Hoisting Cable Wear Mitigation via Ballast Draft Adjustment
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Solution Overview
Problem
Offshore hoisting systems experience significant cable wear and fatigue due to reciprocating motion over high-stress locations, leading to operational disruptions and increased costs when cable replacement is necessary, especially during long-term operations like well testing and workover.
Innovation Solution
The method involves adjusting the ballast system of an offshore vessel to vary its draft, causing a predetermined length of cable to slip through the hoisting system while maintaining a target overpull, thereby repositioning worn sections away from high-stress areas without interrupting operations, using an active heave compensation system to control the drawworks and accommodate vessel motions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If active heave compensation is used to maintain payload position during vessel motions, then payload position stability is improved, but cable wear and fatigue increase due to reciprocating motion over sheaves
Solution Approach 1:
The system proactively manages cable wear by monitoring wear indicators and performing cable replacement before complete failure occurs. The drawworks is controlled to pay out cable at a rate that prevents excessive wear accumulation, replacing cable sections proactively rather than reactively after failure.
Solution Approach 2:
The system changes the operational parameters of the drawworks by controlling it to pay out cable at a specific rate that differs from traditional active heave compensation. This parameter adjustment reduces the reciprocating motion amplitude, thereby reducing cable wear and fatigue while still maintaining payload position stability through coordinated ballast system adjustments.
2Reliability
If cable replacement is performed to address wear and fatigue, then cable reliability is improved, but operational continuity deteriorates due to interruption of hoisting operations
Solution Approach 1:
The system maintains continuous hoisting operations during cable replacement by controlling the drawworks to pay out cable at a rate that keeps the travelling block engaged with the payload. The cable replacement occurs continuously rather than requiring operation shutdown, ensuring uninterrupted productivity while restoring cable reliability.
Solution Approach 2:
The system performs preliminary cable replacement actions before complete cable failure occurs by monitoring wear indicators. This proactive replacement prevents sudden failures that would interrupt operations, maintaining continuous productivity while ensuring cable reliability through preventive maintenance.
3Stability of the object's composition
If traditional active heave compensation controls drawworks to pay in/out cable, then vessel motion compensation is achieved, but cable wear concentrates on specific sections over sheaves
Solution Approach 1:
The system changes the drawworks control parameters by paying out cable at a rate that reduces reciprocating motion amplitude. This parameter modification distributes cable stress more evenly along the cable length rather than concentrating wear at specific sheave contact points, while still achieving vessel motion compensation through ballast system coordination.
Solution Approach 2:
The system dynamically adjusts the cable pay-out rate based on real-time conditions to optimize the distribution of wear along the cable. By making the cable motion more dynamic and less reciprocating, the system reduces localized wear concentration while maintaining the ability to compensate for vessel motions through coordinated ballast adjustments.
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 approach allows for continuous operation while mitigating cable wear and fatigue, reducing the need for frequent cable replacement and associated costs, and improving safety by minimizing personnel intervention during long-term operations.
Implementation Method 1
adjusting a ballast system of an offshore vessel to vary the draft of the vessel
Implementation Method 2
The cable extends from a drawworks and is reeved through one or more pulleys of the crown and travelling blocks, normally with multiple passes to provide a desired mechanical advantage
Data Source
AI summary
A method for mitigating the effects of cable wear in an active heave compensated hoisting system of an offshore vessel in a locked to bottom mode of operation is disclosed. The method comprises supporting an upper end of a string which is connected to a subsea well from a travelling block of the hoisting system, wherein the travelling block is suspended from a crown block via a cable. The method further comprises operating an active heave compensation system to control a drawworks of the hoisting system to pay in and out the cable to compensate for motion of the offshore vessel and maintain a target overpull in the string. The method further comprises adjusting a ballast system of the offshore vessel to vary the draft of the vessel, and controlling the drawworks in accordance with the variation in the draft of the vessel to cause a length of cable to slip through the hoisting system and maintain the target overpull in the string.