Effect of Cutter Shape on the Resistance of PDC Cutters Against Tip Impacts

Abstract

Summary Under harsh downhole conditions, the quasibrittle characteristics of polycrystalline diamond compact (PDC) cutters are a serious drawback, which readily causes the cutters’ premature failure under impact loads. Innovating 3D cutter shapes is an effective solution for optimizing the cutter’s interaction with the rock and improving the impact resistance of PDC cutters. However, the mechanism of how the cutter shape affects the impact resistance is rarely studied or published. In this work, the quantitative energy analysis method was used to create a cutter-impactor interaction model where the interaction was assumed as a process of energy transformation and dissipation. To validate the developed mathematical model, cutters with various geometric shapes were designed and evaluated by laboratory progressive drop tests (PDTs) as well as field trials. The investigations revealed that the predictions of the mathematical model were consistent with both the laboratory results and the field feedback when the relative sharpness evaluation parameter was less than 0.3. The tip impact resistance was positively related to the relative sharpness evaluation parameter. However, when the S is more than 0.3, the cutter shape will present poor tip impact resistance and is not recommended to fabricate in terms of tip impact resistance. In these cases, the protruding tip did not have sufficient support and caused a premature impact failure under the tangential forces. The developed cutter-impactor interaction model filled the technical void of current studies on shaped cutters, which could guide the innovations of the cutter shapes to obtain better tip impact resistance. Field testing indicated that PDC cutters suffered both front and tip impacts under downhole. If the cutter shape matched with the front or tip impact form, the cutters would fulfill satisfactory field performance. Field testing also indicated that the vulnerability of PDC bit under impact loads was strongly related to the regions of the cutting structure. The bit’s impact resistance could be greatly improved by placing the cutters with the right cutter shape at the right regions of the cutting structure. For example, the rhino-horned cutters were placed at the nose and shoulder to fight against the front impacts but were not suggested to deploy at the regions near the gauge because of poor tip impact resistance.