| Title | Reactive Reservoir Systems - Crystal Nucleation and Filter Processes in Geothermal Systems |
|---|---|
| Authors | Philipp ZUBER, Sascha FRANK, Jürgen SCHREUER, Stefan WOHNLICH |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | barite, scaling, crystal nucleation, morphology, filter processes |
| Abstract | During geothermal energy generation, the change of temperature and pressure conditions can lead to supersaturation of the extracted fluids and thus to precipitation of minerals. Well-documented crystalline deposits on the inner walls of pipes are the consequences. In addition, turbulence-induced inhomogeneities and mechanical disturbances also lead to the formation of spontaneous free-floating crystal nuclei. A significant part of them are carried along and reinjected into the reservoir. There, the crystal nuclei are possible centers for crystallization and cementations processes or can accumulate by filter effects. Both processes contribute to scaling effects which limit the use of the geothermal reservoir. So far, such effects have not been considered in hydrogeochemical modelling programs, which are mainly based on the temperature and pressure dependence of solution and reaction equilibria in the reservoir. Our investigations focus on a better understanding of the formation and growth of crystal nuclei in saturated geothermal solutions during thermal and pressure relaxation, and the development of approaches to control crystal nucleation and to minimize filter processes in the reservoir. For this purpose, a high-pressure high-temperature apparatus is used which is based on the working principle of a natural geothermal system. Two separate heating thermostats allow different temperatures to be used in the storage tank of the system and in the pressure vessel in which the rock sample is placed. Furthermore, we have the possibility to inject specific crystal seeds to study the influence of various minerals and their morphologies. Our setup allows pressures of up to 200 bar and temperatures of up to 100 °C. In addition to the determination of hydrochemical parameters, the crystallites and cements produced are characterized by optical methods, scanning electron microscopy and electron microprobe. |