Influence mechanism of microwave irradiation heating on hydrocarbon generation and chemical structure of shale organic matter:a comparative study with conventional heating
In situ heating technology is considered as the most effective means to solve problems for the development of medium to low maturity shale oil.Compared with conventional heating,microwave irradiation heating has the advantages of high heating efficiency and excellent oil quality,and thus has attracted much attention.This study aims to further clarify the effect of microwave irradiation heating on hydrocarbon generation and chemical structure of organic matter in shale,as well as the differences between microwave ir-radiation and conventional heating.Specifically,based on the independently developed microwave pyrolysis instrument of MPS-1 type,in combination with Rock-Eval pyrolysis,total organic carbon,X-ray diffraction,Fourier transform infrared spectroscopy,and hydrocarbon generation kinetics,microwave irradiation heating was carried out on organic rich shale in Member 1 of Qingshankou Formation in Songliao Basin.Meanwhile,conventional heating was performed for comparison.This reveals the hydrocarbon genera-tion yield,product characteristics,and chemical structure evolution characteristics of shale under the two heating conditions.The re-sults show that microwave radiation heating can effectively reduce the activation energy of the reaction and promote a series of chemi-cal reactions during the pyrolysis and hydrocarbon generation process of kerogen,such as methyl side chain and C-C bond cleavage,and thiol group cracking,allowing the shale organic matter to decompose and produce long-chain alkanes and small molecule hydro-carbon compounds earlier.Compared to conventional heating,shale samples heated by microwave irradiation at the same temperature can generate more oil and gas,with higher heating efficiency.The pyrolysis hydrocarbon generation process of shale organic matter is more complete,and the hydrocarbon generation conversion rate is higher.Kerogen has lower aliphatic content and a greater degree of aromatization.Microwave irradiation heating promotes the breaking of aliphatic chain bonds,removal of carboxylic acid structure,and decomposition of long-chain alkanes in kerogens,leading to the generation of more long-chain alkanes in the stage of kerogen cracking,and more small molecule alkanes,especially methane,during the cracking of heavy components.In addition,microwave ir-radiation heating can promote the dehydrogenation of alkanes and the decomposition of thiol groups,leading to the production of more olefin gases and H2S in shale gas components.
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