Secondary recovery of oil by partially miscible phase displacement

Claim 1

IN A METHOD OF SECONDARY RECOVERY OF OIL FROM A FORMATION HAVING AT LEAST ONE INJECTION WELL AND AT LEAST ONE PRODUCTION WELL WHEREIN THERE IS INJECTED INTO SAID FORMATION THROUGH SAID INJECTION WELL FOR PISTONLIKE DISPLACEMENT OF SAID OIL TO SAID PRODUCTION WELL A DISPLACING FLUID WHICH AT THE CONDITIONS WITHIN SAID FORMATION IS GASEOUS AND IS ONLY PARTIALLY MISCIBLE WITHSAID OIL BUT WHEREIN SAID FORMATION IS IN A STATE OF FREE GAS SATURATION WHEREBY SAID DISPLACING FLUID DOES NOT EFFECT PISTONLIKE DISPLACEMENT OF SAID OIL TO SAID PRODUCTION WELL BUT TENDS RATHER TO FLOW THROUGH THE PASSAGES IN SAID FORMATION OCCUPIED BY FREE GAS AND BYPASS AND MIX WITH RATHER THAN DISPLACE SAID OIL AND ADVERSELY AFFECTS THE TOTAL RECOVERY OF SAID OIL, THE STEOPS WHICH COMPRISE: (A) INTRODUCING INTO SAID FORMATION THROUGH SAID INJECTION WELL A HYDROCARBON MATERAL, SAID HYDROCARBON MATERIAL BEING UNDERSATURATED RELATIVE TO SAID FREE GAS IN SAID FORMATION AND WHICH UNDER THE CONDITIONS PREVAILING WITHIN THE FORMATION IS LIQUID, IN A QUANTITY ONLY TO PREVENT FLOW OF SAID DISPLACING FLUID THROUGH THE PASSAGES IN SAID FORMATION OCCUPIED BY SAID FREE GAS AND THEREBY PREVENT BYPASSING AND MIXING WITH RATHER THAN DISPLACING OF SAID OIL AND LESS THAN THE QUANTITY WHICH WILL PASS ENTIRELY THROUGH SAID FORMATION TO SAID PRODUCTION WELL, (B) THEREAFTER INTRODUCING INTO SAID FORMATION THROUGH SAID INJECTION WELL SAID DISPLACING FLUID WHICH IS GASEOUS AND ONLY PARTIALLY MISCIBLE WITH SAID OIL IN SAID FORMATION AT THE CONDITIONS WITHIN SAID FORMATION IN A QUANTITY TO FORM A SLUG WHICH WILL PASS ENTIRELY THROUGH SAID FORMATION AND EFFECT DISPLACEMENT OF SAID OIL BETWEEN SAID INJECTION WELL AND SAID PRODUCTION WELL, AND (C) DRIVING SAID SLUG OF DISPLACING FLUID THROUGH SAID FORMATION TO SAID PRODUCTION WELL TO DISPLACE SAID OIL FROM SAID FORMATION THROUGH SAID PRODUCTION WELL.