Impact of Inorganically Bound Sulfur on Late Shale Gas Generation

Nonisothermal, confined pyrolysis was applied to a mature shale sample from the Ordovician Salgan Formation in Tarim Basin, northwest China. Experiments were conducted using gold-tubes with added water at a very slow heating rate (2 °C/h) and end temperatures between 336 and 600 °C. To investigate the influence of inorganically bound sulfur on the generation of gases and to consider the geological occurrence of sulfur-containing minerals, such as prevalent pyrite in shales, the experiments were carried out with and without admixtures of MgSO₄, CaSO₄, and pyrite. High amounts of methane along with lower amounts of wet gases were formed from highly mature shale without minerals added, demonstrating a huge late gas generation potential at post peak-oil window maturities. In the experiments with added sulfates and pyrite, all organic gases were consumed in varying proportions, resulting in different chemical and stable carbon isotopic compositions. Pyrite treatment affects wet gas (C₂–C₅) evolution directly, but it affects methane (C₁) evolution indirectly. In contrast, sulfate treatments affect C₁–C₅ evolution directly. The cumulative yield ratio of CO₂/H₂S indicates that pyrite impacts on the hydrocarbon gas generation through low valence sulfur such as S⁰ or others, which are associated with H₂S generation. In the pyrite series, the smooth increase in ethane yield at temperatures exceeding 504 °C, together with a concomitant stable carbon isotope reversal, demonstrates a new origin for ethane at high temperatures. The isotopic reversal may come from reactions between water and solid kerogen/coke/pyrobitumen. Isotopic reversal of ethane occurs only in the control and pyrite series but not in the sulfate treatments. This provides evidence that anoxic conditions are required. Thus, one can expect to encounter isotopic reversals in high maturity, unconventional gas shale environments in the presence of pyrite

A comparative study of free and bound bitumens from different mature source rocks with Type III kerogens

The complicated macromolecular structure of kerogen has made it difficult to extract chemical information on bound molecules. The hydropyrolysis (Hypy) technique, which can release considerable amounts of hydrocarbons from kerogen via the mild cleavage method, provides an opportunity to solve this problem. In this study, Type III kerogens with varying degrees of maturation from Lower Carboniferous source rocks in the northern Junggar Basin, China, were subjected to solvent extractions and Hypy experiments. A quantitative comparison of the amount and composition of free and bound bitumen reveals the precise cleavage process of bound molecules from kerogen. As maturation increases, free and bound aliphatic molecules, including biomarkers, decrease markedly as a consequence of continuous cracking and degradation. However, the bound 3-benzene ring compounds are initially enriched and then depleted, consistent with the evolution of the aromatic structure of kerogen. In the early-mature and mature stages, bound bitumen could be a reliable pool of biomarkers, and undoubtedly the bound biomarkers preserve more information about biological inputs. Moreover, due to the protection of the macromolecular structure of kerogen against extreme thermal stress, a few informative biomarkers, especially aliphatic moieties, can be released by Hypy from high-mature kerogens. The rearranged hopane Ts and diasteranes may be present in bound bitumen due to the incorporation of related molecules into the kerogen, possibly during the formation of kerogen. In contrast, C-30 rearranged hopane (C-30(*)) only occurs in free bitumen due to the catalysis by acidic clays during the mature stage. Side chain and ring isomerization of free and bound hopanes and steranes occurring during maturation is more complicated. For example, the configuration changes from R-dominant, to equilibrium R and S configurations, and then to R configuration dominance again. These changes may be controlled by the generation and degradation processes affecting these compounds. However, most aromatic maturity parameters of the bound fractions increase with maturity (i.e. with increasing %Ro). As documented in the literature, kerogen severely suppresses the chiral isomerization of bound aliphatics, but our results show that it does not retard methyl transfer reactions in aromatic rings. (C) 2017 Elsevier Ltd. All rights reserved

Surface Characterization of Aerosol Particles in Guangzhou, China: A Study by XPS

X-ray photoelectron spectroscopy (XPS) is a powerful technique for determining the surface chemical composition of atmospheric particles. In this article, we employed XPS to study atmospheric particles collected from Guangzhou city in typical sites and sea-sons. The results showed that the weight percentage of carbon, oxygen, nitrogen, and sulfur were about 70.5–87.1%, and these species dominated the surface structure of the particles indepen-dent of the collection site and season. Inorganic elements including Si, Na, Ca, Cl, Fe, K, Al, and Cu were also found on the particle surfaces. The high-resolution XPS spectra revealed: (1) High aro-matic and aliphatic C-H, and other oxidized carbons were found on the surface of particles. (2) The nitrogen species were char-acterized by pyridinic, pyrrolic/amide, quaternary type nitrogen functionalities, and nitrate groups, indicating that inorganic and organic N species are both important components of N-containin

Progress in generation kinetics studies of coal-derived gases

Hydrocarbon-generation kinetics is of applicable significance in the study of coal-derived gas pool formation. Its research progress in recent years includes: in combination with geothermal history, it is used as a tool to evaluate source rocks dynamically and depict the change of source kitchen with geological time; according to the carbon isotope fractionation kinetics, a more precise model of identifying coal-derived gas is developed, which contains the kinetic relationship among gas compounds; the combination of compositional kinetics and carbon isotopic kinetics leads to the study method of accumulation processes of coal-derived gases, which is constrained precisely by multi kinetic indices; with the reservoir records, generation kinetics is used to study the whole gas life including generation, charge and alteration. The problems that need investigation are generation kinetics of coal-derived gas at low maturity, pressure effects on gas generation, minerals and water influences, and kinetics of residual soluble organic matter at high maturity. Key words: coal, natural gas, coal-derived gas, generation kinetics, progres