Double-carboxyl double-hydroxyl guar gum thickening agent as well as preparation method and application thereof

Abstract

The invention provides a double-carboxyl double-hydroxyl guar gum thickening agent and a preparation method and application thereof.The thickening agent is of a structure shown in the formula I. The preparation method comprises the steps that guar gum, an alkaline solution and a dispersing solvent are mixed to be subjected to an alkalization reaction under the protective atmosphere, an alkalization product is obtained, and under the protective atmosphere, the alkalization product is subjected to a reaction to obtain the double-carboxyl double-hydroxyl guar gum thickening agent. The alkalization product is mixed with a first etherifying agent solution and a second etherifying agent solution for an etherification reaction, the dicarboxyl dihydroxy guar gum thickening agent is obtained, the first etherifying agent is sodium chloromalonate or sodium chlorosuccinate, and the second etherifying agent is glycidol and / or 3-chloropropanediol. By introducing dicarboxyl and dihydroxyl functional groups, the quick dissolving property of the modified guar gum is improved, the crosslinking strength between the modified guar gum and the crosslinking agent is enhanced, the use concentration of the guar gum in the acidic fracturing fluid is effectively reduced, and the temperature resistance and shear resistance of the acidic guar gum fracturing fluid are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thickeners for oil and gas reservoir fracturing and stimulation, and relates to a dicarboxyl dihydroxy guar gum thickener, its preparation method and application, and particularly relates to a dicarboxyl dihydroxy guar gum thickener for an acidic fracturing fluid system, its preparation method and application. Background Art

[0002] Acidic fracturing fluid is one of the important stimulation measures for reforming carbonate rock (including limestone, dolomite, dolomitic limestone, etc.) reservoirs. The acidic environment can effectively inhibit the swelling and migration caused by the negative charge on the clay surface, reduce the damage to the reservoir, and is of great significance for the continuous stimulation of oil and gas field development.

[0003] For the guar gum acidic fracturing fluid in the prior art, the authorized invention patents protect the fracturing fluid system and the crosslinking agent, and the thickeners in the acidic fracturing fluid are all conventional carboxymethyl hydroxypropyl guar gum. For example, CN102102014B discloses a carboxymethyl hydroxypropyl guar gum acidic fracturing fluid composed of water, carboxymethyl hydroxypropyl guar gum, CJ-2 temperature-resistant enhancer, surfactant, COP-SH clay stabilizer and JL-12 crosslinking agent; CN102329606B discloses a crosslinking agent for carboxymethyl guar gum acidic fracturing fluid and its preparation method; CN111943990B discloses an organic aluminum zirconium boron crosslinking agent in an acidic guar gum fracturing fluid.

[0004] The existing acidic guar gum fracturing fluid system using carboxymethyl hydroxypropyl guar gum has low crosslinking strength, poor temperature resistance of the formed fracturing fluid, and the problem of large consumption of guar gum. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a dicarboxyl dihydroxy guar gum thickener, its preparation method and application, and particularly provide a dicarboxyl dihydroxy guar gum thickener for an acidic fracturing fluid system, its preparation method and application. The present invention improves the rapid dissolution performance of the modified guar gum by introducing dicarboxyl and dihydroxy functional groups, enhances the crosslinking strength between the modified guar gum and the crosslinking agent, effectively reduces the use concentration of guar gum in the acidic fracturing fluid, and improves the temperature and shear resistance of the acidic guar gum fracturing fluid.

[0006] To achieve the purpose of the present invention, the following technical solutions are adopted:

[0007] On the one hand, the present invention provides a dicarboxyl dihydroxy guar gum thickener for an acidic fracturing fluid system, and the thickener has the structure shown in Formula I:

[0008]

[0009] Wherein, R is H, R 1 is an alkyl group of C1-C4, m is an integer of 1-3, n is an integer of 400-10000 (such as 400, 450, 480, 500, 550, 580, 600, 650, 700, 750, 800, 900, 950 or 1000), and * represents the connection site of the group.

[0010] In the present invention, the C1-C4 alkyl group can be a C1, C2, C3 or C4 alkyl group, and can be, for example, a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, etc.

[0011] m is an integer of 1-3, and can be, for example, 1, 2 or 3.

[0012] Preferably, the weight-average molecular weight of the dicarboxy dihydroxy guar gum thickener used in the acidic fracturing fluid system is 200,000-5,000,000, such as 200,000, 300,000, 400,000, 500,000, 800,000, 1,000,000, 1,300,000, 1,500,000, 1,800,000, 2,000,000, 2,300,000, 2,500,000, 2,800,000, 3,000,000, 3,300,000, 3,500,000, 3,800,000, 4,000,000, 4,500,000, 4,800,000 or 5,000,000, and is preferably 1,500,000-2,500,000.

[0013] Preferably, the dicarboxy substitution degree in the dicarboxy dihydroxy guar gum thickener used in the acidic fracturing fluid system is 0.01-3.0, such as 0.01, 0.05, 0.08, 0.1, 0.5, 0.8, 1.3, 1.6, 2.4 or 3.0, and more preferably 0.1-2.0.

[0014] Preferably, the dihydroxy substitution degree in the dicarboxy dihydroxy guar gum thickener used in the acidic fracturing fluid system is 0.01-3.0, such as 0.01, 0.05, 0.08, 0.1, 0.5, 0.8, 1.3, 1.6, 2.4 or 3.0, and more preferably 0.1-2.0.

[0015] On the other hand, the present invention provides the dicarboxy dihydroxy guar gum thickener used in the acidic fracturing fluid system as described above, and the preparation method includes the following steps:

[0016] (1) Under a protective atmosphere, mix guar gum, an alkaline solution and a dispersion solvent for an alkalization reaction to obtain an alkalized product;

[0017] (2) Under a protective atmosphere, mix the alkalized product with a first etherifying agent solution and a second etherifying agent solution for an etherification reaction to obtain the dicarboxy dihydroxy guar gum thickener used in the acidic fracturing fluid system, wherein the first etherifying agent is sodium chloromalonate or sodium chlorobutanedioate, and the second etherifying agent is glycidol and / or 3-chloropropanediol.

[0018] In the present invention, there is no limitation on the sequence of the etherification reaction of the first etherifying agent and the second etherifying agent.

[0019] Preferably, the protective atmosphere in steps (1) and (2) is preferably nitrogen.

[0020] Preferably, the alkaline solution in step (1) includes one or a combination of at least two of an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, and an aqueous tetramethylammonium hydroxide solution.

[0021] In the present invention, the mass concentration of the alkaline solution in step (1) is preferably 2% to 30%, such as 2%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, or 30%.

[0022] In the present invention, the mass ratio of the alkaline solution to guar gum in step (1) is preferably 0.05 to 5:1, such as 0.05:1, 0.08:1, 0.1:1, 0.3:1, 0.5:1, 0.8:1, 1:1, 1.5:1, 1.8:1, 2:1, 2.5:1, 2.8:1, 3:1, 3.5:1, 3.8:1, 4:1, 4.3:1, 4.5:1, 4.8:1, or 5:1.

[0023] Preferably, the dispersion solvent in step (1) includes one or a combination of at least two of water, ethanol, acetone, isopropanol, or dioxane.

[0024] In the present invention, the mass ratio of the dispersion solvent to guar gum in step (1) is preferably 0.2 to 15:1, such as 0.2:1, 0.5:1, 0.8:1, 1:1, 1.3:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, or 15:1.

[0025] In the present invention, the time for the alkalization reaction in step (1) is 0.2 to 2 h, such as 0.2 h, 0.5 h, 0.8 h, 1 h, 1.3 h, 1.5 h, 1.8 h, or 2 h, and the reaction temperature is room temperature.

[0026] In the present invention, the first etherifying agent in step (2) is sodium chloropropanedioate or sodium chlorobutanedioate, and more preferably sodium chloropropanedioate.

[0027] In the present invention, the solvent in the first etherifying agent solution and the second etherifying agent solution includes one or a combination of at least two of water, ethanol, isopropanol, or acetone.

[0028] In the present invention, the mass concentration of the first etherifying agent solution and the second etherifying agent solution is preferably 5% to 100%, such as 5%, 8%, 10%, 15%, 20%, 25%, 28%, 30%, 35%, 40%, 45%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%.

[0029] In the present invention, the mass ratio of the first etherifying agent in the first etherifying agent solution to guar gum is preferably 0.02 to 2.0:1, such as 0.02:1, 0.05:1, 0.08:1, 0.1:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1 or 2.0:1.

[0030] In the present invention, the mass ratio of the second etherifying agent in the second etherifying agent solution to guar gum is preferably 0.05 to 4.0:1, such as 0.05:1, 0.08:1, 0.1:1, 0.5:1, 1:1, 1.5:1, 1.8:1, 2:1, 2.3:1, 2.5:1, 2.8:1, 3.0:1, 3.3:1, 3.5:1, 3.8:1, 4.0:1.

[0031] In the present invention, the temperature of the etherification reaction is preferably 30 to 100 °C, such as 30 °C, 40 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C or 100 °C, more preferably 55 to 90 °C, and the time is preferably 0.5 to 6.0 h, such as 0.5 h, 0.8 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4.0 h, 4.5 h, 5.0 h, 5.5 h or 6.0 h.

[0032] In the present invention, the addition method of the first etherifying agent solution and the second etherifying agent solution is preferably batch addition or simultaneous addition after mixing the two, and more preferably batch addition.

[0033] In the present invention, after the etherification reaction, it further includes adjusting the pH value of the obtained etherification reaction product to 6.0 to 8.5, such as 6.0, 6.2, 6.5, 6.8, 7.0, 7.3, 7.5, 7.8 or 8.0.

[0034] In the present invention, the neutralizing agent used to adjust the pH value to 6.0 to 8.5 preferably includes one or a combination of at least two of acetic acid, carbon dioxide, phosphoric acid, citric acid or polyphosphoric acid.

[0035] Preferably, after adjusting the pH value to 6.0 to 8.5, it further includes washing, drying, pulverizing and sieving in sequence to obtain the dicarboxy dihydroxy guar gum thickener.

[0036] In the present invention, the solvent used for washing preferably includes one or a combination of at least two of water, ethanol, acetone, isopropanol or dioxane.

[0037] The present invention has no special limitation on the specific methods of drying, pulverizing and screening, and the methods well-known to those skilled in the art can be adopted.

[0038] On the other hand, the present invention provides an application of the dicarboxyl dihydroxy guar gum thickener for the acidic fracturing fluid system as described above in the guar gum acidic fracturing fluid system.

[0039] Preferably, the guar gum acidic fracturing fluid system includes a dicarboxyl dihydroxy guar gum thickener, an acidic crosslinking agent, a clay stabilizer, a flowback aid and water. The acidic crosslinking agent is the crosslinking agent for fracturing, organometallic salt JK08 of Kunshan Jingkun Oilfield Chemical Company, and the clay stabilizer and the flowback aid are conventional products on the market.

[0040] Preferably, the mass percentage content of the dicarboxyl dihydroxy guar gum thickener is 0.1 - 0.8%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% or 0.8%.

[0041] Preferably, the mass concentration of the acidic crosslinking agent is 0.20% - 0.65%, such as 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60% or 0.65%.

[0042] Preferably, the mass percentage content of the clay stabilizer is 0.1 - 0.5%, such as 0.1%, 0.2%, 0.3%, 0.4% or 0.5%, and the mass percentage content of the flowback aid is 0.1 - 0.5%, such as 0.1%, 0.2%, 0.3%, 0.4% or 0.5%.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] By introducing dicarboxyl and dihydroxy functional groups, the present invention improves the rapid dissolution performance of the modified guar gum, enhances the crosslinking strength between the modified guar gum and the crosslinking agent, effectively reduces the use concentration of the guar gum in the acidic fracturing fluid, and improves the temperature and shear resistance of the acidic guar gum fracturing fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 1H-NMR spectrum of the sample prepared in Example 1; 1 1H-NMR spectrum;

[0046] Figure 2It is a result graph of the rheological property test of the acidic fracturing fluid system prepared in Example 3 at 120 °C;

[0047] Figure 3 It is a result graph of the rheological property test of the acidic fracturing fluid system prepared in Comparative Example 1 at 120 °C. Detailed implementation manners

[0048] The technical solutions of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the described embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0049] Example 1

[0050] Add 100 parts of guar gum powder, 300 parts of ethanol and 70 parts of 25% sodium hydroxide aqueous solution by mass concentration to the reaction kettle, purge with nitrogen to remove oxygen, carry out alkalization reaction for 30 minutes, heat to raise the material temperature to 80 °C, add 30 parts of 30% sodium chloromalonate aqueous solution by mass concentration, react for 60 minutes, add 60 parts of 3-chloropropanediol with a mass concentration of 75%, continue to react at 80 °C for 120 minutes, after the reaction is completed, cool to below 35 °C, carry out neutralization reaction with 10 parts of 10% acetic acid solution to adjust the pH value between 6.5 and 7.5, after the material is centrifuged to remove the solvent, wash it twice with 80% ethanol, 200 parts each time, and the washed material is dried by air flow and ultrafinely pulverized to obtain the finished product, denoted as Sample No. 1. Figure 1 It is the 1H-NMR spectrum obtained by hydrolyzing Sample No. 1 with trifluoroacetic acid. For Sample No. 1, DS (degree of double carboxyl substitution) = 0.11, DS (degree of double hydroxyl substitution) = 0.48.

[0051] Example 2

[0052] Add 100 parts of guar gum powder, 350 parts of ethanol and 100 parts of 20% sodium hydroxide aqueous solution by mass concentration to the reaction kettle, purge with nitrogen to remove oxygen, carry out alkalization reaction for 30 minutes, heat to raise the material temperature to 85 °C, add 20 parts of 30% sodium chloromalonate aqueous solution by mass concentration, react for 60 minutes, add 40 parts of glycidol with a mass concentration of 75%, continue to react at 80 °C for 120 minutes, after the reaction is completed, cool to below 35 °C, carry out neutralization reaction with 10 parts of 10% acetic acid solution to adjust the pH value between 6.5 and 7.5, after the material is centrifuged to remove the solvent, wash it twice with 80% ethanol, 200 parts each time, and the washed material is dried by air flow and ultrafinely pulverized to obtain the finished product, denoted as Sample No. 2. For Sample No. 2, DS (degree of double carboxyl substitution) = 0.06, DS (degree of double hydroxyl substitution) = 0.35.

[0053] Example 3

[0054] Add 100 parts of guar gum powder, 350 parts of ethanol, and 120 parts of an aqueous sodium hydroxide solution with a mass concentration of 30% to the reaction kettle. Purge with nitrogen to remove oxygen, and carry out the alkalization reaction for 30 minutes. Heat to raise the temperature of the material to 85 °C, add 100 parts of an aqueous sodium chloromalonate solution with a mass concentration of 30%, react for 60 minutes, add 5 parts of glycidol with a mass concentration of 75%, and continue the reaction at 80 °C for 120 minutes. After the reaction is completed, cool to below 35 °C, and carry out a neutralization reaction with 10 parts of a 10% acetic acid solution to adjust the pH value between 6.5 and 7.5. After the material is centrifuged to remove the solvent, wash it twice with 80% ethanol, with a dosage of 200 parts each time. The washed material is dried by air flow and ultrafinely pulverized to obtain the finished product, denoted as Sample No. 3. For Sample No. 3, DS (double carboxyl substitution degree) = 2.95, and DS (double hydroxyl substitution degree) = 0.08.

[0055] Example 4

[0056] Add 100 parts of guar gum powder, 350 parts of ethanol, and 120 parts of an aqueous sodium hydroxide solution with a mass concentration of 30% to the reaction kettle. Purge with nitrogen to remove oxygen, and carry out the alkalization reaction for 30 minutes. Heat to raise the temperature of the material to 85 °C, add 40 parts of an aqueous sodium chloromalonate solution with a mass concentration of 30%, react for 60 minutes, add 300 parts of glycidol with a mass concentration of 75%, and continue the reaction at 80 °C for 120 minutes. After the reaction is completed, cool to below 35 °C, and carry out a neutralization reaction with 10 parts of a 10% acetic acid solution to adjust the pH value between 6.5 and 7.5. After the material is centrifuged to remove the solvent, wash it twice with 80% ethanol, with a dosage of 200 parts each time. The washed material is dried by air flow and ultrafinely pulverized to obtain the finished product, denoted as Sample No. 2. For Sample No. 4, DS (double carboxyl substitution degree) = 0.11, and DS (double hydroxyl substitution degree) = 2.90.

[0057] Comparative Example 1

[0058] Add 100 parts of guar gum powder, 300 parts of ethanol, and 70 parts of an aqueous sodium hydroxide solution with a mass concentration of 25% to the reaction kettle. Purge with nitrogen to remove oxygen, and carry out the alkalization reaction for 30 minutes. Heat to raise the temperature of the material to 80 °C, add 30 parts of an aqueous sodium chloromalonate solution with a mass concentration of 30%, continue the reaction at 80 °C for 180 minutes. After the reaction is completed, cool to below 35 °C, and carry out a neutralization reaction with 10 parts of a 10% acetic acid solution to adjust the pH value between 6.5 and 7.5. After the material is centrifuged to remove the solvent, wash it twice with 80% ethanol, with a dosage of 200 parts each time. The washed material is dried by air flow and ultrafinely pulverized to obtain the finished product, denoted as Sample No. 5. For Sample No. 5, DS (double carboxyl substitution degree) = 0.13.

[0059] Comparative Example 2

[0060] 100 parts of guar gum powder, 300 parts of ethanol and 70 parts of 25% sodium hydroxide aqueous solution were added to a reactor, nitrogen was passed through to deoxidize, alkalization reaction was carried out for 30 minutes, the material temperature was heated to 80°C, 60 parts of 75% 3-chloropropanediol were added, the temperature was continued to react for 180 minutes at 80°C, the temperature was lowered to below 35°C after the reaction, 10 parts of 10% acetic acid solution were used for neutralization reaction to adjust the pH value between 6.5 and 7.5, the material was centrifuged to remove the solvent, and then washed twice with 80% ethanol, each time with 200 parts, and the washed material was dried by air flow and ultrafinely pulverized to obtain a finished product, which was recorded as sample No. 6. Sample No. 6 DS (dihydroxyl substitution degree) = 0.46.

[0061] Performance Testing

[0062] 400 mL of tap water was measured and poured into a stirring cup (Wu Yin mixer or similar products), and the stirring speed was adjusted until the liquid formed a vortex and the top of the stirring shaft could be seen. 1.60 g of the modified guar gum prepared in Examples 1-4 and Comparative Examples 1-2 were weighed respectively, slowly added to the stirring cup, and continued to stir for 3 minutes. The viscosity at 3 minutes was measured and recorded as η 1 Pour the prepared base liquid into a beaker, cover it and place it in a constant temperature water bath at 25℃±1℃ for 4 hours, then measure its viscosity, which is recorded as η 2 . Thickening rate γ = η 1 / η 2 *100%.

[0063] The test results are shown in Table 1. The introduction of dihydroxyl groups is beneficial to improving the solubility of modified guar gum. As the degree of dihydroxyl substitution increases, the viscosity increase rate gradually increases.

[0064] Table 1

[0065] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Viscosity increasing rate 95％ 94％ 90％ 97％ 87％ 93％

[0066] Application Examples

[0067] In this application example, an acidic fracturing fluid system is provided, which includes a dicarboxylic dihydroxy guar gum thickener, an acidic cross-linking agent, a clay stabilizer, a drainage aid and water.

[0068] Measure 400 mL of tap water and pour it into a stirring cup (Wu Yin mixer or similar products), and adjust the stirrer speed until the liquid forms a vortex and the top of the stirrer axis can be seen. Weigh 1.60 g of the modified guar gum prepared in Example 1 and Comparative Examples 1-2 respectively, slowly add them to the stirring cup, then add 1.2 mL of drainage agent and 1.2 mL of clay stabilizer, and continue stirring for 3 minutes. Pour the prepared base liquid into a beaker, cover it, and keep it in a constant temperature water bath at 25°C ± 1°C for 4 hours.

[0069] Take 100 mL of the above base fluid, adjust the pH value of the base fluid to 5.0 with acetic acid, add 0.40 mL of the acidic crosslinking agent for fracturing, i.e., the organometallic salt JK08, and stir. The crosslinking performance results are shown in Table 2.

[0070] Table 2

[0071] Example 1 Comparative Example 1 Comparative Example 2 Crosslinking performance Can be picked up with a glass rod Can be picked up with a glass rod Cannot be picked up

[0072] Perform the temperature and shear resistance performance test on the acidic fracturing fluid system prepared from the modified guar gum of Example 1 at 120 °C. The results are as Figure 2 shown. Perform the rheological property test on the acidic fracturing fluid system prepared from Comparative Example 1 at 120 °C. The results are as Figure 3 shown. By comparison Figures 2 - 3 it can be seen that the gel formed by using 0.40% of the dicarboxyl guar gum base fluid and the crosslinking agent has a gel viscosity lower than 50 mPa·s after shearing for 97 min at 120 °C under the condition of 170 s -1 ; while the gel formed by using 0.40% of the dicarboxyl and dihydroxy guar gum base fluid of the present invention and the crosslinking agent still has a gel viscosity higher than 100 mPa·s after shearing for 120 min at 120 °C under the condition of 170 s -1 . The synergistic effect of dicarboxyl and dihydroxy enhances the crosslinking strength between the modified guar gum and the crosslinking agent. At a lower concentration of guar gum dosage, it can effectively crosslink to form a gel, which has better temperature and shear resistance.

[0073] The applicant declares that the present invention uses the above embodiments to illustrate the dicarboxyl and dihydroxy guar gum thickener of the present invention, its preparation method and application, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of the raw materials selected by the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A double-carboxyl and double-hydroxyl guar gum thickener for an acidic fracturing fluid system, characterized in that, the thickener has the structure shown in Formula I: wherein, R is H, R 1 is an alkyl group having 1 to 4 carbon atoms, m is an integer of 1 to 3, n is an integer of 400 to 10000, and * represents the connection site of the group.

2. The double-carboxyl and double-hydroxyl guar gum thickener for an acidic fracturing fluid system according to claim 1, characterized in that, the weight-average molecular weight of the double-carboxyl and double-hydroxyl guar gum thickener for an acidic fracturing fluid system is 200,000 to 5,000,000, preferably 1,500,000 to 2,500,000.

3. The double-carboxyl and double-hydroxyl guar gum thickener for an acidic fracturing fluid system according to claim 1 or 2, characterized in that, In the dicarboxyl and dihydroxy guar gum thickener for the acid fracturing fluid system, the dicarboxyl has a degree of substitution of 0.01 to 3.0, preferably 0.1 to 2.

0.

4. The double-carboxyl and double-hydroxyl guar gum thickener for an acidic fracturing fluid system according to any one of claims 1-3, characterized in that, The dihydroxy group in the dicarboxyl and dihydroxy guar gum thickener for the acid fracturing fluid system has a degree of substitution of 0.01 to 3.0, preferably 0.1 to 2.

0.

5. The preparation method of the double-carboxyl and double-hydroxyl guar gum thickener for an acidic fracturing fluid system according to any one of claims 1-4, characterized in that, the preparation method includes the following steps: (1) Under a protective atmosphere, mix guar gum, an alkaline solution and a dispersion solvent for an alkalization reaction to obtain an alkalized product; (2) Under a protective atmosphere, mix the alkalized product with a first etherifying agent solution and a second etherifying agent solution for an etherification reaction to obtain the double-carboxyl and double-hydroxyl guar gum thickener for an acidic fracturing fluid system, the first etherifying agent is sodium chloropropanedioate or sodium chlorobutanedioate, and the second etherifying agent is glycidol and / or 3-chloropropanediol.

6. The preparation method according to claim 5, characterized in that, the protective atmosphere in step (1) and step (2) is preferably nitrogen; Preferably, the alkaline solution in step (1) includes one or a combination of at least two of an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution and an aqueous tetramethylammonium hydroxide solution; Preferably, the mass concentration of the alkaline solution in step (1) is 2% to 30%; Preferably, the mass ratio of the alkaline solution to guar gum in step (1) is 0.05 to 5:

1.

7. The preparation method according to claim 5 or 6, characterized in that, the dispersion solvent in step (1) includes one or a combination of at least two of water, ethanol, acetone, isopropanol or dioxane; Preferably, the mass ratio of the dispersion solvent to guar gum in step (1) is preferably 0.2 to 15:1; Preferably, the time of the alkalization reaction in step (1) is 0.2 to 2 h, and the reaction temperature is room temperature.

8. The preparation method according to any one of claims 5-7, characterized in that, the first etherifying agent in step (2) is sodium chloropropanedioate; Preferably, the solvent in the first etherifying agent solution and the second etherifying agent solution includes one or a combination of at least two of water, ethanol, isopropanol or acetone; Preferably, the mass concentration of the first etherifying agent solution and the second etherifying agent solution is preferably 5% to 100%; Preferably, the mass ratio of the first etherifying agent in the first etherifying agent solution to guar gum is preferably 0.02 to 2.0:1; Preferably, the mass ratio of the second etherifying agent in the second etherifying agent solution to guar gum is preferably 0.05 to 4.0:1; Preferably, the temperature of the etherification reaction is preferably 30 to 100 °C, more preferably 55 to 90 °C, and the reaction time is 0.5 to 6.0 h.

9. The preparation method according to any one of claims 5-8, characterized in that the addition method of the first etherifying agent solution and the second etherifying agent solution is preferably batch addition or simultaneous addition after mixing the two, more preferably batch addition; Preferably, after the etherification reaction, it further includes adjusting the pH value of the obtained etherification reaction product to 6.0 to 8.5; Preferably, the neutralizing agent used to adjust the pH value to 6.0 to 8.5 preferably includes one or a combination of at least two of acetic acid, carbon dioxide, phosphoric acid, citric acid or polyphosphoric acid; Preferably, after the pH value is adjusted to 6.0 to 8.5, it further includes washing, drying, pulverizing and sieving in sequence to obtain the dicarboxyl dihydroxy guar gum thickener; Preferably, the solvent used for washing preferably includes one or a combination of at least two of water, ethanol, acetone, isopropanol or dioxane.

10. The application of the dicarboxyl dihydroxy guar gum thickener for acid fracturing fluid system according to any one of claims 1-4 in the guar gum acid fracturing fluid system; Preferably, the guar gum acid fracturing fluid system includes the dicarboxyl dihydroxy guar gum thickener, acid crosslinking agent, clay stabilizer, flowback aid and water of claims 1-4. Preferably, the mass percentage content of the dicarboxyl dihydroxy guar gum thickener in the guar gum acid fracturing fluid system is 0.1 to 0.8%, the mass percentage content of the acid crosslinking agent is 0.1 to 1%, the mass percentage content of the clay stabilizer is 0.1 to 0.5%, and the mass percentage content of the flowback aid is 0.1 to 0.5%.

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