The paper starts by establishing the cost advantages to be gained by applying "weight Reduction Design Techniques". It also establishes the fundamental relationship between topsides equipment and topsides structural steel weights then the relationship between topsides and jacket weights.
The main body of the paper presents a series of philosophies that have been developed. These form the basis of the "Weight Reduction Design Technique". The final part of the paper comprises a demonstration of the weight and cost advantages achievable, in the drilling facilities part of a platform, this is an area where weight reductions can represent cost savings of approximately $50M.
Many senior executives of the oil companies have recently expressed concern, that they must find more economical ways of developing future offshore fields, many of which in the European sector are" of the Marginal type. The pressure to reduce the cost of future marginal field developments has been further increased by lower world oil prices. The words that have been used are that the platforms have got to be "Leaner and meaner", in other words we have to apply "weight Reduction Design Techniques". There are of course many ways of reducing the cost of a development but probably the most important is to design the platforms for lower weight so that they can be built for lower cost.
This paper is not about weight control, which is the function of controlling topsides design weights and centres of gravity within pre-determined weights. Here we are concerned with the achievement of overall lower weights and it is very important therefore that the weight reduction techniques are given major consideration, during front end engineering studies and conceptual design.
The topsides weight analysis, for most platforms will generally indicate that the structural steel represents roughly half the topsides weight. Therefore, based on this generalisation, 1 Tonne of topsides equipment will require 1 Tonne of structural steel to house and support it. A further generalisation is that the previous 2 Tonnes of topsides will require 2 Tonnes of jacket and piles to support it. Obviously the weight of the jacket and piles depends on many factors including water depth but the relationship is useful to demonstrate the value of weight reduction, in that, if we can reduce the weight of topsides equipment by 1 Tonne, we can further reduce the topsides and jacket structure weights by 3 Tonnes.
The next item to consider, is that topsides will cost in the order of $20,000 per tonne, whilst the jacket and piles similar cost will be $13,000 per tonne. These indicative figures include all aspects of getting a platform operational in an offshore location, with the exception of the company?s own management costs.
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Conceptual Design
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Detailed Design
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Follow on Engineering Support
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Procurement
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Fabrication
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Installation
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Hook-up and Commissioning
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All Logistics and Support Services
If we can save 2,000 tonnes of topsides and a corresponding 2,000 tonnes of jacket the effective total cost saving is therefore $66M.
