Downhole Milling System With Stacked Bits
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Solution Overview
Problem
Conventional downhole milling tools require multiple trips and extended rig time due to the need for frequent replacement of single mill bits, which limits efficiency and productivity in milling tubular components in wellbores.
Innovation Solution
A well tool system featuring multiple mill bits stacked along a drill pipe with circulation subs that allow sequential use of each mill bit, where worn-out bits are lowered into the tubular and new bits are engaged, utilizing a circulation fluid pathway and ball-activated sleeve valves to control fluid flow and bit engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single mill bit is used in conventional downhole milling tools, then the tool structure is simple, but multiple trips and extended rig time are required due to frequent replacement of the mill bit
Solution Approach 1:
The milling tool is divided into multiple independent mill bits (first mill bit, second mill bit, third mill bit) stacked along the drill pipe, each capable of independent operation. This segmentation allows one mill bit to be used while others are positioned for sequential engagement, eliminating the need to retrieve and replace the entire tool assembly when a mill bit is consumed.
Solution Approach 2:
Multiple mill bits are nested along the length of the drill pipe in a compact arrangement. The first mill bit is positioned at a first longitudinal end, the second mill bit at a location longitudinally uphole, and the third mill bit at another location longitudinally uphole from the second. This nested configuration allows all mill bits to be carried in a single tool assembly without excessive complexity.
2Loss of time
If multiple mill bits are stacked along the drill pipe for sequential use, then rig time is reduced and productivity increases, but the device complexity increases due to multiple circulation subs and ball-activated valves
Solution Approach 1:
The circulation subs are pre-configured with ball-activated sleeve valves in a specific sequence along the drill pipe. Each circulation sub is positioned to control fluid flow to its corresponding mill bit in advance, so that when a mill bit is consumed, the system can immediately transition to the next mill bit without requiring complex real-time control mechanisms.
Solution Approach 2:
The ball-activated sleeve valves provide automatic circulation control based on the position and consumption of mill bits. As each mill bit is used, the corresponding circulation sub automatically manages fluid flow through the ball mechanism, eliminating the need for external intervention or complex electronic control systems to switch between mill bits.
3Productivity
If worn-out mill bits are lowered into the tubular and new bits are engaged sequentially, then material removal is maximized in a single trip, but the circulation fluid pathway control becomes more complex
Solution Approach 1:
The circulation control function is extracted from a centralized complex system and distributed to individual circulation subs associated with each mill bit. Each circulation sub independently manages fluid flow to its corresponding mill bit through simple ball-activated sleeve valves, reducing the overall system complexity while enabling sequential operation of multiple mill bits.
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 faster and more efficient milling operations by allowing multiple mill bits to be used in a single trip, reducing rig time and maximizing material removal, while maintaining tool durability and adaptability for various tubular profiles.
Implementation Method 1
a circulation fluid pathway through an interior of the well tubing
Implementation Method 2
ball-activated sleeve valves to control fluid flow and bit engagement
Data Source
AI summary
A well tool for milling a tubular includes a well tubing disposed in a wellbore and including a circulation fluid pathway through an interior of the well tubing, a first milling tool coupled to the well tubing at a first longitudinal end of the well tubing, a second milling tool coupled to the well tubing at a location longitudinally uphole from the first milling tool, and a third milling tool coupled to the well tubing at a location longitudinally uphole from the second milling tool. Each of the milling tools include a mill bit and a circulation sub fluidly connected to the circulation fluid pathway. The first milling tool mills a first portion of the tubular, the second milling tool mills a second portion of the tubular, and the third milling tool mills a third portion of the tubular.