Installation of the Brent B Condeep Production Platform
Authors: Eide Ove T. , Larsen Leif G. , Mo Olav 
Published: December 2007

The Condeep production platform was installed in the North Sea's Brentfield in Aug. 1975. The installation phase is described and the results obtained during penetration of the base into the sea bed are presented. Experience gained during this installation will be of use for further work on installing concrete gravity structures.

Introduction

The first concrete gravity structure installed in the northern North Sea was the Ekofisk Doris tank placed for Phillips Petroleum Co. in the summer of 1973. The next Phillips Petroleum Co. in the summer of 1973. The next two installed were the Condeep production platform Beryl A for Mobil Oil Corp. and the Brent B platform for Shell/Esso. Both were installed in the summer of 1975. The water depths at the three fields are 70, 118, and 140 m, respectively.

The greatest concern for installation of the Ekofisk tank was the sea-floor topography and the load distribution on the bottom slab, since the slab was only equipped with 40-cm-high concrete ribs. The sea floor at Ekofisk, however, proved to be almost perfectly flat and no problem related to an uneven sea floor arose. problem related to an uneven sea floor arose. The Condeep structures are equipped with steel skirts. To prevent the skirts from being damaged during installation, steel-pipe dowels extending below skirt-tip level are used. These keep the structure from moving laterally during the first phase of penetration known as "touchdown." The skirts have three basic functions: to improve foundation stability, to reduce the danger of scour or erosion, and to divide the base into compartments for grouting purposes.

The actual installation on the sea floor is a critical phase in the life of the platform and must be included in phase in the life of the platform and must be included in the foundation design analysis. It should be checked that neither the structure nor the foundation soils are damaged or unfavorably affected during installation. This requires comprehensive instrumentation and logging of all important factors, including platform inclination, water pressure in skirt compartments, contact pressure on the base pressure in skirt compartments, contact pressure on the base of the structure, and strain within the structure.

The Brent B Condeep platform was selected for an extended instrumentation program. This research project is sponsored by several oil companies operating in the North Sea, the British Dept. of Energy, Norwegian Contractors, and institutions in both Great Britain and Norway.

Norwegian Contractors and the Aker Group were the general contractors for the Condeep Brent B project. In this joint venture Norwegian Contractors was responsible for the construction, the maritime operations, and the installation at the field. The deck and mechanical fittings were designed and fabricated by the Aker Group. The design concept was developed by A/S Hoyer-Ellefsen. Olav Olsen and his firm were structural consultants for the substructure. The Norwegian Geotechnical Institute acted as geotechnical consultant for the project and was responsible for the installation-phase instrumentation. The Central Institute for Industrial Research developed and produced the monitoring and data acquisition system. The River and Harbour Laboratory at the Technical U. of Norway carried out special model tests for evaluating the environmental loads. This laboratory was also responsible for monitoring the waves at the site during installation. Bloms Oppmaaling A/S was engaged as land surveyor responsible for the navigation and positioning. Det norske Veritas is the certifying society. All these organizations are based in Norway.

JPT

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