A high-temperature resistant, self-degradable composite acidizing fracturing fluid system and its preparation method

Abstract

This invention discloses a high-temperature resistant, self-degradable composite acidizing fracturing fluid system and its preparation method, relating to the field of acidizing fracturing fluid technology. The system includes: a base fluid, a thickener, a complexing agent, a flow aid, a corrosion inhibitor, and a solvent. The base fluid is a citric acid-tartaric acid-hydrochloric acid composite acid solution; the thickener is an AM / DMC / AA / AMPS / NVP pentpolymer; the complexing agent is dihydroxyethylglycine; the flow aid is a fluorocarbon surfactant; the corrosion inhibitor is a compound corrosion inhibitor of imidazoline and pyridine; and the solvent is deionized water. This high-temperature resistant, self-degradable composite acidizing fracturing fluid system exhibits high-temperature retardation, self-degradation characteristics, environmental friendliness, salt and shear resistance, and temperature resistance.

Description

Technical Field

[0001] This invention relates to the field of acid fracturing fluid technology, and in particular to a high-temperature resistant, self-degradable composite acid fracturing fluid system and its preparation method. Background Technology

[0002] Acid fracturing is an effective means of increasing permeability by using acid to chemically dissolve the fracture walls of reservoirs. However, the following technical bottlenecks still exist in practical applications:

[0003] For example, there are several drawbacks: Insufficient acid retardation: Conventional hydrochloric acid systems react too quickly with carbonate rocks, resulting in a short acid action distance and hindering deep reservoir stimulation. Poor thickener temperature resistance: Polyacrylamide-based thickeners, widely used in existing technologies, experience molecular chain breakage at high temperatures, leading to a sharp drop in viscosity and failing to meet the operational requirements of deep-well high-temperature reservoirs. Low environmental compatibility: The cationic monomers in traditional thickeners have poor biodegradability, and residues can easily clog formation pores and pollute the environment, failing to meet current environmental protection requirements for green development. Low flowback efficiency: Existing systems rely on breaker agents to degrade the thickener, but incomplete breaker action can lead to residual adhesive remaining in the formation, reducing the flowback rate and potentially causing secondary pollution of the flowback fluid. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides a high-temperature resistant, self-degradable composite acid fracturing fluid system and its preparation method.

[0005] On the one hand, a high-temperature resistant, self-degradable composite acidizing fracturing fluid system is provided, comprising: base fluid, thickener, complexing agent, drainage aid, corrosion inhibitor, and solvent;

[0006] The base liquid is a citric acid-tartaric acid-hydrochloric acid composite acid solution, the thickener is an AM / DMC / AA / AMPS / NVP pentacetic copolymer, the complexing agent is dihydroxyethylglycine, the discharge aid is a fluorocarbon surfactant, the corrosion inhibitor is a compound corrosion inhibitor of imidazoline and pyridine, and the solvent is deionized water.

[0007] Further, by mass percentage, the thickener is 0.8-1.2%, the complexing agent is 1-2%, the drainage aid is 0.1-0.3%, the corrosion inhibitor is 0.5-1%, the hydrochloric acid in the base solution is 15-20%, the citric acid in the base solution is 10-15%, the tartaric acid in the base solution is 5-10%, and the balance is the solvent.

[0008] Furthermore, in the base solution, the concentration of hydrochloric acid is 15-20%, the concentration of citric acid is 5-8%, and the concentration of tartaric acid is 3-5%.

[0009] Furthermore, the molar ratio of AM, DMC, AA, AMPS, and NVP in the thickener is 85:3:10:1:1.

[0010] Furthermore, the mass ratio of imidazoline to pyridine in the corrosion inhibitor is 2:1.

[0011] On the other hand, a method for preparing the high-temperature resistant, self-degradable composite acidizing fracturing fluid system is provided, comprising the following steps:

[0012] Preparation of AM / DMC / AA / AMPS / NVP pentagonal copolymer;

[0013] Dihydroxyethylglycine was dissolved in deionized water with tartaric acid, citric acid, and hydrochloric acid to obtain a high-temperature resistant acid-based liquid.

[0014] The high-temperature resistant acid base fluid is mixed with deionized water, and then the AM / DMC / AA / AMPS / NVP pentapolymer, fluorocarbon surfactant, and imidazoline and pyridine compound corrosion inhibitor are added sequentially to obtain the high-temperature resistant self-degradable composite acid fracturing fluid system.

[0015] Furthermore, the preparation of the AM / DMC / AA / AMPS / NVP pentagon specifically includes:

[0016] AM, DMC, AA, AMPS, and NVP were dissolved in deionized water in a molar ratio of 85:3:10:1:1. The pH was adjusted to 7.0, and nitrogen was purged for half an hour to remove oxygen. Then, 0.08 wt% of ammonium persulfate-sodium bisulfite initiator was added dropwise at 45°C. The reaction was carried out for 12 hours, granulated, and vacuum dried at 60°C to obtain the AM / DMC / AA / AMPS / NVP pentpolymer.

[0017] The beneficial effects of the technical solution provided by this invention are as follows: The high-temperature resistant self-degradable composite acid fracturing fluid system of this invention has the following characteristics: 1. High-temperature retardation: The multi-acid synergistic complexation retardation mechanism and compound corrosion inhibitor technology take into account both corrosion inhibition efficiency and system stability; 2. Self-degradation characteristics: The rigid segments of NVP and AMPS in the copolymer control the degradation time, eliminating the need for a breaker; 3. Environmental friendliness: DMC replaces traditional toxic cationic monomers, improving the biodegradation rate; 4. Salt and shear resistance: Under high salt conditions, the AMPS sulfonic acid groups inhibit the compression of the double electric layer by salt ions through electrostatic repulsion, resulting in excellent salt resistance; 5. Temperature resistance: The rigid structure of the molecular chain inhibits degradation at high temperatures, resulting in a gradual decrease in viscosity. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is the infrared spectrum of an AM / DMC / AA / AMPS / NVP pentpolymer provided by the present invention;

[0020] Figure 2 This is a molecular structure diagram of an AM / DMC / AA / AMPS / NVP pentagonal copolymer provided by the present invention;

[0021] Figure 3 This is a viscosity comparison chart of a high-temperature resistant, self-degradable composite acid fracturing fluid system provided by this invention and a traditional polyacrylamide fracturing fluid system at different temperatures;

[0022] Figure 4 This is a graph showing the viscosity stability test results of a high-temperature resistant, self-degradable composite acidizing fracturing fluid system under high salinity conditions and a traditional polyacrylamide fracturing fluid system, provided by this invention.

[0023] Figure 5 This is a comparison chart of the sand suspension performance of a high-temperature resistant, self-degradable composite acidizing fracturing fluid system provided by this invention and a traditional polyacrylamide fracturing fluid system.

[0024] Figure 6 This is a comparison chart of the gel breaking performance of a high-temperature resistant, self-degradable composite acid fracturing fluid system provided by this invention and a traditional polyacrylamide fracturing fluid system. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0027] Example 1

[0028] A high-temperature resistant, self-degradable composite acid fracturing fluid system comprises the following components: base fluid, complexing agent, corrosion inhibitor, thickener, drainage aid, and solvent.

[0029] The base solution is a citric acid-tartaric acid-hydrochloric acid composite acid solution, the thickener is an AM / DMC / AA / AMPS / NVP pentacetic copolymer, the complexing agent is dihydroxyethylglycine, the drainage aid is a fluorocarbon surfactant, the corrosion inhibitor is a compound corrosion inhibitor of imidazoline and pyridine, and the solvent is deionized water.

[0030] In this high-temperature resistant, self-degradable composite acidizing fracturing fluid system, by mass percentage, the AM / DMC / AA / AMPS / NVP pentagonal copolymer accounts for 1%, dihydroxyethylglycine for 1.5%, fluorocarbon surfactant for 0.2%, imidazoline and pyridine composite corrosion inhibitor for 0.8%, hydrochloric acid for 18%, citric acid for 12%, tartaric acid for 8%, and the balance is deionized water; among which, the molar ratio of AM, DMC, AA, AMPS, and NVP in the AM / DMC / AA / AMPS / NVP pentagonal copolymer is 85:3:10:1:1, and the mass ratio of imidazoline to pyridine in the imidazoline and pyridine composite corrosion inhibitor is 2:1.

[0031] Among them, the fluorocarbon surfactant is perfluorooctyl sulfonate (PFOS): DuPont Zonyl® FSA (CAS: 29457-72-5), the imidazoline corrosion inhibitor is perfluorooctyl imidazoline quaternary ammonium salt, CAS: N / A, trade name: FluoroImid-12, and the pyridine corrosion inhibitor is hexadecyl bromide pyridine (CPB) (CAS: 140-72-7), trade name: Pyridinium-16.

[0032] The specific preparation method is as follows:

[0033] Step (101): Synthesis of thickener: Add 85 parts AM, 1 part AMPS, 1 part NVP, 3 parts DMC, 10 parts AA and 298 parts deionized water to the reactor, adjust the pH to 7.0, purge with nitrogen for half an hour to remove oxygen, then raise the temperature to 45°C, add 0.5 parts of initiator ammonium persulfate-sodium bisulfite, react for 12 hours, granulate, and vacuum dry at 60°C to obtain a powder with a molecular weight of 10-12 million, which is the target thickener.

[0034] After preparing the thickener, take 1.2g and dissolve it in 200g of experimental water. After it is fully dissolved, use a viscometer to measure its viscosity. Its apparent viscosity is 85mPa·s, indicating a good thickening effect.

[0035] Step (102): Preparation of high-temperature resistant acid base solution: Dihydroxyethylglycine, 4% tartaric acid, 6.5% citric acid, and 18% hydrochloric acid are dissolved in deionized water in the above proportions to obtain the high-temperature resistant acid base solution.

[0036] Step (103): Mix the high-temperature resistant acid base fluid with deionized water, and add the AM / DMC / AA / AMPS / NVP pentapolymer, fluorocarbon surfactant, and imidazoline and pyridine compound corrosion inhibitor in the above proportions in sequence. Let it stand for 2 hours. Finally, the high-temperature resistant self-degradable composite acid fracturing fluid system is obtained.

[0037] Example 2

[0038] A high-temperature resistant, self-degradable composite acidizing fracturing fluid system comprises, by mass percentage, 0.8% AM / DMC / AA / AMPS / NVP pentpolymer, 1% dihydroxyethylglycine, 0.1% fluorocarbon surfactant, 0.5% imidazoline and pyridine composite corrosion inhibitor, 15% hydrochloric acid, 10% citric acid, 5% tartaric acid in the base fluid, and the balance being deionized water; wherein, the molar ratio of AM, DMC, AA, AMPS, and NVP in the AM / DMC / AA / AMPS / NVP pentpolymer is 85:3:10:1:1, and the mass ratio of imidazoline to pyridine in the imidazoline and pyridine composite corrosion inhibitor is 2:1.

[0039] Among them, the fluorocarbon surfactant is perfluorooctyl sulfonate (PFOS): DuPont Zonyl® FSA (CAS: 29457-72-5), the imidazoline corrosion inhibitor is perfluorooctyl imidazoline quaternary ammonium salt, CAS: N / A, trade name: FluoroImid-12, and the pyridine corrosion inhibitor is hexadecyl bromide pyridine (CPB) (CAS: 140-72-7), trade name: Pyridinium-16.

[0040] The specific preparation method is as follows:

[0041] Step (201): Same as in Example 1.

[0042] Step (202): Preparation of high-temperature resistant acid base solution: Dihydroxyethylglycine, 3% tartaric acid, 5% citric acid, and 15% hydrochloric acid are dissolved in deionized water in the above proportions to obtain the high-temperature resistant acid base solution.

[0043] Step (203): Mix the high-temperature resistant acid base fluid with deionized water, and add the AM / DMC / AA / AMPS / NVP pentapolymer, fluorocarbon surfactant, and imidazoline and pyridine compound corrosion inhibitor in the above proportions in sequence. Let it stand for 1 hour. Finally, the high-temperature resistant self-degradable composite acid fracturing fluid system is obtained.

[0044] Example 3

[0045] A high-temperature resistant, self-degradable composite acidizing fracturing fluid system comprises, by mass percentage, 1.2% AM / DMC / AA / AMPS / NVP pentagonal copolymer, 2% dihydroxyethylglycine, 0.3% fluorocarbon surfactant, 1% imidazoline and pyridine compound corrosion inhibitor, 20% hydrochloric acid, 15% citric acid, 10% tartaric acid in the base fluid, and the balance being deionized water; wherein, the molar ratio of AM, DMC, AA, AMPS, and NVP in the AM / DMC / AA / AMPS / NVP pentagonal copolymer is 85:3:10:1:1, and the mass ratio of imidazoline to pyridine in the imidazoline and pyridine compound corrosion inhibitor is 2:1.

[0046] Among them, the fluorocarbon surfactant is perfluorooctyl sulfonate (PFOS): DuPont Zonyl® FSA (CAS: 29457-72-5), the imidazoline corrosion inhibitor is perfluorooctyl imidazoline quaternary ammonium salt, CAS: N / A, trade name: FluoroImid-12, and the pyridine corrosion inhibitor is hexadecyl bromide pyridine (CPB) (CAS: 140-72-7), trade name: Pyridinium-16.

[0047] The specific preparation method is as follows:

[0048] Step (301): Same as in Example 1.

[0049] Step (302): Preparation of high-temperature resistant acid base solution: Dihydroxyethylglycine, 5% tartaric acid, 8% citric acid, and 20% hydrochloric acid are dissolved in deionized water in the above proportions to obtain the high-temperature resistant acid base solution.

[0050] Step (303): Mix the high-temperature resistant acid base fluid with deionized water, and add the AM / DMC / AA / AMPS / NVP pentapolymer, fluorocarbon surfactant, and imidazoline and pyridine compound corrosion inhibitor in the above proportions in sequence. Let it stand for 3 hours. Finally, the high-temperature resistant self-degradable composite acid fracturing fluid system is obtained.

[0051] It should be noted that in the AM / DMC / AA / AMPS / NVP pentpolymer thickener, acrylamide (AM) forms the main chain backbone of the polymer molecule, methacryloyloxyethyltrimethylammonium chloride (DMC) is a cationic modifier of the polymer molecule to enhance adsorption, acrylic acid (AA) increases polymer solubility, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) sulfonic acid groups improve salt resistance, and N-vinylpyrrolidone (NVP) pyrrolidone rings increase chain rigidity and temperature resistance.

[0052] Figure 2 This is the molecular structural formula of the prepared AM / DMC / AA / AMPS / NVP pentagonal copolymer. Figure 1This is the infrared spectrum of the AM / DMC / AA / AMPS / NVP pentpolymer, from... Figure 1 As can be seen, the infrared spectrum confirms the successful synthesis of the copolymer, specifically: 3450 cm⁻¹. -1 The peak at 1668 cm⁻¹ is the NH stretching vibration peak (AM characteristic absorption). -1 The peak at 1180 cm⁻¹ is the C=O stretching vibration peak (characteristic absorption of AA and AMPS). -1 The peak at 1050 cm⁻¹ is the S=O symmetric stretching vibration peak (characteristic absorption of AMPS sulfonic acid group). -1 The peak at this location is the COC stretching vibration peak (characteristic absorption of the DMC cation group).

[0053] In addition, different comparative examples were set up by adjusting the molar ratio of AM, DMC, AA, AMPS, and NVP in the thickener, and a conventional polyacrylamide thickener (molecular weight 10 million) was used as a comparative example to compare the performance with the thickener in Example 1. 0.6% concentration solutions of each thickener were prepared with deionized water, and the viscosity retention rate of each thickener at 120°C was measured to characterize its temperature resistance. The biodegradation rate of each thickener was also measured. The specific results are shown in Table 1.

[0054] Table 1

[0055] Group Thickener type Molecular weight (in ten thousand) Dissolution time (min) Viscosity retention rate at 120℃ (%) Biodegradation rate (30 days, %) Example 1 The molar ratio of AM, DMC, AA, AMPS, and NVP is 85:3:10:1:1. 1100 10 87.2 92.5 Comparative Example 1 The molar ratio of AM, DMC, AA, AMPS, and NVP is 85:4:14:1:1. 1250 15 84.4 71.4 Comparative Example 2 The molar ratio of AM, DMC, AA, AMPS, and NVP is 85:5:13:1:1. 980 18 82.1 43.5 Comparative Example 3 The molar ratio of AM, DMC, AA, AMPS, and NVP is 80:3:15:1:1. 890 15 76.8 85.2 Comparative Example 4 The molar ratio of AM, DMC, AA, AMPS, and NVP is 80:1:17:1:1 750 15 52.3 89.7 Comparative Example 5 Polyacrylamide thickener 1000 38 28.9 39.7

[0056] The data in Table 1 shows the effect of molecular weight on the thickener: excessively high molecular weight (>12 million) leads to difficulty in dissolution, while excessively low molecular weight (<8 million) results in decreased temperature resistance. Regarding environmental impact: when the DMC content is >5%, the biodegradability rate decreases significantly. Therefore, the best overall performance is achieved when the molar ratio of AM, DMC, AA, AMPS, and NVP in the AM / DMC / AA / AMPS / NVP pentpolymer is 85:3:10:1:1. Furthermore, the performance of the thickeners in Example 1 is superior to that of traditional polyacrylamide thickeners.

[0057] It should also be noted that different comparative examples were set by adjusting the mass percentages of dihydroxyethylglycine, tartaric acid, citric acid, and hydrochloric acid in the high-temperature resistant acid base solution, and compared with the high-temperature resistant acid base solutions in steps (102) of Example 1, (202) of Example 2, and (302) of Example 3, to obtain Fe 3+ Comparison of complexation efficiency.

[0058] The experimental procedures are as follows: 1. Preparation of Fe³⁺ solution: Weigh 4.84 g FeCl₃·6H₂O and dissolve it in 1 L of deionized water to prepare a standard solution with a Fe³⁺ concentration of 1000 mg / L. 2. Preparation of acid sample: Prepare a high-temperature resistant acid base solution according to the mass percentages in Table 2. For example, the high-temperature resistant acid base solution in Example 1 is: hydrochloric acid (20%), citric acid (12%), tartaric acid (8%), and dihydroxyethylglycine (1.5%). 3. Mixing and reaction: Mix 50 mL of the high-temperature resistant acid base solution with 50 mL of Fe³⁺ solution (1000 mg / L) and place it in a constant temperature water bath. React at 90℃ for 2 hours. After the reaction, transfer the mixture to a centrifuge tube and centrifuge at 4000 rpm for 15 minutes to separate the precipitate and the supernatant. 4. Fe³⁺ Concentration Determination: The supernatant was filtered (using a 0.45 μm filter membrane), and the free Fe³⁺ concentration was determined using ICP-OES. See Table 2 for specific results.

[0059] Table 2

[0060] Group hydrochloric acid(%) Citric acid (%) tartaric acid(%) Dihydroxyethylglycine (%) Acid viscosity (mPa·s) Fe³⁺ complexation efficiency (%) Example 1 18 12 8 1.5 85 98.2 Example 2 15 10 5 1.0 82 95.7 Example 3 20 15 10 2.0 88 97.5 Comparative Example 1 20 0 20 1.5 72 63.4 (Precipitation formation) Comparative Example 2 25 12 8 0 68 81.3 (Complexation failure) Comparative Example 3 20 8 8 1.5 78 89.6

[0061] In Table 2, the concentrations of hydrochloric acid and tartaric acid in Comparative Example 1 are the same as those in Example 1, and the concentrations of hydrochloric acid, tartaric acid, and citric acid in Comparative Examples 2 and 3 are the same as those in Example 1.

[0062] As can be seen from Table 2, the lack of citric acid (Comparative Example 1) leads to Fe 3+ Precipitation; lack of complexing agent (Comparative Example 2) significantly reduced complexation efficiency. Therefore, as can be seen from Table 2, the synergistic complexation of citric acid-tartaric acid-hydrochloric acid in this invention inhibits hydrolysis precipitation and maintains the acidification effect.

[0063] It should also be noted that, taking the high-temperature resistant self-degradable composite acid fracturing fluid system in Example 1 as an example, different comparative ratios were set by adjusting the type and concentration of corrosion inhibitors. The remaining components were the same as in Example 1. The corrosion rate and stability of each fracturing fluid system were tested. The test method was as follows: N80 steel sheets were immersed in acid solutions containing each fracturing fluid system at 90°C for 4 hours. The corrosion rate was determined according to SY / T 5405-2019. The specific results are shown in Table 3.

[0064] Table 3

[0065] Group Corrosion inhibitor type Total concentration of corrosion inhibitor (%) Corrosion rate (g / m²·h) Stability (precipitation after 72 hours) Example 1 Imidazoline:pyridine = 2:1 0.8 0.75 none Comparative Example 1 Imidazoline:pyridine = 1:1 1.0 0.82 Microflocculation Comparative Example 2 Imidazolin:pyridine = 3:1 1.2 1.05 Precipitation formation Comparative Example 3 Single pyridine 0.8 1.32 none Comparative Example 4 Commercially available corrosion inhibitors 1.5 0.68 Severe stratification

[0066] As can be seen from Table 3, the type of corrosion inhibitor in Example 1 (imidazoline:pyridine = 2:1) balances corrosion inhibition efficiency and system stability.

[0067] In Comparative Example 3, the single pyridine was (bromocetamolpyridine (CPB) (CAS: 140-72-7), trade name: Pyridinium-16), and the commercially available corrosion inhibitor was BASF Keromix series: Keromix 600.

[0068] It should also be noted that the AM / DMC / AA / AMPS / NVP pentpolymer in Example 1 was replaced with commercially available polyacrylamide to form the fracturing fluid system. The remaining components were the same as in Example 1. Salt resistance tests were conducted at different salinity levels on the fracturing fluid system compared to the high-temperature resistant, self-degrading composite acidizing fracturing fluid system in Example 1. The test procedure was as follows: Prepare a fracturing fluid containing 5×10... 4 mg / L, 10×10 4 A 0.6% concentration of a saline solution was added to each fracturing fluid system solution, and the viscosity was measured. The specific results are shown in Table 4.

[0069] Table 4

[0070] Group Mineralization (mg / L) <![CDATA[NaCl:CaCl2 (mass ratio)]]> Initial viscosity (mPa·s) Viscosity after shearing at 120℃ (mPa·s) Complexing agent precipitation Example 1 <![CDATA[5×10 4 ]]> 3:1 83 56 none Example 1 <![CDATA[10×10 4 ]]> 3:1 80 49 none Comparative Example 1 <![CDATA[5×10 4 ]]> 3:1 52 18 Large amount of sediment Comparative Example 1 <![CDATA[10×10 4 ]]> 3:1 48 15 Large amount of sediment

[0071] in addition, Figure 4 This is a graph showing the viscosity stability test results (viscosity after shear at 120℃) of the high-temperature resistant self-degradable composite acidizing fracturing fluid system and the traditional polyacrylamide fracturing fluid system in Example 1. (See attached graph.) Figure 4 According to Table 4, the mineralization degree is 5×10⁻⁶. 4 At a concentration of mg / L, the initial viscosity of the high-temperature resistant self-degrading composite acidizing fracturing fluid system in Example 1 was 83 mPa·s, the viscosity after shearing was 56 mPa·s, and the salinity was 10 × 10⁻⁶ mPa·s. 4 At a concentration of mg / L, the initial viscosity of the high-temperature resistant, self-degradable composite acidizing fracturing fluid system in Example 1 was 80 mPa·s, and the viscosity after shearing was 49 mPa·s. This is because the AMPS sulfonic acid groups inhibit the compression of the electric double layer by salt ions through electrostatic repulsion, resulting in excellent salt resistance. The AMPS sulfonic acid groups can support the system at a concentration of 10 × 10 mg / L. 4 Stable operation at a salinity of mg / L; however, the polyacrylamide in Comparative Example 1 had poor salt resistance, leading to the complexing agent reacting with Ca. 2+ Due to the failure of the traditional polyacrylamide acid fracturing system, which lacks salt-resistant groups, the viscosity is significantly affected by the salting-out effect.

[0072] It should also be noted that the AM / DMC / AA / AMPS / NVP pentpolymer in Example 1 was replaced with commercially available polyacrylamide to form the fracturing fluid system. The remaining components were the same as in Example 1. The viscosity of the fracturing fluid system was compared with that of the high-temperature resistant, self-degrading composite acidizing fracturing fluid system in Example 1 at different temperatures. The fracturing fluid system solution was prepared at a concentration of 0.6% and stirred until completely dissolved using a Wu Yin mixer. After standing for 4 hours, the viscosity values ​​at temperatures (30℃, 60℃, 90℃, 120℃, 150℃) and a shear rate of 170 s⁻¹ were measured using a Fann-35 six-speed rotational viscometer. Specific results can be found in [link to relevant documentation]. Figure 3 ,Depend on Figure 3 It can be seen that the high-temperature resistant self-degradable composite acid fracturing fluid system in Example 1 has an initial viscosity of 86 mPa·s at 30℃ and maintains 52 mPa·s at 150℃, indicating that the viscosity decay is gradual and the rigid molecular chain structure inhibits degradation at high temperatures. In contrast, the traditional polyacrylamide fracturing fluid system has an initial viscosity of 62 mPa·s at 30℃ and only 15 mPa·s at 150℃, indicating that the molecular chain breaks significantly at high temperatures and the viscosity drops sharply.

[0073] Secondly, the proppant suspension performance of the high-temperature resistant self-degradable composite acidizing fracturing fluid system in Example 1 was compared with that of the traditional polyacrylamide fracturing fluid system (quartz sand with a diameter of 0.42~0.84 mm (20~40 mesh) was used as proppant, and the fracturing fluid system to proppant mass ratio was 7:3. The sedimentation time of the sand and gravel was recorded, and the sedimentation rate of the proppant was calculated). For specific results, please refer to [link to relevant documentation]. Figure 5 ,from Figure 5 As can be seen, the initial proppant height was 18cm. In the end, the proppant height of the high-temperature self-degradable composite acidizing fracturing fluid system in Example 1 was 10cm, while the proppant height of the traditional polyacrylamide fracturing fluid system was 1cm. This is because the high-temperature self-degradable composite acidizing fracturing fluid system in Example 1 forms a three-dimensional network structure, which can effectively suspend the proppant. The entanglement of the thickener molecular chains and the synergistic effect of hydrogen bonds can significantly enhance the sand suspension capacity compared to the traditional polyacrylamide fracturing fluid system.

[0074] In addition, the gel-breaking performance of the high-temperature resistant self-degradable composite acidizing fracturing fluid system in Example 1 was compared with that of the traditional polyacrylamide fracturing fluid system (0.15% ammonium persulfate was added to the fracturing fluid solution, and the gel-breaking experiment was conducted at 90°C). For specific results, please refer to [link to relevant documentation]. Figure 6 ,Depend on Figure 6 It can be seen that the high-temperature resistant self-degradable composite acid fracturing fluid system in Example 1 introduces NVP segments to control the degradation rate, achieving controllable self-degradation, and the degradation time reaches the industrial standard within two hours.

[0075] It is worth noting that the experimental data above demonstrates the significant advantages of the high-temperature resistant, self-degradable composite acid fracturing fluid system in this invention in terms of temperature resistance, salt resistance, sand suspension performance, and self-degradation ability.

[0076] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-temperature resistant, self-degradable composite acidizing fracturing fluid system, characterized in that, include: Base liquid, thickener, complexing agent, drainage aid, corrosion inhibitor, and solvent; The base liquid is a citric acid-tartaric acid-hydrochloric acid composite acid liquid, the thickener is an AM / DMC / AA / AMPS / NVP pentacetic copolymer, the complexing agent is dihydroxyethylglycine, the discharge aid is a fluorocarbon surfactant, the corrosion inhibitor is a compound corrosion inhibitor of imidazoline and pyridine, and the solvent is deionized water; The molar ratio of AM, DMC, AA, AMPS, and NVP in the thickener is 85:3:10:1:

1.

2. The high-temperature resistant, self-degradable composite acidizing fracturing fluid system according to claim 1, characterized in that, By mass percentage, the thickener is 0.8-1.2%, the complexing agent is 1-2%, the drainage aid is 0.1-0.3%, the corrosion inhibitor is 0.5-1%, the hydrochloric acid in the base solution is 15-20%, the citric acid in the base solution is 10-15%, the tartaric acid in the base solution is 5-10%, and the balance is the solvent.

3. The high-temperature resistant, self-degradable composite acidizing fracturing fluid system according to claim 2, characterized in that, In the base solution, the concentration of hydrochloric acid is 15-20%, the concentration of citric acid is 5-8%, and the concentration of tartaric acid is 3-5%.

4. The high-temperature resistant, self-degradable composite acidizing fracturing fluid system according to claim 3, characterized in that, The mass ratio of imidazoline to pyridine in the corrosion inhibitor is 2:

1.

5. A method for preparing the high-temperature resistant, self-degradable composite acidizing fracturing fluid system according to any one of claims 1-4, characterized in that, Includes the following steps: The preparation of AM / DMC / AA / AMPS / NVP pentagonal copolymers specifically includes: AM, DMC, AA, AMPS, and NVP were dissolved in deionized water at a molar ratio of 85:3:10:1:1 and a molecular weight of 11 million. The pH was adjusted to 7.0, and nitrogen was purged for half an hour to remove oxygen. Ammonium persulfate-sodium bisulfite initiator was added dropwise at 45°C, and the reaction was carried out for 12 hours. The mixture was then granulated and dried under vacuum at 60°C to obtain the AM / DMC / AA / AMPS / NVP pentpolymer. Dihydroxyethylglycine was dissolved in deionized water with tartaric acid, citric acid, and hydrochloric acid to obtain a high-temperature resistant acid-based liquid. The high-temperature resistant acid base fluid is mixed with deionized water, and then the AM / DMC / AA / AMPS / NVP pentapolymer, fluorocarbon surfactant, and imidazoline and pyridine compound corrosion inhibitor are added sequentially to obtain the high-temperature resistant self-degradable composite acid fracturing fluid system.

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