Method of drilling a borehole using gelled polymers

Claim 1

IN A METHOD FOR DRILLING A BOREHOLE INTO THE EARTH WHEREIN A DRILL BIT IS ACTUATED IN SAID BOREHOLE AND PENETRATES A SUBTERRANEAN FORMATION IN THE PRESENCE OF A DRILLING FLUID, AND SAID DRILLING FLUID, TOGETHER WITH FORMATION SOLIDS ENTRAINED THEREIN, IS REMOVED FROM SAID BOREHOLE, THE IMPROVEMENT WHEREIN SAID DRILLING FLUID COMPRISES AS AQUEOUS GEL, AND WHEREIN SAID GEL COMPRISES WATER TO WHICH THERE HAS BEEN ADDED: A WATER THICKENING AMOUNT OF A WATER-DISPERSIBLE POLYMER SELECTED FROM THE GROUP CONSISTING OF: POLYACRYLAMIDES AND POLYMETHACRYLAMIDES WHEREIN UP TO ABOUT 75 PERCENT OF THE CARBOXAMIDE GROUPS CAN BE HYDROLYZED TO CARBOXYL GROUPS; CROSSLINKED POLYACRYLAMIDES AND CROSSLINKED POLYMETHACRYLAMIDES WHEREIN UP TO ABOUT 75 PERCENT OF THE CARBOXAMIDE GROUPS CAN BE HYDROLYZED TO CARBOXYL GROUPS; POLYACRYLIC ACID AND POLYMETHACRYLIC ACID; POLYACRYLATES; POLYMERS OF N-SUBSTITUTED ACRYLAMIDES WHEREIN THE NITROGEN ATOMS IN THE CARBOXAMIDE GROUPS CAN HAVE FROM 1 TO 2 ALKYL SUBSTITUTENTS WHICH CONTAIN FROM 1 TO 4 CARBON ATOMS; CAPOLYMERS OF ACRYLAMIDE WITH ANOTHER ETHYLENICALLY UNSATURATED MONOMER COPOLYMERIZABLE THEREWITH, SUFFICIENT ACRYLAMIDE BEING PRESENT IN THE MONOMER MIXTURE TO IMPART SAID WATER-DISPERSIBLE PROPERTIES TO THE RESULTING COPOLYMER WHEN IT IS MIXED WITH WATER, AND WHEREIN UP TO ABOUT 75 PERCENT OF CARBOXAMIDE GROUPS CAN BE HYDROLYZED TO CARBOXYL GROUPS; AND MIXTURES OF SAID POLYMERS; A SENSIBLE AMOUNT OF WATER-SOLUBLE COMPOUND OF A POLYVALENT METAL WHEREIN THE METAL PRESENT IS CAPABLE OF BEING REDUCED TO A LOWER POLYVALENT VALENCE STATE AND WHICH IS SUFFICIENT TO GEL SAID WATER WHEN THE VALENCE OF AT LEAST A PORTION OF SAID METAL IS REDUCED TO SAID LOWER VALENCE STATE; AND AN AMOUNT OF A WATER-SOLUBLE REDUCING AGENT WHICH IS EFFECTIVE TO REDUCE AT LEAST A PORTION OF SAID METAL TO SAID LOWER VALENCE STATE.