HYDROCARBON ACCUMULATION PROCESS IN SOUTH STEEP SLOPE, BIYANG SAG, NANXIANG BASIN

Evolution history of hydrocarbon source rocks and tectonics dominates hydrocarbon accumulation in the south steep slope of the Biyang Sag,the Nanxiang Basin.In the slope,early paleo-reservoirs are formed by small-scale hydrocarbon charging during the late Eh¹-Eh² of Paleogene.The middle key reservoirs of Eh³ are formed by relatively larger volume of hydrocarbon charging during the late El uplifting stage of early Paleogene.The shallow secondary oil and gas reservoirs are formed by destruction and redistribution of paleo-reservoirs due to late Himalayan tectonic movement at late Neogene.In ge-neral,it is the early and middle uplifts during late Eh¹-Eh² of Paleogene which control oil and gas accumulation in the south steep slope,while the structural adjustment in the late stage dominates the pre-sent distribution of oil and gas.The small-sized uplifts developed in shallow formations,the lithologic traps developed in flanks of large-sized uplifts as well as the fracture traps developed in bedrock are important targets for future exploration.