Well fluids and additive therefor

Claim 1

AN IMPROVED PROCESS FOR DRILLING A WELL THROUGH A HEAVING SHALE FORMATION WHICH COMPRISES THE STEPS OF CIRCULATING A WELL FLUID COMPRISING AN AQUEOUS SUSPENSION OF A HYDRATABLE CLAY MATERIAL THROUGH THE WELL WHILE DRILLING DOWN TO A LEVEL ADJACENT TO THE HEAVING SHALE FORMATION; THEN DILUTING THE WELL FLUID WITH WATER, ADDING TETRAHYDROXYETHYLETHYLENEDIAMINE AND A WATER-SOLUBLE ZINC SALT SEPARATELY TO THE WELL FLUID IN SUBSTANTIALLY STOICHIOMETRIC PROPORTIONS REQUIRED TO FORM A ZINC CHELATE BY REACTION OF THE ZINC SALT AND TETRAHYDROXYETHYLETHYLENEDIAMINE, FORMING SUCH ZINC CHELATE IN SITU; CONTROLLING THE PROPORTIONS OF TETRAHYDROXYETHYLETHYLENEDIAMINE AND WATER-SOLUBLE ZINC SALT ADDED TO PRODUCE SAID ZINC CHELATE IN EXCESS OF THE AMOUNT ABSORBED ON THE CLAY MATERIAL; ADDING ATTAPULGITE TO THE WELL FLUID IN THE QUANTITY TO INCREASE WEIGHT-SUPPORTING POWER; AND ADDING A FLUID-LOSSREDUCING AMOUNT OF CARBOXYMETHYL CELLULOSE.