Patent CA-2089509-A1 (CA)
Inventor: SCOTT WILLIAM A
IPC: E02B17/00
Filed: 1993-02-15
Abstract: ABSTRACT   A submersible mobile caisson having ice crush resistance for adapting semi-submersible mobile offshore drilling units and mobile offshore oil well production rigs, which are ice crush sensitive for use in ice bearing offshore ocean waters, is provided. The caisson comprises: i) a floatable generally four-sided caisson with a fixed upstanding front outer wall and fixed upstanding opposing side outer walls and an upstanding rear outer wall having a removable entrance door, ii) the caisson is of a height to permit offshore drilling and/or production when said caisson is submersed to rest on an ocean floor, iii) the outer walls are reinforced to withstand crushing forces exerted by ice bearing offshore oceans and the outer wall height is sufficient to turn back a maximum design wave. The outer walls have an inwardly sloping wall portion about caisson perimeter above and below submersed water level to wedge upwardly advancing ice, iv) the upstanding front and rear walls and the opposing side walls define a cavity, access to which is provided by removing the entrance door, v) the cavity has a base, a front inner wall, opposing side inner walls and a rear inner wall on the entrance door. The inner walls are spaced from corresponding outer walls of the front and opposing sides with an upper support deck spanning the spaced apart outer and inner walls. The front and rear including the door and the side inner and outer walls define a caisson perimeter structure, the interior space of the cavity being protected from ice crushing forces by the caisson perimeter structure, vi) the perimeter structure and the base have a plurality of ballast compartments to float the caisson and when the compartments are filled with a ballast liquid, the caisson sinks towards and rests on the ocean floor where the caisson perimeter structure is of a height to provide above water level a sea break to safeguard operating facilities and personnel, vii) the base of said cavity is positioned relative to said deck to provide sufficient draft when the caisson is floating and the door is open to permit entrance and exit of semi-submersible mobile offshore drilling units and/or production units, viii) the deck along each of the opposing sides has at least one drilling/production service hatch, ix) each of the side portions of the perimeter structure has extending vertically therethrough, a drilling/production moon pool system which extends from and is in communication with the corresponding service hatch, x) the caisson perimeter structure comprises an ocean floor perimeter foot portion of solid reinforced structural material. The cavity base of reinforced structural material tied into the perimeter foot portion, xi) the inner and outer walls to at least above submersed water level when the perimeter foot is resting on ocean floor are of reinforced structural material, the plurality of the ballast compartments being provided between the inner and outer walls with a majority of each ballast compartment being below submersed water level when the perimeter foot is resting on ocean floor.