Patent ID: 7381332

Claim:
A method of separating a solid phase and a liquid phase in an oil-based mud comprising the steps of: (i) contacting said oil-based mud with a water-in-oil emulsion comprising a polymer derived from at least one water-soluble monomer, wherein said polymer is not dissolved prior to contact with said oil-based mud, wherein the polymer is prepared by water-in-oil emulsion polymerization, and wherein the emulsion comprises polymer particles of average discrete phase particle size of less than about 10 microns; (ii) mixing said water-in-oil emulsion and said oil-based mud; (iii) separating the solid phase and the liquid phase; wherein said at least one water-soluble monomer is selected from (alkyl)acrylamide, (allyl)acrylic acid, N-vinylpyrrolidone, N-vinylacetamide, N-vinylformamide, acrylonitrile, fumaric acid, crotonic acid, maleic acid, hydroxyalkyl methacrylates, 2-acrylamido-2-alkylsulfonic acids wherein the alkyl group contains 1 to 6 carbon atoms, styrene sulfonic acids; and salts of any of the foregoing thereof; or monomers having the structure of formulas I, II or III wherein R 1 , R 2 , and R 5 are each independently hydrogen or a C 1 to C 6 alkyl; R 3 and R 4 are each independently hydrogen, a C 1 to C 12 alkyl, aryl, arylalkyl or hydroxyethyl; and R 2 and R 4 or R 2 and R 3 can combine to form a cyclic ring containing one or more hetero atoms; Z is the conjugated base of an acid, X is oxygen or —NR 6 wherein R 6 is hydrogen or a C 1 to C 6 alkyl; and A is a C 1 to C 12 alkylene; and further comprising adding a surfactant.