Abstract
It is generally considered that injection-induced seismicity is related to injection duration, injection volume, geological settings, and spatial relationships between the wells and preexisting faults. The seismicity in the Changning shale gas field, which is the largest shale gas field in China, has increased significantly since 2012. A 3D finite element model based on this area is established in our study for calculating the effect of injection on the regional stress field. The modelling results show that the permeability of sedimentary rock is a key factor for determining the fluid diffusion range and affects the stress field in deeper strata by controlling the gravity load. This effect is sufficient to induce earthquakes under critical conditions. Under a reasonable permeability (1.45 × 10−15 m2), injection may induce shallow-focus earthquakes (<3 km) by pore pressure increase and deep-focus earthquakes by increasing the gravity load. In addition, the low-permeability detachment surface below the injection well may buffer the perturbation of the stress field beneath it during injection.
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