Reservoir triggering events for coupling geomechanical and fluid flow simulations

Abstract

The traditional coupled geomechanical analysis of a reservoir depends on the solution of a fluid flow problem and a stress problem. We present a methodology which takes into account the triggering events history in the reservoir dynamics. Normally changes in the state of stress in a reservoir are relatively smooth and gradual during production, until some field development or geological events of mechanical importance take place. These events may trigger abrupt changes in the state of stress of the reservoir solid framework and the pore pressure, requiring a tighter coupling. These changes prompted to devise a smart strategy to define the critical times in the reservoir history to couple, thus allowing to reduce the time step when large changes in stress happen or to relax the time step when small gradual changes are taking place. This strategy reduces significantly the computational cost of the analysis. Typically, the fluid flow problem for reservoir simulations is solved using finite volume method (e.g. Eclipse®). For the geomechanical solution we developed a finite element simulator which is parallel and capable of solving several millions of unknowns. The two simulators were coupled with a C++ interface code enforcing different coupling strategies. For this study, a generic case study was simulated applying one-way coupling and two-way coupling schemes. In the one way coupling, only the resulting pore pressure from the reservoir simulator is communicated to the Geomechanics simulator at the specified time steps defined by the triggering events. In the two-way coupling, in addition to the communication from the fluid flow simulator, the Geomechanics simulator communicates the pore/perm updates back to the fluid flow simulator. A comparative summary of the results from our method with selected published data will be presented.