Microseismic Signatures of Nonlinear Pore Pressure Diffusion

Modelling and analysis of microseismic signatures based on the nonlinear pore pressure diffusion equation in 2D is studied. The nonlinear diffusion equation is solved by using a finite element method on an irregular grid. Following the seismicity-based reservoir characterization approach microseismic earthquakes are triggered and analyzed regarding their spatio-temporal distribution. We find that there are significant differences in the microseismic signatures of linear and nonlinear pore pressure diffusion. It is shown that the microseismic event distribution is governed by two event triggering processes. One process interpreted as a fracturing front changing significantly the fluid transport properties and induces a large number of microearthquakes. Another triggering front that induces only a small number of microearthquakes ahead of the fracturing front. For the Fenton Hill hydrofrac experiment we demonstrate the existence of these nonlinear pore pressure diffusion signatures.