Flexible catenary riser having distributed sag bend ballast

Abstract

The present disclosure relates to a subsea catenary and a method of distributing ballast on a pipe. The subsea catenary includes a flexible pipe, and a selected amount of ballast attached to the flexible pipe, in which the ballast is distributed in a wave pattern on a sag bend of the subsea catenary. The method includes identifying a position of a sag bend in a flexible pipe of the subsea catenary, and applying ballast in a wave distribution along the subsea pipe at the identified position.

1 . A subsea catenary, comprising:
 a flexible pipe, and   a selected amount of ballast attached to the flexible pipe,   wherein the ballast is distributed in a wave pattern on a sag bend of the subsea catenary.   
     
     
         2 . The subsea catenary of  claim 1 , wherein the wave pattern comprises half-wave segments of ballast and half-wave segments of bare pipe. 
     
     
         3 . The subsea catenary of  claim 2 , wherein the wave pattern comprises at least three half-wave segments of ballast and at least three half-wave segments of bare pipe. 
     
     
         4 . The subsea catenary of  claim 1 , wherein the wave pattern is determined by dynamic riser analysis. 
     
     
         5 . The subsea catenary of  claim 1 , wherein wave segments of the wave pattern are of uniform length. 
     
     
         6 . The subsea catenary of  claim 1 , wherein wave segments of the wave pattern are of varying weight. 
     
     
         7 . The subsea catenary of  claim 1 , further comprising a selected amount of buoyancy modules attached to the flexible pipe, wherein the buoyancy modules are distributed in the wave pattern on the sag bend of the subsea catenary. 
     
     
         8 . The subsea catenary of  claim 1 , wherein the wave pattern comprises partial-wave segments of ballast and partial-wave segments of bare pipe. 
     
     
         9 . A method to apply ballast weight to a subsea catenary, the method comprising:
 identifying a position of a sag bend in a flexible pipe of the subsea catenary; and   applying ballast in a wave distribution along the subsea pipe at the identified position.   
     
     
         10 . The method of  claim 9 , wherein the wave distribution comprises half-wave segments of ballast and half-wave segments of bare pipe. 
     
     
         11 . The method of  claim 10 , wherein the wave distribution comprises at least three half-wave segments of ballast and at least three half-wave segments of bare pipe. 
     
     
         12 . The method of  claim 9 , further comprising modeling an optimum wave distribution of ballast. 
     
     
         13 . The method of  claim 12 , wherein the applying the ballast in a wave distribution is according the optimum wave distribution. 
     
     
         14 . The method of  claim 9 , further comprising applying buoyancy modules in the wave distribution. 
     
     
         15 . The subsea catenary of  claim 1  wherein the flexible pipe comprises composite flexible pipe. 
     
     
         16 . The subsea catenary of  claim 1  wherein the subsea catenary comprises a riser. 
     
     
         17 . The subsea catenary of  claim 1  wherein the subsea catenary is installed in a water depth greater than 500 meters and the subsea catenary is hanging from a floating production vessel. 
     
     
         18 . The method of  claim 9 , wherein the flexible pipe comprises composite flexible pipe. 
     
     
         19 . The method of  claim 9 , wherein the subsea catenary comprises a riser. 
     
     
         20 . The method of  claim 9 , wherein the subsea catenary is installed in a water depth greater than 500 meters and the subsea catenary is hanging from a floating production vessel.