Variation characteristics of coal rock layer and gas extraction law of surface well under mining pressure relief

Abstract

In order to study the variation characteristics of coal rock layers and gas extraction law of surface well under mining pressure relief, in Taoyuan Coal Mine of Huaibei mining area, this paper carried out the researches of bottom hole flow pressure and extraction parameter monitoring of surface extraction wells and FLAC3D stress numerical simulation under mining pressure relief and obtained variation data of the bottom hole flow pressure, the extraction volume, and the in situ stress in mining progress. Based on on-site monitoring and numerical simulation results, the changes of coal rock layers in mining affected areas are divided into seven stages. The four stages in front of the mining position are the pressure relief stage (mining position to 15 m in front), the stress concentration stage (15 ~ 40 m in front), the pressure relief stage (40 ~ 65 m in front), and the stage near the original condition (> 65 m in front). The three stages behind mining position are the pressure relief stage (mining position ~ − 40 m), stress recovery stage (− 40 ~ − 250 m), and post-compaction stability stage (> − 250 m). It is found that the gas extraction curve of surface well in mining pressure relief has a positive skew distribution. The extraction stage can be divided into three stages: initial gas production, high production, and gas production attenuation. It is believed that the methane in gas mainly comes from the upper coal seam in initial stage and the main mining seam in the late mining period. According to researches, it is recommended that the “one well multi-purpose” surface gas extraction method can be actively explored in mining affected areas.