Polymer microspheres for profile control and displacement and a preparation method thereof

Abstract

The application provides a polymer microsphere for profile control and flooding and a preparation method thereof. The preparation method comprises the following steps: preparing a first aqueous phase mixed solution by mixing acrylamide, N-isopropyl acrylamide and nanocellulose subjected to TEMPO oxidation modification; mixing an oil phase solvent and an emulsifier to obtain an oil phase solution; mixing a crosslinking agent, an initiator and the first aqueous phase mixed solution to obtain a second aqueous phase mixed solution; adding the second aqueous phase mixed solution into the oil phase solution, stirring at a first rotating speed for a first time, and then reacting under the condition of stirring at a second rotating speed for a second time to obtain a reacted emulsion system; and drying and forming the reacted emulsion system to obtain the polymer microsphere. The polymer microsphere for profile control and flooding is prepared by the preparation method. The polymer microsphere is a novel profile control agent, has good temperature resistance and salt resistance, has rigidity and flexibility, can enter the inside of an oil layer, and has good application in the field of profile control and water plugging.

Description

Technical Field

[0001] This invention relates to a polymer microsphere for regulating and driving and its preparation method, belonging to the field of oilfield chemical technology. Background Technology

[0002] In the mid-to-late stages of oilfield development, due to the heterogeneity of the formation, the water drive process during water injection is uneven both horizontally and vertically. Furthermore, the clay swelling and sand transport caused by long-term water erosion further exacerbate the heterogeneity. In some oil-bearing areas, large or even extra-large channels form, causing premature water flooding of high-permeability layers between injection and production wells. This reduces the sweep potential of injected water to low-permeability layers, leading to increased water cut in surrounding wells, and even water flooding, making it impossible to extract oil from some low-permeability layers. Therefore, in the mid-to-late stages of oilfield water injection development, water shut-off in oil wells that can seal high-permeability formations and increase the sweep area, along with profile control in injection wells, have become important measures to improve oil recovery. In addition, as oilfield water injection development continues to deepen, downhole conditions deteriorate year by year, making many traditional sealing operations impossible. Under these circumstances, the advantages of chemical plugging become increasingly apparent. Therefore, in recent years, the research and application of profile control and water shut-off agents have received widespread attention.

[0003] Currently, commonly used chemical plugging agents in oilfields mainly consist of mobile gels, weak gels, and cross-linked polymer coils formed by the cross-linking polymerization of low-concentration partially hydrolyzed polyacrylamide and aluminum citrate under different conditions. However, due to factors such as high-temperature degradation of polyacrylamide and viscosity reduction caused by high salt and high shear, these plugging agents, whether prepared on-site or polymerized downhole, exhibit poor performance under conditions such as oilfield wastewater and reservoir temperature, sometimes even failing to form cross-linked polymers. Therefore, there is an urgent need to develop a plugging agent that can maintain sufficient strength under high-temperature and high-salt conditions, is not easily degraded, and can penetrate deep into the oil layer. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a polymer microsphere for profile control and its preparation method. The polymer microsphere provided by this invention is a novel type of plugging agent, possessing advantages such as good temperature and salt resistance, combining rigidity and flexibility, and capable of penetrating deep into the oil reservoir, making it well-suited for applications in profile control and water shut-off.

[0005] To achieve the above objectives, the first aspect of the present invention provides a method for preparing polymer microspheres for modulation and driving, comprising the following steps:

[0006] (1) Aqueous phase preparation

[0007] After TEMPO oxidation modification, nanocellulose was mixed with acrylamide (AM) and N-isopropylacrylamide (NIPAM) to prepare a first aqueous phase mixture.

[0008] (2) Oil phase preparation

[0009] The oil phase solvent is mixed with the emulsifier to obtain an oil phase solution;

[0010] (3) Synthesis reaction

[0011] The crosslinking agent, the initiator and the first aqueous phase mixture obtained in step (1) are mixed to obtain the second aqueous phase mixture; the second aqueous phase mixture is added dropwise to the oil phase solution obtained in step (2), and after stirring at the first speed for a first time, it is reacted at the second speed for a second time to obtain the emulsion system after reaction;

[0012] (4) Drying and shaping

[0013] After drying and molding the emulsion system obtained in step (3), the polymer microspheres for regulating and driving are obtained.

[0014] In the above preparation method, preferably, step (1) specifically includes: preparing nanocellulose into a nanocellulose dispersion; mixing sodium carbonate solution and sodium bicarbonate solution to prepare a buffer solution; dissolving TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical) and NaBr in the buffer solution, then mixing it with the nanocellulose dispersion under magnetic stirring, and then adding NaClO to carry out an oxidation reaction. During the oxidation reaction, the pH value of the system is adjusted to 10.0-10.1, and the reaction is stopped after 18-24 hours. After washing the product, gel-like TEMPO oxidized modified nanocellulose is obtained; the gel-like TEMPO oxidized modified nanocellulose is prepared into a TEMPO oxidized modified nanocellulose dispersion; the TEMPO oxidized modified nanocellulose dispersion is mixed with water and ultrasonically vibrated for 10-20 minutes to obtain a uniformly dispersed TEMPO oxidized modified nanocellulose suspension; acrylamide, N-isopropylacrylamide and the TEMPO oxidized modified nanocellulose suspension are mixed to obtain the first aqueous phase mixture.

[0015] In the above preparation method, preferably, in step (1), the solid content of the nanocellulose dispersion is 2% to 6%.

[0016] In the above preparation method, in step (1), the concentration and mixing ratio of the sodium carbonate solution and the sodium bicarbonate solution can be conventionally adjusted by those skilled in the art. For example, the concentrations of the sodium carbonate solution and the sodium bicarbonate solution are 0.1 mol / L, and the mixing volume ratio of the sodium carbonate solution and the sodium bicarbonate solution is 3:2.

[0017] In the above preparation method, preferably, in step (1), the amount of TEMPO is 0.5% to 1.5% of the mass of nanocellulose, the amount of NaBr is 5% to 8% of the mass of nanocellulose, and the amount of NaClO is 50% to 80% of the mass of nanocellulose.

[0018] In the above preparation method, in step (1), the mixing ratio of TEMPO, NaBr, NaClO, buffer solution and nanocellulose dispersion can be conventionally adjusted by those skilled in the art based on the ratio range described above in this invention. For example, 0.064g of TEMPO and 0.4g of NaBr are dissolved in 50mL of buffer solution, and then mixed with 300mL of nanocellulose dispersion (solid content of 2%) under magnetic stirring, and then 28mL of NaClO solution (effective chlorine content ≥10%) is added.

[0019] In the above preparation method, in step (1), the pH value of the system can be adjusted by using a 2 mol / L sodium hydroxide solution during the oxidation reaction.

[0020] In the above preparation method, preferably, in step (1), the mass concentration of the TEMPO oxidative modified nanocellulose dispersion is 10% to 15%.

[0021] In the above preparation method, preferably, in step (1), the mass ratio of the TEMPO oxidative modified nanocellulose, the acrylamide, and the N-isopropylacrylamide is (1.0-2.0):(0.5-1.5):(0.2-0.5).

[0022] In the above preparation method, preferably, in step (1), the diameter of the nanocellulose is 5-70 nm and the length is 100-250 nm.

[0023] The nanocellulose (NCC) used in this invention is a rigid rod-shaped polymer with a diameter of 5–70 nm and a length of 100–250 nm. It not only possesses the basic structure and good properties of cellulose but also exhibits the characteristics of nanoparticles, such as a large specific surface area, high elastic modulus, and high reactivity. In this invention, the nanocellulose is oxidized with TEMPO before the reaction, oxidizing the hydroxymethyl groups on the surface of the nanocellulose to carboxyl groups, thereby increasing its water solubility and oxygen barrier properties. The oxidized nanocellulose of this invention has a large number of negative charges attached to its surface, making its suspension more stable and improving the long-term stability of the microspheres. Therefore, this invention uses TEMPO-oxidized nanocellulose as a reinforcing agent for the blockage regulator, significantly improving the thermal stability, long-term stability, mechanical strength, hardness, rigidity, and flexibility of the blockage regulator.

[0024] In this invention, N-isopropylacrylamide is introduced into the polymer monomer. Due to the presence of hydrophilic amide groups and hydrophobic isopropyl groups in its molecule, the copolymer prepared by this invention has a certain degree of heat sensitivity. The volume of the copolymer changes with temperature, which is beneficial to improving the blocking ability of microspheres at high temperatures.

[0025] In the above preparation method, preferably, in step (2), the oil phase solvent includes a combination of cyclohexane and chloroform. More preferably, the volume ratio of cyclohexane to chloroform is 4:1 to 5:1. In the technique of preparing polyacrylamide microspheres by reverse emulsion polymerization, vegetable oil is usually used as the oil phase. However, the inventors have found that the disadvantage of using vegetable oil as the oil phase is that it is prone to chemical reaction under acidic or alkaline conditions and has a high viscosity. The present invention uses the commonly used organic solvent cyclohexane as the oil phase. However, cyclohexane has poor solubility for the selected Span and Tween series emulsifiers. Therefore, the present invention introduces chloroform, which has strong polarity, and combines it with cyclohexane in a certain proportion to dissolve the emulsifier.

[0026] In the above preparation method, preferably, in step (2), the emulsifier includes a combination of Span60 and Tween60. More preferably, the mass ratio of Span60 to Tween60 is 8:1 to 10:1, and even more preferably 9:1. Generally, an emulsifier with an HLB of 3 to 6 can form a relatively stable W / O type emulsion. The present invention most preferably uses a combination of Span60 and Tween60 with a mass ratio of 9:1, and the HLB of the combined emulsifier is 5.72, which can form a stable W / O type emulsion and is beneficial to the synthesis of polymer microspheres.

[0027] In the above preparation method, preferably, in step (2), the mixing ratio of the emulsifier to the oil phase solvent is (1-2) g: 100 mL.

[0028] In the above preparation method, preferably, in step (3), the crosslinking agent includes one or a combination of several of N,N'-methylenebisacrylamide, N,N'-dicyclohexylcarbodiimide, succinic anhydride and carbodiimide hydrochloride.

[0029] In the above preparation method, preferably, in step (3), the amount of crosslinking agent used is 4% to 10% of the mass of TEMPO oxidative modified nanocellulose in the first aqueous phase mixture.

[0030] In the above preparation method, preferably, in step (3), the initiator includes one or a combination of several of the following: ammonium persulfate, benzoyl peroxide, dimethyl sulfoxide, and tert-butyl peroxide.

[0031] In the above preparation method, preferably, in step (3), the amount of the initiator is (0.1-0.5):(0.5-1.5) of the mass ratio of the initiator to the acrylamide in the first aqueous mixture.

[0032] In the above preparation method, preferably, in step (3), the volume ratio of the second aqueous phase mixture to the oil phase solution is 1:3 to 1:5. In this invention, the volume ratio of the aqueous phase to the oil phase (W / O) affects the dispersion of the aqueous phase. If the volume ratio of the aqueous phase to the oil phase is too large, the aqueous phase droplets in the emulsion will increase, resulting in larger particle size of the synthesized microspheres, which can easily cause precipitation, uneven stirring, and other phenomena. If the volume ratio of the aqueous phase to the oil phase is too small, the yield of microspheres will decrease accordingly. At the same time, if the amount of aqueous phase added is too low, it is not conducive to the formation of a stable emulsion, which affects the synthesis of microspheres. This invention controls the volume ratio of the aqueous phase to the oil phase to be 1:3 to 1:5, which can form a stable emulsion and is conducive to the synthesis of microspheres with suitable particle size and uniform distribution.

[0033] In the above preparation method, preferably, in step (3), the second aqueous phase mixture is added dropwise to the oil phase solution obtained in step (2) at a dropping rate of 3 to 5 mL / min.

[0034] In the above preparation method, preferably, in step (3), the first rotation speed is 900-1200 r / min and the first time is 5-10 min.

[0035] In the above preparation method, preferably, in step (3), the second rotation speed is 600-900 r / min, the reaction temperature is 50-60℃, and the second time is 2-3 h. In this invention, as the reaction temperature increases, the hydrogen bonds and intermolecular forces between the molecular chain segments of the TEMPO-oxidized modified nanocellulose particles are continuously weakened, and the surface molecular chains can freely extend into the aqueous solution, increasing the number of active sites for the crosslinking reaction. Moreover, a higher reaction temperature is also beneficial to the diffusion of initiators and crosslinking agents and the acceleration of free radical generation. However, an excessively high reaction temperature will also increase the homopolymerization rate of the crosslinking agent, resulting in a decrease in yield and degree of crosslinking. This invention controls the reaction temperature at 50-60℃, which is conducive to the smooth progress of the reaction and ensures an appropriate degree of reaction, thereby synthesizing polymer microspheres with better performance in all aspects.

[0036] Currently, common methods for synthesizing polymer microspheres include reverse emulsion method, reverse microemulsion method, and reverse suspension method. This invention employs the reverse emulsion method to synthesize polymer microspheres, which has advantages such as simple operation and readily available reaction system.

[0037] In the above preparation method, preferably, step (3) further includes: at the beginning and end of the reaction, taking a small amount of emulsion and dropping it into the aqueous phase and oil phase respectively to check the emulsion type. Commonly used methods for determining the emulsion type include the dilution method and the conductivity method. The dilution method involves dropping two drops of emulsion into the aqueous phase and oil phase respectively. If it can be diluted by the aqueous phase, it is an oil-in-water (O / W) type, and otherwise it is a water-in-oil (W / O) type. The conductivity method involves measuring the conductivity of the emulsion with a conductivity meter. If the conductivity is higher, it is an oil-in-water (O / W) type, and otherwise it is a water-in-oil (W / O) type. This invention uses the dilution method to determine the emulsion type, which is simple and intuitive.

[0038] In the above preparation method, preferably, step (4) involves spray drying the emulsion system obtained in step (3) to form the polymer microspheres for displacement. More preferably, step (4) specifically includes: dispersing the emulsion system in a first organic solvent, discarding the supernatant, adding a second organic solvent, spraying the resulting solution into an inert gas stream to form small droplets, and then controlling the temperature to remove the first and second organic solvents to obtain the polymer microspheres for displacement. Further preferably, the first organic solvent includes anhydrous ethanol; the volume ratio of the first organic solvent to the emulsion system is 1:1 to 1:4; the emulsion system is dispersed in the first organic solvent by magnetic stirring; the second organic solvent includes acetone; the volume ratio of the second organic solvent to the emulsion system is 1:1 to 1:4; and the temperature for removing the first and second organic solvents is controlled at 20 to 35°C. This invention uses spray drying to dry and shape microspheres, and employs two organic solvents to reduce surface morphology damage caused by rapid dehydration of the microspheres, which is beneficial for obtaining microspheres with complete spherical shape and uniform particle size distribution.

[0039] In the above preparation method, preferably, in step (4), the particle size of the polymer microspheres for driving is 50-150 μm.

[0040] A second aspect of the present invention provides a polymer microsphere for regulating and driving, which is prepared by the above-described preparation method.

[0041] According to a specific embodiment of the present invention, preferably, the particle size of the polymer microspheres for regulating and driving is 50–150 μm. The polymer microspheres of the present invention can be stored in a dry, sealed container at room temperature.

[0042] This invention provides a polymer microsphere for regulating and controlling blockages and its preparation method. This invention overcomes the shortcomings of existing polyacrylamide-based crosslinked polymer blockage control technologies. This invention utilizes an oil-reverse emulsion method, where nanocellulose is TEMPO-modified. Acrylamide monomers and N-isopropylacrylamide monomers are introduced into a TEMPO-modified nanocellulose suspension after ultrasonic vibration. An initiator and a crosslinking agent are then added, and the mixture is mixed with the oil phase to form an emulsion under the action of an emulsifier. At a specific reaction temperature, the TEMPO-modified nanocellulose, acrylamide monomers, and N-isopropylacrylamide monomers undergo a copolymerization reaction through the crosslinking agent. The reacted system is then treated with spray drying to obtain polymer microspheres, which are a novel type of blockage control agent.

[0043] Nanocellulose, as a novel bio-based functional material, possesses excellent mechanical properties, a large specific surface area, and extremely strong reactivity. The exposed hydroxyl groups on the cellulose surface give nanocellulose enormous potential for chemical modification. Based on the properties of hydroxyl groups, various chemical modifications can be performed on nanocellulose to graft various functional groups, creating nanocellulose grafted materials with high strength, high thermal stability, and high mechanical properties. However, current nanocellulose grafted materials may not meet the needs of oilfield profile control and oil displacement. This invention modifies nanocellulose with TEMPO oxidation, oxidizing the hydroxymethyl groups on the nanocellulose surface to carboxyl groups, thereby increasing its water solubility and oxygen barrier properties. The nanocellulose surface after this oxidation modification has a large number of negative charges, making its suspension more stable and improving the long-term stability of the microsphere plugging agent.

[0044] Polyacrylamide is a water-soluble linear polymer that can polymerize into a three-dimensional network structure under appropriate conditions. However, due to the linear nature of its molecules, polyacrylamide has the ability to change the morphology of its molecular chains, resulting in a flexible structure. This flexible structure of polyacrylamide has both advantages and disadvantages in modulated oil recovery (MOR) applications. Flexibility means that the molecules can deform and penetrate deep into the oil layer for deep MOR, but it also leads to weaker plugging performance and insufficient molecular rigidity, making it prone to shearing and viscosity reduction.

[0045] This invention creatively combines TEMPO-modified nanocellulose and acrylamide, and introduces N-isopropylacrylamide monomer. The acrylamide monomer, N-isopropylacrylamide monomer, and semi-rigid TEMPO-modified nanocellulose are uniformly mixed in a certain proportion, and graft copolymerization occurs in a reverse emulsion system. After drying and molding, polymer microspheres are obtained. This invention controls the mixing ratio of acrylamide, N-isopropylacrylamide, and TEMPO-modified nanocellulose. By adjusting the ratio of the three components within the controlled range of this invention, polymer microspheres with different particle sizes and strengths can be obtained. The polymer microspheres prepared by this invention are white powdery particles that are soluble in water when stirred, and the aqueous solution is a white emulsion. The polymer microspheres of this invention are spherical particles with a particle size of 50–150 μm. Experiments show that in this invention, TEMPO-modified nanocellulose, acrylamide, and N-isopropylacrylamide undergo cross-linking copolymerization, and the resulting microspheres have submicron-sized particle sizes. The introduction of TEMPO-oxidized modified nanocellulose gives the microspheres a certain rigidity, strong plugging performance, and long-term stability. The introduction of acrylamide gives the microspheres a certain elasticity, allowing them to deform under pressure differential and penetrate deep into the main channel of reservoir flow. The introduction of N-isopropylacrylamide gives the microspheres a certain degree of thermal sensitivity, with their volume changing with temperature, which is beneficial to improving the plugging ability of the microspheres at high temperatures. After the microspheres are broken, they can also release nanocellulose crystals, which have a nanoscale effect and can further penetrate into the micropore channels to displace the remaining oil.

[0046] The technical solution of the present invention has at least the following beneficial technical effects:

[0047] Compared with existing polymer microspheres, the polymer microspheres for profile control and water shut-off of this invention not only have controllable particle size and good uniformity, but also offer advantages such as good temperature and salt resistance, wide availability of raw materials, and low cost. Furthermore, the polymer microspheres combine the rigidity of nanocellulose macromolecules with the flexibility and deformability of acrylamide, exhibiting a balance of rigidity and flexibility, and also possess a certain degree of thermal sensitivity. Moreover, after absorbing water and swelling, the polymer microspheres can penetrate further into the oil reservoir. They possess a certain elasticity and can deform under pressure differential, penetrating deep into the main flow channels within the reservoir. The volume of the polymer microspheres changes with temperature, which is beneficial for enhancing their sealing ability at high temperatures. Upon breakage, the polymer microspheres can release nanocellulose crystals, exhibiting a nanoscale effect, which can further penetrate into micropores and channels. In addition, the polymer microspheres are not easily degraded and possess strong sealing performance. Based on these advantages, the polymer microspheres for profile control and water shut-off of this invention have good applications in the field of profile control and water shut-off. Attached Figure Description

[0048] Figure 1 The image shows the morphology of the polymer microspheres for driving in water prepared in Example 1.

[0049] Figure 2 and Figure 3 The image shows the morphology of the polymer microspheres for regulation and displacement prepared in Example 1 in a saline solution with a mineralization of 4000 mg / L.

[0050] Figure 4 The sealing curve is the result of an experiment on a sand tube filled with an aqueous solution of the polymer microspheres for driving prepared in Example 1. Detailed Implementation

[0051] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0052] In the following examples and comparative examples, the experimental materials and reagents used mainly included: nanocellulose, TEMPO, NaBr, NaClO, sodium carbonate, sodium bicarbonate, sodium hydroxide, acrylamide, N-isopropylacrylamide, cyclohexane, chloroform, deionized water, N,N'-methylenebisacrylamide (MBAA), Span 60, Tween 60, ammonium persulfate (APS), etc.; the experimental instruments used mainly included: constant temperature water bath, digital display electric stirrer, constant temperature drying oven, analytical balance, infrared spectrometer, etc.

[0053] Example 1

[0054] (1) Aqueous phase preparation:

[0055] Prepare a 2% solids concentration nanocellulose dispersion (300 mL) using deionized water and nanocellulose (5–70 nm in diameter, 100–250 nm in length); prepare a 200 mL buffer solution by mixing 0.1 mol / L sodium carbonate solution and 0.1 mol / L sodium bicarbonate solution at a volume ratio of 3:2; weigh 0.064 g TEMPO and 0.4 g NaBr, dissolve them in 50 mL of buffer solution, and then pour the solution into the 300 mL nanocellulose dispersion under magnetic stirring. Add 2... An oxidation reaction was carried out using 8 mL of NaClO solution (effective chlorine content ≥10%). During the reaction, the pH of the system was adjusted to 10.0–10.1 using 2 mol / L sodium hydroxide solution. The pH was adjusted every 10 min in the initial stage of the reaction and every 20–30 min after 3 h. The reaction was stopped after 18 h. The product was thoroughly washed with deionized water by filtration to obtain gel-like TEMPO oxidized modified nanocellulose. The product was then transferred to 50 mL of deionized water to obtain a TEMPO oxidized modified nanocellulose dispersion with a mass concentration of 12%.

[0056] Weigh out a TEMPO-oxidized nanocellulose dispersion containing 1.0 g of TEMPO-oxidized nanocellulose, add an appropriate amount of deionized water, and sonicate for 10 min to obtain a uniformly dispersed TEMPO-oxidized nanocellulose suspension; weigh out 1.5 g of acrylamide and 0.5 g of N-isopropylacrylamide and add them to the TEMPO-oxidized nanocellulose suspension, and sonicate to obtain 20 mL of the first aqueous phase mixture;

[0057] (2) Preparation of oil phase: 80 mL of cyclohexane and 20 mL of chloroform were weighed, and 1.0 g of Span60 and Tween60 compound emulsifier (mass ratio of Span60 to Tween60 is 9:1) was added. The emulsifier was heated and stirred under a constant temperature water bath at 60℃ to dissolve it and obtain an oil phase solution.

[0058] (3) Synthesis reaction: Weigh 0.1g of crosslinking agent MBAA and add it to 20mL of the first aqueous phase mixture. Stir magnetically to dissolve it. Then weigh 0.3g of initiator APS and add it to the first aqueous phase mixture. After dissolving, the second aqueous phase mixture is obtained. The second aqueous phase mixture is rapidly added dropwise to the oil phase solution within 5min (dropping rate is 4mL / min). First, maintain a high speed of 900r / min for 5min, then adjust the speed to 600r / min and react in a constant temperature water bath at 60℃ for 2h to obtain the emulsion system after reaction. At the beginning and end of the reaction, take a small amount of emulsion with a dropper and add it to the aqueous phase and oil phase respectively to check the emulsion type.

[0059] (4) Drying and molding: The emulsion system after reaction is dried and molded by spray drying. Specifically, after the reaction is completed, the emulsion system after reaction is poured into a beaker, 30 mL of anhydrous ethanol is added, and the mixture is magnetically stirred for 0.5 h. The supernatant is discarded, and 30 mL of acetone is added. The resulting solution is sprayed into an inert gas stream to form small droplets. The temperature is then controlled at room temperature to remove anhydrous ethanol and acetone. The white powder is collected to obtain polymer microspheres for driving.

[0060] The polymer microspheres prepared in this embodiment are white powdery particles that dissolve in water upon stirring, forming a white emulsion in aqueous solution. The microspheres in the aqueous solution of the polymer microspheres in this embodiment were observed using an optical microscope, as shown... Figure 1 As shown, the microspheres are spherical particles with a particle size of approximately 50–150 μm. Adding salt to an aqueous solution of the polymer microspheres to a salinity of 4000 mg / L and observing under an optical microscope reveals that the salt solution increases the swelling ratio of the microspheres. Figure 2 and Figure 3 As shown.

[0061] Example 2

[0062] (1) Aqueous phase preparation: The preparation steps of the TEMPO oxidized modified nanocellulose dispersion with a mass concentration of 12% are the same as in Example 1. Weigh 2.0g of TEMPO oxidized modified nanocellulose dispersion, add an appropriate amount of deionized water, and sonicate for 10min to obtain a uniformly dispersed TEMPO oxidized modified nanocellulose suspension; Weigh 0.5g of acrylamide and 0.4g of N-isopropylacrylamide and add them to the TEMPO oxidized modified nanocellulose suspension. After sonication, 20mL of the first aqueous phase mixture is obtained.

[0063] (2) Preparation of oil phase: 80 mL of cyclohexane and 20 mL of chloroform were weighed, and 1.0 g of Span60 and Tween60 compound emulsifier (mass ratio of Span60 to Tween60 is 9:1) was added. The emulsifier was heated and stirred under a constant temperature water bath at 60℃ to dissolve it and obtain an oil phase solution.

[0064] (3) Synthesis reaction: Weigh 0.2g of crosslinking agent MBAA and add it to 20mL of the first aqueous phase mixture. Stir magnetically to dissolve it. Then weigh 0.4g of initiator APS and add it to the first aqueous phase mixture. After dissolving, the second aqueous phase mixture is obtained. The second aqueous phase mixture is rapidly added dropwise to the oil phase solution within 5min (dropping rate is 4mL / min). First, maintain a high speed of 900r / min for 5min, then adjust the speed to 600r / min and react in a constant temperature water bath at 60℃ for 2h to obtain the emulsion system after reaction. At the beginning and end of the reaction, take a small amount of emulsion with a dropper and add it to the aqueous phase and oil phase respectively to check the emulsion type.

[0065] (4) Drying and molding: The emulsion system after reaction is dried and molded by spray drying. Specifically, after the reaction is completed, the emulsion system after reaction is poured into a beaker, 30 mL of anhydrous ethanol is added, and the mixture is magnetically stirred for 0.5 h. The supernatant is discarded, and 30 mL of acetone is added. The resulting solution is sprayed into an inert gas stream to form small droplets. The temperature is then controlled at room temperature to remove anhydrous ethanol and acetone. The white powder is collected to obtain polymer microspheres for driving.

[0066] Example 3

[0067] (1) Aqueous phase preparation: The preparation steps of the TEMPO oxidized modified nanocellulose dispersion with a mass concentration of 12% are the same as in Example 1. Weigh 1.5g of TEMPO oxidized modified nanocellulose dispersion, add an appropriate amount of deionized water, and sonicate for 10min to obtain a uniformly dispersed TEMPO oxidized modified nanocellulose suspension; Weigh 1g of acrylamide and 0.4g of N-isopropylacrylamide and add them to the TEMPO oxidized modified nanocellulose suspension. After sonication, 20mL of the first aqueous phase mixture is obtained.

[0068] (2) Preparation of oil phase: 80 mL of cyclohexane and 20 mL of chloroform were weighed, and 1.5 g of Span60 and Tween60 compound emulsifier (mass ratio of Span60 to Tween60 is 9:1) was added. The emulsifier was heated and stirred under a constant temperature water bath at 60℃ to dissolve it and obtain an oil phase solution.

[0069] (3) Synthesis reaction: Weigh 0.15g of crosslinking agent MBAA and add it to 20mL of the first aqueous phase mixture. Stir magnetically to dissolve it. Then weigh 0.5g of initiator APS and add it to the first aqueous phase mixture. After dissolving, the second aqueous phase mixture is obtained. The second aqueous phase mixture is rapidly added dropwise to the oil phase solution within 5min (dropping rate is 4mL / min). First, maintain a high speed of 900r / min for 5min, then adjust the speed to 600r / min and react in a constant temperature water bath at 60℃ for 3h to obtain the emulsion system after reaction. At the beginning and end of the reaction, take a small amount of emulsion with a dropper and add it to the aqueous phase and oil phase respectively to check the emulsion type.

[0070] (4) Drying and molding: The emulsion system after reaction is dried and molded by spray drying. Specifically, after the reaction is completed, the emulsion system after reaction is poured into a beaker, 30 mL of anhydrous ethanol is added, and the mixture is magnetically stirred for 0.5 h. The supernatant is discarded, and 30 mL of acetone is added. The resulting solution is sprayed into an inert gas stream to form small droplets. The temperature is then controlled at room temperature to remove anhydrous ethanol and acetone. The white powder is collected to obtain polymer microspheres for driving.

[0071] Comparative Example 1

[0072] This comparative example is basically the same as Example 1, except that: no TEMPO oxidation modification is performed on the nanocellulose; instead, a nanocellulose dispersion containing 1.0g of nanocellulose with a mass concentration of 12% is used, an appropriate amount of deionized water is added, and the mixture is ultrasonically vibrated for 10 minutes to obtain a uniformly dispersed nanocellulose suspension; 1.5g of acrylamide and 0.5g of N-isopropylacrylamide are weighed and added to the nanocellulose suspension, and after ultrasonic vibration, 20mL of the first aqueous phase mixture is obtained; the remaining steps are the same as in Example 1 to prepare polymer microspheres for driving.

[0073] Comparative Example 2

[0074] This comparative example is basically the same as Example 1, except that N-isopropylacrylamide monomer is not used. The remaining steps are the same as in Example 1, and polymer microspheres for driving are prepared.

[0075] Comparative Example 3

[0076] This comparative example is basically the same as Example 1, except that N-isopropylacrylamide is replaced with acrylic acid, and the amount is also 0.5g. The remaining steps are the same as in Example 1, and polymer microspheres for driving are prepared.

[0077] Comparative Example 4

[0078] This comparative example is basically the same as Example 1, except that N-isopropylacrylamide is replaced with (3-acrylamidopropyl)trimethylammonium chloride, and the amount is also 0.5g. The remaining steps are the same as in Example 1, and polymer microspheres for regulating and driving are prepared.

[0079] Comparative Example 5

[0080] This comparative example is basically the same as Example 1, except that N-isopropylacrylamide is replaced with dimethylacrylamide, and the amount is also 0.5g. The other steps are the same as in Example 1, and polymer microspheres for regulating drive are prepared.

[0081] Test Example 1

[0082] Physical model experiments were used to evaluate the plugging performance of the polymer microspheres prepared in Examples 1-3 and Comparative Examples 1-5. A microsphere aqueous solution with a microsphere content of 1000 ppm and a mineralization of 4000 mg / L was prepared, thoroughly stirred, and placed in a 45℃ constant temperature incubator for 24 hours to swell. Quartz sand of different mesh sizes was used to fill 100 cm sand tubes, which were then placed in a 45℃ constant temperature incubator and flushed with formation water at an appropriate flow rate for 48 hours to simulate a formation undergoing long-term water injection development. The permeability of the sand tubes was measured to be 1.5D. The microsphere aqueous solution was injected into the sand tubes at a flow rate of 0.4 L / min, and the pressure changes at various pressure measurement points in the sand tubes were recorded.

[0083] The experimental results of Example 1 are as follows: Figure 4 As shown, for a 1000 ppm polymer microsphere solution, the pressure fluctuations at each pressure measurement point in the sand pipe increase with the increase of the injection volume. When the injection volume reaches 4.0 Vp, the pressures at the three pressure measurement points along the streamline direction rise from 6.8 kPa, 5.7 kPa, and 5.6 kPa to 29.8 kPa, 17.3 kPa, and 10.5 kPa, respectively. After the injection of the microsphere aqueous solution is completed and the formation water is injected, the pressure drops slightly. This indicates that the aqueous solution containing 1000 ppm of the polymer microspheres of Example 1 of this invention can penetrate deeply into a filled sand pipe with a permeability of 1.5 D and form a good seal for the sand pipe, exhibiting good regulation and displacement performance.

[0084] The experimental results of Example 2 are as follows: For a 1000 ppm polymer microsphere solution, the pressure fluctuations at each pressure measuring point in the sand pipe increased with the increase of the injection volume; when the injection volume reached 4.0 Vp, the pressures at the three pressure measuring points along the streamline direction increased from 7.6 kPa, 5.6 kPa, and 5.5 kPa to 35.4 kPa, 15.6 kPa, and 8.4 kPa, respectively. After the injection of the microsphere aqueous solution was completed and the formation water was injected, the pressure decreased slightly.

[0085] The experimental results of Example 3 are as follows: For a 1000 ppm polymer microsphere solution, the pressure fluctuation at each pressure measuring point in the sand pipe increased with the increase of the injection volume; when the injection volume reached 4.0 Vp, the pressure at the three pressure measuring points along the streamline direction increased from 5.2 kPa, 4.3 kPa, and 4.1 kPa to 25.3 kPa, 19.3 kPa, and 12.4 kPa, respectively. After the injection of the microsphere aqueous solution was completed and the formation water was injected, the pressure decreased slightly.

[0086] The experimental results of Comparative Example 1 are as follows: For a 1000 ppm polymer microsphere solution, the pressure fluctuations at each pressure measuring point in the sand pipe increased with the increase of the injection volume; when the injection volume reached 4.0 Vp, the pressures at the three pressure measuring points along the streamline direction increased from 5.3 kPa, 4.0 kPa, and 3.9 kPa to 18.3 kPa, 11.2 kPa, and 6.7 kPa, respectively. After the injection of the microsphere aqueous solution was completed and the formation water was injected, the pressure decreased slightly.

[0087] The experimental results of Comparative Example 2 are as follows: For a 1000 ppm polymer microsphere solution, the pressure fluctuations at each pressure measuring point in the sand pipe increased with the increase of the injection volume; when the injection volume reached 4.0 Vp, the pressures at the three pressure measuring points along the streamline direction increased from 6.6 kPa, 5.4 kPa, and 5.2 kPa to 22.3 kPa, 12.4 kPa, and 7.7 kPa, respectively. After the injection of the microsphere aqueous solution was completed and the formation water was injected, the pressure decreased slightly.

[0088] The experimental results of Comparative Example 3 are as follows: For a 1000 ppm polymer microsphere solution, the pressure fluctuations at each pressure measuring point in the sand pipe increased with the increase of the injection volume; when the injection volume reached 4.0 Vp, the pressures at the three pressure measuring points along the streamline direction increased from 6.2 kPa, 5.2 kPa, and 5.1 kPa to 26.5 kPa, 11.7 kPa, and 6.8 kPa, respectively. After the injection of the microsphere aqueous solution was completed and the formation water was injected, the pressure decreased slightly.

[0089] The experimental results of Comparative Example 4 are as follows: For a 1000 ppm polymer microsphere solution, the pressure fluctuations at each pressure measuring point in the sand pipe increased with the increase of the injection volume; when the injection volume reached 4.0 Vp, the pressures at the three pressure measuring points along the streamline direction increased from 5.8 kPa, 4.1 kPa, and 4.0 kPa to 24.3 kPa, 10.6 kPa, and 5.2 kPa, respectively. After the injection of the microsphere aqueous solution was completed and the formation water was injected, the pressure decreased slightly.

[0090] The experimental results of Comparative Example 5 are as follows: For a 1000 ppm polymer microsphere solution, the pressure fluctuations at each pressure measuring point in the sand pipe increased with the increase of the injection volume; when the injection volume reached 4.0 Vp, the pressures at the three pressure measuring points along the streamline direction increased from 6.8 kPa, 5.6 kPa, and 5.5 kPa to 28.7 kPa, 10.7 kPa, and 5.6 kPa, respectively. After the injection of the microsphere aqueous solution was completed and the formation water was injected, the pressure decreased slightly.

[0091] Test Example 2

[0092] The temperature resistance of the polymer microspheres in Example 1 was evaluated using physical model experiments. A microsphere aqueous solution with a microsphere content of 1000 ppm and a mineralization of 4000 mg / L was prepared, thoroughly stirred, and placed in a 90℃ constant temperature oven for 24 hours to swell. Quartz sand of different mesh sizes was used to fill 100 cm sand tubes, which were then placed in a 90℃ constant temperature oven and flushed with formation water at an appropriate flow rate for 48 hours to simulate a formation undergoing long-term water injection development. The permeability of the sand tubes was measured to be 1.5D. The microsphere aqueous solution was injected into the sand tubes at a flow rate of 0.4 L / min, and the pressure changes at various pressure measurement points were recorded.

[0093] The experimental results of Example 1 show that for a 1000 ppm polymer microsphere solution, the pressure fluctuations at each pressure measurement point in the sand tube increase with the increase of the injection volume. When the injection volume reaches 4.0 Vp, the pressures at the three pressure measurement points along the streamline direction rise from 7.2 kPa, 5.9 kPa, and 5.8 kPa to 31.4 kPa, 15.3 kPa, and 9.6 kPa, respectively. After the injection of the microsphere aqueous solution is completed and the formation water is injected, the pressure drops slightly. This indicates that the aqueous solution containing 1000 ppm of the polymer microspheres of Example 1 of this invention can still penetrate deep into a filled sand tube with a permeability of 1.5 D and form a good seal for the sand tube under 90°C conditions, demonstrating good temperature resistance.

[0094] Test Example 3

[0095] Physical model experiments were used to evaluate the long-term stability of the polymer microspheres in Example 1. A microsphere aqueous solution with a microsphere content of 1000 ppm and a mineralization of 4000 mg / L was prepared, thoroughly stirred, and placed in a 90℃ constant temperature incubator for 30 days to swell. Quartz sand of different mesh sizes was used to fill 100 cm sand tubes, which were then placed in a 90℃ constant temperature incubator and flushed with formation water at an appropriate flow rate for 48 hours to simulate a formation undergoing long-term water injection development. The permeability of the sand tubes was measured to be 1.5D. The microsphere aqueous solution was injected into the sand tubes at a flow rate of 0.4 L / min, and the pressure changes at various pressure measurement points in the sand tubes were recorded.

[0096] The experimental results of Example 1 show that for a 1000 ppm polymer microsphere solution, the pressure fluctuations at each pressure measurement point in the sand pipe increase with the increase of the injection volume. When the injection volume reaches 4.0 Vp, the pressures at the three pressure measurement points along the streamline direction rise from 8.5 kPa, 6.3 kPa, and 6.1 kPa to 27.5 kPa, 15.4 kPa, and 9.5 kPa, respectively. After the injection of the microsphere aqueous solution is completed and the formation water is injected, the pressure drops slightly. This indicates that the aqueous solution containing 1000 ppm of the polymer microspheres of Example 1 of this invention still has strong plugging performance after standing at 90°C for 30 days, and can deeply fill the sand pipe to form a certain degree of plugging, exhibiting good long-term stability.

[0097] Currently, the polymer microspheres prepared by this invention have undergone multiple sets of indoor evaluation experiments on plugging and modulating flow. The experimental results show that the polymer microspheres of this invention can form effective plugging and can penetrate deep into the formation. After switching to water flooding, they can still maintain a high residual resistance coefficient, withstand 90℃ and have good long-term stability. They are a good new type of modulating flow plugging material.

Claims

1. A method for preparing polymer microspheres for modulating and driving, comprising the following steps: (1) Aqueous phase preparation A TEMPO-oxidized modified nanocellulose dispersion was mixed with water and ultrasonically vibrated for 10-20 min to obtain a uniformly dispersed TEMPO-oxidized modified nanocellulose suspension. Acrylamide and N-isopropylacrylamide were mixed with the TEMPO-oxidized modified nanocellulose suspension to obtain a first aqueous phase mixture. The TEMPO-oxidized modified nanocellulose dispersion was obtained by TEMPO-oxidizing nanocellulose, and the nanocellulose had a diameter of 5-70 nm and a length of 100-250 nm. The mass ratio of TEMPO-oxidized modified nanocellulose, acrylamide, and N-isopropylacrylamide in the TEMPO-oxidized modified nanocellulose suspension was (1.0-2.0):(0.5-1.5):(0.2-0.5). (2) Preparation of oil phase An oil phase solvent and an emulsifier are mixed to obtain an oil phase solution; wherein the oil phase solvent is a combination of cyclohexane and chloroform, and the volume ratio of cyclohexane to chloroform is 4:1 to 5:1; the emulsifier is a combination of Span60 and Tween60. (3) Synthesis reaction The crosslinking agent, the initiator and the first aqueous phase mixture obtained in step (1) are mixed to obtain the second aqueous phase mixture; the second aqueous phase mixture is added dropwise to the oil phase solution obtained in step (2), the volume ratio of the second aqueous phase mixture to the oil phase solution is 1:3 to 1:5, and after stirring at the first speed for a first time, the mixture is reacted at the second speed for a second time to obtain the emulsion system after reaction. (4) Drying and shaping The emulsion system obtained in step (3) is dried and shaped by spray drying to obtain the polymer microspheres for driving.

2. The preparation method according to claim 1, wherein, The preparation steps of the TEMPO oxidative modified nanocellulose dispersion specifically include: preparing the nanocellulose into a nanocellulose dispersion; mixing sodium carbonate solution and sodium bicarbonate solution to prepare a buffer solution; dissolving TEMPO and NaBr in the buffer solution, then mixing them with the nanocellulose dispersion under magnetic stirring, and then adding NaClO to carry out an oxidation reaction. During the oxidation reaction, the pH value of the system is adjusted to 10.0-10.1, and the reaction is completed after 18-24 hours. After washing, the product yields gel-like TEMPO oxidative modified nanocellulose; and preparing the gel-like TEMPO oxidative modified nanocellulose into a TEMPO oxidative modified nanocellulose dispersion.

3. The preparation method according to claim 2, wherein, In step (1), the amount of TEMPO is 0.5% to 1.5% of the mass of nanocellulose, the amount of NaBr is 5% to 8% of the mass of nanocellulose, and the amount of NaClO is 50% to 80% of the mass of nanocellulose.

4. The preparation method according to claim 1, wherein, In step (2), the mass ratio of Span60 to Tween60 is 8:1 to 10:

1.

5. The preparation method according to claim 1, wherein, In step (2), the mixing ratio of the emulsifier to the oil phase solvent is (1~2)g:100mL.

6. The preparation method according to claim 1, wherein, In step (3), the crosslinking agent includes one or a combination of several of N,N'-methylenebisacrylamide, N,N'-dicyclohexylcarbodiimide, succinic anhydride and carbodiimide hydrochloride.

7. The preparation method according to claim 1, wherein, In step (3), the amount of crosslinking agent used is 4% to 10% of the mass of TEMPO oxidative modified nanocellulose in the first aqueous phase mixture.

8. The preparation method according to claim 1, wherein, In step (3), the initiator includes one or a combination of several of ammonium persulfate, benzoyl peroxide and tert-butyl peroxide.

9. The preparation method according to claim 1, wherein, In step (3), the mass ratio of the initiator to the acrylamide in the first aqueous mixture is (0.1~0.5):(0.5~1.5).

10. The preparation method according to claim 1, wherein, In step (3), the second aqueous phase mixture is added dropwise to the oil phase solution obtained in step (2) at a dropping rate of 3~5 mL / min.

11. The preparation method according to claim 1, wherein, In step (3), the first rotational speed is 900~1200 r / min, and the first time is 5~10 min.

12. The preparation method according to claim 1, wherein, In step (3), the second rotation speed is 600~900 r / min, the reaction temperature is 50~60℃, and the second time is 2~3h.

13. The preparation method according to claim 1, wherein, Step (4) specifically includes: dispersing the emulsion system after the reaction in a first organic solvent, discarding the supernatant, adding a second organic solvent, spraying the resulting solution into an inert gas stream to form small droplets, and then controlling the temperature to remove the first and second organic solvents to obtain the polymer microspheres for driving.

14. The preparation method according to claim 13, wherein, In step (4), the first organic solvent includes anhydrous ethanol; the volume ratio of the first organic solvent to the emulsion system after reaction is 1:1 to 1:4; the emulsion system after reaction is dispersed in the first organic solvent by magnetic stirring; the second organic solvent includes acetone; the volume ratio of the second organic solvent to the emulsion system after reaction is 1:1 to 1:4; the temperature for removing the first organic solvent and the second organic solvent is controlled at 20 to 35°C.

15. A polymer microsphere for modulated driving, which is prepared by the method for preparing polymer microspheres for modulated driving according to any one of claims 1-14; wherein the particle size of the polymer microsphere for modulated driving is 50~150μm.

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