Analysis of diamond drill bit operation in well drilling under complicated conditions

Abstract

The purpose of the study has been to analyze the operation of diamond drill bits of a PDC type (polycrystalline diamond cutters) in the regions with a complex geological section, and to develop recommendations on optimizing the drill bits. The PDC drill bits are originally designed for soft to medium-hard rocks, thus being ineffective for complex geological sections. As part of the research, the mechanics of the build-up formation on the drill bit cutter and its impact on the rock destruction have been studied. The influence of the pumped drilling mud volume and the pressure differential in the downhole motor on the mechanical drilling speed of the PDC bit has been analyzed. Proposals on improving the geometry and orientation of the tool cutters and optimizing the design of the cutting structure calibratation site and the bit blades have been given; measures on reducing the bottomhole vibrations of the bit during its operation have been suggested. As a result of the study, the mechanism of the build-up formation on the cutter’s working edge and its advance influence on the fracturing in the rock volumetric stratum has been determined. It has been found that the maximum feed of the drilling mud results in the complete absence of the build-up formation and a sharp increase in the mechanical speed of drilling. The study has shown the high performance of high-torque downhole screw motors and defined the optimum range of the pressure differential for the PDC drill bits as a function of the drilling mud flow rate. The authors have suggested the ways to reduce the vibration and stabilize the PDC drill bits by optimizing the structure and geometry of the tool’s cutters and blades, and by using hybrid cutters as auxiliary ones. The conclusion is that the optimization of the PDC drill bits enhances their operation performance under complicated geological-engineering conditions in Eastern Siberia and Yakutia.