Multiple Mill System for Single Trip Subterranean Tubular Section Milling
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Solution Overview
Problem
Existing methods for extending a well in a new direction, such as section milling, face challenges with multiple tubulars due to risks of cuttings causing mill obstruction and inflexibility in multi-mill assemblies, leading to potential damage and inefficient cutting processes.
Innovation Solution
A multiple mill system is introduced, featuring an intermediate watermelon mill to grind cuttings and provide flexible mounting for the second mill, allowing it to center and extend arms only after the initial cut, ensuring precise cutting of multiple nested tubulars in a single trip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple mills are run into the well at the same time, then the cutting efficiency is improved, but the risk of cuttings balling up the mill increases
Solution Approach 1:
The cutting system is segmented into multiple mills operating simultaneously at different depths, with each mill responsible for cutting a specific tubular string. This segmentation allows parallel processing of multiple cutting tasks, improving overall productivity while maintaining individual mill reliability through proper spacing and cutting direction control.
Solution Approach 2:
The mills are configured to cut in the opposite direction of conventional single-mill operation, with the smallest section mill cutting first to generate smaller cuttings that are less likely to ball up the larger mills below. This inverted sequence resolves the contradiction by making the cutting process itself prevent mill obstruction.
2Stability of the object's composition
If a rigid multi-mill assembly is used, then structural stability is improved, but the flexibility to center the second mill is reduced
Solution Approach 1:
The multi-mill assembly incorporates dynamic elements including pivoting arms and flexible connections that allow the second mill to adjust its position and center itself within the annular space created by the first mill's cutting action. This dynamic design maintains overall assembly stability while providing necessary adaptability for proper mill positioning.
Solution Approach 2:
The connection between mills utilizes flexible mechanical elements that resemble flexible shells, allowing the assembly to bend and adapt to the wellbore geometry while maintaining structural integrity. This flexibility enables the second mill to center itself without compromising the stability of the overall multi-mill system.
3Ease of manufacture
If section milling is done in a downhole direction, then the cutting process is simplified, but the hole diameter increases requiring higher circulating fluid rates
Solution Approach 1:
The cutting direction is inverted from the conventional downhole direction to an uphole direction. This reversal allows the mills to cut while being pulled upward, maintaining constant hole diameter and eliminating the need to increase circulating fluid rates. The cutting process remains simplified through the use of powered mills that can efficiently cut in this reversed direction.
Data Source
AI summary
Multiple section mills are run in a single trip with an intervening mill preferably a watermelon mill to grind up any cuttings that get past the first mill in a direction toward the second mill below it. The blades of the second mill are held by the innermost tubular until the location of the initial cut is reached at which point the longer arms of the second mill can be extended and its body centralizes due to the flexibility of the connection between the mills.