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Mechanisms Inducing Earthquakes in the Weiyuan Shale Gas Field, Sichuan, China, Inferred From Dense Array Recordings

Session: Mechanisms of Induced Seismicity: Pressure Diffusion, Elastic Stressing and Aseismic Slip IV

Type: Oral

Date: 4/20/2021

Presentation Time: 06:15 PM Pacific

Description: 

As one of the major shale gas blocks in China, the Weiyuan shale gas field has been actively developed since 2010, accompanying numerous hydraulic fracturing (fracking) activities. Accordingly, the number of earthquakes has been increasing drastically, with a few damaging earthquakes (M>4) in 2019, some of which led to fatalities in the region. Due to the relatively sparse seismic network, locations of these earthquakes bear appreciable uncertainties, in particular on focal depths. Thus, it remains unclear what mechanisms are dominant of inducing earthquakes in Weiyuan. Since April 2020, we have deployed a dense temporary array consisting of more than 130 short-period seismometers, forming a number of mini arrays. During the two-month deployment period, numerous earthquakes with magnitudes up to 3 have been recorded. We apply the machine learning detector, PhaseNet, to identify P and S arrivals. Then we associate the events and locate them by the double-difference method. The location results show a few different earthquake clusters. One cluster that well located within our mini-array stations exhibits clear lineations and temporal migration parallel to the horizontal wells, indicating that they are fracking-induced earthquakes. The earthquakes delineate dipping geometries and locate within 1 km below the Wufeng-Longmaxi formation where fracking was conducted, suggesting that they are likely induced by pore pressure diffusion. Benefiting from the temporary dense array, our location results with unprecedented resolution in the region advance our understanding of mechanisms of induced earthquakes in the Weiyuan shale gas field.

Presenting Author: Hongfeng Yang

Student Presenter: No

Authors