Lazy Wave Riser Buoyancy for Deepwater Disconnection
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Solution Overview
Problem
Existing deepwater hydrocarbon transportation systems, particularly those using hybrid risers, are complex, costly, and require heavy installation vessels, with a need for a cost-effective alternative that ensures the integrity and safe disconnection of components without damage or impact between floating bodies.
Innovation Solution
A system utilizing three or more groups of equally spaced mooring lines with polyester rope parts, a substantially rigid catenary riser supported by a buoy with distributed buoyancy for a lazy wave configuration, and fairings to reduce drag and prevent riser compression, allowing quick and safe connection and disconnection, with the buoyancy ensuring the riser and mooring lines float below the wave active zone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a hybrid riser concept is used for disconnectable FPSO, then the system can be disconnected from the vessel, but the design becomes more complex and requires more hardware
Solution Approach 1:
The riser system is divided into distinct segments: a rigid lower section for structural support and a flexible upper section for motion accommodation. This segmentation allows the system to achieve disconnectable FPSO capability while reducing overall complexity by using standardized components in each segment.
Solution Approach 2:
A flexible intermediary section is introduced between the rigid riser and the floating vessel. This intermediary component absorbs relative motions and enables safe disconnection without requiring complex mechanical coupling mechanisms, thereby reducing system complexity while maintaining adaptability.
2Adaptability or versatility
If a hybrid riser concept is used, then disconnectable FPSO is achieved, but heavy installation vessels are required and CAPEX increases
Solution Approach 1:
The riser system parameters are optimized by changing the material properties and geometric dimensions of the flexible section to reduce its weight and size. This allows the system to maintain disconnectable FPSO capability while reducing the requirements for heavy installation vessels and lowering CAPEX.
Solution Approach 2:
The riser system uses composite construction combining rigid and flexible materials with optimized properties. This composite approach enables achieve disconnectable FPSO capability while reducing the overall system weight and installation requirements, thereby lowering costs.
3Reliability
If the buoy is disconnected from the turret, then the riser and mooring lines can float below the wave active zone, but the payload on the buoy increases
Solution Approach 1:
Buoyancy elements are strategically positioned in the flexible riser section to provide upward counteracting forces. This reduces the net payload on the buoy when disconnected, allowing the riser and mooring lines to float below the wave active zone while maintaining system integrity and reducing buoy payload.
4Adaptability or versatility
If the riser is in a catenary configuration, then it can accommodate vessel motions, but drag forces increase
Solution Approach 1:
The riser system applies different mechanical properties to different sections: the lower section is rigid for structural support, while the upper section is flexible for motion accommodation. This local differentiation reduces drag forces in the flexible section while maintaining motion accommodation capability.
Solution Approach 2:
The flexible riser section is designed with a curved, catenary configuration that optimizes its hydrodynamic properties. This curvature reduces the exposed surface area to wave forces and minimizes drag forces while maintaining the ability to accommodate vessel motions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces the payload on the buoy, minimizes drag, and allows for safe and efficient hydrocarbon transfer with reduced risk of damage during disconnection, enabling faster and safer reconnection while maintaining system integrity, and is designed to handle high pressures and volumes.
Implementation Method 1
the buoy being provided with buoyancy means ensuring that when disconnected from the turret, the buoy with attached substantially rigid riser and grouped mooring lines floats below the wave active zone
Implementation Method 2
fairings to reduce drag and prevent riser compression
Data Source
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AI summary
The invention relates to a system (1) for transporting hydrocarbons from reserves located under the sea floor (2) to a turret (3) connected to a hydrocarbon production vessel floating at the sea surface, the hydrocarbons being transferred through at least one rigid catenary riser (4) extending from the sea floor (2) to a buoy (6), said system for transporting hydrocarbons comprising an upper section of the at least one substantially rigid riser (4) directly attached to the buoy and provided with fairings, a middle section of the rigid riser (4) is provided with buoyancy modules (8) so to give it a lazy wave shape and a lower section of the substantially rigid riser (4) 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 means.