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, kg, 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 kg ranging from 8.684 to 62.350 × 10− 15 m2. Total porosity shows a significant positive correlation with kg 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.