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However, these methods tend to focus on the distinction between biogenic and thermogenic gas. The natural thermal evolution of and hydrocarbon generation from organic matter in open, semi-open, and closed systems have been simulated in numerous experiments (Schenk and Horsfield, 1993; Behar et al., 1995; Tang and Behar, 1995; Lewan and Ruble, 2002). The organic material in coal is relatively aggregated and exhibits high sorption ability, which led Hill et al. (2003) to argue that coal is typically generated in closed or semiclosed systems. Generally, hydrous pyrolysis experiments can only be conducted in closed systems (Lewan et al., 1979; Lewan, 1985). Meanwhile, considering the vitrinite reflectance of pyrolyzed kerogens change in a manner similar to that observed in the natural system, the relationship between hydrocarbon yield and temperature obtained from hydrous pyrolysis experiments in closed systems can be applied practically (Lewan and Williams, 1987). The present study aims to understand the geochemical characteristics of CBM and identify its source (i.e.,

The hydrogeochemical characteristics of coalbed-produced water can provide insights into the sources of ions and water, the groundwater environments, hydrodynamic conditions, and water-rock interactions of depositional basins. To study the water-rock reaction process and reveal whether there is a microbial activity in the groundwater, a case of the Dafosi biogenic gas field was chosen by testing the ionic concentrations and hydrogen and oxygen isotopic compositions of coalbed-produced water and employing R-type cluster and principal component analyses. The results showed that Na+, Cl − , and HCO3- are the principal ions in the coalbed-produced water, while the water type is mainly a Na–Cl. Due to the hydrolysis of HCO3-, the pH in this region was controlled primarily by HCO3-. As the main cation in water, Na+ contributed substantially to the total dissolved solids. Na+ is also related to the exchange between rock-bound Na+ and Ca2+ and Mg2+ in water or surrounding rocks. The coalbed-produced water’s oxygen isotopes displayed a characteristic 18O drift and enrichment, indicating that the 16O isotope in the water was preferentially exchanged with the coal organic matter. Early evaporation is also contributed to the enrichment of TDS (total dissolved solids) and 18O in the water. The central part of the study area, including the Qijia anticline, was affected by the Yanshanian uplift and denudation and subsequently developed a water-conducting fissure zone and was recharged atmospheric precipitation; these conditions were conducive to the formation of secondary biogenic gas.

The formation environment and preservation conditions of sedimentary organic matter (OM) play an important role in the accumulation of shale gas. In the present study, inorganic and organic geochemical data were analyzed to determine the origin and preservation environment of sedimentary OM in the Wc-1 well of the Wufeng–Longmaxi (WF–LMX) Formation in northeastern Chongqing, China. In a biomarkers analysis, the numerical characteristics of n-alkanes ( n-C17/ n-C31>4.0), tricyclic terpenes (C23TT/C30H>1.0), and steranes (C27/C29St>1.0) suggested that the main origin of OM in the black shale was planktonic algae. High values of P/Ti and BaXS in the paleoproductivity indices suggested that primary productivity in the WF–LMX Formation was relatively high, peaking in the lower LMX Formation. Relative enrichment in U, V, and Mo, and the changing trends in V/(V+Ni) and Ni/Co suggested that the redox conditions for the bottom water, which changed from the WF Formation to the lower and upper LMX Formation, were oxic/dysoxic to anoxic and dysoxic, respectively. The relationship between total organic carbon and the above indexes indicates that different key factors controlled OM enrichment in the WF–LMX Formation. In the WF Formation, oxic bottom water was not conducive to the preservation of sedimentary OM. In the lower LMX Formation, the highest paleoproductivity and anoxic bottom water conditions promoted the enrichment and preservation of sedimentary OM. In the upper LMX Formation, excessive terrigenous inputs and relatively low paleoproductivity limited the enrichment of sedimentary OM.

LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) became a research hot point because of its low cost, environmental friendliness, and excellent electrochemical performance. However, Li + /Ni 2+ intermixing is an essential factor affecting its applicability. Doping could be an important method to improve the electrochemical performance of NCM811-based cathode materials. In this work, La and Al co-doped NCM811 was prepared by a solid-state method. Results from X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) and electrochemical performance were discussed in depth. These showed that when La and Al doping concentrations were 1 and 0.5%, the samples showed the best performance. The as-improved performances were mainly attributed to the reduced Li + /Ni 2+ intermixing, suppressed phase transition, and decreased potential polarization and impedance.

The exploration and development of coalbed methane (CBM) is often associated with the thermogenic gas. Because the mixed CBM derived from thermogenic and secondary biogenic gases was discovered in many coal-bearing basins of the world, secondary biogenic CBM which makes a significant contribution to the gas content is becoming a hot topic. In the present study, the origin of the gas in the Luling coalfield of China was first identified through molecular and stable isotope testing. Then, based on the basin evolution history, the generation process of thermogenic CBM and mixed CBM from biogenic and thermogenic gases was analyzed using two calculations. The results show that the carbon isotopic ratios of methane and carbon dioxide in Luling coalfield range from −67.6‰ to −50.5‰ and from −12.6‰ to −8.7‰, respectively, and the hydrogen isotopic ratios of methane range from −228‰ to −206‰. The isotope data indicate that the CBM in the Luling coalfield consists of both biogenic and thermogenic gases. Moreover, the generation process of mixed CBM can be divided into three stages: primary biogenic gas, thermogenic gas, and secondary biogenic gas. Cap outburst dissipation was determined to be the main migration mechanisms of hybrid CBM in Luling coalfiled, whereas diffusion was along with the whole process of CBM generation. Various factors, including maturity, temperature, and the time required for allochthonous methanogenic bacteria to move through the coal bed, were discussed in affecting the generation of secondary biogenic gas. These factors control the quantity, rate, and start and end of secondary biogenic CBM generation, respectively.

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