Wellhead Seal Locking Rings for Thermal Expansion
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Solution Overview
Problem
Existing seal assemblies for casing annuli in wellheads are unreliable due to upward movement of the casing hanger caused by thermal expansion of downhole fluids, which disrupts the sealing process.
Innovation Solution
A seal assembly with radially movable locking rings that axially connect the seal assembly to both the wellhead and the casing hanger, using a running tool to move the locking rings into grooves in the wellhead and hanger, ensuring secure sealing despite axial movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional seal assembly is used to seal the casing annulus, then the sealing structure is simple, but the seal assembly becomes unreliable due to upward movement of the casing hanger caused by thermal expansion
Solution Approach 1:
The seal assembly is divided into multiple functional components: a seal body with sealing elements, and separate locking rings (C-rings) that can independently engage with grooves in the wellhead and casing hanger. This segmentation allows the sealing function and locking function to operate independently, ensuring reliable sealing even when the casing hanger moves axially due to thermal expansion.
Solution Approach 2:
The locking rings are designed to be radially movable between a retracted position and an engaged position. During installation, the running tool actuates the locking rings to move radially outward into the grooves, creating a dynamic locking mechanism that can accommodate axial movement while maintaining the seal's position relative to the wellhead.
2Adaptability or versatility
If the casing hanger is allowed to move axially upward due to thermal expansion, then the system accommodates thermal effects, but the seal assembly can no longer reliably seal the casing annulus at the intended location
Solution Approach 1:
The locking mechanism operates in the radial dimension, while the thermal expansion occurs in the axial dimension. By engaging the locking rings radially into grooves, the seal assembly is constrained in the axial direction without preventing the casing hanger from expanding thermally. This dimensional separation allows the system to accommodate thermal effects while maintaining sealing integrity.
Solution Approach 2:
The locking rings serve as intermediary elements between the seal assembly and the wellhead/casing hanger. These rings transfer and distribute the locking forces, allowing the seal assembly to remain axially fixed relative to the wellhead while the casing hanger can move axially due to thermal expansion. The intermediary locking rings absorb the dimensional changes without compromising the seal.
3Reliability
If locking rings are added to axially connect the seal assembly to the wellhead and casing hanger, then axial connection reliability is improved, but the device complexity increases
Solution Approach 1:
The locking rings serve multiple functions: they provide axial connection between the seal assembly and the wellhead, prevent upward movement of the seal assembly, and can be actuated by a standardized running tool. This multi-functionality reduces the need for additional specialized components, balancing the added complexity with versatile functionality.
Solution Approach 2:
The locking rings are designed to be self-locking once engaged in the grooves. The C-shaped configuration with the open end facing downward allows the rings to automatically lock into position without requiring additional locking mechanisms or complex actuation systems, reducing overall system complexity while maintaining reliable axial connection.
Data Source
AI summary
A seal assembly (30) and a running tool (20) are provided for sealing a casing annulus in a wellhead (14). A casing hanger (12) includes a radially external groove therein, and wellhead has a radially internal groove therein. A locking ring (36) may be actuated by the running tool to move into the internal recess in the wellhead and thereby axially connect the seal assembly and the wellhead. Another locking ring (40) is radially movable to connect the seal assembly to the casing hanger. The seal assembly seals the casing annulus while being interconnected with the wellhead and the casing hanger.