The heterogeneity of the microscopic pore structure in tight sandstone reservoirs is a key factor limiting the efficient development of natural gas. This study focuses on the tight sandstone of the Denglouku Formation in the Lower Cretaceous region of the Xujiaweizi Fault Depression in the northern Songliao Basin. This research integrates petrographic thin sections, scanning electron microscopy (SEM), high-pressure mercury intrusion experiments, and fractal models to systematically reveal the pore structure characteristics and the response patterns of fractal dimensions in the reservoir. The results indicate that the Denglouku Formation reservoir is a typical tight sandstone reservoir, with pore types mainly consisting of residual intergranular pores and micropores, and throat types dominated by narrow lamellar and tubular structures. The pore–throat structure in the study area exhibited typical three-segment fractal characteristics, reflecting the complexity and multi-scale heterogeneity of the reservoir’s pore–throat system. The higher the fractal dimension, the poorer the storage performance and permeability. By constructing a multivariate classification model including porosity, permeability, displacement pressure, and sorting coefficient, the reservoir was divided into three categories. The results of this study provide a theoretical basis for quantitative classification evaluation and development strategy optimization of the continental tight sandstone reservoirs.

In recent years, substantial hydrocarbon discoveries have been documented in Member 4 of the Yingcheng Formation (Ying IV) in the northern Songliao Basin. To fully understand the developmental characteristics of the Yingcheng Formation source rocks and clarify the main controlling factors of their formation, this study focuses on typical wells in the Xujiaweizi Fault Depression. By integrating core data, organic geochemistry, elemental geochemistry, and paleoenvironmental parameter reconstruction, we determined the paleoenvironment, key controls, and organic matter enrichment model during the deposition of Ying IV. The results show that the total organic carbon (TOC) content of the source rocks ranges from 1.46% to 4.34% (average 2.65%). The paleoclimate during deposition was predominantly warm and humid, with low oxygen, reduced water conditions, freshwater-to-brackish salinity, and a deep-lake environment. Paleoproductivity was moderate to high. Relationship analysis indicates that TOC content was jointly controlled by paleoclimate (warm and humid conditions promoting biological proliferation) and paleoproductivity (nutrient supply from volcanic activity and terrigenous clastics). The positive feedback between elevated productivity under warm-humid conditions and deep-lake reducing environments led to organic matter enrichment in the source rocks of Ying IV, following a productivity-controlled model. This study provides critical geological insights for deep natural gas exploration in the Songliao Basin.

The tight sandstone reservoir of the Fuyu Oil Layer in the Quantou Formation of the Cretaceous in the Bayan Chagan area displays intricate microscopic pore structures and pronounced heterogeneity, limiting hydrocarbon exploration and development efficiency. Utilizing core CT scanning digital core technology integrated with field emission scanning electron microscopy (FE–SEM) and whole-rock/clay mineral X-ray diffraction (XRD) analysis, this research performs multi-scale quantitative characterization on 15 representative rock samples from the study area, systematically elucidating reservoir pore structure diversity and its formation mechanisms. The study demonstrates that reservoirs in the study area can be categorized into three types: A, B, and C, exhibiting progressively declining reservoir performance. Type A reservoirs are characterized primarily by dissolution-formed large to medium pores, where macropores (radius > 5 μm) account for more than 92% of storage capacity, average coordination numbers reach 0.27~0.45, and connectivity is optimal. Type B reservoirs are influenced by siliceous cementation, featuring developed residual intergranular pores, macropore volume share declining to 88%, and coordination numbers decreasing to 0.11~0.20. Type C reservoirs experience intense compaction and illite cementation modification, where micropores (radius < 1 μm) constitute 5.6% numerically, yet macropore volume share is merely 76%, coordination numbers drop to 0.02–0.03, and connectivity is minimal. Mineralogical analysis reveals that quartz content exhibits a positive correlation with reservoir properties, as its rigid grain framework effectively resists compaction. Illite content rises with increasing burial depth, and plastic illite occupies pores and segment throats, resulting in Type C reservoir permeability reduction to 0.01~0.25 mD. Dissolution intensity (Type A > Type B > Type C) and cementation types (quartz cementation prevailing in Type B, illite cementation prevailing in Type C) represent crucial factors governing reservoir quality differentiation. This research confirms the reliability of digital core technology for tight reservoir classification and assessment, developing a discrimination model founded on “pore structure-mineral composition-diagenesis”. It provides a geological basis for sweet spot prediction and efficient development in the study area.