Wellhead Seal Lock Preventing Thermal Backout
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In hydrocarbon production wells, thermal expansion and cyclic loads cause the seal energizing ring to back out of the seal pocket, leading to leaks due to the lack of a self-locking feature in metal-to-metal seals, which compromises the integrity of the annulus seal.
Innovation Solution
A system that transfers the load from the inner wellhead member to the wellhead housing through a U-shaped metal-to-metal seal, utilizing a lock energizing ring and an independent lock ring to retain the seal energizing ring in place, thereby maintaining the seal integrity under thermal expansion and pressure loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal-to-metal seal with U-shaped cross section is used, then the seal can withstand high pressure loads, but the seal lacks self-locking feature and allows thermal expansion to back out the energizing ring
Solution Approach 1:
The seal assembly is divided into separate functional components: the U-shaped seal body, the energizing ring, and the lock ring. This segmentation allows each component to perform its specific function - the seal body provides pressure containment, the energizing ring maintains sealing force, and the lock ring prevents thermal backout, resolving the contradiction between pressure strength and seal integrity.
Solution Approach 2:
The lock ring acts as an intermediary component between the energizing ring and the seal pocket. It mediates the thermal expansion forces by providing a dedicated locking interface that prevents the energizing ring from backing out, while not interfering with the pressure sealing function of the U-shaped seal body.
2Force
If the inner wellhead member is secured with slips, then the member can be held in place, but thermal expansion causes the member to lift upwards and back the energizing ring out
Solution Approach 1:
The lock ring is pre-installed on the energizing ring before the seal assembly is placed in the seal pocket. This preliminary action ensures that when thermal expansion occurs, the energizing ring is already constrained and cannot back out, maintaining position stability despite the upward lift force from thermal expansion.
Solution Approach 2:
The solution addresses the vertical displacement problem by adding a radial constraint through the lock ring. The lock ring engages with the energizing ring in a radial direction, preventing axial backout caused by thermal expansion in the vertical dimension, thus stabilizing the seal assembly against multi-directional forces.
3Adaptability or versatility
If cyclic loads and pressures are applied, then the seal operates under realistic conditions, but the energizing ring backs away from the annulus seal causing leaks
Solution Approach 1:
The lock ring provides preliminary anti-action by pre-constraining the energizing ring against the seal pocket. This prevents the harmful backing out motion before it can occur during cyclic loading operations, maintaining seal effectiveness under varying pressure and load conditions.
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 effectively prevents the seal energizing ring from backing out, ensuring the seal integrity is retained, even under thermal expansion and cyclic loads, thus preventing leaks and maintaining the seal's effectiveness.
Implementation Method 1
A seal energizing ring is pressed into the seal pocket to force the legs apart and into sealing engagement with the bore and with the exterior of the casing hanger
Implementation Method 2
During operations, thermal expansion of the inner wellhead member can cause the upper end of the inner wellhead member to lift upwards
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A wellhead assembly (10) includes an outer wellhead member (12), the outer wellhead member having a locking profile (15) on an inner surface. An inner tubular wellhead member (16) lands within the outer wellhead member, defining a seal pocket (22) between the inner tubular wellhead member and the outer wellhead member. A seal ring (30) is located in the seal pocket. A seal energizing ring (46) urges the seal ring into sealing engagement with the outer wellhead member and the inner tubular wellhead member. An annular lock ring (62) is carried with the seal energizing ring and engages the locking profile. A lock energizing ring (52) retains the annular lock ring in engagement with the locking profile.