Main Controlling Factors of Shale Oil and Gas Enrichment in Chang 7 Member,Southeastern Ordos Basin
In order to clarify the main controlling factors of shale oil and gas enrichment,the degree and mechanisms of shale oil and gas enrichment in the Chang 7 member in southeastern Ordos basin were analyzed using the data of drilling,logging,and core.Desorbed shale gas content is positively correlated with the total organic carbon content(TOC)of source rocks,the organic matter content controls the total content of shale oil and gas,and abundant pores are developed in organic matter,and shale oil and gas exist in both adsorbed and free states in these organic pores.The pore structure and porosity of the reservoir affect the content and occurrence state of shale oil and gas.Ad-sorbed oil and gas mainly exist in micropores,while free oil and gas in mesopores and macropores.The content of free gas in mesopores is higher than that in macropores,and the larger the porosity,the higher the absolute content of oil and gas in shale.The configuration be-tween sandstone interlayers and organic-rich shale controls the enrichment positions of shale oil and gas.Based on the distribution of silt-stone,fine sandstone and shale in the reservoir,the shale oil and gas in Chang 7 member can be classified into two types:near-source and in-source.The in-source shale oil and gas can be further divided into hydrocarbons from sandstone interbedded with shale,shale intercalated with sandstone,and pure shale.Sand bodies underlying the organic-rich shale and lenticular sand bodies exhibit the best potential of oil and gas,followed by sand bodies overlying the organic-rich shale or those tongue-shaped or finger-shaped ones in contact with shale.
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