Drilling method

Claim 1

IN THE DRILLING OF A BORE HOLE WHEREIN A DRILLING FLUID IS PASSED THROUGH THE BORE HOLE DURING THE DRILLING OPERATION INTO CONTACT WITH THE WALL OF SAID BORE HOLE, THE IMPROVEMENT WHICH COMPRISES EMPLOYING A FIRST AQUEOUS DRILLING FLUID CONTAINING HYDRATABLE CLAYEY MATERIAL DISPERSED IN A FIRST ALKALINE AQUEOUS PHASE WHICH CONSISTS ESSENTIALLY OF A SATURATED AQUEOUS CALCIUM HYDROXIDE SOLUTION, SAID FIRST AQUEOUS HASE HAVING A PH GREATER THAN 12.6 AND HAVING DISSOLVED THEREIN A CALCIUM ION CONCENTRATION NOT GREATER THAN 200 PARTS PER MILLION BY WEIGHT, SAID FRIST ALKALINE AQUEOUS PHASE BEING PRODUCED BY THE ADDITION TO SAID FIRST AQUEOUS DRILLING FLUID OF AN AMOUNT OF LIME SUFFICIENT TO FORM THEREIN A SATURATED AQUEOUS SOLUTION OF CALCIUM HYDROXIDE AND BY THE ADDITION OF AN AMOUNT OF SODIUM HYDROXIDE SUFFICIENT TO RENDER THE PH OF THE RESULTING FIRST AQUEOUS PHASE GREATER THAN 12.6, SUBSEQUENTLY WHEN THE BORE HOLE BEING DRILLED PENETRATES OR IS ANTICIPATED TO PENETRATED A HEAVING SHALE FORMATION AND DURING THE AFORESAID DRILLING OPERATION CONVERTING SAID FIRST DRILLING FLUID TO A SECOND AQUEOUS DRILLING FLUID CONTAINING HYDRATABLE CLAYEY MATERIAL DISPERSED IN A SECOND ALKALINE AQUEOUS PHASE WHICH CONSISTS ESSENTIALLY OF A SATURATED AQUEOUS CALCIUM HYDROXIDE SOLUTION, SAID SECOND AQUEOUS PHASE HAVING DISSOLVED THEREIN A CALCIUM ION CONCENTRATION GREATER THAN 200 PARTS PER MILLION BY WEIGHT AND HAVING A PH NOT GREATER THAN 12.6, THE AFORESAID CONVERSION HAVING BEEN EFFECTED DURING THE AFORESAID DRILLING OPERATION BY THE ADDITION TO SAID FIRST DRILLING FLUID OF AN AMOUNT OF A WATER SOLUBLE CALCIUM SALT HAVING A SOLUBILITY IN WATER GREATER THAN THAT OF CALCIUM HYDROXIDE SUFFICIENT TO INCREASE THE DISSOLVED CALCIUM ION CONCENTRATION IN THE RESULTING SECOND AQUEOUS PHASE TO A VALUE GREATER THAN 200 PARTS PER MILLION BY WEIGHT.