Enhanced hydrocarbon recovery by in situ combustion of oil sand formations

Abstract

The present invention is a method and apparatus for the enhanced recovery of petroleum fluids from the subsurface by in situ combustion of the hydrocarbon deposit, from injection of an oxygen rich gas and drawing off a flue gas to control the rate and propagation of the combustion front to be predominantly vertical and propagating horizontally guided by the vertical highly permeable hydraulic fractures. Multiple propped vertical hydraulic fractures are constructed from the well bore into the oil sand formation and filled with a highly permeable proppant containing hydrodesulfurization and thermal cracking catalysts. The oxygen rich gas is injected via the well bore into the top of the propped fractures, the in situ hydrocarbons are ignited by a downhole burner and the generated flue gas extracted from the bottom of the propped fractures through the well bore and mobile oil gravity drains through the propped fractures to the bottom of the well bore and pumped to the surface. The combustion front is predominantly upright, providing good vertical and lateral sweep, due to the flue gas exhaust control provided by the highly permeable propped fractures.

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 the enhanced recovery of petroleum fluids from the subsurface by the injection of an oxygen enriched gas into the oil sand formation for in situ combustion of 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 rate and growth of the combustion front, the flue gas composition, the flow of produced hydrocarbons through a hot spent previously combusted zone containing a catalyst for promoting in situ hydrodesulfurization and thermal cracking, the operating reservoir pressures of the in situ process, thus resulting in increased production and quality of the produced petroleum fluids from the subsurface formation as we...

AI Technical Summary

Benefits of technology

[0026] The combustion front generates significant heat, which diffuses into the bitumen ahead of the combustion front and heats the bitumen sufficient for mobile oil to flow under gravity. The bitumen softens and flows by gravity through the oil sands and the propped fractures to the well bore. The generated flue gases and produced hydrocarbons flow down the propped fractures to the well bore heating the proppant in the process. The radial and downward growth of the combustion front consumes the in situ hydrocarbon first near the well bore and then progressively extends radially outwards. Thus the proppant in the lower portions of the propped fractures have been significantly heated by the passage of the combustion front and thus are at sufficiently high a temperature to induce thermal cracking of the cooler produced hydrocarbons draining by gravity through this cracking zone to the well bore. A catalyst placed as the proppant in the fractures or placed in a canister in the well bore will further promote hydrodesulfurization and thermal cracking and thus upgrading in situ the quality of the produced hydrocarbon product. Such catalysts are really available as HDS (hydrodesulfurization) metal containing catalysts and FCC (fluid catalytic cracking) rare earth aluminum silica catalysts.

[0027] The in situ produced hydrocarbon product and flue gas are extracted from the bottom section of the well bore, with the rate of flue gas extraction controlling the rate and growth of the combustion front and the resultant oxygen content of the flue gas. The injected gas could be air or an enriched oxygen injected gas to limit degrading influences that air injection has on the resulting the mobilized oil's viscosity. The process can operate close to ambient reservoir pressures, so that water inflow into the process zone can be minimized. Catalysts for hydrodesulftirization and thermal cracking are contained in the proppant of the hydraulic fractures or within a canister in the well bore. The proppant zone in the lower portions of the hydraulic fractures will be raised to combustion temperatures as the combustion front moves through this zone in a radial growth direction. Therefore the produced hydrocarbons will flow through this hot spent area and thus the catalysts will promote upgrading of the mobile oil by hydrodesulfurization and thermal cracking of some portions of the produced hydrocarbon.

[0029] Therefore, the present invention provides a method and apparatus for enhanced recovery of petroleum fluids from the subsurface by the injection of an oxygen enriched gas in the oil sand formation for the in situ combustion of 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, by controlling the rate and growth of the combustion front, by controlling the flue gas composition, by controlling the flow of produced hydrocarbons through a hot spent previously combusted zone containing a catalyst for promoting in situ hydrodesulfurization and thermal cracking, and by controlling the operating reservoir pressures of the in situ process, thus resulting in increased production and quality of the produced 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 difficulties experienced by the various disclosed methods are: 1) initiating connection of the injector, the combustion zone, and producer to get the process started, 2) the potential for a liquid and / or gravity block, i.e. mobile hydrocarbons can not flow to the producer or combustion (flue) gases rise vertically rather than flow to the producer, and 3) the difficulty of raising the temperature of the produced hydrocarbons to initiate some form of hydrodesulfurization and / or thermal cracking.

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.

In situ combustion methods all suffer from poor connection between the injected gas location, combustion zone, and producer especially at initiation, and during propagation and growth of the combustion front if barren or shale lenses are present or if the oil sands have intrinsically low vertical permeability.

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.

Images