US 4,733,724 A · Viscous oil recovery method

Abstract

Our invention concerns a method for treating a well completed in a subterranean petroleum-containing formation which will improve the rate at which steam can be injected into the formation for a steam push-pull or steam drive oil recovery method. This preconditioning process is applied to formations exhibiting very limited steam receptivity because the formation contains high oil viscosity and has high oil saturation and is completely liquid filled. The method involves injecting a mixture of a non-condensable oil-insoluble gas such as nitrogen and an oil soluble gas such as carbon dioxide all in the gaseous phase into the formation at a controlled rate which will avoid permanently fracturing the formation and also avoid the immediate formation of an oil bank due to dissolution of the injected oil soluble gaseous fluid into the oil. Ideally by controlling the injection rate, the gaseous mixture first displaces water from the flow channels and then carbon dioxide slowly dissolves in the oil while nitrogen remains in the flow channels. Steam injection can then be applied to the formation without the previously experienced loss in steam injectivity.

Claims18

Dependent claims

In a steam stimulation method for recovering petroleum from a subterranean, viscous petroleum containing formation having some water filled flow channels and very low gas saturation, penetrated by at least one injection well, said formation having low stem injectivity, the improvement for preconditioning the formation to increase the receptivity of the formation to steam which comprises:

(a) introducing a predetermined quantity of a gaseous phase treating fluid heated to a temperature above the temerature at which the treating fluid would condense at formation conditions, into the formation via the injection well, said treating fluid comprising a mixture of at least one non-condensable gas which is insoluble in formation petroleum and at least one non-condensable gas which is soluble in the formation petroleum, at a pressure equal to 50 to 95% of the fracture pressure of the formation which produces a treating fluid injection rate which accomplishes displacement of water from the water saturated flow channels of the formation;
(b) leaving the injected treating fluid in the formation flow channels from which water was displaced for a period of time sufficient to allow absorption of the oil soluble gas from the treating fluid into the petroleum, which causes reduction in the petroleum viscosity;
and
(c) thereafter injecting steam into the formation via the injection well;
and
(d) recovering petroleum from the formation.

3 more elements

Dependencies are inferred from the claim text.

Viscous oil recovery method

Life of this patent

Viscous oil recovery method

Life of this patent

Abstract

Claims18