ABSTRACT

The installation of the deepwater Boxer Platform is documented. The objective is to provide a record of the installation plans and some of the reasoning behind the selected approach, as well as to indicate what worked well in the field and what did not. It is hoped the paper will be of assistance to those planning for the installation of future deepwater platforms.

INTRODUCTION

The Boxer Platform is a self-contained drilling and production platform recently installed in the Gulf of Mexico, approximately 140 miles south of Morgan City, Louisiana. The water depth at the Green Canyon Block 19 site is 750 feet. The platform is basically a conventional template type structure, but a specific effort was made to minimize the wave force area near the water surface by reducing the dimensions of the top end of the jacket.

The platform is supported by twelve 72-inch diameter skirt piles and contains twenty-one driven well conductors. There are no piles located in the main jacket legs. The jacket framing is depicted in Figure 1. There are six legs at the top of the jacket, eight legs below elevation minus 170 feet, where the launch trusses begin, and ten legs between elevation minus 470 feet and the mudline. The nominal lateral dimensions at the top of the jacket are only 55.5 by 90 feet, compared to 246 by 243 feet at the base. An impressive characteristic of the jacket, prior to launch, was the relative sizes of the two ends.

The platform is owned and operated by Shell Offshore Inc. The structural jacket design was prepared by the Civil Engineering Group of Shell Oil Company with assistance from Hudson Engineering Corporation. McDermott Marine Construction was the contractor for the fabrication (excluding the decks), transportation and installation of the platform. The decks were designed by Shell Offshore Inc. and fabricated by Avondale Shipyards. McDermott's responsibilities included the development of the installation procedures as well as the design and provision of most of the installation aids and appurtenances.

SUMMARY OF INSTALLATION PROCEDURE

All of the piles and the initial conductor sections were preinstalled in the jacket at the fabrication site with both ends of each sealed to maximize the contribution to jacket buoyancy. The combination of pile buoyancy at the top of the jacket and selected free flooding of structural elements at the lower end allowed the jacket to "self upend" after launch. Four tugs, which were connected to the top of the jacket prior to launch, were used to tow the vertical jacket to the installation site. Positioning slings preinstalled on the jacket were connected to the main block of the crane on McDermott's Derrick Barge No. 22. The jacket was properly positioned using surface surveying techniques and lowered to bottom with the crane while ballasting through the use of manually operated flood valves.

The preinstalled piles were held in open guides by temporary gates. After the piles were flooded and the lower closures removed, the gates were retrieved with preinstalled rigging.

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