Black shale with extraordinarily high organic matter (EHOM) content is prevalent in the Chang 7 Member of the Middle Triassic Yanchang Formation, Ordos Basin. This interval shows significant potential for hydrocarbon generation; however, mechanisms for EHOM accumulation of these black shales remain highly debated. In order to reconstruct the depositional environment of the basin and investigate the mechanisms behind the EHOM enrichment, a comprehensive analysis encompassing elemental carbon and sulfur, major elements, mineral and microbiological fossils, and biomarkers was conducted on 45 shale samples of the Chang 7 Member from a well located in the north slope break belt of the basin. The results indicate that EHOM of these shales has evolved into the mature stage, with a notable potential for hydrocarbon generation. Their OM has mixed-source origins, primarily derived from algal matter, with a significant contribution from higher plants. During the deposition of the Chang 7 Member, the prevailing climate was warm and humid, with moderate weathering intensity and relatively low paleosalinity, fresh-brackish water depositional environment. In semi-deep to deep lake environments, the organic matter enrichment in the Chang 73 sub-member shale follows a medium-high palaeoproductivity and anoxic preservation model. During the Chang 72 depositional period, water depth decrease leads to the deterioration of preservation conditions, resulting in a significant reduction in the abundance of organic matter. During the deposition of the Chang 71 period, the increase in organic matter abundance is mainly attributed to the decrease of terrestrial debris dilution and medium-high paleoproductivity. The enrichment of EHOM is related to volcanic activity, in conjunction with a warm and humid climate, low salinity level, minor terrigenous detritus input, anoxic conditions, algal blooms, and an elevated paleoproductivity sedimentary environment.

The Chang 8 Member in the Longdong area of the Ordos Basin hosts significant petroleum resources, demonstrating substantial potential for tight oil exploration and development. Astronomical forcing exerts a discernible influence on the evolution of its petroleum system. To elucidate the impact of Milankovitch orbital cycles on organic enrichment and the development of source rocks, reservoirs and cap rocks, we conducted a high-resolution cyclostratigraphic analysis of the Chang 8 Member stratigraphy. This study utilized gamma-ray (GR) well log series as the primary dataset. This lacustrine succession preserves distinct Milankovitch cycles, including similar to 405 ka long eccentricity, similar to 125 ka short eccentricity, obliquity, and precession periods, with eccentricity cycles showing particularly strong expression. These diagnostic eccentricity signals provided the framework for delineating high-frequency sequences. Subsequent astronomical tuning and base-level reconstruction constrain the depositional age of the Chang 8 Member to 242.22-241.23 +/- 1.4 Ma. During this interval, the lacustrine system exhibited a pronounced trend of base-level fall followed by rise, punctuated by higher-frequency fluctuations. Milankovitch cycles govern the development of high-quality reservoirs and cap rocks and organic enrichment by modulating climate and lake-level fluctuations. These orbital forcings drive weathering processes, control fluvial sediment supply and lacustrine accommodation space, and influence biological productivity. Our results demonstrate a pronounced association between the long eccentricity cycle (similar to 405 ka) and enhanced reservoir quality development, while the short eccentricity cycle (similar to 125 ka) exhibits a stronger correlation with organic matter enrichment, cap rocks, and source rock formation. Ultimately, the interplay of eccentricity cycles jointly governs the formation of the hydrocarbon system within the continental Chang 8 Member.

Lacustrine spits are one of the important hydrocarbon reservoir types, yet their formation mechanisms remain poorly understood, which has constrained further oil and gas exploration and development. This study aims to elucidate their formative processes and sedimentary evolution through investigations of modern lacustrine spits. The Erlangjian (Elj) spit at Qinghai Lake, located on the northeastern Qinghai-Tibetan Plateau, initially formed 2,370 yr BP and has continuously evolved to the present day. This spit serves as an ideal model for reconstructing the evolutionary history of lacustrine spits and understanding associated sediment transport. This study employs ground-penetrating-radar surveys, historical satellite images, and contemporary beach observations to investigate the formation and evolution of the lacustrine spit. Results indicate that lake-level variations control periodic changes in sediment supply and accommodation space, which strongly influence spit formation. Lateral accretion of the spit occurs due to the welding of sandbars during a low lake-level stage. As the lake level rises, large-scale recurved ridges develop on the low-stand-generated swash bars, resulting in vertical spit accretion. Sediments are sourced primarily from the southern proximal alluvial fan and are transported alongshore by wind-driven waves and currents. Additionally, changes in topography alter hydrodynamic conditions on the landward side of the spit, which in turn reshape the original spit. Thus, cyclical lake-level fluctuations are critical to the growth and complex architecture of spits in Qinghai Lake. This study contributes to a more comprehensive understanding of sedimentary evolution and sediment transport mechanisms for lacustrine spits.

Understanding cement paragenesis is crucial to the study of the porosity evolution in low-permeability sandstone reservoirs. Carbon and oxygen isotope analysis with micro-drilling sampling, electron probe microanalysis, and laser Raman spectroscopy microanalysis was used to clarify the origin of cements and their relationship with reservoir quality of the Chang 8 tight sandstone reservoir in the Longdong area of the Ordos Basin. The predominant cements are chlorite, illite, kaolinite, quartz, and carbonate, which occur in 3 forms: grain rim, overgrowth, and filling of intergranular pore and intragranular dissolved pore. The quantitative paragenesis of the cements is established based on the formation temperature of cements obtained through fluid inclusion, oxygen isotope, chemical composition and Raman parameters. The main source of carbon for carbonate cements is the decarboxylation of organic matter in the adjacent mudstone interlayers. The conversion of smectite to illite and the dissolution of feldspar and previous carbonates provide Ca2+, Mg2+, and Fe3+ ions for carbonate cements and authigenic chlorite, and the authigenic chlorite rim continuously grows from the grain surface outward. The porosity reduction by the cements mainly occurs during the main hydrocarbon filling period (80-120 degrees C), and the reservoir belongs to the type of "hydrocarbon accumulation prior to significant porosity reduction". This study provides a new approach for studying the temporal and spatial evolution of clastic rock diagenesis.

The clastic rocks of the Yanchang Formation in the Ordos Basin display poor physical properties but are rich in petroleum resources, exhibiting significant exploration potential. However, due to the existence of multiple sets of oil-bearing formations, hydrocarbon-generating formations, and a large longitudinal span, elucidating the correspondence between crude oil and source rocks is vital for further exploration. This study concentrates on the Lower Yanchang Formation of Triassic in the Yan'an area of the Ordos Basin, aiming to perform refined oil-source correlation. The findings indicate that the relative contents of diasteranes [DiaC27 beta alpha (20S + 20R), DiaC28 beta alpha (20S + 20R), and DiaC29 beta alpha (20S + 20R)] are instrumental in categorizing hydrocarbon sources. By examination of the biomarker characteristics of crude oils in the Lower Yanchang Formation, it is detected that there are variations in hydrocarbon source contributions across the Wuqi, Shunning, and Xihekou areas and among different formations. In conclusion, the oils within the lower assembly in the study area primarily originate from a composite source, which includes Chang-7 black mudstone in the center of the lake basin, Chang-9 black mudstone in the Wuqi region, and Chang-9 dark mudstone in other areas. The Chang-7 dark mudstone in other areas plays a minor role in the lower assembly crude oil genesis, while the Chang-10 dark mudstone has a negligible influence on the lower assembly oil source of the Yanchang Formation.

To predict the mobility of radiocesium (RCs) in the environment, it is essential to understand the adsorption and desorption processes. In this study, we focused on the effects of certain environmental factors, including typical cations (K + , Na + , and NH 4 + ) and low molecular weight organic acids (LMWOAs) such as acetic acid, malic acid, and citric acid on the behavior of RCs on montmorillonite and vermiculite. The results showed that montmorillonite possesses the strongest adsorption capacity for Cs + than that of vermiculite. Since K + and NH 4 + exhibit similar physicochemical properties to Cs + , there is a significant inhibition of Cs + adsorption on montmorillonite and vermiculite during the competitive interaction with K + and NH 4 + . Compared to NH 4 Cl, the desorption ratios of Cs + on montmorillonite and vermiculite are higher in the presence of KCl as the background solution. Low molecular weight organic acids can cover the surfaces of montmorillonite and vermiculite to different extents, which effectively blocks the adsorption sites for Cs + , and leads to an obvious decrease in the adsorption and desorption of Cs + . Due to the high expandable performance, Cs + is primarily reversibly adsorbed by montmorillonite. Nevertheless, the adsorption of Cs + on vermiculite exhibits typical irreversible characteristics due to the interlayer collapse. After the adsorption of LMWOAs on montmorillonite and vermiculite, the irreversible adsorption of Cs + is increased obviously, mainly due to the blocking effect of organic matters on the adsorption sites with high affinity to Cs + .

The Yanchang Formation, which records the whole evolutionary history of the Middle–Late Triassic lacustrine basin in the western part of the North China Block, provides an opportunity to understand the relationship between the tectono-sedimentary evolution and massive organic matter burial in lacustrine systems. The present study investigates the changes in the lithofacies association, provenance, regional tectonism, depositional environment, and organic matter accumulation in the lower-middle part of the Yanchang Formation, aiming to unravel their links. As a result of the rapid deepening of the southern Ordos Basin, the deposits in the depocenter of the basin shifted dramatically from shallow lacustrine sandstones of the lower part of the Yanchang Formation (i.e., Chang 8 Member) to deep lacustrine shales and gravity flow deposits of the middle part of the Yanchang Formation (i.e., Chang 7 Member). The provenance of the overlying Chang 7 Member is distinct from that of the underlying Chang 8 Member. It is proposed that crustal extension caused by the southwestward rollback of an oceanic slab in the eastern Paleo-Tethys may have triggered the rapid extensional subsidence in the southern Ordos Basin during the early Ladinian. In response to this deep geodynamic process, the depositional environment of the contemporaneous Ordos Basin changed significantly, as reflected by improved primary productivity, enhanced bottom-water anoxia, as well as reduced terrigenous clastic supply in the Ordos Lake. The coupling of these processes further led to the enrichment of organic matter in the Chang 7 Member.

The uptake of radiocesium (RCs) by plants is key to the assessment of its environmental risk. However, the transfer process of RCs in the water-vegetable system still remains unclear. In this work, the uptake and accumulation processes of Cs+ (0-10 mM) in lettuce were explored under different conditions by using hydroponics. The results showed that the higher exposure concentration of Cs+ could lead to a faster uptake rate and would be beneficial to the uptake and accumulation of Cs+. The uptake of K+ by roots and leaves was inhibited significantly when Cs+ concentration increased, but unapparent for Ca2+ and Mg2+. It was found that the higher K+ and Ca2+ concentration was, the higher inhibition was found for the uptake of Cs+ in root. The uptake of Cs+ leads the decrease of chlorophyll content and brought a negative effect on plant photosynthesis, consequently, a negative effect on lettuce morphology and obvious decrease of biomass and root length. The contents of glutathione (GSH), malondialdehyde (MDA), and root vitality were increasing during the growth following stress of high concentrations of Cs+, which caused stresses on the antioxidant system of lettuce. The enrichment coefficient for Cs+ in leaves was in the range of 8-217. Moreover, the transfer factor was in the range of 0.114-0.828, which suggested that the high Cs+ concentration could enhance the transfer of Cs+ from lettuce root to leaf. This study provides more information on the transfer of RCs from water to food chain, promoting the understanding of the potential risk of RCs.

Water, in ultra-deep layers of the earth and in layers receiving abnormally high heat, can exist in a supercritical state. Supercritical water (SCW) can participate in the transformations of organic compounds not only as a solvent but also as a reactant, influencing petroleum formation and the evolution of sedimentary organic matter. Here, we carried out hydrous pyrolysis experiments in both SCW and water vapor (WV) using two organic-rich marine rocks under closed conditions, to quantitatively evaluate the generation potential of hydrocarbons in a supercritical state and to clarify the effect of water phase on hydrous pyrolysis experiments. The results showed that SCW promoted gaseous and liquid hydrocarbon generation and facilitated the cracking of aliphatic hydrocarbons. For gaseous hydrocarbons, the action of SCW became stronger as the temperature increased. For liquid hydrocarbons, the peak yields of bitumen were enhanced by the SCW, and the temperature corresponding to peak yield in SCW was lower than that in WV. These results were attributed to the supply of hydrogen and oxygen from SCW for the petroleum formation and cracking. The δ13C and δD values of gases were also influenced by SCW. However, these values obtained in SCW did not always become positive as their yields increased. Generally, methane (CH4) was enriched in 12C and 1H. The influence of SCW on the isotopic fractionation of ethane (C2H6) and propane (C3H8) was more complex. The water phase is an important factor affecting the experimental results of hydrous pyrolysis. From these findings, it can be concluded that SCW allowed for increased conversion of sedimentary organic matter to gaseous and liquid hydrocarbons in ultra-deep layers and layers affected by volcanic-hydrothermal activity.

Lacustrine beach ridges are often used to reconstruct past lake levels. However, the sedimentary architecture involved in their sedimentary evolution remains unclear, particularly for embayed beaches. To better understand the sedimentary processes, the sedimentary architecture and geomorphology of an embayed beach on the southern of Qinghai Lake were investigated using ground penetrating radar (GPR), trenches, and modern beach observation. The embayed beach's deposits are composed of three major sedimentary facies: washover deposition, fair-weather swash deposition, and lagoonal deposition. According to the variations in sedimentary facies, the formation of the embayed beach can be divided into two stages: lake-level highstand and lake-level lowstand. During lake-level highstand stage, geomorphic changes primarily occur in the cross-shore direction. A single beach ridge with washover lobes and sheets developed along the entire embayed beach. During lake-level lowstand stage, the sediments are mainly transported alongshore within the embayed beach. The northern end shows progradational complex deposits including beach ridge, lagoon and beach system, while only a beach ridge is present at the southern end. Hydrodynamic changes in two stages lead to the heterogeneity of sediment distribution, reflected in the morphology and the sedimentary architecture. The interaction of topography and hydrodynamics controls the formation and evolution of the embayed beach. This study improves the understanding of the sedimentary processes involved in embayed beaches.

The Zhidan area in the Ordos Basin is enriched with unconventional hydrocarbon resources. However, there is a lack of research on oil–source correlation and specific petroleum secondary migration paths in the Chang 10 member, which restricts the exploration and development of petroleum resources in the area. Gas chromatography–mass spectrometry was used to determine the biomarker characteristics of 28 samples and the carbazole ratios of 14 oil sand extracts. Inductively coupled plasma–mass spectrometry was used to determine the rare earth element (REE) compositions of the oil sands and source rock extracts. Oil–source correlation analyses based on biomarkers and REE compositions were cross-validated, and the results showed that the Chang 10 oil in the study area originated from mixed source rocks of the Chang 7 and Chang 9 members, or from separate source rocks in either the Chang 7 or Chang 9 member. Based on the oil–source correlation, 11 secondary migration paths of Chang 10 oil were determined by applying carbazole parameters. The secondary migration path of oil shows that the Zhidan area's eastern part is the preferential oil accumulation area.

The uptake of radiocesium (RCs) by plants is key to the assessment of its environmental risk. However, the transfer process of RCs in the water-vegetable system still remains unclear. In this work, the uptake and accumulation processes of Cs + (0-10 mM) in lettuce were explored under different conditions by using hydroponics. The results showed that the higher exposure concentration of Cs + could lead to a faster uptake rate and would be beneficial to the uptake and accumulation of Cs + . The uptake of K + by roots and leaves was inhibited significantly when Cs + concentration increased, but unapparent for Ca 2+ and Mg 2+ . It was found that the higher K + and Ca 2+ concentration was, the higher inhibition was found for the uptake of Cs + in root. The uptake of Cs + leads the decrease of chlorophyll content and brought a negative effect on plant photosynthesis, consequently, a negative effect on lettuce morphology and obvious decrease of biomass and root length. The contents of glutathione (GSH), malondialdehyde (MDA), and root vitality were increasing during the growth following stress of high concentrations of Cs + , which caused stresses on the antioxidant system of lettuce. The enrichment coefficient for Cs + in leaves was in the range of 8-217. Moreover, the transfer factor was in the range of 0.114-0.828, which suggested that the high Cs + concentration could enhance the transfer of Cs + from lettuce root to leaf. This study provides more information on the transfer of RCs from water to food chain, promoting the understanding of the potential risk of RCs.

The concentric layers of ooids from the modern environment are mostly aragonite and those from the ancient are mostly calcite and Mg-calcite. Dolomitic ooids are rare and are usually formed via the replacement of aragonite or calcite. Here, dolomitic ooids were found in the Pliocene Shizigou Formation in the Qaidam Basin, Northern Tibet Plateau. This paper focuses on whether the dolomitic ooids is a primary precipitate. Optical microscope and scanning electron microscope observation, combined with X-ray diffraction and cathodoluminescence analyses, indicate that the primary mineral of the ooid cortices is poorly ordered dolomite. Extracellular polymeric substances and pyrite were found in the ooids, indicating that the microbe participation was involved in the formation of the ooids. Firstly, the ooids grow on the offshore lake floor. Due to the involvement of sulfate-reducing bacteria and dissolved silica, the nanominerals were precipitated on extracellular polymeric substances. Then, the ooids were transported to strong hydrodynamic surf zones, where the random nanominerals were abraded to form flattened plates as a new polished layer. In addition, a comparison between the carbon and oxygen isotopic compositions and minerals of ooids from different periods indicate that the Pliocene lakes had a lower salinity and were more humid than Pleistocene lakes. Therefore, ooids may be an effective proxy for reflecting the climatic change and uplift history of the Tibet Plateau.

Understanding the content, component features, and controlling factors of hydrocarbons in different occurrence states is a key element in assessing the resource potential, mobility, and engineering exploitability of shale oil. X-ray diffraction, bulk geochemistry, multi-isothermal stage pyrolysis experiments, and total hydrocarbon chromatographic analyses were performed on a set of muddy siltstone (MS), fine sandstone (FS), dark mudstone (DM), and black shale (BS) from the Chang 73 subsection in the Huachi area to investigate the content, component features, and controlling factors of hydrocarbons in different occurrence forms and estimate the shale oil engineering producibility under different production technical methods. The results show that the residual hydrocarbon content in FS, BS, MS, and DM decreased in turn. Mudstone and shale (Mu&Sh) samples featured lower quartz and chlorite contents as well as more pyrite and mixed layer I/S than siltstone and sandstone (Si&Sa) samples. Free and weakly adsorbed hydrocarbons constitute the mainstay of the hydrocarbons in BS and DM, while free hydrocarbons were dominant in MS and FS. The pyrolytic gases were chiefly CO2 and methane. The (Sat. + Aro.)/(Res. + Asp.) ratios and plagioclase and chlorite contents jointly show a positive effect on the free/adsorbed hydrocarbon ratios, while the TOC, clay mineral, and mixed layer I/S contents were inversely proportional. In general, geochemical features and mineral composition chiefly affect adsorbed hydrocarbon yields to control the free/adsorbed hydrocarbon ratio, the only exception of which is that the (Sat. + Aro.)/(Res. + Asp.) ratios affect free hydrocarbon yields. Si&Sa has good shale oil resource potential under volume fracturing because of its relatively high free hydrocarbon and brittle mineral contents and gas oil ratio. The weakly adsorbed hydrocarbons in Mu&Sh will be better transformed to the free state under pyrolysis conditions at 400 °C, which is more suitable for in situ heating conversion production. This study provides a new reference and basis for the occurrence and mobility evaluation of Chang 73 shale oil under different exploitation methods.

Ooids are coated carbonate grains, which exist in shallow water marine and lacustrine environments. There is an ongoing debate about whether the origin of ooids is inorganic or organic. Qinghai Lake is the largest inland lake in China, and ooids are seen on the lake shore. This paper focuses on whether environmental energy has an impact on the growth and size of ooids. Through hydrochemical analysis, thin section observation, and scanning electron microscope, the carbonate coats of beach sands from Qinghai Lake were studied. The research shows that the carbonate-coated grain content from the different shores of the lake present variations. The hydrodynamics and particularly the waves seem to control the distribution of carbonate coats in the lake shore, not the hydrochemical condition. In addition, the integrity and thickness of carbonate coats from the shores with a strong hydrodynamic force are high and thick, respectively. The carbonate coats are often observed on medium-grained sands, and the maximum carbonate-coated grain occurred under the strongest waves, indicating that ooids can be produced only when hydrodynamic force and particle size are well matched. Bacteria or extracellular polymeric substances are not observed within the ooid cortices by scanning electron microscopy. So, bacteria may not be a major factor in the formation and growth of ooids, but hydrodynamic forces appear to play a great role in carbonate grain coat distribution, integrity, thickness, and ooid grain size.

Understanding the content, component features, and controlling factors ofhydrocarbons in different occurrence states is a key element in assessing the resourcepotential, mobility, and engineering exploitability of shale oil. X-ray diffraction, bulkgeochemistry, multi-isothermal stage pyrolysis experiments, and total hydrocarbonchromatographic analyses were performed on a set of muddy siltstone (MS),finesandstone (FS), dark mudstone (DM), and black shale (BS) from the Chang 73subsection in the Huachi area to investigate the content, component features, andcontrolling factors of hydrocarbons in different occurrence forms and estimate the shaleoil engineering producibility under different production technical methods. The resultsshow that the residual hydrocarbon content in FS, BS, MS, and DM decreased in turn.Mudstone and shale (Mu&Sh) samples featured lower quartz and chlorite contents aswell as more pyrite and mixed layer I/S than siltstone and sandstone (Si&Sa) samples.Free and weakly adsorbed hydrocarbons constitute the mainstay of the hydrocarbons inBS and DM, while free hydrocarbons were dominant in MS and FS. The pyrolytic gaseswere chieflyCO2and methane. The (Sat. + Aro.)/(Res. + Asp.) ratios and plagioclase and chlorite contents jointly show a positiveeffect on the free/adsorbed hydrocarbon ratios, while the TOC, clay mineral, and mixed layer I/S contents were inverselyproportional. In general, geochemical features and mineral composition chieflyaffect adsorbed hydrocarbon yields to control thefree/adsorbed hydrocarbon ratio, the only exception of which is that the (Sat. + Aro.)/(Res. + Asp.) ratios affect free hydrocarbonyields. Si&Sa has good shale oil resource potential under volume fracturing because of its relatively high free hydrocarbon and brittlemineral contents and gas oil ratio. The weakly adsorbed hydrocarbons in Mu&Sh will be better transformed to the free state underpyrolysis conditions at 400 degrees C, which is more suitable for in situ heating conversion production. This study provides a new referenceand basis for the occurrence and mobility evaluation of Chang 73shale oil under different exploitation methods.

Organic matter enrichment in black shales has frequently been linked with hydrothermal activity. However, it is poorly understood how hydrothermal activity affected paleo-environments and the enrichment of organic matter in ancient lacustrine sediments. The hydrothermal activity recorded in the Middle Permian Lucaogou Formation (LCGF) in the Jimusar Sag, Junggar Basin, Northwest China, provides an ideal sedimentary archive to explore this issue. The mineralogical composition, major and trace element, total organic carbon, and sulfur content of forty-three shale samples of the LCGF were investigated to better understand how hydrothermal activity influences organic matter enrichment in lacustrine shales. The terrigenous influx, redox conditions, paleoproductivity, hydrothermal effects, and organic matter enrichment mechanisms are discussed. The results show that the terrigenous influx is insufficient overall, and the lower section of the LCGF has less detrital materials than the upper section. The redox conditions of the bottom water of the lake in the Jimusar Sag during deposition of the LCGF were suboxic to anoxic, which, combined with relatively high paleoproductivity, is favorable for organic matter enrichment. Hydrothermal activity occurred more frequently during deposition of the lower section compared with the upper section of LCGF. Hydrothermal fluids provided sufficient nutrients to enhance organic matter production during deposition of the LCGF and resulted in organic matter enrichment.

The provenance study of the sediments from Qinghai Lake is of great significance for the understanding of geological and climatic evolution processes of the Tibet Plateau on the one hand and for evaluating the controlling factors of the sediment components on the other hand. The samples were collected from five rivers, foreshore, beach, beach bar, and aeolian sand dune in the Qinghai Lake. The bulk geochemical composition, petrography, and mineralogy features of the samples are analyzed. The results show that: 1) Qinghai Lake sediments experienced low-intensity chemical weathering from the source areas to the deposition sites and were affected by some recycled detrital materials and 2) the source rocks for the sediments include felsic rocks (granite, granodiorite, and felsic volcanic rocks), carbonate, metamorphic rocks (marble and meta-volcanic rocks), and clastic rocks with the felsic source rocks to have the most important impact on the chemical compositions of the sediments. The geochemical indicator of Al2O3/TiO2 reflects that the provenance of fine-grained sediments from the center of Qinghai Lake is more mafic than the coarse-grained sediments from the margin of the Qinghai Lake, suggesting that the hydraulic sorting of grain size probably plays an important role in the geochemical compositions of the sediments. The mafic elements were probably preferentially enriched in muds.

Pore network modeling based on digital rock is employed to evaluate the mobility of shale oil in Qingshankou Formation, Songliao Basin, China. Computerized tomography technology is adopted in this work to reconstruct the digital rock of shale core. The pore network model is generated based on the computerized tomography data. We simulate the dynamics of fluid flow in a pore network model to evaluate the mobility of fluid in shale formation. The results show that the relative permeability of oil phase increases slowly in the initial stage of the displacement process, which is mainly caused by the poor continuity of the oil phase. In the later stages, with the increase in the oil phase continuity, the range of relative permeability increases. With the increase of organic matter content, the permeability of the water phase remains unchanged at low water saturation, but gradually increases at high water saturation. At the same time, it can be seen that, with the increase in organic matter content, the isosmotic point of the oil–water phase permeability shifts to the left, indicating that the wettability to water phase gradually weakens.