Gravity flow sedimentary system and petroleum exploration prospect of deep water area in the Qiongdongnan Basin, South China Sea

Deep water petroleum exploration is still in start-up phase in China, and the study on the gravity flow theory of deep water sedimentation needs to be strengthened. In this paper, based on the seismic, coring, cuttings analysis and logging data, the gravity flow development conditions and sedimentary features of deep water area in the Qiongdongnan Basin were comprehensively analyzed, and the petroleum accumulation conditions of gravity flow realm in Central Depression of the deep water area were investigated in respect of the key factors like hydrocarbon source, reservoir and migration restricting the deep water hydrocarbon accumulation. The study results are obtained in three aspects. First, large reservoirs are developed in the deep water area, mainly including three gravity flow sedimentary systems, i. e. Huangliu Formation turbidite channel sand sedimentary system in the Central Canyon, Meishan Formation-Yinggehai Formation subsea apron sedimentary system in the Lingshui sag, and Lingshui Formation and Sanya Formation subsea apron sedimentary system in the Baodao-Changchang sag. Second, Lower Oligocene Yacheng Formation marine-terrestrial transitional facies coal-measure strata and semi-closed neritic facies mudstones are the important source rocks of deep water area in the Basin; Lingshui Formation subsea apron, Sanya Formation subsea apron, Meishan Formation subsea apron, Huangliu Formation canyon channel, and Yinggehai Formation subsea apron sandstone developed in Oligocene-Pliocene deep water area and the overlying bathyal-abyssal mudstone form five sets of regional reservoir-caprock assemblages; and proximal diapir and proximal fault are two kinds of efficient vertical source-connection modes in the deep water area. Third, the successful exploration of Lingshui 17-2 Gas Field in Central Canyon reveals that the gravity flow realm in Central Depression of the Qiongdongnan Basin represented by Central Canyon has a favorable exploration prospect. Conclusions are reached that the subsea aprons in both Ledong-Lingshui sag and Baodao-Changchang sag also have good petroleum accumulation conditions and exploration potential, and should be the future exploration targets in deep water area. ©, 2015, Natural Gas Industry Journal Agency. All right reserved.