WO2018165747A1

WO2018165747A1 - Coal bed methane extraction and carbon capture

Info

Publication number: WO2018165747A1
Application number: PCT/CA2018/050293
Authority: WO
Inventors: Mackenzie Millar; Jose Lourenco
Original assignee: 1304342 Alberta Ltd.; 1304338 Alberta Ltd.
Priority date: 2017-03-16
Filing date: 2018-03-12
Publication date: 2018-09-20

Abstract

A method to establish an adsorption/desorption process by injecting carbon dioxide into a coal bed involves injecting a carbon dioxide stream in a coal bed such that it is adsorbed by the coal bed and such that methane stored in the coal bed is desorbed and displaced. The displaced methane is extracted and processed for distribution.

Description

COAL BED METHANE EXTRACTION AND CARBON CAPTURE

FIELD [0001] This relates to a process that displaces and extracts methane from a coal bed by storing carbon dioxide delivered by compression such as from a pipeline such as the Alberta Carbon Trunk Line. The pipeline delivered carbon dioxide stream is injected into coal beds for sequestration and storage BACKGROUND

[0002] The generation of electricity in North America and in most parts of the world is primarily provided by the combustion of coal, a cheap and abundant fossil fuel. Coal is typically mined and transported to a power plant where it is processed before combustion. The coal is combusted in a furnace to generate heat for the production of high pressure dry steam. The produced dry and superheated steam drives a steam turbine generator to produce electricity. Coal is a high carbon content fuel, therefore a large emitter of carbon dioxide as well as NOx and SOx, greenhouse gases (GHG). Rapidly increasing concentrations of GHG's in the atmosphere and emerging evidence of global warming is now triggering international action to reduce GHG's emissions into the atmosphere. The combustion of coal to generate electricity is identified as a main contributor of GHG emissions, resulting in industry action being taken to reduce GHG emissions from the use of coal combustion. Recently, the government of Alberta has mandated that coal usage for power generation be terminated by the year 2030. [0003] Coal bed methane extraction provides an alternative method to recover energy from coal in a safe, efficient and environmentally acceptable manner. Coal bed methane extraction is typically employed in un-mineable coal beds. Conventional coal bed methane recovery methods are based on reservoir pressure reduction, where methane is desorbed from the coal surface by reducing the reservoir pressure. [0004] In the current standard mode of coal bed methane extraction, wells are drilled into a coal bed. The methane is extracted by desorption from coal surfaces where the reservoir pressure is first decreased by dewatering. The decrease in pressure allows the methane to desorb from the coal and flow as a gas to the well. The gas is processed at surface and compressed in a natural gas pipeline network for delivery to markets. More recently, to enhance coal bed methane extraction new methods have been developed. As described by U.S. patent no. 5,085,274 (Puri et al.) entitled "Recovery of methane from solid carbonaceous subterranean of formations", U.S. patent no. 5,332,036 (Shirley et al.) entitled "Method of recovery of natural gases from underground coal formations" and U.S. patent no. 5,014,785 (Puri et al.) entitled "Methane production from carbonaceous subterranean formations", the use of carbon dioxide diluted with inert gases enhances coal bed methane recoveries by reducing the partial pressure of methane and injecting other gases such as nitrogen, resulted in a substantial increment in production.

SUMMARY

[0005] There is provided a method and system for safely storing carbon dioxide, and for extracting stored methane and other volatile hydrocarbons in a coal bed. The method injects carbon dioxide into a coal bed in a condition to be sequestered and stored, and to extract stored methane in the coal bed. The conditions under which the carbon dioxide is injected will depend on one or more of: coal bed depth relative to pressure and methane extraction relative to temperature. The extracted methane and other volatile hydrocarbons may then be recovered, processed and routed to natural gas pipeline distribution systems.

[0006] As coal has a stronger affinity for carbon dioxide, it establishes an adsorption/desorption process where carbon dioxide displaces and frees the methane from the coal bed to be recovered, processed and distributed to natural gas pipeline distribution systems. The objective of the method and system is to permit carbon dioxide to be sequestered and stored. In one example, the proposed Alberta Carbon Trunk Pipeline may be used to transport carbon dioxide recovered due to local carbon-generating activities. The carbon dioxide may then be injected into coal beds to establish an adsorption/desorption process where carbon dioxide is stored in the coal bed by displacing methane and other volatile hydrocarbons, which may then be recovered and processed, such as for pipeline transport and distribution.

[0007] In one example, carbon dioxide recovered and delivered by pipeline is injected at desired pressure and temperature conditions into a coal bed for carbon dioxide adsorption and methane desorption, such that carbon dioxide is stored, and methane is extracted from the coal bed.

[0008] In one aspect, the process comprises the following steps:

(a) injecting carbon dioxide at optimum pressure and temperature for adsorption into a coal bed;

(b) displacing and producing methane by desorption of stored methane and other volatile hydrocarbons at optimum pressure and temperature in the coal bed; and

(c) processing the coal bed extracted hydrocarbon gas.

[0009] In another aspect, there is provided a method of storing carbon dioxide in a coal bed by absorption to coal in the coal bed, and to desorb, displace and extract methane stored in the coal bed, the method comprising the steps of:

providing a supply of carbon dioxide from a source of carbon dioxide to a coal bed site for storage the carbon dioxide having a pressure and temperature that falls within a predetermined pressure and temperature range;

delivering the pressure and temperature conditioned carbon dioxide stream to the coal bed by an injection well;

extracting methane desorbed from the coal bed; and

delivering the extracted methane to a gas processing unit. [0010] In another aspect, there is provided a method of carbon capture and methane production, comprising the steps of:

providing a source of carbon dioxide gas having a pressure and temperature that falls within a predetermined pressure and temperature range;

injecting the conditioned carbon dioxide gas into a coal bed such that the carbon dioxide gas adsorbs to coal in the coal bed and desorbs methane from the coal; and

capturing the desorbed methane for transport or processing.

[0011] According to other aspects, the method may comprise one or more of the following features: the methane may be extracted from the coal bed by a production well, and at least one of the injection well and the production well comprises slots; the source of carbon dioxide may be a pipeline that transports carbon dioxide under pressure; the source of carbon dioxide may comprise at least 50% carbon dioxide gas, at least 80% carbon dioxide gas, or at least 95% carbon dioxide gas; the pressure and temperature of the carbon dioxide may be selected to be optimized for adsorption to coal in the coal bed; the extracted methane may be extracted and processed for distribution; and providing the supply of carbon dioxide may comprise compressing the carbon dioxide gas in a compressor; carbon dioxide may be injected after production of methane has ceased to store additional carbon dioxide in the coal bed. [0012] The process described herein may be used to store carbon dioxide and extract stored methane in a coal bed. The extracted methane is processed and distributed as a fossil fuel derived from coal. The process stores carbon dioxide and extracts stored methane in coal beds, thus contributing to the production of clean abundant energy from a very concentrated carbon fuel. The process is considered to be clean since coal can store two or more moles of carbon dioxide for every mole of methane displaced. Coal can store up to 10 moles of carbon dioxide per mole of methane stored in coal, thus making it a carbon negative process.

[0013] As will hereinafter be further described, carbon dioxide is first delivered by a pipeline, such as the Alberta Carbon Trunk Line, and injected for adsorption into a coal bed for storage and desorption of stored methane from the coal bed. The desorbed and extracted coal bed methane may then be processed for distribution. The process may be used to safely store carbon dioxide in a coal bed by adsorption and also, by desorption, extract and process the coal bed hydrocarbons for distribution as a result of the carbon dioxide being injected.

BRIEF DESCRIPTION OF THE DRAWING

[0014] These and other features will become more apparent from the following description in which reference is made to the appended drawing, the drawing is for the purpose of illustration only and is not intended to in any way limit the scope of the invention to the particular embodiment or embodiments shown, wherein:

FIG. 1 is a schematic diagram of a pipeline delivered carbon dioxide stream injected into a coal bed for storage by adsorption and methane extraction by desorption. It includes a gas processing unit to treat the extracted coal bed hydrocarbons for distribution.

DETAILED DESCRIPTION OF THE PREFERRED EMB ODF ENT

[0015] The method described may be used to safely store carbon dioxide that is produced, recovered and transported by pipeline in such as may occur in a carbon capture process by adsorbing carbon dioxide into a coal bed. It will be understood that a coal bed may also be referred to as a coal seam, or other deposit of coal that is accessible from surface, such as by a well drilled from surface. Furthermore, the hydrocarbons that may be produced form a coal bed are referred to herein as methane or coal bed methane, although the methane may also include a relatively small proportion of other, heavier hydrocarbons or other gases as is known in the art with respect to coalbed methane gas. In addition, the source of carbon dioxide is preferably a source of captured carbon dioxide, such as may be obtained from a power plant or other industrial activity. As it is primarily carbon dioxide that adsorbs to the coal and causes the methane to desorb, the source of carbon dioxide is preferably at least 90% carbon dioxide gas, and preferably more, such as 95% or more. The actual composition of the source of carbon dioxide gas may vary depending on the source and any applicable regulations, but may also include other gases, such as oxygen, nitrogen, nitrogen-based gases, other carbon-based gases, etc. [0016] Coal can store two or more moles of carbon dioxide per mole of methane stored in coal. When carbon dioxide is adsorbed in coal, the methane stored in coal is desorbed and freed to be extracted and processed. The disclosed method provides an alternative solution to safely store carbon dioxide. For example, the Alberta Carbon Trunk Line to be commissioned in 2017 was built to collect and transport carbon dioxide produced in Alberta at major industrial sites for storage in deep saline aquifers and/or for use in EOR (enhanced oil recovery) operations. The proposed method offers a different approach in a unique and innovative variant to store carbon dioxide that may become available from resources such as the Alberta Carbon Trunk Line and other sources of carbon dioxide. The system here described takes advantage of safely storing carbon dioxide in coal beds by an adsorption/desorption process that also produces methane stored in the same coal beds.

[0017] In 2016, Shell Canada commissioned Quest, a carbon capture and storage process where the carbon dioxide captured from its oil upgrading and refinery processes is compressed and stored in underground caverns. The Alberta Carbon Trunk Line is under construction and due to be commissioned in 2017. The objective of this line is to transport and distribute recovered carbon dioxide from Alberta facilities to store in deep saline aquifers and/or EOR (Enhanced Oil Recovery) at oil wells. The use of carbon dioxide to enhance oil production is well documented and in operation since 2000 with success at Estevan, Saskatchewan. However, the use of carbon dioxide in EOR results in the continuous recycling and recompression of carbon dioxide into the oil formation. Historical records at Estevan showed that only 30 to 40% of the carbon dioxide injected is stored under pressure in the oil reservoir, requiring a continuous recycling compression step.

[0018] Coal beds have an affinity to absorb carbon dioxide and hence are an ideal storage resource. Furthermore, the injection of carbon dioxide into a coal bed can be used to establish an adsorption/desorption process that frees the methane and other volatile hydrocarbons stored in coal to be recovered, processed and distributed. [0019] The method described herein provides a process that uses carbon dioxide that may be produced, recovered and transported for storage in coal fields and to extract stored methane and other volatile hydrocarbons from the coal beds. Carbon dioxide recovered from industrial activities and transported by, for example a pipeline such as the Alberta Carbon Trunk Line, may be injected into coal beds to enhance coal bed methane extraction while storing the carbon dioxide, unlike the pipeline proposed practice of compressing it into saline aquifers or oil wells. Coal bed methane extraction works by replacing sorbed methane molecules with more strongly sorbed carbon dioxide molecules. The process is beneficial as coal selectivity of carbon dioxide to methane is greater than 2 to 1, coal adsorbs and stores 2 molecules or more of carbon dioxide for every molecule of methane displaced, and the carbon dioxide remains adsorbed in the coal and displaces the methane. The extracted methane may then be captured, processed and routed to natural gas pipeline distribution systems. The proposed method meets a need to first store carbon dioxide safely and secondly to recover coal stored methane gas and volatile hydrocarbons from a coal bed economically. [0020] The composition of the carbon dioxide gas may vary, depending on the sources available. However, it will be understood that the higher the concentration of carbon dioxide that is injected, the higher the concentration of methane will be produced, as the produced methane will be less diluted. In many cases, sources of carbon dioxide produced from industrial or commercial processes will be 95% (by weight) or more, depending on the equipment used to separate carbon dioxide, and it is these sources that are preferably used in the process. However, the process may also be used with a source of carbon dioxide that has a concentration of carbon dioxide greater than that present in atmospheric air, such as 50%, and more preferably greater than 80%. [0021] The present method provides an alternative to store large volumes of recovered carbon dioxide safely, such as may be delivered by Alberta Carbon Trunk Line or other sources of carbon dioxide, and simultaneously extract methane from the coal beds for distribution. The description of application of the method herein should, therefore, be considered as an example.

[0022] FIG. 1 depicts a preferred method of storing carbon dioxide produced, recovered and transported by a resource such as the Alberta Carbon Trunk Line from industrial plants in Alberta. [0023] Carbon dioxide is transported and distributed by Alberta Carbon Trunk Line through stream 1 into a coal bed site and compressed, if required, by compressor 2 to meet optimum pressure conditions. If the carbon dioxide is at a suitable pressure, the stream of carbon dioxide may bypass the compressor via an optional bypass valve 14. In some cases, if it is known that the carbon dioxide will be at a suitable pressure and temperature, one or both of the compressor 2 and heat exchanger 4 may be omitted. The pressurized carbon dioxide stream 3 flows through a fin fan heat exchanger 4 to meet coal bed optimum temperature conditions for adsorption of carbon dioxide and desorption of methane stored in coal bed. The optimal pressure and temperature conditions may be determined based on coal bed depth and methane production flow. By varying the temperature and pressure conditions, a range of acceptable conditions may be defined. This range may vary from well to well. For example, as the depth of the well increases, the pressure the carbon dioxide will be increased, as there must be sufficient pressure in order to be able to inject the carbon dioxide into the well.

[0024] The pressure and temperature controlled carbon dioxide stream 5 is injected into well 6 and distributed through slots 7 into the coal bed 8. The injected pressure and temperature controlled carbon dioxide stream is adsorbed in coal bed 8 and the desorbed methane and other volatile hydrocarbon gases are displaced across the coal bed 8 and through slots 9 into production well 10. The extracted methane is routed through production well 10 and through stream 11 into gas processing unit 12. The processed gas exits gas processing unit 12 through stream 13 to gas pipeline for distribution. Note that, while FIG. 1 depicts a vertical well, the actual shape or configuration of the well that is drilled into coal bed 8 may vary. For example, the well may be formed using directional drilling to have a horizontal or angled section, multiple wells may be drilled into the same formation, etc. In addition, while the well 6 is shown with a liner having slots 7, the liner may have different openings, or a different way of distributing carbon dioxide within the coal bed may be used.

[0025] As production proceeds and the methane in the coal bed is depleted, the flow of methane from the well will slow. However, because coal is able to store stores 2 or more mols of carbon dioxide for every mol of methane, injection of carbon dioxide may continue even after the flow of methane has stopped or slowed to negligible levels in order to use the coal bed for as carbon storage. As such, carbon dioxide may be injected until a sufficient flow of carbon dioxide is produced from production well 10 to show that the coal bed is sufficiently saturated. [0026] As noted, prior to injecting the carbon dioxide into the coal bed 8, it is conditioned through compression and temperature control. This is preferably done to achieve an optimal amount of carbon dioxide adsorption, which will in turn enhance methane production. The optimal temperature and pressure conditions may be selected by analysing the coal formation, or through experimentation. Optimization may also include an analysis of the energy required to condition the carbon dioxide and any effect the compression and temperature control has on downstream transport or processing.

[0027] In one example, the process may be implemented by: first, storing carbon dioxide delivered from the Alberta Carbon Trunk Line by adsorption in a coal bed; second, desorbing and extracting stored methane from the coal bed; and third, processing and distributing the extracted coal bed methane. This process allows an efficient use of an abundant supply of recovered carbon dioxide for safe storage and simultaneous extraction of stored methane from the coal bed by establishing an adsorption/desorption process where carbon dioxide displaces and frees methane stored in a coal bed to flow into a production well. This process provides for coal beds to be a safe storage resource for carbon dioxide and to recover a clean source of energy from coal in the form of methane.

[0028] In this patent document, the word "comprising" is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article "a" does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.

[0029] The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given a broad purposive interpretation consistent with the description as a whole.

Claims

What is claimed is:

1. A method of storing carbon dioxide in a coal bed by absorption to coal in the coal bed, and to desorb, displace and extract methane stored in the coal bed, the method comprising the steps of:

delivering the pressure and temperature conditioned carbon dioxide stream to the coal bed by an inj ection well;

extracting methane desorbed from the coal bed; and

delivering the extracted methane to a gas processing unit.

2. The method of Claim 1, wherein the methane is extracted from the coal bed by a production well.

3. The method of Claim 1, wherein at least one of the injection well and the production well comprises slots.

4. The method of Claim 1, where the source of carbon dioxide is a pipeline that transports carbon dioxide under pressure.

5. The method of Claim 1, where the source of carbon dioxide comprises at least 50% carbon dioxide gas.

6. The method of Claim 1, where the source of carbon dioxide comprises at least 80% carbon dioxide gas.

7. The method of Claim 1, where the source of carbon dioxide comprises at least 95% carbon dioxide gas.

8. The method of Claim 1, where the pressure and temperature of the carbon dioxide is selected to be optimized for adsorption to coal in the coal bed.

9. The method of Claim 1, where the extracted methane is extracted and processed for distribution.

10. The method of Claim 1, wherein the supply of carbon dioxide is conditioned using a compressor and a heat exchanger.

11. The method of Claim 1, further comprising the step of continuing to injecting carbon dioxide after production of methane has ceased to store additional carbon dioxide in the coal bed.

12. A method of carbon capture and methane production, comprising the steps of:

capturing the desorbed methane for transport or processing.

13. The method of Claim 12 wherein the conditioned carbon dioxide gas is injected into the coal bed through an injection well and produced from a production well.

14. The method of Claim 12, wherein the source of carbon dioxide gas is a pipeline.

15. The method of Claim 12, wherein the pressure and temperature of the carbon dioxide gas is selected to achieve optimized conditions for adsorption to the coal.

16. The method of Claim 12, where the source of carbon dioxide comprises at least 50% carbon dioxide gas.

17. The method of Claim 12, where the source of carbon dioxide comprises at least 80% carbon dioxide gas.

18. The method of Claim 12, where the source of carbon dioxide comprises at least 95% carbon dioxide gas.

19. The method of Claim 12, wherein providing the supply of carbon dioxide comprises compressing the carbon dioxide gas in a compressor.

20. The method of Claim 12, further comprising the step of continuing to injecting carbon dioxide after production of methane has ceased to store additional carbon dioxide in the coal bed.