A salt-sensitive self-thickening weighted acid acidizing system, a preparation method and application thereof

Abstract

The application provides a salt-sensitive self-thickening weighted acid fracturing system as well as a preparation method and application thereof, and belongs to the technical field of oil field acidification and fracturing. The salt-sensitive self-thickening weighted acid fracturing system comprises the following components in parts by weight: 27-40.5 parts of hydrochloric acid aqueous solution, 10-50 parts of a weighting agent, 1-4 parts of a thickening agent, 1-4 parts of an inhibitor, and 1.5-55 parts of water. The acid fracturing system has the characteristics of high density, low corrosion rate, good high-temperature stability, excellent compatibility and the like, and is suitable for acid fracturing reconstruction of deep high-temperature and high-pressure carbonate rock reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of oilfield acid fracturing technology, specifically relating to a salt-sensitive self-thickening weighted acid fracturing system, its preparation method, and its application. Background Technology

[0002] Deep and even ultra-deep reservoirs, with depths exceeding 4,500 meters, hold enormous resource potential and represent the main battleground for future oil and gas reserve enhancement and production. However, deep oil and gas reservoirs typically exhibit extreme geological characteristics such as high temperature, high pressure, high stress, and low permeability, posing unprecedented challenges to reservoir stimulation technologies.

[0003] Acid fracturing, a key technique for enhancing oil and gas production in carbonate reservoirs, involves injecting acid into the formation and fracturing fractures. The acid's non-uniform dissolution of the fracture walls creates highly conductive acid channels, significantly increasing oil and gas yields. However, in deep formations, the fracturing pressure is extremely high, and the density of conventional acid solutions is typically around 1.05-1.10 g / cm³. 3 The resulting fluid column pressure is insufficient to overcome formation pressure, leading to reservoir failure and fluid ingress difficulties, placing extremely demanding requirements on surface fracturing equipment. To address this bottleneck, acid weighting technology has emerged. This technology increases fluid column pressure by adding high-density substances to the acid, effectively reducing wellhead drilling pressure and providing an effective means of deep reservoir stimulation.

[0004] Currently, the most widely used weighting technology both domestically and internationally employs soluble salts, such as calcium chloride, calcium bromide, and formate. These materials have high solubility and can significantly increase the density of acid solutions to 1.3 g / cm³. 3 The above, some even reaching 1.5g / cm³ 3 The above. However, this technical route has a series of inherent defects that are difficult to overcome: (1) Strong corrosivity: High concentrations of salt, especially chloride ions, will greatly aggravate the risk of electrochemical corrosion and stress corrosion cracking of downhole tubing, tools and equipment in high-temperature acidic environments, seriously threatening production safety and shortening equipment life. (2) Poor compatibility: High-salt environments cause acid to become ultra-high mineralization systems, which causes many conventional additives such as polymer thickeners and corrosion inhibitors to have reduced performance or failure due to salting-out effect, resulting in system instability and a significant drop in performance. (3) Environmental and cost pressures: High-efficiency weighting agents such as zinc bromide and potassium iodide are expensive, and the backflow fluid is difficult to treat, which is not environmentally friendly. Chinese patent document CN102399551A discloses a weighting acid, which is composed of industrial hydrochloric acid, inorganic salt weighting agent, corrosion inhibitor, corrosion inhibitor synergist and iron ion stabilizer, with a density of 1.5 g / cm³. 3It increases the density and weighting capacity of the acid solution, but only simple tests were conducted on its corrosiveness, and the corrosiveness data is unknown. In addition, it still has problems such as poor compatibility with other conventional additives and high environmental and cost pressures.

[0005] In recent years, nanomaterials have attracted attention as an emerging type of weighting agent. Their theoretical advantages lie in their small particle size and large specific surface area, enabling density enhancement with relatively low addition amounts, while also effectively improving system compatibility. However, practical experience shows that existing nanomaterials, such as nano-silica and nano-barium sulfate, generally suffer from poor dispersion stability and are prone to agglomeration and sedimentation in strong acid and high-temperature environments. Agglomerates not only lose their nano-effects but may also clog reservoir micropores, causing secondary damage. Furthermore, their density enhancement capacity per unit mass is limited, making it difficult to independently achieve the density targets required for deep acid fracturing, and their low cost-effectiveness restricts their industrial application. Chinese patent document CN103788932A discloses an oilfield nano-weighting agent, which is composed of surfactants, stabilizers, activators, weighting materials, dispersants, and water. The surfactants, dispersants, stabilizers, and activators chemically modify the surface of the weighting material, causing a double electron layer to form on the surface of the weighting agent particles. This increases the electrostatic repulsion between particles, significantly reducing the tendency for particle sedimentation. The particles form a colloid in the solution, creating a kinetically stable system under the combined effects of electrostatic repulsion and Brownian motion, making it highly suitable for use in harsh environments such as high temperature, high pressure, and high salinity. While chemically modifying the surface of the nano-weighting material can effectively alleviate problems such as high-temperature agglomeration and sedimentation of nanoparticles, the nanomaterials themselves have weak weighting capacity and limited density enhancement capabilities, making it difficult to meet the requirements of deep acid fracturing.

[0006] Therefore, the core challenge currently facing the field of deep acid fracturing technology is that while traditional salt-based weighting methods can achieve high density, they are accompanied by unacceptably strong corrosivity and compatibility issues; while emerging nanomaterial weighting technologies are still immature due to limitations in stability and weighting efficiency. Developing a novel weighting acid system that can balance high density, weak corrosion, good high-temperature stability, and excellent compatibility has become an urgent need to overcome the technological bottlenecks in the efficient development of deep oil and gas resources, and is also a key challenge that researchers in this field are striving to solve. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of strong corrosivity, poor compatibility, and insufficient high-temperature stability of existing weighting acids, and to propose a salt-sensitive self-thickening weighting acid fracturing system, its preparation method, and its application. The acid fracturing system of this invention features high density, low corrosion rate, good high-temperature stability, and excellent compatibility, making it suitable for acid fracturing stimulation of deep, high-temperature, and high-pressure carbonate reservoirs.

[0008] The technical solution of the present invention is as follows:

[0009] In a first aspect, the present invention provides a salt-sensitive self-thickening and weighting acid pressure system, comprising the following components in parts by weight: 27-40.5 parts of hydrochloric acid aqueous solution, 10-50 parts of weighting agent, 1-4 parts of thickener, 1-4 parts of corrosion inhibitor, and 1.5-55 parts of water.

[0010] According to a preferred embodiment of the present invention, the salt-sensitive self-thickening and weighting acid pressure system comprises the following components in parts by weight: 27-40.5 parts of hydrochloric acid aqueous solution, 50 parts of weighting agent, 4 parts of thickener, 4 parts of corrosion inhibitor, and 1.5-15 parts of water.

[0011] According to a preferred embodiment of the present invention, the hydrochloric acid aqueous solution has a mass concentration of 36-38%, and is industrial hydrochloric acid.

[0012] According to the present invention, the weighting agent is one or a combination of potassium formate or anhydrous calcium chloride; preferably, the weighting agent is a combination of potassium formate and anhydrous calcium chloride, wherein the mass ratio of potassium formate to anhydrous calcium chloride is 1:2.3-7, preferably 3:7.

[0013] According to a preferred embodiment of the present invention, the thickener is one of N,N,N-trimethylglycine or cocamidopropyl betaine.

[0014] According to a preferred embodiment of the present invention, the corrosion inhibitor is a propynyl alcohol ethoxy compound and an imidazoline quaternary ammonium salt. Preferably, the mass ratio of the propynyl alcohol ethoxy compound to the imidazoline quaternary ammonium salt is 1:0.5-2.

[0015] According to a preferred embodiment of the present invention, the density of the gravimetric acid stress system is 1.203-1.507 g / cm³. 3 .

[0016] Secondly, the present invention provides a method for preparing a salt-sensitive self-thickening and weighted acid pressure system, comprising the following steps:

[0017] Add hydrochloric acid aqueous solution to water, add weighting agent, and stir at 60°C until completely dissolved; add thickener, and stir at 60°C until completely dissolved; add corrosion inhibitor, and stir at 60°C until completely dissolved to obtain a salt-sensitive self-thickening weighted acid pressure system.

[0018] According to a preferred embodiment of the present invention, the stirring rate is 450-550 rpm / min.

[0019] Thirdly, this invention provides an application of a salt-sensitive self-thickening and weighted acid fracturing system in acid fracturing of carbonate reservoirs; the temperature of the carbonate reservoir is greater than or equal to 60°C.

[0020] The technical features and beneficial effects of this invention are as follows:

[0021] 1. This invention uses hydrochloric acid, a weighting agent, a thickener, and a corrosion inhibitor as core raw materials. By controlling the order of addition and the stirring intensity, a low-corrosion weighting acid system with outstanding weighting ability and good corrosion inhibition effect can be prepared. The preparation method of this invention is simple, the raw materials are inexpensive, the backflow liquid is easy to treat, it is environmentally friendly, and it is conducive to industrial production.

[0022] 2. The weighting agent used in this invention has dual functions of density regulation and rheological control. The metal cations it provides are not only the basis for achieving high density, but also act as activators for the salt-sensitive thickener cocamidopropyl betaine. The "cocamidopropyl" portion of the thickener cocamidopropyl betaine provides a long hydrophobic chain, with more tightly packed chains. Van der Waals forces are proportional to the interaction area, forming more stable and compact worm-like micelles. Cocamidopropyl betaine molecules are cross-linked together in solution by van der Waals forces. At the same time, under acidic conditions, the high-valence cations dissociated from the weighting agent efficiently stimulate betaine molecules to form long worm-like micelles and construct a dynamic three-dimensional physical network throughout the system through charge shielding. Macroscopically, this manifests as high viscosity and good thickening effect, effectively reducing the mass transfer and diffusion of hydrogen ions in the system, alleviating the corrosion of metal tubing by acid, and reducing the acid-rock reaction rate. In corrosion inhibitors, propynyl alcohol ethoxy compounds preferentially adsorb onto highly active sites on the metal surface most susceptible to corrosion. The terminal alkyne group (-C≡CH) forms a covalent bond with iron atoms on the metal surface, polymerizing to form a dense polyalkyne film. The imidazoline quaternary ammonium salt fills the gaps, and the quaternary ammonium cation covers the areas not covered by propynyl alcohol through electrostatic adsorption. The long alkyl chain carried by the quaternary ammonium salt molecule undergoes hydrophobic interpenetration with the polyalkyne chain, blocking the pores and achieving a good corrosion inhibition effect.

[0023] 3. The density of the acid system in this invention can reach up to 1.5 g / cm³. 3 , in the range of 1.2-1.5 g / cm 3 Adjustable within a certain range to meet the needs of high-temperature and high-pressure reservoirs; maintains high corrosion inhibition rate even at 150℃; the salt introduced by the weighting agent shields the electrostatic repulsion of cocamidopropyl betaine, resulting in thickening upon contact with salt, maintaining high viscosity without the need for adding polymers, while also avoiding the problems of de-gelling agents and potential residue damage required by traditional thickening acids. Furthermore, cocamidopropyl betaine is an amphoteric surfactant that does not interfere with the main acid reaction and has good compatibility with other additives; the compound corrosion inhibitor has good stability at high temperatures, is not easily decomposed, and forms a protective film with high corrosion inhibition efficiency and good durability; acid-rock reaction kinetic parameters show that the acid fracturing system of this invention has slow-speed deep acid corrosion characteristics, and is particularly suitable for deep carbonate reservoirs.

[0024] 4. The acid fracturing system of this invention features high density, low corrosion rate, good high-temperature stability, and excellent compatibility, making it suitable for acid fracturing stimulation of deep, high-temperature, and high-pressure carbonate reservoirs. The superior effects of this invention can only be achieved through the combined action of specific raw material types and proportions; if the raw material types or proportions are unsuitable, or if a certain raw material is omitted, the performance of the resulting acid fracturing system will decrease. Attached Figure Description

[0025] Figure 1 This is a photograph of the appearance of the acid-pressure system prepared in Example 1 at 60°C.

[0026] Figure 2 This is a 3D laser scan image of the core end face after the rotating rock disk experiment in the experimental example.

[0027] Figure 3 This is a comparison chart of single-factor analysis of acid-rock reaction in the experimental examples. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the embodiments.

[0029] In the embodiments, unless otherwise specified, all materials used are commercially available, and all methods used are conventional methods in the art.

[0030] Example 1:

[0031] A salt-sensitive self-thickening and weighting acid pressure system comprises the following components by mass: 27g of a 37% hydrochloric acid aqueous solution (industrial hydrochloric acid), 15g of potassium formate as a weighting agent, 35g of anhydrous calcium chloride as a weighting agent, 4g of cocamidopropyl betaine as a thickener, 4g of a corrosion inhibitor (propynyl alcohol ethoxylate compound and imidazoline quaternary ammonium salt, mass ratio 1:1), and 15g of deionized water.

[0032] The preparation method of the above-mentioned salt-sensitive self-thickening and gravimetric acid pressure system includes the following steps: (1) Add industrial hydrochloric acid to deionized water to obtain a dilute hydrochloric acid solution; (2) At 60°C, first add anhydrous calcium chloride and stir until completely dissolved, then add potassium formate and continue stirring until completely dissolved to obtain the first product liquid; (3) At 60°C, long-chain cocamidopropyl betaine was added to the first product liquid, and the mixture was stirred at a constant speed of 500 rpm until the solution thickened significantly and only a few bubbles appeared on the surface, thus obtaining the second product liquid. (4) At 60°C, add propynyl alcohol ethoxy compound and imidazoline quaternary ammonium salt to the second product liquid, and stir at a constant speed of 500 rpm for 30 minutes until the solution is completely dissolved to obtain a salt-sensitive self-thickening and weighted acid pressure system.

[0033] The appearance of the gravimetric acid stress system prepared in this embodiment at 60°C is shown in the following photograph. Figure 1 As shown.

[0034] Example 2:

[0035] A salt-sensitive self-thickening and weighting acid pressure system comprises the following components by mass: 27g of a 37% hydrochloric acid aqueous solution (industrial hydrochloric acid), 15g of potassium formate as a weighting agent, 35g of anhydrous calcium chloride as a weighting agent, 4g of cocamidopropyl betaine as a thickener, 1g of a corrosion inhibitor (propynyl alcohol ethoxylate compound and imidazoline quaternary ammonium salt, mass ratio 1:1), and 18g of deionized water.

[0036] The preparation method of the above-mentioned salt-sensitive self-thickening and weighted acid pressure system is the same as that in Example 1, except that it is the same as above.

[0037] Example 3:

[0038] A salt-sensitive self-thickening and weighting acid pressure system comprises the following components by mass: 27g of a 37% hydrochloric acid aqueous solution (industrial hydrochloric acid), 15g of potassium formate as a weighting agent, 35g of anhydrous calcium chloride as a weighting agent, 1g of cocamidopropyl betaine as a thickener, 4g of a corrosion inhibitor (propynyl alcohol ethoxylate compound and imidazoline quaternary ammonium salt, mass ratio 1:1), and 18g of deionized water.

[0039] The preparation method of the above-mentioned salt-sensitive self-thickening and weighted acid pressure system is the same as that in Example 1, except that it is the same as above.

[0040] Example 4:

[0041] A salt-sensitive self-thickening and weighted acid pressure system is described in Example 1, except that the thickener cocamidopropyl betaine is replaced with N,N,N-trimethylglycine; the composition of other raw materials is the same as in Example 1.

[0042] The preparation method of the above-mentioned salt-sensitive self-thickening and weighted acid pressure system is the same as that in Example 1, except that it is the same as above.

[0043] Example 5:

[0044] A salt-sensitive self-thickening and weighting acid pressure system comprises the following components by mass: 40.5g of a 37% hydrochloric acid aqueous solution (industrial hydrochloric acid), 35g of anhydrous calcium chloride as a weighting agent, 4g of cocamidopropyl betaine as a thickener, 4g of a corrosion inhibitor (propynyl alcohol ethoxylate and imidazoline quaternary ammonium salt, mass ratio 1:1), and 16.5g of deionized water.

[0045] The preparation method of the above-mentioned salt-sensitive self-thickening and weighted acid pressure system is the same as that in Example 1, except that it is the same as above.

[0046] Example 6:

[0047] A salt-sensitive self-thickening acid pressure system, as described in Example 1, except that the mass ratio of the corrosion inhibitor propynyl alcohol ethoxy compound and imidazoline quaternary ammonium salt is replaced with 1:2; the composition of other raw materials is the same as in Example 1.

[0048] The preparation method of the above-mentioned salt-sensitive self-thickening and weighted acid pressure system is the same as that in Example 1, except that it is the same as above.

[0049] Example 7:

[0050] A salt-sensitive self-thickening acid pressure system, as described in Example 1, except that the mass ratio of the corrosion inhibitor propynyl alcohol ethoxy compound and imidazoline quaternary ammonium salt is replaced with 2:1; the composition of other raw materials is the same as in Example 1.

[0051] The preparation method of the above-mentioned salt-sensitive self-thickening and weighted acid pressure system is the same as that in Example 1, except that it is the same as above.

[0052] Example 8:

[0053] A salt-sensitive self-thickening and weighting acid pressure system comprises the following components by mass: 40.5g of a 37% hydrochloric acid aqueous solution (industrial hydrochloric acid), 15g of potassium formate as a weighting agent, 35g of anhydrous calcium chloride as a weighting agent, 4g of cocamidopropyl betaine as a thickener, 4g of a corrosion inhibitor (propynyl alcohol ethoxylate and imidazoline quaternary ammonium salt, mass ratio 1:1), and 1.5g of deionized water.

[0054] The preparation method of the above-mentioned salt-sensitive self-thickening and heavy acid pressure system is the same as that in Example 1.

[0055] Example 9:

[0056] A salt-sensitive self-thickening and weighting acid pressure system comprises the following components by mass: 33.8 g of a 37% hydrochloric acid aqueous solution (industrial hydrochloric acid), 15 g of potassium formate as a weighting agent, 35 g of anhydrous calcium chloride as a weighting agent, 4 g of cocamidopropyl betaine as a thickener, 4 g of a corrosion inhibitor (propynyl alcohol ethoxylate and imidazoline quaternary ammonium salt, mass ratio 1:1), and 8.2 g of deionized water.

[0057] The preparation method of the above-mentioned salt-sensitive self-thickening and heavy acid pressure system is the same as that in Example 1.

[0058] Comparative Example 1

[0059] A salt-sensitive self-thickening and weighted acid pressure system is described in Example 1, except that the thickener cocamidopropyl betaine is replaced with cationic polyacrylamide (average molecular weight 12 million, ionicity 10%); the composition of other raw materials is the same as in Example 1.

[0060] The preparation method of the above-mentioned salt-sensitive self-thickening and weighted acid pressure system is the same as that in Example 1, except that it is the same as above.

[0061] Comparative Example 2

[0062] A salt-sensitive self-thickening acid-pressure system, as described in Example 1, except that the corrosion inhibitor is replaced with water-soluble imidazoline; the composition of other raw materials is the same as in Example 1.

[0063] The preparation method of the above-mentioned salt-sensitive self-thickening and weighted acid pressure system is the same as that in Example 1, except that it is the same as above.

[0064] Comparative Example 3

[0065] A salt-sensitive self-thickening acid pressure system is described in Example 1, except that the corrosion inhibitor is replaced with propynyl alcohol ethoxylate in an amount of 4g, and imidazoline quaternary ammonium salt is not added; the composition of other raw materials is the same as in Example 1.

[0066] The preparation method of the above-mentioned salt-sensitive self-thickening and weighted acid pressure system is the same as that in Example 1, except that it is the same as above.

[0067] Comparative Example 4

[0068] A salt-sensitive self-thickening acid pressure system is described in Example 1, except that the corrosion inhibitor is replaced with imidazoline quaternary ammonium salt at a dosage of 4g, and propynyl alcohol ethoxy compound is not added; the composition of other raw materials is the same as in Example 1.

[0069] The preparation method of the above-mentioned salt-sensitive self-thickening and weighted acid pressure system is the same as that in Example 1, except that it is the same as above.

[0070] Test case

[0071] 1. Density test of the weighted acid system Based on the optimal example 1, an acid pressing system was prepared by varying the amount of weighting agent added; the density of the obtained acid pressing system was measured at 60°C. The instrument used in the experiment was a 25ml density bottle. The prepared acid pressing system was poured into the density bottle, kept at 60°C to ensure that no air bubbles were present, and its density was calculated by weighing. The average value was taken from three repeated experiments, and the results are shown in Table 1.

[0072] Table 1. Densities of acid fracturing systems under different weighting agent dosages

[0073]

[0074] Anhydrous calcium chloride exhibits excellent solubility under high-temperature conditions and also possesses a certain weight-adding ability. As shown in Table 1, when added alone, the system density reaches 1.451 g / cm³ at a mass concentration of 35%. 3As the amount of calcium chloride increases, the density also increases significantly, but this also leads to a substantial increase in the system's mineralization. High-mineralization acid solutions may reduce or degrade the performance of some additives. Therefore, it is considered to appropriately reduce the amount of calcium chloride and combine it with potassium formate, which has excellent weight-adding properties, to increase the density while minimizing the system's mineralization. With the continuous addition of potassium formate, the system density continues to increase, reaching a maximum of 1.507 g / cm³ when the potassium formate concentration is 15%. 3 To achieve the target density of 1.5 g / cm³ 3 Furthermore, when anhydrous calcium chloride is used alone for weighting, its density can reach 1.2-1.4 g / cm³. 3 With adjustable density, when used in combination with potassium formate, a density range of 1.2-1.5 g / cm³ can be achieved. 3 Adjustable within a certain range to meet the density requirements of deep acid fracturing.

[0075] 2. Viscosity performance testing of the weighted acid system

[0076] To analyze the thickening ability and high-temperature stability of the systems, using the 4500-meter reservoir temperature as a boundary, the systems prepared in Examples 1, 3, 4, and Comparative Example 1 were first heated to 150°C, then cooled to room temperature. They were then heated to the corresponding test temperatures, and the viscosity of the systems was measured using a rotational viscometer. The instrument used in the experiment was a Brookfield DV2T rotational viscometer (USA). During the experiment, the system volume was 20g, and the shear rate was kept constant at 170s during the viscosity test. -1 The results are shown in Table 2.

[0077] Table 2 Viscosity of different acid-fusing systems at different temperatures

[0078] As shown in Table 2, the salt-sensitive self-thickening and weighted acid fracturing system prepared by this invention maintains a viscosity of 4.58-19.52 mPa·s even after being subjected to a high temperature of 150℃. This viscosity is significantly higher than that of the system prepared with conventional polyacrylamide in Comparative Example 1, indicating that the salt-sensitive self-thickening and weighted acid fracturing system prepared by this invention has better high-temperature stability and can maintain high viscosity even after high temperatures. With increasing test temperature, the system viscosity decreases significantly. During the heating process, as the temperature rises from 60℃ to 90℃, the system viscosity decreases from 19.52 mPa·s to 11.36 mPa·s, a decrease of 41.8%, indicating that the viscosity is more sensitive to temperature at high temperatures. Under constant shear rate conditions, the viscosity remained at 11.36 mPa·s at 90℃, indicating that the acid fracturing system possesses good high-temperature shear stability. The high viscosity of the fluid creates significant flow resistance within the formation pores, which helps reduce acid loss to the formation during fracturing and improves acid efficiency. Simultaneously, increased viscosity slows the mass transfer and diffusion of hydrogen ions to the rock surface, thus reducing the acid-rock reaction rate. This combination of rheological properties suggests that the system can achieve deeper acid penetration and a more gradual and effective reaction in practical applications.

[0079] 3. Testing the corrosion inhibition performance of the acid-based system

[0080] The corrosion inhibition performance of the systems prepared in Examples 1-2, 6, and 7, and Comparative Examples 2, 3, and 4 was tested using N80 steel sheets to simulate a wellbore. The specific steps were as follows: N80 steel sheets with dimensions of 50 × 25 × 2 mm and a surface area of ​​28 cm² were used. 2 The N80 steel sheet was sanded to ensure a uniform surface finish, then rinsed with water, degreased with acetone, and soaked in anhydrous ethanol for about 2-3 minutes before being removed and air-dried. It was then wrapped in filter paper and placed in an oven to dry. Finally, it was weighed and the weight recorded. The treated N80 steel sheet was placed in a polytetrafluoroethylene-lined tank, and the prepared acid pressing system was slowly poured into the tank to cover the steel sheet. The tank was then sealed and placed in a high-temperature container and heated in an oven. After the experiment, the steel sheet was immediately removed and rinsed with water multiple times. The loose product film on the surface of the steel sheet was removed with a soft eraser, and it was degreased in acetone. The steel sheet was then soaked in an acid pickling solution for 5 minutes. After being removed from the acid pickling solution, the surface residual acid was immediately rinsed off with water, and the sheet was immediately immersed in NaOH solution. After removal, it was soaked in anhydrous ethanol for 5 minutes to clean and dehydrate. The steel sheet was then removed, placed on filter paper to dry, and placed in a desiccator for 30 minutes before being weighed. Repeat the above method to conduct experiments on different systems and record the experimental data. Calculate the corrosion inhibition rate of the steel sheet according to the corrosion rate calculation method in the petroleum and natural gas industry standard SY / T5405-2019 "Test Methods and Evaluation Indicators for the Performance of Corrosion Inhibitors for Acidification". The experiment time was 4 hours for all experiments. The results are shown in Table 3.

[0081] Table 3 Corrosion inhibition rates of different acid fracturing systems at different temperatures

[0082]

[0083] Table 3 shows that the salt-sensitive self-thickening and weighted acid fracturing system prepared in this invention significantly improves the corrosion inhibition rate and reduces the corrosion rate of the steel sheet compared to the acid fracturing systems of Comparative Examples 2, 3, and 4. Data from Examples 1 and 2 show that when the temperature increases from 120℃ to 150℃, the corresponding corrosion inhibitor concentration needs to increase from 1% to 4% to maintain a high corrosion inhibition rate. Maintaining the experimental temperature at 150℃ and the experimental time at 4 hours, Examples 1, 6, 7 and Comparative Examples 2, 3, and 4 show that when the corrosion inhibitor concentration is 4%, the effect of the compound corrosion inhibitor is better than that of the single corrosion inhibitor. Furthermore, the ratio of propynyl alcohol ethoxylate compound and imidazoline quaternary ammonium salt in the compound corrosion inhibitor also affects the corrosion inhibition effect, with the corrosion inhibition effect being 1:1 > 2:1 > 1:2 (by mass ratio). This invention demonstrates that the compound corrosion inhibitor in the salt-sensitive self-thickening and weighted acid fracturing system exhibits the best synergistic effect, superior to systems using a single corrosion inhibitor. It forms a denser and more comprehensive protective film on the steel surface. Furthermore, due to the ionic strength effect, the reduced hydrogen ion activity allows calcium ions to preferentially adsorb onto the steel surface, generating protective corrosion products. In practical applications, the compound corrosion inhibitor in the salt-sensitive self-thickening and weighted acid fracturing system forms a more protective film, effectively protecting downhole equipment during acid fracturing injection and production operations, reducing the probability of equipment damage, and extending equipment lifespan.

[0084] 4. Analysis of factors influencing acid-rock reaction kinetics

[0085] The salt-sensitive self-thickening and weighted acid fracturing system of Example 1 of this invention was used, keeping other components constant, but the amounts of hydrochloric acid aqueous solution and deionized water added were changed to alter the concentration of hydrochloric acid in the entire fracturing system (as in Examples 8 and 9 of this invention). A four-factor, three-level orthogonal experiment was designed along with three variables: reaction time, reaction temperature, and rotation speed, to conduct acid-rock reaction kinetic experiments and determine the reaction rate constant, reaction order, reaction kinetic equation, and activation energy. Experimental conditions are shown in Table 4. The instrument used in the experiment was the SYF-3 type rotating rock disk apparatus for acid-rock reaction from Jiangsu Lianyou Scientific Instruments Co., Ltd. This instrument reproduces the temperature and pressure conditions of the formation, causing the rock disk to rotate at high speed in the acid solution. By controlling the rotation speed, the flow state of the acid solution on the rock surface (laminar or turbulent) is adjusted, and the acid solution reacts chemically with the rock (carbonate rock reacts with hydrochloric acid to generate CO2). By measuring parameters such as rock disk mass loss and acid solution concentration changes, the reaction rate and acid etching efficiency were calculated. This test employed a four-factor, three-level orthogonal experiment to evaluate the priority of the effects of temperature, concentration, rotation speed, and reaction time on the acid-rock reaction, and used the acid-rock reaction rate as an indicator to evaluate the acid-rock reaction efficiency of the acid-pressing system. The specific steps are as follows: The core was washed, dried, and weighed. The core was fixed on the rock disk, and the acid-pressing system was poured into the reactor, which was then sealed. Different reaction conditions were set for the experiment. After the experiment, the core was removed, washed, dried, and weighed. The reaction rate was calculated using the core mass loss. Based on the rotating rock disk theory (Levich equation), the reaction kinetic equation was obtained, and the surface reaction activation energy was calculated. The results are shown in Table 4. The cores obtained after the experiment under the conditions in Table 4 were subjected to 3D laser end-face scanning, and the results are shown in Table 4. Figure 2 .

[0086] Table 4. Orthogonal experimental reaction conditions and acid-rock reaction rates

[0087]

[0088] Figure 2 This is a 3D laser scan image of the core face used in the experiment. The chromatographic bands on the left represent height differences, with colors ranging from dark to light as the height difference increases. Compare the data in Table 4 with... Figure 2 It can be seen that the higher the reaction rate, the brighter the corresponding core end face, indicating a deeper etching of the core. Table 4 shows that the salt-sensitive self-thickening and weighted acid fracturing system prepared in this invention exhibits the highest reaction rate and the deepest etching under reaction conditions of 150℃, 15%, 600 r / s, and 5 min.

[0089] Univariate analysis (based on the conditions and data in Table 4): With a single variable fixed, a range analysis was performed on the response rate at different levels of this variable. Range plots of different variables on response rates were then generated. The results are shown in [Table 4]. Figure 3 . Figure 3The first graph in the first row presents a single-factor analysis of reaction time, performing a range analysis on the results of three experimental groups with the same reaction time to compare the effects of three levels of reaction time on the reaction rate. The second graph in the first row presents a single-factor analysis of rotational speed, performing a range analysis on the results of three experimental groups with the same rotational speed to compare the effects of three levels of rotational speed on the reaction rate. The first graph in the second row presents a single-factor analysis of reaction temperature, performing a range analysis on the results of three experimental groups with the same reaction temperature to compare the effects of three levels of reaction temperature on the reaction rate. The second graph in the second row presents a single-factor analysis of the mass concentration of hydrochloric acid in the acid-pressurization system, performing a range analysis on the results of three experimental groups with the same concentration to compare the effects of three levels of hydrochloric acid mass concentration in the acid-pressurization system on the reaction rate. From... Figure 3 It can be seen that the range of single-factor level changes in the first graph of the first row and the second graph of the second row is relatively large, corresponding to the significant influence of reaction time and concentration on mass loss and reaction rate; the range of single-factor level changes in the second graph of the first row and the first graph of the second row is relatively small, corresponding to the weaker influence of rotation speed and reaction temperature on mass loss and reaction rate; the priority of acid-rock reaction factors is: concentration > reaction time > temperature > rotation speed. Based on the rotating rock disk theory (Levich equation), when the rotation speed is 900 r / s, the diffusion control stage is broken and the surface reaction control stage is entered.

[0090] Using a double logarithmic coordinate analysis method, a linear regression equation was constructed between concentration and reaction rate, yielding the reaction rate constant K = 1.4312 × 10⁻⁶. -6 (mol / L) -1.4524 ·mol / (cm 2 Given that the reaction order m = 1.4524, the kinetic equation for the reaction between the core and the acid-treated rock can be obtained as J = 1.4312 × 10⁻⁶ s⁻¹. -6 C 1.4524 The typical kinetic rate of conventional hydrochloric acid-rock reaction is 10. -5 -10 -4 mol / (cm 2 The reaction constant of this system is on the order of ·s, which is an order of magnitude smaller than that of the conventional hydrochloric acid system, indicating that the acid-rock reaction rate is slower than that of conventional hydrochloric acid. Using the Arrhenius equation, a linear regression model of the logarithm of the reaction rate and the reciprocal of the thermodynamic temperature was established, thus yielding the acid-rock reaction frequency factor K0 = 0.000067 (mol / L). -1.4524 ·mol / (cm 2The activation energy of the acid-rock reaction, Ea, is 12249.52 J / mol, which is at the lower limit of the typical range (10-60 kJ / mol) for acid-rock reactions. The minimum energy barrier that needs to be overcome for the acid to dissolve a unit mass of mineral to undergo a chemical reaction is relatively small. This slow-speed characteristic is conducive to achieving deep acid etching, proving that the system has a good deep acidification effect.

[0091] The above embodiments illustrate that the preparation method of the salt-sensitive self-thickening weighted acid fracturing system provided by the present invention has a simple process and is easy to mass-produce. Compared with the weighting of nanomaterials, it has the advantages of low cost, simple process, good dispersion stability, good corrosion inhibition effect, certain viscosity and other characteristics. The acid-rock reaction rate is slow, which is conducive to the non-uniform etching behavior of the acid system on the rock wall, optimizes the acid etching conductivity, and can meet the needs of deep acid fracturing modification.

[0092] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A salt-sensitive self-thickening weighted acid acidizing fluid system characterized in that, The components include the following parts by weight: 27-40.5 parts hydrochloric acid aqueous solution, 50 parts weighting agent, 4 parts thickener, 4 parts corrosion inhibitor, and 1.5-15 parts water; The weighting agent is a combination of potassium formate and anhydrous calcium chloride, with a mass ratio of 3:7; the thickener is cocamidopropyl betaine; and the corrosion inhibitor is propynyl alcohol ethoxylate and imidazoline quaternary ammonium salt, with a mass ratio of 1:

1. The mass concentration of the hydrochloric acid aqueous solution is 36-38%; the density of the weighted acid acidizing system is 1.507 g / cm 3 .

2. The method of preparing a salt-sensitive self-thickening overbased acid fracturing fluid system of claim 1, wherein, Including the following steps: Add hydrochloric acid aqueous solution to water, add weighting agent, and stir at 60°C until completely dissolved; add thickener, and stir at 60°C until completely dissolved; add corrosion inhibitor, and stir at 60°C until completely dissolved to obtain a salt-sensitive self-thickening weighted acid pressure system.

3. Use of the salt-sensitive self-thickening brined acid acidizing system in the acid fracturing of carbonate reservoirs according to claim 1, characterized in that, The temperature of carbonate reservoirs is greater than or equal to 60℃.

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