RELATIONSHIPS BETWEEN THE PROXIMITY OF WASTEWATER DISPOSAL AND HYDRAULIC FRACTURING TO CRYSTALLINE BASEMENT AND INDUCED SEISMICITY, CENTRAL AND EASTERN UNITED STATES

Over the past decade, the dramatic rise in seismicity in the central and eastern US has been attributed to industry operations associated with wastewater injection and hydraulic fracturing. While most of the observed seismicity has occurred in sedimentary basins that have experienced overall increases in oil and gas development (e.g. the Anadarko and Ft. Worth basins), other basins with similar activity (e.g. the Williston and northern Appalachian basins) have experienced very little, if any, induced seismicity. While hydro-geomechanical modeling indicates that induced seismicity may be related to the proximity of critically stressed faults in the crystalline basement, recent studies have interpreted that there is no correlation and concluded that nearly all induced seismicity is a result of high-rate fluid injection. To test these interpretations we evaluated water disposal and well completion records from the Appalachian, Illinois, and Williston basins, and compared them with induced seismic sequences identified through seismic template matching of known or suspected induced events. Research results indicate a strong correspondence between induced seismic events and the proximity of subsurface wastewater injection/hydraulic fracturing targets to crystalline basement rocks. For example, in the northern Appalachian Basin, of the >20 identified induced seismic sequences, all but two were associated with injection/completion targets located at depths within ~1 km of the basement. In parts of the basin where target intervals are at depths >1 km from basement, induced events have been recorded only in proximity to basement-involved faults. In addition, in the Williston Basin most disposal interval/hydraulic fracturing targets are >1 km above the crystalline basement which may explain the lack of induced seismic events in the region. Collectively, the results of our investigation suggest that proximity to basement is an important variable in considering the likelihood of induced seismicity associated with wastewater disposal and hydraulic fracturing. This has important implications regarding induced-seismic risk assessment related to the siting of new disposal wells and/or the production of hydrocarbon from near-basement reservoirs.