Uncertainty Analysis of Thermal Recharge by Free Convection in Geothermal Reservoirs

Abstract

This study investigates the thermal recharge of deep geothermal reservoirs by free convection. A coupled numerical model that is built in Comsol Multiphysics is presented in order to estimate the thermal recharge during the first 30 years of production from a typical high enthalpy geothermal reservoir. A sensitivity analysis was carried out to find which parameters have most significant impact on the thermal recharge by free convection and reservoir lifetime. The sensitivity analysis is mainly focussed on fault properties. The developed model consists of a reservoir with two confining layers and vertical faults. This model is used to calculate the produced energy, extracted energy from the reservoir and the recharge by conduction based on which the thermal recharge by free convection can be calculated. Results show that free convection is a significant part of the produced energy. Therefore, it is important to take free convection into account by estimating the recoverable energy. From the results can also be concluded that fault aperture, fault height, fault permeability and thermal conductivity of the confining layers have a significant impact on the thermal recharge by free convection of a faulted geothermal system. Fault density also has impact on the thermal recharge, but the relation between fault density and thermal recharge by free convection is less clear. Thermal conductivity of the reservoir rock has no impact on the thermal recharge by free convection according to the results of this model.