The term “carbon sequestration” is used to describe both natural and deliberate processes by which CO2 is either removed from the atmosphere or diverted from emission sources and stored in the ocean, terrestrial environments (vegetation, soils, and sediment), and geologic formations. Scientists at the U. S. Geological Survey (USGS) are working to assess both the potential capacities and the potential limitations of the various forms of carbon sequestration and to evaluate their geologic, hydrologic, and ecological consequences. In accordance with the Energy Independence and Security Act of 2007, the USGS has developed scientifically based methods for assessment of biologic and geologic carbon sequestration capacities.
Biologic carbon sequestration refers to the assimilation and storage of atmospheric carbon in vegetation, soils, woody products, and aquatic environments. Fluxes of carbon dioxide and other greenhouse gases (GHG) in ecosystems are a function of natural ecosystem processes and anthropogenic activities. Section 712 of the EISA legislation mandates the U. S. Department of the Interior (DOI) to develop a methodology and conduct an assessment of carbon storage, carbon sequestration, and fluxes of three principal GHG for the Nation’s ecosystems. The three principal GHG are CO2, methane (CH4), and nitrous oxide (N2O). A biological carbon sequestration assessment methodology has been developed to fulfill the first part of the EISA requirements. The national assessment for biological carbon sequestration will be conducted in the course of the next 3-4 years beginning in fiscal year 2011.
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. Using the new methodology, the USGS has started the national assessment of geologic carbon sequestration storage potential. In the course of this assessment, USGS will work with a number of organizations to develop the geologic models needed for the assessment. These organizations include the U. S. Department of Energy, National Energy Technology Laboratory, U. S. Environmental Protection Agency, Bureau of Land Management, Bureau of Ocean Energy Management, Regulation and Enforcement, and State Geological Surveys and Universities.