US 20070199700 A1
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.
1. A method for the in situ recovery of hydrocarbons from a hydrocarbon containing formation, comprising:
a. drilling a bore hole in the formation to a predetermined depth to define a well bore with a casing;
b. installing one or more vertical proppant and diluent filled hydraulic fractures from the bore hole to create a process zone within the formation by injecting a fracture fluid into the casing;
c. injecting an oxygen rich gas into a section of the bore hole connected to the hydraulic fractures;
d. igniting the hydrocarbon deposit;
e. exhausting a combustion gas from the formation;
f. recovering a hydrocarbon from the formation.
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15. A well in a formation of unconsolidated and weakly cemented sediments, comprising:
a. a bore hole in the formation to a predetermined depth;
b. an injection casing grouted in the bore hole at the predetermined depth, the injection casing including multiple initiation sections separated by a weakening line and multiple passages within the initiation sections and communicating across the weakening line for the introduction of a fracture fluid to dilate the casing and separate the initiation sections along the weakening line;
c. a source for delivering the fracture fluid into the injection casing with sufficient fracturing pressure to dilate the injection casing and the formation and initiate a vertical hydraulic fracture, having a fracture tip, at an azimuth orthogonal to the direction of dilation to create a process zone within the formation, for controlling the propagation rate of each individual opposing wing of the hydraulic fracture, and for controlling the flow rate of the fracture fluid and its viscosity so that the Reynolds Number Re is less than 1 at fracture initiation and less than 2.5 during fracture propagation and the fracture fluid viscosity is greater than 100 centipoise at the fracture tip;
d. a source of oxygen rich gas connected to the casing and the propped hydraulic fractures;
e. an ignition source for igniting the hydrocarbon deposit in the presence of the oxygen rich gas, wherein a resulting combustion gas from the formation is exhausted through the casing and petroleum hydrocarbons from the formation are recovered through the casing.
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This application is a continuation-in-part of copending U.S. patent application Ser. No. 11/363,540, filed Feb. 27, 2006.
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 well as limiting water inflow into the process zone.
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 is extremely large in the trillions of barrels, with recoverable reserves estimated by current technology in the 300 billion barrels for Alberta, Canada and a similar recoverable reserve for Venezuela. These vast heavy oil (defined as the liquid petroleum resource of less than 20° API gravity) deposits are found largely in unconsolidated sandstones, being high porosity permeable cohensionless sands with minimal grain to grain cementation. The hydrocarbons are extracted from the oils sands either by mining or in situ methods.
The heavy oil and bitumen in the oil sand deposits have high viscosity at reservoir temperatures and pressures. While some distinctions have arisen between tar or oil sands, bitumen and heavy oil, these terms will be used interchangeably herein. The oil sand deposits in Alberta, Canada extend over many square miles and vary in thickness up to hundreds of feet thick. Although some of these deposits lie close to the surface and are suitable for surface mining, the majority of the deposits are at depth ranging from a shallow depth of 150 feet down to several thousands of feet below ground surface. The oil sands located at these depths constitute some of the world's largest presently known petroleum deposits. The oil sands contain a viscous hydrocarbon material, commonly referred to as bitumen, in an amount that ranges up to 15% by weight. Bitumen is effectively immobile at typical reservoir temperatures. For example at 15° C., bitumen has a viscosity of ˜1,000,000 centipoise. However at elevated temperatures the bitumen viscosity changes considerably to be ˜350 centipoise at 100° C. down to ˜10 centipoise at 180° C. The oil sand deposits have an inherently high permeability ranging from ˜1 to 10 Darcy, thus upon heating, the heavy oil becomes mobile and can easily drain from the deposit.
In situ methods of hydrocarbon extraction from the oil sands consist of cold production, in which the less viscous petroleum fluids are extracted from vertical and horizontal wells with sand exclusion screens, CHOPS (cold heavy oil production system) cold production with sand extraction from vertical and horizontal wells with large diameter perforations thus encouraging sand to flow into the well bore, CSS (cyclic steam stimulation) a huff and puff cyclic steam injection system with gravity drainage of heated petroleum fluids using vertical and horizontal wells, streamflood using injector wells for steam injection and producer wells on 5 and 9 point layout for vertical wells and combinations of vertical and horizontal wells, SAGD (steam assisted gravity drainage) steam injection and gravity production of heated hydrocarbons using two horizontal wells, VAPEX (vapor assisted petroleum extraction) solvent vapor injection and gravity production of diluted hydrocarbons using horizontal wells, and the THAI (toe heel air injection), a vertical injector well located near the base of a horizontal producer well for an in situ combustion process, and combinations of these methods.
Cyclic steam stimulation and steamflood hydrocarbon enhanced recovery methods have been utilized worldwide, beginning in 1956 with the discovery of CSS, huff and puff or steam-soak in Mene Grande field in Venezuela and for steamflood in the early 1960s in the Kern River field in California. These steam assisted hydrocarbon recovery methods including a combination of steam and solvent are described, see U.S. Pat. No. 3,739,852 to Woods et al, U.S. Pat. No. 4,280,559 to Best, U.S. Pat. No. 4,519,454 to McMillen, U.S. Pat. No. 4,697,642 to Vogel, and U.S. Pat. No. 6,708,759 to Leaute et al. The CSS process raises the steam injection pressure above the formation fracturing pressure to create fractures within the formation and enhance the surface area access of the steam to the bitumen. 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.
Descriptions of the SAGD process and modifications are described, see U.S. Pat. No. 4,344,485 to Butler, and U.S. Pat. No. 5,215,146 to Sanchez and thermal extraction methods in U.S. Pat. No. 4,085,803 to Butler, U.S. Pat. No. 4,099,570 to Vandergrift, and U.S. Pat. No. 4,116,275 to Butler et al. The SAGD process consists of two horizontal wells at the bottom of the hydrocarbon formation, with the injector well located approximately 10-15 feet vertically above the producer well. The steam injection pressures exceed the formation fracturing pressure in order to establish connection between the two wells and develop a steam chamber in the oil sand formation. 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.
A thermal steam extraction process referred to a HASDrive (heated annulus steam drive) and modifications thereof are described to heat and hydrogenate the heavy oils insitu in the presence of a metal catalyst, see U.S. Pat. No. 3,994,340 to Anderson et al, U.S. Pat. No. 4,696,345 to Hsueh, U.S. Pat. No. 4,706,751 to Gondouin, U.S. Pat. No. 5,054,551 to Duerksen, and U.S. Pat. No. 5,145,003 to Duerksen. It is disclosed that at elevated temperature and pressure the injection of hydrogen or a combination of hydrogen and carbon monoxide to the heavy oil in situ in the presence of a metal catalyst will hydrogenate and thermal crack at least a portion of the petroleum in the formation.
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. Therefore a less energy intensive oil recovery process is desirable.
Solvents applied to the bitumen soften the bitumen and reduce its viscosity and provide a non-thermal mechanism to improve the bitumen mobility. Hydrocarbon solvents consist of vaporized light hydrocarbons such as ethane, propane, or butane or liquid solvents such as pipeline diluents, natural condensate streams, or fractions of synthetic crudes. The diluent can be added to steam and flashed to a vapor state or be maintained as a liquid at elevated temperature and pressure, depending on the particular diluent composition. While in contact with the bitumen, the saturated solvent vapor dissolves into the bitumen. This diffusion process is due to the partial pressure difference in the saturated solvent vapor and the bitumen. As a result of the diffusion of the solvent into the bitumen, the oil in the bitumen becomes diluted and mobile and will flow under gravity. The resultant mobile oil may be deasphalted by the condensed solvent, leaving the heavy asphaltenes behind within the oil sand pore space with little loss of inherent fluid mobility in the oil sands due to the small weight percent (5-15%) of the asphaltene fraction to the original oil in place. Deasphalting the oil from the oil sands produces a high grade quality product by 3°-5° API gravity. If the reservoir temperature is elevated the diffusion rate of the solvent into the bitumen is raised considerably being two orders of magnitude greater at 100° C. compared to ambient reservoir temperatures of ˜15° C.
Solvent assisted recovery of hydrocarbons in continuous and cyclic modes are described including the VAPEX process and combinations of steam and solvent plus heat, see U.S. Pat. No. 4,450,913 to Allen et al, U.S. Pat. No. 4,513,819 to Islip et al, U.S. Pat. No. 5,407,009 to Butler et al, U.S. Pat. No. 5,607,016 to Butler, U.S. Pat. No. 5,899,274 to Frauenfeld et al, U.S. Pat. No. 6,318,464 to Mokrys, U.S. Patent No. 6,769,486 to Lim et al, and U.S. Pat. No. 6,883,607 to Nenniger et al. The VAPEX process generally consists of two horizontal wells in a similar configuration to SAGD; however, there are variations to this including spaced horizontal wells and a combination of horizontal and vertical wells. 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.
Direct heating and electrical heating methods for enhanced recovery of hydrocarbons from oil sands have been disclosed in combination with steam, hydrogen, catalysts, and/or solvent injection at temperatures to ensure the petroleum fluids gravity drain from the formation and at significantly higher temperatures (300° to 400° range and above) to pyrolysis the oil sands. See U.S. Pat. No. 2,780,450 to Ljungström, U.S. Pat. No. 4,597,441 to Ware et al, U.S. Pat. No. 4,926,941 to Glandt et al, U.S. Pat. No. 5,046,559 to Glandt, U.S. Pat. No. 5,060,726 to Glandt et al, U.S. Pat. No. 5,297,626 to Vinegar et al, U.S. Pat. No. 5,392,854 to Vinegar et al, and U.S. Pat. No. 6,722,431 to Karanikas et al
In situ combustion processes have been disclosed. See U.S. Pat. No. 4, 454,916 to Shu, U.S. Pat. No. 4,474,237 to Shu, U.S Pat. No. 4,566,536 to Holmes et al, 4,598,770 to Shu et al, U.S. Pat. No. 4,625,800 to Venkatesan, U.S. Pat. No. 4,993,490 to Stephens et al, U.S. Pat. No. 5,211,230 to Ostapovich et al, U.S. Pat. No. 5,273,111 to Brannan et al, U.S. Pat. No. 5,339,897 to Leaute, U.S. Pat. No. 5,413,224 to Laali, U.S. Pat. No. 5,626,191 to Greaves et al, U.S. Pat. No. 5,824,214 to Paul et al, U.S. Pat. No. 5,871,637 to Brons, U.S. Pat. No. 5,954,946 to Klazinga et al, and U.S. Pat. No. 6,412,557 to Ayasse et al. Many of these disclosed methods involve in situ combustion of the in situ hydrocarbon deposit with a combination of vertical and horizontal wells. The process involves the injection of an oxygen rich injection gas, igniting the in situ hydrocarbons, either by direct ignition from a standard downhole burner, or from self ignition, and drawing the produced flue gas off to create a gas pressure gradient to control the rate and progress of the combustion front. 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. Some of the disclosed processes overcome some of these difficulties by heating a zone and thus connecting the injector and producer prior to injection of the oxygen rich gas injection and ignition of the hydrocarbon formation. Other methods force the produced hydrocarbons to flow through a spent previously combusted zone to raise the temperature to induce some form of cracking process, while others propose placement of a catalyst in the producer well to promote further cracking at the elevated temperatures. The THAI (toe heel air injection) combustion process has been demonstrated in laboratory tests for application to oil sands, involving air injection in a vertical well with the producer being a horizontal well at a deeper depth and the combustion front progressing horizontally along the alignment of the producer and downwards towards the producer.
In situ processes involving downhole heaters are described in U.S. Pat. No. 2,634,961 to Ljungström, U.S. Pat. No. 2,732,195 to Ljungström, U.S. Pat. No. 2,780,450 to Ljungström. Electrical heaters are described for heating viscous oils in the forms of downhole heaters and electrical heating of tubing and/or casing, see U.S. Pat. No. 2,548,360 to Germain, U.S. Pat. No. 4,716,960 to Eastlund et al, U.S. Pat. No. 5,060,287 to Van Egmond, U.S. Pat. No. 5,065,818 to Van Egmond, U.S. Pat. No. 6,023,554 to Vinegar and U.S. Pat. No. 6,360,819 to Vinegar. Flameless downhole combustor heaters are described, see U.S. Pat. No. 5,255,742 to Mikus, U.S. Pat. No. 5,404,952 to Vinegar et al, U.S. Pat. No. 5,862,858 to Wellington et al, and U.S. Pat. No. 5,899,269 to Wellington et al. Surface fired heaters or surface burners may be used to heat a heat transferring fluid pumped downhole to heat the formation as described in U.S. Pat. No. 6,056,057 to Vinegar et al and U.S. Pat. No. 6,079,499 to Mikus et al.
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. Thus the reasons for raising steam pressures above the fracturing pressure in CSS and during steam chamber development in SAGD, are to increase surface area of the steam with 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. Therefore, the methods, heat and solvent, or a combination thereof, would greatly benefit from a substantial increase in contact surface area with the in place bitumen. Hydraulic fracturing of low permeable reservoirs has been used to increase the efficiency of such processes and CSS methods involving fracturing are described in U.S. Pat. No. 3,739,852 to Woods et al, U.S. Pat. No. 5,297,626 to Vinegar et al, and U.S. Pat. No. 5,392,854 to Vinegar et al. Also during initiation of the SAGD process, overpressurized conditions are usually imposed to accelerated the steam chamber development, followed by a prolonged period of underpressurized condition to reduce the steam to oil ratio. Maintaining reservoir pressure during heating of the oil sands has the significant benefit of minimizing water inflow to the heated zone and to the well bore.
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 in situ combustion method would benefit greatly from having good connection between the injected gas location, combustion zone, and the producer both at the initiation configuration and throughout the propagation and growth of the combustion front. Highly permeable vertical propped hydraulic fractures extending radially from the injector would greatly benefit the process by providing a connection to control the rate and growth of the combustion front and thus guide the combustion front radially between the propped fracture system.
Hydraulic fracturing of petroleum recovery wells enhances the extraction of fluids from low permeable formations due to the high permeability of the induced fracture and the size and extent of the fracture. A single hydraulic fracture from a well bore results in increased yield of extracted fluids from the formation. Hydraulic fracturing of highly permeable unconsolidated formations has enabled higher yield of extracted fluids from the formation and also reduced the inflow of formation sediments into the well bore. Typically the well casing is cemented into the bore hole, and the casing perforated with shots of generally 0.5 inches in diameter over the depth interval to be fractured. The formation is hydraulically fractured by injecting the fracture fluid into the casing, through the perforations, and into the formation. 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. Creating a hydraulic fracture in the formation that is well connected hydraulically to the well bore will increase the yield from the well, result in less inflow of formation sediments into the well bore, and result in greater recovery of the petroleum reserves from the formation.
Turning now to the prior art, hydraulic fracturing of subsurface earth formations to stimulate production of hydrocarbon fluids from subterranean formations has been carried out in many parts of the world for over fifty years. The earth is hydraulically fractured either through perforations in a cased well bore or in an isolated section of an open bore hole. The horizontal and vertical orientation of the hydraulic fracture is controlled by the compressive stress regime in the earth and the fabric of the formation. It is well known in the art of rock mechanics that a fracture will occur in a plane perpendicular to the direction of the minimum stress, see U.S. Pat. No. 4,271,696 to Wood. At significant depth, one of the horizontal stresses is generally at a minimum, resulting in a vertical fracture formed by the hydraulic fracturing process. It is also well known in the art that the azimuth of the vertical fracture is controlled by the orientation of the minimum horizontal stress in consolidated sediments and brittle rocks.
At shallow depths, the horizontal stresses could be less or greater than the vertical overburden stress. If the horizontal stresses are less than the vertical overburden stress, then vertical fractures will be produced; whereas if the horizontal stresses are greater than the vertical overburden stress, then a horizontal fracture will be formed by the hydraulic fracturing process.
Hydraulic fracturing generally consists of two types, propped and unpropped fracturing. Unpropped fracturing consists of acid fracturing in carbonate formations and water or low viscosity water slick fracturing for enhanced gas production in tight formations. Propped fracturing of low permeable rock formations enhances the formation permeability for ease of extracting petroleum hydrocarbons from the formation. Propped fracturing of high permeable formations is for sand control, i.e. to reduce the inflow of sand into the well bore, by placing a highly permeable propped fracture in the formation and pumping from the fracture thus reducing the pressure gradients and fluid velocities due to draw down of fluids from the well bore. Hydraulic fracturing involves the literally breaking or fracturing the rock by injecting a specialized fluid into the well bore passing through perforations in the casing to the geological formation at pressures sufficient to initiate and/or extend the fracture in the formation. The theory of hydraulic fracturing utilizes linear elasticity and brittle failure theories to explain and quantify 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. The fluids used in hydraulic fracturing vary depending on the application and can be water, oil, or multi-phased based gels. Aqueous based fracturing fluids consist of a polymeric gelling agent such as solvatable (or hydratable) polysaccharide, e.g. galactomannan gums, glycomannan gums, and cellulose derivatives. The purpose of the hydratable polysaccharides is to thicken the aqueous solution and thus act as viscosifiers, i.e. increase the viscosity by 100 times or more over the base aqueous solution. A cross-linking agent can be added which further increases the viscosity of the solution. The borate ion has been used extensively as a cross-linking agent for hydrated guar gums and other galactomannans, see U.S. Pat. No. 3,059,909 to Wise. Other suitable cross-linking agents are chromium, iron, aluminum, zirconium (see U.S. Pat. No. 3,301,723 to Chrisp), and titanium (see U.S. Pat. No. 3,888,312 to Tiner et al). A breaker is added to the solution to controllably degrade the viscous fracturing fluid. Common breakers are enzymes and catalyzed oxidizer breaker systems, with weak organic acids sometimes used.
Oil based fracturing fluids are generally based on a gel formed as a reaction product of aluminum phosphate ester and a base, typically sodium aluminate. The reaction of the ester and base creates a solution that yields high viscosity in diesels or moderate to high API gravity hydrocarbons. Gelled hydrocarbons are advantageous in water sensitive oil producing formations to avoid formation damage that would otherwise be caused by water based fracturing fluids.
The method of controlling the azimuth of a vertical hydraulic fracture in formations of unconsolidated or weakly cemented soils and sediments by slotting the well bore or installing a pre-slotted or weakened casing at a predetermined azimuth has been disclosed. The method disclosed that a vertical hydraulic fracture can be propagated at a pre-determined azimuth in unconsolidated or weakly cemented sediments and that multiple orientated vertical hydraulic fractures at differing azimuths from a single well bore can be initiated and propagated for the enhancement of petroleum fluid production from the formation. See U.S. Pat. No. 6,216,783 to Hocking et al, U.S. Pat. No. 6,443,227 to Hocking et al, U.S. Pat. No. 6,991,037 to Hocking, and Hocking U.S. patent application Ser. Nos. 11/363,540, 11/277,308, 11/277,775, 11/277,815, and 11/277,789. The method disclosed that a vertical hydraulic fracture can be propagated at a pre-determined azimuth in unconsolidated or weakly cemented sediments and that multiple orientated vertical hydraulic fractures at differing azimuths from a single well bore can be initiated and propagated for the enhancement of petroleum fluid production from the formation. It is now known that unconsolidated or weakly cemented sediments behave substantially different from brittle rocks from which most of the hydraulic fracturing experience is founded.
Accordingly, there is a need for a method and apparatus for enhancing the extraction of hydrocarbons from oil sands by in situ combustion, direct heating, steam, and/or solvent injection or a combination thereof and controlling the subsurface environment, both temperature and pressure, to optimize the hydrocarbon extraction in terms of produced rate, efficiency, and produced product quality, as well as limit water inflow into the process zone.
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, by injecting an oxygen rich gas, and by drawing off a flue gas to control the rate and progation of the combustion front to be predominantly radially away from the well bore and downwards to the bottom of the well bore, from which the produced flue gas and hydrocarbons are extracted. Multiple propped hydraulic fractures are constructed from the well bore into the oil sand formation and filled with a highly permeable proppant. 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 are extracted from the bottom of the propped fractures through the well bore. A mobile oil zone forms in front of the combustion front, and the oil, under the influence of gravity, drains through the propped fractures to the bottom of the well bore and is pumped to the surface. The injection gas is injected into the well bore and into the propped fractures at or near the ambient reservoir pressure but substantially below the reservoir fracturing pressure. The flue gas is extracted at a rate to control the propagation and shape of the combustion front and the resultant oxygen content of the flue gas. The upright and nearly vertical combustion front propagates horizontally contacting the oil sands and in situ bitumen between the vertical faces of the propped fractures. The combustion front is predominantly upright, providing good vertical sweep and advances radially in the horizontal direction with good lateral sweep, due to the flue gas exhaust control provided by the highly permeable propped fractures. Basically the combustion front is guided by the radially entending vertical hydraulic fractures. The flue gas is composed of combustion gases consisting of carbon monoxide, carbon dioxide, sulfur dioxide, and water vapor.
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.
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.
Although the present invention contemplates the formation of fractures which generally extend laterally away from a vertical or near vertical well penetrating an earth formation and in a generally vertical plane, those skilled in the art will recognize that the invention may be carried out in earth formations wherein the fractures and the well bores can extend in directions other than vertical.
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.
Other objects, features and advantages of the present invention will become apparent upon reviewing the following description of the preferred embodiments of the invention, when taken in conjunction with the drawings and the claims.
Several embodiments of the present invention are described below and illustrated in the accompanying drawings. 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, by injecting an oxygen rich gas, and by drawing off a flue gas to control the rate and progation of the combustion front to be predominantly horizontal away from the well bore. Multiple propped hydraulic fractures are constructed from the well bore into the oil sand formation and filled with a highly permeable proppant. 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, the generated flue gas is extracted from the bottom of the propped fractures through the well bore, and the mobile oil drains by gravity through the propped fractures to the bottom of the well bore and is pumped to the surface. The combustion front is predominantly upright, providing good vertical sweep and advances radially in the horizontal direction with good lateral sweep, due to the flue gas exhaust control provided by the highly permeable propped vertical fractures.
Referring to the drawings, in which like numerals indicate like elements,
The outer surface of the injection casing 1 should be roughened or manufactured such that the grout 4 bonds to the injection casing 1 with a minimum strength equal to the down hole pressure required to initiate the controlled vertical fracture. The bond strength of the grout 4 to the outside surface of the casing 1 prevents the pressurized fracture fluid from short circuiting along the casing-to-grout interface up to the ground surface 6.
The hydraulic fractures will be initiated and propagated by an oil based fracturing fluid consisting of a gel formed as a reaction product of aluminum phosphate ester and a base, typically sodium aluminate. The reaction of the ester and base creates a solution that yields high viscosity in diesels or moderate to high API gravity hydrocarbons. Gelled hydrocarbons are advantageous in water sensitive oil producing formations to avoid formation damage, that would otherwise be caused by water based fracturing fluids. Alternatively a water based fracturing fluid gel can be used.
The pumping rate of the fracturing fluid and the viscosity of the fracturing fluid needs to be controlled to initiate and propagate the fracture in a controlled manner in weakly cemented sediments such as oil sands. The dilation of the casing and grout imposes a dilation of the formation that generates an unloading zone in the oil sand, and such dilation of the formation reduces the pore pressure in the formation in front of the fracturing tip. The variables of interest are v the velocity of the fracturing fluid in the throat of the fracture, i.e. the fracture propagation rate, w the width of the fracture at its throat, being the casing dilation at fracture initiation, and tt the viscosity of the fracturing fluid at the shear rate in the fracture throat. The Reynolds number is Re=pvw/μ. To ensure a repeatable single orientated hydraulic fracture is formed, the formation needs to be dilated orthogonal to the intended fracture plane, and the fracturing fluid pumping rate needs to be limited so that the Re is less than 1.0 during fracture initiation and less than 2.5 during fracture propagation. Also if the fracturing fluid can flow into the dilatant zone in the formation ahead of the fracture and negate the induce pore pressure from formation dilation then the fracture will not propagate along the intended azimuth. In order to ensure that the fracturing fluid does not negate the pore pressure gradients in front of the fracture tip, its viscosity, at fracturing shear rates within the fracture throat of ˜1-20 sec−1, needs to be greater than 100 centipoise.
The fracture fluid forms a highly permeable hydraulic fracture by placing a proppant in the fracture to create a highly permeable fracture. Such proppants are typically clean sand for large massive hydraulic fracture installations or specialized manufactured particles (generally resin coated sand or ceramic in composition) that are designed also to limit flow back of the proppant from the fracture into the well bore. Due to the high temperatures experienced by the proppant during the combustion process, the proppant material will be specially selected to be temperature compatible with the process and consist of clean strong sands, ceramic beads, HDS and FCC catalysts, or a mixture thereof. The fracture fluid-gel-proppant mixture is injected into the formation and carries the proppant to the extremes of the fracture. Upon propagation of the fracture to the required lateral extent 31 and vertical extent 32, the predetermined fracture thickness may need to be increased by utilizing the process of tip screen out or by re-fracturing the already induced fractures. The tip screen out process involves modifying the proppant loading and/or fracture fluid properties to achieve a proppant bridge at the fracture tip. The fracture fluid is further injected after tip screen out, but rather then extending the fracture laterally or vertically, the injected fluid widens, i.e. thickens, and fills the fracture from the fracture tip back to the well bore.
The combustion zone 10 grows horizontally/radially from the well bore casing 1, i.e. parallel to the propped fractures 30, and becomes larger with time until eventually the bitumen within the lateral 31 and vertical 32 extent of the propped fracture system is completely mobilized or spent by the combustion process. Upon growth of the combustion zone radially to the lateral extent 31 and vertical 32 extent of the propped fractures 30, the influence of the hydraulic fractures on the connection between the various zones falls off dramatically. It is at this stage that the process may be stopped due to the limited lateral reach of the process compared to the height of the combusted pay zone. That is, the injected gas may preferentially short circuit to the flue gas extraction location at the bottom of the well bore rather than flow to the combustion front some large lateral distance away. The optimum configuration of the process, i.e. its maximum lateral reach, will depend on the height of the pay zone, the horizontal and vertical permeabilities of the pay zone, the extent of barren or shale lenses within the pay zone, and the ratio of propped fracture permeability to host oil sand permeability.
Another embodiment of the present invention is shown on
Finally, it will be understood that the preferred embodiment has been disclosed by way of example, and that other modifications may occur to those skilled in the art without departing from the scope and spirit of the appended claims.