Research On Controlled Theory Of Positive Displacement Motor Drilling In Coal Mine For Nearly Horizontal Directional Borehole

For assuring safety production and high efficiency in gas drainage, coal minecondition was specially explored, the accuracy on the extent range of gas drainage drilltrack was gradually raised. It is an available approach to solve the above problems innearly horizontal directional drilling(HDD) technology with positive displacement motor(PDM) and relevant equipments.The advantage of PDM assembly in directional drilling was educed in this paper, with it's appliance actuality induced, the infection factor and bend condition of drill track summarized, PDM assembly in horizontal directional drilling chosen and optimized. The capability characteristics of PDM were studied, the two common outside diameters of 73mm PDM in home and abroad that suit for HDD of gas drainage were selected in optimization, and indoor experiment on them was summed and validated, main borehole and lateral borehole directional bore-forming technics method of PDM were studied.Mechanical model was formed by analyzing static force and distortion under two dimensional and three dimensional with continuous beam theory for PDM assembly with bent housing. Quantitative parametric sensitivity analysis under two dimensional was made on factors influencing drilling tool structure, bore-hole structure and drilling technology with Visual C++ 6.0 software and least squares theory, and relevant software was designed. Both of them offered useful theoretic exploratory for drill track. Indoor simulation test and two field directional drilling tests using PDM were done finally, fulfilling six main boreholes and five lateral boreholes, total length of 4226m and main borehole with the biggest length of 1046m. Combined with theory research and field practice, staggered fruit has been gained by analysis on the effect of directional test.In this paper, controlled theory of PDM drilling in coal mine for nearly HDD borehole was comprehensive analysed and successful applicated. It was proved that correct application of PDM and relevant equipments in nearly HDD would relieve the strain situation of unbalance proportion of the discharging, picking, mining, so it is important to improve the ability of gas drainage.