The potential of high-temperature storage systems in depleted oil reservoirs in the Upper Rhine Graben

Summary HT-ATES (high-temperature aquifer thermal energy storage) systems represent a future technology to shift large amounts of excess heat from summer to winter using reservoirs in the deep underground. Among others, depleted hydrocarbon-bearing reservoir formations may constitute favorable storage conditions for HT-ATES. This study characterizes these reservoirs in the Upper Rhine Graben (URG) and quantifies their heat storage potential numerically. Assuming a doublet system with semi-annual injection and production cycles, injection at 140 °C in a reservoir with an ambient temperature of 70 °C leads to an annual storage capacity of up to 12 GWh and significant recovery efficiencies increasing up to 82 % after ten years of operation. Our sensitivity analysis of operational conditions identifies reservoir conditions (e.g. permeability or thickness) and the drilling configuration (horizontal/vertical) as the most influencing parameters. With about 90 % of the investigated reservoirs in the URG potentially transferable into HT-ATES systems, our analyses reveal a large storage potential of these oil reservoirs.