Oil recovery by surfactant flooding - using aq. preflush contg. hydrophilic polymer and having controlled salinity and pH

摘要

A surfactant flooding type oil recovery process comprises (a) determining the range of salinity and polyvalent ion concn. at which the surfactant produces the minimum interfacial tension between water and formation oil, (b) injecting into the formation an aq. preflush soln. contg. a hydrophilic polymeric viscosity increasing material (selected from polyacrylamide, polysaccharide, methyl cellulose, CMC, polyvinyl aromatic sulphonate and polyethylene oxide), the preflush having a salinity and a polyvalent ion concn. within the optimum performance range as determined in step (a), and (c) injecting the surfactant soln. into the formation. Improved sweep efficiencies are achieved, and many chemicals (such as detergents, foaming agents, emulsifiers, etc.) which provide optimum performance only in a narrow range of hardness and salinity, may be used in formations contg. water whose salinity and/or hardness is incompatible with an specific surfactant to be used.