Analysis of the Causes of Altered Coal Seam Permeability Based on On‐Site Directional Long‐Drill Hydraulic Fracturing Tests

Abstract

This study aims to explore the problem of gas extraction from coal seams. Based on the engineering background of Longfeng coal mine in Guizhou Province, hydraulic fracturing test and DC method test are carried out in 5922 wind tunnel of Longfeng coal mine's second mining area, according to which a drainage model is established to simulate the process of gas drainage from a single hole, in order to evaluate the effect of gas drainage after the completion of the hydraulic fracturing tests. According to the test results, it can be seen that the fracturing is mainly concentrated on both sides of borehole No. 9‐4, with an impact area of up to 30 m and a resistance increase in the range of 100–400 Ωm. After calculation, the theoretical value of effective gas extraction radius after fracturing is 4.83 m, which is increased by 49%; the permeability coefficient after fracturing is increased to 2.64 times of that of the original coal seam. In addition, the average concentration of extracted gas is 68%, which is 7.5 times higher than that without fracturing. Therefore, this research result can provide technical reference for the management of low permeability coal seams under similar geological conditions.