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Updated: Aug 14, 2025
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A Uniaxial Compression Experiment with CO2-Bearing Coal Using a Visualized and Constant-Volume Gas-Solid Coupling Test System
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Experiment, Model, and Mechanism of Multiscale Dynamic Diffusion-Permeability in Coal under Different Fluids
Zhiqiang Li1,2,3,4, Pengfei Li1, Lin Wang1,2,3,4
1MOE Engineering Center of Mine Disaster Prevention and Rescue, Henan Polytechnic University, Jiaozuo, Henan454000, China.
ACS Omega
|January 16, 2023
Summary
Coal permeability shows multiscale characteristics due to micro/nanopores. A new model explains how fluid flow dynamics in these pores affect gas extraction, crucial for predicting coalbed methane production.
Area of Science:
- Geosciences
- Petroleum Engineering
- Materials Science
Background:
- Coal permeability exhibits complex multiscale characteristics influenced by micro and nanopores.
- Understanding fluid seepage-diffusion in coal is vital for efficient gas extraction engineering.
- Common engineering fluids in coal seams include water, free gas, and adsorbed gas.
Purpose of the Study:
- To investigate the multiscale characteristics and mechanisms of seepage-diffusion for different fluids (He, CH4, water) in coal.
- To propose a novel model for multiscale dynamic apparent diffusion applicable to various fluids.
- To elucidate the mechanism of dynamic seepage-diffusion based on a multiscale pore geometrical model.
Main Methods:
- Experimental seepage-diffusion tests were conducted on cylindrical coal samples (ϕ50 × 100 mm) using Helium, Methane, and water.
- A novel model of multiscale dynamic apparent diffusion was developed to describe the full-time flow process.
- A geometrical model of multiscale pores was proposed to explain the seepage-diffusion mechanisms.
Main Results:
- Apparent diffusion coefficients for He, CH4, and water dynamically decay with time, independent of fluid properties but dependent on coal pore structure.
- Fluid flow transitions from larger external pores to micro/nanopores within the coal matrix over time, decreasing effective flow pathways.
- Initial apparent permeability (K0) for He/CH4 shows a U-shaped dependency on gas pressure, influenced by slip effects and pressure gradients.
Conclusions:
- The study proposes a multiscale dynamic apparent diffusion model accurately describing fluid flow in coal over time.
- The findings explain the dynamic attenuation of apparent permeability and its significance for late-stage coalbed methane production decline.
- Understanding these multiscale flow mechanisms is crucial for accurate coalbed methane productivity prediction.
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