Cement Acoustic Wavespeed Estimation Using Attenuation Dispersion
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Solution Overview
Problem
Existing cement evaluation methods in wellbore systems face ambiguity in determining cement acoustic properties due to sensitivity to environmental factors and the use of one-dimensional models, leading to inaccurate estimation of cement wavespeed and zonal isolation.
Innovation Solution
A method and system for estimating cement wavespeed by acquiring and processing acoustic waveforms to extract casing arrival signals, calculating attenuation dispersion, detecting discontinuities, and compensating for lateral beam spreading, allowing for accurate estimation of cement properties and wavespeed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the decay of flexural mode amplitude is used to determine cement properties, then the cement evaluation can be performed, but the result is ambiguous and double-valued
Solution Approach 1:
The patent introduces an intermediary parameter (attenuation dispersion of casing arrival signal) that mediates between the measured flexural mode decay and the cement acoustic impedance. This intermediary provides additional independent information that resolves the ambiguity in the inversion result, allowing unique determination of cement properties.
2Measurement precision
If the inversion method is used to estimate cement acoustic impedance, then the cement properties can be determined, but the estimation is not robust due to sensitivity to environmental effects
Solution Approach 1:
The patent changes the parameter being measured from direct acoustic impedance to attenuation dispersion of the casing arrival signal. This parameter change makes the measurement less sensitive to environmental effects such as mud acoustic impedance variations, thereby improving robustness while maintaining measurement precision.
3Device complexity
If the one-dimensional model is used for inversion, then the processing is simplified, but the results are inaccurate due to modeling errors
Solution Approach 1:
The patent replaces the mechanical inversion process based on one-dimensional models with an acoustic field-based approach using attenuation dispersion analysis. This substitution eliminates the need for simplified geometric models and their associated errors, achieving accurate cement wavespeed estimation without excessive complexity.
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
This approach provides unambiguous and robust estimation of cement wavespeed, enabling effective evaluation of cement conditions and zonal isolation, and predicting the longevity of the cement sheath, while reducing errors from environmental and modeling uncertainties.
Implementation Method 1
acquiring, at a plurality of acoustic receivers in the cement evaluation system, acoustic waveforms that have propagated through a casing, the annulus, or both
Implementation Method 2
calculating an attenuation dispersion (which may be a spectral amplitude ratio in some embodiments) of the casing arrival signal
Data Source
AI summary
Embodiments of the disclosure may include systems and methods for estimating an acoustic property of an annulus in a cement evaluation system. In one embodiment, a casing arrival signal is acquired at acoustic receivers a cement evaluation tool. A spectral amplitude ratio is calculated based on the casing arrival signal. The spectral amplitude ratio is scanned to detect and identify discontinuities. If discontinuities are detected, the frequency at the discontinuity may be used to estimate a wavespeed of the annulus. If discontinuities are not detected, attenuation dispersions are calculated and estimated, and an estimated wavespeed and parameters are updated until the calculated and estimated attenuation dispersions match.