CA2962169A1

CA2962169A1 - Coal bed methane extraction and carbon capture

Info

Publication number: CA2962169A1
Application number: CA2962169A
Authority: CA
Inventors: Mackenzie Millar; Jose Lourenco
Original assignee: 1304342 Alberta Ltd; 1304338 Alberta Ltd
Current assignee: 1304342 Alberta Ltd; 1304338 Alberta Ltd
Priority date: 2017-03-16
Filing date: 2017-03-28
Publication date: 2018-09-16
Also published as: CA2960997A1

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 r elates to a p rocess th at d isplaces an d ex tracts m ethane from a coal b ed b y storing c arbon dioxide delivere d by compression such as fr om a pipel ine such as t he Alberta Carbon Trunk Line. The pipeline delivered carbon dioxide stream is injected into coal beds for sequestration and storage BACKGROUND

[0002] The ge neration of electri city in Nort h Arne rica a nd in most part s of the world i s primarily provided by the combustion of coal, a cheap and abundant fossil fuel. Coal is typically mined and t ransported to a powe r plant where it is processed befo re combustion. The coal is combusted i n a fur nace to genera te heat for the producti on of high pressure dr y steam. The produced dr y and s uperheated st eam drives a steam t urbine ge nerator to pr oduce electrici ty.
Coal is a high carbon content fuel, therefore a large emitter of carbon dioxide as well as NOx and S0x, greenhouse gases ( GHG). Rapidly increasin g concentrations of GHG's in the at mosphere and e merging evi dence of gl obal war ming is no w triggering international action to reduce GHG's e missions i nto the at mosphere. The c ombustion of coal to generate electricity is identified as a m ain contributor of GHG em issions, resulting in industry action bei ng taken t o reduce GHG em issions from the use of coal coin bustion. Recently, the government of Alberta has mandated that coal usage for power generation be terminated by the year 2030.

[0003] Coal bed methane ext raction provides an alternati ve method to recover energy fro m coal in a safe, effici ent and environmentally acceptable manner. Coal be d methane extraction is typically employed in un-mineable coal beds. Conventional coal bed methane recovery methods are based on reser voir pressure reduction, where methane is desor bed from t he coal sur face by reducing the reservoir pressure.

[0004] In the current standard mode of coal bed met hane extraction, wells are drilled into a coal bed. The met hane is extracted by deso rption fro m coal sur faces wher e the reser voir 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 processe d at surface and compressed in a natural gas pipeli ne net work for delivery t o ma rkets. More recent ly, to enhance coal be d methane ext raction ne w m ethods have be en devel oped. As descri bed by U.S.
patent no.

5,085,274 (Puri et al.) entitled " Recovery of methane from solid carbonaceous subterranean of formations", U.S. pate nt no. 5, 332,036 (Shirley et al.) ent itled "Method of recovery of natural gases from underground coal form ations" and U.S. patent no. 5,014, 785 (Puri et al.) entitled "Methane production from carbonaceous subterranean form ations", the use of c arbon dioxide diluted with inert gases enhances coal bed methane recoveries by reducing the partial pressure of methane and inj ecting other gases suc h a s nit rogen, res ulted ina s ubstantial increment in production.
SUMMARY
[0005] There is provide d a me thod and s ystem fo r s afely storing ca rbon di oxide, and for extracting st ored met hane and other volati le hydr ocarbons i n a coal be d.
T he method injects carbon diox ide into a coal bed in a condition to be sequestered and s tored, 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 an d methane extraction relative to temperature. The extracted m ethane and other volatile hydr ocarbons may then be recovered, processed and routed to natural gas pipeline distribution systems.

[0006] As coal has a str onger affi nity fo r carbon dioxide, it establishes an adsorption/desorption pr ocess where carbon di oxide displaces and frees the methane fr om t he coal bed t o be rec overed, processed and distri buted to nat ural gas pipeli ne distribution systems.
The objective of the method and system is to permit carbon dioxide to be sequestered and stored.

In one e xample, the propose d Al berta Carbon Tru nk Pipeline may be used to trans port carbon dioxide rec overed due t o local car bon-generating activities. The carbon dioxide m ay then be injected i nto coal beds t o establi sh an adso rption/desorption proc ess whe re car bon di oxide i s 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 tern perature for adsorption into a coal bed;
(b) displacing and producing m ethane by desorpti on of stored m ethane 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 met hod of storing carbon di oxide in a coal bed by absorption to coal in the coal bed, and t o desorb, displace and extract met hane stored in t he coal bed, the method comprising the steps of:
providing a supply of carbon dioxide from a source of car bon dioxide to a coal bed site for stor age the carbon dioxide havi ng a pressu re and temperat ure th at f alls within a predetermined pressure and temperature range;
delivering the pressure and temperature conditione d 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] ln another aspect, ther e is provided a m ethod of carbon capture and m ethane 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 t he conditi oned carbon dioxide ga s into a coal bed such t hat 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 a spects, the met hod may comprise one or more of the following features: the methane may be extr acted 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 car bon dioxide may be a pi peline that tra nsports car bon dioxide unde r pressure; the source of carbon dioxide m ay comprise at least 50% carbon di oxide gas, at least 80% ca rbon di oxide gas, or at le ast 95%
carbon di oxide gas; the pres sure and te mperature of the car bon dioxide ma y be sele cted to be optimized for adsor ption to coal in t he coal be d; the extr acted methane may be extr acted and processed for di stribution; a nd pr oviding th e supply of carbon di oxide ma y comprise compressing the car bon dioxide gas in a comp ressor; car bon dioxide ma y 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 extra ct stored methane i n a coal bed. The ex tracted m ethane is p rocessed an d distri buted as a fossil fuel derived from coal. The proces s stores carbon dioxi de and extracts stored methane in coal be ds, thus c ontributing to the producti on of clea n abundant energy from a very concentrated carbon fuel. The pr ocess is consider ed to be clean si nce coal can st ore two or more moles o f carbon dioxide for every mole of m ethane displaced. Coal can st ore up to 10 moles of carbon dioxide per mole of methane stored in coal, thus making it a carbon negative process.

[0013] As will hereinaft er be furt her de scribed, c arbon di oxide is fir st delive red by a pipeline, such as the Al berta Carbon Trunk Line, and i njected for adsorption into a coal bed for storage and desorption of st ored methane from the coal bed. The desor bed and extr acted coal bed methane m ay then be proces sed for di stribution. The pr ocess may be used to s afely store carbon dioxide in a c oal bed by a dsorption 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 i nvention 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 EMBODIMENT

[0015] The method descr ibed may be used t o safely store carbon dioxide that is produc ed, recovered a nd tra nsported by pipel ine in such as may occ ur in a car bon ca pture proc ess by adsorbing c arbon dioxide into a coal bed. It w ill be unders tood that a coal bed ma y also be referred to as a coal seam, or ot her deposit of coal t hat i s accessible from sur face, 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 i nclude a relatively small proportion of other, heavier hydro carbons or other gase s as is known i n the art with respect to coalbed met hane gas. In additi on, the source of car bon dioxide is pre ferably a source of c aptured carbon dioxide , sue h as ma y be obtained fr om a power pla nt or ot her industrial activity. As it is pr imarily carbon dioxide that adsorb s to the coal and causes the methane to des orb, the s ource of car bon dioxide is preferably at least 90%
carbon di oxide gas, and preferably more, such as 95% or m ore. Th e actual composition oft he source of car bon dioxide ga s may vary depe nding on the s ource and any a pplicable regul ations, but may al so 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 mo le of methane stored in coal. When carbon dioxi de is adsorbed in coal, the methane stored in coal is desorbed and freed to be extr acted and proc essed. The disci osed method provides an alter native 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 s aline aquifers and/or for use in EOR (e nhanced oil recovery) operations. Th e proposed method offers a different approach in a unique and i nnovative variant to store carbon dioxide that may become available from resources such as the Alberta Carbon Trunk Line and other source s of ca rbon dioxide. The syste m her e des cribed take s advantage of safely storing carbon di oxide i n c oal beds by a n a dsorption/desorption process tha t al so produc es met hane stored in the same coal beds.

[0017] In 2016, S hell Canada comm issioned Quest, a carb on capture and stor age pr ocess where the carbon dioxide captur ed from its oil upgrading and ref inery processes is compres sed and stored in underground caverns. The Al berta Carbon Tr unk Line is under construction and due to be c ommissioned in 2017 . T he objective of th is lin e is to transport and distribute recovered carbon dioxide f rom Al berta facilities to store in deep saline aquif ers and/or EOR
(Enhanced Oil Recovery) at oil wel Is. The use of car bon di oxide to enhance oil pr oduction 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 r ecompression 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 a ffinity to absorb carbon di oxide and hence are an ideal st orage resource. Furthermore, the injection of carbon dioxide into a coal bed can be used to establish an adsorption/desorption process that frees the meth ane and other volatile h ydrocarbons stored in coal to be recovered, processed and distributed.

[0019] The method described herein provides a pr ocess that uses carbon dioxide that may be produced, recove red and transported for st orage in coal fiel ds and to extract stored methane and other volatile h ydrocarbons 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 m ethane extr action while storing the carbon dioxide, unlike the pipeline proposed practice of compressing it into saline aquifers or oil wells.
Coal bed m ethane extraction works by replaci ng so rbed m ethane molecules with m ore strongly sorbed carbon dioxide m olecules. The pr ocess is beneficial as coal selectivity of carbon dioxide to methane is greater than 2 to 1, coal adsorbs and stores 2 m olecules or more of carbon dioxide for ev ery molecule of m ethane displaced, and th e carbon dioxide rem ains 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 st ored methane gas and volatile hydrocarbons from a coal bed economically.

[0020] The co mposition oft he carbon dioxi de ga s may var y, de pending on the sourc es available. However, it will be understood that the higher the concentration of carbon dioxide that is injected, the higher the cone entration of methane will be pr oduced, as the pr oduced methane will be less diluted. In many c ases, s ources of car bon di oxide pr oduced fr om i ndustrial or commercial processes wi 11 be 95 % (by wei ght) or more , depending on the equipme nt 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 pre ferably greater than 80%.

[0021] The pres ent m ethod pr ovides a n altemati ve to store lar ge vol umes 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 t he 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 res ource suc h as t he Al berta Ca rbon Tr unk Li ne from industrial plants i n Alberta.

[0023] Carbon dioxide is transported and distributed by Alberta Car bon Trunk Line through stream 1 into a coal bed site and compres sed, i f required, by compressor 2 to meet opti mum pressure conditions. If the carbon dioxide is at a suitable pressure, the st ream 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 me et coal be d opti mum temperature conditi ons for adsorption o f carbon dioxide and de sorption of met hane st ored in c oal bed. The opti mal pr essure and temperature conditions may be determ ined ba sed on coal bed depth and methane productio n flow. By varying the temperature and pressure conditions, a range of acceptable conditions may be de fined. Thi s range ma y vary fr om well to well. For e xample, a s t he dept h of the wel I
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 a nd distributed through sl ots 7 i nto the c oal bed 8. The i Mected pressure and t emperature controlled carbon dioxide stream is adsorbed in coal bed 8 and the des orbed methane and other volatile hydrocar bon gases are displaced acr oss the coa I bed 8 a nd through sl ots 9 i nto production well 10. The extracted methane is r outed through pr oduction well 10 a nd through stream 11 into gas proce ssing unit 12. The processed gas exits gas processing unit I 2 throug h 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 in to the same form ation, etc. In add ition, while the well 6 is shown with a liner having slots 7, the liner ma y have di fferent openings, or a di fferent way of di stributing carbon dioxide within the coal bed may be used.

[0025] As pr oduction procee ds and th e methane in the co al be d i s de pleted, the flow of methane from the well will slow. Ho wever, because coal is able to store 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 su ch, carbon dioxide may be injected until a su fficient flow of carbon dioxide is produced from production well 10 to show that the coal bed is sufficiently saturated.

[0026] As noted, prior to inj ecting the car bon dioxide into the coal bed 8, it is conditione d through compres sion and te mperature control. Th is is preferably done to achieve an optimal amount of c arbon di oxide a dsorption, whi ch will in tur n e nhance met hane pr oduction. The optimal temperature and pressure conditions may be selected by an alysing the coal formation, or through experi mentation. Opt imization may also include an anal ysis of the energy required to condition the carbon dioxi de and any eff ect th e compression and temperature control has on downstream transport or processing.

[0027] In one exa mple, t he pr ocess may be i mplemented by: first , storing car bon dioxi de delivered from the Alberta Carbon Trunk Line by a dsorption in a coal bed;
second, desorbing and extracti ng stor ed methane fr om the coal bed; and third, processing and di stributing the extracted coal bed methane. This pr ocess al lows an e fficient use of an abundant suppl y o f recovered carbon dioxide for s afe storage and simultaneous extraction of stored met hane from the coal bed by esta blishing an ads orption/desorption proce ss where car bon dioxide displaces and frees methane stored in a co al bed to flow i nto a production well. This proc ess 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 5 mean that items following the wor d are incl uded, but items not specific ally mentioned are not excluded. A reference to an elem ent by the indefinite article "a" does not exclude the possibility that more than one of the elemen t is present, unless the context cl early requires that there be one and only one of the elements.
10 [0029] The scope of the claims should not be limited by the preferred embodiments set forth in the exa mples, but shoul d be given a broa d purposive i nterpretation 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:
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.

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:
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.

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.