A defoaming agent for natural gas well produced water and a preparation method thereof

Abstract

This invention discloses an defoamer for produced water from natural gas wells and its preparation method, relating to the field of oil and gas field water treatment technology. The defoamer comprises modified organosilicon, modified hydrogenated rosin glycerol ester, modified alkyl glycoside, potassium pyrophosphate, polyethylene glycol monooleate, plant-based dicarboxylic acid ester, and deionized water. The modified organosilicon is obtained by grafting polydimethylsiloxane with terminal hydroxyl polyether and then modifying it with low-carbon carboxylic anhydride. The modified hydrogenated rosin glycerol ester is obtained by esterifying hydrogenated rosin with glycerol and then modifying it with polyoxyethylene branching. The modified alkyl glycoside is obtained by etherification and condensation of alkyl glycoside with small-molecule polyol and then modifying it with weak phosphonate. This invention addresses the complex conditions of high-altitude gas fields, characterized by high temperature, low pressure, high fine silica particles, and high humic content. It solves the problems of existing defoamers, such as easy solidification and stratification at low temperatures, poor fluidity, decreased activity, easy clogging of pipelines, and difficulty in breaking complex foams, making it suitable for the complex conditions of high-altitude gas fields.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field water treatment technology, specifically a defoamer for produced water from natural gas wells and its preparation method. Background Technology

[0002] With the continuous increase in domestic natural gas energy development efforts, and in order to further expand clean energy supply capacity and improve the energy extraction layout in western China, the country has gradually increased its exploration and development efforts for natural gas resources in plateau areas. Several plateau gas field development blocks have been successively developed, including the Longmenshan production area in western Sichuan, the Songpan production area in northwestern Sichuan, and the Lunpola Basin gas field in northern Tibet. In actual plateau gas field extraction operations, produced water contains formation particles and various natural substances. To ensure stable extraction, various commonly used oilfield additives such as foaming agents and corrosion inhibitors are added during construction. These substances mix together, easily generating large amounts of stable foam at the gas-liquid contact point. Excessive foam in the produced water directly leads to poor gas-liquid separation, deviations in gas delivery metering, and can easily cause problems such as liquid-laden unit operation and back-end processing equipment malfunctions, seriously affecting the normal extraction progress. Therefore, effective defoaming treatment of produced water in plateau gas fields is essential.

[0003] Most existing conventional defoamers are formulated with organosilicon and common polyether as the main raw materials. They can be used by adding them at room temperature and are generally suitable for defoaming scenarios in produced water from flat oil and gas fields with mild climates, simple water composition, and low solid impurity content. However, when applying these conventional defoamers to the aforementioned plateau gas field development sites, the following technical problems are encountered due to the special local environment and produced water quality: Firstly, the plateau region is in a cold environment all year round, with the overall ambient temperature mostly in the range of -20℃ to 20℃. Under low temperature conditions, conventional defoamers are prone to solidification and stratification, and their fluidity becomes poor. Direct injection can easily clog the agent pipeline and slow down the diffusion speed of the agent. The ability to quickly break bubbles on site is greatly reduced, making it difficult to meet the real-time defoaming needs under the low temperature conditions of the plateau.

[0004] Secondly, the strata of the plateau gas field are mainly composed of sandstone, carbonate rock, and shale. Long-term natural weathering has resulted in a loose geological structure, leading to the presence of a large amount of fine silica particles in the produced water. Simultaneously, the widespread distribution of permafrost in the plateau environment allows for the full decomposition of alpine plant remains such as *Kobresia*, *Stipa*, and *Juniperus* under low-temperature anaerobic conditions, enriching the produced water with abundant natural humic substances, primarily humic acid, fulvic acid, and humin. This natural organic matter, combined with various extraction aids added on-site and mixed with the large amount of fine silica particles in the water, can collectively form a structurally stable foam layer. Conventional defoamers can only break down the lightweight foam formed by ordinary aids and have difficulty penetrating this composite foam layer. Furthermore, the active ingredients of defoamers are easily adsorbed onto the surface of silica particles and lose their effectiveness, significantly reducing the defoaming effect. They can also easily form viscous impurities that clog pipelines and separation equipment, increasing the workload of on-site cleaning and maintenance.

[0005] Third, the low atmospheric pressure in plateau regions enhances foam stability and delays natural foam collapse. At the same time, low pressure accelerates the loss of small amounts of volatile additives in defoamers, shortening their effective duration. When faced with sudden large amounts of foam caused by fluctuations in gas well production, long-term foam suppression is impossible, and the phenomenon of repeated foam generation is quite prominent.

[0006] Therefore, developing a special defoamer for natural gas well produced water that is specifically adapted to the aforementioned high-altitude environment and can efficiently solve existing technical problems is of great practical significance. Summary of the Invention

[0007] The purpose of this invention is to provide a defoamer for produced water from natural gas wells and its preparation method. This defoamer can maintain good fluidity and stable activity under low temperature and low pressure environments, effectively penetrate the composite foam layer formed by high silica particles and high humic substances, and at the same time reduce the adhesion and blockage of the agent in the pipeline. It is suitable for the complex water quality and environmental conditions of plateau gas fields, achieves rapid foam breaking and long-term foam suppression, ensures gas-water separation efficiency and continuous and stable operation of production, and effectively solves the defects of existing conventional defoamers that are difficult to adapt to the complex working conditions of high temperature, low pressure, high fine silica particles and high humic substances in plateau gas fields.

[0008] The objective of this invention is achieved through the following technical solution: An antifoaming agent for produced water from natural gas wells comprises the following components in parts by weight: 45-65 parts modified organosilicon, 10-18 parts modified hydrogenated rosin glycerol ester, 6-12 parts modified alkyl glycoside, 4-10 parts potassium pyrophosphate, 3-7 parts polyethylene glycol monooleate, 1-4 parts plant-based dicarboxylic acid ester, and 20-30 parts deionized water; The modified organosilicon is obtained by grafting polydimethylsiloxane with terminal hydroxyl polyether and then modifying it with low-carbon carboxylic anhydride. The modified hydrogenated rosin glycerol ester is obtained by glycerol esterification of hydrogenated rosin, followed by modification with polyoxyethylene branch chains of degree of polymerization 3-6. The modified alkyl glycoside is obtained by etherification condensation reaction of alkyl glycoside and small molecule polyol, followed by modification with weak phosphonate.

[0009] This invention addresses the complex operating conditions of high-altitude gas fields, characterized by extreme cold, low gas pressure, high levels of fine silica particles, and high humic content. It provides a suitable defoamer for produced water from natural gas wells, effectively solving technical problems associated with existing conventional defoamers, such as easy solidification and stratification at low temperatures, poor fluidity, decreased activity, easy clogging of pipelines, and difficulty in breaking down complex foams. The specific functions of the components are as follows: In modified organosilicon, organosilicon itself can reduce the gas-liquid interfacial tension and achieve rapid defoaming; grafting modification with terminal hydroxyl polyether can improve the low-temperature fluidity and diffusion ability of organosilicon, solving the problems of easy solidification of organosilicon and easy blockage of injection pipeline in high-altitude and cold environments; further modification of organosilicon with low-carbon carboxylic anhydride with 1 to 6 carbon atoms can enhance the interfacial spreading ability and anti-volatilization stability of organosilicon, improve the low-temperature activity and long-term defoaming performance of organosilicon in high-altitude and low-pressure environments, and enable organosilicon to penetrate the composite foam layer formed by high humus in high-altitude produced water.

[0010] In modified hydrogenated rosin glycerol esters, hydrogenated rosin is first esterified to produce hydrogenated rosin glycerol esters, solving the problem of hydrogenated rosin's strong oiliness and tendency to precipitate oil in high-altitude, low-temperature, and low-ion environments. The resulting product improves emulsification and dispersibility and can be adsorbed at the foam interface, playing a role in assisting foam breaking. Then, polyoxyethylene branches with a degree of polymerization of 3-6 are introduced to modify the hydrogenated rosin glycerol esters, weakening the ineffective association between hydrogenated rosin glycerol esters and humic substances, enhancing the ability of hydrogenated rosin glycerol esters to penetrate and disintegrate the composite foam layer, reducing the risk of pipeline adhesion and blockage, and making it suitable for high-altitude water quality with high humic substances and high silica fine particles. In practical applications, hydrogenated rosin glycerol esters and polyethylene glycol monooleate are prone to local enrichment, low-temperature settling turbidity, and organic matter adhesion to pipelines. Plant-based dicarboxylic acid esters can disperse local aggregates of components, eliminate settling turbidity, and form a spatial isolation layer on the outer layer of the molecule, reducing organic matter entrainment and mitigating pipeline adhesion.

[0011] In modified alkyl glycosides, the alkyl glycosides themselves can regulate the particle interface in water and assist in defoaming. However, in high-altitude, high-silica, fine-particle water, the combination of alkyl glycosides and potassium pyrophosphate easily causes secondary flocculation of fine suspended particles (including silica particles and organic particles) in the water, crowding out defoaming active sites and reducing defoaming efficiency. This invention first modifies the alkyl glycosides by small-molecule polyol etherification condensation to improve the molecular structural stability of the alkyl glycosides and enhance their resistance to low temperatures and water quality fluctuations; then, through weak phosphonate modification, it reduces the surface activity of particles and the adsorption of active components by chelating metal ions adsorbed on the surface of silica particles, weakening the excess surface activity of the system, effectively improving the tendency of fine suspended particles to agglomerate, avoiding the adsorption and consumption of defoaming active components, and ensuring stable defoaming performance.

[0012] Potassium pyrophosphate can chelate water ions, disperse fine silica particles, and regulate the interface state of silica particles. In synergy with modified alkyl glycosides, it can stabilize the particle interface, reduce particle aggregation, and improve the dispersion uniformity of the system.

[0013] Polyethylene glycol monooleate can promote the drainage of foam liquid film, enhance the foam breaking and foam suppression effect, improve the low-temperature fluidity of the system, delay foam regeneration, and is suitable for high-altitude low-temperature and fluctuating gas production conditions.

[0014] In summary, the components of this invention are synergistically formulated and have complementary properties. They can be stably dispersed at room temperature, making them suitable for the low temperature, low pressure, high silica fine particles, and high humic content conditions of produced water in plateau gas fields. This enables rapid foam breaking, long-term foam suppression, and anti-clogging, improving gas-water separation and ensuring continuous and stable operation of the production process.

[0015] As some possible implementations of this application, in the modified organosilicon, the mass ratio of polydimethylsiloxane, hydroxyl-terminated polyether, and low-carbon carboxylic anhydride is 10:(3-5):(1-2).

[0016] As some possible embodiments of this application, in the modified hydrogenated rosin glycerol ester, the mass ratio of hydrogenated rosin, glycerol, and polyoxyethylene branched chain is 10:(2-3):(1-1.5).

[0017] As some possible embodiments of this application, in the modified alkyl glycoside, the mass ratio of alkyl glycoside, small molecule polyol, and weak phosphonate is 10:(2-4):(0.5-1).

[0018] As some possible embodiments of this application, the small molecule polyol is ethylene glycol or propylene glycol, the weak phosphonate is an alkali metal salt of hydroxyethylidene diphosphonic acid, and the low-carbon carboxylic anhydride is a saturated fatty acid anhydride with 1 to 6 carbon atoms. In this scheme, ethylene glycol or propylene glycol is selected as the small molecule polyol. After etherification and condensation, flexible hydrophilic short chains can be introduced onto the alkyl glycoside molecule, improving its low-temperature stability and dispersibility in water, and reducing low-temperature stratification. The selection of the weak phosphonate as an alkali metal salt of hydroxyethylidene diphosphonic acid can effectively passivate the surface activity of silica particles, effectively improve the agglomeration and flocculation of fine particles, and avoid the adsorption and consumption of defoaming active components. The selection of a saturated fatty acid anhydride with 1 to 6 carbon atoms as the low-carbon carboxylic anhydride has moderate polarity and stable modification effect, which can enhance the interfacial spreading ability and low-pressure anti-volatilization stability of organosilicon, and improve low-temperature activity and composite foam penetration ability.

[0019] As some possible embodiments of this application, the plant-based dicarboxylic acid ester is a palmitic acid diester, which is a diester compound synthesized from palmitic acid and ethylene glycol or propylene glycol.

[0020] Furthermore, to achieve the above objectives, the present invention also provides a method for preparing an antifoaming agent for produced water from natural gas wells, comprising the following steps: At room temperature, first add deionized water to the mixing container, then add potassium pyrophosphate and stir until completely dissolved; then add modified organosilicon, modified hydrogenated rosin glycerol ester, modified alkyl glycoside, plant-based dicarboxylic acid ester, and polyethylene glycol monooleate in sequence, and stir until the system is homogeneous. After standing to remove bubbles and filtering, the finished product is obtained.

[0021] As some possible implementations of this application, the settling and degassing time is 10-15 minutes; the filtration uses a 100-120 mesh filter cloth.

[0022] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a suitable defoamer for produced water from natural gas wells, addressing the complex conditions of high altitude, low pressure, high fine silica particles, and high humus in plateau gas fields. It aims to solve the technical problems of existing conventional defoamers, such as easy solidification and stratification at low temperatures, poor fluidity, decreased activity, easy clogging of pipelines, and difficulty in breaking down complex foams. Specifically, this invention utilizes the synergistic formulation of modified organosilicon, modified hydrogenated rosin glycerol ester, and modified alkyl glycosides to produce an antifoaming agent with excellent low-temperature stability. After standing at -20℃ for 72 hours, it exhibits no stratification, solidification, or precipitation; its freezing point is ≤-27.1℃, and its low-temperature viscosity is ≤342 mm² / s, demonstrating good low-temperature fluidity and preventing solidification and pipeline blockage issues in high-altitude and frigid environments; its 1-minute foam breaking rate is ≥92.7%, and its 5-minute foam suppression height is ≤21 mm, allowing for rapid penetration of the composite foam layer formed by high-silica particles and high-humic substances; its 30-minute foam recovery rate is ≤2.8%, demonstrating strong anti-volatilization ability and excellent long-term foam suppression performance, effectively solving the problem of repeated foam generation under low pressure in high-altitude environments; and its pipeline adhesion rate is ≤2.6%, effectively reducing the adhesion of viscous impurities and lowering the risk of pipeline and equipment blockage. It is fully adaptable to the low temperature, low pressure, high silica fine particles, and high humic conditions of plateau gas fields, and can achieve rapid foam breaking, long-term foam suppression, and anti-clogging, ensuring gas-liquid separation effect and continuous and stable operation of production. Detailed Implementation

[0023] High-altitude gas fields are generally characterized by complex operating conditions such as high temperature, low pressure, high concentration of fine silica particles, and high humus content. Existing conventional defoamers are difficult to adapt to such complex environments, exhibiting problems such as easy solidification and stratification at low temperatures, poor fluidity, rapid activity decay, severe pipeline adhesion and blockage, and difficulty in breaking down complex foams, which seriously affect gas-water separation efficiency and the stability of production operations. Therefore, this invention provides a defoamer for produced water from natural gas wells and its preparation method. Through the synergistic formulation of specific modified components, the above-mentioned technical defects are effectively solved. The following specific embodiments further illustrate the technical solution and effects of this invention.

[0024] Example 1 1. Preparation of non-commercially available components (components whose preparation methods are not mentioned are all commercially available). (1) Preparation of modified organosilicon: according to polydimethylsiloxane (viscosity 500 mPa) The modified organosilicon was prepared by mixing polydimethylsiloxane (polydimethylsiloxane), hydroxyl-terminated polyether (polyoxyethylene-polyoxypropylene block ether, molecular weight 2000 Da), and low-carbon carboxylic anhydride (acetic anhydride, purity ≥99%) in a mass ratio of 10:4:1.5. First, polydimethylsiloxane was added to a reactor, followed by 0.7% (by mass) of 85% phosphoric acid. The mixture was heated to 80°C and stirred at 400 r / min. The hydroxyl-terminated polyether was then slowly added dropwise, and the reaction was maintained at 80°C for 3 h. After the reaction was complete, the temperature was lowered to 60°C, and 0.7% (by mass) of zinc isooctanoate was added, followed by acetic anhydride. The reaction was maintained at 500 r / min for 2 h. The temperature was then lowered to 50°C, and low-boiling-point substances were removed under reduced pressure. The mixture was cooled and discharged to obtain the modified organosilicon.

[0025] (2) Preparation of modified hydrogenated rosin glycerol ester: The materials were prepared according to the mass ratio of hydrogenated rosin (softening point 80℃, degree of hydrogenation ≥95%), glycerol, and polyoxyethylene branched chain (polyethylene glycol, degree of polymerization 4) of 10:2.5:1.2. The hydrogenated rosin was heated to 140℃ to melt, glycerol was added, and esterification reaction was carried out at 240℃ for 4 h; the temperature was lowered to 120℃, polyethylene glycol was added, and grafting reaction was carried out at 120℃ for 3 h under nitrogen protection; after cooling, it was crushed through a 200-mesh sieve to obtain modified hydrogenated rosin glycerol ester. (3) Preparation of modified alkyl glycoside: The materials were prepared according to the mass ratio of alkyl glycoside (C12 alkyl glycoside, based on 100% effective ingredient), small molecule polyol (ethylene glycol), and weak phosphonate (hydroxyethylidene diphosphonate, HEDP). The alkyl glycosides were prepared in a mass ratio of 10:3:0.8 (Na4). A 40% aqueous solution was prepared and dissolved by stirring at 60°C and 400 r / min. Ethylene glycol was added, and the mixture was heated to 75°C and etherified at 500 r / min for 2 h. HEDP was then added. Na4 was stirred at 75°C for 1.5 h; the mixture was concentrated under reduced pressure until it became dry, cooled, and then pulverized through a 200-mesh sieve to obtain the modified alkyl glycoside.

[0026] (4) Preparation of palmitic acid diester: In a reaction vessel equipped with a stirrer, reflux condenser and water separator, 1 mol of ethylene glycol and 2.05 mol of palmitic acid were added, and the mixture was stirred and heated to 70°C to melt the solid. 0.5% of 85 phosphoric acid was added, and the temperature was raised to 140-150°C. The reaction was maintained for 4-6 h. During the reaction, the generated water was removed in time through the water separator. After the reaction was completed, the unreacted small amount of palmitic acid and residual water were removed by vacuum distillation (-0.08 to -0.1 MPa). The mixture was cooled to room temperature to obtain a white waxy solid palmitic acid diester with an esterification rate ≥95%.

[0027] 2. Preparation of defoamer.

[0028] Under normal temperature conditions, first add 20 parts of deionized water to the mixing container, then add 7 parts of potassium pyrophosphate, and stir at 300 r / min for 10 min; then add 55 parts of modified organosilicon, 14 parts of modified hydrogenated rosin glycerol ester, 9 parts of modified alkyl glycoside, 2.5 parts of plant-based dicarboxylic acid ester, and 5 parts of polyethylene glycol monooleate (degree of polymerization 20) in sequence, stir at 350 r / min for 15 min, then let stand to degas for 12 min, and finally filter through a 110 mesh filter cloth to obtain the finished product.

[0029] Example 2 Compared to Example 1, only the following parameters are adjusted; the rest are the same as in Example 1: 1. Preparation of non-commercially available components. (1) Modified organosilicon: polydimethylsiloxane, hydroxyl-terminated polyether, and acetic anhydride in a mass ratio of 10:3:1. (2) Modified hydrogenated rosin glycerol ester: hydrogenated rosin, glycerol, and polyethylene glycol (degree of polymerization 3) in a mass ratio of 10:2:1. (3) Modified alkyl glycoside: alkyl glycoside, ethylene glycol, and HEDP. The mass ratio of Na4 is 10:2:0.5.

[0030] 2. Preparation of defoamer. Raw material ratio (parts by weight): 45 parts modified organosilicon, 10 parts modified hydrogenated rosin glycerol ester, 6 parts modified alkyl glycoside, 4 parts potassium pyrophosphate, 3 parts polyethylene glycol monooleate, 1 part palmitate diester, 25 parts deionized water.

[0031] Example 3 Compared to Example 1, only the following parameters are adjusted; the rest are the same as in Example 1: 1. Preparation of non-commercially available components. (1) Modified organosilicon: polydimethylsiloxane, hydroxyl-terminated polyether, and acetic anhydride in a mass ratio of 10:5:2. (2) Modified hydrogenated rosin glycerol ester: hydrogenated rosin, glycerol, and polyethylene glycol (degree of polymerization 6) in a mass ratio of 10:3:1.5. (3) Modified alkyl glycoside: alkyl glycoside, propylene glycol, and HEDP. The mass ratio of Na4 is 10:4:1.

[0032] 2. Preparation of defoamer. Raw material ratio (parts by weight): 65 parts modified organosilicon, 18 parts modified hydrogenated rosin glycerol ester, 12 parts modified alkyl glycoside, 10 parts potassium pyrophosphate, 7 parts polyethylene glycol monooleate, 4 parts palmitate diester, 30 parts deionized water.

[0033] It is worth noting that: Structural characterization verified that the modified organosilicones prepared in Examples 1-3 all had infrared spectra in the range of 1090–1110 cm⁻¹. -The characteristic peaks of polyether COC stretching vibrations appear in the ¹ range, and also in the 1720–1740 cm⁻¹ range. - The presence of a characteristic absorption peak for the carbonyl group of carboxylic ester in the ¹ region confirms the success of both polyether grafting and carboxylic anhydride modification.

[0034] The modified hydrogenated rosin glycerol esters prepared in Examples 1-3 all had acid values ​​≤8 mgKOH / g and esterification degrees ≥92%, indicating that the esterification reaction was complete. The measured molecular weights of the modified alkyl glycosides prepared in Examples 1-3 were all stably controlled within the range of 1500-2000 Da, and the etherification condensation modification effect was uniform.

[0035] Comparative Example 1 Compared with Example 1: the modified organosilicon was replaced with an equal mass of unmodified polydimethylsiloxane, and the remaining raw material ratios and preparation processes were exactly the same as in Example 1.

[0036] Comparative Example 2 Compared with Example 1: the modified organosilicon was replaced with an equal mass of organosilicon that was only grafted with terminal hydroxyl polyether and not modified with low-carbon carboxylic anhydride, while the other raw material ratios and preparation processes were exactly the same as in Example 1.

[0037] Comparative Example 3 Compared with Example 1: In the preparation of modified hydrogenated rosin glycerol ester, the polyoxyethylene branching step was omitted, and only the glycerol esterification reaction was carried out. The rest was the same as in Example 1.

[0038] Comparative Example 4 Compared with Example 1: In the preparation of modified alkyl glycosides, the weak phosphonate modification step was omitted, and only the ethylene glycol etherification condensation reaction was carried out, while the rest was the same as in Example 1.

[0039] Comparative Example 5 Compared with Example 1: the modified alkyl glycoside component was directly removed, while the remaining raw material ratios and preparation processes were exactly the same as in Example 1.

[0040] Comparative Example 6 Compared with Example 1: the plant-based dicarboxylic acid ester component was directly removed, while the remaining raw material ratios and preparation processes were exactly the same.

[0041] Experimental Example The defoamers prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to the following tests on the defoamer stock solution and the defoaming performance evaluation experiments on produced water from plateau gas fields (the experimental results are shown in Table 1): 1. Low-temperature performance test of defoamer concentrate.

[0042] ①Low temperature stability: Take 50 mL of defoamer stock solution and place it in a sealed transparent sample bottle. Put the sample bottle in a low temperature constant temperature chamber that is maintained at a stable temperature of -20℃. After standing for 72 hours, take it out and observe whether the defoamer stock solution shows stratification, solidification or precipitation.

[0043] ② Freezing point: Take 50 mL of defoamer stock solution and place it in a freezing point test tube. Use a low-temperature freezing point tester to slowly cool it down. Observe the sample state throughout the process and record the temperature at which the defoamer stock solution completely loses its fluidity and solidifies. The unit is ℃.

[0044] ③ Low temperature viscosity: Take 50 mL of defoamer stock solution and place it in a constant temperature container. Keep the container temperature stable at -20℃ and let it stand at the constant temperature for 2 hours to make the sample temperature uniform. Then, use a rotational viscometer to measure its kinematic viscosity, with the unit being mm² / s.

[0045] 2. Defoaming experiment (measuring cylinder method).

[0046] This experiment used the 1000 mL transparent stoppered graduated cylinder method and was conducted entirely in a closed cryogenic and low-pressure chamber at an ambient temperature of -20℃ and a system pressure of 0.7 atm. The specific procedures are as follows: A 1000 mL stoppered graduated cylinder with a precision of 1 mL was used. Three graduated cylinders were set up in parallel for each group of experiments, with a relative standard deviation of ≤5%. The experimental results were averaged. 800 mL of simulated plateau gas field produced water was injected into each graduated cylinder (this simulated plateau gas field produced water was used in the examples and comparative examples). Stable foam was generated using nitrogen aeration, with nitrogen purity ≥99.9%, aerator orifice diameter of 0.5 mm, aeration flow rate controlled at 1.5 L / min, and continuous aeration for 5 min, forming an initial foam height of 220 mm. Subsequently, the corresponding defoamer (dosage of 100 mg / L) was added, and the mixture was stirred using an electric stirrer. First, it was rapidly stirred at 200 r / min for 2 min to fully mix the defoamer with the water. Then, it was slowly stirred at 80 r / min for 5 min. After stirring, the following defoaming-related performance tests were carried out.

[0047] ① 1 min foam breaking rate: After stirring in the graduated cylinder, keep the ambient temperature at -20℃ and the system pressure at 0.7 atm constant, let it stand for 1 min, read the height of the remaining foam layer in the graduated cylinder, and calculate the foam breaking rate according to the formula: foam breaking rate = (initial foam height - remaining foam height after standing for 1 min) / initial foam height × 100%.

[0048] ②5 min foam suppression height: After stirring in the graduated cylinder, keep the ambient temperature at -20℃ and the system pressure at 0.7 atm constant, let it stand for 5 min, and directly read the height of the foam layer in the graduated cylinder, in mm.

[0049] ③ 30-minute foam recovery rate: After completing the 5-minute foam suppression height test, continue to stand for 30 minutes, read the foam height, and calculate the recovery rate: Recovery rate (%) = (30-minute foam height - 5-minute foam height) ÷ initial foam height × 100%.

[0050] ④ Pipeline adhesion rate: After stirring in the graduated cylinder, a portion of the mixture was injected into a stainless steel circulation pipeline system and continuously circulated for 48 hours at a flow rate of 1.2 m / s under conditions of -20℃ and 0.7 atm. After the experiment, the initial total mass of the circulation system and the remaining total mass of the system after circulation were weighed, and the adhesion rate was calculated according to the formula: Adhesion rate = (initial total mass of the circulation system - remaining total mass of the system after circulation) / initial total mass of the circulation system × 100%.

[0051] The produced water from the simulated plateau gas field described above has the following specific composition: Fine silica particles: 1000 mg / L, particle size not greater than 5 μm, composed of sandstone, carbonate rock and mudstone in a mass ratio of 6:3:1; Humic acid: 490 mg / L, of which macromolecules with a molecular weight ≥500 Da account for more than 30% of the total humic acid; Fulvic acid: 400 mg / L; Humin: 200 mg / L; Lignin derivatives: 150 mg / L; Phenolic compounds: 50 mg / L; Foaming agent: 300 mg / L, sodium fatty alcohol polyoxyethylene ether sulfate; Corrosion inhibitor: 150 mg / L, an imidazoline corrosion inhibitor; Mineralization: 8500 mg / L, prepared from a mixture of sodium chloride, calcium chloride and magnesium chloride; Water pH: 7.0–7.5.

[0052] Table 1: As can be seen from Table 1: Examples 1-3 show that the defoamers prepared under the synergistic effect of modified organosilicon, modified hydrogenated rosin glycerol ester, and modified alkyl glycoside exhibit excellent low-temperature stability. After standing at -20℃ for 72 hours, there is no stratification, solidification, or precipitation. The freezing point is ≤-27.1℃, and the low-temperature viscosity is ≤342 mm² / s, demonstrating good low-temperature fluidity and avoiding solidification and pipeline blockage issues in high-altitude and cold environments. The foam breaking rate is ≥92.7% in 1 minute, and the foam suppression height is ≤21 mm in 5 minutes, allowing for rapid penetration of the composite foam layer formed by high-silica particles and high-humic substances. The foam recovery rate is ≤2.8% in 30 minutes, demonstrating strong anti-volatilization ability and excellent long-term foam suppression performance, effectively solving the problem of repeated foam generation under low pressure in high-altitude environments. The pipeline adhesion rate is ≤2.6%, effectively reducing the adhesion of viscous impurities and lowering the risk of pipeline and equipment blockage. It is fully adaptable to the low temperature, low pressure, high silica fine particles, and high humic conditions of plateau gas fields, and can achieve rapid foam breaking, long-term foam suppression, and anti-clogging, ensuring gas-liquid separation effect and continuous and stable operation of production.

[0053] In Comparative Example 1, no modified organosilicon was used; only unmodified polydimethylsiloxane was employed. This resulted in poor low-temperature compatibility and flowability, weak anti-volatilization ability, poor low-temperature stability, a high freezing point, increased viscosity, a significantly decreased defoaming rate, an extremely high foam recovery rate, and a markedly increased pipeline adhesion rate. In Comparative Example 2, the organosilicon was only grafted with terminal hydroxyl polyether without modification with low-carbon carboxylic anhydride. This resulted in insufficient anti-volatilization stability under low environmental pressure, weak low-temperature activity and interfacial spreading ability, poor long-term foam suppression performance, significant foam recovery, and reduced defoaming and foam suppression efficiency. In Comparative Example 3, hydrogenated rosin glycerol ester was not modified with polyoxyethylene branches, making it prone to ineffective association with humic substances. This resulted in weak composite foam penetration ability, poor long-term foam suppression effect, a high pipeline adhesion rate, and decreased anti-clogging performance. In Comparative Example 4, the alkyl glycosides were not modified with weak phosphonates, which failed to effectively passivate the surface activity of silica particles. Fine suspended particles easily agglomerated, and the defoaming active components were easily adsorbed and consumed, resulting in insufficient long-term foam suppression stability and reduced defoaming efficiency. In Comparative Example 5, the lack of modified alkyl glycoside components led to insufficient dispersion and interface regulation of silica particles, significant particle aggregation, easy consumption of defoaming activity, poor long-term foam suppression effect, and increased risk of pipe adhesion. In Comparative Example 6, the lack of plant-based dicarboxylic acid ester components resulted in localized enrichment of the components, easy turbidity upon low-temperature standing, difficulty in forming a molecular isolation layer, prominent problems with organic matter adhering to the pipes, weak long-term foam suppression stability, and a high pipe adhesion rate.

Claims

1. A defoamer for produced water from natural gas wells, characterized in that, Includes the following components by weight: 45-65 parts modified organosilicon, 10-18 parts modified hydrogenated rosin glycerol ester, 6-12 parts modified alkyl glycoside, 4-10 parts potassium pyrophosphate, 3-7 parts polyethylene glycol monooleate, 1-4 parts plant-based dicarboxylic acid ester, and 20-30 parts deionized water; The modified organosilicon is obtained by grafting polydimethylsiloxane with terminal hydroxyl polyether and then modifying it with low-carbon carboxylic anhydride. The modified hydrogenated rosin glycerol ester is obtained by glycerol esterification of hydrogenated rosin, followed by modification with polyoxyethylene branch chains of degree of polymerization 3-6. The modified alkyl glycoside is obtained by etherification condensation reaction of alkyl glycoside and small molecule polyol, followed by modification with weak phosphonate.

2. The defoamer for produced water from natural gas wells according to claim 1, characterized in that, In the modified organosilicon, the mass ratio of polydimethylsiloxane, hydroxyl-terminated polyether, and low-carbon carboxylic anhydride is 10:(3-5):(1-2).

3. The defoamer for produced water from natural gas wells according to claim 1, characterized in that, In the modified hydrogenated rosin glycerol ester, the mass ratio of hydrogenated rosin, glycerol, and polyoxyethylene branched chain is 10:(2-3):(1-1.5).

4. The defoamer for produced water from natural gas wells according to claim 1, characterized in that, In the modified alkyl glycoside, the mass ratio of alkyl glycoside, small molecule polyol, and weak phosphonate is 10:(2-4):(0.5-1).

5. The defoamer for produced water from natural gas wells according to claim 1, characterized in that, The small molecule polyol is ethylene glycol or propylene glycol, the weak phosphonate is an alkali metal salt of hydroxyethylidene diphosphonic acid, and the low carbon carboxylic anhydride is a saturated fatty acid anhydride with 1 to 6 carbon atoms.

6. The defoamer for produced water from natural gas wells according to claim 1, characterized in that, The plant-based dicarboxylic acid ester is a palmitic acid diester, which is a diester compound synthesized from palmitic acid and ethylene glycol or propylene glycol.

7. A method for preparing an antifoaming agent for produced water from natural gas wells according to any one of claims 1-6, characterized in that, Includes the following steps: At room temperature, first add deionized water to the mixing container, then add potassium pyrophosphate and stir until completely dissolved; then add modified organosilicon, modified hydrogenated rosin glycerol ester, modified alkyl glycoside, plant-based dicarboxylic acid ester, and polyethylene glycol monooleate in sequence, and stir until the system is homogeneous. After standing to remove bubbles and filtering, the finished product is obtained.

8. The method for preparing the defoamer for produced water from natural gas wells according to claim 7, characterized in that, The settling and degassing time is 10-15 minutes; the filtration uses a 100-120 mesh filter cloth.

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