Parallel Simulation of Thermal-Hydrological-Mechanical (THM) Processes in Geothermal Reservoirs

Abstract

Geothermal energy reservoir recovery involves multiple physical processes, including multiphase fluid flow, heat transfer, and rock mechanical deformation. To accurately capture the highly nonlinear THM effect, reservoir simulation will need millions of gridblocks with each gridblcok containing several equations. The above problem results in a very large equation system, which is expensive to solve. Therefore, parallel computing is highly demanded in large scale geothermal reservoir simulation. In this paper, we discuss a massively-parallelized, fully-coupled THM simulator that is capable to conduct reservoir-scale simulation. The simulator is written in Fortran 90 with MPI communication scheme. In the simulator, the governing equations are solved using Integral Finite Difference Method (IFDM). Mechanical deformation effect is captured by solving a mean stress equation, which is efficient in computation and accurate enough in reservoir flow application. The phase behavior of water-air system is simulated by a dual-phase EOS module. The simulator has implemented an efficient parallel computation scheme, in which METIS is used to conduct domain decomposition while Aztec package is adopted to solve linear systems. The simulator has been tested on PCs and clusters with computational performance speedup up to hundreds.