Deep water and ultra deep water mooring system

Abstract

A mooring and flowline system is disclosed for mooring a floating production and/or storage vessel ( 10 ) to the seabed ( 12 ) and one or more flowlines ( 22, 24 ) for connection to one or more producing wells or to a facility. The system comprises at least two anchors in the sea bed ( 12 ) and a respective anchor riser ( 14 ) extending from each of the anchors to a common mooring node member ( 18 ). A mooring pendant ( 20 ) extends from the common mooring node member ( 18 ), where the mooring pendant ( 20 ) has an upper end for connection, in use, to the vessel ( 10 ). Each flowline ( 22, 24 ) comprises a lower flowline ( 22 ) and a flowline riser ( 24 ) extending from the lower flowline ( 22 ) to the vessel ( 10 ). Each flowline riser ( 24 ) has part of its length secured to the mooring pendant ( 20 ) by one or more guide frames ( 32 ) to control sideways and rotational movement. Furthermore, buoyancy is provided on, in-between, for or by at least one of the guide frames ( 32 ), wherein the buoyancy is sufficient to support the common mooring node member ( 18 ) and mooring pendant ( 20 ) below the surface of the sea and above the seabed ( 12 ) when the mooring pendant ( 20 ) is disconnected from the vessel ( 10 ).

1 . A mooring and flowline system comprising:
 means for mooring a floating production and/or storage vessel to the seabed;   one or more flowlines for connection to one or more producing wells or to a facility;   the mooring means comprising at least two anchors in the sea bed and a respective anchor riser extending from each of the anchors, each of the anchor risers having one end secured to its anchor and the other end secured to a common mooring node member;   a mooring pendant extending from the common mooring node member, the mooring pendant having an upper end for connection, in use, to the vessel; each flowline comprising a lower flowline extending from the direction of the well or facility partway toward the vessel into the vicinity of the mooring means, and a flowline riser extending from the lower flowline to the vessel;   wherein each flowline riser has part of its length secured to the mooring pendant by one or more guide frames to control sideways and rotational movement so that, in use, each flowline riser is capable of helixing around the mooring pendant in response to turning of the vessel;   wherein buoyancy means are provided on, in-between, for or by at least one of the one or more guide frames; and,   wherein the buoyancy afforded by the buoyancy means is sufficient to support the common mooring node member and mooring pendant below the surface of the sea and above the seabed when the mooring pendant is disconnected from the floating production and/or storage vessel.   
     
     
         2 . A system according to  claim 1 , wherein the buoyancy means comprises two or more sealed pressure vessels. 
     
     
         3 . A system according to  claim 2 , wherein the buoyancy means comprises between six and twelve sealed pressure vessels. 
     
     
         4 . A system according to  claim 2 , wherein the buoyancy of the one or more sealed pressure vessels can be adjusted to control the position in use, of the common mooring node member and mooring pendant below the surface of the sea and above the seabed, when the mooring pendant is disconnected from the floating production and/or storage vessel. 
     
     
         5 . A system according to  claim 2 , wherein the mooring and flowline system is arranged such that when the mooring pendant is connected to the floating production and/or storage vessel, in use, at least one of the sealed pressure vessels is located above the surface of the sea and at least one of the sealed pressure vessels is located below the surface of the sea. 
     
     
         6 . A system according to  claim 2 , wherein one or more of the sealed pressure vessels support the mooring pendant when disconnected from the floating production and/or storage vessel. 
     
     
         7 . A system according to  claim 2 , wherein the sealed pressure vessels are filled with air or foam. 
     
     
         8 . A system according to  claim 1 , wherein the buoyancy means are distributed along the length of the mooring pendant. 
     
     
         9 . A system according to  claims 8 , wherein the buoyancy means are distributed between the common mooring node member and the upper end of the mooring pendant for connection to the vessel. 
     
     
         10 . A system according to  claim 8 , wherein the buoyancy means are distributed equi-distant along the length of the mooring pendant. 
     
     
         11 . A system according to  claim 1 , wherein further buoyancy means is provided for, on or by the mooring means and/or the anchor risers. 
     
     
         12 . A system according to  claim 1  adapted for operation at depths between 1000 and 1500 m of water. 
     
     
         13 . A system according to  claim 1  adapted for disconnection to be made without the need to lower the system into the water using a winch. 
     
     
         14 . A system according to  claim 1 , comprising a riser jumper which provides fluid communication between each riser tower and the floating production and/or storage vessel. 
     
     
         15 . A system according to  claim 14 , wherein each riser jumper is a continuous conduit with a single axial rotational coupling, located between the uppermost guide frame and a riser jumper hang-off point on the vessel. 
     
     
         16 . A system according to  claim 11  wherein the further buoyancy comprises buoyancy tanks. 
     
     
         17 . A system according to  claim 16 , wherein the buoyancy tanks support a connection between the riser tower and the riser jumper at a depth of 150 m. 
     
     
         18 . A system according to  claim 16 , wherein the buoyancy tanks pull on the connection via 20 m of chain. 
     
     
         19 . A system according to  claim 1  comprising at least three anchors in an angular array. 
     
     
         20 . A system according to  claim 19 , comprising three anchors at mutual 120° spacing. 
     
     
         21 . A system according to  claim 20 , wherein the anchors are arranged to point north, south-west and south-east. 
     
     
         22 . A system according to  claim 1 , wherein the common mooring node member is a plain ring, shackle or plate. 
     
     
         23 . A system according to  claim 1 , wherein the production vessel is a tanker 
     
     
         24 . A system according to  claim 1 , wherein the anchor risers are chains between 120 and 147 mm in diameter of Grade R3 higher strength material. 
     
     
         25 . A system according to  claim 1 , wherein the mooring pendant comprises a chafe chain which is 147 mm in diameter of Grade R3 or higher strength material. 
     
     
         26 . (canceled)