ABSTRACT

This paper presents a study in more realistic techniques for fatigue analysis and how they could enable the installation of steel catenary risers (SCR) in ultra-deepwaters without imposing any significant risks, since simplified analysis may reject feasible solutions due to the overestimation of damage. Also, investigation in an upgraded design to improve fatigue results, called upset-end pipe (UEP), applied close to the touchdown zone (TDZ), is shown. Additionally, results from implementation of an SCR in ultra-deepwater in offshore Brazil is presented.

INTRODUCTION

Ever since the first oil well was built in the Campos Basin in 100 metres of water in 1974, technology advancements have made it easier to move farther away from shore in pursuit of new oil reserves. Since then, offshore operations have continued to creep farther out into deeper water depths and the use of SCR has significantly increased. However, free hanging catenary performance became a challenge for ultra-deepwater due to strength loads and high fatigue damage at the TDZ, where Steel Lazy Wave Risers (SLWR) have gained popularity as a viable market solution to improve SCR's performance. Despite SLWR being a popular solution, the procurement and logistics of large amount of buoyancy modules, increased installation time, more operational risks – dealing with lift and assemblies – make it costly, while SCR provides a simpler and cost-effective riser system solution.

Recently, strength performance of SCR has been improved by alternatives such as: residual curvature riser (RCR), Ramiro et al. (2021), and gimbal joint riser (GJR), Cruz et al. (2019). To enhance fatigue life those alternatives could also be combined with extra tools. In principle, fatigue life may be improved by design changes, fabrication process improvements and refined analysis methods (DNV, 2021). Limited understanding of the influence of the various input parameters, such as soil stiffness and seabed profile, on fatigue damage numerical prediction and simplifications, by concentrating damage accumulation ignoring effect of draught and offset of the Floating Production Unit (FPU), leads to unnecessarily high conservatism in design and some feasible efficient solutions may be rejected.

This content is only available via PDF.
You can access this article if you purchase or spend a download.