A self-suspending material for CO2 fracturing, its preparation method and application

Abstract

This invention discloses a self-suspending material for CO2 fracturing, its preparation method, and its application, belonging to the field of CO2 fracturing fluids. The self-suspending material for CO2 fracturing and its application utilize spherical quartz sand as a mechanical compressive strength support material, polyamino acids forming a hollow structure through water solubility, and a polymer obtained by polymerizing hydroxybenzoic acid and formaldehyde to protect the quartz sand, improve its compressive strength, and reduce its density. The polymer obtained by polymerizing hydroxybenzoic acid and formaldehyde is a rigid polymer that is insoluble in water and does not increase the viscosity of the fracturing fluid, effectively preventing reservoir damage. The unique hollow structure reduces the material's density, achieving a self-suspending effect. In obtaining the hollow structure, water is used as a template removal agent, effectively avoiding the corrosion problems to the quartz sand caused by using acids or alkalis to remove the template.

Description

Technical Field

[0001] This invention belongs to the field of CO2 fracturing fluid, and in particular to a self-suspending material for CO2 fracturing, its preparation method and application. Background Technology

[0002] With the continuous increase in domestic and international demand for oil and gas, the difficulty of oil and gas extraction is constantly increasing, especially in the face of highly dense and low-permeability oil and gas reservoirs. Under the new circumstances of energy structure adjustment, strong oil and gas demand, and rapid technological development, how to increase oil and gas production has become an important research area. Hydraulic fracturing technology can effectively develop highly dense and low-permeability oil and gas reservoirs, achieving the goal of increasing oil and gas production. Globally, hydraulic fracturing has been the main oil and gas development method in recent decades. However, hydraulic fracturing brings water resource consumption and pollution risks, easily causing reservoir damage such as water lock-in and water sensitivity, and difficulties in fracturing network formation. More importantly, my country's main oil and gas reservoirs are highly dense and low-permeability, making hydraulic fracturing insufficient to meet current extraction requirements and energy demands. Carbon dioxide (CO2) has a better rock-breaking ability than water, allowing CO2 fracturing to produce a more complex fracture network than hydraulic fracturing, thereby improving oil and gas permeability and recovery rate, and holding promise for the efficient extraction of highly dense and low-permeability oil and gas reservoirs. CO2 fracturing can effectively alleviate water resource pressure, is pollution-free, reduces reservoir damage, and sequesters CO2. However, the low density and low viscosity of CO2 result in poor proppant-carrying capacity, which is a bottleneck restricting its widespread application. Therefore, how to improve the proppant-carrying capacity of CO2 is a key scientific problem facing this field.

[0003] CO2 fracturing typically involves Newtonian fluids, power-law fluids, and viscoelastic fracturing fluids. To improve the proppant-carrying capacity of CO2, the fracturing material must be kept in suspension, which requires reducing its settling velocity. This can be achieved by increasing fluid viscosity, increasing fluid density, increasing the diameter of the fracturing material, and reducing the mass of the proppant. Increasing fluid viscosity and density improves CO2 proppant-carrying capacity by altering the properties of the fracturing fluid; increasing the diameter and reducing the mass of the fracturing material improves CO2 proppant-carrying capacity by altering the properties of the fracturing material. However, simply increasing the viscosity of the CO2 fracturing fluid can damage the reservoir and increase costs. Designing a low-density (less than 1.20 g / cm³) fracturing fluid is a better approach. 3Self-suspending materials can suspend in fracturing fluid without increasing its viscosity, offering advantages such as improved proppant carrying capacity and reduced reservoir damage. Currently, no research has been found on self-suspending materials for CO2 fracturing; however, information on self-suspending materials for hydraulic fracturing is available. Hydraulic fracturing self-suspending materials are typically used in clean water fracturing, employing a method of coating water-swellable polymers with quartz sand to suspend the sand in clean water. However, the swelling polymers easily dissolve or suspend in the fracturing fluid, increasing its viscosity and potentially causing reservoir damage. This is detrimental to widespread and long-term hydraulic fracturing applications. Furthermore, since the swelling polymers can only swell in clean water and cannot swell in brine, brines, foamed CO2 fracturing fluids, or liquid CO2 fracturing fluids, they cannot achieve self-sustaining properties and are therefore unsuitable for use in CO2 fracturing. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a self-suspending material for CO2 fracturing, its preparation method, and its application.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for preparing a self-suspended material for CO2 fracturing includes the following steps:

[0007] (1) Disperse quartz sand in a fatty alcohol solution, then add amino acid monomers, and react at 60℃~80℃ for 1~2h to obtain a core-shell structured composite of quartz sand@polyamino acid.

[0008] (2) After the reaction in step (1) is completed, hydroxybenzoic acid and formaldehyde are added to the system. The hydroxybenzoic acid and formaldehyde are polymerized on quartz sand@polyamino acid at 60-80℃ for 24-48h to obtain a core-shell structured composite of quartz sand@polyamino acid@polymer.

[0009] (3) Collect the core-shell structure composite of quartz sand@polyamino acid@polymer, and then soak or wash it with water. The polyamino acid in the core-shell structure composite of quartz sand@polyamino acid@polymer undergoes hydrolysis and forms a hollow structure in its original position. Finally, the core-shell structure composite of quartz sand@polymer is obtained, which is a self-suspended material for CO2 fracturing.

[0010] Furthermore, in step (1), the mass ratio of quartz sand to fatty alcohol is 1:1.

[0011] Furthermore, the mass ratio of quartz sand to amino acid monomers is 1000:(2-5).

[0012] Furthermore, in step (1), the amino acid monomer is glutamic acid, lysine, or arginine.

[0013] Furthermore, the fatty alcohol solution mentioned in step (1) is one or more of methanol, ethanol, propanol, and n-butanol.

[0014] Furthermore, in step (2), the mass ratio of hydroxybenzoic acid, formaldehyde and quartz sand is (15-30): (2-5): 1000.

[0015] A method for preparing a self-suspended material for CO2 fracturing, characterized in that it is prepared according to the method for preparing a self-suspended material for CO2 fracturing according to the present invention.

[0016] Furthermore, it is used as a self-suspending material in foamed CO2 fracturing fluid.

[0017] Furthermore, it is used as a self-suspending material in liquid CO2 fracturing fluid.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention relates to a self-suspending material for CO2 fracturing and its application. It utilizes spherical quartz sand as a mechanical compressive strength support material, polyamino acids to form a hollow structure through water solubility, and a polymer obtained by polymerizing hydroxybenzoic acid and formaldehyde to protect the quartz sand, improve its compressive strength, and reduce its density. The polymer obtained from the polymerization of hydroxybenzoic acid and formaldehyde is a rigid polymer that is insoluble in water and does not increase the viscosity of the fracturing fluid, effectively preventing reservoir damage. The unique hollow structure reduces the material's density, achieving a self-suspending effect. In obtaining the hollow structure, water is used as a template removal agent, effectively avoiding the corrosion problems to the quartz sand caused by using acids or alkalis to remove the template.

[0020] This invention provides a method for preparing self-suspended materials for CO2 fracturing, which has the advantages of simple synthesis method, simple process flow and excellent self-suspending performance, which is conducive to promotion in the field of CO2 fracturing and has broad application prospects. Attached Figure Description

[0021] Figure 1 These are photographs taken under a confocal microscope according to Embodiment 3 of the present invention;

[0022] Figure 2 These are transmission electron microscope (TEM) images from Embodiment 3 of the present invention;

[0023] Figure 3 These are images showing the suspension performance of Embodiment 3 of the present invention in clear water, wherein... Figure 3 (a) is the initial state. Figure 3 (b) shows the state after 10 minutes;

[0024] Figure 4These are images showing the suspension performance of Example 3 of the present invention in foamed CO2, wherein... Figure 4 (a) is the initial state. Figure 4 (b) shows the state after 10 minutes;

[0025] Figure 5 These are images showing the suspension performance of Embodiment 3 of the present invention in liquid CO2, wherein... Figure 5 (a) is the overall view. Figure 5 (b) is an enlarged view;

[0026] Figure 6 This is a schematic diagram of the implementation process of the present invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0028] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0029] Currently, no research has been found on self-suspending materials for CO2 fracturing. Existing technologies only cover self-suspending materials used in hydraulic fracturing, which are commonly used in fresh water fracturing. This involves coating quartz sand with water-swellable polymers to suspend the quartz sand in fresh water. However, the swellable polymers easily dissolve or suspend in the fracturing fluid, increasing the fluid viscosity and potentially causing reservoir damage. This is not conducive to widespread and long-term hydraulic fracturing applications. Furthermore, since the swellable polymers can only swell in fresh water and cannot swell in brine, brines, foamed CO2 fracturing fluids, or liquid CO2 fracturing fluids, they cannot achieve self-sustaining properties and are therefore unsuitable for use in CO2 fracturing. This invention provides a self-suspending material for CO2 fracturing, its preparation method, and its application. Addressing the current bottlenecks in CO2 fracturing technology—namely, the poor proppant-carrying capacity of CO2 due to its low density and viscosity, and the problems of simply increasing the viscosity of the CO2 fracturing fluid causing reservoir damage and increased costs—this invention offers a novel approach by designing a self-suspending material for CO2 fracturing, its preparation method, and its application. Combined with… Figure 6 Let's take a look. Figure 6 This is a schematic diagram of the implementation process of the present invention. The invention uses spherical quartz sand as a mechanical compressive strength support material, polyamino acids to form a hollow structure through water solubility, and a polymer obtained by polymerizing benzoic acid and formaldehyde to protect the quartz sand, improve its compressive strength, and reduce its density. The polymer obtained by polymerizing benzoic acid and formaldehyde is a rigid polymer that is insoluble in water and does not increase the viscosity of the fracturing fluid, effectively preventing reservoir damage. The unique hollow structure reduces the material's density, achieving self-suspension in CO2 fracturing fluids (including foamed CO2 fracturing fluids and liquid CO2 fracturing fluids). In obtaining the hollow structure, water is used as a template removal agent, effectively avoiding the corrosion of the quartz sand caused by using acids or alkalis to remove the template. This invention provides a self-suspension material for CO2 fracturing, its preparation method, and its application. The resulting material effectively avoids the problem of reservoir damage caused by increased CO2 fracturing fluid viscosity. It has advantages such as simple synthesis method, easy process flow, and excellent self-suspension performance, making it suitable for widespread application in the field of CO2 fracturing and possessing broad application prospects.

[0030] The present invention will now be described in further detail with reference to the accompanying drawings:

[0031] This invention provides a method for preparing a self-suspending material for CO2 fracturing, comprising the following steps:

[0032] (1) Weigh quartz sand, amino acid monomers, hydroxybenzoic acid, and formaldehyde in a mass ratio of 1000:(2~5):(15~30):(2~5);

[0033] (2) Wash the quartz sand with water until it is neutral, then wash the quartz sand with acetone or petroleum ether 3 to 5 times, and then wash the quartz sand with water 3 to 5 times.

[0034] (3) Place the quartz sand from step (2) into a fatty alcohol solution with a mass ratio of quartz sand to fatty alcohol of 1:1. Stir in a constant temperature water bath at 60℃~80℃ for 5~10 min at a stirring rate of 100r / min~500r / min. Then place the amino acid monomer into a fatty alcohol solution containing quartz sand and stir in a constant temperature water bath at 60℃~80℃ for 1~2 h.

[0035] (4) After the reaction in step (3) is completed, hydroxybenzoic acid and formaldehyde are placed in the system at the same time, and the reaction is stirred and maintained in a constant temperature water bath of 60℃~80℃ for 24h~48h.

[0036] (5) After the reaction in step (4) is completed, cool the system to room temperature, filter the solution to obtain a solid substance, and place it in an oven to dry at 80℃~100℃ for 8h~12h to obtain the dried "core-shell" structure intermediate.

[0037] (6) The dried “core-shell” structure intermediate is soaked in water with a mass of ten times its weight, or washed with water for 1 to 2 hours, and then dried at 80°C to 100°C to obtain an “eggshell” structure, which is a self-suspended material for CO2 fracturing.

[0038] Among them, the quartz sand in step (1) is fracturing material quartz sand, with specifications including 20 / 40 mesh, 30 / 50 mesh, 40 / 70 mesh, and 70 / 140 mesh, as a mechanical compressive support material;

[0039] The polyamino acid in step (3) is an intermediate template structure that can dissolve in water and is used to obtain a hollow structure, which can reduce the density of the self-suspended material. The polyamino acid is obtained by polymerizing amino acid monomers in a fatty alcohol solution. The amino acid monomers include glutamic acid, lysine, and arginine.

[0040] The polymer obtained by polymerizing hydroxybenzoic acid and formaldehyde in step (4) is the outermost protective layer of the self-suspending material, which has the functions of protecting the quartz sand, improving its compressive strength, and reducing the density of the material. The polymer obtained by polymerizing hydroxybenzoic acid and formaldehyde is obtained by polymerizing in a fatty alcohol solution. The hydroxybenzoic acid can be monohydroxybenzoic acid or hydroxybenzoic acid.

[0041] The core-shell intermediate in step (5) is the structure of a polymer obtained by polymerizing quartz sand, polyamino acid, hydroxybenzoic acid and formaldehyde. It is an intermediate process for obtaining self-suspended materials for CO2 fracturing. After soaking or washing with water, the polyamino acid is removed to obtain a hollow "eggshell" structured self-suspended material.

[0042] Quartz sand, amino acid monomers, hydroxybenzoic acid, and formaldehyde are prepared in a mass ratio of 1000:(2-5):(15-30):(2-5); the fatty alcohol solution is one or more of methanol, ethanol, propanol, and n-butanol, and the mass ratio of quartz sand and fatty alcohol solution is 1:1; the polyamino acid is obtained by reacting amino acid monomers in a fatty alcohol solution at 60-80℃ for 1-2 hours; after obtaining the polyamino acid, hydroxybenzoic acid and formaldehyde are reacted in a fatty alcohol solution at 60-80℃ for 24-48 hours to obtain a polymer of hydroxybenzoic acid and formaldehyde; the "core-shell" structure intermediate is obtained by drying the polymerized hydroxybenzoic acid and formaldehyde at 80-100℃ for 8-12 hours; the "eggshell" structure is obtained by soaking the "core-shell" structure intermediate in water ten times its mass, or by continuously washing it with water for 1-2 hours, and then drying it at 80-100℃.

[0043] Example

[0044] This invention provides multiple embodiments to further explain and illustrate the self-suspended CO2 fracturing material, its preparation method, its application, and the beneficial effects thereof.

[0045] Because the density of self-suspended materials used in CO2 fracturing is less than 1.20 g / cm³ 3 The key to the self-suspension of materials in CO2 fracturing fluid is the ratio of quartz sand, amino acid monomers, hydroxybenzoic acid, and formaldehyde, which has a significant impact on the density of self-suspension materials for CO2 fracturing. By controlling a single variable, the influence of the ratio on density is explained. Examples 1-4 show the influence of changing the amount of amino acid monomer on density while keeping other ratios constant. Examples 3, 5-8 show the influence of changing the amount of hydroxybenzoic acid and formaldehyde on density while keeping other ratios constant.

[0046] Example 1

[0047] Weigh 1000g of 70 / 140 mesh quartz sand, 2g of lysine monomer, 30g of hydroxybenzoic acid, and 5g of formaldehyde according to a mass ratio of 1000:2:30:5, and set aside. Wash the quartz sand with water until neutral, then wash it three times with acetone or petroleum ether, followed by three more washes with water. Place the quartz sand in 1000g of n-butanol solution and stir for 10 minutes in an 80℃ constant temperature water bath at a stirring rate of 500r / min. Then, place the amino acid monomer in the n-butanol solution containing the quartz sand and stir in an 80℃ constant temperature water bath. The reaction was maintained for 2 hours. After the reaction was complete, hydroxybenzoic acid and formaldehyde were simultaneously added to the system, and the mixture was stirred and maintained in an 80°C constant temperature water bath for 48 hours. After the reaction was complete, the system was cooled to room temperature, the solution was filtered to obtain a solid substance, which was then placed in an oven and dried at 100°C for 12 hours to obtain a dried "core-shell" structure intermediate. The dried "core-shell" structure intermediate was then immersed in water with a mass ten times its weight, or continuously washed with water for 1 hour, and then dried at 80°C to obtain an "eggshell" structure, which is the self-suspended material for CO2 fracturing. The density results are shown in Table 1.

[0048] Example 2

[0049] The difference between this embodiment and Example 1 is that the preparation process was carried out by weighing 1000g of quartz sand, 3g of amino acid monomer, 30g of hydroxybenzoic acid, and 5g of formaldehyde in a mass ratio of 1000:3:30:5. The resulting density is shown in Table 1.

[0050] The test results are shown in Tables 1 to 3.

[0051] Example 3

[0052] The difference between this embodiment and Example 1 is that the preparation process was carried out by weighing 1000g of quartz sand, 4g of amino acid monomer, 30g of hydroxybenzoic acid, and 5g of formaldehyde in a mass ratio of 1000:4:30:5. The resulting density is shown in Table 1.

[0053] Example 4

[0054] The difference between this embodiment and Example 1 is that the mass ratio of 1000g of quartz sand, 5g of amino acid monomer, 30g of hydroxybenzoic acid, and 5g of formaldehyde were weighed to complete the preparation process. The resulting density is shown in Table 1.

[0055] Table 1. Densities of self-suspending materials for CO2 fracturing in Examples 1-4

[0056] <![CDATA[Density (g / cm 3 )]]> Detection value 1 Detection value 2 Detection value 3 average value Example 1 1.18 1.20 1.18 1.19 Example 2 1.11 1.09 1.08 1.09 Example 3 1.02 1.04 1.03 1.03 Example 4 1.04 1.03 1.03 1.03

[0057] As can be seen from Examples 1-4, the density of the self-suspended material for CO2 fracturing shows a continuous decreasing trend as the amount of amino acid monomers increases, until the density decreases to 1.03 g / cm³. 3 A density reduction plateau appeared. This may be because as the amount of amino acid monomers increases, the amount of polyamino acids increases, leading to an increase in the template. After removing the template, the hollow structure increases, thus reducing the density. Further increasing the amount of amino acid monomers does not increase the hollow structure, resulting in the density reduction plateau. Therefore, it is evident that in Example 3, when the amount of amino acid is 4g, i.e., the mass ratio of quartz sand, amino acid monomers, hydroxybenzoic acid, and formaldehyde is 1000:4:30:5, the resulting self-suspended CO2 fracturing material has the lowest density, and the mass ratio of 1000:4:30:5 is the optimal condition.

[0058] Characterization results from Example 3 Figures 1-5 It is possible to obtain the microstructure and self-suspending properties of the material. Figure 1 These are confocal images of the material. The central particle in the image is quartz sand, and the slightly lighter-colored surrounding particles are polymer shells. There is a certain space between the core and the shell, indicating that the material has an "eggshell" structure. Figure 2 The TEM image of the material shows that the central black opaque core is a quartz sand core, the black outer shell is a polymer shell, and the transparent area between the core and the shell is the hollow structure after the template is removed, proving that the material has an "eggshell" structure. Figure 3 Images showing the suspension properties of the material in clear water. Figure 3 (a) is the initial state. Figure 3 (b) shows the state after 10 minutes, indicating that the material remains suspended on various surfaces of the clear water. Tests show that the suspension can be maintained for more than 10 minutes. The foamed CO2 is a prepared foamed CO2 fracturing fluid, composed of water, nonionic surfactant, and saturated CO2 gas. Figure 4 It can be seen that the material can be suspended in foamed CO2. Figure 4 (a) is the initial state. Figure 4 (b) shows the state after 10 minutes. The suspension performance is comparable to that in clear water, and it can remain suspended for more than 10 minutes. Figure 5 It describes the suspension performance of the material in liquid CO2. Figure 5 (a) is the overall view. Figure 5 (b) is a magnified view. Under a certain pressure, liquid CO2 was obtained, and the material can be seen to be suspended in the liquid CO2. The magnified view shows that the material is uniformly dispersed in the liquid CO2 and can remain suspended for more than 5 minutes. These test results indicate that the obtained material has a distinct "eggshell" structure, achieving the goal of suspension in CO2.

[0059] Example 5

[0060] Weigh 1000g of 70 / 140 mesh quartz sand, 4g of lysine monomer, 40g of hydroxybenzoic acid, and 6g of formaldehyde according to a mass ratio of 1000:4:40:6, and set aside. Wash the quartz sand with water until neutral, then wash it three times with acetone or petroleum ether, followed by three more washes with water. Place the quartz sand in 1000g of n-butanol solution and stir in an 80℃ constant temperature water bath for 10 minutes at a stirring rate of 500r / min. Then, place the amino acid monomer in the n-butanol solution containing the quartz sand and stir in an 80℃ constant temperature water bath. The reaction was maintained for 2 hours. After the reaction was complete, hydroxybenzoic acid and formaldehyde were simultaneously added to the system, and the mixture was stirred and maintained in an 80°C constant temperature water bath for 48 hours. After the reaction was complete, the system was cooled to room temperature, the solution was filtered to obtain a solid substance, which was then placed in an oven and dried at 100°C for 12 hours to obtain a dried "core-shell" structure intermediate. The dried "core-shell" structure intermediate was then immersed in water with a mass ten times its weight, or continuously washed with water for 1 hour, and then dried at 80°C to obtain an "eggshell" structure, which is the self-suspended material for CO2 fracturing. The density results are shown in Table 2.

[0061] Example 6

[0062] The difference between this embodiment and Example 5 is that the preparation process was completed by weighing 1000g of quartz sand, 4g of amino acid monomer, 25g of hydroxybenzoic acid, and 4g of formaldehyde in a mass ratio of 1000:4:25:4. The resulting density is shown in Table 2.

[0063] Example 7

[0064] The difference between this embodiment and Example 5 is that the preparation process was completed by weighing 1000g of quartz sand, 4g of amino acid monomer, 20g of hydroxybenzoic acid, and 3g of formaldehyde in a mass ratio of 1000:4:20:3. The resulting density is shown in Table 2.

[0065] Example 8

[0066] The difference between this embodiment and Embodiment 5 is that the preparation process was carried out by weighing 1000g of quartz sand, 4g of amino acid monomer, 15g of hydroxybenzoic acid, and 2g of formaldehyde in a mass ratio of 1000:4:15:2. The resulting density results are shown in Table 2.

[0067] Table 2. Effect of density on CO2 fracturing self-suspending material density in Examples 3 and 5-8.

[0068]

[0069]

[0070] As can be seen from Examples 5-8, as the dosage of hydroxybenzoic acid and formaldehyde continuously decreases, the density of the self-suspended material for CO2 fracturing shows a continuous increasing trend, until it increases to 1.14 g / cm³. 3 Approximately 1.20 g / cm³ 3 This may be because as the amount of hydroxybenzoic acid and formaldehyde decreases, the polymer shell layer gradually reduces, resulting in a polymer density below 1.00 g / cm³. 3 Reducing the amount of polymer is detrimental to the reduction of material density. As can be seen from Examples 3 and 5, with the increase of hydroxybenzoic acid and formaldehyde dosage, the density of the self-suspended material for CO2 fracturing does not change significantly, remaining at 1.03 g / cm³. 3 This may be because increasing the ratio of hydroxybenzoic acid to formaldehyde to 30:5, further increasing the amounts of hydroxybenzoic acid and formaldehyde does not increase the polymer content, making it difficult to further reduce the material's density, thus resulting in a density reduction plateau. In Example 3, when the amino acid content was 4g, i.e., the mass ratio of quartz sand, amino acid monomer, hydroxybenzoic acid, and formaldehyde was 1000:4:30:5, the resulting self-suspended CO2 fracturing material had the lowest density, and the mass ratio of 1000:4:30:5 was the optimal condition.

[0071] The comparison of the results from the above embodiments shows that the self-suspended material for CO2 fracturing, the preparation method, and the application provided by this invention can achieve a reduction in material density to less than 1.20 g / cm³. 3 Targets suspended in foam CO2 and liquid CO2.

[0072] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a self-suspended material for CO2 fracturing, characterized in that, Includes the following steps: (1) Disperse quartz sand in a fatty alcohol solution, then add amino acid monomers, and react at 60 ℃~80 ℃ for 1~2 h to obtain a core-shell structured composite of quartz sand@polyamino acid. (2) After the reaction in step (1) is completed, hydroxybenzoic acid and formaldehyde are added to the system. The hydroxybenzoic acid and formaldehyde are polymerized on quartz sand@polyamino acid at 60~80 ℃ for 24~48 h to obtain a core-shell structured composite of quartz sand@polyamino acid@polymer. The mass ratio of hydroxybenzoic acid, formaldehyde and quartz sand is (15~30):(2~5):1000; (3) Collect the core-shell structure composite of quartz sand@polyamino acid@polymer, and then soak or wash it with water. The polyamino acid in the core-shell structure composite of quartz sand@polyamino acid@polymer undergoes hydrolysis and forms a hollow structure in its original position. Finally, the core-shell structure composite of quartz sand@polymer is obtained, which is a self-suspended material for CO2 fracturing.

2. The method for preparing the self-suspended material for CO2 fracturing according to claim 1, characterized in that, In step (1), the mass ratio of quartz sand to fatty alcohol is 1:

1.

3. The method for preparing the self-suspended material for CO2 fracturing according to claim 1, characterized in that, The mass ratio of quartz sand to amino acid monomers is 1000:(2~5).

4. The method for preparing the self-suspended material for CO2 fracturing according to claim 1, characterized in that, In step (1), the amino acid monomers are glutamic acid, lysine, or arginine.

5. The method for preparing the self-suspended material for CO2 fracturing according to claim 1, characterized in that, The fatty alcohol solution mentioned in step (1) is one or more of methanol, ethanol, propanol, and n-butanol.

6. A self-suspending material for CO2 fracturing, characterized in that, The material is prepared according to the method for preparing self-suspended CO2 fracturing material according to any one of claims 1-5.

7. The application of the self-suspending material for CO2 fracturing according to claim 6, characterized in that, It is used as a self-suspending material in foamed CO2 fracturing fluid.

8. The application of the self-suspending material for CO2 fracturing according to claim 6, characterized in that, It is used as a self-suspending material in liquid CO2 fracturing fluid.

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