Thermodynamic analysis of carbon dioxide storage in salt caverns to improve the Power-to-Gas process

In the current energy transition context, one of the most promising technological solutions to the main complication of the Power-to-Gas process, namely, the supply of carbon dioxide, is to temporarily store carbon dioxide in underground facilities such as salt caverns. However, despite extensive studies on the thermodynamic characteristics of carbon dioxide, the way this gas behaves in a salt cavern has never been described. Such information is essential to enable efficient monitoring of a cavern in accordance with the power demand. This article aims to provide a first analysis of the behavior and specificities of storing carbon dioxide in a salt cavern and subsequently compare the storage behavior of carbon dioxide to that of methane, which is already well known. The comparison is first achieved numerically by simulating the predictive thermodynamic behaviors of both products under different contexts: despite some similarities, no relevant analogy can be easily established between carbon dioxide and methane. The main reasons explaining the different behaviors of the two products are related to their critical point and their capacity of interactions with brine. This last observation is also investigated experimentally by reproducing a cavity at the laboratory scale according to the Pressure-Decay method. The performed experiments show that the phenomenon of mass transfer from dissolution creates a drop in the gas pressure, which is too substantial for carbon dioxide to be neglected. This pressure drop must be accurately characterized to avoid any confusion with pressure drops induced by leakage anomalies in practice.