Cascade/Chinook Disconnectable FPSO: Free Standing Hybrid Risers Monitoring via Acoustic Control/Communications

Abstract

This paper presents the history of and lessons learned from the challenge of designing, implementing and operating the acoustically controlled monitoring system used to verify performance, validate design and track motions and tensions of five Free Standing Hybrid Risers (FSHR), their Buoyancy Can connecting chain tension and disconnectable FPSO's Turret Buoy, which are components of the Cascade & Chinook Production Facilities. For impending threats such as named storms, the FPSO disconnects from the geostationary turret buoy, which sinks to a neutral depth below wave and winds affected zone, while the FPSO sails to safe waters. The system continues to monitor all parameters when the buoy is submerged. While connected, buoy originated real time data and risers originated quasi real time data received via acoustic communications is collected by the monitoring system computers on the FPSO. While disconnected data is recorded at the buoy and FSHRs and is downloaded to the monitoring system computers upon reconnection and prior to resuming production. All data is transmitted to shore via satellite where behavior of the components is analyzed to validate designs for normal and severe weather conditions. The data collected provides a significant database of riser and Turret Buoy behavior in the range of experienced environmental conditions. In this paper the performance of the monitoring system since its installation will be addressed, including how the alarm from this unique monitoring system initiated the discovery of the accidental release of the Chinook 1 FSHR Buoyancy Can. This innovative monitoring system contributes a significant step forward for future designs of FSHRs, by facilitating comparison of actual FSHR behavior in real environmental conditions to engineering model predictions. This monitoring system is being used and can be used for a variety of submerged production equipment without the use of umbilicals and is especially appropriate for use in severe weather locations and when verification of behavior and operability of the risers must be confirmed prior to restarting production. Introduction The Cascade and Chinook Fields are located in the Walter Ridge Block, 300 km south of Louisiana coast in the Gulf of Mexico with Lower Tertiary reservoirs. The development of these fields presented a considerable challenge, due to the water depth, reservoir depth, distance from shore, furrowed seabed and exposed to threats from hurricanes, eddies and loop currents. Both fields are producing to a floating production, storage and offloading facility (FPSO) that is single point (turret) moored 5 km from the Cascade Field and about 20 km from the Chinook field, in 2500 m water depth. Produced oil is shuttled by dedicated tankers to ports in the United States.