Design Of A New Concept Of Underwater Oil Storage Tank In 300M Water Depth With Rubberized Diaphragm
Authors: Bozzo G.M. , Cannavaciuolo A.M. , Faso O.M. 
Published: October 2008

The paper describes the main technical and experimental results of a comprehensive research project leading to the design of a new concept of underwater oil storage tank suitable for 300 m water depth and over.

The all-steel fixed gravity tank has been designed for the North Sea conditions and has a capacity of about 180000 cubic meters divided into eight independent storage cells. An alternative solution suit able for 600 m W.O. for different meteoceanographic al conditions is also described.

The water displacement principle is adopted. In each cell the oil is separated from the water by a rubberized diaphragm to completely avoid sea water po11ution.

Installation procedure is illustrated together with the relevant results of 1:80 scale model tests performed at the Netherlands Ship Model Basin.

The experimental results of a test on a 1:10 scale model of one cell of the tank with the rubberized diaphragm are also presented.

The results of such tests confirm the feasibility of the concept with special reference to the fabrication, installation and operating procedures.

INTRODUCTION

The continuous extension of the activities of exploration and exploitation of offshore oil fields to deeper waters and to increasing distance from the shore have emphasized the demand for new technologies to solve oil storage problems.

Marginal petroleum reservoirs have not been developed since the use of pipelines and onshore terminal is not an economical production. Floating and under water storage tanks can solve such problems.

In presence of severe meteoceanographical conditions and with the increasing of the oil field water depth floating tanks become uneconomical and the oil storage may be conveniently solved by adopting fixed underwater storage tanks, based on the water displacement principle.

For this purpose TECNOMARE S.p.A. has developed a new concept of underwater oil storage tank suitable for 300 m W.O. and over. The design, construction, towing, installation and operation of such a structure comes from the integrated solution of different problems concerning: general configuration, storage process system, design methods, construction towing and installation procedures, maintenance, antipollution and reliability requirements. The paper presents the main technical and experimental results of the TECNOMARE underwater oil storage tank design developed within a three years research project.

DESIGN PREMISES

The 300 m W.O. storage tank has been considered as a part of a deep water exploitation system (3) which also includes a floating drilling and production platform, wellheads cluster, sea-line and mooring buoy for shuttle tanker loading (Fig. l). The structure has been designed in order to meet the following requirements:–to have a total capacity of about 180,000 m ;–to be installed at sea bottom at 300 m W.O.;–to be entirely prefabricated in a dry dock;–to be towed at the installation site;–to be installed with a highly reliable system and with a minimum surface support.