Design Optimization of Top-Tensioned Risers for Deepwater HPHT Applications: Part 1

Dry-tree solutions with top-tensioned risers (TTRs) have been successfully used with floating production systems (FPS), such as Spars and TLPs, in a wide range of deepwater applications. Both single-casing and dual-casing top-tensioned risers are field-proven in existing field developments. The top-tensioned risers bring technical advantages and operational cost benefits. However, recent oil and gas developments that have high pressure and high temperature (HPHT) in combination with severe environmental loads push the design limits of conventional steel pipes in deepwater risers. High-strength steel pipes are therefore considered for risers for both technical and economic reasons. This paper discusses the impact of the above requirements on design of top-tensioned risers, and proposes feasible design concepts for top tensioned risers with extremely high pressure requirements. Part I of the topic here addresses strategies of top-tensioned riser sizing and weight management, and design considerations for TTR specialty joints. Part II of this topic will follow for top-tensioned riser tensioning system configuration and tension performance optimization, as well as coupled motion compensation on the host platform. The objective of the study that forms the basis for this paper is to provide top-tensioned riser system configurations that meet the challenges of the extremely high operational pressure and environmental loads in deep and ultra-deep waters.