InterPore2026

Impacts of Gravity on Gas Continuity Evolution during Injection-Retraction Cycles

19 May 2026, 15:05

1h 30m

Poster Presentation (MS09) Pore-Scale Physics and Modeling Poster

Speaker

Kangdi Xu (Peking University)

Description

Underground hydrogen storage (UHS) executes hydrogen injection into/retraction from subsurface porous reservoirs aiming to stabilize renewable energy. Topological continuity of gas governs its mobility in porous media and thus affects UHS efficiency. Gas continuity exhibits hysteresis effect over injection-retraction cycles, and factors affecting hysteresis, such as porous geometry, flow rate and wettability, have been extensively studied.
Here we demonstrate that gravity, which was previously overlooked, may have a major impact on gas hysteresis during UHS. For instance, in a porous medium with pore size 100μm, gravity can prevail over capillarity (i.e. Bond number $Bo>1$) in a distance as small as 10cm, which is much smaller than the typical representative elementary volume (REV) size. Therefore, for accurate analysis of UHS at the reservoir scale, gravitational effect should be incorporated in governing equations.
In our study, a 3D quasi-static pore network modelling (PNM) method is developed to unveil how gravity affects continuity evolution, quantified by normalized Euler characteristic $\hat{\chi}$, during injection-retraction cycles. This PNM accounts for meniscus curvature variation in different height that follows a linear relationship $\Delta \kappa=\Delta\rho g\Delta z/\sigma$ as validated by Wang and Xu[1]. Simulation results show a distinct asymmetry that gas continuity diminishes during retraction as gas phase fragments into disconnected ganglia, whereas it rises during injection due to the reconnection of injected gas with residual clusters in porous media. Analysis across varying Bond numbers illustrates that residual saturation as well as hysteresis increases with Bond number which stems from vertical gradients in capillary pressure. Specifically, during injection, higher capillary pressure encourages gas to preferentially breakthrough and form a substantial gas cap in the upper region. Conversely, during retraction, gas tends to firstly flinch from the lower region due to lower capillary pressure, which prematurely disconnects pathways of gas cap and thus entraps significant volumes of gas in the upper part of the medium.
In summary, we utilize a 3D PNM to illustrate how gravity influences continuity evolution of gas during multiple cycles in porous media. It is suggested that gravity-induced capillary pressure gradient facilitates disconnection after retraction. This results in increasing hysteresis of non-wetting fluid and residual loss of hydrogen in UHS. Furthermore, the quantitative relationship between Bond number and hysteresis can be acquired based on hysteresis loops under various Bond number and helps refine performance of reservoir-scale simulation.

References
1. Wang, C. and K. Xu, Ganglion startup in porous media. Chemical Engineering Science, 2024. 292.