Propoxylated ethoxylated surfactants and method of recovering oil therewith

The method of enhanced oil recovery which comprises injecting a microemulsion containing an effective amount of surfactant having the general formula:

• R.sub.1 O(C.sub.3 H.sub.6 O).sub.m (C.sub.2 H.sub.4 O).sub.n YX
• wherein
• R.sub.1 is a C.sub.10-16 branched chain alkyl radical having at least two branching groups;
• m has an average value of between about 2 and about 6;
• n has an average value of between about 2 and about 6;
• Y is the sulfate or sulfonate group;
• and
• X is a cation;
• and
• driving said microemulsion through said formation to displace oil to a producing well.

A formulation suitable for injection into a hydrocarbon-bearing formation for enhanced recovery operations which comprises:

• (a) 0.25-90% by volume of oil;
• (b) 1-95% by volume water;
• (c) 1-20% by volume of a surfactant having the general formula:
• R.sub.1 O(C.sub.3 H.sub.6 O).sub.m (C.sub.2 H.sub.4 O).sub.n YX
• wherein
• R.sub.1 is a linear or branched alkyl radical, an alkenyl radical, or an alkyl or alkenyl substituted benzene radical, the non-aromatic portion of the radical containing from 6 to 24 carbon atoms;
• m has an average value of from about 1 to about 10;
• n has an average value of from about 1 to about 10;
• Y is a sulfate, sulfonate, phosphate or carboxylate group;
• and
• X is a cation;
• (d) 0-250 g/l inorganic salts;
• (e) 0-15% by volume of a co-surfactant;
• and
• (f) 0-2% by volume of a thickener.