Interpretation Of Long Offset Avo Attributes

AVO effects in large offset P-wave data (up to 60°) is<br>investigated. In addition to conventional P-wave<br>AVO attributes (A and B) a third term (C) is exa mined.<br>Background trends for crossplots of the attributes<br>are related to rock property relationships. Exact<br>expressions are given for the first 3 terms, (A, B, C),<br>of the expansion of Knott-Zoeppritz equations of the<br>reflected P-wave energy. These exact expressions are<br>compared to the commonly used linearized (first<br>order contrasts of rock properties) attributes. The<br>effect of variation in water saturation and porosity in<br>a sandstone embedded in shale is investigated in a<br>numerical example, based on rock physics models of<br>a well log. The AVO attributes show promise to distinguish<br>so-called fizz-gas (low saturated gas sands)<br>from commercial gas and differentiate porosity in<br>reservoir rocks.