Analyzing Seismic Azimuthal Amplitude by Fourier Decomposition

HTI media yield azimuth-dependent reflectivities which may relate to fracture parameters. However, azimuthal information in seismic data is susceptible to bias resulting from acquisition or processing.

This paper describes a method which analyses azimuthal information in seismic data. This method is designed to QC azimuthal information and to detect and potentially characterise bias. The method can analyse the effect of each processing stage on amplitude-azimuth behaviour. It requires large azimuthal coverage and was thus developed using OBC data.

We first eliminate the cross-talk between azimuth and offset. We then apply an iterative irregular Fourier Transform to amplitude-azimuth data. The magnitude and phase of each Fourier mode characterises the azimuthal information.

Application of the method to a North Sea OBC dataset reveals signs of potential bias. The presence of strong odd Fourier modes is potentially indicative of multiple contamination and acquisition geometry is found to dominate azimuthal behaviour. The impact of typical processes, including Radon and residual moveout corrections, are also assessed.