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. 2026 Sep 16;11(38):57631–57641. doi: 10.1021/acsomega.6c06451

Preparation, Characterization of Janus GO, and Its Interfacial Synergies with Surfactants in Chemical Enhanced Oil Recovery

Mingchen Ding †,‡,*, Zhenyu Zhang §, Yutan Shen ∥, Hui Chen ⊥, Guilin Liu §, Haicheng Liu ⊥, Hanchao Wu #
PMCID: PMC13629373  PMID: 42825131

Abstract

In this work, Janus graphene oxide (JRGO) was synthesized through a simple interface modification method to enhance oil recovery. The JRGO nanosheets were characterized by Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffractometer technology (XRD), and X-ray photoelectron spectroscopy (XPS). In addition, the interface properties of JRGO were evaluated by interfacial tension (IFT), wettability alteration, and emulsion stability. Due to the amphiphilic Janus structure, JRGO possesses superior interfacial tension (IFT) reduction capacity compared with pristine GO, and it can effectively convert oil-wet solid surfaces to water-wet ones. In addition, the interaction of JRGO with different surfactants, including anionic surfactants (SDBS), nonionic surfactants (AEO), and zwitterionic surfactants (EAB), was investigated. Experimental verification confirms that the synergistic effect of the JRGO/EAB system reduces IFT to 3.9 × 10–3 mN/m, and the wettability alteration ability is further improved. Therefore, the synergistic effect of JRGO and EAB can be used as an efficient system to enhance oil recovery.

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1. Introduction

Heavy oil resources are widely distributed globally, contributing approximately 10% of the nation’s annual crude oil production, which is crucial for stabilizing and boosting crude oil production. Owing to the high viscosity of heavy oil, the injection fluid is prone to viscous fingering and water channeling, which is greatly complicating the oil recovery process. Efficient development of heavy oil has thus become a major challenge.

The development of chemical flooding for conventional heavy oil has progressed from theoretical exploration to industrial application, undergoing multiple stages and continuously overcoming technical challenges. Chemical flooding for conventional heavy oil is tailored to the characteristics of heavy oil reservoirs, utilizing chemical agents to alter the oil/water interfacial tension, reduce oil viscosity, or improve reservoir wettability, thereby enhancing the recovery of heavy oil. Polymer flooding, polymer/surfactant combination flooding, and viscosity reduction combination flooding have been developed to enhance heavy oil recovery. The interfacial properties of chemical flooding for heavy oil play a significant role in enhancing the recovery efficiency of conventional heavy oil. , Cao et al. verified that low interfacial tension is conducive to emulsion formation and interface expansion through microscopic model oil displacement experiments. Due to the existence of an elastic oil/water interface film, emulsion stability increases and oil droplet shedding decreases. These phenomena drive microscopic heterogeneous residual oil and thin-film residual oil better than other solutions. Liu et al. proved that the stronger the emulsification ability, the smaller the droplet particle size, the better the viscoelasticity, the stronger the O/W emulsion stability, and the better the chemical flooding heavy oil recovery. This is mainly because the most effective stage of action is when the chemical flood is injected into the formation before the O/W emulsion front flow reaches the production exit. During this period, the emulsification amount of heavy oil, the width of the emulsion zone, and the properties of the O/W emulsion formed affect the flooding efficiency of heavy oil. Therefore, when screening chemical flooding agents, emulsification rate, droplet size, and viscoelasticity of formed O/W emulsions are the main evaluation factors.

Recent advances in nanotechnology have offered a promising technical route for enhancing heavy oil recovery by virtue of nanomaterials with unique physicochemical properties. The main nanomaterials used to improve the recovery of heavy oil are nanocatalysts and nanofluids. The high catalytic activity of nanocatalysts can effectively hydrolyze heavy oil. The oil recovery of nanofluids can be improved by changing rock wettability, reducing interfacial tension, forming emulsion, and improving mobility ratio. Nanomaterials have attracted significant attention in the field of enhanced oil recovery (EOR) due to their ability to form Pickering emulsions with crude oil when dispersed in water. Among these, Janus particles, particularly Janus graphene oxide (Janus GO), have garnered widespread attention due to their asymmetric surface characteristics. Janus GO features both hydrophilic and hydrophobic domains, enables it to effectively regulate interfacial behaviors in complex oil–water systems, such as altering wettability and reducing interfacial tension (IFT), thereby offering advantages in stabilizing emulsions. Because of the characteristics of sheet nanomaterials, it can form a stable interface film at the oil/water interface compared with other nanomaterials and is more conducive to stabilizing the emulsion. Cao et al. prepared Janus sulfonated graphene oxide nanosheets (JSGO) using a simple method. JSGO exhibits excellent dispersibility and stability. Additionally, due to its amphiphilicity, JSGO shows outstanding interfacial properties. On one hand, JSGO can reduce interfacial tension and form a robust interfacial film at the oil/water contact. On the other hand, JSGO has a strong wettability alteration ability. Jia et al. synthesized a series of Janus GO (JGO) with different degrees of modification and studied the interfacial properties of JGO by measuring IFT, dilatational modulus, contact angle, and EOR efficiency. Their research found that JGO exhibits excellent oil/water interfacial activity to form 2D interfacial films and 3D climbing films. Furthermore, the highly modified JGO showed superior wettability alteration efficiency. The formation of climbing films and good wettability alteration capabilities can enhance JGO’s insertion to the oil/rock interface and effectively separate oil from rock surfaces. Additionally, for heavy oil reservoirs, JGO showed greater interfacial activity than unmodified GO. Molecular dynamics simulation results indicated that the strong interaction between JGO and asphaltenes can promote JGO adsorption at the heavy oil/water interface. Moreover, JGO and DTAB exhibited excellent synergistic effects in the heavy oil/water system, reducing the IFT to 8 × 10–3 mN/m, while also demonstrating relatively good salt and temperature resistance. Cumulative literature demonstrates that Janus GO possesses excellent interfacial performance, capable of reducing IFT, reverse the wettability, and forming stable emulsions, demonstrating significant potential in enhancing heavy oil recovery.

In this work, Janus GO (JRGO) was prepared by a simple interfacial modification method, systematically investigating the interfacial behavior of JRGO paired with conventional heavy oil, including its ability to reduce IFT, change wettability, and stabilize emulsion. Additionally, the synergistic effects of JRGO combined with different types of surfactants were studied to evaluate their impact on the interfacial performance. Finally, the effect of JRGO combined with EAB on improving the displacement efficiency of heavy oil was emphasized. The findings are expected to provide new insights into the application of Janus GO in enhanced heavy oil recovery.

2. Experimental Methods

2.1. Materials

Graphene oxide was prepared by the modified Hummers method. Catechol, diaminoethane (DAE), octadecylamine (ODA), and kerosene were provided from Sinophram Chemical Reagent Co., Ltd. Sodium dodecyl benzenesulfonate (SDBS), alcohol ethoxylate (AEO), and erucamidopropyl betaine (EAB) were collected from Shandong Usolf Chemical Technology Co., Ltd. Heavy oil samples were obtained from Shengli Oilfield (viscosity: 731 mPa·s at 70 °C). The composition of formation water is provided in Table .

1. Composition of the Formation Water.

ions Cl– HCO3 – CO3 2– Na++K+ Ca2+ Mg2+ TDS
concentration (mg/L) 3435 725 38 2299 157 27 6681
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2.2. Synthesis of JRGO Nanosheets

JRGO was prepared by interface modification: first, the poly­(diaminoethane-catechol) (PDC) aqueous solution was prepared by adding DAE to 0.1 mg/mL catechol solution according to the molar ratio of 1:2 and stirring at room temperature for 12 h (see Table ). PDC solution and 4 mg/mL ODA-kerosene solution were then added to a 1 mg/mL GO dispersion. The mixture was stirred at room temperature for 12 h and then washed sequentially with petroleum ether, ethanol, and deionized water. Finally, the product was freeze-dried for 24 h to obtain the JRGO. The preparation process diagram of JRGO is shown in Figure .

2. Analysis of the Elemental Content of GO and JRGO.

element C (%) O (%) N (%)
GO 50.76 49.24 -
JRGO 52.88 31.77 15.35
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Synthesis mechanism of JRGO.

2.3. Characterization

The chemical composition and structure of JRGO were characterized by Fourier transform infrared spectroscopy (FT-IR, Bruker Tensor 27, Germany) within the wavenumber range of 4000–400 cm–1. The thermal stability of JRGO was assessed by thermogravimetric analysis (TGA, Mettler Toledo, Switzerland) under a nitrogen atmosphere from 40–800°C. The morphology of JRGO was observed by scanning electron microscopy (SEM, Quanta 200, USA). X-ray diffraction (XRD, Bruker D8 Advance) was employed to analyze the diffraction peaks in the wide-angle range (5° to 80°) to determine the reduction degree of graphene oxide before and after modification. The elemental composition of JRGO was analyzed by X-ray photoelectron spectroscopy (XPS) analysis (ThermoFisher, Nexsa), and the functional group changes of JRGO were analyzed by XPS PEAK.

2.4. Interface Performance Experiments

Oil/water interfacial tension (IFT) was measured using a spinning drop interfacial tensiometer (TX-500C) at 6000 rpm and 70 °C. In addition, 5 mL of kerosene and 5 mL of JRGO dispersion were added to the screw bottle and shake slightly. Then, the changes of the oil/water interface were observed.

The wettability of JRGO was measured by the interface capture method. The ability of JRGO to change wettability was measured by a SL200 K contact angle instrument. The detailed experimental procedures of JRGO to change wettability on the core surface are described as follows: the core slices were cut and polished using sandpapers with different mesh sizes; subsequently, the treated core slices were immersed in heavy crude oil at 70 °C for 72 h; finally, JRGO dispersion was dropped onto the core surfaces to investigate its wettability reversal performance.

The stability of the emulsion was tested by the water precipitation rate test and microscopic observation. 5 mL of heavy oil and 5 mL of 300 mg/L JRGO were added to the measuring cylinder. By shaking violently, it was fully emulsified to form an emulsion. The system was placed at 70 °C to observe the water evolution rate at different times. At the same time, the morphology of emulsions at different time was observed by a microscope.

2.5. Oil Film Peeling Experiments

The 2.5 cm × 5 cm slide was repeatedly rinsed with distilled water and ethanol, then evenly coated with heavy oil on one side, and naturally aged at 70 °C for 72 h to form an oil film. The aged slide pieces were immersed in different systems, and the oil film peeling state was recorded by a digital camera. The remaining oil film area at different time was calculated by graphic analysis software (PhotoShop), and the oil film stripping ratio was obtained by weighing the oil film stripping before and after.

2.6. Heavy Oil Recovery Experiments

The heavy oil displacement experiment was carried out in the following steps: the sand-pack model was filled with quartz sand and saturated with formation water, so the pore volume, porosity, and permeability were calculated; heavy oil was saturated into the sand-pack at a rate of 0.5 mL/min at 70 °C until the water cut at the outlet end was 0% and aged at 70 °C for 24 h; water flooding was carried out at the injection rate of 0.5 mL/min; 0.3% combination system of 0.3 PV was injected into the model; and subsequent water flooding was conducted at the injection rate of 0.5 mL/min. All steps are recorded by recording the volume of oil and water in the production fluid at the outlet to calculate the recovery rate and water cut and recording the change in injection pressure.

3. Results and Discussion

3.1. Characterization of JRGO

Catechol is easily oxidized to catechol quinone, and after adding DAE, PDC is obtained by the phenol–amine reaction. At this time, the PDC solution appears brownish-yellow and shows no precipitation, indicating the successful preparation of PDC, which possesses a small molecular weight and is water soluble. After adding GO dispersion and ODA-kerosene solution, the PDC aqueous solution and ODA-kerosene solution can easily form a uniform emulsion under intense agitation, while GO can easily migrate to the oil/water interface due to its nanosheet structure. Moreover, because the GO surface contains a large number of epoxy groups, it is easy to have ring-opening reactions with the amines or phenolic hydroxyl groups of PDC and ODA. PDC and ODA are grafted to both sides of GO, respectively (PDC to the hydrophilic surface, ODA to the hydrophobic surface).

Figure a shows the FT-IR spectra of GO and JRGO. Compared with GO, JRGO exhibited characteristic peaks at 1200 cm–1 and 1650 cm–1, which represent C–N stretching vibration and N–H bending vibration, respectively. This proved that amines were successfully introduced to the GO surface. At the same time, the peaks at 1070 cm–1 (C–O–C) and 1727 cm–1 (CO) were weakened, proving that PDC and ODA were modified through the reduction reaction with oxygen-containing groups. TGA analysis revealed the thermal decomposition processes of GO and JRGO (Figure b). At room temperature to 200 °C, GO and JRGO showed similar weight loss processes, mainly due to the evaporation of free water. When the temperature increased, the weight loss process was mainly due to the decomposition of active groups such as oxygen-containing groups. At this temperature range, JRGO exhibited a lower weight loss rate than GO, mainly because the modification of PDC and ODA reduced the density of oxygen-containing groups. In addition, when the temperature continues to rise, JRGO shows a period of obvious weight loss, mainly due to the destruction of relatively stable long carbon chains in this temperature range.

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Fourier transform infrared spectrometry (FTIR) (a) and TGA (b) of GO and JRGO.

The 2-D nanosheet structures of GO and JRGO are shown in Figure . The abundant surface oxygen-containing groups on GO generate strong interlayer interactions, leading to a stacked and folded structure. Moreover, the modified folded state displayed a large specific surface area, which provided a reaction site for amphiphilic modification. After amphiphilic modification, the surface became smooth and the dispersion was more uniform.

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SEM images of GO (a) and JRGO (b).

Figure shows the XRD patterns of GO and JRGO. GO exhibited a sharp peak at 8°, representing an obvious oxidation characteristic peak of GO and indicating the oxidation degree of GO. For JRGO, the sharp peaks at 8° were significantly reduced, showing a reduction in the oxidation degree of GO and proving that GO was reduced. At the same time, the amorphous carbon peak envelope at 20° was significantly enhanced, which also indicated that GO had been reduced to JRGO.

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XRD patterns of GO and JRGO.

Figure shows the XPS spectra of GO and JRGO. The presence of the N element in JRGO compared to GO indicated that GO was successfully modified (Figure a). Because of grafted modification of ODA and PDC on the GO surface and the introduction of a large number of C and N elements, the O element content of JRGO was reduced. At the same time, the reduction of the C–O–C peak and the proportion of the C–OH peak obtained by high-resolution O 1s spectral analysis proved that ODA and PDC were grafted onto the GO surface through reduction reaction and ring-opening reaction of epoxy groups.

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XPS full spectrum (a) and high-resolution O 1s spectrum of GO and JRGO (b).

3.2. Interfacial Activity of JRGO

The different wettability of the two sides of JRGO validated the amphiphilic Janus properties. As shown in Figure , the contact angle of water on the hydrophobic side of JRGO was 110.9°, while the contact angle on the hydrophilic side of JRGO was 36.6°, indicating that JRGO possessed two distinct surfaces. In addition, the interface between the nanofluid and the oil was concave before shaking, showing a high IFT. After shaking, JRGO nanosheets migrate from water to oil/water boundary, and the oil/water interface between the JRGO nanofluid and oil flattened, indicating that the oil/water IFT decreases. At the same time, because of its amphiphilicity, JRGO nanosheets spontaneously aggregated at the oil/water interface to form a stable interface film.

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JRGO’s interfacial behavior in oil and water systems and surface wettability.

Long-term immersion of reservoir rock substrates in crude oil gradually enhances surface lipophilicity, rendering the rock permanently oil-wet. Therefore, efficiently altering the wettability of the rock, transforming the surface from oil-wet to water-wet, could significantly reduce adhesion work and flow resistance. This allowed the oil to detach more easily from the rock surface, thereby enhancing oil recovery. To investigate the effect of JRGO on the wettability alteration of the oil-wet surface, the contact angle between JRGO nanofluid and the oil-wet surface was measured (Figure ). The glass slides were coated with heavy oil and aged, resulting in intrinsically oil-wet surfaces with an initial water contact angle of 118.8°. After immersion in GO and JRGO, the hydrophobic surface exhibited the ability to change the wettability. Because of its amphiphilic structure, JRGO demonstrated a greater ability to alter wettability than GO. With the increase of JRGO concentration, the water contact angle gradually decreased, and when the JRGO concentration increases to 300 mg/L, the contact angle dropped to 48.3°. When JRGO nanosheets were adsorbed, the hydrophobic part interacted with the oil-wet surface, and the hydrophilic part was exposed to the surface, forming a water film. This resulted in the wettability changing from oil-wet to water-wet, and the contact angle gradually decreased. When the JRGO concentration exceeded 300 mg/L, the contact angle gradually decreased, indicating that the adsorption sites on solid surfaces were fully saturated by JRGO nanosheets, and further increasing the JRGO concentration did not significantly enhance wettability alteration. Furthermore, JRGO exhibits a slightly superior wettability reversal performance on oil-wet core slices compared with oil-wet glass slides. This is primarily attributed to the higher surface roughness of core slices: rough rock surfaces can adsorb more modified graphene oxide nanosheets to form a continuous and compact hydrophilic film, which facilitates the transformation toward a water-wet interface.

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Effect of the concentration of JRGO on contact angle (a) and wettability alteration process (b).

To further analyze the interface behavior of JRGO, the IFT between heavy oil and JRGO was measured, as shown in Figure . The IFT between heavy oil and formation water reached 57.7 mN/m. Both GO and JRGO were capable of gradually lowering the IFT as the concentration increased. At the same time, JRGO showed better IFT reduction ability than GO, at a concentration of 300 mg/L, the IFT of JRGO dropped to 6.7 mN/m, while that of GO remained at 34.3 mN/m. This indicated that JRGO nanosheets exert favorable regulatory effects on the interaction between heavy oil and water molecules at the interface. The hydrophobic surface of JRGO interacts with the oil phase, while the hydrophilic surface binds tightly to the aqueous phase, giving JRGO a stronger affinity toward the oil/water interface compared to GO. Thereby, IFT is reduced. As the concentration increased, more JRGO nanosheets adsorbed at the oil/water interface, leading to a further decrease in IFT.

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IFT between crude oil and different fluids as a function of concentration.

Emulsion stability plays an active role in the development of heavy oils. Favorable emulsion stability can improve the fluidity of heavy oil in the formation and help improve the recovery rate of heavy oil. At the same time, emulsion stability determines the migration distance of the O/W emulsion within the reservoir, enabling efficient delivery of dispersed oil droplets to production facilities.

Figure shows the evolution of water precipitation rate over time. It was observed that for GO, the water precipitation rate increased rapidly with time. At 30 min, the water precipitation rate exceeded 50% and surpassed 90% at 120 min, indicating the poor emulsion stability of GO. In contrast, for JRGO, the water precipitation rate increased moderately over time. At 60 min, the water precipitation rate was only 40%, and it reached merely 60% after 150 min. This outcome verifies the outstanding emulsion-stabilizing performance of JRGO. Owing to the presence of both hydrophilic and hydrophobic surfaces, it allowed JRGO to adsorb stably onto the emulsion surface, forming a rigid interfacial film. This further enhances the stability of the emulsion. The stability of emulsion was also determined by microscopic observation. Figure shows the morphology of the emulsion formed by GO and JRGO with heavy oil as a function of time. The O/W emulsion formed with JRGO displayed uniform droplet distribution and small size, with an average particle size of less than 30 μm. The particle size barely grew over time, with the average particle size being about 50 μm after 90 min. However, the O/W emulsion formed by GO exhibited a heterogeneous and large particle size, with an average particle size of 130 μm under initial conditions, severe coalescence of oil droplets occurred after 90 min of standing. This proved that JRGO had a strong ability to stabilize the emulsion. Due to its unique amphiphilic property, the hydrophobic group was firmly adsorbed in the oil phase, while the hydrophilic group was firmly adsorbed in the water phase. Therefore, JRGO could stably exist at the oil/water interface and improve the ability to stabilize O/W emulsion.

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Water precipitation rate of the heavy oil and GO/JRGO plotted as a function of time.

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Emulsion morphologies formed by GO at 5 min (a), GO at 30 min (b), GO at 90 min (c), JRGO at 5 min (d), JRGO at 30 min, (e) and JRGO at 90 min (f).

3.3. Interaction with Surfactants

Although JRGO possesses distinctive interfacial properties, it does not reach the ultra-low IFT, which is important in the process of enhanced recovery of heavy oil. Therefore, three types of surfactants (anionic surfactant: SDBS, nonionic surfactant: AEO, zwitterionic surfactant: EAB) were compounded with JRGO to study the synergistic effect.

The initial IFT between the JRGO (300 mg/L) and heavy oil was measured as 6.7 mN/m (Figure ). As presented in Figure , the addition of surfactants significantly reduced IFT, with further reductions observed as surfactant concentration increased. The synergistic combination of surfactants and JRGO achieved lowered IFT compared to surfactants alone. SDBS and EAB, due to their large-surface charges, interacted with JRGO via electrostatic interactions, promoting the migration of surfactant and JRGO to the oil/water interface to reduce IFT. However, the JRGO/SDBS system failed to reach ultra-low IFT. In contrast, EAB achieved ultra-low IFT, and its combination with JRGO further reduced IFT to 3.9 × 10–3 mN/m at 3000 mg/L. As a nonionic surfactant without surface charge, AEO interacted with JRGO through hydrogen bonding, resulting in competitive adsorption at the interface and restricts further IFT reduction. While AEO alone could achieve ultra-low IFT, its combination with EAB showed limited additional reduction. Among all systems, the JRGO/EAB combination achieved the ultra-low IFT, making it the focus of subsequent experiments.

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Effects of combining JRGO with different surfactants to reduce IFT.

As shown in Figure , the contact angle between JRGO and the oil film is 34.1°, indicating its favorable wettability-altering capacity. With the addition of EAB, the contact angle between the system and the oil film decreased further. When the concentration of EAB increased to 3000 mg/L, the contact angle stabilized below 20°. This demonstrated that the addition of EAB enhanced the interaction of positive and negative charges on the surface, promoting the adsorption of the system at the oil/water interface and further improving the wettability alteration. The interaction of positive and negative charges on the surface promoted the adsorption. However, when the concentration exceeded 3000 mg/L, the system adsorption at the oil/water interface reached saturation and further increases in the concentration did not significantly reduce the contact angle.

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Effects of combining JRGO with different concentration of EAB to change wettability.

In heavy oil development, after the use of conventional EOR methods, there will still be a lot of oil film remaining on the rock surface, which is also the bottleneck of further improvement of oil recovery. In order to further improve oil recovery, it is necessary to efficiently peel the oil film adsorbed on the rock surface. , As shown in Figures and , based on pixel and mass analysis results, it was observed that after JRGO treatment, a relatively evident oil film peeling phenomenon occurred on the slides. Over time, the oil film gradually peeled off and its color became lighter. However, some unpeeled areas with darker coloration remained, with more than 35% of the surface being used and approximately 50% of the oil film being peeled off. In contrast, after the EAB treatment, the oil film peeling phenomenon was more pronounced. While there were no clearly visible peeled areas, more than 75% of the oil film was peeled in terms of the mass. The JRGO/EAB system combined the advantages of both materials, demonstrating a stronger oil-film-peeling effect. Pixel and mass analyses showed that the stripping area exceeded 50%, and the mass fraction of removed oil reached 88.7%.

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Oil film peeling process of different systems.

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Oil film peeling capacity of different systems: pixel analysis (a) and mass analysis (b).

This phenomenon is primarily attributed to the amphiphilic structure of JRGO, which facilitates its rapid migration to the oil/water interface. Meanwhile, EAB, containing abundant positive and negative charges, experienced charge attraction and repulsion, making its adsorption at the oil/water interface unstable and providing a driving force for the oil film peeling. Additionally, the combination of JRGO and EAB exhibited outstanding IFT reduction and wettability reversal capabilities, significantly increasing the contact angle of oil droplets on the slide surface, reducing the adhesion work, and making the oil film easier to peel off. Finally, JRGO adsorbed onto the slide surface to form a water film, preventing the stripped oil film from re-adhering and achieving efficient oil film removal.

3.4. Heavy Oil Recovery Experiments

Based on the above results, three systems: JRGO, EAB, and JRGO/EAB, were selected for sand-pack experiments to evaluate their potential applications in EOR for conventional heavy oil reservoirs. During the experiment, changes in injection pressure, water cut, and recovery were recorded as the injection pore volume (PV) increased (Figure ). The main physical characteristics of the sand-pack, including permeability (k), porosity (Φ), initial oil saturation (S 0), and oil recovery factor, are summarized in Table .

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Cumulative oil recovery factor, water cut, and injection pressure as a function of injection volume: HPAM (a), JRGO system (b), EAB system (c), and JRGO/EAB system (d).

3. Summary of Oil Recovery Experiments.

mixtures
 k (μm2)
 Φ (%)
 S 0 (%)
 oil recovery factor (%)
        water flooding recovery chemical flooding recovery total
HPAM 1.33 30.6 80.2 44.1 9.6 53.7
JRGO system 1.13 29.0 79.1 46.3 13.2 59.5
EAB system 1.45 31.3 71.7 46.9 11.2 58.1
JRGO/EAB system 1.13 30.6 75.5 48.6 17.1 65.7
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Both pure JRGO and EAB solutions feature low viscosity, and the low viscosity of the flooding fluids restricts sufficient interaction between the system and heavy oil during combination flooding. To address this limitation, 0.15% HPAM was added to the system to enhance its interaction with heavy oil.

The abilities of the JRGO system and the EAB system to enhance heavy oil recovery were not significantly different. Although the two materials exhibited markedly different interaction abilities with heavy oil, the JRGO/EAB system demonstrated a superior ability to enhance the heavy oil recovery. Experimental results confirmed that the synergistic effect of JRGO and EAB significantly improved the oil recovery. As shown in Figure , the addition of the polymer cannot alter the interfacial tension (IFT) and contact angle of the system by orders of magnitude. Over time, the contact angle decreases from an initial value of 0.012 to 0.005, achieving an ultralow interfacial tension state. Furthermore, the presence of the polymer inhibits rapid variation of the contact angle, resulting in a slow descending rate.

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Effect of HPAM on IFT and contact angle of the JRGO/EAB system.

During the initial stage of water flooding, the injection pressure rose sharply and then dropped after 0.2 PV as the injected water began to break through and water production started at the sand-pack outlet. As the water flooding process continued, the injection pressure decreased, the oil recovery factor increased slowly, and the water cut increased. At this point, the oil recovery factor was ∼47%. After the injection of 0.3 PV of the combination system, the injection pressure increased significantly due to the increase in system viscosity, and the oil recovery factor further improved. Following an additional 0.2 PV of water flooding, the injection pressure gradually decreased, the water cut increased, and the oil recovery factor increased slowly. The results demonstrated that the combination of JRGO and EAB could achieve ultra-low IFT, with enhanced wettability alteration ability. Additionally, the nanosheet structure of JRGO contributed to the emulsion stabilization. The synergistic effect of these properties resulted in the highest oil recovery factor for the JRGO/EAB system (17.1%), which was higher than those of the JRGO system (13.2%) and the EAB system (11.2%). The incremental oil recovery factor of polymer flooding reaches only 9.6%, which is substantially lower than that of the other three systems. The obvious disparity in incremental recovery factors further demonstrates the superior performance of the JRGO/EAB system.

3.5. Enhanced Heavy Oil Recovery Mechanism

The heavy oil displacement mechanism of the JRGO/EAB system is schematically illustrated in Figure . Due to the nanosheet structure of JRGO and the unique zwitterionic surfactant characteristics of EAB, the synergistic effect of JRGO and EAB significantly reduces the interfacial tension (IFT), alters the wettability of the rock surface, and enables the oil adhered to the rock surface to stretch easily, forming oil filaments that ultimately break into oil droplets. This process prevents the detached oil droplets from reattaching to the rock surface. Additionally, because of Brownian motion and electrostatic repulsion between the nanosheets, the nanosheets create a wedge structure under the confinement of the three-phase (oil/nanofluid/rock) contact area. This wedge structure generates a disjoining pressure gradient, which facilitates the diffusion of nanofluids and accelerates oil film peeling from the rock surface. Furthermore, JRGO forms a stable rigid film structure on the oil/water (O/W) emulsion, making the oil droplets resistant to coalescence. This property enhances the migration ability of the O/W emulsion, further contributing to the efficiency of the heavy oil recovery.

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EOR mechanism of enhancing heavy oil recovery by JRGO/EAB.

4. Conclusions

In this work, Janus GO (JRGO) was prepared by a simple interface modification method, and the interaction between JRGO and heavy oil was studied. The main conclusions can be summarized as follows:

  • (1)

    The JRGO was characterized by FTIR, TG, SEM, XRD, and XPS. The results show that JRGO has some interfacial properties in an oil/water system. Compared with GO, JRGO has stronger ability to reduce IFT, change wettability, and emulsion stability.

  • (2)

    The results of combination with different surfactants showed that JRGO and EAB showed an excellent ability to reduce IFT and a better ability to change wettability. At the same time, JRGO + EAB has an excellent oil film stripping ability. In the heavy oil displacement experiments, the EOR enhancement capability of the JRGO/EAB system is significantly higher than that of the single system.

Acknowledgments

The authors thank Oil & Gas Major Project (2025ZD1406403) and the National Science and Technology Major Project of New Oil and Gas Exploration and Development (Grant No. 2025ZD1406203) for their financial support.

Mingchen Ding: writingoriginal draft, methodology, investigation, formal analysis, and conceptualization. Zhenyu Zhang: funding acquisition. Yutan Shen: funding acquisition, visualization, and validation. Hui Chen: visualization and validation. Guilin Liu: visualization and validation. Haicheng Liu: visualization and validation. Hanchao Wu: visualization and validation.

The authors declare no competing financial interest.

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