Hydromechanical modelling of salt caverns subjected to cyclic hydrogen injection and withdrawal

Abstract

The present work is devoted to the study of underground hydrogen storage in salt caverns. Based on the hydromechanical characteristics of rock salts obtained from some laboratory experiments, we propose a novel model that includes short- and long-term mechanical behaviour. Specifically, the short-term part incorporates the elastoplastic and instantaneous damage mechanisms. Concerning the long-term behaviour, in addition to the primary and secondary creep phases, the tertiary phase takes into account a delayed damage mechanism.As application, we performed hydromechanical modelling of two vertical salt caverns with different depths based on existing hydrogen gas caverns, which are subjected to cyclic hydrogen injection and withdrawal (seasonal and daily scenarios). Gas transport is also modelled taking into account diffusion and advection mechanisms. Mechanical results indicate that the stability problem of a very deep cavern is more worrying in comparison with a shallow cavern, as expected. However, the gas extension is the same for both caverns because the gas flow is mainly by diffusion transport, while the permeability does not significantly increase. Since field data at very depths are limited, a sensibility analysis of material properties was carried out to provide insight into key mechanisms that may occur. Typically, a decrease in mechanical properties increases the extent of the damage around deep cavern but did not lead to significant increase in the extent of gas leakage. Under the assumptions made, these findings suggest that the use of salt caverns for green hydrogen storage, even with aggressive operating conditions to regulate variations between renewable energy production and peak power demands, should not significantly affect the stability of salt cavern nor promote an increase in hydrogen loss.