COMPARISON OF ACCURACIES OF ELASTIC IMPEDANCE

摘要

In this study, we examine the accuracies of three approximations for elastic impedance by comparing EI for various interfaces and PP-wave reflection coefficients for three typical classes of AVO models. Three approximations for the PP-wave elastic impedance are respectively derived by Connolly (1999), Ma (2004) and Santos and Tygel (2004) are examined, the later two were developed with an attempt to improve the accuracy of Connolly's original approximation. We find that for most practical applications, i.e., incident angles less than 40°, Connolly's equation is the most accurate equation for Classes Ⅰ and Ⅱ AVO models. The approximations of Ma (2004) and Santos and Tygel (2004) are accurate in determining the critical angles for large incident angles for Classe Ⅲ AVO for incident angles up to at least 70°. Connolly's equation is only accurate for incident angles up to 20°. This study provides a useful guide to choosing the equations for PP-wave elastic impedance. Finally, we have developed an inversion procedure to invert V_P and V_S from 2D seismic data based on the EI equations. We applied the elastic impedance derived AVO inversion to marine 2D data and can invert V_P and V_S from seismic data.