中国石油

The molecular-level differentiation characteristics and genetic mechanisms between expelled and retained oils in saline lacustrine shale remain poorly constrained, which restricts the accurate evaluation of in-situ shale oil accumulation potential. To fill this research gap, the objectives are to reveal the molecular geochemical differences between expelled and retained oils during thermal evolution and establish a valid discriminant system for saline lacustrine shale oil. Taking the Lower Ganchaigou Formation (E-3(2)) shale of the Qaidam Basin as the research object, we adopted semi-closed pyrolysis simulation combined with gas chromatography-mass spectrometry (GC-MS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to conduct systematic molecular geochemical analysis across a wide thermal maturity range (Ro = 0.54%-2.74%).Obvious molecular differentiation signatures between retained and expelled oils are identified. Retained oil is featured by a low Sigma nC(21)(-)/Sigma nC(22)(+) ratio, high C-29 regular sterane proportion, lagged sterane isomerization (C-29-20S/(20S + 20R) < 0.33; C-29-alpha beta beta/(alpha alpha alpha + alpha beta beta) < 0.28), bimodal double bond equivalent (DBE) distribution of N-1 heteroatomic compounds (peaks at DBE = 9 and 12), and a sharp increase in 4-MDBT/1-MDBT ratio (up to 19.73) at high maturity. In contrast, expelled oil is enriched in light saturated hydrocarbons, characterized by a high Sigma nC(21)(-)/Sigma nC(22)(+) ratio, dominant low-DBE (DBE = 1) O-2 compounds (accounting for up to 74.7%), and no abnormal elevation of 4-MDBT/1-MDBT ratio. Small-molecule, low-polarity components (light n-alkanes, low-DBE O-2 compounds) are preferentially expelled owing to high fluid mobility, whereas large-molecule, polar components (heavy hydrocarbons, high-DBE N-1 compounds) are trapped in shale reservoirs. For retained oil, the confined nanoscale pore environment restricts sterane conformational rotation (leading to maturity lag effect) and promotes selective methyl cleavage in dibenzothiophenes. Additionally, the favorable in-situ shale oil accumulation window of E-3(2) shale is determined as Ro = 0.7%-1.0%, with quantitative thresholds of retained oil content > 200 mg/g and N-1 class relative abundance of 25%-59%. This study establishes the first molecular discriminant system for expelled and retained oils in saline lacustrine sedimentary environments, clarifies the multi-factor controlled differential evolution mechanism, and provides key theoretical support and practical indicators for shale oil exploration and sweet spot evaluation in the Qaidam Basin and other similar saline lacustrine basins worldwide.

Developing multifunctional aerogels with simultaneously ultralow thermal conductivity, exceptional mechanical robustness, and scalable processability remains a formidable challenge for advanced thermal management in lithium-ion batteries (LIBs). Herein, we report a three-dimensional (3D) networked BMS (boric acid/melamine/SiO2) aerogel featuring radially aligned SiO2 frameworks, fabricated via an in situ sol-gel method coupled with freeze-drying. The radial alignment of SiO2 nanofibers along the preformed aerogel matrix leads to a unique three-dimensional interconnected porous architecture reinforced by synergistic Si-O-Si covalent bonds and hydrogen bonding networks. This structural design not only enhances the load-bearing capacity of the fibrous skeleton but also dramatically extends the heat transfer path for phonons and reduces solid-phase heat conduction, resulting in a low thermal conductivity of 0.0395 W/m & centerdot;K and a low density of 0.0615 g/cm3. The stabilized SiO2 frameworks further improve thermal stability upon thermal decomposition of the organic components. In addition, the incorporation of phase change materials (PCMs) enhances the thermal buffering performance of the BMS aerogel without compromising its porosity, enabling a significant reduction in the battery surface temperature at discharge rates of 1.5 C and 2 C. During nine consecutive cycles of 2 C discharge, a 1 mm-thick BMS/PEG composite phase change material (cPCM) layer achieves a maximum peak temperature reduction of 5.5 degrees C. This work presents a robust and scalable strategy for the design of high-performance aerogel-based thermal regulators, which exhibit excellent flame retardancy and thermal insulation performance.

Interactions between extracellular polymeric substances (EPS) and clay minerals promote the aggregation of mineral particles. The aggregation process is influenced by various crystal structures of clay minerals. In this study, we conducted a 30-day incubation by using Rhodotorula mucilaginosa (Rho, a fungus with a high ability to produce EPS) and two types of clay minerals, i.e., the layered montmorillonite (Mt) and the fibrous palygorskite (Pal). The D50 size of Mt consistently increased from 55.6 mu m (Mt@CK) to 127.0 mu m (Mt@30d). Meanwhile, evident yellow-red growth clusters gradually appeared after the addition of montmorillonite. This phenomenon is likely attributed to the promotion of fungal growth by the layered structure of montmorillonite. In contrast, after the addition of palygorskite, the D50 size of Pal slightly decreased from 50.6 mu m (Pal@CK) to 33.9 mu m (Pal@10d). This decrease was likely due to the sorption of relatively small fibrous palygorskite particles that restricted fungal nutrient intake. In addition, ATR-FTIR spectra confirmed the intense adsorption of EPS onto the montmorillonite particles. Evident shifts were clearly observed in the FTIR spectra of the Mt@20d and Mt@30d samples. Moreover, the intense symmetric COO- stretching vibrations (1318 cm-1) indicated that a polysaccharide-montmorillonite complex was formed. At the genetic level, the STE7 and STE11 genes (which facilitate EPS secretion) exhibited higher levels of upregulation in the treatment with the addition of montmorillonite than in that with palygorskite. These findings provide new insights into the roles of different clay minerals during the fungal-assisted aggregation process.

The inherent thermal dissipation during long-distance CO2 pipeline transport poses significant challenges to operational safety and efficiency, particularly regarding hydrate formation and pipeline blockages. Careful thermal management is essential to deal with these challenges, which requires a deep understanding of the thermal dissipation characteristics. In this study, we established a thermal dissipation model for long-distance gaseous CO2 pipeline transport to understand the thermal attenuation patterns under different thermal management strategies, and quantitatively evaluate the thermal dissipation intensity along the pipeline. Numerical results show that CO2 temperature decay generally follows an exponential relation with distance. For a common situation with the inlet temperature of 295 K, the ambient temperature of 275 K, and a pipeline length of 30 km, the distance for an 80% decay in gas temperature is about 10 km. Regarding extending the distance without hydrate formation risk, intermediate heating after the temperature decay reaches 80% provides more effective thermal compensation than raising the inlet temperature of CO2. Increasing the inlet temperature by 10 K only extends the distance with a temperature above the hydrate phase equilibrium temperature by 42%, but intermediate heating increases the distance by 89%. Passive thermal protection also shows substantial mitigation effects. Increasing the thickness of the insulation layer from 0 to 0.025 m extends the distance by 21 km, while optimizing the insulation thermal conductivity from 0.15 to 0.05 W/(m K) extends this distance by 17 km. Findings enhance understanding of thermal dissipation in long-distance CO2 pipelines and offer insights for developing thermal management strategies.

Water-invaded underground gas-storage (UGS) reservoirs face challenges, including complex fluid mobilization and capillary trapping under cyclic injection-withdrawal. Here, we propose a microscopic two-phase pore-scale simulation method to elucidate these mechanisms. Cyclic gas injection and withdrawal induce increasingly complex gas-liquid flow and spatial distribution, complicating accurate evaluation of storage capacity and posing challenges for accurately determining storage capacity parameters. The study employs pore-scale simulations to investigate the dynamic mobilization mechanisms of gas and water in two key regions: the gas-drive expansion zone and the gas-water transition zone. In the gas-drive expansion zone, rapid cyclic gas injection and withdrawal mobilize residual liquids by expanding gas interfaces, displacing water into the main flow channels. Trapped water droplets in fine pores gradually coalesce and migrate along the pore walls, increasing accessible gas-storage space. In the gas-water transition zone, high-shear interactions between gas and water induce the formation of gas-water interlocking foams within narrow throats. This increases the flow resistance and inhibits complete gas recovery. Based on these insights, a theoretical model describing the spatial mobilization of fluids in water-injected UGS was developed. This model provides a reliable foundation for evaluating key storage performance indicators and optimizing operational strategies. Applied to a representative UGS field, the model yields a calculated maximum mobile inventory of 33.2 & times; 108 m3, closely matching the measured value of 35.1 & times; 108 m3 (94.6% accuracy). These results demonstrate the strong applicability of the model and provide guidance for the precision design and efficient operation of similar gas-storage systems in China.