Drilling fluid systems with improved fluid loss properties

摘要

A drilling fluid system comprising a brine and a quantity of cationic copolymers comprising a ratio of acrylamide monomers to cationic derivatives of acrylamide monomers, wherein the quantity and the ratio are effective to maintain effective rheology and fluid loss control in said drilling fluid system at temperatures of at least about 250° C. for at least about 16 hours.