Correlations between seismic parameters, EM parameters, and petrophysical/petrological properties for sandstone and carbonate at low water saturations

Abstract

Empirical relations are found between measured petrophysical/petrologic, seismic, and electrical properties of sandstone and carbonate samples by least‐squares fitting at room pressure and ambient saturation. The measured parameters include porosity (φ), fluid permeability (k), clay content (C), grain density (ρg), bulk density (ρb), P‐wave velocity (Vp), electrical conductivity (σ), and dielectric constant (κ). The samples are from reservoir analog sites in the Ferron Sandstone in central Utah and the Ellenburger carbonate in central Texas. Crossplots and regression analysis are done separately for the sandstone and the carbonate samples. For the sandstone samples, predictions with correlation coefficients (R2) greater than 0.75 include ρb from φ, ln k from φ and C, κ from ln k and φ, κ from ρb and C, and κ from ln k. Predictions with 0.65 < R2 < 0.75 include κ from Vp and ρb, κ from Vp and φ, Vp from ln k and C, κ from ln φ, and κ from ρb. In general, σ is difficult to predict, with the best R2(0.48) obtained in a prediction of σ from ln k. Relationships for the carbonate samples are generally less reliable, which is attributed to a complex history of multiple phases of karsting and burial. The largest R2 values obtained are 0.67 for prediction of σ from κ, and 0.36 for prediction of σ from ρg. All the other R2 values are ≤0.19. Both the sandstone and the carbonate data show σ‐φ; relations with negative coefficients, rather than positive as predicted by Archie's law, because of the very low water saturations. In the sandstone, the water connectivity is reduced with increasing grain surface area (with increasing φ and k), so σ decreases. In the carbonate, σ correlates with the degree of dolomitization, and the water content is too low to contribute to σ.