Laminae Control on Pore Space Heterogeneity in Lacustrine Lucaogou Formation: Insights from SANS Studies

Abstract Laminated shales in the Lucaogou Formation exhibit strong pore heterogeneity, and the quantitative relationship between lamina types and pore structure remains poorly constrained. This study investigates how different laminae control pore distribution, connectivity, and heterogeneity in shale reservoirs by using samples from the Lucaogou Formation in the Jimusaer Depression, Junggar Basin. Mineralogy, composition, and lamina structures were analyzed through X-ray diffraction, scanning electron microscopy (SEM), and small-angle neutron scattering (SANS) with contrast matching (CM-SANS). In this research, three lamina types were identified, namely felsic laminae, calcite-clay coupled laminae, and clay-rich laminae. Pore structure varies systematically with lamina type. Calcite-clay coupled laminae are associated with higher total porosity and enhanced spatial heterogeneity, whereas felsic laminae tend to exhibit relatively uniform pore distributions. Clay-rich laminae are dominated by nanoscale pores and relatively poor pore connectivity. Pores in the 10–100 nm range contribute most to total pore volume, and represent the scale with the most pronounced heterogeneity. In addition, porosity varied more strongly along the bedding direction than perpendicular to bedding. Calcite-clay coupled laminae exhibited the greatest spatial heterogeneity, whereas felsic and clay-rich laminae showed more uniform pore distributions. These results indicate that lamina-scale mineralogical and structural contrasts exert an important control on pore distribution and connectivity in the lacustrine shale reservoirs.