A Statistical Model for Seismic Hazard Assessment of Hydraulic-Fracturing-Induced Seismicity

Abstract:

We analyze the inter event time distribution of hydraulic-fracturing-induced seismicity collected during 18 stages at four different injection locations. We identify the statistical process describing the distribution of hydraulic-fracturing-induced events in time and develop a statistical model to compute the occurrence probability of hydraulic fracturing-induced seismicity. This model can be used to assess the seismic hazard associated with hydraulic fracturing operations. We observe a universal distribution of waiting times between subsequently occurring events. The distribution is given by the exponential distribution of the homogeneous Poisson process (HPP). Moreover, the process of event occurrence in the injection volume domain is a HPP. Our findings suggest that hydraulic-fracturing-induced seismicity is directly triggered by the relaxation process of stress and pore pressure perturbation that initially was created at the injection source. Compared to this relaxation process the stress transfer, caused by the occurrence of preceding seismic events, is insignificant for the seismogenesis of subsequently occurring events. It means that no aftershock triggering has to be included in the statistical model. This is an important difference to naturally occurring earthquakes, which has to be considered during seismic hazard assessment of fluid injection-induced seismicity.