天山南、北两侧库车和准南前陆盆地流体动力场与构造应力场、瞬时流场的耦合及对油气成藏的影响

As fluid mineral resource, the hydrocarbon migration and accumulation are controlled mainly by fluid dynamic field in basin. In western foreland basins of China, because of being underwent multi-stage structural compressional movements, faulting effect, fast uplift and subsidence of basin, their fluid pressure has been increased, fluid and pressure have been conducted by faulting, so that the fluid dynamic compositions in western foreland basins are usually more complicated than other kinds of sedimentary basins. In structurally mild and strong activity stage of western foreland basins, there were very complex distribution of fluid dynamics and its effects on hydrocarbon migration and accumulation, and the obvious difference of distribution among different tectonic elements and lithologies. The Kuqa and Zhunnan foreland basins from southern and northern flank of Tianshan mountain are selected as study objects, in which the feature of foreland thrust belt in Kuqa and foredeep-slope in Zhunnan were developed respectively, the fluid dynamic field during major accumulation periods would be coupled with structural stress field and instantaneous flow field in faulting activity, characteristics and differences of “three fields” couple in foreland basins from southern and northern flank of Tianshan mountain, and their effects on hydrocarbon migration and accumulation would be summarized and contrasted. This study would provide a new research idea and method on fluid dynamic field study in western foreland basins, and understand deeply the distribution rule of hydrocarbon migration and accumulation.

油气作为流体矿产，其运移、成藏主要受控于盆地的流体动力场特征。在中国西部前陆盆地内，由于经历了多期的构造挤压运动、断裂作用以及盆地的快速抬升和沉降，引起流体压力增加，断裂活动引起流体和压力的传导，从而使得前陆盆地的流体动力构成比其它类型的沉积盆地更为复杂。在前陆盆地的构造和缓期和构造强烈活动期，流体动力分布及对油气运移、成藏的影响十分复杂，且在不同构造单元和岩性内，其差异性明显。本项目以天山南、北两侧的库车、准南前陆盆地作为研究对象，突出库车的前陆冲断带和准南的前渊-斜坡带特色，试图将主要成藏期的流体动力场与构造应力场、断裂活动中的瞬时流场进行耦合，总结、对比天山南、北两侧前陆盆地“三场”耦合的特点和差异性，及其对油气运移、成藏的影响。该研究将对西部前陆盆地流体动力场的研究提供新的研究思路和方法，也将深化认识其中的油气运移、成藏规律。

油气作为流体矿产，其运移、成藏主要受控于盆地的流体动力场特征。在中国西部前陆盆地内，由于经历了多期的构造挤压运动、断裂作用以及盆地的快速抬升和沉降，引起流体压力增加，断裂活动引起流体和压力的传导，从而使得前陆盆地的流体动力构成比其它类型的沉积盆地更为复杂。本项目以天山南、北两侧的库车、准南前陆盆地作为研究对象，突出构造挤压过程对流体动力场的影响——构造挤压增压与断裂引起的压力传递，通过盆地模拟的手段，将流体动力场与构造应力场、断裂活动中的瞬时流场进行耦合。总结天山南、北两侧前陆盆地“三场”耦合的特点和差异性，及其对油气运移、成藏的影响。该研究将对西部前陆盆地流体动力场的研究提供新的研究思路和方法，也将深化认识其中的油气运移、成藏规律。取得以下重要认识和成果：.（1）库车与准南前陆盆地是两个最具天然气勘探潜力的地区，超压成因相同，主要为欠压实、生烃作用、构造挤压、断裂传递，但贡献存在差异，特别是断裂传递型超压，在库车地区传递型超压的增压幅度主要集中在30MPa~40MPa，而在准南地区主要分布在8MPa~15MPa。.（2）耦合构造挤压后，库车前陆盆地的源储压差显著增高，增量普遍在30MPa左右，有利于油气的垂向运移；克深地区形成一个巨大的低气势、低势梯度的“空腔”，有利于油气的聚集。耦合构造挤压后，准南前陆盆地流体动力分布格局有明显变化，构造增压导致高气势区向冲断带扩展，紫泥泉子组与清水河组气势梯度有所降低，为石油的聚集提供了保障，而超深层侏罗系气势梯度增加，有利于油气的侧向运移。.（3）断裂活动将深浅流体动力系统以“地震泵”的形式进行沟通，将深部超压流体/油气高效输导至浅层。耦合断裂活动后，库车前陆盆地断裂的高效输导与膏盐层良好的封闭能力相匹配，是库车前陆盆地油气成藏的关键；而断裂活动期，断层对浅部盖层封闭性的破坏，导致油气的大量散失，导致准南前陆盆地浅层油气成藏效果不佳。