Degradable Multifunctional Nanoemulsion and Its Preparation Method and Application

Abstract

The present invention provides a degradable multi-functional nanoemulsion, a preparation method thereof and an application thereof. Based on 100% of the total weight of the nanoemulsion, it comprises: 5-15% of a first surfactant, 5-15% of a second surfactant, 10-30% of a co-surfactant, 5-20% of an oil phase and 30-75% of water; wherein, the first surfactant comprises a glycolipid biosurfactant; the second surfactant comprises one or a combination of several of dodecyl glucoside, alkanolamide, fatty acid methyl ester sulfonate and fatty amide alkyl betaine. The present invention also provides an application of the nanoemulsion in a fracturing fluid and / or an oil displacement agent. The nanoemulsion of the present invention can effectively reduce the viscosity of crude oil and enhance the imbibition effect of a heavy oil reservoir, and has the advantages of being completely biodegradable, having low reservoir damage, being safe and non-toxic, having a simple preparation, and having a low recovery and treatment cost, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of oil extraction, and particularly to a degradable multi-effect nanoemulsion, a preparation method thereof, and an application thereof. Background Art

[0002] Tight oil and gas reservoirs mostly develop nano-scale pores. The heavy components in crude oil are complex and the viscosity of crude oil is high, resulting in large reservoir seepage resistance and low recovery rate. Economic development can only be achieved through hydraulic fracturing. As an additive for fracturing fluid, nanoemulsion is widely used in the fracturing operation of tight oil and gas reservoirs due to its advantages of small particle size, low adsorption, and high flowback efficiency, which can increase the oil and gas production per well and improve the development effect of tight oil and gas reservoirs. When nanoemulsion is added to fracturing fluid as an additive, it reduces the viscosity of crude oil after fully interacting with reservoir crude oil while forming artificial fracture networks, enhancing its fluidity. In the hydraulic fracturing operation, tens of thousands of cubic meters of fracturing fluid are pumped into the reservoir and communicate with groundwater through fractures or pores. During the fracturing fluid flowback stage after the production of oil and gas wells, 20% - 50% of the fracturing fluid is flowback to the ground for treatment. Therefore, the biodegradability of nanoemulsion not only affects the safety of groundwater resources and ecological environment, but also relates to the recovery and treatment cost of fracturing fluid.

[0003] Nanoemulsion is a kinetically stable dispersion system formed by dispersing nano-scale droplets in water after mixing surfactants, co-surfactants, and oil phase in a certain proportion. Among them, surfactants are the components with a relatively high proportion in nanoemulsion. The surfactant components used in existing nanoemulsion systems are mostly alkyl sulfonates, alkyl carboxylates, alkyl ammonium salts, imides, alkylphenol polyoxyethylene ethers, etc. (CN108114617A, CN104419395A, CN104667772A), but these surfactant components cannot be completely biodegradable, have a long degradation time, are easy to cause serious pollution to water bodies and soil, and even pose a hazard to human beings. Among them, alkylphenol polyoxyethylene ether substances have been banned in many countries due to their poor biodegradability. The nanoemulsion disclosed in CN108114617A also adds block copolymers, which further reduces the overall biodegradability of the nanoemulsion system. Although a single bio-based surfactant has a relatively high degradation rate (>70%), due to its strong hydrophilicity and low interfacial tension, its degradation period is long, making it difficult to meet the environmental protection quality requirements for hydraulic fracturing construction. Summary of the Invention

[0004] To solve the above technical problems, the purpose of the present invention is to provide a degradable multi-effect nanoemulsion, a preparation method thereof, and an application thereof. The nanoemulsion of the present invention has the characteristics of being completely biodegradable, good viscosity reduction effect, small reservoir damage, high imbibition efficiency, etc., and can effectively improve the recovery rate of heavy oil reservoirs.

[0005] To achieve the above object, a first aspect of the present invention provides a degradable multi-effect nanoemulsion. Based on 100% of the total weight of the nanoemulsion, it comprises the following components: 5-15% of a first surfactant, 5-15% of a second surfactant, 10-30% of a co-surfactant, 5-20% of an oil phase, and 30-75% of water;

[0006] Among them, the first surfactant includes glycolipid biosurfactants; the second surfactant includes one or a combination of several of dodecyl glucoside, alkanolamide, fatty acid methyl ester sulfonate, and fatty amide alkyl betaine, etc.

[0007] In the above-mentioned degradable multi-effect nanoemulsion, preferably, the mass ratio of the first surfactant to the second surfactant is (1-3):1.

[0008] In the above-mentioned degradable multi-effect nanoemulsion, preferably, the first surfactant includes one or a combination of several of sophorolipid, rhamnolipid, trehalolipid, and mannitol erythritol lipid, etc.

[0009] In the above-mentioned degradable multi-effect nanoemulsion, preferably, the co-surfactant includes alcohol compounds. More preferably, the co-surfactant includes one or a combination of several of isopropanol, propylene glycol, glycerol, propylene glycol monobutyl ether, polypropylene glycol, sorbitol, and menthol, etc.

[0010] In the above-mentioned degradable multi-effect nanoemulsion, preferably, the oil phase includes one or a combination of several of limonene, myrcene, ocimene, isododecane, isotetradecane, and isohexadecane, etc.

[0011] In the above-mentioned degradable multi-effect nanoemulsion, preferably, the water used can include deionized water or can also include brine. The brine can be prepared by those skilled in the art according to the formation salinity, and the present invention does not specifically limit its specific composition.

[0012] According to the specific embodiments of the present invention, preferably, the particle size (i.e., droplet particle size) of the degradable multi-effect nanoemulsion is 5-70 nm.

[0013] A second aspect of the present invention provides a preparation method of the above-mentioned degradable multi-effect nanoemulsion, which comprises the following steps:

[0014] Mix the first surfactant, the second surfactant, the co-surfactant, the oil phase, and the water according to the weight percentages of each component to obtain the above-mentioned degradable multi-effect nanoemulsion.

[0015] According to a specific embodiment of the present invention, preferably, the preparation method of the degradable multi-effect nanoemulsion comprises the following steps: according to the weight percentages of the components, at normal temperature and with a stirring speed of 100 - 500 rpm, the first surfactant, the second surfactant, the co-surfactant and the oil phase are mixed uniformly to form an oil-phase micelle solution, and then the oil-phase micelle solution is added to water at one time and mixed uniformly to obtain the degradable multi-effect nanoemulsion.

[0016] In the degradable multi-effect nanoemulsion of the present invention, the first surfactant is mainly a surfactant with emulsifying and solubilizing effects, and the second surfactant is mainly a surfactant with viscosity-reducing effects. When the first surfactant and the second surfactant are compounded according to the mass ratio of the present invention, it helps the first surfactant and the second surfactant to produce a synergistic effect, so that the prepared bio-based nanoemulsion has the effects of emulsifying and solubilizing and reducing the viscosity of crude oil. Specifically, after the first surfactant and the second surfactant in the nanoemulsion of the present invention come into contact with the polar substances in the crude oil, since the lipophilic group of the surfactant is similar to the molecular structure of the polar substances in the crude oil, the solubility of the polar substances is enhanced, and the polar substances are fully emulsified to form an oil-in-water emulsion. In addition, when used in hydraulic fracturing, after the polar components in the crude oil are emulsified, they are uniformly dispersed in the water phase, thus effectively reducing the viscosity of the crude oil. However, when the mass ratio of the first surfactant to the second surfactant in the present invention is not within the above range of the present invention, the coordination of these two aspects cannot be achieved well, and finally the emulsifying and solubilizing and crude oil viscosity-reducing effects of the corresponding fracturing fluid become poor and do not meet the actual use requirements. In addition, the first surfactant used in the nanoemulsion of the present invention is mainly a bio-based surfactant. Due to its large hydrophilic-lipophilic balance (HLB) value, its hydrophilicity is too strong, so that the nanoemulsion described in the present invention cannot be formed by using only a single bio-based surfactant. Therefore, it is necessary to add the second surfactant of the present invention to adjust the HLB value of the whole system, so as to form the nanoemulsion system described in the present invention by the low-energy emulsification method.

[0017] Meanwhile, the oil phase in the present invention has a similar polarity and molecular structure to the resin and asphaltene components in the crude oil, and the solubility of the heavy components in the crude oil is increased through the similar-phase solubility effect, thereby effectively reducing the viscosity of the crude oil. The co-surfactant of the present invention inserts into the interfacial film of the oil-in-water emulsion formed by the crude oil and the nanoemulsion, enhancing the strength of the crude oil-nanoemulsion interfacial film and the flexibility of the interfacial film.

[0018] Moreover, the combination of a specific co-surfactant and the oil phase in the present invention can provide a more favorable environment for the growth of microorganisms, accelerating the reproduction rate of microorganisms. Among them, the acidic substance formed after the co-surfactant of the present invention is decomposed by bioenzymes can adjust the pH value of the environment, while the oil phase of the present invention provides an energy source that is more easily absorbed and transformed for the growth of microorganisms, accelerating the growth and reproduction rate of microorganisms. Under the combined action of these two favorable effects, the nanoemulsion of the present invention has a faster biodegradation rate.

[0019] Therefore, the nanoemulsion of the present invention has the characteristics of complete biodegradability, good viscosity reduction effect, small reservoir damage, high imbibition efficiency, etc., and can effectively improve the recovery rate of heavy oil reservoirs.

[0020] The preparation method of the degradable multi-effect nanoemulsion of the present invention does not require additional ultrasonic or heating treatment. Instead, by first fully mixing the first surfactant, the second surfactant, the co-surfactant and the oil phase to form an oil-phase micelle solution, and then adding the oil-phase micelle solution to the water phase at one time, the chemical potential energy difference generated during the phase transition of the oil-phase micelles is used to promote the bending of the interfacial film, so that the oil phase is dispersed to form an oil-in-water nanoemulsion. The preparation method of the nanoemulsion of the present invention has the advantages of simple operation and low production cost, and can meet the requirements of large-scale industrial production of nanoemulsions.

[0021] The third aspect of the present invention provides the application of the above-mentioned degradable multi-effect nanoemulsion in a fracturing fluid and / or an oil displacement agent.

[0022] The degradable multi-effect nanoemulsion provided by the present invention can be used as a multi-effect additive not only for hydraulic fracturing but also for oil displacement agents in chemical flooding and other fields of oil exploitation.

[0023] The fourth aspect of the present invention provides a flowback aid for a fracturing fluid. Based on the total weight of the flowback aid for a fracturing fluid being 100%, it includes the following components: 0.1-1% of the above-mentioned degradable multi-effect nanoemulsion, and 99-99.9% of water.

[0024] In the above-mentioned flowback aid for a fracturing fluid, preferably, the water used can include deionized water or can also include brine. The brine can be prepared by those skilled in the art according to the formation salinity, and the present invention does not specifically limit its specific composition.

[0025] The present invention also provides a preparation method of the above-mentioned flowback aid for a fracturing fluid, which includes the following steps:

[0026] Based on the total weight of the flowback aid for a fracturing fluid being 100%, add 0.1-1% of the degradable multi-effect nanoemulsion to 99-99.9% of water, and mix evenly to obtain the flowback aid for a fracturing fluid.

[0027] The beneficial effects of the technical solution of the present invention mainly include: (1) achieving the complete biodegradation of the nanoemulsion, shortening the time required for complete biodegradation, and reducing the recovery and treatment cost of the fracturing fluid; (2) achieving the viscosity reduction of crude oil, reducing the seepage resistance of crude oil, and enhancing the flow ability of crude oil; (3) enhancing the imbibition displacement effect of the fracturing fluid, and increasing the imbibition recovery rate and the crude oil production per well. Therefore, the biodegradable multi-effect nanoemulsion of the present invention and the imbibition aid for fracturing fluid containing the same can effectively reduce the viscosity of crude oil and enhance the imbibition effect of heavy oil reservoirs, and have the advantages of complete biodegradability, low reservoir damage, safety and non-toxicity, simple preparation, and low recovery and treatment cost. Description of the Drawings

[0028] Figure 1 It is the change curve of the biodegradation rate with time for Example 1 and Comparative Example 1;

[0029] Figure 2 It is the change curve of the biodegradation rate with time for Example 2 and Comparative Example 2;

[0030] Figure 3 It is the change curve of the biodegradation rate with time for Example 3 and Comparative Example 3;

[0031] Figure 4 It is the change curve of the biodegradation rate with time for Example 4 and Comparative Example 4;

[0032] Figure 5 It is the change curve of the biodegradation rate with time for Example 5 and Comparative Example 5;

[0033] Figure 6 It is the comparison chart of the time required for complete degradation for Examples 1-5 and Comparative Examples 1-5;

[0034] Figure 7 It is the comparison chart of the crude oil viscosity reduction rate for Examples 1-5 and Comparative Examples 1-5;

[0035] Figure 8 It is the comparison chart of the imbibition recovery rate for Examples 1-5 and Comparative Examples 1-5;

[0036] Figure 9 It is the comparison chart of the permeability damage rate for Examples 1-5 and Comparative Examples 1-5;

[0037] Figure 10 It is the comparison chart of the imbibition recovery rate and the crude oil viscosity reduction rate for Example 1 and Comparative Examples 6, 7, and 8. Detailed Embodiments

[0038] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the following detailed description of the technical solution of the present invention is provided, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0039] Example 1

[0040] This example provides a degradable multi-functional nanoemulsion, which is prepared through the following steps:

[0041] By weight percentage, 10% rhamnolipid, 10% dodecyl glucoside, 10% glycerol, and 10% limonene are placed in a reactor and stirred thoroughly at room temperature at a stirring speed of 100 - 500 rpm to mix evenly and form an oil-phase micelle solution. Then, the oil-phase micelle solution is added to 60% deionized water at one time and mixed evenly to obtain a clear and transparent degradable multi-functional oil-in-water nanoemulsion.

[0042] This example also provides a flowback aid for fracturing fluid, which is prepared through the following steps:

[0043] By weight percentage, 1.0% of the nanoemulsion provided in this example is dropped into 99.0% deionized water, stirred and mixed evenly for dilution to obtain the flowback aid for fracturing fluid.

[0044] The average particle size of the nanoemulsion in the flowback aid for fracturing fluid is measured to be 25.5 nm using a Malvern Zetasizer Nano nanoparticle size analyzer; the change in its biodegradability over time is tested in accordance with the national standard GB / T 15818 - 2018, and the results show that its final biodegradability is 100%, and the time required for complete degradation is 12 days (as Figure 1 shown).

[0045] Example 2

[0046] This example provides a degradable multi-functional nanoemulsion, which is prepared through the following steps:

[0047] By weight percentage, 5% sophorolipid, 5% rhamnolipid, 5% coconut oil fatty acid diethanolamide, 5% glycerol, 5% sorbitol, 10% limonene, and 5% myrcene are placed in a reactor and stirred thoroughly at room temperature at a stirring speed of 100 - 500 rpm to mix evenly and form an oil-phase micelle solution. Then, the oil-phase micelle solution is added to 60% deionized water at one time and mixed evenly to obtain a clear and transparent degradable multi-functional oil-in-water nanoemulsion.

[0048] This example also provides a flowback aid for fracturing fluid, which is prepared through the following steps:

[0049] In terms of weight percentage, 1.0% of the nanoemulsion provided in this embodiment is added dropwise to 99.0% of deionized water, and the mixture is stirred and mixed to be evenly diluted to obtain the drainage aid for fracturing fluid.

[0050] The average particle size of the nanoemulsion in the fracturing fluid drainage agent was measured by the Malvern Zetasizer Nano nanoparticle size analyzer to be 45.0 nm; the change of its biodegradability over time was tested according to the national standard GB / T 15818-2018, and the results showed that its final biodegradability was 100%, and the time required for complete degradation was 18 days (such as Figure 2 shown).

[0051] Example 3

[0052] This embodiment provides a degradable multi-effect nanoemulsion, which is prepared by the following steps:

[0053] In terms of weight percentage, 10% of trehalose lipid, 5% of α-sulfo fatty acid methyl ester sodium salt, 5% of cocamidopropyl betaine, 10% of isopropanol, 5% of sorbitol, 10% of ocimene and 5% of isododecane are placed in a reactor, fully stirred at a stirring speed of 100-500 rpm at room temperature, mixed evenly to form an oil phase micelle solution, and then the oil phase micelle solution is added into 50% of deionized water at one time, mixed evenly, and a clear and transparent degradable multi-effect water-in-oil type nanoemulsion is obtained.

[0054] This embodiment also provides a drainage aid for fracturing fluid, which is prepared by the following steps:

[0055] In terms of weight percentage, 1.0% of the nanoemulsion provided in this embodiment is added dropwise to 99.0% of deionized water, and the mixture is stirred and mixed to be evenly diluted to obtain the drainage aid for fracturing fluid.

[0056] The average particle size of the nanoemulsion in the fracturing fluid drainage agent was measured by the Malvern Zetasizer Nano nanoparticle size analyzer to be 65.0 nm; the change of its biodegradability over time was tested according to the national standard GB / T 15818-2018, and the results showed that its final biodegradability was 100%, and the time required for complete degradation was 16 days (such as Figure 3 shown).

[0057] Example 4

[0058] This embodiment provides a degradable multi-effect nanoemulsion, which is prepared by the following steps:

[0059] Place 5% rhamnolipid, 5% mannitol erythritol lipid, 5% cocamidopropyl betaine, 5% polypropylene glycol (PPG200), 15% menthol, 5% limonene, and 10% isododecane in a reactor by weight percentage. Stir well at room temperature at a stirring speed of 100 - 500 rpm to mix evenly and form an oil-phase micelle solution. Then, add the oil-phase micelle solution to 50% deionized water at once and mix evenly to obtain a clear and transparent biodegradable multi-effect oil-in-water nanoemulsion.

[0060] This example also provides a flowback aid for fracturing fluid, which is prepared through the following steps:

[0061] Drop 1.0% of the nanoemulsion provided in this example into 99.0% deionized water by weight percentage, stir and mix evenly for dilution to obtain the flowback aid for fracturing fluid.

[0062] The average particle size of the nanoemulsion in the flowback aid for fracturing fluid is measured to be 65.3 nm using a Malvern Zetasizer Nano nanoparticle sizer; test the change of its biodegradability over time according to GB / T 15818 - 2018 of the national standard. The results show that its final biodegradability is 100%, and the time required for complete degradation is 10 days (as Figure 4 shown).

[0063] Example 5

[0064] This example provides a biodegradable multi-effect nanoemulsion, which is prepared through the following steps:

[0065] Place 5% rhamnolipid, 5% sophorolipid, 5% cocamidopropyl betaine, 10% glycerol, 10% isopropanol, 10% limonene, and 5% isododecane in a reactor by weight percentage. Stir well at room temperature at a stirring speed of 100 - 500 rpm to mix evenly and form an oil-phase micelle solution. Then, add the oil-phase micelle solution to 50% deionized water at once and mix evenly to obtain a clear and transparent biodegradable multi-effect oil-in-water nanoemulsion.

[0066] This example also provides a flowback aid for fracturing fluid, which is prepared through the following steps:

[0067] Drop 1.0% of the nanoemulsion provided in this example into 99.0% deionized water by weight percentage, stir and mix evenly for dilution to obtain the flowback aid for fracturing fluid.

[0068] The average particle size of the nanoemulsion in the flowback aid for fracturing fluid was measured to be 10.0 nm using a Malvern Zetasizer Nano particle size analyzer; the change in its biodegradability over time was tested in accordance with GB / T 15818-2018, and the results showed that its final biodegradability was 100%, and the time required for complete degradation was 7 days (as Figure 5 shown).

[0069] Comparative Example 1

[0070] This comparative example provides a dilution solution of a single surfactant, which is prepared by the following steps:

[0071] By weight percentage, 10% of rhamnolipid and 90% of deionized water were placed in a reactor, stirred and mixed evenly to obtain the dilution solution of the single surfactant.

[0072] This comparative example also provides a flowback aid for fracturing fluid, which is prepared by the following steps:

[0073] By weight percentage, the dilution solution of the single surfactant provided in this comparative example was added dropwise to 99.0% of deionized water, stirred and mixed evenly for dilution to obtain a comparative product with the same first surfactant concentration as in Example 1, which is the flowback aid for fracturing fluid of this comparative example.

[0074] The change in the biodegradability of the flowback aid for fracturing fluid over time was tested in accordance with GB / T 15818-2018, and the results showed that its final biodegradability was 100%, and the time required for complete degradation was 20 days (as Figure 1 shown).

[0075] Comparative Example 2

[0076] This comparative example provides a dilution solution of a compound surfactant, which is prepared by the following steps:

[0077] By weight percentage, 5% of sophorolipid, 5% of rhamnolipid, 5% of coconut oil fatty acid diethanolamide and 85% of deionized water were placed in a reactor, stirred and mixed evenly to obtain the dilution solution of the compound surfactant.

[0078] This comparative example also provides a flowback aid for fracturing fluid, which is prepared by the following steps:

[0079] A dilution solution of the compound surfactant of this comparative example was added dropwise to 99.0% deionized water at a weight percentage of 1.0%, and stirred and mixed evenly for dilution to obtain a comparative product with the same concentrations of the first surfactant and the second surfactant as in Example 2, which is the flowback aid for fracturing fluid of this comparative example.

[0080] According to the national standard GB / T 15818-2018, the change of the biodegradability of the flowback aid for fracturing fluid with time was tested. The results showed that its final biodegradability was 100%, and the time required for complete degradation was 25 days (as Figure 2 shown).

[0081] Comparative Example 3

[0082] This comparative example provides a dilution solution of a compound surfactant, which is prepared by the following steps:

[0083] At a weight percentage, 10% trehalose lipid, 5% sodium α-sulfo fatty acid methyl ester, 5% cocoamidopropyl betaine and 80% deionized water were placed in a reactor, stirred and mixed evenly to obtain the dilution solution of the compound surfactant.

[0084] This comparative example also provides a flowback aid for fracturing fluid, which is prepared by the following steps:

[0085] A dilution solution of the compound surfactant of this comparative example was added dropwise to 99.0% deionized water at a weight percentage of 1.0%, and stirred and mixed evenly for dilution to obtain a comparative product with the same concentrations of the first surfactant and the second surfactant as in Example 3, which is the flowback aid for fracturing fluid of this comparative example.

[0086] According to the national standard GB / T 15818-2018, the change of the biodegradability of the flowback aid for fracturing fluid with time was tested. The results showed that its final biodegradability was 100%, and the time required for complete degradation was 22 days (as Figure 3 shown).

[0087] Comparative Example 4

[0088] This comparative example provides a dilution solution of a compound surfactant, which is prepared by the following steps:

[0089] At a weight percentage, 5% rhamnolipid, 5% mannitol erythritol lipid, 5% cocoamidopropyl betaine and 85% deionized water were placed in a reactor, stirred and mixed evenly to obtain the dilution solution of the compound surfactant.

[0090] This comparative example also provides a flowback aid for fracturing fluid, which is prepared by the following steps:

[0091] A dilution solution of the compound surfactant of this comparative example was added dropwise to deionized water at 99.0% by weight percentage, and stirred and mixed evenly for dilution to obtain a comparative product with the same concentrations of the first surfactant and the second surfactant as in Example 4, which is the flowback aid for fracturing fluid of this comparative example.

[0092] According to GB / T 15818-2018, the change of the biodegradability of the flowback aid for fracturing fluid with time was tested. The results showed that its final biodegradability was 100%, and the time required for complete degradation was 15 days (as Figure 4 shown).

[0093] Comparative Example 5

[0094] This comparative example provides a dilution solution of a compound surfactant, which is prepared by the following steps:

[0095] Rhamnolipid at 5%, sophorolipid at 5%, cocoamidopropyl betaine at 5% and deionized water at 85% were placed in a reactor by weight percentage, and stirred and mixed evenly to obtain the dilution solution of the compound surfactant.

[0096] This comparative example also provides a flowback aid for fracturing fluid, which is prepared by the following steps:

[0097] A dilution solution of the compound surfactant of this comparative example was added dropwise to deionized water at 99.0% by weight percentage, and stirred and mixed evenly for dilution to obtain a comparative product with the same concentrations of the first surfactant and the second surfactant as in Example 5, which is the flowback aid for fracturing fluid of this comparative example.

[0098] According to GB / T 15818-2018, the change of the biodegradability of the flowback aid for fracturing fluid with time was tested. The results showed that its final biodegradability was 100%, and the time required for complete degradation was 9 days (as Figure 5 shown).

[0099] Comparative Example 6

[0100] This comparative example provides a degradable nanoemulsion, which is prepared by the following steps:

[0101] Taking 20% rhamnolipid, 10% glycerol, and 10% limonene by weight percentage, place them in a reactor, and stir well at room temperature at a stirring speed of 100 - 500 rpm to mix evenly, forming an oil-phase micellar solution. Then, add the oil-phase micellar solution to 60% deionized water all at once and mix evenly to obtain a clear and transparent biodegradable oil-in-water nanoemulsion. Compared with Example 1, this nanoemulsion contains only the first surfactant and no second surfactant.

[0102] This comparative example also provides a flowback aid for fracturing fluid, which is prepared through the following steps:

[0103] Taking 1.0% of the nanoemulsion provided by this comparative example by weight percentage, drop it into 99.0% deionized water, stir and mix evenly for dilution to obtain the flowback aid for fracturing fluid.

[0104] Comparative Example 7

[0105] This comparative example provides a biodegradable nanoemulsion, which is prepared through the following steps:

[0106] Taking 20% dodecyl glucoside, 10% glycerol, and 10% limonene by weight percentage, place them in a reactor, and stir well at room temperature at a stirring speed of 100 - 500 rpm to mix evenly, forming an oil-phase micellar solution. Then, add the oil-phase micellar solution to 60% deionized water all at once and mix evenly to obtain a clear and transparent biodegradable oil-in-water nanoemulsion. Compared with Example 1, this nanoemulsion contains only the second surfactant and no first surfactant.

[0107] This comparative example also provides a flowback aid for fracturing fluid, which is prepared through the following steps:

[0108] Taking 1.0% of the nanoemulsion provided by this comparative example by weight percentage, drop it into 99.0% deionized water, stir and mix evenly for dilution to obtain the flowback aid for fracturing fluid.

[0109] Comparative Example 8

[0110] This comparative example provides a biodegradable nanoemulsion, which is prepared through the following steps:

[0111] Put 5% rhamnolipid, 20% dodecyl glucoside, 10% glycerol and 10% limonene into a reactor by weight percentage, stir well at room temperature with a stirring speed of 100 - 500 rpm to mix evenly, forming an oil-phase micelle solution. Then add the oil-phase micelle solution to 55% deionized water at one time and mix evenly to obtain a clear and transparent biodegradable oil-in-water nanoemulsion. Compared with Example 1, the mass ratio of the first surfactant to the second surfactant of this nanoemulsion is 0.25:1.

[0112] This comparative example also provides a flowback aid for fracturing fluid, which is prepared through the following steps:

[0113] Drop 1.0% of the nanoemulsion provided by this comparative example into 99.0% deionized water by weight percentage, stir and mix evenly for dilution to obtain the flowback aid for fracturing fluid.

[0114] Time required for complete degradation in Test Example 1

[0115] This test example tests the biodegradation rates of the nanoemulsions prepared in Examples 1 - 5 and the single / mixed surfactant solutions prepared in Comparative Examples 1 - 5, including the following test steps:

[0116] Test the biodegradation rates of the flowback aids for fracturing fluid in Examples 1 - 5 and Comparative Examples 1 - 5 according to the test method for biodegradability of surfactants GB / T 15818 - 2018. The test interval is 1 day, and record the number of days required when the biodegradation rate of the sample reaches 100%, denoted as T c 。

[0117] The data of the time required for complete degradation of the flowback aids for fracturing fluid prepared from the nanoemulsions prepared in Examples 1 - 5 and the single / mixed surfactant solutions prepared in Comparative Examples 1 - 5 are as Figure 6 shown. It can be seen that the time required for complete degradation of the nanoemulsion of the present invention is 7 - 18 days, which is shorter than that of the single / mixed surfactant solution, and has a faster biodegradation rate.

[0118] Crude oil viscosity reduction rate in Test Example 2

[0119] This test example tests the crude oil viscosity reduction rates of the nanoemulsions prepared in Examples 1 - 5 and Comparative Examples 1 - 8 and the single / mixed surfactant solutions, including the following test steps:

[0120] (1) Measure a certain volume of crude oil and deionized water according to the volume ratio of oil to water of 1:9. Use a high-speed electric stirrer to fully mix the oil and water at a speed of 2000 rpm to form a crude oil emulsion. Then, take an appropriate amount of the upper-layer emulsion and measure the viscosity of the crude oil emulsion at 100 r / min according to the provisions of GB / T 16783.1 using a six-speed viscometer, denoted as η 1 .

[0121] (2) Take the prepared nanoemulsion or single / mixed surfactant solution. Measure a certain volume of crude oil and deionized water according to the volume ratio of oil to water of 1:9. Add the nanoemulsion or single / mixed surfactant solution with an addition amount of 0.1% (weight percentage) to the mixture of crude oil and deionized water. Use a high-speed electric stirrer to fully mix the oil and water at a speed of 2000 rpm to form a crude oil emulsion. Then, take an appropriate amount of the upper-layer emulsion and measure the viscosity of the crude oil emulsion at 100 r / min according to the provisions of GB / T 16783.1 using a six-speed viscometer, denoted as η 2 .

[0122] (3) Calculate the viscosity reduction rate of the crude oil by the nanoemulsion (or single / mixed surfactant solution) as follows:

[0123]

[0124] In the formula: Φ 降黏 is the viscosity reduction rate of the crude oil by the nanoemulsion (or single / mixed surfactant solution), in percentage; η 1 is the initial viscosity of the crude oil emulsion, in mPa·s; η 2 is the viscosity of the crude oil emulsion after adding the nanoemulsion (or single / mixed surfactant solution), in mPa·s.

[0125] The viscosity reduction rate data of the crude oil by the nanoemulsions and single / mixed surfactant solutions prepared in Examples 1-5 and Comparative Examples 1-5 are as Figure 7 shown. It can be seen that the viscosity reduction rate of the crude oil by the nanoemulsion of the present invention can reach 55-80%, which is higher than that of the single / mixed surfactant solution, and has a better crude oil viscosity reduction effect. The viscosity reduction rate data of Examples 1 and Comparative Examples 6, 7, and 8 are as Figure 10 shown.

[0126] Test Example 3 Imbibition Recovery

[0127] This test example tests the imbibition recovery of the nanoemulsions and single / mixed surfactant solutions prepared in Examples 1-5 and Comparative Examples 1-8, including the following test steps:

[0128] (1) Core saturated with oil: Take an artificial quartz sandstone core with a permeability of 0.5 mD and a porosity of 10%, place it in a constant temperature oven at 105 °C and dry it to a constant weight and weigh it, denoted as m 1 . Then place the dried core in a pressurized container filled with oil, and conduct vacuum saturation of the core with oil for 7 days through a vacuum pump and a hydraulic pump. The pressurization pressure for oil saturation is 10 MPa. Take out the core saturated with oil, wipe off the floating oil on the surface with absorbent paper and weigh it, denoted as m 2 , then the volume of oil saturated in the core can be calculated by the following formula:

[0129]

[0130] In the formula, B oil is the volume of oil saturated in the core, mL; m 2 is the mass of the core saturated with oil, g; m 1 is the mass of the dry core, g; ρ oil is the density of the crude oil, g / cm 3 .

[0131] (2) Spontaneous imbibition experiment: Place the above-mentioned core saturated with oil in a spontaneous imbibition bottle, and fill the spontaneous imbibition bottle with a nanoemulsion (or a single / mixed surfactant solution). Measure the volume of the crude oil produced by imbibition through the glass graduated tube at the upper part of the spontaneous imbibition bottle until the volume of the produced crude oil is constant, denoted as V f .

[0132] (3) Calculation of imbibition recovery rate: By comparing the volume of the crude oil produced by imbibition with the volume of oil saturated in the core, the imbibition recovery rate of the nanoemulsion (or a single / mixed surfactant solution) can be obtained, as shown in the following formula:

[0133]

[0134] In the formula, Φ 渗吸 is the imbibition recovery rate of the nanoemulsion (or a single / mixed surfactant solution), in percentage; V f is the volume of the crude oil produced by imbibition, mL; V oil is the volume of oil saturated in the core, mL.

[0135] The imbibition recovery rate data of the nanoemulsions and single / mixed surfactant solutions prepared in Examples 1 to 5 and Comparative Examples 1 to 5 are as Figure 8 shown. It can be seen that the imbibition recovery rate of the nanoemulsion of the present invention can reach 21-35%, which is higher than that of the single / mixed surfactant solution, and has a better imbibition displacement effect. The imbibition recovery rate data of Example 1 and Comparative Examples 6, 7, and 8 are as Figure 10 shown.

[0136] Figure 10 It shows the comparison data of imbibition recovery rate and crude oil viscosity reduction rate between Example 1 prepared by using the first surfactant and the second surfactant of the present invention simultaneously, Comparative Example 6 prepared by using only the first surfactant, Comparative Example 7 prepared by using only the second surfactant, and Comparative Example 8 where the mass ratio of the first surfactant to the second surfactant is not within the above range of the present invention. From Figure 10 It can be seen that Example 1 has higher imbibition recovery rate and crude oil viscosity reduction rate compared with Comparative Examples 6, 7, and 8. The increase range of imbibition recovery rate is 27% - 133%, and the increase range of crude oil viscosity reduction rate is 23% - 106%. This result indicates that the nanoemulsion prepared by compounding the first surfactant and the second surfactant of the present invention under the condition of the mass ratio defined by the present invention has stronger imbibition production increase and crude oil viscosity reduction effects than the nanoemulsion prepared by using only a single surfactant and the nanoemulsion prepared when the mass ratio of the first surfactant to the second surfactant is not within the range of the present invention, indicating that there is a synergistic effect between the first surfactant and the second surfactant of the present invention.

[0137] For Comparative Example 8, the mass ratio of the first surfactant to the second surfactant is not within the range of the present invention, and the recovery rate and viscosity reduction rate are much lower than those of Comparative Examples 6 and 7. This is mainly because under different surfactant ratio conditions, the structural parameters of the mixed micelles formed by the two surfactants have large differences, resulting in changes in the structure of the nanoemulsion mother liquor formed, that is, from a bicontinuous type to an oil-in-water type. This affects the emulsification and solubilization performance of the formed nanoemulsion for crude oil, and also reduces its wetting reversal performance to a certain extent, thus ultimately resulting in obvious differences in the recovery rate and viscosity reduction rate effects when the surfactant ratio of Comparative Example 8 changes compared with the examples of the present invention.

[0138] Test Example 4 Permeability Damage Rate

[0139] This test example tests the permeability damage rate of the nanoemulsions prepared in Examples 1 - 5 and the single / mixed surfactant solutions prepared in Comparative Examples 1 - 5, including the following test steps:

[0140] (1) Sample preparation: Prepare formation water according to the formation water salinity, and use the formation water to prepare a drainage aid for fracturing fluid. The contents of nanoemulsion and single / mixed surfactant solution in the drainage aid for fracturing fluid are the same as those in Examples 1 - 5 and Comparative Examples 1 - 5 above. Use aviation kerosene as the flowing medium. Use natural outcrop cores as experimental cores.

[0141] (2) Conduct the permeability damage rate test according to the water-based fracturing fluid performance evaluation method SY / T 5107 - 2016.

[0142] The data of the permeability damage rates of the nanoemulsions prepared in Examples 1 to 5 and the single / mixed surfactant solutions prepared in Comparative Examples 1 to 5 are as Figure 9 shown. The permeability damage rates of Examples 1 to 5 are between 8% and 14%, and the permeability damage rates of Comparative Examples 1 to 5 are between 10% and 18%. It can be seen that the bio-based nanoemulsion of the present invention causes less damage to the reservoir compared with the comparative examples, and can more effectively reduce the reservoir damage caused by the fracturing fluid.

[0143] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to enumerate all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A degradable multi - effect nano - emulsion. Based on 100% of the total weight of the nano - emulsion, it comprises the following components: 5 - 15% of a first surfactant, 5 - 15% of a second surfactant, 10 - 30% of a co - surfactant, 5 - 20% of an oil phase, and 30 - 75% of water; Wherein, the first surfactant includes glycolipid - type biosurfactants; the second surfactant includes one or a combination of several of dodecyl glucoside, alkanolamide, fatty acid methyl ester sulfonate, and fatty amide alkyl betaine; the co - surfactant includes alcohol compounds; the mass ratio of the first surfactant to the second surfactant is (1 - 3):1; the degradable multi - effect nano - emulsion is an oil - in - water nano - emulsion, and the particle size of the degradable multi - effect nano - emulsion is 5 - 70 nm.

2. The degradable multi - effect nano - emulsion according to claim 1, wherein, the first surfactant includes one or a combination of several of sophorolipid, rhamnolipid, trehalolipid, and mannosylerythritol lipid.

3. The degradable multi - effect nano - emulsion according to claim 1, wherein, the co - surfactant includes one or a combination of several of isopropanol, propylene glycol, glycerol, propylene glycol butyl ether, polypropylene glycol, sorbitol, and menthol.

4. The degradable multi - effect nano - emulsion according to claim 1, wherein, the oil phase includes one or a combination of several of limonene, myrcene, ocimene, isododecane, isotetradecane, and isohexadecane.

5. The degradable multi - effect nano - emulsion according to claim 1, wherein, the water includes deionized water or brine.

6. A preparation method of the degradable multi - effect nano - emulsion according to any one of claims 1 - 5, which comprises the following steps: According to the weight percentages of each component, at room temperature and with a stirring speed of 100 - 500 rpm, the first surfactant, the second surfactant, the co - surfactant, and the oil phase are mixed evenly to form an oil - phase micelle solution, and then the oil - phase micelle solution is added to water at one time and mixed evenly to obtain the degradable multi - effect nano - emulsion.

7. Application of the degradable multi - effect nano - emulsion according to any one of claims 1 - 5 in a fracturing fluid and / or an oil displacement agent.

8. A flow - back aid for a fracturing fluid. Based on 100% of the total weight of the flow - back aid for a fracturing fluid, it comprises the following components: 0.1 - 1% of the degradable multi - effect nano - emulsion according to any one of claims 1 - 5, and 99 - 99.9% of water.

9. The flow - back aid for a fracturing fluid according to claim 8, wherein, the water includes deionized water or brine.

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