Geological Architecture And Its Controls Upon Distribution Of Hydrocarbon In The Northern Segment Of Western Sichuan Basin

The northern segment of western Sichuan Basin is located at the eastern edge of Longmenshan and the south edge of Micangshan,and it includes two rows structure in the expanded deformation belt and the depression in the northwest of Sichuan Basin.It is a key area for studying the expanded deformation in Longmenshan and its interaction with the Sichuan Basin.At the same time,the northern segment of western Sichuan Basin,as a typical example of the Cenozoic tectonic activity,is a window revealing the transformation of new tectonic activities to old structures.Moreover,petroleum exploration in the northern segment of western Sichuan Basin has continued to make breakthroughs in recent years.Based on this,this paper develops the research on the geological structure of the northern segment of western Sichuan Basin and its controls upon petroleum.Based on fault-related fold theory,integrated with the latest surface geology,magnetic,seismic and drilling data,this paper well interpreted surface geology and seismic reflection profiles and analyzed the structural geometry characteristics and restored the tectonic evolution of typical structures and analyzed the deformation time and shortening rate of different structures and analyzed the petroleum geological conditions and their relationship on time and space.Based on the above research contents,this paper mainly draws the following understandings:The northern segment of western Sichuan Basin shows the characteristics of detached deformation,and the main detachment layers are the former Sinian,Cambrian,and Jialingjiang formation.The Beichuan fault slips off from the former Sinian,the depth of the detachment surface is about 4 seconds(about 9km).The buried fault is combined with the Jiangyou-Majiaoba fault at 3.5 seconds(about 7.8km),and slip off to a uniform detachment surface,the detachment surface depth is about 5s(about 11.2km).The source-reservoir-cap assemblage is divided into upper,middle,and lower reservoir forming assemblage the northern segment of western Sichuan Basin.The upper reservoir forming assemblage is mainly composed of sandstones of the 2nd and 4th member of the Xujiahe formation and conglomerate of the Baitianba formation of the Lower Jurassic.The middle reservoir forming assemblage is mainly composed of the dolomite and the limestone of the Maokou formation and the Qixia formation of the the Middle Permian and the dolomitization organic reef bank of the Changxing formation of the Upper Permian and the bioclastic limestone of the the third member of the Feixianguan formation.The lower reservoir forming assemblage is mainly composed of the bioclastic limestone of the Baota formation of the Middle Ordovician.The northern segment of western Sichuan Basin is divided into the expanded deformation belt of the Longmenshan front and the depression in the northwest of Sichuan Basin.The expanded deformation belt is greatly affected by the deformation of the Longmenshan,and deformed intensely,and the main structural styles are the imbricate structure,the duplex structure,and the inversion structure in the expanded deformation belt.The deformation of the depression in the northwest of Sichuan Basin is weak,and the main structural styles are broad anticlines and synclines,and there is no fault to surface.The northern segment of western Sichuan Basin is divided into four tectonic evolution stages.The expanded deformation belt was rifting stage before the Late Triassic and developed the normal fault.The pre-existing normal fault was reversal in the early Late Triassic.The structural wedge was formed in the Cambrian-Permian at the end of the Late Triassic.Backward imbricate structure and basement structure wedge was formed on the west side of the piedmont belt in the Cenozoic.By restoring the tectonic evolutionary stages of the typical structural belts in the northern segment of western Sichuan Basin,the total shortening rate is at 35-51% since the Late Triassic.The expanded deformation belt of the Longmenshan front,especially the west slope of the Zitong depression has a good prospect for petroleum exploration.