Scaling and Corrosion Behavior of Metallic Materials after Long-term Exposure to the Geothermal Fluid of the North German Basin

摘要

The suitability of the geothermal fluid of the North German Basin for heat and power generation has been demonstrated. Nevertheless, due to the combined effect of high temperatures inherent to geothermal operations and the high salinity present in this hydrothermal fluid, corrosion and scaling might affect the technical equipment involved in these processes. Preliminary evaluation of materials in terms of corrosion resistance and scaling susceptibility represents therefore a valuable strategy to ensure a reliable operation of the facilities. Until now the corrosion resistance of possible construction materials for exploration, completion and production equipment subjected to this highly saline geothermal fluid has been evaluated only in the laboratory using artificial conditions. Based on these experimental results, high-alloyed materials such as super austenitic stainless steels and nickel-based alloys were recommended for downhole and surface equipment. To confirm the corrosion and scaling susceptibility of several construction materials under real service conditions, one long-term exposure test was conducted in Gross Schoenebeck, a well located in the geothermal area of the North German Basin. This paper discusses the observed corrosion and scaling behavior of five different metallic materials including one micro alloyed steel, the stainless steels UNS S31600, the Nickel-based alloy UNS N07718, a Cu-alloy and one cemented carbide grade after 3.5 years in contact with the geothermal fluid of the North German Basin.