Floating Deep Draft Semi-Submersible Offshore Platforms and Methods for Assembling and Deploying Same

Abstract

A semi-submersible platform for offshore operations includes a buoyant hull including an adjustably buoyant base and a plurality of adjustably buoyant columns extending vertically from the base. In addition, the platform includes a deck moveably coupled to the columns. The deck is configured to move vertically up and down relative to the hull.

What is claimed is: 
     
         1 . A semi-submersible platform for offshore operations, the platform comprising:
 a buoyant hull including an adjustably buoyant base and a plurality of adjustably buoyant columns extending vertically from the base;   a deck moveably coupled to the columns of the hull, wherein the deck is configured to move vertically up and down relative to the hull.   
     
     
         2 . The platform of  claim 1 , further comprising a plurality of jack-up assemblies moveably coupling the deck to the columns, wherein each jack-up assembly moveably couples the deck to one of the columns 
     
     
         3 . The platform of  claim 2 , further comprising a deck sub-structure moveably coupled to the columns, wherein the deck is seated on the deck-substructure and each jack-up assembly moveably couples the deck sub-structure to one of the columns. 
     
     
         4 . The platform of  claim 3 , wherein each jack-up assembly comprises:
 a toothed rack fixably secured to the corresponding column; and   a powered pinion gear coupled to the deck sub-structure, wherein the powered pinion gear mates and engages the corresponding toothed rack.   
     
     
         5 . The platform of  claim 4 , wherein each toothed rack is oriented parallel to the corresponding column and has an upper end proximal an upper end of the corresponding column and a lower end disposed between the upper end and a lower end of the corresponding column. 
     
     
         6 . The platform of  claim 3 , wherein each jack-up assembly comprises a hydraulic jacking system or a strand jack system. 
     
     
         7 . The platform of  claim 1 , wherein the hull has a vertical height H h  measured from a lower end of the hull to an upper end of the hull, wherein the vertical height H h  is greater than 150 ft. 
     
     
         8 . The platform of  claim 7 , wherein the deck is configured to move relative to the hull between an uppermost position and a lowermost position;
 wherein the deck is disposed at a vertical height H u  measured from the lower end of the hull at the uppermost position;   wherein the deck is disposed at a vertical H l  measured from the lower end of the hull at the lowermost position;   wherein the vertical height H u  is greater than 150 ft. and the vertical height H l  is less than 150 ft.   
     
     
         9 . The platform of  claim 8 , wherein the vertical height H l  is less than 120 ft. 
     
     
         10 . The platform of  claim 8 , wherein the uppermost position of the deck is vertically spaced from the lowermost position of deck by a vertical distance D d  greater than 25 ft. 
     
     
         11 . The platform of  claim 1 , wherein the deck is not buoyant and is not adjustably buoyant. 
     
     
         12 . The platform of  claim 1 , wherein the deck is configured to move relative to the hull between an uppermost position and a lowermost position;
 wherein a portion of each column extending below the lowermost position of the deck has an outer surface comprising strakes.   
     
     
         13 . A method comprising:
 (a) floating a buoyant hull in water at a dockside location, wherein the buoyant hull has a draft less than 40 ft. at the dockside location;   (b) moveably coupling a deck to the hull during (a) to form the semi-submersible offshore platform, wherein the deck is configured to move vertically relative to the hull.   
     
     
         14 . The method of  claim 13 , further comprising:
 (c) floating the semi-submersible platform from the dockside location to an operating site in the water after (b);   (d) adjusting the draft of the semi-submersible hull to maintain stability during (c) or during installation at the operating site; and   (e) raising the deck vertically relative to the hull at the operating site.   
     
     
         15 . The method of  claim 14 , wherein (e) is performed simultaneous with (d). 
     
     
         16 . The method of  claim 14 , wherein (c) comprises:
 (c 1 ) floating the semi-submersible platform from the dockside location to a second location;   (c 2 ) increasing the draft of the hull at the second location; and   (c 3 ) floating the semi-submersible platform from the second location to the operating site after (c 2 ).   
     
     
         17 . The method of  claim 14 , wherein (d) comprises increasing the draft of the hull to a predetermined depth of at least 150 ft. 
     
     
         18 . The method of  claim 17 , wherein (e) comprises raising the deck to a predetermined height above the waterline. 
     
     
         19 . The method of  claim 18 , wherein (e) comprises raising the deck between 25 ft. and 75 ft. relative to the hull. 
     
     
         20 . The method of  13 , wherein the hull includes an adjustably buoyant base and a plurality of columns extending vertically from the base;
 wherein (b) comprises:
 (b 1 ) moving the deck horizontally between a pair of adjacent columns; 
 (b 2 ) raising the deck with a lifting crane at the dockside location; and 
 (b 3 ) coupling the deck to the hull at a height less than a maximum lifting height of the lifting crane. 
   
     
     
         21 . The method of  claim 20 , wherein the maximum lifting height of the lifting crane is less than 200 ft. 
     
     
         22 . The method of  claim 13 , wherein the deck is non-buoyant. 
     
     
         23 . A method comprising:
 (a) floating the semi-submersible platform to the operating site, wherein the platform comprises a buoyant hull and a non-buoyant deck moveably coupled to the hull, wherein the hull is disposed at a draft D during (a);   (b) ballasting the hull at the operating site after (a) to increase the draft D of the hull at the operating site; and   (c) raising the deck vertically relative to the hull at the operating site.   
     
     
         24 . The method of  claim 23 , wherein (c) is performed simultaneous with (b). 
     
     
         25 . The method of  claim 23 , wherein (b) comprises increasing the draft of the hull to a predetermined depth; and
 wherein (c) comprises raising the deck to a predetermined height to set an airgap between the deck and the waterline.   
     
     
         26 . The method of  claim 23 , wherein (c) comprises jacking the deck upward relative to the hull with a plurality of jack-up assemblies that moveably couple the deck to a plurality of vertical columns of the hull.