Application of Composites to Deepwater Top Tensioned Riser Systems

As offshore exploration and production activities head to deeper water, extensive efforts have been focused on mitigating the potential challenges associated with deep- and ultra deep-water riser systems. Such challenges include overcoming the hydrostatic stresses associated with the increased length of water column as well as the increase in overall riser system weight. The implementation of composites in offshore applications is perceived as a promising path forward with composite materials offering many advantages including high specific strength and stiffness, lighter weight, enhanced corrosion resistance, high thermal insulation, improved structural damping and favorable fatigue performance characteristics. This paper focuses on evaluating the potential of composite materials for applications to deepwater top tensioned riser systems from the standpoint of possible impact on overall system cost and reliability. Many deepwater development concepts utilize top tensioned production riser systems, mainly, for conveying production fluids from the wellhead to the surface processing facilities in a dry tree based field development solution. Top tensioned risers can be configured as dual or single barrier systems and can either be hydraulically or hydro-pneumatically supported as on a typical TLP system or pneumatically supported through positively buoyant air cans as on a Spar riser system. Many advantages can be derived from the use of composites on buoyancy can systems. Such advantages include a reduced system weight, higher net lift, smaller diameter cans, improved efficiency and a positive impact on required inspection frequency. Main advantages of using composites for an entire TLP riser system include a significant reduction in both tension requirement and tensioner weight resulting in substantial reduction in total deck loads. An overall assessment of the economic and structural impact of using composites as an alternative to steel will be presented for riser systems and riser system components of both deepwater development concepts.