Riser tensioning system

Abstract

A riser tensioning system for providing a tensioning to a riser connected to a floating installation via a tension ring. The riser tensioning system includes at least one riser tensioner assembly. Each of the at least one riser tensioner assembly includes a riser tensioning cylinder comprising a cylinder rod, at least one sheave, and a wireline with a first end and a second end. The first end is fixed to the tension ring, and the second end is fixed to the cylinder rod. The wireline extends between the tension ring and the cylinder piston via the at least one sheave.

What is claimed is: 
     
       1. A floating installation comprising:
 a riser tensioning system for providing a tensioning to a riser connected to the floating installation via a tension ring, the riser tensioning system comprising:
 at least one riser tensioner assembly, each of the at least one riser tensioner assembly comprising,
 a riser tensioning cylinder comprising a cylinder rod which is configured to work in tension, 
 at least one sheave, and 
 a wireline comprising a first end and a second end, the first end being fixed to the tension ring, and the second end being fixed to the cylinder rod, the wireline being configured to extend between the tension ring and the cylinder piston via the at least one sheave; 
 
 
 a moon pool; and 
 a base structure configured to extend at least partly around the moon pool and below a waterline, 
 wherein, 
 the riser tensioning cylinder of the at least one riser tensioner assembly is arranged in the base structure of the floating installation, and 
 the riser tensioning cylinder is positioned in the base structure at least partly below the waterline. 
 
     
     
       2. The floating installation as recited in  claim 1 , wherein the at least one sheave is, during a use, configured to be pivotable around an axis which is parallel to the riser. 
     
     
       3. The floating installation as recited in  claim 1 , wherein,
 the wireline comprises a wireline diameter, 
 at least one of the at least one sheave comprises a sheave diameter, and 
 a ratio between the wireline diameter and the sheave diameter is at least 30. 
 
     
     
       4. The floating installation as recited in  claim 1 , wherein the at least one riser tensioner assembly comprises 4, 6, 8 or 10 riser tensioner assemblies. 
     
     
       5. The floating installation as recited in  claim 1 , further comprising:
 a physical boundary that at least partly covers the riser tensioning cylinder of the at least one riser tensioner assembly, the physical boundary being configured to at least partly block any direct exposure of ambient water onto the riser tensioning cylinder during a use. 
 
     
     
       6. The floating installation as recited in  claim 5 , wherein the riser tensioning system further comprises:
 at least one guide element configured to guide the cylinder rod in a linear direction. 
 
     
     
       7. The floating installation as recited in  claim 6 , wherein the at least one guide element is fixed to the physical boundary. 
     
     
       8. The floating installation as recited in  claim 5 , wherein,
 the moon pool comprises walls, and 
 the physical boundary also comprises the walls of the moon pool. 
 
     
     
       9. The floating installation as recited in  claim 1 , further comprising:
 a drill floor; and 
 a deck, 
 wherein, 
 the riser tensioning cylinder of the at least one riser tensioner assembly is arranged below the drill floor and the deck of the floating installation. 
 
     
     
       10. The floating installation as recited in  claim 1 , wherein the floating installation is a drilling vessel. 
     
     
       11. A floating installation comprising:
 a riser tensioning system for providing a tensioning to a riser connected to a floating installation via a tension ring, the riser tensioning system comprising:
 at least one riser tensioner assembly, each of the at least one riser tensioner assembly comprising,
 a riser tensioning cylinder comprising a cylinder rod which is configured to work in tension, 
 at least one first sheave fixed to the cylinder rod, 
 at least one second sheave, and 
 a wireline comprising a first end and a second end, the first end being fixed to the tension ring, and the second end being fixed to the floating installation, the wireline being configured to extend between the tension ring and the cylinder piston via at least one of the at least one first sheave and the at least one second sheave; 
 
 
 a moon pool; 
 a base structure configured to extend at least partly around the moon pool and below a waterline; and 
 a wall arranged in the base structure above the riser tensioning cylinder, the wall being configured to at least partly cover the riser tensioning cylinder so as to protect the riser tensioning cylinder from exposure to seawater, 
 wherein, 
 the riser tensioning cylinder of the at least one riser tensioner assembly is arranged in the base structure of the floating installation, and 
 the riser tensioning cylinder is positioned in the base structure at least partly below the waterline. 
 
     
     
       12. The floating installation as recited in  claim 11 , wherein the at least one second sheave, during a use, is configured to be pivotable around an axis which is parallel to the riser. 
     
     
       13. The floating installation as recited in  claim 11 , wherein,
 the wireline comprises a wireline diameter, 
 at least one of the at least one first sheave and the at least one second sheave comprises a sheave diameter, and 
 a ratio between the wireline diameter and the sheave diameter is at least 30. 
 
     
     
       14. The floating installation system as recited in  claim 11 , wherein the at least one riser tensioner assembly comprises 4, 6, 8 or 10 riser tensioner assemblies. 
     
     
       15. The floating installation as recited in  claim 11 , further comprising:
 a physical boundary that at least partly covers the riser tensioning cylinder of the at least one riser tensioner assembly, the physical boundary being configured to at least partly block any direct exposure of ambient water onto the riser tensioning cylinder during a use. 
 
     
     
       16. The floating installation as recited in  claim 15 , wherein the riser tensioning system further comprises:
 at least one guide element configured to guide the cylinder rod in a linear direction. 
 
     
     
       17. The floating installation as recited in  claim 16 , wherein the at least one guide element is fixed to the physical boundary. 
     
     
       18. The floating installation as recited in  claim 15 , wherein,
 the moon pool comprises walls, and 
 the physical boundary also comprises the walls of the moon pool. 
 
     
     
       19. The floating installation as recited in  claim 11 , further comprising:
 a drill floor; and 
 a deck, 
 wherein, 
 the riser tensioning cylinder of the at least one riser tensioner assembly is arranged below the drill floor and the deck of the floating installation. 
 
     
     
       20. The floating installation as recited in  claim 11 , wherein the floating installation is a drilling vessel.