Status and development of intelligent drilling tools for coal mine

As an important part of intelligent drilling, the intelligence of drilling tool system plays a crucial role in the intelligent development of coal mine underground drilling. In order to deeply explore the development direction of intelligent drilling tools, the research results and technical characteristics of intelligent drilling tools in coal mines were systematically sorted out from the aspects of directional drilling tools, measurement while drilling (MWD) system, intelligent drilling pipes and drill bits with reference to the experience in development of oil and gas industry, and the existing shortcomings were also summarized. It is pointed out that screw motor is mainly used at present in most of the intelligent directional drilling tools in coal mines, the research focuses on the geometric design of screw motor, the fatigue resistance of stator elastomer and customization of different technologies, and the development of rotary steerable drilling tools is in start-up phase, greatly deferring from the oil and gas industry. The MWD system can monitor few parameters, and the monitored data is mainly composed of the trajectory parameters. Therefore, Gamma formation identification was introduced gradually. The data was mainly transmitted by wire and mud pulse, with the problems of small data capacity and low transmission efficiency. However, the data transmission by wireless electromagnetic wave is only applicable in case of short distance, only satisfying the requirements of boreholes within 500 m. The research of intelligent drilling pipe was to optimize and improve the cable drill pipe, and the research of intelligent drill bit has not yet been carried out. In order to realize the intelligent drilling of coal mine, it was proposed to carry out the research on the orientation system of drilling tools based on the rotary steerable system and the comprehensive application of a variety of directional drilling tools. The MWD system should integrate the functions, such as gas monitoring, groundwater detection, ground stress sensing, and special requirements of coal mine drilling. Meanwhile, research was conducted on the MWD system with coexistence of multiple transmission methods to adapt to different drilling technologies, improve the transmission speed and realize the high-speed bidirectional transmission of information. Further, the intelligent drill pipe with load self-monitoring and the intelligent drill bit with self-monitoring of rock breaking parameters were also studied. Thereby, an intelligent drilling tool system with two-way communication and adaptive regulation that integrates the efficient rock breaking drilling, dynamic adjustment of drilling trajectory, drilling tool self-condition monitoring, and real-time monitoring of gas, groundwater and in-situ stress was developed through the optimal combination of drilling tool systems. The above research results will enrich the comprehensive understanding of the intelligent drilling tool system in coal mine, and provide the basis and guidance for the subsequent development of the intelligent drilling tool system.