Mechanism of Polycrystalline Diamond Compact and Diamond Impregnated Cutter Hybrid Bit Composite Rock Breaking

Abstract

Rock breaking efficiency of drill bits is an important index for measuring the drilling efficiency in the oil and gas drilling field, and it is influenced by many factors, such as structure and material. This study developed a calculation model and an experimental model of rock breaking of polycrystalline diamond compact (PDC) and diamond impregnated cutter (DIC) hybrid bit to reveal the influence of bit structure and material on tangential force, axial force and wear height. On the basis of the calculation model of the co-rail arrangement of the PDC – DIC hybrid bit and the rock breaking mode, a rock breaking mechanical parameter prediction model and a rock breaking performance test model were established. Rock stress calculation method, rock failure criterion, and mechanical specific energy (MSE) calculation method were used to analyze the rock stress and the relationship between MSE and tangential force, axial force, and wear height during combined rock breaking. The accuracy of the model was verified by experiments. Results show that the specific work of rock breaking of the PDC-DIC hybrid bit is less than that of PDC, and a reverse nonlinear relationship exists between specific work of rock breaking and wear height. The energy required for hybrid bit to break rock is less than that of PDC bit. A positive nonlinear relationship exists between the energy of PDC-DIC hybrid bit and the wear height, whereas the cutting depth and the wear height show a negative nonlinear relationship. The stress distribution of PDC rock breaking is uniform, and the maximum equivalent stress is up to 104 MPa. The stress distribution of rock breaking of the hybrid PDC-DIC is extremely nonuniform, and stress concentration occurs with a minimum equivalent stress of 84 MPa and a maximum stress of 161 MPa, which is beneficial to rock breaking. Rock breaking of PDC-DIC hybrid bit can promote the generation and development of rock cracks, thereby reducing the crushing strength of the rock. The study provides a design method and theoretical basis for designing a new type of PDC-DIC hybrid bit, with certain reference for exploring the rock breaking mechanism of various bits