The anatomy of AVO crossplots
| Autor: | Rob Simm, Roy E. White, Richard Uden |
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| Rok vydání: | 2000 |
| Předmět: | |
| Zdroj: | The Leading Edge. 19:150-155 |
| ISSN: | 1938-3789 1070-485X |
| DOI: | 10.1190/1.1438557 |
| Popis: | AVO crossplots are a simple and elegant way of representing AVO data. Offset variations in amplitude for reflecting interfaces are represented as single points on a crossplot of intercept and gradient. The advantage of this type of plot is that a great deal of information can be presented and trends can be observed in the data that would be impossible to see with a standard offset (or angle) versus amplitude plot. The crossplot is an ideal way of examining differences in AVO responses that may be related to lithologic or fluid-type variations. Commonly used techniques for revealing these differences include color-coding samples from the crossplot and using this as an overlay to a seismic display or creating weighted (or “equivalent angle”) stacks (i.e., linear combinations of intercept (R0) and gradient (G). The early literature approached AVO crossplots from the point of view of rock properties. Acentral concept that emerged from this work was the “fluid line,” a hypothetical trend based on a consideration of brine-filled rock properties together with simplifications of the reflectivity equations (Figure 1). If the intercept is plotted on the x axis and the gradient on the y axis, then for consolidated sand/shale rocks the top and base reflections form a trend from the upper left to the lower right quadrant of the crossplot that passes through the origin. When it was realized that data points for equivalent hydrocarbon-filled rocks plot to the left of this line, it became clear that normalizing the data against the fluid line might provide an optimum AVO indicator. Figure 1. AVO classes and the AVO crossplot. The similarity of the fluid-line trend to trends on time-window AVO crossplots generated from seismic was compelling, and many assumed these are the same. In fact, both models and real data examples show that in general this … |
| Databáze: | OpenAIRE |
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