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OTO 2001/062

Comparative evaluation of minimum structures and jackets

Due to their low fabrication and installation costs, there has been a trend in recent years to use Minimum Facility Platforms (MFPs) for the "fast track" development of marginal oil and gas fields in water depths of up to 60 m. Compared to traditional jackets, minimum structures are characterised by a slender layout, low stiffness, and a low level of redundancy. There are concerns that these structures may be very sensitive to damage and defects which may occur due to design, construction or operational errors. There is therefore a need to understand the performance of these structures with regard to reliability, life-cycle costs and risks, so that informed decisions can be made about their feasibility for a particular field development.
The Joint Industry Project was set up with the overall objective of evaluating and comparing the system reliability levels of three minimum structures against a standard four-pile jacket under extreme storm, fatigue and ship collision conditions. The study also considered the potential for errors due to human and organisational factors during design, construction, and operation of minimum structures, and to quantify their effect on the reliability of these structures. The structural concepts considered are: (i) 3-pile Monotower, (ii) Vierendeel Tower, (iii) Braced Caisson, and (iv) a conventional 4-pile

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Updated 2010-03-19