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The paleovegetation and paleoclimate characteristics are studied in the Palaeogene strata of Hetao Basin, Subei Basin and Qaidam Basin in China, and the Cretaceous Guyang Formation (K1g) in the Hetao Basin. These three basins receive high attention, different distribution areas, representative. Pollen evidence shows that: (1) The sporopollen assemblage of Palaeogene Linhe Formation (E3l) in Hetao Basin is characterised by Pinaceae-Ephedripites-Ulmipollenites-Chenopodipollis. It reflects that the ancient vegetation types were mainly coniferous and evergreen woody plants, and the climate was cold temperature. The sporopollen assemblage characteristics of the upper member of the Palaeogene Xiaganchaigou Formation (E32) in the Qaidam Basin are similar to it. (2) The sporopollen characteristics of the K1g in the Hetao Basin reflect that its ancient vegetation was dominated by evergreen woody plants and belongs to a warm and humid subtropical climate. (3) The assemblage of Palaeocene Funing Formation (E1f) in Subei Basin was Pterisisporites undulatus-Ulmipollenites minor-Taxodiaceaepollenites hiatus. The climate type was humid north temperate climate, vegetation was mainly deciduous trees and evergreen woody plants. (4) Leiosphaeridia/Granodiscus, Pediastrum and Botryococcus were also detected in the E1f of Subei Basin. The appearance of these algae indicates the special saline water environment and good hydrocarbon potential. [ABSTRACT FROM AUTHOR]

The study of mixed natural gas can clarify the specific sources of natural gas accumulation and provide the basis for the exploitation of natural gas resources. Analysis of gas compositions and carbon isotopic ratios of different components of mixed natural gas shows that the carbon isotopic fractionation of methane and ethane from different sources has a small difference after mixing. This conclusion is derived from the experimental data in Table 1, 0.88 is the average of all Ro values. Well DN8 and DN9 produced light oil with a density between 0.75 and 0.82 g/cm3 and viscosity between 1.63 and 3.3 MPa. Generally, in the high maturity stage of organic matter, the carbon isotopic fractionation values of methane and ethane of natural gas from a single source should display a difference of at least 4.0% to 5.0%. The δ13C value of methane and ethane in well DN8 are only 1.6%. It is considered that the mixing of natural gas from different sources causes this phenomenon. [ABSTRACT FROM AUTHOR]

With the global expansion of shale oil and gas exploration, analyzing the geochemical characteristics of different types of shale has seized extensive attention. Taking the Chang 7 Member and Shanxi Formation in the Ordos Basin as examples, this study investigated the geochemical and hydrocarbon expulsion characteristics of different types of shale. The results show that the Chang 7 shale is mainly type I. The total organic carbon (TOC) distribution of the Chang 7 shale in the study area was between 0.72% and 27.5%, with an average of 7.46%, and the vitrinite reflectance (Ro) ranged from 0.45% to 1.28%. It is a good source rock in immature to mature stages. The Shanxi shale is mainly type III. The TOC distribution of the Shanxi shale was between 0.6% and 58.5%, with an average of 8.92%, and the Ro distribution was between 0.42% and 2.39%, indicating good immaturity over mature source rock. The average hydrocarbon expulsion efficiencies of the Chang 7 shale calculated using the hydrocarbon generation potential method and the original hydrocarbon generation potential method were 82.49% and 94.81%, respectively. Simultaneously, a correlation analysis of hydrocarbon expulsion efficiency with organic matter abundance, maturity, and type found that when TOC was less than 5%, hydrocarbon expulsion efficiency increased with increased organic matter abundance and maturity. When the TOC exceeds 5%, the hydrocarbon expulsion efficiency is mainly related to maturity. The hydrocarbon expulsion efficiency of the sapropelic shale was much higher than that of the humic shale. This study is significant for evaluating shale gas and shale oil resources in similar areas. [ABSTRACT FROM AUTHOR]

The well-developed mudstone and gypsum mudstone in the Oligocene Linhe Formation (E3l) in the Hetao Basin are the main source rocks for gypsum. However, the sedimentary environment and organic matter (OM) enrichment factors of E3l are not clear, and this inhibits the prediction of hydrocarbon source rock distribution and resource calculation. Major and trace elements, total organic carbon (TOC), pyrolysis using the Rock-Eval II, and saturated hydrocarbon gas chromatography–mass spectrometry (GC–MS) analyses were performed in this study. The results show that E3l was deposited in brackish water and saline–ultrasaline water, with weak oxidation reduction in an arid and hot environment. Terrestrial input inhibits OM enrichment, while the redox, paleosalinity, paleoclimate, and paleoproductivity play a catalytic role. The main controlling factors of the same lithologic source rocks are different: terrestrial input and paleoclimate have a greater impact on mudstone, and the redox and paleosalinity were more favorable to gypsum mudstone. Although the main controlling factors are different for different lithologies, their OM enrichment characteristics are still consistent. The E3l water body was deep, and the contribution of nutrients from terrigenous debris to OM enrichment was less. In addition, the water retention environment changed significantly during the E3l sedimentary period, resulting in fewer nutrients, which limited the improvement of surface water paleoproductivity. The arid climate increased water evaporation and salinity, which to some extent prevented consumption and decomposition. Weak oxidation-reduction fluctuations and the stratification of the water body were obvious, and this was not only conducive to the enrichment of OM but also to its preservation. [ABSTRACT FROM AUTHOR]