The use of a gravity-assisted-storage-extraction protocol for hydrogen storage in saline aquifers

Abstract

The hydrogen gas produced through the electrolysis of water using excess energy could serve as a prospective source to meet peak energy demand during certain seasons. Because of the large storage capacity and ease of accessibility, saline aquifers are a highly desirable geological storage option for hydrogen. Common challenges encountered in aquifer-based hydrogen storage systems during production include the notable lateral migration of the hydrogen plume caused by the high mobility of hydrogen, as well as the occurrence of gravity override due to the low density of hydrogen and the subsequent production of significant amounts of water during withdrawal. The proposed approach for mitigating water coning and increasing hydrogen production is a gravity-assisted-storage-extraction (GASE) protocol. This involves injecting the working hydrogen gas from the lower region of the formation and extracting it from the top region using a horizontal well. The proposed process capitalizes on the gravitational effects that facilitate the vertical migration of hydrogen, creating a gas-enriched zone within the aquifer. This results in improved hydrogen production as the lateral flow of water and hydrogen is restricted. The implementation of GASE protocol is demonstrated by numerical simulation experiment based on an actual hydrogen storage site at San Pedro belt. The results of simulations conducted on the numerical model indicate that if the GASE protocol is implemented, it has the potential to recover over 93% of the working gas, which is a 20–30% improvement compared to the data that has been previously published. The major limitation of the GASE protocol is the potential capital cost increments due to the drilling and completion of the horizontal wells, which makes it more suitable for a hydrogen storage project with long-term and sustainable hydrogen supplies.