Floating Jacket-- A New Concept for the Design of a Floating Production, Storage and Offloading Platform in Deepwater
Authors: Lou Jack Y.K. , Racine Florian , Xu Fred Y.F. , Cao Peimin 
Published: October 2008

The most unique feature of the new FLOATING JACKET concept is to place much of the needed buoyancy/ballast deep below the ocean surface. The deck and production equipment are supported by a jacket structure which is in turn erected on top of a huge buoyancy/ballast tank deeply submerged. This simple concept offers many very attractive futures and is particularly suitable for the design of floating production, torage and offloading systems in deepwater.

INTRODUCTION

Currently more than 30% of world's consumption of oil and gas is produced from offshore wells. As more oil and gas are discovered in deeper water than ever before, the offshore industry has become increasingly interested in the design of advanced offshore production facilities. For deepwater operations, conventional fixed offshore platforms are no longer suitable and several innovative platform design concept shave emerged. For water depths up to 1000 m, it seems that the tension-leg platform (TLP) appears to be most promising and several TLPs have been installed in water depth up to 1000m.

The TLP is a veqy complex structure system that will require a huge sum of capital investment. Therefore, it is only economically viable for very large reservoirs in deepwater. Furthermore, the TLP is very sensitive to water depth. Its effectiveness in greater water depths is questionable due to excessive weight, buoyancy, and hydro dynamic loads. Thus, for greater water depths and smaller or marginal fields, less expensive platform configurations must h developed. Several new concepts have been suggested as alternatives. Among these, the spar buoy seems to have received the widest attention recently.

Although the spar concept does have its merits, several drawbacks and limitations render this concept less attractive. Among the most severe drawbacks is the excessive wave and current loads. This will require higher initial tension in the tethers and thus increasesthe initial cost.

A new design concept tentatively called FLOATING JACKET(FO as shown in Figure 1 is suggested here in. Instead of using a single large cylindrical structure as in the spar cm.tlguration, the FJ utilizes a jacket-type fkamed structure supported by a bouyancy/storage tank deep below the ocean sutiaee, This simple concept offers many attractive features. Analytical and experimental investigations have been carried out to examine the motions of the platform in regular and random waves. The results indicate that the new FJ concept is indeed a superior platform configuration so far as the sea keeping characteristic sand station keeping requirements are concerned. However, in order to evaluate ita overall merits, practical design considerations and cost factors must be examined are fiddly.

MERITS OF THE FJ CONCEPT

The most important fature of the new FJ concept is to place much of the required buoyancy and ballast deep below the ocean surface. The deck and the production equipment are supported by a jacket structure made of small cylindrical members whichis in turn erected on top of a large, deeply submerged buoyancy ballast tank as shown in Figure 1. This simple concept offers several very attractive features. Some of these are briefly described below.