Borehole drilling fluid and method

Claim 1

In a method for drilling a borehole wherein a drilling fluid is circulated within said borehole while drilling, the improvement comprising circulating in said borehole an aqueous composition comprising an effective amount of an emulsion polymerized polymer in water latex consisting of (1) an interpolymer of an olefinically unsaturated carboxylic acid monomer selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof and at least one other non-carboxylated polymerizable monomer having the general formula: ##STR10## wherein R 1 is a member of the class consisting of alkyl groups having from 1 to 30 carbon atoms and R 2 is hydrogen or a methyl group, said interpolymer having a molecular weight of from about 1,000,000 to about 4,000,000, and (2) water the API apparent viscosity of an aqueous dispersion of said latex containing 0.5 lbs. of polymer solids per barrel of said dispersion in a pH range above about 6 being at least 600% greater than the API apparent viscosity of said mixture in a pH range below about 6, the pH of said aqueous composition being above about 7, said latex serving to viscosify said drilling fluid without the addition of a clay viscosifier.

Claim 12

A method of preparing a water-based drilling fluid useful in drilling a borehole comprising: incorporating into an aqueous carrier an effective amount of an emulsion polymerized polymer in water latex consisting of (1) an interpolymer of an olefinically unsaturated carboxylic monomer selected from the class consisting of acrylic acid, methacrylic acid and mixtures thereof and at least one other, non-carboxylated polymerizable monomer having the general formula: ##STR11## wherein R 1 is a member of the class consisting of alkyl groups having from 1 to 30 carbon atoms and R 2 is hydrogen or a methyl group, said interpolymer having a molecular weight of from about 1,000,000 to about 4,000,000, and (2) water, the apparent API viscosity of an aqueous dispersion of said latex containing 0.5 lbs. of polymer solids per barrel of said mixture in a pH range above about 6 being at least 600% greater than the API apparent viscosity of said dispersion in a pH range below about 6, said latex serving to viscosify said drilling fluid without the addition of a clay viscosifier; adding to said aqueous carrier-latex composition a basic material in an amount such that the pH of said aqueous carrier-latex composition is at least about 7; and incorporating in said aqueous carrier-latex composition a sufficient amount of suspended, finely divided solids to form a filter cake on the wall of said borehole.

Claim 13

A method of preparing a water-based drilling fluid useful in drilling a borehole comprising: incorporating into an aqueous carrier an effective amount of an emulsion polymerized polymer in water latex consisting of (1) an interpolymer of an olefinically unsaturated carboxylic monomer selected from the class consisting of acrylic acid, methacrylic acid and mixtures thereof and at least one other, non-carboxylated polymerizable monomer having the general formula: ##STR11## wherein R 1 is a member of the class consisting of alkyl groups having from 1 to 30 carbon atoms and R 2 is hydrogen or a methyl group, said interpolymer having a molecular weight of from about 1,000,000 to about 4,000,000, and (2) water, the apparent API viscosity of an aqueous dispersion of said latex containing 0.5 lbs. of polymer solids per barrel of said mixture in a pH range above about 6 being at least 600% greater than the API apparent viscosity of said dispersion in a pH range below about 6, said latex serving to viscosify said drilling fluid without the addition of a clay viscosifier; adding to said aqueous carrier-latex composition a basic material in an amount such that the pH of said aqueous carrier-latex composition is at least about 7; and incorporating in said aqueous carrier-latex composition a sufficient amount of suspended, finely divided solids to form a filter cake on the wall of said borehole.