Back-Up Ring Sheath Structure for High-Pressure Extrusion Resistance
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Solution Overview
Problem
Conventional back-up ring systems for elastomer elements in downhole tools face issues such as extrusion, limited anti-extrusion coverage, high energy consumption during setting, and reduced sealing performance under high pressure, particularly due to the limitations of foldback rings, 'V' profiled C-Rings, garter springs, and mesh rings.
Innovation Solution
A back-up ring system featuring a '7' shaped cross-sectional profile ring sheath with a blocking segment and angularly offset rupture points, providing enhanced extrusion resistance and stability through a tapered design that minimizes extrusion gaps and maintains sealing performance under high pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional back-up ring systems (foldback rings, V-profiled C-Rings, garter springs, mesh rings) are used, then the elastomer element can be supported, but extrusion occurs and sealing performance is reduced under high pressure
Solution Approach 1:
The back-up ring system is divided into multiple functional segments: an outer C-ring with a first rupture point, an inner C-ring with a second rupture point angularly offset from the first, and a ring sheath with a cut-out region. This segmentation allows each component to perform specific functions in preventing extrusion while managing the forces during setting and operation.
Solution Approach 2:
The inner C-ring is designed with an asymmetric blocking segment that angularly offsets the first and second rupture points. The ring sheath features a '7' shaped cross-sectional profile with a cut-out region that mates with the blocking segment. This asymmetric design creates angularly offset rupture points that work together to prevent extrusion gaps while maintaining structural integrity under high pressure.
2Stress or pressure
If the elastomer element is compressed between metal gauge rings to seal against high pressures, then sealing capability is achieved, but the elastomer element extrudes into the gap without sufficient support
Solution Approach 1:
The back-up ring system is pre-configured with rupture points positioned at angular offsets before the setting operation. During the setting process, as the elastomer element is compressed and expands radially, the rupture points break in a controlled sequence, allowing the back-up rings to expand and lock into position against the wellbore or casing, creating preliminary support structures that prevent extrusion before high pressure sealing is required.
Solution Approach 2:
The solution transitions from considering only radial support to incorporating angular positioning of rupture points. The inner C-ring's blocking segment and the ring sheath's cut-out region create a three-dimensional configuration where rupture points are offset in the angular dimension, preventing the elastomer element from extruding into gaps that would form if rupture points were aligned.
3Reliability
If the back-up ring system is designed to prevent extrusion, then sealing performance is maintained, but the system complexity increases
Solution Approach 1:
The outer C-ring, inner C-ring, and ring sheath are merged into a single integrated back-up ring system that functions as a unified extrusion prevention mechanism. The components are designed to mate together, with the ring sheath's cut-out region fitting onto the inner C-ring's blocking segment, creating a cohesive structure that prevents extrusion while maintaining manageable complexity through functional integration.
Data Source
AI summary
A back-up ring system incudes an outer C-ring, an inner C-ring that mates with the outer C-ring, the inner C-ring including a first rupture port, and a ring sheath that fits onto the inner C-ring, the ring sheath including a cut-out region, and a second rupture point. The inner C-ring further includes a blocking segment that angularly offsets the first and second rupture points. The cut-out region of the ring sheath mates with the blocking segment of the inner C-ring. The ring sheath further incudes a ‘7’ shaped cross-sectional profile.