Abstract:

The first member of the Dainan Formation in the Qintong Sag of the Subei Basin, characterized by its shallow burial and excellent physical properties, is identified as a key exploration target for high-quality hydrocarbon reserves. This study applies basic theories and technical methods such as sequence stratigraphy, sedimentology, and geochemistry, and integrates seismic, drilling core, and logging data to conduct a comprehensive analysis of sedimentary microfacies and oil and gas accumulation conditions under the sequence stratigraphic framework of the first member of Dainan Formation in Qintong Sag. The study shows that the fan delta front facies belt is a favorable area for the development of lithologic oil reservoirs, and the sand shale interbed near the largest lake flooding surface is the optimal reservoir cap combination vertically, The formation of oil and gas reservoirs in the first member of Dainan Formation is jointly controlled by the structural background, sedimentary facies belts, and regional strike slip structural belts. The study categorizes the oil reservoirs into two major categories and five subcategories. After drilling, it has been confirmed that large-scale integrated structural lithologic oil reservoirs have been discovered, and the exploration results are significant.

Key words: Subei Basin, Qintong Sag, Paleogene, first member of Dainan Formation, enrichment regularity