Coupled Geomechanics and Reservoir Simulation for Gigantic Naturally Fractured Reservoirs

Abstract The objective of this work is to introduce the features of a new in-house geomechanics simulator. In this work, the capabilities of the new simulator will be demonstrated by applying it to coupled geomechanics and reservoir simulation models based on large-scale naturally fractured reservoirs. The 3D geomechanics simulator presented here utilizes the finite element method (FEM) and was developed in C++. The geomechanical grid is created by extending the reservoir into burdens. The simulator is fully parallel using the message passing interface (MPI) library. The geomechanics simulator is developed as a standalone module and the data exchange (pressure, permeability) with reservoir simulator is performed using the multiple program multiple data (MPMD) paradigm. Faults and discrete fractures are modelled by ‘equivalent material’ constitutive relation, in which multi-fractures are included in a straightforward manner. Plasticity is modelled using an implicit closest point projection algorithm in the finite element context. The in-house geomechanics simulator supports three modes: initialization only, one-way coupling, and two-way coupling. It supports poroelastic and poroplastic modeling for intact rock and discontinuities (faults and discrete fracture), e.g., transversely isotropic material (TIV) and Mohr-Coulomb plasticity. It allows users to specify burden grids and stress boundary conditions. It provides permeability correlations for intact rock and discontinuities, including classic correlations like Kozeny-Carman. Users can also define the permeability correlation through table input. The simulator outputs 3D stresses, strains and plastic strains, displacements, and faults displacements and strains. Results can be visualized using industry standard tools as well as open-source tools such as ParaView. Results of the coupled simulation have been verified against industry-standard simulators. The simulation of a billion-cell model has been performed to demonstrate the capability of the in-house simulator for studying gigantic field models. This work introduces a new in-house geomechanics simulator that is coupled to an in-house reservoir simulator. It demonstrates the capability to simulate billion cell reservoir models with natural fractures. Use of the multiple program multiple data (MPMD) paradigm via MPI offers a significant improvement in performance and efficiency when compared to a traditional file-based approach.