Surfactant Foam Research Articles

Repulsive, but sticky – Insights into the non-ionic foam stabilization mechanism by superchaotropic nano-ions

HypothesisThe superchaotropic Keggin polyoxometalate α-SiW12O404− (SiW) was recently shown to stabilize non-ionic surfactant (C18:1E10) foams owing to electrostatic repulsion that arises from the adsorption of SiW-ions to the foam interfaces. The precise mechanism of foam stabilization by SiW however remained unsolved. ExperimentsImaging and conductimetry were used on macroscopic foams to monitor the foam collapse under free drainage and small angle neutron scattering (SANS) at a given foam height allowed for the tracking of the evolution of film thickness under quasi-stationary conditions. Thin film pressure balance (TFPB) measurements enabled to quantify the resistance of single foam films to external pressure and to identify intra-film forces. FindingsAt low SiW/surfactant ratios, the adsorption of SiW induces electrostatic repulsion within foam films. Above a concentration threshold corresponding to an adsorption saturation, excess of SiW screens the electrostatic repulsion that leads to thinner foam films. Despite screened electrostatics, the foam and single foam films remain very stable caused by an additional steric stabilizing force consistent with the presence of trapped micelles inside the foam films that bridge between the interfaces. These trapped micelles can serve as a surfactant reservoir, which promotes self-healing of the interface leading to much more resilient foam films in comparison to bare surfactant foams/films.

Experimental Study and Molecular Simulation of the Effect of Temperature on the Stability of Surfactant Foam

Temperature changes in CO2 foam-fracturing construction can easily affect surfactant foam stability. To investigate the effect of temperature on the foam stability of different types of surfactants, this study measured the foam half-life and viscosity of four typical surfactants, CTAB, LAS-30, HSB1214, and TX-10, using a novel self-designed and built foam performance measurement device. The effects of temperature on foam half-life and viscosity were studied. The results show that as the temperature increased, the half-life shortened, and the viscosity of the liquid phase decreased, which led to a decrease in foam stability. Moreover, using Materials Studio, a type of molecular simulation software, an interfacial model of the foam film was constructed to calculate the IFE and the self-diffusion coefficient of water molecules at 300 ps after the equilibrium of the foam system to investigate the mechanism of temperature influence on the stability of the foam. The results show that, for CTAB, LAS-30, HSB1214, and TX-10, the temperature increases from 15 °C to 45 °C, the IFE is enhanced by −50.05%, −59.10%, −64.21%, and −44.26%, respectively, the interfacial system changes from a low-energy state to a high-energy state, and the interfacial stability decreases. Meanwhile, Dwater increased 1.10-fold, 0.78-fold, 1.43-fold, and 0.64-fold, respectively, which accelerated the diffusion and migration of water molecules, weakened the intermolecular forces, and accelerated the instability of the foam system.

Applications of functional nanoparticle–stabilized surfactant foam in petroleum-contaminated soil remediation

Surfactant foam (SF) can be used to remediate petroleum-contaminated soil because of its easy transfer to inhomogeneous and low-permeability formations. Nanoparticles (NPs) not only stabilize SF under extreme conditions but also impart various functions, aiding the removal of petroleum contaminants. This review discusses the stabilization mechanisms of nanoparticle-stabilized SF (NP-SF) as well as the effects of NP size, chargeability, wettability, and NP-to-surfactant ratio on foam stability. SF stabilized by inert SiO2 NPs is most commonly used to remediate soil contaminated with crude oil and diesel. Low dose of SF stabilized by nano zero-valent iron is cost-effective for treating soil contaminated with chlorinated organics and heavy metal ions. The efficiency and recyclability of Al2O3/Fe3O4 NPs in the remediation of diesel and crude oil contamination could be enhanced by applying a magnetic field. This review provides a theoretical basis and practical guidelines for developing functional NP-SF to improve the remediation of petroleum-contaminated soils. Future research should focus on the structural design of photocatalytic NPs and the application of catalytic NP-SF in soil remediation.

Surfactant-Containing Foam Effectively Enhanced the Removal of Polycyclic Aromatic Hydrocarbons from Heavily Contaminated Soil.

Surfactant remediation has an excellent record of removing polycyclic aromatic hydrocarbons (PAHs). By using simulation experiments, we investigated the properties and mechanism of a surfactant-containing foam and its effect on PAH removal. Our results suggest that the optimal conditions by foam washing are as follows: 40 mmol·L-1 of rhamnolipid and fulvic acid mixed surfactant (V: V = 3:1), with 70:3 and 20:3 foam gas-liquid ratio for naphthalene and phenanthrene, respectively (pH 6, 50°C, 2 h). Under the optimal conditions, 60.1% and 56.68% removal efficiencies were achieved against naphthalene and phenanthrene from contaminated soil, respectively. These values were lower than those from the simulated media (76.69% and 70.43% for naphthalene and phenanthrene, respectively). The strong PAH adsorption on the soil particles antagonized volatilization, the key PAH removal mechanism by foam leaching. Therefore, this research provides relevant information for using surfactant foam to remediate heavily PAH-contaminated soils.

Sustainable Strategy for Gas Supply in China: Based on Foam Drainage Gas Recovery Technology

With the increasing demand of natural gas in China, its production is extremely important to fulfill the requirement of society. However, in reality, the natural gas production from the gas well in the gas field is often accompanied by the production of formation water. For gas well with low production, the gas flow rate in the well is too low to carry out the formation water from the bottom of the well. The water will thus accumulate in the well bore and the gas production will be greatly diminished. To solve this problem, based on the developing status of M gas field in China, foaming surfactant Z301 is synthesized and then foaming agent ZK3012 is developed through combination of Z301 with CAT after optimization experiments. After that, the compatibility tests are conducted to ensure that ZK3012 can work together well with formation fluids, and the water carrying rate tests are conducted concerning the optimum concentration of ZK3012. Finally, pilot test is conducted in 2 gas wells on site in M gas field, good results are obtained that accumulated water is discharged by foam drainage and the gas well production is increased. Studies demonstrate the main steps involved for application of this technology. In regard to the high external dependence degree of China in gas supply, operators of gas fields should give prominence to related studies of this technology to achieve sustainable development.

An Overview on the Treatment of Oil Pollutants in Soil Using Synthetic and Biological Surfactant Foam and Nanoparticles.

Oil-contaminated soil is one of the most concerning problems due to its potential damage to human, animals, and the environment. Nanoparticles have effectively been used to degrade oil pollution in soil in the lab and in the field for a long time. In recent years, surfactant foam and nanoparticles have shown high removal of oil pollutants from contaminated soil. This review provides an overview on the remediation of oil pollutants in soil using nanoparticles, surfactant foams, and nanoparticle-stabilized surfactant foams. In particular, the fate and transport of oil compounds in the soil, the interaction of nanoparticles and surfactant foam, the removal mechanisms of nanoparticles and various surfactant foams, the effect of some factors (e.g., soil characteristics and amount, nanoparticle properties, surfactant concentration) on remediation efficiency, and some advantages and disadvantages of these methods are evaluated. Different nanoparticles and surfactant foam can be effectively utilized for treating oil compounds in contaminated soil. The treatment efficiency is dependent on many factors. Thus, optimizing these factors in each scenario is required to achieve a high remediation rate while not causing negative effects on humans, animals, and the environment. In the future, more research on the soil types, operating cost, posttreatment process, and recycling and reuse of surfactants and nanoparticles need to be conducted.

Preparation for the introduction of SWAG at the fields of PJSC «Tatneft»

The results of laboratory studies of filtration processes on models of a terrigenous reservoir are presented in order to develop optimal compositions for simultaneous water and gas injection and foam assisted water alternating gas injection on the reservoir. The experiments were carried out on rock samples drilled from the core of terrigenous deposits of the Kynovsko-Pashiy horizon. The use of water-gas mixtures with foam-forming surfactants taking into account the field conditions of the fields of PJSC TATNEFT has been established will make it possible to obtain the greatest increase in oil recovery. Studies of the multiplicity and stability of foam systems have shown that non-ionic foaming surfactants TN-PO-1, TN-PO-2 and AF9-12 are best suited for use in FAWAG of the reservoir. The results of studies of the properties of foams depending on the concentration of surfactants are presented, recommendations are given on the use of specific reagents for the implementation of FAWAG, taking into account the conditions of specific fields. The use of SWAG and FAWAG technologies is not only increase oil recovery, but also significantly reduce the volume of irrationally used associated petroleum gas, which is one of the most important tasks for sustainable development goals. Keywords: enhanced oil recovery; filtration studies; simultaneous water and gas injection; foam assisted water alternating gas injection; foaming surfactants.

Remediation of Diesel-contaminated soil using zero-valent nano-nickel and zero-valent nano copper particles-stabilized Tween 80 surfactant foam

This paper uniquely reports the remediation of diesel-contaminated desert soil by aqueous Tween 80 (TW80) surfactant foams stabilized by zero–valent nickel (Ni0) and zero–valent copper (Cu0) nanoparticles (NPs). The sizes of synthesized nanoparticles, ∼21 nm (Cu0), ∼20 nm (Ni0), are determined by XRD and FE-SEM. The impact of these NPs (1 mg, 2 mg concentrations) on foaming characteristics, remediation of diesel-contaminated soils is explored at 2 vol% TW80 surfactant concentration. With 2 mg concentration of Ni0, Cu0 NPs and 2 vol% TW80 surfactant, it is found that 98.73 and 99.38 % diesel contaminants are removed.

Progress in research of sulfobetaine surfactants used in tertiary oil recovery

AbstractThe synthesis of sulfobetaine surfactants and their application in tertiary oil recovery (TOR) are summarized in this paper. The synthesis of sulfobetaine surfactants was classified into three categories of single hydrophobic chain sulfobetaine surfactants, double hydrophobic chain sulfobetaine surfactants and Gemini sulfobetaine surfactants for review. Their application in TOR was classified into surfactant flooding, microemulsion flooding, surfactant/polymer (SP) flooding and foam flooding for review. The sulfonated betaine surfactants have good temperature resistance and salt tolerance, low critical micelle concentration (cmc) and surface tension corresponding to critical micelle concentration (γcmc), good foaming properties and wettability, low absorption, ultralow interfacial tension of oil/water, and excellent compatibility with other surfactants and polymers. Sulfobetaine surfactants with ethoxyl structures, hydroxyl and unsaturated bonds, and Gemini sulfobetaine surfactants will become an important direction for tertiary oil recovery because they have better interfacial activity in high‐temperature (≥90°C) and high‐salinity (≥104 mg/L) reservoirs. Some problems existing in the synthesis and practical application were also reviewed.

Assessment of bimetallic Zn/Fe0 nanoparticles stabilized Tween-80 and rhamnolipid foams for the remediation of diesel contaminated clay soil

Diesel contamination of soil due to oil spills, disposal of refinery waste, oil exploration constitutes a major environmental problem. This paper reports the remediation of diesel contaminated clay soil using Zn/Fe0 bimetallic nanoparticle stabilized Rhamnolipid (RMLP) and Tween-80 (TW-80) surfactant foams. Fe0, and Zn (x wt%)/Fe0 (x = 0.2, 2.0, and 10.0) bimetallic nanoparticles are synthesized by using sodium borohydride reduction method. The average particle size (from FESEM) is calculated to be 62, 57, 42 and 35 nm for the Fe0, Zn (0.2)/Fe0, Zn (2)/Fe0 and Zn (10)/Fe0 nanopowders, respectively. The highest foamability and foam stability of 109.6 and 108.5 mL, respectively are observed for the RMLP (12 mg/l) surfactant foam stabilized with 6 mg/l Zn (10)/Fe0 nanoparticles. The surface tension values reduce to the lowest value of 28.1 and 31.4 mN/m with the addition of 6 mg/l of Zn (10)/Fe0 powder in RMLP and TW-80 solutions of 12 mg/l, respectively. The maximum diesel removal efficiency of 83.8 and 59%, is achieved by RMLP (12 mg/l) foam stabilized by Zn (10)/Fe0 nanoparticles (6 mg/l) for the clay soil contaminated with 100 and 500 μl/g of diesel, respectively. The physicochemical properties of the nanoparticles are studied to explain the foam properties and the remediation behavior. These findings regarding the nanoparticle stabilized foams can offer a cost-effective environment friendly commercial solution for soil remediation in the future.

Law and Mechanism Study on Salt Resistance of Nonionic Surfactant (Alkyl Glycoside) Foam

In this paper, the effects of three cations, Ca2+, Mg2+, and Na+, on the stability of APG foams were investigated experimentally. The results show that cations can slow down the process of liquid drainage and coarsening of APG foam, which is beneficial to the stability of the foam. The salt resistance mechanism of nonionic surfactant (APG) was investigated by molecular dynamics simulation and compared with that of anionic surfactant (SDS) foam. Firstly, the distribution characteristics of cations in APG foam and SDS foam were explored. It was found that the cations in the APG foam were mainly distributed in the water layer away from the head groups, and the cations in the SDS foam were more likely to appear near the head groups. Then, the hydration of the head groups and the cation was investigated. The results show that cations have little effect on the number of water molecules in the hydration layer of APG head groups but will reduce the diffusion capacity of water molecules and increase the water retention capacity of the foam film, thereby enhancing the foam stability. The addition of cations will reduce the water retention capacity of the SDS foam film. In addition, the behavior of surfactant head and tail groups was also analyzed. It was found that the cations made the head groups of APG more inclined to be aligned perpendicular to the liquid interface, and the tail groups were more inclined to realize a cross-arrangement and cover the gas–liquid interface. This can not only slow down the gas phase mass transfer process of the adjacent foam and slow down the coarsening process of the foam but also increase the viscoelasticity and anti-disturbance ability of the foam film. The cations will weaken the staggered arrangement of the SDS molecular tail groups, and at the same time, will cause the SDS molecules to aggregate, which greatly reduces the stability of the foam.

Influence of calcium chloride in coal on guar-based foam fracturing fluid rheological property: An experimental study

To investigate the influence of calcium chloride (CaCl2) in coal seams on the rheological property of a foam fracturing fluid, the guar powder was used as a foam stabilizer, and the anionic and cationic surfactants were used as foaming agents. The impact of CaCl2 concentrations on the foaming volume, half-life, viscosity, and surface tension of foam was investigated. The results show that CaCl2 has a more significant effect on the foaming amount and foam stability of the anionic surfactant-prepared foam. When the concentration of CaCl2 exceeds 0.25%, the viscosity of the base fluid shows a downward trend and gradually tends to a stable level below 10 mPa s. The foam half-life increases as the shape parameter an in the gamma function increases and decreases as the scale parameter b increases. The effect of CaCl2 on the bubble size of the anionic surfactant foam fracturing fluid is significantly greater than that of the cationic surfactant foam fracturing fluid. For coal reservoir foam fracturing, a foaming agent with better CaCl2 compatibility should be employed to reduce the influence of CaCl2 in the formation water on fracturing performance.

Excellent foaming properties of anionic-zwitterionic-Gemini cationic compound surfactants for gas well deliquification: Experimental and computational investigations

Foams are often employed as an efficient and cleaner method to remove the liquid accumulated at the bottom of the gas wells and promote the production of natural gas. However, the extreme conditions (e.g., high content of condensate, high salinity, high temperature, etc.) in the wells would retard the performance of the foaming agents. Usually, mixtures of different foaming surfactants were used to achieve high performances under those extreme conditions. In this paper, foams stabilized by surfactant mixtures containing alpha-olefin sulfonate (AOS), synthesized green cocamidopropyl betaine (CAPB) and modified quaternary ammonium Gemini surfactant (CAGB) in a proportion of 0.2:0.2:0.2 (wt%/wt%/wt%) were developed to evaluate their industrial application potential in gas well deliquification. The ternary surfactant (CAPB-CAGB-AOS) foam exhibited higher stability than the other dual surfactant foams and singular surfactant foams. Additionally, the foaming efficiency (defined as the ratio of the mass of water converted into foam to the mass of the initial liquid) and liquid unloading efficiency of the CAPB-CAGB-AOS mixture could be improved with the presence of condensate. Salts and methanol had a weak influence on the performance of the CAPB-CAGB-AOS foam. The introduction of ethylenediamine tetraacetic acid disodium (EDTA‧2Na) can enhance the performance of the CAPB-CAGB-AOS foam against salts. The temperature (> 60 °C) favored the foaming efficiency and liquid unloading efficiency of the CAPB-CAGB-AOS mixture, which reached up to 100% and 88.5% at 90 °C. These results indicated that the synergy effect of these three surfactants on the stability and liquid unloading efficiency of the foam can be confirmed. Moreover, the synergy effect can also be confirmed by the surface tension test, the foam's microstructure observation and the computational studies on calculated binding energies and electrostatic interactions.

Visualization study of CO2-EOR in carbonate reservoirs using 2.5D heterogeneous micromodels for CCUS

Carbon dioxide enhanced oil recovery (CO2-EOR) is one of the significant technologies to increase oil production and also to reduce greenhouse gas emissions. Carbonate reservoirs distribute widely in the world and show an extremely potential for CO2 geological sequestration and enhanced oil recovery, which is a promising technology for CCUS. However, the complex interfacial properties and strong heterogeneity of carbonate reservoirs lead to serious CO2 channeling, resulting in poor carbon sequestration. Microfluidic experiments in synthetic characterization of strongly heterogeneous reservoirs are a novel method to study multiphase flow in porous media. In this study, a heterogeneous micromodel was prepared using sequential photolithography and calcium carbonate (CaCO3) in-situ growth technique, which was used to construct CaCO3 layer by crystallization on the microchannel surface. The micromodel was represented by a 2.5-dimensional (2.5D) network of pores and fractures at different depths, which was used to simulate the natural structure of carbonate reservoir. The morphological and structural characteristics of the 2.5D micromodel were characterized using scanning electron microscopy, atomic force microscopy, and profilometer. The surface wettability was characterized by determining the contact angle. The results showed that a 1–2 μm layer of CaCO3 grew on the microchannel surface, and the channel surface tended to hydrophobicity. The flow behavior of CO2 in reservoirs and the capacity of foam to control CO2 mobility were simulated using 2.5D micromodels. Among them, CO2 channeling is more obvious and realistic in micromodel. Accordingly, foams with and without nanoparticles (NPs) armor were used to control CO2 mobility. The bubble disproportionation, and liquid drainage of bare surfactant foam induced gas–liquid separation in fractures and pores. Subsequent big and soft bubbles illustrated poor CO2 mobility control performance, and the micro-fractures and pores were not effectively swept and stored with CO2. Extremely stable CO2 foam was obtained with the construction of NPs-armor on foam films, more conducive to the trapping of CO2 in bubbles. The findings of this study can help understand complex CO2 flow behavior in carbonate reservoirs and presents a promising method with NPs-armor stabilized CO2 foams for carbon sequestration and enhanced oil recovery in carbonate reservoirs.

The particular foamed cement formulation by acid for oil/gas wells cementing jobs: an experimental approach

Foamed cements are coarse dispersions of a base cement slurry, a gas (usually air or nitrogen), a foaming surfactant and other materials A new foamed cement, designed for oil/gas well liners and casing cementing jobs, was formulated. Ultra-lightweight cement pastes (such as foamed cements) are appropriate for formation damage prevention in fractured and depleted reservoirs. In this work, foamed cements were prepared at high shear rates using a foaming agent primarily composed of sodium lauryl ether sulfate, boric acid and a retarder (JR120). This formulation was called FBJ. The samples were subjected to tests for density, rheology, free water, settling, thickening time, compressive strength (CS), fluid loss, porosity and permeability, along with microscopic photography and computed tomography scanning. Compared with other drilling cements, the FBJ was found to have one of the lowest densities (1200 kg/m3), a CS of 8963 kPa and a thickening time of about 3 h. The rheology of the FBJ improved under high-pressure and high-temperature conditions. Examinations of the set FBJ also showed that the pores were not interconnected, the porosity of the FBJ was greater than 73% and 28% of the FBJ was matrix. Moreover, cement permeameter tests indicated that the permeability of the FBJ was just 0.0109 mD (1 mD ≈ 1 × 10−12 cm2). All of these results show that the formulated FBJ has acceptable properties for oil/gas wells cementing applications.

Effect of hydroxyl group on foam features of hydroxyl-based anionic ionic liquid surfactant: Experimental and theoretical studies

Ionic liquid surfactant (ILS) shows potential application in surfactant enhancing oil recovery (SEOR). The structure–activity relationship between structural characteristics and foam feature is significant for the design and selection of favorable ILS for foam enhanced oil recovery (FEOR). In this paper, the effect of structural substituent groups of anionic ILSs on foam features was established through experimental methods and Density functional theory (DFT) simulations. Physicochemical features of hydroxyl-based anionic ILS, 1-(2,3-dihydroxypropyl)-3-butylimidazolium dodecyl sulfate ([DPbim][DS]) was detected. By surface tensiometry, the critical micelle concentration (CMC) value of [DPbim][DS] was 0.427 mmol/L. Foam properties of three ILSs ([DPbim][DS], [Hmim][DS] (1-hexyl-3-methylimidazolium dodecyl sulfate), and [Bmim][DS] (1-butyl-3- methylimidazolium dodecyl sulfate), and sodium dodecyl sulfate (SDS) were established. The foam features of ILSs and SDS followed: [DPbim][DS] > [Hmim][DS] > [Bmim][DS] > SDS. ILS hydrates showed tendency: [Bmim][DS](H2O)n > [Hmim][DS](H2O)n > [DPbim][DS](H2O)n. D0 values followed the tendency: [DPbim][DS](H2O)n > [Hmim][DS](H2O)n > [Bmim][DS](H2O)n. Experimental and DFT results verified the introduction of hydroxyl group and longer alkyl chain length in imidazolium cation was favorable for foam features of ILSs. This information will help to screen new foam surfactants for FEOR.

Utilization of a biosurfactant foam/nanoparticle mixture for treatment of oil pollutants in soil.

Oil contamination has become a primary environmental concern due to increased exploration, production, and use. When oil enters the soil, it may attach or adsorb to soil particles and stay in the soil for an extended period, contaminating the soil and surrounding areas. Nanoparticles have been widely used for the treatment of organic pollutants in the soil. Surfactant foam has effectively been employed to remediate various soil contaminants or recover oil compounds. In this research, a mixture of biosurfactant foam/nanoparticle was utilized for remediation of oil-contaminated soil. The results demonstrated that the biosurfactant/nanoparticle mixture and nitrogen gas formed high-quality and stable foams. The foam stability depended on the foam quality, biosurfactant concentration, and nanoparticle dosage. The pressure gradient change in the soil column relied on the flowrate (N2 gas + surfactant/nanoparticle mixture), foam quality, and biosurfactant concentration. The optimal conditions to obtain good quality and stable foams and high oil removal efficiency involved 1 vol% rhamnolipid, 1 wt% nanoparticle, and 1 mL/min flowrate. Biosurfactant foam/nanoparticle mixture was effectively used to remediate oil-contaminated soil, whereas the highest treatment efficiency was 67%, 59%, and 52% for rhamnolipid biosurfactant foam/nanoparticle, rhamnolipid biosurfactant/nanoparticle, and only rhamnolipid biosurfactant, respectively. The oil removal productivity decreased with the increase of flowrate due to the shorter contact time between the foam mixture and oil droplets. The breakthrough curves of oil pollutants in the soil column also suggested that the foam mixture's maximum oil treatment efficiency was higher than biosurfactant/nanoparticle suspension and only biosurfactant.

Enhancing the Aqueous foam Stability Using Nanoparticles: A Review

Today, there is much demand for stabilised foam globally. The primary concern for surfactant foam in enhanced oil recovery (EOR) is its foam stability. The applications of surfactant-nanoparticles mixture for foam stabilisation have been increased significantly because of the combined role of nanoparticles (NPs) and surfactant in the mechanism of foam stabilisation. This paper focuses on enhancing the aqueous foam stability by NPs and respective mechanisms of the aqueous foam stability. Nanoparticles have unique physical and chemical properties, so they alter the surface and rheological properties of the fluid system. It is the outcome of various research that nanoparticles adhere to the gas-liquid interface of the foam to improve foam stability. Therefore, NPs can enhance the stability of surfactant-stabilised foams. The use of nanoparticles increases foam stability, but its drawbacks cannot be ignored. Probable, the synthesis and production technique of nanoparticles is steeply-priced, which have to be made cheap using cutting-edge technology.

Temperature and salt resistant CO2 responsive gas well foam: Experimental and molecular simulation study

Synergism has developed to be an important means to improve the foaming, stabilizing and responsive deforming characteristics of foam. Here, CO2/N2 responsive surfactants with tunable lengths of carbon chains are synthesized. Through forming and deforming testing, the obtained 11-dimethylamino-undecyl sulfate sodium (11-DUSNa) with 11 carbons on the linear tail chain has the best comprehensive performance. 11-DUSNa is then mixed with Cocamidopropyl Hydroxyl Sulfobetaine (CHSB) to produce a compound foam with enhanced temperature and salt tolerance. Experimental observations show that the compound foam has the largest stability by adding 3.2 mol/L divalent salts (Ca2+, Mg2+), and has improved temperature resistance from 20 to 100 °C compared to singular surfactant foam. The compound foam defoams in response to the injection of CO2 within 2200 s. The foaming and defoaming processes can be cycled many times by repeat addition of NaOH for deprotonation and CO2 for protonation of amino groups. Molecular dynamics simulations show that Ca2+ and Mg2+ cations distributing around the head groups of surfactants form a stable network liquid film wall, explaining why the compound foam is salt tolerant. The synergistic effect of CHSB and anions increases the liquid film wall thickness and therefore leads to better temperature resistance.

Dual-energy CT scan protocol optimization to monitor transient fluid saturation distributions during three-phase flow in sand columns

Surfactant foam injection is a promising in situ remediation technique for aquifers impacted by Non-Aqueous Phase Liquids (NAPL). Though the viscous properties of foam can promote immiscible displacement, pore plugging by foam is a concern in an environmental remediation (ER) context, as maintaining flow conditions may require the application of pressures that exceed soil matrix failure thresholds. Optimization of the technology for ER may be furthered by gaining a better understanding of the relationship between foam morphology and NAPL desaturation. This relationship is poorly understood, partly because the interactions between organic phases and foam occurring at specific positions within the flow field at any given time are difficult to assess quantitatively. A Dual-energy X-ray Computed Tomography (CT) technique was developed to enable the measurement of sand column characteristics, as well as transient fluid saturation profiles within the porous medium during foam injection. The available settings of a medical CT scanner were systematically explored in order to identify the acquisition and reconstruction parameters best suited to image the fluids of interest: 0.4 mm slice thickness, a medium kernel (U40u), peak tube voltages of 140 kVp and 80 kVp, and the addition of a doping agent to the NAPL at a concentration of 20 wt%. Using datasets produced by imaging sand columns at various stages of foam injection experiments, an algorithm was developed in order to extract saturation profiles from CT images. The algorithm included multiple scan averaging to reduce image noise, image registration, and specific matrix operations required for calculating fluid saturation values in two- and three-phase systems. The accuracies of the CT-extracted porosity and fluid saturation data were compared to, and found to be in good agreement with, experimentally determined average porosity and saturation values. The scan parameter optimization method developed here can be applied to future studies involving any combination of site-specific natural materials.