Method for enhanced oil recovery in reservoirs containing dissolved divalent metal cations

Claim 1

A method for recovering petroleum from a subterranean reservoir penetrated by an injection well and at least one spaced production well comprising: (a) injecting into said reservoir through said injection well a 0.1 to 0.5 pore volume slug consisting essentially of an aqueous solution containing about 0.1 to 5 percent by weight of a water-soluble alkaline material selected from the group consisting of ammonium and alkali metal hydroxides, and alkaline alkali metal silicates having a molar ratio of M 2 O/SiO 2 of 1 or above wherein M is an alkali metal atom, about 0.01 to 0.6 percent by weight of a chelating agent comprising an aminopolycarboxylic acid or a water-soluble salt thereof, and the remainder water, (b) thereafter injecting an aqueous flooding medium into said injection well to drive the aqueous solution of (a) toward said spaced production well, and (c) recovering fluids from the reservoir via said production well.

Claim 2

A method for recovering petroleum from a subterranean reservoir penetrated by an injection well and at least one spaced production well comprising: (a) injecting into said reservoir through said injection well a 0.1 to 0.5 pore volume slug consisting essentially of an aqueous solution containing about 0.1 to 5 percent by weight of a water-soluble alkaline material selected from the group consisting of ammonium and alkali metal hydroxides, and alkaline alkali metal silicates having a molar ratio of M 2 O/SiO 2 of 1 or above wherein M is an alkali metal atom, about 0.01 to 0.6 percent by weight of a chelating agent comprising an aminopolycarboxylic acid or a water-soluble salt thereof, and the remainder water, (b) thereafter injecting an aqueous flooding medium into said injection well to drive the aqueous solution of (a) toward said spaced production well, and (c) recovering fluids from the reservoir via said production well.

Claim 10

A method for recovering tertiary oil from a subterranean reservoir penetrated by an injection well and at least one spaced production well, which reservoir has been subjected to a waterflood, comprising producing the production well while sequentially injecting into said reservoir through said injection well: (a) a 0.1 to 0.5 pore volume slug of a preflush comprising an aqueous solution of water containing divalent cations and an effective amount of nitrilotriacetic acid chelating agent or a sodium salt thereof, (b) a 0.2 to 0.4 pore volume slug of an aqueous solution containing about 0.05 to 0.5 percent by weight nitrilotriacetic acid chelating agent or a sodium salt thereof and about 0.3 to 1.5 percent by weight sodium orthosilicate or sodium hydroxide, said aqueous solution being prepared by adding said chelating agent to the aqueous solution before addition thereto of the sodium orthosilicate or sodium hydroxide, (c) a 0.1 to 0.5 pore volume slug of an afterflush comprising an aqueous solution of water containing divalent cations and an effective amount of nitrilotriacetic acid chelating agent or a sodium salt thereof, and (d) an aqueous drive fluid.

Claim 11

A method for recovering tertiary oil from a subterranean reservoir penetrated by an injection well and at least one spaced production well, which reservoir has been subjected to a waterflood, comprising producing the production well while sequentially injecting into said reservoir through said injection well: (a) a 0.1 to 0.5 pore volume slug of a preflush comprising an aqueous solution of water containing divalent cations and an effective amount of nitrilotriacetic acid chelating agent or a sodium salt thereof, (b) a 0.2 to 0.4 pore volume slug of an aqueous solution containing about 0.05 to 0.5 percent by weight nitrilotriacetic acid chelating agent or a sodium salt thereof and about 0.3 to 1.5 percent by weight sodium orthosilicate or sodium hydroxide, said aqueous solution being prepared by adding said chelating agent to the aqueous solution before addition thereto of the sodium orthosilicate or sodium hydroxide, (c) a 0.1 to 0.5 pore volume slug of an afterflush comprising an aqueous solution of water containing divalent cations and an effective amount of nitrilotriacetic acid chelating agent or a sodium salt thereof, and (d) an aqueous drive fluid.

Claim 12

A method for recovering petroleum from a subterranean reservoir penetrated by an injection well and at least one spaced production well comprising: (a) injecting into said reservoir through said injection well a 0.1 to 0.5 pore volume slug of preflush comprising an aqueous solution of water containing divalent cations and an effective amount of an aminopolycarboxylic acid or a water-soluble salt thereof, (b) injecting a 0.1 to 0.5 pore volume slug of an aqueous solution containing about 0.1 to 5 percent by weight of a water-soluble alkaline material selected from the group consisting of ammonium and alkali metal hydroxides, and alkaline alkali metal silicates having a molar ratio of M 2 O/SiO 2 of 1 or above wherein M is an alkali metal atom, and about 0.01 to 0.6 percent by weight of a chelating agent comprising an aminopolycarboxylic acid or a water-soluble salt thereof, (c) thereafter injecting an aqueous flooding medium into said injection well to drive the aqueous solution of (b) toward said spaced production well, and (d) recovering fluids from the reservoir via said production well.

Claim 13

A method for recovering petroleum from a subterranean reservoir penetrated by an injection well and at least one spaced production well comprising: (a) injecting into said reservoir through said injection well a 0.1 to 0.5 pore volume slug of preflush comprising an aqueous solution of water containing divalent cations and an effective amount of an aminopolycarboxylic acid or a water-soluble salt thereof, (b) injecting a 0.1 to 0.5 pore volume slug of an aqueous solution containing about 0.1 to 5 percent by weight of a water-soluble alkaline material selected from the group consisting of ammonium and alkali metal hydroxides, and alkaline alkali metal silicates having a molar ratio of M 2 O/SiO 2 of 1 or above wherein M is an alkali metal atom, and about 0.01 to 0.6 percent by weight of a chelating agent comprising an aminopolycarboxylic acid or a water-soluble salt thereof, (c) thereafter injecting an aqueous flooding medium into said injection well to drive the aqueous solution of (b) toward said spaced production well, and (d) recovering fluids from the reservoir via said production well.