Abstract
Coal mine gas disasters have severely restricted production safety. Improving gas extraction efficiency can effectively reduce disasters. Scholars have confirmed that CO2 successfully displaces coal seam CH4. This study conducted displacement and in situ experiments and compared gas drainage under different injection pressures. The displacement experiments indicated that CH4 production rates increased under increased pressures while the displacement ratios decreased. The pressure had a positive effect on sweep efficiency. The in situ experiment showed that CH4 and CO2 concentration trends in the inspection hole remained consistent. Through observing the data of the original and inspection holes, the average gas drainage concentration during low- and medium-pressure injections increased by 0.61 times and 1.17 times, respectively. The low-pressure average gas drainage scalar was increased by 1.08 times. During the medium-pressure injection, the average gas drainage purity increased by 1.94 times. The diffusion ranges of CO2 under low- and medium-pressure injections were 20–25 m and 25–30 m, respectively. The sweep efficiency of medium-pressure injection was 26% better than that of the low-pressure injection, with average pressures of 2.8 MPa and 1.4 MPa, respectively, for sweep efficiency. This study proposes an effective method for improving coal mine gas drainage efficiency.
Highlights
Gas disasters are one of the most important factors affecting the safety of coal mining.Gas drainage is the most direct and effective method for controlling gas disasters and is an effective way to obtain clean energy [1]
The displacement ratios (CO2 storage volume/CH4 production volume) of CH4 in the coal samples injected at different pressures were 3.85, 3.15, and 2.45, respectively
The displacement ratios decreased by 18.2% and
Summary
Gas disasters are one of the most important factors affecting the safety of coal mining. Domestic and foreign scholars have developed a variety of coal seam permeability enhancements and gas drainage technologies and have carried out field tests in many mining areas to improve coalbed methane recovery. These include pore fracture reconstruction technologies such as hydraulic fracturing, explosive blasting, shock wave fracturing, L-CO2 blasting, and L-CO2 fracturing [8–14], and gas desorption technologies such as gas injection, heat injection, and acoustic waves [15–19]. Detonation wave fracturing can result in the formation of a stress-concentrated area in the coalbed, increasing the possibility of accidents These technologies do not significantly improve the efficiency of coalbed methane recovery in coal seams. This study provides a theoretical basis for L-CO2 displacing coal seam CH4 technology and new technical methods to improve gas drainage efficiency
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