Enhanced hydrocarbon recovery by convective heating of oil sand formations

Abstract

The present invention involves a method and apparatus for enhanced recovery of petroleum fluids from the subsurface by convective heating of the oil sand formation and the heavy oil and bitumen in situ by a downhole electric heater. Multiple propped vertical hydraulic fractures are constructed from the well bore into the oil sand formation and filled with a diluent. The heater and downhole pump force thermal convective flow of the heated diluent to flow upward and outward into the propped fractures and circulating back down and back towards the well bore heating the oil sands and in situ bitumen on the vertical faces of the propped fractures. The diluent now mixed with produced products from the oil sand re-enters the bottom of the well bore and passes over the heater element and is reheated to continue to flow in the convective cell. Thus the heating and diluting of the in place bitumen occurs predominantly circumferentially, i.e. orthogonal to the propped fracture, by diffusion from the propped vertical fracture faces progressing at a nearly uniform rate into the oil sand deposit. In situ hydrogenation and thermal cracking of the in place bitumen can provide a higher grade produced product. The heated low viscosity oil is produced through the well bore at the completion of the active heating phase of the process.

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 convective heating of the oil sand formation and the viscous heavy oil and bitumen in situ, more particularly to a method and apparatus to extract a particular fraction of the in situ hydrocarbon reserve by controlling the reservoir temperature and pressure, while also minimizing water inflow into the heated zone and well bore, resulting in increased production of petroleum fluids from the subsurface formation. 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 Venezuela, Indonesia, China and Russia. The hydrocarbon reserves of the oil sand deposit i...

AI Technical Summary

Benefits of technology

[0024] The processes active at the contact of the diluent with the bitumen in the oil sand are predominantly diffusive, being driven by partial pressure gradients and thermal gradients, resulting in the diffusion of diluent components into the bitumen and the conduction of heat from the diluent into the bitumen and oil sand formation. Upon softening of the bitumen, the oil will become mobile and additional smaller convective cells will developed providing better mixing of the diluent in the propped fracture and the every expanded zone of mobile oil in the native oil sand formation.

[0025] The diluent would preferably be an on site diluent, light oil, or natural gas condensate stream or a mixture thereof, with its selected composition to provide a primarily liquid phase of the diluent in the process zone at the imposed reservoir temperatures and pressures. The diluent could be derived from synthetic crude if available. The prime use of the diluent is to transfer by convection, heat from the well bore to the process zone, heat and dilute the produced product to yield a mixture that will flow readily at the elevated temperatures through the oil sands and propped fractures back to the well bore. The selected range of temperatures and pressures to operate the process will depend on reservoir depth, ambient conditions, quality of the in place heavy oil and bitumen, composition of the diluent, and the presence of nearby water bodies. The process can be operated at a low temperature range of ˜100° C. for a heavy oil rich oil sand deposit and at a moderate temperature range of ˜150°-180° C. for a bitumen rich oil sand deposit, basically to reduce the bitumen viscosity and thus mobilized the in place oil. However, the process can be operated a much higher temperatures >270° C. to pyrolysis the in place hydrocarbon in the presence of hydrogen and / or catalysts. The operating pressure of the process may be selected to closely match the ambient reservoir conditions to minimize water inflow into the process zone and the well bore. However, the process operating conditions may deviate from this pressure in order to maintain the diluent and produced mixture in a predominantly liquid state, i.e. the diluent is to remain in most part soluble in the produced heavy oil or bitumen at the operating process temperatures and pressures.

[0026] To accelerate the process, forced convection by a pump can assist and transfer additional heat into the propped fracture convective cells, by pumping the diluent and produced product at greater velocities past the heater and into the propped fractures and mobile zone within the oil sands.

[0028] The prime benefits of the above process are to provide an efficient low temperature heating phase to mobilize the hydrocarbon in situ, to produce a higher grade petroleum product, and to maintain ambient reservoir pressure conditions and thus limit water inflow into the process zone. The disadvantage of the process is that only minimal quantities of hydrocarbons are extracted from the subsurface during the active heating phase of the process since the majority of the hydrocarbons are produced near the end of the process.

[0030] Therefore, the present invention provides a method and apparatus for enhanced recovery of petroleum fluids from the subsurface by convective heating of the oil sand formation and the viscous heavy oil and bitumen in situ, more particularly to a method and apparatus to extract a particular fraction of the in situ hydrocarbon reserve by controlling the reservoir temperature and pressure, while also minimizing water inflow into the heated zone and well bore resulting in increased production of petroleum fluids from the subsurface formation.

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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