Understanding Injection-induced Seismicity Effects on Fault Damage Zones: Beyond Poroelastic Models

Robert L. Walker, Mahshad Samnejad, & Fred Aminzadeh

Submitted August 15, 2018, SCEC Contribution #8793, 2018 SCEC Annual Meeting Poster #184

A rise in earthquake activity attributed to anthropogenic causes has stressed the the need for physics based hazard mitigation, based on robust predictive models. Recent efforts have addressed the problem of modeling injection-induced fault slip using poroelastic coupled computations. Current models commonly represent faults as frictional planes of a dimension lower than the overall model, necessarily neglecting the existence and/or the evolution of fault damage zones. Despite this, near-fault regions have been demonstrated to be critical to the complete picture of fault stress change and rupture, and thus accurate modeling of fluid migration and pore pressure change in these off-fault areas represent important factors in the analysis of fault stability.

We go beyond conventional poroelastic simulations by addressing the varying physical characteristics of material with progression from the linear fault plane in a discrete fashion. We differentiate between fault rupture planes, fault damage zone, and host rock by means of differing physical models. As it has been shown that the inelastic deformation of fault damage zone material can drastically couple with pore pressure evolution in the subsurface, we also include material nonlinearity for the fault damage zone in our model, which is critical to understanding fault hydromechanics.

Our multiphysics modeling toolset allows for the assignment of heterogeneous characteristic hydromechanical properties to damaged zone elements. Similarly, nonlinear material properties may be solved for as auxiliary variables, dependent on the resultant primary variables (e.g. displacement and pore fluid pressure) of a given iteration, or in a manner fully coupled with the primary variables, should it be deemed necessary.

We analyze pore pressure and stress state changes spatiotemporally by applying a continuum damage mechanics workflow to our computational simulation framework, which allows the integration of multi-scale physical processes, such as flow, deformation, and crack growth. We will conclude with safe injection design implications with respect to well placement and flow rate for various representative cases.

Key Words
Induced seismicity, faults, poro-elasto-plasticity, damage, waste injection, fluid flow multiphysics

Citation
Walker, R. L., Samnejad, M., & Aminzadeh, F. (2018, 08). Understanding Injection-induced Seismicity Effects on Fault Damage Zones: Beyond Poroelastic Models. Poster Presentation at 2018 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)