Spectral and Phase Decomposition Case Studies

Evaluating the quality of seismic data based on the amplitude spectrum alone can be misleading, especially when comparing independently acquired and processed datasets. Spectral decomposition and frequency-dependent coherence can be combined to compare stratigraphic and structural details as a function of frequency. When this approach is applied to two 3D seismic datasets (2011 Legacy and 2015 Broadband) from the Chinook Field in the Gulf of Mexico, although the legacy and the broadband data have the same peak frequency and high-frequency cutoff, iso-frequency volumes from the Continuous Wavelet Transform and frequency-dependent coherence attributes indicate that the broadband data has better geological interpretability at high frequency. When phase decomposition is applied to pre-stack attributes on a 2D line across a thin 8-meter thick, gas-saturated reservoir in eastern Alberta, Canada, amplitude variation with angle is magnified on the -90o phase component, showing a stronger amplitude-versus-angle effect. The -90o far-offset component allows better mapping of the lateral extent of the reservoir. This amplification is also seen on the -90o phase component of the gradient attribute. The results are corroborated by seismic modeling which shows the same phase component relationships for near and far angle stacks and the gradient attribute.