Abstract

Analysis of the spatiotemporal distribution of seismic events in Youngstown, Ohio, from previous studies has revealed that the seismicity was triggered by injection during January through December 2011 into a brine-disposal well (North Star #1 well). Investigation of the hypocenters of induced earthquakes, which were substantially deeper than the injection zones in the well, brings the question of how pore pressure could migrate more than a kilometer below the injection zone into the Precambrian basement rock to cause induced seismicity. By doing numerical modeling of brine injection into the North Star #1 well, it is possible to better understand the relationship among induced-seismicity hypocenter locations, pressure diffusion, and formation geology. The effects of geologic and geomechanical characteristics of subsurface formations have been studied, the potential of hydraulic fracturing during brine injection has been considered, and the potential presence of conductive fault or fractured zones has been evaluated. Results show that conductive fractures and faults could be considered one of the main causes of deep induced seismicity by serving as conduits to the deeper, critically stressed basement faults. In addition, heterogeneity along the fault zone could be one of the reasons for lateral migration of earthquake hypocenters over time.

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