Novel dual-network anti-shearing gel microsphere modifying and flooding agent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of modifying and flooding agents, in particular to a novel dual-network anti-shearing gel microsphere modifying and flooding agent and a preparation method and application thereof, and the novel dual-network anti-shearing gel microsphere modifying and flooding agent comprises amphiphilic starch, acrylamide, allyl beta-cyclodextrin, a cross-linking agent, an initiator, a surfactant and distilled water. According to the novel dual-network anti-shearing gel microsphere profile control and flooding agent adopting the components and the preparation method and application thereof, a three-dimensional structure in the formed profile control agent comprises a physical cross-linked structure and a covalent cross-linked structure, a starch chain is slightly rigid, an olefin chain is slightly flexible, and the strength of the three-dimensional network structure is improved through the synergistic effect of the starch chain and the olefin chain. A physical cross-linked structure generated by hydrophobic groups on the amphiphilic starch and the allyl beta-cyclodextrin can be broken under the high-shear action to release stress, when the high-shear action is reduced, the hydrophobic groups and the allyl beta-cyclodextrin can be cross-linked again, and the dynamic cross-linking characteristic can improve the shear failure resistance of the microsphere modifying and flooding agent.

Description

Technical Field

[0001] The present invention relates to the technical field of flooding agents, and in particular to a novel double-network shear-resistant gel microsphere flooding agent, a preparation method thereof, and an application thereof. Background Art

[0002] Profile control involves mechanically or chemically limiting or reducing the water absorption capacity of high-permeability zones or sections of water injection wells. This approach adjusts the water absorption profile of the wells and, in turn, improves the waterflood sweep volume. The core material used in this process is a profile control agent. Most oilfields utilize waterflooding for development. Long-term waterflooding can exacerbate formation heterogeneity, leading to water production or flooding in oil wells, severely reducing oilfield production. Relying solely on injection-production control measures to increase oil production is extremely limited. Therefore, water plugging and profile control technology is widely used in oilfields to increase oil production and reduce water loss.

[0003] Profile control agents are chemical additives used in oilfield development, primarily to improve fluid distribution during water or gas injection, thereby increasing the swept volume and recovery rate of a reservoir. Currently, the most widely used plugging agents are chemically cross-linked gel profile control systems, such as gels, pre-cross-linked gel particles, and weak gels. After absorbing water and swelling, gel particles possess a certain degree of deformation capacity. Under a certain pressure differential, they can deform and migrate deep into the formation. Deep within the formation, as formation pressure gradually decreases, the particles continue to absorb water and swell, becoming trapped in large pores and blocking them, thereby adjusting formation permeability and redirecting deep fluid flow. However, during on-site injection construction and deep migration within complex reservoirs, fully hydrated and swollen gel particles can break due to shear and extrusion, making them easily washed out by subsequently injected fluids. This can lead to unstable or poor fracture sealing capabilities and deep profile control effects. Summary of the Invention

[0004] The purpose of the present invention is to provide a novel double-network shear-resistant gel microsphere flooding agent, its preparation method and application. The physical cross-linking structure of the microsphere flooding agent can be broken under high shear to release stress, and can be cross-linked again when the high shear effect is reduced. The shear resistance of the microsphere flooding agent is improved through dynamic cross-linking.

[0005] To achieve the above objectives, the present invention provides a novel double-network shear-resistant gel microsphere flooding agent and its preparation method and application, comprising amphiphilic starch, acrylamide, propylene β-cyclodextrin, a crosslinking agent, an initiator, a surfactant and distilled water.

[0006] Preferably, the surfactant includes one or more of Span-80, Tween-20, sodium lauryl sulfate, and cetyltrimethylammonium bromide.

[0007] The preparation method of the novel double-network anti-shear gel microsphere flooding agent comprises the following steps:

[0008] S1. Preparation of amphiphilic starch: dissolving starch in water and adjusting the pH to greater than 10, heating to 80-100° C., and maintaining the temperature for 1-3 hours to obtain a starch solution, adding a modifier dropwise to the starch solution after cooling, stirring at a constant temperature, adjusting the pH to 7, and cooling to obtain a starch paste, dropping the starch paste into a precipitant for precipitation, and washing and drying the solid after centrifugation to obtain the amphiphilic starch;

[0009] S2. Preparation of propenyl β-cyclodextrin: dissolving β-cyclodextrin in N,N-dimethylformamide, adding sodium hydride with stirring under a water bath, then adding 3-bromopropylene dropwise to react to obtain a reaction solution, dispersing the reaction solution in acetone at room temperature, filtering, washing with ethanol, and purifying to obtain propenyl β-cyclodextrin;

[0010] S3, preparation of oil phase: dissolve the surfactant in kerosene, stir evenly under a constant temperature water bath to obtain the oil phase for later use;

[0011] S4, preparation of aqueous phase: dissolving the amphiphilic starch prepared in S1, the propylene β-cyclodextrin prepared in S2, acrylamide, a crosslinking agent and an initiator in distilled water in sequence, stirring at room temperature to obtain an aqueous phase for later use;

[0012] S5. Under nitrogen protection, pour the aqueous phase in S4 into the oil phase in S3, stir at high speed to obtain an emulsion, reduce the speed to 800 r / min and then heat to 45-60°C, react for 10-15 hours, stop stirring, and cool to room temperature to obtain a microsphere displacement agent.

[0013] Preferably, in S1, the modifier includes one or more of hexadecyl glycidyl ether, tetradecyl glycidyl ether, dodecyl glycidyl ether, stearic anhydride, hexadecanol, octadecyl alcohol and palmitic acid.

[0014] Preferably, in S1, the volume ratio of the precipitant to the starch paste is 3-5:1, and the dropping rate of the starch paste is 20-40 mL / min.

[0015] Preferably, in S1, the precipitant is one of anhydrous ethanol, isopropanol, methanol, acetone, ethyl acetate and n-butanol.

[0016] Preferably, in S2, the temperature of the water bath is 0°C, and the purification is performed by adding the ethanol-washed product dropwise into acetone, and repeating the purification 2-5 times.

[0017] Preferably, in S3, the surfactant is a mixture of Span-80 and Tween-20 in a volume ratio of 1:0.5-2.

[0018] Preferably, in S4, the mass ratio of the amphiphilic starch prepared in S1, the propylene β-cyclodextrin prepared in S2, and acrylamide is 1:1:1.

[0019] Preferably, in S5, the high-speed shear stirring is performed at a rotation speed of 1300-1600 r / min and for a time of 20-50 min.

[0020] The above-mentioned new type of double-network shear-resistant gel microsphere displacement agent is used for profile control and displacement control in heterogeneous high water-content oil fields.

[0021] Therefore, the present invention adopts the above-mentioned novel double-network shear-resistant gel microsphere flooding agent and its preparation method and application. The obtained microsphere flooding agent includes a physical cross-linking structure between the hydrophobic groups on the amphiphilic starch and propylene β-cyclodextrin, and a covalent cross-linking structure between the amphiphilic starch, acrylamide, propylene β-cyclodextrin, and N,N'-methylenebisacrylamide.

[0022] In the three-dimensional structure formed by physical cross-linking structure and covalent cross-linking structure, starch chains are relatively rigid and olefin chains are relatively flexible. The synergistic effect of starch chains and olefin chains improves the strength of the three-dimensional network structure. The physical cross-linking structure generated by the hydrophobic groups on the amphiphilic starch and propylene β-cyclodextrin can be broken under high shear to release stress. When the high shear effect is reduced, the hydrophobic groups on the amphiphilic starch and propylene β-cyclodextrin can be cross-linked again. This dynamic cross-linking feature can improve the shear damage resistance of the microsphere displacement agent.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the infrared spectrum of the amphiphilic starch and starch in Example 1 of the present invention;

[0025] Figure 2 is the infrared spectrum of propenyl β-cyclodextrin and β-cyclodextrin in Example 1 of the present invention;

[0026] Figure 3 This is the infrared spectrum of the microsphere displacement agent in Example 1 of the present invention;

[0027] Figure 4 This is an electron microscope image of the microsphere displacement agent in Example 1 of the present invention;

[0028] Figure 5 is a particle size distribution diagram of the microsphere displacement agent in Example 1 of the present invention;

[0029] Figure 6 It is a schematic diagram of the physical simulation displacement experimental device;

[0030] Figure 7 This is a graph showing the injection pressure-time curve of the microsphere displacement agent in Example 1 of the present invention;

[0031] Figure 8 This is a graph showing the injection pressure-time curve of conventional acrylamide gel microspheres in Comparative Example 1 of the present invention;

[0032] Figure 9 is an SEM image of the double-crosslinked starch gel in Comparative Example 2 of the present invention;

[0033] Figure 10 This is a comparison chart of the particle size of the microsphere displacement agent before and after shearing in Example 1 of the present invention;

[0034] Figure 11 This is a comparison chart of the pressure difference of the microsphere displacement agent breaking through the microporous filter membrane before and after shearing in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to the accompanying drawings and examples. Unless otherwise defined, technical or scientific terms used herein shall have the same meanings as those commonly understood by persons of ordinary skill in the art to which the present invention pertains. The above-mentioned features or features described in the specific examples of the present invention may be combined in any manner. These specific examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention.

[0036] Example 1

[0037] S1. Preparation of amphiphilic starch: 5 g of starch was dissolved in 100 mL of distilled water, and NaOH solution was added dropwise to adjust the pH to greater than 10. The mixture was heated to 90° C. and kept at this temperature for 2 h to obtain a starch solution.

[0038] The starch solution was cooled to 45°C and 15 mL of the modifier hexadecyl glycidyl ether was added dropwise to the solution. The mixture was stirred at a constant temperature for 24 hours. The pH was adjusted to 7 with hydrochloric acid and then cooled to obtain a starch paste. The starch paste was then added dropwise to 3-5 volumes of anhydrous ethanol as a precipitant at a rate of 30 mL / min. The solid after centrifugation was washed with anhydrous ethanol and dried to obtain an amphiphilic starch.

[0039] S2. Preparation of Propylene β-cyclodextrin: Dissolve 3 g of β-cyclodextrin in 40 mL of N,N-dimethylformamide. Add 0.3 g of sodium hydride in a 0°C water bath and stir for 45 minutes. Then, add 1 mL of 3-bromopropene dropwise and allow to react for 7 hours to obtain a reaction solution. Warm the mixture to room temperature and disperse it in 400 mL of acetone at room temperature. Filter, wash with ethanol, and then purify the mixture by repeatedly adding the solution dropwise to 400 mL of acetone three times to obtain a white solid of propenyl β-cyclodextrin.

[0040] S3. Preparation of oil phase: surfactants Span-80 and Tween-20 were mixed in a volume ratio of 1:0.5-2, dissolved in 50 mL of kerosene, and stirred evenly in a constant temperature water bath at 45° C. to obtain an oil phase for later use.

[0041] S4. Preparation of aqueous phase: 2 g of the amphiphilic starch prepared in S1, 2 g of the propylene β-cyclodextrin prepared in S2, 2 g of acrylamide, 0.2 g of cross-linking agent N,N'-methylenebisacrylamide and 0.1 g of initiator ammonium persulfate were dissolved in 20 mL of distilled water in sequence, and stirred at room temperature to obtain an aqueous phase for use.

[0042] S5. Under nitrogen protection, pour the aqueous phase in S4 into the oil phase in S3, and stir at a high speed of 1500 r / min for 30 min to obtain an emulsion. After reducing the speed to 800 r / min, raise the temperature to 50°C to carry out a free radical-initiated polymerization reaction. Stop stirring after 12 h of reaction, and cool to room temperature to obtain a microsphere displacement agent.

[0043] Comparative Example 1

[0044] Mix 6 mL of Span-80 and 6 mL of Tween-20 evenly, dissolve in 50 mL of kerosene, pour into a 250 mL three-necked flask, stir and mix in a constant temperature water bath at 45°C, and use as the oil phase for inverse emulsion polymerization.

[0045] Weigh 6g acrylamide, 0.2g N,N'-methylenebisacrylamide, and 0.1g ammonium persulfate and dissolve them in 20mL of distilled water, stirring them thoroughly at room temperature to prepare the aqueous phase. Pour the aqueous phase into the oil phase under nitrogen protection at a speed of approximately 1500 rpm. Continue high-speed shear stirring for 30 minutes. Once the emulsion is fully formed, reduce the speed to 800 rpm and heat to 50°C for free radical-initiated polymerization. After 12 hours, stop stirring and cool to room temperature. The reaction is complete, forming conventional acrylamide gel microspheres.

[0046] Comparative Example 2

[0047] Preparation of double cross-linked starch gel:

[0048] 2 g of amphiphilic starch, 2 g of propylene β-cyclodextrin, 2 g of acrylamide, 0.2 g of N,N'-methylenebisacrylamide, and 0.1 g of ammonium persulfate were dissolved in 20 mL of distilled water in sequence, stirred evenly at room temperature, and heated to 50 °C for free radical-initiated polymerization. The reaction was completed after 12 h to form a double-crosslinked starch gel with a double-crosslinked structure.

[0049] Test Example 1

[0050] a. Infrared spectrum test of starch and amphiphilic starch

[0051] Depend on Figure 1 It can be seen that there are three main changes in the infrared spectrum of amphiphilic starch compared with starch: First, at 3300cm -1The stretching vibration peak of the hydroxyl group at 2900 cm-1 shifted to the left. -1 The stretching vibration peak of the methylene group at 1050cm -1 The absorption peak at was enhanced, indicating that the hydrophobic alkane chain was introduced into the starch structure.

[0052] b. Infrared spectrum test of β-cyclodextrin and propylene β-cyclodextrin

[0053] from Figure 2 It can be seen that at 3400cm -1 At 3050cm -1 At 1650cm -1 At 1050cm, it is the stretching vibration absorption peak of C=C bond; at 1050cm -1 It is the vibration absorption peak of C-O on the β-cyclodextrin molecule, and the propene group has been successfully bonded to the β-cyclodextrin molecule.

[0054] c. Infrared spectrum test of microsphere flooding agent

[0055] Combine Figure 1 、 Figure 2 and Figure 3 It can be seen that the microsphere flooding agent contains propylene β-cyclodextrin molecules, amphiphilic starch molecules and acrylamide chains.

[0056] d, SEM and particle size distribution

[0057] like Figure 4 As shown, it can be seen that the microsphere control agent has good sphericity. Since the three-dimensional network structure of the microsphere control agent is difficult to observe, the comparative example 2 with the same components is used as the object to observe the characteristics of the covalent cross-linked structure. Figure 9 As shown, the double-crosslinked starch gel in Comparative Example 2 has both a lamellar network structure and a wired network structure, and the formed microstructure is denser and tighter, and the microstructure layers are more obvious.

[0058] 5 mL of the prepared microsphere displacement agent was sampled and dissolved in 20 mL of distilled water. The particle size was measured and the obtained particle size distribution diagram was shown as follows: Figure 5 As shown, the particle size distribution of the microsphere displacement agent is 30-120 μm, and the main particle size is 60 μm.

[0059] e. Migration characteristics test of microsphere flooding agent and conventional acrylamide gel microspheres in 50mD sand filling pipe

[0060] Use as Figure 6The migration characteristics test was performed using the physical simulation displacement experimental device shown. The sand filling pipe in the simulation displacement experimental device has a Z-shaped structure. Pressure measuring point 1 is located at the entrance of the sand filling pipe, and pressure measuring points 2 and 3 are located at the two inflection points of the sand filling pipe, respectively. The distances between pressure measuring point 1 and pressure measuring point 2, and between pressure measuring point 2 and pressure measuring point 3 are both 1 m, and the diameter of the sand filling pipe is 2.5 cm.

[0061] The migration characteristics of the microsphere displacement agent in Example 1 and the conventional acrylamide gel microspheres in Comparative Example 1 in a sand-filled pipe with a permeability of 50 mD were tested. The injection rate during the test was 0.2 mL / min, and the injection was continued until the pressure at the three pressure measuring points stabilized and the displacement experiment was stopped.

[0062] The test results of microsphere flooding agent in porous media with a permeability of 50mD are as follows: Figure 7 As shown, the injection pressure at pressure measuring point 1 is 15 MPa, the injection pressure at pressure measuring point 2 is 10 MPa, and the injection pressure at pressure measuring point 3 is 5 MPa. The pressure gradient between pressure measuring points 1 and 2 is 5 MPa / m, the pressure gradient between pressure measuring points 2 and 3 is 5 MPa / m, and the pressure gradient between pressure measuring point 3 and the outlet is 5 MPa / m.

[0063] The test results of conventional acrylamide gel microspheres in a porous medium with a permeability of 50 mD in Comparative Example 1 are as follows: Figure 8 It can be seen that the injection pressure at pressure measuring point 1 is 10.5 MPa, the injection pressure at pressure measuring point 2 is 7 MPa, and the injection pressure at pressure measuring point 3 is 3.5 MPa. The pressure gradient between pressure measuring points 1 and 2 is 3.5 MPa / m, the pressure gradient between pressure measuring points 2 and 3 is 3.5 MPa / m, and the pressure gradient between pressure measuring point 3 and the outlet is 3.5 MPa / m.

[0064] In summary, the microsphere flooding agent in Example 1 has a stronger plugging ability in a porous medium with a permeability of 50 mD than the conventional acrylamide gel microspheres in Comparative Example 1.

[0065] f. Microporous membrane pressure difference experiment

[0066] The microsphere displacement agent in Example 1 was subjected to a microporous membrane pressure difference experiment. A 300 mg / L microsphere displacement agent solution was prepared with distilled water and the rheometer was used to measure the pressure difference at 100 s. -1 The particles were sheared for 24 hours, and then the particle size and the pressure through the microporous membrane were measured. The particle size test results before and after shearing are as follows: Figure 10 As shown in the figure, the test results of the microporous membrane before and after shearing are as follows Figure 11 As shown, the results hardly change.

[0067] Therefore, the present invention adopts the above-mentioned novel double-network shear-resistant gel microsphere flooding agent and its preparation method and application, including a physical cross-linking structure and a covalent cross-linking structure. In the three-dimensional structure formed by the two, the starch chain is relatively rigid and the olefin chain is relatively flexible. The synergistic effect of the starch chain and the olefin chain improves the strength of the three-dimensional network structure. The physical cross-linking structure generated by the hydrophobic groups on the amphiphilic starch and the propylene β-cyclodextrin can be broken under high shear to release stress and improve the shear resistance of the microsphere flooding agent.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A new type of double-network shear-resistant gel microsphere flooding agent, characterized by: The invention comprises amphiphilic starch, acrylamide, propylene beta-cyclodextrin, a cross-linking agent, an initiator, a surfactant and distilled water.

2. The novel double-network shear-resistant gel microsphere flooding agent according to claim 1, characterized in that: The surfactant includes one or more of Span-80, Tween-20, sodium lauryl sulfate, and cetyltrimethylammonium bromide.

3. The method for preparing a novel double-network shear-resistant gel microsphere flooding agent according to any one of claims 1-2, characterized in that: The following steps are included: S1. Preparation of amphiphilic starch: dissolving starch in water and adjusting the pH to greater than 10, heating to 80-100° C., and maintaining the temperature for 1-3 hours to obtain a starch solution, adding a modifier dropwise to the starch solution after cooling, stirring at a constant temperature, adjusting the pH to 7, and cooling to obtain a starch paste, dropping the starch paste into a precipitant for precipitation, and washing and drying the solid after centrifugation to obtain the amphiphilic starch; S2. Preparation of propenyl β-cyclodextrin: dissolving β-cyclodextrin in N,N-dimethylformamide, adding sodium hydride with stirring under a water bath, then adding 3-bromopropylene dropwise to react to obtain a reaction solution, dispersing the reaction solution in acetone at room temperature, filtering, washing with ethanol, and purifying to obtain propenyl β-cyclodextrin; S3, preparation of oil phase: dissolve the surfactant in kerosene, stir evenly under a constant temperature water bath to obtain the oil phase for later use; S4, preparation of aqueous phase: dissolving the amphiphilic starch prepared in S1, the propylene β-cyclodextrin prepared in S2, acrylamide, a crosslinking agent and an initiator in distilled water in sequence, stirring at room temperature to obtain an aqueous phase for later use; S5. Under nitrogen protection, pour the aqueous phase in S4 into the oil phase in S3, stir at high speed to obtain an emulsion, reduce the speed to 800 r / min and then heat to 45-60°C, react for 10-15 hours, stop stirring, and cool to room temperature to obtain a microsphere displacement agent.

4. The method for preparing a novel double-network shear-resistant gel microsphere flooding agent according to claim 3, characterized in that: In S1, the modifier includes one or more of hexadecyl glycidyl ether, tetradecyl glycidyl ether, dodecyl glycidyl ether, stearic anhydride, hexadecanol, octadecyl alcohol and palmitic acid.

5. The method for preparing a novel double-network shear-resistant gel microsphere flooding agent according to claim 3, characterized in that: In S1, the volume ratio of the precipitant to the starch paste is 3-5:1, and the dropping speed of the starch paste is 20-40 mL / min.

6. The method for preparing a novel double-network shear-resistant gel microsphere flooding agent according to claim 3, characterized in that: In S2, the temperature of the water bath is 0°C, and the purification is performed by adding the ethanol-washed product dropwise into acetone, and repeating the purification 2-5 times.

7. The method for preparing a novel double-network shear-resistant gel microsphere flooding agent according to claim 3, characterized in that: In S3, the surfactant is a mixture of Span-80 and Tween-20 in a volume ratio of 1:0.5-2.

8. The method for preparing a novel double-network shear-resistant gel microsphere flooding agent according to claim 3, characterized in that: In S4, the mass ratio of the amphiphilic starch prepared in S1, the propylene β-cyclodextrin prepared in S2, and acrylamide is 1:1:

1.

9. The method for preparing a novel double-network shear-resistant gel microsphere flooding agent according to claim 3, characterized in that: In S5, the high-speed shear stirring is performed at a rotation speed of 1300-1600 r / min for 20-50 min.

10. Use of a novel double-network shear-resistant gel microsphere flooding agent according to any one of claims 1-2, characterized in that: Applied to profile control and flooding control in heterogeneous high water-content oil fields.

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