Patent ID: 6855671

Claim:
A drilling system fluid comprising: water as a continuous phase; a first amount of a multivalent metal salt; a second amount of a monovalent salt, said second amount being sufficient to increase gas hydrate suppression and decrease density when compared to said fluid consisting essentially of said multivalent salt in the absence of said monovalent salt; a quantity of water soluble polyacrylamide copolymer having a cationic charge density of at least about 1% and having the following general structure: wherein R and R 1 independently are selected from the group consisting of hydrogen, acrylamide groups, acrylate groups, polyacrylamide groups, and polyacrylate groups, and copolymers thereof; R 2 independently is selected from the group consisting of moieties effective to maintain said water solubility under use conditions; R 3 is selected from groups comprising a charge in the range of from about +1 to about +4; and n independently is at least 1.