Key Takeaways & Executive Findings
- •• A fractal-based permeability model for rough fracture networks accurately predicts single-phase and two-phase flow with deviations under 10%. • Fracture number, tortuosity, and aperture are the dominant geometric parameters controlling permeability. • Flow regimes significantly influence relative permeability in gas-water two-phase systems. • The framework offers a practical, physically based method for analyzing multiphase seepage in fractured rock, applicable to field-scale systems.
Abstract
Quantifying two-phase fluid flow in fractured rocks is essential for resource reutilization in abandoned mines, subsurface energy recovery and underground waste isolation. This study develops a mathematical framework for predicting the permeability of rough fracture networks by integrating fractal geometry with single-phase and two-phase seepage theory. A permeability model for rough fracture networks is first established, and its sensitivity to key geometric parameters is analyzed. A second model is then formulated to relate water-phase saturation to measurable variables, enabling the estimation of two-phase permeability from Reynolds number and aperture. Model predictions show deviations of less than 10% from numerical simulations for both single-phase and two-phase flow, demonstrating the accuracy and robustness of the proposed approach. The results highlight the dominant roles of fracture number, tortuosity and aperture in controlling permeability, as well as the influence of flow regimes on relative permeability. The proposed framework provides a practical and physically based method for analyzing multiphase seepage in fractured rock and offers a foundation for further applications to field-scale fractured systems.
1. Introduction
The phenomenon of two-phase fluid flow is widespread in the development of oil and gas resources [1], underground waste storage [2], hydrogeology, and groundwater flow [3]. Understanding two-phase fluid-flow behaviour in underground rock masses and reliably evaluating the permeability of two-phase fluids in rocks are important for the long-term stable operation of related engineering systems [4].
To reduce carbon dioxide emissions, China has gradually adjusted its energy structure by eliminating and closing numerous coal mines with outdated production capacity or depleted resources [5]. According to conservative estimates, by 2030, China will have approximately 7.2 billion m3 of underground space in closed mines, 140 million m3 of solution-mined salt caverns, and 34 billion m2 of porous saline aquifers, all of which represent significant potential sites for CO2 geological storage and large-scale physical energy storage. In addition, closed mines in China will contain legacy coal resources totalling approximately 42 billion tons, with gas reserves potentially reaching 500 billion m3 [6,7]. Closed mines possess unique advantages such as large storage capacity, great depth, high airtightness, strong shielding performance, high rock-mass strength, and favourable engineering conditions. However, the direct abandonment of these mines not only results in the waste of valuable energy resources but also poses environmental risks due to the leakage of residual gases and other harmful emissions into the atmosphere [8]. Proper disposal of closed coal mines to enable the reuse of waste resources is an urgent scientific challenge for the sustainable development of the coal industry [9]. The residual voids within closed mines are typically subjected to a complex environment where solid, liquid, and gas phases coexist. Water from the overlying strata in closed mines flows downward t
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XUE Kangsheng, PU Hai, LI Ming, LIU Lulu, LIU Xiaoyan, LIU Dejun (2026). Investigation of multiphase fluid seepage behaviour in abandoned mines: Insights from single fracture to network scale. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2026.01.006
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Frequently Asked Questions
What is the main objective of this study?
The study develops a mathematical framework to predict permeability in rough fracture networks, integrating fractal geometry with single-phase and two-phase seepage theory, to analyze multiphase fluid flow in abandoned mines.
How accurate are the proposed permeability models?
The models show deviations of less than 10% from numerical simulations for both single-phase and two-phase flow, demonstrating their accuracy and robustness.
Which geometric parameters most influence permeability?
Fracture number, tortuosity, and aperture are identified as the dominant geometric parameters controlling permeability.
What is the significance of this research for abandoned mines?
The framework provides a practical method for analyzing multiphase seepage in fractured rock, which is essential for resource reutilization, CO2 storage, and environmental safety in abandoned mines.
How does the model relate water-phase saturation to measurable variables?
The model relates water-phase saturation to Reynolds number and aperture, enabling estimation of two-phase permeability from these measurable variables.
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