In response to the 2007 Energy Independence and Security Act, the U.S. Geological Survey (USGS) conducted a national assessment of potential geologic storage resources for carbon dioxide (CO2). Storage of CO2 in subsurface saline formations is one important method to reduce greenhouse gas emissions and curb global climate change. This report provides updates and implementation details of the assessment methodology of Brennan and others (2010, http://pubs.usgs.gov/of/2010/1127/) and describes the probabilistic model used to calculate potential storage resources in subsurface saline formations.
The U.S. Geological Survey (USGS), in accordance with the Energy Independence and Security Act of 2007, developed a methodology to estimate storage potential that could be applied uniformly to geologic formations across the United States. An initial methodology was developed and published in March 2009 (Burruss and others, 2009), and public comments were received. The report was then sent to a panel of experts for external review.
This current report is in response to those external comments and reviews and describes the revised methodology. The resource that is assessed is the technically accessible storage resource, which is defined as the mass of CO2 that can be stored in the pore volume of a storage formation. The methodology that is presented in this report is intended to be used for assessments at scales ranging from regional to subbasinal in which storage assessment units are defined on the basis of common geologic and hydrologic characteristics. The methodology does not apply to site-specific evaluation of storage resources or capacity (see section 1.2). Calculations of subsurface pore volume for potential CO2 storage have been described in a number of publications (Bachu, 2003; Bradshaw, 2004; Bachu and others, 2007; U.S. Department of Energy, National Energy Technology Laboratory, 2008; van der Meer and Egberts, 2008). The methodology in this report is different in that it uses fully probabilistic methods to incorporate geologic uncertainty in calculations of storage potential.
The USGS has developed a methodology to assess the nation's resources for geologic carbon sequestration in oil and gas reservoirs and saline formations. The methodology estimates storage resource potential that can be applied uniformly to geologic formations across the United States. The assessed resource is the volume of pore space into which CO2 can be injected and retained for tens of thousands of years. The methodology builds geologic models of the areas to be assessed and then uses probabilistic methods to account for the uncertainties associated with natural variations in geologic storage formations. In addition, the range of numbers of likely storage sites and their potential sizes are statistically evaluated to estimate the distribution of the storage resource. The estimated mass of storage resource is further evaluated with parameters that describe the probability of successful containment of CO2 above a minimum size. This assessment methodology for CO2 storage resources focuses on what will be called the technically accessible resource, not a total in-place resource volume. This is a resource that may be available using present day geological and engineering knowledge and technology for CO2 injection into geologic formations. No economic factors are used in the estimation of the volume of storage resource.
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