歧口凹陷古近纪构造演化及其对油气成藏的影响

摘要

歧口凹陷古近纪构造活动以断陷为主,演化形成的NW—SE方向多次凹复式箕状断陷结构和N—S方向歧口主凹双断复式地堑结构.通过分析其演化趋势和伸展断裂过程,发现歧口凹陷古近纪受伸展旋转走滑的双重构造作用影响,沧东伸展断裂系统对其的影响大于歧口伸展断裂系统,形成一个菱形或多边形的断陷湖盆,断陷边缘及内部发育一系列构造带.断陷湖盆的持续性沉降,使得烃源岩大量发育.主干断层切割生油层,为油气运移提供输导通道.歧口凹陷古近系断陷构造形成多凸多凹、多物源、近物源的古地理背景,在断陷演化的不同阶段,有多种类型砂岩储集体发育.在断陷湖盆的陡坡带、缓坡带、断阶带、盆内坡折带形成4种油气成藏模式.针对歧口凹陷古近系断陷构造演化的特点,优选勘探目标区,经钻探实例验证,取得良好效果.%The analyses of the mode of structural evolution in Qikou sag showed that,graben faulting of Paleogene generate complex half graben-like framework on NW-SE orientation and complex duplex fault graben on N-S orientation in Qikou sag.The tectonic framework of the convex,concave and concave-uplift alternately formed in Qikou sag,which created favorability for the formation of the lithologic reservoir.The high-quality source rocks developed in the sedimentary center were material foundation of the development of the lithologic oil reservoirs.Synsedimentary fault and its configuration decided the characters of gullies controlling sources,transform zones controlling fans and faulted slopes controlling sands,and that the middle of subaqueous fan,delta front and infralittoral subaqueous fan were the most favorable hydrocarbon accumulation zones.The development of the faults make the deep oil-gas accumulation more favorable,which provided effective reservoir space for the development of the lithologic oil reservoir.Tectonic activity and sedimentary evolution formed the optimal configuration relationships of the source-reservoir-cap,which created favorable conditions for the formation of multi-types lithologic oil reservoirs.According to the lithologic oil reservoir types,spatial distribution characteristics and oil accumulation characters in Tanan sag,four kinds of lithologic oil reservoir forming modes are summarized,including the fault terrace-steep slope-break belt,fault terrace-gentle slope-break belt,cliffsteep slope-break belt and inner basin slope,break belt reservoir forming mode of Qikou sag,combining the geological structure characters.In Qikou sag,4 types of oil-gas accumulation modes are formed:accumulation of shelving,accumulation of actic region,accumulation of fault flight of stairs,accumulation of break in slope of Qikou sag.