Early attempts to monitor coiled tubing (CT) fatigue in open-water interventions relied on basic statistical methods with a constant damage rate and broad generalizations of sea conditions. The new CT fatigue management system (FMS) comprises hardware and software that improve fatigue tracking. It tracks high-cycle fatigue (HCF) and low-cycle fatigue (LCF) simultaneously and in real time, elevating the accuracy, immediacy, and reliability of CT fatigue monitoring in open-water interventions.
The hardware monitors vessel pitch and roll in real time and relays the data to an acquisition system where they are combined with CT depth and circulating pressure. The new acquisition software consumes these data as well as a CT string fatigue life database and geometry and positions of the CT string, work drum, and payout sheave. LCF and HCF are accurately modeled, and the string fatigue life is updated in real time. That information allows the operation to strategically cycle the CT pipe to manage fatigue more efficiently and extend the time before a trim is necessary.
The traditional statistical method recorded a cumulative CT fatigue damage of 16% over a 14-hour job. In that same timeframe, the CT FMS measured a cumulative fatigue of 3.8%. Since the CT FMS updates damage rate continuously in response to vessel dynamics and uses a nonlinear methodology to combine HCF and LCF, it reduces inaccuracy and eliminates unnecessary safety factors associated with the statistical method. By improving precision and reliability, the real-time CT FMS safely extended the useful life of CT pipes by 75%.
The CT FMS also improves operational integrity by introducing alarm threshold settings and custom material parameters. Alarms are raised reflecting fatigue life growth, tubing payout, and changes to sea conditions. This provides the operator with real-time, actionable data to ensure a more even distribution of the fatigue along the CT. Besides extending useful life, this reduces the risk of CT failure, which can lead to costly downtime, reputational damage, and production losses. The string's operating limits are more accurately monitored, which extends the capacity of the CT into harsher environments, longer operations, and riserless interventions of wider workscope. The CT FMS automates workflows that previously required a dedicated technician, reducing crew size on board.
The introduction of CT in open-water interventions brought with it the risk of CT failure, which is inherent to any operation that handles CT pipe. This industry first, real-time CT FMS combines HCF and LCF monitoring and is a step change from the traditional methods to address these CT-related risks. Furthermore, the CT FMS elevates overall operational integrity, increases operational efficiency, and extends the operational envelope and application of CT in open-water interventions.
