Increasing Permeability of Coal Seam and Improving Gas Drainage Using a Liquid Carbon Dioxide Phase Transition Explosive Technology

Abstract

The low permeability of coal seams makes gas drainage difficult in lots of coal mines. This study presents a low-temperature, safe, and efficient liquid carbon dioxide phase transition explosive technology (LCDPTET) to increase the permeability of coal, thereby improving the efficiency of gas drainage and eliminating the dangers of coal and gas outburst. Meanwhile, an integrated approach for experimental determination, numerical simulation, and field testing was applied to study the damage ranges of coal and to determine a reasonable spacing between the gas drainage hole and blast hole. A numerical simulation model of liquid carbon dioxide phase transition explosion (LCDPTE) was built, and the damage index M was introduced to analyze the degree and range of coal damage after explosion at different spacings between the blast hole and the gas drainage hole. Furthermore, another aim was the assessment of the permeability changes and comparison of the gas drainage effects of different borehole spacings. The results showed that as the borehole spacing became smaller, the degree of coal damage around the gas drainage hole increased, and the gas drainage effect improved. However, to avoid the collapse of the gas drainage hole, the gas drainage holes should not be located in the crushing zone caused by LCDPTE. Based on the numerical analysis conducted to guide the borehole arrangement of the field test, the latter was carried out to study the increasing ranges of permeability of coal and the drainage effect after explosion. The results indicated that LCDPTET could greatly improve the permeability of the coal seam and gas drainage efficiency. In addition, this new technology could not only improve the safety and efficiency of mine production but could also turn carbon dioxide into an effective energy source worthy of popularization and application.

Rock Breaking and Dynamic Response Characteristics of Carbon Dioxide Phase Transition Fracturing Considering the Gathering Energy Effect

“…In addition, it can absorb heat and suppress fire during the whole process. In short, CDPTF is a safe, green and reliable rock breaking technology [6][7][8].…”

Positive Phase Pressure Function and Pressure Attenuation Characteristic of a Liquid Carbon Dioxide Blasting System

“…Equation 16is still simple and can match the observed parameters more precisely. Equations (17) through (19) are more and more complex, but they can be adjusted to approximate experimental or theoretical values. The author thinks that scholars should adopt the simplest form that is compatible with the accuracy required for any given analysis.…”

“…Nowadays, the research of liquid carbon dioxide blasting mainly focuses on coal seam anti-reflection, thermodynamic properties, energy calculation, pressure characteristic, mechanism of fracture, and its application. Lu et al [2], Chen et al [16], He et al [17], Kang et al [18], Wang et al [19], Zhao [20], Huo [21], and Dong et al [22] studied the permeability improvement of liquid carbon dioxide phase transition on the basis of foreign liquid carbon dioxide blasting systems, gave two energy calculation equations, and analyzed the trinitrotoluene (TNT) equivalent of liquid carbon dioxide phase change process and the mechanism of fracture. Based on the Span and Wagner carbon dioxide equation of state [23] and the thermodynamics of explosions, the influence of thermodynamic properties of liquid carbon dioxide and the explosion of energy during the phase transition was further investigated through experimental methods, the conclusion that the carbon dioxide in the blasting tube is supercritical before the rupture disc broken was obtained, and a more accurate method was proposed to calculate the energy of explosion of liquid carbon dioxide blasting systems [6].…”

A new cross‐borehole hydraulic caving technique in the coal seam with a soft layer for preventing coal and gas outbursts during coal roadway excavation

“…At present, methods of coal seam permeability enhancement include N 2 injection, deep hole presplitting blasting, hydraulic fracturing, hydraulic flushing, hydraulic slotting, and other methods . The permeability has shown a trend of increasing sharply, slightly decrease, and then stable at a constant value after injecting N 2 in CO 2 ‐rich low permeable seam .…”

“…10,11 Therefore, how to enhance the permeability of coal seam and improve the efficiency of gas drainage, especially complex geological conditions(eg, coal seam with a soft layer), is a difficult problem for experts and scholars all over the world. 12 At present, methods of coal seam permeability enhancement include N 2 injection, deep hole presplitting blasting, 13 hydraulic fracturing, 14 hydraulic flushing, 15,16 hydraulic slotting, and other methods. [17][18][19][20][21][22] The permeability has shown a trend of increasing sharply, slightly decrease, and then stable at a constant value after injecting N 2 in CO 2 -rich low permeable seam.…”