Investigation on water–rock interaction under geothermal hot dry rock conditions with a novel testing method

Geothermal technology has been developed for many years for fields in a range of geological settings. In the past, geothermal energy was considered environmentally friendly. Today problems due to corrosion and scaling have made people aware of the importance of fluid composition in geothermal system. The purpose of this work is to develop a novel testing method and study the fluid–rock interaction as a part of the geothermal model while heat energy is extracted from subsurface geothermal sources. The following aspects were considered in the experiment design: (1) effect of flow rate on fluid chemistry; (2) variations of pH, TDS; (3) influence of water–rock contact time or residence time; (4) dissolution and precipitation or occurrences of solubility equilibrium. For the purpose of this study, a novel testing setup has been developed and tested. Three different rock samples are used which include Rotliegend sandstone and two other different types of sandstones. It has been shown that the setup can mimic the hot downhole conditions found in German EGS system, and the preliminary results have shown some interesting results, for example, scaling produced by temperature variations. These results will have a great impact on future design of geothermal well systems.

► Design a setup to perform water–rock interaction under hot dry rock conditions. ► Setup was tested and worked well up to 130 °C. ► Long contact time between water and rock can enhance TDS or conductivity of liquid. ► Higher temperature can enhance dissolution and precipitation.