Multi-Start Thread Formation for Downhole Tool Alignment
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Solution Overview
Problem
Downhole tools with thin-walled core barrels suffer from thread weakening and damage due to excessive drill torque, leading to flaring or belling, which can prevent proper engagement and cause galling, especially when using multi-start threads to increase strength, as incorrect alignment can result in thread damage and separation during drilling operations.
Innovation Solution
A multi-start thread formation with a first thread start operatively rotationally advanced by at least 5°, allowing partial engagement before the second thread engages, and featuring a unique thread start configuration to facilitate alignment and reduce axial force on the shoulder, thereby alleviating flaring or belling damage and preventing galling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If thin-walled core barrels are used to maximize core sample diameter, then core sample diameter increases, but thread strength decreases causing flaring or belling damage
Solution Approach 1:
The thread formation is divided into multiple independent thread starts (first thread, second thread, third thread) that are circumferentially spaced apart. This segmentation allows the threading load to be distributed across multiple discrete engagement points rather than concentrated at a single location, thereby reducing the axial force on each individual thread start and preventing flaring or belling damage to the thin-walled pipe sections.
Solution Approach 2:
The patent transitions from a single-start thread (one-dimensional engagement) to a multi-start thread configuration where multiple thread starts are arranged in the circumferential dimension. This dimensional change enables simultaneous engagement of multiple threads at different circumferential positions, distributing the axial load across multiple thread engagements and reducing the force concentration that causes damage in thin-walled sections.
2Strength
If multi-start threads are used to increase thread strength, then thread strength improves, but alignment precision decreases causing incorrect engagement and galling
Solution Approach 1:
The thread starts are positioned asymmetrically in the circumferential direction at specific angular intervals (e.g., 120 degrees apart for a three-start thread). This asymmetric arrangement creates a predetermined engagement sequence where threads engage in a controlled manner during assembly, guiding proper alignment and preventing incorrect engagement or galling while maintaining the strength benefits of multi-start threading.
Solution Approach 2:
The circumferential spacing and angular positioning of multiple thread starts are designed in advance to create a predetermined engagement sequence. During assembly, this preliminary configuration ensures that threads engage in the correct sequence and orientation, preventing misalignment and galling before they can occur, while still providing the strength advantages of multi-start threads.
3Power
If thread engagement is increased to distribute torque, then torque distribution improves, but axial load on shoulder increases causing flaring damage
Solution Approach 1:
The thread formation is segmented into multiple independent thread starts that are circumferentially spaced apart. This segmentation allows the torque transmission to be divided across multiple discrete thread engagements, distributing the axial force on the shoulder among multiple thread starts rather than concentrating it at a single location, thereby reducing flaring damage while maintaining effective torque distribution.
Solution Approach 2:
The patent distributes thread engagement across the circumferential dimension by positioning multiple thread starts at different angular intervals. This dimensional approach allows torque to be transmitted through multiple simultaneous thread engagements around the circumference, effectively distributing the axial load on the shoulder and reducing the concentration force that causes flaring damage.
Data Source
AI summary
The disclosure relates to a thread formation and to a downhole tool comprising a hollow tubular pipe section having an end on which the thread formation is provided. The thread formation comprises a first thread having a first thread start and a second thread having a second thread start, wherein the first thread start is operatively rotationally in advance of the second thread start. Accordingly, the first thread is configured to engage at least partially with a complementary thread formation on another downhole tool before the second thread engages with the complementary thread formation.