From Installation to Operation: A Full-Scale Finite Element Modeling of Deep-Water Pipe-in-Pipe System

Developments of deep water oil reservoirs are presently being considered in the Gulf of Mexico (GoM). Pipe-in-Pipe (PIP) systems are widely used and planned as the tie-back flowline for high pressure and high temperature production (HPHT) due to their exceptional thermal insulation capabilities. The installation of PIP flowline in deep water, disregarding the laying method, can present real challenges because of the PIP string weight. The effect of the lowering displacement as well as the lock-in compressive load acting on the inner pipe for the commonly used un-bonded PIP is also a major concern. Such effects will enhance the total flowline compression when the high temperature and high pressure are applied after start-up; they greatly increase the severity of the global buckling and result in local plastic collapse at a larger bending curvature section or strain localization area. An even greater concern is that industry fails to realize the seriousness of such failure potential, and the PIP is generally treated as a composite single pipe which does not evaluate the PIP load response correctly, especially the inner pipe lock-in compression omitted. It could result in an unsafe design for HPHT production. This paper endeavors to provide a trustworthy solution for the HPHT PIP systems from installation to operation by using the advanced analysis tool — “Simulator”, an ABAQUS based in-house Finite Element Analysis (FEA) engine. “Simulator” allows the PIP pipes being modeled individually with realistic interaction between the pipes. A systematic process was introduced by using a generic deep-water PIP flowline as a working example of J-Lay installation and HPHT production. The load and stress responses of the PIP at all installation stages were calculated with a high level of accuracy, they were then included in the global buckling analysis for the HPHT operation. The study demonstrated the effectiveness of Loadshare, an industry-leading solution; which reduces or eliminates the inner pipe lock-in compression and improves the PIP compressive load capacity for the high temperature operation.