Hydraulic fracturing is an effective technique for shale gas development, which breaks tight shale by injecting a large amount of fracturing fluid under high pressure. The potential impacts of hydraulic fracturing on the surrounding environments (such as hydraulic fracturing induced earthquakes) have aroused extensive attentions. Hence it is necessary to study on the evolution rules of reservoir in-situ stress and fault stability during the water injection process of hydraulic fracturing.
In this work, a three-dimensional geomechanical model of a shale gas reservoir which located in Southwestern China is established firstly; Based on the in-situ stress field, numerical simulations on the influence of local in-situ stress and fault stability during quasi-dynamic and dynamic water injection are made. With the calculated shear strain distribution, a workflow for evaluating the seismic moment response in the fault region during water injection is proposed.
Hydraulic fracturing (HF) is an effective technique for shale gas development, which breaks tight shale by injecting a large amount of fracturing fluid under high pressure. The potential impacts of HF on the surrounding environments (such as HF induced earthquakes) have aroused extensive attentions. The mechanisms of fault activation caused by HF mainly includes pore pressure diffusion and pore elastic stress transmission (Ellsworth et al., 2013). Scuderi et al. (2016) conducted an indoor water injection test at centimeter scale, and the results show that aseismic slide induced by pore pressure diffusion can activate the sliding of the fault in the non-pressurized faults. Similar conclusion can also be found in Barros et al. (2018) indoor experiments at ten meters scale. Through in-situ and indoor water injection tests and numerical simulation studies that the friction properties of the fault change with fluid injection, and the shear stress of the fault increases with the propagation of seismic sliding, which ultimately induces seismic sliding in the non-pressurized area of the fault (Cappa et al., 2015, 2019). Through the research on the 2016 Alberta earthquake of magnitude WM4.1 induced by hydraulic fracturing in Canada, confirmed that the seismic sliding in the area affected by pore pressure diffusion of the fault on a kilometer scale can activate the seismic sliding in the non-pressurized area at the far end of the fault (Eyre et al., 2019).
