Hydrogen (H2) storage in subsurface formations has recently gained attention as a promising large-scale energy storage solution. Although previous studies have revealed distinct displacement behaviors between H2 and other gases such as nitrogen (N2) and carbon dioxide (CO2) in high-permeability sandstones, the mechanisms governing H2 migration in tight formations remain largely unexplored. To provide experimental observations that may help improve the understanding of H2 migration in tight reservoirs, we conducted H2 flooding experiments on a tight sandstone sample from the Ordos Basin under pore fluid pressures of 0.5, 1, and 2 MPa. Dynamic core flooding processes were monitored using a low-field nuclear magnetic resonance (NMR) analysis system. The capillary number (Nc) in this work ranged from 1.7 × 10−9 to 3.4 × 10−9, indicating a capillarity-dominated flow. H2 saturation in the tight sandstone increased from 41.9% to 53.3% and then to 57.7% with increasing pore fluid pressure. Under a pore fluid pressure of 0.5 MPa, H2 initially displaced water in small pores (T2 < 10.5 ms), leading to prolonged fluctuations in water content over 136 min before significant displacement occurred in large pores (10.5 ms < T2 < 6579.3 ms). In contrast, at a pore fluid pressure of 2 MPa, the water in large pores was more significantly impacted, with a marked decrease in water saturation observed after 8 min of flooding. These findings provide direct experimental evidence of pressure-dependent and pore-scale selective displacement patterns of H2 in tight sandstone, offering new insights into the fluid dynamics that control hydrogen injectivity and storage efficiency in low-permeability reservoirs.
Shi et al. (Tue,) studied this question.