Subsea Tree Cap Wedge Seal System for ROV Deployment
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Solution Overview
Problem
Current subsea sealing systems, particularly those using elastomeric seals, lack durability and reliability in extreme temperature, pressure, and chemical environments, and metal sealing systems require significant external forces or complex tools for effective sealing, making them impractical for deep well installations and difficult to deploy with remote-operated vehicles (ROVs).
Innovation Solution
A tree cap wedge seal system that employs an annular cage member with a cam element and hydraulic actuation to compress an annular seal against an actuation member, using hydraulic fluid pressure to create a pressure barrier, and includes a locking mechanism and accumulator for maintaining seal energization, allowing for reliable sealing in extreme conditions and easy deployment by ROVs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If elastomeric seals are used to seal subsea equipment, then ease of manufacture and installation are improved, but durability and reliability under extreme temperature, pressure, and chemical conditions deteriorate
Solution Approach 1:
The patent changes the material parameter from elastomeric to metal (specifically Inconel 625), fundamentally altering the seal's ability to withstand extreme conditions. This material substitution enables the seal to maintain reliability under high temperature, pressure, and chemical exposure while remaining manufacturable through processes like laser welding and precision machining.
Solution Approach 2:
The invention employs composite construction by combining Inconel 625 metal seal with stainless steel tree cap components, creating a hybrid system that leverages the corrosion resistance and strength of Inconel 625 while maintaining compatibility with standard stainless steel wellhead equipment. This composite approach optimizes both reliability and manufacturability.
2Reliability
If metal seals are used to withstand extreme conditions, then reliability is improved, but device complexity and weight increase due to required energizing mechanisms
Solution Approach 1:
The metal seal is designed to be self-energizing through a wedge-shaped geometry that converts the closing force during tree cap installation directly into sealing pressure. The seal's own deformation under compression creates the necessary contact pressure against the wellhead bore, eliminating the need for external energizing devices, hydraulic systems, or complex actuation mechanisms.
Solution Approach 2:
The seal incorporates a curved, wedge-shaped profile that transforms linear compression force into radial sealing pressure. This geometric curvature enables the seal to automatically generate the necessary contact pressure distribution against the bore surface, simplifying the overall system by eliminating separate energizing components.
3Reliability
If high degree of interference fit is used to create sealing stresses, then reliability is improved, but ease of operation deteriorates due to requirement of significant external load
Solution Approach 1:
The seal design transitions from a static interference fit requiring pre-compression to a dynamic self-energizing system where the seal progressively deforms and generates increasing sealing pressure as the tree cap closes. The wedge geometry converts the closing motion into escalating radial pressure, automatically achieving the necessary interference fit effect without requiring external pre-loading.
4Reliability
If U-shaped metal seals are used for pressure containing, then reliability is improved, but ease of manufacture deteriorates for small tree bores less than five inches
Solution Approach 1:
Instead of using the conventional U-shaped seal that requires complex forming processes for small diameters, the invention inverts the approach by using a solid wedge-shaped metal seal that can be manufactured through simpler processes like bar stock machining or laser cutting. This inverted geometry is inherently more suitable for small bore applications while maintaining pressure containing reliability.
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 system provides a robust, reliable, and adaptable metal sealing solution that can function in extreme environments, seal surfaces with defects, and is easily deployable by ROVs, ensuring effective sealing across various tree bore diameters.
Implementation Method 1
The cam element selectively energizes the annular seal by compressing the annular seal axially against the actuation member to form a pressure barrier in the bore
Implementation Method 2
A hydraulic piston having an actuation surface and a retrieval surface is positioned in a cavity of the housing and configured to move axially in response to application of hydraulic fluid pressure to the actuation and retrieval surfaces
Implementation Method 3
an accumulator to store at least one of hydraulic fluid pressure and gas pressure, and a charge valve in communication with the accumulator to selectively supply at least one of hydraulic fluid pressure and gas pressure to the accumulator
Data Source
AI summary
A tree cap has a wedge type annular metal seal for capping and sealing a subsea tree and associated methods to energize the same. The tree cap includes a cam element having a lower end with a conical profile adapted to be disposed within a respective bore of the subsea tree. The cam element moves along an axis of the bore. The annular metal seal is disposed on an outer diameter of the cam element so that the cam element may compress the annular metal seal against an actuation member to seal the bore of the subsea tree. The tree cap includes a housing adapted to be disposed on and secure to the subsea tree. The housing carries the cam element and exerts an axial force on the cam element to deform the annular metal seal into sealing engagement between the tree cap and the subsea tree.