Drilling and Production Platforms for Arctic Offshore Development

Abstract

Rapidly expanding development is taking place in the Arctic and sub-Arctic seas of Alaska and Canada, driven by the discovery of immense resources of oil and gas and favorable geophysical conditions in adjoining areas. The Arctic regions are dominated by sea ice, from the central polar pack to the pressure ridges and rubble piles that form in the shear zone along the periphery. In the east, adjoining Labrador and Newfoundland, icebergs are encountered. Storm waves and surges during the summer, strong seismicity in certain areas, and weak and construction-difficult soils in many areas combine to make the design and construction of platforms abnormally difficult. Existing platforms for offshore exploration include sand and gravel islands in shallow-water areas, floating drillships accompanied by icebreakers, a concrete-caisson-retained island in the Canadian Beaufort Sea, and a converted VLCC, grounded on a prepared embankment and given additional protection by artificially constructed ice rubble. At the present time, two steel caissons, designed to be filled with sand after founding, and one floating drilling structure are under construction. In the design and planning stage are a number of new concepts for caissons, mostly constructed of prestressed lightweight concrete, designed to resist global forces in the range of 150 000 kips or more and local concentrated forces of 800 to 1000 psi over small areas. Prestressed lightweight concrete appears well suited to the demands of Arctic service. The towing, deployment, founding, and subsequent removal of exploratory platforms demands consideration of a wide variety of naval architectural aspects. One of the more critical areas facing designers is how to determine the forces and displacements caused by impact from a large ice floe or berg. The compliance of the structure and the hydrodynamic dissipation of kinetic energy need to be considered, as well as the crushing of the ice. The successful development of the Arctic demands consideration not only of a wide range of engineering and naval architectural aspects but also their integration with ecological, social, political and economic considerations.