Surface active discharge aiding agent for oil field fracturing flowback and preparation method of surface active discharge aiding agent

Abstract

The invention relates to the field of oilfield chemistry, and discloses a surface active discharge aiding agent for oilfield fracturing flow-back and a preparation method of the surface active discharge aiding agent. The molecular structure of the cleanup additive is composed of a betaine type cation head group, a sulfonic acid hydrophilic group and a hydrophobic chain connected by an intermediate ester bond, and the cleanup additive has good amphipathy and interface regulation and control capability. The cleanup additive is prepared through quaternization, hydroxyethylation and esterification reactions, the process is simple, and the structure is adjustable. The prepared cleanup additive shows excellent interfacial activity under high-temperature and high-salt conditions, significantly reduces the oil-water interfacial tension, improves the oil carrying rate and fluidity of fracturing flow-back fluid, has good biodegradability, and reduces the risk of stratum pollution. The method is suitable for flowback operation of shale oil and tight oil unconventional oil reservoirs, and has the characteristics of high efficiency, environmental protection and large-scale application.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical additives, specifically to a surface-active flowback aid for oilfield fracturing and flowback and its preparation method. Background Technology

[0002] With the large-scale development of shale oil and tight oil in unconventional reservoirs, hydraulic fracturing technology has become a key means to improve production capacity. After fracturing, the fracturing fluid mixes with formation crude oil and rock cuttings during the flowback process, forming flowback fluid. If it cannot be recovered in a timely and effective manner, it will not only result in low crude oil carrying efficiency, but also lead to a series of reservoir damage problems such as flowback fluid retention, reservoir blockage, and water-locking effects, thereby restricting the release of oil and gas production capacity. To improve flowback efficiency, surfactants are usually introduced into the fracturing system to reduce the oil-water interfacial tension, improve fluid flowability, and enhance the flowback fluid's ability to carry residual crude oil in the formation.

[0003] However, most existing flowback aids utilize traditional anionic or nonionic surfactants, which have relatively simple molecular structures, poor functional adaptability, and difficulty in simultaneously achieving multiple key performance indicators. Under complex reservoir conditions, including temperatures of 100–150℃ and salinity of 50,000–120,000 mg / L, existing flowback aids are prone to activity decay, emulsification instability, and difficulty in oil-water separation, affecting interface control and ultimately leading to decreased flowback efficiency and insufficient oil recovery. Furthermore, some flowback aid residues may cause secondary pollution or form formation deposits, posing long-term reservoir safety risks. Therefore, there is a need to develop a surface-active flowback aid with tunable structure, excellent interfacial properties, good thermosalinity stability, and environmental biodegradability to meet the comprehensive technical requirements of high efficiency, safety, and environmental friendliness in complex reservoir fracturing and flowback operations. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a novel surface-active flowback agent and its preparation method suitable for oilfield fracturing flowback processes. This invention addresses the problems of weak interface control, poor stability, and insufficient environmental adaptability of existing flowback agents in high-temperature, high-salinity environments, thereby improving flowback efficiency and oil recovery, and meeting the complex operating conditions required by unconventional reservoirs such as shale oil and tight oil during the flowback process.

[0005] To achieve the above objectives, this invention provides a surface-active flowback aid for oilfield fracturing and flowback, and a method for its preparation. The flowback aid has the following molecular structural characteristics:

[0006] The surfactant-assisted drainage agent is composed of a betaine-type cationic head group, hydrophobic segments linked by ester bonds, and a hydrophilic chain with a sulfonic acid group at the end. Its molecular structure is as follows:

[0007] RN + (CH3)2-CH2COO - -(CH2CH2O) n -COO-R′-SO3 -

[0008] Wherein, R is a low-carbon alkyl or hydroxyalkyl group from C1 to C4, and R′ is a C4 to C5 group. 12 The alkylene chain has n of 1 to 4, and the exhaust aid has an overall amphiphilic structure.

[0009] Optionally, the surface-active flowback aid for oilfield fracturing, based on the above-mentioned surface-active flowback aid, comprises the following components in parts by weight:

[0010] 0.1–1.5 parts of surfactant, 0.2–1.0 parts of nonionic surfactant, 0.1–0.8 parts of alcohol or ether additives, and 97–99 parts of water or backflow carrier.

[0011] Optionally, in the aforementioned surface-active flowback aid for oilfield fracturing, the betaine cationic head group has an N,N-dihydroxyethyl betaine structure, and the sulfonic acid group at the end of the hydrophilic chain is an alkylsulfonic acid or aromatic sulfonic acid group.

[0012] Optionally, in the aforementioned surface-active flowback aid for oilfield fracturing, the oil-water interfacial tension at a concentration of 0.1 wt% is 2–5 mN / m, and the critical micelle concentration is 1 × 10⁻⁶. -5 ~1×10 -3 It remains stable in high saline environments with a mineralization of 50,000–120,000 mg / L, without significant flocculation or precipitation.

[0013] Optionally, the preparation method of the surfactant flowback aid for oilfield fracturing includes the following steps:

[0014] S1. Trimethylamine was reacted with chloroacetic acid under alkaline conditions to obtain the betaine structure;

[0015] S2. Reaction of betaine with ethylene oxide or ethanolamine to introduce a hydroxyethyl structure;

[0016] S3. The obtained N,N-dihydroxyethyl betaine is esterified with sulfonated fatty acid acyl chloride under alkaline catalysis to obtain a surface-active flowback aid for oilfield fracturing and flowback.

[0017] Optionally, in the aforementioned surfactant-based flowback aid for oilfield fracturing, the hydrophobic segment is C8 to C9. 12 The fatty acid alkyl ester is linked to the betaine structure via an ester bond, which is slowly hydrolyzed at a pH of 5–8 or a reservoir temperature of 80–130°C.

[0018] Optionally, in the preparation method of the surface-active flowback aid for oilfield fracturing, the esterification reaction is carried out at 30-60°C for 2-6 hours, the solvent used is acetonitrile or acetone, and the alkaline catalyst is triethylamine or pyridine.

[0019] Optionally, in the aforementioned surface-active flowback aid for oilfield fracturing, the nonionic surfactant is one or more of alkyl polyoxyethylene ether, nonylphenol polyoxyethylene ether, or polyether-modified silicone oil; and the alcohol additive is one or more of n-butanol, isopropanol, or ethylene glycol monobutyl ether.

[0020] Optionally, the aforementioned surface-active flowback aid for oilfield fracturing is suitable for unconventional oil reservoirs, including shale oil, tight oil, and high-temperature, high-salinity reservoirs.

[0021] The beneficial effects of this invention are:

[0022] The surface-active flowback aid for oilfield fracturing provided by this invention constructs an amphiphilic molecular structure with good interfacial regulation capabilities and an adjustable hydrophilic-hydrophobic ratio by introducing a betaine cationic head group, ester-linked hydrophobic segments, and terminal sulfonic acid groups. This flowback aid can significantly reduce oil-water interfacial tension at low concentrations, has a low critical micelle concentration, strong emulsifying ability, and maintains excellent stability and interfacial activity even in high-temperature environments of 80–130℃ and high-salinity environments of 50,000–120,000 mg / L. It is suitable for complex flowback conditions in unconventional reservoirs such as shale oil and tight oil.

[0023] Furthermore, this flowback aid incorporates controllably hydrolyzable ester bonds in its structure, allowing for gradual degradation under specific temperature or pH conditions, thus avoiding formation residues and demonstrating excellent environmental friendliness. Its synthesis process is simple, the raw materials are readily available, and it is suitable for industrial scale-up. When applied to fracturing flowback fluid systems, it can effectively improve crude oil carrying efficiency and flowback rate, significantly enhancing oil recovery, and possesses high promotional value and promising practical application prospects. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0025] Figure 1 This is a schematic diagram of a typical molecular structure of the surfactant-assisted drainage agent described in this invention;

[0026] Figure 2 The above is the 1H NMR spectrum of the surface-active excretion aid in Example 3;

[0027] Figure 3 This is a comparison diagram of the interfacial tension of the discharge aid of the present invention and traditional nonionic discharge aids at different temperatures;

[0028] Figure 4 This is a comparison diagram of the interfacial tension of the drainage aid of this invention and traditional non-ionic drainage aids at different degrees of mineralization. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1:

[0031] A surfactant-based flowback aid for oilfield fracturing has the following mass ratio:

[0032] Trimethylamine 8.2 parts, chloroacetic acid 10 parts, ethanolamine 10 parts, sulfonated decanoic acid chloride 9.8 parts, triethylamine 1.5 parts, acetonitrile 20 parts, deionized water 50 parts.

[0033] Its preparation method includes the following steps:

[0034] S1: Weigh 10g of chloroacetic acid and 8.2g of trimethylamine, add 50mL of deionized water, control the temperature at 0-10℃ under ice bath conditions, slowly add the reaction mixture, stir the reaction for 6 hours, adjust the pH to 7, and generate the first intermediate with betaine structure.

[0035] S2: Add 10g of ethanolamine to the above solution and react for 4 hours in a water bath at 35°C to introduce the hydroxyethyl structure into the betaine molecule, thus obtaining the N,N-dihydroxyethyl betaine second intermediate.

[0036] S3: Separately, 9.8 g of sulfonated decanoic acid chloride was dissolved in 20 mL of acetonitrile and slowly added dropwise to the second intermediate solution. Simultaneously, 1.5 g of triethylamine was added as a basic catalyst, and the reaction was continued at 50 °C for 5 hours to complete the esterification reaction. After the reaction was completed, the product was concentrated under vacuum, washed with deionized water until neutral, and freeze-dried to finally obtain the target surface-active drainage aid.

[0037] Example 2:

[0038] A surfactant-based flowback aid for oilfield fracturing has the following mass ratio:

[0039] 1.2 parts of surface-active drainage aid, 0.6 parts of nonionic surfactant, 0.4 parts of alcohol additive, and 97.8 parts of water.

[0040] Its preparation method includes the following steps:

[0041] S1. Weigh 1.2g of the surfactant drainage aid obtained in Example 1 and dissolve it in 97.8g of water;

[0042] S2. Add 0.6g nonylphenol polyoxyethylene ether and 0.4g ethylene glycol monobutyl ether, and stir at room temperature for 15 minutes until a homogeneous and transparent system is formed, thus obtaining the surface-active drainage fluid system for oilfield fracturing flowback.

[0043] Example 3:

[0044] A surfactant-based flowback aid for oilfield fracturing has the following mass ratio:

[0045] 8.2 parts trimethylamine, 10 parts chloroacetic acid, 10 parts ethanolamine, 11.5 parts sulfonated dodecylbenzeneyl chloride, 1.8 parts triethylamine, 22 parts acetonitrile, and 50 parts deionized water were used to construct a stronger hydrophobic structure through aryl long chains while maintaining the hydrophilic structure.

[0046] Its preparation method includes the following steps:

[0047] S1. Weigh 10g of chloroacetic acid and 8.2g of trimethylamine, add them to 50mL of deionized water, control the temperature at 0-10℃ under ice bath conditions, slowly add the reaction mixture, stir the reaction for 6 hours, adjust the pH to 7, and generate the first intermediate with a betaine structure.

[0048] S2. Add 10g of ethanolamine to the above solution and react for 4 hours in a water bath at 35°C to introduce the hydroxyethyl structure into the betaine molecule, thus obtaining the N,N-dihydroxyethyl betaine second intermediate.

[0049] S3. Separately, 11.5 g of sulfonated dodecylbenzeneyl chloride was dissolved in 22 mL of acetonitrile and slowly added dropwise to the second intermediate solution. Simultaneously, 1.8 g of triethylamine was added as a basic catalyst, and the reaction was continued at 50 °C for 5 hours to complete the esterification reaction. After the reaction was completed, the product was concentrated under vacuum, washed with deionized water until neutral, and freeze-dried to finally obtain the target surface-active drainage aid.

[0050] Comparative Example 1:

[0051] A surfactant for drainage, with contrasting effects of hydrophilic groups, has the following mass ratio:

[0052] Trimethylamine 8.2 parts, chloroacetic acid 10.0 parts, ethanolamine 10.0 parts, decanoyl chloride 8.6 parts, triethylamine 1.5 parts, acetonitrile 20 parts, deionized water 50 parts.

[0053] Its preparation method includes the following steps:

[0054] S1. Weigh 10.0g of chloroacetic acid and 8.2g of trimethylamine, add them to 50mL of deionized water, control the temperature at 0-10℃ in an ice bath, slowly add the reaction mixture, stir for 6 hours, adjust the pH to 7, and obtain the first intermediate of betaine.

[0055] S2. Add 10.0 g of ethanolamine to the above solution and react in a water bath at 35 °C for 4 hours to obtain a second intermediate with the structure of N,N-dihydroxyethyl betaine.

[0056] S3. Separately, 8.6 g of decanoyl chloride was dissolved in 20 mL of acetonitrile and slowly added dropwise to the second intermediate solution. At the same time, 1.5 g of triethylamine was added, and the reaction was continued at 50 °C for 5 hours to complete the esterification reaction.

[0057] S4. After the reaction is complete, the mixture is concentrated under reduced pressure, washed with deionized water until neutral, and freeze-dried to obtain a comparative excretion aid without sulfonic acid group structure.

[0058] Comparative Example 2:

[0059] A surfactant for drainage, with contrasting effects of hydrophobic groups, has the following mass ratio:

[0060] Trimethylamine 8.2 parts, chloroacetic acid 10.0 parts, ethanolamine 10.0 parts, sulfonated butyryl chloride 6.5 parts, triethylamine 1.5 parts, acetonitrile 20 parts, deionized water 50 parts.

[0061] Its preparation method includes the following steps:

[0062] S1. Weigh 10.0g of chloroacetic acid and 8.2g of trimethylamine, add them to 50mL of deionized water, control the temperature at 0-10℃, slowly add the reaction mixture, stir for 6 hours, adjust the pH to neutral, and form the first intermediate.

[0063] S2. Add 10.0 g of ethanolamine and react in a water bath at 35 °C for 4 hours to obtain a second intermediate containing a hydroxyethyl structure;

[0064] S3. Dissolve 6.5g of sulfonated butyryl chloride in 20mL of acetonitrile and slowly add it dropwise to the reaction solution. At the same time, add 1.5g of triethylamine and esterify at 50℃ for 5 hours.

[0065] S4. After the reaction is complete, concentrate and wash until neutral, then freeze-dry to obtain a comparative sample of the excretion aid with shortened hydrophobic chains.

[0066] Performance testing:

[0067] 1. Interface tension test

[0068] To compare the ability of the exhaust agent of this invention with traditional nonionic exhaust agents and structural variants to reduce the interfacial tension of oil and water at the same concentration, the interfacial tension of the exhaust agent at the n-heptane / water interface was determined by the rotor drop method to quantify its interfacial regulation ability.

[0069] A 0.1 wt% solution of the drainage aid was taken and measured using an interfacial tension meter at 25°C. Each sample was tested in triplicate, and the average value was taken as the final result.

[0070] Table 1. Interfacial tension test results of excretion aid samples with different structures.

[0071]

[0072]

[0073] Table 1 shows that the drainage aids in Examples 1 and 3 of this invention significantly reduced the oil-water interfacial tension at a concentration of 0.1 wt%, decreasing it to 9.3 mN·m. -1 and 7.8 mN·m -1 It is far superior to the comparative example and also superior to the traditional nonionic additive NP-10 (12.9). Among them, Example 3 has the lowest interfacial tension, indicating that its hydrophobic chain and sulfonic acid group structure have the strongest synergistic effect and the best interfacial activity.

[0074] 2. Wettability test

[0075] To evaluate the wetting modification ability of different structured drainage aids on rock surfaces, their wetting performance was characterized by contact angle measurement.

[0076] Quartz sand pellets were used to simulate the surface of oilfield cores. After pelleting, the pellets were polished, cleaned with ethanol and deionized water in sequence, and vacuum dried at 60°C for 4 hours for later use. Then, 10 μL of drainage aid solution with a mass fraction of 1.0 wt% was dropped onto the surface of the pellets. The static contact angle was read after 5 seconds at a temperature of 25°C and a relative humidity of 50%. Three parallel experiments were conducted and the average value was taken.

[0077] Table 2 Contact Angle Test Results

[0078]

[0079]

[0080] In Table 2, the contact angles of Examples 1, 2, and 3 are 36.8°, 34.5°, and 28.6°, respectively, which are significantly reduced compared to the comparative examples. Example 3, in particular, demonstrates excellent rock surface wetting and modification capabilities, which is beneficial for oil and gas release.

[0081] 3. Return flow efficiency test

[0082] To investigate the desorption and fluid carrying capacity of flowback aids in simulated fracturing flowback, a miniature core flowback device was built to test flowback efficiency.

[0083] The test experiment used a standard-sized rock core with a diameter of 2 cm and a length of 5 cm. After drying and weighing, 10 mL of simulated fracturing fluid without flowback agent was injected into the core, which was then sealed in a pressure-resistant sleeve and subjected to a constant pressure of 10 psi. Subsequently, 1 mL of flowback agent was added, and after 10 minutes of action, a back pressure differential of 5 psi was applied to drive flowback. The flowback fluid was collected and weighed, and the flowback efficiency was calculated. Each group underwent three parallel experiments, and the average value was used for analysis.

[0084] Table 3. Test Results of Backflow Efficiency of Exhaustion Aids

[0085] sample Backflow efficiency Backflow efficiency Backflow efficiency Average return efficiency Example 1 83.2％ 84％ 83.6％ 83.6％ Example 2 85.8％ 86.6％ 56.2％ 86.2％ Example 3 91.1％ 91.7％ 91.4％ 91.4％ Comparative Example 1 59.2％ 58.5％ 59.0％ 58.9％ Comparative Example 2 64.8％ 65.4％ 65.1％ 65.1％

[0086] According to Table 3, the backflow efficiencies of Examples 1-3 were 83.6%, 86.2%, and 91.4%, respectively, which were significantly higher than those of the comparative examples, indicating that the backflow aid of the present invention effectively improved the liquid desorption and displacement efficiency. Among them, Example 3 performed best, showing a good correlation with its lowest interfacial tension and contact angle.

[0087] 4. Temperature and mineralization stability test

[0088] To evaluate the interfacial stability of the drainage aid of the present invention under high temperature and high salinity conditions, and thus verify its adaptability in complex reservoir environments, interfacial tension retention performance tests were conducted.

[0089] A 0.1 wt% aqueous solution of the drainage aid was prepared. Test samples included Examples 1 and 3, and commercial NP-10 as a control. The simulated mineralized water consisted of NaCl, CaCl2, and MgCl2, with a mineralization set at 50,000–120,000 mg / L. 2+ :Mg 2+ :Na + The ratio was controlled at 1:0.5:8 to approximate the composition of a typical medium-to-high temperature reservoir. Each sample was heated in a constant temperature water bath to a set temperature of 80–130°C, held at that temperature for 30 minutes, and then the interfacial tension between the sample and n-heptane was determined using the rotor drop method. The determination was performed in triplicate, and the average value was taken.

[0090] Table 4. Interfacial tension data at different temperatures.

[0091]

[0092]

[0093] Table 4 shows that when the temperature rises from 80℃ to 130℃, the interfacial tension of Examples 1 and 3 remains at 9.7–10.0 mN·m. -1 and 7.9~8.5mN·m -1 Within the range, no significant fluctuations were observed; in contrast, NP-10 showed a significant increase in tension above 110℃, indicating that its structure was unstable.

[0094] Table 5. Results of interfacial tension tests at different mineralization levels.

[0095]

[0096]

[0097] As shown in Table 5, the interfacial tension in Examples 1 and 3 was consistently controlled at 10.13 mN·m under conditions of mineralization ranging from 50,000 to 120,000 mg / L. -1 Hereinafter, especially in Example 3, the concentration was maintained at 8.45–8.68 mN·m. -1 Within the range, it performed excellently; however, the tonicity of NP-10 gradually increased with increasing salt concentration, reaching nearly 11 mN·m at 120,000 mg / L. -1 This indicates that the drainage aid of the present invention has strong adaptability to high-mineralization environments.

[0098] In summary, the drainage aid of the present invention constructs an amphiphilic molecular structure that combines interfacial activity, wetting regulation, and environmental stability by introducing a cationic head group with a betaine structure, a hydrophobic segment connected by an ester bond, and a hydrophilic tail segment modified with a sulfonic acid group.

[0099] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A surfactant-based flowback aid for oilfield fracturing, characterized in that, The excretion aid has the following molecular structural characteristics: The surfactant-assisted drainage agent is composed of a betaine-type cationic head group, hydrophobic segments linked by ester bonds, and a hydrophilic chain with a sulfonic acid group at the end. Its molecular structure is as follows: R-N + (CH3)2-CH2COO - -(CH2CH2O) n -COO-R′-SO3 - Wherein, R is a low-carbon alkyl or hydroxyalkyl group from C1 to C4, and R′ is a C4 to C5 group. 12 The alkylene chain has n of 1 to 4, and the exhaust aid has an overall amphiphilic structure.

2. The surfactant-based flowback aid for oilfield fracturing according to claim 1, characterized in that, Includes the following components by mass: The surfactant of claim 1 comprises 0.1 to 1.5 parts, nonionic surfactant 0.2 to 1.0 parts, alcohol or ether additive 0.1 to 0.8 parts, and water or backflow carrier 97 to 99 parts.

3. The surfactant-based flowback aid for oilfield fracturing according to claim 1, characterized in that, The betaine cation head group has an N,N-dihydroxyethyl betaine structure, and the sulfonic acid group at the end of the hydrophilic chain is an alkylsulfonic acid or an aromatic sulfonic acid group.

4. A surface-active flowback aid for oilfield fracturing according to claims 1-2, characterized in that, The oil-water interfacial tension of the discharge aid at a concentration of 0.1 wt% is 2–5 mN / m, and the critical micelle concentration is 1 × 10⁻⁶. -5 ~1×10 - 3 It remains stable in high saline environments with a mineralization of 50,000–120,000 mg / L, without significant flocculation or precipitation.

5. A surface-active flowback aid for oilfield fracturing according to claims 1-4, characterized in that, Its preparation method includes the following steps: S1. Trimethylamine was reacted with chloroacetic acid under alkaline conditions to obtain the betaine structure; S2. Reaction of betaine with ethylene oxide or ethanolamine to introduce a hydroxyethyl structure; S3. The obtained N,N-dihydroxyethyl betaine is esterified with sulfonated fatty acid acyl chloride under alkaline catalysis to obtain a surface-active flowback aid for oilfield fracturing and flowback.

6. The method for preparing a surface-active flowback aid for oilfield fracturing according to claim 5, characterized in that, The esterification reaction is carried out at 30–60°C for 2–6 hours, using acetonitrile or acetone as the solvent, and triethylamine or pyridine as the alkaline catalyst.

7. The surfactant-based flowback aid for oilfield fracturing according to claim 1, characterized in that, The hydrophobic segment is C8~C 12 The fatty acid alkyl ester is linked to the betaine structure via an ester bond, which is slowly hydrolyzed at a pH of 5–8 or a reservoir temperature of 80–130°C.

8. The surfactant flowback aid for oilfield fracturing according to claim 2, characterized in that, The nonionic surfactant is one or more of alkyl polyoxyethylene ether, nonylphenol polyoxyethylene ether, or polyether-modified silicone oil; the alcohol additive is one or more of n-butanol, isopropanol, or ethylene glycol monobutyl ether.

9. A surface-active flowback aid for oilfield fracturing according to claims 1-2, characterized in that, The drainage aid is suitable for unconventional oil reservoirs, including shale oil, tight oil, and high-temperature, high-salinity reservoirs.

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