by fonnula ~4) above.

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Example 1 Preparation of sodium nonyl benzene polyethoxyol sulfonate containing 5.4 ethylene oxide units.
One mole of ethoxylated nonyl phenol containing -~
an average of 5.4 ethylene oxide units per molecule -(available from GAF Corp. as "Igepal C0-520" ) was mixed with 1.5 moles of acetic anhydride. The mixture was stirred and heated under reflux for 2 hours and the volatile materials (acetic acid and excess acetic anhydride) then -were distilled off under vacuum. The resulting material had no free hydroxyls as indicated by infrared spectroscopy and consisted of the acetylated derivative of the starting ethoxylated nonyl phenol. This material was mixed with two volumes o fuming sulfuric acid (10% S03) with cooling so that the temperature did nbt rise over ~0C. The mixture was stirred at room temperature for about five hours and was then partially neutralized to a pH of about 5 by the cautious addition of sodium hydroxide. The resulting mixture was extracted three times with chloroform, the chloroorm extracts were combined and the chloroform was distilled off. The residue was dissolved in 5 volumes of water containing two equivalents of sodium hydroxide and was re1ux~d for two hours. The water was finally evaporated of to yield the desired product in an overall yield o about 80~.

*Trademark --\ ( Example 2 Pre~aration of sodium nonyl benzene polyethoxyol sulfonate containing 6 ethylene oxide units.
This material was prepared in the same fashion i as described in Exa~ple '1, except that the starting material was an ethoxylated nonyl phenol containing an average of ~.0 ethylene oxide units available from GAF
Corp. as"Igepal c0-530~*.
Exa~ple 3 ) Preparation of sodium dodecyl benzene polyethoxyol sulonate containing 3 ethylene oxide units.
The acetate ester of commercially available

2-~2-(2-chloroethoxy)-ethoxy]-ethanol was prepared by reaction with acetic anhydridP and then purified by j distillation. This material (1 mole) was--added to a solution of 1 mole of the sodium salt of dodecyl phenol (prepared from , , dodecyl phenol and sodium hydride) in tetrahydrofurane. The ~ixture was heated under reflux for five hours, the residue ( odium chloride) was filtered off and the solvent was 0 evaporated to yield the acetate ester of dodecyl phenol ethoxylated ~ th exactly three etnylene oxide units.' ~his estcr was then sul~onated and neutralized similarly a~ d~scribed in Example 1 to yield the desired 'surface active material.
It will be recognized that similar reaction routes can be employed in synthesizing the various other aliphatic aryl polyalko~yol sul'onates which may be employed *Trademark .

~.08G~46 9192 in accordance with the present invention. For example, the succinimi~o linked surfactants characterized by formula (2) above can be prepared by reacting the appropriate aliphatic substituted succinic acid anhydride with an amino phenol to yield a compound of type (B).
This can be ethoxylated by methods well known in the art to yield a compound of type (C) as indicated by the following reaction:

H~N~OH R~ ~ 0}1 e~hy (B) .. . .
O
R ~ 7 ~ OCH2CH2~n OH --The product (C) of this reaction can then be sulfonated ~o the desired surface-active material by the method outlined in Example 1.
To demonstrate the effect of total salinity lS ttotal dissolved solids content) and divalent metal ion concentrations on the anionic-nonionic surfactants employed in the present invention, surface tension and inter~acial ~ension measurements were taken at various surfactant concentrations and in various brine solutions. The brine solutions employed in this experimental work were prepared .. .

-19- ~

6~4~6 9192 from a s~ock mixed brine solution containing 19.3 weight 1l.
percent sodium chloride, 7.7 weight percent calcium chlorideg and 3.0 weight percent magnesium chloride to pro~ide a total salinity of 30 weight percent. The stock solution was mixed S with distilled water to form the brines of the various salinities used in the experimental work. The anionic- I
nonionic surfactants employed in this experimental work I -were the nonyl benzene polyethoxyol sulfonates prepared in accordance with Examples 1 and 2 above and the dodecyl benzene polyethoxyol sulfonate prepared in accordance with Example 3 Surface tension measurements were taken ~or alL
~hree of these surfactants and interfacial tension measurements against normal hexadecane and against a crude oil, respectively, were taken for the surfactants produced in accordance with Examples 2 and 3.
The surface tension measurements taken fo~ aqueous solutions o the surfactants produced in accordance with Examples 1, 2, and 3 are set forth in FIGS. 1, 2, and 3, respecti~ely. In each of FIGS. 1, 2, and 3, th~ surace tension, S, ilt dynes per centimeter is plotted on the ordinate versus the log of the surfactant concen~ration, C~
in weight percent on the abscissa. Also in each of these figures~ a separate ordinate scale is provided for each of the curves shown.
2S In ~IG. l, curve 8 is a plot of surfactant concentration versus surface tension for an aqueous solution oL the surfactant in distilled water. Curves 9, lO, ~l, l ., . . _ , .

~36~L6 9192 and 12 are similar plots for surfactant solutions exhibiting total salinities of 3.6, 8.4, 14.43 and 20.4 weight percent, respectively. The curves are drawn interpolatively to provide two line segments which intersect at the critical micelle concentration. Curves 11 and 12 axe drawn for the data points indicated by the legend ~. The data points indicated by the legend X represent measurements taken after the surfactant solutions were aged for several months, In FIG, 2, curve 14 shows the surace tensions observed for the surfactant dissolved in distilled wa~er and curves 15, 16, 17, and 18 show the surface tensions measured for salinities of 4.8, 8.4, 14.4, and 20.4 weight percent, respectively. With respect to curves 14, 15, 16, and 17, the data points indicated by the legend show the surface I
tensions observed within one or two days~ater solution preparation and the data points indicated b~ the legend X
indicate measurements taken about one month after the sur~actant solutions were prepared. With respect to curve l~, the data points indicated by the legend ~ were taken within one day after ~he solu~ions were prepared and ~ ¦
the da~a points indicated by the legend X were taken about t one week ~ater. As in the case of FIG. 1, the curves 14 through 18 are interpolative curves ~rawn for the data points indicated by 0 with little weight given to those indicated by X.
FIG. 3 presents sur~ace tension measurements obtained or aqueous solutions of the dodecyl benze.le .

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9192 polyethoxyol sulfonate of Example 3. In FIG. 3, curve 22 sho~s the surface tensions measured for the sur~actant in distilled water and curves 23 and 24 show the surace ~ .
tensions measured for the surfactant in 2.4 weight percent and 4.8 ~eight percent brine, respectively. With respect to each of these curves, the data points. indicated by the legend ~ reflect measurements taken within one day after the solutions were prepared and those data points indicated .
by X indicate measurements taken Eive or si~ days ater .10 solution preparation. As in the previous figures, curves 22, ¦.
23, and 24 are drawn through the data points indica~ed by ¦.
the legend ~
As can~be seen by an examination of the data presented in FIGS. 1, 2, and 3, t~e anionic-nonionic surfactant samples o the present ~nvention e~hibit surace activities in br-nes as high as about 20 percent, c~rresponding ~o. a di~7alent metal ion concentration o~ abou~ 24,000 parts per million. In addition, the various.sur~ac~ant so~utions tl . ~ested were aged under room temperature condi~ions for ¦~
.- 20 periods ranging ~rom several days to several months and . ~ j showed no evidence of precipitation. .. . .
FIG. 4 illustrates the results o~ inter~acial tens;on measurements taken or aqueous solutions of the nonyl benzene polyethoxyol sulonate produced in accordance 2S with Example 2 against normal hexadecane. The interfacial ~ensior. measurements ~ere taken by the microsessile drop procedure. In FIG. 4, cu w es 26, 27, and ~8 indicate the "

~6~16 ~192 interfacial tensions observed for the surfactant in brines of 6.6, 9.6, and 20.4 weight percent~ respectively. The interfacial tension~ I, in dynes per centimeter is plotted f on the ordinate versus the log of surfactant concentration, C, ~`
in weight percent on the abscissa. For the data illustrated by curve 26, the surfactant solutions were aged 8 or 9 days.
and the interfacia.l tension measurements were taken immediately after the oil drops were formed (indicated by -data points ~) and b~ measuring the same oil drops after standing for 16 hours (indicated by data points X). The .
data illustrated by curve 27 were obtained in a similar fashion after the surfactant solutions were aged for 10 to . 12 days with the data points ~ indicating measurements ..
taken immediately after drop formation and the data points X
indicating measurements taken with respect to the same oil ~
drops a~er standing for 16 hours. The ~ata points .
associated with curve 28 were-taken after the solutions. -were aged ar a period of three weeks. Curves 26 and 27 .
are interpolative curves drawn through ~he data points l indicated by the legend O. .
Interfacial tensions measurements were also talcen or a series of solutions containing 0.06 weight percent of t~e previously described.dodecyl benzene polyethoxyol sulfona~e in increasin~ brine concen~rations against a 2S crucle oil. Mos~ of the interfacial ~ension values were ~ithin the range oE 0.6 to 0.$ dyne per centimeter and the~e was no apparent effeçt oE brine concentration on .
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0~6 9192 interfacial tension. The oil drops were hard to keep on quartz surfaces indicating that the contact angle through the oil phase was apparently 180, i.e. the quartz was perfectly water-wet. I
The foregoing laboratory data i~dicate that the aliphatic aryl alkoxyol sulfonates of ~he present invention tolerate high brine environments and retain their surface activ;~y in these environments with little or no decrease in surface activity observed for increasing salini~ies and divalent metal ion concentrations. While in theory any - decrease in oil-water interfacial tension will result in better microscopic displacement o the reservoir oil by the injected water, it is desirable that the oil~water -interfacial tension be reduced to a value of 0.1 dyne per lS centimeter or less in order ~o achieve a signiicant increase in microscopic displacement efficiency~ It is preferred tha~ the interfacial tension be reduced to a value of 0.005 dyne per centimeter or less to a~rive at opt~mum conditions for microscopic displacemen~ efficiency.
It will be recalled from the previously presented da~a that the dodecyl substituted surfactant with its relatively shor~ polyalkoxyol chain produced considerably lower in~erfacial tensions than those observed ~or the nonyl substituted suractants having from 5 to 6 monomex UllitS in the polyalkoxyol chains. ~hile the surfactants o~ ~he present invention, lil~e other surfactants employed - in low Lension waterflooding procedures, may be expected .

~ 0 ~ 6 9192 to.be specific ~ith regard to the particular reservoir involved, this data would appear t~ indicaté the desirability ~.
of employing,somewhat longer chain-linked aliphatic groups in order to achieve lower interfacial ~ensions. More S ' speciically, it is preferred in carrying out the present , .
invention to employ aliphatic aryl polyalkoxyol sulfonates having an aliphatic group containing from 14-20 carbon .
atoms. Preferably the polyalkoxyol group, particularly i~ - ",, . the case of ffhe polyethylene o~ide derivative, will contain ' 10 ' from 5-15 monomer units., - , . .
In view of the compatibility of .the aliphatic aryl polyalkoxyol sulfonates of the present invention . ' with di~alent metal ions, a preferred application of the present invention is in reservoirs i~ which the connate' water contains significant divalent ion c~oncentrations and , in situations where the ,available floo~ing medium contains divalent metal ions inconsistent with the use of conventional ' , anionic surfactants such as petroleum sulfonates. Thus a '' preferred applicakion of thè present invention is in those . A
situations in which the reservoir waters and/or the waters ' ' - employed in formulating the ~looding medi.um exhibi~ a divalent metal ion concentration within the range of 500 to 2~,000 parts per million. .
The aliphatic aryl polyalkoxyol sulfonates may be ~i employed .in accordance with the present invention in any suitable concentration dependii~g upon the characteristics oi ~he particulsr reservoir involved snd such f-ctors as ' ~

~ 60~6 9192 surfactant consumption, e.g. by adsorption, and dispersion of the surfactant into the reservoir watersr In most cases, it will be preferred to employ the aliphatic aryl polyalkoxyol ' sulfonate in a concentration within the range of 0.1 to S 2 0 weight percent.
l~hile the aqueous solution o aliphatic aryl polyalkoxyol sulfonate may be employed as the sole displacing fluid, 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 least 0.05 pore volume. Typically the siæe of the surfactant slug will be within the range of 0.05 to 0.6 pore volume.
Where an aqueous mobility control slug having a viscosity equal to or greàter than the viscosity of the reservoir oil is employed, it normally' will be inje'cted after the surfactant slu~ in an 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 1uids through '- the formation The driving fluid typically may be any water which is locally available and is not incompatible with the ~ormation. The driving fluid is injected in such amount as ' necessary to carry ~he recovery process to its conclusion~ ' The surfactant'slug may contain the anionic-nonionic sur~actant as the sole surfactant component or it may conta;n ~S ~ther ~lrfactant additives. However, the use of mixtures of several surfactants is subjectto the problem of chromatographic separa~ion noted earlier. Accordingly, if a mixture o -26~ ' .~ ' ' ~' ~ ` ~LOB6~46 9192 surfactants ;s employed, the alipha~ic aryl polyalkoxyol sulfonate should be present in at least a predominant amount with respect ~o the other surfactant(s) present.
The present invention may be carried out utilizing injection and production systems as de~ined by any suitable arrangement of wells. One well arrangement commonly used in water~looding operations and suitable for use in carrying out the present invention is an integrated five-spot pattern of ~he type illustrated in U.S. Patent No. 3,927g716 ~o Burdyn et al Other well arrangements may be used in carrying out the present invention, e~amples of which are set forth in the Burdyn ~t al. patent. ~By the ~erm l'pore volume" as used herein, it is meant that volume of the portion of the ormation underlying the well pattern employed, as-described in greater detail in the Burdyn et al. patent.
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Claims

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 a substantially oil-free aqueous liquid containing a water-soluble anionic-nonionic surfactant having a terminal nonionic polyalkylene oxide hydrophilic group and a terminal anionic sulfonate hydrophilic group, said nonionic group and said anionic group being separately molecularly linked to a common lipophilic base.

2. The method of Claim 1 wherein said surfactant comprises an aliphatic aryl polyalkoxyol sulfonate in which the polyalkoxyol chain contains at least 3 alkylene oxide units having 2 or 3 carbon atoms therein.

3. The method of Claim 2 wherein said subterranean oil reservoir contains water having from 500 to 24,000 parts per million of divalent metal ions therein.

4. The method of Claim 2 wherein said aqueous liquid contains from 500 to 24,000 parts per million of divalent metal ions.

5. 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 a substantially oil-free aqueous liquid containing a water-soluble anionic-nonionic surfactant characterized by the formula wherein R is an aliphatic group, an aliphatic-substituted succinimido group, or the corresponding succinamic acid derivative of said aliphatic-substituted succinimido group, Ar is a mononuclear or condensed ring dinuclear aryl group, Ao is a polyalkylene oxide having a terminal hydroxyl group and containing at least 3 alkylene oxide units having 2 or 3 carbon atoms therein, n is 1 or 2, M is an alkali metal, ammonium, or substituted ammonium ion, and n1 is 1 or 2.

6. The method of Claim 5 wherein R is an aliphatic group containing from 8 to 30 carbon atoms.

7. The method of Claim 6 wherein Ao is a polyethylene oxide group containing from 3 to 20 ethylene oxide units.

8. The method of Claim 5 wherein R is an aliphatic-substituted succinimido group, or its succinamic acid derivative in which the aliphatic substituent contains from 8 to 25 carbon atoms.

9. The method of Claim 8 wherein Ao is a polyethylene oxide group containing from 3 to 20 ethylene oxide units.

10. 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 a substantially oil-free aqueous liquid containing a water-soluble anionic-nonionic surfactant characterized by the formula wherein R2 is an aliphatic group containing from 8 to 30 carbon atoms, n2 is a number within the range of 3 to 20, and M is an alkali metal, ammonium, or substituted ammonium ion.

11. The method of Claim 10 wherein R2 is an aliphatic group containing from 14 to 20 carbon atoms.

12. The method of Claim 11 wherein n2 is a number within the range of 5 to 15.

13. The method of Claim 12 wherein said subterranean oil reservoir contains water having from 500 to 24,000 parts per million divalent metal ions therein.

14. The method of Claim 12 wherein said aqueous liquid contains from 500 to 24,000 parts per million of divalent metal ions.