Abstract: The Paleogene-Neogene sedimentary basins in northeastern Yunnan province have good exploration prospects of biogenic gas, among which the representative one is Qujing basin. Through tectonic and sedimentary interpretations by 2D seismic lines, combining with geologic data and well logs, this paper discusses the tectonic/structural features and the basinal formation and evolution, and analyzes the relation between the tectonic/structural evolution and biogas accumulation. The study shows that during the fault-depression stage of Early-Middle Oligocene, the Caijiachong formation with mass lacustrine dark mudstone was deposited, which was as a major gas source rock. From Late Oligocene to Early Pliocene, as a result of cooling due to the entire uplift and erosion of this basin, the over-consumption of the organic matters in this formation was avoided, providing the organic materials for biogas accumulation since Quaternary. In the depression stage of Late Pliocene, the Ciying formation was deposited, which was the main period of forming its secondary coal-measure gas source rock, reservoir rock, cap rock and lithologic traps. In the end of Pliocene, the basin underwent the stage of compressionshearing uplift and shrinkage, characterized by the development of structural traps like fault-anticline and fault nose and structurallithologic traps. In the Quaternary, the basin was in steady subsidence stage, which was a period of biogas accumulation. The rate of biogas generation from gas source rocks, the vertical conductivity of faults, the preserving conditions of traps and their dynamic assemblages could be the key factors for controlling the late-stage biogas accumulation in this basin.

Key words: Qujing basin, Paleogene, Neogene, Tertiary, structural evolution, biogas, hydrocarbon accumulation, condition