From the Summary: "This report answers frequently asked questions about the geologic storage of carbon dioxide (CO2). The questions are broadly representative of typical inquiries regarding the process and mechanics of storing CO2 underground, how much might be stored, and what might happen to CO2 once it is injected underground. Geologic storage is one step in a process termed 'carbon capture and storage', or CCS. Following capture and transportation, CO2 would be injected into geologic formations that have suitable volume, or pore space, to retain large quantities of the captured gas. Currently, the most promising reservoirs for storing CO2 are oil and gas fields, deep saline reservoirs, and unmineable coal seams. Preventing CO2 from escaping would require careful reservoir characterization. Knowledge gained from over 30 years of injecting CO2 underground to enhance oil recovery would be applied to storing CO2 for CCS purposes. Given the complexity of most geologic reservoirs, and the potentially huge volumes of CO2 that may be injected, risk of some CO2 leakage over time may never completely be eliminated. A variety of techniques are available for monitoring leaks from a reservoir; however, the long-term (hundreds to thousands of years) fate of CO2 stored underground is not thoroughly understood."
CRS Report for Congress, RL34218