Multi-mode Inversion for Shear Anisotropy Logging
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Solution Overview
Problem
Current acoustic logging techniques face challenges in accurately determining formation anisotropy and shear slowness in hydrocarbon reservoirs, particularly in anisotropic formations, which affects the precision of subsurface imaging and reservoir delineation.
Innovation Solution
The implementation of multi-mode inversion methods and shear slowness analysis using acoustic logging systems that generate and detect various wave modes, such as compressional and flexural waves, to derive accurate dispersion curves and determine shear wave anisotropy and slowness, accounting for factors like mud speed and borehole conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional acoustic logging techniques are used, then the logging process is simple, but the measurement precision of formation anisotropy and shear slowness deteriorates in anisotropic formations
Solution Approach 1:
The acoustic logging system segments the measurement process by separately measuring compressional wave velocity and shear wave velocity using different transducer configurations. Compressional waves are measured using axial transducers, while shear waves are measured using radial transducers, allowing independent optimization of each measurement mode for improved precision in anisotropic formations.
Solution Approach 2:
The system transitions from single-mode to multi-mode acoustic measurement by incorporating both compressional and shear wave measurements. This dimensional expansion in measurement space enables the system to capture the full elastic tensor properties of anisotropic formations, resolving the precision limitation of conventional single-mode logging.
2Measurement precision
If multi-mode inversion methods are implemented, then the accuracy of subsurface imaging improves, but the processing complexity increases
Solution Approach 1:
The system performs preliminary separation of compressional and shear wave signals before inversion processing. By pre-processing the raw acoustic data to isolate different wave modes and their respective velocity components, the subsequent inversion process becomes more tractable and computationally efficient, reducing the complexity burden of multi-mode inversion.
Solution Approach 2:
The inversion method transforms the complex anisotropic formation characterization problem into a series of parameter estimation problems by changing from direct tensor inversion to sequential estimation of elastic constants (Vp, Vs, anisotropy parameters). This parameter transformation simplifies the mathematical complexity while maintaining imaging accuracy.
3Loss of information
If shear wave anisotropy analysis is performed, then the delineation of reservoirs and formation boundaries improves, but the time required for data processing increases
Solution Approach 1:
The system extracts shear wave anisotropy information as a separate, dedicated measurement component from the full acoustic log data. By isolating and specifically analyzing shear wave propagation characteristics independent of compressional wave data, the system efficiently extracts critical formation boundary and reservoir delineation information without requiring exhaustive processing of all acoustic parameters.
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 enhances the accuracy of subsurface imaging by providing detailed logs of shear wave anisotropy and slowness, enabling better delineation of reservoirs and identification of formation boundaries, fractures, and improving the economic value of hydrocarbon reservoirs.
Implementation Method 1
An acoustic source generates acoustic waves that propagate primarily in a compressional and a Stoneley wave mode
Implementation Method 2
The monopole transmitter generates waveform signals that propagate primarily in a compressional and a Stoneley wave mode; The multi-pole transmitter generates waveform signals that propagate in a flexural or higher-order mode
Implementation Method 3
The receiver array converts the acoustic waves into electrical signals
Data Source
AI summary
Acoustic logging systems and methods are provided with multi-mode inversion for at least vertical shear slowness and shear anisotropy. At least some method embodiments acquire waveforms for multiple acoustic wave modes as a function of tool position in a borehole, derive position-dependent mode dispersion curves from the waveforms, match the derived dispersion curves with parameterized dispersion curves to determine a vertical shear slowness and a shear anisotropy as a function of position, and displaying a borehole log that represents at least one of the vertical shear slowness and the shear anisotropy as a function of position. The objective function employed for the inversion is evaluated across multiple wave propagation modes and mud slownesses and may employ an adaptive, frequency-dependent weighting based on distance between the derived dispersion curves and the parameterized dispersion curves.