Department of Petroleum Technology, Dibrugarh University, Dibrugarh, 786004, India.
Sci Rep. 2023 Jan 31;13(1):1795. doi: 10.1038/s41598-022-26670-5.
Coil tubing (CT) is widely regarded as one of the most effective servicing tools for dealing with a variety of oil and gas production issues, and it is also commonly used for oil well workover operations in India's upper Assam basin. The current work considers QT 800 to be the CT material used for actual oil well operations. With reference to actual operations carried out in some of the oil wells in the upper Assam basin, the current research analyses the limitations of CTs (QT 800, QT 900, and QT 1000) based on developing limit curves that can depict the operating limit and infer CT failure probability. This study also includes fatigue analysis to determine the likelihood of damage from hot oil circulation, water injection, and nitrogen shot operations while performing them using the CTs (QT 700, QT 800, QT 900, and QT 1000). The current work adopts the methodology of CT assessment based on a computational model built in MATLAB with respect to different oil well parameters in the upper Assam basin. This study takes an innovative approach by taking downhole temperature into account when determining the CT limit for QT 800, which signifies novelty in the current work. According to the computational analysis used in the study on CT limits, mechanical strain, thermal strain, and the combined strain of the CT material all affect CT elongation. This observation was often found to be a research gap in different research works as this aspect in previous studies was not considered while analysing CT operations. The findings of the present study highlight and draw the conclusion that temperature variations in the well and the CTU's circulating fluid contribute linearly to CT strain. CT's working limit diminishes with increasing internal and external pressure and diametrical growth, which eventually causes fatigue damage.
连续油管（CT）被广泛认为是处理各种油气生产问题的最有效作业工具之一，在印度阿萨姆邦上部油井修井作业中也经常使用。目前的工作认为 QT800 是用于实际油井作业的 CT 材料。参考阿萨姆邦上部一些油井的实际作业，当前的研究根据开发极限曲线来分析 CT（QT800、QT900 和 QT1000）的局限性，这些极限曲线可以描绘操作极限并推断 CT 失效概率。本研究还包括疲劳分析，以确定在使用 CT（QT700、QT800、QT900 和 QT1000）进行热油循环、注水和氮气喷射作业时发生损坏的可能性。目前的工作采用了基于 MATLAB 中建立的计算模型对阿萨姆邦上部不同油井参数进行 CT 评估的方法。本研究通过在确定 QT800 的 CT 极限时考虑井下温度，从而在当前工作中采取了创新方法，这一点是新颖的。根据对 CT 极限进行的计算分析，机械应变、热应变和 CT 材料的组合应变都会影响 CT 的伸长。这一观察结果经常被发现是不同研究工作中的一个研究空白，因为在分析 CT 作业时，以前的研究没有考虑到这一方面。本研究的结果强调并得出结论，井内和 CTU 循环流体中的温度变化与 CT 应变呈线性关系。随着内部和外部压力以及直径增长的增加，CT 的工作极限会减小，最终导致疲劳损坏。
