Geologic framework for the national assessment of carbon dioxide storage resources

The 2007 Energy Independence and Security Act (Public Law 110–140) directs the U.S. Geological Survey (USGS) to conduct a national assessment of potential geologic storage resources for carbon dioxide (CO₂) and to consult with other Federal and State agencies to locate the pertinent geological data needed for the assessment. The geologic sequestration of CO₂ is one possible way to mitigate its effects on climate change. The methodology used for the national CO₂ assessment (Open-File Report 2010-1127; http://pubs.usgs.gov/of/2010/1127/) is based on previous USGS probabilistic oil and gas assessment methodologies. The methodology is non-economic and intended to be used at regional to subbasinal scales. The operational unit of the assessment is a storage assessment unit (SAU), composed of a porous storage formation with fluid flow and an overlying sealing unit with low permeability. Assessments are conducted at the SAU level and are aggregated to basinal and regional results. This report identifies and contains geologic descriptions of SAUs in separate packages of sedimentary rocks within the assessed basin and focuses on the particular characteristics, specified in the methodology, that influence the potential CO₂ storage resource in those SAUs. Specific descriptions of the SAU boundaries as well as their sealing and reservoir units are included. Properties for each SAU such as depth to top, gross thickness, net porous thickness, porosity, permeability, groundwater quality, and structural reservoir traps are provided to illustrate geologic factors critical to the assessment. Although assessment results are not contained in this report, the geologic information included here will be employed, as specified in the methodology, to calculate a statistical Monte Carlo-based distribution of potential storage space in the various SAUs. Figures in this report show SAU boundaries and cell maps of well penetrations through the sealing unit into the top of the storage formation. Wells sharing the same well borehole are treated as a single penetration. Cell maps show the number of penetrating wells within one square mile and are derived from interpretations of incompletely attributed well data, a digital compilation that is known not to include all drilling. The USGS does not expect to know the location of all wells and cannot guarantee the amount of drilling through specific formations in any given cell shown on cell maps.