Construction Of Artificial Islands As Beaufort Sea Drilling Platforms
Authors: Garratt D.H. , Kry P.R. 
Published: March 2010

The Beaufort Sea environment imposes unique constraints for drilling operations. Activity in the area must overcome wave attacks, multi-year pack ice invasion in the summer and moving ice sheets in the winter. As well, drilling systems must contend with a very short marine season (July to October).

For its Beaufort Sea acreage, Imperial Oil Limited decided to use artificial sand islands as drilling platforms. The islands have been designed to withstand waves in the area plus loading of ice sheets up to 7 feet thick. Imperial has constructed 14 islands in' water depths ranging from 5 to 42 feet employing three different construction techniques.

Three of the islands were winter-constructed islands. Ice blocks were removed at the site and the island till was placed with material hauled by trucks from onshore gravel deposits. Eight islands were summer-constructed "conventional" islands. An Imperial conventional island consists of sand fill and uses large sandbags to retain a portion of the fill and protect the slopes. Three islands were summer-constructed "sacrificial beach" islands, where the island is protected from wave attack by gradually sloping beaches that force the waves to break, so that their energy is dissipated before they reach the island's working surface.

Introduction

Potential oil and gas reserves have provided incentive for exploration drilling in the Mackenzie Delta region since the mid 1960's. After several years of onshore activity, the first offshore location was drilled by Imperial Oil Limited in 1,973, from an artificial island.(1,2)

In the five years since starting the offshore drilling program, Imperial has constructed fourteen islands in water depths from 5 feet (1.5 m) to 42 feet (12.8 m). Drilling has occurred from thirteen of these islands and has been able to proceed uninterrupted through all seasons.

The Arctic offshore environment to which the islands are exposed is harsh and its features have dictated the applicability of islands and influenced their design.

Environment of the Southern Beaufort

Figure 1 is a map of the area of interest to Imperial. The permit acreage is limited to the shallow waters of the Beaufort Sea, roughly extending from Shingle Point on the Yukon Coast east to the northern tip of the Tuktoyaktuk Peninsula. The northern boundary approximately follows, the 60-foot (18-m) water depth contour, Island construction to date has been concentrated in the Mackenzie Bay and Kugmallit Bay areas.

Sea Conditions

The open water period usually extends from mid July to early October. About 1 year in 5, the open water season is half the average, with break-up two to three weeks late and freeze-up two to three weeks early.(3)

Wave conditions in the Beaufort Sea are quite mild when compared with other ocean areas, because ‘both’ the fetch and the water depth are limited. The available fetch is restricted by the closeness of the Polar ice pack in the summer (usually within 200 miles). In the shallow water regions, the significant wave height is limited to 40% (±5%) of the water depth. Higher waves break and dissipate their energy.