Iron-based high-temperature delayed cross-linking agent as well as preparation method and application thereof

Abstract

The invention discloses an iron-based high-temperature delayed cross-linking agent as well as a preparation method and application thereof, and belongs to the technical field of oilfield chemistry. The preparation method comprises the following steps: dissolving ferric salt in deionized water to prepare a solution A; dissolving the ligand composition in deionized water, and adjusting the pH value to a set pH value by using a pH regulator to prepare a solution B; wherein the ligand composition is prepared from potassium thiocyanate, sodium oxalate, sodium citrate and disodium ethylenediaminetetraacetate; and mixing the solution A and the solution B, maintaining a set pH value, carrying out a reaction, and carrying out reduced pressure distillation after the reaction is finished, so as to prepare the iron-based high-temperature delayed cross-linking agent. The high-temperature delayed cross-linking agent has the characteristics of low-temperature inertia, high-temperature response and environmental friendliness, and is used for solving the technical problem of contradiction between low-viscosity resistance reduction in a shaft and high-viscosity sand carrying in a reservoir of deep fracturing fluid.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield chemistry, and specifically relates to an iron-based high-temperature delayed crosslinking agent, a preparation method thereof, and an application thereof. Background Art

[0002] With the deep exploration and development of deep oil and gas resources towards high-temperature reservoirs, the fracturing fluid system faces the contradiction between "low viscosity and drag reduction in the wellbore" and "high viscosity and sand carrying in the reservoir". The fracturing fluid needs to maintain low-viscosity linear flow in the wellbore as much as possible to reduce the pipe string friction, while after entering the high-temperature reservoir, it needs to quickly form a high-strength polymer crosslinked network structure to achieve long-distance sand carrying. As a core thickening agent of the fracturing fluid, polyacrylamide has excellent viscosity-increasing and shear-thinning properties. However, in high-temperature reservoirs, the entanglement degree of polyacrylamide molecular chains decreases due to the intensified thermal motion, and the amide groups are hydrolyzed to generate carboxylate groups, which will cause a sharp attenuation of viscosity. It is necessary to construct a three-dimensional network through a crosslinking agent to improve the thermal stability.

[0003] In the existing crosslinking agent technology, transition metal crosslinking agents represented by organic zirconium / titanium still dominate. They can form a stable three-dimensional network structure with groups such as carboxyl groups in the polyacrylamide molecular chain. However, their premature crosslinking characteristics lead to too rapid an increase in the fluid viscosity in the wellbore, which not only increases the pumping pressure, but also weakens the final sand-carrying capacity due to the high-speed shear damage of the crosslinked structure, forming a double dilemma of "increased resistance at low temperature - loss of viscosity at high temperature". Some of the disclosed crosslinking technologies can achieve delayed crosslinking by adjusting the ligand and pH, but the existing ligand regulation mechanism cannot effectively inhibit low-temperature crosslinking. For example, an organic zirconium crosslinking agent disclosed in the Chinese invention patent with the publication number CN 117024478 A, although the crosslinking time is regulated by a multi-component ligand, it still crosslinks with polyacrylamide below 60°C, resulting in too rapid an increase in the system viscosity during the pumping process, seriously affecting the pumping efficiency. In addition, raw materials of transition metal crosslinking agents such as zirconium, titanium, and cadmium have disadvantages such as high cost, large environmental hazards, and insufficient high-temperature stability.

[0004] Therefore, there is an urgent need to develop a new type of high-temperature delayed crosslinking agent with low-temperature inertness, high-temperature responsiveness, and environmental friendliness to solve the contradiction between "low viscosity and drag reduction in the wellbore" and "high viscosity and sand carrying in the reservoir" of deep fracturing fluids, which has become a key requirement for breaking through the technical bottleneck of deep fracturing fluids. Summary of the Invention

[0005] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an iron-based high-temperature delayed crosslinking agent, a preparation method thereof, and an application thereof. The high-temperature delayed crosslinking agent has the characteristics of low-temperature inertness, high-temperature responsiveness, and environmental friendliness, so as to solve the technical problem of the contradiction between "low viscosity and drag reduction in the wellbore" and "high viscosity and sand carrying in the reservoir" of deep fracturing fluids.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The present invention provides a preparation method of an iron-based high-temperature delayed crosslinking agent, comprising the following steps:

[0008] Dissolve an iron salt in deionized water to obtain solution A;

[0009] Dissolve the ligand composition in deionized water, and adjust it to a set pH value with a pH regulator to obtain solution B; wherein, the ligand composition consists of potassium thiocyanate, sodium oxalate, sodium citrate, and disodium ethylenediaminetetraacetate;

[0010] Mix solution A and solution B and maintain the set pH value, carry out the reaction, and carry out vacuum distillation after the reaction to obtain the iron-based high-temperature delayed crosslinking agent.

[0011] In one embodiment, the iron salt is at least one of ferric sulfate or ferric chloride; the molar concentration of iron ions in solution A is 0.5 - 1.5 mol / L; the total molar concentration of the ligand composition in solution B is 4.3 - 20 mol / L.

[0012] In one embodiment, the molar ratio of potassium thiocyanate, sodium oxalate, sodium citrate, and disodium ethylenediaminetetraacetate is (4 - 16):(0.1 - 1):(0.1 - 1):(0.1 - 2).

[0013] In one embodiment, the volume ratio of solution A to solution B is 1:1.

[0014] In one embodiment, the iron salt is stirred and dissolved in deionized water at 25 - 30 °C; the ligand composition is stirred and dissolved in deionized water at 30 - 40 °C; the set pH value is 3.5 - 5.5.

[0015] In one embodiment, the pH regulator is one of acetic acid, citric acid, sodium bicarbonate, or ammonia water; the temperature of the reaction is 40 - 60 °C, and the reaction time is 1 - 2 h.

[0016] In one embodiment, the temperature of the vacuum distillation is 50 - 60 °C, and the part of the solvent removed by the vacuum distillation is 10 - 30% of the total volume of the solvent in the product after the reaction.

[0017] The present invention also provides an iron-based high-temperature delayed crosslinking agent prepared by the preparation method of the iron-based high-temperature delayed crosslinking agent as described above.

[0018] In one embodiment, the iron-based high-temperature delayed crosslinking agent is used for crosslinking anionic polyacrylamide. When used for crosslinking anionic polyacrylamide, the anionic polyacrylamide solution is used as the base fluid, and the addition amount of the iron-based high-temperature delayed crosslinking agent is 0.3 - 2% of the base fluid, and the crosslinking temperature is 70 - 100 °C.

[0019] The present invention also provides the application of the iron-based high-temperature delayed crosslinking agent prepared by the preparation method of the iron-based high-temperature delayed crosslinking agent as described above in the oilfield fracturing process.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a preparation method of an iron-based high-temperature delayed crosslinking agent. By using iron salts and multi-component ligands such as potassium thiocyanate, sodium oxalate, and disodium ethylenediaminetetraacetate, a high-temperature delayed crosslinking agent is prepared. Based on the different complexation strengths of the ligands, a hierarchical complexation system is constructed with Fe3+, and the coordination dissociation process of Fe3+ is dominated by different ligands in different temperature ranges. The temperature-responsive control of the crosslinking behavior is achieved by adjusting the ligand ratio. At low temperatures (less than 60 °C), each ligand inhibits the release of iron ions through synergistic complexation to form an iron-based complex with good stability; when the temperature gradually increases, weak ligands such as thiocyanate ions and oxalate ions first dominate the release of part of Fe3+, and then strong ligands such as EDTA gradually release Fe3+. By adjusting the compounding ratio of each ligand, the release of Fe3+ at different temperatures can be controlled. The released Fe3+ undergoes coordination crosslinking with groups such as carboxyl groups (COO-) on the polymer molecular chain, and a large number of thiocyanate ions further produce bridging effects to promote crosslinking, thereby forming a high-strength crosslinked network structure. The present invention achieves the purpose of high-temperature delayed crosslinking through multi-ligand synergistic complexation and temperature-responsive dissociation of Fe3+, providing an efficient and environmentally friendly solution for the fracturing of deep high-temperature oil and gas reservoirs. Description of the Drawings

[0022] Figure 1 It is the SME scanning image of the uncrosslinked polyacrylamide solution;

[0023] Figure 2 It is the SME image after crosslinking the polyacrylamide solution at 120 °C with the iron-based high-temperature delayed crosslinking agent prepared in Example 3. Detailed Embodiments

[0024] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art for the present invention. When there is a conflict, the definition in this specification shall prevail.

[0025] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0026] In this text, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values (including integers and fractions) within the range.

[0027] In this text, unless otherwise specified, terms such as "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0028] In this text, for the sake of more concise description, all possible combinations of all technical features in each embodiment or example are not described in detail. However, this does not mean that these combinations do not exist or are not covered by the present invention. On the contrary, as long as the combinations of these technical features are logically reasonable and free of contradictions, then they can be combined arbitrarily. All such possible combinations should be regarded as being within the scope described in this specification and are the objects protected and implemented by the present invention.

[0029] The present invention provides an iron-based high-temperature delayed crosslinking agent, its preparation method, and its application.

[0030] In the first aspect of the present invention, a preparation method of an iron-based high-temperature delayed crosslinking agent is provided, and the preparation method includes the following steps:

[0031] S1: Dissolve an iron salt in deionized water, and stir at 25 - 30 °C until completely dissolved to obtain solution A.

[0032] S2: Dissolve a ligand composition in deionized water, stir and dissolve at 30 - 40 °C, and adjust the pH of the system to 3.5 - 5.5 with a pH regulator to obtain solution B.

[0033] S3: Slowly add solution A to solution B at a volume ratio of 1:1, and maintain the pH of the system at 3.5 - 5.5. React at 40 - 60 °C for 1 - 2 h. After the reaction ends, remove part of the solvent by vacuum distillation to obtain an iron-based high-temperature delayed crosslinking agent.

[0034] Further, the iron salt is at least one of ferric sulfate or ferric chloride, and the molar concentration of iron ions in solution A is 0.5 - 1.5 mol / L.

[0035] Further, the ligand composition includes potassium thiocyanate, sodium oxalate, sodium citrate, and disodium ethylenediaminetetraacetate, and their molar ratio is (4 - 16):(0.1 - 1):(0.1 - 1):(0.1 - 2).

[0036] Further, the total molar concentration of the ligand substance in Solution B is 4.3 - 20 mol / L.

[0037] Further, the pH regulator is one of acetic acid, citric acid, sodium bicarbonate, and ammonia water.

[0038] Further, the vacuum distillation is carried out at 50 - 60 °C to remove 10 - 30% of the total volume of the solvent in the product after the reaction.

[0039] Based on the synergistic complexation of multi-ligands to form an iron-based complex with good stability under low-temperature conditions, the present invention constructs a hierarchical complexation system through different complexation strengths and compounding ratios of ligands to achieve the temperature-responsive release of Fe3+. The released Fe3+ undergoes coordination crosslinking with groups such as carboxyl groups. In addition, some ligands further enhance the network density through bridging effects, and finally a crosslinking system with both high-temperature delayed crosslinking and a stable three-dimensional network is constructed. Moreover, the iron-based system adopted in the present invention can avoid heavy metal pollution, and the preparation process is simple and efficient, with high efficiency, environmental protection, and industrial feasibility.

[0040] In the second aspect of the present invention, an iron-based high-temperature delayed crosslinking agent prepared by the above preparation method is provided. This crosslinking agent is mainly used for crosslinking anionic polyacrylamide, and the recommended addition amount is 0.3 - 2% of the base fluid, and the crosslinking temperature can be controlled at 70 - 100 °C.

[0041] In the third aspect of the present invention, an application of the iron-based high-temperature delayed crosslinking agent prepared by the above preparation method in fields such as oilfield fracturing is provided.

[0042] This iron-based high-temperature delayed crosslinking agent has excellent low-temperature stability and high-temperature responsiveness. Based on the synergistic complexation of ferric salts and multi-ligands, a stable composite complex is formed under low-temperature conditions; by adjusting the complexation strength of different ligands and the ligand ratio, the controllable release of Fe3+ in a high-temperature environment is achieved. It also has excellent crosslinking effects. The released Fe3+ can undergo coordination crosslinking with groups such as carboxyl groups (COO-) on the polymer molecular chain. At the same time, a relatively high concentration of composite ligands produces a bridging effect, further promoting the formation of a high-strength crosslinked network structure. And this iron-based high-temperature delayed crosslinking agent also has excellent environmental protection and industrial feasibility. The innovative iron-based crosslinking system adopted in the present invention can avoid heavy metal pollution, has good environmental friendliness, the preparation process is simple and efficient, the raw materials are easily available, has good economic benefits, and meets the dual requirements of "low-viscosity drag reduction - high-viscosity sand carrying" for deep fracturing, providing a green and efficient solution for the development of high-temperature oil reservoirs.

[0043] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0044] In the following embodiments, conventional instruments and equipment in the art are used. For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are the conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0045] Example 1

[0046] Add 1 mol of ferric chloride to 1 L of water and stir at 25 °C until completely dissolved to obtain solution A; then add 4 mol of potassium thiocyanate, 0.1 mol of sodium oxalate, 0.1 mol of sodium citrate, and 0.1 mol of disodium ethylenediaminetetraacetate to 1 L of water and stir at 30 °C until completely dissolved, adjust the pH of the system to 5.5 to obtain solution B. Finally, slowly add solution A to solution B at a volume ratio of 1:1, maintain the pH of the system at 5.5, react at 40 °C for 1 h, and after the reaction is completed, remove 30% of the solvent by vacuum distillation at 60 °C to obtain an iron-based high-temperature delayed crosslinking agent.

[0047] Example 2

[0048] Add 1 mol of ferric chloride to 1 L of water and stir at 30 °C until completely dissolved to obtain solution A; then add 16 mol of potassium thiocyanate, 1 mol of sodium oxalate, 1 mol of sodium citrate, and 2 mol of disodium ethylenediaminetetraacetate to 1 L of water and stir at 40 °C until completely dissolved, adjust the pH of the system to 3.5 to obtain solution B. Finally, slowly add solution A to solution B at a volume ratio of 1:1, maintain the pH of the system at 3.5, react at 60 °C for 2 h, and after the reaction is completed, remove 10% of the solvent by vacuum distillation at 50 °C to obtain an iron-based high-temperature delayed crosslinking agent.

[0049] Example 3

[0050] Add 1 mol of ferric chloride to 1 L of water and stir at 30 °C until completely dissolved to obtain solution A; then add 12 mol of potassium thiocyanate, 0.3 mol of sodium oxalate, 1 mol of sodium citrate, and 1 mol of disodium ethylenediaminetetraacetate to 1 L of water and stir at 40 °C until completely dissolved, and adjust the pH of the system to 4 to obtain solution B. Finally, slowly add solution A to solution B at a volume ratio of 1:1, maintain the pH of the system at 4, react at 50 °C for 1 h, and after the reaction, distill off 15% of the solvent under reduced pressure at 50 °C to obtain an iron-based high-temperature delayed crosslinking agent.

[0051] Example 4

[0052] Add 0.5 mol of ferric chloride to 1 L of water and stir at 30 °C until completely dissolved to obtain solution A; then add 12 mol of potassium thiocyanate, 0.3 mol of sodium oxalate, 1 mol of sodium citrate, and 1 mol of disodium ethylenediaminetetraacetate to 1 L of water and stir at 40 °C until completely dissolved, and adjust the pH of the system to 4.5 to obtain solution B. Finally, slowly add solution A to solution B at a volume ratio of 1:1, maintain the pH of the system at 4.5, react at 40 °C for 1 h, and after the reaction, distill off 15% of the solvent under reduced pressure at 50 °C to obtain an iron-based high-temperature delayed crosslinking agent.

[0053] Example 5

[0054] Add 1.5 mol of ferric chloride to 1 L of water and stir at 30 °C until completely dissolved to obtain solution A; then add 16 mol of potassium thiocyanate, 0.5 mol of sodium oxalate, 0.5 mol of sodium citrate, and 0.1 mol of disodium ethylenediaminetetraacetate to 1 L of water and stir at 40 °C until completely dissolved, and adjust the pH of the system to 4.5 to obtain solution B. Finally, slowly add solution A to solution B at a volume ratio of 1:1, maintain the pH of the system at 4.5, react at 50 °C for 1 h, and after the reaction, distill off 15% of the solvent under reduced pressure at 50 °C to obtain an iron-based high-temperature delayed crosslinking agent.

[0055] Example 6

[0056] Add 1 mol of ferric chloride to 1 L of water and stir at 30 °C until completely dissolved to obtain solution A; then add 12 mol of potassium thiocyanate, 0.5 mol of sodium oxalate, 0.5 mol of sodium citrate, and 0.8 mol of disodium ethylenediaminetetraacetate to 1 L of water and stir at 40 °C until completely dissolved, and adjust the pH of the system to 4.5 to obtain solution B. Finally, slowly add solution A to solution B at a volume ratio of 1:1, maintain the pH of the system at 4.5, react at 50 °C for 1 h, and after the reaction, distill off 15% of the solvent under reduced pressure at 50 °C to obtain an iron-based high-temperature delayed crosslinking agent.

[0057] Example 7

[0058] Add 1 mol of ferric sulfate to 1 L of water and stir at 25 °C until completely dissolved to obtain solution A; then add 12 mol of potassium thiocyanate, 0.5 mol of sodium oxalate, 0.5 mol of sodium citrate, and 0.8 mol of disodium ethylenediaminetetraacetate to 1 L of water and stir at 40 °C until completely dissolved. Adjust the pH of the system to 3.5 to obtain solution B. Finally, slowly add solution A to solution B at a volume ratio of 1:1 and maintain the pH of the system at 3.5. React at 50 °C for 2 h. After the reaction, remove 15% of the solvent by vacuum distillation at 50 °C to obtain an iron-based high-temperature delayed crosslinking agent.

[0059] Example 8

[0060] Add 1 mol of ferric sulfate to 1 L of water and stir at 25 °C until completely dissolved to obtain solution A; then add 16 mol of potassium thiocyanate, 1 mol of sodium oxalate, 1 mol of sodium citrate, and 1 mol of disodium ethylenediaminetetraacetate to 1 L of water and stir at 40 °C until completely dissolved. Adjust the pH of the system to 5.5 to obtain solution B. Finally, slowly add solution A to solution B at a volume ratio of 1:1 and maintain the pH of the system at 5.5. React at 60 °C for 1 h. After the reaction, remove 10% of the solvent by vacuum distillation at 50 °C to obtain an iron-based high-temperature delayed crosslinking agent.

[0061] Example 9

[0062] Add 1 mol of ferric sulfate to 1 L of water and stir at 25 °C until completely dissolved to obtain solution A; then add 16 mol of potassium thiocyanate, 1 mol of sodium oxalate, 1 mol of sodium citrate, and 1 mol of disodium ethylenediaminetetraacetate to 1 L of water and stir at 40 °C until completely dissolved. Adjust the pH of the system to 5.5 to obtain solution B. Finally, slowly add solution A to solution B at a volume ratio of 1:1 and maintain the pH of the system at 5.5. React at 60 °C for 1 h. After the reaction, remove 15% of the solvent by vacuum distillation at 50 °C to obtain an iron-based high-temperature delayed crosslinking agent.

[0063] Performance Evaluation

[0064] To characterize the high-temperature delayed crosslinking effect of the iron-based high-temperature delayed crosslinking agent prepared in the present invention, a 0.5 wt% anionic polyacrylamide solution was prepared as the base fluid, and then 0.5 wt% of the crosslinking agents prepared in Examples 1-5 were added to the base fluid and stirred evenly. Using a high-temperature rheometer (HAAKE MARS 40 / 60 type), at a fixed shear rate of 170 s-1, the temperature was raised from 30 °C to 120 °C at a rate of 3 °C / min, and the apparent viscosity (mPa·s) was recorded in real time.

[0065]

[0066] As can be seen from the above experimental results, the iron-based high-temperature delayed crosslinking agents prepared in Examples 1-6 all have good high-temperature delayed crosslinking effects in the polyacrylamide base fluid. At the initial stage of heating (when the temperature is less than 70 °C), there is a slight decrease in the viscosity of the system, and at this time, the crosslinking agent does not undergo crosslinking, showing good low-temperature inertness. The crosslinking temperature of the system can be adjusted by changing the ligand ratio. When the temperature rises to the designed trigger point, the crosslinking agent begins to produce crosslinking, causing a significant increase in the viscosity of the system. For example, the ligand ratio in Example 1 is the lowest, and crosslinking starts at 70 °C. In Example 3, the crosslinking temperature is delayed to 100 °C by adjusting the ligand ratio. In Example 4, by optimizing the ratio of sodium citrate / EDTA, excellent high-temperature stability is exhibited after crosslinking is triggered at 80 °C, ensuring both delay and better maintaining the strength of the crosslinking network. Comparing Figure 1 and Figure 2 the SEM images of the polyacrylamide solution before and after crosslinking with the crosslinking agent, it can be found that the iron-based crosslinking agent prepared in the present invention can form a highly dense three-dimensional network structure for polyacrylamide, endowing the gel system with higher mechanical strength.

[0067] Overall, in view of the technical bottlenecks of the existing crosslinking agents such as premature crosslinking at low temperature, instability at high temperature, and high environmental cost, the present invention innovatively develops an iron-based high-temperature delayed crosslinking agent with multi-level ligand synergistic regulation. Combining the hierarchical complexation design of Fe3+ and ligands, it realizes chemical inertness at low temperature, precise temperature response control in the range of 70-100 °C, and has both high-temperature delay, temperature resistance, and environmental friendliness, providing an efficient and low-cost technical solution for fracturing fluids in deep high-temperature oil and gas reservoirs.

[0068] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an iron-based high-temperature delayed crosslinking agent, characterized in that: The following steps are involved: Dissolve iron salt in deionized water to prepare solution A; The ligand composition is dissolved in deionized water, and the pH value is adjusted to a set value by using a pH adjuster to prepare a solution B; wherein the ligand composition is composed of potassium thiocyanate, sodium oxalate, sodium citrate, and disodium oxalate tetraacetate; The solution A and the solution B are mixed and maintained at a set pH value to react, and after the reaction is completed, reduced pressure distillation is performed to obtain an iron-based high-temperature delayed cross-linking agent.

2. The method for preparing the iron-based high-temperature delayed cross-linking agent according to claim 1, characterized in that: The iron salt is at least one of ferric sulfate and ferric chloride; the molar concentration of iron ions in the solution A is 0.5-1.5 mol / L; and the total molar concentration of the ligand composition in the solution B is 4.3-20 mol / L.

3. The method for preparing the iron-based high-temperature delayed cross-linking agent according to claim 1, characterized in that: The molar ratio of potassium thiocyanate, sodium oxalate, sodium citrate and disodium oxalate tetraacetate is (4-16): (0.1-1): (0.1-1): (0.1-2).

4. The method for preparing the iron-based high-temperature delayed cross-linking agent according to claim 1, characterized in that: The volume ratio of solution A to solution B is 1:

1.

5. The method for preparing the iron-based high temperature delayed cross-linking agent according to claim 1, characterized in that: The iron salt is stirred and dissolved in deionized water at 25-30° C.; the ligand composition is stirred and dissolved in deionized water at 30-40° C.; and the set pH value is 3.5-5.

5.

6. The method for preparing the iron-based high-temperature delayed cross-linking agent according to claim 1, characterized in that: The pH regulator is one of acetic acid, citric acid, sodium bicarbonate or ammonia water; the reaction temperature is 40-60° C., and the reaction time is 1-2 hours.

7. The method for preparing an iron-based high-temperature delayed cross-linking agent according to claim 1, characterized in that: The temperature of the vacuum distillation is 50-60° C., and the part of the solvent removed by the vacuum distillation is 10-30% of the total volume of the solvent in the product after the reaction is completed.

8. An iron-based high-temperature delayed cross-linking agent obtained by the preparation method of the iron-based high-temperature delayed cross-linking agent according to any one of claims 1 to 7.

9. The iron-based high temperature delayed cross-linking agent according to claim 8, characterized in that: The iron-based high temperature delayed crosslinking agent is used for crosslinking of anionic polyacrylamide. When used for crosslinking of anionic polyacrylamide, anionic polyacrylamide solution is used as base liquid, the addition amount of the iron-based high temperature delayed crosslinking agent is 0.3-2% of the base liquid, and the crosslinking temperature is 70-100°C.

10. Use of the iron-based high-temperature delayed cross-linking agent prepared by the method for preparing the iron-based high-temperature delayed cross-linking agent according to any one of claims 1 to 7 in an oil field fracturing process.

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