Dual Mill Bottom Hole Assembly Selective Actuation
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Solution Overview
Problem
Existing solutions for sequentially operating primary and secondary mills with pressure-actuated blades are costly and complex, often requiring independent operating systems with RFID tags and sensors, which increase tool size and cost, making them unsuitable for all applications.
Innovation Solution
The solution involves locking the actuator of the backup mill until the primary mill is spent, then shifting the support string to defeat the lock and allow the backup mill's blades to extend, using fluid pressure to continue milling, and employing a removable pressure barrier like a valve or plug to enable backup mill operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If a single mill is run, then tool cost is reduced, but rig time increases due to pulling out of hole for blade replacement
Solution Approach 1:
The patent implements a dual-mill system where the primary mill blades are discarded after wear and the secondary mill automatically activates to complete the milling operation. This eliminates the need to pull out of hole for blade replacement, thereby reducing rig time while managing tool cost through strategic use of backup capacity.
Solution Approach 2:
The secondary mill is prepared in advance within the same tool assembly, with its blades held in a retracted position by a mechanism that prevents premature activation. When the primary mill becomes worn, the secondary mill is already positioned and ready to immediately take over, eliminating downtime for tool replacement.
2Loss of time
If a backup mill is included in the tool assembly, then rig time is reduced, but device complexity and cost increase
Solution Approach 1:
The patent combines both primary and secondary mills into a single integrated tool assembly, sharing common structural components, housing, and control mechanisms. This merging approach reduces overall device complexity compared to having separate tools, while maintaining the ability to switch between mills to minimize rig time.
Solution Approach 2:
The tool assembly is designed with multi-functionality, where a single device can perform milling operations using either the primary or secondary mill depending on blade wear conditions. This universal design eliminates the need for multiple separate tools, reducing overall system complexity while providing backup capability.
3Ease of operation
If fluid pressure is used to operate both mills, then ease of operation is improved, but premature blade extension of the backup mill occurs
Solution Approach 1:
The patent segments the fluid pressure system into separate pathways for the primary and secondary mills. Each mill has its own pressure-actuated piston and blade extension mechanism, allowing independent control. This segmentation enables simple fluid pressure operation for each mill while preventing premature activation of the secondary mill through isolated pressure channels.
Solution Approach 2:
The patent introduces intermediary mechanisms such as retractable tabs, locks, and flow restrictors that mediate between the common fluid pressure source and the secondary mill's blade extension system. These intermediaries prevent premature pressure transmission to the secondary mill while maintaining ease of operation through the unified fluid pressure control system.
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
This approach allows for cost-effective, reliable sequential operation of dual section mills, reducing rig time and tool size by maintaining fluid pressure operation while preventing premature blade extension of the backup mill until necessary, thus minimizing operational costs and maintaining tool efficiency.
Implementation Method 1
The internal piston using the flow through the tool maintains a contact force on the surrounding tubular as the blades pivot as the milling progresses
Implementation Method 2
A return spring takes over when flow is cut off to again allow the blades to retract to the point where they can be held retracted for tool removal
Implementation Method 3
When the primary mill is spent the support string is shifted to defeat a lock on an actuation piston for the backup mill so that its blades can extend and continue to mill
Data Source
AI summary
Dual section mills are selectively sequentially operated by locking an actuator for the backup mill as the primary mill has blades extended with internal flow through a housing. When the primary mill is spent the support string is shifted to defeat a lock on an actuation piston for the backup mill so that its blades can extend and continue to mill to finish the job. The blades of the primary mill continue to rotate in the already milled portion of the window as the secondary mill enlarges the window. Another way the secondary mill is actuated is to open access to flow to the secondary mill by removing a pressure barrier such as a valve or a disappearing plug, for example.