Downhole Mill with Reverse Flow Debris Removal
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Solution Overview
Problem
Current downhole milling tools face challenges in effectively removing small debris generated during milling operations, as existing systems are limited by fluid flow rates and prone to clogging, especially when trying to retrieve milled components like packers, which can lead to equipment damage and increased costs due to stuck debris in wellbores and safety devices.
Innovation Solution
A mill design featuring large debris passages and radially extending blades, allowing reverse flow to collect cuttings in an annular space around a retention nut, with a slotted bushing and tubular structure that increases flow area, enabling efficient debris removal and supporting retrieval of milled tools while minimizing clogging risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If forward circulation is used to remove cuttings, then cuttings can be removed from the well bore, but cuttings become stuck in the well bore and damage equipment
Solution Approach 1:
The patent inverts the conventional forward circulation method by implementing reverse circulation, where fluid and cuttings flow upward through the mill in reverse direction. This inversion prevents cuttings from becoming stuck in the well bore and equipment, while maintaining effective cuttings removal capability
2Productivity
If milling is done at fast rate to remove large amount of metal, then productivity increases, but large cuttings are generated that must be removed by forward circulation
Solution Approach 1:
The patent applies reverse circulation to handle the large cuttings generated during fast milling operations. By inverting the flow direction, large cuttings are efficiently transported upward through the mill without becoming stuck, maintaining high productivity while managing the harmful effect of large cuttings generation
3Productivity
If conventional mill design is used, then milling operation can be performed, but debris passages become clogged and prevent effective debris removal
Solution Approach 1:
The patent transitions from conventional two-dimensional debris passages to a three-dimensional annular space between the mill housing and retention nut. This dimensional change provides significantly larger flow area for debris transport, preventing clogging while maintaining milling operation capability
4Ease of repair
If packer retrieval is attempted after milling, then tool can be recovered, but debris may become stuck and prevent retrieval
Solution Approach 1:
The patent extracts debris from the potential retrieval path by channeling it through the annular space and out through the workstring. The retention nut and slotted bushing configuration actively removes debris from the area where it could interfere with packer retrieval operations
Solution Approach 2:
The patent uses reverse circulation to transport debris upward during retrieval operations, inverting the conventional flow direction. This prevents debris from becoming stuck and interfering with packer retrieval, ensuring reliable tool recovery
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 design enhances debris removal efficiency, reduces the risk of clogging, and allows for the retrieval of milled tools, such as packers, by providing a larger flow area for debris to be collected and transported to a debris removal tool, using reverse circulation, thus reducing operational costs and equipment damage.
Implementation Method 1
reverse circulation takes cuttings into the large open area between the blades
Implementation Method 2
a mill such as a pilot mill, a section mill, or a junk mill
Data Source
AI summary
A mill is configured to have large debris passages disposed among a series of radially extending blades. The mill center is adapted to accept a retention nut that supports a tool that secures the downhole tool being milled out, such as a packer. Reverse flow takes cuttings into the large open area between the blades to pass up in an annular space around a support for the retention nut. The passage then opens up to a maximum dimension leaving only the tubular wall needed for structural strength to support the mill and conduct cuttings into a debris removal tool.