十万大山地区构造演化和含油气评价

Structural Evolution and Petroleum Assessment in Shiwandashan Region

十万大山盆地的构造演化过程为:在华夏被动大陆边缘发育的弧间洋盆基础上,经东吴、印支和燕山期碰撞造山运动,形成晚古生代—中生代前陆盆地,又经过短暂的弧后陆内裂谷阶段,形成了喜马拉雅期右列张扭性盆地。其原型盆地经历了镶嵌、交错、披盖、再镶嵌等四个叠置过程。其构造发展由正反转向负反转变化,以多次构造运动叠加后保留的基底部分卷入的冲断—推覆构造形态占主导,并发育典型的楔状前陆盆地、斜坡带及前陆隆起。盆地的圈闭类型有四种:于东吴期形成的与前陆隆起有关的背斜圈闭;于印支期形成的与褶皱推覆有关的断弯褶皱圈闭;于燕山期形成的正断层下盘逆牵引断鼻圈闭及逆冲推覆造成的掩覆带及掩覆褶皱圈闭。成烃史配套研究表明,在印支期形成并于燕山期定型的断弯褶皱,是油气聚集的有利场所。此外,南带的前陆盆地巨厚前渊碎屑岩将是寻找深盆气及二氧化碳气藏的有利目标。

Structural evolution of the basin is as follows,in the foundation of interarc oceanic basin developed on Huaxia passive continental margin,the basin has undergone Dongwu, Indosinian and Yanshan collision orogenies,a Later Paleozoic- Mesozoic foreland basin was then formed.After a short period of backarc intracontinental rift,right-laterally arranged tenso- shear basins were finally formed in Himalayan Age.The prototype basin has undergone mosaic,cross,drape and mosaic four superimposed processes.The structural development is characterized by a change from positive reverse-rotation to negative reverse-rotation;thrust-nappe structures based on remains after multiple structural movement superimposition dominate over the structural style.It is also developed with typical wedge foreland basins,slope zones and foreland uplifts.There are four types of traps in the basin: anticline traps formed in Dongwu,related to foreland uplift; faulted-bend fold traps formed in Indosinian,related with folding and napping;faulted-nose traps caused by down block reverse draging of normal fault in Yanshan;thrust-nappe zones and thrust-nappe fold traps caused by thrust and nappe, formed in Yanshan Age.It is shown that the faulted-bend fold traps formed in Indosinian and finalized in Yanshan are the most favorable for oil-gas accumulation from hydrocarbon-forming history.In addition,a huge thickness of foredeep clastic rock in southern foreland basin is a favorable place of exploration of deep-basin gas and carbon dioxide gas pools.