Research on the Analysis of Coiled Tubing Fatigue Life

Abstract

Coiled tubing (CT) and coiled tubing units (CTU) technology has been widely used in oil and gas field since World War II. Coiled tubing fatigue failure is one of the constraints on promoting used. CT bears complex loads, leading to multiple plastic deformations when operating. Then the fatigue damage cannot be ignored. Through the mechanics analysis of CT with finite element method (FEM) in working state at the wellhead, the results show that high stress and high strain are the main factors which cause CT failure. Based on the analysis, the fatigue life is predicted for CT without defects by using Manson-Coffin formula. The results of CT with different inner pressure show that simulations result is closer to the actual working conditions.

Computational analysis of coiled tubing concerns during oil well intervention in the upper Assam basin, India

“…In order to account for the ovality impact, a greater safety factor was applied to the collapse region in the current work. Figures 16,17,18,19,20,21,22,23, 24 depict the inner-working limit curve with a safety factor. Table 7 provides the values of ΔP with and without taking into account the safety factor calculated with the F a set at 10,000 lb for each CT material.…”

“…. While examining limit curve trends, taking SF into account, CTs exhibited similar results in being prone to collapse failure (Figs 16,17,18,19,20,21,. 22, 23, 24) (Table…”

“…Furthermore, material overload and material inadequacies are the two most typical causes of CT string failure 20 . Many studies find that the primary cause of CT failure is fatigue degradation caused by mechanical causes in addition to the corrosion effect on it 19,21 . Because CT is subjected to axial force, internal pressure, and bending strain while in operation, fatigue damage is unavoidable 21 .…”

“…Many studies find that the primary cause of CT failure is fatigue degradation caused by mechanical causes in addition to the corrosion effect on it 19 , 21 . Because CT is subjected to axial force, internal pressure, and bending strain while in operation, fatigue damage is unavoidable 21 . The routine examination of CTs following each well intervention may aid in the procedure involving the least amount of risk.…”

Improvement and determination of the influencing factors of coiled tubing fatigue life prediction

“…After years of development, the CT fatigue life model has three main fatigue calculation models: the Tipton model developed by S Tipton (Tulsa University), the Avakov model developed by V Avakov (Haliburton), and the Coiled tubing simulation software provides life prediction (CIRCA) model developed by BJ/Nowsco. [3][4][5] All three fatigue models are applied to the life prediction of CT in field operations, which reduces fatigue failure to some extent.…”