The Study Of Structure Modeling In Western Sichuan Depression Based On Analyzing The Seismic Images

Western Sichuan depression lies in the west of Sichuan basin, which is the abundance zone for gas. Its western border is Longmenshan thrust structural belt, eastern bored is next to Longquanshan, Micangshan thrust structural belt is the northern border, southern border is closed to Emei-Liangshan fault-block. Guided by theories, method of modern seismology,tectonic geology, Western Sichuan depression is the target. On basis of loggings,drilings and seismic datas having been researched detailedly, synthetic seismogram of 18 wells have been made,and formations calibrating are done, according to the methods ,including feature recognition of seismic reflection waves,introducing from adjacent areas etc, interpret the seismic-geologic horizons in western Sichuan depression. Based on prestack migration seismic images, analyzing the main feature of fault and structural mode by elaborate structure interpretation using regional geologic information, structural maps of the bottom of Jurassic,Upper Triassic Maantang,Middle Triassic Leikoupo,Upper Permian,Permian and Presinian have been made up. The study region can be divided into five structural zone : Longmenshan thrust belt,Longquanshan fault and fold belt,Pengxian deep hollow belt,southeast slope belt and arched area in the middle of Sichuan basin, there are some typical structural mode, such as imbricate structure,fault-propagation folds,pop up,arrested anticline .From the study I also find that faults show a zonality in plane, vertically the structural deformation appears in different levels, Guankou fault,Pen??n fault,Anxian fault and Longquanshan fault play an important role in local structures, which primarily distribute in the west or middle of the study region. Furthermore, Dayuanbao,Yazihe,Pengxian,Anxian,Longquanshan,Hexingchang,Xinchang etc local structure are carried out. Based on confirming structural feature and structural mode in western Sichuan depression, I not only build the structure modeling but also use the 3D visual soft to show the main structure and the changes of the formations in the space. According to the isopach map and balanced section, I think the structure evolution in western Sichuan depression can have several periods by studying the evolution in Longmenshan and western Sichuan foreland basin, which are Hercynian,Indo Chinese epoch,Yanshannian and Himalayan movements. It is relative stablility at the Hercynian in western Sichuan depression. Because of the Indosinian movement, large faults and folds had begun to form, the orogen of Longmenshan had generated, meanwhile, foreland basin had subsided. Through the Yanshannian and Himalayan movements, the forming of Longmenshan had became more and more intense, the number of faults had increased obviously, fault displacement had extended continuously, the border of orogenic belt had spreaded to basin, at the same time foreland basin had subsided deeply, finally it have developed and fallen into today's pattern .