Kim Seunghee, Zhang Jingtao, Ryu Sangjin
Department of Civil and Environmental Engineering, Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
Department of Civil and Environmental Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
Micromachines (Basel). 2023 Jul 18;14(7):1441. doi: 10.3390/mi14071441.
Geologic subsurface energy storage, such as porous-media compressed-air energy storage (PM-CAES) and underground hydrogen storage (UHS), involves the multi-phase fluid transport in structurally disordered or heterogeneous porous media (e.g., soils and rocks). Furthermore, such multi-phase fluid transport is likely to repeatedly occur due to successive fluid injections and extractions, thus, resulting in cyclic drainage-imbibition processes. To complement our preceding study, we conducted a follow-up study with microfluidic pore-network devices with a square solid shape (Type II) to further advance our understanding on the effect of the pore shape (aspect ratio, Type I: 5-6 > Type II: 1), pore-space heterogeneity (coefficient of variation, COV = 0, 0.25, and 0.5), and flow rates (Q = 0.01 and 0.1 mL/min) on the repetitive two-phase fluid flow in general porous media. The influence of pore shape and pore-space heterogeneity were observed to be more prominent when the flow rate was low (e.g., Q = 0.01 mL/min in this study) on the examined outcomes, including the drainage and imbibition patterns, the similarity of those patterns between repeated steps, the sweep efficiency and residual saturation of the nonwetting fluid, and fluid pressure. On the other hand, a higher flow rate (e.g., Q = 0.1 mL/min in this study) appeared to outweigh those factors for the Type II structure, owing to the low aspect ratio (1). It was also suggested that the flow morphology, sweep efficiency, residual saturation, and required pressure gradient may not severely fluctuate during the repeated drainage--imbibition processes; instead, becoming stabilized after 4-5 cycles, regardless of the aspect ratio, COV, and Q. Implications of the study results for PM-CAES and UHS are discussed as a complementary analysis at the end of this manuscript.
地质地下储能，如多孔介质压缩空气储能（PM-CAES）和地下氢储能（UHS），涉及在结构无序或非均质多孔介质（如土壤和岩石）中的多相流体传输。此外，由于连续的流体注入和提取，这种多相流体传输可能会反复发生，从而导致循环排水-吸水过程。为补充我们之前的研究，我们使用方形固体形状的微流控孔隙网络装置（II型）进行了后续研究，以进一步加深我们对孔隙形状（纵横比，I型：5-6 > II型：约1）、孔隙空间非均质性（变异系数，COV = 0、0.25和0.5）以及流速（Q = 0.01和0.1 mL/min）对一般多孔介质中重复两相流体流动影响的理解。当流速较低时（如本研究中的Q = 0.01 mL/min），观察到孔隙形状和孔隙空间非均质性对所研究结果的影响更为显著，这些结果包括排水和吸水模式、重复步骤之间这些模式的相似性、非湿相流体的波及效率和残余饱和度以及流体压力。另一方面，对于II型结构，由于纵横比低（约1），较高的流速（如本研究中的Q = 0.1 mL/min）似乎超过了这些因素的影响。研究还表明，在重复排水-吸水过程中，流动形态、波及效率、残余饱和度和所需压力梯度可能不会剧烈波动；相反，无论纵横比、COV和Q如何，在4-5个循环后都会趋于稳定。在本文末尾，作为补充分析讨论了研究结果对PM-CAES和UHS的意义。
