1 This article was downloaded by: [Srivastava, Rameshwar D.] On: 27 August 2010 Access details: Access Details: [subscription number ] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Encyclopedia of Soil Science Publication details, including instructions for authors and subscription information: Geologic Carbon Capture and Storage Sean I. Plasynski a ; John T. Litynski b ; Timothy R. Carr c ; Howard G. McIlvried d ; Rameshwar D. Srivastava d a National Energy Technology Laboratory, U.S. Department of Energy, Pittsburgh, Pennsylvania, U.S.A. b National Energy Technology Laboratory, U.S. Department of Energy, Morgantown, West Virginia, U.S.A. c Department of Geology and Geography, West Virginia University, Morgantown, West Virginia, U.S.A. d KeyLogic Systems, Pittsburgh, Pennsylvania, U.S.A. Online publication date: 06 April 2010 To cite this Section Plasynski, Sean I., Litynski, John T., Carr, Timothy R., McIlvried, Howard G. and Srivastava, Rameshwar D.(2010) 'Geologic Carbon Capture and Storage', Encyclopedia of Soil Science, 1: 1, 1 5 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
2 Geologic Carbon Capture and Storage Sean I. Plasynski National Energy Technology Laboratory, U.S. Department of Energy, Pittsburgh, Pennsylvania, U.S.A. John T. Litynski National Energy Technology Laboratory, U.S. Department of Energy, Morgantown, West Virginia, U.S.A. Timothy R. Carr Department of Geology and Geography, West Virginia University, Morgantown, West Virginia, U.S.A. Howard G. McIlvried Rameshwar D. Srivastava KeyLogic Systems, National Energy Technology Laboratory, Pittsburgh, Pennsylvania, U.S.A. Introduction Abstract An option that has been proposed to combat the buildup of greenhouse gases in the atmosphere is the capture of CO 2 at large stationary sources, such as power plants, and injection into a geologic formation for permanent storage generally referred to as carbon capture and storage (CCS). This article provides an overview of the major geologic targets in sedimentary basins for long-term storage of CO 2. These targets are oil and gas reservoirs, deep coal beds, and deep saline formations saturated with brackish water or brine. Atmospheric levels of CO 2 have risen significantly from preindustrial levels of 280 parts per million (ppm) to present levels of 384 ppm.  Evidence suggests the observed rise in atmospheric CO 2 levels is the result of expanded use of fossil fuels for energy. Predictions of increased global energy use during this century indicate a continued increase in carbon emissions  and rising concentrations of CO 2 in the atmosphere unless major changes are made in the way we produce and use energy in particular, how we manage carbon. [3,4] One approach to managing carbon is to use energy more efficiently to reduce our reliance on the major carbon emissions source fossil fuel combustion. Another option is to increase our use of low-carbon and carbonfree fuels and technologies (nuclear power and renewable sources, such as solar energy, wind power, and biomass fuels). The third strategy is to manage carbon through geologic storage (GS), sometimes referred to as geologic sequestration. Geologic storage is part of the process of carbon capture and storage (CCS), which involves separation and capture of CO 2 at the point of emission followed by injection and storage in a deep underground geologic formation (Fig. 1).  Carbon dioxide (CO 2 ) sinks are a natural part of the carbon-cycle; however, due to present concerns about global climate change related to greenhouse gas (GHG) emissions, efforts are underway to better utilize CO 2 sinks as a form of carbon management to offset emissions derived from fossil fuel combustion and other human activities. The concept of carbon sinks has become more widely known because the Kyoto Protocol  under the United Nations Framework Convention on Climate Change  allows the use of engineered CO 2 sinks as a form of carbon offset. Natural sinks include the oceans, plants and other photosynthetic organisms, and geologic formations. In 2006, about 28 billion metric tons of CO 2 was emitted globally into the atmosphere, the United States share being about 5.6 billion metric tons.  About half of this came from large stationary sources, primarily coal-fired power plants, which produce flue gases with a low CO 2 concentration (<20%). Geologic storage of CO 2 to limit atmospheric emissions has been underway for more than a decade with projects that have provided significant data and experience, such as Sleipner in Norway,  In Salah in Algeria,  and a joint U.S. Canadian effort at the Dakota Gasification facility and Weyburn field,  Numerous field projects in saline formations, oil reservoirs, and coal seams are being developed in the United States and Canada through the U.S. Department of Energy s (DOE s) Regional Carbon Sequestration Partnerships initiative.  It is expected that large numbers of new power plants and processing facilities based on coal and other non-liquid hydrocarbons (i.e., coal-to-liquid fuels and coal-to-synthetic natural gas plants) will be built in the coming decades, both in the developing world and some areas of the Encyclopedia of Soil Science DOI: /E-ESS Copyright 2010 by Taylor & Francis. All rights reserved.
3 Geologic Carbon Capture and Storage Fig. 1 Illustration of carbon capture and storage (CCS) process showing major pathways for geologic and terrestrial storage. Source: Carbon sequestration atlas of the United States and Canada.  developed world. These new facilities have the potential for being appropriately fitted, during design and construction, with efficient CCS technologies.  Existing plants can be retrofitted for CO 2 capture. If we are to effectively manage the CO 2 emissions from all these plants, the use of geologic carbon sinks will be required. Geologic storage is most efficient at depths greater than 2600 ft (800 m) because CO 2 increases in density and becomes a supercritical fluid at pressures that naturally exist at such depths (Fig. 2). Supercritical fluids take up much less volume and diffuse better through the pore spaces in storage formations than gases or ordinary liquids. Geologic Storage Targets Geologic storage requires a reservoir and seal (caprock) to trap CO 2 for long periods of time. Geologic storage can take place in three major geologic targets in sedimentary basins  : deep saline formations, saturated with brackish water or brine; oil and gas reservoirs; and deep coal beds (Fig. 1). Basalt formations and organic rich shales have been proposed as potential GS options, but their utility and suitability need to be demonstrated. [5,14] Keeping the CO 2 in the subsurface requires geologic conditions that create a trap consisting of one or more layers of impermeable rock (caprocks), which are layers of sediments (shale or evaporates) that impede CO 2 movement and act to trap the CO 2 for millennia. Saline Formations Saline formations are layers of porous rock, such as sandstone and limestone, which are saturated with brine. They are much more extensive than coal seams or oil- and gasbearing reservoirs and represent an enormous potential for CO 2 storage. However, much less is known about saline formations because of a lack of characterization data, such as that acquired through resource recovery from oil and gas reservoirs and coal seams. Therefore, there is greater uncertainty regarding the volume and suitability of saline formations for CO 2 storage. 
4 Geologic Carbon Capture and Storage Fig. 2 CO 2 injected at depths below 2600 ft (800 m) increases in density with depth and becomes a supercritical fluid. Supercritical fluids take up much less space and diffuse better than either gases or ordinary liquids through the tiny pore spaces in storage rocks. The blue numbers show the volume of CO 2 at each depth compared to a volume of 100 at the surface. Source: Data from CO2CRC ( The suitability of deep saline formations for the storage of CO 2 is the result of various physical and chemical mechanisms that act on different time scales, such as dissolution and mineral precipitation. In stratigraphic and structural traps, CO 2 storage capacity can be estimated following procedures similar to those for oil and gas reservoirs, but still involves an understanding of temperature, pressure, and salinity constraints. In the large areas that do not have well-defined traps, a general rough estimate of capacity can be achieved through time-discounted estimates of dissolution potential. With time, increasingly secure physical and chemical trapping mechanisms come into play, and the overall security of storage in saline formations increases (Fig. 3). However, it is critical to understand the displacement and migration of saline water and the injected CO 2 within these deep formations. The GS potential of saline formations is very large, but accurate capacity estimates require significant local refinement and modeling. The GS potential for saline formations in portions of the United States has been estimated to range from 900 billion to more than 3300 billion metric tons.  Oil and Gas Reservoirs Mature oil and gas reservoirs have held crude oil and natural gas over millions of years. They consist of a layer of permeable rock with a layer of non-permeable rock (caprock) above, such that the nonpermeable layer forms a trap that holds the hydrocarbons in place. Oil and gas fields have many characteristics that make them excellent target locations for GS of CO 2. The geologic conditions that trap oil and gas are also the conditions that are conducive to CO 2 storage. As a value-added benefit, CO 2 injected into a mature oil reservoir can enable incremental oil recovery. A small amount of CO 2 will dissolve in the oil, increasing the bulk volume and decreasing the viscosity, thereby facilitating flow to the wellbore. Typically, primary oil recovery and secondary recovery via water flooding produce 30 40% of a reservoir s original oil in place (OOIP). A CO 2 flood allows recovery of an additional 10 15% of the OOIP. Oil and gas reservoirs are the best understood of the potential GS options as a result of exploration for, and production of, hydrocarbons. The volume of CO 2 that can be stored in
5 Geologic Carbon Capture and Storage The suitability of a coal seam for CO 2 GS can be evaluated on technical, economic, and regulatory (resource protection) criteria. [14,15] However, limited operating experience with ECBM technology and poor understanding of CO 2 /coal interactions under reservoir conditions has limited storage applications. A number of pilot projects in coal seams are underway or planned to address gaps in knowledge. An initial estimate of GS potential of coal seams in the United State is billion metric tons.  Fig. 3 As time passes, increasingly secure trapping mechanisms come into play, and overall storage security increases. This is especially important in saline formations where relatively well understood structural and stratigraphic trapping operates over short time frames. Source: Data from CO2CRC ( an oil and gas reservoir can be estimated based primarily on the reservoir s depth and size and the volume of produced fluids.  Over the past 30 years, enhanced oil recovery (EOR) using CO 2 flooding has proven to be valuable technology in areas with natural CO 2 supplies, as miscible and immiscible CO 2 flooding can revitalize mature oil fields. At present, limited availability of CO 2 in most regions constrains production from CO 2 -based EOR. However, carbon capture applied to advanced electric power generation facilities and other industrial processes could produce large quantities of CO 2, which could be sold to oil and gas producers for use in enhanced oil and gas recovery while at the same time storing CO 2 in reservoirs deep beneath the earth s surface. An initial estimate of GS potential of oil and gas fields in the United State exceeds 83 billion metric tons.  Coal Seams Unminable coal seams are seams that are too deep or too thin to be economically mined. All coals have varying amounts of methane adsorbed onto pore surfaces, and wells can be drilled into unminable 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 CO 2. Depending on coal rank and properties, two or more molecules of CO 2 are adsorbed for each molecule of methane released, thereby providing an excellent storage site for CO 2 with the additional benefit of enhanced coalbed methane (ECBM) recovery. Similar to maturing oil reservoirs, unminable coalbeds are good value-added candidates for CO 2 storage. Monitoring, Verification, and Accounting Geologic storage of CO 2 requires monitoring, verification, and accounting (MVA) activities at the storage site, as well as risk assessment and development of mitigation strategies that can be implemented should a problem arise. Effective application of MVA technologies ensures the safety of sequestration projects, with respect to both human health and the environment, and provides the basis for establishing carbon credits on trading markets for sequestered CO 2. Monitoring methods, such as subsurface pressure monitoring, geochemical monitoring, well logging, and surface monitoring, will help demonstrate that the CO 2 is contained in the storage formation and not leaking. Other techniques, such as seismic imaging and electromagnetic imaging, provide an indication of where the CO 2 plume might migrate in the formation so that the monitoring strategies can be modified during the project s life. Risk assessment focuses on identifying and quantifying potential risks to humans and the environment associated with geologic CO 2 storage and helps to ensure that these risks remain low. For well-selected, designed, and managed GS sites, risks are estimated to be comparable to those associated with current hydrocarbon activities.  Conclusion Geologic storage is one of several strategies for reducing CO 2 emissions to the atmosphere. Several projects injecting CO 2 into geologic formations have been underway for more than a decade, and more than 30 years of industrial experience has demonstrated that CO 2 can be safely transported and injected into the deep subsurface. There are a number of challenges to the widespread implementation of the GS of CO 2, including reducing capital and operating costs, improving understanding of long-term CO 2 behavior in the subsurface, improving monitoring methods, developing a satisfactory regulatory environment, establishing long-term custody of the stored CO 2, and keeping the public informed and accepting of the technology (Fig. 4). Numerous pilot and large-scale field projects are underway or planned throughout the United States  and the world  over the next few years. Information from these projects
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