Summary

Development of a shale gas rock physics model is extremely difficult because organic-rich shales are often observed to be strongly anisotropic due to the partial alignment of clay minerals and the bedding-parallel lamination of organic material within the shale, and the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure. This paper presents an anisotropic rock physics model for estimating elastic stiffness of organic shales. The model combines the Reuss-Voigt-Hill average, the anisotropic self-consistent approximation (SCA) and differential effective medium (DEM) theory in order to take mineralogy, kerogen, pores and fluid into consideration. The elastic moduli of fully aligned clay-fluid composite with ellipsoidal inclusions are obtained by the combination of SCA and DEM, after which the Reuss-Voigt-Hill average is applied to calculate the elastic moduli of mineral composite (kerogen, quartz, feldspar et al.) assuming that they are discrete spherical inclusions in a clay-fluid background. Finally, the mineral composite is added into the shale matrix using the anisotropic DEM model. The predicted elastic constants are in good agreement with experimental measurements, which indicates our method has the potential to model organic-rich shales.