Sulfate rocks and organic sulfur from sedimentary organic matter are conventionally assumed as the original sulfur sources for hydrogen sulfide （H2S） in oil and gas reservoirs. However, a few recent experiments prel...Sulfate rocks and organic sulfur from sedimentary organic matter are conventionally assumed as the original sulfur sources for hydrogen sulfide （H2S） in oil and gas reservoirs. However, a few recent experiments preliminarily indicate that the association of pyrite and hydrocarbons may also have implications for H2S generation, in which water effects and natural controls on the evolution of pyrite sulfur into OSCs and H2S have not been evaluated. In this study, laboratory experiments were conducted from 200 to 450°C to investigate chemical interactions between pyrite and hydrocarbons under hydrothermal conditions. Based on the experimental results, preliminary mechanism and geochemical implications were tentatively discussed. Results of the experiments showed that decomposition of pyrite produced H2S and thiophenes at as low as 330°C in the presence of water and n-pentane. High concentrations of H2S were generated above 450°C under closed pyrolysis conditions no matter whether there is water in the designed experiments. However, much more organic sulfur compounds （OSCs） were formed in the hydrous pyrolysis than in anhydrous pyrolysis. Generally, most of sulfur liberated from pyrite at elevated temperatures was converted to H2S. Water was beneficial to breakdown of pyrite and to decomposition of alkanes into olefins but not essential to formation of large amounts of H2S, given the main hydrogen source derived from hydrocarbons. In addition, cracking of pyrite in the presence of 1-octene under hydrous conditions was found to proceed at 200°C, producing thiols and alkyl sulfides. Unsaturated hydrocarbons would be more reactive intermediates involved in the breakdown of pyrite than alkanes. The geochemistry of OSCs is actually controlled by various geochemical factors such as thermal maturity and the carbon chain length of the alkanes. This study indicates that the scale of H2S gas generated in deep buried carbonate reservoirs via interactions between pyrite and natural gas should be much smaller than that of thermochemical sulfate reduction （TSR） due to the scarcity of pyrite in carbonate reservoirs and the limited amount of long-chained hydrocarbons in natural gas. Nevertheless, in some cases, OSCs and/or low contents of H2S found in deep buried reservoirs may be associated with the deposited pyrite-bearing rock and organic matters （hydrocarbons）, which still needs further investigation.展开更多
H2S-rich gas in carbonate reservoirs is usually attributed to thermochemical sulfate reduction (TSR). In this paper, thermal simulation experiments on the reaction system of CH4-MgSO4-H2O were carried out using autocl...H2S-rich gas in carbonate reservoirs is usually attributed to thermochemical sulfate reduction (TSR). In this paper, thermal simulation experiments on the reaction system of CH4-MgSO4-H2O were carried out using autoclave at 425℃―525℃. The threshold temperature for initiating TSR is much lower than our previous studies (550 ℃ ). Properties of the reaction products were analyzed by microcoulometry, gas-chromatography (GC), Fourier transform-infrared spectrometry (FT-IR) and X-ray diffraction (XRD) methods. Thermodynamics and reaction kinetics of TSR processes were investigated on the basis of the experimental data. The results show that thermochemical reduction of magnesium sulfate with methane can proceed spontaneously to produce magnesium oxide, hydrogen sulfur, and carbon diox-ide as the main products, and high temperature is thermodynamically favorable to the reaction. Ac-cording to the reaction model, the calculated activation energy of TSR is 101.894 kJ/mol, which is lower than that by most previous studies. Mg2+ may have played a role of catalytic action in the process of TSR. The elementary steps of TSR and reaction mechanism were discussed tentatively. The study can provide important information on the explanation of geochemical depth limit for natural gas and on the generation of high H2S gas in deep carbonates reservoirs.展开更多
基金the National Natural Science Foundations of China(No.41472095 and No.40902034)the Foundation of State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing(No.PRP/open-1508)PetroChina Innovation Foundation(No.2012D-5006-0104)
文摘Sulfate rocks and organic sulfur from sedimentary organic matter are conventionally assumed as the original sulfur sources for hydrogen sulfide （H2S） in oil and gas reservoirs. However, a few recent experiments preliminarily indicate that the association of pyrite and hydrocarbons may also have implications for H2S generation, in which water effects and natural controls on the evolution of pyrite sulfur into OSCs and H2S have not been evaluated. In this study, laboratory experiments were conducted from 200 to 450°C to investigate chemical interactions between pyrite and hydrocarbons under hydrothermal conditions. Based on the experimental results, preliminary mechanism and geochemical implications were tentatively discussed. Results of the experiments showed that decomposition of pyrite produced H2S and thiophenes at as low as 330°C in the presence of water and n-pentane. High concentrations of H2S were generated above 450°C under closed pyrolysis conditions no matter whether there is water in the designed experiments. However, much more organic sulfur compounds （OSCs） were formed in the hydrous pyrolysis than in anhydrous pyrolysis. Generally, most of sulfur liberated from pyrite at elevated temperatures was converted to H2S. Water was beneficial to breakdown of pyrite and to decomposition of alkanes into olefins but not essential to formation of large amounts of H2S, given the main hydrogen source derived from hydrocarbons. In addition, cracking of pyrite in the presence of 1-octene under hydrous conditions was found to proceed at 200°C, producing thiols and alkyl sulfides. Unsaturated hydrocarbons would be more reactive intermediates involved in the breakdown of pyrite than alkanes. The geochemistry of OSCs is actually controlled by various geochemical factors such as thermal maturity and the carbon chain length of the alkanes. This study indicates that the scale of H2S gas generated in deep buried carbonate reservoirs via interactions between pyrite and natural gas should be much smaller than that of thermochemical sulfate reduction （TSR） due to the scarcity of pyrite in carbonate reservoirs and the limited amount of long-chained hydrocarbons in natural gas. Nevertheless, in some cases, OSCs and/or low contents of H2S found in deep buried reservoirs may be associated with the deposited pyrite-bearing rock and organic matters （hydrocarbons）, which still needs further investigation.
基金the National Natural Science Foundation of China (Grant Nos. 40472076 and 40702019)Item of Cooperative Fund of Beijing Educational Committee (Grant No. XK114140479)
文摘H2S-rich gas in carbonate reservoirs is usually attributed to thermochemical sulfate reduction (TSR). In this paper, thermal simulation experiments on the reaction system of CH4-MgSO4-H2O were carried out using autoclave at 425℃―525℃. The threshold temperature for initiating TSR is much lower than our previous studies (550 ℃ ). Properties of the reaction products were analyzed by microcoulometry, gas-chromatography (GC), Fourier transform-infrared spectrometry (FT-IR) and X-ray diffraction (XRD) methods. Thermodynamics and reaction kinetics of TSR processes were investigated on the basis of the experimental data. The results show that thermochemical reduction of magnesium sulfate with methane can proceed spontaneously to produce magnesium oxide, hydrogen sulfur, and carbon diox-ide as the main products, and high temperature is thermodynamically favorable to the reaction. Ac-cording to the reaction model, the calculated activation energy of TSR is 101.894 kJ/mol, which is lower than that by most previous studies. Mg2+ may have played a role of catalytic action in the process of TSR. The elementary steps of TSR and reaction mechanism were discussed tentatively. The study can provide important information on the explanation of geochemical depth limit for natural gas and on the generation of high H2S gas in deep carbonates reservoirs.
