断裂复合汇聚脊对新近系油气远距离富集的控制作用——以珠江口盆地阳江东凹与恩平凹陷为例

Controls of Faulted Composite Accumulation Ridge on the Long Distance Migration and Accumulation of Neogene Hydrocarbon:A Case Study of the Eastern Yangjiang Sag and the Enping Sag in the Pearl River Mouth Basin

珠江口盆地珠一坳陷北部断阶带在近40年的勘探实践中一直未获商业发现,近年来在阳江东凹与恩平凹陷北部相继获得重大油气发现,且油气具有远源富集特征。本文提出"断裂复合汇聚脊"是该地区新近系油气远源富集的关键控制因素。"断裂复合汇聚脊"是受多条断裂切割复杂化的一类汇聚脊,具有4个特征:(1)汇聚脊三面分别被恩平17洼、恩平21洼、恩平14洼等三个已证实或潜在富生烃洼陷环绕,油气来源充足;(2)汇聚脊西侧发育7条北倾的反向断裂,东侧发育6条南倾的顺向断裂,整体由南向北逐级抬升,两侧地势较低,油气能从多个方向持续汇聚;(3)汇聚脊南端的断裂深切洼陷,且新近纪强烈活动,能将洼陷内部的油气大规模调节至新近系;(4)汇聚脊东西两侧断裂上升盘发育一系列断鼻圈闭,利于捕获油气。勘探实践证实,断裂复合汇聚脊是该地区油气远源富集的关键要素,由此作者建立了油气成藏模式,该模式丰富了新近系油气成藏理论,这一发现对珠江口盆地类似地区的勘探具有一定借鉴意义。

After 40 years of exploration in the faulted-terrain zone of the northern ZhuⅠDepression,Pearl River Mouth Basin,significant discoveries have been made recently in the eastern Yangjiang Sag and the northern Enping Sag.The characteristics of the newly found oil and gas show that they were likely originated from source rocks out of this area.Therefore,a hypothesis of faulted composite accumulation ridge was put forward to explain the oil and gas accumulation from a remote Neogene source in this region.The faulted composite accumulation ridge is a type of accumulation ridge which is commonly difficult to identify due multiple-stage faulting and far-reaching extending.The faulted composite accumulation ridge in this study area has four characteristics.First,the accumulation ridge is surrounded by three potential or proven hydrocarbon-generating sags,such as the Enping 17 Sag,the Enping 21 Sag and the Enping 14 Sag,and hosts abundant sources of oil and gas.Secondly,there are 7 north-dipping antithetic faults on the west side of the accumulation ridge,and 6 south-dipping synthetic faults on the east side.The accumulation ridge as a whole is gradually uplifted from south to north.The terrains on both sides are relatively low,which partly controls the migration of the oil and gas.Thirdly,the faults in the south of the accumulation ridge penetrate into the sag at depth,whereas its strong activity in Neogene resulted in the redistribution of the oil and gas in the sag.Finally,a series of faulted-nose-like traps developed on both the east-and west-side uplifts of the accumulation ridge favored the capture oil and gas.The exploration practice show that the faulted composite accumulation ridge is the key factor controlling accumulation of the oil and gas originated from a remote source area.In conclusion,the mechanism for oil and gas accumulation established for the study area might be applicable for future exploration in other regions of the Pearl River Mouth Basin as well.