Choice of hydrogen energy storage in salt caverns and horizontal cavern construction technology

This study investigated the large-scale hydrogen storage in several forms of underground space (depleted gas reservoirs, aquifers, hard rock caverns, and salt caverns,). according to relevant geological, technical, environmental, health and financial factors, different alternatives of underground hydrogen storage were evaluated. It is pointed out that salt caverns are the most favorable underground space for large-scale hydrogen storage, so at least at present, we should pay more attentions to the scientific research and engineering practice of underground hydrogen storage in salt caverns. China is rich in salt resources, but most of these resources have the characteristics of bedded structures, thin salt layers, and complicated geological conditions, which make it very difficult to construct energy storage caverns in the these strata. Moreover, salt mining and gas storage have occupied a large part of salt resources with large thickness and high ore grade. Three methods of salt cavern construction were detailed described and compared, which consists of Single-well-vertical, Two-well-vertical (TWV), and Two-well-horizontal. Therefore, for the construction of hydrogen storage caverns in China, we suggest to adopt the technology of Two-well-horizontal cavern, which is more suitable for the construction of caverns in the remaining thinly bedded salt rocks. The highlights of Two-well-horizontal caverns method were presented and it has better construction efficiency and larger cavern volume. Influencing factors of construction technology were summarized: water injection direction, tubing/oil-blanket lifting, water injecting rate and inter-well distance. Based on “TWHSMC V2.0”, a series of tests were carried out, and multi-factor influences analysis were also carried out. The recommended process parameters in the process of Two-well-horizontal cavern construction are: repeatedly alternating “Injection” and “Withdrawal” operation every 30 days; lifting tubings/oil-blanket every 30 days; setting the inter-well distance to 130 m and water injecting rate at 300 m3/h. This study shows that Two-well-horizontal cavern has higher cavern construction rate than traditional Single-well-vertical cavern, and has high suitability in thinly bedded salt rocks, thus it is capable of providing caverns for ample scale hydrogen storage in China.