Search

Carbazole compounds are widely used in determining the direction of petroleum migration, but the effect of thermal maturity on carbazoles is still ambiguity. In this paper, using compaction pyrolysis simulation experiments, artificial mature samples with vitrinite reflectance (Ro) range from 0.38 to 3.0% were acquired. And the content and composition change characteristics of carbazole compounds were analyzed in coal source rocks. The experimental results showed that thermal maturity controls the generation of a large amount of carbazole compounds in coal rocks. Compared with the low mature stage, the content of carbazole compounds was about 10–100 times higher in the mature stage. With the increasing maturity, in the coal sample, the content of carbazole compounds showed a trend of first increasing and then decreasing. In derivatives of carbazole, the corresponding maturity for the maximum generation of ethylcarbazole (EC), dimethylcarbazole (DMCA), methylcarbazole (MCA), carbazole (CA) and benzocarbazole (BCA) performed the increasing sequence. With the increasing maturity, the relative abundance of 2-MCA, 1,7-DMCA and benzo[a]carbazole increased with the increasing maturity, while 4-MCA, 1,4-DMCA and benzo[c]carbazole gradually decreased. Benzocarbazole ratio [a]/[a] +[ c] varies only in a narrow range 0.36–0.61 in the entire maturity range, suggesting limited maturity dependence. The experimental conclusion provides more theoretical basis for future geochemical analysis using carbazole compounds. [ABSTRACT FROM AUTHOR]

Sulfate reduction by activated carbon (AC), a model compound for solid bitumen (pyrobitumen) without gas generative potential, was studied experimentally for the first time. The simulation experiments show that hydrogen sulfide (H2S) is produced from hydrothermal reduction of calcium sulfate (CaSO4) by AC at elevated temperatures. This result demonstrates that water can also act as a hydrogen source for H2S generation in addition to hydrocarbons. The formation mechanism of H2S may undergo a three-stage sequential process with calcium sulfide (CaS) as the unstable intermediate. The reactivity of carbon is thermodynamically higher than that of methane at ≥ 150 oC but lower than that of ethane or propane in sedimentary basins. Carbon-initiated sulfate reduction follows a zero–order reaction with an apparent activation energy Ea of 172.36 kJ/mol. When extrapolated to the temperature range of typical oil and gas reservoirs (100–200 oC), the order of the rate constant is determined as propane > ethane > solid bitumen > methane in the TSR of CaSO4. Although solid bitumen contributes little to hydrocarbon gas generation, H2S derived from carbon-initiated sulfate reduction may act as an indispensable catalyst for the consequent alteration of methane by TSR in deep buried gas reservoirs with high dryness coefficient. [ABSTRACT FROM AUTHOR]

In this study, thermal reduction of MgSO by NHCl was operated in the presence of water at 350 °C for 168 h. It was found that NHCl reacted with MgSO to produce HS, N and MgCl as the main products. Based on the experimental results and the assumption that the MgSO-NHCl reaction could approach a state of chemical equilibrium in natural environments over geological time scales, thermochemical program HSC 6.0 was utilized to model this geochemical process occurring in sedimentary basins. The results indicate that NH thermodynamically more easily participates in the reduction of SO than C-C normal alkanes of oil and gas at reservoir temperatures. The heat liberated from the reaction of MgSO-NHCl was estimated as 200.40-270.50 J/mol MgSO in typical oil and gas reservoirs (100-200 °C), which is much smaller than previous studies. In comparison with the minimum temperature range (100-140 °C) for conventional thermochemical sulfate reduction (TSR) using hydrocarbons, the inferred threshold temperature for initiating reduction of SOby NH in geological settings is only about 50-60 °C. The present study shows NH may play an additional role in TSR process by serving as an inorganic reductant, which has substantial implications for the formation of HS and N in sedimentary basins. [ABSTRACT FROM AUTHOR]

Factors affecting the abundance and the distribution of pyrrolic N compounds in sediments and crude oils have been traditionally attributed to palaeoenvironment of deposition, thermal maturity and source characteristics, as well as to migration effects. In this paper, experiments simulating reactions between pyrrole and hydrogen sulfide (HS) were conducted using a Hastelloy alloy tube confined system to investigate the effect of organic-inorganic interactions on the alteration of pyrrolic N compounds in real subsurface reservoirs. Experimental results showed that thermochemical N-S atom exchange evidently occurred at 400 °C in the pyrrole-HS system, with thiophene and ammonium hydrosulfide as the main products. Kinetic analysis of experimental data according to the integral composite method showed that the conversion of pyrrole into thiophene is best described by the second-order reaction model. The calculated apparent activation energy was about 39.010 kJ/mol and the frequency factor A was estimated equal to 5.935 × 10 s. This study indicates that pyrrolic N compounds may be susceptible to hydrogen sulfide under the conditions of real subsurface reservoirs, which is of great relevance to the stability of reservoir pyrrolic N compounds. [ABSTRACT FROM AUTHOR]

H2-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°C-525°C. The threshold temperature for initiating TSR is much lower than our previous studies (550°C). 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 dioxide as the main products, and high temperature is thermodynamically favorable to the reaction. According 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. [ABSTRACT FROM AUTHOR]

The TSR process may be one of the reasons to result in the natural gas destruction in deep carbonate reservoirs. The work on this field has been the subject of much research in recent years. In this paper, thermal simulation experiments on the reaction of CH4-CaSO4 were carried out using autoclave at high temperature and high pressure. The products were characterized by some advanced analytical methods. The thermodynamics and kinetics were discussed and the reaction mechanism was investigated tentatively. It is found that the reaction can proceed spontaneously to produce H2S, H2O and CaCO3 as the main products at the temperature range of 550–700°C. The activation energy and geological reaction ? action rate calculated from the kinetic model can be compared with those from previous work. The results obtained in this paper can provide important information on the explanation of geochemical depth limit for natural gas and on the exploration of gas reservoirs. [ABSTRACT FROM AUTHOR]