Nano-polyacrylamide microspheres for profile control based on microchannel reactor and preparation method thereof

Abstract

The present invention discloses nano-polyacrylamide microspheres for profile control based on a microchannel reactor and a preparation method thereof. The preparation method is as follows: an oil phase and a composite emulsifier are added to a first flask to form a stable oil phase system; a mixed monomer and a crosslinking agent and / or an initiator are pre-dissolved uniformly in water in a second flask and the pH is adjusted to 7 to form a neutral aqueous phase system; an initiator is dissolved in water in a third flask to form an initiating phase system; the prepared aqueous phase system and the oil phase system are pumped into a mixer together to form a reverse microemulsion; the reverse microemulsion and the initiating phase system are pumped into a microchannel reactor together to react to obtain a crude product emulsion; the crude product emulsion is demulsified, centrifuged, and dried to obtain nano-polyacrylamide microspheres. The present invention uses a microchannel reactor to prepare nano-polyacrylamide microspheres for profile control. The synthesized product has a smaller particle size, a more convergent distribution, and has better stability, anti-aging and other properties.

Description

Technical Field

[0001] The present invention relates to the field of oil reservoir exploitation, and in particular to nano-polyacrylamide microspheres for profile control based on a microchannel reactor and a preparation method thereof. Background Art

[0002] During reservoir development, most reservoirs contain layers of varying permeability. Even within the same layer, it can be heterogeneous or have multiple dominant flow paths. During primary and secondary oil production, repeated water injection washes away fine sand particles and cements in the underlying oil layers, altering the reservoir's internal structure. Subsurface cracks and pore throats widen, creating heterogeneity and increasing permeability. Highly permeable zones, such as large and extra-large pores, can even emerge. This can lead to water inrush and water channeling, severely impacting oil recovery and forcing oil development into a high-water-cut phase.

[0003] In such situations, injected water tends to flow along high-permeability layers and along preferred flow paths, leading to pronounced differences between layers. This makes it difficult to achieve effective profile control and oil recovery using conventional chemical flooding agents. Low-permeability zones remain untouched, and over 70% of the residual oil remains in these untouched areas. Therefore, improving oil recovery in heterogeneous reservoirs and enhancing the efficiency of untouched areas are crucial. How to exploit the residual oil in reservoirs, increase crude oil recovery, and enhance the economic benefits of oil extraction have always been a concern. Especially in today's rapidly developing economy, with total crude oil reserves increasingly depleted, improving oil recovery efficiency has become even more critical.

[0004] Most oil fields in my country have undergone years of waterflooding, resulting in a steady increase in the water content of produced fluids. While tertiary oil recovery (TER) techniques have increased crude oil production over the past decade, the water content in most fields has risen to 80%, resulting in a rapid drop in formation pressure and a severe shortage of production pressure. The generally low permeability of formations in my country has been a major challenge for researchers. While some oil fields have abundant reserves, the vast majority of their crude oil lies in tight or ultra-tight reservoirs, where rock permeability is typically very low or ultra-low, presenting significant challenges for oilfield recovery. Studies have shown that over half of my country's oil reserves lie in low- and ultra-low-permeability fields, making conventional recovery methods inadequate. Compared to fields with higher permeabilities, low-permeability fields are generally more challenging to exploit, primarily due to inadequate technical research and insufficient injection product performance, making conventional chemical reagents difficult to use effectively.

[0005] After long-term development, the geological volume of the oil field deteriorates, and a large number of large pores, large cracks and high-permeability channels appear. These lead to problems such as bypass, coning and flooding of the oil layer during the subsequent injection of water. Traditional water plugging and profile control technology cannot meet the needs of the later development of the oil field, resulting in a significant reduction in oil recovery efficiency.

[0006] Researching new gel microsphere profile control agents that are low-cost, environmentally friendly, long-lasting, and applicable to different reservoir conditions is also a practical problem that needs to be urgently solved in today's oilfield field.

[0007] Therefore, by studying the development and research status of plugging agents at home and abroad, summarizing the types and characteristics of existing plugging agents, evaluating the advantages and disadvantages of various technologies, and combining the use requirements of low permeability oilfields, we carried out research based on the point of supplementing the deficiencies of existing technologies and types, and found that efficient profile control agents are an urgent goal to be achieved. Summary of the Invention

[0008] In view of the above problems, one of the objectives of the present invention is to provide a method for preparing nano-polyacrylamide microspheres for profile control based on a microchannel reactor.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] A method for preparing nano-polyacrylamide microspheres for profile control based on a microchannel reactor, comprising the following steps:

[0011] (1) Add the oil phase and composite emulsifier into flask No. 1 to form a stable oil phase system;

[0012] (2) In flask No. 2, pre-dissolve the mixed monomers and cross-linking agent and / or initiator in water, stir evenly, and adjust the pH value to 7 to form a neutral aqueous phase system;

[0013] (3) Dissolve the initiator in water in flask No. 3 to form an initiating phase system;

[0014] (4) pumping the prepared aqueous phase system and oil phase system into a mixer to mix and form an inverse microemulsion;

[0015] (5) pumping the reverse microemulsion and the initiating phase system into a microchannel reactor to react and obtain a crude product emulsion;

[0016] (6) The crude product emulsion is subjected to demulsification, centrifugation, and drying to obtain the nano-polyacrylamide microspheres.

[0017] Preferably, the specific weight parts of the raw materials involved in the preparation process are as follows:

[0018] 20-60 parts of oil phase, 12-24 parts of composite emulsifier, 18-34 parts of water, 1-3 parts of initiator, 8-15 parts of mixed monomer, and 1-2 parts of crosslinking agent.

[0019] Preferably, the oil phase is one of mineral white oil, vegetable oil, kerosene or liquid paraffin;

[0020] The composite emulsifier is composed of a Span emulsifier and a Tween emulsifier in a mass ratio of (2-4):1;

[0021] The initiator is a redox or azo initiator;

[0022] The mixed monomer is a non-ionic monomer;

[0023] The cross-linking agent is N,N-methylenebisacrylamide.

[0024] Preferably, the mixed monomer is a plurality of acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, 2-acrylamido-2-methyl-1-propanesulfonic acid, 3-(4-hydroxy-2-methylphenyl)-2-propenoic acid, vinylbenzenesulfonic acid, vinylsulfonic acid, and vinylphosphonic acid.

[0025] Preferably, the Span emulsifier is one or more of Span-20, Span-40, Span-60, Span-80 and Span-85, and the Tween emulsifier is one or more of Tween-20, Tween-40, Tween-60 and Tween-80.

[0026] Preferably, the specific process of step (1) is as follows: add the oil phase and the composite emulsifier into flask No. 1, mix and disperse them evenly, seal the bottle mouth with a rubber stopper, and use a double-row tube to perform vacuum and nitrogen filling operations to ensure that the system is a complete nitrogen environment, thereby forming a stable oil phase system.

[0027] Preferably, the dimensions of the microchannel reactor in step (5) are as follows: inner diameter 30-50 mm, length 200-1000 m.

[0028] Preferably, the reaction temperature of the microchannel reactor in step (5) is 20-80° C., and the residence time is 10-200 min.

[0029] Preferably, the specific process of step (6) is as follows:

[0030] The crude product emulsion is demulsified with methanol or ethanol and then centrifuged at high speed. The oil phase in the product is removed by washing with ethanol and then dried to obtain nano-polyacrylamide microspheres.

[0031] The second purpose of the present invention is to provide nano-polyacrylamide microspheres for profile control based on a microchannel reactor.

[0032] In order to achieve the above object, the present invention provides the following technical solutions:

[0033] The nano-polyacrylamide microspheres for profile control based on a microchannel reactor are prepared by the above-mentioned preparation method, and the particle size of the nano-polyacrylamide microspheres is 50-90 nm.

[0034] The beneficial effects of the present invention are:

[0035] Compared to batch synthesis in traditional kettle reactors, the present invention uses a microchannel reactor to prepare polyacrylamide nanospheres for profile control based on the reverse microemulsion polymerization method. The emulsion system is mixed more thoroughly and evenly, the reaction effect is better, the synthesized product has a smaller particle size, a more convergent distribution, and better stability, anti-aging and other properties. It is not easy to agglomerate to form large particles, and can better meet the application requirements of actual oil field profile control. Microchannel reactors have high mass and heat transfer efficiency and excellent control over the reaction process; the reaction residence time is uniform and controllable, the polymerization process is easy to adjust, and the product characteristics are better controlled; it is convenient for continuous and large-scale production, with flexible output to meet the needs of different users; and it is easy to monitor the reaction process online in real time to ensure product quality uniformity.

[0036] Therefore, compared with the traditional batch reaction process, the use of microchannel reactors to prepare nano-scale polyacrylamide microspheres for profile control has obvious process advancement, superiority and technical competitiveness, and has broad prospects and application potential to replace the existing batch process. It is very likely to subvert the existing production method of polyacrylamide microspheres for profile control.

[0037] The polyacrylamide microspheres produced by the present invention have a uniform particle size distribution, a high solid content, and a nanometer-level particle size. The average initial particle size is between 50 and 90 nm, and the distribution is concentrated. The resulting emulsion product is stable during long-term storage, without sedimentation, stratification, or precipitation, making it easy to store. Even during aging in brine with a high salt content, it maintains a relatively stable swelling state, with a swelling ratio of ≥10. This product has excellent application effects and promising prospects.

[0038] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 The process flow chart of the preparation method of the present invention is shown;

[0041] Figure 2 Shown is a scanning electron microscope image of the product of Example 1;

[0042] Figure 3 Shown is a scanning electron microscope image of the product of Example 2;

[0043] Figure 4 Shown is a scanning electron microscope image of the product of Example 3;

[0044] Figure 5 Shown is a scanning electron microscope image of the product of Example 4;

[0045] Figure 6 The scanning electron microscope image of the product of Comparative Example 1 is shown. DETAILED DESCRIPTION

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0047] The present invention discloses a nano-polyacrylamide microsphere for profile control based on a microchannel reactor, wherein the particle size is 50-90 nm. The specific weight parts of the raw materials involved in the preparation process are as follows:

[0048] 20-60 parts of oil phase, 12-24 parts of composite emulsifier, 18-34 parts of water, 1-3 parts of initiator, 8-15 parts of mixed monomer, and 1-2 parts of crosslinking agent.

[0049] The oil phase is one of mineral white oil, vegetable oil, kerosene or liquid paraffin, and a reasonable selection range can be any oil-like substance that can act on inverse emulsion polymerization; the composite emulsifier is composed of a Span emulsifier and a Tween emulsifier in a mass ratio of (2-4):1; the initiator is a redox initiator such as ammonium persulfate and sodium bisulfite, and an azo initiator such as azobisisobutyronitrile; the mixed monomer is a non-ionic monomer; and the crosslinking agent is N,N-methylenebisacrylamide.

[0050] Preferably, the Span emulsifier is a sorbitan fatty acid ester, specifically one or more of Span-20, Span-40, Span-60, Span-80, and Span-85. The Tween emulsifier is a sorbitan monooleate polyoxyethylene ether, specifically one or more of Tween-20, Tween-40, Tween-60, and Tween-80.

[0051] Preferably, the mixed monomer is one or more of acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, 2-acrylamido-2-methyl-1-propanesulfonic acid, 3-(4-hydroxy-2-methylphenyl)-2-propenoic acid, vinylbenzenesulfonic acid, vinylsulfonic acid, and vinylphosphonic acid.

[0052] The present invention also discloses a method for preparing nano-polyacrylamide microspheres for profile control based on a microchannel reactor, the flow chart of which is as follows: Figure 1 As shown, combined Figure 1 The specific process of the preparation method is described as follows:

[0053] (1) Adding the oil phase and the composite emulsifier to flask No. 1 to form a stable oil phase system; preferably, the specific process of this step is as follows: adding the oil phase and the composite emulsifier to flask No. 1, uniformly mixing and dispersing, sealing the bottle mouth with a rubber stopper, and performing vacuuming and nitrogen filling operations using a double-row tube to ensure that the system is in a complete nitrogen environment, thereby forming a stable oil phase system. Preferably, the vacuuming and nitrogen filling operations are repeated at least three times, with a single operation time of 5-10 minutes.

[0054] (2) In flask No. 2, pre-dissolve the mixed monomers and cross-linking agent and / or initiator in water, stir evenly, and adjust the pH value to 7 to form a neutral aqueous phase system;

[0055] (3) Dissolve the initiator in water in flask No. 3 to form an initiating phase system;

[0056] (4) pumping the prepared aqueous phase system and oil phase system into a mixer to mix and form an inverse microemulsion;

[0057] (5) Pumping the reverse microemulsion and the initiating phase system into a microchannel reactor for reaction to obtain a crude product emulsion; preferably, the microchannel reactor has the following dimensions: an inner diameter of 30-50 mm and a length of 200-1000 m, and the microchannel reactor is made of materials including but not limited to glass, polytetrafluoroethylene, and metal. The reaction temperature of the microchannel reactor is 20-80° C., and the residence time is 10-200 min.

[0058] (6) Demulsifying the crude product emulsion, centrifuging, and drying to obtain the nano-polyacrylamide microspheres. Preferably, the specific process of this step is as follows: demulsifying the crude product emulsion with methanol or ethanol, centrifuging at high speed, washing with ethanol to remove the oil phase in the product, and drying to obtain the nano-polyacrylamide microspheres.

[0059] It should be noted that: preferably, when the initiator is a redox initiator, the oxidizing component is added to flask No. 2 and the reducing component is added to flask No. 3. When the initiator is an azo initiator, no initiator is added to flask No. 2 and all the initiator can be added to flask No. 3.

[0060] In order to better understand the technical solution of the present invention, the following specific embodiments are given to specifically describe the solution of the present invention as follows:

[0061] Example 1

[0062] To a small flask, 29 g of 7# white oil, 7.5 g of Span 80, and 2.5 g of Tween 80 were added, and the oil phase was stirred until completely dispersed. The bottle mouth was sealed with a rubber stopper, and vacuum and nitrogen were filled using a double-row tube. This operation was repeated three times to ensure that the system was in a complete nitrogen environment and mixed evenly. To a second flask, 5.94 g of acrylamide, 0.66 g of 2-acrylamido-2-methyl-1-propanesulfonic acid, 0.45 g of N,N-methylenebisacrylamide, 0.075 g of ammonium persulfate, and 3.4 g of water were added, and the pH was adjusted to 7 to prepare the aqueous phase. To a third flask, sodium bisulfite and an appropriate amount of water were added to prepare a solution to serve as the initiating phase system. The reaction liquids in flasks No. 1 and No. 2 are mixed evenly through a mixer under the action of a feed pump, and are pumped into a microchannel reactor with an inner diameter of 40 mm and a length of 900 m together with the subsequent initiator in flask No. 3. The reaction temperature is controlled at 40°C, the residence time is 120 min, and the reaction obtains a crude product emulsion.

[0063] Methanol was added to the crude product emulsion to break the emulsion, and after being stirred evenly, the mixture was centrifuged, washed three times with anhydrous ethanol, and dried to obtain a white powdery microsphere product (nano-polyacrylamide microspheres) which was then subjected to characterization tests.

[0064] The sample powder obtained in Example 1 was dispersed in ethanol and ultrasonicated for 15 minutes. The particle size was measured by dynamic light scattering. The initial particle size was about 100-300 nm, with a wide distribution. The white precipitate obtained by the initial demulsification and centrifugal washing was dispersed in ethanol, fully diluted, and the microsphere powder obtained after natural evaporation was photographed by field emission scanning electron microscopy. Figure 2 As shown, from Figure 2 It can be seen that the particle size distribution of the microspheres is uneven and the size differences are large.

[0065] Example 2

[0066] To a small flask No. 1, 22 g of kerosene, 6 g of Span 60, and 3 g of Tween 80 were added, and the oil phase was stirred until completely dispersed. The bottle mouth was sealed with a rubber stopper, and vacuuming and nitrogen filling were performed using a double-row tube. This operation was repeated three times to ensure that the system was in a complete nitrogen environment and mixed evenly. To a second flask, 6.3 g of acrylamide, 0.7 g of 2-acrylamido-2-methyl-1-propanesulfonic acid, 0.25 g of N,N-methylenebisacrylamide, 0.1 g of ammonium persulfate, and 2 g of water were added, and the pH was adjusted to 7 to prepare the aqueous phase. To a third flask, sodium bisulfite and an appropriate amount of water were added to prepare a solution to serve as the initiating phase system. The reaction liquids in flasks No. 1 and No. 2 are evenly mixed through a mixer under the action of a feed pump, and are pumped into a microchannel reactor with an inner diameter of 35 mm and a length of 900 m together with the subsequent initiator in flask No. 3. The reaction temperature is controlled at 40°C, the residence time is 100 min, and the reaction obtains a crude product emulsion.

[0067] Methanol was added to the crude product emulsion to break the emulsion, and after being stirred evenly, the mixture was centrifuged and washed three times with anhydrous ethanol and dried to obtain a white powder microsphere product which was then subjected to characterization tests.

[0068] The sample powder obtained in Example 2 was dispersed in ethanol and subjected to ultrasound for 15 minutes. The particle size was measured by dynamic light scattering. The initial particle size was about 70-100 nm, with a narrow distribution. The white precipitate obtained by the initial demulsification and centrifugal washing was dispersed in ethanol, fully diluted, and the microsphere powder obtained after natural evaporation was photographed by field emission scanning electron microscopy. Figure 3 As shown, from Figure 3 Nanospheres of similar size can be seen in the sample, and some of the microspheres agglomerate to form large particles with a diameter of about 1 μm.

[0069] Example 3

[0070] To a small flask No. 1, 26 g of liquid paraffin, 7.5 g of Span 80, and 3 g of Tween 60 were added, and the oil phase was stirred until completely dispersed. The bottle mouth was sealed with a rubber stopper, and vacuum and nitrogen were filled using a double-row tube. This operation was repeated three times to ensure that the system was in a complete nitrogen environment and mixed evenly. To a second flask, 7.2 g of acrylamide, 0.8 g of 2-acrylamido-2-methyl-1-propanesulfonic acid, 0.25 g of N,N-methylenebisacrylamide, 0.01 g of ammonium persulfate, and 4 g of water were added, and the pH was adjusted to 7 to prepare the aqueous phase. To a third flask, sodium bisulfite and an appropriate amount of water were added to prepare a solution to serve as the initiating phase system. The reaction liquids in flasks No. 1 and No. 2 are evenly mixed by a mixer under the action of a feed pump, and are pumped into a microchannel reactor with an inner diameter of 50 mm and a length of 900 m together with the subsequent initiator in flask No. 3. The reaction temperature is controlled at 40°C, the residence time is 120 min, and the reaction obtains a crude product emulsion.

[0071] Methanol was added to the crude product emulsion to break the emulsion, and after being stirred evenly, the mixture was centrifuged and washed three times with anhydrous ethanol and dried to obtain a white powder microsphere product which was then subjected to characterization tests.

[0072] The sample powder obtained in Example 3 was dispersed in ethanol and subjected to ultrasound for 15 minutes. The particle size was measured by dynamic light scattering. The initial particle size was about 100 nm. The white precipitate obtained by the initial demulsification and centrifugal washing was dispersed in ethanol, fully diluted, and the microsphere powder obtained after natural evaporation was photographed by field emission scanning electron microscopy. Figure 4 As shown, from Figure 4 It can be seen that there is slight agglomeration and the shape is not regular.

[0073] Example 4

[0074] To small flask No. 1, add 24 g of kerosene, 8 g of Span 60, and 2 g of Tween 80, stir the oil phase until completely dispersed, seal the bottle with a rubber stopper, and use a double-row tube to evacuate and fill with nitrogen three times to ensure a complete nitrogen environment and uniform mixing. To flask No. 2, add 2.55 g of acrylamide, 2 g of 2-acrylamido-2-methyl-1-propanesulfonic acid, 0.35 g of N,N-methylenebisacrylamide, 0.25 g of ammonium persulfate, and 2 g of water, and adjust the pH to 7 to prepare the aqueous phase. To flask No. 3, add sodium bisulfite and an appropriate amount of water to prepare a solution to serve as the initiating phase system. The reaction liquids in flasks No. 1 and No. 2 are evenly mixed by a mixer under the action of a feed pump, and are pumped into a microchannel reactor with an inner diameter of 40 mm and a length of 900 m together with the subsequent initiator in flask No. 3. The reaction temperature is controlled at 40°C, the residence time is 90 min, and the reaction obtains a crude product emulsion.

[0075] Methanol was added to the crude product emulsion to break the emulsion, and after being stirred evenly, the mixture was centrifuged and washed three times with anhydrous ethanol and dried to obtain a white powder microsphere product which was then subjected to characterization tests.

[0076] The sample powder obtained in Example 4 was dispersed in ethanol and subjected to ultrasound for 15 minutes. The particle size was measured by dynamic light scattering. The initial particle size was about 50-70 nm. The white precipitate obtained by the initial demulsification and centrifugal washing was dispersed in ethanol, fully diluted, and the microsphere powder obtained after natural evaporation was photographed by field emission scanning electron microscopy. Figure 5 As shown, from Figure 5 Nanospheres of similar size can be seen, and the particle size is relatively uniform.

[0077] The powders of Example 1, Example 2, Example 3, and Example 4 were respectively dissolved in water and dispersed in simulated underground mineral water with a mineralization of 25,000 mg / L. Salt aging resistance tests were carried out. Table 1 below shows the expansion properties at different times at 60°C.

[0078] Table 1 Comparison of expansion properties

[0079]

[0080] As can be seen from Table 1, comparing the results of Example 1, Example 2, Example 3, and Example 4, firstly, the reduction in the proportion of the mixed monomer concentration, the increase in the content of the composite emulsifier, and the increase in the cross-linking agent are conducive to the production of microsphere emulsions with smaller particle size; and the swelling ratio and speed are also improved to a certain extent, and the maximum swelling ratio is also relatively stable at around 24; the results of scanning electron microscopy also confirm that the microspheres produced after adjusting the parameters are more uniform, with distinct particles and less agglomeration.

[0081] Comparative Example 1

[0082] In a small flask, 29g of 7# white oil, 7.5g of Span80, and 2.5g of Tween80 were added, and the oil phase was stirred until completely dispersed. The bottle mouth was sealed with a rubber stopper, and vacuum and nitrogen were filled with a double-row tube three times to ensure that the system was in a complete nitrogen environment. In a second flask, 5.94g of acrylamide, 0.66g of 2-acrylamido-2-methyl-1-propanesulfonic acid, and 0.45g of N,N-methylenebisacrylamide were added, and 3.4g of water was added, and the pH was adjusted to 7 for the aqueous phase. In flasks 3 and 4, ammonium persulfate / sodium bisulfite were added respectively and prepared into a solution for the initiator. The flasks were placed in a constant temperature magnetic stirring water bath, the speed was adjusted to 1500 rpm, and the aqueous phase was evenly and slowly added. The mixture was stirred for more than 30 minutes until a uniform emulsion was uniformly dispersed and formed. The composite initiator was slowly added and the reaction started for 90 minutes to obtain a microsphere emulsion.

[0083] Methanol was added to the emulsion to break the emulsion, and after being stirred evenly, the mixture was centrifuged and washed three times with anhydrous ethanol and dried to obtain a white powder microsphere product which was then subjected to characterization tests.

[0084] The sample powder obtained in Comparative Example 1 was dispersed in ethanol and ultrasonicated for 15 minutes. The particle size was measured by dynamic light scattering. The initial particle size was about 70-100 μm, with a wide distribution and a large particle size. The white precipitate obtained by the initial demulsification and centrifugal washing was dispersed in ethanol, fully diluted, and the microsphere powder obtained after natural evaporation was photographed by field emission scanning electron microscopy. Figure 6 As shown, from Figure 6 Large nano-micron particles with serious agglomeration can be seen.

[0085] Comparing the results of Examples 1, 2, 3, and 4 with those of Comparative Example 1, compared with the traditional polymerization method, the microchannel reactor does provide a good place for inverse microemulsion polymerization, making the emulsion system more thoroughly and evenly mixed, the reaction effect is better, and nano-scale polyacrylamide microspheres can be better obtained with smaller particle size and more convergent distribution. Scanning electron microscopy observation shows that in the microchannel reactor, the microsphere particles are distinct and not easy to agglomerate to form large particles, which can better meet the actual application requirements of profile control and improved water flooding, and has good application prospects and potential.

[0086] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing nano-polyacrylamide microspheres for profile control based on a microchannel reactor, characterized in that: The specific steps are as follows: (1) Add the oil phase and composite emulsifier into flask No. 1 to form a stable oil phase system; (2) In flask No. 2, pre-dissolve the mixed monomers and cross-linking agent and / or initiator in water, stir evenly, and adjust the pH value to 7 to form a neutral aqueous phase system; (3) Dissolve the initiator in water in flask No. 3 to form an initiating phase system; (4) Pumping the prepared aqueous phase system and oil phase system into a mixer together to form an inverse microemulsion; (5) pumping the reverse microemulsion and the initiating phase system into a microchannel reactor to react and obtain a crude product emulsion; (6) breaking the crude product emulsion, centrifuging, and drying to obtain the nano-polyacrylamide microspheres; The specific weight parts of the raw materials involved in the preparation process are as follows: 20-60 parts of oil phase, 12-24 parts of composite emulsifier, 18-34 parts of water, 1-3 parts of initiator, 8-15 parts of mixed monomer, and 1-2 parts of crosslinking agent; The mixed monomers are acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid; The composite emulsifier is composed of a Span emulsifier and a Tween emulsifier in a mass ratio of (2-4):1; The reaction temperature of the microchannel reactor in step (5) is 20-80° C., and the residence time is 10-200 min.

2. The method for preparing nano-polyacrylamide microspheres for profile control based on a microchannel reactor according to claim 1, characterized in that: The oil phase is one of mineral white oil, vegetable oil, kerosene or liquid paraffin; The initiator is a redox or azo initiator; The cross-linking agent is N,N-methylenebisacrylamide.

3. The method for preparing nano-polyacrylamide microspheres for profile control based on a microchannel reactor according to claim 2, characterized in that: The Span emulsifier is one or more of Span-20, Span-40, Span-60, Span-80 and Span-85, and the Tween emulsifier is one or more of Tween-20, Tween-40, Tween-60 and Tween-80.

4. The method for preparing nano-polyacrylamide microspheres for profile control based on a microchannel reactor according to claim 1, characterized in that: The specific process of step (1) is as follows: add the oil phase and the composite emulsifier into flask No. 1, mix and disperse them evenly, seal the bottle mouth with a rubber stopper, and use a double-row tube to vacuum and fill with nitrogen to ensure that the system is a complete nitrogen environment to form a stable oil phase system.

5. The method for preparing nano-polyacrylamide microspheres for profile control based on a microchannel reactor according to claim 1, characterized in that: The dimensions of the microchannel reactor in step (5) are as follows: inner diameter 30-50 mm, length 200-1000 m.

6. The method for preparing nano-polyacrylamide microspheres for profile control based on a microchannel reactor according to claim 1, characterized in that: The specific process of step (6) is as follows: the crude product emulsion is demulsified with methanol or ethanol and then centrifuged at high speed, and the oil phase in the product is removed by washing with ethanol, and then dried to obtain nano-polyacrylamide microspheres.

7. A nano-polyacrylamide microsphere for profile control based on a microchannel reactor prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The particle size of the nano-polyacrylamide microspheres is 50-90nm.

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