琼东南盆地深水区重力流沉积体系及油气勘探前景

我国深水油气勘探还处于起步阶段,对于深水沉积重力流理论的研究亟待加强。为此,利用地震、新钻井岩心、壁心、岩屑化验分析及测井等资料,综合分析了琼东南盆地深水区重力流发育条件、沉积特征,并围绕烃源、储层、运移等制约深水油气成藏的关键因素对深水区中央坳陷重力流领域成藏条件进行了研究。结果表明:①深水区大型储集体发育,主要发育了中央峡谷黄流组浊积水道砂沉积体系、乐东陵水凹陷梅山组莺歌海组海底扇沉积体系和长昌宝岛凹陷陵水组、三亚组海底扇沉积体系等三大重力流沉积体系;②该盆地早渐新统崖城组海陆过渡相煤系地层和半封闭浅海相泥岩地层是深水区重要的烃源岩,渐新统上新统深水区发育的陵水组海底扇、三亚组海底扇、梅山组海底扇、黄流组峡谷水道、莺歌海组海底扇砂岩与上覆半深海、深海泥岩形成了5套区域性储盖组合,近源底辟、近源断裂是深水区两种垂向高效通源模式;③中央峡谷陵水17-2气田的勘探成功,揭示了以中央峡谷为代表的琼东南盆地中央坳陷重力流领域具有良好的油气勘探前景。结论认为,乐东一陵水凹陷和宝岛一长昌凹陷海底扇领域同样具有良好的油气成藏条件和勘探潜力,是深水区下一步油气勘探的突破方向。

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.