Method for improving areal sweep efficiency in solvent recovery processes

Claim 1

IN A METHOD OF RECOVERING CRUDE OIL FROM A HYDROCARBON-CONTAINING WATER-WET RESERVOIR HAVING A PRODUCING WELL AND AN INJECTION WELL EXTENDING INTO SAID RESERVOIR, THE IMPROVEMENT WHICH COMPRISES FIRST INJECTING WATER INTO SAID RESERVOIR THROUGH SAID INJECTION WELL IN AN AMOUNT SUFFICIENT TO FORM A BANK OR FRONT OF LIQUID WATER OF RELATIVELY LOW MOBILITY IN THE NIEGHBORHOOD OF SAID INJECTION WELL, THE AMOUNT OF INJECTED WATER NOT EXCEEDING 10 PERCENT OF THE HYDROCARBON PORE VOLUME OF SAID RESERVOIR, THEREAFTER INJECTING INTO SAID RESERVOIR VIA SAID INJECTION WELL A NORMALLY GASEOUS HYDROCARBON SOLVENT FOR SAID OIL IN AN AMOUNT SUFFICIENT AND UNDER CONDITIONS ADEQUATE TO FORM A LIQUID SOLVENT BANK CONTIGUOUS TO SAID WATER BANK, NEXT INJECTING INTO SAID RESERVOIR VIA SAID INJECTION WELL A FLUID DRIVE AGENT AT A PRESSURE SUFFICIENT TO CAUSE FINGER-LIKE STREAKS FROM SAID SOLVENT BANK TO EXTEND THROUGHOUT SAID WATER BANK AND TO THERAFTER EMERGE FROM SAID WATER BANK IN THE DIRECTION OF SAID PRODUCING WELL WHEREBY SAID SOLVENT TENDS TO DISTRIBUTE ITSELF IN A MORE UNIFORM BANK AT THE LEADING EDGE OF THE WATER BANK, CONTINUING THE INTRODUCTION OF SAID AGENT VIA SAID INJECTION WELL UNDER THE AFORESAID CONDITIONS TO DRIVE SAID SOLVENT BANK THROUGH SAID RESERVOIR AND TOWARD SAID PRODUCING WELL, AND WITHDRAWING CRUDE OIL FROM SAID PRODUCING WELL.