Analysis Of Hydrocarbon Accumulation Characteristics Of Middle Jurassic In Muli Depression,South Qilian Basin

The Muli depression is located between the South Qilian structural unit and the middle Qilian structural unit.In the Middle Jurassic,it was in a relatively stable stage,dominated by depression subsidence,and the formation generally deposited shale and coal bearing seam of Yaojie formation.In recent years,with the deepening of the investigation of natural gas hydrate,it is considered that the Middle Jurassic source rock in Muli depression has a high degree of thermal evolution,which is the main source rock of hydrate.However,due to the fact that no oil and gas reservoir has been drilled in Muli depression,the Research on conventional oil and gas has not been effectively broken through.The aim of this paper is to study the source rock,reservoir characteristics and reservoir forming period of the Middle Jurassic Jiaojie formation in Muli depression,.the following conclusions are obtained:(1)According to the evaluation and analysis of trace elements and organic matter in source rocks,it is considered that the sedimentary environment of Middle Jurassic source rocks is mainly continental sedimentary environment,and The water medium conditions are generally open oxidation brackish water environment;the organic matter type in the study area is generally considered to be humic organic matter,and the organic matter abundance of Middle Jurassic mudstone and carbonaceous mudstone is medium source rock,the coal seam is poor source rock,and the main body of source rock is mature Stage,a small number of high maturity stage.(2)From the analysis of geochemical parameters of source rocks,the source material of the rearranged hopane compounds in the source rocks is generally more closely related to the lower organisms(such as algae),and the increase of partial oxidation,brackish water sedimentary environment and maturity is conducive to the formation and enrichment of rearranged hopane,?? steranes and short chain sterane compounds.(3)Through thin section observation and analysis,it is considered that the reservoir space in the study area mainly includes intergranular pores and dissolution pores,followed by relatively developed fractures,which are conducive to the migration and accumulation of oil and gas,and the overall reservoir physical properties are unevenly distributed,which is relatively medium level;According to the petrography and composition characteristics,the fluid inclusions in the reservoir can be divided into five subtypes: yellow fluorescent hydrocarbon inclusions,blue fluorescent hydrocarbon inclusions and methane gas Inclusions,hydrocarbon bearing brine inclusions and brine inclusions.(4)The results of fluid inclusion temperature measurement show that there is no obvious discontinuity between 90? and 180?,and the distribution of the peak value of homogenization temperature in different periods is continuous,which indicates that the homogenization temperature distribution of the reservoir fluid inclusions in Yaojie formation in the study area experienced a period of oil and gas filling at 90-180?,and the hydrocarbon filling time is about 120-20 Ma,i.e.from Late Cretaceous to late Cretaceous Neogene,and oil and gas filling is a continuous process.