Abstract
SUMMARY Combining electrical and elastic measurements can be instrumental in lowering the uncertainty of subsurface characterization. Many commonly used rock physics relations for joint electrical–elastic properties are at least partly empirical and often rely on the estimation of porosity as an intermediate step. We combine differential effective medium schemes that relate, respectively, elastic and electrical properties to porosity and pore shape. The resulting expressions are independent of porosity, depending only on pore aspect ratio. Analysis of published joint electrical–elastic data shows that a single aspect ratio model performs well for clean sandstones, allowing us to model Vp/Vs ratios as a function of resistivity. Clay-bearing sandstones are more complex, but our modelling can still identify the correct trends. We speculate about the potential to extend our approach to produce additional cross-property relations.
Highlights
Electrical-elastic multiphysics modelling, for example through the integration of controlled-source electromagnetic (CSEM) data into marine seismic reservoir characterisation workflows, can lead to reduced uncertainty in reservoir characterisation (Alcocer et al 2013)
SC porosity models; a method originally used by Sevostianov & Kachanov (2002), and more recently U by Han (2018), who modelled anisotropic electrical-elastic measurements made on artificial porous N sandstones with aligned fractures
We show the single model parameter, equivalent pore aspect ratio, D is weakly sensitive to clay volume fraction in this data set
Summary
Electrical-elastic multiphysics modelling, for example through the integration of controlled-source electromagnetic (CSEM) data into marine seismic reservoir characterisation workflows, can lead to reduced uncertainty in reservoir characterisation (Alcocer et al 2013). RI Carcione et al (2007) presented a set of electrical-elastic cross-property models with no explicit porosity terms by substituting pre-existing resistivity-porosity models into pre-existing velocity-. The problem of modelling a rock’s shear modulus and Vp/Vs ratio from electrical resistivity measurements alone by a simple model derived from first principles remains unsolved. A et al (2007) for cross-property modelling - which in the case of DEM equates to applying the chain IN rule - to obtain new electrical-elastic DEM expressions which predict elastic moduli from electrical conductivity measurements. We predict a Vp/Vs trend for mixed, wet sandstones in the absence of porosity and density measurements using the modelled elastic moduli and the Gardner et al (1974) velocity-density relation for sandstones. We solve the inverse problem numerically to estimate electrical resistivity from measured elastic moduli and assess the effect of clay content on the inverse solution
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