Geological structure of Zhusi Depression in ultra-deep water area on the continental margin of the northern South China Sea and its control on the development of source rocks

The overall water depth of Zhusi Depression in the Pearl River Mouth Basin is more than 1500 m with very low degree of the exploration. The oil and gas revealed by drilling has shown the existence of source rocks in this area, and seismic data present a vast and thick source rocks in the Paleogene strata. As a new oil and gas exploration area marching towards ultra-deep water in the north of the South China Sea, we analyzed the advantages and disadvantages of petroleum geological conditions in each depression. Based on the knowledge of the formation mechanism of six types of fault depressions in the Pearl River Mouth Basin, Zhusi Depression were divided into three representative fault depression structural styles: inter crustal ductile rheological type of Atlantic magma-poor continental margin, supracrustal magmatic underplating type of Atlantic magma-rich continental margin, and pre-existing splicing type of supracrustal magmatic on Atlantic magma-poor continental margin. Using the 2Dmove software and decompaction technology, the subsidence rate and extension rate of each depression were restored. Combining a large number of seismic profiles, the geological structure of Zhusi Depression and its impact on the development of source rocks were studied in depth, and the differences of source rock development background under different fault depression structures were clarified. Results show that the development conditions of source rocks in Liwan and Heshan depressions are superior, which can be regarded as an important exploration breakthrough point in the ultra-deep water area in the north of the South China Sea.