An amphiphilic copolymer for natural gas hydrate fracturing fluid, preparation method and use thereof

Abstract

The invention discloses an amphiphilic copolymer for natural gas hydrate fracturing fluid, a preparation method thereof and use thereof in natural gas hydrate fracturing fluid, wherein the amphiphilic copolymer is a ternary or tetrapolymer formed by polymerization of acrylamide monomer, 2-acrylamide-2-methylpropanesulfonic acid monomer, enol polyether amphiphilic monomer and polyether diunsaturated acid ester monomer, and has a general structural formula (I). The copolymer can well improve the viscoelastic properties of the solution, enhance the anti-shear performance of the solution, and the formed fracturing fluid system has the advantages of strong sand suspension capacity, low transport friction, low formation damage and effective reduction of interfacial tension.

Description

Technical Field

[0001] The invention belongs to the field of petrochemical industry, and in particular relates to an amphiphilic copolymer for natural gas hydrate fracturing fluid, a preparation method thereof and application of the amphiphilic copolymer in natural gas hydrate fracturing in oilfield chemistry. Background Art

[0002] Natural gas hydrates are widely distributed in nature, existing in continental permafrost, slope zones of islands, uplifts of continental margins, polar continental shelves, and deep-water environments of oceans and some inland lakes. At present, fossil fuels are becoming increasingly depleted, energy consumption is surging, and fossil fuel prices are rising. Natural gas hydrates are hailed as an emerging and promising unconventional alternative energy source due to their wide distribution, abundant reserves, and high fuel utilization rate. Natural gas hydrate reservoirs are similar to lockers in the global carbon cycle, containing most of the world's methane and accounting for one-third of the earth's mobile organic carbon. Natural gas hydrates are one of the largest methane reservoirs in the global carbon cycle. At standard temperature and pressure, 1 cubic meter of natural gas hydrate contains no less than 160 cubic meters of natural gas. This means that the carbon content in natural gas hydrates is twice that of the world's mixed fossil fuels. Exploiting methane hydrate in the ocean is a world-class problem. The principle of exploitation is mainly to change the temperature and pressure of the methane hydrate reservoir, break its phase equilibrium, and decompose the methane hydrate to obtain methane gas. In the ocean, the main difficulties in exploitation are stratum collapse and pore siltation and sand blockage. Fracturing is a technology that improves the permeability of reservoirs by applying pressure to create cracks. Combining fracturing technology with conventional mining methods can increase the mining cycle and provide gas migration channels.

[0003] Artificially synthesized polymers are widely available and have advantages such as good temperature resistance, strong sand suspension ability, and thorough gel breaking, making them a hot topic in fracturing fluid research. Conventional polymers currently have disadvantages such as weak thickening ability and great shear influence. In order to overcome these disadvantages, functional monomers are often introduced to modify the polymers. Hydrophobic associating copolymers are water-soluble polymers with a small amount of hydrophobic groups introduced into the hydrophilic long chain. The hydrophobic groups spontaneously aggregate in water due to polarity reasons, and the copolymers form a network structure. Therefore, they have good thickening and shear resistance properties, which can meet increasingly stringent mining conditions. The structure and type of hydrophobic monomers will greatly affect the performance of hydrophobic associating polymers. The hydrophobic monomers reported so far are often based on long-chain alkyl and benzene ring structures. Polymers with benzene rings as side chains (Zhong Chuanrong et al., Characterization and heat resistance of AM-STD-NaAMPS ternary hydrophobic associating copolymers. Polymer Materials Science and Engineering, 2003, 19(6): 126-130) have rigid benzene rings, which can effectively improve the temperature resistance and shear resistance of polymers. However, the benzene rings are too close to the main chain of the molecule. Such a structure is not conducive to the copolymerization of hydrophobic monomers and acrylamide, resulting in poor thickening effect. Hydrophobic associating copolymers containing long-chain alkyl groups (Hu Jun et al., Preparation and application of hydrophobic associating cross-linked acid thickeners. Oilfield Chemistry, 2020, 37(3): 403-408) can effectively improve the viscosity of the solution, but they have poor solubility, low content of introduced monomers, weak associative ability, and poor shear resistance.

[0004] The present invention designs and synthesizes a novel amphiphilic copolymer with long-chain polyoxypropylene or polyoxybutylene as a hydrophobic group and polyoxyethylene as a hydrophilic group, which can overcome the shortcomings of poor solubility, limited associative ability and poor shear resistance of traditional hydrophobic associative copolymers with long-chain alkyl or benzene ring as hydrophobic groups. More amphiphilic monomers can be introduced into the molecular structure, so that the copolymer exhibits more excellent viscoelasticity and stronger sand suspension ability. With polyoxyethylene and polyoxypropylene as amphiphilic groups and flexible side chains, the copolymer can easily form a spontaneously assembled associative structure, and under the action of high-speed shear, it has the advantages of low transport friction and easy shear recovery, and can effectively reduce the oil-water interfacial tension, with low damage to the formation, and can improve the compatibility of fracturing fluid with other oilfield agents. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention proposes an amphiphilic copolymer for natural gas hydrate fracturing fluid, which can well improve the viscoelastic properties of the solution and enhance the shear resistance of the solution. The formed fracturing fluid system has the advantages of strong sand suspension ability, low transportation friction, low formation damage and effective reduction of interfacial tension.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] According to one aspect of the present invention, an object of the present invention is to provide an amphiphilic copolymer for natural gas hydrate fracturing fluid, wherein the amphiphilic copolymer is a ternary or tetrapolymer prepared by polymerizing acrylamide monomer, 2-acrylamido-2-methylpropanesulfonic acid monomer, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer, and has a general structural formula (I):

[0008]

[0009] Formula (I) wherein X is H, Y is CH3 or C2H5, and Z is H or CH3; m=1-30, n=0-30, e=1-20, and f=0-20, respectively representing the number of blocks derived from oxyethylene groups, blocks derived from oxypropylene groups, or blocks derived from oxybutylene groups in the random polyether block, wherein when n and f are 0, it indicates that the amphiphilic copolymer structure may not contain the block; a, b, c, and d represent the degree of polymerization of each monomer, wherein a:b:c:d=50-90:5-50:5-30:0-30, wherein when d is 0, it indicates that the block may not be contained, and the weight average molecular weight range of the amphiphilic copolymer is 500,000-12,000,000.

[0010] As a preferred technical solution, the enol polyether amphiphilic monomer is prepared by polymerization of unsaturated alcohol with ethylene oxide and propylene oxide or butylene oxide under inert gas protection, temperature of 90°C to 150°C, pressure of 0.1 to 0.4 MPa and the presence of a catalyst for 4 to 9 hours.

[0011] Preferably, in the preparation of the enol polyether amphiphilic monomer, the catalyst is selected from at least one of NaOH, KOH, LiOH, Mg(OH)2, Ca(OH)2, Ba(OH)2, AlCl3 or sulfuric acid and the like, wherein NaOH or KOH is preferred.

[0012] Preferably, in the preparation of the enol polyether amphiphilic monomer, the inert gas is selected from argon or nitrogen, preferably nitrogen.

[0013] Preferably, in the preparation of the enol polyether amphiphilic monomer, the unsaturated alcohol is selected from vinyl alcohol, propenol, butenol, pentenol or hexenol, and isomers thereof.

[0014] Preferably, in the preparation of the enol polyether amphiphilic monomer, the etherification temperature of ethylene oxide is 120°C, and the etherification temperature of propylene oxide or butylene oxide is 135°C.

[0015] As a preferred technical solution, the polyether diunsaturated acid ester monomer is mixed with an unsaturated acid such as acrylic acid or methacrylic acid and a polyether in a molar ratio of 1:0.8-3 and then added to a reaction container, 20-80% of a solvent, 0.5-5% of an acid catalyst and a small amount of an inhibitor are added in sequence, and then the temperature is raised to 70°C-120°C for esterification, the reaction is performed for 2-6 hours, and the product is washed and extracted to obtain.

[0016] Preferably, in the preparation of the polyether diunsaturated acid ester monomer, the acid catalyst is selected from at least one of concentrated sulfuric acid, concentrated phosphoric acid, concentrated hydrochloric acid, boric acid, p-toluenesulfonic acid, aminosulfonic acid, and citric acid.

[0017] Preferably, in the preparation of the polyether diunsaturated acid ester monomer, the solvent is selected from alkanes or aromatic hydrocarbons, preferably at least one of n-hexane, cyclohexane, n-heptane, n-octane, toluene and xylene.

[0018] Preferably, in the preparation of the polyether diunsaturated acid ester monomer, the polymerization inhibitor is selected from at least one of hydroquinone, p-hydroxyanisole, 2-tert-butylhydroquinone, p-benzoquinone and methylhydroquinone.

[0019] The present invention also provides a method for preparing the amphiphilic copolymer for natural gas hydrate fracturing fluid, comprising the following steps:

[0020] Acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid monomer, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer are added into a reaction container according to a set ratio, water is added, and after stirring evenly, the temperature is slowly increased, and then an initiator is added dropwise. Under nitrogen protection, an amphiphilic copolymer is obtained by polymerization reaction at a reaction temperature of 30°C to 100°C and a reaction time of 4 to 9 hours.

[0021] As a preferred technical solution, acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid monomer, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer are added in a weight percentage ratio of 30-90%: 5-50%: 5-50%: 0-20%, wherein the proportion of polyether diunsaturated acid ester monomer is 0, indicating that the monomer is not included, and the sum of the weight percentages of the four monomers is 1.

[0022] As a preferred technical solution, based on the total weight of the added monomers, the weight percentage of the added solvent water is 40-80%, and the weight percentage of the initiator is 0.2-3%.

[0023] As a preferred technical solution, the initiator is selected from at least one of sodium persulfate, ammonium persulfate, potassium persulfate, sodium persulfate / sodium bisulfite or hydrogen peroxide / ferrous sulfate.

[0024] According to another aspect of the present invention, another object of the present invention is to provide use of the amphiphilic copolymer in preparing a natural gas hydrate fracturing fluid.

[0025] According to another aspect of the present invention, another object of the present invention is to provide a natural gas hydrate fracturing fluid, wherein the natural gas hydrate fracturing fluid is an aqueous solution comprising the amphiphilic copolymer according to the present invention in a concentration of 0.01% to 0.5% by weight.

[0026] Compared with the prior art, the advantages and positive effects of the present invention are:

[0027] 1. The copolymer provided by the present invention is obtained by a direct polymerization method based on the simultaneous introduction of polyoxyethylene polyoxypropylene or polyoxybutylene long chains on the copolymer chain. It can significantly enhance the viscoelasticity of the solution and has good shear resistance. The formed fracturing fluid system has the advantages of strong sand suspension ability, low transportation friction, low formation damage and effective reduction of interfacial tension.

[0028] 2. The preparation method of the copolymer provided by the present invention is simple, the reaction is stable, the price is low and it is suitable for industrial processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 The viscosity-concentration relationship curves of the amphiphilic copolymer A1 solution prepared according to Example 1 and the commercial polyacrylamide (PAM) solution;

[0031] Figure 2 The temperature and shear resistance curves of the amphiphilic copolymer A1 solution and the commercial polyacrylamide (PAM) solution prepared according to Example 1;

[0032] Figure 3 : is the viscoelasticity curve of the amphiphilic copolymer A1 solution prepared according to Example 1. DETAILED DESCRIPTION

[0033] Hereinafter, the present invention will be described in detail. Before describing, it should be understood that the terms used in this specification and the appended claims should not be interpreted as being limited to the general meaning and dictionary meaning, but should be interpreted according to the meaning and concept corresponding to the technical aspects of the present invention on the basis of the principle that the inventor is allowed to appropriately define the terms for the best interpretation. Therefore, the descriptions presented here are only preferred examples for illustrative purposes and are not intended to limit the scope of the present invention, so that it should be understood that other equivalents or improvements can be obtained therefrom without departing from the spirit and scope of the present invention.

[0034] As used herein, the terms "include", "comprising", "having", "containing" or any other similar terms are open-ended transitional phrases, which are intended to cover non-exclusive inclusions. For example, a composition or article containing multiple elements is not limited to the elements listed herein, but may also include other elements that are not explicitly listed but are generally inherent to the composition or article. In addition, unless otherwise expressly stated, the term "or" refers to an inclusive "or" rather than an exclusive "or". For example, any of the following situations satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and both A and B are true (or exist). In addition, as used herein, the terms "include", "comprising", "having", and "containing" should be interpreted as having been specifically disclosed and simultaneously covering closed or semi-closed transitional phrases such as "consisting of" and "consisting essentially of".

[0035] In this article, all features or conditions defined in the form of numerical ranges or percentage ranges are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be deemed to have covered and specifically disclosed all possible secondary ranges and individual values ​​within the range, especially integer values. For example, the range description of "1 to 8" should be deemed to have specifically disclosed all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., especially secondary ranges defined by all integer values, and should be deemed to have specifically disclosed individual values ​​such as 1, 2, 3, 4, 5, 6, 7, 8, etc. within the range. Unless otherwise specified, the above interpretation method applies to all contents of the entire present invention, regardless of whether the range is broad or not.

[0036] If the quantity or other numerical value or parameter is expressed as a range, a preferred range or a series of upper and lower limits, it should be understood that all ranges consisting of any upper limit or preferred value of the range and the lower limit or preferred value of the range have been specifically disclosed herein, regardless of whether these ranges are disclosed separately. In addition, if a numerical range is mentioned herein, unless otherwise specified, the range should include its endpoints and all integers and fractions within the range.

[0037] In this document, under the premise of achieving the purpose of the invention, numerical values ​​should be understood to have the accuracy of the number of significant digits of the numerical value. For example, the number 40.0 should be understood to cover the range from 39.50 to 40.49.

[0038] Meanwhile, in the present invention, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are polystyrene conversion molecular weights analyzed by gel permeation chromatography (GPC), and the molecular weight distribution can be calculated from the ratio Mw / Mn.

[0039] The present invention provides an amphiphilic copolymer for fracturing, which is a ternary or tetrapolymer prepared by polymerizing acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, an enol polyether amphiphilic monomer, and a polyether diunsaturated acid ester, and has a general structural formula (I):

[0040]

[0041] Formula (I) wherein X is H, Y is CH3 or C2H5, and Z is H or CH3; m=1-30, n=0-30, e=1-20, and f=0-20, respectively representing the number of blocks derived from oxyethylene groups, blocks derived from oxypropylene groups, or blocks derived from oxybutylene groups in the random polyether block, wherein when n and f are 0, it indicates that the amphiphilic copolymer structure may not contain the block; a, b, c, and d represent the degree of polymerization of each monomer, wherein a:b:c:d=50-90:5-50:5-30:0-30, wherein when d is 0, it indicates that the block may not be contained, and the weight average molecular weight range of the amphiphilic copolymer is 500,000-12,000,000.

[0042] in

[0043] The molecular formula of acrylamide monomer is:

[0044] The molecular formula of 2-acrylamide-2-methylpropanesulfonic acid monomer is:

[0045] The molecular formula of the amphiphilic monomer of enol polyether is:

[0046]

[0047] The molecular formula of polyether diunsaturated acid ester monomer is:

[0048]

[0049] wherein m, n, e, f, X, Y and Z are defined the same as in formula (I).

[0050] When d in formula (I) is 0, it means that the amphiphilic copolymer may not contain a block formed by a polyether diunsaturated acid ester, that is, the amphiphilic copolymer is represented by the following formula (II), and in this case, the amphiphilic copolymer is a ternary polymer:

[0051]

[0052] wherein a, b, c, m, n, X, and Y have the same definitions as in formula (I).

[0053] For example, the amphiphilic copolymer for natural gas hydrate fracturing fluid according to the present invention is polymerized from acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester, and the specific structure of the obtained amphiphilic copolymer is limited, wherein the number of oxyethylene groups, oxypropylene groups, or oxybutylene groups is specifically limited, and the weight average molecular weight of the copolymer is controlled within the above range by controlling the degree of polymerization of each monomer represented by a, b, c, and d, so as to obtain an amphiphilic copolymer for fracturing with expected excellent performance.

[0054] In a preferred embodiment, the unsaturated acid in the polyether diunsaturated acid ester is selected from acrylic acid or methacrylic acid, and the polyether is selected from polyoxyethylene, polyoxypropylene, polyoxybutylene or a block polyether thereof.

[0055] In a preferred embodiment, the unsaturated alcohol in the amphiphilic monomer of the enol polyether is selected from vinyl alcohol, propenol, butenol, pentenol or hexenol, and isomers thereof, among which propenol is preferred, and the polyether is selected from polyoxyethylene, polyoxypropylene, polyoxybutylene or block polyethers thereof.

[0056] After selecting the above optimized groups to participate in the reaction, a fracturing fluid with better performance can be obtained. It is understandable that those skilled in the art can adjust the unsaturated acid and unsaturated alcohol used according to the actual desired reaction.

[0057] In a preferred embodiment, a method for preparing an enol polyether amphiphilic monomer is provided, wherein the method is prepared by polymerization of unsaturated alcohol with ethylene oxide and propylene oxide or butylene oxide under inert gas protection, temperature of 90°C to 150°C, pressure of 0.1 to 0.4 MPa and catalyst presence for 4 to 9 hours. It is understandable that in order to obtain a suitable enol polyether amphiphilic monomer that can participate in the reaction, it is necessary to reasonably select the temperature, pressure and catalyst in its preparation method, wherein the temperature can also be 110°C, 120°C, 130°C, etc., the pressure can also be 0.2MPa, 0.3MPa, etc., and the catalyst can be selected from at least one of NaOH, KOH, LiOH, Mg(OH)2, Ca(OH)2, Ba(OH)2, AlCl3 or sulfuric acid and other acidic and basic compounds or Lewis acidic and basic compounds, wherein NaOH or KOH can be preferred. However, it should be noted that the preparation method of the polyoxyethylene-polyoxypropylene ether of unsaturated alcohol provided by the present invention is not limited to the above-mentioned method, and other feasible preparation methods can also be selected.

[0058] Preferably, in the preparation of the enol polyether amphiphilic monomer, the inert gas is selected from argon or nitrogen, preferably nitrogen.

[0059] Preferably, in the preparation of the enol polyether amphiphilic monomer, the unsaturated alcohol is selected from vinyl alcohol, propenol, butenol, pentenol or hexenol, and isomers thereof.

[0060] Preferably, in the preparation of the enol polyether amphiphilic monomer, the etherification temperature of ethylene oxide is 120°C, and the etherification temperature of propylene oxide or butylene oxide is 135°C.

[0061] In a preferred embodiment, the polyether diunsaturated acid ester is prepared by mixing an unsaturated acid such as acrylic acid or methacrylic acid with a polyether in a molar ratio of 1:0.8-3 and adding the mixture into a reaction vessel. Then, 20-80% of a monomer synthesis solvent, 0.5-5% of an acid catalyst and a small amount of an inhibitor are added in sequence. The temperature is then raised to 70°C-120°C for esterification. The reaction is performed for 2-6 hours, and the product is washed and extracted to obtain the product.

[0062] In the preparation method of the polyether diunsaturated acid ester, the amount of each monomer participating in the reaction, the amount of catalyst and the amount of solvent for monomer synthesis are limited, and the reaction temperature and reaction time are also limited. Wherein, the amount of solvent for monomer synthesis includes alkanes or aromatic hydrocarbons, for example, at least one of n-hexane, cyclohexane, n-heptane, n-octane, toluene and xylene, preferably toluene. The acidic catalyst is selected from at least one of concentrated sulfuric acid, concentrated phosphoric acid, concentrated hydrochloric acid, boric acid, p-toluenesulfonic acid, aminosulfonic acid, and citric acid, preferably concentrated sulfuric acid or p-toluenesulfonic acid. However, it should be noted that the preparation method of the polyether diunsaturated acid ester provided by the present invention is not limited to the above-mentioned methods, and other feasible preparation methods can also be selected.

[0063] According to one embodiment of the present invention, there is also provided a method for preparing the amphiphilic copolymer as described in the above embodiment, comprising the following steps: adding acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester into a reaction container according to a set ratio, adding a solvent, stirring evenly, slowly heating up, and then dropping an initiator, and under nitrogen protection, performing a polymerization reaction at a reaction temperature of 30°C to 100°C and a reaction time of 4 to 9 hours to obtain the amphiphilic copolymer.

[0064] In the preparation method of the above-mentioned amphiphilic copolymer, three or four monomers are directly polymerized under the action of water and an initiator to obtain a ternary or tetrapolymer. In the above-mentioned preparation method, in order to avoid the influence of the ambient atmosphere on the reactants, the entire reaction is carried out under the protection of an inert gas, preferably nitrogen, and the reaction temperature and reaction time are also limited. The preferred reaction temperature is 30°C to 100°C, and the reaction time is 4 to 9h, so as to ensure that the weight average molecular weight of the amphiphilic copolymer obtained by the reaction is within a suitable range. It can be understood that, depending on the weight average molecular weight of the desired amphiphilic copolymer, the reaction temperature can also be 35°C, 45°C, 55°C, 65°C, 75°C, etc., and the reaction time can also be 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, etc., and those skilled in the art can adjust according to the actual reaction situation.

[0065] In a preferred embodiment, acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, enol polyether amphiphilic monomer, polyether diunsaturated acid ester are added in a ratio of 30-90% by weight: 5-50% by weight: 5-50% by weight: 0-20% by weight, wherein the ratio of polyether diunsaturated acid ester monomer is 0, indicating that the monomer is not included, and the sum of the weight percentages of the four monomers is 1. In this embodiment, in order to obtain the expected amphiphilic copolymer structure, the addition amount of the four reactive monomers is limited, and the sum of the addition amount of the four reactive monomers is 1 as a whole. As a specific but non-limiting example, the added enol polyether amphiphilic monomer can be 5%, 15%, 25%, 35%, etc., and the added polyether diunsaturated acid ester can be 5%, 10%, 15%, 20%, etc., and those skilled in the art can make adjustments according to the actual required reaction conditions.

[0066] In a preferred embodiment, the weight percentage of water added as a solvent is 40-80%, and the weight percentage of the initiator is 0.2-3%. In this embodiment, in order to ensure that the reaction is fully and stably carried out, the amount of the added solvent and the amount of the initiator are also specifically limited, wherein the amount of the added solvent can also be 30%, 40%, 50%, 60%, 70%, etc., as long as it can ensure that each reaction monomer can be fully dissolved and mixed to meet the required amount of the reaction, and the amount of the added initiator can also be 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc., as long as it can fully initiate the reaction.

[0067] In a preferred embodiment, the initiator is selected from at least one of sodium persulfate, ammonium persulfate, potassium persulfate, sodium persulfate / sodium bisulfite or hydrogen peroxide / ferrous sulfate. In this embodiment, the selection of the initiator described in the above embodiment is limited, but it can be understood that this embodiment is not limited to the initiators listed, and can also be initiators that can be replaced with each other and are known to those skilled in the art in combination with common knowledge in the art.

[0068] In a preferred embodiment, the enol polyether amphiphilic monomer is prepared by polymerization of unsaturated alcohol with ethylene oxide and propylene oxide or butylene oxide at a temperature of 90° C. to 150° C. and a pressure of 0.1 to 0.4 MPa in the presence of a catalyst.

[0069] The following examples are only listed as examples of embodiments of the present invention and do not constitute any limitation to the present invention. It can be understood by those skilled in the art that modifications within the scope of the essence and concept of the present invention fall within the scope of protection of the present invention. Unless otherwise specified, the reagents and instruments used in the following examples are commercially available products.

[0070] Example 1

[0071] Preparation of Enol Polyether Amphiphilic Monomers

[0072] Put 1 mol of propylene alcohol into a high-pressure reactor, add NaOH as a catalyst, evacuate, purge with N2 three times, gradually heat up to 110°C, continuously introduce ethylene oxide, then heat up to 130°C and continuously introduce propylene oxide, maintain the reaction pressure at 0.1MPa, after the feeding reaction is completed, evacuate to remove the reaction residue, finally add acetic acid to neutralize, and the polyoxyethylene polyoxypropylene ether amphiphilic monomer of propylene alcohol can be obtained.

[0073] Preparation of polyether diunsaturated acid ester monomer

[0074] Methacrylic acid and polyoxyethylene polyoxypropylene block polyether are mixed in a molar ratio of 1:2.1, 60% of toluene is added as a solvent, and then 1% of p-toluenesulfonic acid is mixed with the above raw materials, and the mixture is put into a four-necked flask, and an inhibitor hydroquinone is added. The temperature is gradually raised to 90°C for reflux dehydration. The reaction is stopped after the water output reaches the theoretical value after reacting for 5 hours. The mixture is washed with a Na2CO3 solution and then with water. The organic phase is extracted to obtain a polyether diunsaturated methacrylate monomer.

[0075] Preparation of amphiphilic copolymers

[0076] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer are mixed in a weight ratio of 60:20:10:10, with a total monomer mass fraction of 20% in the aqueous solution, 0.5% potassium persulfate is used as an initiator, the temperature is raised to 60° C. under nitrogen protection, the initiator is slowly added, and the polymerization is carried out for 8 hours and then the temperature is lowered to obtain an amphiphilic copolymer A1;

[0077] Acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer were mixed in a ratio of 60:10:5:15, with the mass fraction of the total monomers in the aqueous solution being 20%. 1% ammonium persulfate was used as an initiator. Under nitrogen protection, the temperature was raised to 80°C, the initiator was slowly added, and the polymerization was performed for 6 hours before cooling to obtain an amphiphilic copolymer A2.

[0078] Example 2

[0079] Preparation of Enol Polyether Amphiphilic Monomers

[0080] Put 1 mol of butenol into a high-pressure reactor, add KOH as a catalyst, evacuate, purge with N2 three times, gradually heat up to 120°C, continuously introduce ethylene oxide, then heat up to 140°C and continuously introduce butylene oxide, maintain the reaction pressure at 0.2MPa, after the feeding reaction is completed, evacuate to remove the reaction residue, finally add acetic acid to neutralize, and you can get the polyoxyethylene polyoxybutylene ether amphiphilic monomer of butenol.

[0081] Preparation of polyether diunsaturated acid ester monomer

[0082] Acrylic acid and polyoxyethylene polyoxypropylene block polyether are mixed in a molar ratio of 1:1.5, 70% of xylene is added as a solvent, and then 2% of concentrated sulfuric acid is mixed with the above raw materials, and the raw materials are put into a four-necked flask together, and an inhibitor p-hydroxyanisole is added. The temperature is gradually raised to 100°C for reflux dehydration. After the water output reaches the theoretical value after the reaction for 5 hours, the reaction is stopped, and the mixture is washed with a Na2CO3 solution and then with water. The mixture is layered and extracted to obtain an organic phase, thereby obtaining a polyether diunsaturated acrylate monomer.

[0083] Preparation of amphiphilic copolymers

[0084] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer were mixed in a ratio of 50:20:20:10, with a total monomer mass fraction of 20% in the aqueous solution, 0.7% potassium persulfate and sodium bisulfite were used as initiators, the temperature was raised to 40°C under nitrogen protection, the initiator was slowly added, and the polymerization lasted for 9 hours before cooling to obtain an amphiphilic copolymer B1;

[0085] Acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, enol polyether amphiphilic monomer and polyether diunsaturated acid ester monomer were mixed in a ratio of 50:10:20:20, with the mass fraction of the total monomers in the aqueous solution being 20%. 1.1% ammonium persulfate was used as an initiator. Under nitrogen protection, the temperature was raised to 90°C, the initiator was slowly added, and the polymerization was performed for 5 hours before cooling to obtain an amphiphilic copolymer B2.

[0086] Example 3

[0087] Preparation of Enol Polyether Amphiphilic Monomers

[0088] Put 1 mol of pentenol into a high-pressure reactor, add LiOH as a catalyst, evacuate, purge with N2 three times, gradually raise the temperature to 125°C, continuously introduce ethylene oxide, then raise the temperature to 135°C and continuously introduce butylene oxide, maintain the reaction pressure at 0.5MPa, after the feeding reaction is completed, evacuate to remove the reaction residue, finally add acetic acid to neutralize, and the polyoxyethylene polyoxybutylene ether amphiphilic monomer of pentenol can be obtained.

[0089] Preparation of polyether diunsaturated acid ester monomer

[0090] Acrylic acid and polyoxyethylene polyoxybutylene block polyether are mixed in a molar ratio of 1:1.5, 50% of hexane is added as a solvent, and then 2% of concentrated phosphoric acid is mixed with the above raw materials, and the mixture is put into a four-necked flask, and an inhibitor p-benzoquinone is added. The temperature is gradually raised to 110°C for reflux dehydration. The reaction is stopped after the water output reaches the theoretical value after 6 hours of reaction. The mixture is washed with a Na2CO3 solution and then with water. The organic phase is extracted to obtain a polyether diunsaturated acrylate monomer.

[0091] Preparation of amphiphilic copolymers

[0092] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer were mixed in a ratio of 50:15:15:20, with a total monomer mass fraction of 20% in the aqueous solution, 1.2% ammonium persulfate and ferrous sulfate were used as initiators, the temperature was raised to 45°C under nitrogen protection, the initiator was slowly added, and the polymerization lasted for 9 hours before cooling to obtain an amphiphilic copolymer C1;

[0093] Acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, enol polyether amphiphilic monomer and polyether diunsaturated acid ester monomer were mixed in a ratio of 70:10:10:10, with the mass fraction of the total monomers in the aqueous solution being 20%. 1.8% sodium persulfate was used as an initiator. Under nitrogen protection, the temperature was raised to 70°C, the initiator was slowly added, and the polymerization was performed for 6 hours before cooling to obtain an amphiphilic copolymer C2.

[0094] Example 4

[0095] Preparation of Enol Polyether Amphiphilic Monomers

[0096] 1 mol of hexenol was added into a high-pressure reactor, NaOH was added as a catalyst, vacuum was drawn, N2 was purged three times, the temperature was gradually raised to 100°C, ethylene oxide was continuously introduced, and then the temperature was raised to 125°C and propylene oxide was continuously introduced, and the reaction pressure was maintained at 0.3 MPa. After the feeding reaction was completed, the reaction residue was removed by vacuum drawing, and finally citric acid was added for neutralization to obtain the polyoxyethylene polyoxypropylene ether amphiphilic monomer of hexenol.

[0097] Preparation of polyether diunsaturated acid esters

[0098] Methacrylic acid and polyoxyethylene polyoxybutylene block polyether are mixed in a molar ratio of 1:1.2, 70% of n-heptane is added as a solvent, and then 1.5% of boric acid is mixed with the above raw materials, and the mixture is put into a four-necked flask together. Methyl hydroquinone, an inhibitor, is added, and the temperature is gradually raised to 90°C for reflux dehydration. The reaction is stopped after the water output reaches the theoretical value after 6 hours of reaction, and the mixture is washed with a Na2CO3 solution and then with water. The mixture is layered and extracted to obtain an organic phase, thereby obtaining a polyether diunsaturated methacrylate monomer.

[0099] Preparation of amphiphilic copolymers

[0100] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer were mixed in a ratio of 50:10:10:30, with a total monomer mass fraction of 20% in the aqueous solution, 0.8% ammonium persulfate and ferrous sulfate were used as initiators, the temperature was raised to 50°C under nitrogen protection, the initiator was slowly added, and the polymerization lasted for 5 hours before cooling to obtain an amphiphilic copolymer D1;

[0101] Acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, enol polyether amphiphilic monomer and polyether diunsaturated acid ester monomer were mixed in a ratio of 80:10:10:0, with the mass fraction of the total monomers in the aqueous solution being 20%. 0.7% sodium persulfate was used as an initiator. Under nitrogen protection, the temperature was raised to 80°C, the initiator was slowly added, and the polymerization was performed for 6 hours before cooling to obtain an amphiphilic copolymer D2.

[0102] Example 5

[0103] Preparation of Enol Polyether Amphiphilic Monomers

[0104] Put 1 mol of propylene alcohol into a high-pressure reactor, add NaOH as a catalyst, evacuate, purge with N2 three times, gradually heat up to 105°C, continuously introduce ethylene oxide, then heat up to 120°C and continuously introduce propylene oxide, maintain the reaction pressure at 0.3MPa, after the feeding reaction is completed, evacuate to remove the reaction residue, finally add hydrochloric acid to neutralize, and you can get the polyoxyethylene polyoxypropylene ether amphiphilic monomer of hexenol.

[0105] Preparation of polyether diunsaturated acid esters

[0106] Methacrylic acid and polyoxyethylene polyoxybutylene block polyether are mixed in a molar ratio of 1:1.7, 70% of n-octane is added as a solvent, and then 1% of aminosulfonic acid is mixed with the above raw materials, and the mixture is put into a four-necked flask, and an inhibitor hydroquinone is added. The temperature is gradually raised to 110°C for reflux dehydration, and the reaction is stopped after the water output reaches the theoretical value after 6 hours of reaction. The mixture is washed with a Na2CO3 solution and then with water, and the organic phase is extracted to obtain a polyether diunsaturated methacrylate monomer.

[0107] Preparation of amphiphilic copolymers

[0108] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer were mixed in a ratio of 70:15:5:10, with a total monomer mass fraction of 20% in the aqueous solution, 0.3% sodium persulfate was used as an initiator, the temperature was raised to 65°C under nitrogen protection, the initiator was slowly added, and the polymerization lasted for 8 hours before cooling to obtain an amphiphilic copolymer E1;

[0109] Test Example 1

[0110] (1) Thickening effect of amphiphilic copolymers

[0111] The amphiphilic copolymer A1 in Example 1 and commercially available polyacrylamide (PAM) were prepared into 0.01%, 0.03%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% copolymer solutions, respectively. -1 Under the conditions of , the viscosity-concentration relationship curve of the copolymer solution was measured using Anton Paar MCR302 rheometer. The results are as follows Figure 1 As shown. Figure 1 It can be seen that copolymer A1 has strong hydrophobic association and significant viscosity-increasing effect, and the viscosity of 0.5wt% copolymer solution reaches 550mPa·s.

[0112] (2) Temperature and shear resistance of amphiphilic copolymer solution

[0113] The amphiphilic copolymer A1 in Example 1 and the purchased commercial polyacrylamide (PAM) were respectively prepared into 0.5 wt% copolymer solutions, and sheared continuously for two hours at a temperature rising from 25°C to 80°C at a shear rate of 170s -1 Under the conditions of , the viscosity-time curve of the copolymer solution was measured using the Anton Paar MCR302 rheometer. After two hours of shearing, the viscosity was still 190mPa·s, which is much higher than the 50mPa·s specified in the Chinese petroleum and natural gas industry standard SY / T6376-2008 "General Technical Specifications for Water-Based Fracturing Fluids". The results are as follows Figure 2 shown.

[0114] (3) Viscoelastic properties of amphiphilic copolymer solutions

[0115] The amphiphilic copolymer A1 in Example 1 was prepared into a 0.5 wt% copolymer solution. The storage modulus and loss modulus of the copolymer solution were measured at 25°C using an Anton Paar MCR302 rheometer to measure the relationship between the angular frequency, which represents the viscoelasticity of the copolymer A1 solution. The frequency was 6.3 rad·s -1 That is, at 1Hz, G′ and G″ are 4.31Pa and 1.13Pa respectively, which are much higher than the Chinese petroleum and natural gas industry standard SY / T6376-2008 "General Technical Indicators of Water-Based Fracturing Fluids" G′≥1.5Pa, G″≥0.3Pa. The results are as follows Figure 3 shown.

[0116] (4) Degelling performance of amphiphilic copolymer solution

[0117] The amphiphilic copolymers A1, B1, and E1 in Examples 1, 2, and 5 were respectively prepared into 0.5 wt% copolymer solutions. A breaker was added to the copolymer solutions at 70°C, the breaking time was measured, and the viscosity of the breaking solution was measured using an Anton Paar MCR302 rheometer. The copolymer solutions can break quickly and completely. The results are shown in Tables 1, 2, and 3.

[0118] Table 1 Gel breaking performance of amphiphilic copolymer A1

[0119]

[0120] Table 2 Gel breaking performance of amphiphilic copolymer B1

[0121]

[0122] Table 3 Gel breaking performance of amphiphilic copolymer E1

[0123]

[0124]

[0125] (5) Sand-carrying performance of amphiphilic copolymer solution

[0126] The amphiphilic copolymers A1, B1, and E1 in Examples 1, 2, and 5 were respectively prepared into 0.5 wt% copolymer solutions. At 25°C, 30-mesh ceramsite was selected as a proppant, the ceramsite and the copolymer solution were uniformly mixed, and the ceramsite sinking rate was measured to indicate its sand-carrying performance. The ceramsite did not sink within six hours, indicating that the copolymer solution had a good sand-carrying performance.

[0127] (6) Filtration performance of amphiphilic copolymer solution

[0128] The amphiphilic copolymers A1, B1 and E1 in Example 1, Example 2 and Example 5 were respectively prepared into 0.5 wt% copolymer solutions, and the filtration coefficient and filtration rate were measured at 25°C, 50°C and 80°C. The filtration loss of the solution within 36 minutes at different temperatures was measured using a GGS71-A high temperature and high pressure filtration meter, and the filtration coefficient and filtration rate were lower than the requirements of the Chinese petroleum and natural gas industry standard SY / T6376-2008 "General Technical Indicators for Water-Based Fracturing Fluids". The results are shown in Tables 4, 5 and 6.

[0129] Table 4 Filtration properties of amphiphilic copolymer A1 solution

[0130]

[0131] Table 5 Filtration properties of amphiphilic copolymer B1 solution

[0132]

[0133] Table 6 Filtration properties of amphiphilic copolymer E1 solution

[0134]

[0135]

[0136] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An amphiphilic copolymer for natural gas hydrate fracturing fluid, wherein the amphiphilic copolymer is a quaternary copolymer prepared by polymerizing acrylamide monomer, 2-acrylamide-2-methylpropanesulfonic acid monomer, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer, and has the general structural formula (I): Formula (I) wherein, X is H, Y is CH3 or C2H5, and Z is H or CH3; m=1-30, n=0-30, e=1-20, and f=0-20, respectively representing the number of blocks derived from oxyethylene groups, blocks derived from oxypropylene groups, or blocks derived from oxybutylene groups in the random polyether block, wherein n and f are not 0; a, b, c, and d represent the degree of polymerization of each monomer, wherein a:b:c:d=50-90:5-50:5-30:0-30, wherein d is not 0, and the weight average molecular weight range of the amphiphilic copolymer is 500,000-12,000,000.

2. The amphiphilic copolymer for natural gas hydrate fracturing fluid according to claim 1, wherein the amphiphilic enol polyether monomer is prepared by polymerization of unsaturated alcohol with ethylene oxide and propylene oxide or butylene oxide under inert gas protection, at a temperature of 90° C. to 150° C., at a pressure of 0.1 to 0.4 MPa and in the presence of a catalyst for 4 to 9 hours; In the preparation of the enol polyether amphiphilic monomer, the catalyst is selected from at least one of NaOH, KOH, LiOH, Mg(OH)2, Ca(OH)2, Ba(OH)2, AlCl3 or sulfuric acid; In the preparation of the enol polyether amphiphilic monomer, the inert gas is selected from argon or nitrogen; In the preparation of the enol polyether amphiphilic monomer, the unsaturated alcohol is propenol; In the preparation of the enol polyether amphiphilic monomer, the etherification temperature of ethylene oxide is 120°C, and the etherification temperature of propylene oxide or butylene oxide is 135°C.

3. The amphiphilic copolymer for natural gas hydrate fracturing fluid according to claim 2, wherein: In the preparation of the enol polyether amphiphilic monomer, the catalyst is selected from NaOH and KOH.

4. The amphiphilic copolymer for natural gas hydrate fracturing fluid according to claim 2, wherein: In the preparation of the enol polyether amphiphilic monomer, the inert gas is nitrogen.

5. The amphiphilic copolymer for natural gas hydrate fracturing fluid according to claim 1, wherein the polyether diunsaturated acid ester monomer is added to a reaction container by mixing acrylic acid or methacrylic acid with polyether in a molar ratio of 1:0.8-3, and 20-80% of a solvent, 0.5-5% of an acidic catalyst and a small amount of a polymerization inhibitor are added in sequence, and then the temperature is raised to 70° C. to 120° C. for esterification, and the reaction is performed for 2-6 hours, and the product is washed and extracted to obtain; In the preparation of the polyether diunsaturated acid ester monomer, the acid catalyst is selected from at least one of concentrated sulfuric acid, concentrated phosphoric acid, concentrated hydrochloric acid, boric acid, p-toluenesulfonic acid, aminosulfonic acid, and citric acid; the solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, n-octane, toluene, and xylene; and the inhibitor is selected from at least one of hydroquinone, p-hydroxyanisole, 2-tert-butylhydroquinone, p-benzoquinone, and methylhydroquinone.

6. A method for preparing an amphiphilic copolymer for natural gas hydrate fracturing fluid according to any one of claims 1 to 5, comprising the following steps: Acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid monomer, enol polyether amphiphilic monomer, and polyether diunsaturated acid ester monomer are added into a reaction container according to a set ratio, water is added, and after stirring evenly, the temperature is slowly increased, and then an initiator is added dropwise. Under nitrogen protection, an amphiphilic copolymer is obtained by polymerization reaction at a reaction temperature of 30°C to 100°C and a reaction time of 4 to 9 hours.

7. The method for preparing an amphiphilic copolymer for natural gas hydrate fracturing fluid according to claim 6, wherein: Acrylamide monomer, 2-acrylamide-2-methylpropanesulfonic acid monomer, enol polyether amphiphilic monomer and polyether diunsaturated acid ester monomer are added in a weight percentage ratio of 30-90%: 5-50%: 5-50%: 0-20%, and the sum of the weight percentages of the four monomers is 1.

8. The method for preparing an amphiphilic copolymer for natural gas hydrate fracturing fluid according to claim 6, wherein: Based on the total weight of the added monomers, the weight percentage of the added solvent water is 40-80%.

9. The method for preparing an amphiphilic copolymer for natural gas hydrate fracturing fluid according to claim 6, wherein: Based on the total weight of the added monomers, the weight percentage of the initiator is 0.2-3%.

10. The method for preparing an amphiphilic copolymer for natural gas hydrate fracturing fluid according to claim 6, wherein: The initiator is selected from at least one of sodium persulfate, ammonium persulfate, potassium persulfate, sodium persulfate / sodium bisulfite or hydrogen peroxide / ferrous sulfate.

11. Use of the amphiphilic copolymer according to any one of claims 1 to 5 in the preparation of natural gas hydrate fracturing fluid.

12. A natural gas hydrate fracturing fluid, which is an aqueous solution comprising the amphiphilic copolymer according to any one of claims 1 to 5 in a concentration of 0.01% to 0.5% by weight.

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