Three-dimensional Structural Analysis Of Dayi In Front Of Longmen Mountain

Dayi structure locate in the southwest of Sichuan basin and it belongs to the south part of the Longmenshan hidden belt.The study area is rich in structural phenomena,complex stratum deformation,Abundant oil and gas resources make it become the key local structure for oil and gas exploration in the front belt of Longmenshan.Previous studies mainly focused on the identification of fractures,fracture types,fracture development characteristics and natural gas accumulation conditions in the Dayi structural reservoir,but rarely analyzed the tectonic evolution of Dayi structure and most of them were two-dimensional seismic data.Based on the 3D seismic data,this paper analyzes the structural style and variation in Dayi area,and based on the theory of fault-related folds,the kinematics forward modelling of typical seismic sections is carried out by using the balanced cross section technology,so as to reproduce the movement process of Dayi anticline.Combined with 3D seismic data,3D structural geometry modeling was carried out by using structural modeling software to display the spatial distribution pattern of strata and faults in Dayi region.On the basis of 3D structural geometry model,structural restoration was carried out to restore the ancient morphology of Dayi region.The thickness of the four sections of Xujiahe formation(T3x4)and Baitlanba formation(J1b)of Dayi anticline are characterized by thin top and thick wings,and there is stratum penetrating phenomenon in deep Leikoupo formation and Jialingjiang formation.Based on the structural geometry analysis and structural restoration of the typical seismic reflection section,it is found that a concealed transition fault is developed in the deep of Dayi anticline.In construction,on the basis of the analysis of tectonic evolution and kinematics forward modeling,Dayi region since indo-chinese epoch mainly experienced three times of tectonic activities:the late indosinian process of low angle thrust nappe tectonic activities occurred in the Xujiahe formation(T3x4)in the upper sedimentary period,fault deformation plate of yanchang formation occurred;Himalayan ? act,blined fault activity again and it caused the differences of deformation between Jurassic and the underlying Triassic.Himalayan ? act,passed forward regional stress field of the longmenshan tectonic belt,Dayi area form high angle thrust fault,fault along the deep slip layer in Dayi upward thrust to the surface,the early blined fault is disconnected,accompanied by secondary faults,recoil fault is generated.The main faults in the study area are all developed with fault slope-fault slope structural geometry,and the two wings of the anticline are developed with high and steep thrust faults,which end at the bottom of T2l.From the southern section to the middle section of the anticline,a NE strike recoil fault developed in the front wing and an NNE strike recoil fault developed in the rear wing.The distance between the two groups of recoil faults increased with the widening of the anticline.In the northern section,the front and rear wing recoil faults gradually disappear,and a new recoil fault is formed at the rear wing syncline.In three dimensional space,the anticlinal wings are truncated by high and steep recoil faults,and the recoil faults of two groups with different strike trends are distributed as conjugate fault systems.The Dayi anticline was formed in the T3X4 period.During the yanshanian to xiashan period,the Dayi anticline continued its folding process inheritingly on the basis of the late indo-chinese anticline.