Subsea Riser Buoyancy Support for Lazy-Wave Hogbend Installation
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Solution Overview
Problem
The installation of subsea risers, particularly lazy-wave risers, is hindered by the complexity and cost of attaching buoyancy modules, which requires multiple workers and expensive vessels, and is prone to delays and risks due to sea dynamics and vessel movements.
Innovation Solution
A method involving a buoyant support structure with pivotable elements and deballasting to lift the riser portion away from the seabed, allowing for the formation of a hogbend region without the need for extensive surface-based assembly or expensive vessels, using a low-cost vessel to deploy and deballast the support elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If buoyancy modules are attached to the riser using conventional methods, then the hogbend can be formed and supported, but the installation process becomes complex, expensive, and time-consuming requiring multiple workers and expensive vessels
Solution Approach 1:
The buoyancy support system is divided into multiple discrete buoyancy modules that can be independently attached to the riser at different locations. Each module can be installed separately using simplified procedures, reducing the overall complexity of the installation process while maintaining reliable hogbend support.
Solution Approach 2:
A temporary support structure or positioning device is used as an intermediary during installation to hold the riser in the correct position while buoyancy modules are being attached. This mediator facilitates the installation process without requiring complex vessel operations or multiple workers simultaneously.
2Reliability
If buoyancy modules are attached using conventional methods, then the riser can be supported at the hogbend, but the installation is prone to delays and risks due to sea dynamics and vessel movements
Solution Approach 1:
Buoyancy modules are pre-assembled and pre-positioned on the riser before deployment to the installation site. This preliminary preparation reduces the time required during actual installation and minimizes the window of exposure to sea dynamics and vessel movement risks.
Solution Approach 2:
The buoyancy modules are designed to be self-attaching or self-positioning on the riser, reducing the need for complex manual assembly operations during installation. This self-service capability minimizes installation time and reduces risks associated with worker safety and vessel stability during the attachment process.
3Reliability
If conventional installation methods are used, then buoyancy modules can be attached to form the hogbend, but expensive vessels and multiple workers are required increasing project cost
Solution Approach 1:
The buoyancy modules are designed as simple, lightweight components that can be attached using basic tools and equipment rather than expensive specialized vessels. The modules themselves are relatively simple structures that can be manufactured and installed cost-effectively, reducing overall project expenditure while maintaining reliable hogbend formation.
Solution Approach 2:
The complex and expensive vessel operations are extracted from the installation process. The buoyancy modules are designed to be installed using simpler, more cost-effective methods that do not require expensive specialized vessels, thereby reducing project costs while maintaining the ability to form and support the hogbend.
4Ease of manufacture
If a free-hanging catenary riser configuration is used, then installation is simple and least expensive, but top tension is high and the riser is susceptible to damage from vessel motion
Solution Approach 1:
Buoyancy modules are attached to the riser to provide an upward buoyant force that counteracts the downward gravitational force and reduces top tension. This counterweight effect of buoyancy allows the riser to maintain a simpler installation configuration while improving durability by reducing stress and susceptibility to damage from vessel motion.
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 method simplifies the installation of subsea risers by reducing the need for expensive vessels and minimizing delays, enabling efficient installation of buoyancy modules and reducing operational risks, while allowing for the use of lower-cost vessels and eliminating the requirement for deadweight, thus improving project operability and reducing costs.
Implementation Method 1
A method involving a buoyant support structure with pivotable elements and deballasting to lift the riser portion away from the seabed
Data Source
Figure 1a~1c
Figure 1d~1f
Figure 2~3
AI summary
A method of installing a subsea riser comprises 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 comprises 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.