ACCUMULATION CONDITIONS OF BURIED-HILL HYDROCARBON RESERVOIRS ON THE LINGNAN LOW UPLIFT IN THE DEEP WATER AREAS OF QIONGDONGNAN BASIN

Buried hill reservoirs are quite common in the deep water areas of Qiongdongnan Basin, where sandstone reservoirs are rare. This paper is specially devoted to the forming conditions and geological models of buried-hill hydrocarbon reservoirs on the Lingnan Low Uplift. By careful correlation of the oil and gas exploration results and existing problems of the Songnan Low Uplift buried-hills in Northeast China, geological conditions for buried-hill oil and gas accumulations in the Qiongdongnan basin are comprehensively evaluated by means of the reservoir forming model and its characteristics. The study shows that the buried-hill on the Lingnan Low Uplift is surrounded by matured source rocks. Hydrocarbon is supplied by the Ledong-Lingshui hydrocarbon-rich sag next to it. There is a coupled reservoir cap assemblage composed of Mesozoic granite buried-hill reservoir and Neogene thick cover of marine mudstone. There also occurs a smooth migration and accumulation system composed of large source-connected faults and large inherited structural ridges. Large pressure difference occurs between the source and storage that ensure the reservoir directly to be charged by near source oil and gas. Compared with the buried-hill reservoir on the Songnan Low Uplift, which has been successfully explored, the reservoir forming conditions are excellent in the study area. It could be compared with the large Baihu buried-hill oilfield in Vietnam and the Bozhong 19-6 buried-hill condensate gas field in the Bohai Sea. The petroleum geological conditions of the Lingnan Low Uplift, which is "rich in mud and poor in sand", may be favorable for the formation of large-scale and contiguous buried-hill oil and gas reservoirs in the deep water areas in addition to the Central Canyon of the Qiongdongnan Basin.