SCRs have been widely used in the deep water offshore industry due to their reliability, low cost, and robust design. Field data, however, indicates that riser fatigue damage is often overpredicted at the critical touchdown region. This can lead to expensive solutions like CRA cladding and vessel upgrades, resulting in unnecessarily higher costs for operators.
2H Offshore kicked off the STREAM (STeel Riser Enhanced Analytics using Measurements) JIP in 2017 to help establish a measurement-based foundation for SCR design with the goal of increasing the accuracy of fatigue assessments. The project provides significant value addition to new projects’ schedules and costs as reduced conservatism will enables safer, simpler and more efficient new designs. The findings also provide an engineering basis for life extension of existing SCRs.
Phase 1 – Smarter Data Analytics Reduces Conservatism
Full-scale field data from six deep water SCR systems was provided by the Phase 1 participants, including ExxonMobil, Shell, Anadarko, and Chevron. The monitoring systems on each riser varied in configuration but included different combinations of motion only and motion and strain measurement devices.
Our first step was to apply proven riser response data analytics methods to benchmark design, identify gaps and derive ‘best fit’ modelling parameters. We then developed a set of improved SCR fatigue analysis parameters that reduce conservatism compared to typical design parameters, and reduce the variability in wave fatigue predictions. As shown below, the updated parameters reduce fatigue damage rates near the TDZ by over a factor of 3.
In addition, the Phase 1 datasets revealed frequent VIV occurrences, including occurrences of inline and higher harmonic response events. SHEAR7 v4.9b analysis was conducted with site-specific currents and compared to measured fatigue. Strake and fairing suppression effectiveness was also evaluated.
Phase 2 – Expanding the Data to Semi-Submersible and FPSO Risers
The second phase of the STREAM JIP is being planned for mid-2018 and will include at least 2 more datasets. The new datasets will consist of a lazy wave riser attached to a semi-submersible and an FPSO with an SCR. Phase 1 considered risers with TLPs and spars. The scope of Phase 2 is going to cover:
- Validation of wave fatigue assessment parameters with additional SCR and SLWR datasets
- The addition of extreme hurricane storm events in wave fatigue validation exercise
- Characterization of Heave Induced Vibration (HIV) occurrences and assessment methodology development
- Calibration of SHEAR7 to obtain a consistent set of conservative parameters
- Contribution from inline and higher harmonic VIV
- Further investigation of ‘unexplained’ response identified during Phase 1.
Intelligent Use of Riser Data
“The modern subsea market is evolving, and there is a need for smarter, more efficient solutions,” vice president, Mike Campbell said. “At 2H, we are leading these changes by combining our domain expertise with the intelligent use of data.”
“Data is critical to bridge the gap between numerical analysis and actual response in the field for deep water SCRs. The STREAM JIP is providing a platform for operators to work together to achieve an industry consensus on optimal design parameters.”
If you are interested in participating in Phase 2 of the STREAM JIP, please contact:
Dhyan Deka | +1 281 258 2035 | email@example.com