Search

Shale reservoirs contain petroleum that undergoes losses through oil expulsion and evaporation, with uncertain implications on shale oil reserves and mobility evaluation. This study focuses on understanding the influence of these losses on open‐system pyrolysis, the primary method for assessing shale oil content and mobility. Comprehensive analyses were performed on 26 lacustrine shale samples from the Chang7 Member, encompassing total organic carbon (TOC), programmed pyrolysis, solvent extraction, and gas chromatography–mass spectrometry (GC–MS). The research examines the impact of petroleum losses on petroleum fractions, the oil saturation index (OSI), and multi‐step pyrolysis outcomes. The findings indicate that Chang7 shale with TOC content above 7% experiences more substantial petroleum losses than those with TOC below 7%. Petroleum losses result in significant fractional distillation of crude oil in the shale, leading to the deterioration of shale oil properties and a notable reduction in free oil content in S1, ultimately causing a decline in OSI values. As a result, Chang7 shale with TOC below 7% demonstrates a higher potential for shale oil recovery, whereas Chang7 shale with TOC exceeding 7% should be considered more significant as a hydrocarbon source rock. Moreover, multi‐step pyrolysis is not suitable for assessing petroleum mobility in shale with low free oil content (OSI values below 100 mg/g). This limitation arises from the loss of free low‐boiling components in Chang7 shale, and the currently detected low‐boiling pyrolysis products may predominantly exist in an adsorbed state. [ABSTRACT FROM AUTHOR]

Ultra‐deep Sinian carbonate rocks are rich in natural gas, and the Deng‐4 Member of the Central Sichuan Basin has been shown to have an extremely high degree of thermal evolution. They are characterized by dry gas produced due to the thermal cracking of palaeo‐oil reservoirs (PORs). The distribution of PORs as materials for the formation of cracked gas reservoirs remains unclear. The complex multistage evolution process and limited drilling data make it challenging to precisely and systematically recover a range of PORs. Based on basin and petroleum system modelling (BPSM), the bottom‐up migration and accumulation method was used to investigate the distribution of PORs. Research shows that the PORs in the Sinian Deng‐4 Member were mainly formed in the Early–Middle Triassic under the mixed contribution of Cambrian and Sinian source rocks, and the coupling of palaeostructural and trap settings controlled its accumulation. Generally, the distribution of PORs can be divided into two categories: one is located at the core of the uplift zone and is controlled by structural‐stratigraphic composite traps, whereas the other is controlled by a series of lithologic traps formed in the slope area. Sensitivity analysis showed that the distribution patterns of the PORs were mostly related to the facies conditions (physical characteristics) of the reservoirs. The widely distributed PORs provide necessary and sufficient material conditions for the formation of cracked Sinian gas reservoirs in the Central Sichuan Basin, and the North Slope area has great potential for natural gas exploration in the future. [ABSTRACT FROM AUTHOR]

Network embedding aspires to learn a low‐dimensional vector of each node in networks, which can apply to diverse data mining tasks. In real‐life, many networks include rich attributes and temporal information. However, most existing embedding approaches ignore either temporal information or network attributes. A self‐attention based architecture using higher‐order weights and node attributes for both static and temporal attributed network embedding is presented in this article. A random walk sampling algorithm based on higher‐order weights and node attributes to capture network topological features is presented. For static attributed networks, the algorithm incorporates first‐order to k‐order weights, and node attribute similarities into one weighted graph to preserve topological features of networks. For temporal attribute networks, the algorithm incorporates previous snapshots of networks containing first‐order to k‐order weights, and nodes attribute similarities into one weighted graph. In addition, the algorithm utilises a damping factor to ensure that the more recent snapshots allocate a greater weight. Attribute features are then incorporated into topological features. Next, the authors adopt the most advanced architecture, Self‐Attention Networks, to learn node representations. Experimental results on node classification of static attributed networks and link prediction of temporal attributed networks reveal that our proposed approach is competitive against diverse state‐of‐the‐art baseline approaches. [ABSTRACT FROM AUTHOR]

The Upper Triassic Chang 7 Member lacustrine organic-rich shale of the Yanchang Formation of the Ordos Basin is a significant hydrocarbon source rock containing abundant of tuff intervals ranging from millimeters to tens of centimeters thick. The present study relies upon petrographic and geochemical data of Chang 7 tuff intervals and organic-rich shale to consider fertilization of the lake surface by volcanic debris as a triggering mechanism of black shale sedimentation. Paleoproductivity proxies, including P/Al, Ni/Al, and Cu/Al, display elevated values in association with tuff intervals, suggesting increased productivity induced by volcanic nutrient seeding of the lake surface. Moreover, vertical variations of TOC mimic trends of paleoproductivity proxies, indicating that primary productivity was critical to organic carbon enrichment of the Chang 7 Member. Previous studies have postulated that lake bottom redox conditions were predominantly oxic--suboxic during deposition of the Chang7and that these deposits accumulated slowly, neitherofwhich would have favored the export and preservation of organic matter in the absence of enhanced productivity. Accumulation of the organic-rich Chang 7 shale demonstrates the critical role that intensified primary productivity triggered by volcanism can play in the accumulation of carbonaceous sediment.Le shale lacustre riche en matiere organique du membre Chang 7 du Trias superieur de la Formation de Yanchang du bassin d'Ordos est une importante roche-mere d'hydrocarbures renfermant d'abondants intervalles de tuf d'epaisseur millime-trique a decimetrique. Nous utilisons des donnees petrographiques et geochimiques d'intervalles de tuf et de shale riche en matiere organique du membre Chang 7 pour examiner la fertilisation de la surface de lacs par des debris volcaniques comme mecanisme declencheur du depot de shale noir. Des variables substitutives de la paleoproductivite, dont les rapports P/Al, Ni/Al et Cu/Al, presentent des valeurs elevees associees aux intervalles de tuf, ce qui indiquerait une productivite accrue induite par l'ensemencement de la surface de lacs par des nutriments d'origine volcanique. Les variations verticales du COT suivent en outre les tendances des variables de paleoproductivite, ce qui indique que la productivite primaire jouait un role cle dans l'enrichissement en carbone organique du membre Chang 7. Des etudes anterieures ont postule que les conditions d'oxydoreduction du fond des lacs etaient principalement oxiques a suboxiques durant le depot du membre Chang 7 et que ces sediments se sont accumules lentement, ni l'une ni l'autre de ces situations ne favorisant l'exportation et la preservation de matiere organique en l'absence d'une productivite accrue. L'accumulation du shale riche en matiere organique du membre Chang 7 demontre le role cle que l'intensification de la productivite primaire causee par le volcanisme peut jouer dans l'accumulation de sediments carbones. [Traduit par la Redaction], IntroductionThe association of volcanic ash deposits or tuff intervals and organic-rich hydrocarbon source rocks has been described from basins of various ages and locations (Dawson 2000; Su et al. 2003; [...]

The organic matter (OM) enrichment mechanisms and depositional environment characteristics of lacustrine source rocks in the western Bozhong Sag, Bohai Bay Basin in Northeast China remain controversial. To address these issues, based on Rock‐Eval pyrolysis, kerogen macerals, H/C and O/C ratios, GC‐MS, major and trace elements, the Dongying Formation Member (Mbr) 3 (E3d3), the Shahejie Formation mbrs 1 and 2 (E2s1+2), and the Shahejie Mbr 3 (E2s3) source rocks in the western Bozhong Sag were studied. The above methods were used to reveal their geochemical properties, OM origins and depositional environments, all of which indicate that E2s1+2 and E2s3 are excellent source rocks, and that E3d3 is of the second good quality. E3d3 source rocks were formed under a warm and humid climate, mainly belong to fluvial/delta facies, the E3d3 sediments formed under weakly oxidizing and freshwater conditions. Comparatively, the depositional environments of E2s1+2 source rocks were arid and cold climate, representing saline or freshwater lacustrine facies, and the sediments of E2s1+2 belong to anoxic or suboxic settings with large evaporation and salinity. During the period of E2s3, the climate became warm and humid, indicating the freshwater lacustrine facies, and E2s3 was characterized by freshwater and abundant algae. Moreover, compared with other intervals, the OM origin of E3d3 source rocks has noticeable terrestrial input. The OM origin of the E2s1+2 and E2s3 are mainly plankton and bacteria. Tectonic subsidence and climate change have affected the changes of the depositional environment in the western Bozhong Sag, thus controlling the distribution of the source rocks, the geochemical characteristics in the three intervals of lacustrine source rocks have distinct differences. Overall, these factors are effective to evaluate the paleoenvironmental characteristics of source rocks by biomarkers, major and trace elements. The established models may have positive implications for research of lacustrine source rocks in offshore areas with few drillings. [ABSTRACT FROM AUTHOR]