Drilling mud comprising tetrapolymer consisting of N-vinyl-2-pyrrolidone, acrylamidopropanesulfonic acid, acrylamide, and acrylic acid

Claim 1

A water-based drilling fluid comprising a) a clayey mineral and water in amounts effective to form a water-based drilling fluid; and b) a tetrapolymer provided in an amount effective to provide water-loss control wherein the tetrapolymer is the product of a polymerization of the following four monomer components: (i) 2-acrylamido-2-methylpropane sulfonic acid and alkali salts thereof present in an amount in the range of from about 15 weight percent to about 45 weight percent; (ii) N-vinyl-2-pyrrolidone present in an amount in the range of from about 10 weight percent to about 30 weight percent; (iii) acrylamide present in an amount in the range of from about 20 weight percent to about 45 weight percent; and (iv) acrylic acid and alkali salts thereof present in an amount in the range of from about 10 to about 20 weight percent.

Claim 5

A method for drilling a well utilizing a rotary drill comprising circulating through said well a water-based drilling fluid containing an effective amount of a clayey material to form a water-based drilling fluid and an effective amount of tetrapolymer to control water-loss wherein the tetrapolymer is the product of a polymerization of the following four monomer components: (i) 2-acrylamido-2-methylpropane sulfonic acid and alkali salts thereof present in an amount in the range of from about 15 weight percent to about 45 weight percent; (ii) N-vinyl-2-pyrrolidone present in an amount in the range of from about 10 weight percent to about 30 weight percent; (iii) acrylamide present in an amount in the range of from about 20 weight percent to about 45 weight percent; (iv) acrylic acid and alkali salts thereof present in an amount in the range of from about 10 to about 20 weight percent; and said water-based drilling fluid will form a filter cake on the wall of said well.

Claim 6

A method for drilling a well utilizing a rotary drill comprising circulating through said well a water-based drilling fluid containing an effective amount of a clayey material to form a water-based drilling fluid and an effective amount of tetrapolymer to control water-loss wherein the tetrapolymer is the product of a polymerization of the following four monomer components: (i) 2-acrylamido-2-methylpropane sulfonic acid and alkali salts thereof present in an amount in the range of from about 15 weight percent to about 45 weight percent; (ii) N-vinyl-2-pyrrolidone present in an amount in the range of from about 10 weight percent to about 30 weight percent; (iii) acrylamide present in an amount in the range of from about 20 weight percent to about 45 weight percent; (iv) acrylic acid and alkali salts thereof present in an amount in the range of from about 10 to about 20 weight percent; and said water-based drilling fluid will form a filter cake on the wall of said well.