Installation of Subsea Risers

Abstract

A method of installing a subsea riser includes placing an elongate negatively-buoyant support on the seabed and, when laying the riser on the seabed, guiding a riser portion onto the support to extend along and be cradled by the support. A hogbend region of the riser is then formed by conferring positive buoyancy on the support to lift the support and the riser portion away from the seabed. An element of the support includes a riser support disposed in a longitudinally extending open-ended gap between buoyancy volumes disposed on opposite sides of the gap. Coupling formations such as hinge portions can couple the element to a like element. When so coupled, the gaps of those elements align to define an upwardly opening, longitudinally extending groove to receive the riser.

1 - 39 . (canceled) 
     
     
         40 . A method of installing a subsea riser, comprising:
 placing an elongate support on the seabed;   when laying the riser on the seabed, guiding a riser portion onto the support to extend along and be cradled by the support; and   forming a hogbend region of the riser by conferring positive buoyancy on the support to lift the support and the riser portion away from the seabed.   
     
     
         41 . The method of  claim 40 , comprising cradling the riser portion in an upwardly-opening groove formation of the support. 
     
     
         42 . The method of  claim 41 , wherein the riser portion enters the groove formation from above as the riser is being laid. 
     
     
         43 . The method of  claim 41 , comprising holding the riser portion in the groove formation by virtue of gravity and tension acting on the riser against buoyant upthrust acting on the support. 
     
     
         44 . The method of  claim 40 , comprising holding the support against movement along the riser by frictional engagement between the support and the riser portion. 
     
     
         45 . The method of  claim 40 , comprising holding the support against movement along the riser by mechanical engagement between the support and the riser portion. 
     
     
         46 . The method of  claim 45 , comprising attaching one or more engagement formations to the riser portion after guiding the riser portion onto the support. 
     
     
         47 . The method of  claim 40 , comprising applying buoyant upthrust to the support on opposite sides of the riser portion when conferring positive buoyancy on the support. 
     
     
         48 . The method of  claim 47 , wherein the buoyant upthrust is applied to the support substantially equally on the opposite sides of the riser portion. 
     
     
         49 . The method of  claim 47 , wherein the buoyant upthrust acts through centres of buoyancy on the opposite sides of the riser portion, which centres of buoyancy are above a centre of gravity of the riser portion. 
     
     
         50 . The method of  claim 47 , comprising conferring positive buoyancy substantially simultaneously on the opposite sides of the riser portion. 
     
     
         51 . The method of  claim 50 , comprising removing ballast from the support on the opposite sides of the riser portion. 
     
     
         52 . The method of  claim 51 , comprising distributing a deballasting fluid between the opposite sides of the riser portion. 
     
     
         53 . The method of  claim 52 , comprising introducing a flow of the deballasting fluid into the support through an inlet and then dividing the flow between the opposite sides of the riser portion. 
     
     
         54 . The method of  claim 40 , comprising bending the support along its length to conform to curvature of the hogbend region. 
     
     
         55 . The method of  claim 54 , comprising bending the support by pivoting rigid elements of the support relative to each other. 
     
     
         56 . The method of  claim 55 , comprising constraining movement between the elements to pivotal movement about a substantially horizontal pivot axis. 
     
     
         57 . The method of  claim 40 , comprising assembling the support from elements on the seabed. 
     
     
         58 . The method of  claim 40 , comprising laying the riser using a different vessel to that used for placing the support and/or for conferring positive buoyancy on the support. 
     
     
         59 . The method of  claim 58 , wherein the vessel used for placing the support and/or for conferring positive buoyancy on the support is not equipped for laying the riser. 
     
     
         60 . A hogbend support for a subsea riser, the hogbend support comprising at least two hogbend support elements that are coupled end-to-end to allow relative pivotal movement, each support element comprising:
 a riser support disposed in a longitudinally extending open-ended gap between buoyancy volumes of the support element that are disposed on opposite sides of the gap; and   coupling formations on at least one end of the support element for coupling the support element to a like support element to allow relative pivotal movement between the coupled support elements, so that the gaps of those coupled support elements align to define an upwardly opening, longitudinally extending groove.   
     
     
         61 . The support of  claim 60 , wherein the buoyancy volumes are substantially symmetrical about an upright longitudinal plane that extends along the riser support. 
     
     
         62 . The support of  claim 60 , wherein each buoyancy volume has a centre of buoyancy at a level above a base of the riser support. 
     
     
         63 . The support of  claim 60 , wherein the riser support is suspended between the buoyancy volumes. 
     
     
         64 . The support of  claim 63 , wherein the riser support is defined by a band that extends sinuously across the gap between the buoyancy volumes. 
     
     
         65 . The support of  claim 60 , wherein the riser support is formed integrally with the buoyancy volumes. 
     
     
         66 . The support of  claim 60 , wherein the riser support has downwardly converging walls. 
     
     
         67 . The support of  claim 66 , wherein the walls of the riser support are at an angle of from 50° to 80° to the horizontal. 
     
     
         68 . The support of  claim 60 , wherein the coupling formations are arranged for hinged connection to complementary coupling formations of a like support element. 
     
     
         69 . The support of  claim 60 , wherein each support element further comprises an inlet for deballasting fluid, in fluid communication with both of the buoyancy volumes. 
     
     
         70 . The support of  claim 69 , wherein each support element further comprises a manifold between the inlet and the buoyancy volumes for distributing an incoming flow of the deballasting fluid. 
     
     
         71 . The support of  claim 60 , wherein the buoyancy volumes of each support element are separate from each other. 
     
     
         72 . The support of  claim 60 , wherein the buoyancy volumes of each support element are conjoined with each other. 
     
     
         73 . The support of  claim 60 , wherein the buoyancy volumes of each support element are in fluid communication with each other. 
     
     
         74 . The support of  claim 60 , wherein buoyancy volumes of different support elements are in fluid communication with each other. 
     
     
         75 . A subsea riser made by the method of  claim 40 . 
     
     
         76 . The riser of  claim 75 , being of wave configuration. 
     
     
         77 . The riser of  claim 76 , being of lazy-wave configuration. 
     
     
         78 . A subsea riser incorporating the support of  claim 60  positioned under a hogbend region of the riser. 
     
     
         79 . The riser of  claim 78 , being of wave configuration. 
     
     
         80 . The riser of  claim 79 , being of lazy-wave configuration.