Modeling the non-linear thermo-mechanical behavior of faults

ABSTRACT: Induced seismicity is a common consequence of geo-engineering activities and is a highly coupled multi-physics phenomenon in the subsurface. We present a methodology to deterministically study the risk of induced seismicity in dry nuclear waste disposal repositories. The problem is decomposed into the superposition of an in-situ stress state and a stress change induced by heating, reducing the complexity to a pair of sequentially coupled one-dimensional problems. The rock mass is modeled as a visco-thermo-elastic material with an elastic volumetric response, a visco-elastic Burgers deviatoric response, and temperature-dependent material properties. The frictional fault interfaces are modeled using Chester's extension to rate-and-state friction laws. A custom fully-coupled monolithic implicit finite element model is employed to solve the problem numerically. The thermal pulse is shown to induce tensile and compressive changes in stress which vary non-monotonically in both time and space. The mean in-situ stress is shown to be the most important factor in reducing the risk of inducing slipping events, and extreme ratios between the components of the in-situ stress increase the risk of slipping events.