Viscous oil recovery using electric heating and solvent injection

Abstract

To recover in situ viscous oil from an underground reservoir, electricity is conducted through the underground reservoir by at least two electrodes in an amount that would, in the absence of solvent injection, cause water in the reservoir to vaporize adjacent to the electrodes, and injecting solvent into the reservoir to mitigate water vaporization adjacent to the electrodes by vaporizing solvent in this region. Oil and solvent are produced through one or more production wells.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority from Canadian Patent Application number 2,707,283 filed Jun. 11, 2010, entitled Viscous Oil Recovery Using Electric Heating and Solvent Injection, the entirety of which is incorporated by reference herein.FIELD OF THE INVENTION[0002]The present invention relates generally to in situ recovery of hydrocarbons. More particularly, the present invention relates to the use of electric heating to recover in situ hydrocarbons including viscous oil such as bitumen.BACKGROUND OF THE INVENTION[0003]Recovering viscous oil from a subterranean reservoir in an economic manner typically requires reducing the in situ viscosity of the oil. Most commonly, this is accomplished by steam injection. Steamflooding (see for example U.S. Pat. No. 3,705,625 (Whitten)), cyclic steam stimulation (CSS) (see, for example, U.S. Pat. No. 4,280,559 (Best)), and steam assisted gravity drainage (SAGD) (see for example U.S. Pat. No. 4,344,485...

AI Technical Summary

Benefits of technology

[0020]According to an aspect of the present invention, there is provided a method of recovering hydrocarbons from a subterranean reservoir by the synergistic use of electrothermal heating and solvent injection. The method requires that a conductive brine exist between electrodes disposed within the reservoir. The conductive brine may be naturally occurring or may comprise injected brine. The conductivity of the brine should be such that fluid-filled reservoir rock has a low electrical resistivity, for example less than 100 ohm-meters, 10 ohm-meters, or even 1 ohm-meter. The solvent is used to limit vaporization of water in the brine adjacent to one or more of the electrodes so as to maintain good electrical conductivity between electrodes. Sufficient electricity is supplied that would, in the absence of solvent injection, cause water to vaporize within the reservoir adjacent to the one or more electrodes. The electro-thermal heating reduces the viscosity of the oil. Sufficient solvent is injected to keep the reservoir adjacent to the one or more electrodes below the boiling point temperature of water at reservoir pressure conditions. Finally, oil and solvent are produced through one or more production wells.

Problems solved by technology

Steam injection, however, is not always an appealing method.

Steam generation requires large upfront capital expenditures for water handling and clean-up facilities.

Additionally, steam is costly to distribute over a large field due to thermal losses in pipes.

This patent does not envision pressure-driven flow of solvent through the reservoir nor use of resistive heating of the reservoir.

However, radio frequency heating is significantly more complex than ohmic heating due to the need for high-frequency alternating current to be generated and sent down into the subsurface.

However, conduction ceases if the brine sufficiently heats that it boils away.

This is particularly an issue near electrodes where, due to geometric factors, the electrical current is concentrated and thus maximum heating may occur.

Being limited to modest temperatures may result in insufficient viscosity reduction of the oil and thus cause unacceptably slow oil production rates.

However, brine injection near an electrode may be problematic since the heating may cause salts to precipitate and foul the injection well and the near-wellbore region.

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