"Three Soft" Outburst Coal Seam Gas Drainage Hole Deflection Law And Engineering Application

In the process of gas control borehole construction,the actual gas drainage borehole trajectory often has a certain deviation from the design,causing the borehole to be deviated,which makes it easy to produce blind areas for gas drainage,and there are hidden safety hazards.Based on the engineering research background of Xinzheng Coal and Electricity Co,Ltd.in Xinzheng City,Henan Province,this paper uses theoretical analysis and numerical simulation to study the law of borehole deflection and engineering application of gas drainage in the "three-soft" outburst coal seam.(1)Based on the monitoring data of the field data,the trajectory changes of the gas drainage borehole angles of 15°,30°,45°,60°,75°,90° with the depth of the hole are obtained and the function relationship between the inclination of the borehole and the inclination of the borehole,In this way,the amount of change in the inclination of the gas drainage borehole corresponding to the different inclination of the gas drainage borehole is calculated.(2)Analyze the deflection mechanism of the drilling rig during the drilling process according to the mechanical bending,geometric bending and other factors that affect the deflection of the drilling hole;The mechanical model of the gas drainage drilling rig in vertical upward,horizontal,and different inclination angles is obtained.The research results found that the main influencing parameters of drilling deflection are the weight on bit and the weight of the drill pipe.It provides a theoretical basis for the main influencing parameters that cause deflection in the drilling process.Among them,geological factors are the main influencing factors,but the objectivity is strong,and the controllability is weak.The equipment factors and human factors are subjective and easy to control.Therefore,the deflection of the gas drainage boreholes is mainly reduced from the equipment factors and human factors.(3)According to the AHP analysis model,the geological factors affecting(4)the deflection of the borehole trajectory of gas drainage boreholes are obtained: rock anisotropy,soft and hard interbeds,and rock angle;equipment factors: equipment installation,drilling tool structure,drilling tool weight;Human factors: the weight ratio of drilling method,drilling parameters,WOB selection,and drilling speed selection.(5)In the FLAC3 D numerical simulation experiment,the displacement around the borehole is small,the borehole area is relatively stable,and basically remains unchanged.The overall stress distribution presents the characteristics of layered distribution,which basically corresponds to the distribution of rock layers.The areas of stress concentration are mainly the rock layer change area,the coal seam area and the location of drilling holes.The drilling holes are prone to deflection in these areas.