Deepwater RCM and SRI Performance on Production Rigid Flowline Loops

Deepwater High Pressure High Temperature (HPHT) rigid flowlines laid on large slope seabed morphology, with complex operational loading and multiple subsea well tie-in locations, pose significant design challenges. This paper demonstrates the effective performance of a novel thermomechanical design for the production flowline loops of a project in West Africa, based on the surveys which were carried out post pipelay, pressure test and thermal loading. The design employed the Residual Curvature Method (RCM) to control lateral buckling and Subsea Rock Installation (SRI) to partially restrain the flowlines and control the flowline displacements at the tie-ins. This paper focuses on the as-laid configuration of the RC sections and the initial formation of the engineered lateral buckles, for a large range of RC section as-landed angles, considering also the formation of soil berms. Furthermore, the effect of the cooldown of thick insulated flowlines, on the seabed just after pipelay from as-laid to ambient seawater temperature, is quantified. Additionally, the performance of the rock berms, during the pressure test and the first thermal loading, is evaluated. Moreover, the benefits of gradually heating up the flowline loops during hot-commissioning are discussed, considering the response of the flowlines and the objectives of this thermal preconditioning (TPC) operation. Finally, this paper provides recommendations for future RCM and SRI designs based on lessons learned from this project.