Effects of Oscillating Pore Pressure of Fluid Injection on Fault Slip Described by Rate and State Friction

The injection of fluid into the Earth’s crust for the exploitation of subsurface resources can induce seismicity. These earthquakes can be relatively small, but their occurrence can prompt the interruption or termination of injection activities. Therefore, improving seismic mitigation strategies related to fluid injection operations is of paramount importance. A fundamental factor of interaction between fluid injection and seismic events is the fluid oscillation amplitude and period at which slip occurs. Here, we use a frictional sliding model to simulate laboratory tests on cylindrical samples of sandstone subjected to fluctuating fluid pressure. Samples contain a sliding surface inclined to the axis cylinder created by a saw-cut. Advance of the vertical piston causes slip on the surface. High amplitudes and frequencies of pore fluid pressure oscillation facilitate the triggering of fault slip. In particular, the number of rapid events increases if period of pore pressure oscillation decreases. Also, the increase in normal stress promotes the occurrence of rapid episodes. Results provide insights into and support experimental observations. They help understanding the conditions for the occurrence of seismic events and their magnitude.