Crawl-down installation method for a tension leg platform

Abstract

A method for installing or removing a tension-leg platform with at least three tendon porches, and its tendons, the method includes grasping each of three or more extended tendons by a respective one jacking tool on one tendon porch, wherein the platform is being stabilized by at least three jacking tools each applying tension on the respective extended tendon. Extended tendons are created by connecting one or more tendon extension piece end-to-end from a tendon.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
         1 . A method for installing or removing tendons and a tension leg platform which comprises three or more tendon porches, the method comprising:
 grasping each of three or more extended tendons by a respective one jacking tool on one tendon porch, wherein the platform is being stabilized by at least three jacking tools each applying tension on the respective extended tendon.   
     
     
         2 . A method for installing tendons and a tension leg platform with three or more tendon porches, the method comprising:
 a) connecting one or more tendon extension pieces to an end of a tendon forming an extended tendon, and placing the extended tendon on a tendon porch, wherein the jacking tool grasps the tendon extension piece; and   b) repeating step a) for at least three tendons; and   c) when each of three or more extended tendons have been placed within a respective jacking tool on a respective tendon porch, three or more of the jacking tools crawl down the one more tendon extension pieces of the extended tendon placed therein to tension the respective extended tendon while lowering the platform to submerge the tendon porches below a water surface.   
     
     
         3 . The method of  claim 2 , wherein the tendon extension piece is a rigid pipe section. 
     
     
         4 . The method of  claim 2 , further comprising adding ballast to the tension leg platform while the jacking tools are lowering the platform. 
     
     
         5 . The method of  claim 2 , wherein the platform comprises a primary ballast tank and an installation ballast tank, the method further comprising filling the primary ballast tank before the installation ballast tank. 
     
     
         6 . The method of  claim 5 , further comprising removing ballast from the installation ballast tank after the platform is at the installation depth. 
     
     
         7 . The method of  claim 2 , comprising towing the platform to the installation site in a waterplane stabilized condition. 
     
     
         8 . The method of  claim 2 , wherein a sum of lengths of the tendon and the one or more tendon extension pieces is equal to or greater than a depth from a tendon anchor to the water surface. 
     
     
         9 . The method of  claim 2 , while the platform is floating on the surface of the water, the tendon is connected to a first pipe section forming an extended tendon, the jacking tool then lowers the extended tendon, and a second pipe section is connected to an upper end of the first pipe section while in the jacking tool, and lowered, and subsequent pipe sections are connected and lowered in series until a length of the extended tendon is equal to or greater than a depth from a tendon anchor to the surface of the water. 
     
     
         10 . The method of  claim 9 , further comprising attaching a bottom end of the tendon to an anchor and using the jacking tool to apply tension on the extended tendon while the jacking tool crawls down the pipe sections. 
     
     
         11 . The method of  claim 10 , further comprising, using the jacking tool to lower the platform to the installation depth, and removing a pipe section after the jacking tool has crawled below a connection between adjacent pipe sections. 
     
     
         12 . The method of  claim 2 , further comprising monitoring a tension of the extended tendon during lowering of the platform. 
     
     
         13 . A method for installing tendons and a tension leg platform with three or more tendon porches, the method comprising:
 a) connecting a tendon extension piece to an end of a tendon to form an extended tendon;   b) placing the extended tendon on a tendon porch, wherein the jacking tool grasps the tendon extension piece;   c) the jacking tool crawls up the tendon extension piece, and tendon extension pieces are added to the extended tendon in series until a length of the extended tendon is sufficient to attach the tendon to an anchor;   d) for each of at least three tendons, steps a) through c) are performed;   e) after each of the at least three tendons has been attached to a respective anchor, each jacking tool crawls down the series of tendon extension pieces connected thereto to lower the platform; and   f) after lowering the platform to the installation draft, each of the tendons is locked to the respective one of the tendon porches.   
     
     
         14 . A method for removing tendons and a tension leg platform with three or more tendon porches, the method comprising:
 a) installing a jacking tool on at least three tendon porches;   b) connecting one or more tendon extension pieces to an end of a tendon to create an extended tendon;   c) repeating step b) for at least three tendons;   d) grasping the tendon extension pieces of each of three or more extended tendons by a respective one jacking tool on one tendon porch,   e) unlocking each of the tendons from the respective tendon porches;   f) wherein the platform is being stabilized by at least three jacking tools each applying tension on the respective extended tendon; and   g) three or more of the jacking tools crawl up the one more tendon extension pieces of the extended tendon placed therein while the platform rises.   
     
     
         15 . A method for removing tendons and a tension leg platform with at least three tendon porches, the method comprising:
 a) installing a jacking tool on at least three tendon porches;   b) connecting one or more tendon extension pieces to an end of a tendon to create an extended tendon;   c) repeating step b) for at least three tendons;   d) three or more of the jacking tools crawl up the tendon extension piece of each extended tendon while the platform rises, and tendon extension pieces are continually added to each of the extended tendons until a length of extended tendon is sufficient for the platform to reach the surface of the water.   
     
     
         16 . The method of  claim 15 , further comprising disconnecting an extended tendon from a respective anchor, and the jacking tool crawls down the tendon extension piece thereby raising the disconnected extended tendon. 
     
     
         17 . The method of  claim 16 , further comprising disconnecting a tendon extension piece of the disconnected extended tendon after the jacking tool passes by a connection between two tendon extension pieces. 
     
     
         18 . The method of  claim 15 , further comprising adding ballast to the platform to reduce pre-tension to avoid overloading the jacking tools and extended tendons. 
     
     
         19 . The method of  claim 15 , further comprising removing ballast from the platform to allow the platform to rise. 
     
     
         20 . The method of  claim 18 , further comprising monitoring a tension of the tendon during removing the ballast from the platform.