Targeted tackifying type polyacrylamide microcapsule as well as preparation method and application thereof

Abstract

The invention discloses a targeted tackifying polyacrylamide microcapsule which comprises a core material and a wall material wrapping the core material, and the core material is a water phase solution containing a monomer and an initiator; and the wall material is an oil-phase solution containing an oil-soluble surfactant. The invention also discloses a preparation method of the targeted tackifying type polyacrylamide microcapsule, which comprises the following steps: (1) adding 1-1.4 parts of monomer and 0.05-0.15 part of initiator into 8-10 parts of water, and uniformly stirring to obtain a water phase solution as a fluid L1; (2) adding 1 part of an oil-soluble surfactant into 30-49 parts of oil, and uniformly stirring to obtain an oil-phase solution serving as a fluid L2; (3) enabling the fluid L1 as a dispersed phase to pass through a central channel of the flow focusing microchip, enabling the fluid L2 as a continuous phase to pass through peripheral channels of the flow focusing microchip, and preparing a water-in-oil emulsion; and (4) irradiating the water-in-oil emulsion by an ultraviolet lamp, and curing.

Description

Technical Field

[0001] The present invention belongs to the field of microcapsule preparation, and particularly relates to a targeted viscosity-increasing polyacrylamide microcapsule, a preparation method thereof, and an application thereof. Background Art

[0002] Petroleum, known as the "industrial blood", is a non-renewable resource, a power resource for economic development and social operation, and also an important lifeline related to the national economy and people's livelihood.

[0003] China is a large populous country, and the demand for petroleum is increasing day by day with the economic development: in 1993, China imported 9.88 million tons of crude oil; in 1997, China imported 39.71 million tons of crude oil; in 2003, China's imported crude oil reached 100 million tons; in 2010, China's imported crude oil reached 239 million tons, and the external dependence of China's petroleum reached 56%. Therefore, in addition to exploring new oil reservoirs, improving the recovery rate of the discovered old oil fields has become the best solution.

[0004] At present, the exploitation of the discovered old oil fields in China has entered the middle and late stages. The reservoir conditions are poor, the reservoir heterogeneity is strong, and the exploitation of low-permeability, ultra-low-permeability and complex fault-block sandstone oil reservoirs is difficult. In addition, the expansion of petroleum exploitation to high-temperature and high-salt oil reservoirs at home and abroad has put forward higher requirements for new polymers for enhanced oil recovery.

[0005] Due to its good viscosity-increasing performance, low price, and large-scale industrialization, polyacrylamide has been widely used in oilfield exploitation. For example, Chinese Patent Application CN 104861950A discloses a supramolecular linear polyacrylamide enhanced oil recovery agent, which is composed of the following components: adamantane-capped polyacrylamide, β-cyclodextrin dimer, additives, deoxidizer, and water; a preparation method of a supramolecular linear polyacrylamide enhanced oil recovery agent, which consists of the following steps: a. preparing adamantane-capped polyacrylamide; b. adding additives and deoxidizer to water, stirring evenly, adding adamantane-capped polyacrylamide, stirring and then standing for reaction, adding β-cyclodextrin dimer, stirring and then standing for reaction, and the obtained solution is the supramolecular linear polyacrylamide enhanced oil recovery agent. However, among the commonly used polyacrylamide polymers at present, the products that can resist high temperature and high salt generally have a large molecular weight or a significant increase in viscosity after association, and have poor anti-shearing performance and anti-sulfide iron performance after injection into the formation, which do not meet the requirements for injection into low-permeability oil reservoirs. Small molecular weight polymers have poor high-temperature resistance, generally only up to 70 °C, and poor anti-shearing performance, and their performance is greatly affected by the environment.

[0006] Microcapsule polymers protect polymer molecules by using a microcapsule shell to embed the polymer molecules for oil displacement inside the microcapsules, so that the polymer molecules will not be degraded by shear and oxidation effects in the near-wellbore zone, and slowly release in the far-wellbore zone to achieve targeted viscosity increase, with excellent shear resistance and slow-release performance. The structure of the microcapsules, the binding mode with the polymer for oil displacement, and its embedding rate directly affect the physical and chemical properties and targeted viscosity-increasing ability of the polymer.

[0007] Microcapsule technology refers to the technology of using natural or synthetic polymer materials to encapsulate dispersed solid, liquid, or even gaseous substances to form tiny particles with semi-permeable or sealed capsule membranes, so as to facilitate the storage, transportation, and use of the core substances, protect the internal substances from the external environment, improve the stability of the core material, reduce the diffusion of the core material to the external environment, extend the storage time of the core material, and at the same time, through diffusion, dissolution, degradation, stimulation, etc., achieve the controlled release of the core material, which is an important feature of microcapsule technology.

[0008] Currently, the main methods for embedding polyacrylamide microcapsules are emulsion polymerization and inverse emulsion polymerization. For example, Chinese Patent Application CN108311068A discloses a temperature-sensitive intelligent microcapsule, including a microcapsule with a poly N-hydroxymethylacrylamide functional polymer as the film capsule wall substrate, and temperature-sensitive submicron spheres are embedded in the film capsule wall of the microcapsule. The temperature-sensitive submicron spheres are poly N-isopropylacrylamide or poly N-isopropylacrylamide polymerized with other hydrophilic monomers. Another example is that Chinese Patent Application CN101167706A discloses a method for synthesizing chitosan nanomicrocapsules. The preparation steps are as follows: A. Prepare an oil-in-water inverse microemulsion system solution by a conventional method; B. Drop chitosan or chitosan derivatives into the microemulsion system and disperse them by the interfacial energy of the microemulsion system itself; C. Add a cross-linking agent TPP, and chitosan or chitosan derivatives and the cross-linking agent TPP in the microemulsion system solution automatically attract each other through positive and negative charges to form capsules; D. Centrifuge the solution in step C, discard the supernatant to obtain chitosan / TPP nanomicrocapsules or chitosan derivative / TPP nanomicrocapsules, and finally wash and store the nanomicrocapsules with absolute ethanol. However, the above technical solutions cannot achieve precise regulation of the core and shell layers, and the uniformity effect is not good. During the preparation process, it is difficult to achieve real-time observation and control, and the operation is relatively complicated. Summary of the Invention

[0009] Object of the Invention: Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides a targeted viscosity-increasing polyacrylamide microcapsule, its preparation method and application.

[0010] Based on a flow-focusing microchip, for the inner aqueous phase and the outer oil phase, the structure of the emulsion is controlled by regulating the flow rate of each phase to obtain a water-in-oil emulsion, and the water-in-oil emulsion is cured by ultraviolet light to obtain targeted viscosity-increasing polyacrylamide microcapsules. The obtained targeted viscosity-increasing polyacrylamide microcapsules have a controllable structure, a high encapsulation rate, good monodispersity, controllable release, and good shear resistance and viscosity-increasing properties.

[0011] Technical solution: A targeted viscosity-increasing polyacrylamide microcapsule, the targeted viscosity-increasing polyacrylamide microcapsule includes a core material and a wall material wrapping the core material, wherein:

[0012] The core material is an aqueous solution containing monomers and initiators;

[0013] The wall material is an oil-phase solution containing an oil-soluble surfactant.

[0014] Further, the monomer is one or more of acrylic acid, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid;

[0015] The initiator is one of ammonium persulfate and potassium persulfate;

[0016] The aqueous solution contains water, and the mass ratio of the monomer, initiator, and water in the core material is (1 - 1.4):(0.05 - 0.15):(8 - 10).

[0017] Further, the oil-phase solution containing an oil-soluble surfactant contains oil, and the mass ratio of the oil-soluble surfactant to the oil is 1:(30 - 49), wherein:

[0018] The oil-soluble surfactant is one of Span80, TX-100, and Tween80;

[0019] The oil is one of mineral oil, fluorocarbon oil, silicone oil, and white oil.

[0020] The preparation method of the targeted viscosity-increasing polyacrylamide microcapsule according to any one of the above, in parts by mass, includes the following steps:

[0021] (1), Add 1 - 1.4 parts of monomers and 0.05 - 0.15 parts of initiators to 8 - 10 parts of water, stir evenly to obtain an aqueous solution, which is used as fluid L1;

[0022] (2), Add 1 part of oil-soluble surfactant to 30 - 49 parts of oil, stir evenly to obtain an oil-phase solution, which is used as fluid L2;

[0023] (3), Make fluid L1 pass through the central channel of the flow-focusing microchip as the dispersed phase, and make fluid L2 pass through the surrounding channels of the flow-focusing microchip as the continuous phase to prepare a water-in-oil emulsion;

[0024] (4) After irradiating the water-in-oil emulsion with an ultraviolet lamp and curing it, a targeted viscosity-increasing polyacrylamide microcapsule is obtained.

[0025] Furthermore, it further includes step (5): washing the targeted viscosity-increasing polyacrylamide microcapsule obtained in step (4) with n-hexane and drying it naturally.

[0026] Furthermore, the monomer in step (1) is one or more of acrylic acid, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid.

[0027] Furthermore, the initiator in step (1) is one of ammonium persulfate and potassium persulfate.

[0028] Furthermore, the oil in step (2) is one of mineral oil, fluorocarbon oil, silicone oil, and white oil.

[0029] Furthermore, the oil-soluble surfactant in step (2) is one of span80, TX-100, and Tween80.

[0030] Furthermore, in step (3), the size and structure of the targeted viscosity-increasing polyacrylamide microcapsule are controlled by regulating the flow rates of fluid L1 and fluid L2, where:

[0031] The flow rate of fluid L1 is controlled at 1 - 120 μL / min, and the flow rate of fluid L2 is controlled at 100 - 550 μL / min.

[0032] Furthermore, the process conditions for ultraviolet curing in step (4) are: irradiating under a high-pressure mercury lamp with a power of 400 - 600 W and a main wavelength of 320 - 400 nm for 12 - 80 min.

[0033] The targeted viscosity-increasing polyacrylamide microcapsule is prepared by the preparation method described in any one of the above.

[0034] The application of the targeted viscosity-increasing polyacrylamide microcapsule described in any one of the above as a displacement agent in oil exploitation.

[0035] Beneficial effects: A targeted viscosity-increasing polyacrylamide microcapsule and its preparation method and application disclosed by the present invention have the following beneficial effects:

[0036] 1. Based on a flow-focusing microchip, the core structure and shell structure of the targeted viscosity-increasing polyacrylamide microcapsule can be controlled by adjusting the flow rates of two phases, and the obtained targeted viscosity-increasing polyacrylamide microcapsule has good sphericity and high monodispersity;

[0037] 2. The encapsulation rate of the prepared polyacrylamide is as high as 100%;

[0038] 3. By adjusting the water-oil ratio in the pre-emulsion and the flow rates of each phase in the flow-focusing microchip, the monomer content in the targeted viscosity-increasing polyacrylamide microcapsules is controlled, enabling the targeted viscosity-increasing polyacrylamide microcapsules to have good shear resistance and viscosity-increasing properties;

[0039] 4. The microcapsules can be cured non-destructively and quickly online through ultraviolet curing. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the preparation method of the targeted viscosity-increasing polyacrylamide microcapsules disclosed in the present invention.

[0041] Figure 2a It is a graph showing the relationship between the inner-phase flow velocity and the particle size of the targeted viscosity-increasing polyacrylamide microcapsules.

[0042] Figure 2b It is a graph showing the relationship between the outer-phase flow velocity and the particle size of the targeted viscosity-increasing polyacrylamide microcapsules.

[0043] Figure 2c It is a graph showing the relationship between the curing time and the particle size of the targeted viscosity-increasing polyacrylamide microcapsules.

[0044] Figure 2d It is a graph showing the relationship between the initiator concentration and the particle size of the targeted viscosity-increasing polyacrylamide microcapsules.

[0045] Figure 3 It is an infrared spectrum of the targeted viscosity-increasing polyacrylamide microcapsules prepared in Example 1.

[0046] Figure 4 It is a thermogravimetry-differential thermal analysis graph of the targeted viscosity-increasing polyacrylamide microcapsules prepared in Example 1.

[0047] Figure 5a It is a broken-line graph showing the relationship between the viscosity and the aging time of the targeted viscosity-increasing polyacrylamide microcapsules prepared in Example 1.

[0048] Figure 5b It is a broken-line graph showing the relationship between the viscosity and the aging time of the targeted viscosity-increasing polyacrylamide microcapsules prepared in Example 2.

[0049] Figure 6 It is a schematic diagram showing the change in the sustained-release performance and viscosity of the targeted viscosity-increasing polyacrylamide microcapsules prepared in Example 1 with the curing time. DETAILED DESCRIPTION OF THE INVENTION

[0050] The following is a detailed description of the specific embodiments of the present invention.

[0051] The flow-focusing microchip in this application is a flow-focusing type channel used in the field of microfluidics.

[0052] The flow focusing microchip is assembled from a glass slide, a square glass capillary, a cylindrical glass capillary, a dispensing needle, and AB glue. The main preparation steps of the flow focusing microchip include the following steps:

[0053] (1) Use a capillary stretcher to heat and stretch a cylindrical glass capillary (0.95mm×0.6mm) to form a tip with an outer diameter less than 0.1mm, and then use sandpaper to polish its tip to about 0.1mm and about 0.4mm respectively. Among them, the glass capillary with a tip outer diameter of 0.1mm is used as injection tube I, and the glass capillary with a tip outer diameter of 0.4mm is used as collection tube III;

[0054] (2) Insert injection tube I and collection tube III into the left and right ends of square glass capillary II (1.0mm×1.0mm) in the opposite direction, so that the tip of injection tube I is embedded in the tip of collection tube III, and adjust to an appropriate depth while ensuring a high degree of coaxiality between the two;

[0055] (3) Cut the bottom of the dispensing needle so that the capillary can be embedded in it. Place dispensing needle A at the inlet end of injection tube I, and place dispensing needle B at the interface between injection tube I and square glass capillary II, which are used as the injection ports for the inner-phase fluid and the outer-phase fluid respectively. Under the condition of ensuring a high degree of coaxiality between injection tube I and collection tube III, fix the dispensing needle with AB glue, and at the same time block the interface between collection tube III and square glass capillary II;

[0056] (4) Let it stand for 8h until the AB glue is completely cured, and a two-phase flow glass capillary flow focusing microchannel is successfully prepared.

[0057] The formation process of its two-phase emulsion is as follows: the inner-phase fluid is introduced into injection tube I, and the outer-phase fluid is introduced into the gap between injection tube I and square glass capillary II. The two fluids converge at the tip of injection tube I. Under the action of fluid pressure, interfacial tension, and viscous shear force, the two fluids shear each other to form droplets, and finally flow out from the orifice of collection tube III.

[0058] The "range" disclosed by the present invention is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 10 - 50 is listed for a specific parameter, ranges of 10 - 40 and 20 - 50 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations.

[0059] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0060] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0061] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0062] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also only include or comprise the listed components.

[0063] If there is no special instruction, the reaction is carried out under normal temperature and normal pressure conditions.

[0064] If there is no special instruction, all parts or percentages are by weight or weight percentage.

[0065] In the present invention, all the substances used are known substances and can be purchased or synthesized by known methods.

[0066] In the present invention, all the devices or equipment used are conventional devices or equipment known in the art and can be purchased.

[0067] A targeted viscosity-increasing polyacrylamide microcapsule, which comprises a core material and a wall material wrapping the core material, wherein:

[0068] The core material is an aqueous solution containing monomers and initiators;

[0069] The wall material is an oil-phase solution containing an oil-soluble surfactant.

[0070] Furthermore, the particle size of the targeted viscosity-increasing polyacrylamide microcapsule is 72 - 248 microns.

[0071] Furthermore, the monomer is any one of acrylic acid, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid;

[0072] The initiator is one of ammonium persulfate and potassium persulfate;

[0073] The aqueous solution contains water, and the mass ratio of the monomer, initiator, and water in the core material is (1 - 1.4):(0.05 - 0.15):(8 - 10).

[0074] Furthermore, the oil-phase solution containing an oil-soluble surfactant contains oil, and the mass ratio of the oil-soluble surfactant to the oil is 1:(30 - 49), wherein:

[0075] The oil-soluble surfactant is one of Span80, TX-100, and Tween80;

[0076] The oil is one of mineral oil, fluorocarbon oil, silicone oil, and white oil.

[0077] The preparation method of the targeted viscosity-increasing polyacrylamide microcapsule described in any one of the above, in parts by mass, comprises the following steps:

[0078] (1) Add 1 - 1.4 parts of monomers and 0.05 - 0.15 parts of initiators to 8 - 10 parts of water, stir evenly to obtain an aqueous solution, which is used as fluid L1;

[0079] (2) Add 1 part of an oil-soluble surfactant to 30 - 49 parts of oil, stir evenly to obtain an oil-phase solution, which is used as fluid L2;

[0080] (3) Pass the fluid L1 as the dispersed phase through the central channel of the flow focusing microchip, and pass the fluid L2 as the continuous phase through the peripheral channels of the flow focusing microchip to prepare a water-in-oil emulsion;

[0081] (4) After irradiating the water-in-oil emulsion with an ultraviolet lamp and curing it, a targeted viscosity-increasing polyacrylamide microcapsule is obtained.

[0082] Further, it further includes step (5): washing the targeted viscosity-increasing polyacrylamide microcapsules obtained in step (4) with n-hexane and drying them naturally.

[0083] Further, in step (1), the monomer is one or more of acrylic acid, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid.

[0084] Further, in step (1), the initiator is one of ammonium persulfate and potassium persulfate.

[0085] Further, in step (2), the oil is one of mineral oil, fluorocarbon oil, silicone oil, and white oil.

[0086] Further, in step (2), the oil-soluble surfactant is one of span80, TX-100, and Tween80.

[0087] Further, in step (3), the size structure of the targeted viscosity-increasing polyacrylamide microcapsules is controlled by regulating the flow rates of the fluid L1 and the fluid L2, where:

[0088] The flow rate of the fluid L1 is controlled at 1 - 120 μL / min, and the flow rate of the fluid L2 is controlled at 100 - 550 μL / min.

[0089] Further, the process conditions for ultraviolet curing in step (4) are: irradiating under a high-pressure mercury lamp with a power of 400 - 600 W and a main wavelength of 320 - 400 nm for 12 - 80 min.

[0090] The targeted viscosity-increasing polyacrylamide microcapsules are prepared by the preparation method described in any one of the above.

[0091] The application of the targeted viscosity-increasing polyacrylamide microcapsules described in any one of the above as a displacement agent in oil recovery.

[0092] In one embodiment, a targeted viscosity-increasing polyacrylamide microcapsule, the targeted viscosity-increasing polyacrylamide microcapsule includes a core material, and a wall material wrapping the core material, where:

[0093] The core material is an aqueous solution containing monomers and initiators;

[0094] The wall material is an oil-phase solution containing an oil-soluble surfactant.

[0095] Further, the particle size of the targeted viscosity-increasing polyacrylamide microcapsules is 72 microns.

[0096] Further, the monomer is acrylic acid;

[0097] The initiator is ammonium persulfate;

[0098] The aqueous solution contains water, and the mass ratio of the monomer, initiator, and water in the core material is 1:0.05:8.

[0099] Further, the oil-phase solution containing the oil-soluble surfactant contains oil, and the mass ratio of the oil-soluble surfactant to the oil is 1:30, where:

[0100] The oil-soluble surfactant is Span80;

[0101] The oil is mineral oil.

[0102] The preparation method of the targeted viscosity-increasing polyacrylamide microcapsules according to any one of the above, in parts by mass, includes the following steps:

[0103] (1) Add 1 part of the monomer and 0.05 part of the initiator to 8 parts of water, stir evenly to obtain an aqueous solution, which is used as fluid L1;

[0104] (2) Add 1 part of the oil-soluble surfactant to 30 parts of oil, stir evenly to obtain an oil-phase solution, which is used as fluid L2;

[0105] (3) Make fluid L1 as the dispersed phase pass through the central channel of the flow-focusing microchip, and make fluid L2 as the continuous phase pass through the peripheral channels of the flow-focusing microchip to prepare a water-in-oil emulsion;

[0106] (4) After irradiating the water-in-oil emulsion with an ultraviolet lamp and curing, the targeted viscosity-increasing polyacrylamide microcapsules are obtained.

[0107] Further, it also includes step (5): washing the targeted viscosity-increasing polyacrylamide microcapsules obtained in step (4) with n-hexane and drying naturally.

[0108] Further, the monomer in step (1) is acrylic acid.

[0109] Further, the initiator in step (1) is ammonium persulfate.

[0110] Further, the oil in step (2) is mineral oil.

[0111] Further, the oil-soluble surfactant described in step (2) is span80.

[0112] Further, in step (3), the size and structure of the targeted viscosity-increasing polyacrylamide microcapsules are controlled by regulating the flow rates of fluid L1 and fluid L2, where:

[0113] The flow rate of fluid L1 is controlled at 1 μL / min, and the flow rate of fluid L2 is controlled at 100 μL / min.

[0114] Further, the process conditions for ultraviolet curing in step (4) are: irradiating under a high-pressure mercury lamp with a power of 400 W and a main wavelength of 320 nm for 80 min.

[0115] The targeted viscosity-increasing polyacrylamide microcapsules are prepared by the preparation method described in any one of the above.

[0116] The application of the targeted viscosity-increasing polyacrylamide microcapsules described in any one of the above as a displacement agent in oil recovery.

[0117] In another embodiment, a targeted viscosity-increasing polyacrylamide microcapsule, the targeted viscosity-increasing polyacrylamide microcapsule includes a core material and a wall material wrapping the core material, where:

[0118] The core material is an aqueous solution containing monomers and initiators;

[0119] The wall material is an oil-phase solution containing an oil-soluble surfactant.

[0120] Further, the particle size of the targeted viscosity-increasing polyacrylamide microcapsules is 248 microns.

[0121] Further, the monomer is acrylamide;

[0122] The initiator is potassium persulfate;

[0123] The aqueous solution contains water, and the mass ratio of the monomer, initiator, and water in the core material is 1.4:0.15:10.

[0124] Further, the oil-phase solution containing an oil-soluble surfactant contains oil, and the mass ratio of the oil-soluble surfactant to the oil is 1:49, where:

[0125] The oil-soluble surfactant is TX-100;

[0126] The oil is fluorocarbon oil.

[0127] The preparation method of the targeted viscosity-increasing polyacrylamide microcapsules described in any one of the above, in parts by mass, includes the following steps:

[0128] (1) Add 1.4 parts of monomers and 0.15 parts of initiator to 10 parts of water. After stirring evenly, an aqueous solution is obtained as fluid L1;

[0129] (2) Add 1 part of oil-soluble surfactant to 49 parts of oil. After stirring evenly, an oil-phase solution is obtained as fluid L2;

[0130] (3) Let fluid L1 be the dispersed phase and pass through the central channel of the flow-focusing microchip, and let fluid L2 be the continuous phase and pass through the surrounding channels of the flow-focusing microchip to prepare a water-in-oil emulsion;

[0131] (4) After irradiating the water-in-oil emulsion with an ultraviolet lamp and curing it, a targeted viscosity-increasing polyacrylamide microcapsule is obtained.

[0132] Further, it also includes step (5): Wash the targeted viscosity-increasing polyacrylamide microcapsule obtained in step (4) with n-hexane and dry it naturally.

[0133] Further, the monomer in step (1) is acrylamide.

[0134] Further, the initiator in step (1) is potassium persulfate.

[0135] Further, the oil in step (2) is fluorocarbon oil.

[0136] Further, the oil-soluble surfactant in step (2) is TX-100.

[0137] Further, in step (3), the size structure of the targeted viscosity-increasing polyacrylamide microcapsule is controlled by regulating the flow rates of fluid L1 and fluid L2, where:

[0138] The flow rate of fluid L1 is controlled at 120 μL / min, and the flow rate of fluid L2 is controlled at 550 μL / min.

[0139] Further, the process conditions for ultraviolet curing in step (4) are: irradiate under a high-pressure mercury lamp with a power of 600 W and a main wavelength of 400 nm for 12 min.

[0140] The targeted viscosity-increasing polyacrylamide microcapsule is prepared by the preparation method described in any one of the above.

[0141] The application of the targeted viscosity-increasing polyacrylamide microcapsule described in any one of the above as a displacement agent in oil recovery.

[0142] In yet another embodiment, a targeted viscosity-increasing polyacrylamide microcapsule, the targeted viscosity-increasing polyacrylamide microcapsule includes a core material and a wall material wrapping the core material, where:

[0143] The core material is an aqueous solution containing monomers and initiators;

[0144] The wall material is an oil-phase solution containing oil-soluble surfactants.

[0145] Further, the particle size of the target-viscosity-increasing polyacrylamide microcapsules is 120 microns.

[0146] Further, the monomer is 2-acrylamido-2-methyl-1-propanesulfonic acid;

[0147] The initiator is ammonium persulfate;

[0148] The aqueous solution contains water, and the mass ratio of the monomer, initiator, and water in the core material is 1.2:0.1:9.

[0149] Further, the oil-phase solution containing oil-soluble surfactants contains oil, and the mass ratio of the oil-soluble surfactant to the oil is 1:39, where:

[0150] The oil-soluble surfactant is Tween80;

[0151] The oil is silicone oil. In another embodiment, the oil is white oil.

[0152] The preparation method of the target-viscosity-increasing polyacrylamide microcapsules according to any one of the above, in parts by mass, includes the following steps:

[0153] (1) Add 1.2 parts of monomers and 0.1 part of initiator to 9 parts of water, stir evenly to obtain an aqueous solution, which is used as fluid L1;

[0154] (2) Add 1 part of oil-soluble surfactant to 39 parts of oil, stir evenly to obtain an oil-phase solution, which is used as fluid L2;

[0155] (3) Make fluid L1 as the dispersed phase pass through the central channel of the flow-focusing microchip, and make fluid L2 as the continuous phase pass through the surrounding channels of the flow-focusing microchip to prepare a water-in-oil emulsion;

[0156] (4) After irradiating the water-in-oil emulsion with an ultraviolet lamp and curing it, the target-viscosity-increasing polyacrylamide microcapsules are obtained.

[0157] Further, it also includes step (5): Wash the target-viscosity-increasing polyacrylamide microcapsules obtained in step (4) with n-hexane and dry them naturally.

[0158] Further, the monomer in step (1) is 2-acrylamido-2-methyl-1-propanesulfonic acid. In another embodiment, the monomer in step (1) is a mixture of acrylic acid, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid in an equal mass ratio.

[0159] Further, the initiator in step (1) is ammonium persulfate.

[0160] Further, the oil in step (2) is silicone oil. In another embodiment, the oil in step (2) is white oil.

[0161] Further, the oil-soluble surfactant in step (2) is Tween 80.

[0162] Further, in step (3), the size and structure of the target viscosity-increasing polyacrylamide microcapsules are controlled by regulating the flow rates of fluid L1 and fluid L2, where:

[0163] The flow rate of fluid L1 is controlled at 60 μL / min, and the flow rate of fluid L2 is controlled at 200 μL / min.

[0164] Further, the process conditions for ultraviolet curing in step (4) are: irradiating for 40 min under a high-pressure mercury lamp with a power of 500 W and a main wavelength of 365 nm.

[0165] The target viscosity-increasing polyacrylamide microcapsules are prepared by the preparation method described in any one of the above.

[0166] The application of the target viscosity-increasing polyacrylamide microcapsules described in any one of the above as a displacement agent in oil recovery.

[0167] Example 1

[0168] As Figure 1 shown, the preparation method of the target viscosity-increasing polyacrylamide microcapsules includes the following steps:

[0169] (1), Add 1 part of monomer and 0.1 part of initiator to 9 parts of water, stir evenly to obtain an aqueous solution, which is used as fluid L1;

[0170] (2), Add 1 part of oil-soluble surfactant to 39 parts of oil, stir evenly to obtain an oil-phase solution, which is used as fluid L2;

[0171] (3), Use fluid L1 as the dispersed phase to pass through the central channel of the flow focusing microchip, and use fluid L2 as the continuous phase to pass through the surrounding channels of the flow focusing microchip to prepare a water-in-oil emulsion;

[0172] (4) After irradiating the water-in-oil emulsion with an ultraviolet lamp and curing it, a targeted viscosity-increasing polyacrylamide microcapsule is obtained.

[0173] Further, it further includes step (5): washing the targeted viscosity-increasing polyacrylamide microcapsule obtained in step (4) with n-hexane and drying it naturally, and its particle size is 80 μm.

[0174] Further, in step (1), the monomers are a mixture of acrylic acid, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid, and their mass ratio is 7:1:1.

[0175] Further, in step (1), the initiator is ammonium persulfate.

[0176] Further, in step (2), the oil is mineral oil.

[0177] Further, in step (2), the oil-soluble surfactant is span80.

[0178] Further, in step (3), the size structure of the targeted viscosity-increasing polyacrylamide microcapsule is controlled by regulating the flow rates of fluid L1 and fluid L2, where:

[0179] The flow rate of fluid L1 is controlled at 3 μL / min, and the flow rate of fluid L2 is controlled at 150 μL / min.

[0180] Further, the process conditions for ultraviolet curing in step (4) are: irradiating under a high-pressure mercury lamp with a power of 500 W and a main wavelength of 400 nm for 12 min.

[0181] Example 2

[0182] As Figure 1 shown, a preparation method of a targeted viscosity-increasing polyacrylamide microcapsule includes the following steps:

[0183] (1) Add 1 part of monomers and 0.1 part of initiator to 9 parts of water, stir evenly to obtain an aqueous solution, which is used as fluid L1;

[0184] (2) Add 1 part of oil-soluble surfactant to 39 parts of oil, stir evenly to obtain an oil-phase solution, which is used as fluid L2;

[0185] (3) Make fluid L1 pass through the central channel of the flow-focusing microchip as the dispersed phase, and make fluid L2 pass through the surrounding channels of the flow-focusing microchip as the continuous phase to prepare a water-in-oil emulsion;

[0186] (4) After irradiating the water-in-oil emulsion with an ultraviolet lamp and curing it, a targeted viscosity-increasing polyacrylamide microcapsule is obtained.

[0187] Further, it further includes step (5): washing the target viscosity-increasing polyacrylamide microcapsules obtained in step (4) with n-hexane and drying naturally, and the particle size thereof is 150 μm.

[0188] Further, the monomer in step (1) is a mixture of acrylic acid, acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid, and the mass ratio thereof is 7:1:1.

[0189] Further, the initiator in step (1) is ammonium persulfate.

[0190] Further, the oil in step (2) is mineral oil.

[0191] Further, the oil-soluble surfactant in step (2) is span80.

[0192] Further, in step (3), the size structure of the target viscosity-increasing polyacrylamide microcapsules is controlled by regulating the flow rates of fluid L1 and fluid L2, wherein:

[0193] The flow rate of fluid L1 is controlled at 10 μL / min, and the flow rate of fluid L2 is controlled at 550 μL / min.

[0194] Further, the process conditions for ultraviolet curing in step (4) are: irradiating under a high-pressure mercury lamp with a power of 500 W and a main wavelength of 365 nm for 20 min.

[0195] Example 3

[0196] As Figure 1 shown, a preparation method of target viscosity-increasing polyacrylamide microcapsules includes the following steps:

[0197] (1), adding 1 part of monomer and 0.1 part of initiator into 9 parts of water, and stirring evenly to obtain an aqueous solution as fluid L1;

[0198] (2), adding 1 part of oil-soluble surfactant into 39 parts of oil, and stirring evenly to obtain an oil phase solution as fluid L2;

[0199] (3), using fluid L1 as the dispersed phase to pass through the central channel of the flow focusing microchip, and using fluid L2 as the continuous phase to pass through the peripheral channels of the flow focusing microchip to prepare a water-in-oil emulsion;

[0200] (4), irradiating the water-in-oil emulsion with an ultraviolet lamp, and after curing, target viscosity-increasing polyacrylamide microcapsules are obtained.

[0201] Further, it further includes step (5): washing the target viscosity-increasing polyacrylamide microcapsules obtained in step (4) with n-hexane and drying naturally, and the particle size thereof is 250 μm.

[0202] Further, the monomer in step (1) is a mixture of acrylic acid, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid, and their mass ratio is 7:1:1.

[0203] Further, the initiator in step (1) is ammonium persulfate.

[0204] Further, the oil in step (2) is mineral oil.

[0205] Further, the oil-soluble surfactant in step (2) is span80.

[0206] Further, in step (3), the size structure of the targeted viscosity-increasing polyacrylamide microcapsules is controlled by regulating the flow rates of fluid L1 and fluid L2, where:

[0207] The flow rate of fluid L1 is controlled at 10 μL / min, and the flow rate of fluid L2 is controlled at 100 μL / min.

[0208] Further, the process conditions for ultraviolet curing in step (4) are: irradiating for 80 min under a high-pressure mercury lamp with a power of 500 W and a main wavelength of 320 nm.

[0209] Performance characterization:

[0210] 1. Influence of the inner-phase flow velocity, outer-phase flow velocity, curing time, and initiator concentration on the particle size of the targeted viscosity-increasing polyacrylamide microcapsules

[0211] According to the technical solution of Example 1, while keeping other process parameters unchanged, the influences of the inner-phase flow velocity, outer-phase flow velocity, curing time, and initiator concentration on the targeted viscosity-increasing polyacrylamide microcapsules were studied respectively.

[0212] Figure 2a It is a relationship diagram of the inner-phase flow velocity and the particle size of the targeted viscosity-increasing polyacrylamide microcapsules. From Figure 2a It can be seen that as the inner-phase flow velocity increases, the particle size of the targeted viscosity-increasing polyacrylamide microcapsules continuously increases.

[0213] Figure 2b It is a relationship diagram of the outer-phase flow velocity and the particle size of the targeted viscosity-increasing polyacrylamide microcapsules. From Figure 2b It can be seen that as the outer-phase flow velocity increases, the particle size of the targeted viscosity-increasing polyacrylamide microcapsules continuously decreases.

[0214] Figure 2c It is a relationship diagram of the curing time and the particle size of the targeted viscosity-increasing polyacrylamide microcapsules. From Figure 2cIt can be seen that with the increase of the curing time, the particle size of the targeted viscosity-increasing polyacrylamide microcapsules continuously decreases.

[0215] Figure 2d It is a relationship diagram of the initiator concentration and the particle size of the targeted viscosity-increasing polyacrylamide microcapsules. From Figure 2d It can be seen that with the increase of the initiator concentration, the particle size of the targeted viscosity-increasing polyacrylamide microcapsules continuously increases.

[0216] 2. High encapsulation efficiency

[0217] As Figure 1 shown, the encapsulation efficiency of the targeted viscosity-increasing polyacrylamide microcapsules prepared in Examples 1-3 was examined, and all of them achieved 100% encapsulation.

[0218] 3. Good monodispersity

[0219] As Figure 1 shown, the monodispersity of the targeted viscosity-increasing polyacrylamide microcapsules prepared in Examples 1-3 was examined, and uniformly, stably and well-monodispersed targeted viscosity-increasing polyacrylamide microcapsules were obtained.

[0220] 4. Controllable release

[0221] The slow-release performance of the targeted viscosity-increasing polyacrylamide microcapsules is related to the change trend of its viscosity with the curing time.

[0222] Since the greater the crosslinking density, the smaller the swelling degree of the microcapsules and the worse the viscosity-increasing performance. According to the technical scheme of Example 1, by fixing the reaction conditions such as the monomer ratio, monomer concentration, crosslinking agent concentration, initiator concentration and internal and external phase flow rates, the curing times were respectively selected as 12 min and 20 min, so that the targeted viscosity-increasing polyacrylamide microcapsules presented a low-density state of agglomeration and a high-density state of smooth dispersion respectively.

[0223] In simulated formation water, the viscosity of two targeted viscosity-increasing polyacrylamide microcapsules with different degrees of density was measured respectively using a high-temperature rotary rheometer, and the viscosities of the aqueous solutions of the two targeted viscosity-increasing polyacrylamide microcapsules with different degrees of density at different curing times were investigated. It can be seen that the microcapsules with a curing time of 12 min had an earlier release time (less than 24 h), while the microcapsules with 20 min started to release after 36 h, and the viscosity-increasing performance of the microcapsules with 12 min was better than that of the targeted viscosity-increasing polyacrylamide microcapsules with a curing time of 20 min.

[0224] 5. Infrared characterization

[0225] Figure 3 It is the infrared spectrum of the targeted viscosity-increasing polyacrylamide microcapsules prepared in Example 1. As Figure 3As shown, the characteristic absorption peaks of the target-viscosity-increasing polyacrylamide microcapsules prepared in Example 1 at around 1141 cm -1 , 1025 cm -1 and 622 cm -1 correspond to the stretching vibrations of the S=O bond and the C-S bond respectively. It can be obtained that the microcapsules contain sulfonic acid groups and polyacrylamide groups, indicating the successful curing of the microcapsules.

[0226] 6. Thermogravimetric Characterization

[0227] Figure 4 Figure 4 is the thermogravimetric-differential thermal diagram of the target-viscosity-increasing polyacrylamide microcapsules prepared in Example 1. As Figure 4 shown, the thermogravimetric curve of the target-viscosity-increasing polyacrylamide microcapsules can be divided into three stages. The first stage is between 30 - 247 °C, and the mass loss in this part comes from the volatilization of the free water contained in the microcapsules, indicating that the microcapsules are not prone to thermal decomposition within 240 °C.

[0228] 7. Relationship between Viscosity and Aging Time

[0229] Test method: Prepare a target-viscosity-increasing polyacrylamide microcapsule polymer solution with a concentration of 2500 mg / L using simulated formation water, stir it for 1 h under a stirrer at 300 r / min, transfer it to a sealed container after deoxygenation, and finally place it in an oven at 75 °C for constant temperature storage. The aging days are set as: 0 day, 1 day, 3 days, 5 days, 7 days, 10 days, 15 days, and its viscosity is measured.

[0230] Figure 5a Figure 5 is the broken-line relationship diagram between the viscosity and the aging time of the target-viscosity-increasing polyacrylamide microcapsules prepared in Example 1. From Figure 5a it can be seen that when placed in simulated formation water at 75 °C, the shell breaks after 1 day, and the liquid viscosity increases significantly. Its viscosity reaches a peak value of 4.7 mPa·s at the 10th day.

[0231] As Figure 5a shown, within the aging time range of 0 - 15 days, when the aging temperature is 75 °C, the viscosity of the aqueous solution of the target-viscosity-increasing polyacrylamide microcapsules first increases and then decreases with the increase of the aging time. This is because in the initial stage of aging, the target-viscosity-increasing polyacrylamide microcapsules have a certain thermal stability and can maintain their original morphology without swelling, so no obvious viscosity-increasing performance is shown; when the aging time extends to 6 days, the target-viscosity-increasing polyacrylamide microcapsules show a swelling phenomenon due to water absorption and swelling, showing viscosity-increasing performance. With the increase of the aging time, the viscosity of the target-viscosity-increasing polyacrylamide microcapsules increases, and its viscosity-increasing performance becomes more obvious. When the aging time is 10 days, the viscosity of the target-viscosity-increasing polyacrylamide microcapsules reaches a peak value of 4.7 mPa·s.

[0232] Figure 5b Line graph showing the relationship between the viscosity of the target-viscosity-increasing polyacrylamide microcapsules prepared in Example 2 and the aging time. As Figure 5b shown, when placed in simulated formation water at 75 °C, the capsule shell breaks after 3 days, the liquid viscosity increases, and its viscosity reaches a peak of 3.9 mPa·s at the 10th day.

[0233] Obviously, the above embodiments of the present invention enable those skilled in the art to implement or use the present invention, rather than limiting the implementation manners of the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and it is impossible to enumerate all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

[0234] The above has described the implementation manners of the present invention in detail. However, the present invention is not limited to the above implementation manners, and various changes can be made without departing from the gist of the present invention within the knowledge scope of those of ordinary skill in the art.

Claims

1. A targeted viscosity-increasing polyacrylamide microcapsule, characterized in that, the targeted viscosity-increasing polyacrylamide microcapsule comprises a core material and a wall material wrapping the core material, wherein: the core material is an aqueous solution containing monomers and initiators; the wall material is an oil-phase solution containing an oil-soluble surfactant.

2. The targeted viscosity-increasing polyacrylamide microcapsule according to claim 1, characterized in that, the monomer is one or more of acrylic acid, acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid, and / or the initiator is one of ammonium persulfate and potassium persulfate, and / or the aqueous solution contains water, and the mass ratio of the monomer, initiator and water in the core material is (1 - 1.4):(0.05 - 0.15):(8 - 10), and / or the oil-phase solution containing the oil-soluble surfactant contains oil, and the mass ratio of the oil-soluble surfactant to the oil is 1:(30 - 49), wherein: the oil-soluble surfactant is one of Span80, TX-100, Tween80, and the oil is one of mineral oil, fluorocarbon oil, silicone oil, white oil.

3. A method for preparing the targeted viscosity-increasing polyacrylamide microcapsule according to claim 1 or 2, characterized in that, by mass, it comprises the following steps: (1) Add 1 - 1.4 parts of monomers and 0.05 - 0.15 parts of initiators to 8 - 10 parts of water, stir evenly to obtain an aqueous solution, as fluid L1; (2) Add 1 part of oil-soluble surfactant to 30 - 49 parts of oil, stir evenly to obtain an oil-phase solution, as fluid L2; (3) Make fluid L1 as the dispersed phase pass through the central channel of the flow-focusing microchip, and make fluid L2 as the continuous phase pass through the surrounding channels of the flow-focusing microchip to prepare a water-in-oil emulsion; (4) After irradiating the water-in-oil emulsion with an ultraviolet lamp and curing, the targeted viscosity-increasing polyacrylamide microcapsule is obtained.

4. The method for preparing the targeted viscosity-increasing polyacrylamide microcapsule according to claim 3, characterized in that, it further comprises step (5): washing the targeted viscosity-increasing polyacrylamide microcapsule obtained in step (4) with n-hexane and drying it naturally.

5. The method for preparing the targeted viscosity-increasing polyacrylamide microcapsule according to claim 3, characterized in that, the monomer in step (1) is one or more of acrylic acid, acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid, and / or the initiator in step (1) is one of ammonium persulfate and potassium persulfate.

6. The method for preparing the targeted viscosity-increasing polyacrylamide microcapsule according to claim 3, characterized in that, the oil in step (2) is one of mineral oil, fluorocarbon oil, silicone oil, white oil, and / or the oil-soluble surfactant in step (2) is one of span80, TX-100, Tween80.

7. The method for preparing the targeted viscosity-increasing polyacrylamide microcapsule according to claim 3, characterized in that, In step (3), the size and structure of the targeted viscosity-increasing polyacrylamide microcapsules are controlled by regulating the flow rates of fluid L1 and fluid L2, where: The flow rate of fluid L1 is controlled at 1 - 120 μL / min, and the flow rate of fluid L2 is controlled at 100 - 550 μL / min.

8. A method for preparing a targeted viscosity-increasing polyacrylamide microcapsule according to claim 3, characterized in that In step (4), the process conditions for ultraviolet curing are: irradiating under a high-pressure mercury lamp with a power of 400 - 600 W and a main wavelength of 320 - 400 nm for 12 - 80 min.

9. A targeted viscosity-increasing polyacrylamide microcapsule, characterized in that It is prepared by the preparation method described in any one of claims 3 - 8.

10. The application of the targeted viscosity-increasing polyacrylamide microcapsule described in any one of claims 1 - 2, 9 as a displacement agent in oil recovery.

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