Effects of Lamellar Stratification on Pore Systems and Fluid Flow Behavior in Shale Reservoirs

To clarify lithofacies and fluid mobility in Ordos Basin lamellar shales, an integrated characterization workflow was developed using image texture analysis, gas adsorption, mercury injection porosimetry, and low-field nuclear magnetic resonance. The results identify three lithofacies: high-density, medium-density, and low-density lamellar shale. The high-density type has a perimeter ratio <0.007; the medium-density type has a horizontal variation coefficient >0.23; and the low-density type has a vertical variation coefficient >0.09 and an aspect ratio >1.00. The average pore diameters are 4.09 μm, 2.65 μm, and 2.52 μm for the three types, respectively, suggesting that more developed mineral lamination leads to a larger average pore size. All types show main pore diameter peaks around 500 nm, with the highest peak observed in high-density shale. Medium-density shale contains relatively abundant micropores and mesopores, resulting in a moderate average diameter. Regarding fluid availability, high-density shale exhibits good mobility, medium-density shows an unclear trend, and low-density demonstrates poor mobility. These findings offer a reference for classifying laminated shale lithofacies and aid in evaluating fluid flow capacity.