Radially Expandable Stop Collar for Cement Seal Integrity
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Solution Overview
Problem
Existing systems for mounting stop collars and tool assemblies on liners in oil and gas wells face challenges in ensuring a complete and continuous cement seal, particularly in deviated wells where centralizers may not maintain adequate clearance and lead to voids or thin cement portions, allowing fluid migration.
Innovation Solution
The development of a collar system with radially expandable gripping members that engage the tubular member through opposing thrust surfaces, allowing for secure frictional engagement without penetrating or creating electrolytic contact, and incorporating mechanisms to prevent loosening of threaded connections, such as pawls and detents or set screws, to ensure stable centralization and sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional stop collars are used to limit centralizer movement, then centralizer positioning is achieved, but the cement seal becomes discontinuous with voids or thin portions allowing fluid migration
Solution Approach 1:
The stop collar incorporates a radially expandable gripping member that transitions from a compressed state during installation to an expanded state for securing the centralizer. This dynamic expansion allows the collar to adapt to the tubular member diameter while maintaining a secure grip, preventing centralizer movement without creating cement seal discontinuities
Solution Approach 2:
The gripping member changes its radial dimension through compression and expansion. During installation, it is compressed to allow passage over the tubular member, then expands to engage the tubular member surface and prevent centralizer movement. This parameter change enables effective positioning while maintaining cement seal integrity
2Object-affected harmful factors
If the gripping member expands radially inward to engage the tubular member, then frictional engagement is achieved without penetration, but electrolytic contact may occur between dissimilar metals
Solution Approach 1:
The gripping member acts as an intermediary element between the stop collar and the tubular member. It provides frictional engagement through radial expansion while the collar's threaded connection serves as a mediator to secure the assembly without direct metal-to-metal contact, thereby preventing electrolytic corrosion
Solution Approach 2:
The invention replaces direct mechanical engagement (metal-to-metal contact) with frictional engagement through the expandable gripping member. The threaded connection provides mechanical security without requiring the gripping member to penetrate or create electrolytic contact with the tubular member
3Reliability
If threaded connections are used to secure the collar, then adjustable positioning is achieved, but the connections may loosen under downhole conditions
Solution Approach 1:
The connection system is segmented into two functional parts: threaded connections for adjustable positioning and locking mechanisms (pawls and detents or set screws) for preventing loosening. This segmentation allows each component to perform its specific function effectively while maintaining overall system reliability
Solution Approach 2:
The locking mechanisms (pawls and detents or set screws) are designed to prevent loosening of the threaded connection before it can occur under downhole conditions. The pawls engage with detents to block rotational movement, while set screws mechanically prevent the threaded connection from backing out, thereby preemptively counteracting loosening 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
This solution enhances the formation of a continuous cement sheath around the liner, reducing fluid migration and improving the stability of centralizers by providing a secure, non-corrosive, and non-penetrating grip, thus maintaining effective sealing and preventing electrolytic corrosion.
Implementation Method 1
The members may be drawn laterally together to cause the thrust surfaces to bear on the gripping member. As the thrust surfaces bear on the gripping member that will expand it radially inward into frictional engagement with the tubular member
Data Source
AI summary
Stop collars may be fixedly mounted on a liner or other tubular member. The stop collar comprises a first sleeve and a second sleeve. The sleeves are adapted to extend around the outer circumference of the tubular member and are engaged by threaded connections. The sleeves provide opposing inner thrust surfaces. The collar further comprises a radially expandable gripping member disposed between the opposing thrust surfaces. The sleeves may be drawn together by rotation about the threaded connection to cause the thrust surfaces to bear on the gripping member and expand the gripping member radially inward into frictional engagement with the tubular member.