Petroleum geology of the Zengmu basin in the southern South China Sea

Abstracts：The Zengmu basin is a large Cenozoic sedimentary basin located in the southern South China Sea, characterized by a high sedimentation rate and great thickness. Recent petroleum exploration and research indicate that the Zengmu basin has very favorable geological conditions for the formation of petroleum, where there occur mainly two groups of source rocks, including Oligocene paralic carbonaceous shale, coal layers and marine mudstones and lower-middle Miocene marine mudstones, and two types of reservoirs, namely, Oligocene-middle Miocene sandstones and middle-upper Miocene limestone or reef limestone. The Kangxi depression and Eastern Balinjian depression are two primary hydrocarbon-generating zones. Vertically, petroleum mostly occurs in lower Miocene sandstone and middle-upper Miocene carbonates, with the formar mainly containing oil and the latter mainly containing gas. Laterally, the petroleum distribution in the Zengmu Basin is characterized by occurrence of oil in the south and gas in the north. Gas fields are mainly distributed in the Nankan mesa in the east and the western slope, while oil fields mainly occur in the Balinjian area. The distinct zonal distribution of oil and gas is primarily related to structures in different tectonic units and difference in sedimentation in the basin.