An integrated scale inhibitor and bactericide fracturing fluid and its preparation method

Abstract

The present invention discloses an integrated scale and bacteria inhibition fracturing fluid and its preparation method. The fracturing fluid includes a thickening agent, a crosslinking agent, a surfactant, an anti-swelling agent, a breaker, and water. The preparation method includes montmorillonite treatment and in-situ polymerization of montmorillonite. To simultaneously address the scale formation and bacterial corrosion during the actual water-based fracturing application process, the thickening agent of the present invention adopts a combination of PAAVV polymer with amide, sulfonic acid, phosphonic acid, and quaternary phosphonium salt ionic liquid and montmorillonite. The sulfonic acid monomer provides salt resistance, the phosphonic acid monomer provides crosslinking sites and antibacterial properties, the quaternary phosphonium salt ionic liquid monomer simultaneously provides additional thickening, antibacterial, and solubility requirements, and the interlayer force of montmorillonite has the effect of transferring shear force, thereby ensuring that the viscosity of the thickening agent decreases less under long-term shear and remains above 35 mPa·s. In summary, the fracturing fluid product of the present invention realizes the organic combination of multiple functions such as scale prevention, bacteria inhibition, thickening, sand carrying, and gel breaking.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic fracturing fluids and their production technologies, and particularly relates to an anti-scaling and bactericidal integrated fracturing fluid and a preparation method thereof. Background Art

[0002] A fracturing fluid refers to a heterogeneous and unstable chemical system formed by a variety of additives in a certain ratio, and is a working fluid used for fracturing and reforming oil and gas reservoirs. Its main function is to transfer the high pressure formed by surface equipment into the formation, causing the formation to fracture to form cracks and transporting proppants along the cracks.

[0003] The following technical requirements are generally required for the formulation of water-based fracturing fluids:

[0004] 1) Anti-scaling: With the in-depth development of oil and gas fields, especially the exploitation of unconventional oil and gas resources such as shale gas, the composition of the fracturing fluid flowback fluid is complex, containing a large amount of inorganic salts, organic substances, heavy metal ions, etc. When flowing in equipment and pipelines, these substances are extremely likely to scale under specific conditions, causing serious corrosion and blockage to the equipment, affecting production efficiency and the service life of the equipment. Therefore, anti-scaling has become an important issue in the application of fracturing fluids.

[0005] 2) Antibacterial: The composition of the oilfield flowback fluid is complex, containing a large amount of petroleum substances, heavy metal ions, chemical additives (such as demulsifiers, corrosion inhibitors, etc.) and microorganisms. The growth of microorganisms will cause the deterioration of the flowback fluid quality, produce odors, corrode pipelines and equipment, and the microorganisms will aggregate to form a biofilm, which will block the formation pores, reduce the oil layer permeability, and affect the subsequent exploitation efficiency of the oilfield.

[0006] 3) Shear resistance of thickening agent: If the shear resistance of the thickening agent in the drilling fluid is low, the viscosity of the drilling fluid will drop sharply during the circulation process, especially when passing through high-speed shear parts such as the drill bit nozzle, and it will not be able to effectively carry cuttings, resulting in the precipitation of cuttings, which may block the wellbore, affect the normal progress of drilling operations, and may also cause the instability of the wellbore wall and trigger accidents such as well collapse.

[0007] However, the amide thickening agent in the existing fracturing fluid is prone to viscosity loss under high temperature and high shear, and is also prone to amide hydrolysis or degradation. At the same time, scale inhibitors and antibacterial agents are added to the thickening agent in the form of mixing small molecules or small particles, and are prone to wall sticking and penetration when entering the formation, resulting in the lack of long-term anti-scaling and antibacterial performance of the fracturing fluid, which urgently needs to be improved. Summary of the Invention

[0008] The purpose of the present invention is to solve the deficiencies existing in the prior art, and to propose an anti-scaling and bactericidal integrated fracturing fluid and a preparation method thereof.

[0009] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0010] The present invention first proposes an integrated scale and bacteria inhibition fracturing fluid, which comprises the following components by weight percentage: thickening agent 0.5 - 0.8%, crosslinking agent 0.3 - 0.4%, surfactant 0.4 - 0.6%, swelling inhibitor 1 - 2%, breaker 0.01 - 0.05%, and the balance is water;

[0011] To simultaneously address the problems of scaling and bacterial corrosion in the actual water-based fracturing application process, the thickening agent adopts a combination of PAAVV polymer with amide, sulfonic acid, phosphonic acid and quaternary phosphonium salt ionic liquid and montmorillonite, and at the same time overcomes the high-shear thickening effect. The specific preparation process is as follows:

[0012] S1. Montmorillonite treatment:

[0013] Quaternary ammonium salt intercalation: According to twice the cation exchange capacity of sodium montmorillonite (Na-MMT), prepare an aqueous solution of cetyltrimethylammonium bromide (CTAB) with a weight ratio of 20%, and add it to a sodium montmorillonite aqueous suspension with a weight ratio of 3%. Stir at 500 r / min, keep warm in a water bath at 60 °C for 4 h. The precipitate obtained from the reaction is separated by centrifugation, filtered and washed until there is no bromide ion. The obtained product is dried in a blast oven at 60 °C for 24 h, ground and sieved through a 200-mesh sieve to obtain organic montmorillonite A (OMMT);

[0014] S2. In-situ polymerization of montmorillonite:

[0015] 1) Mix and soak the dried organic montmorillonite A and water in a weight ratio of 1:1, then add 4-vinylbenzyltributylphosphonium chloride (VBP-Bu), dissolve at 60 °C, and grind to obtain a mixed slurry B;

[0016] 2) Under nitrogen protection, acrylamide (AM), vinylphosphonic acid (VPA), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) are successively added to deionized water. The amount of deionized water added is 3 times the total weight of acrylamide, vinylphosphonic acid and 2-acrylamido-2-methylpropanesulfonic acid. Add sodium hydroxide to adjust the pH of the system to 8 - 9, add the mixed slurry B. The ratio of organic montmorillonite A in the mixed slurry B to the total weight of acrylamide, vinylphosphonic acid and 2-acrylamido-2-methylpropanesulfonic acid is 1:4. The molar ratio of 4-vinylbenzyltributylphosphonium chloride in the mixed slurry B to acrylamide, vinylphosphonic acid and 2-acrylamido-2-methylpropanesulfonic acid is 0.3 - 0.8:10:1.6 - 2.3:0.9 - 1.2. Add ammonium persulfate, and the dosage of ammonium persulfate accounts for 1.5 - 2.5% of the total weight of the system. React at 75 °C for 5 h to obtain a gel-like product C;

[0017] 3) The gel-like product C is soaked in water for 10 h, the ions are replaced, and the treatment is carried out 3 times. The surface pH of the wet gel D is measured to be 7.5 - 8.5;

[0018] 4) Through a colloid mill, wet gel D and deionized water are mixed at a weight ratio of 1:1. The deionized water is added and ground in 5 portions while grinding, to obtain a viscous colloid E with bubbles inside.

[0019] 5) The viscous colloid E is hot roll-pressed into a film with a thickness < 10 mm, dried with hot air at 60 °C, cut and crushed to obtain a flaky granular product, which is the finished thickening agent.

[0020] Preferably, the cross-linking agent is a compound of borax and EDTA at a specific gravity of 2:1. Both borax and EDTA cross-link the phosphonic acid groups in the PAAVV polymer. Among them, the amino group of EDTA has a strong linking effect on the phosphonic acid group, and EDTA has a complexing effect with calcium, magnesium, barium and other ions, further improving the scale inhibition effect.

[0021] Preferably, the surfactant is a compound of a sulfonate surfactant and a quaternary ammonium salt surfactant at a ratio of 4:1. The quaternary ammonium salt surfactant includes any several of cetyltrimethylammonium chloride (1631), polyquaternium-17, benzalkonium bromide or cetylpyridinium bromide. The quaternary ammonium salt surfactant has both antibacterial agent functions and has good bactericidal, corrosion inhibition and clay stabilization properties, and has remarkable effects in preventing formation clay swelling and particle migration.

[0022] The sulfonate surfactant is sodium alkylbenzene sulfonate (LAS), α-olefin sulfonate (AOS) or alkyl sulfonate (AS), which has good surface activity and the ability to reduce surface tension, has strong sand-carrying capacity, low filtration loss, high fracturing efficiency, relatively low cost, and is used in water-based fracturing fluids.

[0023] Preferably, the swelling inhibitor is a small cationic swelling inhibitor HJZ-500 (Kaifeng Hengju Biotechnology Co., Ltd.) or a quaternary ammonium salt type clay stabilizer HJZ-500-1 (Kaifeng Hengju Biotechnology Co., Ltd.). The small cationic swelling inhibitor HJZ-500 is composed of a cationic polymer and a variety of additives. The quaternary ammonium salt type clay stabilizer HJZ-500-1 is composed of a quaternary ammonium salt cationic polymer and a variety of additives, which are used to prevent the swelling and migration of fine particles in reservoirs such as shale, and at the same time increase the degree of ionization of the system and increase the scale inhibition effect.

[0024] Preferably, the breaker is an enzyme breaker or a redox breaker.

[0025] A more preferred solution is that the molar ratio of 4-vinylbenzyltributylphosphonium chloride to acrylamide, vinylphosphonic acid and 2-acrylamido-2-methylpropanesulfonic acid in the mixed slurry B is 0.5:10:2:1.

[0026] A more preferred solution is that the dosage of ammonium persulfate in S2 accounts for 2% of the total weight of the system.

[0027] The present invention also provides a preparation method of the above-mentioned scale and bacteria resistant integrated fracturing fluid, which comprises the following steps: water, surfactant, swelling inhibitor, breaker are mixed according to percentages and stirred at high speed in a stirrer, and then a thickening agent in a corresponding proportion is slowly added. After swelling is completed, a crosslinking agent is added, and finally the scale and bacteria resistant integrated fracturing fluid is obtained.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. Firstly, through group screening, the present invention selects four monomers with amide, sulfonic acid, phosphonic acid and quaternary phosphonium salt ionic liquid for copolymerization. The amide monomer provides thickening performance and solubility requirements, the sulfonic acid monomer provides salt resistance, the phosphonic acid monomer provides crosslinking sites (with borax) and antibacterial properties, and the quaternary phosphonium salt ionic liquid monomer simultaneously provides additional thickening, antibacterial and solubility requirements. According to the polymerization effect and anti-shear test, the problem of high-shear debonding can be initially overcome.

[0030] 2. At the same time, the present application also uses montmorillonite intercalated with long-chain quaternary ammonium salt, and utilizes the high permeability of the ionic liquid for in-situ polymerization of polymer-montmorillonite. Through the degumming experiment, it is proved that the polymer phase and the inorganic phase are evenly distributed and cannot be separated. On the one hand, the adhesion (or intercalation) of the polymer improves the solubility of montmorillonite, and on the other hand, the supporting force of montmorillonite provides anti-pressure and the interlayer force has the effect of transferring shear force, so as to ensure that the viscosity of the thickening agent decreases less under long-term shear and is guaranteed to be above 35 mPa·s.

[0031] 3. The scale and bacteria resistant integrated fracturing fluid of the present invention realizes the organic combination of multiple functions such as scale prevention, bacteria killing, thickening, sand carrying and breaking through optimizing the formula and process, which is specifically embodied as:

[0032] 1) High scale prevention performance: phosphonic acid groups and sulfonic acid groups are introduced into the thickening agent, and these functional groups can form stable chelates with calcium, magnesium, barium and other ions in the formation, effectively preventing the formation of scale layers; the crosslinking agent adopts the compound of borax and EDTA. The amino group of EDTA has a strong connection effect on the phosphonic acid group, and at the same time EDTA can coordinate with metal ions to further improve the scale prevention performance.

[0033] 2) High antibacterial property:

[0034] The intercalated montmorillonite itself has a high ion adsorption capacity, especially has a high adsorption efficiency for alkaline earth metal ions, and the long-chain quaternary ammonium salt between layers also has long-term antibacterial properties. The quaternary phosphonium salt ionic liquid monomer has high biological cell permeability and bactericidal effect;

[0035] The surfactant is a mixture of sulfonate and quaternary ammonium salt surfactants. The quaternary ammonium salt surfactant has good antibacterial properties, can effectively inhibit the growth of bacteria, and reduce biological corrosion;

[0036] 3) Enhanced thickening and proppant-carrying capacity:

[0037] The thickening agent is a PAAVV polymer with amide, sulfonic acid, phosphonic acid and quaternary phosphonium salt ionic liquids. Combining with the nano-enhancing effect of montmorillonite, it can maintain good thickening performance under high-shear conditions and improve the proppant-carrying capacity;

[0038] Through the in-situ polymerization process of montmorillonite, the prepared thickening agent has higher mechanical stability and shear resistance. Description of the Drawings

[0039] Figure 1 It is the infrared spectrum of the thickening agent in the embodiment of the present invention;

[0040] Figure 2 It is the graph of the influence of concentration on the viscosity of the thickening agent aqueous solution in the embodiment of the present invention;

[0041] Figure 3 It is the graph of the influence of shear time on the viscosity of the thickening agent aqueous solution in the embodiment of the present invention;

[0042] Figure 4 It is the graph of the influence of temperature on the viscosity of the thickening agent aqueous solution in the embodiment of the present invention;

[0043] Figure 5 It is the graph of the influence of NaCl concentration on the viscosity of the thickening agent aqueous solution in the embodiment of the present invention;

[0044] Figure 6 It is the graph of the influence of CaCl2 concentration on the viscosity of the thickening agent aqueous solution in the embodiment of the present invention. Detailed Embodiments

[0045] Next, with reference to the existing well-known technologies, the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0046] I. Preparation of shear-resistant thickening agent:

[0047] 1. Preparation process:

[0048] S1. Montmorillonite treatment:

[0049] Quaternary ammonium salt intercalation: Sodium-based montmorillonite. According to twice the cation exchange capacity (CEC) of sodium-based montmorillonite, a cetyltrimethylammonium bromide solution with a weight ratio of 25% was prepared and added to a sodium-based montmorillonite suspension with a weight ratio of 5%. Stir at 500 r / min, keep warm in a water bath at 60 °C for 4 h. The precipitate obtained from the reaction was separated by centrifugation, filtered and washed until there was no bromide ion. The obtained product was dried in a blast dryer at 60 °C for 24 h, ground and passed through a 200-mesh sieve to obtain organic montmorillonite A (OMMT);

[0050] S2. In-situ polymerization

[0051] The dried organic montmorillonite A and water were mixed and infiltrated according to a weight ratio of 1:1, and then 4-vinylbenzyltributylphosphonium chloride was added. After dissolving at 60 °C, it was ground to obtain a mixed slurry B;

[0052] Under nitrogen protection, acrylamide (AM), vinylphosphonic acid (VPA), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) were successively added to deionized water. The amount of deionized water added was 3 times the total weight of acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid. Sodium hydroxide was added to adjust the pH of the system to 8-9. Mixed slurry B was added. The ratio of organic montmorillonite A in mixed slurry B to the total weight of acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid was 1:4 (this ratio was set according to the maximum dissolution degree of montmorillonite). The molar ratio of 4-vinylbenzyltributylphosphonium chloride (VBP-Bu) in mixed slurry B to acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid was 0.3-0.8:10:1.6-2.3:0.9-1.2. Ammonium persulfate as an initiator (accounting for 2% of the total system weight) was added, and the reaction was carried out at 75 °C for 5 h to obtain a gel-like product C;

[0053] The gel-like product C was soaked in water for 10 h to replace ions, and this process was carried out 3 times. The surface pH of the wet gel D was measured to be 7.5-8.5;

[0054] Through a colloid mill, the wet gel D and deionized water were mixed according to a weight ratio of 1:1. The deionized water was added and ground 5 times to obtain a viscous colloid E with bubbles inside;

[0055] The viscous colloid E was hot roll-pressed into a film with a thickness < 10 mm, dried in hot air at 60 °C, cut and crushed to obtain a flaky granular product, which was the finished thickening agent.

[0056] Reagent source:

[0057] Sodium-based montmorillonite (Na-MMT, 325 mesh), Hebei Leijiang New Material Technology Co., Ltd.;

[0058] Cetyltrimethylammonium bromide (CTAB, purity 99%), Shandong Guohua Chemical Co., Ltd.;

[0059] Acrylamide (AM), absolute ethanol, sodium hydroxide, sodium chloride, calcium chloride, ammonium persulfate, with a purity of AR each, Shanghai Macklin Biochemical Co., Ltd.;

[0060] Acrylamido-2-methylpropanesulfonic acid (AMPS), purity > 99%, Shanghai Hongzhuang Chemical Technology Co., Ltd.;

[0061] Vinylphosphonic acid (VPA), purity > 99%, Hubei Hongxin Ruiyu Fine Chemical Co., Ltd.;

[0062] 4-Vinylbenzyltributylphosphonium chloride (VBP-Bu ionic liquid, in white powder form, melting into ionic liquid form at 60 °C), purity > 99%, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0063] According to the above steps, the thickener formulations of each preparation example are as shown in Table 1 below:

[0064] Table 1. Components of the thickener

[0065]

[0066] To verify the effects of various reagents and treatment processes on thickening performance, scale inhibition, and sterilization performance, etc., the thickeners of the following comparative preparation examples are set:

[0067] Comparative Preparation Example 1:

[0068] It has the same components and steps as Preparation Example 2. The difference is that the sodium-based montmorillonite is not treated by quaternary ammonium salt intercalation.

[0069] Comparative Preparation Example 2:

[0070] It has the same components and steps as Preparation Example 2. The difference is that the thickener does not use sodium-based montmorillonite. The specific process is as follows:

[0071] Mix and soak the dried organic montmorillonite A and water in a weight ratio of 1:1, then add 4-vinylbenzyltributylphosphonium chloride. After dissolving at 60 °C, grind to obtain a mixed slurry B;

[0072] Under nitrogen protection, acrylamide (AM), vinylphosphonic acid (VPA), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) were successively added to deionized water. The amount of deionized water added was 3 times the total weight of acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid. Sodium hydroxide was added to adjust the pH of the system to 8-9. 4-Vinylbenzyltributylphosphonium chloride (VBP-Bu) was added, and ammonium persulfate (2% of the total system weight) was added as an initiator. The reaction was carried out at 75 °C for 5 h to obtain a gel-like product, which was soaked in water, rinsed, filtered, and dried to obtain a granular product, which was the finished thickening agent.

[0073] Comparative Preparation Example 3:

[0074] It was the same as Preparation Example 2 in terms of components and steps. The difference was that the wet gel D was directly dried and crushed. The specific process was as follows:

[0075] S1. Montmorillonite treatment:

[0076] Quaternary ammonium salt intercalation: For sodium-based montmorillonite, a 25% cetyltrimethylammonium bromide solution was prepared according to twice the cation exchange capacity (CEC) of sodium-based montmorillonite and added to a 5% sodium-based montmorillonite suspension. Stir at 500 r / min and keep warm in a 60 °C water bath for 4 h. The precipitate obtained from the reaction was centrifuged, filtered, and washed until there were no bromide ions. The obtained product was dried in a blast dryer at 60 °C for 24 h, ground, and sieved through a 200-mesh sieve to obtain organic montmorillonite A (OMMT);

[0077] S2. In-situ polymerization

[0078] The dried organic montmorillonite A and water were mixed and infiltrated at a weight ratio of 1:1, and then 4-vinylbenzyltributylphosphonium chloride was added. After dissolving at 60 °C, it was ground to obtain a mixed slurry B;

[0079] Under nitrogen protection, acrylamide (AM), vinylphosphonic acid (VPA), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) were successively added to deionized water. The amount of deionized water added was 3 times the total weight of acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid. Sodium hydroxide was added to adjust the pH of the system to 8-9. The mixed slurry B was added. The ratio of organic montmorillonite A in the mixed slurry B to the total weight of acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid was 1:4 (this ratio was set according to the maximum dissolution degree of montmorillonite). The molar ratio of 4-vinylbenzyltributylphosphonium chloride (VBP-Bu) in the mixed slurry B to acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid was 0.3-0.8:10:1.6-2.3:0.9-1.2. Ammonium persulfate (2% of the total system weight) was added as an initiator. The reaction was carried out at 75 °C for 5 h to obtain a gel-like product C;

[0080] The gel-like product C is soaked in water for 10 h, the ions are replaced, and the treatment is carried out 3 times. The surface pH of the wet gel D is tested to be 7.5 - 8.5; the wet gel D is dried and crushed to obtain the finished thickening agent.

[0081] 2. Detection of the thickening agent:

[0082] 1) Mixed properties:

[0083] The finished thickening agent is prepared into an aqueous solution with a mass fraction of 5%, and it does not settle within 10 days, while the sedimentation times of the sodium-based montmorillonite suspension and the organophilic montmorillonite A suspension with the same specific gravity are 18 min and 70 min respectively;

[0084] Degumming experiment: The finished thickening agent is prepared into an aqueous solution with a mass fraction of 0.5%, filtered through a 150-mesh sieve, and rinsed 3 times with deionized water. The obtained filter cake is still gel-like and has particles inside. The particles cannot be separated from the transparent colloid, indicating that the polymer network and the montmorillonite matrix are wound and combined well and will not fall off.

[0085] 2) FT-IR characterization: The KBr tablet pressing method is adopted, and the infrared spectrum of the sample is measured using a WQF-520 Fourier transform infrared spectrometer. Infrared detection is carried out on sodium-based montmorillonite, organophilic montmorillonite A, and the finished thickening agent respectively.

[0086] Refer to Figure 1 , the bulk infrared of sodium-based montmorillonite (MMT) and the quaternary ammonium salt in organophilic montmorillonite A (OMMT) are both reflected. The strong absorption band of the broad peak at 1039 cm -1 is the Si-O-Si framework vibration, which is the characteristic absorption peak of montmorillonite; at 2928 cm -1 , 2854 cm -1 , 1469.6 cm -1 are the absorption peaks of -CH2 of the quaternary ammonium salt, and the layered silicate framework of montmorillonite has not changed, indicating that the quaternary ammonium salt has indeed been embedded between the montmorillonite layers;

[0087] PAAVV-MMT (abbreviation: PMMT): 3430 cm -1 and 3210 cm -1 are the characteristic peaks of the amide group. The S=O bond in AMPS is at 1184 cm -1 and 1043 cm -1 , the P=O bond is at 1250 - 1300 cm -1 , and the C=O of the amide group is at 1660 - 1680 cm -1 and other absorption peaks will still be reflected in the infrared spectrum. Only due to the interference of the montmorillonite inorganic phase, the position and intensity of the absorption peaks will change to a certain extent.

[0088] 3) Performance Evaluation of Polymer PAAVV

[0089] ① Thickening performance test: The thickeners in Preparation Examples 1-5 were used to prepare aqueous solutions of polymer PAAVV with different mass fractions. The apparent viscosity was measured by a six-speed rotational viscometer at room temperature (25 °C) and a shear rate of 170 s -7 as shown in Figure 2 ;

[0090] ② Crosslinking property test: Prepare a PAAVV polymer solution with a controlled mass fraction of 0.5%. After complete dissolution, adjust its pH value to 6 with 3 wt% dilute hydrochloric acid. Prepare an aqueous borax solution with a mass fraction of 0.4%. Add the aqueous borax solution to the PAAVV polymer solution according to a volume ratio of 100:5. Stir quickly with a glass rod at 30 °C and record the reaction time (stopwatch reading) when the crosslinked product can be picked up and does not form lumps (indicating good crosslinking effect). The crosslinking times of the thickeners in Preparation Examples 1-5 and Comparative Preparation Examples 1-3 are shown in Table 2 below:

[0091] Table 2: Crosslinking Property of Thickener

[0092]

[0093] Among them, the crosslinking time of Comparative Preparation Example 1 was shorter, but obvious particle aggregation was visible to the naked eye, and there was a small amount of particle deposition at the bottom of the PAAVV polymer solution after standing for 3 days; the product of Comparative Preparation Example 3 was not subjected to grinding and pre-shearing treatment. When preparing the aqueous solution, the dissolution and diffusion rate was slower than that of Preparation Example 2. After the PAAVV polymer solution was left standing for 10 days, there were suspended aggregates inside the solution. The grinding process of the colloid mill was beneficial to the uniform distribution of the polymer phase and the montmorillonite matrix.

[0094] ③ Shear resistance performance test: Taking Preparation Example 2 and Comparative Preparation Example 2 as examples, prepare a PAAVV polymer solution with the thickener, with a controlled mass fraction of 0.5%. Measure the apparent viscosity at different shear times at room temperature (25 °C) and a shear rate of 170 s -7 as shown in Figure 3 .

[0095] ④ Temperature resistance performance test: Prepare a PAAVV polymer solution with a controlled mass fraction of 0.5%. Use a six-speed rotational viscometer to measure the apparent viscosity of the solution at different temperatures, and control the shear rate at 170 s -1 as shown in Figure 4 .

[0096] ⑤ Salt tolerance performance test: Taking Preparation Example 2 and Comparative Preparation Example 2 as examples, a polymer PAAVV solution was prepared, and its mass fraction was controlled at 0.5%. NaCl or CaCl2 was continuously added, and a six-speed rotational viscometer was used to measure the change in the apparent viscosity of the solution, where the conditions were controlled at room temperature (25 °C) and a shear rate of 170 s -1 , as shown respectively in Figure 5 and Figure 6 , and the concentration in the figure is the proportion (wt%) of NaCl or CaCl2 in the solution system.

[0097] 3. Formulation screening process of thickening agent:

[0098] 1) From the crosslinking degree of the thickening agent prepared according to Figure 2 and Preparation Examples 1-5, as the amount of VBP-Bu increases, the viscosity of the thickening agent increases slightly (comparison of Preparation Examples 1-3);

[0099] 2) As the amount of ammonium persulfate increases, the thickening agent with a higher molecular weight (Preparation Example 4) has a better thickening effect at low concentrations, and the thickening agent with a smaller molecular weight (Preparation Example 5) has a better thickening effect at high concentrations;

[0100] 3) According to Figure 4 , Preparation Examples 1-5 still maintain around 70 mPa·s at high temperatures, meeting the requirements for high-temperature fracturing fluids;

[0101] 4) According to Figure 5 and Figure 6 , when montmorillonite is added, the salt resistance of the thickening agent is significantly improved, and the apparent viscosity remains above 35 mPa·s in high-concentration salt;

[0102] 5) According to Figure 3 and combining the above data, when montmorillonite is added, the shear resistance of the thickening agent is significantly improved, and according to the usage amount of the existing thickening agent in the fracturing fluid and the requirements for the number of amides or ions, Preparation Example 2 is tentatively determined as the preferred formulation.

[0103] II. Preparation of fracturing fluid:

[0104] Thickening agent: Taken from Preparation Examples 1-5 and Comparative Preparation Examples 1-3 for comparison.

[0105] Crosslinking agent: Composed of borax (2000 mesh, Langfang Pengcai Fine Chemical Co., Ltd.) and EDTA (AR, Langfang Pengcai Fine Chemical Co., Ltd.) in a ratio of 2:1. Both borax and EDTA crosslink the phosphonic acid groups in the PAAVV polymer. Among them, the amino group of EDTA has a strong bonding effect on the phosphonic acid groups, and EDTA has a complexing effect with calcium, magnesium, barium and other ions, further improving the scale prevention effect;

[0106] Surfactant: A compound prepared by mixing sulfonate surfactants and quaternary ammonium salt surfactants at a ratio of 4:1;

[0107] Quaternary ammonium salt surfactant: Cetyltrimethylammonium chloride (1631), polyquaternium-17, benzalkonium bromide, or cetylpyridinium bromide, which also functions as an antibacterial agent and has good bactericidal, corrosion inhibition, and clay stabilization properties, and is highly effective in preventing formation clay swelling and particle migration;

[0108] Sulfonate surfactant: Sodium alkylbenzene sulfonate (LAS), α-olefin sulfonate (AOS), or alkyl sulfonate (AS), which has good surface activity and the ability to reduce surface tension, strong sand-carrying capacity, low filtration loss, high fracturing efficiency, relatively low cost, and is used in water-based fracturing fluids.

[0109] Swelling inhibitor: Small cationic swelling inhibitor HJZ-500 (Kaifeng Hengju Biotechnology Co., Ltd.) or quaternary ammonium salt type clay stabilizer HJZ-500-1 (Kaifeng Hengju Biotechnology Co., Ltd.). The small cationic swelling inhibitor HJZ-500 is composed of a cationic polymer and various additives, and the quaternary ammonium salt type clay stabilizer HJZ-500-1 is composed of a quaternary ammonium salt cationic polymer and various additives, which are used to prevent the swelling and migration of fine particles in reservoirs such as shale, and at the same time increase the degree of ionization of the system and enhance the scale inhibition effect;

[0110] Gel breaker: Enzyme gel breaker (oil fracturing gel breaker, enzyme activity 50,000 u, Nantong Yingruida Biotechnology Co., Ltd.), redox gel breaker (ammonium persulfate capsule gel breaker, Dongying Yiming Chemical Co., Ltd.).

[0111] The fracturing fluid formulations used in the specific examples and comparative examples are as shown in Table 3 below:

[0112] Table 3. Fracturing fluid formulations

[0113]

[0114] Scale inhibition test: Prepare a simulated aqueous solution with solute weight percentages of 1% potassium chloride, 1.5% sodium chloride, 0.5% magnesium chloride, and 0.2% calcium chloride. The solvent is the backflow fluid from Well No. 7 of Gansu Haishiwan hydraulic fracturing oil production mine (where the water weight content is 89.1 wt% and the sulfate content is 1.2 wt%). Mix various fracturing fluids into the simulated aqueous solution, with the weight ratio of fracturing fluid to simulated aqueous solution being 1:9. Observe the metal content m1 in the sediment weight (after drying), the metal content m2 in the solute, and the scale inhibition rate θ = (m2 - m1) / m2, calculated based on CaSO4;

[0115] Antibacterial test: The produced water from Well 7 of the hydraulic fracturing oil production in Haishiwan, Gansu (where the water weight content is 89.1 wt% and the sulfate content is 1.2 wt%) was used. The bacterial solution concentration was measured with a colony counter (Interscience Scan100 from France) to be 7.5×10 5 CFU / ml for Flavobacterium C, which served as the blank standard solution. The fracturing fluids of Examples 1 - 5 and Comparative Examples 1 - 5 were respectively added to this produced water to obtain the test solutions;

[0116] The blank standard solution and each test solution were cultured at 37°C for 7 days. Then, the stock solution was diluted successively by a factor of 100 times, and the colony counts in the petri dishes were measured respectively. Referring to the calculation formula for the cell concentration: Cell concentration (CFU / mL) = Visual count of cells in the counting chamber × 10* × Dilution factor, the cell concentrations of each test solution were calculated as S n , the cell concentration of the test solution was S0, and the bactericidal rate τ = (S n - S0) / S0.

[0117] The specific data are shown in Table 4 below:

[0118] Table 4. Scale inhibition and bactericidal properties of fracturing fluids

[0119]

[0120] From Table 4 combined with Figure 2 - 6 it can be seen that by comparing Examples 1 - 5, it is proved that the increase in the content of VPA phosphonic acid is beneficial to the increase in antibacterial property, meeting the antibacterial property requirements of polyphosphonic acid. At the same time, it is also proved that the scheme of using phosphonic acid instead of the existing carboxylic acid as the crosslinking site (crosslinking with borax) is feasible.

[0121] By comparing Comparative Examples 1 and 3 with Example 2, reducing the amount of quaternary ammonium salt in the system reduces the bactericidal ability, while montmorillonite improves the ion inclusion ability of the effective components of the fracturing fluid, especially suitable for oil wells with high salt content.

[0122] By comparing Comparative Example 2 with Example 2, pre - grinding treatment is beneficial to the uniform distribution of montmorillonite and the polymer phase, further enhancing the ion adsorption ability.

[0123] By comparing Comparative Examples 4 / 5 with Example 2, trace amounts of EDTA further enhance the scale inhibition function, and trace amounts of cetyltrimethylammonium chloride further increase the bactericidal rate.

[0124] The above - mentioned are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. An anti-scaling and sterilizing integrated fracturing fluid, characterized in that: The invention comprises the following components in weight percentage: 0.5-0.8% of thickener, 0.3-0.4% of crosslinking agent, 0.4-0.6% of surfactant, 1-2% of anti-swelling agent, 0.01-0.05% of gel breaker, and the balance is water; the crosslinking agent is prepared by mixing borax and EDTA in a ratio of 2:1; The preparation process of the thickener is as follows: S1. Montmorillonite treatment: Quaternary ammonium salt intercalation: according to the cation exchange capacity of twice the sodium montmorillonite, a 20% by weight aqueous solution of hexadecyltrimethylammonium bromide was prepared, added to a 3% by weight aqueous suspension of sodium montmorillonite, stirred at 500 r / min, kept warm in a 60°C water bath for 4 h, the precipitate obtained by the reaction was separated by centrifugation, filtered and washed until there was no bromide ion, the obtained product was dried at 60°C for 24 h, ground and sieved through a 200-mesh sieve to obtain organic montmorillonite A; S2, montmorillonite in-situ polymerization: 1) Mix and infiltrate dried organic montmorillonite A and water in a weight ratio of 1:1, then add 4-vinylbenzyltributylphosphonium chloride, dissolve at 60°C, and grind to obtain a mixed slurry B; 2) Under nitrogen protection, acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid are sequentially added into deionized water, wherein the amount of deionized water added is 3 times the total weight of acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid, sodium hydroxide is added to adjust the pH of the system to 8-9, and mixed slurry B is added, wherein the ratio of the total weight of organic montmorillonite A to acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid in the mixed slurry B is 1:4, and the molar ratio of 4-vinylbenzyltributylphosphonium chloride to acrylamide, vinylphosphonic acid, and 2-acrylamido-2-methylpropanesulfonic acid in the mixed slurry B is 0.3-0.8:10:1.6-2.3:0.9-1.2, and ammonium persulfate is added, wherein the amount of ammonium persulfate accounts for 1.5-2.5% of the total weight of the system, and the reaction is carried out at 75°C for 5 hours to obtain a gel product C; 3) The gel product C was soaked in water for 10 h, ion was replaced, and the surface pH of the wet gel D was tested to be 7.5-8.5; 4) Using a colloid mill, wet gel D and deionized water were mixed in a weight ratio of 1:1, and deionized water was added five times while grinding to obtain a viscous colloid E with bubbles inside; 5) The viscous colloid E is hot-rolled into a film with a thickness of less than 10 mm, dried with hot air at 60°C, cut into pieces, and crushed to obtain a flake granular product, i.e., the finished thickener.

2. The anti-scaling and sterilizing integrated fracturing fluid according to claim 1, characterized in that: The surfactant is prepared by compounding a sulfonate surfactant and a quaternary ammonium salt surfactant in a ratio of 4:1, and the quaternary ammonium salt surfactant includes any of cetyltrimethylammonium chloride, polyquaternium-17, benzalkonium bromide or cetylpyridinium bromide; The sulfonate surfactant is sodium alkylbenzene sulfonate, α-olefin sulfonate or alkyl sulfonate.

3. The anti-scaling and sterilizing integrated fracturing fluid according to claim 1, characterized in that: The anti-swelling agent is a small cationic anti-swelling agent HJZ-500 or a quaternary ammonium salt type clay stabilizer HJZ-500-1.

4. The anti-scaling and sterilizing integrated fracturing fluid according to claim 1, characterized in that: The breaker is an enzyme breaker or a redox breaker.

5. The anti-scaling and sterilizing integrated fracturing fluid according to claim 1, characterized in that: The molar ratio of 4-vinylbenzyltributylphosphonium chloride to acrylamide, vinylphosphonic acid and 2-acrylamido-2-methylpropanesulfonic acid in the mixed slurry B is 0.5:10:2:

1.

6. The anti-scaling and sterilizing integrated fracturing fluid according to claim 1, characterized in that: The amount of ammonium persulfate in S2 accounts for 2% of the total weight of the system.

7. The method for preparing an anti-scaling and sterilizing integrated fracturing fluid according to any one of claims 1 to 6, characterized in that: The following steps are involved: Water, surfactant, anti-swelling agent and degelling agent are mixed according to percentage and stirred at high speed in a stirrer, and then a corresponding proportion of thickener is slowly added. After swelling is completed, a cross-linking agent is added to finally obtain an anti-scaling and sterilization integrated fracturing fluid.

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