Directional Sonic Logging With Monopole Screening for Low-SNR Dipole Data
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Solution Overview
Problem
Conventional LWD dipole measurements suffer from low signal-to-noise ratio (SNR) due to the averaging of azimuthal information, making them azimuthally insensitive and ineffective for directional measurements.
Innovation Solution
A method involving a directional sonic logging tool with a multipole transmitter and receiver arrays, which includes noise component evaluation, monopole screening, and data processing techniques such as time and frequency domain stacking to improve SNR by discarding noisy waveforms and aligning orthogonal pairs of measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stacking (averaging) multiple waveforms is used to improve SNR, then signal-to-noise ratio is improved, but azimuthal information is lost making measurements azimuthally insensitive
Solution Approach 1:
The patent segments the waveform data by separating it into monopole and dipole components through decomposition. This allows selective stacking of monopole components for noise reduction while preserving the dipole components that contain azimuthal information, thus resolving the contradiction between improving SNR and maintaining azimuthal sensitivity.
Solution Approach 2:
The patent extracts the monopole noise component from the total waveform signal and removes it through selective stacking. By taking out only the monopole portion for averaging while keeping the dipole portion intact, the method improves SNR without losing the azimuthal information contained in the dipole measurements.
2Object-affected harmful factors
If conventional stacking methods are applied to dipole measurements, then noise is reduced, but directional sensitivity is eliminated
Solution Approach 1:
The patent applies segmentation by decomposing the waveform into monopole and dipole modes. The monopole component is subjected to stacking for noise reduction, while the dipole component is preserved to maintain directional sensitivity, allowing both noise reduction and azimuthal measurement capabilities to coexist.
Solution Approach 2:
The patent applies local quality by treating different components of the waveform differently. The monopole portion undergoes aggressive noise reduction through stacking, while the dipole portion maintains its original characteristics to preserve azimuthal information, thus applying different processing qualities to different parts of the signal.
3Loss of information
If un-stacked dipole waveforms are used to maintain azimuthal sensitivity, then directional information is preserved, but signal-to-noise ratio becomes very low
Solution Approach 1:
The patent segments the waveform into monopole and dipole components, allowing the dipole component to be preserved unstacked to maintain azimuthal sensitivity while the monopole component is stacked to improve overall SNR, thus resolving the trade-off between noise reduction and directional information preservation.
Solution Approach 2:
The patent extracts and removes the monopole noise component through selective stacking while leaving the dipole component intact. This extraction approach improves the overall signal quality by reducing noise without compromising the azimuthal information contained in the unstacked dipole measurements.
Data Source
AI summary
A method for acoustic logging a wellbore includes making a plurality of directional sonic logging measurements while rotating an acoustic logging tool in a wellbore. A noise component of each of the measurements is compared with a threshold. Measurements for which the noise component is greater than the threshold are discarded. Measurements for which the noise component is less than the threshold are retained.