Crude Oil Source and Accumulation Models for the Wenchang Formation, Southern Lufeng Sag, Pearl River Mouth Basin, (Offshore) China

In recent years, a large amount of industrial oil and gas resources have been discovered in the Paleogene Wenchang Formation (WC) of the southern Lufeng sag, confirming that the WC resources are promising prospects for petroleum exploration. However, because of the complex lithology, multiple sources of crude oil and multi-period charging characteristics in the WC, the accumulation process and model have not been clearly understood. Therefore, in this study, the main sources of crude oil and the process of hydrocarbon accumulation in key oil accumulation periods are determined by combining biomarker and geological analyses. Finally, the model of oil and gas accumulation is systematically summarized. The obtained results show that the source rock of the WC is the main source of hydrocarbons in the study area. The crude oil types in the southern Lufeng sag are classified into three types. Type A crude oil comes from source rocks of Wenchang Formation Members 3 and 4. Type B crude oil comes partly from source rocks of Wenchang Formation Members 1, 2, and 3 and partly from source rocks of Wenchang Formation Members 5 and 6. Type C crude oil is a mix of type A and type B crude oil. There are three accumulation periods that typify the study area: in the first period, accumulation was with vertical migration by fault; in the second period, accumulation was with lateral migration by sand body; and in the third period, accumulation was with vertical migration by sand body and adjacent to the source. The methodology and results of the accumulation process in southern Lufeng sag can support offshore oil and gas exploration.