Rotational Locking Backup Rings for Downhole Seal Extrusion

The backup ring is divided into an inner backup ring and an outer backup ring that work together. The inner backup ring has slots that receive the elastomeric seal, while the outer backup ring has flanges that overlap with the inner ring's slots. This segmentation allows each ring to perform a specific function, with the inner ring providing primary support and the outer ring preventing extrusion through overlapping flanges, thereby improving reliability without excessive complexity.

The inner backup ring is nested within the outer backup ring, creating a concentric arrangement. The inner ring fits inside the outer ring's internal diameter, allowing the elastomeric seal to be received by the inner ring's slots while the outer ring's flanges provide additional extrusion prevention. This nesting approach maximizes space utilization and improves extrusion resistance while maintaining a compact design.

The backup rings are designed to be expandable rather than fixed. The inner backup ring can expand radially to maintain contact with the elastomeric seal, and the outer backup ring's flanges can expand to overlap with the inner ring's slots. This dynamic expansion capability allows the backup rings to adapt to different operating conditions and maintain effective extrusion prevention throughout multiple operational cycles.

The backup rings utilize radial expansion as an additional dimension of control. By expanding in the radial direction, the inner ring's slots can accommodate the elastomeric seal more effectively, and the outer ring's flanges can overlap with these slots to prevent extrusion. This radial dimension adds a new degree of freedom for extrusion prevention without significantly increasing axial or circumferential complexity.

The inner and outer backup rings are designed with asymmetric features that enable rotational locking. The inner ring has slots at specific angular positions, and the outer ring has flanges that correspond to these slot positions. When expanded, the flanges naturally align with and lock into the slots, preventing relative rotation between the rings. This asymmetric design provides automatic rotational locking without requiring additional complex locking mechanisms.

The rotational locking function is achieved through the inherent geometry of the slots and flanges themselves. When the backup rings expand, the flanges of the outer ring automatically engage with the slots of the inner ring, creating a self-locking mechanism that prevents extrusion gaps. This self-service approach eliminates the need for separate locking components or complex assembly procedures.