Subsea Tree Cap Locking Mechanism for ROV Installation
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Solution Overview
Problem
The installation and retrieval of tree caps on subsea tree spools are challenging due to weight and alignment issues, and existing solutions do not effectively secure the cap, prevent fluid trapping, or protect seals during installation.
Innovation Solution
A locking tree cap design featuring deflectable collet fingers, moveable stabs with sealing members, and a secondary locking mechanism, which can be installed and secured using a ROV, includes ports for fluid management and seal testing to address weight, alignment, and fluid trapping problems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a heavy tree cap is used to ensure structural integrity and sealing capability, then the sealing and structural strength are improved, but the ease of installation and retrieval by ROV deteriorates
Solution Approach 1:
The patent applies buoyancy material (foam) integrated into the tree cap structure to counteract the weight of the cap. This allows the tree cap to be installed and retrieved by ROV despite maintaining sufficient structural integrity for sealing and operational purposes. The buoyant material provides upward force that offsets the downward gravitational force on the cap.
2Reliability
If deflectable collet fingers are used to secure the tree cap, then the locking reliability is improved, but the complexity of the locking mechanism increases
Solution Approach 1:
The collet fingers are designed to be deflectable rather than rigid, allowing them to dynamically adapt during the locking process. The fingers deflect outward during installation to accommodate misalignment, then snap inward to engage with recesses in the tree spool, providing reliable locking without requiring complex actuation mechanisms.
3Reliability
If multiple sealing members and stabs are added to secure the tree cap and prevent fluid leakage, then the sealing reliability is improved, but the device complexity increases
Solution Approach 1:
The sealing system is divided into discrete sealing members positioned at different locations (e.g., at the interface between tree cap and tree spool, and within bore openings). Each sealing member is a separate component that can be independently positioned and adjusted, allowing for reliable sealing without requiring a single complex sealing mechanism.
4Object-affected harmful factors
If ports are added to the tree cap for fluid management, then the ability to prevent fluid trapping and enable flushing is improved, but the device complexity increases
Solution Approach 1:
Ports are extracted as separate functional elements from the tree cap structure, allowing fluid to be introduced or removed through dedicated openings. This enables fluid management functions (flushing, bleeding, injecting inhibitors) without requiring complex integrated fluid handling systems within the cap body.
5Manufacturing precision
If alignment features such as funnels and pins are added to the tree spool, then the alignment precision during installation is improved, but the complexity of the tree spool structure increases
Solution Approach 1:
Alignment features such as funnels and pins are pre-formed as integral parts of the tree spool structure during manufacturing. These features guide the tree cap into proper alignment during installation, ensuring precise positioning before the final locking action occurs, without requiring complex active alignment systems.
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 design facilitates easier installation and retrieval, ensures secure locking, prevents fluid-related issues, and protects seals, enhancing operational efficiency and reliability in subsea oil and gas production.
Implementation Method 1
The tree cap may have integral buoyancy to help the underwater transport of the tree cap. For example, a buoyant material such as foam may be attached to reduce the underwater weight of the tree cap.
Implementation Method 2
provide deflectable collet fingers that are adapted to snap into a recess when the tree cap has been landed
Implementation Method 3
The at least one sealing member forms a seal between the at least one stab and the bore when the at least one stab is in the second stab position
Data Source
AI summary
A locking tree cap for use on a subsea tree. The tree cap may be installed and retrieved using a remote operated vehicle. The tree cap may include deflectable collet fingers that lock the tree cap to a tree spool. The deflectable collet fingers may be adapted, such as with enlarged heads, to extend into recesses of the tree spool when the tree cap has been landed on the tree spool. The tree cap may be locked onto a tree spool before energizing sealing members within the bores of the subsea tree, thereby protecting the sealing members from damage during the installation of the tree cap onto the tree spool. The tree cap may include soft landing means such as a plastic cap, on the end of stabs to protect the sealing members as the tree cap is landed. The tree cap may include a secondary locking mechanism used to further secure the tree cap to the tree spool.