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<p>To overcome the limitations of traditional hydraulic fracturing—high water consumption, groundwater pollution risks, and coal seam water-blocking damage—this study investigates a water-free fracturing technology combining liquid nitrogen (LN<sub>2</sub>) and microwave treatment for enhanced coalbed methane (CBM) extraction from low-permeability seams. Using nuclear magnetic resonance, uniaxial compression, and acoustic emission (AE) tests, the fracturing effects and damage mechanisms of three treatments (microwave-only, LN<sub>2</sub>-only, and combined cyclic treatment) were systematically compared. Results show that after treatment, the <i>T</i><sub>2</sub> spectrum peak of coal decreases with prolonged relaxation time, while the fractal dimensions of large and medium pores diminish with increasing treatment intensity. Higher microwave power, longer LN<sub>2</sub> cooling, and more cycles progressively reduce uniaxial compressive strength and elastic modulus. Both LN<sub>2</sub> and microwave significantly raise AE event frequency and energy release during loading, shifting energy release from near peak strength to a stepped distribution. Microwave treatment selectively heats coal, generating thermal stress that expands existing fractures and creates new ones while also promoting mineral decomposition and material migration. LN<sub>2</sub> induces thermal shock and pressure via low-temperature contraction and vaporization, accelerating fracture propagation. Their synergy forms a complex fracture network, markedly improving coal seam permeability. This study provides theoretical and technical support for efficient CBM extraction, positioning LN<sub>2</sub>-microwave synergetic fracturing as a promising alternative to conventional hydraulic methods.</p>

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Experimental Investigation on Damage Evolution and Mechanical Properties of Coal Treated by Liquid Nitrogen-Microwave Synergy

  • 期刊论文

  • 发表日期：

    2026年4月6日

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  • Yuxin Liang,
  • Yang Liu,
  • Peng Hou,
  • Quansheng Liu,
  • Zhijun Wu,
  • Xuhai Tang,
  • Mukhammedrakhym Rabatuly

摘要

To overcome the limitations of traditional hydraulic fracturing—high water consumption, groundwater pollution risks, and coal seam water-blocking damage—this study investigates a water-free fracturing technology combining liquid nitrogen (LN2) and microwave treatment for enhanced coalbed methane (CBM) extraction from low-permeability seams. Using nuclear magnetic resonance, uniaxial compression, and acoustic emission (AE) tests, the fracturing effects and damage mechanisms of three treatments (microwave-only, LN2-only, and combined cyclic treatment) were systematically compared. Results show that after treatment, the T2 spectrum peak of coal decreases with prolonged relaxation time, while the fractal dimensions of large and medium pores diminish with increasing treatment intensity. Higher microwave power, longer LN2 cooling, and more cycles progressively reduce uniaxial compressive strength and elastic modulus. Both LN2 and microwave significantly raise AE event frequency and energy release during loading, shifting energy release from near peak strength to a stepped distribution. Microwave treatment selectively heats coal, generating thermal stress that expands existing fractures and creates new ones while also promoting mineral decomposition and material migration. LN2 induces thermal shock and pressure via low-temperature contraction and vaporization, accelerating fracture propagation. Their synergy forms a complex fracture network, markedly improving coal seam permeability. This study provides theoretical and technical support for efficient CBM extraction, positioning LN2-microwave synergetic fracturing as a promising alternative to conventional hydraulic methods.