DESIGN STUDY OF A DEEPWATER COMPLIANT VERTICAL ACCESS RISER FOR THE GULF OF MEXICO

摘要

This paper presents the results of a design study of a compliant vertical-access riser (CVAR) for the deepwater Gulf of Mexico area. The CVAR concept modifies traditional, tensioned risers by providing vertical compliancy through its geometric shape that is achieved by elongating the riser and providing buoyancy along the lower section. A major benefit of this geometric compliancy is that surface trees can be fixed relative to the floating vessel. Also, there is a potential for significant cost savings as compared to alternate, top-tensioned riser systems. A key design feature is the tapering of the buoyancy transition to create a nearly neutrally buoyant region. This tapering reduces bending stress between the weighted and buoyant regions of the CVAR. The design basis for this study is a production riser system for a deep draft caisson vessel (DDCV) in 4900 feet of water. The design study begins by establishing a base configuration for operational conditions. This configuration is then checked for extreme loading and fatigue due to DDCV motions and riser VIV. The potential for riser interference is also checked. The study also includes a brief assessment of fabrication and installation procedures. Finally, a cost estimate is made for comparison with alternate production riser systems.