CA1248341A

CA1248341A - Oil recovery agent

Info

Publication number: CA1248341A
Application number: CA000469701A
Authority: CA
Inventors: Howard P. Angstadt; Donald F. Rugen; John L. Cayias
Original assignee: Sun Refining and Marketing Co
Current assignee: Sunoco Inc R&M
Priority date: 1983-12-22
Filing date: 1984-12-10
Publication date: 1989-01-10
Also published as: FR2557198A1; FR2557198B1

Abstract

ABSTRACT OF THE DISCLOSURE

There is provided herein a process and composition for the enhanced recovery of oil from subterranean formations comprising injecting in combination with steam a composition comprising (a) an anionic surfactant and (b) a hydrotrope.

Description

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BACKGROUND OF THE lNVEN~ION

FIELD OF THE INVENTION

This invention relates to novel surfactant compositions and methods of using the s2me to enhance the secondary and ~ertiary recovery of oil from subterranean formations. More particularly, this invention comprises injecting novel combinations of anionic ~urfactants and hydrotropes with steam into oil-bearing formations to greatly increase heavy oil recovery as compared with the use of s~eam alone.

DESCRIPTION OF:THE PRIOR ART

The use of 6econdary and tertiary oil recovery techniqués, with or without the addition of various reagents such as surfactants, water thickeners and the like to recover crude oil left behind in fonmations ~fter the "pri~ry~ oil has been withdrawn i~ well e~t~blished in the ~rt. These displacement methods have been improved by the addition of surfactant compo~ition~ ~ln bctb secoDdary nd tertiary proce~ses, for example where a fonmation hss already been waterflooded ~t le~t once.

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Representative of these prior art compositions and methods are those taught in U.S. Patents 3,348,611 to Reifiburg; 3,885,626 to Gale et al;
3,901,317 to Plummer et al; 3,994,342 to Healy et al; and 4,295,980 to ~otz, all of which teach aqueous flooding techniques with st least one surfactant, and in some cases, with viscosity modifiers, co-surfactants or the like. Finally, in an unrelated field, U.S. Patent 3,501,409 teache~ a liquid washing detergent composi~ion comprising said detergent in combination with a hydrotrope.

In addition to the aforedescribed aqueous flooding technigues, the art has also employed ~team for 6econdary and tertiary oil recovery, utilizing the effect of heat to obtain heavy oil from the formations in which it is found. See, for example, ~.S. Patents 3,357,487 and 3,994,345. However, the mechanism and effects of surfactants under these hi8h temperatures 3nd diverse formation eonditions remain unclear, ~nd thus make it impossible to predict from a knowledge of the effects of aqueous surfactant systems which surfactants, if any, can advantageously be employed in these steam recovery conditions. This is even more true in the choice of sny ~odifiers which might enhance the effectiveness of the surfactant.

It i~, therefore, an obJect of this invention to provide a novel ~urfactant composition useful for enhancing ~tesm rec~very processes for secondary or tertiary recovery of heavy oil from subterranean fonmatioDs, ~s compared with t~e use of 6team ~lone.

~S1146 3 It is a further object of this inv~ntion to provide an i~proved steam recovery process for enhanced oil recovery, utilizing the novel compositions pr~vided herein.

Further objects and advantages of the compositions and methods of the present invention will become apparent in ~he course of the following detailed de~cription thereof.

SUMMARY 0~ THE INVENTION

In accordance with the present invention, there is provided herein a novel surfactant composition useful in steam recovery processes for the enhanced recovery of typical heavy crude oil comprising (1) an anionic surfactant and (2) a hydrotrope, wherein the anionic surfactant is preferably selected from the group consisting of long chain alkyl aryl sulfonates~ petroleum sulfonates, and olefin 6ulfonates, including derivatives of ~aid olefin sulfonates ~uch 3S ether sulfonates, ethoxylated sulfonates and propoxylated fiulfonates. The hydrotropes, a~
described in further detail hereinbelow, are also a sulfonated compound, but differing from the surfactants defined above in having considerably lower molecular weight, being extremely water soluble, having very short side chains, And performing poorly as surfactants.

As will be evident from the examples and following description, the novel compo6ltion and proce~e~ of this invention comprising 6aid anionic ~LZ~3'~

surfaotants and a hydrotrope, when employed in a steam recovery process, exhibit unexpected benefits o~er what would be expected from the combined effects of each component, i.e., a synergistic effect as fompared with the results of steam alone. For instance, in Example 9 the percent increased recovery over steam alone was 55%, while the percent increased recovery of the individual components, added together, totals only 26%.
As discussed further below, since a hydrotrope by definition is a compound which increases the solubility of a ~urfactant in water, the enhanced effect disclosed herein is particularly surprising because it would normally be supposed that the hydrotrope would thus increase the solubility of the surfactant in the aqueous portion of the ~team, and decrease its solubility in the oil phase, thus rendering it less effective in oil recovery.

Moreover, apart from the mechanism of the hydrotrope, steam recovery æystems themselves differ from water recovery ~ystems in many ways.
Thus, for example, steam is present in a gas phase, which itself provides different oil recovery mecbanisms than does water. Also, since it is in a ~a~ phase, the steam has considerably faster flow rates, allowing physical effects such as aspiration to occur. Further, condensation of the steam allows for much greater and more efficient heat ~ransfer to the formation and the oil, so that the whole system can be heated hotter and faster than with water. Since the steam is hotter and less viscou~ than water, lt can reach parts of the reservoir which are inacces6ible to water. Also, steam c~n effect distillation of lighter fraction~ of ~2~

crude oil, prod~cing unpredictable effects. Finally, ~team can move heavy oils, which have different compositions from light oils moved by water, also with different effects. Thus, it will be seen that as between steam and water recovery systems, significant differences exist, the results of which are unpredictable from one system to the other.

DESCRIPTION OF THE PRE~ERRED EMBODIMENTS

Amongst the anionic surfactants useful in the composition and methods of this invention one preferred embodiment comprises long chain alkyl aryl sulfonates where the alkyl aryl sulfonate is most preferably either a benzene or toluene sulfonate, bec~use of their high heat stability in the steam environment in which they are to be used.
Conversely, alkyl xylene sulfonates exhibit much less heat stability and are thus not as effective within the scope of this invention.

By the term "long chain alkyl" is meant ~hat the alkyl moiety of the alkyl aromatic sulfonate (which may be branched or straight-chain) should desirably have from 12 to 30 carbon atoms, and most preferably an average of about 16 to 20 carbon atoms. The term "average" is thus meant to signify that the alkyl moiety may be derived from mixtures of hydrocarbons having a weighted average of from about 16 to 20 carbon atoms, even though shorter or longer chain lengths may be present in the mixture. Alternatively, pure olefins used as the source of the alkyl group having exactly tbe desired number of carbon atoms within thi~

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range may also be employed. Thus, in one embodiment of the invention, the alkyl moiety may be derived from a mixed C14_20 OC-olefin source in which the molecular weight distribution is such that the resultant alkylate side chain has an average of 16 carbon atoms, even though lesser amounts of somewhat shorter or longer chain lengths may be present in the alkylated product.

One preferred alkylate, having an average number of carbon atoms of about 16.2 in the side chain, may be derived from a wax-cracked C14 18 CX~ -ole~in, and has the following weight distribution:

Carbon Atoms in Side Chain Weight Distribution (%) -Alternatively, the alkylate may be prepared from a C14 18 mixture derived from the polymerization of ethylene in a known manner, wherein the average alkyl group i8 16.0, and wherein the ~ixture is further characterized by alkyl groups having even-numbered carbon atoms only.

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A typical weight distribution of such a mixture is 8S follow6:

Carbon Atoms in Side Chain Weigbt Distribution (~) Alternatively, the alkylate may have a side chain derived from the oligomerization of propylene by known processes, as for example using phosphoric scid as the catalyst, or the like, wherein the side-chaiD may be either a single carbon number species which is ~ multiple of C3, l.e.
Cl2, Cl5, Cl8, or C2l, or a blend of these branched oligomers, such that the average molecular weight of the ~ide chain is in the C15 18 range.

In place of the alkyl aryl sulfonates there may be employed as ~he anionic surfactant in the compositions of this invention petroleum sulfonates. The petroleum sulfonates encompass a broad range of compounds which are well known in the art, and which are geDerally obtained by the sulfonation of naturally occurring petroleum streams derived from crude oil. Typical of this broad range are those petroleum aulfonates described in U.S. Patents 3,302,713; 3,508,~12; 3,648,772; and 3,901,317 i LS1146 ~z~

Thus, ~he term "natural petroleum sulfonates" is a co~mercial designation of petroleum sulfonates which are obtained by a treatment of petroleum fractions, particularly solvent-treated aromatic fractions, with, for example, sulfuric acid, fuming sulfuric acid, or sulfur trioxide. Upon sulfonation ~wo types of general products are thereby formed which are known in the art as mahogany acid sulfonates and green acid sulfonates, respectively, based on their color and solubility in oil or water.

A third type of anionic surfactant which may be used in the compositions disclosed herein are, as mentioned above, olefin sulfonates which are generally commercially available materials, as for example those obtained from olefins made by the "SHOP" process available from Shell Oil Co. Typically, these olefins ~ay have the followin~
~tructures: R-CH=CH-Rl, R-CH=CH2, or R- C = CH2, Rl wherein R and ~l may be hydrogen, or alkyl groups having from 8-28 carbon atoms, and may be the same or different. Preferred amongst these sre those alkyl ~roups having a total of from 10 to 16 carbon atoms.
While the methods or preparing these olefins are generally well known, the olefin ~ulfonates may best be described as the sulfonation products o~ wax-cracked hydrocarbons having from about 12 to 30 carbon atoms, or alternatively of ethylene oligomers, e.g., those obtained by Ziegler-type polymeri~ationfi and having fro~ about 12 to 30 carbon atoms. Also contemplated within the scope of the invention are known dèrivatives o said olefin sulfonates 6uch as ether ~ulfonates; ethoxylated sulfonates;
or proproxylated æulfonates. In general, these compounds may be prepared by well-kno~n procedures.

The preparation of the anionic surfactants, i.e., the alkylation and sulfonation of the aromatic moiety, or the prepartion of the olefin or petroleum sulfonates, are conventional techniques well known in the art which need not be described further herein. It is preferred, though, not essential, that for purposes of this in~entiGn the sulfonates are in the form of their alkali metal salts.

The second component of the novel composition claimed herein, to be used in combination with the anionic surfact2nts, is a hydrotrope, i.e.
those compounds characterized in the art by their ability to increase the 601ubility of surfactants in a~ueous systems. See, for example, the description in "Synthetic Detergents", Davidsohn et al, 6th Ed., Wiley and Sons, pages 79, 80. Included amongst these compounds are both aryl and non-aryl compounds. The aryl compounds are generally aryl sulfonates or 6hort chain alkyl aryl sulfonates in the form of their alkali ~etal salts, in which there may be present from 1 to 3 al~yl groups containing from 1 to about 3 carbon atoms, and in which the aryl component may be benzene, toluene, xylene, cumene, or naphthalene. Included amongst these aryl hydrotropes are such preferred compounds as sodium xylene sulfonate, 60dium toluene ~ulfonate, sodium benzene ~ulfonate, and the like. The non-aryl hydrotropes which may likewise be satisfactorily .

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employed include such compounds as fiodium isethionate, butQne sulfonate, hexane sulfonate, and the like, i.e. sulfonates whose alkyl ~oiety contains from about 1 to 8 carbon atoms.

The mechanism by which these hydrotropes operate to enhance steam-driven surfactant systems in an essentially non-aqueous liquid oil environment i6 not known. Also, as stated above, since hydrotropes increase the çolubility of sufactants in water, it should render them less effective in oil recovery for the reasons stated. However, as ~ill be shown in the examples below, when a hydrotrope is combined with e.g., a C14 18 alkyl aryl sulfonate, a significant increase in oil recovery results over the added effects of the two components alone.

The ~ole ratio of the anionic surfactant to hydrotrope in the composition of this invention is desirably from about 1:0.1 to Q~:l.0, and prefer~bly about 1:0.5 to 1:1.5, although this a~ount may be varied conæiderably, depending upon the properties of the oil field being treated, as well as the nature of the selected hydrotrope, and the nature of the resulting composition therefrom. To this mixture is then desirably added ~ solvent in order to prepare an easily handled solution to add to the steam to be injected into the underground formation. This ~olvent is desirably water, although li~hter-weight hydrocarbon solvents such as kerosene, toluene, naphtha, petroleum ether, lube oil base stocks, or li~e inert hydrocarbon streams may be used instead. Thus, ~Z~3391~

for example, one preparatiou representing a preferred comp~sition ready ~o be added to steam comprises 35% by weight of hexadecyltoluene sulfonate; 17% sodium xylene sulfonate, snd the balance water.

In addition to the two major components of the composition there may optionally be included minor amounts of materials such as known stabiliz-ers, bacteriostats, anti-oxidants. These materials, alone or in combina-tion, may be added in amounts of up to 10-15% by weight of the total surfactant composition.

As described above~ the surfactant system of this invention is desirably injected into ~he subterranean formations ad~ixed in ~team, wherein the ~team recovery process is carried out either as a cyclic process or a steam drive process, and the heavy crude oil recovered in a generally well-known manner. Thus, in a typical cyclic steam process, oil is produced from the same well from which the steam was previously added, while in a typical steam drive process the oil production well is remo~e ~rom the steam injection well.

The a=ount of the surfactant-hydrotrope composition of this invention admixed with the steam may vary widely according to the characteristics of the formation, but desirably is in the range of from about O.l to l-X~ by weight, based on the 6urfactant, of an aqueous solution of the composition, and preferably about a 0.5-5X concentration. This , '~ ' . .

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concentration, in turn, is achieved by metering it into the steam at those levels fr~m a more concentrated aqueous solution, as described ~bove, which is prepared beforehand.

In practice, the process of this invention may be applied equally to steam drive processes among multiple wells or to a cyclic process involv-ing an individual well.

The composition and method of ~his invention will now be illustrated by reference to the following examples, which are presented by way of illustration only and not by way of limitation on the scope of the invention.

EXAMPIES

In the following examples, some of which are comparative, while others are illustrative of the invention, the same basic method to evaluate the usefulness of the composition was used wherein a tube having a diameter of 2" and a length of 18" was packed with oil-saturated No.
140-mesh Ottowa sand. The water-wet sand was roated with Midway Sunset crude oil to between 60-65% residual oil saturation. The top 15g of the tube was filled with clean sand to ~imulate a zone of high per~eability frequently found in stesm reservoirs. The tube was insulated to reduce heat losses, and then either a 40-50% quality steam alone or a 40-50%
quality 6team i~ combinatio~ with various surfactant systems was passed .' ~' through the sand pack in concentrations of 1 weight percent ~urfactant based on total water equivalent of the steam, and at appropriate rates until no more oil was evident exiting from the apparatus. The amount of 3il recovered was measured in one or both of two ways: (1) total liquid oil obtsined from the pack; or (2) the oil remaining on ~he sand at the end of the experiment was determined, and the amount recovered calculated as the difference from the value determined to be on ~he sand at the start of the experiment. The percent of oil recovered, for each system, based on the amount of oil originally in the pack, is summarized in Table I below.

In the following examples, Examples 1 to 7 are ~omparative, while Exampl~s 8 to 13 illustrate the composition and method of this invention.

It will be seen from the results of these examples that not only is there a very substantial increase of almost 55% in oil recovery utilizing the surfactant system of this invention (Examples 8 to 13) as compared with the use of steam alone (EXAmP1e 1), snd as much as a 46% greater oil recovery than witb various prior art surfactants alone having alkyl chain lengths averaging less than 16 (Examples 2, 3 and 4), but also there is an equally significant improvement shown when the effects of the individ-ual components of the composition (Examples 5, 6 and 7) are compared with the results demonstrated in the aforementioned Examples 8 to 13.

, Employing the general procedures described above, and passing steam alone through the sandpack containing the Midway Sunset oil, in a series of runs an average of 44.5% of this oil was recovered.

Employing the procedures of Example 1~ but adding to the steam 9.24cc. (100% surfactant-ac~ive basis) of an O~-olefin sulfonate diluted such that the final concentration was 1% by weight in the æteam (based on the water equivalent), 48.4% of original oil in place was recovered, i.e., an increase of 9Z based upon the recovery obtained by steam alone.

The cC-olefin sulfonate was a sulfonated C12_1~ OC olefin prepared from a mixture of ~-oleins whose carbon chain length~ are C12, Cl~, and C16, wherein the olefin has an average of 14 carbon atoms.

Employing the procedures of Example 1, but adding to the steam 9 24 cc. (100% surfactant-active basis) of a C12_14 alkyltoluene ~ulfonate diluted such that the final concentration was l~ by weight in the steam (based on the water equivalent), 49.6% of the original oil in place was recovered, i.e., an increase of 12~ based upon the recovery obtained by steam alone.

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The alkylate nsed in the preparation of the surfactant wa~ a wax-12-14 ~-olefin having an average of 12.8 carbon atoms.

EXAMPLE h Employing the procedures of Example 1, but adding to the steam 9.24 cc. (100X surfactant-active basis) of a Cl~ 18 alkyltoluene sulfonate diluted ~uch that the final concentration was 1% by weight in the fiteam (based on the water equivalent), 58.4% of the original oil in place was recovered, i.e., an increase of 31g based upon ~he recovery obtained by steam alone.

The alkylate used in the preparation of the surfactant was derived from a C10-Cl8C~-olefin prepared by the polymerization of ethylene; this mi~ture, consisting of even-numbered carbon chains only, had an average of 14.0 carbon atoms.

~XAMPLE 5 Employing the procedures of Example 1, but sdding to the steam 9.24 cc. (100% surfactant-active basisj of a Cl4 18 alkyltoluene sulfonate diluted such that the final concentration W9S 1% by weight in the steam (based on the water e~uivalent), in two runs an sveraee of 57.4~ of the original oil in place was recovered, i.e., an increase of 29~ based upon the recovery obtained by steam~alone.

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The alkylate used in the preparation of ~he ~urfac~ant WB~ derived m a wax cracked C14_18 ~ -olefin having an average of 16.2 carbon ~toms.

Employing the procedures of Example 1, but &dding to the steam 9.24 cc. (100% surfactant-active basi8) of a C14_18 alkYltlUene sulfonate diluted such ~hat the final concentration was 1% by weight in the steam (based on the water equivalent), 53.5Z of the original oil in place was recovered, i.e., an increase of 20% based upon the recovery obtained by steam alone.

The alkylate used i~ the preparation of the surfactant was derived from a mixture consisting of even-numbered carbon chains only, a C14 18 C-olefin obtained irom the polymeriæation of ethylene and had an average 16.0 earbon atoms.

Employing the procedures of Example 1, but adding to the steam 9.24 cc. (100~ ~urfactant-active basi6) of sodiu~ xylene sulfonate~
diluted such that the i~sl~co~centration was 1% by weight in ~he ~team (based on the water equivale~t), 47.0% of the original oil in place was recovered, i.e., a~ increase of 6~ b~sed upo~ the recovery Dbtai~ed by ~team lone.

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EXAMPL~ 8 The procedures of Example 1 were employed, but the C14 18 alkyl toluene sulfonate of ~xample 5 was used in combination with the sodium xylene sulfonate of Example 7 in a 1:1 molar ratio, i.e., g.24cc of the alkyl toluene sulfonate (100% surfactant-active basis~ was mixed with an equivalent molar amount of the sodium xylene sulfonate hydrotrope. This mixture was diluted to p~ovide a final concentration in the steam (based on the water equivalent) of 1% by weight based on the surfactant. When added to the steam, 67.3~ of the original oil in place was recovered, i.e, an increase of 51% based upon the recovery obtained by steam above.

In accordance with the 6ame procedures used in Example 8, but using instead Cl4 18 slkyl toluene sulfonate of Example 6 in combination with the sodium xylene sulfonate of E~ample 7 in the same 1:1 molar ratio, 69Z
of the original oil in place W8S recovered, i.e., an increase of 55%
based upon the recovery obtained by steam alone.

In accordance with the procedures of Example 8, but substituting sodium toluene sulfonate for sodium xylene sulfonate, 67.5~ of the original oil in place was recovered, i.e., an increase of 52% based upon the recovery obtained by steam alone.

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~AMPL~ 1 1 In accordance with the procedures of Example 8, but ~ubstituting sodium cumene sulfonate for sodium xylene 6ulfonate, 68.4% of the origi-nal oil in place was recovered, i.e., an increase of 54% based upon the recovery obtained by steam alone.

Employing the procedures of Example 8, but sdding 4b of ethylene glycol to the surfactant-hydrotrope system of E~ample 9, and adding this combination to the steam, 68.1% of the original oil in place was recovered, i.e., an increase of 52~ based upon the recovery obtained by s~eam alone.

Employing the Q~-olefin of Example 2 in combination with sodium xylene sulfonate in accordance with the procedures of Example 8, there was recovered 6~.8% of the original oil ia place, i.e., an increase of 50% based upon the recovery obt-ined by the use of steam alone.

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The percentage yields of recovered oil sho~n ln the above examples are sum~arized as follows:

TABLE I
Oil Recovered Example Surfactant Compositlon Oil Recovered (% Improvement)**
(% OOIP)*
1 Steam Alone 44.5

2 C12 1~ O~-olefin 48.4 9

3 C12-14 AlkYltlUene Sulfonate 49.6 12

4 Cl0-l8 Alkyltoluene Sulfonate 58.4 31 C14_1B Alkyltoluene Sulfonate 57.4 29 6 C14_18 Alkyltoluene Sulfonate 53.5 20 7 ~a Xylene Sulfonate 47.0 6 8 Ex. 5 + Ex. 7 Sulfonates 67.3 51 9 Ex. 6 + Ex. 7 Sulfonates 69.0 55 Ex. 6 + Na Toluene Sulfonate 67.5 52 11 Ex. 6 + Ma Cumene Sulfonate 68.4 54 12 Ex. 9 + Ethylene Glycol 67.5 52 13 Ex. 2 ~ Na Xylene Sulfonate 66.8 50 * OOIP ~ original oil in place ** Based Upon Steam Alone LS1146 ~ 20 .: ~ :

Claims

WHAT WE CLAIM IS:

1. An improved method for the enhanced recovery of oil from subterranean formations whereby steam is injected into said formations, the improvement comprising incorporating in the steam an effective amount of a mixture comprising:

a. an anionic surfactant hydrocarbon containing a sulfur moiety, and b. a sulfonated hydrocarbon hydrotrope containing fewer than 10 carbon atoms

2. The process of claim 1 wherein the anionic surfactant is an alkyl aryl sulfonate having 12 to 30 carbon atoms in the alkyl group, a petroleum sulfonate, or a C8-30 .alpha.-olefin sulfonate.

3. The process of claim 2 wherein the alkyl aryl sulfonate is an alkyl benzene sulfonate or alkyl toluene sulfonate, and the alkyl group has from about 16 to 20 carbon atoms.

4. The process of claim 3 wherein the alkyl aryl sulfonate is an alkyl toluene sulfonate, wherein the alkyl group has an average of about 16 carbon atoms.

5. The process of claim 3 wherein the alkyl aryl sulfonate is an alkyl benzene sulfonate, wherein the alkyl group has an average of about 16 carbon atoms.

6. The process according to claim 1 wherein the hydrotrope is an aryl sulfonate.

7. The process according to claim 6 wherein the hydrotrope is an alkali metal xylene sulfonate, an alkali metal toluene sulfonate, or an alkali metal cumene sulfonate.

8. The process according to claim 1 wherein the hydrotrope is an alkali metal isethionate, an alkali metal butane sulfonate or an alkali metal hexane sulfonate.

9. The process according to claim 1 wherein the mole ratio of anionic surfactant to hydrotrope is in the range of from about 1:0.1 to 0.1:1.

10. The process according to claim 1 wherein the concentrstion of the surfactant-hydrotrope mixture in the steam is in the range of from about 0.1 to 10.0% by weight, based on the surfactant.

11. An improved method for the enhanced recovery of oil from subterranean formations whereby steam is injected into said formations, the improvment comprising incorporating in the steam an effective amount of a mixture comprising about a 1:1 mole ratio of a C16-20 alkyl toluene sulfonate or alkyl benzene sulfonate and an alkali metal xylene sulfonate, an alkali metal toluene sulfonate, or an alkali metal cumene sulfonate.

12. The process according to claim 11 wherein the alkyl moiety has an average of about 16 carbon atoms.

13. An improved method for the enhanced recovery of oil from subterranean formations by the injection of steam into said formations, the improvement comprising incorporating in said steam an effective amount of a mixture comprising about a 1:1 mole ratio of a C8-30 .alpha.-olefin sulfonate and an alkali metal xylene sulfonate, an alkal 0 metal toluene sulfonate, or an alkali metal cumene sulfonate.

14. The process according to claim 13 wherein the olefin has an average of about 16 carbon atoms.

15. A surfactant composition useful in the enhanced steam recovery of oil from subterranean formations comprising: ;

a. an anionic surfactant selected from the group consisting of C12-30 alkyl aryl sulfonates, having 12 to 30 carbon atoms in the alkyl group, petroleum sulfonates, and C8-30 .alpha. -olefin sul-fonates; and b. a sulfonated hydrocarbon hydrotrope containing fewer than 10 carbon atoms.

16. The composition of claim 15 wherein the C12-30 alkyl aryl sulfonate is a toluene sulfonate or a benzene sulfonate, and the alkyl group has an average of about 16 carbon atoms.

17. The composition of claim 15 wherein the hydrotrope is an alkali metal salt of a xylene sulfonate, a toluene sulfonate, and a cumene sulfonate.

18. The composition of claim 15 wherein the hydrotrope is an alkaki metal isethionate, an alkali metal butane sulfonate, or an alkali metal hexane sulfonate.

19. The composition of claim 15 wherein the mole ratio of surfac-tant to hydrotrope is in the range of about 1:0.1 to 0.1:1.

20. A surfactant composition useful in the enhanced steam recovery of oil from subterranean formations comprising:

a. an alkyl toluene sulfonate or alkyl benzene sulfonate, wherein the alkyl group has an average of about 16 carbon atoms; and b. an alkali metal xylene sulfonate.

21. The composition of claim 20 wherein the mole ratio of sulfo-nates is about 1:1.

22. A surfactant composition useful in the enhanced steam recovery of oil from subterranean formations comprising:

a. an alkyl toluene sulfonate, or alkyl benzene sulfonate, wherein the alkyl group has an average of about 16 carbon atoms; and b. an alkali metal toluene sulfonate.

23. The composition of claim 22 wherein the mole ratio of sulfo-nates is about 1:1.

24. A surfactant composition useful in the enhanced steam recovery of oil from subterranean formations comprising:

a. an alkyl toluene sulfonate, or alkyl benzene sulfonate, wherein the alkyl group has an average of about 16 carbon atoms; and b. an alkali metal cumene sulfonate.

25. The composition of claim 24 wherein the mole ratio of sulfo-nates is about 1:1.

26. A surfactant composition useful in the enhanced steam recovery of oil from subterranean formations comprising:

a. an .alpha.-olefin sulfonate, wherein the olefin has an average of from about 8 to 30 carbon atoms or petroleum sulfonate; and b. an alkali metal aryl sulfonate containing fewer than 10 carbon atoms.

27. The composition of claim 26 wherein the .alpha.-olefin has an average of from about 14 to 20 carbon atoms, and the alkali metal aryl sulfonate is sodium xylene sulfonate.

28. The composition of claim 26 wherein the mole ratio of sulfo-nates is about 1:1.