Casing Coupling Thread Profile for Higher Make-Up Torque
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Solution Overview
Problem
Casing string connections in oil and gas wells have low torque capacity, leading to mechanical integrity issues, particularly during hydraulic fracturing completions, where high internal pressure and tension loads are applied, resulting in frequent failures at connections.
Innovation Solution
A threaded coupling design featuring a first and second thread profile with the last two threads near the second end reduced in height according to an extra machining angle, providing increased make-up torque and stress reduction, while maintaining standard dimensions and configuration for oil country tubular goods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If standard API couplings are used, then manufacturing is economical and standard dimensions are maintained, but torque capacity is low leading to connection failures
Solution Approach 1:
The coupling applies local quality by modifying only the last two threads near the second end with an extra machining angle to reduce height, while maintaining standard thread profiles elsewhere. This localized modification increases make-up torque capacity without requiring complete redesign of the entire coupling, thus improving strength while preserving ease of manufacture for the majority of the component.
Solution Approach 2:
The invention changes the geometric parameter of the thread height for the last two threads by applying an extra machining angle. This parameter change increases the make-up torque capacity of the coupling while maintaining compatibility with standard API dimensions and configurations, resolving the contradiction between improved strength and manufacturing ease.
2Strength
If thread height is reduced at the second end, then make-up torque is increased, but manufacturing precision requirements increase
Solution Approach 1:
The extra machining angle is applied only to the last two threads near the second end of the coupling, creating a localized zone of modified thread height. This localized approach concentrates the torque-enhancing geometry where it is most effective while limiting the scope of precision requirements to a small portion of the overall coupling, thereby reducing overall manufacturing precision demands.
Solution Approach 2:
Rather than modifying all threads uniformly, the invention applies the extra machining angle to only the last two threads - a partial action that provides sufficient make-up torque improvement without requiring high-precision control across the entire thread length. This partial modification achieves the necessary torque capacity while relaxing precision requirements compared to a full-thread modification approach.
Data Source
AI summary
A threaded coupling comprising a first end, a second end, a first portion of the threaded coupling defining a first thread profile, a second portion of the threaded coupling defining a second thread profile different from the first thread profile, where at least two threads of the second thread profile proximate to the second end are reduced in height according to an extra machining angle.