TSG-Integrated Storage Platform for Early Production in the North Sea
Authors: Agostoni Alberto , Gnone Enzo 
Published: December 2007

Since 1975, several proposals have been made concerning the exploitation of the Maureen field in the British sector of the North Sea. Tecnomare SpA has designed, on behalf of Phillips Petroleum Co. E and A. a steel gravity platform, with integrated oil storage, to be installed in the Maureen field. In 1977 the operating company, Phillips, carried out detailed studies on two basic development concepts:a work over and production platform installed over a subsea template with predrilled wells anda drilling and production platform installed on a bare seabed.

Both concepts incorporated storage facilities and a tanker-mooring and offshore-loading system. While the latter is a conventional field development, the former is an application of the early-production philosophy.

We concluded that the early-production concept was practicable and that the Tecnomare steel gravity (TSG) platform was the more suitable.

Basic Philosophy

The early-production concept aims at shortening the field-development time and hastening the investment-cost recovery, which is particularly important in rendering profitable the exploitation of marginal fields. Moreover, in most cases, marginal fields require storage capacity and loading systems because the long distance from the coast or from larger offshore facilities does not justify the use of submarine pipeline for transportation. These requirements can be met bydrilling the production wells and fabricating the platform at the same time;using a topside facility fully equipped onshore, thus minimizing the time-lag from installation to production start-up; andproviding the storage required.

Point 1 calls for a platform that can be installed over a template of predrilled wells; Point 2 requires a platform that can transport an integrated topside deck; and Point 3 demands a platform with integrated storage capacity.

The Maureen TSG platform is now under onshore hook-up operations in Scotland and will be installed over the template, through which the production wells have been drilled and capped. Production casings will be tied back to surface conventional wellheads.

All the critical problems concerning the installation of a platform over a template, such as the required accuracy and the necessity to avoid damage to the template itself, are solved positively by the TSG platform, which features:a self-contained ballasting and mooring system that allows the platform positioning and setting to be controlled by an operator console on the platform temporary deck;a particularly good floating dynamic behavior better than that of a semisubmersible of comparable displacement when a proper draft is reached; anda foundation base divided into three separate circular pads, providing space and easy accessibility for the installation over existing underwater equipment.

The Maureen TSG platform also will transport to the field the drilling and production topside facility, consisting of an integrated deck fully equipped onshore. The deck loaded onto a single barge will be mated with the TSG substructure in the calm water of Kishom. The substructure basic configuration has been modified to accommodate the hideck and to perform the mating operation.

The cylinders of the Maureen TSG platform ensure a total storage capacity of 650,000 bbl (103 342 m3). In general, the available storage and the transportable payload are related - the larger the payload to be accommodated, the larger the built-in storage available. In the Maureen case, the required storage provides the platform with the buoyancy and the naval stability needed for safe transpose of the payload.

JPT

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