WATER-BASED POLYMER DRILLING FLUID AND METHOD OF USE
A water-based drilling fluid comprises a polymer which is a non-ionic polymer or an anionic polymer. The polymer can be a polyaerylamide. The fluid is used for drilling subterranean formations containing heavy crude oil and bitumen-rich oil sands, and may comprise additional fluid components.
1 - 38 . (canceled)
39 . A water-based drilling fluid comprising an anionic polyacrylamide polymer.
40 . A water-based drilling fluid according to claim 39 , wherein the anionic polyacrylamide has a general formula 3
wherein: R 4 to R 9 are each independently selected from H and a C 1 to C 6 linear, branched, saturated, unsaturated or cyclic alkyl group optionally containing at least one heteroatom; and
m1 and m2 each independently range from 10,000 to 1,000,000; and
X + is selected from the group consisting of Li + , Na + , K + and a quaternary ammonium ion.
41 . A water-based drilling fluid according to claim 39 , wherein the anionic polyacrylamide is of formula 4:
wherein: m1 and m2 each independently range from 10,000 to 1,000,000.
42 . A water-based drilling fluid according to claim 39 , wherein the fluid has a pH of about 8 or lower.
43 . A water-based drilling fluid according to claim 39 , wherein the fluid has a pH from about 5 to about 7.
44 . A water-based drilling fluid according to claim 39 , wherein the anionic polyacrylamide has an anionicity between 0 to 100%.
45 . A water-based drilling fluid according to claim 39 , wherein the anionic polyacrylamide has a molecular weight from about 8 to about 10 million.
46 . A water-based drilling fluid according to claim 39 further comprising a compound selected from the group consisting of organic acid, inorganic acid, organic salt, inorganic salt and mixtures thereof.
47 . A water-based drilling fluid according to claim 39 further comprising a compound selected from the group consisting of fluid additives, viscosifiers, fluid loss additives, weighting materials, clay formation control agents, bactericides, defoamers, lost circulation materials, bridging agents and mixtures thereof.
48 . A method of drilling subterranean formations containing heavy crude oil or bitumen, the method comprising the steps of:
operating a drilling rig to drill a wellbore in a formation, the formation containing heavy crude or bitumen;
circulating a water-based drilling fluid to the drill bit operation of the drilling rig, the water-based drilling fluid comprising an anionic polyacrylamide polymer; and
maintaining the pH of the circulating drilling fluid below about 8.
49 . A method according to claim 48 , wherein the pH of the circulating drilling fluid is maintained between from about 5 to about 7.
50 . A method according to claim 48 , wherein the anionic polyacrylamide has a general formula 3:
wherein R 4 to R 9 are each independently selected from H and a C 1 to C 6 linear, branched, saturated, unsaturated or cyclic alkyl group optionally containing at least one heteroatom; and
m1 and m2 each independently range from 10,000 to 1,000,000; and
X + is selected from the group consisting of Li + , Na + , K + and a quaternary ammonium ion.
51 . A method according to claim 48 , wherein the anionic polyacrylamide is of formula 4:
wherein m1 and m2 each independently range from 10,000 to 1,000,000.
52 . A method according to claim 48 , wherein the anionic polyacrylamide has an anionicity of between 0 and 100.
53 . A method according to claim 48 , wherein the polyacrylamide has a molecular weight of between about 8 million and about 10 million.
54 . A method according to claim 48 , wherein the drilling fluid further comprises a compound selected from the group consisting of organic acid, inorganic acid, organic salt, inorganic salt and mixtures thereof.
55 . A method according to claim 48 , wherein the drilling fluid further comprises a compound selected from the group consisting of fluid additives, viscosifiers, fluid loss additives, weighting materials, clay formation control agents, bactericides, defoamers, lost circulation materials, bridging agents and mixtures thereof.
56 . A method as in claim 48 , wherein the step of maintaining the pH of the circulating drilling fluid below 8 comprises addition of sulphamic acid to the drilling fluid.
57 . A method as in claim 48 , wherein the polyacrylamide polymer has an anionicity of less than about 1%.
58 . A method as in claim 48 , wherein the polyacrylamide polymer is present in the drilling fluid at a concentration of less than 4.5 kg/m 3 .
59 . A method as in claim 48 , wherein the polyacrylamide polymer is present in the drilling fluid at a concentration between about 0.5 kg/m 3 and about 2.2 kg/m 3 .
60 . A method as in claim 48 , wherein bentonite is not present in significant quantities in the drilling fluid.