Method of offshore platform construction using a tension-moored barge

Abstract

A method of installing an integrated deck onto an offshore platform substructure. The integrated deck is held by a support structure on a barge and transported to a preinstalled offshore platform substructure which is adapted to receive the barge and allow aligning of the integrated deck with the substructure for mating operations. Once the barge is positioned within the substructure, tethers are connected between the barge and anchoring foundation elements to moor the barge. Then the tethers are tensioned to minimize both vertical movement and lateral movement caused by wave action. Mating of the integrated deck and the substructure proceeds while tension loads in the tethers are maintained.

We claim: 
     
       1. A method of installing an integrated deck onto an offshore platform substructure having a slot in an upper end thereof for receiving a barge carrying said integrated deck, comprising the steps of: (a) positioning said barge within said slot in said offshore platform substructure such that said integrated deck is approximately aligned with said offshore platform substructure;   (b) installing a plurality of tethers between said barge and a plurality of foundation elements;   (c) tensioning said tethers such that said barge is maintained at a deeper draft than would be provided by the buoyancy of said barge alone;   (d) lowering said integrated deck to contact said offshore platform substructure; and   (e) ballasting said barge to assist in transferring the weight of said deck onto said offshore platform substructure.   
     
     
       2. The method of claim 1, wherein said method further comprises the steps of: (f) disconnecting said integrated deck from said barge;   (g) disconnecting said tethers from said barge; and   (h) removing said barge from said slot in said offshore platform substructure.   
     
     
       3. The method of claim 1, wherein said step (b) is replaced with the step of: (b) installing a plurality of tethers between said barge and a plurality of anchor piles driven into the seafloor.   
     
     
       4. The method of claim 1, wherein said step (b) is replaced with the step of: (b) installing a plurality of tethers between said barge and a plurality of tether base structures incorporated into said offshore platform substructure.   
     
     
       5. The method of claim 1, wherein said tethers are tensioned by deballasting said barge. 
     
     
       6. The method of claim 1, where said tethers are tensioned by jacking against said barge. 
     
     
       7. The method of claim 1, wherein said integrated deck structure is lowered onto said offshore platform substructure by simultaneous ballasting of said barge and jacking of said tethers against said barge. 
     
     
       8. The method of claim 1, wherein said integrated deck structure is supported on said barge by a deck-to-barge support system and is lowered by lowering means incorporated into the deck-to-barge support system. 
     
     
       9. The method of claim 1, wherein said integrated deck structure is supported on said barge by a deck-to-barge support system and is lowered by a plurality of sand jacks incorporated into the deck-to-barge support system. 
     
     
       10. The method of claim 1, wherein said integrated deck structure is supported on said barge by a deck-to-barge support system and is lowered by a plurality of hydraulic jacks incorporated into the deck-to-barge support system. 
     
     
       11. A method of installing an integrated deck onto an offshore platform substructure, comprising a steel jacket substructure anchored to the seafloor, and having a slot in an upper end thereof for receiving a barge carrying said integrated deck, said method comprising the steps of: (a) positioning said barge within said slot in said offshore platform substructure such that said integrated deck is approximately aligned with said offshore platform substructure;   (b) installing a plurality of tethers between said barge and a plurality of foundation elements;   (c) tensioning said tethers such that said barge is maintained at a deeper draft than would be provided by the buoyancy of said barge alone;   (d) lowering said integrated deck to contact said offshore platform substructure; and   (e) ballasting said barge to assist in transferring the weight of said deck onto said offshore platform substructure.   
     
     
       12. A method of installing an integrated deck onto an offshore platform substructure, comprising a gravity base substructure resting on the seafloor, and having a slot in an upper end thereof for receiving a barge carrying said integrated deck, said method comprising the steps of: (a) positioning said barge within said slot in said offshore platform substructure such that said integrated deck is approximately aligned with said offshore platform substructure;   (b) installing a plurality of tethers between said barge and a plurality foundation elements;   (c) tensioning said tethers such that said barge is maintained at a deeper draft than would be provided by the buoyancy of said barge alone;   (d) lowering said integrated deck to contact said offshore platform substructure; and   (e) ballasting said barge to assist in transferring the weight of said deck onto said offshore platform substructure.   
     
     
       13. A method of installing an integrated deck onto an offshore platform substructure, comprising a tension leg platform substructure tension-moored to the seafloor, and having a slot in an upper end thereof for receiving a barge carrying said integrated deck, said method comprising the steps of: (a) positioning said barge within said slot in said offshore platform substructure such that said integrated deck is approximately aligned with said offshore platform substructure;   (b) installing a plurality of tethers between said barge and a plurality of foundation elements;   (c) tensioning said tethers such that said barge is maintained at a deeper draft than would be provided by the buoyancy of said barge alone;   (d) lowering said integrated deck to contact said offshore platform substructure; and   (e) ballasting said barge to assist in transferring the weight of said deck onto said offshore platform substructure.   
     
     
       14. A method of installing an integrated deck onto an offshore platform substructure having a slot in an upper end thereof for receiving a barge carrying said integrated deck, comprising the steps of: (a) positioning said barge within said slot in said offshore platform substructure such that said integrated deck is approximately aligned with said offshore platform substructure;   (b) installing a plurality of tethers between said barge and a plurality of foundation elements;   (c) tensioning said tethers such that said barge is maintained at a deeper draft than would be provided by the buoyancy of said barge alone;   (d) lowering said integrated deck to contact said offshore platform substructure;   (e) transferring the weight of said deck onto said offshore platform substructure; and   (f) removing said barge from said slot in said offshore platform substructure.   
     
     
       15. The method of claim 14, wherein step (f) comprises: (a) disconnecting said integrated deck from said barge; and   (b) disconnecting said tethers from said barge.