Wellhead Seal Assembly Lockdown and Slotted Arrangement
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Solution Overview
Problem
High pressures and thermal expansion in wellhead assemblies can cause the casing hanger to move axially, compromising the annular seal and leading to leaks, as existing lockdown mechanisms often direct upward forces into the wellhead housing, damaging the sealing ability.
Innovation Solution
A wellhead assembly with a radially expandable annular lockdown member and a casing hanger seal featuring slots in its extension, which reduces axial stiffness and redirects upward forces through the lockdown member into the wellhead housing, thereby enhancing the sealing capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lockdown mechanism is used to prevent axial movement of the casing hanger, then reliability is improved, but the upward forces are directed into the wellhead housing which damages the sealing ability
Solution Approach 1:
The extension is segmented by forming slots through it, dividing the solid extension into multiple sections. This segmentation reduces the axial stiffness of the extension, allowing it to flex and redirect upward forces away from the seal interface while maintaining the lockdown function.
Solution Approach 2:
The axial stiffness parameter of the extension is changed by introducing slots. This parameter change allows the extension to deform under axial load, redirecting forces through a different path that does not compromise the seal between the casing hanger and wellhead housing.
2Strength
If the extension is made rigid to maintain structural integrity, then strength is improved, but axial stiffness increases which directs more upward forces into the wellhead housing
Solution Approach 1:
The extension is divided into sections by slots, creating a segmented structure that maintains overall strength while reducing continuous axial stiffness. The slots allow controlled flexing without compromising the structural integrity of the extension or its connection to the casing hanger.
Solution Approach 2:
The extension combines rigid material with slot openings to create a composite-like structure that has both strength and flexibility. The solid portions maintain structural integrity while the slot regions provide flexibility to reduce axial stiffness and redirect forces.
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 solution effectively reduces axial stiffness and redirects upward forces, improving the sealing ability of the casing hanger by distributing the forces more efficiently, reducing the likelihood of leaks and maintaining a secure seal under high pressures and thermal conditions.
Implementation Method 1
The lockdown member has an upward and inward facing cam surface. The extension on a lower end of the casing hanger seal has a downward and outward facing cam surface that engages the cam surface on the lockdown ring. The cam surface on the seal extension moves the lockdown member to the expanded position while the casing hanger seal is moved into the seal pocket.
Implementation Method 2
A plurality of slots are formed in the extension. The slots have upper and lower sides that are in planes perpendicular to the axis. The slots are axially spaced apart from each other a distance at least equal to a dimension between the upper and lower sides of each of the slots.
Data Source
Figure 1
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AI summary
A wellhead assembly has a casing hanger for supporting a string of casing, the casing hanger having an external upward-facing shoulder. A radially movable annular lockdown member is carried on the shoulder for movement between a retracted position while the casing hanger is being run and an expanded position. In the expanded position, the lockdown member is in engagement with a lockdown profile shoulder in a wellhead housing. A casing hanger seal is carried by the casing hanger above the lockdown member. The casing hanger seal has a lower extension that includes a connection leg and a nose ring. The nose ring has a cam surface that engages and moves the lockdown member to the expanded position while the casing hanger seal is being lowered into a set position. Slots are formed in the extension to reduce the axial stiffness.