Abstract
•Confocal can be a standard 3D pore-scale characterization method for carbonates.•Fluorophore, objective, and medium are the key controls for confocal image quality.•Confocal resolved carbonates’ macro- and micropores, and their interconnectivity.•PSD from confocal demonstrated bimodality of IL, while PSD from μ-CT did not.•Multi-scale image registration corroborated rock properties at different resolutions.
Pore space characterization of carbonate materials is of fundamental importance to a wide range of earth science and engineering applications. In this study, we show how confocal microscopy can be used as a reliable tool to visualize and quantify the heterogeneous pore space in carbonate materials. In confocal imagery, the quality of pore space images is controlled by various factors including the choice of fluorophore, objective lens, and medium of imaging. Our experiments demonstrated that there is no “fit-for-all” dye. The red dye provides more depth of investigation, while the blue dye can capture large pores more efficiently. Our investigation indicated that quantitative pore space description from confocal images can be significantly influenced by imaging artifacts associated with imaging the heterogeneous and complex pore space in carbonates. By applying image deconvolution, we mitigated the confocal imaging artifacts (e.g., spherical aberration, and resolution deviation), and extracted a more reliable 3D pore-network model of the carbonate sample. We employed our optimized confocal imaging protocol to visualize and quantify macro- and micropores, and more importantly their interconnectivity within an Indiana limestone (IL) sample. The computed pore-throat size distribution (PSD) from the 3D confocal images was able to capture the inherent bimodal distribution of IL.