Subsea Running Tool Emergency Release Mechanism
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Solution Overview
Problem
Subsea well operations face challenges in retrieving casing strings or pipes due to frictional and suction effects, making it difficult to disconnect the rig or vessel from the wellhead, especially in deteriorating weather conditions, which can lead to hardware damage and increased crew danger.
Innovation Solution
A running tool with a redundant emergency release mechanism, featuring a hollow mandrel and moveable dogs, where a transition part is releasably attached to a first part using shearable members or a split ring, allowing separation under predetermined pressure, enabling safe disconnection by applying pressure within the mandrel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the running tool is mechanically connected to the wellhead for stable insertion, then the reliability of component insertion is improved, but the ease of operation for disconnection deteriorates when frictional and suction effects prevent retrieval
Solution Approach 1:
The mandrel is divided into separate parts (first part and transition part) that can detach from each other. The transition part can separate from the first part under predetermined pressure, allowing the dogs to be released from the wellhead without requiring direct manual intervention on the stuck component.
Solution Approach 2:
The transition part acts as an intermediary between the first part of the mandrel and the dogs. It transmits pressure from the bore to release the dogs from engagement with the wellhead, mediating the force transmission to achieve disconnection.
2Strength
If the dogs are firmly engaged with the wellhead to hold the casing string, then the strength of connection is improved, but the ease of operation for emergency release deteriorates
Solution Approach 1:
The system changes the pressure parameter within the mandrel to trigger release. When pressure exceeds a predetermined threshold, the transition part separates from the first part, automatically releasing the dogs from their engaged state without requiring mechanical manipulation.
Solution Approach 2:
The mechanical system for releasing dogs is replaced with a pressure-actuated system. Instead of using mechanical keys or external tools to disengage the dogs, the invention uses fluid pressure transmitted through the mandrel to automatically trigger the release mechanism.
3Strength
If the transition part is securely attached to the first part to maintain structural integrity, then the strength of the mandrel is improved, but the reliability of emergency release deteriorates
Solution Approach 1:
The attachment means between the transition part and first part are designed with predetermined shear strength that will fail under emergency pressure conditions. This preliminary design ensures that under normal operation the mandrel maintains structural integrity, but under emergency conditions the attachment automatically fails to enable release.
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
Enables safe and controlled disconnection of the running tool from the wellhead, mitigating the risks of damage and crew safety by allowing release of the locking dogs and transition part under increased pressure, ensuring operational safety during adverse conditions.
Implementation Method 1
The means which respond may comprise a shearable member or assembly which has a shear strength selected so that it shears to allow release of the transition part from the first part in response to a predetermined pressure within the mandrel.
Implementation Method 2
Alternatively the means may comprise a split ring which in an expanded state locks the transition part to the first part but is arranged to be compressed radially, to allow release of the transition part from the part in response to a sufficient bore pressure.
Implementation Method 3
During subsea completion operations it is very difficult, and often practically impossible, to recover a casing string or pipe once it has been run into a well, owing to frictional and suction effects acting on the outer wall of the casing string or pipe.
Implementation Method 4
During subsea completion operations it is very difficult, and often practically impossible, to recover a casing string or pipe once it has been run into a well, owing to frictional and suction effects acting on the outer wall of the casing string or pipe.
Data Source
AI summary
A running tool for use in the insertion of an object such as a casing hanger into a subsea well includes a body and a hollow mandrel moveable within the body. Engagement dogs are supported within the body and are moveable to engage the object, the mandrel having a first part and a transition part, the transition part being shaped to cause out-ward movement of the dogs when the mandrel is in a given position within the body and to allow movement of the dogs for position of the mandrel spaced form the given position. The tool has an emergency release feature wherein the transition part is releasably attached to the first part by shear pins which shear in response to a sufficient increase in pressure within the mandrel to allow the transition part to separate from the first part.