Workshop “Geothermal fluids in saline systems”

Abstract Earth’s crust offers a vast resource of heat that can be used and converted into energy both for electricity and heating/cooling purposes. The utilization of this geothermal energy can make an important contribution to meet the targets of the envisaged energy turnaround. So-called “conventional” geothermal plants exploiting hot hydrothermal reservoirs have long been a fully commercial contributor to the energy provision in favorable geological settings such as Iceland or Tuscany/Italy. The concept of Enhanced Geothermal Systems, however, is a much younger approach to make the heat stored in Earth’s crust available for a stable supply of heat and power, independent of specific geological conditions. Such systems offer an enormous potential for a sustainable energy concept since they provide base-load energy and therefore constitute an important cornerstone in a future energy mix as counterpart to the increasing share of fluctuating energy sources being furthermore poor on CO2 emissions and practically inexhaustible. This Geothermal Energy article collection is intended to document a workshop held at the Karlsruhe Institute of Technology (KIT) on the 24th and 25th of November 2016. The workshop was planned as a discussion platform for the Helmholtz Program “Renewable Energies; RE” Topic 4 “Geothermal Energy Systems” with the partners German Research Centre for Geosciences (GFZ), KIT and Helmholtz Centre for Environmental Research (UFZ) jointly working together over the Helmholtz Program-Oriented Research (POF-3) funding period 2015–2019

The element-release mechanisms of two pyrite-bearing siliciclastic rocks from the North German Basin at temperatures up to 90 °C under oxic and anoxic conditions

Abstract Leaching tests with synthetic brines (25 g/L NaCl) between 25 °C and 90 °C were performed under oxic and anoxic conditions over 7 days on two pyrite-bearing siliciclastic rocks from the Lower Jurassic Hettangian and Sinemurian stages in the North German Basin. The release mechanisms of the mobile elements Al, As, Ba, Ca, Cu, Fe, Mn, Ni, Si, and Pb were studied and explained by means of numerical simulations of the leaching tests. The study was performed in the context of aquifer thermal energy storage (ATES) to improve the understanding of water–rock interactions during heat storage. Results showed that release patterns of Ba, Ca, Cu, Fe, Ni, and Pb were predominantly controlled by the dissolution of pyrite under oxic conditions and iron hydroxides under anoxic conditions. The mobilizations of Al and Mn could be explained by a combination of desorption and the dissolution of hydroxides. Si was mainly released from amorphous silica. The mobilization of Ca was governed by pH-sensitive desorption and calcite dissolution in one of the samples. Arsenic was immobile in both studied rocks. In general, elemental release was augmented by the presence of oxygen and the subsequent dissolution of pyrite and reduction of pH, which should therefore be avoided in ATES systems

Geochemical Characterization of the Lower Jurassic Aquifer in Berlin (Germany) for Aquifer Thermal Energy Storage Applications

AbstractHydrogeochemical processes associated with the potential seasonal storage of 90°C hot water in a Lower Jurassic aquifer (Lower Sinemurian/ Hettangian stages) in the city of Berlin, Germany, are characterized and evaluated to determine possible sources of mineral precipitation resulting in aquifer damage (clogging). Laboratory leaching tests with material from the sandstone aquifer and the pelitic hanging aquiclude obtained from the wellbore “Am Reichstag 2/98” were conducted over a period of 28 days under anoxic conditions. A hydrogeochemical batch reaction simulation of the leaching test was set up with the commercial software PHREEQC and matched to the experimental results. Laboratory experiments show a strong pH decrease and sulfur mobilization as well as precipitation of reddish-brown iron hydroxides. This is most likely the consequence of pyrite oxidation. PHREEQC simulations can reproduce acidification and hematite precipitation if a minor diffusion of oxygen into the system is assumed