Recovery of viscous unsaturated crude by intermittent gas injection

Claim 1

THE PROCESS FOR THE RECOVERY OF A VISCOUS UNSATURATED CRUDE FROM SUBTERRANEAN FORMATIONS, HAVING A PLURALITY OF WELLS DRILLED THEREIN, SAID WELLS BEING EQUIPPED FOR INJECTION AND RECOVERY OPERATIONS COMPRISING IN COMBINATION: (A) INJECTION GASEOUS HYDROCARBON SOLVENT, IN A PORTION OF SAID WELLS HAVING 1-4 CARBON ATOMS IN THE AMOUNT OF FROM ABOUT 10% TO ABOUT 25% FORMATION PORE VOLUME, INTO A TREATMENT ZONE IMMEDIATELY ADJACENT THE WELL BORE; (B) ALLOWING THE TREATMENT ZONE TO REMAIN ESSENTIALLY QUIESCENT FOR FROM ABOUT 2 TO ABOUT 4 HOURS WHILE SUBSTANTIALLY MAINTAINING THE PRESSURE WITHIN THE TREATMENT ZONE AND THEREAFTER; (C) WITHDRAWING A MIXTURE OF SOLVENT AND PETROLEUM FROM ANOTHER PORTION OF WELLS AND THEREAFTER; (D) REVERSING THE FLOW BY INJECTION A GASEOUS HYDROCARBON SOLVENT CONTAINING 1 TO 4 CARBON ATOMS INTO THE PORTION OF SAID WELLS THAT WERE PREVIOUSLY PRODUCTION WELLS AND RECOVERING THE MIXTURE OF SOLVENT AND PETROLEUM THROUGH THE PORTION OF SAID WELLS PREVIOUSLY USED AS INJECTION WELLS WITH; (E) REPETITION OF STEPS (A)-(D) ABOVE WITH SUCCESSIVE CYCLES.