By: Wan Mohd Shaharizuan b. Mat Latif 831107115535 / MY131031

From SPE-159700

“A New Family of Anionic Surfactants for Enhanced Oil Recovery Applications” Bo Gao, Upstream Research Company at ExxonMobil, and Mukul M. Sharma, University of Texas at Austin

OBJECTIVE OF THIS RESEARCH: 1. To compare the interfacial properties between

conventional surfactant and seven different anionic Gemini surfactants; different length of hydrophobic tail and linking spacer towards reducing IFT and static adsorption and retention.

2. To find the best Gemini surfactant among 7 types.

3. Discuss the IFT, phase behavior (precipitation) and adsorption behavior of Gemini surfactants series.

PROBLEM OF NORMAL SURFACTANT FLOODING: 1. High concentration of surfactant (0.2 ~ 2% wt or

2000 ~ 20,000 ppm) to achieve CMC. 2. High adsorption on rock which loss the surfactant. 3. High retention on rock which loss the surfactant. 4. Less effective in high temperature (85~120oC) and

high salinity (up to 200,000 mg/L) and hard to find surfactant at low salinity (below 5000 mg/L). Therefore, it’s hard to find surfactants for producing ultra low crude oil/water IFT at this reservoir conditions.

CONVENTIONAL ANIONIC SURFACTANT: 1. Anionic surfactant are most widely used in chemical EOR process because low adsorption on sandstone rock whose surface charge is negative. 2. Nonionic primarily serve as co-surfactant to improve system phase behavior. 3. Quite often, a mixture of anionic and nonionic is used to increase the tolerance to salinity. 4. Cationic surfactants can strongly adsorb in sandstone rock, therefore they used in the carbonate rock to change the wettability from oil wet to water wet. (Sheng, J. 2011).

RECENT ADVANCED SURFACTANT FLOODING FOR HARSH CONDITION RESERVOIR WITH LARGE HYDROPHOBIC :

1. Dimeric / Gemini surfactants (Iglauer et al, 2010; Gao et al, 2012,

Wei, 2012; Zana, 2002; Bae et al, 1989). 2. Polymeric surfactants (Wang et al, 2010; Elraies et al, 2011; Zhang

et al, 2010; Zeron et al, 2012). 3. Oligometric surfactants. 4. Guerbet alkoxy sulfates. 5. Guerbet alkoxy carboxylates (Lu et al, 2012; Adkins et al, 2012). 6. Alkoxy carboxylates and/or sulfonates (Weerasooriya et al, 2012;

Berger et al, 2007, 2009).

To the best of our knowledge, these surfactants are not being utilized in commercial applications till now; nevertheless, the price of surfactant is still too high. Therefore, new surfactants types and techniques must be developed for an economically viable EOR process. (SPE169051-MS).

GEMINI SURFACTANT: 1. Gemini surfactant consist of two

covalently linked “conventional” surfactants by means of a spacer.

2. The hydrocarbon tail can vary in length, the spacer group can be flexible or rigid, hydrophilic or hydrophobic, the polar group can be anionic, cationic, nonionic or zwitterionic.

3. This Gemini surfactants have significant water solubility, form micelles, substantially reduce the surface tension, and exhibit more interesting rheological properties behavior.

GEMINI SURFACTANT EXPERIMENT METHODS: 1. Gemini surfactant solutions are prepared by weighing the surfactant

in distilled water and stirring with a magnetic stirrer at the desired experimental temperature.

2. The oil phase used in IFT measurements was pure hydrocarbons purchased from Sigma Aldrich.

3. Salt that used to make the brine (NaCl, CaCl2) were obtained from the Fisher Chemical and used as received.

4. Then, blend the surfactants at reservoir temperature using equal volumes of reservoir brine and crude oil.

5. Recorded the Krafft temperature and CMC for each Gemini surfactants and changed for different temperature.

6. Measured the IFT of after increased the temperature. 7. Changed the alkyl length and recorded the IFT. 8. Changed the salinities of monovalent and divalent ions and recorded

the change of IFT, adsorption and phase behavior (precipitation). 9. Changed the spacer length and recorded the adsorption. 10. Recorded all data.

RESULT AND DISCUSSION (NORMAL VS. 7 GEMINI SURFACTANTS:

1. The solubility of ionic surfactants is commonly characterized by the Krafft temperature, Tk which is the minimal temperature at which surfactants form micelles. 2. Anionic Gemini surfactants synthesized in the current study have Tk lower than 20oC (Gao 2012). 3. The low Tk of these surfactants can be explained by the concept of hydrophilic/lipophilic balance (HLB) (Becher 1984). 4. Although bearing the same tail carbon chain and head group, the Gemini surfactants show much higher HLB values and thus correspondingly better aqueous solubility, compared with conventional counterparts.

THE KRAFFT POINT:

1. Below the Krafft point the solubility of the surfactants is too low for micellization so solubility alone determines the surfactant monomer concentration.

2. As temperature increase the solubility increases until at Tk the CMC is reached. At this temperature a relatively large amount of surfactant can be dispersed in micelles and solubility increases greatly.

3. Above the Krafft point maximum reduction in surface or IFT occurs at the CMC because the CMC then determines the surfactants monomer concentration.

HYDROPHILE–LIPOPHILE BALANCE (HLB)

1. The hydrophile–lipophile balance (HLB) has been used to characterize surfactants. This number indicates relatively the tendency to solubilize in oil or water and thus the tendency to form water-in-oil or oil-in-water emulsions. Low HLB numbers are assigned to surfactants that tend to be more soluble in oil and to form water-in-oil emulsions. When the formation salinity is low, a low HLB surfactant should be selected. Such a surfactant can make middle-phase microemulsion at low salinity. When the formation salinity is high, a high HLB surfactant should be selected. Such a surfactant is more hydrophilic and can make middle-phase microemulsion at high salinity. 2. Surfactants HLB is determined by calculating values for the different regions of the molecule, as described by Griffin (1949, 1954). Other methods have been suggested, notably by Davies (1957). Griffin’s equation to calculate HLB for nonionic surfactants is

HLB = 20 MWh / MW where MWh is the molecular mass of the hydrophilic portion of the molecule, and MW is the molecular mass of the whole molecule, giving a result on an arbitrary scale of 0 to 20. An HLB value of 0 corresponds to a completely hydrophobic molecule, and a value of 20 corresponds to a molecule made up completely of hydrophilic components. The HLB value can be used to predict the following surfactant properties: ● A value from 0 to 3 indicates an antifoaming agent. ● A value from 4 to 6 indicates a W/O emulsifier. ● A value from 7 to 9 indicates a wetting agent. ● A value from 8 to 18 indicates an O/W emulsifier. ● A value from 13 to 15 is typical of detergents. ● A value of 10 to 18 indicates a solubilizer or hydrotrope. (Sheng, J. 2011).

CRITICAL MICELLE CONCENTRATION:

1. Another important characteristic of a surfactant is critical micelle concentration (CMC) which show the effectiveness of the surfactant.

2. It is defined by minimum concentration of surfactant (mg/L) to get the minimum IFT between oil and water (dynes/cm).

3. The standard IFT of waterflooding is from 10-30 dynes/cm and the Gemini surfactant must be reduce to 0.001 dynes/cm or less.

CRITICAL MICELLE CONCENTRATION:

1. Upon reaching CMC, any further addition of surfactants will just increase the number of micelles (in the ideal case), as shown in Figure 7.1. In other words, before reaching the CMC, the surface tension decreases sharply with the concentration of the surfactant.

2. After reaching the CMC, the surface tension stays more or less constant. (Sheng, J. 2011).

EFFECT OF TEMPERATURE ON IFT GEMINI SURFACTANTS:

1. The IFT of Gemini surfactants decreased from 1 to less than 0.001 dyne/cm when the temperature increased from 55oC to 85oC.

2. Obviously, even at an extremely low concentration level, Gemini surfactants (at least for the 18-4-18 molecule), are still capable of reducing the IFT to ultralow levels (less than 0.001 dyne/cm).

3. In all measurements that follow, a surfactant concentration of 0.02 wt% (approximately 200 mg/L) will be used to make sure we stay safely above CMC, and in the meantime still remain much lower than concentration typically used in a conventional surfactants.

IMPACT OF ALKYL LENGTH ON IFT:

1. As the alkyl chain get longer, we see a gradual decrease in IFT. 2. Indeed, as the hydrophobes get larger, the HLB is adjusted in such a

way that the surfactant molecule become more lipophilic, and thus have a higher tendency to move from the bulk aqueous phase onto the oil/water interface.

3. Once there, they can orient themselves so that the large hydrophobes point toward the oil phase to reduce the free energy of the system.

IMPACT OF MONOVALENT SALT (NaCl) CONCENTRATION TOWARD IFT:

1. Figure 8 show the positive impact of a higher NaCl concentration on lowering the tension of an oil/water interface.

2. The solubility of Gemini surfactants in highly saline solutions should be noted. As more NaCl is added, the IFT steadily goes down.

1. Divalent ions such as Ca2+ and Mg2+ are more efficient in driving surfactant molecules onto the oil/water interface than monovalent ions.

2. Most conventional EOR surfactants do not work well at high concentrations of divalent ions, often showing precipitation or phase separation upon the addition of Ca2+ and Mg2+ to their aqueous solutions.

3. First and most importantly, no solubility problems were encountered in these test, even when the CaCl2 when as high as 4%.

4. The addition of divalent ions help further reduce the IFT, and ultralow IFT observed.

IMPACT OF DIVALENT SALT (CaCl2) CONCENTRATION TOWARD IFT:

IMPACT OF SALINITY ON PRECIPITATION (PHASE BEHAVIOR):

1. Even a salinity as high as 20 wt%, no phase separation or precipitation take place, showing the high salinity (and/or hardness) of this molecule. 2. No obvious transition in microemulsion appearance (volume and color) was observed from low to high surfactant concentrations because no visually discernible middle phase can be identified across the board.

ADSORPTION COMPARISON

1. Maximal adsorption densities of the three surfactants follow the trend of 16-4-16 < SHS < S13-C.

2. First of all, Gemini surfactants are much more hydrophilic than their conventional counterparts. Therefore, they will have a higher tendency to go into the bulk aqueous phase than conventional surfactants, which makes it more difficult for Gemini to get adsorbed at the solid surface.

3. Second, the two sulfate head groups in one molecule make a Gemini effectively a bifunctional ion.

4. Therefore, one Gemini molecule can potentially interact with more than two adsorption sites on the solid surface, and thus saturate the adsorption sites more efficiently.

5. However, the different is only little compared with other two conventional surfactants.

EFFECT OF SPACER LENGTH ON THE ADSORPTION OF GEMINIS:

1. As can be seen on above figure, the molecule with a shorter space has a smaller plateau adsorption density for basically the same reason mentioned previously; stronger intermolecular interactions and reduced solubility.

2. Longer spacer groups promote surfactant adsorption.

CONCLUSION:

1. These 7 molecules of anionic Gemini surfactants showed excellent aqueous stability even in high salinity and hard brines.

2. The IFT of Gemini surfactants decreased from 1 to less than 0.001 dyne/cm when the temperature increased from 55oC to 85oC.

3. As the alkyl chain get longer, we see a gradual decrease in IFT.

4. As the salinity of monovalent ion increased, IFT decreased (same effect with conventional surfactant).

5. As the salinity of divalent ion increase, IFT also decreased (contrast effect with conventional surfactant).

6. Even with extremely high concentration of NaCl (up to 20 wt%) and or CaCl2 (up to 5 wt%), no phase separation or precipitation of any kind was observed for all the samples prepared.

7. Showed lower maximal adsorption densities than the conventional single chain surfactants. However, the amount is quite small (1~2 mg/g).

CONCLUSION (continued):

8. With increasing brine salinity, at a fixed temperature, the CMC decreased. 9. Only used 0.02% (200 ppm) of Gemini Surfactant to achieve CMC, compared with conventional surfactant (0.2 ~ 2% wt or 2000 ~ 20,000 ppm). 10. The molecular interaction between Gemini and conventional surfactants provides mutual benefits that contribute to aquoues stability and interfacial activity. This leads to a new possibility of making use of Gemini surfactants as co-solvents that help improve the performance of the surfactant mixture. 11. All the Gemini surfactant synthesized are very hydrophilic. 12. The HLB could be further adjusted through modifications to the tail length and changes in the head group for better performance. 13. Gemini surfactant shows a lower plateau adsorption density than conventional EOR surfactants. 14. Lower adsorption can be achieved by decreasing the solution salinity.

RECOMMENDATION:

1. Due to the potential of using this surfactant at low concentration and in harsh reservoir conditions (high T and salinity – commonly encountered in oil reservoirs around the world), it’s compulsory to do the lab core analysis as to measure the oil recovery before propose to pilot field test.

2. Besides, the table 2 data also inaccurate for the Krafft point comparison, due to Gemini surfactant used year 2001 data but the conventional surfactant used 1971 data. (Supposedly to do at the same time for better apple to apple comparison).

OTHER REFERENCES: Adkins, S., et al. 2010. A New Process for Manufacturing and Stabilizing High Performance EOR Surfactants at Low Cost for High Temperature, High Salinity Oil Reservoir. Paper SPE 129923 presented at the SPE Improved Recovery Symposium, Tulsa, Oklahoma, USA, 24-28 April 2010. Li, Y., et al. 2014. Mixtures of Anionic-Cationic Surfactants: A New Approach for Enhanced Oil Recovery in Low Salinity, High Temperature Sandstone Reservoir. Paper SPE 169051-MS presented at the SPE Improved Recovery Symposium, Tulsa, Oklahoma, 12-16 April 2014. Liu, S. 2007. Alkaline Surfactant Polymer Enhanced Oil Recovery Process, MS Thesis, The University of Rice at Houston, Texas, January 2008. Noll, L.A. 1991. The Effect of Temperature, Salinity, and Alcohol on the Critical Micelle Concentration of Surfactants. Paper SPE 21032-MS was prepared for presentation at the SPE International Symposium of Oilfield Chemistry held in Anaheim, California, 20-22 February 1991. Sheng, J. 2011. Modern Chemical Oil Recovery, USA: Gulf Professional Publishing.

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