Fault-Controlled on Hydrocarbon Migration and Accumulation of Baodao Northern Slope in the Qiongdongnan Basin, South China Sea

Based on the oil-gas exploration data of Baodao Northern Slope in Qiongdongnan basin, the abundance of the adsorbed hydrocarbon and the abundance of brine inclusions with hydrocarbon were evaluated by quantitative grain fluorescence experiment. Combined with stages of fault activities, fault sealing capacity and the oil-gas charging time, the fault control on hydrocarbon migration and accumulation characteristics of Baodao Northern Slope was analyzed. The results show that the oil and gas reservoirs of the N1m–N1s Formation (21–10 Ma) of Baodao Northern Slope were formed very late, so, the particle surface adsorbed hydrocarbon abundance of shallow N1m–N1s Formation is prevalent and high with a low abundance of intragranular hydrocarbon. However, the oil and gas reservoirs of E3l Formation (30–21 Ma), close to the Baodao Sag, were formed earlier but most of them were destroyed later, and therefore the hydrocarbon abundance characteristics are different. Because of the limited migration ability, the oil and gas generated from the Baodao Sag mainly contributed to the south of Baodao Northern Slope, and they have little contribution to the northern part. The hydrocarbon generated from Oligocene source rock migrated vertically through the widely developed faults rather than along the lateral delta front sands.