Calibrating Sonic Log Anisotropy with Walkaway VSP Data
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Solution Overview
Problem
Current methods for determining elastic anisotropy in subsurface formations, such as the ANNIE model, often fail to accurately represent Thomsen's delta parameter and require assumptions that may not be universally applicable, leading to incomplete characterization of elastic properties.
Innovation Solution
A method that combines sonic logging and borehole seismic data by receiving seismic and sonic measurements, making initial assumptions about the subsurface formation's anisotropy, calculating elastic constants, comparing sonic and seismic data attributes, and adjusting these assumptions to derive effective elastic constants through upscaling, thereby avoiding the limitations of existing models.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the ANNIE model is used to determine elastic anisotropy from sonic logging data, then the processing is simplified and only three parameters are required, but Thomsen's delta parameter cannot be accurately determined and the model may not be universally applicable
Solution Approach 1:
The patent combines sonic logging data with walkaway VSP seismic data to determine elastic anisotropy parameters. By merging these two data sources, the method overcomes the limitation of the ANNIE model which cannot accurately determine Thomsen's delta parameter, while avoiding the complexity of using all four parameters from both methods independently.
Solution Approach 2:
The patent uses an iterative optimization process where the elastic anisotropy parameters are initially determined from sonic logging data, then compared with walkaway VSP data, and adjusted through feedback until the parameters satisfy both data sets. This feedback mechanism ensures accurate determination of Thomsen's delta parameter while maintaining processing efficiency.
2Loss of information
If all four elastic anisotropy parameters (C44, C66, mC33, N) are used from sonic logging, then complete characterization is achieved, but the data cannot be directly compared with walkaway VSP data without additional processing
Solution Approach 1:
The patent transforms the four elastic anisotropy parameters (C44, C66, mC33, N) derived from sonic logging into Thomsen's anisotropy parameters (ε, δ, γ) which can be directly compared with walkaway VSP data. This parameter transformation maintains complete characterization of elastic properties while enabling direct comparison between the two data sources.
3Measurement precision
If conventional VSP methods are used to extract anisotropy parameters, then four parameters can be obtained, but horizontally polarized shear wave behavior (Thomsen's gamma) cannot be measured
Solution Approach 1:
The patent uses dipole sonic logging tools that can measure multiple wave types including compressional waves, shear waves, and horizontally polarized shear waves. This multi-functional capability allows determination of all three Thomsen parameters (ε, δ, γ), making the method universally applicable to different wave types and more versatile than conventional VSP methods.
Data Source
AI summary
Methods and related systems are described relating to processing subsurface sonic and seismic data. The described techniques use anisotropy estimates derived from a walkaway VSP to calibrate elastic properties derived from sonic logs. An empirical relationship between the sonic derived anisotropy parameters is modified until the upscaled elastic properties from the sonic log data best matches the anisotropy parameters measured with the walkway VSP. The result is a set of elastic constants consistent with the walkaway VSP measurements.