Reducing fluid loss in downhole cementing

Cementing compositions having improved fluid loss capabilities for use in oil, gas, water and other well cementing operations comprise water, hydraulic cement and a fluid-loss additive comprising a graft polymer comprised of a backbone of lignin, lignite, derivatized cellulose and various synthetic polymers selected from the group consisting of polyvinyl alcohol, polyethylene oxide, polypropylene oxide and polyethyleneimine. The grafted pendant groups comprise at least one member selected from the group of homopolymers, copolymers and terpolymers of 2-acrylamido-2-methylpropane-sulfonic acid, acrylonitrile, N,N-dimethylacrylamide, acrylic acid, N,N-dialkylaminoethylmethacrylate and their salts. The backbone comprises from about 5 to about 95 percent by weight of the graft polymer, and the pendant groups can comprise from about 5 to about 95 percent by weight of the graft polymer.