High-temperature-resistant antioxidant scale inhibitor for fracturing, fracturing fluid system containing high-temperature-resistant antioxidant scale inhibitor and preparation method of high-temperature-resistant antioxidant scale inhibitor

Abstract

The invention belongs to the technical field of oil and gas field scale inhibition, and relates to a high-temperature-resistant antioxidant scale inhibitor for fracturing, a fracturing fluid system containing the same and a preparation method of the high-temperature-resistant antioxidant scale inhibitor. The scale inhibitor comprises amino trimethylene phosphate alkyl ester, hydroxy ethylidene diphosphate alkyl ester, ethylenediamine tetramethylene phosphate alkyl ester and an emulsifier. Dissolving an emulsifier in pure water to form a water phase solution; and stirring and mixing amino trimethylene ethyl phosphate, hydroxy ethylidene ethyl diphosphate and ethylenediamine tetramethylene ethyl phosphate, and then mixing and stirring with the aqueous phase solution to form the high-temperature-resistant antioxidant scale inhibitor for fracturing. The scale inhibitor is esterified organophosphate, has water insolubility, forms an oil-in-water emulsion under the action of an emulsifier, and can release organophosphoric acid through a slow hydrolysis reaction at a high temperature of a stratum after entering the stratum along with fracturing fluid, so that the scale inhibitor is prevented from being damaged by an oxidation reaction of a gel breaker after entering the stratum; the high-stability scale inhibition and prevention performance is still kept, so that the damage of the fracturing fluid to the stratum is reduced.

Description

Technical Field

[0001] This invention belongs to the field of scale inhibition technology in oil and gas fields, and specifically relates to a high-temperature resistant and antioxidant scale inhibitor for fracturing, a fracturing fluid system containing the inhibitor, and a method for preparing the inhibitor. Background Technology

[0002] When fracturing fluid enters the formation, it easily reacts with formation water in situ to form insoluble precipitates, thereby blocking oil and gas channels and causing a decrease in reservoir permeability.

[0003] To prevent scale buildup from occurring in the formation of fracturing fluids, researchers have developed "scale-inhibiting fracturing fluid systems" by adding scale inhibitors, such as organophosphates and small-molecule polycarboxylates, to conventional fracturing fluids. Additionally, conventional fracturing fluids often contain strong oxidizing breaker agents, such as ammonium persulfate. The hydroxyl radicals generated by these breaker agents at high formation temperatures indiscriminately oxidize and degrade the organic agents in the fracturing fluid. Therefore, the scale inhibitors added to the fracturing fluid will also be oxidized and degraded by the breaker agents, thus losing their original function.

[0004] Currently, there is no specific solution to the problem of scale inhibitors in fracturing fluids being oxidized and degraded by breaker agents at high formation temperatures. Summary of the Invention

[0005] The purpose of this invention is to provide a high-temperature resistant and antioxidant scale inhibitor for fracturing, a fracturing fluid system containing the same, and a method for preparing the same, thereby solving the problem of scale inhibitors in fracturing fluids being oxidized and degraded by breaker agents at high formation temperatures.

[0006] This invention is achieved through the following technical solution:

[0007] A high-temperature resistant, antioxidant, and scale inhibitor for fracturing, comprising the following components by weight:

[0008] 5-15 parts of aminotrimethylphosphonic acid alkyl ester, 5-15 parts of hydroxyethylidene diphosphonic acid alkyl ester, 5-15 parts of ethylenediaminetetramethylene phosphonic acid alkyl ester, 5-15 parts of emulsifier, and 40-90 parts of water.

[0009] Furthermore, the molecular structural formula of aminotrimethylphosphoalkyl ester is as follows:

[0010]

[0011] Wherein, the R group is methyl or ethyl.

[0012] Furthermore, when the R group is methyl, hydroxyethylidene is suitable for reservoirs at 70-90°C; when the R group is ethyl, hydroxyethylidene is suitable for reservoirs at temperatures above 90°C.

[0013] The hydrolytic ability of methyl aminotrimethylphosphonate is stronger than that of ethyl aminotrimethylphosphonate. Furthermore, the molecular structural formula of alkyl ethylenediaminetetramethylene phosphate is:

[0014]

[0015] Wherein, the R group is methyl or ethyl.

[0016] Furthermore, the molecular structural formula of alkyl hydroxyethylidene diphosphate is as follows:

[0017]

[0018] Wherein, the R group is methyl or ethyl.

[0019] Furthermore, when the R group is methyl, hydroxyethylidene is suitable for reservoirs at 70-90°C; when the R group is ethyl, hydroxyethylidene is suitable for reservoirs at temperatures above 90°C.

[0020] The hydrolytic ability of methyl hydroxyethylidene diphosphate is stronger than that of ethyl hydroxyethylidene diphosphate.

[0021] Furthermore, the emulsifier is a water-soluble surfactant that can stabilize the oil-in-water emulsion.

[0022] Furthermore, the emulsifiers are nonylphenol polyoxyethylene and sodium dodecyl sulfate.

[0023] This invention also discloses a method for preparing the high-temperature resistant, antioxidant, and scale inhibitor for fracturing, comprising the following steps:

[0024] Dissolve the emulsifier in pure water and heat it to 50-60℃ to form an aqueous solution.

[0025] Ethyl aminotrimethylphosphonic acid, ethyl hydroxyethylidene diphosphate, and ethyl ethylenediaminetetramethylene phosphate were stirred and mixed to obtain a mixture; the mixture was then mixed with an aqueous solution to form a high-temperature resistant, antioxidant, and scale inhibitor for fracturing.

[0026] The present invention also discloses a fracturing fluid system comprising the aforementioned high-temperature resistant, antioxidant, and scale inhibitor for fracturing, wherein the hydrolysis reaction time of the high-temperature resistant, antioxidant, and scale inhibitor in the fracturing fluid system is later than the oxidation reaction time of the breaker.

[0027] Compared with the prior art, the present invention has the following beneficial technical effects:

[0028] This invention discloses a high-temperature resistant, antioxidant, and scale inhibitor for fracturing, comprising aminotrimethylmylate, hydroxyethylidene diphosphate, ethylenediaminetetramethylene phosphate, and an emulsifier. The three organic alkyl phosphates—aminotrimethylmylate, hydroxyethylidene diphosphate, and ethylenediaminetetramethylene phosphate—undergo hydrolysis upon entering the reservoir, transforming into aminotrimethylmylate, hydroxyethylidene diphosphate, and ethylenediaminetetramethylene phosphate, respectively. These three substances are currently relatively efficient and widely used scale inhibitors, capable of forming stable complexes with calcium and magnesium ions in water, thereby preventing them from forming scale deposits on pipes, equipment, and other surfaces, effectively reducing scale formation and deposition.

[0029] Compared with conventional scale inhibitors, the scale inhibitor of this invention is an esterified organic phosphate ester, which is water-insoluble and forms an oil-in-water emulsion under the action of an emulsifier. After entering the formation with the fracturing fluid, it can release the organic phosphate with high-efficiency scale inhibitor function through a slow hydrolysis reaction at the high temperature of the formation. Since the hydrolysis reaction time is 2-3 hours, while the oxidation reaction time of the breaker in the fracturing fluid is about 30-60 minutes, the scale inhibitor is effectively prevented from being destroyed by the oxidation reaction of the breaker after entering the formation, and still maintains high and stable scale inhibition and prevention performance, thereby reducing the damage of fracturing fluid to the formation.

[0030] Furthermore, the R group of aminotrimethylphosphonic acid alkyl ester, hydroxyethylidene diphosphonic acid alkyl ester, and ethylenediaminetetramethylene phosphonic acid alkyl ester is methyl or ethyl. When the R group is methyl, it is suitable for medium-temperature reservoirs of 70-90℃, with a stronger hydrolysis rate; when the R group is ethyl, it is suitable for high-temperature reservoirs above 90℃, with a weaker hydrolysis rate. Scale inhibitors with different hydrolysis release rates are added according to the different reservoir temperatures. Scale inhibitors containing organophosphate ethyl esters with a slower hydrolysis rate are added under high-temperature conditions, while scale inhibitors containing organophosphate methyl esters with a faster hydrolysis rate are added under medium-temperature reservoir conditions.

[0031] Furthermore, this invention uses nonylphenol polyoxyethylene ether and sodium dodecylbenzenesulfonate as emulsifiers. These substances enable thorough mixing of the oil and water phases, forming a stable oil-in-water emulsion. This allows the different components of the scale inhibitor to be evenly distributed throughout the system, preventing localized excessively high or low concentrations and ensuring the stability of the scale inhibitor's performance during use. The stable emulsion system also prevents the scale inhibitor from undergoing stratification, precipitation, or deterioration during storage, extending its shelf life.

[0032] Emulsifiers enable scale inhibitors to disperse better in fracturing fluids, thereby increasing the contact opportunities between the scale inhibitor and the scale. This helps the scale inhibitor to adsorb more effectively onto the scale surface, preventing further scale growth and deposition.

[0033] Emulsifiers can reduce the surface tension of fracturing fluids, making it easier for scale inhibitors to penetrate into formation pores and fractures, thus preventing and treating potential scale formation sites.

[0034] In high-temperature environments, emulsifiers can stabilize emulsion systems and prevent other components in scale inhibitors from decomposing or becoming ineffective due to high temperatures.

[0035] Enhance system stability: Stabilize the emulsion system to prevent demulsification or phase separation during storage and transportation, thereby ensuring the shelf life of the scale inhibitor product. Attached Figure Description

[0036] Figure 1 The pH dynamic curves of hydrolysates of three scale inhibitors are shown.

[0037] Figure 2 This is the APS decomposition rate curve. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0039] The detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0040] This invention discloses a high-temperature resistant, antioxidant, and scale inhibitor for fracturing, comprising the following components:

[0041] 5-15 parts of aminotrimethylphosphonic acid alkyl ester, 5-15 parts of hydroxyethylidene diphosphonic acid alkyl ester, 5-15 parts of ethylenediaminetetramethylene phosphonic acid alkyl ester, 5-15 parts of emulsifier, and 40-90 parts of water.

[0042] The high-temperature resistant, antioxidant, and scale inhibitor for fracturing of the present invention is a compound mixture of the above components, formulated into an oil-in-water emulsion.

[0043] The aforementioned aminotrimethylphosphoalkyl ester has the following molecular structural formula:

[0044]

[0045] Wherein, the R group is methyl or ethyl.

[0046] When the R group is methyl, aminotrimethylphosphophosphate has a strong methyl hydrolysis ability and is suitable for lower temperature reservoirs of 70-90℃.

[0047] When the R group is ethyl, the ethyl aminotrimethylphosphophosphate has a weak hydrolytic ability and is suitable for high-temperature reservoirs above 90℃.

[0048] Furthermore, the alkyl hydroxyethylidene diphosphate has the following molecular structural formula:

[0049]

[0050] Wherein, the R group is methyl or ethyl;

[0051] When the R group is methyl, hydroxyethylidene diphosphate has a strong hydrolytic ability and is suitable for lower temperature reservoirs of 70-90℃.

[0052] When the R group is ethyl, the hydrolytic ability of ethyl hydroxyethylidene diphosphate is relatively weak, making it suitable for high-temperature reservoirs above 90℃.

[0053] The alkyl ethylenediaminetetramethylene phosphate described above has the following molecular structural formula:

[0054]

[0055] The R group is either methyl or ethyl.

[0056] When the R group is methyl, ethylenediaminetetramethylene phosphate has a strong methyl hydrolysis ability and is suitable for lower temperature reservoirs of 70-90℃.

[0057] When the R group is ethyl, the ethyl ethylenediaminetetramethylene phosphate has a weak hydrolytic ability and is suitable for high-temperature reservoirs above 90°C.

[0058] The emulsifier is a water-soluble surfactant that can stabilize oil-in-water emulsions.

[0059] Specifically, the emulsifiers are nonylphenol polyoxyethylene and sodium dodecyl sulfate.

[0060] The high-temperature resistant, antioxidant, and scale inhibitor for fracturing of the present invention has the following functions:

[0061] I. High-efficiency scale inhibition performance

[0062] The three components—aminotrimethylammonium phosphate alkyl ester, hydroxyethylimide diphosphate alkyl ester, and ethylenediaminetetramethylene phosphate alkyl ester—work together to inhibit scale formation. They can bind with scale-forming ions in water (such as calcium and magnesium) to form stable complexes, preventing scale formation and deposition. This synergistic effect can effectively inhibit various types of scale, such as calcium carbonate, calcium sulfate, and calcium phosphate, thus improving scale inhibition efficiency.

[0063] Wide applicability: Due to its excellent complexing ability for various scale-forming ions, this scale inhibitor is suitable for fracturing operations under different water quality conditions. Whether it's hard water or water containing other impurities, it effectively prevents scale formation, ensuring the smooth progress of the fracturing process.

[0064] II. High Temperature Resistance

[0065] Stability of the Special Structure: The components in this scale inhibitor exhibit good stability at high temperatures. The molecular structures of components such as aminotrimethylmethylene phosphate alkyl ester, hydroxyethylidene diphosphate alkyl ester, and ethylenediaminetetramethylene phosphate alkyl ester remain stable under high-temperature environments, and are not easily decomposed or ineffective. This allows the scale inhibitor to maintain its effective scale inhibition function during high-temperature fracturing operations, ensuring the smooth flow of equipment and pipelines.

[0066] High-temperature oxidation resistance: Under high-temperature conditions, the emulsifiers and other components in the scale inhibitor also possess certain antioxidant properties, preventing the scale inhibitor itself from being oxidized and thus reducing its performance. Simultaneously, it also reduces the oxidation of other components in the fracturing fluid, extending the service life of the fracturing fluid.

[0067] III. Good emulsifying properties

[0068] Stabilized Emulsion System: The presence of emulsifiers enables scale inhibitors to form stable oil-in-water emulsion systems. This type of emulsion system facilitates the uniform dispersion of components, improving the performance stability of the scale inhibitor. Simultaneously, emulsifiers can reduce the surface tension of fracturing fluids, improving their flowability and permeability, allowing the scale inhibitor to more easily penetrate the formation and exert its scale inhibition effect.

[0069] Enhanced Formation Compatibility: Excellent emulsifying properties allow the scale inhibitor to have better compatibility with fluids in the formation, reducing damage to the formation. During fracturing operations, the scale inhibitor can interact with water and oil in the formation to form a stable mixture, avoiding formation blockage or other problems caused by incompatibility.

[0070] IV. Environmental friendliness

[0071] Low toxicity: The scale inhibitor uses relatively environmentally friendly ingredients with low toxicity to humans and the environment. During use, it will not cause serious harm to the health of operators, nor will it cause significant pollution to the surrounding environment.

[0072] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0073] Example 1

[0074] This invention discloses a method for preparing a high-temperature resistant, antioxidant, and scale inhibitor, comprising the following steps:

[0075] Dissolve 3 parts of nonylphenol polyoxyethylene and 2 parts of sodium dodecyl sulfate in 60 parts of pure water and heat to 60°C to form an aqueous solution.

[0076] Mix 15 parts of aminotrimethylphosphonic acid ethyl phosphate, 10 parts of hydroxyethylidene diphosphate ethyl phosphate, and 15 parts of ethylenediaminetetramethylene phosphate ethyl phosphate for 30 minutes. Slowly add the mixture to the aqueous solution while stirring. After the addition is complete, increase the stirring intensity and maintain for 1 hour to form an antioxidant scale inhibitor resistant to temperatures above 90°C, code: NGZ-1.

[0077] Example 2

[0078] This invention discloses a method for preparing a high-temperature resistant, antioxidant, and scale inhibitor, comprising the following steps:

[0079] Dissolve 3 parts of nonylphenol polyoxyethylene and 2 parts of sodium dodecyl sulfate in 60 parts of pure water and heat to 50°C to form an aqueous solution.

[0080] Mix 7 parts of aminotrimethylmycin phosphate, 7 parts of aminotrimethylmycin phosphate, 5 parts of hydroxyethylidene diphosphate, 5 parts of hydroxyethylidene diphosphate, 5 parts of ethylenediaminetetramethylene phosphate, and 5 parts of ethylenediaminetetramethylene phosphate for 30 minutes. Slowly add the mixture to the aqueous solution while stirring. After the addition is complete, increase the stirring intensity and maintain for 1 hour to form an antioxidant scale inhibitor resistant to 80-90℃, code: NGZ-2.

[0081] Example 3

[0082] This invention discloses a method for preparing a high-temperature resistant, antioxidant, and scale inhibitor, comprising the following steps:

[0083] Dissolve 5 parts of nonylphenol polyoxyethylene and 5 parts of sodium dodecyl sulfate in 90 parts of pure water and heat to 50°C to form an aqueous solution.

[0084] Mix 15 parts of aminotrimethylphosphonic acid methyl ester, 15 parts of hydroxyethylidene diphosphate methyl ester, and 10 parts of ethylenediaminetetramethylene phosphate methyl ester for 30 minutes. Slowly add the mixture to the aqueous solution while stirring. After the addition is complete, increase the stirring intensity and maintain for 1 hour to form an antioxidant scale inhibitor resistant to 70-80℃, code: NGZ-3.

[0085] Example 4

[0086] This invention discloses a method for preparing a high-temperature resistant, antioxidant, and scale inhibitor, comprising the following steps:

[0087] Dissolve 5 parts of nonylphenol polyoxyethylene and 10 parts of sodium dodecyl sulfate in 40 parts of pure water, and heat to 50°C to form an aqueous solution.

[0088] Mix 5 parts of aminotrimethylphosphonic acid methyl ester, 5 parts of hydroxyethylidene diphosphate methyl ester, and 5 parts of ethylenediaminetetramethylene phosphate methyl ester for 30 minutes. Slowly add the mixture to the above aqueous solution while stirring. After the addition is complete, increase the stirring intensity and maintain for 1 hour to form an antioxidant scale inhibitor resistant to 70-80℃, code: NGZ-4.

[0089] Example 5

[0090] This invention discloses a method for preparing a high-temperature resistant, antioxidant, and scale inhibitor, comprising the following steps:

[0091] Dissolve 5 parts of nonylphenol polyoxyethylene and 5 parts of sodium dodecyl sulfate in 70 parts of pure water and heat to 50°C to form an aqueous solution.

[0092] Mix 10 parts of aminotrimethylphosphonic acid methyl ester, 8 parts of hydroxyethylidene diphosphate methyl ester, and 9 parts of ethylenediaminetetramethylene phosphate methyl ester for 30 minutes. Slowly add the mixture to the aqueous solution while stirring. After the addition is complete, increase the stirring intensity and maintain for 1 hour to form an antioxidant scale inhibitor resistant to 70-80℃, code: NGZ-5.

[0093] Comparative Example

[0094] Standard scale inhibitor preparation:

[0095] 15 parts of aminotrimethylphosphonic acid, 10 parts of hydroxyethylidene diphosphonic acid, 10 parts of ethylenediaminetetramethylene phosphoric acid, and 65 parts of water are mixed at 60°C for 30 minutes to form a conventional scale inhibitor, code: CZJ.

[0096] The scale inhibitors prepared in Examples 1-5 and the comparative examples were evaluated.

[0097] I. Evaluation of High Temperature Resistance and Antioxidant Properties

[0098] Prepare a solution containing 1000 ppm scale inhibitor, 4 ppm anhydrous calcium chloride, 30 ppm anhydrous calcium chloride, 6.28 ppm sodium carbonate, 73.35 ppm sodium sulfate, 2.06 ppm sodium sulfate, 2.8 ppm barium chloride, ammonium buffer solution (54 g ammonium chloride + 350 ml ammonia water, then diluted to 1000 ml), chrome black T indicator, calcium indicator, EDTA standard solution, 1% ammonium persulfate (APS) solution, and 0.01 M EDTA-MgNa2.

[0099] Antioxidant and scale inhibition experimental evaluation:

[0100] 1. Blank group 1:

[0101] Add 200ml of distilled water and 5ml of APS to a 250ml volumetric flask, seal tightly, and place in a 95℃ water bath for 1 hour. After cooling to room temperature, add 6ml of 4ppm calcium chloride, shake well, let stand for 10 minutes, add 6ml of sodium carbonate, dilute to 250ml, shake well, seal the flask, and place it in a 95℃ water bath. After half an hour, open the stopper to release the gas, then seal the flask again and let it stand for 16 hours. If significant evaporation is observed, add distilled water to the mark of the volumetric flask and shake well before use.

[0102] 2. Blank group 2:

[0103] Add 200ml of distilled water and 5ml of APS to a 250ml volumetric flask, seal tightly, and place in a 95℃ water bath for 1 hour. After cooling to room temperature, add 6ml of 4ppm calcium chloride, shake well, let stand for 10 minutes, dilute to 250ml, shake well, seal the flask, and place it in a 95℃ water bath. After half an hour, open the stopper to release the gas, then seal the flask again and let it stand for 16 hours. If significant evaporation is observed, add distilled water to the mark of the volumetric flask and shake well before use.

[0104] 3. Experimental Group 1:

[0105] Add 100ml of distilled water and 7.5ml of NGZ-1 scale inhibitor to a 250ml volumetric flask, seal tightly, and place in a 95℃ water bath for 1 hour. Cool to room temperature. In a sealed reagent bottle, add 5ml of APS to 100ml of distilled water, cap, and place in a 95℃ water bath for 1 hour. After cooling to room temperature, pour the solution into the volumetric flask above. Add 6ml of 4ppm calcium chloride, shake well, and let stand for 10 minutes. Add 6ml of sodium carbonate, dilute to 250ml, shake well, seal, and place in a 95℃ water bath. After half an hour, open the stopper to release the gas, then seal again and let stand for 16 hours. If significant evaporation is observed, add distilled water to the mark of the volumetric flask and shake well before use.

[0106] 4. Experimental Group 2

[0107] Add 200ml of distilled water and 5ml of APS to a 250ml volumetric flask, then add 7.5ml of NGZ-1 scale inhibitor. Seal the flask and place it in a 95℃ water bath for 1 hour. After cooling to room temperature, add 6ml of 4ppm calcium chloride, shake well, and let stand for 10 minutes. Add 6ml of sodium carbonate, dilute to a final volume of 250ml, shake well, seal the flask, and place it in a 95℃ water bath. After half an hour, open the stopper to release the gas, then seal the flask again and let it stand for 16 hours. If significant evaporation is observed, add distilled water to the mark of the volumetric flask and shake well before use.

[0108] Titration / Calculation:

[0109] The supernatants of the above four solutions were filtered through qualitative filter paper, and the filtrate was collected. 25 ml of the filtrate was accurately transferred to a 250 ml Erlenmeyer flask, 5 ml of 0.5 M sodium hydroxide was added, along with a small amount of calcium indicator. The solution was shaken well until it turned a wine-red color. The solution was titrated with EDTA-2Na standard solution until a pure blue endpoint was reached, and the volume of EDTA-2Na consumed, V, was recorded. If significant evaporation was observed, distilled water was added to the mark of the volumetric flask, and the solution was shaken well before use.

[0110] Conventional scale inhibition rate calculation: X1 = (Vexperiment 1 - Vblank 1) / (Vblank 2 - Vblank 1) * 100%

[0111] Calculation of oxidation scale inhibition rate: X2 = (Vexperiment 2 - Vblank 1) / (Vblank 2 - Vblank 1) * 100%

[0112] Scale inhibition attenuation rate = (X1-X2) / X1*100%

[0113] The scale inhibitor NGZ-1 in the above evaluation process was replaced with CZJ scale inhibitor, and another scale inhibition evaluation was performed. The scale inhibition performance of the two scale inhibitors at 95℃ was compared and shown in Table 1.

[0114] Table 1 Comparison of Scale Inhibition Performance at 95℃

[0115]

[0116] As shown in Table 1, the scale inhibitor NGZ-1 prepared in this invention has a scale inhibition rate of 80.1%, which is slightly lower than the 88.7% scale inhibition rate of the conventional high-performance scale inhibitor CZJ. However, under the influence of high temperature and APS, the scale inhibition performance of conventional scale inhibitors decreases to 46.3% and 47.8%, respectively, while the scale inhibitor NGZ-1 prepared in this invention still maintains 67.4% under the influence of high temperature and APS, with a scale inhibition performance decrease of only 15.8%.

[0117] The water bath temperature in the scale inhibition evaluation method was adjusted to 85℃, while the other methods remained unchanged. The scale inhibition performance of NGZ-2 scale inhibitor and CZJ scale inhibitor was compared. The scale inhibition performance of the two scale inhibitors at 85℃ was compared, as shown in Table 2.

[0118] Table 2 Comparison of Scale Inhibition Performance at 85℃

[0119]

[0120] As shown in Table 2, the scale inhibitor NGZ-2 prepared in this invention has a scale inhibition rate of 82.2%, which is slightly lower than the 89.1% scale inhibition rate of the conventional high-performance scale inhibitor CZJ. However, under the influence of high temperature and APS, the scale inhibition performance of conventional scale inhibitors decreases to 49.5% and 39.6%, respectively, while the scale inhibitor NGZ-2 prepared in this invention still maintains 76.7% under the influence of high temperature and APS, with a scale inhibition performance decrease of only 5.5%.

[0121] The water bath temperature in the scale inhibition evaluation method was adjusted to 75℃, while the other methods remained unchanged. The scale inhibition performance of NGZ-3 scale inhibitor and CZJ scale inhibitor was compared. The scale inhibition performance of the two scale inhibitors at 75℃ was compared, as shown in Table 3.

[0122] Table 3 Comparison of Scale Inhibition Performance at 75℃

[0123]

[0124] As shown in Table 3, the scale inhibitor NGZ-3 configured in this invention has a scale inhibition rate of 83.4%, which is slightly lower than the 90.5% scale inhibition rate of the conventional high-performance scale inhibitor CZJ. However, under the influence of high temperature and APS, the scale inhibition rate of conventional scale inhibitors decreases to 67.6%, a decrease of 22.9%, while the scale inhibitor NGZ-2 configured in this invention still maintains 79.8% under the influence of high temperature and APS, with a scale inhibition performance decrease of only 3.6%.

[0125] The water bath temperature in the scale inhibition evaluation method was adjusted to 80℃, while the other methods remained unchanged. The scale inhibition performance of NGZ-4 scale inhibitor and CZJ scale inhibitor was compared. The scale inhibition performance of the two scale inhibitors at 75℃ was compared, as shown in Table 4.

[0126] Table 4 Comparison of Scale Inhibition Performance at 80℃

[0127]

[0128] As shown in Table 4, the scale inhibitor NGZ-4 configured in this invention has a scale inhibition rate of 72.4%, which is slightly lower than the 87.8% scale inhibition rate of the conventional high-performance scale inhibitor CZJ. However, under the influence of high temperature and APS, the scale inhibition rate of conventional scale inhibitors decreases to 47.2%, a decrease of 40.6%, while the scale inhibitor NGZ-4 configured in this invention still maintains 68.6% under the influence of high temperature and APS, with a scale inhibition performance decrease of only 3.8%.

[0129] The water bath temperature in the scale inhibition evaluation method was adjusted to 70℃, while the other methods remained unchanged. The scale inhibition performance of NGZ-5 scale inhibitor and CZJ scale inhibitor was compared. The scale inhibition performance of the two scale inhibitors at 75℃ was compared, as shown in Table 5.

[0130] Table 5 Comparison of Scale Inhibition Performance at 70℃

[0131]

[0132] As shown in Table 5, the scale inhibitor NGZ-5 configured in this invention has a scale inhibition rate of 73.1%, which is slightly lower than the 90.1% scale inhibition rate of the conventional high-performance scale inhibitor CZJ. However, under the influence of high temperature and APS, the scale inhibition rate of conventional scale inhibitors decreases to 67.6%, a decrease of 22.5%, while the scale inhibitor NGZ-5 configured in this invention still maintains 68.9% under the influence of high temperature and APS, with a scale inhibition performance decrease of only 4.2%.

[0133] II. Evaluation of hydrolysis rate:

[0134] Take three 250mL volumetric flasks and add 7.5mL of NGZ-1, NGZ-2, NGZ-3, NGZ-4, and NGZ-5 respectively. Then, bring the volume to 250mL and shake thoroughly. Place each flask in a water bath at 95℃, 85℃, 80℃, 75℃, and 70℃ respectively. Start timing each flask. Remove the liquid every 15 minutes and measure the pH using a pH meter. The change in pH indicates the degree of hydrolysis. Figure 1 As shown, the hydrolysis time of the five scale inhibitor formulations is approximately 3 hours.

[0135] III. Evaluation of the decomposition rate of ammonium persulfate (APS)

[0136] Prepare five 500ml beakers of 0.4% APS solution and place them in water at 95℃, 85℃, 80℃, 75℃, and 70℃ respectively. Every 5 minutes, 10ml of solution is removed and cooled in an iodine flask. The decomposition rate of APS at different temperatures is determined using the method described below. The results are as follows: Figure 2 The decomposition rate-time curve is shown.

[0137] Take 10 mL of 0.4% APS in an iodine flask, add 20 mL of deionized water and 4 g (accurate to 0.01 g) of KI, shake well, and let stand in the dark for 30 min. Add 2 mL of 36% acetic acid to the settled solution, and titrate with standard sodium thiosulfate solution. Near the endpoint, add 3 mL of starch indicator and continue titrating until the blue color of the solution disappears. Record the volume of sodium thiosulfate standard solution consumed, V1. Perform a blank test under the same experimental conditions using deionized water instead of the sample solution, and record the volume of sodium thiosulfate standard solution consumed, V2.

[0138] The APS decomposition rate is calculated using the following formula 1:

[0139]

[0140] In the formula:

[0141] n—Decomposition rate, %;

[0142] The actual concentration of the CO-sodium thiosulfate standard solution, in mol / L;

[0143] The volume of sodium thiosulfate standard solution consumed by V1—CJJN-3, in mL;

[0144] V2—The volume of sodium thiosulfate standard solution consumed in the blank test, in mL;

[0145] Under the same experimental conditions, two parallel experiments are conducted, and the relative error between the two measurements is no greater than 5%. The arithmetic mean of the results is taken.

[0146] Figure 2 This indicates that the complete decomposition time of APS at 95℃, 85℃, 80℃, 75℃, and 70℃ is 30min-100min, which means that the oxidation reaction can be completed before the scale inhibitor is completely released, thus avoiding large-scale contact between APS and the scale inhibitor.

[0147] The above results indicate that the scale inhibitor provided by this invention has a delayed release effect due to hydrolysis, and the hydrolysis release time is approximately 2-3 hours, slower than the decomposition time of the breaker APS (approximately 1 hour). Therefore, it can continue to release the scale inhibitor through hydrolysis after the breaker has completely decomposed, avoiding oxidation and destruction of the scale inhibitor by the breaker. Compared to conventional scale inhibitors, the scale inhibitor provided by this invention is better able to maintain highly stable scale inhibition and prevention performance under high formation temperatures and breaker oxidation, thereby reducing the damage of fracturing fluid to the formation.

[0148] Adding esterified organophosphate scale inhibitors to the fracturing fluid system allows the scale inhibitor molecules to be slowly released after hydrolysis upon entering the formation, thus preventing the organophosphate scale inhibitors from being destroyed by the rapid oxidation reaction of the breaker.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-temperature resistant, antioxidant, and scale inhibitor for fracturing, characterized in that, Based on parts by mass, it includes the following components: 5-15 parts of aminotrimethylphosphonic acid alkyl ester, 5-15 parts of hydroxyethylidene diphosphonic acid alkyl ester, 5-15 parts of ethylenediaminetetramethylene phosphonic acid alkyl ester, 5-15 parts of emulsifier, and 40-90 parts of water.

2. The high-temperature resistant, antioxidant, and scale inhibitor for fracturing according to claim 1, characterized in that, The molecular structural formula of aminotrimethylphosphoalkyl ester is: Wherein, the R group is methyl or ethyl.

3. The high-temperature resistant, antioxidant, and scale inhibitor for fracturing according to claim 2, characterized in that, When the R group is methyl, hydroxyethylidene is suitable for reservoirs at 70-90℃; When the R group is ethyl, the hydroxyethylidene is suitable for reservoirs above 90°C; The hydrolytic ability of aminotrimethylphosphomethyl is stronger than that of aminotrimethylphosphoethyl.

4. The high-temperature resistant, antioxidant, and scale inhibitor for fracturing according to claim 1, characterized in that, The molecular structural formula of alkyl ethylenediaminetetramethylene phosphate is: Wherein, the R group is methyl or ethyl.

5. The high-temperature resistant, antioxidant, and scale inhibitor for fracturing according to claim 1, characterized in that, The molecular structural formula of alkyl hydroxyethylidene diphosphate is: Wherein, the R group is methyl or ethyl.

6. The high-temperature resistant, antioxidant, and scale inhibitor for fracturing according to claim 5, characterized in that, When the R group is methyl, hydroxyethylidene is suitable for reservoirs at 70-90℃; When the R group is ethyl, the hydroxyethylidene is suitable for reservoirs above 90°C; The hydrolytic ability of methyl hydroxyethylidene diphosphate is stronger than that of ethyl hydroxyethylidene diphosphate.

7. The high-temperature resistant, antioxidant, and scale inhibitor for fracturing according to claim 1, characterized in that, The emulsifier is a water-soluble surfactant that can stabilize oil-in-water emulsions.

8. The high-temperature resistant, antioxidant, and scale inhibitor for fracturing according to claim 7, characterized in that, The emulsifiers are nonylphenol polyoxyethylene and sodium dodecyl sulfate.

9. A method for preparing the high-temperature resistant, antioxidant, and scale inhibitor for fracturing according to any one of claims 1-8, characterized in that, The process includes the following: Dissolve the emulsifier in pure water and heat it to 50-60℃ to form an aqueous solution. Ethyl aminotrimethylphosphonic acid, ethyl hydroxyethylidene diphosphate, and ethyl ethylenediaminetetramethylene phosphate were stirred and mixed to obtain a mixture; the mixture was then mixed with an aqueous solution to form a high-temperature resistant, antioxidant, and scale inhibitor for fracturing.

10. A fracturing fluid system comprising the high-temperature resistant, antioxidant, and scale inhibitor for fracturing according to any one of claims 1-8, characterized in that, In fracturing fluid systems, the hydrolysis reaction time of high-temperature resistant, antioxidant, and scale inhibitors is later than the oxidation reaction time of the breaker.

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