A Coupled Control-Volume Finite Element Geomechanical Model for Discrete-Fracture Reservoir Simulators

摘要

The effects of geomechanical parameters on reservoir properties are usually not consideredin conventional reservoir simulation.This may have ramifications in reservoirs wherecompaction drive is essential or for reservoirs where fracture flow is dominant and is stronglypressure sensitive. Discrete-fracture network representations of a fractured reservoir are examplesof the latter; geomechanical effects are expected to have significant impact on productionperformance. In this paper, we systematically explore a number of different methodologies for incorporatingstress dependence into reservoir properties. A finite element, geomechanical modelbased on force balance principles is interfaced with a control-volume finite element, discretefracturereservoir simulator. The geomechanical module that has been developed is able toconsider any standard thermo-poroelastic constitutive relationship or stress-strain correlation,and accounts for both fracture and matrix constitutive properties. The pressure and saturationinformation from the flow model are communicated to the geomechanical model and the matrix/fracture properties are updated. Several different approaches for coupling are demonstratedand compared; from explicit exchange to communication between modules. Examples from fracturedtight gas formations are used to demonstrate the model and for assessing the importanceand effectiveness of each type of coupling. It is shown that the relevant geomechanical informationis incorporated into the reservoir model in a computationally efficient manner by allowingtimely communication, not necessarily after every time step. The impact of aperture changesof the fractures is shown to be considerable - resulting in significant local changes in effectivepermeability and connectivity during production. The influence of fracture aperture change, associatedwith the geomechanical module on capillarity and other rock-fluid phenomena lead to anumber of interesting observations concerning water block, fluid trapping, producible rates andultimate production. It is significant in dealing with dynamic changes in fracture networks infractured reservoirs.