Organic Geochemistry And Reservoir Characteristics Research Of The Middle Ordovician Yanxi Formation Shale,Central Hunan

Shale gas is a kind of very important unconventional natural gas resources.Its exploration and development work is related to China's energy structure even affects all aspects of the economic society.The Yanxi formation shale of Middle Ordovician Epoch in central Hunan is widely distributed and has a large deposition thickness.Previous researchers have done little research on it.In view of this,this paper takes it as the research object.Based on sedimentology and geochemistry,this paper analyzes its geological sedimentary environment,organic geochemistry and reservoir performance.Finally,select the favorable area.Based on the investigation to the field profiles and summarizing previous research results we have obtained stratigraphic development,structural features,sedimentary facies,sedimentary facies and sedimentary evolution patterns.The Yanxi formation can be divided into five sections and the third and fourth sections are better.The results of organic geochemistry research show that organic carbon content is generally high,the highest is 8.17%,the average is 2.12%,belongs to high quality source rock category.The type of organic matter is?.The equivalent vitrinite reflectance is 1.83%³.77%,the average is 3.15%,the degree of evolution is at a high maturity stage.The results of molecular biomarker analysis show that n-alkanes are bimodal.The phytane advantage is obvious indicating strong reduction of Marine sedimentary environment.Terpene abundance sequence is pentacyclic triterpene>tricyclic terpene>tetracyclic terpane.The ratio of gamma-paraffin divided by C₃₀0 hopane was generally greater than 0.3,indicating that its sedimentary mother was dominated by plankton and Marine autotrophic bacteria.It contains some algae.The regular sterane C₂₇>C₂₉>C₂₈8 indicates that its parent source is mainly derived from shallow Marine life.In all samples,progesterone,progesterone,sterane and 4-methylsterane were detected,indicating that they may have undergone microbial degradation.Test it through the experiment of shale mineral composition,porosity,permeability and microscopic pore structure,it is concluded that the brittle shale mineral content is rich,clay mineral content is moderate.It is advantageous to the fracturing operation and has excellent conditions for shale gas reservoir physical properties.Based on the above studies,it is concluded that the shale gas in the region has good organic material foundation,good reservoir performance and later development physical condition.Through the analysis of the selection of shale gas reservoir main control factors and the evaluation system of the discussion,finally think Lingling blocks and Shuangpai block areas are favorable for shale gas reservoir.In the later stage,it is recommended to give preference.