Flow Assurance Issues Related to Flexible Riser and Pipeline System Configuration

Abstract

Abstract Flexible riser and pipeline systems have been proposed as a promising solution for offshore oil and gas production systems in various harsh and challenging marine environments. They have many advantages compared with traditional rigid riser and pipeline systems, including: relatively low axial bending stiffness; ability to spool on a reel for easy transport and faster installation; and suitability for various floating systems. Flexible riser and pipeline systems typically have buoyancy modules to produce a lazy wave or similar configuration in the riser to decouple the floating vessel motions from the touchdown point. However, the buoyancy modules may move or even drag the riser in the horizontal direction, which may cause the riser shape to change or the riser bottom to move on the seabed. The riser shape/configuration may change, even slightly, with the movement of buoyancy modules or flexible riser, resulting in potentially significant changes in flow assurance design issues related to slugging and system blowdown. Case studies were carried out using transient multiphase simulation software, as reported in this paper, to investigate the slugging issues impacted by slight variations in the riser configuration in flexible pipeline/riser systems, including slight uphill and downhill riser base configurations. These small changes in the riser shape/configuration can also cause significant differences in the resulting residual pressures in the subsea pipeline and riser after blowing down the system. The results from this paper suggest that the riser shape/configuration in flexible pipe systems has a significant impact on flow assurance concerns, especially the impact of slugging and blowdown residual pressures related to hydrate prevention and mitigation. Consequently, the sensitivity of riser shape/configuration in flexible riser and pipeline systems should be considered in early design phases to understand the impact on key flow assurance strategies.