Numerical Simulation of Induced Seismicity Due to Hydraulic Fracturing of Shale Gas Reservoirs

Microseismic events in shale-gas hydraulic fracturing are due to propagation of induced fractures. Larger and noticeable seismic events are less likely to occur, but the probability of occurrence will increase in the presence of a pre-stressed fault. Intersection of an undetected and pre-existing fault/fracture with the production well is the main cause for upward extension of induced fractures. This upward extension of fractures may lead to reactivation of existing faults and can increase the induced seismicity potential. This study investigates the induced seismicity and fault reactivation potential associated with hydraulic fracturing operations when a limited-dimension fault exists close to the fracturing site. For this purpose, a 2D, fully coupled, hydro-mechanical, numerical model was developed to simulate changes in the stress distribution in the fractured zone and fault. The results obtained from the numerical simulations were used to determine the fault responses. Seismological theories were adopted along with the fault slips obtained from the numerical simulations to estimate the magnitude of induced seismic events. Parametric study was performed to investigate the impact of injection rate and fault permeability on the magnitude of an induced seismic event. In all cases which were examined, the magnitude of induced earthquake was very low and never reached to the level of a noticeable seismic event.