AVA analysis and interpretation of a carbonate reservoir: northwest Java']Java basin, Indonesia

A detailed analysis is performed of amplitude variation with angle (AVA) observations in six common-midpoint gathers with reflection points that are over and beside carbonate reefs in the Parigi Formation in the northwest Java basin. Both empirical analysis and full-wavefield modeling of the AVA data suggest that the presence of gas affects AVA by reducing the bulk density of the reservoir, decreasing of the overburden V-p/V-s ratio and by local attenuation caused by gas sieving through the overlying sediments. The slopes of AVA curves for reflections from the top of the Parigi are negative for brine saturation and strongly positive for gas saturation.