Surfactant, preparation method thereof and permeability-enhancing fracturing fluid system

Abstract

The invention relates to the technical field of oil and gas well reservoir transformation, and provides a surfactant, a preparation method thereof and a permeability-increasing fracturing fluid system, and the surfactant is obtained by sulfonating a product synthesized by maleic anhydride, diethylenetriamine and alkyl polyoxyethylene polyoxypropylene alcohol. The surfactant provided by the invention is a gemini surfactant synthesized from maleic anhydride, diethylenetriamine, alkyl polyoxyethylene polyoxypropylene alcohol and a sulfonating reagent, the molecular structure contains two or more pairs of hydrophilic groups and hydrophobic groups, and contains multiple hydrophilic groups such as amino, sulfonic group and polyoxyethylene propylene ether group; the surfactant has the advantages of high molecular surface activity and strong molecular structure controllability, can be used as a shale gas permeation enhancing surfactant, and has the advantages of lower critical micelle concentration and better surface activity compared with the conventional surfactant. The method can be widely applied to the petroleum and natural gas industry, can be used for tertiary oil recovery, dialysis agents and the like, and is not applied to the aspect of improving the recovery efficiency of shale gas reservoirs.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well reservoir stimulation technology, specifically to a surfactant, its preparation method, and a permeability-enhancing fracturing fluid system. Background Technology

[0002] Shale gas reservoirs have a dense rock matrix with pore sizes ranging from a few nanometers to hundreds of nanometers. Capillary action, leading to extensive seepage during fracturing in shale gas reservoirs, significantly impacts gas migration, causing rapid production decline and reducing both initial and cumulative well production. Research indicates that shale reservoirs possess a unique "hydration effect," where fracturing fluid injected into the reservoir migrates deeper into the shale before well opening and blowout testing, increasing the complexity of artificial fractures. This represents an emerging direction for improving shale gas recovery. Since shale reservoirs are generally hydrophilic, further enhancing the fracturing fluid's fracture-creating effect requires the development of more potent surfactants. Summary of the Invention

[0003] Based on this, the present invention proposes a surfactant, its preparation method and a permeation-enhancing fracturing fluid system, which has excellent surface properties, better wetting performance and practical application value, targeting the characteristics of shale reservoirs.

[0004] According to a first aspect of the present invention, a surfactant is provided, said surfactant being obtained by sulfonation of a product synthesized from maleic anhydride, diethylenetriamine and alkyl polyoxyethylene polyoxypropylene alcohol; The surfactant comprises the following structure: ; Where p = m = 0 or p = 6~12, m = 6~12; n=0 or n=6~12; The number of carbon atoms in the alkyl chain R is 8 to 16.

[0005] According to an embodiment of the present invention, the alkyl polyoxyethylene polyoxypropylene alcohol is one of alkyl polyoxyethylene alcohol, alkyl polyoxypropylene alcohol and alkyl polyoxyethylene polyoxypropylene block copolymer alcohol; And / or, the molar ratio of the maleic anhydride to the diethylenetriamine is 2.1~2.2:1.

[0006] According to a second aspect of the present invention, a method for preparing the above-described surfactant is provided, comprising the following steps: Maleic anhydride, alkyl polyoxyethylene polyoxypropylene alcohol and the first catalyst are dissolved in a first organic solvent to obtain a first mixture; The first mixture reacts to yield diethylenetriamine maleic acid monoester; The diethylenetriamine maleate monoester, alkyl polyoxyethylene polyoxypropylene alcohol, and the second catalyst are dissolved in a second organic solvent to obtain a second mixture; The second mixture reacts to yield diethylenetriamine maleate dialkyl polyoxyethylene polyoxypropylene ester; The diethylenetriamine maleate dialkyl polyoxyethylene polyoxypropylene ester was mixed with a sulfonating agent, and the surfactant was obtained after sulfonation.

[0007] According to an embodiment of the present invention, the first organic solvent includes one or more solvents such as methanol, ethanol, and propanol; The first organic solvent accounts for 65wt to 75wt% of the first mixture.

[0008] According to an embodiment of the present invention, the first catalyst and the second catalyst are solid acids; Both the first catalyst and the second catalyst comprise one of phosphotungstic acid / silica, sulfuric acid / titanium dioxide, sodium molybdate, and phosphotungstic acid; The first catalyst is 0.5 wt% to 1.0 t% of the mass of the maleic anhydride. The second catalyst is 0.5 wt to 1.0 wt% of the mass of the alkyl polyoxyethylene polyoxypropylene alcohol.

[0009] According to an embodiment of the present invention, the reaction conditions of the first mixture include: a reaction temperature of 90°C and a reaction time of 4 hours; The reaction conditions for the second mixture include: reaction temperature 100~120℃, reaction time 4~6h, and stirring speed 800r / min.

[0010] According to an embodiment of the present invention, the sulfonating agent is sodium bisulfite; The molar ratio of the diethylenetriamine maleate dialkyl polyoxyethylene polyoxypropylene ester to the sulfonating agent is 1:2.1~2.2.

[0011] According to an embodiment of the present invention, the molar ratio of diethylenetriamine maleate monoester to alkyl polyoxyethylene polyoxypropylene alcohol is 1:2.3~2.6.

[0012] According to an embodiment of the present invention, the second organic solvent is one or more solvents selected from chlorobenzene, dichloromethane, trichloromethane, etc. The second organic solvent accounts for 55 wt% to 70 wt% of the total mass of the second mixture.

[0013] According to an embodiment of the present invention, the reaction conditions for the sulfonation reaction include: The reaction temperature is 120~130℃, the reaction time is 2.5~3h, and the stirring rate is 800r / min.

[0014] According to a third aspect of the present invention, a fracturing fluid system employing the above-mentioned surfactant is provided, comprising, by mass fraction: 0.08-0.3% drag reducer, 1.0% surfactant and 0.05% bactericide, with the remainder being water.

[0015] As can be seen from the above technical solutions, the surfactant, its preparation method, and the permeation-enhancing fracturing fluid system provided by the present invention have the following beneficial effects: The surfactant provided by this invention is a gemini surfactant synthesized from maleic anhydride, diethylenetriamine, alkyl polyoxyethylene polyoxypropylene alcohol, and sulfonating agents. Its molecular structure contains two or more pairs of hydrophilic and hydrophobic groups, and includes various hydrophilic groups such as amino, sulfonic acid, and polyoxyethylene propylene ether groups. It exhibits high surface activity and strong controllability of its molecular structure, making it suitable for use as a permeability-enhancing surfactant in shale gas. Compared to conventional surfactants, it has a lower critical micelle concentration and better surface activity. It can be widely applied in the oil and gas industry, including in enhanced oil recovery (EOR) and as a permeation agent, but it has not yet been used in shale gas reservoir enhanced oil recovery. Attached Figure Description

[0016] Figure 1 A flowchart illustrating the preparation of a permeability-enhancing surfactant for shale gas fracturing, provided in an embodiment of the present invention. Figure 2 This is a graph showing the self-absorption curves of different concentrations of permeability-enhancing surfactant aqueous solution for shale gas fracturing compared with water and drag-reducing agent solution, provided in Example 4 of the present invention. Figure 3 This is a self-absorption curve of the permeation-enhancing surfactant aqueous solution composite system for shale gas fracturing provided in Example 4 of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0018] Currently, there exists a highly efficient permeation and drag reduction water system suitable for shale gas reservoirs, in which a mixture of polyoxyethylene fatty alcohol ether, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate plays a permeation conditioning role. However, this type of composite surfactant mixture is subject to adsorption in the formation due to chromatographic separation effects, thus affecting the surface activity of the mixture. Patent CN 114350340A discloses a fracturing permeation enhancer and its preparation method. First, polyoxyethylene and refined powdered aminosulfonic acid are mixed in the solvent dimethylformamide for a first-step esterification reaction; then, a certain amount of long-chain alkyl acyl chloride is added to the reaction solution for a second-step reaction, finally obtaining the target product. The product decomposes into aminosulfonic acid, polyoxyethylene, and long-chain alkyl acids at high temperatures, exhibiting a certain dissolving effect on the formation. However, it also suffers from instability at high temperatures. Patent CN114315937A describes a biomass nano-permeability enhancer for pressure displacement and fracturing, obtained by dissolving sucrose in water, adding ethyl acetate and an acid-binding agent, and slowly adding phosphorus oxychloride dropwise at low temperature. After the addition is complete, the reaction is controlled at temperature for a period of time. After the reaction is complete, the product is concentrated, purified, separated, and vacuum dried. This method has good biocompatibility and environmental friendliness, but the product degrades rapidly at high temperatures, resulting in a short-lived surface activity. Patent CN114045163A describes the synthesis of a multi-branched twinned amphoteric surfactant. The synthesis method involves reacting fatty acids with N,N-dimethylaminopropylamine to obtain an intermediate tertiary amine, then adding dichloroethyl ether to the intermediate to conduct a twinning reaction to obtain a twinned tertiary amine. The twinned tertiary amine is then refluxed with isopropanol and sodium chloroacetate to obtain the target product. This agent possesses both permeability enhancement and desorption capabilities. In addition to the permeability enhancer, this product requires the addition of various additives such as nano-synergists and mutual solvents.

[0019] Rock reservoirs are generally hydrophilic reservoirs. In order to further improve the fracturing effect of fracturing fluid, a surfactant with stronger surface activity is needed.

[0020] According to a first aspect of the present invention, a surfactant is provided, which is obtained by sulfonation of a product synthesized from maleic anhydride, diethylenetriamine and alkyl polyoxyethylene polyoxypropylene alcohol; Surfactants include the following structures: ; Where p = m = 0 or p = 6~12, m = 6~12; n=0 or n=6~12; The number of carbon atoms in the alkyl chain R is 8 to 16.

[0021] The surfactant provided by this invention is a gemini surfactant synthesized from maleic anhydride, diethylenetriamine, alkyl polyoxyethylene polyoxypropylene alcohol, and sulfonating agents. Its molecular structure contains two or more pairs of hydrophilic and hydrophobic groups, and includes various hydrophilic groups such as amino, sulfonic acid, and polyoxyethylene propylene ether groups. It exhibits high surface activity and strong controllability of its molecular structure, making it suitable for use as a permeability-enhancing surfactant in shale gas. Compared to conventional surfactants, it has a lower critical micelle concentration and better surface activity. It can be widely applied in the oil and gas industry, including in enhanced oil recovery (EOR) and as a permeation agent, but it has not yet been used in shale gas reservoir enhanced oil recovery.

[0022] According to an embodiment of the present invention, the alkyl polyoxyethylene polyoxypropylene alcohol is one of alkyl polyoxyethylene alcohol, alkyl polyoxypropylene alcohol and alkyl polyoxyethylene polyoxypropylene block copolymer alcohol.

[0023] According to an embodiment of the present invention, the molar ratio of maleic anhydride to diethylenetriamine is 2.1~2.2:1.

[0024] According to a second aspect of the invention, such as Figure 1 As shown, a method for preparing the above-mentioned surfactant is provided, comprising the following steps: S1: Dissolve maleic anhydride, alkyl polyoxyethylene polyoxypropylene alcohol and the first catalyst in the first organic solvent to obtain the first mixture; S2: The first mixture reacts to obtain diethylenetriamine maleic acid monoester, as shown in Formula 1; (Equation 1) S3: Dissolve diethylenetriamine maleate monoester, alkyl polyoxyethylene polyoxypropylene alcohol and the second catalyst in the second organic solvent to obtain the second mixture; S4: The second mixture reacts to obtain diethylenetriamine maleate dialkyl polyoxyethylene polyoxypropylene ester, as shown in Formula 2;

[0025] (Equation 2) S5: Diethylenetriamine maleate dialkyl polyoxyethylene polyoxypropylene ester is mixed with a sulfonating agent, and the surfactant is obtained after sulfonation reaction, as shown in Formula 3.

[0026] (Equation 3).

[0027] According to an embodiment of the present invention, in S1, the first organic solvent includes one or more solvents such as methanol, ethanol, and propanol.

[0028] According to an embodiment of the present invention, in S1, the first organic solvent accounts for 65wt to 75wt% of the first mixture.

[0029] According to an embodiment of the present invention, in S1 and S3, the first catalyst and the second catalyst are solid acids.

[0030] According to an embodiment of the present invention, in S1 and S3, both the first catalyst and the second catalyst include one of phosphotungstic acid / silica, sulfuric acid / titanium dioxide, sodium molybdate, and phosphomolybdic acid.

[0031] According to an embodiment of the present invention, in S1 and S3, the first catalyst is 0.5 wt to 1.0 t of maleic anhydride by mass.

[0032] According to an embodiment of the present invention, in S3, the second catalyst is 0.5 wt to 1.0 wt% of the mass of alkyl polyoxyethylene polyoxypropylene alcohol.

[0033] According to an embodiment of the present invention, in S1, the reaction apparatus may be a three-necked flask equipped with a stirrer and a thermometer and a reflux condenser.

[0034] According to an embodiment of the present invention, in S2, the reaction conditions of the first mixture include: a reaction temperature of 90°C and a reaction time of 4 hours.

[0035] According to an embodiment of the present invention, in S3, the second organic solvent is one or more solvents such as chlorobenzene, dichloromethane, and trichloromethane.

[0036] According to an embodiment of the present invention, in S3, the second organic solvent accounts for 55wt to 70wt% of the total mass of the second mixture.

[0037] According to an embodiment of the present invention, in S4, the reaction conditions of the second mixture include: reaction temperature of 100~120℃, reaction time of 4~6h, and stirring rate of 800r / min.

[0038] According to an embodiment of the present invention, in S4, the reaction is carried out for a certain period of time under conditions of vigorous stirring and heating, and the water generated by the reaction is continuously separated.

[0039] According to an embodiment of the present invention, in S5, the sulfonating agent is sodium bisulfite.

[0040] According to an embodiment of the present invention, in S5, the molar ratio of diethylenetriamine maleate dialkyl polyoxyethylene polyoxypropylene ester to sulfonating agent is 1:2.1~2.2.

[0041] According to an embodiment of the present invention, in S5, the molar ratio of diethylenetriamine maleate monoester to alkyl polyoxyethylene polyoxypropylene alcohol is 1:2.3~2.6.

[0042] According to an embodiment of the present invention, in S5, the reaction conditions for the sulfonation reaction include: a reaction temperature of 120~130℃, a reaction time of 2.5~3h, and a stirring rate of 800r / min.

[0043] According to an embodiment of the present invention, in S5, the sulfonation reaction requires nitrogen protection.

[0044] According to an embodiment of the present invention, in S5, the reaction time and reaction temperature vary depending on the structure of diethylenetriamine maleate dialkyl polyoxyethylene polyoxypropylene ester.

[0045] According to a third aspect of the present invention, a fracturing fluid system employing the above-mentioned surfactant is provided, comprising, by mass fraction: 0.08-0.3% drag reducer, 1.0% surfactant and 0.05% bactericide, with the remainder being water.

[0046] When the drag-reducing agent concentration is 0.1%, it is a low-viscosity slickwater permeability-enhancing fracturing fluid system; when the drag-reducing agent concentration is 0.3%, it is a medium-viscosity slickwater permeability-enhancing fracturing fluid system. During field operations, the drag-reducing agent concentration can be adjusted from 0.08% to 0.3% according to the water quality used for preparing the fluid.

[0047] The technical solution of the present invention will be described in detail below through preferred embodiments. It should be noted that the specific embodiments in the following text are for illustrative purposes only and are not intended to limit the present invention.

[0048] Example 1 Maleic anhydride, diethylenetriamine, and methanol were added to a three-necked flask equipped with a stirrer, thermometer, and reflux condenser. Methanol accounted for 70 wt% of the total mass. The molar ratio of maleic anhydride to diethylenetriamine was 2.1:1. A sulfuric acid / titanium dioxide catalyst was added, with a catalyst mass of 0.6 wt% of the maleic anhydride mass. The mixture was heated to 90 °C under stirring and reacted for 4 h, resulting in an amide reaction to produce diethylenetriamine maleic acid monoester.

[0049] Diethylenetriamine maleate monoester and dodecyl polyoxyethylene alcohol (R=12, m=6, n=p=0) were dissolved in chloroform at a molar ratio of 1:2.3, with chloroform accounting for 60 wt% of the total mass. A catalyst of sulfuric acid / titanium dioxide was added, with the catalyst accounting for 0.65 wt% of the mass of the dodecyl polyoxyethylene alcohol. The mixture was heated to 105 °C, stirred at 800 rpm, and reacted for 4 h, continuously separating the water produced in the reaction to obtain diethylenetriamine maleate didodecyl polyoxyethylene ester.

[0050] Diethylenetriamine maleate didodecyl polyoxyethylene ester was mixed with an aqueous solution of sodium bisulfite at a molar ratio of 1:2.1. Under nitrogen protection, the mixture was heated to 120°C and stirred at 800 rpm for 2.5 h to obtain the target product.

[0051] Example 2 Similar to Example 1, except that diethylenetriamine maleate monoester and dodecyl polyoxyethylene alcohol (R=12, m=10, n=p=0) were dissolved in chloroform at a molar ratio of 1:2.4, with chloroform accounting for 65 wt% of the total mass. A catalyst, sulfuric acid / titanium dioxide, was added, with the catalyst accounting for 0.65 wt% of the mass of the dodecyl polyoxyethylene alcohol. The temperature was raised to 110°C, the stirring speed was 800 r / min, and the reaction was carried out for 4.5 h, with water continuously separated to obtain diethylenetriamine maleate didodecyl polyoxyethylene ester.

[0052] Example 3 Similar to Example 1, except that diethylenetriamine maleate monoester and dodecyl polyoxyethylene alcohol (R=12, m=12, n=p=0) were dissolved in chloroform at a molar ratio of 1:2.3, with chloroform accounting for 65 wt% of the total mass. A catalyst of sulfuric acid / titanium dioxide was added, with the catalyst accounting for 0.65 wt% of the mass of the dodecyl polyoxyethylene alcohol. The mixture was heated to 110°C, stirred at 800 rpm, and reacted for 4 hours, continuously separating the water produced in the reaction to obtain diethylenetriamine maleate didodecyl polyoxyethylene ester.

[0053] Example 4 Similar to Example 1, except that diethylenetriamine maleate monoester and octyl polyoxyethylene polyoxypropylene alcohol (R=8, m=n=6) were dissolved in chloroform at a molar ratio of 1:2.4, with chloroform accounting for 70 wt% of the total mass. A catalyst of sulfuric acid / titanium dioxide was added, with the catalyst accounting for 0.65 wt% of the mass of the dodecyl polyoxyethylene alcohol. The temperature was raised to 120°C, the stirring speed was 800 r / min, and the reaction was carried out for 4 h, continuously separating the water generated in the reaction to obtain diethylenetriamine maleate dioctyl polyoxyethylene polyoxypropylene ester.

[0054] Diethylenetriamine maleate dioctyl polyoxyethylene polyoxypropylene ester was mixed with an aqueous solution of sodium bisulfite at a molar ratio of 1:2.1. Under nitrogen protection, the mixture was heated to 130°C and stirred at 800 r / min for 2.5 h to obtain the target product.

[0055] Example 5 Similar to Example 1, except that diethylenetriamine maleate monoester and dodecyl polyoxyethylene polyoxypropylene alcohol (R=16, m=n=6) were dissolved in chloroform at a molar ratio of 1:2.5, with chloroform accounting for 70 wt% of the total mass. A catalyst of sulfuric acid / titanium dioxide was added, with the catalyst accounting for 0.8 wt% of the mass of the dodecyl polyoxyethylene alcohol. The temperature was raised to 120°C, the stirring speed was 800 r / min, and the reaction was carried out for 4 h, continuously separating the water generated in the reaction to obtain diethylenetriamine maleate didodecyl polyoxyethylene polyoxypropylene ester.

[0056] Diethylenetriamine maleate didodecyl polyoxyethylene polyoxypropylene ester was mixed with an aqueous solution of sodium bisulfite at a molar ratio of 1:2.1. Under nitrogen protection, the mixture was heated to 130°C and stirred at 800 r / min for 3 hours to obtain the target product.

[0057] Example 6 Similar to Example 5, except that diethylenetriamine maleate monoester and hexadecyl polyoxyethylene alcohol (R=16, m=n=6) were dissolved in chloroform at a molar ratio of 1:2.6.

[0058] Diethylenetriamine maleate dihexadecyl polyoxyethylene polyoxypropylene ester was mixed with an aqueous solution of sodium bisulfite at a molar ratio of 1:2.1. Under nitrogen protection, the mixture was heated to 120°C and stirred at 800 rpm for 3 hours to obtain the target product.

[0059] Comparative Example 1 We selected a commercially available gemini surfactant product, which is a sulfonate gemini surfactant.

[0060] Comparative Example 2 We selected a commercially available gemini surfactant product, which is a polyether-based gemini surfactant.

[0061] Experimental example: Construction of Permeation-Enhancing Fracturing Fluid System A low-viscosity slickwater fracturing fluid system (0.1% drag reducer + 1.0% Gemini surfactant + 0.05% bactericide) was used to conduct indoor shale face self-absorption tests. The injection volume of a constant-speed, constant-pressure pump was recorded by computer at different times. The cumulative flow rate at different time points represented the shale's absorption at that time, allowing for analysis of the absorption patterns. Finally, based on the shale sample's physical properties and the experimentally measured dynamic absorption, a self-absorption rate was defined to quantitatively characterize the absorption capacity, i.e., the percentage (I) of the absorption volume relative to the core pore volume. The percentage of permeation to the core pore volume I through Calculated by multiplying by 100%.

[0062] In the formula, V represents the volume of water entering the core; A represents the porosity of the core; A represents the cross-sectional area of ​​the core; L represents the length of the core.

[0063] Example Product Performance Evaluation Gemini surfactants' surface tension γCMC, critical micelle concentration CMC, and contact angle After dissolving the permeation-enhancing surfactants provided in Examples 1-6 and the gemini surfactants provided in Comparative Examples 1-2 in water, the surface tension γ was measured using an automatic tension meter.CMC The critical micelle concentration (CMC) and the results are shown in Table 1.

[0064] Table 1 Surface tension and critical micelle concentration of products in each example

[0065] The surface tension γCMC, critical micelle concentration CMC, and contact angle of the products obtained in each embodiment were compared. Table 1 shows that the surface tension γCMC, critical micelle concentration CMC, and contact angle of this type are all lower than those of the comparative example, exhibiting superior surface activity. In the gemini surfactant, with a constant alkyl chain length, the contact angle and critical micelle concentration decrease with increasing polyoxyethylene content (Examples 1-3), demonstrating good wetting properties. In the gemini surfactant molecule, the number of polyoxyethylene and polyoxypropylene groups is consistent; with increasing alkyl chain length, the surface tension γCMC, critical micelle concentration CMC, and contact angle all decrease, resulting in enhanced wetting performance. A suitable gemini surfactant structure can be selected based on specific application conditions and cost considerations.

[0066] Shale end face self-absorption performance test The product from Example 4 was selected as a shale gas permeability enhancer for shale face self-absorption performance testing. The results are as follows: Figure 2 and Figure 3 As shown.

[0067] Depend on Figure 2 It is known that shale itself is hydrophilic. The addition of drag-reducing agent solution reduces the hydrophilicity of the rock surface, as evidenced by the fact that the cumulative self-absorption of the drag-reducing agent solution is less than that of pure water. Different concentrations of permeability-enhancing agent solution can further improve the hydrophilicity of shale rock samples, and the cumulative self-absorption increases with the increase of permeability-enhancing agent concentration. Figure 3 The cumulative self-absorption capacity of the composite system of permeability enhancer and drag reducer was investigated. The drag reducer, a macromolecule of acrylamide, competes with the permeability enhancer for adsorption on the shale surface. Compared with the permeability enhancer solution, the cumulative self-absorption capacity of the composite system was lower, increasing with the increase of the permeability enhancer concentration. This indicates that adding permeability-enhancing Gemini surfactants to a conventional fracturing fluid system forms a permeability-enhancing fracturing fluid, which can increase the self-absorption capacity of shale reservoirs. This allows for further enhancement of the complexity of artificial fractures by utilizing shale hydration, thereby improving gas testing results.

[0068] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A surfactant, characterized in that, The surfactant is obtained by sulfonation of the product synthesized from maleic anhydride, diethylenetriamine and alkyl polyoxyethylene polyoxypropylene alcohol. The surfactant comprises the following structure: ； Where p = m = 0 or p = 6~12, m = 6~12; n=0 or n=6~12; The number of carbon atoms in the alkyl chain R is 8 to 16.

2. The surfactant according to claim 1, characterized in that, The alkyl polyoxyethylene polyoxypropylene alcohol is one of alkyl polyoxyethylene alcohol, alkyl polyoxypropylene alcohol and alkyl polyoxyethylene polyoxypropylene block copolymer alcohol; And / or, the molar ratio of the maleic anhydride to the diethylenetriamine is 2.1~2.2:

1.

3. A method for preparing the surfactant according to claim 1 or 2, characterized in that, Includes the following steps: Maleic anhydride, alkyl polyoxyethylene polyoxypropylene alcohol and the first catalyst are dissolved in a first organic solvent to obtain a first mixture; The first mixture reacts to yield diethylenetriamine maleic acid monoester; The diethylenetriamine maleate monoester, alkyl polyoxyethylene polyoxypropylene alcohol, and the second catalyst are dissolved in a second organic solvent to obtain a second mixture; The second mixture reacts to yield diethylenetriamine maleate dialkyl polyoxyethylene polyoxypropylene ester; The diethylenetriamine maleate dialkyl polyoxyethylene polyoxypropylene ester was mixed with a sulfonating agent, and the surfactant was obtained after sulfonation.

4. The preparation method according to claim 3, characterized in that, The first organic solvent includes one or more solvents such as methanol, ethanol, and propanol; The first organic solvent accounts for 65wt to 75wt% of the first mixture.

5. The preparation method according to claim 3, characterized in that, The first catalyst and the second catalyst are solid acids; Both the first catalyst and the second catalyst comprise one of phosphotungstic acid / silica, sulfuric acid / titanium dioxide, sodium molybdate, and phosphotungstic acid; The first catalyst is 0.5 wt% to 1.0 t% of the mass of the maleic anhydride. The second catalyst is 0.5 wt to 1.0 wt% of the mass of the alkyl polyoxyethylene polyoxypropylene alcohol.

6. The preparation method according to claim 3, characterized in that, The reaction conditions for the first mixture include: a reaction temperature of 90°C and a reaction time of 4 hours; The reaction conditions for the second mixture include: reaction temperature 100~120℃, reaction time 4~6h, and stirring speed 800r / min.

7. The preparation method according to claim 3, characterized in that, The sulfonating agent is sodium bisulfite; The molar ratio of the diethylenetriamine maleate dialkyl polyoxyethylene polyoxypropylene ester to the sulfonating agent is 1:2.1~2.2; The molar ratio of diethylenetriamine maleic acid monoester to alkyl polyoxyethylene polyoxypropylene alcohol is 1:2.3~2.

6.

8. The preparation method according to claim 3, characterized in that, The second organic solvent is one or more solvents selected from chlorobenzene, dichloromethane, trichloromethane, etc. The second organic solvent accounts for 55 wt% to 70 wt% of the total mass of the second mixture.

9. The preparation method according to claim 3, characterized in that, The reaction conditions for the sulfonation reaction include: The reaction temperature is 120~130℃, the reaction time is 2.5~3h, and the stirring rate is 800r / min.

10. A permeation-enhancing fracturing fluid system using the surfactant described in claim 1 or 2, characterized in that, The components by mass fraction are: 0.08-0.3% drag-reducing agent, 1.0% surfactant as described in claims 1-2, and 0.05% bactericide, with the remainder being water.

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