Variation Of Interfacial Tension Research Articles

Investigation of ionic liquid adsorption and interfacial tension reduction using different crude oils; effects of salts, ionic liquid, and pH

The results revealed the significant effect of NaCl, KCl, CaCl2, MgCl2, CaSO4, MgSO4, and Na2SO4 and pH values of 3.5–11 on the interfacial tension (IFT) reduction using three types of neutral, acidic, and basic crude oils, especially for acidic crude oil (crude oil II) as the pH was changed from 3.5 to 11 (due to saponification process). The findings showed the highest impact of pH on the IFT of crude oil II with a reducing trend, especially for the pH 11 when no salts exist. The results revealed that the salts except MgCl2 and CaCl2 led to a similar IFT variation trend for the case of distilled water/crude oil II. For the MgCl2 and CaCl2 solutions, a shifting point for IFT values was inevitable. Besides, the dissolution of 1-dodecyl-3-methyl imidazolium chloride ([C12mim][Cl]) with a concentration of 100–1000 ppm eliminates the effect of pH on IFT which leads to a reducing trend for all the examined crude oils with minimum IFT of 0.08 mN/m. Finally, the [C12mim][Cl] adsorption (under pH values) for crude oils using only Na2SO4 was measured and the minimum adsorption of 0.41 mg surfactant/g Rock under the light of saponification process was obtained.

Development of a multi-stage model for freezing of a suspended binary solution droplet

The importance of developing spray freeze-drying technology for extending the shelf life of biological and pharmaceutical materials has never been greater, given the increasing food shortage and the strong demand for pharma processes. In particular, the optimal thermal design and application of spray freeze-drying technologies now depend on the estimation of nucleation behavior for droplet solidification (especially the droplets of binary mixtures). Although earlier nucleation models could estimate the nucleation rate and temperature of solidifying droplets, few considered extreme environmental factors, such as extremely low ambient temperatures below −60C∘. To ensure the preservation and storage of biological and pharmaceutical products, such as vaccines and protein drugs, these conditions are essential. Hence, developing an accurate and trustworthy mathematical framework for simulating nucleation is paramount. In this study, a multi-stage, hybrid analytical-numerical model for droplet solidification is developed while coupled with a gradient-based optimization algorithm. Specifically, the five-stage solidification of binary mixtures is simulated (including supercooling of liquid, nucleation, recalescence, equilibrium freezing, and subcooling of solid), which captures the dynamic behaviors of temperature and composition or solute concentration during phase change. The heterogeneous nucleation of a binary-mixture droplet in a frigid environment is predicted and validated against a series of experiments on single suspended droplets at a wide range of ambient temperatures between −20 and −160C∘. The freezing curves of different solute concentrations are also validated against experimental data. It is found that significant variations in interfacial tension lead to abrupt changes in nucleation temperature for extremely cold environments. Further, the effects of the concentration, contact angle, droplet size, and heat transfer coefficient are investigated.

Development of methodological solutions for the efficient development of gas condensate deposits in low-permeability reservoirs with complex phase behavior of reservoir fluid

Efficient production of gas and condensate from deep deposits requires the solution of a set of scientific and methodological problems, including the assessment of distribution of the initial fluid composition and properties within the deposit; predicting the complex phase behavior of the reservoir fluid at near-critical conditions and under the influence of the porous medium; modeling the formation of condensate banks in multiphase flows, taking into account velocity effects, variable interfacial tension, non-equilibrium phase transitions and complex well completions; etc. The paper presents the developments of Oil and Gas Research Institute of the Russian Academy of Sciences in this area, with an emphasis on recovery of the unique hydrocarbon reserves of the Achimov deposits of the Urengoy oil and gas condensate field.

Magnetically recyclable polydopamine-polyquaternium modified Fe3O4 nanoparticles for demulsification of asphaltene-rich ASP flooding produced water

The asphaltene-rich alkaline-surfactant-polymer (ASP) flooding produced water has been identified with high interfacial stability and severe secondary emulsification, which poses great difficulties in its demulsification process. This leads to an urgent need to develop targeted and efficient demulsifiers. In this research, a novel polydopamine-polyquaternium modified Fe3O4 (PQA-PDA@Fe3O4) nanoparticle integrates the electrical neutralization, interfacial adsorption and magnetic aggregation functionalities was prepared to dispose this emulsion. Primarily, structural and surface properties of the PQA-PDA@Fe3O4 demulsifier were systemically characterized by a series of analytical techniques, which presents its core-shell, hydrophilic and positively charged characters. When employing PQA-PDA@Fe3O4 to treat the produced water that contained 500 mg/L emulsified oil, a demulsification efficiency of 90.5 % was achieved at 200 mg/L dosage. It was found that the PQA-PDA@Fe3O4 nanoparticles could coalesce the fine oil droplets into large and dense aggregates, as demonstrated by the raised fractal dimension values. By monitoring the interfacial properties (interfacial tension, zeta potential and interfacial film elastic modulus) variations, the demulsification mechanism was further explored. The PQA-PDA@Fe3O4 nanoparticle could spontaneously migrate to the oil/water interface and reassemble a loose interfacial film, thus leading the oil droplets destabilization and aggregation. Notably, the magnetic force between the PQA-PDA@Fe3O4 nanoparticles significantly accelerates the oil droplets aggregation and inhibits the secondary emulsification process, so as to achieve the outstanding demulsification efficiency. Moreover, this PQA-PDA@Fe3O4 nanoparticle exhibited acceptable magnetic recyclability. These results provided an effective and alternative protocol to demulsify the asphaltene-rich ASP flooding emulsions.

Role of concentration and hydrophobic nature of weak polyelectrolytes on adsorption structure and thermodynamics at oil-water interface: Study of several carboxylate polymers

Intermolecular structure, conformations, solvation and adsorption characteristics of four partially ionized polycarboxylic acids syndiotactic-poly(acrylic acid) (s-PAA), syndiotactic-poly(methacrylic acid) (s-PMA), isotactic-poly(methacrylic acid) (i-PMA) and atactic-poly(ethacrylic acid) (a-PEA) at oil (CCl4) - water interface is studied by molecular dynamics simulations over the range from dilute to monolayer coverage. Linearity and slope of Θ-Γ curves are correlated to conformational invariance and extent of adsorption (partial vs complete) respectively, within the range of concentration of study. Adsorption of i-PMA and a-PEA chains occurs deeper into the oil-side of interface region as driven by the greater hydrophobicity of these polymers. Higher tendency of highly extended s-PMA to desorb from the interface as compared to strong adsorption of compact coiled i-PMA is driven by their solvation behavior dictated by aspects of structural partitioning of chemical groups with respect to the solvents of the two phases. Hydrophobic side-group in the polyelectrolyte chain is responsible for the slower dynamics of the backbone. The observed variation in thickness of adsorbed layer and fractional interface coverage with concentration suggest partial adsorption of chain segments beyond saturation of interface rather than coiling of chains to accommodate additional chains. While a-PEA exhibits greater variation in interfacial tension, the change in electric potential difference across the interface indicates weak adsorption by s-PMA. The influence of the tacticity of PMA on dynamics and distribution of counter-ions is in agreement with experimental results. Results provide a significant advancement in our understanding of polyelectrolyte and polymer adsorption at oil-water liquid interface.

Inhibition of asphaltene deposition by Al2O3 nanoparticles during CO2 injection

Carbon dioxide flooding is of interest due to its high oil-sweep efficiency for enhanced oil recovery and contribution to the reduction of greenhouse gas emissions. However, when CO2 is injected into deep geological strata, asphaltene may precipitate. In this work, the effect of Al2O3 nanoparticles on the deposition of asphaltene was examined by assessing the variations of bond number and interfacial tension at different pressures and a temperature of 60 °C. The asphaltene onset point and intensity were characterized using the bond number, which proved a better indicator of changes in oil droplet shape and interfacial tension with gravity. Synthesized mixtures of toluene and n-heptane that contained two different kinds of asphaltenes were used as M and D oil samples. A 0.06 mass% addition of Al2O3 nanoparticles, which worked best for reduction of interfacial tension, was also applied at various pressures. Addition of nanoparticles to the oils prevented asphaltene precipitation in both synthetic samples by altering the slope of the plot of interfacial tension with pressure by 49.7% for the M sample and 9.0% for the D sample. The Al2O3 nanoparticles were found to be more effective at inhibiting asphaltene precipitation for the M oil sample due to its lower H/C ratio and higher nitrogen content.

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.

Pore-scale Analysis of CO2-brine Displacement in Berea Sandstone and Its Implications to CO2 Injectivity

For storage in deep saline formations, where CO2 is injected into the pore spaces of rocks previously occupied by saline groundwater (brine), relative permeability is a key input parameter for predictive models. CO2 injectivity is considered to reach the maximum value at the CO2 endpoint relative permeability when brine saturation becomes irreducible. The objective of this study is to investigate the effect of viscosity ratio, interfacial tension and wettability on relative permeability during CO2-brine drainage. A multiphase lattice Boltzmann model (LBM) is employed to numerically measure pore-scale dynamics in CO2-brine flow in the sample of Berea sandstone. CO2/brine with interfacial tension from 30 to 45 mN/m and viscosity ratio from 0.05 to 0.17 (the range of values expected for typical storage reservoirs conditions) are carried out to systematically assess the influence on the relative permeability curves. Although CO2 storage in sandstone saline aquifers is predominantly water wet, there are contradictory results as to the magnitude of the contact angle and its variation with fluid conditions. Therefore, the range of wetting conditions is studied to gain a better insight into the effect of wettability on supercritical CO2 displacement. In this study, it is observed that interfacial tension variations play a trivial impact while both of viscosity ratio and wettability are likely to have a significant effect on relative permeability curves under representative condition of storage reservoirs. We also perform a near-wellbore scale geomechanics analysis to investigate the impact of relative permeability on CO2 injectivity. The result shows that water-wet condition facilitates the CO2 injection when there is no fracture induced.

Study on the dynamic interfacial tension with micro interface sensor

In two-phase dispersion process coupling with interphase mass transfer, the dynamic variation of interfacial tension is a key parameter to determine the flow behavior. Simultaneous determination of the dynamic interfacial tension (DIFT) and the transient fluid concentration is the fundamental for understanding and predicting the DIFT, which is seldom reported in previous study. In this study, a novel method was developed to achieve the goal during the interphase mass transfer. Micro interface sensor was applied as a probe to detect the transient droplet concentration and the DIFT simultaneously. Based on the new method, the DIFT was studied in the process of the solute diffuses from the droplet to the continuous phase, and vice-versa. The transient concentration of the droplet was found to significantly affect the interfacial tension. Besides, the molecular movement across the interface may also affect the interfacial tension, which is seldom reported in previous studies. The method was demonstrated to be reliable and simple. It provides a promising approach to deeply understand the DIFT.

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.

Toward low-salinity waterflooding predictive capability development in carbonates for fast screening of oil-brine-rock candidates

Despite numerous studies on the low-salinity waterflooding (LSWF) technique, a robust predictive capability has not yet been established. Predictive capability development is essential to reduce costs and time during the early screening or prioritization of candidate fields for LSWF in the opportunity realization process (ORP). This study aims at proposing a set of screening methods that offer the best LSWF predictive capability for various crude oil-brine-carbonate rock systems. In this regard, the robustness of different methods for predicting oil recovery factor (RF) from core-scale spontaneous imbibition (SI) experiments in carbonate rocks was investigated here. The relevant small-scale screening methods were divided into two distinct categories. The first category includes methods based on rock/fluid interactions: wettability assessment based on flotation and contact angle measurement, and geochemical assessment to identify mineral dissolution (and pH change). The second group includes methods based on probing fluid/fluid interactions: oil-brine interfacial tension (IFT) and viscoelasticity, and micro-dispersion formation. The most common types of carbonate rocks, including dolomite, limestone, and chalk, were used to comprehensively evaluate the response of each carbonate rock type to brines of different salinities. Each rock type could be distinguished with its particular microscopic texture, pore-size, grain type, and carbonate mineral structure. According to the SI results, oil recovery strongly depends not only on brine salinity but also on the rock type. The oil RF for Indiana limestone was found to be higher than that for other rock types but showed less sensitivity to the degree of dilution. Additionally, RF from dolomite and chalk plugs showed the most and the least sensitivity to the degree of brine dilution, respectively. We introduced a brine efficiency index based on the SI results to compare the results for different rock types and salinities. The results of the systematic tests performed here showed that variation of IFT and viscoelasticity (expressed as phase angle) with brine salinity reduction was neither significant nor monotonic, and did not correlate with the brine efficiency index. Also, minor/negligible mineral dissolution was observed upon brine-rock contact. On the other hand, wettability results based on contact angle measurement and flotation, as well as microdispersion results strongly correlated with the brine efficiency index over a wide range of brine salinities, which indicates these techniques can quickly predict the potency of a system toward low salinity effect (LSE). It is hypothesized, therefore, that the techniques which involve rock explicitly would be more robust because they capture the rock-type dependency of LSE too. The findings from this study can be used for quick screening of the candidate formations for LSWF, before performing the costly and time-intensive special core analysis (SCAL) experiments. The data provided by this research can also enrich the SCAL data bank toward developing robust data-driven predictive models.

Thermotaxis of a deformable droplet in a confined Poiseuille flow

A droplet under a thermal gradient is known to migrate in a preferential direction, as governed by the variation of its interfacial tension with temperature. Contradicting the outcome of reported asymptotic analysis, here we show that the calculation of the droplet migration by considering the variation of interfacial tension with the imposed thermal field alone may be fundamentally incorrect. This error is attributed to the dynamically evolving interfacial temperature field due to a two-way coupling between the thermal field and the flow field, mediated by the droplet deformation and thermal diffusion. By directly capturing an inherent nonlinear coupling between the thermal field and the flow field using explicit interface tracking in a three-dimensional space, our boundary integral based analysis reveals that a linearly decreasing temperature profile imposed along the direction of a plane Poiseuille flow enhances the migration speed of the droplet in both the axial and cross-stream directions. This is in sharp contrast to a prediction of decelerated motion of the droplet under the same imposed thermal field, as obtained from asymptotic theory. We attribute this discrepancy to an alteration of the surface tension mediated interfacial stress due to the locally evolving temperature field, and a consequent concomitant alteration in the interfacial viscous stress to realize a tangential force balance at the interface. From scaling arguments, we show that the resulting change in the viscous drag force may occur over an order of magnitude, disrupting the outcome as compared to that obtained from asymptotic analysis. These results are likely to bear significant implications in controllable separation and sorting of deformable entities in confined fluidic media.

Diffusiophoresis of a highly charged conducting fluid droplet

Diffusiophoresis of a perfectly conducting droplet-like liquid metal in electrolyte solutions is investigated theoretically, focusing on the chemiphoresis component, the very heart of diffusiophoresis, where the droplet motion is induced solely by the chemical gradient. The resulting electrokinetic equations are solved with a pseudo-spectral method based on Chebyshev polynomials. For the isothermal electrokinetic system of a perfectly conducting droplet considered here, there is no Marangoni effect, which is a motion-inducing effect due to the variation of interfacial tension along the droplet surface. No Maxwell traction is present as well. The droplet motion is full of hydrodynamic nature. It is found, among other things, that contrary to a dielectric droplet, a conducting droplet always moves up the chemical gradient toward the region with a higher concentration of ions in chemiphoresis. This implies that a perfectly conducting droplet like a gallium or its alloy droplet is superior to the commonly utilized dielectric droplet like a liposome in drug delivery in terms of self-guarding itself toward the desired destination of injured or infected area in the human body, as specific ionic chemicals are often released there. Optimum droplet size yielding the fastest migration rate is predicted.

Morphology of MoS2 nanosheets and its influence on water/oil interfacial tension: A molecular dynamics study

Plate-shaped nanoparticles exhibit huge potential for a broad range of cutting-edge applications in interfacial-based science and technology, such as enhanced oil recovery in hydrocarbon reservoirs, owing to their remarkable features in superior affinity toward interfaces. Understanding the adsorption behavior of nanosheets (NSs) self-assembled at the water/oil interface (W/O interface) is crucial to elucidate the variation of interfacial tension (IFT) and establish special design criteria for efficient industrial use of NSs. Here we present a molecular dynamics study to reveal the morphology of carbon-chain modified molybdenum disulfide (MoS2) nanosheets. The stress exerted on a nanosheet is analyzed. The simulation results demonstrate a significant decrease in interfacial tension after adding NSs to the water/oil system, followed by a noticeable fluctuation with increased NS concentration. Surprisingly, the carbon-chain modified MoS2 nanosheets do not show a greater ability in altering IFT compared to unmodified ones. The IFT fluctuation is found strongly linked to the competition between the effects of interface coverage rate of adsorbed nanosheets and the intersection angle arising from non-uniform forces acting on a nanosheet.

Systematic investigation on the abnormal surface and interfacial activity of fatty acid ionic liquids

Ionic liquids are regarded as the promising and efficient additives to use in various aspects of petroleum industry, especially in chemical EOR. In this investigation, three novel fatty acid ionic liquids (FAILs), methyltrioctylammonium octanoate ([N8881][C8:0]), methyltrioctylammonium laurate ([N8881][C12:0]) and methyltrioctylammonium palmitate ([N8881][C16:0]), were selected and evaluated for their performances in terms of surface/interfacial activity, temperature and salt resistances. The three FAILs could cause remarkable reduction of surface tension to ~30mN/m in their aqueous solutions, and the [N8881][C8:0] with the shortest anionic alkane chain exhibited the greatest surface activity among three FAILs. Then the size-match effect and intermolecular interaction were employed to explain the abnormal variations, which were confirmed by the control experiments using mixed surfactants and the molecular dynamics simulation. It was found that the binding energy in [N8881][C8:0] (−28.961 kcal/mol) was larger than that in [N8881][C16:0] (−22.942 kcal/mol), which should be responsible for their different surface activity. Moreover, the crude oil/water interfacial tension (IFT) could be decreased to the much level (4.9 ×10−3 mN/m and 1.7 × 10−2 mN/m) even at high-temperature conditions (80 °C) and at high-salinity conditions (100,000 mg/L), indicating the FAILs might be the ideal candidate for the EOR used surfactants with great temperature and salt tolerances. Meanwhile, the variations of IFT results further verified our proposed mechanism.

Stable Electrospinning of Core-Functionalized Coaxial Fibers Enabled by the Minimum-Energy Interface Given by Partial Core-Sheath Miscibility.

Core–sheath electrospinning is a powerful tool for producing composite fibers with one or multiple encapsulated functional materials, but many material combinations are difficult or even impossible to spin together. We show that the key to success is to ensure a well-defined core–sheath interface while also maintaining a constant and minimal interfacial energy across this interface. Using a thermotropic liquid crystal as a model functional core and polyacrylic acid or styrene-butadiene-styrene block copolymer as a sheath polymer, we study the effects of using water, ethanol, or tetrahydrofuran as polymer solvent. We find that the ideal core and sheath materials are partially miscible, with their phase diagram exhibiting an inner miscibility gap. Complete immiscibility yields a relatively high interfacial tension that causes core breakup, even preventing the core from entering the fiber-producing jet, whereas the lack of a well-defined interface in the case of complete miscibility eliminates the core–sheath morphology, and it turns the core into a coagulation bath for the sheath solution, causing premature gelation in the Taylor cone. Moreover, to minimize Marangoni flows in the Taylor cone due to local interfacial tension variations, a small amount of the sheath solvent should be added to the core prior to spinning. Our findings resolve a long-standing confusion regarding guidelines for selecting core and sheath fluids in core–sheath electrospinning. These discoveries can be applied to many other material combinations than those studied here, enabling new functional composites of large interest and application potential.

Tracking of Nanoparticle Diffusion at a Liquid-Liquid Interface Adsorbed by Nonionic Surfactants.

Emulsions stabilized by both nanoparticles and surfactants often display longer shelf life than those stabilized by nanoparticles or surfactants alone. Although numerous works have been conducted to understand the effect of nanoparticles and surfactants on the variation of interfacial tension, little is known about interfacial diffusion when both nanoparticles and surfactants are present at interfaces. In this work, we used single-particle fluorescence tracking to study the lateral diffusion of individual hydrophobic nanoparticles at hexane-glycerol interfaces adsorbed by different amounts of nonionic surfactants. When the surfactant concentration is over a threshold, we found that the nanoparticle diffusion exhibits a two-regime behavior involving short-time Brownian and the emergence of subdiffusive, non-Gaussian, and dynamically anticorrelated diffusion in the long lag time regime. A stepwise analysis rationalized diffusion in different lag time regimes, leading to a mechanistic interpretation regarding the two-regime behavior. These results could provide insight into the understanding of the synergistic effect for the surfactant-assistant Pickering emulsion.

Hydrodynamic Properties of Tris(2-methylbutyl) Phosphate and Tri-n-alkyl Phosphates in n-Dodecane – A Comparative Investigation between Unirradiated and Gamma Irradiated Solvent Systems

ABSTRACT The physicochemical parameters of tris(2-methylbutyl) phosphate (T2MBP), a molecule possessing the essential characteristics required to be considered as a promising extractant in the solvent extraction stage of fast reactor fuel reprocessing, have been evaluated in the present study. In this context, the density, viscosity and interfacial tension (IFT), which are considered to be few among the important solvent selection criteria prior to its deployment in the plant scale have been measured for T2MBP in n-dodecane (n-DD) based systems. Similar studies have been performed with its straight chain isomer, tri-n-amyl phosphate (TAP) as well as the widely utilized commercial extractant, tri-n-butyl phosphate (TBP) so as to emphasize on the structural effects. Though the trends on the physicochemical behaviour of TBP based systems (temperature and ligand concentration effects) are well known in the literature, the data on TBP have been generated in the present work for comparison with the T2MBP results under similar experimental conditions. Solutions of trialkyl phosphates (TalP) in n-DD of different concentrations have been used to generate the data on the variation of density, IFT and viscosity with the change in the ligand concentration. In addition, the transformation in their properties has been assessed after subjecting the solvents to various levels of gamma absorbed doses. Overall, it has been observed that there was no significant variation in the density of the irradiated TalPs; however, there was a significant rise in the viscosity and reduction in the IFT of the TalP samples upon irradiation. The data on the Gibbs energy change of activation of various 1.1 M TalP/n-DD solutions have been generated by fitting their respective dynamic viscosity value as a function of temperature using Andrade’s equation. Moreover, from the IFT value, the parameters relating to the interfacial activity of TalP/n-DD solutions have been determined using the Szyszkowski adsorption isotherm.

Pore-doublet computational fluid dynamic simulation of the effects of dynamic contact angle and interfacial tension alterations on the displacement mechanisms of oil by low salinity water

Using our recently developed model, for the first time in the literature, the effect of fluid/fluid and rock/fluid interactions on the performance of Low Salinity Waterflooding (LSWF, as an Enhanced Oil Recovery process) at pore-doublet scale is investigated. The model is incorporated into OpenFOAM and both the Navier-Stokes equation for oil/water two-phase flow and the advection-diffusion equation for ion transport (at both fluid/fluid and rock/fluid interface) are solved via direct numerical simulation (DNS).The model is validated against imbibition and drainage pore-doublet experiments reported in the literature, and then applied to investigate the sole effect of wettability alteration as well as its coupled effect with interfacial tension (IFT) variations on the redistribution and transport of phases within the model. Different degrees of contact angle alteration, different trends of IFT variations reported in the literature, as well as different injection scenarios (secondary or tertiary) are considered.Simulation results show that in the case of high salinity water flooding (HSWF), IFT (within the range of 30 to 5 mN.m−1) has very limited effect on the residual oil saturation of the investigated model. For the case of HSWF in the oil-wet pore-doublet model (contact angle = 140°), significant amount of oil will be trapped in the small pores of the model. This residual oil cannot be produced in the absence of wettability alteration, no matter how much the IFT be reduced during LSWF (even as low as 0.1 mN.m−1). However in the absence of any IFT variation (IFT = 10 mN.m−1), the residual oil ganglia can be displaced with the sufficient degree of wettability alteration (contact angles below or equal to 30°). Nevertheless, in the presence of adequate contact angle reduction, fluid/fluid interactions (different IFT variation) can affect the outcome of the enhanced oil recovery. The LSWF performance boosts under appropriate degree of fluid/fluid and rock/fluid interactions as it leads to the coalescence of the detached or partially detached residual oil blobs and progress of chasing water front in both small and large pores of the doublets towards the downstream of the model. The results confirm the importance of fluid/fluid interactions such as IFT variation on such coalescence and dynamic LSWF, especially in the case of secondary LSWF.

Model for Interfacial Tension of Nanoconfined Lennard-Jones Fluid

Understanding and controlling the interfacial tension (IFT) of nanoconfined fluids has tremendous implications in scientific research and engineering applications. On the basis of the physical meaning of the equimolar dividing surface and the density distribution characteristic at the interface, we propose a simple model for the density profile at the vapor–liquid interface. The equimolar dividing surface and the surface of tension are assumed to coincide with each other in this work since the inhomogeneity of the interface is characterized by the proposed density profile model. Then, on the basis of the density distribution model, the density function theory (DFT) and the extended Peng–Robinson equation of state (PR EOS, which considers the effects of critical properties shift and capillary pressure) are used to estimate the confined interfacial properties and phase behavior in nanopores. Besides, the influences of temperature, pore radius, and wettability on IFT and capillarity are addressed. The developed model is validated as reliable for IFT calculation through comparison with the experimental data in the literature. Results show the following: (i) The IFT decreases with the reduction of pore size and the increase of temperature, and the decreasing rate is larger in smaller pores and higher temperatures. (ii) Capillary pressure increases with the decreasing pore size and the decreasing temperature, and it is more sensitive to pore size compared with the IFT. (iii) In the liquid phase-wet condition, as the contact angle decreases, the IFT decreases, while the capillary force increases, and the change rate is more obvious in smaller pores. Compared with other methods, the model for nanoconfined IFT proposed in this work, which is derived from the underlying physics mechanism, has a simper formulation with the similar reliability. Particularly, this work sheds light on the variation of IFT of hydrocarbons confined in nanopores of shale gas reservoirs, which provides an insight into the means of enhanced gas recovery in petroleum engineering.