珠江口盆地阳江凹陷不同成藏期次原油成因及混源比例分析

阳江凹陷为珠江口盆地近两年来获得油气勘探重大突破的新区。采用饱和烃色谱—质谱实验、流体包裹体系统分析和全油气相色谱法混源油定量配比实验相结合，对阳江凹陷不同成藏期次原油成因进行系统分析，并对已获得混源油藏的混源比例进行了测算。阳江凹陷发生两期原油充注，充注时间分别为12.0～7.5 Ma和6.5～0 Ma。第一期原油来源于恩平20洼始新统文昌组文三段中浅湖相烃源岩，主要在中新统珠江组储层中聚集成藏；第二期原油来源于文一段和文二段中深湖相烃源岩，在中新统珠江组—韩江组储层中均有成藏。通过混源油定量配比实验建立混源比例测算模板，计算结果表明，B20-1、B20-2油田韩江组油藏均为第二期充注，B20-1油田珠江组油藏第一期和第二期充注量占比分别为39%和61%。关键成藏时期断裂活动强度、圈闭发育层段及有效烃源岩三者耦合关系共同控制着圈闭富集程度。 

Origin and mixing ratio of crude oils in different charging episodes of Yangjiang Sag of Pearl River Mouth Basin

The oil and gas exploration in the Yangjiang Sag of Pearl River Mouth Basin has successfully carried out and breakthroughs have been achieved in the past two years.The generation mechanisms of crude oils of multiple charging episodes were studied and the sources,mixing ratios were quantitatively calculated by the using of analytical results of gas chromatography-mass spectrometry(GC-MS)for the saturated hydrocarbon fractions,fluid inclusion system analysis and whole-oil gas chromatography(GC-FID)for mixed-source oil proportion experiment.Results showed that there were two episodes of crude oil charging in the Yangjiang Sag,12.0-7.5 Ma and 6.5-0 Ma.In the first stage,crude oils came from the medium-shallow deposited lacustrine source rocks in the third member of Wenchang Formation in the Enping 20 sub-sag,and mainly were accumulated in the Zhujiang Formation.In the second stage,crude oil came from the medium-deep deposited lacustrine source rocks of the first and second members of Wenchang Formation,and accumulated in the Zhujiang and Hanjiang formations.A template for the calculation of mixed propotion of oils was established through quantitative experiments.It was concluded that the Hanjiang reservoirs in the B20-1 and B20-2 oil fields were mainly charged during the second episode,while the Zhujiang reservoirs in the B20-1 oil field were charged during both the first and the second episodes,accounting for 39%and 61%,respectively.The coupling relationship among fault activity intensity,trap development interval and effective source rock controlled the degree of enrichment.