A new approach to assess geothermal reservoir potential: An integrated core and analogue study for the Buntsandstein Formation of the Campine Basin (NE Belgium)

Geothermal energy can allow Flanders to make the transition towards a sustainable and low-carbon economy, either through the production of geothermal electricity or heat. Geothermal reservoirs in Flanders are either made of siliciclastic sediments or carbonate rocks, of which the former will be investigated during this research. In general, this project focuses on siliciclastic geothermal reservoirs, which are suitable for low-temperature Aquifer Thermal Energy Storage (ATES) (I) or high-temperature ATES (II). These ATES systems allow to temporarily store thermal energy in shallow aquifers, either daily or seasonal. Low-temperature ATES projects have a strong application potential in Flanders, especially for heating and cooling of residential or office buildings.

Inherent to all geothermal installations are the changes in fluid temperatures, which lead to altered chemical equilibrium conditions within the reservoir. The latter could give rise to water-rock interactions within the reservoir itself, leading to well clogging, scaling, leaching, etc. Precipitation of iron and manganese (hydr)oxides has been reported by several authors, leading to well-clogging and affecting the lifetime and probability of ATES systems. Mineral reactions are thus a poorly understood and widespread phenomenon plaguing several geothermal installations. In addition, the circulation of geothermal fluids, which are not in equilibrium with reservoir conditions, can influence groundwater quality. Furthermore, these reactions can cause the degradation of reservoir performance, defined as the set of petrophysical properties which evolve during the lifetime of a geothermal project. Pore-blocking cements can for example lower reservoir performance, decreasing productivity and injectivity of a geothermal system. In order to understand these mineral reactions and the consequence they have, empiric core-flooding tests will be performed during this Ph.D. These allow us to simulate reservoir conditions and to study the reactions within different mineralogical types of reservoir rocks. In general, there are five important mineralogical groups of siliciclastic sediments in Flanders, being carbonate-cemented sand(stone), organic-rich sand(stone), arkosic sand(stone), glauconitic sand(stone) and iron-rich sand(stone).

The main goals of this Ph.D. are thus to build a core-flooding set-up at the division of Geology at the KU Leuven, empirically assess the reactivity of the 5 major mineralogical groups of siliciclastic sediments and to understand how ATES exploitation affects groundwater quality