Research on Pore-Fracture Structure Alteration and Gas Emission Homogenization in an Outburst Coal Seam Induced by CO2 Gas Fracturing

Considering the alarming frequency of coal mine gas disasters globally, there is an urgent need to develop efficient gas control technologies to ensure mining safety. This study focuses on the problem of high peak gas emission restriction in the process of coal roadway tunneling in outburst coal seams, taking the No. 15 outburst coal seam of the Pingshu Coal Mine as the research object. Based on coal sample testing analysis and the application of CO2 gas fracturing (CO2-Frac) in coal mines, a comprehensive evaluation was conducted on pore-fracture structure alteration and homogenization gas emission effect induced by CO2-Frac, providing technical solutions for coal mine safety production. The results are as follows: (1) CO2-Frac induces fracture propagation and the development of three types of fracture structures: Tri-Wing Fracture, Damage Markers, and Coal Matrix Fragmentation. (2) Following CO2-Frac at 150 MPa, the pore volume and average diameter of pores in the 100-10,000 nm range increased by 128% and 61%, respectively, compared to the pre-CO2-Frac state. (3) During the excavation period, continuous monitoring of the airflow for 3 days showed a significant homogenization of gas emission, with a maximum value of 0.450% and a variance value of 0.0031, indicating a reduction of 31% and 68%, respectively. These results reveal several key findings: The pore-fracture structure alteration enhances gas diffusion and permeation, providing high-speed pathways for gas migration, resulting in a substantial increase in gas extraction efficiency. During coal cutting, the modified coal exhibits homogenized gas emission, eliminating the high peak phenomenon and achieving safe and efficient mining. These findings demonstrate that CO2-Frac has broad potential in gas emission homogenization for widespread application in coal mines with similar gas geological conditions.