A nanoemulsion, its preparation method and working solution system containing it.

Abstract

This invention provides a nanoemulsion, its preparation method, and a working fluid system containing it. The nanoemulsion comprises benzenesulfonic acid-based polybutadiene, anionic surfactant, long-chain alkyl compound, monophenyl compound, and water.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction, and in particular to a nanoemulsion for shale oil extraction. Background Technology

[0002] As global conventional oil and gas resources are gradually depleted and the demand for energy from economic and social development continues to grow, unconventional resources are receiving increasing attention and importance.

[0003] Shale oil refers to petroleum resources contained in shale formations, which are mainly composed of shale. It is an important unconventional oil and gas resource and a potential substitute for traditional petroleum resources. Shale oil includes petroleum in the pores and fractures of mudstone and shale, as well as petroleum resources in adjacent and interlayered layers of dense carbonate rocks or clastic rocks in mudstone and shale formations.

[0004] The most effective development methods are horizontal wells and staged fracturing technology. However, existing fracturing technologies have the following drawbacks: poor sand-carrying capacity, difficulty in proppant delivery, and excessively high sand ratios can easily cause sand blockage, while excessively low sand ratios result in low proppant concentration and low fracture conductivity, which in turn affects fracturing effectiveness. Therefore, improvements in the performance of pre-fracturing fluid and fracturing fluid are necessary. First, pre-fracturing fluid is injected to flush the wellbore to ensure good cementing quality, which is a prerequisite for fracturing operations. Then, a fracturing working fluid with strong sand-carrying capacity is injected to transport the proppant to the fracture, improving fracture conductivity.

[0005] In the field of solid minerals, shale oil is a synthetic petroleum product, a brown, viscous liquid with a distinctive pungent odor, formed by the thermal decomposition of organic matter during the dry distillation of shale. China's continental basins contain vast shale oil resource potential, with estimated recoverable resources reaching (30–60) × 10⁻⁶. 8 Tons. The latest exploration and development results show that industrial oil flow wells have been drilled in several regions of my country, indicating the enormous potential for shale oil extraction. However, due to the unique physical characteristics of shale and mudstone reservoirs, such as their extremely low porosity and permeability, shale oil flow in tight reservoirs is difficult. Shale and mudstone reservoirs are also susceptible to damage from external working fluids, resulting in generally low single-well production and rapid production decline, making it difficult to achieve industrial-scale production. Compared to the high cost of shale oil extraction, current production is far from meeting economic standards. Therefore, shale oil extraction relies on effective artificial fracturing techniques to improve the physical properties of shale oil reservoirs and promote shale oil flow. Especially in the Shengli Oilfield, where shale oil reservoirs reach depths of over 6000 meters, shale oil extraction depends on effective fracturing technology, which places higher demands on cementing and completion techniques. Summary of the Invention

[0006] One aspect of the present invention provides a nanoemulsion comprising benzenesulfonic acid-based polybutadiene, a first anionic surfactant, a long-chain alkyl compound, a monophenyl compound, and water.

[0007] In one specific embodiment, the benzenesulfonic acid-based polybutadiene has a weight-average molecular weight of 2000 to 3000.

[0008] In one specific embodiment, the first anionic surfactant is at least one of sodium dodecyl sulfate, dodecylbenzene sulfonic acid, anionic polyacrylamide, fatty acid salt, sulfonate, sodium fatty alcohol sulfate, and sulfate; the long-chain alkyl compound is at least one of butane, hexane, pentane, and heptane; and the monophenyl compound is at least one of toluene, ethylbenzene, and xylene.

[0009] In one specific embodiment, 100 parts by mass of water, 30 to 35 parts by mass of benzenesulfonic acid-based polybutadiene, 0.1 to 0.2 parts by mass of the first anionic surfactant, and 3 to 5 parts by mass of the total amount of the long-chain alkyl compound and the monophenyl compound.

[0010] In one specific embodiment, the mass ratio of the long-chain alkyl compound to the monophenyl compound is 1:4 to 4:1.

[0011] The second aspect of the present invention provides a method for preparing a nanoemulsion according to any one of the present inventions, comprising the following steps:

[0012] 1) Mix benzenesulfonic acid-based polybutadiene and water evenly, add the first anionic surfactant, mix evenly, and let stand to obtain a pre-hydration treatment solution;

[0013] 2) The pre-hydration treatment liquid is mixed evenly with long-chain alkyl compounds and monophenyl compounds to obtain the nanoemulsion.

[0014] In one specific embodiment, in step 1), the mixture is mixed at 50 to 70°C and then left to stand at ambient temperature.

[0015] In one specific implementation, the settling time is 20 to 24 hours.

[0016] The third invention provides a shale oil fracturing working fluid system, which includes independently composed pre-flush fluid, proppant-carrying fluid, and depolymerization fluid, wherein,

[0017] The pre-emulsion is a nanoemulsion as described in any one of the present inventions or a nanoemulsion prepared by the preparation method described in the second invention.

[0018] The sand-carrying fluid includes polyacrylamide, a second anionic surfactant, and water;

[0019] The depolymerization solution comprises a depolymerizing agent, a third anionic surfactant, and water.

[0020] In one specific embodiment, the polyacrylamide has a weight-average molecular weight of 100,000 to 120,000.

[0021] In one specific embodiment, the depolymerizing agent is di-tert-butyl peroxide and / or benzoyl peroxide.

[0022] In one specific embodiment, the amount of water in the sand-carrying solution is 100 parts, the amount of polyacrylamide is 0.11 to 0.17 parts by mass, and the amount of the second anionic surfactant is 0.1 to 0.2 parts by mass.

[0023] In one specific embodiment, the amount of water in the depolymerization solution is 100 parts, the amount of the depolymerization agent is 0.11 to 0.17 parts by mass, and the amount of the third anionic surfactant is 0.1 to 0.2 parts by mass.

[0024] In one specific embodiment, the second anionic surfactant and the third surfactant are independently at least one selected from sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, dodecylbenzene sulfonic acid, anionic polyacrylamide, fatty acid salt, sulfonate, sodium fatty alcohol sulfate, and sulfate.

[0025] The beneficial effects of this invention are:

[0026] With the exploration and development of shale oil in oilfields, low-permeability, ultra-low-permeability, and complex and sensitive reservoirs are gradually increasing. Conventional guar gum fracturing fluid leaves a large amount of residue in the fractures and fracture walls during fracturing operations, causing reservoir damage, reducing formation permeability and productivity, and directly affecting fracturing efficiency. Reducing the amount of thickener will reduce the content of solids entering the formation, effectively reducing the damage of fracturing fluid filtrate and residue to fractures and reservoirs. This invention uses low molecular weight polyacrylamide as a thickener for the proppant-carrying fluid. After fracturing and filling, a depolymerizing agent is injected to degrade the polyacrylamide, minimizing the damage of the fracturing fluid to the matrix supporting the fractures and fracture walls while ensuring fracture creation and proppant carrying. Therefore, this invention provides a residue-free, low-friction, high-efficiency, low-damage low molecular weight polyacrylamide clean proppant-carrying fluid, which is of great significance for greatly improving reservoir protection.

[0027] Because the emulsions currently used have large particle sizes and large adsorption losses, it is difficult to improve the oil washing efficiency of emulsion flooding in low-permeability reservoirs. Therefore, there is an urgent need to develop an oil washing system with small particle size and high oil washing efficiency, which is suitable for cleaning oil stains on the well wall using nano-emulsion pre-cleaning fluid. The nano-emulsion of the present invention has obvious effects in permeation and adsorption oil displacement and can be used as a pre-cleaning fluid for cleaning the well wall. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments. However, the embodiments of the present invention are merely illustrative examples and should not be construed as limiting the present invention under any circumstances.

[0029] Benzenesulfonic acid-based polybutadiene was purchased from Evonik Degussa.

[0030] Nanoemulsion

[0031] Example 1

[0032] Measure 100 parts by mass of water, heat it to 50℃, add 30 parts by mass of benzenesulfonic acid-based polybutadiene with a weight average molecular weight of 2000 under electric stirring at 5000 r / min, stir for 10 minutes (first stirring), then add 0.125 parts by mass of sodium dodecyl sulfate, stir for another 10 minutes (second stirring), and let it stand at ambient temperature for 24 hours for pre-hydration treatment; then heat it to 50℃ again and add 3.0 parts by mass of heptane and toluene (where the mass ratio of heptane to toluene is 1:1) under low speed electric stirring at 1000 r / min, and then stir for 20 minutes under electric stirring at 5000 r / min (third stirring) to prepare the nanoemulsion.

[0033] Example 2

[0034] Measure 100 parts by mass of water, heat it to 60℃, add 30 parts by mass of benzenesulfonic acid-based polybutadiene with a weight average molecular weight of 2000 under electric stirring at 3000 r / min, stir for 10 minutes (first stirring), then add 0.125 parts by mass of sodium dodecyl sulfate, stir for another 10 minutes (second stirring), and let it stand at ambient temperature for 24 hours for pre-hydration treatment; then heat it to 60℃ again and add 3.0 parts by mass of heptane and toluene (where the mass ratio of heptane to toluene is 1:1) under low speed electric stirring at 1000 r / min, and then stir for 20 minutes under electric stirring at 3000 r / min (third stirring) to prepare the nanoemulsion.

[0035] Example 3

[0036] Measure 100 parts by mass of water, heat it to 60℃, add 35 parts by mass of benzenesulfonic acid-based polybutadiene with a weight average molecular weight of 2000 under electric stirring at 3000 r / min, stir for 10 minutes (first stirring), then add 0.125 parts by mass of sodium dodecyl sulfate, stir for another 10 minutes (second stirring), and let it stand at ambient temperature for 24 hours for pre-hydration treatment; then heat it to 60℃ again and add 3.0 parts by mass of heptane and toluene (where the mass ratio of heptane to toluene is 1:1) under low speed electric stirring at 1000 r / min, and then stir for 20 minutes under electric stirring at 3000 r / min (third stirring) to prepare the nanoemulsion.

[0037] Example 4

[0038] Measure 100 parts by mass of water, heat it to 60℃, add 30 parts by mass of benzenesulfonic acid-based polybutadiene with a weight average molecular weight of 2000 under electric stirring at 3000 r / min, stir for 10 minutes (first stirring), then add 0.1 parts by mass of sodium dodecyl sulfate, stir for another 10 minutes (second stirring), and let it stand at ambient temperature for 24 hours for pre-hydration treatment; then add 3.0 parts by mass of heptane and toluene (where the mass ratio of heptane to toluene is 1:1) under low speed electric stirring at 1000 r / min, and then stir at 3000 r / min for 20 minutes (third stirring) to prepare the nanoemulsion.

[0039] Example 5

[0040] Measure 100 parts by mass of water, heat it to 60℃, add 30 parts by mass of benzenesulfonic acid-based polybutadiene with a weight average molecular weight of 2000 under electric stirring at 3000 r / min, stir for 10 minutes (first stirring), then add 0.2 parts by mass of sodium dodecyl sulfate, stir for another 10 minutes (second stirring), and let it stand at ambient temperature for 24 hours for pre-hydration treatment; then heat it to 60℃ again and add 3.0 parts by mass of heptane and toluene (where the mass ratio of heptane to toluene is 1:1) under low speed electric stirring at 1000 r / min, and then stir for 20 minutes under electric stirring at 3000 r / min (third stirring) to prepare the nanoemulsion.

[0041] Example 6

[0042] Measure 100 parts by weight of water, heat it to 60℃, add 30 parts by weight of benzenesulfonic acid-based polybutadiene with a weight average molecular weight of 3000 under electric stirring at 3000 r / min, stir for 10 minutes (first stirring), then add 0.125 parts by weight of sodium dodecyl sulfate, stir for another 10 minutes (second stirring), and let it stand at ambient temperature for 24 hours for pre-hydration treatment; then heat it to 60℃ again and add 3.0 parts by weight of heptane and toluene (where the mass ratio of heptane to toluene is 4:1) under low speed electric stirring at 1000 r / min, and then stir for 20 minutes under electric stirring at 3000 r / min (third stirring) to prepare the nanoemulsion.

[0043] Example 7

[0044] Measure 100 parts by mass of water, heat it to 60℃, add 30 parts by mass of benzenesulfonic acid-based polybutadiene with a weight average molecular weight of 2000 under electric stirring at 3000 r / min, stir for 10 minutes (first stirring), then add 0.125 parts by mass of sodium dodecyl sulfate, stir for another 10 minutes (second stirring), and let it stand at ambient temperature for 24 hours for pre-hydration treatment; then heat it to 60℃ again and add 3.0 parts by mass of heptane and toluene (where the mass ratio of heptane to toluene is 1:4) under low speed electric stirring at 1000 r / min, and then stir at 3000 r / min for 20 minutes (third stirring) to prepare the nanoemulsion.

[0045] Example 8

[0046] Measure 100 parts by mass of water, heat it to 70℃, add 30 parts by mass of benzenesulfonic acid-based polybutadiene with a weight average molecular weight of 2000 under electric stirring at 2000 r / min, stir for 10 minutes (first stirring), then add 0.125 parts by mass of sodium dodecyl sulfate, stir for another 10 minutes (second stirring), and let it stand at ambient temperature for 24 hours for pre-hydration treatment; then heat it to 70℃ again and add 3.0 parts by mass of heptane and toluene (where the mass ratio of heptane to toluene is 1:1) under low speed electric stirring at 1000 r / min, and then stir for 20 minutes under electric stirring at 2000 r / min (third stirring) to prepare the nanoemulsion.

[0047] Sand-carrying liquid

[0048] Example 9

[0049] Take 100 parts by weight of water, at ambient temperature, and add 0.11 parts by weight of polyacrylamide with a weight average molecular weight of 120,000 under electric stirring at 2000-5000 r / min. After stirring for 10 minutes (first stirring), add 0.2 parts by weight of sodium dodecyl sulfonate and stir for another 10 minutes (second stirring) to prepare the sand-carrying solution.

[0050] Example 10

[0051] Take 100 parts by weight of water, at ambient temperature, and add 0.15 parts by weight of polyacrylamide with a weight average molecular weight of 120,000 under electric stirring at 2000-5000 r / min. Stir for 10 minutes (first stirring), then add 0.1 parts by weight of sodium dodecyl sulfonate, and stir for another 10 minutes (second stirring) to prepare the sand-carrying solution.

[0052] Example 11

[0053] Take 100 parts by weight of water, at ambient temperature, and add 0.17 parts by weight of polyacrylamide with a weight average molecular weight of 120,000 under electric stirring at 2000-5000 r / min. After stirring for 10 minutes (first stirring), add 0.1 parts by weight of sodium dodecyl sulfonate and stir for another 10 minutes (second stirring) to prepare the sand-carrying solution.

[0054] Example 12

[0055] Take 100 parts by weight of water, at ambient temperature, and add 0.11 parts by weight of polyacrylamide with a weight average molecular weight of 100,000 under electric stirring at 2000-5000 r / min. Stir for 10 minutes (first stirring), then add 0.2 parts by weight of sodium dodecyl sulfonate, and stir for another 10 minutes (second stirring) to prepare the sand-carrying solution.

[0056] Example 13

[0057] Take 100 parts by weight of water, at ambient temperature, and add 0.17 parts by weight of polyacrylamide with a weight average molecular weight of 100,000 under electric stirring at 2000-5000 r / min. After stirring for 10 minutes (first stirring), add 0.1 parts by weight of sodium dodecyl sulfonate and stir for another 10 minutes (second stirring) to prepare the sand-carrying solution.

[0058] Depolymerization liquid

[0059] Example 14

[0060] Take 100 parts by weight of water, at ambient temperature, add 0.11 parts by weight of di-tert-butyl peroxide under electric stirring at 2000-5000 r / min, stir for 10 minutes (first stirring), then add 0.2 parts by weight of sodium dodecylbenzenesulfonate, and stir for another 10 minutes (second stirring) to prepare the depolymerization solution.

[0061] Example 15

[0062] Take 100 parts by weight of water, at ambient temperature, add 0.15 parts by weight of di-tert-butyl peroxide under electric stirring at 2000-5000 r / min, stir for 10 minutes (first stirring), then add 0.1 parts by weight of sodium dodecylbenzenesulfonate, and stir for another 10 minutes (second stirring) to prepare the depolymerization solution.

[0063] Example 16

[0064] Take 100 parts by weight of water, at ambient temperature, add 0.17 parts by weight of di-tert-butyl peroxide under electric stirring at 2000-5000 r / min, stir for 10 minutes (first stirring), then add 0.1 parts by weight of sodium dodecylbenzenesulfonate, and stir for another 10 minutes (second stirring) to prepare the depolymerization solution.

[0065] Example 17

[0066] Take 100 parts by weight of water, at ambient temperature, add 0.11 parts by weight of benzoyl peroxide under electric stirring at 2000-5000 r / min, stir for 10 minutes (first stirring), then add 0.2 parts by weight of sodium dodecylbenzenesulfonate, and stir for another 10 minutes (second stirring) to prepare the depolymerization solution.

[0067] Example 18

[0068] Take 100 parts by weight of water, at ambient temperature, add 0.15 parts by weight of benzoyl peroxide under electric stirring at 2000-5000 r / min, stir for 10 minutes (first stirring), then add 0.1 parts by weight of sodium dodecylbenzenesulfonate, and stir for another 10 minutes (second stirring) to prepare the depolymerization solution.

[0069] Example 19

[0070] Take 100 parts by weight of water, at ambient temperature, add 0.17 parts by weight of benzoyl peroxide under electric stirring at 2000-5000 r / min, stir for 10 minutes (first stirring), then add 0.2 parts by weight of sodium dodecylbenzenesulfonate, and stir for another 10 minutes (second stirring) to prepare the depolymerization solution.

[0071] Performance testing

[0072] 1. Determination of the particle size of nanodroplets in nanoemulsions

[0073] The particle size of nanodroplets in the nanoemulsions prepared in Examples 1 to 8 was determined using a laser scattering system (DLS), and the median particle size was obtained. The results are shown in Table 1.

[0074] According to the results in Table 1, the particle size of the nanodroplets in the nanoemulsions prepared in Examples 1 to 8 was measured, and the median particle size was found to be between 40 and 100 nanometers.

[0075] 2. Measurement of interfacial tension

[0076] The nanoemulsions prepared in Examples 1 to 8 were diluted with water to 0.5 wt%, that is, 0.5 g of nanoemulsion was mixed with 99.5 g of water, stirred evenly at 5000 r / min at 80 °C, and then allowed to stand at 80 °C for 30 minutes to obtain the diluted nanoemulsion.

[0077] The interfacial tension of the diluted nanoemulsion was measured using a rotating drop interfacial tensiometer, and the results are shown in Table 1.

[0078] As shown in Table 1, the nanoemulsions of Examples 1 to 8 exhibited good interfacial tension reduction properties. Low interfacial tension can effectively reduce the adhesion work between the oil phase and the rock surface, thereby enhancing oil washing ability.

[0079] 3. Determination of dispersion stability

[0080] The nanoemulsions prepared in Examples 1 to 8 were diluted with water to 0.5 wt%, i.e., 0.5 g of nanoemulsion was mixed with 99.5 g of water to obtain diluted nanoemulsions. The diluted nanoemulsions were then allowed to stand for 3 days at ambient temperature and 80°C, respectively, and it was observed whether they separated into layers or formed precipitates. The results are shown in Table 1.

[0081] According to the results in Table 1, the median particle size of the emulsion is between 40 and 100 nanometers, the minimum interfacial tension is 2.0 mN / m, the emulsion has good stability, and there is no stratification or precipitation.

[0082] Table 1

[0083] Example Median particle size / nm Interfacial tension / mN / m Is it layered? Does precipitation occur? Example 1 40 4.0 no no Example 2 45 3.5 no no Example 3 43 3.0 no no Example 4 55 2.0 no no Example 5 61 2.5 no no Example 6 81 2.6 no no Example 7 90 3.3 no no Example 8 100 4.8 no no

[0084] 4. Oil displacement effect

[0085] 4.1 Oil displacement effect at different dilution rates

[0086] The nanoemulsion prepared in Example 1 was diluted with water to 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, and 0.5 wt%, and stirred evenly at 80°C and a stirring speed of 5000 r / min to obtain diluted nanoemulsions.

[0087] Core samples (5.0 cm long, 2.5 cm in diameter) with pre-determined porosity and permeability were vacuum-pressurized and saturated with formation crude oil (0.7 mPa·s viscosity at room temperature, 0.713 g / cm³ density). 3 The weight of the core sample before saturation with formation crude oil was recorded. The difference between the weight of the core sample and the weight of the formation crude oil adsorbed was M1. The core sample was then aged in an 80℃ constant temperature chamber for more than 24 hours. After saturation, the core sample was wrapped with copper wire and placed in water and diluted nanoemulsions of various concentrations for 2 hours at 80℃. The weight of the diluted nanoemulsions before and after percolation was measured. The difference between the weight of the core sample and the weight of the diluted nanoemulsions was M2. The washing efficiency was calculated using the formula M2 / M1×100%. The results are shown in Table 2.

[0088] Table 2

[0089] Diluted nanoemulsion Porosity <![CDATA[Permeability / 10 -3 μm 2 > Oil washing efficiency 0 9.3％ 1.80 21.00％ 0.1％ 10.1％ 0.59 35.12％ 0.2％ 7.3％ 0.19 46.32％ 0.3％ 7.8％ 0.12 55.06％ 0.4％ 8.0％ 0.22 60.88％ 0.5％ 8.6％ 0.32 60.12％

[0090] 4.2 Oil displacement effect of nanoemulsions in different embodiments

[0091] The nanoemulsions prepared in Examples 1 to 8 were diluted with water to 0.4 wt% and stirred evenly at 80°C and a stirring speed of 5000 r / min to obtain diluted nanoemulsions.

[0092] The oil washing efficiency of each nanoemulsion was determined using the same procedure as in section 4.1 above, and the results are shown in Table 3.

[0093] Table 3

[0094] Example Porosity <![CDATA[Permeability / 10 -3 μm 2 > Oil washing efficiency Example 1 7.3％ 0.19 61％ Example 2 7.3％ 0.19 62％ Example 3 7.3％ 0.19 58％ Example 4 7.3％ 0.19 56％ Example 5 7.3％ 0.19 63％ Example 6 7.3％ 0.19 68％ Example 7 7.3％ 0.19 70％ Example 8 7.3％ 0.19 54％

[0095] 5. Degradation rate determination

[0096] The sand-carrying liquid of Example 9 and the depolymerization liquid of Example 14 were mixed at a mass ratio of 1:1. After being mixed evenly, the mixture was placed at 50°C for 24 hours to obtain the degradation liquid. The residue was observed and the results are shown in Table 4.

[0097] The sand-carrying liquid of Example 10 and the depolymerization liquid of Example 15 were mixed at a mass ratio of 1:1 and degraded under the same conditions as above to obtain the degradation liquid. The residue was observed and the results are shown in Table 4.

[0098] The sand-carrying liquid from Example 11 and the depolymerization liquid from Example 16 were mixed at a mass ratio of 1:1 and degraded under the same conditions to obtain the degradation liquid. The residue was observed, and the results are shown in Table 4.

[0099] The sand-carrying liquid of Example 12 and the depolymerization liquid of Example 17 were mixed at a mass ratio of 1:1 and degraded under the same conditions as above to obtain the degradation liquid. The residue was observed and the results are shown in Table 4.

[0100] The sand-carrying liquid of Example 13 and the depolymerization liquid of Example 18 were mixed at a mass ratio of 1:1 and degraded under the same conditions as above to obtain the degradation liquid. The residue was observed and the results are shown in Table 4.

[0101] The sand-carrying liquid of Example 9 and the depolymerization liquid of Example 19 were mixed at a mass ratio of 1:1 and degraded under the same conditions as above to obtain the degradation liquid. The residue was observed and the results are shown in Table 4.

[0102] Prepare aqueous solutions of polyacrylamide with gradient concentrations, measure the peak area using high-performance liquid chromatography, and plot a standard curve of polyacrylamide concentration.

[0103] The concentration of polyacrylamide in each degradation solution was determined by high performance liquid chromatography according to the above standard curve. Then, the degradation rate of polyacrylamide was calculated based on the concentration of polyacrylamide in each degradation solution. The results are shown in Table 4.

[0104] Table 4

[0105] Example Example Observe the residue Degradation rate Example 9 Example 14 none 80％ Example 10 Example 15 none 85％ Example 11 Example 16 none 90％ Example 12 Example 17 none 81％ Example 13 Example 18 none 79％ Example 9 Example 19 none 75％

[0106] While the present invention has been described with reference to specific embodiments, those skilled in the art will understand that various changes can be made without departing from the true spirit and scope of the invention. Furthermore, numerous modifications can be made to the subject, spirit, and scope of the invention to suit specific situations, materials, material compositions, and methods. All such modifications are included within the scope of the claims of the present invention.

Claims

1. A nanoemulsion comprising benzenesulfonic acid-based polybutadiene, a first anionic surfactant, a long-chain alkyl compound, a monophenyl compound, and water; The weight-average molecular weight of the benzenesulfonic acid-based polybutadiene is 2000 to 3000. The first anionic surfactant is at least one of sodium dodecyl sulfate, dodecylbenzene sulfonic acid, anionic polyacrylamide, and fatty acid salt; The long-chain alkyl compound is at least one of butane, hexane, pentane, and heptane; The monophenyl compound is at least one of toluene, ethylbenzene, and xylene; The amount of the benzenesulfonic acid-based polybutadiene is 30 to 35 parts by mass, the amount of the first anionic surfactant is 0.1 to 0.2 parts by mass, and the total amount of the long-chain alkyl compound and the monophenyl compound is 3 to 5 parts by mass, based on 100 parts by mass of water.

2. The nanoemulsion according to claim 1, characterized in that, The mass ratio of the long-chain alkyl compound to the monophenyl compound is 1:4 to 4:

1.

3. The method for preparing the nanoemulsion according to claim 1 or 2, comprising the following steps: 1) Mix benzenesulfonic acid-based polybutadiene and water evenly, add the first anionic surfactant, mix evenly, and let stand to obtain a pre-hydration treatment solution; 2) The pre-hydration treatment liquid is mixed evenly with long-chain alkyl compounds and monophenyl compounds to obtain the nanoemulsion.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the long-chain alkyl compound to the monophenyl compound is 1:4 to 4:

1.

5. The preparation method according to claim 3 or 4, characterized in that, In step 1), the mixture is mixed at 50°C to 70°C and then left to stand at ambient temperature.

6. The preparation method according to claim 5, characterized in that, The settling time is 20 to 24 hours.

7. A shale oil fracturing working fluid system, comprising independently composed pre-flush fluid, proppant-carrying fluid, and depolymerization fluid, wherein, The pre-emulsion is the nanoemulsion as described in claim 1 or 2, or the nanoemulsion prepared by the preparation method described in any one of claims 3 to 6; The sand-carrying fluid includes polyacrylamide, a second anionic surfactant, and water; The depolymerization solution comprises a depolymerizing agent, a third anionic surfactant, and water; The weight-average molecular weight of the polyacrylamide is 100,000 to 120,000. The depolymerizing agent is di-tert-butyl peroxide and / or benzoyl peroxide; The amount of water in the sand-carrying solution is 100 parts, the amount of polyacrylamide is 0.11 to 0.17 parts by mass, and the amount of the second anionic surfactant is 0.1 to 0.2 parts by mass. The amount of water in the depolymerization solution is 100 parts by mass, the amount of the depolymerization agent is 0.11 to 0.17 parts by mass, and the amount of the third anionic surfactant is 0.1 to 0.2 parts by mass. The second anionic surfactant and the third surfactant are independently at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, dodecylbenzene sulfonic acid, anionic polyacrylamide, and fatty acid salt.