Failure resistance research of the dual-stage hybrid bit

Abstract

Vibration failure is mainly the abnormal fracture failure of cutters, including brittle fracture, impact spalling, impact fatigue fracture, and cutter loss. The weak core area of the existing drill bit is prone to develop into core failure. Vibration failure and core failure will seriously affect drilling performance of the drill bit. To limit vibration and improve stability, we proposed a dual-stage hybrid bit with a polycrystalline diamond compact bit as the primary cutting unit and a tri-cone bit as the secondary cutting unit. Polycrystalline diamond compact bit only breaks the outer rock to form a central rock pillar, while the tri-cone bit breaks the central rock pillar. The existence of the central rock pillar enables the hybrid bit to have a larger lateral contact area with the bottom hole, which can reduce lateral force and limit lateral vibration. The tri-cone bit strengthens the impact and wear resistance of the core area, which can effectively prevent core failure. The experimental results showed that the working parameters of the dual-stage hybrid bit fluctuated less, its drilling stability was better. The experiment verified that the lateral force of the dual-stage hybrid bit was smaller. The vibration test results showed that, with small weight-on-bit, the vibration accelerations of the two drill bits were relatively close. With higher weight-on-bit, the accelerations in all directions of the dual-stage hybrid bit were smaller than those of the polycrystalline diamond compact bit. Specifically, the lateral acceleration differed by more than 40%, which proved the lateral vibration resistance of the dual-stage hybrid bit. The axial and tangential accelerations were reduced accordingly. In the validation experiments, the lateral force of the dual-stage hybrid bit decreased by 11.7%, 21.3% and 26.7%, its vibration acceleration reduced by 12.2%, 26.4% and 14.9%. Therefore, the dual-stage hybrid bit could reduce vibration and enhance stability.