Abstract: We studied the microscopic pore structure of the organic-rich Longmaxi Formation shale in Sichuan Basin through Argon Ion milling-Field Emission Scanning Electron Microscopy characterization with different SEM parameters,and investigated the effect of electron microscopic parameter variation on the quantitative evaluation of the microscopic pores of shale based on the pore data extracted by the "optimal threshold method" within the same field of view.The results show that the probe current and accelerating voltage among these electron microscopic parameters,have greater influence on the accuracy of quantitative pore data extraction.When the beam exceeds 170PA,the higher the voltage is adjusted to,the smaller the large pore area is extracted.When the voltage exceeds 15KV,the beam current is lower,and the pores extracted are relatively more complete; while as the beam current is lower than 86PA,the longer the scanning time is,the more completely the pore is extracted,but as it exceeds 86PA,the scanning time has little effect on pore extraction.In addition,luminance and contrast values of excessive lowness or highness are detrimental to pore extraction,and the pore extraction comes to the most complete when their values are 47.5 and 85 respectively.In conclusion,the parameters of electron microscopy have a remarkable influence on the extraction of organic pores,and the proper selection of parameters can significantly improve the accuracy of quantitative data extraction for shale micropores,in a bid to obtain more realistic data of shale micropore structure.

Key words: Field Emission Scanning Electron Microscopy, SEM parameter, accelerating voltage, electron beam current, micropore extraction, shale, Longmaxi Formation, Sichuan Basin