Investigation on the unsteady-state two-phase fluid transport in the nano-pore system of natural tight porous media

• Published in: Journal of hydrology (Amsterdam) 2022-04, Vol.607, p.127516, Article 127516
• Main Authors: Qiao, Juncheng, Zeng, Jianhui, Jiang, Shu, Yang, Guangqing, Zhang, Yongchao, Feng, Xiao, Feng, Sen
• Format: Article
• Language: English
• Subjects: Dynamic gas accessibility; Fluid mobility potential; Micro-nanometer pore system; Primary gas intrusion; Tight porous sandstone; Unsteady-state two-phase fluid transport
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2022.127516

•Low-velocity non-linear flow presents in unsteady-state gas–water flow.•Gas can access to 71.22–97.66% of the connected pore system of tight sandstone.•Movement of inner layer of weakly bound water in the connected pore system governs the continuous two-phase fluid flow.•Water flow in the outer layer of bound water zone dominates dynamic gas accessibility increases.•Unsteady-state two-phase flow is highly susceptible to the tortuosity of connected pore network. Fluid transport across the natural tight micro-nanometer porous media governs numerous subsurface geological and industrial activities. The unsteady-state two-phase fluid flow at the very initial stage of non-wetting phase fluid intrusion, governing the hydrocarbon accumulation and CO2 geological sequestration process, remains uncertain. A modified unsteady-state pressurization gas displacement experiment incorporating systematic pore structure description combining mercury porosimetry, nuclear magnetic resonance, and X-ray computed tomography is conducted on the tight sandstone cores to investigate the fluid flow behaviors and to uncover their pore-scale controls. The results indicate that the unsteady-state gas–water flow deviates from Darcy’s law, in which the threshold for the onset of continuous non-wetting phase fluid intrusion (ISTP) can be observed and degree of water movement and gas intrusion strongly depend on the injection pressure. Analyses under circular pore assumption, water layer distribution model based on DLVO theory, effective flow assumption, and overall pore connectivity evaluation suggest that the water movement and gas accessibility increases are dominated by the water displacement in the free water layer zone when injection pressure