Abstract

MENA-NEGRETE, J.; VALDIVIEZO-MIJANGOS, O. C.; COCONI-MORALES, E.  and  NICOLAS-LOPEZ, R.. Micromechanical modeling of ultrasonic velocity for pore-structure and porosity characterization considering anisotropy in carbonate samples. Geofís. Intl [online]. 2021, vol.60, n.4, pp.294-319.  Epub Jan 31, 2022. ISSN 2954-436X.  https://doi.org/10.22201/igeof.00167169p.2021.60.4.2118.

This work presents an approach to characterize the pore-structure and anisotropy in carbonate samples based on the Effective Medium Method (EMM). It considers a matrix with spheroidal inclusions which induce a transverse anisotropy. The compressional wave (VP), vertical (VSV) and horizontal (VSH ) shear wave velocities are estimated, taking into account parameters as characteristic length, frequency, wave incidence angle, aspect ratio, mineralogy, and pore-filling fluid to predict pore shape in carbonates. Ranges of aspect ratios are shown to discriminate different pore types: intercrystalline, intergranular, moldic, and vuggy. The wave incidence angle is a determinant parameter in the estimation of VP (0°,45°,90°), VSV (0°) and VSH (90°) to calculate dynamic anisotropic Young's modulus (E33) and Poisson's ratio (v31), together with the Thomsen parameters, ε, γ, and δ for quantification of the anisotropic pore-structure. The obtained results establish that the size and the pore-structure have a more significant impact on the elastic properties when the porosity takes values greater than 4% for the three ranges of frequency, ultrasonic, sonic, and seismic. This investigation predicts the pore-structure and pore-size to improve the characterization and elastic properties modeling of carbonate reservoirs. The validation of results includes porosity measurements and ultrasonic velocity data of different carbonate samples.

Keywords : anisotropy; ultrasonic velocity; pore-structure and carbonate rocks.