Process for acidizing injection wells

Claim 1

IN THE TREATMENT OF GEOLOGICAL FLUID-BEARING FORMATIONS HAVING INTRAZONE PERMEABILITY DIFFERENTIALS RESULTING FROM THE OCCURRENCE WITHIN SAID FORMATION OF ADJACENT STREAKS OF VARYING PERMEABILITY, A METHOD FOR SELECTIVELY ACIDIZING THE LESS PERMEABLE STREAKS OF SAID FORMATION TRAVERSED BY AN INJECTION WELL WHICH COMPRISES INJECTING A LIQUID INTO SAID FORMATION AR A PRESSURE SUBSTANTIALLY IN EXCESS OF NORMAL FORMATION PRESSURE, REDUCING SAID PRESSURE SUBSTANTIALLY BELOW AMBIENT FORMATION PRESSURE WHEREBY A TRANSIENT BACK-PRESSURE IS PRODUCED IN SAID FORMATION BY THE BACKFLOW OF THE INJECTED FLUID INTO SAID INJECTION WELL, INJECTING INTO SAID INJECTION WELL A TEMPORARY SEALING AGENT AFTER THE TRANSIENT BACK-PRESSURE IN THE MORE PERMEABLE STREAKS HAS DISSIPATED TO A PRESSURE SUFFICIENT TO PERMIT THE INTRODUCTION OF SAID SEALING AGENT INTO SAID MORE PERMEABLE STREAKS WHEREBY THE TRANSIENT BACK-PRESSURE REMAINING IN SAID FORMATION IS SUFFICIENT TO PREVENT THE INIMICAL PENETRATION OF SAID SEALING AGENT INTO THE LESS PERMEABLE STREAKS, MAINTAINING THE SEALING AGENT WITHIN THE STREAKS PENETRATED THEREBY FOR A TIME SUFFICIENT TO EFFECT THE SOLIDIFICATION OF THE SEALING AGENT, AND THEREAFTER FORCING INTO THE UNSEALED STREAKS AN ACIDIC FORMATION PENETRATOR CAPABLE OF REACTING WITH THE CONSTITUENTS OF SAID FORMATION IN AN AMOUNT SUFFICIENT TO INCREASE THE PERMEABILITY OF SAID UNSEALED, LESS PERMEABLE STREAKS.