Numerical modelling of coupled hydro-thermal processes of the Soultz heterogeneous geothermal system

Abstract

This paper presents an application of the finite element method (FEM) in modelling coupled, hydro-thermal (HT) processes of the Soultz heterogeneous geothermal system, using different working fluids. A two-dimensional (2-D) model of the geothermal system was developed in the Multiphysics FEM application solver (COMSOL), and the geometry comprises of three wells with five geological layers. Also, two discrete fractures were incorporated in the geometry, each with a 2mm thickness. The model mesh consists of various types of elements, including triangular elements, edge elements and vertex elements. The working fluids used in the study were water (H2O) and supercritical carbon dioxide (SCCO2), using constant density and viscosity. Moreover, other field variables employed in the work were those available in the literature of the geothermal site considered. A long-term simulation of 30 years was applied, and the temperature, pressure, and enthalpy distribution in the production well were studied. The results obtained showed the superiority of water, concerning energy production, when constant density was used. On the other hand, the pressure of the supercritical carbon dioxide in the production wellbore is far superior to that of water. Therefore, supercritical carbon dioxide can serve as a surrogate to water in the future because of its lower pumping cost in comparison to water. Further studies of other parameters are required to affirm the practicability of the scheme.