The amplitude variation with offset analysis has long been used in the world of exploration, especially in mapping gas reservoir distribution. The behavior of this amplitude anomalies occur due to presence of gas in the pores of rocks which also changes the value of Poisson’s ratio (equivalence of Vp/Vs ratio). Unfortunately, this method comes not without limitations, in some cases shows that the amplitude anomalies were associated with the presence of gas accumulation value that is not economically valuable. A modeling has been done to get the velocity and density response for varying gas saturation , it shows that the difficulty of separating the reservoir from high and low gas accumulation is due to response of pwave where it drops dramatically by presence of 5-10% gas and slightly increase for higher gas saturation. The density behaves differenly where it has slightly linear declination trend for different saturation percentage so we hope that by having this attribut we will be able to differenciate gas with various saturation level. There are number of methods to derive density attribute where two of them are using AVO method and prestack inversion. Based on modeling for unconsolidated sand layer the density reflectivity derived from AVO is more sensitive compare to density property derived from prestack inversion. By applying local background trend calibration to density property the higher sensitivity can be achieved with about 155%.
Keyword: Density, AVO, Prestack inversion
Author : Irfan H, Syudkirman