Enhanced Wettability Alteration by Surfactants with Multiple Hydrophilic Moieties

The main production mechanism during water flooding of naturally fractured oil reservoirs is the spontaneous imbibition of water into matrix blocks and resultant displacement of oil into the fracture system. This is an efficient recovery process when the matrix is strongly water-wet. However, in mixed- to oil-wet reservoirs, secondary recovery from water flooding is often poor. Oil production can be improved by dissolving low concentrations of surfactants in the injected water. The surfactant alters the wettability of the reservoir rock, enhancing the spontaneous imbibition process. Our previous study revealed that the two main mechanisms responsible for the wettability alteration are ion-pair formation and adsorption of surfactant molecules through interactions with the adsorbed crude oil components on the rock surface. Based on the superior performance of surfactin, an anionic biosurfactant with two charged groups on the hydrophilic head, it was hypothesized that the wettability alteration process might be further improved through the use of dimeric or gemini surfactants, which have two hydrophilic head groups and two hydrophobic tails. We believe that when ion-pair formation is the dominant wettability alteration mechanism, wettability alteration in oil-wet cores can be improved by increasing the charge density on the head group(s) of the surfactant molecule since the ion-pair formation is driven by electrostatic interactions. At a concentration of 1.0 mmol L⁻¹ a representative anionic gemini surfactant showed oil recoveries of up to 49% original oil-in-place (OOIP) from oil-wet sandstone cores, compared to 6 and 27% for sodium laureth sulfate and surfactin, respectively. These observations are consistent with our hypothesis.     

Effect of surfactants on the thermodynamic properties of Methyl Orange dye in buffered solutions

The apparent thermodynamic parameters of ionisation and the association constants of the two forms of Methyl Orange were evaluated in the presence of different surfactants (TX-100 as nonionic, CTAB as cationic and SDS as anionic). The enthalpy of ionisation of the dye in aqueous solution and at different surfactant concentrations is obtained from a novel thermochromic method and is found to decrease in aqueous medium in CTAB and TX-100 micelles and to increase in the case of SDS micelles. The apparent ionisation constant of the dye is evaluated spectrophotometrically for each surfactant concentration and type. The apparent Gibbs free energy, entropy of ionisation and association constants are also calculated. The results are discussed in light of the stabilisation of the two forms of the dye in the micellar core of the different surfactants and their effect on properties of the bulk solution is examined.     

Altering the wettability of bitumen-treated glass surfaces with ionic surfactants

The abilities of three ionic surfactants—sodium methylnaphthalene sulfonate (SMNS), sodium dodecyl sulfate (SDS), and cetyl trimethylammonium bromide (CTAB)—to alter the wettability of bitumen-treated glass surfaces was examined. Surface wettability was characterized by contact angles, and all measurements were carried out under alkaline conditions by having sodium carbonate (Na₂CO₃) dissolved in the aqueous phase. It was found that Na₂CO₃ alone could slightly increase the hydrophilcity of bitumen-treated glass surfaces. With surfactants added to the system, it was demonstrated that SMNS and SDS (both anionic surfactants) were much more effective in enhancing the water wettability of bitumen-treated glass in comparison to CTAB (a cationic surfactant). X-ray photoelectron spectroscopy (XPS) analyses were also conducted to determine the functional groups and relative mass concentrations of various elements on the glass substrates. Based on these results, we speculate that most or all of the adsorbed hydrocarbon material could be removed from a glass substrate through synergistic effects between sodium carbonate, which provides the alkaline condition, and anionic surfactants, which likely interacted with adsorbed cationic materials. This resulted in dramatic alteration in the wettability of bitumen-treated glass surfaces—from oil-wet to water-wet.     

A new surfactant wettability alteration model for reservoir simulators

Surfactants enhance oil recovery in naturally-fractured oil-wet rocks by wettability alteration and interfacial tension reduction. The oil-wet state is ascribed to the adsorption of soap on the rock surface. Soaps are the dissociated forms of carboxylic acids in the crude oil, that is, carboxylate surfactants. This paper describes a new mechanistic surfactant wettability alteration model that was developed for and implemented in a reservoir simulator. The model captures the geochemical reactions of acid/soap, the formation of mixed micelles, Henry's law adsorption, and the formation of cationic surfactant-anionic soap ion-pairs. A new wettability scaling factor is used to interpolate between the oil-wet and water-wet relative permeability and capillary pressure curves. The new model also accounts for the effect of salinity and pH, so it should also be useful for modeling low-salinity flooding without surfactant. Previous surfactant wettability alteration models ignored the underlying mechanisms and were not predictive. Simulations of both static and dynamic imbibition were performed to better understand the key surfactant parameters and the dynamics of wettability alteration, microemulsion phase behavior, and interfacial tension reduction on oil recovery. Optimizing surfactant formulations for wettability alteration is discussed.     

不同因素对CTAB/TX-100微乳液相图的影响

用ε-β"鱼状"相图法研究了阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)与非离子表面活性剂辛基苯酚聚氧乙烯(10)醚(TX-100)以不同摩尔比复配形成的CTAB/TX-100/醇/油/NaCl水溶液微乳液体系的相行为和增溶性能.结果表明,随着醇浓度的增加,体系由水包油型(O/W)(winsor Ⅰ or (2-)...     

Wettability reversal of reservoir rock surface through surfactant stabilized microemulsion

In the process of the tertiary recovery of oil and gas resources, it is necessary to use external fluids to displace the crude oil in the reservoir. Whether the crude oil on the surface of the rock can be effectively displaced and the wettability of the rock can be changed to avoid re-adsorption by the crude oil is directly related to the level of oil recovery. Therefore, it is critical to study the cleaning and wettability reversal of reservoir rock surface. Because microemulsions have outstanding performance in changing the wettability of rocks and solubilizing crude oil, this paper uses cetyl trimethyl ammonium bromide (CTAB) as a surfactant and n-butanol as a co-surfactant to prepare microemulsions. The performance of microemulsions with different microstructures on the cleaning and wettability changes of crude oil on the rock surface were studied. The results show that the water-in-oil (W/O) microemulsion has good cleaning efficiency, and the oil removal rate on the sandstone core surface can reach 79.65%. In terms of changing the wettability of the rock surface, W/O, bi-continuous phase (B.C.) and oil-in-water (O/W) microemulsions can change the core surface from lipophilic to hydrophilic. And the effects of the B.C. and O/W microemulsions are more obvious. The microemulsion system that was prepared based on cationic surfactants has a good application prospect in changing the wettability of the reservoir and cleaning the adsorbed crude oil.     

Synergistic Effect of Mixed Surfactant Systems on Foam Behavior and Surface Tension

Foam and surface tension behaviors of different ionic/nonionic surfactant solutions along with their different combinations have been investigated. Among different surfactants, sodium dodecyl sulfate showed the highest foamability over other surfactants. Mixed surfactant systems were always found to have higher foamability than the individual surfactant. It was also noticeable that nonionic surfactants show good foamability when they combine with anionic and cationic surfactants. In the case of mixed surfactant systems, nonionic/cationic surfactant mixtures showed lower surface tension than nonionic/anionic surfactant mixture due to a synergistic effect.     

Wettability alteration and reducing water blockage in tight gas sandstone reservoirs using mixed cationic Gemini/nonionic fluorosurfactant mixtures

The unrecovered hydraulic fracturing fluid will invade the matrix and induce water blockage, creating formation damage and hindering the oil or gas production rate. First, the synergistic effect of cationic Gemini surfactant (MQAS) and nonionic fluorosurfactant (N-2821) mixtures on reducing the surface tension and wettability alteration was investigated in this paper. The critical micelle concentration (CMC) of the surfactant mixture is one or two orders of magnitude lower than that of N-2821 and MQAS, indicating that the MQAS/N-2821 mixtures exhibit an apparent synergistic effect in reducing surface tension. Moreover, the maximal contact angle of MQAS/N-2821 mixtures reached 83.55° at α_N-2821 = 0.5, and the total surfactant concentration of 1 × 10⁻⁴ mol/L due to the adsorption of surfactant. The adsorption mechanism of surfactants on the surface of quartz sand was then examined. The adsorption kinetics is consistent with the pseudo-second-order model at different surfactant concentrations, while the Freundlich model is suitable for describing the adsorption behavior of surfactants on the sandstone surface. This finding indicates that surfactant adsorption is multilayered. The MQAS/N-2821 surfactant mixtures have excellent surfactant activity due to the relationship of the capillary pressure to the surface tension, pore radius, and contact angle; thus, the addition of surfactant mixtures can reduce the liquid saturation effectively. Furthermore, the sequential imbibition experiments indicate that MQAS/N-2821 mixtures alter the wettability of the core plug, which results from the adsorption of surfactants. Compared with brine water, the MQAS/N-2821 mixtures decreased the liquid saturation and increased the permeability recovery ratios of the core plug.     

Laboratory Studies to Determine Suitable Chemicals to Improve Oil Recovery from Garzan Oil Field

Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated.     

Effect of Surfactants on Catalytic Activity of Diastase α-Amylase

The enzyme amylase is one of the hydrolyzing enzymes used in detergent formulation in order to remove soil based on polysaccharides. The effectiveness of the enzyme depends on its compatibility with other ingredients of the formulation. Among the studied additives, comprising anionic surfactants sodium dodecyl hydrogen sulfate (SDS) and dioctyl sodium sulfosuccinate, the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), nonionic surfactants polyoxyethylene sorbitan monooleate and polyoxyethylene octyl phenyl ether, carboxy methyl cellulose and sodium sulfate, only the anionic surfactant SDS and cationic surfactant CTAB showed catalytic enhancement of α-amylase. The kinetic parameters, K _m and k _cat, showed an increase in catalytic activity in the micellar pseudophase. The decrease in optimum temperature from 55 to 30 °C and the shift in optimum pH from 5.5 to 7 on the addition of SDS and CTAB for the hydrolysis of starch are very favorable to enhance the washing characteristics.     

Wettability alterations due to crude oil composition and an anionic surfactant in petroleum reservoirs

In this study, dual-drop dual-crystal (DDDC) contact-angle measurements have been made using dolomite rock and fluid samples from the Yates reservoir (West Texas) and in the presence of an anionic (ethoxy sulfate) surfactant. The experiments have been conducted at Yates reservoir conditions (4.8 MPa and 27.8°C) and using live synthetic oil to provide realistic measurements of in situ reservoir wettability. Stocktank crude oil has also been used at reservoir conditions to study the oil compositional effects on wettability. An advancing contact angle of 152° measured for Yates dolomite rock, stocktank oil and synthetic reservoir brine showed a strong oil-wet nature. However, experiments with Yates live synthetic oil resulted in an advancing contact angle of 55°, indicating a weakly water-wet behavior. In the rock-fluids system consisting of Yates stocktank oil, the surfactant altered the wettability to less oil-wet by decreasing the advancing contact angle to 135°. For rock-fluids system with Yates live synthetic oil, the surfactant altered the wettability from weakly water-wet to strongly oil-wet by increasing the advancing contact angle from 55° to 165°. The oil-wet behavior observed with Yates live synthetic oil due to the surfactant indicates a significant wettability altering capability of the surfactant.     

Studies on aggregation of AOT and NaDEHP via the energy transfer between AO and RB molecules

The aggregation behaviours of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and sodium bis(2-ethylhexyl)phosphate (NaDEHP) solutions are studied via the energy transfer of acridine orange (AO) and rhodamine B(RB) molecules. The approximate apparent energy transfer efficiency (ϕ_a) of the dye molecules reaches its maximum value when the concentrations of AOT and NaDEHP are far lower than their cmc. This might be caused by the formation of surfactant–dye mixtures. The anionic surfactants (SDS, AS, AOT and NaDHEP), cationic surfactant (CTAB) and nonionic surfactant (Triton-X-100) are chosen to investigate the effect of the structure of surfactant on the ϕ_a between AO and RB molecules. The results indicate that the effective energy transfer may occur in the anionic surfactant systems and it is not obvious in the nonionic and cationic surfactant systems.     

Effects of surfactants on the microstructures of electrospun polyacrylonitrile nanofibers and their carbonized analogs

In this study, the influence of surfactants on the processability of electrospun polyacrylonitrile (PAN) nanofibers and their carbonized analogs was investigated. The surfactants employed in this effort are Triton X‐100 (nonionic surfactant, SF‐N), sodium dodecyl sulfate (SDS) (anionic surfactant, SF‐A), and hexadecyltrimethylammonium bromide (HDTMAB) (cationic surfactant, SF‐C). Interactions between electrospun PAN and the surfactants, reflected in effects on as‐spun and carbonized nanofiber morphologies and microstructures, were explored. The results show that uniform nanofibers are obtained when cationic and anionic surfactants (surfactant free and nonionic surfactants) are utilized in the preparation of electrospun PAN. In contrast, a bead‐on‐a‐string morphology results when the aniconic and cationic surfactants are present, and defect structure is enhanced with cationic surfactant addition. Moreover, fiber breakage is observed when the nonionic surfactant Triton X‐100 is employed for electrospinning. After carbonizaition, the PAN polymers were observed to have less ordered structures with addition of any type of surfactant used for electrospinning and the disorder becomes more pronounced when the anionic surfactant is utilized. Owing to the fact that microstructure defects create midband gap states that enable more electrons to be emitted from the fiber, an enhancement of electron emission is observed for PAN electrospun in the presence of the anionic surfactant. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3726–3735, 2013     

油水界面上阴/阳离子型复配表面活性剂体系的分子动力学模拟

采油过程中阴/阳离子型表面活性剂复配使用可显著增强驱油效果,对其微观机理的深入研究有助于驱油用表面活性剂的结构优化设计及使用。采用分子动力学方法研究了不同摩尔比的阴离子表面活性剂聚醚羧酸钠(PECNa)和阳离子表面活性剂十八烷基三甲基氯化铵(OTAC)复配体系在油水界面上的分子行为和物理性质。结果表明,复配体系比单种表面活性剂体系更有利于降低油水界面张力。不同复配比体系中,两种表面活性剂头基相反电荷间的吸引作用使表面活性剂之间对各自反离子的静电吸引作用减弱,且等摩尔比体系尤为明显。阴离子表面活性剂的亲水头基对阳离子表面活性剂亲水头基形成的水化层内水分子的结构取向无显著影响,反之亦然。通过调节两种离子型表面活性剂的复配比例,可调整油水界面吸附层微观结构,有望降低油水界面张力,提高采收率。     

Synergism and Performance for Systems Containing Binary Mixtures of Anionic/Cationic Surfactants for Enhanced Oil Recovery

The surfactant structure–performance relationship and application properties in enhanced oil recovery (EOR) for binary mixtures of anionic and cationic surfactants are presented and discussed. A polyoxyethylene ether carboxylate anionic surfactant was blended with a quaternary ammonium chloride cationic surfactant and tested for a high-temperature, low-salinity, and high-hardness condition as found in an oil reservoir. These mixtures were tailored by phase behavior tests to form optimal microemulsions with normal octane (n-C8) and crude oil having an API gravity of 48.05°. The ethoxy number of the polyoxyethylene carboxylate anionic surfactant and the chain length of the cationic surfactant were tuned to find an optimal surfactant blend. Interfacial tensions with n-C8 and with crude oil were measured. Synergism between anionic and cationic surfactants was indicated by surface tension measurement, CMC determination, calculation of surface excess concentrations and area per molecule of individual surfactants and their mixtures. Molecular interactions of anionic and cationic surfactants in mixed monolayers and aggregates were calculated by using regular solution theory to find molecular interaction parameters β ^σ and β ^M . Morphologies of surfactant solutions were studied by cryogenic TEM. The use of binary mixtures of anionic/cationic surfactants significantly broadens the scope of application for conventional chemical EOR methods.     

Morphology,structure, and conductivity of polypyrrole prepared in the presence of mixed surfactants in aqueous solutions

Polypyrrole (PPy) was prepared from different mixed‐surfactant solutions with ammonium persulfate as an oxidant. Three types of combinations were selected, including cationic/anionic, cationic/nonionic, and anionic/nonionic mixed‐surfactant solutions. The surfactants used in the experiments included cetyltrimethylammonium bromide (cationic surfactant), sodium dodecyl sulfate (anionic surfactant), sodium dodecyl sulfonic acid salt (anionic surfactant), poly(vinyl pyrrolidone) (nonionic surfactant), and poly(ethylene glycol) (nonionic surfactant). The morphology, structure, and conductivity of the resulting PPy were investigated in detail with scanning electron microscopy, Fourier transform infrared spectra, and the typical four‐probe method, respectively. The results showed that the interaction between the different surfactants and the interaction between the surfactants and the polymer influenced the morphology, structure, and conductivity of the resulting polymer to different degrees. The cationic surfactant favored the formation of nanofibers, the addition of anionic surfactants produced agglomeration but enhanced the doping level and conductivity, and the presence of a nonionic surfactant weakened the interaction between the other surfactant and the polymer in the system. In comparison with the results for monosurfactant solutions, the polymerization of pyrrole in mixed‐surfactant solutions could modulate the morphologies of PPy, which ranged from nanofibers of different lengths to nanoparticles showing various states of aggregation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1987–1996, 2007     

Adsorption mechanism of surfactants on nonwoven fabrics

For improved surface properties, nonwoven fabrics of polypropylene and poly(ethylene terephthalate) were treated with several kinds of surfactants, including anionic, cationic, and nonionic types. The adsorption isotherms of the anionic, cationic, and nonionic surfactants on the nonwoven fabrics were different. The adsorption isotherm of the cationic surfactant (dodecyl dimethylbenzyl/ammonium chloride) exhibited a maximum. The adsorption isotherm of the anionic surfactant (sodium dodecylbenzene sulfonate) was in the shape of the fifth Brunauer adsorption isotherm, and that of the nonionic surfactant (alkylphenol/ethylene oxide condensate) was similar to the fourth Brunauer adsorption isotherm. The time of the adsorption equilibrium was constant for the same types of adsorbate and adsorbent, and it was not related to the initial concentration. The specific surface resistance of the nonwoven fabrics decreased substantially after the adsorption of ionic surfactants. The nonwoven fabrics with the surfactants were characterized with scanning electron microscopy and X‐ray photoelectron spectroscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3210–3215, 2003     

Degradation of tricyclazole by colloidal manganese dioxide in the absence and presence of surfactants

The kinetics of the degradation of tricyclazole by water soluble colloidal MnO₂ in acidic medium (HClO₄) has been studied spectrophotometrically in the absence and presence of surfactants. The experiments have been performed under the pseudo-first-order reaction conditions with respect to MnO₂. To determine the rate constant as functions of [tricyclazole], [MnO₂] and [HClO₄], the pseudo-first-order reaction conditions have been maintained throughout the entire kinetic runs. The degradation has been observed to be first-order with respect to MnO₂ while fractional-order in both tricyclazole and HClO₄. The anionic surfactant, sodium dodecyl sulfate (SDS) has been observed to be ineffective whereas nonionic surfactant, Triton X-100 (TX-100) accelerates the reaction rate. However, the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) causes flocculation with oppositely charged colloidal MnO₂ and therefore could not be studied further. The catalytic effect of TX-100 has been discussed in the light of the mathematical model proposed by Tuncay et al. [25]. The kinetic data have been exploited to generate the various activation parameters for the oxidative degradation of tricyclazole by colloidal MnO₂.     

Mechanistic Studies of Particulate Soil Detergency: I. Hydrophobic Soil Removal

The mechanism of particulate soil detergency using aqueous surfactant systems is not well understood. In this research, carbon black (model hydrophobic soil) removal from a hydrophilic (cotton) and hydrophobic (polyester) fabric is studied using anionic, nonionic, and cationic surfactants. The zeta potential, solid/liquid spreading pressure, contact angle and surfactant adsorption of both soil and fabric are correlated to detergency over a range of surfactant concentrations and pH levels. Electrostatic repulsion between fabric and soil is generally found to be the dominant mechanism responsible for soil removal for all surfactants and fabrics. Steric effects due to surfactant adsorption are also important for nonionic surfactants for soil detachment and antiredeposition. Solid/liquid interfacial tension reduction due to surfactant adsorption also aids in detergency in cationic surfactant systems. Wettability is not seen as being an important factor and SEM photos show that entrapment of soil in the fabric weave is not significant; the particles are only attached to the fabric surface. Anionic surfactants perform best, then nonionic surfactants. Cationic surfactants exhibit poor detergency which is attributed to low surfactant rinseability.     

Effects of surface activity on aquatic toxicity of binary surfactant mixtures

The purpose of this study was to discuss the effects of surface activity on the aquatic toxicity of binary surfactant mixtures comprising anionic, nonionic, and cationic surfactants. Surface tension was measured to determine the cmc (critical micelle concentration), and acute aquatic toxicity tests were conducted on Daphnia magna to obtain 24h-EC(50) (24h 50% effective concentration). TU (toxic unit) was calculated to evaluate the toxicity of the mixture. Most of the surfactant mixtures showed no synergistic increase in the aquatic toxicity. The mixture of anionic/nonionic surfactants showed synergistic interfacial activity with decreasing cmc, but the toxicity did not increase. The surface tension of the mixture at 24h-EC(50) (γ(tox)), which was used as an indicator of the toxic concentration, decreased considerably and TU was >1, indicating decreased toxicity. γ(tox) of the anionic/anionic surfactant mixture decreased when tested with hard water (hardness of 625 ppm). γ(tox) could not be used as a toxic indicator for the anionic/cationic surfactant mixtures because they showed aquatic toxicity before their surface tension began to decrease.