Radial Shear Velocity Profiling via Flexural Mode Dispersion
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Solution Overview
Problem
Current formation evaluation methods using sonic well logging face challenges in accurately determining shear wave velocity profiles in alteration zones around boreholes, where material and structural discontinuities lead to complex acoustic properties, making it difficult to characterize near-field shear velocities effectively.
Innovation Solution
The method involves using a dipole acoustic tool to measure flexural wave phase velocities, generating dispersion curves, and constructing sensitivity kernels to estimate shear wave slowness radial profiles through a linear approximation model, allowing for improved characterization of shear velocities in the alteration zone by inverting constrained linear equations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sonic well logging methods are used to measure wave velocities in alteration zones, then basic formation properties can be obtained, but the accuracy of shear wave velocity profiles deteriorates due to material and structural discontinuities
Solution Approach 1:
The alteration zone is divided into multiple radial layers, each with potentially different acoustic properties. The measurement system segments the complex heterogeneous zone into manageable discrete layers, allowing independent characterization of shear wave velocity in each layer while accounting for material discontinuities and structural variations.
Solution Approach 2:
The invention measures multiple wave velocity parameters (compressional wave velocity, shear wave velocity, Stoneley wave velocity) and uses their relationships to derive accurate shear wave velocity profiles. By changing from single-parameter to multi-parameter measurement and utilizing the interrelationships between different wave types, the system overcomes the limitations of conventional methods in complex alteration zones.
2Loss of information
If detailed radial profiling of shear velocities is implemented, then formation characterization improves, but measurement and processing complexity increases
Solution Approach 1:
The dipole acoustic tool is designed to perform multiple measurement functions simultaneously - measuring compressional wave velocities, shear wave velocities, and Stoneley wave velocities using the same physical device. This multi-functionality allows comprehensive formation characterization without requiring separate specialized tools for each measurement type, thus improving information quality while controlling device complexity.
Solution Approach 2:
The invention uses measured wave velocity data as an intermediary to indirectly determine shear wave velocity profiles in the alteration zone. Rather than directly measuring difficult-to-obtain parameters, the system measures accessible wave velocities and uses theoretical relationships and inversion techniques to derive the desired shear wave velocity information, simplifying the direct measurement challenge.
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 and efficiency of formation evaluation by providing detailed radial shear wave velocity profiles, enabling better analysis of formation properties and improving drilling operations.
Implementation Method 1
emitting acoustic energy to generate flexural waves in a surrounding formation
Implementation Method 2
measuring velocities of the returning flexural waves
Data Source
AI summary
A method is disclosed for radiaiiy profiling shear velocities of flexural wave modes in a formation. The method includes establishing sensitivity kernels with two non-dimensionalized parameters and using said sensitivity kernels to perform an inversion for radial shear wave velocity profiles. This method may be used for LWD, MWD, or wireline logging operations.