High-viscosity Oil Research Articles

COMPARISON OF MEASURED AND CALCULATED HIGH-VISCOSITY CRUDE OIL TEMPERATURE VALUES IN A PIPELINE DURING CONTINUOUS PUMPING AND SHUTDOWN MODES

The paper investigates the stationary and non-stationary cooling processes of high-viscosity crude oil temperature in the Severnye Buzachi – Karazhanbas pipeline during both pump operations and pump shutdowns. To transport high-viscosity crude oil through pipelines, the hot pumping method is employed. During oil transportation and pump shutdowns, the oil temperature decreases due to heat exchange with the environment, leading to an increase in oil viscosity. As viscosity rises, more power is required from the pumps to move the thickened oil, resulting in higher electricity consumption. To avoid increased operational costs after pump shutdowns, it is crucial to accurately calculate the oil cooling temperature in order to determine the safe shutdown duration and a critical temperature threshold. The Shukhov formula is used to calculate oil temperature during transportation, while a modified version is applied during pump shutdowns. To verify the accuracy of the obtained oil temperature results, the calculated values were compared with the measured values from pipeline sensors in both stationary and non-stationary cases. The novelty of the work is in determining the methodology for calculating the safe shutdown time of a pipeline for high-viscosity oil. The proposed formula was validated using experimental data from SCADA system sensors in real-time.

Preparation of Superhydrophobic and Multifunctional Sponges for Oil/Water Separation and Oil Absorption.

For settling the recycling problem of waste polyurethane sponges (PU) and environment pollution of oil spills simultaneously, this work exploited the multifunctional superhydrophobic PU materials via the dip-coating method, which were prepared by anchoring modified Fe3O4 and expandable graphite (EG) on PU sponges under the adhesion effect of polydimethylsiloxane (PDMS). The water contact angle and sliding angle of as-prepared PU sponges reached 154.1 ± 1.6 and 8°, respectively. Most importantly, the superhydrophobic PU sponges were endowed with the multipath oil treatment ability, which consisted of magnetically driven, gravity-driven, peristaltic pump-driven, and photothermally driven modes. Besides, the light oil absorption capacity, separation flux, and efficiency for superhydrophobic PU sponges reached 23.9 g/g, 27779 L m-2 h-1, and 99.5%, respectively. Owing to the photothermal conversion ability of Fe3O4 and EG, the temperature of superhydrophobic PU sponges was raised to 71.5 °C within 233 s under 1.2 solar irradiation (1200 W/m2), demonstrating its absorption potential for high-viscosity crude oils. In addition, the prepared sponges exhibited good chemical/mechanical stability, self-cleaning, and flame retardancy. In a nutshell, this article has evolved an environmentally benign and practical method for fabricating the multifunctional materials in oil spill treatment, which will efficiently accomplish the targets of low carbon and environmental management.

Development of a demulsifier and technological process study for the preparation of highly viscous heavy oils for refinement

One of the challenges in the petroleum industry is the production of highly viscous heavy oils, often accompanied by undesirable emulsion formation with very high aggregate stability. To prepare the crude oils for refinement, the oils must be destroyed. The destruction of aqueous emulsions containing highly viscous heavy oils is an intricate task owing to the comparatively small disparity in water and oil densities, as well as the high viscosity of the dispersive medium and its high content of mechanical impurities. The problem of the destruction of petroleum emulsions arises desperately during the desalination and dehydration of crude oils with a high content of emulsifiers (resins, asphalts, paraffin, etc.) The creation of a highly efficient demulsifier and the development of an optimal technological process for the preparation of highly emulsifying oils that are distinguished by the composition and quantity of emulsifiers of West Siberian oils, which are widely refined in Russia, are the ways to resolve this challenging and timely issue. This study focuses on the viscous heavy oil of the Verbliouje deposit in the Astrakhan region. It also explains the creation of an effective demulsifier for the destruction of petroleum emulsions characterized by a very high emulsifying power and the fundamental principles of the development of deep dehydration technology and desalination of such high-viscosity heavy oils.

Fundamental study on dielectric oil viscosity for high-performance wire EDM

AbstractDielectric oil has been recently used in wire electrical discharge machining (wire EDM) for achieving high-precision machining. However, the influence of dielectric oil properties on wire EDM characteristics has not been clarified sufficiently. This study fundamentally investigated the influence of dielectric oil viscosity on wire EDM characteristics. In this study, three types of dielectric oil differing only in viscosity were prepared and examined. Linear cutting experiment results showed that the removal rate and the machined surface roughness increase with dielectric oil viscosity. Then, the influence of viscosity on crater removal volume was investigated to discuss the cause of the change in removal rate, and it was found that crater removal volume increases with the viscosity. Furthermore, CFD (computational fluid dynamics) analysis results and discharge observation results showed that the debris exclusion becomes worse in higher viscosity oil, and the discharge concentration occurs frequently, resulting in the deterioration in machined surface roughness. Next, the difference in machining accuracy with dielectric oil viscosity was investigated. It was found that the corner shape accuracy deteriorates with the increase of viscosity while the machined surface waviness and straightness improve slightly. Structural analysis results showed that wire deflection increases with viscosity, resulting in the deterioration in corner shape accuracy. On the other hand, high-speed observation of wire vibration was carried out, and it was found that the wire vibration decreases in the case of higher viscosity, which leads to the improvement in machined surface waviness and straightness.

Importance of Clay Swelling on the Efficacy of Cyclic Steam Stimulation in the East Moldabek Formation in Kazakhstan

Both steam and hot water flooding of high-viscosity oils in the presence of swelling clays are difficult methods for producing oil efficiently because of potential formation permeability reduction. This paper pertains to heavy oil recovery from the East Moldabek formation where the oil API gravity is about 22 and is inundated with swelling clays. To achieve this, we used the IntersectTM reservoir simulator to compare oil recovery economics using both hot water and steam injection as a function of steam cycle duration, temperature, and steam dryness. We also studied clay swelling in the East Moldabek formation where clay poses a significant challenge due to its impact on permeability reduction. In this research, we developed an equation based on experimental data to establish a relationship between water mineralization and permeability in the East Moldabek formation. The equation provides valuable insight on how to mitigate clay swelling which is crucial for enhancing oil recovery efficiency—especially in sandstone reservoirs. Our modeling studies provide the recovery efficiencies for salinities of the hot water EOR versus cyclic steam EOR methods in a formation containing swelling clays. Specifically, the reduction in formation permeability as a function of the distilled water fraction is the controlling parameter in hot water or steam flooding—when the formation water mixture becomes less saline, oil recovery decreases. Our research shows that clay swelling can significantly impact cyclic steam stimulation outcomes, potentially reducing its effectiveness, while hot water flooding may offer a more cost-effective and operationally feasible solution in formations where clay swelling is a concern. Economic analysis reveals the potential for achieving an optimal favorable condition for hot water injection. Therefore, this paper provides a guideline on how to conduct thermal oil recovery for heavy oils in fields with high clay content such as the East Moldabek deposit.

Impact of a compound droplet on a solid surface: The effect of the shell on the core

The dynamic behavior of compound droplets impacting a solid surface was studied via experiments over κ (defined as the ratio of the compound droplet shell thickness h to the diameter D0 of compound droplet) ranging from 0 to 0.34, We ranging from 25 to 325 and Re ranging from 165.3 to 3405.2. The spreading diameter ratio, the maximum spreading dynamic contact angle and spreading speed of the core were investigated. Four modalities of the core of compound droplets were observed on the solid surface, including a) core rebound, b) no rebound, c) core splitting rebound, d) core splitting. The results revealed that the thickness of the shell, We, and the viscosity of the shell have a significant effect on the rebound and spreading processes of the core of the compound droplet. The high viscosity oil shell is conducive to its spreading. As the thickness of the oil shell increases, its cushioning effect on the water core also increases. In addition,κ=0.02254We0.503,κ=-0.336e-We121.056+0.319 and κ=0.06086e-We121.056+0.07716e-We121.70598+0.01595 were used to divide the modal boundary of the compound droplet core. Further analysis reveals the correlation between We, Re, βm and.κ,12+Weβm=8+31-cos22.78+84.57κβm3+0.955We1.05Reβm6.5.

Microbubbles enhance oil-in-water emulsion separation in fibrous coalescers

The principle of fibrous coalescers is to induce the coalescence and growth of small oil droplets in oil-in-water emulsions to achieve oil–water separation. However, they are poorly adaptable to emulsions containing high-viscosity oil. In this study, pressurized air is dissolved in the oil-in-water emulsion, microbubbles are released by reducing the pressure, and the emulsion is subsequently processed through a fibrous coalescer. Adding microbubbles altered the oil removal mechanism within the fibrous bed from oil droplet coalescence and growth to oil droplet–microbubble floc flotation, which significantly improved the emulsion separation efficiency of the fibrous bed, especially in complex emulsions containing surfactants and low salinity. Notably, the decrease in the interfacial energy of the oil droplet–microbubble floc caused oil droplets adhered to fibers to detach and renew quickly. Moreover, the curved interfacial tension increased oil droplet buoyancy and kinetic energy collectively drove the detachment of oil droplets from the fibrous bed. Effective, dynamic anti-fouling of the fibrous bed was able to maintain high throughput during long-term emulsion separation. This study provides a theoretical basis for the industrial application of fibrous coalescers for the treatment of oily wastewater produced during extraction high-viscosity crude oil.

Nickel-cobalt hydrogen phosphate membrane with outstanding anti-crude oil-fouling capability and its microscopic anti-fouling mechanism

Oil/water separation membranes with superior anti-fouling properties against highly viscous oils are crucial for the efficient treatment of oily wastewater. Herein, the effects of functional groups in an inorganic superhydrophilic membrane on the anti-fouling properties of the membrane are investigated. Using a facile one-step electrochemical deposition method, Ni1-xCoxHPO4·3H2O membranes were formed on a Cu(OH)2 microneedle-coated copper mesh (CCNC–P) with superhydrophilic and underwater superoleophobic properties. All CCNC–P membranes with different Co2+ contents showed outstanding anti-fouling capability for oily wastewater such as those containing crude oil. The CCNC–P(x = 0.5) membrane exhibited high separation efficiency reaching 99.7 % across five oil–water mixtures and oil-in-water emulsions, concurrently presenting an ultrahigh flux of 61695 L m−2 h−1 for crude oil–water mixture. Moreover, the membrane consistently maintained its separation performance during the long-term crude oil–water separation process. The flux decline ratio was below 1 %, and the flux recovery ratio approached 99.4 %. The CCNC–P membranes possessed superior chemical, thermal, and mechanical stability, suggesting significant potential for the industrial treatment of oily wastewater. Density functional theory calculation revealed that the HPO42− group in CCNC–P can strongly adsorb water molecules. The resultant stabilized hydration layer impeded the contact between the membrane surface and oil droplets, while the metal ions scarcely influenced the adsorption of water molecules on CCNC–P. These findings provide new insights into the development of novel oil–water separation membranes with higher anti-fouling capabilities against high-viscosity oils.

Oil storage and debrining process in insoluble sediment voids for underground salt cavern energy storage: An experimental study

Large salt cavern oil storage is an effective underground oil storage method, which has been widely used in the United States, Germany, and France. However, the insoluble impurity sediment particles at the bottom of the salt cavern will occupy plenty of oil storage space. To enhance the oil storage capacity, the sediment void oil storage (SVOS) method was proposed. The debrining process from the sediment void prerequisite of the SVOS. It will affect the feasibility of oil injection into the sediment void and the operation efficiency of SVOS. Thus, a self-made debrining device of SVOS was built, and the dynamic debrining process in the sediment void was investigated to explore the debrining process from the sediment void. Six debrining parameters (oil-brine interface change, oil injection rate, brine discharge rate, oil viscosity, the second oil injection quantity, and ground temperature) were proposed and considered. Two kinds of oils (diesel and petrolatum) were conducted in the SVOS debrining experiments. The experimental results showed that the debrining rate remained stable, and it was relevant to the oil injection rate and the interaction of oil and sediments. The average debrining rate of the initial diesel debrining, second diesel debrining, and petrolatum debrining were 2.5 g/s, 2.55 g/s and 2.40 g/s, respectively. The 50 °C of ground temperature sped the debrining rate of high-viscosity oil storage in the sediment void. The oil-brine interface kept balance from the macro perspective, and the oil did not penetrate the inner brine. The oil-brine interface drops ratio of the initial diesel debrining, second diesel debrining, and petrolatum debrining process were 0.586 mm/s, 0.629 mm/s and 0.592 mm/s, respectively. The oil in the sediment voids generated movable and immobile bubbles. The petrolatum flow in the sediment void was easier than the diesel due to the low viscosity at 50 °C. The research has a certain reference value for the development of underground salt cavern oil storage.

Biomimetic structural aerogel derived from green tide enteromorpha-prolifera: Multi-sided unidirectional freeze casting and solar-driven viscous oil spill remediation

The development of environmental remediation materials from renewable biowaste, especially for the cleanup of viscous oil spills in an eco-friendly manner, marks a substantial advancement in functional materials. This study proposes a biomass aerogel (M−MCEP) transformed from Enteromorpha prolifera (EP) in green tides for solar-driven recovery of high-viscosity oil spills. Inspired by the lamella-bridge architecture of Thalia dealbata stems, a biomimetic structure with multi-domain, long-range aligned lamella-bridge interconnections is constructed by a multi-sided unidirectional freeze-casting technique. Multi-scale interface optimization between rigid photothermal fillers and soft lamellar layers achieves multiple reinforcements, providing aerogel with a perfect balance of elasticity and strength. The multidomain low tortuosity channels and photothermal effects enhance M−MCEP’s photothermal conversion (95.2 %) and thermal conductivity (0.3517 W/m·K), reducing oil flow resistance and achieving high oil retention efficiency (>92 %). Under 1 sun irradiation, M−MCEP rapidly heats to 67.3 °C, effectively reducing the viscosity of crude oil in situ, with a crude oil adsorption rate of 1843 mL/m2 within 30 s. Moreover, M−MCEP captures emulsified oil in oil-in-water emulsions through high-speed repeated oscillations, achieving a separation efficiency of 96.42–99.21 %. Renewable resources and unique structural designs provided by nature drive the development of advanced biomimetic aerogels for efficiently remedying catastrophic oil spills.

Research for the Enhanced Oil Recovery Mechanism of Heavy Oil after Composite Huff and Puff Assisted by Edge-Bottom Water Displacement

Abstract In the late stage of exploiting heavy oil reservoirs with edge-bottom water, we are faced with problems such as high crude oil viscosity, channeling of bottom water, and rapid rise in water cut. To clarify the synergistic effect of N2, CO2, N2 foam, and viscosity reducer in water control and oil increase, and solve the problem of edge-bottom water rushing into production wells, one-dimensional sand-pack huff and puff experiments were carried out. First, the N2 foam huff and puff experiment evaluated the effect of N2 foam on controlling bottom water. Then the viscosity reducer assisted CO2 huff and puff experiment analyzed the synergistic viscosity reduction ability between the two to mobilize the remaining heavy oil. Next, the N2 foam-viscosity reducer-CO2 huff and puff experiment clarified the synergistic effect between the three. Finally, the N2 foam-viscosity reducer-CO2-N2 huff and puff experiment solved the problem of insufficient reservoir energy based on synergistic precipitation and oil increase. Experimental results show that N2 foam-viscosity reducer-CO2-N2 huff and puff is the optimal water control and oil increase solution. This solution can significantly reduce water production and increase oil production. In the one-dimensional sand-pack experiment, this technical solution reduced the water content by 68% and increased the recovery rate by 16.09%. The research results provide a reference for the development of exploitation technology schemes for similar edge-bottom water heavy oil reservoirs after entering high water cut.

The Influencing Factors and Mechanism of Anionic and Zwitterionic Surfactant on Viscosity Reduction in Heavy O/W Emulsions.

The high viscosity of heavy crude oil has been an obstacle to its safe production and economic transportation. In this work, a screened emulsified viscosity reducer system is conducted. Experimental results demonstrate that the most effective viscosity reducing agent comprises sodium oleate (NaOl) and cocamidopropyl betaine (CAB-35) in a ratio of 1:2, achieving a viscosity reduction rate of 94.65%. Additionally, the interfacial tension between oil and water decreases from 27 to 4 mN/m with 0.1 mass % TEOA and NaOH in a 1:1 ratio. The oil droplet size is uniformly distributed with D mean is 14 μm and D 50 is 11 μm. Droplets flocculate as the salinity increases to 0.2 mol/L, which corresponds to the apparent increase of viscosity. The adsorption of long alkyl chain lipophilic groups on surfactant molecules at the oil-water interface and the water film alters the wettability of pipe steel to water-wet, further enhancing the application of emulsification and viscosity reduction effects. The primary mechanism behind the viscosity reduction in emulsification is attributed to strong electrostatic interactions stemming from molecular electrostatic potential distributions.

Viscometric studies of heavy oil in the presence of compositions consisting of amphiphilic compounds and organic solvents

The chemical composition of high-viscosity heavy oil has been studied by IR spectroscopy and X-ray fluorescence spectrometry. It is found that characteristic absorption bands are available and characterize aliphatic structures and aromatic cycles, sulfur- and organophosphorus compounds, and the presence of compounds containing heteroatoms P, V, Ca, Pd, Ni, Ru, Mo, Fe, Cu and Zn in its composition is found. The method of rotational viscometry has established the Newtonian nature of the oil flow in the studied range of the velocity up to 300 s–1. At the same time, according to the densitometry results (ρ = 0.954 g/cm3 ), studied heavy oil belongs to the bituminous type characterized by a complex rheological behavior under long- and high-term deformation conditions. In order to regulate the studied oil viscosity properties, composite additives based on amphiphilic reagents of cationic and amphoteric type and organic solvents have been developed, their influence on dynamic and kinematic viscosity has been examined. It has been established that compositions with surfactants simultaneously containing a large amount of amino and phosphate groups dissolved in a non-polar aromatic solvent (toluene) or an organic mixture (catalytic reforming gasoline) have a maximum modifying effect of the colloidal structure of bituminous oil. The interaction of functional groups of amphiphilic reagents with oil heteroatoms leads to the dispersion of resinous-asphaltene substances, a decrease in the structural and mechanical strength of the system, an increase in the molecular mobility of aggregates, which results in improving the investigated oil quality and viscosity characteristics by 7.0 and 12.6 % according to the composition efficiency index.

STUDY OF TEMPERATURE FIELDS NEAR A WELL DURING FILTRATION OF VISCOPLASTIC OIL

The work examines the time variation of fluid temperature during non-isothermal filtration of viscoplastic oil near a well. It is known that a characteristic feature of modern oil production is an increase in the share of hard-to-recover oil reserves, which include viscoplastic oils. According to their rheological characteristics, such oils are non-Newtonian liquids and, therefore, their filtration process is not described by Darcy’s linear law. When filtering fluids that are not described by Darcy's law, it is necessary to use nonlinear filtration laws, which make it possible to more adequately describe the processes occurring in productive formations when hydrocarbons are displaced from them. To describe the nonlinear filtration law, empirical formulas obtained by approximating data from laboratory experiments are usually used.In the works of V.V. Devlikamov and his co-authors provide experimental data on the dependence of viscosity on shear stress for high-viscosity oils. They have been shown to be approximated quite well by a sigmoid function. However, the problem then becomes significantly nonlinear. Subsequently, in order to simplify finding a solution to the problem of filtration of high-viscosity oil, experimental data were obtained by V.V. Devlikamov and his co-authors were approximated by broken lines.In this work, the experimental data are approximated by a sigmoid function, which allows for more accurate calculations. Assuming that the viscosity and density of oil do not depend on temperature, which is typical for natural development modes, the results of calculations of temperature changes over time near the well are presented. It is shown that the temperature of viscoplastic oil in the first hours after starting a well differs significantly from the temperature of Newtonian oil (oil with constant viscosity). Thus, if the temperature of Newtonian oil continuously increases, then the temperature of viscoplastic oil immediately after starting a well increases and coincides with the temperature of oil with constant viscosity, then drops and after some time begins to increase again. The work shows that such an unusual change in the temperature of viscoplastic oil over time is associated with a change in the zone of destruction of the formation structure.

ANALYSIS OF THE CHANGE IN THE RHEOLOGICAL CURVE OF THE FLOW OF NON-NEWTONIAN OILS IN THE FIELDS OF WESTERN KAZAKHSTAN

In order to improve oil recovery technologies, the task of studying the rheological properties of oil, which largely determine the development indicators of the development target, namely, the rate of oil withdrawal, the stability and nature of the movement of the front of displacement of oil by water or gas, and, as a result, final oil recovery, is becoming urgent. In this regard, there is a need for in-depth studies of the rheoviscidity properties of produced oils.This article presents the results of laboratory studies to study the rheological characteristics of both high-paraffin and heavy high-viscosity oils using the example of oil from fields in Western Kazakhstan. Since structured oils are thixotropic systems, all experiments were carried out with the same degree of structure destruction in oil, both anhydrous oils and those with different water cuts were studied. The authors also showed the nature of the change in the rheological curve of the flow of oil emulsion of various water cuts to identify the temperature interval where non-Newtonian properties of various oils are manifested. Their main physical and chemical properties are also given, and kinematic viscosities of oil with different densities are compared. The results of laboratory studies of viscosity change with temperature increase for Karazhanbas oil emulsion with different water cut are considered. Despite differences in viscosity values of different degrees of watered samples of highly paraffinic oil, the tendency of oil viscosity change depending on the shear gradient is the same. The formation of structured systems of resin and asphaltene particles is observed in flows with relatively low shear gradients. As a result, oil viscosity dependence on the shear gradient in the range of low values from 0 to 20 s-1 must be taken into account when solving tasks for high-paraffin production. The results obtained are of practical interest, since when creating a compositional model and technological modeling of the collection and transport system, the rheological characteristics of the oil of a particular field, as well as the presence of thixotropic properties, must be taken into account.

Highly transparent inorganic superhydrophilic coatings with sustainable anti-fogging and mechanically robust underwater anti-oil-fouling capabilities

Inorganic coatings with high transparency and superhydrophilicity have attracted tremendous attention because of their potential applications in marine environment monitoring, and oily wastewater treatment. However, the transparency and superhydrophilicity are usually mutually exclusive. Herein, we present a new facile strategy for fabricating highly transparent and mechanically robust superhydrophilic inorganic coatings with outstanding anti-fogging ability and anti-oil-fouling performance for high-viscosity oils. In this strategy, amorphous calcium phosphate (ACP) coatings are mineralized on the surface of polydopamine and polyethylenimine (PDA/PEI) membranes under the synergistic effect of magnesium ions, citric acid, and poly(acrylic acid) at room temperature, forming an organic-inorganic composite structure with a uniform texture on various substrates. Owing to the strong hydration capacity of ACP, these coatings are highly efficient at preventing surface fogging and avoiding underwater crude oil fouling. Meanwhile, the ACP coating without grain boundaries or pores can reduce light scattering, thus maintaining the high transparency of the substrate. Moreover, the organic-inorganic composite structure endows the coatings with robust mechanical properties. This PDA/PEI-ACP mineralized coating can be deposited on various substrates, showing potential applications in underwater optical lenses, oily wastewater treatment, microfluidic devices, and other areas.

Experimental investigation on the oil extraction process for a novel underground oil storage method: Oil storage in salt cavern insoluble sediment voids

Large-scale underground oil storage is vital for addressing the energy crisis. Leveraging the insoluble sediment space at the bottoms of salt caverns for oil storage is particularly effective in high-impurity salt mines, enhancing oil storage capacity. The process of extracting oil from the sediment void is essential for utilizing this resource. Three experimental devices were developed to investigate this extraction process. We conducted experiments on oil extraction processes and rates for various oil types, analyzing weight changes and influencing factors. The sediment and water content in the extracted oil were also evaluated. Results indicated that extracting oil from the sediment void is feasible, yielding average recovery rates over 90.0 %. High-viscosity oil at 50 °C exhibited three stages: initial stability, a rapid rise, and final stability. Low-viscosity oil correlated with brine injection rates, displaying a rapid rise, stable phase, and subsequent decline. Petrolatum extraction was easier than diesel extraction, and ground temperature improved recovery rates. Changes in water and sediment content had minimal impact on oil quality. This research provides insights for large-scale underground energy storage.

Oscillation-free implicit pressure explicit concentration discontinuous Galerkin methods for compressible miscible displacements with applications in viscous fingering

The system of compressible miscible displacements is widely adopted to model surfactant flooding in enhanced oil recovery techniques, where a low-viscosity fluid is injected underground to replace the high-viscosity oil. When the mobility ratio of the injected fluid to oil is high, the waterflood front tends to be unstable and exhibits a finger-like growth pattern, known as viscous fingering. Due to its unstable nature, the viscous fingering phenomenon is sensitive to mesh orientation and numerical discretization. Therefore, high-order numerical methods are preferable to reduce numerical artifacts and mesh dependence. In this paper, we propose a high-order discontinuous Galerkin method for the coupled nonlinear system of compressible miscible displacements to simulate the viscous fingering fluid instability in porous media. We adopt the IMplicit Pressure Explicit Concentration time marching approach based on implicit-explicit Runge-Kutta methods to achieve high-order temporal accuracy. Additionally, we introduce an oscillation-free damping term to control the spurious oscillations encountered in the waterflood front due to the large gradient of saturation. We have conducted ample numerical tests in two space dimensions to demonstrate the effectiveness and robustness of the proposed schemes in recovering viscous fingering.

Effect of Grease Composition on Impact-Sliding Wear

Impact-sliding experiments were performed by using four self-made lithium-based greases, namely Yangtze Grease 1, Yangtze Grease 2, Yangtze Grease 3, and Yangtze Grease 4. The influence of base oil viscosity, thickener content, and morphology of thickener fiber clusters on the lubricating state were visually explored, combined with field-emission microscopy and two-light interference technology. The grease film distribution at the middle section was measured using Dichromatic Interference Intensity Modulation (DIIM) software. All experiments were executed in a completely flooded environment. The results show that among the components of grease, the base oil’s viscosity has the greatest impact on the anti-wear performance of the grease. As the viscosity of the base oil increases, the grease exhibits better anti-wear performance. The grease film thickness under the condition of high-viscosity base oil is about 10 times higher than that under the condition of low-viscosity base oil. Secondly, the content of thickener in the grease needs to be controlled within a reasonable range. The experiments indicate that the effect of thickener content on the grease’s film-forming properties becomes more pronounced at higher speeds. From the experiment using YG 4, it can be seen that a higher thickener content under high-speed conditions increases the thickness of the lubricating grease film by about 10 times. The dimensions of the thickener fibers and the density of their entanglement structure significantly influence the rheological properties and load-bearing capacity of the grease. Larger fiber sizes and higher entanglement densities result in reduced grease fluidity and recovery but enhance its load-bearing capabilities. In order to obtain the best anti-wear performance during impact-sliding motion, the size of the thickener fiber and the density of the entanglement structure need to be controlled within an appropriate range.

Photothermally responsive, magnetic and flame-retardant MOF-based polyurethane sponges for oil/water separation and emulsion purification

The development of a multifunctional sponge with photothermal effect for adsorbing high-viscosity oil, as well as magnetic drive and excellent flame-retardant property, is significant in the field of oil/water separation, but also extremely challenging. In this work, a multifunctional MOF-based polyurethane (PU) sponge was successfully prepared using a simple method. Fe3O4-loaded NH2-MIL-101(Fe) nanoparticles were immobilized on PU sponge via low surface energy polydimethylsiloxane (PDMS) to obtain superhydrophobic NH2-MIL-101(Fe)@Fe3O4@PDMS@PU sponge (WCA = 155.6°), which exhibited excellent oil absorption, oil/water selectivity and reusability. The introduction of NH2-MIL-101(Fe)@Fe3O4 endowed the modified sponge with excellent photothermal properties, which was manifested in that with the help of solar energy, the sponge heated up rapidly and could achieve efficient adsorption of high viscosity oil. The magnetic property of the modified sponge made it effectively separate oil and water mixture along a certain path under the control of a magnetic field. In addition, the NH2-MIL-101(Fe)@Fe3O4@PDMS coating made the sponge exhibit excellent flame retardancy, which could effectively improve the safety of the modified PU sponge in practical applications. In summary, NH2-MIL-101(Fe)@Fe3O4@PDMS@PU sponge has potential application prospects in the oil/water separation field.