CN115286750A - A kind of self-degrading temporary plugging agent and preparation method and application thereof - Google Patents

Abstract

The invention discloses a self-degrading temporary plugging agent and a preparation method and application thereof. Based on 100 parts of the total mass, the raw material consists of the following components by weight: 19.4-20 parts of hydrophilic polymerized monomers, modified nanoparticles 10.5-1 part of NP-, 0.1-0.5 part of hydrophobic monomer, 0.12-0.2 part of crosslinking agent, 0.8-1 part of initiator, and the balance is water; the hydrophilic polymerizable monomer is acrylamide and/or acrylic acid; The hydrophobic monomer is selected from one or more of cetyldimethylallyl ammonium chloride, dimethyl diallyl ammonium chloride, and methacryloyloxyethyltrimethylammonium chloride. The crosslinking agent is polyethylene glycol diacrylate; the modified nanoparticle NP-1 is nano-SiO ₂ hydrophobically modified by a silane coupling agent. The temporary plugging agent can have a certain plugging strength under the condition of high pressure difference, and can self-degrade into a low-viscosity solution in a wide temperature range (40℃～120℃) Multifunctional self-degrading temporary plugging agent and its preparation methods and applications.

Description

A kind of self-degradation temporary plugging agent and its preparation method and application

technical field

The invention relates to the field of oil field chemistry, in particular to a self-degradable temporary plugging agent and its preparation method and application, and more specifically to a self-degrading temporary plugging agent which has a certain plugging strength under reservoir conditions and can be used in a wide temperature range ( 40°C～120°C), a multifunctional self-degradable temporary plugging agent that degrades itself into a low-viscosity solution, its preparation method and application.

Background technique

The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

After a period of water injection in the oil reservoir, the crude oil controlled by the old fractures has been almost fully recovered, and the fractures have become the main water outlet channels, which reduces the development benefits, but there is still a large amount of remaining oil in the matrix. In order to further control water and increase oil production, and give full play to the production capacity of oil wells, the refracturing technology of plugging old fractures and opening new ones has been gradually formed. The essence of refracturing is to use a plugging agent to selectively enter and seal old fractures, and then perform fracturing to open new fractures, thereby providing seepage channels for unused remaining oil. The implementation of this process requires a temporary plugging agent with excellent performance.

At present, the most commonly used water-soluble temporary plugging agent is ordinary gel particles, and gel breakers are often used for plugging removal. This method has the following disadvantages: the plugging strength is small, the rubber is broken unevenly, and it is easy to form a large rubber plug, which may cause potential damage to the oil layer. In recent years, some people have proposed self-degrading temporary plugging agents. Self-degrading temporary plugging agents can be well dispersed in water or fracturing fluids, and have certain plugging strength under high pressure differential conditions. After a period of time, they can be used in reservoir conditions Self-degradation into a low-viscosity solution, reducing formation pollution and residue damage. However, the existing self-degrading temporary plugging agents still have disadvantages such as the expansion time and degradation time are not easy to control, and the temporary plugging strength is uncontrollable.

Contents of the invention

In order to solve the above problems, the present invention proposes a self-degrading temporary plugging agent and its preparation method and application. ℃～120 ℃), a multifunctional self-degrading temporary plugging agent that degrades itself into a low-viscosity solution, its preparation method and application.

In order to achieve the above object, the present invention is achieved through the following technical solutions:

In the first aspect, the present invention provides a self-degrading temporary plugging agent. Based on 100 parts of the total mass, its raw materials are composed of the following components by weight: 19.4 to 20 parts of hydrophilic polymerized monomers, modified nanoparticles NP-1 0.5-1 part, 0.1-0.5 part of hydrophobic monomer, 0.12-0.2 part of cross-linking agent, 0.8-1 part of initiator, and the balance is water;

The hydrophilic polymer monomer is acrylamide and/or acrylic acid;

The hydrophobic monomer is selected from one or more of hexadecyl dimethyl allyl ammonium chloride, dimethyl diallyl ammonium chloride, methacryloxyethyl trimethyl ammonium chloride kind;

The cross-linking agent is polyethylene glycol diacrylate;

The modified nanoparticle NP-1 is nano SiO ₂ hydrophobically modified by a silane coupling agent.

Second aspect, the present invention provides a kind of preparation method of self-degradation temporary plugging agent, comprises the steps:

Dissolving the hydrophilic polymer monomer in water, and adjusting the solution to weak alkalinity with water, to obtain a hydrophilic polymer monomer solution;

Adding the hydrophobic monomer, the modified nanoparticle NP-1 and the cross-linking agent in sequence to the hydrophilic polymerization monomer solution, mixing and dissolving to obtain a mixed solution;

The initiator is added to the mixed solution, and the reaction is heated to obtain the product.

In the third aspect, the present invention provides the application of the temporary plugging agent in repeated fracturing of oil layers.

The beneficial effects obtained by one or more embodiments of the present invention are as follows:

According to the reservoir fracture parameters, select temporary plugging agent particles with appropriate particle size, then disperse the temporary plugging agent particles in the injection fluid according to the injection plan, stir rapidly to form a relatively stable suspension, and then inject them into the oil-water well through the operation string , the temporary plugging agent particles enter the plugging target layer, continue to absorb water and expand rapidly to form a high-strength temporary plugging layer, and after a certain period of time, they can degrade by themselves after repeated fracturing. The injection rate is determined according to the injection pressure, and the reservoir temperature range for the temporary plugging agent is 40°C to 120°C.

In the present invention, the self-degradation temperature of the temporary plugging agent is 40° C. to 120° C., the self-degradation temperature range is wide, and the oil reservoir is applicable to a wide range. In the present invention, the self-degrading temporary plugging agent absorbs water and swells at the reservoir temperature and maintains its strength for a period of time. Then, as time goes by, the crosslinking agent fails to cross-link under the reservoir temperature, and the temporary plugging agent Degraded into a linear polymer, the final viscosity is reduced, and the self-degradation of the temporary plugging agent is realized.

In the present invention, the expansion and degradation time of the temporary plugging agent can be controlled. In the present invention, the particles of the temporary plugging agent absorb water and swell after being added to water. Since the hydrophobic monomer contains hydrophobic groups, the water absorption rate and water absorption capacity of the temporary plugging agent are reduced, thereby reducing the expansion capacity of the temporary plugging agent. Therefore, the expansion performance and expansion rate of the temporary plugging agent can be adjusted by adjusting the amount of hydrophobic monomer added. In the present invention, the crosslinking agent used is polyethylene glycol diacrylate containing ester bonds. The ester bonds are broken at a certain temperature, the three-dimensional network structure of the temporary plugging agent is destroyed, and finally becomes a low-viscosity solution, so it can be By adjusting the amount of cross-linking agent, the cross-linking density of the temporary plugging agent is adjusted, and then the self-degradation time of the temporary plugging agent is regulated.

In the present invention, the temporary plugging strength of the temporary plugging agent is controllable. In the present invention, the surface of the modified nanoparticles is rich in double bonds, which can be connected to the skeleton structure of the temporary blocking agent through free radical polymerization, increasing the stability of the three-dimensional network structure of the temporary blocking agent and increasing the strength of the temporary blocking agent , in addition, as the degree of modification increases, the number of double bonds on the modified nanoparticles increases, which can be used as a cross-linking agent to connect polymer chains, further increasing the strength of the temporary plugging agent. Therefore, we can adjust the temporary plugging strength of the temporary plugging agent by adjusting the amount and modification degree of the modified nanoparticles.

Description of drawings

The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute improper limitations to the present invention.

Fig. 1 is the self-degradation temporary plugging agent expansion performance test result prepared by embodiment 1-4;

Fig. 2 is the comparison chart of elastic modulus of the self-degradation temporary plugging agent prepared by embodiment 1-4;

Fig. 3 is the flow chart of temporary plugging agent plugging and unblocking experimental device prepared in embodiment 1-4;

Fig. 4 is the pressure change curve of the temporary plugging agent plugging process that embodiment 1-4 prepares;

Fig. 5 is the pressure change curve of the temporary plugging agent unblocking process that embodiment 1-4 prepares;

Fig. 6 is a schematic diagram of the structure of the temporary plugging agent prepared in Example 4.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the present invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

In the first aspect, the present invention provides a self-degrading temporary plugging agent. Based on 100 parts of the total mass, its raw materials are composed of the following components by weight: 19.4 to 20 parts of hydrophilic polymerized monomers, modified nanoparticles NP-1 0.5-1 part, 0.1-0.5 part of hydrophobic monomer, 0.12-0.2 part of cross-linking agent, 0.8-1 part of initiator, and the balance is water;

The hydrophilic polymer monomer is acrylamide and/or acrylic acid;

The hydrophobic monomer is selected from one or more of hexadecyl dimethyl allyl ammonium chloride, dimethyl diallyl ammonium chloride, methacryloxyethyl trimethyl ammonium chloride kind;

The cross-linking agent is polyethylene glycol diacrylate;

The modified nanoparticle NP-1 is nano SiO ₂ hydrophobically modified by a silane coupling agent.

The hydrophilic group in the hydrophilic polymerization monomer is used to absorb water, so that the temporary plugging agent absorbs water and expands, and the hydrophobic group in the hydrophobic monomer is used to reduce the water absorption rate and water absorption capacity of the temporary plugging agent, thereby inhibiting the water absorption of the temporary plugging agent swell. The hydrophilic group and the hydrophobic group cooperate with each other to adjust the expansion performance and expansion rate of the temporary plugging agent.

The cross-linking agent contains ester bonds. When the ester bond breaks at a certain temperature, the three-dimensional network structure of the temporary plugging agent is destroyed, and finally becomes a low-viscosity solution. Therefore, by adjusting the amount of the cross-linking agent, the Cross-linking density, and then adjust the self-degradation time of temporary plugging agent.

The main structure of the particle skeleton is an acrylamide structure, and the purpose of adding acrylic acid is to increase water absorption and improve swelling performance.

Cetyl dimethyl allyl ammonium chloride, dimethyl diallyl ammonium chloride, and methacryloyloxyethyl trimethyl ammonium chloride have better salt tolerance.

The strength of the temporary plugging agent is regulated by the following methods: the most obvious regulation is through nano-particles, mainly to control the amount of particles added and the degree of modification. Secondly, the addition amount of hydrophilic monomer, crosslinking agent, hydrophobic monomer, initiator, reaction temperature, and reaction time can also be changed. The surface of the modified nano-SiO ₂ is rich in double bonds, which can be connected to the skeleton structure of the temporary plugging agent through free radical polymerization, increasing the stability of the three-dimensional network structure of the temporary blocking agent and increasing the strength of the temporary blocking agent. As the degree of stability increases, the number of double bonds on the modified nanoparticles increases, which can be used as a cross-linking agent to connect polymer chains, further increasing the strength of the temporary plugging agent. Therefore, by adjusting the amount of modified nanoparticles and the degree of modification, the temporary plugging strength of the temporary plugging agent can be adjusted to increase the amount of cross-linking agent, which can increase the cross-linking density of the polymer chain, thereby increasing the strength of the temporary plugging agent particles. .

As a cross-linking agent, polyethylene glycol diacrylate not only contains ester bonds, but also contains double bonds at both ends of the molecular chain. The polymer chain can be connected to the two ends of the cross-linking agent through free radical polymerization to form a three-dimensional Spatial network structure. Moreover, this kind of ester has high cross-linking efficiency, a stable cross-linked structure can be obtained only by adding a small amount, the cross-linking speed is suitable, it is stable during process treatment and storage, and no harmful reaction and aggregation will occur. Non-toxic, non-irritating, non-polluting environment.

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

In some embodiments, the degree of modification of the nano-SiO ₂ hydrophobically modified by the silane coupling agent is 20%-70%. The purpose of the modification is to introduce double bonds on the nano-SiO ₂ so that it can participate in the reaction, or be connected to the polymer chain, or be used as a cross-linking agent to connect the polymer chain. If the degree of modification is too low, the nano-SiO ₂ will The efficiency of participating in the reaction is reduced, and the degree of modification is too high, most of the nano-SiO ₂ will participate in the reaction as a cross-linking agent, which reduces the self-degradation ability of the temporary plugging agent. After optimization, nano-SiO ₂ with a modification degree of 20% to 70% is selected.

In some embodiments, the hydrophobic monomer is cetyldimethylallyl ammonium chloride. This kind of hydrophobic monomer has strong hydrophobicity, which can provide hydrophobic side groups for the polymer chain to ensure that the polymer chain has certain hydrophobic characteristics. In water, the hydrophobic groups are aggregated due to the hydrophobic effect to form a spatial network structure, thereby To provide the necessary viscoelasticity. Moreover, the long-chain alkyl group has antibacterial properties, which can effectively prevent it from being degraded by microorganisms underground.

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

Preferably, the initiator is ammonium persulfate.

Second aspect, the present invention provides a kind of preparation method of self-degradation temporary plugging agent, comprises the steps:

Dissolving the hydrophilic polymer monomer in water, and adjusting the solution to weak alkalinity with water, to obtain a hydrophilic polymer monomer solution;

Adding the hydrophobic monomer, the modified nanoparticle NP-1 and the cross-linking agent in sequence to the hydrophilic polymerization monomer solution, mixing and dissolving to obtain a mixed solution;

The initiator is added to the mixed solution, and the reaction is heated to obtain the product.

In some embodiments, the pH value of the hydrophilic polymerization monomer is adjusted to 7.2-8, preferably 7.4-7.8, more preferably 7.5.

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

In some embodiments, the temperature of the polymerization reaction is 40-60° C., and the reaction time is 3-6 hours.

In some embodiments, the step of drying, grinding and pulverizing the prepared product is also included.

In the third aspect, the present invention provides the application of the temporary plugging agent in repeated fracturing of oil layers.

In some embodiments, the method for temporarily plugging oil reservoir fractures by using the temporary plugging agent includes the following steps: screening temporary plugging agent particles with a set particle size range, uniformly dispersing them in water to form a stable suspension,

The suspension is injected into the oil-water well, so that the temporary plugging agent particles enter the plugging target layer, continue to absorb water and expand, and form a high-strength temporary plugging layer to plug the fracture.

The appearance of the self-degrading temporary plugging agent provided by the invention is powdery, and after being dissolved in water, it forms a heterogeneous system with low viscosity and good fluidity, which is easy to pump. It maintains strength inside and seals fractures. After the operation is over, it can be degraded into a linear polymer at the reservoir temperature, and the final viscosity is reduced. The self-degradation temperature is 40 ° C ~ 120 ° C, no need to add a breaker, and the process is simple. Little damage to ground.

The present invention will be further described below in conjunction with specific examples.

Example 1

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

Step 1. In parts by weight, weigh 10 parts of acrylic acid, 10 parts of acrylamide, and 30 parts of distilled water, and use 15% sodium hydroxide solution to adjust the pH value of the solution to 7.5 to obtain a hydrophilic polymer monomer solution;

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;

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

Step 4. Dry the reaction product and grind it to obtain temporary plugging agent particles with different meshes, named SD-TPA-1.

Example 2

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

Step 1. In parts by weight, weigh 10 parts of acrylic acid, 9.5 parts of acrylamide, 30 parts of distilled water, and use 15% sodium hydroxide solution to adjust the pH value of the solution to 7.5 to obtain a hydrophilic polymer monomer solution;

Step 2, add 0.5 part of modified nanoparticles NP-1 (nano- _SiO2 modified by silane coupling agent hydrophobically, the degree of modification is 30%), 0.12 parts in the hydrophilic polymer monomer solution obtained in step 1 Cross-linking agent-polyethylene glycol diacrylate, stirred until completely dissolved;

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

Step 4. Dry the reaction product and grind it to obtain temporary plugging agent particles of different meshes, which are named SD-TPA-2.

Example 3

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

Step 1. In parts by weight, weigh 10 parts of acrylic acid, 9.9 parts of acrylamide, and 30 parts of distilled water, and use 15% sodium hydroxide solution to adjust the pH value of the solution to 7.5 to obtain a hydrophilic polymer monomer solution;

Step 2, add 0.1 part of hydrophobic monomer-hexadecyl dimethyl allyl ammonium chloride, 0.12 part of crosslinking agent-polyethylene glycol diacrylic acid to the hydrophilic polymer monomer solution obtained in step 1 Esters, stirred until completely dissolved;

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

Step 4. Dry the reaction product and grind it to obtain temporary plugging agent particles of different meshes, which are named SD-TPA-3.

Example 4

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

Step 1. Weigh 10 parts of acrylic acid, 9.4 parts of acrylamide, and 30 parts of distilled water in parts by weight, and adjust the pH value of the solution to 7.5 with 15% sodium hydroxide solution to obtain a hydrophilic polymer monomer solution;

Step 2, add 0.5 part of modified nanoparticles NP-1, 0.1 part of hydrophobic monomer-hexadecyl dimethyl allyl ammonium chloride, 0.12 part to the hydrophilic polymer monomer solution obtained in step 1 Cross-linking agent-polyethylene glycol diacrylate, stirred until completely dissolved;

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

Step 4. Dry the reaction product and grind it to obtain temporary plugging agent particles of different meshes, which are named SD-TPA-4.

Performance Testing

Performance Test Trial 1

This test example is to select the multifunctional self-degradation temporary plugging agent prepared in the embodiment to test the expansion and self-degradation performance.

Add 0.5 parts of dried and ground four temporary plugging agent particle powders to the prepared 25mL plugged colorimetric tube, and then add 20 parts of formation water with a salinity of 21276.87mg/L to the colorimetric tube. The ionic composition of water is shown in Table 1. After sealing the colorimetric tube, shake it fully and evenly. Finally, place them in an incubator at 80°C, record the expansion volume of the temporary blocking agent particles in the colorimetric tube at regular intervals, and calculate the expansion multiple according to the following formula.

In the formula, α _V -expansion multiple, V ₁ -maximum expansion volume, V ₀ -initial volume.

Add 0.5 parts of dried and ground four kinds of temporary plugging agent particle powders to the prepared 25mL plugged colorimetric tube, and then add 20 parts of formation water with a salinity of 21276.87mg/L to the colorimetric tube, and After the colorimetric tube is sealed, shake it fully and evenly. Finally, place them in an incubator at 80°C, record the expansion volume of the temporary blocking agent particles in the colorimetric tube at regular intervals, and record the time of complete degradation. After complete degradation, calculate the degradation rate according to the following formula .

In the formula, α-degradation rate, m ₁ -mass after complete degradation, m ₀ -initial mass.

Table 1 is the ion composition of formation water.

Table 1

Table 2 is the test results of self-degradation performance of self-degradation temporary plugging agent.

Table 2

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

The synthesized temporary plugging agent particles are a three-dimensional network structure formed by chemical cross-linking of polymer chains and entanglement of polymers. Its swelling in water can be divided into two main stages: the first stage is that after the solvent molecules come into contact with the particles, they hydrate with the hydrophilic groups in the particles to form hydrogen bonds. This stage is short, fast, and accompanied by thermal effects. The second stage is due to the expansion of the three-dimensional polymer network, in which the hydrophilic ionic groups are hydrolyzed to form free ions. The presence of these ions causes a difference in the concentration of ions inside and outside the particle, thereby forming an osmotic pressure difference. Under the action of osmotic pressure, free water enters the polymer network structure of the particles, and continues to interact with the hydrophilic groups in the particles to form hydrogen bonds, which further promotes the occurrence of hydrolysis and the formation of osmotic pressure differences, causing water molecules to continuously enter the particles , the particle size increases. At the initial stage, the osmotic pressure difference inside and outside the particles is large, and the rate of water swelling is fast; after a period of time, the osmotic pressure difference decreases, the rate of particle expansion slows down, and finally reaches equilibrium.

Figure 1 shows the experimental results of the expansion performance of the temporary plugging agent, and Table 2 shows the experimental results of the self-degradation performance of the temporary plugging agent. Both the expansion multiple and the degradation time can be adjusted. It does not mean that the higher the expansion multiple, the better or the shorter the degradation time, the better. It is determined according to the actual needs of the mine, but the higher the plugging strength, the better. There are many factors affecting the plugging strength. The core of the temporary plugging agent of the present invention is that the expansion ratio, expansion rate and degradation rate can be adjusted without affecting the plugging strength.

Figure 1 regularly compares the maximum expansion multiples and expansion rates of the _four temporary plugging agents. It can be seen that the expansion multiples decrease after adding modified nanoparticles. It contains double bonds, which can be connected to the skeleton structure of the temporary plugging agent through free radical polymerization, which increases the stability of the three-dimensional network structure of the temporary plugging agent and weakens its ability to absorb water and expand. After adding hydrophobic monomers, the hydration capacity is weakened, which reduces the water absorption capacity, thereby reducing the expansion rate and expansion multiple, which is conducive to entering deep reservoirs.

Table 2 compares the four temporary plugging agents according to the rules. The formula with modified nano- _SiO2 added has a longer complete degradation time than the formula without modified nano- _SiO2 , and the degradation rate is lower than the formula without modified nano- _SiO2 . This is because the modified nano- _SiO2 can be connected to the polymer chain, or as a cross-linking agent to connect the polymer chain, increasing the stability of the three-dimensional network structure of the temporary blocking agent and increasing the strength of the temporary blocking agent.

Comparing the plugging strength and permeability after plugging removal of the four temporary plugging agents in Table 3, the plugging ability of the temporary plugging agent added with modified nano-SiO ₂ is much better than that of the non-added temporary plugging agent, and basically does not affect Permeability recovery rate. This shows that adding modified nano-SiO ₂ can significantly increase the plugging strength, and on this basis, changing the amount of hydrophobic monomer can realize the regulation of expansion multiple, expansion rate and degradation rate.

Performance Test Trial 2

This test example is a rheological experiment of functional self-degrading temporary plugging agent.

The viscoelasticity and yield stress of temporary plugging agent particles were measured by the flat plate system of MCR301 rheometer. The specific experimental operation steps are as follows: put the synthesized 4 different temporary plugging agent particles in formation water with a salinity of 21276.87mg/L at 80°C to absorb water and swell, and use a rubber dropper to take test tubes of different samples at different times The solid particles at the bottom are placed on a flat plate system, and the wetness of the particles is maintained during the test. The rheological properties of temporary plugging agent particles were measured on MCR301 rheometer by dynamic oscillation method. The experimental temperature was set at 80 °C. The shear rate was set at 7.74 s ^-1 .

The experimental results show that the elastic modulus of SD-TPA-1, SD-TPA-2, SD-TPA-3, and SD-TPA-4 are 27Pa, 28Pa, 27Pa, and 113Pa, respectively, and the temporary plugging agent particles SD-TPA- The elastic modulus of 4 is the largest, and the elastic modulus is 113Pa.

Figure 2 is a comparison chart of the elastic modulus of three temporary plugging agent particles SD-TPA-1, SD-TPA-2, and SD-TPA-4 when they reach full expansion. It can be seen from the figure that in the same oscillation Under the frequency, the elastic modulus of SD-TPA-4 particles is the largest, and the elastic modulus of SD-TPA-1 is the smallest. This is because the strength of temporary plugging agent particles is increased after adding modified nanoparticles.

Performance Test Trial 3

This example is the experimental result of plugging and unplugging with a multifunctional self-degrading temporary plugging agent.

The plugging and plugging removal performance of self-degradable temporary plugging agent in porous media was evaluated by core displacement experiment. A 2.5cm×10cm fractured core was placed in a core holder, and the confining pressure was set to 10MPa.

(1) Place the core in an oven at 80°C to dry for 24 hours. After drying completely, use a balance to accurately weigh the dry weight of the core, which is recorded as m ₀ . The wet weight of the rock core is denoted as m, the radius r and length l of the rock core are measured, and the porosity of the rock core is calculated, and the calculation formula is as follows:

(2) Place a gasket with a thickness of 0.03 mm on the cut surface of the core, simulate a crack of 0.03 mm, place the core in the core holder, and connect the instrument as shown in Figure 3.

(3) Use a constant flow pump to inject formation water into the core at a constant flow rate of 0.5mL/min, read the pressure at the injection end, and when the displacement pressure is stable, record the pressure at this time and calculate the permeability. The calculation formula is as follows:

其中，k为渗透率，μm²；Q为流体流速，cm³/s；μ为流体黏度，0.001Pa·s；ΔL为岩心长度，cm；A为岩心裂缝截面积，cm²；ΔP为岩心两端压差，10⁵Pa；

Among them, k is permeability, μm ² ; Q is fluid velocity, cm ³ /s; μ is fluid viscosity, 0.001Pa·s; ΔL is core length, cm; A is core fracture cross-sectional area, cm ² ; ΔP is core Pressure difference across the two ends, 10 ⁵ Pa;

(4) Inject a temporary plugging agent with a concentration of 0.5wt.% into the core at a constant flow rate of 0.5mL/min after the expansion is complete, and the injection rate is 0.5FV;

(5) After the injection of the temporary plugging agent is completed, re-inject formation water into the core at a constant flow rate of 0.5mL/min until the injection pressure becomes stable again; Blocking rate, the formula for calculating the blocking rate is as follows:

其中，Φ₀为初始渗透率，μm²，Φ为封堵后渗透率，μm²。

Among them, Φ ₀ is the initial permeability, μm ² , and Φ is the permeability after plugging, μm ² .

其中，Φ₀为初始渗透率，μm²，Φ’为解堵后渗透率，μm²。(6) Aging the core holder with the remaining temporary plugging agent in an oven at 80°C for 72 hours. After the temporary plugging agent is completely degraded, inject formation water again until the injection pressure is stable, test the permeability recovery rate of the core, and press The following formula is calculated:

Among them, Φ ₀ is the initial permeability, μm ² , and Φ' is the permeability after plugging removal, μm ² .

Table 3 Plugging and plugging removal performance

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A self-degradation temporary plugging agent is characterized in that: the raw materials comprise the following components in parts by weight based on 100 parts of the total mass: 19.4 to 20 portions of hydrophilic polymerization monomer, 0.5 to 1 portion of modified nano particle NP-, 0.1 to 0.5 portion of hydrophobic monomer, 0.12 to 0.2 portion of cross linker, 0.8 to 1 portion of initiator and the balance of water;

the hydrophilic polymerization monomer is acrylamide and/or acrylic acid;

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

the cross-linking agent is polyethylene glycol diacrylate;

the modified nano-particle NP-1 is nano SiO hydrophobically modified by silane coupling agent ₂ 。

2. The self-degrading temporary plugging agent according to claim 1, wherein: the hydrophilic polymerization monomer is a combination of acrylamide and acrylic acid, and the mass ratio of the acrylamide to the acrylic acid is 1:0.8-1.2.

3. The self-degrading temporary plugging agent according to claim 1, wherein: nano SiO hydrophobically modified by silane coupling agent ₂ The degree of modification of (a) is 20 to 70%.

4. The self-degrading temporary plugging agent according to claim 1, wherein: the hydrophobic monomer is hexadecyl dimethyl allyl ammonium chloride.

5. The self-degrading temporary plugging agent according to claim 1, wherein: the initiator is selected from one or more of potassium persulfate, sodium thiosulfate, ammonium persulfate and sodium bisulfite.

6. The self-degrading temporary plugging agent according to claim 5, wherein: the initiator is ammonium persulfate.

7. The process for preparing a self-degradable temporary plugging agent according to any one of claims 1 to 6, wherein: the method comprises the following steps:

dissolving a hydrophilic polymerization monomer in water, and adjusting the solution to be alkalescent to obtain a hydrophilic polymerization monomer solution;

sequentially adding a hydrophobic monomer, the modified nano-particle NP-1 and a cross-linking agent into the hydrophilic polymerization monomer solution, and mixing and dissolving to obtain a mixed solution;

and adding an initiator into the mixed solution, and heating for reaction to obtain a product.

8. The method for preparing a self-degrading temporary plugging agent according to claim 7, wherein: adjusting the pH value of the hydrophilic polymerization monomer to 7.2 to 8, preferably 7.4 to 7.8, and more preferably 7.5;

preferably, the base is sodium hydroxide solution, the concentration of which is 10-20%, preferably 15%.

9. The method for preparing a self-degrading temporary plugging agent according to claim 7, wherein: the temperature of the polymerization reaction is 40-60 ℃, and the reaction time is 3-6h.

10. Use of the temporary plugging agent of any one of claims 1 to 6 in repeated fracturing of a reservoir;

preferably, the method for temporarily blocking the oil layer fracture by using the temporary blocking agent comprises the following steps: screening the temporary plugging agent particles with a set particle size range, uniformly dispersing the temporary plugging agent particles in water to form a stable suspension,

and injecting the suspension into an oil-water well, so that the temporary plugging agent particles enter a plugging target layer, continuously absorbing water and expanding to form a high-strength temporary plugging layer, and plugging cracks.

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