A responsive oil field pH sensitive corrosion inhibition and corrosion prevention additive, its preparation method and application

Abstract

The application discloses a responsive oilfield pH-sensitive corrosion inhibition and prevention additive, and a preparation method and application thereof. The responsive oilfield pH-sensitive corrosion inhibition and prevention additive has a core-shell structure and contains the following raw materials in parts by weight based on 100 parts of total weight: long-chain alkyl imidazoline 25-32 parts, momordica grosvenori polyphenol 2-4 parts, pH-sensitive shell emulsion 52-57 parts, hydrophobic modified nano silicon dioxide 2-4 parts, polyethylene glycol 4-6 parts, and tetrahydropyran carboxylic acid 2-4 parts. The pH-sensitive shell emulsion is a dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion. The corrosion inhibition and prevention additive can quickly release the drug and efficiently prevent corrosion in an acidic medium with pH less than 6.5, and can slowly inhibit corrosion and protect the drug for a long time in a neutral medium with pH 6.5-8.5. The single-time drug addition can protect for more than 90 days, and the corrosion inhibition and prevention additive has good stability.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical agents technology, specifically relating to a responsive pH-sensitive corrosion inhibitor and preservative agent for oilfields, its preparation method, and its application. Background Technology

[0002] In oil and gas extraction and gathering systems, acidic gases such as hydrogen sulfide and carbon dioxide contained in the formation dissolve in produced fluids and wastewater media, causing the pH of the system to fluctuate repeatedly in the acidic (pH < 6.5) and neutral (pH 6.5~8.5) range. This leads to a combined failure problem of electrochemical corrosion and microbial corrosion in carbon steel equipment, which significantly shortens the service life of oilfield equipment and increases the operation and maintenance costs of oil and gas extraction.

[0003] Currently, most mainstream oilfield pH-responsive corrosion inhibitors on the market use rare earth metal salts, which have a single corrosion inhibition synergistic effect and can only assist in film formation, without antioxidant or ion shielding properties. Conventional corrosion inhibitors have poor interfacial adsorption stability and are prone to detachment under high sulfur and high mineralization conditions, resulting in rapid decay of the agent's corrosion inhibition performance. Under neutral conditions, the agent has a high loss rate and weak long-term protection capability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a responsive pH-sensitive corrosion inhibitor for oilfields, its preparation method, and its application. By constructing a synergistic corrosion inhibition system, it overcomes the deficiencies of existing corrosion inhibitors, such as poor pH response and weak long-term protection capabilities.

[0005] A responsive pH-sensitive corrosion inhibitor for oilfields, the responsive pH-sensitive corrosion inhibitor for oilfields having a core-shell structure, comprising the following raw materials in parts by weight per 100 parts total: 25-32 parts of long-chain alkyl imidazoline, 2-4 parts of monk fruit polyphenols, 52-57 parts of pH-sensitive shell emulsion, 2-4 parts of hydrophobically modified nano silica, 4-6 parts of polyethylene glycol, and 2-4 parts of tetrahydropyranoic acid. The pH-sensitive shell emulsion is a dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion.

[0006] Preferably, the dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion is prepared by the following method: mixing dimethylaminoethyl methacrylate, acrylic acid, and modified chitosan evenly, adding anhydrous ethanol and an initiator, and stirring.

[0007] Preferably, the mass ratio of dimethylaminoethyl methacrylate, acrylic acid, modified chitosan, anhydrous ethanol, and initiator is (18-25):(8-14):10:(40-60):(0.6-1.2).

[0008] Preferably, the modified chitosan is prepared by the following method: chitosan is dissolved in glacial acetic acid solution and dissolved at a constant temperature of 60-65°C under a nitrogen atmosphere. Then, cerium ammonium nitrate and dimethylaminoethyl methacrylate are added sequentially. Dimethylaminoethyl methacrylate is used to graft pH-responsive tertiary amine groups onto the chitosan. The reaction is continued at a constant temperature for 4-4.5 hours, purified by dialysis, and freeze-dried.

[0009] Preferably, in the preparation of modified chitosan, the mass ratio of chitosan, glacial acetic acid solution, cerium ammonium nitrate, and dimethylaminoethyl methacrylate is 10:(50-55):(0.5-0.8):(22-25); and the concentration of the glacial acetic acid solution is 1 wt%.

[0010] Preferably, the hydrophobically modified nano-silica is prepared by the following method: adding a silane coupling agent to a mixture of ethanol and water, stirring for 40-45 min, then adding nano-silica, refluxing at 70-75°C for 2 h, centrifuging, washing with ethanol, and vacuum drying; wherein the mass ratio of silane coupling agent to nano-silica is (4-6):100.

[0011] Preferably, the initiator is an oil-soluble azo initiator.

[0012] More preferably, the initiator is azobisisobutyronitrile (AIBN).

[0013] The long-chain alkyl imidazoline can be selected from one or more of oleic acid imidazoline, tetradecyl imidazoline, octadecyl imidazoline, and castor oil imidazoline, with oleic acid imidazoline being preferred.

[0014] The preparation method of the aforementioned responsive pH-sensitive corrosion inhibitor for oilfields includes the following steps: (1) Preparation of corrosion-inhibiting active core: Long-chain alkyl imidazoline and monk fruit polyphenols are added to water and stirred at 50-55℃ for 30-35 min to obtain corrosion-inhibiting active core solution, which is kept warm for later use; (2) Core-shell microsphere polymerization: The core active liquid is dropped into the pH-sensitive shell emulsion, sheared and dispersed for 40-45 min at a shearing speed of 8000-9000 r / min, and then isothermal polymerization reaction is carried out at 65-68℃ for 3-3.5 h to obtain the core-shell microsphere primary product; (3) Modification and post-treatment: Hydrophobic modified nano silica, polyethylene glycol and tetrahydropyranoic acid are added sequentially to the core-shell microsphere primary product, ultrasonically dispersed for 25-30 min, and stirred at a constant temperature for 60-70 min; after natural cooling, it is centrifuged, washed and vacuum dried.

[0015] Preferably, in step (1), the total mass ratio of long-chain alkyl imidazoline and monk fruit polyphenols to water is 1:(1.2-1.8).

[0016] The application of the responsive pH-sensitive corrosion inhibitor in oilfield corrosion prevention: The responsive pH-sensitive corrosion inhibitor is added to the oilfield gas well shaft, gathering and transmission pipeline, and sewage reinjection system medium at a concentration of 50-80 mg / L.

[0017] Preferably, the responsive oilfield pH-sensitive corrosion inhibitor is applied using either continuous or intermittent dosing.

[0018] Advantages of this invention: (1) The corrosion inhibitor provided by the present invention can release the drug quickly and provide efficient corrosion protection in acidic media with pH < 6.5; in neutral media with pH 6.5-8.5, the agent slows down corrosion and provides long-term protection. The long-term protection period after a single application can be more than 90 days. (2) The corrosion inhibitor provided by the present invention does not agglomerate, separate into layers or precipitate when placed in a high-mineralization oil-water system for a long time, and has good stability; (3) It is suitable for working temperatures of 40-120℃ and can withstand working conditions with total mineralization of medium >100000mg / L and H2S concentration >100ppm. Detailed Implementation

[0019] Example 1: 1. A responsive pH-sensitive corrosion inhibitor for oilfields, having a core-shell structure, comprising the following raw materials in parts by weight per 100 parts total: The mixture contains 29 parts of imidazoline oleate, 3 parts of monk fruit polyphenols, 57 parts of pH-sensitive shell emulsion, 3 parts of hydrophobically modified nano-silica, 5 parts of polyethylene glycol, and 3 parts of tetrahydropyranoic acid; the pH-sensitive shell emulsion is a dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion. The dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion is prepared by the following method: dimethylaminoethyl methacrylate, acrylic acid, and modified chitosan are mixed evenly, anhydrous ethanol and an initiator are added, and the mixture is stirred at a constant speed of 150 r / min for 20 min; wherein the mass ratio of dimethylaminoethyl methacrylate, acrylic acid, modified chitosan, anhydrous ethanol, and initiator is 22:10:10:50:0.9. The modified chitosan was prepared by the following method: chitosan was dissolved in glacial acetic acid solution and dissolved at a constant temperature of 60°C under a nitrogen atmosphere. Then, cerium ammonium nitrate and dimethylaminoethyl methacrylate were added sequentially, and the reaction was continued at a constant temperature for 4 hours. Dialysis purification was performed using a regenerated cellulose dialysis bag with a molecular weight cutoff of 8000-14000 Da. The dialysate was deionized water, and the dialysate was changed every 4 hours until no monomers or metal ions were detected in the dialysate. The modified chitosan was then freeze-dried to obtain pure modified chitosan. The mass ratio of chitosan, glacial acetic acid solution, cerium ammonium nitrate, and dimethylaminoethyl methacrylate was 10:50:0.5:22, and the concentration of the glacial acetic acid solution was 1 wt%. The hydrophobically modified nano-silica was prepared by the following method: silane coupling agent KH-550 was added to a mixture of ethanol and water, stirred for 40 min, then nano-silica was added, refluxed at 70 °C for 2 h, centrifuged, washed with ethanol, and vacuum dried at 70 °C to constant weight; wherein the mass ratio of silane coupling agent to nano-silica was 4:100. 2. The preparation method of the aforementioned responsive oilfield pH-sensitive corrosion inhibitor includes the following steps: (1) Preparation of corrosion-inhibiting active core: Oleic acid imidazoline and monk fruit polyphenols were added to water and stirred at 50℃ and 280r / min for 30min to obtain corrosion-inhibiting active core liquid, which was kept warm for later use; wherein, the total mass ratio of oleic acid imidazoline and monk fruit polyphenols to water was 1:1.2. (2) Core-shell microsphere polymerization: The core active liquid is dropped into the pH-sensitive shell emulsion, and dispersed by high-speed shearing at 8000 r / min for 40 min. Then, the core-shell microsphere primary product is obtained by isothermal polymerization at 65℃ for 3 h. (3) Modification and post-treatment: Hydrophobic modified nano-silica, polyethylene glycol and tetrahydropyranoic acid were added sequentially to the core-shell microsphere primary product, ultrasonically dispersed for 25 min, and stirred at a constant temperature for 60 min; after natural cooling, the product was centrifuged, washed, and vacuum dried at 70℃ to constant weight. The resulting pH-sensitive corrosion inhibitor with a core-shell structure had a particle size of 200-500 nm.

[0020] Example 2: 1. A responsive pH-sensitive corrosion inhibitor for oilfields, having a core-shell structure, comprising the following raw materials in parts by weight per 100 parts total: The mixture contains 32 parts of oleic acid imidazoline, 4 parts of monk fruit polyphenols, 52 parts of pH-sensitive shell emulsion, 4 parts of hydrophobically modified nano-silica, 6 parts of polyethylene glycol, and 2 parts of tetrahydropyranoic acid; the pH-sensitive shell emulsion is a dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion. The dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion is prepared by the following method: dimethylaminoethyl methacrylate, acrylic acid, and modified chitosan are mixed evenly, anhydrous ethanol and an initiator are added, and the mixture is stirred at a constant speed of 150 r / min for 20 min; wherein the mass ratio of dimethylaminoethyl methacrylate, acrylic acid, modified chitosan, anhydrous ethanol, and initiator is 18:8:10:40:0.6. The modified chitosan was prepared by the following method: chitosan was dissolved in glacial acetic acid solution and dissolved at a constant temperature of 65°C under a nitrogen atmosphere. Then, cerium ammonium nitrate and dimethylaminoethyl methacrylate were added sequentially, and the reaction was continued at a constant temperature for 4.5 hours. Dialysis purification was performed using a regenerated cellulose dialysis bag with a molecular weight cutoff of 8000-14000 Da. The dialysate was deionized water, and the dialysate was changed every 4 hours until no monomers or metal ions were detected in the dialysate. The modified chitosan was then freeze-dried to obtain pure modified chitosan. The mass ratio of chitosan, glacial acetic acid solution, cerium ammonium nitrate, and dimethylaminoethyl methacrylate was 10:55:0.8:25, and the concentration of the glacial acetic acid solution was 1 wt%. The hydrophobically modified nano-silica was prepared by the following method: adding silane coupling agent KH-550 to a mixture of ethanol and water, stirring for 45 min, then adding nano-silica, refluxing at 75 °C for 2 h, centrifuging, washing with ethanol, and vacuum drying at 70 °C to constant weight; wherein the mass ratio of silane coupling agent to nano-silica is 6:100. 2. The preparation method of the aforementioned responsive oilfield pH-sensitive corrosion inhibitor includes the following steps: (1) Preparation of corrosion-inhibiting active core: Oleic acid imidazoline and monk fruit polyphenols were added to water and stirred at 55℃ and 280r / min for 35min to obtain corrosion-inhibiting active core liquid, which was kept warm for later use; wherein, the total mass ratio of oleic acid imidazoline and monk fruit polyphenols to water was 1:1.8. (2) Core-shell microsphere polymerization: The core active liquid is dropped into the pH-sensitive shell emulsion, dispersed by high-speed shearing at 9000 r / min for 45 min, and then polymerized at 68℃ for 3.5 h. The core-shell microsphere primary product is obtained through interfacial crosslinking reaction. (3) Modification and post-treatment: Hydrophobic modified nano silica, polyethylene glycol and tetrahydropyranoic acid were added sequentially to the core-shell microsphere primary product, ultrasonically dispersed for 30 min, and stirred at constant temperature for 70 min; after natural cooling, the product was centrifuged, washed, and vacuum dried at 70℃ to constant weight. The resulting pH-sensitive corrosion inhibitor with core-shell structure had a particle size of 200-500 nm.

[0021] Example 3: 1. A responsive pH-sensitive corrosion inhibitor for oilfields, having a core-shell structure, comprising the following raw materials in parts by weight per 100 parts total: The mixture contains 25 parts of imidazoline oleate, 4 parts of monk fruit polyphenols, 57 parts of pH-sensitive shell emulsion, 4 parts of hydrophobically modified nano-silica, 6 parts of polyethylene glycol, and 4 parts of tetrahydropyranoic acid; the pH-sensitive shell emulsion is a dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion. The dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion is prepared by the following method: dimethylaminoethyl methacrylate, acrylic acid, and modified chitosan are mixed evenly, anhydrous ethanol and an initiator are added, and the mixture is stirred at a constant speed of 150 r / min for 20 min; wherein the mass ratio of dimethylaminoethyl methacrylate, acrylic acid, modified chitosan, anhydrous ethanol, and initiator is 25:14:10:60:1.2. The modified chitosan and hydrophobically modified nano-silica are the same as in Example 1; 2. The preparation method of the responsive oilfield pH-sensitive corrosion inhibitor is the same as that in Example 1.

[0022] Example 4: A responsive pH-sensitive corrosion inhibitor for oilfields, having a core-shell structure, comprising the following raw materials in parts by weight per 100 parts total: The mixture contains 32 parts of imidazoline oleate, 2 parts of monk fruit polyphenols, 56 parts of pH-sensitive shell emulsion, 2 parts of hydrophobically modified nano-silica, 4 parts of polyethylene glycol, and 4 parts of tetrahydropyranoic acid; the pH-sensitive shell emulsion is a dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion. Everything else is the same as in Example 1.

[0023] Comparative Example 1: Lanthanum chloride was used instead of monk fruit polyphenols, and benzotriazole (BTA), a conventional auxiliary corrosion inhibitor, was used instead of tetrahydropyranoic acid. Everything else was the same as in Example 1.

[0024] Comparative Example 2: Benzotriazole (BTA) was used instead of tetrahydropyranoic acid, and everything else was the same as in Example 1.

[0025] Comparative Example 3: Lanthanum chloride was used instead of monk fruit polyphenols, and everything else was the same as in Example 1.

[0026] Performance testing To visually verify the pH-responsive drug release characteristics, wide temperature adaptability, high sulfur and high mineralization tolerance, and storage stability of the adjuvant of this invention, multiple sets of supporting evaluation tests were designed. The complete test methods and test results are as follows: Unified Explanation of Basic Experimental Conditions Corrosion substrate: Standard N80 carbon steel plate; Simulated produced fluid formulation: total mineralization 120,000 mg / L, H2S concentration 120 ppm; Reference test temperature: 90℃; Dosage regimen: Initial concentration of 60 mg / L is uniform, with intermittent supplementation, and the same concentration of adjuvant is added every 7 days; pH setting: pH is fixed at 5.5 under acidic conditions and 7.5 under neutral conditions; single-group alternating cycle process: acidic soaking for 2 hours → neutral soaking for 2 hours, the equipment is automatically controlled by a program to run 6 cycles per day, continuously for 90 days. Core detection indicators and calculation methods: Corrosion inhibition efficiency: calculated using the weight loss method of the coupon; Reagent loss rate: The remaining content of the long-chain alkyl imidazoline (oleic imidazoline) active component was quantitatively determined by ultraviolet spectrophotometry using periodic sampling of the medium. The proportion of active agent lost per unit period was calculated, which is the loss rate. Loss rate = 1 - (remaining content of active component ÷ initial content of active component), in percentage terms (%). Shell swelling degree: The corrosion inhibitor was freeze-dried, the core and shell were separated, and the shell was equilibrated in simulated produced fluid media with pH 5.5 and pH 7.5 for 24 h. The swelling ratio was calculated by weighing. Swelling ratio = mass after swelling ÷ mass before swelling. The higher the swelling ratio in acidic conditions, the faster the drug release. The lower the swelling ratio in neutral conditions, the better the drug locking and storage effect. 4) Drug release rate: Combining the swelling degree of the shell and the increase of long-chain alkyl imidazoline (oleic acid imidazoline) in the medium, the release rate of active components at different pH values ​​is quantified. The drug release rate directly determines the short-term corrosion inhibition efficiency.

[0027] 1. pH alternating cycle response sustained-release performance test Experimental groups: Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Initial corrosion inhibition efficiency after 2 hours in acidic conditions, agent loss rate in neutral conditions, long-term corrosion inhibition efficiency after 90 days of alternating corrosion, and swelling ratio of the acidic / neutral shell were simultaneously measured. This multi-dimensional assessment demonstrated the differentiated pH-responsive drug release behavior. The results are as follows: Comparative Example 1: Lacks pH-differentiated drug release regulation capability and cannot construct a reversible swelling-shrinkage shell structure; at acidic pH=5.5, the shell swelling ratio is only 1.12, with low pore expansion, insufficient release of active components within 2 hours, and an initial corrosion inhibition efficiency of only 90.8%; after switching to neutral pH=7.5, the shell has no shrinkage and locking effect, active components continue to leak, and the ineffective loss rate of the agent is as high as 21%; after 90 days of continuous pH alternation operation, the corrosion inhibition efficiency drops to 83.8%; in high-sulfur and high-mineralized media, the protective film is easily penetrated by corrosive ions, and local pitting corrosion occurs with each pH switch; there is no obvious gradient in the drug release rate under acidic and neutral conditions, and it does not have a pH-stimulated response sustained release effect; Comparative Example 2: In acidic environment, the shell swelling ratio was 1.25, with limited improvement in drug release and slight improvement in pH-responsive release efficiency, but the initial corrosion inhibition efficiency increased to 94.2%. In neutral conditions, the shell's ability to close and lock in the drug was insufficient, with a drug loss rate of 17.3%. After 90 days of alternating cycles, the corrosion inhibition efficiency was 88.5%. During acid-base switching, the reversibility of shell swelling and contraction was poor, the drug release rate differentiation was low, and the improvement in sulfur resistance and long-term pH adaptive ability was small, failing to achieve differentiated response of "rapid drug release in acidic conditions and long-term drug storage in neutral conditions." It is evident that single mogroside polyphenols are insufficient to perfect the pH-sensitive shell structure, and a synergistic effect system is lacking. Comparative Example 3: The swelling ratio of the acidic shell was 1.21, the release rate of the active component was only slightly improved, and the initial corrosion inhibition efficiency was 93.5%; the shell lock-in effect was poor under neutral conditions, and the agent loss rate was 18.1%; after 90 days of continuous operation, the corrosion inhibition efficiency was 87.6%; the film's antioxidant and ion shielding performance was weak, the reversibility of the shell's swelling and shrinkage under alternating acid and alkali conditions was poor, the release rate gradient was not obvious, and the long-term protection stability was insufficient; it can be seen that tetrahydropyranoic acid alone has obvious shortcomings in constructing a polymer shell pH reversible control structure; Example 1: Under acidic pH 5.5 conditions, the shell rapidly protonated and swelled, reaching a swelling ratio of 1.86, fully opening the drug release channels and rapidly releasing a large amount of corrosion-inhibiting active components within 2 hours, with an initial corrosion inhibition efficiency as high as 97.8%. When switching to neutral pH 7.5, the shell automatically deprotonated and contracted, reducing the swelling ratio to 1.03 and blocking the drug release channels. The ineffective drug loss rate under neutral conditions decreased to 13.2%, achieving low-speed, long-lasting drug storage protection. After continuous 90-day pH alternating cycle operation, the corrosion inhibition efficiency remained stable at over 92.5%. Under high sulfur and 120,000 mg / L high mineralization conditions, the protective film on the metal surface was dense and stable, with no ion penetration or film detachment failure after multiple acid-base switching. This demonstrates that the synergistic stabilization of the polymer pH-sensitive shell reversible swelling-contraction structure by mogroside polyphenols and tetrahydropyranoic acid exhibits a clear and controllable pH-stimulated response slow-release characteristic. In summary: Monk fruit polyphenols can form a dense, multi-layered protective film, compensating for the insufficient antioxidant and ion-shielding performance of traditional rare earth salts; tetrahydropyranoic acid enhances the interfacial adsorption of active components and improves sulfur resistance; the combination of the two achieves a pH-adaptive function of rapid acidic drug release and long-term neutral drug locking protection, with corrosion inhibition efficiency, long-term stability, and adaptability to high sulfur conditions significantly superior to single additives or alternative component systems.

[0028] 2. Wide temperature range adaptability test Using the simulated produced fluid of 120,000 mg / L and 120 ppm H2S, 60 mg / L of the additive from Example 1 was added, and the samples were kept at 40℃, 70℃, 90℃, and 120℃ for 72 h respectively. The corrosion inhibition efficiency was determined by the weight loss method. The corrosion inhibition efficiencies at 40℃, 70℃, 90℃, and 120℃ were 97.9%, 97.2%, 96.5%, and 94.1%, respectively. This indicates that the corrosion inhibition efficiency of this additive is higher than 94% in the entire temperature range of 40-120℃, with a wide temperature tolerance range. The pH response release structure is not damaged at high temperatures, making it suitable for high-temperature downhole and gathering pipeline conditions in oil fields.

[0029] 3. High mineralization and high hydrogen sulfide tolerance test Simulated produced fluids with total salinity of 50,000 mg / L, 100,000 mg / L, 120,000 mg / L, and 150,000 mg / L, corresponding to H2S concentrations of 20 ppm, 60 ppm, 100 ppm, and 120 ppm, were prepared in gradients and kept at a constant temperature of 90℃ for 72 h. In Example 1, 60 mg / L was added, and the corrosion inhibition efficiency was tested: Under extreme conditions of total salinity of 150,000 mg / L and H2S concentration of 120 ppm, the corrosion inhibition efficiency still reached 93.6%; This proves that this additive can stably withstand the harsh oilfield corrosive media with total salinity >100,000 mg / L and H2S >100 ppm, and its pH-responsive film-forming performance under high sulfur and high salinity environments showed no significant attenuation.

[0030] 4. Long-term storage stability test Take the finished additive from Example 1, and let it stand at room temperature in the dark for 90 days. Observe the appearance and test the particle size and corrosion inhibition efficiency at 0 days, 30 days, 60 days and 90 days. The corrosion inhibition efficiency is the 90-day alternating long-term corrosion inhibition efficiency in the above pH alternating cycle response slow-release performance test. 0 days: The liquid is uniform and clear, without stratification or precipitation; the microspheres have a particle size of 260-420 nm; and the alternating corrosion inhibition efficiency is 92.5% after 90 days. 30 days: The system was uniform with no flocculation, no sedimentation or stratification, no significant increase in particle size, and a corrosion inhibition efficiency of 92.1%; 60 days: No agglomeration or clumping, no precipitates at the bottom, corrosion inhibition efficiency 91.7%; 90 days: The liquid does not separate into layers, and there is no white silica slag / polymer precipitate. Only the microspheres with a particle size of 280~460nm float to the surface, and the corrosion inhibition efficiency is 90.9%. This demonstrates that the additive does not agglomerate, separate into layers, or precipitate when left to stand for a long time in a high-mineralized oil-water simulation system, exhibiting excellent storage stability.

Claims

1. A responsive pH-sensitive corrosion inhibitor for oilfields, characterized in that: The responsive oilfield pH-sensitive corrosion inhibitor has a core-shell structure and comprises the following raw materials in parts by weight per 100 parts: 25-32 parts of long-chain alkyl imidazoline, 2-4 parts of monk fruit polyphenols, 52-57 parts of pH-sensitive shell emulsion, 2-4 parts of hydrophobically modified nano silica, 4-6 parts of polyethylene glycol, and 2-4 parts of tetrahydropyranoic acid. The pH-sensitive shell emulsion is a dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion.

2. The responsive oilfield pH-sensitive corrosion inhibitor according to claim 1, characterized in that: The dimethylaminoethyl methacrylate-acrylic acid-chitosan copolymer emulsion is prepared by the following method: dimethylaminoethyl methacrylate, acrylic acid, and modified chitosan are mixed evenly, anhydrous ethanol and an initiator are added, and the mixture is stirred.

3. The responsive oilfield pH-sensitive corrosion inhibitor according to claim 2, characterized in that: The mass ratio of dimethylaminoethyl methacrylate, acrylic acid, modified chitosan, anhydrous ethanol, and initiator is (18-25):(8-14):10:(40-60):(0.6-1.2).

4. The responsive oilfield pH-sensitive corrosion inhibitor according to claim 2, characterized in that: The modified chitosan was prepared by the following method: chitosan was dissolved in glacial acetic acid solution and dissolved at a constant temperature of 60-65°C under a nitrogen atmosphere. Then, cerium ammonium nitrate and dimethylaminoethyl methacrylate were added sequentially, and the reaction was continued at a constant temperature for 4-4.5 hours. The mixture was then purified by dialysis and freeze-dried.

5. The responsive oilfield pH-sensitive corrosion inhibitor according to claim 4, characterized in that: The mass ratio of chitosan, glacial acetic acid solution, cerium ammonium nitrate, and dimethylaminoethyl methacrylate is 10:(50-55):(0.5-0.8):(22-25); the concentration of the glacial acetic acid solution is 1 wt%.

6. The responsive oilfield pH-sensitive corrosion inhibitor according to claim 1, characterized in that: The hydrophobically modified nano-silica is prepared by the following method: adding a silane coupling agent to a mixture of ethanol and water, stirring for 40-45 min, then adding nano-silica, refluxing at 70-75℃ for 2 h, centrifuging, washing with ethanol, and vacuum drying; wherein the mass ratio of silane coupling agent to nano-silica is (4-6):

100.

7. The responsive oilfield pH-sensitive corrosion inhibitor according to claim 3, characterized in that: The initiator is azobisisobutyronitrile.

8. The preparation method of the responsive oilfield pH-sensitive corrosion inhibitor as described in claim 1, characterized in that: Includes the following steps: (1) Preparation of corrosion-inhibiting active core: Long-chain alkyl imidazoline and monk fruit polyphenols are added to water and stirred at 50-55℃ for 30-35 min to obtain corrosion-inhibiting active core solution, which is kept warm for later use; (2) Core-shell microsphere polymerization: The core active liquid is dropped into the pH-sensitive shell emulsion, sheared and dispersed at 8000-9000 r / min for 40-45 min, and then polymerized at 65-68℃ for 3-3.5 h to obtain the core-shell microsphere primary product; (3) Modification and post-treatment: Hydrophobic modified nano silica, polyethylene glycol and tetrahydropyranoic acid are added sequentially to the core-shell microsphere primary product, ultrasonically dispersed for 25-30 min, and stirred at a constant temperature for 60-70 min; after natural cooling, it is centrifuged, washed and vacuum dried.

9. The preparation method of the responsive oilfield pH-sensitive corrosion inhibitor according to claim 8, characterized in that: In step (1), the total mass ratio of long-chain alkyl imidazoline and monk fruit polyphenols to water is 1:(1.2-1.8).

10. The application of the responsive pH-sensitive corrosion inhibitor of oilfields as described in claim 1 in oilfield corrosion prevention, characterized in that: The responsive pH-sensitive corrosion inhibitor for oilfields is added to the media in oilfield gas well shafts, gathering and transmission pipelines, and sewage reinjection systems at a concentration of 50-80 mg / L.