Fluid loss reducer for high temperature high pressure water based-mud application

The present invention concerns a water-based drilling mud for utilization in the drilling of oil wells comprising an aqueous phase wherein the aqueous phase contains an oil soluble polymer in the form of a gel as a fluid loss reducer. The subject invention further reveals a process for preparing an oil soluble polymer fluid loss control agent comprising the steps of dissolving at least one polymer in a hydrocarbon oil to form a clear solution or a gel, adding an emulsifier to the solution or the gel, and keeping the mixture under conditions of agitation until a clear creamy mixture is obtained; wherein said oil soluble polymer fluid loss control agent contains up to 50 percent water based on the weight of the control agent; wherein the emulsifier is present at a level which is within the range of 3 percent to 30 percent based upon the weight of the control agent; and wherein the polymer is prepared from monomers selected from the group consisting of styrene, substituted styrene, alkyl acrylate, substituted alkyl acrylate, alkyl methacrylate, substituted alkyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, isoprene, butadiene, ethylene, vinyl acetate, and vinyl esters of versatic acids containing from 9 to 19 carbon atoms.