Experimental Study on Hysteresis During Cyclic Injection in Hierarchical
Porous Media
Abstract
Cycle injection schemes are often encountered in underground gas
storage, and the involved hysteresis directly impacts storage and
extraction efficiency. The geological formation generally has
hierarchical features containing multiple-level pore sizes.
Nevertheless, we still lack a comprehensive understanding of this
phenomenon and the pore-scale mechanism behind the geometry affects
saturation hysteresis and its cyclic responses. In this work, by 3D
printing technology, we fabricate a hierarchically structured porous
media chip with dual permeability and uniform one for comparison.
Gas-liquid injection cycles are performed to investigate the impact of
hierarchical structure on invasion behavior. The phase morphology shows
the preferential invasion in 1st-order structure and the capillary
trapping in 2nd-order structure, which are supported by the phase
saturation at each level of the hierarchical structure. Furthermore,
ganglion motion is suppressed in the hierarchical chip while they are
significant in the uniform one. Through analysing local invasion
behaviors, the connect-jump invasion mode is identified as the primary
reason for this suppression. Then, the hysteresis effect is quantified
based on the Land model, revealing a weaker saturation hysteresis effect
in the hierarchical structure compared with the uniform structure.
Finally, the upward trend of relative permeability with saturation is
fitted by the van Genuchten model. The model parameter in the
hierarchical structure is higher than that in the uniform structure,
which is caused by extra pore space in 2nd-order structure. The findings
improve the understanding of the hysteresis effect and can promote
optimizing strategies for storage and extraction in underground hydrogen
storage (UHS).