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<p>Liquid CO₂ (L-CO₂), with its phase-transition expansion and low viscosity, is a promising preconditioning fluid for permeability enhancement and dust reduction by coal seam water injection. However, liquid CO₂ fracturing (LCF) still has challenges, such as high-pressure phase behavior control and a lack of systematic testing system. Moreover, the mechanisms of liquid CO₂ and water cyclic fracturing (LCWCF) remain unclear. To address these gaps, a novel coal testing system for low-temperature fluid cyclic fracturing and wetting enhancement was developed. The functions and working principles of each module were introduced, and key technical issues, such as pulse-free cyclic injection and thermo-hydro-mechanical (THM) multi-field coupling, were resolved. Hydraulic fracturing (HF), LCF, and LCWCF experiments were conducted with synchronous acquisition of pressure and acoustic emission (AE) data. The results show that the system can precisely control stress and temperature to reproduce in situ coal seam conditions at the laboratory scale. Alternating injection of L-CO₂ and water overcame the limitations of a single fluid mode. Compared with HF, both LCF and LCWCF achieved higher fracturing efficiency. LCWCF, combining L-CO₂ phase transformation and water stress transmission, enabled faster fracture initiation, with a first-cycle breakdown pressure of 18.21&#xa0;MPa, and reduced pressure demand in subsequent cycles. Moreover, LCWCF produced a step-like cumulative AE response, with 31.99% of the AE counts concentrated between the two pressure peaks. This work demonstrates the reliability of the system and provides an experimental basis for developing advanced permeability enhancement and dust reduction technologies.</p>

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A Novel Coal Testing System for Low-Temperature Fluid Cyclic Fracturing and Wetting Enhancement and Its Application

  • 期刊论文

  • 发表日期：

    2026年1月29日

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  • Hui Wang,
  • Hetang Wang,
  • Yulai Zhang,
  • Jianglong Tan,
  • Haoen Ma,
  • Kai Jin,
  • An Shi,
  • Junzhe An,
  • Haiming Xu,
  • Wendong Zhou

摘要

Liquid CO₂ (L-CO₂), with its phase-transition expansion and low viscosity, is a promising preconditioning fluid for permeability enhancement and dust reduction by coal seam water injection. However, liquid CO₂ fracturing (LCF) still has challenges, such as high-pressure phase behavior control and a lack of systematic testing system. Moreover, the mechanisms of liquid CO₂ and water cyclic fracturing (LCWCF) remain unclear. To address these gaps, a novel coal testing system for low-temperature fluid cyclic fracturing and wetting enhancement was developed. The functions and working principles of each module were introduced, and key technical issues, such as pulse-free cyclic injection and thermo-hydro-mechanical (THM) multi-field coupling, were resolved. Hydraulic fracturing (HF), LCF, and LCWCF experiments were conducted with synchronous acquisition of pressure and acoustic emission (AE) data. The results show that the system can precisely control stress and temperature to reproduce in situ coal seam conditions at the laboratory scale. Alternating injection of L-CO₂ and water overcame the limitations of a single fluid mode. Compared with HF, both LCF and LCWCF achieved higher fracturing efficiency. LCWCF, combining L-CO₂ phase transformation and water stress transmission, enabled faster fracture initiation, with a first-cycle breakdown pressure of 18.21 MPa, and reduced pressure demand in subsequent cycles. Moreover, LCWCF produced a step-like cumulative AE response, with 31.99% of the AE counts concentrated between the two pressure peaks. This work demonstrates the reliability of the system and provides an experimental basis for developing advanced permeability enhancement and dust reduction technologies.