An acrylamide emulsion based on an alcohol-based dispersion liquid and a preparation method thereof

Abstract

The present invention belongs to the technical field of oil and gas field fracturing material development, and discloses a polyacrylamide emulsion based on an alcohol-based dispersion liquid and a preparation method thereof. The polyacrylamide fracturing fluid based on the alcohol-based dispersion liquid, by mass fraction, comprises 41.0% - 53.0% of polyethylene glycol, 1.0% - 4.0% of a surfactant, 1.0% - 4.0% of a suspending aid, 35.0% - 40% of polyacrylamide dry powder, 5.0% - 8.0% of an organic alcohol with a relative molecular mass of 30 - 200, and the balance of water. By optimizing the component compounding, the fracturing fluid significantly improves water solubility, dispersion stability, and functions such as demulsification and water blockage removal, effectively reducing the damage to the reservoir. Especially under low-temperature conditions, the fracturing fluid can maintain good solubility and fluidity, solving the technical problems of difficult dissolution and unstable viscosity of existing alcohol-based fracturing fluids at low temperatures, and having potential engineering application value for improving oil recovery rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field fracturing material development, and relates to a polyacrylamide emulsion based on an alcohol-based dispersion liquid and a preparation method thereof. Background Technique

[0002] As an important functional additive for oil and gas fracturing development, polyacrylamide is mainly used in the stimulation fracturing link in oil and gas field exploitation. In the hydraulic fracturing system, it can effectively improve the conductivity of fractures, reduce the friction during fracturing, reduce energy loss, improve fracturing efficiency. At the same time, its high viscosity can improve the sand-carrying performance of fracturing fluid, ensuring the uniform distribution of proppants in fractures, which helps to form a wider, longer and more complex fracture network, and improve the permeability and productivity of oil and gas wells. In addition, as an environmentally friendly chemical additive, polyacrylamide has good biodegradability, can reduce the use of harmful chemicals, and reduce environmental pollution, so it has received extensive attention.

[0003] In order to pursue simplicity and high efficiency in construction, in industrial applications, inverse emulsion type and oil suspension type polyacrylamide are mainly used. However, the dispersibility of polyacrylamide in water is poor. Therefore, mineral oil and emulsifier need to be added to both inverse emulsion type polyacrylamide fracturing fluid and oil suspension type polyacrylamide fracturing fluid. Among them, the combination of mineral oil and emulsifier can enhance the dispersibility of polyacrylamide, can carry and disperse polyacrylamide particles, prevent their agglomeration and precipitation, form a stable emulsion, and at the same time regulate the viscosity of polyacrylamide, making the fracturing fluid have better fluidity and pumpability, which helps to achieve more efficient construction in applications such as oil and gas fracturing development. However, the mineral oil and emulsifier in the polyacrylamide emulsion disperse into the fracturing fluid system and then enter the reservoir. The mineral oil and emulsifier will cause the emulsification of crude oil in the formation, and at the same time adsorb and block the rock pores, causing irreversible damage to the reservoir. Therefore, the development of a more clean and environmentally friendly fracturing fluid system with low damage to the reservoir has received extensive attention.

[0004] Chinese Patent CN117050742B discloses a fracturing fluid based on modified polyacrylamide and its preparation method. The fracturing fluid based on modified polyacrylamide includes 1 - 2 parts of modified polyacrylamide, 15 - 20 parts of zwitterionic surfactant, 10 - 15 parts of co - surfactant, 15 - 20 parts of inorganic salt, 10 - 15 parts of organic solvent, and 120 - 150 parts of water. This fracturing fluid mainly improves the dispersion uniformity of polyacrylamide by modifying it and avoids the use of mineral oil and emulsifier. However, in the process of modifying polyacrylamide, first, using aminobenzenesulfonic acid as the raw material, it reacts with epichlorohydrin, dodecyldimethyl tertiary amine, and acrylic acid in sequence to obtain a functional monomer containing a rigid benzene ring group, a sulfonic acid group, a long - chain quaternary ammonium salt group, and an acrylate group in its structure. Further, the functional monomer is polymerized with acrylamide and 2 - acrylamido - 2 - methylpropanesulfonic acid to obtain modified polyacrylamide. The synthesis process is complex, the yield is low, and the synthesis process requires strict control of conditions, resulting in large performance differences in the obtained modified polyacrylamide. Therefore, the stability of the fracturing solution is insufficient. Moreover, under low - temperature conditions, the existing polyacrylamide emulsion system is prone to freezing, resulting in poor stability of the fracturing fluid, seriously affecting the use of the fracturing fluid. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides a polyacrylamide emulsion based on an alcohol - based dispersion liquid and its preparation method, thereby solving the technical problems that when polyacrylamide is used as a fracturing fluid in the prior art, adding mineral oil and emulsifier causes emulsification of crude oil in the formation, blockage of rock pores, and damage to the reservoir at the same time, and the existing polyacrylamide emulsion is prone to freezing at low temperature, resulting in poor stability of the fracturing fluid.

[0006] The present invention is realized through the following technical solutions:

[0007] A polyacrylamide emulsion based on an alcohol - based dispersion liquid, calculated by mass fraction, includes 41.0% - 53.0% of polyethylene glycol, 1.0% - 4.0% of surfactant, 1.0% - 4.0% of suspending agent, 35.0% - 40% of polyacrylamide dry powder, 5.0% - 8.0% of organic alcohol with a relative molecular mass of 30 - 200, and the balance of water.

[0008] Preferably, the organic alcohol is one of methanol, ethanol, ethylene glycol, and isopropyl alcohol.

[0009] Preferably, the polyethylene glycol is one of polyethylene glycol 100, polyethylene glycol 200, polyethylene glycol 300, and polyethylene glycol 400.

[0010] Preferably, the surfactant is one of coconut diethanolamide, nonylphenol polyoxyethylene ether, and alkylphenol polyoxyethylene ether.

[0011] Preferably, the suspending agent is one or two of organic clay, carboxymethyl cellulose, hydroxyethyl cellulose, and polyvinyl butyral.

[0012] Preferably, when the suspending agent is a mixture of hydroxyethyl cellulose and polyvinyl butyral, the mass ratio of hydroxyethyl cellulose to polyvinyl butyral is (2 - 3):(0.3 - 1.5).

[0013] Preferably, the polyacrylamide dry powder is one or two of hydrophobically associating polyacrylamide dry powder, post - hydrolyzed polyacrylamide dry powder, and salt - resistant polyacrylamide dry powder.

[0014] Preferably, the relative molecular mass of the polyacrylamide dry powder is 5 million - 10 million.

[0015] In the above - mentioned method for preparing a polyacrylamide emulsion based on an alcohol - based dispersion, by mass fraction, the organic alcohol, polyethylene glycol, surfactant, and suspending agent are added to water, stirred and dissolved to obtain an alcohol - based dispersion, and then polyacrylamide dry powder is added and stirred evenly to obtain the polyacrylamide emulsion based on the alcohol - based dispersion.

[0016] The above - mentioned application of a polyacrylamide emulsion based on an alcohol - based dispersion in fracturing of unconventional oil and gas reservoirs. When in use, the polyacrylamide emulsion based on the alcohol - based dispersion is added to water to be formulated into an aqueous solution with a mass concentration of 0.1% - 0.8% and used as slickwater and sand - carrying fracturing fluid for on - site fracturing, that is, as the on - site fracturing fluid.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects:

[0018] The present invention discloses a polyacrylamide emulsion based on an alcohol-based dispersion liquid. In the first aspect, among its components, polyethylene glycol (PEG) serves as the main solvent of the dispersion liquid, with a mass fraction as high as 41.0% - 53.0%, which is a key component in the formulation. First of all, as a high molecular polymer, PEG has a long molecular chain with certain flexibility and entanglement ability. In the system, the PEG molecular chain interacts with the polyacrylamide molecular chain, which can effectively reduce the overall viscosity of the system. The organic alcohol with a relative molecular mass of 30 - 200 has a relatively small molecular mass and can penetrate between the polyacrylamide molecular chains, destroying the intermolecular forces, thereby reducing the viscosity of the system. Secondly, the ether bonds on the PEG molecular chain and the organic alcohol can both form hydrogen bonds with the polar groups on the polyacrylamide molecular chain, thereby enhancing the solvation effect of polyacrylamide in the system. Therefore, based on the good water solubility of PEG and the synergistic effect with the organic alcohol with a relative molecular mass of 30 - 200, the solubility of polyacrylamide dry powder in the system is effectively improved. Especially under low-temperature conditions, the addition of PEG can significantly improve the solubility of polyacrylamide, solving the technical problem that the alcohol-based fracturing fluid is prone to freezing at low temperatures, resulting in poor stability of the fracturing fluid.

[0019] In the second aspect, the organic alcohol with a relative molecular mass of 30 - 200, in addition to serving as a solvent and synergizing with PEG to improve the solubility of polyacrylamide dry powder and solving the technical problem that the fracturing fluid is prone to freezing at low temperatures, resulting in poor stability of the fracturing fluid, can also effectively achieve demulsification and water lock removal, prevent the emulsifier in the fracturing fluid from emulsifying the formation crude oil, effectively protect the oil and gas reservoir, thus avoiding reservoir damage, releasing the water trapped in the reservoir, and improving the oil and gas flow efficiency.

[0020] In the third aspect, the addition of a surfactant further improves the dissolution and dispersion properties of the dispersion liquid. The surfactant can reduce the interfacial tension of the system, promote the mutual fusion of each component, thereby improving the overall performance of the fracturing fluid; the suspending agent promotes the formation of the network structure of the dispersion liquid and the increase in viscosity. By forming a stable network structure, the suspending agent can effectively improve the suspension of polyacrylamide dry powder, prevent it from settling or aggregating during the fracturing process, thereby maintaining the uniformity and stability of the fracturing fluid.

[0021] In summary, in the formulation of the present invention, polyacrylamide dry powder, solvents such as polyethylene glycol and organic alcohols, and additives such as surfactants and suspending agents act synergistically to form a fracturing fluid (emulsion) system with excellent performance. Through the compounding and optimization of each component, the use of this emulsion to prepare fracturing fluid not only improves the water solubility and dispersibility of the dry powder, but also enhances functions such as demulsification and water blockage removal, effectively reducing the damage of external fluids to the reservoir. Especially under low-temperature conditions, due to the synergistic effect of organic alcohols and polyethylene glycol, the fracturing fluid can maintain good solubility and fluidity, thus solving the problem that existing alcohol-based fracturing fluids are difficult to dissolve at low temperatures, that is, the problem of easy icing, and having potential engineering application value in improving oil recovery rate.

[0022] Furthermore, the present invention also discloses the application of the above-mentioned polyacrylamide emulsion based on alcohol-based dispersion liquid in the fracturing of unconventional oil and gas reservoirs; during use, the polyacrylamide emulsion based on alcohol-based dispersion liquid is added to water and formulated into an aqueous solution with a mass concentration of 0.1% - 0.8% as slickwater and sand-carrying fracturing fluid for on-site fracturing. According to industry standards, this concentration can enable the fracturing fluid to carry sand sufficiently and also has good fluidity to achieve a drag reduction effect. The use process of this polyacrylamide emulsion based on alcohol-based dispersion liquid is convenient, and it can be directly formulated according to industry standards without complex operation processes, which is conducive to large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0024] Figure 1 Photographs before (A) and after (B) centrifugation of the alcohol-based polyacrylamide emulsion prepared in Example 3 of the present invention;

[0025] Figure 2 Photographs of the alcohol-based polyacrylamide emulsion prepared in Example 3 of the present invention (A), the photograph of the 0.5% on-site fracturing fluid prepared (B), and the photograph of the fracturing fluid after on-site fracturing (C);

[0026] Figure 3 Drag reduction performance test results of the 0.1% on-site fracturing fluid prepared from the alcohol-based polyacrylamide emulsion prepared in Example 3 of the present invention;

[0027] Figure 4Results of shear viscosity test at 90 °C for the field fracturing fluid prepared by formulating the alcohol-based polyacrylamide emulsion obtained in Example 3 of the present invention into a 0.6% solution;

[0028] Figure 5 Results of shear viscosity test at 120 °C for the field fracturing fluid prepared by formulating the alcohol-based polyacrylamide emulsion obtained in Example 3 of the present invention into an 0.8% solution;

[0029] Figure 6 Results of suspension performance test for the field fracturing fluid prepared by formulating the alcohol-based polyacrylamide emulsion obtained in Example 3 of the present invention into an 0.8% solution, with 20% - 50% proppant in it. Detailed implementation manners

[0030] To enable those skilled in the art to understand the features and effects of the present invention, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflicts, the definitions in this specification shall prevail.

[0031] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0032] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values (including integers and fractions) within the range.

[0033] In this article, unless otherwise specified, "comprising", "including", "containing", "having" or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0034] In this article, for the sake of concise description, not all possible combinations of all technical features in each embodiment or example are described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as within the scope described in this specification.

[0035] The present invention provides a polyacrylamide emulsion based on an alcohol-based dispersion liquid, which, by mass fraction, comprises 41.0% - 53.0% of polyethylene glycol, 1.0% - 4.0% of surfactant, 1.0% - 4.0% of suspending agent, 35.0% - 40% of polyacrylamide dry powder, 5.0% - 8.0% of organic alcohol with a relative molecular mass of 30 - 200, and the balance of water.

[0036] The proportion of water in this system is 3% - 5%. Additionally, the water is preferably deionized water, and its main function is to fully mix the alcohol, surfactant, and suspending agent.

[0037] In a preferred embodiment, by mass fraction, it comprises 44.0% - 51.0% of polyethylene glycol, 3.0% of surfactant, 2.0% of suspending agent, 35.0% - 40% of polyacrylamide dry powder, 6.0% of organic alcohol with a relative molecular mass of 30 - 200, and the balance of water.

[0038] The organic alcohol is one of methanol, ethanol, ethylene glycol, and isopropyl alcohol, preferably isopropyl alcohol. Its main functions are to improve the fluidity and anti-freezing performance of the dispersion liquid. These small-molecule alcohols not only have good demulsification and water-lock release functions, but also methanol, ethanol, ethylene glycol, and isopropyl alcohol have good lubricating properties. During the fracturing process, these alcohol compounds can reduce the friction coefficient between the fracturing fluid and the formation rock, playing a lubricating role. This helps to reduce the energy consumption during the fracturing operation, and at the same time reduces the wear and damage of the fracturing fluid to the formation rock, thereby reducing the risk of formation damage. At the same time, as additives to clean fracturing fluids, these organic alcohols contribute to the formation of a cleaner and more environmentally friendly fracturing fluid system. Compared with traditional fracturing fluids, clean fracturing fluids have less impact on the environment, which is beneficial to protecting underground water resources and the ecological environment.

[0039] The polyethylene glycol is one of polyethylene glycol 100, polyethylene glycol 200, polyethylene glycol 300, and polyethylene glycol 400. As the main solvent of the dispersion liquid, polyethylene glycol 100, polyethylene glycol 200, polyethylene glycol 300, and polyethylene glycol 400 can form a good synergistic effect with the organic alcohol to improve the dispersion uniformity of the polyacrylamide dry powder. Additionally, polyethylene glycol 300 is preferably used.

[0040] The surfactant is one of coconut fatty acid diethanolamide, nonylphenol polyoxyethylene ether, and alkylphenol polyoxyethylene ether, preferably coconut fatty acid diethanolamide. The wetting, demulsification, and drainage-aiding effects of the surfactant can improve the permeability and fracture propagation ability of the fracturing fluid, promote the backflow ability, reduce the damage to the formation, and effectively eliminate foam, preventing the foam from affecting the stability and construction effect of the fracturing fluid. At the same time, it improves the dissolution and dispersion properties of the dispersion liquid.

[0041] The suspending agent is one or two of organic clay, carboxymethyl cellulose, hydroxyethyl cellulose, and polyvinyl butyral. This suspending agent can also be called a suspension aid, which can increase the viscosity of the dispersion medium, effectively prevent particle flocculation, and at the same time promote the uniform dispersion of particles. The organic clay here includes sodium-based bentonite or lithium-based bentonite.

[0042] More preferably, the suspending agent is a mixture of hydroxyethyl cellulose and polyvinyl butyral. Hydroxyethyl cellulose is used to improve the network structure of the dispersion liquid, and polyvinyl butyral is used to increase the viscosity of the dispersion. The suspension property of polyacrylamide dry powder is improved in two ways. The suspending agent being a mixture of hydroxyethyl cellulose and polyvinyl butyral enables the fracturing fluid to better form and maintain fractures during oil and gas exploitation, improve the permeability of oil and gas, and thus increase the production of oil and gas. When the suspending agent is a mixture of hydroxyethyl cellulose and polyvinyl butyral, the mass ratio of hydroxyethyl cellulose to polyvinyl butyral is (2 - 3):(0.3 - 1.5), which can effectively form a polymer with a three-dimensional network structure. Specifically, after they are dissolved in water, the hydroxyl groups on the molecular chains of hydroxyethyl cellulose and polyvinyl butyral form hydrogen bonds with water molecules, promoting the full extension and mutual entanglement of the polymer chains to form a polymer with a three-dimensional network structure. Here, both hydroxyethyl cellulose and polyvinyl butyral are high-molecular chain polymers containing hydroxyl groups. In an aqueous system, the hydroxyl groups on the molecular chains of hydroxyethyl cellulose and polyvinyl butyral form hydrogen bonds with water molecules, enabling the molecular chains of hydroxyethyl cellulose and polyvinyl butyral to fully extend and mutually entangle, forming a polymer with a three-dimensional network structure from a chain polymer. More preferably, the mass ratio of hydroxyethyl cellulose to polyvinyl butyral is 2:0.3.

[0043] More preferably, a polyacrylamide emulsion based on an alcohol-based dispersion liquid includes 3 g of water, 6 g of isobutanol, 45.7 g of polyethylene glycol 300, 2.8 g of coconut fatty acid diethanolamide, 2 g of hydroxyethyl cellulose, 0.3 g of polyvinyl butyral, and 40 g of polyacrylamide dry powder.

[0044] The polyacrylamide dry powder is selected from one or two of hydrophobic associative polyacrylamide dry powder, post-hydrolyzed polyacrylamide dry powder, and salt-resistant polyacrylamide dry powder, and hydrophobic associative polyacrylamide dry powder is further preferred; the relative molecular mass of the polyacrylamide dry powder is 5 million - 10 million.

[0045] The hydrophobic associative polyacrylamide dry powder is a special polyacrylamide. Hydrophobic groups are introduced into its molecules, enabling the formation of aggregates through hydrophobic interactions between molecules. These aggregates have a certain stability and viscosity in the solution, thus endowing polyacrylamide with new properties, having high sand-carrying capacity, low frictional resistance, and shear resistance.

[0046] In addition, according to the construction needs, water can be replaced with concentrated solutions such as swelling inhibitors, flowback aids, and scale inhibitors. Through compounding technology, an integrated multifunctional fracturing fluid can be directly obtained using an alcohol-based polyacrylamide dispersion, which greatly simplifies the procedure of adding additional additives during the actual construction process. The alcohol-based polyacrylamide dispersion solution meets the industry standards of fracturing fluids, and the solution is clear and transparent, meeting the requirements of clean fracturing fluids.

[0047] The preparation method of the above-mentioned polyacrylamide emulsion based on an alcohol-based dispersion is as follows: By mass fraction, add the organic alcohol, polyethylene glycol, surfactant, and suspending agent into water, and stir for 30 min to uniformly mix the monomers to obtain an alcohol-based dispersion. Then add polyacrylamide dry powder and stir with a high-speed shear mixer for 15 min to uniformly disperse the polyacrylamide dry powder in the alcohol-based dispersion, thereby obtaining the polyacrylamide emulsion based on the alcohol-based dispersion.

[0048] In addition, the present invention also discloses the preparation method of the above-mentioned polyacrylamide emulsion based on an alcohol-based dispersion. By mass fraction, add the polyethylene glycol, surfactant, suspending agent, and organic alcohol with a relative molecular mass of 30 - 200 into water, stir and dissolve to obtain an alcohol-based dispersion. Then add the polyacrylamide dry powder and stir evenly to obtain the polyacrylamide emulsion based on the alcohol-based dispersion. This emulsion preparation method is simple, convenient to operate, and easy to industrialize.

[0049] Meanwhile, the present invention also discloses the application of the above-mentioned polyacrylamide emulsion based on an alcohol-based dispersion in fracturing of unconventional oil and gas reservoirs. During use, add the polyacrylamide emulsion based on the alcohol-based dispersion into water and prepare an aqueous solution with a mass concentration of 0.1% - 0.8% as slickwater and sand-carrying fracturing fluid for on-site fracturing applications.

[0050] This fracturing fluid has good stability. After continuous testing for 10 min, its drag reduction rate is 70% - 80%, showing good drag reduction stability. In addition, the shear viscosity of the prepared fracturing fluid is 60 - 89 mPa·s at 90 °C and 50 - 70 mPa·s at 120 °C. It can be seen that under high-temperature conditions, it has good temperature and shear resistance, indicating that the alcohol-based dispersant in the system has no impact on the fracturing fluid.

[0051] In view of the irreversible damage caused by the current fracturing polyacrylamide emulsion containing a large amount of mineral oil and emulsifier to unconventional complex oil and gas reservoirs, an alcohol-based dispersion is prepared by using polyethylene glycol, water, small molecule alcohol, and surfactant as dispersants. The polyacrylamide dry powder is evenly dispersed in the alcohol-based solvent to prepare a polyacrylamide emulsion of the alcohol-based dispersion. Further, a clear and transparent clean fracturing fluid can be formulated by using the polyacrylamide emulsion of the alcohol-based dispersion. The prepared fracturing fluid has good drag reduction and sand-carrying performance. In addition, concentrated aqueous additives such as swelling inhibitor, flowback aid, and scale inhibitor can be dispersed into the alcohol-based dispersion to realize the multifunctionalization of the fracturing fluid system. The alcohol-based dispersion does not contain mineral oil and emulsifier, is more environmentally friendly, and promotes the simple, environmentally friendly, and efficient development of unconventional complex oil and gas.

[0052] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and will not limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also belong to the scope defined by the appended claims of this application.

[0053] Conventional instruments and equipment in the art are used in the following embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise specified, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0054] Example 1

[0055] This example provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: Weigh 3 g of deionized water, 6 g of isobutanol, 51.2 g of polyethylene glycol 300, 2.5 g of coconut fatty acid diethanolamide, 2 g of hydroxyethyl cellulose, and 0.3 g of polyvinyl butyral using a beaker, and stir with an electric stirrer at 100 r / min for 30 min to fully mix and dissolve various monomers to obtain an alcohol-based dispersion. Weigh 35 g of a hydrophobic associative polyacrylamide dry powder with a molecular weight of 10 million, adjust the rotation speed to 3000 r / min, slowly add it to the alcohol-based dispersion, and continue to stir for 15 min to obtain an alcohol-based polyacrylamide dispersion with a content of 35%.

[0056] In addition, when applied to fracturing of unconventional oil and gas reservoirs, the alcohol-based polyacrylamide dispersion is added to water to prepare a field fracturing fluid with a mass concentration of 0.1%. The drag reduction rate of this field fracturing fluid is 72%, and it has good drag reduction stability. The shear viscosities of the fracturing fluid with a concentration of 0.8% at 90 °C and 120 °C are 65.21 mPa·s and 55.42 mPa·s, respectively.

[0057] Example 2

[0058] This example provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: Weigh 3 g of deionized water, 6 g of isobutanol, 47.9 g of polyethylene glycol 300, 2.8 g of coconut oil diethanolamide, 2 g of hydroxyethyl cellulose, and 0.3 g of polyvinyl butyral using a beaker. Stir with an electric stirrer at 100 r / min for 30 min to fully mix and dissolve various monomers to obtain an alcohol-based dispersion. Weigh 38 g of a hydrophobic associative polyacrylamide dry powder with a molecular weight of 10 million, adjust the rotation speed to 3000 r / min, slowly add it to the alcohol-based dispersion, and continue stirring for 15 min to obtain an alcohol-based polyacrylamide dispersion with a content of 38%.

[0059] In addition, when applied to fracturing of unconventional oil and gas reservoirs, the alcohol-based polyacrylamide dispersion is added to water to prepare a field fracturing fluid with a mass concentration of 0.1%. The drag reduction rate of this field fracturing fluid is 74%, and it has good drag reduction stability. The shear viscosities of the fracturing fluid with a concentration of 0.8% at 90 °C and 120 °C are 71.51 mPa·s and 62.57 mPa·s, respectively.

[0060] Example 3

[0061] This example provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: Weigh 3 g of deionized water, 6 g of isobutanol, 45.7 g of polyethylene glycol 300, 2.8 g of coconut oil diethanolamide, 2 g of hydroxyethyl cellulose, and 0.3 g of polyvinyl butyral using a beaker. Stir with an electric stirrer at 100 r / min for 30 min to fully mix and dissolve various monomers to obtain an alcohol-based dispersion. Weigh 40 g of a hydrophobic associative polyacrylamide dry powder with a molecular weight of 10 million, adjust the rotation speed to 3000 r / min, slowly add it to the alcohol-based dispersion, and continue stirring for 15 min to obtain an alcohol-based polyacrylamide dispersion with a content of 40%.

[0062] In order to verify the performance of the polyacrylamide fracturing fluid based on the alcohol-based dispersion in the present invention, the following tests are conducted:

[0063] The stability test was carried out on the alcohol-based polyacrylamide emulsion prepared in Example 3 (i.e., the effective content of alcohol-based polyacrylamide was 40%). Specifically, the alcohol-based polyacrylamide emulsion prepared in Example 3 was centrifuged for 10 min at a rotational speed of 1000 r / min, and the stability result of its system was observed. The test results are as Figure 1 shown. Among them, Figure (A) is before centrifugation, and Figure (B) is after centrifugation. It can be seen from Figure 1 that there is no obvious stratification in the alcohol-based polyacrylamide dispersion after centrifugation and no solid precipitation is formed at the bottom, indicating good stability.

[0064] Then, the alcohol-based polyacrylamide emulsion prepared in Example 3 was used as a fracturing fluid for performance testing. Specifically, the alcohol-based polyacrylamide dispersion with a mass concentration of 40% prepared in Example 3 was formulated into a field fracturing fluid with a mass concentration of 0.5%, and its appearance was observed. The alcohol-based polyacrylamide dispersion with a mass concentration of 40% prepared in Example 3 of the present invention is as Figure 2 shown in Figure (A) therein, the formulated 0.5% field fracturing fluid is shown in Figure (B), and the fracturing fluid after on-site fracturing is shown in Figure (C). It can be seen from Figure 2 that the formulated 0.5% field fracturing fluid is clear and transparent, and the fracturing fluid after on-site fracturing is still crystal clear, indicating that the liquid performance of the fracturing fluid is stable during the on-site construction process, and the gel breaking is complete after fracturing, which can meet the requirements of the on-site drilling and sand addition scale.

[0065] Furthermore, in order to test the drag reduction performance of the fracturing fluid prepared by the present invention, the dispersion prepared in Example 3 was formulated into a 0.1% field fracturing fluid, and its drag reduction performance, that is, the drag reduction rate, was tested. The test process of this drag reduction performance refers to the test of the drag reduction rate in 7.12.4 of the National Petroleum and Natural Gas Industry Standard SY / T5107-2016 "Evaluation Method for the Performance of Water-Based Fracturing Fluids" of the People's Republic of China. The test results are shown in Figure 3 . It can be seen from the figure that after continuous testing for 10 min, the drag reduction rate of this field fracturing fluid is greater than 70%, indicating good drag reduction stability, which shows that the alcohol-based polyacrylamide fracturing fluid in the present invention not only has excellent fracturing and gel breaking performance, but also has excellent drag reduction performance.

[0066] In addition, the dispersion prepared in Example 3 was formulated into field fracturing fluids with mass concentrations of 0.6% and 0.8%, and the shear viscosity of the 0.6% field fracturing fluid at 90 °C and the shear viscosity of the 0.8% field fracturing fluid at 120 °C were tested. The test results are shown in Figure 4 and Figure 5It can be known that the shear viscosity of 0.6% of the on-site fracturing fluid at 90 °C is 62.89 mPa·s, and the shear viscosity of 0.8% of the on-site fracturing fluid at 120 °C is 70.57 mPa·s. It can be seen that under high-temperature conditions, the viscosity maintains good stability, indicating that the alcohol-based dispersant in the system has no effect on the fracturing fluid.

[0067] Furthermore, according to the on-site drilling and production technical standards, that is, the industry standard of the People's Republic of China for oil and gas SY / T5107-2016 "Evaluation Method for the Performance of Water-Based Fracturing Fluids", the dispersion liquid prepared in Example 3 was configured into an on-site fracturing fluid with a mass concentration of 0.8%, and a suspension performance test was carried out using 20% - 50% of the proppant. Here, the proppant is quartz sand, and the test results are as Figure 6 shown. As can be seen from the figure, no obvious settlement of the proppant was observed in 30 minutes, indicating that the alcohol-based polyacrylamide dispersion liquid meets the fracturing fluid industry standard.

[0068] Example 4

[0069] This example provides a preparation method of a polyacrylamide emulsion based on an alcohol-based dispersion liquid: 5 g of 60% fluorocarbon surfactant solution is used instead of deionized water, 6 g of isobutanol, 43.7 g of polyethylene glycol 300, 2.8 g of coconut fatty acid diethanolamide, 2 g of hydroxyethyl cellulose, 0.3 g of polyvinyl butyral. Using an electric stirrer, stir at 100 r / min for 30 minutes to fully mix and dissolve various monomers to obtain an alcohol-based dispersion liquid. Weigh 40 g of hydrophobic associative polyacrylamide dry powder with a relative molecular mass of 5 million, adjust the rotation speed to 3000 r / min, and slowly add it to the alcohol-based dispersion liquid, and continue to stir for 15 minutes to obtain an alcohol-based polyacrylamide dispersion liquid with a content of 40% and a drainage-aid function.

[0070] In addition, when applied to fracturing of unconventional oil and gas reservoirs, the alcohol-based polyacrylamide dispersion liquid is formulated into a fracturing fluid with a mass concentration of 0.1%. The drag reduction rate of this on-site fracturing fluid is 76%, and it has good drag reduction stability; the shear viscosities of the fracturing fluid with a concentration of 0.8% at 90 °C and 120 °C are 70.43 mPa·s and 61.53 mPa·s respectively.

[0071] Example 5

[0072] This example provides a polyacrylamide emulsion based on an alcohol-based dispersion: 5 g of a 70% scale inhibitor (1-hydroxyethylidene diphosphonic acid, HEDP) solution is used instead of deionized water, 6 g of isobutanol, 43.7 g of polyethylene glycol 300, 2.8 g of coconut oil diethanolamide, 2 g of hydroxyethyl cellulose, 0.3 g of polyvinyl butyral. Using an electric stirrer, stir at 100 r / min for 30 min to fully mix and dissolve various monomers to obtain an alcohol-based dispersion. Weigh 40 g of a hydrophobic associative polyacrylamide dry powder with a molecular weight of 8 million, adjust the rotation speed to 3000 r / min, slowly add it to the alcohol-based dispersion, and continue stirring for 15 min to obtain an alcohol-based polyacrylamide dispersion with a scale inhibition function and a content of 40%.

[0073] In addition, when applied to fracturing of unconventional oil and gas reservoirs, the alcohol-based polyacrylamide dispersion is formulated into a field fracturing fluid with a mass concentration of 0.7%. The drag reduction rate of this field fracturing fluid is 78%, and it has good drag reduction stability; the shear viscosities of the fracturing fluid with a concentration of 0.8% at 90 °C and 120 °C are 71.05 mPa·s and 62.75 mPa·s, respectively.

[0074] Example 6

[0075] This example provides a preparation method for a polyacrylamide emulsion based on an alcohol-based dispersion: Use a beaker to weigh 5 g of water, 6 g of isobutanol, 47 g of polyethylene glycol 100, 3 g of nonylphenol polyoxyethylene ether, 4 g of sodium bentonite. Using an electric stirrer, stir at 100 r / min for 30 min to fully mix and dissolve various monomers to obtain an alcohol-based dispersion. Weigh 35 g of a hydrophobic associative polyacrylamide dry powder with a molecular weight of 10 million, adjust the rotation speed to 3000 r / min, slowly add it to the alcohol-based dispersion, and continue stirring for 15 min to obtain an alcohol-based polyacrylamide dispersion with a content of 35%.

[0076] In addition, when applied to fracturing of unconventional oil and gas reservoirs, the alcohol-based polyacrylamide dispersion is formulated into a field fracturing fluid with a mass concentration of 0.1%. The drag reduction rate of this field fracturing fluid is 75%, and it has good drag reduction stability; the shear viscosities of the fracturing fluid with a concentration of 0.8% at 90 °C and 120 °C are 78.04 mPa·s and 62.86 mPa·s, respectively.

[0077] Example 7

[0078] This embodiment provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: Weigh 5 g of water, 10 g of isobutanol, 55 g of polyethylene glycol 200, 5 g of coconut fatty acid diethanolamide, and 4.5 g of carboxymethyl cellulose using a beaker, and stir with an electric stirrer at 100 r / min for 30 min to fully mix and dissolve various monomers to obtain an alcohol-based dispersion. Weigh 45 g of hydrophobic associative polyacrylamide dry powder with a molecular weight of 10 million, adjust the rotation speed to 3000 r / min, slowly add it to the alcohol-based dispersion, and continue stirring for 15 min to obtain an alcohol-based hydrophobic associative polyacrylamide dispersion with a content of 36%.

[0079] In addition, when applied to fracturing of unconventional oil and gas reservoirs, the alcohol-based polyacrylamide dispersion is formulated into a fracturing fluid with a mass concentration of 0.1%. The drag reduction rate of this on-site fracturing fluid is 80%, and it has good drag reduction stability; the shear viscosities of the fracturing fluid with a concentration of 0.8% at 90 °C and 120 °C are 68.21 mPa·s and 63.31 mPa·s respectively.

[0080] Example 8

[0081] This embodiment provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: Weigh 8 g of water, 11 g of isobutanol, 93 g of polyethylene glycol 400, 7 g of alkylphenol polyoxyethylene ether, 4 g of hydroxyethyl cellulose, and 2 g of polyvinyl butyral using a beaker, and stir with an electric stirrer at 100 r / min for 30 min to fully mix and dissolve various monomers to obtain an alcohol-based dispersion. Weigh 35 g of hydrophobic associative polyacrylamide dry powder with a relative molecular weight of 10 million, adjust the rotation speed to 3000 r / min, slowly add it to the alcohol-based dispersion, and continue stirring for 15 min to obtain an alcohol-based hydrophobic associative polyacrylamide dispersion with a content of 39%.

[0082] In addition, when applied to fracturing of unconventional oil and gas reservoirs, the alcohol-based polyacrylamide dispersion is formulated into an on-site fracturing fluid with a mass concentration of 0.1%. The drag reduction rate of this on-site fracturing fluid is 82%, and it has good drag reduction stability; the shear viscosities of the fracturing fluid with a concentration of 0.8% at 90 °C and 120 °C are 78.62 mPa·s and 70.25 mPa·s respectively.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polyacrylamide emulsion based on an alcohol-based dispersion liquid, characterized in that, By mass fraction, it includes 41.0% - 53.0% of polyethylene glycol, 1.0% - 4.0% of surfactant, 1.0% - 4.0% of suspending agent, 35.0% - 40% of polyacrylamide dry powder, 5.0% - 8.0% of organic alcohol with a relative molecular mass of 30 - 200, and the balance of water; The organic alcohol is one of methanol, ethanol, ethylene glycol and isopropanol; The polyethylene glycol is one of polyethylene glycol 100, polyethylene glycol 200, polyethylene glycol 300 and polyethylene glycol 400; The suspending agent is one or two of organic clay, carboxymethyl cellulose, hydroxyethyl cellulose and polyvinyl butyral; The organic clay includes sodium-based bentonite or lithium-based bentonite; The polyacrylamide dry powder is one or two of hydrophobic associative polyacrylamide dry powder, post-hydrolyzed polyacrylamide dry powder and salt-resistant polyacrylamide dry powder; The relative molecular mass of the polyacrylamide dry powder is 5 million - 10 million.

2. The polyacrylamide emulsion based on an alcohol-based dispersion liquid according to claim 1, characterized in that, The surfactant is one of coconut fatty acid diethanolamide, nonylphenol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

3. A polyacrylamide emulsion based on an alcohol-based dispersion liquid according to claim 1, wherein When the suspending agent is a mixture of hydroxyethyl cellulose and polyvinyl butyral, the mass ratio of hydroxyethyl cellulose to polyvinyl butyral is (2 - 3):(0.3 - 1.5).

4. A method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion liquid according to any one of claims 1 to 3, characterized in that, By mass fraction, add the polyethylene glycol, surfactant, suspending agent and organic alcohol with a relative molecular mass of 30 - 200 into water, stir and dissolve to obtain an alcohol-based dispersion liquid, and then add the polyacrylamide dry powder and stir evenly to obtain the polyacrylamide emulsion based on the alcohol-based dispersion liquid.

5. Use of a polyacrylamide emulsion based on an alcohol-based dispersion liquid according to any one of claims 1 to 3 in fracturing of unconventional oil and gas reservoirs, characterized in that, During use, add the polyacrylamide emulsion based on the alcohol-based dispersion liquid into water to prepare an aqueous solution with a mass concentration of 0.1% - 0.8% as slickwater and sand-carrying fracturing fluid for on-site fracturing.

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