Evaluation of Representative Elementary Volumes for Characterizing Tight Sandstone Microstructure via 3D CT Reconstruction

Determining the representative elementary volume (REV) of tight sandstone remains challenging because CT resolution and field of view impose competing constraints on pore-structure characterization. In this study, six tight sandstone samples were examined using multi-resolution micro-CT with voxel sizes of 0.556, 3.98, and 10.5 μm. A unified stability-index method was used to evaluate geometric, topological, and hydraulic parameters, including porosity, fractal dimension, anisotropy, pore-size distribution, specific surface area, coordination number, sphericity, tortuosity, and permeability. The results show that both CT resolution and field of view influence REV estimates. High-resolution images preserve more micropores, narrow throats, and irregular boundaries, whereas low-resolution images lose fine-pore information but better capture larger-scale structural heterogeneity. Hydraulic parameters generally require larger REVs. Porosity and coordination number show scale-dependent trends similar to those of the hydraulic parameters, indicating that pore-space abundance and network connectivity jointly influence the representative scale of flow. Pore-size distribution and anisotropy provide more reliable REV estimates at high resolution, while fractal dimension, specific surface area, and sphericity are more sensitive to changes in resolution. Therefore, flow-related REV evaluation in tight sandstone should account for resolution limitations and integrate multiple geometric, topological, and hydraulic parameters rather than relying solely on porosity.