Effect of Chamfer Geometry of PDC Cutters on the Impact Resistance, Wear Resistance and Rock Cutting Efficiency

Abstract

ABSTRACT: Polycrystalline diamond compact (PDC) drill bit is widely applied in drilling engineering. Under harsh downhole conditions, the quasi-brittle characteristics of PDC cutters may be a severe drawback of drill bits, which readily causes premature impact failure. In order to improve the durability of PDC cutters without compromising the cutter aggressiveness, the planar diamond table with modified cutter edge geometry was experimentally investigated. The experiment included progressive drop test (PDT) and vertical turret lathe (VTL) wear test. The cutting forces were measured using a dynamometer load cell. Overall test results were compared together. The results showed that a single-chamfer cutter performs best under the dry VTL test without coolant and generates a lower cutting force. The dual chamfer geometries showed a significant impact resistance without compromising other properties. Because the commonly used mechanical specific energy (MSE) has a negative relationship with cutting efficiency, therefore, the ratio between the volume of rock cuttings and energy consumed on rock cutting process was calculated to represent the cutting efficiency or namely aggressiveness, so as overall analysis performances with same correlation trend between cutting edge geometry and cutter properties. From the overall comparison, it is found that cutters with a sharper edge can enhance the aggressiveness but has a worse impact resistance; Cutters with complex and large edge size bring a good impact resistance but lead to lower aggressiveness. 1. INTRODUCTION It is well known that PDC drill bits are becoming more widely used to drill oil & gas wellbores. As the key component of PDC drill bits, PDC cutter is composed of a polycrystalline diamond layer and a cobalt-cemented tungsten carbide substrate. The PDC cutter is sintered under high-pressure (typically 5-8 GPa) and high-temperature (typically 1400-1650 °C) conditions. During sintering, the cobalt that existed in the substrate turns molten and wets through the diamond powder bed at a short duration. All diamond particles are then bonded together to form a solid polycrystalline structure (Shin et al. 2004; Hong et al. 1991; Akaishi et al. 1991). Enhancing the physical properties of PDC cutters will undoubtedly make the bits drill faster and deeper. The physical properties of PDC cutters play an important or even predominant role in the drilling performance of PDC bits.