Bit-Weighting Sub for Controlled Milling Force in Wellbore Casing
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Solution Overview
Problem
Current methods for milling holes in wellbore casings, such as using motor-driven knuckle joint drive assemblies, face challenges like poor stabilization, high operational skill requirements, torque inefficiencies, and limitations in deep or deviated wells, leading to increased costs and complexity.
Innovation Solution
A bit-weighting sub assembly is integrated with coiled tubing to provide a consistent weight transfer to the milling bit through a rotary drive, allowing for controlled and efficient hole milling by compressing a spring or using hydraulic force, independent of the tubing weight, enabling quicker and cost-effective operations in deviated or deep wells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a motor-driven knuckle joint drive assembly is used for milling, then the milling operation can be performed, but the assembly is poorly stabilized and requires significant operator skill
Solution Approach 1:
The milling system is divided into separate functional components: a stabilization assembly with stabilizing elements (feet) that contacts the wellbore wall independently of the milling bit, and a knuckle joint drive assembly. This segmentation allows the stabilization function to be performed separately from the milling function, improving overall stability without interfering with the milling operation.
Solution Approach 2:
The stabilizing elements are positioned to contact the wellbore wall at multiple points, creating a stable platform that equalizes the operational conditions. By distributing the load and contact points along the wellbore wall, the system achieves better stabilization and reduces the skill required to maintain proper positioning during milling.
2Power
If a knuckle joint drive assembly is used, then milling can be performed, but torque is lost to frictional drag from the joint assembly and coiled tubing
Solution Approach 1:
The stabilizing function is extracted from the knuckle joint drive assembly and placed in a separate stabilization assembly. This allows the knuckle joint to focus solely on power transmission for milling, while the stabilization elements handle positioning and support, reducing parasitic frictional losses in the joint assembly.
Solution Approach 2:
The stabilization assembly acts as an intermediary between the knuckle joint drive and the wellbore environment. It provides a stable reference frame and support structure that reduces unnecessary movement and friction, allowing more of the motor torque to be effectively used for the milling operation.
3Ease of operation
If standard size coiled tubing is used to lower the knuckle drive, then the equipment can be deployed, but the operator has virtually no feel over the milling operations
Solution Approach 1:
The stabilization elements provide mechanical feedback to the operator by contacting the wellbore wall and creating resistance that can be sensed through the drill string. This tactile feedback allows the operator to sense when the stabilizers are properly positioned and when the bit is making effective contact with the casing, improving control without requiring specialized skills.
4Adaptability or versatility
If a knuckle joint drive assembly is used in high angle or horizontal wells, then milling can be attempted, but the assembly cannot be effectively stabilized and weight cannot be transferred to the bit
Solution Approach 1:
The stabilization elements extend radially outward from the drill string in directions perpendicular to the longitudinal axis, providing contact with the wellbore wall in multiple dimensions. This geometric arrangement allows the stabilizers to effectively support the assembly in high-angle and horizontal wells by distributing forces across multiple contact points, enabling weight transfer to the bit even in challenging wellbore geometries.
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 solution enables faster, more controlled, and cost-effective hole milling in wellbore casings, reducing operator skill requirements and allowing for milling in previously challenging environments like deviated or horizontal wells, while minimizing torque demands on the motor.
Implementation Method 1
A bit-weighting sub assembly is integrated with coiled tubing to provide a consistent weight transfer to the milling bit through a rotary drive, allowing for controlled and efficient hole milling by compressing a spring or using hydraulic force
Implementation Method 2
A bit-weighting sub assembly is integrated with coiled tubing to provide a consistent weight transfer to the milling bit through a rotary drive, allowing for controlled and efficient hole milling by compressing a spring or using hydraulic force
Data Source
AI summary
An apparatus and method for improving control over the milling force applied to a milling bit that is turned through a rotary drive to form a hole in a wellbore casing. A bit-weighting sub is applied between the tubing used to lower the rotary drive's motor into the wellbore and the rotary drive itself, the sub serving to take the weight of the tubing off the rotary drive when the motor lands in operative connection with the drive, and further serving to apply a known milling force to the drive (and thus to the bit) independent of the weight of the tubing. In a preferred form the sub includes a spring that is compressed against the drive when the tubing and motor are landed.