Treatment of water-sensitive formations

Claim 1

IN A METHOD FOR THE PREVENTION OF CLAY BLOCKING IN A WATER-SENSITIVE UNDERGROUND CLAY FORMATION CONTAINING NATIVE WATER IN WHICH AT LEAST ABOUT 5 PERCENT OF THE SOLIDS DISSOLVED IN SAID NATIVE WATER REPRESENT DIVALENT CATION SALTS, THE IMPROVEMENT WHICH COMPRISES: INJECTING INTO SAID FORMATION A LIQUID HAVING A SALINITY OF NOT MORE THAN ABOUT 15,000 P.P.M. OF WHICH AT LEAST ABOUT 5 PERCENT OF THE DISSOLVED SALTS IN SAID LIQUID ARE DIVALENT CATION SALTS, SAID LIQUID BEING INJECTED INTO SAID FORMATION IN AN AMOUNT CORRESPONDING TO AT LEAST ABOUT 0.5 GALLON PER LINEAR FOOT THICKNESS OF FORMATION BEING TREATED, REPEATING SAID INJECTION STEP A PLURALITY OF TIMES UNDER THE AFORESAID CONDITIONS WHILE REDUCING THE DISSOLVED SOLIDS CONCENTRATION CONTAINED IN THE LIQUID THUS INJECTED AT EACH SUCH STEP, MAINTAINING THE CONCENTRATION OF SAID DIVALENT CATION SALTS AT LEAST ABOUT 5 PERCENT OF THE DISSOLVED SOLIDS CONTAINED IN THE LIQUID FOR ANY GIVEN INJECTION STEP, AND CONTINUING THIS CYCLE UNTIL THE LIQUID BEING INJECTED HAS REACHED THE DESIRED DEGREE OF DILUTION WITH RESPECT TO THE DISSOLVED SOLIDS IN SAID FORMATION.