Fluorine-free solid mud acid and application thereof

Abstract

This invention belongs to the field of fluorine-free solid soil acid technology, specifically relating to a fluorine-free solid soil acid and its applications. The fluorine-free solid soil acid is prepared from 20-22 parts of solid organic acid, 7-9 parts of metal salt catalyst, 1-3 parts of chelating agent, 0.5-0.7 parts of silicate inhibitor, and 65.3-71.5 parts of water. The solid organic acid is selected from one or more of maleic anhydride, maleic acid, hydroxyethylidene diphosphonic acid, and aminotrimethylene phosphonic acid. The metal salt catalyst is selected from one or more of aluminum chloride, polyaluminum chloride, ferric chloride, and zirconium oxychloride. The silicate inhibitor is selected from one or more of polyepoxysuccinic acid and polyacrylic acid. The fluorine-free solid soil acid of this invention does not generate secondary precipitation of fluorosilicates and fluoroaluminates, thus avoiding formation damage. Furthermore, the dissolution rate after 18 hours of reaction is 14.72%-16.99%, and the raw materials are solid with low toxicity and corrosiveness, which is beneficial for transportation, storage, and construction.

Description

Technical Field

[0001] This invention belongs to the field of fluorine-free solid soil acid technology, specifically relating to a fluorine-free solid soil acid and its applications. Background Technology

[0002] Acidizing sandstone reservoirs is an important measure to remove near-wellbore contamination and increase oil and gas well production. Conventional soil acid is a mixture of hydrochloric acid and hydrofluoric acid, which can effectively dissolve siliceous minerals and clay. Conventional soil acid easily reacts with formation minerals to generate secondary precipitates such as fluorosilicates and fluoroaluminates, causing formation damage. The article “Zhao Haijian, Liu Pingli, Fan Kerui, et al. Evaluation of the effect of soil acid acidizing on unblocking of water injection well reservoirs [J]. Progress in Fine Petrochemicals, 2012, 13(12):17-19” reported that AlF 2+ SiF4 is the most basic product, and the formation of the product is affected by the pH of the acid solution and the F of the solution. - The effects are significant. When the volume ratio of HCl to HF is less than 6:1, a large amount of AlF3 precipitate is formed; when it is greater than 6:1, clay swelling is likely to occur. In addition, hydrofluoric acid is extremely toxic and corrosive, and is liquid at room temperature, which poses safety hazards for transportation, storage, and on-site construction, especially limiting its application in remote areas such as offshore platforms.

[0003] Therefore, existing soil acids are prone to generating secondary precipitation of fluorosilicates and fluoroaluminates, causing formation damage. Furthermore, the raw materials are liquid, highly toxic and corrosive, which is not conducive to transportation, storage and construction. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a fluorine-free solid acid and its applications.

[0005] The purpose of this invention is to provide a fluorine-free solid organic acid, which is made from the following raw materials in parts by weight: 20 to 22 parts of solid organic acid, 7 to 9 parts of metal salt catalyst, 1 to 3 parts of chelating agent, 0.5 to 0.7 parts of silicate inhibitor, and 65.3 to 71.5 parts of water.

[0006] The solid organic acid is selected from one or more of maleic anhydride, maleic acid, hydroxyethylidene diphosphonic acid, and aminotrimethylene phosphonic acid. Maleic anhydride and maleic acid have similar chemical properties, as do hydroxyethylidene diphosphonic acid and aminotrimethylene phosphonic acid; the former two can be used in combination with the latter two.

[0007] The metal salt catalyst is selected from one or more of aluminum chloride, polyaluminum chloride, ferric chloride, and zirconium oxychloride. The anions of the metal salt catalysts are all chloride ions, exhibiting similar catalytic activity, and do not introduce fluoride ions.

[0008] The chelating agent is selected from one or more of sodium hydroxyethylidene diphosphonate, ethylenediaminetetraacetic acid, tetrasodium glutamate diacetate, and polyaspartic acid.

[0009] The silicate inhibitor is selected from one or more of polyepoxysuccinic acid and polyacrylic acid.

[0010] This invention uses solid organic acid, metal salt catalyst, chelating agent, silicate inhibitor, and water as raw materials. It is fluorine-free and will not produce secondary fluoride precipitation during use, thus avoiding pollution. Furthermore, the organic acid prepared in this invention is solid and has no strong corrosiveness or toxicity, which is beneficial for transportation, storage, and construction use.

[0011] Preferably, the total amount of the solid organic acid, metal salt catalyst, chelating agent, silicate inhibitor and water is 100 parts.

[0012] Preferably, the composition comprises 21 parts of solid organic acid, 8 parts of metal salt catalyst, 2 parts of chelating agent, 0.6 parts of silicate inhibitor, and 68.4 parts of water.

[0013] Preferably, the solid organic acid is obtained by mixing maleic acid and sodium hydroxyethylidene diphosphonate in a mass ratio of 20:1 or 1:20.

[0014] Preferably, the metal salt catalyst is obtained by mixing polyaluminum chloride and zirconium oxychloride in a mass ratio of 7:1 or 1:7.

[0015] Preferably, the chelating agent is a mixture of tetrasodium glutamate diacetate and polyaspartic acid in a mass ratio of 2:1 or 1:2.

[0016] Preferably, the silicate inhibitor is polyepoxysuccinic acid and polyacrylic acid in a mass ratio of 5:2 or 2:5.

[0017] Another objective of this invention is to provide an application of fluorine-free solid soil acid in water injection well unblocking, wellbore unblocking, sandstone reservoir matrix acidification, and pre-fracturing pressure reduction.

[0018] Preferably, the method for applying the fluorine-free solid soil acid in sandstone reservoir matrix acidification includes the following steps: The solid organic acid, metal salt catalyst, chelating agent, silicate inhibitor, and water are mixed in the specified proportions to obtain fluorine-free solid soil acid. This fluorine-free solid soil acid is then injected into the sandstone reservoir matrix to acidify it.

[0019] After fluorine-free solid soil acid enters the sandstone reservoir matrix, its solid components gradually dissolve and react under hydration, generating a slow-release acid system in situ deep within the sandstone reservoir matrix. This in-situ generated acid system can achieve deep and slow dissolution of silicate mineral plugging materials, thereby effectively relieving deep reservoir blockage. After shutting in the well and allowing the reaction to proceed fully, the residual solution is flowed back to complete the acidizing operation. This method utilizes the in-situ generation of slow-release acid after the solid composition is delivered to the reservoir, avoiding the rapid reaction and excessive corrosion of conventional soil acid systems, and achieving deep and uniform unblocking of the reservoir.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. The fluorine-free solid organic acid of the present invention is made from the following raw materials in parts by weight: 20-22 parts solid organic acid, 7-9 parts metal salt catalyst, 1-3 parts chelating agent, 0.5-0.7 parts silicate inhibitor, and 65.3-71.5 parts water. The silicate inhibitor disrupts the crystal structure of silicate minerals and weakens the Si-O bonds. The solid organic acid and chelating agent strongly complex and dissolve the metal cations, such as Al, that connect the mineral framework. 3+ Fe 3+ This causes lattice collapse. The metal salt catalyst provides continuous reaction motive force through the slow release of catalytic protons and inhibits clay swelling. Continuous dissolution of sandstone is achieved through the synergistic effect of silicate inhibitors, solid organic acids, and metal salt catalysts. Simultaneously, it avoids the damage to the formation caused by secondary precipitation such as fluorosilicates in traditional soil acids, and the solid form significantly improves the safety of storage, transportation, and construction. The fluorine-free solid soil acid of this invention exhibits a dissolution rate of 14.72%~16.99% after 18 hours of reaction, maintaining a high dissolution rate over a long period.

[0021] The solid organic acid described in this invention is selected from one or more of maleic anhydride, maleic acid, hydroxyethylidene diphosphonic acid, and aminotrimethylene phosphonic acid. The metal salt catalyst is selected from one or more of aluminum chloride, polyaluminum chloride, ferric chloride, and zirconium oxychloride. The chelating agent is selected from one or more of sodium hydroxyethylidene diphosphonate, ethylenediaminetetraacetic acid, tetrasodium glutamate diacetate, and polyaspartic acid. This invention uses solid organic acid, metal salt catalyst, chelating agent, silicate inhibitor, and water as raw materials. It is fluorine-free and will not produce secondary fluoride precipitation during use, thus avoiding pollution. Furthermore, the organic acid prepared in this invention is solid and has no strong corrosiveness or toxicity, which is beneficial for transportation, storage, and construction use.

[0022] The functions of each substance in the fluorine-free solid acid of this invention are as follows: Solid organic acids, such as aminotrimethylenephosphonic acid, have extremely strong chelating abilities and can dissolve calcium in silicate minerals. 2+ Mg 2+ Fe 3+ Al3+ The removal of metal ions by aminotrimethylenephosphonic acid disrupts the "bridges" connecting silicon-oxygen tetrahedra. When these crucial metal cations are removed from the mineral lattice by aminotrimethylenephosphonic acid, the entire silicate crystal structure becomes unstable and may even collapse, indirectly dissolving silicate rocks. Furthermore, the phosphate groups in aminotrimethylenephosphonic acid have a strong adsorption capacity for rock minerals, forming a dense adsorption film on the rock surface that blocks H+ ions. + Contact with the rock surface significantly reduces the reaction rate between the acid and the rock, thereby achieving deep acidification.

[0023] Metal salt catalysts, such as zirconium oxychloride, can catalyze the dissociation of hydroxyl groups or water molecules in organic acid molecules, thereby slowly and continuously releasing highly active protons. This prevents the acid from being rapidly consumed near the wellbore, allowing it to penetrate deeper into the reservoir for unblocking. Furthermore, its excellent clay stability effectively inhibits clay swelling and particle migration caused by acid erosion.

[0024] Chelating agents, such as maleic acid for Fe 3+ It possesses extremely strong chelating ability, effectively preventing the formation of ferric hydroxide precipitate, and is more heat-resistant than commonly used citric acid. When polymerized, the resulting copolymer significantly increases the viscosity of the acid solution and greatly reduces H₂O. + The diffusion rate towards the rock surface is slowed down, thus extending the depth of action.

[0025] Silicate inhibitors, as organic synergists that promote the dispersion or structural dissociation of silicate minerals, can specifically break the Si-O bonds in silicate minerals in sandstone, making their structure more porous. This creates conditions for subsequent solid organic acid and metal salt catalysts to more effectively dissolve and complex metal cations in silicate crystals, thereby achieving efficient and synergistic unblocking of the sandstone matrix.

[0026] In summary, the fluorine-free solid soil acid of this invention completely avoids the formation of insoluble precipitates such as calcium fluoride and fluorosilicates that are easily generated in traditional soil acid reactions, effectively preventing pore blockage caused by secondary precipitation. It not only has strong dissolving power but also broader formation adaptability, which is beneficial for long-term reservoir protection. The product exists in solid form, significantly reducing the inherent strong corrosiveness and leakage risk of liquid acids, making transportation and storage safer and more convenient, and particularly suitable for the operational needs of offshore and remote oilfields.

[0027] 2. The fluorine-free solid soil acid of this invention fills the technological gap in the field of oilfield unblocking using fluorine-free soil acid systems. It combines efficient dissolution and long-term unblocking characteristics, and can completely avoid the risk of formation damage caused by the formation of fluoride precipitates such as fluorosilicates and fluoroaluminates generated by the reaction of HF and HCl in traditional soil acids. At the same time, it has the advantages of convenient storage and transportation, low harm to personnel and the environment, long effective unblocking time, and strong dissolution ability. It provides a safer, more environmentally friendly, and more economical technical option for onshore and offshore oilfields, with huge market application potential and broad prospects. Attached Figure Description

[0028] Figure 1 The diagram shows the static reaction dissolution rate of acid rocks in Examples 1 to 6 and Comparative Example 1 of the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the following detailed description, in conjunction with preferred embodiments and accompanying drawings, provides a clear and complete account of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0031] I. Experimental Materials The main materials used in this invention are maleic acid, polyaluminum chloride, zirconium oxychloride, tetrasodium diacetate of glutamic acid, polyaspartic acid, polyepoxysuccinic acid, and polyacrylic acid.

[0032] Among them, maleic acid, analytical grade, CAS number: 110-16-7, purchased from Maclean's Company; polyaluminum chloride, 98% purity, CAS number: 1327-41-9, purchased from Maclean's Company; zirconium oxychloride, 98% purity, CAS number: 13520-92-8, purchased from Maclean's Company; tetrasodium glutamate diacetate, ≥45% purity, CAS number: 51981-21-6, purchased from Keenu Biotechnology Co., Ltd.; polyaspartic acid, molecular weight 2000Da~4000Da, purity 95%, CAS number: 25608-40-6, purchased from Guangdong Xingfu Chemical Reagent Co., Ltd.; and polyepoxysuccinic acid, molecular weight 1500Da~2500Da, analytical grade, CAS number: 1528-98-7, purchased from Shanghai Ron Chemical Reagent Co., Ltd. Polyacrylic acid, molecular weight 3000Da~5000Da, purity laboratory grade, CAS number: 9003-01-4, purchased from McLean Company.

[0033] II. Experimental Methods 1. Dissolution rate detection The erosion rate of the fluorine-free solid clay acid prepared in Examples 1 to 6 and Comparative Example 1 under static reaction was tested. The specific test method is as follows: The fluorine-free solid clay acid of Examples 1 to 6 and Comparative Example 1 were respectively prepared with water to form an acid solution with a mass fraction of 25%. The bentonite and the acid solution were mixed at a solid-liquid ratio of 1:20 and sealed. The reaction was carried out at 60°C. Samples were taken, dried and weighed at 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h and 18h ​​of reaction. The erosion rate was calculated according to formula (1).

[0034] Formula (1): Dissolution rate = (Initial bentonite mass - Dried bentonite mass) / Initial bentonite mass × 100%.

[0035] 2. Secondary sedimentation damage assessment Weigh 5g of bentonite and add it to a sealed plastic bottle. Prepare 25% (w / w) acid solutions using the fluorine-free solid clay acid prepared in Examples 1-6 and the clay acid prepared in Comparative Example 1, respectively, and add them to the bentonite. Seal the bottle and place it in a 60℃ water bath. React for 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, and 18h, respectively. Rinse the reacted bentonite with distilled water and dry it to obtain the reaction product. Perform elemental analysis on the reaction product and compare the changes in fluorine content in the reaction product and bentonite to determine the degree of secondary damage caused by the acid solution. The more fluoride precipitate, the higher the fluorine content, indicating a higher level of secondary damage.

[0036] Example 1 A method for preparing a fluorine-free solid oxalic acid includes the following steps: 20 parts maleic acid, 7 parts polyaluminum chloride, 1 part tetrasodium glutamate diacetate, 0.5 parts polyepoxysuccinic acid, and 70.5 parts water were mixed thoroughly to obtain fluorine-free solid silicic acid. The fluorine-free solid silicic acid had a dissolution rate of 16.34% after 18 hours of reaction.

[0037] Example 2 A method for preparing a fluorine-free solid oxalic acid includes the following steps: 20 parts maleic acid, 1 part hydroxyethylidene diphosphonic acid, 7 parts polyaluminum chloride, 1 part zirconium oxychloride, 1 part tetrasodium glutamate diacetate, 1 part polyaspartic acid, 0.5 parts polyepoxysuccinic acid, 0.1 parts polyacrylic acid, and 67.4 parts water were mixed evenly to obtain fluorine-free solid tereic acid. The fluorine-free solid tereic acid had a solubility of 16.64% after 18 hours of reaction.

[0038] Example 3 A method for preparing a fluorine-free solid oxalic acid includes the following steps: 20 parts maleic acid, 2 parts hydroxyethylidene diphosphonic acid, 7 parts polyaluminum chloride, 2 parts zirconium oxychloride, 1 part tetrasodium glutamate diacetate, 2 parts polyaspartic acid, 0.5 parts polyepoxysuccinic acid, 0.2 parts polyacrylic acid, and 64.3 parts water were mixed thoroughly to obtain fluorine-free solid tereic acid. The fluorine-free solid tereic acid exhibited a dissolution rate of 16.99% after 18 hours of reaction.

[0039] Example 4 A method for preparing a fluorine-free solid oxalic acid includes the following steps: 20 parts of hydroxyethylidene diphosphonic acid, 7 parts of zirconium oxychloride, 2 parts of polyaspartic acid, 0.5 parts of polyacrylic acid, and 70.5 parts of water were mixed evenly to obtain a fluorine-free solid terephthalic acid. The fluorine-free solid terephthalic acid had a dissolution rate of 14.72% after 18 hours of reaction.

[0040] Example 5 A method for preparing a fluorine-free solid oxalic acid includes the following steps: One part maleic acid, 20 parts hydroxyethylidene diphosphonic acid, 1 part polyaluminum chloride, 7 parts zirconium oxychloride, 1 part tetrasodium glutamate diacetate, 2 parts polyaspartic acid, 0.5 parts polyacrylic acid, 0.1 parts polyepoxysuccinic acid, and 67.4 parts water were mixed thoroughly to obtain fluorine-free solid tereic acid. The fluorine-free solid tereic acid exhibited a dissolution rate of 15.11% after 18 hours of reaction.

[0041] Example 6 A method for preparing a fluorine-free solid oxalic acid includes the following steps: Two parts maleic acid, 20 parts hydroxyethylidene diphosphonic acid, 2 parts polyaluminum chloride, 7 parts zirconium oxychloride, 2 parts tetrasodium glutamate diacetate, 2 parts polyaspartic acid, 0.5 parts polyacrylic acid, 0.2 parts polyepoxysuccinic acid, and 64.3 parts water were mixed thoroughly to obtain a fluorine-free solid tereic acid. The fluorine-free solid tereic acid exhibited a dissolution rate of 15.65% after 18 hours of reaction.

[0042] Comparative Example 1 A method for preparing an oxalic acid includes the following steps: 12 parts hydrochloric acid, 3 parts hydrofluoric acid, and 85 parts water were mixed thoroughly to obtain terpineic acid. The terpineic acid had a dissolution rate of 13.79%.

[0043] Comparative Example 2 A method for preparing a fluorine-free solid oxalic acid includes the following steps: The 20 parts maleic acid in Example 1 were replaced with 20 parts citric acid, while other conditions remained the same as in Example 1, to obtain fluorine-free solid citric acid. The fluorine-free solid citric acid had a dissolution rate of 8.23% after 18 hours of reaction. Compared with Example 1, the type of solid organic acid in Comparative Example 1 was replaced, resulting in a decrease in the dissolution rate of the fluorine-free solid citric acid from 16.34% to 8.23%. This is because solid organic acids are both highly efficient metal ion chelating agents, directly destroying the silicate structure, and excellent retarders, controlling reaction kinetics through surface adsorption. After being replaced with citric acid, its relatively weaker chelating ability led to a decrease in the efficiency of destroying the mineral lattice. At the same time, its poor adsorption and retarding ability resulted in an excessively rapid acid reaction and insufficient depth of action, leading to a decrease in the dissolution rate.

[0044] Comparative Example 3 A method for preparing a fluorine-free solid oxalic acid includes the following steps: In Example 2, 7 parts polyaluminum chloride and 1 part zirconium oxychloride were adjusted to 8 parts sodium chloride, while other conditions remained the same as in Example 2, to obtain fluorine-free solid teracid. The resulting fluorine-free solid teracid exhibited a dissolution rate of 7.28% after 18 hours of reaction, with a significant decrease in the dissolution rate during the early stages of the reaction. Compared to Example 2, the metal salt catalyst in Comparative Example 2 was replaced, leading to a decrease in the dissolution rate of the fluorine-free solid teracid from 16.64% to 7.28%. This is because the metal salt catalyst plays a crucial role in catalyzing proton release and maintaining reaction kinetics in the fluorine-free solid teracid; replacing it with other metal salts weakened or eliminated this catalytic effect, resulting in a decrease in the dissolution rate.

[0045] Comparative Example 4 A method for preparing a fluorine-free solid oxalic acid includes the following steps: In Example 3, 2 parts of tetrasodium glutamate diacetate and 2 parts of polyaspartic acid were adjusted to 4 parts of sodium citrate, while other conditions remained the same as in Example 3, to obtain fluorine-free solid tereic acid. The obtained fluorine-free solid tereic acid exhibited a dissolution rate of 9.17% after 18 hours of reaction, and a small amount of Fe was observed in the reaction product. 3+ Precipitation. Compared to Example 3, the chelating agent in Comparative Example 3 was replaced, resulting in a decrease in the dissolution rate of the fluorine-free solid oxalic acid from 16.99% to 9.17%. This is because the chelating agent has the ability to complex metal ions and a retarding effect. The replaced sodium citrate, with its weaker complexing ability, led to the formation of Fe³⁺ precipitate, causing not only secondary damage but also reducing the utilization rate of the effective components. On the other hand, its lack of a retarding function resulted in insufficient depth of acid action, leading to a decrease in the dissolution rate.

[0046] Comparative Example 5 A method for preparing a fluorine-free solid oxalic acid includes the following steps: The polyacrylic acid in Example 4 was adjusted to 0.5 parts sodium silicate, while other conditions remained the same as in Example 4, to obtain fluorine-free solid bentonite acid. The fluorine-free solid bentonite acid had a dissolution rate of 6.19% after 18 hours of reaction. Compared with Example 4, the silicate inhibitor in Comparative Example 5 was replaced, resulting in a decrease in the dissolution rate of the fluorine-free solid bentonite acid from 14.72% to 6.19%. This is because the silicate inhibitor can specifically break Si-O bonds, creating structural conditions for subsequent dissolution. After replacement, the bentonite structure was not effectively destroyed, which reduced the dissolution rate of the fluorine-free solid bentonite acid.

[0047] Comparative Example 6 A method for preparing a fluorine-free solid oxalic acid includes the following steps: 20 parts citric acid, 8 parts ammonium chloride, 2 parts disodium EDTA, 1 part sodium silicate, and 69 parts water were mixed thoroughly to obtain fluorine-free solid citric acid. The fluorine-free solid citric acid had a solubility of 4.32% after 18 hours of reaction, and a precipitate appeared in the product after the reaction.

[0048] The results of Comparative Examples 2 to 6 show that replacing any key component of the present invention with other substances leads to a significant decrease in dissolution rate, insufficient reaction kinetics, or an increased risk of secondary precipitation. The types and proportions of the solid organic acid, metal salt catalyst, chelating agent, and silicate inhibitor in the fluorine-free solid acid of the present invention achieve multiple functions of synergistic slowing, long-term dissolution, structural dissociation, and precipitation inhibition among the components. It is a non-obvious, highly efficient, safe, and environmentally friendly solid acidification system with significant technological advancements and industrial application value.

[0049] To illustrate the beneficial effects of the present invention, the following experiments were also conducted.

[0050] The raw material ratios of Examples 1 to 6 of the present invention are shown in Table 1.

[0051] Table 1. Raw material ratios for Examples 1 to 6 1. Dissolution rate detection The changes in the static reaction dissolution rate of acid rocks in different acid systems in Examples 1-6 and Comparative Example 1 over time are as follows: Figure 1 As shown, the fluorine-free solid soil acid systems of Examples 1 to 6 of the present invention exhibit a significantly and sustained increase in dissolution rate with increasing reaction time, reaching a high level after 18 hours of reaction. In contrast, although the dissolution rate of the conventional soil acid system in Comparative Example 1 increases rapidly in the early stage, the duration is short and the dissolution rate continues to decrease, ultimately falling below that of the embodiments of the present invention.

[0052] The mineral compositions of the fluorine-free solid soil acids prepared in Examples 1-6 and the soil acid prepared in Comparative Example 1 after reaction with bentonite are shown in Table 2. The results show that bentonite itself does not contain fluorine (F), but fluorine is produced after reaction with the traditional soil acid system. However, no fluorine is produced after reaction with Examples 1-6. This indicates that the present invention avoids the risk of formation damage caused by fluoride precipitation, such as fluorosilicates and fluoroaluminates, during the acidification process of traditional soil acid reactions.

[0053] Table 2. Mass percentage of mineral composition after reaction of bentonite with different acid solutions (%) In summary, this invention presents a fluorine-free solid soil acid system composed of a solid organic acid, a metal salt catalyst, a chelating agent, and a silicate inhibitor. The finished product is a stable solid powder under normal conditions, and its properties after water solubility are similar to those of liquid soil acid. The product has advantages such as convenient storage and transportation, and simple construction. It can effectively avoid the formation of insoluble byproducts such as calcium fluoride and fluorosilicates that clog pores in conventional fluorine-containing soil acids, thereby inhibiting secondary precipitation. It has strong dissolving power, good adaptability to formations, enriches the acidification product series, fills a technological gap in the industry, and has significant value for promotion and application.

[0054] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the inventive concept of this invention, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0055] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If such modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A fluorine-free solid acid, characterized in that, It is made from the following raw materials in parts by weight: 20 to 22 parts solid organic acid, 7 to 9 parts metal salt catalyst, 1 to 3 parts chelating agent, 0.5 to 0.7 parts silicate inhibitor, and 65.3 to 71.5 parts water; The solid organic acid is selected from one or more of maleic anhydride, maleic acid, hydroxyethylidene diphosphonic acid, and aminotrimethylene phosphonic acid; The metal salt catalyst is selected from one or more of aluminum chloride, polyaluminum chloride, ferric chloride, and zirconium oxychloride; The chelating agent is selected from one or more of sodium hydroxyethylidene diphosphonate, ethylenediaminetetraacetic acid, tetrasodium glutamate diacetate, and polyaspartic acid; The silicate inhibitor is selected from one or more of polyepoxysuccinic acid and polyacrylic acid.

2. The fluorine-free solid acid according to claim 1, characterized in that, The total amount of the solid organic acid, metal salt catalyst, chelating agent, silicate inhibitor and water is 100 parts.

3. The fluorine-free solid acid according to claim 1, characterized in that, The composition consists of 21 parts solid organic acid, 8 parts metal salt catalyst, 2 parts chelating agent, 0.6 parts silicate inhibitor, and 68.4 parts water.

4. The fluorine-free solid acid according to claim 3, characterized in that, The solid organic acid is obtained by mixing maleic acid and sodium hydroxyethylidene diphosphonate in a mass ratio of 20:1 or 1:

20.

5. The fluorine-free solid acid according to claim 3, characterized in that, The metal salt catalyst is obtained by mixing polyaluminum chloride and zirconium oxychloride in a mass ratio of 7:1 or 1:

7.

6. The fluorine-free solid acid according to claim 3, characterized in that, The chelating agent is obtained by mixing tetrasodium glutamate diacetate and polyaspartic acid in a mass ratio of 2:1 or 1:

2.

7. The fluorine-free solid acid according to claim 3, characterized in that, The silicate inhibitor is composed of polyepoxysuccinic acid and polyacrylic acid in a mass ratio of 5:2 or 2:

5.

8. The application of the fluorine-free solid soil acid according to claim 1 in unblocking water injection wells, unblocking wellbores, acidizing sandstone reservoir matrix, or reducing pressure before fracturing.

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