Uncertainties in the quantitative interpretation of lithology probability volumes

Abstract

The interpretation of deterministic seismic inversion results can be greatly enhanced through the generation of lithology probability cubes (e.g., Avseth et al., 2005). This is particularly true when there are more than two lithology types or when the inversion has produced estimates of P-impedance and S-impedance (or some combination of these). One method to generate the lithology probabilities is to derive probability density functions (PDFs) that relate the inverted elastic properties of the rocks to the probability of each lithology type (e.g., Sams and Saussus, 2010). These are applied to the elastic property volumes, within a Bayesian framework, to produce volumes of lithology probability. Ideally the process captures all of the uncertainties in the data, as well as those resulting from the inversion workflow and due to limited seismic resolution. The resultant lithology probability volumes can be visualized and manipulated for improved qualitative interpretation. For example, the sand probability cube in Figure 1a has been derived from the P-and S-impedance volumes shown in Figure 1a and 1b. The probability volume is intuitively easier to understand and therefore interpret than the elastic property volumes, particularly for those who have little insight into the elastic properties of rocks. Thresholds on probability and 3D connectivity criteria can be imposed to provide potential shapes of geological bodies.