Study On The Relationship Between Tectonic Evolution And Hydrocarbon Accumulation In Feixianguan Formation In Northeast

The Northeastern Sichuan area is located at the intersection of Dabashan frontal arcuate fold belt and Northeast Sichuan arcuate fold belt, and its tectonic position lies in the margin of the Yangtze plate. It has experienced a number of complex tectonic movements, and then a large number of thrust fault and typical compressional structures were formed, so currently geological structural features are complicated and divers. With the guide of seismic exploration, structural geology, and petroleum geology and in the combination of geology, core analyses, seismic data and a variety of other testing data in the study, the main structural features, tectonic evolution and accumulation of Feixianguan formation member were investigated and evaluated, and then some following conclusions have been made:(1)Tectonic movements such as, Caledonian-Hercynian, Indo-Chinese, Yanshanian and Himalayan, taking place within the study area, have affected the formation of structure a lot., and current tectonic pattern is caused by a variety of superimposed transformation.(2)The study area with diverse structure is located at the intersection of two fold belts. Two different tectonic systems were developed in the direction of north-west and north-east within the area. In the North-West trending structure, the structure of surface is consistent with local structures underground, and there are just some differences between the magnitude and intensity structure. However, the poor agreement between the structure of surface and subsurface structure is presented and performance of abdominal structures is complicated.(3)Tectonic stress field in the study area is mainly compressional stress field, where the folds, fault-bend folds, fault-propagation folds, imbricate thrust faults were developed.(4)The region of Northeast Sichuan experienced a multi-phase structure of tectonic movements, now the north-east and north-west trending structures were achieved by a multi-stage evolution. The study illustrates that the north-east trending structure has come into being at Indo-Chinese epoch, and eventually finalized in the early Himalayan period; the North-West trending structure began to form in the late Yanshanian period, finalized in late Himalayan period.(5)The accumulation of hydrocarbon is quite relative with tectonic evolution and tectonic pattern. The reservoir forming condition at north-east trending structure is significantly better than at the north-west trending structure in northeastern region of Sichuan. From the perspective of structural history, the north-east trending structure has come into being at Indo-Chinese epoch, and has been formed in the mid Yanshanian period, and then the timing of tectonic development is in agreement with hydrocarbon generation peak in the region. Moreover, it is shown that tectonic axis and fault strike is consistent with the direction of main hydrocarbon migration, which indicates good conditions to accumulate the oil and gas. However, the NW-trending structures formed in the late Yanshanian period didn’t match with the peak period of hydrocarbon, so missed the best time for hydrocarbon accumulation. The results of oil and gas exploration have also shown that oil and gas resources in the north-east trending structures (Luojiazhai structure) are much better in the north-west trending structures (jinzhupin structure).