Drilling fluid containing a copolymer filtration control agent

Claim 2

In a method of drilling a well into a subterranean formation in which an aqueous drilling fluid containing clayey material is circulated into the well, the steps of forming a filter cake on the wall of the well to decrease loss of fluid from the drilling fluid, which comprises: (1) admixing with said drilling fluid an amount of at least about 0.5 weight percent of a copolymer of: (a) from between about 70 mole percent and about 100 mole percent of a (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof; and (b) from between about 30 mole percent and about 1 mole percent of N,N-dialkyl(meth)acrylamide, a 0.3 percent by weight aqueous solution of said copolymer having a viscosity at about 25° C. of from between about 18 centipoises and about 32 centipoises, as determined at a shear rate of 511 reciprocal seconds, the number of carbon atoms in the alkyl portion of the acrylamido-alkyl sulfonic acid or alkali metal salt thereof being about four, and the number of carbon atoms in the alkyl portion of the N,N-dialkyl(meth)acrylamide being from between about 1 and about 3.

Claim 3

The method of claim 1 wherein the amount of said (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof is about 90 mole percent and the amount of said dialkyl(meth)acrylamide is about 10 mole percent.

Claim 4

The method of claim 1 wherein said (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof is sodium 2-acrylamido-2-methyl propane sulfonate.

Claim 5

The method of claim 1 wherein said N,N-dialkyl(meth)acrylamide is N,N-dimethyl acrylamide.

Claim 6

The method of claim 1 wherein said (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof is sodium 2-acrylamido-2-methyl propane sulfonate in an amount of about 90 mole percent and said N,N-dialkyl(meth)acrylamide is N,N-dimethyl acrylamide in the amount of about 10 mole percent.

Claim 7

In a method of drilling a well into a subterraranean formation in which an aqueous drilling fluid containing clayey material is circulated into the well, the steps of forming a filter cake on the wall of the well to decrease loss of fluid from the drilling fluid, which comprises: (1) admixing with said drilling fluid an amount of at least about 0.25 pounds per 42-gallon barrel of a cross-linked copolymer of: (a) from between about 70 mole percent and about 100 mole percent of a (meth)acrylamide alkyl sulfonic acid or alkali metal salt thereof; (b) from between about 10 mole percent and about 1 mole percent of a N,N-dialkyl(meth)acrylamide; and (c) from about 0.1 mole percent of a cross-linking agent selected from the class consisting of N,N'-methylenebisacrylamide, divinyl benzene, N-(isobutoxymethyl)acrylamide and N-(methylol)acrylamide, a 0.3 percent by weight aqueous solution of said copolymer having a viscosity at about 25° C. between about 15 centipoises and about 84 centipoises, as determined at a shear rate of 511 reciprocal seconds, the number of carbon atoms in the alkyl portion of the acrylamido-alkyl sulfonic acid or alkali metal salt thereof being about four, and the number of carbon atoms in each alkyl portion of the N,N-dialkyl(meth)acrylamide being between from about 1 and about 3 and (2) circulating said drilling fluid in said well.

Claim 8

In a method of drilling a well into a subterraranean formation in which an aqueous drilling fluid containing clayey material is circulated into the well, the steps of forming a filter cake on the wall of the well to decrease loss of fluid from the drilling fluid, which comprises: (1) admixing with said drilling fluid an amount of at least about 0.25 pounds per 42-gallon barrel of a cross-linked copolymer of: (a) from between about 70 mole percent and about 100 mole percent of a (meth)acrylamide alkyl sulfonic acid or alkali metal salt thereof; (b) from between about 10 mole percent and about 1 mole percent of a N,N-dialkyl(meth)acrylamide; and (c) from about 0.1 mole percent of a cross-linking agent selected from the class consisting of N,N'-methylenebisacrylamide, divinyl benzene, N-(isobutoxymethyl)acrylamide and N-(methylol)acrylamide, a 0.3 percent by weight aqueous solution of said copolymer having a viscosity at about 25° C. between about 15 centipoises and about 84 centipoises, as determined at a shear rate of 511 reciprocal seconds, the number of carbon atoms in the alkyl portion of the acrylamido-alkyl sulfonic acid or alkali metal salt thereof being about four, and the number of carbon atoms in each alkyl portion of the N,N-dialkyl(meth)acrylamide being between from about 1 and about 3 and (2) circulating said drilling fluid in said well.

Claim 9

The method of claim 6 wherein the amount of said (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof is about 90 mole percent; the amount of said N,N-dialkyl(meth)acrylamide is about 10 mole percent; and the amount of said cross-linking agent is about 0.02 mole percent.

Claim 10

The method of claim 6 wherein said (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof is sodium 2-acrylamido-2-methyl propane sulfonate.

Claim 11

The method of claim 6 wherein said N,N-dialkyl(meth)acrylamide is N,N-dimethylacrylamide.

Claim 12

The method of claim 6 wherein said cross-linking agent is N,N'-methylenebisacrylamide.

Claim 13

The method of claim 6 wherein said (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof is sodium 2-acrylamido-2-methyl propane sulfonate in an amount of about 90 mole percent; said N,N-dialkyl(meth)acrylamide in the amount of about 10 mole percent; and said cross-linking agent is N,N'-methylenebisacrylamide in an amount of about 0.05 mole percent.

Claim 14

An aqueous drilling fluid comprising water, a clayey substance suspended in said water, and at least about 0.25 pounds per 42-gallon barrel of a copolymer of: (a) from between about 70 mole percent and about 100 mole percent of a (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof; and (b) from between about 30 mole percent and about 1 mole percent of N,N-dialkyl(meth)acrylamide, a 0.5 percent by weight aqueous solution of said copolymer having a viscosity of about 25° C. of from between about 15 centipoises and about 32 centipoises as determined at a shear rate of 511 reciprocal seconds, the number of carbon atoms in the alkyl portion of the acrylamidoalkyl sulfonic acid or alkali metal salt thereof being about four, and the number of carbon atoms in each alkyl portion of the N,N-dialkyl(meth)acrylamide being from between about 1 and about 3.

Claim 15

An aqueous drilling fluid comprising water, a clayey substance suspended in said water, and at least about 0.25 pounds per 42-gallon barrel of a copolymer of: (a) from between about 70 mole percent and about 100 mole percent of a (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof; and (b) from between about 30 mole percent and about 1 mole percent of N,N-dialkyl(meth)acrylamide, a 0.5 percent by weight aqueous solution of said copolymer having a viscosity of about 25° C. of from between about 15 centipoises and about 32 centipoises as determined at a shear rate of 511 reciprocal seconds, the number of carbon atoms in the alkyl portion of the acrylamidoalkyl sulfonic acid or alkali metal salt thereof being about four, and the number of carbon atoms in each alkyl portion of the N,N-dialkyl(meth)acrylamide being from between about 1 and about 3.

Claim 16

The drilling fluid of claim 12 wherein the amount of said N,N-dimethyl acrylamide or (meth) is about 10 mole percent.

Claim 17

The drilling fluid of claim 12 wherein the amount of said (meth)acrylamido alkyl sulfonic acid or alkali metal salt there of is about 90 mole percent and the amount of said N,N-dialkyl(meth)acrylamide is about 10 mole percent.

Claim 18

The drilling fluid of claim 12 wherein said (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof is sodium 2-acrylamido-2-methyl propane sulfonate.

Claim 19

The drilling fluid of claim 12 wherein said N,N dialkyl(meth)acrylamide is N,N-dimethyl acrylamide.

Claim 20

The drilling fluid of claim 12 wherein said (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof is sodium 2-acrylamido-2-methyl propane sulfonate in an amount of about 90 mole percent and said N,N-dialkyl(meth)acrylamide is N,N-dimethyl acrylamide in an amount of about 10 mole percent.

Claim 21

An aqueous drilling fluid comprising water, a clayey substance suspended in said water, and at least about 0.25 pounds per 42-gallon barrel of cross-linked copolymer of: (a) from between about 70 mole percent and about 100 mole percent of a (meth)acrylamide alkyl sulfonic acid or alkali metal salt thereof; (b) from between about 30 mole percent and about 1 mole percent of a N,N-dialkyl(meth)acrylamide; and (c) from between about 0.01 to about 0.05 mole percent of a cross-linking agent selected from N,N'-methylenebisacrylamide, divinyl benzene, N-(iso-butoxymethyl)acrylamide or N-(methylol)acrylamide, a 0.5 percent by weight aqueous solution of said copolymer having a viscosity at about 25° C. of from between about 15 centipoises and about 84 centipoises, as determined at a shear rate of 511 reciprocal seconds, the number of carbon atoms in the alkyl portion of the acrylamidoalkyl sulfonic acid or alkali metal salt thereof being about four, and the number of carbon atoms in each alkyl portions of the N,N-dialkyl(meth)acrylamide being from between about 1 and about 3.

Claim 22

An aqueous drilling fluid comprising water, a clayey substance suspended in said water, and at least about 0.25 pounds per 42-gallon barrel of cross-linked copolymer of: (a) from between about 70 mole percent and about 100 mole percent of a (meth)acrylamide alkyl sulfonic acid or alkali metal salt thereof; (b) from between about 30 mole percent and about 1 mole percent of a N,N-dialkyl(meth)acrylamide; and (c) from between about 0.01 to about 0.05 mole percent of a cross-linking agent selected from N,N'-methylenebisacrylamide, divinyl benzene, N-(iso-butoxymethyl)acrylamide or N-(methylol)acrylamide, a 0.5 percent by weight aqueous solution of said copolymer having a viscosity at about 25° C. of from between about 15 centipoises and about 84 centipoises, as determined at a shear rate of 511 reciprocal seconds, the number of carbon atoms in the alkyl portion of the acrylamidoalkyl sulfonic acid or alkali metal salt thereof being about four, and the number of carbon atoms in each alkyl portions of the N,N-dialkyl(meth)acrylamide being from between about 1 and about 3.

Claim 23

The drilling fluid of claim 18 wherein the amount of said (meth)acrylamido alkyl sulfonic acid or alkali metal salt there of is about 90 mole percent; the amount of said N,N-dialkyl(meth)acrylamide is about 10 mole percent; and the amount of said cross-linking agent is about 0.02 mole percent.

Claim 24

The drilling fluid of claim 18 wherein said (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof is sodium 2-acrylamido-2-methyl propane sulfonate.

Claim 25

The drilling fluid of claim 18 wherein said N,N-dialkyl(meth)acrylamide is N,N-dimethyl acrylamide.

Claim 26

The drilling fluid of claim 18 wherein said cross-linking agent is N,N'-methylenebisacrylamide.

Claim 27

The drilling fluid of claim 18 wherein said (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof is sodium 2-acrylamido-2-methyl propane sulfonate in an amount of about 90 mole percent; said N,N-dialkyl acrylamide is N,N-dimethylacrylamide in an amount of about 10 mole percent; and said cross-linking agent is N,N'-methylenebisacrylamide in an amount of about 0.02 mole percent.