Azimuthal Simultaneous Elastic Inversion for Anisotropic Fracture Characterization
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Solution Overview
Problem
Conventional seismic data processing methods provide limited and biased estimates of elastic attributes in anisotropic subterranean formations, particularly due to assumptions of isotropic media and reliance on near offset approximations, leading to reduced resolution and systematic errors in fracture information.
Innovation Solution
A computer-implemented method for azimuthal simultaneous elastic inversion that calculates reflectivity using the anisotropic Zoeppritz equation, incorporating alternative parameterizations such as Thomsen parameters and rock physics models like penny-shaped crack theory, to accurately estimate elastic parameters in HTI anisotropic media without near offset approximations, thereby reducing ambiguity and improving stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional isotropic inversion methods are used, then the processing is simpler and faster, but the estimation of elastic parameters in anisotropic formations is biased and has reduced resolution
Solution Approach 1:
The patent transforms the inversion problem from estimating traditional elastic parameters (Vp, Vs, density) to estimating anisotropic parameters (Thomsen parameters ε, δ, γ and symmetry axis orientation). This parameter transformation enables accurate characterization of anisotropic formations by changing the fundamental variables being inverted, thereby resolving the bias inherent in isotropic methods while maintaining computational feasibility through specialized algorithms.
2Reliability
If near offset approximations are used, then the inversion is more stable, but systematic errors are introduced in fracture information
Solution Approach 1:
The patent implements a two-stage inversion approach where a preliminary isotropic inversion is performed first to obtain initial models, followed by an anisotropic inversion that refines the estimates. This partial action strategy allows the method to benefit from the stability of simpler initial estimates while progressively incorporating the more accurate but computationally intensive anisotropic corrections, thereby reducing systematic errors without sacrificing overall stability.
3Loss of information
If azimuthal AVO inversion is performed, then fracture information can be obtained, but the bandwidth is limited and resolution is reduced
Solution Approach 1:
The patent merges azimuthal AVO inversion with full waveform inversion (FWI) techniques, combining the fracture-sensitive azimuthal information with the high-resolution bandwidth capabilities of FWI. This integration allows the method to simultaneously recover both fracture characteristics (through anisotropic parameters) and high-frequency elastic properties, thereby overcoming the bandwidth limitations of conventional azimuthal AVO while maintaining complete fracture information.
4Measurement precision
If anisotropic Zoeppritz equations are used, then accurate reflectivity calculation is achieved, but the computational complexity increases
Solution Approach 1:
The patent performs preliminary linearization of the anisotropic Zoeppritz equations before the inversion process, deriving approximate reflection coefficient expressions that are linear in the anisotropic parameters. This preliminary action transforms the complex nonlinear problem into a more tractable linear or weakly nonlinear system, maintaining accuracy for small-to-moderate anisotropy while significantly reducing computational complexity and enabling faster inversion processing.
Data Source
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AI summary
An improved method for analyzing seismic data to obtain elastic attributes is disclosed. In one embodiment, a reflectivity series is determined for at least one seismic trace of seismic data obtained for a subterranean formation, where the reflectivity series includes anisotropy properties of a formation. One or more synthetic seismic traces are obtained by convolving the reflectivity series with a source wavelet. The one or more synthetic seismic traces are inverted to obtain elastic parameters estimates. According to one aspect, the data inputs are angle-azimuth stacks. According to another aspect, the data inputs are azimuthal Fourier coefficients, un, vn.