Enhanced hydrocarbon recovery by vaporizing solvents in oil sand formations

Abstract

The present invention involves a method and apparatus for enhanced recovery of petroleum fluids from the subsurface by injecting a hydrocarbon solvent vapor in contact with the oil sand formation and the heavy oil and bitumen in situ. Multiple propped vertical hydraulic fractures are constructed from the well bore into the oil sand formation. The hydrocarbon solvent vapor and a non-condensing diluent gas are injected into the well bore, fill the hydraulic fractures, and thus contact and diffuse into the in situ bitumen. The hydrocarbon solvent vapors diffuse into the bitumen from the vertical faces of the propped fractures. The bitumen softens and flows by gravity to the well bore, exposing fresh surface of bitumen for the process to progressively soften and mobilizes the bitumen in a predominantly circumferentially, i.e. orthogonal to the propped fracture, diffusion direction at a nearly uniform rate into the oil sand deposit. The mobile oil may be deasphalted by the condensed solvent, leaving the heavy asphaltenes behind in the oil sand pore space with little loss of inherent fluid mobility in the processed oil sands. The processed product is produced with the dissolved solvent along with a tail diluent gas. The tail diluent gas is enriched with hydrocarbon solvent and re-injected into the process zone and the cycle repeated.

Description

RELATED APPLICATION [0001] This application is a continuation-in-part of copending U.S. patent application Ser. No. 11 / 363,540, filed Feb. 27, 2006.TECHNICAL FIELD [0002] The present invention generally relates to enhanced recovery of petroleum fluids from the subsurface by vaporized solvents placed in the oil sand formation contacting the viscous heavy oil and bitumen in situ, and more particularly to a method and apparatus to extract a particular fraction of the in situ hydrocarbon reserve by controlling the access to the in situ bitumen, the solvent composition, and operating temperatures and pressures of the in situ process, resulting in increased production of petroleum fluids from the subsurface formation as well as limiting water inflow into the process zone. BACKGROUND OF THE INVENTION [0003] Heavy oil and bitumen oil sands are abundant in reservoirs in many parts of the world such as those in Alberta, Canada, Utah and California in the United States, the Orinoco Belt of Ven...

AI Technical Summary

Benefits of technology

[0028] Therefore, the present invention provides a method and apparatus for enhanced recovery of petroleum fluids from the subsurface by vaporized solvents placed in the oil sand formation contacting the viscous heavy oil and bitumen in situ, and more particularly to a method and apparatus to extract a particular fraction of the in situ hydrocarbon reserve by controlling the access to the in situ bitumen, the solvent composition, and operating temperatures and pressures of the in situ process, resulting in increased production of petroleum fluids from the subsurface formation as well as limiting water inflow into the process zone.

Problems solved by technology

Successive steam injection cycles reenter earlier created fractures and thus the process becomes less efficient over time.

CSS is generally practiced in vertical wells, but systems are operational in horizontal wells, but have complications due to localized fracturing and steam entry and the lack of steam flow control along the long length of the horizontal well bore.

Similar to CSS, the SAGD method has complications, albeit less severe than CSS, due to the lack of steam flow control along the long section of the horizontal well and the difficulty of controlling the growth of the steam chamber.

Thermal recovery processes using steam require large amounts of energy to produce the steam, using either natural gas or heavy fractions of produced synthetic crude.

Burning these fuels generates significant quantities of greenhouse gases, such as carbon dioxide.

Also, the steam process uses considerable quantities of water, which even though may be reprocessed, involves recycling costs and energy use.

The startup phase for the VAPEX process can be lengthy and take many months to develop a controlled connection between the two wells and avoid premature short circuiting between the injector and producer.

The VAPEX process with horizontal wells has similar issues to CSS and SAGD in horizontal wells, due to the lack of solvent flow control along the long horizontal well bore, which can lead to non-uniformity of the vapor chamber development and growth along the horizontal well bore.

The thermal and solvent methods of enhanced oil recovery from oil sands, all suffer from a lack of surface area access to the in place bitumen.

Similarly the VAPEX process is limited by the available surface area to the in place bitumen, because the diffusion process at this contact controls the rate of softening of the bitumen.

Likewise during steam chamber growth in the SAGD process the contact surface area with the in place bitumen is virtually a constant, thus limiting the rate of heating of the bitumen.

The hydraulic connectivity of the hydraulic fracture or fractures formed in the formation may be poorly connected to the well bore due to restrictions and damage due to the perforations.

At significant depth, one of the horizontal stresses is generally at a minimum, resulting in a vertical fracture formed by the hydraulic fracturing process.

Such theories and models are highly developed and generally sufficient for the art of initiating and propagating hydraulic fractures in brittle materials such as rock, but are totally inadequate in the understanding and art of initiating and propagating hydraulic fractures in ductile materials such as unconsolidated sands and weakly cemented formations.

Hydraulic fracturing has evolved into a highly complex process with specialized fluids, equipment and monitoring systems.

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