Deepwater disconnectable turret system with improved riser configuration

Patent metadata

Field	Value
Publication number	US-9797203-B2
Application number	US-201414889048-A
Country	US
Kind code	B2
Filing date	Apr 28, 2014
Priority date	May 6, 2013
Publication date	Oct 24, 2017
Grant date	Oct 24, 2017

Abstract

A system for transporting hydrocarbons from reserves located under the sea floor to a turret connected to a hydrocarbon production vessel floating at the sea surface, the hydrocarbons being transferred through at least one rigid catenary riser extending from the sea floor to a buoy, the system for transporting hydrocarbons includes an upper section of the at least one substantially rigid riser directly attached to the buoy and provided with fairings, a middle section of the rigid riser is provided with buoyancy modules so to give it a lazy wave shape and a lower section of the substantially rigid riser is in contact with the seafloor at a distance X from the buoy vertical axis that is smaller than a distance Y between the buoy vertical axis and the mooring lines anchoring elements.

First claim

The invention claimed is:

1. A system ( 1 ) for transporting hydrocarbons from reserves located under the sea floor ( 2 ) to a turret ( 3 ) that is rotatably connected to a hydrocarbon production vessel that is floating at the sea surface, comprising at least one substantially rigid catenary riser ( 4 ) extending from the sea floor ( 2 ) for transport of said hydrocarbons to the turret, said system comprising:
three or more groups of mooring lines equally spaced apart, each group of mooring lines containing at least two individual mooring lines with polyester rope parts, the mooring lines each comprising two chain parts at the end, a polyester part between the chain parts and a spring buoy, wherein the lower ends of the mooring lines are anchored to the sea floor,
said groups of mooring lines having open sectors therebetween in which the at least one substantially rigid catenary riser ( 4 ) is located, wherein the substantially rigid catenary riser ( 4 ) and the grouped mooring lines have upper ends connected to and supported by one buoy ( 6 ) which is adapted to be connected to and disconnected from the lower part of the turret ( 3 ), wherein said buoy, when connected to the turret, is partially accommodated within the turret and held in position with respect to the turret by one or more structural connectors ( 14 ),
the upper part of the buoy being provided with a fluid connector that is in fluid connection with the upper end of the substantially rigid catenary riser ( 4 ) connector, for attachment to the fluid transfer system of the turret ( 3 ) to allow said transfer of hydrocarbons from the seabed to the production vessel, the buoy having a buoyancy such that when disconnected from the turret ( 3 ), the buoy with attached substantially rigid riser ( 4 ) and grouped mooring lines floats below the wave active zone in the upper half part of the water-depth, wherein,
groups of the substantially rigid risers are connected to the lower part of the buoy ( 6 ),
an upper section of each of the substantially rigid risers ( 4 ) is directly attached to the buoy,
a middle section of each substantially rigid riser ( 4 ) is provided with buoyancy modules ( 8 ) so to give each substantially rigid riser ( 4 ) a lazy wave shape, and a lower section of each of the substantially rigid risers ( 4 ) is in contact with the sea floor at a radial distance X from the buoy vertical axis that is smaller than the radial distance Y between the buoy vertical axis and the location wherein the lower ends of the mooring lines are anchored to the sea floor, and
the lazy wave shape of the substantially rigid riser is located below sea level.

2. The system for transporting hydrocarbons according to claim 1 , wherein the height of the lazy wave riser ( 4 ) is between 80% and 100% of the radial distance X.

3. The system for transporting hydrocarbons according to claim 1 , wherein a lower part of the lazy wave riser ( 4 ) is placed horizontally on the sea floor and can be at one end lifted off from the sea floor while the other end stays connected to the sea floor.

4. The system for transporting hydrocarbons according to claim 1 , wherein the fluid transfer system comprises at least one lazy wave production riser ( 4 ) for transfer of hydrocarbons from a reserve to the vessel, at least one lazy wave riser ( 4 ) for exporting the produced gas from the vessel via a subsea pipeline and at least one lazy wave riser ( 4 ) for injection of water into a sub sea floor hydrocarbon reserve.

5. The system for transporting hydrocarbons according to claim 1 , wherein the departure angle at the buoy of the mooring line is less than 60 degrees, preferably less than 45 degrees, more preferably less than 30 degrees with the vertical when the buoy is connected to the vessel.

6. The system for transporting hydrocarbons according to claim 1 , wherein the buoy with attached substantially rigid riser ( 4 ) and grouped mooring lines floats below the wave active zone in the upper quarter part of the water-depth.

7. The system for transporting hydrocarbons according to claim 1 , wherein the height of the lazy wave riser ( 4 ) is between 100% and 300% of the radial distance X.

8. The system for transporting hydrocarbons according to claim 1 , wherein, with the buoy connected to the vessel, the lazy wave risers ( 4 ) and mooring system combined allow the vessel a maximal offset of 8% of the water depth.

Assignees

• Single Buoy Moorings

Inventors

• Cao Peimin
• Lavagna Philippe

Classifications

• E21B17/012 Primary

  with buoyancy elements (E21B17/015 takes precedence) · CPC title

• E21B17/015

  Non-vertical risers, e.g. articulated or catenary-type · CPC title

• B63B21/508 Primary

  connected to submerged buoy (mooring buoys per se B63B22/02) · CPC title

• B63B22/24

  container type, i.e. having provision for the storage of material · CPC title

• E21B19/004

  supporting a riser from a drilling or production platform · CPC title