Geomechanics simulation of stress regime change in hydraulic fracturing: a case study

Unconventional geomechanics has attracted research interests in shale gas development, owing to the potential to mitigate drilling risk and optimize hydraulic fracturing. In the Yichang shale gas reservoir, one of the tough challenges in shale gas exploitation is the low gas production rate after hydraulic fracturing. To address mechanisms behind this problem, a comprehensive 3D geomechanics model which accounts for the anisotropy and spatial heterogeneity of shale is established. Shale anisotropy is characterized by the inversion of sonic data, and heterogeneity is achieved by using seismic velocity as a controlling trend among wells. Various scales of natural factures are incorporated from geophysical inversion, which have impacts on stress disturbance and the propagation of hydraulic fracturing networks. The established geomechanics model is validated with the detected pore pressure, minimum horizontal stress, and drilling risks field data. The model is then used to quantify the vertical stress barrier in hydraulic fracturing. To uncover the poor hydraulic fracturing effect in the Yichang shale gas reservoir, a coupled geomechanics and hydraulic fracturing simulation is also made. Results show that the “stress shadow” impacts the propagation of the hydraulic fracturing network in the adjacent hydraulic fracturing stage. The change of stress regime from strike-slip to reverse fault after hydraulic fracturing inhibits the propagation of fracturing network horizontally, and results in a low-gas production rate.