A pinning nanomaterial, a preparation method and application thereof

Abstract

The application belongs to the technical field of oil development, and particularly relates to a pinning nanomaterial and a preparation method and application thereof, the preparation method comprising the following steps: carboxylation of MoS2 and dopamine hydrochloride under alkaline conditions to make dopamine self-oxidize and polymerize to form a polydopamine coating, centrifugal collection and washing of the precipitate, addition of a protective agent, pre-freezing for 2-4 hours, and freezing drying to obtain MoS2@PDA; addition of an alpha-hydroxy-omega-amino polypropylene glycol solution to a dispersion of MoS2@PDA, reaction at 50-60 DEG C for 8-12 hours, addition of anhydrous ethanol, stirring, centrifugal collection and washing of the precipitate, addition of 3wt% trehalose and 1.5wt% mannitol, pre-freezing for 3-5 hours, and freezing drying to obtain the pinning nanomaterial; and the pinning nanomaterial of the application makes the water phase capillary force in the pores a resistance and the oil phase capillary force a power, thereby inhibiting the flow of the water phase in the reservoir and strengthening the flow of the oil phase.

Description

Technical Field

[0001] This invention belongs to the field of petroleum development technology, specifically relating to a pinning nanomaterial, its preparation method, and its application. Background Technology

[0002] China's medium- to low-permeability oil reservoirs are widely distributed and are key resources for ensuring energy security. These reservoirs suffer from uneven natural fracture development, resulting in almost no natural production capacity. Decades of development have exacerbated their heterogeneity, and the inability to control water and extract oil remains a bottleneck hindering their efficient development. Existing plugging agents, which alter fluid properties and pore structure, often exhibit poor oil-water selectivity, short-lasting effects, and can damage the reservoir and impair permeability. To address these issues, relative permeability modifiers form a hydrophobic chemical film on the rock surface, adjusting the oil-water flow path and increasing relative oil permeability while decreasing relative water permeability without significantly reducing overall permeability. However, their size is not suitable for all low-permeability reservoir conditions. Therefore, optimizing the size and dispersion stability of the modifier is crucial for "water control and oil enhancement" in medium- to low-permeability reservoirs and a prerequisite for long-term controllability.

[0003] MoS2 possesses a high specific surface area and anisotropic interfacial interactions, making it more advantageous for spreading and forming films on pore-throat surfaces and for interface control compared to spherical nanoparticles, thus attracting considerable attention. However, the functionalization approach of MoS2 for basic nanomaterial units is still mainly based on water-wet modification, making it difficult to achieve differentiated control of oil and water phases. Summary of the Invention

[0004] To address the above problems, this invention provides a pinning nanomaterial, its preparation method, and its application.

[0005] A method for preparing pinned nanomaterials includes the following steps: Carboxylated MoS2 and dopamine hydrochloride react in an alkaline solution to induce dopamine to undergo auto-oxidative polymerization to form a polydopamine coating. The precipitate is collected by centrifugation and washed. A protective agent is added, and the mixture is pre-frozen at -85℃ to -75℃ for 2 to 4 hours. After freeze-drying, MoS2@PDA with strong adsorption pinning groups is obtained. An α-hydroxy-ω-aminopolypropylene glycol solution was added to a dispersion of MoS2@PDA and reacted at 50℃~60℃ for 8h~12h. The flexible segments of α-hydroxy-ω-aminopolypropylene glycol were stably grafted onto the surface of MoS2@PDA via Michael addition reaction. After the reaction was completed, anhydrous ethanol was added, the mixture was stirred, the precipitate was collected by centrifugation and washed, 3wt% trehalose and 1.5wt% mannitol were added, and the mixture was pre-frozen at -75~-85℃ for 3h~5h. The mixture was then freeze-dried at -40~-50℃ and 0.05mbar for about 32~36h to obtain a "pinned" nanomaterial with strong hydrophobic function.

[0006] This invention introduces strong hydrophobic groups to improve the controllability of the material for both oil and water effects, making the capillary force of the water phase in the pores a resistance and the capillary force of the oil phase a driving force, thereby inhibiting the flow of the water phase in the reservoir and enhancing the flow of the oil phase. In addition, the pinned nanomaterials regulate the balanced flow of oil and water by adsorbing and forming a film on the pore surface.

[0007] Preferably, the mass ratio of the carboxylated MoS2 to dopamine hydrochloride is 1:2~3.

[0008] Preferably, the reaction time of carboxylated MoS2 and dopamine hydrochloride in alkaline solution is 20h~30h.

[0009] Preferably, the mass ratio of HO-PPO-NH2 to MoS2@PDA is 6~10:2~3.

[0010] Preferably, the protective agent is trehalose.

[0011] Preferably, the preparation steps of the carboxylated MoS2 are as follows: Add 3.0 g of mercaptopropionic acid to the dispersion of MoS2, sonicate for 24 hours, collect the precipitate by centrifugation, wash and dry to obtain carboxylated MoS2; The mass ratio of MoS2 to mercaptopropionic acid is 1:2~3.

[0012] Preferably, the ultrasound conditions are: 50℃~60℃, 35kHz~40kHz, 60W~100W.

[0013] The pinning nanomaterials prepared by the aforementioned method.

[0014] The application of the aforementioned pinning nanomaterials as plugging agents in oil production.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes an integrated size control approach combining "reaction condition regulation + surface confinement + differential centrifugation fractionation." By controlling reaction temperature, time, pH, and reactant ratios, high-density nucleation and confined growth are induced, allowing for controlled initial size of MoS2 nanosheets. Simultaneously, the introduction of a dispersant synergistically inhibits sheet aggregation and secondary growth. After gentle ultrasonic exfoliation, the product undergoes further precise screening using differential centrifugation fractionation, resulting in small-sized MoS2 nanosheets with concentrated size and excellent dispersibility. Furthermore, the basic nanomaterial unit undergoes synergistic functionalization with "strong adsorption-strong hydrophobicity." Traditional plugging materials block both water and oil, lacking selectivity, with short water-blocking periods and easy degradation under shear, resulting in loss of viscosity. This invention introduces strongly hydrophobic groups to improve the controllability of both water and oil phases, making the capillary force of the aqueous phase in the pores a resistance and the capillary force of the oil phase a driving force, thereby inhibiting the aqueous phase in the reservoir. The invention enhances the flow of the oil phase and strengthens the flow of the water phase. The introduction of strong adsorption groups allows the pinned nanomaterials to be strongly anchored to the pore surface like "nails," making them difficult to desorb and providing long-lasting effects. Furthermore, while traditional plugging agents damage the reservoir and affect the two-phase flow capacity of oil and water, the pinned nanomaterials of this invention regulate the balanced flow of oil and water by adsorbing and forming a film on the pore surface. Unlike traditional organic / inorganic plugging agents that alter the flow path through blockage and retention, this invention does not damage the reservoir. Therefore, it is reservoir-friendly, has a long-lasting effect, and strong selectivity, providing a new and feasible technical path for long-term water control and oil enhancement in medium- to low-permeability reservoirs. Attached Figure Description

[0016] Figure 1 TEM images of the MoS2@PDA nanosheets obtained in Examples 1-3.

[0017] Figure 2 The curves showing the change in the stability index of the "pinned" nanomaterials in Examples 1-3 over time are shown. Detailed Implementation

[0018] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0019] Unless otherwise specified, the experimental methods described in the various embodiments of this invention are all conventional methods; Unless otherwise specified, "room temperature" in this invention refers to 25-30°C.

[0020] Unless otherwise specified, all reagents used in this invention are commercially available. Tris(hydroxymethyl)aminomethane, dopamine hydrochloride, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, α-hydroxy-ω-aminopolypropylene glycol, polyvinylpyrrolidone, and trehalose were purchased from Shanghai Maclean Biochemical Co., Ltd.; ammonium heptamolybdate, thioacetamide, mercaptopropionic acid, N,N-dimethylformamide, carbodiimide, and mannitol were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; ethanol and hydrochloric acid were standard laboratory reagents, and deionized water was prepared in the laboratory. Abbreviations for each material are shown in Table 1.

[0021] Table 1: Chinese Abbreviation Comparison Table The technical solution of the present invention will be further illustrated by the following embodiments.

[0022] Example 1: A method for preparing "pinned" nanomaterials includes the following steps: (1) Preparation of precursor solution.

[0023] 1.65 g of ammonium heptamolybdate was used as the molybdenum source, and 4.5 g of thioacetamide was used as the sulfur source, so that the Mo:S molar ratio was about 1:7. The two were dissolved in 105 mL of deionized water. 0.66 g of cetyltrimethylammonium bromide was added as a dispersant, and the pH of the solution was adjusted to 4.5 with 0.1 mol / L hydrochloric acid. The solution was stirred at 700 rpm for 1 hour under magnetic stirring to obtain a homogeneous precursor solution.

[0024] (2) Hydrothermal reaction synthesis and size regulation.

[0025] The obtained precursor solution was transferred to a 250 mL polytetrafluoroethylene-lined hydrothermal reactor and reacted at 200 °C for 12 hours, then naturally cooled to room temperature. After centrifuging the reaction product at 3000 × g for 10 min to remove large particles, the supernatant was collected and centrifuged again at 8000 × g for 18 min to collect the precipitate. The precipitate was redispersed in a mixed solvent of deionized water / anhydrous ethanol at a volume ratio of 8 / 2 (solid-liquid ratio 10 mg / mL). 0.05 wt% polyvinylpyrrolidone was added as a dispersion stabilizer. After pre-dispersing under magnetic stirring for 10 min, the mixture was treated with an ultrasonic bath at 40 kHz and 80 W for 5 min, with the system temperature controlled to not exceed 30 °C.

[0026] After ultrasonic treatment, the undispersed large particles were removed by centrifugation at 2000×g for 5 min. The supernatant was collected, and then the final precipitate was collected by centrifugation at 8000×g for 15 min. The precipitate was washed three times each with 0.1 mol / L hydrochloric acid solution and anhydrous ethanol, followed by two washes with deionized water to remove residual ions and surfactants. The washed sample was redispersed with deionized water, and 3 wt% trehalose and 0.05 wt% PVP were added as cryoprotectants. After pre-freezing at -80℃ for 3 h, the sample was freeze-dried at -35℃ and 0.08 mbar for about 28 h to obtain loose black MoS2.

[0027] (3) "Pinning" modification on the surface of nanosheets.

[0028] 1.0 g of the prepared MoS2 was dispersed in 50 mL of deionized water, and 3.0 g of mercaptopropionic acid was added. The mixture was continuously ultrasonicated at 60 °C, 40 kHz, and 80 W for 24 hours to achieve carboxylation modification of the MoS2 surface. After the reaction, the precipitate was collected by centrifugation at 8000 × g for 20 min. The product was washed alternately with deionized water and anhydrous ethanol 3-5 times until the washing solution was neutral and odorless. The washed sample was dried overnight in a vacuum drying oven at 60 °C for later use, yielding carboxylated MoS2 nanosheets.

[0029] 1 g of carboxylated MoS2 nanosheets were dispersed in 100 mL of 0.05 mol / L Tris buffer (pH 8.5). 3.0 g of dopamine hydrochloride was added, and the mixture was magnetically stirred until homogeneous. The mixture was then stirred continuously at room temperature for 24 h to allow dopamine to undergo auto-oxidative polymerization under alkaline conditions to form a polydopamine coating. After the reaction was complete, the product was collected by centrifugation at 8000 × g for 20 min. The product was washed 3-5 times alternately with deionized water and ethanol until the washings were clear and colorless. 5 wt% trehalose was added as a protective agent, and the mixture was pre-frozen at -80℃ for 3 h. Then, it was freeze-dried at -35℃ and 0.06 mbar for approximately 32 h to obtain MoS2@PDA nanosheets with strongly adsorbed "pinning" groups.

[0030] (4) Hydrophobic alkyl linkages.

[0031] 100 mg of dried MoS2@PDA nanosheets were ultrasonically dispersed in a solvent consisting of 6.7 mL of anhydrous N,N-dimethylformamide and 2.2 mL of anhydrous ethanol at a volume ratio of 3:1 to prepare a MoS2@PDA dispersion. Separately, 30 mg of HO-PPO-NH2 (molecular weight approximately 1000) was dissolved in 5 mL of anhydrous DMF, and 5 mg of carbodiimide was added. The mixture was magnetically stirred at room temperature for 2-3 h to obtain a HO-PPO-NH2 solution. Subsequently, under nitrogen protection, the HO-PPO-NH2 solution was slowly added dropwise to the MoS2@PDA dispersion. After the addition was complete, the mixture was magnetically stirred at 55 °C for 10 h to stably graft flexible segments onto the MoS2@PDA surface via a Michael addition reaction. After the reaction was complete, excess anhydrous ethanol (20 mL) was added to the system, and stirring was continued for 30 min to terminate the reaction and promote product precipitation. The product was centrifuged at 8000×g for 10 min to collect the precipitate, and then washed alternately with anhydrous ethanol and deionized water 4-5 times. 3wt% trehalose and 1.5wt% mannitol were added, and the mixture was pre-frozen at -80℃ for 4 hours. Then, it was freeze-dried at -40℃ and 0.05mbar for about 34 hours to obtain “pinned” nanomaterials with strong hydrophobic function.

[0032] Example 2: A method for preparing "pinned" nanomaterials includes the following steps: (1) Preparation of precursor solution.

[0033] 1.2 g of ammonium heptamolybdate was used as the molybdenum source, and 3.3 g of thioacetamide was used as the sulfur source, so that the Mo:S molar ratio was about 1:7. The two were dissolved in 105 mL of deionized water. 0.40 g of hexadecyltrimethylammonium bromide was added as a dispersant, and the pH of the solution was adjusted to 4.5 with 0.1 mol / L hydrochloric acid. The solution was stirred at 700 rpm for 1 h under magnetic stirring to obtain a homogeneous precursor solution.

[0034] (2) Hydrothermal reaction synthesis and size regulation.

[0035] The obtained precursor solution was transferred to a 250 mL polytetrafluoroethylene-lined hydrothermal reactor and reacted at 210 °C for 14 h, then naturally cooled to room temperature. The reaction product was centrifuged at 3000 × g for 10 min to remove large particles, and the supernatant was then centrifuged at 6000 × g for 15 min to collect the precipitate. The precipitate was redispersed in a mixed solvent of deionized water / anhydrous ethanol (volume ratio = 8 / 2) at a solid-liquid ratio of 12 mg / mL. 0.03 wt% polyvinylpyrrolidone was added as a dispersion stabilizer, and the mixture was pre-dispersed under magnetic stirring for 10 min, followed by ultrasonic treatment at 35 kHz and 60 W for 5 min, with the system temperature controlled to not exceed 30 °C.

[0036] After ultrasonic treatment, the undispersed large particles were removed by centrifugation at 2000×g for 5 min. The supernatant was collected, and the final precipitate was collected by centrifugation at 6000×g for 12 min. The precipitate was washed three times each with 0.1 mol / L hydrochloric acid solution and anhydrous ethanol, followed by two washes with deionized water to remove residual ions and surfactants. The washed sample was redispersed with deionized water, and 3 wt% trehalose and 0.05 wt% PVP were added as cryoprotectants. After pre-freezing at -80℃ for 3 h, the sample was freeze-dried at -35℃ and 0.08 mbar for about 28 h to obtain loose black MoS2.

[0037] (3) "Pinning" modification on the surface of nanosheets.

[0038] 1.0 g of the previously prepared MoS2 was dispersed in 40 mL of deionized water, and 2.5 g of mercaptopropionic acid was added. The mixture was continuously ultrasonicated at 55 °C, 40 kHz, and 100 W for 18 h to achieve carboxylation modification of the MoS2 surface. After the reaction, the precipitate was collected by centrifugation at 8000 × g for 20 min. The product was washed alternately with deionized water and anhydrous ethanol 3-5 times until the washing solution was neutral and odorless. The washed sample was dried overnight in a vacuum drying oven at 60 °C for later use, yielding carboxylated MoS2 nanosheets.

[0039] 1 g of carboxylated MoS2 nanosheets were dispersed in 80 mL of 0.04 mol / L Tris buffer (pH 8.5). 2.0 g of dopamine hydrochloride was added, and the mixture was magnetically stirred until homogeneous. The mixture was then stirred continuously at room temperature for 24 hours to allow dopamine to undergo auto-oxidative polymerization under alkaline conditions to form a polydopamine coating. After the reaction was complete, the product was collected by centrifugation at 8000 × g for 20 min. The product was washed 3-5 times alternately with deionized water and ethanol until the washings were clear and colorless. 5 wt% trehalose was added as a protective agent, and the mixture was pre-frozen at -80℃ for 3 h. Then, it was freeze-dried at -35℃ and 0.06 mbar for approximately 32 h to obtain MoS2@PDA nanosheets with strongly adsorbed "pinning" groups.

[0040] (4) Hydrophobic alkyl linkages.

[0041] 80 mg of dried MoS2@PDA nanosheets were ultrasonically dispersed in 5.0 mL of a solvent consisting of anhydrous N,N-dimethylformamide and 1.7 mL of anhydrous ethanol at a volume ratio of 3:1 to prepare a MoS2@PDA dispersion. Separately, 25 mg of HO-PPO-NH2 (molecular weight approximately 1000) was dissolved in 4 mL of anhydrous DMF, and 4 mg of carbodiimide was added. The mixture was magnetically stirred at room temperature for 2-3 h to obtain a HO-PPO-NH2 solution. Subsequently, under nitrogen protection, the HO-PPO-NH2 solution was slowly added dropwise to the MoS2@PDA dispersion. After the addition was complete, the mixture was magnetically stirred at 50 °C for 10 h to stably graft the flexible segments onto the MoS2@PDA surface. After the reaction was complete, excess anhydrous ethanol (15 mL) was added to the system, and stirring was continued for 30 min to terminate the reaction and promote product precipitation. The product was centrifuged at 8000×g for 10 min to collect the precipitate, and washed 4-5 times alternately with anhydrous ethanol and deionized water. 3wt% trehalose and 1.5wt% mannitol were added, and the mixture was pre-frozen at -80℃ for 4 hours. Then, it was freeze-dried at -40℃ and 0.05mbar for about 34 hours to obtain “pinned” nanomaterials with strong hydrophobic function.

[0042] Example 3: A method for preparing "pinned" nanomaterials includes the following steps: (1) Preparation of precursor solution.

[0043] 1.10 g of ammonium heptamolybdate was used as the molybdenum source, and 3.00 g of thioacetamide was used as the sulfur source, so that the Mo:S molar ratio was about 1:7. The two were dissolved in 105 mL of deionized water. 0.30 g of cetyltrimethylammonium bromide was added as a dispersant, and the pH of the solution was adjusted to 4.5 with 0.1 mol / L hydrochloric acid. The solution was stirred at 600 rpm for 1 h under magnetic stirring to obtain a homogeneous precursor solution.

[0044] (2) Hydrothermal reaction synthesis and size regulation.

[0045] The obtained precursor solution was transferred to a 250 mL polytetrafluoroethylene-lined hydrothermal reactor and reacted at 225 °C for 18 h, then naturally cooled to room temperature. The reaction product was centrifuged at 2000 × g for 12 min to remove large particles, and the supernatant was then collected by centrifugation at 4500 × g for 15 min to collect the precipitate. The precipitate was redispersed in a mixed solvent of deionized water / anhydrous ethanol at a volume ratio of 8 / 2 (solid-liquid ratio 10 mg / mL). 0.03 wt% polyvinylpyrrolidone was added as a dispersion stabilizer, and the mixture was pre-dispersed under magnetic stirring for 10 min, followed by ultrasonic treatment at 35 kHz and 60 W for 5 min, with the system temperature controlled to not exceed 30 °C.

[0046] After ultrasonic treatment, the undispersed large particles were removed by centrifugation at 2000×g for 5 min. The supernatant was collected and then centrifuged at 4500×g for 15 min to collect the final precipitate. The precipitate was washed three times each with 0.1 mol / L hydrochloric acid solution and anhydrous ethanol, followed by two washes with deionized water to remove residual ions and surfactants. The washed sample was redispersed with deionized water, and 3 wt% trehalose and 0.05 wt% PVP were added as cryoprotectants. After pre-freezing at -80℃ for 3 h, the sample was freeze-dried at -35℃ and 0.08 mbar for about 28 h to obtain a loose black MoS2 powder.

[0047] (3) "Pinning" modification on the surface of nanosheets.

[0048] 1.0 g of the prepared MoS2 nanosheets were dispersed in 60 mL of deionized water, and 2.0 g of mercaptopropionic acid was added. The mixture was continuously ultrasonicated at 50 °C, 35 kHz, and 60 W for 14 h to achieve carboxylation modification of the MoS2 surface. After the reaction, the precipitate was collected by centrifugation at 8000 × g for 18 min. The product was washed alternately with deionized water and anhydrous ethanol 3-5 times until the washing solution was neutral and odorless. The washed sample was dried overnight in a vacuum drying oven at 60 °C for later use, yielding carboxylated MoS2 nanosheets.

[0049] 1 g of carboxylated MoS2 nanosheets were dispersed in 100 mL of 0.03 mol / L Tris buffer (pH 8.5). 2.0 g of dopamine hydrochloride was added, and the mixture was magnetically stirred until homogeneous. The mixture was then stirred continuously at room temperature for 12 h to allow dopamine to undergo auto-oxidative polymerization under alkaline conditions to form a polydopamine coating. After the reaction was complete, the product was collected by centrifugation at 8000 × g for 18 min. The product was washed 3-5 times alternately with deionized water and ethanol until the washings were clear and colorless. 5 wt% trehalose was added as a protective agent, and the mixture was pre-frozen at -80 °C for 3 h. Then, it was freeze-dried at -35 °C and 0.06 mbar for approximately 32 h to obtain MoS2@PDA nanosheets with strongly adsorbed "pinning" groups.

[0050] (4) Hydrophobic alkyl linkages.

[0051] 60 mg of dried MoS2@PDA nanosheets were ultrasonically dispersed in 4.0 mL of a solvent consisting of anhydrous N,N-dimethylformamide and 1.3 mL of anhydrous ethanol at a volume ratio of 3:1 to prepare a MoS2@PDA dispersion. Separately, 20 mg of HO-PPO-NH2 (molecular weight approximately 1000) was dissolved in 3 mL of anhydrous DMF, and 3 mg of carbodiimide was added. The mixture was magnetically stirred at room temperature for 2-3 h to obtain a HO-PPO-NH2 solution. Subsequently, under nitrogen protection, the HO-PPO-NH2 solution was slowly added dropwise to the MoS2@PDA dispersion. After the addition was complete, the mixture was magnetically stirred at 50 °C for 8 h to stably graft the flexible segments onto the MoS2@PDA surface. After the reaction was complete, excess anhydrous ethanol (12 mL) was added to the system, and stirring was continued for 30 min to terminate the reaction and promote product precipitation. The product was centrifuged at 8000×g for 8 min to collect the precipitate, and then washed 4-5 times alternately with anhydrous ethanol and deionized water. 3wt% trehalose and 1.5wt% mannitol were added, and the mixture was pre-frozen at -80℃ for 4 hours. Then, it was freeze-dried at -40℃ and 0.05mbar for about 34 hours to obtain “pinned” nanomaterials with strong hydrophobic function.

[0052] Effect verification: To further illustrate the effect of "pinning" nanomaterials in this invention, experiments were conducted on the prepared nanomaterials, including morphology testing of MoS2@PDA nanosheets, nanofluid stability testing, interfacial tension testing, wettability testing, and oil-water interpenetration experiments, to further demonstrate the scientific validity and effectiveness of the present invention.

[0053] 1. Nanosheet morphology testing.

[0054] To further verify the structural characteristics and preparation effect of the "pinned" nanomaterials in this invention, the MoS2@PDA nanosheets obtained in Examples 1-3 were characterized by transmission electron microscopy (TEM). The results are as follows: Figure 1 As shown, all three samples exhibit a typical layered two-dimensional sheet structure with complete morphology and clear crystal boundaries. The lateral size and layer thickness of the nanosheets vary with different reaction conditions.

[0055] In Example 1, the lateral dimension of the nanosheets was approximately 25 nm; in Example 2, the nanosheet size was approximately 42 nm; and in Example 3, the nanosheet size was approximately 58 nm. TEM showed that there was a continuous amorphous low-contrast outer layer of approximately 1 nm at the edge of the MoS2 sheets, consistent with the PDA coating, as shown by the white arrow in the figure; layered stripes of MoS2 were visible within the sheets.

[0056] 2. Nanofluid stability test.

[0057] The "pinned" nanomaterials obtained in Examples 1-3 were freeze-dried and then dispersed in deionized water at a mass fraction of 0.6 wt%. A uniform nanofluid dispersion was prepared by magnetic stirring and ultrasonic dispersion. After standing for 12 hours, the dispersion stability of the nanofluid dispersion was tested using a multiple light scattering instrument. The dispersion was placed in a standard sample tube, and the scan time was set from 0 min to 360 min, with data collected at 10-min intervals. The stability index change curve over time is shown below. Figure 2 As shown, the stability index is abbreviated as TSI. The system in Example 1 exhibits the best dispersibility, minimal agglomeration and sedimentation, and the best nanofluid stability; Example 2 shows moderate dispersion stability; in Example 3, the nanoparticles show a certain degree of agglomeration or sedimentation.

[0058] 3. Interface tension test.

[0059] Under conditions of 70℃ and a mineralization of 20000 mg / L, with a divalent cation content of 4500 mg / L, and using simulated formation water as a solvent, the "pinned" nanomaterials prepared in Examples 1-3 were respectively prepared into nano-solutions with a concentration of 0.6 wt%. These solutions were then thoroughly ultrasonically dispersed to achieve uniform mixing, resulting in "pinned" nanofluids. The interfacial tension between the nano-solutions prepared in different examples and crude oil was tested using a rotating drop interfacial tensiometer at a constant temperature of 70℃. The viscosity of the crude oil at room temperature was 70 mPa·s. Crude oil was injected through a micro-syringe to form a suspended droplet. After the interface stabilized, the equilibrium interfacial tension was recorded. The measurement was repeated three times, and the average value was taken (see Table 2). The results show that the effect of reducing interfacial tension decreases sequentially with increasing nanosheet size, decreasing interfacial coverage and rearrangement capacity.

[0060] Table 2: Test results of interfacial tension between "pinned" nanofluid and crude oil in different embodiments 4. Contact angle test.

[0061] A clean, initially wet quartz plate measuring 2.5 × 2.5 × 0.5 cm was used as the test substrate. Quartz sheets were immersed in 0.6 wt% "pinned" nanofluid prepared from the "pinned" nanomaterials of the above-mentioned different embodiments, and treated in a 70°C water bath for 24 h, 48 h, 72 h, 96 h, 120 h, 144 h, 168 h, 192 h, 216 h, and 240 h. Each group had an independent sample bottle. After immersion, the quartz sheets were removed, gently rinsed with deionized water, dried, and immediately subjected to contact angle testing. Crude oil was dropped onto the surface of the quartz sheet in water, and the static contact angle of the oil droplet on the surface of the quartz sheet was measured using a contact angle measuring instrument. To reduce error, five different positions were measured for each quartz sheet, and the average value was taken as the data for that group. The results are shown in Table 3. In Example 1, the sheet diameter was small, the surface nonpolarity was stronger, and the contact angle was the largest; in Examples 2 and 3, the size increased, the coverage per unit area and the rearrangement decreased, and the oil wetting degree was relatively weakened.

[0062] Table 3: Contact Angle Test Results of "Pinned" Nanofluid-Crude Oil in Different Embodiments 5. Oil-water interpenetration test.

[0063] Prepare 4 artificial homogeneous cores, averaging 30.0 cm in diameter and 2.5 cm in diameter, with a K... g =50mD, experimental temperature 70℃, unsteady-state oil-water relative permeability experiment was conducted. Simulated formation water was first injected until saturation, then crude oil was injected until no water production was observed, obtaining the initial Sd. wi Subsequently, the core samples were subjected to constant-rate water flooding and "pinned" nanofluid flooding, respectively, and the cumulative oil production, cumulative fluid production, and displacement pressure differential were recorded at different times. The water breakthrough time was accurately recorded, and recording was intensified after water breakthrough. The recording time was appropriately extended as the oil production decreased until the water cut at the outlet section exceeded 99.95%, at which point the experiment was stopped. Data were processed using the JBN method to obtain oil-water and oil-"pinned" nanofluid phase permeability curves. The Brook-Corey equation was used to fit the phase permeability curves to obtain the phase permeability curve parameter n. w n o K rw * and K ro * The results are shown in Table 4. Compared to the water-drive baseline, the "pinned" nanofluid of this invention can significantly reduce the relative permeability of the aqueous phase endpoint and increase the relative permeability of the oil phase endpoint.

[0064] Table 4: Variation of relative permeability parameters for water-driven and "pinned" nanofluidic flooding Existing methods for preparing MoS2 nanomaterials, such as mechanical exfoliation and chemical vapor deposition, often suffer from wide size distributions and poor dispersion stability, making it difficult to meet the pore throat size requirements of some low-permeability reservoirs. While hydrothermal methods can synthesize MoS2 in batches, the product sizes are typically large, ranging from 50 to 500 nm. This invention utilizes an integrated size control route combining "reaction condition regulation + surface confinement + differential centrifugation fractionation." By controlling the reaction temperature, time, pH, and reactant ratios, high-density nucleation and confined growth are induced, allowing for controlled initial sizes of MoS2 nanosheets. Simultaneously, the introduction of a dispersant synergistically inhibits sheet aggregation and secondary growth. After gentle ultrasonic exfoliation, the product is further precisely screened using differential centrifugation fractionation, resulting in small-sized MoS2 nanosheets with concentrated size and excellent dispersibility.

[0065] It should be noted that when numerical ranges are mentioned in the claims of this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. To avoid redundancy, the present invention describes preferred embodiments.

[0066] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0067] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing pinned nanomaterials, characterized in that, Includes the following steps: Carboxylated MoS2 and dopamine hydrochloride react in an alkaline solution to induce dopamine to undergo auto-oxidative polymerization to form a polydopamine coating. The precipitate is collected by centrifugation and washed. A protective agent is added, and the mixture is pre-frozen at -85℃ to -75℃ for 2 to 4 hours. After freeze-drying, MoS2@PDA with strong adsorption pinning groups is obtained. An α-hydroxy-ω-aminopolypropylene glycol solution was added to a dispersion of MoS2@PDA and reacted at 50℃~60℃ for 8h~12h. Flexible segments from α-hydroxy-ω-aminopolypropylene glycol were grafted onto the surface of MoS2@PDA via Michael addition reaction. After the reaction was complete, anhydrous ethanol was added, the mixture was stirred, the precipitate was collected by centrifugation and washed, 3wt% trehalose and 1.5wt% mannitol were added, and the mixture was pre-frozen at -85℃~-75℃ for 3h~5h. After freeze-drying, pinned nanomaterials with strong hydrophobic properties were obtained.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the carboxylated MoS2 to dopamine hydrochloride is 1:2~3.

3. The preparation method according to claim 1, characterized in that, The reaction time of carboxylated MoS2 and dopamine hydrochloride in alkaline solution is 20-30 h.

4. The preparation method according to claim 1, characterized in that, The mass ratio of HO-PPO-NH2 to MoS2@PDA is 6~10:2~3.

5. The preparation method according to claim 1, characterized in that, The protective agent is trehalose.

6. The preparation method according to claim 1, characterized in that, The preparation steps of the carboxylated MoS2 are as follows: Mercaptopropionic acid was added to the dispersion of MoS2, and the mixture was sonicated for 24 hours. The precipitate was collected by centrifugation, washed, and dried to obtain carboxylated MoS2. The mass ratio of MoS2 to mercaptopropionic acid is 1:2~3.

7. The preparation method according to claim 6, characterized in that, The ultrasound conditions are: 50℃~60℃, 35kHz~40kHz, 60W~100W.

8. The pinning nanomaterial prepared by the preparation method according to claim 1.

9. The application of the pinning nanomaterial as a plugging agent in oil production according to claim 8.

Images