Velocity-dependent frictional behavior and slip magnitude of a fault affected by fluid injection activities

Abstract:

Fluid injection is performed or planned for various activities, such as CO2 sequestration, gas storage, waste water disposal, and engineered geothermal system.
Static stress and pressure perturbation due to the fluid injection may cause different scale earthquake phenomena, from instrumental recorded micro-seismicity to triggering of human-felt events.
With this study we present a sensitivity analysis of the slip magnitude for the fluid injection in a reservoir-like structure. The reservoir, confined within impervious rock units, is composed by a porous rock mass laterally bounded by a fault. The fault is hydraulically connected to the fluid hosting unit.
The numerical analysis is based on fully explicit sequential coupling between a multiphase fluid flow and a hydromechanical finite element calculation code. When the system conditions approaches failure, the simulation is performed in a fully dynamic mode.
The coupling allows simulating change in permeability due to stress/strain change, as well as the slip on the fault due to overpressure and associated stress changes.
Interface elements have been used to include the constitutive law characterizing the frictional behaviour of the fault. 
The change in friction with different slip velocities has been derived from laboratory results.
Velocity- and strain-dependent frictional behavior of different patches of the fault influence the system evolution, resulting in larger or smaller slip length for the same injected volume.