Fracture Characteristics And Construal Styles In Southern Sichuan Area

The Southern Sichuan area is a favorable oil-gas-bearing area of the middle Yangzi,which is highly modified in the later stage and complex in structure,which restricts oil and gas exploration work in this area.Based on geological,drilling,logging,and 2D seismic data,we fully investigated the previous literature on fault characteristics and structural styles in the area,combined with the theoretical methods and technical knowledge of petroleum tectonic analysis,through explaining the distribution characteristics of fault planes,the classification of fault grades,the division of fault stages,the plane combination patterns of faults,the structural styles of faults,the formation mechanism of typical structural belts and the production of plane profiles,we can focus on the study of fault development characteristics and the regular pattern of tectonic evolution in southern Sichuan area.The southern Sichuan area has a complex fault system,characterized by "basic fault control,obvious strike-slip,double-layer slip".The distribution of faults on the plane is controlled by the basement faults,which mainly develops near north-east,near north-west and east-west faults,all the faults are divided into five different fault development zones;According to the scale of the fault(break the horizons,the size of the gap and the vertical change,the extension length)and the effect on the structure and sedimentation,the fault is divided into three levels,including the first-level controlled basin fault,the second-level controlled area fault and the third-level adjusted fault.The main stages of fault development in the study area were studied,it can be divided into the Caledonian movement period,the late Yanshan movement period,the early Himalayan movement period and the late Himalayan movement period.The structural styles in southern Sichuan are rich in development,with a variety of types distributed on the plane and plane combination patterns with different characteristics.The types are oblique fault combinations,near-parallel fault types,en echelon fault combinations,and broom fault combinations;The vertical distributions has obvious zoning features,which can be divided into upper structural belt,middle structural belt and lower structural belt.Includin g nearly 10 types of construction styles: single-punch type,recoil type(positive and negative "Y" characters),hedging type,back-punching type,half-flower shape,positive flower shape(wide and narrow),upright sliding and reverse typeIn the typical structural belt developed in southern Sichuan,the structural styles developed in each structural belt are obviously different and the structural styles developed in different parts of the structural belt are also different,the genetic mechanism is also obviously different.The tectonic evolution of the southern Sichuan area shows that this area was formed at the base of the Sinian,the uplift prototype appeared in the early Caledonian movement,and the early upright strike-slip faults were formed;before the Middle Triassic,it maintained a stable structural form and developed a series of small faults,Since the late Triassic,with the intense squeezing movement of the Yanshan-Himalayan movement,the faults formed in the early period reversed,the strata were obviously uplifted,and various structural belts and structural styles were basically formed,forming the current structural pattern.