Continuous USAXS-SAXS-WAXS scanning of pore structure and mineral heterogeneity in laminated shale

Laminated lacustrine shales exhibit strong vertical heterogeneity in mineral composition and pore structure over very short distances, making lamina-scale reservoir characterization challenging. This study aims to obtain co-located, continuous profiles of pore structure and mineral variation in a laminated shale from the Dongying Sag using integrated USAXS-SAXS-WAXS scanning. A total of 81 adjacent points were measured along a 1.6 cm transect, and the scattering results were integrated with SEM, XRF elemental mapping, and QEMSCAN observations. The sample consists mainly of alternating carbonate-rich and mixed/clay-rich laminae, with average thicknesses of 176 μm and 255 μm, respectively. These thickness statistics define the lamina-scale structural framework of the scanned interval and demonstrate that multiple lamina cycles occur over a very short vertical distance, which is fundamental to the observed microscale pore-mineral heterogeneity. XRF and mineral mapping show rhythmic alternation between Ca-Sr-P-enriched carbonate layers and Si-K-Al-enriched clay-rich layers. Integrated USAXS-SAXS-WAXS analysis reveals pronounced heterogeneity in pore structure and mineral distribution, with standard deviations of total porosity and specific surface area of 2.33% and 36.2 m 2 /g, respectively. Porosity shows a bimodal distribution, dominated by the 2-50 nm pore range, whereas specific surface area is contributed mainly by pores smaller than 50 nm. Clay-rich laminae are commonly associated with abundant nanoscale pores and higher specific surface area, whereas calcite-rich laminae are more often associated with relatively larger pores or pore–fracture spaces. These results demonstrate the value of integrated USAXS-SAXS-WAXS scanning for continuous multi-scale characterization of pore–mineral heterogeneity in laminated shale.