Coupled Forward Simulation of Seismicity: a Stick-Slip Model for Fractures and Transient Geomechanics

Summary Seismic deformation in poroelastic media may be triggered by a variety of physical events including stick-slip frictional instabilities in fracture. While in the context of simulation-aided engineering to mitigate the risks of induced-seismicity, it is sufficient to be able to resolve the onset of seismic slip using quasi-static assumptions, applications involving microseismicity require inertial models throughout the intended operational activity. In this work, we develop a fully-dynamic (inertial), time-adaptive, and coupled numerical model incorporating transient poromechanics and multiphase flow in fractured reservoirs. The model is applied to simultaneously assimilate well-performance and dynamic seismic event sequences, thereby informing about the causal event dynamics. First, we extend the mixed XFEM-EDFM numerical scheme to time-dependent mechanics. A stable and second-order implicit Newark method is developed in time. The pressure-dependent contact forces in fracture are treated using Lagrange multiplier constraints, and a Polynomial Projection Method is developed to stabilize the computation of contact traction. A temporal adaptivity indicators is developed to resolve preseismic triggering and coseismic spontaneous rupture. The model is validated empirically (for accuracy, consistency, and computational efficiency). Numerical examples are presented to benchmark the proposed dynamic model relative to predictions from a quasi-static approach. In particular, it is demonstrated that computed waveforms can differ to first-order. Furthermore, in simulation test cases with water injection, coseismic rupture and microseismic signals are detected and in-situ stress migration is observed. We outline implications towards unifying toolchains and workflows for combined geophysical, well completions design, and reservoir performance analysis.