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Study on Methane Diffusion Characteristics and Lost Methane Estimation Model for Coals with Different Structures

Qiao Wang1, Haiyang Cai1, Pengfei Wang1

  • 1School of Resource and Environment and Safety Engineering, Hunan University of Science and Technology, Xiangtan, Hunan 411201, China.

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Summary

Accurate coal seam methane prediction is vital for preventing outbursts. A new tortuosity-based model (τ-STDM) improves lost methane estimation by considering coal structure and diffusion, enhancing safety.

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Area of Science:

  • Geology and Mining Engineering
  • Petroleum Engineering
  • Materials Science

Background:

  • Coal seam methane content is a critical indicator for predicting coal and gas outbursts.
  • Existing models for estimating lost methane are inaccurate due to variations in coal pore structure and methane diffusion behavior.
  • These inaccuracies compromise the reliability of outburst prediction, posing significant safety risks.

Purpose of the Study:

  • To develop a more accurate model for estimating lost methane in coals with varying structural types.
  • To quantitatively analyze the relationship between coal pore structure, tortuosity, and methane diffusion capacity.
  • To establish a reliable method for predicting coal and gas outbursts by improving methane content determination.

Main Methods:

  • Selected four coal samples with different degrees of structural destruction.
  • Conducted low-temperature liquid nitrogen adsorption experiments to characterize pore structure.
  • Performed methane desorption tests under various pressures and compared unipore, bidisperse, and time-dependent diffusion models.
  • Developed a tortuosity-based lost methane estimation model (τ-STDM) based on quantitative analysis of diffusion distance.

Main Results:

  • Increased coal destruction led to more micropores and small pores, increased total pore volume and surface area, and enhanced methane desorption and diffusion.
  • The effective diffusion coefficient (D_e) increased linearly with pressure.
  • The time-dependent diffusion model best described methane release dynamics.
  • The τ-STDM model achieved a maximum lost methane estimation error of only 7.82%, significantly outperforming the √t model (35.85%).

Conclusions:

  • Coal destruction significantly influences pore structure and methane diffusion capacity, with shorter diffusion distances enhancing diffusion.
  • The proposed τ-STDM model accurately estimates lost methane in coals with different structures, providing a theoretical basis for reliable outburst prediction.
  • This study enhances the accuracy of methane content determination in composite coal seams, contributing to improved mine safety.