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GLOBAL PLATFORM DESIGN.

Introduction  Design strategy  Small platforms  Medium platforms  Large platforms  Previous page

Introduction: 

 

The traditional platform designs vary from the ultra-small "flag pole" type of platforms to the really heavy ones with topsides weight of some 50000 ton.  There are fixed platforms and floating platforms, semi-rigid and tension leg platforms, all made to serve their different purposes; fighting the budgets as well as ambient conditions.

 

Most of the platforms are designed with two main objectives in mind; low investment cost and sufficient integrity to withstand the ambient forces, wear and tear.

 

Since most projects are judged by their potential generated "cash flow after tax" or Net Present Value (NPV), the focus is set on factors like investment cost and date of first oil. In order to accommodate the need of an optimal NPV and low project risk, TRC has looked into a different platform design strategy.

 

If you click on the curve,  you can see the importance of reduced investment cost and first oil on the NPV. Since the NPV is the discounted cash flow, it is obvious that  "money now" has a higher value than "money later".

 

By a click on the curves, you will see indicated high- and low budget cash flows. Since it is difficult to know the value of the produced oil and gas during the life cycle of the field, designing the complete platform for any of these events may increase the project risk and lower the profit. 

Would it not be wise to select a strategy that proved to be advantageous for the possible development of the field by making the production systems, hence the platform more flexible in terms of adapting to the field production rate and the market cost of the products ? 

The main issue here is therefore to design the "backbone" of the platform, the support, strong enough to accept the higher weight needed for the best case production budget, and to design the topsides with the flexibility of accepting a rapid and low-cost stepwise increase in production, accommodate the need for water injection, gas lift, adding more wells, satellites, etc ? 

 

A new way to look at fixed platforms. 

 

- A fixed platform is in fact a "crane" standing on the sea bed, so why do we need the huge floating cranes to install the topsides ? 

 

- If we design the platform topsides support structure with members in tension rather than members in compression, could we not save structural weight ? 

 

- Since the fabrication cost of module- and cellar deck type of structures is higher than jacket type of structures, why not let a jacket fabricator make the topsides support structure as an integrated part of the jacket ? 

 

- Since parallel activity type of fabrication schedules are more flexible and time saving than the series-type of schedules used to day, why not take advantage of that, and save project execution time as well ? 

 

- If we use open or closed system cassettes instead of modules, would it not be relatively easy to increase the production capacity by adding cassettes ? 

 

 

These are some of the questions we have made during the process of optimizing the global platform designs.

 

TRC platform designs and efficient fabrication methods for platforms will reduce initial capital expenditure, reduce time between project start and first oil, lower the cost of maintenance, lower the cost of platform- and system extensions and make the platform and its systems re-usable thus also considerably improving the project Net Present Value.  

 

The small PEF platform designs: 

 

 

No, this is not a platform, but a portion of a Stay-Bridge during construction ! 

You can see two of the stay wires running from the top of the tower down to the center of the bridge section. The complete span is really suspended in those stay-wires.

The ultimate load of such a stay bridge wire is close to 17,100 kN and the specific weight only 85 kg per meter ! 

The reason for this exercise is obvious, since the way the bridge was designed, also may help us save structural steel weight in the platforms. 

Take a look at this platform !

(Click on the pictures to enlarge.)

 

This patented platform design is a typical result of the TRC development strategy. Look at the topsides. All cassettes are hanging from the horizontal support truss connected to the platform legs by stays or cables in tension. 

 

 

The platform jacket is fabricated in one piece from the bottom and up to the stay-bridge like connections to the hanger system that supports the topsides cassettes. The platform may be installed by using supply vessels. One proposal is to install a platform template, perform drilling, and then pull the platform with positive buoyancy down to the template using lifting jacks fitted to the top of the jacket. 

 

The lifting system for the cassettes is always present, and will lift the cassettes up from a supply vessel. The cassettes may be installed in the middle of the platform, or hanging from the support system in two directions. Cassettes may also be installed above the horizontal support beam level. All kind of cassettes may b used. On the picture, a combined living quarter and workshop cassette is temporarily installed during hook-up or maintenance periods. 

 

 

The cassettes may easily be removed and brought onshore by a supply vessel for major overhaul. 

 

The saving potential in topsides structural weight is some 70%, and the cost saving abt. 40% compared to a traditional platform. Further, the platform may be developed sequentially, or moved to other locations if needed. 

 

If you wish to read more about this particular platform design, order the CD information package, or look at the PEF platform report.

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The medium size PEF platform designs: 

 

This platform topsides design is a hybrid between the integrated topsides and closed cassette principle. The idea was to design a platform with a basic production system, but with a built-in option to install additional two cassettes at a later stage. Since the support structure was planned to be a GBS, a fully integrated truss system was proposed as support for the topsides. 

 

 

The platform in the foreground is based on the integrated topsides principle. It has no cellar deck, but the structure contains and supports fully developed open system cassettes. The main deck area has been reserved for later installations. Here, the load transfer of one cassette deck takes place.

 

 

As can be seen from the picture, a system cassette deck is being installed into one of the topsides compartments.

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The The large PEF platform designs: 

 

There are two particular types of large integrated topsides platform designs (IPEF). One made for a PEF type of installation on a steel jacket, and one for GBS type of platforms. 

 

 

The integrated topsides on this platform is designed with system compartments, but as the other designs, the system cassette decks may be introduced from the underside or horizontally into the structure at time of assembly or later. The complete topsides may be fabricated onshore and most of the systems tested before installation on the jacket.  The topsides carry its own lifting equipment, which is connected to the connecting truss or leg extension of the jacket at arrival. 

 

 

The topsides is then transferred to the lifting system and elevated according to the PEF method. The topsides may be removed later using the method in reverse. 

 

 

The GBS platform adoption of the fully integrated topsides also take advantage of the strength in the very high truss system and compartments for the system cassettes and at the same time benefit from the open access fabrication and installation principles with a parallel activities type of schedule. 

 

 

As may be seen from this schedule, the system decks may be inserted into the structure very late in the process, even at-shore, in-shore or offshore. The savings in structural steel and improvement in fabrication productivity is very significant.

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TR Consulting, Joh. Falkb.gt. 10, 5538 Haugesund, Norway. Tel: +47 52729124, Fax: +47 52724196, C.E.O. Cell phone.  +47 90 616969  e-mail: trcons@online.no or trcons@start.no