珠江口盆地阳江凹陷油气重大发现与成藏启示

Discoveries of Hydrocarbon Accumulation in the Yangjiang Sag of the Pearl River Mouth Basin and Implications

珠江口盆地阳江凹陷近两年先后发现了多个中型油田和含油构造,短短两年时间里从一个沉寂了近四十年的勘探新区成为珠江口盆地(东部)的热点探区。主力含油层段韩江组下段和珠江组上段储层物性良好,以中高孔、中高渗储层为主,油气产量高。这些油田的发现对珠江口盆地的新区勘探具有重要借鉴意义。(1)良好的烃源发育背景是新区突破的前提:阳江凹陷东段恩平20洼和恩平21洼文昌组沉积期以盆内物源为主,强烈的断陷活动和相对小的物源供给形成欠补偿环境,半深湖相烃源岩继承性发育、连片展布,为大中型油气田的发现提供充足的油气源。(2)大型海相三角洲为大中型油气田提供优质储集条件:受古珠江三角洲影响,阳江凹陷珠江组上段和韩江组下段以三角洲前缘沉积为主,水下分流河道和河口坝提供了优质储集体。(3)断裂差异性控制油气富集层系和富集程度的差异性:断裂通源能力控制油气富集层段,长期活动断裂系统是阳江凹陷最优质的油源断裂,能够将油气运移至浅层韩江组;断裂封闭能力控制油气的富集程度, NW向张扭断裂侧向封堵能力强,有利于油气的大规模富集。

A number of medium-sized oilfields and oil-bearing structures have been discovered in the Yangjiang Sag of the Pearl River Mouth Basin in the past two years,which is a breakthrough of the nearly 40 years of exploration in the Pearl River Mouth Basin(east area).The physical property of main oil-bearing intervals in the Miocene Hanjiang and Zhujiang Formations is well characterized by primarily medium-high porosity and medium-high permeability.And the oil and gas production is high.These discoveries are of great significance for the future exploration of the Pearl River Mouth Basin.First of all,a good hydrocarbon source rocks is the prerequisite for successful exploration operations.Provenances within the basins dominate the sedimentation during the depositional period of the Wenchang Formation of the Enping 20 Sub-sag and the Enping 21 Sub-sag in the eastern Yangjiang Sag.The strong faulting and relatively small provenances form an under-compensation environment.The semi-deep lacustrine facies source rocks are successively developed and connectively distributed,offering abundant sources for the large and medium-sized oil and gas fields.Secondly,the large marine delta supplies favorable storage conditions for large-and medium-sized oil and gas fields.Influenced by the ancient Pearl River delta,the Miocene Hanjiang and Zhujiang Formations in the Yangjiang area mainly develop underwater distributary channels and estuary dam sandstones in the delta front,providing the high-quality reservoir.Thirdly,the difference of fault activities controls the stratigraphic sequence and the degree of the oil and gas enrichment.The capacity of faults that cut through the source rocks controls the oil and gas enrichment intervals.The long-term active fault system is of highest quality for faults that connect the source rock in the Yangjiang Area,enabling oil and gas to be transported to the shallow Miocene Hanjiang Formation.The sealing ability of the faults controls the degree of oil and gas enrichment.The lateral sealing ability of the NW-striking transtensional faults is strong,which is beneficial for large scale oil and gas accumulation.