Flow-through experiments on the interaction of sandstone with Ba-rich fluids at geothermal conditions

It is commonly known that heat extraction and decompression can lead to mineral precipitation and reservoir clogging in geothermal systems. In the Upper Rhine Graben, the precipitating minerals are mainly barite and calcite. This study focuses on clogging processes due to mineral precipitation in porous reservoir rocks, i.e., sandstone. The goal is to develop, build, and put into operation the HydRA apparatus, a facility for performing experiments on forced precipitation of barite in the pore spaces of sandstone under geothermally relevant pressure and temperature conditions. Barite precipitation during the flow-through is provoked by using barite-supersaturated solutions with a saturation index (SI) of 1.75. Scanning electron microscopy (SEM) investigations are used to detect barite crystal agglomerations and clogging of the pore spaces by overgrowths on these agglomerates. Following this, different crystal shapes are observed. The results are confirmed by permeability analyses before and after the flow-through experiments. Comparison of the major and trace element compositions of the original and reacted sandstones indicates element mobility due to water-rock interaction, even during the short-time experimental runs (max. 24 h).