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Microseismic monitoring at the Illinois Basin-Decatur Project (IBDP) is accomplished using a combination of commercially available components that are integrated to provide real-time analysis and remote processing capabilities by means of a purpose-built data management system and secure web portal. The processing workflow consists of real-time, remote access, and inhouse processing components, which provides a seamless path from in-field quality control to final locations with short turnaround times. Event location is performed using an adaptation of the Geiger method, which is designed to be robust for the sparse but localized observation sets typically encountered with injection monitoring. Observed microseismicity displayed distinct linear clustering and increased in distance from the injection well over time, presenting challenges for location accuracy of more distal events. The velocity model, a key component in event location and characterization, evolved through early stages of the project as new wells were drilled providing the opportunity for improved observation geometry and acquisition of additional controlled energy source points for model calibration. The experience gained at IBDP highlights the importance of field systems and processing flows that allow adaptation to evolving operational conditions and microseismic event activity.

The Illinois Basin-Decatur Project (IBDP) is a large-scale carbon dioxide (CO 2) injection and storage demonstration project. Over a three-year period one million metric tons of CO 2 were injected deep into the Mt. Simon Sandstone, a deep saline reservoir in the Illinois Basin. This study examines the microseismic data gathered for the period from May 2010 to November 2011, which preceded the CO2 injection. Microseismic events are detected through permanent geophone arrays installed in two wells. A CO 2 injection well drilled to the depth of 7,236 feet (2,205 m) is outfitted with a 4-component geophone array. Situated approximately 185ft away (56m), the 3,502 feet (1,067m) deep geophysical monitoring well contains a 3-component geophone array. During the pre-injection period, a total of 7,894 microseismic events were detected and 99% of these correlate with drilling and other well-related operations. Eight local microseismic events were identified that appear unrelated to well activity and appear representative of the background level of microseismicity. Regional seismicity was also examined by changing triggering parameters and producing a second dataset. Under this configuration, the system detected twelve regional seismic events that correlate to the United States Geological Survey (USGS) earthquake record, and approximately 1,100 distant events are believed associated with quarry-related blasting operations.

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