Directional Sonic Logging Waveform Stacking for Azimuthal SNR
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Solution Overview
Problem
Conventional LWD dipole measurements suffer from low signal-to-noise ratio (SNR) due to averaging out 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 screening for excessive noise, identifying orthogonal pairs of measurements, rotating and stacking waveforms in the time and frequency domains to improve SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional stacking methods are used to improve SNR, then signal-to-noise ratio is improved, but azimuthal information is averaged out making measurements azimuthally insensitive
Solution Approach 1:
The patent segments the dipole measurements into orthogonal pairs (e.g., X-X, X-Y, Y-X, Y-Y components) and processes each pair separately through rotation and stacking. This segmentation allows preservation of azimuthal directional information while still achieving noise reduction through stacking within each orthogonal pair, thereby resolving the contradiction between improving SNR and maintaining azimuthal sensitivity.
2Loss of information
If un-stacked dipole waveforms are used to preserve azimuthal information, then azimuthal sensitivity is maintained, but signal-to-noise ratio becomes very low
Solution Approach 1:
The patent applies dynamic rotation of the dipole measurements to align orthogonal pairs with the tool orientation, then dynamically stacks the rotated waveforms. This dynamic processing approach allows the system to adaptively preserve azimuthal information while improving SNR, rather than using static conventional stacking methods that would average out directional sensitivity.
3Object-affected harmful factors
If conventional stacking is applied to dipole measurements, then noise is reduced, but transverse anisotropy detection capability is lost
Solution Approach 1:
The patent introduces a rotational dimension to the stacking process by rotating dipole measurements into orthogonal pairs before stacking. This dimensional transformation allows the system to stack waveforms for noise reduction while maintaining the ability to detect transverse anisotropy through the preserved orthogonal component relationships, thus resolving the contradiction between noise reduction and anisotropy detection capability.
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 plurality of orthogonal pairs of measurements are identified among the measurements. Each of the orthogonal pairs includes a first measurement having a measured angle of a transmitter firing direction that is perpendicular with a measured angle of a transmitter firing direction of a second measurement within a predetermined tolerance. A set of 4C component waveforms is compiled for each of the identified orthogonal pairs and mathematically rotated to align with predefined axes. Selected ones of the rotated waveforms are then stacked in the time domain.