Deposition Pattern and Differential Thermal Evolution of Source Rocks, Deep Water Area of Qiongdongnan Basin

The deep water area of the Qiongdongnan Basin is currently a hot spot for natural gas exploration,but the lack of understanding of sedimentary model、evolution characteristics of the source rocks constrains the exploration results. In order to identify and evaluate source rocks in the deep waters of the Qiongdongnan Basin,Comprehensive application of seismic sedimentology,organic geochemistry and structural geology analysis methods,the parent materials of hydrocarbon and formation settings of the Oligocene-containing coal delta-shallow marine mudstones and their corresponding relationships with the discovered oil and gas are analyzed. The research shows that the distribution of coal-series and terrigenous type dominated marine source rocks controlled by the development scale and paleo-geomorphology of the Oligocene delta,and semi-closed shallow sea environment in the transition period of the fault-depression is conducive to formed the Oligocene terrestrial marine source rocks which are characterized by gas-prone and oil coproduct; The terrigenous type dominated marine source rocks distribution、thermal evolution as well as hydrocarbon generation processes of deep water have controlled the characteristics of natural gas potential. Hereby,gas-prone sags are evaluated by classification and Ledong、Lingshui and Songnan are gas- rich sags of Ⅰtype.