Development Of PDC Bit For Horizontal Hole Drilling In Coal Mine Synchronously With Pipe

Coal mining is often accompanied by gas which seriously threatens the safety of coal mine.It is necessary to drill gas drainage holes in advance to remove gas in coal seam.At present,most of the gas drainage holes have the shortcomings of small size and inadequate holes depth,which restrict the gas extraction efficiency and affect the safety of coal mining.However,direct drilling of large diameter drainage holes is easy to induce gas outburst,holes wall collapse and accident risk of drilling equipment jamming.Synchronized pipe-following drilling technology is a new horizontal drilling technology and new technology,which can effectively solve the problem of large-scale gas drainage deep hole drilling in coal mines,and is of great significance to increase the efficiency of gas drainage in coal mines and ensure mining safety.However,the existing drilling tools cannot be directly used in synchronous pipe-following drilling because of the drawbacks of difficult recovery,poor reliability and low quality of drilling.In this paper,an expandable PDC bit for synchronous tracing drilling of horizontal holes in coal mines is developed according to the field drilling conditions of gas drainage holes and the requirements of new technology.The main research contents include:(1)A new type of rotary transverse expandable PDC bit with open core design was proposed.The open expandable structure adopted by the tool reduces the risk of blocking during bit shrinkage and has good bearing capacity for both compression and tension during drilling.(2)The design and research of the expansion and control structure of the expandable PDC bit were carried out.The rotary blade is adopted as the expansion and expansion structure of the drill bit,and the expansion of the blade is controlled by drill pressure shearing pin.When the bit starts out,it is recovered under the extrusion of the pipe orifice,and the extension condition is limited by the structure of the shearing pin.The distribution and shearing pin experiments showed that the method is not only simple and easy to operate,but also ensures that the drill bit will not scratch the pipe wall when it moves horizontally in the pipe.In order to achieve multiple drilling operations by replacing copper pins after the bit starts out.(3)The design and study of cutting structure and hydraulic structure of the expandable PDC bit were carried.In the extended state,the overall cutting profile is smooth,short parabolic cutting profile,which has good adaptability to coal seam drilling and strong inclination building ability,and can meet the matching requirements of rotary steering tools and steering drilling requirements.The theoretical analysis results showed that the bit breaking efficiency in coal seam is high and the hydraulic cleaning effect is good.(4)The manufacture of TGZS 245/320mm expandable PDC bit has been successfully completed.The developed expandable PDC bit provides strong technical support for drilling large-scale gas drainage holes,improving coal seam gas extraction rate and ensuring coal mine safety,and lays a solid foundation for the follow-up study of the expandable bit for directional synchronous pipe-following drilling.