Offshore production risers are generally designed considering a large margin of conservatism to account for the uncertainty in the design parameters and to ensure robust design. As the Oil & Gas Industry is advancing toward ultra-deepwater there may be a necessity to adopt new technologies and riser configurations to develop the field. Project teams may elect to quantify the degree of conservatism in the designs as an additional measure to improve confidence in the safe and reliable service over the life of the field. Such validation provides confidence in the design performed based on theoretical concepts and software predictions.
This paper presents a novel approach that has been undertaken to validate the design of the Caesar-Tonga Steel Lazy Wave Risers (SLWR) tied back to the Anadarko Petroleum Company (APC) operated Constitution Spar located in the Green Canyon Area of the Gulf of Mexico. These risers represent the first application of the steel lazy wave riser technology in the Gulf of Mexico, and it was the first such application tied back to a spar platform.
The procedure is based on the monitoring of motion and strain data measured at critical locations along the risers. The measured data is post-processed to identify significant riser motion events that occurred during the observation period. Met- ocean data during this time period is also evaluated to correlate back to the riser motion events. Vessel motions and current data corresponding to these identified events are used to drive a Finite Element (FE) model of the riser, and the corresponding riser motions and strains are calculated. The calculated motions and strains are compared with measured motions and strains to provide confidence in the design methodologies. The procedure as well as the results of the comparison between predicted performance and measured performance is discussed in detail in the paper. The procedure can be applied for design validation and performance and integrity assessment of newly-built or existing risers.