Wide Bandwidth Borehole Dipole Source Design

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Solution Overview

Problem

Current dipole sources for borehole acoustic logging lack wide bandwidth and high modal purity, particularly in generating low-frequency shear waves with strong signal strength, leading to inadequate measurement accuracy in hydrocarbon content analysis.

Innovation Solution

A dipole source design featuring a cylindrical shell with a center beam and a movable projector inside, utilizing a magneto-motive force to generate a wide bandwidth acoustic wave with high modal purity, including a cavity for acoustic insulation and a control unit for data processing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If piezo-electric bender bars are used as dipole sources, then the device structure is simple and reliable, but the frequency bandwidth is narrow (1 kHz to 3 kHz)

Engineering Contradiction:

Improvedevice reliabilityVSAvoidfrequency bandwidth

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent replaces the piezo-electric mechanical system with a electromagnetic system consisting of a voice coil motor, permanent magnet, and movable mass. This substitution enables wide bandwidth operation through electromagnetic force generation while maintaining structural reliability, resolving the contradiction between simple reliable structure and wide frequency bandwidth.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If piston radiators are used to provide wider bandwidth, then the frequency range increases, but mode purity deteriorates with monopole, quadrupole and higher order modes

Engineering Contradiction:

Improvefrequency bandwidthVSAvoidmode purity

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent employs asymmetric positioning of the movable mass relative to the center beam, creating a pure dipole moment configuration. This asymmetric arrangement ensures that only dipole modes are excited while eliminating monopole and quadrupole modes, thereby achieving high mode purity across wide bandwidth.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The center beam acts as an intermediary element that couples the movable mass to the cylindrical shell. This intermediary structure efficiently transmits the dipole moment from the movable mass to the surrounding medium while filtering out unwanted acoustic modes, maintaining high mode purity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If shaker sources are used to produce shear waves, then the device can generate acoustic waves, but the driving mechanism interferes with the logging tool body requiring acoustic isolators

Engineering Contradiction:

Improveacoustic wave generationVSAvoidmechanical interference

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts the harmful mechanical interference by suspending the movable mass and voice coil assembly within the cylindrical shell using elastic elements. This isolation technique separates the driving mechanism from the tool body, eliminating mechanical interference while preserving acoustic wave generation capability.

Inventive Principle:

Principle #2Taking out (Extraction)

4Strength

If shaker sources with mass are used, then the device structure is robust, but dipole radiation strength becomes inadequate

Engineering Contradiction:

Improvestructural robustnessVSAvoiddipole radiation strength

Core Design Contradiction:

StrengthVSForce

Solution Approach 1:

The patent optimizes the parameters of the movable mass, permanent magnet, and voice coil to maximize electromagnetic force generation. By carefully selecting and adjusting these parameters, the system achieves strong dipole radiation while maintaining structural robustness, resolving the contradiction between structural strength and radiation capability.

Inventive Principle:

Principle #35Parameter changes

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 provides a strong, low-frequency dipole signal with high signal-to-noise ratio, enabling accurate shear wave measurements and improved hydrocarbon content analysis in both wireline and logging-while-drilling applications.

Implementation Method 1

propelling a projector to impact a center beam using a magneto-motive force generated by the current

Methodology Applied

Scientific EffectMagneto-motive force: Electromagnetic Induction

Implementation Method 2

a cavity acoustically insulating the interior of the cylindrical shell from the exterior of the cylindrical shell

Methodology Applied

Scientific EffectAcoustic insulation: Acoustic Absorption

Data Source

PatentUS10288758B2Wide bandwidth borehole dipole source for acoustic logging

Publication Date: 2019.05.14 HALLIBURTON ENERGY SERVICES INC

AI summary

A dipole source for borehole acoustic logging includes a cylindrical shell, a center beam coupled to the cylindrical shell, a movable projector inside the cylindrical shell to impact the center beam, and a cavity acoustically insulating the interior of the cylindrical shell from the exterior of the cylindrical shell. An acoustic logging tool for making measurements of a substrate surrounding a borehole with a body insertable in the borehole is also provided. The body includes an acoustic detector and a dipole source as above, along the axial length. The acoustic logging tool may include a control unit to process data collected from the acoustic detector and obtain information about the substrate surrounding the borehole.