Extension of the algebraic dual-energy gamma-ray tomography model for reservoir rock characterization

This study presents an extension of an algebraic model-previously developed for dual-energy gamma-ray transmission tomography-to estimate the effective atomic number (Z_eff) and physical density (ρ) of complex materials. In contrast to earlier validation based solely on elemental materials, the current work investigates the method's applicability to a broader range of samples, including phantoms (acrylic, water, aluminum oxide, calcium oxide, and polytetrafluoroethylene) and heterogeneous geological materials, notably carbonate rocks used as analogs of oil and gas reservoir formations. These samples pose additional challenges due to their compositional heterogeneity and complex internal structures. The methodology applies the algebraic model independently to projection profiles acquired from a gamma-ray scanner (241 Am and 137 Cs) and an X-ray microtomography (μCT-XR) system operated at two distinct tube voltages to estimate Z_eff and ρ from measured attenuation coefficients. The results show strong agreement with reference values for materials within the calibration ranges, with deviations generally below 8% for both parameters. Materials outside these calibration bounds exhibit larger discrepancies, emphasizing the importance of appropriate calibration scope. The findings confirm the robustness of the approach and its potential application to reservoir rock characterization in petrophysical and geomechanical studies.