Thermal effect of a borehole thermal energy store on the subsurface

Background The thermal effect on the subsurface of a large borehole thermal energy store (BTES) has been investigated by coupling measured rock properties with an enhanced FEFLOW simulation. Methods The finite element model has been validated against measured data from a 2-year operation period. The thermal changes in the subsurface have been predicted by simulation for a 30-year operation period. The model is based on three 80-m core sections drilled in Triassic carbonates, which have been analyzed in detail with respect to lithology, facies, and thermal and hydraulic parameters. Results The model shows thermal effects of the BTES on the subsurface at a distance of approximately 350 m after 10 years and a distance of approximately 850 m after 30 years of operation. At a distance of 100 m, the temperature of the subsurface rises by 2 K after 30 years. Conclusions The simulation describes the real BTES in an accurate manner and is suited for predicting the thermal changes in the subsurface for long-term operational durations.