Full scale pore throat characterization incorporating a dynamic shape factor and permeability prediction in tight rocks

Tight reservoirs represent a significant component of unconventional resources, yet their development is challenged by multiscale and highly heterogeneous pore-throat systems that govern fluid flow. To address this, we integrated MIP, NMR and micro-CT scanning to capture the multi-scale pore structure. Micro-CT analysis reveals that tight sandstones are dominated by micro- and nano-pores, with pores smaller than 10 μm in radius accounting for over 95% of the total pores. Pore morphology classification is not limited by CT scanning resolution: small throats are predominantly regular and plate-like, while macropores exhibit more complex and irregular geometries. MIP data indicate a triple-segment fractal dimension for the throat system, reflecting strong heterogeneity in large throats and weaker heterogeneity in medium and small throats. The pore surfaces are smooth and stable, and permeability is primarily controlled by throats within the 0.1–0.4 μm radius range, whose sorting coefficient shows a logarithmic relationship with permeability. Building on these insights, the core contribution of this study is a novel full-scale pore-throat characterization method that incorporates a dynamic shape factor to quantify throat geometry. By integrating MIP and NMR data within this new framework, we successfully derived the complete pore-throat distribution. Results show that plate-like throats are mainly distributed between 0.0015 μm and 1.23 μm, while the critical radius of plate-like pore is about 1 μm. In contrast, heterogeneous pores exhibit radii exceeding 15 μm, with a peak around 40 μm. The accuracy of the full-scale distribution was validated using a modified Kozeny-Carman model, which predicts permeability within less than 10% error compared to experimental measurements. This study provides a robust and accurate workflow for pore structure characterization, advancing the quantitative evaluation of tight sandstone reservoirs and enhancing our fundamental understanding of fluid transport mechanisms.