Characteristics Of Soluble Organic Matter In Shale And Its Effect On Methane Adsorption Behavior

Methane is predominantly adsorbed in shale in an adsorbed state,and the ability of methane adsorption is often used to indirectly evaluate shale gas resources.Organic matter in shale is a key factor in the control of methane adsorption.The influence of soluble organic matter on methane adsorption in shale is studied,which has certain reference significance for hydrocarbon-generating and hydrocarbon expulsion theory of organic matter.In this paper,shale is taken as the research object,and the samples are extracted to the stepwise extraction in the order of n-hexane,dichloromethane and tetrahydrofuran.Using gas chromatography-mass spectrometry test?GC/MS?,field emission scanning electron microscopy?FE-SEM?,low temperature nitrogen adsorption test and isothermal adsorption experiment and other analysis methods,analyzed the soluble organic components at various levels and their effects on the adsorption behavior of methane.The results show that:?1?Dissolved products of?-level extraction are normal alkane hydrocarbons of fatty hydrocarbons(C₁₃^C₂₅ n-alkanes).?-level extraction leaching?-level extraction of aliphatic hydrocarbons,while the dissolution of aromatics and some non-hydrocarbon components.aliphatic hydrocarbons are mainly C₂₃^C₂₅ n-alkanes and branched-chain alkanes,aromatic hydrocarbons are mainly monocyclic or bicyclic naphthalene Department-based;?-level extraction further dissolves soluble hetero atomic compounds,including hydroxyl group?-OH?,ether group?-O-?,carboxyl group?-COOH?,ester group?-COO-?,carbon carbon double bond?=C=C=?and aromatic ring(-C₆H₅)etc..?2?Under the electron microscope,irregular marginal pores were observed in the raffinate.Dissolution of soluble organic matter has a certain "hole enlarging" and "pore increasing" effect on shale pore.After extraction,volume and average pore diameter of BJH are increased for shale,while BET specific surface area no obvious change.Compared with original sample,the content of mesoporous pore volume and specific surface area of?-level extraction was decreased,and the macropore one was increased.In the range of mesopore,With the increase of extraction stages,The aperture of 2¹0nm decreases,the aperture of 10³0nm changes less,and the aperture of 30⁵0nm increases obviously.The complexity of pores was decreased and surface roughness of pores was too.?3?The methane adsorption curves of raw-samples and extracted-samples are basically "inverted" adsorption,and the maximum adsorptive capacity of extracted-samples is larger than that of residue at all levels.?4?With the increase of solvent polarity,the methane adsorption decreases first and then increases,which is related to the dissolution of soluble organic matter and the change of pore structure.Hydrocarbons in soluble organic matter have a certain role in promoting the adsorption of methane,and heteroatom organic compounds with strong molecular polarity are not conducive to the adsorption of methane.The dissolution of soluble organic matter changed the original pore structure and had a certain influence on the adsorption capacity of methane.The increase in the volume of micropores and mesopores increases the maximum methane adsorption,whereas the increase in pore volume of macropores is not conducive to the maximum methane adsorption.