A B S T R A C TWe measured in the laboratory ultrasonic compressional and shear-wave velocity and attenuation (0.7-1.0 MHz) and low-frequency (2 Hz) electrical resistivity on 63 sandstone samples with a wide range of petrophysical properties to study the influence of reservoir porosity, permeability and clay content on the joint elasticelectrical properties of reservoir sandstones. P-and S-wave velocities were found to be linearly correlated with apparent electrical formation factor on a semi-logarithmic scale for both clean and clay-rich sandstones; P-and S-wave attenuations showed a bell-shaped correlation (partial for S-waves) with apparent electrical formation factor. The joint elastic-electrical properties provide a way to discriminate between sandstones with similar porosities but with different clay contents. The laboratory results can be used to estimate sandstone reservoir permeability from seismic velocity and apparent formation factor obtained from co-located seismic and controlled source electromagnetic surveys.

A B S T R A C TImprovements in the joint inversion of seismic and marine controlled source electromagnetic data sets will require better constrained models of the joint elastic-electrical properties of reservoir rocks. Various effective medium models were compared to a novel laboratory data set of elastic velocity and electrical resistivity (obtained on 67 reservoir sandstone samples saturated with 35 g/l brine at a differential pressure of 8 MPa) with mixed results. Hence, we developed a new three-phase effective medium model for sandstones with pore-filling clay minerals based on the combined selfconsistent approximation and differential effective medium model. We found that using a critical porosity of 0.5 and an aspect ratio of 1 for all three components, the proposed model gave accurate model predictions of the observed magnitudes of P-wave velocity and electrical resistivity and of the divergent trends of clean and clay-rich sandstones at higher porosities. Using only a few well-constrained input parameters, the new model offers a practical way to predict in situ porosity and clay content in brine saturated sandstones from co-located P-wave velocity and electrical resistivity data sets.