Petroleum geological conditions and prospects in the Zhongjiannan basin in the western South China Sea

Abstract：The Zhongjiannan basin, located in a continental shelf-slope area of the western South China Sea, inherits the geological characteristics of the tectonic domain of the northern continental slope and Nansha sea area of the South China Sea and its development was controlled by the western South China Sea marginal fault. So the Zhongjiannan basin has very complex structure. Study indicates that: various sedimentary systems such as continental facies, transition facies and marine facies are developed in the Zhongjiannan basin; in the basin there are swampy, lagoonal, shallow lake (sea)-semi-deep lake (sea) and semi-deep lake (sea)-deep lake (sea) environments, which are favorable for the growth of source rocks; intermediate to high geothermal gradients made kerogen mature easily; the main reservoirs are fluvial, fan, deltaic sandstone and weathered bedrocks and carbonate rocks. Controlled by the combined action of the global geodynamic systems produced by the interaction of the Pacific plate, Indian-Australian plate and Eurasian plate and affected by the regional stresses produced by sea-floor spreading of the South China Sea, the basin evolution has the features of polycyclic evolution, which resulted in the formation of several good source-reservoir-cap assemblages, fault systems and many types of trap. These geological elements provide excellent material conditions and storage spaces for the petroleum-bearing system of the Zhongjiannan basin. According to seismic exploration information of China and other countries, gas shows have been found in the uplift in the northwest of the basin and many places in the central and southern parts of the basin. In addition, Wu Bihao et al. of the Chinese Academy of Geological Sciences found bitumen fragments with fresh fractured surfaces in samples from the column of the surface of the sea floor of the Zhongjiannan basin. It was identified as stearine bitumen by the fluorescence microscope. All of these prove that the Zhongjiannan basin has the potential of hydrocarbon generation. In a word, the Zhongjiannan basin has good petroleum prospects and high value for petroleum exploration.