Cross-linking agent, preparation method thereof and fracturing fluid containing cross-linking agent

Abstract

The invention provides a cross-linking agent, a preparation method thereof and fracturing fluid containing the cross-linking agent. The cross-linking agent provided by the invention is a reaction product of boric acid glycol ester, a polyamine compound and a nonionic amphiphilic compound; wherein the structural formula of the nonionic amphiphilic compound is shown as a formula I: # imgabs0 #, in the formula I, d is an integer from 2 to 10, and e is an integer from 1 to 15. The fracturing fluid provided by the invention comprises the cross-linking agent, a thickening agent, a pH regulator and water, and has good high-temperature rheological property, the gel breaking fluid of the fracturing fluid obtained after gel breaking has good compatibility with gel breaking residual acid of cross-linked acid, and after the gel breaking fluid and the cross-linked acid are mixed, the fracturing fluid has an excellent thickened oil viscosity reduction effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield chemistry, and particularly relates to a crosslinking agent, a preparation method thereof, and a fracturing fluid containing the same. Background Art

[0002] Oil is currently the most widely used and most extensively applied energy source in the world, and its advantages in use and fundamental role are still irreplaceable in the coming period. Carbonate rock formations are widely distributed in China, with rich oil and gas reserves. Increasing the development of carbonate reservoirs can effectively ensure the supply of oil and gas resources. For the development of carbonate reservoirs, acid fracturing has unique advantages. It can not only connect natural fractures in the reservoir through fracturing, but also form acid-etched fractures, effectively improving reservoir heterogeneity and forming highly conductive fractures for oil and gas. Therefore, acidification technology has been widely applied in carbonate reservoirs and achieved good results.

[0003] Carbonate oilfields mainly consist of heavy oil and extra-heavy oil reservoirs. To improve the oil recovery rate, it is necessary to reduce the viscosity of crude oil by chemical methods, mainly including emulsion viscosity reduction and dilution viscosity reduction. Emulsion viscosity reduction is a method of reducing the viscosity of heavy oil by adding hydrophilic surfactants to form an oil-in-water emulsion. However, this method often has problems such as being only applicable to wellbore viscosity reduction and increasing the difficulty of treating produced fluids. Dilution viscosity reduction is a method of reducing the viscosity of heavy oil by mixing with light oil to reduce the concentration of resins and asphaltenes in the crude oil. However, this method often has problems such as limited viscosity reduction effect, large amount of light oil added, and high comprehensive cost. In addition, through acidification operations, the dehydration difficulty of acid-containing heavy oil produced fluids increases, and ordinary thermochemical processes alone cannot meet the process requirements. Therefore, higher requirements are put forward for fracturing fluids and acid fluids on-site. Existing technologies generally achieve heavy oil viscosity reduction by compounding with surfactants or microorganisms, but there are the following deficiencies: microorganisms have a narrow applicable temperature range, harsh growth conditions, a long cycle for producing surface active substances through microbial metabolism, and a narrow applicable heavy oil viscosity range for the products; surfactants have a large dosage, high cost, a small applicable heavy oil viscosity, and a large difficulty in treating produced fluids. Therefore, for the development of carbonate heavy oil reservoirs, existing acid fracturing working fluid systems often need to mix with light oil, add surfactants, etc. to achieve heavy oil viscosity reduction, which increases the construction cost and reduces the development efficiency. Summary of the Invention

[0004] One aspect of the present invention provides a crosslinking agent, which is a reaction product of ethylene glycol borate, a polyamine compound, and a nonionic amphiphilic compound; wherein, the structural formula of the nonionic amphiphilic compound is as shown in Formula I:

[0005]

[0006]

[0007] In Formula I, d is an integer from 2 to 10, and e is an integer from 1 to 15.

[0008] According to a specific embodiment of the present invention, in Formula I, d is an integer from 6 to 9 (such as 6, 8, 9), and e is an integer from 5 to 11 (such as 5, 8, 11).

[0009] According to a specific embodiment of the present invention, the mass ratio of the polyamine compound, ethylene glycol borate, and nonionic amphiphilic compound is 1:(0.1 - 10):(0.02 - 10);

[0010] Preferably, the mass ratio of the polyamine compound, ethylene glycol borate, and nonionic amphiphilic compound is 1:(0.5 - 5):(0.1 - 3.5);

[0011] More preferably, the mass ratio of the polyamine compound, ethylene glycol borate, and nonionic amphiphilic compound is 1:(1.25 - 2.5):(0.25 - 1).

[0012] According to a specific embodiment of the present invention, the polyamine compound is selected from at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, heptaethyleneoctamine, octaethylenenonamine, and polyethyleneimine;

[0013] Preferably, the polyamine compound is selected from at least one of pentaethylenehexamine, triethylenetetramine, hexaethyleneheptamine, tetraethylenepentamine, and polyethyleneimine.

[0014] The second aspect of the present invention provides a method for preparing the crosslinking agent as described in the first aspect of the present invention, which includes the following steps:

[0015] 1) React the polyamine compound and the ethylene glycol borate to obtain an intermediate product;

[0016] 2) React the intermediate product and the nonionic amphiphilic compound to obtain the crosslinking agent.

[0017] According to a specific embodiment of the present invention, the mass ratio of the polyamine compound, ethylene glycol borate, and nonionic amphiphilic compound is 1:(0.1 - 10):(0.02 - 10); and / or

[0018] The conditions for the first reaction are to react at 120 - 180 °C for 1 - 18 h; and / or

[0019] The conditions for the second reaction are to react at 30 - 80 °C for 2 - 24 h;

[0020] Preferably, the mass ratio of the polyamine compound, ethylene glycol borate and nonionic amphiphilic compound is 1:(0.5-5):(0.1-3.5); and / or

[0021] The conditions for the first reaction are to react at 135-170°C for 2-10 h; and / or

[0022] The conditions for the second reaction are to react at 30-65°C for 3-12 h;

[0023] Preferably, the mass ratio of the polyamine compound, ethylene glycol borate and nonionic amphiphilic compound is 1:(1.25-2.5):(0.25-1); and / or

[0024] The conditions for the first reaction are to react at 140-155°C for 3-6 h; and / or

[0025] The conditions for the second reaction are to react at 50-60°C for 6-8 h.

[0026] The third aspect of the present invention provides a fracturing fluid, which includes a crosslinking agent, a thickening agent, a pH regulator and water;

[0027] The crosslinking agent is the crosslinking agent described in the first aspect of the present invention or the crosslinking agent prepared by the method described in the second aspect of the present invention.

[0028] According to a specific embodiment of the present invention, the mass ratio of the thickening agent, crosslinking agent, pH regulator and water is 1:(0.2-3):(0.01-0.5):(20-500);

[0029] Preferably, the mass ratio of the thickening agent, crosslinking agent, pH regulator and water is 1:(0.35-1.8):(0.01-0.2):(50-500);

[0030] Preferably, the mass ratio of the thickening agent, crosslinking agent, pH regulator and water is 1:(0.6-1.13):(0.037-0.16):(100-160).

[0031] According to a specific embodiment of the present invention, the thickening agent is hydroxypropyl guar gum co-modified with a cationic modifier and a nonionic modifier; and / or

[0032] The molecular weight of the hydroxypropyl guar gum is 500,000-10,000,000;

[0033] Preferably, the cationic modifier and the nonionic modifier are compounds represented by Structural Formulas II and III in sequence;

[0034]

[0035] In Formula II, R1 and R2 are methyl, ethyl, propyl or benzyl, a is 5 - 17, and X is Cl or Br;

[0036]

[0037] In Formula III, b is 2 - 15 and c is 1 - 5;

[0038] Preferably, in Formula II, R1 and R2 are methyl, ethyl or benzyl, a is 11 - 15 (such as 11, 15), and X is Cl or Br;

[0039] Preferably, in Formula III, b is 6 - 12 (such as 6, 8, 12), and c is 1.5 - 4 (such as 1.5, 2, 4).

[0040] According to a specific embodiment of the present invention, the pH regulator is an inorganic base;

[0041] Preferably, the pH regulator is a hydroxide (preferably sodium hydroxide).

[0042] Application of any one of the crosslinking agent according to the first aspect of the present invention, the crosslinking agent prepared by the method according to the second aspect of the present invention, and the fracturing fluid according to the third aspect of the present invention in the development of carbonate rock heavy oil reservoirs, especially in acid fracturing.

[0043] The fourth aspect of the present invention provides a thickening agent, which is hydroxypropyl guar gum co - modified by a cationic modifier and a non - ionic modifier;

[0044] Preferably, the cationic modifier and the non - ionic modifier are compounds represented by Formula II and Formula III in sequence;

[0045]

[0046] In Formula II, R1 and R2 are methyl, ethyl, propyl or benzyl, a is 5 - 17, and X is Cl or Br;

[0047]

[0048] In Formula III, b is 2 - 15 and c is 1 - 5;

[0049] Preferably, in Formula II, R1 and R2 are methyl, ethyl or benzyl, a is 11 - 15 (such as 11, 15), and X is Cl or Br;

[0050] Preferably, in Formula III, b is 6 - 12 (such as 6, 8, 12), and c is 1.5 - 4 (such as 1.5, 2, 4).

[0051] According to a specific embodiment of the present invention, the mass ratio of the hydroxypropyl guar gum, the cationic modifier and the non-ionic modifier is 1:(0.005 - 5):(0.001 - 1);

[0052] Preferably, the mass ratio of the hydroxypropyl guar gum, the cationic modifier and the non-ionic modifier is 1:(0.03 - 2):(0.01 - 0.5);

[0053] Preferably, the mass ratio of the hydroxypropyl guar gum, the cationic modifier and the non-ionic modifier is 1:(0.2 - 0.9):(0.1 - 0.4).

[0054] The fifth aspect of the present invention provides a method for preparing the thickener as described in the fourth aspect of the present invention, which comprises the following steps:

[0055] A. Mix the hydroxypropyl guar gum, the organic solvent, water and the base to obtain a hydroxypropyl guar gum solution;

[0056] B. Carry out a third reaction on the cationic modifier, the anionic modifier and the hydroxypropyl guar gum solution to obtain the thickener.

[0057] According to a specific embodiment of the present invention, the mass ratio of the hydroxypropyl guar gum, the organic solvent, water and the base is 1:(1 - 100):(1 - 80):(0.001 - 0.1); and / or

[0058] the mass ratio of the hydroxypropyl guar gum, the cationic modifier and the non-ionic modifier is 1:(0.005 - 5):(0.001 - 1);

[0059] Preferably, the mass ratio of the hydroxypropyl guar gum, the organic solvent, water and the base is 1:(5 - 70):(4 - 30):(0.002 - 0.05); and / or

[0060] the mass ratio of the hydroxypropyl guar gum, the cationic modifier and the non-ionic modifier is 1:(0.03 - 2):(0.01 - 0.5);

[0061] Preferably, the mass ratio of the hydroxypropyl guar gum, the organic solvent, water and the base is 1:(10 - 20):(5 - 18):(0.01 - 0.03); and / or

[0062] the mass ratio of the hydroxypropyl guar gum, the cationic modifier and the non-ionic modifier is 1:(0.2 - 0.9):(0.1 - 0.4).

[0063] According to a specific embodiment of the present invention, the organic solvent is tetrahydrofuran; and / or

[0064] the base is a hydroxide (preferably sodium hydroxide).

[0065] According to a specific embodiment of the present invention, in step B, the reaction product obtained from the third reaction is filtered, dried, and pulverized to obtain the thickening agent.

[0066] According to a specific embodiment of the present invention, the conditions of the third reaction are to react at 40 - 80 °C for 1 - 24 h;

[0067] Preferably, the conditions of the third reaction are to react at 40 - 65 °C for 3 - 15 h;

[0068] Preferably, the conditions of the third reaction are to react at 50 - 60 °C for 4 - 5 h.

[0069] Application of the thickening agent according to the fourth aspect of the present invention or the thickening agent prepared by the method according to the fifth aspect of the present invention in the development of carbonate heavy oil reservoirs, especially in acid fracturing.

[0070] Advantages of the present invention:

[0071] Aiming at the problems of unsatisfactory viscosity reduction effect and high viscosity reduction cost of the existing viscosity reduction means in the acid fracturing of carbonate heavy oil reservoirs, the present invention provides a crosslinking agent, a preparation method thereof, and a fracturing fluid containing the same. Through the structural design and formulation design of the crosslinking agent and the fracturing fluid, the fracturing fluid prepared by the present invention has the following advantages:

[0072] 1. The fracturing fluid provided by the present invention has an apparent viscosity of 91 - 229 mPa·s after shearing for 90 min at 140 °C for 170 s. The relatively high apparent viscosity reflects that the fracturing fluid has good high-temperature rheological properties; -1 After shearing for 90 min, the apparent viscosity is 91 - 229 mPa·s, and the relatively high apparent viscosity reflects that the fracturing fluid has good high-temperature rheological properties;

[0073] 2. The compatibility between the gel-breaking fluid obtained after the gel-breaking of the fracturing fluid provided by the present invention and the gel-breaking residual acid of the crosslinked acid is good. After mixing the two, the viscosity reduction rates for No. 1 heavy oil and No. 2 heavy oil with viscosities of 28300 mPa·s and 51700 mPa·s at 50 °C are 90.6% - 98.8% and 92.1% - 99.2% respectively. The viscosity reduction rates are all above 90%, and the heavy oil viscosity reduction effect is excellent;

[0074] 3. The gel-breaking fluid obtained after the gel-breaking of the fracturing fluid provided by the present invention can achieve the heavy oil viscosity reduction effect only by mixing with the gel-breaking residual acid of the crosslinked acid generated after acid fracturing, making use of the organic components in the gel-breaking fluid. There is no need to additionally incorporate light oil, surfactant, etc., which is beneficial to reducing the cost of acid fracturing heavy oil viscosity reduction and is applicable to the acid fracturing application scenario of carbonate heavy oil reservoirs. Specific embodiments

[0075] The present invention will be further described below in conjunction with embodiments. However, the embodiments of the present invention are only exemplary descriptions, and this implementation manner does not constitute a limitation to the present invention under any circumstances.

[0076] Unless otherwise specified, the experimental methods used in the following experimental evaluations are all conventional methods.

[0077] The hydroxypropyl guar gum (HG-25) used in the following examples was purchased from Beijing Baofengchun Petroleum Technology Co., Ltd., and its molecular weight was 500,000 - 10,000,000.

[0078] The amphiphilic non-ionic compound used in the following examples was purchased from Jiangsu Haian Petrochemical Factory, the cationic modifier was purchased from Jiangsu Fumiao Technology Co., Ltd., and the non-ionic modifier was purchased from Jiangsu Haian Petrochemical Factory. Other materials, reagents, etc., unless otherwise specified, can be obtained from commercial channels.

[0079] The crosslinked acid agents used in the following experimental evaluations, including thickening agent (PEJ-3), crosslinking agent (PCA-1), corrosion inhibitor (PHT-2), corrosion inhibitor synergist (PHTA-2), high-temperature stabilizer (PTR), and iron ion stabilizer (PFAA), were all purchased from Puyang Lutong Petrochemical Co., Ltd. Other materials, reagents, etc., unless otherwise specified, can be obtained from commercial channels.

[0080] Preparation of crosslinking agent

[0081] Example 1

[0082] 1) Add 50 g of pentaethylenehexamine and 75 g of ethylene glycol borate to a three-necked glass bottle equipped with a stirrer, a condenser, and a thermometer, stir and mix evenly, control the temperature at 155 °C, and react for 3 h to obtain an intermediate product;

[0083] 2) Cool the temperature to 50 °C, add 25 g of amphiphilic non-ionic compound (in formula I, d = 6, e = 8) to the intermediate product obtained in step 1), and react for 8 h to obtain a crosslinking agent.

[0084] Example 2

[0085] Replace 50 g of pentaethylenehexamine in step 1) of Example 1 with a mixture of 30 g of triethylenetetramine and 30 g of hexaethyleneheptamine, and the others are the same as in Example 1 to obtain a crosslinking agent.

[0086] Example 3

[0087] Replace 50 g of pentaethylenehexamine in step 1) of Example 1 with a mixture of 20 g of tetraethylenepentamine and 30 g of polyethyleneimine, and the others are the same as in Example 1 to obtain a crosslinking agent.

[0088] Example 4

[0089] Adjust the addition amount of ethylene glycol borate in step 1) of Example 1 to 125 g, and keep other conditions the same as those in Example 1 to obtain a crosslinking agent.

[0090] Example 5

[0091] Replace 25 g of the nonionic amphiphilic compound (in formula Ⅰ, d = 6, e = 8) in step 2) of Example 1 with 50 g of the nonionic amphiphilic compound (in formula Ⅰ, d = 9, e = 5), and keep other conditions the same as those in Example 1 to obtain a crosslinking agent.

[0092] Example 6

[0093] Replace 25 g of the nonionic amphiphilic compound (in formula Ⅰ, d = 6, e = 8) in step 2) of Example 1 with 12.5 g of the nonionic amphiphilic compound (in formula Ⅰ, d = 8, e = 11), and keep other conditions the same as those in Example 1 to obtain a crosslinking agent.

[0094] Example 7

[0095] Adjust the reaction conditions in step 1) and step 2) of Example 1 to react at 140 °C for 6 h and at 60 °C for 6 h in sequence, and keep other conditions the same as those in Example 1 to obtain a crosslinking agent.

[0096] Preparation of fracturing fluid

[0097] Example 8

[0098] Preparation of thickening agent:

[0099] A. Add 50 g of hydroxypropyl guar gum HG-25, 500 g of tetrahydrofuran, 450 g of deionized water and 0.5 g of sodium hydroxide into a three-necked glass bottle equipped with a stirrer, a condenser and a thermometer, and stir at 40 °C for 30 min to obtain a hydroxypropyl guar gum solution;

[0100] B. Add 25 g of cationic modifier (in formula Ⅱ, R1, R2 are methyl groups, a = 11, X = Cl) and 10 g of nonionic modifier (in formula Ⅲ, b = 8, c = 2), control the temperature at 50 °C, react for 5 h, filter, dry and crush the product to obtain a thickening agent.

[0101] Preparation of fracturing fluid:

[0102] Add 5 g of the thickening agent prepared in this example, 3 g of the crosslinking agent prepared in Example 1 and 0.3 g of sodium hydroxide into 800 g of water, and dissolve them fully under stirring to obtain a fracturing fluid.

[0103] Example 9

[0104] Preparation of thickening agent:

[0105] Adjust the addition amount of tetrahydrofuran in step A of Example 8 to 1000 g, and keep other conditions the same as those in Example 8 to obtain a thickening agent.

[0106] Prepare a fracturing fluid:

[0107] Add 5 g of the thickening agent prepared in this example, 3 g of the crosslinking agent prepared in Example 1, and 0.3 g of sodium hydroxide to 800 g of water, and fully dissolve them under stirring to obtain a fracturing fluid.

[0108] Example 10

[0109] Prepare a thickening agent:

[0110] Adjust the addition amount of deionized water in step A of Example 8 to 900 g, and keep other conditions the same as those in Example 8 to obtain a thickening agent.

[0111] Prepare a fracturing fluid:

[0112] Add 5 g of the thickening agent prepared in this example, 3 g of the crosslinking agent prepared in Example 1, and 0.3 g of sodium hydroxide to 800 g of water, and fully dissolve them under stirring to obtain a fracturing fluid.

[0113] Example 11

[0114] Prepare a thickening agent:

[0115] Adjust the addition amount of deionized water in step A of Example 8 to 250 g, and keep other conditions the same as those in Example 8 to obtain a thickening agent.

[0116] Prepare a fracturing fluid:

[0117] Add 5 g of the thickening agent prepared in this example, 3 g of the crosslinking agent prepared in Example 1, and 0.3 g of sodium hydroxide to 800 g of water, and fully dissolve them under stirring to obtain a fracturing fluid.

[0118] Example 12

[0119] Prepare a thickening agent:

[0120] Adjust the addition amount of sodium hydroxide in step A of Example 8 to 1.5 g, and keep other conditions the same as those in Example 8 to obtain a thickening agent.

[0121] Prepare a fracturing fluid:

[0122] Add 5 g of the thickening agent prepared in this example, 3 g of the crosslinking agent prepared in Example 1, and 0.3 g of sodium hydroxide to 800 g of water, and fully dissolve them under stirring to obtain a fracturing fluid.

[0123] Example 13

[0124] Prepare a thickening agent:

[0125] Adjust the 25 g of cationic modifier in step B of Example 8 (in formula II, R1 and R2 are methyl groups, a is 11, and X is Cl) to 45 g of cationic modifier (in formula II, R1 and R2 are benzyl groups, a is 15, and X is Br), and keep other conditions the same as in Example 8 to obtain a thickening agent.

[0126] Prepare a fracturing fluid:

[0127] Add 5 g of the thickening agent prepared in this example, 3 g of the crosslinking agent prepared in Example 1, and 0.3 g of sodium hydroxide to 800 g of water, and dissolve them thoroughly under stirring to obtain a fracturing fluid.

[0128] Example 14

[0129] Prepare a thickening agent:

[0130] Adjust the 25 g of cationic modifier in step B of Example 8 (in formula II, R1 and R2 are methyl groups, a is 11, and X is Cl) to 10 g of cationic modifier (in formula II, R1 and R2 are ethyl groups, a is 11, and X is Cl), and keep other conditions the same as in Example 8 to obtain a thickening agent.

[0131] Prepare a fracturing fluid:

[0132] Add 5 g of the thickening agent prepared in this example, 3 g of the crosslinking agent prepared in Example 1, and 0.3 g of sodium hydroxide to 800 g of water, and dissolve them thoroughly under stirring to obtain a fracturing fluid.

[0133] Example 15

[0134] Prepare a thickening agent:

[0135] Adjust the 10 g of non-ionic modifier in step B of Example 8 (in formula III, b is 8 and c is 2) to 20 g of non-ionic modifier (in formula III, b is 12 and c is 1.5), and keep other conditions the same as in Example 8 to obtain a thickening agent.

[0136] Prepare a fracturing fluid:

[0137] Add 5 g of the thickening agent prepared in this example, 3 g of the crosslinking agent prepared in Example 1, and 0.3 g of sodium hydroxide to 800 g of water, and dissolve them thoroughly under stirring to obtain a fracturing fluid.

[0138] Example 16

[0139] Prepare a thickening agent:

[0140] Adjust the 10 g of non-ionic modifier in step B of Example 8 (in formula III, b is 8 and c is 2) to 5 g of non-ionic modifier (in formula III, b is 6 and c is 4), and keep other conditions the same as in Example 8 to obtain a thickening agent.

[0141] Prepare a fracturing fluid:

[0142] Add 5 g of the thickening agent prepared in this example, 3 g of the crosslinking agent prepared in Example 1, and 0.3 g of sodium hydroxide to 800 g of water, and fully dissolve them under stirring to obtain a fracturing fluid.

[0143] Example 17

[0144] Prepare a thickening agent:

[0145] Adjust the reaction temperature in Step B of Example 8 to 60 °C and the reaction time to 4 h. Keep other conditions the same as in Example 8 to obtain a thickening agent.

[0146] Prepare a fracturing fluid:

[0147] Add 5 g of the thickening agent prepared in this example, 3 g of the crosslinking agent prepared in Example 1, and 0.3 g of sodium hydroxide to 800 g of water, and fully dissolve them under stirring to obtain a fracturing fluid.

[0148] Example 18

[0149] Prepare a fracturing fluid:

[0150] Add 5 g of the thickening agent prepared in Example 8, 3 g of the crosslinking agent prepared in Example 2, and 0.3 g of sodium hydroxide to 800 g of water, and fully dissolve them under stirring to obtain a fracturing fluid.

[0151] Example 19

[0152] Prepare a fracturing fluid:

[0153] Add 5 g of the thickening agent prepared in Example 8, 3 g of the crosslinking agent prepared in Example 3, and 0.3 g of sodium hydroxide to 800 g of water, and fully dissolve them under stirring to obtain a fracturing fluid.

[0154] Example 20

[0155] Prepare a fracturing fluid:

[0156] Add 5 g of the thickening agent prepared in Example 8, 3 g of the crosslinking agent prepared in Example 4, and 0.3 g of sodium hydroxide to 800 g of water, and fully dissolve them under stirring to obtain a fracturing fluid.

[0157] Example 21

[0158] Prepare a fracturing fluid:

[0159] Add 5 g of the thickening agent prepared in Example 8, 3 g of the crosslinking agent prepared in Example 5, and 0.3 g of sodium hydroxide to 800 g of water, and fully dissolve them under stirring to obtain a fracturing fluid.

[0160] Example 22

[0161] Prepare a fracturing fluid:

[0162] Add 5 g of the thickening agent prepared in Example 8 of 5G, 3 g of the crosslinking agent prepared in Example 6, and 0.3 g of sodium hydroxide to 800 g of water, and dissolve them thoroughly with stirring to obtain a fracturing fluid.

[0163] Example 23

[0164] Prepare a fracturing fluid:

[0165] Add 5 g of the thickening agent prepared in Example 8 of 5G, 3 g of the crosslinking agent prepared in Example 7, and 0.3 g of sodium hydroxide to 800 g of water, and dissolve them thoroughly with stirring to obtain a fracturing fluid.

[0166] Example 24

[0167] Prepare a fracturing fluid:

[0168] Successively adjust the dosages of the thickening agent prepared in Example 8 used in Example 8 and the crosslinking agent prepared in Example 1 to 8 g and 9 g respectively, and keep other conditions the same as those in Example 8 to obtain a fracturing fluid.

[0169] Example 25

[0170] Prepare a fracturing fluid:

[0171] Successively adjust the dosages of the crosslinking agent prepared in Example 1 used in Example 8 and sodium hydroxide to 4.5 g and 0.8 g respectively, and keep other conditions the same as those in Example 8 to obtain a fracturing fluid.

[0172] Evaluation of the performance of the fracturing fluid

[0173] 1. Evaluation of the high-temperature rheological properties of the fracturing fluid

[0174] According to the provisions of SY / T 5107-2016 "Evaluation Method for the Performance of Water-Based Fracturing Fluids", shear for 90 min at 140 °C for 170 s -1 and then measure the apparent viscosity of the fracturing fluid.

[0175] 2. Evaluation of the viscosity reduction performance of the fracturing fluid for viscous oil

[0176] ⅰ Viscous oil samples for the test

[0177] Two dehydrated and degassed crude oils from a certain block in the Northwest Oilfield, numbered 1# viscous oil and 2# viscous oil;

[0178] The viscosity of 1# viscous oil measured by a rotary viscometer at 50 °C is 28,300 mPa·s;

[0179] The viscosity of 2# viscous oil measured by a rotary viscometer at 50 °C is 51,700 mPa·s;

[0180] ⅱ Preparation of the gelled fracturing fluid breaker

[0181] Weigh 1 g of sodium persulfate and add 500 g of the fracturing fluid prepared in any one of Examples 8 to 25 into a wide-mouth bottle. After stirring evenly, place it at 90 °C for aging. When the viscosity of the system is less than 5 mPa·s at 25 °C, stop aging to obtain the gelled fracturing fluid breaker fluid;

[0182] According to the steps in ii, use the fracturing fluids prepared in Examples 8 to 25 to prepare fracturing fluid breaker fluids -1 to -18 for standby respectively;

[0183] ⅲ Preparation of crosslinked acid breaker spent acid

[0184] (1) Crosslinked acid formula: 400 g of hydrochloric acid (20%), 8 g of thickening agent PEJ-3, 12 g of crosslinking agent PCA-1, 8 g of corrosion inhibitor PHT-2, 4 g of corrosion inhibitor synergist PHTA-2, 10 g of high-temperature stabilizer PTR, 6 g of iron ion stabilizer PFAA, and 1 g of breaker ammonium persulfate;

[0185] (2) Preparation of crosslinked acid breaker spent acid: Weigh 500 g of the crosslinked acid in (1), add it to a wide-mouth bottle, then add an appropriate amount of calcium carbonate blocks to the crosslinked acid, and place it at 90 °C for aging. When the viscosity of the system is less than 5 mPa·s and the pH is greater than 3 at 25 °C, stop aging, filter and collect the filtrate to obtain the crosslinked acid breaker spent acid for standby;

[0186] ⅳ Determination of viscosity reduction rate of heavy oil

[0187] a. Prepare an oil-water mixture: Weigh 100 g of any one of the fracturing fluid breaker fluids from fracturing fluid breaker fluid -1 to -18, 100 g of crosslinked acid breaker spent acid, and 200 g of heavy oil 1# or heavy oil 2# and mix them to obtain an oil-water mixture;

[0188] b. Stir at 50 °C and 500 rpm for 15 min, and measure the viscosity of the oil-water mixture by a rotational rheometer. The viscosity reduction rate is calculated according to the following formula.

[0189]

[0190] In the formula, VR—viscosity reduction rate (%),

[0191] μ o —viscosity of heavy oil (mPa·s),

[0192] μ m —viscosity of the oil-water mixture (mPa·s).

[0193] The evaluation results of the high-temperature rheological properties and heavy oil viscosity reduction properties of the fracturing fluid are shown in Table 1.

[0194] Table 1. Evaluation results of high-temperature rheological properties and heavy oil viscosity reduction properties of fracturing fluid

[0195] Example Apparent viscosity (mPa·s) Viscosity reduction rate of heavy oil 1# (%) Viscosity reduction rate of heavy oil 2# (%) Example 8 125 93.6 95.3 Example 9 109 94.7 95.9 Example 10 138 93.2 94.9 Example 11 120 94.1 95.6 Example 12 102 95.0 96.5 Example 13 91 96.8 97.4 Example 14 153 90.6 93.0 Example 15 114 95.4 96.1 Example 16 146 92.5 94.0 Example 17 118 94.3 95.8 Example 18 145 93.2 94.9 Example 19 138 93.1 94.0 Example 20 156 90.7 92.1 Example 21 121 95.1 97.1 Example 22 133 92.7 94.5 Example 23 119 94.0 95.6 Example 24 229 98.8 99.2 Example 25 150 94.1 95.7

[0196] As can be seen from Table 1, the fracturing fluid further prepared from the crosslinking agent provided by the present invention still has a relatively high apparent viscosity after being sheared for 90 min at 140 °C for 170 s -1 indicating that it has good shear resistance at high temperatures not higher than 140 °C and good high-temperature rheological properties. In addition, after the gel-breaking fluid of the fracturing fluid further prepared from the crosslinking agent provided by the present invention is mixed with the gel-breaking residual acid of the crosslinked acid further prepared from the crosslinked acid, the viscosity reduction rates of the No. 1 heavy oil and the No. 2 heavy oil are both above 90%, and the highest can reach 99.2%, showing excellent heavy oil viscosity reduction effect. It is proved that the fracturing fluid further prepared from the crosslinking agent provided by the present invention has the characteristics of good salt and acid resistance of the gel-breaking fluid of the fracturing fluid, good compatibility with the gel-breaking residual acid of the crosslinked acid, and good heavy oil viscosity reduction of the mixed liquid of the gel-breaking fluid of the fracturing fluid and the gel-breaking residual acid of the crosslinked acid, and can meet the integrated requirements of acid fracturing and viscosity reduction in carbonate rock reservoirs.

[0197] Although the present invention has been described with reference to specific embodiments, those skilled in the art should understand that various changes can be made without departing from the true spirit and scope of the present invention. In addition, various changes can be made to the subject matter, spirit and scope of the present invention to adapt to specific situations, materials, material compositions and methods. All such changes are included within the scope of the claims of the present invention.

Claims

1. A crosslinking agent which is a reaction product of ethylene glycol borate, a polyamine compound and a nonionic amphiphilic compound; wherein, The structural formula of the nonionic amphiphilic compound is shown in Formula I: In Formula I, d is an integer from 2 to 10, and e is an integer from 1 to 15.

2. The crosslinking agent according to claim 1, wherein The mass ratio of the polyamine compound, ethylene glycol borate and nonionic amphiphilic compound is 1:(0.1 - 10):(0.02 - 10); Preferably, the mass ratio of the polyamine compound, ethylene glycol borate and nonionic amphiphilic compound is 1:(0.5 - 5):(0.1 - 3.5).

3. The crosslinking agent according to claim 1 or 2, characterized in that, The polyamine compound is selected from at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, heptaethyleneoctamine, octaethylenenonamine, and polyethyleneimine.

4. A method for preparing the crosslinking agent according to any one of claims 1 to 3, which comprises the following steps: 1) Subject the polyamine compound and the ethylene glycol borate to a first reaction to obtain an intermediate product; 2) Subject the intermediate product and the nonionic amphiphilic compound to a second reaction to obtain the crosslinking agent.

5. The method according to claim 4, wherein The mass ratio of the polyamine compound, ethylene glycol borate and nonionic amphiphilic compound is 1:(0.1 - 10):(0.02 - 10); and / or The conditions for the first reaction are to react at 120 - 180 °C for 1 - 18 h; and / or The conditions for the second reaction are to react at 30 - 80 °C for 2 - 24 h; Preferably, the mass ratio of the polyamine compound, ethylene glycol borate and nonionic amphiphilic compound is 1:(0.5 - 5):(0.1 - 3.5).

6. A fracturing fluid, which comprises a crosslinking agent, a thickening agent, a pH regulator and water; The crosslinking agent is the crosslinking agent according to any one of claims 1 to 3 or the crosslinking agent prepared by the method according to claim 4 or 5.

7. The fracturing fluid according to claim 6, wherein, The mass ratio of the thickening agent, crosslinking agent, pH regulator and water is 1:(0.2 - 3):(0.01 - 0.5):(20 - 500); Preferably, the mass ratio of the thickening agent, crosslinking agent, pH regulator and water is 1:(0.35 - 1.8):(0.01 - 0.2):(50 - 500).

8. The fracturing fluid according to claim 6 or 7, characterized in that, The thickening agent is hydroxypropyl guar gum co-modified by a cationic modifier and a nonionic modifier; and / or The molecular weight of the hydroxypropyl guar gum is 500,000 - 10,000,000; Preferably, the cationic modifier and the nonionic modifier are compounds shown in Formula II and Formula III respectively; In Formula II, R1 and R2 are methyl, ethyl, propyl or benzyl, a is 5 - 17, and X is Cl or Br; In Formula III, b is 2 - 15 and c is 1 - 5.

9. The fracturing fluid according to any one of claims 6 to 8, characterized in that, The pH regulator is an inorganic base; Preferably, the pH regulator is a hydroxide.

10. Use of any one of the crosslinking agent according to any one of claims 1 to 3, the crosslinking agent prepared by the method according to claim 4 or 5, and the fracturing fluid according to any one of claims 6 to 9 in the development of carbonate heavy oil reservoirs, especially in acid fracturing.

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