Marine riser

Abstract

The invention relates to a production riser system wherein the riser ( 1 ), at the touchdown point ( 5 ), has a bottom flexjoint ( 8 ) so that the dynamic motion of the riser ( 1 ) is absorbed by angular excursion ( 9 ) of the flexjoint ( 8 ) and not by the interaction of the sag bend ( 10 ) with the seabed ( 6 ). The surface end of the riser may be fixed, or coupled by a second flexjoint to a production and storage vessel.

1 . A riser system comprising a continuous metallic riser conduit ( 1 ) extending substantially from seabed to surface, to connect a surface installation ( 3 ) to a seabed installation wherein, where the riser reaches the seabed ( 6 ), there is incorporated at least a joint which allows relative angular rotation between the riser conduit and conduit supported by the seabed, so as to fix the point at which the riser reaches the seabed during expected excursions of the surface support position.  
     
     
         2 . A riser system as claimed in  claim 1  wherein the riser is coupled to the surface support by means of a second joint which allows relative angular rotation between the riser and the surface support.  
     
     
         3 . A riser system as claimed in  claim 1  or  2  wherein said riser conduit is made of steel pipe, and follows substantially a catenary path.  
     
     
         4 . A riser system as claimed in  claim 1 ,  2  or  3 , in use as a permanent production system for hydrocarbons.  
     
     
         5 . A riser system as claimed in any preceding claim, wherein said surface support is controlled so as to maintain a minimum horizontal displacement from the relative to the touchdown point.  
     
     
         6 . A riser system as claimed in any preceding claim, wherein the surface support comprises a dynamically positioned vessel.  
     
     
         7 . A riser system as claimed in any preceding claim, wherein the surface support comprises a moored vessel.  
     
     
         8 . A riser system as claimed in any preceding claim, wherein said first joint provides at least two angular degrees of freedom.  
     
     
         9 . A method of controlling the touchdown point of a substantially continuous catenary riser conduit, wherein a joint is incorporated which allows relative angular rotation between the riser and a conduit supported on the seabed.  
     
     
         10 . A method as claimed in  claim 8  wherein the riser conduit is coupled to a surface support by means of a second joint which allows relative angular rotation between the riser conduit and the surface support.  
     
     
         11 . A method as claimed in  claim 8  or  9  wherein said riser conduit is made of steel pipe, and follows substantially a catenary path.  
     
     
         12 . A method as claimed in  claim 8 ,  9  or  10  wherein said riser conduit forms part of a permanent production system for hydrocarbons.  
     
     
         13 . A method as claimed in any of  claims 8  to  11 , wherein the surface support is controlled so as to maintain a minimum horizontal displacement from the relative to the touchdown point.  
     
     
         14 . A method as claimed in any of  claims 8  to  11 , wherein the surface support comprises a dynamically positioned vessel.  
     
     
         15 . A method as claimed in any of  claims 8  to  13 , wherein the surface support comprises a moored vessel.  
     
     
         16 . A method as claimed in any of  claims 8  to  14 , wherein said first joint provides at least two angular degrees of freedom.