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

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.