Search Results (709)

This study addresses the challenges of low-pressure oil well workover operations, namely, severe loss of water-based workover fluid, significant reservoir damage from conventional temporary plugging agents, and slow production recovery, by focusing on the yet-mechanistically unclear “fuzzy-ball workover fluid.” Laboratory experiments combined with field data were used to evaluate its plugging performance and reservoir-protective mechanisms. In sand-filled tubes (diameter 25 mm, length 20–100 cm) sealed with the fuzzy-ball fluid, the formation’s bearing capacity increased by 3.25–18.59 MPa, showing a positive correlation with the plugging radius. Compatibility tests demonstrated that mixtures of crude oil and workover fluid (1:1) or crude oil, workover fluid, and water (1:1:1) held at 60 °C for 80 h exhibited only minor apparent viscosity reductions of 4 mPa·s and 2 mPa·s, respectively, indicating good stability. After successful plugging, a 1% ammonium persulfate solution was injected for 2 h to break the gel; permeability recovery rates reached 112–127%, confirming low reservoir damage and effective gel-break de-blocking. Field data from five wells (formation pressure coefficients 0.49–0.64) showed per-well fluid consumption of 33–83 m³ and post-workover liquid production index recoveries of 5.90–53.30%. Multivariate regression established mathematical relationships among bearing capacity, production index recovery, and fourteen geological engineering parameters, identifying the plugging radius as a key factor. Larger radii enhance both temporary plugging strength and production recovery without harming the reservoir, and they promote production by expanding the cleaning zone. In summary, the fuzzy-ball workover fluid achieves an integrated “high-efficiency plugging–low-damage gel-break–synergistic cleaning” mechanism, resolving the trade-off between temporary-plugging strength and production recovery in low-pressure wells and offering an innovative, environmentally friendly solution for the sustainable and efficient exploitation of oil–gas resources. Full article

This study systematically investigates the structure–performance relationship of PMA (PolyMethacrylate) viscosity index improvers in new energy vehicle (NEV) transmission fluids. We developed an integrated analytical framework combining spectroscopic and chromatographic techniques to simultaneously characterize its side chain length distribution, molecular weight polydispersity, and branching architecture. Key findings reveal that the kinematic viscosity of formulated oils positively correlates with PMA molecular weight, low-temperature performance is governed by side-chain length (≥C14 fatty alcohols), shear stability is predominantly determined by molecular weight, and nitrogen-modified PMA enhances oxidation resistance by mitigating kinematic viscosity increase. These insights provide actionable guidance for the molecular design of viscosity index improvers and the formulation optimization of advanced lubricants to meet the stringent demands of electric vehicle transmission systems. Full article

To address the challenges of decarbonization in the global transportation sector and disposal of waste tires, warm asphalt rubber (WAR) with low viscosity and high performance was prepared. In particular, the preparation and rheological behavior of WAR incorporating composite warm mix systems at relatively high crumb rubber contents have not been thoroughly documented. In this study, WAR prepared under such conditions was systematically examined. A five-factor, three-level segmented orthogonal experimental design (OED) was employed to investigate the effects of preparation parameters on hot mix asphalt rubber (AR) properties. Based on the optimized AR formulation, a composite warm mix system combining Ultra-Warm Mix additive (UWM) and Sasobit was developed, and control groups containing 5% UWM only and 1.5% Sasobit only were prepared for comparison. Conventional physical tests together with rheological characterization, including Dynamic Shear Rheometer (DSR), Multiple Stress Creep Recovery (MSCR), and Bending Beam Rheometer (BBR) tests, were conducted to evaluate the high- and low-temperature performance of WAR. Results show that the optimal preparation process consisted of aromatic oil content 5%, crumb rubber content 30%, shear temperature 220 °C, shear time 120 min, and reaction time 90 min. The composite warm mix system notably enhanced WAR performance, with the WAR-5U1.5S group exhibiting the most balanced properties. A marked reduction in rotational viscosity was achieved while maintaining a stable softening point, and satisfactory ductility and elastic recovery were also retained. DSR and MSCR tests confirmed improved high-temperature deformation resistance, an increase in percent recovery R, and a decrease in non-recoverable creep compliance J_nr. BBR test further verified that the composite system maintained good low-temperature cracking resistance, meeting all specification requirements. Overall, these results indicate that, compared with the optimized AR, WAR can reduce mixing viscosity without sacrificing rutting or cracking performance, while alleviating the limitations observed for single warm mix additives. This study provides essential technical support for promoting WAR that integrates low-carbon construction with superior pavement performance. Full article

Under high-temperature conditions in deep well formations, oil-based drilling fluids tend to show degraded rheological properties and reduced suspension capacity, which may impair wellbore cleanliness and circulation pump pressure and hinder drilling. To address this issue, a three-component composite thickener including fatty acid polymers and clay activator was developed, and then the composite agents were used as the core component in formulating a thermo-thickening oil-based drilling fluid. Experimental results demonstrated that at up to 200 °C and 153 MPa, the fluid’s low-shear-rate viscosity and yield point increased steadily, while high-shear-rate viscosity and plastic viscosity remained nearly unchanged. The composite thickener largely enhanced the fluid’s storage modulus and inner structural force, thus improving its rheological properties and suspension capacity under high-temperature and high-pressure conditions. Based on these findings, the thermo-thickening oil-based drilling fluid was supposed to address the critical diminished rheological stability and suspension capacity of conventional oil-based drilling fluids in complex formations with promising application prospects. Full article

CO₂ miscible flooding provides dual advantages in enhancing oil recovery and facilitating geological sequestration, and has become a key technical approach for developing low-permeability oil reservoirs and carbon emission reduction. The pore-scale flow mechanisms governing CO₂ behavior during miscible flooding are crucial for achieving efficient oil recovery and secure geological storage of CO₂. In this study, pore-scale two-phase flow simulations of CO₂ miscible flooding in porous media are performed using a coupled laminar-flow and diluted-species-transport framework. The model captures the effects of diffusion, concentration distribution, and pore structure on the behavior of CO₂ miscible displacement. The results indicate that: (1) during miscible flooding, CO₂ preferentially displaces oil in larger pore throats and subsequently invades smaller throats, significantly improving the mobilization of oil trapped in small pores; (2) increasing the injection velocity accelerates the displacement front and improves oil utilization in dead-end and trailing regions, but a “velocity saturation effect” is observed—when the inject velocity exceeds 0.02 m/s, the displacement pattern stabilizes and further gains in ultimate recovery become limited; (3) higher injected CO₂ concentration accelerates CO₂ accumulation within the pores, enlarges the miscible sweep area, promotes a more uniform concentration field, leads to a smoother displacement front, and reduces high-gradient regions, thereby suppressing local instabilities, and improves displacement efficiency, although its effect on overall recovery remains modest; (4) CO₂ dynamic viscosity strongly influences flow stability: low-viscosity conditions promote viscous fingering and severe local bypassing, whereas higher viscosity stabilizes flow but increases injection pressure drop and energy consumption, indicating a necessary trade-off between flow stability and operational efficiency. Full article

A series of poly(5-n-butyl-2-norbornene) oils with controlled molecular weights was synthesized via metathesis polymerization, fully hydrogenated, and characterized in terms of viscosity and tribological performance. In contrast to established lubricant base stocks—such as poly(α-olefins) and multiply alkylated cyclopentanes—these novel norbornene-based polymers remain underexplored, despite their promising anti-wear activity. Based on differential scanning calorimetry (DSC) data, all the synthesized products are amorphous compounds whose thermograms show a single glass transition temperature. The effect of molecular weight and temperature on the viscosity of poly(5-n-butyl-2-norbornene) oils was quantified over an extended temperature range, including extra-cold conditions down to −80 °C. The pour points of the oils were determined and can be as low as −66 °C, indicating excellent low-temperature fluidity. The tribological performance of the synthesized oils was evaluated using the four-ball test, with friction coefficient and wear scar diameter measured to assess anti-wear and antifriction properties. The tribological results were benchmarked against commercially available polyalphaolefin (PAO) oils (PAO-4, PAO-20, and PAO-80). Metathesis and hydrogenated poly(5-n-butyl-2-norbornene) oils outperform conventional PAOs by up to 67% in wear protection and 30% in friction reduction. These findings establish alicyclic molecular strain as a viable design parameter for next-generation lubricating oils, thereby expanding the toolbox for material development beyond conventional chemical functionalization. Full article

Studying the propagation behavior of hydraulic fracturing fractures is of great significance for understanding the mechanism of fracture propagation in deep unconventional reservoirs. The goal of unconventional oil and gas reservoir fracturing transformation is to form a complex fracture network system and increase the effective transformation volume of the reservoir. This article conducts physical model experiments on fracturing under different reservoir stress conditions to determine whether complex pressure fractures can be formed. The main controlling factors for the formation of complex pressure fractures are analyzed, and the influence of each factor is quantitatively studied through numerical simulation. The results indicate that the difference in geostress has a significant impact on the formation of pressure cracks. As the difference in geostress increases, the lateral extension range of pressure cracks significantly decreases, resulting in a phenomenon parallel to the direction of maximum horizontal geostress. As the injection volume decreases, the phenomenon of early fracturing bifurcation propagation gradually decreases, with a small number of bifurcations appearing. In the subsequent fracturing process, the main trend of fracture extension is more pronounced in reservoirs with lower fluid injection rates. In addition, low-viscosity fracturing fluids seem to be more prone to forming fracture zones with more developed branching fractures. This study can provide technical support and reference for fracturing construction in deep tight oil reservoirs. Full article

The research problem concerning oils used for lubricating piston combustion engines is still very current and important. The proper selection of oil and its properties have a significant impact on engine reliability and durability, their efficiency, effective operating parameters, fuel consumption, environmental impact, and the proper operation of the turbocharger and exhaust system. The work concerned determining the effect of temperature and operating time on the dynamic viscosity of oils: mineral, semi-synthetic, and synthetic, used in compression-ignition engines (diesel engines). Dynamic viscosity tests were conducted for new oils, after a mileage of seven thousand kilometers, and after a mileage of fifteen thousand kilometers. The range of temperature measurement conditions used was from 0 to 50 °C and the shear transmission rate was 1000 s⁻¹. This range allows the oil to be preserved at low and medium temperatures, which are crucial for engine operation during start-up and short operating cycles. As the conducted studies showed, both temperature and operating time have a very large influence on the dynamic viscosity of oils. It was demonstrated that as the operating time of the oils in the engine increased, their dynamic viscosity decreased, and increasing the viscosity measurement temperature results in smaller absolute changes in it. Full article

This article presents the results of experimental studies examining the effectiveness of low-concentration nanoemulsions for enhanced oil recovery (EOR). The maximum volume concentration of diesel fuel in the emulsions did not exceed 1% by volume. The volume concentration of the emulsifier ranged from 0.05% to 0.4%. A method for preparing stable nanoemulsions was developed. The colloidal stability, viscosity, interfacial tension, wettability, and capillary imbibition rate of low-concentration nanoemulsions were studied. Filtration experiments were conducted to study oil displacement on microfluidic chips simulating a porous medium and core samples. This is the first systematic study of the properties of nanoemulsions containing diesel fuel. It was demonstrated that the developed emulsions have high potential for EOR. It was shown that increasing the emulsifier concentration reduces the contact angle from 35 to 16 degrees and halves the surface tension coefficient. Experiments studying the capillary imbibition of oil-saturated cores with nanoemulsions also confirmed their ability to reduce interfacial tension and improve rock wettability. Oil displacement efficiency during capillary imbibition increases by 22%. Filter tests on microfluidic chips and core samples confirmed the high efficiency of the developed nanoemulsions. Increasing the emulsifier concentration in the emulsion to 0.4% increases the displacement efficiency from 32% for water displacement to 57% for nanoemulsion displacement. Core tests showed that additional injection of nanoemulsions significantly increases the oil displacement efficiency by 10–14%, depending on the emulsifier concentration in the nanoemulsion. It was also established that the use of an aqueous solution of an emulsifier without a hydrocarbon phase does not provide such a significant increase in the displacement coefficient as in the emulsion composition. Full article

This paper presents a comprehensive review of forced convective heat-transfer phenomena in fluids, emphasizing the influence of fluid properties, tube geometries, and flow orientations under varying Prandtl numbers. Key governing parameters—including velocity, viscosity, thermal conductivity, density, specific heat, surface area, and flow regime (laminar or turbulent)—are expressed through dimensionless groups such as the Nusselt (Nu), Reynolds (Re), and Prandtl (Pr) numbers. The review encompasses heat-transfer characteristics of low-, medium-, and high-Prandtl-number fluids flowing through circular, square, triangular, and elliptical tubes in both horizontal and vertical orientations, aiming to critically evaluate the effectiveness and trends reported in previous studies. Where applicable, symmetry correlations—based on equivalent thermal and hydrodynamic behaviour along geometrically symmetric boundaries—were considered to interpret flow uniformity and heat-transfer distribution across cross-sectional profiles. Analysis reveals that over 84% of the reviewed studies emphasize on horizontal configurations and 55% on circular geometries, with medium-Prandtl-number fluids dominating experimental investigations. While these studies provide valuable insights, significant research gaps remain. Limited attention has been given to vertical orientations, where buoyancy effects may alter flow behaviour due to temperature and pressure gradients arising from variations in fluid density and viscosity, to non-circular geometries that enhance boundary-layer disruption, and to extreme-Prandtl-number fluids such as liquid metals and heavy oils, which are vital in advanced industrial applications. Bridging these gaps presents opportunities to design and optimize diverse engineering systems requiring efficient convective heat transfer. Practical examples include coolant flow in nuclear reactors, heat dissipation in high-performance CPUs, and high-speed airflow over automotive radiators. This review therefore underscores the need for future research extending forced-convection studies beyond conventional configurations, with particular emphasis on vertical orientations, complex geometries, and underexplored Prandtl-number regimes. Full article

CCUS-EOR combines emission reduction with economic benefits, making it one of the key technologies for addressing global climate change. Addressing the lack of systematic comparative studies on the differences in geological endowments and engineering conditions between China and North America in existing literature, this paper systematically reviews the progress of North American CO₂-EOR in areas such as gas source structure transformation, capture technologies, and pipeline network construction, based on a self-constructed database of typical projects. It then conducts a quantitative comparative analysis of typical projects in China and the United States from three dimensions: reservoir geological endowment, gas source composition, and infrastructure. The study reveals that the advancement of U.S. CO₂-EOR projects benefits from increasing industrial CO₂ supply and the construction of cross-regional pipeline networks. Comparative analysis indicates that North American projects primarily feature miscible displacement in medium-to-low temperature and light oil reservoirs. This contrasts fundamentally with the characteristics of China’s continental reservoirs, which exhibit “strong heterogeneity, high viscosity, and high minimum miscibility pressure (MMP)”. Currently, China’s CCUS-EOR is transitioning from engineering demonstration to commercial application. However, gaps persist compared to more mature international systems in areas such as low-concentration CO₂ capture, pipeline network construction for source-sink matching, and suitability for continental reservoir EOR. Moving forward, China can draw on U.S. CCUS-EOR development experience, accelerate research on relevant technologies tailored to its continental reservoir characteristics, and establish a differentiated whole-industry-chain CCUS-EOR technology system. Full article

The current rise in global energy demand and environmental degradation has highlighted the need to use renewable energy as an alternative to fossil fuels. Ricinus communis L. (castor bean oil) has emerged as a promising source for biofuels production due to high oil content (45–55%), ability to grow on marginal soils, and resistance to adverse conditions. This review analyzes 93 relevant studies from 2019 to 2025, selected by the PRISMA method (Preferred Reporting Items for Systematic reviews and Meta-Analyses) from databases such as Google Scholar and Web of Science. There were identified that agronomic techniques such as optimized plant spacing, balanced fertilization, and elicitation can significantly increase productivity. Among the production methods used, heterogeneous catalysis (96.8%) and enzymatic processes (90%) stand up for their sustainability and efficiency. However, the main limitation remains the high viscosity of castor biodiesel (14–18 mm²/s at 40 °C), which exceeds international quality standards. Even so, castor biodiesel offers excellent lubricity (reduces injection wear by 20%), has standard oxidative stability, and has a relatively low cetane number (38–42), which poses challenges for ignition quality. Improvement strategies such as blending, enzymatic modification, and additive incorporation have shown potential to mitigate these limitations. The review also addresses environmental benefits, regulatory challenges, and market opportunities where the castor biodiesel offers competitive advantages. Enhancing research and innovation, supported by targeted public policies and technical standards, is essential to overcome current barriers and enable the commercial adoption of castor biodiesel as part of a more sustainable and diversified energy future. Full article

This study examines the flow behavior of water-lubricated heavy oil transport utilizing the core annular flow (CAF) technique. The goal is to enhance efficiency and minimize risks in pipeline operations. The flow was numerically simulated in a horizontal pipe using a Large Eddy Simulation (LES) model within a commercial Computational Fluid Dynamics (CFD) framework. The Geo Reconstruct scheme is employed to accurately capture the oil–water interface, and both oil and water initialization methods were assessed against experimental data. Results show that the LES model accurately reproduces the main flow features observed experimentally, particularly for low-viscosity oil–water systems. This suggests that the model can be a reliable tool for predicting flow behaviour in similar fluid systems. Further validation with varying parameters could enhance its applicability across a broader range of conditions. In cases of heavy oil, the velocity profile remains nearly constant within the oil core, indicating rigid body-like motion surrounded by a turbulent water annulus. Turbulence intensity and oil volume fraction distributions were closely related, with higher turbulence in water and lower in oil. Although wall adhesion modelling limited fouling prediction, simulations confirmed that fouling can significantly increase pressure losses. This illustrates the value of considering both fluid dynamics and material interactions in such systems. Future studies could explore the impact of varying temperature and pressure conditions on fouling behaviour to further refine predictive models. Overall, the LES approach proved suitable for analysing turbulent CAF, offering insights for optimizing viscosity ratios, flow rates, and design parameters for safer and more efficient heavy oil transport. Full article

As a key medium in industry, lubricating oil plays a significant role in reducing friction, cooling sealing and transmitting power, which directly affects equipment life and energy efficiency. Traditional mineral-based lubricating oils rely on non-renewable petroleum, and they have high energy consumption and poor biodegradability (<30%) during the production process. They can easily cause lasting pollution after leakage and have a high carbon footprint throughout their life cycle, making it difficult to meet the “double carbon” goal. Bio-based lubricating oil uses renewable resources such as cottonseed oil and waste grease as raw materials. This material offers three significant advantages: sustainable sourcing, environmental friendliness, and adjustable performance. Its biodegradation rate is over 80%, and it reduces carbon emissions by 50–90%. Moreover, we can control its properties through processes like hydrogenation, isomerization, and transesterification to ensure it complies with ISO 6743 and other relevant standards. However, natural oils and fats have regular molecular structure, high freezing point (usually > −10 °C), and easy precipitation of wax crystals at low temperature, which restricts their industrial application. In recent years, a series of modification studies have been carried out around “pour point depression-viscosity preservation”. Catalytic isomerization can reduce the freezing point to −42 °C while maintaining a high viscosity index. Epoxidation–ring-opening modification introduces branched chains or ether bonds, taking into account low-temperature fluidity and oxidation stability. The deep dewaxing-isomerization dewaxing process improves the base oil yield, and the freezing point drops by 30 °C. The synergistic addition of polymer pour point depressant and nanomaterials can further reduce the freezing point by 10–15 °C and improve the cryogenic pumping performance. The life cycle assessment shows that using the “zero crude oil” route of waste oil and green hydrogen, the carbon emission per ton of lubricating oil is only 0.32 t, and the cost gradually approaches the level of imported synthetic esters. In the future, with the help of biorefinery integration, enzyme catalytic modification and AI molecular design, it is expected to realize high-performance, low-cost, near-zero-carbon lubrication solutions and promote the green transformation of industry. Full article

Prolonged water injection in conventional heavy oil reservoirs typically leads to high water cut and a substantial reduction in recovery rate. This study explores the synergistic effects of a composite flooding process, where associated gas-assisted surfactant-polymer (SP) flooding is enabled by prior gel conformance control, to enhance oil recovery in these reservoirs. Through high-temperature, high-pressure microscopic visualization experiments and heterogeneous core flooding tests, the oil displacement mechanisms and enhanced recovery effects of this composite system were systematically investigated. The results show that SP flooding, through viscosity enhancement and reduction in interfacial tension, achieves the highest microscopic oil displacement efficiency, with an oil recovery of 81% and a significant reduction in clustered residual oil to just 9%. Associated gas flooding improves oil mobility by reducing viscosity and promoting expansion through gas dissolution, resulting in a recovery efficiency of 62%, which outperforms traditional viscosity reducers (58%). Heterogeneous core flooding experiments demonstrate that a composite strategy involving gel plugging, associated gas assistance, and SP flooding increases recovery by 24% compared to water flooding. The system also exhibits excellent flow control and maintains a low water cut, confirming the promising potential of this gel-conformance-controlled, associated gas-assisted SP flooding strategy as an effective method for enhancing recovery in high-water-cut heavy oil reservoirs. Full article