Polyacrylamide emulsion based on alcohol-based dispersion liquid and preparation method thereof

Abstract

The 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 of the polyacrylamide emulsion based on the alcohol-based dispersion liquid. Comprising 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 dry polyacrylamide powder, 5.0%-8.0% of organic alcohol with the relative molecular mass of 30-200 and the balance of water. According to the fracturing fluid, by optimizing component compounding, the water solubility, dispersion stability, demulsification, water lock removal and other functions are remarkably improved, damage to a reservoir stratum is effectively reduced, particularly, under the low-temperature condition, the fracturing fluid can keep good solubility and fluidity, the technical problems that an existing alcohol-based fracturing fluid is difficult to dissolve at the low temperature and unstable in viscosity are solved, and the fracturing fluid has good application prospects. The potential engineering application value of improving the oil recovery rate is realized.

Description

Technical Field

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

[0002] As an important functional additive for oil and gas fracturing development, polyacrylamide is mainly used in the production-enhancing fracturing process in oil and gas field exploitation. In the hydraulic fracturing system, it effectively improves the conductivity of the fractures, reduces the friction during the fracturing process, reduces energy loss, and improves the fracturing efficiency. At the same time, its high viscosity can improve the sand-carrying performance of the fracturing fluid and ensure the uniform distribution of the proppant in the fractures, which helps to form a wider, longer, and more complex fracture network and improve the permeability and production capacity 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 widespread attention.

[0003] In order to pursue simple and efficient construction, inverse emulsion type and oil suspension type polyacrylamide are mainly used in industrial applications. However, the dispersibility of polyacrylamide in water is poor. Therefore, mineral oil and emulsifiers need to be added to 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, carry and disperse polyacrylamide particles, prevent their agglomeration and precipitation, form a stable emulsion, and regulate the viscosity of polyacrylamide at the same time, so that the fracturing fluid has better fluidity and pumpability, which is helpful to achieve more efficient construction in applications such as oil and gas fracturing development. However, the mineral oil and emulsifier in the polyacrylamide emulsion are dispersed 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 cleaner, more environmentally friendly and less damaging fracturing fluid system to the reservoir has attracted much attention.

[0004] Chinese patent CN117050742B discloses a fracturing fluid based on modified polyacrylamide and a preparation method thereof. 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. The fracturing fluid mainly improves the dispersion uniformity of polyacrylamide by modifying polyacrylamide, and avoids the use of mineral oil and emulsifier. However, in the process of modifying polyacrylamide, aminobenzenesulfonic acid is first used as a raw material, and 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 the structure, and the functional monomer is further polymerized with acrylamide and 2-acrylamide-2-methylpropanesulfonic acid to obtain a modified polyacrylamide. The synthesis process is complicated and the yield is low. The synthesis process requires strict control of conditions, resulting in large differences in the performance of the modified polyacrylamide obtained, thereby making the stability of the fracturing solution insufficient. Moreover, under low-temperature conditions, the existing polyacrylamide emulsion system is prone to freezing, resulting in poor stability of the fracturing fluid, which seriously affects the use of the fracturing fluid. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a polyacrylamide emulsion based on an alcohol-based dispersion and a preparation method thereof, thereby solving the technical problems in the prior art that when polyacrylamide is used as a fracturing fluid, the addition of mineral oil and an emulsifier causes emulsification of crude oil in the formation, blocks rock pores, and damages the reservoir, and the existing polyacrylamide emulsion is easy to freeze at low temperatures, resulting in poor stability of the fracturing fluid.

[0006] The present invention is achieved through the following technical solutions: A polyacrylamide emulsion based on an alcohol-based dispersion comprises, by mass fraction, 41.0% to 53.0% polyethylene glycol, 1.0% to 4.0% surfactant, 1.0% to 4.0% suspending agent, 35.0% to 40% polyacrylamide dry powder, 5.0% to 8.0% organic alcohol with a relative molecular mass of 30 to 200, and the remainder water.

[0007] Preferably, the organic alcohol is one of methanol, ethanol, ethylene glycol and isopropanol.

[0008] Preferably, the polyethylene glycol is one of polyethylene glycol 100, polyethylene glycol 200, polyethylene glycol 300 and polyethylene glycol 400.

[0009] Preferably, the surfactant is one of coconut oil diethanolamide, nonylphenol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

[0010] Preferably, the suspending agent is one or two of organoclay, carboxymethyl cellulose, hydroxyethyl cellulose and polyvinyl butyral.

[0011] 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).

[0012] 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.

[0013] Preferably, the relative molecular mass of the polyacrylamide dry powder is 5 million to 10 million.

[0014] The above-mentioned method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion comprises adding the organic alcohol, polyethylene glycol, a surfactant and a suspending agent into water according to mass fraction, stirring to dissolve, to obtain an alcohol-based dispersion, and then adding polyacrylamide dry powder, stirring evenly, to obtain the polyacrylamide emulsion based on the alcohol-based dispersion.

[0015] The above-mentioned polyacrylamide emulsion based on alcohol-based dispersion is used in unconventional oil and gas reservoir fracturing. When used, the polyacrylamide emulsion based on alcohol-based dispersion is added to water to prepare an aqueous solution with a mass concentration of 0.1% to 0.8%, and is used as a slippery water and sand-carrying fracturing fluid for on-site fracturing, that is, as an on-site fracturing fluid.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention discloses a polyacrylamide emulsion based on an alcohol-based dispersion. In a first aspect, among its components, polyethylene glycol (PEG) is used as a main solvent of the dispersion, and its mass fraction is as high as 41.0% to 53.0%, which is a key component in the formula. Firstly, as a high molecular polymer, PEG has a long molecular chain and has 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 to 200 has a small relative molecular mass and can penetrate between the polyacrylamide molecular chains to destroy the molecular The interaction force between the chains can reduce the viscosity of the system; secondly, the ether bonds on the PEG molecular chain and the organic alcohol can 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, it synergizes with the organic alcohol with a relative molecular mass of 30-200 to effectively improve the solubility of polyacrylamide dry powder in the system. Especially under low temperature conditions, the addition of PEG can significantly improve the solubility of polyacrylamide, solving the technical problem that alcohol-based fracturing fluid is easy to freeze at low temperatures, resulting in poor stability of the fracturing fluid.

[0017] Secondly, organic alcohols with a relative molecular mass of 30 to 200, in addition to acting as solvents, work together with PEG to improve the solubility of polyacrylamide powder, solving the technical problem that fracturing fluids are prone to freezing at low temperatures, resulting in poor stability of the fracturing fluids. At the same time, they can also effectively break emulsification and release water locks, preventing the emulsifier in the fracturing fluid from emulsifying the formation crude oil, effectively protecting the oil and gas reservoirs, thereby avoiding reservoir damage, releasing the bound water in the reservoirs, and improving the flow efficiency of oil and gas.

[0018] Thirdly, the addition of surfactants further improves the solubility and dispersibility of the dispersion. Surfactants can reduce the interfacial tension of the system and promote the mutual fusion of the components, thereby improving the overall performance of the fracturing fluid. Suspending agents promote the formation of the network structure of the dispersion and the increase of viscosity. By forming a stable network structure, suspending agents can effectively improve the suspension of polyacrylamide dry powder and prevent it from settling or agglomerating during the fracturing process, thereby maintaining the uniformity and stability of the fracturing fluid.

[0019] In summary, in the formula of the present invention, polyacrylamide dry powder, solvents such as polyethylene glycol and organic alcohol, and additives such as surfactants and suspending agents work synergistically to form a fracturing fluid (emulsion) system with excellent performance. The present invention optimizes the compounding of each component and uses the emulsion to prepare the fracturing fluid, which not only improves the water solubility and dispersibility of the dry powder, but also enhances the functions of demulsification and water lock release, effectively reducing the damage of foreign fluids to the reservoir. Especially under low temperature conditions, due to the synergistic effect of organic alcohol and polyethylene glycol, the fracturing fluid can maintain good solubility and fluidity, thereby solving the problem that the existing alcohol-based fracturing fluid is difficult to dissolve at low temperatures, that is, the problem of easy freezing, and has potential engineering application value in improving oil recovery rate.

[0020] Furthermore, the present invention also discloses the use of the above-mentioned polyacrylamide emulsion based on alcohol-based dispersion in unconventional oil and gas reservoir fracturing; when used, the polyacrylamide emulsion based on alcohol-based dispersion is added to water to prepare an aqueous solution with a mass concentration of 0.1% to 0.8%, and used as a slippery water and sand-carrying fracturing fluid for on-site fracturing. According to industry standards, this concentration can make the fracturing fluid fully carry sand, and also has good fluidity to achieve a drag reduction effect. The use process of the polyacrylamide emulsion based on alcohol-based dispersion is convenient, and it can be directly prepared according to industry standards without complicated operation processes, which is conducive to large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 The photographs are of the alcohol-based polyacrylamide emulsion prepared in Example 3 of the present invention before (A) and after (B) centrifugation; Figure 2 The photograph (A) of the alcohol-based polyacrylamide emulsion prepared in Example 3 of the present invention, the photograph (B) of the 0.5% on-site fracturing fluid, and the photograph (C) of the fracturing fluid after on-site fracturing; Figure 3 The drag reduction performance test results of the alcohol-based polyacrylamide emulsion prepared in Example 3 of the present invention as a 0.1% on-site fracturing fluid; Figure 4 The shear viscosity result of the alcohol-based polyacrylamide emulsion prepared in Example 3 of the present invention prepared as a 0.6% on-site fracturing fluid tested at 90°C; Figure 5The shear viscosity result of the alcohol-based polyacrylamide emulsion prepared in Example 3 of the present invention prepared as a 0.8% on-site fracturing fluid tested at 120°C; Figure 6 The alcohol-based polyacrylamide emulsion prepared in Example 3 of the present invention is formulated into a 0.8% on-site fracturing fluid, and the suspension performance test results of 20% to 50% of the proppant therein are shown. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0024] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0025] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0026] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0027] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0028] The invention provides a polyacrylamide emulsion based on an alcohol-based dispersion, which comprises, by mass fraction, 41.0%-53.0% of polyethylene glycol, 1.0%-4.0% of a surfactant, 1.0%-4.0% of a suspending agent, 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 remainder of water.

[0029] The proportion of water in the system is 3% to 5%. In addition, water is preferably deionized water, and its main function is to fully mix the alcohol, surfactant, and suspending agent.

[0030] In a preferred embodiment, the composition includes, by mass fraction, 44.0% to 51.0% polyethylene glycol, 3.0% surfactant, 2.0% suspending agent, 35.0% to 40% polyacrylamide powder, 6.0% organic alcohol with a relative molecular mass of 30 to 200, and the remainder water.

[0031] The organic alcohol is one of methanol, ethanol, ethylene glycol and isopropanol, preferably isopropanol, and its main function is to improve the fluidity and antifreeze performance of the dispersion. These small molecule alcohols not only have good demulsification and water lock functions, but also methanol, ethanol, ethylene glycol and isopropanol have good lubrication properties. During the fracturing process, these alcohol compounds can reduce the friction coefficient between the fracturing fluid and the formation rock, and play a lubricating role, which helps to reduce the energy consumption in the fracturing operation, and at the same time reduce the wear and damage of the fracturing fluid to the formation rock, thereby reducing the risk of damage to the formation; at the same time, as an additive for clean fracturing fluid, these organic alcohols help to form 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 conducive to protecting groundwater resources and ecological environment.

[0032] 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. In addition, the polyethylene glycol is preferably polyethylene glycol 300.

[0033] The surfactant is one of coconut oil diethanolamide, nonylphenol polyoxyethylene ether and alkylphenol polyoxyethylene ether, preferably coconut oil diethanolamide. The wetting, demulsification and drainage effects of the surfactant can improve the permeability and crack expansion ability of the fracturing fluid, promote the backflow ability and reduce the damage to the formation, and effectively eliminate foam, prevent the foam from affecting the stability and construction effect of the fracturing fluid, and at the same time improve the solubility and dispersibility of the dispersion.

[0034] The suspending agent is one or two of organic clay, carboxymethyl cellulose, hydroxyethyl cellulose and polyvinyl butyral, which can also be called a suspending agent, which can increase the viscosity of the dispersion medium, thereby effectively preventing the flocculation of particles and promoting uniform dispersion of particles. The organic clay here includes sodium bentonite or lithium bentonite.

[0035] 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, polyvinyl butyral is used to improve the viscosity of the dispersion, and the suspension of polyacrylamide powder is improved in two ways. The suspending agent is a mixture of hydroxyethyl cellulose and polyvinyl butyral, which can enable the fracturing fluid to better form and maintain cracks during oil and gas production, improve the permeability of oil and gas, and thus increase the output 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 the two 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 polymer chains to fully stretch and entangle with each other to form a polymer with a three-dimensional network structure. Here, hydroxyethyl cellulose and polyvinyl butyral are both high molecular weight chain polymers containing hydroxyl groups. In a water system, the hydroxyl groups on the molecular chains of hydroxyethyl cellulose and polyvinyl butyral form hydrogen bonds with water molecules, so that the molecular chains of hydroxyethyl cellulose and polyvinyl butyral can be fully extended and entangled with each other, and a polymer with a three-dimensional network structure is formed by the chain polymer. More preferably, the mass ratio of hydroxyethyl cellulose to polyvinyl butyral is 2:0.3.

[0036] More preferably, a polyacrylamide emulsion based on an alcohol dispersion includes 3 g of water, 6 g of isobutyl alcohol, 45.7 g of polyethylene glycol 300, 2.8 g of coconut oil diethanolamide, 2 g of hydroxyethyl cellulose, 0.3 g of polyvinyl butyral, and 40 g of polyacrylamide dry powder.

[0037] The polyacrylamide dry powder is selected from one or two of hydrophobically associated polyacrylamide dry powder, post-hydrolyzed polyacrylamide dry powder, and salt-resistant polyacrylamide dry powder, and hydrophobically associated polyacrylamide dry powder is further preferred; the relative molecular mass of the polyacrylamide dry powder is 5 million to 10 million.

[0038] The hydrophobic associating polyacrylamide dry powder is a special polyacrylamide, in which hydrophobic groups are introduced into the molecules, so that the molecules can form an association body through hydrophobic interaction. This association body has a certain stability and viscosity in the solution, thereby giving the polyacrylamide new properties, such as high sand carrying, low friction and shear resistance.

[0039] In addition, according to construction needs, water can be replaced with concentrated liquids such as anti-swelling agents, drainage aids, and scale inhibitors. The alcohol-based polyacrylamide dispersion can be used to directly obtain an integrated multifunctional fracturing fluid through compounding technology, which greatly simplifies the procedure of adding additional additives during actual construction. The alcohol-based polyacrylamide dispersion solution meets the industry standards for fracturing fluids, and the solution is clear and transparent, meeting the requirements for clean fracturing fluids.

[0040] The above-mentioned method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion is specifically as follows: according to the mass fraction, the organic alcohol, polyethylene glycol, surfactant and suspending agent are added to water, stirred for 30 minutes to mix the monomers evenly, and an alcohol-based dispersion is obtained; then, polyacrylamide powder is added, and stirred for 15 minutes using a high-speed shearing machine to evenly disperse the polyacrylamide powder in the alcohol-based dispersion to obtain the polyacrylamide emulsion based on the alcohol-based dispersion.

[0041] In addition, the present invention also discloses a method for preparing the polyacrylamide emulsion based on the alcohol-based dispersion. According to the mass fraction, the polyethylene glycol, the surfactant, the suspending agent and the organic alcohol with a relative molecular mass of 30 to 200 are added into water, stirred and dissolved to obtain the alcohol-based dispersion, and then the polyacrylamide dry powder is added and stirred evenly to obtain the polyacrylamide emulsion based on the alcohol-based dispersion. The emulsion preparation method is simple, convenient to operate and easy to industrialize.

[0042] At the same time, the present invention also discloses the use of the above-mentioned alcohol-based dispersion polyacrylamide emulsion in unconventional oil and gas reservoir fracturing. When used, the alcohol-based dispersion polyacrylamide emulsion is added to water to prepare an aqueous solution with a mass concentration of 0.1% to 0.8%, and used as slick water and sand-carrying fracturing fluid for on-site fracturing.

[0043] The fracturing fluid has good stability. After continuous testing for 10 min, its drag reduction rate is 70%~80%, and it has good drag reduction stability. In addition, the shear viscosity of the prepared fracturing fluid is 60~89 mPa·s at 90 ℃, and the shear viscosity at 120 ℃ is 50~70 mPa·s. 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 effect on the fracturing fluid.

[0044] The invention combines the irreversible damage problem of unconventional complex oil and gas reservoirs caused by a large amount of mineral oil and emulsifier in the polyacrylamide emulsion currently used in fracturing, and uses polyethylene glycol, water, small molecule alcohol and surfactant as dispersants to prepare an alcohol-based dispersion, and evenly disperses polyacrylamide powder in an alcohol-based solvent to prepare a polyacrylamide emulsion of the alcohol-based dispersion. The polyacrylamide emulsion of the alcohol-based dispersion can be further used to prepare a clear and transparent clean fracturing fluid. The prepared fracturing fluid has good drag reduction and sand carrying performance. In addition, aqueous auxiliary agent concentrates such as anti-swelling agents, drainage agents and scale inhibitors can be dispersed into the alcohol-based dispersion to realize the multifunctionality of the fracturing fluid system. The alcohol-based dispersion does not contain mineral oil and emulsifiers, is more environmentally friendly, and promotes the simple, environmentally friendly and efficient development of unconventional complex oil and gas.

[0045] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only intended 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 may make various changes or modifications to the present invention, and these equivalent forms belong to the scope limited by the appended claims of the application equally.

[0046] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0047] Example 1 The present embodiment provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: use a beaker to weigh 3 g of deionized water, 6 g of isobutyl alcohol, 51.2 g of polyethylene glycol 300, 2.5 g of coconut oil diethanolamide, 2 g of hydroxyethyl cellulose, and 0.3 g of polyvinyl butyral, use an electric stirrer to 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 hydrophobic associating polyacrylamide powder with a molecular weight of 10 million, adjust the 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%.

[0048] In addition, when used in unconventional oil and gas reservoir fracturing, 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 the field fracturing fluid is 72%, and it has good drag reduction stability; the shear viscosity of the fracturing fluid with a concentration of 0.8% at 90 ℃ and 120 ℃ is 65.21 mPa·s and 55.42 mPa·s, respectively.

[0049] Example 2 The present embodiment provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: 3 g of deionized water, 6 g of isobutyl alcohol, 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 are weighed in a beaker, and stirred at 100 r / min for 30 min using an electric stirrer to fully mix and dissolve various monomers to obtain an alcohol-based dispersion, 38 g of hydrophobically associating polyacrylamide powder with a molecular weight of 10 million is weighed, the rotation speed is adjusted to 3000 r / min, and the mixture is slowly added to the alcohol-based dispersion, and stirring is continued for 15 min to obtain an alcohol-based polyacrylamide dispersion with a content of 38%.

[0050] In addition, when used in unconventional oil and gas reservoir fracturing, 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 the field fracturing fluid is 74%, and it has good drag reduction stability; the shear viscosity of the fracturing fluid with a concentration of 0.8% at 90 ℃ and 120 ℃ is 71.51 mPa·s and 62.57 mPa·s, respectively.

[0051] Example 3 The present embodiment provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: 3 g of deionized water, 6 g of isobutyl alcohol, 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 are weighed in a beaker, and stirred at 100 r / min for 30 min using an electric stirrer to fully mix and dissolve various monomers to obtain an alcohol-based dispersion, 40 g of hydrophobically associating polyacrylamide powder with a molecular weight of 10 million is weighed, the rotation speed is adjusted to 3000 r / min, and the mixture is slowly added to the alcohol-based dispersion, and stirring is continued for 15 min to obtain an alcohol-based polyacrylamide dispersion with a content of 40%.

[0052] In order to verify the performance of the polyacrylamide fracturing fluid based on the alcohol-based dispersion in the present invention, the following tests were performed: The alcohol-based polyacrylamide emulsion prepared in Example 3 (i.e., the effective content of the alcohol-based polyacrylamide is 40%) was subjected to a stability test. Specifically, the alcohol-based polyacrylamide emulsion prepared in Example 3 was centrifuged at a speed of 1000 r / min for 10 min to observe the stability of the system. The test results are as follows: Figure 1 As shown, (A) is before centrifugation, (B) is after centrifugation. Figure 1 It can be seen that the alcohol-based polyacrylamide dispersion after centrifugation has no obvious stratification and no solid precipitation is formed at the bottom, which shows good stability.

[0053] 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 prepared 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 was as follows: Figure 2 As shown in Figure (A), the prepared 0.5% on-site fracturing fluid is shown in Figure (B), and the fracturing fluid after on-site fracturing is shown in Figure (C). Figure 2 It can be seen that the configured 0.5% on-site fracturing fluid is clear and transparent, and the fracturing fluid after on-site fracturing is still crystal clear, which shows that the liquid performance of the fracturing fluid is stable during the on-site construction process, and the gel is completely broken after fracturing, which can meet the requirements of on-site drilling and sand adding scale.

[0054] Further, in order to test the drag reduction performance of the fracturing fluid prepared by the present invention, the dispersion prepared in Example 3 was prepared as a 0.1% on-site fracturing fluid, and its drag reduction performance, i.e., the drag reduction rate, was tested. The test process of the drag reduction performance refers to the test of the drag reduction rate in 7.12.4 of the Petroleum and Natural Gas Industry Standard SY / T5107-2016 of the People's Republic of China "Method for Evaluating the Performance of Water-Based Fracturing Fluids", and the test results are shown in Figure 3 As can be seen from the figure, after continuous testing for 10 minutes, the drag reduction rate of the on-site fracturing fluid is greater than 70%, and it has good drag reduction stability, indicating 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.

[0055] In addition, the dispersion prepared in Example 3 was prepared 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. Figure 4 as well as Figure 5It can be seen that the shear viscosity of the 0.6% on-site fracturing fluid at 90 °C is 62.89 mPa·s, and the shear viscosity of the 0.8% 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.

[0056] Further, according to the on-site drilling and production technical standards, that is, the People's Republic of China Petroleum and Natural Gas Industry Standard SY / T5107-2016 "Water-based Fracturing Fluid Performance Evaluation Method", the dispersion prepared in Example 3 was configured as a field fracturing fluid with a mass concentration of 0.8%, and 20% to 50% of a proppant was used for suspension performance testing. The proppant here is quartz sand. The test results are as follows: Figure 6 As shown in the figure, there is no obvious sedimentation of the proppant after 30 minutes, indicating that the alcohol-based polyacrylamide dispersion solution meets the industry standards for fracturing fluids.

[0057] Example 4 The present embodiment provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: 5 g of a 60% fluorocarbon surfactant solution is used instead of deionized water, 6 g of isobutyl alcohol, 43.7 g of polyethylene glycol 300, 2.8 g of coconut oil diethanolamide, 2 g of hydroxyethyl cellulose, and 0.3 g of polyvinyl butyral, and an electric stirrer is used to stir at 100 r / min for 30 min to fully mix and dissolve various monomers to obtain an alcohol-based dispersion, 40 g of hydrophobically associating polyacrylamide dry powder with a relative molecular mass of 5 million is weighed, the rotation speed is adjusted to 3000 r / min, and the powder is slowly added to the alcohol-based dispersion, and stirring is continued for 15 min to obtain an alcohol-based polyacrylamide dispersion with a drainage function having a content of 40%.

[0058] In addition, when used in unconventional oil and gas reservoir fracturing, the alcohol-based polyacrylamide dispersion is formulated into a fracturing fluid with a mass concentration of 0.1%. The drag reduction rate of the on-site fracturing fluid is 76%, and it has good drag reduction stability; the shear viscosity of the fracturing fluid with a concentration of 0.8% at 90 ℃ and 120 ℃ is 70.43 mPa·s and 61.53 mPa·s, respectively.

[0059] Example 5 This embodiment provides a polyacrylamide emulsion based on an alcohol-based dispersion: 5 g of 70% scale inhibitor (1-hydroxyethyl diphosphonic acid, HEDP) solution is used instead of deionized water, 6 g of isobutyl alcohol, 43.7 g of polyethylene glycol 300, 2.8 g of coconut oil diethanolamide, 2 g of hydroxyethyl cellulose, and 0.3 g of polyvinyl butyral are stirred at 100 r / min for 30 min using an electric stirrer to fully mix and dissolve various monomers to obtain an alcohol-based dispersion, 40 g of hydrophobically associated polyacrylamide dry powder with a relative molecular mass of 8 million is weighed, the rotation speed is adjusted to 3000 r / min, and the mixture is slowly added to the alcohol-based dispersion, and stirring is continued for 15 min to obtain an alcohol-based polyacrylamide dispersion with a scale inhibition function having a content of 40%.

[0060] In addition, when used in unconventional oil and gas reservoir fracturing, the alcohol-based polyacrylamide dispersion is formulated into a field fracturing fluid with a mass concentration of 0.7%. The drag reduction rate of the field fracturing fluid is 78%, and it has good drag reduction stability; the shear viscosity of the fracturing fluid with a concentration of 0.8% at 90 ℃ and 120 ℃ is 71.05 mPa·s and 62.75 mPa·s, respectively.

[0061] Example 6 The present embodiment provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: 5 g of water, 6 g of isobutyl alcohol, 47 g of polyethylene glycol 100, 3 g of nonylphenol polyoxyethylene ether, and 4 g of sodium bentonite are weighed in a beaker, and stirred at 100 r / min for 30 min using an electric stirrer to fully mix and dissolve various monomers to obtain an alcohol-based dispersion, 35 g of hydrophobically associating polyacrylamide powder with a molecular weight of 10 million is weighed, the rotation speed is adjusted to 3000 r / min, and the mixture is slowly added to the alcohol-based dispersion, and stirring is continued for 15 min to obtain an alcohol-based polyacrylamide dispersion with a content of 35%.

[0062] In addition, when used in unconventional oil and gas reservoir fracturing, the alcohol-based polyacrylamide dispersion is formulated into a field fracturing fluid with a mass concentration of 0.1%. The drag reduction rate of the field fracturing fluid is 75%, and it has good drag reduction stability; the shear viscosity of the fracturing fluid with a concentration of 0.8% at 90 ℃ and 120 ℃ is 78.04 mPa·s and 62.86 mPa·s, respectively.

[0063] Example 7 The present embodiment provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: 5 g of water, 10 g of isobutyl alcohol, 55 g of polyethylene glycol 200, 5 g of coconut oil diethanolamide, and 4.5 g of carboxymethyl cellulose are weighed in a beaker, and stirred at 100 r / min for 30 min using an electric stirrer to fully mix and dissolve various monomers to obtain an alcohol-based dispersion, 45 g of hydrophobically associating polyacrylamide dry powder with a molecular weight of 10 million is weighed, the speed is adjusted to 3000 r / min, and the powder is slowly added to the alcohol-based dispersion, and stirring is continued for 15 min to obtain an alcohol-based hydrophobically associating polyacrylamide dispersion with a content of 36%.

[0064] In addition, when used in unconventional oil and gas reservoir fracturing, the alcohol-based polyacrylamide dispersion is formulated into a fracturing fluid with a mass concentration of 0.1%. The drag reduction rate of the on-site fracturing fluid is 80%, and it has good drag reduction stability; the shear viscosity of the fracturing fluid with a concentration of 0.8% at 90 ℃ and 120 ℃ is 68.21 mPa·s and 63.31 mPa·s, respectively.

[0065] Example 8 The present embodiment provides a method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion: 8 g of water, 11 g of isobutyl alcohol, 93 g of polyethylene glycol 400, 7 g of alkylphenol polyoxyethylene ether, 4 g of hydroxyethyl cellulose, and 2 g of polyvinyl butyral are weighed in a beaker, and stirred at 100 r / min for 30 min using an electric stirrer to fully mix and dissolve various monomers to obtain an alcohol-based dispersion, 35 g of hydrophobically associating polyacrylamide dry powder with a relative molecular mass of 10 million is weighed, the rotation speed is adjusted to 3000 r / min, and the powder is slowly added to the alcohol-based dispersion, and stirring is continued for 15 min to obtain an alcohol-based hydrophobically associating polyacrylamide dispersion with a content of 39%.

[0066] In addition, when used in unconventional oil and gas reservoir fracturing, the alcohol-based polyacrylamide dispersion is formulated into a field fracturing fluid with a mass concentration of 0.1%. The drag reduction rate of the field fracturing fluid is 82%, and it has good drag reduction stability; the shear viscosity of the fracturing fluid with a concentration of 0.8% at 90 ℃ and 120 ℃ is 78.62 mPa·s and 70.25 mPa·s, respectively.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A polyacrylamide emulsion based on an alcohol-based dispersion, characterized in that: Calculated by mass fraction, it includes 41.0%~53.0% polyethylene glycol, 1.0%~4.0% surfactant, 1.0%~4.0% suspending agent, 35.0%~40% polyacrylamide powder, 5.0%~8.0% organic alcohol with a relative molecular mass of 30~200, and the balance water.

2. The polyacrylamide emulsion based on an alcohol-based dispersion according to claim 1, characterized in that: The organic alcohol is one of methanol, ethanol, ethylene glycol and isopropanol.

3. The polyacrylamide emulsion based on alcohol-based dispersion according to claim 1, characterized in that: The polyethylene glycol is one of polyethylene glycol 100, polyethylene glycol 200, polyethylene glycol 300 and polyethylene glycol 400.

4. The polyacrylamide emulsion based on alcohol-based dispersion according to claim 1, characterized in that: The surfactant is one of coconut oil diethanolamide, nonylphenol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

5. The polyacrylamide emulsion based on alcohol-based dispersion according to claim 1, characterized in that: The suspending agent is one or two of organic clay, carboxymethyl cellulose, hydroxyethyl cellulose and polyvinyl butyral.

6. The polyacrylamide emulsion based on alcohol-based dispersion according to claim 5, characterized in that: When the suspending agent is a mixture of hydroxyethyl cellulose and polyvinyl butyral, the mass ratio of the hydroxyethyl cellulose to the polyvinyl butyral is (2-3):(0.3-1.5).

7. The polyacrylamide emulsion based on alcohol-based dispersion according to claim 1, characterized in that: The polyacrylamide dry powder is one or two of hydrophobic association type polyacrylamide dry powder, post-hydrolysis type polyacrylamide dry powder and salt-resistant type polyacrylamide dry powder.

8. The polyacrylamide emulsion based on alcohol-based dispersion according to claim 1, characterized in that: The relative molecular mass of the polyacrylamide dry powder is 5 million to 10 million.

9. The method for preparing a polyacrylamide emulsion based on an alcohol-based dispersion according to any one of claims 1 to 8, characterized in that: According to the mass fraction, the polyethylene glycol, surfactant, suspending agent and organic alcohol with a relative molecular mass of 30 to 200 are added to water, stirred to dissolve, and an alcohol-based dispersion is prepared. Then, the polyacrylamide dry powder is added and stirred evenly to prepare the polyacrylamide emulsion based on the alcohol-based dispersion.

10. The use of a polyacrylamide emulsion based on an alcohol-based dispersion according to any one of claims 1 to 8 in unconventional oil and gas reservoir fracturing, characterized in that: When in use, the polyacrylamide emulsion based on the alcohol-based dispersion is added into water to prepare an aqueous solution with a mass concentration of 0.1% to 0.8%, and is used as a slippery water and sand-carrying fracturing fluid for on-site fracturing.

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