Retarded foamed acid, preparation method thereof and application of retarded foamed acid in stratum blockage removal or augmented injection

Abstract

The invention discloses a retarded foam acid, a preparation method thereof and an application of the retarded foam acid in stratum plug removal or augmented injection. The retarded foam acid comprises the following raw material components in percentage by mass: 0.2-1.0% of a foaming agent, 5-10% of hydrochloric acid, 8-12% of authigenic acid, 0.2-1.0% of a corrosion inhibitor, 0.2-1.0% of an iron ion stabilizer and the balance of water. The preparation method comprises the following steps: dissolving hydrochloric acid in water, adding the rest components into the solution in proportion, uniformly mixing, introducing nitrogen or carbon dioxide, and stirring for foaming. The application method for removing blocking or increasing injection of the stratum comprises the following steps that a blocking removing or increasing injection tubular column is put down, the retarded foamed acid is injected into the stratum through a cement truck, displacement fluid is injected to squeeze all the retarded foamed acid in the tubular column into the stratum, then a well is closed, the cement truck is stopped, and the stratum is waited for acidification reaction; and injecting water into the stratum after the reaction is finished. The retarded foamed acid disclosed by the invention is good in permeability, moderate in acid rock reaction speed and long in acidification distance.

Description

TECHNICAL FIELD

[0001] The present application relates to a retarded foam acid, a preparation method thereof and an application of performing formation plugging removal or injection increase, and belongs to the technical field of oil and gas well acidification stimulation. BACKGROUND

[0002] With the continuous development and maturity of acid fracturing technology, it has become an indispensable key technology in the process of oil and gas exploration and development. Acidizing technology mainly solves the problem of oil well pollution and plugging, and uses acid to dissolve organic or inorganic pollutants in rock voids to improve reservoir permeability. Conventional acidizing uses hydrochloric acid and mud acid, however, such acid has strong corrosion, potential damage to the reservoir, too fast acid-rock reaction rate leading to small acidizing range and uneven acidizing, etc. The foam acid has high viscosity, preferentially blocks high permeability layers, makes acid enter low permeability layers, and has slow acid-rock reaction and small filtration loss, etc., so it becomes an important part of acid fracturing technology.

[0003] At present, relevant technical personnel has developed various foam acid systems, and obtained foam acid with slow acid-rock reaction rate, improved acidizing depth and uniformity. For example, the Chinese invention patent with publication number CN 108165250B discloses "a nano foam acid and its preparation method and use method", the nano foam acid uses amphoteric long-chain imidazoline betaine as a foaming agent, and hydrophilic nano silicon dioxide as a foam enhancer. The nano silicon dioxide and the long-chain imidazoline betaine have adsorption and synergistic effect, which improves the stability of the foam and can tolerate higher oil and gas well temperature, thereby expanding the depth of oil and gas drilling and development. Moreover, the nano silicon dioxide can form a relatively dense filter cake in the acid, effectively reducing the filtration loss of the acid.

[0004] The Chinese invention patent with publication number CN 107474811B discloses "a micro-foam acid and a preparation method thereof", the foam acid is composed of hydrochloric acid, a compound foaming agent, a foam stabilizer, a thickening agent and water. The micro-foam acid has good foaming, foam stability, viscosity retention, and temperature resistance, salt resistance, etc.

[0005] The Chinese invention patent application with publication number CN 118813236A discloses "an ultra-stable foam acid and a preparation method thereof", the system uses hydrochloric acid as the base fluid and adds a polymer as the foam stabilizer, and has good temperature resistance and salt resistance, excellent foam stability. However, the above foam acid only improves the foam stability and tolerance, and does not optimize the acid base fluid itself, so the acidizing uniformity and acidizing distance still need to be improved. SUMMARY

[0006] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the invention of this application, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0007] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0008] The primary purpose of the present invention is to overcome the problems existing in the prior art and provide a slow foam acid that has good permeability, moderate acid-rock reaction speed and long acidizing distance when used for formation acidizing.

[0009] To solve the above technical problems, the invention provides a slow foaming acid, which comprises the following components by mass percentage: 0.2-1.0% of a foaming agent, 5-10% of hydrochloric acid, 8-12% of autogenous acid, 0.2-1.0% of a corrosion inhibitor, 0.2-1.0% of an iron ion stabilizer, and the remainder is water.

[0010] In some embodiments, the foaming agent is prepared by compounding a long-chain alkylamidopropyl betaine and an anionic surfactant.

[0011] In some embodiments, the structural formula of the long carbon chain alkylamidopropyl betaine is:

[0012]

[0013] Wherein, R1 is a C8-C16 alkyl group.

[0014] In some embodiments, the anionic surfactant includes at least one of sodium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium dodecylbenzenesulfonate, and sodium fatty alcohol polyoxyethylene ether sulfate, and the mass ratio of long-chain alkylamidopropyl betaine to the anionic surfactant is 1:1.

[0015] In some embodiments, the autogenous acid comprises an ammonium salt and an oxidizing agent.

[0016] In some embodiments, the ammonium salt in the autogenous acid includes one or more of ammonium fluoride, ammonium chloride, ammonium dihydrogen phosphate, ammonium sulfate, ammonium acetate, and ammonium trifluoroacetate; the oxidant in the autogenous acid includes one of hypochlorite, chlorate, and bromate; the molar ratio of the ammonium salt to the oxidant is 2:1, and the ammonium salt in the autogenous acid and the oxidant generate various organic acids or inorganic acids under acidic conditions. The general reaction formula is as follows:

[0017] 2NH4X+ClO3 - → Nitrogen + Cl - +2HX+3H2O

[0018] HX is one of ammonium fluoride, ammonium chloride, ammonium dihydrogen phosphate, ammonium sulfate, ammonium acetate and ammonium trifluoroacetate.

[0019] In some embodiments, the corrosion inhibitor is one of imidazoline corrosion inhibitor or quinoline corrosion inhibitor.

[0020] In some embodiments, the iron ion stabilizer is one of citric acid, disodium ethylenediaminetetraacetate or trisodium nitrilotriacetate.

[0021] Another object of the present application is to provide a preparation method of the retarded foam acid to overcome the problems in the prior art.

[0022] To solve the above technical problems, the present application provides a preparation method of the retarded foam acid, which comprises the following steps: dissolving hydrochloric acid in water, and then adding the other components in the solution and mixing them evenly, and finally stirring and foaming by nitrogen or carbon dioxide.

[0023] Another object of the present application is to provide an application of the retarded foam acid in formation plugging or injection to overcome the problems in the prior art.

[0024] To solve the above technical problems, the present application provides an application of the retarded foam acid in formation plugging or injection, which comprises the following steps in sequence:

[0025] S1, a plugging or injection string;

[0026] S2, preparing the retarded foam acid;

[0027] S3, injecting the retarded foam acid into the formation by a cement truck;

[0028] S4, after the retarded foam acid is injected into the string, displacing fluid is used to squeeze all the retarded foam acid in the string into the formation;

[0029] S5, closing the well, stopping the cement truck, and waiting for the acidification reaction of the formation;

[0030] S6, after the acidification reaction is completed, water is injected into the formation.

[0031] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application at least include: the retarded foam acid provided by the present application takes high-viscosity foam as a carrier, on the one hand, the foam system can effectively plug high-permeability layers, which is beneficial to the acid liquid to enter and penetrate into low-permeability layers, thereby realizing uniform acidizing; on the other hand, the foam fluid can significantly increase the volume of the fluid, thereby improving the flowability thereof. This is helpful for the acid liquid to be more uniformly distributed and propagated in the fractures, especially in a complex fracture network, which can ensure that the acid liquid covers a wider area.

[0032] In addition, the self-generating acid is used as an effective component of the retarded foam acid in the present application, and the ammonium salt and the oxidizing agent react to generate organic acid (such as acetic acid and trifluoroacetic acid) or inorganic acid (such as hydrochloric acid, hydrofluoric acid and sulfuric acid) under acidic conditions. By slowly generating and releasing the acidic component, the reaction with the rock can be continued for a longer time and space, thereby enhancing the deep acidizing effect. By utilizing the advantages of foam fluid mobility control and acid-carrying uniformity and the advantages of the self-generating acid system in continuously generating acid and prolonging the acid etching distance, the retarded foam acid is endowed with excellent retarded acidizing performance by the synergistic effect of the two. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of these drawings. The drawings are provided for reference and illustration only, and are not intended to limit the present application.

[0034] In the formula, R represents a C1-C4 alkyl group, and n represents an integer of 1-3.

[0035] Figure 1 Shear viscosity graph of the retarded foam acid of the present application at 20℃;

[0036] Figure 2 Shear viscosity graph of the retarded foam acid of the present application at 150℃. DETAILED DESCRIPTION

[0037] The technical solutions of the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0038] In the following description of the embodiments, the term "and / or" is used to describe the association relationship of associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the cases of A existing alone, B existing alone and A and B existing simultaneously. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it.

[0039] In the following description of the embodiments, the term "at least one" means one or more, and "multiple" means two or more. "At least one of the following (one)" or similar expressions means any combination of these items, including any combination of single (one) or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b and c can be single or multiple.

[0040] The terms used in the embodiments of the present application are merely for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0041] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of the serial numbers does not mean the order of execution, and some or all steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0042] Those skilled in the art should understand that the numerical ranges in the embodiments of the present application should be understood as also specifically disclosing each intermediate value between the upper limit and the lower limit of the range. Each smaller range within any stated value or stated range of values and any other stated value or stated range of values between the stated values and the stated range of values is also included in the present application. The upper limit and the lower limit of these smaller ranges can be independently included or excluded from the range.

[0043] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as generally understood by those skilled in the art to which the present application belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present application. All documents mentioned in the specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of conflict between any incorporated document and the content of the specification, the content of the specification shall prevail.

[0044] Embodiment 1

[0045] Prepare raw materials in the following mass percentages: dodecyl amido propyl betaine 0.5%; sodium dodecyl sulphate 0.5%; hydrochloric acid 5%; ammonium chloride + sodium chlorate 12% (molar ratio of both 2:1); quinoline corrosion inhibitor 0.3%; citric acid 0.3%, with the remainder being water; dissolve the hydrochloric acid in water first, then add the other components in proportion to the solution and mix well, and then stir and foam with nitrogen gas.

[0046] Example 2

[0047] Prepare raw materials in the following mass percentages: dodecyl amido propyl betaine 0.5%; sodium dodecyl sulphate 0.5%; hydrochloric acid 5%; ammonium chloride + sodium chlorate 12% (molar ratio of both 2:1); quinoline corrosion inhibitor 0.3%; citric acid 0.3%, with the remainder being water; dissolve the hydrochloric acid in water first, then add the other components in proportion to the solution and mix well, and then stir and foam with nitrogen gas.

[0048] Example 3

[0049] Prepare raw materials in the following mass percentages: dodecyl amido propyl betaine 0.5%; sodium dodecyl sulphate 0.5%; hydrochloric acid 5%; ammonium chloride + sodium chlorate 12% (molar ratio of both 2:1); quinoline corrosion inhibitor 0.3%; citric acid 0.3%, with the remainder being water; dissolve the hydrochloric acid in water first, then add the other components in proportion to the solution and mix well, and then stir and foam with nitrogen gas.

[0050] Example 4

[0051] Prepare raw materials in the following mass percentages: dodecyl amido propyl betaine 0.5%; sodium dodecyl sulphate 0.5%; hydrochloric acid 5%; ammonium chloride + sodium chlorate 12% (molar ratio of both 2:1); quinoline corrosion inhibitor 0.3%; citric acid 0.3%, with the remainder being water; dissolve the hydrochloric acid in water first, then add the other components in proportion to the solution and mix well, and then stir and foam with nitrogen gas.

[0052] Example 5

[0053] Prepare raw materials in the following mass percentages: dodecyl amido propyl betaine 0.5%; sodium dodecyl sulphate 0.5%; hydrochloric acid 5%; ammonium chloride + sodium chlorate 12% (molar ratio of both 2:1); quinoline corrosion inhibitor 0.3%; citric acid 0.3%, with the remainder being water; dissolve the hydrochloric acid in water first, then add the other components in proportion to the solution and mix well, and then stir and foam with nitrogen gas.

[0054] Example 6

[0055] Prepare the raw materials in the following mass percentages: tetradecyl amido propyl betaine 0.4%; sodium dodecyl alcohol polyoxyethylene ether sulfate 0.4%; hydrochloric acid 8%; ammonium dihydrogen phosphate + sodium hypochlorite 12% (molar ratio of 2:1); quinoline corrosion inhibitor 0.8%; citric acid 0.8%, and the rest is water; first dissolve the hydrochloric acid in water, then add the other components to the solution in proportion and mix well, and then stir and foam with carbon dioxide.

[0056] Example 7

[0057] Use the retarded foam acid of Example 6 to perform formation plugging removal or injection enhancement, which successively includes the following steps:

[0058] S1, lower the plugging removal or injection string;

[0059] S2, prepare the retarded foam acid;

[0060] S3, inject the retarded foam acid into the formation by the cement truck;

[0061] S4, after the retarded foam acid is completely injected into the string, the displacement fluid is used to squeeze all the retarded foam acid in the string into the formation;

[0062] S5, shut in the well, stop the cement truck, and wait for the formation to perform acidizing reaction;

[0063] S6, after the acidizing reaction is completed, inject water into the formation.

[0064] Take a water injection well in a certain block as an example: after three hours of retarded foam acid washing, the daily water injection amount is increased by 60 m 3 , and the average water injection amount is increased by more than 30%, and the water injection pressure is reduced from 20 MPa to 16 MPa.

[0065] Comparative Example 1

[0066] In contrast to Example 1, this example provides a foam acid without self-generating acid, and the other components are the same as those in Example 1, which is formed by dissolving the following raw materials in water in the following mass ratio:

[0067] Dodecyl amido propyl betaine 0.5%; sodium dodecyl sulfate 0.5%; hydrochloric acid 5%; quinoline corrosion inhibitor 0.3%; citric acid 0.3%.

[0068] Comparative Example 2

[0069] In contrast to Example 1, this example provides an acid solution without foam, and the other components are the same as those in Example 1, which is formed by dissolving the following raw materials in water in the following mass ratio:

[0070] Hydrochloric acid 5%; ammonium chloride + sodium chlorate 12% (molar ratio of 2:1); quinoline corrosion inhibitor 0.3%; citric acid 0.3%.

[0071] Comparative Example 3

[0072] This example provides a conventional hydrochloric acidizing fluid formed by dissolving the following raw materials in water in a mass ratio: hydrochloric acid 12%; quinoline corrosion inhibitor 0.5%; citric acid 0.5%.

[0073] Comparative Example 4

[0074] This example provides a conventional mud acid acidizing fluid formed by dissolving the following raw materials in water in a mass ratio: hydrochloric acid 12% + hydrofluoric acid 3%; quinoline corrosion inhibitor 0.8%; citric acid 0.8%.

[0075] To verify the actual performance of the retardation foam acid of the present application, after the retardation foam acid of Examples 1-6 is dissolved in clean water and ultrasonically treated, the foaming performance is tested according to SY / T 5350-2009 “Evaluation Procedure for Foaming Agent for Drilling Fluids”, and the acid-rock reaction speed, average acid-rock reaction speed and retardation rate of the retardation foam acid are tested according to SY / T 5886-2018 “Performance Evaluation Method for Acidizing Working Fluid”.

[0076] 1.1, the test method of foaming performance includes: foaming volume and half-life period using stirring method, taking 100 mL of prepared foam acid solution, stirring in a high-speed stirrer at 7000 r / min for 3 min, pouring the generated foam into a graduated cylinder, and recording the maximum foaming volume and half-life period (time for 50 mL of solution to be precipitated).

[0077] 1.2, the test method of core dissolution rate of the retardation foam acid includes: using laboratory self-provided rock sample, taking 3 mL of foam acid solution per square centimeter of rock sample surface area, placing in the reaction tank of a rotary rock disc experiment instrument, and measuring the core dissolution rate of the foam acid at 90°C and 12 MPa. The acid-rock reaction speed Va is calculated according to Formula 1, the average acid-rock reaction speed is calculated according to Formula 2, and the retardation rate K is calculated according to Formula 3.

[0078]

[0079] In the formula, Δm is the dissolution mass of the rock sample (g); S is the total surface area of the rock sample (cm 2 ); and Δt is the reaction time (s).

[0080]

[0081] In the formula, n is the number of experiments.

[0082]

[0083] In the formula, K is the retardation rate (%); Average acid-rock reaction rate (mg / (cm 2 ·s) of blank acid liquid; Average acid-rock reaction rate (mg / (cm 2 ·s) of retarding foam acid.

[0084] 1.3, the test results are shown in Table 1 and Table 2.

[0085] Table 1: foaming and stability test results of foam acid of Examples 1-6

[0086] Slow foaming acid Foaming volume / mL Half-life / min Example 1 375 39 Example 2 365 36 Example 3 360 42 Example 4 365 44 Example 5 355 45 Example 6 380 21

[0087] Table 2: average acid-rock reaction rate and retarding rate of retarding foam acid of Examples 1-3 and Comparative Examples 1-4

[0088]

[0089] According to Table 1, using long carbon chain alkyl amide propyl betaine and anionic surfactant as a foaming agent can obtain higher bubble volume and half-life, and the foam performance can be effectively improved, which is the basis of the acid liquid carrier.

[0090] According to Table 2, the average acid-rock reaction rate of the 12% hydrochloric acid base liquid in Comparative Example 3 is 1.089 x 10 -3 mg / (cm 2 ·s), the acid-rock reaction rate of the 12% hydrochloric acid + 3% hydrofluoric acid base liquid in Comparative Example 4 is the highest, reaching 1.412 x 10 -3 mg / (cm 2 ·s), which is mainly due to the fact that the soil acid can dissolve the quartz matrix rock sample, and the dissolution amount is increased. After replacing the hydrofluoric acid in the soil acid with the self-generating acid (Comparative Example 2), the average acid-rock reaction rate is reduced to 5.752 x 10 -4 , and the retarding rate is reduced to 47.19%; and based on Comparative Example 3, the foam fluid is added (Comparative Example 1), and the average acid-rock reaction rate can be further reduced to 3.688 x 10 -4 , and the retarding rate is increased to 66.15%. Therefore, after adding the foam fluid or the self-generating acid system to the conventional acid liquid base liquid, the acid-rock reaction rate can be reduced to different degrees, and the retarding rate can be increased. By comparing the preferred Examples 1-3, the average acid-rock reaction rate of the retarding foam acid is reduced by two orders of magnitude, and the retarding rate is more than 92.27%, which shows that the addition of the foam fluid and the self-generating acid system can significantly improve the performance of the acid liquid, effectively reduce the acid-rock reaction rate, and have a good retarding effect.

[0091] 1.4, shear viscosity test

[0092] The slow foaming acid solution of the present application was subjected to shear viscosity test. The test method is: using Anton Paar rheometer to test the slow foaming acid prepared in Examples 1 to 3 at 20°C and 150°C at a variable shear rate of 10-150s -1 The viscosity under the conditions is automatically measured by the computer to test the viscosity of the prepared slow foaming acid. After the measurement is completed, the data is recorded and the results are saved. Figure 1 、 Figure 2 As shown, Figure 1 is the shear viscosity change of the foam at 20°C, Figure 2 is the shear viscosity change of the foam at 150°C.

[0093] Depend on Figure 1 It can be seen that when the shear rate is less than 30s -1 As the shear rate increases, the viscosity of the foam decreases rapidly; when the shear rate exceeds 30s -1 After that, the viscosity of the foam decreases slowly. As a typical pseudoplastic fluid, the foam will show shear dilution when flowing in the formation. -1 The shear viscosity test curve at 150°C shows a similar pattern, indicating that the foam acid system of the present invention has good temperature resistance.

[0094] In summary, the retarded foam acid prepared in the examples of this application has excellent foaming and retarding properties, is expected to solve the problem of oil and gas well blockage, and play an important role in the field of oil and gas well production increase. The retarded foam acid system described in the present invention is of great significance for ensuring the production of oil and gas wells.

[0095] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0096] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A slow foaming acid, characterized in that The invention comprises the following components by mass percentage: 0.2-1.0% of a foaming agent, 5-10% of hydrochloric acid, 8-12% of autogenous acid, 0.2-1.0% of a corrosion inhibitor, 0.2-1.0% of an iron ion stabilizer, and the rest is water.

2. A slow foaming acid according to claim 1, characterized in that: The foaming agent is prepared by compounding a long carbon chain alkylamidopropyl betaine and an anionic surfactant.

3. A slow foaming acid according to claim 2, characterized in that: The structural formula of the long carbon chain alkyl amidopropyl betaine is: Wherein, R1 is a C8-C16 alkyl group.

4. A slow foaming acid according to claim 2, characterized in that: The anionic surfactant includes at least one of sodium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium dodecylbenzenesulfonate, and sodium fatty alcohol polyoxyethylene ether sulfate, and the mass ratio of the long carbon chain alkylamidopropyl betaine to the anionic surfactant is 1:

1.

5. A slow foaming acid according to claim 1, characterized in that: The autogenous acid includes an ammonium salt and an oxidizing agent.

6. A slow foaming acid according to claim 5, characterized in that: The ammonium salt in the authigenic acid includes one or more of ammonium fluoride, ammonium chloride, ammonium dihydrogen phosphate, ammonium sulfate, ammonium acetate, and ammonium trifluoroacetate; the oxidant in the authigenic acid includes one of hypochlorite, chlorate, and bromate; the molar ratio of the ammonium salt to the oxidant is 2:1, and the ammonium salt in the authigenic acid and the oxidant generate various organic acids or inorganic acids under acidic conditions, and the general reaction formula is as follows: 2NH4X+ClO3 - → Nitrogen + Cl - +2HX+3H2O Wherein, HX is one of ammonium fluoride, ammonium chloride, ammonium dihydrogen phosphate, ammonium sulfate, ammonium acetate, and ammonium trifluoroacetate.

7. A slow foaming acid according to claim 1, characterized in that: The corrosion inhibitor is one of an imidazoline corrosion inhibitor or a quinoline corrosion inhibitor.

8. A slow foaming acid according to claim 1, characterized in that: The iron ion stabilizer is one of citric acid, disodium edetate or trisodium nitrilotriacetate.

9. A method for preparing slow foaming acid, characterized in that: The raw material components include, by mass percentage, 0.2-1.0% of a foaming agent, 5-10% of hydrochloric acid, 8-12% of autogenous acid, 0.2-1.0% of a corrosion inhibitor, 0.2-1.0% of an iron ion stabilizer, and the rest being water. The hydrochloric acid is first dissolved in water, and then the rest of the components are added to the solution in proportion and mixed evenly, and then nitrogen or carbon dioxide is introduced for stirring and foaming.

10. An application of slow foam acid for formation blockage removal or injection, characterized in that: The steps are as follows: S1, lower the plugging or injection string; S2. Prepare slow foaming acid; S3, injecting slow foam acid into the formation through a cement truck; S4. After all the slow foam acid is injected into the tubing string, the displacement fluid is injected to squeeze all the slow foam acid in the tubing string into the formation; S5. Shut down the well, stop the cement truck, and wait for the formation to undergo acidification reaction; S6. After the acidification reaction is completed, water is injected into the formation.

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