Title: Fatigue failure analysis based on coupling vibration of drill string in ultra-deep wells

Authors: Guojie Cui; Hongshan Zhao; Runfeng Cai; Donghong Guo; Sheng Zhong; Wenchang Wang

Addresses: CNOOC, Ltd., 2121# Haichuan Road, Binhai New Area, Tianjin City, China ' Drilling Technology Research Institute, Sinopec Shengli Oilfield Service Corporation, 827# Beiyi Road, Dongying City, Shandong Province, China ' CNOOC Enertech-Drilling & Production Co., 2121# Haichuan Road, Binhai New Area, Tianjin City, China ' CNOOC Enertech-Drilling & Production Co., 2121# Haichuan Road, Binhai New Area, Tianjin City, China ' CNOOC Enertech-Drilling & Production Co., 2121# Haichuan Road, Binhai New Area, Tianjin City, China ' School of Mechanics and Engineering Science, Shanghai University, 147# Yanchang Road, Shanghai City, China

Abstract: Fatigue failure of drill string occurs frequently in deep wells. However, the commonly used fatigue ratio is difficult to evaluate drill string fatigue safety accurately. In this paper, considering the characteristics of super slenderness ratio of drill string and collision with the wellbore wall, the coupling vibration of drill string is studied, and the vortex characteristics and dynamic stress of the drill string are calculated more accurately. On this basis, combined with the calculation method of fatigue coefficient under asymmetric variable stress amplitude, the strength criterion of fatigue failure of drill string under dynamic condition is established. The results show that this method can better understand the working state of the drill string in the wellbore and predict the risk position of fatigue failure of whole drill string more accurately in vertical wells. [Received: March 28, 2023; Accepted: February 13, 2024]

Keywords: drill string; coupled vibration; dynamic stress; fatigue failure.

DOI: 10.1504/IJOGCT.2024.140276

International Journal of Oil, Gas and Coal Technology, 2024 Vol.36 No.2, pp.152 - 169

Received: 27 Mar 2023
Accepted: 13 Feb 2024
Published online: 01 Aug 2024 *

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