Elemental dissolution characteristics of granite and gabbro under high-temperature water-rock interactions

Abstract

In the process of developing hot dry rock (HDR) through enhanced geothermal systems (EGS), it is necessary to inject circulating water to complete thermal energy extraction. However, the injected water will react with the high-temperature rock and produce mineral dissolution, which can destroy the artificial reservoir and affect the development of geothermal energy. To explore the influence of temperature on the solution composition and mineral dissolution after water-rock reaction, this study conducted water-rock interaction experiments on gabbro and granite at different heat treatment temperatures. Subsequently, the changes of solution composition and mineral dissolution with temperature after the reaction were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and XRD. The results demonstrated that Si, Na, Ca, K, Al, and Mg did not enter the aqueous solution at the same dissolution rate. Si was the primary solute in the solution, mainly resulting from the dissolution of quartz, and the dissolution rates of metallic elements were lower. In the granite-water interaction system, metallic elements such as Na, K, Ca, and Al showed a tendency to enter the solution at low temperatures, i.e., 150–180 °C, and the dissolution rate of Si reached its peak when the water was close to the supercritical state. With the increase in temperature, the dissolution rates of Si and metallic elements showed an initial increasing trend followed by a decrease. When water is in the subcritical to the supercritical state, abrupt fluctuations in the physical properties of water can strongly affect the dissolution of minerals or rocks. The results of this study provide insights into rock corrosion fatigue and mineral scaling in EGS water environment.