National assessment of geologic carbon dioxide storage resources: Summary

The U.S. Geological Survey (USGS) recently completed an evaluation of the technically accessible storage resource (TASR) for carbon dioxide (CO2) for 36 sedimentary basins in the onshore areas and State waters of the United States (fig. 1). The TASR is an estimate of the geologic storage resource that may be available for CO2 injection and storage and is based on current geologic and hydrologic knowledge of the subsurface and current engineering practices. By using a geology-based probabilistic assessment methodology, the USGS assessment team members obtained a mean estimate of approximately 3,000 metric gigatons (Gt) of subsurface CO2 storage capacity that is technically accessible below onshore areas and State waters; this amount is more than 500 times the 2011 annual U.S. energy-related CO2 emissions of 5.5 Gt (U.S. Energy Information Administration, 2012).

In 2007, the Energy Independence and Security Act (Public Law 110–140) directed the U.S. Geological Survey to conduct a national assessment of geologic storage resources for CO2 in consultation with the U.S. Environmental Protection Agency (EPA), the U.S. Department of Energy (DOE), and State geological surveys. The USGS developed a methodology to estimate storage resource potential in geologic formations in the United States (Burruss and others, 2009; Brennan and others, 2010; Blondes, Brennan, and others, 2013). In 2012, the USGS completed the assessment, and the results are summarized in this Fact Sheet (fig. 2A,B; tables 1, 2) and are provided in more detail in companion reports (U.S. Geological Survey Geologic Carbon Dioxide Storage Resources Assessment Team, 2013a,b).

Figure 2. Pie charts showing mean estimates by the U.S. Geological Survey in 2012 of technically accessible storage resources (TASR) for carbon dioxide (CO2) in the United States by (A) type and class and (B) region. Resources were estimated for eight geographic regions shown in figure 1. A mean total of 3,000 metric gigatons (Gt) of storage resources was estimated to exist in buoyant and residual storage types. The known recovery replacement storage resource (KRRSR) is not shown in part A but is included in the buoyant storage type. Resources in federally owned offshore areas were not assessed. Mean values sum to totals but are reported to only two significant figures. Percentages were calculated from unrounded resource estimates.

The goal of this project was to conduct an initial assessment of storage capacity on a regional basis, and results are not intended for use in the evaluation of specific sites for potential CO2 storage. The national assessment was a geology-based examination of all sedimentary basins in the onshore and State waters area of the United States that contain storage assessment units (SAUs) that could be defined according to geologic and hydrologic characteristics. Although geologic storage of CO2 may be possible in some areas not assessed by the USGS, the SAUs identified in this assessment represent those areas within sedimentary basins that met the assessment criteria. A geologic description of each SAU was prepared; descriptions for SAUs in several basins are in Warwick and Corum (2012).

The resources were estimated without consideration either of accessibility due to land-management or regulatory restrictions or of economic viability. Thus, if storage of CO2 within a formation is feasible with current technology, it was considered for this report. Because the legislation that mandated this assessment (Public Law 110–140) required that the assessment incorporate EPA regulations about underground sources of drinking water, a substantial percentage of potential storage formations containing water with less than 10,000 milligrams per liter (mg/L) of total dissolved solids (TDS) (considered freshwater for the purpose of this assessment) was disqualified as a protected underground source of potential drinking water.

The SAU is a mappable volume of rock that consists of a porous reservoir and a bounding regional sealing formation. The upper vertical limit chosen for this assessment was 3,000 feet (914 meters) because CO2 at this depth is typically subjected to temperatures and pressures that maintain the CO2 in a supercritical state and maximize the storage resource per unit volume. The lower vertical limit for the SAU of 13,000 ft (3,962 m) is based on the potential CO2 injection depth at pipeline pressures without additional compression at the surface. Standard SAUs are between depths of 3,000 ft (914 m) and 13,000 ft (3,962 m). If reservoir rock properties suggested that a viable storage resource is present at depths below 13,000 ft (3,962 m), the assessment geologist may have added an additional deep SAU for this deeper reservoir.

Sedimentary rocks of deep saline formations and of existing oil and gas fields were evaluated. Specifically, 33 sedimentary basins, or combined basin areas, within 8 regions of the United States were assessed (table 2). Numerous other basins (study areas shown in bluish gray in fig. 1) were evaluated but not assessed because existing geologic conditions and available data indicated that the areas failed to meet the minimum requirements for CO2 storage as outlined in Brennan and others (2010). Within the assessed basins, 202 SAUs were identified as having good storage potential because of the presence of a robust regional seal, adequate reservoir rock, and sufficient areas containing saline formation waters. Ten of the SAUs did not have sufficient data to build a robust geologic model to accurately estimate the storage resource and were designated as nonquantitative SAUs; no storage resources were estimated for the 10 nonquantitative SAUs. Three basins (Central California Coast Basins; Columbia Basin of Oregon, Washington, and Idaho; and Raton Basin) contain only nonquantitative SAUs, bringing the total number of basins shown in figure 1 to 36. For nonquantitative SAUs, surficial geographic boundaries were defined and a geologic description was prepared.

Two general storage types, buoyant and residual, were defined in the methodology used in this assessment. Buoyantly trapped CO2 can be held in place in porous formations by top and lateral seals. Residually trapped CO2 can be held in porous formations as individual droplets within pores by capillary forces. The residual storage resource consists of three injectivity classes based on reservoir permeability: residual trapping class 1 (R1SR) represents storage in rocks with permeability greater than 1 darcy (D); residual trapping class 2 (R2SR) represents storage in rocks with moderate permeability, defined as permeability between 1 millidarcy (mD) and 1 D; and residual trapping class 3 (R3SR) represents storage in rocks with low permeability, defined as permeability less than 1 mD.

The known recovery replacement storage resource (KRRSR) is the mass of CO2 that can be stored in existing hydrocarbon reservoirs. The KRRSR is a minimum range of values that represent the amount of CO2 at subsurface conditions that could replace the volume of known hydrocarbons in petroleum reservoirs. KRRSR is determined from production volumes rather than the geologic model of buoyant and residual resources that make up the TASR. The same type of resource is also included in the buoyant storage type estimated from a geologic model.

Regions with the largest technically accessible storage resources (TASR) are the Coastal Plains Region (mean estimate of 1,900 Gt, of which about 1,800 Gt, or 91 percent, is in the U.S. Gulf Coast) and the Alaska Region (mean estimate of 270 Gt), where the resource is almost entirely in the Alaska North Slope. Most (89 percent) of the TASR is in the residual trapping class 2 storage resource category (mean estimate of 2,700 Gt; fig. 2A). Residual trapping classes 1 and 3 account for 5 and 4 percent of the TASR, respectively. The USGS team obtained a mean estimate of 44 Gt for storage in buoyant traps, BSR. The mean estimate for KRRSR storage resources available in petroleum reservoirs within the assessed areas is 13 Gt (table 1).

The 44 Gt (mean estimate) of buoyant trapping storage resources includes non-hydrocarbon-bearing reservoir formations, but most of the resources are well defined by hydrocarbon exploration data. Existing oil in hydrocarbon reservoirs may be produced in the near future by using enhanced-oil-recovery technology that utilizes anthropogenic CO2 (fig. 3), and then the reservoirs could be used for CO2 storage. Because of the depth of knowledge about the hydrocarbon reservoirs, buoyant trapping storage resources in these reservoirs may be more attractive for storage of CO2 than residual trapping storage resources.

By U.S. Geological Survey Geologic Carbon Dioxide Storage Resources Assessment Team

Peter D. Warwick, Project Chief Madalyn S. Blondes Sean T. Brennan Marc L. Buursink Steven M. Cahan James L. Coleman Troy A. Cook Margo D. Corum Jacob A. Covault William H. Craddock Christina A. DeVera Colin Doolan Ronald M. Drake II Lawrence J. Drew Joseph A. East Philip A. Freeman Christopher P. Garrity Kevin J. Gooley Mayur A. Gosai Hossein Jahediesfanjani Celeste D. Lohr John C. Mars Matthew D. Merrill Ricardo A. Olea Tina L. Roberts-Ashby William A. Rouse Paul G. Schruben John H. Schuenemeyer Ernie R. Slucher Brian A. Varela Mahendra K. Verma

For information, please contact:

Mail Stop 956 12201 Sunrise Valley Drive Reston, VA 20192

Telephone: (703) 648–6469 E-mail: pwarwick@usgs.gov

Director, Eastern Energy Resources Science Center

Mail Stop 956 12201 Sunrise Valley Drive Reston, VA 20192

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