Si / c quantum dot oil displacement agent, and preparation method therefor and use thereof

Abstract

A Si / C quantum dot oil displacement agent, and a preparation method therefor and a use thereof. On the basis of the total weight of the Si / C quantum dot oil displacement agent being 100%, the concentration of Si / C quantum dots is 4-26%; under the condition that the absorbance is greater than or equal to 2.5, the peak wavelength of an ultraviolet absorption spectrum of the Si / C quantum dot oil displacement agent is 275 ± 3 nm, and under the condition that the excitation wavelength is 375 ± 3 nm, the peak wavelength of a fluorescence emission spectrum of the Si / C quantum dot oil displacement agent is 445 ± 3 nm; and the Zeta potential of the Si / C quantum dot oil displacement agent is −4.45 ± 0.5 mV. The Si / C quantum dot oil displacement agent has the characteristics of weak adsorption and weak retention, has ultrahigh stability, and can improve recovery efficiency.

Description

A Si / C quantum dot oil displacement agent, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202510138099.X, filed on February 7, 2025, entitled "A Carbon Silicon Quantum Dot Oil Displacement Agent and Its Preparation Method and Application", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to a Si / C quantum dot oil displacement agent, its preparation method and application, belonging to the field of oil displacement technology. Background Technology

[0003] In recent years, low-permeability / tight reservoirs have gradually become the main focus of oil and gas development and a key to stable oil production. Most newly added oil resources are in low-permeability / tight reservoirs, but about 30% of these reservoirs cannot be injected with water. Conventional water injection is insufficient to establish an effective displacement relationship, and conventional enhanced oil recovery (EOR) technologies are largely ineffective in high-temperature, high-salinity, low-permeability / tight reservoirs where water cannot be injected or extracted. Therefore, there is an urgent need to develop new EOR technologies. Currently, researchers have turned their attention to quantum dot flooding technology, primarily aiming to obtain structurally stable and uniformly dispersed quantum dots that can adapt to harsh reservoir environments such as high temperature and high salinity; to obtain quantum dots with sufficiently small size, strong permeability, and long diffusion range to facilitate their entry into micro / nanopores and expand their reach; and to obtain quantum dot flooding agents with good oil washing effects, in order to further improve crude oil recovery. The goal is to apply these obtained quantum dots to low-permeability / tight reservoir flooding to form an effective EOR technology.

[0004] The applicant will briefly introduce some prior art that is closely related to this invention, so that those skilled in the art can better understand the situation of the prior art and the drawbacks of the prior art.

[0005] US11718782B2 discloses a polymeric silicon-based quantum dot synthesized using polyfluorene-o-benzothiadiazole and / or polystyrene-conmaleic anhydride as raw materials via a nanoprecipitation method. The initial particle size is 25 nm, increasing to approximately 33 nm at a salinity of 100,000, and reaching approximately 44 nm at 80°C. When used for oil displacement, this polymeric silicon-based quantum dot improves oil recovery by 15.03% compared to waterflooding. However, this type of polymeric silicon-based quantum dot uses organic and silicon materials as raw materials and requires dispersion in a surfactant, limiting the product's temperature and salt resistance. Furthermore, the nanoprecipitation method limits the quantum dot's particle size, resulting in a relatively large particle size and thus a limited effect on improving oil recovery.

[0006] CN113528107A discloses a method for synthesizing coal-based carbon quantum dots using coal and / or coal-based derivatives plus oxidants such as organic acids as raw materials, employing top-down methods such as arc discharge, chemical oxidation, and electrochemical oxidation. The resulting particles have a diameter of approximately 10 nm and a temperature resistance of up to 80℃, but a salt tolerance of only 3.2 × 10⁻⁶. 3 The concentration of mg / L indicates poor salt tolerance. This suggests that the carbon quantum dots provided by this existing technology still have certain shortcomings in salt tolerance.

[0007] Analysis of the existing technologies reveals that the performance differences of quantum dots are primarily influenced by the selection of raw materials and the choice of synthesis methods. On one hand, the inherent defects in the materials' resistance to mineralization—for example, the weak bond energy and low strength of carbon-carbon bonds in carbon quantum dots or silicon-silicon bonds in silicon quantum dots—lead to poor environmental tolerance of organic molecules, resulting in instability and easy aggregation of the quantum dot system under high mineralization conditions. On the other hand, the reaction conditions and intensity of the preparation process also play a role. For instance, the aforementioned redox reactions or nanoprecipitation methods involve complex and difficult-to-control reaction processes, resulting in larger and uncontrollable quantum dot particle sizes. Therefore, the selection of raw materials and the choice of synthesis methods comprehensively affect the oil displacement performance of quantum dots.

[0008] Given the shortcomings of the above-mentioned quantum dot oil displacement agents, providing a novel Si / C quantum dot oil displacement agent, its preparation method, and its application has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] To address the aforementioned shortcomings and deficiencies, the present invention aims to provide a Si / C quantum dot oil displacement agent, its preparation method, and its application. The technical solution provided by this invention can at least solve the problems of existing conventional quantum dot oil displacement agents, such as large particle size, poor dispersion stability in high-salt reservoir environments, easy agglomeration failure, and low oil displacement efficiency.

[0010] To achieve the above objectives, on the one hand, the present invention provides a Si / C quantum dot oil displacement agent, which is an aqueous solution of Si / C quantum dots, wherein, based on the total weight of the Si / C quantum dot oil displacement agent as 100%, the concentration of Si / C quantum dots is 4-26%;

[0011] Among them, under the condition of absorbance (A) ≥ 2.5, the dominant wavelength of the ultraviolet absorption spectrum of the Si / C quantum dot oil displacement agent is 275±3nm, and under the condition of excitation wavelength of 375±3nm, the dominant wavelength of the fluorescence emission spectrum of the Si / C quantum dot oil displacement agent is 445±3nm.

[0012] The zeta potential of the Si / C quantum dot oil displacement agent is distributed between -4.45±0.5mV.

[0013] As a specific embodiment of the Si / C quantum dot oil displacement agent described above in this invention, the particle size of the Si / C quantum dots is less than 10 nm.

[0014] As a specific embodiment of the Si / C quantum dot oil displacement agent described above in this invention, the Si / C quantum dot oil displacement agent has an average oil displacement efficiency of 64-90% in ultra-low permeability cores, wherein the permeability of the ultra-low permeability cores is greater than or equal to 1.0 × 10⁻⁶. -3 μm 2 Less than 10.0 × 10 -3 μm 2 .

[0015] As a specific embodiment of the Si / C quantum dot oil displacement agent described above in this invention, the Si / C quantum dot oil displacement agent has an adsorption efficiency of 20-55% in low-permeability cores and 21-50% in ultra-low-permeability cores, wherein the permeability of the low-permeability core is 10.0 × 10⁻⁶. -3 -30.0×10 -3 μm 2 The permeability of ultra-low permeability cores is greater than or equal to 1.0 × 10⁻⁶. -3 μm 2 Less than 10.0 × 10 -3 μm 2 .

[0016] In one specific embodiment of the Si / C quantum dot oil displacement agent described above in this invention, the sweep range of the Si / C quantum dot oil displacement agent is 30-35% in the microfluidic perforated plate model.

[0017] As a specific embodiment of the Si / C quantum dot oil displacement agent described above in this invention, the Si / C quantum dot oil displacement agent can remain stable without agglomeration or precipitation under conditions where the temperature is not higher than 85°C and the mineralization is not higher than 300,000 mg / L.

[0018] On the other hand, the present invention also provides a method for preparing the Si / C quantum dot oil displacement agent described above, wherein the preparation method includes:

[0019] Step (1): Add carbon source and silicon source to water at a mass ratio of 4-15:1-7 and let them dissolve completely to obtain carbon-silicon mixture;

[0020] Step (2): The carbon-silicon mixture is subjected to hydrothermal reaction at a pressure of 1-2 MPa and a temperature of 100-250℃ for 4-24 hours;

[0021] Step (3): After cooling the reaction product obtained in step (2), an aqueous solution of Si / C quantum dots is obtained, which is the Si / C quantum dot oil displacement agent.

[0022] In one specific embodiment of the preparation method described above in this invention, the mass ratio of the carbon source to the silicon source is 4-10:1-3.

[0023] As a specific embodiment of the preparation method described above in this invention, the carbon source includes one or a combination of several of the following: coal, graphite powder, sucrose, xylose, starch, citric acid, glutaraldehyde, rhodamine, amino acids, o-phenylenediamine, sodium p-toluenesulfonate, and amaranth.

[0024] As a specific embodiment of the preparation method described above in this invention, the silicon source includes one or a combination of several of the following: 3-aminopropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, sodium metasilicate, triphenylsilanol, and sodium silicate.

[0025] In one specific embodiment of the preparation method described above in this invention, the carbon source and silicon source are fully dissolved in water by ultrasound, wherein the power of the ultrasound is 1000-2000W and the time is 10-60min.

[0026] In one specific embodiment of the preparation method described above in this invention, the ultrasonic power is 1000-1500W and the duration is 10-30min.

[0027] In one specific embodiment of the preparation method described above in this invention, the water may be distilled water or the like.

[0028] In one specific embodiment of the preparation method described above in this invention, the temperature of the hydrothermal reaction is 120-250℃.

[0029] In one specific embodiment of the preparation method described above in this invention, the hydrothermal reaction can be carried out in a high-temperature and high-pressure reactor.

[0030] In one specific embodiment of the preparation method described above in this invention, the cooling is natural cooling to room temperature.

[0031] As a specific embodiment of the preparation method described above in this invention, the preparation method further includes: purifying the cooled reaction product, wherein the purification is a three-stage purification process of centrifugation, filtration, and ultrafiltration. The centrifugation speed is 2000-10000 rpm, and the time is 5-30 min. The filtration is performed sequentially using a filter membrane with a pore size of 0.45 μm and a filter membrane with a pore size of 0.22 μm, and the number of filtrations is 1-10. The ultrafiltration is performed 1-10 times using an ultrafiltration membrane with a pore size of 0.01 μm.

[0032] In a specific embodiment of the preparation method described above in this invention, the centrifugation speed is 5000-10000 rpm, the time is 10-20 min, the filtration is performed 5-10 times, and the ultrafiltration is performed 5-10 times.

[0033] In some embodiments of the present invention, the filtration can be achieved using a syringe-type membrane filter having a filter membrane with a pore size of 0.45 μm and a filter membrane with a pore size of 0.22 μm, and the ultrafiltration can be achieved using an ultrafiltration cup having an ultrafiltration membrane with a pore size of 0.01 μm. The "syringe-type membrane filter having a filter membrane with a pore size of 0.45 μm and a filter membrane with a pore size of 0.22 μm" and the "ultrafiltration cup having an ultrafiltration membrane with a pore size of 0.01 μm" can be respectively referred to as "syringe-type membrane filter (0.45 μm and 0.22 μm)" and "ultrafiltration cup (0.01 μm)".

[0034] In another aspect, the present invention also provides the application of the Si / C quantum dot oil displacement agent described above in unconventional reservoir oil displacement.

[0035] Compared with the prior art, the beneficial technical effects that the technical solution of the present invention can achieve include at least the following:

[0036] 1. This invention innovatively prepares Si / C quantum dot oil displacement agents using silicon and carbon sources as raw materials. Carbon is widely available for synthesis, while silicon is inexpensive, providing abundant resources for low-cost and large-scale synthesis. Compared with other quantum dots, the Si / C quantum dot oil displacement agent provided by this invention is non-toxic, environmentally friendly, and biocompatible. For example, the Zeta potential of the Si / C quantum dot oil displacement agent provided by this invention is distributed between -4.45±0.5mV, exhibiting weak electrochemical properties and weak adsorption and retention characteristics.

[0037] 2. This invention innovatively combines silicon and carbon materials to obtain a Si / C quantum dot oil displacement agent, overcoming the shortcomings of single-component materials. By leveraging the higher bond energy and stronger interaction of silicon-carbon bonds, as well as the inherent stability of the raw materials, the stability of the product is further improved. For example, the Si / C quantum dot oil displacement agent provided by this invention can remain stable without agglomeration or precipitation under conditions where the temperature does not exceed 85℃ and the mineralization does not exceed 300,000 mg / L, indicating that it has extremely strong salt and temperature resistance.

[0038] 3. The Si / C quantum dot oil displacement agent provided by this invention has specific fluorescence absorption and emission spectral wavelengths. Specifically, under the condition of A≥2.5, the dominant wavelength of the ultraviolet absorption spectrum of the Si / C quantum dot oil displacement agent is 275±3nm, and under the condition of excitation wavelength of 375±3nm, the dominant wavelength of the fluorescence emission spectrum of the Si / C quantum dot oil displacement agent is 445±3nm. Therefore, based on the specific excitation wavelength and dominant wavelength of the fluorescence emission spectrum of the Si / C quantum dot oil displacement agent, fluorescence detection of the Si / C quantum dot oil displacement agent in oilfield produced fluid can be performed to further track the migration patterns of fluids in the reservoir from the produced fluid. That is, the Si / C quantum dot oil displacement agent provided by this invention can also be used as an oilfield tracer, exhibiting the characteristic of multi-purpose application and promising prospects.

[0039] 4. The Si / C quantum dot oil displacement agent provided by this invention exhibits excellent enhanced oil recovery performance. In a microfluidic orifice plate model, the sweep range of the Si / C quantum dot oil displacement agent provided by this invention is 30-35%. Specifically, the Si / C quantum dot oil displacement agent provided in Example 1 achieves a sweep range of 34.22% in a microfluidic orifice plate model, which is 47.25% higher than the water-drive sweep range, demonstrating a significant ability to expand sweep capacity. The Si / C quantum dot oil displacement agent is effective in ultra-low permeability cores (permeability greater than or equal to 1.0 × 10⁻⁶). -3 μm 2 Less than 10.0 × 10 -3 μm 2 The average oil displacement efficiency in the core is not less than 64%, and in a preferred embodiment it can be as high as 85.9%, which is 24.5 percentage points higher than that of waterflooding; the Si / C quantum dot oil displacement agent is effective in low-permeability cores (permeability of 10.0 × 10⁻⁶ m³ / s). -3 -30.0×10 -3 μm 2 The permeation efficiency in the core is not less than 20%, and in a preferred embodiment it can be as high as 53.9%, which is 37.4 percentage points higher than that of formation water permeation. This is particularly important for ultra-low permeability cores (permeability greater than or equal to 1.0 × 10⁻⁶). -3 μm 2 Less than 10.0 × 10 -3μm 2 The percolation efficiency in the Si / C quantum dot oil displacement agent is no less than 21%, and in a preferred embodiment it can reach as high as 47.4%, which is 23.7 percentage points higher than that of formation water percolation. This indicates that the Si / C quantum dot oil displacement agent provided by the present invention, relying on its small size and weak retention characteristics, can effectively enter areas that water-driven flooding cannot reach, and enter the micro-nano pores in the core, thereby expanding the coverage area. At the same time, the Si / C quantum dot oil displacement agent, relying on its own strong Brownian motion, can enhance the interaction between the oil-water interface and the oil-solid interface, which is conducive to percolation into the matrix and the mobilization and stripping of crude oil. That is, the Si / C quantum dot oil displacement agent provided by the present invention has a dual oil displacement effect of "percolation + displacement", which can improve the recovery rate from the two aspects of expanding the coverage area and improving the oil displacement efficiency. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 is a particle size distribution diagram of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention.

[0042] Figure 2a shows the fluorescence spectra of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention under formation water conditions with different salinity.

[0043] Figure 2b shows the fluorescence spectra of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention under different storage time conditions.

[0044] Figure 3a is a graph showing the permeation efficiency of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention as a function of time.

[0045] Figure 3b is a graph showing the change in infiltration efficiency over time when formation water (mineralization of 100,000 mg / L) is absorbed.

[0046] Figure 4 is a graph showing the relationship between the oil displacement efficiency and the injection ratio of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention.

[0047] Figure 5a shows the results of fluorescence performance evaluation of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention.

[0048] Figure 5b is a graph showing the relationship between absorbance and wavelength of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention.

[0049] Figure 5c is a graph showing the relationship between the fluorescence intensity and wavelength of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention.

[0050] Figure 6 is an infrared spectrum of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention.

[0051] Figure 7 shows the Zeta potential analysis spectrum of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention. Detailed Implementation

[0052] It should be noted that the term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0053] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0054] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0055] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0056] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0057] In this invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying tables, drawings, and embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0059] Example 1

[0060] This embodiment provides a Si / C quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0061] Step (1): Add 10 mg of xylose and 3 mg of 3-aminopropyltrimethoxysilane to 20 mL of double-distilled water, stir and sonicate to dissolve and disperse, and obtain a carbon-silicon mixture.

[0062] Step (2): Then the carbon-silicon mixture is transferred to a high-temperature and high-pressure reactor and subjected to hydrothermal reaction at 1.4 MPa and 180°C for 5 hours;

[0063] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, the clear liquid is taken to obtain a quantum dot solution, namely Si / C quantum dot oil displacement agent.

[0064] Example 2

[0065] This embodiment provides a Si / C quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0066] Step (1): Add 10 mg of amaranth red and 1 mg of sodium metasilicate to 20 mL of double-distilled water, stir and sonicate to dissolve and disperse, and obtain a carbon-silicon mixture;

[0067] Step (2): Then the carbon-silicon mixture is transferred to a high-temperature and high-pressure reactor and subjected to hydrothermal reaction at 1.5 MPa and 190°C for 12 hours;

[0068] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, the clear liquid is taken to obtain a quantum dot solution, namely Si / C quantum dot oil displacement agent.

[0069] Example 3

[0070] This embodiment provides a Si / C quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0071] Step (1): Add 4 mg of amaranth red and 3 mg of 3-aminopropyltrimethoxysilane to 20 mL of double-distilled water, stir and sonicate to dissolve and disperse, and obtain a carbon-silicon mixture.

[0072] Step (2): Then the carbon-silicon mixture was transferred to a high-temperature and high-pressure reactor and subjected to a hydrothermal reaction at 1.3 MPa and 180°C for 4 hours;

[0073] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, the clear liquid is taken to obtain a quantum dot solution, namely Si / C quantum dot oil displacement agent.

[0074] Example 4

[0075] This embodiment provides a Si / C quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0076] Step (1): Add 4 mg xylose and 1 mg sodium metasilicate to 20 mL of double-distilled water and sonicate to dissolve completely to obtain a carbon-silicon mixture;

[0077] Step (2): Then the carbon-silicon mixture was transferred to a high-temperature and high-pressure reactor and subjected to a hydrothermal reaction at 1.2 MPa and 150 °C for 4 hours;

[0078] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, it is first centrifuged at 6000 rpm for 15 min, then filtered 5 times with a syringe filter membrane filter (0.45 μm and 0.22 μm), and finally ultrafiltered 5 times with an ultrafiltration cup (0.01 μm) to obtain a quantum dot solution, namely Si / C quantum dot oil displacement agent.

[0079] Example 5

[0080] This embodiment provides a Si / C quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0081] Step (1): Add 6 mg xylose and 2 mg sodium metasilicate to 20 mL of double-distilled water and sonicate to dissolve completely to obtain a carbon-silicon mixture;

[0082] Step (2): Then the carbon-silicon mixture is transferred to a high-temperature and high-pressure reactor and subjected to hydrothermal reaction at 1.3 MPa and 180°C for 12 hours;

[0083] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, the clear liquid is taken to obtain a quantum dot solution, namely Si / C quantum dot oil displacement agent.

[0084] Example 6

[0085] This embodiment provides a Si / C quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0086] Step (1): Add 8 mg of xylose and 2 mg of 3-aminopropyltrimethoxysilane to 20 mL of double-distilled water and sonicate to dissolve completely to obtain a carbon-silicon mixture;

[0087] Step (2): Then the carbon-silicon mixture was transferred to a high-temperature and high-pressure reactor and subjected to a hydrothermal reaction at 1.3 MPa and 160°C for 5 hours;

[0088] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, the clear liquid is taken to obtain a quantum dot solution, namely Si / C quantum dot oil displacement agent.

[0089] Comparative Example 1

[0090] This comparative example provides a carbon quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0091] Step (1): Add 8 mg of citric acid to 20 mL of double-distilled water, stir and sonicate to dissolve and disperse, and obtain a mixture;

[0092] Step (2): Then the mixture is transferred to a high-temperature and high-pressure reactor and subjected to hydrothermal reaction at 1.2 MPa and 150°C for 10 h;

[0093] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, it is first centrifuged at 8000 rpm for 15 min, then filtered 5 times with a syringe filter membrane filter (0.45 μm and 0.22 μm), and finally ultrafiltered 5 times with an ultrafiltration cup (0.01 μm) to obtain a quantum dot solution, namely carbon quantum dot oil displacement agent.

[0094] Comparative Example 2

[0095] This comparative example provides a silicon quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0096] Step (1): Add 3 mg of 3-glycidyloxypropyltrimethoxysilane to 20 mL of double-distilled water, stir and sonicate to dissolve and disperse, and obtain a mixture;

[0097] Step (2): Then the mixture is transferred to a high-temperature and high-pressure reactor and subjected to hydrothermal reaction at 0.9 MPa and 130°C for 8 hours;

[0098] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, it is first centrifuged at 8000 rpm for 15 min, then filtered 5 times with a syringe filter membrane filter (0.45 μm and 0.22 μm), and finally ultrafiltered 5 times with an ultrafiltration cup (0.01 μm) to obtain a quantum dot solution, namely silicon quantum dot oil displacement agent.

[0099] Comparative Example 3

[0100] This comparative example provides a Si / C quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0101] Step (1): Add 1 mg of glutaraldehyde and 10 mg of sodium metasilicate to 20 mL of double-distilled water and sonicate to dissolve completely to obtain a carbon-silicon mixture.

[0102] Step (2): Then the carbon-silicon mixture was transferred to a high-temperature and high-pressure reactor and subjected to a hydrothermal reaction at 1.3 MPa and 150°C for 4 hours;

[0103] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, it is first centrifuged at 6000 rpm for 15 min, then filtered 5 times with a syringe filter membrane filter (0.45 μm and 0.22 μm), and finally ultrafiltered 5 times with an ultrafiltration cup (0.01 μm) to obtain a quantum dot solution, namely Si / C quantum dot oil displacement agent.

[0104] Comparative Example 4

[0105] This comparative example provides a Si / C quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0106] Step (1): Add 10 mg of glutaraldehyde and 2 mg of sodium metasilicate to 20 mL of double-distilled water and sonicate to dissolve completely to obtain a carbon-silicon mixture.

[0107] Step (2): Then the carbon-silicon mixture was transferred to a high-temperature and high-pressure reactor and subjected to a hydrothermal reaction at 1.1 MPa and 80°C for 4 hours;

[0108] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, it is first centrifuged at 6000 rpm for 15 min, then filtered 5 times with a syringe filter membrane filter (0.45 μm and 0.22 μm), and finally ultrafiltered 5 times with an ultrafiltration cup (0.01 μm) to obtain a quantum dot solution, namely Si / C quantum dot oil displacement agent.

[0109] Comparative Example 5

[0110] This comparative example provides a Si / C quantum dot oil displacement agent, which is prepared by a method including the following specific steps:

[0111] Step (1): Add 10 mg of glutaraldehyde and 2 mg of sodium metasilicate to 20 mL of double-distilled water and sonicate to dissolve completely to obtain a carbon-silicon mixture.

[0112] Step (2): Then the carbon-silicon mixture is transferred to a high-temperature and high-pressure reactor and subjected to hydrothermal reaction at 1.3 MPa and 150°C for 3 hours;

[0113] Step (3): After the reaction product obtained in step (2) is naturally cooled to room temperature, it is first centrifuged at 6000 rpm for 15 min, then filtered 5 times with a syringe filter membrane filter (0.45 μm and 0.22 μm), and finally ultrafiltered 5 times with an ultrafiltration cup (0.01 μm) to obtain a quantum dot solution, namely Si / C quantum dot oil displacement agent.

[0114] Test Example 1

[0115] This test example measures the particle size of quantum dots in the Si / C quantum dot oil displacement agents provided in Examples 1-6 of the present invention and the quantum dot oil displacement agents provided in Comparative Examples 1-5, including the following steps:

[0116] First, clean the measuring cup with ethanol, then rinse it with distilled water, and finally rinse the measuring cup twice with the quantum dot oil displacement agent solutions provided in the examples and comparative examples, respectively, and set it aside. Add the quantum dot oil displacement agent solutions provided in the examples and comparative examples to the measuring cup according to the amount of 2 / 3 of the volume of the measuring cup. Select the particle size analysis test program, put the measuring cup into the nanoparticle size analyzer for particle size measurement, repeat three times, and take the average value as the final particle size result.

[0117] In this test example, the particle size results of each Si / C quantum dot oil displacement agent and each carbon quantum dot oil displacement agent are shown in Table 1 and Figure 1 below. Figure 1 is a particle size distribution diagram of the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention.

[0118] Test Example 2

[0119] This test example evaluates the temperature and salt resistance of the quantum dots in the quantum dot oil displacement agents provided in Examples 1-6 and Comparative Examples 1-5 of this invention. Since salt ions affect the measurement accuracy of the nanoparticle size analyzer under high salinity conditions, this test example does not use a nanoparticle size analyzer to measure particle size changes. Because the fluorescence spectrum of quantum dots can well reflect the stable particle size of quantum dots, the stability of the system is evaluated in this test example by fluorescence intensity, including the following steps:

[0120] Preparation of formation water:

[0121] 88.93 g of NaCl, 8.71 g of CaCl2, and 4.32 g of MgCl2·6H2O (all analytical grade, manufactured by Sinopharm Group) were added to water and fully dissolved. The solution was then diluted to 1 L with water to obtain formation water with a mineralization of approximately 100,000 mg / L. Formation water with different mineralizations can be prepared by scaling up or down the amounts of the above components proportionally.

[0122] Evaluation test of the temperature and salt resistance properties of quantum dots:

[0123] The absorption wavelength (peak position) and fluorescence intensity (peak height) of various quantum dot oil displacement agent solutions were examined under different formation temperatures, formation water salinities, and storage times. When the absorption wavelength (peak position) and fluorescence intensity (peak height) of each quantum dot oil displacement agent solution remained essentially unchanged, it indicated that each quantum dot oil displacement agent was relatively stable with minimal performance differences. The corresponding temperature and salinity at this point represent the maximum temperature resistance and maximum salt concentration tolerance of each quantum dot oil displacement agent. The different formation temperatures included 25℃ and 60℃. Formation water with different mineralizations, including 30,000 mg / L, 50,000 mg / L, 80,000 mg / L, 100,000 mg / L, 150,000 mg / L, 200,000 mg / L, 250,000 mg / L, and 300,000 mg / L, was used at temperatures of 70℃, 80℃, and 85℃. The quantum dot oil displacement agents were then formulated into solutions with concentrations of 0.3wt%, 0.5wt%, 1.0wt%, and 1.5wt%, and placed for different durations, including 1 day, 3 days, 5 days, and 7 days.

[0124] In this test example, the highest temperature resistance and highest salt concentration resistance of each quantum dot oil displacement agent are shown in Table 1 and Figures 2a-2b below. Figure 2a shows the fluorescence spectrum of the Si / C quantum dot oil displacement agent provided in Example 1 of this invention under different formation water salinity conditions (concentration of 0.3wt%, temperature of 25℃, and placement time of 7 days). Figure 2b shows the fluorescence spectrum of the Si / C quantum dot oil displacement agent provided in Example 1 of this invention under different placement time conditions (salinity of 100,000 mg / L, concentration of 0.3wt%, and temperature of 85℃). As can be seen from Figure 2a, under different formation water salinity conditions, the fluorescence spectra of each quantum dot oil displacement agent are relatively dense, and the peak values ​​do not change much, indicating that the system is relatively stable. As can be seen from Figure 2b, each quantum dot oil displacement agent can maintain system stability when placed at 85℃ for different times.

[0125] Test Example 3

[0126] This test example evaluates the permeation and absorption performance of quantum dots in the quantum dot oil displacement agents provided in Examples 1-6 and Comparative Examples 1-5 of the present invention, including the following steps:

[0127] Step 1): Wipe dry the tight sandstone core saturated with crude oil (this core should be a low-permeability core or an ultra-low-permeability core, where the permeability of the low-permeability core is 20.0-30.0 × 10⁻⁶). -3 μm 2 The permeability of ultra-low permeability cores is greater than or equal to 1.0 × 10⁻⁶. -3 μm 2 Less than 10.0 × 10 -3 μm 2 The surface oil was immediately measured and recorded using an electronic balance.

[0128] Step 2): Transfer the core to a horizontally placed percolation bottle, slowly push the core to the bottom, place the percolation bottle vertically, and ensure that the core does not tilt against the bottle wall.

[0129] Step 3): After assembling the upper and lower parts of the osmosis bottle, seal the joint with Vaseline to prevent leakage.

[0130] Step 4): Inject the percolation liquid (which is the quantum dot oil displacement agent obtained by diluting each quantum dot oil displacement agent in the examples and comparative examples to a concentration of 0.3 wt% using formation water with a salinity of 100,000 mg / L) into the percolation bottle through the rubber tube at the bottom, and add the percolation liquid to a position above the 0 mark.

[0131] Step 5): After checking and confirming that there is no leakage, place the percolation bottle in an 85℃ oven to start the percolation experiment and prepare for the next set of experiments.

[0132] Step 6): Record the time when the core is placed in the percolation bottle, and record the amount of oil percolated every 2 hours. Observe the experimental phenomena and take photos.

[0133] In this test case, the percolation efficiency is calculated according to the following formula 1):

[0134] In Formula 1), η is the percolation efficiency, %; V is the core percolation oil discharge volume, mL; V o The original oil-bearing volume of the core is expressed in mL.

[0135] In this test, the permeation efficiency results of each quantum dot oil displacement agent are shown in Table 1 and Figures 3a-3b below. Figure 3a is a curve showing the permeation efficiency of the Si / C quantum dot oil displacement agent provided in Example 1 of this invention as a function of time, and Figure 3b is a curve showing the permeation efficiency of formation water with a salinity of 100,000 mg / L as a function of time.

[0136] Test Example 4

[0137] This test example evaluates the oil displacement performance of quantum dots in the quantum dot oil displacement agents provided in Examples 1-6 and Comparative Examples 1-5 of the present invention, including the following steps:

[0138] Step 1): Select natural low-permeability / tight cores with gas permeability less than 10 mD as experimental cores. After thorough cleaning, perform saturated water and saturated oil operations to simulate the original oil-bearing state of the reservoir.

[0139] Step 2): At 85℃, perform one water flooding operation, injecting formation water with a salinity of 100,000 mg / L to continuously drive out the oil inside the core channels until no more oil is produced. Once the water flooding operation is completed, record the amount of oil produced and calculate the oil recovery rate of the water flooding operation.

[0140] Step 3): Use quantum dot oil displacement agent to drive oil. Inject a certain number of quantum dot oil displacement agents (which are obtained by diluting each quantum dot oil displacement agent in the examples and comparative examples to a concentration of 0.3wt% using formation water with a salinity of 100,000 mg / L) to drive oil, record the amount of oil produced, and calculate the recovery rate of the quantum dot oil displacement agent.

[0141] Step 4): Water flood again, inject formation water with a salinity of 100,000 mg / L until no oil is produced. Record the oil production and calculate the final recovery rate / displacement efficiency.

[0142] In this test case, the waterflooding efficiency, the oil displacement efficiency of the oil displacement agent, and the final recovery rate were calculated according to the following formulas 2)-4):

[0143] In Formula 2), η1 is the water-driven oil displacement efficiency, %; V1 is the water-driven oil output volume, mL; V o The original oil-bearing volume of the core is expressed in mL.

[0144] In Formula 3), η2 is the oil displacement efficiency of the oil displacement agent, %; V2 is the volume of oil displaced by the oil displacement agent, mL; V o The original oil-bearing volume of the core is expressed in mL.

[0145] In formula 4), η 总 V1 is the final recovery rate, %; V2 is the volume of oil removed by water flooding, mL; V3 is the volume of oil removed by the oil displacement agent, mL; V4 is the final recovery rate, %; V5 is the final recovery rate, %; V6 is the final recovery rate, %; V7 is the final recovery rate, %; V8 is the final recovery rate, %; V9 is the final recovery rate, %; V1 is the volume of oil removed by water flooding, mL; V2 is the o The original oil-bearing volume of the core is expressed in mL.

[0146] In this test example, the oil displacement efficiency results of each quantum dot oil displacement agent are shown in Table 1 and Figure 4 below. The oil displacement efficiency in Table 1 is calculated under the condition that the injection amount of quantum dot oil displacement agent is 5.2 PV. Figure 4 is a curve showing the relationship between the oil displacement efficiency and the injection multiple of the Si / C quantum dot oil displacement agent provided in Example 1 of this invention.

[0147] Test Example 5

[0148] This test example directly evaluated the fluorescence intensity of the Si / C quantum dot oil displacement agents provided in Examples 1-6 and Comparative Examples 1-5 of this invention. The dominant wavelengths (A≥2.5) of the ultraviolet absorption spectrum and the dominant wavelengths (excitation wavelength 375±3nm) of the fluorescence emission spectrum of each Si / C quantum dot oil displacement agent are shown in Table 2 below. The results of the fluorescence intensity evaluation of the Si / C quantum dot oil displacement agent provided in Example 1 of this invention are shown in Figures 5a-5c. Figure 5a shows the results of the fluorescence performance evaluation of the Si / C quantum dot oil displacement agent provided in Example 1 of this invention; Figure 5b shows the relationship between absorbance and wavelength of the Si / C quantum dot oil displacement agent provided in Example 1 of this invention; and Figure 5c shows the relationship between fluorescence intensity and wavelength of the Si / C quantum dot oil displacement agent provided in Example 1 of this invention.

[0149] As can be seen from Table 2, under the condition that A≥2.5, the dominant wavelength of the ultraviolet absorption spectrum of the Si / C quantum dot oil displacement agent provided in the embodiments of the present invention is 275±3nm, and under the condition that the excitation wavelength is 375±3nm, the dominant wavelength of the fluorescence emission spectrum of the Si / C quantum dot oil displacement agent provided in the embodiments of the present invention is 445±3nm.

[0150] As can be seen from Figures 5a-5c, the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention can emit blue fluorescence under ultraviolet light irradiation. The position of maximum ultraviolet absorption, i.e., the dominant wavelength of the ultraviolet absorption spectrum (A≥2.5), is at 275nm, and the position of maximum fluorescence intensity, i.e., the dominant wavelength of the fluorescence emission spectrum (excitation wavelength is 375±3nm), is at 445nm, indicating that it has good fluorescence phenomenon.

[0151] Test Example 6

[0152] This test example performs infrared spectroscopy analysis on the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention, and the obtained infrared spectrum is shown in Figure 6. It can be clearly seen from Figure 6 that the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention has C-Si bonds located at 1070 cm⁻¹. -1 and less than 1070cm -1 At 1268cm -1 The characteristic absorption peak at 1638 cm⁻¹ belongs to the CO bending vibration. -1 The characteristic absorption peak at 1597 cm⁻¹ is due to the C=O tensile vibration. -1 The characteristic absorption peak at 3532 cm⁻¹ corresponds to the NH₂ shear vibration. -1 3422cm -1 and 3368cm -1 The characteristic absorption peak at the point can be attributed to the OH stretching vibration. This indicates that the Si / C quantum dot oil displacement agent provided in Example 1 of the present invention not only has C-Si bonds, but also contains hydroxyl, carbonyl and amino groups on its surface.

[0153] Infrared spectroscopy analysis further proves that the embodiments of the present invention first break down the carbon source and silicon source molecules in a high temperature and pressure environment, and then rely on the fact that the carbon-silicon bond energy is greater than the carbon-carbon bond energy and the silicon-silicon bond energy to make it easier for carbon and silicon to combine and recombine to form a carbon-silicon composite quantum dot oil displacement agent.

[0154] Test Example 7

[0155] This test example performs Zeta potential analysis on the Si / C quantum dot oil displacement agents provided in Examples 1-6 and Comparative Examples 1-5 of the present invention, including the following steps:

[0156] First, clean the measuring cup with ethanol, then rinse it with distilled water, and finally rinse the measuring cup twice with the quantum dot oil displacement agent provided in Example 1 before use. Add the quantum dot oil displacement agent provided in Example 1 to the measuring cup at a volume of 2 / 3 of the measuring cup volume. Select the Zeta analysis test program, put the measuring cup into the Zeta potential analysis for Zeta potential measurement, repeat three times, and take the average value as the final Zeta potential analysis.

[0157] The specific values ​​of the Zeta potential of the Si / C quantum dot oil displacement agents provided in Examples 1-6 and Comparative Examples 1-5 of this invention are shown in Table 1 below, and the Zeta potential analysis spectrum of the Si / C quantum dot oil displacement agent provided in Example 1 of this invention is shown in Figure 7. It can be clearly seen from Figure 7 that the Zeta potential of the Si / C quantum dot oil displacement agent provided in Example 1 of this invention is distributed at approximately -4.55 mV, indicating that it has obvious electroweak characteristics.

[0158] Test Example 8

[0159] This test example performs sweep range tests on the Si / C quantum dot oil displacement agents provided in Examples 1-6 and Comparative Examples 1-5 of the present invention, including the following steps:

[0160] ① The experiment used a PDMS microfluidic model with a length of 1.000cm, a width of 0.500cm, and a height of 0.010cm.

[0161] ② Vacuum saturate the formation water to determine the original water saturation Sw of the model.

[0162] ③ Use the oil-displacement method to drive water to a bound water state, record the pressure during oil-displacement, calculate the original oil saturation of the core, observe the oil-water distribution pattern, and determine the permeability of the oil phase. Inject 3-5 times the pore volume of experimental oil, generally until water is no longer produced, then inject more than one times the pore volume of oil. Subsequently, use the grid method to calculate the oil and water area in the core, calculate the original oil saturation Soi and bound water saturation Swi in the model, and take pictures.

[0163] ④ Let it sit for 7 days to restore its wettability, in order to simulate the wettability under formation conditions.

[0164] ⑤ Water drive oil to the residual oil state. Usually, more than twice the pore volume of water is injected until no more oil is produced. The oil and water distribution is observed under a microscope, and then the water area in the model is counted using the grid method under a microscope.

[0165] ⑥ Continue to use the oil displacement agent to displace the oil until no more oil is produced. Observe the oil and water distribution under a microscope, and use the grid method to count the water area in the model under a microscope to end the experiment.

[0166] For the Si / C quantum dot oil displacement agent provided in Example 1 of this invention, tests show that the aqueous phase sweep area after water flooding is 0.1162 cm². 2 The aqueous phase swept area after Si / C quantum dot oil displacement agent is 0.1711 cm². 2 The corresponding sweep ranges (sweep range = sweep area / area of ​​PDMS microfluidic model × 100%) were 23.24% and 34.22% respectively, indicating that the sweep range growth rate can reach 47.25%.

[0167] In this test example, the sweep range data of the Si / C quantum dot oil displacement agents provided in Examples 1-6 and Comparative Examples 1-5 of the present invention are also shown in Table 1 below.

[0168] Table 1 Performance evaluation results of various quantum dot oil displacement agents

[0169] Table 2 Fluorescence properties of various quantum dot oil displacement agents

[0170] As shown in Table 1, the particle size distribution of each Si / C quantum dot in the Si / C quantum dot oil displacement agents provided in the embodiments of the present invention is below 10 nm, indicating that the particle size distribution of the Si / C quantum dot oil displacement agents provided in the embodiments of the present invention is more uniform. For the Si / C quantum dot oil displacement agent provided in Example 1, as shown in Figure 1, its particle size distribution is around 4.032 nm, accounting for 100% of the total particle size, indicating that the synthesis method provided in the embodiments of the present invention can obtain quantum dot oil displacement agents with uniform and fine particle size.

[0171] As shown in Table 1, the Si / C quantum dot oil displacement agents provided in the embodiments of the present invention can achieve a maximum temperature and salt resistance of 300,000 mg / L and 85°C, indicating that they have strong temperature and salt resistance properties. Their temperature resistance is generally superior to that of the carbon quantum dot oil displacement agents provided in the comparative examples, and their salt resistance is significantly superior. For the Si / C quantum dot oil displacement agent provided in Example 1, as shown in Figures 2a and 2b, under conditions of a salinity of 300,000 mg / L and a temperature of 85°C, the absorption wavelength (peak position) and fluorescence intensity (peak height) remain essentially unchanged, indicating that the Si / C quantum dot oil displacement agent is relatively stable with minimal performance differences. Comparing the temperature and salt resistance data of the Si / C quantum dot oil displacement agents provided in Example 4 of the present invention and Comparative Examples 3-5, it can be seen that the temperature and salt resistance properties of the Si / C quantum dot oil displacement agent provided in Example 4 of the present invention are significantly superior to those of the Si / C quantum dot oil displacement agents provided in Comparative Examples 3-5.

[0172] As shown in Table 1, under a temperature of 85℃, the Si / C quantum dot oil displacement agents provided in the embodiments of the present invention all exhibited an adsorption efficiency of over 20% in low-permeability cores, with a maximum of nearly 54%, while the oil displacement efficiency was over 64%, with a maximum of nearly 86%. Both the adsorption and oil displacement efficiencies were superior to the carbon quantum dot oil displacement agents provided in Comparative Examples 1-5. For the Si / C quantum dot oil displacement agent provided in Example 1, as shown in Figures 3a-3b and 4, under 85℃, its adsorption efficiency in low-permeability cores reached a maximum of nearly 54%, which is 37.4 percentage points higher than that of formation water adsorption (as shown in Figure 3b, the adsorption efficiency of formation water adsorption was only 16.4%). This is particularly evident in ultra-low permeability cores (permeability greater than or equal to 1.0 × 10⁻⁶). -3 μm 2 Less than 10.0 × 10 -3 μm 2 The absorption efficiency of this material can reach 47.4%, which is 23.7 percentage points higher than that of formation water absorption; it is also effective in ultra-low permeability cores (permeability greater than or equal to 1.0 × 10⁻⁶). -3 μm 2 Less than 10.0 × 10 -3 μm 2 The average oil displacement efficiency can reach nearly 86%, which is 22.5 percentage points higher than that of water flooding, indicating that it has strong enhanced oil recovery performance. In summary, compared with the Si / C quantum dot oil displacement agents provided in the embodiments of this invention, the carbon quantum dot oil displacement agents provided in Comparative Examples 1-5 have disadvantages such as weak salt resistance, resulting in poor oil displacement effect.

[0173] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical inventions, and technical inventions in this invention can be freely combined and used.

Claims

1. A Si / C quantum dot oil displacement agent, which is an aqueous solution of Si / C quantum dots, wherein, The total weight of the Si / C quantum dot oil displacement agent is 100%, and the concentration of Si / C quantum dots is 4-26%. Specifically, under the condition of absorbance ≥ 2.5, the dominant wavelength of the ultraviolet absorption spectrum of the Si / C quantum dot oil displacement agent is 275±3nm, and under the condition of excitation wavelength 375±3nm, the dominant wavelength of the fluorescence emission spectrum of the Si / C quantum dot oil displacement agent is 445±3nm. The zeta potential of the Si / C quantum dot oil displacement agent is distributed between -4.45±0.5mV.

2. The Si / C quantum dot oil displacement agent according to claim 1, wherein, The particle size of Si / C quantum dots is less than 10 nm.

3. The Si / C quantum dot oil displacement agent according to claim 1 or 2, wherein, The Si / C quantum dot oil displacement agent has an average oil displacement efficiency of 64-90% in ultra-low permeability cores, wherein the permeability of the ultra-low permeability cores is greater than or equal to 1.0 × 10⁻⁶. -3 μm 2 Less than 10.0×10 -3 μm 2 .

4. The Si / C quantum dot oil displacement agent according to claim 1 or 2, wherein, The Si / C quantum dot oil displacement agent exhibits an adsorption efficiency of 20-55% in low-permeability cores and 21-50% in ultra-low-permeability cores, wherein the permeability of the low-permeability core is 10.0 × 10⁻⁶. -3 -30.0×10 -3 μm 2 The permeability of ultra-low permeability cores is greater than or equal to 1.0 × 10⁻⁶. -3 μm 2 Less than 10.0×10 -3 μm 2 .

5. The Si / C quantum dot oil displacement agent according to claim 1 or 2, wherein, The sweep range of the Si / C quantum dot oil displacement agent is 30-35%.

6. The Si / C quantum dot oil displacement agent according to claim 1 or 2, wherein, The Si / C quantum dot oil displacement agent can remain stable without agglomeration or precipitation under conditions where the temperature is not higher than 85℃ and the mineralization is not higher than 300,000 mg / L.

7. The method for preparing the Si / C quantum dot oil displacement agent according to any one of claims 1-6, wherein, The preparation method includes: Step (1): Add carbon source and silicon source to water at a mass ratio of 4-15:1-7 and dissolve them completely to obtain carbon-silicon mixture; Step (2): The carbon-silicon mixture is subjected to hydrothermal reaction at a pressure of 1-2 MPa and a temperature of 100-250℃ for 4-24 hours; Step (3): After cooling the reaction product obtained in step (2), an aqueous solution of Si / C quantum dots is obtained, which is the Si / C quantum dot oil displacement agent.

8. The preparation method according to claim 7, wherein, The mass ratio of the carbon source to the silicon source is 4-10:1-3.

9. The preparation method according to claim 7, wherein, The carbon source includes one or more of the following: coal, graphite powder, sucrose, xylose, starch, citric acid, glutaraldehyde, rhodamine, amino acids, o-phenylenediamine, sodium p-toluenesulfonate, and amaranth.

10. The preparation method according to claim 7, wherein, The silicon source includes one or a combination of several of the following: 3-aminopropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, sodium metasilicate, triphenylsilanol, and sodium silicate.

11. The preparation method according to claim 7, wherein, The carbon and silicon sources are fully dissolved in water by ultrasound, with a power of 1000-2000W and a duration of 10-60 minutes.

12. The preparation method according to claim 11, wherein, The ultrasound power is 1000-1500W, and the duration is 10-30 minutes.

13. The preparation method according to claim 7, wherein, The temperature for hydrothermal reactions is 120-250℃.

14. The preparation method according to claim 7, wherein, The preparation method further includes: purifying the cooled reaction product, wherein the purification is a three-stage purification process of centrifugation, filtration, and ultrafiltration. The centrifugation speed is 2000-10000 rpm, and the time is 5-30 min. The filtration is performed sequentially using a filter membrane with a pore size of 0.45 μm and a filter membrane with a pore size of 0.22 μm, and the number of filtrations is 1-10. The ultrafiltration is performed 1-10 times using an ultrafiltration membrane with a pore size of 0.01 μm.

15. The preparation method according to claim 14, wherein, The centrifugation speed is 5000-10000 rpm, the time is 10-20 min, the filtration is performed 5-10 times, and the ultrafiltration is performed 5-10 times.

16. The application of the Si / C quantum dot displacement agent according to any one of claims 1-6 in unconventional reservoir displacement.

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