Drill String Vibration Mitigation via Mode Shape Modification

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Solution Overview

Problem

High frequency torsional vibrations in drill strings and bottomhole assemblies during oil field drilling can cause damage and are difficult to mitigate with existing methods.

Innovation Solution

A method involving the construction of a mathematical model of the drill tubular system to calculate and modify its mass distribution, stiffness, and damping, using a predefined damping criterion that includes the ratio of drill bit deflection and eigenfrequency to increase effective damping and reduce vibrations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high frequency torsional vibrations occur in drill strings during drilling, then drilling operations can proceed, but downhole tools may be damaged and system reliability decreases

Engineering Contradiction:

Improvedownhole tool reliabilityVSAvoidtorsional vibrations

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent modifies the vibratory mode shapes of the drill string by changing physical parameters including mass distribution (adding mass at specific locations), stiffness (modifying structural properties), and damping characteristics. These parameter changes alter the natural frequencies and mode shapes to avoid resonance with excitation frequencies, thereby reducing torsional vibrations and preventing downhole tool damage.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies vibration theory to analyze and control the vibratory behavior of the drill string. By calculating mode shapes and eigenfrequencies, and by intentionally modifying these vibratory characteristics through mass and stiffness changes, the system transforms harmful high-frequency torsional vibrations into less harmful vibration patterns, reducing the risk of tool damage.

Inventive Principle:

Principle #18Mechanical vibration

2Object-affected harmful factors

If the drill string system is modified to reduce vibrations, then vibration mitigation is achieved, but the complexity of the drill string design increases

Engineering Contradiction:

ImprovevibrationsVSAvoiddrill string design complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

Rather than adding complex active control systems or multiple components, the patent achieves vibration mitigation by modifying fundamental physical parameters of existing drill string components - specifically mass distribution and stiffness characteristics. This approach reduces vibrations while maintaining relatively simple drill string design, as it involves adjusting parameters of existing elements rather than adding complex new systems.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11021945B2Method to mitigate bit induced vibrations by intentionally modifying mode shapes of drill strings by mass or stiffness changes

Publication Date: 2021.06.01 BAKER HUGHES CO

AI summary

A method for reducing vibrations in a drill tubular coupled to a drill bit configured to drill a borehole in a formation includes: constructing a model of a system having the drill tubular, the model having a mass distribution, a stiffness, and/or a damping of the drill tubular; and calculating a plurality of modes using the model. The method also includes increasing an effective damping of the drill tubular for the plurality of modes by modifying at least one of the mass distribution, the stiffness, and the damping of the drill tubular using a predefined damping criterion, wherein the predefined damping criterion includes a ratio, the ratio having a deflection at the drill bit of at least one mode in the plurality and an eigenfrequency of the at least one mode in the plurality, wherein the deflection at the drill bit is raised to a power other than one.