南海北部珠江口盆地烃源岩成因:阳江凹陷的资源潜力

Formation of Source Rocks in the Pearl River Mouth Basin,Northern South China Sea:Resource Potential of the Yangjiang Sag

本文基于最新的三维地震资料和钻井等资料,对阳江凹陷古近系烃源岩的形成条件与资源潜力进行分析和评价。作者从盆地分析入手,明确了走滑拉分的成盆模式有利于烃源岩形成,并首次利用Badlands盆地模拟揭示了阳江凹陷古地貌及沉积发育特征,指出该区属于典型有利于烃源岩的形成和发育的内源沉积;并利用三维地震资料,精细解析其断裂体系,在井震结合进行烃源岩层位标定和层序划分的基础上,结合沉积体系的研究结果,在阳江凹陷文昌组中识别出深湖和半深湖相沉积,说明阳江凹陷古近系烃源岩主要分布在文昌组,文昌组自下而上可为文三段、文二段和文一段;根据钻井资料揭示的烃源岩特征,在地震剖面上识别出烃源岩的地震相反射特征,然后通过对地震属性的分析,确定文昌组烃源岩的分布特征;最后基于以上研究,利用Petromod盆地模拟技术对文昌组烃源岩的生烃潜力进行模拟。结果显示:文昌组烃源岩具有良好的生烃潜力,文一段烃源岩在16Ma成熟,开始生油;文二段和文三段烃源岩在23Ma成熟,开始生油,且文二段烃源岩为最好的生烃潜力层段。结合生烃史模拟结果,表明恩平20洼为生烃潜力最好的洼陷,是未来勘探的重点。

The formation of the Paleogene source rocks of the Yangjiang Sag is analyzed and their resource potentials are evaluated based on the latest 3D seismic and drilling data.Basin analysis showed that the tectonic model of strike slip-pull apart basin is very favorable for the formation of the source rocks.The Software Badlands basin simulation was exploited for the first time to delineate the paleo-topography and sedimentary characteristics,and the results also indicated the endogenous deposition in this area is favorable for the formation of the source rocks.Through detailed investigations of faults and structures,sequence division of source rocks,and sedimentary facies on the basis of the seismic-drilling data,we recognized a lot of deep lake and semi-deep lake sedimentary facies in the Wenchang Formation which are favorable source rocks in the Yangjiang Sag.The Wenchang Formation is divided into three members,namely the Wen-3,Wen-2 and Wen-1 members from the bottom to top.The distribution and characteristics of the source rocks in the Wenchang Formation are determined on the bases of the geochemical characteristics and seismic facies of the source rocks.Finally,petromod simulation showed that the source rocks in the Wenchang Formation have good hydrocarbon generating potential,within which the source rocks in the Wen-1 Member have been matured at 16 Ma,and source rocks in the Wen-2 and Wen-3 Members have been matured at 23 Ma,while the source rocks in the Wen-2 Member in the eastern Yangjiang Sag is the most favorable member to generate hydrocarbon.In addition,the simulation results of the hydrocarbon generation history demonstrated that the Enping 20 Sub-sag is the most promising area and should be the focus of future hydrocarbon exploration.