Patent ID: 7943554

Claim:
A wellbore fluid having a continuous aqueous phase, and comprising at least one polymer which: (a) has a number average molecular weight in the range of from 10,000 to less than 100,000; (b) contains hydrophilic units such that the polymer is at least 2% soluble in water at a temperature of 20° C. wherein none of said hydrophilic units comprise —CH 2 .CH 2 .O— units; and (c) contains pendant alkyl groups having at least 10 carbon atoms, the combined molecular weight of said pendant alkyl groups being in the range of from 15 to 70% by weight based on the weight of the polymer; and wherein the polymer is selected from the group consisting of: (A) a homopolymer of a compound of general formula HO(O)CCH═CHC(O)OR where R is a C 10 to C 40 alkyl group; and (B) a copolymer of (i) at least one hydrophilic monomer selected from the group consisting of acrylic acid, methacrylic acid, hydroxyethylmethacrylate, hydroxypropylmethacrylate, maleic acid, maleic anhydride, fumaric acid, itaconic acid, vinyl acetate, acrylamide, N,N-dimethylacrylamide, and N-vinyl pyrrolidone, and (ii) at least one hydrophobic monomer that provides a pendant alkyl group selected from the group consisting a C 12 to C 40 alpha-olefin, a C 10 to C 24 alkyl vinyl ether, an acrylamide of the general formula CH 2 ═CR 5 C(O)NHR 6 (I) where R 5 is selected from the group consisting of H and C 1 to C 4 alkyl groups and R 6 is a C 10 to C 40 alkyl group, and an acrylate of the general formula CH 2 ═CR 7 C(O)OR 8 (II) where R 7 is H or methyl and R 8 is a C 10 to C 40 alkyl group; and additionally comprising at least one additive selected from the group consisting of additional fluid loss control agents, bridging particulate materials, finely dispersed additives for increasing the fluid density, thinners, and shale inhibitors.