Underground retorting for secondary oil recovery

Claim 1

PROCESS FOR THE RECOVERY OF HYDROCARBONS FROM POROUS FORMATIONS CONTAINING THE SAME AND INTO WHICH HAVE BEEN DRILLED A PRODUCING WELL, A PRIMARY INJECTION WELL, AND A PLURALITY OF SECONDARY INJECTION WELLS ADJACENT SAID PRODUCING AND PRIMARY INJECTION WELLS, COMPRISING THE STEPS OF INJECTING A FUEL GAS INTO SAID FORMATION BY MEANS OF SAID PRIMARY INJECTION WELL TOGETHER WITH A GAS CONTAINING AN AMOUNT OF OXYGEN SUFFICIENT TO MAINTAIN COMBUSTION WITHIN SAID FORMATION, IGNITING THE MIXTURE OF OXYGEN AND FUEL GAS IN SAID FORMATION, IMPOSING A FIRST PRESSURE DIFFERENCE BETWEEN SAID PRIMARY INJECTION WELL AND SAID PRODUCING WELL GREATER THAN THE PRESSURE DROP EXISTING THEREBETWEEN IN A MANNER TO CAUSE THE INJECTED GASES TO FLOW IN THE DIRECTION OF SAID PRODUCING WELL AND TO ADVANCE A ZONE OF COMBUSTION IN A PATH BETWEEN SAID PRIMARY INJECTION WELL AND SAID PRODUCING WELL, INJECTING INERT GASES HAVING AN AMOUNT OF OXYGEN INSUFFICIENT TO MAINTAIN COMBUSTION WITHIN SAID FORMATION INTO SAID FORMATION THROUGH A PLURALITY OF SAID SECONDARY INJECTION WELLS, IMPOSING A SECOND PRESSURE DIFFERECE BETWEEN SAID SECONDARY INJECTION WELLS AND SAID PRODUCING WELL GREATER THAN THE PRESSURE DROP EXISTING BETWEEN SAID SECONDARY INJECTION WELLS AND SAID PRODUCING WELL TO CAUSE SAID LATTER GASES TO FLOW IN THE DIRECTION OF SAID PRODUCING WELL, WHEREBY FLOW OF GASES FROM SAID COMBUSTION ZONE TOWARD SAID SECONDARY INJECTION WELLS IS PREVENTED, THE PRESSURE DIFFERENCES BETWEEN SAID PRIMARY INJECTION WELL AND EACH OF SAID SECONDARY INJECTION WELLS IMPOSED BY VIRTUE OF THE IMPOSITION OF SAID FIRST AND SECOND PRESSURE DIFFERENCES BEING LESS THAN THE PRESSURE DROP BETWEEN SAID PRIMARY INJECTION WELL AND EACH OF SAID SECONDARY INJECTION WELLS, AND RECOVERING HYDROCARBON FROM SAID PRODUCING WELL.