Supported surfactant microcapsule and preparation method thereof

Abstract

The invention relates to the technical field of oil exploitation, and discloses a surfactant-loaded microcapsule and a preparation method thereof. The preparation method of the microcapsule loaded with the surfactant comprises the following steps: respectively injecting an inner phase, an intermediate phase and an outer phase into a micro-fluidic chip for contact, and then separating to obtain the microcapsule, wherein the inner phase is an aqueous solution containing a surfactant I; the intermediate phase is a solution containing a hydrophobic material; the external phase is an aqueous solution containing a surfactant II; the inner phase and the outer phase are both insoluble with the intermediate phase; the flow velocity ratio of the inner phase to the middle phase is 1: (0.5-8); the flow velocity ratio of the inner phase to the outer phase is 1: (5-30); the concentration of the intermediate phase is 5-100 wt%. According to the microcapsule prepared by adopting a microfluidic technology, the adsorption of a surfactant in a near wellbore area is greatly reduced, so that the microcapsule fully plays an oil displacement role in a deep reservoir, and the recovery efficiency of an oil field is improved.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum extraction, and in particular to a surfactant-loaded microcapsule and a preparation method thereof. Background Art

[0002] During the development of oil fields, as water injection development continues, a large amount of crude oil (about 70%) remains underground and is difficult to be effectively extracted. This is because the high permeability areas in the reservoir are preferentially occupied by water, forming an invalid circulation path. At the same time, the hydrophilic rock surface gradually turns into an oil-wet surface due to the adsorption of components such as colloids and asphalt, resulting in the residual oil being tightly adsorbed on these rocks and difficult to strip off, which seriously restricts the further improvement of crude oil recovery.

[0003] Surfactants are widely used to improve the oil recovery rate in the later stage of water flooding due to their properties of emulsification and solubilization, changing the wettability of rock surface and reducing the oil-water interfacial tension. However, in actual applications, the strong adsorption of rocks to surfactants causes a large amount of surfactants to be adsorbed at the beginning of injection, resulting in oil recovery effects far less than expected and greatly increasing production costs. Although calcium lignin sulfonate and Chaser International CD1045 have been developed, TM , sodium polyacrylate and other sacrificial agents to reduce adsorption, but the adsorption loss problem of surfactants has not been fundamentally solved, and the improvement of oil recovery efficiency is still limited. Especially for non-ionic and amphoteric surfactants, the adsorption loss problem is more serious.

[0004] In recent years, microcapsule technology has provided new ideas for the application of surfactants due to its unique encapsulation and sustained-release properties. Microcapsule technology can not only reduce the direct adsorption of surfactants in the initial injection stage by encapsulating surfactants to form a protective shell, but also achieve continuous and stable release of surfactants by controlling the rupture and dissolution of the shell. However, traditional microcapsule preparation methods such as interfacial polymerization, spray drying, solvent evaporation and self-assembly have disadvantages such as uneven size distribution, limited morphology control, poor reproducibility and difficulty in achieving directional release. Especially in the face of the complex and changeable underground environment of oil fields, microcapsules prepared by traditional methods are often difficult to meet actual needs. For this reason, microfluidic technology has gradually entered the research field of view with its advantages of precise control of fluid behavior and efficient preparation of uniform microcapsules. However, the existing technology of microcapsules synthesized by microfluidics still has deficiencies in controlling the release rate and optimizing the membrane structure. These deficiencies limit the application effect of microcapsules in the field of oil field flooding, and it is difficult to fully achieve its goal of reducing surfactant adsorption and improving recovery.

[0005] Therefore, developing a microcapsule loaded with non-ionic and amphoteric surfactants with sustained release, anti-adsorption and crude oil response characteristics based on microfluidic technology, and regulating the release rate by precisely controlling its preparation parameters has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] The purpose of the present invention is to overcome the serious adsorption loss of nonionic and amphoteric surfactants in the near-wellbore area in the prior art, and the problem that the method of the prior art is difficult to accurately adjust the preparation parameters of microcapsules to control the release rate of microcapsules, and provide a surfactant-loaded microcapsule and a preparation method thereof. The method described in the present invention uses microfluidic technology to coat the surfactant, accurately controls the microfluidic preparation process, and prepares microcapsules with uniform size, controllable morphology, good sustained release performance, anti-adsorption performance and oil response performance, which greatly reduces the adsorption of surfactants in the near-wellbore area, enables it to fully exert its oil displacement effect in deep reservoirs, and improves oil field recovery.

[0007] In order to achieve the above object, the first aspect of the present invention provides a method for preparing surfactant-loaded microcapsules, the method comprising:

[0008] The inner phase, the middle phase and the outer phase are respectively injected into a microfluidic chip for contact, and then separated to obtain microcapsules; wherein the inner phase is an aqueous solution containing surfactant I; the middle phase is a solution containing a hydrophobic material; the outer phase is an aqueous solution containing surfactant II; and the inner phase and the outer phase are both immiscible with the middle phase;

[0009] Wherein, the flow rate ratio of the inner phase to the middle phase is 1:0.5-8; the flow rate ratio of the inner phase to the outer phase is 1:5-30; and the concentration of the middle phase is 5-100wt%.

[0010] The second aspect of the present invention provides a surfactant-loaded microcapsule prepared by the method described in the first aspect.

[0011] Through the above technical solution, the present invention has the following beneficial effects:

[0012] (1) The preparation method of the surfactant-loaded microcapsules provided by the present invention uses microfluidic technology to wrap the surfactant in a specific film, and uses a specific emulsification technology to accurately control the size, composition and structure of the emulsion to prepare microcapsules with uniform size, controllable morphology, good sustained release performance, anti-adsorption performance and oil response performance, which greatly reduces the high adsorption of surfactants, especially non-ionic and amphoteric surfactants in the near-wellbore area, so that they can fully play the role of oil displacement in deep reservoirs, improve oil field recovery, and reduce production costs.

[0013] (2) The method for preparing surfactant-loaded microcapsules provided by the present invention changes the particle size and shell thickness of the microcapsules in real time by controlling the flow rate of the injected fluid and the concentration of the solution containing the hydrophobic material, thereby quickly obtaining microcapsules with the desired structure; and the degradation rate of the outer film of the microcapsules in water is slow, which effectively controls the release of the surfactant and ensures its sustained-release effect.

[0014] (3) The microcapsules prepared by the preparation method of the surfactant-loaded microcapsules provided by the present invention have excellent adaptability to high temperature and high salt conditions and good responsiveness to oil, which expands the application scenarios of the microcapsules and is suitable for operations in high temperature areas, such as being used in high temperature and high salt oil reservoir environments to improve oil recovery. In addition, the shell layer of the microcapsule has a certain elasticity, which ensures the encapsulation ability of the surfactant during transportation and ensures the integrity of the microcapsules when passing through different narrow gap formations such as the capillary wall of the oil reservoir, and is not easy to break. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention.

[0016] Figure 1 Schematic diagram of the structure of the microfluidic chip of the present invention;

[0017] Figure 2 This is a diagram showing the internal structure of the main part of the microfluidic chip of the present invention;

[0018] Figure 3 The curve diagram of the shell thickness change of microcapsules under different flow rate ratios of the intermediate phase and the internal phase;

[0019] Figure 4 is the release curve of the surfactant in the microcapsule at different flow rate ratios of the intermediate phase and the internal phase;

[0020] Figure 5 is the release curve of the surfactant in the microcapsule at different mesophase concentrations;

[0021] Figure 6 The release curve of the surfactant in the microcapsule in water at different temperatures when the mesophase concentration is 20wt%;

[0022] Figure 7 The graph is a release relationship graph of the surfactant in the microcapsules in the simulated oil at different temperatures when the mesophase concentration is 20wt%;

[0023] Figure 8 This is a curve diagram of the release relationship of the surfactant in the microcapsules prepared in Example 15 at different mineralization degrees.

[0024] Reference numerals

[0025] 1External phase syringe 2Intermediate phase syringe 3Inner phase syringe

[0026] 4 square tube 5 injection end capillary 6 collection end capillary

[0027] 7 glass sheet 8 external phase fluid injection tube 9 intermediate phase fluid injection tube

[0028] 10 internal phase fluid injection pipe 11 collection pipe 12 collection container DETAILED DESCRIPTION

[0029] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0030] The first aspect of the present invention provides a method for preparing surfactant-loaded microcapsules, the method comprising:

[0031] The inner phase, the middle phase and the outer phase are respectively injected into a microfluidic chip for contact, and then separated to obtain microcapsules; wherein the inner phase is an aqueous solution containing surfactant I; the middle phase is a solution containing a hydrophobic material; the outer phase is an aqueous solution containing surfactant II; and the inner phase and the outer phase are both immiscible with the middle phase;

[0032] Wherein, the flow rate ratio of the inner phase to the middle phase is 1:0.5-8; the flow rate ratio of the inner phase to the outer phase is 1:5-30; and the concentration of the middle phase is 5-100wt%.

[0033] In the present invention, the surfactant is wrapped in a specific film by adopting microfluidic technology, and the size, composition and structure of the emulsion are precisely controlled by a specific emulsification technology to prepare microcapsules with uniform size, controllable morphology, good sustained release performance, anti-adsorption performance and oil response performance; by controlling the flow rate of the injected fluid and the concentration of the solution containing the hydrophobic material, the particle size and shell thickness of the microcapsules are changed in real time, and microcapsules with the desired structure are quickly obtained, which greatly reduces the adsorption of surfactants, especially non-ionic surfactants and zwitterionic surfactants in the prepared microcapsules in the near-wellbore area, so that the microcapsules can fully exert their oil displacement effect in deep reservoirs, improve the oil field recovery rate, and reduce production costs.

[0034] In the present invention, the method for testing the sustained-release performance of microcapsules comprises: measuring the absorbance of the supernatant containing microcapsules by using an ultraviolet-visible spectrophotometer until the absorbance is stable, thereby determining the concentration (wt%) of the surfactant released from the microcapsules.

[0035] In the present invention, the oil-responsiveness testing method of the microcapsules comprises: S1, preparing a water-absorbing hydrogel substrate: mixing a sodium alginate aqueous solution (2wt%) and a calcium chloride aqueous solution (1wt%) in a mass ratio of 1-4:1, and preparing the water-absorbing gel substrate with no water precipitation as the judging standard; S2, placing 0.1g of microcapsules on the water-absorbing hydrogel substrate, adding 3g of simulated oil (toluene and n-decane mixed in a mass ratio of 1:1), and placing it at the test temperature for a period of time; S3, at different time periods, sucking out the upper layer of simulated oil, adding 3g of formation water and mixing evenly, and testing the absorbance value of the supernatant with a UV-visible spectrophotometer until the absorbance value is stable, thereby determining the concentration of the surfactant released in the microcapsules.

[0036] In the present invention, the method for testing the anti-adsorption characteristics of microcapsules includes: S1, preparing 90g of a 0.3wt% surfactant aqueous solution and 90g of an aqueous solution loaded with surfactant microcapsules, ensuring that the total amount of surfactant in the two solutions is consistent; S2, preparing simulated formation sand: washing and drying quartz sand of different particle sizes with distilled water to prepare simulated formation sand; S3, mixing 30g of simulated formation sand with 90g of a 0.3wt% surfactant aqueous solution or an aqueous solution loaded with surfactant microcapsules at a constant temperature of 80°C and shaking for 24h, then standing for 30min, taking the supernatant to measure the interfacial tension with the crude oil in the target block, and measuring the anti-adsorption effect of the microcapsules by comparing the interfacial tension value with the surfactant aqueous solution.

[0037] In some embodiments of the present invention, preferably, the flow rate ratio of the inner phase to the middle phase is 1:0.5-8, for example, it can be 1:0.5, 1:0.6, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, and any value in the range of any two values, preferably 1:0.6-7.

[0038] In the present invention, the ratio of the inner phase flow rate to the middle phase flow rate is controlled within the above range, which can ensure that the generated double emulsion droplets have a relatively uniform size, and improve the stability of the microcapsules, thereby preparing microcapsules with uniform structure and controllable morphology, which is beneficial to improving the anti-adsorption properties of the microcapsules, and is beneficial to accurately control the release rate of the surfactant in the microcapsules, ensuring that the surfactant can be stably and continuously released when needed. The preferred range described in the present invention has a more excellent effect.

[0039] In some embodiments of the present invention, preferably, the flow rate ratio of the inner phase to the outer phase is 1:5-30, for example, it can be 1:5, 1:6, 1:8, 1:12, 1:15, 1:18, 1:21, 1:24, 1:27, 1:28, 1:30, and any value in the range of any two numerical values, preferably 1:6-27.

[0040] In the present invention, controlling the ratio of the inner phase flow rate to the outer phase flow rate within the above range is conducive to forming a stable double emulsion structure, thereby facilitating the preparation of microcapsules with uniform size, controllable morphology, good sustained release performance, anti-adsorption performance and oil response performance. The preferred range described in the present invention has a more excellent effect.

[0041] In some embodiments of the present invention, preferably, the internal phase flow rate is 200-2500 μL / h, for example, it can be 200 μL / h, 300 μL / h, 500 μL / h, 800 μL / h, 1000 μL / h, 1500 μL / h, 2000 μL / h, 2500 μL / h, and any value in the range consisting of any two values, preferably 300-2000 μL / L.

[0042] In some embodiments of the present invention, preferably, the intermediate phase flow rate is 180-5000 μL / h, for example, it can be 180 μL / h, 500 μL / h, 800 μL / h, 1000 μL / h, 2000 μL / h, 3000 μL / h, 4000 μL / h, 5000 μL / h, and any value in the range composed of any two values, preferably 600-3000 μL / h.

[0043] In some embodiments of the present invention, preferably, the external phase flow rate is 5000-15000 μL / h, for example, it can be 5000 μL / h, 6000 μL / h, 7000 μL / h, 8000 μL / h, 10000 μL / h, 12000 μL / h, 13000 μL / h, 15000 μL / h, and any value in the range composed of any two values, preferably 6000-12000 μL / L.

[0044] In the present invention, on the basis that the ratio of the inner phase flow rate, the outer phase flow rate and the middle phase flow rate meets the above range, the inner phase flow rate, the middle phase flow rate and the outer phase flow rate are precisely controlled within the above range, which is more conducive to improving the stability of the microcapsules, accurately regulating the release rate of the surfactant in the microcapsules, greatly reducing the adsorption of the surfactant in the near-wellbore area, making it fully play the role of oil displacement in the deep reservoir, and improving the oil field recovery rate. The preferred range described in the present invention has a more excellent effect.

[0045] In some embodiments of the present invention, preferably, the mesophase concentration is 5-100wt%, for example, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 60wt%, 70wt%, 80wt%, 90wt%, 100wt%, and any value in the range of any two values, preferably 10-50wt%. In the present invention, unless otherwise specified, the mesophase concentration refers to the concentration of the hydrophobic material.

[0046] In the present invention, controlling the concentration of the mesophase within the above range is conducive to forming a stable microcapsule structure, avoiding rupture or too fast release caused by too thin a microcapsule shell, and too slow a release rate caused by too thick a microcapsule shell, improving its physical stability in a complex underground environment, and reducing structural damage caused by environmental changes (such as temperature, salinity, etc.); and is conducive to achieving continuous and stable release of surfactants, allowing the surfactants to play a role for a longer time, and having good anti-adsorption performance, improving oil displacement efficiency. The preferred range of the present invention is conducive to making the prepared microcapsules have a more suitable shell thickness, good sustained release performance, anti-adsorption performance, oil-responsive performance and stability.

[0047] In some embodiments of the present invention, preferably, the internal phase concentration is 1-10wt%, for example, it can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, and any value in the range of any two values, preferably 1-5wt%.

[0048] In the present invention, unless otherwise specified, the internal phase concentration refers to the concentration of surfactant I. Controlling the internal phase concentration within the above range is conducive to ensuring the stability of the formed double emulsion and achieving continuous and stable release of the surfactant in the microcapsule.

[0049] In the present invention, the molecular weight of the surfactant in the internal phase affects the stability of the emulsion and the performance of the microcapsules. Surfactants with larger molecular weights increase the viscosity of the emulsion and reduce its fluidity, which increases its injectability and encapsulation difficulty. Preferably, when the number average molecular weight of the surfactant I is 100-10000 g / mol, the content of the surfactant I in the internal phase is 1-5wt%, preferably 1-4wt%; when the number average molecular weight of the surfactant I is greater than 10000 g / mol, the content of the surfactant I in the internal phase is 5-10wt%, preferably 5-8wt%.

[0050] In the present invention, the external phase concentration has a wide selection range. Preferably, the external phase concentration is 1-20wt%. Preferably, 3-10wt%. In the present invention, controlling the external phase concentration within the above range is beneficial to improving the structural stability of the microcapsules, ensuring the compactness and integrity of the microcapsule shell, achieving continuous and stable release of the surfactant in the microcapsules, giving full play to the oil displacement effect of the surfactant, and reducing the adsorption of the surfactant in the near-wellbore area.

[0051] In the present invention, the ratio of the inner phase concentration to the middle phase concentration has a wide range of selection. Preferably, the ratio of the inner phase concentration to the middle phase concentration is 1:5-100, for example, it can be 1:5, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, and any value in the range of any two values, preferably 1:10-50.

[0052] In the present invention, controlling the ratio of the internal phase concentration to the intermediate phase concentration within the above range is beneficial to accurately control the structure of the microcapsules, ensuring that the internal phase surfactant is effectively encapsulated inside the microcapsules without causing the internal phase surfactant to be excessively diluted or lost due to excessive external phase concentration, which is beneficial to further improve the stability of the microcapsules, accurately control the release rate of the surfactant in the microcapsules, give full play to the oil displacement effect of the surfactant, and reduce the adsorption of the surfactant in the near-wellbore area.

[0053] In the present invention, the ratio of the inner phase concentration to the outer phase concentration has a wide selection range. Preferably, the ratio of the inner phase concentration to the outer phase concentration is 1:1-20, preferably 1:1-10.

[0054] In the present invention, the ratio of the inner phase concentration to the outer phase concentration is further limited within the above range, which is more conducive to improving the structural stability of the microcapsules, achieving continuous and stable release of the surfactant in the microcapsules, giving full play to the oil displacement effect of the surfactant, and reducing the adsorption of the surfactant in the near-wellbore area.

[0055] In the present invention, the shape of the microcapsule is not particularly limited, and can be microcapsules of various shapes formed by microfluidics technology. Preferably, the microcapsule is spherical.

[0056] In the present invention, the particle size of the microcapsule has a wide selection range, and the flow rate ratio of the inner phase to the middle phase, the flow rate ratio of the inner phase to the outer phase, the concentration of the middle phase and the composition of each phase are limited to the aforementioned range. The particle size of the prepared microcapsule is preferably 50-300 μm, for example, it can be 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, and any value in the range composed of any two values, preferably 50-200 μm. In the present invention, unless otherwise specified, the particle size of the microcapsule is measured using imageJ software.

[0057] In the present invention, the shell thickness of the microcapsule has a wide selection range, and the flow rate ratio of the inner phase to the middle phase, the flow rate ratio of the inner phase to the outer phase, the concentration of the middle phase and the composition of each phase are limited to the aforementioned range. The shell thickness of the prepared microcapsule is preferably 0.5-50 μm, for example, it can be 0.5 μm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, and any value in the range of any two values, preferably 0.5-10 μm. In the present invention, unless otherwise specified, the shell thickness of the microcapsule is measured using imageJ software.

[0058] In the present invention, the hydrophobic material is dissolved in a solvent as an intermediate oil phase. The hydrophobic material is preferably selected from hydrophobic monomers and / or hydrophobic polymers having a sustained release effect and an anti-adsorption effect. More preferably, the hydrophobic material is selected from at least one of polylactic acid, polybutylene succinate, glycidyl methacrylate, ethoxylated trimethylolpropane triacrylate, polyethylene glycol diacrylate and ethyl cellulose. More preferably, ethoxylated trimethylolpropane triacrylate and / or polyethylene glycol diacrylate are selected.

[0059] In the present invention, the hydrophobic material is easy to form a microcapsule shell layer, and the formed microcapsule shell layer has good stability, which is conducive to the continuous and stable release of the surfactant coated by the microcapsule, fully exerting the oil displacement effect of the surfactant, and reducing the adsorption of the surfactant in the near-wellbore area.

[0060] In the present invention, the type of the solvent in the mesophase is not particularly limited, as long as the solvent is slightly soluble or insoluble in water. Preferably, the solvent in the mesophase is an oil solvent and / or an organic solvent, preferably mineral oil, silicone oil, paraffin, C6-C 10 At least one of alkanes, dichloromethane and toluene, more preferably at least one selected from mineral oil, paraffin, cyclohexane, dichloromethane and toluene.

[0061] In some embodiments of the present invention, preferably, the mesophase optionally contains an initiator. In the present invention, the term "optionally" means that the mesophase may contain an initiator or may not contain an initiator. Preferably, the mesophase contains an initiator.

[0062] In the present invention, in the microfluidic chip, when the inner phase, the middle phase and the outer phase are in contact under specific conditions, the initiator in the middle phase will quickly initiate a polymerization reaction, forming a shell layer at the interface to wrap the inner phase material to form the microcapsule, thereby shortening the preparation time of the microcapsule and improving production efficiency.

[0063] In the present invention, the amount of the initiator has a wide range of selection. Preferably, based on the total amount of the mesophase, the content of the initiator is 0.5-5wt%, preferably 0.5-2wt%. In the present invention, controlling the content of the initiator within the above range is beneficial to optimizing the reaction rate while avoiding rapid polymerization, thereby increasing the preparation rate of microcapsules.

[0064] In the present invention, the type of the initiator has a wide selection range. Preferably, the initiator is selected from at least one of benzophenone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, benzoin dimethyl ether and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone. In the present invention, the initiator is more conducive to improving the preparation efficiency of the microcapsules and the stability of the microcapsules.

[0065] In the present invention, the surfactant I is dissolved in water as the internal aqueous phase. The type of the surfactant I of the present invention is not particularly limited, and can be at least one of various anionic surfactants, cationic surfactants, zwitterionic surfactants and nonionic surfactants conventionally used in the art, preferably nonionic surfactants and amphoteric surfactants, more preferably at least one selected from Tween 80, Triton 100, polyvinyl alcohol, fatty alcohol polyoxyethylene ether and betaine.

[0066] In the present invention, the polyvinyl alcohol can be various polyvinyl alcohols commonly used in the art. Preferably, the polyvinyl alcohol is selected from at least one of polyvinyl alcohol with a number average molecular weight of 13kDa-23kDa, polyvinyl alcohol with a number average molecular weight ≥20000g / mol, high-viscosity polyvinyl alcohol and low-viscosity polyvinyl alcohol.

[0067] In some embodiments of the present invention, preferably, the inner phase optionally contains sodium chloride. In the present invention, by optionally adding sodium chloride, the osmotic pressure inside and outside the microcapsule is adjusted to achieve the regulation of the controlled release of the hydrophobic material to meet the needs of different application scenarios.

[0068] In the present invention, the amount of sodium chloride has a wide range of selection, and those skilled in the art can select it according to actual conditions. Preferably, the concentration of sodium chloride is 0.01-1wt%, preferably 0.05-0.5wt%.

[0069] In the present invention, unless otherwise specified, the substances described in the present invention can be purchased commercially or prepared using existing technologies.

[0070] In the present invention, preferably, the surfactant II is dissolved in water as the external aqueous phase. The type of the surfactant II of the present invention is not particularly limited, and may be the same as the surfactant I or different from the surfactant I. Preferably, the surfactant II is different from the surfactant I. Preferably, the surfactant II is a nonionic surfactant and an amphoteric surfactant, more preferably at least one selected from Tween 80, Triton 100, polyvinyl alcohol, fatty alcohol polyoxyethylene ether and betaine, and further preferably selected from Triton 100 and / or polyvinyl alcohol.

[0071] In the present invention, preferably, the external phase optionally contains sodium chloride. In the present invention, by optionally adding sodium chloride, the osmotic pressure inside and outside the microcapsule is adjusted to achieve the regulation of the controlled release of the hydrophobic material to meet the needs of different application scenarios. In the present invention, the amount of sodium chloride has a wide selection range. Preferably, the concentration of sodium chloride is 0.01-1wt%, preferably 0.05-0.5wt%.

[0072] In the present invention, preferably, the preparation method of the surfactant-loaded microcapsules comprises: flowing the inner phase and the intermediate phase into the microfluidic chip in the same direction, and at the same time, flowing the outer phase solution into the microfluidic chip in the opposite direction to form a water-in-oil-in-water (W / O / W) double emulsion system, i.e., double emulsion droplets, collecting the double emulsion droplets to obtain the surfactant-loaded microcapsules. The method of the present invention realizes precise control of the microfluidic preparation process, prepares microcapsules with uniform size, controllable morphology, good sustained release performance, anti-adsorption performance and oil response performance, greatly reduces the adsorption of surfactants in the near-wellbore area, enables it to fully exert its oil displacement effect in deep reservoirs, and improves oil field recovery.

[0073] In the present invention, preferably, the method further comprises: washing and separating the collected double emulsion droplets. The washing method and conditions of the present invention are not particularly limited, and the washing methods and conditions conventionally used in the art can be adopted, as long as the surfactant residue on the surface of the microcapsule can be removed, and the unreacted hydrophobic material and other additives can be removed. Preferably, the double emulsion droplets are washed with water. The separation method of the present invention is not particularly limited, as long as the microcapsules can be separated. Preferably, the separation method is centrifugal separation.

[0074] In the present invention, the type of the microfluidic chip is not particularly limited, as long as the inner phase, the intermediate phase and the outer phase can be brought into contact to obtain the microcapsule. Preferably, the microfluidic chip is a microfluidic chip with a coaxial channel structure. More preferably, the microfluidic chip comprises two circular glass capillaries and a square glass capillary, one end of the two circular glass capillaries is drawn into a cone, and the tapered ends of the two drawn capillaries are inserted into the square glass capillary in relative directions. In the present invention, the two circular glass capillaries are respectively an injection end capillary and a collection end capillary. Preferably, the microfluidic chip comprises an injection end capillary, a collection end capillary and an outer square capillary.

[0075] In the present invention, the capillary diameter of the microfluidic chip has a wide range of selection. Preferably, the inner diameter of the capillary at the injection end is 0.2-0.6μm, preferably 0.5-0.6μm; the diameter of the tapered end of the capillary at the injection end is 30-100μm, preferably 40-90μm; the inner diameter of the capillary at the collection end is 0.2-0.6μm, preferably 0.5-0.6μm; the diameter of the tapered end of the capillary at the collection end is 120-300μm, preferably 130-290μm; the inner diameter of the outer square capillary is 1.05-1.5μm, preferably 1.05-1.1μm. In the present invention, the inner diameter of the outer square capillary refers to the height and width of the outer square capillary. The source of the microfluidic modified chip is not particularly limited, and it can be commercially purchased or prepared using existing technology.

[0076] In a preferred embodiment of the present invention, the overall structure of the microfluidic chip is as follows Figure 1 As shown, the internal structure is as Figure 2 Specifically, the microfluidic chip includes two circular glass capillaries and a square glass capillary and a glass sheet 7, which are respectively an injection end capillary 5, a collection end capillary 6 and a square tube 4. A needle puller is used to pull one end of the two circular glass capillaries into a cone shape, and the cone ends of the two drawn capillaries are inserted into the square glass capillary in opposite directions, and the spacing between the cone ends is 60-150 μm. A three-way head and an adhesive are used to connect and encapsulate the three glass tubes.

[0077] In the present invention, preferably, the method for preparing double emulsion droplets using the microfluidic chip includes (eg Figure 1 and Figure 2 As shown): use the inner phase syringe 3, the middle phase syringe 2 and the outer phase syringe 1 to extract the inner phase, the middle phase and the outer phase respectively, fix the three syringes on the syringe pump, and then connect the three syringes to the three-phase polyethylene tubes respectively, turn on the syringe pump, inject the inner phase from the inner phase fluid injection tube 10 into the left end opening of the injection end capillary 5, and inject the middle phase from the middle phase fluid injection tube 9 into the annular space between the injection end capillary 5 and the square tube 4. At the same time, reversely inject the outer phase from the outer phase fluid injection tube 8 into the annular space between the injection end capillary 6 and the square tube 4. The three-phase fluid forms double emulsion droplets, which enter the collection container 12 from the collection end capillary 6 through the connected collection tube 11 to obtain double emulsion droplets. In the present invention, preferably, the middle phase containing the initiator needs to be UV cross-linked and cured before entering the collection container 12 through the connected collection tube 11.

[0078] The second aspect of the present invention provides a surfactant-loaded microcapsule prepared by the method described in the first aspect.

[0079] In the present invention, the surfactant-loaded microcapsules prepared by the preparation method greatly reduce the high adsorption of surfactants, especially non-ionic and amphoteric surfactants in the near-wellbore area, so that they can fully exert their oil displacement effect in deep reservoirs and improve the oil field recovery rate; the surfactant-loaded microcapsules have excellent adaptability to high temperature and high salt conditions, and have good oil responsiveness, and are suitable for operations in high temperature areas, such as being used in high temperature and high salt oil reservoir environments to improve oil recovery rates, and the microcapsule shell has a certain elasticity, which ensures the encapsulation ability of the surfactant during transportation, and ensures the integrity of the microcapsules when passing through different narrow gap formations such as the capillary wall of the oil reservoir, and is not easy to break.

[0080] The present invention will be described in detail below through examples.

[0081] The raw materials used in the following examples and comparative examples are all commercially available.

[0082] The microcapsule particle size and microcapsule shell thickness were determined using ImageJ software.

[0083] Test method for sustained-release performance of microcapsules: Use a UV-visible spectrophotometer to measure the absorbance of the supernatant containing microcapsules until the absorbance is stable, thereby determining the mass concentration of the surfactant released from the microcapsules.

[0084] Microcapsule oil responsiveness test method: S1. Prepare a water-absorbing hydrogel substrate: mix a sodium alginate aqueous solution (2wt%) and a calcium chloride aqueous solution (1wt%) in a mass ratio of 3:1, and prepare a water-absorbing gel substrate with no water precipitation as the criterion; S2. Place 0.1g of microcapsules on the water-absorbing hydrogel substrate, add 3g of simulated oil (toluene and n-decane mixed in a mass ratio of 1:1), and place it at the test temperature for a period of time; S3. At different time periods, suck out the upper layer of simulated oil, add 3g of formation water and mix evenly, and use a UV-visible spectrophotometer to test the absorbance value of the supernatant until the absorbance value stabilizes, thereby determining the concentration of the surfactant released in the microcapsule.

[0085] Test method for anti-adsorption characteristics of microcapsules: S1. Prepare 90g of 0.3wt% aqueous surfactant solution and 90g of aqueous solution loaded with surfactant microcapsules, ensuring that the total amount of surfactant in the two solutions is consistent; S2. Prepare simulated formation sand: wash and dry quartz sand of different particle sizes with distilled water to prepare simulated formation sand (as shown in Table 1); S3. Mix 30g of simulated formation sand with 90g of 0.3wt% aqueous surfactant solution or aqueous solution loaded with surfactant microcapsules at a constant temperature of 80°C and shake for 24h, then let it stand for 30min, take the supernatant to measure the interfacial tension with the target block crude oil, and measure the anti-adsorption effect of the microcapsules by comparing the interfacial tension value with the surfactant aqueous solution.

[0086] Microfluidic chip: homemade, such as Figure 1 As shown, the inner diameter of the capillary at the injection end is 0.56 μm, the inner diameter of the capillary at the collection end is 0.56 μm, the diameter of the tapered end of the capillary 6 at the collection end is 220 μm, the diameter of the tapered end of the capillary 5 at the injection end is 80 μm, the spacing between the tapered ends is 80 μm, and the height and width inside the square tube are 1.05 μm and 1.05 μm respectively.

[0087] Example 1

[0088] (1) Preparation of the internal surfactant solution: 5 g of fatty alcohol polyoxyethylene ether (molecular weight 315 g / mol) was dissolved in 100 g of distilled water, and the prepared solution was placed in an ultrasonic device for 5 minutes;

[0089] (2) Preparation of hydrophobic material solution: 4 g of polyethylene glycol diacrylate and 0.2 g of 2-hydroxy-2-methylpropiophenone were dissolved in 15.8 g of dichloromethane as membrane material and stored in the dark;

[0090] (3) Preparation of external surfactant solution: Dissolve 10 g of low-viscosity polyvinyl alcohol in 90 g of distilled water, and ultrasonicate the prepared solution in an ultrasonic device for 5 minutes;

[0091] (4) Preparation of double emulsion droplets: 20 g of the surfactant solvent prepared in step (1) is injected as the inner phase from the injection end capillary, and 10 g of the hydrophobic material solution prepared in step (2) is injected as the middle phase from the annular space between the injection end capillary and the square tube into the microfluidic chip, and at the same time, 20 g of the surfactant solution prepared in step (3) is reversely flowed into the microfluidic chip from the annular space between the collection end capillary and the square tube, and the inner phase flow rate, the middle phase flow rate, and the outer phase flow rate are controlled to be 1000 μL / h, 1000 μL / h, and 8000 μL / h, to form a water-in-oil-in-water (W / O / W) double emulsion system, thereby obtaining double emulsion droplets;

[0092] (5) Preparation of microcapsules: A collection container is connected to the discharge end of the microfluidic chip to collect the double emulsion droplets formed in step (4) and wash them to obtain the surfactant-loaded microcapsules.

[0093] The microcapsules prepared in this example are spherical, with an average particle size of 119 μm and a shell thickness of 3 μm.

[0094] According to the test, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 8 wt %, and the release rate was slow.

[0095] After testing, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 15 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0096] According to the test, the interfacial tension between the microcapsules prepared in this embodiment and crude oil at 80° C. is 18.68 mN / m, and the interfacial tension between the surfactant and crude oil is 6.47 mN / m, indicating that the microcapsules have good anti-adsorption properties.

[0097] Example 2

[0098] (1) Preparation of surfactant solution: 5 g of fatty alcohol polyoxyethylene ether (molecular weight 315 g / mol) was dissolved in 95 g of distilled water, and the prepared solution was ultrasonicated in an ultrasonic device for 5 minutes;

[0099] (2) Preparation of hydrophobic material solution: 10 g of polyethylene glycol diacrylate and 0.4 g of 2-hydroxy-2-methylpropiophenone were dissolved in 9.6 g of dichloromethane as membrane material and stored in the dark;

[0100] (3) Preparation of external surfactant solution: Dissolve 10 g of low-viscosity polyvinyl alcohol in 90 g of distilled water, and ultrasonicate the prepared solution in an ultrasonic device for 5 minutes;

[0101] (4) Preparation of double emulsion droplets: 20 g of the surfactant solvent prepared in step (1) as the inner phase is injected into the microfluidic chip from the injection end capillary, and 10 g of the hydrophobic material solution prepared in step (2) as the middle phase is injected into the microfluidic chip from the annular space between the injection end capillary and the square tube. At the same time, 20 g of the surfactant solution prepared in step (3) as the outer phase is reversely flowed into the microfluidic chip from the annular space between the collection end capillary and the square tube. The inner phase flow rate is controlled to be 500 μL / h, the middle phase flow rate is controlled to be 1500 μL / h, and the outer phase flow rate is controlled to be 8000 μL / h, so as to form a water-in-oil-in-water (W / O / W) double emulsion system, thereby obtaining double emulsion droplets;

[0102] (5) Preparation of microcapsules: A collection container is connected to the discharge end of the microfluidic chip to collect the double emulsion droplets formed in step (4) and wash them to obtain the surfactant-loaded microcapsules.

[0103] The microcapsules prepared in this example are spherical, with an average particle size of 109 μm and a shell thickness of 8.6 μm.

[0104] According to the test, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 2 wt %, and the release rate was slow.

[0105] After testing, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 5 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0106] Example 3

[0107] (1) Preparation of surfactant solution: 3 g fatty alcohol polyoxyethylene ether (molecular weight 315 g / mol) was dissolved in 97 g distilled water, and the prepared solution was placed in an ultrasonic device for 5 minutes;

[0108] (2) Preparation of hydrophobic material solution: 2 g of polyethylene glycol diacrylate and 0.1 g of 2-hydroxy-2-methylpropiophenone were dissolved in 17.9 g of dichloromethane as membrane material and stored in the dark;

[0109] (3) Preparation of external surfactant solution: Dissolve 10 g of low-viscosity polyvinyl alcohol in 90 g of distilled water, and ultrasonicate the prepared solution in an ultrasonic device for 5 minutes;

[0110] (4) Preparation of double emulsion droplets: 20 g of the surfactant solvent prepared in step (1) as the inner phase is injected into the microfluidic chip from the injection end capillary, and 10 g of the hydrophobic material solution prepared in step (2) as the middle phase is injected into the microfluidic chip from the annular space between the injection end capillary and the square tube. At the same time, 20 g of the surfactant solution prepared in step (3) as the outer phase is reversely flowed into the microfluidic chip from the annular space between the collection end capillary and the square tube. The inner phase flow rate is controlled to be 500 μL / h, the middle phase flow rate is controlled to be 600 μL / h, and the outer phase flow rate is controlled to be 8000 μL / h, so as to form a water-in-oil-in-water (W / O / W) double emulsion system, thereby obtaining double emulsion droplets;

[0111] (5) Preparation of microcapsules: A collection container is connected to the discharge end of the microfluidic chip to collect the double emulsion droplets formed in step (4) and wash them to obtain the surfactant-loaded microcapsules.

[0112] The microcapsules prepared in this example are spherical, with an average particle size of 96 μm and a shell thickness of 3.6 μm.

[0113] According to the test, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 20 wt %, and the release rate was slow.

[0114] After testing, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 35 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0115] Example 4

[0116] In the manner described in Example 1, except that,

[0117] In step (4), the inner phase flow rate is controlled to be 1200 μL / h and the middle phase flow rate is controlled to be 800 μL / h.

[0118] The microcapsules prepared in this example are spherical, with an average particle size of 119 μm and a shell thickness of 2.8 μm.

[0119] According to the test, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 26 wt %, and the release rate was slow.

[0120] After testing, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 43 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0121] Example 5

[0122] In the manner described in Example 1, except that,

[0123] In step (4), the inner phase flow rate is controlled to be 800 μL / h and the middle phase flow rate is controlled to be 1200 μL / h.

[0124] The microcapsules prepared in this example are spherical, with an average particle size of 120 μm and a shell thickness of 4.6 μm.

[0125] According to the test, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 12 wt %, and the release rate was slow.

[0126] After testing, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 22 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0127] Example 6

[0128] In the manner described in Example 1, except that,

[0129] In step (4), the inner phase flow rate is controlled to be 500 μL / h and the middle phase flow rate is controlled to be 1500 μL / h.

[0130] The microcapsules prepared in this example are spherical, with an average particle size of 119 μm and a shell thickness of 7 μm.

[0131] According to the test, the microcapsules prepared in this embodiment were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 9 wt %, and the release speed was relatively fast.

[0132] After testing, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 17 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0133] Example 7

[0134] In the manner described in Example 1, except that,

[0135] In step (4), the inner phase flow rate is controlled to be 300 μL / h and the middle phase flow rate is controlled to be 1700 μL / h.

[0136] The microcapsules prepared in this example are spherical, with an average particle size of 121 μm and a shell thickness of 10 μm.

[0137] According to the test, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 4 wt %, and the release speed was relatively fast.

[0138] After testing, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 7 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0139] Example 8

[0140] In the manner described in Example 1, except that,

[0141] In step (2), 2 g of polyethylene glycol diacrylate and 0.2 g of 2-hydroxy-2-methylpropiophenone were dissolved in 17.8 g of dichloromethane as membrane material.

[0142] The microcapsules prepared in this example are spherical, with an average particle size of 85 μm and a shell thickness of 5 μm.

[0143] According to the test, the microcapsules prepared in this embodiment were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 17 wt %, and the release speed was relatively accelerated.

[0144] After testing, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 31 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0145] Example 9

[0146] In the manner described in Example 1, except that,

[0147] In step (2), 3 g of polyethylene glycol diacrylate and 0.2 g of 2-hydroxy-2-methylpropiophenone were dissolved in 16.8 g of dichloromethane as membrane material.

[0148] The microcapsules prepared in this example are spherical, with an average particle size of 95 μm and a shell thickness of 5 μm.

[0149] According to the test, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 14 wt %, and the release rate was slow.

[0150] According to the test, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 28 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0151] Example 10

[0152] In the manner described in Example 1, except that,

[0153] In step (2), 5 g of polyethylene glycol diacrylate and 0.2 g of 2-hydroxy-2-methylpropiophenone were dissolved in 14.8 g of dichloromethane as membrane material.

[0154] The microcapsules prepared in this example are spherical, with an average particle size of 120 μm and a shell thickness of 5 μm.

[0155] According to the test, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 5 wt %, and the release rate was slow.

[0156] According to the test, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 9 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0157] Embodiment 11

[0158] In the manner described in Example 1, except that,

[0159] In step (2), 6 g of polyethylene glycol diacrylate and 0.2 g of 2-hydroxy-2-methylpropiophenone were dissolved in 13.8 g of dichloromethane as membrane material.

[0160] The microcapsules prepared in this example are spherical, with an average particle size of 138 μm and a shell thickness of 5 μm.

[0161] According to the test, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 3.6 wt %, and the release rate was slow.

[0162] After testing, the microcapsules prepared in this embodiment were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 6 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0163] Example 12

[0164] (1) Preparation of surfactant solution 1: dissolve 6 g of Tween 80 in 94 g of distilled water; preparation of surfactant solution 2: dissolve 2 g of low-viscosity polyvinyl alcohol in 98 g of distilled water; the prepared solutions are ultrasonicated in an ultrasonic device for 5 minutes;

[0165] (2) Preparation of hydrophobic material solution: 2.5 g of polylactic acid was dissolved in 47.5 g of dichloromethane as the membrane material and stored in the dark;

[0166] (3) Preparation of external surfactant solution: Dissolve 10 g of low-viscosity polyvinyl alcohol in 90 g of distilled water, and ultrasonicate the prepared solution in an ultrasonic device for 5 minutes;

[0167] (4) Preparation of double emulsion droplets: 10 g of the surfactant solvent 1 prepared in step (1) and 10 g of the surfactant solvent 2 prepared in step (1) are mixed and injected into the microfluidic chip from the injection end capillary as the inner phase, and 20 g of the hydrophobic material solution prepared in step (2) is injected into the microfluidic chip from the annular space between the injection end capillary and the square tube as the intermediate phase. At the same time, 20 g of the surfactant solution prepared in step (3) is reversely injected into the microfluidic chip from the annular space between the collection end capillary and the square tube. The flow rate of the inner phase, the flow rate of the intermediate phase, and the flow rate of the outer phase are controlled to be 500 μL / h, 500 μL / h, and 7000 μL / h, to form a water-in-oil-in-water (W / O / W) double emulsion system, thereby obtaining double emulsion droplets;

[0168] (5) Preparation of microcapsules: A collection container is connected to the discharge end of the microfluidic chip to collect the double emulsion droplets formed in step (4) and wash them to obtain the surfactant-loaded microcapsules.

[0169] The surfactant-loaded microcapsules prepared in this example are spherical, with an average particle size of 79 μm and a shell thickness of 3 μm.

[0170] According to the test, the microcapsules prepared in this embodiment were placed in water at room temperature (25° C.) for one day, and the release concentration of the surfactant in the microcapsules was 12 wt %, and the release speed was relatively fast.

[0171] After testing, the microcapsules prepared in this example were placed in simulated oil at room temperature (25° C.) for one day, and the release concentration of the surfactant in the microcapsules was 25 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0172] Example 13

[0173] The method described in Example 2 is different in that

[0174] In step (2), 1 g of polybutylene succinate was dissolved in 19 g of dichloromethane as a membrane material;

[0175] In step (4), the inner phase flow rate is controlled to be 700 μL / h, the middle phase flow rate is controlled to be 700 μL / h, and the outer phase flow rate is controlled to be 9000 μL / h, so as to form a water-in-oil-in-water (W / O / W) double emulsion system, that is, to obtain double emulsion droplets;

[0176] (5) Preparation of microcapsules: A collection container is connected to the discharge end of the microfluidic chip to collect the double emulsion droplets formed in step (4) and wash them to obtain the surfactant-loaded microcapsules.

[0177] The surfactant-loaded microcapsules prepared in this example are spherical, and the average particle size of the microcapsules is 105 μm and the shell thickness is 5 μm.

[0178] After testing, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for one day, and the release concentration of the surfactant in the microcapsules was 5 wt %, and the release rate was relatively fast.

[0179] After testing, the microcapsules prepared in this example were placed in simulated oil at room temperature (25° C.) for one day, and the release concentration of the surfactant in the microcapsules was 12 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0180] Embodiment 14

[0181] The method described in Example 2 is different in that

[0182] In step (2), 5 g of polylactic acid was dissolved in 45 g of dichloromethane as the membrane material.

[0183] The surfactant-loaded microcapsules prepared in this example are spherical, with an average particle size of 92 μm and a shell thickness of 6 μm.

[0184] After testing, the microcapsules prepared in this example were placed in water at room temperature (25° C.) for one day, and the release concentration of the surfactant in the microcapsules was 8 wt %, and the release rate was relatively fast.

[0185] After testing, the microcapsules prepared in this example were placed in simulated oil at room temperature (25° C.) for one day, and the release concentration of the surfactant in the microcapsules was 17 wt %, the release speed was accelerated, and the microcapsules had oil-responsive characteristics.

[0186] Embodiment 15

[0187] The method described in Example 1 is different in that

[0188] In step (4), the flow rate of the inner phase, the flow rate of the middle phase, and the flow rate of the outer phase were controlled to be 800 μL / h, 800 μL / h, and 6000 μL / h.

[0189] The surfactant-loaded microcapsules prepared in this example are spherical, with an average particle size of 85 μm and a shell thickness of 5.4 μm.

[0190] According to the test, the microcapsules prepared in this embodiment were placed in water at 50° C. for 10 days, and the release concentration of the surfactant in the microcapsules was 26 wt %, and the release rate was relatively slow even at high temperature.

[0191] According to the test, the microcapsules prepared in this embodiment are placed in simulated oil at 50° C. for 10 days, and the release concentration of the surfactant in the microcapsules is 50wt%, the release speed is accelerated, and the microcapsules have oil-responsive characteristics.

[0192] Example 16

[0193] The method described in Example 1 is different in that

[0194] In step (4), the inner phase flow rate is controlled to be 800 μL / h, the middle phase flow rate is 800 μL / h, and the outer phase flow rate is 6000 μL / h. The surfactant-loaded microcapsules prepared in this embodiment are spherical, with an average particle size of 85 μm and a shell thickness of 5.4 μm.

[0195] According to the test, the microcapsules prepared in this embodiment were placed in water at 80° C. for 10 days, and the release concentration of the surfactant in the microcapsules was 35 wt %, and the release rate was relatively slow even at high temperature.

[0196] According to the test, the microcapsules prepared in this embodiment were placed in simulated oil at 80° C. for 10 days, and the release concentration of the surfactant in the microcapsules was 68 wt %, and the release speed was accelerated, showing the microcapsules had oil-responsive characteristics.

[0197] Embodiment 17

[0198] (1) Preparation of surfactant solution 1: dissolve 6 g of Tween 80 and 1.2 g of sodium chloride in 92.8 g of distilled water; preparation of surfactant solution 2: dissolve 2 g of low-viscosity polyvinyl alcohol in 98 g of distilled water, and place the prepared solutions in an ultrasonic device for 5 minutes;

[0199] (2) Preparation of hydrophobic material solution: 3 g of polyethylene glycol diacrylate and 0.2 g of 2-hydroxy-2-methylpropiophenone were dissolved in 16.8 g of dichloromethane as membrane material and stored in the dark;

[0200] (3) Preparation of external surfactant solution: Dissolve 10 g of low-viscosity polyvinyl alcohol in 90 g of distilled water, and ultrasonicate the prepared solution in an ultrasonic device for 5 minutes;

[0201] (4) Preparation of double emulsion droplets: 10 g of the surfactant solvent 1 prepared in step (1) and 10 g of the surfactant solvent 2 prepared in step (1) are mixed and injected into the microfluidic chip from the injection end capillary as the inner phase, and 20 g of the hydrophobic material solution prepared in step (2) is injected into the microfluidic chip from the annular space between the injection end capillary and the square tube as the intermediate phase. At the same time, 0.12 g of sodium chloride and 19.88 g of the external phase surfactant solution prepared in step (3) are mixed and injected into the microfluidic chip from the annular space between the collection end capillary and the square tube as the external phase. The flow rate of the inner phase, the flow rate of the intermediate phase, and the flow rate of the external phase are controlled to be 800 μL / h, 800 μL / h, and 8000 μL / h, to form a water-in-oil-in-water (W / O / W) double emulsion system, thereby obtaining double emulsion droplets;

[0202] (5) Preparation of microcapsules: A collection container is connected to the discharge end of the microfluidic chip to collect the double emulsion droplets formed in step (4) and wash them to obtain the surfactant-loaded microcapsules.

[0203] The surfactant-loaded microcapsules prepared in this example are spherical, with an average particle size of 99 μm and a shell thickness of 4.5 μm.

[0204] After testing, the microcapsules prepared in this example have a release concentration of 70 wt % of the surfactant in the microcapsules at a mineralization of 5000 mg / L for 10 days. The release rate of the microcapsules is accelerated at a high mineralization (5 times the mineralization of the internal phase).

[0205] According to the test, the interfacial tension between the microcapsules prepared in this example and crude oil at 80° C. is 15.06 mN / m, and the interfacial tension between the surfactant and crude oil is 7.93 mN / m, indicating that the microcapsules have good anti-adsorption properties.

[0206] Embodiment 18

[0207] In the manner described in Example 1, except that,

[0208] In step (1), 5 g of fatty alcohol polyoxyethylene ether was replaced by betaine (molecular weight 435 g / mol);

[0209] In step (4), the flow rate of the inner phase is controlled to be 800 μL / h, the flow rate of the middle phase is controlled to be 600 μL / h, and the flow rate of the outer phase is controlled to be 8000 μL / h.

[0210] The microcapsules prepared in this example are spherical, with an average particle size of 53 μm and a shell thickness of 3.3 μm.

[0211] According to the test, the microcapsules prepared in this embodiment were placed in water at 80° C. for 7 days, and the release concentration of the surfactant in the microcapsules was 28 wt %, and the release speed was slow.

[0212] Comparative Example 1

[0213] The method described in Example 1 is different in that

[0214] In step (3), the flow rate of the inner phase is controlled to be 200 μL / h, the flow rate of the middle phase is controlled to be 80 μL / h, and the flow rate of the outer phase is controlled to be 800 μL / h.

[0215] The microcapsules prepared in this comparative example are spherical, with an average particle size of 86 μm and a shell thickness of 1.6 μm.

[0216] According to the test, the microcapsules prepared in this comparative example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 60 wt %, with a relatively fast release rate.

[0217] Comparative Example 2

[0218] The method described in Example 1 is different in that

[0219] In step (2), 1 g of polyethylene glycol diacrylate and 0.2 g of 2-hydroxy-2-methylpropiophenone were dissolved in 23.8 g of dichloromethane as membrane materials.

[0220] According to the test, the microcapsules prepared in this comparative example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 64 wt %, with a relatively fast release rate.

[0221] After testing, the microcapsules prepared in this comparative example were placed in simulated oil at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 89 wt %, the release rate remained substantially unchanged, and the microcapsules did not have oil-responsive characteristics.

[0222] Comparative Example 3

[0223] The method described in Example 1 is different in that

[0224] In step (2), 0.5 g of polyethylene glycol diacrylate and 0.2 g of 2-hydroxy-2-methylpropiophenone were dissolved in 19.3 g of dichloromethane as membrane materials;.

[0225] In step (4), the flow rate of the inner phase is controlled to be 200 μL / h, the flow rate of the middle phase is controlled to be 500 μL / h, and the flow rate of the outer phase is controlled to be 5000 μL / h.

[0226] According to the test, the microcapsules prepared in this comparative example were placed in water at room temperature (25° C.) for 10 days, and the release concentration of the surfactant in the microcapsules was 71 wt %, with a relatively fast release rate.

[0227] Table 1 Composition of simulated formation sand

[0228]

[0229] Figure 3 is a graph showing the change in shell thickness of the microcapsules prepared in Example 1 and Examples 4-7 of the present invention at different flow rate ratios of the intermediate phase to the internal phase, Figure 3 It can be seen that when the flow rate ratio of the intermediate phase to the internal phase is not higher than 1, the shell thickness does not change significantly with the increase of the flow rate ratio of the intermediate phase to the internal phase, and the shell thickness of the microcapsule is 2-4 μm; when the flow rate ratio of the intermediate phase to the internal phase is higher than 1, and with the increase of the flow rate ratio of the intermediate phase to the internal phase, the shell thickness of the microcapsule increases significantly.

[0230] Figure 4 is a release curve of the surfactant in the microcapsules at different flow rate ratios of the intermediate phase and the internal phase of the microcapsules prepared in Example 1 and Examples 4-7 of the present invention, Figure 4 It can be seen that as the flow rate ratio of the intermediate phase to the internal phase increases, the shell thickness of the microcapsule increases, the diffusion resistance increases, and the release of the surfactant in the microcapsule becomes slower. However, if the shell thickness of the microcapsule is too large, the release of the surfactant is too slow, which will affect its use.

[0231] Figure 5 is a release curve of the surfactant in the microcapsules at different mesophase concentrations of the microcapsules prepared in Example 1 and Examples 8-11 of the present invention, Figure 5 It can be seen that the higher the content of hydrophobic material in the mesophase, the smaller and denser the membrane pore size, and the slower the release rate of the surfactant in the microcapsule. However, if the content of hydrophobic material is too high, the release of the surfactant will be too slow, which will affect its use.

[0232] Figure 6 is a graph showing the release relationship of the surfactant in the microcapsules in water at different temperatures when the mesophase concentration (the content of the hydrophobic material in the mesophase) of the microcapsules prepared in Examples 1, 15 and 16 of the present invention is 20 wt%. Figure 6 It can be seen that when the content of the hydrophobic material in the mesophase is 20 wt %, the release rate of the surfactant in the microcapsule is slightly accelerated as the temperature rises, and the release rate is relatively slow at high temperatures.

[0233] Figure 7is a graph showing the release relationship of the surfactant in the microcapsules in simulated oil at different temperatures when the intermediate phase product concentration (the content of the hydrophobic material in the intermediate phase) of the microcapsules prepared in Examples 1, 15 and 16 of the present invention is 20 wt%. Figure 7 It can be seen that when the concentration of the hydrophobic material in the mesophase is 20 wt %, the release rate of the surfactant in the microcapsule is faster than that in water, and it also has oil-responsive characteristics at high temperatures.

[0234] Test Example 1

[0235] The microcapsules prepared in Example 15 were tested for sustained release performance under different mineralizations. The specific testing method includes: adding the microcapsules into bottles containing sodium chloride solutions with concentrations of 0.05wt%, 0.1wt%, 0.2wt%, and 0.5wt%, respectively, simulating different mineralization conditions by changing the salt concentration to explore the effect on the release rate of the microcapsules, and measuring the absorbance of the sodium chloride solution containing the microcapsules with a UV-visible spectrophotometer until the absorbance is stable, thereby determining the concentration of the surfactant released in the microcapsules. The test results are shown in Table 2.

[0236] Table 2

[0237]

[0238] Figure 8 is a graph showing the release relationship of the surfactant in the microcapsules at different mineralizations of the microcapsules obtained in Example 15 of the present invention, combined with Figure 8 It can be seen from Table 2 that when the mesophase concentration (the content of hydrophobic material in the mesophase) is 20wt%, the higher the mineralization, the faster the release rate of the surfactant in the microcapsule; when the mineralization of the microcapsule is not higher than 1000mg / L, the release rate of the surfactant in the microcapsule is slow; when the mineralization of the microcapsule reaches 5000mg / L, the release rate of the surfactant in the microcapsule is fast.

[0239] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing surfactant-loaded microcapsules, characterized in that: The method includes: The inner phase, the middle phase and the outer phase are respectively injected into a microfluidic chip for contact, and then separated to obtain microcapsules; wherein the inner phase is an aqueous solution containing surfactant I; the middle phase is a solution containing a hydrophobic material; the outer phase is an aqueous solution containing surfactant II; and the inner phase and the outer phase are both immiscible with the middle phase; Wherein, the flow rate ratio of the inner phase to the middle phase is 1:0.5-8; the flow rate ratio of the inner phase to the outer phase is 1:5-30; and the concentration of the middle phase is 5-100wt%.

2. The method according to claim 1, wherein: The flow rate ratio of the inner phase to the middle phase is 1:0.6-7; Preferably, the flow rate ratio of the inner phase to the outer phase is 1:6-27; Preferably, the flow rate of the inner phase is 200-2500 μL / h, preferably 300-2000 μL / h; Preferably, the flow rate of the intermediate phase is 180-5000 μL / h, preferably 600-3000 μL / h; Preferably, the flow rate of the external phase is 5000-15000 μL / h, preferably 6000-12000 μL / h.

3. The method according to claim 1 or 2, wherein: The internal phase concentration is 1-10wt%, preferably 1-5wt%; Preferably, when the number average molecular weight of the surfactant I is 100-10000 g / mol, the content of the surfactant I in the internal phase is 1-5wt%, preferably 1-4wt%; when the number average molecular weight of the surfactant I is greater than 10000 g / mol, the content of the surfactant I in the internal phase is 5-10wt%, preferably 5-8wt%; Preferably, the mesophase concentration is 10-50wt%; Preferably, the external phase concentration is 1-20 wt%, preferably 3-10 wt%.

4. The method according to any one of claims 1 to 3, wherein: The ratio of the inner phase concentration to the middle phase concentration is 1:5-100, preferably 1:10-50; Preferably, the ratio of the inner phase concentration to the outer phase concentration is 1:1-20, preferably 1:1-10.

5. The method according to any one of claims 1 to 4, wherein: The microcapsules are spherical and have a particle size of 50-300 μm, preferably 50-200 μm; Preferably, the shell thickness of the microcapsule is 0.5-50 μm, preferably 0.5-10 μm.

6. The method according to any one of claims 1 to 5, wherein: The hydrophobic material is selected from at least one of polylactic acid, polybutylene succinate, glycidyl methacrylate, ethoxylated trimethylolpropane triacrylate, polyethylene glycol diacrylate and ethyl cellulose, preferably ethoxylated trimethylolpropane triacrylate and / or polyethylene glycol diacrylate; Preferably, the solvent of the mesophase is an oil solvent and / or an organic solvent, preferably mineral oil, silicone oil, paraffin, C6-C 10 At least one of alkanes, dichloromethane and toluene, more preferably at least one selected from mineral oil, paraffin, cyclohexane, dichloromethane and toluene; Preferably, the surfactant I is selected from at least one of Tween 80, Triton 100, polyvinyl alcohol, betaine and fatty alcohol polyoxyethylene ether; Preferably, the surfactant II is selected from at least one of Tween 80, Triton 100, polyvinyl alcohol, betaine and fatty alcohol polyoxyethylene ether, preferably selected from Triton 100 and / or polyvinyl alcohol.

7. The method according to any one of claims 1 to 6, wherein: The mesophase optionally contains an initiator; Preferably, based on the total amount of the mesophase, the content of the initiator is 0.5-5wt%, preferably 0.5-2wt%; Preferably, the initiator is selected from at least one of benzophenone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, benzoin dimethyl ether and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone.

8. The method according to any one of claims 1 to 7, wherein: The internal phase optionally contains sodium chloride; Preferably, the concentration of sodium chloride is 0.01-1 wt%, preferably 0.05-0.5 wt%.

9. The method according to any one of claims 1 to 8, wherein: The microfluidic chip is a microfluidic chip with a coaxial channel structure; Preferably, the microfluidic chip comprises an injection end capillary, a collection end capillary and an outer square capillary; Preferably, the inner diameter of the capillary at the injection end is 0.2-0.6μm, preferably 0.5-0.6μm; the diameter of the tapered end of the capillary at the injection end is 30-100μm, preferably 40-90μm; the inner diameter of the capillary at the collection end is 0.2-0.6μm, preferably 0.5-0.6μm; the diameter of the tapered end of the capillary at the collection end is 120-300μm, preferably 130-290μm; the inner diameter of the outer square capillary is 1.05-1.5μm, preferably 1.05-1.1μm.

10. A surfactant-loaded microcapsule prepared by the method according to any one of claims 1 to 9.

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