Surface drilling is one of the main technical means to solve the problem of gas extraction in the goaf and mining area. It can not only extract the gas in the goaf, but also extract the pressure relief gas in the adjacent layer to realize the gas extraction in the coal seam group, which is the commonly used pressure relief gas extraction technology in Lianghuai mining area. The practice shows that the larger the well diameter, the larger the mixture and pure amount of gas extraction, and the lower the gas concentration in the upper corner. However, due to the constraints of large-diameter well drilling technology, borehole stability under mining conditions, casing anti-crushing ability, large-diameter cavitation technology, etc., the borehole diameter of pressure relief gas mining Wells is limited.
In cooperation with Huaibei Mining Group, CCTEG Xi'an Research Institute (Group) Co., Ltd. has applied the drilling technology of surface large diameter well to the construction of gas mining well, and carried out special technical research. The research has formed the mud wall protection technology of large diameter well, multi-stage reaming technology of PDC bit, hole cutting technology of rechangeable tool wing type bit, casing running technology of lifting buoyancy method and efficient cementing technology of large aperture well. The technology has been applied to the construction of two large-diameter gas mining Wells, 1077-13 and 1077-18, in Yangliu Coal Mine, Huaibei Mining area. The two Wells have a drilling diameter of 444.5mm, a hole cutting section diameter of 550mm, and a completion casing of φ339.7mm, which is the largest caliber gas mining well reported in China. At present, Wells 1077-13 have been mined at the mining face, and the extraction effect is remarkable. The daily gas extraction amount and total gas extraction amount are 3 ~ 4 times that of ordinary surface Wells at the same mining line position. The gas extraction rate of the working face increases from 80% to over 90%, and the gas concentration in the goaf decreases from 0.86% to 0.48% at the upper corner beam pipe pressure depth of 25m. The upper corner basically realizes the negative pressure state.
The 1077-13# and 1077-18# surface pressure relief gas mining Wells successfully implemented by Xi 'an Research Institute in Yangliu Coal Mine fill the gap in the construction and application of large-caliber surface gas Wells in China, and provide reliable data support and theoretical basis for realizing the maximum extraction of surface Wells in coal mines.
