Casing Thread Connection Surfaces for Gas-Tight Make-Up Under Load
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Solution Overview
Problem
Existing thread connections for casings in oil, gas, and gas-condensate wells fail to maintain tightness, especially gas tightness, under multidirectional combined mechanical loads, and suffer from jamming and surface damage during assembly and operation.
Innovation Solution
The thread connection features male and female elements with tapered trapezoidal threads and an internal sealing unit, including additional surfaces such as taper and spherical surfaces, which reduce jamming and surface damage by distributing contact stresses and ensuring accurate alignment and positioning, thereby maintaining high tightness and preventing galling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional tapered trapezoidal threads with parallel crests and roots are used, then the thread connection can be assembled, but jamming occurs at the initial stage of make-up and sealing surfaces get damaged under mechanical loads
Solution Approach 1:
The patent introduces a chamfered surface at the entry of the female thread element that precedes the main sealing surface. This chamfered surface performs the preliminary action of guiding the male element into proper alignment and distributing initial contact stresses, preventing jamming before the sealing surfaces engage. The chamfered surface is positioned ahead of the sealing surface in the make-up direction, preparing the connection for smooth assembly.
Solution Approach 2:
The patent divides the end face surface of the female element into multiple functional zones: a chamfered surface zone at the entry, a sealing surface zone, and a shoulder surface zone. This segmentation allows each zone to perform its specific function - the chamfered zone handles initial alignment and stress distribution, the sealing zone maintains tightness, and the shoulder zone provides structural support, thereby preventing jamming and surface damage.
2Reliability
If sealing surfaces are made to contact directly under mechanical loads, then tightness is achieved, but galling and damage occur on contact surfaces
Solution Approach 1:
The chamfered surface performs preliminary stress distribution before the sealing surfaces engage under full mechanical loads. By providing a gradual transition zone, the chamfered surface prevents sudden stress concentration on the sealing surfaces, thereby maintaining sealing integrity while distributing loads more evenly across the contact areas.
Solution Approach 2:
The chamfered surface acts as a cushioning zone that absorbs and distributes mechanical stresses before they reach the sealing surfaces. This beforehand cushioning prevents direct transmission of high mechanical loads to the sealing surfaces, reducing the risk of galling and damage while maintaining the necessary contact pressure for gas tightness.
3Adaptability or versatility
If multiple make-up and break-out cycles are performed, then field assembly flexibility is improved, but damages accumulate on thread and sealing surfaces
Solution Approach 1:
The chamfered surface performs preliminary alignment and stress distribution during each make-up cycle, preventing damage accumulation. By consistently guiding the male element into proper position and distributing contact stresses at the entry zone, the chamfered surface protects the sealing surfaces from repeated impact and misalignment damages during multiple assembly cycles.
Solution Approach 2:
The chamfered surface provides beforehand cushioning during each make-up/break-out cycle, absorbing repetitive mechanical stresses before they reach the sealing surfaces. This cushioning effect prevents fatigue and damage accumulation on the critical sealing surfaces, maintaining reliability over multiple assembly cycles.
Data Source
AI summary
A thread connection for casings used for construction of vertical, directional and horizontal wells. The connection includes male and female elements, whose ends, both externally and internally, are produced correspondingly with tapered trapezoidal threads, sealing, transition and shoulder end surfaces. Crests and roots of the thread turn profile are parallel to the axial line of thread. Additional surfaces are formed as a taper surface on the female element and a taper surface or convex spherical surface on the male element. Transition from the sealing surfaces to additional surfaces are formed as concave spherical surface on the male element and of convex spherical surface on the female element. High tightness of the connection under sufficient mechanical loads is achieved by improving characteristics of the connection make-up, prevention of jamming of the connection at the initial stage of make-up, lack of damages (galling) of sealing surfaces.