Compositions and methods for enhanced oil recovery from low permeability formations
The present invention provides compositions and methods for enhancing oil recovery from low permeability subterranean formation using three mechanisms: repressurization; reduction of interfacial tension; and increased permeability. The subject compositions comprise a chelating agent, a biosurfactant, a carbonate or bicarbonate salt, water, and a pH adjusting substance, which when applied to an oil-bearing formation according to the methods of the subject invention, allow for controlled release of carbon dioxide within the formation without complicated machinery or gas-producing microorganisms.
1. A method for enhancing oil recovery from an oil-bearing subterranean formation, the method comprising obtaining a composition comprising EDTA (ethylenediaminetetraacetic acid), a sophorolipid biosurfactant, sodium bicarbonate, and water, adding an amount of sodium hydroxide to the composition sufficient to adjust the pH of the composition to at least about 9.5;
injecting the composition into the formation,
injecting an acid solution into the formation, wherein the acid solution is added at a quantity such that the pH of the composition is reduced to 7.0 or below and causes the controlled release of carbon dioxide gas inside the formation,
injecting a plugging composition comprising 1.0-1.5% sodium alginate dissolved in water into the formation, and
wherein the formation pressure is increased.
2. The method of claim 1 , wherein the acid solution is injected prior to injection of the composition.
3. The method of claim 1 , wherein the acid solution is injected after injection of the composition.
4. The method of claim 1 , further comprising injecting water or brine to push the composition and acid solution deep into the formation.
5. The method of claim 1 , wherein the acid solution is water or brine having a pH of 3.0 or below.
6. The method of claim 1 , wherein the plugging composition further comprises one or more biopolymers selected from xanthan gum and guar gum.
7. The method of claim 1 , further comprising shutting the formation for 3 to 30 days.
8. The method of claim 1 , wherein once carbon dioxide release has stopped inside the formation, pumping of oil begins after about 1 to 2 days.
9. The method of claim 1 , wherein the formation has a permeability of 10 mD or lower.