Influence of Mechanical Deformation and Mineral Dissolution/precipitation on Reservoir Thermal Energy Storage
Authors: Jin W. , Atkinson T. , Neupane G. , McLing T. , Doughty C. , Spycher N. , Dobson P. , Smith R. 
Published: October 2022

ABSTRACT:
Reservoir thermal energy storage (RTES) is a promising technology to balance the mismatch between energy supply and demand. In particular, high temperature (HT) RTES can stabilize the grid with increasing penetration of renewable energy generation. This paper presents the investigation of the mechanical deformation and chemical reaction influences on the performance of HT-ATES for the Lower Tuscaloosa site. Thermo-hydraulic (TH), thermo-hydro-mechanical (THM), and thermo-hydro-chemical (THC) coupled simulations were performed with different operational modes and injection rates for a fixed five-spot well configuration and a seasonal cycle. The results show that (1) geomechanical-induced porosity change is mainly contributed by effective stress change, and the porosity change is distributed through the whole system; (2) geochemistry-induced porosity change is located near the hot well, and its change is one order of magnitude higher than the geomechanical effect; (3) both the operation mode and the injection rate have a huge influence on the RTES performance and lower injection rate with push-pull operation mode has the best performance with recovery factor around 70% for this RTES system. These results shed light on the deployment of HT-RTES in the US and around the world.

1 INTRODUCTION
The concept of reservoir thermal energy storage (RTES), also known as geological thermal energy storage (GeoTES) or aquifer thermal energy storage (ATES), to mitigate the mismatch between energy supply and demand has been applied around the world since the 1960s with mixed success. Given its nearly unlimited storage capacity and easy accessibility, RTES has the potential to become an indispensable component to achieve the goal of carbon-neutral energy.
Most successful deployments of RTES are operated at low temperatures (LT) (&lt; 25°C), mainly to heat buildings by storing excess thermal energy during the low-use periods (summer) and recovering it during peak energy demand periods (winter). As reviewed by Fleuchaus et al. (2018), there are currently more than 2800 RTES systems worldwide, and 99% are LT-RTES. However, only high-temperature (HT) RTES has the capacity to serve as an earth battery for stabilizing the grid as indicated in McLing et al. (2019). The research and development of HT-RTES have mainly focused on site suitability studies and performance optimization by only considering fluid flow and heat transfer. For example, Schout et al. (2014) extended the widely adopted Rayleigh number - recovery factor relationship for identifying site suitability of LT-RTES systems (Gutierrez-Neri et al., 2011) to HT-RTES systems. Sheldon et al. (2021) further improved the Rayleigh number relationship to consider daily cycles for HT-RTES systems. In addition to recovery factor, the performance metrics of HT-RTES include storage capacity, operational duration, etc. Jin et al. (2021, 2022) performed stochastic thermo-hydraulic simulations and used a machine learning algorithm to directly correlate formation parameters and operational conditions with multiple HT-RTES performance metrics using the simulated big data. All these investigations can facilitate the deployment of HT-RTES. However, geomechanical response and geochemical reactions involved during the operation of a HT-RTES system can potentially induce risks as identified by Fleuchaus et al. (2020), and their effects on HT-RTES performance have not been systematically reported.