Pore-structure controls on absolute permeability of 1-mm digital sandstone subsamples under a fixed CT field of view

Absolute permeability is a key index for evaluating the fluid transmission capacity of sandstone reservoirs. However, what determines its value is not just the pore volume itself, but also whether the effective flow-transmission space is formed, whether the dominant throats are unobstructed, and whether the pore network organization is favorable for flow connectivity. In this paper, we take 20 1 mm × 1 mm × 1 mm digital sub-samples cropped from the fixed CT field of view of 5 parent sandstone samples as the research object. Based on X-ray micro-CT, we built digital core models, finished pore space characterization, pore structure parameter extraction and single-phase seepage simulation with Avizo software, and used the geometric mean of three-directional absolute permeability, k_g, to characterize the overall seepage capacity of the sub-samples. The results show that the 20 digital sub-samples present obvious differences in pore space development degree, effective flow-transmission space scale, dominant throat size and network topology organization, with k_g ranging from 8.684 to 62.350 × 10^- 15 m². Total porosity shows a significant positive correlation with k_g overall, but under similar porosity conditions, the permeability can still differentiate further. Further redundancy elimination screening indicates that, after controlling for connected porosity, the median throat radius still retain a statistically detectable incremental explanatory effect, whereas Euler number also preserved an additional but more marginal contribution within the current dataset, with partial correlation coefficients of 0.466 ( P = 0.038) and 0.447 ( | r |, P = 0.048), respectively. Under the current sample system and unified processing conditions, the differences in absolute permeability of millimeter-scale digital sandstone sub-samples can be interpreted primarily by connected porosity, median throat radius, and Euler number, which correspond to three complementary aspects: effective flow-transmission space, dominant channel size, and network organization. However, the incremental contribution of Euler number should be understood with appropriate caution under the present sample size.