Polymers for use as filtration control aids in drilling muds

Claim 2

A polymer having an intrinsic viscosity of 1.0 to 7.0 dl/g in I.OM NaCI and prepared from: (A) 2.5 to 45% by weight of at least one unsaturated carboxylic acid or its salt; (B) 5.0 to 85% by weight of at least one unsaturated sulfonic acid or its salt; (C) 2.5 to 15% by weight of at least one unsaturated cationic-containing monomer; and (D) 0 to 90% by weight of at least one unsaturated non-ionic monomer.

Claim 3

A polymer as claimed in Claim 1 having an intrinsic viscosity of 1.5 to 5.0 dl/g in 1.OM NaCl.

Claim 4

A polymer as claimed in Claim 1 or 2 prepared from 25 to 35% by weight of component (A); 25 to 40% by weight of component (B); 5 to 10% by weight of component (C); and 15 to 45% by weight of component (D).

Claim 5

A polymer as claimed in any preceding claim in which component (A) is acrylic acid, methacrylic acid, vinyl acetic acid, allyl acetic acid, 4-methyl-4-pentenoic acid, a-haloacrylic acid, maleic acid, itaconic acid, fumaric acid, B-hydroxyethyl acrylate, B-carboxyethyl acrylate, a salt of such an acid or a mixture of two or more such compounds; component (B) is 2-acrylamido-2-methyl-propanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid, a sulfoalkylacrylate, a sulfoalkylmethacrylate, allylsulfonic acid, methallylsulfonic acid, 3-methacrylamido-2-hydroxypropylsulfonic acid, a salt of such an acid or a mixture of two or more such compounds; component (C) is dimethyldiallylammonium chloride, diethyldiallylammonium chloride, methacryloyloxyethyl-trimethylammonium methosulfate, methacrylamidopropyl-trimethylammonium chloride, acryloyloxyethyl-trimethylammonium chloride, methacryloyloxyethyl-trimethylammonium chloride, acrylamidomethylpropyl-trimethylammonium chloride, acrylamidomethylbutyl-trimethylammonium chloride, or a mixture of two or more such compounds; and component (D) is acrylamide, methacrylamide or N,N-dimethylacrylamide.

Claim 6

A polymer as claimed in any preceding claim in which the cationic-containing monomer is a monomer containing a pendant tertiary amine that had been quaternized subsequent to polymerization.

Claim 7

An aqueous drilling fluid comprising an aqueous clay dispersion and a polymer as claimed in any one of Claims 1 to 5.

Claim 8

A method for drilling a well in a subterranean formation, comprising circulating into the well, during drilling, an aqueous drilling fluid as claimed in Claim 6.