Estimation of the density contrast by AVO inversion beyond the linearized approximation: An indicator of gas saturation

Abstract

The density parameter may reveal important and crucial information about the presence and saturation of hydrocarbon. But in seismic analysis the importance of the density parameter is generally ignored. The main reason is the difficulty to estimate reliably the density parameter from the seismic data. Because of the complexity some approximations to the Knott-Zoeppritz equation are very often used for the AVO analysis. However, AVO inversions based on the linearized approximations fail to generate reliable estimate of the density contrast parameter. In this paper, we use a reparametrization of the Knott-Zoeppritz equation without any approximation in terms of a background and three contrast parameters: P-velocity, S-velocity and density contrasts (Lavaud, Kabir and Chavent, 1999). Synthetic data example shows that a reliable estimation of the density contrast is possible by using higher angles of incidence data and performing a nonlinear inversion. The example also shows that the density contrast can be potentially used as an indicator of the gas saturation in a reservoir.