Salt-resistant guar gum fracturing fluid crosslinker aqueous solution, and preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of petrochemical industry, and in particular to a salt-resistant guar gum fracturing fluid crosslinker aqueous solution, and a preparation method therefor and a use thereof. The salt-resistant guar gum fracturing fluid crosslinker aqueous solution comprises water and a salt-resistant guar gum fracturing fluid crosslinker. The salt-resistant guar gum fracturing fluid crosslinker is prepared by a flue gas desulfurization and denitrification product reacting with a complexone epoxy-alkyl borate ester, the flue gas desulfurization and denitrification product introduces a quaternary ammonium group into the crosslinker, the quaternary ammonium group and the complexone epoxy-alkyl borate ester group are linked by means of a short carbon chain, and the boron atom in the borate ester group is linked to the short carbon chain to form a boron-carbon bond. According to the salt-resistant guar gum fracturing fluid crosslinker aqueous solution provided by the present invention, when being added into a fracturing fluid, the complexone alkenyl borate ester in the salt-resistant guar gum fracturing fluid crosslinker is hydrolyzed in contact with an alkali to generate a complexone and a boric acid functional group, the complexone coordinates with magnesium ions in the reservoir to achieve the effect of mineralization resistance, and the boric acid group provides a delayed crosslinking effect.

Description

A salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution and its preparation method and application Technical Field

[0001] The invention relates to the technical field of petrochemical industry, in particular to a salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution and a preparation method and application thereof. Background Art

[0002] Fracturing technology is one of the essential and important measures for oil and gas field development. Fracturing fluid, as an important component of fracturing technology, is the key to the success of fracturing.

[0003] Most commonly used guar gum crosslinkers are composed of borates, including borax and organoboron. Organoboron contains numerous boric acid groups, which act as crosslinking agents with guar gum. Boron atoms are linked to oxygen and nitrogen atoms. While this increases the crosslinker's chain length, the boron-oxygen and boron-nitrogen bonds are susceptible to hydrolysis in the presence of heat, acid, and alkali, limiting their application in high-temperature reservoirs and acidic and alkaline conditions. Guar gum fracturing fluids commonly use inorganic salts such as KCl as anti-swelling agents, placing salt tolerance requirements on guar gum. To minimize reservoir damage, guar gum must be used in conjunction with a fungicide. Therefore, developing a salt-, heat-, and alkali-resistant guar gum fracturing fluid crosslinker that combines both anti-swelling and fungicide functions has become a critical issue.

[0004] Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution and its preparation method and application. The crosslinking agent is prepared by reacting a desulfurization and denitrification product with an aminocarboxylic acid complexing agent epoxy alkyl borate, and has good alkali stability and heat resistance. The aminocarboxylic acid complexing agent borate group in the crosslinking agent is hydrolyzed in the presence of alkali to form an aminocarboxylic acid complexing agent, which is coordinated with calcium and magnesium ions to achieve the effect of mineralization resistance. The desulfurization and denitrification product introduces a quaternary ammonium group into the crosslinking agent, and the nitrogen atom therein can serve as both an anti-swelling agent and a bactericide, thereby achieving a multi-purpose effect with one dose.

[0006] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0007] A salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution comprises water and a salt-resistant guar gum fracturing fluid crosslinking agent, wherein the salt-resistant guar gum fracturing fluid crosslinking agent is prepared by reacting a flue gas desulfurization and denitrification product with an aminocarboxyl complexing agent epoxyalkyl borate, wherein the flue gas desulfurization and denitrification product is used to introduce a quaternary ammonium group into the crosslinking agent, wherein the quaternary ammonium group and the aminocarboxyl complexing agent epoxyalkyl borate group are connected via a short carbon chain, and the boron atom in the borate group is connected to the short carbon chain to form a boron-carbon bond.

[0008] Specifically, the chemical formula of the salt-resistant guar gum fracturing fluid cross-linker is:

[0009] The present invention provides a salt-resistant guar gum fracturing fluid cross-linking agent aqueous solution. The aminocarboxylic acid complexing agent alkenyl borate in the salt-resistant guar gum fracturing fluid cross-linking agent, after being added to the fracturing fluid, is hydrolyzed in alkali to generate an aminocarboxylic acid complexing agent and a boric acid functional group. The aminocarboxylic acid complexing agent can coordinate with the magnesium ion in the reservoir to achieve the effect of mineralization resistance, and the boric acid group provides the cross-linking agent with a delayed cross-linking effect. The boron atom in the boric acid group is connected to the short carbon chain to form a boron-carbon bond, which has higher alkali stability and heat resistance than the boron-nitrogen bond and boron-oxygen bond in the existing commonly used boron-containing cross-linking agent. At the same time, the nitrogen atoms in the flue gas desulfurization and denitrification products enable the cross-linking agent to serve as both an anti-swelling agent and a bactericide, achieving a one-dose multi-purpose effect.

[0010] The present invention also provides a method for preparing the above-mentioned salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution, comprising the following steps:

[0011] S1. Treatment of the aminocarboxylic acid complexing agent alkenyl borate: The aminocarboxylic acid complexing agent alkenyl borate is added to a polar organic solvent, stirred and cooled to obtain a suspension, peracetic acid is added to the suspension, heated and stirred to obtain a mixture, the organic phase is separated, dried, filtered, concentrated in vacuo, and then purified by chromatography to obtain the desired crystalline solid, i.e., the aminocarboxylic acid complexing agent epoxyalkyl borate;

[0012] S2. The flue gas desulfurization and denitrification product was stirred and heated, and then the crystalline solid obtained in step S1 was added dropwise, deionized water was added, and the reaction was kept warm to obtain a salt-resistant guar gum fracturing fluid crosslinker aqueous solution;

[0013] The flue gas desulfurization and denitrification product is one of the following: sulfate of THEED (tetrahydroxyethylethylenediamine), nitrate of THEED, sulfate of bipy (4,4'-bipyridine) or nitrate of bipy;

[0014] The aminocarboxylic acid complexing agent alkenyl borate is allyl boric acid methyliminodiacetate;

[0015] The molar ratio of the flue gas desulfurization and denitrification product to the aminocarboxylic acid complexing agent epoxyalkyl borate is 1:2.

[0016] In the preparation method provided by the present invention, allylboronic acid methyliminodiacetate is first treated with peracetic acid, and the specific reaction formula is as follows:

[0017] The aminocarboxylic acid complexing agent in the alkenyl borate can be not only the above-mentioned methyliminodiacetic acid (MIDA), but also other commonly used aminocarboxylic acid complexing agents, such as sodium ferrocenylmethyliminodiacetic acid (FIDA), ethylenediaminetetraacetic acid (EDTA), propylenediaminetetraacetic acid (PDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraaminehexaacetic acid (TTHA) or other commonly used aminocarboxylic acid complexing agents.

[0018] Preferably, in step S1, the polar organic solvent is selected from dichloromethane. Further preferably, the ratio of the polar organic solvent to the aminocarboxylic acid complexing agent, alkenyl borate, is (15-25) mol:1 mol.

[0019] Preferably, in step S1, the suspension temperature is -10°C to 0°C;

[0020] The molar ratio of peracetic acid to aminocarboxylic acid complexing agent alkenyl borate is (3-4):1;

[0021] The heating and stirring specifically includes heating to 20° C. to 40° C. and stirring for 15 h to 20 h.

[0022] Further preferably, the suspension temperature is 0°C;

[0023] The molar ratio of peracetic acid to aminocarboxylic acid complexing agent alkenyl borate is 3:1;

[0024] The heating and stirring step specifically includes heating to 23° C. and stirring for 18 h.

[0025] Preferably, in step S1, the specific operation of separating the organic phase is as follows:

[0026] The mixture was poured into a separatory funnel containing sodium bicarbonate solution, diluted with ethyl acetate, and shaken to separate the aqueous phase and the organic phase. The aqueous phase was extracted and separated with ethyl acetate, and the organic phase was washed with sodium bicarbonate solution to obtain the product.

[0027] Preferably, in step S1, the stationary phase in the chromatography column is silica, and the solvent is a mixture of diethyl ether and acetonitrile in a volume ratio of 3:2.

[0028] Preferably, in step S2, the temperature is raised to 25°C to 50°C with stirring, and the insulation reaction time is 0.5h-3h;

[0029] More preferably, the temperature is raised to 35° C. with stirring and the reaction is kept at this temperature for 2 h.

[0030] Preferably, in step S2, the concentration of the prepared salt-resistant guar gum fracturing fluid crosslinker aqueous solution is 100 mg / L-700 mg / L, and more preferably 500 mg / L.

[0031] The present invention also provides an application of the above-mentioned salt-resistant guar gum fracturing fluid crosslinker aqueous solution or the salt-resistant guar gum fracturing fluid crosslinker aqueous solution prepared by the above-mentioned preparation method, wherein the salt-resistant guar gum fracturing fluid crosslinker aqueous solution is mixed with the guar gum fracturing fluid and injected into the formation, and the concentration of the salt-resistant guar gum fracturing fluid crosslinker in the salt-resistant guar gum fracturing fluid crosslinker aqueous solution is 100 mg / L-700 mg / L.

[0032] Preferably, the concentration of the salt-resistant guar gum fracturing fluid cross-linking agent in the salt-resistant guar gum fracturing fluid cross-linking agent aqueous solution is 500 mg / L.

[0033] Beneficial effects of the present invention:

[0034] 1. The invention provides a salt-resistant guar gum fracturing fluid crosslinker aqueous solution. After being added to the fracturing fluid, the aminocarboxylic acid complexing agent alkenyl borate is hydrolyzed in alkali to generate an aminocarboxylic acid complexing agent and a boric acid functional group. The aminocarboxylic acid complexing agent can coordinate with the magnesium ion in the reservoir to achieve the effect of mineralization resistance, and the boric acid group provides the crosslinker with a delayed crosslinking effect. The boron atom in the boric acid group is connected to the short carbon chain to form a boron-carbon bond, which has higher alkali stability and heat resistance than the boron-nitrogen bond and boron-oxygen bond in the existing commonly used boron-containing crosslinkers. At the same time, the nitrogen atom in the flue gas desulfurization and denitrification product introduces a quaternary ammonium group into the crosslinker, allowing the crosslinker to serve as both an anti-swelling agent and a bactericide, achieving a multi-purpose effect with one dose, avoiding the use of inorganic salt anti-swelling agents, and reducing the salt resistance requirements of the guar gum fracturing fluid.

[0035] 2. The raw materials of the present invention are flue gas desulfurization and denitrification products, which turns waste into treasure and effectively controls the manufacturing cost of the cross-linking agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 is a curve showing the relationship between the cross-linking agent concentration and the viscosity of guar gum in Experimental Example 2.

[0037] FIG2 is a curve showing the relationship between the pH value of the fracturing fluid system and the viscosity of guar gum in Experimental Example 3.

[0038] FIG3 is a curve showing the relationship between the temperature of the fracturing fluid system and the viscosity of guar gum in Experimental Example 4.

[0039] FIG4 is a curve showing the relationship between crosslinking time and guar gum viscosity in Experimental Example 5.

[0040] FIG5 is a relationship curve between shear time and guar gum viscosity in Experimental Example 6.

[0041] FIG6 is a curve showing the relationship between the salinity of the fracturing fluid system and the viscosity of guar gum in Experimental Example 7.

[0042] FIG7 is an infrared spectrum of the cross-linking agent in Example 2.

[0043] FIG8 is an infrared spectrum of the cross-linking agent in Example 4. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0045] It should be noted that the experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents, materials and equipment described are all commercially available unless otherwise specified.

[0046] 1. Anti-swelling rate test method: Determine the anti-swelling performance of the crosslinking agent according to SY / T 5971-2016 "Performance Evaluation Method of Clay Stabilizers for Oil and Gas Field Fracturing, Acidizing and Water Injection".

[0047] 2. Test method for bactericidal rate: The bactericidal performance of the crosslinker is obtained according to the performance evaluation method of oilfield bactericides in Q / SW 050-2020 "Oilfield Bactericides".

[0048] 3. Fracturing fluid performance evaluation: Determine the retarded crosslinking performance of organic amine boron crosslinked fracturing fluid according to SY / T 5107-2016 "Water-based fracturing fluid performance evaluation method".

[0049] Example 1:

[0050] A salt-resistant guar gum fracturing fluid crosslinker aqueous solution comprises water and a salt-resistant guar gum fracturing fluid crosslinker, wherein the salt-resistant guar gum fracturing fluid crosslinker is prepared by reacting THEED nitrate with allyl boric acid methyliminodiacetate, and has the following chemical formula:

[0051] The salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution is prepared by the following method:

[0052] S1. 1.00 mmol of allylboronic acid methyliminodiacetate and 20 mL of dichloromethane were placed in a 50 mL Schlenk flask equipped with a stirring bar, stirred to obtain a suspension, and then cooled to 0°C. 3 mmol of peracetic acid was added to the suspension, heated to 23°C, and stirred for 18 h to obtain a mixture. The mixture was poured into a separatory funnel containing 10 mL of 0.05 mol / L sodium bicarbonate solution, diluted with 40 mL of ethyl acetate, and shaken to separate the aqueous and organic phases. The aqueous phase was extracted and separated with 80 mL of ethyl acetate, and the remaining organic phase was washed with 5 mL of 0.05 mol / L sodium bicarbonate solution, dried over magnesium sulfate, filtered, and concentrated in vacuo. The mixture was then purified by flash chromatography on a silica column using a mixture of ether and acetonitrile in a volume ratio of 3:2 to obtain 147 mg of colorless crystalline solid of glycidylboronic acid methyliminodiacetate.

[0053] S2. Prepare an aqueous solution of 0.5 mmol THEED nitrate, stir and heat to 35°C, add the crystalline solid obtained in step S1, add 20 mL of deionized water dropwise, and react at 35°C for 2 hours to obtain a salt-resistant guar gum fracturing fluid crosslinker aqueous solution with a concentration of 500 mg / L.

[0054] In this embodiment, the reaction involved in step S2 is as follows:

[0055] Example 2:

[0056] A salt-resistant guar gum fracturing fluid crosslinker aqueous solution comprises water and a salt-resistant guar gum fracturing fluid crosslinker, wherein the salt-resistant guar gum fracturing fluid crosslinker is prepared by reacting THEED sulfate with allyl boric acid methyliminodiacetate, and has the same chemical formula as that of Example 1.

[0057] The salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution is prepared by the following method:

[0058] S1. 1.00 mmol of allylboronic acid methyliminodiacetate and 15 mL of dichloromethane were placed in a 50 mL Schlenk flask equipped with a stirring bar, stirred to obtain a suspension, and then cooled to -10°C. 4 mmol of peracetic acid was added to the suspension, heated to 20°C, and stirred for 20 h to obtain a mixture. The mixture was poured into a separatory funnel containing 10 mL of 0.05 mol / L sodium bicarbonate solution, diluted with 40 mL of ethyl acetate, and shaken to separate the aqueous and organic phases. The aqueous phase was extracted and separated with 80 mL of ethyl acetate, and the remaining organic phase was washed with 5 mL of 0.05 mol / L sodium bicarbonate solution, dried over magnesium sulfate, filtered, and concentrated in vacuo. The mixture was then purified by flash chromatography on a silica column using a mixture of ether and acetonitrile in a volume ratio of 3:2 to obtain 147 mg of colorless crystalline solid of glycidylboronic acid methyliminodiacetate.

[0059] S2. Prepare an aqueous solution of 0.5 mmol THEED sulfate, stir and heat to 25°C, add the crystalline solid obtained in step S1, add 20 mL of deionized water dropwise, and react at 25°C for 3 hours to obtain a salt-resistant guar gum fracturing fluid crosslinker aqueous solution with a concentration of 500 mg / L.

[0060] The infrared spectrum of the crosslinking agent is shown in Figure 7, where 2959 cm -1 The peak at 3067 cm corresponds to the boron-carbon bond between the borate ester group and the short carbon chain. -1 to 3079cm -1 The peak between 1304 cm and 1306 cm corresponds to the cyclic structure of the MIDA boronate group. -1 to 1461cm -1 The peaks in between correspond to the quaternary ammonium groups between the boron atoms.

[0061] Example 3:

[0062] A salt-resistant guar gum fracturing fluid crosslinker aqueous solution comprises water and a salt-resistant guar gum fracturing fluid crosslinker, wherein the salt-resistant guar gum fracturing fluid crosslinker is prepared by reacting bipy sulfate with allyl boric acid methyliminodiacetate, and has the following chemical formula:

[0063] The salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution is prepared by the following method:

[0064] S1. 1.00 mmol of allylboronic acid methyliminodiacetate and 20 mL of dichloromethane were placed in a 50 mL Schlenk flask equipped with a stirring bar, stirred to obtain a suspension, and then cooled to 0°C. 3 mmol of peracetic acid was added to the suspension, heated to 23°C, and stirred for 18 h to obtain a mixture. The mixture was poured into a separatory funnel containing 10 mL of 0.05 mol / L sodium bicarbonate solution, diluted with 40 mL of ethyl acetate, and shaken to separate the aqueous and organic phases. The aqueous phase was extracted and separated with 80 mL of ethyl acetate, and the remaining organic phase was washed with 5 mL of 0.05 mol / L sodium bicarbonate solution, dried over magnesium sulfate, filtered, and concentrated in vacuo. The mixture was then purified by flash chromatography on a silica chromatography column using a mixture of ether and acetonitrile in a volume ratio of 3:2 to obtain 147 mg of colorless crystalline solid of epoxypropylboronic acid methyliminodiacetate;

[0065] S2. Prepare 0.5 mmol Bipy sulfate into an aqueous solution, stir and heat to 35 ° C, add the crystalline solid obtained in step S1, add 20 mL of deionized water dropwise, and react at 35 ° C for 2 hours to obtain a salt-resistant guar gum fracturing fluid crosslinker aqueous solution with a concentration of 500 mg / L.

[0066] In this embodiment, the reaction involved in step S2 is as follows:

[0067] Example 4:

[0068] A salt-resistant guar gum fracturing fluid crosslinker aqueous solution comprises water and a salt-resistant guar gum fracturing fluid crosslinker, wherein the salt-resistant guar gum fracturing fluid crosslinker is prepared by reacting bipy nitrate with allyl boric acid methyliminodiacetate, and the chemical formula is the same as that of Example 2.

[0069] The salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution is prepared by the following method:

[0070] S1. 1.00 mmol of allylboronic acid methyliminodiacetate and 15 mL of dichloromethane were placed in a 50 mL Schlenk flask equipped with a stirring bar, stirred to obtain a suspension, and then cooled to -5°C. 3.5 mmol of peracetic acid was added to the suspension, heated to 40°C, and stirred for 15 h to obtain a mixture. The mixture was poured into a separatory funnel containing 10 mL of 0.05 mol / L sodium bicarbonate solution, diluted with 40 mL of ethyl acetate, and shaken to separate the aqueous and organic phases. The aqueous phase was extracted and separated with 80 mL of ethyl acetate, and the remaining organic phase was washed with 5 mL of 0.05 mol / L sodium bicarbonate solution, dried over magnesium sulfate, filtered, and concentrated in vacuo. The mixture was then purified by flash chromatography on a silica chromatography column using a mixture of ether and acetonitrile in a volume ratio of 3:2 to obtain 147 mg of colorless crystalline solid of epoxypropylboronic acid methyliminodiacetate;

[0071] S2. Prepare an aqueous solution of 0.5 mmol bipy nitrate, stir and heat to 50°C, add the crystalline solid obtained in step S1, add 20 mL of deionized water dropwise, and react at 50°C for 0.5 h to obtain a salt-resistant guar gum fracturing fluid crosslinker aqueous solution with a concentration of 500 mg / L.

[0072] The infrared spectrum of the crosslinking agent is shown in Figure 8, where 2928 cm -1 to 2989cm -1 The peak between 3016 cm corresponds to the boron-carbon bond between the borate ester group and the short carbon chain. -1 to 3027cm -1 The peak between 1494 cm and 1494 cm corresponds to the cyclic structure of the MIDA boronate group. -1 to 1635cm -1 The peaks in between correspond to the pyridine rings between the boron atoms.

[0073] Example 5:

[0074] As provided in any one of Examples 1 to 4, the salt-tolerant guar gum fracturing fluid crosslinking agent aqueous solution is used, and the salt-tolerant guar gum fracturing fluid crosslinking agent aqueous solution is mixed with the guar gum fracturing fluid and injected into the formation.

[0075] After the salt-resistant guar gum fracturing fluid crosslinker aqueous solution is mixed with the guar gum fracturing fluid, the salt-resistant guar gum fracturing fluid crosslinker is hydrolyzed in the presence of alkali to produce boric acid groups and MIDA. MIDA can chelate with calcium and magnesium ions in the formation to promote the right shift of the hydrolysis equilibrium, thereby better improving the fracturing fluid's resistance to mineralization and delayed crosslinking. The reaction formula is as follows:

[0076] Among them, formula (IV) is the reaction principle of the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution provided in Example 1 or Example 2, and formula (V) is the reaction principle of the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution provided in Example 3 or Example 4.

[0077] Experimental Example 1:

[0078] The salt-tolerant guar gum fracturing fluid crosslinker aqueous solutions prepared in Examples 2 and 4, as well as the crosslinker provided in "Synthesis and Application of Organic Amine Boron Crosslinker AB-1," were prepared into aqueous solutions and then crosslinked with guar gum. The pH of the crosslinker aqueous solutions and guar gum combined to form the fracturing fluid system was 12, the crosslinker aqueous solutions had a mass concentration of 500 mg / L, and the guar gum concentration was 5000 mg / L. The fracturing fluid system containing the crosslinker provided in "Synthesis and Application of Organic Amine Boron Crosslinker AB-1" also contained 4% KCl as an anti-swelling agent and 1% glutaraldehyde as a bactericide, as Comparative Example 1.

[0079] The anti-swelling rate and sterilization rate of the above fracturing fluid were measured, and the results are shown in Table 1:

[0080] Table 1 Anti-swelling rate and sterilization rate of each group

[0081] As can be seen from the table, Example 2 has a 33.8% higher sterilization rate and a 47.3% higher anti-swelling rate than Comparative Example 1. Example 4 has a 31.1% higher sterilization rate and a 43.6% higher anti-swelling rate than Comparative Example 1. The introduction of quaternary ammonium functional groups into the cross-linking agent effectively provides both anti-swelling and sterilization benefits, achieving a multi-purpose, cost-effective solution without the need for additional anti-swelling agents or bactericides. Furthermore, the salt tolerance and compatibility requirements of guar gum are reduced.

[0082] Experimental Example 2:

[0083] 1. Experimental purpose: To investigate the effect of cross-linker concentration on cross-linker performance.

[0084] 2. Experimental method: Based on Example 2, Example 4 and Comparative Example 1, the concentration of the cross-linking agent was changed, and the configuration method of the fracturing fluid system was the same as that of Example 2, Example 4 and Comparative Example 1 in the experimental examples.

[0085] III. Experimental Results: As shown in Figure 1, at a cross-linker concentration of 500 mg / L, the viscosity of the fracturing fluid increased significantly with concentration. The viscosity of the fracturing fluid in Example 2 was 43.9% higher than that in Comparative Example 1, and the viscosity of the fracturing fluid in Example 4 was 47.4% higher than that in Comparative Example 1. The longer molecular chains of the cross-linker in this invention enhance cross-linking. However, considering economic and field safety considerations, the cross-linker concentration is preferably 500 mg / L.

[0086] Experimental Example 3:

[0087] 1. Experimental purpose: To investigate the effect of pH value on the performance of cross-linking agent.

[0088] 2. Experimental method: Based on Example 2, Example 4 and Comparative Example 1, the pH value was changed and the configuration method of the fracturing fluid system was the same as that of Example 2, Example 4 and Comparative Example 1 in the experimental examples.

[0089] III. Experimental Results: As shown in Figure 2, the crosslinking agent in the present invention produces the highest viscosity fracturing fluid at pH 12. The viscosity decreases less with increasing pH than in Comparative Example 1, which produces the highest viscosity at pH 10. The carbon-nitrogen chains between boron atoms in the present invention are more resistant to alkaline hydrolysis than those in Comparative Example 1. The present invention can hydrolyze in a highly alkaline environment to produce boric acid groups that crosslink with guar gum, resulting in greater alkaline resistance. The optimal pH for crosslinking is 12.

[0090] Experimental Example 4:

[0091] 1. Experimental purpose: To investigate the effect of temperature on the performance of cross-linking agent.

[0092] 2. Experimental method: Based on Example 2, Example 4 and Comparative Example 1, the temperature was changed and the configuration method of the fracturing fluid system was the same as that of Example 2, Example 4 and Comparative Example 1 in the experimental examples.

[0093] III. Experimental Results: As shown in Figure 3, the viscosity of the fracturing fluid using the crosslinker of the present invention decreased less significantly than that of Comparative Example 1. The carbon-nitrogen bonds between the boron atoms in the present invention are more resistant to hydrolysis upon heating than those in Comparative Example 1. At temperatures above 70°C, the crosslinker hydrolyzes to produce a large number of boric acid groups that crosslink with guar gum, slowing the rate of viscosity decrease with temperature.

[0094] Experimental Example 5:

[0095] 1. Experimental purpose: To investigate the delayed cross-linking performance.

[0096] 2. Experimental method: Based on Example 2, Example 4 and Comparative Example 1, the concentration of guar gum at different cross-linking times was measured. The configuration method of the fracturing fluid system was the same as that of Example 2, Example 4 and Comparative Example 1 in the experimental examples.

[0097] III. Experimental Results: As shown in Figure 4, the viscosity of the fracturing fluid in Comparative Example 1 increased significantly from 20 minutes, reaching a maximum at 50 minutes. The viscosity of the fracturing fluid in the present invention increased significantly from 50 minutes, reaching a maximum at 80 minutes, a delay of 30 minutes compared to Comparative Example 1. The boron atoms in the crosslinker in the present invention are tightly complexed with MIDA, requiring a longer time to dissociate the boronic acid groups, thus achieving a better delayed crosslinking effect.

[0098] Experimental Example 6:

[0099] 1. Experimental purpose: To investigate the effect of shear time on the performance of crosslinking agent.

[0100] 2. Experimental method: Based on Example 2, Example 4 and Comparative Example 1, the concentration of guar gum at different shear times was measured. The configuration method of the fracturing fluid system was the same as that of Example 2, Example 4 and Comparative Example 1 in the experimental examples.

[0101] III. Experimental Results: As shown in Figure 5, after 50 minutes of shearing, the viscosity of Comparative Example 1 decreased to 62.5%, the viscosity of Example 2 decreased to 74.3%, and the viscosity of Example 4 decreased to 83.8%. This is because the presence of pyridine functional groups in the cross-linking agent prepared in Example 4 gives it stronger molecular rigidity, resulting in better shear resistance than that of Example 2 and a smaller decrease in the viscosity of the fracturing fluid system. Therefore, the cross-linking agent prepared in Example 4 is preferred.

[0102] Experimental Example 7:

[0103] 1. Experimental purpose: To investigate the effect of mineralization on the performance of cross-linking agent.

[0104] 2. Experimental method: Formation water was prepared according to the water quality of S oil field C-1. On the basis of Example 2, Example 4 and Comparative Example 1, the salinity of the solution was changed. The preparation method of the fracturing fluid system was the same as that of Example 2, Example 4 and Comparative Example 1 in the experimental example.

[0105] 3. Experimental results: As shown in Figure 6. When the salinity of the fracturing fluid system is less than 100 g / L, the viscosity of the fracturing fluid in Comparative Example 1 decreases with the salinity, while the viscosity of the fracturing fluid in the present invention increases with the salinity. MIDA produced by the hydrolysis of the cross-linking agent provided by the present invention chelates with calcium and magnesium ions, preventing them from affecting the performance of the fracturing fluid. When the concentration of calcium and magnesium ions is high, the hydrolysis equilibrium of the cross-linking agent shifts to the right, promoting the hydrolysis of the cross-linking agent to produce boric acid groups that cross-link with guar gum. Therefore, the fracturing fluid system configured with the cross-linking agent provided by the present invention has better salt tolerance.

Claims

1. A salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution, characterized in that: The invention comprises water and a salt-resistant guar fracturing fluid crosslinking agent, wherein the salt-resistant guar fracturing fluid crosslinking agent is prepared by reacting a flue gas desulfurization and denitration product with an aminocarboxylic acid complexing agent epoxy alkyl borate, the flue gas desulfurization and denitration product is used to introduce a quaternary ammonium group into the crosslinking agent, the quaternary ammonium group and the aminocarboxylic acid complexing agent epoxy alkyl borate group are connected through a short carbon chain, and the boron atom in the borate group is connected to the short carbon chain to form a boron-carbon bond, Specifically, the chemical formula of the salt-resistant guar gum fracturing fluid cross-linking agent is:

2. A method for preparing the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution as claimed in claim 1, characterized in that: The steps include: S1. Adding an aminocarboxylic acid complexing agent alkenyl borate into dichloromethane, stirring and cooling to obtain a suspension, adding peracetic acid to the suspension, heating and stirring to obtain a mixture, separating the organic phase, drying, filtering, and concentrating in vacuo, and purifying by a chromatography column to obtain the desired crystalline solid, i.e., an aminocarboxylic acid complexing agent epoxyalkyl borate; S2. The flue gas desulfurization and denitrification product is stirred and heated, and then the crystalline solid obtained in step S1 is added, deionized water is added dropwise, and the reaction is kept warm to obtain a salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution; The products of flue gas desulfurization and denitrification are sulfate of THEED, nitrate of THEED, sulfate of bipy or One of the nitrates; The aminocarboxylic acid complexing agent alkenyl borate is allyl boric acid methyliminodiacetate; The molar ratio of the flue gas desulfurization and denitrification product to the aminocarboxylic acid complexing agent epoxy alkyl borate is 1:

2.

3. The method for preparing the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution according to claim 2, characterized in that: In step S1, the ratio of dichloromethane to aminocarboxylic acid complexing agent alkenyl borate is (15-25) L:1 mol.

4. The method for preparing the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution according to claim 2, characterized in that: In step S1, the suspension temperature is -10°C to 0°C; The molar ratio of peracetic acid to aminocarboxylic acid complexing agent alkenyl borate is (3-4):1; The heating and stirring specifically includes heating to 20° C. to 40° C. and stirring for 15 h to 20 h.

5. The method for preparing the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution according to claim 2, characterized in that: In step S1, the specific operation of separating the organic phase is as follows: The mixture was poured into a separatory funnel containing a sodium bicarbonate solution, diluted with ethyl acetate, and shaken to separate the aqueous phase and the organic phase. The aqueous phase was extracted and separated with ethyl acetate, and the organic phase was washed with a sodium bicarbonate solution to obtain the product.

6. The method for preparing the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution according to claim 2, characterized in that: In step S1, the stationary phase in the chromatography column is silica, and the solvent is a mixture of diethyl ether and acetonitrile in a volume ratio of 3:

2.

7. The method for preparing the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution according to claim 2, characterized in that: In step S2, the temperature is raised to 25°C to 50°C with stirring, and the reaction time is kept at this temperature for 0.5h to 3h.

8. The method for preparing the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution according to claim 2, characterized in that: In step S2, the concentration of the prepared salt-resistant guar gum fracturing fluid cross-linking agent aqueous solution is 100 mg / L to 700 mg / L.

9. Use of the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution according to claim 1 or the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution prepared by the method for preparing the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution according to any one of claims 2 to 8, characterized in that: The salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution is mixed with the guar gum fracturing fluid and injected into the formation, and the concentration of the salt-resistant guar gum fracturing fluid crosslinking agent in the salt-resistant guar gum fracturing fluid crosslinking agent aqueous solution is 100 mg / L to 700 mg / L.

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