Abstract: A method for installing a pipeline for transporting a warm fluid, such as newly-produced oil, across arctic seafloor underlain by a permafrost zone without danger of rupture of the pipeline caused by thawing in the supporting permafrost zone comprises (1) drilling a series of boreholes along the seafloor through a thawed zone of subsea soil so as to penetrate a distance into a zone of permafrost lying thereunder, (2) circulating a warm fluid through each borehole so as to cause a zone of prethawing in the permafrost zone and thereby create a slump trough on the surface of the seafloor along a path marked by the series of boreholes; and (3) installing a warm fluid bearing pipeline along the bottom of the slump trough. Usually a temperature differential between the warm fluid and the bottom of the borehole of at least 2 degrees Fahrenheit is required to assure economical prethawing of the permafrost zone.

Abstract: Method and apparatus for building a thickened ice mass, such as a grounded ice island, at a cold offshore location, in which water is pumped through a fluid flow conduit and discharged from a rotating swing arm section of the conduit onto selected areas of a natural ice sheet to form circular and/or annular thickened ice bodies. The fluid flow conduit includes a first water supply line disposed in the water body between the ice sheet and the marine bottom, and, if required, a second water supply line which is installed along the top surface of the ice island after the grounding of the ice body forces abandonment of the first water supply line.

Abstract: An ice island for use in offshore operations in cold waters includes an operations pad and a surrounding containment barrier, the bases of which are grounded on the marine bottom. The island is constructed by accumulating ice in confined areas defined on a sheet of native ice until the mass of the accumulated ice causes the ice underlying and adjacent to the confined area to be depressed with respect to the main body of ice and be grounded on the marine bottom.