Modeling Dynamic Shear Rupture and Microseismic Source Responses on Discontinuities Induced by Quasi-Static Flow-Driven Stress in Fractured Porous Media

The problem of dynamic shear (mode II) rupture on a non-growing fracture embedded in a solid continuum is traditionally solved using a standard split-node finite element method by permitting displacement discontinuity on the fracture while imposing contact constraint via a Lagrangian multiplier or a penalty regularization. In the presence of fluid pressure, this framework can be adjusted accordingly using an effective stress formulation, hence, in principle, can be used for modeling a rupture process in a fluid-filled porous medium and the associated microseismic source responses. However, if the porous medium is subjected to pressure spatial variations, the pressure gradient then acts as a body force, as naturally predicted by the force balance law, generating additional flow-driven stress in the medium. Moreover, when fractures are present, the pressure gradient across fractures is often discontinuous, further complicating the flow-driven stress state. Such coupling effects are rarely included in currently available rupture codes, hence limiting their applications to fluid-induced seismicity. In this study, we take into account flow-driven stress and provide a numerical modeling framework for fluid-induced quasi-static triggering and dynamic shear rupture processes on pre-existing discontinuities. Through a simple configuration in which two natural fractures intersect a hydraulic fracture, we illustrate how a flow-driven rupture process can be used to understand microseismic source responses, estimate permeability enhancement, as well as provide potential explanations for some curious injection-related geophysical observations.