Field Performance of New Coiled Tubing Technology and a New Grade for Improved Sour Service

Abstract

A new coiled tubing (CT) manufacturing technology was developed and introduced to commercial field operations in 2015. The new technology uses new steels and new heat treatment processes for complete microstructure transformation to produce significantly improved and uniform microstructure and properties along the entire coiled tubing string, including bias welds. Numerous straight and tapered wall thickness CT strings have been commercially deployed and used in various field operations and environments. Information has been collected for CT field performance evaluation of the new technology 125-ksi and 110-ksi minimum yield strength CT grades. Field results show new technology CT performance and utilization far beyond any conventional CT capability and experience. Additionally, testing of CT strings after extensive field use shows significant remaining string life and confirms observations and conclusions from previous extensive laboratory and field testing. The new CT manufacturing technology also has been extended to produce a new, 95-ksi yield strength CT grade. This new CT grade has significantly better general performance than comparable conventional CT grades. It also has substantially better performance in sour, aqueous H2S-containing environments. Non-sour and sour test results for the new CT grade and comparisons with other CT grades are presented in the paper. Sour fatigue tests were conducted on full-body CT samples after 4-day sour exposure. Sulfide stress cracking and sour fatigue testing in H2S environments show that the new 95-ksi CT grade has much better sour performance than the conventional 90-ksi grade that is currently the highest CT grade regularly used in sour environments.

Fatigue Life Analysis of Coiled Tubing in Deep Well Jet Plugging Removal

“…In the process of coiled tubing operation, it is inevitable to have mechanical damage on the outer surface, such as clamping block injuries, bumps, scratches, and furrows [9] [10] [11]. These defects will produce stress or strain concentration when the coiled tubing continues to work, which will affect the service life of the coiled tubing.…”