Safety Joint Moveable Seal Prevents Hydraulic Lock
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Solution Overview
Problem
Downhole safety joints face hydraulic lock issues due to trapped wellbore fluid between seals, leading to reduced tightening torque and accidental disconnection when reengaged in a downhole environment, with existing solutions either compromising thread protection or seal integrity.
Innovation Solution
A safety joint design featuring a moveable seal with a spring and sealing member, such as an O-ring and extrusion ring, that maintains a constant volume between seals, preventing hydraulic lock by allowing the seal to travel in a groove and compressing the spring to balance fluid pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two seals are installed on both sides of the threaded connection to prevent washout and fluid loss, then thread protection and fluid sealing are improved, but hydraulic lock occurs during reengagement due to trapped wellbore fluid compression
Solution Approach 1:
The second seal is designed as a moveable seal that can shift axially within the box end. During reengagement, as the pin end axially moves into the box end, the moveable seal travels axially to maintain a constant volume between the two seals, preventing fluid compression and hydraulic lock while maintaining thread protection
Solution Approach 2:
A spring is introduced as an intermediary element between the moveable seal and the box end shoulder. The spring provides a yieldable connection that allows the seal to move axially in response to fluid pressure changes during engagement, absorbing pressure variations and preventing hydraulic lock
2Ease of operation
If both seals are removed to prevent hydraulic lock, then reengagement is improved, but thread washout and fluid loss occur
Solution Approach 1:
The moveable seal design allows one seal to remain in place for thread protection while eliminating hydraulic lock. The seal's ability to move axially maintains constant fluid volume between seals, preventing pressure buildup that would otherwise require seal removal
3Ease of operation
If one seal is removed to prevent hydraulic lock, then reengagement is improved, but thread corrosion and reduced thread life occur
Solution Approach 1:
The moveable seal maintains thread protection by remaining in place while preventing hydraulic lock through its axial movement capability. This eliminates the need to remove seals, thereby preserving thread life and preventing corrosion
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
Ensures reliable reconnection and disconnection of safety joints downhole without hydraulic lock, maintaining seal integrity and preventing thread washout, while minimizing pressure increase and corrosion risks.
Implementation Method 1
a moveable seal with a spring and sealing member, such as an O-ring and extrusion ring, that maintains a constant volume between seals, preventing hydraulic lock by allowing the seal to travel in a groove and compressing the spring to balance fluid pressure
Data Source
AI summary
Provided is a safety joint with a moveable seal designed to prevent hydrostatic locking. The safety joint is primarily made up assembling a pin end having a first seal, a threaded connection, and a second, moveable seal to a box end. The moveable seal is disposed in a recess formed in the pin end and includes an O-ring and a spring. When the safety joint is assembled downhole, a volume of fluid may become trapped between the first seal and the second seal. The trapped fluid in turn pushes the O-ring towards the spring, thereby limiting pressure build-up by substantially maintaining the volume trapped between the first and second seals.