Laboratory Modeling of Induced Microseismicity in the Illinois Basin
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The CarbonSAFE Macon County Project is evaluating the potential for injecting and geologically storing commercial quantities of CO2 captured from large industrial emitters in the Illinois Basin. Determining the potential for induced seismicity is an important component of this evaluation. Microseismic activity recorded from previous demonstration projects appears to be related to development on planes of weakness in the low-permeable Precambrian crystalline basement that lies below the injection formation. To evaluate induced seismicity risk for the development of large commercial projects, detailed investigations of fault stability should be performed case specifically before injection starts. In the case of Illinois Basin, industrial scale projects could potentially involve carbon dioxide injection of several million tonnes CO2 per year, so both the geomechanical properties of rocks and fault material and the stress state should be properly characterized. In this study, the cores of Precambrian rhyolite are recovered from more than 2 km depth in CarbonSAFE Macon County Well and preliminary X-ray CT scanning shows presence of sealed fractures in some of them, while others appear to be intact. The influence of fractures on rock's poroelastic and strength properties is investigated. Laboratory data is used in a numerical code to simulate the reservoir and basement response and explain the observed induced seismicity.The CarbonSAFE Macon County project is evaluating the potential for injecting and geologically storing CO2 captured from large industrial emitters in the Illinois Basin. A consideration of this evaluation is the potential to induce seismic activity as a result of increased reservoir pressures from commercial-scale injection. Induced seismicity is of a major concern, because it is believed that even small- to moderate-sized earthquakes threaten the seal integrity of CO2 repositories, possessing significant risk on large scale storage operations (Zoback and Gorelick, 2012). A demonstration carbon capture and storage (CCS) project the Illinois Basin Decatur Project (IBDP) injected approximately 1MT CO2 over three years into a Cambrian sandstone reservoir about 2,100 m deep in the Illinois Basin (Bauer et al., 2016), underlain mainly by the Eastern Granit-Rhyolite province (Leetaru and Freiburg, 2014). Deep wellbore geophones at IBDP detected microseismic activity believed to be concentrated in the crystalline basement (Goertz-Allmann et al., 2017; Bauer et al., 2019) right below the injection formation. The basement has small porosity (<0.02) and permeability (<1019 m2), therefore, it could be possible that reservoir overpressure transfers to the basement through preexisting fractures.
