Lessons Learned From 12 Years of Operations of a Prestressed High-Performance-Concrete Floating Production Unit

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper IPTC 12546, "Lessons Learned From 12 Years of Operations of a Huge Floating-Production Unit Made of Prestressed High-Performance Concrete," by Bertrand Lanquetin, Heidi Dendani, and Pascal Collet, Total, and Jose Esteve, Bureau Veritas, prepared for the 2008 International Petroleum Technology Conference, Kuala Lumpur, 3-5 December. The paper has not been peer reviewed. Lessons learned from use of a floating-production unit (FPU), made of pre-stressed high-performance concrete, in operation for Total E&P Congo are pre-sented. The unit has been in use for 12 years on the N'Kossa oil field in 170-m water depth. The focus is on structural-modeling techniques, aging processes, and development of an inspection program. The paper is not intended to make a recommendation between steel and concrete, which would entail many other considerations. Introduction The FPU NKP is 220 m long, 46 m wide, and 16 m high, with a displacement of 107 000 tonnes. It contains 27 000 m3 of concrete, 2350 tonnes of prestressed steel, and 5000 tonnes of passive steel. During its 12 years of operation, the FPU has undergone one technical stop for process maintenance, as scheduled in the design; otherwise, it has been in uninterrupted service. The unit, shown in Fig. 1, was built in southern France in 1994–95 and installed 1 year later in the N'Kossa oil field in 170-m water depth, 60 km off the Congo coast. The production facilities and living quarters for 160 people are fitted on the 10 000-m2 deck, which for construction purposes was subdivided into six modules: accommodation and central control, utilities, electric-power generation, gas compression for re-injection, crude oil, and gas. Design production is 16 000 tonne/d of oil and 1300 tonne/d of liquefied petroleum gas. The unit is held in place, 70 m away from the NKF2 platform, with a spread-moored configuration by means of 12 mooring lines. Asset-Integrity Management A special method was developed to analyze and monitor the condition of the units. The aim of the floating-units integrity-management process is to ensure management and continuous follow-up of floating units from safety, environmental, operational, maintenance, and quality-management view-points. It includes recommendations on inspection, maintenance, and repairs. This process calls for the following.Structural and anchoring modeling and analysisQualitative [risk-based inspection (RBI)]Yearly reviews of the inspection, repair, and maintenance (IRM) planData management and storage (including reports)Assistance for emergency responseFramework for analysis