Beneficial effects of wettability altering surfactants in oil-wet fractured reservoirs

In fractured reservoirs, an effective matrix-fracture mass transfer is required for oil recovery. Surfactants have long been considered for oil recovery enhancement, mainly in terms of their ability to reduce oil–water interfacial tension. These surfactants are effective when the fractured formations are water-wet, where capillary imbibition of surfactants from the fracture into the matrix contributes to oil recovery. However, another beneficial aspect of surfactants, namely their ability to alter wettability, remains to be explored and exploited. Surfactants capable of altering wettability can be especially beneficial in oil-wet fractured formations, where the surfactant in the fracture diffuses into the matrix and alters the wettability, enabling imbibition of even more surfactant into the matrix. This sequential process of initial diffusion followed by imbibition continues well into the matrix yielding significant enhancements in oil recovery.In order to test this hypothesis of sequential diffusion–imbibition phenomenon, Dual-Drop Dual-Crystal (DDDC) contact angle experiments have been conducted using fractured Yates dolomite reservoir fluids, two types of surfactants (nonionic and anionic) and dolomite rock substrates. A new experimental procedure was developed in which crude oil equilibrated with reservoir brine has been exposed to surfactant to simulate the matrix-fracture interactions in fractured reservoirs. This procedure enables the measurements of dynamic contact angles and oil–water interfacial tensions, in addition to providing the visual observations of the dynamic behavior of crude oil trapped in the rock matrix as it encounters the diffusing surfactant from the fractures. Both the measurements and visual observations indicate wettability alterations of the matrix surface from oil-wet to less oil-wet or intermediate wet by the surfactants. Thus this study is of practical importance to oil-wet fractured formations where surfactant-induced wettability alterations can result in significant oil recovery enhancements. In addition, this study has also identified the need to include contact angle term in the dimensionless Bond number formulations for better quantitative interpretation of rock–fluids interactions.     

The Interaction of Glymes with Surfactant Micelles

The critical micelle concentrations (CMC) values and counterion dissociation (α values) have been determined for a number of mixed micellar systems consisting of two typical ionic surfactants and glycol ethers (glymes) as cosurfactants, namely diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. Conductance experiments were used to determine the CMC and α values of the mixed micelles as a function of glyme concentration in the aqueous mixed solvent. Favorable interactions between sodium dodecyl sulfate micelles and glyme cosurfactants were deduced from the decreases in the CMC values and the large increase in the α values of these systems as a function of increasing glyme concentration in the mixed solvents. In contrast to the anionic surfactant/glyme systems, in general, there appeared to be little favorable interactions between the surfactant and glymes when micelles of the cationic surfactant dodecyltrimethylammonium bromide were formed in water/glyme solvent systems containing an increasing amount of the glymes. The interaction of glymes with the surfactant micelles was examined closely via ¹³C nuclear magnetic resonance (NMR) chemical shifts for both surfactant and glyme carbons; these chemical shifts changes were interpreted in terms of the distribution and the localization of the glymes in the aggregates. Finally, partition constants, determined from two-dimensional diffusion-oriented spectroscopy (2D-DOSY) experiments, were used to calculate thermodynamic quantities of transfer of the glymes between the bulk phase and the self-assembled aggregates. All these results are interpreted in terms of the key contributions that both the glyme ethoxylated groups and alkyl endgroups make to the hydrophobic interactions.     

混合指示剂单相滴定法测定烷基磷酸酯钾盐

本研究用混合指示剂单相滴定法测定ISO标准方法所不能测定的磷酸盐阴离子表面活性剂的浓度.测定PK、E502A、昆山PK的常数K分别为355.lg/M、420.7g/M和344.0g/M,变异系数分别为1.45%、0.59%和1.26%,测定实际试样的加标回收率为98.2～103.9%.方法准确、简单、快速,不需用毒性较大的有机溶剂,本法适用于化纤油剂和涤纶短纤维上油率等的测定.     

Thermal analysis of montmorillonites modified with quaternary phosphonium and ammonium surfactants

The thermal stability of seven organically modified montmorillonites (‘organoclays’) has been investigated using differential thermal analysis, differential scanning calorimetry, and thermogravimetry in conjunction with X-ray diffractometry. Six organoclays were synthesised by replacing the interlayer inorganic cations, initially present, with quaternary phosphonium and ammonium surfactant cations. The samples modified with tetrabutylphosphonium (TBP), and butyltriphenylphosphonium (BTPP) ions have an appreciably higher thermal stability than the octadecyltrimethylammonium (ODTMA)-modified clays. Thus, in the case of TBP- and BTPP-modified montmorillonites, the onset temperature of decomposition is close to 300 °C. Samples modified with hexadecyltributylphosphonium (HDTBP) ions have a lower onset temperature of decomposition of 225 °C. In comparison, the onset temperature for ODTMA-montmorillonites (obtained at different concentrations of ODTMA-bromide) ranges from 158 to 222 °C, being highest where the concentration of intercalated surfactant is lowest. The onset temperature for a commercial alkylsilane-treated quaternary ammonium-modified organoclay (S-BEN N-400FP) is 207 °C. The basal spacing of the TBP- and BTPP-modified clays is 1.7–1.8 nm, indicating a monolayer arrangement of quaternary phosphonium ions in the interlayer space, while the value of 2.5 nm for HDTBP-montmorillonite indicates a more open structure. The ODTMA-modified samples have basal spacings ranging from 1.9 to 2.1 nm, indicative of a bilayer to pseudo-trilayer arrangement. The exceptionally high basal spacing of 3.4 nm for the S-BEN N-400FP organoclay might be due to interlayer penetration of organosilane hydrolysis products during synthesis. The thermal properties of organoclays are apparently related to the nature of the surfactants and their arrangement in the interlayer space of montmorillonite.     

脂肪酸烷基醇酰胺硫酸酯的合成及性能研究

脂肪酸烷基醇酰胺硫酸酯是一类性能优异的新型阴离子型表面活性剂，尤其具有良好的钙皂分散性及乳化性。本文报道了其合成工艺条件，测定了有关物性     

Synthesis of mesoporous ZnS synergistically templated by butylamine and alkanols

Pore size and pore volume adjustable mesoporous ZnS was synthesized through a co-template method, which was achieved by the combined interaction between butylamine and some alkanols with proper lengths of the straight carbon chain. The pore size for mesoporous ZnS templated by butyl amine alone was 4.29 nm, and could be enlarged to 6.96 and 8.33 nm respectively through adding certain amounts of hexanol and octanol. Correspondingly, the pore volume also exhibited an augmentation with increasing carbon chain lengths of alkanols from C₆ to C₈. However, the pore size and pore volume dropped abruptly when decanol was added as the auxiliary agent. The formation of mesopores for ZnS prepared using butylamine molecules as the only templating agent is considered to be attributed to the coordination between N atoms in amines and Zn²⁺ ions at the surfaces of zinc suphide. The templating effect of butylamines might be improved by adding hexanols and octanols to form aggregates through solubilization to tailor the pore size and pore volume of ZnS effectively, while the function of decanols for changing the porous structure is restricted by its low solubility.     

Advantage of Sodium Polyoxyethylene Lauryl Ether Carboxylate as a Mild Cleansing Agent

Five anionic surfactants widely used in commercial skin cleansers were studied: sodium polyoxyethylene lauryl ether carboxylate (EC), sodium polyoxyethylene alkyl ether sulfate (ES), sodium dodecyl sulfate, potassium laurate, and N-cocoyl-l-glutamic acid monosodium salt. The amount of surfactant from aqueous solution adsorbed into the stratum corneum (SC), the degree of SC swelling, the change of the secondary structure of SC proteins (denaturation). The surface tension of surfactant–zein mixed solutions, and the solubilization behavior of zein were measured. Results showed that EC had the lowest adsorption into SC, the lowest SC swelling, and lowest denaturation of SC proteins. Low interactions between surfactants and SC proteins were also observed for EC/ES mixture solutions as well as. Mixing EC with ES good foaming performance. The EC/ES mixture, at about 1:1 ratio, is an excellent surfactant system for skin cleanser applications having cleansing characteristics and mildness to the skin.     

Enhanced Mn2+ solidification and NH4+-N removal from electrolytic manganese metal residue via surfactants

Electrolytic manganese metal residue (EMMR) harmless treatment has always lacked a low-cost and quick processing technology. In this study, surfactants, namely tetradecyl trimethylammonium chloride (TTC), sodium dodecyl benzene sulfonate (SDBS), sodium lignin sulfonate (SLS), and octadecyl trimethylammonium chloride (OTC), were used in the solidification of Mn²⁺ and removal of NH₄⁺-N from EMMR. The Mn²⁺ and NH₄⁺-N concentrations under different reaction conditions, Mn²⁺ solidification and NH₄⁺-N removal mechanisms, and leaching behavior were studied. The results revealed that the surfactants could enhance the Mn²⁺ solidification and NH₄⁺-N removal from EMMR, and the order of enhancement was as follows: TTC > SDBS > OTC > SLS. The NH₄⁺-N and Mn²⁺ concentrations were 12.3 and 0.05 mg·L^-1 with the use of 60.0 mg·kg^-1 TTC under optimum conditions (solid–liquid ratio of 1.5:1, EMMR to BRM mass ratio of 100:8, temperature of 20 ℃, and reaction duration of 12 h), which met the integrated wastewater discharge standard (GB8978-1996). Mn²⁺ was mainly solidified as Mn(OH)₂, MnOOH and MnSiO₃, and NH₄⁺-N in EMMR was mostly removed in the form of ammonia. The results of this study could provide a new idea for cost-effective EMMR harmless treatment.     

Effect of Nanoparticles on Viscosity and Interfacial Tension of Aqueous Surfactant Solutions at High Salinity and High Temperature

Surfactant flooding has widely been used as one of the chemically enhanced oil recovery (EOR) techniques. Surfactants majorly influence the interfacial tension, γ, between oil and brine phase and control capillary number and relative permeability behavior and, thus, influence ultimate recovery. Additives, such as nanoparticles, are known to affect surfactant properties and are regarded as promising EOR agents. However, their detailed interactions with surfactants are not well understood. Thus, in this work, we examined the influence of silica nanoparticles on the ability of surfactants to lower γ and to increase viscosity at various temperatures and salinities. Results show that the presence of nanoparticles decreased γ between n-decane and various surfactant formulations by up to 20%. It was found that γ of nanoparticles–surfactant solutions passed through a minimum at 35 °C when salt was added. Furthermore, the viscosity of cationic surfactant solutions increased at specific salt (1.5 wt.%) and nanoparticle (0.05 wt.%) concentrations. Results illustrate that selected nanoparticles–surfactant formulations appear very promising for EOR as they can lower brine/n-decane interfacial tension and act as viscosity modifiers of the injected fluids.     

Impact of surfactants on the lipase digestibility of gum arabic-stabilized O/W emulsions

The bioavailability of lipids from an emulsion can be controlled and regulated by the property of the stabilizing interfacial layer. Here we evaluate how low-molecular weight surfactants including hexadecyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Tween 80 (T80) influence the interfacial behavior of lipase and bile extract on the surface of lipid droplets stabilized with gum arabic (GA). The lipolysis behavior was influenced by surfactant type and concentration. The results showed that anionic SDS could completely displace GA from droplet surface. Cationic CTAB might either adsorb onto existing GA layers or displace GA, whereas non-ionic T80 could co-adsorb with GA on the interface. When the concentration of surfactants was much higher than the critical micelle concentration (CMC), all the surfactants would form a dense adsorption layer on the droplet interface to prevent lipase from the direct contact with lipids. A considerable amount of surfactant in the aqueous phase may also compete with the bile salt and lipase, thus leading to suppressed digestion of lipids. Ionic surfactants would denature the lipase resulting in reduced enzyme activity, and T80 micelles may interact with the lipase, hindering their adsorption onto the droplet interface as well. These results were confirmed both by the digestion model and interfacial techniques. The results provided guidance for the development of emulsion-based delivery systems for functional lipid foods.