Imidazolyl polycarboxylic acid chelating agents, processes for their preparation and use, and scale removal agents, processes for their preparation and use

Abstract

The application relates to the field of oil field chemistry, and discloses an imidazole-based polycarboxylic acid chelating agent, a preparation method and application thereof, and a scale remover and a preparation method and application thereof. The imidazole-based polycarboxylic acid chelating agent provided by the application is a compound shown in formula (1), wherein R is a hydroxyl group, an amino group, a carboxyl group, an amido group or an alkoxy group, and n is an integer of 1-5. The chelating agent contains multiple electron-donating groups such as carboxyl groups and amino groups in the structure, can realize stable chelation with metal ions, and forms a multidentate chelate. The scale remover contains a scale inhibitor component, plays a chelation synergistic role, and the surfactant is used for washing oily substances on the scale sample surface, and increases the chelating agent action area. The scale remover has a wide application range, and can be applied to efficient scale dissolving and plugging of calcium carbonate, calcium sulfate and barium sulfate under high-temperature (60-180 DEG C) conditions in oil and gas wells.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemistry, specifically to an imidazole-based polycarboxylic acid chelating agent, its preparation method and application, as well as a scale remover, its preparation method and application. Background Technology

[0002] With the continuous advancement of oil extraction technology, in the actual production process of oil and gas fields, factors such as high mineralization of formation water, incompatibility of groundwater and injected water ions, and rising system temperature can all lead to the formation of inorganic scale, which can seriously block oil and gas field production and gathering pipelines, affecting the normal production of oil and gas fields.

[0003] Compared to physical deblocking, chemical deblocking offers advantages such as high efficiency and short operation time, proving particularly effective for blockages in near-wellbore reservoirs of oil and gas fields and areas inaccessible to physical deblocking techniques. Traditional chemical deblocking primarily utilizes acid systems, which offer rapid scale dissolution, but are highly corrosive to metal pipelines, especially at high temperatures. While these systems effectively dissolve scale, they also accelerate corrosion. Corrosion inhibitors are typically added to mitigate this, but repeated acid deblocking still increases the risk of pipeline failure. To address the corrosiveness of acid solutions, non-acidic descaling systems have begun to be used in major oilfields. These systems primarily utilize chelation mechanisms to form chelates with inorganic metal ions, thereby dissolving insoluble inorganic scale. Commonly used chelation descaling systems are generally alkaline, with a pH of around 12 required for effective descaling. Moreover, most chelates are phosphonic acids or other amino polyacids. Phosphorus can cause stress corrosion damage to some metals at high temperatures. Furthermore, some large-molecule amino polyacid compounds are difficult to degrade, posing a significant impact on the ecological environment and thus limiting their widespread use.

[0004] Therefore, finding an environmentally friendly descaling agent with a wide range of applications, low corrosivity, and good scale dissolving effect to solve the scale blockage problem in oil and gas fields is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of high metal corrosivity and difficulty in degradation of existing chelating descaling systems, and to provide an imidazole-based polycarboxylic acid chelating agent, its preparation method and application, as well as a descaling agent and its preparation method and application. This imidazole-based polycarboxylic acid chelating agent has multiple carboxyl groups, has strong chelating ability, can form stable chelates, and has strong scale dissolving and descaling capabilities.

[0006] To achieve the above objectives, a first aspect of the present invention provides an imidazole-based polycarboxylic acid chelating agent, wherein the imidazole-based polycarboxylic acid chelating agent is a compound represented by formula (1).

[0007]

[0008] Where R is a hydroxyl, amino, carboxyl, amide, or alkoxy group, and n is an integer from 1 to 5.

[0009] A second aspect of this invention provides a method for preparing an imidazole polycarboxylic acid chelating agent, the method comprising the following steps:

[0010] (1) Histidine was mixed with an acylation reagent in an organic solvent to carry out the first reaction, and intermediate 1 was obtained;

[0011] (2) The intermediate 1 is mixed with chloroacetic acid or ethyl chloroacetate to carry out a second reaction to obtain the imidazole polycarboxylic acid chelating agent;

[0012] The acylation reagent is a compound represented by formula (2).

[0013]

[0014] Wherein, the definitions of R and n are the same as those in the first aspect of the present invention, and R1 is Cl or OH.

[0015] The third aspect of the present invention provides the application of the imidazole polycarboxylic acid chelating agent provided by the present invention or the imidazole polycarboxylic acid chelating agent prepared by the preparation method provided by the present invention as a descaling agent.

[0016] A fourth aspect of the present invention provides a descaling agent comprising an imidazole polycarboxylic acid chelating agent, a scale inhibitor, a surfactant, and water; wherein the imidazole polycarboxylic acid chelating agent is the imidazole polycarboxylic acid chelating agent provided by the present invention or an imidazole polycarboxylic acid chelating agent prepared by the preparation method provided by the present invention.

[0017] The fifth aspect of the present invention provides a method for preparing a descaling agent, the method comprising the following steps: mixing an imidazole polycarboxylic acid chelating agent, a scale inhibitor, a surfactant and water to obtain the descaling agent.

[0018] The sixth aspect of this invention provides the application of the imidazole polycarboxylic acid chelating agent or the scale remover provided by this invention in oil and gas field unblocking.

[0019] The beneficial effects of the present invention through the above technical solution are as follows:

[0020] The imidazole-based polycarboxylic acid chelating agent provided by this invention meets the requirements of green environmental protection. This compound contains imidazole groups and multiple carboxyl groups, giving it strong coordination and chelating abilities, enabling it to form stable chelates and exhibiting strong scale-dissolving and descaling capabilities. The imidazole groups can adsorb onto various metal ions, especially iron ions, forming a film on metal pipes. This promotes the detachment of scale from the pipe wall and effectively prevents scale deposition. The imidazole ring also plays a role in corrosion inhibition by adsorbing and forming a film on the metal surface.

[0021] Combining imidazole polycarboxylic acid chelating agents with scale inhibitors and surfactants can leverage their synergistic effects, thereby improving scale dissolution and removal efficiency. The scale inhibitor primarily prevents the deposition of smaller scale particles, acting as a dispersant and preventing the formation of scale-forming cations. The addition of surfactants enhances the surface activity of the scale, cleaning away organic deposits and increasing the contact area between the chelating agent and inorganic scale, thus improving chelation efficiency.

[0022] In a preferred embodiment of the present invention, by selecting appropriate types and proportions of components in the descaling agent, the present invention enables each component to better exert its synergistic effect, thereby further improving the descaling rate of the descaling agent. By using a pH adjuster to adjust the pH of the descaling agent to around 7-8, not only can the chelation reaction of the chelating agent be promoted, but the descaling agent also exhibits lower corrosiveness compared to acidic descaling and will not cause damage to the formation. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] To achieve the above objectives, a first aspect of the present invention provides an imidazole-based polycarboxylic acid chelating agent, wherein the imidazole-based polycarboxylic acid chelating agent is a compound represented by formula (1).

[0025]

[0026] Where R is a hydroxyl, amino, carboxyl, amide, or alkoxy group, and n is an integer from 1 to 5.

[0027] According to the present invention, preferably, the imidazole polycarboxylic acid chelating agent is selected from the compounds shown below.

[0028]

[0029] A second aspect of this invention provides a method for preparing an imidazole polycarboxylic acid chelating agent, the method comprising the following steps:

[0030] (1) Histidine was mixed with an acylation reagent in an organic solvent to carry out the first reaction, and intermediate 1 was obtained;

[0031] (2) The intermediate 1 is mixed with chloroacetic acid or ethyl chloroacetate to carry out a second reaction to obtain the imidazole polycarboxylic acid chelating agent;

[0032] The acylation reagent is a compound represented by formula (2).

[0033]

[0034] Wherein, the definitions of R and n are the same as those in the first aspect of the present invention, and R1 is Cl or OH.

[0035] According to a specific embodiment of the present invention, the imidazole polycarboxylic acid chelating agent The preparation process is illustrated below:

[0036]

[0037] According to a specific embodiment of the present invention, when the acylation reagent is 2-cyanoacetyl chloride, the imidazole polycarboxylic acid chelating agent... The preparation process is illustrated below:

[0038]

[0039] Since the cyano group undergoes hydrolysis to generate a carboxyl group during the second reaction, the resulting structure is: Imidazole polycarboxylic acid chelating agents.

[0040] According to the present invention, preferably, in step (1), the molar ratio of histidine to the acylation reagent is 1:(1-1.2).

[0041] According to the present invention, preferably, the organic solvent is selected from at least one of acetonitrile, N,N-dimethylformamide and isopropanol, and preferably acetonitrile.

[0042] According to the present invention, preferably, the amount of organic solvent is 1-2 parts by weight, based on the total weight of histidine and the acylation reagent being 1 part by weight.

[0043] According to the present invention, preferably, the temperature of the first reaction is 75-85°C and the time is 4-5 hours. When the conditions of the first reaction meet the above range, high reaction purity and yield can be guaranteed.

[0044] According to the present invention, preferably, in step (2), the molar ratio of intermediate 1 to chloroacetic acid or ethyl chloroacetate is 1:(2-2.2).

[0045] According to the present invention, preferably, the temperature of the second reaction is 80-90°C and the time is 4-5 hours. When the conditions of the second reaction meet the above range, the purity of the final chelating agent can be ensured.

[0046] Preferably, the second reaction is carried out at a pH of 9-10.

[0047] According to the present invention, preferably, the preparation method further includes: in step (2), the intermediate 1 and chloroacetic acid are first mixed with neutralizing agent 1 and neutralizing agent 2 respectively to obtain solution 1 and solution 2, and then solution 1, solution 2 and neutralizing agent 3 are mixed to carry out the second reaction. The addition of neutralizing agent 1, neutralizing agent 2 and neutralizing agent 3 can ensure that the reaction proceeds in the forward direction, thereby reducing the generation of by-products.

[0048] According to the present invention, preferably, the weight ratio of the neutralizing agent 1 to the intermediate 1 is (0.5-0.7):1.

[0049] According to the present invention, preferably, the weight ratio of the neutralizing agent 2 to chloroacetic acid is (0.5-0.7):1.

[0050] According to the present invention, preferably, the neutralizing agent 1 and the neutralizing agent 2 are sodium carbonate aqueous solutions with a sodium carbonate content of 40-50 wt%.

[0051] According to the present invention, preferably, the amount of neutralizing agent 3 is 0.3-0.5g, based on the total weight of intermediate 1 and chloroacetic acid being 1g.

[0052] According to the present invention, preferably, the neutralizing agent 3 is an aqueous solution of sodium hydroxide with a sodium hydroxide content of 30-50 wt%.

[0053] According to the present invention, preferably, the preparation method further includes: adjusting the pH of the reaction mixture obtained after the second reaction to 1-2 to obtain the imidazole polycarboxylic acid chelating agent.

[0054] The third aspect of the present invention provides the application of the imidazole polycarboxylic acid chelating agent provided by the present invention or the imidazole polycarboxylic acid chelating agent prepared by the preparation method provided by the present invention as a descaling agent.

[0055] The imidazole-based polycarboxylic acid chelating agent provided by this invention meets the requirements of green environmental protection. This compound contains imidazole groups and multiple carboxyl groups, giving it strong coordination and chelating abilities, enabling it to form stable chelates and exhibiting strong scale-dissolving and descaling capabilities. The imidazole group can adsorb onto various metal ions, especially iron ions, forming a film on metal pipes. This promotes the detachment of scale from the pipe wall and effectively prevents scale deposition. The film formed by the imidazole ring on the metal surface also provides a certain degree of corrosion inhibition.

[0056] A fourth aspect of the present invention provides a descaling agent comprising an imidazole polycarboxylic acid chelating agent, a scale inhibitor, a surfactant, and water; wherein the imidazole polycarboxylic acid chelating agent is the imidazole polycarboxylic acid chelating agent provided by the present invention or an imidazole polycarboxylic acid chelating agent prepared by the preparation method provided by the present invention.

[0057] Combining imidazole polycarboxylic acid chelating agents with scale inhibitors and surfactants can leverage their synergistic effects, thereby improving scale dissolution and removal efficiency. The scale inhibitor primarily prevents the deposition of smaller scale particles, acting as a dispersant and preventing the formation of scale-forming cations. The addition of surfactants enhances the surface activity of the scale, cleaning away organic deposits and increasing the contact area between the chelating agent and inorganic scale, thus improving chelation efficiency.

[0058] According to the present invention, preferably, the pH value of the descaling agent is 7-8.

[0059] According to the present invention, preferably, the descaling agent comprises the following components in parts by weight: 8-13 parts of the imidazole polycarboxylic acid chelating agent, 2-3 parts of the scale inhibitor, 1-2 parts of the surfactant, 2-5 parts of the pH adjuster, and 77-87 parts of water. When the components meet the above proportions, the components can better exert their synergistic effect.

[0060] By using a pH adjuster to adjust the pH of the descaling agent to around 7-8, not only can the chelation reaction of the chelating agent be promoted, but the descaling agent also has lower corrosive properties compared to acidic descaling agents, and will not cause damage to the formation.

[0061] According to the present invention, preferably, the scale inhibitor is selected from polyepoxysuccinic acid and / or maleic acid-acrylic acid copolymer, and more preferably a mixture of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer. Using a mixture of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer as a scale inhibitor can accelerate the dispersion of scale in the descaling agent solution and has a better scale inhibition ability.

[0062] According to the present invention, preferably, the polyepoxysuccinic acid has a weight-average molecular weight of 900-1200 g / mol. According to the present invention, preferably, the maleic acid-acrylic acid copolymer has a weight-average molecular weight of 1500-2000 g / mol.

[0063] When the weight-average molecular weight of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer meets the above range, the descaling agent can be guaranteed to have good scale inhibition and dispersion effects.

[0064] Preferably, the weight ratio of structural units from maleic acid to structural units from acrylic acid in the maleic acid-acrylic acid copolymer is (2-3):(3-4). Meeting this range ensures the descaling agent has strong scale inhibition and dispersing capabilities; otherwise, the solubility and dispersing / chelating ability of the descaling agent will be affected.

[0065] According to the present invention, preferably, the weight ratio of the polyepoxysuccinic acid and the maleic acid-acrylic acid copolymer is (6-7):(3-4). When the weight ratio meets the above range, the synergistic effect of the two can be better exerted; otherwise, it is not conducive to the synergistic effect of the scale inhibitor.

[0066] According to the present invention, preferably, the surfactant is a succinate sulfonate, more preferably potassium isooctyl succinate sulfonate. Using potassium isooctyl succinate sulfonate as a surfactant enables the descaling agent to have stronger penetrating power.

[0067] According to the present invention, preferably, the pH adjuster is a mixture of ammonium chloride and ammonia or sodium acetate, and more preferably a mixture of ammonium chloride and ammonia.

[0068] According to the present invention, preferably, in the mixture of ammonium chloride and ammonia, the weight ratio of ammonium chloride to ammonia is 1:(1-1.2).

[0069] The fifth aspect of the present invention provides a method for preparing a descaling agent, the method comprising the following steps: mixing an imidazole polycarboxylic acid chelating agent, a scale inhibitor, a surfactant and water to obtain the descaling agent.

[0070] According to the present invention, preferably, the preparation method includes the following steps: first mixing 8-13 parts of imidazole polycarboxylic acid chelating agent, 2-3 parts of scale inhibitor, 2-5 parts of pH adjuster and 77-87 parts of water, and then second mixing with 1-2 parts of surfactant to obtain the scale remover.

[0071] According to the present invention, preferably, the temperatures of the first mixture and the second mixture are each independently 60-70°C.

[0072] According to the present invention, preferably, the first mixing time is 30-60 min.

[0073] According to the present invention, preferably, the second mixing time is 20-40 min.

[0074] According to a specific embodiment of the present invention, the preparation method includes the following steps: adding water to a reaction vessel, and sequentially adding an imidazole polycarboxylic acid chelating agent, a scale inhibitor, and a pH adjuster; heating to 60-70°C; stirring for 30-60 minutes; measuring the pH of the system; and when the pH of the system reaches 7-8, adding a surfactant; continuing to stir for 20-40 minutes; and then cooling to room temperature to obtain the scale remover.

[0075] The sixth aspect of this invention provides an application of the imidazole polycarboxylic acid chelating agent or the scale remover provided by this invention in oil and gas field unblocking; preferably, it is applied to remove inorganic scale plugs in oil and gas wells under medium and low temperature (60-180℃) conditions, especially calcium carbonate, calcium sulfate and barium sulfate scale plugs.

[0076] The present invention will be described in detail below through examples and comparative examples. Unless otherwise specified, all methods used in the following examples and comparative examples are conventional; the reagents and materials used are commercially available unless otherwise specified. The specific determination methods involved in the following examples and comparative examples are as follows:

[0077] Descaling rate determination method:

[0078] (1) Sample preparation: Dry the analytical grade scale sample and the field scale sample at 105℃ to constant weight.

[0079] (2) Weigh 2g of scale sample, add 100mL of descaling agent, let stand, place in a constant temperature water bath or constant temperature drying oven at the set temperature, react for 24h, cool down, filter, weigh, and calculate the descaling rate. The descaling rate is calculated according to the following formula (1):

[0080]

[0081] In the formula: m1 is the mass before the reaction, and m2 is the mass after the reaction, both in g.

[0082] Example 1

[0083] Preparation of imidazole polycarboxylic acid chelating agents:

[0084] (1) Weigh 0.5 mol of histidine and acetonitrile (the amount of acetonitrile is the same as the total weight of histidine and 2-cyanoacetyl chloride) into a reaction flask, start stirring, and add 0.6 mol of 2-cyanoacetyl chloride dropwise. After the addition is complete, heat the reaction system to reflux, control the reaction temperature at 85℃, and continue stirring for 5 h. Evaporate the solvent by vacuum distillation, wash with ethyl acetate, filter, and dry to obtain intermediate 1 with a yield of 90 wt%.

[0085] (2) Weigh 0.5 mol of intermediate 1 and add it to the reaction flask, along with a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to intermediate 1 is 0.5:1). Simultaneously, mix 1.1 mol of chloroacetic acid with a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to chloroacetic acid is 0.5:1) and add the mixture to the reaction flask. Start stirring and add a 30 wt% sodium hydroxide aqueous solution (the ratio of the amount of sodium hydroxide aqueous solution to the total weight of intermediate 1 and chloroacetic acid is 0.5:1) to make the pH of the reaction system 9.8. Heat to 90℃ and react for 4 hours. Stop the reaction, adjust the pH to 1 with hydrochloric acid, filter, and dry to obtain the imidazole polycarboxylic acid chelating agent. The product yield was 85 wt%.

[0086] Preparation of descaling agent:

[0087] Add 77 parts of water to the reactor, and then add 13 parts of imidazole polycarboxylic acid chelating agent, 3 parts of scale inhibitor, and 5 parts of pH adjuster in sequence. Heat to 70°C for the first mixing. After stirring for 60 minutes, the pH of the system is measured to reach 7. Then add 2 parts of surfactant for the second mixing. After stirring for 40 minutes, stop and cool to room temperature to obtain descaling agent P1.

[0088] The scale inhibitor is a mixture of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer in a weight ratio of 3:2; the weight average molecular weight of polyepoxysuccinic acid is 1200 g / mol, the weight average molecular weight of maleic acid-acrylic acid copolymer is 2000 g / mol, and the weight ratio of structural units from maleic acid to structural units from acrylic acid is 2:3.

[0089] The surfactant is potassium isooctyl succinate sulfonate; the pH adjuster is a mixture of ammonium chloride and ammonia water in a weight ratio of 1:1.

[0090] Example 2

[0091] Preparation of imidazole polycarboxylic acid chelating agents:

[0092] (1) Weigh 0.5 mol of histidine and acetonitrile (the amount of acetonitrile is twice the total weight of histidine and 2-cyanoacetyl chloride) into a reaction flask, start stirring, and add 0.5 mol of 2-cyanoacetyl chloride dropwise. After the addition is complete, heat the reaction system to reflux, control the reaction temperature at 75°C, and continue stirring for 4 hours. Evaporate the solvent by vacuum distillation, wash with ethyl acetate, filter, and dry to obtain intermediate 1 with a yield of 87 wt%.

[0093] (2) Weigh 0.5 mol of intermediate 1 and add it to the reaction flask, and add a 40 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to intermediate 1 is 0.7:1). At the same time, take 1 mol of chloroacetic acid and mix it with a 40 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to chloroacetic acid is 0.7:1) and add it to the reaction flask. Start stirring and add a 50 wt% sodium hydroxide aqueous solution (the ratio of the amount of sodium hydroxide aqueous solution to the total weight of intermediate 1 and chloroacetic acid is 0.3:1) to make the pH of the reaction system 9.6. Heat to 80°C and react for 5 h. Stop the reaction, adjust the pH to 1 with hydrochloric acid, filter, dry, and obtain the imidazole polycarboxylic acid chelating agent with the same structural formula as in Example 1, with a yield of 82 wt%.

[0094] Preparation of descaling agent:

[0095] Add 87 parts of water to the reactor, and then add 8 parts of imidazole polycarboxylic acid chelating agent, 2 parts of scale inhibitor, and 2 parts of pH adjuster in sequence. Heat to 60°C for the first mixing. After stirring for 30 minutes, measure that the pH of the system reaches 7. Then add 1 part of surfactant for the second mixing. After stirring for 20 minutes, stop and cool to room temperature to obtain descaling agent P2.

[0096] The composition of the scale inhibitor, surfactant, and pH adjuster is the same as in Example 1.

[0097] Example 3

[0098] Preparation of imidazole polycarboxylic acid chelating agents:

[0099] Step (1) is the same as in Example 1.

[0100] Step (2): Weigh 0.5 mol of intermediate 1 and add it to the reaction flask. Add a 45 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to intermediate 1 is 0.55:1). At the same time, mix 1.05 mol of chloroacetic acid with a 45 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to chloroacetic acid is 0.6:1) and add it to the reaction flask. Start stirring and add a 40 wt% sodium hydroxide aqueous solution (the ratio of the amount of sodium hydroxide aqueous solution to the total weight of intermediate 1 and chloroacetic acid is 0.4:1) to make the pH of the reaction system 9.3. Heat to 85°C and react for 4.5 h. Stop the reaction, adjust the pH to 1 with hydrochloric acid, filter, and dry to obtain an imidazole polycarboxylic acid chelating agent with the same structural formula as in Example 1, with a yield of 84 wt%.

[0101] Preparation of descaling agent:

[0102] Add 83 parts of water to the reactor, and then add 10 parts of imidazole polycarboxylic acid chelating agent, 2.5 parts of scale inhibitor, and 3 parts of pH adjuster in sequence. Heat to 65°C for the first mixing. After stirring for 50 minutes, the pH of the system reaches 7. Add 1.5 parts of surfactant for the second mixing. After stirring for 30 minutes, stop and cool to room temperature to obtain descaling agent P3.

[0103] The scale inhibitor is a mixture of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer in a weight ratio of 7:3; the weight average molecular weight of polyepoxysuccinic acid is 1000 g / mol, the weight average molecular weight of maleic acid-acrylic acid copolymer is 1800 g / mol, and the weight ratio of structural units from maleic acid to structural units from acrylic acid is 3:4.

[0104] The surfactants and pH adjusters are the same as in Example 1.

[0105] Example 4

[0106] The preparation of the imidazole polycarboxylic acid chelating agent was the same as in Example 3, resulting in an imidazole polycarboxylic acid chelating agent with the same structural formula as in Example 1.

[0107] Preparation of descaling agent:

[0108] Add 84 parts of water to the reactor, and then add 10 parts of imidazole polycarboxylic acid chelating agent, 2 parts of scale inhibitor, and 3 parts of pH adjuster in sequence. Heat to 70°C for the first mixing. After stirring for 30 minutes, measure that the pH of the system reaches 7. Then add 1 part of surfactant for the second mixing. After stirring for 30 minutes, stop and cool to room temperature to obtain descaling agent P4.

[0109] The composition of the scale inhibitor, surfactant, and pH adjuster is the same as in Example 1.

[0110] Example 5

[0111] Preparation of imidazole polycarboxylic acid chelating agents:

[0112] (1) Weigh 0.5 mol of histidine and acetonitrile (the amount of acetonitrile is the same as the total weight of histidine and 2-cyanoacetyl chloride) into a reaction flask, start stirring, and add 0.55 mol of 2-cyanoacetyl chloride dropwise. After the addition is complete, heat the reaction system to reflux, control the reaction temperature at 80℃, and continue stirring for 4 h. Evaporate the solvent by vacuum distillation, wash with ethyl acetate, filter, and dry to obtain intermediate 1 with a yield of 89 wt%.

[0113] (2) Weigh 0.5 mol of intermediate 1 and add it to the reaction flask, and add a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to intermediate 1 is 0.5:1). At the same time, mix 1.05 mol of chloroacetic acid with a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to chloroacetic acid is 0.5:1) and add it to the reaction flask. Start stirring and add a 30 wt% sodium hydroxide aqueous solution (the ratio of the amount of sodium hydroxide aqueous solution to the total weight of intermediate 1 and chloroacetic acid is 0.3:1) to make the pH of the reaction system 9.2. Heat to 80°C and react for 4 h. Stop the reaction, adjust the pH to 1 with hydrochloric acid, filter, and dry to obtain an imidazole polycarboxylic acid chelating agent with the same structural formula as in Example 1, with a yield of 86 wt%.

[0114] Preparation of descaling agent:

[0115] Add 82 parts of water to the reactor, and then add 10 parts of imidazole polycarboxylic acid chelating agent, 3 parts of scale inhibitor, and 3 parts of pH adjuster in sequence. Heat to 70°C for the first mixing. After stirring for 30 minutes, measure that the pH of the system reaches 7. Then add 2 parts of surfactant for the second mixing. After stirring for 30 minutes, stop and cool to room temperature to obtain descaling agent P5.

[0116] The scale inhibitor is a mixture of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer in a weight ratio of 7:3; the weight average molecular weight of polyepoxysuccinic acid is 1100 g / mol, the weight average molecular weight of maleic acid-acrylic acid copolymer is 1600 g / mol, and the weight ratio of structural units from maleic acid to structural units from acrylic acid is 3:5.

[0117] The surfactants and pH adjusters are the same as in Example 1.

[0118] Example 6

[0119] Preparation of imidazole polycarboxylic acid chelating agents:

[0120] (1) Weigh 0.5 mol of histidine and acetonitrile (the amount of acetonitrile is the same as the total weight of histidine and 2-cyanoacetyl chloride) into a reaction flask, start stirring, and add 0.5 mol of 2-cyanoacetyl chloride dropwise. After the addition is complete, heat the reaction system to reflux, control the reaction temperature at 75℃, and continue stirring for 5 h. Evaporate the solvent by vacuum distillation, wash with ethyl acetate, filter, and dry to obtain intermediate 1 with a yield of 88 wt%.

[0121] (2) Weigh 0.5 mol of intermediate 1 and add it to the reaction flask, and add a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to intermediate 1 is 0.5:1). At the same time, take 1 mol of chloroacetic acid and mix it with a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to chloroacetic acid is 0.5:1) and add it to the reaction flask. Start stirring and add a 30 wt% sodium hydroxide aqueous solution (the ratio of the amount of sodium hydroxide aqueous solution to the total weight of intermediate 1 and chloroacetic acid is 0.3:1) to make the pH of the reaction system 9.3. Heat to 80°C and react for 5 h. Stop the reaction, adjust the pH to 1 with hydrochloric acid, filter, and dry to obtain an imidazole polycarboxylic acid chelating agent with the same structural formula as in Example 1, with a yield of 84 wt%.

[0122] Preparation of descaling agent:

[0123] Add 81 parts of water to the reactor, and then add 12 parts of imidazole polycarboxylic acid chelating agent, 2 parts of scale inhibitor, and 3 parts of pH adjuster in sequence. Heat to 70°C for the first mixing. After stirring for 30 minutes, the pH of the system is measured to reach 7. Then add 2 parts of surfactant for the second mixing. After stirring for 30 minutes, stop and cool to room temperature to obtain descaling agent P6.

[0124] The composition of the scale inhibitor, surfactant, and pH adjuster is the same as in Example 1.

[0125] Example 7

[0126] The imidazole polycarboxylic acid chelating agent and the descaling agent were prepared according to the method of Example 1, except that the descaling agent consisted of 13 parts imidazole polycarboxylic acid chelating agent, 2 parts scale inhibitor, 2 parts surfactant, 5 parts pH adjuster, and 78 parts water. Descaling agent P7 was obtained.

[0127] Example 8

[0128] The imidazole polycarboxylic acid chelating agent and the descaling agent were prepared according to the method of Example 1, except that the descaling agent consisted of 12 parts imidazole polycarboxylic acid chelating agent, 3 parts scale inhibitor, 1 part surfactant, 4.5 parts pH adjuster, and 79.5 parts water. Descaling agent P8 was obtained.

[0129] The scale inhibitor is a mixture of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer in a weight ratio of 7:3; the weight average molecular weight of polyepoxysuccinic acid is 1200 g / mol, the weight average molecular weight of maleic acid-acrylic acid copolymer is 2000 g / mol, and the weight ratio of structural units from maleic acid to structural units from acrylic acid is 2:3.

[0130] Example 9

[0131] The imidazole polycarboxylic acid chelating agent and the descaling agent were prepared according to the method of Example 1, except that the descaling agent consisted of 13 parts imidazole polycarboxylic acid chelating agent, 3 parts scale inhibitor, 2 parts surfactant, 4.5 parts pH adjuster, and 77.5 parts water. Descaling agent P9 was obtained.

[0132] The scale inhibitor is a mixture of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer in a weight ratio of 7:3; the weight average molecular weight of polyepoxysuccinic acid is 1200 g / mol, the weight average molecular weight of maleic acid-acrylic acid copolymer is 2000 g / mol, and the weight ratio of structural units from maleic acid to structural units from acrylic acid is 2:3.

[0133] Example 10

[0134] The imidazole polycarboxylic acid chelating agent and the descaling agent were prepared according to the method of Example 1, except that the descaling agent consisted of 10 parts imidazole polycarboxylic acid chelating agent, 2 parts scale inhibitor, 2 parts surfactant, 3 parts pH adjuster, and 83 parts water. Descaling agent P10 was obtained.

[0135] The scale inhibitor is a mixture of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer in a weight ratio of 7:3; the weight average molecular weight of polyepoxysuccinic acid is 1200 g / mol, the weight average molecular weight of maleic acid-acrylic acid copolymer is 2000 g / mol, and the weight ratio of structural units from maleic acid to structural units from acrylic acid is 2:3.

[0136] Example 11

[0137] The imidazole polycarboxylic acid chelating agent and the descaling agent were prepared according to the method of Example 1, except that the descaling agent consisted of 8 parts imidazole polycarboxylic acid chelating agent, 3 parts scale inhibitor, 1 part surfactant, 2 parts pH adjuster, and 86 parts water. Descaling agent P11 was obtained.

[0138] Example 12

[0139] The imidazole-based polycarboxylic acid chelating agent and the scale remover were prepared according to the method in Example 1, except that in the preparation of the imidazole-based polycarboxylic acid chelating agent, 2-cyanoacetyl chloride was replaced with an equimolar amount of 2-hydroxyacetamide, thus obtaining the imidazole-based polycarboxylic acid chelating agent. And descaling agent P12.

[0140] Example 13

[0141] The imidazole-based polycarboxylic acid chelating agent and the scale remover were prepared according to the method in Example 1, except that in the preparation of the imidazole-based polycarboxylic acid chelating agent, 2-cyanoacetyl chloride was replaced with an equimolar amount of 2-aminoacetyl chloride, thus obtaining the imidazole-based polycarboxylic acid chelating agent. And descaling agent P13.

[0142] Example 14

[0143] The imidazole polycarboxylic acid chelating agent and descaling agent were prepared according to the method of Example 1, except that the proportions of the components were different when preparing the descaling agent. Specifically, the descaling agent consisted of: 15 parts imidazole polycarboxylic acid chelating agent, 3 parts scale inhibitor, 3 parts surfactant, 5 parts pH adjuster, and 74 parts water. Descaling agent P14 was obtained.

[0144] Example 15

[0145] The imidazole polycarboxylic acid chelating agent and descaling agent were prepared according to the method in Example 1, except that the proportions of the components were different when preparing the descaling agent. Specifically, the descaling agent consisted of: 5 parts imidazole polycarboxylic acid chelating agent, 3 parts scale inhibitor, 2 parts surfactant, 2 parts pH adjuster, and 88 parts water. Descaling agent P15 was obtained.

[0146] Example 16

[0147] The imidazole polycarboxylic acid chelating agent and descaling agent were prepared according to the method of Example 1, except that the proportions of the components were different when preparing the descaling agent. Specifically, the descaling agent consisted of 12 parts imidazole polycarboxylic acid chelating agent, 1 part scale inhibitor, 1 part surfactant, 3 parts pH adjuster, and 83 parts water. Descaling agent P16 was obtained.

[0148] Example 17

[0149] The imidazole polycarboxylic acid chelating agent and descaling agent were prepared according to the method in Example 1, except that the proportions of the components were different when preparing the descaling agent. Specifically, the descaling agent consisted of: 12 parts imidazole polycarboxylic acid chelating agent, 2 parts scale inhibitor, 5 parts surfactant, 4 parts pH adjuster, and 77 parts water. Descaling agent P17 was obtained.

[0150] Example 18

[0151] The imidazole-based polycarboxylic acid chelating agent and descaling agent were prepared according to the method of Example 1, except that the ratio of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer in the scale inhibitor was different. Specifically, the scale inhibitor was a mixture of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer in a weight ratio of 3:7; the weight average molecular weight of polyepoxysuccinic acid was 1200 g / mol, the weight average molecular weight of maleic acid-acrylic acid copolymer was 2000 g / mol, and the weight ratio of structural units from maleic acid to structural units from acrylic acid was 2:3. Descaling agent P18 was obtained.

[0152] Example 19

[0153] The imidazole-based polycarboxylic acid chelating agent and descaling agent were prepared according to the method of Example 1, except that the polyepoxysuccinic acid and maleic acid-acrylic acid copolymer contained in the scale inhibitor had different weight-average molecular weights. Specifically, the polyepoxysuccinic acid had a weight-average molecular weight of 2000 g / mol, and the maleic acid-acrylic acid copolymer had a weight-average molecular weight of 1200 g / mol. Descaling agent P19 was obtained.

[0154] Example 20

[0155] The imidazole polycarboxylic acid chelating agent and descaling agent were prepared according to the method of Example 1, except that the weight ratio of structural units from maleic acid to structural units from acrylic acid in the maleic acid-acrylic acid copolymer was 2:1. Descaling agent P20 was obtained.

[0156] Example 21

[0157] An imidazole polycarboxylic acid chelating agent and a descaling agent were prepared according to the method in Example 1, except that sodium octadecyl sulfate was used as the surfactant. Descaling agent P21 was obtained.

[0158] Example 22

[0159] Preparation of imidazole polycarboxylic acid chelating agents:

[0160] (1) Weigh 0.5 mol of histidine and acetonitrile (the amount of acetonitrile is the same as the total weight of histidine and 2-cyanoacetyl chloride) into a reaction flask, start stirring, and add 0.4 mol of 2-cyanoacetyl chloride dropwise. After the addition is complete, heat the reaction system to reflux, control the reaction temperature at 75℃, and continue stirring for 5 h. Evaporate the solvent by vacuum distillation, wash with ethyl acetate, filter, and dry to obtain intermediate 1 with a yield of 70 wt%.

[0161] (2) Weigh 0.5 mol of intermediate 1 and add it to the reaction flask, and add a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to intermediate 1 is 0.5:1). At the same time, take 0.9 mol of chloroacetic acid and mix it with a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to chloroacetic acid is 0.5:1) and add it to the reaction flask. Start stirring and add a 30 wt% sodium hydroxide aqueous solution (the ratio of the amount of sodium hydroxide aqueous solution to the total weight of intermediate 1 and chloroacetic acid is 0.3:1) to make the pH of the reaction system 9.3. Heat to 80°C and react for 5 h. Stop the reaction, adjust the pH to 1 with hydrochloric acid, filter, and dry to obtain an imidazole polycarboxylic acid chelating agent with the same structural formula as in Example 1, with a yield of 75 wt%.

[0162] Example 23

[0163] Preparation of imidazole polycarboxylic acid chelating agents:

[0164] (1) Weigh 0.5 mol of histidine and acetonitrile (the amount of acetonitrile is the same as the total weight of histidine and 2-cyanoacetyl chloride) into a reaction flask, start stirring, and add 0.55 mol of 2-cyanoacetyl chloride dropwise. After the addition is complete, heat the reaction system to reflux, control the reaction temperature at 75°C, and continue stirring for 3 hours. Evaporate the solvent by vacuum distillation, wash with ethyl acetate, filter, and dry to obtain intermediate 1 with a yield of 68 wt%.

[0165] (2) Weigh 0.5 mol of intermediate 1 and add it to the reaction flask, and add a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to intermediate 1 is 0.5:1). At the same time, mix 1.05 mol of chloroacetic acid with a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to chloroacetic acid is 0.5:1) and add it to the reaction flask. Start stirring and add a 30 wt% sodium hydroxide aqueous solution (the ratio of the amount of sodium hydroxide aqueous solution to the total weight of intermediate 1 and chloroacetic acid is 0.3:1) to make the pH of the reaction system 9.3. Heat to 80°C and react for 3 h. Stop the reaction, adjust the pH to 1 with hydrochloric acid, filter, and dry to obtain an imidazole polycarboxylic acid chelating agent with the same structural formula as in Example 1, with a yield of 71 wt%.

[0166] Example 24

[0167] Preparation of imidazole polycarboxylic acid chelating agents:

[0168] (1) Weigh 0.5 mol of histidine and acetonitrile (the amount of acetonitrile is the same as the total weight of histidine and 2-cyanoacetyl chloride) into a reaction flask, start stirring, and add 0.55 mol of 2-cyanoacetyl chloride dropwise. After the addition is complete, heat the reaction system to reflux, control the reaction temperature at 60℃, and continue stirring for 5 h. Evaporate the solvent by vacuum distillation, wash with ethyl acetate, filter, and dry to obtain intermediate 1 with a yield of 65 wt%.

[0169] (2) Weigh 0.5 mol of intermediate 1 and add it to the reaction flask, and add a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to intermediate 1 is 0.5:1). At the same time, take 0.9 mol of chloroacetic acid and mix it with a 50 wt% sodium carbonate aqueous solution (the weight ratio of sodium carbonate aqueous solution to chloroacetic acid is 0.5:1) and add it to the reaction flask. Start stirring and add a 30 wt% sodium hydroxide aqueous solution (the ratio of the amount of sodium hydroxide aqueous solution to the total weight of intermediate 1 and chloroacetic acid is 0.3:1) to make the pH of the reaction system 9.3. Heat to 60°C and react for 5 h. Stop the reaction, adjust the pH to 1 with hydrochloric acid, filter, and dry to obtain an imidazole polycarboxylic acid chelating agent with the same structural formula as in Example 1, with a yield of 69 wt%.

[0170] Comparative Example 1

[0171] The imidazole polycarboxylic acid chelating agent and descaling agent were prepared according to the method of Example 1, except that no scale inhibitor was added. Specifically, the descaling agent consisted of 13 parts imidazole polycarboxylic acid chelating agent, 2 parts surfactant, 5 parts pH adjuster, and 80 parts water. Descaling agent D1 was obtained.

[0172] Comparative Example 2

[0173] The imidazole polycarboxylic acid chelating agent and descaling agent were prepared according to the method of Example 1, except that no surfactant was added. Specifically, the descaling agent consisted of 13 parts imidazole polycarboxylic acid chelating agent, 3 parts scale inhibitor, 5 parts pH adjuster, and 79 parts water. Descaling agent D2 was obtained.

[0174] Comparative Example 3

[0175] The descaling agent was prepared according to the method of Example 1, except that a different chelating agent was used. Specifically, the chelating agent with the following structural formula was selected. The chelating agent was used to obtain descaling agent D3.

[0176] Test case

[0177] The composition of descaling agents P1-P21 and D1-D3 and the test results of their descaling rates on calcium carbonate and barium sulfate scale in the Tarim Oilfield are shown in Table 1.

[0178] Table 1

[0179]

[0180]

[0181] As shown in Table 1, Comparative Examples 1-3 represent the cases without scale inhibitor, without surfactant, and with different chelating agents, respectively. The scale removers D1-D3 in Comparative Examples 1-3 all showed a scale removal rate below 70% for calcium carbonate and below 55% for barium sulfate. However, the scale removers P1-P13 prepared using the imidazole polycarboxylic acid chelating agents of Examples 1-13 of this invention exhibit excellent scale removal effects on both calcium carbonate and barium sulfate scales, with a scale removal rate above 81% for calcium carbonate and above 72% for barium sulfate. The imidazole polycarboxylic acid chelating agent provided by this invention significantly improves the scale removal effect of the scale remover.

[0182] Furthermore, Example 14 altered the proportions of the components in the descaling agent, with higher contents of imidazole polycarboxylic acid chelating agent, scale inhibitor, surfactant, and pH adjuster. Compared to Example 1, the descaling agent showed a lower descaling rate for both calcium carbonate and barium sulfate. In Example 15, the descaling agent P15 had a reduced imidazole polycarboxylic acid chelating agent content; in Example 16, the descaling agent P16 had a reduced scale inhibitor content; and in Example 17, the descaling agent P17 had an increased surfactant content. Compared to Example 1, the descaling agents showed a lower descaling rate for both calcium carbonate and barium sulfate. Example 18 changed... Example 19 changed the weight-average molecular weight of the polyepoxysuccinic acid and maleic acid-acrylic acid copolymer in the scale inhibitor. Example 20 changed the weight ratio of structural units from maleic acid to structural units from acrylic acid in the maleic acid-acrylic acid copolymer. Compared with Example 1, the scale inhibitor showed a decrease in the scale removal rate of both calcium carbonate and barium sulfate. Example 21 changed the type of surfactant. Compared with Example 1, the scale inhibitor showed a decrease in the scale removal rate of both calcium carbonate and barium sulfate. This shows that under specific ratios, the components in a scale inhibitor can better synergistically exert each other and maximize their effectiveness.

[0183] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An imidazole-based polycarboxylic acid chelating agent, characterized in that, The imidazole-based polycarboxylic acid chelating agent is selected from the compounds shown below. , or .

2. A method for preparing the imidazole polycarboxylic acid chelating agent according to claim 1, characterized in that, The preparation method includes the following steps: (1) Histidine is mixed with an acylation reagent in an organic solvent to carry out the first reaction, to obtain intermediate 1; (2) The intermediate 1 is mixed with chloroacetic acid or ethyl chloroacetate to carry out a second reaction to obtain the imidazole polycarboxylic acid chelating agent; Wherein, the acylation reagent is the compound shown in formula (2), Equation (2), Where R is a hydroxyl, carboxyl, or amino group, n=1, and R1 is Cl or OH; Intermediate 1 is a compound as shown below. 。 3. The preparation method according to claim 2, characterized in that, In step (1), the molar ratio of histidine to the acylation reagent is 1:(1-1.2). And / or, the organic solvent is selected from at least one of acetonitrile, N,N-dimethylformamide and isopropanol; And / or, based on a total weight of histidine and the acylation reagent of 1 part by weight, the amount of the organic solvent is 1-2 parts by weight; And / or, the temperature of the first reaction is 75-85°C, and the time is 4-5 hours.

4. The preparation method according to claim 3, characterized in that, In step (1), the organic solvent is acetonitrile.

5. The preparation method according to any one of claims 2-4, characterized in that, In step (2), the molar ratio of intermediate 1 to chloroacetic acid or ethyl chloroacetate is 1:(2-2.2). And / or, the temperature of the second reaction is 80-90℃, and the time is 4-5h.

6. The preparation method according to any one of claims 2-4, characterized in that, The second reaction was carried out at a pH of 9-10.

7. The preparation method according to claim 5, characterized in that, The second reaction was carried out at a pH of 9-10.

8. The preparation method according to any one of claims 2-4 and 7, characterized in that, The preparation method further includes: in step (2), the intermediate 1 and chloroacetic acid are first mixed with neutralizing agent 1 and neutralizing agent 2 respectively to obtain solution 1 and solution 2 respectively, and then solution 1, solution 2 and neutralizing agent 3 are mixed to carry out the second reaction; Neutralizing agent 1 and neutralizing agent 2 are sodium carbonate aqueous solutions with a sodium carbonate content of 40-50 wt%, and neutralizing agent 3 is a sodium hydroxide aqueous solution with a sodium hydroxide content of 30-50 wt%.

9. The preparation method according to claim 5, characterized in that, The preparation method further includes: in step (2), the intermediate 1 and chloroacetic acid are first mixed with neutralizing agent 1 and neutralizing agent 2 respectively to obtain solution 1 and solution 2 respectively, and then solution 1, solution 2 and neutralizing agent 3 are mixed to carry out the second reaction.

10. The preparation method according to claim 6, characterized in that, The preparation method further includes: in step (2), the intermediate 1 and chloroacetic acid are first mixed with neutralizing agent 1 and neutralizing agent 2 respectively to obtain solution 1 and solution 2 respectively, and then solution 1, solution 2 and neutralizing agent 3 are mixed to carry out the second reaction.

11. The preparation method according to any one of claims 2-4, 7, and 9-10, characterized in that, The preparation method further includes: adjusting the pH of the reaction mixture obtained after the second reaction to 1-2 to obtain the imidazole polycarboxylic acid chelating agent.

12. The preparation method according to claim 5, characterized in that, The preparation method further includes: adjusting the pH of the reaction mixture obtained after the second reaction to 1-2 to obtain the imidazole polycarboxylic acid chelating agent.

13. The preparation method according to claim 6, characterized in that, The preparation method further includes: adjusting the pH of the reaction mixture obtained after the second reaction to 1-2 to obtain the imidazole polycarboxylic acid chelating agent.

14. The preparation method according to claim 8, characterized in that, The preparation method further includes: adjusting the pH of the reaction mixture obtained after the second reaction to 1-2 to obtain the imidazole polycarboxylic acid chelating agent.

15. The use of an imidazole polycarboxylic acid chelating agent according to claim 1 or an imidazole polycarboxylic acid chelating agent prepared by any one of claims 2-14 as a descaling agent.

16. A descaling agent, characterized in that, The descaling agent includes an imidazole polycarboxylic acid chelating agent, a scale inhibitor, a surfactant, and water; The imidazole polycarboxylic acid chelating agent is the imidazole polycarboxylic acid chelating agent according to claim 1 or the imidazole polycarboxylic acid chelating agent prepared by any one of claims 2-14.

17. The descaling agent according to claim 16, characterized in that, The descaling agent has a pH value of 7-8; And / or, the descaling agent comprises the following components in parts by weight: 8-13 parts of the imidazole polycarboxylic acid chelating agent, 2-3 parts of the scale inhibitor, 1-2 parts of the surfactant, 2-5 parts of pH adjuster, and 77-87 parts of water.

18. The descaling agent according to claim 16 or 17, characterized in that, The scale inhibitor is selected from polyepoxysuccinic acid and / or maleic acid-acrylic acid copolymer; And / or, the surfactant is a succinate sulfonate; And / or, the pH adjuster is a mixture of ammonium chloride and ammonia or sodium acetate.

19. The descaling agent according to claim 18, characterized in that, The scale inhibitor is a mixture of polyepoxysuccinic acid and maleic acid-acrylic acid copolymer; And / or, the weight-average molecular weight of the polyepoxysuccinic acid is 900-1200 g / mol; And / or, the weight-average molecular weight of the maleic acid-acrylic acid copolymer is 1500-2000 g / mol; And / or, the weight ratio of structural units from maleic acid to structural units from acrylic acid in the maleic acid-acrylic acid copolymer is (2-3):(3-4); And / or, the weight ratio of the polyepoxysuccinic acid to the maleic acid-acrylic acid copolymer is (6-7):(3-4).

20. The descaling agent according to claim 18, characterized in that, The surfactant is potassium isooctyl succinate sulfonate.

21. The descaling agent according to claim 19, characterized in that, The surfactant is potassium isooctyl succinate sulfonate.

22. The descaling agent according to claim 18, characterized in that, The pH adjuster is a mixture of ammonium chloride and ammonia.

23. The descaling agent according to claim 22, characterized in that, In the mixture of ammonium chloride and ammonia, the weight ratio of ammonium chloride to ammonia is 1:(1-1.2).

24. The descaling agent according to any one of claims 19-21, characterized in that, The pH adjuster is a mixture of ammonium chloride and ammonia.

25. The descaling agent according to claim 24, characterized in that, In the mixture of ammonium chloride and ammonia, the weight ratio of ammonium chloride to ammonia is 1:(1-1.2).

26. A method for preparing a descaling agent, characterized in that, The preparation method includes the following steps: mixing the imidazole polycarboxylic acid chelating agent according to claim 1 or the imidazole polycarboxylic acid chelating agent prepared by any one of the preparation methods of claims 2-15, the scale inhibitor, the surfactant, and water to obtain the scale remover.

27. The preparation method according to claim 26, characterized in that, The preparation method includes the following steps: mixing 8-13 parts of imidazole polycarboxylic acid chelating agent, 2-3 parts of scale inhibitor, 2-5 parts of pH adjuster and 77-87 parts of water in the first mixing, and then mixing with 1-2 parts of surfactant in the second mixing to obtain the scale remover.

28. The preparation method according to claim 27, characterized in that, The temperatures of the first mixture and the second mixture are each independently 60-70°C; And / or, the first mixing time is 30-60 min; And / or, the second mixing time is 20-40 min.

29. The application of an imidazole polycarboxylic acid chelating agent according to claim 1 or a descaling agent according to any one of claims 16-25 in oil and gas field unblocking.

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