Prestack Seismic Wave Separation via Anisotropic Rotation
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Solution Overview
Problem
In three-dimensional three-component seismic exploration, the 'mode leakage' phenomenon occurs due to azimuthal anisotropy in subsurface structures, leading to errors in predicting fracture parameters as P and split S-waves interfere and project onto all components, making traditional surface processing amplitude non-preserving and inaccurate.
Innovation Solution
A prestack separating method that projects P-wave, S1-wave, and S2-wave into a Z-R-T coordinate system, forms composite vectors, transforms them into an anisotropic wave vector matrix, and performs an affine coordinate system rotation to generate a wave separation matrix, assuming no orthogonal polarization, thereby separating seismic waves into true wave vector directions of pure P-wave, S1-wave, and S2-wave.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional RT rotation is used to process 3-C seismic data under isotropic, flat-layered, and low-velocity assumptions, then S-wave can be received by R-component and T-component only receives noises, but the assumption is not acceptable in most 3-C seismic explorations due to azimuthal anisotropy and tilted strata
Solution Approach 1:
The patent changes the fundamental parameters of wave separation by abandoning the traditional RT rotation approach based on isotropic assumptions and adopting a new method that explicitly accounts for azimuthal anisotropy and tilted strata. The new approach uses different rotation matrices for P-waves and S-waves, with S-wave separation considering both fast (S1) and slow (S2) modes, thereby improving reliability while maintaining operational feasibility
Solution Approach 2:
The patent segments the wave separation process into distinct components: P-wave separation using one rotation matrix, and S-wave separation using another rotation matrix that accounts for anisotropy. This segmentation allows each wave type to be processed with appropriate assumptions and methods, improving overall accuracy without overwhelming complexity
2Productivity
If S1-wave and S2-wave are separated from stacked SV-section and SH-section in traditional surface processing, then fracture parameters can be predicted, but amplitude is not preserving and great errors occur due to mode leakage from tilted strata
Solution Approach 1:
The patent performs wave separation at the prestack level before stacking and imaging operations, rather than separating waves after stacking. This preliminary separation ensures that P-waves and S-waves (including S1 and S2 modes) are isolated in their pure forms before any processing that could cause mode leakage, thereby preserving amplitude accuracy and enabling reliable fracture parameter prediction
Solution Approach 2:
The patent introduces rotation matrices as intermediary transformation tools that systematically convert seismic data from the recorded coordinate system to the wave propagation coordinate system. These rotation matrices serve as mediators that properly account for azimuthal anisotropy and tilted strata, preventing mode leakage and preserving amplitude information throughout the processing workflow
Data Source
AI summary
The present disclosure provides a prestack separating method for a seismic wave, including: receiving P-wave, S1-wave and S2-wave of the seismic wave, wherein the P-wave, S1-wave and S2-wave are reflected from different points; projecting the P-wave, S1-wave and S2-wave into a Z-R-T coordinate system, so as to generate a projection matrix, wherein Z is a vertical component, R is a component of a source-to-receiver azimuth and T is a component orthogonal to the R component; forming vectors of the P-wave, S1-wave and S2-wave as a composite vector; transforming the composite vector to an anisotropic wave vector matrix according to base vectors on the vector directions of the P-wave, S1-wave and S2-wave; and performing a rotation transformation of an affine coordinate system on the anisotropic wave vector matrix to generate a wave separation matrix, thereby solving a problem of error prediction result of fracture parameters caused by the “mode leakage” phenomenon.