UCST gel particles for profile control and water plugging, preparation method and application thereof

Abstract

The present invention belongs to the technical field of profile control and water plugging in oil and water wells, and specifically relates to a UCST gel particle for profile control and water plugging, and a preparation method and application thereof. The preparation method of the UCST gel particle for profile control and water plugging of the present invention combines a multi-hydrogen bond donor monomer and a multi-hydrogen bond acceptor monomer to form a UCST gel particle with a double network structure of multi-hydrogen bond entanglement. This structure can effectively inhibit the gel from absorbing water and swelling at low temperatures, slow down the expansion rate of the gel particles in a low temperature environment, and achieve effective deep migration. As the temperature rises, the hydrogen bonds are gradually broken due to the influence of temperature, resulting in the gradual disappearance of the hydrogen bond entanglement network. At this time, the gel network is transformed from a two-phase structure to a single-phase structure, and the hydrophilicity increases accordingly, the water absorption and swelling capacity of the gel particles is enhanced, and slow expansion at high temperature is achieved. The gel particles have the characteristics of low-temperature anti-swelling, high-temperature expansion, adaptability to a wide range of reservoir types, and the ability to achieve deep migration, and are suitable for application in profile control and water plugging in oil and water wells.

Description

Technical Field

[0001] The invention belongs to the technical field of profile control and water plugging of oil and water wells, and particularly relates to UCST gel particles for profile control and water plugging, and a preparation method and application thereof. Background Art

[0002] In the context of the current tertiary oil recovery stage in domestic oil fields, water injection has become an important means to improve oil recovery. However, long-term water injection operations will lead to increased reservoir heterogeneity, which in turn affects the recovery effect of the oil field. The root of this problem lies in the flow characteristics of the injected water, which makes it easy for water channels to form in the high permeability layer, resulting in the low permeability layer failing to obtain sufficient injection pressure, thereby reducing the recovery rate of crude oil. In addition, excessive water production may also cause corrosion, scaling and other problems, increase the cost of oil and water treatment, and further affect the technical environment and economic life of the production well.

[0003] Therefore, improving the heterogeneity of the formation, increasing the water drive sweep coefficient, and thus improving the recovery rate are the primary goals of comprehensive oilfield management. In recent years, researchers have developed a series of new gel particle plugging agents, which have better elastic deformation properties than traditional rigid inorganic particles, and can more effectively plug high permeability layers and promote water injection in low permeability layers.

[0004] With the improvement of exploration level and the rising demand for oil and gas resources, the heterogeneity and temperature of oil reservoirs are also increasing, and the technical performance requirements for water plugging particles are increasing. During the water injection process of deep oil wells, the water absorption and expansion rate of traditional polyacrylamide gel particles or resins is often too fast, resulting in the particles expanding before reaching the target layer, making it difficult to achieve effective deep migration. In addition, the mechanical properties of such particles decrease after expansion, and they are easily sheared and broken during transportation.

[0005] UCST (Utmost Critical Solution Temperature) gel particles have shown great application potential in oil and water well profile control and water plugging technology due to their special temperature response characteristics. How to prepare more adaptable and cost-effective profile control and water plugging gel particles through new methods or processes to achieve smooth migration in deep formations and maintain good mechanical properties has important research and application value. Summary of the invention

[0006] The first purpose of the present invention is to provide a method for preparing UCST gel particles for profile control and water plugging. The preparation method is simple, the raw materials are easily obtained, and the cost is low. The UCST gel particles are combined with part of the solvent through strong hydrogen bonding on the polymer network of multiple hydrogen bonding sites to form a dense hydrogen bonding structure, thereby enhancing the mechanical strength of the gel particles and improving the plugging ability of the gel particles.

[0007] The second purpose of the present invention is to provide a UCST gel particle for profile control and water plugging. The gel particle has the characteristics of low-temperature resistance to swelling, high-temperature expansion, low cost, adaptability to a wide range of oil reservoir types and ability to achieve deep migration, and is suitable for use in profile control and water plugging in oil and water wells.

[0008] The third object of the present invention is to provide an application of gel particles for profile control and water plugging in oil and water wells. The gel particles achieve effective deep migration and are suitable for application in profile control and water plugging in oil and water wells.

[0009] The present invention is achieved through the following technical solutions:

[0010] In a first aspect, the present invention provides a method for preparing UCST gel particles for profile control and water plugging.

[0011] a: adding a multi-hydrogen bond donor monomer into water and stirring evenly to obtain a multi-hydrogen bond donor monomer aqueous solution with a molar concentration of 1 mol / L-6 mol / L;

[0012] b: adding a multi-hydrogen bond acceptor monomer to a solvent, stirring evenly to obtain a multi-hydrogen bond acceptor monomer solution with a molar concentration of 1 mol / L to 8 mol / L;

[0013] c: adding a crosslinking agent and an initiator to the multi-hydrogen bond donor monomer aqueous solution and the multi-hydrogen bond acceptor monomer solution respectively, and stirring them evenly to obtain a hydrogel precursor solution A and a gel precursor solution B;

[0014] d: polymerizing the solution A to obtain hydrogel A;

[0015] e: soaking the hydrogel A in solution B for 16-72 hours to polymerize to obtain UCST gel, and then drying, grinding and granulating in sequence to obtain UCST gel particles for profile control and water plugging;

[0016] The molar ratio of the multi-hydrogen bond donor monomer to the multi-hydrogen bond acceptor monomer is 1:(0.2-4).

[0017] Furthermore, in a preferred embodiment of the present invention, the multi-hydrogen bond donor monomer is selected from amide compounds.

[0018] Furthermore, in a preferred embodiment of the present invention, the multi-hydrogen bond acceptor monomer is selected from amide compounds and / or carboxylic acid compounds.

[0019] Furthermore, in a preferred embodiment of the present invention, the polymerization time of the above solution A to obtain the hydrogel A is 1-5h.

[0020] Furthermore, in a preferred embodiment of the present invention, the multi-hydrogen bond donor monomer is selected from at least one of methacrylamide, acrylamide and isopropylacrylamide.

[0021] Furthermore, in a preferred embodiment of the present invention, the multi-hydrogen bond acceptor monomer is selected from at least one of isopropyl acrylamide, N,N-dimethyl acrylamide, N-hydroxymethyl acrylamide and acrylic acid.

[0022] Furthermore, in a preferred embodiment of the present invention, the solvent in the above step b is water, an organic solution or a mixture of water and an organic solution.

[0023] Furthermore, in a preferred embodiment of the present invention, the stirring speeds of the above steps a, b, and c are respectively 200-1000 r / min.

[0024] In a second aspect, the present invention provides a UCST gel particle for profile control and water plugging, wherein the gel particle is prepared by the above-mentioned preparation method of the UCST gel particle for profile control and water plugging.

[0025] In a third aspect, the present invention provides an application of gel particles for profile control and water plugging in oil and water wells.

[0026] Furthermore, the application mass concentration of the above-mentioned gel particles for profile control and water plugging in oil and water wells is 5%-19%; preferably, the application mass concentration can be selected from 5%, 7%, 9%, 11%, 13%, 15%, 17%, and 19%.

[0027] Compared with the prior art, the present invention has at least the following technical effects:

[0028] The present invention provides a method for preparing UCST gel particles for profile control and water plugging, which has the following advantages: the preparation method is simple, the process flow is clear, and the operation is convenient; the required raw materials are widely available and easy to obtain, thereby reducing the production cost; and the cost is low: the overall production cost is low and is suitable for large-scale application.

[0029] Through this preparation method, multi-hydrogen bond donor monomers are combined with hydrogen bond acceptor monomers to form UCST gel particles with a multi-hydrogen bond entangled double network structure. This structure can effectively inhibit the water absorption and expansion of the gel particles at low temperatures and slow down the expansion rate of the gel particles in a low temperature environment. As the temperature rises, the hydrogen bonds are gradually broken by the temperature, resulting in the gradual disappearance of the hydrogen bond entanglement network. At this time, the gel network changes from a tightly entangled polymer network to a stretched polymer network, the hydrophilic groups are exposed, the hydrophilicity increases, the water absorption and expansion ability of the gel particles is enhanced, and slow expansion at high temperatures is achieved. In addition, this gel particle also has excellent mechanical strength, which can effectively enhance its plugging ability. Even after absorbing water and expanding to dozens of times its own weight, the gel particles still maintain a high mechanical strength, can withstand external pressure without leakage, and are extremely suitable for use in oil and water well profile control and water plugging application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 , schematic diagram of the mechanism of UCST gel particles for profile control and water plugging in Example 3.

[0031] Figure 2 , a graph showing the relationship between the water absorption multiples of the gel particles prepared in Example 1 and time at 90°C and 25°C.

[0032] Figure 3 , a graph showing the relationship between the water absorption multiples of the gel particles prepared in Example 2 and time at 90°C and 25°C.

[0033] Figure 4 , a graph showing the relationship between the water absorption multiples of the gel particles prepared in Example 3 and time at 90°C and 25°C.

[0034] Figure 5 , a graph showing the relationship between the water absorption multiples of the gel particles prepared in Example 4 and time at 90°C and 25°C.

[0035] Figure 6 , a graph showing the relationship between the water absorption multiples of the gel particles prepared in Example 5 and time at 90°C and 25°C.

[0036] Figure 7 , a graph showing the relationship between the water absorption multiples of the gel particles prepared in Example 6 and time at 90°C and 25°C.

[0037] Figure 8 , a graph showing the relationship between the water absorption multiples of the gel particles prepared in Example 7 and time at 90°C and 25°C.

[0038] Fig. 9 , a graph showing the relationship between the water absorption multiples of the gel particles prepared in Example 8 and time at 90°C and 25°C.

[0039] Fig.10 , Comparative Example 1 shows the relationship between the water absorption multiples of the gel particles prepared at 90°C and 25°C and time.

[0040] Fig.11 , Comparative Example 2 shows the relationship between the water absorption multiples of the gel particles prepared at 90°C and 25°C and time.

[0041] Fig.12 , Swelling equilibrium diagram of the gel particles at different temperatures after changing the mass of the hydrogen bond donor monomer in Example 3.

[0042] Fig.13 , Swelling equilibrium diagram of the gel particles at different temperatures after changing the mass of the hydrogen bond acceptor monomer in Example 3.

[0043] Fig.14 , Swelling photos of the gel particles after changing the mass of the hydrogen bond donor monomer in Example 3 at 60°C and 100°C before swelling.

[0044] Fig.15 , Swelling photos of the gel particles after changing the mass of the hydrogen bond acceptor monomer in Example 3 at 60°C and 100°C before swelling.

[0045] Fig.16 , the compressive stress-strain curve of the gel particles before swelling after changing the mass of the hydrogen bond donor monomer in Example 3.

[0046] Fig.17 , the compression stress-strain curve of the gel particles after swelling after changing the mass of the hydrogen bond donor monomer in Example 3.

[0047] Fig.18 , Temperature scanning diagram of the gel particles prepared in Example 3 under a high temperature rheometer.

[0048] Fig.19 , displacement experiment diagram of the gel particles prepared in Example 3. DETAILED DESCRIPTION

[0049] The embodiments of the present invention will be described in detail below in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. The specific conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0050] The technical solutions of the specific implementation modes of the present invention are as follows:

[0051] A method for preparing UCST gel particles for profile control and water plugging,

[0052] a: adding a multi-hydrogen bond donor monomer into water and stirring evenly to obtain a multi-hydrogen bond donor monomer aqueous solution with a molar concentration of 1 mol / L-6 mol / L;

[0053] b: adding a multi-hydrogen bond acceptor monomer to a solvent, stirring evenly to obtain a multi-hydrogen bond acceptor monomer solution with a molar concentration of 1 mol / L to 8 mol / L;

[0054] c: adding a crosslinking agent and an initiator to the multi-hydrogen bond donor monomer aqueous solution and the multi-hydrogen bond acceptor monomer solution respectively, and stirring them evenly to obtain a hydrogel precursor solution A and a gel precursor solution B;

[0055] d: polymerizing the solution A to obtain hydrogel A;

[0056] e: soaking the hydrogel A in solution B for 16-72 hours to polymerize to obtain UCST gel, and then drying, grinding and granulating in sequence to obtain UCST gel particles for profile control and water plugging;

[0057] The molar ratio of the multi-hydrogen bond donor monomer to the multi-hydrogen bond acceptor monomer is 1:(0.2-4).

[0058] When the molar concentration of the multi-hydrogen bond donor monomer is less than 1 mol / L, the monomer concentration is insufficient and the gel cannot be effectively formed, thus affecting the subsequent preparation process of the double network. When the molar concentration exceeds 6 mol / L, violent polymerization will occur during the gelation process, resulting in a large number of pores inside the gel and the structure becoming extremely fragile. At the same time, at high concentrations, the solubility of the monomer decreases significantly and cannot be completely dissolved into a gel precursor solution of the required concentration.

[0059] For multi-hydrogen bond receptor monomers, when the molar concentration is lower than 1 mol / L, the number of receptor sites is small, and the prepared double network gel lacks sufficient hydrogen bond interactions, so the temperature response performance is not obvious. When the molar concentration exceeds 8 mol / L, the water in the gel will be exchanged in large quantities after immersion, resulting in excessive monomer concentration, which in turn affects the subsequent polymerization reaction.

[0060] In addition, in the technical solution of the present invention, steps a and b are not in order, and steps a and b can be interchanged. Step c is also specifically divided into two steps, and there is no order in which the hydrogel precursor solution A can be prepared first, or the gel precursor solution B can be prepared first. Those skilled in the art can adjust the steps of this solution as needed;

[0061] Preferably, the molar concentration of the above-mentioned multi-hydrogen bond donor monomer aqueous solution is 2mol / L-5.5mol / L; specifically, the molar concentration of the above-mentioned multi-hydrogen bond donor monomer aqueous solution is 2.0mol / L, 2.5mol / L, 3.0mol / L, 3.5mol / L, 4.0mol / L, 4.5mol / L, 5mol / L, 5.5mol / L;

[0062] Preferably, the molar concentration of the multi-hydrogen bond acceptor monomer solution is 1.5 mol / L-8 mol / L; specifically, the molar concentration of the hydrogen bond site acceptor can be 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L, 5.0 mol / L, 5.5 mol / L, 6.0 mol / L, 6.5 mol / L, 7.0 mol / L, 7.5 mol / L, 8.0 mol / L;

[0063] Preferably, the molar ratio of the above-mentioned multi-hydrogen bond donor monomer to the multi-hydrogen bond acceptor monomer is 1:(0.5-2); more preferably, the molar ratio of the multi-hydrogen bond donor monomer to the multi-hydrogen bond acceptor monomer is 1:(0.7-1.5);

[0064] When the molar ratio of multi-hydrogen bond donor monomer to multi-hydrogen bond acceptor monomer is close to 1:1, the hydrogen bond cross-linking between polymers in the double network gel forms a more stable network structure, which increases the density of hydrogen bonds. Such a structure not only reduces the hydrogen bonding between hydrophilic groups (such as amino groups, carbonyl groups, etc.) and water, but also enhances the internal entanglement of the polymer network. This means that in a low-temperature environment, the hydrophobicity of the gel is improved, effectively inhibiting the swelling phenomenon, thereby ensuring that it maintains good anti-swelling properties before entering the high-temperature formation.

[0065] In addition, as the UCST transition temperature increases, the gel can maintain stability at higher formation temperatures, which is particularly important for certain engineering applications (such as oil extraction, geothermal energy utilization, etc.). The strong hydrogen bond network also gives the gel particles excellent mechanical properties, increasing their breakthrough pressure, allowing them to still play their due role in high-pressure environments. These properties combined make this UCST gel have a wide range of application potential in complex formation conditions.

[0066] Preferably, the multi-hydrogen bond donor monomer is selected from amide compounds; further preferably, the multi-hydrogen bond donor monomer is selected from at least one of methacrylamide, acrylamide and isopropyl acrylamide.

[0067] Preferably, the multi-hydrogen bond acceptor monomer is selected from amide compounds and / or carboxylic acid compounds; preferably, the multi-hydrogen bond acceptor monomer is selected from at least one of isopropyl acrylamide, N,N-dimethyl acrylamide, N-hydroxymethyl acrylamide and acrylic acid. Further preferably, the multi-hydrogen bond acceptor monomer is selected from amide compounds;

[0068] Preferably, the polymerization time of the above solution A to obtain the hydrogel A is 1-5 hours. Preferably, the polymerization time can be selected from 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours.

[0069] Preferably, the polymerization method of the above solution A can be photo-initiated polymerization or thermal-initiated polymerization; the photo-initiated polymerization can be polymerization under ultraviolet light, and the polymerization temperature is 40-50°C.

[0070] The selection of a suitable initiator and a suitable temperature is conducive to the full progress of the polymerization reaction.

[0071] Preferably, the solvent in the above step b is water, an organic solution or a mixture of water and an organic solution. Further preferably, the solvent in the above step b is an organic solution or a mixture of water and an organic solution.

[0072] The organic solvent can be any solvent capable of dissolving the multi-hydrogen bond acceptor monomer, and can be selected from dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, glutaraldehyde, ethyl acetate or methanol; more preferably, the organic solvent is at least one of dimethyl sulfoxide, N,N-dimethylformamide and N,N-dimethylacetamide;

[0073] Among them, the solvent of the above step b is selected from an organic solution or a mixture of an organic solution and water, because during the immersion of the receptor monomer in the organic mixed solution, the amino group and the carbonyl group on the amide group can be effectively combined through strong hydrogen bonds, and the organic solvent's ability to snatch hydrogen bond sites is much greater than that of water, so that it can effectively form a strong hydrogen bond structure with the amide monomer. Before the UCST transition temperature, the hydrophilic group combines with the polymer and organic matter in large quantities to form a strong hydrophobic effect, so that the gel can effectively enter the deep formation. The UCST temperature transition requires greater energy, that is, a higher temperature is required, so as to achieve suitability for different formation temperatures, further increasing the formation profile control effect of the UCST gel particles.

[0074] Preferably, the solvent is a mixture of an organic solution and water, wherein the mass fraction of the organic solution added is 0%-90% of the solvent; 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%;

[0075] Preferably, the stirring temperature obtained in the above step C is 40-80°C.

[0076] Further preferably, the crosslinking agent can be selected from at least one of bisphenol A epoxy resin, divinylbenzene, dimethylaminopropylamine, trimethyl propane trimethyl acrylate and methylene bisacrylamide; the initiator is I 2959 (Chinese name: 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone) and / or 2,2-diethoxyacetophenone. The appropriate initiator is selected to make the obtained gel particles for profile control and water plugging have good performance.

[0077] Further preferably, the amount of the crosslinking agent or initiator added can be any value between 0.1% and 2% of the mass of the hydrogel precursor solution A.

[0078] Preferably, the stirring speeds of steps a, b and c are respectively 200-1000 r / min.

[0079] Preferably, the hydrogel A is immersed in solution B for 18-48 hours. The purpose of immersing for a certain period of time is to ensure that the gel precursor of the hydrogen bond acceptor network fully enters the hydrogen bond donor gel, effectively forming a double network gel with UCST transition at a certain molar ratio.

[0080] In a second aspect, the present invention provides a UCST gel particle for profile control and water plugging, wherein the gel particle is prepared by the above-mentioned preparation method of the UCST gel particle for profile control and water plugging.

[0081] In a third aspect, the present invention provides an application of gel particles for profile control and water plugging in oil and water wells, wherein the application mass concentration of the gel particles for profile control and water plugging in oil and water wells is 5%-19%, for example, 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%.

[0082] Example 1

[0083] This embodiment provides a method for preparing gel particles for UCST profile control and water plugging:

[0084] Step 1: Weigh 0.5 g of methacrylamide and dissolve it in 2 mL of deionized water, and stir it magnetically at 60 ° C for 60 minutes to make it dissolve evenly, to obtain a methacrylamide monomer aqueous solution;

[0085] Step 2: Weigh 0.4 g of acrylic acid and 2 ml of dimethyl sulfoxide and dissolve them in 2 mL of deionized water, and stir them magnetically at 40 °C for 60 min to make them dissolve evenly to obtain an organic solution;

[0086] Step 3: Add 25 mg of crosslinker methylenebisacrylamide and 25 mg of initiator 2,2-diethoxyacetophenone to the solutions prepared in step 1 and step 2, respectively, and stir them magnetically at 60 °C for 30 min to dissolve them uniformly, to obtain hydrogel precursor solution A and gel precursor solution B, respectively;

[0087] Step 4: Pour the gel precursor solution A obtained in step 3 into a circular mold and polymerize under 365UV light for 6 hours to obtain hydrogel A;

[0088] Step 5: Soak the hydrogel A obtained in step 4 in the gel precursor solution B prepared in step 3 for 24 hours and photoinitiate polymerization for 4 hours to obtain UCST gel;

[0089] Step 6: Dry, grind and granulate the gel in step 5 to prepare UCST gel particles for profile control and water plugging.

[0090] Example 2

[0091] This embodiment provides a method for preparing gel particles for UCST profile control and water plugging:

[0092] Step 1: Weigh 0.5 g of methacrylamide and dissolve it in 2 mL of deionized water, and stir it magnetically at 60 ° C for 120 min to make it dissolve evenly, to obtain a methacrylamide monomer aqueous solution;

[0093] Step 2: Weigh 0.4 g of acrylic acid and 2 ml of N,N-dimethylformamide and dissolve them in 2 mL of deionized water, and stir them magnetically at 40°C for 120 min to make them dissolve evenly, to obtain an organic solution;

[0094] Step 3: Add 25 mg of crosslinking agent methylene bisacrylamide and 25 mg of initiator 2,2-diethoxyacetophenone to the solutions prepared in step 1 and step 2, respectively, and stir them magnetically at 60 °C for 30 min to dissolve them uniformly, to obtain hydrogel precursor solution A and gel precursor solution B;

[0095] Step 4: Pour the hydrogel precursor solution A obtained in step 3 into a circular mold and polymerize it under 365UV light for 6 hours to obtain hydrogel A;

[0096] Step 5: Soak the hydrogel A obtained in step 4 in the gel precursor solution B prepared in step 3 for 24 hours and photoinitiate polymerization for 4 hours to obtain UCST gel;

[0097] Step 6: Dry, grind and granulate the gel in step 5 to prepare UCST gel particles for profile control and water plugging.

[0098] Example 3

[0099] This embodiment provides a method for preparing gel particles for UCST profile control and water plugging:

[0100] Step 1: Weigh 0.67 g of methacrylamide and dissolve it in 2 mL of deionized water, and stir it magnetically at 60 ° C for 60 minutes to make it dissolve evenly, to obtain a methacrylamide monomer aqueous solution;

[0101] Step 2: Weigh 0.4 g N,N-dimethylacrylamide and 2 ml dimethyl sulfoxide and dissolve them in 2 mL deionized water, and stir them magnetically at 60 °C for 100 min to make them dissolve evenly to obtain an organic solution;

[0102] Step 3: Add 25 mg of crosslinking agent methylene bisacrylamide and 25 mg of initiator 2,2-diethoxyacetophenone to the solutions prepared in step 1 and step 2, respectively, and stir them magnetically at 60 °C for 30 min to dissolve them uniformly, to obtain hydrogel precursor solution A and gel precursor solution B;

[0103] Step 4: Pour the hydrogel precursor solution A obtained in step 3 into a circular mold and polymerize it under 365UV light for 6 hours to obtain hydrogel A;

[0104] Step 5: Soak the hydrogel A obtained in step 4 in the gel precursor solution B prepared in step 3 for 48 hours and photoinitiate polymerization for 2 hours to obtain UCST gel;

[0105] Step 6: Dry, grind and granulate the gel in step 5 to obtain UCST gel particles for profile control and water plugging.

[0106] Example 4

[0107] This embodiment provides a method for preparing gel particles for UCST profile control and water plugging:

[0108] Step 1: Weigh 1 g of methacrylamide and dissolve it in 2 mL of deionized water, and stir it magnetically at 60 °C for 60 min to make it dissolve evenly, to obtain a methacrylamide monomer aqueous solution;

[0109] Step 2: Weigh 0.4 g of N,N-dimethylacrylamide in 4 mL of deionized water, and stir magnetically at 40 °C for 60 min to dissolve the monomer evenly, to obtain an N,N-dimethylacrylamide aqueous solution;

[0110] Step 3: Add 25 mg of crosslinking agent methylene bisacrylamide and 25 mg of initiator 2,2-diethoxyacetophenone to the solutions prepared in step 1 and step 2, respectively, and stir them magnetically at 60 °C for 30 min to dissolve them uniformly, to obtain hydrogel precursor solution A and gel precursor solution B;

[0111] Step 4: Pour the hydrogel precursor solution A obtained in step 3 into a circular mold and polymerize it under 365UV light for 6 hours to obtain hydrogel A;

[0112] Step 5: Soak the hydrogel A obtained in step 4 in the gel precursor solution B prepared in step 3 for 24 hours and photoinitiate polymerization for 4 hours to obtain UCST gel;

[0113] Step 6: Dry, grind and granulate the gel obtained in step 5 to obtain UCST gel particles for profile control and water plugging.

[0114] Example 5

[0115] This embodiment provides a method for preparing gel particles for UCST profile control and water plugging:

[0116] Step 1: Weigh 0.5 g of acrylamide and dissolve it in 2 mL of deionized water, and stir it magnetically at 60 ° C for 60 min to make it dissolve evenly, to obtain a methacrylamide monomer aqueous solution;

[0117] Step 2: Weigh 0.2 g of N,N-dimethylacrylamide and 2 ml of dimethyl sulfoxide and dissolve them in 2 mL of deionized water, and stir them magnetically at 40 °C for 60 min to uniformly dissolve the monomers to obtain an organic solution;

[0118] Step 3: Add 25 mg of crosslinking agent methylene bisacrylamide and 25 mg of initiator 2,2-diethoxyacetophenone to the solutions prepared in step 1 and step 2, respectively, and stir them magnetically at 60 °C for 30 min to dissolve them uniformly, to obtain hydrogel precursor solution A and gel precursor solution B;

[0119] Step 4: Pour the gel precursor solution A obtained in step 3 into a circular mold and polymerize it under 365UV light for 6 hours to obtain hydrogel A;

[0120] Step 5: Soak the hydrogel A obtained in step 4 in the gel precursor solution B prepared in step 3 for 24 hours and photoinitiate polymerization for 4 hours to obtain UCST gel;

[0121] Step 6: Dry, grind and granulate the gel obtained in step 5 to obtain UCST gel particles for profile control and water plugging.

[0122] Example 6

[0123] This embodiment provides a method for preparing gel particles for UCST profile control and water plugging:

[0124] Step 1: Weigh 0.5 g of isopropyl acrylamide and dissolve it in 2 mL of deionized water, and stir it magnetically at 60 ° C for 60 minutes to make it dissolve evenly, to obtain a methacrylamide monomer aqueous solution;

[0125] Step 2: Weigh 0.4 g of N,N-dimethylacrylamide and 2 ml of dimethyl sulfoxide and dissolve them in 2 mL of deionized water, and stir them magnetically at 40 °C for 60 min to uniformly dissolve the monomers to obtain an organic solution;

[0126] Step 3: Add 25 mg of crosslinking agent methylene bisacrylamide and 25 mg of initiator 2,2-diethoxyacetophenone to the solutions prepared in step 1 and step 2, respectively, and stir them magnetically at 60 °C for 30 min to dissolve them uniformly, to obtain hydrogel precursor solution A and gel precursor solution B;

[0127] Step 4: Pour the gel precursor solution A obtained in step 3 into a circular mold and polymerize it under 365UV light for 6 hours to obtain hydrogel A;

[0128] Step 5: Soak the hydrogel A obtained in step 4 in the gel precursor solution B prepared in step 3 for 24 hours and photoinitiate polymerization for 6 hours to obtain UCST gel;

[0129] Step 6: Dry, grind and granulate the gel obtained in step 5 to obtain the UCST gel particles for profile control and water plugging.

[0130] Example 7

[0131] This embodiment provides a method for preparing gel particles for UCST profile control and water plugging:

[0132] Step 1: Weigh 0.5 g of methacrylamide and dissolve it in 2 mL of deionized water, and stir it magnetically at 60 ° C for 60 minutes to make it dissolve evenly, to obtain a methacrylamide monomer aqueous solution;

[0133] Step 2: Weigh 0.6 g of N-hydroxymethyl acrylamide, 1 ml of N,N-dimethyl acrylamide and 1 ml of acrylic acid and dissolve them in 2 mL of deionized water, and stir them magnetically at 40 °C for 60 min to evenly dissolve the monomers to obtain an organic solution;

[0134] Step 3: Add 25 mg of crosslinking agent methylene bisacrylamide and 25 mg of initiator 2,2-diethoxyacetophenone to the solutions prepared in step 1 and step 2, respectively, and stir them magnetically at 60 °C for 30 min to dissolve them uniformly, to obtain hydrogel precursor solution A and gel precursor solution B;

[0135] Step 4: Pour the hydrogel precursor solution A obtained in step 3 into a circular mold and polymerize it under 365UV light for 6 hours to obtain hydrogel A;

[0136] Step 5: Soak the hydrogel A obtained in step 4 in the gel precursor solution B prepared in step 3 for 24 hours and photoinitiate polymerization for 4 hours to obtain UCST gel;

[0137] Step 6: Dry, grind and granulate the gel obtained in step 5 to obtain the UCST gel particles for profile control and water plugging.

[0138] Example 8

[0139] This embodiment provides a method for preparing gel particles for UCST profile control and water plugging:

[0140] Step 1: Weigh 0.5 g of methacrylamide and dissolve it in 2 mL of deionized water, and stir it magnetically at 60 ° C for 60 minutes to make it dissolve evenly, to obtain a methacrylamide monomer aqueous solution;

[0141] Step 2: Weigh 0.6 g of isopropyl acrylamide, 1 g of N-hydroxymethyl acrylamide and 1 ml of acrylic acid, dissolve them in 2 mL of deionized water, and stir them magnetically at 40 °C for 60 min to uniformly dissolve the monomers to obtain a monomer solution;

[0142] Step 3: Add 25 mg of crosslinking agent methylene bisacrylamide and 25 mg of initiator 2,2-diethoxyacetophenone to the solutions prepared in step 1 and step 2, respectively, and stir them magnetically at 60 °C for 30 min to dissolve them uniformly, to obtain hydrogel precursor solution A and gel precursor solution B;

[0143] Step 4: Pour the gel precursor solution A obtained in step 3 into a circular mold and polymerize it under 365UV light for 6 hours to obtain a hydrogel;

[0144] Step 5: Soak the hydrogel A obtained in step 4 in the gel precursor solution B prepared in step 3 for 24 hours and photoinitiate polymerization for 6 hours to obtain UCST gel;

[0145] Step 6: Dry, grind and granulate the gel obtained in step 5 to obtain the UCST gel particles for profile control and water plugging.

[0146] Comparative Example 1

[0147] A gel particle for profile control and water plugging, which differs from Example 3 in that step 2 and step 5 are omitted, and other substances, dosages and preparation methods are the same as those in Example 3:

[0148] Step 1: Weigh 0.67 g of methacrylamide and dissolve it in 2 mL of deionized water, and stir it magnetically at 60 ° C for 60 minutes to make it dissolve evenly, to obtain a methacrylamide monomer aqueous solution;

[0149] Step 2: Add 25 mg of crosslinking agent methylene bisacrylamide and 25 mg of initiator 2,2-diethoxyacetophenone to the solution prepared in step 1, and stir magnetically at 60 °C for 30 min to dissolve them uniformly to obtain a hydrogel precursor solution A;

[0150] Step 3: Pour the hydrogel precursor solution A obtained in step 2 into a circular mold and polymerize it under 365UV light for 6 hours to obtain hydrogel A;

[0151] Step 4: Dry, grind and granulate the hydrogel A in step 3 to obtain gel particles for profile control and water plugging.

[0152] Comparative Example 2

[0153] A gel particle for profile control and water plugging, which is different from Example 3 in that the hydrogen bond donor and the hydrogen bond acceptor are directly mixed, and the copolymer single network gel is prepared by a one-pot method, and the dosage and reaction method are the same as those in Example 3:

[0154] Step 1: Weigh 0.67 g of methacrylamide and dissolve it in 2 mL of deionized water, and stir it magnetically at 60 ° C for 60 minutes to make it dissolve evenly, to obtain a methacrylamide monomer aqueous solution;

[0155] Step 2: Weigh 0.4 g N,N-dimethylacrylamide and 2 ml dimethyl sulfoxide and dissolve them in 2 mL deionized water, and stir them magnetically at 60 °C for 100 min to make them dissolve evenly to obtain an organic solution;

[0156] Step 3: The solutions obtained in step 1 and step 2 were mixed evenly, 50 mg of cross-linking agent methylene bisacrylamide and 50 mg of initiator 2,2-diethoxyacetophenone were added, and magnetic stirring was performed at 60 ° C for 30 min to make them dissolve evenly, to obtain a gel precursor solution;

[0157] Step 4: Pour the gel precursor solution obtained in step 3 into a round mold and polymerize it under 365UV light for 6 hours to obtain a gel;

[0158] Step 5: Dry, grind and granulate the gel in step 4 to obtain gel particles for profile control and water plugging.

[0159] In order to illustrate that the gel particles provided in this application have the effect of profile control and water plugging, the following performance experiments are conducted:

[0160] (1) Swelling properties

[0161] The schematic diagram of high temperature slow expansion of UCST gel particles prepared in Example 3 is as follows Figure 1 As shown;

[0162] The water absorption expansion multiple of the gel particles will increase with the increase of water contact time, but because there are multiple hydrogen bond network cross-links in the hydrophilic polymer network, the water absorption expansion multiple of the gel particles remains stable before the hydrogen bonds break. Under the action of high temperature, the hydrogen bond network breaks, and the hydrophilicity of the gel particles slowly increases, which enhances the water absorption performance of the gel particles, thereby extending the swelling time of the gel particles.

[0163] The gel particles prepared in Examples 1-7 and Comparative Examples 1-2 were placed in a high-temperature pressure-resistant tube containing water and swelled at 90°C and 25°C. The water absorption and swelling tests were performed at regular intervals. The swelling performance test results are shown in FIG. Figure 2-11As shown. According to the experimental results, the gel particles of Examples 1-7 have double network gel particles with strong hydrogen bonds, and have obvious swelling differences at low and high temperatures. The hydrophobic effect at low temperatures is conducive to entering the deep oil well for profile control and water plugging; at high temperatures above the UCST transition, the double network gel is transformed from a hydrophobic network to a hydrophilic network. When the specified formation temperature is reached, the gel absorbs a large amount of water and expands, forming a plug for the high permeability layer of the formation, achieving the purpose of profile control and improving the water injection oil recovery rate.

[0164] The results of Comparative Examples 1-2 are as follows Fig.10 and Fig.11 As shown, the results show that the single network gel in comparative example 1 fails to have a good hydrophobic effect at low temperatures, causing the gel to absorb water and swell, forming a blockage before entering the formation where the profile adjustment is required, and cannot effectively improve the water injection and oil recovery problem. Comparative example 2 shows a partial water absorption inhibition effect at low temperatures, and the water absorption and swelling at high temperatures are not much different from the water absorption and swelling at low temperatures. This is because the copolymer linear network formed by the one-pot method fails to have a large number of hydrogen bonds between polymers, and the polymer chain also exposes a large number of hydrophilic groups at low temperatures, resulting in insufficient hydrophobic effect.

[0165] (2) Effect of the content of multi-hydrogen bond donor monomer on the water absorption and swelling ratio of gel particles

[0166] The gel particles were prepared by changing the amount of the multi-hydrogen bond donor monomer methacryloyl in step 1 of Example 3 (0.35 g, 0.5 g, 0.67 g, and 1 g were added respectively), and swelled to the maximum equilibrium swelling at different temperatures. The water absorption expansion multiples were tested. The test results are as follows: Fig.12 As shown:

[0167] according to Fig.12 It can be seen that different monomer masses have a significant effect on the transition point of the gel. The number of hydrogen bonds between the two polymers and the cross-linking network density of the monomers affect the final swelling multiple and the UCST transition temperature. When the monomer mass of the hydrogen bond donor is close to the mass of the hydrogen bond acceptor, it has better expansion performance and a higher temperature transition point.

[0168] (3) Effect of hydrogen bond acceptor monomer content on the water absorption and swelling ratio of gel particles

[0169] The gel particles were prepared by changing the amount of the multi-hydrogen bond acceptor monomer N,N-dimethylacrylamide in step 2 of Example 3 (0.2 g, 0.4 g, 0.6 g, 0.8 g, and 1 g were added respectively), and swelled to the maximum equilibrium swelling at different temperatures. The water absorption expansion multiples were tested. The test results are as follows: Fig.13 Show:

[0170] according to Fig.13It can be seen that different multi-hydrogen bond acceptor monomer masses have a significant effect on the UCST (upper critical solution temperature) transition point of the gel, but have little difference in the final swelling rate; therefore, the multi-hydrogen bond acceptor monomer mass has a significant effect on the UCST transition point and swelling response time of the gel, but has little effect on the final swelling rate. The final swelling multiple of the gel mainly depends on the content of the multi-hydrogen bond donor.

[0171] Fig.14 and 15 The swelling photos can clearly show the changes in the transmittance and volume of the gel. Before swelling and at low temperature, it remains in a white hydrophobic state, and after high temperature swelling, it becomes a hydrophilic network with better transmittance.

[0172] (4) Mechanical properties

[0173] The amount of the multi-hydrogen bond donor monomer methacryloyl in step 1 of Example 3 was changed (0.35 g, 0.5 g, 0.67 g, and 1 g were added respectively) to prepare the gel particles, and the above gel particles were made into gel blocks with a diameter of 2 cm and a height of 1 cm, and the compression test was carried out by a universal testing machine. The test results are as follows: Figure 16-17 shown; according to Fig.16 It can be seen from the stress-strain curve that the more hydrogen bond donor monomers there are in the bulk expanded particles, the higher the mechanical strength is, and the maximum can reach 17.13MPa at 75% strain. Fig.17 The stress of the gel particles with 1g of monomer added after expansion is 0.713MPa under a strain of 75%, and the swollen gel maintains continuous compression with a strain of up to 80%, indicating that the gel particles have a high mechanical strength before expansion and are not easily damaged during transportation in the formation. After expansion, the gel particles still maintain a certain mechanical strength and can effectively block the hyperpermeability channels.

[0174] (5) Rheological properties

[0175] The gel particles obtained in Example 3 were prepared into gel blocks with a length of 5 cm, a width of 5 cm, and a height of 2 mm, and temperature scanning was performed under a high temperature rheometer. Fig.18 As shown, the storage modulus and loss modulus decrease at around 80°C, which means that the strong hydrogen bonds in the gel are broken, resulting in a decrease in the two moduli, but the elastic state is always maintained, indicating that the gel has good temperature response performance and good elasticity and can smoothly enter deep into the formation.

[0176] (6) Displacement experiment

[0177] The gel particles obtained in Example 3 were used to conduct a simulation test of plugging in a crack in a stainless steel core with a crack opening of 2 mm, a crack width of 10 mm, and a crack length of 50 mm. The gel particles that passed through a 200-mesh sieve were selected and prepared into a 10% aqueous solution by mass. The solution was transported into the crack through a displacement device and maintained at 100°C for 7 days. The displacement experiment was then conducted to measure the breakthrough pressure of the plugging. The experimental results are shown in Figure 2. Fig.19 As shown, it is shown that the gel particles prepared by the present invention can achieve deep profile control and water plugging.

[0178] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing UCST gel particles for profile control and water plugging, characterized in that: The following steps are included: a: adding a multi-hydrogen bond donor monomer into water and stirring evenly to obtain a multi-hydrogen bond donor monomer aqueous solution with a molar concentration of 1 mol / L-6 mol / L; b: adding a multi-hydrogen bond acceptor monomer to a solvent, stirring evenly to obtain a multi-hydrogen bond acceptor monomer solution with a molar concentration of 1 mol / L to 8 mol / L; c: adding a crosslinking agent and an initiator to the multi-hydrogen bond donor monomer aqueous solution and the multi-hydrogen bond acceptor monomer solution respectively, and stirring them evenly to obtain a hydrogel precursor solution A and a gel precursor solution B; d: polymerizing the solution A to obtain hydrogel A; e: soaking the hydrogel A in solution B for 16-72 hours to polymerize to obtain UCST gel, and then drying, grinding and granulating in sequence to obtain UCST gel particles for profile control and water plugging; The molar ratio of the multi-hydrogen bond donor monomer to the multi-hydrogen bond acceptor monomer is 1:(0.2-4); The polymerization method of the solution A is photo-induced polymerization.

2. The method for preparing UCST gel particles for profile control and water plugging according to claim 1, characterized in that: The multi-hydrogen bond donor monomer is selected from amide compounds.

3. The method for preparing UCST gel particles for profile control and water plugging according to claim 1, characterized in that: The multi-hydrogen bond acceptor monomer is selected from amide compounds and / or carboxylic acid compounds.

4. The method for preparing UCST gel particles for profile control and water plugging according to claim 1, characterized in that: The polymerization time of the solution A to obtain the hydrogel A is 1-5 hours.

5. The method for preparing UCST gel particles for profile control and water plugging according to claim 2, characterized in that: The multi-hydrogen bond donor monomer is selected from at least one of methacrylamide, acrylamide and isopropylacrylamide.

6. The method for preparing UCST gel particles for profile control and water plugging according to claim 3, characterized in that: The multi-hydrogen bond acceptor monomer is selected from at least one of isopropyl acrylamide, N,N-dimethyl acrylamide, N-hydroxymethyl acrylamide and acrylic acid.

7. The method for preparing UCST gel particles for profile control and water plugging according to claim 1, characterized in that: The solvent in step b is water, an organic solution or a mixture of water and an organic solution.

8. The method for preparing UCST gel particles for profile control and water plugging according to claim 1, characterized in that: The stirring speeds of steps a, b and c are respectively 200-1000 r / min.

9. UCST gel particles for profile control and water plugging, the gel particles being prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the UCST gel particles for profile control and water plugging as claimed in claim 9 in oil and water wells.

Images