Abstract
The tight sandstone reservoir exhibits a complex pore structure and strong heterogeneity. Accurate characterization of its pore structure is crucial for improving the efficiency of tight oil development. This study investigates tight sandstone samples exhibiting different oil-bearing levels from the Fuyu oil reservoir of the fourth member of the Quantou Formation in the Xinmiao area, located in the southern Songliao Basin. The influence of pore structure on oil-bearing capacity was investigated through a series of systematic experiments, including low-pressure nitrogen adsorption (LPN(2)A), high-pressure mercury intrusion (HPMI), constant-rate mercury intrusion (CRMI), nano-computed tomography (nano-CT), and nuclear magnetic resonance (NMR). The results show that: (1) The microscopic pore structure influences the macroscopic oil-bearing capacity. As the oil-bearing level of the sample increases, the corresponding pore structure gradually improves, and the oil saturation increases to 32.93%, 40.36%, 42.61%, and 50.80%, respectively. (2) The oil saturation of fluorescent samples was primarily contributed by small pores (T(2) < 10 ms), with a contribution rate of 78.17%. The oil saturation of oil trace and oil flecked samples was mainly contributed by small pores and medium pores (10 < T(2) < 100 ms), with combined contribution rates of 93.75% and 84.35%, respectively. The oil saturation of oil immersion samples was primarily contributed by medium pores and large pores (T(2) > 100 ms), with a contribution rate of 54.45%. (3) Pore-throat connectivity and its heterogeneity are the key factors influencing the oil-bearing capacity of tight sandstone in the study area. The pore-throat radius, connected pore throat volume percentage and NMR fractal dimension are the best parameters to characterize oil-bearing capacity. (4) The lower limit for oil-bearing capacity in the tight sandstone reservoir of the study area is oil trace, and the corresponding threshold values of a pore-throat radius of 1.19 μm, a connected pore-throat volume percentage of 47.5%, and an NMR fractal dimension of 2.8169. This research establishes a quantitative linkage between pore-throat structure and oil-bearing capacity, providing diagnostic parameters for tight oil evaluation.