Anisotropic three-term amplitude-variation-with-offset projections: A case study

Abstract

A seismic amplitude-variation-with-offset (AVO) analysis is an important element in seismic reservoir characterization and has been successfully applied in many fields. Traditionally, AVO studies are based on AVO intercept ( A) and gradient ( B) only; curvature ( C) is neglected because it is very sensitive to noise and avoiding noisy C is very difficult in practice. The recently introduced concept of three-term (3T) AVO projections, combined with continuous improvements in seismic data acquisition and processing, allows interpreters to effectively use C by optimizing projection angles based not only on rock physics but also on seismic noise. The effectiveness of the 3T AVO projection, in which A, B, and C are used as the triplet of reflectivities that are summed in the projection, and the impact of random noise on the 3T AVO projection were investigated using data from an offshore Western Australian field. The 3T AVO projection was used in the framework of the extended elastic impedance. Because the study area is known to have nonnegligible differences in anisotropy parameters between the various lithologies, its impact on B and C was taken into account. First, the 3T projection angle targeting lithology fraction logs was optimized using well-log data. Analyses using synthetic seismograms were then performed to investigate the impact of seismic noise. Finally, the method was applied to field data. The results find that (1) C is an important component of seismic reservoir characterization even if it appears unusable and (2) seismic noise must be taken into account when optimizing the projection angle.

Sandstone detection using three‐term amplitude variation with offset projection: A case study

“…One of the important attributes of 3T AVO projection is that noise in A, B and C is correlated and can be suppressed by summing A, B and C using optimum projection angles. Figure 2 shows the logarithm of the scalar noise variance of the 3T AVO projection for various projection angles, assuming random noise that is not correlated between angle stacks (see Ball et al, 2018 andAsaka, 2022 for details of calculating the scalar noise variance). The incident angle range was 12˚, 22˚, 29˚, 36˚, 42˚and 47˚, based on synthetic angle stacks used in the next section.…”

“…Other important examples include fluid response (Ball et al., 2018) and correlation with some rock property (e.g. Asaka, 2022).…”