Multiscale modeling of heat and mass transfer in fractured media for enhanced geothermal systems applications

Abstract

• Multiscale modeling of heat and mass transfer in complex 2D and 3D fractured media. • Extension of Generalized Multiscale Finite Element Method (GMsFEM) to include heat transfer equation. • Accurate fluid pressure and temperature solution compared to fine scale. In this work, heat and mass transfer in a hypothetical Enhanced Geothermal System with complex fracture network is considered. Fracture networks have complex geometries , exist in the multiple scales and have a significant impact on the heat and mass transfer processes. Predictive capacity of numerical models for EGS operations rely directly on how accurately the heat and mass transfer in fractures and their surrounding matrix are resolved. For numerical solution, we generate a fine grid model using finite element approximation . The fine grid explicitly resolves the fractures; however, simulation of the process leads to computationally prohibitive simulations. To reduce dimension of the system of equations, we further expand Generalized Multiscale Finite Element Method (GMsFEM) to include heat transfer equation. Multiscale basis functions for the coarse grid approximation of the equations are constructed and accurate solution fluid pressure and temperature are obtained for two and three-dimensional model problems. To the best knowledge of authors, there are only few application of multiscale methods for geothermal heat recovery operations. Therefore the developed GMsFEM for EGS applications will provide a platform to develop predictive tools for fully coupled thermo-hydro-mechanical-chemical (THMC) processes.