Abstract: High H₂S-bearing natural gas is usually referred to the thermochemical sulfate reduction (TSR). The thermosimulation experimental study of reaction between natural gas and magnesium sulfate is made in unsaturated water vapor of HTHP. Its possible reaction pathways are determined, and the geochemical characteristics of natural gas in TSR are presented. The possible geologic factors influencing the process of TSR are investigated. The results show that MgO, H₂S, CO₂ and coke are the main products of such a reaction. With the simulated temperature increasing, the degree of conversion of TSR is increasing, and the total hydrocarbon content in natural gas is decreasing, showing CH₄ gas ratio is gradually increasing, accompanied by the decreasing of contents of C₂H₆ and C₃H₈ The apparent positive correlation between the gas dryness and CO₂ content, the low positive correlation between gas dryness and H₂S content, and CO₂ and H₂S content indicate there are different control factors in different stages of TSR. The study shows that the origin and evolution of high H₂S-bearing natural gas are probably controlled by temperature, carbochain length, metallic ion, water content and H₂S concentration in geologic settings.

Key words: sulfate, thermosimulation, natural gas, HS, geochemistry, experiment, test