ABSTRACT

As Dome Petroleum Limited and others discover the potentially rich hydrocarbon resources of the offshore Arctic areas it becomes a priority to develop the specialized production systems required for this unique area. This paper describes a platform design which could form an integral part of such an Arctic production system.

This Arctic Production Monocone (APM) has been designed for year round operation in the Beaufort Sea in medium water depths up to 250 feet. The platform is comprised of three basic components; a doughnut shaped base, a bottle shaped superstructure, and a removable jack-up deck.

The base section provides the foundation for the structure, and may be either a piled or gravity base depending on the in-situ soil conditions. The submerged conical mid-section of the superstructure is designed to minimize the ice forces by causing ice ridges to fail in flexure. The surface piercing cylindrical shaft provides support for the jack-up production deck and fails sheet ice in the crushing mode.

It is unlikely that a structure installed in the Beaufort Sea would be endangered by an ice island. However, the feasibility of avoiding an ice island by disconnecting the superstructure and the deck from the base was investigated. During disconnect the base-section would remain in place to protect the subsea wellheads which would be installed on the sea floor. In order to maintain stability during towing and disconnect procedures the deck must he removed from the main structure. A jacking system has been designed to accomplish the deck installation and removal.

This paper will discuss in some detail the following features of the Arctic Production Monocone:

  1. Environmental design criteria,

  2. Structural design,

  3. Foundation design,

  4. Cone/base connection mechanisms,

  5. Deck jack-up systems,

  6. Construction and installation.

The platform described in this paper incorporates many novel features which make it especially suitable for ice covered seas. The studies that have been carried out to date show that the concept is technically and economically feasible and should thus be of interest to other operators in the offshore Arctic regions.

INTRODUCTION

Several kinds of structures have been proposed for use in the Beaufort Sea, including artificial islands, caissons, ice islands, monocones and floating vessels. Most of these have been intended as drilling platforms and, with the exception of the floating vessels, they have been designed for relatively shallow water. Two of these concepts, artificial islands and floating vessels, are presently used in the Beaufort Sea as exploration drilling platforms. Artificial islands have been used since 1974 by Imperial Oil Limited, and moored drill ships have been used by Dome Petroleum Limited since 1976.

Exploration to date has shown that a number of promising geological formations lie in the 150-250 foot water depth range. This paper describes a bottom founded platform that is capable of year-round operation in the Beaufort Sea in water depths ranging from 150 to 250 feet. The region for which this structure was developed is shown in Figure 1.

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