四川盆地米仓山前陆冲断带成藏条件分析

本文运用层序地层学、平衡剖面分析与缩短量计算和生烃史恢复等方法,从区域构造分析和地震剖面解释入手,通过野外地质调查、地震资料解释、典型剖面平衡剖面分析和缩短量计算,结合成藏条件的分析和生烃史恢复,探讨了米仓山前陆冲断带构造演化特征,揭示该带的成藏条件和天然气富集特征。提出了米仓山演化模式,认为米仓山前陆冲断带成藏条件优越,可供钻探的圈闭发育,天然气勘探潜力巨大,储层、保存条件是成藏关键。其中,二叠系为主要烃源岩,二叠系生屑灰岩和飞仙关组鲕粒灰岩为主要储集层,雷口坡组和嘉陵江组膏盐岩层为主要盖层。并且,冲断带构造演化的时序性表现为由西向东变形强度、缩短量变小,变形时间变晚,同时前陆盆地的不同构造单元间的相互关系发生变化,造成勘探目的层系、圈闭幅度、类型的相应变化。

Analysis of Pool-Forming Factors of the Micangshan Thrust Belt in the Sichuan Basin

Foreland basins are one kind of petroleum enrichment basins all over the world. The Sichuan Basin is located in the southwest of China, and on the northern margin of the basin three foreland basins are well developed. Of the three foreland basins, the Micangshan foreland basin is between the Longmen Mountains and the Daba Mountains, which is more poorly developed. With only two small gas fields, the Jiulongshan and Hewanchang gas fields, and Chuanfu 82 and Shejianhe gas-enriched traps have been found in the basin. According to recent seismic survey data along the mountain, many structure traps have been found in the thrust belts in the area, but the key factors in gas pools formation need to be studied. Based on sequence stratigraphy, balanced section analysis, calculation of shorten amount of strata, petroleum generation modeling techniques, in combination of synthetic study of pool forming factors, the paper studies the evolution features of the thrust belt and proposes an evolution mode of Micang Mountain, which indicates that the thrust belt began to evolve from west to east, and the distortion intensity, shortening amount became less from west to east with the evolution. According to systemic studies, the paper pointes out that the pool-forming factors are good, traps are well developed and there is a huge gas potential in the thrust belt. Reservoirs and conservation conditions are the key factors of the formation of pools. The main gas generation layer is Permian rocks. Permian biologic clastic limestone and Triassic oolite are the best reservoirs and the main cover strata are salt rocks in the Leikoupo and Jialingjiang Formations of Triassic.