Lower Mill Spaced Cutting Ring Structure for Extended Window Height
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Solution Overview
Problem
Conventional window milling technologies face challenges in creating a long, large diameter window cut due to excessive bending stress and torque, which leads to premature wear and reduced cutting efficiency, especially at the top of the whipstock where the angle change is abrupt, causing interference and limiting the size of drilling assemblies that can pass through.
Innovation Solution
The use of a lower mill with a cutting structure arranged in parallel rows of sharper and more durable inserts, spaced to increase contact stress and promote longer window extension, allowing fewer inserts to penetrate deeper and maintain cutting effectiveness as rows wear down, combined with a smaller diameter design to reduce bending stress and enhance milling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the lower mill diameter is increased to cut deeper and extend the window higher, then the window height is improved, but the bending stress and torque increase excessively
Solution Approach 1:
The cutting structure is segmented into multiple rows of inserts arranged circumferentially and axially on the lower mill. This segmentation allows the cutting load to be distributed across multiple rows, reducing the bending stress and torque on any single row while still achieving the required window height extension through cumulative cutting action.
Solution Approach 2:
The inserts are arranged with varying axial spacing to create local quality differences in the cutting action. The circumferential arrangement with specific axial spacing creates zones of different contact stress, allowing optimal cutting performance at different locations while managing overall bending stress and torque on the lower mill.
2Length of stationary object
If the lower mill diameter is increased to cut deeper and extend the window higher, then the window height is improved, but the torque increases excessively
Solution Approach 1:
The cutting structure is segmented into multiple rows of inserts arranged circumferentially and axially on the lower mill. This segmentation allows the cutting load to be distributed across multiple rows, reducing the bending stress and torque on any single row while still achieving the required window height extension through cumulative cutting action.
Solution Approach 2:
Multiple rows of inserts provide partial cutting action at different axial positions, with each row contributing to the overall window extension. This distributed partial action reduces the torque requirement compared to a single row attempting to cut the entire depth, while still achieving the desired window height.
3Length of stationary object
If more inserts are used to cut deeper and extend the window higher, then the window height is improved, but the wear on inserts increases
Solution Approach 1:
The cutting structure is segmented into multiple rows of inserts arranged circumferentially and axially on the lower mill. This segmentation allows the cutting load to be distributed across multiple rows, reducing the bending stress and torque on any single row while still achieving the required window height extension through cumulative cutting action.
Solution Approach 2:
The multiple rows of inserts provide continuous cutting action as the lower mill rotates and progresses through the casing. Each row contributes to the cutting process at different stages, ensuring continuous material removal and extending insert life by distributing the wear across multiple inserts rather than concentrating it on a single row.
4Stress or pressure
If the lower mill diameter is reduced to decrease bending stress, then the bending stress is reduced, but the cutting depth and window extension are limited
Solution Approach 1:
The cutting structure utilizes both circumferential and axial dimensions to achieve window extension. Instead of relying solely on increased mill diameter, the invention arranges inserts in multiple rows along the axial direction and circumferentially, allowing the lower mill to cut deeper through cumulative axial progression while maintaining a diameter that limits bending stress.
5Strength
If conventional dense insert arrangement is used, then the cutting structure is robust, but the contact stress is insufficient to penetrate casing wall effectively
Solution Approach 1:
The inserts are arranged with varying axial spacing to create local quality differences in the cutting action. The circumferential arrangement with specific axial spacing creates zones of different contact stress, allowing optimal cutting performance at different locations while managing overall bending stress and torque on the lower mill.
Solution Approach 2:
The invention changes the spatial parameters of insert arrangement from conventional dense packing to a distributed pattern with specific circumferential and axial spacing. This parameter change increases the contact stress at each insert-casing interface, enabling effective penetration of the casing wall while maintaining structural robustness through the distributed arrangement.
Data Source
AI summary
The cutting structure on the lower mill is arrayed in rows that are preferably parallel. The cutting structure in each row is made sharper and more durable than prior designs with the objective of cutting the window higher than where the window mill started the window. The use of the rows increases the contact stress of the inserts on the casing inside wall because at any given time fewer and sharper inserts are cutting the casing wall to lengthen the window. As a row wears down the next row takes over to continue the cutting where the previous row was active and to further penetrate the casing wall. The cutout angle can also increase as this occurs. As a result a decreased insert density results in more effective casing wall cutting to extend the window to allow larger tools to exit into the window off the whipstock.