Ultrasonic Televiewer Wood-Grain Reduction via Ringdown Subtraction
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Solution Overview
Problem
Acoustic logging tools face challenges in reducing the 'wood-grain' interference pattern in ultrasonic images of borehole sidewalls due to transducer ringdown and eccentricity, which limits image quality and feature detection.
Innovation Solution
A method involving the construction of a background modulation template using peak amplitude and arrival time values, followed by estimation and subtraction of an azimuthally varying interference pattern to mitigate ringdown effects, allowing for improved image quality and feature preservation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If a pulse-echo transducer is excited to obtain echo signals from the borehole formation, then the desired formation information is obtained, but transducer ringdown and reverberation noise are generated that interfere with the echo signals and create a wood-grain pattern in the image
Solution Approach 1:
The patent extracts and removes the interfering ringdown and reverberation components from the received signal. By identifying and separating these harmful noise components from the desired echo signal, the method preserves the formation information while eliminating the wood-grain interference pattern that degrades image quality
Solution Approach 2:
The patent introduces an intermediary processing step that models and subtracts the ringdown and reverberation effects from the received signal. This intermediary approach allows the desired echo information to be recovered by treating the noise components as separate entities that can be mathematically removed
2Productivity
If the televiewer rotates at a desired rate to continuously scan the borehole sidewall, then continuous imaging coverage is achieved, but the echo signal arrival time changes with instrument centralization and borehole shape, causing modulation by stationary noise
Solution Approach 1:
The patent performs preliminary processing to determine the actual arrival time of each echo signal before image construction. By calculating the precise arrival time of reflected acoustic energy for each azimuthal position, the method compensates for variations caused by tool eccentricity and borehole geometry, ensuring accurate positioning of features in the final image
Solution Approach 2:
The patent dynamically adjusts the arrival time determination for each echo signal based on its specific temporal position and azimuthal location. Rather than using a fixed time window, the method adapts the signal processing to account for varying travel times caused by changing tool-formation geometry during rotation, maintaining measurement precision throughout the scanning process
3Measurement precision
If higher acoustic frequencies are used to achieve better resolution in the confined borehole space, then spatial resolution is improved, but the acoustic energy is severely attenuated by borehole fluid contaminated with drill cuttings, air bubbles and foreign matter
Solution Approach 1:
The patent replaces purely hardware-based signal enhancement with a software-based signal processing approach. By using digital signal processing techniques to remove ringdown and reverberation noise, the method enables the use of higher frequencies for improved resolution without being limited by the additional energy loss from contaminated borehole fluid, as the processing compensates for the degraded signal quality
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 method effectively reduces 'wood-grain' interference, enhancing image quality and enabling better detection of borehole features, even in legacy data without requiring raw waveforms, thus improving interpretation and analysis.
Implementation Method 1
A beam of acoustic pulses is launched along the normal to the borehole sidewall as the transducer scans the interior surface of the borehole. The insonified borehole sidewall returns pulses reflected therefrom, back to the transducer
Implementation Method 2
Transducer ringdown is related to transmitter construction, internal damping and transducer and load impedance mismatches. When a pulse-echo transducer is excited, a series of reflections of the transmit pulse within the transducer are generated, and superimposed upon the received echo
Implementation Method 3
the borehole fluid is contaminated by drill cuttings, air bubbles and foreign matter which may severely attenuate the acoustic energy via scattering because the physical dimensions of the contaminants are comparable to the wavelength of the wavefields emitted by the transducer
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
Systems, devices, and methods for evaluating an earth formation intersected by a borehole using signals produced at a plurality of borehole depths by an ultrasonic transducer in the borehole, the signals produced by the transducer including ringdown signals from the ultrasonic transducer and echo signals from a wall of the borehole from a plurality of azimuthal orientations. Methods include using peak amplitude values and arrival time values from the signals to construct a background modulation template corresponding to at least one depth; estimating, for each respective depth of the plurality of borehole depths, an azimuthally varying interference pattern predominantly resulting from a ringdown signal for each respective depth by mapping the modulation template to arrival time values corresponding to the respective depth; and subtracting, for each respective depth, the estimated varying interference pattern from the peak amplitude values corresponding to the respective depth to generate adjusted peak amplitudes.