Composite fracturing fluid and preparation method thereof

Abstract

The present application relates to the technical field of fracturing fluid, and specifically discloses a composite fracturing fluid and a preparation method thereof. A preparation method of a composite fracturing fluid comprises the following steps: 1) amino-modifying nano-silicon dioxide to obtain amino-modified nano-silicon dioxide; 2) reacting amino-modified nano-silicon dioxide with a polyethylene glycol derivative to obtain a precursor; 3) mixing guar gum, precursor, and water evenly to obtain a base fluid, and then adding glycerol glucoside, micro-nano metal powder, organic base, and cross-linking agent, and mixing evenly to obtain a composite fracturing fluid. The composite fracturing fluid prepared in the present application has the advantages of temperature resistance, salt resistance, and good sand carrying performance.

Description

Technical Field

[0001] The present application relates to the technical field of fracturing fluid, and more specifically, to a composite fracturing fluid and a preparation method thereof. Background Art

[0002] With the continuous increase in global energy demand and the improvement of environmental protection awareness, the oil and gas extraction industry has an increasing demand for more efficient and environmentally friendly fracturing technology. Clean fracturing fluid, as an environmentally friendly fracturing fluid, has gradually gained attention in oil and gas field exploitation, and the research and application of clean fracturing fluid has also continued to develop and mature.

[0003] Compared with traditional fracturing fluid, clean fracturing fluid has poor salt and temperature resistance, high material cost, and large formation filtration loss. In response to this, technicians have attracted widespread attention by adding nanoparticles to improve the performance of fracturing fluid. After introducing nanoparticles into the fracturing fluid, the cross-linking between the nanoparticles and the fracturing fluid and the synergistic effect between the surfactants can form a reversibly cross-linked stable structure between the solution micelles, thereby improving the viscosity and temperature resistance of the fracturing fluid system to a certain extent.

[0004] For example, a Chinese patent application document with application publication number CN110527504A discloses a nano-composite displacement fracturing fluid, comprising the following components in parts by weight: 0.25-0.5 parts of a dissolving agent, 1-1.6 parts of an emulsion thickener, 0.4-0.8 parts of a cross-linking agent, 0.2-0.25 parts of a nano-displacing agent, and the remainder of liquid water, wherein the nano-displacing agent is a nano-scale multi-component synthetic additive, and the nano-displacing agent comprises an organic solvent, a surfactant, a polybasic organic acid, a strong oxidant, a corrosion inhibitor, an iron ion stabilizer, a clay stabilizer, a chelating agent, and a slag inhibitor, and the obtained fracturing fluid has good temperature and shear resistance.

[0005] Another example is a Chinese patent application document with application publication number CN109097019A, which discloses a nanoparticle composite high-temperature guar gum fracturing fluid, which is composed of a base fluid and a cross-linking agent, wherein the base fluid is composed of the following components by mass percentage: a thickener, water-soluble nanoparticles, a clay stabilizer, a surfactant, a temperature stabilizer, and the rest is water. Nanoparticles are used to enhance the network structure of the fracturing fluid, thereby improving its temperature resistance and shear resistance.

[0006] At present, with the complexity and diversity of oil and gas reservoir environments, the challenges faced by traditional nanoparticle-modified fracturing fluids are gradually emerging. For example, fracturing construction in high-temperature and high-salt areas often requires fracturing fluids to have stronger temperature and salt resistance. Therefore, how to improve the performance of nano-composite fracturing fluids is a technical problem that still needs to be solved. Summary of the invention

[0007] In order to further improve the temperature and salt resistance of the nanocomposite fracturing fluid, the present application provides a composite fracturing fluid and a preparation method thereof.

[0008] In a first aspect, the present application provides a method for preparing a composite fracturing fluid, which adopts the following technical solution:

[0009] A method for preparing a composite fracturing fluid comprises the following steps:

[0010] 1) Amino-modified nano-silica to obtain amino-modified nano-silica;

[0011] 2) reacting the amino-modified nano-silica with a polyethylene glycol derivative to obtain a precursor;

[0012] 3) Take guar gum, precursor material and water and mix them evenly to obtain base fluid, then add glycerol glucoside, micro-nano metal powder, organic base and cross-linking agent, mix them evenly to obtain composite fracturing fluid.

[0013] Preferably, in the step 1), the amino modification of the nano-silica is: firstly modifying the surface of the nano-silica with hydroxyl groups, and then reacting the surface hydroxyl-modified nano-silica with a silane coupling agent to obtain amino-modified nano-silica;

[0014] And / or, in step 1), the average particle size of the nano-silicon dioxide is 10-50 μm;

[0015] And / or, in the step 1), the particle size distribution of nano-silicon dioxide is: the particle size range of [10-30) μm accounts for 30-50%, and the particle size range of [30-50] μm accounts for 50-70%.

[0016] Preferably, the polyethylene glycol derivative is one of polyethylene glycol monomethyl ether, carboxyl-terminated polyethylene glycol, and amino-terminated polyethylene glycol;

[0017] And / or, in the step 2), the mass ratio of amino-modified nano-silica to polyethylene glycol derivative is 1:0.15-0.35;

[0018] And / or, in the step 2), reacting the amino-modified nano-silica with the polyethylene glycol derivative comprises the following steps: first dispersing the amino-modified nano-silica and the polyethylene glycol derivative in anhydrous ethanol, then adding triethylamine, reacting under the protection of an inert gas, washing with anhydrous ethanol after the reaction, and drying to obtain the product.

[0019] Preferably, in step 3), the mass ratio of the guar gum, the precursor, and the water is 3-3.5:2-5:1000;

[0020] And / or, in step 3), the guar gum is one of hydroxypropyl guar gum, carboxymethyl hydroxypropyl guar gum, and sulfonic acid hydroxypropyl guar gum;

[0021] And / or, in step 3), the content of micro-nano metal powder in the composite fracturing fluid is 0.01-0.025wt%;

[0022] And / or, in step 3), the average particle size of the micro-nano metal powder is 150-300 nm;

[0023] And / or, in step 3), the organic base is one of triethylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide;

[0024] And / or, in the step 3), the crosslinking agent is one of an organic boron crosslinking agent, an organic zirconium crosslinking agent, and an organic boron-zirconium composite crosslinking agent.

[0025] Preferably, in step 3), the micro-nano metal powder is prepared by the following steps:

[0026] S1: grinding the metal raw powder and sodium tetraborate at a low speed and dispersing them in anhydrous ethanol to prepare a feed liquid;

[0027] S2: slowly add a mixed solution of carrageenan and urea into the feed liquid, stir, freeze-dry, crush and grind to obtain.

[0028] Preferably, the metal raw powder is one or more of iron powder, aluminum powder, copper powder, zinc powder, nickel powder and gallium powder.

[0029] Preferably, the metal raw powder is composed of aluminum powder and gallium powder in a mass ratio of 1:0.05-0.1.

[0030] Preferably, in step S1, the mass ratio of the metal raw powder to sodium tetraborate is 1:0.05-0.1.

[0031] Preferably, in step S2, the mass ratio of the feed liquid, carrageenan and urea is 1:0.2-0.3:0.1-0.15.

[0032] In a second aspect, the present application provides a composite fracturing fluid, which is prepared by the above-mentioned preparation method and has good temperature and salt resistance.

[0033] In summary, this application has the following beneficial effects:

[0034] 1. The present application uses a precursor material and guar gum to form an inorganic-organic hybrid crosslinking system. First, the inorganic particles of the precursor material are used to enhance the interfacial compatibility and improve the crosslinking strength. Secondly, the crosslinking network of guar gum itself is used to provide flexibility and self-repairing performance. Then, the two work together effectively to greatly improve the temperature and salt resistance of the fracturing fluid. In addition, the precursor material of the present application is prepared by reacting amino-modified silica with a polyethylene glycol derivative, which can form branched grafts on the surface of nano-silica, thereby entangled with the molecular chains of the guar gum network system, and obtain better sand carrying performance and temperature and salt resistance.

[0035] 2. In the preparation process of the precursor material of the present application, nano-silica of different particle size ranges is used, so that the nano-silica of large and small particle sizes are evenly distributed in the cross-linked system. Compared with inorganic particles of uniform particle size, these particles of different sizes can form a number of sites with different creeping resistance in the cross-linked system, which is beneficial to the relative movement between the molecular chains of the cross-linked system, reduces the adverse effects of various environments on the system during the fracturing construction process, and can improve the sand carrying, temperature and salt resistance of the fracturing fluid.

[0036] 3. Based on the hybrid system of precursor and guar gum, the present application also introduces micro-nano metal powders. These micro-nano metal powders can form uniform anchoring sites in the cross-linking system. In the early stage of cross-linking, these anchoring sites only play a physical stabilizing role. As time goes by, the sodium tetraborate and carrageenan on the surface of the metal raw powder will gradually be released into the fracturing fluid. On the one hand, the metal surface has high activity and can form a complex with a large number of hydroxyl groups in the guar gum system to further stabilize the cross-linking system; on the other hand, the sodium tetraborate and carrageenan released into the fracturing fluid will undergo secondary auxiliary cross-linking, thereby further improving the comprehensive performance of the fracturing fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a test data chart of the temperature and salt resistance of the composite fracturing fluid of Example 3 and Comparative Example 1 of the present application.

[0038] Figure 2 It is the SEM picture of nano-silicon dioxide of Example 1 and Example 2 of the present application.

[0039] Figure 3 It is a TEM image of the composite fracturing fluid of Examples 1-3 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0040] The present application is further described in detail below with reference to the embodiments.

[0041] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0042] The inventors of this application have conducted a large number of experiments and have found that by constructing an inorganic-organic hybrid crosslinking system within the guar gum crosslinking system, the sand carrying performance and temperature and salt resistance of the fracturing fluid have been greatly improved. In addition, the solid phase damage of the fracturing fluid after demulsification is relatively small, making it suitable for high-salt and high-temperature fracturing operations.

[0043] The present application provides a method for preparing a composite fracturing fluid, comprising the following steps:

[0044] 1) Amino-modified nano-silica to obtain amino-modified nano-silica;

[0045] 2) reacting the amino-modified nano-silica with a polyethylene glycol derivative to obtain a precursor;

[0046] 3) Take guar gum, precursor material and water and mix them evenly to obtain base fluid, then add glycerol glucoside, micro-nano metal powder, organic base and cross-linking agent, mix them evenly to obtain composite fracturing fluid.

[0047] Preferably, in the step 1), the amino modification of the nano-silica is: firstly modifying the surface of the nano-silica with hydroxyl groups, and then reacting the surface hydroxyl-modified nano-silica with a silane coupling agent to obtain amino-modified nano-silica;

[0048] And / or, in step 1), the average particle size of the nano-silicon dioxide is 10-50 μm;

[0049] And / or, in the step 1), the particle size distribution of the nano-silicon dioxide is: the particle size range of [10-30) μm accounts for 30-50%, and the particle size range of [30-50] μm accounts for 50-80%.

[0050] In some specific embodiments, in step 1), the particle size distribution of nano-silicon dioxide is: the particle size range of [10-30) μm may account for 30%, 35%, 40%, 45%, 50%, and the particle size range of [30-50] μm may account for 50%, 55%, 60%, 65%, 70%. More preferably, in step 1), when the particle size distribution of nano-silicon dioxide is: the particle size range of [10-30) μm accounts for 35%, and the particle size range of [30-50] μm accounts for 65%, a better experimental effect can be obtained.

[0051] Preferably, the polyethylene glycol derivative is one of polyethylene glycol monomethyl ether, carboxyl-terminated polyethylene glycol, and amino-terminated polyethylene glycol;

[0052] And / or, in the step 2), the mass ratio of amino-modified nano-silica to polyethylene glycol derivative is 1:0.15-0.35;

[0053] And / or, in the step 2), reacting the amino-modified nano-silica with the polyethylene glycol derivative comprises the following steps: first dispersing the amino-modified nano-silica and the polyethylene glycol derivative in anhydrous ethanol, then adding triethylamine, reacting under the protection of an inert gas, washing with anhydrous ethanol after the reaction, and drying to obtain the product.

[0054] In some specific embodiments, in the step 2), the mass ratio of amino-modified nano-silica to the polyethylene glycol derivative can be 1:0.15-0.2, 1:0.2-0.25, 1:0.25-0.3, 1:0.3-0.35. More preferably, in the step 2), the mass ratio of amino-modified nano-silica to the polyethylene glycol derivative can be 1:0.15, 1:0.18, 1:0.2, 1:0.23, 1:0.25, 1:0.27, 1:0.3, 1:0.32, 1:0.35. More preferably, when the mass ratio of amino-modified nano-silica to the polyethylene glycol derivative is 1:0.25, the experimental effect is better.

[0055] Preferably, in step 3), the mass ratio of the guar gum, the precursor, and the water is 3-3.5:2-5:1000;

[0056] And / or, in step 3), the guar gum is one of hydroxypropyl guar gum, carboxymethyl hydroxypropyl guar gum, and sulfonic acid hydroxypropyl guar gum;

[0057] And / or, in step 3), the content of micro-nano metal powder in the composite fracturing fluid is 0.01-0.025wt%;

[0058] And / or, in step 3), the average particle size of the micro-nano metal powder is 150-300 nm;

[0059] And / or, in step 3), the organic base is one of triethylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide;

[0060] And / or, in the step 3), the crosslinking agent is one of an organic boron crosslinking agent, an organic zirconium crosslinking agent, and an organic boron-zirconium composite crosslinking agent.

[0061] In some specific embodiments, in step 3), the mass ratio of the guar gum, the precursor, and water can be 3:2:1000, 3:2.5:1000, 3:3:1000, 3:3.5:1000, 3:4:1000, 3:4.5:1000, 3:5:1000, 3.2:2:1000, 3.2:2.5:1000, 3.2:3:1000, 3.2:3.5:1000, 3.2:4:1000. 0, 3.2:4.5:1000, 3.2:5:1000, 3.5:2:1000, 3.5:2.5:1000, 3.5:3:1000, 3.5:3.5:1000, 3.5:4:1000, 3.5:4.5:1000, 3.5:5:1000. More preferably, under normal circumstances, when the mass ratio of the guar gum, the precursor and the water is 3:3.5:1000, better experimental results can be obtained.

[0062] In some specific embodiments, in the step 3), the content of micro-nano metal powder in the composite fracturing fluid can be 0.01-0.015wt%, 0.015-0.02wt%, 0.02-0.025wt%. More preferably, the content of micro-nano metal powder in the composite fracturing fluid can be 0.01wt%, 0.012wt%, 0.015wt%, 0.018wt%, 0.02wt%, 0.025wt%. Under normal circumstances, when the content of micro-nano metal powder in the composite fracturing fluid is 0.02wt%, better experimental results can be obtained.

[0063] Preferably, in step 3), the micro-nano metal powder is prepared by the following steps:

[0064] S1: grinding the metal raw powder and sodium tetraborate at a low speed and dispersing them in anhydrous ethanol to prepare a feed liquid;

[0065] S2: slowly add a mixed solution of carrageenan and urea into the feed liquid, stir, freeze-dry, crush and grind to obtain.

[0066] Preferably, the metal raw powder is one or more of iron powder, aluminum powder, copper powder, zinc powder, nickel powder and gallium powder.

[0067] Preferably, the metal raw powder is composed of aluminum powder and gallium powder in a mass ratio of 1:0.05-0.1.

[0068] Preferably, in step S1, the mass ratio of the metal raw powder to sodium tetraborate is 1:0.05-0.1.

[0069] Preferably, in step S2, the mass ratio of the feed liquid, carrageenan and urea is 1:0.2-0.3:0.1-0.15.

[0070] Example 1

[0071] The preparation method of the composite fracturing fluid of this embodiment comprises the following steps:

[0072] 1) Add 30g of nano-silica to a mixed solution of hydrogen peroxide and sulfuric acid in a three-necked flask equipped with a stirrer, a thermometer, and a dropping funnel, wherein the volume ratio of hydrogen peroxide to sulfuric acid is 3:7, stir for 3h, then wash with deionized water until neutral, and then quickly freeze-dry to obtain the treated nano-silica; disperse the treated nano-silica in toluene, then add 20mL of silane coupling agent ADMS, react at 110°C under nitrogen protection for amino modification, wash with anhydrous ethanol after the reaction, and obtain amino-modified nano-silica after drying;

[0073] 2) Add 5g of amino-modified nano-silica, 1.25g of polyethylene glycol derivative, 100mL of anhydrous ethanol to a four-necked flask equipped with a condenser, a thermometer, a stirrer, and a dropping funnel, and then add a small amount of triethylamine, react at 115°C for 12h under nitrogen protection, centrifuge after the reaction, wash, and then dry in a vacuum drying oven at 25°C to obtain a precursor;

[0074] 3) Take 3g of guar gum, 3.5g of precursor material, and 1kg of deionized water and add them into a stirring tank, mix them evenly at a stirring speed of 200rpm to obtain a base fluid, then add 1.5g of glycerol glucoside, 0.2g of micro-nano metal powder, 5mL of organic base, and 5g of cross-linking agent, mix them evenly to obtain a composite fracturing fluid.

[0075] The average particle size of nano silicon dioxide is 30 μm. The polyethylene glycol derivative is carboxyl-terminated polyethylene glycol with a weight average molecular weight of 600. The guar gum is carboxymethyl hydroxypropyl guar gum. The micro-nano metal powder is aluminum powder with an average particle size of 200 nm. The organic base is triethylamine. The cross-linking agent is an organic zirconium cross-linking agent.

[0076] Example 2

[0077] The preparation method of the composite fracturing fluid of this embodiment comprises the following steps:

[0078] 1) Add 30g of nano-silica to a mixed solution of hydrogen peroxide and sulfuric acid in a three-necked flask equipped with a stirrer, a thermometer, and a dropping funnel, wherein the volume ratio of hydrogen peroxide to sulfuric acid is 3:7, stir for 3h, then wash with deionized water until neutral, and then quickly freeze-dry to obtain the treated nano-silica; disperse the treated nano-silica in toluene, then add 20mL of silane coupling agent ADMS, react at 110°C under nitrogen protection for amino modification, wash with anhydrous ethanol after the reaction, and obtain amino-modified nano-silica after drying;

[0079] 2) Add 5g of amino-modified nano-silica, 1.25g of polyethylene glycol derivative, 100mL of anhydrous ethanol to a four-necked flask equipped with a condenser, a thermometer, a stirrer, and a dropping funnel, and then add a small amount of triethylamine, react at 115°C for 12h under nitrogen protection, centrifuge after the reaction, wash, and then dry in a vacuum drying oven at 25°C to obtain a precursor;

[0080] 3) Take 3g of guar gum, 3.5g of precursor material, and 1kg of deionized water and add them into a stirring tank, mix them evenly at a stirring speed of 200rpm to obtain a base fluid, then add 1.5g of glycerol glucoside, 0.2g of micro-nano metal powder, 5mL of organic base, and 5g of cross-linking agent, mix them evenly to obtain a composite fracturing fluid.

[0081] The particle size distribution of nano-silicon dioxide is as follows: the particle size range of [10-30) μm accounts for 35%, and the particle size range of [30-50] μm accounts for 65%. The polyethylene glycol derivative is polyethylene glycol monomethyl ether, and the weight average molecular weight is 750. The guar gum is sulfonic acid hydroxypropyl guar gum. The micro-nano metal powder is aluminum powder, and the average particle size is 200 nm. The organic base is tetrabutylammonium hydroxide. The cross-linking agent is an organic boron zirconium cross-linking agent.

[0082] Example 3

[0083] The preparation method of the composite fracturing fluid of this embodiment comprises the following steps:

[0084] 1) Add 30g of nano-silica to a mixed solution of hydrogen peroxide and sulfuric acid in a three-necked flask equipped with a stirrer, a thermometer, and a dropping funnel, wherein the volume ratio of hydrogen peroxide to sulfuric acid is 3:7, stir for 3h, then wash with deionized water until neutral, and then quickly freeze-dry to obtain the treated nano-silica; disperse the treated nano-silica in toluene, then add 20mL of silane coupling agent ADMS, react at 110°C under nitrogen protection for amino modification, wash with anhydrous ethanol after the reaction, and obtain amino-modified nano-silica after drying;

[0085] 2) Add 5g of amino-modified nano-silica, 1.25g of polyethylene glycol derivative, 100mL of anhydrous ethanol to a four-necked flask equipped with a condenser, a thermometer, a stirrer, and a dropping funnel, and then add a small amount of triethylamine, react at 115°C for 12h under nitrogen protection, centrifuge after the reaction, wash, and then dry in a vacuum drying oven at 25°C to obtain a precursor;

[0086] 3) Take 3g of guar gum, 3.5g of precursor material, and 1kg of deionized water and add them into a stirring tank, mix them evenly at a stirring speed of 200rpm to obtain a base fluid, then add 1.5g of glycerol glucoside, 0.2g of micro-nano metal powder, 5mL of organic base, and 5g of cross-linking agent, mix them evenly to obtain a composite fracturing fluid.

[0087] The micro-nano metal powder of this embodiment is prepared by the following steps:

[0088] S1: 100 g of metal raw powder and 55 g of sodium tetraborate were ground at a low speed under vacuum conditions and then dispersed into anhydrous ethanol to prepare a feed solution;

[0089] S2: Add 100 g of feed liquid into a beaker, then slowly add a mixed solution consisting of 25 g of carrageenan and 15 g of urea into the feed liquid, stir and centrifuge to obtain a solid isolate, then freeze-dry the solid isolate, crush and grind it to obtain.

[0090] The particle size distribution of nano-silicon dioxide is as follows: the particle size range of [10-30) μm accounts for 35%, and the particle size range of [30-50] μm accounts for 65%. The polyethylene glycol derivative is polyethylene glycol monomethyl ether, and the weight average molecular weight is 750. The guar gum is sulfonic acid hydroxypropyl guar gum. The metal raw powder is composed of aluminum powder and gallium powder in a mass ratio of 1:0.075, and the average particle size of the ground micro-nano metal powder is 200nm. The organic base is tetrabutylammonium hydroxide. The cross-linking agent is an organic boron zirconium cross-linking agent.

[0091] Comparative Example 1

[0092] The preparation method of the composite fracturing fluid of this comparative example comprises the following steps:

[0093] 1) Add 30g of nano-silica to a mixed solution of hydrogen peroxide and sulfuric acid in a three-necked flask equipped with a stirrer, a thermometer, and a dropping funnel, wherein the volume ratio of hydrogen peroxide to sulfuric acid is 3:7, stir for 3h, then wash with deionized water until neutral, and then quickly freeze-dry to obtain the treated nano-silica; disperse the treated nano-silica in toluene, then add 20mL of silane coupling agent ADMS, react at 110°C under nitrogen protection for amino modification, wash with anhydrous ethanol after the reaction, and obtain amino-modified nano-silica after drying;

[0094] 2) Take 3g of guar gum, 3.5g of amino-modified nano-silica, and 1kg of deionized water and add them into a stirring tank, mix them evenly at a stirring speed of 200rpm to obtain a base fluid, then add 1.5g of glycerol glucoside, 0.2g of micro-nano metal powder, 5mL of organic base, and 5g of cross-linking agent, mix them evenly to obtain a composite fracturing fluid.

[0095] The average particle size of nano silicon dioxide is 30 μm. The guar gum is carboxymethyl hydroxypropyl guar gum. The micro-nano metal powder is aluminum powder with an average particle size of 200 nm. The organic base is triethylamine. The cross-linking agent is an organic zirconium cross-linking agent.

[0096] Comparative Example 2

[0097] The preparation method of the composite fracturing fluid of this comparative example comprises the following steps:

[0098] 1) Add 30g of nano-silica to a mixed solution of hydrogen peroxide and sulfuric acid in a three-necked flask equipped with a stirrer, a thermometer, and a dropping funnel, wherein the volume ratio of hydrogen peroxide to sulfuric acid is 3:7, stir for 3h, then wash with deionized water until neutral, and then quickly freeze-dry to obtain the treated nano-silica; disperse the treated nano-silica in toluene, then add 20mL of silane coupling agent ADMS, react at 110°C under nitrogen protection for amino modification, wash with anhydrous ethanol after the reaction, and obtain amino-modified nano-silica after drying;

[0099] 2) Add 5g of amino-modified nano-silica, 1.25g of polyethylene glycol derivative, 100mL of anhydrous ethanol to a four-necked flask equipped with a condenser, a thermometer, a stirrer, and a dropping funnel, and then add a small amount of triethylamine, react at 115°C for 12h under nitrogen protection, centrifuge after the reaction, wash, and then dry in a vacuum drying oven at 25°C to obtain a precursor;

[0100] 3) Take 3g of guar gum, 3.5g of precursor material, and 1kg of deionized water and add them into a stirring tank, mix them evenly at a stirring speed of 200rpm to obtain a base fluid, then add 5mL of organic base and 5g of cross-linking agent, mix them evenly to obtain a composite fracturing fluid.

[0101] The average particle size of nano silicon dioxide is 30 μm. The polyethylene glycol derivative is carboxyl-terminated polyethylene glycol with a weight average molecular weight of 600. The guar gum is carboxymethyl hydroxypropyl guar gum. The organic base is triethylamine. The crosslinking agent is an organic zirconium crosslinking agent.

[0102] Performance testing

[0103] 1. Temperature and salt resistance performance test

[0104] 1.1. Temperature resistance test

[0105] Take the composite fracturing fluid of Example 3 and Comparative Example 1, take 3g of guar gum and 1kg of deionized water and mix them evenly to prepare a blank group fracturing fluid. Use a HAAKE MARSⅢ rheometer at a shear rate of 170s -1 , the test temperature is 120℃, and the apparent viscosity of the composite fracturing fluid after shearing at different times is tested. The test results are as follows Figure 1 As shown in the above figure, it can be seen that the composite fracturing fluid of the present application has better temperature resistance than the fracturing fluid of Comparative Example 1.

[0106] 1.2. Salt resistance test

[0107] According to the preparation method of the composite fracturing fluid of Example 3 and Comparative Example 1, deionized water is replaced with standard brine for preparation. The mass fractions of sodium chloride, calcium chloride, magnesium chloride and potassium chloride in the standard brine are 5.5%, 0.55%, 0.45% and 2.0% respectively, and the mineralization of the standard brine is 5000mg / L, 10000mg / L, 15000mg / L, 20000mg / L, 25000mg / L, 30000mg / L, 35000mg / L, 40000mg / L, 45000mg / L and 50000mg / L respectively. In addition, 3g of guar gum and 1kg of standard brine with different mineralizations are mixed and uniformly prepared into a blank group fracturing fluid. At a temperature of 25°C, a rotational viscometer is used to measure the apparent viscosity of each sample fracturing fluid at different mineralizations. The test results are as follows: Figure 1 As shown in the figure below, it can be seen that the composite fracturing fluid of the present application has better salt resistance.

[0108] 2. Sand carrying performance test

[0109] Take the composite fracturing fluid and base fluid of Examples 1-3 and Comparative Examples 1-2, take 3g of guar gum and 1kg of deionized water and mix them evenly to prepare a blank group fracturing fluid, and then place them in 500mL measuring cylinders, the measuring cylinder height H=24.5cm, and the static sand carrying performance characterization method is used to test the free settling rate of the proppant 20 / 40 mesh Carbo ceramsite in the composite fracturing fluid, base fluid and gel. The results are shown in Table 1.

[0110]

[0111] It can be seen that a relatively stable hybrid cross-linking system is constructed in the composite fracturing fluid of the present application, thereby increasing the "viscoelasticity" of the fracturing fluid to a certain extent, and having better and more stable sand carrying performance.

[0112] 3. Microscopic performance testing

[0113] 3.1. Nano-silicon dioxide particle size distribution test

[0114] The nano-silicon dioxide of Example 1 and Example 2 was tested by scanning electron microscope. The results are as follows: Figure 2 As shown ( Figure 2 Wherein A is Example 1, Figure 2 B is Example 2), it can be seen that the particle size distribution range of the nano silicon dioxide in Example 2 is different from that in Example 1, and is composed of small particle sizes and large particle sizes in a corresponding proportion, which can improve the temperature and salt resistance and sand carrying performance of the fracturing fluid.

[0115] 3.2. Microscopic performance testing of fracturing fluid

[0116] The composite fracturing fluids of Examples 1-3 and Comparative Example 1 were tested by transmission electron microscopy. The results are as follows: Figure 3 As shown, (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Comparative Example 1. It can be seen that the particle components of Examples 1-3 of the present application are more evenly distributed in the cross-linked system in the fracturing fluid, the distribution state is better than that of the comparative example, and the comprehensive performance of the fracturing fluid is better.

[0117] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for preparing a composite fracturing fluid, characterized in that: The steps include: 1) Amino-modifying nano-silica to obtain amino-modified nano-silica; 2) reacting the amino-modified nano-silica with a polyethylene glycol derivative to obtain a precursor; the polyethylene glycol derivative is one of polyethylene glycol monomethyl ether, carboxyl-terminated polyethylene glycol, and amino-terminated polyethylene glycol; 3) Take guar gum, precursor material and water and mix them evenly to obtain base fluid, then add glycerol glucoside, micro-nano metal powder, organic base and cross-linking agent, mix them evenly to obtain composite fracturing fluid; the micro-nano metal powder is prepared by the following steps: S1: grinding the metal raw powder and sodium tetraborate at a low speed and dispersing them in anhydrous ethanol to prepare a feed liquid; S2: slowly add a mixed solution of carrageenan and urea into the feed liquid, stir, freeze-dry, crush and grind to obtain.

2. The method for preparing a composite fracturing fluid according to claim 1, characterized in that: In the step 1), the amino modification of the nano-silica is: firstly modifying the surface of the nano-silica with hydroxyl groups, and then reacting the surface hydroxyl-modified nano-silica with a silane coupling agent to obtain amino-modified nano-silica; And / or, in step 1), the average particle size of the nano-silicon dioxide is 10-50 μm; And / or, in the step 1), the particle size distribution of the nano-silicon dioxide is: the particle size range of [10,30) μm accounts for 30-50%, and the particle size range of [30,50] μm accounts for 50-70%.

3. The method for preparing a composite fracturing fluid according to claim 1, characterized in that: In the step 2), the mass ratio of amino-modified nano-silica to polyethylene glycol derivative is 1:0.15-0.35; And / or, in the step 2), reacting the amino-modified nano-silica with the polyethylene glycol derivative comprises the following steps: first dispersing the amino-modified nano-silica and the polyethylene glycol derivative in anhydrous ethanol, then adding triethylamine, reacting under the protection of an inert gas, washing with anhydrous ethanol after the reaction, and drying to obtain the product.

4. The method for preparing a composite fracturing fluid according to claim 1, characterized in that: In the step 3), the mass ratio of the guar gum, the precursor material and the water is 3-3.5:2-5:1000; And / or, in step 3), the guar gum is one of hydroxypropyl guar gum, carboxymethyl hydroxypropyl guar gum, and sulfonic acid hydroxypropyl guar gum; And / or, in step 3), the content of micro-nano metal powder in the composite fracturing fluid is 0.01-0.025wt%; And / or, in step 3), the average particle size of the micro-nano metal powder is 150-300 nm; And / or, in step 3), the organic base is one of triethylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide; And / or, in the step 3), the crosslinking agent is one of an organic boron crosslinking agent, an organic zirconium crosslinking agent, and an organic boron-zirconium composite crosslinking agent.

5. The method for preparing a composite fracturing fluid according to claim 1, characterized in that: The metal raw powder is one or more of iron powder, aluminum powder, copper powder, zinc powder, nickel powder and gallium powder.

6. The method for preparing a composite fracturing fluid according to claim 5, characterized in that: The metal raw powder is composed of aluminum powder and gallium powder in a mass ratio of 1:0.05-0.

1.

7. The method for preparing a composite fracturing fluid according to claim 1, characterized in that: In the step S1, the mass ratio of the metal raw powder to sodium tetraborate is 1:0.05-0.

1.

8. The method for preparing a composite fracturing fluid according to claim 1, characterized in that: In step S2, the mass ratio of the feed liquid, carrageenan and urea is 1:0.2-0.3:0.1-0.

15.

9. A composite fracturing fluid, characterized in that: The method is prepared by any one of claims 1 to 8.

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