Patent ID: 7220708

Claim:
A method of reducing the water permeability of a formation comprising: forming a well bore in a formation using a drilling fluid comprising a polymer, wherein the polymer comprises: (i) a hydrophobically modified hydrophilic monomer selected from the group consisting of alkyl dimethylammoniumethyl methacrylate halides and alkyl dimethylammonium propylmethacrylamide halides, wherein the alkyl groups have from about 4 to about 22 carbon atoms; and (ii) a hydrophilic monomer selected from the group consisting of 2-acrylamido-2-methyl propane sulfonic acid, N,N-dimethylacryl amide, vinyl pyrrolidone, dimethylaminoethyl methacrylate, acrylic acid, dimethylaminopropylmethacrylamide, trimethylammoniumethyl methacrylate chloride, methacrylamide and hydroxyethyl acrylate; and allowing the drilling fluid to enter the formation, thereby allowing the polymer to be adsorbed into the formation, which adsorption causes a reduction in the water permeability of the formation without substantially reducing the hydrocarbon permeability thereof.