COUPLED FLUID FLOW AND GEOMECHANICAL MODELING OF FAULT ACTIVATED INDUCED SEISMICITY
ABSTRACT
Many unconventional shale applications in the oil and gas industry require coupling of reservoir fluid flow with geomechanics simulations for a holistic study of formation stability. Since traditional reservoir simulation packages normally do not fully support geomechanical effects resulting from pore pressure change and varying stress states, finite difference flow simulators which handle multi-phase regimes with varying fluid saturation need to be supplemented with finite element analysis software applications that include geomechanics capabilities but might be limited to single phase fluid flow regimes. The general theme in events leading to induced seismicity from human interaction with the environment involves pore pressure, strain change, total stress and effective stress variations in a reservoir system with underlying faults, undergoing fluid injection and extraction. The objective of the current research study is to couple fluid flow with geomechanical effects to model pore pressure, stress variations and strain change using commercially available finite element analysis in Abaqus and finite difference analysis in CMG for comparison. Reservoir material properties and output strain results from both CMG and Abaqus coupled models are used to calculate induced seismic moments during unbalanced waste water injection and brine production in a reservoir system with an underlying fault. Results suggest that a combination of fluid flow and geomechanics can have an impact on induced seismicity. Near fault basement strain change depends more on production pattern compared to injection pattern variations as more compaction occurs. Unbalanced target formation injection-production activity can lead to increased strain change and seismicity in the basement. Induced seismicity is more related to strain change as opposed to pore pressure change for the cases studied here.
