High temperature viscosifying and fluid loss controlling additives for well cements, well cement compositions and methods

A method of cementing a subterranean zone penetrated by a well bore comprising the steps of:

• (a) providing a cement composition comprising a hydraulic cement, water present in an amount sufficient to form a slurry and a viscosifying and fluid loss controlling additive comprising a mixture of a polymer comprised of at least one monomer which is calcium tolerant, anionic and disperses basic cement slurries, at least one monomer which hydrolyzes in basic cement slurries to generate anionic carboxylate groups that bind with calcium and viscosify the slurries, and at least one monomer which generates non-ionic pendant groups on the polymer upon hydrolyzing in basic cement slurries to prevent polymer precipitation selected from the group consisting of N-alkyl-N-vinyl-acetamide wherein the alkyl group is selected from C1 to C6 alkyl groups, allyl glycidyl ether, and vinylacetate;
• and a homopolymer of a monomer which hydrolyzes in basic cement slurries to generate anionic carboxylate groups that bind with calcium, viscosify the slurries and prevent settling in the slurries;
• (b) placing said cement composition in said subterranean zone;
• and
• (c) allowing said cement composition to set therein.