LWD Acoustic Dipole Source for Anisotropic Formation Shear Direction
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Solution Overview
Problem
Current logging-while-drilling (LWD) acoustic measurement tools face challenges in obtaining complete anisotropy characterization of formations due to strong interference and coupling from collar modes, inability to maintain cross-dipole orthogonal firing, tool eccentering, and signal-to-noise ratio issues, limiting their ability to determine fast and slow shear slownesses and azimuthal directions.
Innovation Solution
The implementation of a time-domain and frequency-domain workflow for LWD acoustic measurement tools, which includes non-orthogonal dipole firings and multi-component waveform rotation algorithms to extract the fast shear azimuth direction, allowing for the estimation of fast and slow shear slownesses and complete anisotropy characterization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional LWD acoustic measurement tools are used, then drilling efficiency is improved, but complete anisotropy characterization cannot be achieved due to collar mode interference and other limitations
Solution Approach 1:
The acoustic source is segmented into multiple dipole elements arranged in specific orientations (e.g., orthogonal or non-orthogonal configurations). This segmentation allows independent excitation of different wave modes and directions, enabling separation of collar modes from formation modes and achieving complete anisotropy characterization while maintaining drilling efficiency
Solution Approach 2:
The patent transitions from conventional single-component or two-component measurements to multi-component waveform measurements (e.g., four-component or more). This dimensional expansion in measurement space provides additional independent equations to solve for multiple unknowns including fast and slow shear slownesses and azimuthal directions, resolving the contradiction between speed and measurement completeness
2Measurement precision
If cross-dipole orthogonal firing is implemented, then shear directionality measurement is improved, but tool complexity and operational difficulty increase
Solution Approach 1:
The dipole element array is designed to perform multiple functions: it can excite both collar modes and formation modes, measure both fast and slow shear waves, and determine azimuthal directions. This multi-functionality eliminates the need for separate measurement systems, reducing overall device complexity while maintaining high measurement precision
Solution Approach 2:
The patent employs dynamic signal processing techniques including time-domain and frequency-domain workflows that can adapt to varying tool orientations and formation properties. The system dynamically adjusts processing parameters based on real-time measurements, simplifying operational procedures while maintaining accurate shear directionality determination
3Productivity
If conventional monopole and quadrupole measurements are used, then processing speed is improved, but complete anisotropy characterization is not achieved
Solution Approach 1:
The system performs preliminary separation of collar modes and formation modes in the raw signal before detailed analysis. By pre-processing the signals to isolate formation responses and remove collar mode contamination, the subsequent anisotropy characterization can be performed quickly and accurately without losing critical information
Solution Approach 2:
The patent uses intermediate processing steps including waveform rotation algorithms and dispersion analysis as mediators between raw multi-component measurements and final anisotropy parameters. These intermediary processes efficiently transform complex multi-dimensional data into meaningful geological information, maintaining both speed and information completeness
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 enables the determination of fast and slow shear slownesses and azimuthal directions, providing a comprehensive characterization of anisotropic formations, overcoming the limitations of existing LWD tools and improving the accuracy of formation evaluation.
Implementation Method 1
the at least one dipole acoustic source is operated to excite a time-varying pressure field in the anisotropic formation surrounding the borehole
Implementation Method 2
The array of receivers are used to measure waveforms arising from the time-varying pressure field in the anisotropic formation surrounding the borehole
Data Source
AI summary
Methods are provided for determining properties of an anisotropic formation (including both fast and slow formations) surrounding a borehole. A logging-while-drilling tool is provided that is moveable through the borehole. The logging-while drilling tool has at least one dipole acoustic source spaced from an array of receivers. During movement of the logging-while-drilling tool, the at least one dipole acoustic source is operated to excite a time-varying pressure field in the anisotropic formation surrounding the borehole. The array of receivers is used to measure waveforms arising from the time-varying pressure field in the anisotropic formation surrounding the borehole. The waveforms are processed to determine a parameter value that represents shear directionality of the anisotropic formation surrounding the borehole.