Patent ID: 7388045

Claim:
A well cement composition comprising: water; a cement; and a fluid loss control additive comprising a graft polymer, the graft polymer comprising: a backbone comprising a lignite; a first grafted monomer selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid, salts thereof and combinations thereof; a second grafted monomer comprising diallyldimethylammonium chloride; a third grafted monomer comprising acrylamide; and a fourth grafted monomer selected from the group consisting of vinylphosphonic acid, salts thereof and combinations thereof, wherein the graft polymer has a first grafted monomer-second grafted monomer-third grafted monomer-fourth grafted monomer mole ratio in the range of from about 4:2:4:1 to about 4:0.1:1:0.1.