High-temperature heat storage capacity in the depleted hydrocarbon fields in the Upper Rhine Graben

Geothermal energy offers a growing opportunity to meet the future energy demand. High-temperature reservoir thermal energy storage (HT-RTES) can decrease seasonal mismatches between heat generation and usage while supporting the stability of the power network. In Upper Rhine Graben, HT-RTES is favored from suitable geological conditions, permeable reservoirs and formation temperatures which makes these reservoirs appropriate for injection temperatures above 100 °C.

The study incorporates data from wells within the Leopoldshafen depleted field as well as two additional wells Eggenstein 1 and Stutensee 1 (EG 1 and ST 1) located approximately 2 and 4 km from the main Leopoldshafen study area. These wells target two Oligocene stratigraphic formations: the Niederrödern formation, deposited in a meandering system, and the Karlsruhe subformation, characterized by marine depositional environments.

Through integration of the existing borehole logging data, we developed an approach to identify potential sandstone reservoir horizons and to evaluate regional heat storage capacity. This methodology relies primarily on the interpretation of self-potential (SP) logs, which enables the identification of sandstone bodies, their internal architecture, and lateral continuity. Based on the newly acquired core- and plug porosity and permeability measurements, the observed reservoir heterogeneity reflects significant variability associated with the distribution of different sedimentary facies.

As a result, a three-dimensional facies-based geological model was constructed to identify the most suitable storage horizons and their associated channel geometries, which also enabled estimation of the potentially storable heat volumes.