Modelling coupled Component Based Multiphase and Reactive Transport Processes in Deep Geothermal Reservoirs using OpenGeoSys

Abstract

In deep geothermal reservoirs, artificial fracture networks are often stimulated and the enhanced during the well construction, in order to facilitate efficient heat transfer from the host rock to the heat carrying fluid. However, throughout the life span of a geothermal power plant, the geochemical reactions on the fracture surfaces will gradually control the hydraulic and mechanical behavior of the fractures, thus further affect the energy output of the reservoir. The numerical simulation of such long term behavior of the reservoir imposes several challenges to the modelers. First, it is a coupled non-isothermal system that often contains multiple fluid and solid phases. In addition to that, controlled by the pressure and temperature conditions, phase change process may happen in certain part of the modeling domain. To further increase the non-linearity of the system, the long term fluid-rock geochemical reactions have to be included in the consideration and the model must be able to account for their feedback to the hydraulic and flow field. Within the framework OpenGeoSys software, we extend the traditional phase volume based multiphase flow module to chemical component based formulations. This allows a further coupling with geochemical processes on the fracture surface. The developed code will be verified against several benchmark cases, which involves non-isothermal multiphase flow involving phase change and mineral-water geochemical reactive transport processes. The simulation of coupled processes in fracture network dominated geothermal reservoirs will also be presented.