Mechanistic Study of Wettability Alteration of ... - ACS Publications

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Mechanistic Study of Wettability Alteration of Quartz Surface Induced by Nonionic Surfactants and Interaction between Crude Oil and Quartz in the Presence of Sodium Chloride Salt Achinta Bera, Kissmathulla S, Keka Ojha, T. Kumar, and Ajay Mandal* Department of Petroleum Engineering, Indian School of Mines, Dhanbad-826004, India ABSTRACT: Experimental investigations have been conducted in order to elucidate the mechanism responsible for wettability alteration of quartz surface in the presence of nonionic surfactants. The wettability alteration has been verified by measuring the contact angle on a quartz−crude oil−distilled water system by systematic variation of surfactants, temperature, and water salinity. In all cases, contact angle decreases with elapse of time. As ethylene oxide number of nonionic surfactant increases the initial equilibrium contact angle decreases. Results also show that as temperature increases, contact angle decreases due to reduction of oil viscosity. With increasing water salinity, contact angle decreases up to a certain salinity and then increases. This salinity may be termed as optimal salinity for the system. Scanning electron microscopy analysis shows the roughness of the quartz surface. Infrared spectroscopy analysis of the quartz sample indicates the presence of Si−O groups. Fourier transform infrared (FTIR) spectroscopy and acid number analysis of crude oil suggest the acidic nature of the oil. Critical micelle concentrations of the surfactants were also measured by the surface tension method. The lowest surface tension value achieved by Tergitol 15-S-12 is 28 mN m−1.

1. INTRODUCTION Wettability of solid surfaces can be modified by introducing surface active agents or surfactants and ionic substances into the solid−liquid systems and also by regulating the thermodynamic parameters such as temperature.1−3 According to Craig,4 wettability is defined as “the tendency of one fluid to spread on or adhere to a solid surface in presence of other immiscible fluids”. Wettability of a solid surface relates directly to the solid−fluid and fluid−fluid interactions. The interaction between two immiscible phases implies the interfacial energy. Attraction between the substrates causes lower interfacial energy, and repulsion forces result in a higher energy surface. The interfacial forces in a three-phase system relate to one another in a famous equation known as Young’s law,5−7 σ − σSO cos θ = SW σ WO (1)

another immiscible liquid such as water. The Young’s equation is valid at equilibrium conditions for an ideal state of a perfectly smooth, chemically homogeneous, rigid, insoluble, and nonreactive surface. Understanding the mechanism of spreading of a liquid over a solid substrate is crucial in several engineering applications. Some of these applications are enhanced oil recovery (EOR), lubrication emulsion, and film coating as in pulp and paper, photographic emulsions, and plastic. In the oil recovery process, wettability alteration of reservoir rocks by surfactants is very much important as it controls the multiphase flow problems regarding the oil migration from source rocks to primary production, capillary pressure, imbibitions, drainage, dispersion, irreducible water saturation, residual oil saturation, and EOR. The factors which can play major role on the reservoir rock wettability are the presence of surface active agent in the crude oil, type of mineral surfaces in the reservoir, presence of salts in formation fluids, temperature, and pH value of brine and cementing clay. Sodium chloride (NaCl) salt causes an increased tendency to form a monolayer, which decreases liquid−liquid interfacial tension, and an increased tendency to accumulate the surface active agents produced from crude oil; these two trends act together to alter wettability of solid surfaces. An interesting property that enables the surfactants to alter wettability of solid surfaces is amphiphilicity. The amphiphilicity of surfactants makes them form a multitude of different structures in solution and adsorb at interfaces.8 Such an adsorption makes the surface of solids more nonpolar. The formation of the adsorbed film on polar or ionic solid surface causes changes in the surface free energy of the solid, solid−

where θ is contact angle and σ values indicate the interfacial tensions between solid−water (σSW), solid−oil (σSO), and water−oil (σWO) interfaces. Figure 1 illustrates the situation where the oil drop will reside on solid surface in the presence of

Received: March 19, 2012 Revised: April 24, 2012 Published: April 25, 2012

Figure 1. Illustration of contact angle in three-phase system on a solid surface. © 2012 American Chemical Society

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dx.doi.org/10.1021/ef300472k | Energy Fuels 2012, 26, 3634−3643

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Table 1. Physicochemical Properties of the Surfactants Employed in this Work chemical name secondary alcohol ethoxylate secondary alcohol ethoxylate secondary alcohol ethoxylate secondary alcohol ethoxylate

linear formula and molecular weight C12−14H25−29O[CH2CH2O]5H EON = 5 MW = 415 C12−14H25−29O[CH2CH2O]7H EON = 7 MW = 515 C12−14H25−29O[CH2CH2O]9H EON = 9 MW = 584 C12−14H25−29O[CH2CH2O]12H EON = 12 MW = 738

trade name

HLB value

category

Tergitol 15-S-5

10.6

nonionic

Tergitol 15-S-7

12.1

nonionic

Tergitol 15-S-9

13.3

nonionic

Tergitol 15-S-12

14.7

nonionic

analysis of quartz has been performed to know the presence of Si−O groups. Critical micelle concentrations of the employed nonionic surfactants were also measured by the surface tension method. Physicochemical properties of crude oil have been studied by viscosity, asphaltene content, acid number, and API gravity measurements, and FTIR of crude oil has been done to summarize the information about the chemical groups that are present.

liquid interfacial free energy, surface tension of water, and decreases the spreading coefficient. Due to presence of polyethylene oxide chain in nonionic surfactants in which a hydrophobic part is attached are widely used in technological applications.9−12 The hydrophilic−lipophilic balance (HLB) of the nonionic surfactant also plays an important role on wettability alteration of a solid surface. However, there are many studies available dealing with wettability of solids and the acid−base intermolecular interactions in the presence of the surfactants, but until now, proper explanation was not satisfactory.3,13−21 Reservoir rocks as a whole may not show the same wettability. It depends upon the reservoir rock properties, oil chemistry, and water salinity of the system. The rocks may be oil-wet, water-wet, or intermediate-wet. This wetting behavior depends upon interaction between rock and crude oil. In the case of the silica surface, the surface charge of silica in water is positive at low pH but negative at high ph value. The silica surface remains negatively charged at neutral pH and hence the affinity to adsorb organic acids which are naturally occurring in the oil. A number of investigators have been working on wettability alteration by adsorption from crude oil.22−30 Different experimental methods such as contact angle measurement, the Li and Horne method, Amott wettability index (AWI), USBM (U.S. Bureau of Mines) wettability index for quantitative results and imbibitions rate, flotation, microscopic examination, capillary pressure curves, reservoir logs, permeability, saturation relationship, nuclear resonance, and dye adsorption for qualitative results have been used to measure the surface wettability of a system.31−34 For most of the cases, the contact angle method (sessile drop method) is commonly used to measure the wetting properties of the solid surface with respect to a liquid in presence of another immiscible liquid. Water salinity also affects the contact angle on a quartz−crude oil−distilled water system. The effect of water salinity on contact angle using different concentrations of NaCl has been studied by several researchers,35,36 and they reported that the contact angle can be noticeably influenced by variation of NaCl concentration. Temperature has an important effect on the contact angle of solid/crude oil/water system due to change in viscosity and density of oil, and this effect introduces an additional force on the oil drop. In the present paper, wettability alteration of the quartz surface has been determined by sessile drop method to study the effect of different nonionic surfactants, water salinity, and temperature. The effect of ethylene oxide number (EON) on contact angle between solid−liquid systems has also been examined. Scanning electron microscopy (SEM) images were taken for surface morphology study. Infrared spectroscopy

2. EXPERIMENTAL SECTION 2.1. Materials Used. Four nonionic surfactants such as Tergitol 15-S-5, Tergitol 15-S-7, Tergitol 15-S-9, and Tergitol 15-S-12 were procured from Sigma-Aldrich, Germany. The details physicochemical properties of the surfactants have been given in Table 1, and all the surfactants are 99.9% pure in nature. Sodium chloride (NaCl) with 99% purity was used for preparation of different concentration of brines, and it was supplied by Qualigens Fine Chemical, India. Quartz was used as solid surfaces for contact angle measurement. The crude oil sample collected from Ahmadabad oil field, India, was used in the experiment. Reverse osmosis water from Millipore water system (Millipore SA, 67120 Molshein, France) was used for preparation of solutions. 2.2. Apparatus and Methodology. 2.2.1. Characterization of Crude Oil and Quartz. The crude oil sample used for this work was characterized by measurement of its density, viscosity, API gravity, and total acid number. Density of the crude oil was determined by pycnometer and from the density data. API gravity was calculated. Viscosity of the crude oil at different temperature was measured by Rheometer (Physica MC1). The asphaltenes content was determined by n-pentane precipitation. The physical properties of the crude oil are listed in Table 2. FTIR analysis of the crude oil was also done to determine the functional groups that are present.

Table 2. Physical Properties of the Crude Oil asphaltene content (wt %) sulfur content (wt %) viscosity at 45 °C (mPa·s) density at 22 °C (kg/m3) ° API gravity total acid number (mg KOH/g)

0.20 0.50 51.02 855.05 33.987 0.040

Microscopic images of quartz sample were taken in a sophisticated SEM (Hitachi S-3400N Scanning Electron Microscope) for morphological studies of the quartz surface. Infrared spectra of the quartz and crude oil samples were recorded between 400 and 4000 cm−1 using KBr pellet techniques on a Buck Scientific infrared (IR) spectrophotometer, M500. The spectra were interpreted using the Ganz and Kalkreuth method. 2.2.2. Measurement of Surface Tension. Measurement of surface tension is a very useful supplementary test method for determination of critical micelle concentration (CMC). It is particularly useful when only very small quantities of an experimental surfactant are available. 3635


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Figure 2. Schematic diagram of the apparatus used to measure the contact in solid−liquid systems.

Figure 3. FTIR spectra of the employed crude oil in this experiment. in direct contact with the flat horizontal solid surface of quartz which is hanging from the clamp of the stand attached with a glass rod and the solid surface and the droplet of oil were completely submerged under the water. After submerging the attached system, photographs were taken few minutes later on reaching the equilibrium. The angle between the solid surface and oil−water interface was measured on an enlarged photograph of the drop. Photographs were taken by a high resolution and magnification digital camera (Sony DSC-HX100 V). The quartz was cleaned in boiling concentrated nitric acid and then washed with distilled water and stored in that distilled water. The dynamic contact angle was measured in different time intervals for all the solutions. To test the temperature effect on the contact angle, a

In the present study surface tension of the different concentrated surfactant solutions were measured by a programmable tensiometer (Kruss GmbH, Germany, model: K20 EasyDyne) under atmospheric pressure by the Du Noüy ring method. During the measurement, the experimental temperature was maintained at 298 K. The platinum ring was thoroughly cleaned with acetone and flame-dried before each measurement. In all cases, the standard deviation did not exceed ±0.1 mN/m. 2.2.3. Measurement of Contact Angle. The schematic diagram of the experimental setup of contact angle method used to measure the wettability of solid surfaces is shown in Figure 2. The contact angle was measured by placing crude oil droplet (constant volume of 20 μL) 3636


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wavenumber range of 3700−3100 cm−1 is due to the presence of a small amount of phenolic functional groups.39 There are weak bands at 1590−1470 cm−1 because of the presence of CC ring stretching. The presence of acidic groups in crude oil has been identified by FTIR analysis of crude oil. This is also supported by the total acid number (0.040 mg of KOH/g) of the crude oil. 3.2. Surface Morphology and Quantitative Analysis of Quartz Sample. SEM images in Figures 4a and b show the morphology of clean quartz plate before aging with surfactant at 500× and 1500× magnifications, respectively. It can be observed from the figure that clean substrate has a surface containing quartz particles with sharp edges. The roughness of the quartz surface influences the contact angle. The effect of roughness on contact angle was investigated by Wenzel40 who stated that in a simple equation as

water bath was used; the system was placed in the water bath, and measurements were carried out at different temperatures.

3. RESULTS AND DISCUSSION 3.1. Characterization of Crude Oil. The chemical groups present in the crude oil were determined by FTIR spectra. FTIR spectra of the crude oil used in the present study were recorded between 400 and 4000 cm−1. In the FTIR spectrum, certain groups of chemical bonding give rise to bands at or near the same frequency, regardless of the structure of the rest of the molecule. The absorption bands of aliphatic C−H bonds, with additional bands originating from groups containing aromatics, oxygen, sulfur, and nitrogen, usually dominate the spectra of crude oils.37,38 A typical FTIR spectrum of the crude oil is shown in Figure 3. The prominent functional groups present in the oil are given in Table 3. The major functional groups

wavelength of absorption (cm−1)

mode of vibration

2852−2852

CH stretching

2922−2923

CH stretching

1460

CH deformation

1376 722

CH symmetric deformation CH bending

1640−1800

CO stretching

3700−3100 1470−1590

OH stretching CC ring stretching

(2)

cos θ* = r cos θ

Table 3. Functional Group in the IR Spectra of the Crude Oil

where θ* is contact angle on the rough surface and r is the roughness factor. The roughness is a difference between advancing and receding angle. From the Wenzel wetting equation, as the surface roughness increased, the solid liquid contact area increased, leading to a large contact angle. The roughness of the surfaces, as obvious from SEM image in Figure 4, is related to the surface morphology of the surface. Therefore, after treatment with surfactant, the surface properties have been changed due to formation of a surfactant layer over the quartz surface leading to reduced contact angle. The infrared spectra of clean quartz and surfactant treated quartz are shown in Figures 5 and 6. The spectra of the quartz before and after surfactant treatment used in the present study were recorded between 400 and 4000 cm−1. The band assignments are listed in Table 4. The difference between the two spectra is the additional peak at 3450 cm−1 of O−H stretching of treated quartz sample. This is due to adsorption of ethoxylated secondary nonionic surfactant on quartz surface. Band intensities were determined by the baseline method and the characteristic absorption values were calculated. No internal reference band was found in the infrared spectra of quartz because all band intensities were changed by the action of grinding. The quartz band at 1095 cm−1 occurs as a shoulder because it partly overlaps the strongest absorption band of quartz at 1085 cm−1. The Si−O asymmetric stretching and bending vibrations have been found at 1095 and 465 cm−1. On

functional group CH2 and CH3 of the saturate CH2 and CH3 of the saturate CH2 and CH3 of the saturate CH2 of the saturate CH of substituted benzene CO of carbonyl/ carboxylic groups OH of phenolic groups CC of aromatics

identified on the FTIR spectra of the oil include C−H stretching of the saturate (2923 and 2852 cm−1), C−H deformation of the saturate (1460 cm−1), and C−H symmetric deformation of the saturate (1376 cm−1). The peak at 722 cm−1 indicates the presence of long-chain alkyl groups, (CH2)n, with n > 4, in saturates. The region between 1800 and 1640 cm−1 corresponds to carbonyl groups such a carboxylic acids. The absorption at 1643 cm−1 is due to vibration of the carboxylic acid group present in the crude oil. The absorption at the

Figure 4. SEM images of a clean quartz sample. (a) 500× magnification and (b) 1500× magnification. 3637


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Figure 5. Infrared spectra of a quartz sample before surfactant treatment.

Figure 6. Infrared spectra of a quartz sample after surfactant treatment.

present study, the same result has been also found in the case of the employed nonionic surfactants that with increasing EON, the CMC value of the surfactant increases. The CMC values for the surfactants with EON 5, 7, 9, and 12 are 0.002, 0.0031, 0.0042, and 0.0051 wt %, respectively. 3.4. Factors Influencing the Contact Angle (θc). The effect of surfactants and their ethylene oxide number, water salinity, and temperature on wettability of quartz surface has been determined by measuring the contact angles. The contact angles are largely influenced by the above factors. The effects of the above factors are discussed below. 3.4.1. Effect of Surfactants and their EON. Wettability of solid surface is largely affected by application of surfactants. The interfacial crude oil−aqueous solution−solid substrate interactions are characterized by the formation of a contact angle on a solid surface. Understanding contact angle behavior, in general, is one of the challenging problems in surface science due to its role in all processes involved in three-phase interfacial phenomena. Two fundamental problems can be associated with contact angle behavior. The first is related to solid substrate

the other hand, the Si−O symmetric stretching and bending vibrations have been found at 785 and 695 cm−1. Examination of a number of quartz infrared spectra showed that the resolution of this shoulder appears to be very sensitive to the crystallinity of the quartz sample. 3.3. Reduction of Surface Tension by the Surfactants. It is well-known that the surfactants reduce the surface tension of water by getting adsorbed on the liquid−gas interface. The critical micelle concentration (CMC), one of the main parameters for surfactants, is the concentration at which surfactant solutions begin to form micelles in large amounts.41 Surface tensions of the above three surfactant (Tergitol 15-S-5, Tergitol 15-S-7, Tergitol 15-S-9, and Tergitol 15-S-12) solutions at different concentrations were measured and plotted as a function of concentration in Figure 7. The concentration at the inflection point of the curve is critical micelle concentration. The lowest surface tension value achieved by Tergitol 15-S-12 is 28 mN m−1 which is significantly lower than the surface tension value of water. For ethoxylated nonionic surfactant CMC increases with increase in EON of the surfactant.42 In the 3638


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Table 4. Band Assignments of Quartz and Surfactant Treated Quartz samples quartz

wave number (cm−1) 2930 1095 785 695 465

quartz with Tergitol 15-S-7

3450 2930 1095 785 695 465

assignments C−H stretching Si−O asymmetrical stretching vibration Si−O symmetrical stretching vibration Si−O symmetrical bending vibrations Si−O asymmetrical bending vibration O−H stretching C−H stretching Si−O asymmetrical stretching vibration Si−O symmetrical stretching vibration Si−O symmetrical bending vibrations Si−O asymmetrical bending vibration

Figure 8. Effect of surfactants on dynamic contact angles on the quartz surface at 298 K.

Figure 9. Effect of ethylene oxide number on contact angle on the quartz surface at 298 K after 2 h of equilibrium.

Figure 7. Surface tension of the surfactants with variation of their concentration and CMC determination.

equilibrium in each surfactants solution at their critical micelle concentration value. The figure shows that with increase in ethylene oxide number of the surfactants, contact angle decreases. As ethylene oxide number increases, the surface activity of the surfactant increases and also the wetting property of the solid surface is modified to be more oil-wet. An example of the attained photographs of the variation of contact angles over different time intervals is shown in Figure 10 for Tergitol 15-S-7.

structure and its surface roughness, whereas the second is associated with the mutual interactions of immiscible liquids in contact with the solid substrate. The investigation has been made on the fundamental problems related to crude oil− aqueous solution interfacial interactions in the close vicinity to the contact line with solid substrate. Figure 8 shows the contact angle behavior versus time of rest on the quartz substrate for crude oil droplets in the presence of nonionic surfactants (Tergitol 15-S-5, Tergitol 15-S-7, Tergitol 15-S-9, and Tergitol 15-S-5). The contact angle decreases initially sharply for all surfactant but for water the effect is not so prominent. In the case of water, contact angle decreases due to interaction of Si− O groups with water molecules that makes the quartz surface oil-wet. In the presence of surfactants, the solid surface has been become more oil-wet by lowering the contact angle. After an hour the lowering of the contact angle shows the time independent behavior up to 3 h. In Figure 9, the surface activity of the surfactants has been plotted as contact angle versus ethylene oxide number. The values were recorded after 2 h of

Figure 10. Photographs of sessile oil droplets in Tergitol 15-S-7 surfactant over time on quartz surface. 3639


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active agents from crude oil to solution also increases which can decrease the contact angle. After a certain time, the behavior of contact angle decrease is independent of time due to completion of transfer of surface active agent into the solution phase. In addition with this, there are several types of interactions available in crude oil−quartz−liquid systems such as polar interactions that dominate in the absence of a water film between oil and solid, surface precipitation which depends on mainly crude oil solvent properties with respect to the asphaltenes, acid/base interactions that control surface charge at oil/water and solid/water interfaces, and ion bonding or specific interactions between charged sites and higher valence ions. These two types of interaction are shown in Figure 12. In Figure 13, a contact angle versus salinity curve is depicted. It is clear from the figure that with increase in salinity contact angle decreases up to a certain salinity and then increases. This salinity can be assigned as the optimal salinity for the system. This reduction in contact angle can be attributed to the effect of salt on the interfacial tension between crude oil and aqueous phases. The presence of salts in the aqueous phase has a strong ability to increase the accumulation of the surface-active species; these are available in crude oil, at the crude oil− aqueous phase interface, and thereby reduce the interfacial tension and contact angle.43 As the salinity concentration rises to more than 6 wt %, then the repulsive electrostatic doublelayer forces and repulsive hydration forces increase to avoid the spreading of crude oil. This influence causes a significant increase in contact angle over the range of NaCl concentrations of 6−8 wt %. When NaCl concentration increases to exceed 8 wt %, it prevents the surface-active material from dissolving into the aqueous phase. Therefore, the activity of the nonionic surfactant as well as produced surfactant from the crude oil has been reduced and it could not further reduce the contact angle. Instead, the surface-active material will adsorb onto the solid surface, which will enhance the oil-wetting behavior on the solid surface. 3.4.3. Effect of Temperature. The effect of temperature on contact angle has been investigated in water solution. Figure 14 depicts the variation of contact angle with temperature. The figure shows that with increase in temperature the contact angle gradually decreases. Temperature influences the oil property as well as bath solution property. The interfacial interaction between crude oil and solution is also influenced by temperature. The reduction in contact angle may also be attributed to the reduction in oil viscosity with the increase in temperature. Temperature also affects the density of the phases differently along with viscosity, which in turn will affect the contact angle. Equation 1 shows that contact angle is related to oil−water interfacial tension. Again interfacial tension is directly related to liquid density. As temperature influences the density of liquids, interfacial tension between oil−water will be also affected by temperature and contact angle will also be exaggerated. In addition to this, a thermal gradient acts behind the phenomena. On a thermal gradient, the drop will move from the warm side to the cool side. It does this because liquid−liquid interfacial tension is affected by temperature. As temperature increases, interfacial tension decreases, and vice versa. On each area element at the liquid−liquid interface, there are two forces pulling in opposite directions trying to reduce the surface area of the drop. Since interfacial tension decreases with increasing temperature, the tension pulling in the cold direction (γcold) is stronger than the one pulling in the warm direction (γwarm). This results in a flow around the edge of the

On the other hand, the HLB value of the surfactant also increases with increasing EON. As HLB value is related to wetting ability of surfactant, with an increase in the HLB value the surfactant makes the solid surface more oil-wet. In the presence of surfactants, the wettability alteration of quartz follows a different mechanistic path. Quartz wettability is connected with adsorption of surfactants at water−air and quartz−water interfaces. Surfactant adsorption at the water−air interface causes a decrease of the water surface tension; however, the quartz−water interface tension can increase or decrease under the influence of the surfactant depending on the orientation of its molecules in the adsorbed layer. The monoand bilayer adsorption model are responsible for the mechanism of the wettability alteration of the solid quartz surface. The mechanism of monolayer adsorption suggests that at a low concentration of surface active agents they are adsorbed on the quartz surface, and their hydrophobic parts are arranged parallelly to the quartz−water interface. When the concentration of surfactant in the bulk phase increases, the density of the surface layer increases, too, and the hydrophobic part of the adsorbed surfactant becomes oriented into the solution, making thus a larger number of active sites available for adsorption. In such a way the quartz−water interface tension increases and make the quartz surface oil-wet. In the bilayer mechanism, the initial stage of adsorption of surface active cations at the quartz−water interface is similar to that of the monolayer. However, it is assumed that after neutralization of the surface charges the adsorption of the surface active cations proceeds further on the hydrophobic parts of the previously adsorbed ions. So a second adsorbed layer is formed, where the charged hydrophilic parts of ions are oriented toward the solution. It causes a decrease of the quartz−solution interface tension and simultaneous increase the oil-wet property of the quartz surface. 3.4.2. Effect of Water Salinity. The effect of salinity on contact angle for a constant volume (20 μL) oil droplet has been measured on quartz surface. The variation of the contact angle with time has been measured with different salinity systems, and the results are depicted in Figure 11. With the progression of time, the interaction between crude oil and salt present in solution increases, and hence, the transfer of surface

Figure 11. Effect of salinity on dynamic contact angles on quartz surface at 298 K. 3640


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Figure 12. Mechanism of interaction between crude oil component, salt, and solid surfaces: (a) acid/base interactions; (b) ion-bonding.

Figure 15. Schematic diagram of effect of temperature gradient on contact angle.

crude oil−aqueous phase interface, and thereby reduce the interfacial tension and contact angle. In the presence of surfactants, the accumulation of the produce surfactant from crude oil shows good activity to reduce contact angle. Two types of interactions act behind the wettability alteration of solid surfaces such as acid/base interaction and ion bonding. The major functional groups identified on the FTIR spectra of the oil include C−H stretching of the saturate (2923 and 2852 cm−1), C−H deformation of the saturate (1460 cm−1), and C− H symmetric deformation of the saturate (1376 cm−1). The peak at 722 cm−1 indicates the presence of long-chain alkyl groups, (CH2)n, with n > 4, in saturates. The presence of acidic groups in crude oil has been identified by FTIR analysis of crude oil. This is also supported by the total acid number (0.040 mg of KOH/g) of the crude oil. It can be observed from SEM study that clean substrate has a surface containing quartz particles with sharp edges. The difference between the two spectra of quartz before and after surfactant treatment is due to adsorption of ethoxylated secondary nonionic surfactant on quartz surface. An empirical relation has been established between ethylene oxide numbers of nonionic surfactant and wettability of quartz. The increase of HLB value and ethylene oxide number of nonionic surfactant makes the quartz surface more oil-wet. A new concept about the optimal salinity has been drawn from contact angle method for determination of wettability. Water salinity has systematic effects on contact angle at a particular temperature. Temperature has noticeable effect on contact angle. As temperature of the container liquid increases, the contact angle decreases due to reduction of oil viscosity.

Figure 13. Effect of salinity on contact angles on quartz surface at 298 K.

Figure 14. Effect of temperature on contact angles on quartz surface in water.

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drop, as shown in Figure 15. This flow pushes against the surface under the bottom of the drop and the reaction force from the surface pushes the drop along the thermal gradient.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 91-326-2296632.

4. CONCLUSIONS Accumulation of surface active agents produced from crude oil plays a vital role on wettability alteration of solid surface. Adsorption of crude oil components alters the wetting behavior of the solid surface. The presence of salts in the aqueous phase has the strong ability to increase the accumulation of the surface-active species; these are available in crude oil, at the

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge the financial assistance provided by University Grant Commission [F. No. 37-203/ 2009(SR)], New Delhi to the Department of Petroleum 3641


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Engineering, Indian School Of Mines, Dhanbad, India. Thanks are also extended to all individuals associated with the project.

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