Research of genesis of hydrocarbon accumulations located within pre-Cenozoic basement of the South China Sea shelf (Vietnam) presented. Formation of hydrocarbon deposits is confined to the protrusive massifs of granites that have undergone structural and tectonic processing at the stage of prototectonics and postmagmatic tectonics. The totality of post-structure-forming processes led to a change in the viscosity properties of rocks, to their tectonic and material heterogeneity and stratification and, as a consequence, to vertical and lateral redistribution in space with the formation of granite protrusions. The mechanisms of formation of voids and oil and gas traps within the protrusions are considered. Based on the similarity of the geochemical characteristics and biomarker parameters of the oils and organic matter in the Oligocene-Miocene sediments and in the basement rocks, a conclusion has been made about the organic nature of the oils in the basement of the shelf of the South China Sea (Vietnam). Possible mechanisms of migration and accumulation of hydrocarbons in basement rocks are considered. It is confirmed that the formation of hydrocarbon deposits occurred due to lateral and downward migration of hydrocarbons through the contact area from the Oligocene-Miocene source rocks into crystalline massifs — into voids and increased fracture zone in the protrusions.
The main controlling factors and developmental models of Oligocene source rocks in the Qiongdongnan Basin, northern South China Sea
