InterPore2025

Molecular insights into cyclic H2 injection and extraction in shale nanocomposite pore and the role of cushion gas in UHS

20 May 2025, 10:05

1h 30m

Poster Presentation (MS23) Advances in Experimental, Computational, and Analytical Approaches for Underground Hydrogen Storage Poster

Speaker

Mr Qiujie Chen (College of Energy, Chengdu University of Technology)

Description

Molecular insights into cyclic H2 injection and extraction in shale nanocomposite pore and the role of cushion gas in UHS
Qiujie Chen a, Lei Wang a, , Liang Huang a, , Zhenyao Xu a, Sirun An a, Xinni Feng a, Haiyan Zhu a
a State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation & College of Energy, Chengdu University of Technology, Chengdu 610059, P.R. China.
* E-mail: wanglei@cdut.edu.cn (Lei Wang); huangliang@cdut.edu.cn (Liang Huang).
Abstract: Hydrogen energy plays a pivotal role in energy transition; nevertheless, large-scale and long-term storage of H2 remains a challenge. Depleted shale reservoirs are considered as promising sites for large-scale underground hydrogen storage (UHS). However, the microscopic characteristics of H2 injection and extraction in shale composite pores and the influence of CO2 as a cushion gas on UHS remains unclear. In this study, a molecular model of the composite nanopore was constructed to examine the competitive gas sorption interactions between organic and inorganic shale constituents. A molecular simulation scenario was proposed to reproduce the process of cyclic H2 injection and extraction by combining grand canonical Monte Carlo and molecular dynamics simulations, marking the first investigation of its kind in the shale composite nanopore model. The microscopic characteristics of the injection and extraction of pure H2 in shale nanocomposite were elucidated, shedding light on the impacts of CO2 as a cushion gas on these critical processes. The results show that depleted shale gas reservoirs are a promising option for UHS with 71% of the cumulative injected H2 recovered after 5 cycles and as much as 98% of H2 is recovered in the 5th cycle alone. In the shale composite medium, the quartz surface shows a higher affinity for H2 compared to the kerogen surface. However, kerogen, with its internal structure, serves as the predominant storage site for sorbed H2. The recovery ratios of sorbed and free H2 are nearly equal, suggesting that sorbed H2 is readily recoverable with minimal sorption loss. The storage stability of H2 decreases in tandem with an increase in the H2 injection/extraction cycle. The order of H2 diffusion capacity in various storage states is: free H2 > adsorbed H2 on the kerogen surface > adsorbed H2 on the quartz surface > absorbed H2 in the kerogen matrix. H2 injection into shale boosts CH4 production as an additional benefit, resulting in an approximately 17% increment in CH4 recovery after 5 cycles. CO2, adopted as a cushion gas, maintains reservoir pressure but negatively impacts the storage capacity of H2 and degrades the purity of the produced gas, making it an unsuitable cushion gas option in depleted shale reservoirs. This molecular modeling study deepens the comprehension of H2 storage in depleted shale gas reservoirs and the role of cushion gas in UHS.
Keywords: Underground hydrogen storage; depleted shale gas reservoir; H2 injection and extraction; CO2; Cushion gas; Molecular simulationion gas in UHS.