Method and product for low-temperature preparation of ceramic fracturing proppant with SiO2-Al2O3 mullite phase

Abstract

This invention provides a method and product for preparing ceramic fracturing proppant with a SiO2-Al2O3 mullite phase at low temperature. The method includes: placing a mixture of SiO2, Al2O3, and a transient sintering aid in a low-temperature sintering apparatus; with the pressure relief port of the pressure shaft closed, performing a first pressurization treatment on the sintering chamber using the pressure shaft, controlling the gas pressure inside the sintering chamber to be higher than the gas pressure outside the sintering chamber, obtaining a first pressurization treatment product; then opening the pressure relief port, adjusting the gas pressure inside and outside the sintering chamber to be consistent, and performing a second pressurization treatment, obtaining a mullite phase fracturing proppant with excellent mechanical properties, low breakage rate, stable physical and chemical properties, and resistance to chemical corrosion. This preparation method has the advantages of simple synthesis, ease of implementation, low sintering temperature, and energy saving, which is conducive to its promotion in the field of fracturing in the oil and gas industry and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of fracturing materials in the oil and gas industry, and more specifically, to a method and product for preparing ceramic fracturing proppant with SiO2-Al2O3 mullite phase at low temperature. 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. Fracturing technology can effectively develop highly dense and low-permeability oil and gas reservoirs, thereby achieving the goal of increasing oil and gas production.

[0003] Globally, hydraulic fracturing has been a major oil and gas development method in recent decades, effectively increasing oil and gas well production. Fracturing proppant is a key construction material commonly used in hydraulic fracturing. Quartz sand and ceramic fracturing proppant account for over 90% of the total proppant usage. However, quartz sand fracturing proppant, being a natural product, has poor mechanical properties, making it difficult to apply to high-yield wells and unable to increase oil and gas production.

[0004] Ceramsite fracturing proppant is a high-performance product obtained through artificial sintering. Due to its excellent mechanical properties, it has been widely used in high-yield wells and for increasing oil and gas production. However, the sintering temperature of ceramsite fracturing proppant is typically between 900℃ and 1300℃. The excessively high sintering temperature resulting from traditional sintering methods leads to high production costs, limiting the application range of ceramsite fracturing proppant.

[0005] Furthermore, ceramsite fracturing proppant is mostly prepared using silica. Although silica has a theoretical hardness of 7, which is an apparent hardness, it cannot be achieved in actual artificial synthesis. Moreover, silica itself has low mechanical properties, poor toughness, and is brittle. Fracturing proppant is often used in oil and gas formations with complex acid and alkali compositions. Due to silica's poor alkali resistance, it easily forms soluble salts with alkalis, making it unsuitable for use in complex and variable environments. Therefore, although silica is commonly used as a fracturing material and has good rigidity, it still has certain shortcomings in toughness, mechanical strength, and alkali resistance. It may not be able to meet the demands of more complex acid and alkali environments or higher mechanical performance requirements, necessitating further performance improvements in fracturing materials.

[0006] Therefore, as oil and gas extraction develops in a more complex and variable direction, it is very important to address the problems of excessively high sintering temperature of ceramic fracturing proppant and the inability of fracturing materials to meet higher application requirements in terms of toughness, mechanical strength, and alkali resistance. Summary of the Invention

[0007] The main objective of this invention is to provide a method and product for preparing ceramic fracturing proppant with SiO2-Al2O3 mullite phase at low temperature, in order to solve the problems in the prior art that ceramic fracturing proppant cannot be prepared under sintering conditions at lower temperatures, and that the fracturing materials cannot meet higher application requirements in terms of toughness, mechanical strength and alkali resistance.

[0008] To achieve the above objectives, according to a first aspect of the present invention, a method for preparing a ceramic fracturing proppant having a SiO2-Al2O3 mullite phase at low temperature is provided. The method includes: placing a mixture of SiO2, Al2O3, and a transient sintering aid in a low-temperature sintering apparatus; with the pressure relief port of a pressure shaft closed, performing a first pressurization treatment on the sintering chamber using the pressure shaft, wherein during the first pressurization treatment, the gas pressure inside the sintering chamber is controlled to be higher than the gas pressure outside the sintering chamber, resulting in a first pressurization treatment product; opening the pressure relief port, adjusting the gas pressure inside and outside the sintering chamber to be consistent, and performing a second pressurization treatment on the first pressurization treatment product using the pressure shaft, resulting in the ceramic fracturing proppant; the temperature of the first pressurization treatment and / or the second pressurization treatment is 90-120°C, and the temperature of the first pressurization treatment is higher than the temperature of the second pressurization treatment. The instantaneous sintering aid includes: water, siloxane, silicic acid, ethyl orthosilicate, and alkali; preferably, the mass of the instantaneous sintering aid accounts for 1-4% of the sum of the mass of SiO2, Al2O3, and the instantaneous sintering aid.

[0009] Furthermore, the particle size of SiO2 and Al2O3 is independently ≤10μm; preferably, the molar ratio of SiO2 to Al2O3 is 1:2-5.

[0010] Furthermore, before the first and second pressurization processes are performed, the temperature in the sintering chamber is preheated to the temperature required for either the first or second pressurization process using a heating device.

[0011] Further, the pressure of the first pressurization treatment is 100-500 MPa; preferably, the time of the first pressurization treatment is 2-4 hours; preferably, the pressure of the second pressurization treatment is 100-500 MPa; preferably, the time of the second pressurization treatment is 1-4 hours.

[0012] Furthermore, the low-temperature sintering apparatus includes: a pressure shaft, a sintering chamber, an upper end face, and a lower end face; the pressure shaft is located on the side of the upper end face near the lower end face, and the sintering chamber is located on the side of the lower end face near the upper end face; the pressure shaft is hollow and can be inserted into the sintering chamber and move vertically like a piston; a pressure relief port is provided on the side wall of the pressure shaft, which is connected to the gas passage outlet at the end of the pressure shaft near the sintering chamber, forming a gas passage.

[0013] Furthermore, the sintering chamber is provided with multiple sintering tanks for holding sintering raw materials; multiple sintering tank pressure shafts are provided at one end of the pressure shaft near the sintering chamber, and the multiple sintering tank pressure shafts can be inserted into the multiple sintering tanks one by one and perform piston movement in the vertical direction; preferably, the sintering tanks and the sintering tank pressure shafts are both cylindrical, and the diameters of the sintering tanks and the sintering tank pressure shafts are each independently 100-800μm.

[0014] Furthermore, the low-temperature sintering apparatus also includes a press; the press includes an upper press and a lower press, the upper press being in detachable contact with the side of the upper end face away from the lower end face, and the lower press being in detachable contact with the side of the lower end face away from the upper end face.

[0015] Furthermore, the low-temperature sintering apparatus also includes a heating device; the heating device is fitted around the outer periphery of the sintering chamber and is used to provide heat to the sintering chamber; preferably, the heating device also includes a temperature display element, which is selected from a thermometer, a sensor or a digital temperature display.

[0016] Furthermore, the gas channel is a single hollow structure set inside the pressure shaft, and the longitudinal projection of the gas channel cannot fall into the sintering tank, and the horizontal projection of the gas channel does not overlap with the sintering tank; preferably, the gas channel is cylindrical, and the diameter of the gas channel outlet and the pressure relief port is less than 100μm; preferably, the upper end face and the lower end face are connected by a lead screw.

[0017] Furthermore, the low-temperature sintering device also includes inner end faces. There are two inner end faces: one inner end face is located between the upper end face and the pressure shaft on the side near the lower end face, and the other inner end face is located between the lower end face and the sintering chamber on the side near the upper end face.

[0018] Furthermore, the pressure relief port has two states: open and closed. The opening and closing of the pressure relief port can be controlled by the connection between the nut and the internal thread of the pressure relief port or by the buckle set on the outside of the pressure relief port.

[0019] To achieve the above objectives, according to a second aspect of the present invention, a ceramic fracturing proppant having a SiO2-Al2O3 mullite phase is provided using the above-described preparation method, wherein the relative density of the ceramic fracturing proppant is greater than 90%; preferably, under the test method for performance testing of proppants for hydraulic fracturing and gravel filling operations (SY / T5108-2014), the breakage rate of the ceramic fracturing proppant is less than 10%.

[0020] The present invention involves mixing a transient sintering aid with raw materials. The mixture is first pre-pressurized, ensuring the pressure inside the sintering chamber is higher than the external pressure. Under high pressure and low temperature, the transient sintering aid in the sintering chamber forms a relatively dense fracturing proppant with the raw materials. Then, by adjusting the vent of the pressure shaft to an open state, the pressure inside the low-temperature sintering device is made consistent with the external pressure, further pressurizing the fracturing proppant to densify it. This allows for the production of a relatively dense ceramic fracturing proppant at a lower temperature. This preparation method has the advantages of simple synthesis, ease of implementation, low sintering temperature, and energy saving, making it suitable for widespread application in the fracturing field of the oil and gas industry and possessing broad application prospects. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, 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 undue limitation of the invention. In the drawings:

[0022] Figure 1 A front view of the low-temperature sintering apparatus used in the embodiments is shown;

[0023] Figure 2 A horizontal cross-sectional view of the sintering chamber of the low-temperature sintering apparatus used in the embodiments is shown.

[0024] Figure 3 A side view of the pressure shaft of the low-temperature sintering apparatus used in the embodiment is shown;

[0025] Figure 4 The SEM image of the ceramic fracturing proppant obtained in Example 3 of the present invention is shown;

[0026] Figure 5 The XRD pattern of the ceramic fracturing proppant obtained in Example 3 of the present invention is shown;

[0027] The above figures include the following reference numerals:

[0028] 1. Press; 2. Heating device; 3. Pressure shaft; 4. Pressure relief port; 5. Sintering chamber; 6. Upper end face; 7. Lower end face; 8. Lead screw; 9. Inner end face; 10. Sintering tank; 11. Gas passage; 12. Sintering tank pressure shaft; 13. Gas passage outlet. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0030] As mentioned in the background section, existing ceramic fracturing proppants are mostly prepared using silica. Although silica has a theoretical hardness of 7, which is an apparent hardness, it cannot be achieved in actual artificial synthesis. Furthermore, silica itself has low mechanical properties, poor toughness, and is brittle. Fracturing proppants are often used in oil and gas formations with complex acid and alkali compositions. Due to silica's poor alkali resistance, it easily forms soluble salts with alkalis, making it unsuitable for use in complex and variable environments. Therefore, although silica is commonly used as a fracturing material and has good rigidity, it still has certain shortcomings in toughness, mechanical strength, and alkali resistance. It may not be able to meet the demands of more complex acid and alkali environments or higher mechanical performance requirements, necessitating further performance improvements in fracturing materials.

[0031] Furthermore, current methods for preparing ceramsite fracturing proppant still rely on high-temperature sintering, typically between 900℃ and 1300℃. This excessively high sintering temperature leads to high production costs, limiting the application range of ceramsite proppant, hindering the further development of hydraulic fracturing, and failing to meet current oil and gas extraction requirements and energy demands. Because current technology has not achieved a fundamental breakthrough, the sintering temperature must be between two-thirds and the melting point of the sintering material to achieve particle densification. This results in excessively high sintering temperatures for ceramsite proppant. Without advanced sintering technology, dense, high-quality ceramsite proppant cannot be obtained when the sintering temperature does not exceed two-thirds of the melting point of the sintering material.

[0032] However, although existing cold sintering technology exists, it is mostly used in the electronics field to prepare conductive materials. However, the equipment used cannot meet the morphology requirements of ceramsite fracturing proppant, and the sintering temperature is still higher than 300°C, making it impossible to obtain dense ceramic materials at lower temperatures (90-120°C). In addition, the raw materials of existing cold sintering technology are different from those of the ceramsite fracturing proppant in this application, and the sintering temperature is still relatively high (greater than 300°C), making it difficult to apply it to the preparation of ceramsite fracturing proppant in this application.

[0033] Beneficial effects

[0034] Therefore, addressing the current technical bottleneck in the field of ceramsite proppant, namely the excessively high sintering temperature, typically exceeding 900℃, this invention aims to provide a method and product for low-temperature preparation of ceramsite proppant. This invention utilizes a self-made low-temperature sintering device, using SiO2 powder and Al2O3 powder as raw materials, supplemented by a transient sintering aid. The sintering process achieves densification, generating a mullite phase with high mechanical properties and densifying the ceramsite grains.

[0035] Mullite refers to a series of minerals composed of aluminosilicates. Its molecular formula is SiO2-Al2O3. It is the most important binary system in ceramics. It has the characteristics of uniform expansion, good thermal shock stability, high load softening point, low high temperature creep, high hardness, stable physical and chemical properties, and good chemical corrosion resistance. It can be used in the complex and variable environment of oil and gas extraction.

[0036] Existing methods for synthesizing mullite phases require sintering at 1300-1400℃ under normal pressure. However, this application ingeniously combines solvothermal (water) sintering with low-temperature sintering to obtain the SiO2-Al2O3 mullite phase ceramic fracturing proppant of this application at a lower temperature (90-120℃). Specifically, during the first stage of pressurization, SiO2 and Al2O3 powders, under the self-generated pressure of the instantaneous sintering aid, low-temperature assisted sintering, and solvothermal (water) action, undergo pressure holding and temperature holding to initially obtain a densified SiO2-Al2O3 mullite phase. Subsequently, during the second stage of pressurization, the entire densification process is completed through low-temperature sintering, thereby obtaining a SiO2-Al2O3 mullite phase fracturing proppant with excellent mechanical properties, low breakage rate, stable physical and chemical properties, and resistance to chemical corrosion at 90-120℃. This SiO2-Al2O3 mullite phase fracturing proppant is suitable for various harsh working conditions with complex formations and variable environments, providing strong technical support for research and development in this field.

[0037] The principle of sintering using a transient sintering aid is as follows: The transient sintering aid in this application must be able to leave / escape from the grain surface and grain boundaries in a gaseous or liquid form under certain conditions, leaving only the grains and grain boundaries. This prevents the introduction of unknown impurities due to transient sintering aid residue. This application can complete the densification process of SiO2 and Al2O3 at low temperatures, thereby obtaining a fracturing proppant with low breakage rate, good mechanical properties, and high strength.

[0038] By utilizing low-temperature sintering equipment to simultaneously provide constant pressure and temperature, external conditions are provided for the sintering process. The volatility and binding properties of the instantaneous sintering aid provide material conditions for the densification process. The combined effect of these two aspects allows the ceramsite grains to reach a densification degree at 90-120℃, resulting in ceramsite fracturing proppant with a relative density greater than 0.90 and a breakage rate of less than 10% under the performance test method of proppant for hydraulic fracturing and gravel filling operations in SY / T5108-2014.

[0039] This invention eliminates the need for a high-temperature process, effectively reducing the sintering temperature of the ceramic proppant. It achieves a dense, high-quality ceramic proppant at a sintering temperature below two-thirds of the melting point of the sintering material. Overall, this invention offers advantages such as simple synthesis, ease of implementation, low sintering temperature, and energy saving, making it suitable for widespread application in the fracturing field of the oil and gas industry and possessing broad application prospects.

[0040] In a first typical embodiment of this application, a method for preparing ceramsite fracturing proppant at low temperature is provided. The method includes: placing a mixture of SiO2, Al2O3, and a transient sintering aid in a low-temperature sintering apparatus; with the pressure relief port of a pressure shaft closed, performing a first pressurization treatment on the sintering chamber using the pressure shaft, wherein during the first pressurization treatment, the gas pressure inside the sintering chamber is controlled to be higher than the gas pressure outside the sintering chamber; obtaining a first pressurization treatment product under the first pressurization treatment conditions; opening the pressure relief port, adjusting the gas pressure inside and outside the sintering chamber to be consistent, and performing a second pressurization treatment on the first pressurization treatment product using the pressure shaft to obtain the ceramsite fracturing proppant; the temperature of the first pressurization treatment and / or the second pressurization treatment is 90-120°C, and the temperature of the first pressurization treatment is higher than the temperature of the second pressurization treatment. Preferably, the temperature of the first pressurization treatment is 110°C.

[0041] The pressure applied during the sintering process is divided into two stages: In the first stage, the pressure shaft of the sintering tank is subjected to a constant pressure of 100-500 MPa because the pressure generated spontaneously by the instantaneous sintering aid does not need to contact the mixture of SiO2 powder and Al2O3 powder in the sintering tank. The pressure relief port is closed and the pressure is maintained for more than 2 hours. After that, the pressure is released by opening the pressure relief port to the same pressure as atmospheric pressure, and the second stage is immediately carried out.

[0042] The second process involves releasing pressure spontaneously generated by the instantaneous sintering aid through a pressure relief port, promoting densification. The sintering chamber integrates a sintering tank to hold a mixture of SiO2 and Al2O3 powders. A pressure shaft in the sintering tank then transmits pressure to the corresponding mixture of SiO2 and Al2O3 powders within the sintering chamber. The pressure shaft needs to contact the mixture of SiO2 and Al2O3 powders in the sintering tank, applying a constant pressure of 100-500 MPa, keeping the pressure relief port open, and maintaining this pressure for at least 30 minutes. After removing the pressure and allowing natural cooling, a dense ceramic fracturing proppant with a mullite phase is obtained.

[0043] The pressure relief port is a small hole located on the pressure shaft that can be opened and closed. When the pressure relief port is open, the pressure inside the sintering chamber is the same as the outside pressure. When the pressure relief port is closed, the pressure inside the sintering chamber is greater than the outside pressure. The pressure relief port is closed only in the first pressurization process, and the remaining pressure relief ports are in the open state.

[0044] It is important to emphasize that this invention employs the two-stage pressurization process described above. This not only avoids the problem of insufficient structural densification caused by the inability to stably control the low-temperature sintering environment during a single pressurization process, but also avoids the drawbacks of three or more multi-stage pressurization processes, such as increased process complexity and excessive energy consumption.

[0045] This application mixes a transient sintering aid with raw materials in a sintering chamber. Using a pressure shaft with internal gas channels, the pressure relief port on the side wall is closed to pre-pressurize the mixture, making the pressure inside the sintering chamber higher than the external pressure. Under high pressure and low temperature, the transient sintering aid boils, forming a relatively dense initial fracturing proppant with the raw materials. Simultaneously, the transient sintering aid is completely separated from the fracturing proppant through volatilization or adhesion, without causing any contamination. After pre-pressurization, the pressure relief port is opened to release gas. The gas channels inside the pressure shaft bring the pressure inside the sintering chamber back to the external pressure, and further mechanical pressure is applied to densify the initial fracturing proppant, resulting in a relatively dense ceramic fracturing proppant at a lower temperature. Any low-temperature sintering apparatus capable of pre-pressurizing and releasing gas after pre-pressurizing the mixture of sintering raw materials and transient sintering aid, followed by further mechanical application, is suitable for this application. In a preferred embodiment, this application utilizes... Figure 1-3 The low-temperature sintering apparatus shown is used for the preparation of ceramic fracturing proppant.

[0046] The transient sintering aid in this application must, under certain conditions (such as 100-500 MPa and 20-120°C in this application), be able to leave / escape from the grain surface and grain boundaries in a gaseous or liquid form, leaving only the grains and grain boundaries. This prevents the introduction of unknown impurities due to residual transient sintering aid. This application can complete the densification process of SiO2 and Al2O3 at low temperatures, thereby obtaining a fracturing proppant with low fragmentation rate, good mechanical properties, and high strength.

[0047] In a preferred embodiment, the transient sintering aid is selected from one of the following: water, siloxane, silicic acid, silicic acid derivatives (such as ethyl orthosilicate), and alkali (ammonia, urea, and NaOH). Preferably, the transient sintering aid is selected from one of silicic acid, ethyl orthosilicate, or NaOH. To make the sintered product more dense, in a preferred embodiment, the mass of the transient sintering aid accounts for 1-4% of the sum of the mass of SiO2, Al2O3, and the transient sintering aid, preferably 3%, and more preferably, when the transient sintering aid is water, the mass of the transient sintering aid accounts for 3% of the sum of the mass of silicon dioxide and the transient sintering aid.

[0048] Different types of siloxane molecules produce ceramsite fracturing proppants with varying properties due to their different structures. Siloxanes with long chains and unsaturated bonds (such as KH570) benefit from the fact that the long chains avoid the steric hindrance effect on densification, while the unsaturated bonds facilitate the condensation reaction; both contribute to densification, thereby increasing relative density and reducing breakage rate. Ceramsite fracturing proppants made from siloxanes without long chains and unsaturated bonds (such as A171) generally exhibit moderate performance. Ceramsite fracturing proppants made from siloxanes with long chains but no unsaturated bonds (such as silicone oil) have moderate relative density and breakage rate performance.

[0049] Silicic acid and its derivatives can generate SiO2 and H2O through hydrolysis. The newly generated SiO2 and the volatile H2O can improve the compactness of the ceramic fracturing proppant during sintering, while filling the voids.

[0050] The alkaline substances used, such as ammonia water and urea, can effectively volatilize NH3 and H2O at temperatures above 100°C, promoting grain densification. If NaOH, which can react to form a binder, is used, the binder properties of the product Na2SiO3 can be utilized to promote grain densification.

[0051] To achieve a denser ceramic proppant, in a preferred embodiment, the particle size of both SiO2 and Al2O3 is independently ≤10μm. In another preferred embodiment, the raw materials are SiO2 and Al2O3, with a molar ratio of SiO2 to Al2O3 of 1:2-5. Specifically, when the molar ratio of SiO2 to Al2O3 is less than or equal to 0.5, sintering SiO2 and Al2O3 together as raw materials can form a mullite phase with high mechanical properties, thereby achieving densification of the ceramic grains in the proppant.

[0052] In order to efficiently sinter the ceramic fracturing proppant and reduce energy consumption, in a preferred embodiment, the temperature in the low-temperature sintering apparatus is preheated to the temperature required for the first or second pressurization treatment before the first or second pressurization treatment is performed, and the preheating rate is 10°C / min.

[0053] In order to efficiently complete sintering, in a preferred embodiment, the pressure of the first pressurization treatment is 100-500 MPa; preferably, the time of the first pressurization treatment is 2-4 hours; the pressure of the second pressurization treatment is 100-500 MPa; preferably, the time of the second pressurization treatment is 1-4 hours, and more preferably 3 hours.

[0054] In a preferred embodiment, this application provides a low-temperature sintering apparatus, which includes: a pressure shaft 3, a sintering chamber 5, an upper end face 6, and a lower end face 7; the pressure shaft 3 is disposed on the side of the upper end face 6 near the lower end face 7, and the sintering chamber 5 is disposed on the side of the lower end face 7 near the upper end face 6; the pressure shaft 3 is hollow and can be inserted into the sintering chamber 5 and move vertically like a piston; a pressure relief port 4 is provided on the side wall of the pressure shaft 3, which communicates with the gas channel outlet 13 at the end of the pressure shaft near the sintering chamber 5 to form a gas channel 11.

[0055] The low-temperature sintering apparatus of this application, by setting a pressure relief port and a gas channel on the pressure shaft, can easily adjust the gas pressure state in the sintering chamber during sintering, thereby enabling the sintering preparation of ceramsite fracturing proppant at a lower temperature. By creating a different gas pressure inside the sintering chamber 5 compared to the outside, a higher gas pressure can be maintained inside the sintering chamber 5, allowing the raw materials to be sintered under high pressure and at a lower temperature. This effectively reduces the sintering temperature of the ceramsite proppant and can obtain ceramsite proppant of qualified quality, reducing the production cost of ceramsite proppant and the difficulty of scaling up production.

[0056] Since this application aims to obtain a product with a three-dimensional structure and to improve product production efficiency, in a preferred embodiment, the sintering chamber 5 is provided with multiple sintering tanks 10 for holding sintering raw materials. The number of sintering tanks 10 in the sintering chamber 5 can be adjusted according to actual production needs.

[0057] To ensure uniform pressure in each sintering tank 10 and a denser structure of the fracturing proppant, in a preferred embodiment, a plurality of sintering tank pressure shafts 12 are provided at the end of the pressure shaft 3 near the sintering chamber 5. These pressure shafts 12 can be inserted into the respective sintering tanks 10 and move vertically in a piston-like motion. By uniformly distributing the pressure transmitted by the pressure shaft 3 to each sintering tank 10 through the pressure shafts 12, the problem of uneven force distribution, which can lead to porous product structures and inconsistent quality, is avoided when a single pressure shaft 3 acts on multiple sintering objects simultaneously.

[0058] Since this application aims to obtain cylindrical fracturing proppant, in a preferred embodiment, both the sintering tank 10 and the sintering tank pressure shaft 12 are cylindrical, and the diameters of the sintering tank 10 and the sintering tank pressure shaft 12 are each independently 100-800 μm. The sintering tank 10 and the sintering tank pressure shaft 12 can be adjusted accordingly based on the desired size and shape of the product.

[0059] To provide more stable pressure for the fracturing proppant, in a preferred embodiment, the low-temperature sintering apparatus further includes a press 1. Furthermore, to achieve a more dense and uniform structure in the fracturing proppant, in a preferred embodiment, the press 1 includes an upper press and a lower press. The upper press is in separable contact with the side of the upper end face 6 away from the lower end face 7, and the lower press is in separable contact with the side of the lower end face 7 away from the upper end face 6. Applying a certain pressure to both the upper and lower ends of the sintering tank allows for a more uniform and compact structure of the sintered fracturing proppant.

[0060] Since heat needs to be provided to the sintering environment and maintained at a certain temperature during the sintering process, in a preferred embodiment, the low-temperature sintering apparatus further includes a heating device 2, which is fitted around the outer periphery of the sintering chamber 5 to provide heat to the sintering chamber 5. The heating device 2 includes an electric heating system and a hydrothermal system, which conduct heat to the sintering chamber 5 to maintain the sintering process therein.

[0061] In order to monitor the temperature inside the sintering chamber 5 in a timely manner and make timely adjustments to the sintering process, in a preferred embodiment, the heating device 2 further includes a temperature display element, which is selected from a thermometer, a sensor or a digital temperature display.

[0062] To prevent gas in the gas channel from damaging the sintering density of the fracturing proppant in the sintering tank 10 of the sintering chamber 5, the gas channel should not overlap with the sintering tank 10 in spatial position. In a preferred embodiment, the pressure shaft gas channel 11 is a single hollow structure disposed inside the pressure shaft 3, and the longitudinal projection of the gas channel 11 does not fall into the sintering tank 10, and the horizontal projection of the gas channel 11 does not overlap with the sintering tank 10. Any gas channel capable of facilitating gas flow between the inside of the sintering chamber 5 and the outside is only applicable to this application. In a preferred embodiment, the gas channel 11 is cylindrical, and the diameter of the gas channel outlet 13 and the pressure relief port 4 is less than 100 μm.

[0063] To facilitate more accurate adjustment of the horizontal position of the upper end face 6 and the lower end face 7, in a preferred embodiment, the upper end face 6 and the lower end face 7 are connected by a lead screw 8.

[0064] To further secure the pressure shaft 3 and the sintering chamber 5, in a preferred embodiment, the low-temperature sintering apparatus further includes inner end faces 9. There are two inner end faces 9: one is located between the pressure shaft 3 and the side of the upper end face 6 near the lower end face 7, and the other is located between the sintering chamber 5 and the side of the lower end face 7 near the upper end face 6. The pressure shaft 3 and the sintering chamber 5 are respectively fixed on the side of the inner end face 9 away from the upper end face 6 or the lower end face 7, making the pressure shaft 3 and the sintering chamber 5 more stable during pressure sintering.

[0065] To adjust the internal pressure of the sintering chamber 5, the pressure relief port 4 has two states: open and closed. Any setting that can achieve the switching between open and closed states of the pressure relief port 4 is applicable to this application. In a preferred embodiment, the opening and closing of the pressure relief port 4 is controlled by the connection between the nut and the internal thread of the pressure relief port 4 or by a snap fastener located on the outside of the pressure relief port 4.

[0066] In a second typical embodiment of this application, a ceramic fracturing proppant with a SiO2-Al2O3 mullite phase is provided, prepared using the above-described method. The relative density of the ceramic fracturing proppant is greater than 90%. Preferably, under the test method of SY / T5108-2014 for proppant performance in hydraulic fracturing and gravel-filling operations, the breakage rate of the ceramic fracturing proppant is less than 10%. The above-described preparation method enables the acquisition of a ceramic fracturing proppant with good performance, i.e., high density, at a relatively low temperature.

[0067] It should be noted that the related apparatus or equipment used in the aforementioned preparation method of this application can be implemented using the improved low-temperature sintering apparatus described above, or can be reasonably selected from existing equipment capable of achieving the corresponding effects, depending on the required conditions of each step. In some preferred embodiments, the low-temperature sintering apparatus provided above in this application is used.

[0068] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Based on the exemplary description, the following embodiments adopt the methods of this application as described above. Figures 1-3 The low-temperature sintering apparatus shown completes the sintering process. However, this is not a limiting statement and does not preclude the possibility that prior art equipment with similar functions can also achieve the sintering process of this application.

[0069] Utilize Figures 1-3 The sintering process of the low-temperature sintering apparatus shown is as follows:

[0070] Adjust the position of the low-temperature sintering device to make it horizontal.

[0071] Weigh appropriate amounts of SiO2 powder, Al2O3 powder, and combustion improver, mix them thoroughly to obtain a mixture (where the particle size of SiO2 powder and Al2O3 powder is ≤10μm, the molar ratio of SiO2 powder to Al2O3 powder is 1:2-5, and the mass of the combustion improver accounts for 1-4% of the sum of the masses of the three). Then place the mixture in each sintering tank 10 of the sintering chamber 5.

[0072] Close the pressure relief port 4, start the press 1, adjust the pressure shaft 3 to apply the pressure of the first pressurization treatment (100-500MPa) in the longitudinal direction, and at the same time turn on the heating device 2 to raise the temperature to the temperature of the first pressurization treatment (90-120℃). Maintain the pressure and temperature for 2-4 hours to carry out the first pressurization treatment. Adjust the pressure shaft 3 longitudinally upward so that the pressure shaft 12 of the sintering tank does not contact the sintering tank 10. Open the pressure relief port 4. After the pressure in the sintering chamber 5 is completely released from the gas channel 11, that is, the same as the atmospheric pressure outside the sintering chamber 5, maintain the temperature at the temperature of the first pressurization treatment.

[0073] Keep the pressure relief port 4 open, adjust the pressure shaft 3 to apply the pressure of the second pressurization process (100-500MPa) in the longitudinal direction, so that the pressure shaft 12 of the sintering tank contacts the sintering tank 10, raise the temperature to the temperature of the second pressurization process (90-120℃), and maintain the pressure and temperature for 1-4 hours. After the second pressurization process is completed, stop the operation of the press 1, remove the pressure, and take out the sintered product from the sintering tank 10.

[0074] Example 1

[0075] The sintering process is completed using the low-temperature sintering apparatus of this application, such as... Figures 1-3 As shown.

[0076] Adjust the positions of the upper end face 6, lower end face 7, inner end face 9 and lead screw 8 to keep the low-temperature sintering device on a horizontal plane.

[0077] Weigh 350g of SiO2 powder with a particle size of 1μm and 1200g of Al2O3 powder with a particle size of 1μm, mix them thoroughly to obtain mixed powder A, then add 15.5g of water to A and mix thoroughly to obtain mixture B, then place the mixture evenly in each sintering tank 10 of sintering chamber 5.

[0078] Close the pressure relief port 4, start the press 1, adjust the pressure shaft 3 to apply a pressure of 500MPa in the longitudinal direction, and at the same time turn on the heating device 2 to raise the temperature to 110℃ at 10℃ / min. Maintain the pressure and temperature for 3 hours to perform the first pressurization process. Adjust the pressure shaft 3 to be longitudinally upward so that the pressure shaft 12 of the sintering tank does not contact the sintering tank 10. Open the pressure relief port 4. After the pressure in the sintering chamber 5 is completely released from the gas channel 11, that is, the same as the atmospheric pressure outside the sintering chamber 5, maintain the temperature at 110℃.

[0079] With the pressure relief port 4 open, the pressure shaft 3 was adjusted to apply a longitudinal pressure of 500 MPa, so that the pressure shaft 12 of the sintering tank contacted the sintering tank 10. The temperature was increased to 110°C at a rate of 10°C / min, and the pressure and temperature were maintained for 2 hours. After the second pressurization process was completed, the press 1 was stopped, the pressure was removed, and the sintered product was taken out of the sintering tank 10. The performance results of the obtained samples are shown in Table 1.

[0080] Example 2

[0081] The difference between this embodiment and Example 1 is that the amount of water used is 2%, or 31g. The performance results of the obtained samples are shown in Table 1.

[0082] Example 3

[0083] The difference between this embodiment and Example 1 is that the amount of water used is 3%, or 46.5g. The performance results of the obtained samples are shown in Table 1.

[0084] Example 4

[0085] The difference between this embodiment and Example 1 is that the amount of water used is 4%, or 62g. The performance results of the obtained samples are shown in Table 1.

[0086] Table 1 Performance results of samples from Examples 1-4

[0087] Example relative density Breakage rate (%) 1 0.86 14 2 0.92 8 3 0.96 4 4 0.96 4

[0088] The relative density was determined using the method outlined in SY / T5108-2014, "Test Method for Performance of Proppants for Hydraulic Fracturing and Gravel Packing Operations," which tested the apparent density. The apparent density was then divided by the density of the dense pure SiO2 material (2.2 g / cm³). 3 The relative density is obtained through calculation.

[0089] The breakage rate was tested using the method described in SY / T5108-2014, "Test Method for Performance of Proppants Used in Hydraulic Fracturing and Gravel Filling Operations".

[0090] Examples 1-4 show that increasing the amount of water can increase the relative density of the ceramsite proppant, indicating improved compactness. This increased compactness leads to a lower breakage rate, demonstrating effective improvement in mechanical properties. In particular, the ceramsite proppant obtained in Example 3 achieved a relative density of 0.96, with a breakage rate reduced to 4%. This is because, under the action of the instantaneous sintering aid, pressure and heat preservation can produce the mullite phase (…). Figure 4 and Figure 5 Through further sintering, after removing the instantaneous sintering aid, a densified ceramic support is obtained. Figure 5 ).from Figure 4 It can be seen that the sample obtained in Example 3 has a grain size of about 1 μm, a dense microstructure, and few pores, consistent with the results of higher relative density, which helps to reduce the breakage rate. Figure 5It can be seen that the sample obtained in Example 3 is a mullite phase with sharp diffraction peaks, indicating a high degree of crystallinity, which helps improve the mechanical properties of the sample. When the water content reaches 4%, the results are the same as those obtained with 3%, so there is no need to indiscriminately increase the water content. The results show that when the pressure of the first pressurization treatment is 500 MPa, the temperature is 110°C, the pressure of the second pressurization treatment is 500 MPa, and the instantaneous sintering aid is water, the optimal dosage is 3% (Example 3).

[0091] Examples 3, 5-7 control a single variable: the instantaneous sintering aid is water, with a dosage of 3%; the pressure of the first pressurization treatment is 500 MPa; the pressure of the second pressurization treatment is 500 MPa, which remains constant; the variable is the temperature, which is 90℃, 100℃, 110℃, and 120℃. These examples illustrate the effect of changing the temperature on the compactness (evaluated by relative density) and breakage rate of the ceramsite proppant.

[0092] Example 5

[0093] The difference between this embodiment and Embodiment 3 is that the temperature is 90℃. The performance results of the obtained samples are shown in Table 2.

[0094] Example 6

[0095] The difference between this embodiment and Embodiment 3 is that the temperature was 100℃. The performance results of the obtained samples are shown in Table 2.

[0096] Example 7

[0097] The difference between this embodiment and Embodiment 3 is that the temperature was 120℃. The performance results of the obtained samples are shown in Table 2.

[0098] Table 2 Performance results of samples 3, 5-7 in Examples 2

[0099]

[0100]

[0101] Examples 3, 5-7 show that increasing the temperature increases the relative density of the ceramsite proppant, indicating improved compactness. Increased compactness leads to a lower breakage rate, demonstrating effective improvement in mechanical properties. The results obtained at 120°C are the same as those obtained at 120°C, therefore, it is unnecessary to indiscriminately increase the temperature. The results show that maintaining a water content of 3%, a first pressurization pressure of 500 MPa, a second pressurization pressure of 500 MPa, and an optimal temperature of 110°C are optimal.

[0102] Examples 3, 8-10 control a single variable: the instantaneous sintering aid is water, with a dosage of 3%; the pressure of the first pressurization treatment is 500 MPa, and the temperature is 110°C; the pressure of the second pressurization treatment is 500 MPa, which remains constant; the change is that the pressure holding time of the first pressurization treatment is 1 h, 2 h, 3 h, and 4 h. These examples illustrate the effect of changing the pressure holding time of the first pressurization treatment on the compactness (evaluated by relative density) and breakage rate of the ceramsite proppant.

[0103] Example 8

[0104] The difference between this embodiment and Embodiment 3 is that the pressure holding time for the second pressurization treatment is 1 hour. The performance results of the obtained samples are shown in Table 3.

[0105] Example 9

[0106] The difference between this embodiment and Embodiment 3 is that the pressure holding time for the second pressurization treatment is 2 hours. The performance results of the obtained samples are shown in Table 3.

[0107] Example 10

[0108] The difference between this embodiment and Embodiment 3 is that the pressure holding time for the second pressurization treatment is 4 hours. The performance results of the obtained samples are shown in Table 3.

[0109] Table 3 Performance results of samples 8-10 in Examples 3

[0110] Example relative density Breakage rate (%) 3 0.96 4 8 0.93 7 9 0.95 5 10 0.96 4

[0111] As can be seen from Examples 3, 8-10, extending the pressure holding time of the first pressurization treatment can increase the relative density of the ceramsite proppant, indicating improved compactness. Increased compactness leads to a lower breakage rate, indicating effective improvement in mechanical properties. This is because the pressure holding time of the first pressurization treatment is for the formation of the mullite phase. Under the influence of pressure, temperature, and a transient sintering aid, extending the time is beneficial for the formation of the mullite phase. When the pressure holding time of the first pressurization treatment is extended to 4 hours, the results are the same as those obtained with 3 hours. Therefore, it is unnecessary to indiscriminately extend the pressure holding time of the second pressurization treatment. The results show that maintaining a water content of 3%, a temperature of 110°C, a pressure of 500 MPa for both the first and second pressurization treatments, and a pressure holding time of 3 hours for the first pressurization treatment are optimal.

[0112] Examples 11-31 control a single variable: the amount of instantaneous sintering aid is 3%, the pressure of the first pressurization treatment is 500 MPa, the temperature is 110°C, and the pressure of the second pressurization treatment is 500 MPa, which remains constant. The change is that the instantaneous sintering aid is a siloxane, namely KH570, A171, and silicone oil (polydimethylsiloxane). The siloxane plays a role in volatilization and binding during sintering. At temperatures above 80°C, the siloxane can combine with the surface of the mixed powder B and undergo a condensation reaction. The generated H2O can be effectively volatilized, while the condensation product remains on the surface of the mixed powder B and plays a binding role. Both aspects work together to promote the densification of the ceramsite grains. These examples illustrate the effect of changing the type of instantaneous sintering aid on the densification (evaluated by relative density) and breakage rate of the ceramsite support.

[0113] Example 11

[0114] The difference between this embodiment and Embodiment 3 is that the instantaneous sintering aid is KH570. The performance results of the obtained samples are shown in Table 4.

[0115] Example 12

[0116] The difference between this embodiment and Embodiment 3 is that the instantaneous sintering aid is A171. The performance results of the obtained samples are shown in Table 4.

[0117] Example 13

[0118] The difference between this embodiment and Embodiment 3 is that the instantaneous sintering aid is silicone oil. The performance results of the obtained samples are shown in Table 4.

[0119] Table 4 Performance results of samples from Examples 11-12

[0120] Example relative density Breakage rate (%) 11 0.98 2 12 0.96 4 13 0.97 3

[0121] As can be seen from Examples 11-13, when all the instantaneous sintering aids are siloxanes, the relative density and breakage rate of the ceramic proppant vary due to the different molecular structures of different types of siloxanes. KH570 molecules have long chains and unsaturated bonds; the long chains avoid the steric hindrance effect on densification, and the unsaturated bonds facilitate the condensation reaction. Both contribute to densification, thereby increasing the relative density and reducing the breakage rate. A171 molecules have no long chains and no unsaturated bonds, resulting in a lower degree of densification compared to KH570, thus reducing the relative density and increasing the breakage rate. Silicone oil molecules have long chains but no unsaturated bonds, resulting in a moderate relative density and breakage rate for the ceramic proppant. Therefore, under the same external conditions and when the instantaneous sintering aid is an organic compound, the sample performance is mainly affected by whether the instantaneous sintering aid molecules have long chains and unsaturated bonds.

[0122] Examples 14-15 control a single variable: the amount of instantaneous sintering aid is 3%, the pressure of the first pressurization treatment is 500 MPa, the temperature is 110°C, and the pressure of the second pressurization treatment is 500 MPa, which remains constant; the changes are: the instantaneous sintering aid is silicic acid and ethyl orthosilicate, respectively; through hydrolysis, silicic acid is converted into SiO2 and H2O. During the sintering process, SiO2 is distributed around the grains (i.e., at the grain boundaries), which fills the voids, and the generated H2O can be effectively volatilized at temperatures above 100°C. Both effects work together to promote densification; the examples illustrate the effect of changing the type of instantaneous sintering aid on the densification (evaluated by relative density) and breakage rate of the ceramsite support.

[0123] Example 14

[0124] The difference between this embodiment and Embodiment 3 is that the instantaneous sintering aid is silicic acid. The performance results of the obtained samples are shown in Table 5.

[0125] Example 15

[0126] The difference between this embodiment and Example 3 is that the instantaneous sintering aid is ethyl orthosilicate. The performance results of the obtained samples are shown in Table 5.

[0127] Table 5 Performance results of samples from Examples 14-15

[0128] Example relative density Breakage rate (%) 14 0.98 2 15 0.99 1

[0129] As can be seen from Examples 14-15, when the instantaneous sintering aid is silica or ethyl orthosilicate, the hydrolysis product SiO2 occupies the position of the pores at the grain boundaries, fills the voids, and promotes densification, thereby obtaining a fracturing proppant with a relative density as high as 0.99 and a breakage rate of only 1%.

[0130] Examples 16-18 control a single variable: the amount of instantaneous sintering aid is 3%, the pressure of the first pressurization treatment is 500 MPa, the temperature is 110°C, and the pressure of the second pressurization treatment is 500 MPa, which remains constant; the changes are: the instantaneous sintering aid is ammonia, urea, and NaOH, respectively; the volatilization of ammonia and urea promotes densification; NaOH and SiO2 grains can form a binder, and the generated H2O can be effectively volatilized at temperatures above 100°C, both of which jointly promote grain densification; these examples illustrate the effect of changing the type of instantaneous sintering aid on the densification (evaluated by relative density) and breakage rate of the ceramsite support.

[0131] Example 16

[0132] The difference between this embodiment and Embodiment 3 is that the instantaneous sintering aid is ammonia. The performance results of the obtained samples are shown in Table 6.

[0133] Example 17

[0134] The difference between this embodiment and Embodiment 3 is that the instantaneous combustion aid is urea. The performance results of the obtained samples are shown in Table 6.

[0135] Example 18

[0136] The difference between this embodiment and Embodiment 3 is that the instantaneous sintering aid is NaOH. The performance results of the obtained samples are shown in Table 6.

[0137] Table 6 Performance results of samples 16-18 in Examples 16-18

[0138] Example relative density Breakage rate (%) 16 0.97 3 17 0.97 3 18 0.98 2

[0139] As can be seen from Examples 16-18, when the instantaneous sintering aid is ammonia or urea, the generated NH3 and H2O can be effectively volatilized at temperatures above 100°C, promoting grain densification. When the instantaneous sintering aid is NaOH, Na2SiO3 and H2O can be generated around the SiO2 grains. Na2SiO3 is a binder, and H2O can be effectively volatilized at temperatures above 100°C. Both effects work together to promote grain densification.

[0140] Comparative Examples 1-18

[0141] The raw material used in Comparative Examples 1-18 was 1000g of SiO2 powder with a particle size of 1μm. The pressure of the first pressurization treatment was 300MPa, the time of the first pressurization treatment was 40min, the pressure of the second pressurization treatment was 500MPa, and the temperature of the second pressurization treatment was 20℃.

[0142] The remaining conditions and the properties of the prepared silica fracturing proppant are shown in Table 7 below:

[0143] Table 7 Conditional variables and performance results for Comparative Examples 1-18

[0144]

[0145] As can be seen from Table 7 above, when the raw material used for fracturing proppant is only SiO2 powder, even if the preparation method is the same as that of this application, which is a two-stage pressurization process (as compared with Comparative Examples 5-10 in Examples 5-10), and using the same mass and type of instantaneous combustion accelerant (as compared with Comparative Examples 1-4, 11-18 in Examples 1-4, 11-18), the performance parameters of relative density and breakage rate of the silica fracturing proppant obtained by Comparative Examples 1-18 are worse than those of Examples 1-18 in this application.

[0146] The SiO2-Al2O3 mullite phase fracturing proppant of this application exhibits superior quality in relative density and fragmentation rate compared to ordinary silica fracturing proppants, enabling it to perform effectively in more demanding application environments. Specifically, the preparation raw materials of this application also include Al2O3 powder. Under the first pressurization treatment, the SiO2 powder, through the self-generated pressure of the instantaneous sintering aid, low-temperature assisted sintering, and the action of solvothermal (water) heat, undergoes pressure holding and temperature maintenance to initially obtain a densified SiO2-Al2O3 mullite phase. Subsequently, during the second pressurization process, low-temperature sintering completes the entire densification process. Thus, a SiO2-Al2O3 mullite phase fracturing proppant with excellent mechanical properties, low fragmentation rate, stable physical and chemical properties, and resistance to chemical corrosion is obtained at 90-120℃. This makes the SiO2-Al2O3 mullite phase fracturing proppant suitable for harsh operating conditions such as complex formations and variable environments.

[0147] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: The instantaneous sintering aid is mixed with the raw materials, and the mixture is first pre-pressurized to make the gas pressure in the sintering chamber higher than the external gas pressure. Under high pressure and low temperature, the instantaneous sintering aid in the sintering chamber forms a mullite phase with high mechanical properties with the raw materials, and densifies the ceramic particle grains. Then, the gas pressure in the low-temperature sintering device is made consistent with the external pressure, further pressurizing the fracturing proppant to densify it, so that a relatively dense ceramic fracturing proppant can be obtained at a lower temperature, thereby effectively reducing the breakage rate of the ceramic fracturing proppant. The low-temperature sintering device can simultaneously provide constant pressure and constant temperature, providing external conditions for the sintering process. The volatility and binding properties of the instantaneous sintering aid provide material conditions for the densification process, enabling the silica grains to achieve a degree of densification at a lower temperature, with a relative density greater than 0.90 and a breakage rate of less than 10%.

[0148] The technical solution of this application eliminates the need for a high-temperature process, effectively reducing the sintering temperature of the ceramic proppant. By achieving a sintering temperature below two-thirds of the melting point of the sintering material, a dense ceramic proppant with low breakage rate, high strength, and good mechanical properties can be obtained. Overall, the technical solution of this application has the advantages of simple synthesis, ease of implementation, low sintering temperature, and energy saving, making it suitable for promotion in the fracturing field of the oil and gas industry and possessing broad application prospects.

[0149] 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. A method for preparing ceramic fracturing proppant with SiO2-Al2O3 mullite phase at low temperature, characterized in that, The method includes: A mixture of SiO2, Al2O3 and a transient sintering aid is placed in a low-temperature sintering apparatus; The pressure relief port of the pressure shaft is in a closed state. The pressure shaft is used to perform a first pressurization treatment on the sintering chamber. During the first pressurization treatment, the air pressure inside the sintering chamber is controlled to be higher than the air pressure outside the sintering chamber, and a first pressurization treatment product is obtained. With the pressure relief port in an open state, the air pressure inside the sintering chamber and outside the sintering chamber is adjusted to be consistent, and the first pressurized product is subjected to a second pressurization treatment using the pressure shaft to obtain the ceramic fracturing proppant. The temperature of the first pressurization treatment and / or the second pressurization treatment is 90-120°C, and the temperature of the first pressurization treatment is higher than the temperature of the second pressurization treatment; The instantaneous sintering aid is selected from one of the following: water, siloxane, silicic acid, ethyl orthosilicate, and alkali; The mass of the instantaneous sintering aid accounts for 1-4% of the sum of the masses of SiO2, Al2O3 and the instantaneous sintering aid.

2. The method according to claim 1, characterized in that, The particle size of SiO2 and Al2O3 is independently ≤10μm.

3. The method according to claim 2, characterized in that, The molar ratio of SiO2 to Al2O3 is 1:2-5.

4. The method according to any one of claims 1-3, characterized in that, Before performing the first and second pressurization processes, the temperature in the sintering chamber is preheated to the temperature required for the first or second pressurization processes using a heating device.

5. The method according to claim 4, characterized in that, The pressure of the first pressurization process is 100-500 MPa.

6. The method according to claim 5, characterized in that, The first pressurization process takes 2-4 hours.

7. The method according to claim 5, characterized in that, The pressure of the second pressurization process is 100-500 MPa.

8. The method according to claim 5, characterized in that, The second pressurization process takes 1-4 hours.

9. The method according to claim 1, characterized in that, The low-temperature sintering apparatus includes: Pressure shaft (3), sintering chamber (5), upper end face (6) and lower end face (7); The pressure shaft (3) is located on the side of the upper end face (6) near the lower end face (7); The sintering chamber (5) is located on the side of the lower end face (7) near the upper end face (6); The pressure shaft (3) is hollow and can be inserted into the sintering chamber (5) and move like a piston in the vertical direction; A pressure relief port (4) is provided on the side wall of the pressure shaft (3), which is connected to the gas channel outlet (13) at the end of the pressure shaft (3) near the sintering chamber (5) to form a gas channel (11).

10. The method according to claim 9, characterized in that, The sintering chamber (5) is provided with multiple sintering tanks (10) for holding sintering raw materials. The pressure shaft (3) is provided with a plurality of sintering tank pressure shafts (12) at one end near the sintering chamber (5). The plurality of sintering tank pressure shafts (12) can be inserted into the plurality of sintering tanks (10) one by one and perform piston movement in the vertical direction.

11. The method according to claim 10, characterized in that, The sintering tank (10) and the sintering tank pressure shaft (12) are both cylindrical, and the diameters of the sintering tank (10) and the sintering tank pressure shaft (12) are each independently 100-800μm.

12. The method according to claim 9, characterized in that, The low-temperature sintering apparatus also includes a press (1). The press (1) includes an upper press and a lower press. The upper press is in detachable contact with the side of the upper end face (6) away from the lower end face (7). The lower press is in detachable contact with the side of the lower end face (7) away from the upper end face (6).

13. The method according to claim 9, characterized in that, The low-temperature sintering device also includes a heating device (2); The heating device (2) is fitted around the outer periphery of the sintering chamber (5) to provide heat to the sintering chamber (5).

14. The method according to claim 13, characterized in that, The heating device (2) also includes a temperature display element.

15. The method according to any one of claims 9-14, characterized in that, The gas channel (11) is a single hollow structure disposed inside the pressure shaft (3), and the longitudinal projection of the gas channel (11) cannot fall into the sintering tank (10), and the horizontal projection of the gas channel (11) does not overlap with the sintering tank (10).

16. The method according to claim 15, characterized in that, The gas channel (11) is cylindrical, and the diameter of the gas channel outlet (13) and the pressure relief port (4) is less than 100 μm.

17. The method according to claim 15, characterized in that, The upper end face (6) and the lower end face (7) are connected by a lead screw (8).

18. The method according to claim 15, characterized in that, The low-temperature sintering device also includes an inner end face (9), which has two inner end faces (9). One inner end face (9) is located between the upper end face (6) and the pressure shaft (3) on the side near the lower end face (7), and the other inner end face (9) is located between the lower end face (7) and the sintering chamber (5) on the side near the upper end face (6).

19. The method according to claim 15, characterized in that, The pressure relief port (4) has two states: open and closed. The opening and closing of the pressure relief port (4) can be controlled by the connection between the nut and the internal thread of the pressure relief port (4) or by the buckle set on the outside of the pressure relief port (4).

20. A ceramic fracturing proppant with a SiO2-Al2O3 mullite phase obtained by the method according to any one of claims 1-19, characterized in that, The relative density of the ceramic fracturing proppant is greater than 90%.

21. The ceramic fracturing proppant according to claim 20, characterized in that, Under the test method for proppant performance in hydraulic fracturing and gravel-filled operations (SY / T5108-2014), the breakage rate of the ceramsite fracturing proppant is less than 10%.

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