Mesoporous silica-rhamnolipid oil-displacing agent and preparation method and application thereof

Abstract

The invention discloses a mesoporous silica-rhamnolipid oil-displacing agent as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing mesoporous silica by adopting a sol-gel method; adding rhamnolipid into the dispersion liquid of the mesoporous silica for reaction; and after the reaction is finished, washing the precipitate, and drying to obtain the mesoporous silica-rhamnolipid oil-displacing agent. The rhamnolipid is loaded by using the high specific surface area and the pore structure of the mesoporous silica, so that the problem of large adsorption loss in the process of injecting the biosurfactant into the oil reservoir is effectively solved. Experiments show that the oil-displacing agent can significantly reduce the oil-water interfacial tension, changes the rock surface from lipophilicity to neutral wetting, and shows good temperature resistance, salt resistance and emulsion stability. When the concentration of rhamnolipid is 1000 mg / L, the adsorption loss of the rhamnolipid on the surface of quartz sand can be reduced by about 40.92%, the oil washing efficiency can reach about 77.82%, and the rhamnolipid has remarkable advantages and potential application value in the aspect of improving the crude oil recovery efficiency.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction technology, specifically to a mesoporous silica-rhamnolipin oil displacement agent, its preparation method, and its application. Background Technology

[0002] Petroleum is a crucial raw material for the chemical industry and has played a vital role in global economic development over the past century. The number of new oil field discoveries is decreasing annually, and most currently developed oil fields are in the middle to late stages of extraction, resulting in increasingly lower crude oil recovery rates. Although primary and secondary oil recovery processes have extracted some crude oil, approximately two-thirds of it remains unrecovered in the reservoirs, further compounded by the growing difficulty of discovering new oil fields. Therefore, developing new oil recovery technologies to improve the recovery rate of existing oil fields has become a key research direction in oil and gas extraction.

[0003] Biosurfactants (such as rhamnolipids) possess excellent oil displacement properties, are environmentally friendly, and can replace chemical surfactants in enhancing oil recovery. For example, the unique properties of rhamnolipids allow them to reduce the surface tension of water from 70 mN / m to 30 mN / m, while simultaneously reducing the interfacial tension with kerosene to 10 mN / m. -3 Below mN / m. This significant reduction effect makes rhamnolipids a promising candidate for enhanced oil recovery. However, biosurfactants are more expensive to produce than chemical surfactants, and during the injection process, they are easily adsorbed by the reservoir, leading to losses and further increasing oil displacement costs, thus greatly limiting the application of biosurfactant-assisted oil recovery technology.

[0004] In recent years, nanomaterials have been gradually applied in enhancing oil recovery. Silica (SiO2) nanoparticles have been the most widely studied in oilfield development (Bila et al., Experimental Investigation of Polymer-Coated Silica Nanoparticles for Enhanced Oil Recovery. Nanomaterials, 2019, 9(6):822). Because silica is the main component of quartz and sandstone in reservoirs, it is more compatible with porous media. Silica synthesis methods are simple, low-cost, non-toxic, and environmentally friendly. Regarding the application of nanoparticles in enhancing oil recovery, more research focuses on the combined use of chemical surfactants and nanoparticles (Wan Lu et al., Application of biosurfactants and their compound systems in tertiary oil recovery, Bioprocessing, 2024, 22(3):271-277). Recently, a small number of researchers have prepared a bio-based nanofluid oil displacement agent by mixing SiO2 nanoparticles with rhamnolipin biosurfactants, which can improve the oil recovery rate of low-permeability reservoirs and reduce injection pressure (Chinese Patent ZL201810838339.7).

[0005] While the aforementioned technologies have improved oil recovery rates to some extent, existing technologies simply use SiO2 nanoparticles and rhamnolipin biosurfactants in a simple compounding process, without considering adsorption losses and nanoparticle aggregation during injection. Studies have found that nanoparticles are prone to aggregation in aqueous environments, and the ability of aggregated SiO2 nanoparticles to load rhamnolipin is greatly reduced, which also easily clogs oil displacement pores (Wan Lu et al., Application of biosurfactants and their compounding systems in tertiary oil recovery, Bioprocessing, 2024, 22(3): 271-277). In recent years, mesoporous materials have attracted widespread attention from researchers. Materials with ordered mesoporous structures in the pore size range of 2~50 nm are called mesoporous materials. Mesoporous silica (HMSN) has shown unique potential in the field of enhanced oil recovery (EOR) due to its unique morphological characteristics and physicochemical properties, such as ultra-high specific surface area and pore volume, adjustable size and shape, easy surface functionalization, and rich surface chemical properties (Li Di et al., Characteristics of mesoporous SiO2 nanomaterials and their application progress in EOR. Applied Chemical Industry, 2023, 52(05): 1447-1453). Chinese patent application No. 2025108775035 discloses a high-temperature and high-salt nano-permeabilizer and its preparation method, which includes aminated modified mesoporous silica nanoparticles, nanocellulose, rhamnolipids, etc. The synergistic effect of rhamnolipids and anionic surfactants reduces the oil-water interfacial tension. In addition, the introduction of amino functional groups significantly improves the surface activity and anti-adsorption properties of the carrier.

[0006] In summary, a few researchers have made some progress in preparing oil displacement agents by combining SiO2 nanoparticles with rhamnolipid biosurfactants in the existing technology. However, the existing oil displacement agents based on aminated mesoporous silica nanoparticles, nanocellulose, rhamnolipids, etc., are very complicated to prepare. Furthermore, the amination modification process uses expensive amination reagents (such as 3-aminopropyltriethoxysilane), which not only increases the production cost of the oil displacement agent, but also the residual amination reagents may cause greater environmental pollution problems. Whether a simpler process based on the combination of mesoporous silica nanoparticles and biosurfactants can be developed, resulting in an oil displacement agent with simple composition, convenient preparation, and relatively low cost, while also reducing adsorption loss of biosurfactants during injection and releasing the biosurfactants upon reaching the oil layer to maximize their effectiveness, remains a technical challenge. Summary of the Invention

[0007] Technical problem solved: In view of the problems of cumbersome preparation process, large adsorption loss and high oil production cost in the oil recovery process using biosurfactants in the above-mentioned existing technology, the present invention proposes a mesoporous silica-rhamnolipin oil displacement agent and its simple preparation method and application. The oil displacement agent has extremely high stability in the aqueous phase and can rapidly release rhamnolipin after contacting the oil phase, thereby greatly reducing the adsorption loss of rhamnolipin during the injection process, reducing the use cost and significantly improving the oil displacement efficiency.

[0008] Technical solution: The first objective of this invention is to provide a method for preparing a mesoporous silica-rhamnolipin oil displacement agent, the steps of which are as follows:

[0009] Step 1: Prepare mesoporous silica (HMSN) using the sol-gel method;

[0010] Step 2: Add rhamnolipin (RL) to the dispersion of mesoporous silica and stir at 50°C for 6 hours. The mass ratio of mesoporous silica to rhamnolipin is 50-100:1-50.

[0011] Step 3: After the reaction is complete, the precipitate is washed with anhydrous ethanol and deionized water, and dried to obtain the mesoporous silica-rhamnolipin oil displacement agent (HMSN-RL oil displacement agent).

[0012] The mesoporous silica-rhamnolipin oil displacement agent provided by this invention has undergone characterization, performance testing, and oil washing performance testing. FT-IR and XRD results show that RL was successfully incorporated into HMSN. Scanning electron microscopy observation and particle size distribution revealed that RL loading increased the average particle size of HMSN-RL, and RL was partially attached to the surface, indicating the successful preparation of HMSN-RL. Simultaneously, this HMSN-RL oil displacement agent can reduce the oil-water interface to approximately 10 mN / m at a temperature of 80℃ and a salinity of 50000 mg / L, exhibiting temperature and salt resistance and excellent interfacial properties. Treatment with HMSN-RL can change the contact angle from oil-wet (114°) to water-wet (76.57°), further reducing interfacial tension. HMSN-RL can be effectively adsorbed at the oil-water interface, enhancing the strength of emulsion droplets and improving the stability of the emulsion. HMSN-RL achieves an oil washing efficiency of approximately 77.82% and reduces adsorption loss on the quartz sand surface by about 40.92% when the rhamnolipin concentration is 1000 mg / L, demonstrating its significant application potential in enhancing oil recovery.

[0013] Preferably, the preparation of mesoporous silica in step one using the sol-gel method is as follows:

[0014] S1. Mix anhydrous ethanol and distilled water, then add ammonia water, mix well, add tetraethyl orthosilicate, stir and react at room temperature for 1 hour, and finally centrifuge, wash with water and ethanol to collect the precipitate for later use.

[0015] S2. Disperse the precipitate obtained in step S1 in distilled water to prepare a precipitate dispersion, then add hexadecyltrimethylammonium bromide aqueous solution and triethanolamine, stir at room temperature for 1 h, heat to 80 °C and add tetraethyl orthosilicate dropwise, then place the reaction solution in a 50 °C water bath for reaction, add anhydrous sodium carbonate to etch, react for 3 h, after the reaction is completed, separate by centrifugation, wash the precipitate several times and place it in an oven to dry;

[0016] S3. The surfactant CTAB was removed by acid extraction. The precipitate was dispersed in a methanol solution containing concentrated hydrochloric acid and stirred at room temperature for 12 h. The sample was collected by centrifugation, washed with methanol and centrifuged 3 times, and then dried under vacuum to obtain mesoporous silica.

[0017] Preferably, in step S1, the ratio of anhydrous ethanol, distilled water, 25 wt% ammonia, and tetraethyl orthosilicate is 75 mL: 10 mL: 2 mL: 2 mL; in step S2, the ratio of the precipitate, hexadecyltrimethylammonium bromide, triethanolamine, tetraethyl orthosilicate, and anhydrous sodium carbonate is 0.45 g: 0.6 g: 0.25 g: 0.5 mL: 0.3 g; and in step S3, the ratio of the precipitate to the methanol solution containing concentrated hydrochloric acid is 1:30, and the mass ratio of concentrated hydrochloric acid, methanol, and water in the methanol solution containing concentrated hydrochloric acid is 1:556:36.

[0018] Preferably, the mass ratio of mesoporous silica to rhamnolipin is 2:1.

[0019] The second objective of this invention is to provide a mesoporous silica-rhamnolipin oil displacement agent prepared by the above method.

[0020] Preferably, the mesoporous silica has an average particle size of 460-500 nm.

[0021] The third objective of this invention is to provide the application of the above-mentioned mesoporous silica-rhamnolipin oil displacement agent as an oil displacement agent in petroleum extraction.

[0022] Preferably, the application includes formulating the oil displacement agent into a nanofluid and injecting it into the oil layer to reduce the oil-water interfacial tension, change the wettability of the rock surface, improve the emulsification stability of crude oil, and increase the oil washing efficiency.

[0023] An oil displacement composition for oil extraction, comprising an effective amount of the aforementioned mesoporous silica-rhamnolipin oil displacement agent.

[0024] Preferably, the effective amount of the mesoporous silica-rhamnolipin oil displacement agent is 250-1000 mg / L.

[0025] Beneficial effects: Compared with traditional oil displacement agents obtained by combining nanomaterials and biosurfactants, the present invention uses mesoporous silica materials and rhamnolipids to prepare oil displacement agents. The resulting oil displacement agents have extremely high stability in the aqueous phase and rapidly release rhamnolipids after contact with the oil phase, thereby greatly reducing the adsorption loss of rhamnolipids during the injection process, reducing usage costs, and significantly improving oil displacement efficiency. Attached Figure Description

[0026] Figure 1 UV spectra of rhamnolipin (50, 100, 150, 200, 250 mg / L) (a) and standard curve of rhamnolipin concentration measured by phenol-sulfuric acid method (b);

[0027] Figure 2 SEM images of HMSN (a, 100×) and HMSN-RL (b, 100×) and particle size distribution of HMSN (c) and HMSN-RL (d).

[0028] Figure 3 FT-IR spectra (a), XRD patterns (b), and TG analysis (c) of HMSN and HMSN-RL;

[0029] Figure 4 The adsorption-desorption curves (a) and pore size distribution diagram (b) of HMSN and HMSN-RL are shown.

[0030] Figure 5 The graph shows the changes in stability and UV transmittance of the HMSN and HMSN-RL dispersions over time. In the graph, (a) shows the change in stability of the dispersion (water → HMSN → HMSN-RL) over time; and (b) shows the change in UV transmittance over time.

[0031] Figure 6 The figure shows the interfacial tension diagrams of HMSN, RL and HMSN-RL at different concentrations. In the figure, (a) is the interfacial tension diagram of HMSN, RL and HMSN-RL at different concentrations; (b) is a magnified view of the interfacial tension between RL and HMSN-RL at different concentrations.

[0032] Figure 7 The figure shows the interfacial tension between oil and water of HMSN-RL at different temperatures and sodium ion concentrations. In the figure, (a) shows the interfacial tension between oil and water of HMSN, RL, and HMSN-RL at different temperatures; and (b) shows the interfacial tension between oil and water of HMSN-RL at different sodium ion concentrations.

[0033] Figure 8The graph shows the effect of different concentrations of RL, HMSN, and HMSN-RL on the contact angle.

[0034] Figure 9 Optical micrographs of HMSN, RL, and HMSN-RL emulsified diesel oil and the relationship between the water separation rate of the emulsion and time are shown in the figure. (a)-(c) are optical micrographs of HMSN, RL, and HMSN-RL emulsified diesel oil (magnification 10×40); (d) is the relationship between the water separation rate of the emulsion and time.

[0035] Figure 10 The figure shows the washing oil test and washing oil efficiency diagrams for HMSN-RL, HMSN, and RL. (a) shows the washing oil test for HMSN-RL, HMSN, and RL; (b) shows the washing oil efficiency diagram.

[0036] Figure 11 A comparison of adsorption losses of RL and HMSN-RL on the surface of quartz sand. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific embodiments, but there are no limitations on the present invention.

[0038] Unless otherwise specified, the raw materials and reagents used in the embodiments of this invention are all from commercially available products.

[0039] Example 1: Preparation of HMSN and HMSN-RL

[0040] This embodiment provides a method for preparing a mesoporous silica-rhamnolipin oil displacement agent, the specific steps of which are as follows:

[0041] Step 1: Preparation of mesoporous silica (HMSN):

[0042] The mesoporous silica was synthesized based on existing research (Xu Youqiang, Regulation of Drug Release Behavior in Curcumin Hollow Mesoporous Silica Drug Delivery System, Master's Thesis, Hebei University of Science and Technology, 2022), with slight modifications. The specific steps are as follows:

[0043] Solid silica spheres were synthesized using the sol-gel method: First, a mixture of 75 mL of anhydrous ethanol and 10 mL of distilled water was added to a round-bottom flask, followed by 2.0 mL of ammonia (25% by mass). The mixture was thoroughly mixed, and then 2.0 mL of tetraethyl orthosilicate was slowly added dropwise over 2 minutes at 100 rpm. The reaction was continued at room temperature (25°C) for 1.0 h with stirring. After the reaction was complete, the precipitate was centrifuged, washed three times with water and ethanol, dried, and collected for later use (the product weighed 0.45 g, yield approximately 83%).

[0044] The obtained precipitate was dispersed in deionized water to obtain a precipitate dispersion with a mass ratio of precipitate to deionized water of 1:10. Then, 0.6 g of hexadecyltrimethylammonium bromide (CTAB) was weighed and dissolved in deionized water to obtain a CTAB aqueous solution with a concentration of 30 mg / mL. After the CTAB was completely dissolved, 0.25 g of triethanolamine and the precipitate dispersion were added, and the mixture was stirred at room temperature for 1.0 h (100 rpm). Then, the temperature was raised to 80 °C, and 0.50 mL of tetraethyl orthosilicate was added dropwise, and the reaction was allowed to proceed for 1.0 h. The reaction solution was then placed in a 50 °C water bath for further reaction, and 0.3 g of anhydrous sodium carbonate was added for etching. The reaction was allowed to proceed for 3.0 h. After the reaction was completed, the precipitate was separated by centrifugation, washed several times, and then dried in an oven at 60 °C.

[0045] Finally, the surfactant CTAB was removed by acid extraction. The dried precipitate (approximately 0.51 g) was dispersed in 15 mL of methanol (containing 0.75 mL of concentrated hydrochloric acid, concentration 0.6 mol / L), and the mixture was stirred at room temperature for 12 h. The sample was collected by centrifugation, washed three times with methanol, and dried under vacuum at 60 °C to obtain HMSN. The powder was then ground again thoroughly in an agate mortar and dried in a drying oven at 60 °C for later use.

[0046] Step 2: Preparation and optimization of rhamnolipid-mesoporous silica displacement agent (HMSN-RL):

[0047] First, the standard curve of rhamnolipid concentration was determined using the phenol-sulfuric acid method, as follows:

[0048] Preparation of rhamnolipin standard stock solution: Accurately weigh the rhamnolipin standard and dilute it to 1000 mg / L with distilled water in a volumetric flask. Then, serially dilute it to 50 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L.

[0049] Phenol-sulfuric acid method: Take 1.00 mL of sample solution into a colorimetric tube, add 0.5 mL of 5% phenol aqueous solution and mix well, quickly add 2.50 mL of concentrated sulfuric acid and mix well, react at 80 ℃ for 15 min, let stand at room temperature for about 15 min, and scan the full wavelength using an ultraviolet spectrophotometer.

[0050] Construction of the rhamnolipin standard curve: Transfer 4 mL, 5 mL, 6 mL, 7 mL, 8 mL, 9 mL, 10 mL, 11 mL, and 12 mL of rhamnolipin standard stock solution into 50 mL volumetric flasks, respectively, and dilute to volume with distilled water. Measure the absorbance of the solutions at the maximum absorption wavelength using the phenol-sulfuric acid method described above. Plot the standard curve with the measured absorbance value on the ordinate and the concentration of rhamnolipin on the abscissa.

[0051] like Figure 1As shown, the maximum absorption wavelength of RL is approximately λ = 482 nm. The absorbance (A) of rhamnolipids shows a linear relationship with its mass concentration (C), yielding a standard curve y = 0.0024x + 0.1552. The fitted correlation coefficient is: R 2 =0.9857, which can be used to determine the concentration of rhamnolipids.

[0052] Subsequently, orthogonal experiments (see Table 1) were used to optimize the preparation conditions of the rhamnolipin-mesoporous silica displacement agent (HMSN-RL), including four experimental factors: A (HMSN concentration), B (RL concentration), C (reaction temperature), and D (reaction time). The RL encapsulation efficiency and loading of the obtained HMSN-RL under different experimental conditions were investigated.

[0053] The specific steps are as follows: Different masses of mesoporous silica were weighed and dispersed in 10 mL of anhydrous ethanol, resulting in silica concentrations of 0 mg / mL, 0.5 mg / mL, 1 mg / mL, and 2 mg / mL, respectively. The silica was then sonicated for 30 min using an ultrasonic cleaner to ensure complete dissolution. Next, different masses of rhamnolipid (RL) were added to the above solution, resulting in RL concentrations of 0.5 mg / mL, 1 mg / mL, 2 mg / mL, and 5 mg / mL, respectively. Subsequently, the resulting mixture was stirred at different temperatures (50 ℃, 65 ℃, 80 ℃) for different times (stirring speed 100 rpm, for 3 h, 6 h, and 9 h, respectively). After the reaction was complete, the precipitate was collected by centrifugation (8000 rpm, 10 min), washed repeatedly with anhydrous ethanol and deionized water, and dried in an oven for 24 h to obtain rhamnolipid-loaded mesoporous silica (HMSN-RL).

[0054] Table 1 Design of Orthogonal Experiments

[0055]

[0056] Calculation of encapsulation ratio, load capacity, and overall score:

[0057] Simultaneously, the supernatant obtained from the centrifugation was collected, and the residual unencapsulated RL in the supernatant was determined using the phenol-sulfuric acid method. The encapsulation efficiency (EE, %) and loading (LC, %) in the rhamnolipin displacement system were calculated using the following formulas:

[0058]

[0059]

[0060] The overall score (Y, %) is calculated using the following formula:

[0061]

[0062] Where Y1 represents the encapsulation efficiency (%), Y 1i Y1i represents the encapsulation rate of the i-th group (i=1, 2, 3, ..., 9) in the orthogonal experiment, and ∑y1i represents the sum of the encapsulation rates of all groups; Y2 represents the loading (%), Y2i represents the loading of the i-th group (i=1, 2, 3, ..., 9) in the orthogonal experiment, and ∑y2i represents the sum of the loadings of all groups.

[0063] An orthogonal experimental design (Table 1) and results analysis (Table 2) were performed using IBM SPSS Statistics 22. Range analysis was conducted on the experimental results in Table 2, resulting in Tables 3-5. Based on the k-value of the comprehensive score, the optimal combination was determined to be A3B2C1D2, i.e., HMSN concentration 2 mg / mL, RL concentration 1 mg / mL, reaction temperature 50 ℃, and reaction time 6 h. The order of importance of the factors was determined by the R-value: reaction time (D) > reaction temperature (C) > rhamnolipin concentration (B) > HMSN concentration (A). Analysis of variance was performed on the experimental results in Tables 2-5, resulting in Tables 6-8. The results showed that rhamnolipin concentration (B), reaction temperature (C), and reaction time (D) had significant effects on encapsulation efficiency and comprehensive score; rhamnolipin concentration (B), reaction temperature (C), and reaction time (D) had significant effects on loading, while HMSN concentration (A) had no significant effect on loading.

[0064] The optimal combination A2B1C2D2 obtained from the orthogonal experiment was used for verification. The results showed that the encapsulation efficiency of HMSN-RL was 90.30±0.27% and the loading was 32.37±0.07%, which was in line with the expected results.

[0065] The optimal experimental method is as follows:

[0066] Weigh 20 mg of mesoporous silica into a three-necked flask (pre-filled with 10 mL of anhydrous ethanol) and sonicate for 30 min using an ultrasonic cleaner to ensure complete dissolution. Then add 10 mg of rhamnolipin (RL) to the three-necked flask, with a mass ratio of rhamnolipin to mesoporous silica of 1:2. Stir at 50 °C for 6 h. After the reaction is complete, wash repeatedly with anhydrous ethanol and deionized water, collect the precipitate, and dry it in an oven for 24 h to obtain rhamnolipin-loaded mesoporous silica (HMSN-RL).

[0067] Table 2. Results of the orthogonal experiment

[0068]

[0069] Note: A is the HMSN concentration; B is the rhamnolipin concentration; C is the reaction temperature; D is the reaction time;

[0070] Table 3 Range analysis of encapsulation efficiency

[0071]

[0072] Note: A is the HMSN concentration; B is the rhamnolipin concentration; C is the reaction temperature; D is the reaction time;

[0073] Table 4 Load Range Analysis

[0074]

[0075] Note: A is the HMSN concentration; B is the rhamnolipin concentration; C is the reaction temperature; D is the reaction time;

[0076] Table 5 Range Analysis of Comprehensive Scores

[0077]

[0078] Note: A is the HMSN concentration; B is the rhamnolipin concentration; C is the reaction temperature; D is the reaction time;

[0079] Table 6. Analysis of variance of encapsulation efficiency

[0080]

[0081] Table 7. Analysis of Variance of Load Quantity

[0082]

[0083] Note: A is the HMSN concentration; B is the rhamnolipin concentration; C is the reaction temperature; D is the reaction time;

[0084] Table 8. Analysis of Variance of Overall Scores

[0085]

[0086] Note: A is the HMSN concentration; B is the rhamnolipin concentration; C is the reaction temperature; D is the reaction time;

[0087] Characterization results:

[0088] The microstructure of HMSN and HMSN-RL was observed using a scanning electron microscope (FEI Quanta 250, FEI Corporation, USA; ZEISS Sigma 300, Germany). A small amount of gold was sputtered onto the samples to improve image quality. The particle size distribution of HMSN and HMSN-RL was obtained using a nanoparticle size analyzer (Nano ZS90, Malvern Instruments, UK). Before measurement, the samples were diluted in water and ultrasonically dispersed at 25 °C for 10 min. The FT-IR spectra of the samples were obtained using a Fourier transform infrared spectrometer (Nicolet IS-5, Thermo Fisher Scientific, USA), with a wavenumber range of 4000–500 cm⁻¹. -1 2 cm resolution -1 Against a pure potassium bromide background, the XRD patterns of HMSN and HMSN-RL were measured using an X-ray diffractometer (D8 Advance, Bruker, Germany). Samples were laid flat on a glass support and compacted with coverslips. The tube voltage was 40 kV, the current 40 mA, the measurement range was 10° to 80°, and the scan rate was 0.01° / min. The nitrogen-desorption curves, specific surface area, and pore size of the samples were determined using an automated specific surface area and porosity analyzer (Micromeritics ASAP 2460, USA). Thermogravimetric analysis (TGA) of the samples was performed using a simultaneous thermal analyzer (NETZSCH STA 409PC, Germany) at a flow rate of 20 mL / min, a heating rate of 10 °C / min, and a maximum temperature of 800 °C.

[0089] The morphology and particle size distribution of HMSN and HMSN-RL are as follows: Figure 2 As shown. The morphology of the sample was observed using a scanning electron microscope to determine the microstructure of the crystal. Figure 2 As shown in (a), HMSN consists of spherical particles with a rough outer surface, good particle dispersion, and relatively uniform size distribution; while Figure 2 (b) The HMSN-RL shown is also spherical, with particulate matter adhering to its surface and is more rough. Figure 2 (c) and (d) show the hydrated particle size distribution of HMSN and HMSN-RL. The average particle size of HMSN is approximately 465.96 ± 2.12 nm, while the average particle size of HMSN-RL is approximately 497.24 ± 3.52 nm. After loading RL, the spherical particles become larger. This difference may be because when RL is loaded into HMSN, some RL enters the pores of HMSN, while a small portion adsorbs on the surface of the HMSN microspheres, resulting in larger spherical shapes.

[0090] The surface functional groups of HMSN, RL, and HMSN-RL were analyzed using Fourier transform infrared spectroscopy, such as... Figure 3 As shown in (a), in the HMSN infrared spectrum, a broad peak appears at a wavelength of 3436 cm⁻¹.-1 The position of this structure originates from the adsorption of water molecules from the air by mesoporous silica. The -OH groups in these water molecules cause this adsorption through their unique antisymmetric stretching vibrations. And 963 cm⁻¹ -1 1086 cm -1 And 807 cm -1 The absorption peaks are attributed to the bending vibrations of the Si-OH bond, the antisymmetric stretching vibrations of the Si-O-Si bond, and the symmetric stretching vibrations of the Si-O bond, respectively. In the RL infrared spectrum, the peak at 2930 cm⁻¹ is [missing value]. -1 and 2857 cm -1 The two sharp absorption peaks at the 1731 cm⁻¹ position are caused by the CH stretching vibration of the alkane chain. -1 The absorption peak at 1577 cm⁻¹ indicates the presence of a carbonyl group (-C=O) in the ester. -1 and 1402 cm -1 The absorption peak at 1731-983 cm⁻¹ is due to the stretching vibration of the -C=O group of carboxylic acid; and the absorption peak at 1731-983 cm⁻¹ is due to the stretching vibration of the -C=O group of carboxylic acid. -1 The characteristic absorption peak at 2930 cm⁻¹ confirms the presence of a bond between a carbon atom and a hydroxyl group in the chemical structure of the rhamnose ring. In HMSN-RL, the peak at 2930 cm⁻¹... -1 and 2857 cm -1 The two sharp absorption peaks, -CH3 and -CH2, appear at 1731 cm⁻¹. -1 An absorption peak for the carbonyl group (-C=O) of the ester appeared at 963 cm⁻¹. -1 1086 cm -1 And 807 cm -1 Absorption peaks also appeared at the Si-OH bending vibration, the antisymmetric stretching vibration of the Si-O-Si bond, and the symmetric stretching vibration of the Si-O bond, indicating the successful preparation of HMSN-RL.

[0091] The crystalline state information of HMSN and HMSN-RL at the 2θ scale was obtained by X-ray diffraction, such as... Figure 3 As shown in (b), the X-ray diffraction spectra of HMSN and HMSN-RL are as follows. Figure 3 As shown in (b), the figure shows that HMSN has a relatively broad diffraction peak at 2θ of approximately 22°, and no other diffraction peaks appear nearby, indicating that it is an amorphous structure. The diffraction peaks of HMSN-RL are similar to those of HMSN, and no other characteristic peaks appear, indicating that the structure of HMSN was not destroyed after being loaded with RL, and RL exists in an amorphous state within the mesoporous channels of HMSN.

[0092] The thermal stability of the prepared HMSN and HMSN-RL was studied, and the experimental results are as follows: Figure 3As shown in (c), both samples HMSN and HMSN-RL exhibited mass loss between 25 and 100 °C. This mass loss was attributed to the evaporation of adsorbed water and organic reagents. The loss was greater in HMSN than in HMSN-RL, possibly because HMSN was not sufficiently dried, resulting in a higher adsorbed water content. The weight loss of HMSN between 200 and 800 °C corresponded to condensed water between the silanol groups in the pores and a small amount of residual organic components. HMSN-RL experienced a weight reduction of approximately 23.13% between 200 and 500 °C, which may be due to the breaking of molecular bonds within RL itself, indicating the successful preparation of HMSN-RL.

[0093] The pore size information of HMSN and HMSN-RL was obtained using an automated specific surface area and porosity analyzer. Figure 4 (a) Shows the nitrogen adsorption-desorption isotherms of HMSN and HMSN-RL. Besides having a high proportion of silanol groups, silica also possesses a well-defined mesoporous structure and a high specific surface area, which are important characteristics of a good adsorbent. Figure 4 (a) shows that the nitrogen adsorption-desorption curve of HMSN is Type IV, consistent with the characteristic adsorption curve of mesoporous materials. At lower relative pressures (P / P0 < 0.05), the rate of nitrogen adsorption increases rapidly. When the relative pressure exceeds 0.6, nitrogen molecules are adsorbed on the outer layer of the mesoporous material in a monolayer-to-bilayer manner. With further increases in relative pressure, the effect of nitrogen molecules in the medium gradually stabilizes. Figure 4 (b) It can be seen that the pore size distribution of mesoporous nano-SiO2 is uniform, and the diameter of the pores is mainly 3.388 nm.

[0094] HMSN-RL also exhibits type IV, indicating that RL loading did not change the pore shape, and the nitrogen adsorption capacity of HMSN-RL decreased after loading. Table 9 shows that compared to HMSN, HMSN-RL has a smaller specific surface area and pore volume, indicating that RL has been adsorbed into the pores of HMSN, reducing the pore space and surface area. The pore size of HMSN-RL increased, possibly due to RL filling the pores during loading, leading to an increase in the apparent average pore size, or possibly due to thermal expansion and contraction caused by prolonged immersion in the solvent during loading and subsequent drying.

[0095] Table 9 Mesoporous parameters of HMSN and HMSN-RL

[0096]

[0097] Example 2: Stability Test of HMSN-RL

[0098] The stability of the samples prepared in Example 1 was evaluated using direct observation and UV-transmittance methods. The states of the two different nanofluids were evaluated within different time ranges, thereby expressing the stability of the nanofluids.

[0099] The stability testing method is as follows:

[0100] Using 10 mL of deionized water as the reference solution, 2 mg of HMSN and 2 mg of HMSN-RL were weighed and dissolved separately in 10 mL of deionized water. The mixture was stirred with a magnetic stirrer for 10 min to disperse the nanoparticles. The nanoparticle suspension was then ultrasonically cleaned and sonicated for 30 min to obtain nanofluid. 2 mL of sample was pipetted into a cuvette using a dropper. The transmittance was measured at 400 nm using a UV spectrophotometer, with the aqueous solution as a reference (100% transmittance). Samples were taken from the middle of the sample vial, and each sample was repeated three times.

[0101] according to Figure 5 (a) shows that, overall, the dispersibility of 200 mg / L HMSN and 200 mg / L HMSN-RL remained largely unchanged, indicating a stable state. The stability of HMSN and HMSN-RL in aqueous solution was investigated; throughout the measurement experiment, both nanofluids remained clearly and transparently dispersed in the aqueous solution, with minimal change in transmittance over time, less than 20% within 6 hours. Figure 5 (b) Therefore, the overall stability is relatively good. The transmittance of HMSN and HMSN-RL increased slightly with time, and the overall transmittance change was small, which is basically consistent with the directly observed stability of nanofluids.

[0102] Example 3: Interface Performance Test of HMSN-RL

[0103] The interface performance of HMSN-RL, HMSN, and RL prepared in Example 1 was tested:

[0104] According to the Chinese petroleum and natural gas industry standard SY / T5370-2018 "Methods for Determination of Surface and Interfacial Tension", the interfacial tension between nanofluid and diesel fuel was determined using the platinum ring method. The specific operating steps are as follows: Prepare 200 mg / L HMSN and 200 mg / L HMSN-RL nanofluids separately, and ultrasonically treat them in an ultrasonic cleaner for 30 min to ensure thorough dispersion and dissolution. Before sample testing, the instrument needs to be calibrated. Distilled water and diesel fuel are added to the sample cup for testing. Once an accurate result is obtained for the interfacial tension between diesel fuel and water, the interfacial tension of the sample is measured. Add 10 mL of nanofluid to the sample cup, adjust the height of the platinum ring so that the platinum ring is submerged in the nanofluid, add approximately 10 mL of diesel fuel, and begin measurement after 1 min of contact between the two. Record the interfacial tension between the nanofluid and diesel fuel.

[0105] Depend on Figure 6 As shown in (a) and (b), pure HMSN has a very small effect on reducing the oil-water interfacial tension, only decreasing it from 42.235 mN / m to 37.686 mN / m. This indicates that the removal of the template CTAB during HMSN preparation was thorough, avoiding the influence of CTAB on the oil-water interfacial tension. In contrast, RL and HMSN-RL significantly reduced the oil-water interfacial tension. When both concentrations were 100 mg / L, the oil-water interfacial tension decreased significantly, reaching the lower limit of instrument measurement, i.e., 1 mg / L. Analysis suggests that pure HMSN has a simple surface structure and lacks interfacial activity, resulting in a relatively high interfacial tension between HSMN and diesel oil. HMSN-RL, loaded with RL, exhibits amphiphilic properties, allowing it to adsorb autonomously onto the oil-water interface, reducing the surface energy of the interface and thus lowering the interfacial tension down to the detection limit. Comparing HMSN-RL and RL, HMSN-RL demonstrates a better effect in reducing oil-water interfacial tension, indicating a synergistic effect between the two, effectively reducing interfacial tension. In conclusion, HMSN-RL nanofluids can reduce oil-water interfacial tension, decrease the adsorption of crude oil by reservoir rocks, and improve crude oil recovery.

[0106] Example 4: Temperature and salt resistance tests of HMSN-RL

[0107] In actual production, both the injected water and formation water have specific temperatures and salinity levels. Therefore, the performance of nanomaterials under different temperatures and salinities is an important indicator. This example tests the temperature and salt resistance of HMSN-RL, HMSN, and RL prepared in Example 1.

[0108] Temperature resistance: Following the aforementioned method, a 10 mg / L HMSN-RL nanofluid was prepared and treated in an ultrasonic cleaner for 30 minutes to ensure uniform dispersion. It was then dispensed into centrifuge tubes and heated in a water bath at different temperatures (30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃). The interfacial tension was evaluated using a fully automated interfacial tensiometer. If the interfacial tension value increases with increasing temperature, it indicates poor temperature resistance of the nanofluid; conversely, it indicates good temperature resistance.

[0109] Salt tolerance: NaCl solutions of 5000 mg / L, 10000 mg / L, 20000 mg / L, 30000 mg / L, 40000 mg / L, and 50000 mg / L were prepared and mixed with 10 mg / L HMSN-RL nanomaterials to prepare nanofluids. These mixtures were treated in an ultrasonic cleaner for 30 minutes to ensure uniform dispersion. The interfacial tension of these nanofluids was then measured using an interfacial tensiometer. An increase in interfacial tension with increasing temperature indicated poor salt tolerance of the nanofluid, and vice versa.

[0110] Figure 7 (a) shows the interfacial tension variation curves of different nanofluids at different temperatures. It can be seen that with increasing temperature, the interfacial tension between HMSN (10 mg / L) and RL (10 mg / L) does not change significantly, while the interfacial tension of HMSN-RL first decreases and then tends to stabilize, indicating potential for improved oil recovery. Figure 7 (b) It can be seen that with the increase of salt concentration, the interfacial tension between diesel and nanofluid first decreases and then increases, and then tends to stabilize; HMSN-RL adsorbs at the oil-water interface, which reduces IFT. When the concentration gradually increases, the adsorption of surface active substances at the oil-water interface reaches its maximum. Sodium chloride is an inert substance at the interface, and its large influx offsets some of the active components of the surface active substances, resulting in a rebound of interfacial tension. Compared with the interfacial tension between oil and water (40 mN / m), nanofluid can reduce the interfacial tension between oil and water, and can still maintain a relatively stable interfacial tension level when the sodium ion concentration is 50000 mg / L, which has the potential to improve the recovery rate under reservoir conditions.

[0111] Example 5: Wetting performance test of HMSN-RL

[0112] This embodiment tests the wetting properties of HMSN-RL, HMSN, and RL prepared in Example 1:

[0113] According to the Chinese petroleum and natural gas industry standard SY / T 5153-2017 "Methods for Determining the Wettability of Reservoir Rocks", the contact angle method was used to study the effect of nanofluid modification on the wettability of reservoir rock surfaces. The specific operation was as follows: A suitable amount of glass slide was taken and immersed in a 1% (volume fraction) dilute hydrochloric acid solution for 4.0 h. The surface was then washed with deionized water to remove residual hydrochloric acid and dried. The dried slide was then placed in a 5% (volume fraction) dimethyl silicone oil ethanol solution and aged at 60 ℃ for 7 days. After aging, it was removed, ultrasonically dispersed, dried, and then dried in an oven to simulate the surface of an oleophilic reservoir rock. The contact angle of water droplets was measured using a contact angle meter, and the data were recorded. The slides were then aged in different nanofluids for 48 h and dried in an oven at 60 ℃. The contact angle of water droplets was then measured, and the wettability was evaluated by comparing the changes in contact angle.

[0114] Depend on Figure 8 It can be seen that the contact angles after oil-wetting treatment were 112.72°, 113.57°, and 115.70°, respectively, all showing oleophilicity. After soaking in a 60 ℃ drying oven for 48 h with nanofluid, the contact angles of HMSN were 99.98°, 97.21°, and 98.36°, the contact angles of RL cores were 82.45°, 84.36°, and 84.92°, and the contact angles of HMSN-RL cores were 75.95°, 77.41°, and 76.34°. The wettability of HMSN did not change much, while the wettability of RL and HSMN-RL changed significantly, from oleophilic to moderately wettable. Analysis suggests that the presence of numerous hydrophilic groups such as hydroxyl and carboxyl groups on the surface of HMSN gives it its hydrophilic properties. Furthermore, HMSN-RL and RL loaded with RL exhibit a hydrophilic head and a hydrophobic tail, altering the wettability of the reservoir rock surface and allowing crude oil to detach from the rock and flow out with the displacing fluid. Therefore, the wettability of HMSN-RL nanofluid changes from oleophilic to moderately wettable, making it highly promising for enhanced oil recovery.

[0115] Example 6: Emulsification performance test of HMSN-RL

[0116] This embodiment tests the emulsification properties of HMSN-RL, HMSN, and RL prepared in Example 1:

[0117] Following the Chinese petroleum and natural gas industry standard SY / T6424-2014 "Performance Determination Method of Composite Oil Displacement System", the emulsification performance of nanofluids was studied using the water separation method. The specific operating steps are as follows: First, 500 mg / L solutions of HMSN, RL, and HMSN-RL were prepared and ultrasonically treated for 30 minutes to ensure thorough dispersion. Then, the nanofluid and diesel oil were added to a beaker at a volume ratio of 7:3 and homogenized using a high-speed homogenizer at a speed of 1000 r / min for 5 minutes to prepare a homogeneous emulsion. Subsequently, the prepared emulsion was transferred to a sample bottle, and the height of the separated water was measured using a ruler. The height of the separated water was recorded at time points of 10 min, 20 min, 30 min, 1 h, 2 h, 3 h, 6 h, 12 h, and 24 h, and the water separation rate was calculated to examine the stability of the emulsion. The formula for calculating the water separation rate is as follows:

[0118]

[0119] in:

[0120] X – Water separation rate, %

[0121] V w —Total aqueous phase volume added to the system, mL;

[0122] V wi —The volume of the water layer at a certain moment, in mL;

[0123] The emulsifying properties of HMSN, RL, and HMSN-RL were studied using the water separation method, and the results are as follows: Figure 9 As shown. By Figure 9 (a)-(c) are optical micrographs of HMSN, RL, and HMSN-RL emulsified diesel oil, respectively. HMSN-RL shows the smallest emulsion droplets. The average particle size of the emulsion is related to its stability; the smaller the particle size, the higher the stability. Therefore, HMSN-RL exhibits excellent emulsion stability. Figure 9(d) shows the change in the water separation rate of the emulsion over time. It can be seen that the water separation rate of the emulsion treated with HMSN-RL changes significantly. The water separation rate of HMSN reaches 82.05% within 5 minutes, while the modified HMSN-RL system remains stable within 30 hours. After 30 hours, water separation begins in the emulsion system, and the water separation rate slowly increases. At 72 hours, the water separation rate slows down and gradually stabilizes. Analysis suggests that HMSN-RL, due to the interaction between nanoparticles and the biosurfactant rhamnolipid, effectively adsorbs at the oil-water interface. The presence of HMSN enhances the strength of the emulsion droplets, effectively improving the stability of the emulsion, thus giving it excellent emulsifying properties and demonstrating great application potential in improving oil recovery.

[0124] Example 7: Oil washing efficiency test of HMSN-RL

[0125] Oil wash efficiency is a key indicator directly reflecting the effectiveness of oil displacement, typically referring to the ability of surfactants to strip crude oil from the surface of rock pores within their effective range. This indicator plays a crucial role in the laboratory research, evaluation, and screening of oil displacement agents. Evaluating oil wash efficiency provides a better understanding of the overall performance and effectiveness of oil displacement agents, offering strong support for practical applications.

[0126] This embodiment tests the oil washing efficiency of HMSN-RL, HMSN, and RL prepared in Example 1:

[0127] HMSN, RL, and HMSN-RL were added to each flask containing 2 g of oil sand. The flasks were then shaken at 90 rpm and 70 °C for 24 hours. The oil removed from the solution was transferred to a new container, and the residual oil in the sand was further extracted overnight with 50 mL of petroleum ether at 90 rpm. Simultaneously, crude oil was extracted directly from 2 g of oil sand using 50 mL of petroleum ether. The oil content washed from the quartz sand by the surfactant was calculated by measuring the absorbance, as shown in Equation 4.

[0128]

[0129] In the formula:

[0130] X—washing rate;

[0131] K—Oil content in oil sands (mass fraction);

[0132] W0—The mass of the oil sand (in grams);

[0133] W1—Residual oil content in the oil sand inside the colorimetric tube;

[0134] Oil washing experiments were conducted using crude oil from Shengli Oilfield to prepare oil sands, and the washing efficiency of nanofluids was evaluated. The washing effect and washing efficiency of HMSN, RL, and HMSN-RL are shown in the figures below. Figure 10 As shown in Figure 10(a), the oil sand surface of HMSN-RL is clean and clear, while that of HMSN-treated sand is black and still covered by crude oil, indicating that the oil washing effect is significantly improved after being subjected to RL loading. Figure 10 As shown in (b), 1000 mg / L HMSN, RL and HMSN-RL can remove approximately 37.35%, 64.71% and 77.82% of the oil in the oil sands, respectively. These results indicate that HMSN-RL can significantly improve the oil washing efficiency.

[0135] Example 8: Anti-adsorption performance test of HMSN-RL

[0136] During enhanced oil recovery (EOR) processes, injected surfactants interact with rocks, oil sands, and other materials, adsorbing and remaining on the reservoir surface. This leads to significant surfactant adsorption losses during injection, directly increasing costs and severely impacting EOR, especially for high-cost biosurfactants. Therefore, this study investigated the adsorption of RL and HMSN-RL in quartz sand.

[0137] This embodiment tests the anti-adsorption properties of HMSN-RL, HMSN, and RL prepared in Example 1:

[0138] Different concentrations of RL and HMSN-RL nanofluids were prepared. The nanofluid solution was mixed with quartz sand at a ratio of 5:1 and added to an Erlenmeyer flask. After constant temperature shaking at 65 °C for 3 h, the mixture was allowed to stand for 24 h. The upper liquid in the Erlenmeyer flask was transferred to a centrifuge tube, centrifuged, and the supernatant was collected. The absorbance was measured, and the concentration was calculated by comparing with the standard curve. The adsorption amount was then calculated.

[0139] The adsorption behavior of RL on the sandstone surface was determined by static adsorption method, and the adsorption amount q was calculated according to formula 5:

[0140]

[0141] Where: q—adsorption capacity, mg / g;

[0142] CO—Concentration of surfactant before adsorption, mg / L;

[0143] C—Concentration of surfactant after adsorption, mg / L;

[0144] V—Volume of surfactant, mL;

[0145] M—Mass of sandstone, in grams.

[0146] The results are as follows Figure 11 As shown, when the concentration is 250 mg / L, the adsorption capacity of rhamnolipin is 0.175 g / g, while that of HMSN-RL is only 0.020 g / g, reducing adsorption loss by about 88%. When the concentration is 1000 mg / L, the adsorption capacity of rhamnolipin is 0.672 g / g, while that of HMSN-RL is only 0.397 g / g, reducing adsorption loss by about 40.92%. With the increase of RL concentration, the adsorption capacity also gradually increases. This may be because when surfactant molecules approach the surface of quartz sand, the charge distribution on the surface becomes uneven, resulting in surfactant molecules being adsorbed on the surface by electrostatic attraction. With the increase of surfactant concentration, more and more RL and HMSN-RL are adsorbed on the surface of quartz sand, resulting in greater adsorption loss. In comparison, pure rhamnolipin solution has a greater adsorption loss in quartz sand, while RL after loading can reduce adsorption loss, thereby allowing more RL to interact with crude oil, thus achieving a better oil displacement effect.

[0147] Example 9: Comparison of oil washing efficiency and anti-adsorption performance of HMSN-RL and SiO2 nanoparticle-RL composite nanofluids

[0148] The method described in reference (Chinese Patent ZL201810838339.7) was used to prepare a 1000 mg / L SiO2 nanoparticle-RL composite nanofluid. The method is briefly described below. The SiO2 nanoparticles (purchased from Beijing Zhongke Keyou Technology Co., Ltd., with an average particle size of ~18 nm) were used. The 1000 mg / L SiO2 nanoparticle-RL composite nanofluid was prepared using simulated mineralized water containing 30000 mg / L NaCl. The oil washing efficiency and anti-adsorption performance of the 1000 mg / L SiO2 nanoparticle-RL composite nanofluid were tested according to the aforementioned method and compared with those of 1000 mg / L HMSN-RL.

[0149] The results are shown in Table 10. It can be seen that the oil washing efficiency of HMSN-RL is significantly higher than that of SiO2 nanoparticle-RL composite nanofluid.

[0150] Table 10 Comparison of oil washing efficiency between HMSN-RL and SiO2 nanoparticle-RL composite nanofluids

[0151]

[0152] Similarly, the adsorption loss of the 1000 mg / L SiO2 nanoparticle-RL composite nanofluid was analyzed and compared with that of the 1000 mg / L HMSN-RL. The results showed that the adsorption loss of HMSN-RL was significantly lower than that of the SiO2 nanoparticle-RL composite nanofluid (Table 11).

[0153] Table 11 Comparison of adsorption losses (mg / g) of HMSN-RL and SiO2 nanoparticle-RL composite nanofluids

[0154]

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a mesoporous silica-rhamnolipin oil displacement agent, characterized in that, The steps are as follows: Step 1: Prepare mesoporous silica using the sol-gel method; Step 2: Add rhamnolipin to the dispersion of mesoporous silica and stir at 50°C for 6 h. The mass ratio of mesoporous silica to rhamnolipin is 50-100:1-50. Step 3: After the reaction is complete, the precipitate is washed with anhydrous ethanol and deionized water, and dried to obtain the mesoporous silica-rhamnolipin oil displacement agent.

2. The preparation method of the mesoporous silica-rhamnolipin oil displacement agent according to claim 1, characterized in that, The preparation of mesoporous silica using the sol-gel method in step one is as follows: S1. Mix anhydrous ethanol and distilled water, then add ammonia water, mix well, add tetraethyl orthosilicate, stir and react at room temperature for 1 hour, and finally centrifuge, wash with water and ethanol to collect the precipitate for later use. S2. Disperse the precipitate obtained in step S1 in distilled water to prepare a precipitate dispersion, then add hexadecyltrimethylammonium bromide aqueous solution and triethanolamine, stir at room temperature for 1 h, heat to 80 °C and add tetraethyl orthosilicate dropwise, then place the reaction solution in a 50 °C water bath for reaction, add anhydrous sodium carbonate to etch, react for 3 h, after the reaction is completed, separate by centrifugation, wash the precipitate several times and place it in an oven to dry; S3. The surfactant CTAB was removed by acid extraction. The precipitate was dispersed in a methanol solution containing concentrated hydrochloric acid and stirred at room temperature for 12 h. The sample was collected by centrifugation, washed with methanol and centrifuged 3 times, and then dried under vacuum to obtain mesoporous silica.

3. The preparation method of the mesoporous silica-rhamnolipin oil displacement agent according to claim 2, characterized in that, In step S1, the ratio of anhydrous ethanol, distilled water, 25 wt% ammonia, and tetraethyl orthosilicate is 75 mL:10 mL:2 mL:2 mL; in step S2, the ratio of the precipitate, hexadecyltrimethylammonium bromide, triethanolamine, tetraethyl orthosilicate, and anhydrous sodium carbonate is 0.45 g:0.6 g:0.25 g:0.5 mL:0.3 g; in step S3, the ratio of the precipitate to the methanol solution containing concentrated hydrochloric acid is 1:30, and the mass ratio of concentrated hydrochloric acid, methanol, and water in the methanol solution containing concentrated hydrochloric acid is 1:556:

36.

4. The preparation method of the mesoporous silica-rhamnolipin oil displacement agent according to claim 1, characterized in that, The mass ratio of mesoporous silica to rhamnolipin is 2:

1.

5. A mesoporous silica-rhamnolipin oil displacement agent prepared by the method according to any one of claims 1-4.

6. The mesoporous silica-rhamnolipin oil displacement agent according to claim 5, characterized in that, The average particle size of the mesoporous silica is 460-500 nm.

7. The application of the mesoporous silica-rhamnolipin oil displacement agent according to claim 5 as an oil displacement agent in petroleum extraction.

8. The application according to claim 7, characterized in that, The application includes formulating the oil displacement agent into a nanofluid and injecting it into the oil layer to reduce the oil-water interfacial tension, change the wettability of the rock surface, improve the emulsification stability of crude oil, and increase the oil washing efficiency.

9. An oil displacement composition for oil extraction, characterized in that, Includes an effective amount of the mesoporous silica-rhamnolipin oil displacement agent of claim 5.

10. The oil displacement composition for oil extraction according to claim 9, characterized in that, The effective amount of mesoporous silica-rhamnolipin oil displacement agent is 250-1000 mg / L.

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