DOE OSTI2014
The studies summarized herein were conducted during 2009–2014 to investigate the utility of the Knox Group and St. Peter Sandstone deeply buried geologic strata for underground storage of carbon dioxide (CO 2 ), a practice called CO 2 sequestration (CCS). In the subsurface of the midwestern United States, the Knox and associated strata extend continuously over an area approaching 500,000 sq. km, about three times as large as the State of Illinois. Although parts of this region are underlain by the deeper Mt. Simon Sandstone, which has been proven by other Department of Energy-funded research as a resource for CCS, the Knox strata may be an additional CCS resource for some parts of the Midwest and may be the sole geologic storage (GS) resource for other parts. One group of studies assembles, analyzes, and presents regional-scale and point-scale geologic information that bears on the suitability of the geologic formations of the Knox for a CCS project. New geologic and geo-engineering information was developed through a small-scale test of CO 2 injection into a part of the Knox, conducted in western Kentucky. These studies and tests establish the expectation that, at least in some locations, geologic formations within the Knox will (a) accept a commercial-scale flow rate of CO 2 injected through a drilled well; (b) hold a commercial-scale mass of CO 2 (at least 30 million tons) that is injected over decades; and (c) seal the injected CO 2 within the injection formations for hundreds to thousands of years. In CCS literature, these three key CCS-related attributes are called injectivity, capacity, and containment. The regional-scale studies show that reservoir and seal properties adequate for commercial-scale CCS in a Knox reservoir are likely to extend generally throughout the Illinois and Michigan Basins. Information distinguishing less prospective subregions from more prospective fairways is included in this report. Another group of studies report the results of reservoir flow simulations that estimate the progress and outcomes of hypothetical CCS projects carried out within the Knox (particularly within the Potosi Dolomite subunit, which, in places, is highly permeable) and within the overlying St. Peter Sandstone. In these studies, the regional-scale information and a limited amount of detailed data from specific boreholes is used as the basis for modeling the CO 2 injection process (dynamic modeling). The simulation studies were conducted progressively, with each successive study designed to refine the conclusions of the preceding one or to answer additional questions. The simulation studies conclude that at Decatur, Illinois or a geologically similar site, the Potosi Dolomite reservoir may provide adequate injectivity and capacity for commercial-scale injection through a single injection well. This conclusion depends on inferences from seismic-data attributes that certain highly permeable horizons observed in the wells represent laterally persistent, porous vuggy zones that are vertically more common than initially evident from wellbore data. Lateral persistence of vuggy zones is supported by isotopic evidence that the conditions that caused vug development (near-surface processes) were of regional rather than local scale. Other studies address aspects of executing and managing a CCS project that targets a Knox reservoir. These studies cover well drilling, public interactions, representation of datasets and conclusions using geographic information system (GIS) platforms, and risk management.
54 ENVIRONMENTAL SCIENCES↗