Causes and predictability of the extreme heatwave over the Sichuan Basin in Late Summer 2024

Evolution of pore structure and methane adsorption in thermally matured shales: A case study of low-mature Dalong shale in Sichuan Basin, China

Over the past two decades, despite significant fluctuations in China's soybean planting area, high-resolution assessments quantifying the spatially heterogeneous and nonlinear impacts of compounding economic, climatic, and policy drivers remain scarce. To fill this gap, this study uses satellite remote sensing data (2000–2022) to map 1 km gridded soybean areas across China’s three main producing regions: the Northeast China Plain (NEP), Huang-Huai and Middle-Lower Yangtze Plains (HH-MLYP), and Sichuan Basin (SCB). Integrating yield and cost‒price data, we calculated the comparative economic benefit (CEB) between soybean and maize. A random forest model with SHapley additive explanations (SHAP) quantified the contributions of CEB, climatic, and topographical variables. Results revealed that CEB, growing season precipitation, and growing degree days were the most influential drivers, explaining 14.88%, 14.47%, and 13.70% of area variation, respectively. These impacts exhibit strong spatial heterogeneity: economic factors dominate in the NEP, whereas climate is more critical in the HH-MLYP and SCB. Subsidy policies effectively expanded planting in the NEP, despite diminishing marginal effects. These findings provide a scientific basis for optimizing planting strategies and designing targeted subsidies.

In-situ constraints on the occurrence and mineralization of critical elements in Late Triassic coals from the Sichuan Basin, China

High-resolution imaging of the seismogenic fault of three earthquakes in Luxian, Sichuan Basin, China, from data recorded by dense linear arrays and methane sources

Shifting relative importance of vegetation filtering and cold trapping in PCB deposition along a 1000 km transect toward the Qinghai-Tibet Plateau.

Structural characteristics and evolution processes of intracratonic strike-slip fault systems: A case from central Sichuan Basin, SW China

Fluid sources and formation mechanisms of fracture veins in the Upper Ordovician-Lower Silurian Wufeng-Longmaxi shales, southeastern Sichuan Basin, China

Microbial communities inhabiting hydraulically fractured subsurface waters are increasingly recognized as important components of unconventional oil and gas systems because they can influence water quality, infrastructure integrity, and biogeochemical processes during flowback and production. However, a quantitative cross-basin understanding of their taxonomic diversity, ecological organization, and potential functional variation remains limited. In this study, we analyzed 16S rRNA gene amplicons, metagenomes, and geochemical data from flowback and produced water (FPW) from the Sichuan Basin, China, and conducted a quantitative comparison to data previously reported from the same basin and hydraulic fracturing (HF) regions in North America. Our findings revealed strong co-occurrence patterns among fermentative, sulfidogenic, and methanogenic microorganisms, which emerged as core members of microbial communities across all fractured subsurface environments. Notably, microbial diversity and selected metabolic traits differed across basins in the low-salinity systems of China, whereas high-salinity basins in North America exhibited reduced diversity and more constrained metabolic capabilities. These differences are consistent with salinity acting as an important ecological filter across the analyzed basins. Our results indicate that basin-specific geochemical context, particularly salinity, is closely associated with cross-basin differences in microbial diversity, community composition, and selected metabolic traits in fractured subsurface waters. These findings support the value of integrating geological, geochemical, and microbiological information when interpreting microbial risks and water-management strategies in hydraulic fracturing systems.

The Gufeng Formation of the Permian in the northern Sichuan Basin hosts a high-carbonate shale reservoir, representing a key emerging target for unconventional gas exploration in the basin. However, the mechanisms governing organic pore development in this unit remain poorly understood. In this study, samples from the Gufeng and Longmaxi formations were analyzed using organic petrology, scanning electron microscopy (SEM), and nitrogen adsorption experiments. Three groups of samples were prepared for comparative treatment: original, chloroform-extracted, and acid-treated. This approach enabled a comparative assessment of the integrated effects of bioprecursor types, early cementation, bitumen filling, and mineral-organic interactions on organic pore development. The main findings are as follows: (1) bioprecursor types control the characteristics of kerogen-hosted pore development. Benthic algae retain a relatively complete biological structure, with well-developed internal pores (>100 nm). In contrast, pores developed in planktonic algae are concentrated in the 10-50 nm range. The Gufeng Formation contains a higher proportion of planktonic algae (>30%), resulting in lower kerogen pore-generation potential compared to the Longmaxi Formation. (2) Cementation and bitumen infilling cause significant damage to organic pores. In the Gufeng Formation, microcrystalline calcite infilling occurs within various kerogen types, leading to over 60% loss of mesopores and macropores. Additionally, during the oil window stage, bitumen primarily fills pores <10 nm, causing a further 7-12% pore loss. Although bitumen-hosted pores in the Gufeng Formation increase with maturity (Ro 0.7-2.0%), pore volume shows no significant correlation with Ro, reflecting the combined effects of early cementation and bitumen infilling. (3) Mineral-organic interactions induce differentiation in organic pore development. In the Longmaxi Formation, clay minerals promote hydrocarbon generation and pore formation in mineral-associated organic matter through an "adsorption-catalysis" mechanism, resulting in well-developed organic pores. In the Gufeng Formation, Lewis acid sites on carbonate mineral surfaces may promote early hydrocarbon generation, but they cannot sustain continuous pore development during mid-to-late hydrocarbon generation stages. Surface complexation enhances the thermal stability of organic matter, thereby delaying hydrocarbon generation and organic pore development. This study reveals a multifactor synergistic mechanism responsible for limited organic pore development in carbonate-rich shales, providing a new perspective for reservoir evaluation and favorable target selection in high-to-overmature carbonate-rich shale systems.

During the development of shale gas fields, horizontal wells drilling through highly fractured shale formations are prone to drilling abnormal conditions such as borehole collapse and lost circulation, which significantly increase drilling risks and operational complexity. Therefore, this study investigates the shale of the Wufeng-Longmaxi Formations in the Sichuan Basin to identify the specific intervals where highly fractured shale develops and their development characteristics by analyzing data from drilling, logging while drilling (LWD), wireline logging, and core analysis. Furthermore, it analyzes the generation mechanism of highly fractured shale and the induced causes of drilling abnormal conditions, and develops a real-time drilling identification method based on LWD technology. The study shows that the top interval of the Wufeng Formation belongs to highly fractured shale, characterized by frequent abnormal conditions and a low gas production contribution rate. Moreover, bedding fractures at the top of the Wufeng Formation are more developed than those in the overlying Longmaxi Formation, and the Wufeng Formation exhibits stronger heterogeneity relative to the Longmaxi Formation. This leads to discontinuous or uneven rock strength where fractures develop or lithology changes drastically, making the rock mass susceptible to fracturing when the external environment changes, thereby forming highly fractured shale. Based on the LWD response characteristics of highly fractured shale, a mechanical specific energy (MSE) evaluation model can be established using drilling engineering theory. Combining this model with near-bit and far-bit γ ray (GR) and gas show parameters can effectively identify highly fractured shale, and the feasibility of this method is verified through field cases. The study results can meet the needs of field engineers for real-time evaluation, providing a new method and technical approach for the evaluation of highly fractured formations.

Contrasting 2001 and 2020 land cover states: Impacts on heterogeneous HONO chemistry and nitrate formation in China.

Nitrogen-containing organic aerosols (NOAs) significantly affect air quality and climate, but their formation mechanisms remain unclear. Here, we investigated the chemical characteristics and light absorption of water-soluble NOA (WSOAN) in PM2.5 from three Sichuan Basin cities of China, Chengdu, Yibin, and Nanchong, during winter 2023, to elucidate both regional consistence and intercity differences of WSOAN formation. Our results showed that the water-soluble organic nitrogen (WSON) of PM2.5 was 0.8-1.0 μg N m-3, and WSOAN accounted for 15.4-38.4% of WSOA. Four WSOAN subclass fragments (amines, amides, amino acids, and imidazoles (IMs)) were identified. The concentration of IMs increased by 1.3-1.4 times during the regional heavy haze event (HHE). Aqueous secondary formation dominated WSOAN production during HHE, contributing 45-58% of total WSON. Chengdu showed a much lower apparent IMs yield than Yibin and Nanchong, mainly due to stronger aerosol acidity and higher levels of dicarbonyls and aerosol liquid water. WSOA light absorption at λ365nm increased linearly with WSON, with a larger slope in Yibin and Nanchong, indicating a stronger light-absorbing of WSOAN in the two cities. Our study revealed abundant NOA pollution in inland China, which is strongly light-absorbing and largely produced from aerosol aqueous-phase reactions.

Atmospheric circulation and local meteorology strongly influence the transport and evolution of volatile organic compounds (VOCs) in mountainous environments, yet their vertical distribution and controlling factors in southwest China remain poorly characterized. Here, we conducted synchronous online measurements of VOCs and related air pollutants at the foot (550m a.s.l.) and top (2119m a.s.l.) of Mt. Fanjing during autumn and winter 2024, providing a rare side-by-side characterization of VOCs under contrasting atmospheric conditions in the background region of the Yunnan-Guizhou Plateau. The mean VOC concentration at the mountain top was 14.1 ± 4.8 ppbv, 17.5% lower than that at the mountain foot. Source apportionment showed that vehicles, biomass burning, and industrial-related sources together contributed more than 50% of VOCs at the foot site, whereas the relative contributions of aged traffic plume and solvent evaporation increased at the mountain top, reflecting the combined influence of transport and atmospheric processing. Elevated VOC species at both sites were mainly associated with emissions from the border region of Guizhou, Hunan, and Chongqing, in agreement with the emission inventory analysis. Mt. Fanjing was primarily affected by easterly and westerly background winds. Under westerly background conditions, air masses passing through the Sichuan Basin, Chongqing, and Yunnan enhanced the vertical gradient of VOCs at Mt. Fanjing and increased near-surface VOC accumulation, particularly during periods with pronounced diurnal evolution of local circulation. These results demonstrate that the vertical contrast in VOCs over Mt. Fanjing is jointly controlled by regional transport, background wind regimes, and thermally driven local circulation. The findings highlight that elevated mountain sites cannot be regarded simply as clean background environments and have important implications for regional air-quality assessment, ozone and secondary aerosol formation, and pollutant exposure in mountainous and ecologically sensitive areas.

Sinian microbialites represent crucial archives for investigating the co-evolution of life and the environment after the Marinoan glaciation, but their porous facies also form significant hydrocarbon reservoirs worldwide. The giant gas accumulation in the fourth member of the Upper Sinian Dengying Formation (Deng-4 Member, Z2dn4) in the Penglai area, Sichuan Basin, is hosted within such a reservoir. Reservoir development, however, is constrained by a complex interplay of tectono-sedimentary factors, generating notable heterogeneity. To elucidate the depositional model and the corresponding reservoir control mechanisms, this study presents a systematic analysis integrating core descriptions, petrographic thin sections, petrophysical measurements, and geophysical surveys. This investigation establishes a 'step-like carbonate platform' depositional model for the Deng-4 Member. The model reveals a multi-level, step-like palaeogeomorphic framework. This framework was shaped by the interplay of near north-south trending relict escarpments formed during earlier tectonic movements, and slope breaks created by near east-west trending, syn-sedimentary strike-slip faults. This complex palaeogeomorphology governed the type, evolution, and spatial arrangement of sedimentary facies, which in turn controlled the reservoir development and heterogeneity. This control operated through three principal mechanisms: Firstly, the sedimentary facies determined the origin and assemblages of pore spaces. Microbial mounds developed framework and vuggy porosity, enhanced by later bedding-parallel and honeycomb-like dissolution vugs. In contrast, grain shoals generated a 'pin-point' pore system comprising intergranular and intragranular dissolution pores. The inter-mound sea facies, composed of dense micritic dolomite, lacks effective reservoir space. Secondly, the facies framework directed the spatio-temporal differentiation of reservoir properties. The Deng-4 Member constitutes a single shallowing-upward depositional sequence, transitioning from relatively deeper-water grain shoals in the lower sub-member to widespread shallower-water microbial mounds in the upper sub-member. The vertical facies succession forced the locus of premium reservoir quality to migrate from the lower grain shoals to the upper microbial mounds. Thirdly, the sedimentary facies controlled the macroscopic reservoir distribution. The thickest effective reservoir zones correspond spatially to the dominant facies in each interval, matching the grain shoal distribution in the lower sub-member and the extensive microbial mound belts in the upper sub-member. The proposed depositional model provides a robust geological framework for predicting high-quality sweet spots in complex, deep to ultra-deep carbonate reservoirs.

Urban greenness and heavy PM2.5 events in China: A national long-term panel study on burden, severity, and within-event dynamics.

Summary As a major high-sulfur natural gas province in China, the Sichuan Basin frequently experiences severe tubing corrosion in producing wells due to the coexistence of H2S and CO2. Especially in high-temperature, high-pressure gas reservoirs with medium concentrations of H2S/CO2, such as the M Block in central Sichuan, corrosion-induced tubing failure and wellbore plugging have severely affected the long-term safe production and economic development of gas wells. Despite extensive studies on single-gas corrosion and mixed-corrosive environments, reliable models that accurately predict the H2S-CO2 synergistic corrosion rate under representative wellbore conditions remain scarce. To this end, this study takes the MX-X11 well in the M block as a case example. First, through wall thickness measurements of the entire well section of the tubing, combined with X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS), the corrosion mechanism of the tubing under the synergistic effect of H2S and CO2 was analyzed. Subsequently, a semiempirical corrosion rate prediction model considering temperature-pressure coupling was established, and the influencing factors of corrosion were simulated and analyzed. On this basis, a corrosion rate prediction model is developed and integrated with coupled temperature-pressure profiles to enable corrosion prediction along the wellbore. The results demonstrate that the tubing corrosion rate exhibits strong depth dependence. Corrosion products vary systematically with depth, indicating distinct corrosion regimes. In shallow intervals, corrosion products are dominated by FeS2, indicating an H2S-dominated environment. In deeper intervals, the products progressively shift to FeCO3, accompanied by FeS and Fe3O4, suggesting an increasing contribution from CO2-driven corrosion. By quantifying the synergistic effects of H2S and CO2 partial pressures, a corrosion rate prediction model incorporating both gases’ partial pressure terms is established. The model captures corrosion behavior across a wide range of partial pressure conditions and yields corrosion rate profiles that are generally consistent with field-derived average corrosion rates from the MX-X11 well. In addition, the proposed corrosion rate model is coupled with a tubing temperature-pressure model to simulate corrosion behavior under different operating conditions. Temperature exerts a pronounced effect on corrosion rate: The rate is low at lower temperatures, increases with temperature, and is suppressed at higher temperatures due to the formation of a dense corrosion product film. With respect to gas partial pressures, the interaction between H2S and CO2 significantly affects the corrosion rate. Different partial pressure ratios promote corrosion product films with different compositions, thereby modifying corrosion kinetics. These findings provide a scientific basis for predicting tubing corrosion in the M Block of the Sichuan Basin and in comparable sour gas reservoirs, supporting full life cycle corrosion management of tubing systems. Further optimization and independent validation of the proposed model using additional wells will enable more robust guidance for corrosion mitigation in oil and gas fields. It should be noted that the corrosion rate prediction model proposed in this study is primarily applicable to the prediction of uniform corrosion rates. For the evaluation of localized pitting corrosion in practical engineering, pitting depth measurements should still be incorporated.

Late Paleozoic stratigraphic hiatuses and carbon isotope chemostratigraphy in the northwestern Sichuan Basin: Implications for the Tectono-sedimentary evolution of the Eastern Tethyan

The genesis and source of tight sandstone gas in the third member of Xujiahe Formation in Zitong Sag, NW Sichuan Basin: Constraints from geochemical evidence

Absolute ages of multiple deformation events in the eastern Sichuan Basin by U–Pb dating of slickenfiber calcite