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.

Coiled tubing has been traditionally characterized by its mechanical properties in order to guarantee that the structural response of the tubing is uniform and satisfies current standards along its full length. Also the tubing is generally fatigued tested in order to characterize its responses under simulated field conditions. As coiled tubing applications become more challenging, there is a need for higher mechanical properties, better resistance to severe environments and a better relative fatigue performance in the tube body and bias weld. The limitations to develop a product that satisfies these new requirements can not be understood solely based on coiled tubing mechanical properties, but extensive metallurgical analysis must be performed.In this study, the relevance of the metallurgy basis in each of the production steps was reviewed in order to understand the limitations of current manufacturing process. This understanding, coupled with the goal of developing new products that satisfy new market demands, has resulted in a complete redesign of the manufacturing process. Preliminary results of a new manufacturing process have proven to provide a path for current and future innovative products.

A new type of coiled tubing (CT) failure mechanism has appeared in the past four years. The failures occur in CT strings used for frac plug milling in extended reach horizontal wells. Although significant effort has been put into understanding these failures in the past several years, the mechanism that leads to them is still not well understood. Different hypotheses have been discussed among the industry, like the impact the use of extended reach tools (ERT) have on the low cycle fatigue performance of the CT [1] [2] [3]. The objective of this paper is to further investigate possible causes for these failures focusing on the analysis of the effects of circulating pressure and strain on the mechanical properties of the CT that could eventually contribute to a premature failure.