Method of polymer flooding

Claim 1

IN A PROCESS FOR RECOVERING CRUDE OIL FROM A SUBTERRANEAN OIL-BEARING RESERVOUR HAVING AT LEAST ONE INJECTION MEANS IN FLUID COMMUNICATION WITH AT LEAST ONE PRODUCTION MEANS AND WHEREIN AN AQUEOUS SOLUTION OF A HIGH MOLECULAR WEIGHT COPOLYMER OF AN ETHYLENICALLY UNSATURATED CARBOXYLIC ACID OR SALT THEREOF AND AN ETHYLENICALLY UNSATURATED NON-CARBOXYLIC COMPOUND IS INJECTED INTO THE FORMATION TO DISPLACE CRUDE OIL TOWARD THE AT LEAST ONE PRODUCTION MEANS AND WHEREIN THE COPOLYMER HAS A PREDETERMINED AVERAGE MOLECULAR WEIGHT WITH AT LEAST 5 PERCENT BY WEIGHT OF THE COPOLYMER HAVING AN AVERAGE MOLECULAR WEIGHT AT LEAST ABOUT 1.2 TIMES GREATER THAN THE AVERAGE MOLECULAR WEIGHT AT LEAST ABOUT 1.2 TIMES GREATER THA THE AQUEOUS SOLUTION AND WHEREIN THE AT LEAST 5 PERCENT PORTION CONRIBUTES SIGNIFICANTLY TO REDUCING THE PERMEABLILITY OF THE SUBTERTANEAN OIL-BEARING FORMATION, THE IMPROVEMENT COMPRISING SUBJECTING THE COPOLYMER SOLUTION TO SUFFICIENT SHEAR FORCE TO SUBSTANTIALLY SHEAR ALL OF THE LEAST 5 PERCENT PORTION OF THE COPOLYMER, THEREBY REDUCING THE AVERAGE MOLECULAR WEIGHT OF THE AT LEAST 5 PERCENT PORTION OF THE COPOLYMER AND THEREAFTER INJECTING THE COPOLYMER, INTO THE RESERVOIR AND DISPLACING IT TOWARD THE PRODUCTION MEANS, THE OVERALL EFFECT BEING TO INHIBIT THE TENDENCY OF THE COPOLYMER TO SUBSTANTIALLY REDUCE THE PERMEABILITY OF THE RESERVOIR.