Long distance running technology of large-diameter casingwith near horizontal drilling in underground coal mine

The sealing of drill hole casing is the basis of drilling construction and safety guarantee. The key factors affecting the installation success rate of large diameter casing with near horizontal and long distance in coal mine are the passing capacity of large diameter casing, the deviation control of hole trajectory and the effect of slag discharge.In order to improve the pasing success rate of casing with near horizontal and long distance.The rigid and elastic models of large diameter casing were established, and the passing capacity of ø178mm,ø146 mm and ø127mm casing in the underground coal mine was obtained. The causes of easy deviation and difficult slag discharge in near horizontal and large diameter casing borehole section were analyzed, and the technical scheme of using large diameter auger drill rod and concave PDC drill bit for straightening drilling and efficient slagging was introduced. The related drilling tools were developed, the drilling tool assembly was also made, and the mechanism of straight drilling and high-efficiency slag discharge was analyzed. Field test was carried out in Zhaogu No.1 coal mine, and three boreholes were completed for it. Compared with the conventional process, the construction time of casing borehole section was reduced from 110 to 21 shifts, the trajectory deflection was only 0.042 °/m. The success rate reaches 100%, which effectively solves the problem of large-diameter casing with near horizontal and long distance and provides reference for similar casing borehole section construction.