Sedimentary Facies Characteristics and Hydrocarbon Accumulation Model of the Chang 2 Member in the Antaolin Area, Ordos Basin

The Chang 2 Member of the Triassic Yanchang Formation is an important oil-bearing interval in the Ordos Basin, and it serves as one of the key targets for tight oil exploration and development in China. The Antaolin area, located in the central part of the northern Shaanxi slope, exhibits relatively low well control but demonstrates good hydrocarbon potential based on drilling and testing results. In this study, core, well logging, thin section, and experimental data were comprehensively integrated to analyze the stratigraphic division, sedimentary facies, reservoir petrology and physical properties, and hydrocarbon accumulation characteristics of the Chang 2 Member in the Antaolin area. The results indicate that the Chang 2 Member was deposited during the stage of lake basin shrinkage and extinction, dominated by a delta depositional system, particularly the delta front subfacies. Subfacies types mainly include subaqueous distributary channels, mouth bars, interdistributary bays, and sheet sands, with sand bodies trending NE–SW. Subaqueous distributary channel and mouth bar sand bodies serve as the major reservoir units. Lithologically, the reservoirs are dominated by feldspathic sandstones, with cementation mainly by calcite and chlorite. Pore types include intergranular residual pores, dissolution pores, moldic pores, and microfractures. Reservoir properties are characterized by low porosity and low permeability, with strong heterogeneity. Hydrocarbon accumulation is controlled by the “source below, reservoir above” assemblage, with structural–lithological composite traps serving as the main trap type. Multiple charging events occurred, with late-stage charging playing a dominant role in accumulation. Based on the integration of depositional, structural, and diagenetic characteristics, a hydrocarbon accumulation model for the Chang 2 Member in the Antaolin area was established, providing a geological basis for future exploration and development.