Discussion on Significant Geological Events during Carboniferous-Permian Transition and Main Controlling Factors of Shale Gas Enrichment in Eastern Margin of Ordos Basin
With the ongoing advancement of research on the coupling effect of unconventional oil and gas enrichment with multi-geological(biological)events,it has increasingly been confirmed that the deposition process of unconventional oil and gas"sweet spots"in black shale formations is frequently accompanied by volcanic eruptions,hydrothermal activities,ocean anoxia,climate change,biological prosperity,and extinctions,among various global or regional geological(biological)events.The Carboniferous-Permian transition in the eastern margin of the Ordos basin is endowed with multiple sets of marine-continental shale formations,which are significant targets for the exploration and development of shale gas in the country.In this paper it provides a review of the major geological events during the Carboniferous-Permian transition in order to discuss their potential impact on shale gas enrichment in the eastern margin of the Ordos basin.The Study shows that the changes in the glacial sea-level,paleoclimate during the Carboniferous-Permian transition have impacted on the surface primary productivity of organic matter and the bottom redox conditions in different degrees.Given the positive correlation between gas content and total organic carbon(TOC)content in the Carboniferous Jinci Section(Zhaoxian Shale)and Permian Shan23 Subsection shale formations in the eastern margin of the Ordos basin,it discusses the potential influence of paleoproductivity and paleoenvironment on the enrichment of marine-continental transition shale gas deposits:vegetation flourished organic matter,and with the relative rise in sea level,a hypoxic-anoxic water environment is easily formed,conducive to the deposition and enrichment of organic matter,thereby ultimately facilitating the formation of the"sweet spots"for shale gas in the region.
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