Hydraulic and thermal performance of high-temperature aquifer thermal energy storage in a stratified geothermal reservoir: The case study of the North Alpine Foreland Basin

A numerical analysis is performed to capture the driving physical processes controlling the hydrothermal response of High-Temperature Aquifer Thermal Energy Storage (HT-ATES) and to predict the system performance under a stratified reservoir configuration. The coupled thermal-hydraulic numerical models, constrained by the geometry and physical properties of the Lower Cretaceous/Upper Jurassic geothermal reservoir (North Alpine Foreland Basin) and further encompassing a site-adapted operational scheme, provide a predictive evaluation of HT-ATES application in the reservoir. Implications on the computed physical state field, stemming from varying the spatial distribution of hydraulic properties in the reservoir zones, the well-screen length, or omitting variations in the fluid properties, are inferred. The computations predict a zone-distinct heterogeneous distribution of the thermal front propagation, and dominance of forced convection. Beyond the commonly evaluated thermal performance in terms of heat recovery factor, our approach further resolves the hydraulic performance of the HT-ATES system through the productivity and injectivity indexes. Results indicate that improvement in the hydraulic contribution of the lower-permeability zones induces a decline in the estimated thermal performance. The retrieved geometrical features of the developing thermal perturbation corroborate this analysis. The hydraulic performance is primarily controlled by the reservoir transmissibility, superimposed by additional effects from fluid-property variations that induce a transient component over the simulation. Computations disregarding fluid-property variations yield physically inconsistent predictions of the primary state field, introducing consequently discrepancies in the estimated thermal and hydraulic performance. We, therefore, prove the relevance of considering fluid-property variations even in absence of influential free convective patterns for HT-ATES applications.