Model Set-Up to Determine Dissolution Rates at a Salt Dome under Changing Climatic Conditions

The assessment of future dissolution rates is an important aspect in the long-term forecast of the evolution of a salt dome, as a potential host rock for a nuclear waste repository. Dissolution or leaching occurs under the influence of undersaturated groundwater on saline rocks. In this way, dissolution reduces the thickness of salt formations and could be significant for the thickness of the host rock. Higher dissolution rates are possible, on the one hand, with continuous salt rise or regional uplift with erosion of the overlying rock. On the other hand, higher dissolution rates can occur with saline solutions flowing away from the area of the salt level due to groundwater flow, for example, through the formation of fractures in the cap rock and overlying rock and the resulting altered permeability. Hydrogeological conditions could change in the future due to altered climatic conditions (higher groundwater recharge rates) and affect dissolution.

This project intends to deepen the understanding of the conditions under which dissolution occurs at the salt interface and to determine dissolution rates depending on the hydrogeological conditions caused by climate. This is done through the simulation of different boundary conditions over time. Different climatic developments for the next 150,000 years are defined. These are meant to cover the two extremes, namely a warm period with no cold period and an early onset of a cold period, as well as certain glacial configurations, such as direct ice coverage or a glacier margin, and variations regarding a tunnel valley and the formation and depth of permafrost. The aim is to investigate how changes in hydrogeological conditions under different climatic settings affect dissolution rates at a salt dome, or whether dissolution occurs at all. An existing generic 2D geological model of a salt dome with overlying rock is adapted to the respective question, meaning, for example, that in the case of considering the impact of a tunnel valley, the existing model is geometrically modified to incorporate a tunnel valley with infill as a structure. Variable fluid viscosities around the salt dome due to variations in salinities and temperature will be considered. Furthermore, the impact of more permeable transition zones in between the salt dome and adjacent units will be analysed. We show here the set up of the 2D geological model and defined scenarios for the simulation.

Resulting dissolution rates can be scaled to the observation period of 1 million years based on assumptions about climatic development to determine maximum dissolution rates.