关键词: 采动卸压, 下组煤, 煤层气, 水平井, 钻井技术

Abstract: As the scale of coal mining is gradually shifting to the deep in China, the problems of gas prevention and the exploitation and utilization of coalbed methane (CBM) resources in deep coal mining remain to be resolved urgently.Taking Sihe mine in Jincheng, Shanxi Province as an example, the stress distribution, fracture evolution and permeability change of the underlying strata of No. 3 Sihe Mine Field after mining pressure relief were analyzed. The feasibility of reducing gas content by surface extraction of CBM from the lower coal group has been studied, and research on the deployment method of surface extraction CBM wells from the lower coal group, drilling techniques and drainage key technologies has been carried out.The results showed that the permeability in No. 15 lower coal group has been increased by about 2.20 times, which is beneficial to the surface CBM pre-drainage of No. 15 coal seam. According to the requirements of CBM development project, based on the method of comprehensive analysis of surface wells, the deployment of CBM extraction wells in the horizontal wells of the lower coal group through the coal wedge was optimized, the structure of the three section drilling well body was conceived, the design of borehole trajectory and drilling trajectory control technology was evaluated, and drilling technologies such as drilling fluid system, leak plugging and graded cementing process of fracture development section for different drilling layers was investigated.In order to effectively reduce the wear resistance of the string in the drainage of L-shaped horizontal Wells, the technology of "well buttoning positive + two-way protection rod collar prevention eccentric wear + guider torque reduction" was adopted. The maximum daily gas output of the horizontal well through coal pillar of the lower coal group is 9522 cubic meters, and the cumulative gas output is 2.2 million cubic meters within 14 months. The gas production effect is ideal, which proves the feasibility of the technology and has a certain degree of implications for CBM exploitation of the lower coal group in the research area and the similar areas in China.