NATCARB
CO2 Storage Formations
CO2 Storage Resource Methodology
DOE's Regional Carbon Sequestration Partnerships (RCSPs) were charged with providing a high-level, quantitative estimate of carbon dioxide (CO2) storage resource available in subsurface environments of their regions. Environments considered for CO2 storage were categorized into five major geologic systems: saline formations, oil and gas reservoirs, unmineable coal areas, shale, and basalt formations. Where possible, CO2 storage resource estimates have been quantified for oil and gas reservoirs, saline formations, and unmineable coal areas in the third edition of the Carbon Sequestration Atlas of the United States and Canada (Atlas III). Shale and basalt formations are presented as future opportunities and are not assessed (please see disclaimer on the NATCARB homepage).
The methodology employed by the RCSPs is based on volumetric methods for estimating subsurface volumes. Subsurface storage volume estimates depend on geologic properties and storage efficiency. Storage efficiency for this methodology was determined using Monte Carlo sampling, which includes efficiency terms to define the pore volume that is amenable to geologic storage and displacement terms to define the pore volume immediately surrounding a single CO2 injection well.
Methodologies used in Atlas IIIare intended to produce high-level, regional- and national- scale CO2 resource estimates of potential geologic storage in the United States and Canada. At this scale, the estimates of CO2 geologic storage have a high degree of uncertainty. Because of this uncertainty, estimates from Atlas IIIare not intended to be used as a substitute for site-specific characterization and assessment. As CO2 storage sites move through the site characterization process, additional site-specific data is collected and analyzed, reducing uncertainty. Incorporation of this site-specific data allows for the refinement of CO2 storage resource estimates and development of CO2 storage capacities by future potential commercial project developers.
More information on the RCSPs' CO2 storage methodology is available in Atlas III's Appendix B: Summary of the Methodology for Development of Geologic Storage Estimates for Carbon Dioxide. Detailed CO2 storage resource estimates are available in Atlas III's Appendix C: CO2 Stationary Source and Geologic Storage Resource Estimates by States/Province.
All data, metadata, and high resolution jpgs are available on NATCARB's Data Download and Custom Maps Request webpage.
Sedimentary Basins
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| Sedimentary Basins |
DOE's RCSPs have identified and examined the location of potential CO2 geologic storage injection sites in different sedimentary basins throughout the United States and Canada. Sedimentary basins are areas where sediments accumulate over time and lithify to become sedimentary rocks. If these sedimentary rocks are porous or fractured, they can be saturated with brine (water with a high total dissolved solids [TDS] concentration), oil, or gas. If the sedimentary rock is also permeable (interconnected pores) it could be a target for CO2 injection. If the sedimentary rock is impermeable (lack of or minimal connected pores), it can act as a seal to prevent CO2 migration. Necessary conditions for a CO2 storage site are the presence of both a reservoir with sufficient porosity and permeability and presence of an impermeable seal to prevent migration.
CO2 Storage Geologic Formations
Saline Formations
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| Saline Formations |
Saline formations are porous rock that is saturated with brine. They are much more extensive than coal areas or oil- and gas-bearing rock and represent an enormous potential for CO2 geologic storage. However, less is known about saline formations because they lack the characterization experience that industry has acquired through resource recovery from oil and gas reservoirs and coal seams. Therefore, there is an amount of uncertainty regarding the suitability of saline formations for CO2 storage.
While not all saline formations in the United States have been examined, the RCSPs have documented the locations of saline formations with an estimated CO2 storage resource ranging from 1,653 billion metric tons to more than 20,213 billion metric tons (from 1,822 billion tons to more than 22,281 billion tons) of CO2. At current CO2 emission rates, calculations indicate more than 450 years of storage potential in assessed saline formations. For details on saline formation CO2 storage resource by state, see Appendix C of the 2010 Carbon Sequestration Atlas of the United States and Canada – Third Edition.
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| Data current as of November 2010 |
Oil and Gas Reservoirs
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| Oil and Gas Reservoirs |
Sedimentary rocks that contain oil and gas have an impermeable seal that holds the oil or gas in place. The characteristics that have held this oil and gas in the reservoir for millions of years make them excellent target locations for geologic CO2 storage. An added benefit of oil and gas reservoirs is that they have been extensively explored, which generally results in a wealth of data available to plan and manage proposed CCS efforts.
While not all mature oil and gas reservoirs in all states and provinces have been examined, the RCSPs have documented the location of almost 143 billion metric tons (155 billion tons) of CO2 storage resource in 29 states and 4 provinces. At current CO2 emission rates, calculations indicate more than 40 years of storage potential in assessed oil and gas reservoirs. For details on oil and gas storage by state, see Appendix C of the 2010 Carbon Sequestration Atlas III of the United States and Canada – Third Edition.
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| Data current as of November 2010 |
Unmineable Coal Areas
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| Unmineable Coal Areas |
Coal is an organic sedimentary rock that forms mainly from the accumulation of plant debris in an anoxic environment. Unmineable coals are too deep or too thin to be economically mined with today's state-of-the-art technology and are potentially viable for CO2 storage. All coals have varying amounts of methane adsorbed onto pore surfaces. Wells can be drilled into unmineable coalbeds to recover this coalbed methane (CBM). Initial CBM recovery methods, such as dewatering and depressurization, leave a considerable amount of methane in the formation. Additional recovery can be achieved by sweeping the coalbed with CO2. Depending on coal rank, 3 to 13 molecules of CO2 are adsorbed for each molecule of methane released, thereby providing an excellent storage site for CO2 along with the additional benefit of enhanced coalbed methane (ECBM) recovery. The adsorption process bonds the CO2 to the coals, causing the CO2 to be physically and permanently trapped on the coal provided sufficient pressure is maintained. The adsorption process coupled with the recovery of economically valuable methane gas makes unmineable coal seams attractive options for CCS.
While not all unmineable coal areas have been examined, the RCSPs have documented the location of 60 billion to 117 billion metric tons (65 billion to 128 billion tons) of potential CO2 storage resource in unmineable coal areas distributed over 21 states and 1 province. At current CO2 emission rates, calculations indicate more than 15 years of storage potential in assessed coal areas. For details on unmineable coal area storage by state, see Appendix C of the 2010 Carbon Sequestration Atlas III of the United States and Canada – Third Edition.
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| Data current as of November 2010 |
Future Opportunities for CO2 Storage Geologic Storage
Basalt Formations
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| Basalt Formations |
Another potential CO2 storage option DOE is investigating is basalt formations. The relatively large amount of potential storage resource in basalts, along with their geographic distribution, make them an important formation type for possible CO2 storage, particularly in the Pacific Northwest and the Southeastern United States. Basalt formations are geologic formations of solidified lava. These formations have a unique chemical makeup that could potentially convert all of the injected CO2 to a solid mineral form, thus isolating it from the atmosphere permanently. Some key factors affecting the capacity and injectivity of CO2 into basalt formations are effective porosity of flow top layers and interconnectivity. DOE's current efforts are focused on enhancing and utilizing the mineralization reactions and increasing CO2 flow within basalt formations. Before basalt formations can be considered viable storage targets, a number of questions relating to the basic geology, the CO2 trapping mechanisms and their kinetics, and monitoring and modeling tools need to be addressed. As such, Atlas III presents a map of these potential future storage opportunities, but provides no CO2 storage resource values for basalt formations.
Shale Basins
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| Organic Shale Basins |
As CCS moves toward commercialization, additional CO2 storage options may be explored. One option already under consideration is the possibility of utilizing organic-rich shales. Shales are formed from silicate minerals that are degraded into clay particles that accumulate in areas of still water over millions of years. The plate-like structure of these clay particles causes them to accumulate in a flat manner, resulting in rock layers with extremely low permeability in the vertical direction. Therefore, shales are most often used in a geologic storage system as a confining seal or caprock. Before organic-rich shale basins can be considered viable storage targets, a number of questions relating to the basic geology, the CO2 trapping mechanisms and their kinetics, and monitoring and modeling tools need to be addressed. As such, Atlas III presents a map of these potential future storage opportunities, but provides no CO2 storage resource values for organic-rich shale basins.
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