Technology and application of L-shaped well ground gas extraction for pressure relief in coal mining areas

WANG Yi; ZHANG Yuanzhi; ZHANG Jing

doi:10.11799/ce202511010

Abstract：Ground L-shaped well gas extraction and pressure relief is an important technical means for gas extraction in coal mining areas.In response to the current problems of low drainage efficiency,difficult well completion and large difficulty in well deviation control during the gas extraction process of ground L-shaped horizontal wells,the technical principle of L-shaped horizontal well gas extraction was analyzed and three key technical points,including well location deployment,key technologies for drilling and well completion,and negative pressure drainage technology,are summarized.According to the gas migration law,the L-shaped well layout range was optimized;the three-casing wellbore structure design was sorted out and proposed,the wellbore trajectory control technology was optimized,the anti-pressing directional drilling technology,well completion and well washing technology,and cementing technology of L-shaped wells were studied,and the L-shaped well drilling technology system was established.According to the characteristics of gas extraction and pressure relief by L-shaped wells,two negative pressure extraction modes and negative pressure extraction control management systems at different stages were proposed,namely the general-specific mode,and specific-general mode.The"flow rate guarantee and negative pressure variation"control method was adopted at each stage.The gas extraction effect of ground L-shaped wells in Huaibei mining area was studied and analyzed.The pure gas extraction volume of Guobei Coal Mine reached 2.7×106 m3,and the pure gas extraction volume of a group of L-shaped horizontal wells implemented in Zhuxianzhuang Coal Mine was up to 5875 m3 per day,achieving safe mining.On this basis,the future development direction of L-shaped well technology was proposed,mainly including the precision of design parameters,precise control of horizontal section trajectory,large displacement horizontal well drilling,refined drainage management,and joint ground-surface L-shaped mining-induced well gas extraction technology.