Seismic anisotropy in Trinidad:
Processing and interpretation  

Tariq Alkhalifah and Dave Rampton

ABSTRACT

The lithology of offshore Trinidad is formed of alternating sequences of sand and shale dominated layers. Average (effective) anisotropy is much lower in Trinidad compared to the prevoiusly studied area of offshore Angola due to the large amount of sand in the subsurface. Nevertheless, accounting for anisotropy in seismic processing results in improved imaging of structural and stratigraphic features. The imaging improvement is shown for two different lines from that region. Inversion for an interval value of the anisotropy parameter ($\eta$), suggests that low values are correlated with sands (or any other isotropic material), while high interval $\eta$ values are correlated with shales. Correlation between separate independent measurements for $\eta$ across common midpoints (CMPs) enhances the credibility of such estimates as a representation of real geologic parameters. Finally, the $\eta$ curve agrees well with gamma-ray well-log measurements used as a shale estimate. This result confirms the hypothesis that anisotropy is due to shales in the subsurface, and the inversion for interval $\eta$ can subsequently be used to predict lithology.