Low Profile Internal Tree Cap for Subsea Wellhead Sealing
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Solution Overview
Problem
The installation of subsea tree caps is challenging due to potential damage to seals during the process, requires complex steps for securing and energizing seals, and may result in trapped fluid and corrosion, with conventional tree caps not being suitable for gas lift operations due to fluid pressure issues.
Innovation Solution
A low-profile internal tree cap design with a split latch ring and bulk seal mechanism that allows for secure attachment to a tree spool without energizing seals initially, includes a flow passage for fluid removal and pressure equalization, and features bi-directional metal-to-metal seals for gas lift compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional tree cap installation steps are followed (land, secure, then energize seals), then seal reliability is improved, but installation time and complexity increase
Solution Approach 1:
The patent combines the securing and seal-energizing operations into a single simultaneous action. The tree cap is designed with a bulk seal that is automatically energized when the cap is secured to the tree spool, eliminating the need for separate energizing steps and reducing installation time while maintaining seal reliability
Solution Approach 2:
The bulk seal is pre-positioned and pre-loaded in such a way that it is automatically energized during the securing operation itself. The seal engagement surfaces and loading mechanisms are designed to ensure proper seal activation occurs as part of the initial installation, not as a subsequent step
2Ease of operation
If tree cap projects above tree spool for easy installation, then ease of operation is improved, but obstruction to other equipment increases
Solution Approach 1:
The patent transitions from a protruding tree cap design to a low-profile design where the cap sits substantially flush with the tree spool surface. This dimensional change eliminates obstruction to other equipment while maintaining installation ease through redesigned engagement features and sealing mechanisms that work effectively in the constrained space
3Stress or pressure
If tree cap creates fluid barrier for pressure containment, then pressure control is improved, but trapped fluid causing corrosion increases
Solution Approach 1:
The patent extracts the trapped fluid problem by incorporating drainage features that allow fluid to be removed from the cavity between the tree cap and tree spool. Drain holes or channels are provided that enable fluid to drain away, preventing accumulation and subsequent corrosion of the VX gasket and internal components while maintaining the pressure containment function
4Weight of moving object
If lightweight tree cap material is used, then ease of installation is improved, but susceptibility to fluid trapping and corrosion increases
Solution Approach 1:
The patent converts the potential harm of fluid trapping into a benefit by designing the lightweight cap with integrated drainage features. The same lightweight materials that make installation easier are combined with drainage holes and channels that turn the previously harmful fluid accumulation into a controlled drainage system, allowing fluid to escape and preventing corrosion
Data Source
AI summary
An internal tree cap having a running configuration and a latched configuration to be selectively secured to a tree spool. The tree cap may include an inner sleeve movable between upper and lower positions. The movement of the inner sleeve to the lower position may simultaneously engage a locking profile within the tree spool and energize a sealing element around the exterior of the tree cap. The tree cap may be a low profile tree cap that is flush with the top of the tree spool when installed. The tree cap may provide a collateral beneficial locking means to secure a tubing hanger within the tree spool. A lower housing may be attached to the tree cap to seal on the exterior of the upper neck of the tubing hanger. The tree cap may include a profile to accept a wireline plug.