The evolution, migration and accumulation regularity of oil and gas in Zhujiangkou basin, northeastern South China Sea

Abstract：The Zhujiangkou basin is a special tectonic location of passive continental margin with complex regional background and oil and gas geological conditions. The region has not only basic characteristics of Cenozoic continental rift and fault basin in eastern China but also its unique features. Because oil and gas geological conditions are different in different basin zones, there exist the regularity of migration and accumulation of oil in the north and that of gas in the south, and the characteristics of association and superimposition of various resources are obvious: The north rift zone and the East Sha uplift shallow water zone constitute the thinning location of the continental crust, with the scale of the fault depression and sedimentation being smaller than that of the deep water area in the north rift zone; in addition, the area has low geothermal gradient and small heat flow, its thermal evolution of source rocks is in the range of oil window, and it produces large quantities of oil accompanied by a small amount of oil type gas, thus forming a petroleum accumulation zone in the sallow water of north continental shelf, which mainly includes Wenchang, Yunping, Xijiang, Huizhou, Lufeng and Liuhua oil fields. The exotic source mechanism of the oil and gas migration and accumulation system is the Oligocene delta sandstone and Miocene reef limestone in the area. There exist large quantities of natural gas and a small amount of light oil, which mainly include gas reservoirs of LW3-1, LH34-2 and LH29-1 and oil reservoir of LH16-2 in eastern Baiyun depression and a small gas reservoir group in Panyu uplift of Baiyun depression, which constitute a rich natural gas district with resource potential of oil and oil-gas in the south rift zone and the south uplift zone. Because the south rift zone and the deep water zone of southern uplift constitute the location of near-ocean crust characterized by thin crust and large-scale fault depression, the area has more marine hydrocarbon source rocks than northern shallow water. There exist high geothermal gradient and large heat flow in this area, and the thermal evolution of the source rocks is at the stage of mature-highly mature condensate oil and wet gas; besides, there is mixed source mechanism of hydrocarbon migration and accumulation characterized by the hydrocarbon system of Oligocene delta coastal sandstone and the deep-water fan system, and there also exists the paragenetic and superimposition relationship between gas hydrates in the seafloor and shallow gas and conventional oil and gas in the deep water.