EVALUATION OF ELASTIC IMPEDANCE ATTRIBUTES IN OFFSHORE HIGH ISLAND, GULF OF MEXICO
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In certain areas, seismic AVO alone is not sufficient for interpretative purposes. This necessitates the use of other seismic attributes. The High Island Field, a Tertiary basin in the Gulf of Mexico, has values of acoustic impedance for shale and gas-saturated sands that are approximately equal. Conventional 3-D seismic data has had limited success in detecting hydrocarbons in this area. Also, synthetic seismograms are difficult if not impossible to tie to seismic data. To solve these problems, I employed the elastic impedance and extended elastic impedance attributes. Results from this research show significant amplitude increase with offset for a gas-saturated reservoir as compared to brine-saturated reservoir. The elastic impedance volume derived from the far-angle stack delineates the reservoir better than the elastic impedance volume from the near-angle stack. With respect to reservoir characterization, the five seismic attributes (Vp/Vs, bulk modulus, shear modulus, Lamé, and shear impedance) generated from the extended elastic impedance inversion helped to determine the lithology and predict the pore-fluid type of the reservoir. In conclusion, the use of additional seismic attributes (elastic impedance and extended elastic impedance) helps to achieve a better reservoir characterization especially in a Class 2 environment.