南海北部琼东南盆地深水区烃源条件及天然气成藏机制

近年来，南海北部琼东南盆地深水西区天然气勘探取得了重大突破，证实深水区具备良好的烃源和油气成藏条件。但由于地质条件的复杂性，琼东南盆地深水区烃源岩规模及生烃潜力、油气成藏机制及分布规律、下一步勘探突破领域依然不是很清楚。针对上述关键问题，本研究综合运用地球化学与地质分析方法，开展琼东南盆地深水区烃源条件与油气成藏机制研究，进而指出琼东南盆地深水区下一步有利的油气勘探突破领域。研究认为：琼东南盆地中央坳陷深水区发育始新统湖相、渐新统崖城组海陆过渡相及半封闭浅海相2套3种类型的烃源岩，其规模大、热演化程度高，生烃潜力巨大，为琼东南盆地深水区天然气勘探提供了坚实的物质基础。琼东南盆地深水区油气成藏条件优越，但深水西区与深水东区油气成藏机制存在一定差异。深水西区乐东_陵水凹陷中央峡谷周缘上中新统轴向水道、海底扇岩性圈闭带和陵水凹陷南部斜坡古近系/潜山圈闭带以及深水东区的宝岛凹陷宝南断阶带、长昌凹陷西部环A洼圈闭带为下一步油气勘探的重要突破领域。上述成果对于解决琼东南盆地深水区天然气勘探瓶颈问题、指明下一步勘探突破方向具有重要的科学和勘探实践意义。

Hydrocarbon source condition and accumulation mechanism of natural gas in deepwater area of Qiongdongnan Basin,northern South China Sea

There has major breakthrough of natural gas exploration in western deepwater area of Qiongdongnan Basin resent years.This verified favorable source and accumulation conditions in the deepwater area of Qiongdongnan Basin.But because of the complicated geologic settings,the scale of source rocks and the hydrocarbon potential,accumulation mechanism and regularities of hydrocarbon distribution and exploration breakthrough fields in deepwater area of Qiongdongnan Basin are still indistinct.In this article,a serials of geochemical and geological methods are used.Research result shows that three types of source rocks such as Eocene lacustrine deposit,marine-continental transitional deposit and neritic deposit in Yacheng Formation of Oligocene developed in the central depression of Qiongdongnan Basin.Huge hydrocarbon potential provided a solid material basis for natural gas exploration in deepwater area of Qiongdongnan Basin.Deepwater area in Qiongdongnan Basin has favorable reservoir formation conditions with certain degree of differences.Axial channel deposited in the Upper Miocene around central canyon,submarine fan lithologic traps and Palaeogene traps in western deepwater area of Ledong and Lingshui Sags,step-fault zone in southern Baodao Sag and trap zone around western A sub-sag in western Changchang Sag of eastern deepwater area are significant exploration breakthrough field.