Seismic amplitude variation with offset: Its effects on weighted stacking, and its uses in characterization of sandstone and carbonate reservoirs

An algorithm for weighted stacking, which is not particularly expensive in terms of computer time or memory and can be easily incorporated into routine processing is proposed. A comprehensive comparison of the proposed weighted stacking algorithm and the conventional stacking algorithm is conducted through testing on synthetics and a real data set from New Mexico, USA. This weighted stacking algorithm achieves the primary goal of signal-to-noise ratio improvement while at the same time providing better resolution, wider bandwidth, and a higher signal-to-noise ratio than the conventional stack.; A novel hydrocarbon indicator [the water-filled porosity (S _wv)], which is estimated from the ratio of P-velocity to S-velocity (V_p/V_s), is proposed and applied to characterize clastic hydrocarbon reservoirs in the North Sea. The separation between pore fluids and lithologies is enhanced by mapping from V _p/V_s to S_wv using an empirical crossplot-derived relationship. The S_wv-V _p/V_s plane still does not produce unique interpretations in many situations. However, the critical distinction, which is between hydrocarbon-bearing sands and all other geologic/reservoir configurations, is defined.; Porosity is the dominant factor controlling reservoir signature for carbonate rocks. Acoustic impedance and seismic amplitudes are porosity and lithology indicators. Angle-dependent reflectivity effects are introduced for determination of fluid charactersitics by simultaneous elastic impedance inversion of three non-overlapping migrated common-angle stacked sections for P- and S-impedance (I_p and I_s). Deviations of points from a water-filled baseline in the I_p-I _s plane define a gas potential section that is used for direct identification of gas zones in the dolomitized limestone reservoirs of the Turner Valley Formation in southern Alberta, Canada. There is consistency with the known gas production at a well and agreement with gas index sections obtained through the use of Lamé parameter data sets derived by the (λρ, μρ) method. A composite gas index produced by combining the three individual indices, is shown to be a better gas indicator than any of the others is alone, because it enhances the salient character of the potential gas-filled zones in the dolomitized limestones.