Design of deepwater risers involves the use of multiple conservative design parameters to account for the uncertainty in the understanding of behavior of their complex structures in challenging environments. Due to the oil industry going into deeper and harsher waters, the challenges in design of risers are ever increasing and design tolerances are being stretched. In an effort to counter and better understand this, some deepwater developments are monitoring vessel and riser response. Measured vessel response can be used to drive riser models and calibrate design software by comparing analysis predictions against field measurements. For a Spar with pulltubes the riser behavior is dictated by vessel motions at the keel. Hence, the measured vessel motions have to be transferred to the keel prior to conducting riser analysis. The limitations of existing spar vessel monitoring systems to provide data reliable for the purpose of software benchmarking is demonstrated and alternate benchmarking methodologies are proposed in this paper.
Chevron is monitoring the response of a steel catenary riser (SCR) on one of its production platforms in the Gulf of Mexico (GoM) with the aim to improve understanding of the SCR behavior to validate the design methodology, as discussed in Karayaka et al. (2009). The current riser design analysis is based on simplified empirically derived models for soil structure interaction and hydrodynamics. These models are derived using either laboratory scale experiments or limited section field tests and are known to be conservative. One of the goals from the riser monitoring program is to obtain measurements of riser response in the field, compare against analysis predictions and improve our riser design methods such that excessive conservatism is minimized. The location of the vessel monitoring system is dictated by installation logistics and to date has typically been on the vessel deck.
