Nonlinear Pore Pressure Diffusion and Associated Microseismicity in Rocks with Pressure-dependent Permeability

The fluid transport properties of fractured porous rocks usually show a strong dependence on the effective pressure and thus on the pore pressure. Consequently the process of pore pressure diffusion initiated by fluid injection experiments is governed by the non-linear diffusion equation. The spatio-temporal evolution of microseismicity associated with the process of nonlinear pore pressure diffusion is analyzed. In particular, it is shown that the process of nonlinear pore pressure diffusion allows to define two triggering fronts. One corresponding to the triggering of microseismic events without changing the fluid transport properties significantly, another one that triggers the majority of microseismic events and that alters the fluid transport properties significantly. The applicability of this model for the interpretation of microseismicity observed during hydraulic fracturing treatments is discussed.