Borehole Elastic Wave Anisotropy Determination

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Solution Overview

Problem

Determining anisotropic seismic velocities in earth formations is challenging due to poor data quality and low frequencies in surface seismic data, and traditional wireline logging methods struggle to independently measure P-wave velocity components in arbitrary borehole inclinations.

Innovation Solution

A method and apparatus using a logging tool with transducers to generate elastic waves at inclined angles in boreholes, measuring voltage and current to estimate parameters like compressional and shear wave velocities and impedances, which can be used to create an anisotropic velocity model for improved seismic imaging.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If surface seismic data is used to determine anisotropic velocities, then coverage of the subsurface can be obtained, but the data quality is poor and frequencies are low making accurate velocity determination difficult

Engineering Contradiction:

Improvevelocity determination accuracyVSAvoiddata quality

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent introduces borehole measurements as an intermediary between surface seismic data and anisotropic velocity determination. The borehole measurements serve as a high-quality reference that mediates the extraction of anisotropic parameters from surface seismic data, allowing accurate velocity determination without directly relying on the poor quality surface data alone.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If traditional wireline logging is used in vertical boreholes, then the vertical P-wave velocity can be obtained, but velocities in arbitrary directions cannot be independently measured

Engineering Contradiction:

Improvemeasurement direction flexibilityVSAvoidvelocity component separation

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent segments the velocity measurement problem by using multiple boreholes with different orientations (vertical, horizontal, and arbitrary inclinations). Each borehole configuration is optimized to measure specific velocity components, and the results are combined to fully characterize the anisotropic velocity model. This segmentation allows independent measurement of velocity components that would be coupled in a single vertical borehole.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent adds the dimension of borehole orientation to the measurement system. By measuring velocities in boreholes with different inclinations and azimuths, the system transitions from measuring only vertical velocity (1D) to measuring velocity components in multiple directions (3D), enabling full characterization of anisotropic properties.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Measurement precision

If conventional acoustic logging is used in horizontal boreholes, then the horizontal P-wave velocity component can be obtained, but complete anisotropic velocity characterization is insufficient

Engineering Contradiction:

Improvehorizontal velocity measurementVSAvoidvelocity model completeness

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent merges measurements from multiple borehole configurations (vertical, horizontal, and arbitrarily inclined) to create a complete anisotropic velocity model. Each borehole type contributes specific velocity components, and by combining these measurements, the system achieves comprehensive velocity characterization that no single borehole configuration could provide alone.

Inventive Principle:

Principle #5Merging (Combining)

4Measurement precision

If anisotropic velocity models are not used in seismic imaging, then processing is simpler, but imaging accuracy in anisotropic formations deteriorates

Engineering Contradiction:

Improveimaging accuracyVSAvoidvelocity model complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent changes the parameters of the velocity model from isotropic (single velocity value) to anisotropic (multiple velocity components including vertical, horizontal, and intermediate velocities). This parameter change enables accurate imaging in anisotropic formations by accounting for direction-dependent velocity variations, while the systematic approach to measuring these parameters keeps the complexity manageable.

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

Enables accurate determination of seismic velocities as a function of propagation angle, enhancing the quality of seismic data and facilitating better subsurface imaging by accounting for anisotropy in seismic velocity models.

Implementation Method 1

An elastic wave is generated into the earth formation at an angle inclined to a longitudinal axis of the borehole by activating at least one transducer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

The parameter of interest is estimated using a voltage and a current in the at least one transducer

Methodology Applied

Scientific EffectElectrical impedance measurement: Electrical Impedance Tomography

Data Source

PatentUS7626886B2P-wave anisotropy determination using borehole measurements

Publication Date: 2009.12.01 BAKER HUGHES CO

AI summary

A phased array of transducers is used to generate elastic waves into the earth formation in a selected direction. The impedance measured at the input to the transducer array is indicative of the elastic impedance of the earth formation in the selected direction.