Assessing the Geochemical Impact of Injection of Cooled Triassic Brines into the Dogger Aquifer (Paris Basin, France): A 2D Reactive Transport Modeling Study

Abstract

The Triassic sandstone reservoirs of the Paris Basin (France) have attractive geothermal potential for district heating. However, previous exploitations of these reservoirs have revealed re-injection problems preventing from further geothermal operations. To avoid these crucial problems, a possible option would be to inject the exploited Triassic brines in the Dogger aquifer characterized by better re-injection properties. However, this solution might trigger geochemical reactions that may impact negatively the properties of the Dogger aquifer, notably its porosity.
This study, based on numerical simulations, aims to identify and quantify the possible consequences of the thermo-hydro-geochemical processes induced by the re-injection of the cooled Triassic brines into the Dogger aquifer.
Initial batch simulations show potential occurrences of precipitation/dissolution reactions that could potentially impact the Dogger porosity: dissolution of disordered dolomite and calcium sulfate; precipitation of silicates, barium sulfate and sulfides.
In a second step, 2D reactive transport modeling was performed. The results obtained up to now suggest that the impact of the Triassic re-injection could be limited to the first fifty meters around the injection well and be insignificant in terms of porosity variation (< 0.14 percentage point). However, at this stage, species which are sensitive to redox conditions, such as iron and sulfur, are not yet considered. Therefore, this reactive transport model does not take into account some of the reactions identified in the batch modeling as potentially induced during the Triassic re-injection into the Dogger, such as barium sulfate and sulfides precipitation. This is planned to be done in upcoming modeling tasks.