Paleoenvironmental conditions significantly influence the distribution patterns and organic matter enrichment of shale. This study investigated the vertical variations of major elements, trace elements, and total organic carbon (TOC) in the Lower Carboniferous marine shale from the Yaziluo Rift Trough, South China, to understand the paleoenvironmental conditions, including redox conditions, terrigenous detrital input, paleoproductivity, and paleo-seawater depth. The Lower Carboniferous formation consists of three sedimentary facies: basin facies, lower slope facies, and upper slope facies. From the basin to the lower slope and then to the upper slope facies, TOC, quartz, and pyrite contents gradually decrease, whereas the carbonate mineral content shows an increasing trend. A continuous decline in paleo-seawater depth transformed a deep-water anoxic environment with high paleoproductivity and low detrital input in the basin facies into a semi-deep-water environment with dysoxic-oxic conditions and moderate detrital influx in the lower slope facies, evolving further into a suboxic environment with high detrital flux in the upper slope facies. The geochemistry results suggest that anoxic conditions and high paleoproductivity were the primary controls on organic matter enrichment in the siliceous shale of the basin facies. In contrast, redox conditions significantly influenced organic matter accumulation in the mixed shale of the lower slope facies, attributed to relatively low paleoproductivity in a more restricted marine setting. Additionally, the adsorption of carbon components by clay minerals facilitated the preservation of organic matter in the calcareous shale of the upper slope facies.

The reliability of bulk geochemical proxies for provenance analysis in heterogeneous clastic systems remains a critical yet underexplored issue. This study investigates the Lower Permian Shanxi Formation in the Southern North China Basin (SNCB) using an integrated approach combining major and trace element geochemistry, rare earth elements (REEs), and detrital zircon U–Pb geochronology. The results show that major element compositions have been significantly modified by diagenetic processes in tidal flat environments, limiting their applicability in tectonic discrimination. In contrast, immobile trace elements and REE patterns provide more robust constraints on source rock composition, suggesting predominantly felsic upper continental crustal sources. Detrital zircon age spectra reveal two dominant populations at 290–440 Ma and 1800–2500 Ma, indicating mixed provenance from the North Qinling Region (NQR) and the North China Craton (NCC). However, the application of classical discrimination diagrams is challenged by lithological heterogeneity, as the mixed presence of sandstone, sandy mudstone, and mudstone introduces compositional bias. Spatial variations among wells suggest differential contributions from continental island arc and active continental margin, likely controlled by paleogeographic configuration and sediment transport pathways. This study emphasizes the necessity of multi-proxy integration for reliable provenance reconstruction in complex sedimentary systems.

Natural fractures serve as important storage spaces and primary flow channels in hydrocarbon reservoirs. However, fracture identification using conventional well logs remains challenging due to complex logging responses and the limited number of fracture samples. Logging responses exhibit two important characteristics: different logging variables show complex nonlinear relationships, while fracture-related anomalies tend to vary continuously within local depth intervals. Motivated by these characteristics, an intelligent fracture prediction method based on a hybrid iTransformer-LSTM network combined with Gaussian Mixture Model (GMM)-based sample augmentation is proposed. The iTransformer module is used to capture inter-feature dependencies among different logging variables, while the LSTM module further models sequential variations along the depth direction. In addition, GMM-based sample augmentation is applied to the training fracture samples to learn their multivariate distribution and generate statistically consistent synthetic samples, thereby alleviating the influence of limited fracture samples. The proposed method was evaluated on two wells from the C7 target interval. On the WELL1 test set, it achieved an accuracy of $0.714\pm 0.038$, a Macro-F1 score of $0.708\pm 0.093$, and an AUC of $0.816\pm 0.042$. On the independent WELL2 blind well, it achieved an accuracy of $0.816\pm 0.093$, a Macro-F1 score of $0.502\pm 0.034$, an AUC of $0.734\pm 0.016$, and a fracture recall of $0.813\pm 0.163$. These results suggest potential for fracture identification under highly imbalanced conditions.

China has focused on the exploration and development of shale gas resources to reduce its reliance on coal and shift to cleaner energy sources. While significant progress has been made in the Sichuan Basin, unlocking the shale gas potential in other regions of South China has proven challenging due to the complex geology and mountainous terrain. In 2021, Well QSD-1 was deployed in southwestern Guizhou and achieved a daily shale gas flow of 11,011 m³ in the Dawuba Formation, marking the first time an industrial gas flow had been obtained from shale gas drilling in the marine strata of the Upper Paleozoic in China. This breakthrough has deepened the understanding of the southern China Carboniferous marine strata and highlighted key aspects of the formation: (1) Sedimentation occurred in alternating platforms and basins, with most organic-rich shale developed in sloping and basin areas; (2) the formation exhibits favorable static indicators, with a relatively thick section (over 200 m), and an organic carbon content of approximately 1%; (3) the intercalation of argillaceous limestone and shale intervals is conducive to the preservation of shale gas within the formation. These results demonstrate the potential for the Upper Paleozoic in South China to become a significant shale gas producer, which could contribute significantly to China’s energy security. Furthermore, exploring shale gas in the region may have positive economic and environmental impacts, including reducing China’s dependence on coal and decreasing greenhouse gas emissions.