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Application of nano particle for enhancement of foam stability in the presence of crude oil: Experimental investigation
Accepted Manuscript Application of nano particle for enhancement of foam stability in the presence of crude oil: Experimental investigation
Sepideh Babamahmoudi, Siavash Riahi PII: DOI: Reference:
S0167-7322(17)36049-X doi:10.1016/j.molliq.2018.04.093 MOLLIQ 8996
To appear in:
Journal of Molecular Liquids
Received date: Revised date: Accepted date:
20 December 2017 16 April 2018 18 April 2018
Please cite this article as: Sepideh Babamahmoudi, Siavash Riahi , Application of nano particle for enhancement of foam stability in the presence of crude oil: Experimental investigation. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Molliq(2017), doi:10.1016/j.molliq.2018.04.093
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ACCEPTED MANUSCRIPT
Application of Nano Particle for Enhancement of Foam
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Investigation
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Stability in the presence of Crude Oil: Experimental
Sepideh Babamahmoudi+, Siavash Riahi+
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+ Institute of Petroleum Engineering, School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran
Corresponding author: Siavash Riahi P.O Box: 113654563 Email address: [email protected] Phone number: +982161114714
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Abstract The use of gas is one of the most common methods in the oil industry for enhancing oil recovery.
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However, problems such as gas uptake due to the low density of the gas reduce the efficiency of
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this method. The formation of foam reduces the relative permeability of the gas and improves
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this technique. The foam generated by the combination of water and gas does not show enough stability, and thus surfactant injection method has been used for many years. However, foam
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stabilized by the surfactant is problematic in the presence of oil. The advent of nano technology
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has shown that the foam stabilized by nanoparticles can tolerate the presence of oil. In this project, the foam generated by nanoparticle and the surfactant is studied. Then, the effect
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of different kinds of crude oils, with different viscosities on foam structure, has been
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investigated. For studying the foamability and foam stability, the static method of “mixing” is used with the experimental setup designed for this job. Then, by measuring the interfacial tension
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(IFT) and surface tension (ST) between solutions, oil and the air, the entering coefficient (E),
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spreading coefficient (S), lamella number (L) and bridging coefficient (B) are calculated, and the relations between obtained values and the observed behaviors has been investigated.
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The results show that the solution containing Cetyltrimethyl ammonium bromide (CTAB) and nano silica is undispersed, so the foam studies are not carried out for this system. But the solution containing Sodium dodecyl sulfate (SDS) and nano silica is completely dispersed and generates a desirable foam. In addition, nano silica increases the foamability and foam stability of the SDS solution. Regarding the effects of crude oil, the presence of crude oil reduces foam stability and by increasing oil saturation, the stability reduction is observed to be greater. It is also observed that by increasing oil viscosity, foam stability and foam properties improve. 2
ACCEPTED MANUSCRIPT Keywords: Foam; Nano Particle; Surfactant; Crude Oil; Enhanced Oil Recovery (EOR)
1. Introduction Gas injection into reservoirs is one of the most widely used methods in enhanced oil recovery. If
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the gas is miscible with oil, it can replace that in the swept volume. However, the undesirable
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mobility rate of the gas, due to the reservoir heterogeneity and its low viscosity, leads to the gas
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fingering and reduction in the sweep efficiency [1]. Using foam, the disadvantages of gas injection including low sweep efficiency will decrease [2]. However, immediately after foam
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generation, the liquid will start to drain out of the liquid films, which are called lamella. This can
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cause foam rupture [3].
Surfactants are surface-active components which can be used to prevent foam collapse [4]. When
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surfactant is injected, the required energy to form the gas-liquid interface has been decreased and
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thus a more stable foam is formed [5]. By increasing the surfactant concentration near the “critical micelle concentration (CMC)”, the surface tension is reduced and thus the required
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energy for foam generation is decreased [6]. Along with the positive effects of surfactants,
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several factors limit the use of them. The factors such as surfactant adsorption on the reservoir rock and surfactant break down under the harsh condition of the reservoir, like high pressure and
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high temperature [7-9].
In recent years, new applications of nanoparticles as foam stabilizers became clear [10]. Studies showed that the nano particles, unlike surfactants, can be used without adsorption or chemical break down [11-13]. Since the adhesion force at the surface between two fluids in the presence of nano particles is more than that in the presence of surfactants, these foams have longer stability [14]. So far, nano silica has been used mostly in the EOR process in order to improve the foam properties [15, 16]. 3
ACCEPTED MANUSCRIPT Ma et al. studied the assembly of nano particle and surfactant at air-water interface. They first investigated the effects of nano silica on the surface tension. During the experiment, it was found that the nano silica does not show a great impact on the effective surface tension. They understood that because the nano silica is hydrophilic, it has no tendency to get in the water-air
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interface [17]. Another important part of their work was studying the amount of adsorption in the
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water-air interface when the system has both nano particle and surfactant. For this purpose,
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anionic surfactant SDS was selected and the results were compared with Ravera et al. results that had used the cationic surfactant CTAB [18]. It was found that, in the nano silica and CTAB
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system, because of the attractive force between nano silica with negative charge and CTAB with
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positive charge, the surfactants stuck to the surface of the nano silica and dramatically reduced the system’s efficiency. But in the nano silica and SDS system, the repulsive force between
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negatively charged nano silica and SDS resulted in more surfactant adsorption on the water-air
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interface and caused increase of the system’s efficiency [17]. Kumar et al. also investigated the interaction between nano silica with negative charge and
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different surfactants in aqueous solutions. Actually, the strong attraction force between nano
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silica with negative charge and Dodecyltrimethylammonium bromide (DTAB) with positive charge led to the accumulation of nano particles in the system. In the case of non-ionic surfactant
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C12E10, the non-electrostatic interaction between nano particles and surfactant micelles also led to the adsorption of surfactants on the nano particles. But no significant interaction was observed between nano silica and SDS with the same negative charge [19]. Foam Stability in The Presence of Oil Crude oils have complex compositions and properties. Presence of oil may influence the stability of foam which is applied for EOR process [20-22]. 4
ACCEPTED MANUSCRIPT Oil can be solubilized in the micelles, or it can remain as emulsions or as a continuous phase in the foam liquid films. The properties of the oil are important factors for judging whether the oil will influence the foam structure, or not [23]. Vikingstad investigated the interaction between crude oil and foam solution containing 0.5wt.%
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Alpha Olefin Sulfonate (AOS) using the static method of studying foam. She used six different
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crude oil samples with various properties and different viscosities. According to her experiment,
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the effect of crude oils with different physical and chemical properties on foam structure was so complex, and there was no obvious trend to explain the interaction between crude oil and foam
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[24].
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Farzaneh et al. studied the foam performance in the presence of light and heavy oil. Also, they examined the effects of different concentrations of various types of surfactants. Based on their
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experiments, in the presence of crude oil the anionic surfactant generates better foam in
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comparison with the nonionic surfactant. They also observed that by increasing the surfactant concentration, the foams half-time increases. But, this trend is not permanent and there is an
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optimum concentration for each surfactant. Regarding to the crude oil, the presence of crude oil
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reduced the foam stability, but by increasing the oil viscosity, this negative effect decreased [25]. Yekeen et al. examined the influence of two kinds of nano particles, Al2O3 and SiO2, on SDS
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foam stability in a glass micro model. The experiment has been conducted in the presence of different oils. According to their results, the presence of nano particle is effective in improving the stability of foam, and SiO2 is more effective than Al2O3 [26]. In addition, by increasing the oil viscosity, foam stability will also increase [27]. Generally, the interaction between foam and oil is not clearly understood and many different types of experiments are required to clarify the interaction [28]. There are some main theories, which explain foam stability in the presence of oil: 5
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Spreading and Entering Coefficients
Based on this theory, the stability of foam in the presence of oil is related to the spreading coefficients (S) and entering coefficients (E) [20, 22, 24, 29-39] (equations 1 and 2). S = σw/g − σw/o − σo/g
(1)
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E = σw/g + σw/o − σo/g w/o
is the interfacial tension between water
and oil, and σo/g is the surface tension between oil and gas.
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σw/g is the surface tension between water and gas, σ
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(2)
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According to this theory, if the entering coefficient is positive, the oil will be attracted into the lamella between two adjoining bubbles, and if the spreading coefficient is positive, the oil will
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spread at the surface and break the foam films [40]. S and E are interdepending as below
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(equation 3).
(3)
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E=S+2σw/o
It shows that the entering coefficient is always greater than or equal to the spreading coefficient.
Lamella Number
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So, a negative entering coefficient implies a negative spreading coefficient [41-47].
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The procedure of oil emulsification with foam lamella can be described using the balance of forces and in terms of a dimensionless number called the lamella number [23, 39, 44, 45, 48, 49]. Lamella number (L) can be defined as follows: (4) Where, rp is the radius of curvature of the plateau border and ro is the oil drop radius. It was found in the literatures that ro/rp ratio is constant for all the foams yielding about 0.15 [23, 48]. So, it will be obtained: 6
ACCEPTED MANUSCRIPT (5) Based on this theory, oils can give unstable foam, moderately stable foam or they can show little interaction with the foam. From experiments, three types of foams, A, B, and C have been defined which were shown in Figure S-1.
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Type A foams: L<1
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Type B foams: 1
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Type C foams: L> 7
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In type A foams, both entering and spreading coefficients are negative. Type B foams have a negative spreading coefficient and a positive entering coefficient. Type C foams have an unstable
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structure. Both spreading and entering coefficient are positive for these foams and it leads to
Bridging Coefficient
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lamella ruptures [23, 49].
Another theory, which explains the antifoam effect of oil additives on to foam, is the bridging
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coefficient (B) [50-53]. The equation for the bridging coefficient is given as:
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(6)
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A schematic of an oil bridge is illustrated in Figure S-2. Based on this theory, for oil to behave as an antifoaming agent, the bridging coefficient should be positive and a negative value of bridging coefficient results in a stable foam [23, 54, 55] Based on experiments, when B is positive, E is also positive [32, 53]. But a positive entering coefficient does not insure a positive bridging coefficient [32, 53].
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Pseudo-Emulsion Film Theory
Pseudo-emulsion film theory relates foam stability in the presence of oil to the stability of a pseudo-emulsion film. A pseudo-emulsion film is the thin liquid film between the oil droplet and the gas phase. If the pseudo-emulsion film is ruptured, the oil may form a lens at the gas-water
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interface; and this can break down the foam [28, 46, 56-58]. Formation and rupture of a pseudo
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emulsion film is shown in Figure S-3 [24]. Foam Destabilization
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Foam destabilization can occur due to several reasons. Gravity forces can cause liquid drainage from the foam structure and result in liquid accumulation under the structure [59]. Also, Laplace
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pressure, due to the pressure difference, diffuses the gas from smaller bubbles to the larger ones
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[60].
In addition, foam has an unstable structure because of osmotic pressure. This pressure causes the
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liquid to flow from lamella toward the plateau, because the concentration varies inside the foam
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structure. In addition, disjoining pressure breaks the liquid films. These factors can lead to the
structures [61].
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rearrangement of the foam structure and cause the bubbles to assemble and create larger
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Rybczynski and Hadamar developed an equation to calculate the velocity of bubbles that rise inside the foam with the assumption that the bubbles are spherical with a radius r. The simplified relation is as below:
(7) In this equation, u is the rising velocity of the bubbles, ρ is liquid density, ῃ is the viscosity of liquid in the lamellas and g is gravity acceleration [61].
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ACCEPTED MANUSCRIPT According to this equation, the viscosity and radius of the bubbles have an inverse and direct relation with the rising velocity of the bubbles, respectively. Foam Stability Measurement Methods Foam stability can be examined by various methods. Micro visual cell observations, simulations,
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core flooding and bulk foam experiments are some of these methods [5, 44].
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Bulk foam experiments can be static or dynamic. Dynamic foam is defined as a foam in which a dynamic equilibrium exists between the rate of foam generation and foam decay. Core flooding
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is a method for studying the dynamic foam. Static foam is defined as a foam in which the rate of foam generation is zero and the foam is allowed to decay after its generation without
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regeneration. Some of the methods for studying the static foam are mixing method, Ross-mile
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test, vibration test and etc [5, 44].
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Generally, few studies have been done on the de-foaming effect of crude oil on the nanosurfactant foam in oil-water systems. But, the effect of oil on surfactant-foam has been widely
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investigated. Therefore, in the present work, the foam composed of nano particle and surfactant
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is examined and the effect of nano particles on foam structure in the presence of different crude oils with different viscosities is investigated. For this purpose, the static method of “mixing” is
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choosed and the foamability and foam stability is measured by the setup, which is designed for this purpose by the concept of “t2/3”. Then, the IFT of the solutions and oils is measured and E, S, B and L are calculated, then the relation between obtained values and observed behavior of foam is explained. Finally, the foam structure is examined visually for all various kinds of oils and the differences in their structures are explained.
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ACCEPTED MANUSCRIPT 2. Experiments 2.1.
Material
The nano particle used in this paper is nano silica with 20-30 nm diameter and purity above 98% as a solid powder provided from Nanosany Company. Based on the literature, the isoelectric
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point of this nano particle is at about pH=2 [62]. The range of pH in all solutions is between 5
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and 6, so the nano silica has negative charge in all experiments. Anionic surfactant, SDS, with
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the purity above 99% and cationic surfactant, CTAB, with the purity above 98% as a solid powder is provided from Merk Company. Three types of crude oil with the specific gravities of
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20, 28.5 and 49.9 ◦API are obtained from a field in the south of Iran. N2 gas used in this project is
Experimental Procedure
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2.2.
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99% pure and the water used in all experiments is deionized water with the quality of 0.1 µs/cm.
In this paper, the static method “mixing” has been used and a setup has been designed for this
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purpose. Nano particle in two concentrations of 0 and 0.1 wt.%, surfactant in three
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concentrations of 0.115, 0.23 and 0.345 wt.% and three different kinds of crude oil at three weight percent of 15, 25 and 35 wt.% with respect to water are used. These oil concentrations are
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close to oil saturation in general reservoirs. The properties of these three crude oils are shown in
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Table 1. In each experiment, 200 cc of the foam generating solution is poured into the graduated cylinder. Then a certain amount of oil is added to it. The rate of gas injection into the solution is controlled by MFC and is equal to 200 ml/min at the pressure of 14.7 psi for all experiments. Concurrent with the gas injection from one direction, the air in the cylinder is emptied from the other direction. Gas injection lasts for 5 minutes to be sure that the whole space of cylinder is filled by nitrogen. At the end of this stage, all inlets and outlets are closed and the stirrer blends the foam generating solution which contains oil, by the speed of 600 rpm for 2 minutes. After 10
ACCEPTED MANUSCRIPT that, the stirrer is turned off and the foam height is recorded at different time steps to measure the foam stability. Pictures are taken by Dino light AD-4113TL-MA1 Digital camera and an Image J software is used to measure the average bubbles’ size. A schematic of the setup designed for measuring the static properties of the foam is shown in
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pH Measurement
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Figure 1.
The pH measured values are reported in Table 2. All values are between 5 and 6 and since the
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isoelectric point for nano silica is at the pH of 2 and 3, the silica nano particles have negative
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charge in all solutions. Conductivity Test
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The critical micelle concentration of SDS is obtained by this test. In each step, a certain amount
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of SDS is dissolved in deionized water and the conductivity of the solution is measured with a
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conductivity meter (Figure 2). In this figure, the intersection of two lines with different slopes shows the critical micelle concentration for SDS.
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By increasing the SDS concentration before the micelle formation, the electric charge of solution and thus the electrical conductivity will increase. At the moment of micelle formation, a change
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occurs in conductivity which is visible as a deflection in the graph (Figure 2). The critical micelle concentration obtained in this experiment is completely matched with the value reported in the literatures [63, 64].
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ACCEPTED MANUSCRIPT 3. Results and Discussion 3.1.
Study of Static Foam
t2/3 As a Criterion for Foam Stability Analysis Generally, the concept of “half-time” is used to compare the stability of foams. “half-time”
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means the time it takes for the foam to reach half of its primary height. But in this paper, using
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this concept can cause misunderstanding. Because as it is shown in Figure 3, foam stability in the
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second half of its life is much more than in the first half. So, using the term “half-time” is
time it takes for the foam to lose
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completely misleading in this case. Thus, a “t2/3” criteria is used to avoid this issue. “t2/3” is the of its original height. To explain how to calculate the “t2/3”
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criteria, the foam formed from the solution containing 0.1 wt.% nano silica, 0.115 wt.% SDS and
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15 wt.% oil “c” is investigated (Figure 3). As it is shown in this figure, t1/2 occurs 360 seconds
describe the foam stability.
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after foam generation but t2/3 happens after 8640 seconds, so t2/3 is a more suitable term to
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The Effect of Surfactant Type on Foamability in the Presence of Nano Silica
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In the solution containing CTAB and nano silica all particles remain undispersed in the solution
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due to the attractive force between CTAB with positive charge and nano silica with negative charge. For this reason, the foam of CTAB-nano silica system has not been studied. But the solution containing SDS and nano silica is completely dispersed and generates a desirable foam. It is because of the repulsive forces between negatively charged nano silica and SDS which persuade the surfactants to be adsorbed more on the water-air interface and increase the system’s efficiency (Figure S-4).
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ACCEPTED MANUSCRIPT The Effect of SDS Concentration on the Foamability and Foam Stability As it is illustrated in Figure 4 and Figure 5, by increasing the concentration of SDS to the critical micelle concentration, the foamability and stability of the foam will increase significantly. However, with a further increase in the SDS concentration above CMC, these parameters do not
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increase much. Because after the formation of spherical shaped micelles at CMC, increasing the
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SDS concentration above CMC leads to form the aggregates and reorganization of the spherical
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shaped micelles to more complex structures whereas the concentration of the unassociated monomers remains almost constant [24]. Thus, new micelle structures and aggregates remain in
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the bulk volume and do not migrate to the interface. So, increasing the SDS concentration above
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CMC has little impact on the foamability and stability of foam. This trend is observed for all
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concentrations of oil. As an example, the figures related to 35 wt.% of the oils are shown.
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The Effect of Nano Silica Concentration on the Foamability
The foamability in the solution containing nano silica and SDS is slightly more than the
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foamability in the solution containing solely surfactant (Figure S-5). The reason is the presence
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of nano silica with negative charge alongside the anionic SDS, which persuades the SDS to be adsorbed more on the interface and act better and more efficient. This trend is observed for all
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surfactant and oil concentrations. As an example, the figures related to 15 wt.% oil and 1 CMC surfactant are shown.
The Effect of Nano Silica Concentration on the Foam Stability The effect of nano silica concentration on the foam stability in the absence and presence of oil is shown in Figure 6 to Figure 9.
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ACCEPTED MANUSCRIPT As it is shown in Figure 6, in the absence of oil, the foam stability in the presence of nano silica is much more than the foam stability in the absence of nano particles. The amount of t2/3 for foam with nano silica is about 38800 seconds, but this value for foam without nano silica is 26220 seconds. This means that a 40% increase in stability is observed for foam containing nano silica.
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But in the presence of oil, the case will be very complicated. Figure 7 shows the foam stability in
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the presence of oil “a”. The API gravity and viscosity of oil “a” is 49/9 ◦API and 1.17 cp,
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respectively. So in the comparison with the other oils, it is considered as a light oil. When foam is formed, this oil easily penetrates through the foam structure, moves in the lamellas and
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collapses the liquid films. This occurrence (foam collapse) happens in a short time, so the nano
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particles do not find the opportunity to enter the interface and increase the foam stability. Figure 8 is the foam in the presence of oil “b”. The API gravity and viscosity of this oil are equal to
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28/5◦ API and 23.88 cp, respectively. So, this oil is heavier than oil “a”. As it is clear in Figure 8,
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although in the first part of the foam life, the foam containing only surfactant has a better performance, but with the passing of time, nano particles find the required time to enter the foam
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structure and increase the foam stability. So in the second part of foam life, foam containing both
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nano particles and surfactant will have a better performance in comparison with the foam containing solely surfactant. As it is obvious in Figure 9, foam stability in the presence of oil “c”
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is very high. The API gravity and viscosity of oil “c” are equal to 20 ◦API and 627.25 cp, respectively. So oil “c” is a heavier oil in comparison with oil “a” and “b”. This oil has a high viscosity; thus, it has a low tendency to move through the foam structure and collapse the lamellas. So in the presence of this oil, foam preserves its structure and nano particles find the opportunity to enter the foam structure. As a result, foam stability in the presence of both nano particle and surfactant is much more than the stability in the presence of only surfactant.
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ACCEPTED MANUSCRIPT This trend is observed for all surfactant and oil concentrations. As an example, the figures related to 25 wt.% oil and 1 CMC surfactant is shown.
The Effect of Oil Concentration and Oil Viscosity on the Foam Stability Oil has a destructive effect on foam structure and with increasing the oil saturation, this
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destructive effect significantly increases. This effect is observed in all concentration of surfactant
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and nano particle and for all three types of oils (Figure 10, Figure S-6 and Figure S-7). In conjunction with the oil type, foam stability is the highest in the presence of oil “c” and is the
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lowest in the presence of oil “a”. It is because of the difference in the oils’ viscosities. Generally, oil has a destructive effect on the foam structure. But, this effect is less in the oils
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with higher viscosity and density. Because oil with a higher viscosity and density has less
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mobility, its tendency to move in the liquid films and collapsing the foam structure is less. This
3.2.
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observation is completely in agreement with Yekeen et al studies [26, 27]. Spreading, Entering and Bridging Coefficient and Lamella Number Evaluation
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Among the theories mentioned in section 1.1, entering, spreading and bridging coefficient and
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lamella number are the main theories which are measured in this part. Table 3 shows the measured values. Positive entering coefficient means that the oil droplets enter the foam structure
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and positive spreading coefficient means that entered oil droplets can move in the lamellas, spread in the liquid films and collapse the foam structure. According to Table 3, oil “a” has the highest entering and spreading coefficient and oil “c” has the lowest E and S values. So, the defoaming effect of oil “a” is the most and oil “c” is the lowest. This occurrence is completely in agreement with the observations and experiments. In relation with lamella number, all values are between 1 and 7, so all three foams are considered as type B foams; but both entering and spreading coefficients are positive, and it is not in 15
ACCEPTED MANUSCRIPT agreement with the type B foam concept, which tells about a positive entering coefficient and negative spreading coefficient. About the bridging coefficient, the obtained values do not provide a good description of the foam performance observed in this investigation. This situation was reported before [24] .
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Foam Structure
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3.3.
The foam structure can be defined as bubble size, which is an important parameter for
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determining the strength of the generated foam. The smaller the bubbles’ size, the stronger
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the foam[65]. Also according to equation 7, the radius of bubbles has a direct relation with the rising velocity of the bubbles and foam instability. This means that by passing of time, the
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bubbles’ size increase and thus the rising velocity of the bubbles and the foam instability
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increases. The increasing trend of bubbles’ size is shown in Figure 11 and Figure S-8. As it is clear from these figures, the average radius of bubbles has increased from 0.3 mm to 5.5 mm
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after 24 hours.
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(7)
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According to this equation the viscosity of the liquid has an inverse relation with the rising velocity of the bubbles and by increasing the viscosity of the liquid in the foam films, the rising
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velocity of bubbles will decrease and the foam ruptures at a later time (Figure 12). Among these three oils, oil “a” with the lowest viscosity shows the most destructive effect on foam structure in comparison with oil “b” and “c”, and oil “c” with the highest viscosity creates the most stable and regular structure compared to oil “a” and “b”. This is as a result of the reduction in tendency of oil “c” to move inside the lamellas due to its high viscosity. The rising velocity of the bubbles in the presence of oil “a”, “b” and “c” is presented in Table 4. These results confirm the claim mentioned above. 16
ACCEPTED MANUSCRIPT The oil movement inside the lamellas can be seen in Figure 13. This aspect is just shown for oil “b”. Because in the presence of oil “a”, the oil movement could not be recorded due to the high speed of lamella collision and for oil “c” the oil movement in the lamellas was so slow that it
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was not significant enough to be possible to record.
In the system containing nano silica and CTAB, the solution remains undispersed. But the
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4. Conclusion
solution containing nano silica and SDS is completely dispersed and creates a desirable foam
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and in this system, by increasing the SDS concentration to the critical micelle concentration,
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the foamability and foam stability will increase significantly. But with a further increase in the SDS concentration to an amount above CMC, these parameters do not increase much. Nano silica increases the foamability and foam stability of SDS solution in the absence of oil.
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In the presence of oil “a” which is a light oil, the foam collapse happens in a short time. So,
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the nano particles do not find the opportunity to enter the interface and increase the foam
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stability. Oil “b” is heavier than oil “a”. The foam generated in the presence of oil “b” is more stable than the foam generated in the presence of oil “a” and although the nano particles cannot have any effect at first, but they find the time to enter the foam structure and prevent
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But in the presence of oil the case will be much more complicated.
the foam collision with the passage of time. The foam stability in the presence of oil “c” is very high. Oil “c” is a heavier oil in comparison with oil “a” and “b”. This oil has such a high viscosity that its tendency to move in the foam structure and collapse the lamellas is low. For this reason, in the presence of this oil, foam preserves its structure and nano particles find the opportunity to enter the foam structure and enhance the foam stability.
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The presence of crude oil reduces foam stability and by increasing oil saturation, the stability reduction will become greater.
Generally, oil has a destructive effect on the foam structure. This effect is less in the oils with higher viscosity. According to the results, the measured entering and spreading coefficients are completely
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compatible with the results observed from the foam performance in the presence of all three
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oils. But the bridging coefficients and lamella numbers do not provide a good description of
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foam performance in this investigation.
The viscosity of the liquid has an inverse relation and the radius of the bubbles has a direct
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relation with the rising velocity of the bubbles. So the bubbles with bigger radius are most prone to rupture and by increasing the fluid viscosity, the foam collision will happen at a
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later time.
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All told, it is important to mention that crude oil has a complicated structure and it behaves in
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different manners. So the results obtained in this paper are valid for these three special crude oils
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and they may be different for other crude oils.
5. Acknowledgment
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The authors would like to thank the “Institute of Petroleum Engineering in University of Tehran” and “Iran National Science Foundation, INSF” for all the supports to do this investigation.
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Koval, E., A method for predicting the performance of unstable miscible displacement in heterogeneous media. Society of Petroleum Engineers Journal, 1963. 3(02): p. 145-154. DOI: https://doi.org/10.2118/450-PA.
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ACCEPTED MANUSCRIPT Patzek, T.W., Field applications of steam foam for mobility improvement and profile control. SPE Reservoir Engineering, 1996. 11(02): p. 79-86. DOI: https://doi.org/10.2118/29612-PA.
3.
Schramm, L.L., Emulsions, foams, and suspensions: fundamentals and applications. 2006: John Wiley & Sons. DOI: 10.1002/cphc.200500530.
4.
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Wasan, D., et al. Foams: Fundamentals and Application in the Petroleum Industry. in ACS Symp. Ser. 1994. Koehler, S.A., S. Hilgenfeldt, and H.A. Stone, A generalized view of foam drainage: experiment and theory. Langmuir, 2000. 16(15): p. 6327-6341. DOI: 10.1021/la9913147.
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Yekeen, N., et al., Bulk and bubble-scale experimental studies of influence of nanoparticles on foam stability. Chinese Journal of Chemical Engineering, 2017. 25(3): p. 347-357. DOI: https://doi.org/10.1016/j.cjche.2016.08.012.
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AlYousef, Z.A., M.A. Almobarky, and D.S. Schechter, The effect of nanoparticle aggregation on surfactant foam stability. Journal of colloid and interface science, 2018. 511: p. 365-373. DOI: https://doi.org/10.1016/j.jcis.2017.09.051.
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Figure 1: A schematic of the designed setup for static measurement of foam properties
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Conductivity (µs)
CE
700 600 500 400
CMC=0.23 wt.%
300 200 100 0 0
0.1
0.2
0.3
0.4
0.5
Surfactant concentration (wt.%)
Figure 2: CMC determination for SDS by means of conductivity test
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Relative foam height
0.80
t2/3=8640 S 0.60 0.40
0.00 4000
8000
12000
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0
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0.20
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time (s)
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Figure 3: Change of foam height versus time, foam generating from the solution containing 0.1 wt.% nano silica, 0.115 wt.% SDS and 15 wt.% oil “c”
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30 24
18.7 19.5 19.6
18 12 6
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0
36.5
ED
36
41 41.8
17.2
19.3 20
17.5
oil "a"
19.4 19.6
Oil "b" Oil "c"
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Initial Foam Height (cm)
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0.5
1
1.5
no oil
0.5
1
1.5
0.5
1
1.5
0.5
1
1.5
SDS Concentration (CMC)
Figure 4: Foamability in the absence and presence of 35 wt.% oil “a”, “b” & “c”, foam generating from the solution containing 0.1 wt.% nano silica and different concentration of SDS
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23100
20000
24050
18300
15000
t2/3 (s)
oil "a" Oil "b"
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10000
3087 3600
66.5 121 132
1200
1069
0 1
1.5
0.5
1
1.5
0.5
1
1.5
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0.5
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5000
Oil "c"
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0.5
no oil
1
1.5
SDS Concentration (CMC)
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Figure 5: Foam stability in the absence and presence of 35 wt.% oil “a”, “b” & “c”, foam generating from the solution containing 0.1 wt.% nano silica and different concentration of SDS
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0.8
CE
0.6 0.4
0.1 %wt nano, 1 CMC SDS 0 %wt nano, 1 CMC SDS
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Relative foam height
1.0
0.2 0.0
0
4000
8000
12000
16000
Time (s)
Figure 6: The effect of nano silica concentration on foam stability in the absence of oil
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0.8 0.6
0.1 %wt nano, 1 CMC SDS
0.4
0 %wt nano, 1 CMC SDS
0.2
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Relative foam height
1.0
0
100
200
300
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0.0 400
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Time (s)
500
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Figure 7: The effect of nano silica concentration on the foam stability in the presence of 25 wt.% oil “a”
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0.8 0.6
0.1 %wt nano, 1 CMC SDS 0 %wt nano, 1 CMC SDS
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0.4 0.2 0.0
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0
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Relative foam height
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2000
4000
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Time (s)
Figure 8: The effect of nano silica concentration on the foam stability in the presence of 25 wt.% oil “b”
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0.8 0.1 %wt nano, 1 CMC SDS
0.4
0 %wt nano, 1 CMC SDS
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0.2
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Relative foam height
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0
4000
8000
12000
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Time (s)
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Figure 9: The effect of nano silica concentration on the foam stability in the presence of 25 wt.% oil “c”
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4000
CE
t2/3 (s)
8000 6000
8640
ED
10000
2000
15 % wt 3960
25 %wt 2124 1481 1069
1200
35 %wt
173 111.5 66.5
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0
a
b
c
oil type
Figure 10: Foam stability in different saturation of oil “a”, “b” and “c”, foam generating from the solution containing 0.1 wt.% nano silica and 0.115 wt.% SDS
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Figure 11: Change in bubbles’ size by passing time
Figure 12: Foam structure in the presence of oils with different viscosities, 150 second after foam generation
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Figure 13: Oil movement in the lamellas
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ACCEPTED MANUSCRIPT Table 1: Properties of oil “a”, oil “b” and oil “c” Surface tension (mN/m)
Viscosity (cp)
Density (gr/cm3)
A
49.90
1.17
0.78
22.05
B
28.50
23.88
0.88
28.94
C
20
627.25
0.93
30.93
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Table 2: The measured values of pH
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API
◦
Crude oil
Nano silica concentration (wt.%)
SDS concentration (wt.%)
pH
1
0.1
0.115
5.34
2
0.1
3
0.1
4
0
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Experiment No.
5.21 5.15
0.23
5.21
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0.23
0.345
Entering Coefficient (mN/m)
Spreading Coefficient (mN/m)
Lamella Number
Bridging Coefficient (mN/m)2
a
14.07
6.87
1.35
584.48
4.57
2.69
5.18
-128.78
2.95
0.24
3.59
102.99
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Crude Oil
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Table 3: The spreading, entering and bridging coefficient and lamella number at the equilibrium state for the foam containing 0.1 wt.% nano silica and 0.23 wt.% SDS and oil
b
CE
c
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Table 4: The rising velocity of the bubbles in the presence of oil “a”, “b” & “c” 150 second after foam generation Crude Oil
a
b
c
Average bubbles’ diameter (mm)
5.2
4.7
3.7
The rising velocity of the bubbles (cm/s)
9.08
0.44
0.01
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ACCEPTED MANUSCRIPT Highlights
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Foam generated by nano silica and two kinds of surfactants, SDS and CTAB was studied. The effect of different kinds of crude oils on foam structure was studied. Nano silica increased the foamability and foam stability of SDS solution. The presence of crude oil reduced the foam stability. Among oils with different viscosities, high viscous oil is beneficial to give better foam properties.
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Sepideh Babamahmoudi, Siavash Riahi PII: DOI: Reference:
S0167-7322(17)36049-X doi:10.1016/j.molliq.2018.04.093 MOLLIQ 8996
To appear in:
Journal of Molecular Liquids
Received date: Revised date: Accepted date:
20 December 2017 16 April 2018 18 April 2018
Please cite this article as: Sepideh Babamahmoudi, Siavash Riahi , Application of nano particle for enhancement of foam stability in the presence of crude oil: Experimental investigation. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Molliq(2017), doi:10.1016/j.molliq.2018.04.093
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ACCEPTED MANUSCRIPT
Application of Nano Particle for Enhancement of Foam
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Investigation
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Stability in the presence of Crude Oil: Experimental
Sepideh Babamahmoudi+, Siavash Riahi+
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+ Institute of Petroleum Engineering, School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran
Corresponding author: Siavash Riahi P.O Box: 113654563 Email address: [email protected] Phone number: +982161114714
1
ACCEPTED MANUSCRIPT
Abstract The use of gas is one of the most common methods in the oil industry for enhancing oil recovery.
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However, problems such as gas uptake due to the low density of the gas reduce the efficiency of
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this method. The formation of foam reduces the relative permeability of the gas and improves
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this technique. The foam generated by the combination of water and gas does not show enough stability, and thus surfactant injection method has been used for many years. However, foam
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stabilized by the surfactant is problematic in the presence of oil. The advent of nano technology
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has shown that the foam stabilized by nanoparticles can tolerate the presence of oil. In this project, the foam generated by nanoparticle and the surfactant is studied. Then, the effect
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of different kinds of crude oils, with different viscosities on foam structure, has been
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investigated. For studying the foamability and foam stability, the static method of “mixing” is used with the experimental setup designed for this job. Then, by measuring the interfacial tension
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(IFT) and surface tension (ST) between solutions, oil and the air, the entering coefficient (E),
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spreading coefficient (S), lamella number (L) and bridging coefficient (B) are calculated, and the relations between obtained values and the observed behaviors has been investigated.
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The results show that the solution containing Cetyltrimethyl ammonium bromide (CTAB) and nano silica is undispersed, so the foam studies are not carried out for this system. But the solution containing Sodium dodecyl sulfate (SDS) and nano silica is completely dispersed and generates a desirable foam. In addition, nano silica increases the foamability and foam stability of the SDS solution. Regarding the effects of crude oil, the presence of crude oil reduces foam stability and by increasing oil saturation, the stability reduction is observed to be greater. It is also observed that by increasing oil viscosity, foam stability and foam properties improve. 2
ACCEPTED MANUSCRIPT Keywords: Foam; Nano Particle; Surfactant; Crude Oil; Enhanced Oil Recovery (EOR)
1. Introduction Gas injection into reservoirs is one of the most widely used methods in enhanced oil recovery. If
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the gas is miscible with oil, it can replace that in the swept volume. However, the undesirable
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mobility rate of the gas, due to the reservoir heterogeneity and its low viscosity, leads to the gas
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fingering and reduction in the sweep efficiency [1]. Using foam, the disadvantages of gas injection including low sweep efficiency will decrease [2]. However, immediately after foam
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generation, the liquid will start to drain out of the liquid films, which are called lamella. This can
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cause foam rupture [3].
Surfactants are surface-active components which can be used to prevent foam collapse [4]. When
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surfactant is injected, the required energy to form the gas-liquid interface has been decreased and
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thus a more stable foam is formed [5]. By increasing the surfactant concentration near the “critical micelle concentration (CMC)”, the surface tension is reduced and thus the required
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energy for foam generation is decreased [6]. Along with the positive effects of surfactants,
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several factors limit the use of them. The factors such as surfactant adsorption on the reservoir rock and surfactant break down under the harsh condition of the reservoir, like high pressure and
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high temperature [7-9].
In recent years, new applications of nanoparticles as foam stabilizers became clear [10]. Studies showed that the nano particles, unlike surfactants, can be used without adsorption or chemical break down [11-13]. Since the adhesion force at the surface between two fluids in the presence of nano particles is more than that in the presence of surfactants, these foams have longer stability [14]. So far, nano silica has been used mostly in the EOR process in order to improve the foam properties [15, 16]. 3
ACCEPTED MANUSCRIPT Ma et al. studied the assembly of nano particle and surfactant at air-water interface. They first investigated the effects of nano silica on the surface tension. During the experiment, it was found that the nano silica does not show a great impact on the effective surface tension. They understood that because the nano silica is hydrophilic, it has no tendency to get in the water-air
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interface [17]. Another important part of their work was studying the amount of adsorption in the
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water-air interface when the system has both nano particle and surfactant. For this purpose,
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anionic surfactant SDS was selected and the results were compared with Ravera et al. results that had used the cationic surfactant CTAB [18]. It was found that, in the nano silica and CTAB
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system, because of the attractive force between nano silica with negative charge and CTAB with
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positive charge, the surfactants stuck to the surface of the nano silica and dramatically reduced the system’s efficiency. But in the nano silica and SDS system, the repulsive force between
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negatively charged nano silica and SDS resulted in more surfactant adsorption on the water-air
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interface and caused increase of the system’s efficiency [17]. Kumar et al. also investigated the interaction between nano silica with negative charge and
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different surfactants in aqueous solutions. Actually, the strong attraction force between nano
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silica with negative charge and Dodecyltrimethylammonium bromide (DTAB) with positive charge led to the accumulation of nano particles in the system. In the case of non-ionic surfactant
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C12E10, the non-electrostatic interaction between nano particles and surfactant micelles also led to the adsorption of surfactants on the nano particles. But no significant interaction was observed between nano silica and SDS with the same negative charge [19]. Foam Stability in The Presence of Oil Crude oils have complex compositions and properties. Presence of oil may influence the stability of foam which is applied for EOR process [20-22]. 4
ACCEPTED MANUSCRIPT Oil can be solubilized in the micelles, or it can remain as emulsions or as a continuous phase in the foam liquid films. The properties of the oil are important factors for judging whether the oil will influence the foam structure, or not [23]. Vikingstad investigated the interaction between crude oil and foam solution containing 0.5wt.%
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Alpha Olefin Sulfonate (AOS) using the static method of studying foam. She used six different
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crude oil samples with various properties and different viscosities. According to her experiment,
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the effect of crude oils with different physical and chemical properties on foam structure was so complex, and there was no obvious trend to explain the interaction between crude oil and foam
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[24].
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Farzaneh et al. studied the foam performance in the presence of light and heavy oil. Also, they examined the effects of different concentrations of various types of surfactants. Based on their
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experiments, in the presence of crude oil the anionic surfactant generates better foam in
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comparison with the nonionic surfactant. They also observed that by increasing the surfactant concentration, the foams half-time increases. But, this trend is not permanent and there is an
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optimum concentration for each surfactant. Regarding to the crude oil, the presence of crude oil
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reduced the foam stability, but by increasing the oil viscosity, this negative effect decreased [25]. Yekeen et al. examined the influence of two kinds of nano particles, Al2O3 and SiO2, on SDS
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foam stability in a glass micro model. The experiment has been conducted in the presence of different oils. According to their results, the presence of nano particle is effective in improving the stability of foam, and SiO2 is more effective than Al2O3 [26]. In addition, by increasing the oil viscosity, foam stability will also increase [27]. Generally, the interaction between foam and oil is not clearly understood and many different types of experiments are required to clarify the interaction [28]. There are some main theories, which explain foam stability in the presence of oil: 5
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Spreading and Entering Coefficients
Based on this theory, the stability of foam in the presence of oil is related to the spreading coefficients (S) and entering coefficients (E) [20, 22, 24, 29-39] (equations 1 and 2). S = σw/g − σw/o − σo/g
(1)
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E = σw/g + σw/o − σo/g w/o
is the interfacial tension between water
and oil, and σo/g is the surface tension between oil and gas.
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σw/g is the surface tension between water and gas, σ
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(2)
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According to this theory, if the entering coefficient is positive, the oil will be attracted into the lamella between two adjoining bubbles, and if the spreading coefficient is positive, the oil will
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spread at the surface and break the foam films [40]. S and E are interdepending as below
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(equation 3).
(3)
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E=S+2σw/o
It shows that the entering coefficient is always greater than or equal to the spreading coefficient.
Lamella Number
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So, a negative entering coefficient implies a negative spreading coefficient [41-47].
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The procedure of oil emulsification with foam lamella can be described using the balance of forces and in terms of a dimensionless number called the lamella number [23, 39, 44, 45, 48, 49]. Lamella number (L) can be defined as follows: (4) Where, rp is the radius of curvature of the plateau border and ro is the oil drop radius. It was found in the literatures that ro/rp ratio is constant for all the foams yielding about 0.15 [23, 48]. So, it will be obtained: 6
ACCEPTED MANUSCRIPT (5) Based on this theory, oils can give unstable foam, moderately stable foam or they can show little interaction with the foam. From experiments, three types of foams, A, B, and C have been defined which were shown in Figure S-1.
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Type A foams: L<1
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Type B foams: 1
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Type C foams: L> 7
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In type A foams, both entering and spreading coefficients are negative. Type B foams have a negative spreading coefficient and a positive entering coefficient. Type C foams have an unstable
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structure. Both spreading and entering coefficient are positive for these foams and it leads to
Bridging Coefficient
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lamella ruptures [23, 49].
Another theory, which explains the antifoam effect of oil additives on to foam, is the bridging
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coefficient (B) [50-53]. The equation for the bridging coefficient is given as:
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(6)
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A schematic of an oil bridge is illustrated in Figure S-2. Based on this theory, for oil to behave as an antifoaming agent, the bridging coefficient should be positive and a negative value of bridging coefficient results in a stable foam [23, 54, 55] Based on experiments, when B is positive, E is also positive [32, 53]. But a positive entering coefficient does not insure a positive bridging coefficient [32, 53].
7
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Pseudo-Emulsion Film Theory
Pseudo-emulsion film theory relates foam stability in the presence of oil to the stability of a pseudo-emulsion film. A pseudo-emulsion film is the thin liquid film between the oil droplet and the gas phase. If the pseudo-emulsion film is ruptured, the oil may form a lens at the gas-water
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interface; and this can break down the foam [28, 46, 56-58]. Formation and rupture of a pseudo
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emulsion film is shown in Figure S-3 [24]. Foam Destabilization
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Foam destabilization can occur due to several reasons. Gravity forces can cause liquid drainage from the foam structure and result in liquid accumulation under the structure [59]. Also, Laplace
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pressure, due to the pressure difference, diffuses the gas from smaller bubbles to the larger ones
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[60].
In addition, foam has an unstable structure because of osmotic pressure. This pressure causes the
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liquid to flow from lamella toward the plateau, because the concentration varies inside the foam
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structure. In addition, disjoining pressure breaks the liquid films. These factors can lead to the
structures [61].
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rearrangement of the foam structure and cause the bubbles to assemble and create larger
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Rybczynski and Hadamar developed an equation to calculate the velocity of bubbles that rise inside the foam with the assumption that the bubbles are spherical with a radius r. The simplified relation is as below:
(7) In this equation, u is the rising velocity of the bubbles, ρ is liquid density, ῃ is the viscosity of liquid in the lamellas and g is gravity acceleration [61].
8
ACCEPTED MANUSCRIPT According to this equation, the viscosity and radius of the bubbles have an inverse and direct relation with the rising velocity of the bubbles, respectively. Foam Stability Measurement Methods Foam stability can be examined by various methods. Micro visual cell observations, simulations,
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core flooding and bulk foam experiments are some of these methods [5, 44].
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Bulk foam experiments can be static or dynamic. Dynamic foam is defined as a foam in which a dynamic equilibrium exists between the rate of foam generation and foam decay. Core flooding
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is a method for studying the dynamic foam. Static foam is defined as a foam in which the rate of foam generation is zero and the foam is allowed to decay after its generation without
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regeneration. Some of the methods for studying the static foam are mixing method, Ross-mile
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test, vibration test and etc [5, 44].
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Generally, few studies have been done on the de-foaming effect of crude oil on the nanosurfactant foam in oil-water systems. But, the effect of oil on surfactant-foam has been widely
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investigated. Therefore, in the present work, the foam composed of nano particle and surfactant
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is examined and the effect of nano particles on foam structure in the presence of different crude oils with different viscosities is investigated. For this purpose, the static method of “mixing” is
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choosed and the foamability and foam stability is measured by the setup, which is designed for this purpose by the concept of “t2/3”. Then, the IFT of the solutions and oils is measured and E, S, B and L are calculated, then the relation between obtained values and observed behavior of foam is explained. Finally, the foam structure is examined visually for all various kinds of oils and the differences in their structures are explained.
9
ACCEPTED MANUSCRIPT 2. Experiments 2.1.
Material
The nano particle used in this paper is nano silica with 20-30 nm diameter and purity above 98% as a solid powder provided from Nanosany Company. Based on the literature, the isoelectric
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point of this nano particle is at about pH=2 [62]. The range of pH in all solutions is between 5
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and 6, so the nano silica has negative charge in all experiments. Anionic surfactant, SDS, with
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the purity above 99% and cationic surfactant, CTAB, with the purity above 98% as a solid powder is provided from Merk Company. Three types of crude oil with the specific gravities of
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20, 28.5 and 49.9 ◦API are obtained from a field in the south of Iran. N2 gas used in this project is
Experimental Procedure
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2.2.
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99% pure and the water used in all experiments is deionized water with the quality of 0.1 µs/cm.
In this paper, the static method “mixing” has been used and a setup has been designed for this
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purpose. Nano particle in two concentrations of 0 and 0.1 wt.%, surfactant in three
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concentrations of 0.115, 0.23 and 0.345 wt.% and three different kinds of crude oil at three weight percent of 15, 25 and 35 wt.% with respect to water are used. These oil concentrations are
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close to oil saturation in general reservoirs. The properties of these three crude oils are shown in
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Table 1. In each experiment, 200 cc of the foam generating solution is poured into the graduated cylinder. Then a certain amount of oil is added to it. The rate of gas injection into the solution is controlled by MFC and is equal to 200 ml/min at the pressure of 14.7 psi for all experiments. Concurrent with the gas injection from one direction, the air in the cylinder is emptied from the other direction. Gas injection lasts for 5 minutes to be sure that the whole space of cylinder is filled by nitrogen. At the end of this stage, all inlets and outlets are closed and the stirrer blends the foam generating solution which contains oil, by the speed of 600 rpm for 2 minutes. After 10
ACCEPTED MANUSCRIPT that, the stirrer is turned off and the foam height is recorded at different time steps to measure the foam stability. Pictures are taken by Dino light AD-4113TL-MA1 Digital camera and an Image J software is used to measure the average bubbles’ size. A schematic of the setup designed for measuring the static properties of the foam is shown in
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pH Measurement
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2.3.
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Figure 1.
The pH measured values are reported in Table 2. All values are between 5 and 6 and since the
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isoelectric point for nano silica is at the pH of 2 and 3, the silica nano particles have negative
2.4.
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charge in all solutions. Conductivity Test
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The critical micelle concentration of SDS is obtained by this test. In each step, a certain amount
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of SDS is dissolved in deionized water and the conductivity of the solution is measured with a
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conductivity meter (Figure 2). In this figure, the intersection of two lines with different slopes shows the critical micelle concentration for SDS.
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By increasing the SDS concentration before the micelle formation, the electric charge of solution and thus the electrical conductivity will increase. At the moment of micelle formation, a change
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occurs in conductivity which is visible as a deflection in the graph (Figure 2). The critical micelle concentration obtained in this experiment is completely matched with the value reported in the literatures [63, 64].
11
ACCEPTED MANUSCRIPT 3. Results and Discussion 3.1.
Study of Static Foam
t2/3 As a Criterion for Foam Stability Analysis Generally, the concept of “half-time” is used to compare the stability of foams. “half-time”
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means the time it takes for the foam to reach half of its primary height. But in this paper, using
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this concept can cause misunderstanding. Because as it is shown in Figure 3, foam stability in the
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second half of its life is much more than in the first half. So, using the term “half-time” is
time it takes for the foam to lose
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completely misleading in this case. Thus, a “t2/3” criteria is used to avoid this issue. “t2/3” is the of its original height. To explain how to calculate the “t2/3”
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criteria, the foam formed from the solution containing 0.1 wt.% nano silica, 0.115 wt.% SDS and
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15 wt.% oil “c” is investigated (Figure 3). As it is shown in this figure, t1/2 occurs 360 seconds
describe the foam stability.
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after foam generation but t2/3 happens after 8640 seconds, so t2/3 is a more suitable term to
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The Effect of Surfactant Type on Foamability in the Presence of Nano Silica
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In the solution containing CTAB and nano silica all particles remain undispersed in the solution
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due to the attractive force between CTAB with positive charge and nano silica with negative charge. For this reason, the foam of CTAB-nano silica system has not been studied. But the solution containing SDS and nano silica is completely dispersed and generates a desirable foam. It is because of the repulsive forces between negatively charged nano silica and SDS which persuade the surfactants to be adsorbed more on the water-air interface and increase the system’s efficiency (Figure S-4).
12
ACCEPTED MANUSCRIPT The Effect of SDS Concentration on the Foamability and Foam Stability As it is illustrated in Figure 4 and Figure 5, by increasing the concentration of SDS to the critical micelle concentration, the foamability and stability of the foam will increase significantly. However, with a further increase in the SDS concentration above CMC, these parameters do not
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increase much. Because after the formation of spherical shaped micelles at CMC, increasing the
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SDS concentration above CMC leads to form the aggregates and reorganization of the spherical
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shaped micelles to more complex structures whereas the concentration of the unassociated monomers remains almost constant [24]. Thus, new micelle structures and aggregates remain in
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the bulk volume and do not migrate to the interface. So, increasing the SDS concentration above
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CMC has little impact on the foamability and stability of foam. This trend is observed for all
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concentrations of oil. As an example, the figures related to 35 wt.% of the oils are shown.
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The Effect of Nano Silica Concentration on the Foamability
The foamability in the solution containing nano silica and SDS is slightly more than the
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foamability in the solution containing solely surfactant (Figure S-5). The reason is the presence
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of nano silica with negative charge alongside the anionic SDS, which persuades the SDS to be adsorbed more on the interface and act better and more efficient. This trend is observed for all
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surfactant and oil concentrations. As an example, the figures related to 15 wt.% oil and 1 CMC surfactant are shown.
The Effect of Nano Silica Concentration on the Foam Stability The effect of nano silica concentration on the foam stability in the absence and presence of oil is shown in Figure 6 to Figure 9.
13
ACCEPTED MANUSCRIPT As it is shown in Figure 6, in the absence of oil, the foam stability in the presence of nano silica is much more than the foam stability in the absence of nano particles. The amount of t2/3 for foam with nano silica is about 38800 seconds, but this value for foam without nano silica is 26220 seconds. This means that a 40% increase in stability is observed for foam containing nano silica.
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But in the presence of oil, the case will be very complicated. Figure 7 shows the foam stability in
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the presence of oil “a”. The API gravity and viscosity of oil “a” is 49/9 ◦API and 1.17 cp,
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respectively. So in the comparison with the other oils, it is considered as a light oil. When foam is formed, this oil easily penetrates through the foam structure, moves in the lamellas and
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collapses the liquid films. This occurrence (foam collapse) happens in a short time, so the nano
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particles do not find the opportunity to enter the interface and increase the foam stability. Figure 8 is the foam in the presence of oil “b”. The API gravity and viscosity of this oil are equal to
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28/5◦ API and 23.88 cp, respectively. So, this oil is heavier than oil “a”. As it is clear in Figure 8,
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although in the first part of the foam life, the foam containing only surfactant has a better performance, but with the passing of time, nano particles find the required time to enter the foam
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structure and increase the foam stability. So in the second part of foam life, foam containing both
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nano particles and surfactant will have a better performance in comparison with the foam containing solely surfactant. As it is obvious in Figure 9, foam stability in the presence of oil “c”
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is very high. The API gravity and viscosity of oil “c” are equal to 20 ◦API and 627.25 cp, respectively. So oil “c” is a heavier oil in comparison with oil “a” and “b”. This oil has a high viscosity; thus, it has a low tendency to move through the foam structure and collapse the lamellas. So in the presence of this oil, foam preserves its structure and nano particles find the opportunity to enter the foam structure. As a result, foam stability in the presence of both nano particle and surfactant is much more than the stability in the presence of only surfactant.
14
ACCEPTED MANUSCRIPT This trend is observed for all surfactant and oil concentrations. As an example, the figures related to 25 wt.% oil and 1 CMC surfactant is shown.
The Effect of Oil Concentration and Oil Viscosity on the Foam Stability Oil has a destructive effect on foam structure and with increasing the oil saturation, this
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destructive effect significantly increases. This effect is observed in all concentration of surfactant
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and nano particle and for all three types of oils (Figure 10, Figure S-6 and Figure S-7). In conjunction with the oil type, foam stability is the highest in the presence of oil “c” and is the
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lowest in the presence of oil “a”. It is because of the difference in the oils’ viscosities. Generally, oil has a destructive effect on the foam structure. But, this effect is less in the oils
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with higher viscosity and density. Because oil with a higher viscosity and density has less
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mobility, its tendency to move in the liquid films and collapsing the foam structure is less. This
3.2.
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observation is completely in agreement with Yekeen et al studies [26, 27]. Spreading, Entering and Bridging Coefficient and Lamella Number Evaluation
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Among the theories mentioned in section 1.1, entering, spreading and bridging coefficient and
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lamella number are the main theories which are measured in this part. Table 3 shows the measured values. Positive entering coefficient means that the oil droplets enter the foam structure
AC
and positive spreading coefficient means that entered oil droplets can move in the lamellas, spread in the liquid films and collapse the foam structure. According to Table 3, oil “a” has the highest entering and spreading coefficient and oil “c” has the lowest E and S values. So, the defoaming effect of oil “a” is the most and oil “c” is the lowest. This occurrence is completely in agreement with the observations and experiments. In relation with lamella number, all values are between 1 and 7, so all three foams are considered as type B foams; but both entering and spreading coefficients are positive, and it is not in 15
ACCEPTED MANUSCRIPT agreement with the type B foam concept, which tells about a positive entering coefficient and negative spreading coefficient. About the bridging coefficient, the obtained values do not provide a good description of the foam performance observed in this investigation. This situation was reported before [24] .
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Foam Structure
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3.3.
The foam structure can be defined as bubble size, which is an important parameter for
CR
determining the strength of the generated foam. The smaller the bubbles’ size, the stronger
US
the foam[65]. Also according to equation 7, the radius of bubbles has a direct relation with the rising velocity of the bubbles and foam instability. This means that by passing of time, the
AN
bubbles’ size increase and thus the rising velocity of the bubbles and the foam instability
M
increases. The increasing trend of bubbles’ size is shown in Figure 11 and Figure S-8. As it is clear from these figures, the average radius of bubbles has increased from 0.3 mm to 5.5 mm
ED
after 24 hours.
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(7)
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According to this equation the viscosity of the liquid has an inverse relation with the rising velocity of the bubbles and by increasing the viscosity of the liquid in the foam films, the rising
AC
velocity of bubbles will decrease and the foam ruptures at a later time (Figure 12). Among these three oils, oil “a” with the lowest viscosity shows the most destructive effect on foam structure in comparison with oil “b” and “c”, and oil “c” with the highest viscosity creates the most stable and regular structure compared to oil “a” and “b”. This is as a result of the reduction in tendency of oil “c” to move inside the lamellas due to its high viscosity. The rising velocity of the bubbles in the presence of oil “a”, “b” and “c” is presented in Table 4. These results confirm the claim mentioned above. 16
ACCEPTED MANUSCRIPT The oil movement inside the lamellas can be seen in Figure 13. This aspect is just shown for oil “b”. Because in the presence of oil “a”, the oil movement could not be recorded due to the high speed of lamella collision and for oil “c” the oil movement in the lamellas was so slow that it
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was not significant enough to be possible to record.
In the system containing nano silica and CTAB, the solution remains undispersed. But the
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4. Conclusion
solution containing nano silica and SDS is completely dispersed and creates a desirable foam
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and in this system, by increasing the SDS concentration to the critical micelle concentration,
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the foamability and foam stability will increase significantly. But with a further increase in the SDS concentration to an amount above CMC, these parameters do not increase much. Nano silica increases the foamability and foam stability of SDS solution in the absence of oil.
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In the presence of oil “a” which is a light oil, the foam collapse happens in a short time. So,
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the nano particles do not find the opportunity to enter the interface and increase the foam
CE
stability. Oil “b” is heavier than oil “a”. The foam generated in the presence of oil “b” is more stable than the foam generated in the presence of oil “a” and although the nano particles cannot have any effect at first, but they find the time to enter the foam structure and prevent
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But in the presence of oil the case will be much more complicated.
the foam collision with the passage of time. The foam stability in the presence of oil “c” is very high. Oil “c” is a heavier oil in comparison with oil “a” and “b”. This oil has such a high viscosity that its tendency to move in the foam structure and collapse the lamellas is low. For this reason, in the presence of this oil, foam preserves its structure and nano particles find the opportunity to enter the foam structure and enhance the foam stability.
17
ACCEPTED MANUSCRIPT
The presence of crude oil reduces foam stability and by increasing oil saturation, the stability reduction will become greater.
Generally, oil has a destructive effect on the foam structure. This effect is less in the oils with higher viscosity. According to the results, the measured entering and spreading coefficients are completely
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compatible with the results observed from the foam performance in the presence of all three
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oils. But the bridging coefficients and lamella numbers do not provide a good description of
US
foam performance in this investigation.
The viscosity of the liquid has an inverse relation and the radius of the bubbles has a direct
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relation with the rising velocity of the bubbles. So the bubbles with bigger radius are most prone to rupture and by increasing the fluid viscosity, the foam collision will happen at a
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later time.
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All told, it is important to mention that crude oil has a complicated structure and it behaves in
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different manners. So the results obtained in this paper are valid for these three special crude oils
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and they may be different for other crude oils.
5. Acknowledgment
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The authors would like to thank the “Institute of Petroleum Engineering in University of Tehran” and “Iran National Science Foundation, INSF” for all the supports to do this investigation.
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Kruglyakov, P. and N. Vilkova, The relation between stability of asymmetric films of the liquid/liquid/gas type, spreading coefficient and surface pressure. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999. 156(1): p. 475-487. DOI: https://doi.org/10.1016/S0927-7757(99)00105-3.
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Bergeron, V., M. Fagan, and C. Radke, Generalized entering coefficients: a criterion for foam stability against oil in porous media. Langmuir, 1993. 9(7): p. 1704-1713. DOI: 10.1021/la00031a017.
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Mannhardt, K. and I. Svorstøl. Foam propagation in Snorre reservoir core-effects of oil saturation and ageing. in IOR 1997-9th European Symposium on Improved Oil Recovery. 1997. DOI: 10.3997/2214-4609.201406794.
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Aarra, M., P. Ormehaug, and A. Skauge. Foams for GOR control-improved stability by polymer additives. in IOR 1997-9th European Symposium on Improved Oil Recovery. 1997. DOI: 10.3997/2214-4609.201406787.
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Mannhardt, K., J. Novosad, and L. Schramm, Comparative evaluation of foam stability to oil. SPE Reservoir Evaluation & Engineering, 2000. 3(01): p. 23-34. DOI: https://doi.org/10.2118/60686-PA.
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Farajzadeh, R., A. Andrianov, and P. Zitha, Investigation of immiscible and miscible foam for enhancing oil recovery. Industrial & Engineering chemistry research, 2009. 49(4): p. 1910-1919. DOI: 10.1021/ie901109d.
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Duan, X., et al., Evaluation of oil-tolerant foam for enhanced oil recovery: Laboratory study of a system of oil-tolerant foaming agents. Journal of Petroleum Science and Engineering, 2014. 122: p. 428-438. DOI: https://doi.org/10.1016/j.petrol.2014.07.042.
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Osei-Bonsu, K., N. Shokri, and P. Grassia, Foam stability in the presence and absence of hydrocarbons: From bubble-to bulk-scale. Colloids and Surfaces A: Physicochemical and
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p.
514-526.
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Lau, H. and S. O'Brien, Effects of spreading and nonspreading oils on foam propagation through porous media. SPE reservoir engineering, 1988. 3(03): p. 893-896. DOI: https://doi.org/10.2118/15668-PA.
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Dalland, M., J.E. Hanssen, and T.S. Kristiansen, Oil interaction with foams under static and flowing conditions in porous media. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1994. 82(2): p. 129-140. DOI: https://doi.org/10.1016/09277757(93)02628-R.
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Basheva, E.S., et al., Role of betaine as foam booster in the presence of silicone oil drops. Langmuir, 2000. 16(3): p. 1000-1013. DOI: 10.1021/la990777.
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Singh, R. and K.K. Mohanty, Synergy between nanoparticles and surfactants in stabilizing foams for oil recovery. Energy & Fuels, 2015. 29(2): p. 467-479. DOI: 10.1021/ef5015007.
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Raterman, K. An investigation of oil destabilization of nitrogen foams in porous media. in SPE Annual Technical Conference and Exhibition. 1989. Society of Petroleum Engineers. DOI: https://doi.org/10.2118/19692-MS.
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Wasan, D., K. Koczo, and A. Nikolov, Mechanisms of aqueous foam stability and antifoaming action with and without oil: a thin-film approach. Advances in Chemistry Series, 1994. 242: p. 47-47. DOI: 10.1021/ba-1994-0242.ch002.
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Wasan, D., et al. Foams: Fundamentals and Application in the Petroleum Industry. in ACS Symp. Ser. 1994. Koehler, S.A., S. Hilgenfeldt, and H.A. Stone, A generalized view of foam drainage: experiment and theory. Langmuir, 2000. 16(15): p. 6327-6341. DOI: 10.1021/la9913147.
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62.
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Domínguez, A., et al., Determination of critical micelle concentration of some surfactants by three techniques. J. Chem. Educ, 1997. 74(10): p. 1227. DOI: 10.1021/ed074p1227.
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AlYousef, Z.A., M.A. Almobarky, and D.S. Schechter, The effect of nanoparticle aggregation on surfactant foam stability. Journal of colloid and interface science, 2018. 511: p. 365-373. DOI: https://doi.org/10.1016/j.jcis.2017.09.051.
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Figure 1: A schematic of the designed setup for static measurement of foam properties
AC
Conductivity (µs)
CE
700 600 500 400
CMC=0.23 wt.%
300 200 100 0 0
0.1
0.2
0.3
0.4
0.5
Surfactant concentration (wt.%)
Figure 2: CMC determination for SDS by means of conductivity test
24
ACCEPTED MANUSCRIPT 1.00 t1/2=360 S
Relative foam height
0.80
t2/3=8640 S 0.60 0.40
0.00 4000
8000
12000
CR
0
IP
T
0.20
US
time (s)
M
AN
Figure 3: Change of foam height versus time, foam generating from the solution containing 0.1 wt.% nano silica, 0.115 wt.% SDS and 15 wt.% oil “c”
PT
30 24
18.7 19.5 19.6
18 12 6
AC
0
36.5
ED
36
41 41.8
17.2
19.3 20
17.5
oil "a"
19.4 19.6
Oil "b" Oil "c"
CE
Initial Foam Height (cm)
42
0.5
1
1.5
no oil
0.5
1
1.5
0.5
1
1.5
0.5
1
1.5
SDS Concentration (CMC)
Figure 4: Foamability in the absence and presence of 35 wt.% oil “a”, “b” & “c”, foam generating from the solution containing 0.1 wt.% nano silica and different concentration of SDS
25
ACCEPTED MANUSCRIPT 25000
23100
20000
24050
18300
15000
t2/3 (s)
oil "a" Oil "b"
T
9282
10000
3087 3600
66.5 121 132
1200
1069
0 1
1.5
0.5
1
1.5
0.5
1
1.5
US
0.5
CR
5000
Oil "c"
IP
7440
0.5
no oil
1
1.5
SDS Concentration (CMC)
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Figure 5: Foam stability in the absence and presence of 35 wt.% oil “a”, “b” & “c”, foam generating from the solution containing 0.1 wt.% nano silica and different concentration of SDS
PT
0.8
CE
0.6 0.4
0.1 %wt nano, 1 CMC SDS 0 %wt nano, 1 CMC SDS
AC
Relative foam height
1.0
0.2 0.0
0
4000
8000
12000
16000
Time (s)
Figure 6: The effect of nano silica concentration on foam stability in the absence of oil
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ACCEPTED MANUSCRIPT
0.8 0.6
0.1 %wt nano, 1 CMC SDS
0.4
0 %wt nano, 1 CMC SDS
0.2
T
Relative foam height
1.0
0
100
200
300
IP
0.0 400
CR
Time (s)
500
AN
US
Figure 7: The effect of nano silica concentration on the foam stability in the presence of 25 wt.% oil “a”
M ED
0.8 0.6
0.1 %wt nano, 1 CMC SDS 0 %wt nano, 1 CMC SDS
PT
0.4 0.2 0.0
AC
0
CE
Relative foam height
1.0
2000
4000
6000
8000
Time (s)
Figure 8: The effect of nano silica concentration on the foam stability in the presence of 25 wt.% oil “b”
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ACCEPTED MANUSCRIPT
0.8 0.1 %wt nano, 1 CMC SDS
0.4
0 %wt nano, 1 CMC SDS
T
0.6
0.2
IP
Relative foam height
1.0
0
4000
8000
12000
16000
US
Time (s)
CR
0.0
M
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Figure 9: The effect of nano silica concentration on the foam stability in the presence of 25 wt.% oil “c”
PT
4000
CE
t2/3 (s)
8000 6000
8640
ED
10000
2000
15 % wt 3960
25 %wt 2124 1481 1069
1200
35 %wt
173 111.5 66.5
AC
0
a
b
c
oil type
Figure 10: Foam stability in different saturation of oil “a”, “b” and “c”, foam generating from the solution containing 0.1 wt.% nano silica and 0.115 wt.% SDS
28
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ACCEPTED MANUSCRIPT
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Figure 11: Change in bubbles’ size by passing time
Figure 12: Foam structure in the presence of oils with different viscosities, 150 second after foam generation
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Figure 13: Oil movement in the lamellas
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ACCEPTED MANUSCRIPT Table 1: Properties of oil “a”, oil “b” and oil “c” Surface tension (mN/m)
Viscosity (cp)
Density (gr/cm3)
A
49.90
1.17
0.78
22.05
B
28.50
23.88
0.88
28.94
C
20
627.25
0.93
30.93
IP
Table 2: The measured values of pH
T
API
◦
Crude oil
Nano silica concentration (wt.%)
SDS concentration (wt.%)
pH
1
0.1
0.115
5.34
2
0.1
3
0.1
4
0
CR
Experiment No.
5.21 5.15
0.23
5.21
AN
US
0.23
0.345
Entering Coefficient (mN/m)
Spreading Coefficient (mN/m)
Lamella Number
Bridging Coefficient (mN/m)2
a
14.07
6.87
1.35
584.48
4.57
2.69
5.18
-128.78
2.95
0.24
3.59
102.99
PT
ED
Crude Oil
M
Table 3: The spreading, entering and bridging coefficient and lamella number at the equilibrium state for the foam containing 0.1 wt.% nano silica and 0.23 wt.% SDS and oil
b
CE
c
AC
Table 4: The rising velocity of the bubbles in the presence of oil “a”, “b” & “c” 150 second after foam generation Crude Oil
a
b
c
Average bubbles’ diameter (mm)
5.2
4.7
3.7
The rising velocity of the bubbles (cm/s)
9.08
0.44
0.01
31
ACCEPTED MANUSCRIPT Highlights
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Foam generated by nano silica and two kinds of surfactants, SDS and CTAB was studied. The effect of different kinds of crude oils on foam structure was studied. Nano silica increased the foamability and foam stability of SDS solution. The presence of crude oil reduced the foam stability. Among oils with different viscosities, high viscous oil is beneficial to give better foam properties.
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