Surfactant waterflooding enhanced oil recovery process

Claim 1

A method for recovering petroleum from a subterranean, petroleum-containing formation, said formation being penetrated by an injection well and a spaced-apart producing well containing water having salinity greater than 20,000 parts per million total dissolved solids, comprising injecting into the formation via the injection well an aqueous saline surfactant fluid containing from 0.1 to 10.0 percent by weight of an alkoxylated and sulfonated surfactant having the following formula: RO(R'O).sub.n R'SO.sub.3.sup.- X.sup.+ wherein R is an alkylaryl group having from 6 to 20 carbon atoms in the alkyl chain, R' is ethylene or a mixture of ethylene and higher alkylene with relatively more ethylene than higher alkylene, n is an integer closest numerically to the average degree of alkoxylation at which the surfactant is effective for oil recovery at the formation water salinity, R' is ethylene, propylene, hydroxy propylene or butylene, S is sulfur, O is oxygen, and X is a monovalent cation, wherein the alkoxylated and sulfonated surfactant is prepared by blending together at least two reaction products of different average degrees of alkoxylation, said reaction products each being comprised of molecular species of varying degrees of alkoxylation, the reaction products being blended in a predetermined ratio to produce a mixture of molecular species differing in the degree of alkoxylation and containing molecules having degrees of alkoxylation ranging from less than n-2 to n+10, wherein from 14 to 20 weight percent of the molecules have degrees of alkoxylation less than n-1, from 16 to 25 weight percent have degree of alkoxylation equal to n-1; from 16 to 25 weight percent of the molecules have degree of alkoxylation equal to n; from 12 to 17 percent have degree of alkoxylation equal to n+1; and from 15 to 25 percent have degree of alkoxylation greater than n+1, said surfactant fluid displacing petroleum through the formation, and recovering the petroleum displaced by the surfactant solution from the formation via the producing well.

Claim 2

A method for recovering petroleum from a subterranean, petroleum-containing formation, said formation being penetrated by an injection well and a spaced-apart producing well containing water having salinity greater than 20,000 parts per million total dissolved solids, comprising injecting into the formation via the injection well an aqueous saline surfactant fluid containing from 0.1 to 10.0 percent by weight of an alkoxylated and sulfonated surfactant having the following formula: RO(R'O).sub.n R'SO.sub.3.sup.- X.sup.+ wherein R is an alkylaryl group having from 6 to 20 carbon atoms in the alkyl chain, R' is ethylene or a mixture of ethylene and higher alkylene with relatively more ethylene than higher alkylene, n is an integer closest numerically to the average degree of alkoxylation at which the surfactant is effective for oil recovery at the formation water salinity, R' is ethylene, propylene, hydroxy propylene or butylene, S is sulfur, O is oxygen, and X is a monovalent cation, wherein the alkoxylated and sulfonated surfactant is prepared by blending together at least two reaction products of different average degrees of alkoxylation, said reaction products each being comprised of molecular species of varying degrees of alkoxylation, the reaction products being blended in a predetermined ratio to produce a mixture of molecular species differing in the degree of alkoxylation and containing molecules having degrees of alkoxylation ranging from less than n-2 to n+10, wherein from 14 to 20 weight percent of the molecules have degrees of alkoxylation less than n-1, from 16 to 25 weight percent have degree of alkoxylation equal to n-1; from 16 to 25 weight percent of the molecules have degree of alkoxylation equal to n; from 12 to 17 percent have degree of alkoxylation equal to n+1; and from 15 to 25 percent have degree of alkoxylation greater than n+1, said surfactant fluid displacing petroleum through the formation, and recovering the petroleum displaced by the surfactant solution from the formation via the producing well.