A method for characterizing the earthquake-inducing capacity of hydraulic fracturing

The seismicity rate in the Southern Sichuan Basin, China (SSBC), has increased by orders of magnitude within the past a few years accompanying the rapidly growing hydraulic fracturing (HF) operations. However, there is currently no appropriate method to directly determine whether a HF platform has induced seismicity and to quantitatively describe its potential of inducing earthquakes. In this study, by taking advantage of a more complete seismic catalog constructed from temporary short-period seismic stations and broadband stations for two adjacent well pads in the SSBC, we investigate a new statistical metrics for detailed studies of earthquake clusters on the "pre- and post-fracture" time scales to characterize their earthquake-inducing capacity. After declustering the earthquake catalog, a small-scale “Spatiotemporal Association Filter (SAF)” is designed to obtain seismic data closely associated with six independent fracturing well groups, and an “Unit Seismic Energy Release (USER)” index is established to evaluate the potential to induce earthquakes. Comparing the differences in the index before and after fracturing, as well as the nonparametric statistical test of each well group’s “Interevent time (IET)” and historical IET, four of the well groups are considered “induced-seismic”, and the other two are “anti-seismic”. The HF well with the largest USER value has the largest inducing capacity. The paired result of the nonparametric test shows that the p values are less than 0.001, indicating significant statistical differences between the IET series before and after the HF process around the four induced-seismic wells. To sum up, our method can conveniently distinguish the earthquake-inducing capacity of different HF wells, and thus offer practical advice for HF operation in the SSBC.