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Supercritical CO2 pipeline transportation is a crucial link in Carbon Capture, Utilization, and Storage (CCUS). Compared with traditional oil and gas pipelines, if a supercritical CO2 pipeline is shut down for an excessively long time, the phase state of CO2 may transform into a gas–liquid two-phase state. It is urgently necessary to conduct research on the phase change mechanism and safety control during the restart process of gas–liquid two-phase CO2 pipelines. Based on a certain planned supercritical carbon dioxide pipeline demonstration project, this paper proposes a new pipeline safety restart scheme that actively seeks the liquefaction of gaseous CO2 inside the pipeline by injecting liquid-phase CO2 at the initial station. Through numerical simulation and experimental methods, the co-variation laws of parameters such as temperature, pressure, density, and phase state during the pipeline restart process were revealed. It was found that the pipeline shutdown and restart process could be subdivided into four stages: shutdown stage, liquefaction stage, pressurization stage, and displacement stage. The phase transition line would form a closed curve that is approximately trapezoidal. It is suggested to optimize the restart scheme from aspects such as reducing the restart time, controlling the pressure rise rate, and saving CO2 consumption. It is proposed that the liquid holdup of CO2 fluid in the pipe at the initial moment of restart and the mass flow rate of CO2 injected at the initial station during the restart process are the main controlling factors affecting the evolution of the phase path of pipeline restart. For the demonstration project, the specific critical threshold values are given. The research results can provide a certain theoretical guidance and reference basis for the safe restart method of supercritical CO2 pipelines.

During the surface gathering and transportation of CO2-enhanced oil recovery (CO2-EOR) under ambient temperature conditions, pressure drops caused by valves or elbows result in significant throttling effects in multiphase flows with high CO2 content, which critically impact the safe operation of the gathering system. Using a high-pressure sapphire autoclave experimental setup, this study analyzes the effects of phase state, CH4 content, gas-liquid ratio, and water content on the throttling characteristics. The results indicate that under ambient temperature conditions, the final throttling temperature of liquid CO2 is primarily influenced by the final throttling pressure, with no significant correlation to the pressure drop. For throttling without phase change, liquid CO2 exhibits a weaker throttling effect, with a throttling coefficient (Di) of approximately 0.6℃/MPa, whereas gaseous CO2 demonstrates a stronger effect, with Diranging between 10-12℃/MPa. Furthermore, the influence of CH4 content on the throttling temperature drop varies with the initial pressure. At high initial pressures (16 MPa), Diis approximately 1.3-5.4℃/MPa, and the addition of CH4 enhances the throttling effect of the mixed gas. At lower initial pressures (5 MPa and 4 MPa), Di is approximately 3.4-11.9℃/MPa, and the addition of CH4 weakens the throttling effect. An increase in the gas-liquid ratio and a decrease in water content both lead to a greater throttling temperature drop, with the gas-liquid ratio having a particularly significant impact.

In order to meet the differentiated demand of oil refiners for crude oil, improve the operating load ratio of long-distance pipelines, and reduce one-time investment, sequential transportation process has been widely used in long-distance crude oil pipelines in China. There are many studies on the calculation method of the mixed oil quantity of sequential transportation of refined oil, but due to its complex influencing factors, there is no general calculation model accepted by everyone. For the sequential transportation of crude oil pipelines, most of them have the characteristics of variable temperature and low Reynolds number, and it is more difficult to accurately calculate the mixed oil quantity than the refined oil pipeline. Through the analysis of the characteristics of oil mixing and hydraulic characteristics of sequential oil transportation, combined with the operation example of an oil pipeline in China, the calculation results of the diffusion theory formula, the Austin-Palfrey empirical formula and the equivalent pipeline length formula were compared and analyzed. The results show that the “equivalent pipeline length method” considers the influence of flow, pipe diameter and conveying distance on oil mixing, and takes into account the oil mixture caused by the change of initial oil mix and Reynolds number, which is more suitable for calculating the mixed oil quantity of sequential transportation of crude oil pipelines. However, for the sequential transportation of crude oil pipelines with low Reynolds number and variable temperature, the amount of oil mixed will be increased. According to the comparative analysis of actual cases, the correction coefficient is increased by 1.5 times on the basis of theoretical calculation, and the calculated value is in good agreement with the actual value, and the deviation is within 5%. It can be used as a reference for the design and operation management of variable temperature and low Reynolds number crude oil sequential transportation pipeline.

To ensure the safety of supercritical CO2 pipelines and address the limitations of full-scale fracture tests, such as high risk and substantial investment, software for evaluating the crack arrest toughness of CO2 pipelines containing impurities was developed based on the Battelle Two-Curve Model (BTCM) in this study. The software is programmed in Python (v.3.12.4), with a graphical user interface (GUI) built using PyQt6 (v.6.10.0) and a three-tier architecture design. It integrates the resistance curve model and the decompression wave model. To determine the thermodynamic state of the fluid, a large property database covering pure components and various mixtures is embedded, incorporating state equations such as PR, HEOS, and GERG-2008. The software can generate pressure drop curves, decompression curves, and resistance curves. The pressure plateau can be quickly identified by examining the pressure drop curve. Whether the pipeline can achieve self-crack arrest can be rapidly judged by comparing the positional relationships between the decompression curve and the resistance curve. To verify the accuracy of the software’s calculation results, comparisons were conducted with previous decompression wave experimental data, full-scale burst test data of a CO2 pipeline, and the international HLP model. The calculation error of the software is within 10%. The development and application of this software provide a convenient, efficient, and accurate practical tool for the calculation of crack arrest toughness and crack arrest evaluation of supercritical CO2 pipelines.

In the context of global energy demands, the efficient demulsification of highly stable heavy crude oil emulsions remains a critical challenge. This study systematically investigated the demulsification mechanisms of two demulsifiers (P1# and P2#) through multi-dimensional characterisation and performance evaluation. The results indicated that asphaltenes and resins can strengthen the oil–water interfacial film and stabilise the emulsion due to their unique structural properties. FTIR and 1HNMR analyses showed that both demulsifiers contained polar groups and alkyl chains; however, P1# exhibited higher viscosity and lower surface tension, which favored its rapid adsorption at the interface. Demulsification tests at 60 °C demonstrated that P1# achieved superior efficiency (92.44% demulsification efficiency (DE) in 120 min versus 82.31% for P2#), attributable to its enhanced ability to displace asphaltene/resin at the oil-water interface. Turbiscan stability analysis and microscopic observations confirmed that P1#-treated emulsions underwent faster droplet coalescence and significant interfacial film disruption. Mechanistic studies indicated that the demulsifiers competitively adsorb at the interface, thereby weakening film cohesion through steric hindrance and charge redistribution. XRD and FTIR analyses suggested that interactions between the demulsifier and the asphaltene/resin increased interlayer spacing and reduced crystallinity. Zeta potential and interfacial tension measurements further highlighted P1#’s ability to neutralize negative charges (from −14.52 mV to +8.3 mV) and reduce the IFT (from 28.5 mN/m to 12.1 mN/m), thereby promoting droplet aggregation. This study helps elucidate the mechanism of emulsion phase transition induced by demulsifiers and provides theoretical support for improving the demulsification efficiency of crude oil emulsions.

During the surface gathering and transportation of CO 2 -enhanced oil recovery (CO 2 -EOR) under ambient temperature conditions, pressure drops caused by valves or elbows result in significant throttling effects in multiphase flows with high CO 2 content, which critically impact the safe operation of the gathering system. Using a high-pressure sapphire autoclave experimental setup, this study analyzes the effects of phase state, CH 4 content, gas-liquid ratio, and water content on the throttling characteristics. The results indicate that under ambient temperature conditions, the final throttling temperature of liquid CO 2 is primarily influenced by the final throttling pressure, with no significant correlation to the pressure drop. For throttling without phase change, liquid CO 2 exhibits a weaker throttling effect, with a throttling coefficient ( D i ) of approximately 0.6℃/MPa, whereas gaseous CO 2 demonstrates a stronger effect, with D i ranging between 10-12℃/MPa. Furthermore, the influence of CH 4 content on the throttling temperature drop varies with the initial pressure. At high initial pressures (16 MPa), D i is approximately 1.3-5.4℃/MPa, and the addition of CH 4 enhances the throttling effect of the mixed gas. At lower initial pressures (5 MPa and 4 MPa), D i is approximately 3.4-11.9℃/MPa, and the addition of CH 4 weakens the throttling effect. An increase in the gas-liquid ratio and a decrease in water content both lead to a greater throttling temperature drop, with the gas-liquid ratio having a particularly significant impact.

After gas channeling during CO2 flooding, CO2 gas content in the produced liquid will gradually increase. Research on desorption law of CO2 in crude oil has not yet appeared in the literature. In the design of gas-liquid separator, in order to desorb CO2 gas effectively, the retention time of produced liquid in gas-liquid separator has to be prolonged appropriately just based on the experience, and the effect is usually not good, leading to serious corrosion of the follow-up equipment. In this paper, the study key point is the desorption law of CO2 in crude oil. The gas desorption experimental device of CO2 flooding produced liquid is set up, using the method of depressurization for desorption, gas desorption process of the produced liquid in gas liquid separator can be simulated in the condition of gathering temperature and pressure. How the CO2 desorption rate and desorption percentage change with time is determined. Finally, the desorption rule of CO2 in water and crude oil is obtained. The experimental results show that at the moment of the depressurization, high desorption rate peak of CO2 appears with short duration. What's more, with the pressure rapidly reducing, desorption rate is falling rapidly. During most of the time when the pressure is the atmospheric pressure, which is the end of the desorption pressure, desorption rate of CO2 in water and crude oil are both below 0.025 Ncm3/(cm2·s), and respectively after 20.9 min and 58.60 min, their desorption rates reduce to zero, the desorption percentage reaching only 62.13% and 22.92%. CO2 gas desorption from crude oil is more difficult than that from the water, and the higher oil content in produced liquid is, the more difficult the CO2 gas desorption is. So even if the retention time of produced liquid in the separator is far more than that stated in the specification, most of CO2 still cannot desorb from the produced liquid. By studying the characteristics of desorption of CO2 in crude oil, it is found clearly that only relying on stepdown desorption and prolonging retention time of produced liquid in the separator cannot solve the problem of effective desorption of CO2. It is recommended to take some measures in the process of gas liquid separation to promote gas desorption. Thus, this paper provides a theoretical basis for the further research on methods of gas desorption.

Increases in backfill soil's thermal conductivity can cause sharply higher heating station fuel costs on heavy oil crude pipelines because the higher conductivity requires a higher initial temperature to keep the crude's terminal temperature stable. Excavation and filling change not only the compactness and water content of backfill soil, but also its thermal conductivity. Backfill soil's thermal conductivity in turn affects the cooling of a hot oil pipeline, and through this, its energy consumption, safety, and budget. This article analyzes the characteristics of backfill soil thermal conductivity along a buried pipeline, explains the principle of the line heat source method used for measuring soil thermal conductivity, and introduces field thermal needle system FTNO1 as a tool for determining thermal conductivity. Taking soil thermal conductivity field testing results at the Niger hot oil pipeline project as an example, the article summarizes distribution rules and the main factors influencing backfill soil thermal conductivity in the West Africa tropical desert, tropical grassland, and farmland areas. The testing and analysis methods introduced can be used to determine backfill soil thermal conductivity distribution along new or existing pipelines.

As urban rail transit networks age, understanding the synergistic impacts of multi-defect interactions on tunnel structural safety has become critical for underground infrastructure maintenance. This study investigates defect interaction mechanisms in shield tunnels and cross passages of Beijing Metro Line 8, integrating field monitoring, numerical simulations, and Bayesian network analysis. Long-term field surveys identified spatiotemporal coupling characteristics of four key defects—lining leakage, structural voids, material deterioration, and deformation—while revealing typical defect propagation patterns such as localized leakage at track beds and drainage pipe-induced voids. A 3D fluid–solid coupling numerical model simulated multi-defect interactions, demonstrating that defect clusters in structurally vulnerable zones (e.g., pump rooms) significantly altered pore pressure distribution and intensified displacement, whereas void expansion exacerbated lining uplift and asymmetric ground settlement. Stress concentrations were notably amplified at tunnel–cross passage interfaces. The Bayesian network risk model further validated the dominant roles of defect volume and burial depth in controlling structural safety. Results highlight an inverse correlation between defect severity and structural integrity. Based on these findings, a coordinated maintenance framework combining priority monitoring of high-stress interfaces with targeted grouting treatments is proposed, offering a systematic approach to multi-defect risk management that bridges theoretical models with practical engineering solutions.

Energy security has emerged as a critical concern amid intensifying climate risks and surging energy demand driven by economic growth. This study examines the impact of climate risk on energy security by constructing a panel dataset covering 30 Chinese provinces from 2006 to 2022. Using the instrumental variable generalized method of moments (IV-GMM) model, we estimate the marginal impact of climate risk on energy security and further investigate its asymmetric, direct, and indirect relationships via panel quantile regression and mediation analysis. Our key findings are as follows: (1) Climate risk exerts a significant negative impact on energy security, indicating an inverse relationship. (2) The effect of climate risk is asymmetric, with a stronger adverse impact in regions with lower levels of energy security. (3) Climate risk undermines energy security by reducing energy accessibility, affordability, sustainability, and technological efficiency. (4) Energy transition and energy efficiency serve as critical mediators in the relationship between climate risk and energy security, offering insights into potential mitigation pathways. Unlike previous studies that primarily examine energy security in isolation or focus on single dimensions, this research integrates a multidimensional indicator system and advanced econometric techniques to uncover both direct and mediated pathways, thereby filling a key gap in understanding the climate–energy nexus at the provincial level in China. Based on these findings, we propose targeted policy recommendations to enhance energy security by improving climate resilience, accelerating the deployment of renewable energy, and optimizing energy infrastructure investments.