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