Tension leg platform having modified wave response characteristics

Abstract

A modified tension leg platform (referred to as “Soft TLP”)for the exploration of, drilling of, and production from offshore subterranean reservoirs. The buoyant section has been positioned below 100 feet of water depth, to provide this Soft TLP with a reduced surface area in the first 100 feet of water depth to reduce the effect of wave forces on the structure.

We claim:  
     
         1 . An offshore platform comprising: 
 (A) a deck for supporting hydrocarbon exploration, drilling or production equipment;    (B) a buoyant member;    (C) an open support structure positioned between the deck and buoyant member, comprising an upper end connected to the deck, and comprising a lower end connected to the buoyant member;    (D) a plurality of tendons connected to the buoyant member suitable for anchoring the platform;    wherein when the platform is positioned offshore, the deck is supported above the waterline, the upper end of the open structure is positioned above the water line, with the lower end positioned at least 100 feet below the waterline; and the heave resonance of the platform is at least 6 seconds.    
     
     
         2 . The platform of  claim 1 , wherein the heave resonance of the platform is in the range of about 6 to about 10 seconds.  
     
     
         3 . The platform of  claim 1 , wherein the heave resonance of the platform is in the range of about 7 to about 9 seconds.  
     
     
         4 . The platform of  claim 1 , wherein when the platform is positioned offshore, the lower end is positioned at least 150 feet below the waterline.  
     
     
         5 . The platform of  claim 4 , wherein the heave resonance of the platform is in the range of about 6 to about 10 seconds.  
     
     
         6 . The platform of  claim 4 , wherein the heave resonance of the platform is in the range of about 7 to about 9 seconds.  
     
     
         7 . The platform of  claim 1 , wherein when the platform is positioned offshore, the lower end is positioned at least 200 feet below the waterline.  
     
     
         8 . The platform of  claim 7 , wherein the heave resonance of the platform is in the range of about 6 to about 10 seconds.  
     
     
         9 . The platform of  claim 7 , wherein the heave resonance of the platform is in the range of about 7 to about 9 seconds.  
     
     
         10 . A method of exploring an offshore target zone for hydrocarbons, the method comprising: 
 (A) positioning a platform offshore near the target zone;    (B) conducting exploration activities from the platform,    wherein the platform comprises: 
 (i) a deck for supporting hydrocarbon exploration equipment;  
 (ii) a buoyant member;  
 (iii) an open support structure positioned between the deck and buoyant member, comprising an upper end connected to the deck, and comprising a lower end connected to the buoyant member;  
 (iv) a plurality of tendons connected to the buoyant member suitable for anchoring the platform;  
 wherein when the platform is positioned offshore, the deck is supported above the waterline, the upper end of the open structure is positioned above the water line, with the lower end positioned at least 100 feet below the waterline; and the heave resonance of the platform is at least 6 seconds.  
   
     
     
         11 . The method of  claim 10 , wherein the heave resonance of the platform is in the range of about 6 to about 10 seconds.  
     
     
         12 . The method of  claim 10 , wherein the heave resonance of the platform is in the range of about 7 to about 9 seconds.  
     
     
         13 . The method of  claim 10 , wherein when the platform is positioned offshore, the lower end is positioned at least 150 feet below the waterline.  
     
     
         14 . The method of  claim 13 , wherein the heave resonance of the platform is in the range of about 6 to about 10 seconds.  
     
     
         15 . The method of  claim 13 , wherein the heave resonance of the platform is in the range of about 7 to about 9 seconds.  
     
     
         16 . The method of  claim 10 , wherein when the platform is positioned offshore, the lower end is positioned at least 200 feet below the waterline.  
     
     
         17 . The method of  claim 16 , wherein the heave resonance of the platform is in the range of about 6 to about 10 seconds.  
     
     
         18 . The method of  claim 16 , wherein the heave resonance of the platform is in the range of about 7 to about 9 seconds.  
     
     
         19 . A method of drilling for or production of hydrocarbons from an offshore target zone, the method comprising: 
 (A) positioning a platform offshore near the target zone;    (B) conducting drilling or production activities from the platform,    wherein the platform comprises: 
 (i) a deck for supporting hydrocarbon exploration equipment;  
 (ii) a buoyant member;  
 (iii) an open support structure positioned between the deck and buoyant member, comprising an upper end connected to the deck, and comprising a lower end connected to the buoyant member;  
 (iv) a plurality of tendons connected to the buoyant member suitable for anchoring the platform;  
 wherein when the platform is positioned offshore, the deck is supported above the waterline, the upper end of the open structure is positioned above the water line, with the lower end positioned at least 100 feet below the waterline; and the heave resonance of the platform is at least 6 seconds.  
   
     
     
         20 . The method of  claim 19 , wherein the heave resonance of the platform is in the range of about 6 to about 10 seconds.  
     
     
         21 . The method of  claim 19 , wherein the heave resonance of the platform is in the range of about 7 to about 9 seconds.  
     
     
         22 . The method of  claim 19 , wherein when the platform is positioned offshore, the lower end is positioned at least 150 feet below the waterline.  
     
     
         23 . The method of  claim 22 , wherein the heave resonance of the platform is in the range of about 6 to about 10 seconds.  
     
     
         24 . The method of  claim 22 , wherein the heave resonance of the platform is in the range of about 7 to about 9 seconds.  
     
     
         25 . The method of  claim 19 , wherein when the platform is positioned offshore, the lower end is positioned at least 200 feet below the waterline.  
     
     
         26 . The method of  claim 25 , wherein the heave resonance of the platform is in the range of about 6 to about 10 seconds.  
     
     
         27 . The method of  claim 25 , wherein the heave resonance of the platform is in the range of about 7 to about 9 seconds.