Micro-nano capsule, preparation method thereof and sustained-release gel containing same

Abstract

The present invention provides a micro-nano capsule, a preparation method thereof, and a sustained-release gel containing the micro-nano capsule. The micro-nano capsule comprises amphiphilic silica micro-nano particles as a capsule shell and a crosslinker solution as a content, with the content being encapsulated by the capsule shell. The preparation method of the nano-microcapsule comprises preparing a crosslinker solution, stirring the solution with the amphiphilic silica micro-nano particles at a speed of 10,000 to 19,000 r / min for 1 to 2 minutes to obtain the micro-nano capsule. The sustained-release gel comprises the micro-nano capsule, a partially hydrolyzed polyacrylamide solution, and an oxygen scavenger solution. The sustained-release gel has a gelation time of up to 144 hours at 120°C.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield chemicals, and in particular relates to a micro-nano capsule, a preparation method thereof and a sustained-release gel containing the micro-nano capsule. Background Art

[0002] After long-term waterflooding, many oil fields and wells have entered a period of high water content, resulting in severe reservoir heterogeneity and increasing water content in produced fluids. Polyacrylamide-based plugging control systems are the most commonly used plugging control agents in oil fields. By adding a crosslinker to a partially hydrolyzed polyacrylamide (HPAM) solution, a network-like structure is formed between the polymer chains, locking in water and ultimately forming a polymer gel. This effectively blocks high-permeability reservoirs and large pores, reducing water content and improving the recovery efficiency of medium- and low-permeability reservoirs. During the process of plugging control agent entry into the reservoir, the gelation rate should not be too rapid due to the pressure resistance of the wellbore and injection equipment. Furthermore, if the plugging control agent crosslinks in the wellbore and pipeline, the injection pressure will increase sharply. Once the triggering pressure of the medium- and low-permeability layers is reached, the plugging control agent will enter the medium- and low-permeability layers and cause contamination. Furthermore, for deep profile control, the plugging control agent must be injected into the target reservoir before crosslinking occurs. Excessively rapid crosslinking can compromise the effectiveness of deep profile control. Therefore, delayed crosslinking technology for gels is particularly important. Numerous methods exist in the prior art for delaying the gelation time of polymer gels, but they still present numerous drawbacks. For example, the method of adding a competitive inclusion agent is too specific and difficult to apply to various crosslinker systems. The W / O / W multiple emulsion method can delay the gelation time at low temperatures, but the emulsion's stability and the crosslinker's sustained release performance cannot be guaranteed at high temperatures. There is an urgent need for a material that delays the gelation time of polymer gels, features a limited number of raw materials, a simple process, is applicable to various crosslinker systems, and exhibits excellent thermal stability. Summary of the Invention

[0003] One aspect of the present invention provides a micro-nano capsule, comprising a capsule shell and contents; the capsule shell is amphiphilic silica micro-nano particles, the contents are a cross-linking agent solution; the contents are wrapped by the capsule shell.

[0004] In one embodiment, the mass ratio of the contents to the capsule shell is (10 to 50):1; and / or

[0005] In the cross-linking agent solution, the concentration of the cross-linking agent is 0.1 wt % to 1.0 wt %.

[0006] In one embodiment, a portion of the continuous surface area of ​​the amphiphilic silica micro-nanoparticles is bonded to the hydrophilic groups, and another portion of the continuous surface area is bonded to the hydrophobic groups.

[0007] In one embodiment, the hydrophilic group is an amino group; and / or the hydrophobic group is a long-chain alkyl group;

[0008] Preferably, the long chain alkyl is C 12 to C 18 Alkyl;

[0009] Preferably, the long chain alkyl is C 12 to C 18 of straight-chain alkyl;

[0010] Preferably, the long-chain alkyl group is a dodecyl group.

[0011] In one embodiment, the amphiphilic silica micro-nanoparticles are obtained by modifying nano-silica with a silane coupling agent containing an amino group and a long-chain alkyl carboxylic acid;

[0012] Preferably, the particle size of the nano-silicon dioxide is 7 nm to 40 nm; and / or

[0013] The long-chain alkyl carboxylic acid is C 12 to C 18 Alkyl carboxylic acids;

[0014] Preferably, the amino-containing silane coupling agent is 3-aminopropyltriethoxysilane; and / or

[0015] The long-chain alkyl carboxylic acid is C 12 to C 18 of straight-chain alkyl carboxylic acids;

[0016] Preferably, the long-chain alkyl carboxylic acid is dodecanoic acid;

[0017] Preferably, the CAS number of the nano-silicon dioxide is 60676-86-0.

[0018] In one embodiment, in the cross-linking agent solution, the cross-linking agent is selected from at least one of chromium chloride, chromium acetate, zirconium acetate, aluminum citrate, a mixture of hexamethylenetetramine and resorcinol, a mixture of phenol and formaldehyde, a phenolic resin and polyethyleneimine; and / or

[0019] The solvent in the cross-linking agent solution is water;

[0020] Preferably, the mass ratio of hexamethylenetetramine to resorcinol, and the mass ratio of phenol to formaldehyde are independently (1 to 3): (3 to 1);

[0021] Preferably, the solvent in the cross-linking agent solution is formation water with a pH of 2 to 10;

[0022] Preferably, the mass ratio of hexamethylenetetramine to resorcinol and the mass ratio of phenol to formaldehyde are independently 1:1.

[0023] In one embodiment, the median particle size of the micro-nanocapsules is 680 nm to 3110 nm; and / or

[0024] The median particle size of the amphiphilic silica micro-nanoparticles is 80 nm to 120 nm.

[0025] The second aspect of the present invention provides a method for preparing the micro-nanocapsules according to the first aspect of the present invention, which comprises the following steps:

[0026] 1) preparing a cross-linking agent solution to obtain the contents;

[0027] 2) mixing the amphiphilic silica micro-nano particles and the contents to obtain the micro-nano capsules.

[0028] In one embodiment, in step 2), mixing is performed by stirring;

[0029] Preferably, the stirring speed is 10000 r / min to 19000 r / min; and / or

[0030] The stirring time is 1 min to 2 min.

[0031] In one embodiment, the amphiphilic silica micro-nanoparticles are prepared by the following method:

[0032] a. subjecting the nano-silica and the amino-containing silane coupling agent to a first reaction to obtain hydrophilic silica micro-nanoparticles;

[0033] b. The hydrophilic silica micro-nanoparticles and paraffin are dispersed in water and emulsified to obtain solidified paraffin microspheres;

[0034] c. subjecting the solidified paraffin microspheres to a second reaction with a long-chain alkyl carboxylic acid to obtain hydrophobically modified paraffin microspheres;

[0035] d. dissolving the paraffin in the hydrophobically modified paraffin microspheres with an organic solvent to obtain the amphiphilic silica micro-nanoparticles.

[0036] In one embodiment, the mass ratio of the nano-silica to the amino-containing silane coupling agent is (1 to 2): (0.3 to 0.6); and / or

[0037] The mass ratio of the hydrophilic silica micro-nanoparticles to paraffin is (1 to 2): (5 to 6); and / or

[0038] The mass of the amino-containing silane coupling agent is calculated as 100%, and the amount of the long-chain alkyl carboxylic acid is 70wt% to 100wt%;

[0039] Preferably, the mass ratio of the nano-silica to the amino-containing silane coupling agent is 1:0.4; and / or

[0040] The mass ratio of the hydrophilic silica micro-nanoparticles to paraffin is 1:5; and / or

[0041] The weight of the amino-containing silane coupling agent is calculated as 100%, and the amount of the long-chain alkyl carboxylic acid is 83.5 wt%.

[0042] In a specific embodiment, the organic solvent is selected from at least one of an alkane organic solvent (such as diesel, gasoline), an aromatic organic solvent (such as xylene) and a halogenated hydrocarbon organic solvent (such as chloroform).

[0043] In one embodiment, in step a, the nano-silica and the amino-containing silane coupling agent are hydrolyzed separately and then mixed, and then the first reaction is carried out; and / or

[0044] The reaction liquid obtained by the first reaction is filtered twice, and the filter residue obtained by the second filtration is dried to obtain the hydrophilic silica micro-nano particles;

[0045] Preferably, the nano-silica is mixed with ethanol and hydrolyzed; and / or the amino-containing silane coupling agent is mixed with an ethanol aqueous solution and hydrolyzed; and / or

[0046] Wash the filter residue obtained from the first filtration and then perform the second filtration;

[0047] Preferably, the duration of the hydrolysis of the nano-silica and the duration of the hydrolysis of the amino-containing silane coupling agent are independently 2 h to 3 h; and / or

[0048] The pressure of the first filtration and the second filtration are independently 0.5 MPa to 0.7 MPa; and / or

[0049] The duration of the first filtration and the duration of the second filtration are independently 30 min to 45 min; and / or

[0050] Washing the filter residue obtained by the first filtration with acetone; and / or

[0051] The filter residue obtained by the second filtration is dried at 70°C to 80°C;

[0052] Preferably, in the ethanol aqueous solution, the volume ratio of water to ethanol is 1:9.

[0053] In one embodiment, in step b, the emulsification is followed by cooling to solidify the paraffin on the surface of the paraffin microspheres to obtain the solidified paraffin microspheres; and / or

[0054] In step c, the solidified paraffin microspheres are added to the ethanol solution of the long-chain alkyl carboxylic acid to carry out the second reaction; and / or the mass fraction of the long-chain alkyl carboxylic acid in the ethanol solution of the long-chain alkyl carboxylic acid is 2 wt%; and / or

[0055] The second reaction is carried out under stirring conditions; and / or

[0056] Filtering the reaction solution obtained from the second reaction, collecting the filter residue and washing it with ethanol to obtain the hydrophobically modified paraffin microspheres; and / or

[0057] In step d, the paraffin in the hydrophobically modified paraffin microspheres is dissolved with an organic solvent, the mixture is centrifuged, the lower precipitate is collected, and the precipitate is dried to obtain the amphiphilic silica micro-nanoparticles;

[0058] Preferably, the stirring speed is 200 r / min to 300 r / min; and / or

[0059] The drying condition of the lower precipitate is vacuum drying at 60° C. to 80° C.

[0060] In one embodiment, in step a, the first reaction is refluxed at 80° C. for 4 h; and / or

[0061] In step b, the emulsification conditions are: stirring at a speed of 3000 r / min to 4500 r / min for 45 min to 30 min at 70° C. to 80° C.; and / or

[0062] The temperature of the water in which the hydrophilic silica micro-nanoparticles and paraffin are dispersed is 75° C. to 80° C.;

[0063] In step c, the temperature of the second reaction is 20° C. to 30° C.; and / or the reaction time is 36 h to 48 h.

[0064] The third aspect of the present invention provides a sustained-release gel comprising a partially hydrolyzed polyacrylamide solution and micro-nanocapsules;

[0065] The micro-nano capsule is the micro-nano capsule described in one embodiment of the present invention or the micro-nano capsule prepared by the method described in the second embodiment of the present invention.

[0066] In one embodiment, in the partially hydrolyzed polyacrylamide solution, the hydrolysis degree of the partially hydrolyzed polyacrylamide is 20% to 25%; and / or the weight average molecular weight is 8×10 6 to 1.2×10 7 .

[0067] In one embodiment, the sustained-release gel further comprises an oxygen scavenger solution;

[0068] Preferably, the solvent in the partially hydrolyzed polyacrylamide solution and the solvent in the oxygen scavenger solution are independently water;

[0069] Preferably, the solvent in the partially hydrolyzed polyacrylamide solution is formation water with a pH of 2 to 10; and / or

[0070] The solvent in the deoxidizer solution is formation water with a pH of 2 to 9.

[0071] In one embodiment, based on the mass of the sustained-release gel, the sustained-release gel comprises 25 to 50 parts by mass of a partially hydrolyzed polyacrylamide solution, 10 to 40 parts by mass of micro-nanocapsules, and 10 to 50 parts by mass of an oxygen scavenger solution;

[0072] Preferably, in the partially hydrolyzed polyacrylamide solution, the concentration of the partially hydrolyzed polyacrylamide is 1 wt% to 2 wt%; and / or

[0073] In the deoxidizer solution, the concentration of the deoxidizer is 0.4 wt % to 2.0 wt %.

[0074] Generally, commercially available oxygen scavengers can be used in the present invention. If listed, the oxygen scavenger is at least one of thiourea, bisulfite (such as sodium bisulfite, potassium bisulfite or ammonium bisulfite), isoascorbic acid, isoascorbate (such as sodium isoascorbate), ascorbic acid and ascorbate (such as sodium ascorbate).

[0075] The application of at least one of the micro-nanocapsules according to the first invention, the micro-nanocapsules prepared by the method according to the second invention, and the slow-release gel according to the third invention in oil reservoir plugging control, especially as a plugging control agent. The beneficial effects of the present invention are as follows:

[0076] To address the problems of existing gel delayed cross-linking technologies, such as numerous raw materials, complex processes, limited availability of suitable cross-linking agent systems, and poor thermal stability, the present invention provides a micro-nanocapsule, a preparation method, and a sustained-release gel containing the same. The micro-nanocapsule comprises amphiphilic silica micro-nanoparticles as a capsule shell and a cross-linking agent solution as a content; the content is encapsulated by the capsule shell. The micro-nanocapsules can be applied with various crosslinker systems, such as chromium acetate, zirconium acetate, aluminum citrate, urotropine / resorcinol, phenol / formaldehyde, phenolic acid resin, and polyethyleneimine, and have strong universal applicability. The method for preparing the micro-nanocapsules provided by the present invention is simple: a crosslinker solution is prepared, the crosslinker solution is mixed with amphiphilic silica micro-nanoparticles, and the mixture is stirred at a speed of 10,000 to 19,000 r / min for 1 to 2 minutes to obtain the micro-nanocapsules. The sustained-release gel is obtained by mixing the micro-nanocapsules, a partially hydrolyzed polyacrylamide solution, and an oxygen scavenger solution. After the sustained-release gel is formed, synergistic enhancement exists between the amphiphilic silica micro-nanoparticles and the partially hydrolyzed polyacrylamide gel, thereby enhancing the rigidity and thermal stability of the sustained-release gel after formation. The sustained-release gel has excellent thermal stability and can gel at temperatures between 60 and 120°C. The gelation time of the sustained-release gel at 120°C is extended to 144 hours at most, which is 288 times longer than the gelation time of a partially hydrolyzed polyacrylamide gel without the micro-nanocapsules added at 120°C. Furthermore, the sustained-release gel provided by the present invention achieves a gel strength of Grade I after gelation at 120°C, with an elastic modulus of 307 Pa and a viscous modulus of 36 Pa at 30°C, 1.0 Hz, and 1.0 Pa. The micro-nanocapsules provided by the present invention can not only significantly delay the gelation time of the polymer gel, but also effectively enhance the strength of the gel, improving the sealing effect of the hypertonic layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 Infrared spectra of the amphiphilic silica micro-nanoparticles prepared by the present invention, the hydrophilic silica micro-nanoparticles prepared in the preparation process of the amphiphilic silica micro-nanoparticles, and the nano-silica used;

[0078] Figure 2 This is an image of fluorescent micro-nanocapsules formed by amphiphilic silica micro-nanoparticles encapsulating fluorescent dyes under a laser confocal microscope;

[0079] Figure 3 The contents of the micro-nanocapsules prepared in Example 1 (i.e., the cross-linking agent solution);

[0080] Figure 4 The upper middle portion is the amphiphilic silica micro-nanoparticles used in Example 1, and the lower portion is deionized water;

[0081] Figure 5The micro-nano capsules obtained by encapsulating the contents with amphiphilic silica micro-nano particles in Example 1;

[0082] Figure 6 This is a microscope image of the micro-nanocapsules prepared in Example 1;

[0083] Figure 7 This is an image of the micro-nanocapsules prepared in Example 1 under a scanning electron microscope;

[0084] Figure 8 This is an image of the partially hydrolyzed polyacrylamide gel prepared in Comparative Example 3 without the addition of micro-nanocapsules after gelation under a scanning electron microscope at a magnification of 500;

[0085] Figure 9 This is an image of the partially hydrolyzed polyacrylamide gel prepared in Comparative Example 3 without the addition of micro-nanocapsules after gelation under a scanning electron microscope at a magnification of 1000;

[0086] Figure 10 This is an image of the sustained-release gel containing micro-nanocapsules prepared in Example 15 after gelation under a scanning electron microscope at a magnification of 500;

[0087] Figure 11 This is an image of the sustained-release gel containing micro-nanocapsules prepared in Example 15 after gelation under a scanning electron microscope at a magnification of 1000;

[0088] Figure 12 This is an image of the micro-nanocapsules prepared in Comparative Example 4 after gelation under a scanning electron microscope at a magnification of 500;

[0089] Figure 13 This is an image of the micro-nanocapsules prepared in Comparative Example 4 after gelation under a scanning electron microscope at a magnification of 1000; DETAILED DESCRIPTION

[0090] The present invention will be further described below with reference to examples. However, the examples are merely illustrative and do not limit the present invention in any way.

[0091] Nanosilica used in the preparation of amphiphilic silica micro-nanoparticles was purchased from Beijing Huawei Ruike Chemical Co., Ltd. with a purity (Hydr) of 99.8% and a specific surface area (BET) of 300 m 2 / g, CAS number is 60676-86-0, and particle size is 7 to 40 nm.

[0092] Preparation of amphiphilic silica micro-nanoparticles

[0093] 1) 6 g of nano-SiO2 was dispersed in 100 mL of ethanol and hydrolyzed for 2 h. 2.394 g of 3-aminopropyltriethoxysilane (APTES) was dissolved in a mixed solution of water and ethanol with a volume ratio of 1:9 and hydrolyzed for 2 h. The mixture was heated to 80° C. and refluxed for 4 h. The resulting reaction solution was filtered for a first time at 0.5 MPa for 45 min, the first filtration residue was collected, washed with acetone, and then filtered for a second time at 0.5 MPa for 30 min. The second filtration residue was collected. The second filtration residue was dried in an oven at 80° C. to obtain hydrophilic silica micro-nanoparticles.

[0094] 2) Dispersing 6 g of hydrophilic silica micro-nanoparticles and 30 g of paraffin wax in 100 g of distilled water at 80° C., stirring and emulsifying the mixture at 3000 rpm for 45 min using a high-speed stirrer, and cooling the paraffin wax to solidify the mixture, thereby obtaining solidified paraffin wax microspheres;

[0095] 3) adding all the solidified paraffin microspheres obtained in step 2) to 100 g of a 2 wt % ethanol solution of dodecanoic acid, stirring at 300 rpm for 36 h at room temperature (25° C.), filtering, and washing the filter residue with ethanol to obtain hydrophobically modified paraffin microspheres;

[0096] 4) The hydrophobically modified paraffin microspheres obtained in step 3) were immersed in chloroform to dissolve the paraffin, centrifuged, and the lower precipitate was collected and vacuum-dried at 60° C. for 12 h to obtain amphiphilic silica micro-nanoparticles with a median particle size of 80 nm.

[0097] Preparation of micro-nanocapsules

[0098] Example 1

[0099] 1) mixing 0.4 g of chromium acetate and 99.6 g of formation water having a pH value of 7 to obtain a chromium acetate aqueous solution having a mass fraction of 0.4 wt % of chromium acetate, which is the content;

[0100] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0101] Example 2

[0102] 1) mixing 1.0 g of chromium acetate and 99 g of formation water having a pH value of 4 to obtain a chromium acetate aqueous solution having a mass fraction of chromium acetate of 1.0 wt %, which is the content;

[0103] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0104] Example 3

[0105] 1) mixing 0.4 g of chromium acetate and 99.6 g of formation water having a pH value of 7 to obtain a chromium acetate aqueous solution having a mass fraction of 0.4 wt % of chromium acetate, which is the content;

[0106] 2) 5 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 1,268 nm.

[0107] Example 4

[0108] 1) mixing 0.4 g of chromium acetate and 99.6 g of formation water having a pH value of 7 to obtain a chromium acetate aqueous solution having a mass fraction of 0.4 wt % of chromium acetate, which is the content;

[0109] 2) 2 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 680 nm.

[0110] Example 5

[0111] 1) mixing 0.25 g of chromium acetate and 99.75 g of formation water having a pH value of 7 to obtain a chromium acetate aqueous solution having a mass fraction of 0.25 wt % of chromium acetate, which is the content;

[0112] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 19,000 rpm for 2 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0113] Example 6

[0114] 1) mixing 0.4 g of phenolic resin and 99.6 g of formation water having a pH value of 7 to obtain a phenolic resin aqueous solution having a mass fraction of 0.4 wt % of phenolic resin, which is the content;

[0115] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0116] Example 7

[0117] 1) mixing 0.4 g of chromium chloride and 99.6 g of formation water having a pH value of 7 to obtain a chromium chloride aqueous solution having a mass fraction of 0.4 wt % of chromium chloride, which is the content;

[0118] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0119] Example 8

[0120] 1) mixing 0.1 g of zirconium acetate and 99.9 g of formation water having a pH of 2 to obtain a zirconium acetate aqueous solution having a mass fraction of zirconium acetate of 0.1 wt %, which is the content;

[0121] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0122] Example 9

[0123] 1) mixing 0.2 g of aluminum citrate and 99.8 g of formation water having a pH value of 7 to obtain an aluminum citrate aqueous solution having a mass fraction of 0.2 wt % of aluminum citrate, which is the content;

[0124] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0125] Example 10

[0126] 1) mixing 0.075 g of methenamine, 0.225 g of resorcinol, and 99.7 g of formation water having a pH value of 7 to obtain a mixed aqueous solution of methenamine and resorcinol having a total mass fraction of 0.3 wt % of methenamine and resorcinol, which is the content;

[0127] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0128] Example 11

[0129] 1) mixing 0.375 g of phenol, 0.125 g of formaldehyde, and 99.5 g of formation water having a pH value of 9 to obtain a mixed aqueous solution of phenol and formaldehyde having a total mass fraction of phenol and formaldehyde of 0.5 wt %, which is the content;

[0130] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0131] Example 12

[0132] 1) mixing 0.4 g of polyethyleneimine and 99.6 g of formation water having a pH value of 7 to obtain a polyethyleneimine aqueous solution having a polyethyleneimine mass fraction of 0.4 wt %, which is the content;

[0133] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 15,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0134] Example 13

[0135] 1) mixing 0.4 g of chromium acetate and 99.6 g of formation water having a pH value of 10 to obtain a chromium acetate aqueous solution having a mass fraction of 0.4 wt % of chromium acetate, which is the content;

[0136] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 16,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0137] Example 14

[0138] 1) mixing 0.4 g of chromium acetate and 99.6 g of formation water having a pH value of 7 to obtain a chromium acetate aqueous solution having a mass fraction of 0.4 wt % of chromium acetate, which is the content;

[0139] 2) 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 10,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 3110 nm.

[0140] Preparation of sustained-release gel

[0141] The partially hydrolyzed polyacrylamide used in Examples 15 to 28 and Comparative Examples 1 to 4 had a hydrolysis degree of 25% and a weight average molecular weight of 8×10 6 .

[0142] Example 15

[0143] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0144] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0145] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 1 were mixed and stirred uniformly to obtain a sustained-release gel.

[0146] Example 16

[0147] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 4 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0148] 2) mixing 0.5 g of sodium bisulfite and 99.5 g of simulated formation water having a pH of 4 to obtain a 0.5 wt % aqueous solution of sodium bisulfite;

[0149] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 8 g of the 0.5 wt % sodium bisulfite aqueous solution prepared in this example, and 2 g of the micro-nanocapsules prepared in Example 2 were mixed and stirred uniformly to obtain a sustained-release gel.

[0150] Example 17

[0151] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0152] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0153] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 3 were mixed and stirred uniformly to obtain a sustained-release gel.

[0154] Example 18

[0155] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0156] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0157] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 4 were mixed and stirred uniformly to obtain a sustained-release gel.

[0158] Example 19

[0159] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of 1 wt % of the hydrolyzed polyacrylamide;

[0160] 2) mixing 2 g of sodium bisulfite with 98 g of simulated formation water having a pH of 7 to obtain a 2 wt % aqueous solution of sodium bisulfite;

[0161] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 2 g of the 2 wt % sodium bisulfite aqueous solution prepared in this example, and 8 g of the micro-nanocapsules prepared in Example 5 were mixed and stirred uniformly to obtain a sustained-release gel.

[0162] Example 20

[0163] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0164] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0165] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 6 were mixed and stirred uniformly to obtain a sustained-release gel.

[0166] Example 21

[0167] 1) mixing 2 g of partially hydrolyzed polyacrylamide and 98 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 2 wt %;

[0168] 2) mixing 0.4 g of sodium bisulfite with 99.6 g of simulated formation water having a pH of 7 to obtain a 0.4 wt % aqueous solution of sodium bisulfite;

[0169] 3) 5 g of the 2 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 10 g of the 0.4 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 7 were mixed and stirred uniformly to obtain a sustained-release gel.

[0170] Example 22

[0171] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 2 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0172] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 2 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0173] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 8 were mixed and stirred uniformly to obtain a sustained-release gel.

[0174] Example 23

[0175] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0176] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0177] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 9 were mixed and stirred uniformly to obtain a sustained-release gel.

[0178] Example 24

[0179] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0180] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0181] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 10 were mixed and stirred uniformly to obtain a sustained-release gel.

[0182] Example 25

[0183] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 9 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0184] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0185] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 11 were mixed and stirred uniformly to obtain a sustained-release gel.

[0186] Example 26

[0187] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0188] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0189] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 12 were mixed and stirred uniformly to obtain a sustained-release gel.

[0190] Example 27

[0191] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 10 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0192] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0193] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 13 were mixed and stirred uniformly to obtain a sustained-release gel.

[0194] Example 28

[0195] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0196] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0197] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this example, and 5 g of the micro-nanocapsules prepared in Example 14 were mixed and stirred uniformly to obtain a sustained-release gel.

[0198] Comparative Example 1

[0199] Preparation of micro-nanocapsules:

[0200] 1) mixing 0.4 g of chromium acetate and 99.6 g of formation water having a pH value of 7 to obtain a chromium acetate aqueous solution having a mass fraction of 0.4 wt % of chromium acetate, which is the content;

[0201] 2) 1 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm was mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 10,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 390 nm.

[0202] Preparation of sustained-release gel:

[0203] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0204] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0205] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this comparative example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this comparative example, and 5 g of the micro-nanocapsules prepared in this comparative example were mixed and stirred uniformly to obtain a sustained-release gel.

[0206] Comparative Example 2

[0207] Preparation of micro-nanocapsules:

[0208] 1) mixing 0.4 g of phenolic resin and 99.6 g of formation water having a pH of 12 to obtain a chromium acetate aqueous solution having a mass fraction of chromium acetate of 0.4 wt %, which is the content;

[0209] 2) 2 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with 100 g of the contents prepared in step 1), and stirred at a speed of 19,000 rpm for 1 min to obtain micro-nanocapsules with a median particle size of 680 nm.

[0210] Preparation of sustained-release gel:

[0211] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 12 to obtain a partially hydrolyzed polyacrylamide aqueous solution having a mass fraction of partially hydrolyzed polyacrylamide of 1 wt %;

[0212] 2) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0213] 3) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this comparative example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this comparative example, and 5 g of the micro-nanocapsules prepared in this comparative example were mixed and stirred uniformly to obtain a sustained-release gel.

[0214] Comparative Example 3

[0215] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to prepare a partially hydrolyzed polyacrylamide aqueous solution with a mass fraction of the partially hydrolyzed polyacrylamide of 1 wt %;

[0216] 2) mixing 0.4 g of chromium acetate with 99.6 g of formation water having a pH of 7 to obtain a chromium acetate aqueous solution having a mass fraction of 0.4 wt % of chromium acetate;

[0217] 3) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0218] 4) 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this comparative example was added with 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this comparative example and 5 g of the 0.4 wt % chromium acetate solution prepared in this comparative example, and the mixture was stirred uniformly to obtain a partially hydrolyzed polyacrylamide gel system.

[0219] Comparative Example 4

[0220] 1) mixing 1 g of partially hydrolyzed polyacrylamide with 99 g of simulated formation water having a pH of 7 to prepare a partially hydrolyzed polyacrylamide aqueous solution with a mass fraction of the partially hydrolyzed polyacrylamide of 1 wt %;

[0221] 2) mixing 0.4 g of chromium acetate with 99.6 g of formation water having a pH of 7 to obtain a chromium acetate aqueous solution having a mass fraction of 0.4 wt % of chromium acetate;

[0222] 3) mixing 0.8 g of sodium bisulfite and 99.2 g of simulated formation water having a pH of 7 to obtain a 0.8 wt % aqueous solution of sodium bisulfite;

[0223] 4) To 10 g of the 1 wt % partially hydrolyzed polyacrylamide aqueous solution prepared in this comparative example, 5 g of the 0.8 wt % sodium bisulfite aqueous solution prepared in this comparative example and 4.55 g of the 0.4 wt % chromium acetate solution prepared in this comparative example were added, and the mixture was stirred uniformly to obtain a content; 0.45 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm was then added, and the mixture was stirred at 16,000 rpm for 1 minute to obtain micro-nanocapsules, a sustained-release gel system.

[0224] Experimental evaluation

[0225] 1. Structural Characterization of Amphiphilic Silica Micro-Nanoparticles

[0226] The KBr pellet method was used and the wavelength range was 4000 to 500 cm-1 using a Nexus Fourier transform infrared spectrometer. -1 The amphiphilic silica micro-nano particles prepared by the present invention were subjected to infrared spectroscopy, and the hydrophilic silica micro-nano particles prepared in the process of preparing the amphiphilic silica micro-nano particles and the nano silica used were subjected to infrared spectroscopy. Figure 1 .

[0227] Figure 1 The infrared spectra of nano-silica, hydrophilic silica micro-nanoparticles and amphiphilic silica micro-nanoparticles are shown in Figure 2. According to the infrared results, the curve of nano-silica particles has an average wavelength of 3480 cm -1 The peak at 3310 cm-1 can be attributed to the absorption of OH bonds on the surface of nano-silica. In the infrared spectrum of hydrophilic silica micro-nanoparticles, this peak shifts to the right and is at 3310 cm-1. -1 The peak at 2905 cm-1 can be attributed to the absorption of NH bonds on the particle surface; the amino absorption peak on the infrared spectrum of amphiphilic silica micro-nanoparticles becomes weaker, and its peak at 2905 cm-1 is -1 and 2580cm -1 The peak at 1680cm is the absorption peak of the alkyl group in dodecanoic acid. -1 and 1605cm -1 The peak at 1140 cm is attributed to the vibration of SiO-H; -1 The peak at 800 cm is attributed to the asymmetric stretching vibration of Si-O-Si; -1 The above analysis of the infrared spectrum shows that the present invention first prepares hydrophilic silica micro-nano particles (i.e., amino-modified nano-silica particles) based on nano-silica, and finally prepares amphiphilic silica micro-nano particles.

[0228] 2. Characterization of the encapsulation ability of amphiphilic silica micro-nanoparticles for aqueous solutions

[0229] Confocal laser scanning microscopy (CLSM) without vacuum conditions was used to characterize the encapsulation capacity of amphiphilic silica micro-nanoparticles. The specific steps are as follows:

[0230] i. Preparation of contents: Mix 0.2 g of fluorescent dye Nile Blue A stain with 100 g of water and stir to obtain the contents;

[0231] ii. 10 g of amphiphilic silica micro-nanoparticles with a median particle size of 80 nm were mixed with the contents prepared in step 1), and stirred at a speed of 16,000 r / min for 2 min to obtain micro-nanoparticles encapsulating fluorescent dyes with amphiphilic silica micro-nanoparticles as capsule shells.

[0232] The fluorescent dye-encapsulated micro-nanocapsules prepared in this experiment were observed using a confocal laser scanning microscope in fluorescence mode. Figure 2 As shown: The micro-nanocapsules encapsulating fluorescent dyes prepared in this experiment actually appear magenta (corresponding to Figure 2The gray and white areas shown in the figure demonstrate that the amphiphilic silica micro-nanoparticles successfully encapsulate the contents containing the fluorescent dye - Nile Blue A dye inside, demonstrating the encapsulation ability of the amphiphilic silica micro-nanoparticles for aqueous solutions.

[0233] Figures 3 to 5 The following are the actual pictures of the cross-linking agent solution, amphiphilic silica micro-nanoparticles and micro-nanocapsules in Example 1. Figure 3 is a crosslinker solution, Figure 4 The upper middle part is amphiphilic silica micro-nanoparticles. Figure 5 These are the micro-nanocapsules prepared in Example 1. It can be seen that the crosslinker solution is a dark liquid, the amphiphilic silica micro-nanoparticles are white, nearly powdery fine particles, and the micro-nanocapsules are white, spherical particles. The dark crosslinker liquid is not observed, indicating that the crosslinker solution is encapsulated by the amphiphilic silica micro-nanoparticles.

[0234] 3. Observation of the morphology of micro-nanocapsules, sustained-release gels, and amphiphilic silica micro-nanoparticles

[0235] 1) Observation of micro-nanocapsule morphology

[0236] First, the micro-nanocapsules prepared in Examples 1 to 14, Comparative Examples 1, 2 and Comparative Example 4 were observed using a microscope and a scanning electron microscope.

[0237] Figure 6 、 Figure 7 The images of the micro-nanocapsules prepared in Example 1 under a microscope and a scanning electron microscope are respectively. Figure 6 The distribution state of micro-nanocapsules under a microscope; Figure 7 The micro-nano capsules were observed under a scanning electron microscope with a magnification of 1000 times. Figure 7 The micro-nanocapsules are shown after dehydration; Figure 6 It can be seen that the micro-nanocapsules wrapped with the cross-linking agent aqueous solution are mostly spherical or ellipsoidal, and there is a slight agglomeration phenomenon; Figure 7 It can be seen that the surface of the micro-nanocapsules after dehydration under vacuum conditions is slightly rough, and the irregularity of the shape is greater than that of the Figure 6 The observed amount of micro-nanocapsules without water loss increased slightly, but the agglomeration phenomenon was reduced.

[0238] The micro-nanocapsules prepared in Examples 2 to 14, Comparative Examples 1, 2 and Comparative Example 4 can be observed under a microscope and a scanning electron microscope. Figure 6 、 Figure 7 The morphology is similar to that of the micro-nanocapsules prepared in Example 1.

[0239] 2) Observation of the morphology of the sustained-release gel after gelation

[0240] The morphologies of the partially hydrolyzed polyacrylamide gel without micro-nanocapsules prepared in Comparative Example 3, the sustained-release gels with micro-nanocapsules prepared in Examples 15 to 28, Comparative Examples 1 and 2, and the micro-nanocapsules prepared in Comparative Example 4 after gelation were observed using a scanning electron microscope.

[0241] Figures 8 to 11 These are images of the partially hydrolyzed polyacrylamide gel without micro-nanocapsules prepared in Comparative Example 3 after gelation and the sustained-release gel with micro-nanocapsules prepared in Example 15 after gelation, magnified 500 times and 1000 times, respectively. Figure 8 、 Figure 9 The images of the partially hydrolyzed polyacrylamide gel prepared in Comparative Example 3 without adding micro-nanocapsules after gelation under a scanning electron microscope at magnifications of 500 times and 1000 times are shown respectively; Figure 10 、 Figure 11 Scanning electron microscope images of the sustained-release gel prepared in Example 15, containing micro-nanocapsules, at magnifications of 500x and 1000x are shown. It can be observed that the hydrolyzed polyacrylamide gel without micro-nanocapsules forms a dense three-dimensional network structure after gelation. The sustained-release gel containing micro-nanocapsules exhibits a large number of nanoparticles attached to the chain segments of its network structure, significantly enhancing the strength of the sustained-release gel network and making the three-dimensional network more compact. This comparative analysis demonstrates that the addition of micro-nanocapsules enhances the strength of the sustained-release gel system.

[0242] The morphology of the sustained-release gels with added micro-nanocapsules prepared in Examples 16 to 28 and Comparative Examples 1 and 2 after gelation is similar to the morphology of the sustained-release gel with added micro-nanocapsules prepared in Example 15 after gelation. It can also be observed that a large number of nanoparticles are attached to the chain segments of the hydrolyzed polyacrylamide network structure, which is beneficial to improving the strength of the sustained-release gel.

[0243] Figure 12 、 Figure 13 The images of the micro-nanocapsules prepared in Comparative Example 4 after gelation under a scanning electron microscope at magnifications of 500 times and 1000 times are shown in sequence. Figure 10 、 Figure 11 As can be seen in the image, the gel prepared using the method of Comparative Example 4 exhibits a network structure, but relatively few particles are attached to it. Analysis suggests that during the gelation process, the particles were encapsulated by a relatively small amount of gel solution, preventing effective gelation. However, after the particles released the gel solution, a large amount of solution aggregated and sank, initiating gelation and forming a network structure. Some particles became attached to this network, but this only limited improvement in the rigidity of the network structure.

[0244] 4. Determination of gelation time, gelation strength and viscoelastic properties of sustained-release gel

[0245] 1) Determination of gelation time and gelation strength

[0246] The gel strength visual code method was used to evaluate the gelation time and gelation strength of the sustained-release gels prepared in Examples 15 to 28, Comparative Examples 1 and 2, the partially hydrolyzed polyacrylamide gel without micro-nanocapsules prepared in Comparative Example 3, and the micro-nanocapsules prepared in Comparative Example 4. The specific method is as follows:

[0247] ⅰTest water: simulated water from a formation in a block of Chunfeng Oilfield, with a salinity of 40,000 mg / L, of which the calcium and magnesium ion concentrations were 6,600 mg / L;

[0248] ⅱ Visual code method for gel strength: 20 g each of the sustained-release gels prepared in Examples 15 to 28, Comparative Examples 1 and 2, the partially hydrolyzed polyacrylamide gel without micro-nanocapsules prepared in Comparative Example 3, and the micro-nanocapsules prepared in Comparative Example 4 were added to ampoule bottles, sealed with a cap, and the gel formation was determined by inverting the ampoule bottle at 120°C and observing the change in the gel state over time.

[0249] The gels were divided into 10 grades based on their different flow, suspension, and tongue-out states, as shown in Table 1. The initial gelation time of the gel was defined as the time it took for the gel to transform from a solution state to a strength code of E.

[0250] Table 1. Gel strength codes

[0251]

[0252]

[0253] The gelation time and gelation strength of the sustained-release gels prepared in Examples 15 to 28, Comparative Examples 1 and 2, the partially hydrolyzed polyacrylamide gel without micro-nanocapsules prepared in Comparative Example 3, and the micro-nanocapsules prepared in Comparative Example 4 are shown in Table 2.

[0254] 2) Viscoelastic properties test

[0255] The viscoelastic properties of the sustained-release gels prepared in Examples 15 to 28, Comparative Examples 1 and 2, the partially hydrolyzed polyacrylamide gel without micro-nanocapsules prepared in Comparative Example 3, and the micro-nanocapsules prepared in Comparative Example 4 after gelation at 120°C were tested using a MARS III rheometer from HAAKE, Germany. The test temperature was 30°C, the shear frequency was 1.0 Hz, and the shear stress was 1.0 Pa.

[0256] See Table 2 for specific results.

[0257] Table 2. Gelation time, gel strength, and viscoelastic properties

[0258]

[0259] Analysis of the data in Table 2 shows that as the amount of amphiphilic silica micro-nanoparticles used in the micro-nanocapsule preparation process increases, the elastic modulus and viscous modulus of the sustained-release gel after gelation with the corresponding micro-nanocapsules increase accordingly. Furthermore, the elastic modulus and viscous modulus of the sustained-release gels prepared in Examples 15 to 28 and Comparative Examples 1 and 2 with the addition of micro-nanocapsules are both greater than those of the partially hydrolyzed polyacrylamide gel in Comparative Example 3 without the use of micro-nanocapsule technology. This demonstrates that amphiphilic silica micro-nanoparticles significantly enhance the viscoelastic properties of the sustained-release gel. However, despite the addition of micro-nanocapsules, the sustained-release gels prepared in Comparative Examples 1 and 2 exhibit significantly lower elastic moduli and viscous moduli than those in Examples 15 to 28, likely due to the low content of amphiphilic silica micro-nanoparticles in the micro-nanocapsules and the high pH of the formation water used, which may affect the gelation strength and gelation time of the sustained-release gel. Compared to the partially hydrolyzed polyacrylamide gel in Comparative Example 3, which did not utilize micro-nanocapsulation technology, the sustained-release gels prepared in Examples 15 to 28 exhibited significantly longer gelation times at 120°C than the partially hydrolyzed polyacrylamide gel in Comparative Example 3. The sustained-release gel prepared in Example 15 exhibited the longest gelation time at 120°C, specifically 144 hours. This extended the gelation time by 288 times compared to Comparative Example 3. Furthermore, the sustained-release gel prepared in Example 15 achieved Grade I gel strength after gelation at 120°C, with an elastic modulus of 307 Pa and a viscous modulus of 36 Pa at 30°C, 1.0 Hz, and 1.0 Pa. The sustained-release gels prepared in Examples 15 to 28 exhibited superior gelation times at 120°C, gel strength after gelation, and elastic and viscous moduli at 30°C, 1.0 Hz, and 1.0 Pa, compared to the hydrolyzed polyacrylamide gel in Comparative Example 3, which did not utilize micro-nanocapsulation technology. The micro-nanocapsules prepared in Comparative Example 4 are actually a sustained-release gel system, the gel strength of which only reaches Grade H, and the gel strength is relatively low. The elastic modulus and viscous modulus are also significantly lower than those of Examples 15 to 28.

[0260] Although the present invention has been described with reference to specific embodiments, those skilled in the art will appreciate that various modifications may be made without departing from the true spirit and scope of the invention. Furthermore, the subject matter, spirit, and scope of the invention may be modified in various ways to adapt to specific circumstances, materials, combinations of materials, and methods. All such modifications are intended to be within the scope of the claims.

Claims

1. A micro-nanocapsule comprising a capsule shell and contents; the capsule shell is amphiphilic silica micro-nano particles, the contents are a crosslinking agent solution; the contents are wrapped by the capsule shell; The mass ratio of the contents to the capsule shell is (10 to 50):1; The amphiphilic silica micro-nanoparticles are obtained by modifying nano-silica with a silane coupling agent containing an amino group and a long-chain alkyl carboxylic acid: a. subjecting the nano-silica and the amino-containing silane coupling agent to a first reaction to obtain hydrophilic silica micro-nanoparticles; b. The hydrophilic silica micro-nanoparticles and paraffin are dispersed in water and emulsified to obtain solidified paraffin microspheres; c. subjecting the solidified paraffin microspheres to a second reaction with a long-chain alkyl carboxylic acid to obtain hydrophobically modified paraffin microspheres; d. dissolving the paraffin in the hydrophobically modified paraffin microspheres with an organic solvent to obtain the amphiphilic silica micro-nanoparticles; The mass ratio of the nano-silica to the amino-containing silane coupling agent is (1 to 2): (0.3 to 0.6); The mass ratio of the hydrophilic silica micro-nanoparticles to paraffin is (1 to 2):(5 to 6); The weight of the amino-containing silane coupling agent is calculated as 100%, and the amount of the long-chain alkyl carboxylic acid is 70wt% to 100wt%; The particle size of the nano-silicon dioxide is 7nm to 40nm; The long-chain alkyl carboxylic acid is C 12 to C 18 Alkyl carboxylic acids; In the cross-linking agent solution, the concentration of the cross-linking agent is 0.1 wt % to 1.0 wt %; The cross-linking agent is selected from at least one of chromium chloride, chromium acetate, zirconium acetate, aluminum citrate, a mixture of hexamethylenetetramine and resorcinol, a mixture of phenol and formaldehyde, phenolic resin and polyethyleneimine; The solvent in the cross-linking agent solution is water.

2. The micro-nano capsule according to claim 1, characterized in that The amino-containing silane coupling agent is 3-aminopropyltriethoxysilane; and / or The long-chain alkyl carboxylic acid is C 12 to C 18 of straight-chain alkyl carboxylic acids.

3. The micro-nanocapsule according to claim 1, characterized in that The long-chain alkyl carboxylic acid is dodecanoic acid.

4. The micro-nanocapsule according to claim 1, characterized in that The CAS number of the nano silicon dioxide is 60676-86-0.

5. The micro-nanocapsule according to any one of claims 1 to 4, characterized in that The median particle size of the micro-nano capsule is 680 nm to 3110 nm; and / or The median particle size of the amphiphilic silica micro-nanoparticles is 80 nm to 120 nm.

6. A method for preparing the micro-nanocapsule according to any one of claims 1 to 5, comprising the following steps: 1) preparing a cross-linking agent solution to obtain the contents; 2) mixing the amphiphilic silica micro-nano particles and the contents to obtain the micro-nano capsules.

7. The method according to claim 6, characterized in that In the step 2), mixing by stirring; The stirring speed is 10000 r / min to 19000 r / min; and / or The stirring time is 1 min to 2 min.

8. A sustained-release gel comprising a partially hydrolyzed polyacrylamide solution and micro-nanocapsules; The micro-nano capsule is the micro-nano capsule according to any one of claims 1 to 5 or the micro-nano capsule prepared by the method according to claim 6 or 7.

9. The sustained-release gel according to claim 8, characterized in that The sustained-release gel also includes an oxygen scavenger solution.

10. The sustained-release gel according to claim 9, characterized in that The solvent in the partially hydrolyzed polyacrylamide solution and the solvent in the oxygen scavenger solution are independently water.

11. The sustained-release gel according to claim 9, characterized in that Based on the mass of the sustained-release gel, the sustained-release gel comprises 25 to 50 parts by mass of a partially hydrolyzed polyacrylamide solution, 10 to 40 parts by mass of micro-nanocapsules, and 10 to 50 parts by mass of an oxygen scavenger solution.

12. The sustained-release gel according to claim 9, characterized in that In the partially hydrolyzed polyacrylamide solution, the concentration of the partially hydrolyzed polyacrylamide is 1 wt % to 2 wt %; and / or In the deoxidizer solution, the concentration of the deoxidizer is 0.4 wt % to 2.0 wt %.

13. Use of any one of the micro-nanocapsules according to any one of claims 1 to 5, the micro-nanocapsules prepared by the method according to claim 6 or 7, and the sustained-release gel according to any one of claims 8 to 12 in oil reservoir plugging control, characterized in that Application as a plugging agent.

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