Chapter 6: Multicomponent AVO
Published:January 01, 1993
Exploration and exploitation of hydrocarbon reserves is becoming increasingly complex. To be successful, an increasing amount of information is required. In recent years much attention has been devoted to the information present in reflection amplitude variation with offset (AVO) (Balogh et al., 1986; Gelfand et al., 1986; Spratt, 1987; Chiburis, 1987; Ball, 1987; Lörtzer and Berkhout, 1988, 1989; Haas and Berkhout, 1988, 1989; Rijssen and Herman, 1988; SEG workshop, 1988). In principle, the offset variations of the P-P reflection amplitudes contain information on all the elastic parameter contrasts (P-wave velocity, S-wave velocity, and density), while the zero-offset reflection amplitude contains only information on the acoustic impedance.
Figures & Tables
Offset-Dependent Reflectivity–Theory and Practice of AVO Analysis
“The P-wave reflection coefficient at an interface separating two media is known to vary with angle of incidence. The manner in which it varies is strongly affected by the relative values of Poisson’s ratio of the two media. For moderate angles of incidence, the relative change in reflection coefficient is particularly significant when Poisson’s ratio differs greatly between the two media.
Theory and laboratory measurements indicate that gas sands tend to exhibit abnormally low Poisson’s ratios. Embedding a low velocity gas sand into sediments having ‘normal’ Poisson’s ratios should result in an increase in reflected P-wave energy with angle of incidence. This phenomenon has been observed on conventional seismic data recorded over known gas sands.”
With these words, W. J. Ostrander ushered in a new era in seismic interpretation. Although many workers were aggressively moving forward with amplitude variation with offset (AVO) analysis before 1982, Ostrander’s presentation at the 52nd Annual International Meeting of the Society of Exploration Geophysicists popularized the concept as an exploration tool. The presentation proved to be a precursor to the avalanche of literature on the subject which has appeared during the past decade.