Analysis on the CBM extraction effect of the horizontal wells in the coal seam roof in Luling coal mine in Huaibei

Huaibei Luling Coal Mine is a mine with high risk of gas outburst. The coal seams are broken and soft have low permeability, the gas extraction is difficult. The high-efficiency gas extraction technology of staged hydraulic fracturing horizontal well next to seam roof, developed during the 12th Five Year Plan, was applied. The pilot test achieved a breakthrough in gas production. However, there are few researches on the effect of horizontal well drainage on the prevention and control of gas disasters. In this paper, the reservoir characteristics of the target coal seams and the gas production law of the pilot horizontal well were analyzed. Then, the numerical simulation technology was employed to historically match the production data. On this basis, the horizontal well production was predicted for ten years. The change law of coalbed methane gas content and reservoir pressure over time in the process of horizontal well extraction was analyzed. And the effect of coalbed methane extraction on coal mine gas control was evaluated. The results show that:The influence area of horizontal well drainage is mainly near the hydraulic fracture and wellbore, and the area outside the wellbore-fracture system is less affected; The influence area of horizontal well gradually increases with the production time. It is predicted that the area of influence scope of 1 a, 3 a, 5 a, 8 a, and 10 a is 0.113, 0.193, 0.242, 0.311, 0.350 km², respectively; With the drainage time, the gas content and reservoir pressure gradually decrease. It is predicted that after 5 years of production, the gas content within the control range of the horizontal well can be reduced to 2.86 m³/t at the lowest, and the average can be reduced to 4.2 m³/t, with a reduction ratio of 50.6%. The reservoir pressure can be reduced to 0.85 MPa at the lowest, and 2.30 MPa on average, with a reduction ratio of 66.2%; Coal seam roof horizontal well technology has significant effects on coalbed methane development and gas disaster prevention and control, and is an effective method to achieve ground pre-drainage of gas from broken, soft and low-permeability coal seams.