Seismic Monitoring at the Decatur, IL, Geologic Carbon Dioxide Sequestration Site
Wednesday, 17 December 2014: 5:37 PM
The viability of carbon capture and storage (CCS) depends on safely sequestering large quantities of carbon dioxide over geologic time scales. One concern is the potential for induced seismicity. We report on seismic monitoring by the U.S. Geological Survey (USGS) at a CCS demonstration site in Decatur, IL. This is the first (and to date only) CCS project in the U.S. to inject large volumes of CO2 into an extensive undisturbed saline reservoir, and thus serves as an important test for future industrial-scale CCS projects. At Decatur, supercritical CO2 is injected at 2.1 km depth into the Mt. Simon Sandstone, which directly overlies granitic basement. The primary sealing cap is the Eau Claire Shale at a depth of about 1.5 km. The Illinois State Geological Survey (ISGS) manages the ongoing Illinois Basin - Decatur Project, a three-year project beginning in November 2011 during which CO2 is injected at an average rate of 1000 metric tons/day. Archer Daniels Midland (ADM) manages the nearby Illinois Industrial Carbon Capture and Storage project, which, pending permit approval, plans to inject 3000 metric tons/day for five years. The USGS seismic network was installed starting in July 2013 and consists of 12 stations, three of which include borehole sensors at depths of 150 m. The aperture of this network is roughly 8 km, centered on the injection well. A one-dimensional velocity model was derived from a vertical seismic profile survey acquired by ADM and the ISGS to a depth of 2.2 km, tied into acoustic logs from a deep observation well and the USGS borehole stations. This model was used together with absolute and double-difference techniques to locate seismic events. These events group into two clusters: 0.4 to 1.0 km NE and 1.8 to 2.6 km WNW from the injection well, with moment magnitudes ranging from -0.8 to 1.1. Most of these events are in the granitic basement, well below the cap rock, and are unlikely to have compromised the integrity of the seal.