Dissymmetrical Threaded Connection for Well Casing Pressure Sealing
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Solution Overview
Problem
Existing threaded connections for deep well casings face challenges in machining complexity and assembly tolerances, particularly in achieving high resistance to internal and external pressures while maintaining effective sealing, especially in large diameter tubes used in oil and gas exploration.
Innovation Solution
A threaded tubular connection design featuring male and female tool joints with specific helix pitch and tooth width ratios, along with unique thread profiles and sealing surfaces, that allows for efficient assembly and enhanced resistance to pressures, while minimizing machining complexity and assembly variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If dovetail threading with different pitch values for load flank and stabbing flank is used, then resistance to internal and external pressures is improved, but machining difficulty and assembly complexity increase significantly
Solution Approach 1:
The patent applies asymmetry by defining different pitch values for the load flank (LFLp) and stabbing flank (SFLp) of the helical threading. Specifically, the load flank pitch LFLp is different from the stabbing flank pitch SFLp, creating an asymmetric thread profile that optimizes both pressure resistance and machining feasibility. This asymmetric design allows the thread to better distribute loads while maintaining manufacturability compared to symmetric dovetail threads.
Solution Approach 2:
The patent changes the pitch parameter of the helical threading to resolve the contradiction. By setting specific pitch values for different flanks (LFLp for load flank, SFLp for stabbing flank) and establishing relationships between these parameters and other geometric parameters (such as tooth width Wtp, outer diameter OD, inner diameter ID), the patent achieves optimal pressure resistance while keeping machining within reasonable complexity limits.
2Strength
If intermediate abutment with negative angle is used, then resistance to pressures is improved, but sealing performance and assembly tolerances deteriorate
Solution Approach 1:
The patent segments the tool joint into distinct functional zones: a first sealing zone with radial interference between conical surfaces, a second sealing zone with additional radial interference, and an intermediate abutment region. This segmentation allows each zone to perform its specific function optimally - sealing zones provide reliable sealing while the intermediate abutment provides pressure resistance, resolving the contradiction between these competing requirements.
Solution Approach 2:
The patent applies local quality by giving different geometric characteristics to different regions of the tool joint. The sealing zones have specific conical surface angles optimized for sealing, while the intermediate abutment has a negative angle optimized for pressure resistance. This localized optimization of geometric parameters in different regions allows simultaneous achievement of sealing performance and pressure resistance.
3Reliability
If self-locking wedge thread with progressively increasing tooth width is used, then locking effectiveness is improved, but machining complexity and assembly tolerance control become very difficult
Solution Approach 1:
The patent applies partial action by implementing self-locking characteristics through a controlled progression of tooth width over a limited portion of the thread engagement, rather than throughout the entire thread length. The tooth width Wtp progressively increases over at least two consecutive turns to provide locking effectiveness, while maintaining manageable geometric complexity and machining feasibility by limiting the progression to a partial engagement length.
Data Source
AI summary
Threaded tubular connection for the casing of hydrocarbon wells obtained by makeup of a male tool joint with a female tool joint, the connection comprising a threaded portion, such that the male and respectively female threaded portions each comprise a helix provided with a load flank, a thread crest, a stabbing flank, a thread root, such that a pitch of the load flank (LFLp, LFLb) and a pitch of the stabbing flank (SFLp, SFLb) fulfills the following condition: [Math 14] SFLb=LFLb=SFLp=LFLp=k, A tooth width (Wtp) of the male helix and a tooth width of the female helix (Wtb) are such that [Math 15] 50%<Wtp/Wtb<80% or [Math 16] 50%<Wtb/Wtp<80% and [Math 17] Wtp Wtb<k.