Study on combined rock-breaking and rock carrying by high-pressure water jet and PDC single blade

Abstract:

High-pressure water jet can not only clean the bottom of wells but also significantly enhance the drilling speed， thus substantially improving the drilling efficiency. At present， however， the research on the combined rock-breaking of high-pressure water jet and PDC （Polycrystalline Diamond Compact） bits mainly centers on analyzing with PDC cutters as the basic cutting unit. This approach fails to comprehensively reflect the impact of high-pressure water jet on operation of the overall PDC bit. Therefore， in this study， the entire PDC single blade is regarded as the basic cutting unit. A numerical model for the combined rock-breaking of high-pressure water jet and PDC single blade is established using the SPH-FEM（Smooth Particle Hydrodynamics-Finite Element Method）. The reliability of the model was verified by the cutting force and the size of the water jet fracture pit， and the error between the model and the experiment was only 9.29%. Furthermore， based on this numerical model， the rock-breaking and rock-carrying mechanism of the high-pressure water jet and PDC single blade was analyzed through cutting force， rock stress field， rock strain field and bottom hole flow field. This method can basically reflect the influence of high-pressure water jet on the entire PDC bit， and verify the enhancement of the rock-breaking and rock-carrying capacity of the PDC bit by high-pressure water jet.