Hydrology of the Forest City basin, Mid-Continent, USA: implications for CO_2 sequestration in the St. Peter Sandstone

摘要

The central United States contain numerous coal-burning electric power plants that emit large amounts of CO_2 for which a nearby suitable disposal site would be desirable. The results of a reconnaissance study reported here indicate that the St. Peter Sandstone in the Forest City basin has potential large-scale CO_2 sequestration capacity, despite the basin's overall relatively shallow depth. A three-dimensional stratigraphic model of the basin constructed from published well logs reveals that about 59 % of the St. Peter in the basin lies below a depth of 750 m, where CO_2 would exist in a supercritical state for increased storage efficiency. Based on a porosity of 15 % and a storage efficiency factor of 5.4 %, the St. Peter in the basin could potentially sequester upto ～ 830 M tonnes of CO_2, equating to upto 23,500 tonnes of CO_2 per km~2. A three-dimensional hydrologic model coupling groundwater flow, heat transport, and salinity transport provided insights into how CO_2 might be transported in the basin. The results show a consistent pattern of predominantly southwestward groundwater flow in the northern part of the basin and predominantly eastward flow in the southern part of the basin. Groundwater average linear velocities are known with much less confidence, but in the St. Peter are mostly under 10 m/year and lack a strong vertical component. Mineralogical analysis shows the St. Peter to be composed almost entirely of quartz, suggesting that the St. Peter would be resistant to dissolution by CO_2-enriched fluids and accompanying increases in porosity and permeability.