Enriched gas drive recovery process

Claim 2

A PROCESS FOR RECOVERING HYDROCARBONS FROM A HYDROCARBON-BEARING RESERVOIR HAVING A HYDROCARBON LIQUID PHASE AND A GAS SATURATION, TRAVERSED BY AT LEAST ONE INJECTION WELL AND ONE PRODUCTION WELL, COMPRISING THE STEPS OF: A. DETERMINING THE COMPOSITION OF A HYDROCARBON SOLVENT THAT IS CONDITIONALLY MISCIBLE WITH SAID LIQUID PHASE AT THE TEMPERATURE AND PRESSURE OF SAID RESERVOIR B. INJECTING INTO SAID RESERVOIR VIA SAID INJECTION WELL A SLUG OF SAID HYDROCARBON SOLVENT IN AN AMOUNT SUFFICIENT TO ESTABLISHED A MISCIBLE TRANSITION ZONE OF SAID SLUG WITH SAID HYDROCARBON LIQUID PHASE, C. INJECTING INTO SAID RESERVOIR A DRIVE FLUID AT A PRESSURE AND IN AN AMOUNT SUFFICIENT TO MAINTAIN A DRIVE OF SAID SLUG AND SAID RESERVOIR HYDROCARBONS TOWARD SAID PRODUCTION WELL AND D. RECOVERING SAID HYDROCARBONS VIA SAID PRODUCTION WELL.

Claim 3

The process of claim 1 wherein said hydrocarbon solvent comprises a mixture of methane and at least one hydrocarbon having from 2 to 6 carbon atoms per molecule.

Claim 4

The process of claim 1 wherein said hydrocarbon solvent contains methane, natural gas, carbon dioxide, hydrogen sulfide, sulfur dioxide, separator gas and mixtures thereof.

Claim 5

The process of claim 1 wherein water, brine, thickened water, thickened brine and mixtures thereof are injected simultaneously or alternately with said hydrocarbon solvent.

Claim 6

The process of claim 1 wherein said drive fluid is selected from the Group consisting of methane, natural gas, carbon dioxide, nitrogen, air, flue gas and mixtures thereof.

Claim 7

The process of claim 1 wherein said drive fluid is water, brine, thickened water, thickened brine and mixtures thereof.

Claim 8

The process of claim 1 wherein said drive fluid is a gas and water injected as a mixture.

Claim 9

The process of claim 1 wherein said drive fluid is a gas and water, said gas and water being injected alternately.

Claim 10

The process of claim 1 wherein step (a) is preceded by pressure depletion to a pressure less than the reservoir bubble point pressure.

Claim 11

A process for recovering hydrocarbons from a hydrocarbon-bearing reservoir, said reservoir being traversed by at least one injection well and one production well, comprising the steps of: a. producing said reservoir by pressure depletion to a pressure at which a gas saturation and a hydrocarbon liquid phase are established in said reservoir, b. determining the composition of a hydrocarbon solvent that is conditionally miscible with said liquid phase at the temperature and pressure of said reservoir, c. injecting into said reservoir via said injection well a slug of said hydrocarbon solvent in an amount sufficient to establish a transition zone of said slug with said liquid phase, d. injecting into said reservoir a drive fluid at a pressure and in an amount sufficient to maintain a drive of said slug and said reservoir hydrocarbons toward said production well and, e. recovery of said hydrocarbons via said production well.

Claim 12

A process for recovering hydrocarbons from a hydrocarbon-bearing reservoir, said reservoir being traversed by at least one injection well and one production well, comprising the steps of: a. producing said reservoir by pressure depletion to a pressure at which a gas saturation and a hydrocarbon liquid phase are established in said reservoir, b. determining the composition of a hydrocarbon solvent that is conditionally miscible with said liquid phase at the temperature and pressure of said reservoir, c. injecting into said reservoir via said injection well a slug of said hydrocarbon solvent in an amount sufficient to establish a transition zone of said slug with said liquid phase, d. injecting into said reservoir a drive fluid at a pressure and in an amount sufficient to maintain a drive of said slug and said reservoir hydrocarbons toward said production well and, e. recovery of said hydrocarbons via said production well.

Claim 13

The process of claim 10 wherein said pressure depletion is continued to a pressure in the range of from the bubble point pressure to a pressure at which the gas saturation is about 30 percent of the hydrocarbon pore volume.

Claim 14

The process of claim 10 wherein said hydrocarbon solvent comprises a mixture of methane and at least one hydrocarbon having from 2 to 6 carbon atoms per molecule.

Claim 15

The process of claim 10 wherein said hydrocarbon solvent contains methane, natural gas, carbon dioxide, hydrogen sulfide, sulfur dioxide, separator gas and mixtures thereof.

Claim 16

The process of claim 10 wherein water, brine, thickened water, thickened brine and mixtures thereof are injected simultaneously or alternately with said hydrocarbon solvent.

Claim 17

The process of claim 10 wherein said drive agent is selected from the group consisting of methane, natural gas, carbon dioxide, nitrogen, air, flue gas and mixtures thereof.

Claim 18

The process of claim 10 wherein said drive fluid is water, brine, thickened water, thickened brine and mixtures thereof.

Claim 19

The process of claim 10 wherein said drive fluid is a gas and water, injected as a mixture.

Claim 20

The process of claim 10 wherein said drive fluid is a gas and water, said gas and water being injected alternately.