Desorption analysis of shale and its geochemical characteristics: A case study of the Chang 7 member shale in thecentral south Ordos basin
FAN Bojiang
WANG Xiangzeng
WU Xiaobin
Abstract：The Chang 7 member shale containing abundant gas is highly developed in the central south Ordos basin.Based on chemical and isotopic composition analyses,the content variations of gas components and their isotopic compositions during desorption were obtained to study the gas generation,migration and accumulation process.It is demonstrated that in the course of desorption,the content of methane gradually decreases while that of heavy hydrocarbon increases;the gas drying coefficient declines slowly;the methane carbon isotope has no obvious change.The results show that the carbon dioxide volume fraction,nitrogen volume fraction,gas drying coefficient and methane carbon isotope ranges from 0.53％ to 5.15％,1.24％ to 4.64 ％,0.43 to 0.82,and-51.6‰ to-33.9‰ respectively.Based on desorption characteristics,Chang 7 member shale gas is oil-prone pyrolysis gas generated from humic matter,and has the strongest absorption for carbon dioxide,followed by methane,and then nitrogen.Gases with small molecules migrate faster and easier than those composed of larger molecules.Shale gases in three kinds of existing phase including dissolved gas,absorbed gas and free gas keeps on transforming and adjusting throughout the geological history.The average shale gas content in Chang 7 member shale is 1.90 m3/t.
Keywords：Ordosshale gasgas chemistrycarbon isotopehosting phasesgas adsorbing
Publication Date：2017-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：10( 554-562,577 )