Microemulsion, preparation method thereof, nanoemulsion infiltration agent and application

Abstract

The application provides a microemulsion, a preparation method thereof, a nanoemulsion infiltration agent and application. The raw materials of the microemulsion comprise a main surfactant, a co-surfactant, an oil phase and water; the main surfactant comprises anionic surfactant and nonionic surfactant with a mass ratio of 1:(1-1.5); the mass ratio of the co-surfactant to the main surfactant is 1:(4-6); the mass ratio of the sum of the mass of the main surfactant and the co-surfactant to the mass of the oil phase is (4-6):1; and the mass ratio of the sum of the mass of the main surfactant, the co-surfactant and the oil phase to the mass of the water is 1:(0.1-0.15). The nanoemulsion infiltration agent prepared from the microemulsion has strong temperature resistance, can still maintain a small particle size after high-temperature treatment, has the effects of reducing the oil-water interfacial tension, changing the wettability, and has strong anti-formation adsorption performance and infiltration effect, and can improve the recovery ratio of super-low-permeability and tight oil reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of ultra-low permeability tight oilfield development, specifically relating to a microemulsion and its preparation method, a nanoemulsion permeation agent and its application. Background Technology

[0002] Infiltration-driven oil recovery has been recognized as a crucial technique for the effective development of tight oil reservoirs. Compared to conventional reservoirs, tight oil reservoirs, influenced by crustal movement and sedimentary diagenesis, exhibit characteristics such as low porosity, low permeability, and strong heterogeneity. Furthermore, they possess a wide distribution of nanoscale pores and complex pore structures, leading to challenges such as fluid flow not conforming to Darcy's law, high flow resistance, difficulty in water injection, and difficulty in crude oil flow. In addition, current tight reservoirs are predominantly terrestrial sedimentary, with poor physical properties, numerous thin interbedded layers, and complex sand body distribution. This results in significant differences in geothermal gradients and pressure coefficients among different strata within the same basin, with most areas belonging to overpressured, high-temperature (>80℃) environments.

[0003] While traditional chemical flooding technologies (such as surfactant flooding) can drive the retention of crude oil, their application in high-temperature tight reservoirs still faces fundamental challenges. For example, conventional surfactants are structurally unstable at high temperatures and are prone to formation adsorption, severely impacting development costs and effectiveness. With the rapid development of nanotechnology, nanofluids are playing an increasingly prominent role in enhancing oil recovery. Nanofluids typically refer to uniformly dispersed systems with high stability, small particle size, and large specific surface area, including nanoparticle dispersions and nanoemulsions. Nanoparticles, however, suffer from dispersion stability issues, easily depositing during transport and causing contamination and irreversible damage to the matrix surface. Nanoemulsions, with their nanoscale effect, can effectively penetrate dense matrices to achieve full-area coverage, thus attracting widespread attention; however, many technical problems still need to be solved.

[0004] Patent application No. 201510050795.1 discloses a method for preparing high-temperature resistant nanoemulsions via ultrasonic emulsification. However, this method has limitations, requiring high external energy input and resulting in an average particle size greater than 200 nm for the ultrasonically dispersed emulsion. Patent application No. 202010468936.2 discloses a temperature- and salt-resistant nanoemulsion for fracturing fluids prepared through heating and distribution assembly. However, its preparation process is time-consuming, and the average particle size distribution is between 25-50 nm. Therefore, while the above methods can ensure the temperature resistance of the nanoemulsion system to a certain extent, they cannot effectively prepare nanoemulsion permeation systems with particle sizes of a few nanometers. The nanoemulsion systems prepared by these methods may still not be effectively injected into the deep matrix. Furthermore, the small pore size of ultra-low permeability / tight oil reservoirs often results in a large specific surface area, leading to formation adsorption losses, a problem that the above methods cannot overcome.

[0005] Therefore, how to provide a nanoscale permeabilizer suitable for high-temperature, ultra-low permeability / tight oil reservoirs remains a problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a microemulsion and its preparation method, a nanoemulsion permeabilizer, and its applications. This nanoemulsion permeabilizer exhibits strong temperature resistance, maintaining a small particle size and stability even at high temperatures.

[0007] To achieve the above objectives, the present invention provides a microemulsion, wherein the raw materials of the microemulsion include a main surfactant, a co-surfactant, an oil phase, and water;

[0008] The main surfactant comprises anionic surfactants and nonionic surfactants in a mass ratio of 1:(1-1.5);

[0009] The mass ratio of the co-surfactant to the main surfactant is 1:(4-6);

[0010] The mass ratio of the sum of the main surfactant and the co-surfactant to the oil phase is (4-6):1;

[0011] The mass ratio of the sum of the main surfactant, co-surfactant, and oil phase to water is 1:(0.1-0.15).

[0012] In some specific embodiments, preferably, the main surfactant comprises anionic surfactant and nonionic surfactant in a mass ratio of 1:(1-1.2).

[0013] In some specific implementations, preferably, the mass ratio of the sum of the main surfactant and the co-surfactant to the mass of the oil phase is (5-6):1.

[0014] According to a specific embodiment of the present invention, preferably, the anionic surfactant comprises sodium fatty alcohol polyoxyethylene ether sulfate and / or sodium secondary alkyl sulfonate. The general formula of the sodium fatty alcohol polyoxyethylene ether sulfate (AES) is RO(CH2CH2O). n -SO3Na, n=2 or 3, R is an alkyl group with 12-15 carbon atoms, and the secondary alkyl sulfonate sodium (SAS) has the structural formula C 12-16 H 25-33 A mixture of SO3 and Na.

[0015] According to a specific embodiment of the present invention, preferably, the nonionic surfactant includes fatty alcohol polyoxyethylene ether and / or alkylphenol polyoxyethylene ether. In this invention, by selecting appropriate surfactant types for compounding, the subsequently prepared nanoemulsion permeabilizer can achieve strong anti-adsorption performance, effectively solving the adsorption loss problem existing in ultra-low permeability tight oil reservoirs.

[0016] According to a specific embodiment of the present invention, preferably, the fatty alcohol polyoxyethylene ether includes one or more of AEO7, AEO9, and AEO15.

[0017] According to a specific embodiment of the present invention, preferably, the alkylphenol polyoxyethylene ether comprises OP10 and / or OP12.

[0018] According to a specific embodiment of the present invention, preferably, the co-surfactant comprises one or a combination of two or more of ethylene glycol, triethylene glycol, and butanol. In this invention, the addition of the co-surfactant can enhance the strength of the interfacial film.

[0019] According to a specific embodiment of the present invention, preferably, the oil phase includes one or more of white oil, acrylate, n-hexane, and limonene.

[0020] According to a specific embodiment of the present invention, preferably, the acrylate comprises one or a combination of two or more of methyl 9-decenoate, ethyl 9-decenoate, and methyl 2-decenoate.

[0021] The present invention also provides a method for preparing the above-mentioned microemulsion, wherein the preparation method includes:

[0022] The anionic surfactant, nonionic surfactant, and co-surfactant are first mixed to obtain an emulsifier; the emulsifier is then second mixed with the oil phase and water to obtain a microemulsion.

[0023] According to a specific embodiment of the present invention, preferably, the first mixing process includes: mixing the anionic surfactant and the nonionic surfactant to obtain the main surfactant, then mixing the co-surfactant with the main surfactant, stirring until clear, to obtain the emulsifier; more preferably, the stirring speed is 200-300 r / min.

[0024] According to a specific embodiment of the present invention, preferably, the second mixing process includes: mixing the emulsifier with the oil phase to form a microemulsion initial phase, then adding water to the microemulsion initial phase, heating and stirring until clear, to obtain a microemulsion; more preferably, the stirring temperature is 30-50℃, and the stirring speed is 300-500 r / min. In the present invention, adding a small amount of deionized water to the microemulsion initial phase promotes the self-assembly process, and the oil encapsulates the water to form a uniform water-in-oil (W / O) microemulsion. Through stepwise feeding and the self-assembly process, it is helpful to further efficiently prepare nanoemulsion permeators with small particle size, narrow distribution, and high stability.

[0025] This invention also provides a nanoemulsion permeabilizer, wherein the components of the nanoemulsion permeabilizer include brine and the aforementioned microemulsion; the mass ratio of the microemulsion to the brine is (0.05-0.5):(99.95-99.5). In this invention, by optimizing the ratio of surfactant shell to encapsulate the oil phase, a "Trojan horse effect" can be achieved. The resulting core-shell structure can reduce adsorption retention loss and improve temperature resistance, thereby giving the prepared nanoemulsion permeabilizer good anti-adsorption properties and deep migration ability, significantly improving the permeation recovery rate and sweep efficiency.

[0026] According to a specific embodiment of the present invention, preferably, the concentration of the brine is 0.05-0.3 wt%. In the present invention, the brine is slowly added for dilution under continuous stirring, which can induce a phase transition in the structure, transforming the oil-in-water phase into a water-in-oil phase, thereby obtaining a homogeneous, semi-transparent or transparent oil-in-water (O / W) nanoemulsion permeabilizer.

[0027] In some specific embodiments, preferably, the salt dissolved in the brine includes one or more of the following: calcium chloride, sodium chloride, ferric chloride, sodium sulfate, calcium sulfate, ferric sulfate, and potassium sulfate.

[0028] According to a specific embodiment of the present invention, preferably, after the nanoemulsion permeabilizer is aged at 80-120°C for 24-72 hours, it meets one or a combination of two of the following conditions: the particle size of the nanoemulsion permeabilizer is less than 20 nm (more preferably 5-16 nm); the cloud point of the nanoemulsion permeabilizer is less than 2 (more preferably 0.01-1.5). In this invention, the ratio of anionic surfactant to nonionic surfactant is the key to determining the temperature resistance of the subsequent nanoemulsion permeabilizer, and it can also affect the particle size distribution of the nanoemulsion permeabilizer, resulting in a nanoemulsion permeabilizer with a smaller particle size. In addition, the ratio of emulsifier to oil phase can also affect the particle size of the subsequently prepared nanoemulsion permeabilizer.

[0029] The present invention also provides the application of the above-mentioned microemulsion or nanoemulsion permeation agent in the permeation of ultra-low permeability tight oil reservoirs, wherein the core permeability of the ultra-low permeability tight oil reservoir is less than or equal to 0.1 mD.

[0030] In some specific embodiments, preferably, the formation adsorption capacity of the nanoemulsion permeabilizer is less than 1 mg / g, more preferably 0.2-0.6 mg / g.

[0031] In some specific implementations, preferably, the nanoemulsion permeation agent achieves an oil recovery rate of over 33% in ultra-low permeability tight oil reservoirs.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The microemulsion preparation method provided by this invention, by optimizing the ratio of anionic to nonionic surfactants, the ratio of the sum of the mass of the main surfactant and co-surfactant to the oil phase, and the appropriate type of surfactant, can obtain a stable microemulsion. This results in a nanoemulsion permeabilizer with small particle size, narrow distribution, high stability, and excellent injection performance. The preparation process is simple, efficient, and has low operating costs.

[0034] The nanoemulsion permeabilizer provided by this invention exhibits strong temperature resistance, maintaining good kinetic stability and a small particle size even after high-temperature treatment. It also retains the effects of reducing oil-water interfacial tension and altering wettability at high temperatures, making it suitable for ultra-low permeability / tight oil reservoir environments. Furthermore, this nanoemulsion permeabilizer demonstrates strong resistance to formation adsorption and a strong permeation effect, along with structural stability. This enhances permeation oil recovery and improves the recovery rate of ultra-low permeability / tight oil reservoirs, showing broad application prospects in the development of high-temperature ultra-low permeability / tight oil reservoirs. Attached Figure Description

[0035] Figure 1 The particle size distribution diagram is shown for the nanoemulsion permeating agent prepared in Example 1.

[0036] Figure 2 The particle size distribution diagram is shown for the nanoemulsion permeating agent prepared in Example 2.

[0037] Figure 3 The particle size distribution diagram is shown for the nanoemulsion permeating agent prepared in Example 3.

[0038] Figure 4 The particle size distribution of the nanoemulsion permeating agent prepared for Comparative Example 2 is shown in the figure.

[0039] Figure 5 The particle size distribution diagram is shown for the nanoemulsion permeating agent prepared in Example 3.

[0040] Figure 6 The image shows the scanning electron microscopy morphology of the nanoemulsion permeating agent prepared in Example 3.

[0041] Figure 7 Interfacial tension test curves of the emulsion penetrants prepared in Examples 1-3 and Comparative Examples 2-3.

[0042] Figure 8 The wetting angle test diagrams are for the emulsion penetrants prepared in Examples 1-3 and Comparative Examples 2-3.

[0043] Figure 9 The formation adsorption curves are for the emulsion permeation agents prepared in Examples 1-3 and Comparative Examples 2-3.

[0044] Figure 10 The recovery rate test curves are for the emulsion permeation agents prepared in Examples 1-3 and Comparative Examples 2-3. Detailed Implementation

[0045] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0046] It should be noted that, unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0047] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0048] It should be understood that the terms “comprising,” “including,” and / or “containing” as used herein specify the presence of the stated features, integers, steps, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

[0049] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0050] The sources of the main raw materials in the following examples and comparative examples are as follows:

[0051] Sodium alkyl sulfonate (SAS): 60%-70%, purchased from Clariant Chemicals (China) Co., Ltd.

[0052] Sodium fatty alcohol polyoxyethylene ether sulfate (AES): 60%-70%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0053] OP10: Analytical purity, purchased from Shanghai Maclean Biotechnology Co., Ltd.

[0054] Limonene: Analytical grade, purchased from China Huawi Ruike Chemical Co., Ltd.

[0055] AEO9: Analytical grade, purchased from Aladdin Reagent Co., Ltd., China.

[0056] Acrylate (methyl 9-decenoate): analytical grade, purchased from Shanghai Aoye Petroleum Technology Co., Ltd.

[0057] n-Hexane: Analytical grade, purchased from Aladdin Reagent Co., Ltd., China.

[0058] Betaine (TMG): Analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0059] Example 1:

[0060] This embodiment provides a method for preparing a microemulsion, the specific steps of which are as follows:

[0061] The anionic surfactant sodium alkyl sulfonate (SAS) and the nonionic surfactant OP10 were compounded at a mass ratio of 1:1.5 and stirred evenly to obtain the main surfactant; triethylene glycol and the main surfactant were mixed at a mass ratio of 1:5 and stirred at 30°C with a magnetic stirrer at a speed of 200 r / min until clear to obtain the emulsifier.

[0062] The above emulsifier and oil phase limonene were mixed at a mass ratio of 5:1 to form a microemulsion initial phase; finally, deionized water was added to the microemulsion initial phase, wherein the mass ratio of deionized water to the above microemulsion initial phase was 0.1:1; the mixture was stirred at 300 r / min at a temperature of 30°C until it became clear and transparent, thus obtaining a water-in-oil (W / O) microemulsion.

[0063] This embodiment also provides a nanoemulsion permeation agent, the specific steps of which are as follows:

[0064] Take 0.1 g of the microemulsion prepared in this example and dilute it with 99.9 g of 0.2% NaCl aqueous solution to obtain 0.1% nanoemulsion permeabilizer S-1.

[0065] Example 2:

[0066] This embodiment provides a method for preparing a microemulsion, the specific steps of which are as follows:

[0067] The anionic surfactant sodium fatty alcohol polyoxyethylene ether sulfate (AES) and the nonionic surfactant AEO9 were compounded at a mass ratio of 1:1 and stirred evenly to obtain the main surfactant; triethylene glycol and the main surfactant were mixed at a mass ratio of 1:5 and stirred at 30°C with a magnetic stirrer at a speed of 200 r / min until clear to obtain the emulsifier.

[0068] The above emulsifier and the oil phase methyl 9-decenoate were mixed at a mass ratio of 6:1 to form the microemulsion initial phase; finally, deionized water was added to the microemulsion initial phase, wherein the mass ratio of deionized water to the above microemulsion initial phase was 0.1:1; the mixture was stirred at 300 r / min at 30°C until it became clear and transparent, thus obtaining a water-in-oil (W / O) microemulsion.

[0069] This embodiment also provides a nanoemulsion permeation agent, the specific steps of which are as follows:

[0070] Take 0.2 g of the microemulsion prepared in this example and dilute it with 99.8 g of 0.2% NaCl aqueous solution to obtain 0.2% nanoemulsion permeabilizer S-2.

[0071] Example 3:

[0072] This embodiment provides a method for preparing a microemulsion, the specific steps of which are as follows:

[0073] Nonionic surfactants AEO9 and OP10 were compounded at a mass ratio of 1:1. Then, anionic surfactant sodium fatty alcohol polyoxyethylene ether sulfate (AES) was mixed with the compounded nonionic surfactant at a mass ratio of 1:1.2 and stirred until homogeneous to obtain the main surfactant. Triethylene glycol and the main surfactant were mixed at a mass ratio of 1:5 and stirred at 30°C with a magnetic stirrer at a speed of 200 r / min until clear to obtain the emulsifier.

[0074] The above emulsifier was mixed with the oil phase n-hexane at a mass ratio of 5:1 to form the microemulsion initial phase; finally, deionized water was added to the microemulsion initial phase, wherein the mass ratio of deionized water to the above microemulsion initial phase was 0.1:1; the mixture was stirred at 300 r / min at a temperature of 30°C until it became clear and transparent, thus obtaining a water-in-oil (W / O) microemulsion.

[0075] This embodiment also provides a nanoemulsion permeation agent, the specific steps of which are as follows:

[0076] Take 0.3 g of the microemulsion prepared in this example and dilute it with 99.7 g of 0.2% NaCl aqueous solution to obtain 0.3% nanoemulsion permeabilizer S-3.

[0077] Comparative Example 1:

[0078] This comparative example provides a method for preparing a microemulsion, which is basically the same as the preparation steps in Example 1, except that the ratio of anionic surfactant and nonionic surfactant in the main surfactant is changed.

[0079] Specifically, the mass ratio of SAS to OP10 will be adjusted to 1:3.

[0080] The remaining steps and parameters remain unchanged to obtain a water-in-oil (W / O) microemulsion.

[0081] This comparative example also provides an emulsion permeabilizer, which is basically the same as the preparation steps in Example 1, except that the microemulsion is replaced with the microemulsion prepared in this comparative example, while the other steps and parameters remain unchanged, and finally diluted to obtain an emulsion permeabilizer DB-1 with a concentration of 0.1%.

[0082] Comparative Example 2:

[0083] This comparative example provides a method for preparing a microemulsion, which is basically the same as the preparation steps in Example 1, except that the mass ratio of emulsifier to oil phase in the initial phase of the microemulsion is changed.

[0084] Specifically, the mass ratio of emulsifier to oil phase is adjusted to 3:1;

[0085] The remaining steps and parameters remain unchanged to obtain a water-in-oil (W / O) microemulsion.

[0086] This comparative example also provides an emulsion permeabilizer, which is basically the same as the preparation steps in Example 1, except that the microemulsion is replaced with the microemulsion prepared in this comparative example, while the other steps and parameters remain unchanged, and finally diluted to obtain an emulsion permeabilizer DB-2 with a concentration of 0.1%.

[0087] Comparative Example 3:

[0088] This comparative example provides a method for preparing a microemulsion, which is basically the same as the preparation steps in Example 1, except that the type of surfactant in the main surfactant is changed.

[0089] Specifically, the anionic surfactant is replaced with the same effective amount of the amphoteric surfactant betaine (TMG); the effective amount can be calculated based on the purity of the surfactant reagent.

[0090] The remaining steps and parameters remain unchanged to obtain a water-in-oil (W / O) microemulsion.

[0091] This comparative example also provides an emulsion permeabilizer, which is basically the same as the preparation steps in Example 1, except that the microemulsion is replaced with the microemulsion prepared in this comparative example, while the other steps and parameters remain unchanged, and finally diluted to obtain an emulsion permeabilizer DB-3 with a concentration of 0.1%.

[0092] The performance of the emulsion permeabilizers prepared in Examples 1-3 and Comparative Examples 1-3 was tested as follows:

[0093] (1) Temperature resistance and particle size distribution test:

[0094] The prepared emulsion permeating agents S-1, S-2, S-3, DB-1, DB-2, and DB-3 were placed in a high-temperature environment of 120℃ for 3 days. The degree of clarity and transparency of the above samples was then observed by a turbidimeter, and the turbidity point of the samples was recorded in Table 1.

[0095] The particle size distribution of the sample was determined using a nanolaser particle size / ZETA potentiometer, and the results are as follows: Figures 1 to 5 As shown, the results are summarized in Table 1. The particle size and morphology of the nanoemulsion permeabilizer prepared in Example 3 were observed using a scanning electron microscope, and the results are as follows. Figure 6 As shown, from Figure 6 It can be seen that a core-shell structure is formed inside the nanoemulsion absorbent.

[0096] As can be seen from Table 1, due to the unsuitable ratio of anionic surfactant to nonionic surfactant in Comparative Example 1, the prepared emulsion penetrant DB-1 became turbid after high-temperature aging treatment, with a cloud point of about 160.5. Subsequently, obvious phase separation occurred, and it did not have the effect of temperature resistance.

[0097] In contrast, the nanoemulsion permeabilizer S-1 in Example 1, after high-temperature aging treatment, had a cloud point of only 0.01, and was composed of... Figure 1 It can be seen that the median particle size of S-1 is 15.76 nm; the nanoemulsion permeabilizer S-2 in Example 2, after high-temperature aging treatment, has a cloud point of 0.1, and is composed of... Figure 2 It can be seen that the median particle size of S-2 is 8.34 nm; the nanoemulsion permeabilizer S-3 in Example 3, after high-temperature aging treatment, has a cloud point of 1.5, and is composed of... Figure 3 It can be seen that the median particle size of S-3 is 7.31 nm. Therefore, the above results show that the nanoemulsion permeators prepared in Examples 1-3 can all achieve good temperature resistance and maintain a small particle size at high temperatures, exhibiting good stability.

[0098] Furthermore, in Comparative Example 2, where the emulsifier-to-oil phase ratio was inappropriate, although the cloud point could be maintained at around 0.9 after high-temperature aging treatment, demonstrating temperature resistance, however, due to... Figure 4It can be seen that the median particle size of DB-2 is 157.7 nm, which cannot maintain a small particle size. Similarly, Comparative Example 3, which uses other types of surfactants, although its cloud point can be maintained at around 0.8 after high-temperature aging treatment, demonstrating temperature resistance, still exhibits... Figure 5 It can be seen that the median particle size of DB-3 is 533.9 nm, which is insufficient to maintain a small particle size.

[0099] (2) Interfacial tension performance test:

[0100] The prepared emulsion penetrants S-1, S-2, S-3, DB-2, and DB-3 were placed in a CNTGX700 rotating droplet interfacial tensiometer. The experimental temperature was set to 90℃, and the rotation speed was maintained at 6000 r / min with a time interval of 1 min. The rotating shaft carried the liquid and spun at a rotation speed ω. The lens focal length and field of view were adjusted to observe the droplet position, and the interfacial tension value was calculated. The calculation formula is shown in Equation I.

[0101] (Formula I);

[0102] In Equation I, σ represents the interfacial tension, mN / m; Δρ represents the density difference, kg / m³. 3 ω is the actual speed of the motor, r / min; R0 is the radius of the cylinder, m.

[0103] The results of measuring the interfacial tension of the above samples are as follows: Figure 7 As shown in the table, the results are summarized in Table 1. Table 1 shows that the emulsion permeators prepared in Examples 1-3 all reduce surface / interfacial tension, with Example 2 showing a more significant effect in reducing interfacial tension; while the emulsion permeators prepared in Comparative Examples 2-3 have a weaker ability to reduce interfacial tension. Therefore, the nanoemulsion permeator provided by this invention can significantly reduce the interfacial tension between the nanoemulsion and crude oil.

[0104] (3) Wetting and reversal performance test:

[0105] Referring to the "Method for Determining the Wettability of Reservoir Rocks" (SY / T 5153—2017), the wetted contact angle of a 2 mm thick, 25 mm diameter core slice was measured using a contact angle meter to determine the wettability of the core slice. First, the core slice was vacuum-sealed and aged in simulated oil for 7 days. The aged core slice was then immersed in different nanoemulsion permeabilizers S-1, S-2, S-3, DB-2, and DB-3, respectively, at an experimental temperature of 90℃. The contact angle and final contact angle of the core slice surface were measured after one day of immersion.

[0106] The contact angles of the above samples were measured using an E5637-C contact angle meter, and the results are as follows: Figure 8 As shown, the results are summarized in Table 1. Figure 8Table 1 shows that the nanoemulsion permeators prepared in Examples 1-3 can modify oleophilic surfaces into hydrophilic surfaces by their wetting angles, exhibiting wetting reversal ability. Among them, Example 3 has the smallest wetting angle and the strongest wetting reversal ability. In contrast, the nanoemulsion permeators prepared in Comparative Examples 2-3 have poor wetting reversal ability. Therefore, the nanoemulsion permeators provided by this invention can effectively change the wettability of oil reservoirs.

[0107] (4) Adsorption performance test:

[0108] The absorbance of nanoemulsion permeabilizers with mass fractions of 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, and 1.0 wt% at characteristic wavelengths was determined using a UV spectrophotometer, and a concentration-spectrophotometric standard curve was established. 50 mL of each of the nanoemulsion permeabilizers S-1, S-2, S-3, DB-2, and DB-3 were taken as samples to be tested. Each sample was thoroughly mixed with 2 g of quartz sand in a blue-capped bottle, and after thorough shaking in an 80℃ constant-temperature shaker, the supernatant was collected and centrifuged. The absorbance of the supernatant of each sample was measured, and the concentration values ​​at different adsorption times were calculated according to the standard curve. The static equilibrium adsorption capacity per unit mass of sandstone powder was then obtained using Formula II. Figure 9 The results are recorded in Table 1.

[0109] (Formula II);

[0110] Where τ is the adsorption amount, mg / g; C1 is the concentration of the emulsion permeabilizer before adsorption, mg / L; C2 is the concentration of the emulsion permeabilizer after adsorption, mg / L; V is the volume of emulsion permeabilizer added, mL; and m is the weight of quartz sand, g.

[0111] Depend on Figure 9 As shown in Table 1, the formation adsorption capacity of the comparative examples is higher than that of the examples, especially the formation adsorption capacity of comparative example 3, which uses a zwitterionic surfactant, is significantly higher. Therefore, compared with the comparative examples, the nanoemulsion permeators with smaller particle size prepared in Examples 1-3 have lower formation adsorption capacity (<1 mg / g), indicating that they have achieved stronger anti-adsorption performance.

[0112] (5) Immersion effect test:

[0113] Tight sandstone cores with similar reservoir properties were selected, with core mineral composition shown in Table 2 and physical property parameters shown in Table 3. Spontaneous adsorption experiments were conducted at 90℃ for the aforementioned emulsion adsorbents S-1, S-2, S-3, DB-2, and DB-3, recording the adsorption recovery rate at different times until no oil was produced in the core. The recovery rate of different samples was calculated using Formula III, and the results are as follows: Figure 10 As shown, the results are recorded in Table 1.

[0114] (Formula III);

[0115] Where i represents a certain osmosis time, h; R oi Let V be the oil recovery rate at time i; % oi ρ is the cumulative oil permeation and discharge volume at time i, in mL; ρ is the crude oil density, in g / mL; Δm is the core mass difference before and after saturation with crude oil, in g.

[0116] Table 1. Summary of performance test results of emulsion permeabilizers

[0117]

[0118] Table 2. X-ray diffraction analysis of whole-rock minerals

[0119]

[0120] Table 3. Summary of basic physical properties of core samples

[0121]

[0122] Depend on Figure 10 As shown in Table 1, compared with the comparative example, the nanoemulsion permeabilizers with smaller particle size prepared in Examples 1-3 can significantly reduce the adsorption and retention loss of sandstone during formation migration through the "Trojan horse effect", thereby achieving efficient permeabilization oil recovery and improving the recovery rate of ultra-low permeability tight oil reservoirs (>33%).

[0123] The above embodiments illustrate and describe the main features and advantages of the present invention in detail. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of the present invention.

Claims

1. A microemulsion, wherein, The raw materials for this microemulsion include a primary surfactant, a co-surfactant, an oil phase, and water; The main surfactant comprises anionic surfactants and nonionic surfactants in a mass ratio of 1:(1-1.5); The mass ratio of the co-surfactant to the main surfactant is 1:(4-6); The mass ratio of the sum of the main surfactant and the co-surfactant to the oil phase is (4-6):1; The mass ratio of the sum of the main surfactant, co-surfactant, and oil phase to water is 1:(0.1-0.15).

2. The microemulsion according to claim 1, wherein, The anionic surfactant includes sodium fatty alcohol polyoxyethylene ether sulfate and / or sodium secondary alkyl sulfonate.

3. The microemulsion according to claim 1, wherein, The nonionic surfactant includes fatty alcohol polyoxyethylene ether and / or alkylphenol polyoxyethylene ether; Preferably, the fatty alcohol polyoxyethylene ether comprises one or a combination of two or more of AEO7, AEO9, and AEO15; Preferably, the alkylphenol polyoxyethylene ether comprises OP10 and / or OP12.

4. The microemulsion according to claim 1, wherein, The co-surfactant includes one or more of ethylene glycol, triethylene glycol, and butanol.

5. The microemulsion according to claim 1, wherein, The oil phase includes one or more of white oil, acrylate, n-hexane, and limonene; Preferably, the acrylate comprises one or a combination of two or more of methyl 9-decenoate, ethyl 9-decenoate, and methyl 2-decenoate.

6. The method for preparing the microemulsion according to any one of claims 1-5, wherein, The preparation method includes: The anionic surfactant, nonionic surfactant, and co-surfactant are first mixed to obtain an emulsifier; the emulsifier is then second mixed with the oil phase and water to obtain a microemulsion.

7. The preparation method according to claim 6, wherein, The first mixing process includes: mixing the anionic surfactant and the nonionic surfactant to obtain the main surfactant, then mixing the co-surfactant with the main surfactant and stirring until clear to obtain the emulsifier; Preferably, the second mixing process includes: mixing the emulsifier with the oil phase to form a microemulsion initial phase, then adding water to the microemulsion initial phase, heating and stirring until clear, to obtain a microemulsion.

8. A nanoemulsion permeabilizer, wherein, The nanoemulsion permeabilizer comprises saline solution and the microemulsion as described in any one of claims 1-5; the mass ratio of the microemulsion to the saline solution is (0.05-0.5):(99.95-99.5); Preferably, the concentration of the brine is 0.05-0.3 wt%.

9. The nanoemulsion permeabilizer according to claim 8, wherein, After being aged at 80-120℃ for 24-72 hours, the nanoemulsion permeabilizer meets one or a combination of two of the following conditions: The particle size of the nanoemulsion penetrant is less than 20 nm; The cloud point of the nanoemulsion penetrant is less than 2.

10. The application of the microemulsion according to any one of claims 1-5, or the nanoemulsion permeabilizer according to claim 8 or 9, in the permeation of ultra-low permeability tight oil reservoirs, wherein, The core permeability of the ultra-low permeability tight oil reservoir is less than or equal to 0.1 mD.

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