Rotor Catch Assembly for Downhole Motor Rotor Retention
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Solution Overview
Problem
Downhole motor stator connections are prone to failure, leading to the loss of components, which causes delays and increased costs due to the need for costly and time-consuming 'fishing' procedures to retrieve lost components.
Innovation Solution
A catch assembly, including a catch basket with an internal shoulder and threaded end, is integrated into the downhole motor assembly to prevent the rotor from exiting the stator tube by interfering with the rotor knob, and is coupled to the saver sub to retain the rotor in case of connection failures between the stator and saver sub.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a catch assembly is added to prevent rotor loss, then reliability is improved, but device complexity increases
Solution Approach 1:
The catch basket is positioned within the stator assembly, and the rotor knob passes through the catch basket to engage the rotor. This nested configuration allows the catch assembly to be integrated into the existing motor structure without requiring separate external components, thereby improving reliability while minimizing the increase in device complexity.
Solution Approach 2:
The catch basket acts as an intermediary component between the stator and rotor. It provides a mechanical interface that prevents rotor loss while allowing normal motor operation. The catch basket with its internal shoulder creates a stopping mechanism that intervenes only when needed (when rotor detachment occurs), thus improving reliability without significantly complicating the overall device.
2Loss of substance
If fishing procedures are used to retrieve lost components, then component recovery is possible, but loss of time increases
Solution Approach 1:
The catch assembly provides preliminary protection against rotor loss before it can occur. By pre-installing the catch basket with the internal shoulder in the stator, the system creates a preventive mechanism that stops the rotor from detaching in the first place. This eliminates the need for subsequent fishing operations, thereby preventing both component loss and the time loss that would result from retrieval operations.
Solution Approach 2:
The catch assembly is installed in advance during motor assembly, preparing the protection mechanism before any potential failure occurs. The rotor knob is designed to pass through the catch basket during normal operation, and the internal shoulder is positioned to automatically engage if the rotor attempts to move beyond its intended position. This preliminary configuration ensures immediate protection without requiring any additional action during failure scenarios.
3Power
If stator connections are made highly loaded to handle drilling forces, then power transmission is improved, but reliability worsens due to connection failure risk
Solution Approach 1:
The catch basket extracts the function of rotor retention from the stator connection system. By separating the power transmission function (handled by the stator connections) from the rotor retention function (handled by the catch basket), the design allows the stator connections to be optimized for power transmission without compromising overall reliability. The catch basket takes on the additional responsibility of preventing rotor loss independently of the connection integrity.
Data Source
AI summary
A catch assembly is provided for a downhole motor assembly of a drilling system. The catch assembly may include a catch basket that may be coupled to a saver sub. The saver sub may be coupled to a stator tube housing a rotor of a downhole motor. The rotor knob may be coupled to the rotor and include a flange that may be positioned in the catch basket. The flange may be positioned uphole of an internal shoulder of the catch basket. Subsequent to a connection failure in or near the stator tube, the flange may engage the internal shoulder of the catch basket to prevent the rotor from falling downhole.