Cellular tendons for tlp

Abstract

Tendon systems described herein may include a cellular tendon main body system having at least two essentially parallel pipe strings and may be used to moor a floating structure to a seabed. Hybrid tendon systems may include one or more tendon modules, where at least one tendon module includes a cellular tendon main body system. Where more than one module is used, the modules may be different types or designs of tendon systems, such as conventional single-string tendon or cellular tendon, according to the performance requirements of the module. Cellular tendon main body systems described herein enable the overall tendon, and subsequently the floating structure, to be used in ultra-deep waters and/or with heavy topsides.

What is claimed: 
     
         1 . A tendon system, comprising:
 a top tendon section configured to attach to a floating structure;   a tendon bottom section configured to attach to a foundation;   an upper transition unit connected to the top tendon section;   a bottom transition unit connected to the tendon bottom section; and   one or more tendon modules disposed intermediate the upper and bottom transition units, at least one tendon module including a tendon main body system comprising at least two pipe strings connected proximate their upper ends to a first module transition unit, which can be the same or different than the upper transition unit, and proximate their bottom ends to a second module transition unit, which can be the same or different than the bottom transition unit.   
     
     
         2 . The tendon system according to  claim 1 , comprising one tendon module disposed intermediate the upper and bottom transition units, the tendon module including a tendon main body system comprising at least two pipe strings connected proximate their upper ends to the upper transition unit and proximate their bottom ends to the bottom transition unit. 
     
     
         3 . The tendon system according to  claim 1 , comprising two or more tendon modules, including an upper tendon module, a lowermost tendon module, and optionally one or more intermediate tendon modules. 
     
     
         4 . The tendon system of  claim 3 , wherein the lowermost tendon module includes a tendon main body system comprising at least two pipe strings connected proximate their upper ends to a module transition unit and proximate their bottom ends to the bottom transition unit. 
     
     
         5 . The tendon system of  claim 3 , further comprising one or more intermediate tendon modules, comprising:
 the upper tendon module including the top tendon section configured to attach to the floating structure and a lower tendon section configured to attach to one of the intermediate tendon modules;   the intermediate tendon modules:
 attached at their upper ends via an upper transition unit to the lower tendon section of the upper tendon module; 
 attached at their lower ends via a lower transition unit to an upper tendon section of an axially lower tendon module; 
   the lowermost tendon module:
 attached at its upper end to a lower tendon section of an axially higher tendon module; 
 attached at its lower end via the bottom transition unit to the foundation. 
   
     
     
         6 . The tendon system of  claim 1 , wherein the pipe strings are connected to the upper and bottom transition units such that the pipe strings are mechanically coupled. 
     
     
         7 . The tendon system of  claim 1 , wherein the pipe strings are formed from steel, composite, or aluminum. 
     
     
         8 . The tendon system of  claim 1 , the tendon main body system further comprising one or more centralizers disposed along a length of the pipe strings. 
     
     
         9 . The tendon system of  claim 8 , the centralizers configured to space the pipe strings and mechanically couple the pipe strings. 
     
     
         10 . The tendon system of  claim 1 , the tendon main body system further comprising one or more buoyancy modules disposed around at least a portion of the pipe strings. 
     
     
         11 . The tendon system of  claim 1 , the tendon main body system further comprising a buoyancy arrest collar connected to the pipe strings. 
     
     
         12 . The tendon system of  claim 1 , the tendon main body system further comprising one or more guide frames disposed along a length of the pipe strings. 
     
     
         13 . The tendon system of  claim 1 , wherein each of the pipe strings are substantially parallel to each other. 
     
     
         14 . The tendon system of  claim 3 , wherein one or more of the tendon modules comprises a single-string type tendon. 
     
     
         15 . The tendon system of  claim 3 , wherein the upper tendon module comprises a cellular tendon. 
     
     
         16 . A tension leg platform moored to a seabed using a tendon system as claimed in  claim 1 . 
     
     
         17 . A method of mooring a floating structure, comprising:
 transporting a tendon system according to  claim 1  from an onshore assembly location to an offshore location;   submerging the tendon system;   connecting the tendon system to a foundation; and   connecting the tendon system to the floating structure.   
     
     
         18 . The method of mooring a floating structure of  claim 17 , the tendon system comprising two or more tendon modules, including an upper tendon module, a lowermost tendon module, and optionally one or more intermediate tendon modules, the method comprising:
 submerging the lowermost tendon module;   connecting the lowermost tendon module to the foundation;   submerging an upper tendon module;   connecting the upper tendon module to a lower tendon module; and   connecting the upper tendon module to the floating structure.   
     
     
         19 . The method of mooring a floating structure of  claim 17 , wherein the tendon modules of the tendon system are fully assembled onshore prior to transport. 
     
     
         20 . The method of mooring a floating structure of  claim 18 , wherein the upper and lower modules of the tendon system are connected offshore prior to submerging. 
     
     
         21 . A method of assembling a tendon system, comprising:
 assembling a tendon main body section comprising two or more pipe strings;   axially connecting the top and bottom ends of the two or more pipe strings to a tendon top segment and a tendon bottom segment, respectively.   
     
     
         22 . The method of  claim 21 , further comprising:
 disposing an upper transition unit intermediate the top end of the two or more pipe strings and the tendon top segment; and   disposing a bottom transition unit intermediate the bottom end of the two or more pipe strings and the tendon bottom segment.   
     
     
         23 . The method of  claim 21 , further comprising
 terminating the tendon bottom segment with a connector assembly; and   terminating the tendon top segment with a connector assembly.   
     
     
         24 . The method of  claim 21 , wherein assembling the tendon main body system comprises axially connecting two or more pipe segments to form a pipe string. 
     
     
         25 . The method of  claim 24 , the assembling the tendon main body system further comprising spacing apart the two or more pipe segments or the two or more pipe strings using at least one of a guide frame, a buoyancy module, and a centralizer. 
     
     
         26 . The method of  claim 21 , further comprising disposing a bulkhead in at least one of the two or more pipe strings, the tendon top segment, and the tendon bottom segment. 
     
     
         27 . The method of  claim 21 , further comprising disposing a buoyancy arrest collar in at least one of the two or more pipe strings, the tendon top segment, and the tendon bottom segment.