Downhole Tool Selective Connection Using Harmonic Drive
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Solution Overview
Problem
Existing downhole safety subs used in oil and gas exploration are prone to accidental disengagement during normal operations, leading to financial losses due to non-production time required for reconnection.
Innovation Solution
A tool with a drive shaft and housing parts that utilize a transmission mechanism, such as a harmonic drive, to selectively connect or disconnect by rotating the drive shaft, causing axial displacement of housing parts, allowing for a predetermined disconnection time to prevent accidental disengagement and facilitate retrieval of stuck components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spring or friction ring stop device is used to maintain bias between mating parts, then the mating parts remain connected during normal operations, but the risk of accidental disengagement increases due to force imbalances
Solution Approach 1:
The patent transitions from a static spring-based stop device to a dynamic transmission mechanism (harmonic drive) that converts rotational motion into controlled axial displacement. The mechanism engages and disengages based on rotational direction and magnitude, providing reliable connection during normal operations while enabling controlled disconnection when needed, thereby reducing accidental disengagement risk.
Solution Approach 2:
The patent changes the operational parameter from force-based (spring pressure) to motion-based (rotational displacement). By requiring a specific number of rotations (e.g., 5-10 turns) to trigger disengagement, the system becomes insensitive to transient force imbalances that could cause accidental disengagement in force-based systems.
2Ease of operation
If the housing parts are directly connected without transmission means, then the disconnection occurs immediately when force is applied, but there is no time for operator intervention to prevent accidental disengagement
Solution Approach 1:
The patent implements preliminary action by requiring multiple rotations (5-10 turns) before actual disengagement occurs. This creates a buffer period during which operators can detect the rotation and intervene to prevent accidental disengagement, while still enabling relatively quick disconnection when intentionally triggered.
Solution Approach 2:
The transmission mechanism (harmonic drive) acts as an intermediary between the rotational input and the axial disconnection action. It mediates the disconnection process by converting rotations into gradual axial displacement, providing time for operator intervention while ensuring eventual disengagement when the threshold is reached.
3Reliability
If a harmonic drive or gear reduction mechanism is used, then the axial displacement occurs over a predetermined time, but the device complexity increases
Solution Approach 1:
The patent replaces complex multi-component mechanical transmission systems with a harmonic drive, which achieves the same function (converting rotation to axial displacement) with fewer parts. The harmonic drive uses a wave generator and flexible spline instead of multiple gears and shafts, reducing complexity while maintaining the predetermined disconnection time function.
4Strength
If the stop device maintains strong bias between mating parts, then the torsional integrity is maintained, but the force required to disengage the parts increases
Solution Approach 1:
The patent transitions from static force maintenance (spring bias) to dynamic force application. During normal operations, the harmonic drive maintains engagement through rotational locking. For disengagement, rotational force is applied in the opposite direction, dynamically overcoming the engagement force without requiring excessive static force, thus reducing the disengagement force requirement while maintaining torsional integrity.
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
The tool provides a fail-safe mechanism that prevents accidental disengagement, allows for controlled disconnection and reconnection of downhole components, and enables retrieval of stuck parts by providing time for operator intervention and reducing friction during the process.
Implementation Method 1
transmission means being arranged to selectively connect or disconnect the housing parts by rotating the drive shaft. Preferably, said transmission means are arranged so that the rotation of said drive shaft causes a longitudinal displacement of one of the housing parts
Implementation Method 2
said transmission means comprises a gear mechanism arranged for selectively transmitting the torque of said drive shaft to one of said housing parts
Data Source
AI summary
The present invention relates to a tool for selectively connecting or disconnecting components of a downhole workstring comprising a drive shaft (3) and a housing couplable to said drive shaft, and housing comprising first and second housing parts (21, 22) releasably connected to one another, transmission means such as a reduction gear mechanism (52-54) coupled to the drive shaft, the transmission means being arranged to selectively connect or disconnect the housing parts by rotating the drive shaft.