Pore-Scale Resolution Effects on Image-Based Permeability Estimation in Tight Sandstone Using Physical Multiscale SEM Imaging

Reliable image-based permeability estimation in tight porous media depends strongly on how pore and throat geometries are resolved across scales. This study investigates the influence of image resolution on pore characterization and permeability estimation in tight sandstone using true multiscale scanning electron microscopy (SEM). A fixed sandstone region was imaged at three resolutions—S1 (0.1 μm/pixel), S4 (0.05 μm/pixel), and S16 (0.025 μm/pixel)—and spatially registered to ensure the same field of view across scales. Porosity, pore roundness, fractal dimension, pore size distribution, and permeability were extracted and compared. With increasing resolution, more fine pores are identified, porosity rises from 4.6% (S1) to 5.55% (S4) and 6.31% (S16), pore roundness and fractal dimension increase, indicating greater complexity and fine-scale heterogeneity. Meanwhile, the pore size distribution narrows and shifts towards smaller pores as large merged pores at low resolution are decomposed into multiple micropores. Permeability derived from individual images becomes more spatially variable at higher resolutions, but the overall permeability decreases, with only a small additional change from S4 to S16. The values at the S4 and S16 scales (1.77 × 10−17 m2 and 1.72 × 10−17 m2) agree well with the measured gas permeability of 1.85 × 10−17 m2. These results indicate that image resolution exerts systematic control on transport-relevant pore descriptors and image-based permeability. Within the investigated resolution range, further refinement from S4 to S16 reveals additional fine-scale heterogeneity but produces only a limited change in the overall permeability estimate. The findings, therefore, highlight the importance of balancing image resolution and field-of-view representativeness in digital-rock workflows aimed at pore-scale transport analysis and permeability upscaling.