ALKALI POLYMER SURFACTANT SANDWICH
Aspects of the invention relate to methods for enhancing the amount of oil recovered from subterranean reservoirs or reducing the amount of surfactant needed. The method includes injecting a first alkali-polymer slug through a wellbore into a reservoir, followed by injecting a alkali-polymer-surfactant slug through the wellbore into the reservoir, and then injecting a second alkali-polymer slug through the wellbore into the reservoir.
1 . A method for enhancing oil recovery in a subsurface reservoir in fluid communication with a wellbore comprising, in order:
injecting a first alkali-polymer slug through the wellbore into the reservoir;
injecting an alkali-polymer-surfactant slug through the wellbore into the reservoir; and
injecting a second alkali-polymer slug through the wellbore into the reservoir.
2 . The method of claim 1 , further comprising injecting a polymer slug through the wellbore into the reservoir following the second alkali-polymer slug.
3 . The method of claim 1 , wherein the alkali-polymer-surfactant slug comprises less surfactant mass than a predetermined optimal surfactant amount.
4 . The method of claim 3 , wherein the alkali-polymer-surfactant slug comprises the alkali-polymer-surfactant slug may comprise greater than 95%, greater than 90%, greater than 80%, greater than 70%, greater than 60%, or greater than 50%, of the predetermined optimal surfactant amount.
5 . The method of claim 1 , wherein the alkali-polymer-surfactant slug comprises one or more of the group consisting of internal olefin sulfonates, isomerized olefin sulfonates, alkyl aryl sulfonates, medium alcohol (C10 to C17) alkoxy sulfates, alcohol ether [alkoxy]carboxylates, alcohol ether [alkoxy]sulfates, primary amines, secondary amines, tertiary amines, quaternary ammonium cations, cationic surfactants that are linked to a terminal sulfonate or carboxylate group, alkylaryl alkoxy alcohols, alkyl alkoxy alcohols, alkyl alkoxylated esters, and alkyl polyglycosides.
6 . The method of claim 1 , wherein the alkali-polymer-surfactant slug, the first alkali-polymer slug, and/or the second alkali polymer slug comprises one or more of the group consisting of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide, sodium silicate, tetrasodium EDTA, sodium metaborate, sodium citrate, and sodium tetraborate.
7 . The method of claim 1 , wherein the alkali-polymer-surfactant slug, the first alkali-polymer slug, and/or the second alkali polymer slug comprises one or more of the group consisting of xanthan gum, scleroglucan, partially hydrolyzed polyacrylamides, hydrophobically-modified associative polymers, co-polymers of polyacrylamide (PAM), 2-acrylamido 2-methylpropane sulfonic acid, and N-vinyl pyrrolidone (NVP).
8 . The method of claim 1 , wherein the alkali-polymer-surfactant slug, the first alkali-polymer slug, and/or the second alkali polymer slug comprises 0.1 to 10 percent by weight alkali.
9 . The method of claim 1 , wherein the alkali-polymer-surfactant slug, the first alkali-polymer slug, and/or the second alkali polymer slug comprises 250 ppm to 5,000 ppm polymer.
10 . The method of claim 1 , wherein the alkali-polymer-surfactant slug comprises 0.1 to 5 weight percent surfactant.
11 . The method of claim 1 , further comprising receiving production fluid from the reservoir.
12 . The method of claim 13 , wherein greater than 90% of residual oil is recovered from the reservoir.
13 . The method of claim 1 , wherein the first alkali-polymer slug is optimized for the subsurface reservoir by adjusting the concentration of alkali and polymer in the alkali-polymer slug to at least about 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90% of optimal salinity for the reservoir.
14 . The method of claim 1 , wherein the second alkali-polymer slug is optimized for the subsurface reservoir by adjusting the concentration of alkali and polymer to at least about 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90% of optimal salinity for the reservoir.
15 . The method of claim 1 , wherein the alkali-surfactant-polymer slug is optimized for the subsurface reservoir by adjusting one or more of the concentration of alkali, polymer and surfactant to about at least 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90% of optimal salinity for the reservoir.
16 . The method of claim 1 , further comprising, prior to injection of the first alkali-polymer slug,
softening seawater or brine water; and
adding alkali and polymer to the softened seawater to form the first alkali-polymer slug.
17 . The method of claim 1 , further comprising, prior to injection of the first alkali-polymer slug,
softening seawater or brine water; and
adding alkali, polymer, and surfactant to the softened seawater to form alkali-polymer-surfactant slug.
18 . The method of claim 1 , further comprising, prior to injection of the first alkali-polymer slug,
softening seawater or brine water; and
adding alkali and polymer to the softened seawater to form the second alkali-polymer slug.
19 . The method of claim 1 , wherein the first alkali-polymer slug, the second alkali-polymer slug, and/or the alkali-polymer-surfactant slug comprises from about 100 to 150,000 ppm total dissolved solids.