Results of an Environmental Research Program In the Canadian Beaufort Sea
- J. Hnatiuk (Gulf Oil Canada Limited)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- June 1977
- Document Type
- Journal Paper
- 604 - 612
- 1977. Society of Petroleum Engineers
- 2 Well Completion, 5.5.2 Core Analysis, 6.6.2 Environmental and Social Impact Assessments, 4.3.4 Scale, 6.5.5 Oil and Chemical Spills, 5.1.1 Exploration, Development, Structural Geology, 4.6 Natural Gas, 6.7 Fundamental Research in HSSE, 1.6.9 Coring, Fishing, 5.2.1 Phase Behavior and PVT Measurements, 1.6 Drilling Operations
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A $12 million joint industry-government environmental research program consisting of 33 wildlife, biological, oceanographic, meteorological, sea ice, sea bottom, and oil-spill cleanup studies was conducted in the Beaufort Sea during 1974-75. The results were used to set operating constraints for drilling from drillships during open-water periods beginning in 1976.
From 1963 to 1969, Beaufort Sea offshore permits to explore for oil and gas were issued for the majority of the continental shelf. The shelf extends 75 to 100 miles from shore to water depths of about 600 ft, as shown in Fig. 1. In mid-1972, a group of 10 companies, and later, two other companies, applied to the Canadian federal government for approval of floating vessels as exploratory drilling systems for the Beaufort Sea. The first approvalin-principle of a floating drilling system was granted in mid-1973, and was followed by other approvals. These approvals were subject to completion of a number of environmental studies that would serve as the basis for the conditions and constraints to be included in a drilling authority. This environmental research, stipulated in late 1973, consisted of 29 studies estimated to cost $5.3 million, apart from in-house government support. The basis for funding these studies was resolved in Feb. 1974. Following two summers of field work, reports and an environmental assessment were completed early in 1976.
The Beaufort Sea Environment
The southern Beaufort Sea is usually ice-covered 9 months of the year it is during the 3 or 4 months of open water or thin ice that exploratory drilling from a floating vessel is proposed. With the onset of winter in early October, freeze-up typically progresses seaward, with relatively smooth ice extending 15 to 20 miles with an average water depth of 30 ft. Here, a very rough pressure-ridged band of ice grows outward to the 60-ft pressure-ridged band of ice grows outward to the 60-ft water depth where the landfast ice mass stabilizes early in the year. A recurring open-water lead exists at the edge of this landfast ice. Beyond this depth, the ice is fragmented into floes of varying thicknesses. The undisturbed winter ice within the landfast zone reaches a thickness of 6 or 7 ft by May, while the pressure ridges composed of broken blocks of ice may reach up to 40 ft. above sea level and have keels reported to exceed 100 ft. Multiyear ice up to 12 ft thick and glacial ice islands also may be incorporated in the first-year sea ice. Beyond the unstable, ridged first-year ice, a distance of about 100 miles, usually exists the permanent polar pack that is primarily composed of old ice and that rotates in a clockwise motion. Ice movements on the rim of this gyre average less than 2 miles/D but in the spring reach 15 miles/D.
Breakup, which begins in early July, is influenced by the Mackenzie River inflow, the Amundsen Gulf openwater area, southerly winds, and increased temperatures. In severe years, such as 1974, the area remains largely ice-covered as northerly winds replenish the ice in coastal areas. Fig. 2 shows the 1953-75 variation in the useful open-water days at a proposed drilling location 45 miles north of Tuktoyaktuk.
Extreme temperatures range from -50 to 80 degrees F, with an annual mean of 12 degrees F. Winds average 10 knots but, on rare occasions, can reach 75 knots; in large expanses of open water, these extreme winds can generate significant waves up to 20 ft. Visibility is restricted in midsummer by fog and in winter by blowing snow.
The sea bottom consists of clays and silts in the westerly areas and silts and sands in the easterly areas.
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