| Title | Procedure for the Determination of Rock-Fluid Interaction Reactions with Barium Sulfate Supersaturated Fluids |
|---|---|
| Authors | Sabine BAUR, Andrea SEIBT, Christian BUSE, Frank WOLTER, Dietmar KUHN |
| Year | 2024 |
| Conference | Stanford Geothermal Workshop |
| Keywords | barium sulfate scaling, saline fluid, rock-fluid interactions, flow through experiment, inhibitor efficiency, SEM-EDX |
| Abstract | In the German Upper Rhine Graben (URG), the main geothermal reservoirs that are exploited for heat and electricity production are the Middle Bunter sandstone in combination with Rotliegend sediments and the underlaying granitic basement. The produced highly saline fluids are supersaturated in barium sulfate which leads to the precipitation of barite and barite-celestine solid solutions when the fluids are cooled down. In addition, metal sulfides like lead sulfide and even pure lead have been observed. Formation of sulfate scaling in geothermal plants could be prevented through the application of phosphonate-based inhibitors. The precipitation of the other phases could be reduced by simultaneously dosing a corrosion inhibitor. Within the scope of this BMWK-backed R&D-project, inhibitor combinations were formulated and tested for their efficiency. The focus of the research was to evaluate if the corrosion inhibitors are compatible with the phosphonate-based inhibitors and if they have an effect on the reservoir rocks. The research was carried out using the HydRA rock flow through device (Hydrothermal Reaction Apparatus) that was developed at the KIT-ITES. The apparatus allows the flow of an original or synthetic, barium sulfate enriched geothermal brine through a rock sample at reservoir like p-T conditions (up to 420 bar and 250 °C). As a result of the experiments, which each lasted several days, it was possible to show that mineral precipitation in the rock samples could be prevented and that the severity of the formation of new phases depends on the inhibitor concentration. An inhibitor mix with an added corrosion inhibitor did not show any negative influence on the efficiency of the scale inhibitor. In addition to the pressure monitoring on the HydRA apparatus, geochemical analyses of the fluids and SEM-EDX analysis on thin section from rock samples were carried out. The result of the HydRA experiments can also provide information about the application concentration of the inhibitor on site. |