Articulated Offshore Drilling Support Strings for Bending Control
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Solution Overview
Problem
Mobile offshore drilling units experience movement relative to the seabed, leading to drill string damage from bending moments and reduced operational safety due to limited safe operating radii, which can result in the need to halt operations or disconnect the drill string.
Innovation Solution
Incorporating an articulated joint in the elongate support string between the mobile offshore drilling unit and the seabed, allowing for the lower portion to maintain a substantially vertical orientation and accommodate misalignment, thereby increasing the safe operating radius and facilitating safer and more efficient drilling operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rigid support string is used to extend between the mobile offshore drilling unit and the seabed, then the structural strength and stability are maintained, but the safe operating radius is limited and the drill string is susceptible to damage from bending moments when the unit moves
Solution Approach 1:
The support string is divided into multiple segments with articulated joints between them, allowing each segment to move independently. This segmentation enables the drill string to accommodate unit movement through joint articulation rather than rigid bending, increasing the safe operating radius while maintaining structural integrity.
Solution Approach 2:
The articulated joints introduce dynamic flexibility to the previously rigid support string. The joints allow rotational movement and articulation, enabling the drill string to adapt to changing positions of the mobile unit without exceeding bending moment limits, thus expanding the safe operating radius.
2Adaptability or versatility
If the mobile offshore drilling unit moves within the safe operating radius, then operational flexibility is improved, but the drill string is affected by continual bending moments that increase the likelihood of damage from low cycle fatigue
Solution Approach 1:
The articulated joints transform the rigid drill string into a dynamic system that can articulate and rotate to accommodate unit movement. This dynamic capability allows the drill string to maintain alignment with the wellbore while the unit moves, eliminating harmful bending moments and enabling greater operational flexibility.
Solution Approach 2:
The articulated joints act as intermediaries between the mobile unit and the seabed wellbore. These joints absorb and accommodate the relative movement through articulation, preventing the transmission of bending moments to the drill string while maintaining the connection between the unit and the wellbore.
3Productivity
If objects are suspended into the sea column beneath the unit during operations, then the drilling capacity is improved, but the speed at which the unit can move through the sea surface is restricted due to the rigid deployment conduit
Solution Approach 1:
The articulated joints enable the suspended objects and drill string to dynamically adjust their position and orientation as the unit moves. This dynamic flexibility allows the unit to transit at higher speeds without causing excessive bending or stress to the suspended objects, thereby increasing both productivity and transit speed.
4Productivity
If the unit moves beyond the safe operating radius, then operational continuity is maintained, but drilling operations must be halted or the drill string disconnected
Solution Approach 1:
The articulated joints provide the drill string with dynamic flexibility to accommodate larger unit displacements. This enables the unit to operate beyond the traditional safe operating radius while maintaining drill string integrity and alignment with the wellbore, ensuring both operational continuity and safety.
Data Source
AI summary
An offshore method includes providing an elongate support string for extending between a mobile offshore drilling unit and a seabed location. The string has an upper portion and a lower portion, and an articulated joint is provided between the upper portion and the lower portion. The provision of the articulated joint maintains the lower portion of the elongate support string in a substantially vertical orientation and increases the safe operating radius of the mobile offshore drilling unit or increases the speed at which the unit may transit through the sea with objects suspended via the elongate support string.