Alkaline waterflooding process

Claim 2

IN THE RECOVERY OF OIL FROM A SUBSTERRANEAN OIL RESERVOIR PENETRATED BY SPACED INJECTION AND PRODUCTION SYSTEMS AND CONTAINING OIL HAVING AN ACID NUMBER OF AT LEAST 0.167, THE METHOD COMPRISING: A. INTRODUCING INTO SAID RESERVOIR VIA SAID INJECTION SYSTEM AN AQUEOUS ALKALINE SOLUTION IN AN AMOUNT WITHIN THE RANGE OF 0.15 TO 0.65 PORE VOLUME, SAID ALKALINE SOLUTION HAVING A PH WITHIN THE RANGE OF 11.5 TO 13 AND A MONOVALENT SALT SALINITY WITHIN THE RANGE OF 0.5 TO 2.0 WEIGHT PERCENT, B. THEREAFTER INTRODUCING INTO SAID RESERVIOR VIA SAID INJECTION SYSTEM AN AQUEOUS FLOODING MEDIUM TO DISPLACE OIL TO SAID PRODUCTION SYSTEM, AND C. RECOVERING OIL FROM SAID PRODUCTION SYSTEM.

Claim 3

The method of claim 1 wherein said monovalent salt comprises sodium chloride.

Claim 4

The method of claim 2 wherein said aqueous alkaline solution contains an alkali metal hydroxide in a concentration range of 0.005 to 0.1 N.

Claim 5

The method of claim 3 wherein said alkali metal hydroxide is sodium hydroxide.

Claim 6

The method of claim 1 further comprising the step of prior to the injection of said aqueous alkaline solution, introducing into said reservoir via said injection system an aqueous protective slug which is substantially free of divalent salts and exhibits a monovalent salt salinity within the range of 0.5 to 2.0 weight percent.

Claim 7

In the recovery of oil from a subterranean oil reservoir penetrated by spaced injection and production systems and containing oil having an acid number of at least 0.167, the method comprising: a. introducing into said reservoir via said injection system an aqueous initiation slug in an amount within the range of 0.05 to 0.15 pore volume, said initiation slug containing an alkali metal hydroxide in an amount within the range of 0.005 N to 0.1 N and sodium chloride in a concentration within the range of 0.5 to 2.0 weight percent, b. thereafter introducing into said reservoir via said injection system an aqueous mobility control slug in an amount within the range of 0.1 to 0.5 pore volume, at least a portion of said mobility control slug containing a thickening agent in an amount to increase the viscosity thereof to a value greater than the viscosity of said initiation slug, and containing an alkali metal hydroxide in an amount within the range of 0.005 N to 0.1 N and sodium chloride in a concentration within the range of 0.5 to 2.0 weight percent, c. thereafter introducing into said reservoir via said injection system an aqueous flooding medium to displace oil to said production system, and d. recovering oil from said production system.

Claim 8

In the recovery of oil from a subterranean oil reservoir penetrated by spaced injection and production systems and containing oil having an acid number of at least 0.167, the method comprising: a. introducing into said reservoir via said injection system an aqueous initiation slug in an amount within the range of 0.05 to 0.15 pore volume, said initiation slug containing an alkali metal hydroxide in an amount within the range of 0.005 N to 0.1 N and sodium chloride in a concentration within the range of 0.5 to 2.0 weight percent, b. thereafter introducing into said reservoir via said injection system an aqueous mobility control slug in an amount within the range of 0.1 to 0.5 pore volume, at least a portion of said mobility control slug containing a thickening agent in an amount to increase the viscosity thereof to a value greater than the viscosity of said initiation slug, and containing an alkali metal hydroxide in an amount within the range of 0.005 N to 0.1 N and sodium chloride in a concentration within the range of 0.5 to 2.0 weight percent, c. thereafter introducing into said reservoir via said injection system an aqueous flooding medium to displace oil to said production system, and d. recovering oil from said production system.

Claim 9

The method of claim 6 wherein said thickening agent is present in an amount to increase the viscosity of at least a portion of said mobility control slug to a value within the range of 1 to 4 times the viscosity of the oil in said reservoir.

Claim 10

The method of claim 7 wherein the concentration of said thickening agent in a lAtter portion of said mobility control slug is progressively decreased.

Claim 11

The method of claim 8 wherein said alkali metal hydroxide is sodium hydroxide.

Claim 12

The method of claim 6 further comprising the step of prior to the injection of said initiation slug, introducing into said reservoir via said injection system an aqueous protective slug which is substantially free of divalent salts and contains sodium chloride in a concentration within the range of 0.5 to 2.0 weight percent.