Nonlinear Acoustic Borehole Imaging for Fracture Detection
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Solution Overview
Problem
Current methods for characterizing material integrity and imaging around boreholes in oil and gas reservoirs are inadequate for detailed characterization of natural and induced fractures, CO2 sequestration, and assessing mechanical integrity, particularly in discerning mechanically damaged regions and predicting borehole breakout, as they fail to effectively utilize nonlinear acoustic properties.
Innovation Solution
A method and apparatus utilizing high frequency pulses and low frequency acoustic waves to differentiate between linear and nonlinear features in rock formations by inducing elastic nonlinearity, where the high frequency pulses are reflected or backscattered based on changes in acoustic impedance, allowing for three-dimensional imaging and determination of feature orientation and distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional acoustic methods are used for material characterization, then the imaging capability is limited, but the device complexity and measurement precision requirements increase when attempting to discern mechanically damaged regions
Solution Approach 1:
The patent applies parameter changes by utilizing nonlinear acoustic parameters (elastic nonlinearity) instead of conventional linear acoustic parameters. This allows the system to detect mechanically damaged regions through changes in nonlinear acoustic response, improving measurement precision without requiring overly complex device architectures. The nonlinear acoustic properties provide additional diagnostic information that enhances detection capability.
2Measurement precision
If high frequency pulses are used to detect material features, then the detection precision improves, but the energy loss and attenuation increase
Solution Approach 1:
The patent employs periodic action by using a low frequency acoustic wave to periodically modulate the acoustic impedance of material features. This periodic modulation causes the high frequency pulses to be reflected or backscattered in a periodic manner, enabling detection of material features while managing energy attenuation through the use of lower frequency modulation waves that experience less attenuation.
3Measurement precision
If nonlinear acoustic methods are applied to probe material integrity, then the measurement precision for damage detection improves, but the device complexity and operational complexity increase
Solution Approach 1:
The patent applies universality by designing an acoustic interrogation system that can perform both linear and nonlinear acoustic measurements using the same basic hardware configuration. The system uses a combination of low frequency acoustic waves and high frequency pulses that can be processed to extract both linear acoustic properties and nonlinear elastic properties, reducing device complexity while maintaining high measurement precision for damage detection.
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 imaging and characterization of material properties around boreholes, distinguishing between linear and nonlinear features, and detecting mechanical damage, thereby improving the assessment of borehole integrity and reservoir properties.
Implementation Method 1
the elastic nonlinearity of a solid is a measure of the material mechanical damage state. The low frequency acoustic wave induces a corresponding elastic distortion cycle in the material.
Implementation Method 2
the second high frequency pulses are received at the one or more receivers if the first sequence of high frequency pulses encounters the one or more features within the material with a contrast in acoustic impedance that results in reflection or backscattering of energy to the borehole.
Implementation Method 3
one or more features in the material may experience crack shearing that will imprint a signature on the high frequency reflected pulses.
Implementation Method 4
the source of the first acoustic wave can include a vibrating member that is configured to induce elastic nonlinearity in the material.
Data Source
Figure 1
Figure 2a~2b
Figure 3~3c
AI summary
In some aspects of the disclosure, a method and an apparatus is disclosed for investigating material surrounding the borehole. The method includes generating a first low frequency acoustic wave within the borehole, wherein the first low frequency acoustic wave induces a linear and a nonlinear response in one or more features in the material that are substantially perpendicular to a radius of the borehole; directing a first sequence of high frequency pulses, with a frequency 10 to 1000 times that of the low frequency acoustic wave, in a direction perpendicularly with respect to the longitudinal axis of the borehole into the material contemporaneously with the first acoustic wave; and receiving one or more second high frequency pulses at one or more receivers positionable in the borehole produced by an interaction between the first sequence of high frequency pulses and the one or more features undergoing linear and nonlinear elastic distortion due to the first low frequency acoustic wave to investigate the material surrounding the borehole.