Applications of zeolite-zirconia-copper nanocomposites as a new asphaltene inhibitor for improving permeability reduction during CO2 flooding

Using nanoparticles for adsorbing asphaltene was known as an efficient method among researchers for crude oil upgrading. In this study, zeolite-zirconia-copper nanocomposites (NCs) have been synthesized and characterized with Scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and energy-dispersive X-ray (EDX). Then, CO2-oil interfacial tension (IFT) tests, Ultraviolet–visible spectroscopy (UV–Vis) Langmuir and Freundlich isotherm models, asphaltene precipitation tests at static phase, and dynamic CO2 flooding tests were performed in the presence of NCs and the results were compared with zeolite nanoparticles. Based on the characterization results, zirconia-copper particles were distributed at the surface of zeolite with total dimensions less than 30 nm, and the specific surface areas of the NCs (327.82 m2/g) was less than the pure zeolite (369.48 m2/g). It was seen that NCs had a greater asphaltene adsorption capacity and the application of decreasing asphaltene precipitation was higher in comparison to the zeolite nanoparticles. Accordingly, NCs were selected for performing dynamic CO2 tests and investigation of the permeability and porosity reduction parameters at obtained static condition. After adding NCs at the dynamic phase, asphaltene depositions that occured after CO2 injection was decreased and permeability/porosity reduction parameters were improved.


Scientific Reports
| (2022) 12:6209 | https://doi.org/10.1038/s41598-022-09940-0 www.nature.com/scientificreports/ Hosseinpour et al. 28 , shows that zirconia samples with surface acid sites have high BET specific surface area values compared to other nanoparticles such as Fe 2 O 3 , NiO, and WO 3 which shows the strength of interactions between the asphaltenes and this sample. Other nanoparticles which are widely used due to their availability and low cost are copper oxide nanoparticles. Copper oxide nanoparticles have a wide variety of applications including efficient adsorbent [38][39][40][41][42][43] , foam stabilization 44 , EOR 45 , and environmental remediation 46 . Changing composition due to adding CO 2 gas was known as a main concern in porous media, and it was found that asphaltene deposition especially at the inlet part of the core caused formation damage which should be fully considered [47][48][49] . Wang et al. 50 , investigated blockage degree during asphaltene precipitation during CO 2 flooding, and based on the results, asphaltene precipitation which occurs in both large and small sizes correlated with permeability reduction. Moreover, it was found that the agglomeration problem relevant to nanoparticles can be solved by using nanocomposites 51 . In this study, zeolite-zirconia-copper oxide nanocopmosites (NCs) were used for surveying asphaltene adsorption on the surface and removal of asphaltene as an asphaltene inhibitor and the results compared with zeolite nanoparticles as a reference. As NCs had better results in the static phase and were selected for performing dynamic CO 2 tests. Although the application of zeolite, zirconia, copper oxide at different cases were surveyed in previous studies such as asphaltene adsorption, introducing NCs as a possible asphaltene adsorbent and dynamic CO 2 tests were not covered according to our knowledge. In first phase, adsorption behavior during CO 2 -oil IFT tests were observed and results was matched with real natural depletion tests in the presence of NCs and zeolite nanoparticles. Natural depletion was used as the main source of making asphaltene precipitation by changing pressures. The main points in natural depletion tests were selected based on the CO 2 -oil interfacial tension (IFT) tests (higher adsorption potential points). Two tests of CO 2 -oil interfacial tension (IFT) and Ultraviolet-visible spectroscopy (UV-Vis) spectrophotometer were used for describing asphaltene adsorption on the nanoparticles surface, and two different isotherm models of Langmuir and Freundlich were completely surveyed in the presence of NCs and zeolite nanoparticles. Finally, based on the static phase results, NCs were selected for performing dynamic CO 2 tests and improving permeability reduction/porosity reduction parameters.

Materials and methodology
Materials. Crude oil was collected from one of the Iranian oil reservoirs in the west with an oil density of 0.864 g/cm 3 and viscosity of 9.9 cP at 40 °C. Table 1 shows reservoir oil composition and the results of saturatearomatic-resin-asphaltene (SARA).
Gas and brine permeability and porosity results and other specifications carbonate plug which were used in the dynamic CO 2 test were shown in Table 2.
For extracting asphaltenes, the standard IP143 method was used 52  3. Using centrifuge at 3000 ppm and 30 min for separating asphaltene which adsorbed on NCs or zeolite nanoparticles surface. 4. Measuring remaining asphaltene concentration. 5. Calculating the amount of adsorbed asphaltene on nanoparticles surface with Eq. 1 as below: The main items in Eq. 1 and the relevant units are Initial asphaltene concentration ( C o ) , mg/L, asphaltene equilibrium concentration (C e ) , mg/L, volume of solution (V), L, NCs mass (m), mg.
Dynamic experimental CO 2 procedure. A dynamic apparatus schematic of setup that used to perform dynamic CO 2 tests is shown in Fig. 3.
The dynamic set up was contained three different vessels of brine, nanofluids, and crude oil, hydraulic pump, core holder for holding carbonate core plug, pressure and temperature sensors, overburden pump, DP sensors, and acquisition data. Below five steps were used for performing dynamic CO 2 tests in the presence of NCs: 1. Injecting formation water (0.1 cc/min) and calculate water permeability 2. Obtaining residual water saturation with performing oil injection 3. Calculation of effective oil permeability at residual water saturation   For nanocopmosites, the procedure was the same except for step 4 inwhich oil contains NCs 30 ppm at 1700 Psi and 40 °C. Figure 5S show the experimental approach which was used in this study:

Results and discussion
Characterization. Figure 4a, b shows X-ray analysis for detecting the structure of zeolite and NCs nanoparticles, respectively. Zeolite structure is determined through d hkl = 7.5°, 8.5°, 23° and 24° reflections 53  τ, k, λ, β, and θ are crystalline size (nm), shape factor (0.9), x-rays wavelength (0.154 nm), line broadening, and Bragg angle. NCs calculated average size was 30.21 nm. The morphological surface and size of nanoparticles were investigated by SEM. Images obtained from nano zeolite and synthesized zeolite-zirconia-copper nanocomposites (NCs) are shown in Fig. 5. From a morphological point of view as shown in Fig. 5a, the zeolite sample is composed of a large number of coffin-shaped units with relatively similar dimensions of about 50 nm. In this image, it is possible to see the uneven surfaces of the bed and cavities, which will increase the specific surface area and adsorption capacity.About gained SEM image from zeolite-zirconia-copper nanocomposites (NCs) as Fig. 5b, it can be observed that the zirconia-copper particles  www.nature.com/scientificreports/ were uniformly distributed at surface of zeolite with dimensions less than 30 nm. This is a sign of the successful stabilization of nanoparticles on the zeolite substrate. The surface area, pore size, and pore volume of the pure zeolite and zeolite-zirconia-copper nanocomposites (NCs) were measured by BET. The results are summarized in Table 3. The specific surface areas of the NCs (327.82 m 2 /g) are less than the pure zeolite (369.48 m 2 /g) as a result of introducing of ZrO 2 and CuO. An increase in the ZrO 2 and CuO contents decreases the specific surface area due to increasing the crystal size and the pore blockage of the support. Compared to NCs, pure zeolite has a higher specific surface area and higher pore volume, but a lower average pore diameter. Figure 6 and Table 4 show EDX results for zeolite nanoparticles and NCs. Figure 6a shows different elements in the zeolite nanoparticles such as Si (31.49), Al (3.38), Na (16.32) and O (48.81) 55 . Different elements of Al, Si, O, and Na were observed in the NCs composition as Fig. 6b and Table 4. Zirconia and copper were observed in zeolite nanoparticles based on EDX images.

Asphaltene adsorption isotherms in the presence of NCs and zeolite nanoparticles. Langmuir
and Freundlich isotherm models which were used in this study are expressed in Eqs. 3 and 4 56 .
Equations 5 and 6 are expressed in linear form as: Table 3. Textural properties of the prepared materials. NCs = zeolite-zirconia-copper nanocomposites.

Sample
Surface area (m 2 /g) Pore volume (cm 3 /g) Average pore diameter (nm)  www.nature.com/scientificreports/ Asphaltene adsorption on NCs and zeolite's surface (mg/g), equilibrium concentration of NCs and zeolite (mg/L), maximum asphaltene adsorption per grams of NCs or zeolite (mg/g), Langmuir constant of adsorption, the capacity of adsorption in Freundlich isotherm ([mg/g] [L/mg]), and intensity factor in Freundlich isotherm were shown with Q e , Ce, Q m, K L , K F , and 1/n, respectively. Figure 7 shows asphaltene adsorption on the NCs nanocomposites and zeolite's surface in the batch experiment tests up to 1000 ppm. As it is clear from the graph, there is two different slopes below 100 ppm and after that. At first slope (below 100 ppm), the slope was dramatically increased. Then, asphaltene adsorption on the NCs nanocomposites and zeolite's surfaces were reached to around 78.5 mg/g (0.213 mg/m 2 ), and 33 mg/g (0.101 mg/m 2 ), respectively. Accordingly NCs were adsorbed more asphaltene on its surface compared to zeolite nanoparticles. It was concluded from previous research that the type of sorbent is affected on the amount and type of adsorption 19,57,58 . According to the isotherm model results in this study, the adsorption data was adapted well with Langmuir isotherm than Freundlich isotherm, and this shows that adsorption surface was monolayer and homogeneous. Freundlich isotherm occurs in the surface that has different energy with the heterogeneous surface 58 . From the comparison between Freundlich isotherm between zeolite and NCs, it was observed that the data less adopted with NCs in comparison zeolite. Langmuir and Freundlich isotherm linear plots are shown in Figs. 2S and 3S, respectively. All experiments in this study were replicated three times with the maximum uncertainty of ± 5%.
Isotherm parameters of both isotherm models were shown in Table 5. According to the results, NCs have better adsorption capacity than zeolite nanoparticles. The maximum adsorption ratio of NCs to the zeolite (qm NCs/qm zeolite) was 2.41. Furthermore, NCs had higher adsorption capacity in comparison zeolite, and the KF NCs / K F zeolite was 2.5782. Baninaam et al. was investigated the isothermal behavior of ZSM-5, and based on their results, q m was 21.7024 mg/g which is less than both nanoparticles in this study 59 . Nanoparticles adsorption before and after asphaltene adsorption. To   www.nature.com/scientificreports/ Figure 8 shows asphaltene adsorption before and after asphaltene adsorption. In the presence of NCs, contact angles had higher results in comparison to the zeolite which were in a good agreement with batch adsorption experiment (Fig. 7). In other words, as NCs had more contact angle due to adsorb more asphaltene on its surface in comparison to zeolite.

Effect of nanoparticles concentration and pressure on CO 2 -crude oil interfacial tension.
The effects of NCs and zeolite nanoparticles on the CO 2 -Oil IFT was shown in Fig. 9. As can be seen from Figure, two main slopes were observed with/without nanoparticles. The slope of second region was decreased at high pressures. In other words, at high pressure asphaltene adsorbed on the nanoparticles surface and have not tend to aggregated in compared to first region and low pressure. Slope in the second region was increased but not as much as first region which shows that nanoparticles reduced asphaltene precipitation. Other main point is that, although nanoparticles decreased asphaltene precipitation but it did not stop it completely 61 . According to the results, there are two different ranges from 200 to 2600 Psi. Interfacial tension of CO 2 -Oil was decreased due to dissolving CO 2 in the crude oil. The slope in this graph was changed due to forming the aggregate of asphaltene particles. According to Fig. 9, NCs were changed the slope in the second region more than Na-ZSM-5 zeolite, and in other words adsorbed higher amounts of asphaltene on its surface. As it was mentioned in the previous section, NCs had the better asphaltene adoption in comparison to zeolite nanoparticles which confirmed these results. Moreover, one of the other essential results from the results was delaying agglomeration in the presence of NCs and zeolite nanoparticles, and it was confirmed that NCs had better results than zeolite. Previously Kazemzadeh et al. was seen the same results in the presence of Fe 3 O 4 nanoparticles 61 . Based on their results, the main mechanism of IFT reduction in the presence of nanocopmosites and zeolite nanoparticle were asphaltene adsorption onto the surface of the nanocomposites. Seven pressures from the second region (1700-2600 Psi) were selected for obtaining the relation between these high adsorber points with adsorption in the real crude oil in natural depletion tests. As it was mentioned, there are two different slopes of CO 2 -Oil in the base and both nanoparticles of NCs and zeolite, and Table 6 summarized different equations in these two regions. 2nd to 1st slope ratio was 19.403% at the base case, and 2nd to 1st ratio increased to 20.895% and 30.303% in the presence of NCs and zeolite at 30 ppm, respectively. Thus, NCs had better performance with regards adsorbing asphaltene on its surface in comparison zeolite. Natural depletion tests in the presence of nanoparticles. As it was mentioned in the previous section, seven pressure of 1700, 1850, 2000, 2150, 2300, 2450, and 2600 Psi have selected as high adsorption points for static phase and performing natural depletion tests in the presence of NCs and zeolite nanoparticles. Asphaltene precipitation content versus pressures at static pressure were shown in Fig. 10, and effects of both NCs and  www.nature.com/scientificreports/ zeolite nanoparticles were observed according to this graph. It was seen asphaltene precipitation of NCs and zeolite nanoparticles decreased from (5.10 wt%, 14.34 wt%) to (3.78 wt%, 8.40 wt%) and (2.8 wt%, 6.25 wt%), respectively during pressure reduction from 2600 to 1700 Psi. Accordingly, based on the results, NCs had better results for decreasing asphaltene precipitation in the static phase in comparison to zeolite, and it can be in a direct relation with higher adsorption potential in the previous steps.

Dynamic CO 2 tests in the presence of NCs.
According to the static phase results, NCs had better results than zeolite in aspect of asphaltene adsorption and asphaltene precipitation reduction. Thus it was selected for   www.nature.com/scientificreports/ surveying permeability/porosity reduction parameters. As it is clear from the Table 7, NCs had better results in lower pressure for asphaltene precipitation at 1700 Psi, 40 °C, and 30 ppm were selected for performing CO 2 flooding at dynamic phase. One of the essential factors in porous media is considering deposition condition. As it was shown in the static phase, NCs had better performance in comparison to zeolite. Accordingly, it was selected for surveying its effect on the deposition rate in porous media. Dynamic displacement tests were used for CO 2 flooding in the presence of NCs. As it is clear from Fig. 11, asphaltene deposition in the presence of gas was increased during CO 2 flooding. By measuring the asphaltene content of injected and produced oil samples, one can estimate the amount of deposition in porous media. The asphaltene of produced oil was measured by the IP143 standard technique. After adding NCs in crude oil, asphaltene precipitation was reduced. As CO 2 gas volume was increased from 1 to 6 pore volume, asphaltene precipitation (wt%) was decreased from (15.12, 18.12) to (11.85, 14.44), respectively.
As it was mentioned before, after saturation of carbonate core sample with brine, recombined oil and CO 2 [25 Mole % which was more than initial onset value (20 Mole %) at static phase] displaced through the low permeability carbonate core and initial permeability reduction was recorded. Then, same procedure was performed in the presence of NCs [dispersed in oil] at 30 ppm, 1700 Psi, and 40 °C as Figs. 12 and 13. Many other cases and laboratory studies have been reported on precipitation and deposition of asphaltenes in porous media during immiscible or miscible gas flooding operations [62][63][64][65][66][67] . Figure 12 shows permeability reduction in the presence of NCs, and based on the results, NCs improved permeability reduction in porous media. Figure 13 shows differential pressure between inlet and outlet cores for both tests. As it is clear from the graph, most pressure drop was occurs at initial part which asphaltene deposition problem was severe at this point. Moreover, NCs decreased pressure drop successfully in comparison to base CO 2 flooding. The precipitated asphaltenes left in the reservoir core plugs reaches its lowest value. An explanation for this phenomenon is that the total density Asphaltene precipitaƟon ( wt%)

Pressure (Psi)
Base zeolite nanoparticles Ncs Figure 10. Effects of NCs and zeolite nanoparticles on asphaltene precipitation during natural depletion tests. There is direct relation between porosity reduction and asphaltene deposition rate. Figure 14 shows the porosity variations of low permeability carbonate reservoir versus the amounts of pore volume. As it was observed in the previous steps, NCs was decreased asphaltene precipitation in static phase at 30 ppm, and at same concentration asphaltene deposition was decreased in carbonate reservoir. Moreover, higher porosity reduction was seen at higher asphaltene deposition points.

Conclusions
Zeolite-zirconia-copper oxide nanocomposites (NCs) have been synthesized successfully with average size of 30 nm and it was used for asphaltene adsorption and solving asphaltene precipitation problems and the results compared with zeolite nanoparticles. Results show that NCs nanoparticles adsorbed higher amount of asphaltene and asphaltene precipitation decreased more in the presence of NCs nanoparticles than zeolite nanoparticles which reveal this point that these nanocomposites can be used efficiently as an asphaltene inhibitor and the agglomeration process was delayed efficiently. Adsorption data fitted well with the Langmuir model compared to the Freundlich model, which shows that the adsorption occurs on a homogeneous surface with monolayer coverage in the presence of both nanoparticles. Based on the BET results, NCs has lower surface area, higher pore volume but higher diameter in comparison to zeolite nanoparticles. EDX analysis confirmed that NCs synthesized successfully. There is two different slope in CO 2 -oil IFT readings as pressure increases (200 Psi-2600 Psi), and the second slope is slower than the first one which is due to aggregation of asphaltene.  www.nature.com/scientificreports/ with regards adsorbing asphaltene on its surface and decreasing asphaltene precipitation during natural depletion in comparison to zeolite nanoparticles, and it was selected for performing CO 2 dynamic tests. In dynamic phase. It was observed that NCs had high potential material for improving permeability impairment, porosity reduction, and asphaltene deposition rate during CO 2 flooding tests.