Tight oil is the most viable target for unconventional oil and gas exploration, but the complexity of micro-/nanopore throat systems significantly affects the oil content of reservoirs. To investigate the causes of heterogeneity in oil-bearing reservoirs, a high-pressure mercury injection experiment combined with fractal theory was conducted to analyze the micro pore throat structure characteristics of the tight sandstone of Chang 7 Member reservoirs in the Ordos Basin. The factors controlling the variations in oil content among tight sandstone samples were identified based on mineral composition characteristics. The results indicate that the pore throat radius distribution is mainly unimodal an bimodal. In oil-bearing samples, the pore throat distributions align well with the corresponding permeability contribution curves, while in oil-free samples, there is a clear deviation from these curves. Mesopore throats exert the greatest influence on seepage capacity. Differences in fractal characteristics are primarily reflected in D1 values, with oil-free samples exhibiting D1 values close to 3, indicating an extremely nonuniform pore throat structure at this scale. The content of quartz, plagioclase, and chlorite is significantly higher in oil-bearing samples than in oil-free samples, whereas calcite content is lower in oil-bearing samples. There is a positive correlation between the contents of quartz, plagioclase, and chlorite with D1; their increased presence contributes to a more favorable pore throat structure. Conversely, the calcite contents show an inverse relationship with D1. Cementation increases the complexity of pore throat structures, while multiple diagenetic processes simultaneously control these characteristics, leading to variations in oil content.

Lacustrine shale oil and gas are important fields for unconventional exploration and development in China, and organic-rich shale deposition lays down the critical foundation for hydrocarbon generation. There are two sets of shale, the Dongyuemiao and Da’anzhai Members, in the Ziliujing Formation in the Sichuan Basin. To identify the differential enrichment characteristics of organic matter and clarify its controlling factors, geochemical analyses of organic and inorganic geochemical analyses were performed. The results showed that the total organic carbon content of the Dongyuemiao shale (1.36%) is slightly higher than that of the Da’anzhai shale (0.95%). The enrichment of organic matter in the two shales resulted from the comprehensive controls of paleoproductivity, paleoenvironment, and terrigenous input, but different factors have different effects. In addition, driven by climate, the change in the sulfate concentration in the bottom water further led to the different intensities of bacterial sulfate reduction in early diagenesis. This made a great difference regarding organic matter accumulation in the two members. In general, climate may have played a dominant role in organic matter enrichment in the two sets of shale.