On CO2 Behavior in the Subsurface, Following Leakage from aGeologic Storage Reservoir
The amounts of CO2 that would need to be injected intogeologic storage reservoirs to achieve a significant reduction ofatmospheric emissions are very large. A 1000 MWe coal-fired power plantemits approximately 30,000 tonnes of CO2 per day, 10 Mt per year(Hitchon, 1996). When injected underground over a typical lifetime of 30years of such a plant, the CO2 plume may occupy a large area of order 100km2 or more, and fluid pressure increase in excess of 1 bar(corresponding to 10 m water head) may extend over an area of more than2,500 km2 (Pruess, et al., 2003). The large areal extent expected for CO2plumes makes it likely that caprock imperfections will be encountered,such as fault zones or fractures, which may allow some CO2 to escape fromthe primary storage reservoir. Under most subsurface conditions oftemperature and pressure, CO2 is buoyant relative to groundwaters. If(sub-)vertical pathways are available, CO2 will tend to flow upward and,depending on geologic conditions, may eventually reach potablegroundwater aquifers or even the land surface. Leakage of CO2 could alsooccur along wellbores, including pre-existing and improperly abandonedwells, or wells drilled in connection with the CO2 storage operations.The pressure increases accompanying CO2 injection will give rise tochanges in effective stress that could cause movement along faults,increasing permeability and potential for leakage.Escape of CO2 from aprimary geologic storage reservoir and potential hazards associated withits discharge at the land surface raise a number of concerns, including(1) acidification of groundwater resources, (2) asphyxiation hazard whenleaking CO2 is discharged at the land surface, (3) increase inatmospheric concentrations of CO2, and (4) damage from a high-energy,eruptive discharge (if such discharge is physically possible). In orderto gain public acceptance for geologic storage as a viable technology forreducing atmospheric emissions of CO2, it is necessary to address theseissues and demonstrate that CO2 can be injected and stored safely ingeologic formations. This requires an understanding of the risks andhazards associated with geologic storage, and a demonstration that therisks are acceptably small or can be mitigated. Much work is currentlyunderway to develop comprehensive approaches towards risk assessment froma systems analysis perspective, which in general requires a simplifieddescription of physical and chemical processes (Maul, et al., 2004,Espie, 2004; Wildenborg, et al., 2004; Walton, et al., 2004). This typeof approach is very important, but needs to be complemented withdevelopment of an understanding of the physical and chemical processesassociated with CO2 storage and leakage (Evans, et al.,2004).
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE. Assistant Secretary for Fossil Energy.Coal
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 920245
- Report Number(s):
- LBNL-59628; R&D Project: G22401; BnR: AA1505000; TRN: US200825%%456
- Country of Publication:
- United States
- Language:
- English
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