Wednesday, July 16, 2008
Given the supplies of coal available to the US and China, it is critical that effective carbon capture and sequestration technologies be developed and that effective environmental protections be put in place to regulate those technologies. While some have suggested ocean sequestration of CO2, the preferred type of carbon capture and sequestration is geologic sequestration. With geological sequestration, CO2 is captured from flue gas produced by fossil-fueled power plants or industrial facilities, compressed to convert it from a gaseous state to a supercritical fluid, and transported to the sequestration site, usually by pipeline. The fluid CO2 is then injected into deep subsurface rock formations through one or more wells, likely at depths greater than approximately 800 meters where pressure and temperature are sufficient to keep the CO2 in a supercritical state. When injected, CO2 is sequestered by a combination of physical and geochemical trapping processes. Physical trapping occurs when the relatively buoyant CO2 rises in the formation until it reaches a low-permeability layer that inhibits further upward migration, or when residual CO2 is immobilized in formation pore spaces. Geochemical trapping occurs when chemical reactions between the dissolved CO2 and minerals in the formation lead to the precipitation of solid carbonate minerals. Similarly, naturally-occurring CO2 deposits have been physically and geochemically trapped in geologic formations for millions of years.
Injection of any substance into a well is regulated under the Underground Injection Control regulations promulgated under the Safe Drinking Water Act. EPA believes that the relative buoyancy of CO2, its corrosivity in the presence of water, the potential presence of impurities in captured CO2, its mobility within subsurface formations, and large injection volumes anticipated at full scale deployment warrant specific requirements tailored to this new practice. So, EPA has proposed a new class of UIC well for GS, a Class VI well, and requirements for such wells. Proposed UIC CO2 Rule