Pretensioned Shear Coupling for Downhole Torque and Bending
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Solution Overview
Problem
Conventional shear couplings fail to withstand axial, torsional, and bending stresses in downhole applications, particularly in deviated wellbores, leading to premature failure and interruptions in wellbore production, and are not designed for use with both rotary and reciprocating downhole pumps.
Innovation Solution
A flexible shear coupling using a shear nut and connecting member as the shear element, with a polygonal shaft and hub profile for torque transmission, and pretensioning to isolate the shear nut from alternating stresses, providing increased resistance to bending and torsional stresses while protecting from corrosive environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional shear couplings use shear pins or grooves as shear elements, then the coupling can break at a pre-set axial load, but the shear element becomes a stress concentrator that causes fatigue and unexpected failure under combined axial, torsional, and bending stresses
Solution Approach 1:
The patent extracts the shear element (shear pin or groove) from the load-bearing path by introducing a separate sacrificial shear element that breaks first. The main coupling members are designed with reinforced geometry to withstand combined stresses, while the isolated shear element absorbs the breaking function without concentrating stress in the main structural components.
Solution Approach 2:
The patent introduces a sacrificial shear element as an intermediary component between the coupling members. This intermediary breaks at a predetermined load to separate the coupling, protecting the main coupling members from stress concentration and fatigue that would occur if the shear function were integrated into the structural members themselves.
2Adaptability or versatility
If conventional shear couplings are designed for axial loads only, then the shear element can break at a pre-set axial load, but the coupling cannot adequately transmit torque or resist bending stresses in deviated wellbores
Solution Approach 1:
The patent designs the coupling members with multiple functional features: a polygonal drive interface for torque transmission, reinforced geometry for bending resistance, and a sacrificial shear element for axial load breaking. This multi-functional design allows the same coupling to be used with both progressive cavity pumps and sucker rod pumps across various well conditions including deviated wellbores.
Solution Approach 2:
The patent employs composite construction by combining different material properties and structural features within the coupling assembly. The coupling members use high-strength materials with specific geometric reinforcement for torsional and bending resistance, while the sacrificial shear element uses a lower-strength material designed to break at a predetermined load, creating a composite system that handles multiple stress types.
3Ease of operation
If the shear element is exposed to the wellbore environment, then the coupling can function as designed, but the shear element is subjected to corrosive conditions that reduce its reliability
Solution Approach 1:
The patent extracts the sacrificial shear element into a protected position within the coupling assembly, shielded from direct exposure to the corrosive wellbore environment. The coupling members and drive interface remain exposed for proper operation, while the shear element is positioned in a less corrosive zone, extending its service life and reliability.
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 shear coupling effectively resists axial, bending, and torsional stresses, ensuring reliable operation with both rotary and reciprocating pumps and protecting the shear element from corrosion, thereby enhancing the durability and performance of downhole operations.
Implementation Method 1
The length of the connecting member, especially when pretensioned, and a reduced cross-section that may be formed on the outer surface of the shear coupling increase the overall flexibility of the shear coupling, thereby making the shear coupling more resistant to bending stress.
Implementation Method 2
The shear nut is isolated from large alternating stresses due to pretensioning of the connecting member.
Implementation Method 3
The coupling members may be connected by a polygonal shaft profile on one coupling member and matching polygonal hub profile on the other coupling member to transmit torque in a rotary application.
Data Source
AI summary
A shear coupling can be used with reciprocating and rotary pumps. The shear coupling uses a shear nut and connecting member as the shear element. The connecting member and shear nut are located inside the axial bore of the shear coupling to protect from corrosive wellbore elements. The coupling members may be connected by matching polygonal shaft and hub profiles on the coupling members to transmit torque. The shaft and hub may have octagonal profiles for better torque transmission capacity. The shear nut may be isolated from large alternating stresses due to pretensioning of the connecting member. The length of the connecting member, especially when pretensioned, and a reduced cross-section that may be formed on the outer surface of the shear coupling increase the overall flexibility of the shear coupling, thereby increasing the resistance to bending stress.