松辽盆地徐家围子断陷断裂变形特征及控藏机理

徐家围子断陷为“西断东超”的箕状断陷，伸展断裂和走滑断裂这2种性质断裂对天然气成藏具有明显的控制作用。伸展断裂系统在控盆同时控制有效烃灶分布，近SN向张扭断裂即徐西断裂与NNE向断裂共同控制了沙河子组煤层分布，形成有效烃源灶。走滑断层为火山喷发的通道，徐中断裂和徐东断裂控制营一段和营三段火山分布，与之相交的北北东向断裂有诱导火山喷发作用，交点位置火山规模最大。徐中断裂在泉头组沉积晚期到青山口组沉积早期再次强烈活动，右旋走滑变形使火山岩产生大量裂缝，特别是在断层交点处最发育，形成优质储层。徐东断裂此时无明显活动，优质储层不受裂缝控制。与此同时断裂强烈活动配合沙河子组气源岩大量生排气，成为气源断层，徐中断裂是最主要的气源断裂，由于岩性对接封闭作用，天然气主要分布在气源断裂下盘，因此，天然气围绕倾向变化的徐中断裂两盘呈“正弦曲线”状分布。反转断层和盖层控制天然气富集层位，火山岩顶面的“混岩”盖层品质好，在反转断层不发育区使天然气富集在火山岩储层中。反转断层发育区，易将火山岩中天然气调整到青山口组区域性盖层下的扶杨油层中聚集，调整期为明水组沉积末期。走滑断裂是天然气成藏的主控因素，明水末期没发生强烈反转是保存的关键。

Fault Deformation Features and Reservoir-controlling Mechanisms of Xujiaweizi Fault Depression in Songliao Basin

Xujiaweizi fault depression is a dustpan\|shape graben which ruptures at the west and overlaps at the east.Two kinds of fault have a significant controlling effect on the gas accumulation,namely extensional fault and strike-slip fault.The extensional fault system controls the basin boundary and the distribution of effective hydrocarbon kitchen.The distribution of the Shahezi coal is controlled by the NS transtensional fault named Xuxi fault and the NNE faults,which is an effective hydrocarbon kitchen.The strike\|slip faults are the channels of volcanic eruption.Xuzhong fault and Xudong fault control the volcanoes′ distribution in the first and third members of Yingcheng Formation,while the NNE faults intersected with them have the effect of inducing volcanic eruption.And the scale of the volcanic is the largest at the intersection.Xuzhong fault has a strong movement from the late Quantou to early Qingshankou,whose dextral strike slip deformation makes the volcanic rock to form a great number of fractures,especially at the fault intersection,forming high quality reservoir.Xudong fault has no obvious activity at this moment,where high quality reservoir is not controlled by fractures.The intense activities combined with abundant gas generation and expulsion from the Shahezi source rocks make the faults as gas |source faults.Xuzhong fault is the most significant gas source fault.Gas accumulates at the footwall of gas source faults because of the lithology juxtaposition.The trend of Xuzhong fault changes,so the gas distributes like a “sine curve” around the Xuzhong fault.Inverted faults and cap rocks control the layer of gas enrichment.The top lithology of volcanic rock named “mix litholoty” has a good sealing quality,which seals the gas at the volcanic rock reservoir at the area lack of inverted faults.In the inverted faults area,the gas in volcanic rock is easily adjusted to Fuyang oil layer sealed by regional cap rocks,Qingshankou Formation.And the adjustment happened at the late deposition stage of Mingshui Formation.Strike slip fault is the controlling factor of gas accumulation.There is no strong inversion at the end of Mingshui deposition,which is crucial for preservation.