Study on interfacial properties of Imidazolium ionic liquids as surfactant and their application in enhanced oil recovery

Accepted Manuscript Title: Study on evaluating potential of Imidazolium ionic liquids as a surfactant in Enhanced Oil Recovery Author: Shilpa K. Nandwani Naved I. Malek V.N. Lad Mousumi Chakraborty Smita Gupta PII: DOI: Reference:

S0927-7757(16)31080-9 http://dx.doi.org/doi:10.1016/j.colsurfa.2016.12.037 COLSUA 21244

To appear in:

Colloids and Surfaces A: Physicochem. Eng. Aspects

Received date: Revised date: Accepted date:

28-10-2016 17-12-2016 21-12-2016

Please cite this article as: Shilpa K.Nandwani, Naved I.Malek, V.N.Lad, Mousumi Chakraborty, Smita Gupta, Study on evaluating potential of Imidazolium ionic liquids as a surfactant in Enhanced Oil Recovery, Colloids and Surfaces A: Physicochemical and Engineering Aspects http://dx.doi.org/10.1016/j.colsurfa.2016.12.037 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Study on evaluating potential of Imidazolium ionic liquids as a surfactant in Enhanced Oil Recovery

Shilpa K. Nandwania, Naved I. Malekb, V. N. Lada, Mousumi Chakrabortya,*, Smita Guptaa,* a

Department of Chemical Engineering, bDepartment of Applied Chemistry

Sardar Vallabhbhai National Institute of Technology Surat – 395 007, Gujarat, India

* Corresponding authors. Tel.: +912612201610; fax: +91 261 2227334 (Mousumi Chakraborty), Tel.: +912612201717; fax: +91 261 2227334 (Smita Gupta). E-mail addresses: [email protected] (Mousumi Chakraborty), [email protected] (Smita Gupta)

GRAPHICAL ABSTRACT

1

Highlights 

Potential of the ionic liquid, C16mimBr, in reducing interfacial tension between oil and aqueous system was studied.



C16mimBr was found to have higher potential than conventional cationic surfactant, CTAB, by significantly reducing IFT even under harsh reservoir conditions.



Improved oil recovery rates when using C16mimBr as surfactants in a CEOR process were attributed to the formation of oil in water emulsions.



Occurrence of emulsions was confirmed by performing video microscopy of fluid flowing through microchannels, modeled as porous structures present in the core.

Abstract Enhanced oil recovery is a tertiary method for recovering oil trapped in porous rock of the reservoir. This oil becomes trapped in porous media because of capillary forces. The reduction of these forces by surfactants is an important aspect of enhanced oil recovery. The development of ionic liquid -based surfactants has gained significant interest in their use as cationic surfactants in analytical methods and separations. In the current study, functionality of long chain imidazolium ionic liquids as surfactants have been investigated by measuring, dynamic interfacial tension of water/ oil system and their ability to reduce IFT under harsh conditions of salinity and temperature. In the present study, an advantage of 1-hexadecyl-3methyl imidazolium bromide (C16mimBr) over traditional cationic surfactant (CTAB) has been highlighted. The efficiency of both (C16mimBr & CTAB) in recovering additional oil when used in an EOR process has been found out by conducting lab-scale core flooding experiments. Also, small Poly (dimethylsiloxane), (PDMS) microchannels have been prepared and moduled as oil filled porous structures in the reservoir. Microscopic images of surfactant solutions flowing through these channels have been recorded to find out whether they form emulsions while flowing. The experiments revealed that C16mimBr is more efficient in reducing interfacial tension between water/ oil system and thus recovering more entrapped oil than traditional cationic surfactant CTAB. The results obtained here reflect high interfacial activity, high oil solubility due to the formation of emulsions and stability under harsh reservoir conditions for the IL in consideration. Keywords: Interfacial tension, Surfactant flooding, Imidazolium ionic liquids, Emulsion. 2

___________________________________________________________________________ 1. Introduction The percentage of oil remaining in a reservoir varies from field to field. However many field case studies have reported that after primary and secondary-oil recovery processes about 50 to 80% of original oil in place (OOIP) would be still left behind as residual oil trapped in the pores of the reservoir rock [1-4]. The percentage of residual oil left behind depends largely on the type of hydrocarbons (light oil, heavy oil or tar sands). Enhanced oil recovery (EOR) is a propitious method for recovering significant amount of this residual oil. EOR is oil recovery by the injection of materials not normally present in the reservoir viz., gases or chemicals and/or thermal energy. Thermal, miscible, and chemical enhanced oil recoveries (CEOR) are three main types of EOR techniques. Crude oil prices and cost effectiveness are the two main factors governing EOR processes. The majority of EOR processes used today were first intoduced in the early 1970’s when the oil prices were high and the interest gradually declined in the late 1980s when the oil price dropped [5]. Chemical EOR methods popularized in the 1980’s, most of them in sandstone reservoirs. Chemical methods involve process wherein a chemical formulation capable enough in reducing mobility ratio and/or increasing capillary number is injected in the reservoir as displacing fluid. The different chemicals usually employed are polymers, surfactants, low salinity water and alkalines. The most renowned ones among the chemical EOR methods are polymer flooding followed by microemulsion-polymer flooding and alkaline-surfactantpolymer flooding [5]. Therefore and despite the volatility of oil prices, chemical EOR is fast gaining attention due to its well-deserved option for almost complete oil field extraction. Recent developments in chemical EOR, especially in the field of surfactant flooding, have made even further developments making the processes comparatively safer, cleaner and more cost efficient. Surfactants are considered as good candidates for EOR since years because they can significantly lower the interfacial tensions and alter wetting properties [4]. Surfactant flooding systems are basically classified into, low-surfactant concentration systems and highsurfactant concentration systems. At low-surfactant concentration (0.1 - 0.2 wt %), system appears to be a two phase system, whereas at high surfactant concentration systems (around 4-8 wt % surfactant concentration) a middle phase microemulsion exists in equilibrium with excess oil and brine [6]. One of the main challenges in chemical EOR by surfactant flooding

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is the loss of surfactant due to adsorption on formation rocks and adsorption of such toxic substances on the reservoir rock. In addition high cost of surfactants makes the entire process uneconomical. In light of these serious drawbacks there are some additional issues regarding the functionality of conventional surfactants being used in an EOR process. Most of the ionic as well as nonionic surfactants loose stability at high salinity. It is thus clear that vast amount of work needs to be done in the area of designing specific surfactants which are able to tolerate harsh reservoir conditions, adsorb less on the reservoir rock and are less toxic, thus optimizing the entire process [7]. Petroleum industry is among one of the energy suppliers to the world and in the last decades it has shown profound interest towards transforming into a more clean and “green industry” around the world. Ionic liquids are substances that consist of ions having weak bonds amongst themselves. Most of the ionic liquids have melting points below 100⁰C however some of them are in a liquid state at room temperature. Ionic liquids are receiving importance due to a number of characteristics they own, namely an extremely low vapor pressure, low melting temperatures, wide liquid temperature range, good chemical and thermal stabilities and the ability of being doctored for a specific application by switching ions or designing specific functionalities in their structures [8]. The amphiphilic nature of ionic liquids and their ability to self organize in solutions opens additional perspectives for applications in chemical synthesis, catalysis, electrochemistry, extraction and chromatography, in the synthesis of polymer materials, nanomaterials etc [9]. For their versatility and properties, it is found from literature that ionic liquids have vast potential for different application in petroleum industry such as to inhibit the deposition of asphaltenes and paraffins [10], in crude oil dehydration and desalting [11], refining [12], as well as catalysts and solvents for petrochemical processes [13, 14]. Ionic liquids can also replace organic surfactant in breaking water/oil emulsions in oil refining process [15]. Micelle formation of ionic liquid solution enables them to act as emulsifying agents and make them capable enough to solubilise and disperse otherwise non-compatible materials like oil. More recently, ionic liquids have received interests as a green alternative to conventional emulsifying agents for EOR purposes. Many researchers have reported that ionic liquids are capable of decreasing interfacial tension between crude oil and formation water. Also they are more effective in high saline formation brine even at very low concentration of 100 ppm and have minor adsorption in the rock surface [7, 16-23]. In a recent study, Iago Rodriguez et al. [22], reported about the interfacial properties of the ionic liquid, 1-dodecyl-3-methyl 4

imidazolium acetate (C12mimOAc) for enhanced oil recovery. The effect of different variables, namely the concentration of ionic liquid, electrolytes (NaCl) and alkalis (NaOH, Na2CO3), and temperature had been analyzed. They found significant lowering of interfacial tension and stability of ionic liquid under harsh reservoir conditions [22]. Most of the efforts on evaluating ionic liquids as suitable alternatives of traditional surfactants in EOR process focus on the imidazolium family of ionic liquids. Imidazolium ionic liquids behave like typical cationic surfactants in that their aggregation behaviour is similar to that of alkyltrimethylammonium salts (CnTAX) [9]. Based on these findings, in the present work surface activity of some long chain imidazoliums, 1-alkyl-3-methylimidazolium bromides (CnmimBr (n = 12, 14, 16)) has been investigated. The imidazolium ionic liquid which reduces the interfacial tension (IFT) between oil and surfactant solution the most, was then chosen for further study viz., C16mimBr. The dynamic interfacial tensions between aqueous solution of the C16mimBr and paraffin liquid light oil (henceforth mentioned as oil), under harsh reservoir conditions has been evaluated. On this basis, efficiency of C16mimBr in recovering residual oil has been examined by carrying out lab-scale core flooding experiments. Although much research has been done in the past few years where scientists have tried to evaluate the amphiphilic character of different ionic liquids and its application in oil recovery, it is rare that a direct comparison of surface active ionic liquids had been made with traditional surfactants. Hence in the present study, the potential of C16mimBr to act like a surfactant in an EOR process was evaluated and was then compared with a traditional cationic surfactant, Cetyl trimethylammonium bromide (CTAB) for the first time for enhanced oil recovery. Further, to confirm formation of emulsions different surfactant solutions were flooded through small Poly(dimethylsiloxane) PDMS microchannels already containing oil. These microchannels have been moduled as oil filled porous structures in the reservoir. 2. Experimental 2.1 Materials used Paraffin liquid light oil (Finar Chemicals) was used as the oil phase. Sodium chloride (99%), Cetyl trimethylammonium bromide (CTAB) (99%) was purchased from SigmaAldrich (India). Three long-chain imidazolium-based ionic liquids, 1-alkyl-3methylimidazolium bromides, C12mimBr, C14mimBr and C16mimBr, were prepared and purified as mentioned elsewhere [24]. Aqueous solutions of the ionic liquids were prepared 5

by weighing on an analytical balance in degassed Millipore-grade water. Sand (50 mesh size) used in the sand pack column was purchased from Sunrise Glass Factory, India. Iso-propanol (Finar Chemicals Ltd.,India) was used as micro-channel swelling agent. 2.2 Experimental technique 2.2.1 Interfacial/ surface tension measurements: In the present study interfacial tension (both static and dynamic) between oil phase and brine phase was measured using a KRUSS-T9 Tensiometer (Germany), (Du-Nuoy ring method) under atmospheric pressure. The platinum ring was cleaned and flame-dried before each measurement. In all cases, more than three successive measurements were carried out. 2.2.2 Droplet size distribution analysis and stability of microemulsion Different ratios of oil and surfactant solutions were homogenized using an IKA ULTRA-TURRAX T-25 homogenizer for 5 mins at a speed of 6500 rpm. A sample of the microemulsion phase was then extracted using a micro-pipette. Emulsion size distribution measurements were performed using laser diffraction method of Zetasizer Ver. 6.00 (Malvern Instruments Ltd., Worcestershire, UK). The physical stability of the blends was analyzed on scanning the sample by light rays of 880 nm wavelength using Turbiscan classic MA 2000 (Formulaction, France). All the experiments were conducted at 298 K. 2.2.3 Sand pack column assays Two types of vertical sand pack columns were used to perform the EOR tests in this work. The large scale setup was an acrylic column vertically placed (FIG. 1). The dimensions of both the setups are given in TABLE 1.

2.2.4 Method of preparing microchannels PDMS Sylgard 184 (containing silicon elastomer and curing agent, Dow Corning, Midland, USA) was used for the fabrication of the microchannels as per the method elaborated in detail by YueFei et al. [25], Ralekar (S. Ralekar, M. Tech. Dissertation, Sardar Vallabhbhai National Institute of Technology-Surat, India, 2015) and Lad and Ralekar [26]. Conceptually, the silicon elastomer base and curing agent were mixed in the ratio 10:1, followed by pouring the mixture in the moulds. Moulds were also prepared by using small 6

aluminum containers, wires, micropipette tips, sealing agent (Resibond-SL330, Bondtite, India) as detailed therein [26]. Curing at 65˚C, followed by de-moulding and swelling in isopropyl alcohol as per the protocol [26] resulted in the microchannels of 384 µm diameter. The microchannel was fed at constant flow rates through accurately controlled pumping using a syringe pump NE-4000 (New Era Pump Systems Inc., USA). Firstly, oil was flown in the channel at a constant flow rate of 0.5ml/min, following which different surfactant solutions (yellow coloured due to addition of methyl orange dye) were passed through the micro-channel at the same flow rate. An inverted microscope Nikon Eclipse TS100 (Japan) equipped with a microscopic camera DS-Fi2 (Nikon, Japan) was used to observe formation of emulsion inside miniature channels. Microscopic images were analysed by NIS element documentation 4.3 microscope (Nikon, Japan) supported software (FIG. 2). 3. Results and discussions 3.1 Aggregation in water First, the aggregation behaviour of three ionic liquids, CnmimBr (n = 12, 14, 16) in water was evaluated by means of surface tension (Ɣ). Surface tension was measured for different concentrations at 298 K and results are presented in FIG. 3. At very low surfactant concentrations, the dissolved surfactant molecules are dispersed as monomers. When surfactant quantity increased to a critical concentration called the critical micelle concentration (CMC) the molecules starts to aggregate and forms micelles. After CMC of the surfactant in an aqueous solution is reached there is no appreciable change in the surface tension and it almost remains constant [27]. For each ionic liquid, the surface tension progressively decreased with the increase in the ionic liquid concentration up to a plateau region, above which a nearly constant value (Ɣ CMC) was obtained. Absence of a minimum around the breakpoint confirms the high purities of these long-chain imidazolium ionic liquids. From the surface tension plot, other important parameters, i.e., the effectiveness of surface tension reduction, ΠCMC and the surface excess concentration of surfactant at saturation, Γmax were calculated. The values obtained for all these properties are presented in TABLE 2 together with literature values [28, 29] for the same ionic liquids.

7

From TABLE 2, it is evident that the CMC values decrease in the order C12mimBr >C14mimBr >C16mimBr, which is in accordance with the literature reported [28, 29]. A reason for this is increase in hydrophobicity due to elongation of hydrocarbon chain, thus favouring micelle formation. Thus a larger hydrophobic domain would result in a lower CMC [29]. When compared with traditional cationic surfactants having the same hydrocarbon chain length the CMC values for [Cnmim]X salts are lower than for CnTAX with the same n value [28,30], for e.g. CTAB had a CMC of 0.89mM [31] compared to 0.57mM of C16mimBr presented in this work. A lower CMC of imidazolium ionic liquids as compared to conventional cationic surfactants of the same chain length implies that the less polar methyl imidazolium head group makes micelle formation energetically more favourable. From the above study it is observed that C16mimBr is superior to, or at least comparable to, traditional cationic surfactant CTAB in their capability for micelle formation. 3.2 Effect of Ionic Liquid on Interfacial tension (IFT) in paraffin oil /water and paraffin oil /brine solution systems The effect of ionic liquid concentration on the IFT between ionic liquid solution in distilled water/brine water and paraffin oil were investigated (FIG.4).The results revealed that the measured IFT for C12mimBr, C14mimBr and C16mimBr decreased from 43.97 mN/m to 9.1mN/m, 7.2 mN/m and 4.7 mN/m respectively as the concentration of ionic liquid increased in distilled water and above the CMC, no decrease in IFT was observed (Figure inset). It was also observed that there is a sharp reduction in CMC, around 500 ppm for C14mimBr and around 250 ppm for C16mimBr. It means, as the length of the alkyl chain increased the capability of the ionic liquid to reduce the IFT increased. This might be due to strong adsorption at the interface of surfactants with higher alkyl chain length. As a consequence, even a small amount of surfactant arriving at the interface causes a large decrease in the IFT. Heazve et al. [20] in their work also observed a similar behaviour and thus concluded that as the length of the chain increases the capability of the ionic liquid to reduce the IFT increases, longer tails are more effective at low concentrations; that is, less surfactant is needed to achieve the same IFT. The salinity of the displacing fluid has a strong influence on the oil/aqueous systems interfacial tension. For this reason, various experiments were carried out for 1-Alkyl-3methylimidazolium bromides ((CnmimBr) with n = 12, 14, 16) at a constant NaCl concentration (3 wt %), FIG. 4. 8

The results revealed that under same operating conditions the measured IFT for C12mimBr decreased slightly from 9.1 mN/m (distilled water) to 8.7 mN/m (brine water), 7.2 mN/m (distilled water) to 5.9 mN/m (brine water) for C14mimBr, while the IFT for C16mimBr experienced significant reduction from 4.7 mN/m (distilled water) to 3.9 mN/m (brine water). From FIG. 4 it is clear that the presence of ion not only increased the strength of ionic liquid to reduce the IFT but also lowered the CMC for all the three ionic liquids. It is worth mentioning that CMC of C16mimBr reduced from 250 ppm to about 100 ppm. Similar results were obtained by Heazve et al [20], as they measured the IFT between crude oil and four different ionic liquid solutions, C12mimCl, C8mimCl, C12PyCl and C8PyCl in the presence and absence of salinity. The effect of change in concentration of C16mimBr on IFT between oil and brine solution (varying salinity from 0 ppm to 30000ppm ~ 3 wt %) was studied. It was observed that as the salinity increased the counter-ions (Cl-) available for neutralizing the charge of surfaces increased and decreased CMC. It was found that at 3 wt %salinity, the CMC had reduced to about 100 ppm. Hence further studies were limited to C16mimBr and a traditional cationic surfactant having the same hydrocarbon chain length CTAB. 3.3 Comparison of C16mimBr with CTAB in reducing IFT under high salinity conditions. Anionic surfactants have a negative headgroup and get less adsorbed on the sandstone rocks (surface charge of sand being negative). Hence are most widely used in chemical EOR processes. However, anionic surfactants cannot render ultralow interfacial tension under high salinity conditions. In a recent study Zhao et al [32], observed such antagonism between inorganic salt and Dodec-MNS surfactant (anionic). Cationic surfactants have a positive headgroup and get strongly adsorbed in sandstone rocks. They are generally not used in sandstone reservoirs, but can be used in carbonate rocks for recovering residual trapped in the reservoir. In recent investigation, it has been proved that cationic surfactants like CTAB performed better than anionic surfactants in altering the wettability of the carbonate rock to a more water wet [33]. As mentioned earlier, imidazolium ionic liquids behave like typical cationic surfactants in that their aggregation behaviour is similar to that of alkyltrimethylammonium salts. Hence when evaluating efficiency of C16mimBr in reducing IFT, it was compared with a conventional cationic surfactant having the same hydrocarbon chain length and same anion type Br, CTAB. The results obtained are shown in FIG. 5.

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As seen in FIG. 5, C16mimBr was found to be more efficient in reducing interfacial tension (3.8mN/m) between oil and surfactant solution systems under high salinity conditions. From FIG. 5 it is seen that CTAB showed a larger IFT (7.7mN/m) under same salinity conditions. Thus, the obtained results suggest C16mimBr as a novel candidate for the chemical EOR processes dealing with the harsh conditions of salinity. 3.4 The Dynamic Interfacial Tension (DIFT) Once the displacing fluid is injected in the reservoir, the two immiscible fluids generate a new interface. However the equilibrium interfacial tension is not instantly reached. Equilibrium interfacial tension is reached only after the surfactant molecules from the displacing fluid diffuse to the newly generated interfacial layer, get adsorbed and further orient themselves. These steps are characterized by dynamic interfacial tension (DIFT). In this stage, the effect of NaCl concentrations (0.2- 3 wt %) on the DIFT of the IL/ oil system were evaluated at a constant concentration of the C16mimBr (0.01 wt %). FIG. 6 shows that as NaCl concentration in the IL solution increased the DIFT reduced. It was seen that for the IL solution, the DIFT reaches its equilibrium value in less than 15 mins even under high salinity conditions.

Zhao et al. [32] reported that with increasing inorganic salt mass concentration, the time required for the anionic surfactants DIFT to reach the ultimate value increases. It was observed that IFT between oil and IL solution almost remained constant with time at a given brine concentration (0.5 wt % NaCl-3.5 wt% NaCl). Nevertheless, the profiles of the dynamic interfacial tension were different for different salinities. Equilibrium interfacial tension stabilized around 7.54 mN/m, when NaCl concentration was set to 0.2 – 0.5 wt %, and stabilized around 6.08- 5.84 mN/ m for NaCl concentrations in the mentioned range 1.5–3.5 wt %. A similar behaviour was reported, wherein increasing NaCl concentration decreased the interfacial tension, however showed a limiting effect as above for 1-dodecyl pyridinium chloride and 1-dodecyl-3-methylimidazolium acetate at much higher NaCl concentrations [20, 22]. In order to test the effect of temperature on the DIFT between oil and IL soution, aqueous solutions of the surfactant ILs were prepared in brine (3wt % NaCl) and a series of experiments were carried out at four different temperatures. The results obtained are shown in 10

FIG. 6 (inset). It is seen that an increase in temperature led to increase in DIFT. An explanation to this behaviour might be that as the temperature increases viscosity of oil decreases. The resistance to mass transfer and surfactant diffusion in the oil phase lowers and above the phase inversion temperature (PIT) emulsion inversion takes place. However, the time required for the surfactant to reach equilibrium remains the same between temperatures 298 K-333 K. This behaviour with temperature was also found in literature for other ionic liquids [18-23]. Heazve et al. [18] attributed this behaviour of imidazolium ionic liquids to the cationic head which is more lipophilic than the cationic head of conventional surfactants. 3.5 Size Distribution of Emulsion Droplet and stability study Lowering interfacial tension with surfactants leads to the formation of emulsions and microemulsions. High oil solubilisation is one of the key characteristic of surfactant used in enhanced oil recovery process. In other words, micelles in the aqueous phase should be able to solubilise oil from the hydrocarbon phase, thus forming emulsions. In this section the size of emulsion formed when the IL solution and oil are homogenized is determined using dynamic light scattering technique. The system under study being a low surfactant concentration system of surfactant flooding, the concentration of C16mimBr was varied from 0.1 wt% - 0.5 wt% in brine (3 wt% NaCl) solution.The reason behind selecting a range well above CMC was to overcome the loss of surfactant due to adsorption on reservoir rock throughout the flooding process. It was observed from Fig.7 that microemulsions have smaller size and narrow droplets size distribution, which indicates stability of the emulsion [34]. The average diameter of dispersed oil droplets formed with 0.3 wt % C16mimBr concentration was found to be 474.5 nm. Thus for further study in core flooding experiments the concentration of C16mimBr and concentration of NaCl was set to 0.3 wt% and 3 wt % respectively. The stability of emulsion was then examined by scanning the sample in a turbiscan for a period of 24 hours. The Transmission profile of the homogenised mixture is elucidated in FIG.8. From FIG. 8 it was observed that the oil in water emulsion in the lower phase broke down gradually with time and separated into water and oil phase after a period of 24 hrs. As separation of phases took place gradually it indicates that emulsion droplets formed in homogenized sample were large enough to be stable. However it took about 6 hrs for the emulsion phase to destabilize, which would be enough for the IL solution to sweep along

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with it some amount of solubilised oil. This solubilised oil would then separate out into an oil bank. 3.6 Core flooding experiment The core flooding experiments were carried out at room temperature. A schematic representation of the sand packed columns is shown in FIG. 1. Pore volume (PV cm3) of sand column was calculated by measuring the volume of water required to saturate the column [17]. The porosity (%) of the column was calculated as PV

𝑃orosity (%) =

Bulk Volume of the sand column

(1)

In the second step, paraffin liquid light oil was injected into the column, until there was no more water coming out from the downstream. Original oil in place (OOIP, cm3) was then calculated from volume of oil retained in the column. Initial oil saturation (Soi %) and initial water saturation (Swi %) were calculated as follows respectively [12] : 𝑆𝑜𝑖 (%) =

𝑂𝑂𝐼𝑃

× 100

(2)

𝑆𝑤𝑖 (%) = 100 − 𝑆𝑜𝑖

(3)

𝑃𝑉

The sand pack column was then sealed with a parafilm and allowed to stand for 24 hrs. After 24 hrs, the sand column was waterflooded until there was no more oil in the effluent stream. The amount of oil recovered after water flooding (ORWF, cm3) was determined volumetrically. The residual oil saturation (Sor, %) was then calculated as follows: The residual oil was then subjected to EOR processes. The column was then flooded with surfactant solutions. The effluent was collected in graduated test tubes (25 cm3). All the fractions recovered correspond to the oil recovered after surfactant flooding (ORSF, cm3). All the results represent average of two independent experiments. The EOR (%) was calculated as follows: 𝑂𝑅𝑆𝐹

𝐸𝑂𝑅 (%) = [(𝑂𝑂𝐼𝑃−𝑂𝑅𝑊𝐹)] × 100

(4)

3.6.1 Effect of different surfactant solutions on oil recovery efficiency The effect of IL concentration on the oil recovery efficiency was investigated by performing three different core flooding tests with gradual increase in volume of IL 12

containing water (pore volume).It is observed that with an increase in the IL concentration from 0.1 to 0.3 wt %, oil recovery improved from 58.75 to 73.25%. These results could be attributed to the IFT reduction, wettabilty alteration and the coacervation process. In the next step, five EOR assays were performed in the small scale setup, using 3 wt % NaCl solution without any surfactant, 0.3 wt % C16mimBr aqueous solution, 0.3 wt % C16mimBr in 3 wt% brine solution, 0.3 wt % CTAB aqueous solution and 0.3wt% CTAB in 3 wt% brine solution. The results obtained are reported in TABLE 3 and FIG. 9. The sand pack column in the small setup had a PV in the range of 32 – 34 cm3and the OOIP was between 17 – 24 cm3. Water –flooding with pure water removed about 60- 75 % of the oil entrapped in the column thus leaving behind only 25- 40% of the initial oil in place. After the secondary water – flooding step, tertiary EOR processes were performed as described above. It was found that in all the assays, after injecting about 4 PV of slug no more oil recovered. As seen from the TABLE 3, surfactant slug containing 0.3 wt % C16mimBr in 3 wt% brine solution recovered the maximum percentage of oil, 71.83%, trapped in the sand packed column after secondary water flooding process. FIG. 9 represents the oil recovery as a function of the volume of surfactant slug injected. Percentage oil recovered when a surfactant slug prepared in brine water was injected through the column was found to be larger than the oil recovered when the same surfactant slug prepared in distilled water was injected. This improvement might be attributed to more to additional decrease in IFT in the presence of NaCl as shown in FIG. 9. The IL solution was found to be more efficient in recovering oil (both in distilled water and brine) when compared with the traditional cationic surfactant CTAB. With oil recovery of 71.83 % the IL solution prepared in brine was found to be the most efficient in an EOR process. To investigate the effect of configuration of the sand pack column, another set of core flooding experiments were performed in a large scale setup, dimensions of which are mentioned in TABLE 1. After packing the sand in the acrylic column tightly, the two ends were sealed with a sieved cap. The fluids were injected into the column at the rate of 2.33 ml/min. For the sand packed in the large scale setup, the PV was approximately 44 cm3. The OOIP (average of two readings) was 20 cm3. After secondary water flooding step, the residual oil saturation (Sor), was found to be approximately 30 %. During the tertiary oil recovery process, an IL slug having composition (0.3 wt% C16mimBr in 3 wt % NaCl solution) was injected into the acrylic column. The oil recovered after the IL-EOR process in a sand bed packed in the acrylic column, was 75.65 % of the residual oil trapped in the pores of the bed after secondary water flooding process, which was almost the same as in the case of small setup. The results are shown in FIG. 9. Similar results were reported in another study 13

where EOR process was carried out by alkaline flooding for Western Canadian heavy oil recovery [35]. 3.7 Recycling of surfactant slugs for CEOR To test the ability of recycling of the surfactant slug as well as its adsorption on sand, a series of experiments was carried out for the two surfactant (CTAB and C16mimBr) slugs on three different sand-pack columns. In the first step, fresh surfactant slug (either 0.3 wt % CTAB or 0.3 wt% C16mimBr in 3 wt % brine solution), Cycle1, was flooded into core 1. Effluent produced at the end of the chemical flooding process from core 1, known as Cycle 2 was then flooded into core 2 during its tertiary oil recovery process. Again effluent collected from core 2, known as Cycle 3, was flushed as a chemical slug into core 3 during the CEOR stage of the latter one. The purpose of doing this was to evaluate the depletion in efficiency of the chemical slug, in recovering oil from the pores which was further attributed to loss of surfactant due to adsorption on sand particles in the reservoir. The results are shown in FIG.10. It was observed that when a chemical slug of 3.5 PV and a composition, 0.3 wt% C16mimBr in 3 wt % brine solution, was injected into core 1, the additional oil recovered was 73.33%. From FIG. 10 it is observed that the efficiency of recovering trapped oil, of Cycle 2 has dropped down to 37.5% in core 2. In core 3, however not a significant depletion in efficiency was observed i.e. Cycle 3 when flooded in core 3 recovered about 32% of the trapped oil. Similar results were obtained for CTAB; however the oil recovered from core 3 reduced drastically to about 8%. From the above results it is evident that both the surfactants, (CTAB and C16mimBr), get adsorbed on the negatively charged sand particles in the packed column. The reason being, that both of them have a headgroup with cationic charge. From FIG. 10 it can be seen that amount of surfactant adsorbed on sand in core 1 was larger as compared to adsorption of surfactants on sand particles in core 2 and core 3 in case of both CTAB and C16mimBr. T. Gu et al.[36] suggested that at low concentrations surfactant molecules adsorb in a linear fashion whereas at higher concentration, the adsorption suddenly increases due to hemimicellization, initiated by some adsorbed surfactant molecules on the surface. Thus it is clear that amount of surfactant adsorbed on the sand particles depends strongly on its concentration in the effluent stream. Thus the IL solution retains its efficiency as compared to CTAB and thus can be reused to serve as a more economical alternative to the traditional cationic surfactant, CTAB. 14

3.8 Fourier Transform Infrared (FTIR) Spectroscopy of light oil and oil recovered after flooding with surfactants (C16mimBr and CTAB) in brine solution. IR spectra of the Paraffin liquid light oil used in the present study were recorded between 400 and 4000 cm-1. A typical IR spectrum of pure oil is shown in FIG. 11. It also shows spectra of oil recovered after flooding with CTAB and C16mimBr in brine solution. FTIR spectra shown in the FIG.11 suggests the newly developed peak between 1600 1700 cm-1, may be due to the interaction between the C-N- C of the surfactants (C16mimBr & CTAB) and CH2 from the oil part. Here it is noteworthy to mention that the micelles of the surfactants (concentration well above CMC, 0.3 wt %) have been injected into in the sand packed column. As general observation, micelles are more hydrophobic than the monomers, the hydrophobic-hydrophobic interaction between the micelles of the surfactants and oil is expected and which are confirmed through the newly generated peak between 1600 -1700 cm-1. The spectrum of the IL treated oil (FIG. 11) gives almost the same peak as that of the CTAB treated oil, but with an improved interaction. It is noted that two bands at 3432 and 3481 cm-1 are due to the asymmetric υ3 and symmetric υ1 stretching modes of water, where the water interacts with the anion via H-bonding in a symmetric complex [37]. In case of C16mimBr, these peaks are merged and present as the single broad band in the recovered oil sample after interacting with C16mimBr. Hence it is clear that C16mimBr might be reacting with the hydrocarbon (oil) inside the packed column and a stronger interaction is responsible for the better oil recovery in case of IL than the other systems studied which is CTAB. 3.9 Flow of surfactants through microchannel A high percentage of oil recovered in surfactant – based enhanced oil recovery is attributed to the formation of emulsions [6]. Emulsions are formed due to decrease in interfacial tension between the oil and surfactant slug. In the present study it had been observed that use of IL as well as CTAB as a surfactant solution improved oil recovery, the two being more efficient under high salinity conditions. From emulsion droplet size distribution experiments (section 3.5); this behaviour might be attributed to formation of emulsions. In order to have a deeper insight on the formation of emulsions, miniature microchannels were prepared and modelled as oil filled porous structure in the reservoir. Slugs were then passed though these PDMS microchannels at the rate of 0.5 ml/min with the help of a syringe pump. The flow of the fluids was recorded to mark formation of emulsions if any. FIG. 12 shows frames of the video captured.

15

It was observed that when pure brine without any surfactant was flown inside the channel, no emulsions were formed. FIG. 12 (a) displays frames when brine solution is passed though the microchannels initially filled with oil. When a high salinity brine solution with strong dipole moment is injected into the column, electrostatic attraction between the negative charge of sand surface and the ionic groups causes an increase in the oil recovery. Zhang et al. [38] also showed that on injecting saline water into the core, oil was recovered. J. Periera[17] in his studies had also observed oil recovery when brine solution was injected into sand packed column after secondary oil recovery. They have attributed this oil recovery to electrostatic attractions between brine solution and the surface charge of the sand particles [17]. When the IL solution containing 0.3 wt % C16mimBr in distilled water was flushed into the channel a clear presence of o/w emulsions was observed. However these emulsions coalesced and gradually disappeared (FIG. 12(b)). Oil drops in the emulsion prepared in the absence of salt were discrete and spherical. However for an IL solution in brine ((0.3 wt %) C16mimBr + (3 wt %) NaCl), number of o/w emulsions formed was larger than those formed in the case of IL solution in distilled water. Also a large variation in the size of these emulsions was observed, FIG.12(c). Similar behaviour of effect of NaCl on emulsion size was also reported by Binks et al. [39], when studying the effect of salt concentration on oilin-water emulsions stabilized solely by nanocomposite microgel particles. They concluded that addition of salt resulted in tight concealing of ionized groups and also increased the degree of ionization of imidazolium groups on the surface of the particles [39]. From FIG. 12 (c) it was observed that degree of flocculation was negligible in brine solution. Thus we can conclude that when chemical flooding with IL in brine solution, a high recovery might be observed due to formation of large number of o/w emulsions. When a surfactant solution containing 0.3 wt% CTAB in brine (3wt% NaCl) was passed through the oil filled microchannels, a cluster of very small o/w emulsions were observed at the interface (FIG. 12(d)). The reasons for a lower efficiency of CTAB in recovering oil as compared to C16mimBr can be attributed to the following reasons:  The imidazolium ionic liquids have a bulky heterocyclic ring as cationic portion; however, CTAB possesses a smaller quaternary ammonium cation. This bulky structure gives

16

the IL more hydrophobicity and consequently more interfacial activity than conventional cationic surfactants [28].  It has been reported that the imidazolium cations are aromatic in nature and have a sextet of π-electrons [40].This aromatic character of ILs acts as driving force for oil solubility. It might be due to the π-π interactions between IL and oil that more amount of oil is solubilised in the o/w emulsions formed.  The FTIR spectra of the oil recovered after CEOR from the sand packed column indicates a stronger interaction between C16mimBr and oil. B.Dong et al. [23], also observed slightly higher micropolarity of the Stern layer for CnmimBr micelles than that for CnTAB micelles owing to the bulkiness of the imidazolium head group. The author concluded that due to this behaviour CnmimBr would serve for potential application of ILs in colloidal systems [28]. 4. Conclusion The surface activity of 1-alkyl-3-methyl imidazolium bromide (CnmimBr), n = 12, 14, 16, was evaluated by means of surface tension. It was found that surface activity of the ionic liquids improved with increase in alkyl chain length. In addition to a lower CMC, interfacial tension between oil and C16mimBr solution were lower than those obtained when using CTAB surfactant solution under high salinity conditions. This interfacial activity of C16mimBr solution was found to sustain even at high temperature conditions unlike other conventional surfactants. Sand-packed columns were moduled as reservoir cores and the potential of the two surfactants (CTAB and C16mimBr) in recovering additional oil in an EOR process were also investigated. Chemical flooding with IL in brine solution extracted more oil trapped in the reservoir when compared to CTAB solution with same composition. FTIR of the recovered oil further pointed out a stronger interaction between C16mimBr and oil, thus validating its increased efficiency. PDMS microchannels were moduled as oil filled pores in the reservoir. Inside the pores, IL solutions solubilise oil by forming o/w emulsions. C16mimBr showed promising results when the effluent from a surfactant flooding process was reused in the CEOR process of another sand packed column. Based on the obtained results it can be concluded that C16mimBr has characteristics which make them a promising candidate for surfactants to be used in EOR processes. However other screening criterion in selection of surfactants for EOR process are: ultralow 17

interfacial tension and low adsorption on reservoir rock. Thus in our ongoing research we are formulating ionic liquid surfactant solution which pass this screening criteria.

Funding: This research did not receive any specific grant from funding agencies in the publc, commercial, or not-for-profit sectors.

REFERENCES [1] V.Pillai, J.R.Kanicky, D.O.Shah, Application of Microemulsion in Enhanced Oil Recovery, in: P.Kumar, K.L.Mittal (Eds.), Handbook of MicroemulsionScience and Technology, Marcel Dekker Inc., New York, 1999, pp. 743-754. [2] D.W. Green, G.P. Willhite, Enhanced Oil Recovery, fourth ed., Henry L. Doherty Memorial Fund of AIME, Society of Petroleum Engineers, 1998. [3] J.J. Sheng, Surfactant-Polymer Flooding, in: J.J. Sheng (Ed.),Enhanced Oil Recovery – Field Case Studies, Elsevier, 117-142 [4] L.L. Schramm, D.G. Marangoni, Surfactants and Their Solutions: Basic Principles, in: L.L.Schramm (Ed.), Surfactants: fundamentals and applications in the petroleum industry, Cambridge University Press, UK, 2000. [5] V. Alvarado, E. Manrique, Enhanced oil recovery: An update review, Energies. 3 (2010) 1529–1575. [6] D.O. Shah, Fundamental aspects of surfactant–polymer flooding process, Keynote paper presented at the European Symposium on Enhanced Oil Recovery, Bournemouth, England, 1981. [7] M.S. Benzagouta, I.M. AlNashef, W. Karnanda, K. Al-Khidir, Ionic liquids as novel surfactants for potential use in enhanced oil recovery, Korean J. Chem. Eng. 30 (2013) 2108– 2117.

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[8]P. Wasserscheid, T. Welton (Eds.), Ionic Liquids in Synthesis, second ed., WileyVCH,Weinheim, 2002. [9] N.A. Smirnova, E.A. Safonova, Ionic liquids as surfactants, Russ. J. Phys. Chem. A 84 (2010) 1695–1704. [10]

M. Boukherissa, F. Mutelet, A. Modarressi, A. Dicko, D. Dafri, M. Rogalski, Ionic

liquids as dispersants of petroleum asphaltenes, Energy Fuels 23 (2009) 2557–2564. [11]R.C.B. Lemos, E.B. Da Silva, A. Dos Santos, R.C.L. Guimarães, B.M.S. Ferreira, R.A. Guarnieri, C. Dariva, E. Franceschi, A.F. Santos, M. Fortuny, Demulsification of water-incrude oil emulsions using ionic liquids and microwave irradiation, Energy Fuels 24 (2010) 4439– 4444. [12] X. Chen, S. Yuan, A.A. Abdeltawab, S.S. Al-Deyab, J. Zhang, L. Yu, G. Yu, Extractive desulfurization and denitrogenation of fuels using functional acidic ionic liquids, Sep. Purif. Technol. 133 (2014) 187–193. [13] H. Olivier-Bourbigou, V. Lecocq, Ionic liquids as new solvents and catalysts for petrochemical and refining processes, Sci. Technol. Catal. 145 (2003) 55–60. [14] P. Painter, P. Williams, A. Lupinsky, Recovery of bitumen from Utah tar sands using ionic liquids, Energy Fuels 24 (2010) 5081–5088. [15] M.H. José-Alberto, A. Jorge, Current knowledge and potential applications ofionic liquids in the petroleum industry, in: P.A. Kokorin (Ed.), Ionic liquids:applications and perspectives,InTech, 2011, pp. 439–456. [16] S. Lago, H. Rodríguez, M.K. Khoshkbarchi, A. Soto, A. Arce, Enhanced oil recovery using the ionic liquid trihexyl(tetradecyl)phosphonium chloride: phase behaviour and properties, RSC Adv. 2 (2012) 9392-9397. [17] J.F.B. Pereira, R. Costa, N. Foios, J.A.P. Coutinho, Ionic liquid enhanced oil recovery in sand-pack columns, Fuel 34 (2014) 196–200. [18] A.Z. Hezave, S. Dorostkar, S. Ayatollahi, M. Nabipour, B. Hemmateenejad, Investigating the effect of ionic liquid (1-dodecyl-3-methylimidazolium chloride ([C12mim] [Cl])) on the water/oil interfacial tension as a novel surfactant, Colloids Surf., A421 (2013) 63–71. 19

[19] A.Z. Hezave, S. Dorostkar, S. Ayatollahi, M. Nabipour, B. Hemmateenejad, Dynamic interfacial tension behavior between heavy crude oil and ionic liquid solution (1-dodecyl-3methylimidazolium chloride ([C12mim][Cl] + distilled or saline water/heavy crude oil)) as a new surfactant, J. Mol. Liq.187 (2013) 83–89. [20] A.Z.Hezave, S. Dorostkar, S. Ayatollahi, M. Nabipour, B. Hemmateenejad, Effect of different families (imidazolium and pyridinium) of ionic liquids-based surfactants on interfacial tension of water/crude oil system, Fluid Phase Equilib.360 (2013) 139–145. [21] A.Z.Hezave, S. Dorostkar, S. Ayatollahi, M. Nabipour, B. Hemmateenejad, Mechanistic Investigation on Dynamic Interfacial Tension Between Crude Oil and Ionic Liquid Using Mass Transfer Concept, J. Dispers. Sci. Technol.35 (2014) 1483–1491. [22] I. Rodríguez-Palmeiro, I. Rodríguez-Escontrela, O. Rodríguez, A. Arce, A. Soto, Characterization and interfacial properties of thesurfactant ionic liquid 1-dodecyl-3methylimidazolium acetate for enhanced oil recovery, RSC Adv. 5 (2015) 37392–37398. [23] M. Bin Dahbag, A. AlQuraishi, M. Benzagouta, Efficiency of ionic liquids for chemical enhanced oil recovery, J. Pet. Explor. Prod. Technol. 5 (2015) 353–361. [24] N.I. Malek, Z.S. Vaid, U.U. More, O.A. El Seoud, Ionic-liquid-based surfactants with unsaturated head group: synthesis and micellar properties of 1-(n-alkyl)-3-vinylimidazolium bromides, Colloid Polym. Sci. 293 (2015) 3213–3224. [25] Y. Jia, J. Jiang, X. Ma, Y. Li, H. Huang, K. Cai, S. Cai, Y. Wu, PDMS microchannel fabrication technique based on microwire-molding, Chin. Sci. Bull. 53 (2008) 3928–3936. [26] V.N. Lad, Ralekar Swati, Controlled evacuation using the biocompatible and energy efficient microfluidic ejector, Biomed. Microdevices 18 (2016) 96. [27] M.J. Rosen (Ed.), Surfactants and Interfacial Phenomena, third ed., John Wiley & Sons, New Jersey, USA, 2004. [28] B. Dong, X. Zhao, L. Zheng, J. Zhang, N. Li, T. Inoue, Aggregation behavior of longchain imidazolium ionic liquids in aqueous solution: Micellization and characterization of micelle microenvironment, Colloids Surf., A 317 (2008) 666–672. [29] R. Vanyúr, L. Biczók, Z. Miskolczy, Micelle formation of 1-alkyl-3-methylimidazolium bromide ionic liquids in aqueous solution, Colloids Surf., A 299 (2007) 256–261. 20

[30] J. Łuczak, J. Hupka, J. Thöming, C. Jungnickel, Self-organization of imidazolium ionic liquids in aqueous solution, Colloids Surf., A 329 (2008) 125–133. [31] V. Mosquera, J.M. del Río, D. Attwood, M. García, M.N. Jones, G. Prieto, M.J. Suarez, F. Sarmiento, A Study of the Aggregation Behavior of Hexyltrimethylammonium Bromide in Aqueous Solution., J. Colloid Interface Sci. 206 (1998) 66–76. [32] Z. Zhao, C. Bi, W. Qiao, Z. Li, L. Cheng, Dynamic interfacial tension behavior of the novel surfactant solutions and Daqing crude oil, Colloids Surf., A 294 (2007) 191–202. [33] D.C. Standnes, T. Austad, Wettability alteration in chalk 2. Mechanism for wettability alteration from oil-wet to water-wet using surfactants, J. Pet. Sci. Eng. 28 (2000) 123–143. [34] E. Chrisman, V. Lima, P. Menechini, Asphaltenes – Problems and Solutions in E&P of Brazilian Crude Oils, in: M. El-Sayed Abdel-Raouf (Eds.), Crude Oil EmulsionsComposition Stability and Characterization, InTech, 2012, pp. 1-25. [35] Q. Liu, M. Dong, S. Ma, Y. Tu, Surfactant enhanced alkaline flooding for Western Canadian heavy oil recovery, Colloids Surf., A 293 (2007) 63–71. [36] T. Gu, Z. Huang, Thermodynamics of Hemimicellization of Cetyltrimethylammonium Bromide at the Silica Gel/ Water Interface, Colloids Surf. 40 (1989) 71–76. [37] L. Cammarata, S.G. Kazarian, P. a. Salter, T. Welton, Molecular states of water in room temperature ionic, Phys. Chem. Chem. Phys. 3 (2001) 5192–5200. [38] Y. Zhang, N.R. Morrow, Comparison of Secondary and Tertiary Recovery with Change in Injection Brine Composition for Crude Oil/ Sandstone Combinations, SPE/DOE Symp. Improv. Oil Recover. (2006). [39] B.P. Binks, R. Murakami, S.P. Armes, S. Fujii, Effects of pH and salt concentration on oil-in-water emulsions stabilized solely by nanocomposite microgel particles, Langmuir 22 (2006) 2050–2057. [40] T.M. Krygowski, W.P. Oziminski, C.A. Ramsden, Sigma- and pi- electron structure of aza-azoles, J. Mol. Model. 17 (2011) 1427–1433.

21

Inner bore

Tight cap

d L

Acrylic column Sand bed Sieve

FIG. 1: Schematic representation of sand pack columns.

22

FIG. 2: Schematic diagram of set-up of recording flow in microchannels; (i) syringe pump NE-4000 holding syringe. (ii) Nikon eclipse microscope TS100 (iii) Desktop showing microscopic image (iv) microchannel.

23

FIG. 3: Surface tension of aqueous solutions of surfactant ionic liquids at 298 K and atmospheric pressure.

24

FIG. 4: Effect of surfactant concentration on IFT between oil and brine water (3 wt% NaCl).

25

FIG. 5: Comparison of C16mimBr with CTAB on the basis of reduction of IFT between oil/distilled water system and oil/ brine water (3 wt% NaCl) system.

26

FIG. 6: Plot of interfacial tension and temperature against time between oil and IL solution (C16mimBr (0.01 wt %)) under varying salinity conditions.

27

Intensity (%)

40 35

0.1 wt%

30

0.2 wt% 0.3 wt%

25

0.4 wt%

20

0.5 wt%

15 10 5 0 200

700 Size(d.nm)

1200

FIG. 7: Influence of change in concentration of C16mimBr on the size of emulsion at constant brine concentration (3 wt %) and a constant WOR (4:1).

28

FIG. 8: Transmission profile of homogenised oil and IL solution.

29

FIG. 9: Comparison of enhanced oil recovery by chemical flooding using different surfactants and different setups.

30

FIG.10. Effect of recycling of surfactant slug on EOR

31

FIG.11: FTIR spectrum of pure oil and oil recovered after surfactant flooding.

32

(a) Sequence of frames after 3 wt% NaCl is passed through the channel filled with oil. The

images are displayed using 4 times magnification for a microchannel of 384 µm diameter.

(b) Sequence of frames after IL solution containing 0.3 wt % C16mimBr in distiiled water

is passed through the channel filled with oil. The images are displayed using 4 times magnification for a microchannel of 384 µm diameter.

(c) Sequence of frames after IL solution containing 0.3 wt % C16mimBr in brine (3 wt % NaCl), is passed through the channel filled with oil. The images are displayed using 4 times magnification for a microchannel of 384 µm diameter.

(d) Sequence of frames after surfactant solution, (0.3 wt %) CTAB + (3 wt %) NaCl, is passed through the channel filled with oil. The images are displayed using 4 times magnification for a microchannel of 384 µm diameter. FIG.12: Flow of different chemical slugs through PDMS microchannels.

33

TABLE 1: Dimensions of the large scale as well as the small scale setup used in the core flooding process.

Large scale setup Small scale setup

Inner diameter (d), (cm) 2.9 2.9

Length of packed sand bed (L), (cm) 22.3 10.9

34

TABLE 2: Surface properties of C12mimBr, C14mimBr, and C16mimBr at 298 K. ƔCMC (mN/m)

П CMC (mN/m)

Γmax (µmol/m²)

Ionic

CMC (mmol/L)

liquids

This

Ref

Ref

This

Ref

Ref

This

Ref

Ref

This

Ref

Ref

work

(28)

(29)

work

(28)

(29)

work

(28)

(29)

work

(28)

(29)

C12mimBr

9.03

10.9

9.8

39.4

39.4

na

32.6

33.6

na

0.42

1.91

na

C14mimBr

2.43

2.8

2.5

39.2

39.2

na

32.8

33.8

na

1.37

1.96

na

C16mimBr

0.54

0.55

0.61

38.6

39.1

na

33.4

33.9

na

1.55

2.03

na

na – not available

35

TABLE 2: Oil recovery in sand pack columns after flooding with NaCl (3 wt %), IL surfactant – C16mimBr, conventional cationic surfactant – CTAB.

33.4050 41.0950

CTAB (0.3 wt %) + NaCl (3 wt %) 33.55 41.27

C16mimBr (0.3 wt %) + NaCl (3 wt %) 33.67 41.455

23.5

21.5

18

19.5

51.58

72.0250

64.355

53.65

57.93

48.42

27.9750

35.6450

46.35

42.07

26.9

29.78

20.93

33.33

36.14

12.61

32.145

62.53

54.87

71.83

Specifications of sand pack column

NaCl (3 wt %)

CTAB (0.3 wt %)

C16mimBr (0.3 wt %)

Pore volume (cm3) Porosity (%) Original oil in place, OOIP (cm3) Initial oil saturation, Soi (%) Initial water saturation, Swi (%) Residual oil saturation, Sor (%) EOR with 4PV injected (%)

33.15 40.78

32.6250 40.135

17.1

36