SPE Copyright 2012, Society of Petroleum Engineers

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1 SPE A Novel Effective Triglyceride Microemulsion for Chemical Flooding Z. Jeirani, SPE, B. Mohamed Jan, SPE, B. Si Ali, and I. Mohd Noor, University of Malaya; and C.H. See, SPE, and W. Saphanuchart, SPE, BCI Chemical Corp. Sdn. Bhd. Copyright 2012, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Asia Pacific Oil and Gas Conference and Exhibition held in Perth, Australia, October This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract This paper presents determination of aqueous phase composition of a new triglyceride microemulsion in which the triglycerides constitute the whole oil-phase of the microemulsion. Palm oil was used as the oil phase of the microemulsion. Experimental results indicate that the optimum triglyceride microemulsion was achieved when equal mass of palm oil and the aqueous phase containing 3wt% sodium chloride, 1wt% alkyl polyglycosides, 3wt% glyceryl monooleate, and 93wt% deionized water were mixed. The formulated composition of the aqueous phase was able to form translucent Winsor Type I microemulsion with palm oil at ambient conditions. The measured interfacial tension between the optimum microemulsion and the model oil, which is n-octane in this study, was mN/m. The maximum tertiary oil recovery of 71.8% was achieved after the injection of the optimum microemulsion formulation to a sand pack. The significant increase in total oil recovery (87%) suggests the effectiveness of the triglyceride microemulsion formulation for enhanced oil recovery. Its capability in recovering additional oil (4.3% of the trapped oil after water flooding) compared to a typical polymer in tertiary oil recovery indicates the efficiency of the optimum triglyceride microemulsion formulation. Introduction Chemical flooding, one of the most successful techniques to enhance oil recovery (Austad and Milter, 2000), involves the injection of a chemical to displace the oil remaining in the reservoir after waterflooding. Microemulsion is one type of formulation, which consists of oil, water, and an amphiphile mixture (Paul and Moulik, 2001). Amphiphile is a substance containing both hydrophilic and hydrophobic parts in its molecular structure. Surfactants and co-surfactants are two examples of amphiphiles. Microemulsion has been used in tertiary oil recovery since the 1970s (Halbert and Inks, 1971; Holm, 1971; Healy et al., 1975; Dreher and Sydansk, 1976; Healy and Reed, 1977; Nelson and Pope, 1978; Glover et al., 1979; Meyers and Salter, 1980; Willhite et al., 1980; Putz et al., 1981; Sayyouh et al., 1991; Osterloh and Jante, 1992; Purwono and Murachman, 2001; Bouabboune et al., 2006; Santanna et al., 2009). A microemulsion slug mobilizes the remaining oil by reducing the interfacial tension (IFT) between oil and water. Microemulsion flooding has been conducted in two distinct ways. In the first method, a microemulsion system is prepared by mixing water, oil, and amphiphile(s) on the surface prior to its injection (Putz et al., 1981; Santanna et al., 2009). In the second method, a microemulsion slug is prepared in the porous media from the formation brine, residual oil, and the injected amphiphile and water (Zhao et al., 2008; Wang et al., 2010). In the 1980s chemical flooding was considered uneconomical due to low oil price, which caused a major halt in scientific publications. On the other hand, in 1990 researchers started to embark on chemical flooding due to the higher oil prices accompanied with the first gulf war. However, at the time microemulsion flooding was not considered as a common chemical flooding. Only recently numerous researchers have started conducting tests to improve microemulsion flooding efficiency by modifying the existing microemulsions in the market or developing a new microemulsion (Iglauer et al., 2009; Wu et al., 2010). It is evident that altering the chemical nature or amount of any component in a microemulsion may result in drastic changes in the IFT, type of microemulsion, and amount of the recovered oil (Kahlweit et al., 1995a; Sottmann and Strey, 1997; Sottmann and Stubenrauch, 2009). New microemulsions were formulated to enhance oil recovery by altering the surfactants and/or co-surfactants (Wang et al., 2010; Iglauer et al., 2010a; Iglauer et al., 2010b); however, the oil-component in the microemulsion prepared on the surface plays an important role not only in the cost of microemulsion preparation but also in the efficiency of the microemulsion flooding due to changes in the IFT. Most researchers in literature used a specific crude oil or a fraction of petroleum such as n-octane as the oil phase of the microemulsion (Putz et al., 1981; Bouabboune et al., 2006).

2 2 SPE Despite extensive attempts made on the formulation of microemulsions with n-alkane or hydrocarbons, there is another attractive option; using triglycerides for the oil phase of the microemulsion. It is not a very common practice in enhanced oil recovery because microemulsions have typically been prepared in situ from the injected chemical slug and the remaining oil in the reservoir. However, microemulsions can be prepared outside before the injection and the oil component of the prepared microemulsion can be either hydrocarbons or triglycerides. The application of a triglyceride microemulsion in tertiary oil recovery was once tested by Santanna et al. (2009) with the use of pine oil (a kind of vegetable oil) as the oil phase of a microemulsion. A great number of triglyceride-based microemulsion formulations have also been carried out in the last decades in applications other than enhanced oil recovery (Kunieda et al., 1988; Joubran et al., 1993; Kahlweit et al., 1995a, 1995b; Hecke et al., 2003; Komesvarakul et al., 2006; Engelskirchen et al., 2007; Do et al., 2009; Fanun, 2010; Phan et al., 2011). Triglycerides are esters of glycerol and three fatty acids. Triglycerides are the major components of palm oil. Triglycerides in palm oil are a mixture of mono-unsaturated, poly-unsaturated, and saturated triglycerides. Compared to n-alkane oil, saturated triglycerides are among the hardest oil to microemulsify since saturated triglyceride molecules have a bulky polar head and three long hydrocarbon chains (Phan et al., 2011). Therefore, the presence of unsaturated triglycerides in palm oil reduces the possibility informing microemulsion. However, if an effective surfactant and a suitable co-surfactant are selected in the microemulsion formulation, an efficient triglyceride microemulsion with low to ultra-low interfacial tensions and a high solubilization parameter could be achieved easily. Various types of surfactants and co-surfactants such as alcohols were used to formulate triglyceride microemulsions in the literature (Kunieda et al., 1988; Joubran et al., 1993; Kahlweit et al., 1995a, 1995b; Hecke et al., 2003; Komesvarakul et al., 2006; Engelskirchen et al., 2007; Do et al., 2009; Fanun, 2010; Phan et al., 2011). The main objective of this paper is to formulate an efficient triglyceride microemulsion on the surface to improve oil production in a tertiary recovery process after its injection. Alkyl polyglycosides was used as the surfactant of the triglyceride microemulsion. In this paper, an attempt has been made to screen and select the most effective co-surfactant from various kinds of co-surfactants such as alcohols and non-ionic surfactants. The highest cumulative tertiary oil recovery and the lowest interfacial tension between the formulated microemulsion and the model oil are the two essential criteria considered in the selection of the co-surfactant. After the co-surfactant screening, the composition of the aqueous phase of the triglyceride microemulsion was optimized to ensure minimum interfacial tension and maximum cumulative tertiary oil recovery are achieved. Finally, the efficiency of the optimum triglyceride microemulsion formulation was compared to a common commercial polymer solution in tertiary oil recovery by conducting a sand pack flooding. In all these steps, the type of the formulated triglyceride microemulsions used is Winsor Type I microemulsion, which exists in equilibrium with the excess palm oil. Experimental tests Materials. The surfactant used in this work was Glucopon 650EC, a mixture of alkyl polyglycosides (APGs) having an average alkyl chain length of 11, hydrophilic-lipophilic balance (HLB) of 11.9, and critical micelle concentration (CMC) of g/l at 37 C (Jurado et al., 2007). It was provided by Cognis (Malaysia) Sdn Bhd which is now part of BASF Chemical Company. The active percentage of the surfactant solution is weight percent (wt%). Sodium chloride (NaCl, A.R. grade) and lower alkanols such as isopropyl alcohol (IPA), isobutyl alcohol (IBA), and normal butyl alcohol (NBA) were supplied by LGC Scientific, Malaysia. In addition, fatty alcohol C8 (FA8), fatty alcohol C8/C10 (FA810), fatty alcohol C12/C14 (FA1214), stearyl alcohol (SA), cetyl alcohol (CA), and ethylene glycol mono-ethyl ether (EGEE) were provided by BCI Chemical Corporation Sdn. Bhd. Furthermore, n-octane, Tween20 (TWN20), Tween80 (TWN80), glycerol (GLY), sorbitan monooleate (SM), glyceryl monooleate (GM), and saponin (SAP) were supplied by Sigma-Aldrich. Palm kernel oil was purchased from Delima Oil Products Sdn. Bhd. in Malaysia. Some properties of the palm kernel oil are tabulated in Table 1. All of the materials were used as supplied without further purification. Triglyceride microemulsion preparation. A triglyceride microemulsion was prepared by mixing 230g of the oil phase with 230g of the aqueous phase. The aqueous phase comprised of surfactant, co-surfactant, sodium chloride, and de-ionized water at various compositions. The oil phase was pure palm oil. After adding all the components at their desired fractions, the sample was shaken with orbital shaking motion. Lab Companion SI-300 Benchtop Shaker at low shaking frequency of 100rpm was used to avoid the appearance of emulsion phase. The triglyceride microemulsion sample was shaken for at least an hour to ensure a well-mixed and uniform mixture because of quite low aqueous solubility of APG, low frequency of mixing, and the relatively large volume of the samples. The sample was then poured into a separating funnel and left undisturbed for at least one week for equilibrium. Since palm oil is a natural component, to avoid the possibility of degradation, sample bottles used during the mixing were sealed with Viton lined screw caps. In addition, separating funnels used in the resting step were sealed with tight lubricated Teflon stopper. The microemulsion phase formed after the equilibrium was Winsor Type I or lower phase microemulsion. Then the microemulsion phase was separated from the upper (excess oil) phase in the separating funnel and was used in the next measurements. Methodology of IFT measurements. Prior to IFT measurements, the density or specific gravity of both the light and heavy phases was determined. The heavy phase was a microemulsion, which is prepared based on the aforementioned methodology

3 SPE and separated from the excess oil phase. The light phase was n-octane, which represents the crude oil in reservoirs (Green and Willhite, 1998). In density measurements, about 1.0 cm 3 of sample was filled into the oscillating U-tube capillary of a Density/Specific Gravity Meter DMA 4500/5000 (Anton Paar, Austria) via syringeat 30 C. Measurement was repeated for all samples of the heavy and light phases. In the next step, interfacial tensions between the heavy and light phases were measured using a Spinning Drop Tensiometer SITE 4 (KRUSS, Germany) at 30 C. As a general procedure, 10 µl of the light phase was injected into the rotating capillary filled with the heavy phase. During the injection, the capillary was rotated at the speed of 1000 to 2000 rpm. The diameter of the droplet was measured at high rotational velocity of 6000 to 8000 rpm after the equilibrium was reached. The system reaches the equilibrium when the diameter of the droplet did not change with time (Drelich et al., 2002). Since in all of the IFT measurements the system reached equilibrium after a very short time of about 10s, the depletion of cosurfactant into the n-octane phase was considered negligible. Measurements were carried out in triplicate. The IFT was estimated using Vonnegut s equation, which relates IFT to the droplet radius, rotational velocity, and the densities of the two phases (Vonnegut, 1942). Table 1 Some Properties of the Palm Kernel Oil Composition (wt%) Monounsaturated fat Polyunsaturated fat Saturated fat Density (g/ml) Viscosity (cp) General structure of triglycerides (Hecke et al., 2003) Sand pack design and microemulsion flooding. Sand pack flooding tests were conducted to investigate the performance of all the formulated microemulsions in oil recovery. The sand used in these experiments was composed of SiO 2 and CaO with particle size of 100mesh or 0.150mm. The sand was packed vertically in a glass sand pack holder 45 cm in length and 5 cm in diameter. Both sides were equipped with stainless steel sieves to prevent any sand flow. The sieve size was 300mesh per inch with sieve opening of 0.053mm. The sand pack was placed horizontally and flooded at atmospheric pressure and room temperature. Fig. 1 shows the experimental setup of the flooding system. The measured properties of the sand pack and floodings are listed in Table 2 (sand pack test #1). Table 2 Summary of the Properties of the Sand Pack Floodings for Sand Pack Test #1 Length 45cm Diameter 5cm Porosity 34% Permeability 25D Pore volume (PV) 299ml Connate water saturation 8% Brine PV (secondary oil recovery) 2 Residual oil ml Flow rate of injections 0.83ml/min Microemulsion PV (tertiary oil recovery) 4 First, brine (1 wt% NaCl) was injected for about 3 pore volumes (PV), followed by 3 PV of n-octane to reach the connate water saturation. For the secondary oil recovery, 2 PV of brine was injected. Then for the tertiary oil recovery, the sand pack was continuously flooded with 4 PV of a prepared triglyceride microemulsion. The flow rates of the injections were kept constant at 0.83ml/min, or about 2 ft/day frontal advance rate in order to mimic real field injection velocities (Iglauer et al., 2010a; Iglauer et al., 2010b; Kumar and Mohanty, 2010). The effluents from the sand pack were collected in sample tubes and the incremental oil recoveries were measured against time by gas chromatography (GC). The gas chromatograph (Agilent Technologies, Model 7890A) was equipped with flame ionization detector (FID) maintained at 300 C. The column was a DB-1 capillary column (J&W, 40m 0.18mm inner diameter 0.4µm film thickness). The column temperature was held at 35 C for 15min, programmed to 70 C at 1.5 C/min and then to 130 C at 30 C/min and held at 130 C for 20min. The carrier gas was helium at speed of 25cm/sec. The amount of recovered oil was quantitatively expressed by the term of cumulative

4 4 SPE tertiary oil recovery, which is the percentage of the volume of produced oil in the tertiary oil recovery step to the volume of residual oil (remaining oil after secondary oil recovery step). The same methodologies of sand pack microemulsion flooding and IFT measurement were conducted for all microemulsion samples to determine the optimum microemulsion formulation. The calculated cumulative tertiary oil recovery and IFT were used as the criteria of selecting the most efficient microemulsion. Fig. 1 Set-up of the experimental flooding system. Co-surfactant screening. The aforementioned methodology of triglyceride microemulsion preparation was applied for various types of co-surfactants, namely IPA, IBA, NBA, TWN20, TWN80, GLY, SM, GM, FA8, FA810, FA1214, SA, CA, EGEE, and SAP at concentrations of 1, 2, 3 and 4wt% of the aqueous phase. The concentration of APG (surfactant) and NaCl were fixed at 1 and 3wt% of the aqueous phase. Cumulative tertiary oil recovery and IFT results were obtained for all of the Winsor Type I microemulsion formulations. The co-surfactant of the microemulsion with the highest tertiary oil recovery and the lowest IFT is selected as the most effective co-surfactant. Optimization of the aqueous phase composition of the triglyceride microemulsion Optimization of salinity. Different microemulsion samples were prepared at various salinities ranging from 0.5 to 12 weight percent of the aqueous phase. The concentration of APG (surfactant) and the selected co-surfactant were fixed at 1 and 2wt% of the aqueous phase. Cumulative tertiary oil recovery and IFT results were obtained for all thewinsor Type I microemulsion formulations. The optimum concentration of NaCl in the aqueous phase is the salinity at which its microemulsion yields the highest tertiary oil recovery and the lowest IFT. Optimization of the co-surfactant concentration. Different microemulsion samples were prepared at various concentrations of co-surfactant ranging from 0.5 to 4 weight percent of the aqueous phase. The concentration of APG was fixed at 1wt% of the aqueous phase. All of the samples were prepared at the determined optimum salinity. Cumulative tertiary oil recovery and IFT results were obtained for all thewinsor Type I microemulsion formulations. The optimum concentration of the cosurfactant in the aqueous phase is the concentration at which its microemulsion yields the highest tertiary oil recovery and the lowest IFT. Optimization of the surfactant concentration. Different microemulsion samples were prepared at various concentrations of surfactant ranging from 0.25 to 2 weight percent of the aqueous phase. The concentrations of co-surfactant and NaCl in the aqueous phase were fixed at their optimum values. Cumulative tertiary oil recovery and IFT results were obtained for all thewinsor Type I microemulsion formulations. The optimum concentration of the surfactant in the aqueous phase is the concentration at which its microemulsion yields the highest tertiary oil recovery and the lowest IFT. Application of the optimum microemulsion formulation. The same flooding procedure mentioned previously was used until the sand pack reached the residual oil saturation after secondary oil recovery by water flooding. In the tertiary recovery, 1 PV of the triglyceride microemulsion with optimized aqueous phase composition was injected to the sand pack, followed by 1 PV of polymer solution (1500ppm xanthan gum in 1 wt% NaCl) to provide mobility control. The viscosity of the polymer solution was 27cP at 30 C and measured using a rotational viscometer (Haake VT550 controlled-rate viscotester, Germany). The viscometer was equipped with a coaxial cylinder sensor system consists of a set of NV cup and stainless steel rotor. Finally 1 PV of brine was injected into the sand pack as the chasing fluid to push all the injected fluids. The flow rates of injections were also kept constant at 0.83ml/min, or about 2ft/day frontal advance rate. The produced oil volume was recorded by GC for both secondary and tertiary oil recovery. The measured properties of the sand pack and floodings are listed in Table 3 (sand pack test #2).

5 SPE Table 3 Summary of the Properties of the Sand Pack Floodings for Sand Pack Test #2 and 3 Sand pack test #2 Sand pack test #3 Length 45cm 45cm Diameter 5cm 5cm Porosity 34% 34% Permeability 25D 25D Pore volume (PV) 299ml 299ml Connate water saturation 8% 8% Brine PV (secondary oil recovery) 2 2 Residual oil ml ml Flow rate of injections 0.83ml/min 0.83ml/min Microemulsion PV (tertiary oil recovery) 1 0 Polymer PV (tertiary oil recovery) 1 4 Viscosity of the polymer solution 27cP 27cP Chasing brine PV 1 0 In the next step, the efficiency of the formulated microemulsion with optimized aqueous phase composition and the same polymer solution (1500ppm xanthan gum in 1 wt% NaCl) in tertiary oil recovery were determined and compared. The same flooding procedure was used until the sand pack reached the residual oil saturation after the secondary oil recovery by water flooding. In the tertiary recovery, the sand pack was continuously flooded with 4 PV of optimum triglyceride microemulsion before being flooded with 4 PV of polymer solution (1500ppm xanthan gum in 1 wt% NaCl).The produced oil was recorded by GC in tertiary oil recovery. The measured properties of the sand pack and floodings are listed in Tables2 and3 (sand pack test #1 for microemulsion flooding and sand pack test #3 for polymer flooding). Results and discussion Co-surfactant screening. Some surfactants do not sufficiently reduce interfacial tension at the oil/water interface to form microemulsions (Myers, 1992).They may not distribute between the aqueous and oil phase properly (Alany et al., 2000). To overcome this, co-surfactant molecules are introduced to sufficiently lower the oil/water interfacial tension, fluidize the rigid hydrocarbon region of the interfacial film, and induce ideal curvature of the interfacial film (Alany et al., 2000). Cosurfactants are molecules with weak surface-active properties that are combined with the surfactants to enhance their ability to reduce the interfacial tension and promote the formation of a microemulsion (Schick, 1987). For a co-surfactant-free triglyceride microemulsion sample, which contains only 1wt% of APG as surfactant and 3wt% NaCl in the aqueous phase, its IFT against n-octane was measured to be mN/m. This value is low but not ultra-low. Thus to reduce the IFT to ultra-low values, it is essential to select an appropriate co-surfactant. Selecting an effective cosurfactant could be the first and the most critical step in synthesizing a triglyceride microemulsion for tertiary oil recovery because the type of co-surfactant might considerably influence the IFT reduction and consequently the tertiary oil recovery efficiency. Figs. 2-6 show the IFT variation of the microemulsion samples with various co-surfactants against n-octane with an increase in the concentration of co-surfactants. Figs show the cumulative tertiary oil recovery of the microemulsion samples with an increase in the concentration of co-surfactants. The whole set of these figures is an indicator of the performance of the co-surfactants used. In general, the observed reduction in IFT with an increase in the volume of the cosurfactants shows good performance of the co-surfactant in reducing the IFT. Increasing of the amount of co-surfactant decreases the hydrophilic-lipophilic balance (HLB) number. The HLB value is an indication of the oil or water solubility of the microemulsion (Griffin, 1949). The HLB value characterizes the relative oil and water solubility of surfactants. Lower HLB number indicates the microemulsion is more oil soluble and vice versa. It is evident that decreasing the HLB number of a nonionic mixture leads to a change in the microstructure of the microemulsion from Winsor Type I to Winsor Type III, and subsequently to Winsor Type II (Wu et al., 2001). While the microstructure is changing, the IFT decreases to a minimum before it starts to increase (Wu et al., 2001). The IFT reaches a minimum in the phase inversion temperature (PIT) point, which is fairly in the middle of Winsor Type III region (Wu et al., 2001). It was observed that for all the co-surfactants except GM, the IFT decreases with the amount of co-surfactant (or decreasing the HLB number). This trend indicates that the microstructure of the microemulsions can be Winsor Type I or Winsor Type III before the PIT at the studied range of co-surfactant. The IFT variation shows a minimum only for GM in co-surfactant range of 1 to 4wt% of the aqueous phase (Fig. 4). The minimum IFT value indicates the appearance of Winsor Type III microemulsion. In other words, the microstructure of the triglyceride microemulsion with co-surfactant of GM is changed from Winsor Type I to Winsor Type III microemulsion in the presence of n-octane. Furthermore, the efficiency of the co-surfactant can also be estimated from the values of either IFT or the tertiary oil recovery.twn80, which yields the highest IFT (Fig.3) and the lowest tertiary oil recovery (Fig. 8) is considered as the worst choice of co-surfactant among the co-surfactants studied. In contrast, GM which yields ultra-low IFT against n-octane (Fig.4) and the highest tertiary oil recovery (Fig. 9) is considered as the most efficient co-surfactant among co-surfactants studied. Therefore, GM is the desired co-surfactant for a triglyceride microemulsion formulation and it is selected to be one of the

6 6 SPE components of the triglyceride microemulsion. An appropriate surfactant blend for formulation of a microemulsion can be selected if the HLB of the candidate surfactant blend (surfactant and co-surfactant) approaches the required HLB of the oily component for a particular system (Schick, 1987). In addition, in the selection of surfactant blend it is more favorable if the lipophilic part of the used surfactant matches the oily component (Prince, 1977). This may be the reason that GM seems to be an effective co-surfactant for a triglyceride microemulsion. Fig. 2 The IFT of microemulsion samples containing the three lower alkanols against n-octane. Fig. 3 The IFT of microemulsion samples containing the Tweens against n-octane. Fig. 4 The IFT of microemulsion samples containing the two monooleates against n-octane.

7 SPE Fig. 5 The IFT of microemulsion samples containing the five fatty alcohols against n-octane. Fig. 6 The IFT of microemulsion samples containing other types of co-surfactants against n-octane. Fig. 7 The cumulative tertiary oil recovery of microemulsion samples containing the three lower alkanols.

8 8 SPE Fig. 8 The cumulative tertiary oil recovery of microemulsion samples containing the Tweens. Fig. 9 The cumulative tertiary oil recovery of microemulsion samples containing the two monooleates. Fig. 10 The cumulative tertiary oil recovery of microemulsion samples containing the five fatty alcohols.

9 SPE Fig. 11 The cumulative tertiary oil recovery of microemulsion samples containing other types of co-surfactants. Optimization of the aqueous phase composition of the triglyceride microemulsion Optimization of salinity. Six microemulsion samples were prepared at salinities of 0.5, 1, 3, 6, 9, and 12wt% of the aqueous phase. In all the samples, the concentration of APG and GM was maintained at 1 and 2wt%, respectively. Fig. 12 shows both the variation of IFT and cumulative tertiary oil recovery with salinity. The IFT values on left-side y-axis of Fig. 12 demonstrate that the IFT of the microemulsion samples against n-octane is fairly constant at various NaCl concentrations. The IFT was observed to be quasi-independent of salinity because the nature of the microemulsion samples is intrinsically nonionic (Kahlweit at al., 1995a; Balzer and Lüders, 2000; Iglauer et al., 2009). The mean of the IFT values was found to be ± mN/m, which is in the ultra-low region (<0.01mN/m). In order to investigate the impact of salinity on the performance of microemulsion flooding in tertiary oil recovery, the sand pack was flushed with all the six microemulsion samples at various salinities individually. The cumulative tertiary oil recovery results on the right-side y-axis of Fig. 12 shows no variation with NaCl concentration. In the other words, the same amount of oil can be attained using microemulsion samples with different salinities. Therefore, the salinity of the microemulsion formulation can be adjusted at any value within the studied range. Thus in this study the salinity of 3wt% NaCl was selected and taken as the optimum salinity of the microemulsion. Fig. 12 IFT of microemulsion samples against n-octane at various salinities (on left-side y-axis); the cumulative tertiary oil recovery of microemulsion samples at various salinities (on right-side y-axis).the concentration of APG and GM was maintained at 1 and 2wt%, respectively. Optimization of co-surfactant concentration. The concentration of GM, the co-surfactant, was also optimized by IFT measurements and microemulsion flooding using8 microemulsion samples at GM concentrations of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, and 4wt% of the aqueous phase. In all of the samples, the concentration of APG and NaCl was kept constant at 1 and 3wt% (optimum salinity), respectively. Fig. 13 shows both the variation of IFT and cumulative tertiary oil recovery with the microemulsion samples at various GM concentrations. The IFT values on left-side y-axis of Fig. 13 decreased to a minimum before it started to increase. In contrast, the cumulative tertiary oil recovery increased to a maximum before it reduced. It is apparent that the point at which the IFT is at its minimum value and tertiary oil recovery efficiency is at its maximum value represents the optimum concentration of GM. Therefore, based on the experimental data obtained, 3wt% GM is selected as

10 10 SPE the optimum concentration of the co-surfactant in the aqueous phase of the microemulsion. Fig. 13 IFT of microemulsion samples against n-octane at various concentrations of GM (on left-side y-axis); the cumulative tertiary oil recovery of microemulsion samples at various concentrations of GM (on right-side y-axis).the concentration of APG and NaCl was kept at 1 and 3wt%, respectively. Optimization of the concentration of surfactant. Eight microemulsion samples were prepared at APG concentrations of 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, and 2wt% of the aqueous phase. In all of the samples, the concentration of GM and NaCl was kept constant at 3 (optimum concentration of co-surfactant) and 3 wt% (optimum salinity), respectively. Both the variation of IFT and cumulative tertiary oil recovery with the microemulsion samples at various APG concentrations are shown in Fig. 14. It was observed that by increasing the APG concentration from 0.25 to 1wt%, the IFT between the microemulsion and n-octane yields to the minimum value of mN/m, while the cumulative tertiary oil recovery reached to the maximum value of 71.8%. When the concentration of APG in the aqueous phase of the microemulsion exceeds 1wt%, the IFT starts to increase and the cumulative tertiary oil recovery starts to decreases continuously. It is obvious that the point at which the IFT and cumulative tertiary oil recovery yield their minimum and maximum values respectively indicates the optimum concentration of APG. Therefore, based on the collected experimental data, 1wt% is selected as the optimum concentration of the surfactant in the aqueous phase of the microemulsion. Fig. 14 IFT of microemulsion samples against n-octane at various concentrations of APG (on left-side y-axis); the cumulative tertiary oil recovery of microemulsion samples at various concentrations of APG (on right-side y-axis).the concentration of GM and NaCl were kept at 3 and 3wt%, respectively. Microemulsion flooding with the optimum microemulsion formulation. The optimum aqueous phase composition of the triglyceride microemulsion is 3wt% NaCl, 3wt% GM, 1wt% APG, and 93wt% de-ionized water. Fig. 15 shows the total

11 SPE cumulative oil recovery in secondary and tertiary recoveries for the triglyceride microemulsion with optimum aqueous phase formulation. The cumulative total oil recovery is the ratio of the produced oil to the initial oil in place (IOIP) expressed as a percentage. The secondary recovery includes water flooding (2PV), and the tertiary recovery includes microemulsion (1PV), polymer (1PV), and water flooding (1PV). Experimental results show that 60.8% of the IOIP was recovered after the secondary recovery with water flooding. About 39.2% of the oil still remained in the sand pack after the initial water flooding. To recover the remaining oil, tertiary recovery was carried out. After the injection of 1PV of microemulsion flooding with optimum aqueous phase formulation and viscosity of 3.3cP, about 46.4% of the remaining trapped oil after the water flooding was recovered. As a result the total cumulative oil recovery increased to about 78% of the IOIP. Then 1PV polymer solution was injected into the sand pack and the total cumulative oil recovery increases to about 84% of the IOIP (59.2% of the trapped oil remaining after water flooding was recovered). Finally, after the injection of 1PV of water, the total cumulative oil recovery reached 87% of the IOIP (66.8% of the trapped oil). The relatively high oil recovery suggests the effectiveness of the optimum triglyceride microemulsion formulation in enhancing oil recovery. Fig. 15 Cumulative total oil recovery in secondary (water flooding) and tertiary (microemulsion, polymer, and water flooding) recoveries. In one of the recent studies on microemulsion formulation (Iglauer et al., 2010b), a microemulsion was prepared from APG, Span20, and n-octane as its surfactant, co-surfactant, and the oil phase, respectively. Injection of the microemulsion into a sand pack resulted in the recovery of 94% of the IOIP (Iglauer et al., 2010b). Although the amount of oil recovery for the triglyceride microemulsion formulation in this work is a bit less than other formulations in the literature, this work is considered crucial as it opens new application of triglyceride microemulsion in tertiary enhanced oil recovery. The new triglyceride microemulsion formulation is also less toxic and more environmentally friendly than other microemulsions with a hydrocarbon or a petroleum fraction as the oil phase (Kahlweit et al., 1995b; Do et al., 2009). The efficiencies of the formulated triglyceride microemulsion with optimized aqueous phase composition and the polymer solution in tertiary oil recovery was investigated by continuous injection (4PV) of the chemical. Fig. 16 shows the recovery results. The cumulative tertiary oil recovery is the ratio of the produced oil to the trapped oil after water flooding (secondary oil recovery) expressed as a percentage. As can be seen in Fig. 16, injection of polymer solution results in higher oil production during the first 1.5 PV than the injection of the microemulsion. This is due to the viscosity difference of the injected microemulsion and polymer. The viscosities of the injected microemulsion and the polymer solution are 3.3cP and 27cP, respectively. Both viscosities are sufficient to sweep oil (with viscosity of 0.55cP) and brine (with viscosity of 1cP). However, because of the higher mobility ratio of polymer compared to microemulsion, higher oil recoveries were observed in the first 1.5 PV of chemical injection. Since the viscosity of polymer solution is higher than microemulsion, it seems the polymer slug moved within the sand pack like a plug flow. The amount of produced oil was less in polymer flooding than microemulsion flooding during further injection of the chemical slug from 1.5 PV up to 4PV. Unlike polymer, the flow of the microemulsion inside the sand pack does not follow plug flow. However, because the triglyceride microemulsion is capable of solubilizing the remaining oil beside sweeping it, the final tertiary oil recovery for microemulsion flooding (71.8% of the trapped oil after water flooding) was found to be higher than that of polymer flooding (67.5% of the trapped oil after water flooding). Therefore, microemulsion flooding tends to recover an additional 4.3% of the trapped oil compared to a polymer flooding.

12 12 SPE Fig. 16 Cumulative tertiary oil recovery in continuous microemulsion and polymer floodings. Conclusions The results of this study showed that palm oil could be used as an oil phase in the formulation of a pre-prepared triglyceride microemulsion for enhanced oil recovery. This is true when the aqueous phase contains APG as its surfactant, and GM as its co-surfactant. A triglyceride microemulsion could be obtained by equal mixing of the oil and aqueous phase, shaking, and standing for 1 week. The aqueous phase composition of the triglyceride microemulsion was optimized to achieve the lowest interfacial tension and highest tertiary oil recovery. Optimum composition of the aqueous phase was found to be 1wt% APG, 3wt% NaCl, 3wt% GM, and 93wt% de-ionized water. The measured IFT between the triglyceride microemulsion at the optimum aqueous phase composition and n-octane is mN/m. This value is considered ultra-low. The cumulative tertiary oil recovery reached to a maximum value of 71.8% by the continuous injection of the triglyceride microemulsion at the optimum aqueous phase composition. Furthermore, the total oil recovery of 87% after the secondary and tertiary oil recovery suggests the feasibility in the application of the optimum triglyceride microemulsion formulation. The oil recovery efficiency for the formulated microemulsion is considered comparable. Finally, based on the sand pack flooding tests conducted in this study, the formulated triglyceride microemulsion is able to recover 4.3% additional oil than a typical polymer in tertiary oil recovery. Acknowledgements The authors would like to acknowledge the financial support of the Bright Sparks Program at University of Malaya. They also would like to acknowledge the support of University of Malaya IPPP grant, project number: PV021/2011B. Appreciation also goes to BCI Chemical Corporation Sdn. Bhd. for providing the flooding set-up. References Alany, R. G., Rades, T., Agatonovic-Kustrin, S., Davies, N. M., and Tucker, I. G Effects of alcohols and diols on the phase behaviour of quaternary systems. International Journal of Pharmaceutics 196(2): Austad, T. and Milter, J Surfactant Flooding in Enhanced Oil Recovery. In Surfactants- Fundamentals and Applications in the Petroleum Industry, L.L. Schramm, 203. Cambridge, UK: Cambridge University Press. Balzer, D. and Lüders, H Nonionic Surfactants: Alkyl Polyglycosides, Surfactant Science Series, 91. New York: Marcel Dekker, Inc. Bouabboune, M. et al Comparison between Microemulsion and Surfactant Solution Flooding Efficiency for Enhanced Oil Recovery in TinFouyé Oil Field. PAPER presented at the Petroleum Society s 7 th Canadian International Petroleum Conference and 57 th Annual Technical Meeting, Calgary, Alberta, June Do, L.D., Withayyapayanon, A., Harwell, J.H., and Sabatini, D.A Environmentally friendly vegetable oil microemulsions using extended surfactants and linkers. Journal of Surfactants and Detergents 12(2): Dreher, K.D. and Sydansk, R.D Observation of Oil-Bank Formation During Micellar Flooding. Paper SPE 5838 presented at the SPE Oil Recovery Symposium, Tulsa, Oklahoma, March Drelich, J., Fang, Ch., and White, C.L Measurement of Interfacial Tension in Fluid-Fluid Systems. In Encyclopedia of Surface and Colloid Science, P. Somasundaran, New York: Marcel Dekker, Inc. Engelskirchen, S., Elsner, N., Sottmann, T., and Strey, R Triacylglycerol microemulsions stabilized by alkyl ethoxylate surfactantsa basic study. Phase behavior, interfacial tension and microstructure. Journal of Colloid and Interface Science 312(1): Fanun, M Formulation and characterization of microemulsions based on mixed nonionic surfactants and peppermint oil. Journal of Colloid and Interface Science 343(2): Glover, C.J., Puerto, M.C., Maerker, J.M., and Sandvik, E.L Surfactant Phase Behavior and Retention in Porous Media. SPE Journal 19(3): Green, D.W. and Willhite, G.P Enhanced Oil Recovery, SPE Textbook Series, Vol. 6. Texas, USA: Society of Petroleum Engineers. Griffin, W.C Classification of Surface-active Agents by HLB. Journal of the Society of Cosmetic Chemists 1: Halbert, W.G. and Inks, C.G Miscible Waterflooding Using a Phosphate Ester Solubilizer. Paper SPE 3697 presented at the SPE 42 nd Annual California Regional Meeting, Los Angeles, California, 4-5 November

13 SPE Healy, R.N. and Reed, R.L Immiscible Microemulsion Flooding. SPE Journal 17(2): Healy, R.N., Reed, R.L., and Carpenter, C.W A Laboratory Study of Microemulsion Flooding. SPE Journal 15(1): Hecke, E.V., Catté, M., Poprawski, J., Aubry, J.M., and Salager, J.L A novel criterion for studying the phase equilibria of non-ionic surfactant-triglyceride oil-water systems. Polymer International 52(4): Holm, L.W Use of Soluble Oils for Oil Recovery. Journal of Petroleum Technology 23(12): Iglauer, S., Wu, Y., Shuler, P., Tang, Y., and Goddard III, W.A Alkyl polyglycoside surfactant-alcohol cosolvent formulations for improved oil recovery. Colloids and Surfaces A 339(1-3): Iglauer, S. et al. 2010a. Alkyl Polyglycoside/1-naphthol Formulations with Ultra-low Interfacial Tensions Against N-octane for Enhanced Oil Recovery. Paper SPE presented at the SPE EUROPEC/EAGE Annual Conference and Exhibition, Barcelona, Spain, June Iglauer, S., Wu, Y., Shuler, P., Tang, Y., and Goddard III, W.A. 2010b. New surfactant classes for enhanced oil recovery and their tertiary oil recovery potential. Journal of Petroleum Science and Engineering 71: Joubran, R.F., Cornell, D.G., and Parris, N Microemulsions of triglyceride and non-ionic surfactant- effect of temperature and aqueous phase composition. Colloids and Surfaces A 80(2-3): Jurado, E., Bravo, V., Luzόn, G., Fernández-Serrano, M., García-Román, M., Altmajer-Vaz, D., and Vicaria, J.M Hard-Surface Cleaning Using Lipases: Enzyme-Surfactant Interactions and Washing Tests. Journal of Surfactants and Detergents 10: Kahlweit, M., Busse, G., and Faulhaber, B. 1995a. Preparing microemulsions with alkyl monoglycosides and the role of n-alkanols. Langmuir 11(9): Kahlweit, M., Busse, G., Faulhaber, B., and Eibl, H. 1995b. Preparing nontoxic microemulsions. Langmuir 11(11): Komesvarakul, N., Sanders, M.D., Szekeres, E., Acosta, E.J., Faller, J.F., Mentlik, T., Fisher, L.B., Nicoll, G., Sabatini, D.A., and Scamehorn, J.F Microemulsions of triglyceride-based oils: The effect of co-oil and salinity on phase diagrams. Journal of Cosmetic Science 57(4): Kumar, R. and Mohanty, K.K ASP Flooding of Viscous Oils. Paper SPE presented at the SPE Annual Technical Conference and Exhibition, Florence, Italy, September Kunieda, H., Asaoka, H., and Shinoda, K Two types of surfactant phases and four coexisting liquid phases in a water/nonionic surfactant/triglyceride/hydrocarbon system. Journal of Physical Chemistry 92(1): Meyers, K.O. and Salter, S.J The Effect of Oil Brine Ratio on Surfactant Adsorption from Microemulsions. SPE Journal 21(4): Myers, D Surfactant Science and Technology, 152. New York: VCH Publishers. Nelson, R.C. and Pope, G.A Phase Relationships in Chemical Flooding. SPE Journal 18(5): Osterloh, W.T., Jante, M.J., Surfactant-Polymer Flooding With Anionic PO/EO Surfactant Microemulsions Containing Polyethylene Glycol Additives. Paper SPE presented at the SPE 8 th Symposium on Enhanced Oil Recovery, Tulsa, Oklahoma, April Paul, B.K. and Moulik, S.P Uses and applications of microemulsions. Current Science 80(8): Phan, T.T., Attaphong, C., and Sabatini, D.A Effect of Extended Surfactant Structure on Interfacial Tension and Microemulsion Formation with Triglycerides. Journal of the American Oil Chemists Society 88(8): Prince, L. M Formulation. In Microemulsions: Theory and Practice, L.M. Prince, New York: Academic Press. Purwono, S. and Murachman, B Development of Non Petroleum Base Chemicals for Improving Oil Recovery in Indonesia. Paper SPE presented at the SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, Indonesia, April Putz, A., Chevalier, J.P., Stock, G., and Philippot, J A Field Test of Microemulsion Flooding, Chateaurenard Field, France. Journal of Petroleum Technology 33(4): Santanna, V.C., Curbelo, F.D.S., Castro Dantas, T.N., Dantas Neto, A.A., Albuquerque, H.S., and Garnica, A.I.C Microemulsion flooding for enhanced oil recovery. Journal of Petroleum Science and Engineering 66(3-4): Sayyouh, M.H. et al Design of a Microemulsion Slug for Maximizing Tertiary Oil Recovery Efficiency. Paper SPE Schick, M.J Nonionic Surfactants Physical Chemistry, 447. New York: Marcel Dekker. Sottmann, T. and Strey, R Ultralow interfacial tensions in water n-alkane surfactant systems. Journal of Chemical Physics 106(20): Sottmann, T. and Stubenrauch, C Phase Behaviour, Interfacial Tension and Microstructure of Microemulsions. In Microemulsions: Background, New Concepts, Applications, Perspectives, C. Stubenrauch. Chichester, UK: John Wiley & Sons, Ltd. Vonnegut, B Rotating Bubble Method for the Determination of Surface and Interfacial Tensions. Review of Scientific Instruments 13(1): 6-9. Wang, D. et al Novel surfactants that attain ultra-low interfacial tension between oil and high salinity formation water without adding alkali, salts, co-surfactants, alcohol and solvents. Paper SPE presented at the SPE EOR Conference at Oil & Gas West Asia, Muscat, Oman, April Willhite, G.P., Green, D.W., Okoye, D.M., and Looney, M.D A Study of Oil Displacement by Microemulsion Systems- Mechanisms and Phase Behavior. SPE Journal 20(6): Wu, B., Cheng, H., Childs J.D., and Sabatini, D.A Surfactant-Enhanced Removal of Hydrophobic Oils from Source Zones. In Physicochemical Groundwater Remediation, J.A. Smith and S.E. Burns, 246. New York: Plenum Publishers. Wu, Y., Iglauer, S., Shuler, P., Tang, Y., and Goddard, W.A Branched Alkyl Alcohol Propoxylated Sulfate Surfactants for Improved Oil Recovery. Tenside Surfactants Detergents 47(3): Zhao, P., Jackson, A.C., Britton, C., Kim, D.H., Britton L.N., Levitt, D.B., Pope, G.A., Development of High-Performance Surfactants for Difficult Oils. Paper SPE presented at the SPE Improved Oil Recovery Symposium, Tulsa, Oklahoma, USA, April