## 5 Conclusions  
(1) The factors that influence the peak pressure of a downhole impact load are explored. Numerical simulation shows that the peak pressure of a downhole impact load increases with the increase in the total amount of ammunition, the increase in wellbore pressure, the increase in rock pressure and the increase in the detonation interval. With the increase in effective explosion range, the peak pressure of a downhole impact load decreases.  
(2) A numerical simulation-based shock loading calculation model is developed for the safety evaluation of perforated string under dynamic load. The analysis of two wells in southwest China shows that the model has high accuracy, and the calculated peak bottom hole pressures are 69.52 MPa and 82.93 MPa, respectively. The results show that the error margin is less than 10% compared with the results of foreign commercial wellbore dynamic software, which confirms the reliability of the model and that it is suitable for engineering applications. This validation highlights the model's ability to predict key parameters such as axial forces and peak pressures under complex impact loads.  
(3) A hybrid safety assessment methodology integrating static strength theory (fourth strength theory) and dynamic response analysis was proposed. By establishing buckling  
Figure 10: Simulation result of shock load.  
and tensile failure criteria, the model effectively evaluated risks such as pipe string buckling (safety factor >1.6) and tensile fracture (safety factor >3.8) under shock loads. This dual approach bridges the gap between theoretical dynamics and practical static standards, offering engineers a robust tool for real-world safety design and risk mitigation.  
(4) At present, there is still a lot of room for improvement in the analysis of pipe dynamics. The study of dynamic response mechanisms is of great significance in solving the difficult problems in the field of pipe safety, and it can also promote the innovation and improvement of theories and methods in the field of pipe mechanics in oil and gas well engineering and help develop more effective measures to ensure the safety and reliability of operations.  
Writing--review and editing, Q.D. and D.Y.; Conceptualization, M.Y.; Formal analysis, G.C. and D.F.; Methodology, B.J. All authors have read and agreed to the published version of the manuscript.  
This study was supported by open foundation project of the Key Laboratory of Polar Geology and Marine Mineral Resources (China University of Geosciences, Beijing), Ministry of Education (Number: PGMR-2024-106); the Key Program of the Hubei Provincial Department of Education, No. D20221303; the Natural Science Foundation of Hubei Province, No. 2022 CFB700; and the Open Foundation of Cooperative Innovation Center of Unconventional Oil and Gas, Yangtze University (Ministry of Education & Hubei Province), No. UOG2024-06.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
Authors [PERSON], [PERSON] and [PERSON] were employed by the company China Petroleum Group Bohai Drilling Engineering Co., Ltd. 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.