Electrical-elastic modelling of rocks using cross-property DEM

The combination of electrical and elastic measurements can be useful in lowering subsurface characterisation uncertainty. The majority of rock physics relations which relate a rock’s electrical and elastic properties, however, rely on the estimation of porosity as an intermediate step. By combining differential effective medium schemes which relate a rock’s electrical and elastic properties to porosity and pore shape, we obtain cross-property expressions which are independent of porosity, depending only on pore aspect ratio. Analysing published joint electrical-elastic measurements shows the cross-property model works well for clean sandstones, and models V_p/V_s ratios as a function of resistivity without porosity. Although clay-bearing sandstones are more complex, our model can still identify the correct trends. On theoretical grounds, it seems our approach has the potential to produce additional cross-property relations; a topic upon which we speculate.