Experience in Float Over Integrated Deck - Flexibility of the concept
Authors: Sigrist J.H. , Thomas P.A. , Naudin J.C. 
Published: October 2008

Since the early 1980's, Technip-Geoproduction (TPG), as a designer or installation contractor. has been successfully using the "UNIDECK-TPG", a float over system for the transportation and installation of integrated decks for offshore platforms, The concept offers the advantages of significant savings in transportation and installation costs by reducing the installation time and offshore hook-up and avoiding the need for a heavy lift derrick barge. This paper describes the concept and the technology, the installation methods, the required engineering studies and the flexibility of the concept which can be adapted to each project requirement and location.

INTRODUCTION

TPG has developed the integrated deck concept, called UNlDECK-TPG, with the objective of minimizing the overall costs by offering the advantage of installing a deck on a jacket as a fully completed and tested single unit, without using a conventional crane barge. The technology combines ballasting and hydraulic jacking - when required - to improve the stability of the cargo barge during the transportation phase and to provide a safe and quick transfer of the deck weight onto the pre-installed jacket. The concept has been successfully used several times in both favorable and more severe sea conditions with deck weight ranging from 2,500 to 9,500 metric tons. This method has been implemented in the Mediterranean sea, in the Arabian Gulf, recently in the Qatar North Field and in West Africa with the COB-PI Production Platform, (9,500 tons) for which TPG acted as a contractor's manager. This deck was first installed early 1996 with 1.2 m significant wave height, a world's premiere in the long swell of the southern Atlantic Ocean. At the present time TPG is designing several other UNIDECKs, one for Adma Opco in Abu Dhabi for the GIP project (4,000T) and two large drilling/production decks (8,500T and 1O,500T) in Malaysia. The UNIDECK-TPG method has proved to be economical in three main categories :in shallow water where there is not sufficient draft for a large derrick barge to enter the site,when heavy lift derrick barges are not readily available resulting in prohibitive mobilization costs,when an integrated deck would be too heavy for existing derrick barges.

In each case, the design of the platform arrangement and the installation method have be adapted to the particular project requirements in terms of layout, topside weight, environmental conditions and final elevation of the deck in order to lower the cost of the operation.

PRELIMINARY ENGINEERING

When designing a large integrated deck, the first task of the engineering is to assess the feasibility of a float over operation considering:the weight and center of gravity of the topside,the meteorological conditions on the site.

The preliminary investigations include:the selection of a suitable transport barge,the evaluation of the need for an additional jackingsystem,the improvement of the deck and jacket arrangement,the evaluation of cost savings.

PLATFORM LAYOUT ARRANGEMENT

When a float over approach with the integrated deck is selected, one primary question shall be resolved : will the barge slot in the jacket be in longitudinal or in the transversal direction?