A novel prediction method of PDC bit 's ROP in directional drilling

Key words:  drilling  PDC bits  drillability anisotropy  well trajectory  ROP  directional drilling

Abstract:

In this study, a novel prediction method of PDC bit 's ROP during directional drilling was established, in which the cutting action of the PDC bit, the mechanical action of BHA and the drillability anisotropy of rock formations were considered based on the instantaneous force balance principle. In the calculation of the total transient force on the PDC bit, the influence of the lateral unbalanced force on bit crown and the lateral force on bit gauge were accounted. The new method was verified using the experimental results of core drilling, in which the predicted well trajectory has a good agreement with the measured one. In using this method, the axial and lateral drilling rate of the PDC bit can be obtained by numerical calculation based on the parameter of the bit design and the drillability anisotropy of the rock formation, and no need to measure the normal formation drilling efficiency of the bit. In consideration of the transient force balance on the bit, the higher the lateral unbalanced force, the harder for well path control. The lateral unbalanced force on the PDC bit can be decreased by optimizing the PDC bit design, and the drift angle of the bit and the variation of the tool face azimuth can be also decreased.