Our research focuses on understanding the chemical implications of injecting water into the hot, deep, crystalline rocks during reservoir stimulation and subsequent long-term circulation. For this we use natural analogues such as the thermal springs at the Grimsel mountain pass, fluid and rock composition data obtained from drilling campaigns (e.g. from the geothermal exploration well at Basel), and fluids obtained during the construction of the Gotthard rail base tunnel. Data are being used to constrain reactive transport models designed to predict the thermal, hydraulic and chemical processes likely to occur in petrothermal systems at conditions anticipated for Switzerland.
Results of numerical simulations of 15 years of operation of a petrothermal system based on the Basel-1 well. The diagram shows predicted changes in mineralogy and porosity along the flow path in the granitic reservoir at 5000 m depth and at 200 °C. The injected water is intially riverwater. Time-integrated changes in volume fractions of minerals are plotted as a function of distance from the base of the injection well. Positive volume fractions indicate mineral precipitation; negative fractions indicate dissolution or porosity decrease (dashed curve) (from Alt-Epping et al. 2013).