Paleogene Reservoir Development Characteristics and Hydrocarbon Accumulation Response in the Sanmenxia Basin, Southern North China

The Sanmenxia Basin, located in the southern margin of the North China Craton, is a typical representative of the numerous Meso–Cenozoic small–to–medium–sized basins in China. In recent years, an exploration breakthrough has been made in this basin through its first hydrocarbon discovery well (Well Yuxiadi–1). Based on core samples and associated analytical data from Well Yuxiadi–1, this study reveals the petrological characteristics and diagenetic evolution of the Paleogene Xiao’an Formation reservoirs and investigates the controlling factors of reservoir development and their impacts on hydrocarbon accumulation. Results demonstrate that the Xiao’an Formation reservoirs are dominated by delta plain channel sandbodies and delta front subaqueous distributary channel sandbodies, with overall medium porosity and permeability. Reservoir development is governed by provenance, deposition and diagenesis: (1) a dual–provenance system dominated by distal clastics from the Qinling orogenic belt delivers quartz–rich components, forming well–sorted fine–grained sandstone frameworks; (2) depositional processes control vertical heterogeneity, with rapidly deposited massive sandbodies in delta plain channels exhibiting optimal porosity–permeability conditions; (3) two–phase calcite cementation and dissolution critically regulate microscopic reservoir properties—syndepositional micritic calcite dissolution enhances effective storage space, while the second–phase sparry calcite cementation (26–30 Ma) significantly degrades pore connectivity. Hydrocarbon accumulation analysis reveals a single–phase charging event during the late Oligocene (24–26 Ma), characterized by fault–controlled vertical migration. The temporal relationship between cementation–dissolution processes and hydrocarbon charging directly governs hydrocarbon enrichment efficiency. This research provides a key case study and scientific basis for deepening the understanding of the petroleum geological characteristics of Meso–Cenozoic small–to–medium–sized basins in China.