US20130025861A1

US20130025861A1 - Methods and Systems for In-Situ Extraction of Bitumen

Info

Publication number: US20130025861A1
Application number: US13/557,842
Authority: US
Inventors: Julian Kift; Mahendra Joshi
Original assignee: Marathon Oil Canada Corp
Current assignee: Shell Canada Energy Ltd; Chevron Canada Ltd
Priority date: 2011-07-26
Filing date: 2012-07-25
Publication date: 2013-01-31
Also published as: CA2783781A1

Abstract

A method for carrying out in-situ bitumen extraction can include a step of forming one or more vertical freeze walls within or around a deposit of bituminous material and establishing a laterally confined deposit of bituminous material; a step of injecting a solvent within the laterally confined deposit of bituminous material; a step of withdrawing a mixture of dissolved bitumen and solvent from within the laterally confined deposit of bituminous material; a step of injecting water within the laterally confined deposit of bituminous material; and a step of withdrawing a mixture of solvent and water from within the laterally confined deposit of bituminous material.

Description

This application claims priority to U.S. Provisional Patent Application No. 61/511,921, filed Jul. 26, 2011, and U.S. Provisional Patent Application No. 61/525,590, filed Aug. 19, 2011. Each application is incorporated herein by reference in its entirety.

BACKGROUND

Deposits of bituminous material can be found throughout the world. including in the United States and Canada. Depending on the depth of the bituminous material, various methods can be used to extract bitumen from bituminous deposits. When the bituminous material is located relatively close to the surface, surface mining can be used to remove the bituminous material from the ground. However, deeper deposits of bituminous material cannot be economically obtained through surface mining. Accordingly, methods involving the use of well bores drilled into the bituminous deposits have been developed.
One such method for obtaining deeper deposits of bituminous material is the Steam Assisted Gravity Drainage (SAGD) method. The SAGD method generally includes injecting steam into the bituminous deposit to warm the bituminous material and make it flowable. Once the viscosity of the bituminous material is sufficiently lowered, the bituminous material can flow downwardly to a horizontal production well that is positioned below the horizontal well used to inject steam into the deposit. While the SAGD method can be relatively effective in extracting bituminous material from bitumen deposits, other methods that do not require the use of water and that provide better bitumen extraction rates are desired.
The use of solvents to extract bitumen from mined oil sands or the like is considered an effective method for separating bitumen from other components of the oil sands material. The solvent is generally used to dissolve the bitumen, after which the bitumen-loaded solvent is separated from the sand, clay, and other components of the oil sands. The injection of solvent into a deposit of oil sands to dissolve the bitumen would appear to be an effective means for extracting bitumen from a bituminous deposit, but several problems are associated with solvent injection into the ground that have prevented the method from being feasible.
One primary problem with injecting solvent into the oil sands deposit is that it has been difficult or impossible to recover a sufficient amount of the injected solvent to make the process economical. For example, in some instances, only 25% of the solvent injected into the deposit can be recovered. The cost of having to replenish large amounts of solvent to continue the process generally makes the process uneconomical.
An additional problem with injecting solvent into the oil sands deposits relates to the environmental concerns of injecting potentially hazardous solvent material into the ground without any effective way of recovering the solvent or preventing the solvent from migrating to a location outside of the oil sands deposit. For example, if the oil sands deposit is near an aquifer, then concerns arise regarding the flow of solvent out of the oils sands deposit and into the aquifer, where potential well water would be contaminated.

SUMMARY

The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.
In some embodiments, a method of in-situ bitumen extraction is disclosed, the method including a step of forming one or more vertical freeze walls within or around a deposit of bituminous material and establishing a laterally confined deposit of bituminous material; a step of injecting a solvent within the laterally confined deposit of bituminous material; a step of withdrawing a mixture of dissolved bitumen and solvent from within the laterally confined deposit of bituminous material; a step of injecting water within the laterally confined deposit of bituminous material; and a step of withdrawing a mixture of solvent and water from within the laterally confined deposit of bituminous material.
In some embodiments, a system for in-situ bitumen extraction is disclosed, the system including a plurality of vertical freeze wall bores formed in a deposit of bituminous material and aligned in a geometric pattern; a refrigerant source in fluid communication with the plurality of vertical freeze wall bores; a plurality of vertical injection bores formed win the deposit of bituminous material and located within the geometric pattern of the plurality of freeze walls; a water source in fluid communication with the plurality of vertical injection bores; a solvent source in fluid communication with the plurality of vertical injection bores; and a plurality of vertical production wells formed in the deposit of bituminous material and located within the geometric pattern of the plurality of freeze walls.
The foregoing and other features and advantages of the present application will become more apparent from the following detailed, description, which proceeds with reference to the accompanying figures. In this regard, it is to be understood that the scope of the invention is to be determined by the claims as issued and not by whether given subject includes any or all features or aspects noted in this Summary or addresses any issues noted in the Background.

BRIEF DESCRIPTION OF THE DRAWING

The preferred and other embodiments are disclosed in association with the accompanying drawings in which:

FIG. 1 is flow chart of embodiments of an in-situ bitumen extraction method described herein;

FIG. 2 is an aerial view of a configuration of well bores formed in a deposit of bituminous material in accordance with some embodiments described herein;

FIG. 3 is an aerial view of a configuration of well bores formed in a deposit of bituminous material, including a two loop refrigerant circulation system according to some embodiments described herein;

FIG. 4 is a cross-sectional view of a bituminous deposit having a vertical injection well and a vertical production well formed therein in accordance with some embodiments described herein;

FIG. 5 is a cross-sectional view of a bituminous deposit having a horizontal injection well and a horizontal production well formed therein in accordance with some embodiments described herein; and

FIG. 6 is a cross-sectional view of a composite injection well according to some embodiments described herein.

DETAILED DESCRIPTION

With reference to FIG. 1, some embodiments of a method of in-situ extraction of bitumen generally include a step 100 of forming one or more vertical freeze walls within or around a deposit of bituminous material and establishing a laterally confined deposit of bituminous material, a step 110 of injecting a solvent within the laterally confined deposit of bituminous material, a step 120 of withdrawing a mixture of dissolved bitumen and solvent from within the laterally confined deposit of bituminous material, a step 130 of injecting water within the laterally confined deposit of bituminous material, and a step 140 of withdrawing a mixture of solvent and water from within the laterally confined deposit of bituminous material. Such embodiments can successfully confine material injected into the bituminous deposit within a prescribed area. Similarly, mixtures of dissolved bitumen and solvent created by injecting material into the bituminous deposit are maintained within the area defined by the freeze walls. Accordingly, contamination of, for example, underground water sources can be mitigated or prevented and recovery of dissolved bitumen can be enhanced by providing barriers around the bitumen deposit being subjected to the bitumen extraction processes.
In step 100, one or more vertical freeze walls are formed within or around a deposit of bituminous material. The vertical freeze walls formed within or around the deposit of bituminous material form a boundary around all or a portion of the deposit of bituminous material and establish a laterally confined deposit of bituminous material. An objective of step 100 is to provide vertical boundaries that will prevent material injected into the deposit of bituminous material and mixture of materials formed within the bituminous deposit from traveling outside of the laterally confined area, thus alleviating environmental concerns of in-situ bitumen extraction and making collection of dissolved bitumen easier.
The deposit of bituminous material in which the vertical freeze walls are formed in step 100 can be any suitable deposit of bituminous material. Suitable deposits of bituminous material include tar sands or oil sands formations, such as those located in the Athabasca region of Canada. In some embodiments, the deposit of bituminous material is a deposit or a portion of a deposit that is located at a depth that is too deep for surface mining but too shallow for traditional in-situ bitumen extraction methods such as steam assisted gravity drainage (SAGD). In some embodiments, the deposit of bituminous material is located at a depth of from between 250 feet and 1,500 feet below the surface.
The one or more freeze walls formed in the deposit of bituminous material can be any type of freeze wall capable of slowing or preventing the movement of fluids through the freeze wall. The freeze walls are typically made from water that is naturally present in the ground in a liquid form. By freezing this water, a barrier of ice is created in the ground. Freeze walls can be formed in deposits of bituminous material because bituminous material (such as oil sands deposits) typically includes a water content.
Any manner of forming the one or more freeze walls known to those of ordinary skill in the art can be used in the embodiments of this method. In an exemplary method, a series of interconnected vertical well bores are constructed within or around the deposit of bituminous material, and a refrigerant is circulated through the vertical well bores until the water in the ground proximate the vertical well bores freezes. The refrigerant can be continuously circulated through the vertical well bores to ensure the water remains frozen and the freeze walls remain intact. Any suitable refrigerant can be used, such as brine or ammonia. In some embodiments, the refrigerant is circulated within the well bores for a period of from 6 weeks to 16 weeks in order to establish the freeze walls.
The arrangement and spacing of the vertical well bores within or around the deposit of bituminous material can be any suitable arrangement for providing freeze walls. In some embodiments, the vertical well bores are spaced close enough together that the water in the area between two adjacent vertical well bores can be frozen to create a vertical freeze wall. In some embodiments, the well bores are spaced apart approximately 2 to 6 meters from one another.
The dimensions of the well bores can vary based on the specific application but are typically selected to ensure that a suitable amount of refrigerant passes through the well bores to freeze the Water in the surrounding ground. In some embodiments, the well bores have a diameter in the range of from 3 to 15 inches. The depth of the well bores can be dependent on a variety of factors. In some embodiments, the depth of the well bores is selected based on the depth of the deposit of bituminous material and/or the depth of any bed rock or other geological formation that might be located beneath the deposit of bituminous material. A bed rock or other geological formation below the deposit of bituminous material can serve as a lower horizontal boundary for the deposit of bituminous material, so it can be beneficial to extend the well bores down to abut a rock formation or the like. Generally speaking, the well bores will have a depth of from 100 to 1,500 feet.
In some embodiments, the vertical well bores are arranged in a closed geometric pattern (when looking down at the vertical well bores from above) to thereby create vertical freeze walls that enclose a deposit of bituminous material. Any suitable closed geometric shape can be used. With reference to FIG. 2, the vertical well bores 200 are arranged in a rectangular shape, with each side of the rectangle including several well bores 200. The well bores 200 are spaced close enough to freeze the area 210 between each well bore 200 and ultimately form a series of vertical freeze walls arranged in a rectangular shape and enclosing a deposit of bituminous material 220.
The well bores used to form the freeze walls are generally constructed by drilling vertical holes into the deposit of bituminous material and providing piping within the drilled holes. The piping can be any suitable type of piping, but is typically of a type that is impermeable to fluids and has good heat transfer for allowing the refrigerant to freeze the water proximate the piping. The piping may also have structural additions to improve heat transfer, such as a plurality of fins extending out from the piping. As noted above, the piping provided in the drilled holes can be interconnected with piping in adjacent drilled holes such that the refrigerant can circulate throughout the plurality of well bores.
In some embodiments, the well bores constructed for establishing freeze walls in the deposit of bituminous material can include a two loop system of interconnected well bores. The two loop system allows for refrigerant to be supplied into the interconnected well bores in a first loop and for refrigerant to be removed from the interconnected well bores in a second loop. With reference to FIG. 3, the two loop system 300 provides a first loop 310 where refrigerant is introduced into the system to flow through the well bores 350 and create and/or maintain freeze walls. The first loop 310 extends around the closed geometric arrangement of well bores 350 and is in fluid communication 315 with each of the well bores 350 such that refrigerant introduced into the first loop 310 can travel to each of the well bores 350 and provide refrigerant into the well bores 350. The two loop system also includes a second loop 320. Like first loop 310, second loop 320 extends around the closed geometric arrangement of well bores 350 and is in fluid communication 325 with each of the well bores 350. Second loop 320 receives refrigerant that has flowed through the well bores 350 and provides a path 360 for the refrigerant to leave the system 300. In some embodiments, the first loop 310 will be in fluid communication at a bottom end of each well bore 350 and the second loop 320 will be in fluid communication with the top end of each well bore 350 such that new refrigerant is introduced into each well bore 350 at the bottom via the first loop 310 and then exits the well bore 350 at the top via the second loop 320. The opposite arrangement can also be used. The two loop system 300 provides a manner for fresh refrigerant to be introduced into the system and for used refrigerant to be taken out of the system, where it can be reconditioned and reinjected back into the well bores 350.
Well bores as described above are not the only mechanism that can be used to create the freeze walls in step 110. In some embodiments, freeze walls can be formed using thermosyphons. Thermosyphons generally include a fully enclosed system having a low temperature fluid (such as liquid CO₂, or ammonia) circulating inside. Natural convection allows the liquid to pick up heat from the bed rock at the bottom of the closed system below and convert to a vapor. The vapor rises to the top of the system, where cooling occurs (such as wind cooling via radiators) to convert the vapor back to liquid. The cooled liquid drains back to the bottom of the system, and the process repeats.
As noted above, bed rock or other geological formations can be used to serve as a lower horizontal barrier of the confined deposit of bituminous material. However, natural harriers may not always be available. Accordingly, in some embodiments, steps can also be taken to form a horizontal freeze wall that will serve as a barrier that vertically confines the deposit of bituminous material. Generally speaking, such a horizontal freeze wall will extend up to or beyond the vertical freeze walls laterally confining the deposit of bituminous material. It can also be preferable to have the horizontal freeze wall abut the bottom end of the vertical freeze walls. In this manner, the material injected into the confined deposit of bituminous material will be prevented from leaving the confined area in both a lateral direction and in a downward direction.
Any suitable manner of forming horizontal freeze walls can be used. In some embodiments, the manner of forming the horizontal freeze wall is similar or identical to the manner in which the vertical freeze walls are used. For example, directional drilling techniques can be used to form a plurality of horizontal well bores through which refrigerant can flow in order to freeze the water in the ground between adjacent horizontal well bores.
In step 100, the vertical freeze walls formed serve to laterally confine a deposit of bituminous material. When bed rock (or other geological formation) or a horizontal freeze wall are used in conjunction with the vertical freeze walls, a “bath tub” configuration is provided that is capable of retaining liquid material within the confined “bath tub” area. Accordingly, when solvents are injected into the confined area of bituminous material, the “bath tub” configuration mitigates or eliminates concerns related to injected solvent drilling out of the area undergoing bitumen extraction and into, for example, underground water sources. Similarly, the “bath tub” configuration helps to keep dissolved bitumen within a confined area, which helps make withdrawing dissolved bitumen from the deposit of bituminous material more effective and efficient.
In step 110, a solvent is injected into the laterally confined deposit of bituminous material. The injected solvent is injected to dissolve bitumen and create a diluted bitumen (or “dilbit”) phase within the deposit. Once dissolved, the mixture of bitumen and solvent can be withdrawn from the deposit to thereby extract bitumen.
The solvent used in step 110 may include a hydrocarbon solvent. Any hydrocarbon solvent or mixture of hydrocarbon solvents that is capable of dissolving bitumen can be used. The hydrocarbon solvent or mixture of hydrocarbon solvents can be economical and relatively easy to handle and store. The hydrocarbon solvent or mixture of hydrocarbon solvents may also be generally compatible with refinery operations.
In some embodiments, the solvent is paraffinic. Any paraffinic solvent suitable for use in dissolving bitumen can be used. In some embodiments, the paraffinic solvent is pentane. Other suitable paraffinic solvents include, but are not limited to, ethane, butane, hexane and heptane
It should be appreciated that the paraffinic solvent need not be 100% paraffinic solvent. Instead, the paraffinic solvent may include a mixture of paraffinic and non-paraffinic compounds. For example, the solvent can include greater than zero to about 100 wt % paraffinic compounds, such as approximately 10 wt % to 100 wt % paraffinic compounds, or approximately 20 wt % to 100 wt % paraffinic compounds.
In some embodiments, a portion or all of the solvent is derived from bitumen recovered by the in-situ bitumen extraction process described herein. The bitumen extracted by the process described herein can be subjected to distillation processing to separate a light end portion of the bitumen that is suitable for use as a solvent in the process described herein. In some embodiments, the light end portion of the recovered bitumen is a fraction of the bitumen having a boiling point temperature in the range of up to 225° C.
Any distillation methods capable of separating fractions of bitumen material known to those of ordinary skill in the art can be used, including the use of atmospheric or vacuum distillation towers. In some embodiments, a make-up solvent, such as any of the above discussed solvents, can be mixed with the light end portion of the bitumen in order to provide a suitable amount of solvent for the process. Obtaining a portion or all of the solvent from the bitumen recovered by the in-situ bitumen extraction process described herein can be useful in that the process can become essentially self-sustainable. Additionally, use of solvent derived from the recovered bitumen can reduce or eliminate environmental concerns associated with using non-indigenous or commercial solvents.
In some embodiments, the solvent can include a mixture of water and peroxide. Suitable peroxides for use as the solvent include those which produce oxygen micro-bubbles upon being mixed with hydrocarbon liquids or solids. Exemplary peroxides suitable for use as solvent include hydrogen peroxide, peroxide salts, and any compounds capable of producing hydrogen peroxide on decomposition in water (e.g., sodium percarbonate). Peroxide can be useful as an extraction solvent at least in part due to its ability to alter surface conditions, such as reducing interfacial tension between hydrocarbon material, water, and inorganic material of the bituminous deposit (including rocks). Reduced interfacial tension can, for example, help release bitumen from within pores in the bituminous deposit. Exothermic heat release associated with the use of the peroxides can also assist in removal of bitumen due to the heat release decreasing the viscosity of the bitumen. The decreased viscosity improves flowability and drainage and ultimately makes the material easier to recover.
The oxygen micro-bubbles formed from the mixing of peroxide and hydrocarbon material can also be useful in stripping hydrocarbon material such as bitumen from inorganic material (such as sand) in the bituminous deposit. It is believed that the oil stripped from the sand will form a film on the oxygen micro-bubbles. The stripped bitumen material can then be recovered in the same manner as other free bitumen in the bituminous deposit, i.e., by injecting additional wash materials (e.g., water) into the bituminous deposit to mix with the oxygen micro-bubbles and carry the stripped bitumen out of the deposit via production wells. The continuous injection of a solvent. including water and peroxide will continue to produce the oxygen micro-bubbles having bitumen films within the deposit of bituminous material and provide additional free bitumen for recovery from subsequent in situ wash cycles.
In some embodiments, the mixture of peroxide and water injected into the deposit as a solvent is from 10 wt % to 60 wt % (including from 3 wt % to 5 wt %) peroxide.
In some embodiments, the desired amount of solvent is injected into the deposit of bituminous material and is then allowed to stay in the deposit of bituminous material for a period of time before production wells are used to remove the mixture of solvent and bitumen. In some embodiments, the solvent is held in the deposit of bituminous material for a period of from 1 day to 1 month.
The amount of solvent injected into the laterally confined deposit of bituminous material can be any suitable amount of solvent needed for dissolving bitumen. In some embodiments, the amount of solvent injected into the deposit of bituminous material will depend on the quality of the deposit of bituminous material (i.e., the bitumen content of the bituminous material). Larger bitumen contents can require larger amounts of solvent to ensure as much bitumen as possible is dissolved into a dilbit phase. The amount of solvent injected into the deposit of bituminous material can also vary on the size of the area being subjected to bitumen extraction. In some embodiments, the amount of solvent injected into the deposit ranges from 0.5:1 to 5:1.
In some embodiments, the desired amount of solvent is injected into the deposit of bituminous material and is then allowed to stay in the deposit of bituminous material for a period of time before production wells are used to remove any dilbit formed. Holding the solvent in the deposit of bituminous material allows for the solvent to migrate to a larger area and have sufficient time to dissolve the bitumen. In some embodiments, the solvent is held in the deposit of bituminous material for a period of from 1 day to 1 month.
Any suitable technique for injecting solvent into the laterally confined deposit of bituminous material can be used in step 110. In some embodiments, one or more injection wells are formed in the laterally confined area, which allows for solvent to flow down and into the bituminous material bound by the freeze walls. Once the solvent is injected into the confined deposit of bituminous material, the solvent works to dissolve the bitumen and create a dilbit phase within the deposit of bituminous material. The injection wells can be paired with production wells capable of drawing the dilbit phase out of the deposit of bituminous material and up to the surface.
The injection wells can be any type of injection wells suitable for injecting solvent into a deposit of bituminous material, and can be constructed by any suitable technique used by those or ordinary skill in the art to construct injection wells. Similarly, production wells used to draw fluid material out of the deposit of bituminous material (such as dilbit) can be any suitable type of production well and can be constructed by any suitable technique for constructing production wells. In some embodiments, the injection wells and productions wells are similar enough that injection wells can be transformed into production wells with minimal modifications.
The dimensions of the production wells and injection wells can be any suitable dimensions needed to carry out the in-situ bitumen extraction. The length of the injection wells and the production wells will generally be equal to or slightly shorter than the depth of the deposit of bituminous material. The diameter of the injection wells and production wells can vary, and in some embodiments, range from 6 to 12 inches.
With reference to FIG. 4, the injection wells formed in the laterally confined area can be vertical injection wells 410 that have a plurality of injection ports 415 located along the height of the injection well 410 for injecting solvent into the deposit of bituminous material 400 at various depths. The injection ports 415 are capable of injecting solvent into the deposit of bituminous material 400, and in some cases will generally inject solvent into the bituminous deposit 400 at a direction perpendicular to the vertical injection well 410. The vertical injection wells 410 can be paired with vertical production wells 430 that are spaced apart a distance from the injection wells 410. In this manner, the vertical production wells can collect the mixture of solvent and dissolved bitumen produced upon injecting solvent into the deposit of bituminous material 400.
With reference to FIG. 5, the injection wells formed in the laterally confined area can also be a series of horizontal injection wells 510. The horizontal injection wells 510 generally have an L-shaped configuration that includes a vertical portion 510 a and a horizontal portion 510 b. Solvent travels down into the deposit of bituminous material 500 via the vertical portion 510 a and is injected into the deposit of bituminous material 500 via the horizontal portion 510 b. In some embodiments, a plurality of injection ports 515 are located along the length of the horizontal portion 510 b of the horizontal injection well 510 such that solvent is injected into the deposit of bituminous material 500 at various locations along the length of the horizontal portion 510 b of the horizontal injection well 510. In some embodiments, the injection ports 515 are oriented to inject solvent upwardly into the bituminous deposit 500. Horizontal production wells 530 can also be included to withdraw the dilbit formed upon the injection of solvent into the deposit of bituminous material 500 via the horizontal injection well 510. In some embodiments, the horizontal production wells 530 have a vertical portion 530 a and horizontal portion 530 b. The horizontal portion 530 b can be located parallel to and below the horizontal portion 510 b of the horizontal injection well 510. The dilbit formed above the horizontal portion 510 b flows downwardly where it collected in the horizontal portion 530 b of the horizontal production well 530. The collected dilbit is then transported up the vertical portion 530 a of the horizontal production well 530 to the surface.
The injection wells and production wells are formed within the area of bituminous material confined by the freeze walls established in step 100. The arrangement of the plurality of injection wells and production wells is generally not limited and can include any arrangement that will provide for multiple solvent injection locations and multiple dilbit production locations. Generally speaking, the injection wells and production wells are located close enough to one another that the production wells can receive the dilbit created by injecting solvent into the deposit of bituminous material via the injection wells. In some embodiments, a production well is located from 50 to 100 feet from an injection well.
In some embodiments, more injection wells than production wells will be provided within the deposit of bituminous material confined by the freeze walls, such as from 2 to 6 injection wells per production well. The arrangement of injection wells and production wells can include various geometric shapes and patterns. One exemplary arrangement involves a hexagonal matrix of production wells surrounding an injection well located in the middle of the hexagon.
In some embodiments where vertical injection wells and production wells are used, the arrangement of injection wells and production wells can be a straight line arrangement of injection wells and a straight line arrangement of production wells parallel to the injection wells and spaced apart a suitable distance. The straight lines of injection wells and production wells can be located relatively close to one of the freeze walls making up the boundary of the confined deposit of bituminous material, and can also be oriented in parallel to that freeze wall. Thus, for example, in a rectangular shaped confined deposit of bituminous material, a straight line of injection wells can be located next to and in parallel with a freeze wall, while a straight line of production wells can be located next to and in parallel with the straight line of injection wells, and further away from the freeze wall then the injection wells. The injection ports on the injection wells can be pointed in a direction towards the production wells (i.e., away from the freeze wall) to extract bitumen from the area closest to the freeze wall. Once this area has been sufficiently treated, the injection wells can be decommissioned, the production wells can be converted to injection wells (including positioning injection ports in a direction away from the freeze wall), and a new straight line of production wells can be formed further into the confined area and in parallel with the straight line of injection wells. The space between the new injection wells and the new production wells can be treated for a sufficient period of time, after which the above described process of converting production wells into injection wells and forming new production wells is repeated. This cycle can be repeated until the entire length of the rectangular confined area is subjected to bitumen extraction. Such a system can be referred to as a “line drive” process of extracting bitumen.
In some embodiments, the injection of solvent is preceded and/or followed by an agitation step. Agitation prior to solvent injection can help top open the formation such that solvent can better penetrate the deposit of bituminous material. Agitation after solvent injection can promote mixing between the solvent and the bituminous material. Any suitable manner of causing agitation within the bituminous deposit can be used. In some embodiments, the agitation step includes a gas injection or gas pulsation step. In both gas injection and gas pulsation, the introduction of the gas into the deposit leads to improved mixing between the solvent and the bituminous material, which in turn leads to more bitumen dissolving in the solvent. When used prior to solvent injection, both the gas injection and gas pulsation can lead to opening of passageways within the deposit to allow for improved penetration of the solvent in the bituminous material.
The gas injection or gas pulsation step can be carried out using the injection wells described in greater detail above. For example, in gas injection, the gas is injected into the deposit via the same injection wells used to inject the solvent into the bituminous deposit. Any gas suitable for use in agitating the solvent in the bituminous deposit can be used. In some embodiments, the gas is unreactive to the materials in the bituminous deposit such that the injection of the gas leads to primarily the mechanical agitation of the solvent and not to the reaction between the gas and the solvent or materials in the bituminous deposit. Exemplary passes that can be used include but are not limited to natural gas, steam, nitrogen, air, and carbon dioxide.
In some embodiments, the gas is preferably injected into the bituminous deposit at relatively high volumes to ensure agitation. In some embodiments, the gas is injected into the bituminous deposit at a rate of 0.20 to 1.45 BCFD depending on the geologic conditions and oil production rate, or, in some embodiments, from 130 BOPD to 600 BOPD per MMCFD of gas injected. When gas pulsation is used, the frequency of the gas pulsation can be between 2 and 10 Hz. The injection of solvent into the bituminous deposit can be carried out in several cycles. In some embodiments, the agitation step is carried out after every cycle of injecting solvent into the bituminous deposit.
In step 120, a mixture of solvent and dissolved bitumen produced from injecting solvent into the deposit of bituminous material in step 110 is withdrawn from within the laterally confined deposit of bituminous material. Any suitable manner of withdrawing the dilbit from within the deposit of bituminous material can be used to carry out step 120. As discussed in greater detail above, in some embodiments the dilbit is withdrawn from within the deposit of bituminous material using production wells that are located proximate the injection wells. Production wells can be operated for extended periods of time, such as up to 9 months, to ensure that the vast majority of the dilbit produced in step 110 is withdrawn from the deposit. In some embodiments, the production wells are operated until 90% of the dilbit produced in step 110 is removed. Step 120 is usually performed after step 110 is completed, but is some embodiments, step 120 can be commenced prior to step 110 being completed.
The fluid material withdrawn from within the deposit of bituminous material in step 120 generally includes solvent and dissolved bitumen. Other materials that can be present in the fluid material include water, and organic and inorganic solids. Generally speaking, the fluid material withdrawn in step 120 includes from 40 to 75% solvent, from 25 to 60% bitumen, from 0 to 5% water, and less than 2% other materials. The rate of withdrawing the fluid material is generally not limited, and in some embodiments, the fluid is withdrawn from within the deposit of bituminous material via the production wells at a rate of from about 5,000 to 25,000 bbls/day.
Once the mixture of dissolved bitumen and solvent is brought to the surface in step 120, various separation steps can take place to separate the bitumen, solvent, and water. Any suitable separation unit or series of separation units can be used to separate the bitumen, solvent, and water, such as distillation towers. Once separated, the bitumen can be further processed, such as by being subjected to upgrading to produce useful lighter hydrocarbons. The recovered solvent can be reused in the bitumen extraction process, such as by reusing the solvent in step 110.
Steps 110 and 120 described above can be repeated several. Performing multiple cycles of injecting solvent and withdrawing a mixture of solvent and bitumen can help to improve the overall amount of bitumen recovered using the methods described herein.
In some embodiments, step 120 will not be capable of withdrawing all of the solvent injected into the deposit of bituminous material in step 110. For example, from 10 to 50% of the solvent injected into the deposit of bituminous material may remain in the deposit after the completion of step 120. For environmental and economical reasons, additional steps should be taken to attempt to remove solvent from the deposit of bituminous material.
In steps 130 and 140, water is injected into the bituminous material to displace the residual solvent towards the production wells, where the solvent and water may then be withdrawn from the laterally confined deposit of bituminous material. The water injected into the deposit can be in the form of steam or as liquid water.
The manner of injecting water is similar or identical to the manner in which the solvent is injected into the deposit of bituminous material. The same injection wells used for injecting solvent can be used to inject water. The amount of water injected into the laterally confined deposit of bituminous material can be any suitable amount of water needed for removing the solvent. In some embodiments, the amount of water injected into the deposit of bituminous material will depend on the amount of residual solvent remaining in the deposit. The amount of water injected into the deposit of bituminous material can also vary based on the size of the area being subjected to bitumen extraction. In some embodiments, the amount of water injected into the deposit ranges from 3:1 to 10:1 on a water:bitumen ratio.
In some embodiments, the desired amount of water is injected into the deposit of bituminous material and is then allowed to stay in the deposit of bituminous material for a period of time before production wells are used to remove the mixture of water and solvent. In some embodiments, the water is held in the deposit of bituminous material for a period of from 1 day to 1 month.
The manner of withdrawing a mixture of water and solvent from within the deposit if bituminous material is similar or identical to the manner in which the mixture of solvent and dissolved bitumen is withdrawn from the deposit of bituminous material. The same production wells used to withdraw dilbit and solvent from the deposit can be used to withdraw a mixture of water and solvent from the deposit.
The fluid material withdrawn from within the deposit of bituminous material in step 140 generally includes water and solvent. Other materials that can be present in the fluid material include water, bitumen, and organic and inorganic solids. Generally speaking, the fluid material withdrawn in step 140 includes from 40 to 90% water, from 60 to 95%, from 2 to 10% bitumen, and less than 2% other materials. The constituency of the fluid withdrawn in step 140 can change over time as the injected water reaches the well head. The rate of withdrawing the fluid material is generally not limited, and in some embodiments, the fluid is withdrawn from within the deposit of bituminous material via the production wells at a rate of from about 500 to 2,000 bbls/day per well head (by gravity drainage).
Once the mixture of water and solvent is brought to the surface in step 140, various separation steps can take place to separate the water from the solvent. Any suitable separation unit or series of separation units can be used to separate the water from the solvent. Once separated, the solvent can be reused in the extraction process.
Any water left in the deposit of bituminous material can remain in the deposit, as the water is generally not considered an environmental concern. In some embodiments, 5 to 50% of the water injected into the deposit in step 130 will remain in the deposit.
The above described method can be performed one or more times on a confined deposit of bituminous material. Similarly, any one step or pairs of steps (e.g. step 110 and 120) can be repeated multiple times before moving on to the next step of the method. Repeating certain steps or pairs of steps may help to increase the bitumen extraction efficiency.
Once a confined deposit of bituminous material has been subjected to the above-described in-situ bitumen extraction process, the same process can be carried out on adjacent deposits of bituminous material. In some embodiments, one or more freeze walls established for carrying out the in-situ bitumen extraction process on a first deposit of bituminous material can be re-used when confining an adjoining deposit of bituminous material. For example, when a confined deposit of bituminous material has a square shape, three of the freeze walls can be decommissioned while a fourth wall can be used as the first wall of a new confined deposit of bituminous material located next to the first deposit.
Additional pretreatment steps can also be carried out prior to or during the method described above. For example, any of a variety of fracturing steps or method to increase porosity can be carried out prior to any of the solvent injection steps in an attempt to create more passageways for solvent and other materials to pass through.
Additionally, hot water or sloppy steam can be injected into the deposit of bituminous material prior to or during the injection of the solvent in an effort to soften the oil sands and the bitumen component or create channels for the subsequently injected solvent to pass through. In some embodiments, the injection wells can be adapted to allow for the simultaneous injection of water and solvent through the same injection wells. The injection wells can be “composite” injection wells that include multiple passage ways within the same general piping. With reference to FIG. 6, a composite injection well 600 can include a co-annular inner passage 610 and a co-annular outer passage 620, with the inner passage 610 having injection ports 615 that extend through the outer passage to the exterior of the injection well 600. In this manner, steam or water can travel down the inner passage 610 of the injection well 600 and be injected into the deposit at the same time that solvent passes down the outer passage 620 of the injection well 600 and is injected into the deposit through standard injection ports 625 in fluid communication with the outer passage 620.
The majority of the system used to carry out the in-situ bitumen extraction methods described herein is discussed above, including the vertical freeze walls, the optional horizontal freeze wall, the plurality of injection bores, and the plurality of production wells. Also discussed above are the separation units that can be provided, including the separator for separating dilbit into bitumen and solvent, a separator for separating a mixture of solvent and water, and distillation units for producing solvent from recovered bitumen.
Additional components that can be part of the system include a refrigerant source, a solvent source, and a water source. Each source can include any type of supply vessel that is capable of supplying the desired fluid needed for the method. The supply vessels may also include recycle inputs for receiving fluid material that is recovered from the process and sent back into the system. The refrigerant source is in fluid communication with the interconnected well bores used to establish the freeze walls and, when a two loop system as described above is used, can include a recycle input for receiving refrigerant that has passed through the two loop system back into the refrigerant source for storage and further use. The solvent and water sources can be in fluid communication with the outer and inner passage of a composite injection well, respectively.
Several advantages can be realized by using the methods and systems described herein. Specifically, the use of a single solvent where the solvent is paraffinic can provide numerous advantages over other solvent bitumen extraction techniques, including those techniques using more than one type of solvent. Firstly, the use of paraffinic solvent can increase the throughput of the method by a factor of 2 or greater. Improved throughput can be realized due to the use of the lighter paraffinic solvent that is capable of solvating the bitumen material faster than heavier solvents and results in reduced viscosity dilbit, which can be recovered from the solids easier. The paraffinic solvent can also advantageously precipitate asphaltenes, further eliminating the heavy viscosity component. In some instances, the paraffinic solvent causes the asphaltenes to precipitate into the solids, and more specifically onto the finer clays. The precipitated asphaltenes are captured by finer clays while the dilbit passes through and out of the bitumen material for successful bitumen extraction. The precipitation of asphaltene can also be beneficial by allowing for the upgrading of bitumen extracted in the dilbit using conventional upgrading processing equipment (i.e., specialized upgrading equipment capable of handling asphaltenes as well as bitumen is not required).
The systems and methods that use a single solvent instead of two different types of solvents can also be advantageous from a capital expenditure (CAPEX) perspective. Single solvent systems typically only require a single distillation unit for the separation and recovery of the single solvent. Single solvent systems, including single solvent systems using a paraffinic solvent, also tend to require smaller distillation units as compared to when heavier solvents are used. Operating expenditures (OPEX) are also reduced when using a single solvent system versus a two solvent system. For example, lower heating duty is required for removing a single, relatively light, solvent from the tailings. Finally, environmental advantages can result from the single solvent system. Carbon dioxide emissions and fugitive solvent loses can be reduced when a single solvent system is used in lieu of a system that uses two different types of solvents.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made without departing from the spirit and scope of the invention.
A presently preferred embodiment of the present invention and many of its improvements have been described with a degree of particularity. It should be understood that this description has been made by way of example, and that the invention is defined by the scope of the following claims.

Claims

1. A method of in-situ bitumen extraction comprising:

forming one or more vertical freeze walls within or around a deposit of bituminous material and establishing a laterally confined deposit of bituminous material;

injecting a solvent within the laterally confined deposit of bituminous material; and

withdrawing a mixture of dissolved bitumen and solvent from within the laterally confined deposit of bituminous material.

2. The method as recited in claim 1, further comprising:

injecting water within the laterally confined deposit of bituminous material; and

withdrawing a mixture of solvent and water from within the laterally confined deposit of bituminous material.

3. The method as recited in claim 1, wherein the solvent comprises a paraffinic solvent.

4. The method as recited in claim 1, wherein the solvent comprises pentante.

5. The method as recited in claim 1, wherein the method further comprises forming one or more horizontal freeze walls within the deposit of bituminous material and vertically confining the laterally confined deposit of bituminous material.

6. The method as recited in claim 1, wherein the one or more vertical freeze walls abut an impervious geological material located below the deposit of bituminous material.

7. The method as recited in claim 1, wherein forming one or more vertical freeze walls within or around the deposit of bituminous material comprises:

drilling a plurality of spaced apart vertical bores within or around the deposit of bituminous material; and

circulating a refrigerant through the vertical bores.

8. The method as recited in claim 1, wherein injecting the solvent within the laterally confined deposit of bituminous material comprises:

drilling one or more vertical injection bores within the laterally confined deposit of bituminous material; and

injecting the solvent within the laterally confined deposit of bituminous material through the one or more vertical injection bores.

9. The method as recited in claim 8, wherein withdrawing the mixture of dissolved bitumen and solvent from within the laterally confined deposit of bituminous material comprises:

drilling one or more vertical production bores within the laterally confined deposit of bituminous material; and

withdrawing the mixture of dissolved bitumen and solvent from the laterally confined deposit of bituminous material through the one or more vertical production bores.

10. The method as recited in claim 9, wherein:

the one or more vertical injection bores are arranged in a straight line;

the one or more vertical production bores are arranged in a straight line parallel to and spaced a distance away from the straight line of vertical injection bores; and

the solvent is injected into the laterally confined deposit of bituminous material in a direction towards the straight line of one or more vertical production bores.

11. The method as recited in claim 1, further comprising:

separating the mixture of dissolved bitumen and solvent withdrawn from within the laterally confined deposit of bituminous material into a bitumen stream and a solvent stream; and

reusing the solvent stream in the step of injecting solvent within the laterally confined deposit of bituminous material.

12. The method as recited in claim 1, wherein the solvent comprises a mixture of water and a peroxide.

13. The method as recited in claim 12, wherein the mixture comprises from 10 wt % to 60 wt % peroxide.

14. The method as recited in claim 12, wherein the peroxide is hydrogen peroxide.

15. The method as recited in claim 1, further comprising

agitating the deposit of bituminous material prior to injecting the solvent within the laterally confined deposit of bituminous material.

16. A system for in-situ bitumen extraction comprising:

a plurality of vertical freeze wall bores formed in a deposit of bituminous material and aligned in a geometric pattern;

a refrigerant source in fluid communication with the plurality of vertical freeze wall bores;

a plurality of vertical injection bores formed win the deposit of bituminous material and located within the geometric pattern of the plurality of freeze walls;

a solvent source in fluid communication with the plurality of vertical injection bores; and

a plurality of vertical production wells formed in the deposit of bituminous material and located within the geometric pattern of the plurality of freeze walls.

17. The system as recited in claim 16, further comprising:

a bitumen-solvent separator in fluid communication with the plurality of vertical production wells.

18. The system as recited in claim 16, wherein the plurality of vertical freeze wall bores are in fluid communication with one another.

19. The system as recited in claim 16, further comprising a water source in fluid communication with the plurality of vertical injection bores.

20. The system as recited in claim 19, wherein the plurality of vertical injection bores each comprises:

an inner passage;

a co-annular outer passage separated from the inner passage by a partition;

a plurality of inner passage injection ports extending from the inner passage to the exterior of the vertical injection bore; and

a plurality of outer passage injection ports extending to the exterior of the vertical injection bore.

21. The system as recited in claim 20, wherein the inner passage is in fluid communication with only the water source and the outer passage is in fluid communication with only the solvent source.