Final report for the DOE GTO funded research on geologic thermal energy storage (GeoTES), or commonly known as reservoir thermal energy storage (RTES).

The results described in this report shed light on various aspects of RTES including project siting, operational performance, mitigation of both subsurface and surface infrastructure issues, and system longevity. Additionally, the reviews of international projects provide valuable lessons associated with exploration, initiation, operation, and sustainable maintenance of RTES. Overall site characterization, THM modeling, risk evaluation, and flexible operations are key aspects to a suitable RTES project. Geochemical modeling supported by laboratory experiments show that understanding the intricacies in brine chemistry and fluid evolution within changing thermal and pressure environments is important because resultant diagenetic reactions and subsequent scaling exist even in unexpected scenarios. Thermo-hydro-chemical (THC) and THM modeling with MOOSE and TOUGH also inform the potential for hydrogeological and geochemical changes within the reservoir and best operational parameters over the life of an RTES system. The results of this study help define future RTES research projects that will facilitate successful future deployment of such systems and make RTES a more viable option for energy storage in the U.S.