NATURAL GAS RESERVOIRS WITH HIGH CO_2 CONCENTRATIONS AS NATURAL ANALOGS FOR CO_2 STORAGE

摘要

Natural gas accumulations with high CO_2 concentrations may be useful natural analogs for the study of long-term CO_2 storage in geologic strata if viewed in the context of "CO_2 systems". Comprehensive evaluation of a CO_2 system involves the identification of the following parameters: (1) the source and timing of CO_2 generation, (2) the CO_2 migration pathways, (3) the timing of CO_2 migration, and (4) the locations and nature of CO_2 traps and seals. The following three examples are described in terms of CO_2 systems: (1) the Ellenburger Fields of West Texas, (2) the Leadville Fields of the Paradox Basin, and (3) the Big Escambia Creek and Flomaton Fields of Mississippi. The USGS is applying this concept to the Indian Creek Field of West Virginia, a natural gas accumulation with a high concentration of CO_2, to determine the length of time that CO_2 has been trapped in the field. This information is crucial for geologic CO_2 storage projects, because it can be used to provide a degree of certainty that the CO_2 will remain in geologic traps for the required hundreds to thousands of years. Studies of CO_2 systems can provide important ground-truth information for future laboratory experiments, models, and CO_2 storage projects. Furthermore, the perspectives of CO_2 systems suggest that some high CO_2 fields can themselves be CO_2 storage sites, because these fields have held CO_2 over geologic time scales.