The Accumulation Process Of Upper Paleozoic Natural Gas In Zhen-jing Area In The South Of The Ordos Basin

The exploration potential of upper Paleozoic natural gas in Zhen-jing area of the Southern Ordos Basin is quite good,while the exploration level remains relatively low.In the present study,by integrated utilization of various geological data in the research area,the burial history,geothermal history,hydrocarbon generation and expulsion history as well as the history of oil and gas accumulation are well investigated.Besides,with the help of homogenization temperature analysis of fluid inclusions,the charging time of upper Paleozoic natural gas in the study area is determined,and the accumulation history is reconstructed.Firstly,the local stratigraphy and well-correlation were conducted,and the distribution characteristics of the sand body in different sedimentary facies were studied;Meanwhile,the burial history of the target strata was analyzed,which can be divided into three stages.On the basis,the differences of the burial evolution process caused by structural uplift between the eastern and western areas and its impact on the natural gas accumulation process were analyzed.Based on the tectonic evolution analysis,the quality of primary Carboniferous-Permian sources rocks in the study area was analyzed.By analyzing paleo-temperature and vitrinite reflectance,it was determined that the source rocks in the study area are now in deep pyrometric gas-gemous stage.Secondly,by utilizing the Basin Mod software,one-dimensional and two-dimensional simulation of the natural gas accumulation were carried out,which revealed that natural gas reservoirs in Zhen-jing area are formed by one-episode of hydrocarbon charge,and the period of hydrocarbon generation is consistent with the main hydrocarbon generation period of the basin,starts from 230 Ma.During the subsequent 140-100 Ma,it experienced an adjustment period.Compared to the one-episodic accumulation in the western area,the two-episodic accumulation in the eastern area is caused by the structural uplift.At the same time,the fluid inclusion is utilized to determine the accumulation periods,which is consistent with the tectonic evolution.Natural gas in Zhen-jing area is mainly accumulated in Shanxi Formation and Shihezi Formation.