Study on technology and effect of gas extraction in horizontal well with segmental hydraulic fracture in roof of coal seam in Huainan mining area

Huainan mining area is a typical high-gas area, with broken soft coal seam, low permeability, high gas content, and difficulty in extraction. In order to probe into the technical feasibility and gas control effect of the horizontal well for segmental hydraulic fracture in roof of coal seam in mining area, a three-dimensional in-situ stress test of coal seam was carried out using the stress relief method based on the analysis of the characteristics of the 13-1 coal reservoir, which was the main coal seam in the mining area. The results shown that, the three-dimensional stress field was mainly σ_h,max > σ_v > σ_h,min, which had sufficient conditions for the implementation of horizontal well with segmental hydraulic fracture in roof of coal seam. MFrac Suite software was used to simulate the fracture parameters of horizontal section at 1, 3 and 5 m from the coal seam. The maximum half-length of the fracture was 107.33 m and the minimum was 89.47 m, which was ideal for fracturing, indicating that the horizontal well with segmental hydraulic fracture had better geological adaptability and feasibility in Huainan mining area. Taking the CBM01 well, a horizontal well with L-type roof segmental fracturing in the 13-1 coal seam of Panyi coal mine, as the research object, the effect of gas control and management was comprehensively analyzed by means of borehole detection and numerical simulation. The results shown that, CBM01 well significantly reduced the gas pressure and gas content of coal seam after 415 d of extraction. The gas pressure at 50 and 65 m from the horizontal well decreased from 6.4 MPa to 2.6 and 2.7 MPa, respectively, by more than 55%. The gas content decreased from 13.5 m³/t to a maximum of 9.11 m³/t, a minimum of 6.92 m³/t, an average of 7.92 m³/t in an area of about 15-20 m on each side of the horizontal section, and decreased to less than 8 m³/t within about 10 m. Finally, a numerical simulation method was used to predict the gas production effect of CBM 01 well extracting for 10 a and the effect with gas control. The cumulative gas production of gas well was about 272.08×10⁴ m³ in 10 a, and the gas content in the range of about 150 m on one side of the horizontal section was reduced to less than 8 m³/t, and the pressure was reduced to less than 3 MPa. Comprehensive research results shown that the horizontal well technology of segmental hydraulic fracturing in roof of coal seam had greater advantage and application effect in gas control and management in Huainan mining area.