Production riser with pre-formed curves for accommodating vessel motion

Abstract

A system for establishing fluid communication between a floating body and a wellhead on the seafloor includes a rigid, self-tensioning riser for fluidly connecting the floating body and the wellhead. The riser defines a major axis extending from the floating body to the wellhead. The riser is formed with a series of pre-formed curves that absorb and release energy in response to the heave and surge of the floating-body by flexing in a direction essentially parallel to the major axis. The series of curves may be in a single plane (e.g., sinusoidal), or in multiple planes (e.g., helical).

I claim:  
     
         1 . A system for establishing a fluid communication between a floating body and a wellhead, the system comprising: 
 a rigid, self-tensioning riser pipe providing fluid communication between the floating body and the wellhead, the riser pipe defining a major axis extending from the floating body to the wellhead; and    a series of pre-formed curves formed in the riser pipe so as to absorb and release energy in response to the heave and surge of the floating body by flexing in a direction essentially parallel to the major axis.    
     
     
         2 . The system of  claim 1 , wherein the series of pre-formed curves comprises a series of single-planar, pre-formed curves in the riser.  
     
     
         3 . The system of  claim 2 , wherein the series of single-planar curves comprises arcs having a substantially constant radius of curvature.  
     
     
         4 . The system of  claim 2 , wherein the series of single-planar curves comprises sinusoidal shaped curves.  
     
     
         5 . The system of  claim 1 , wherein the series of pre-formed curves comprise a series of multi-planar, pre-formed curves in the riser.  
     
     
         6 . The system of  claim 5 , wherein the series of multi-planar curves comprises form a substantially helical curve.  
     
     
         7 . The system of  claim 6 , wherein the helical curve has a curve spacing and a curve diameter, wherein the curve spacing is at least double the curve diameter.  
     
     
         8 . The system of  claim 6 , wherein the riser has an axial length between the seafloor and the floating body, and wherein the helical curve has a curve spacing that increases along the axial length of the riser with the distance above the seafloor.