Hydraulic fracturing-induced seismicity: an overview of recent observations and implications on development
Adam Baig and Ted Urbancic demonstrate that many instruments are insufficient to characterize induced seismicity associated with hydraulic fracturing and that more realistic target magnitudes are needed. An accurate magnitude calculation is critical to assessing the impact of hydraulic fracturing on seismic hazards as well as correctly characterizing the fractures that are activated during the stimulation. Recently, Warpinski (2013) asserted that seismicity associated with hydraulic fracturing rarely attains magnitudes above 0.5; on the other hand Holland (2011) documents hydraulic fracture-induced seismicity in the Eola field in Oklahoma reaching magnitudes of 2.8. While it can be argued that the latter dataset may be unusual, there is a fundamental difference between the datasets considered in that the former data are collected from downhole monitoring arrays utilizing 15Hz geophones, primarily tasked with the routine tasks of hydraulic fracture monitoring of delineating stimulation volumes with event locations; whereas Holland’s study used USArray broadband stations with the low-frequency response necessary to accurately characterize the larger magnitude events. Given the ubiquity of arrays of 10 Hz or 15 Hz geophone arrays for industrial monitoring of hydraulic fracturing, it is an open question whether and how frequently larger-magnitude events (>M0) are generated during these stimulations given the inadequacy of these instruments for characterizing larger-magnitude events.