CO2 Sequestration Potential of Unmineable Coal ...

Available online at www.sciencedirect.com

Energy Procedia 37 (2013) 5134 – 5140

GHGT-11

CO2 Sequestration Potential of Unmineable Coal—State of Knowledge Margo D. Coruma *, Kevin B. Jonesa, Peter D. Warwicka a

USGS, 12201 Sunrise Valley Drive, MS 956, Reston VA 20192, USA

Abstract Currently the U.S. Geological Survey (USGS) national assessment of geological carbon dioxide (CO2) storage resource considers porous sandstones, limestones, and dolomites as potential storage formations. Assessment of an additional potential geologic storage resource within unmineable coal seams was deferred because no consensus exists on what constitutes unmineable coal. Because unmineable coal seams may be considered potential storage resources in future assessments, however, the USGS is researching factors affecting CO2 storage potential in coal. © 2013 The Authors. Published by Elsevier Ltd. © 2013 Battelle Memorial Institute. Published by Elsevier Ltd. All rights reserved. Selection and/or peer-review under responsibility of GHGT Selection and/or peer-review under responsibility of GHGT Keywords: Carbon dioxide; coal; geologic storage assessment; unmineable

1.

Introduction

Carbon dioxide (CO2) is a predominant greenhouse gas in the Earth’s atmosphere. A major source of anthropogenic CO2 is the combustion of fossil fuels to generate electricity: 68% of electricity in the United States (U.S.) is generated using fossil fuels and 42% of electricity in the U.S. is generated using coal [1]. The U.S. emitted 5,471 million metric tons of carbon dioxide in 2011 from fossil fuel combustion [1]. According to the Energy Information Administration (EIA), demand for electricity in the U.S. will increase by approximately 22% from 2012 to 2035 [2]. Carbon capture and storage technologies, including geologic carbon sequestration, can be used to reduce CO2 emissions despite increasing demand for electricity. The Energy Independence and Security Act (EISA, Public Law 110–140) [3] of 2007 mandated the U.S. Geological Survey (USGS) to develop a methodology and conduct a national assessment of the potential geological storage resources for CO2 in consultation with the U.S. Department of Energy (DOE), the U.S. Environmental Protection Agency (EPA), and State geological surveys. The USGS was chosen to perform this assessment because of its long history of assessing water, mineral, and energy resources.

* Corresponding author. Tel.: +1-703-648-6488; fax: +1-703-648-6419. E-mail address: [email protected]. E

1876-6102 © 2013 The Authors. Published by Elsevier Ltd.

Selection and/or peer-review under responsibility of GHGT doi:10.1016/j.egypro.2013.06.428

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In 2009, Burruss et al. [4] developed and published a preliminary methodology to estimate potential geologic storage resources for CO2. Brennan et al. [5] revised this methodology in 2010, using comments from a panel of experts and public review. The USGS is currently assessing the potential CO2 storage capacity resulting from buoyant and residual trapping in porous sandstones, limestones, and dolomites using the Brennan et al. [5] methodology. This methodology omits unmineable coal seams, because no universally accepted criteria for coal minability exist. Because unmineable coal may be addressed in future assessments, the USGS is assembling a body of knowledge on factors affecting CO2 storage potential in coal. 2.

Coal Mineability

Carbon dioxide stored in a coal bed effectively renders the coal unusable for energy purposes in the future—that is, it “sterilizes” the resource. Coal mining, combustion, or gasification would release carbon dioxide stored in the coal, eliminating any benefit derived by such storage. For this reason, EISA specified that only unmineable coal, rather than all coal, be considered for CO2 storage potential [3]. Depending on the definition of coal minability, unmineable coal seams have the potential to store large volumes of CO2 (Table 1). There is no universally accepted quantitative definition of coal minability. Qualitatively, unmineable coal seams cannot be mined economically because they are too deep, thin, or small; are of poor quality; or because of land use restrictions. DOE and DOE’s Big Sky Carbon Sequestration Partnership and Plains CO2 Reduction Partnership define coal as unmineable if it is beneath at least 305 meters (m) of overburden [6]. DOE’s Midwest Geological Sequestration Consortium adds two considerations to their definition: all coals shallower than 152 m are mineable and so are unsuitable for CO2 sequestration, and at 152–305 m deep, coal seams 0.5–1.1 m thick are unmineable and so are reasonable sequestration targets [6]. Changes in technology and economics over time shift the threshold of mineability and therefore complicates attempts to quantify this resource. The USGS needs a generally accepted definition of unmineable coal in order to develop a methodology to assess the storage potential in unmineable coal seams, and a generally accepted definition does not yet exist. Ultimately, it may be more practical to assess the potential storage capacity in all coal, keeping in mind that much of this potential will go unused because the coal will eventually be mined. Table 1. CO2 storage resource estimates for unmineable coal in each Department of Energy Regional Carbon Sequestration Partnership [6] Regional Carbon Sequestration Partnership

Low Estimate

High Estimate

Billion Metric Tons of CO2 storage of Coal

Billion Metric Tons of CO2 storage of Coal

Big Sky Carbon Sequestration Partnership

12

12

Midwest Geological Sequestration Consortium

2

3

Midwest Regional Carbon Sequestration Partnership

1

1

Plains CO2 Reduction Partnership

1

1

Southeast Regional Carbon Sequestration Partnership

33

75

Southwest Regional Partnership on Carbon Sequestration

1

2

West Coast Regional Carbon Sequestration Partnership

10

23

Total

60

117

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Fig. 1. This map displays unmineable coal areas from Department of Energy Regional Carbon Sequestration Partnerships and other sources, compiled by NATCARB [6].

3.

Mechanisms of Storing CO2 in Coal

Carbon dioxide can be stored in coal by sorption and diffusion. Diffusion occurs when CO2 moves through large (greater than 30 nanometer) pores, fractures, and cleats. Sorption of CO2 occurs by adsorption onto internal surfaces; absorption into the molecular structure; free gas in fractures, cleats, and voids; and dissolution of CO2 in groundwater. The process of adsorption causes the CO2 to bond to the coal causing the CO2 to be physically and permanently trapped on the coal provided sufficient pressure is maintained. According to Mastalerz et al. [8] adsorption is considered, by far, the most important mechanism for gas retention. Successful injection of CO2 into a coal seam requires sufficient permeability along pores and fractures. 4.

Storing CO2 in Coal


The DOE Carbon Sequestration Atlas of the United States and Canada [6] (Table 1), estimates 60 billion to 117 billion metric tons of potential CO2 storage in coal seams across 29 U.S. states and 1 Canadian province. DOE also estimates that 82.1 billion metric tons of CO2 can be stored in unmineable coal of the Central Appalachian Basin and 0.72-1.36 billion metric tons of CO2 can be stored in unmineable coal of the Black Warrior Basin [6]. While these numbers appear promising there are both advantages and disadvantages of storing CO2 in coal. Some of the advantages of storing CO2 in coal seams are: Reduce amount of CO2 released into the atmosphere Potential for large CO2 storage resource within the U.S. CO2 readily absorbs to coal more than methane, resulting in a greater volume of CO2 absorbed to the coal via the displacement of methane • this process could stimulate additional extraction of CBM as adsorption of CO2 preferentially displacing previously adsorbed methane, leading to increased fossil fuel production to offset the costs of sequestration Some of the disadvantages of CO2 sequestration in coal are: lack of accepted “unmineable” coal definition causes uncertainty over which coal seams are available for CO2 sequestration successful injection of CO2 into a coal seam requires sufficient permeability along pores and fractures, yet adsorption of CO2 reduces permeability due to swelling of the coal • permeability will also decrease exponentially with depth as a result of increasing lithostatic pressure deeper than approximately 1000 m, pressures and temperatures are such that CO2 is a supercritical fluid • in the supercritical fluid state, CO2 is an organic solvent that can diffuse into and plasticize coal, further reducing coal permeability and porosity applied stress from overburden or other factors can reduce the CO2 sorption capacity of coal [7] injection of CO2 in coal seams in production of enhanced coal bed methane (ECBM) can also cause the coal to shrink effecting permeability CO2 is more water-soluble than methane, which can cause acidification of pore water, dissolution of minerals, and potentially coal failure [9] 5.

Pilot Projects

DOE’s Regional Carbon Sequestration Partnerships (fig. 2) has research projects that are ongoing in the partnership’s study areas for CO2 storage [6]. Several field injection tests and subsequent monitoring in the partnerships locations allow researchers to build on previous theoretical and laboratory studies to better understand the geological and engineering factors affecting CO2 storage in coal. Two injection projects of importance are the San Juan Basin Allison Unit Project and the Black Warrior Basin Project.

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Fig. 2. Map showing DOE’s Regional Carbon Sequestration Partnerships and locations of coal seams, oil & gas bearing formations, and saline formations used for CO2 storage projects [6]. The seven partnerships are the Big Sky Carbon Sequestration Partnership (BSCSP), Midwest Geological Sequestration Consortium (MGSC), Midwest Regional Carbon Sequestration Partnership (MRCSP), Plains CO2 Reduction (PCOR) Partnership, Southeast Regional Carbon Sequestration Partnership (SECARB), Southwest Regional Partnership on Carbon Sequestration (SWP), and West Coast Regional Carbon Sequestration Partnership (WESTCARB) [6]. Several field injection tests and subsequent monitoring in the partnerships locations allow researchers to build on previous theoretical and laboratory studies to better understand the geological and engineering factors affecting CO2 storage in coal. Two injection projects of importance are the San Juan Basin Allison Unit Project and the Black Warrior Basin Project.

The San Juan Basin Allison Unit Project, located in San Juan County, New Mexico, was launched in 2000 as a DOE-sponsored investigation of CO2 storage in deep unmineable coal [10]. The San Juan Basin was ranked as one of the top basins for sequestration due to its high methane content and well developed production, nearby power plants, favorable geology, existing gas and CO2 pipeline, and local expertise on coalbed methane (CBM). Wells produce methane from three coals in the Upper Cretaceous Fruitland Formation. The net thickness of the coal is 23 m over a 53 m interval. The pilot area consisted of sixteen CBM production wells, four CO2 injection wells, and one pressure observation well [10]. This project injected 18,400 tons of CO2 and improved methane recovery by 18%, but injectivity and permeability decreased over time. These factors can be detrimental effect to CBM-sequestration economics.


The Black Warrior Basin Project, located in the Blue Creek Field in Tuscaloosa County, Alabama, was as a DOE-sponsored study of CO2 sequestration in deep, unmineable coal and ECBM recovery potential launched in 2006 [11]. DOE estimated between 0.63-1.36 billion metric tons of potential CO2 storage [6]. The pilot test site consisted of a mature coalbed methane well, deep observation wells, shallow monitoring wells, and surface monitoring stations [11]. The projected injected 252 metric tons of CO2 and 516,709 litres (3,250 bbl) of water into three different coal zones; Black Creek (548 m), Mary Lee (433-457 m), and Pratt Coal (287 m) [11]. The project demonstrated significant injectivity more than 167 billion cubic meters (5.9 trillion cubic feet) of CO2 can be sequestered, and increased the CBM reserves by more than 20% [11]. 6.

Summary

Many in-progress and completed field CO2 injection tests and subsequent monitoring are allowing researchers to build on theoretical work and laboratory studies to better understand geologic and engineering factors affecting CO2 storage in coal seams. For the USGS to develop a methodology to assess the potential of CO2 sequestration in coal it is necessary to use volume (pore space), rock properties, geologic data, processes, geologic models and to define unmineable coal. The current geologic assessment methodology will be used as a guideline, but the details are not fully determined. This increased understanding will form the basis for a future USGS methodology to assess the CO2 storage potential in unmineable coal seams. Acknowledgements The authors would like to thank members of the USGS Geological Carbon Sequestration Assessment and Research teams for their contributions to this work. In addition, the authors would like to thank Sean T. Brennan and Matt Merrill for providing valuable reviews and comments on an earlier version of this paper.

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References [1] U.S. Energy Information Administration. Monthly Energy Review March 2012. U.S. Energy Information Administration DOE/EIA-0035(2012/07); 2012, 212 p. accessed September 30, 2012, at http://www.eia.gov/totalenergy/data/monthly/archive/00351207.pdf. [2] U.S. Energy Information Administration. Annual Energy Outlook 2012 with projections to 2035. U.S. Energy Information Administration DOE/EIA-0383(2012); 2012, 239 p. accessed September 28, 2012, at http://www.eia.gov/forecasts/aeo/pdf/0383(2012).pdf. [3] Public Law 110–140, Energy Independence and Security Act of 2007. U.S. Government Printing Office; 2007, unpaginated, accessed September 10, 2012, at http://frwebgate.access.gpo.gov/cgibin/getdoc.cgi?dbname=110_cong_public_laws&docid=f:publ140.110.pdf. [4] Burruss, RC, Brennan, ST, Freeman, PA, Merrill, MD, Ruppert, LF, Becker, MF, Herkelrath, WN, Kharaka, YK, Neuzil, CE, Swanson, SM, Cook, TA, Klett, TR, Nelson, PH, Schenk, CJ. Development of a probabilistic assessment methodology for evaluation of carbon dioxide storage. U.S. Geological Survey Open-File Report 2009–1035; 2009, 81 p., accessed September 11, 2012, at http://pubs.usgs.gov/of/2009/1035/. [5] Brennan, ST, Burruss, RC, Merrill, MD, Freeman, PA, and Ruppert, LF, 2010. A probabilistic assessment methodology for the evaluation of geologic carbon dioxide storage. U.S. Geological Survey Open-File Report 2010–1127, 31 p., available only at http://pubs.usgs.gov/of/2010/1127. [6] U.S. Department of Energy, National Energy Technology Laboratory.. Carbon sequestration atlas of the United States and Canada (2d ed.; Atlas III). 2010, 162 p., accessed August 10, 2012, at http://www.netl.doe.gov/technologies/carbon_seq/refshelf/atlasIII/ [7] Hol, S, Peach, CJ, and Spiers, CJ. Applied stress reduces the CO2 sorption capacity of coal. International Journal of Coal Geology 2011, 85, 128–142. [8] Mastalerz, M, Gluskoter, H, and Rupp, J. Carbon dioxide and methane sorption in high volatile bituminous coals from Indiana, USA. International Journal of Coal Geology 2004, 60: 43–55. [9] Bustin, RM, Cui, X, and Chikatamarla, L. Impacts of volumetric strain on CO2 sequestration in coals and enhanced CH4 recovery. AAPG Bulletin 2008,92, 15–29 [10] Reeves, SR, and Kopema, GJ, Jr. Geologic Sequestration of CO2 in Deep, Unmineable Coalbeds: An Integrated Research and Commercial-Scale Field Demonstration Project: Advanced Resources International, Inc., 2008, (US DOE DE-FC26-00NT40924). [11] Pashin, JC, McIntyre, MR, Carroll, RE, Clark, PE, Dayan, A, and Esposito, RA. Final Report, Southeastern Regional Carbon Sequestration Partnership (SECARB) Phase II SECARB Black Warrior Test Site Blue Creek Field, Tuscaloosa County, Alabama. Geological Survey of Alabama, 2011, Open-File Report 1101.