Wanhua Chemical (China)

Abstract Carbon capture and storage (CCS) technology harnesses the unique properties of supercritical carbon dioxide (scCO 2 ) under reservoir conditions to achieve efficient geological sequestration and is widely recognized as a vital strategy for reducing CO 2 emissions and addressing climate change. However, the flow behavior of CO 2 within reservoirs is strongly influenced by the heterogeneity of the porous media in reservoir rocks, which serves as a critical factor in determining both the efficiency and safety of sequestration. In this study, permeability heterogeneity models were constructed using random functions, and the Volume of Fluid method was employed to simulate scCO 2 displacement of water and investigate the effects of porous media heterogeneity on the two-phase flow behavior. The results reveal that heterogeneity significantly impacts displacement patterns, dominant flow paths, and displacement efficiency during scCO 2 invasion. At low injection capillary number ( Ca ), capillary forces dominate, resulting in capillary fingering, while at high Ca , viscous forces prevail, leading to viscous fingering. In models with weaker heterogeneity, a transition zone from capillary fingering to viscous fingering is observed at intermediate Ca . Conversely, in models with stronger heterogeneity, no transition zone is detected due to the formation of fixed dominant flow paths. Additionally, the final displacement efficiency increases with Ca but decreases with increasing heterogeneity. Greater heterogeneity intensifies fingering effects, leading to higher residual water saturation and reduced invasion efficiency. These findings provide valuable theoretical insights for optimizing CO 2 geological storage operations, highlighting the importance of tailoring injection strategies to reservoir heterogeneity. Properly adjusting injection parameters can suppress fingering effects and improve sequestration efficiency, thereby enhancing the overall effectiveness of CO 2 storage.

Basalt fibers can significantly enhance the crack resistance of warm-mix recycled asphalt mixtures (WRAM). However, the impact of their morphology on crack resistance and damage behavior still lacks systematic comparison. This study comparatively investigates the differences in crack resistance and damage behavior of WRAM with flocculent basalt fibers (FBF) and chopped basalt fibers (CBF). Based on the edge-notch disc bending test, the impact of fiber morphology on crack resistance was evaluated using parameters such as bending index, peak load, and fracture energy. Combined with digital image correlation (DIC) technology, the strain and strain energy density changes during microcrack initiation, development, and macrocrack propagation were tracked to assess the effect of fiber morphology on external damage. Acoustic emission (AE) technology was used to analyze the changes in internal damage ring-down counts and RA-AF distribution during the external damage phase to evaluate the impact of fiber morphology on internal damage. A correlation between DIC and AE results was established to achieve a quantitative mapping of external and internal damage. Scanning electron microscopy was used to reveal the crack resistance mechanism of the fibers. The results show that FBF enhances pre-crack strength and toughness by increasing the energy threshold and the proportion of internal shear damage during the microcrack development stage. This mechanism arises from the three-dimensional network structure formed, which effectively disperses stress and inhibits microcrack development. CBF enhances post-crack toughness by increasing the energy threshold and the proportion of internal shear damage during the macrocrack propagation stage. The mechanism primarily involves fiber pullout and fracture, redistributing stress and inducing the complexity of crack path curvature. A quantitative mapping relationship between internal and external damage (R² > 0.98) was established to reveal the regulatory mechanism of fiber morphology on the multi-scale damage evolution behavior in WRAM. • The ENDB test effectively evaluated the impact of basalt fiber morphology on the crack resistance of WRAM under low-temperature conditions, providing an accurate basis for assessing crack resistance. • The combination of Digital Image Correlation (DIC) and Acoustic Emission (AE) technologies successfully monitored the changes in external cracks and internal damage types of WRAM under low-temperature conditions, revealing the correlation between the two during the damage evolution process. • Through the analysis of horizontal strain and strain energy density using DIC technology, the evolution of external damage in WRAM was revealed, and the impact of different fiber morphologies on crack resistance behavior was further analyzed. • The evolution of internal damage and damage types in WRAM was revealed through ring-down counts and RA-AF distribution using AE technology, and the regulatory effects of different fiber morphologies on internal damage were further analyzed. • A quantitative relationship between cumulative strain energy density from DIC and cumulative ring-down counts from AE was established, revealing the coupling relationship between external and internal damage, providing a new perspective for understanding damage evolution. • FBF effectively inhibits micro-crack propagation through uniformly dispersed single fibers and strong interface interactions; CBF, on the other hand, delays macro-crack propagation through pull-out and fracture actions. The two fiber types play different roles at various damage stages.

As the central city of the Yellow River Delta, Dongying faces challenges of water scarcity and water pollution. Based on the grey water footprint theory, the paper conducted grey water footprint accounting, factor analysis, and evaluation in Dongying from 2011 to 2023, aiming to clarify the water resources situation. Results indicated that the total grey water footprint in Dongying have decreased from 1.19 billion m3 in 2011 to 235 million m3 in 2023, a reduction of 80.21%. The agricultural, industrial, and domestic grey water footprints decreased by 94 million m3, 88 million m3, and 769 million m3, respectively, with the reduction rates reaching 54.19%, 69.98%, and 86.77%, respectively. The domestic grey water footprint has a significant impact on the dynamics of the total regional grey water footprint. The technical factor, as a negative driving factor, significantly affect the total grey water footprint in Dongying. Economic and population factors, as positive driving factors, have little impact. The water pollution level has been below 100% in recent years, with the grey water footprint sustainability remaining well. The grey water footprint intensity has decreased by 58.00 m3/10,000 CNY, a reduction of 90.60%, indicating significant improvements in water resource utilization efficiency and economic benefits. The paper provides a basis for water resource protection and water environment improvement in the Yellow River Delta region.

Wellbore stability is a crucial factor affecting the safe exploitation of offshore natural gas hydrates. As a sustainable energy source, natural gas hydrate has significant reserves, high energy density, and low environmental impact, making it an important candidate for alternative energy. Although research on the stability of screen pipes during horizontal-well hydrate production is currently limited, its importance in sustainable energy extraction is growing. This study therefore considers the effects of hydrate phase change, gas–water seepage, energy and mass exchange, reservoir deformation, and screen pipe influence and develops a coupled thermal–fluid–solid–chemical field model for horizontal-well natural gas hydrate production. The model results were validated using experimental data and standard test cases from the literature. The results obtained by applying this model in COMSOL Multiphysics 6.1 showed that the errors in all simulations were less than 2%, with errors of 12% and 6% observed at effective stresses of 0.5 MPa and 3 MPa, respectively. The simulation results indicate that the presence of the screen pipe in the hydrate reservoir exerts little effect on the decomposition of gas hydrates, but it effectively mitigates stress concentration in the near-wellbore region, redistributing the effective stress and significantly reducing the instability risk of the hydrate reservoir. Furthermore, the distribution of mechanical parameters around the screen pipe is uneven, with maximum values of equivalent Mises stress, volumetric strain, and displacement generally occurring on the inner side of the screen pipe in the horizontal crustal stress direction, making plastic instability most likely to occur in this area. With other basic parameters held constant, the maximum equivalent Mises stress and the instability area within the screen increase with the rise in the production pressure drop and wellbore size, and the decrease in screen pipe thickness. The results of this study lay the foundation for wellbore instability control in the production of offshore natural gas hydrates via depressurization. The study provides new insights into sustainable energy extraction, as improving wellbore stability during the extraction process can enhance resource utilization, reduce environmental impact, and promote sustainable development in energy exploitation.