Lateral Buckling Control With Residual Curvature Method for Ultra Deep Water Flowlines

The lateral buckling design process for deep and ultra deep water fields has matured in recent years, particularly with steel sleepers and/or distributed buoyancies as the main triggering concepts (buckling initiators). However, depending on field conditions and geographical location, complex engineering, manufacturing, or installation may be encountered. Furthermore, the solution may not be cost-effective, especially for projects requiring a large number of triggers. The residual curvature method (RCM), which offers an economical and practical solution with low environmental impact, has been used frequently for shallow water projects and rarely proposed for deep and ultra deep water. This is essentially due to the challenges in terms of landing orientation of the RCM on very soft soils associated with deep water and the resulting in-place reliability question. This paper will present how the Residual Curvature Method can be used as a reliable buckling control measure for ultra deep water flowlines operating under high internal pressure and high temperature (HPHT) conditions. The case study is the Mero 2 project offshore Brazil. The Mero 2 ultra deep water project includes rigid mechanically lined pipeline (MLP) systems which operate under HPHT for oil production and water alternating gas injection. The pipelines are exposed (unburied) with fully restrained anchoring systems at both ends using pin-piles. They will withstand high operating conditions, including permanent and transient flow regimes with several shutdown/restart cycles predicted during the design life. This induces large compressive axial forces in the pipeline without expansion absorption at either end (no sliding, i.e. fixed-fixed) and requires, therefore, buckle initiators such as RCM to control the lateral buckling behavior. The solutions and measures proposed to ensure acceptable RCM lateral offset, under as-laid conditions, will be presented. The interaction between the residual curvature (RC) and soil, as well as the competition with on-bottom rogue buckles, will be shown. The reliability and robustness of the proposed lateral buckling solution for Mero 2 pipelines will be discussed. In addition, the advantages of the RCM and its limitations will be reviewed.