Seismic Numerical Modelling And Migration Using Frequency-Adaptive Meshes

Seismic numerical modelling and migration are key steps in seismic processing main body and their results are impacted by many factors. For grid-based methods, the grid interval is one of the most important factors controlling the computational efficiency and accuracy. Considering the advantage of frequency-domain methods in efficiency, in this paper we mainly study the influence of different meshes on frequency-domain modelling and migration.First, we introduce relevant theory of the illumination analysis and apply the ray-based illumination analysis in imaging complex media. Results indicate the good performance of the ray-based illumination analysis. Then we use the Pade generalized screen propagator (GSP) as an example. According to results of illumination analysis, modelling and migration, we discuss its numerical stability and investigate the influences of different grid schemes on the image quality under different acquisition geometries, i.e. different trace intervals. Experiments suggest that numerical stability still needs to be considered. Overlook on it may cause severe errors in understanding the migration result. When dealing with insufficient spatial-sampling data, both the regular interpolations among traces and using finer grid are not helpful in improving the migration result.As the main body of this paper, we apply the frequency-adaptive meshes to the GSP modelling and migration. In the frequency-adaptive meshes method, different meshes are used for different frequency computation. Meshes are coarse for low-frequency computation and relatively fine for high-frequency computation. Grid meshes coincide with frequencies. And its key factor is the function describing the grid varying with the frequency. Several examples show its validity in avoiding anomalies of the propagation angle for low-frequency components and the wavefield illusions for high-frequency components produced by regular fixed-mesh GSP. Without modifying the propagator, this approach can be extended to other frequency-domain propagators.