Study on drill pipe oscillation elimination and drilling efficiency enhancement of pressure-relief borehole in coal mines

Pressure-relief borehole construction is one of the most common drilling operations in coal mines, which generally has characteristics such as coarse diameter, multiple construction angles, and large depth. However, due to the limitations of the working environment conditions. Many pressure-relief borehole drilling are difficult to directly use large-scale drilling equipment. The use of small drilling rigs combined with lightweight small diameter drill pipes to complete large-diameter drilling is an effective way to carry out pressure-relief borehole construction in such harsh environmental areas. But there will be severe oscillation of the drill pipe, leading to bending and low efficiency in drilling. In response to such issue, a method for eliminating drill pipe oscillation and increasing drilling efficiency has been proposed. Through comprehensive research methods such as theoretical analysis, numerical simulation, and laboratory experiments. The system analyzed the internal reasons for the low efficiency and poor quality of completing large diameter drilling with small diameter drill pipes, as well as the vibration characteristics and oscillation reduction mechanism of drill pipes in large-diameter pressure-relief borehole drilling. The results indicate that the main reasons for the poor quality and low efficiency of drilling are the bending of borehole and the extra power consumption of the drilling rig caused by the severe oscillation of drilling pipe. The larger the drilling depth, the more severe the drill pipe oscillation, and the lower the drilling efficiency and quality. The oscillation damping device is used to support the drill pipe in the radial direction, which can eliminate the drill pipe oscillation during drilling. The greater the drilling depth, the more obvious the oscillation attenuation effect of the oscillation damping device. When the drilling depth reaches 4m, the drill pipe amplitude is significantly reduced, and the maximum amplitude can be reduced by 80%. Based on this, a static support oscillation absorber suitable for pressure-relief borehole drilling is developed, which has both oscillation attenuation and drill pipe connection functions. It is mainly composed of embedded drill pipe connector, bearing structure, locking gasket and support seat. Under the action of high-speed rotation of drill pipe, the support seat not rotate with the drill pipe and is supported on the hole wall, and drilling cuttings can be discharged smoothly through the chip guide channel. The on-site borehole drilling test results show that using this oscillation absorber, when the drilling depth is 4m, the drilling time is reduced by 28%, effectively improving the drilling efficiency and quality.