Self-generating foam acid system as well as preparation method and evaluation method thereof

Abstract

The invention belongs to the technical field of fracturing fluid chemical systems, and particularly relates to a self-generating foam acid system as well as a preparation method and an evaluation method thereof. The self-generating foam acid system provided by the invention consists of the following reagents in parts by mass: 15-50 wt% of a reagent I, 10-35 wt% of a reagent II, 3-10 wt% of a reagent III, 0.5-5 wt% of a reagent IV and the balance of water, wherein the reagent I is one or more of paraformaldehyde, methyl formate, ethyl formate, methyl acetate, ethyl lactate, chloracetyl and chloromethane; the reagent II is one or more of ammonium chloride and aluminum chloride; the reagent III is NaNO2; and IV is selected from the group consisting of NP-10 and / or FS-3100. The self-generating foam acid system does not generate an acid generation reaction in an environment with the temperature lower than 60 DEG C, corrosion to underground equipment and damage to a stratum are reduced, the limestone reaction rate can be delayed under the high-temperature condition, and the acting distance of acid liquor in the stratum is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of fracturing fluid chemical systems, and in particular relates to a self-generating foaming acid system and a preparation method and an evaluation method thereof. Background Art

[0002] Carbonate reservoirs are widely distributed and hold significant oil and gas reserves, offering significant potential for recovery. However, these reservoirs face challenges such as complex natural fracture and vug structures, strong heterogeneity, and low natural production. To properly release their production capacity, they require reservoir reconstruction. Acid fracturing is a commonly used method for carbonate reservoir reconstruction. The key indicator determining the effectiveness of acidizing in carbonate reservoirs is the penetration distance of the acid into the rock matrix.

[0003] However, the acid systems used in conventional acid fracturing transformation at this stage have the following problems: the traditional hydrochloric acid acid system has a fast acid-rock reaction rate, the acid is consumed too quickly in the formation, and the effective action distance is small; the carbonate reservoir has developed fractures and dissolution pore structures, and the acid is easily lost during the acidization process. Traditional acid will differentially dissolve the reservoir rock matrix and microcracks, increasing the acid loss and affecting the transformation range; when transforming low-pressure reservoirs, traditional acid systems may face the problem of difficult backflow. The presence of acid-rock reaction by-products and residual acid may cause secondary damage to the formation and water lock effect, affecting the normal subsequent oil and gas production.

[0004] In response to the above problems, it is urgent to propose an acid system with the following advantages to improve the acid fracturing effect of carbonate reservoirs: (1) Develop a self-generating acid system with strong continuous acid generation ability to reduce the acid-rock reaction rate, increase the formation acid action distance, and improve the deep reservoir transformation ability; (2) Prepare a self-generating foam acid system to improve the acid flowback capacity and improve the acid loss problem. At present, a single acid fracturing working fluid system is difficult to solve the transformation problems of carbonate reservoirs. Therefore, it is of great practical significance to develop a composite acid system with multiple functions such as slow acidization, control of loss and energy-enhancing flowback. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a self-generating foaming acid system, which is composed of the following reagents in parts by weight: 15-50 wt% of reagent I, 10-35 wt% of reagent II, 3-10 wt% of reagent III, 0.5-5 wt% of reagent IV, and the rest is water;

[0006] Among them, the reagent I is one or more of paraformaldehyde, methyl formate, ethyl formate, methyl acetate, ethyl lactate, chloroacetyl, and methyl chloride; the reagent II is one or more of ammonium chloride and aluminum chloride; the reagent III is NaNO2; and the reagent IV is one or more of NP-10 and FS-3100.

[0007] Furthermore, the self-generating foaming acid system is composed of the following reagents in parts by weight: 27% wt% of reagent I, 24 wt% of reagent II, 6 wt% of reagent III, 0.75 wt% of reagent IV and 21.125 wt% of water;

[0008] The reagent I is a mixture of paraformaldehyde and ethyl lactate, the reagent II is ammonium chloride, the reagent III is NaNO2, and the reagent IV is a mixed solution of NP-10 and FS-3100.

[0009] In a second aspect, the present invention provides a method for preparing a self-generating foaming acid system, which comprises the following steps:

[0010] Reagent II, reagent III and reagent IV are sequentially added to reagent I to form a mixed reagent, and the mixed reagent is stirred at a constant temperature to obtain a self-generating foaming acid system.

[0011] Furthermore, the stirring speed is 500-2000 r·min -1 , stirring time is 1-5min, and stirring temperature is 90-300℃.

[0012] In a third aspect, the present invention provides a method for evaluating a self-generating foaming acid system, wherein the method comprises the following steps:

[0013] After the reaction starts, the supernatant liquid from the foaming acid system is taken at set intervals to test the acid concentration and record the gas production of the foaming acid system;

[0014] Calculating the foam quality of the self-generated foaming acid system according to the gas production of the self-generated foaming acid system;

[0015] A comprehensive index evaluation value of the self-generated foaming acid system is calculated according to the acid concentration and foam quality, and the self-generated foaming acid system is evaluated using the comprehensive index evaluation value.

[0016] Furthermore, the acid concentration of the self-generated foaming acid system is measured by acid-base titration, and the calculation formula is as follows:

[0017]

[0018] Among them, c 碱 is the molar concentration of the titrated alkali solution, mol·L -1 , V 碱 is the volume of standard alkali solution consumed in titration, m 酸 is the mass of the self-generated foaming acid system to be tested, M HCl is the molar mass of HCl.

[0019] Furthermore, the foam quality of the self-generating foaming acid system was calculated using the following formula:

[0020]

[0021] Where Γ is the foam mass; V g V is the gas volume of the self-generated foaming acid system; l is the volume of the liquid phase; V f is the foam volume.

[0022] Furthermore, the comprehensive index evaluation value of the self-generating foaming acid system is calculated using the following formula:

[0023]

[0024] Among them, H end is the acid concentration of the self-generated foaming acid system after 6 hours of reaction; H ref is the commonly used HCl concentration in the field; M foamacid It is the comprehensive index evaluation value of the self-generating foaming acid system.

[0025] Furthermore, the self-generating foaming acid system is evaluated using the comprehensive index evaluation value as follows:

[0026] Set up comprehensive evaluation of quality value of autogenous acid system;

[0027] If the calculated comprehensive index evaluation value is greater than or equal to the set autogenous acid system comprehensive evaluation high quality value, the autogenous foaming acid system is considered to be of high quality.

[0028] The self-generating foaming acid system or the self-generating foaming acid system prepared according to the preparation method is used in the acid fracturing modification process.

[0029] Beneficial effects of the present invention:

[0030] The self-generating foaming acid system proposed in the present invention does not produce an acid reaction in an environment below 60°C, thereby greatly reducing the corrosion to downhole equipment and damage to the formation. In addition, it takes at least 3 hours to stand in a formation above 60°C before reaching the HCl concentration used in conventional formation acidification, greatly slowing the acid-rock reaction rate and extending the action distance of the acid in the formation.

[0031] The foam quality generated by the self-generated foaming acid system proposed in the present invention can reach 97.543%. The rich foam generated after entering the formation helps to reduce the foam loss in the carbonate reservoir and reduce the loss of acid liquid. At the same time, the foam fluid has a higher backflow capacity than conventional liquid acid, which reduces the damage of the acid liquid system to the formation.

[0032] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 A flow chart showing the evaluation method of the self-foaming acid system proposed in the present invention is shown;

[0035] Figure 2 A schematic diagram of a gas production experimental device for a self-generated foaming acid system according to an embodiment of the present invention is shown;

[0036] Figure 3 It shows the acid concentration curve of the self-generated foaming acid system in the embodiment of the present invention;

[0037] Figure 4 The gas production capacity curve of the self-generated foaming acid system in the embodiment of the present invention is shown;

[0038] Figure 5 A comparison chart of the reaction rates of the self-generated foaming acid system, hydrochloric acid, and thickened acid at different acid concentrations in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0040] In view of the shortcomings of the existing technology, the present invention provides a self-generating foaming acid system and an evaluation method. The self-generating foaming acid system proposed by the present invention is composed of the following reagents in parts by weight: reagent I: 15-50wt%, reagent II: 10-35wt%, reagent III: 3-10wt%, reagent IV: 0.5-5wt%, and the rest is water.

[0041] The reagent I is selected from one or more of paraformaldehyde, methyl formate, ethyl formate, methyl acetate, ethyl lactate, chloroacetyl, and methyl chloride; the reagent I can stimulate ammonium chloride to react and generate an aldehyde organic substance of acid solution.

[0042] The reagent II is selected from one or more of ammonium chloride and aluminum chloride;

[0043] Reagent III uses NaNO2; in this invention, NaNO2 serves as the primary gasification agent, providing a source of N2. If NaNO2 is replaced with sodium nitrate, it will still react with ammonium chloride, but the byproducts will be NH3 and NO2, and stable N2 will not be generated. Furthermore, the amount of gas generated is limited.

[0044] The reagent IV is selected from one or more of NP-10 and FS-3100.

[0045] The present invention also provides a method for preparing a self-generating foaming acid system, comprising the following steps:

[0046] Adding reagent II, reagent III and reagent IV to reagent I in sequence to form a mixed reagent IV, and stirring the mixed reagent IV at a constant temperature to obtain a self-generating foaming acid system;

[0047] The specific process is as follows:

[0048] Weigh quantitative reagent I for later use;

[0049] Weigh quantitative reagent II and add it to reagent I to form mixed reagent I;

[0050] Weigh quantitative reagent III and add it to mixed reagent I to form mixed reagent II;

[0051] Weigh quantitative reagent IV and add mixed reagent II to form mixed reagent III;

[0052] Add a certain amount of mixed reagent III to form mixed reagent IV, and stir; the stirring method uses a power agitator JJ-1, and the stirring speed is set to 500-2000 r·min -1 , stirring time is 1-5min, and stirring temperature is 90-300℃.

[0053] The mixed reagent IV is placed in a constant temperature heating stirrer and stirred during the constant temperature process to obtain a self-generated foaming acid system; the constant temperature heating stirrer is a heat-collecting constant temperature heating magnetic stirrer DF-101S.

[0054] The present invention also proposes a method for evaluating a self-generating foaming acid system, such as Figure 1 As shown, the following steps are included:

[0055] S1: After the reaction starts (i.e., when the reaction generates acid and gas), the supernatant liquid from the foaming acid system is taken at set intervals to measure the acid concentration and record the gas production of the foaming acid system; specifically, the set time can be 0.5h; the schematic diagram of the gas production experimental device of the foaming acid system is as follows Figure 2 shown.

[0056] The acid concentration in step S1 is measured using an acid-base titration method. The decomposition of acid in the acid-generating system at high temperature is a dynamic reaction, producing continuous acid. The continuous addition of the alkaline solution promotes the reaction's forward progression. The titration result is the final acid concentration of the reactants at that ratio.

[0057] The specific measurement process is as follows:

[0058] In acid-base titration, the concentration ratio of the consumed reactants is 1:1, so the relationship between the acid and base solutions is as shown in formula (1):

[0059] c 碱 V 碱 =c 酸 V 酸 (1)

[0060] Where c 碱 、c 酸 are the molar concentration of the acid solution to be tested and the molar concentration of the alkali solution, mol·L -1 ; V 碱 、V 酸 are the volumes of standard alkali solution consumed in titration, mL respectively. The alkali solution can be a standard NaOH solution.

[0061] The acid mass fraction x (wt%) and the acid molar concentration c 酸 (mol·L -1 ) is as follows:

[0062]

[0063] Where M HCl is the molar mass of HCl, g·mol -1 ;m 酸 is the mass of the acid to be tested, g; ρ 酸 is the acid density, g·mL -1 .

[0064] Combining equations (1) and (2), the concentration of authigenic acid (i.e., mass fraction x, wt%) can be expressed by equation (3).

[0065]

[0066] S2: Calculate the foam quality of the self-generated foaming acid system according to the gas production of the self-generated foaming acid system:

[0067] Foam mass is the volume of gas contained in a unit volume of foam under certain pressure and temperature conditions, that is, the volume fraction of gas in the foam, as shown in formula (4).

[0068]

[0069] Where, Γ is the foam mass, %; V g is the gas volume, mL; V l is the liquid volume, mL; V f is the foam volume, mL.

[0070] S3: calculating a comprehensive index evaluation value of the self-generated foaming acid system according to the acid concentration and foam quality, and evaluating the self-generated foaming acid system using the comprehensive index evaluation value.

[0071] In step S3, the autogenous foam acid comprehensive index evaluation method is used for evaluation. The HCl concentration of 15 wt% commonly used in carbonate reservoirs is used as a reference value. The acid concentration and foam mass of the system are measured 6 hours after the reaction. The quality value of the autogenous foam acid system is comprehensively evaluated, and 0.8 is used as the high-quality comprehensive evaluation value of the autogenous acid system. The calculation formula for the autogenous foam acid comprehensive index evaluation is shown in formula (5):

[0072]

[0073] Among them, H end is the acid concentration of the self-generated foaming acid system after 6 hours of reaction; H ref is the common HCl concentration in carbonate reservoirs, 15wt%; M foamacid It is the comprehensive index evaluation value of the self-generating foaming acid system.

[0074] The present invention also provides a method for using a carbonate reservoir acid fracturing self-generating foaming acid solution system, comprising the following steps:

[0075] Injecting reagent I, reagent II, reagent III and reagent IV into the reservoir in sequence;

[0076] Then inject water into the reservoir as a spacer fluid and let it stand for 5-15 minutes.

[0077] Example 1

[0078] This embodiment provides a self-generating foaming acid system, comprising the following steps:

[0079] Adding reagent II, reagent III and reagent IV to reagent I in sequence to form a mixed reagent IV, and stirring the mixed reagent IV at a constant temperature to obtain a self-generating foaming acid system 1;

[0080] The specific process is as follows:

[0081] Step (1): Weigh 13.5 g of reagent I for use; in this embodiment, reagent I is 6 g of paraformaldehyde and 7.5 g of ethyl lactate;

[0082] Step (2): Weigh 12.0 g of reagent II and add it to reagent I to form a mixed reagent I; in this embodiment, reagent II is ammonium chloride;

[0083] Step (3): Weigh 3.0 g of reagent III and add it to mixed reagent I to form mixed reagent II; in this embodiment, sodium nitrite is used as reagent III;

[0084] Step (4): Weigh 0.375 g of reagent IV and add it to mixed reagent II to form mixed reagent III; in this embodiment, reagent IV is prepared by 0.3 g of industrial grade (99 wt%) NP-10 + 0.075 g of industrial grade (99 wt%) FS-3100;

[0085] Step (5): Add 21.125 g of water to the mixed reagent III to form the mixed reagent IV, and stir. In this embodiment, the stirring method uses a power agitator JJ-1, and the stirring speed is set to 500 r·min. -1 , the stirring time is 1 min; in other embodiments of the present invention, the stirring speed can also be 1000 r·min -1 or 2000 r·min -1 The stirring time can be 3 minutes, 4 minutes, 5 minutes, etc.

[0086] Step (6): Stir the mixed reagent IV in a heat-collecting constant temperature heating magnetic stirrer DF-101S at 90°C to obtain a self-generated foaming acid system 1. In other embodiments of the present invention, the stirring temperature can be 150°C, 180°C, 200°C, 220°C or 300°C.

[0087] In other embodiments of the present invention, the masses of Reagent I, Reagent II, Reagent III, and Reagent IV used may be 7.5 g, 5 g, 1.5 g, and 0.25 g, respectively, and water 35.75 g;

[0088] In other embodiments of the present invention, the masses of Reagent I, Reagent II, Reagent III and Reagent IV used may be 25 g, 17.5 g, 5 g and 2.5 g, respectively.

[0089] The self-generating foaming acid system 1 prepared in Example 1 was evaluated, and the specific process was as follows:

[0090] Measure the foam parameters and acid concentration of the self-generated foaming acid system. After the reaction starts, take out a small amount of the supernatant of the self-generated foaming acid system every 0.5 hours to test the acid concentration and record the gas production. After 6 hours, take out the self-generated foaming acid system and measure the foam parameters and acid concentration.

[0091] The acid concentration of the self-generated foaming acid system prepared in this embodiment was measured by acid-base titration. The acid concentration at different time points was calculated using the calculation formulas (1) to (3).

[0092] The general experimental steps are as follows:

[0093] ① Prepare 1.0 mol·L -1 NaOH solution is used as standard titrant;

[0094] ② Use a pipette to take 5.0 mL of the autogenous acid to be tested and place it in a beaker, and weigh the mass of the acid;

[0095] ③ Add 2-3 drops of standard phenolphthalein reagent and titrate with standard NaOH solution;

[0096] ④When the last drop of standard NaOH solution is dripped into the beaker, the solution changes from colorless to pink and does not fade within half a minute. This is considered the titration endpoint. Record the volume of standard NaOH solution consumed at this time and calculate the acid concentration. The calculation result is as follows: Figure 3 As shown, it can be seen that within 0-1 h, the acid concentration of the self-generated foaming acid system quickly reached about 10 wt %, and in the subsequent 1-6 h, the acid concentration also increased steadily.

[0097] The foam quality method was used to measure the foam quality of the self-generated foaming acid system prepared in this example at different reaction times. The calculation formula is as follows:

[0098]

[0099] Where, Γ is the foam mass, %; V g is the gas volume, mL; V l is the liquid volume, mL; V f is the foam volume, mL.

[0100] The results are as follows Figure 4 As shown, it can be seen that the foam quality increases rapidly in the first hour, and in the subsequent 5 hours, the foam quality also continues to increase, and the growth rate is slower than that in the first hour. The foam quality generated by the self-generated foaming acid system can reach 97.543%.

[0101] Calculating a comprehensive index evaluation value of the self-generated foaming acid system according to the acid concentration and the foam quality, and evaluating the self-generated foaming acid system using the comprehensive index evaluation value;

[0102] In this example, the HCl concentration of 15 wt% commonly used in carbonate reservoirs was used as a reference value. The acid concentration and foam mass of the system were measured 6 hours after the reaction. The quality of the self-generated foaming acid system was comprehensively evaluated, and 0.8 was used as the high-quality boundary for judgment.

[0103] Formula (5) is used to evaluate the comprehensive index of self-generated foaming acid:

[0104] The comprehensive evaluation index of the self-generated foaming acid in Example 1 can be calculated as follows:

[0105] The comprehensive evaluation quality value of the autogenous acid system in this embodiment is 0.8, and the system in Example 1 is identified as a high-quality autogenous foaming acid system.

[0106] Example 2 The same method as in Example 1 was used to prepare authigenic acid system 2, except that reagent I used in this example was methyl formate, reagent II was aluminum chloride, reagent III was NaNO2, and reagent IV was NP-10. The authigenic foaming acid comprehensive index evaluation value of the authigenic acid system 2 obtained in this example was calculated to be 0.9356, and the acid concentration at 90°C was 8.2%.

[0107] Example 3: Autogenous acid system 3 was prepared by the same method as in Example 1, except that reagent I used in this example was chloroacetyl, reagent II was ammonium chloride and aluminum chloride in a mass ratio of 1:1, reagent III was NaNO2, and reagent IV was FS-3100. The comprehensive index evaluation value of autogenous foaming acid of the autogenous acid system 3 obtained in this example was calculated to be 0.9217, and the acid concentration at 90°C was 5.4%.

[0108] Example 4 The same method as in Example 1 was used to prepare the autogenous acid system 4, except that the reagent I used in this example was methyl chloride, the reagent II was ammonium chloride, the reagent III was NaNO2, and the reagent IV was NP-10. The autogenous foam acid comprehensive index evaluation value of the autogenous acid system obtained in this example was calculated to be 0.5388, and the acid concentration at 90°C was 0%. The system could only generate acid at high temperatures, and the acid concentration at 150°C was 2.4%. The reason here may be that methyl chloride was used as reagent I, and the system was temperature sensitive and would slowly generate acid only when the temperature approached 150°C.

[0109] Example 5 The acid generating capacity (characterized by acid generating concentration) of the self-generating foaming acid system prepared in Example 1 at different temperatures was measured using the same method as that for measuring acid generating concentration in Example 1. The measurement results are shown in Table 1:

[0110] Table 1 Acid generation capacity of self-generated foaming acid system at different temperatures

[0111] drug 60℃ acid concentration / % 90℃ acid concentration / % Acid concentration at 150℃ / % Paraformaldehyde + ammonium chloride 4.2 12.9 19.8

[0112] As can be seen from Table 1, the acid-generating ability of the self-generating foaming acid system at 60°C is relatively weak, only one-third of that at 90°C.

[0113] Example 6 The reaction rates of the self-generated foaming acid system and conventional carbonate acid in the prior art with limestone at different acid concentrations were investigated, and the reaction temperature was 150°C.

[0114] The conventional carbonate acid selected in this embodiment is hydrochloric acid and thickening acid. The self-generating foaming acid system is the self-generating foaming acid system 1 obtained in Example 1. The reaction rate of the limestone acid rock at 150°C with the concentration is shown in the following curve: Figure 5 As shown, it can be seen that the reaction rate of hydrochloric acid and thickened acid with limestone is significantly faster than the reaction rate of the self-generated foaming acid system with limestone, which is consistent with the situation in actual applications. In actual applications, hydrochloric acid and thickened acid are highly acidic after being configured on the ground, and the reaction rate is too fast, which will cause corrosion to the tubing. The self-generated foaming acid proposed in the present invention can only react and become acidic after 30 minutes under reservoir conditions, and will not corrode the tubing during the injection process.

[0115] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A self-generating foaming acid system, characterized in that: The method comprises the following reagents in parts by weight: 15 to 50 wt% of reagent I, 10 to 35 wt% of reagent II, 3 to 10 wt% of reagent III, 0.5 to 5 wt% of reagent IV, and the remainder being water; Among them, the reagent I is one or more of paraformaldehyde, methyl formate, ethyl formate, methyl acetate, ethyl lactate, chloroacetyl, and methyl chloride; the reagent II is one or more of ammonium chloride and aluminum chloride; the reagent III is NaNO2; and the reagent IV is one or more of NP-10 and FS-3100.

2. The self-foaming acid system according to claim 1, characterized in that The composition is composed of the following reagents in parts by weight: 27% wt% of reagent I, 24 wt% of reagent II, 6 wt% of reagent III, 0.75 wt% of reagent IV and 21.125 wt% of water; The reagent I is a mixture of paraformaldehyde and ethyl lactate, the reagent II is ammonium chloride, the reagent III is NaNO2, and the reagent IV is a mixed solution of NP-10 and FS-3100.

3. A method for preparing a self-generating foaming acid system, characterized in that: The method for preparing the self-foaming acid system according to claim 1 or 2 comprises the following steps: Reagent II, reagent III and reagent IV are sequentially added to reagent I to form a mixed reagent, and the mixed reagent is stirred at a constant temperature to obtain a self-generating foaming acid system.

4. The method for preparing the self-foaming acid system according to claim 3, wherein: The stirring speed is 500-2000 r·min -1 , stirring time is 1-5min, and stirring temperature is 90-300℃.

5. A method for evaluating a self-foaming acid system, characterized in that: The self-foaming acid system according to claim 1 or 2 is evaluated, comprising the following steps: After the reaction starts, the supernatant liquid from the foaming acid system is taken at set intervals to test the acid concentration and record the gas production of the foaming acid system; Calculating the foam quality of the self-generated foaming acid system according to the gas production of the self-generated foaming acid system; A comprehensive index evaluation value of the self-generated foaming acid system is calculated according to the acid concentration and foam quality, and the self-generated foaming acid system is evaluated using the comprehensive index evaluation value.

6. The method for evaluating a self-foaming acid system according to claim 5, wherein: The acid concentration of the self-generated foaming acid system is measured by acid-base titration, and the calculation formula is as follows: Among them, c 碱 is the molar concentration of the titrated alkali solution, mol·L -1 , V 碱 is the volume of standard alkali solution consumed in titration, m 酸 is the mass of the self-generated foaming acid system to be tested, M HCl is the molar mass of HCl.

7. The method for evaluating a self-foaming acid system according to claim 5, wherein: The foam quality of the autogenous foaming acid system is calculated using the following formula: Where Γ is the foam mass; V g V is the gas volume of the self-generated foaming acid system; l is the volume of the liquid phase; V f is the foam volume.

8. The method for evaluating a self-foaming acid system according to claim 5, wherein: The comprehensive index evaluation value of the self-generating foaming acid system is calculated using the following formula: Among them, H end is the acid concentration of the self-generated foaming acid system after 6 hours of reaction; H ref is the commonly used HCl concentration in the field; M foamacid It is the comprehensive index evaluation value of the self-generating foaming acid system.

9. The method for evaluating a self-foaming acid system according to claim 5, wherein: The self-generating foaming acid system is evaluated using the comprehensive index evaluation value as follows: Set up comprehensive evaluation quality value of autogenous acid system; If the calculated comprehensive index evaluation value is greater than or equal to the set autogenous acid system comprehensive evaluation high quality value, the autogenous foaming acid system is considered to be of high quality.

10. Use of the self-generating foaming acid system according to claim 1 or 2, or the self-generating foaming acid system prepared according to the preparation method according to claim 3 or 4, in an acidizing and fracturing process.

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