The 2050 Swiss Energy Strategy aims to reduce carbon emissions by embracing renewable energy resources. In Switzerland and worldwide, the heating and cooling sector uses roughly half of the total energy consumed, which is generated primarily by fossil fuels (Quiquerez et al., 2017; Fleuchaus et al., 2018). Aquifer thermal energy storage (ATES) allows low-carbon and/or low-cost heat to be stored until the demand for heat rises, usually in the winter. ATES stores waste heat (e.g. from a power plant, industrial process, or incineration of domestic waste) by injecting hot water into aquifers, and extracting the heat at a later time. ATES is typically operated at moderate temperatures (<25 °C) in thick, unconsolidated aquifers (Fleuchaus et al., 2018). ATES has been shown to be technically and economically successful, and it is becoming widespread in countries such as the Netherlands, which have favorable geologic and legal frameworks (Hartog et al., 2013; Bloemendal et al., 2014; Fleuchaus et al., 2018).
There is interest in expanding ATES to higher temperatures and different reservoir types, like those found in Switzerland. As temperature and pressure increase in ATES systems, the potential for thermo- and poroelastic deformation also increases. We study thermo-hydro-mechanical (THM) effects in high temperature (HT) (>25 °C) ATES systems (Fig. 1). We hope to understand, mitigate, and avoid ground surface deformation, wellbore integrity problems, hydraulic fracturing, and/or induced seismicity, which is important due to the proximity that ATES typically has to cities and infrastructure.
Figure 1: Schematic of THM processes in a HT-ATES system. The temperature and pressure changes lead to mechanical deformations, such as ground uplift.
Methods and Results
Our work involves the use of coupled analytical and numerical models. We use the MOOSE framework to solve the thermo-poro-elastic equations (Gaston et al., 2015; Alger et al., 2019). It is a generalized, parallelized finite element software that facilitates the coupling between different physics. An illustrative example of the numerical model is shown in Figure 2. We collaborate with partners across Europe as part of Geothermcia HEATSTORE. At the national level, we work closely with other universities and industry partners in the Swiss HEATSTORE Consortium. Our models consider input from the energy systems scenario modelers and from the geological understanding at the pilot projects in Geneva and Bern. Likewise, our results inform the experimental design of lab and field work done for these sites. Work is ongoing, but preliminary results have shown:
- The importance of reservoir transmissivity to a successful ATES system
- That a doublet well configuration is preferred over a single well huff and puff, or a 5-spot well pattern
- That the optimal well spacing is achieved when constraints from pumping pressure are balanced with constraints from the amount of heat the reservoir can hold.
Figure 2: Numerical model results. The 3D mesh (a) uses localized refinement near the wells. The pore pressure (b) and temperature (c) affect the deformation (d).
Alger B., Andrš D., Carlsen R. W., Gaston D.R., Kong F., Lindsay A. D., Miller J. M., Permann C. J., Peterson J. W., Slaughter A. E., and Stogner R.: MOOSE Web Page. https://mooseframework.org. (2019).
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