Research Of Construction Technology On Large-diameter Directional Borehole In Coal Mining Areas

Mainly applied as a tunnel connecting surface and underground, the large-diameter directional borehole in coal mining areas, which is different from small-diameter hole in respect of core boring(diameter range from30mm to150mm) and large-diameter shaft(diameter range from3m to10m), generally reaches its completion diameter in the range from550mm to1200mm. It is hard to complete this kind of borehole because of the distinctly different drilling techniques and frequent problems occurring during borehole construction, such as inferior directional drilling accuracy, low reaming efficiency, high drilling accident rate, difficult casing job and low cementation quality, etc. It will be of great significance for coal mine safe construction, generation and emergency management and rescue to research large-diameter directional borehole construction technology in coal mining areas to enhance completion quality and efficiency.This paper relies on the self-financed projects of Xi’an Research Institute, CCTEG to carry out the research work. The procedure of large-diameter borehole drilling as follows: first, drill the pilot hole, then, the diameter of the hole is extended step by step, finally, run casing and cement. It addresses the key technologies, including trajectory of pilot hole control technique, maximum horizontal reaming, casing running and cementing. The paper discusses trajectory of pilot hole control technique and safe drilling technique. Based on theory of rock breaking, the paper analyses the reaming sequence, drilling string safety, drilling parameter and other contents. The corresponding drilling parameter and arrangement of drilling tools are derived via DrillNET software simulation. Necessary float collar and float shoe are developed. Then it optimizes buoyancy method for casing running and corrects casing strength. Also it discusses inner string cementing to improve displacement efficiency and cementing quality.This paper is a theoretical and applied stylistic research project. The construction technology for large-diameter borehole in coal mining area has been optimized by theoretic analysis and industrial field experiment of3drilled correlation boreholes, and this technical support is provided for safety in coal mining areas.