A new method of coring in coal mine: pressure-holding and continuous coring technology

The quality and cost-effectiveness of rock core samples and rapid rock coring are main issues that need to be considered in the special operations of oil and gas fields and coal mines, such as opening coal seams with gas outburst, detecting fault distance or lithologic pinch out. Soft rock coring technology has a lot of work to do to improve coring quality and coring speed. In this study, pressure maintaining continuous coring technology (PHCCT) and equipment was developed, and the new coring method was compared with traditional coring method in terms of coring speed, core quality, and rock quality index (RQD). Compared with traditional coring method, the coring speed of PHCCT was almost doubled, and the RQD value of rock stratum was increased; however, the PHCCT method had little effect on the RQD value of coal bed. In this paper, the process parameters and technological measures of PHCCT were also discussed, the drilling fluid pressure of 6 MPa and the drill bit outer diameter of 94 mm were reasonable, and the drilling fluid pressure-holding of PHCCT was realized through the sealing device of drill pipe and sealing fixing borehole. The PHCCT method has great significance for the coring of coal seam and soft rock stratum.