GB2143563A - Oil recovery process using anionic surfactants - Google Patents

Abstract

A process for enhanced oil recovery using anionic surfactants selected from esters of alpha - sulfocarboxylic acids, more particularly from the mono-and di-esters of the formula: <IMAGE> wherein R is a monovalent hydrocarbon radical R' a monovalent hydrocarbon radical or a (poly-) oxyalkyl radical, R'' a divalent radical or a (poly)oxyalkylene and M<(+)> is an alkali metal cation, an ammonium ion or an alkaline-earth metal half-cation (1 DIVIDED 2 M<2+>). The esters of the alpha -sulfocarboxylic acids may be used as aqueous solutions or microemulsions. They are effective even in the presence of oil field waters having high salinity, particularly a high content of divalent cations (calcium and/or magnesium).

Description

SPECIFICATION Oil recovery process using anionic surfactants This invention relates to a process for recovering oil from subterranean reservoirs and, more particularly, to a process for recovering oil using surfactants. More particularly, this invention concerns a process for recovering oil using one or more anionic surfactants selected from esters of a-sulfocarboxylic acids.

In the recovery of oil from subterranean oil fields, it is usually possible to recover only a small fraction of the oil present by means of the so-called primary recovery methods, which take advantage of the natural forces developed in the field (e.g. fluid pressure release, expansion of dissolved gas, expansion of the gas dome, water drive and the like). The proportion of such recovery is, on average, only 15% of the oil present. Accordingly, a wide variety of additional techniques have been used in order to increase oil recovery. One of the additional recovery methods in general use is flushing with water, requiring water injection into the reservoir.The efficiency of the latter process, particularly the efficiency of the microscopic drive, may be improved by adding a surfactant to the water which will produce a decrease of the water/oil interfacial surface tension and control the capillary force responsible for trapping the oil in the pores of the reservoir rock.

Numerous surfactants have been proposed for enhanced oil recovery, particularly petroleum sulfonates, alkyl-sulfonates, alkylaryl-sulfonates, alkyl-sulfates, alkylaryl-sulfates, polyoxyethyl alkyl- or alkylarylsulfates, alkylpyridinium salts, quaternary ammonium salts, polyoxyethyl alcohols, polyoxyethyl alkylphenols, derivatives being a betaine structure etc.

Many of these surfactants are only satisfactory in a few types of formations, particularly those whose overall salinity and concentration of divalent ions (particularly calcium and magnesium) are relatively low, i.e. generally lower than 5-10 g/i for overall salinity, with a divalent ion concentration lower than 500 ppm.

The major limitation to the use of the most of the hitherto proposed surfactants results from their tendency to precipitate when in the presence of high salt concentrations. Moreover, their performance is adversely affected by the presence of salts, even when the concentration of the latter is substantially lower than that at which precipitation occurs, e.g. between 20 and 30 g/l.

With average or high salinities, it has sometimes been recommended to use certain mixtures of anionic and non-ionic surfactants, but the use of these mixtures gives rise to certain problems. For example, resulting from the selective adsorption of one of the two compounds preferably to the other and from the temperature of the reservoir, the solubility of non-ionic surfactants decreasing with temperature (cloud point).

We have now discovered a process giving enhanced oil recovery usable in formations wherein the salt concentration may vary within wide limits. Thus, the invention provides a process for the recovery of oil from an oil field by injecting therein a liquid containing a surfactant composition, wherein said surfactant composition comprises at least one anionic surfactant selected from esters of a-sulfocarboxylic acids of general formula

or

wherein:: R is am alkyl or arylalkyl radical in which the alkyl chain has from 5 to 25 carbon atoms; R' is an alkyl or arylalkyl radical in which the alkyl chain has from 1 to 25 carbon atoms, or is a radical of the formula 4CH2) Xs e Z (in which x is an integer from 1 to 12, y is an integer from 1 to 56, and Z a hydrogen atom or a methyl or ethyl radical), said radical R' being optionally substituted by at least one monovalent polar organic group, preferably ionisable, such as for example a sulfonic or carboxylic group; R" is an alkylidene or arylalkylidene radical in which the alkylidene chain has from 1 to 25 carbon atoms, or is a radical of the formula 5(CH2)X - 0 hy (CH2ex (in which x is an integer from 1 to 12, and y is an integer from 1 to 50); and Mt is a method cation (an alkali metal or alkaline-earth metal cation, e.g. of lithium, sodium, potassium, magnesium, calcium) or an ammonium ion (e.g. ammonium, triethanolammonium, triethylammonium, pyridinium and the like). In the case of alkaline earth metal salts (i.e. with divalent cations), M is a half-cation i M2+. However, Ml-e is generally a monovalent cation.

The surfactants for use according to the invention offer the advantage of forming a group of products having a high efficiency within a wide range of salt concentrations. It has been found that certain members of the group are stable in formations containing water having a high salts content, particularly with high concentrations of divalent ions, such as calcium or magnesium.

Non-limiting examples of esters which may be used as surfactants for enhanced oil recovery according to the invention include: a-(sodium sulfonate) methyl dodecanoate; a-(potassium sulfonate) ethyl dodecanoate; a-(sodiu m sulfonate) triethyleneglycol mono-dodecanoate; a, a'-(sodium disulfonate) ethyleneglycol didoecanoate; a-(ammonium sulfonate) propyl palmitate; a-(sodiu m su Ifonate) butyl stearate; a-(diethylamine sulfonate) isopropyl myristate; a-(triethanolammonium sulfonate) methyl stearate; a-(sodium sulfonate) methyl palmitate; a-(sodium sulfonate) propyleneglycol monopalmitate; and a-(sodium sulfonate) (sodium sulfonate)-2 ethyl mono-behenate.

The R, R' and R" groups may be selected having regard to the salt concentration of the water of the treated oil field. The a-sulfocarboxylic acid esters for use according to the invention provide a wide choice of products, easily synthesized, whose selection may be "tailored to measure in accordance with the characteristics of the subterranean oil reservoir.

Some of the esters of a-sulfocarboxylic acids for use according to the invention may be prepared from natural raw materials either of animal or vegetable origin, particularly fatty materials, oils and greases, such as tallow, colza, palm, coconut oils and the like. Such esters may thus be prepared from raw materials whose production and price are relatively independent from the fluctuations of the oil market.

The technology for manufacturing the esters of a-sulfonated fatty acids has been the object of numerous published papers (A.J. STIRTON, the Journal of the Amer. Oil Chemists, Vol. 39, Nov. 1962, p. 490-496; W. STEIN and H. BAUMAN, same ref. Vol. 52, Sept. 1975, p 323-329; B.L. KAPUR, J.M. SOLOMON and B.R.BLUESTEIN, same ref., Vol. 55, June 1978, p 549-557) and certain products are already commercially available. US Patents 3 1 28 294 and 3 1 73 940 may also be mentioned.

The esters of a-sulfocarboxylic acids are, unexpectedly, highly resistant to hydrolysis as compared with esters of fatty acids, and this applies over a Ph range from 3.5 to 9.5 and at temperatures up to 80"C or more.

According to the invention the a-sulfocarboxylic esters, either alone or as mixtures, including mixtures with other anionic surfactants (e.g. petroleum sulfonates, olefin sulfonates and the like) or non-ionic surfactants (e.g. polyoxyethyl alkylphenols, polyoxyethyl alcohols and the like) may be used in several techniques.

For example a first technique comprises using an aqueous solution of the surfactant with a concentration of active product preferably of from 0.5 to 10% by weight, the injected volume being preferably from 20 to 30% of the pore volume, the rheological properties of the system being optionally adjusted by adding to the solution a hydrosoluble polymer. A second technique comprises injecting a smaller volume of a solution which may contain, preferably up to 30% by weight of the surfactant (expressed as active material), and variable amounts of water, hydrocarbon, oil and optionally co-surfactant, corresponding to the use of a microemulsion.

When using the surfactants of the invention as micro-emulsions, the co-surfactant may conveniently be selected from those known in the art, particularly from different aliphatic, alicyclic, aromatic-aliphatic mono-alcohols, such as for example isopropyl, butyl, isobutyl, amyl, isoamyl, hexyl, heptyl, octyl alcohols, cyclohexanol and benzyl alcohol or from alkylene-glycol alkyl monoethers, such as for example ethylene-glycol mono-butylether, this list being only illustrative and not limiting. The proportions of co-surfactant are well known in the art, generally 50 or 150 parts by weight of alcohol are advantageously used with 100 parts of surfactant.

The type of hydrocarbon and the optional salinity of the water are generally important in the selection of the surfactant proportions to be used to maintain the microemulsion within the limits of stability. This amount is most frequently, particularly for microemulsions of salt water with paraffinic hydrocarbons, of about 1 to 30 parts by weight per 100 parts of microemulsion mixture. Usually, a proportion of about 1 to 1 5 parts per 100 parts of microemulsion is convenient when hydrocarbon and water are in substantially equal amounts.

The invention is illustrated by the following non-limiting examples. These examples indicate for different a-sulfocarboxylic esters, the optimum salinity and the solubilization parameters.

EXAMPLES 1 TO 8 Polvnhasic mixtures describina transitions

(Winsor notations) are prepared bv increasing the water salinity. Oil and water amounts dissolved in the micellar phase are determined. The salinity for which these amounts are equal is arbitrarily defined as the optimum salinity (O.S.).

The solubilization parameters (S.P.) are calculated as follows: initial water weight - excess water weight S.P. water = initial water weight initial oil weight - excess oil weight S.P. oil = ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ initial oil weight The following composition is prepared: n-dodecane 4.5 g surfactant 0.25 g n-butanol 0.25 g brine 4.5 g The brine consists of water, NaCI and CaC12 in the proportion of 9 parts of NaCI for one part of CaCI2.

In the following table, the type of ester of a-sulfocarboxylic acid used as surfactant and the obtained values of optimum salinity (O.S) and solubilization parameters (S.P.) are indicated for the mentioned temperatures.

EX Ester of &alpha;-sulfo- O.S. (g/l). S.P. carboxylic acid at 250C at 800C at 250C at 800C 1 &alpha;-(sodium sulfonate) - 180 - 0.18 methyl palmitate 2 sodium sulfonate) 135 120 0.16 0.15 ethyl palmitate 3 d-(sodium sulfonate) 75 75 0.17 0.16 isopropyl palmitate 4 (sodium sulfonate) 30 30 0.18 0.18 n-butyl palmitate 5 &alpha; ;/sodium sulfonate) 150 120 0.28 0.27 methyl stearate 6 &alpha;-(sodium sulfonate) 45 30 0.21 0.26 propyl stearate 7 -(sodium sulfonate) 22 18 0.33 0.32 n-butyl stearate 8 sodium sulfonate) 180 - 0.19 methyl tallowate ~

At 80 C, a triphasic system is obtained for salt concentrations from 150 to 200 g/l.

Mixture of fatty acids from tallow.

Claims (14)

1. A process for the recovery of oil from an oil field by injecting therein a liquid containing a surfactant composition, wherein said surfactant composition comprises at least one anionic surfactant selected from esters of a.sulfocarboxylic acids of general formula:

wherein R is an alkyl or arylalkyl radical in which the alkyl chain contains 5 to 25 carbon atoms; R' is an alkyl or arylalkyl radical in which the alkyl chain contains 1 to 25 carbon atoms, or is a radical of the formula t(CH2)x - (in which Z is a hydrogen atom or a methyl or ethyl radical, x is an integer from 1 to 1 2 and y is an integer from 1 to 50), said radical R' being optionally substituted by at least one monovalent polar organic group;R" is an alkylidene or arylalkylidene radical in which the alkylidene chain contains 1 to 25 carbon atoms, or is a radical of the formula 4 (CH2)X - ey ( CH2iX (in which x is an integer from 1 to 12, and y is an integer from 1 to 50); and Mo is an alkali metal cation, an alkaline-earth metal half-cation or an ammonium ion.

2. A process according to claim 1 wherein the ester of the r-sulfocarboxylic acid is selected from: a-(sodium sulfonate) methyl dodecanoate; a-(potassium sulfonate) ethyl dodecanoate; a-(sodium sulfonate) triethyleneglycol mono-dodecanoate; a, a'.(sodium disulfonate) ethyleneglycol didodecanoate; a-(ammonium sulfonate) propyl palmitate; sodium sulfonate) butyl stearate; a-(diethylamine sulfonate) isopropyl myristate; a-(triethanolammonium sulfonate) methyl stearate; a-(sodium sulfonate) methyl palmitate; a-(sodium sulfonate) propyleneglycol monopalmitate; and ee-(sodium sulfonate)(sodium sulfonate)-2 ethyl mono-behenate.

3. A process according to either of claims 1 and 2 wherein the ester of the a-sulfocarboxylic acid is used in an aqueous solution.

4. A process according to claim 3 wherein the concentration of the ester of the asulfocarboxylic acid in said aqueous solution is from 0.5 to 10% by weight.

5. A process according to either of claims 1 and 2 wherein the ester of the a-sulfocarboxylic acid is used in a microemulsion containing, in addition to water, a hydrocarbon oil and optionally a co-surfactant.

6. A process according to claim 5 wherein said co-surfactant is an aliphatic, alicyclic or aromatic-aliphatic mono-alcohol or an alkylene glycol alkyl mono-ether and is used in a proportion of from 50 to 1 50 parts by weight per 100 parts by weight of a-sulfocarboxylic ester.

7. A process according to either of claims 5 and 6 wherein the proportion of surfactant is from 1 to 30 parts by weight per 100 parts by weight of said microemulsion.

8. A process according to any one of claims 5 to 7 wherein the proportions of water and hydrocarbon oil in said microemulsion are substantially equal.

9. A microemulsion for use in oil recovery as defined in any one of claims 5 to 8.

10. A process as defined in claim 1 substantially as herein described,

11. A process for the recovery of oil substantially as herein described with reference to the Examples.

12. A microemulsion as defined in any one of claims 5 to 8 substantially as herein described.

1 3. A microemulsion comprising an ester of an a-sulfocarboxylic acid as defined in claim 1 substantially as herein described in the Examples.

14. Each and every novel process, method, apparatus, product and composition substantially as herein described.