An Integrated Framework of Stress Inversion and Coupled Flow and Geomechanical Simulation for 4D Stress Mapping

A change in pore pressure due to production/injection causes changes in both the total stress and the effective stress in the reservoir. These stress changes, when projected onto a fault, may induce fault failure and seismicity depending on the fault rheology and friction parameters. A seismic event can be characterized by the moment tensor and the focal mechanism, which are related to the change in stress tensor causing the event. The objective of this paper is to use the theories of poroelasticity and stress inversion to develop a framework for mapping spatiotemporal changes in reservoir stresses caused by injection and production processes. We use a poro-elastoplastic simulation approach in CMG STARS to examine stress changes resulting from production in a reservoir with a normal fault. Production-induced increase in the von Mises stress and the effective mean compression cause plastic failure within the fault. We model the shear slip as a function of the plastic strain and compute the moment magnitudes of equivalent microseismic events. The focal mechanisms of these events are used in MSATSI, a MATLAB Package for Stress Inversion, to obtain the magnitudes and directions of three principal stresses. The stress inversion algorithm is modified to calibrate the principal stresses with the stress solution from the poro-elastoplastic simulator. We find that as production continues in the reservoir, the magnitudes and directions of stresses evolve in time. The result is a framework that provides a 4D (time-lapse) stress map of a reservoir while honoring both the production/injection and microseismic data.