Investigation of Rock-Breaking Mechanisms Based on the Adaptive Matching Method for Drilling Loads

Considering stick–slip vibration and the impact loads formed while drilling in strongly heterogeneous formations or soft–hard interbedded formations, an adaptive matching drilling load method is presented in this paper to form dynamic drilling loads to automatically adjust the applied axial load acting on the drill bit. To determine the rock-breaking mechanisms using this method, the structure of a kind of downhole tool was designed and a discrete element simulation model was established with a PDC cutter cutting heterogeneous rock. The effects of the load factor, the applied initial axial force, and the driven force on the variation in the axial force, as well as the moving displacement of the PDC cutter and the rock-breaking characteristic parameters, were studied. The failure states of the simulated rock have a positive correlation with the number of total cracks generated in the rock-breaking process, as opposed to MSE. The decrease in the reaction force suffered by the PDC cutter in the cutting direction was caused by the automatically adapting load, although there was no significant regularity in the axial direction. MSE decreased obviously under the action of the adaptive matching drilling load method so that the contacting states of the PDC cutter could be improved, thus raising the rate of penetration of the PDC bit. This study provides a feasible method for rapidly drilling in highly heterogeneous formations or soft–hard interbedded formations.