Longitudinal Positioning Tool for Rod String Wear Distribution
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Solution Overview
Problem
The existing systems for downhole equipment, such as downhole pumps, face wear issues due to the rod string contacting the tubing string at various elevations, leading to uneven wear distribution and potential failure.
Innovation Solution
A positioning tool is introduced that allows for the longitudinal adjustment of the rod string relative to the tubing string, using a mechanism with sliding tubular mandrels, actuators, and seals to maintain a sealed connection while allowing for the redistribution of wear points, and includes a secondary seal for containment in case of primary seal failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rod string is fixed at a single longitudinal position relative to the tubing string, then the drive head can rotate the rod string efficiently, but the rod string causes concentrated wear at specific contact points on the tubing string
Solution Approach 1:
The positioning tool incorporates a movable inner mandrel that can slide longitudinally within the outer mandrel, allowing the rod string position to be dynamically adjusted. This dynamic positioning capability enables redistribution of wear points along the tubing string while maintaining rotational efficiency, resolving the contradiction between fixed-position rotation and wear distribution.
Solution Approach 2:
The system changes the longitudinal position parameter of the rod string relative to the tubing string by actuating the inner mandrel to different positions. This parameter adjustment allows wear to be distributed across multiple locations along the tubing string, extending its operational life while maintaining the rotational function.
2Reliability
If the rod string longitudinal position is adjusted to redistribute wear, then tubing string life is extended, but the positioning mechanism adds device complexity
Solution Approach 1:
The positioning tool uses a nested structure where the inner mandrel is positioned within the outer mandrel. This nesting approach allows the positioning mechanism to be compact and integrated within the existing rod string assembly, minimizing additional complexity while providing the required adjustment capability.
Solution Approach 2:
The positioning tool acts as an intermediary device between the drive head and the rod string, providing the adjustment function without requiring modification of the existing components. This mediator approach adds functionality while maintaining compatibility with the existing system architecture.
3Reliability
If a seal is used to maintain sealed connection between moving mandrels, then sealing reliability is improved, but the seal may fail and require well shutdown for repairs
Solution Approach 1:
The system incorporates a backup seal arrangement that provides protective cushioning against seal failure. If the primary seal fails, the backup seal prevents catastrophic failure and allows continued operation, cushioning the impact of seal failure and avoiding well shutdown for repairs.
Data Source
AI summary
A rod positioning tool mounts in series between a tubing string and the stuffing box of a drive head. An outer mandrel of the tool mounts to a first flange at the bottom end for connection to the tubing string below and an inner mandral mounts to a second flange for connection to the stuffing box above. The inner mandrel is slidably received within the outer mandrel with primary seals therebetween to vary the overall length of the tool using one or more actuators between the flanges, while maintaining a sealed connection between the tubing string and the stuffing box. Keys on the outer tubular mandrel are longitudinally slidable in keyways on the inner tubular mandrel to resist relative rotation between the mandrels. A secondary seal provides a sealed connection between the second flange and the top end of the outer mandrel in a fully retracted position of the tool.