Surfactant waterflooding oil recovery method

A process for recovering petroleum from an underground permeable reservoir wherein the reservoir is penetrated by at least one injection well and at least one spaced-apart production well, said wells being in fluid communication with said reservoir, and wherein the reservoir contains a brine with from 50 to 220 kg/m.sup.3 salinity comprising:

• a. preparing a surfactant solution wherein the surfactant is an alkylarylpolyalkoxy sulfate or alkylpolyalkoxy sulfate of the formula
• RO(R'O).sub.m SO.sub.3 X
• wherein R is a C.sub.8 to C.sub.22 alkyl or an alkylaryl selected from the group consisting of alkylbenzene, dialkylbenzene, trialkylbenzene, alkyl toluene and dialkyl toluene with each alkyl group containing from 6 to 18 carbon atoms;
• R' is ethylene or a mixture of ethylene and propylene with relatively more ethylene than propylene;
• m is a number from 1 to 12 and X is a cation, said surfactant exhibiting phase stability when mixed with small amounts of crude oil or distilled fractions thereof and a brine, said surfactant solution having a salinity less than that of the reservoir brine and comprising from about 0.05 to 10.0 percent by weight surfactant and a brine or diluted brine having a salinity from 5 to 20 percent less than the salinity required to produce partitioning of from forty to sixty percent of the surfactant solution out of the aqueous phase and into the oil and emulsion phases;
• b. injecting the surfactant solution through the injection well into the underground reservoir said surfactant partitioning into the oil phase of the higher salinity reservoir fluid on contact therewith;
• c. injecting a driving agent;
• and
• d. recovering petroleum from the formation via the production well.