Subsea Tethering System for BOP Fatigue Resistance
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Solution Overview
Problem
Subsea blowout preventers, wellheads, and primary conductors face challenges in strength and fatigue performance due to cyclical loads from riser vibrations and environmental factors, which can compromise the integrity of subsea wells.
Innovation Solution
A tethering system is implemented, comprising anchors, pile top assemblies, and flexible tension members that apply tensile loads to the subsea blowout preventer, wellhead, and primary conductor, thereby resisting lateral loads and bending moments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If subsea BOP, wellhead, and primary conductor are installed without tethering, then device complexity is reduced, but strength and fatigue resistance deteriorate under cyclical loads from riser vibrations and environmental factors
Solution Approach 1:
The tethering system is divided into separate functional components: anchors positioned on the sea floor, flexible tension members connecting anchors to the subsea structure, and tensioning devices for applying and maintaining tension. This segmentation allows each component to be optimized independently and facilitates installation and maintenance operations.
Solution Approach 2:
The tethering system applies counteracting tensile forces through the flexible tension members to balance the cyclical loads from riser vibrations and environmental factors. The anchors provide counterweight-like resistance to lateral movements and bending moments, stabilizing the subsea structure against dynamic loads.
2Force
If anchors and flexible tension members are deployed to tether the subsea structure, then lateral load resistance improves, but ease of operation deteriorates due to complex installation and tensioning procedures
Solution Approach 1:
The flexible tension members are designed to dynamically accommodate lateral movements and vibrations of the subsea structure while maintaining tension. The flexibility allows the system to adapt to changing operational conditions without requiring complex adjustment mechanisms, simplifying operation while maintaining force resistance.
Solution Approach 2:
The flexible tension members act as intermediaries between the fixed anchors and the moving subsea structure, transferring and distributing lateral loads. This intermediary function allows the system to achieve complex force resistance characteristics through relatively simple anchor and tension member components.
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
The tethering system enhances the strength and fatigue resistance of subsea blowout preventers, wellheads, and primary conductors, stabilizing these components against lateral movements and bending moments, thus maintaining the integrity of subsea wells.
Implementation Method 1
flexible tension members that apply tensile loads to the subsea blowout preventer, wellhead, and primary conductor, thereby resisting lateral loads and bending moments
Data Source
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AI summary
A tethering system includes an adapter configured to couple to an upper end of a subsea anchor, a tensioning system, and a flexible tension member having one end coupled to the tensioning system and the other end coupled to the adapter. The tensioning system is operable to pay in and pay out the flexible tension member relative to the tensioning system. The tensioning system can be mounted to the BOP frame, and tension can be applied via a locally or remotely placed winch assembly. Tension can also be applied by gripping the flexible tension member and pulling on the flexible tension member with a hydraulic cylinder.