Heat transfer in salt cavern energy storage coupled with water phase transition: Field experiment and modeling approach

Abstract

Salt cavern energy storage is deemed to be a key method to regulate the intermittency and instability of clean energy. Heat transfer in salt caverns is a key factor as it influences the temperature profile, creep rate of salt rock, and storage capacity inversion. However, existing heat transfer models experience challenges as temperature reversal phenomena near the gas-brine interface were frequently observed in field experiments. Herein, a 183-day field monitoring experiment was presented to reveal the heat transfer characteristics during gas injection, extraction, and shut-in periods. Four variation trends of temperature profiles with depth and negative temperature gradient were observed for the first time. Thus, the cavity was divided into four heat transfer regions, and a new heat transfer model coupled with water phase transition was presented. The average errors of wellhead pressure, cavity pressure, and cavity temperature are ∼2.99 %, ∼1.83 %, and 2.09 %, respectively. A comparison of temperature profiles first confirmed the brine temperature remained noticeably lower than the formation temperature due to the water phase transition, resulting in the inversion of the temperature gradient at the cavity bottom. The average estimation error of the temperature profiles is 1.92 %, which is considerably better than that of the traditional model (3.03 %). A further look at the storage capacity assessment shows that the new model has the smallest error (∼3.09 %), followed by using methane substitution (∼3.55 %) and the geothermal gradient-based method (∼4.28 %). This work offers further insights into thermal performance during gas operation and could serve as a powerful tool for the estimation of storage capacity and developing a digital twin system.