Slim Coupled Casing Connection for Tight Clearance Wells
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Solution Overview
Problem
Existing flush and semi-flush joint connections for casing strings in oil and gas wells are expensive, have limited industry availability, and do not meet performance needs, with low tension efficiency and inadequate torque resistance, especially in tight clearance situations.
Innovation Solution
A slim hole coupled connection design featuring tubulars with turn-down pin ends and couplings with varying thread sections, balancing critical cross-sections to achieve targeted connection tension and pressure efficiencies, including high torque resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If flush or semi-flush integral joint connections are used to meet minimum annular clearance requirements, then the clearance constraint is satisfied, but tension efficiency and torque resistance are significantly reduced
Solution Approach 1:
The connection system is divided into separate components: a coupling device with external threads that connects to box threads on adjacent casing strings. This segmentation allows the coupling to be designed with optimized geometry that maintains both small external diameter for clearance and sufficient internal strength for tension and torque, resolving the contradiction between clearance constraint and mechanical performance
Solution Approach 2:
The coupling device acts as an intermediary component between adjacent casing strings. It provides the threaded connection interface while maintaining a compact external profile, thereby enabling both clearance satisfaction and adequate mechanical strength through its mediating function in the connection system
2Area of stationary object
If flush or semi-flush integral joint connections are used, then annular clearance is maintained, but torque resistance capacity is insufficient
Solution Approach 1:
By separating the connection function into a distinct coupling device with external threads, the design allows optimization of the coupling's internal thread geometry and material properties to provide adequate torque resistance, while the external diameter remains constrained for clearance purposes
Solution Approach 2:
The coupling device employs optimized thread parameters including thread pitch, depth, and profile geometry to maximize torque transmission capacity within the constrained external diameter, thereby achieving sufficient torque resistance while maintaining small clearance envelope
3Strength
If conventional threaded connections are used, then connection strength is achieved, but susceptibility to environmentally-assisted cracking increases
Solution Approach 1:
The coupling device utilizes optimized material selection and heat treatment parameters to achieve a microstructure that provides both high strength and enhanced resistance to environmentally-assisted cracking, while the thread geometry parameters are optimized to reduce stress concentration that could initiate cracking
Solution Approach 2:
The coupling device may employ composite material structures or material combinations that provide both the required mechanical strength and improved resistance to environmentally-assisted cracking, distinguishing it from conventional homogeneous materials used in traditional connections
Data Source
AI summary
A casing string is used within a predetermined annular clearance inside a surrounding casing. Tubulars have turn-down recessed to a smaller diameter than the tubular's outer diameter. Pin ends of the tubulars have pin thread and taper inward to an even smaller diameter at the pin noses of the pin ends. Couplings have an outer diameter to fit with the annular clearance requirement. The through-bore of the coupling has box thread sections tapering outward from a center of the through-bore to the coupling's ends. The pin threads of the pipe ends thread respectively to the box thread sections of the couplings, and the pin noses of the opposing pipe ends engage in contact in the center of the coupling with a contact pressure. Cross-sections of the pin ends are balanced to cross-sections of the coupling so the connection can provide a tension and pressure ratings, such as at least 70 percent, of the pipe body tension and pressure ratings.