Research On Rock Breaking Mechanism Of Composite Drilling PDC Bit

As an effective method for accelerating drilling speed, compound drilling technology has been widely used in drilling engineering. Nevertheless, the accelerating mechanism of compound drilling has not been clearly revealed yet in this field. For one thing, increasing the absolute rotation speed of the PDC bit will directly increase the drilling speed of it, but if drill with the same absolute rotation speed, compound drilling can make the drilling speed higher than the bit motivated by simply the screw or the rotary table. Based on the interaction between the PDC bit and bottom-hole rock, researches on the accelerating mechanism of compound drilling are conducted in this paper.Below are the main job and major achievements of this research:1. Failure features of the PDC bit under the working condition of compound drilling, particularly failure of the center and shoulder area of the bit, are clarified and analyzed.2. Movement laws of the PDC bit in compound drilling, which including the cutting tracks, influencing parameters and the radial overlap of the cutters, are researched, on basis of which, the influencing law of transverse and shimmy vibrations on the motion tracks of PDC cutters in compound drilling is analyzed and revealed.3. The load and deformation on the downhole drilling tools are analyzed and calculated with the method of vertical and horizontal bending, which provides a theoretical basis for calculating the actual slant angle and equivalent arm of the PDC bit in compound drilling.4. The numerical simulation of the interacting process between the bottom-hole rock and the PDC bit in compound drilling is established by utilizing Maltlab platform.5. The rock-breaking simulation program of the PDC bit in compound drilling is developed with related theories, with which the cutting parameters of cutters, as well as the contacting situations between the PDC bit and bottom-hole rock, is simulated and calculated. Furtherly, the rock-breaking mechanism of the PDC bit and the rock features in bottom-hole are concluded, on basis of which the concepts of customized design and application of the PDC bit are discussed.Through the analysis on the movement of the PDC bit and the interaction between the PDC bit and the bottom-hole rock under the condition of compound drilling, the rock-breaking mechanism of the PDC bit in compound drilling is clearly revealed, and furtherly, the concepts of customized design and application of the PDC bit are discussed, which provide reliable scientific basis for the design and application of PDC bits used in actual compound drilling.