This paper presents the numerical investigation of the geological thermal energy storage (GeoTES) by considering well configuration, discrete fracture network (DFN), and mechanical effect. After validated against field experiments, the MOOSE framework was used to simulate the GeoTES with geological properties from the Weber/Tensleep formation. Mono-well, doublets with different well distance, 5-spot with and without discrete fracture network, and 5-spot with and without mechanical deformation were modeled based on annual injection-storage-extraction-rest cycle for over 10 years. Each period in a cycle lasts for one season, and the same amount of water was injected and extracted within each year. Results show that: (1) the highest recovery efficiency 37% is yielded from the mono-well and the 5-spot without DFN, suggesting that extracting thermal energy directly from the injection well is the best practice; (2) the presence of DFN yield less recovery efficiency, and the pore pressure continues to build-up; (3) thermal expansion and mechanical volumetric strain increase upon three months of injection can only increase the formation permeability about 3% at maximum, indicating the influence the mechanical behavior is negligible for the investigated GeoTES. Future work towards a detailed reservoir model with consideration of chemical reaction is undergoing.
Geological Thermal Energy Storage (GeoTES) is a concept where geological formation can be used as a battery, storing energy as the form of heated liquid during the season with excess energy generated, and recovering it during the season with peak energy demand. This GeoTES approach can greatly stabilize the electrical grids to handle the increasing and inconsistent renewable energy generation. In addition to indirect use of GeoTES by electricity generation, direct application of GeoTES by heating and cooling buildings can save energy up to 80 % for cooling and up to 30 % for heating (Schout et al., 2014). With these advantages, GeoTES is internationally accepted as the most economical and practical energy storage technique.
