Improvement of Ca2+-tolerance by the introduction of EO groups for the anionic surfactants: Molecular dynamics simulation

Investigation of the Stability Mechanism of Stimulus-Responsive Wormlike Micelle-CO2 Foams in the Oil Phase

Foam flooding is an important tool for reservoir development. This study aims to further investigate the interaction between stimulus-responsive wormlike micelle (WLM)-CO2 foams and crude oil. We performed micromorphology experiments as our major studies and used molecular dynamics simulations as an auxiliary tool for interfacial analysis. We utilized foam generation, liquid separation, and defoaming as the entry points of experimental research and energy as the quantitative assessment index to investigate the dynamic process of the action of different oil contents and oil phase types in a DOAPA@NaSal-H+ foam system. We also examined the role of NaSal in the generation and development of the foam system. Results indicated that the law of crude oil's effect on foam could be summarized as "low contents are beneficial and high contents are harmful." In addition, although the DOAPA@NaSal-H+ foam system has high compatibility for saturated and aromatic hydrocarbons, it is highly suitable for application in reservoir environments with relatively high asphaltene and resin contents. Through combined experimental and simulation approaches, we clarified the law governing the stability of the DOAPA@NaSal-H+ foam system in different oil-containing environments, identified the key role of NaSal, and provided a reference for the targeted application of the DOAPA@NaSal-H+ foam system in different oil reservoirs.

Interaction, Surface Activity, and Application of Mixed Systems of Alcohol Ether Sulfate Anionic Surfactants with Multiple Ethylene Oxide Groups and Gemini Quaternary Ammonium Surfactant

The surface activities and application properties for the mixtures of cationic surfactants tetramethylene-1,4-bis[N,N-bis(hydroxypropyl)-hexa/decyloxypropylammonium] bromide (GC10-P) and tetramethylene-1,4-bis[N,N-bis(hydroxyethyl)-hexa/decyloxypropylammonium] bromide (GC10-E) and anionic surfactant isomeric sodium fatty alcohol ether sulfates (iso-AE9S) were investigated using both the tensiometry and the conductometry. The interaction parameters and thermodynamic micellization parameters of GC10-P/iso-AE9S and GC10-E/iso-AE9S mixtures were evaluated by Clint-Rubingh and Motomura theoretical models. When the mole fraction of α1 for GC10-P/iso-AE9S mixed system was 0.2, the critical micelle concentration (CMC) reached a minimum of 1.61 × 10-4 mol/L, and the minimum critical micelle concentration of the GC10-E/iso-AE9S mixed system is 2.67 × 10-5 mol/L at α1 = 0.6. The CMC value of the mixed system is 1-2 orders of magnitude lower than that of any single component. The results indicate that the synergistic effects of the investigated mixed systems (evaluated by βm) are in order of GC10-P/iso-AE9S < GC10-E/iso-AE9S, with maximum βm values of -17.98 and -9.78, respectively. The change in zeta potential indicates that the poly(ethylene oxide) chain has weakened the charge density of the hydrophilic headgroup of the anionic surfactant. The interfacial tension at the oil-water interface in the mixed system of anionic/cationic surfactants is lower than that of any single component, exhibiting a higher interfacial activity. The mixed system exhibits a decreased contact angle and superior wetting ability over any single component, and it also enhances foam performance, emulsification performance, and degreasing performance.

Study on the Synthesis, Surface Activity, and Self-Assembly Behavior of Anionic Non-Ionic Gemini Surfactants

The use of surfactants in oil recovery can effectively improve crude oil recovery rate. Due to the enhanced salt and temperature resistance of surfactant molecules by non-ionic chain segments, anionic groups have good emulsifying stability. Currently, there are many studies on anionic non-ionic surfactants for oil recovery in China, but there is relatively little systematic research on introducing EOs into hydrophobic alkyl chains, especially on their self-assembly behavior. This article proposes a simple and effective synthesis method, using 3-aminopropane sulfonic acid, fatty alcohol polyoxyethylene ether, and epichlorohydrin as raw materials, to insert EO into hydrophobic alkyl chains and synthesize a series of new anionic non-ionic Gemini surfactants (CnEO-5, n = 8, 12, 16). The surface activity, thermodynamic properties, and self-assembly behavior of these surfactants were systematically studied through surface tension, conductivity, steady-state fluorescence probes, transmission electron microscopy, and molecular dynamics simulations. The surface tension test results show that CnEO-5 has high surface activity and is higher than traditional single chain surfactants and structurally similar anionic non-ionic Gemini surfactants. Additionally, thermodynamic parameters (e.g., ΔG°mic ΔH°mic ΔS°mic et al. indicate that CnEO-5 molecules are exothermic and spontaneous during the micellization process. DLS, p-values, and TEM results indicate that anionic non-ionic Gemini surfactants with shorter hydrophobic chains (such as C8EO-5) tend to form larger vesicles in aqueous solutions, which are formed in a tail to tail and staggered manner; Negative non-ionic Gemini surfactants with longer hydrophobic chains (such as C12EO-5, C16EO-5) tend to form small micelles. The test results indicate that CnEO-5 anionic non-ionic Gemini surfactants have certain application prospects in improving crude oil recovery.

Mechanism Analysis and Property Prediction of Extended Surfactants Based on the Respectively Optimized Force Field

Extended surfactants represent a novel class of anionic-nonionic surfactants with exceptional performance and unique application value in chemically enhanced oil recovery. Although molecular dynamics (MD) simulations can efficiently screen these surfactants, the current research is limited. Here, it is proven for the first time that existing generic force fields (GAFF and CHARMM) cannot accurately describe extended surfactants, and traditional approaches are insufficient for obtaining precise charge parameters. The concept of the respectively optimized force field (ROFF) with the purports of specialization and accuracy is proposed to construct high-accuracy models for MD simulations, and a new approach is developed to simulate the interface model. By combining the newly specialized alkane model, ROFF-based surfactant models, and the innovative simulation protocol, high accuracy and reliability can be obtained in predicting hydration free energies, minimum of area per molecule, and critical micelle concentration of extended surfactants. Key properties of the newly designed extended surfactants in conventional oil-water interfaces and oil reservoir environments are comprehensively predicted by using advanced analytical and characterization methods. Furthermore, the more rigorous mechanism underlying the special amphiphilicity of the extended surfactant is revealed, potentially offering significant improvements over previous empirical perspectives.

Synergistic Effect of Salt and Anionic Surfactants on Interfacial Tension Reduction: Insights from Molecular Dynamics Simulations

Surfactants are commonly utilized in chemical flooding processes alongside salt to effectively decrease interfacial tension (IFT). However, the underlying microscopic mechanism for the synergistic effect of salt and surfactants on oil displacement remains ambiguous. Herein, the structure and properties of the interface between water and n-dodecane are studied by means of molecular dynamics simulations, considering three types of anionic surfactants and two types of salts. As the salt concentration (ρsalt) increases, the IFT first decreases to a minimum value, followed by a subsequent increase to higher values. The salt ions reduce the IFT only at low ρsalt due to the salt screening effect and ion bridging effect, both of which contribute to a decrease in the nearest head-to-head distance of surfactants. By incorporating salt doping, the IFTs can be reduced by at most 5%. Notably, the IFTs of different surfactants are mainly determined by the hydrogen bond interactions between oxygen atoms in the headgroup and water molecules. The presence of a greater number of oxygen atoms corresponds to lower IFT values. Specifically, for alkyl ethoxylate sulfate, the ethoxy groups play a crucial role in reducing the IFTs. This study provides valuable insights into formulating anionic surfactants that are applicable to oil recovery processes in petroleum reservoirs using saline water.

Study on the effect of SDBS and SDS on deep coal seam water injection

Coal seam water injection, as an important disaster prevention means in the process of coal mining, can effectively suppress coal dust, add water injection additives, can effectively improve the wettability of coal body, improve the permeability of coal body, so as to achieve the prevention of rock burst. To improve the wettability of coal in coal seam water injection, the surfactant is often added to water, but sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) have limitations in improving wettability of deep coal seam by injecting water. Therefore, it is very important to determine the influencing factors of SDBS and SDS to improve the wettability of coal. In this paper, the effects of oxygen-containing functional groups and minerals in coal on the wettability of coal are revealed, and the wettability mechanism of SDBS and SDS is expounded from the microscopic point of view. SEM was used to characterize the interaction between coal surface and surfactant, and the contact angle experiment was used to verify the influence of minerals in coal on wettability. Inductively coupled plasma atomic emission spectroscopy (ICP) and dynamic light scattering (DLS) tests were used to characterize the interaction of SDBS, SDS with minerals and the size of precipitation generated by the interaction of SDBS, SDS and mineral ions. The results showed that SDBS and SDS interact with Ca²⁺ to produce precipitation and block the flow of water in coal, which is not conducive to improving the wettability of deep coal seam to a certain extent. The significant chelating effect of chelating agent and Ca²⁺ provides a feasible solution to this problem.

Effect of Fe(III) Species on the Stability of a Water-Model Oil Emulsion with an Anionic Sulfonate Surfactant as an Emulsifier

The stability of an emulsion has an important effect on enhancing oil recovery. However, the effect of ions with different valences on the stability of the emulsion emulsified by an ionic surfactant is not fully understood. In this study, the effects of Fe(III) species on the stability, microscopic morphology of droplets, interfacial properties, and rheological properties of water-model oil emulsions emulsified by sodium dodecyl benzenesulfonate (SDBS) were explored. The effect of Fe(III) species on the stability of a W/O crude oil emulsion was also explored. The stability experiment results show that the addition of the Fe(III) species impairs the stability of the model oil-in-water (O/W) emulsion, in which the O/W model oil emulsion is inverted to a water-in-model oil (W/O) emulsion at ∼99 ppm. With the increase of Fe(III) species concentration, stable W/O model oil and W/O crude oil emulsions are obtained. The rheological results indicated that the existence of the Fe(III) species has a remarkable effect on the viscosity and viscoelastic behaviors of the water-model oil emulsion. The calculation results based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory are in accord with the stability experiment results. Furthermore, the addition of EO groups makes the phase inversion point appear at a higher Fe(III) species concentration, forming a more stable W/O model oil emulsion and a more unstable O/W model oil emulsion. The experimental results are helpful to comprehensively understand the effect of Fe(III) species on the stability of an emulsion emulsified by an anionic sulfonate surfactant, which can help to enhance the oil recovery.

Comprehensive review on surfactant adsorption on mineral surfaces in chemical enhanced oil recovery

With the increasing demand for efficient extraction of residual oil, enhanced oil recovery (EOR) offers prospects for producing more reservoirs' original oil in place. As one of the most promising methods, chemical EOR (cEOR) is the process of injecting chemicals (polymers, alkalis, and surfactants) into reservoirs. However, the main issue that influences the recovery efficiency in surfactant flooding of cEOR is surfactant losses through adsorption to the reservoir rocks. This review focuses on the key issue of surfactant adsorption in cEOR and addresses major concerns regarding surfactant adsorption processes. We first describe the adsorption behavior of surfactants with particular emphasis on adsorption mechanisms, isotherms, kinetics, thermodynamics, and adsorption structures. Factors that affect surfactant adsorption such as surfactant characteristics, solution chemistry, rock mineralogy, and temperature were discussed systematically. To minimize surfactant adsorption, the chemical additives of alkalis, polymers, nanoparticles, co-solvents, and ionic liquids are highlighted as well as implementing with salinity gradient and low salinity water flooding strategies. Finally, current trends and future challenges related to the harsh conditions in surfactant based EOR are outlined. It is expected to provide solid knowledge to understand surfactant adsorption involved in cEOR and contribute to improved flooding strategies with reduced surfactant loss.

Salt-tolerance of alkyl-glyceryl ether carboxylates hydrotropes and surfactants. Dramatic effect of the methylation of the glyceryl spacer

HYPOTHESIS

The insertion of polyether spacers between the anionic head and the alkyl chain of ionic surfactants significantly improves their salt-tolerance. The aim of this work is to study whether the petro-based polyethoxy spacer can be replaced by a glyceryl ether group for high salinity applications.

EXPERIMENTS

A series of amphiphilic sodium salts of alkyl glyceryl ether carboxylates are synthesized with different alkyl chain lengths from 4 to 12 and various spacers between the glyceryl and the carboxylate groups. Their aggregation behavior is studied by tensiometry and their amphiphilicities are assessed by the PIT-slope method. The dramatic effect of the methylation of the glyceryl spacer on the salt-tolerance is highlighted, and rationalized by DFT calculations and molecular dynamics.

FINDINGS

In contrast to the corresponding sodium soap, n-C₆H₁₃-CO₂Na, and to the non-methylated counterpart, the sodium salt of 1-pentyl-3-methyl glyceryl ether methylene carboxylate ([5.0.1]-CH₂CO₂Na) exhibits an excellent salt-tolerance since it remains water-soluble with NaCl or CaCl₂ concentrations greater than 20 wt% at 25 °C. Amphiphiles with short alkyl chains (<C₈) act as hydrotropes whereas longer compounds behave as surfactants whose CMC are lower than their corresponding isomers with ethoxy spacers n-C_i(EO)₂CH₂CO₂Na.

Revealing the Origin of the Specificity of Calcium and Sodium Cations Binding to Adsorption Monolayers of Two Anionic Surfactants

The studied anionic surfactants linear alkyl benzene sulfonate (LAS) and sodium lauryl ether sulfate (SLES) are widely used key ingredients in many home and personal care products. These two surfactants are known to react very differently with multivalent counterions, including Ca²⁺. This is explained by a stronger interaction of the calcium cation with the LAS molecules, compared to SLES. The molecular origin of this difference in the interactions remains unclear. In the current study, we conduct classical atomistic molecular dynamics simulations to compare the ion interactions with the adsorption layers of these two surfactants, formed at the vacuum-water interface. Trajectories of 150 ns are generated to characterize the adsorption layer structure and the binding of Na⁺ and Ca²⁺ ions. We found that both surfactants behave similarly in the presence of Na⁺ ions. However, when Ca²⁺ is added, Na⁺ ions are completely displaced from the surface with adsorbed LAS molecules, while this displacement occurs only partially for SLES. The simulations show that the preference of Ca²⁺ to the LAS molecules is due to a strong specific attraction with the sulfonate head-group, besides the electrostatic one. This specific attraction involves significant reduction of the hydration shells of the interacting calcium cation and sulfonate group, which couple directly and form surface clusters of LAS molecules, coordinated around the adsorbed Ca²⁺ ions. In contrast, SLES molecules do not exhibit such specific interaction because the hydration shell around the sulfate anion is more stable, due to the extra oxygen atom in the sulfate group, thus precluding substantial dehydration and direct coupling with any of the cations studied.

The rheological characteristics for the mixtures of cationic surfactant and anionic–nonionic surfactants: the role of ethylene oxide moieties

Ethylene oxide moieties in various numbers regulate the rheological characteristics of anionic–nonionic/cationic surfactants solutions by affecting the molecular self-assembly.

Picolinic Acid Promoted Permanganate Oxidation of D-Mannitol in Micellar Medium

Kinetics of permanganate oxidation of D-mannitol have been investigated spectrophotometrically under pseudo-first-order conditions in aqueous acidic media at 30 °C. The spectral analysis of hydrazone derivative of the product indicates the product to be an aldehyde. The observed rate constant value was found to be relatively slow in the uncatalyzed path, which increases by the presence of four isomeric promoters: 2-picolinic acid (2-PA), 4-picolinic acid (4-PA), 2,3-dipicolinic acid (2,3-diPA) and 2,6-dipicolinic acid (2,6-diPA). The catalytic effect of sodium dodecylbenzene sulfonate (SDBS) surfactant on the permanganate oxidation of D-mannitol has been also studied in the presence of the promoters. The critical micelle concentration (CMC) of SDBS alone and in presence of D-mannitol was determined by conductometry and spectrophotometry. The aggregation and morphological changes during reaction were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The variation of the reaction rates for the different promoters in the presence and absence of SDBS micellar catalyst is discussed qualitatively in the terms of partitioning nature of substrate, charge of surfactant and reactants. 2,3-diPA in association with SDBS as micellar catalyst accelerated the reaction velocity compared to the uncatalyzed path.

Synthesis of a novel comb micro-block hydrophobically associating copolymer for Ca2+/Mg2+ resistance

A comb micro-block hydrophobically associating copolymer (CBHAP), which can withstand divalent cations in harsh conditions, was successfully synthesized in this work.

Mixed surfactant modified graphene oxide nanocarriers for DOX delivery to cisplatin-resistant human ovarian carcinoma cells

Mixed surfactant modified graphene oxide nanocarriers based on the nonideal mixed micelle theory of surfactants exhibit great potential in drug delivery.