关键词: 烃类, 蚀变作用, 硫酸盐热化学还原反应, 硫化氢, 碳同位素, 四川盆地, 渤海湾盆地

Abstract: The thermochemical sulfate reduction (TSR) refers to the process of sulfate reaction with hydrocarbons,which is the important mechanism for generating natural gas with high content of H₂S and CO₂.Because TSR is the reaction between hydrocarbons and sulfate under the driving of thermal force,the composition of hydrocarbons gas and the carbon isotope maybe vary correspondingly along with the oxidation and alteration of hydrocarbons.The composition of hydrocarbons gas and the carbon isotope of gas reservoirs with high content of H₂S in the Feixianguan Formation of the lower Triassic (T₁f) in the northeastern area of Sichuan Basin and the formation of Paleozoic Erathem in Bohai Bay Basin were studied.It is proved that the heavy hydrocarbons preferentially participated in the reactions of TSR and led to the drying coefficient of natural gas to increase during the process of hydrocarbon depleted by TSR.In the process of TSR,the bond of ¹²C-¹²C ruptured preferentially and more ¹²C participated in the reactions of TSR,while more ¹³C remained in the residual hydrocarbons,which causes the abundant ¹³C distributed in the residual hydrocarbons.Therefore,the drying coefficients of hydrocarbons gas increased after the alteration of TSR.Meanwhile,the increased values of carbon isotope of hydrocarbons gas are from 2.0‰ to 4.0‰ . Also,the increasing extent of carbon isotope for heavy hydrocarbons is greater than that of methane.

Key words: hydrocarbons, alteration, thermochemical sulfate reduction, hydrogen sulfide, carbon isotope, Sichuan Basin, Bohai Bay Basin