USE OF OLEFIN SULPHONATE COMPOSITIONS IN ENHANCED OIL RECOVERY PROCESSES

Abstract: The invention provides olefin sulphonate compositions comprising an aqueous solution containing 15 to 35%w of a blend of (a) C₁₂₋₂₂ linear alpha-olefin sulphonate and b) alkyl aryl sulphonate of general formula where n is 0, 1 or 2. R is a C₈₋₁₈ alkyl group and M ist an alka­ li metal or ammonium ion, the weight ratio (a):(b) being in the range 90:10 to 60:40; and use of such compositions in foam drive processes of enhanced oil recovery.

Description: OLEFIN SULPHONATE COMPOSITIONS This invention relates to olefin sulphonate compositions and to their use in enhanced oil recovery processes, particularly foam drive processes of enhanced oil recovery. Foam drive processes for enhanced oil recovery are described in US Patents 4,086,964, 4,161,217 and 4,393,937. Such processes typically achieve displacement of oil within an oil-containing subterranean reservoir by flowing a steam-containing fluid containing a surfactant component through a relatively steam-permeable zone within the reservoir. In the process of US Patent 4,393,937, the surfactant component comprises an olefin sulphonate. The olefin sulphonate is conveniently used as a 30 %w solution in water. Alpha-olefin sulphonates, e.g. C10-24, preferably C14¯20, and advantageously C16-18, are disclosed as being particularly suitable. However, although 30 %w aqueous solutions of sodium C16-18 alpha-olefin sulphonates have low viscosities (typically ca 8.5 mm?/s at 200C), they are not stable on storage for 48 hours at 200C. Indeed the minimum storage temperature (MST) is typically 300C, which necessitates transport and storage at elevated temperatures, generally in insulated containers. US Patent 4,161,217 specifically discloses alkyl benzene sulphonates for such processes. However, in addition to having relatively high MST (typically greater than 300C), 30% aqueous solutions of alkyl benzene sulphonates are typically highly viscous (e.g. greater than 6000 mm2/s at 200C). W. German Offenlegungsschrift 2,523,589 discloses a dishwashing composition which comprises (a) Cog,20 alpha-olefin sulphonates and (b) Cog¯24 secondary alkanol sulphonates and/or (Cg-18 alkyl) aryl sulphonates, wherein the weight ratio a:b is in the range 50:50 to 10:90. Canadian Patent 1,031,686 discloses a water-flooding composition for enhanced oil recovery, which comprises an aqueous composition containing a maximum of 5 %w of each of (a) an oilsoluble petroleum sulphonate, (b) a C8-30) preferably Cl2i8, alpha-olefin sulphonate and (c) an oxyalkylated alcohol. It has now surerisinglv been found possible to provide an olefin sulphonate composition having a high concentration of surfactant, which has a minimum storage temperature not greater than 200C while having a viscosity at 200C of less than 1000 mm2/s. Such compositions are of sufficiently low viscosity to be readily transported and handled (e.g. transferred from one container to another), and do not have to be stored at disadvantageous elevated temperatures. According to the present invention therefore there is provided an olefin sulphonate composition comprising an aqueous solution containing 15 to 35 %w of a blend of a) C12-22 linear alpha-olefin sulphonate and b) alkyl aryl sulphonate of general formula EMI2.1 where n is 0, 1 or 2, R is a C8-18 alkyl group and M is an alkali metal or ammonium ion, the weight ratio (a):(b) being in the range 90:10 to 60:40. Linear alpha-olefin sulphonates are known compounds and various examples thereof are described in US Patent 4,393,937, together with outline processes for their preparation. Preferably the olefin sulphonate is a C140 linear alpha-olefin sulphonate, more preferably a Cm6¯18 linear alpha-olefin sulphonate. Suitable olefin sulphonates are conveniently prepared by sulphonation, hydrolysis and neutralisation of C12-22 linear alphaolefins prepared by the "SHELL" Higher Olefins Process ("SHELL" is a registered trade mark). Compounds of formula I are alkyl benzene sulphonates (n is 0), alkyl toluene sulphonates (n is 1) and alkyl xylene sulphonates. Such compounds are also known. Preferably n is 0. It is further preferred for R to be a C1014 alkyl group. Conveniently the compounds of formula I are those prepared by alkylation of benzene, toluene or xylene with linear alpha-olefins prepared by the "SHELL" Higher Olefins Process ("SHELL" is a registered trade mark), followed by sulphonation and neutralisation. The olefin sulphonate (a) and the alkyl aryl sulphonate (b) are alkali metal or ammonium salts. Alkali metal salts may be e.g. potassium or, preferably, sodium salts. Ammonium salts include those derived from ammonia and from primary, secondary or tertiary amines, for example amines bearing one, two or three C1-6 alkyl or hydroxyalkyl moieties, e.g. triethanolamine. Alternative ammonium salts are quaternary salts such as tetramethyl ammonium salts. Sodium salts are very suitable. Preferably the aqueous solution contains at least 20 %w, advantageously at least 25 %w, of the blend of (a) and (b). More preferably the aqueous solution contains substantially 30 %w of -the blend of (a) and (b). The invention further provides the use of an olefin sulphonate composition according to the invention in an enhanced oil recovery process, particularly a foam drive process of enhanced oil recovery, such as the techniques disclosed in US Patents 4,086,964, 4,161,217 and 4,393,937. The invention will be further understood from the following illustrative Examples, in which parts and percentages are by weight (w/w) unless otherwise indicated. EXAMPLES 1 to 4 A C1 6-i 8 linear alpha-olefin sulphonate composition containing 30% active matter and sold by member companies of the Royal Dutch/Shell group of comPanies under the registered trade mark "ENORDET AoS/340", is prepared by sulphonation using vapourised sulphur trioxide, followed by hydrolysis and neutralisation to give the sodium salt, of a mixture of Cl6l8 linear alpha-olefins prepared by the "SHELL" Higher Olefins Process ("SHELL" is a registered trade mark), and characterized by consisting of about 55% C16 about 42% C18 and not greater than 3% of each of C14 and C20 olefins, of which about 94% is linear terminal, about 3% branched terminal and about 2% linear internal. A (C10¯14 linear alkyl) benzene sulphonate solution containing 30g active matter was prepared bv adding 100 g "DOBANIC ACID JNtr (registered trade mark) (containing 97.5% active matter) to 72 g of 16.7% aqueous sodium hydroxide solution and diluting the resulting paste with water to give an aqueous solution of 30% active matter. "DOBANIC ACID JN" is prepared by sulphonation of "DOBANE JN" (registered trade mark) detergent alkylate wherein typically 12% of the alkyl substituents are C10, 28% are C11, 27% are C12, 25% are C13 and 8% are C14. The resulting olefin sulphonate composition and alkyl benzene sulphonate solution were heated at 300C to 600C until homogeneous, and blends were prepared. In each case, of course, the active matter content was 30%. The viscosities of the various compositions were measured using a Ubbelohde viscometer at 200C according to ASTM D445. Minimum storage temperature determination was as follows. The compositions were stored for at least 48 hours in a cooler. The temperature of the cooler was lowered by 1 0C every 48 hours, and the temperature immediately prior to that at which precipitation was observed was noted as the minimum storage temperature (MST). Constitution of the various compositions and results of viscosity and ;i determinations are given in Table I following. TABLE I EMI5.1 <tb> <SEP> Weight <SEP> ratio <SEP> Viscosity <SEP> MST <tb> <SEP> Example <SEP> olefin <SEP> sulphonate: <tb> <SEP> alkyl <SEP> benzene <SEP> sulphonate <SEP> (nan2/s) <SEP> (OC) <SEP> <tb> Comparative <SEP> 100:0 <SEP> 8.5 <SEP> 30 <tb> <SEP> 1 <SEP> 90:10 <SEP> 11.5 <SEP> 20 <tb> <SEP> 2 <SEP> 80:20 <SEP> 28 <SEP> 15 <tb> <SEP> 3 <SEP> 70:30 <SEP> 77 <SEP> 11 <tb> <SEP> 4 <SEP> 60:40 <SEP> 256 <SEP> 8 <tb> Comparative <SEP> 0:100 <SEP> 6840 <SEP> 34 <tb> It can readily be seen that the presence of the alkyl benzene sulphonate confers surprising benefit in terms of reduced MST, whilst viscosity remains conveniently low.

Claims: CLAIMS 1. An olefin sulphonate composition comprising an aqueous solution containing 15 to 35 %w of a blend of (a) C122 linear alpha-olefin sulphonate and (b) alkyl aryl sulphonate of general formula EMI6.1 where n is 0, 1 or 2, R is a C8-18 alkyl grout and M is an alkali metal or ammonium ion, the weight ratio (a):(b) being in the range 90:10 to 60:40. 2. A composition according to claim 1 wherein the olefin sulphonate is a C1420 linear alpha-olefin sulphonate. 3. A composition according to claim 1 or 2 wherein the olefin sulphonate is a Cl6l8 linear alpha-olefin sulphonate. 4. A composition according to claim 1, 2 or 3 wherein in formula I n is 0. 5. A composition according to any of claims 1 to 4 wherein R is a C10-'14 alkyl group. 6. A composition according to any of claims 1 to 5 wherein the olefin sulphonate and the alkyl aryl sulphonate are sodium salts. 7. A composition according to any of claims 1 to 6 wherein the aqueous solution contains at least 25 %w of the blend of (a) and (b). 8. A composition according to any of claims 1 to 7 wherein the aqueous solution contains substantially 30 %w of the blend of (a) and (b). 9. A comnosition according to claim I substantially as hereinbefore described with reference to any of Examples 1 to 4. 10. Use of an olefin sulphonate composition according to any of claims 1 to 9 in an enhanced oil recovery process.

Inventors: CRAVEN, SHEILA MAIRI, FERNLEY, GEORGE WILLIAM
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1984
Main classification: E21B43
IPC codes: C07C309, C09K8, B01F17, C07C67, C07C301