Dynamic evolution of reservoir permeability and deformation in geothermal battery energy storage using abandoned mines

Abstract

Retasking existing subsurface abandoned mines as infrastructure for solar energy storage could be a feasible approach in overcoming the low thermal gradient present in shallow formations. In this work, the potential for thermal storage in the high permeability goaf of abandoned mines through diurnal cyclic injection-then-extraction using coupled thermo-hydro-mechanical modeling was explored by coupling FLAC^3D with TOUGH2. The temperature sensibility of reservoir during 30 days of cyclic injection-then-production was examined at various injection temperatures (ranging from 50 ​°C to 250 ​°C) and rates (ranging from 1 ​kg/s to 10 ​kg/s) and for representative reservoir physical and thermal properties, including variable thermal expansion coefficients. The simulation results reveal that: The principal mechanisms driving reservoir deformation result from the combined influence of thermal poroelastic and thermal effects. With the change of reservoir temperature, the reservoir is perturbed by pressure and thermal stresses causing permeability evolution. Permeability reduces ∼10% for a maximum injection temperature of 250 ​°C – although effects are reduced the lower injection temperatures. The pore pressure fluctuations for an injection rate of 10 ​kg/s is ∼6.5 times that for a rate of 1 ​kg/s. The pressure perturbation of the reservoir during the injection process decreases with the injection rate, and the reservoir is relatively more stable. When the thermal stress becomes predominant, the reservoir volume expands. Uplift displacements 220 ​m above the hot injection well are trivial an of the order of ∼1.5 ​mm at a mean temperature of 163 ​°C.