WORKING TOWARDS AN ASSESSMENT METHODOLOGY FOR CO2 STORAGE CAPACITY IN THE U.S

Geologic storage of CO₂ is a demonstrated method that can be applied to mitigate the millions of tons of CO₂ emitted each year by natural gas processing and coal gasification. Substantively reducing the anthropogenic CO₂ input to the atmosphere will also entail the storage of emissions from coal-powered electrical generating stations, whose collective output is approximately 500 megatonnes of CO₂ per year. Such an effort will require a large number of storage projects, each with a minimum lifetime of 20 to 50 years. To address this challenge, several geologic options will need to be considered, each having limitations. Oil and gas reservoirs represent the storage options with the highest geologic assurance because they possess a proven seal that has held fluids in a trap over long periods of time. Furthermore, the reported known resource for each oil and gas reservoir provides a proven trap volume that could be used for CO₂ storage. However, the majority of oil and gas reservoirs reside in the western U.S. whereas the majority of power plants are located in the eastern U.S. Saline formations collectively offer the highest storage capacity of any geologic target, and are frequently found in close proximity to power plants. However, saline formations lack the clearly defined trap volume and proven seal of oil and gas reservoirs. To successfully match geologic storage options with sequestration projects, a systematic approach to evaluate each option is needed. The USGS is in the process of defining a methodology to assess the storage capacity of geologic formations that incorporates such factors as the integrity of the storage option, location relative to CO₂ sources, and potential for enhanced oil and gas production to offset storage costs. The ability to integrate these factors will provide a systematic evaluation of overall storage “quality” relative to specific CO₂ storage projects. The resultant hierarchical ranking of storage targets will allow for a more robust assessment of storage capacity, going beyond basic calculations of total storage capacity in the U.S., and moving towards identifying the most useful space for the geologic storage of CO₂.