Waterflooding process employing cationic-nonionic copolymers

Claim 1

In a method of recovering oil from an oil-containing subterranean formation penetrated by an injection well and a production well and wherein an aqueous fluid is injected via said injection well into said formation to displace said oil to said production well, the improvement comprising: employing in at least a portion of said aqueous fluid injected via said injection well into said formation a water soluble copolymer having a molecular weight within the range of 50,000 to 500,000, said copolymer being employed in a sufficient amount to thicken said portion of said aqueous fluid and provide improved efficiency in displacing said oil to said production well, said water soluble copolymer being formed of hydrogenated polybutadiene segments and polystyrene segments chemically modified to strong polyelectrolytes with cationic sites fixed onto the polymer backbone, said polystyrene segments having been first chloromethylated by reacting with chloromethyl ether or formaldehyde and hydrogen chloride and then quaterized by reacting with a tertiary amine to form strong polyelectrolytes with cationic sites fixed onto the polymer backbone, said copolymer having the following structural formula: ##STR6## wherein: R 1 , R 2 , and R 3 are alkyl groups containing 1 to 18 carbon atoms, and x to y is a ratio that is equal to or greater than about 1.