Oil recovery method using a surfactant

A method for producing oil from an oil-bearing formation which comprises injecting into the formation a fluid containing a surface-active agent having the formula:

• ##SPC3##
• in which
• R.sub.6 is an alkyl group having from 6 to 24 carbon atoms;
• n has a value of 2 or 3;
• m has an average value of from 2 to 8;
• and
• X is a cation.

A method for producing oil from an oil-bearing formation which comprises injecting into the formation a solution containing a surface-active agent having the formula:

• ##SPC4##
• in which
• R.sub.6 is an alkyl group having 6 to 24 carbon atoms;
• m has an average value of from 2 to 8;
• and
• X is a cation;
• driving said fluid through said formation to displace oil from said formation;
• and recovering the displaced oil.

In a secondary or tertiary method of recovering crude oil from a subterranean formation wherein a microemulsion solution is injected into the formation through at least one injection means to displace crude oil in the formation toward at least one production means, the improvement wherein said microemulsion comprises an oil, an aqueous medium, and in amounts sufficient to produce a single-phase microemulsion a surfactant characterized by the formula:

• ##STR5## wherein R.sub.1 is a benzene, toluene, or xylene radical having a linear or branched alkyl substituent containing from 6 to 24 carbon atoms;
• R.sub.2 is an alkyl, cycloalkyl, alkene or aryl radical containing up to 8 carbon atoms;
• R.sub.3 is a hydrogen atom, a hydroxyl radical, or an aliphatic radical containing from 1 to 8 carbon atoms;
• n has a value of 2 or 3;
• m has an average value of from 1 to 20;
• and
• X is a cation;
• driving said microemulsion solution through said formation to displace oil from said formation and recovering the displaced oil.

A method of recovering residual oil from a subterranean formation which has been subjected to primary depletion and waterflooding which comprises:

• injecting into the flooded out formation through at least one injection means in fluid communication with at least one production means a slug of a single-phase microemulsion comprising an oil and aqueous medium and in an amount sufficient to produce said single-phase microemulsion a surfactant being characterized by the formula:
• ##STR6## wherein R.sub.1 is a benzene, toluene, or xylene radical having a linear or branched alkyl substituent containing from 6 to 24 carbon atoms;
• R.sub.2 is an alkyl, cycloalkyl, alkene or aryl radical containing up to 8 carbon atoms;
• R.sub.3 is a hydrogen atom, a hydroxyl radical, or an aliphatic radical containing from 1 to 8 carbon atoms;
• n has a value of 2 or 3;
• m has an average value of from 1 to 20;
• and
• X is a cation;
• said microemulsion being capable of displacing residual crude oil in said formation toward said production means;
• thereafter injecting thickened water to drive said slug of microemulsion through said formation toward said production means;
• injecting unthickened water subsequent to the injection of said thickened water;
• and recovering residual crude oil through said production means.