Patent ID: 7838597

Claim:
An aqueous concentrate for hydraulic cement to ameliorate fluid loss at elevated temperatures comprising a blend of: a) a polyvinyl alcohol resin having a characteristic viscosity in the range of from about 1 cps to about 25 cps; and b) a fluid loss ameliorating co-resin comprising a sulfonic acid-functionalized co-resin, wherein the sulfonic acid-functionalized co-resin is a copolymer which includes the residues of N,N-dimethylacrylamide (NNDMA) and AMPS, and wherein the copolymer comprises from about 60 to 99 weight percent AMPS monomer units and from about 1 to 40 weight percent NNDMA monomer units; wherein further the blend is fully dissolved in the aqueous concentrate solution; and wherein the total resin content of the concentrate solution is between about 10 and 40 percent by weight, the concentrate solution has a viscosity in the range of from about 10 cps to about 15,000 cps at 20° C., and wherein further the weight ratio of polyvinyl alcohol resin to sulfonic acid-functionalized co-resin is in the range of from about 2.5:1 to about 10:1 and the polyvinyl alcohol resin and the sulfonic acid-functionalized co-resin are selected such that the blend is synergistically effective to reduce API Fluid loss of a cement slurry at elevated temperatures as compared with either component of the blend, with the further proviso that the blend is effective to reduce the API fluid loss of a cement slurry by at least 50% at 170° F. as compared with a slurry with either the polyvinyl alcohol only instead of the blend or the AMPS/NNDMA resin only instead of the blend.