Downhole String Shoe Extension Sub for Jam-Free Milling
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Solution Overview
Problem
During fishing operations, broken coil tubing often jams in the wash-pipe above the milling shoe, preventing further milling and making it impossible to remove stuck tools due to the tapered throat of existing solutions like the Bowen mill extension, which also requires additional components like a grapple and bowl.
Innovation Solution
A string shoe extension sub with a straight bore and cutting elements, such as tungsten carbide buttons, is used in conjunction with a milling shoe to mill and remove broken coil tubing, allowing for continued penetration and retrieval of stuck tools without jamming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a Bowen mill extension with a tapered throat is used, then the fish can be milled away to enable passage, but the tapered throat restricts the bore causing coil tubing to jam
Solution Approach 1:
The patent changes the geometric parameter of the bore from tapered (conventional) to straight (invention). This parameter change allows the bore to accommodate broken coil tubing without restriction, preventing jamming while maintaining the milling capability provided by the cutting elements on the interior wall.
2Productivity
If a Bowen mill extension is used, then milling can proceed, but additional components like grapple and bowl are required
Solution Approach 1:
The string shoe extension sub serves multiple functions: it provides a straight bore that prevents coil tubing jamming, incorporates cutting elements for milling operations, and eliminates the need for separate grapple and bowl components. This multi-functionality reduces device complexity while maintaining productivity.
Solution Approach 2:
The invention extracts and eliminates the unnecessary grapple and bowl components from the system. By integrating all required functions into the extension sub itself, the patent removes redundant components, simplifying the overall device while maintaining effective milling and retrieval capabilities.
3Strength
If a conventional milling shoe is used, then cutting can occur, but broken coil tubing jams in the wash-pipe above the milling shoe
Solution Approach 1:
The string shoe extension sub acts as an intermediary component between the milling shoe and the wash-pipe. Its straight bore design prevents broken coil tubing from jamming during the transition, facilitating smooth passage of the fish into the wash-pipe while the milling shoe performs its cutting function.
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
Enables effective milling and removal of stuck or broken coil tubing by preventing jamming and allowing further penetration, facilitating the release and extraction of stuck tools without the need for additional components like a grapple and bowl.
Implementation Method 1
cutting elements fixed to the interior wall of the tubular and extending into the bore of the tubular... enable the cutting elements to cut material that is inserted into the bore
Data Source
AI summary
An extension sub for a downhole fishing tool, the extension sub comprising a tubular having a threaded pin end and a threaded box end, the tubular having an interior wall defining a bore, and cutting elements fixed to the interior wall of the tubular and extending into the bore of the tubular. Such a device may be referred to as a string shoe.