An integrated composite acid emulsion applied to fracturing fluid and acid fluid and a preparation method thereof

Abstract

The application discloses an integrated composite acid emulsion applied to fracturing fluid and acid liquid and a preparation method thereof, and belongs to the technical field of oil and gas field exploitation. The preparation steps of the emulsion are as follows: S1, organic solvent and composite emulsifier are mixed, stirred, dispersed and uniformly distributed to obtain an oil phase; S2, quaternary ammonium salt unsaturated monomer, sodium benzenesulfonate unsaturated monomer, methacryloyloxyethyl phosphate and a complexing agent are added into water, mixed uniformly and adjusted to have a pH value of 7-9 to obtain an aqueous phase; S3, under the condition of stirring, the aqueous phase is added dropwise into the oil phase to form a water-in-oil emulsion; S4, after nitrogen is passed through the water-in-oil emulsion to remove oxygen, an initiator is added, the temperature is increased to 40-60 DEG C, and stirring reaction is carried out for 4-8 h to obtain the integrated composite acid emulsion. The composite acid emulsion prepared by the inverse emulsion polymerization method has the characteristics of strong thickening, high resistance, high temperature resistance, crosslinking and on-line viscosity change when applied to water and acid liquid, and is an integrated composite acid thickening agent emulsion suitable for fracturing fluid and acid liquid.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and in particular to an integrated composite acid emulsion for use in fracturing fluids and acid solutions, and its preparation method. Background Technology

[0002] In oil and gas reservoir stimulation, hydraulic fracturing and acid fracturing are core technologies for improving recovery efficiency. Thickeners, as key components of fracturing fluids, directly determine the system's proppant carrying capacity, fracture creation effect, and formation adaptability. Currently, fracturing fluids mainly use guar gum and its derivatives, as well as conventional polyacrylamide, as thickeners. While guar gum is inexpensive and has good proppant suspension properties, its residue easily clogs formation pore throats, and it is easily degraded under high temperatures (>90℃) and strong shear. It has almost no viscosity in acidic solutions and also precipitates flocculants. Conventional polyacrylamide thickeners have good temperature and shear resistance in clean water, but their acid resistance is insufficient. In acidic environments, their viscosity is much lower than in aqueous systems, and flocculation or precipitation may even occur, rendering them unusable. Acid fracturing commonly uses acid fluid systems such as thickened acid, emulsified acid, cross-linked acid, diverting acid, and foamed acid. Most of these systems rely on viscosity to reduce the acid-rock reaction rate. However, they also have problems such as long pre-mixing time, high friction, difficulty in pumping, inability to change viscosity in real time, and high formation damage. In addition, conventional acid thickeners do not have good viscosity-enhancing and cross-linking proppant-carrying properties in fracturing fluids.

[0003] With the increasing proportion of deep wells, ultra-deep wells, and complex lithological reservoirs being developed year by year, integrated fracturing and acidizing operations have become the mainstream trend. There is an urgent need for a new type of thickener that combines wide adaptability and convenient operation. It should be able to maintain excellent thickening, proppant carrying, crosslinking, and shear resistance properties in water-based fracturing fluids, and also have good thickening and retardation properties in strong acid environments. At the same time, it should have the characteristics of high temperature resistance, crosslinking, rapid dissolution, and online preparation in acid solutions. This would completely solve the pain points of incompatibility and cumbersome construction of traditional systems, and provide technical support for efficient reservoir stimulation.

[0004] However, current research on thickeners does not yet yield a single thickener that can function as both a fracturing working fluid for slickwater, linear gels, and crosslinked gels, and an acidizing working fluid for acidic slickwater, gelling acid, and crosslinked acid. Therefore, the problems of integrated fracturing and acidizing operations, as well as large-scale online acid fracturing operations, remain unresolved. Summary of the Invention

[0005] To address the problem that existing thickeners cannot achieve integrated fracturing and acidizing operations, this invention provides an integrated composite acid emulsion applicable to fracturing fluids and acid solutions.

[0006] The integrated composite acid emulsion for use in fracturing fluids and acids provided by this invention is prepared by the following method:

[0007] S1. Mix and disperse the organic solvent and composite emulsifier evenly to obtain the oil phase;

[0008] The organic solvent is selected from one or more of No. 3 white oil, No. 5 white oil, No. 10 white oil, and D60 solvent oil. No. 5 white oil is preferred; the amount of No. 5 white oil is 50.2% of the total mass of the water-in-oil emulsion.

[0009] The composite emulsifier is composed of Span-80 and OP-10 in a mass ratio of (2~5):1. The total mass of the composite emulsifier accounts for 2%~5% of the total mass of the water-in-oil emulsion, preferably 4%.

[0010] S2. Add the quaternary ammonium salt unsaturated monomer, sodium benzenesulfonate unsaturated monomer, methacryloyloxyethyl phosphate and complexing agent to water, mix and stir evenly, and adjust the pH of the solution to 7~9 with sodium hydroxide to obtain the aqueous phase.

[0011] The quaternary ammonium salt unsaturated monomer is selected from any one of acryloyloxyethyltrimethylammonium chloride, acrylamidopropyltrimethylammonium chloride, methacrylamidopropyltrimethylammonium chloride, and dimethyldiallylammonium chloride. Acryloyloxyethyltrimethylammonium chloride is preferred.

[0012] The sodium benzenesulfonate unsaturated monomer is selected from any one of sodium p-vinylbenzenesulfonate, sodium p-methacrylamidobenzenesulfonate, and sodium α-methylstyrenesulfonate. Sodium p-vinylbenzenesulfonate is preferred.

[0013] Preferably, the molar ratio of the quaternary ammonium salt unsaturated monomer, sodium benzenesulfonate unsaturated monomer, and methacryloyloxyethyl phosphate is (70-80):(10-20):(1-5). The total mass of the three monomers accounts for 34-35% of the total mass of the water-in-oil emulsion.

[0014] The complexing agent is selected from one of ethylenediaminetetraacetic acid (EDTA), ethylenediaminetetramethylene phosphate (EDTA), sodium aminotriacetate (MTAT), and diethylenetriaminepentacarboxylate (DICA). Preferably, it is disodium EDTA, added at 0.1% of the total mass of the water-in-oil emulsion.

[0015] S3. Under stirring conditions, the aqueous phase is slowly added dropwise to the oil phase at a stirring rate of 1000~1500 r / min. The addition is completed within 30 minutes. Stirring is continued for 2 hours to form a water-in-oil emulsion.

[0016] S4. Adjust the rotation speed to 600 r / min, purge the water-in-oil emulsion with nitrogen to remove oxygen for 1 hour, then raise the temperature to 40℃~60℃, add the initiator, and stir the reaction for 4-8 hours to obtain the integrated composite acid emulsion.

[0017] The initiator is a water-soluble azo initiator, selected from one of azobisisobutyramidine hydrochloride and azobisisobutyramidine imidazoline hydrochloride. Preferably, azobisisobutyramidine imidazoline hydrochloride is used, and the amount added is 0.1-0.5% of the total mass of the three monomers.

[0018] In the above preparation method, three monomers—quaternary ammonium salt unsaturated monomer, sodium benzenesulfonate unsaturated monomer, and methacryloyloxyethyl phosphate—are polymerized to obtain a copolymer, which in turn yields an emulsion containing the copolymer. When the quaternary ammonium salt unsaturated monomer is acryloyloxyethyltrimethylammonium chloride and the sodium benzenesulfonate unsaturated monomer is sodium p-vinylbenzenesulfonate, the molecular structure of the prepared copolymer is as follows:

[0019]

[0020] In the formula, x ranges from 0.70 to 0.85, y ranges from 0.10 to 0.20, and z ranges from 0.01 to 0.05. Preferably, x ranges from 0.75 to 0.85, y ranges from 0.10 to 0.19, and z ranges from 0.03 to 0.05.

[0021] The prepared composite acid emulsion can be used directly as a thickener, or it can be separated and precipitated with acetone / methanol, filtered, washed, dried, and pulverized to obtain a solid powder for use as a thickener.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] The effective component copolymer in the composite acid emulsion of this invention is copolymerized from three functional monomers: quaternary ammonium salt unsaturated monomer, sodium benzenesulfonate unsaturated monomer, and methacryloyloxyethyl phosphate. This avoids the use of conventional acrylamide monomers, preventing the imidization reaction of acrylamide polymers under acidic conditions, which leads to flocculation and precipitation, and thus reduces their temperature resistance under acidic conditions. The use of acryloyloxyethyl trimethylammonium chloride monomer, with its quaternary ammonium salt group making the main chain strongly cationic and possessing large side groups, enhances the thermal stability of the polymer molecules in acidic solutions. The sulfonic acid group of the sodium benzenesulfonate unsaturated monomer is unprotonated in both acidic and neutral environments. The sulfonic acid group is a strong acidic group that can completely dissociate even in acidic environments, exhibiting low affinity for metal ions and high negative charge density, effectively resisting interference from salt ions. It maintains the molecular chain extension through electrostatic repulsion, ensuring good thickening properties in both water and acidic solutions. Simultaneously, the rigid structure of the benzene ring main chain effectively improves the copolymer's high-temperature resistance and shear strength. Methacryloxyethyl phosphate, as a crosslinking functional monomer, allows its phosphate groups to coordinate with metal ions to form a dynamic crosslinking network, enabling the copolymer to crosslink in both water and acidic solutions. Therefore, this copolymer exhibits strong thickening properties, high drag reduction, high temperature resistance, crosslinking capability, and online viscosity enhancement when used in both water and acidic solutions.

[0024] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0025] Figure 1 The image shows the infrared spectrum of the composite acid emulsion copolymer of Example 14.

[0026] Figure 2 This is a diagram showing the crosslinking experiment of the composite acid emulsion in Example 14 in water and acid.

[0027] Figure 3 The figure shows the sand-carrying performance of the composite acid emulsion in Example 14 at 90°C in water.

[0028] Figure 4 The diagram shows the temperature and shear resistance of the fracturing fluid gel formed by the composite acid emulsion in Example 14 at 200°C.

[0029] Figure 5 The graph shows the 0.1% slickwater drag reduction of the composite acid emulsion in Example 14.

[0030] Figure 6 The graph shows the viscosity change of the composite acid emulsion in Example 14 at different stirring times.

[0031] Figure 7 This is a diagram showing the dissolution of a rock core by the composite acid emulsion at a slow rate of 200°C in Example 14.

[0032] Figure 8 The graph shows the temperature and shear resistance of the gelled acid formed by the composite acid emulsion in Example 14 at 200°C.

[0033] Figure 9 The graph shows the temperature and shear resistance of the crosslinked acid formed by the composite acid emulsion in Example 14 at 200°C. Detailed Implementation

[0034] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0035] Examples 1-5: Effect of different initiator dosages on the viscosity of integrated composite acid emulsions in water and acid.

[0036] Example 1

[0037] The preparation method of the integrated composite acid emulsion in this embodiment is as follows: White oil and a composite emulsifier (Span-80 and OP-10 in a mass ratio of 3:1) are added to a three-necked flask and stirred until homogeneous, forming the oil phase. Acryloyloxyethyltrimethylammonium chloride, sodium p-vinylbenzenesulfonate, methacryloyloxyethyl phosphate, and disodium ethylenediaminetetraacetate (EDTA) are added to distilled water and mixed until homogeneous. The pH is adjusted to 7-9 using sodium hydroxide solution; this mixed solution forms the aqueous phase. Stirring is started, and the stirring speed is controlled at 1000-1500 r / min. The aqueous phase is slowly added dropwise to the oil phase, completing the addition within 30 minutes. Stirring continues for 2 hours to prepare a water-in-oil emulsion. After emulsification, the stirring speed is adjusted to 600 r / min, nitrogen is purged for 1 hour, and the temperature is raised to 50°C. A solution of azobisisobutylamidine hydrochloride, pre-dissolved in distilled water as an initiator, is added dropwise, and the reaction is carried out for 6 hours to obtain the integrated composite acid emulsion. The total amount of the three monomers is 34.25% of the emulsion mass. The molar ratio of acryloyloxyethyltrimethylammonium chloride:sodium p-vinylbenzenesulfonate:methacryloyloxyethyl phosphate is 80:17:3. The amount of composite emulsifier is 4% of the emulsion. The complexing agent, disodium ethylenediaminetetraacetate, is 0.1% of the emulsion. The amount of white oil is 50.2%. The amount of initiator is 0.1% of the total mass of the three monomers. The remainder is distilled water.

[0038] Example 2

[0039] The preparation method of Example 1 was followed, except that the amount of initiator was changed to 0.2% of the total mass of the three monomers.

[0040] Example 3

[0041] The preparation method of Example 1 was followed, except that the amount of initiator was changed to 0.3% of the total mass of the three monomers.

[0042] Example 4

[0043] The preparation method of Example 1 was followed, except that the amount of initiator was changed to 0.4% of the total mass of the three monomers.

[0044] Example 5

[0045] The preparation method of Example 1 was followed, except that the amount of initiator was changed to 0.5% of the total mass of the three monomers.

[0046] The integrated composite acid emulsions prepared in Examples 1 to 5 were tested as follows:

[0047] 1) Referring to the methods for preparing thickened acid solutions (6.2) and determining the apparent viscosity of thickened acid (7.5) in the petroleum and natural gas industry standard SY / T 6214-2016, the viscosity of the composite acid emulsion in a 20% hydrochloric acid solution (acid base viscosity) was tested. The amount of composite acid emulsion added accounted for 1.5% of the mass of the hydrochloric acid solution. Subsequent examples were tested using the same method.

[0048] 2) Referring to sections 6.1.1 (base fluid preparation) and 6.2 (apparent viscosity determination) of the energy industry standard NBT 14003.3-2017, the viscosity (fracturing fluid base fluid viscosity) of the composite acid emulsion was tested when dissolved in clean water at 600 r / min for 5 min. The amount of composite acid emulsion added accounted for 0.6% of the mass of clean water. Subsequent examples were tested using the same method.

[0049] The test results are shown in Table 1. It can be concluded that the viscosity of the composite acid emulsion is the highest in water and hydrochloric acid when the initiator content is 0.4%. Therefore, the optimal initiator content is 0.4%.

[0050] Table 1. Viscosities of the composite acid emulsions prepared in Examples 1 to 5 in water and acid solutions.

[0051]

[0052] Examples 6-9: Effect of reaction temperature on the viscosity of integrated composite acid emulsion in water and acid.

[0053] Example 6: Following the same preparation method as in Example 4, only the reaction temperature was adjusted to 40°C to obtain an integrated composite acid emulsion.

[0054] Example 7: Following the same preparation method as in Example 4, only the reaction temperature was adjusted to 45°C to obtain an integrated composite acid emulsion.

[0055] Example 8: Following the same preparation method as in Example 4, only the reaction temperature was adjusted to 55°C to obtain an integrated composite acid emulsion.

[0056] Example 9: Following the same preparation method as in Example 4, only the reaction temperature was adjusted to 60°C to obtain an integrated composite acid emulsion.

[0057] The viscosity of the composite acid emulsions from Examples 6-9 was tested in both water and acid, and compared with the results of Example 4. The test results are shown in Table 2. It can be concluded that the composite acid emulsions obtained at a reaction temperature of 55°C have the highest viscosity in both water and acid. Therefore, the optimal reaction temperature is 55°C.

[0058] Table 2. Viscosities of the composite acid emulsions from Examples 6-9 and Example 4 in water and acid solutions.

[0059]

[0060] Examples 10-12: Effects of composite emulsifier ratio on viscosity and stability of composite acid emulsions in water and acid solutions.

[0061] Example 10: The same preparation method as in Example 8 was used, except that the ratio of composite emulsifiers was adjusted to a mass ratio of Span-80 to OP-10 of 2:1.

[0062] Example 11: The same preparation method as in Example 8 was used, except that the ratio of composite emulsifiers was adjusted to a mass ratio of Span-80 to OP-10 of 4:1.

[0063] Example 12: The same preparation method as in Example 8 was used, except that the ratio of composite emulsifiers was adjusted to a mass ratio of Span-80 to OP-10 of 5:1.

[0064] The viscosity of the integrated composite acid emulsions prepared in Examples 10-12 was measured in both water and acid. The viscosity of the composite acid emulsions (Examples 8, 10, 11, and 12) at 100 r / min was tested using a six-speed rotational viscometer according to Appendix A of SY / T5886-2018. The composite acid emulsions of Examples 8, 10, 11, and 12 were placed in a 45°C water bath for 30 days to observe for stratification or separation. The test results are shown in Table 3. It can be seen that when the composite emulsifier ratio is Span 80∶OP-10 = 3∶1, the viscosity performance and stability of the composite acid emulsion are optimal.

[0065] Table 3 shows the test results of the composite acid emulsions in Examples 8, 10, 11, and 12 in water and acid solutions, including the viscosity of the emulsion, emulsion stability, and bulk viscosity.

[0066]

[0067] Examples 13-20: Effect of monomer molar ratio on viscosity and crosslinking properties of integrated composite acid emulsions in water and acid solutions

[0068] The same preparation method as in Example 8 was used, except that the molar ratio of the three monomers, namely, the molar ratio of acryloyloxyethyltrimethylammonium chloride, sodium p-vinylbenzenesulfonate, and methacryloyloxyethyl phosphate, was adjusted. The monomer molar ratios of each example are shown in Table 4.

[0069] The viscosity of the composite acid emulsions from Examples 13-20 in water and acid solutions was tested and compared with that of Example 8. The results are shown in Table 4. 0.3% crosslinking agent LP-JJL was added to both the obtained acid base solution and fracturing fluid base solution, and the mixtures were stirred thoroughly. The mixtures were then placed in a 90°C water bath, and the crosslinking time and crosslinking adhesion properties of the acid and fracturing fluid were observed. The test results are shown in Table 5.

[0070] Table 4. Viscosities of the composite acid emulsions prepared in Examples 13-20 and Example 8 in water and acid solutions.

[0071]

[0072] Table 5. Crosslinking properties of the composite acid emulsions prepared in Examples 13-20 and Example 8 in water and acid.

[0073]

[0074] It can be seen that the composite acid emulsion prepared in Example 14 has the best viscosity and crosslinking properties, that is, the optimal molar ratio of acryloyloxyethyltrimethylammonium chloride, sodium p-vinylbenzenesulfonate, and methacryloyloxyethyl phosphate is 80:15:5.

[0075] The molecular structure of the composite acid emulsion prepared in Example 14 was characterized and its performance in water and acid was tested.

[0076] The composite acid emulsion obtained in Example 14 was added to methanol to precipitate, separated, washed, filtered, dried, and pulverized to obtain copolymer powder.

[0077] (1) The copolymer powder was used, and the infrared spectrum was determined by the KBr pellet method. The results are as follows: Figure 1 As shown.

[0078] Depend on Figure 1 It can be seen that 3011 cm⁻¹ in the Fourier transform infrared spectrum -1 This is the stretching vibration of unsaturated CH on the benzene ring, 1728 cm⁻¹ -1 The peak at 1635 cm⁻¹ represents the C=O stretching vibration of the ester carbonyl group. -1 The peak at 1480 cm⁻¹ represents the C=C stretching vibration of the benzene ring. -1 The peak for the CH bending vibration of the -CH2- group of DAC quaternary ammonium salt is 1392 cm⁻¹. -1 The absorption peak corresponds to the CH bending vibration peak of the methyl group in the quaternary ammonium salt group -N+(CH3)3, at 1334 cm⁻¹. -1 The peak for the CH bending vibration of -CH3 is 1273 cm⁻¹. -1 The peak is the P=O stretching vibration peak of the phosphate group, at 1120 cm⁻¹. -1 and 1154cm -1 The peak at 952 cm⁻¹ corresponds to the characteristic peak of the S=O stretching vibration of the sulfonate group. -1 The peak is the POH bending vibration peak of the phosphate group, which suggests that the copolymer molecule is consistent with the target structure.

[0079] (2) Molecular weight characterization was performed using the Ubbelohde viscometer method. The copolymer powder was dissolved in 1 mol / L NaCl solution to prepare a 2000 mg / L copolymer solution. Then, 7.5 g of the copolymer solution was added to 92.5 g of a 150 mg / L copolymer target solution. The molecular weight was determined according to GB / T 12005.10 Polyacrylamide Molecular Weight Determination Viscosity Method. The results are shown in Table 6. Table 6 shows that the viscosity-average molecular weight M of the copolymer is... η The value is 11018948.

[0080] Table 6. Molecular weight characterization results of the copolymers in Example 14

[0081]

[0082] (3) Performance of compound acid emulsion in water

[0083] 1) Emulsion viscosity: The viscosity of the composite acid emulsion of Example 14 at 100 r / min was tested using a six-speed rotational viscometer according to Appendix A of SY / T5886-2018. The results are shown in Table 7.

[0084] 2) Viscosity of composite acid emulsions in water at different concentrations: According to the different concentrations of composite acid emulsions shown in Table 8, the viscosity of composite acid emulsions at different concentrations in water was tested, and the results are shown in Table 8.

[0085] 3) Breaking performance test: The composite acid emulsion of Example 14 was added to clean water, with the amount of composite acid emulsion accounting for 0.6% of the mass of clean water. It was stirred at 600 r / min for 5 min to form fracturing fluid base fluid. Then, 0.3% crosslinking agent LP-JJL and 0.3% breaking agent LP-PJ03 were added, and it was treated at 90℃ for 2 h. After cooling to room temperature, the viscosity of the breaking fluid was measured with a capillary viscometer. The results are shown in Table 7.

[0086] 4) Crosslinking performance of fracturing fluid: The test method is the same as the test method for crosslinking performance in Examples 13-20. The crosslinking adhesion performance is as follows: Figure 2 The crosslinking time is shown in Table 7.

[0087] 5) Sand-carrying performance test: Take 200mL of clean water, control the stirring speed at 600r / min, add 40g of 40-70 mesh ceramsite (sand ratio of 20%), add 0.3% of crosslinking agent LP-JJL, and then add 0.6% of the composite acid emulsion from Example 14. Dissolve for 5min, add to a 100ml graduated cylinder, and observe the settling rate at 90℃. The results are as follows. Figure 3 As shown, no sand settles after 2 hours.

[0088] 6) Temperature and Shear Resistance Test of Fracturing Fluid Gel: Prepare 1% fracturing fluid base fluid according to method 2), add 0.3% crosslinking agent LP-JJL, stir evenly, and perform the temperature and shear resistance test at 200℃ according to the provisions of 6.6 in SY / T 5107-2005. The results are as follows: Figure 4 As shown in Table 7.

[0089] 7) Drag reduction rate: The drag reduction rate of the composite acid emulsion of 0.1% in Example 14 was tested according to section 7.13 of SY / T 6376—2008, and the results are as follows. Figure 5 As shown in Table 7.

[0090] Table 7. Performance of the composite acid emulsion hydraulic fracturing fluid in Example 14

[0091]

[0092] Table 8. Viscosity of the composite acid emulsion in clear water at different concentrations in Example 14

[0093]

[0094] (4) Performance of composite acid emulsion in acid solution

[0095] 1) Viscosity of acid solutions prepared from composite acid emulsions of different concentrations: The viscosity of the acid base solution formed by the composite acid emulsion of Example 14 at different concentrations in hydrochloric acid was tested, and the results are shown in Table 9. The concentration of the composite acid emulsion is the percentage of the mass of the composite acid emulsion to the mass of the hydrochloric acid solution.

[0096] Table 9. Viscosity of the acid base liquid in the composite acid emulsion of Example 14 at different concentrations

[0097]

[0098] 2) Viscosity of 3% composite acid emulsion at different times: 20% hydrochloric acid was prepared according to method 4.2 in SY / T 5405—2019. The stirring speed was controlled at 400 r / min. 3% composite acid emulsion was added, and the viscosity was tested at 1 min, 3 min, 5 min, 7 min, 30 min, and 120 min using a six-speed rotational viscometer (100 r / min). The results are as follows: Figure 6 As shown.

[0099] 3) Acid crosslinking performance: Following the acid crosslinking time and crosslinking adhesion test methods in Examples 13-20, the crosslinking adhesion performance is as follows: Figure 2 The crosslinking time is shown in Table 10.

[0100] 4) 200℃ Retarding Rate Test: According to the petroleum and natural gas industry standard SY / T 6526-2019, "Method for Determining the Dynamic Reaction Rate of Hydrochloric Acid with Carbonate Rocks," a 20% blank hydrochloric acid solution and a composite acid solution formed by adding 3% of the composite acid emulsion from Example 14 to hydrochloric acid were tested. The retarding rate was calculated, and the results are as follows: Figure 7 As shown in Table 10. Figure 7 The paper presents a comparison of the dissolution of rock cores by blank hydrochloric acid and composite acid solutions.

[0101] 5) Temperature and shear resistance of gelling acid at 200℃: Prepare a 3% composite acid solution according to 1) above, and test its temperature and shear resistance at 200℃ according to method 7.7 in SY / T 6214-2016. The results are as follows: Figure 8 As shown in Table 10.

[0102] 6) Temperature and shear resistance of crosslinked acid at 200℃: Prepare a 3% composite acid solution as described in 1) above, then add 0.3% crosslinking agent LP-JJL, stir evenly, and test the temperature and shear resistance at 200℃ according to method 7.7 in SY / T 6214-2016. The results are as follows: Figure 9 As shown in Table 10.

[0103] Table 10, Acid Properties of Composite Acid Emulsion in Example 14

[0104]

[0105] In summary, the composite acid emulsion prepared by this invention has the characteristics of strong thickening, high drag reduction, high temperature resistance, cross-linking, and online viscosity change in both water and acid solutions, enabling integrated fracturing and acidizing operations as well as large-scale online acid fracturing operations.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing an integrated composite acid emulsion applicable to fracturing fluids and acid solutions, characterized in that, Includes the following steps: S1. Mix and disperse the organic solvent and composite emulsifier evenly to obtain the oil phase; S2. Add the quaternary ammonium salt unsaturated monomer, sodium benzenesulfonate unsaturated monomer, methacryloyloxyethyl phosphate and complexing agent to water, mix and stir evenly, adjust the pH of the solution to 7-9, and obtain the aqueous phase. The quaternary ammonium salt unsaturated monomer is selected from any one of acryloyloxyethyltrimethylammonium chloride, acrylamidopropyltrimethylammonium chloride, methacrylamidopropyltrimethylammonium chloride, and dimethyldiallylammonium chloride; The sodium benzenesulfonate unsaturated monomer is selected from any one of sodium p-vinylbenzenesulfonate, sodium p-methacrylamidobenzenesulfonate, and sodium α-methylstyrenesulfonate. The molar ratio of quaternary ammonium salt unsaturated monomer, sodium benzenesulfonate unsaturated monomer, and methacryloyloxyethyl phosphate is (70-80): (10-20): (1-5). S3. Under stirring conditions, the aqueous phase is slowly added dropwise to the oil phase, and the addition is completed within 30 minutes. Stirring is continued for 2 hours to form a water-in-oil emulsion. S4. After purging nitrogen gas into the water-in-oil emulsion to remove oxygen for 1 hour, the temperature is raised to 40℃~60℃, an initiator is added, and the mixture is stirred for 4-8 hours to obtain an integrated composite acid emulsion.

2. The method for preparing the integrated composite acid emulsion for use in fracturing fluids and acid solutions as described in claim 1, characterized in that, The organic solvent is selected from one or more of No. 3 white oil, No. 5 white oil, No. 10 white oil, and D60 solvent oil.

3. The integrated composite acid emulsion for use in fracturing fluids and acid solutions as described in claim 1, characterized in that, The composite emulsifier is composed of Span-80 and OP-10 in a mass ratio of (2~5):

1.

4. The method for preparing the integrated composite acid emulsion for use in fracturing fluids and acid solutions as described in claim 1, characterized in that, The complexing agent is selected from one of ethylenediaminetetraacetic acid, ethylenediaminetetramethylene phosphate, sodium aminotriacetate, and diethylenetriaminepentacarboxylate.

5. The method for preparing the integrated composite acid emulsion for use in fracturing fluids and acid solutions as described in claim 1, characterized in that, The initiator is a water-soluble azo initiator, selected from one of azobisisobutyramidine hydrochloride and azobisisobutyramidine imidazoline hydrochloride.

6. The method for preparing the integrated composite acid emulsion for use in fracturing fluids and acid solutions as described in claim 1, characterized in that, The total mass of the three monomers accounts for 34-35% of the total mass of the water-in-oil emulsion.

7. An integrated composite acid emulsion for use in fracturing fluids and acid solutions, characterized in that, It is prepared by any one of the preparation methods described in claims 1-6.

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