Emulsion hydroxyl chitosan-based viscous oil viscosity-reducing treatment agent and method

Abstract

The present application relates to heavy oil exploitation and oil field chemical field, specifically to a heavy oil viscosity reduction treatment agent based on emulsion hydroxyl chitosan and a preparation method thereof; the agent comprises functionalized modified hydroxyl chitosan, a cosolvent, an emulsifying aid and water; the material grafts hydrophobic long-chain alkyl and anionic hydrophilic groups to the hydroxyl chitosan skeleton through chemical bonds, and an amphiphilic polymer emulsion is prepared by combining a high shear emulsification process; the key technical principle is that the hydrophilic and hydrophobic groups are covalently and stably grafted on the same macromolecular skeleton, a high mechanical strength polymer interfacial film is formed in the water phase, the internal association of heavy oil is destroyed through steric hindrance, and the heavy oil is in-situ converted into an oil-in-water emulsion; the present application overcomes the defect that the traditional physical compounding system is prone to chromatographic separation, solves the demulsification failure in high temperature and high salt environment of the formation by using a natural polysaccharide skeleton, and solves the problems of great toxicity and poor degradation of petrochemical products, effectively improves the heavy oil viscosity reduction rate and long-term stability, and meets the development trend of green environmental protection.

Description

Technical Field

[0001] This invention relates to the fields of heavy oil extraction and oilfield chemistry, specifically to a heavy oil viscosity reducing agent and method based on emulsion hydroxy chitosan. Background Technology

[0002] With the decreasing reserves of conventional light crude oil, the proportion of heavy oil resource development in crude oil production is increasing year by year. Heavy oil contains a large amount of gum and asphaltenes. These polar macromolecules associate with each other through hydrogen bonds, π-π stacking and van der Waals forces to form a complex three-dimensional network structure. This causes the viscosity of heavy oil to exceed the conventional extraction threshold and the fluidity to fail to meet the requirements of oil well self-flowing extraction, increasing the process complexity of downhole extraction, lifting and surface gathering and transportation. Currently, the commonly used methods for reducing the viscosity of heavy oil in industry are mainly divided into physical heating and chemical viscosity reduction. Chemical viscosity reduction has attracted much attention due to its low energy consumption and simple operation. However, existing chemical viscosity reducers have significant limitations: the viscosity reduction effect is significantly affected by the high temperature and high salinity of the formation environment, and there is a risk of phase transformation or demulsification failure. Moreover, most of them are petrochemical derivatives, which have problems such as high environmental toxicity and long biodegradation period, which have a negative impact on the formation and ecological environment. Existing systems typically involve the physical compounding of high molecular weight polymers with small molecule surfactants. In the complex flow environment of porous downhole media, due to differences in molecular size and adsorption characteristics, component separation can easily occur due to differences in adsorption and retention. This leads to component separation and microstructure failure in the formulation system during transport, resulting in a significant decrease in viscosity reduction performance. While native chitosan possesses excellent biocompatibility and environmental friendliness, the strong intramolecular and intermolecular hydrogen bonds in native chitosan result in poor water solubility, making it unsuitable for direct use as a surfactant. Although simple hydroxylation modification improves water solubility, the lack of a hydrophobic structure prevents it from effectively penetrating and dissociating the gum / asphaltite network of heavy oil, thus lacking emulsifying and viscosity-reducing capabilities. Therefore, there is an urgent need to develop a novel heavy oil viscosity-reducing agent that is heat-resistant, salt-resistant, chromatographically resistant, and environmentally friendly. Summary of the Invention

[0003] The purpose of this invention is to provide a heavy oil viscosity reducer based on emulsion hydroxy chitosan and its preparation method. This aims to overcome the shortcomings of existing chemical viscosity reducers, which are prone to phase transformation or demulsification failure due to high formation temperature and high salinity. It also aims to improve upon the high environmental toxicity and low biodegradability of existing petrochemical-derived viscosity reducers, avoid the phenomenon of significant decrease in viscosity reduction performance caused by component separation due to differences in adsorption and transport rates in downhole porous media caused by the physical compound system of high molecular weight polymers and small molecule surfactants, and solve the problem that native or simply hydroxylated chitosan lacks a hydrophobic structure and cannot effectively penetrate and disrupt the heavy oil association network for emulsification and viscosity reduction. Specifically, the technical solution of this invention is as follows: The heavy oil viscosity reducing agent based on emulsion hydroxy chitosan comprises the following components by weight percentage: 0.5-15.0% functionalized modified hydroxy chitosan; 0.1-5.0% total amount of cosolvent and emulsifying agent; and the balance being water. The functionalized modified hydroxy chitosan is an amphiphilic polymer prepared by grafting hydrophobic long-chain alkyl groups with 12-16 carbon atoms and anionic hydrophilic groups containing sulfonic acid groups onto hydroxy chitosan as the backbone.

[0004] Preferably, in one specific embodiment, the functionalized modified hydroxy chitosan is prepared by the following method: A. Chitosan powder with a degree of deacetylation ≥ 85% is dispersed in isopropanol, and sodium hydroxide aqueous solution is slowly added dropwise. The mixture is stirred and swelled at 20-25℃ for 1-2 hours to alkalize it. Then, propylene oxide is added dropwise, and the mixture is heated to 60-70℃ and refluxed for 4-6 hours to obtain a hydroxy chitosan intermediate mixture. B. In the hydroxy chitosan intermediate mixture, a long-chain alkylating agent and a phase transfer catalyst are added, and the mixture is refluxed at 70-80℃ for 6-8 hours; then an anionizing agent is added, and the reaction is continued at 70-80℃ for 4-5 hours; after the reaction is completed, the mixture is cooled to room temperature, and the reaction solution is neutralized with glacial acetic acid to a system pH of 7.0. The mixture is then poured into acetone to precipitate the precipitate, which is filtered, washed with anhydrous ethanol, and dried under vacuum to obtain the functionalized modified hydroxy chitosan.

[0005] Preferably, the long-chain alkylating agent is 1-bromododecane or 1,2-epoxyhexadecane; the phase transfer catalyst is tetrabutylammonium bromide; and the anionizing agent is sodium 3-chloro-2-hydroxypropanesulfonate.

[0006] Preferably, based on the mass of 1g of the chitosan powder, the amount of isopropanol used is 8-12mL, the amount of 20% sodium hydroxide aqueous solution used is 3-5mL, the amount of propylene oxide used is 1-2mL, the amount of the long-chain alkylating agent used is 0.6-1.0g, the amount of the phase transfer catalyst used is 0.03-0.08g, and the amount of the anionizing agent used is 0.4-0.8g.

[0007] Preferably, in step B, the washing is performed by extraction and washing in a Soxhlet extractor for 24 hours; the vacuum drying is performed by drying to constant weight in a vacuum drying oven at 60°C.

[0008] Preferably, the cosolvent is ethylene glycol butyl ether; and the emulsifying agent is fatty alcohol polyoxyethylene ether.

[0009] Preferably, the fatty alcohol polyoxyethylene ether is isomeric tridecyl alcohol polyoxyethylene ether.

[0010] Preferably, the water is deionized water.

[0011] Preferably, a method for preparing a heavy oil viscosity reducing agent based on emulsion hydroxy chitosan as described in any one of claims 1-8 comprises the following steps: dissolving the functionalized modified hydroxy chitosan in the water, adding the co-solvent and the emulsifying agent, and shearing and emulsifying for 15-30 minutes at 40-60°C using a high-shear dispersing homogenizer at a rotation speed of 8000-15000 r / min to obtain the heavy oil viscosity reducing agent based on emulsion hydroxy chitosan.

[0012] The beneficial effects of this invention are as follows: The material of this invention, as a macromolecular surfactant, has hydrophobic long-chain alkyl groups that can effectively penetrate into the gum / asphalt molecular layer of heavy oil, disrupting hydrogen bonds and π-π stacking inside the heavy oil through steric hindrance. At the same time, its hydrophilic skeleton, rich in hydroxyl and sulfonic acid groups, is distributed in the aqueous phase, forming a high-mechanical-strength polymeric interfacial film. Under the action of fluid shear force, it can convert the continuous phase of high-viscosity heavy oil into a low-viscosity oil-in-water emulsion in situ, with a viscosity reduction rate of over 95%. Because both hydrophobic and hydrophilic groups are stably grafted onto the same chitosan polymer backbone via covalent bonds, the chromatographic separation problem of the physical compound system in porous media is solved; the introduced sulfonic acid groups are not prone to salting out in high-temperature and high-salinity formation water, and the long-term stability of the emulsion is maintained through strong electrostatic repulsion and steric hindrance; the main agent backbone is derived from natural polysaccharides, which have extremely low biotoxicity and excellent biodegradability compared to traditional petrochemical-based polyacrylamide or large-dose small-molecule surfactants, in line with the development trend of modern green oilfield chemicals. Detailed Implementation

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below; the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0014] Example 1: This embodiment provides a heavy oil viscosity reducing agent based on emulsion hydroxy chitosan, specifically including the following steps: S1. Alkalization and hydroxypropylation of chitosan: Weigh 10.0 g of chitosan with a degree of deacetylation of 90% and add it to 100 mL of isopropanol and disperse for 30 min; slowly add 40 mL of 20% sodium hydroxide aqueous solution to the dispersion system and stir and activate at room temperature for 2 h; add 15 mL of propylene oxide to the alkalized system, heat to 65 °C and reflux for 5 h to obtain a hydroxy chitosan intermediate mixture; This hydroxy chitosan intermediate mixture serves as the backbone for grafting reactions in subsequent processes. The introduced hydroxypropyl groups effectively disrupt the original intramolecular and intermolecular hydrogen bonds of chitosan, improving the polymer's water solubility and reactivity, and providing sufficient active sites for subsequent grafting of hydrophobic long chains and anionic groups. A small amount of the mixture was purified, dried, weighed, and subjected to 1H NMR spectroscopy. The yield of the hydroxy chitosan intermediate was calculated to be 85.6%, and the degree of hydroxypropyl substitution was 0.82. S2. Hydrophobic long-link grafting and anionization grafting: 0.5 g of tetrabutylammonium bromide and 8.0 g of 1-bromododecane were added to the hydroxy chitosan intermediate mixture, and the mixture was refluxed at 75 °C for 7 h; then 6.0 g of sodium 3-chloro-2-hydroxypropanesulfonate was added, and the mixture was reacted at 75 °C for another 4 h; after the reaction was completed, the mixture was cooled to room temperature, and the pH of the system was adjusted to 7.0 with glacial acetic acid. The neutralized mixture was poured into 800 mL of acetone to precipitate the precipitate. After filtration, it was extracted and washed with anhydrous ethanol in a Soxhlet extractor for 24 h. The precipitate was then dried to constant weight in a vacuum drying oven at 60 °C to obtain a pale yellow functionalized modified hydroxy chitosan powder, designated as modified product 1. The product mass was 14.2 g, with a total yield of 78.5%. Infrared spectroscopy analysis showed that the precipitate was precipitated at 2920 cm⁻¹. -1 and 2850cm -1 A distinct absorption peak for the methylene stretching vibration appears at 1045 cm⁻¹. -1 The presence of a characteristic absorption peak for sulfonic acid groups indicates that both dodecyl and sulfonic acid groups have been grafted onto the hydroxy chitosan backbone. Further structural characterization confirmed that the hydrophobic long chain and anionic groups are mainly linked to the amino group at the C2 position of the chitosan molecule through N-substitution. Further calculations using 1H NMR spectroscopy and elemental analysis showed that the grafting rate of the long-chain alkyl group was 15.4% and the degree of substitution of the sulfonic acid group was 0.45. S3. Preparation of emulsion-type viscosity reducing agent: Weigh 5.0g of the powder labeled as modified product 1 and slowly add it to 92.5g of deionized water at 60℃, stirring until completely dissolved; add 2.0g of ethylene glycol butyl ether and 0.5g of isomeric tridecyl alcohol polyoxyethylene ether, and emulsify at 10000r / min for 20min at 50℃ using a high-shear dispersion homogenizer to obtain a milky white homogeneous mother liquor; dynamic light scattering test shows that the average hydrodynamic particle size of the mother liquor is 120nm.

[0015] Example 2: This embodiment provides a heavy oil viscosity reducing agent based on emulsion hydroxy chitosan, specifically including the following steps: S1. Alkalization and hydroxypropylation of chitosan: Weigh 8.0 g of chitosan with a degree of deacetylation of 88%, add it to 80 mL of isopropanol and disperse for 30 min; slowly add 30 mL of 20% sodium hydroxide aqueous solution, stir and activate at room temperature for 1 h; add 10 mL of propylene oxide, heat to 60 °C and reflux for 4 h to obtain a hydroxy chitosan intermediate mixture; The hydroxy chitosan intermediate mixture serves as a macromolecular backbone in subsequent processes. The steric hindrance effect of the hydroxypropyl group weakens the hydrogen bond network, significantly improving the solubility of the system and ensuring the uniformity and efficiency of subsequent grafting reactions of hydrophobic long chains and anionic hydrophilic groups. After purifying and drying a small amount of the mixture, the yield of the hydroxy chitosan intermediate was calculated to be 83.2%, and the degree of hydroxypropyl substitution was 0.76. S2. Hydrophobic long-link grafting and anionization grafting: 0.3 g of tetrabutylammonium bromide and 6.0 g of 1-bromododecane were added to the hydroxy chitosan intermediate mixture, and the mixture was refluxed at 70 °C for 6 h. Subsequently, 4.0 g of sodium 3-chloro-2-hydroxypropanesulfonate was added, and the reaction was continued at 70 °C for 4 h. After the reaction was completed, the mixture was cooled to room temperature, and the pH was adjusted to 7.0 with glacial acetic acid. The mixture was poured into acetone to precipitate the precipitate, filtered, washed with anhydrous ethanol, and vacuum dried at 60 °C to constant weight to obtain functionalized modified hydroxy chitosan powder, designated as modified product 2. The product mass was 10.8 g, and the total yield was 75.3%. Structural characterization calculations showed that the long-chain alkyl grafting rate was 12.8% and the sulfonic acid group substitution degree was 0.38. Furthermore, it was confirmed that the hydrophobic long chain and anionic group were mainly connected to the C2 amino group of the chitosan molecule through N-substitution. S3. Preparation of emulsion-type viscosity reducing agent: Weigh 10.0g of the powder labeled as modified product 2, add it to 89.7g of deionized water, heat to 40℃ and stir to dissolve; add 0.2g of ethylene glycol butyl ether and 0.1g of isomeric tridecyl alcohol polyoxyethylene ether, and shear emulsify at 8000r / min for 15min at 40℃ to obtain the viscosity reducing agent stock solution.

[0016] Example 3: This embodiment provides a heavy oil viscosity reducing agent based on emulsion hydroxy chitosan, specifically including the following steps: S1. Alkalization and hydroxypropylation of chitosan: Weigh 12.0 g of chitosan with a degree of deacetylation of 92% and add it to 120 mL of isopropanol and disperse for 30 min; slowly add 50 mL of 20% sodium hydroxide aqueous solution and stir to activate at room temperature for 2 h; add 20 mL of propylene oxide and reflux at 70 °C for 6 h to obtain a mixture of hydroxy chitosan intermediates; This hydroxy chitosan intermediate mixture not only retains the natural skeletal characteristics of chitosan, but also disrupts the dense crystalline region through the introduction of hydroxypropyl groups, endowing the intermediate with excellent hydrophilicity and reaction accessibility. It is a key basic material to ensure the successful implementation of subsequent amphiphilic functionalization grafting. After purifying and drying a small amount of the mixture, the yield of the hydroxy chitosan intermediate was calculated to be 87.5%, and the degree of hydroxypropyl substitution was 0.88. S2. Hydrophobic long-chain grafting and anionization grafting: 0.8 g of tetrabutylammonium bromide and 10.0 g of 1,2-epoxyhexadecane were added to the hydroxy chitosan intermediate mixture, and the mixture was refluxed at 80 °C for 8 h; then 8.0 g of sodium 3-chloro-2-hydroxypropanesulfonate was added, and the mixture was further reacted at 80 °C for 5 h; after the reaction was completed, the mixture was cooled to room temperature, and the pH was adjusted to 7.0 with glacial acetic acid; the mixture was poured into acetone to precipitate the precipitate, filtered, washed with anhydrous ethanol, and vacuum dried at 60 °C to constant weight to obtain functionalized modified hydroxy chitosan powder, designated as modified product 3, with a product mass of 18.5 g and a total yield of 81.2%; structural characterization calculations showed that the long-chain alkyl grafting rate was 18.2% and the sulfonic acid group substitution degree was 0.52; S3. Preparation of emulsion-type viscosity reducing agent: Weigh 15.0g of the powder labeled as modified product 3, add it to 80.0g of deionized water, heat to 60℃ and stir to dissolve; add 4.0g of ethylene glycol butyl ether and 1.0g of isomeric tridecyl alcohol polyoxyethylene ether, and shear emulsify at 15000r / min for 30min at 60℃ to obtain the viscosity reducing agent stock solution.

[0017] Example 4: This embodiment provides a heavy oil viscosity reducing agent based on emulsion hydroxy chitosan, specifically including the following steps: S1. Alkalization and hydroxypropylation of chitosan: Weigh 10.0 g of chitosan with a degree of deacetylation of 90%, add it to 100 mL of isopropanol and disperse for 30 min; slowly add 40 mL of 20% sodium hydroxide aqueous solution, stir and activate at room temperature for 1.5 h; add 15 mL of propylene oxide, heat to 65 °C and reflux for 5 h to obtain intermediate mixture; S2. Hydrophobic long chain grafting and anionization grafting: 0.5 g of tetrabutylammonium bromide and 8.0 g of 1,2-epoxyhexadecane were added to the above mixture, and the mixture was refluxed at 75 °C for 7 h; then 6.0 g of sodium 3-chloro-2-hydroxypropanesulfonate was added, and the mixture was further reacted at 75 °C for 4 h; after the reaction was completed, the mixture was cooled to room temperature, and the pH was adjusted to 7.0 with glacial acetic acid; the mixture was poured into acetone to precipitate the precipitate, filtered, and then extracted and washed with anhydrous ethanol in a Soxhlet extractor for 24 h. The precipitate was then vacuum dried at 60 °C to constant weight to obtain functionalized modified hydroxy chitosan powder, which was designated as modified product 4; structural characterization confirmed that the hydrophobic long chain and anion group were mainly linked to the C2 amino group of the chitosan molecule through N-substitution. S3. Preparation of emulsion-type viscosity reducing agent: Weigh 8.0g of the powder labeled as modified product 4, add it to 89.8g of deionized water, heat to 55℃ and stir to dissolve; add 1.5g of ethylene glycol butyl ether and 0.7g of isomeric tridecyl alcohol polyoxyethylene ether, and shear emulsify at 12000r / min for 25min at 55℃ to obtain the viscosity reducing agent stock solution.

[0018] Comparative Example 1: The difference between this comparative example and Example 1 is that 1-bromododecane in S2 is omitted, while other operating steps and process parameters are exactly the same as in Example 1; the resulting product is referred to as comparative product 1, which contains only hydroxypropyl and sulfonic acid groups and does not contain hydrophobic long chains.

[0019] Comparative Example 2: The difference between this comparative example and Example 1 is that sodium 3-chloro-2-hydroxypropanesulfonate in S2 is omitted, while other operating steps and process parameters are exactly the same as in Example 1; the resulting product is referred to as comparative product 2, which contains only hydroxypropyl and dodecyl groups and no sulfonic acid groups.

[0020] Comparative Example 3: The difference between this comparative example and Example 1 is that 8.0 g of 1-bromododecane in S2 is replaced with 8.0 g of 1-bromobutane, while the other operating steps and process parameters are exactly the same as in Example 1; the resulting product is referred to as comparative example product 3, and its hydrophobic chain length is shorter than that of Example 1.

[0021] Comparative Example 4: The difference between this comparative example and Example 1 is that isomeric tridecyl alcohol polyoxyethylene ether is not added in S3, while the other operating steps and process parameters are exactly the same as in Example 1.

[0022] Comparative Example 5: The difference between this comparative example and Example 1 is that the rotation speed of the high-shear dispersion homogenizer in S3 is replaced by 3000 r / min instead of 10000 r / min. Other operating steps and process parameters are exactly the same as in Example 1.

[0023] Comparative Example 6: The difference between this comparative example and Example 1 is that a conventional compound viscosity reducer is used instead of the functionalized modified hydroxy chitosan system in Example 1. The commercially available compound viscosity reducer is prepared by mixing anionic polyacrylamide with a molecular weight of 8-10 million and sodium dodecylbenzenesulfonate in a mass ratio of 1:1. The working concentration is the same as in Example 1, and other test conditions are exactly the same.

[0024] Performance Testing and Datasheets Extra-heavy crude oil from a certain oilfield was used as the test sample. The apparent viscosity of the dehydrated crude oil at 50℃ was 125000 mPa·s; the simulated formation water total salinity was 85000 mg / L, of which Ca²⁺… + and Mg² + The total content was 3500 mg / L; the mother liquors prepared in each example and comparative example were diluted with simulated formation water to a working solution with a mass concentration of 0.2%, and mixed with heavy oil at an oil-to-water volume ratio of 7:3. The mixture was then heated at 50°C for 100 seconds. - ¹The apparent viscosity was determined under shear conditions and the viscosity reduction rate was calculated; the emulsion sample was aged at 120℃ for 72h and then cooled to 50℃ to test the viscosity after aging and the water separation rate after 72h of standing. Table 1 Performance test results of each embodiment and comparative example

[0025] Test Result Mechanism Analysis As can be seen from the comparison of the test results of Example 1 and Comparative Example 1 in Table 1, after omitting the hydrophobic long-chain branches, the initial apparent viscosity increased from 185 mPa·s to 12600 mPa·s, and the apparent viscosity increased to 22400 mPa·s after aging, with the water separation rate increasing to 28.5%. The underlying mechanism is that, without the dodecyl hydrophobic chain, the polymer is difficult to effectively insert into the interior of the gum and asphaltenes aggregates, the association structure in the heavy oil cannot be fully dissociated, the bonding force between the formed interfacial film and the oil is weakened, resulting in an increase in the emulsion particle size, insufficient interfacial coverage, and a significant decrease in both viscosity reduction effect and thermal stability. As can be seen from the comparison of the test results of Example 1 and Comparative Example 2 in Table 1, after omitting the sulfonic acid grafting, the initial viscosity reduction rate can still be maintained at a high level, but the apparent viscosity after aging increases from 210 mPa·s to 12600 mPa·s, and the water separation rate increases to 35.4%. The underlying mechanism is that the dodecyl chain can still enter the heavy oil heavy component association layer, so short-term emulsification can still occur; however, after the polymer skeleton lacks sulfonic acid groups, the charge repulsion and hydration ability on the aqueous side are significantly weakened. Under conditions of high salinity and divalent ions, droplets are more likely to aggregate, the interfacial film has insufficient salt resistance, and the emulsion stability decreases significantly during the aging process. As can be seen from the comparison of the test results of Example 1 and Comparative Example 3 in Table 1, after replacing the dodecyl group with butyl, the initial apparent viscosity increased from 185 mPa·s to 4200 mPa·s, and the apparent viscosity increased to 7900 mPa·s after aging. The underlying mechanism is that the hydrophobic interaction of the butyl chain is weaker than that of the dodecyl chain, and the insertion depth and adsorption strength of the butyl chain to the gum and asphaltene layer are insufficient. It is impossible to form hydrophobic adsorption sites with sufficient strength, resulting in insufficiently dense arrangement of polymer at the oil-water interface and insufficient destruction of the internal association structure of heavy oil. Therefore, the emulsification and viscosity reduction ability is significantly reduced. As can be seen from the comparison of the test results of Example 1 and Comparative Example 4 in Table 1, after omitting the emulsifying agent, the average particle size of the mother liquor increased from 120 nm to 290 nm, the initial apparent viscosity and the apparent viscosity after aging both increased, and the water separation rate increased to 14.6%. The underlying mechanism is that although the functionalized modified hydroxy chitosan has an amphiphilic structure, when it relies solely on macromolecular self-assembly during the shear emulsification stage, the interfacial tension decreases slowly, and the restoring ability after droplet breakage is insufficient. Adding an appropriate amount of fatty alcohol polyoxyethylene ether can improve the interfacial spreading speed and synergistically form a composite interfacial film. After omitting this component, the emulsion particle size increases, the particle size distribution becomes wider, and the storage and temperature resistance stability decreases. As can be seen from the comparison of the test results of Example 1 and Comparative Example 5 in Table 1, after reducing the high shear speed from 10000 r / min to 3000 r / min, the average particle size of the mother liquor increased from 120 nm to 520 nm, the initial apparent viscosity increased from 185 mPa·s to 1680 mPa·s, and the apparent viscosity increased to 3180 mPa·s after aging. The underlying mechanism is that when the shear strength is insufficient, the distribution, self-assembly and droplet fragmentation of macromolecular chain segments are limited, the size of the formed droplets is larger, the effective interface area per unit volume decreases, and the interface film is unevenly distributed. Therefore, it is difficult for the continuous phase of crude oil to be fully converted into a stable oil-in-water emulsion. As can be seen from the comparison of the test results of Example 1 and Comparative Example 6 in Table 1, after using the physical compound viscosity reducer, the initial apparent viscosity can be reduced to 430 mPa·s, but after aging, the apparent viscosity rises back to 89000 mPa·s, and the water separation rate reaches 62.0%. The underlying mechanism is that there is no covalent bond between the small molecule surfactant and the polymer, and desorption and component separation easily occur in the high temperature and high salt system. The polyacrylamide molecular chain coils and condenses under high mineralization, and sodium dodecylbenzenesulfonate is easily affected by electrolytes and its interfacial activity decreases. The two cannot maintain the same interfacial film structure, resulting in a rapid rebound in viscosity after the emulsion is destroyed. As can be seen from the comparison of the test results of Examples 1 to 4 in Table 1, after changing the raw material ratio, hydrophobic reagent type and emulsification conditions within the scope of the present invention, each example maintains a high viscosity reduction rate and a low water separation rate, indicating that the technical solution has stable process adaptability. Among them, the comprehensive data of Example 1 shows the best viscosity reduction rate and the lowest water separation rate. The reason is that the degree of hydroxypropylation, the amount of dodecyl grafting, the amount of sulfonic acid group introduction and the emulsification conditions are well matched, which can achieve a relatively balanced result between oil phase adsorption intensity, aqueous phase repulsion stability and droplet size control.

[0026] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any conventional modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A heavy oil viscosity reducer based on emulsion hydroxy chitosan, characterized in that, The product comprises the following components by weight percentage: 0.5-15.0% functionalized modified hydroxy chitosan; 0.1-5.0% total amount of cosolvent and emulsifying agent; and the balance being water. The functionalized modified hydroxy chitosan is an amphiphilic polymer prepared by grafting hydrophobic long-chain alkyl groups with 12-16 carbon atoms and anionic hydrophilic groups containing sulfonic acid groups onto a hydroxy chitosan backbone through chemical bonds.

2. The heavy oil viscosity reducing agent based on emulsion hydroxy chitosan according to claim 1, characterized in that: The functionalized modified hydroxy chitosan was prepared using the following method: A. Chitosan powder with a degree of deacetylation ≥ 85% is dispersed in isopropanol, and sodium hydroxide aqueous solution is slowly added dropwise. The mixture is stirred and swelled at 20-25℃ for 1-2 hours to alkalize it. Then, propylene oxide is added dropwise, and the mixture is heated to 60-70℃ and refluxed for 4-6 hours to obtain a hydroxy chitosan intermediate mixture. B. In the hydroxy chitosan intermediate mixture, a long-chain alkylating agent and a phase transfer catalyst are added, and the mixture is refluxed at 70-80℃ for 6-8 hours; then an anionizing agent is added, and the reaction is continued at 70-80℃ for 4-5 hours; after the reaction is completed, the mixture is cooled to room temperature, and the reaction solution is neutralized with glacial acetic acid to a system pH of 7.

0. The mixture is then poured into acetone to precipitate the precipitate, which is filtered, washed with anhydrous ethanol, and dried under vacuum to obtain the functionalized modified hydroxy chitosan.

3. The heavy oil viscosity reducing agent based on emulsion hydroxy chitosan according to claim 2, characterized in that: The long-chain alkylating agent is 1-bromododecane or 1,2-epoxyhexadecane; the phase transfer catalyst is tetrabutylammonium bromide; and the anionizing agent is sodium 3-chloro-2-hydroxypropanesulfonate.

4. The heavy oil viscosity reducing agent based on emulsion hydroxy chitosan according to claim 2, characterized in that: Based on the mass of 1g of the chitosan powder, the amount of isopropanol used is 8-12mL, the amount of 20% sodium hydroxide aqueous solution used is 3-5mL, the amount of propylene oxide used is 1-2mL, the amount of the long-chain alkylating agent used is 0.6-1.0g, the amount of the phase transfer catalyst used is 0.03-0.08g, and the amount of the anionizing agent used is 0.4-0.8g.

5. The heavy oil viscosity reducing agent based on emulsion hydroxy chitosan according to claim 2, characterized in that: In step B, the washing is performed by extraction and washing in a Soxhlet extractor for 24 hours; the vacuum drying is performed by drying in a vacuum drying oven at 60°C until constant weight.

6. The heavy oil viscosity reducing agent based on emulsion hydroxy chitosan according to claim 1, characterized in that: The cosolvent is ethylene glycol butyl ether; the emulsifying agent is fatty alcohol polyoxyethylene ether.

7. The heavy oil viscosity reducer based on emulsion hydroxy chitosan according to claim 6, characterized in that: The fatty alcohol polyoxyethylene ether is isomeric tridecyl alcohol polyoxyethylene ether.

8. The heavy oil viscosity reducing agent based on emulsion hydroxy chitosan according to claim 1, characterized in that: The water is deionized water.

9. A method for preparing a heavy oil viscosity reducer based on emulsion hydroxy chitosan as described in any one of claims 1-8, characterized in that, The steps are as follows: Dissolve the functionalized modified hydroxy chitosan in the water, add the cosolvent and the emulsifying agent, and emulsify at 40-60℃ using a high-shear dispersion homogenizer at a speed of 8000-15000 r / min for 15-30 min to obtain the heavy oil viscosity reducing agent based on emulsion hydroxy chitosan.

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