ABSTRACT

This paper describes the installation of the Brae 'B' platform in the UK sector of the North Sea. Over 72,000 tonnes of facilities were installed within a period of 67 days in the early summer of 1987. The work included launching a 22,500 tonne jacket, driving 35 piles, depositing 4.5 tonnes of weld metal and lifting 35 modules. Also, a small tripod structure was set and two 50m pipeline spools were successfully connected to the existing pipelines.

INTRODUCTION

Marathon Oil (UK) operates the Brae Field as a joint venture with the following companies:

  • Britoil plc

  • Bow Valley Exploration (UK) Ltd

  • Kerr-McGee Oil (UK) Ltd

  • Dyas Oil UK

  • LL&E (UK) Inc

  • Sovereign Oil and Gas Ltd

  • Norsk Hydro Oil and Gas Ltd

Brae 'B' is the second platform to be installed in the field which is located 155 miles north-east of Aberdeen. The first (Brae 'A') was installed in 1982 and was considered a large platform at the time with a topside design weight of 36,000 tonnes. The Brae 'B' platform, however, surpassed this with a total operating topside weight of 42,000 tonnes. The modules and jackets were fabricated at seven UK sites and a fleet of 16 cargo barges was required to move the components offshore. In all 38 major separate lifts took place to complete the platform which included an off-structure flare tower.

Detailed planning was an important feature of the project. The installation itself was scheduled using a 300 activity probabilistic model which incorporated known weather sensitivity factors. After much fine-tuning the final run showed that the installation period could take up to 95 days. In fact it was accomplished in an overall duration of 67 days which included 18 days downtime. As a result, the platform hook-up was given an early start and first oil is now expected well ahead of the original schedule.

OUTLINE DESIGN

The hydrocarbon reserves in the Brae Field are a complex mix of gas, oil and condensates. The Northern platform, Brae 'B', is expected to be producing 75,000 bpd of condensate and 400 million cubic feet of wet gas by the end of 1990. Because much of this gas will be re-cycled initially, the largest ever offshore gas processing plant is now incorporated on the platform. This includes four Rolls-Royce RB211 gas turbines to handle the compression. A further three RB211 turbines are provided to give the platform 72MW of electrical power. In addition, two complete drilling rigs have been installed to cope with the demands of the Brae reservoirs and the drilling programme. Some of the other vital statistics of this substantial development are given in Figure 1.

INSTALLATION DESIGN

From the outset the installation techniques available were considered before selecting the final shape of the major components of the platform.

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