Seawater-based modified guar gum fracturing fluid and preparation method thereof

Abstract

The invention provides a seawater-based modified guar gum fracturing fluid and a preparation method thereof, and belongs to the technical field of seawater-based fracturing fluids, the fracturing fluid comprises the following components by volume: 100 parts of an organic phosphonic acid hydroxypropyl modified guar gum aqueous solution; 0.1 to 0.3 part of a temperature stabilizer; 0.4 to 1 part of a pH regulator; 0.3 to 0.5 part of a demulsification cleanup additive; 0.2 to 0.8 part of a cross-linking agent; wherein the organic phosphonic acid hydroxypropyl modified guar gum is prepared by carrying out hydroxypropylation and chelating agent grafting modification on guar gum; the chelating agent is N-chloro aminoethyl diphosphonic acid; the cross-linking agent is prepared by carrying out coordination reaction on a ligand and salt containing central ions. The seawater-based fracturing fluid obtained by matching the organic phosphonic acid hydroxypropyl modified guar gum thickener with the cross-linking agent and other components has the characteristics of high hardness resistance and high instant solubility.

Description

Technical Field

[0001] The present invention relates to the technical field of modification of guar gum thickeners and seawater-based fracturing fluids, and particularly to a seawater-based modified guar gum fracturing fluid and a preparation method thereof. Background Art

[0002] With the development of oil and gas exploration and production technologies, the exploitation of offshore oil has gradually increased, and low-permeability and tight oil and gas occupy an important position in offshore oil and gas resources. Offshore low-permeability and tight unconventional oil and gas fields are mainly composed of sandstone reservoirs, which have the characteristics of relatively deep geological burial, relatively high temperature, relatively large shale content, and small rock porosity. Therefore, high-temperature fracturing fluids are required to carry out formation modification to improve the single-well production.

[0003] Currently, most of the fracturing fluids used in offshore fracturing are guar gum fracturing fluids prepared with fresh water. However, fresh water guar gum fracturing fluids have problems such as difficult transportation, long fracturing fluid preparation cycle, and large platform cleaning difficulty; conventional guar gum for preparing seawater-based fracturing fluids has problems such as slow dissolution rate and precipitation during crosslinking. For example, when hydroxypropyl guar gum thickener is dissolved in seawater to prepare a fracturing fluid, usually a relatively large amount of chelating auxiliary is required to chelate hardness ions to avoid precipitation interference of hardness ions with hydroxide radicals during crosslinking. Although carboxymethyl guar gum thickener for preparing fracturing fluid has high temperature resistance, the thickener has a slow dissolution rate in high-hardness water quality and is not suitable for seawater quality with high salinity and high calcium and magnesium ions. At the same time, a relatively large amount of chelating auxiliary is also required to chelate hardness ions. Summary of the Invention

[0004] One object of the present invention is to provide a seawater-based modified guar gum fracturing fluid.

[0005] Another object of the present invention is to provide a preparation method of the seawater-based modified guar gum fracturing fluid.

[0006] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0007] In the first aspect, the present invention provides a seawater-based modified guar gum fracturing fluid, including the following components in parts by volume:

[0008] 100 parts of an aqueous solution of organophosphonic acid hydroxypropyl modified guar gum; the aqueous solution of organophosphonic acid hydroxypropyl modified guar gum is prepared by dissolving organophosphonic acid hydroxypropyl modified guar gum in seawater, and the mass concentration of organophosphonic acid hydroxypropyl modified guar gum in seawater is 0.50%-0.65%;

[0009] 0.1-0.3 part of a temperature stabilizer;

[0010] 0.4-1 part of a pH regulator;

[0011] Demulsifying and drainage aid: 0.3 - 0.5 parts;

[0012] Crosslinking agent: 0.2 - 0.8 parts;

[0013] Calcium and magnesium chelating agent: 0 - 0.8 parts;

[0014] Among them, the organic phosphonic acid hydroxypropyl modified guar gum is obtained by graft modification of guar gum with hydroxypropylation and chelating agent; the chelating agent is N-chloroaminoethyl diphosphonic acid;

[0015] The crosslinking agent is obtained by the coordination reaction of a ligand and a salt containing a central ion.

[0016] The following is a detailed description of each component:

[0017] Organic phosphonic acid hydroxypropyl modified guar gum:

[0018] The organic phosphonic acid hydroxypropyl modified guar gum is obtained after two chemical modifications of guar gum powder. The first step is hydroxypropylation modification, and the second step is grafting chelating groups (i.e., graft modification with chelating agent). The chemical reagent (chelating agent) used for graft modification with chelating agent is N-chloroaminoethyl diphosphonic acid.

[0019] In some embodiments, the organic phosphonic acid hydroxypropyl modified guar gum is prepared by the following method:

[0020] (1) First, hydroxypropylate the guar gum powder, then wash and dry it to obtain hydroxypropylated guar gum;

[0021] (2) Then graft the hydroxypropylated guar gum with an organic phosphonic acid chelating agent, and then wash and dry it.

[0022] Further, step (1) includes: dispersing the guar gum powder in a solvent, adding a catalyst, adding propylene oxide, controlling the reaction temperature and reaction time. After the reaction is completed, cool the system to room temperature, and then wash and dry it to obtain hydroxypropylated guar gum;

[0023] Preferably, the dispersion solvent of the guar gum is isopropyl alcohol, which is 1 - 3 times the mass of the guar gum.

[0024] Preferably, the catalyst is NaOH, and its addition amount is 17 - 25% of the mass of the guar gum, and it is added as a 20% aqueous solution;

[0025] Preferably, the addition amount of propylene oxide is 20 - 30% of the mass of the guar gum;

[0026] Preferably, the reaction temperature is 50 - 70 °C, and the reaction time is 2 - 5 h;

[0027] Preferably, the washing is carried out with an alcohol-water mixture, and the volume ratio of alcohol to water is 65:35 to 80:20. The alcohol can be ethanol, isopropanol, etc.;

[0028] Preferably, the degree of substitution of hydroxypropyl in hydroxypropyl guar gum is 0.25 to 0.35, and the detection method is nuclear magnetic resonance hydrogen spectrum method.

[0029] Furthermore, step (2) includes: dispersing hydroxypropyl guar gum in a solvent, adding a catalyst, adding an organic phosphonic acid chelating agent N-chloroaminoethyl diphosphonic acid, controlling the reaction temperature and reaction time. After the reaction is completed, the system is cooled to room temperature, and then washed, dried, and neutralized to obtain organophosphonic acid hydroxypropyl modified guar gum.

[0030] Preferably, the catalyst is NaOH, and its addition amount is 20 to 25% of the mass of hydroxypropyl guar gum, and it is added as a 20% aqueous solution;

[0031] Preferably, the addition amount of N-chloroaminoethyl diphosphonic acid is 25 to 60% of the mass of hydroxypropyl guar gum;

[0032] Preferably, the reaction temperature is 60 to 75 °C, and the reaction time is 2 to 3 h;

[0033] Preferably, the washing is carried out with an alcohol-water mixture, and the volume ratio of alcohol to water is 65:35 to 75:25. The alcohol can be ethanol, isopropanol, etc.

[0034] The degree of substitution of the grafted organophosphonic acid group is 0.20 to 0.35, and the detection method is nuclear magnetic resonance hydrogen spectrum method.

[0035] The modified thickener, organophosphonic acid hydroxypropyl modified guar gum, has characteristics such as high hardness resistance and rapid solubility. Grafting hydroxypropyl and polyphosphonic acid functional groups onto guar gum reduces the hydrogen bond interaction of guar gum on the one hand, which helps the rapid solubility of guar gum. On the other hand, the polyphosphonic acid functional group can chelate calcium and magnesium ions, further promoting rapid solubility, and significantly reducing or avoiding the use of calcium and magnesium ion chelating agents during the use of fracturing fluids.

[0036] Dissolve the organophosphonic acid hydroxypropyl modified guar gum in seawater to prepare an organophosphonic acid hydroxypropyl modified guar gum aqueous solution, and its mass percentage is, for example, 0.5%, 0.55%, 0.6%, 0.65%, but not limited to this.

[0037] The volume fraction of the organophosphonic acid hydroxypropyl modified guar gum aqueous solution is 100 parts.

[0038] Temperature stabilizer:

[0039] The temperature stabilizer uses an aqueous solution of one or two of imidazoline and pyridinium p-toluenesulfonate. Preferably, the total solute concentration is 10% - 30%.

[0040] The volume fraction of the temperature stabilizer is, for example, 0.1 part, 0.2 part, 0.3 part, but not limited thereto.

[0041] The temperature stabilizer is an electron-donating organic compound. This type of compound can capture oxidation free radicals during the high-temperature operation of the fracturing fluid, etc. After being added to the fracturing fluid system, it will improve the temperature resistance of the fracturing fluid.

[0042] pH regulator:

[0043] In some embodiments, the pH regulator is prepared by compounding ammonia-ammonium chloride buffer solution and ethanolamine.

[0044] In a specific embodiment, the pH regulator is prepared according to the following ratio:

[0045] Dilute 5.4 g of ammonium chloride and 35 mL of ammonia water into an 80 - 95 mL aqueous solution, then add 5 - 15 mL of ethanolamine, and then add water to make up the volume to 100 mL.

[0046] The volume fraction of the pH regulator is, for example, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 part, but not limited thereto.

[0047] Demulsification and drainage aid:

[0048] The demulsification and drainage aid is prepared by compounding a non-ionic surfactant and an aqueous non-ionic demulsifier. The non-ionic surfactant is one or more selected from polyoxyethylene type A7N, alkylphenol polyoxyethylene ether NP-10, alkanolamide type 6502, and polyether type Pluronic PE6100. The aqueous non-ionic demulsifier is fatty alcohol polyether type B-28.

[0049] The volume fraction of the demulsification and drainage aid is, for example, 0.3, 0.4, 0.5 part, but not limited thereto.

[0050] Crosslinking agent:

[0051] The crosslinking agent is prepared by the coordination reaction of a ligand and a salt containing a central ion.

[0052] In some embodiments, the crosslinking agent is prepared by the following method:

[0053] Add the ligand to the salt solution containing the central ion, and react under stirring at a certain temperature to obtain the crosslinking agent;

[0054] Preferably, the ligand is one or several selected from triethanolamine, 2-hydroxypropionic acid, and citric acid;

[0055] Preferably, the salt containing the central ion is one or more selected from sodium borate decahydrate, sodium borate pentahydrate, sodium tetraborate, zirconium sulfate, zirconium acetate, and zirconium carbonate;

[0056] Preferably, the mass ratio of the ligand to the salt containing the central ion is 0.5 to 3;

[0057] Preferably, the reaction temperature is 20 to 50 °C, and the reaction time is 1 to 5 h;

[0058] The volume fraction of the crosslinking agent is, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 parts, but not limited thereto.

[0059] In a second aspect, the present invention provides a preparation method of the above seawater-based modified guar gum fracturing fluid, comprising the following steps:

[0060] (1) Preparation of an aqueous solution of organophosphonic acid hydroxypropyl modified guar gum: Add organophosphonic acid hydroxypropyl modified guar gum to seawater to obtain an aqueous solution of organophosphonic acid hydroxypropyl modified guar gum;

[0061] (2) Add a temperature stabilizer, a pH regulator, a demulsifying and drainage aid, and a crosslinking agent, and a calcium and magnesium chelating agent (not required in some medium and low temperature fracturing fluid formulations) to the aqueous solution of organophosphonic acid hydroxypropyl modified guar gum, and mix evenly to obtain a seawater-based modified guar gum fracturing fluid.

[0062] Each component is as described in the first aspect.

[0063] Beneficial effects

[0064] In the fracturing fluid of the present invention, a modified guar gum thickener with chelating groups and hydroxypropyl groups is designed. The hydroxypropyl groups can effectively break the hydrogen bond action of guar gum and improve its dissolution rate in the aqueous phase. The chelating groups can chelate hardness ions during the dissolution process of the modified guar gum, further enhancing the dissolution rate of guar gum in seawater and significantly reducing or avoiding the addition of additional calcium and magnesium ion chelating agents.

[0065] The present invention has been described in detail above, but the above embodiments are essentially illustrative only and are not intended to limit the present invention. In addition, the present invention is not limited by any theory described in the foregoing prior art or the invention content or the following examples. Specific embodiments

[0066] The following further illustrates the present invention with reference to embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection required by the present invention.

[0067] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the embodiments are all conventional raw materials, reagents, methods in the art.

[0068] The raw materials involved in the examples and comparative examples are as follows:

[0069] The guar gum powder is from Kunming Jingkun Oilfield Chemical Technology Co., Ltd., Jiangsu Kunshan, grade Guar / First Grade;

[0070] N-chloroaminoethyl diphosphonic acid was prepared with reference to the literature "Synthesis and Application of Aminoethylphosphonic Acid Water Treatment Agent";

[0071] Industrial products are used for chemical substances such as imidazoline, pyridinium p-toluenesulfonate, EDTA disodium (8% EDTA disodium as a calcium and magnesium chelating agent, the solution is acidic), alkylphenol polyoxyethylene ether NP-10, alkanolamide type 6502 and polyether type Pluronic PE6100, fatty alcohol polyether type B-28, etc.

[0072] Example 1 160°C seawater-based fracturing fluid

[0073] 1. Preparation of organophosphonic acid hydroxypropyl modified guar gum:

[0074] 100 g of guar gum powder was dispersed in 200 g of isopropanol, 25 g of propylene oxide and 100 g of 20% sodium hydroxide solution were added, and under the protection of N2 gas, at a pressure of 0.05 Mpa and a temperature of 50°C, hydroxypropylation was carried out first for 4 h. After the reaction, the degree of substitution was 0.25, and it was washed and dried with 70% ethanol aqueous solution. Then 100 g of hydroxypropylated guar gum was dispersed in 200 g of isopropanol, 53 g of N-chloroaminoethyl diphosphonic acid and 100 g of 23% sodium hydroxide solution were added, and under the protection of N2 gas, at a pressure of 0.07 Mpa and a temperature of 60°C, grafting reaction was carried out for 2.5 h. After grafting, the degree of substitution of organophosphonic acid groups was 0.30, and it was washed and dried with 75% ethanol aqueous solution. 100 mesh maleic acid was dispersed in the modified guar gum to play a neutralizing role. The viscosity increasing rate of the organophosphonic acid hydroxypropyl modified guar gum in seawater was 89% in 3 minutes.

[0075] 2. Preparation of crosslinking agent:

[0076] 5 g of sodium borate decahydrate, 3 g of zirconium sulfate and 6 g of triethanolamine were dispersed in 60 g of water, then 5 g of 2-hydroxypropionic acid was added and stirred at 40°C for 30 min, and then 21 g of 2% sodium hydroxide solution was added and stirred at 25°C for 1 h to obtain the crosslinking agent.

[0077] 3. Temperature stabilizer: 10% pyridinium p-toluenesulfonate + 5% imidazoline + 85% water;

[0078] 4. pH regulator: 5.4 g of ammonium chloride + 35 mL of ammonia water were diluted to 95 mL of aqueous solution, then 5 mL of ethanolamine and a certain amount of water were added to make up to 100 mL.

[0079] 5. Demulsifying and drainage aid: 3% polyether type Pluronic PE6100 + 3% alkanolamide type 6502 + 5% alkylphenol polyoxyethylene ether NP-10 + 5% fatty alcohol polyether B-28 + 15% ethanol + 69% water.

[0080] Fracturing fluid formulation components: 100 mL of 0.55% organic phosphonic acid hydroxypropyl modified guar gum aqueous solution + 0.6 mL of crosslinking agent + 0.2 mL of temperature stabilizer + 0.8 mL of pH regulator + 0.3 mL of calcium and magnesium chelating agent (8% EDTA disodium solution) + 0.4 mL of demulsifying and drainage aid.

[0081] Through experimental detection: at a temperature of 160 °C and a rotational speed of 100 s -1 The temperature and shear resistance performance is greater than 100 mPa·s, meeting the industry standard for fracturing fluids.

[0082] Example 2 120 °C seawater-based fracturing fluid

[0083] 1. Preparation of organic phosphonic acid hydroxypropyl modified guar gum:

[0084] 100 g of guar gum powder is dispersed in 250 g of isopropanol, 28 g of propylene oxide and 100 g of 21% sodium hydroxide solution are added. Under the protection of N2 gas, at a pressure of 0.05 Mpa and a temperature of 62 °C, hydroxypropylation is carried out first for 3.5 h. After the reaction, the degree of substitution is 0.28, and it is washed and dried with 75% ethanol aqueous solution. Then 100 g of hydroxypropylated guar gum is dispersed in 200 g of isopropanol. 50 g of N-chloroaminoethyl diphosphonic acid and 100 g of 22% sodium hydroxide solution are added. Under the protection of N2 gas, at a pressure of 0.07 Mpa and a temperature of 65 °C, grafting reaction is carried out. After grafting, the degree of substitution of organic phosphonic acid is 0.27. After the reaction product is neutralized, it is washed and dried with 75% ethanol aqueous solution. 100-mesh maleic acid is dispersed in the modified guar gum to play a neutralizing role. The viscosity increasing rate of organic phosphonic acid hydroxypropyl modified guar gum in seawater within 3 minutes is 91%.

[0085] 2. Preparation of crosslinking agent:

[0086] 5 g of sodium borate decahydrate, 1 g of zirconium sulfate and 3 g of triethanolamine are dispersed in 60 g of water, then 2 g of 2-hydroxypropionic acid is added and stirred at 40 °C for 30 min, and then 29 g of 1.5% sodium hydroxide solution is added and stirred at 30 °C for 2 h to obtain the crosslinking agent.

[0087] 3. Temperature stabilizer: 5% pyridinium p-toluenesulfonate + 5% imidazoline + 90% water;

[0088] 4. pH regulator: 5.4 g of ammonium chloride + 35 mL of ammonia water are diluted to 93 mL of aqueous solution, then 7 mL of ethanolamine and a certain amount of water are added to make up to 100 mL.

[0089] 5. Demulsifying and drainage aid: 10% polyether type Pluronic PE6100 + 5% alkylphenol polyoxyethylene ether NP-10 + 5% fatty alcohol polyether B-28 + 10% ethanol + 70% water.

[0090] Fracturing fluid formulation components: 100 mL of 0.45% organic phosphonic acid hydroxypropyl modified guar gum aqueous solution + 0.5 mL of crosslinking agent + 0.1 mL of temperature stabilizer + 0.60 mL of pH regulator + 0.3 mL of demulsifying and drainage aid.

[0091] Through experimental detection: at a temperature of 120 °C and a -1 rotation speed of 100 s, the temperature and shear resistance performance is greater than 90 mPa·s, meeting the fracturing fluid industry standard.

[0092] Comparative Example 1

[0093] The difference between this comparative example and Example 1 is that the organic phosphonic acid hydroxypropyl modified guar gum is replaced by carboxymethylated guar gum.

[0094] 100 g of guar gum powder is dispersed in 250 g of isopropanol, 75 g of sodium chloroacetate and 100 g of 25% sodium hydroxide solution are added, and carboxymethylation is first carried out under the protection of N2 gas, at a pressure of 0.05 Mpa and a temperature of 62 °C for 3.5 h. After the reaction, the degree of substitution is 0.25. After the product is neutralized, it is washed with 75% ethanol aqueous solution and dried. 100-mesh maleic acid is dispersed in the carboxymethylated guar gum to play a neutralizing role. The viscosity increase rate of carboxymethylated guar gum in seawater is 65% in 3 minutes (slow viscosity increase rate).

[0095] Other components are the same as in Example 1.

[0096] Fracturing fluid formulation components: 100 mL of 0.55% carboxymethylated guar gum aqueous solution + 0.6 mL of crosslinking agent + 0.2 mL of temperature stabilizer + 1.3 mL of pH regulator + 0.7 mL of chelating agent (8% EDTA-disodium solution) + 0.4 mL of demulsifying and drainage aid.

[0097] Modified N-chloroaminoethyl diphosphonic acid guar gum is not used, and a relatively large amount of calcium and magnesium chelating agent (EDTA-disodium) is required. The calcium and magnesium chelating agent is acidic, and the dosage of the pH regulator used also increases.

[0098] At a temperature of 160 °C and a -1 rotation speed of 100 s, the temperature and shear resistance performance is greater than 100 mPa·s, meeting the fracturing fluid industry standard, but the viscosity increase rate of carboxymethylation is slow and the dosage of calcium and magnesium chelating agent is large.

[0099] Comparative Example 2

[0100] The difference between this comparative example and Example 2 is that the organic phosphonic acid hydroxypropyl modified guar gum is replaced by hydroxypropyl guar gum.

[0101] 100g guar gum powder was dispersed in 250g isopropanol, 28g propylene oxide and 100g 21% sodium hydroxide solution were added, and hydroxypropylation was first carried out under N2 gas protection, 0.05Mpa pressure, and 62°C. The degree of substitution after the reaction was 0.28. The reaction was carried out for 3.5h, and the mixture was washed with 75% ethanol aqueous solution and dried. 100 mesh maleic acid was dispersed in the modified guar gum to play a neutralizing role. The viscosity of hydroxypropyl guar gum in seawater was 73% in 3 minutes.

[0102] The other components are the same as in Example 2.

[0103] Fracturing fluid formula components: 100 mL of 0.45% hydroxypropyl modified guar gum aqueous solution + 0.5 mL of cross-linking agent + 0.1 mL of temperature stabilizer + 1.2 mL of pH regulator + 0.5 mL of chelating agent (8% EDTA-disodium solution) + 0.3 mL of demulsification and drainage agent.

[0104] 120℃, 100s -1 The temperature and shear resistance under the rotation speed condition is greater than 100mPa.s, which meets the industry standards of fracturing fluid, but the viscosity increase rate of hydroxypropyl guar gum is slow and the amount of calcium and magnesium chelating agent added is large.

[0105] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and essence of the claims of the present invention; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A seawater-based modified guar gum fracturing fluid, characterized in that, Comprising the following components by volume fraction: 100 parts of an aqueous solution of hydroxypropyl-modified guar gum with organic phosphonic acid; the aqueous solution of hydroxypropyl-modified guar gum with organic phosphonic acid is prepared by dissolving hydroxypropyl-modified guar gum with organic phosphonic acid in seawater, and the mass concentration of hydroxypropyl-modified hydroxyguar gum with organic phosphonic acid in seawater is 0.50%-0.65%; 0.1-0.3 parts of a temperature stabilizer; 0.4-1 part of a pH regulator; 0.3-0.5 part of a demulsification and drainage aid; 0.2-0.8 part of a crosslinking agent; 0-0.8 part of a calcium and magnesium chelating agent; Wherein the hydroxypropyl-modified guar gum with organic phosphonic acid is prepared by graft modification of guar gum powder through hydroxypropylation and a chelating agent; the graft-modified chelating agent is N-chloroaminoethyl diphosphonic acid; The crosslinking agent is prepared by a coordination reaction of a ligand and a salt containing a central ion.

2. The seawater-based modified guar gum fracturing fluid according to claim 1, wherein The hydroxypropyl-modified guar gum with organic phosphonic acid is prepared by the following method: (1) First, hydroxypropylate the guar gum powder, then wash and dry it to obtain hydroxypropylated guar gum; (2) Then graft the hydroxypropylated guar gum with a chelating agent, and then wash, dry and neutralize it.

3. The seawater-based modified guar gum fracturing fluid according to claim 2, wherein, Step (1) includes: dispersing the guar gum powder in a solvent, adding a catalyst, adding propylene oxide, controlling the reaction temperature and reaction time, after the reaction is completed, cooling the system to room temperature, and then washing and drying to obtain hydroxypropylated guar gum; Preferably, the dispersion solvent of the guar gum powder is isopropanol, which is 1-3 times the mass of the guar gum; Preferably, the catalyst is NaOH, and its addition amount is 17-25% of the mass of the guar gum, and it is added as an aqueous solution; Preferably, the addition amount of propylene oxide is 20-30% of the mass of the guar gum; Preferably, the reaction temperature is 50-70°C, and the reaction time is 2-5h; Preferably, the washing is carried out with an alcohol-water mixture, and the volume ratio of alcohol to water is 65:35-80:20; Preferably, the degree of substitution of hydroxypropyl in the hydroxypropylated guar gum is 0.25-0.

35.

4. The seawater-based modified guar gum fracturing fluid according to claim 2, wherein, Step (2) includes: dispersing the hydroxypropylated guar gum in a solvent, adding a catalyst, adding the graft-modified chelating agent N-chloroaminoethyl diphosphonic acid, controlling the reaction temperature and reaction time, after the reaction is completed, cooling the system to room temperature, and then washing, drying and neutralizing to obtain hydroxypropyl-modified guar gum with organic phosphonic acid; Preferably, the catalyst is NaOH, and its addition amount is 20-25% of the mass of the hydroxypropylated guar gum, and it is added as an aqueous solution; Preferably, the addition amount of N-chloroaminoethyl diphosphonic acid is 25-60% of the mass of the hydroxypropylated guar gum; Preferably, the reaction temperature is 60-75°C, and the reaction time is 2-3h; Preferably, the washing is carried out with an alcohol-water mixture, and the volume ratio of alcohol to water is 65:35-75:25; The degree of substitution of the organic phosphonic acid group after grafting is 0.20-0.

35.

5. The seawater-based modified guar gum fracturing fluid according to claim 1, wherein The temperature stabilizer is an aqueous solution selected from one or two of imidazoline and pyridinium p-toluenesulfonate.

6. The seawater-based modified guar gum fracturing fluid according to claim 1, wherein The pH regulator is prepared by compounding ammonia-ammonium chloride buffer solution and ethanolamine.

7. The seawater-based modified guar gum fracturing fluid according to claim 1, wherein The demulsification and drainage aid is prepared by compounding a non-ionic surfactant and a water-based non-ionic demulsifier; Preferably, the non-ionic surfactant is one or more selected from polyoxyethylene type A7N, alkylphenol polyoxyethylene ether NP-10, alkanolamide type 6502, and polyether type Pluronic PE6100; Preferably, the aqueous non-ionic demulsifier is fatty alcohol polyether B-28.

8. The seawater-based modified guar gum fracturing fluid according to claim 1, characterized in that, The crosslinking agent is prepared by the following method: Adding a ligand to a salt solution containing a central ion, adjusting the pH value by adding an alkaline solution under a certain temperature condition, and reacting after stirring to obtain the crosslinking agent; Preferably, the mass ratio of the ligand to the salt containing the central ion is 0.5-3; Preferably, the reaction temperature is 20-50 °C and the reaction time is 1-5 h.

9. The seawater-based modified guar gum fracturing fluid according to claim 8, wherein The ligand is one or several selected from triethanolamine, 2-hydroxypropanoic acid, and citric acid; Preferably, the salt containing the central ion is one or several selected from sodium borate decahydrate, sodium borate pentahydrate, sodium tetraborate, zirconium sulfate, zirconium acetate, and zirconium carbonate.

10. The preparation method of the seawater-based modified guar gum fracturing fluid according to any one of claims 1-9, characterized in that, It includes the following steps: (1) Preparation of an aqueous solution of organophosphonic acid hydroxypropyl modified guar gum: Adding organophosphonic acid hydroxypropyl modified guar gum to seawater to obtain an aqueous solution of organophosphonic acid hydroxypropyl modified guar gum; (2) Adding a temperature stabilizer, a pH regulator, a demulsification and drainage aid, a crosslinking agent, and an optional calcium and magnesium chelating agent to the aqueous solution of organophosphonic acid hydroxypropyl modified guar gum, and mixing evenly to obtain a seawater-based modified guar gum fracturing fluid.