Resonance-Based Acoustic Impedance Inversion for Wellbore Cement Evaluation
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Solution Overview
Problem
Conventional acoustic evaluation techniques for wellbore cement integrity are inaccurate in thicker casings and acoustically-attenuative wellbore environments, leading to reduced accuracy in determining zonal isolation and acoustic impedance.
Innovation Solution
A resonance-based inversion workflow that normalizes acoustic waveforms and matches them with reference waveforms to iteratively estimate wellbore parameters such as acoustic impedance and casing thickness, improving the accuracy of cement evaluation in thicker casings and deviated wellbores.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional acoustic evaluation techniques are used, then the measurement process is simple, but the accuracy of zonal isolation and acoustic impedance determination is reduced in thicker casings and acoustically-attenuative wellbore environments
Solution Approach 1:
The patent utilizes acoustic vibrations and resonance phenomena to evaluate cement integrity. The ultrasonic pulse-echo tool transmits broadband pulses to excite thickness resonance modes in the casing, and the resonance-based inversion technique analyzes the resonant frequencies and damping characteristics to determine acoustic impedance and cement quality, thereby improving measurement precision through vibrational analysis
Solution Approach 2:
The patent implements an iterative inversion process where measured acoustic waveforms are continuously compared with modeled waveforms. The resonance-based inversion technique adjusts model parameters (acoustic impedance, casing thickness) based on the difference between measured and modeled resonance characteristics, creating a feedback loop that converges on accurate parameter values, thus resolving the accuracy problem in complex wellbore environments
2Strength
If thicker casings are used, then the structural strength and integrity are improved, but the acoustic behavior becomes more complex and reduces the accuracy of cement evaluation
Solution Approach 1:
The patent employs resonance-based analysis that is particularly effective for thicker casings. By exciting thickness resonance modes and analyzing the resonant frequencies and decay characteristics, the technique can accurately determine acoustic impedance and cement quality even in thicker casing configurations where conventional methods fail, thus resolving the contradiction between structural strength and measurement precision
Solution Approach 2:
The patent changes the analysis parameters from simple pulse transmission time to resonance frequency and damping characteristics. The resonance-based inversion technique uses multiple resonance modes and their frequency shifts to extract accurate parameter information from thicker casings, allowing the measurement precision to be maintained or improved despite the increased casing thickness
3Reliability
If acoustically-attenuative wellbore environments are used, then the wellbore stability and mud weight are improved, but the acoustic signal attenuation increases and reduces measurement accuracy
Solution Approach 1:
The patent utilizes resonance phenomena that are less sensitive to acoustic attenuation than conventional pulse-echo methods. By measuring the resonant frequencies and quality factors of the casing-cement system, the technique can accurately determine acoustic impedance even in acoustically-attenuative environments with heavy muds, thus maintaining measurement precision while ensuring wellbore stability
Solution Approach 2:
The patent converts the harmful effect of acoustic attenuation into a beneficial measurement parameter. By analyzing the damping characteristics and quality factors of resonance modes, the technique can actually improve measurement accuracy by using the attenuation information itself to characterize the wellbore environment and cement properties, turning the harmful attenuation into a useful measurement signal
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 resonance-based inversion technique enhances the accuracy of wellbore parameter estimation, providing more reliable zonal isolation and acoustic impedance measurements, even in challenging wellbore conditions, compared to conventional methods.
Implementation Method 1
Certain acoustic measurements, such as the ultrasonic pulse-echo measurement, have been widely used in cement evaluation to provide the effective acoustic impedance of the annulus material adjacent to the casing
Implementation Method 2
an ultrasonic pulse-echo tool may transmit a broadband pulse, usually between 200 and 700 kHz, to the casing wall to excite a thickness resonance mode in the casing
Data Source
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AI summary
Techniques involve obtaining acoustic data from an acoustic logging tool, where the acoustic data includes waves reflected from the casing, the annular fill material, the formation, and/or interfaces between any of the casing, the annular fill material, one or more interfaces between any of the mud, the casing, and the annular fill material. Techniques include normalizing the acoustic wave to result in a normalized wave having a comparable spectral shape with a reference wave, and comparing the normalized wave with the reference wave. The reference wave may be generated or modeled or produced from a look-up table or database, and may be estimated based on initial estimates of wellbore parameters. Based on the comparison of the normalized wave with the reference wave, a best-fit reference wave substantially matching the normalized wave may be identified. The best-fit reference wave may correspond with a thickness of the casing, an acoustic impedance of the annular fill material, and an acoustic impedance of mud.