ABSTRACT

This paper describes novel methods for the development of offshore oil fields within iceberg infested waters, at locations with water depths of up to 200 metres. The scheme involves the construction of a Protective Barrier which completely surrounds and protects the oil production platform. The production platform facilities, which are located inside the Protective Barrier, may either be supported off a fixed steel structure, or alternatively off a jack-up platform, or alternatively off a specially developed floating production unit. The quite separate Protective Barrier is constructed in a cellular arrangement from reinforced or pre-stressed concrete, and has sufficient mass through its own weight, together with the weight of solid ballast, placed within the cells, to resist external forces due to either icebergs or wave action. The feasibility of the scheme is demonstrated for a typical oil field development in 80 metres of water. The paper provides the overall sizes and quantities of materials used in the construction of the Protective Barrier and of the structure required to support the production facilities, together with a description of the methods of installation of the production platform within the Protective Barrier.

In this development scheme, a major point has been to reduce the overall quantities during construction and hence the anticipated overall development costs, together with a reduction in the overall schedule, as against more conventional methods of offshore field development in these areas. It is considered that the development scheme, as described in the paper, will allow the economic development of offshore oil and gas fields in iceberg infested waters, which hitherto have remained undeveloped for economic reasons.

1. INTRODUCTION

Significant offshore oil and gas fields exist in various parts of the world, in areas where the potential of a large iceberg impact with the production platform must be considered in the design process. The consideration of iceberg impact on a production platform obviously introduces an additional premium in terms of quantities, costs and schedule, when compared with more conventional developments in deep water harsh environments, such as the North Sea. The objective of development in areas with the potential of iceberg impact must therefore be to reduce this additional premium in terms of quantities and costs to a minimum.

One important offshore province, which has hitherto remained undeveloped, is offshore St. John's, Newfoundland. In these areas several interesting oil and gas fields exist, and have the potential for possible development. An outline map showing various fields is given in Figure 1. To date, the schemes and solutions offered for the development of these fields follows a rather "conventional" pattern (1,2,3), bearing in mind the potential for impact from icebergs and the development of large forces due to the movement of very large icebergs in that area.

This paper describes an alternative method of development for such areas (4). The essential feature of this scheme is that the structure, in the form of a Protective Barrier, which is required to resist the impact forces due to icebergs, is quite separate and disconnected from the production platform.

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