The relationship between elastic-wave velocities and density in sedimentary rocks: A proposal

Susan L.M. Miller and Robert R. Stewart

ABSTRACT

When information about density (ρ) is unavailable, it is often estimated from P-wave velocity (Vp) using an empirical relationship such as Gardner's equation. Since access to S-wave velocity is increasing, it is reasonable to consider whether Vs might contribute to improving density estimates. Sandstone and limestone datasets taken from the literature demonstrate correlations between Vp and Vs, Vp and ρ and Vs and ρ. Both sandstone and limestone show strong correlations between Vp and Vs. The correlations between velocity and density are strong for the limestone data, but are scattered for the sandstone data. The sandstone velocity-density correlations improve significantly when the data are categorized by clay content. When measured densities are compared to densities calculated from Gardner's empirical relation, there is a systematic error in both datasets. The error increases as density decreases. Some of the factors which might affect the uncertainty in the density estimates are porosity, clay content, and lithology. Since Vs is also dependent on these factors, we are seeking empirical relationships among Vp, Vs, and ρ. One goal of this investigation is to estimate density from seismically available measurements.

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