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Oil sources and accumulations in complex oil reservoirs of superimposed basins are difficult to identify and recover because of multiple kitchens and multistage charging processes. Constraining the oil sources and characterizing their accumulation patterns is a critical challenge. In this study, 46 crude oils from the Upper Wuerhe Formation, a widely distributed oil reservoir in the Mahu Sag of the Junggar Basin, NW China, are geochemically characterized to assess their sources and spatial distribution. These oils are divided into four groups: group I oils (characterized by high β-carotane and gammacerane concentrations, low C21/C23 and (C19 + C20)/C23 tricyclic terpane ratios, and low Pr/Ph ratios); group II oils (characterized by low β-carotane and gammacerane concentrations, high C21/C23 and (C19 + C20)/C23 tricyclic terpane ratios, and moderate Pr/Ph ratios); group III oils (very high Pr/Ph ratio (>3), the lowest β-carotane and gammacerane concentrations, and low tricyclic terpane concentration, but relatively high C19 and C20 tricyclic terpane abundance); and group IV oils (refered to here as geochemically hybrid, and inferred to be sourced from mixed P1f and C/P1j source rocks). The integration of oil-source correlation and geological framework indicates that oils generated from multiple kitchens are more likely to be near-sourced accumulations, providing a plausible example for oil accumulation in a complex oil reservoir of superimposed basin with several sets of kitchens and multistage oil charging history. The results show that multisource and multistage hydrocarbon accumulation is a common characteristic of prolific superimposed basins. The oil accumulation pattern must be established by carefully characterizing sources and charging processes to reduce the risk of exploration activities. [ABSTRACT FROM AUTHOR]

In order to understand the hydrocarbon generation potential of the siliceous shale in the Permian Gufeng Formation of the South Yellow Sea, the organic geochemistry and organic petrology of the siliceous shale in the Gufeng Formation of the CSDP-2 well were studied and analyzed. It is found that the TOC of the samples is mainly between 9% and 12%, and Tmax is mainly distributed between 510 and 540 °C. The value of the organic microscopic type index (TI) is between 25.71 and 31.00, which is a set of II2 high-quality source rocks with high organic matter abundance in the over mature stage of large-scale gas generation. According to the distribution characteristics of Molecular fossils in siliceous shale of Gufeng Formation of well CSDP-2, bacterial organic matter is the main hydrocarbon generating parent material, and aquatic animal organic matter is an important hydrocarbon generating parent material. The siliceous shale in Gufeng Formation of CSDP-2 well is in the stage of large-scale gas generation; Therefore, the Gufeng Formation in the central uplift of the South Yellow Sea has the material basis for the formation of large-scale shale gas reservoirs. At the same time, the siliceous metasomatism of the siliceous shale reservoir of Gufeng Formation is not conducive to the primary migration of oil, and there is much oil and gas remaining in the reservoir. [ABSTRACT FROM AUTHOR]

The Upper Triassic Xujiahe Formation (T3x) is the most important terrigenous stratum in the Western Sichuan Depression; however, it is still insufficient for the understanding of molecular compositional characteristics of its source rocks. Based on the analysis of both saturated and aromatic fractions of extracts of source rocks from different members of the Xujiahe Formation, the indication is then discussed for sedimentary environment and thermal evolution of source rocks. The distribution of tricyclic terpanes (TTs) and dibenzothiophene/phenanthrene (DBT/P) ratio of the argillaceous source rocks in 2nd to 4th members of the Xujiahe Formation mainly display the signatures of typical lacustrine source rocks, and the relatively high gammacerane/C30 hopane (0.16-0.23), as well as 9-/1-methylphenanthrene (1.16-1.41) ratios suggest relatively high salinity of water body. The parameters such as methylphenanthrene index (MPI1), methylphenanthrene distribution fraction (F1), and methyldibenzothiophene distribution index (MDBI) are effective for the evaluation of thermal maturity, and they show positively and negatively linear correlation with maturity degree before and after Ro=1.35%. The distribution pattern of C27-C29 regular steranes, relative composition of three fluorine series, and methyldibenzothiophene/methyldibenzofuran ratios for high to over-maturity T3x source rocks are distorted due to the effect of thermal maturation.

The middle (Miaolingian) to upper (Furongian) Cambrian Alum Shale Formation in the DBH15/73 core from south-central Sweden was exposed to local heat from a diabase intrusion, providing an opportunity to investigate the molecular geochemical response to thermal stress. Organic petrological observations and biomarker analyses were conducted to study changes in maturity-indicating parameters and the distribution of high molecular weight polycyclic aromatic hydrocarbons (PAHs) during the maturation process. The DBH15/73 samples exhibit a maturity gradient, ranging from immature at the base to mature in the upper part of the Alum Shale Formation. Multiple maturity-based biomarker parameters were analyzed, and Ts/(Ts + Tm), M 30 /(M 30 + H 30), and Hopane H 32 : 22S/(22S + 22R) of saturated hydrocarbon parameters are found to be more reliable. Ratios of alkylnaphthalenes, alkylphenanthrenes, and alkyldibenzothiophenes (MNR, DNR, TMNr, TeMNr, MPI-1, MPR, MDR, and DMDR) also showed consistent correlations with thermal maturity. Thermal maturation impacted the macromolecular structure, resulting in the aromatization and demethylation, leading to MPy/Py, MChy/Chy, and the sum of unsubstituted 5-ring/4-ring PAH ratios changes with maturity. The influence of thermal maturation outweighs that of uranium radiation in this study, and maturity varies mainly with depth. • The behavior of saturated and aromatic maturity-dependent biomarkers within the maturity range of VR eqv < 1.40 % • High molecular weight PAHs ratios in Alum Shale Formation under thermal intrusion • Influence of uranium radiation on biomarker distributions [ABSTRACT FROM AUTHOR]

Climatic fluctuations from the Eocene to the Miocene highlight the importance of investigating the paleoenvironment of the latest Eocene to the Middle Miocene Lark Formation in the Danish North Sea. This study investigates immature sedimentary organic matter in the Lark Formation using 54 cuttings samples and one core sample collected from seven wells in the eastern North Sea Basin. Organic petrography and molecular geochemistry analyses were performed to determine the variations in the quantity and origin of allochthonous and autochthonous organic matter. Additionally, the study assesses the impact of climate fluctuations on marine productivity in the eastern North Sea Basin and land plant vegetation at the basin margins during the latest Eocene to the Middle Miocene. The organic matter in the Lark Formation originated from mixed sources, primarily land plants, with a secondary contribution from marine algae. This is indicated by the maceral composition and the types and abundance of aliphatic and aromatic hydrocarbon biomarker compounds. Moreover, the presence of diterpenoids (gymnosperm biomarkers) and non-hopanoid triterpenoids (angiosperm biomarkers) reveals that the allochthonous organic matter originated from conifers and angiosperms. Climatic impacts on land plants and marine algae during the latest Eocene to the Middle Miocene are revealed by several parameters: the Averaged Chain Length (ACL) of land plant waxes, the proportion of coniferous contribution (C/(C + A)), and the whole rock volume percentages of huminite, inertinite (H + I, vol%) and liptinite (L, vol%). The shifts to cooler and drier climates highlighted the cold adaptation of onshore conifers and resulted in the input of higher molecular weight waxy components into the sediments. However, under these conditions, reduced precipitation and runoff resulted in lower amounts of terrigenous organic matter supplied to the basin. Additionally, the drop in water temperature and the warm-affinity of local algae assemblage led to reduced marine productivity. Together, these factors contributed to an overall decrease in organic richness. In contrast, during shifts to warmer and more humid climates, the trend reversed. The contribution of conifers to the floral assemblage diminished, but higher amounts of terrigenous organic matter were transported to the basin due to increased precipitation and runoff. This was accompanied by warmer water temperatures, boosting the productivity of organic-walled microplankton in the marine environment and contributing to greater organic richness. • 54 drill cuttings and one core were obtained from the eastern North Sea Basin. • Point counting and GC–MS analysis were conducted to identify the biosource. • The biosource includes both land plants (majority) and marine algae (minority). • Contributions from gymnosperms (mainly conifers) and angiosperms were identified. • Climate fluctuations impacted land plants growth and marine productivity. [ABSTRACT FROM AUTHOR]

The Permian Pingdiquan Formation (P 2 p) in Shishugou Sag, Junggar Basin, Northwest China, is a typical example of mixed sedimentary strata formed in a saline lacustrine environment, characterized by complex lithological assemblages and extensive distribution of organic-rich source rocks. To further investigate the differences in oil-source contribution and hydrocarbon generation characteristics of source rocks with different lithologies, studying the difference of their geochemical characteristics and the formation mechanism of organic-rich source rocks is the top priority. Based on a comprehensive analysis of lithologic types, geochemical characteristics, and hydrocarbon generation potential of source rocks using organic petrology, molecular geochemistry and element geochemistry, this paper reveals the formation background and organic matter enrichment mechanism of the P 2 p organic-rich source rocks. The results show that the mixed sedimentary rocks of the P 2 p were deposited under relatively arid and saline lacustrine conditions. Paleoclimatic conditions tended to be more arid and hydrothermal activity became more frequent during the sedimentation process from mudstone, dolomitic mudstone to argillaceous dolomite. Consequently, the water column salinity elevated, leading to an increased proportion of salt-tolerant green algae and slight salt-tolerant cyanobacteria compared to salt-intolerant algae. Frequent changes in paleoclimate and hydrothermal activity control the interbedding deposition of mudstone, dolomitic mudstone and argillaceous dolomite, and the resulting salinity fluctuations contribute to variations in the proportion of salt-tolerant and intolerant algae in source rocks with different lithologies. Furthermore, the source rocks within the mixed sedimentary strata (mudstone, dolomitic mudstone and argillaceous dolomite) all exhibit substantial hydrocarbon generation potential, and there exists heterogeneity among source rocks of the same lithology. The key factor influencing the development of these organic-rich source rocks is the enhancement of palaeoproductivity driven by volcanic activity. Additionally, the water stratification caused by saline water promotes anoxic water columns, also contributing to organic matter enrichment in the source rocks. • The paleoclimate and hydrothermal activity control the lithology and its composition. • The water column salinity controls the variation of algal composition in source rocks. • Volcanic activity promotes organic-rich source rock by controlling paleoproductivity. [ABSTRACT FROM AUTHOR]

The Lower Triassic Montney Formation of the Western Canada Sedimentary Basin (WCSB) is a world-class unconventional hydrocarbon resource in North America. It was deposited on the northwestern margin of Pangaea at mid-latitudes in an arid climate and after major mass extinction at the Late Permian-Triassic boundary. Despite decades of exploration and economic importance, the origin of organic matter and source of accumulated hydrocarbons is not well understood. The Montney Formation is primarily composed of dolomitic siltstone with a mean total organic carbon (TOC) content of ≤1 wt%. In this study, we re-examined samples from an Alberta Geological Survey (AGS) data release in 2010 on Montney Formation organic petrography and expand the sampling and analysis to further investigate organic matter type, thermal maturity, and possible internal hydrocarbon source intervals within the Montney Formation as well as organic matter preservation and depositional environment by integrating programmed pyrolysis, organic petrography, and molecular geochemistry. Organic petrography and molecular geochemistry show that millimeter to centimeter thick mudstone intervals with TOC ≤ 1 wt%, are dominantly comprised of Type II marine kerogen (Prasinophyte and Tasmanites) with minimal terrigenous organic matter. The presence of these organic-rich mudstone beds in central and western Alberta reveals intra-formational sources of hydrocarbons within the Montney Formation, in addition to hydrocarbons sourced from overlying organic-rich source rocks (i.e., Triassic Doig and Jurassic Gordondale). These results confirm that the Montney Formation can be considered as a hybrid unconventional hydrocarbon reservoir with an interbedded source and reservoir. Molecular geochemistry data suggest that photic zone euxinia (PZE) was favorable for the preservation of organic matter during deposition of the Montney Formation. However, in many instances, this only happened during very short periods similar to depositional conditions on the offshore present day Namibian shelf. Traces of terrigenous organic matter were able to reach the basin, likely in the form of inertinite and combustion-derived polycyclic aromatic hydrocarbons (PAHs). Although the results of this study show there are source rock intervals within the Montney Formation, a comprehensive organic petrography and geochemistry study on a series of full-length Montney cores throughout the basin will help to ascertain the major paleo depositional variation and their effect on organic matter preservation as well as hydrocarbon source intervals and their contribution to WCSB petroleum systems. • Organic petrography and molecular geochemistry show the presence of immature/early mature Type II kerogen in the Montney Formation. • Thin (1–10 cm) mudstone intervals contributed to hydrocarbon resources of the Montney Formation. • Short-lived photic zone euxinia was favorable for preservation of organic matter. • The presence of PAHs may be related to combustion-derived materials transported from higher latitudes. [ABSTRACT FROM AUTHOR]

The character of the coal in Tomago and Greta coal measures are similar to other coals from the Sydney Coal Basin, with variation from vitrinite-rich to inertinite-rich coal. A type III organic matter (OM) linked to continental higher plants and a perhydrous type III similar to type II were found by Rock-Eval analysis. The coexistence of inertinite with algae ( Botryococcus ) in the Greta coals explains the high HI in the perhydrous type. The Gangamopteris flora that is reported in the Greta coal measures, grew after plants in a taiga like the recent birch forests in Russia (Retallack, 1980). The Glossopteris flora that is reported in the Tomago coal measures, grew in a swamp forest. Based upon the botanic zonation, this flora was located in the cold temperate biome that was located in Gondwanaland, except for Antarctica which was in the glacial biome. Diterpane analysis results reveal alternation of wet and dry periods existed during the deposition of Lewis coals in the Greta coal measures during the Kungurian, and an increase of dryness is noted from Upper Donaldson to Beresfield in the Tomago coal measures during the Capitanian. Based on analysis of aromatics and diterpanes, the same periods of dryness and wetness alternate during the coal deposition in the Sydney Coal Basin. These climatic changes correspond to high frequency cycles (< 100 ka, Goldhammer et al., 1994). The presence of aromatics linked with combustion in the studied samples confirms the hypothesis of fire in peat land to explain high inertinite content. A low to medium biodegradation by bacteria was observed for saturates and aromatics from the studied samples as noted previously in the Sydney and Bowen Basins. This biodegradation concerns short chain n -alkanes, naphtalenes and phenanthrenes and does not alter the paleoenvironmental and paleoclimatic interpretation. The comparison between biomarkers from coals and isotopes from marine (Birgenheier et al., 2010) and terrestrial (Retallack et al., 2011) deposits allow us to identify precise dry/wet climate and glacial/interglacial periods during the Permian. [ABSTRACT FROM AUTHOR]

The Cap d’Ailly area (Upper Normandy, France) shows several terrestrial–lagoonal sections recording the negative carbon isotope excursion (CIE) associated with the Paleocene–Eocene Thermal Maximum (PETM; 55.8 Ma). A study of the biomarkers and spore/pollen content of the Vasterival section gave complementary information on paleofloral changes that occurred around the Paleocene–Eocene (P–E) boundary. Aliphatic hydrocarbon fractions revealed a high abundance of vascular plant biomarkers, including tricyclic diterpanes derived from conifers, fernenes derived from ferns and des-A-triterpenes derived from angiosperms. Whereas the vegetation of the depositional environment surroundings seemed alternately dominated by ferns and angiosperms (revealed from biomarkers), the regional flora seemed dominated strictly by angiosperms such as Juglandaceae (revealed by pollen). Spore/pollen assemblages revealed no major turnover in the paleovegetation, but slight variation in vegetation composition. However, both biomarkers and spores/pollen exhibited two intervals of rapid floral change: the first occurred around the P–E boundary and the second at the top of the strictly terrestrial unit that coincides with a marine transgression. Comparison of the data with published paleoclimatic results, obtained from the same samples, indicated that the first interval of floral change correlates with strong paleohydrological perturbations, whereas the second is linked to an increasing marine influence. [ABSTRACT FROM AUTHOR]

Abstract: Soil organic matter (SOM) is a key factor in ecosystem dynamics. A better understanding of the global relationship between environmental characteristics, ecosystems and SOM chemistry is vital in order to assess its specific influence on carbon cycles. This study compared the composition of extracted SOM in 18 topsoil samples taken under tundra, taiga, steppe, temperate forest and tropical forest using pyrolysis–GC/MS. Results indicate that SOM from cold climates (tundra, taiga) still resembles the composition of litter, evidenced by high quantities of levosugars and long alkanes relative to N-compounds and a clear odd-over-even dominance of the longer alkanes. Under temperate conditions, increased microbial degradation generally results in a more altered SOM chemistry. SOM formed under temperate coniferous forests shows an accumulation of aromatic and aliphatic moieties, probably induced by substrate limitations. Tropical SOM was characterized by an SOM composition rich in N-compounds and low in lignins, without any accumulation of recalcitrant fractions (i.e. aliphatic and aromatic compounds). Lignin composition moreover varies according to vegetation type. Results were validated against 13 new samples. The humic signature of topsoil organic matter formed under different biomes indicates a dominating effect of (i) SOM input composition related to vegetation, and (ii) SOM breakdown reflecting both climate and input quality. No evidence was found for a chemically stabilized SOM fraction under favorable decomposition conditions (temperate or warm climate with broadleaved vegetation). [Copyright &y& Elsevier]

Abstract: More than one hundred and thirty coal seams and coaly layers occur in the Donets Basin (Donbas). Twenty-eight (52 samples) of them, ranging in age from Serpukhovian (Late Mississipian) to Gzhelian (Late Pennsylvanian), 33 clastics and three limestones were studied in terms of maceral composition, sulphur contents, and biomarker distribution. Diterpanes are used to estimate the contribution of different groups of plants and the height of the water table in the swamp; hopanes are a measure of bacterial activity in the peat; and steranes indicate the relative input of wood and algae. Stratigraphic trends in these parameters are discussed in relation to paleoenvironment, climatic changes, and eustacy. A tropical climate prevailed in the Donbas from Serpukhovian to Kasimovian times. Nevertheless, periods with drier and wetter conditions can be distinguished based on maceral and biomarker data. Relatively dry conditions are observed during Serpukhovian and Vereian times, whereas wetter climates with a maximum of coal deposition occurred during the (late) Bashkirian, most of the Moscovian, and the earliest Kasimovian. No economic coal seams are hosted in upper Kasimovian and Gzhelian deposits, a result of a change to an arid climate. Our data also suggest climatic changes during sequences of different order. For the second-order, third-order, and fourth-order sequences, relatively dry or wet conditions occurred during coal deposition in the lowstand systems tract, an intermediate climate during the transgressive systems tract and the maximum flooding, and a wet climate during the highstand systems tract. The results for high frequency sequences support the Cecil''s paleoclimatic model: an intermediate paleoclimate during LST (sandstone and levee siltstone), a wet climate during early TST (coal), and a dry climate during late TST (limestone), MFS (claystone), and HST (deltaic siltstone). Coals deposited during maximum flooding periods are more enriched in C27 steranes derived from algae, and contain lower proportions of C29 steranes derived from the wood of higher plants. [Copyright &y& Elsevier]

Having studied the biomarker composition and maturity of dissolved hydrocarbons from Ordovician formation waters, the authors presented molecular geochemical evidence for the controversial origin of natural gases in central Ordos Basin. The dissolved hydrocarbons in Well Shan 12 and Well Shan 78 are relatively high in abundance of tricylic terpane, pregnane series and dibenzothiophene series and low in Pr/Ph (<2) and hopane/sterane ratios, indicating the source input of marine carbonates. In contrast, the dissolved hydrocarbons in Well Shan 81 are free from tricyelic terpane and pregnane series, with trace dibenzothiophene series and high Pr/Ph (3.27) and higher hopane/sterane ratios, which are the typical features of terrestrial organic matter. Furthermore, Well Shan 37 and Well Shan 34 are between the two situations, having a mixed source of marine carbonate and terrestrial organic matter. The maturity of biomarkers also supports the above suggestions. These results are consistent with the geological background and source rock distribution in this region. [ABSTRACT FROM AUTHOR]

The recently discovered Shunbei Oilfield is perceived as a remarkable breakthrough in deep marine carbonate petroleum exploration in the Tarim Basin, western China. Constraining the absolute timing of petroleum system evolution is crucial for further hydrocarbon exploration and development in the area. Here, we integrated molecular geochemical correlation, stable carbon isotopes of bulk oil (bitumen) and Re–Os geochronology to trace the petroleum sources, to constrain the absolute timing of hydrocarbon generation, and to reconstruct the petroleum system evolution of the deeply-buried oil accumulations in carbonate reservoirs. Biomarker parameters derived from isoprenoids, terpanes, steranes and aromatic compounds, as well as stable carbon isotopic compositions, revealed that the Ordovician reservoir oils and bitumens were all originated from the same source rock, deposited under a highly-reduced environment with organic matters being predominantly contributed by algae and bacteria. The calculated equivalent vitrinite reflectance (Rc) values of reservoir bitumen and oil samples indicate that the Shunbei Oilfield has experienced at least two hydrocarbon charges. Geochemical characteristics and thermal maturity suggest that the bitumen within the Ordovician Yijianfang Formation reservoirs in the north Shuntuoguole Low Uplift is not originated from thermal cracking, thermochemical sulfate reduction, biodegradation, nor gas washing. Re–Os isotopic data from six reservoir bitumen samples yield an isochron age of 399 ± 12 Ma with an initial 187Os/188Os ratio (Os i) of 1.26 ± 0.11. This age is interpreted to represent the timing of oil generation when compared with the thermal evolution of possible source rocks and other radiometric dating results in the region. A comparison of 187Os/188Os of the 399 Ma-old bitumen and that of possible source rocks at the time of oil generation suggests that the reservoir oil was possibly originated from the lower Cambrian Yuertusi source rock. This work highlights that Re–Os geochronology combining with the initial 187Os/188Os ratio can be used to effectively constrain the timing of hydrocarbon generation in petroleum systems with complex tectonic history, multiple oil charges and alterations. • Oil-bitumen correlations based on biomarkers and δ13C suggested a similar origin. • Bitumen with a moderate thermal maturity was formed by asphaltene precipitation. • The Re–Os age of 399 ± 12 Ma represents the timing of early oil generation. • Reservoir bitumen was derived from the Lower Cambrian Yuertusi Formation shale. [ABSTRACT FROM AUTHOR]

A comprehensive geochemical and petrographic study was performed on 23 clay-rich shale samples collected from 18 wells drilled in the mid-western part of the Ordos Basin to investigate the characteristics and thermal maturity of organic matter as well as the paleo-depositional environment of the Chang 7 Member within the Triassic Yanchang Formation. The samples are characterized by moderate to very high organic carbon (TOC) contents ranging from 0.24% to more than 24.83% (2.72% on average) and total sulfur (TS) contents of 0.06% to 6.51%. Rock-Eval S 1 and S 2 values range from 0.13 to 3.70 mg HC/g rock and 0.62 to 92.50 mg HC/g rock, respectively, implying good to very good hydrocarbon generation potential for most of the samples. Rock-Eval data and petrographical observations reveal that the kerogen is mainly composed of type II to type III, consisting of a mixture of aquatic and terrigenous organic matter. The aliphatic fractions show variable monomodal to bimodal distributions of normal alkanes. Different parameters such as TOC/TS and molecular biomarker data imply that the Chang 7 member is a typical clay-rich source rock deposited in a sulphate-poor lacustrine to fluvio-deltaic environment under oxic to sub-oxic conditions with substantial input of organic matter derived from higher land plants, mainly conifers. Low values of gammacerane further indicate a low salinity of the paleo-lake. Average T max values of 445 °C, vitrinite reflectance values between 0.68% and 0.88%, biomarker parameters, such as sterane ratios of C 29 ααα 20S/(20S + 20R) and C 29 ββ/(ββ + αα), and maturity indices based on aromatic compounds, indicate a thermal maturity within the oil window for the studied samples, showing some regional variability within the mid-western Ordos Basin. • Detailed elemental and molecular composition, organic petrology of the Chang 7 Member • Thermal maturity within oil window uniform over a large area within the Ordos Basin • Lacustrine deposition at high sedimentation rates under oxic-suboxic bottom water • Kerogen originated from a mixture of higher land plants, bacteria and algae [ABSTRACT FROM AUTHOR]

The Chang 6, Chang 8, and Chang 9 reservoirs of the Upper Triassic Yanchang Formation in the Zhenjing area of the Ordos Basin are characterized by low porosity, low permeability, high oil saturation, and large oil reserves, which indicate huge tight oil potential. To comprehensively investigate the hydrocarbon contributors and charging history, fluid inclusions were systemically studied coupled with basin modeling and oil geochemical analysis. According to the petrographic characteristics, two episodes of fluid inclusions occurred in each of the three reservoirs. Microthermometry analysis suggests that the hydrocarbon inclusions of the first episode in each reservoir are distributed mainly along overgrowth quartz or secondary microcracks and exhibit light yellow or light brown fluorescence; the coeval aqueous inclusions display low homogenization temperature (Th) peaks with 80–100 °C. The hydrocarbon inclusions of the second episode in each reservoir are mainly distributed in microcracks that cut across or within quartz grains and exhibit light green or bluish-green fluorescence; the coeval aqueous inclusions are characterized by high Th peaks with 110–120 °C. The different characteristics of the two episodes of the fluid inclusions imply the existence of two episodes of hydrocarbon charging events. The burial and geothermal histories of the various reservoirs were reconstructed using one-dimensional basin modeling and pressure–volume–temperature–composition (PVTX) simulation coupled with the authigenic illite K–Ar dating. The reconstruction implied the time of the two hydrocarbon charging episodes to be Early Cretaceous and Late Cretaceous. Oil-source correlation studies illustrate that the Chang 6, Chang 8, and Chang 9 crude oils all originate from the Chang 7 source rock. The migration characteristics and directions were comprehensively analyzed by using maturity parameters. This explanation of the charging history and oil migration pathway of the Upper Triassic Yanchang Formation in the Zhenjing area provides a theoretical basis for further exploration. • Each reservoir was charged during the Early and Late Cretaceous, respectively. • The crude oils in all reservoirs originated primarily from the Chang 7 source rocks. • The oils are charged along with the faults and the W-dipping monocline. [ABSTRACT FROM AUTHOR]