The use of large-diameter coiled tubing (CT) pipe, 2 inches and greater, as the typical work strings in HP/HT extended reach wells has brought new challenges to the CT intervention industry. The CT strings utilized in this service are expensive and, by nature, short-lived expendables. As well reach increases, the strings become increasingly more sophisticated and costly. Identifying, predicting and controlling the factors that govern the pipe reliability is important to further extend the usable life of strings and contribute to the operational and economical success of CT service providers, CT pipe manufacturers and O&G operators.
Furthermore, if any CT failure takes place, the root cause investigation is essential to the continuous improvement of the service and must be looked at in a holistic, systematic manner . Hence we must understand how the combination of operational procedures, surface equipment, CT pipe manufacturing, and overall well conditions can affect pipe performance.
In this proactive process, a new mechanism that can contribute to failures has been identified. This failure mode is associated with larger outside diameter (OD) CT pipe being subjected to a combination of high hoop stresses, high strain levels and run-in or retrieved from wells at high speeds. These new set of operational dynamic conditions expose the CT pipe material to higher forces, stresses and deformations not considered in the traditional conventional working envelope and in the associated performance tests and models.
This new field CT pipe failure mechanism is presented in this work, its possible origins are explained in addition to laboratory test data reproducing such failures and identifying the potential set of combined operational conditions in which it can take place.
An alternative CT fatigue-data generation procedure is proposed to better predict pipe performance, avoiding failures under field conditions, improve operational procedures, and enhance overall service quality.