A self-degrading temporary plugging agent, a preparation method and application thereof

Abstract

The application discloses a self-degradation temporary plugging agent and a preparation method and application thereof. The raw materials of the self-degradation temporary plugging agent are composed of the following components in parts by weight and the total mass is 100 parts: 19.4-20 parts of hydrophilic polymer monomer, 10.5-1 parts of modified nano-particle NP-1, 0.1-0.5 parts of hydrophobic monomer, 0.12-0.2 parts of crosslinking agent, 0.8-1 parts of initiator, and the balance of water; the hydrophilic polymer monomer is acrylamide and / or acrylic acid; the hydrophobic monomer is selected from one or more of cetyl dimethyl allyl ammonium chloride, dimethyl diallyl ammonium chloride and methacryloyloxyethyl trimethyl ammonium chloride; the crosslinking agent is polyethylene glycol diacrylate; and the modified nano-particle NP-1 is nano-SiO2 which is hydrophobically modified by a silane coupling agent. The temporary plugging agent has a certain plugging strength under high pressure difference conditions and can be self-degraded into a low-viscosity solution in a wide temperature range (40-120 DEG C).

Description

Technical Field

[0001] This invention relates to the field of oilfield chemistry, specifically to a self-degrading temporary plugging agent, its preparation method and application, and more specifically to a multifunctional self-degrading temporary plugging agent that can have a certain plugging strength under reservoir conditions and can self-degrade into a low-viscosity solution within a wide temperature range (40℃~120℃), its preparation method and application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] After a period of water injection and extraction, the crude oil controlled by the old fractures in the oil reservoir has been almost completely extracted, and the fractures have become the main water outlets, reducing development efficiency. However, a large amount of residual oil still exists in the matrix. In order to further control water and increase oil production and fully utilize the production capacity of oil wells, a repeated fracturing technology that plugs old fractures and opens new ones is gradually being developed. The essence of repeated fracturing is to selectively enter and plug old fractures with a plugging agent, and then perform fracturing to open new fractures, thereby providing a seepage channel for the untapped residual oil. The implementation of this process requires a high-performance temporary plugging agent.

[0004] Currently, the most commonly used water-soluble temporary plugging agents are ordinary gel particles, and de-plugging is often done using gel breaker agents. This method has the following drawbacks: relatively low plugging strength, uneven gel breaking, and a tendency to form large gel plugs, potentially damaging the reservoir. In recent years, self-degradable temporary plugging agents have been proposed. These agents can disperse well in water or fracturing fluid, maintain a certain plugging strength under high pressure differential conditions, and after a period of time, self-degrade into a low-viscosity solution under reservoir conditions, reducing formation contamination and residue damage. However, existing self-degradable temporary plugging agents still have drawbacks such as difficulty in controlling expansion and degradation times, and uncontrollable temporary plugging strength. Summary of the Invention

[0005] To address the above problems, this invention proposes a self-degradable temporary plugging agent, its preparation method, and its application. This temporary plugging agent can exhibit a certain plugging strength under high pressure differential conditions and can self-degrade into a low-viscosity solution within a wide temperature range (40℃~120℃). It is a multifunctional self-degradable temporary plugging agent, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a self-degradable temporary plugging agent, which, based on a total mass of 100 parts, comprises the following components in parts by weight: 19.4 to 20 parts of hydrophilic polymerizable monomer, 0.5 to 1 part of modified nanoparticles NP-1, 0.1 to 0.5 parts of hydrophobic monomer, 0.12 to 0.2 parts of crosslinking agent, 0.8 to 1 part of initiator, and the balance being water;

[0008] The hydrophilic polymerizable monomer is acrylamide and / or acrylic acid;

[0009] The hydrophobic monomer is selected from one or more of hexadecyl dimethyl allyl ammonium chloride, dimethyl diallyl ammonium chloride, and methacryloyloxyethyl trimethyl ammonium chloride;

[0010] The crosslinking agent is polyethylene glycol diacrylate;

[0011] The modified nanoparticles NP-1 are nano-SiO2 modified with a silane coupling agent through hydrophobic modification.

[0012] Secondly, the present invention provides a method for preparing a self-degrading temporary plugging agent, comprising the following steps:

[0013] The hydrophilic monomer is dissolved in water and the solution is adjusted to a weakly alkaline state to obtain a hydrophilic monomer solution.

[0014] Hydrophobic monomer, modified nanoparticle NP-1 and crosslinking agent are added sequentially to a hydrophilic polymerizable monomer solution, and the mixture is dissolved to obtain a mixed solution;

[0015] An initiator is added to the mixed solution, and the reaction is heated to obtain the product.

[0016] Thirdly, the present invention provides the application of the temporary plugging agent in repeated fracturing of oil reservoirs.

[0017] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0018] Based on reservoir fracture parameters, temporary plugging agent particles of suitable size are selected. Then, according to the injection plan, the particles are dispersed in the injection fluid and rapidly stirred to form a relatively stable suspension. This suspension is then injected into oil and water wells through the work tubing. The plugging agent particles enter the target layer, continue to absorb water and expand rapidly, forming a high-strength temporary plugging layer. After a certain period, once repeated fracturing is completed, it can degrade spontaneously. The injection rate is determined based on the injection pressure. The applicable reservoir temperature range for the temporary plugging agent is 40℃~120℃.

[0019] In this invention, the self-degradation temperature of the temporary plugging agent is 40℃~120℃, which is a wide range and applicable to a wide range of oil reservoirs. In this invention, the self-degrading temporary plugging agent absorbs water and swells at reservoir temperature, maintaining its strength for a period of time. Subsequently, over time, the crosslinking agent fails to crosslink under the influence of reservoir temperature, degrading the temporary plugging agent into a linear polymer, ultimately reducing its viscosity and achieving self-degradation.

[0020] In this invention, the expansion and degradation time of the temporary plugging agent are controllable. In this invention, the temporary plugging agent particles absorb water and expand upon addition to water. Because the hydrophobic monomer contains hydrophobic groups, the water absorption rate and capacity of the temporary plugging agent are reduced, thereby reducing its expansion capacity. Therefore, the expansion performance and expansion rate of the temporary plugging agent can be adjusted by changing the amount of hydrophobic monomer added. In this invention, the crosslinking agent used is polyethylene glycol diacrylate containing ester bonds. These ester bonds break at a certain temperature, destroying the three-dimensional network structure of the temporary plugging agent, ultimately resulting in a low-viscosity solution. Therefore, the crosslinking density of the temporary plugging agent can be adjusted by changing the amount of crosslinking agent added, thereby controlling the self-degradation time of the temporary plugging agent.

[0021] In this invention, the temporary plugging strength of the temporary plugging agent is controllable. The modified nanoparticles in this invention are rich in double bonds on their surface, which can be linked to the framework structure of the temporary plugging agent via free radical polymerization, increasing the stability of the three-dimensional network structure and thus increasing the strength of the temporary plugging agent. Furthermore, as the degree of modification increases, the number of double bonds on the modified nanoparticles increases, which can act as crosslinking agents to connect polymer chains, further increasing the strength of the temporary plugging agent. Therefore, we can control the temporary plugging strength of the temporary plugging agent by adjusting the amount of modified nanoparticles and the degree of modification. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 These are the expansion performance test results of the self-degradable temporary plugging agents prepared in Examples 1-4;

[0024] Figure 2 This is a comparison chart of the elastic modulus of the self-degradable temporary plugging agents prepared in Examples 1-4;

[0025] Figure 3 This is a flowchart of the experimental apparatus for plugging and unplugging the temporary plugging agents prepared in Examples 1-4;

[0026] Figure 4 These are pressure change curves during the plugging process of the temporary plugging agents prepared in Examples 1-4;

[0027] Figure 5 These are pressure change curves during the unblocking process of the temporary plugging agents prepared in Examples 1-4;

[0028] Figure 6 This is a schematic diagram of the structure of the temporary plugging agent prepared in Example 4. Detailed Implementation

[0029] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] In a first aspect, the present invention provides a self-degradable temporary plugging agent, which, based on a total mass of 100 parts, comprises the following components in parts by weight: 19.4 to 20 parts of hydrophilic polymerizable monomer, 0.5 to 1 part of modified nanoparticles NP-1, 0.1 to 0.5 parts of hydrophobic monomer, 0.12 to 0.2 parts of crosslinking agent, 0.8 to 1 part of initiator, and the balance being water;

[0031] The hydrophilic polymerizable monomer is acrylamide and / or acrylic acid;

[0032] The hydrophobic monomer is selected from one or more of hexadecyl dimethyl allyl ammonium chloride, dimethyl diallyl ammonium chloride, and methacryloyloxyethyl trimethyl ammonium chloride;

[0033] The crosslinking agent is polyethylene glycol diacrylate;

[0034] The modified nanoparticles NP-1 are nano-SiO2 modified with a silane coupling agent through hydrophobic modification.

[0035] The hydrophilic groups in the hydrophilic monomers are used to absorb water, causing the temporary plugging agent to swell. The hydrophobic groups in the hydrophobic monomers are used to reduce the water absorption rate and capacity of the temporary plugging agent, thereby inhibiting its swelling. The hydrophilic and hydrophobic groups work together to adjust the swelling properties and rate of the temporary plugging agent.

[0036] The crosslinking agent contains ester bonds, which break at a certain temperature, destroying the three-dimensional network structure of the temporary plugging agent and eventually turning it into a low-viscosity solution. Therefore, the crosslinking density of the temporary plugging agent can be adjusted by changing the amount of crosslinking agent added, thereby controlling the self-degradation time of the temporary plugging agent.

[0037] The main structure of the granular skeleton is an acrylamide structure. The purpose of adding acrylic acid is to increase water absorption and improve expansion performance.

[0038] The monomers hexadecyl dimethyl allyl ammonium chloride, dimethyl diallyl ammonium chloride, and methacryloyloxyethyl trimethyl ammonium chloride have good salt resistance.

[0039] The strength of temporary plugging agents can be controlled in the following ways: The most significant control is through nanoparticles, primarily by adjusting the amount of particles added and the degree of modification. Secondly, it can be controlled by changing the amount of hydrophilic monomers, crosslinking agents, hydrophobic monomers, initiators, reaction temperature, and reaction time. Modified nano-SiO2 has a surface rich in double bonds, which can be linked to the temporary plugging agent's framework structure via free radical polymerization, increasing the stability of the three-dimensional network structure and thus increasing the agent's strength. Furthermore, as the degree of modification increases, the number of double bonds on the modified nanoparticles increases, which can act as crosslinking agents to connect polymer chains, further increasing the agent's strength. Therefore, the temporary plugging strength can be controlled by adjusting the amount and degree of modification of the nanoparticles. Increasing the amount of crosslinking agent increases the crosslinking density of the polymer chains, thereby increasing the strength of the temporary plugging agent particles.

[0040] Polyethylene glycol diacrylate, as a crosslinking agent, not only contains ester bonds but also double bonds at both ends of the molecular chain. These bonds can be used in free radical polymerization to connect the polymer chains at both ends of the crosslinking agent, forming a three-dimensional network structure. Furthermore, this type of ester exhibits high crosslinking efficiency; a stable crosslinked structure can be obtained with only a small amount. The crosslinking rate is suitable, and it remains stable during processing and storage without causing harmful reactions or aggregation. It is non-toxic, non-irritating, and does not pollute the environment.

[0041] In some embodiments, the hydrophilic polymerizable monomer is a combination of acrylamide and acrylic acid, wherein the mass ratio of acrylamide to acrylic acid is 1:0.8-1.2.

[0042] In some embodiments, the degree of modification of the silane coupling agent-modified hydrophobically modified nano-SiO2 is 20%–70%. The purpose of modification is to introduce double bonds into the nano-SiO2, enabling it to participate in the reaction, either by attaching to the polymer chain or by acting as a crosslinking agent. Too low a degree of modification will reduce the efficiency of the nano-SiO2 in the reaction, while too high a degree of modification will cause most of the nano-SiO2 to participate in the reaction as a crosslinking agent, reducing the self-degradation ability of the temporary plugging agent. After optimization, nano-SiO2 with a modification degree of 20%–70% was selected.

[0043] In some embodiments, the hydrophobic monomer is hexadecyldimethylallylammonium chloride. This hydrophobic monomer has strong hydrophobicity, providing hydrophobic side groups to the polymer chain, ensuring that the polymer chain has certain hydrophobic properties. In water, the hydrophobic groups aggregate due to hydrophobic interactions, forming a spatial network structure, thereby providing the necessary viscoelasticity. Furthermore, the long-chain alkyl group has antibacterial properties, effectively preventing its degradation by microorganisms underground.

[0044] In some embodiments, the initiator is selected from one or more of potassium persulfate, sodium thiosulfate, ammonium persulfate, and sodium bisulfite.

[0045] Preferably, the initiator is ammonium persulfate.

[0046] Secondly, the present invention provides a method for preparing a self-degrading temporary plugging agent, comprising the following steps:

[0047] The hydrophilic monomer is dissolved in water and the solution is adjusted to a weakly alkaline state to obtain a hydrophilic monomer solution.

[0048] Hydrophobic monomer, modified nanoparticle NP-1 and crosslinking agent are added sequentially to a hydrophilic polymerizable monomer solution, and the mixture is dissolved to obtain a mixed solution;

[0049] An initiator is added to the mixed solution, and the reaction is heated to obtain the product.

[0050] In some embodiments, the pH of the hydrophilic polymeric monomer is adjusted to 7.2-8, preferably 7.4-7.8, and more preferably 7.5.

[0051] Preferably, the alkali is a sodium hydroxide solution. The concentration of the sodium hydroxide solution is 10-20%, preferably 15%.

[0052] In some embodiments, the polymerization reaction is carried out at a temperature of 40-60°C for 3-6 hours.

[0053] In some embodiments, the method further includes the steps of drying and grinding the prepared product.

[0054] Thirdly, the present invention provides the application of the temporary plugging agent in repeated fracturing of oil reservoirs.

[0055] In some embodiments, a method for temporarily plugging oil reservoir fractures using the aforementioned plugging agent includes the following steps: screening plugging agent particles within a specified particle size range, uniformly dispersing them in water to form a stable suspension.

[0056] The suspension is injected into the oil and water wells, allowing the temporary plugging agent particles to enter the target layer for sealing. They continue to absorb water and expand, forming a high-strength temporary plugging layer to seal the fractures.

[0057] The self-degradable temporary plugging agent provided by this invention is in powder form. After dissolving in water, it forms a heterogeneous system with low viscosity, good fluidity, and easy pumping. After being injected into the formation, it absorbs water and expands under formation conditions, and maintains its strength for a period of time to seal fractures. After the operation is completed, it can degrade into a linear polymer at reservoir temperature, with a final viscosity reduction. The self-degradation temperature is 40℃~120℃. No breaker is required, the process is simple, and it causes little damage to the formation.

[0058] The present invention will be further described below with reference to specific embodiments.

[0059] Example 1

[0060] This embodiment provides a method for preparing a multifunctional self-degrading temporary plugging agent, comprising the following steps:

[0061] Step 1: Weigh 10 parts acrylic acid, 10 parts acrylamide, and 30 parts distilled water by weight. Adjust the pH of the solution to 7.5 with 15% sodium hydroxide solution to obtain a hydrophilic polymer monomer solution.

[0062] Step 2: Add 0.12 parts of crosslinking agent - polyethylene glycol diacrylate to the hydrophilic polymer monomer solution obtained in Step 1, and stir until completely dissolved;

[0063] Step 3: Add 0.8 parts of initiator-ammonium persulfate to the above solution, heat to 40°C, and react for 5 hours.

[0064] Step 4: After drying the reaction product, grind and pulverize it to obtain temporary plugging agent particles of different mesh sizes, named SD-TPA-1.

[0065] Example 2

[0066] This embodiment provides a method for preparing a multifunctional self-degrading temporary plugging agent, comprising the following steps:

[0067] Step 1: Weigh 10 parts acrylic acid, 9.5 parts acrylamide, and 30 parts distilled water by weight. Adjust the pH of the solution to 7.5 with 15% sodium hydroxide solution to obtain a hydrophilic polymer monomer solution.

[0068] Step 2: Add 0.5 parts of modified nanoparticle NP-1 (silane coupling agent hydrophobically modified nano SiO2, with a modification degree of 30%) and 0.12 parts of crosslinking agent - polyethylene glycol diacrylate to the hydrophilic polymer monomer solution obtained in Step 1, and stir until completely dissolved.

[0069] Step 3: Add 0.8 parts of initiator-ammonium persulfate to the above solution, heat to 40°C, and react for 5 hours.

[0070] Step 4: After drying the reaction product, grind and pulverize it to obtain temporary plugging agent particles of different mesh sizes, named SD-TPA-2.

[0071] Example 3

[0072] This embodiment provides a method for preparing a multifunctional self-degrading temporary plugging agent, comprising the following steps:

[0073] Step 1: Weigh 10 parts acrylic acid, 9.9 parts acrylamide, and 30 parts distilled water by weight. Adjust the pH of the solution to 7.5 with 15% sodium hydroxide solution to obtain a hydrophilic polymer monomer solution.

[0074] Step 2: Add 0.1 parts of hydrophobic monomer - hexadecyl dimethyl allyl ammonium chloride and 0.12 parts of crosslinking agent - polyethylene glycol diacrylate to the hydrophilic polymer monomer solution obtained in Step 1, and stir until completely dissolved;

[0075] Step 3: Add 0.8 parts of initiator-ammonium persulfate to the above solution, heat to 40°C, and react for 5 hours.

[0076] Step 4: After drying the reaction product, grind and pulverize it to obtain temporary plugging agent particles of different mesh sizes, named SD-TPA-3.

[0077] Example 4

[0078] This embodiment provides a method for preparing a multifunctional self-degrading temporary plugging agent, comprising the following steps:

[0079] Step 1: Weigh 10 parts acrylic acid, 9.4 parts acrylamide, and 30 parts distilled water by weight. Adjust the pH of the solution to 7.5 with 15% sodium hydroxide solution to obtain a hydrophilic polymer monomer solution.

[0080] Step 2: Add 0.5 parts of modified nanoparticles NP-1, 0.1 parts of hydrophobic monomer - hexadecyl dimethyl allyl ammonium chloride, and 0.12 parts of crosslinking agent - polyethylene glycol diacrylate to the hydrophilic polymer monomer solution obtained in Step 1, and stir until completely dissolved;

[0081] Step 3: Add 0.8 parts of initiator-ammonium persulfate to the above solution, heat to 40°C, and react for 5 hours.

[0082] Step 4: After drying the reaction product, grind and pulverize it to obtain temporary plugging agent particles of different mesh sizes, named SD-TPA-4.

[0083] Performance testing

[0084] Performance Test Experiment 1

[0085] This experimental example tests the expansion and self-degradation properties of the multifunctional self-degrading temporary plugging agent prepared in the examples.

[0086] Add 0.5 parts of dried and ground temporary plugging agent powder to each of the prepared 25 mL stoppered colorimetric tubes. Then add 20 parts of formation water with a mineralization of 21276.87 mg / L (see Table 1 for the ionic composition of the formation water). Seal the colorimetric tubes and shake them thoroughly. Finally, place them in an 80℃ incubator and record the expansion volume of the temporary plugging agent particles in the colorimetric tubes at regular intervals. Calculate the expansion factor using the following formula.

[0087]

[0088] In the formula α V - Expansion factor, V1 - Maximum expansion volume, V0 - Initial volume.

[0089] Add 0.5 parts of dried and ground temporary plugging agent granules to each of the prepared 25 mL stoppered colorimetric tubes. Then add 20 parts of formation water with a salinity of 21276.87 mg / L to the colorimetric tubes. Seal the colorimetric tubes and shake them thoroughly. Finally, place them in an 80℃ constant temperature incubator. Record the expansion volume of the temporary plugging agent particles in the colorimetric tubes at regular intervals and record the time for complete degradation. After complete degradation, calculate the degradation rate according to the following formula.

[0090]

[0091] In the formula, α is the degradation rate, m1 is the mass after complete degradation, and m0 is the initial mass.

[0092] Table 1 shows the ionic composition of formation water.

[0093] Table 1

[0094]

[0095] Table 2 shows the test results of the self-degradation performance of the self-degrading temporary plugging agent.

[0096] Table 2

[0097] formula Complete degradation time / h Degradation rate / % SD-TPA-1 240 97.14 SD-TPA-2 412 86.91 SD-TPA-3 288 92.13 SD-TPA-4 492 88.13

[0098] The synthesized temporary plugging agent particles are a three-dimensional network structure formed by the chemical cross-linking and entanglement of polymer chains. Its expansion in water can be divided into two main stages: The first stage occurs when solvent molecules come into contact with the particles and hydrate with the hydrophilic groups within the particles, forming hydrogen bonds. This stage is short, rapid, and accompanied by a thermal effect. The second stage occurs due to the expansion of the three-dimensional polymer network, where hydrophilic ionic groups hydrolyze to form free ions. The presence of these ions creates a difference in ion concentration inside and outside the particles, thus forming an osmotic pressure difference. Under the influence of osmotic pressure, free water enters the polymer network structure of the particles and continues to interact with the hydrophilic groups within the particles to form hydrogen bonds, further promoting hydrolysis and the formation of the osmotic pressure difference. This leads to a continuous influx of water molecules into the particles, increasing their volume. Initially, the osmotic pressure difference inside and outside the particles is large, resulting in a rapid water absorption and expansion rate; after a period of time, the osmotic pressure difference decreases, the particle expansion rate slows down, and eventually equilibrium is reached.

[0099] Figure 1Table 1 shows the experimental results of the expansion performance of the temporary plugging agent, and Table 2 shows the experimental results of its self-degradation performance. Both the expansion ratio and degradation time are adjustable; it's not necessarily true that a higher expansion ratio or a shorter degradation time is always better. The choice depends on the actual needs of the mine. However, higher plugging strength is always better. Many factors influence plugging strength. The core of this invention's temporary plugging agent is the ability to control the expansion ratio, expansion rate, and degradation rate without affecting the plugging strength.

[0100] Figure 1 A comparison of the maximum expansion ratio and expansion rate of the four temporary plugging agents reveals that the expansion ratio decreases after the addition of modified nanoparticles. This is because the surface of the nano-SiO2, modified with a silane coupling agent for hydrophobicity, is rich in double bonds, which can be linked to the framework structure of the temporary plugging agent through free radical polymerization, increasing the stability of the three-dimensional network structure and weakening its water absorption and expansion capacity. The addition of hydrophobic monomers further reduces hydration capacity, decreasing water absorption and consequently reducing the expansion rate and expansion ratio, which is beneficial for penetrating deeper reservoirs.

[0101] Table 2 compares the four types of temporary plugging agents. The formulation with modified nano-SiO2 added has a longer complete degradation time and a lower degradation rate than the formulation without modified nano-SiO2. This is because the modified nano-SiO2 can be attached to the polymer chain or act as a crosslinking agent to connect the polymer chain, increasing the stability of the three-dimensional network structure of the temporary plugging agent and increasing the strength of the temporary plugging agent.

[0102] Comparing the plugging strength and post-plugging permeability of the four temporary plugging agents in Table 3, the plugging agent with modified nano-SiO2 added showed significantly better plugging ability than the one without it, and had virtually no impact on the permeability recovery rate. This indicates that adding modified nano-SiO2 can significantly increase the plugging strength, and by changing the amount of hydrophobic monomer added, the expansion ratio, expansion rate, and degradation rate can be controlled.

[0103] Performance Test Experiment 2

[0104] This experimental example is a rheological test of a functional self-degrading temporary plugging agent.

[0105] The viscoelasticity and yield stress of temporary plugging agent particles were measured using a plate system on an MCR301 rheometer. The specific experimental procedures were as follows: Four different synthesized temporary plugging agent particles were placed in formation water with a salinity of 21276.87 mg / L at 80℃ to absorb water and swell. Solid particles from the bottom of test tubes of different samples at different times were collected using a dropper and placed on the plate system, maintaining the wettability of the particles throughout the test. The rheological properties of the temporary plugging agent particles were determined using a dynamic oscillation method on the MCR301 rheometer. The experimental temperature was set to 80℃, and the shear rate was set to 7.74 s⁻¹. -1 .

[0106] Experimental results show that the elastic moduli of SD-TPA-1, SD-TPA-2, SD-TPA-3, and SD-TPA-4 are 27 Pa, 28 Pa, 27 Pa, and 113 Pa, respectively. Among them, the elastic modulus of the temporary plugging agent particle SD-TPA-4 is the largest, with an elastic modulus of 113 Pa.

[0107] Figure 2 This is a comparison of the elastic moduli of three temporary plugging agent particles (SD-TPA-1, SD-TPA-2, and SD-TPA-4) when they reach full expansion. The graph shows that, at the same oscillation frequency, SD-TPA-4 particles have the highest elastic modulus, while SD-TPA-1 has the lowest. This is because the addition of modified nanoparticles increases the strength of the temporary plugging agent particles.

[0108] Performance test experiment 3

[0109] This embodiment presents the experimental results of sealing and unblocking with a multifunctional self-degrading temporary plugging agent.

[0110] Core displacement experiments were used to evaluate the plugging and unplugging performance of self-degrading temporary plugging agents in porous media. A 2.5cm × 10cm fractured core was placed in a core holder, and the confining pressure was set to 10 MPa.

[0111] (1) Place the core in an oven at 80℃ and dry for 24 hours. After it is completely dried, accurately weigh the core with a balance and record it as m0. Then saturate the core with water for 24 hours and accurately weigh the core as m. Measure the radius r and length l of the core and calculate the porosity of the core. The calculation formula is as follows:

[0112]

[0113] (2) Place a 0.03mm thick shim on the core cut surface to simulate a 0.03mm crack, place the core in the core holder, and then... Figure 3 Connect the instruments as shown.

[0114] (3) Inject formation water into the core using a constant flow pump at a constant rate of 0.5 mL / min. Read the pressure at the injection end. When the displacement pressure stabilizes, record the pressure at this time and calculate the permeability. The calculation formula is as follows:

[0115] Where k is the permeability, in μm 2 Q is the fluid velocity, in cm. 3 / s; μ is the fluid viscosity, 0.001 Pa·s; ΔL is the core length, cm; A is the cross-sectional area of ​​the core fracture, cm² 2 ΔP is the pressure difference between the two ends of the core, 105 Pa;

[0116] (4) Inject a 0.5 wt.% temporary plugging agent after it has fully expanded into the core at a constant flow rate of 0.5 mL / min, with an injection volume of 0.5 FV;

[0117] (5) After the temporary plugging agent is injected, formation water is injected again into the core at a constant flow rate of 0.5 mL / min until the injection pressure stabilizes again. During the entire displacement process, the real-time pressure changes are recorded, and the plugging rate is calculated. The plugging rate is calculated using the following formula:

[0118] Where Φ0 is the initial permeability, in μm 2 Φ represents the permeability after plugging, in μm. 2 .

[0119] (6) The core holder with remaining temporary plugging agent was aged in an 80℃ oven for 72 hours. After the temporary plugging agent was completely degraded, formation water was injected again until the injection pressure stabilized. The permeability recovery rate of the core was then tested and calculated using the following formula: Where Φ0 is the initial permeability, in μm 2 Φ' represents the permeability after unblocking, in μm. 2 .

[0120] Table 3. Plugging and Unplugging Performance

[0121]

[0122] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of self-degradable temporary plugging agents in repeated fracturing of oil reservoirs, characterized in that: The method for temporarily plugging oil reservoir fractures using the aforementioned temporary plugging agent includes the following steps: screening self-degradable temporary plugging agent particles within a set particle size range, uniformly dispersing them in water to form a stable suspension; The suspension is injected into oil and water wells, allowing the self-degrading temporary plugging agent particles to enter the target layer for sealing. They continue to absorb water and expand, forming a high-strength temporary plugging layer to seal the fractures. The self-degradable temporary plugging agent, based on a total mass of 100 parts, consists of the following components by weight: 19.4-20 parts hydrophilic polymeric monomer, 0.5-1 parts modified nanoparticles NP-1, The composition consists of 0.1 to 0.5 parts hydrophobic monomer, 0.12 to 0.2 parts crosslinking agent, 0.8 to 1 part initiator, and the balance being water. The hydrophobic monomer is hexadecyl dimethyl allyl ammonium chloride; the crosslinking agent is polyethylene glycol diacrylate. The modified nanoparticles NP-1 are nano-SiO2 modified with a silane coupling agent for hydrophobicity. The hydrophilic polymerizable monomers are a combination of acrylamide and acrylic acid, with a mass ratio of acrylamide to acrylic acid of 1:0.8-1.2; The degree of modification of nano-SiO2 by hydrophobic modification with silane coupling agent is 20%~70%.

2. The application according to claim 1, characterized in that: The initiator is selected from one or more of potassium persulfate, sodium thiosulfate, ammonium persulfate, and sodium bisulfite.

3. The application according to claim 2, characterized in that: The initiator is ammonium persulfate.

4. The application according to claim 1, characterized in that, The preparation method of the self-degrading temporary plugging agent includes the following steps: The hydrophilic monomer is dissolved in water and the solution is adjusted to weak alkalinity with sodium hydroxide solution to obtain a hydrophilic monomer solution. Hydrophobic monomer, modified nanoparticle NP-1 and crosslinking agent are added sequentially to a hydrophilic polymerizable monomer solution, and the mixture is dissolved to obtain a mixed solution; An initiator is added to the mixed solution, and the reaction is heated to obtain the product.

5. The application according to claim 4, characterized in that: Adjust the pH of the hydrophilic polymer monomer to 7.2-8.

6. The application according to claim 5, characterized in that: Adjust the pH of the hydrophilic polymer monomer to 7.4-7.

8.

7. The application according to claim 6, characterized in that: The pH of the hydrophilic polymer monomer was adjusted to 7.

5.

8. The application according to claim 4, characterized in that: The concentration of the sodium hydroxide solution is 10-20%.

9. The application according to claim 8, characterized in that: The concentration of the sodium hydroxide solution is 15%.

10. The application according to claim 4, characterized in that: The polymerization reaction is carried out at a temperature of 40-60℃ for 3-6 hours.

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