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US 4,579,481 AGranted
Mobile offshore drilling structure for the arctic
AssigneeThe Standard Oil Company
InventorsBen C. Gerwick, Robert F. Mast
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AssigneeThe Standard Oil Company
InventorsBen C. Gerwick, Robert F. Mast
Estimating the term…
A mobile platform structure, installation and method for use in arctic waters where the dominant environmental loading threats are posed by winter ice pressures and summer ice floes. The structure includes an ice load bearing, submergible substructure and a platform superstructure of approximately equal lateral dimensions. The substructure has a height approximately equal its depth of submergence when ballasted down onto the sea floor and includes a plurality of peripherally arranged, surface accessible spud guides. The spuds are laterally restrained by the spud guides in the top and bottom walls for transmission of lateral loads therebetween at respective vertically spaced apart fulcrum points and are vertically movable in the spud guides for penetration into high shear soils which may be overlaid by relatively low shear soils whereby the shear capacities of both soils combine with the frictional capacity of the structure/sea floor interface to provide high displacement resistance to lateral ice loads. Provision also is made for extracting the spuds for redeployment of the structure at another arctic installation site and for fixedly but releasably securing the spuds in an elevated position within the spud guides when not in use.
A mobile offshore platform structure for use in arctic waters wherein the dominant environmental loading threats are posed by winter ice pressures and summer ice floe impacts, said structure comprising an ice load bearing, submergible substructure and a deck receiving superstructure supported on said substructure and above sea level when said substructure is submerged onto the sea floor, said substructure including horizontal top and bottom walls, peripheral side walls surrounding said top and bottom walls, and a plurality of vertical bulkheads extending between said top and bottom walls to form a plurality of base compartments, a plurality of vertical spud guides interposed between said vertical bulkheads about the perimeter of said substructure, and a plurality of spuds extending vertically through said spud guides, said spuds operably being vertically movable in respective spud guides for penetration into the sea floor substrate and laterally restrained by said spud guides in said top and bottom walls for transmission of lateral loads therebetween at respective fulcrum points vertically spaced apart to permit flexing of said spuds therebetween.
An arctic offshore platform installation capable of resisting large ice loads, comprising a platform superstructure supported on a ballasted substructure resting on the sea floor for vertical load transfer to the sea floor and also lateral load transfer through friction between the bottom of the substructure and the sea floor, said superstructure and substructure having a vertical through hole defining a moon pool, a well head protecting caisson received at its top end within said moon pool and embedded at its lower end in the sea floor substrate, said caisson being arranged and sized to allow for relative lateral and vertical shifting of the substructure due to vertical and lateral loads thereon, and a plurality of extractable spuds laterally restrained at their upper ends in said substructure and embedded at their lower ends in the sea floor substrate for transfer of lateral loads acting on the substructure to the sea floor substrate.
An arctic structure installation capable of resisting large lateral ice loads at an offshore site having a relatively low shear sea floor foundation layer of substantial depth overlying a considerably higher shear foundation layer, said installation comprising a mobile drilling structure including a platform superstructure supported on a substructure ballasted to rest on the sea floor for vertical load transfer and also lateral load transfer through friction between the bottom of the substructure and the sea floor, said substructure including horizontal top and bottom walls, peripheral side walls surrounding said top and bottom walls, and a plurality of vertical bulkheads extending between said top and bottom walls to form a plurality of base compartments, a plurality of vertical spud guides interposed between said vertical bulkheads about the perimeter of said substructure, and a plurality of spuds extending vertically through said spud guides, said spuds operably being vertically movable in respective spud guides for penetration into the sea floor substrate and laterally restrained by said spud guides in said top and bottom walls for transmission of lateral loads therebetween at respective fulcrum points vertically spaced apart to permit flexing of said spuds therebetween, said spuds extending downwardly through said low shear foundation layer and into said higher shear foundation layer whereby the shear capacities of both foundation layers are combined with the frictional capacity of the substructure/sea floor interface to provide high displacement resistance to large lateral ice loads.
A mobile offshore platform structure for use in arctic waters wherein the dominant environmental loading threats are posed by winter ice pressures and summer ice floe impacts, said structure comprising an ice load bearing, submergible substructure and a deck receiving superstructure supported on said substructure and above sea level when said substructure is submerged onto the sea floor, said substructure including a plurality of vertical guides about the perimeter of said substructure, and a plurality of bending restraints extending vertically through said guides, said bending restraints operably being vertically movable in respective guides for penetration into the sea floor substrate and cantilevered by said guides in said substructure for transmission of lateral loads therebetween while being sufficiently flexible and ductile to displace under high impact loads for energy absorption and balanced distribution of shear loads into the sea floor substrate.
Dependencies are inferred from the claim text.