Pore Pressure Effects on Fault Slip and Earthquake Triggering

Jha and Juanes (2014) present a new computational model to simulate the coupling between multiphase flow and poromechanics of faults and developed a two-way coupled simulator that interlaces a geomechanics simulator, CIG’s open source code PyLith, with a multiphase flow simulator, Stanford’s General Purpose Research Simulator (GPRS).

The coupling between subsurface flow and geomechanical deformation is critical in the assessment of the environmental impacts of groundwater use, underground liquid waste disposal, geologic storage of carbon dioxide, and exploitation of shale gas reserves. In particular, seismicity induced by fluid subsurface technologies that tap into water and energy resources. Faults are represented as surfaces embedded in a three-dimensional medium by using zero-thickness interface elements to accurately model fault slip under dynamically evolving fluid pressure and fault strength. The effect of fluid pressures are incorporated from multiphase flow in the mechanical stability of faults and employ a rigorous formulation of nonlinear multiphase geomechanics that is capable of handling strong capillary effects. The numerical simulation tool couples the two codes by using the unconditionally stable fixed-stress scheme for the sequential solution of two-way coupling between flow and geomechanics. It is unconditionally stable, due to the use of the fixed-stress sequential split between multiphase flow and deformation. The model accounts rigorously for multiphase flow effects through a fully nonlinear poromechanics formulation. The modeling approach is validated through comparison with analytical solutions of the Terzaghi and Mandel Problem as well as test cases that illustrate the onset and evolution of earthquakes from fluid injection and withdrawal.

Contributed by Birendra Jha.