Patent ID: 7098172

Claim:
A process for preventing lost circulation of a drilling fluid to a formation penetrated by a wellbore in the formation while drilling below an earthen surface, the process comprising: (a) stopping the drilling of the hole including stopping the circulation of drilling fluid in the wellbore; (b) admixing components of a flowing gel pill, the pill including a non-cellulose-containing copolymer having at least one phosphonate group, a crosslinking agent active upon the phosphonate group, a crosslink initiator, wherein the crosslink initiator is selected from the group consisting of Bronsted-Lowry bases, Lewis bases, or combinations thereof, wherein the crosslink initiator is substantially free of polyvalent metal ions, and an aqueous solvent for the polymer and the crosslinker, wherein the non-cellulose containing co-polymer is a copolymer comprising monomers selected from the group consisting of: vinyl phosphonate, bis-(β-chloroethyl vinyl phosphonate), bis (hydrocarbyl) vinylphosphonate, 1,1-dichlorovinylethyl phosphate, 1,1-dichlorovinylethyl phosphate, triethanolamino-bis-chlorophosphoric acid, hydrophilic monomers of the formula: in which R1 is hydrogen, methyl or ethyl, and R2 is the group —COOR4, a sulfonyl group, a phosphonyl group, a phosphonyl group esterified by (C1–C4)-alkanol or a group of the formula: and R3 is hydrogen, methyl, ethyl or the carboxyl group; and R4 is hydrogen, amino or hydroxy-(C 1 –C 4 )-alkyl, and R5 is a sulfonyl group, a phosphonyl group or a carboxyl group, or grafting (co)polymerization of one or more hydrophilic monomers of the formula I onto a grafting base, using a free radical initiator which forms three or more free radical sites per molecule, or monomers of the formula: X 2 O 3 PCHYCZ 2 PO 2 XH (III) in which X is H, alkali metal or ammonium, Y and Z are each H, PO 3 X 2 , SO 3 X or CO 2 X and combinations thereof; (c) injecting the flowing gel pill into the wellbore and resuming the circulation of the drilling fluid in the wellbore for a predetermined time period, thereby placing the gel pill at a wellbore face in direct communication with the formation; and (d) forming a nonflowing gel from the flowing gel pill at the face so as to stop the loss of the drilling fluid into the formation; (e) resuming the drilling of the hole including the circulation of the drilling fluid in the wellbore.