| Abstract |
Aquifer Thermal Energy Storage (ATES) is a sustainable technology, capable of fulfilling both cooling and heating demands of buildings. This technology thus possesses a strong potential in Belgium to decrease greenhouse gas emissions This study mainly focusses on the north-eastern part of Flanders, where several suitable siliciclastic reservoirs are present . An inherent process associated with all geothermal installations are changes in fluid temperatures, potentially affecting the chemical equilibrium conditions within these geothermal systems. Changing fluid temperatures in these reservoirs may lead to water-rock interactions, potentially triggering the dissolution and precipitation of minerals such as calcite. Moreover, ATES systems in Flanders are often located in formations that are used as a freshwater reservoir, raising concerns towards their influence on groundwater quality. During this study, a combination of both static reactivity tests and core-flooding experiments are used to empirically assess and quantify this reactivity. These experiments focus on five major types of siliciclastic sediments that are common in Flanders, being carbonate cemented sand(stone), organic-rich sand(stone), arkosic sand(stone), glauconitic sand(stone) and iron-rich sand(stone). During these static reactivity tests sand samples are allowed to react with natural formation water, whilst gradually increasing the temperature of the experimental conditions. As such, static reactivity tests have indicated a variable reactivity strongly depending on the reservoir type which is mainly related to the dissolution of carbonate phases and feldspars. The strength of core-flooding experiments lies in simulating reservoir conditions of ATES projects in a lab environment. In addition, these experiments can also be used to evaluate the effect of ATES exploitation in chemically contaminated formations. The latter allows to study remediation of contaminated sites and assess potential risks towards groundwater degradation. During these core-flooding experiments, the evolution of reservoir material, fluid geochemistry and pore-network are monitored. Micro -Computed Tomography is used to quantify the evolution of pore-networks before and after these core-flooding experiments. The latter can provide valuable information with regard to the reservoir performance of geothermal systems during the exploitation stage. Moreover, the geochemical composition of the fluids is essential in order to numerically model these systems, which will be completed in a next stage. Therefore, PHREEQC will be used to numerically validate these results to verify the observed geochemical evolution of the fluids. |