Increase In Interfacial Tension Research Articles

Wetting Effect Induced Depletion and Adsorption Layers: Diffuse Interface Perspective.

When a multi-component fluid contacts arigid solid substrate, the van der Waals interaction between fluids and substrate induces a depletion/adsorption layer depending on the intrinsic wettability of the system. In this study, we investigate the depletion/adsorption behaviors of A-B fluid system. We derive analytical expressions for the equilibrium layer thickness and the equilibrium composition distribution near the solid wall, based on the theories of de Gennes and Cahn. Our derivation is verified through phase-field simulations, wherein the substrate wettability, A-B interfacial tension, and temperature are systematically varied. Our findings underscore two pivotal mechanisms governing the equilibrium layer thickness. With an increase in the wall free energy, the substrate wettability dominates the layer formation, aligning with de Gennes' theory. When the interfacial tension increases, or temperature rises, the layer formation is determined by the A-B interactions, obeying Cahn's theory. Additionally, we extend our study to non-equilibrium systems where the initial composition deviates from the binodal line. Notably, macroscopic depletion/adsorption layers form on the substrate, which are significantly thicker than the equilibrium microscopic layers. This macroscopic layer formation is attributed to the interplay of phase separation and Ostwald ripening. We anticipate that the present finding could deepen our knowledge on the depletion/adsorption behaviors of immiscible fluids.

Dynamic Interfacial Tension Measurement for the Kinetic Study of Eu(III) Extraction in the NaNO3/Tributyl Phosphate System Based on an Increase in Interfacial Tension.

We demonstrated for the first time that interfacial tension measurements can be used to evaluate the kinetics of the solvent extraction of metal ions. The Eu(III) extraction mechanism in the nitrate ion/tributyl phosphate (TBP) system was investigated on the basis of dynamic interfacial tension. Interestingly, the interfacial tension of the TBP droplet (γ) increased with Eu(III) extraction. This behavior can be explained by the electrocapillary effect. The time dependence of γ was kinetically analyzed, and we demonstrated that the rate-determining process was the interfacial reaction of Eu(III). Furthermore, the dependence of the mass transfer rate constant upon the concentration of the nitrate ions revealed that two nitrate ions were involved in the interfacial reaction during Eu(III) extraction. However, no change in the rate constant upon TBP concentration was observed, because the change in the TBP concentration did not affect the electrocapillary effect. We determined the forward and backward reaction rates to be k1 = (1.5 ± 0.7) × 10-6 m M-2 s-1 and k-MT = (6.9 ± 3.9) × 10-7 m s-1. Therefore, for the first time, we demonstrated that dynamic interfacial tension, which is involved in the electrocapillary effect, can be used to elucidate the kinetics of Eu(III) extraction. We expect that this study will attract the attention of researchers in several fields, including physical and analytical chemistry.

One-step in-situ fabrication of novel food-grade Janus droplets with zein and alginate: Dual effect of phase separation and interfacial equilibrium

Janus droplets exhibit an asymmetric structure, where one droplet has two compartments with different properties. However, food-grade Janus droplets are rarely reported. In this work, food-grade Janus droplets composed of alcohol-soluble protein and alginate were fabricated for the first time by the one-step in-situ method. Segregative phase separation and interfacial equilibrium of zein and alginate solutions were the prerequisites for the formation of food-grade Janus droplets. Segregative phase separation occurred when the concentration of zein and alginate solutions was increased. The zein in the aqueous phase synergistically reduced the oil-water interfacial tension with polyglycerol polyricinoleate (PGPR), but the alginate weakened the interfacial ability of PGPR, resulting in an increase of oil-water interfacial tension. Therefore, the interfacial tension difference between zein/oil and alginate/oil could be regulated by changing the concentration of zein and alginate solutions, which was beneficial to the interfacial equilibrium. The droplet size of food-grade Janus droplets could be adjusted by the concentrations of zein and alginate solutions. In addition, the Janus droplet structure could be further controlled by the volume ratio of zein and alginate solutions. The destabilization of food-grade Janus droplets was dominated by coalescence and sedimentation. The construction of food-grade Janus droplets is expected to provide a structural basis for the construction of food-grade Janus particles and promote the development of food technology.

Tunable Approach to Induce the Formation of Flexible Nanofilms from Small (3 nm) Gold Nanoparticles at Oil-Water Interfaces.

The self-assembly of gold nanoparticles (AuNPs) into thin films at the liquid-liquid interface has promising applications in industries such as catalysis, optics, and sensors. However, precise control over their formation is complex, influenced by several factors which scale differently with core size. Due to their small free energy of adsorption, there are few examples of AuNPs with core diameters <10 nm. The present research evaluates the adsorption of ∼3 nm AuNPs from either side of the oil-aqueous interface with variations in ligand shell composition, the oil phase composition, and the structure of alcohol additives to best drive thin-film formation. Film formation and quality are evaluated, and a recent thermodynamic model is used to gain insight into the primary forces promoting this adsorption. Results demonstrate that longer-chain alcohol additives (namely, n-butanol and n-hexanol) induced adsorption more efficiently than shorter-chain alcohols (ethanol). The volume of alcohol additive needed to induce adsorption was dependent upon the ligand composition, suggesting that the mechanism for induced interfacial adsorption is via interaction with the AuNP ligand shell. Comparison with the thermodynamic model indicates that the driving force for this induced adsorption is the alteration of the three-phase contact angle. Additionally, the use of various oils demonstrates that as oil-water interfacial tension increases, more AuNPs adsorb to the interface. This relationship is also supported by the model. Insight gained for favorable conditions of adsorption for AuNPs < 10 nm as well as the underlying thermodynamic mechanism is important in working toward the ability to fine-tune such films for industrial applications.

Effective cell membrane tension protects red blood cells against malaria invasion.

A critical step in how malaria parasites invade red blood cells (RBCs) is the wrapping of the membrane around the egg-shaped merozoites. Recent experiments have revealed that RBCs can be protected from malaria invasion by high membrane tension. While cellular and biochemical aspects of parasite actomyosin motor forces during the malaria invasion have been well studied, the important role of the biophysical forces induced by the RBC membrane-cytoskeleton composite has not yet been fully understood. In this study, we use a theoretical model for lipid bilayer mechanics, cytoskeleton deformation, and membrane-merozoite interactions to systematically investigate the influence of effective RBC membrane tension, which includes contributions from the lipid bilayer tension, spontaneous tension, interfacial tension, and the resistance of cytoskeleton against shear deformation on the progression of membrane wrapping during the process of malaria invasion. Our model reveals that this effective membrane tension creates a wrapping energy barrier for a complete merozoite entry. We calculate the tension threshold required to impede the malaria invasion. We find that the tension threshold is a nonmonotonic function of spontaneous tension and undergoes a sharp transition from large to small values as the magnitude of interfacial tension increases. We also predict that the physical properties of the RBC cytoskeleton layer-particularly the resting length of the cytoskeleton-play key roles in specifying the degree of the membrane wrapping. We also found that the shear energy of cytoskeleton deformation diverges at the full wrapping state, suggesting the local disassembly of the cytoskeleton is required to complete the merozoite entry. Additionally, using our theoretical framework, we predict the landscape of myosin-mediated forces and the physical properties of the RBC membrane in regulating successful malaria invasion. Our findings on the crucial role of RBC membrane tension in inhibiting malaria invasion can have implications for developing novel antimalarial therapeutic or vaccine-based strategies.

A numerical study on the effect of wall wettability on film formation in liquid–liquid slug flow

This study numerically investigates the effect of the contact angle on the hydrodynamics of liquid–liquid slug flow in a capillary with an internal diameter of 2.4 mm. The finite volume method is used to solve the Navier–Stokes equation, and the volume-of-fluid method is employed for interface capturing. The contact angle varies from 13° to 169°. The aqueous phase is observed as a continuous medium, the organic phase is in a dispersed phase at low contact angles, and the aqueous phase is dispersed as a medium at high contact angles. The slug velocity is lower at partial wetting contact angles than at fully wetting or non-wetting contact angles. The vorticity inside the slug is higher at extreme contact angles (169°/13°) and becomes very pronounced near the interface. At the Weber number Weslug&amp;gt;0.135, fully developed film is observed. The thickness of this film increases as the interfacial tension decreases. Additionally, the pressure within the slug rises with an increase in interfacial tension.

A data-driven model of drop size prediction based on artificial neural networks using small-scale data sets

An artificial neural network (ANN) method is introduced to predict drop size in two kinds of pulsed columns with small-scale data sets. After training, the deviation between calculate and experimental results are 3.8% and 9.3%, respectively. Through ANN model, the influence of interfacial tension and pulsation intensity on the droplet diameter has been developed. Droplet size gradually increases with the increase of interfacial tension, and decreases with the increase of pulse intensity. It can be seen that the accuracy of ANN model in predicting droplet size outside the training set range is reach the same level as the accuracy of correlation obtained based on experiments within this range. For two kinds of columns, the drop size prediction deviations of ANN model are 9.6% and 18.5% and the deviations in correlations are 11% and 15%.

Optimizing chaotic frequency electric fields for deformation analysis of droplets based on numerical modeling

Chaotic pulse group (CPG) electric field has already been proposed to achieve demulsification of water-in-oil (W/O) emulsions; however, the electric field parameters of the CPG electric field for efficient demulsification of emulsions are unknown. Therefore, in this study, the numerical model of droplet deformation under the action of electric field was established by coupling the flow field and electric field, and the effectiveness of the model was verified by comparing with the experimental results. In the numerical model, the electric field parameters are optimized by droplet deformation; moreover, the influence of surface tension and oil viscosity on the optimal electric field parameters is discussed; the deformation of droplets under the optimized CPG electric field was analyzed. The results show that when the droplet radius is 1 mm, the optimal electric field strength is 612 kV/m, the optimal pulse width is 0.023 s, and the optimal pulse rest width is 0.017 s. The increase in interfacial tension leads to the increase in optimal electric field strength, and the decrease in optimal pulse width and pulse rest width. The increase in oil viscosity leads to an increase in the optimal electric field parameters. With the increase in interfacial tension and oil viscosity, their influence on the deformation of droplets gradually decreases. Droplets of different sizes could find their own optimal electric field parameters in the CPG electric field, so as to achieve the maximum deformation. The results provide valuable guidance for the selection of electric field parameters in CPG electric field industrial applications.

Structure and functionality of cinnamaldehyde/chitosan/gum Arabic complex particles

The work aims to study the effects of the mixing order of chitosan, gum Arabic and cinnamaldehyde and the concentration of cinnamaldehyde on the structure and functionality of complex particles. The results showed that non-covalent and Schiff base reactions occurred between cinnamaldehyde, chitosan and gum Arabic. When chitosan and gum Arabic (CS-GA-1:0.3) were mixed first, the complex particles were flat spherical and more compact and existed in aggregate state, with higher particle size, Zeta potential and wettability, and lower interfacial tension. When mixing cinnamaldehyde with chitosan or gum Arabic first (CS-CA-1:0.3 and GA-CA-1:0.3) and adding high concentration of cinnamaldehyde (CS-GA-1:0.9 and CS-GA-1:1.2), the structural compactness and morphological regularity of the complex particles got weakened, leading to the decrease in contact angle and increase in interfacial tension. All complex particles could be effectively used as Pickering emulsion stabilizers. When chitosan:cinnamaldehyde mass ratio reached 1:0.6 and below, the complex particles showed obvious antibacterial properties. The above results laid a foundation for the application of chitosan-based complex particles in the food and medical field.

Fabrication and characterization of food-grade pea protein-ascorbic acid nanoparticles-stabilized Pickering emulsion

In this study, modified pea proteins (PP) were prepared by heat treatment, ultrasound, adjusting the pH to 9, and the addition of ascorbic acid (AA) to stabilize the Pickering emulsion (PE) with a 50% volume fraction of corn oil. The solubility of PP after different treatments was higher in all treatments than in the native state. FTIR and SDS-PAGE results confirmed that a covalent bond (Maillard reaction) was formed between PP and AA, which occurred more strongly in the heat-treated suspensions. The nanoparticles produced from ultrasonication of PP and the PP/AA complexes were able to stabilize the emulsion with a high volume fraction of oil as novel Pickering emulsifiers. In ultrasonicated PP and PP/AA complexes, the reduction of interfacial tension and particle size and increase of contact angle caused a significant improvement in the physical stability of the PE, which can be the result of regular placement of protein particles at the water-oil interface. The treatment corresponds to highly stable PE, heat-treated PP in the presence of AA in alkaline conditions (HPP.AA.pH), increased the contact angle of PP from ∼ 42 to 77, and decreased interfacial tension from ∼ 25 to 14. These PEs showed high physical and oxidative stability. According to CLSM images, the type of PE was oil in water, and PP particles surrounded the oil droplets. The results of this research could be effective in developing PP-based low-fat formulations with improved oxidative stability by utilizing different treatments, including ultrasonic treatment and/or complex formation between PP and AA.

Critical coalescence electric intensity of water droplets adsorbing surfactant molecules under electromagnetic synergy field

Electromagnetic synergy is a more effective physical method than a single AC electric field (ACEF) to enhance oil–water separation. However, the critical coalescence conditions and transformation mechanism of droplets adsorbing surfactant molecules in the synergistic electromagnetic field (EMSF) still lack research. Herein, a series of Triton X-100-adsorbed droplets with different surface tensions were prepared, and the critical coalescence electric intensity (Ec) of the droplets under ACEF and EMSF were compared. Micro high-speed experiments revealed that Ec of droplets under EMSF is higher than under ACEF. The electric intensity, Ec, increased with the increase in interfacial tension γ under both ACEF and EMSF. This study provides valuable results for designing high-performance devices by introducing electromagnetic synergy in water-in-oil emulsion treatment. For the equipment with electromagnetic synergy to strengthen oil–water separation, the allowable optimal voltage should be higher than that of the electrostatic coalescer, and the adjustment range is 2.99%−9.57%.

Experimental study on the effect of high water cut on the emulsifying properties of crude oil

Most waterflooding oilfields have entered the high water cut stage, but significant amounts of crude oil remain in the formation. Therefore, understanding the emulsifying characteristics of crude oil with high water content is crucial. This study investigates the effects of shear time, shear rate, temperature, water content, and re-emulsification at high water content on the emulsifying properties of crude oil. Results indicate that shear time, temperature, and water content play a role in enhancing the emulsifying capacity of crude oil. Additionally, the initial water content of the emulsion affects the solubilization ability of crude oil; lower initial water content leads to stronger solubilization ability, while higher total water content leads to weaker solubilization capacity. Under an optical microscope, the morphology of the emulsion was observed, revealing that an increase in water content resulted in an increase in particle size and quantity of emulsion droplets, leading to more uniform droplets. However, at high water content, the particle size of emulsion decreased, the number of droplets decreased, and the droplets became uneven. Furthermore, the particle size of re-emulsified emulsion was smaller than that of the emulsion with the same moisture content, indicating that re-emulsification can lead to instability. The interfacial characteristics of the emulsion were also analyzed, showing that an increase in water content caused an increase in interfacial tension and expansion modulus of emulsion compared to crude oil. Finally, the study elucidates the influence mechanism of high-water content on the emulsifying performance of crude oil, which includes the destruction of molecular forces on and between interfaces, weakening the steric hindrance effect. Unstable film and non-uniform droplets can promote coalescence and fragmentation of droplets, limiting the emulsifying performance of crude oil. The results of this study provide a better understanding of the formation and fracture process of emulsion under high water cut conditions, offering a theoretical basis for further enhanced oil recovery.

Effects of Entrained Slag Droplets on Slag-Metal Interface in A Gas-Stirred Ladle

This study explores the underlying mechanism between secondary refining efficiency, gas flow rate, and slag properties. The secondary refining efficiency is directly affected by the slag-metal interface area. Traditionally, the slag-metal interface has been limited to the liquid-liquid interface of the ladle cross-section and does not include the interface area between the entrained slag droplets and metal. To investigate the interface area with different slags and metals under various bottom blow rates, a physical model of a single-nozzle gas-stirred ladle was established using oil to simulate slag and water to simulate metal. The roles of relevant variables that affect the volume of entrained oil, the diameter of entrained droplets, and interface area were studied, as well as oil viscosity, interfacial tension, and oil thickness. Experimental data were collected using colorants and image processing techniques. Based on these findings, the increase in gas flow rate and oil layer thickness increased the volume of entrained oil and interface area, while the increase in oil viscosity and interfacial tension decreased these parameters. When the gas flow rate increased, the mean diameter of droplets first increased and then decreased. However, the specific surface area of droplets revealed the opposite trend. Furthermore, the mean diameter and specific surface area increased and decreased with increasing oil-layer thickness.

Interfacial tension of tri-ethylene glycol-water mixtures in carbon dioxide at elevated pressures

The study of interfacial tension (IFT) of fluid/liquid systems is vital to optimize the design and operation of liquid-fluid contactors, and in this case, the design and performance of carbon dioxide (CO2) dehydration by absorption using tri-ethylene glycol (TEG). Several studies on improving CO2 dehydration with an absorption column containing TEG focused on system simulation and modeling but so far neglect the impact of interfacial tension of TEG–CO2 on the overall system performance. This study analyzes the interfacial tension, fluid mixture densities and drop volumes of TEG and TEG + water in CO2 medium. The pendant drop and the oscillating u-tube methods with a high-pressure densitometer were used to measure the IFT and the mixture densities of TEG–CO2 and TEG + water–CO2, respectively, at temperatures ranging from 10 °C to 50 °C and pressures up to 250 bars. The saturated TEG–CO2 and TEG + water–CO2 densities were used to evaluate the IFT from recorded drop profiles. The static IFT of TEG–CO2 shows a strongly decreasing trend from above 40 mN/m to less than 5 mN/m as the pressure increases up to 250 bars at a constant temperature (30 °C) but strongly increases by a factor of nearly 6 as the temperature is raised from 10 °C to 50 °C at a fixed pressure of 70 bars. The same trend is observed for IFT of TEG–water–CO2, although a slight increase in IFT (sim 2 mN/m) is observed due a water content of 5 wt% which would have a negative effect on the mass transfer efficiency. Conversely, a lower interfacial tension at higher pressures and lower temperatures favors the formation of a larger interface which is advantageous for mass transfer. Dynamic IFT of TEG–CO2 attains a constant after around 5 min at 70 bars and 50 °C while the drop volume increases leveling off after 10 min corresponding to a volumetric expansion of nearly 14% which corresponds to a CO2 solubility in TEG of 14%. The drop volume of a pendant drop at higher pressures hardly depends on temperature due to the superposed counteracting effects of a slightly increasing buoyancy and slightly dropping IFT. For a process design, static values of IFT can be applied with a reasonable precision, e.g., for using We-correlations to estimate drop sizes.

Effects of grain size and small-scale bedform architecture on CO2 saturation from buoyancy-driven flow

Small-scale (mm-dm scale) heterogeneity has been shown to significantly impact CO2 migration and trapping. To investigate how and why different aspects of small-scale heterogeneity affect the amount of capillary trapping during buoyancy-driven upward migration of CO2, we conducted modified invasion percolation simulations on heterogeneous domains. Realistic simulation domains are constructed by varying two important aspects of small-scale geologic heterogeneity: sedimentary bedform architecture and grain size contrast between the matrix and the laminae facies. Buoyancy-driven flow simulation runs cover 59 bedform architecture and 40 grain size contrast cases. Simulation results show that the domain effective CO2 saturation is strongly affected by both grain size and bedform architecture. At high grain size contrasts, bedforms with continuous ripple lamination at the cm scale tend to retain higher CO2 saturation than bedforms with discontinuous or cross lamination. In addition, the “extremely well sorted” grain sorting cases tend to have lower CO2 saturation than expected for cross-laminated domains. Finally, both a denser CO2 phase and greater interfacial tension increase CO2 saturation. Again, variation in fluid properties seems to have a greater effect on CO2 saturation for cross-laminated domains. This result suggests that differences in bedform architecture can impact how CO2 saturation values respond to other variables such as grain sorting and fluid properties.

Toward mechanistic understanding of interfacial tension behavior in nanofluid-model oil systems at different asphaltene stability conditions: The roles of nanoparticles, solvent, and salt concentration

Surface phenomena between liquid-liquid phases like interfacial tension (IFT) can significantly affect the recovery factor in hydrocarbon reservoirs. Nanotechnology could be used as a chemical method for enhanced oil recovery (EOR) via IFT reduction and wettability alteration. Nanoparticles could draw the asphaltene molecules to the interface of crude oil and brine water to reduce IFT. Several researches were conducted on SiO2 nanoparticles due to their accessibility with low price and their good performance in wettability alteration. However, the mechanism of IFT changes under different conditions of asphaltene instabilities and in the presence of nanoparticles has not been fully understood yet. In this study, the stability of SiO2 nanofluid in the presence of different NaCl concentrations was evaluated by visual observation, spectral analysis, and measuring the size of the hydrodynamic diameter of the particles. Besides, Fourier transform infrared (FTIR) spectroscopy of asphaltene was measured. Then, the influence of different parameters, including asphaltene content, water salinity, and nanoparticle concentration on the IFT between synthetic oil and nanofluids, was measured by the pendant drop shape method using drop shape analysis apparatus. Furthermore, IFT changes due to asphaltene instability at different n-heptane content and the instabilities of SiO2 nanoparticles at higher salinities were discussed. The IFT between synthetic oil and brine was measured. Results showed that the IFT reduces (about 23 mN/m) at very high salt concentrations due to the presence of free salt ions attracted with the hydrocarbon phase. Also, increasing the instability of asphaltene to a particular n-heptane concentration reduces the IFT variation by NaCl concentration from 5 mN/m to 2.5 mN/m because less potential remains for asphaltene adsorption at the interface. In addition, the increase in n-heptane concentration leads to a decrease and then an increase in IFT. Furthermore, as the nanoparticles become unstable at high salinities, the IFT increases significantly. Moreover, the IFT difference between the case with nanoparticle and the case without it is about 20 mN/m.

Interfacial tension of carbon dioxide - water under conditions of CO2 geological storage and enhanced geothermal systems: A molecular dynamics study on the effect of temperature

In recent years, CO2 injection into geological formations under a wide range of temperature conditions, including super-hot geothermal reservoirs, has attracted much attention (i.e., higher than 500 K). Despite the importance, however, no study has been reported on the interfacial tension (IFT) of CO2 - water systems at temperatures higher than 478 K. In this study, we performed molecular dynamics (MD) simulations to estimate the CO2 - water IFT from 278 to 573 K at 8 to 50 MPa. Our results show the IFT at 10 MPa and 573 K is approximately 80% lower than that at a typical reservoir condition for CO2 geological storage. This indicates that the effect of the capillary pressure on the flow of CO2 and water in the geological formation is expected to be significantly reduced in such a super-hot geothermal reservoir.We discuss a possible mechanism for the IFT variation against temperature, including the maxima around 373 K at 8 to 12 MPa, which is reproduced and tackled by MD simulations for the first time. On the basis of the Gibbs-Duhem relation, the temperature dependence is directly related to the interfacial excess molar entropy. Our analyses show (1) the IFT increase is attributed to the substantial variation of the entropy and density of the bulk CO2 phase near the critical point, and (2) this variation is characterized by the distinct behavior of the molecular ordering and the mobility of CO2 at the interface, consistent with the close relationship between the disorder in molecular arrangement and configurational entropy.

Droplet Microfluidic Technology for the Early and Label-Free Isolation of Highly-Glycolytic, Activated T-Cells.

A label-free, fixation-free and passive sorting method is presented to isolate activated T-cells shortly after activation and prior to the display of activation surface markers. It uses a recently developed sorting platform dubbed “Sorting by Interfacial Tension” (SIFT) that sorts droplets based on pH. After polyclonal (anti-CD3/CD28 bead) activation and a brief incubation on chip, droplets containing activated T-cells display a lower pH than those containing naive cells due to increased glycolysis. Under specific surfactant conditions, a change in pH can lead to a concurrent increase in droplet interfacial tension. The isolation of activated T-cells on chip is hence achieved as flattened droplets are displaced as they encounter a micro-fabricated trench oriented diagonally with respect to the direction of flow. This technique leads to an enrichment of activated primary CD4+ T-cells to over 95% from an initial mixed population of naive cells and cells activated for as little as 15 min. Moreover, since the pH change is correlated to successful activation, the technique allows the isolation of T-cells with the earliest activation and highest glycolysis, an important feature for the testing of T-cell activation modulators and to determine regulators and predictors of differentiation outcomes.

A new dynamic imbibition model for penny-shaped blind pores in shale gas well

Penny-shaped blind pores are common in shale, these pores with the original gas occurrence, including free gas and adsorbed gas, are seriously affected by a large amount of imbibed fracturing fluid. The competitive gas–water adsorption mechanism and the equations of gas-water phase pressures were analyzed statistically to detail the changes in gas–water distribution during imbibition. Based on the Lucas–Washburn equation, a new dynamic imbibition model is established for penny-shaped blind pores in shale gas reservoirs, which first considers the resistance of desorption of adsorbed gas and free gas and the factors of pore shape and fractal characteristics. The experimental validation, dimensionless-type curve, and common features of the new model regarding water imbibition are analyzed in detail. The results indicated that the proposed model is suitable for accurately predicting the imbibition in blind pores, and the dimensionless-type curve can simplify the calculation process for imbibition predictions. Factor analysis showed that penny-shaped pore width and length are two important factors for imbibition, the smaller width and the longer length, the more imbibition. Meanwhile, the increase of gas-water interfacial tension and displacement pressure is conducive to imbibition, the increase of initial gas pressure and desorption of adsorbed gas is obstructive to imbibition. The research is not only applicable in shale gas reservoir but also useful for geological hydrogen storage, carbon dioxide storage and geothermal development.

Effect of bacteria on oil/water interfacial tension in asphaltenic oil reservoirs

Microbial enhanced oil recovery (MEOR), due to the formation of biofilm and the presence of biosurfactants generated by microorganisms in the reservoir, can play a role in reducing interfacial tension (IFT) and wettability alteration. In this work, the fluid-fluid interaction by measuring the IFT has been evaluated for combining two EOR methods, including low salinity water and MEOR, due to the high importance of fluid-fluid interaction in EOR. GeoBacillus stearothermophilus has been used as a bacterium to study changes in IFT. The effect of different salts, including monovalent and divalent cations and anions at different salinities, on biosurfactant performance, is investigated using IFT measurements. Also, the type of oil is evaluated in terms of its acidic and basic properties on the performance of biosurfactants. According to the results of this study, injection of GeoBacillus stearothermophilus bacteria reduces interfacial tension in acidic oil by 10.26% and in basic oil by 5.26%. According to the results, increasing salinity in the presence of oil-containing asphaltene with basic properties increases the IFT of the solution containing GeoBacillus stearothermophilus bacteria, but in the presence of acidic oil, a decrease in IFT is observed. The most significant effect of reducing the IFT of acidic oil and solution containing GeoBacillus stearothermophilus is obtained in the presence of the following salts, respectively: CaCl2 > MgCl2 > NaCl. The results show that with increasing CaCl2 concentration, the IFT between basic oil and GeoBacillus stearothermophilus solution gradually increases. This ascending trend is in the presence of NaCl salt with a lower slope. However, in the presence of MgCl2 salt, dual behavior is observed before and after the concentration of 1000 ppm, so that before this concentration, the IFT increases and then decreases. The findings of this study can help for a better understanding of the interaction of bacteria with asphaltenic oils in the presence of effective salts for low salinity water injection. The results of this study showed that by combining low salinity water with bacteria, less IFT could be obtained than low salinity water or bacteria alone.