Late Reformation And Hydrocarbon Preservation Of Carboniferous-Permian System In The Juyanhai Depression Of Yin'E Basin

The Yin'e(Yingen-ejina)basin is located in the northwest of China,which is a typical reformed-superimposed basin.It is also one of the petroliferous basin with extremely low level of exploration in China.Since 2007,The China Geological Survey has found many sets of source rocks with large thickness,stable lateral distribution and middle-good organic abundance in Permo-Carboniferous in the Yin'e basin and its adjacent areas.In 2016,with the appearance of industrial oil flow in guaican 1 and yanhacan 1 well.It is confirmed that the Permo-Carboniferous in the basin has good petroleum geological conditions.However,the oil and gas exploration has not made a big breakthrough in Yin'e basin because of the complicated geological conditions and the strong reformation.It makes a great significance for oil and gas exploration in this area to reveals the structure of Carboniferous-Permian basin and determining the characteristics of the late reformation.This paper takes the Juyanhai depression as the study area,Study on the geological structure of Carboniferous-Permian basin and the distribution characteristic of Permo-Carboniferous residues and its late reformation based on seismic,drilling,logging data,combine with the characteristics of the outcrop in the adjacent areas.Then we divide the periods of late reformation,define its type,intensity and explore the effect of late reformation on hydrocarbon generation and accumulation.Through the interpretation of seismic profiles.We found that the carboniferous possible characteristic of rift sedimentary and widely distributing in the Juyanhai depression.Permian is relatively continuous,It mainly shows the characteristics of depressed-type sediments.The carboniferous-Permian basin is generally characterized by the tectonic evolution of rift basins.Triassic and Jurassic is missing in the basin.The Lower Cretaceous has obvious stretching effect and overlap,it shows obvious fault depression deposition and has a wide distribution.The Cenozoic strata spread gently with wide distribution and smaller thickness.Based on the geological characteristic in the area.It is considered that Juyanhai depression had undergone six periods of reformation since the Carboniferous-Permian.The first stage occurred from late Permian to middle Triassic,the carboniferous-Permian in theoutcrop develop a serious of tight,inverted and width folds influenced by the compression in the south-north direction,but the carboniferous-Permian deformation is not strong in the overlying area of Juyanhai depression.The second stage from late Triassic to middle Jurassic,the study area is generally uplifted,Permian has a large amount of denudation and there is a large different in the amount of denudation of each sag,locally deposited in the upper Triassic and middle lower Jurassic.The third stage is middle Jurassic to late Jurassic,the early Jurassic and previous strata are strongly deformed,while the Cretaceous are weakly deformed in the area influenced by the compression in the south-north direction.In additions,a series of nappe structures have developed in Beishan and Yin'e area,the strata are strong denuded,accompanied by certain magmatic activities.The fourth stage occurred in the early Cretaceous,Juyanhai depression reformed by superimposed overburden and depositing thick Lower Cretaceous strata.The fifth stage occurred from the end of early Cretaceous to Paleogene,study area suffer from structural reversal,Cretaceous is strongly denuded.The denudation recovery show that the amount of denudation is large in the boundary of sag and small in the subsidence center of sag.The sixth stage from Neogene to Quaternary,Juyanhai depression has entered the sedimentary stage.In general,the first and third stage are the main reformation period.The studies suggest that the uplift-erosion and superimposed overburden has an important influence on hydrocarbon generation of Carboniferous-Permian source rocks in the Juyanhai depression.we found that each sag has similar burial history characterized by pattern of “subsidence,uplift,re-subsidence,re-uplift”.It directly affects the hydrocarbon generation process in Juyanhai depression.In additions,the extensively developed magmatic activities in the indosinian and yanshanian also promoted the thermal evolution of source rocks in the study area.The anticlinal traps formed by compression deformation are important oil and reservoirs in Juyanhai depression.