Acrylamide terpolymer shale stabilizing additive for low viscosity oil and gas drilling operations
AssigneeNalco Chemical Company
InventorsC. Darwin Williamson, Dodd W. Fong, Robert K. Gabel
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Abstract
A low viscosity drilling fluid and method for stabilizing a downhole shale formation are disclosed. The fluid comprises an aqueous solution of a partialy transamidated hydrolyzed acrylamide copolymer, potassium chloride, a weighting agent and an optional viscosifying agent. The copolymer comprises from about 50 to about 98 mole percent primary amide functionality, from about 0.1 to about 15 mole percent secondary amide functionality and from about 2 to about 50 mole percent of the acrylate salt. The drilling fluid has a density out from about 8 to about 18 pounds per gallon and a viscosity of from about 5 to about 30 centistokes.
Claims20
A method for stabilizing a downhole shale formation, comprising the steps of:
- (a) inverting a water-in-oil emulsion comprising a random hydrophobic acrylamide copolymer having the formula:
- ##STR3## wherein R is a hydrogen or methyl group, M is hydrogen, an alkali metal, ammonium or amine group, and R' is an hydrocarbyl group having from 1 to about 6 carbon atoms, said inverted emulsion forming a polymer concentrate, wherein said (A) repeat units comprise from about 2 to about 50 mole percent of said copolymer, said (B) repeat units comprise from about 50 to about 98 mole percent of said copolymer and said (C) repeat units comprise from about 0.1 to about 15 mole percent of said copolymer;
- (b) preparing an aqueous drilling fluid comprising a sufficient amount of said concentrate to give a copolymer concentration of from about 0.04 to about 1.8 pounds per barrel, from about 5 to about 50 pounds per barrel of potassium chloride, and a weighting agent, wherein the drilling fluid has a density from about 8 to about 18 pounds per gallon and a viscosity from about 5 to about 30 centistokes;
- and
- (c) circulating said drilling fluid through a bore in the formation.
The method of claim wherein said R' group has from 2 to about 5 carbon atoms.
An aqueous based drilling fluid suitable for stabilizing a downhole shale formation, comprising:
- (a) from about 0.04 to about 1.8 pounds per barrel of a random hydrophobic acrylamide copolymer having the formula:
- ##STR4## wherein R is a hydrogen or methyl radical, M is hydrogen, an alkali metal, ammonium or amine cation, and R' is an hydrocarbyl radical having from 1 to about 6 carbon atoms, wherein said (A) repeat units comprise from about 2 to about 50 mole percent of said copolymer, said (B) repeat units comprise from about 50 to about 98 mole percent of said copolymer and said (C) repeat units comprise from about 0.1 to about 15 mole percent of said copolymer;
- (b) from about 5 to about 50 pounds per barrel of potassium chloride;
- (c) a weighting agent to provide a density from about 8 to about 18 pounds per gallon;
- wherein the fluid has a viscosity of from about 5 to about 30 centistokes.
In the method of drilling a well bore through a sensitive clay formation comprising preparing a low viscosity drilling fluid containing a shale inhibiting polyacrylamide, and circulating the drilling fluid through the bore in contact with the formation, the improvement wherein the polyacrylamide comprises a random hydrophobic copolymer having the formula:
- ##STR5## wherein R is a hydrogen or methyl group, M is hydrogen, an alkali metal, ammonium or amine group, and R' is an hydrocarbyl group having from 1 to about 6 carbon atoms, wherein said (A) repeat units comprise from about 2 to about 50 mole percent of said copolymer, said (B) repeat units comprise from about 50 to about 98 mole percent of said copolymer and said (C) repeat units comprise from about 0.1 to about 15 mole percent of said copolymer.
Dependencies are inferred from the claim text.