31 natural gases in the western Qaidam Basin of China were collected and analyzed for gas composition including light hydrocarbons (C₅-C₇) and carbon isotopic characteristics. Based on genetic type obtained from C₁-C₃ and C₇ fractions, four types of gases are identified: oil-type gas, coal-type gas, biodegraded gas, and mixed gas. The oil-type gas is the predominant-type gas in the western Qaidam Basin; coal-type gas is mainly distributed in the Zhahaquan and Nanyishan fields; mixed gas is mainly in the Zhahaquan, Wunan, and Nanyishan fields; and biodegraded gas is mainly distributed in the Huatugou and Yuejinerhao fields. According to the empirical relationship between δ¹³C₁ and the equivalent vitrinite reflectance (Ro, %) of source rock, the Ro values of gas range from 0.6% to 1.5%, with an average value of 0.9%. The generation temperatures of major reservoired hydrocarbons (GTMRH) calculated from the C₇ components range from 115.6°C to 141.7°C, with an average value of 126.5°C. These two maturity indicators have relatively positive correlation and reveal that the maturity of gas increases from west to east in the southwestern Qaidam Basin. Moreover, combining GTMRH with the homogenous temperature of petroleum inclusions, it is inferred that major petroleum charge in the western Qaidam Basin mainly occurred during the late period of the Himalayan movement. Deep hydrocarbon fluid sources were found in the Shizigou, Yingdong, Zhahaquan, and Nanyishan fields; thus, the deep reservoirs of paleouplifts adjacent to the hydrocarbon-generating depressions are estimated as a favorable area for further exploration in the western Qaidam Basin.

Organic-rich tuffaceous mudstones are important oil and gas resources. The systematic study of the pyrolysis kinetics and characteristics can not only provide the theoretical basis for the rational development and efficient utilization of these rocks but also is an important complement to the theoretical research on the pyrolysis kinetics of organic-rich rocks. In this study, the pyrolysis kinetics, behavior, and mechanism of the organic-rich tuffaceous mudstone in the Junggar Basin were clarified by thermogravimetric analysis. The organic structure and mineral composition were identified by Rock-Eval, Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The results indicated that the mudstone could be described as a type II kerogen with good hydrocarbon generation potential. The mudstone included up to 80.7% quartz, which is associated with Carboniferous volcanic activity. Four isoconversional methods were used to evaluate the activation energies. A novel and simplified method was proposed to separate the pyrolysis processes using the Coats-Redfern method based on the differences in reaction models and activation energies. The pyrolysis processes were divided into four stages, and the reaction models of each stage were preliminarily clarified. The reaction models were further modified by the accommodation function The results showed the kinetic parameters, and the reaction models of each stage were significantly different. Moreover, the obtained kinetic parameters and optimal reaction models can well characterize the pyrolysis processes and mechanism of the tuffaceous mudstone. The results of thermogravimetric-FTIR (TG-FTIR) indicated that the main pyrolysis hydrocarbon volatiles were methane, C²⁺ aliphatic hydrocarbons, and aromatics. And the types and yields of pyrolysis volatiles differed at each stage.

The geochemical characteristics of mantle degassing observed on the surface of the earth can indicate the origin and migration path of mantle fluids. Compared with the plate boundary tectonic environment, the intraplate tectonic environment does not have a large number of active volcanoes and active faults, and the observation of mantle volatiles in hot spring gas is relatively limited. We selected the Sichuan–Yunnan block to discuss mantle degassing based on the carbon and noble gas isotopes of the spring gases and previous studies on the fault slip rate and geophysical research. A total of five hot spring gas samples (including two free gases and three dissolved gases) were collected from the Sichuan–Yunnan block. Chemical and isotopic compositions were analyzed in N₂-dominant hot spring gases. The ³He/⁴He ratio (0.068–0.541 R_a) indicates the occurrence of mantle-derived helium throughout the Sichuan–Yunnan block, which has been diluted by a crustal radiogenic ⁴He component. The occurrence of mantle-derived helium in the study areas ranges from 0.74 to 5.67%. The lower proportion of mantle-derived helium in YNWQ and HGWQ than that in other spring gases near the Jinghe-Qinghe fault may be caused by the smaller scale of fault around YNWQ and HGWQ than the Jinghe-Qinghe fault. The correlation between ⁴He, ²⁰Ne, and N₂ concentrations implies a common trapping mechanism for ⁴He, ²⁰Ne, and N₂ in hot spring gases. The ⁴⁰Ar/³⁶Ar ratios and N₂/Ar ratios indicate that N₂ and Ar are mostly meteoric, and YNWQ and HGWQ have more crustal-derived Ar contribution (40.56 and 51.49%, respectively). The δ¹³C(CO₂)_o values calculated by Rayleigh fractionation and CO₂ concentration suggest that CO₂ has inorganic and organic origins. The plot of R_c/R_a versus δ¹³C(CO₂) indicates that the spring gas CO₂ origin in the Sichuan–Yunnan block is mainly derived from mixing of limestone and organic sediments with minor mantle CO₂. The δ¹³C(CH₄) versus CH₄/³He values indicate that the origin of methane is thermogenic and microbial oxidation. The low mantle-derived helium distribution pattern is most likely controlled by the weak fault activity rate, the small fault scale, and not obvious magmatic activity in the Sichuan–Yunnan block.

The characteristic of biomarker, stable carbon isotope, and rare earth elements in solid bitumen from the Puguang gas field and organic fraction in source rocks from the same area were investigated. Results show that the solid bitumen was derived from a mixed organic source with greater contributions from marine materials deposited under reducing environments. The enrichment of light rare earth elements seemed related to marine organic matter input. According to the results of principal component analysis, the main source rocks of paleo-oil reservoir in the Puguang gas field were the Upper Permian source rocks.