Synthesis of Iron Oxide (Fe 2 O 3 )-Xanthan Gum Nanoparticle Composites Its Potential as a Chemical Flooding Media in Enhanced Oil Recovery (EOR)

Increasing oil consumption in Indonesia encourages an improvement of production using chemical flooding of Enhanced Oil Recovery (EOR) technology. Chemical flooding is an injection method of materials based on polymer and nanoparticles such as α-Fe 2 O 3 -xanthan gum nanocomposite into the reservoir. In this study, α-Fe 2 O 3 nanoparticles were synthesised and then blended to xanthan gum by sonochemical method through an ex-situ process. The α-Fe 2 O 3 -xanthan gum nanocomposite X-ray diffraction (XRD) shows that there are no additional peaks. Only the α-Fe 2 O 3 and the xanthan gum peaks are detected with the crystallite size of around 16-20 nm. The particle size of α-Fe 2 O 3 -xanthan gum (1:1) nanocomposite as measured by Particle Size Analyzer (PSA) was 228.43 nm with the type of polydisperse. The functional group of the nanocomposite is a combination of the α-Fe 2 O 3 and xanthan gum functional groups which shows there are no other compounds detected in IR spectra. The EOR test showed that xanthan gum had a significant effect on increasing the viscosity of the α-Fe 2 O 3 -xanthan gum nanofluid to 1.964 cP at a 1:2 composition. Based on these results, α-Fe 2 O 3 -xanthan gum nanofluid is the potential material used in the chemical flooding process in the reservoir.


INTRODUCTION
Demands for crude oil in Indonesia will increase with total population growth. However, from 2018 until 2021 there was a decline in crude oil production in Indonesia. This contrasts with an increase in the number of crude oil imports from 2020 to 2021. Indonesia has imported crude oil by 20.14% in 2021 to meet domestic needs (ESDM, 2022). Although, this oil production can still be increased with the Enhanced Oil Recovery (EOR) technology. In oil fields in the United States, EOR technology can increase oil production by 30-60 % more than the total conventional methods (Gov, 2022).
Chemical injection is one type of EOR method by inserting a fluid containing chemical substances into the reservoir. These chemicals include polymers such as xanthan gum or hydrolyzed polyacrylamide (HPAM) and nanoparticles such as Fe2O3, Fe3O4, TiO2, andSiO2 (Jiang et al., 2014: Ali et al., 2015).
Polymer addition will increase the viscosity of working fluid to reduce water permeability due to mechanical entrapment. This will make a good mobility ratio to move the oil from the reservoir to the production well (Kamal et al., 2015). The addition of nanoparticles based on metal catalysts in a working fluid can significantly reduce oil viscosity (Zhao et al., 2021). Nanoparticles also have changed the wettability of the reservoir rock, decreased interfacial tension (IFT) between water and oil, and increased the viscosity of working fluid from previous research (Cheraghian, Rostami, & Afrand, 2020).
The development of chemical flooding materials in EOR technology continues to combine nanoparticles with polymersurfactants. Previous research that has been reported by  showed an increase in oil recovery efficiency by 27% with the addition of Fe3O4 nanoparticles to fluids CTAB. This occurs due to changes in the wettability of the reservoir rock surface which was previously wet with oil to become wet with water. This change allows oil droplets trapped on the rock surface to be solvated by Fe3O4-CTAB material and can be carried out of the reservoir (Pereira, et al., 2020). This phenomenon also occurs in the study of Saha et al, the reetha-xanthan gum-Si material succeeded in increasing the oil recovery efficiency by 24.97% by reducing the wettability of contact angle and IFT, as well as the increasing viscosity of the working fluid (Saha et al., 2019). Furthermore, the study of PAM-grafted-TiO2 material by Corredor et al., can increase oil recovery by 2% compared to using only HPAM as polymer flooding (Corredor et al., 2019). In addition, the incorporation of nanoparticles with surfactants or polymers can also prevent the occurrence of blocking in the pores of the reservoir rock by the aggregation of solid nanoparticles (Gbadamosi, et al., 2021;Rellegadla, et al., 2018).
Fe2O3 nanoparticles studied by Joonaki and Ghanaatian, showed that this material reduces the contact angle of the wettability of the rock by 32 ∘ and lowers the oil-water surface tension from 38.5 dyne/cm to 2.75 dyne/cm. Chemical injection with Fe2O3 nanoparticles can increase the oil recovery from 56.6% to 73.6% (Joonaki & Ghanaatian, 2014). Another material that is often used in chemical injections is xanthan gum. In the study of Jang, et al., xanthan gum can increase the viscosity of the working fluid at room temperature up to 27.8 cp. This figure is much higher than HPAM which is only 10.0 cp (Jang et al., 2014). This increase in viscosity can reduce the permeability of the rock in the reservoir. This reduces the mobility of the working fluid so that it can better push out the oil that is still trapped in the reservoir rock (Jang et al., 2014;(Jang, Zhang, Chon, & Choi, 2014;Rellegadla, et al., 2018). Xanthan gum polymers can also reduce the surface tension (IFT) between oil and water from 19.8 mN/m to 17.2 mN/m (Gbadamosi, et al., 2021).
Research on α-Fe2O3 nanoparticles modified by polymers, especially xanthan gum, has not been widely developed for EOR technology. Therefore, this research will focus on the synthesis of α-Fe2O3xanthan gum nanocomposite. The stages of this research are divided into three, the first is to synthesize α-Fe2O3 nanoparticles. The second part is the mixing of α-Fe2O3 nanoparticles with xanthan gum in the form of composites and nanofluids. The third part is to analyze the effect of mass composition on α-Fe2O3-xanthan gum nanocomposite on changes in viscosity of working fluid and oil.

Synthesis of ɑ-Fe2O3-Xanthan Gum Nanocomposite
The process of synthesizing ɑ-Fe2O3xanthan gum nanocomposite was carried out using a sonochemical that has been proposed by (Hassanjani-Roshan, Vaezi, Shokuhfar, & Rajabali, 2011) with reflux methods. The FeCl3.6H2O (0.1 M) and NaOH (0.1 M) were dissolved in 50 mL of aquadest separately. The NaOH solution dripped slowly into the FeCl3 solution. Then the analyte was sonicated for 30 minutes at 30 C. The solids formed were filtered and dried for 15 minutes at 105 C. Then annealed for 1 hour at 500 C to obtain ɑ-Fe2O3. The ex-situ method was applied to synthesis nanocomposite by mixing the synthesized ɑ-Fe2O3 nanoparticle with xanthan gum in 50 mL of ethanol (mass ratio ɑ-Fe2O3: xanthan gum is 1:1, 2:1, and 1:2) (T. Hanemann and D. V. Szabó, 2010). The mixture was reflux at 65 C for 1 hour and filtered to form ɑ-Fe2O3-xanthan gum nanocomposite.

Nanofluids Preparation
The ɑ-Fe2O3-xanthan gum nanocomposite, ɑ-Fe2O3 nanoparticle, and xanthan gum were dissolved into 100 mL of aquadest with a concentration of 1000 ppm and sonicated for 90 minutes.

Viscosity Measurements
The rotor 0 of NDJ-8s Viscometer was inserted into nanofluids with angular velocity from 30 to 60 rpm. The values of viscosity that are detected by the instrument were recorded.

Identification of ɑ-Fe2O3-Xanthan Gum Nanocomposite and Its Crystallite Size with X-Ray Diffraction (XRD).
The results of ɑ-Fe2O3-xanthan gum nanocomposite that was characterized by XRD can be seen in Figure 1. The pattern of XRD spectrum shows that ɑ-Fe2O3-xanthan gum nanocomposite is a combination of peaks ɑ-Fe2O3 and xanthan gum. The 2θ positions of ɑ-Fe2O3 corresponded to previous research by (Hassanjani et al., 2011) and JCPDS no. 01-105. Indicates that the ɑ-Fe2O3 nanoparticle was successfully synthesized before it is mixed with xanthan gum. However, xanthan gum just has one broad peak at 19.5° which means that xanthan gum is an amorphous polymer. The ɑ-Fe2O3-xanthan gum nanocomposite main spectrum is at positions 24, 33, 35.5, dan 40.7°, describing ɑ-Fe2O3 as a majority structure in nanocomposite for all composition mass. Furthermore, exceeding the mass of xanthan gum in the composite will increase amorphous phase in 1:2 composition (ɑ-Fe2O3: xanthan gum) in the presence of a spectrum at 19,6˚. No other diffraction arises from the impurity compound other than ɑ-Fe2O3 or xanthan gum as shown in Figure 1. Therefore, the crystallinity of the synthesized ɑ-Fe2O3-xanthan gum nanocomposite has a high degree of purity (Ali, Manshad, Imani, Sajadi, & Keshavarz, 2020).
Based on the Scherrer equation, obtained the size of the crystallites in each solid as shown in Table 1 (Mustapa et al., 2019). The crystallite size of ɑ-Fe2O3 nanoparticle has decreased from 19.2 nm to 13.18 nm in ɑ-Fe2O3-xanthan gum nanocomposite 1:1 composition due to presence of xanthan gum. Although the excess addition of xanthan gum has an opposite trend to the previous one. There was an increase in crystallite size of ɑ-Fe2O3xanthan gum nanocomposite becoming 16.86 nm in 1:2 composition.  Identification of particles size in ɑ-Fe2O3xanthan gum nanocomposite with particle size analyzer (PSA).
The particle size of α-Fe2O3 and α-Fe2O3xanthan gum (1:1) is 177.56 and 228.43 nm, respectively ( Table 2). This size classifies that materials synthesis is a type of nanoparticle due to it being in the range of 1-1000 nm (Mahato, 2017). Generally, many researchers categorized material sizes as nanoparticles with sizes under 100 nm. However, particle size analysers (PSA) have a weakness that could not measure particle size. The result of PSA often tends to be larger. Since, it measures sample particle size depending on their diffusion properties in a solvent from the hydrodynamic diameter. The sample tested must be a dispersion so that the measurement of composite solids is only carried out at a 1:1 composition, due to xanthan gum dissolving in water which makes the measurement only determined by α-Fe2O3 (Jindal & Khattar, 2018). Moreover, α-Fe2O3 and α-Fe2O3-xanthan gum (1:1) have a variety in particle size and distribution is polydispersion with a polydispersity index by 0.14 and 0.387, respectively. Analysis of functional groups in ɑ-Fe2O3xanthan gum nanocomposite with fourier transform infrared spectroscopy (FTIR). Figure 2 shows the spectrum of ɑ-Fe2O3xanthan gum nanocomposite, ɑ-Fe2O3 nanoparticle, and xanthan gum. The absorption peaks in ɑ-Fe2O3-xanthan gum nanocomposite have a functional group such as, O-H, C-H sp 3 , C=O, C-O, dan Fe-O in all composition (Faria et al., 2011;Darezereshki et al., 2012). Those functional groups are a combination between ɑ-Fe2O3 and xanthan gum but with different percentage of transmittance that indicate the interaction was occur. In 1727 cm -1 , the transmittance of C=O dropped moderate in ɑ-Fe2O3-xanthan gum nanocomposite when mass of xanthan gum increase and the opposite mass trend of ɑ-Fe2O3. In other regions, the transmittance of Fe-O has a slight shift to the high wavenumber from composition 2:1, 1:1, and 1:2. It represents that the interaction takes place between Fe in α-Fe2O3 with C=O in xanthan gum which the Fe-O bond will be stronger due to this new interaction. Figure 3 describes the effect of xanthan gum on the viscosity of nanofluids. Xanthan gum steeply improved viscosity of fluids to 16.58 cP which is bigger than other nanofluids. This trend has the same impact on nanofluids that dissolved from ɑ-Fe2O3-xanthan gum nanocomposite, in which the viscosity in composition 1:2 is 1.964 and it is greater than others. This is because xanthan gum has a long and large molecular structure due to repeated bonds of the monomer (Patel et al., 2020) When the interaction between molecules or London force is large, it will result in a significant increase in the viscosity value (Khan et al., 2018). The anomaly condition occurred in composition 2:1 and 1:1, where nanofluids 2:1 have a viscosity more than nanofluids 1:1 by 1.334 cP and 1.182 cP, respectively. It can happen, because nanoparticles also can increase the viscosity of fluids with interactions between molecules ɑ-Fe2O3 (Rudyak & Krasnolutskii, 2014). Therefore, it can be concluded that ɑ-Fe2O3-xanthan gum has potential result to in EOR technology based on increasing of the viscosity when compared to Fe2O3 fluid.

CONCLUSIONS
The ɑ-Fe2O3-xanthan gum nanocomposite was successfully synthesized by sonochemical and ex situ methods, respectively. The spectrum of XRD shows that nanocomposite has the main structure as ɑ-Fe2O3 and an additional peak of xanthan gum at 19.6, 24, 33, 35.5, dan 40.7°. This material belongs to the category of nanoparticles with a size of 228.43 nm (PSA). The functional group that has in ɑ-Fe2O3-xanthan gum nanocomposite is O-H, C-H sp 3 , C=O, C-O, and Fe-O, which interaction occurs between Fe from ɑ-Fe2O3 and C=O from xanthan gum. EOR test in this research presents that xanthan gum is a material that has the function to increase the viscosity of fluids. Gumthermore, α-Fe2O3-xanthan gum nanofluid is the potential material used in the chemical flooding process in the reservoir.