56-3 Impact of Hematite Morphology on Coating Architecture of Sandstone and Limestone

Abstract:

Mineral coatings are important components of both carbonate and clastic sedimentary systems, where they can modify pore-surface properties and fluid-rock interactions. Detrital and authigenic iron oxides are widespread in sandstone and carbonate reservoirs and may undergo reductive dissolution, recrystallization, redistribution, and phase transformation during burial diagenesis and hydrocarbon migration. These processes can generate iron oxides with distinct crystal phases, particle morphologies, and surface properties, potentially altering pore geometry, reactive surface area of reservoir rocks, interactions with polar crude-oil components, and reservoir wettability. However, how iron oxide morphology interacts with host-rock surface architecture to control coating development, and how the resulting coating patterns affect pore-scale transport, remain poorly understood.

Hematite is one of the most abundant iron oxides found on Earth’s surface and in the shallow crust, which has been commonly found in both sandstone and carbonate reservoirs. Platelet and cubic hematite particles expose different dominant crystal facets and surface functional groups, potentially leading to morphology- and facet-dependent adsorption, attachment, and coating development on reservoir-rock surfaces. To evaluate these controls, we compared hematite coating development on Berea sandstone (BS), Colton sandstone (CS), Indiana limestone (IL), and Edwards Brown limestone (EBL). Under identical coating conditions, platelet hematite formed broadly continuous coatings on all four substrates, whereas cubic hematite produced patchy, substrate-dependent coatings with coverage ranging from approximately 36% to 71%. Quantitative SEM analysis further revealed differences in coating distribution and spatial texture among hematite morphologies and host-rock types. The observed coating patterns are being incorporated into pore-scale models to evaluate their potential effects on fluid transport and displacement.

This workflow provides a reproducible approach for quantifying coating-related surface heterogeneity in porous geologic materials when direct measurements of surface topography or wettability are limited. Together, these results will provide a basis for linking mineral-coating architecture to pore-scale transport and fluid displacement in clastic and carbonate reservoirs.

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