Alkyl indole polyether carboxylate surfactant and preparation method and application thereof

Abstract

The present invention provides an alkyl indole polyether carboxylate surfactant and a preparation method and application thereof. The alkyl indole polyether carboxylate surfactant has a molecular formula shown in Formula I, wherein R is C1 to C 20 Hydrocarbon group; R2 is hydrogen or C1-C6 hydrocarbon group, R3 is C1-C6 hydrocarbon group; n is any integer from 1 to 20, m is any integer from 0 to 30; M is any one of alkali metal and alkaline earth metal, when M is alkali metal, x is 1, when M is alkaline earth metal, x is 0.5. The alkyl indole polyether carboxylate surfactant of the present invention still has a good solubilization effect under the conditions of alkali-free, high temperature and high salt, and can improve the recovery rate of crude oil. #imgabs0#

Description

Technical Field

[0001] The invention relates to an alkyl indole polyether carboxylate type surfactant and a preparation method and application thereof. Background Art

[0002] Tertiary oil recovery is a comparison between primary oil recovery and secondary oil recovery. In layman's terms, in the early stage of oil recovery, only the natural energy of the formation is used to recover oil, which is called primary oil recovery, and its recovery rate is only about 10%. The method of recovering oil by adding energy to the formation, such as water injection and gas injection, is called secondary oil recovery. At present, a large number of oil fields in the world have adopted secondary oil recovery methods, but the recovery rate can generally only reach about 25% to 40%. Tertiary oil recovery is a method of using physical, chemical and biological means to continue to recover the remaining oil underground to increase the recovery rate of crude oil.

[0003] Among the tertiary oil recovery technologies, composite flooding (polymer-surfactant) has become a hot topic in current research, and practice has proved that this technology can effectively improve the recovery rate of crude oil. The role of the surfactant is to form an ultra-low interfacial tension with crude oil, so that the residual oil (oil film, dead-end oil, etc.) underground after polymer flooding can be restarted, thereby improving the recovery rate.

[0004] According to E r =E v *E d , where E r Indicates recovery factor, %; E v Indicates the sweep coefficient, %; E d For oil washing efficiency, %. Therefore, to improve the recovery rate, it is necessary to improve the sweep coefficient and oil washing efficiency. The properties of surfactants directly determine the oil washing efficiency of composite oil displacement agents in actual production. Therefore, the development of new surfactants is of great significance to my country's tertiary oil recovery industry.

[0005] At present, surfactants have been successfully applied in ordinary oil reservoirs (Class I and II oil reservoirs) (CN1458219A). However, for high-temperature and high-mineralization oil reservoirs, surfactants that are more effective for Class I and II oil reservoirs cannot effectively reduce interfacial tension and improve recovery, and therefore cannot perform the required tasks, which is manifested in variable chemical structures, severe chromatographic separation, and the like. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide an alkyl indole polyether carboxylate type surfactant and a preparation method and application thereof in order to solve the technical problems existing in the prior art. The alkyl indole polyether carboxylate type surfactant of the present invention still has a good solubilization effect under alkali-free, high temperature and high salt conditions, and can improve crude oil recovery.

[0007] The objectives of the present invention are achieved through the following technical solutions.

[0008] In a first aspect, the present invention provides an alkyl indole polyether carboxylate type surfactant, wherein the alkyl indole polyether carboxylate type surfactant has a molecular formula as shown in Formula I,

[0009]

[0010] In Formula I, R is C 1 ~C 20 Hydrocarbon; R 2 is hydrogen or C 1 ~C 6 Hydrocarbon, R 3 C 1 ~C 6 Hydrocarbon group; n is any integer from 1 to 20, m is any integer from 0 to 30; M is any one of an alkali metal and an alkaline earth metal, when M is an alkali metal, x is 1, and when M is an alkaline earth metal, x is 0.5.

[0011] According to the alkyl indole polyether carboxylate surfactant provided by the present invention, wherein in formula I, R is C 1 ~C 20 Alkyl, preferably C 5 ~C 18 Alkyl, more preferably C 12 ~C 18 In some specific embodiments, R in Formula I is hexadecyl.

[0012] According to the alkyl indole polyether carboxylate surfactant provided by the present invention, in Formula I, R 2 is hydrogen or C 1 ~C 6 Alkyl, R 3 C 1 ~C 6 Alkyl. Suitable for use as R in formula I 2 and R 3 C 1 ~C 6 Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, butyl, pentyl, and hexyl.

[0013] According to the alkyl indole polyether carboxylate surfactant provided by the present invention, wherein in formula I, EO represents a polyoxyethylene repeating unit, i.e., -CH 2 CH 2 O-; PO represents polyoxypropylene repeating unit, i.e. -CH(CH 3 )CH 2 O-.

[0014] In some embodiments, in Formula I, n is any integer from 1 to 15, preferably any integer from 2 to 15, and more preferably any integer from 4 to 15.

[0015] In some embodiments, in Formula I, m is any integer from 0 to 20, preferably any integer from 2 to 15, more preferably any integer from 2 to 10, and most preferably any integer from 4 to 10.

[0016] In some embodiments, in Formula I, m+n is any integer from 4 to 30, preferably any integer from 4 to 20, and more preferably any integer from 8 to 18.

[0017] According to the alkyl indole polyether carboxylate surfactant provided by the present invention, the alkali metal is sodium or potassium; and / or the alkaline earth metal is calcium or magnesium.

[0018] In a second aspect, the present invention provides a method for preparing an alkyl indole polyether carboxylate surfactant, wherein the preparation method comprises the following steps:

[0019] a. reacting the alkylphenylhydrazine represented by formula II with the ketone compound represented by formula III in the presence of an acidic catalyst to obtain a first intermediate represented by formula IV;

[0020]

[0021] b. reacting the first intermediate of formula IV with propylene oxide and ethylene oxide in the presence of a basic catalyst A to obtain a second intermediate of formula V;

[0022]

[0023] c. reacting the second intermediate represented by formula V with chloroacetate in the presence of a basic catalyst B to obtain an alkyl indole polyether carboxylate surfactant represented by formula I;

[0024]

[0025] According to the preparation method provided by the present invention, wherein the acidic catalyst in step a) is a protonic acid or a Lewis acid, preferably a Lewis acid. Examples of Lewis acids suitable for use in the present invention include, but are not limited to, zinc chloride.

[0026] In some embodiments, in step a), based on the total weight of the alkylphenylhydrazine shown in II and the ketone compound shown in formula III, the amount of Lewis acid used is 0.1 wt% to 99 wt%, preferably 0.5 to 5 wt%, and more preferably 2 to 4 wt%.

[0027] According to the preparation method provided by the present invention, the reaction in step a) is carried out in the presence of solvent A. The solvent A in step a) can be acetic acid, and the weight ratio of solvent A to the alkylphenylhydrazine shown in formula II and the ketone compound shown in formula III is preferably 1 to 4:1, preferably 1.75 to 2.5:1.

[0028] According to the preparation method provided by the present invention, in step a), the molar ratio of the alkylphenylhydrazine represented by formula II to the ketone compound represented by formula III is 10:1 to 1:10, preferably 2:1 to 1:2.

[0029] According to the preparation method provided by the present invention, the reaction temperature in step a) is 50-80° C., preferably 50-60° C.; the reaction time is 1-6 hours, preferably 4-6 hours.

[0030] According to the preparation method provided by the present invention, the alkaline catalyst A in step b) and the alkaline catalyst B in step c) are the same or different, and are independently alkali metal hydroxides or alkali metal alkoxides.

[0031] Examples of alkali metal hydroxides suitable for use in the present invention include, but are not limited to, sodium hydroxide and potassium hydroxide. Examples of alkali metal alkoxides suitable for use in the present invention include, but are not limited to, sodium methoxide, potassium methoxide, sodium ethoxide, and potassium ethoxide.

[0032] According to the preparation method provided by the present invention, the amount of the alkaline catalyst A in step b) is 0.3-6% by weight based on the weight of the first intermediate.

[0033] According to the preparation method provided by the present invention, the reaction conditions in step b) are as follows: the reaction temperature is 85-160° C., preferably 120-160° C.; the reaction pressure is less than 0.80 MPa gauge pressure, preferably 0.30-0.60 MPa gauge pressure.

[0034] According to the preparation method provided by the present invention, wherein, in step b), propylene oxide and ethylene oxide are added sequentially for reaction. In the present invention, the amount of propylene oxide and ethylene oxide can be determined according to the structure of the target alkyl indole polyether carboxylate surfactant. In particular, propylene oxide is added in an amount of 50-150% excess, such as 90-110% relative to the stoichiometric ratio, and / or ethylene oxide is added in an amount of 0.5-30% excess, preferably 1-20%, more preferably 1-15% excess relative to the stoichiometric ratio.

[0035] According to the preparation method provided by the present invention, wherein in step c), the molar ratio of the second intermediate, the chloroacetate and the alkaline catalyst B is 1:(1-6):(1-6), preferably 1:2-3:2-3.

[0036] According to the preparation method provided by the present invention, the reaction in step c) is carried out in the presence of solvent B. In the present invention, the solvent B in step c) can be selected from at least one of C6-C9 aromatic hydrocarbons, for example, benzene and / or toluene, and the weight ratio of solvent B to the second intermediate and chloroacetate is preferably 0.5-3:1, more preferably 1-2.5:1.

[0037] According to the preparation method provided by the present invention, the reaction conditions in step c) are as follows: reaction temperature 50-200° C., preferably 60-120° C., more preferably 60-90° C.; reaction time 3-15 hours, preferably 4-12 hours.

[0038] In some preferred embodiments, step c) comprises:

[0039] c1) reacting the alkaline catalyst B and the second intermediate represented by formula V at a temperature of 60 to 80° C. for 2 to 4 hours under stirring conditions and in the presence of solvent B to obtain a pre-reaction system;

[0040] c2) adding chloroacetate to the pre-reaction system obtained in step c1) and reacting at a temperature of 70 to 90° C. for 2 to 8 hours.

[0041] According to the preparation method provided by the present invention, in step c), any method known in the art can be used for separation and purification to obtain various product forms of alkyl indole polyether carboxylate surfactants.

[0042] In some embodiments, step c) further comprises:

[0043] c3) adding an acid to the reaction product of the second intermediate represented by formula V and chloroacetate, adjusting the pH of the aqueous phase to 1 to 3, and separating to obtain an organic phase;

[0044] c4) After concentrating the organic phase, adding alkali to obtain the alkyl indole polyether carboxylate surfactant shown in formula I.

[0045] Of course, in step c4), after the organic phase is concentrated, the acid product form of the alkyl indole polyether carboxylate surfactant can be directly obtained.

[0046] In a third aspect, the present invention further provides an application of an alkyl indole polyether carboxylate surfactant or an alkyl indole polyether carboxylate surfactant prepared by the above preparation method in tertiary oil recovery.

[0047] The present invention has the following advantages:

[0048] (1) The alkyl indole polyether carboxylate surfactant of the present invention can still form 10-3 The ultra-low interfacial tension of mN / m has good solubilization effect, good oil displacement effect, can improve crude oil recovery rate, and has excellent temperature and salt resistance.

[0049] (2) The alkyl indole polyether carboxylate surfactant of the present invention can be used for tertiary oil recovery. No alkali is required (no alkali is included) during use, which can greatly reduce the huge damage of alkali to the formation and oil wells, and meets environmental protection requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is the interfacial tension curve of the alkyl indole polyether carboxylate surfactant of the present invention. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with specific embodiments, but they do not constitute any limitation to the present invention.

[0052] Example 1 Synthesis of 2,3-dimethylhexadecyl indole

[0053] To a 2L reactor equipped with a stirring device, 332 g (1 mol) of 4-hexadecylphenylhydrazine, 72 g (1 mol) of butanone and 13.6 g (0.1 mol) of zinc chloride were added, and 808 g of acetic acid was added as a solvent. The mixture was heated to 60°C and reacted for 5 hours. After the raw material disappeared by LC detection, the reaction was stopped by cooling, the organic phase was separated, and the crude product was obtained by rotary evaporation. The crude product was subjected to rapid column chromatography to obtain 2,3-dimethyloctadecylindole with a yield of 85%.

[0054] Example 2 Synthesis of 3-methylhexadecyl indole

[0055] To a 2L reactor equipped with a stirring device, 332 g (1 mol) of 4-hexadecylphenylhydrazine, 58 g (1 mol) of propionaldehyde and 13.6 g (0.1 mol) of zinc chloride were added, and 780 g of acetic acid was added as a solvent. The mixture was heated to 60°C and reacted for 5 hours. After the raw material disappeared by TLC detection, the temperature was lowered to stop the reaction, the organic phase was separated, and the crude product was obtained by rotary evaporation. The crude product was subjected to rapid column chromatography to obtain 3-dimethylhexadecylindole in a yield of 90%.

[0056] Example 3 Synthesis of 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=4)

[0057] 367 g (1 mol) of 2,3-dimethylhexadecyl indole and 5.6 g of potassium hydroxide were added to a 2L pressure reactor equipped with a stirring device. When heated to 85±5°C, the vacuum system was turned on and dehydrated for 1 hour under high vacuum. Then, the system was replaced with nitrogen 3 to 4 times. The reaction temperature of the system was adjusted to 150°C and 469.8 g (8.1 mol) of propylene oxide was slowly introduced, and the gauge pressure was controlled to be ≤0.60 MPa. After the reaction of propylene oxide was completed, the temperature was adjusted to 140°C and 178.2 g (4.05 mol) of ethylene oxide was slowly introduced, and the gauge pressure was controlled to be ≤0.40 MPa. After the reaction was completed, the temperature was lowered to 90°C, low boiling substances were removed in vacuo, and after cooling, the system was neutralized and dehydrated to obtain 770 g of 2,3-dimethylhexadecyl indole polyoxypropylene (4) polyoxyethylene (4) ether, with a yield of 98%.

[0058] Example 4 Synthesis of 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=10)

[0059] 367 g (1 mol) of 2,3-dimethylhexadecyl indole and 5.6 g of potassium hydroxide were added to a 2L pressure reactor equipped with a stirring device. When heated to 85±5°C, the vacuum system was turned on, and dehydrated for 1 hour under high vacuum. Then, the system was replaced with nitrogen 3 to 4 times. The reaction temperature of the system was adjusted to 150°C, and 469.8 g (8.1 mol) of propylene oxide was slowly introduced, and the gauge pressure was controlled to be ≤0.60 MPa. After the reaction of propylene oxide was completed, the temperature was adjusted to 140°C, and 482 g (10.95 mol) of ethylene oxide was slowly introduced, and the gauge pressure was controlled to be ≤0.40 MPa. After the reaction was completed, the temperature was lowered to 90°C, low boiling substances were removed in vacuo, and after cooling, the system was neutralized and dehydrated to obtain 980 g of 2,3-dimethylhexadecyl indole polyoxypropylene (4) polyoxyethylene (4) ether, with a yield of 97%.

[0060] Example 5 Synthesis of 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=13)

[0061] 374 g (1 mol) of 2,3-dimethylhexadecyl indole and 5.6 g of potassium hydroxide were added to a 2L pressure reactor equipped with a stirring device. When heated to 80-90°C, the vacuum system was turned on and dehydrated for 1 hour under high vacuum. Then, the system was replaced with nitrogen 3-4 times. The reaction temperature of the system was adjusted to 150°C and 469.8 g (8.1 mol) of propylene oxide was slowly introduced, and the pressure was controlled to be ≤0.60 MPa. After the reaction of propylene oxide was completed, the temperature was adjusted to 140°C and 602 g (13.68 mol) of ethylene oxide was slowly introduced, and the pressure was controlled to be ≤0.40 MPa. After the reaction was completed, the temperature was lowered to 90°C, low boiling substances were removed in vacuo, and after cooling, the system was neutralized and dehydrated to obtain 1020 g of 2,3-dimethylhexadecyl indole polyoxypropylene (4) polyoxyethylene (13) ether, with a yield of 93.5%.

[0062] Example 6 Synthesis of 2,3-dimethylhexadecyl indole polyoxypropylene (n=4) polyoxyethylene (n=4) carboxylate sodium

[0063] 775 g (about 1 mole) of 2,3-dimethylhexadecyl indole polyoxypropylene (n=4) polyoxyethylene (n=4) was added to a 2L pressure reactor equipped with a stirring device, 1.5L of benzene was added to dissolve, and then 80 g of NaOH was added. After reacting at 80°C for 4 hours, 290 g of sodium chloroacetate was added, the temperature was maintained, and the reaction was performed for 6 hours. Then the temperature was lowered, acidified to a pH of 2 in the aqueous phase, and washed with water to obtain about 500 g of the product 2,3-dimethylhexadecyl indole polyoxypropylene (n=4) polyoxyethylene (n=4) carboxylic acid, with a yield of 96.5%. NaOH was added to obtain sodium 2,3-dimethylhexadecyl indole polyoxypropylene (n=4) polyoxyethylene (n=4) carboxylate.

[0064] Example 7 Synthesis of 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=10) carboxylate sodium

[0065] 520 g (about 0.5 mole) of 2,3-dimethylhexadecyl indole polyoxypropylene (n=10) polyoxyethylene (n=10) was added to a 2L pressure reactor equipped with a stirring device, 1.5L of benzene was added to dissolve, and then 40 g of NaOH was added. After reacting at 80°C for 4 hours, 150 g of sodium chloroacetate was added, the temperature was maintained, and the reaction was performed for 6 hours. Then the temperature was lowered, acidified to a pH of 2 in the aqueous phase, and washed with water to obtain about 520 g of the product 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=10) carboxylic acid, with a yield of 94.8%. NaOH was added to obtain sodium 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=10) carboxylate.

[0066] Example 8 Synthesis of 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=13) carboxylate sodium

[0067] 585 g (about 0.5 mole) of 2,3-dimethylhexadecyl indole polyoxypropylene (n=10) polyoxyethylene (n=4) was added to a 2L pressure reactor equipped with a stirring device, 1.5L of benzene was added to dissolve, and then 45 g of NaOH was added. After reacting at 80°C for 4 hours, 155 g of sodium chloroacetate was added, the temperature was maintained, and the reaction was performed for 6 hours. Then the temperature was lowered, acidified to a pH of 2 in the aqueous phase, and washed with water to obtain a product of about 600 g of 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=13) carboxylic acid, with a yield of 97.7%. NaOH was added to obtain sodium 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=13) carboxylate.

[0068] Example 9

[0069] Simulated brine with different mineralization degrees was prepared respectively, and its composition is shown in Table 1.

[0070] Table 1 Composition of simulated brine

[0071] Simulated salt water Total mineralization (NaCl) mg / L A 0 B 10000 C 20000 D 40000 E 60000 F 80000 G 10000 H 150000 I 200000 J 250000 K 300000

[0072] Using the simulated brine A to K in Table 1, a 4 wt% solution of 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=4) sodium carboxylate (Example 6), and n-octane as the simulated oil, the experimental temperature was 80°C, and a phase experiment was conducted to simulate the surfactant and oil reservoir conditions in the formation to determine the effect of the surfactant on the volume expansion of crude oil. After 30 days of observation, the solubilization effect of the surfactant on the simulated oil in the simulated brine with a total mineralization of 0 to 15W is shown in Table 2.

[0073] Table 2 Solubilization effect of alkyl indole polyether carboxylate surfactants

[0074] Salinity (NaCl) mg / L Water solubilization parameters (volume) Oil solubilization parameters (volume) 20000 7.5 12.5 40000 5 25 60000 2.5 7.5

[0075] It can be seen from Table 2 that as the salinity increases, the solubilization effect decreases. It can be considered that the alkyl indole polyether carboxylate surfactant has a higher surface activity in water with a mineralization degree lower than 15W.

[0076] Example 10

[0077] Prepare the simulated brine A to K in Table 1, 4 wt% 2,3-dimethylhexadecyl indole polyoxypropylene (m=4) polyoxyethylene (n=10) sodium carboxylate solution (Example 7), select n-octane as the simulated oil, and conduct phase state experiments at an experimental temperature of 80°C to simulate the surfactant and oil reservoir conditions in the formation to determine the effect of the surfactant on the volume expansion of crude oil. After 30 days of observation, the solubilization effect of the surfactant on the simulated oil in the simulated brine with a total mineralization of 1 to 10W is shown in Table 3.

[0078] Table 3 Solubilization effect of alkyl indole polyether carboxylate surfactants

[0079] Salinity (NaCl) mg / L Water solubilization parameters (volume) Oil solubilization parameters (volume) 40000 25 5 60000 25 5 80000 25 5 10000 25 2.5

[0080] It can be seen from Table 3 that the alkyl indole polyether carboxylate surfactant of the present invention has a good solubilizing effect.

[0081] Embodiment 11

[0082] (1) Using the synthetic 2,3-dimethylhexadecylindole prepared in Example 1, 2,3-dimethylhexadecylindole polyoxypropylene (m=4) polyoxyethylene (n=7) was prepared according to the preparation method in Example 3, except that the amount of ethylene oxide used was 354 g (8.05 mol). The yield of the obtained 2,3-dimethylhexadecylindole polyoxypropylene (m=4) polyoxyethylene (n=7) was 97.6%.

[0083] (2) The method of Example 7 was used to prepare sodium 2,3-dimethylhexadecylindolepolyoxypropylene (m=4)polyoxyethylene (n=7) carboxylate, except that 0.5 mol of 2,3-dimethylhexadecylindolepolyoxypropylene (m=4)polyoxyethylene (n=7) was used instead of 2,3-dimethylhexadecylindolepolyoxypropylene (n=10)polyoxyethylene (n=4), and the obtained sodium 2,3-dimethylhexadecylindolepolyoxypropylene (m=4)polyoxyethylene (n=7) carboxylate was recorded as "PO4-EO7 COONa".

[0084] PO4-EO7 COONa was prepared into a solution with a concentration of 0.1 wt% using simulated brine C. The interfacial tension between the solution and n-octane as the simulated oil was measured using an American TX-500C spinning drop interfacial tension meter. The results are shown in Figure 1 The test conditions are as follows: temperature 85°C, speed 4500 rpm.

[0085] Depend on Figure 1 It can be seen that the alkyl indole polyether carboxylate surfactant of the present invention can still form 10 -3 Ultra-low interfacial tension of mN / m.

[0086] In summary, the alkyl indole polyether carboxylate surfactant of the present invention still has a good solubilization effect under the conditions of alkali-free, high temperature and high salt, and can improve the recovery rate of crude oil.

[0087] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. Alkyl indole polyether carboxylate surfactant, wherein: The alkyl indole polyether carboxylate surfactant has a structural formula shown in Formula I, In Formula I, R is C5~C 20 Alkyl; R2 is hydrogen or C1-C6 alkyl, R3 is C1-C6 alkyl; n is any integer from 1 to 20, m is any integer from 0 to 20; M is any one of alkali metal and alkaline earth metal, when M is alkali metal, x is 1, when M is alkaline earth metal, x is 0.5; EO represents -CH2CH2O-; PO represents -CH(CH3)CH2O-.

2. The alkyl indole polyether carboxylate surfactant according to claim 1, characterized in that: In Formula I, R is C5~C 18 Alkyl; and / or, In formula I, the C1-C6 alkyl group is selected from methyl, ethyl, propyl, butyl, pentyl or hexyl.

3. The alkyl indole polyether carboxylate surfactant according to claim 2, characterized in that: In Formula I, R is C 12 ~C 18 alkyl.

4. The alkyl indole polyether carboxylate surfactant according to any one of claims 1 to 3, characterized in that: In formula I, n is any integer from 1 to 15; and / or, In formula I, m is any integer between 2 and 15; and / or, In formula I, m+n is any integer from 4 to 30.

5. The alkyl indole polyether carboxylate surfactant according to claim 4, characterized in that: In formula I, n is any integer from 2 to 15; and / or, In formula I, m is any integer between 2 and 10; and / or, In formula I, m+n is any integer from 4 to 20.

6. The alkyl indole polyether carboxylate surfactant according to claim 5, characterized in that: In formula I, n is any integer from 4 to 15; and / or, In formula I, m is any integer from 4 to 10; and / or, In formula I, m+n is any integer between 8 and 18.

7. The alkyl indole polyether carboxylate surfactant according to any one of claims 1 to 3, characterized in that: The alkali metal is sodium or potassium; and / or the alkaline earth metal is calcium or magnesium.

8. The method for preparing the alkyl indole polyether carboxylate surfactant according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: a. reacting the alkylphenylhydrazine represented by formula II with the ketone compound represented by formula III in the presence of an acidic catalyst to obtain a first intermediate represented by formula IV; b. reacting the first intermediate of formula IV with propylene oxide and ethylene oxide in the presence of a basic catalyst A to obtain a second intermediate of formula V; c. reacting the second intermediate represented by formula V with chloroacetate in the presence of a basic catalyst B to obtain an alkyl indole polyether carboxylate surfactant represented by formula I; 9. The preparation method according to claim 8, characterized in that: The acidic catalyst in step a) is a protonic acid or a Lewis acid; and / or In step a), the molar ratio of the alkylphenylhydrazine represented by formula II to the ketone compound represented by formula III is 10:1 to 1:10; and / or The reaction temperature in step a) is 50-80° C. and the reaction time is 1-6 hours.

10. The preparation method according to claim 9, characterized in that: The acidic catalyst in step a) is a Lewis acid; and / or Based on the total weight of the alkylphenylhydrazine represented by formula II and the ketone compound represented by formula III, the amount of Lewis acid used is 0.1 wt% to 99 wt%; and / or In step a), the molar ratio of the alkylphenylhydrazine represented by formula II to the ketone compound represented by formula III is 2:1 to 1:2; and / or The reaction temperature in step a) is 50-60° C. and the reaction time is 4-6 hours.

11. The preparation method according to claim 10, characterized in that: The acidic catalyst in step a) is zinc chloride; and / or Based on the total weight of the alkylphenylhydrazine represented by formula II and the ketone compound represented by formula III, the amount of Lewis acid used is 0.5 to 5 weight %.

12. The preparation method according to claim 11, characterized in that: Based on the total weight of the alkylphenylhydrazine represented by formula II and the ketone compound represented by formula III, the amount of Lewis acid used is 2 to 4 weight %.

13. The preparation method according to any one of claims 8 to 12, characterized in that: The alkaline catalyst A in step b) and the alkaline catalyst B in step c) are the same or different, and are each independently an alkali metal hydroxide or an alkali metal alkoxide; and / or Based on the weight of the first intermediate, the amount of the basic catalyst A in step b) is 0.3 to 6 weight %; and / or The reaction conditions in step b) are as follows: the reaction temperature is 85-160° C.; and the reaction pressure is less than 0.80 MPa gauge pressure.

14. The preparation method according to claim 13, characterized in that: The reaction conditions in step b) are as follows: the reaction temperature is 120-160° C.; and the reaction pressure is 0.30-0.60 MPa gauge pressure.

15. The preparation method according to any one of claims 8 to 12, characterized in that: In step c), the molar ratio of the second intermediate, the chloroacetate and the alkaline catalyst B is 1:(1-6):(1-6); and / or The reaction in step c) is carried out in the presence of a solvent B, wherein the solvent B in step c) is selected from at least one of C6 to C9 aromatic hydrocarbons.

16. The preparation method according to claim 15, characterized in that: In step c), the molar ratio of the second intermediate, the chloroacetate and the alkaline catalyst B is 1:(2-3):(2-3); and / or The solvent B in step c) is selected from benzene and / or toluene; and / or The weight ratio of solvent B to the second intermediate and chloroacetate is (0.5-3):

1.

17. The preparation method according to claim 16, characterized in that: The weight ratio of solvent B to the second intermediate and chloroacetate is (1-2.5):

1.

18. The preparation method according to any one of claims 8 to 12, characterized in that: The reaction conditions in step c) are as follows: reaction temperature 50-200° C.; reaction time 3-15 hours.

19. The preparation method according to claim 18, characterized in that: The reaction conditions in step c) are as follows: reaction temperature is 60-120° C.; reaction time is 4-12 hours; and / or Step c) comprises: c1) reacting the alkaline catalyst B and the second intermediate represented by formula V at a temperature of 60 to 80° C. for 2 to 4 hours under stirring conditions and in the presence of solvent B to obtain a pre-reaction system; c2) adding chloroacetate to the pre-reaction system obtained in step c1) and reacting at a temperature of 70 to 90° C. for 2 to 8 hours.

20. The preparation method according to claim 19, characterized in that: The reaction conditions in step c) are as follows: the reaction temperature is 60-90°C.

21. Use of the alkyl indole polyether carboxylate type surfactant according to any one of claims 1 to 7 or the alkyl indole polyether carboxylate type surfactant prepared by the preparation method according to any one of claims 8 to 20 in tertiary oil recovery.

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