Design Challenges of Top Tensioned Risers in Ultra Deepwater Applications

Abstract

A Top Tensioned Riser (TTR) system provides direct access to subsea wells from a floating platform for drilling, workover, and completion operations. TTRs have been widely used with floating production systems such as Spars and TLPs in deepwater field developments. This paper investigates design challenges of TTRs in ultra deepwater applications. As application moves to ultra deepwater, challenges of TTRs increase in terms of riser design, analysis, installation and global performance. This paper first introduces a typical TTR configuration in ultra deepwater applications. The TTR design issues cover riser wall thickness which is especially driven by extreme high pressure and high temperature, tension limits, high payload, and long tensioner stroke. The installation concerns come from hook capacity limit, riser Vortex-Induced Vibration (VIV) when the riser is disconnected, and riser bottom drift caused by vessel motion during installation. This paper further investigates the coupling between the risers and floating platform, the interference between riser pairs, riser VIV, and tensioner stick-slip phenomenon. Examples are given to illustrate various aspects of TTRs in ultra deepwater applications. In addition, this paper also explores likely solutions to TTR design challenges.