RIASSUNTO
ABSTRACT
Recent discoveries 'of petroleum along the northern coastal areas of Alaska and Canada's Northwest Territories have promoted interest in exploration in the shallow waters of the Beaufort Sea. During the period 1972-1975, Imperial Oil Limited has constructed six earth fill islands in water depth ranging from five to fifteen feet from which exploratory wells have been drilled. Island costs have varied from two to eleven million dollars. This paper describes the design, planning, and unique construction methods employed in building islands which must withstand severe summer storms and forces due to moving ice.
The technology and experience developed in the construction of temporary islands will have application in the development of futurefacilities, and may prove of benefit in other areas where ice conditions make conventional offshore operations unsuitable.
INTRODUCTION
Petroleum exploration activities in the offshore Arctic were initiated in the mid 1960's when permits covering acreage on the Arctic continental shelf were issued to several petroleum exploration companies. (Figure 1). Imperial Oil Limited, at that time, obtained permits in the shallow waters of the Beaufort Sea adjacent to the Mackenzie River Delta. To date our offshore island construction activities have been confined to water depths of less than ten meters as shown on Figure 2. Preliminary studies of offshore drilling feasibility, which were undertaken during the late 1960's soon brought to light the tremendous dearth of knowledge concerning the offshore Arctic environment.
It was apparent that the major problems to be solved while developing the technology required to support offshore Arctic drilling were:
The definition of forces exerted on stationary structures by the mobile annual and multi year ice.
Influence of violent, short duration summer storms.
An apparent scarcity of easily accessible construction materials.
The mobilization of suitable construction equipment which would be effective during the short open water operating season.
In 1969 Imperial initiated data gathering and ice testing programs, followed in succeeding years by many additional studies sponsored by Imperial and other interested Arctic operators.
Numerous concepts, both conventional and unique, were considered for Arctic offshore drilling, including artificial islands, bottom founded mobile structures, monopods, cones, and ice breaking floating vessels. Each of these concepts is feasible and may have application for a specific set of conditions. However, Imperial determined that the dredged artificial island was the safest and most economically attractive type of structure for use in support of its exploration drilling program in the shallow waters of the Beaufort Sea. In 1971 authorization was received to proceed with construction of an experimental island at what was later to become Imperial Immerk B-44 wellsite and construction began early in August, 1972. Drilling operations were not to take place until the stability of the structure under winter ice conditions had been adequately assessed.