Pore Structure Characterization of Low-Permeability Gravity-Flow Reservoirs: A Case Study of the Middle Es3 Member in Daluhu Area, the Dongying Depression, China

The low-permeability gravity-flow sandstone reservoirs in the Dongying Depression, China, contain substantial oil reserves, yet their development is constrained by complex pore structures. In this study, optical and scanning electron microscopy (SEM) observations were integrated with nuclear magnetic resonance (NMR) measurements to investigate the pore system, pore size distribution, and connectivity of Es3z sandstone. By applying a Gaussian multi-peak fitting algorithm to the NMR T2 spectra, parameters that directly capture the physical attributes of the rocks were extracted. Based on the correlation between these parameters and permeability, three distinct pore structure types (A, B, and C) were identified. The results demonstrate the effectiveness of using these NMR T2 spectral parameters for quantitative pore structure characterization and classification, providing a robust framework for evaluating and predicting the quality of low-permeability reservoirs.