# Investigation of Rock-Breaking Mechanisms Based on the Adaptive Matching Method for Drilling Loads
## 4 Conclusions  
1. This study proposes an adaptive matching method of drilling load acting on the PDC drill bit during the process of rock breaking in a bottomhole. The working principle and adjustment mechanism of this method are elaborated upon in detail, complemented by the detailed structural design of a purpose-built tool implementing this adaptive load control.
2. A kind of simulation model of rock breaking under the action of a PDC cutter based on the discrete element method (DEM) is established, incorporating the proposed adaptive matching method of drilling load to dynamically adjust applied axial force according to the reaction force monitored in the cutter. This simulation framework enables systematic investigation of the rock-breaking mechanism under adaptive load conditions.
3. The influential factors of load factor, initial axial force, and driven force on the kinematics and rock fragmentation behavior are clarified based on the proposed method. The use of the proposed method of this kind of tool can systematically decrease the reaction force in the cutting direction, while axial reaction force exhibits non-uniform fluctuations. The total crack count inversely correlates with MSE, and the tensile cracks account for 85% of total failures, consistent with the simulated rock's tensile-dominated failure mode. The cracks generated a decrease while increasing the load factor, which increases linearly with the driven force and follows a parabolic trend with the initial axial force acting on the PDC cutter.
4. The proposed adaptive matching method of drilling load strategy improves the mechanics of PDC cutter-rock contact, thereby enhancing drilling efficiency and the working life through reduced drillstring vibration and reaction force mitigation. This innovation offers a viable solution for optimizing penetration rates in highly heterogeneous formations or soft-hard interbedded formations by dynamically balancing cutting loads and energy consumption.  
**Author Contributions:** Conceptualization, H.H., L.Z. and K.W.; methodology, H.H., G.J., F.S., L.Z. and K.W.; software, L.Z. and K.W.; validation, H.H., G.J. and F.S.; formal analysis, G.J., F.S. and L.Z.; investigation, H.H., L.Z. and K.W.; resources, H.H., G.J. and F.S.; data curation, H.H., G.J. and F.S.; writing--original draft preparation, L.Z. and K.W.; writing--review and editing, H.H., G.J. and K.W.; visualization, F.S. and L.Z.; supervision, H.H., G.J. and L.Z.; project administration, H.H., G.J., F.S. and K.W.; funding acquisition, K.W. All authors have read and agreed to the published version of the manuscript.  
**Funding:** The work of this study was funded by the Foundation of National Engineering Research Center of Oil & Gas Drilling and Completion Technology (No.: NERCDCT202312); the CNPC Programs for Subordinate Institution (No.: CPET2022-10S); the CNPC Major Science and Technology Project \"Development of Key Engineering Technologies and Equipment for Ultra-deep Drilling\" (No.: 2023 ZZ20); and the CNPC Programs for Science and Technology Development \"Research on Key Technologies and Equipment for drilling and Completion of ultra-deep Oil and Gas Resources\" (No.: 2022 ZG06).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the project research hereto being incomplete.  
**Conflicts of Interest:** Authors [PERSON], [PERSON], [PERSON] were employed by CNPC Engineering Technology R&D Company Limited. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.