空气钻井中螺杆钻具输出性能研究

Analysis of Output Properties of PDM for Air Drilling

针对空气螺杆钻具在使用过程中难启动、扭矩不足等问题,为寻求螺杆钻具的最优性能,将空气螺杆简化为一个环形圆筒的等效模型,求出其当量直径,并结合一维可压缩流体的流动特性,求得井下螺杆的压降和实际进气量,进一步得到螺杆转速、扭矩等输出特性。计算结果表明,随着井深的增加,空气螺杆输出扭矩和钻速随之降低。

The PDM （Positive Displacement Motor） usually is used as a motive machine during air drilling, it transforms the energy of compressed air into mechanical energy, then transports the mechanical energy to the bit, and bit breaks rocks. PDM usually faces the problem of hard-starting and the shortage of torque and so on, The analysis of output properties of PDM has an important effects on selecting PDM structure parameters and drilling parameters. In this paper, PDM was simplified as an equivalent annulus between stator and rotor,its equivalent diameter, combined with the characteristics of the dimensional compressible fluid, was derived pressure drop and actual air injecting flow rate of the motor, further output characteristics such as revolution speed and torque were calculated. The results shows that torque and revolution speed decreases with depth increasing.