Analysis On The Difference Of Hydrocarbon Accumulation Of The Ordovician In Tahe Area And Its Peripheral Area,Tarim Basin

The Tarim Basin is the largest petroliferous sedimentary basin in China and is also a typical multi-cycle superimposed complex basin.Tahe area is located in the northern Tarim Basin,the main Ordovician reservoir is one of the most unique large carbonate reservoirs in China.Affected by multi-stage tectonic movement,there are obvious differences in hydrocarbon accumulation between Tahe area and its peripheral area.This paper takes the Tahe area and its peripheral area as the research object,with a focus on the Ordovician Yingshan Formation(O_1-2y)and Yijianfang Formation（O₂yj）as the research horizon.Theoretical guidance is provided by hydrocarbon accumulation dynamics.Through the comparison of source rocks in the study area,the basic properties and types of oil and gas in different tectonic units in the region are analyzed.By using the fluid inclusion system analysis method,the main types of diagenesis and the sequences of diagenesis evolution in the region are defined from a microscopic point of view.On the basis of the diagenesis sequence,the hydrocarbon accumulation period and time of different blocks are determined by combining the homogenization temperature of the coeval aqueous inclusions and hydrocarbon inclusions.Based on the analysis of source rock evolution,tectonic evolution,and reservoir characteristics,the regional differential hydrocarbon accumulation process and accumulation model have been established.Finally,based on the comparison of hydrocarbon accumulation differences in the study area,the main factors controlling these differences are discussed in combination with various conditions.The results show that:（1）There are obvious differences in the distribution of oil and gas basic properties,as well as oil and gas reservoir types,among different blocks in the study area.From south to north,the density of crude oil gradually increases,and the oil quality gradually becomes heavier.From northwest to southeast,the drying coefficient and maturity of natural gas gradually increase.Oil and gas reservoir types transition gradually from south to north,starting with dry（wet）gas reservoirs,followed by condensate gas reservoirs,volatile reservoirs,light oil reservoirs,medium oil reservoirs,and finally heavy oil reservoirs.This transition occurs through an annular distribution.（2）There are some differences in the fluorescence color and maturity of reservoir hydrocarbon inclusions among different blocks in the study area.The fluorescence color of oil inclusions in well YQ8 in the Yuqidong area is mainly blue,indicating high maturity.The fluorescence colors of oil inclusions in well YQX1 in Yuqiixi area are blue,yellow,and orange,indicating high and low maturity.The fluorescence color of oil inclusions in well TS3 in the deep Tahe area is mainly blue,indicating high maturity.The fluorescence color of oil inclusions in well TP18 in Tuoputai area is mainly yellow-green,indicating low maturity.The fluorescence colors of oil inclusions in well YJ1X in the Yuejin area are blue and yellow-green,indicating high and medium-low maturity.（3）The Ordovician oil and gas in the study area have the characteristics of multi-stage accumulation and mixed filling.There are significant differences in the hydrocarbon filling period and filling time among different blocks.Among them,there are three stages of hydrocarbon charging in the Yingshan Formation of well YQ8 in the Yuqidong area.The first stage occurred in the middle Hercynian period（338～305Ma）,the second stage occurred in the middle Yanshanian（130～111 Ma）,and the third stage occurred in the late Himalayan（22～16Ma）.There is one stage of hydrocarbon charging in the Yingshan Formation of well YQX1 in Yuqixi area,mainly in the middle-late Himalayan（31～6Ma）.There are three stages of hydrocarbon charging in the Yingshan Formation of the well TS3 in deep Tahe area.The first stage occurred in the late Caledonian（458～454Ma）,the second stage occurred in the early Yanshanian（191～173Ma）,and the third stage occurred in the late Himalayan（22～18Ma）.There are three stages of hydrocarbon charging in the Yijianfang Formation of well TP18 in Tuoputai area.The first stage occurred in the Indosinian（233～210Ma）,the second stage occurred in the middle Yanshanian（138～123Ma）,and the third stage occurred in the late Himalayan（21～13Ma）.There are two stages of hydrocarbon charging in the Yijianfang Formation of well YJ1X in Yuejin area.The first stage occurred in the middle Yanshanian（134～117Ma）,and the second stage occurred in the late Himalayan（22～12Ma）.（4）The difference in Ordovician hydrocarbon accumulation in the study area is affected by various factors,such as source rock development and tectonic evolution.The difference in hydrocarbon generation evolution controls the difference in hydrocarbon accumulation periods and accumulation times.Additionally,the difference in tectonic evolution controls the types and properties of regional oil and gas reservoirs.Among these factors,multi-stage tectonic activities are the fundamental reason for controlling the complex distribution of oil and gas.