Oilfield composite desulfurizing agent and its preparation method

Abstract

This invention belongs to the field of desulfurizing agent preparation technology, specifically relating to an oilfield composite desulfurizing agent and its preparation method. The oilfield composite desulfurizing agent of this invention, by mass percentage, comprises the following raw materials: 12-14% 6-tetrazyl-1,3,5-triazine-2,4-diamine, 25-27% tetramethylguanidine lactate, 7-9% ferric glutamate-N,N-diacetate, 3.6-4.0% sodium diisooctyl sulfosuccinate, 1.0-1.3% glycerol polyoxypropylene polyoxyethylene ether, and water as the balance. The oilfield composite desulfurizing agent of this invention exhibits a relatively rapid desulfurization speed while also considering desulfurization depth and persistence, avoiding the problems of easy emulsification and poor compatibility with crude oil found in traditional desulfurizing agents.

Description

Technical Field

[0001] This invention belongs to the field of desulfurizing agent preparation technology, specifically relating to an oilfield composite desulfurizing agent and its preparation method. Background Technology

[0002] The main mechanisms of H2S formation in crude oil are as follows: Inorganic hydrogen sulfide is primarily produced through the thermochemical reduction of sulfates and the chemical decomposition of pyrite; organic hydrogen sulfide is mainly generated through thiols or thioethers; and biogenic hydrogen sulfide is generated during petroleum formation through various complex chemical and biochemical processes involving hydrolysis, oxidation, and bacterial degradation, accompanied by H2S formation. In petroleum extraction, bacterial sulfate reduction is a crucial formation mechanism. Under anaerobic conditions in oil reservoirs, sulfate-reducing bacteria can efficiently reduce sulfates, producing large amounts of H2S.

[0003] The presence of hydrogen sulfide during oil extraction and crude oil gathering and transportation is a major challenge that urgently needs to be addressed. The presence of hydrogen sulfide in oil products: ① severely corrodes pipelines and equipment, significantly increasing gathering and transportation costs; ② due to its high toxicity and volatility, it causes severe environmental pollution, directly endangering personal safety; ③ it leads to problems such as excessive sulfur content in refined oil products, poor oil quality, and substandard products. Therefore, how to reduce the hydrogen sulfide content to a minimum before crude oil is extracted from the well and to zero after extraction is a problem that every oilfield must solve.

[0004] Currently, domestic and international methods for treating hydrogen sulfide in oil wells include physical, biological, and chemical methods. Physical methods mainly involve physical adsorption and membrane separation. Biological methods utilize various sulfur-oxidizing bacteria and thiobacilli to treat hydrogen sulfide. Chemical methods mainly include oxidation, acid-base neutralization, and sulfide precipitation. Each method has its advantages and disadvantages. Among them, acid-base neutralization offers rapid desulfurization, safety, and low labor intensity, but its drawback is that if unsuitable raw materials are selected, the desulfurization cost can be relatively high.

[0005] Chinese invention patent CN110564394B discloses a desulfurizing agent for heavy oil thermal recovery wells, which is composed of epoxypropyl biimidazole and nitrate. It can remove hydrogen sulfide and mercaptan. However, its raw material nitrate can be converted into nitrite in high-temperature acidic oil wells, which accelerates equipment corrosion. Moreover, the epoxy groups are prone to ring opening at high temperatures, resulting in a decrease in activity. Since the product was promoted and applied in Gudao Oilfield, although the desulfurization effect in some high-temperature wells is better than that of triazine desulfurizing agents, its treatment effect is still poor.

[0006] Therefore, crude oil must be desulfurized to a safe concentration. Previously used desulfurizing agents were mostly mixed solutions of strongly alkaline organic amines and high-salt content. While desulfurizing, these reacted with acidic substances in the crude oil to form large-molecule organic salts, acting as surfactants and causing severe emulsification of the crude oil. This led to a series of downstream problems such as difficulty in demulsification, difficulty in dehydration and desalting, and poisoning of downstream refining catalysts. Therefore, developing desulfurizing agents that can overcome the defects of easy hydrolysis and poor desulfurization effect has always been a technical challenge for those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a composite desulfurizing agent for oil fields, which has a relatively rapid desulfurization speed while also taking into account the desulfurization depth and persistence. This invention also provides its preparation method.

[0008] The oilfield composite desulfurizing agent of the present invention has the following raw material composition by mass percentage: 12-14% 6-tetrazyl-1,3,5-triazine-2,4-diamine, 25-27% tetramethylguanidine lactate, 7-9% ferric glutamate-N,N-diacetate, 3.6-4.0% sodium diisooctyl sulfosuccinate, 1.0-1.3% glycerol polyoxypropylene polyoxyethylene ether, and water as the balance.

[0009] The structural formula of 6-tridecyl-1,3,5-triazine-2,4-diamine is:

[0010] .

[0011] The preparation method of ferric glutamic acid-N,N-diacetate consists of the following steps:

[0012] ① Dissolve tetrasodium glutamate diacetate in deionized water to prepare a tetrasodium glutamate diacetate solution;

[0013] ② A ferric salt solution was prepared by dissolving ferric chloride hexahydrate in deionized water;

[0014] ③ Under stirring conditions, the iron salt solution prepared in step ② is added to the tetrasodium glutamate diacetate solution, controlling the reaction between the tetrasodium glutamate diacetate and Fe. 3+ The molar ratio of the two components was 1.2:1. Then, sodium hydroxide solution was added to adjust the pH of the reaction system to 9.0. The reaction was carried out at 50-55℃ for 1.5h. After the reaction was completed, the mixture was cooled to room temperature, filtered to remove insoluble matter, and glutamic acid-N,N-diacetic acid iron was prepared.

[0015] Wherein: the mass concentration of the tetrasodium diglutamate solution in step ① is 25%, and the mass concentration of the iron salt solution in step ② is 20%.

[0016] The preparation method of the oilfield composite desulfurizing agent of the present invention comprises the following steps:

[0017] (1) Add 60% of the total mass of deionized water to the reaction apparatus, add tetramethylguanidine lactate while stirring, and stir until completely dissolved;

[0018] (2) Add sodium diisooctyl sulfosuccinate and continue stirring until the solution is clear;

[0019] (3) Add 6-tetrazyl-1,3,5-triazine-2,4-diamine, heat to 40-42℃ and stir until completely dispersed;

[0020] (4) Add glutamic acid-N,N-diacetic acid iron to the reaction system of step (3) and stir to mix well;

[0021] (5) Add glycerol polyoxypropylene polyoxyethylene ether and stir to mix evenly, then add the remaining deionized water and stir evenly to prepare the oilfield composite desulfurizer.

[0022] In step (1), the stirring speed is 400 r / min, the stirring time is 10-13 min, and the stirring temperature is room temperature.

[0023] In step (2), the stirring time is 15-17 min, the stirring speed is 400 r / min, and the stirring temperature is room temperature.

[0024] In step (3), the stirring speed is 800 r / min and the stirring time is 25-30 min.

[0025] In step (4), the stirring speed is 400 r / min, the stirring temperature is 35-38℃, and the stirring time is 10-12 min.

[0026] In step (5), the stirring speed is 400 r / min, the stirring temperature is 40-42℃, glycerol polyoxypropylene polyoxyethylene ether is added, and the mixture is stirred for 10-12 min. Then the remaining deionized water is added and the mixture is stirred for 20-23 min.

[0027] The prepared oilfield composite desulfurizing agent product is a light yellow, transparent, uniform liquid with a pH value of 10.8-11.2. It does not separate into layers after being stored at 40℃ for 30 days.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) The oilfield composite desulfurizer of the present invention uses 6-tridecyl-1,3,5-triazine-2,4-diamine, tetramethylguanidine lactate and glutamic acid-N,N-diacetate iron as the main desulfurizing substances. The three work synergistically. The long-chain alkyl of 6-tridecyl-1,3,5-triazine-2,4-diamine ensures oil phase penetration and undergoes an irreversible chemical reaction with hydrogen sulfide, reducing the concentration of hydrogen sulfide in a very short time. Tetramethylguanidine lactate maintains the alkaline environment of the system, ensuring that 6-tridecyl-1,3,5-triazine-2,4-diamine and glutamic acid-N,N-diacetate iron can work in the optimal pH environment. Its lactate ion can also solubilize and stabilize. Glutamic acid-N,N-diacetate iron can deeply remove the trace amount of H2S remaining after the triazine reaction and convert it into elemental sulfur, thereby improving the desulfurization depth and thoroughness. The three components work synergistically to fundamentally ensure the removal of hydrogen sulfide. In addition, the presence of sodium diisooctyl sulfosuccinate in the raw materials enables the desulfurizer to quickly remove oil film, asphalt, and biofilm, reduce the oil-water interfacial tension, and shorten the time for the desulfurizer to take effect. Glyceryl polyoxypropylene polyoxyethylene ether inhibits foam generated by surfactants during the treatment process, prevents air lock, and ensures that the entire treatment process proceeds smoothly.

[0030] (2) The oilfield composite desulfurizer described in this invention has a relatively rapid desulfurization speed, while also taking into account the desulfurization depth and persistence, thus avoiding the problems of easy emulsification and poor compatibility with crude oil of traditional desulfurizers.

[0031] (3) The preparation method of the oilfield composite desulfurizing agent described in this invention is simple to operate and mild in conditions, which greatly alleviates the problems of subsequent treatment such as demulsification, dehydration and desalination caused by crude oil emulsification due to traditional desulfurizing agents, and saves a lot of comprehensive treatment costs for oilfields. Detailed Implementation

[0032] Example 1

[0033] The oilfield composite desulfurizer described in Example 1 has the following raw material composition by mass percentage: 13% 6-tetrazyl-1,3,5-triazine-2,4-diamine, 26% tetramethylguanidine lactate, 8% ferric glutamate-N,N-diacetate, 3.8% sodium diisooctyl sulfosuccinate, 1.1% glycerol polyoxypropylene polyoxyethylene ether, and water as the balance.

[0034] The structural formula of 6-tridecyl-1,3,5-triazine-2,4-diamine is:

[0035] .

[0036] The preparation method of ferric glutamic acid-N,N-diacetate consists of the following steps:

[0037] ① Dissolve tetrasodium glutamate diacetate in deionized water to prepare a tetrasodium glutamate diacetate solution;

[0038] ② A ferric salt solution was prepared by dissolving ferric chloride hexahydrate in deionized water;

[0039] ③ Under stirring conditions, the iron salt solution prepared in step ② is added to the tetrasodium glutamate diacetate solution, controlling the reaction between the tetrasodium glutamate diacetate and Fe. 3+ The molar ratio of the two components was 1.2:1. Then, sodium hydroxide solution was added to adjust the pH of the reaction system to 9.0. The reaction was carried out at 53℃ for 1.5h. After the reaction was completed, the mixture was cooled to room temperature, filtered to remove insoluble matter, and glutamic acid-N,N-diacetic acid iron was prepared.

[0040] Wherein: the mass concentration of the tetrasodium diglutamate solution in step ① is 25%, and the mass concentration of the iron salt solution in step ② is 20%.

[0041] The preparation method of the oilfield composite desulfurizing agent described in Example 1 consists of the following steps:

[0042] (1) Add 60% of the total mass of deionized water to the reaction apparatus, add tetramethylguanidine lactate while stirring, and stir until completely dissolved;

[0043] (2) Add sodium diisooctyl sulfosuccinate and continue stirring until the solution is clear;

[0044] (3) Add 6-tetrazyl-1,3,5-triazine-2,4-diamine, heat to 41°C and stir until completely dispersed;

[0045] (4) Add glutamic acid-N,N-diacetic acid iron to the reaction system of step (3) and stir to mix well;

[0046] (5) Add glycerol polyoxypropylene polyoxyethylene ether and stir to mix evenly, then add the remaining deionized water and stir evenly to prepare the oilfield composite desulfurizer.

[0047] In step (1), the stirring speed is 400 r / min, the stirring time is 11 min, and the stirring temperature is room temperature.

[0048] In step (2), the stirring time is 16 min, the stirring speed is 400 r / min, and the stirring temperature is room temperature.

[0049] In step (3), the stirring speed is 800 r / min and the stirring time is 27 min.

[0050] In step (4), the stirring speed is 400 r / min, the stirring temperature is 36℃, and the stirring time is 11 min.

[0051] In step (5), the stirring speed is 400 r / min, the stirring temperature is 41℃, glycerol polyoxypropylene polyoxyethylene ether is added, and the mixture is stirred for 11 min. Then the remaining deionized water is added and the mixture is stirred for 21 min.

[0052] The oilfield composite desulfurizing agent prepared in Example 1 is a light yellow, transparent, uniform liquid with a pH value of 11.2. It did not separate into layers after being stored at 40°C for 30 days.

[0053] Example 2

[0054] The oilfield composite desulfurizer described in Example 2 has the following raw material composition by mass percentage: 12% 6-tetrazyl-1,3,5-triazine-2,4-diamine, 25% tetramethylguanidine lactate, 9% ferric glutamate-N,N-diacetate, 4.0% sodium diisooctyl sulfosuccinate, 1.0% glycerol polyoxypropylene polyoxyethylene ether, and water as the balance.

[0055] The structural formula of 6-tridecyl-1,3,5-triazine-2,4-diamine is:

[0056] .

[0057] The preparation method of ferric glutamic acid-N,N-diacetate consists of the following steps:

[0058] ① Dissolve tetrasodium glutamate diacetate in deionized water to prepare a tetrasodium glutamate diacetate solution;

[0059] ② A ferric salt solution was prepared by dissolving ferric chloride hexahydrate in deionized water;

[0060] ③ Under stirring conditions, the iron salt solution prepared in step ② is added to the tetrasodium glutamate diacetate solution, controlling the reaction between the tetrasodium glutamate diacetate and Fe. 3+ The molar ratio of the two components was 1.2:1. Then, sodium hydroxide solution was added to adjust the pH of the reaction system to 9.0. The reaction was carried out at 50℃ for 1.5h. After the reaction was completed, the mixture was cooled to room temperature, filtered to remove insoluble matter, and glutamic acid-N,N-diacetic acid iron was prepared.

[0061] Wherein: the mass concentration of the tetrasodium diglutamate solution in step ① is 25%, and the mass concentration of the iron salt solution in step ② is 20%.

[0062] The preparation method of the oilfield composite desulfurizing agent described in Example 2 consists of the following steps:

[0063] (1) Add 60% of the total mass of deionized water to the reaction apparatus, add tetramethylguanidine lactate while stirring, and stir until completely dissolved;

[0064] (2) Add sodium diisooctyl sulfosuccinate and continue stirring until the solution is clear;

[0065] (3) Add 6-tetrayl-1,3,5-triazine-2,4-diamine, heat to 40°C and stir until completely dispersed;

[0066] (4) Add glutamic acid-N,N-diacetic acid iron to the reaction system of step (3) and stir to mix well;

[0067] (5) Add glycerol polyoxypropylene polyoxyethylene ether and stir to mix evenly, then add the remaining deionized water and stir evenly to prepare the oilfield composite desulfurizer.

[0068] In step (1), the stirring speed is 400 r / min, the stirring time is 10 min, and the stirring temperature is room temperature.

[0069] In step (2), the stirring time is 17 min, the stirring speed is 400 r / min, and the stirring temperature is room temperature.

[0070] In step (3), the stirring speed is 800 r / min and the stirring time is 25 min.

[0071] In step (4), the stirring speed is 400 r / min, the stirring temperature is 38℃, and the stirring time is 12 min.

[0072] In step (5), the stirring speed is 400 r / min, the stirring temperature is 40℃, glycerol polyoxypropylene polyoxyethylene ether is added, and the mixture is stirred for 10 min. Then the remaining deionized water is added and the mixture is stirred for 20 min.

[0073] The oilfield composite desulfurizing agent prepared in Example 2 is a light yellow, transparent, uniform liquid with a pH value of 10.8. It does not separate into layers after being stored at 40°C for 30 days.

[0074] Example 3

[0075] The oilfield composite desulfurizer described in Example 3 has the following raw material composition by mass percentage: 14% 6-tetrazyl-1,3,5-triazine-2,4-diamine, 27% tetramethylguanidine lactate, 7% ferric glutamate-N,N-diacetate, 3.6% sodium diisooctyl sulfosuccinate, 1.3% glycerol polyoxypropylene polyoxyethylene ether, and water as the balance.

[0076] The structural formula of 6-tridecyl-1,3,5-triazine-2,4-diamine is:

[0077] .

[0078] The preparation method of ferric glutamic acid-N,N-diacetate consists of the following steps:

[0079] ① Dissolve tetrasodium glutamate diacetate in deionized water to prepare a tetrasodium glutamate diacetate solution;

[0080] ② A ferric salt solution was prepared by dissolving ferric chloride hexahydrate in deionized water;

[0081] ③ Under stirring conditions, the iron salt solution prepared in step ② is added to the tetrasodium glutamate diacetate solution, controlling the reaction between the tetrasodium glutamate diacetate and Fe. 3+ The molar ratio of the two components was 1.2:1. Then, sodium hydroxide solution was added to adjust the pH of the reaction system to 9.0. The reaction was carried out at 55℃ for 1.5h. After the reaction was completed, the mixture was cooled to room temperature, filtered to remove insoluble matter, and glutamic acid-N,N-diacetic acid iron was prepared.

[0082] Wherein: the mass concentration of the tetrasodium diglutamate solution in step ① is 25%, and the mass concentration of the iron salt solution in step ② is 20%.

[0083] The preparation method of the oilfield composite desulfurizing agent described in Example 3 consists of the following steps:

[0084] (1) Add 60% of the total mass of deionized water to the reaction apparatus, add tetramethylguanidine lactate while stirring, and stir until completely dissolved;

[0085] (2) Add sodium diisooctyl sulfosuccinate and continue stirring until the solution is clear;

[0086] (3) Add 6-tetrazyl-1,3,5-triazine-2,4-diamine, heat to 42°C and stir until completely dispersed;

[0087] (4) Add glutamic acid-N,N-diacetic acid iron to the reaction system of step (3) and stir to mix well;

[0088] (5) Add glycerol polyoxypropylene polyoxyethylene ether and stir to mix evenly, then add the remaining deionized water and stir evenly to prepare the oilfield composite desulfurizer.

[0089] In step (1), the stirring speed is 400 r / min, the stirring time is 13 min, and the stirring temperature is room temperature.

[0090] In step (2), the stirring time is 15 min, the stirring speed is 400 r / min, and the stirring temperature is room temperature.

[0091] In step (3), the stirring speed is 800 r / min and the stirring time is 30 min.

[0092] In step (4), the stirring speed is 400 r / min, the stirring temperature is 35℃, and the stirring time is 10 min.

[0093] In step (5), the stirring speed is 400 r / min, the stirring temperature is 42℃, glycerol polyoxypropylene polyoxyethylene ether is added, and the mixture is stirred for 12 min. Then the remaining deionized water is added and the mixture is stirred for 23 min.

[0094] The oilfield composite desulfurizing agent prepared in Example 3 is a light yellow, transparent, uniform liquid with a pH value of 11.0. It does not separate into layers after being stored at 40°C for 30 days.

[0095] Comparative Example 1

[0096] The preparation method of the oilfield composite desulfurizer described in Comparative Example 1 is the same as that in Example 1, the only difference being the raw material composition. The oilfield composite desulfurizer described in Comparative Example 1, by mass percentage, has the following raw material composition: tetramethylguanidine lactate 26%, ferric glutamate-N,N-diacetate 8%, sodium diisooctyl sulfosuccinate 3.8%, glycerol polyoxypropylene polyoxyethylene ether 1.1%, and water as the balance.

[0097] Comparative Example 2

[0098] The preparation method of the oilfield composite desulfurizer described in Comparative Example 2 is the same as that in Example 1, except that the raw material composition is different. The oilfield composite desulfurizer described in Comparative Example 2, by mass percentage, has the following raw material composition: 13% 6-tetrazyl-1,3,5-triazine-2,4-diamine, 8% ferric glutamic acid-N,N-diacetic acid, 3.8% sodium diisooctyl sulfosuccinate, 1.1% glycerol polyoxypropylene polyoxyethylene ether, and water as the balance.

[0099] Comparative Example 3

[0100] The preparation method of the oilfield composite desulfurizer described in Comparative Example 3 is the same as that in Example 1, the only difference being the raw material composition. The oilfield composite desulfurizer described in Comparative Example 3, by mass percentage, has the following raw material composition: 13% 6-tetrazyl-1,3,5-triazine-2,4-diamine, 26% tetramethylguanidine lactate, 3.8% sodium diisooctyl sulfosuccinate, 1.1% glycerol polyoxypropylene polyoxyethylene ether, and water as the balance.

[0101] The desulfurization capacity testing method refers to ASTM D4810-88 (1999), "Standard Method for Determination of Hydrogen Sulfide Content in Natural Gas by Colorimetric Detection Tube Method". First, 1L of oilfield produced fluid is poured into a sealed container, which is immediately sealed and placed in a shaking chamber for 10 minutes. A gas sample is taken from the top of the sealed container to test the hydrogen sulfide concentration, which is recorded as the blank hydrogen sulfide concentration C0. A certain amount of desulfurizing agent is added to a sealed container, and then 1L of oilfield produced fluid is poured into it. The container is immediately sealed and placed in a shaking chamber for 10 minutes. A gas sample is taken from the top of the container to test the hydrogen sulfide concentration, which is recorded as the hydrogen sulfide concentration C.

[0102] The desulfurization performance of a desulfurizing agent is evaluated by its desulfurization rate; a higher desulfurization rate indicates better desulfurization performance. The desulfurization rate refers to the percentage decrease in hydrogen sulfide content measured before and after adding the desulfurizing agent to an oil sample. The desulfurization rate is calculated using the following formula: X = (C0 - C) / C0 * 100%, where X is the desulfurization rate, C0 is the hydrogen sulfide content measured before adding the desulfurizing agent, and C is the desulfurizing agent content measured after adding the desulfurizing agent. The test platform used crude oil from an oilfield, with a desulfurizing agent concentration of 100 mg / L and a hydrogen sulfide content of 2500 mg / L. The desulfurization rate was tested using the above method, and the results are shown in Table 1 below.

[0103] Table 1. Test results of desulfurization performance of desulfurizing agent

[0104]

[0105] As shown in Table 1 above, the desulfurization rate of the oilfield composite desulfurizer prepared in Examples 1-3 of this application is much higher than that of Comparative Examples 1-3. Comparative Examples 1-3 are missing raw materials 6-tetrazyl-1,3,5-triazine-2,4-diamine, tetramethylguanidine lactate, and glutamic acid-N,N-diacetic acid iron, respectively, which leads to a significant decrease in the desulfurization efficiency of the prepared oilfield composite desulfurizer. Comparative Examples 1-3 show that the raw materials of the oilfield composite desulfurizer prepared in this application have a synergistic effect.

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

Claims

1. An oilfield composite desulfurizing agent, characterized in that: The raw material composition, by mass percentage, is as follows: 12-14% 6-tetrazine-1,3,5-triazine-2,4-diamine, 25-27% tetramethylguanidine lactate, 7-9% ferric glutamate-N,N-diacetate, 3.6-4.0% sodium diisooctyl sulfosuccinate, 1.0-1.3% glycerol polyoxypropylene polyoxyethylene ether, and water as the balance.

2. The oilfield composite desulfurizing agent according to claim 1, characterized in that: The structural formula of 6-tridecyl-1,3,5-triazine-2,4-diamine is: 。 3. The oilfield composite desulfurizing agent according to claim 1, characterized in that: The preparation method of ferric glutamic acid-N,N-diacetate consists of the following steps: ① Dissolve tetrasodium glutamate diacetate in deionized water to prepare a tetrasodium glutamate diacetate solution; ② A ferric salt solution was prepared by dissolving ferric chloride hexahydrate in deionized water; ③ Under stirring conditions, the iron salt solution prepared in step ② is added to the tetrasodium glutamate diacetate solution, controlling the reaction between the tetrasodium glutamate diacetate and Fe. 3+ The molar ratio of the two components was 1.2:

1. Then, sodium hydroxide solution was added to adjust the pH of the reaction system to 9.

0. The reaction was carried out at 50-55℃ for 1.5h. After the reaction was completed, the mixture was cooled to room temperature, filtered to remove insoluble matter, and glutamic acid-N,N-diacetic acid iron was prepared.

4. The oilfield composite desulfurizing agent according to claim 3, characterized in that: In step ①, the mass concentration of the tetrasodium diglutamate solution is 25%, and in step ②, the mass concentration of the iron salt solution is 20%.

5. A method for preparing the oilfield composite desulfurizing agent according to claim 1, characterized in that: It consists of the following steps: (1) Add 60% of the total mass of deionized water to the reaction apparatus, add tetramethylguanidine lactate while stirring, and stir until completely dissolved; (2) Add sodium diisooctyl sulfosuccinate and continue stirring until the solution is clear; (3) Add 6-tetrazyl-1,3,5-triazine-2,4-diamine, heat to 40-42℃ and stir until completely dispersed; (4) Add glutamic acid-N,N-diacetic acid iron to the reaction system of step (3) and stir to mix well; (5) Add glycerol polyoxypropylene polyoxyethylene ether and stir to mix evenly, then add the remaining deionized water and stir evenly to prepare the oilfield composite desulfurizer.

6. The method for preparing the oilfield composite desulfurizing agent according to claim 5, characterized in that: In step (1), the stirring speed is 400 r / min, the stirring time is 10-13 min, and the stirring temperature is room temperature.

7. The preparation method of the oilfield composite desulfurizing agent according to claim 5, characterized in that: In step (2), the stirring time is 15-17 min, the stirring speed is 400 r / min, and the stirring temperature is room temperature.

8. The method for preparing the oilfield composite desulfurizing agent according to claim 5, characterized in that: In step (3), the stirring speed is 800 r / min and the stirring time is 25-30 min.

9. The method for preparing the oilfield composite desulfurizing agent according to claim 5, characterized in that: In step (4), the stirring speed is 400 r / min, the stirring temperature is 35-38℃, and the stirring time is 10-12 min.

10. The method for preparing the oilfield composite desulfurizing agent according to claim 5, characterized in that: In step (5), the stirring speed is 400 r / min, the stirring temperature is 40-42℃, glycerol polyoxypropylene polyoxyethylene ether is added, and the mixture is stirred for 10-12 min. Then the remaining deionized water is added and the mixture is stirred for 20-23 min.

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