Hydrocarbon generation from sedimentary organic matter(SOM)with an original net C oxidation state(OS,-1–-2)is a disproportionation reaction involving the transfer of internal(“organic”)hydrogen and producing oxidiz...Hydrocarbon generation from sedimentary organic matter(SOM)with an original net C oxidation state(OS,-1–-2)is a disproportionation reaction involving the transfer of internal(“organic”)hydrogen and producing oxidized C(up to OS=+4)and reduced C(down to OS=-4).The contribution of extrinsic(“inorganic”)hydrogen could lead to an increase of hydrocarbon yields,but mechanisms and potential sources are still unclear,although it is supported by some experimental evidence.In this study,we have analyzed quantitatively the effect of increasing hydrogen fugacity on the hydrocarbon generation behavior of the Cambro-Ordovician Alum shale at 350℃and 40 MPa.Hydrogen fugacity in the experimental system was controlled by the magnetite-hematite(MH)buffer.The experimental data confirm that a more reducing environment will increase overall hydrocarbon yields and depress CO_(2) yields.The elevated hydrogen fugacity was found to correlate with an increase in δ^(13)C isotopic composition of methane and a decrease of δ^(13)C values in CO_(2),ethane and propane.This demonstrates that elevated hydrogen fugacity constrained by water-rock reaction in sedimentary basins can enhance hydrocarbon generation by“hydrocracking”.This mechanism of hydrocarbon generation by organic-inorganic interactions might be ubiquitous in the deeper sections of sedimentary basins(approximately 4–10 km).Thus,it will extend the connotation of the current theory on petroleum generation.The level of hydrogen fugacity,constrained by water-rock reactions,increases with depth and may thus activate over-maturity sedimentary organic matter to produce more hydrocarbons.The end of hydrocarbon generation will thus move to a greater depth than predicted by the traditional theory.It will be correlated to the capacity of the buffer system,which should,in consequence,be taken into account in petroleum exploration,similar to the hydrogen index(HI)of SOM.This extension of the fundamental theory will help to enlarge the area of petroleum exploration to ultra-deep strata in sedimentary basins.展开更多
基金financially supported by the National Key Research and Development Program of China(Grant No.2017YFC0603102)the Foundation of State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum(Beijing)(Grant No.PRP/indep-3-1715)。
文摘Hydrocarbon generation from sedimentary organic matter(SOM)with an original net C oxidation state(OS,-1–-2)is a disproportionation reaction involving the transfer of internal(“organic”)hydrogen and producing oxidized C(up to OS=+4)and reduced C(down to OS=-4).The contribution of extrinsic(“inorganic”)hydrogen could lead to an increase of hydrocarbon yields,but mechanisms and potential sources are still unclear,although it is supported by some experimental evidence.In this study,we have analyzed quantitatively the effect of increasing hydrogen fugacity on the hydrocarbon generation behavior of the Cambro-Ordovician Alum shale at 350℃and 40 MPa.Hydrogen fugacity in the experimental system was controlled by the magnetite-hematite(MH)buffer.The experimental data confirm that a more reducing environment will increase overall hydrocarbon yields and depress CO_(2) yields.The elevated hydrogen fugacity was found to correlate with an increase in δ^(13)C isotopic composition of methane and a decrease of δ^(13)C values in CO_(2),ethane and propane.This demonstrates that elevated hydrogen fugacity constrained by water-rock reaction in sedimentary basins can enhance hydrocarbon generation by“hydrocracking”.This mechanism of hydrocarbon generation by organic-inorganic interactions might be ubiquitous in the deeper sections of sedimentary basins(approximately 4–10 km).Thus,it will extend the connotation of the current theory on petroleum generation.The level of hydrogen fugacity,constrained by water-rock reactions,increases with depth and may thus activate over-maturity sedimentary organic matter to produce more hydrocarbons.The end of hydrocarbon generation will thus move to a greater depth than predicted by the traditional theory.It will be correlated to the capacity of the buffer system,which should,in consequence,be taken into account in petroleum exploration,similar to the hydrogen index(HI)of SOM.This extension of the fundamental theory will help to enlarge the area of petroleum exploration to ultra-deep strata in sedimentary basins.
