Method for preparing ceramsite fracturing propping agent with SiO2-Al2O3 mullite phase at low temperature and product

Abstract

The invention provides a method for preparing a ceramsite fracturing propping agent with a SiO2-Al2O3 mullite phase at a low temperature and a product. The method comprises the following steps: putting a mixture of SiO2, Al2O3 and an instantaneous sintering aid into a low-temperature sintering device; a pressure relief opening of the pressure shaft is in a closed state, the pressure shaft is used for conducting first pressurization treatment on the sintering chamber, the air pressure in the sintering chamber is controlled to be higher than the air pressure outside the sintering chamber, and a first pressurization treatment product is obtained; the pressure relief opening is in an open state, the air pressure inside the sintering chamber and the air pressure outside the sintering chamber are adjusted to be kept consistent, second pressurization treatment is conducted, and the mullite phase fracturing propping agent which is excellent in mechanical property, low in breakage rate, stable in physical and chemical property and resistant to chemical corrosion is obtained. The preparation method has the advantages of simplicity in synthesis, easiness in implementation, low sintering temperature and energy conservation, is beneficial to popularization in the field of industrial fracturing of petroleum and natural gas, and has a wide application prospect.

Description

Technical Field

[0001] The invention relates to the field of fracturing materials for the petroleum and natural gas industries, and in particular to a method for preparing a ceramsite fracturing proppant having a SiO2-Al2O3 mullite phase at low temperature and a product thereof. Background Art

[0002] With the continuous increase in demand for oil and gas at home and abroad, the difficulty of oil and gas extraction is increasing in the face of high-density and low-permeability oil and gas reservoirs. Under the new situation of energy structure adjustment, strong demand for oil and gas, and rapid technological development, how to increase oil and gas production is an important research field. The use of fracturing technology can effectively develop high-density and low-permeability oil and gas reservoirs and achieve the goal of increasing oil and gas production.

[0003] As the main oil and gas development method in recent decades, hydraulic fracturing can effectively increase the production of oil and gas wells worldwide. Fracturing proppants are key construction materials commonly used in hydraulic fracturing. Among them, the use of quartz sand fracturing proppants and ceramsite fracturing proppants accounts for more than 90% of the total use of fracturing proppants. Since quartz sand fracturing proppants are natural products, their mechanical properties are poor, making them difficult to apply to high-yield wells and unable to increase oil and gas production.

[0004] Ceramic fracturing proppant is a high-performance product obtained through artificial sintering. With its excellent mechanical properties, it has been widely used in high-yield wells and in the field of increasing oil and gas production. However, the sintering temperature of ceramsite fracturing proppant is usually between 900℃ and 1300℃. Due to the high sintering temperature caused by traditional sintering methods, the production cost remains high, which limits the application scope of ceramsite fracturing proppant.

[0005] In addition, ceramsite fracturing proppants are mostly prepared using silica. Although the theoretical hardness of silica is 7, which belongs to the apparent hardness, it cannot be achieved by actual artificial synthesis. Moreover, the mechanical properties of silica itself are relatively low, with poor toughness and brittleness. The application environment of fracturing proppants is mostly oil and gas formations with complex acid and alkali components. Due to the poor alkali resistance of silica, it is easy to form soluble salts with alkali, making it impossible to use it in complex and changeable environments. Therefore, although silica is often used as a fracturing material and has good rigidity, it still has certain deficiencies in toughness, mechanical strength and alkali resistance. It may not be able to cope with more complex acid and alkali environments or higher mechanical performance requirements, and further performance improvement of fracturing materials is needed.

[0006] Therefore, as oil and gas extraction develops in a more complex and changeable direction, how to solve the problems of excessively high sintering temperature of expanded clay fracturing proppants and the inability of fracturing materials to meet higher application requirements in terms of toughness, mechanical strength and alkali resistance is very important for the development of this field. Summary of the invention

[0007] The main purpose of the present invention is to provide a method and product for preparing ceramsite fracturing proppants having SiO2-Al2O3 mullite phase at low temperature, so as to solve the problems in the prior art that ceramsite fracturing proppants cannot be prepared under low temperature sintering conditions, and the toughness, mechanical strength and alkali resistance of the fracturing materials cannot meet higher application requirements.

[0008] In order to achieve the above-mentioned purpose, according to the first aspect of the present invention, there is provided a method for preparing a ceramsite fracturing proppant having a SiO2-Al2O3 mullite phase at a low temperature, the method comprising: placing a mixture of SiO2, Al2O3 and an instantaneous sintering aid in a low-temperature sintering device; the pressure relief port of the pressure shaft is in a closed state, and the sintering chamber is subjected to a first pressurization treatment by means of the pressure shaft, wherein during the first pressurization treatment, the air pressure in the sintering chamber is controlled to be higher than the air pressure outside the sintering chamber to obtain a first pressurized product; the pressure relief port is in an open state, the air pressure in the sintering chamber is adjusted to be consistent with the air pressure outside the sintering chamber, and the first pressurized product is subjected to a second pressurization treatment by means of the pressure shaft to obtain a 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. The instant sintering aid comprises: water, siloxane, silicic acid, hexyl orthosilicate and alkali; preferably, the mass of the instant sintering aid accounts for 1-4% of the sum of the mass of SiO2, Al2O3 and the instant sintering aid.

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

[0010] Furthermore, before the first pressurization treatment and the second pressurization treatment are performed, the temperature in the sintering chamber is preheated to a temperature required for the first pressurization treatment or the second pressurization treatment by a heat supply 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 h; preferably, the pressure of the second pressurization treatment is 100-500 MPa; preferably, the time of the second pressurization treatment is 1-4 h.

[0012] Furthermore, the low-temperature sintering device includes: a pressure shaft, a sintering chamber, an upper end face and a lower end face; the pressure shaft is arranged on the side of the upper end face close to the lower end face, and the sintering chamber is arranged on the side of the lower end face close to the upper end face; the pressure shaft is hollow, can be inserted into the sintering chamber and perform piston movement in the vertical direction; a pressure relief port is arranged on the side wall of the pressure shaft, which is connected to the gas channel outlet at one end of the pressure shaft close to the sintering chamber to form a gas channel.

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

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

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

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

[0017] Furthermore, the low temperature sintering device also includes two inner end surfaces, one inner end surface is arranged between the side of the upper end surface close to the lower end surface and the pressure shaft, and the other inner end surface is arranged between the side of the lower end surface close to the upper end surface and the sintering chamber.

[0018] Furthermore, the pressure relief port has two states of on and off, and the on and off control of the pressure relief port is achieved through the connection between the nut and the thread inside the pressure relief port or the buckle arranged outside the pressure relief port.

[0019] In order to achieve the above-mentioned object, according to the second aspect of the present invention, there is provided a ceramsite fracturing proppant having a SiO2-Al2O3 mullite phase obtained by the above-mentioned preparation method, wherein the relative density of the ceramsite fracturing proppant is greater than 90%; preferably, under the SY / T5108-2014 proppant performance test method for hydraulic fracturing and gravel filling operations, the crushing rate of the ceramsite fracturing proppant is less than 10%.

[0020] By applying the technical solution of the present invention, the instantaneous sintering aid is mixed with the raw material, and the mixture is first pre-pressurized to make the air pressure in the sintering chamber higher than the external air pressure. The instantaneous sintering aid in the sintering chamber forms a relatively dense fracturing proppant with the raw material under high pressure and low temperature. Then, by adjusting the air release port of the pressure shaft to an open state, the air pressure in the low-temperature sintering device is made consistent with the external environment, and the fracturing proppant is further pressurized to densify, so that a relatively dense ceramsite fracturing proppant can be obtained at a relatively low temperature. The preparation method has the advantages of simple synthesis, easy implementation, low sintering temperature, and energy saving, which is conducive to promotion in the field of fracturing in the oil and natural gas industry and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0022] Figure 1 A front view of a low temperature sintering device used in the embodiment is shown;

[0023] Figure 2 A horizontal cross-sectional view of a sintering chamber of a low-temperature sintering device used in an embodiment is shown;

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

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

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

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

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

[0029] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0030] As mentioned in the background technology, the ceramsite fracturing proppant in the prior art is mostly prepared by using silicon dioxide. Although the theoretical hardness of silicon dioxide is 7, which belongs to the apparent hardness, it cannot be achieved by actual artificial synthesis. In addition, the mechanical properties of silicon dioxide itself are relatively low, and its toughness is poor and it is brittle. The application environment of fracturing proppant is mostly oil and gas formations with complex acid-base components. Due to the poor alkali resistance of silicon dioxide, it is easy to generate soluble salts with alkali, making it impossible to use it in complex and changeable environments. Therefore, although silicon dioxide is often used as a fracturing material and has good rigidity, it still has certain deficiencies in toughness, mechanical strength and alkali resistance. It may not be competent in the face of more complex acid-base environments or higher mechanical performance requirements, and further performance improvement of fracturing materials is required.

[0031] In addition, the preparation of ceramsite fracturing proppants still uses a high-temperature sintering method, and the sintering temperature is usually between 900℃ and 1300℃, which results in too high a sintering temperature and high production costs, limiting the scope of application of ceramsite proppants, restricting the further development of hydraulic fracturing, and making it difficult to meet existing oil and gas production requirements and energy needs. Because the existing technology has not made a breakthrough in principle, the sintering temperature is between two-thirds of the melting point of the sintering material and the melting point. The sintering temperature must be reached to meet the densification effect of the sintering material particles, resulting in the sintering temperature of the ceramsite proppants being too high. If advanced sintering technology is not used, when the sintering temperature does not exceed two-thirds of the melting point of the sintering material, it is impossible to obtain a dense, quality ceramsite proppant.

[0032] However, although cold sintering technology exists, it is mostly used in the electronics field to prepare conductive materials, but its equipment cannot meet the morphology requirements of expanded clay fracturing proppants, and the sintering temperature is still higher than 300°C, and it is impossible to obtain dense ceramic materials at a lower temperature (90-120°C); in addition, the raw material types of the existing cold sintering technology and the expanded clay fracturing proppants of the present application are different, and there is a problem that the sintering temperature is still relatively high (greater than 300°C), and there are certain difficulties in transferring it to the present application for the preparation of expanded clay fracturing proppants.

[0033] Beneficial Effects

[0034] Therefore, in view of the technical bottleneck problem existing in the field of ceramsite proppants, that is, the sintering temperature is too high, usually exceeding 900°C, the present invention intends to provide a method and product for preparing ceramsite proppants at low temperature. The present invention uses a self-made low-temperature sintering device, SiO2 powder and Al2O3 powder as raw materials, and an instant sintering aid to achieve densification through the sintering process, generate a mullite phase with high mechanical properties through the sintering process, and densify the ceramsite grains.

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

[0036] The existing synthesis of mullite phase needs to be sintered at 1300-1400°C under normal pressure. However, the present application skillfully combines solvent heat (water) with low-temperature sintering to obtain the SiO2-Al2O3 mullite phase ceramsite fracturing proppant of the present application at a lower temperature (90-120°C). Specifically, in the first pressurization process, SiO2 and Al2O3 powders are subjected to pressure and heat preservation under the action of the self-generated pressure of the instantaneous sintering aid, low-temperature auxiliary sintering, and solvent heat (water), and initially obtain a densified SiO2-Al2O3 mullite phase; thereafter, in the second pressurization process, the entire densification process is completed through the action of 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 chemical corrosion resistance at 90-120°C. The SiO2-Al2O3 mullite phase fracturing proppant is suitable for various harsh working conditions with complex formations and changeable environments, providing strong technical support for research and development in this field.

[0037] The principle of sintering with an instant sintering aid is as follows: the instant sintering aid in the present application must be able to leave / escape from the grain surface and grain boundary in the form of gas or liquid under certain conditions, leaving only the grains and grain boundaries, so that no unknown impurities are introduced due to the residue of the instant sintering aid. The present application can complete the densification process of SiO2 and Al2O3 at low temperature, thereby obtaining a fracturing proppant with low breakage rate, good mechanical properties and high strength.

[0038] Low-temperature sintering equipment is used to provide constant pressure and constant temperature at the same time, providing external conditions for the sintering process, and the volatility and adhesion of the instantaneous sintering aid provide material conditions for the densification process. The two aspects work together to make the expanded clay grains reach a densification degree at 90-120°C, and obtain expanded clay fracturing proppants with a relative density greater than 0.90 and a breakage rate of less than 10% under the SY / T5108-2014 proppant performance test method for hydraulic fracturing and gravel filling operations.

[0039] The present invention does not require a high temperature process, effectively reduces the sintering temperature of the ceramsite proppant, and achieves a dense ceramsite proppant with qualified quality when the sintering temperature is lower than two-thirds of the melting point of the sintering material. The present invention as a whole has the advantages of simple synthesis, easy realization, low sintering temperature, and energy saving, which is conducive to promotion in the field of oil and gas industry fracturing and has broad application prospects.

[0040] In a first typical embodiment of the present application, a method for preparing a ceramsite fracturing proppant at low temperature is provided, the method comprising: placing a mixture of SiO2, Al2O3 and an instantaneous sintering aid in a low-temperature sintering device; the pressure relief port of the pressure shaft is in a closed state, and the sintering chamber is subjected to a first pressure treatment by the pressure shaft, wherein during the first pressure treatment, the gas pressure in the sintering chamber is controlled to be higher than the gas pressure outside the sintering chamber; under the conditions of the first pressure treatment, a first pressure treatment product is obtained; the pressure relief port is in an open state, the gas pressure in the sintering chamber is adjusted to be consistent with the gas pressure outside the sintering chamber, and the first pressure treatment product is subjected to a second pressure treatment by the pressure shaft to obtain a ceramsite fracturing proppant; the temperature of the first pressure treatment and / or the second pressure treatment is 90-120°C, and the temperature of the first pressure treatment is higher than the temperature of the second pressure treatment. Preferably, the temperature of the first pressure treatment is 110°C.

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

[0042] In the second process, the pressure spontaneously generated by the instantaneous sintering aid is released through the pressure relief port to promote the densification process. The sintering chamber is integrated with a sintering tank, which is used to hold a mixture of SiO2 powder and Al2O3 powder. The sintering tank pressure shaft then transmits the pressure to the mixture of SiO2 powder and Al2O3 powder in the corresponding sintering tank of the sintering chamber. The sintering tank pressure shaft needs to contact the mixture of SiO2 powder and Al2O3 powder in the sintering tank, apply a constant pressure of 100-500MPa, keep the pressure relief port open, and maintain the pressure time greater than or equal to 30min. Remove the pressure and cool naturally to obtain a dense ceramsite fracturing proppant with mullite phase.

[0043] Among them, the pressure relief port is a small hole located on the pressure axis that can be opened and closed. When the pressure relief port is opened, the pressure inside the sintering chamber is the same as the external pressure. When the pressure relief port is closed, the pressure inside the sintering chamber is greater than the external pressure. The pressure relief port is closed only in the first pressure application process, and the other pressure relief ports are all open.

[0044] It should be emphasized that the present invention adopts the two-stage pressurization process as described above, which not only avoids the problem that the one-stage pressurization process cannot stably control the stability of the low-temperature sintering environment, which easily leads to insufficient structural densification. At the same time, it also avoids the defects of complicated process and excessive energy consumption caused by three or more stages of pressurization process.

[0045] The present application mixes the instantaneous sintering aid with the raw material in the sintering chamber, and uses a pressure shaft with a gas channel inside to close the pressure relief port on the side wall, and first pre-pressurizes the mixture so that the air pressure in the sintering chamber is higher than the external air pressure. The instantaneous sintering aid in the sintering chamber boils under high pressure and low temperature, and forms a relatively dense initial fracturing proppant with the raw material. At the same time, the instantaneous sintering aid will be completely separated from the fracturing proppant through volatilization or bonding, and will not cause any contamination by impurities. After pre-pressurization, the pressure relief port is opened to release air, and the gas channel inside the pressure shaft is used to make the air pressure in the sintering chamber consistent with the external environment. The initial fracturing proppant is further densified by mechanical force, so that a relatively dense ceramsite fracturing proppant can be obtained at a lower temperature. Among them, low-temperature sintering devices that can satisfy the requirements of pre-pressurizing the mixture of sintering raw materials and instantaneous sintering aid and then releasing air, and further applying mechanical force are applicable to the present application. In a preferred embodiment, the present application utilizes Figure 1-3 The low temperature sintering device shown is used to prepare ceramsite fracturing proppant.

[0046] The instantaneous sintering agent in the present application must be able to leave / escape from the grain surface and grain boundary in the form of gas or liquid under certain conditions (such as 100-500MPa and 20-120°C in the present application), leaving only the grains and grain boundaries, so that no unknown impurities are introduced due to the residue of the instantaneous sintering agent. The present application can complete the densification process of SiO2 and Al2O3 at low temperature, thereby obtaining a fracturing proppant with low breakage rate, good mechanical properties and high strength.

[0047] In a preferred embodiment, the instantaneous sintering aid is selected from the following: water, siloxane, silicic acid, silicic acid derivatives (such as hexyl orthosilicate) and alkali (ammonia, urea and NaOH). Preferably, the instantaneous sintering aid is selected from one of silicic acid, hexyl orthosilicate or NaOH. In order to make the sintered product more compact, in a preferred embodiment, 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, preferably 3%. More preferably, when the instantaneous sintering aid is water, the mass of the instantaneous sintering aid accounts for 3% of the sum of the masses of silicon dioxide and the instantaneous sintering aid.

[0048] Among them, the performance of the ceramsite fracturing proppant obtained from different types of siloxane molecules is different due to their different structures. For siloxanes with long chains and unsaturated bonds (such as KH570), the long chain can avoid the influence of steric hindrance on densification, and the unsaturated bonds are conducive to polycondensation reaction. The two together promote densification, thereby increasing relative density and reducing crushing rate. The performance of ceramsite fracturing proppant obtained from siloxanes without long chains and unsaturated bonds (such as A171) is relatively general. The relative density and crushing rate performance of ceramsite fracturing proppant obtained from siloxanes with long chains but no unsaturated bonds (such as silicone oil) are in the middle.

[0049] Silicic acid and its derivatives can generate SiO2 and H2O due to hydrolysis. The newly generated SiO2 and H2O can volatilize and improve the density of the ceramsite fracturing proppant while filling the voids during the sintering process.

[0050] The alkaline substances used, such as NH3 and H2O generated by ammonia water and urea, can be effectively volatilized at temperatures above 100°C, promoting grain densification; if NaOH, which can reflect the generation of adhesives, is used, the adhesive properties of the product Na2SiO3 can be used to promote grain densification.

[0051] In order to make the generated ceramsite fracturing proppant more compact, in a preferred embodiment, the particle size of SiO2 and Al2O3 is independently ≤10μm. In a preferred embodiment, the raw materials are SiO2 and Al2O3, and the molar ratio of SiO2 to Al2O3 is 1:2-5. Among them, 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, so that the ceramsite grains in the fracturing proppant are densified.

[0052] In order to efficiently sinter to obtain expanded clay fracturing proppant and reduce energy consumption, in a preferred embodiment, the temperature in the low-temperature sintering device is preheated to the temperature required for the first pressure treatment or the second pressure treatment before the first pressure treatment or the second pressure treatment, and the preheating heating 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, the present application provides a low-temperature sintering device, 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 arranged on the side of the upper end face 6 close to the lower end face 7, and the sintering chamber 5 is arranged on the side of the lower end face 7 close to the upper end face 6; the pressure shaft 3 is hollow, can be inserted into the sintering chamber 5 and perform piston movement 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 one end of the pressure shaft close to the sintering chamber 5 to form a gas channel 11.

[0055] The low-temperature sintering device of the present application can conveniently adjust the gas pressure state in the sintering chamber for sintering by setting a pressure relief port and a gas channel on the pressure shaft, thereby achieving the sintering preparation of ceramsite fracturing proppant at a lower temperature. By creating a different gas pressure from the outside in the sintering chamber 5, a higher gas pressure can be maintained in the sintering chamber 5, so that the raw materials can 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 the ceramsite proppant and the difficulty of expanding production.

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

[0057] In order to make the pressure acting on each sintering groove 10 uniform and make the structure of the fracturing proppant more compact, in a preferred embodiment, a plurality of sintering groove pressure shafts 12 are arranged at one end of the pressure shaft 3 close to the sintering chamber 5, and the plurality of sintering groove pressure shafts 12 can be inserted into the plurality of sintering grooves 10 one by one and perform piston movement in the vertical direction. The pressure transmitted by the pressure shaft 3 is uniformly applied to each sintering groove 10 through the sintering groove pressure shafts 12, which can avoid the problem of loose product structure and uneven quality caused by uneven force when only a single pressure shaft 3 contact surface acts on multiple sintering objects at the same time.

[0058] Since the present application is to obtain a columnar fracturing proppant, in a preferred embodiment, 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 independently 100-800 μm. The sintering tank 10 and the sintering tank pressure shaft 12 can be adjusted accordingly according to the size and shape of the required product.

[0059] In order to provide a relatively stable pressure for the fracturing proppant, in a preferred embodiment, the low-temperature sintering device further comprises a press 1. And in order to make the fracturing proppant form a more dense and uniform structure, in a preferred embodiment, the press 1 comprises 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, and the lower press is in detachable contact with the side of the lower end face 7 away from the upper end face 6. Providing a certain pressure on both the upper and lower sides of the sintering tank can make the structure of the sintered fracturing proppant therein more uniform and compact.

[0060] Since it is necessary to provide heat to the sintering environment and maintain it at a certain temperature during the sintering process, in a preferred embodiment, the low-temperature sintering device further includes a heat supply device 2, which is sleeved on the outer periphery of the sintering chamber 5 and is used to provide heat to the sintering chamber 5. The heat supply device 2 includes an electric heating system device and a water heating system device, which conducts heat to the sintering chamber 5 to maintain the sintering process therein.

[0061] In order to timely observe the temperature inside the sintering chamber 5 and adjust the sintering process in time, in a preferred embodiment, the heating device 2 also includes a temperature display element, and the temperature display element is selected from a thermometer, a sensor or a temperature digital display.

[0062] In order to prevent the gas in the gas channel from destroying the sintering density of the fracturing proppant in the sintering groove 10 in the sintering chamber 5, the gas channel should not overlap with the sintering groove 10 in spatial position. In a preferred embodiment, the pressure shaft gas channel 11 is a single hollow structure arranged inside the pressure shaft 3, and the projection of the gas channel 11 in the longitudinal direction cannot fall in the sintering groove 10, and the projection of the gas channel 11 in the horizontal direction does not overlap with the sintering groove 10. Any gas channel that can complete the gas flow between the inside of the sintering groove 5 and the outside is only applicable to this application. In a preferred embodiment, the gas channel 11 is cylindrical, and the diameters of the gas channel outlet 13 and the pressure relief port 4 are less than 100 μm.

[0063] In order to more conveniently and accurately adjust the horizontal positions of the upper end surface 6 and the lower end surface 7 , in a preferred embodiment, the upper end surface 6 and the lower end surface 7 are connected by a screw 8 .

[0064] In order to further fix the pressure shaft 3 and the sintering chamber 5, in a preferred embodiment, the low-temperature sintering device further includes an inner end surface 9, and there are two inner end surfaces 9, one inner end surface 9 is arranged between the side of the upper end surface 6 close to the lower end surface 7 and the pressure shaft 3, and the other inner end surface 9 is arranged between the side of the lower end surface 7 close to the upper end surface 6 and the sintering chamber 5. The pressure shaft 3 and the sintering chamber 5 are respectively fixed on the side of the inner end surface 9 away from the upper end surface 6 or the lower end surface 7, so that the pressure shaft 3 and the sintering chamber 5 are more stable during the pressure sintering process.

[0065] In order to adjust the internal air pressure of the sintering tank 5, the pressure relief port 4 has two states of on and off. Any setting that can realize the on and off state conversion of the pressure relief port 4 is applicable to the present application. In a preferred embodiment, the on and off control of the pressure relief port 4 is realized by the connection relationship between the nut and the thread inside the pressure relief port 4 or the buckle arranged outside the pressure relief port 4.

[0066] In a second typical embodiment of the present application, a ceramsite fracturing proppant having a SiO2-Al2O3 mullite phase obtained by the above-mentioned preparation method is provided, wherein the relative density of the ceramsite fracturing proppant is greater than 90%; preferably, under the SY / T5108-2014 proppant performance test method for hydraulic fracturing and gravel filling operations, the crushing rate of the ceramsite fracturing proppant is less than 10%. The above-mentioned preparation method can be used to obtain a ceramsite fracturing proppant with better performance, i.e., higher density, at a lower temperature.

[0067] It should be noted that the related devices or equipment used in the aforementioned preparation method of the present application can be completed by using the improved low-temperature sintering device mentioned above in the present application, or can be reasonably selected from existing equipment that can achieve the corresponding effect according to the conditions required for each step. In some preferred embodiments, the low-temperature sintering device provided above in the present application is used to complete the process.

[0068] The present application is further described in detail below in conjunction with specific embodiments, and these embodiments cannot be understood as limiting the scope of protection claimed in the present application. Figures 1 to 3 The low-temperature sintering device shown completes the sintering process. However, this is not a restrictive description and does not exclude that the equipment with similar functions in the prior art can also realize the sintering process of the present application.

[0069] Use Figures 1 to 3 The sintering process of the low temperature sintering device shown is as follows:

[0070] Adjust the position of the low-temperature sintering device so that it is on a horizontal plane.

[0071] Weigh appropriate amounts of SiO2 powder, Al2O3 powder and combustion aid, mix them thoroughly to obtain a mixture (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 aid accounts for 1-4% of the sum of the masses of the three), and then place the mixture in each sintering tank 10 of the sintering chamber 5.

[0072] Close the pressure relief port 4, start the press machine 1, adjust the pressure shaft 3 to apply the first pressure treatment pressure (100-500MPa) in the longitudinal direction, and at the same time turn on the heating device 2 to raise the temperature to the first pressure treatment temperature (90-120°C), maintain the pressure and temperature for 2-4 hours, and perform the first pressure treatment; adjust the pressure shaft 3 longitudinally upward so that the sintering tank pressure shaft 12 does not contact the sintering tank 10, open the pressure relief port 4, and wait until 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, and maintain the temperature at the temperature of the first pressure treatment.

[0073] Keep the pressure relief port 4 open, adjust the pressure shaft 3 to apply the second pressure treatment pressure (100-500MPa) in the longitudinal direction, so that the sintering tank pressure shaft 12 contacts the sintering tank 10, heat up to the second pressure treatment temperature (90-120℃), and maintain the pressure and temperature for 1-4h. After completing the second pressure treatment, stop 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 by using the low temperature sintering device of the present application. Figures 1 to 3 shown.

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

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

[0078] Close the pressure relief port 4, start the press machine 1, adjust the pressure shaft 3 to apply a pressure of 500 MPa in the longitudinal direction, and at the same time turn on the heating device 2 to increase the temperature to 110°C at 10°C / min, maintain the pressure and temperature for 3 hours, and perform the first pressurization treatment; adjust the pressure shaft 3 longitudinally upward so that the sintering tank pressure shaft 12 does not contact the sintering tank 10, open the pressure relief port 4, and wait until 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, and maintain the temperature at 110°C.

[0079] Keep the pressure relief port 4 open, adjust the pressure shaft 3 to apply a pressure of 500 MPa in the longitudinal direction, so that the sintering tank pressure shaft 12 contacts the sintering tank 10, increase the temperature to 110°C at 10°C / min, and maintain the pressure and temperature for 2 hours. After the second pressurization treatment is completed, stop the press machine 1, remove the pressure, and take out the sintered product from 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 embodiment 1 is that the amount of water used is 2%, namely 31 g. The performance results of the obtained samples are shown in Table 1.

[0082] Example 3

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

[0084] Example 4

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

[0086] Table 1 Performance results of samples of Examples 1 to 4

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

[0088] The relative density is measured by using the SY / T5108-2014 proppant performance test method for hydraulic fracturing and gravel filling operations to test the apparent density, and then the apparent density is divided by the density of the pure SiO2 dense material (2.2 g / cm 3 ), and the relative density is obtained by calculation.

[0089] The crushing rate is tested by using the SY / T5108-2014 proppant performance test method for hydraulic fracturing and gravel filling operations.

[0090] It can be seen from Examples 1 to 4 that increasing the amount of water can increase the relative density of the ceramsite proppant, indicating that its compactness is improved. The increased compactness reduces the crushing rate, indicating that the mechanical properties are effectively improved. In particular, the relative density of the ceramsite proppant obtained in Example 3 reaches 0.96, and the crushing rate is reduced to 4%. This is because under the action of the instantaneous sintering agent, the mullite phase ( Figure 4 and Figure 5 ), after further sintering and removal of the transient sintering aid, a densified ceramsite proppant ( Figure 5 ).from Figure 4 It can be seen that the grain size of the sample obtained in Example 3 is about 1 μm, with a dense microstructure and fewer pores, which is consistent with the result of high relative density and helps to reduce the breakage rate. Figure 5It can be seen that the sample obtained in Example 3 is a mullite phase, and the diffraction peak is sharp, indicating a high degree of crystallization, which helps to improve the mechanical properties of the sample. When the amount of water reaches 4%, the result is the same as that of 3%, so there is no need to increase the amount of water blindly. From the results, it can be seen that the pressure of the first pressure treatment is kept at 500MPa, the temperature is kept at 110°C, and the pressure of the second pressure treatment is kept at 500MPa. When the instantaneous sintering aid is water, its optimal amount is 3% (Example 3).

[0091] Examples 3, 5 to 7 control a single variable: water is used as the instantaneous sintering aid in an amount of 3%, the pressure of the first pressurized treatment is 500 MPa, and the pressure of the second pressurized treatment is 500 MPa, which remain unchanged; what is changed is: the temperature is 90°C, 100°C, 110°C, and 120°C; the effects of changing the temperature on the compactness (evaluated by relative density) and the crushing rate of the ceramsite proppant are illustrated by way of examples.

[0092] Example 5

[0093] The difference between this embodiment and embodiment 3 is that the temperature is 90° C. 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 is 100° C. 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 is 120° C. The performance results of the obtained samples are shown in Table 2.

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

[0099] Example Relative density Crushing rate (%) 3 0.96 4 5 0.90 10 6 0.92 8 7 0.96 4

[0100] From Examples 3, 5 to 7, it can be seen that increasing the temperature can increase the relative density of the ceramsite proppant, indicating that its compactness is improved, and the increased compactness reduces the crushing rate, indicating that the mechanical properties are effectively improved; when the temperature reaches 120°C, the results are the same as those obtained at 120°C, so there is no need to increase the temperature blindly. From the results, it can be seen that the optimal temperature is 110°C when the water dosage is kept at 3%, the pressure of the first pressure treatment is 500MPa, and the pressure of the second pressure treatment is 500MPa.

[0101] Examples 3, 8 to 10 control a single variable: water is used as the instantaneous sintering aid in an amount of 3%, the pressure of the first pressure treatment is 500 MPa, the temperature is 110°C, and the pressure of the second pressure treatment is 500 MPa, which remain unchanged; what is changed is: the pressure holding time of the first pressure treatment is 1h, 2h, 3h, and 4h; the effects of changing the pressure holding time of the first pressure treatment on the density (evaluated by relative density) and the crushing rate of the ceramsite proppant are illustrated by way of examples.

[0102] Example 8

[0103] The difference between this embodiment and embodiment 3 is that the pressure holding time of the second pressurization treatment is 1 hour. The performance results of the obtained samples are shown in Table 3.

[0104] Example 9

[0105] The difference between this embodiment and embodiment 3 is that the pressure holding time of the second pressurization treatment is 2 hours. The performance results of the obtained samples are shown in Table 3.

[0106] Example 10

[0107] The difference between this embodiment and embodiment 3 is that the pressure holding time of the second pressurization treatment is 4 hours. The performance results of the obtained samples are shown in Table 3.

[0108] Table 3 Performance results of samples of Examples 3, 8 to 10

[0109] Example Relative density Crushing rate (%) 3 0.96 4 8 0.93 7 9 0.95 5 10 0.96 4

[0110] From Examples 3, 8 to 10, it can be seen that extending the pressure holding time of the first pressure treatment can increase the relative density of the ceramsite proppant, indicating that its density has been improved. The increased density reduces the crushing rate, indicating that the mechanical properties have been effectively improved. This is because the pressure holding of the first pressure treatment is to generate the mullite phase. Under the action of pressure, temperature and the instantaneous sintering agent, the extended time is conducive to the generation of the mullite phase; when the pressure holding time of the first pressure treatment is extended to 4h, the result is the same as that obtained by 3h, so there is no need to blindly extend the pressure holding time of the second pressure treatment. From the results, it can be seen that the water dosage is 3%, the temperature is 110℃, the pressure of the first pressure treatment is 500MPa, and the pressure of the second pressure treatment is 500MPa. It is better to extend the pressure holding time of the first pressure treatment to 3h.

[0111] Examples 11 to 31 control a single variable: the amount of instantaneous sintering agent is 3%, the pressure of the first pressurized treatment is 500 MPa, the temperature is 110° C., and the pressure of the second pressurized treatment is 500 MPa, which remain unchanged; what is changed is that the instantaneous sintering agent uses siloxane, namely KH570, A171, and silicone oil (polydimethylsiloxane). Siloxane plays a role of volatilization and bonding during the sintering process. When the temperature is greater than 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, and the condensation product remains on the surface of the mixed powder B and plays a bonding role. The two effects jointly promote the densification of ceramsite grains; the embodiment illustrates the effect of changing the type of instantaneous sintering agent on the density (evaluated by relative density) and the crushing rate of the ceramsite proppant.

[0112] Embodiment 11

[0113] The difference between this embodiment and embodiment 3 is that the instantaneous sintering agent is KH570. The performance results of the obtained samples are shown in Table 4.

[0114] Example 12

[0115] 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.

[0116] Embodiment 13

[0117] The difference between this embodiment and embodiment 3 is that the instantaneous sintering agent is silicone oil. The performance results of the obtained samples are shown in Table 4.

[0118] Table 4 Performance results of samples of Examples 11 to 12

[0119] Example Relative density Crushing rate (%) 11 0.98 2 12 0.96 4 13 0.97 3

[0120] It can be seen from Examples 11 to 13 that when the instantaneous sintering aids are all siloxanes, the relative density and crushing rate of the ceramsite proppant are different due to the different molecular structures of different types of siloxanes; because the KH570 molecule has a long chain and unsaturated bonds, the long chain can avoid the influence of the steric hindrance effect on the densification, and the unsaturated bonds are helpful for the polycondensation reaction. The two together promote densification, thereby increasing the relative density and reducing the crushing rate; the A171 molecule has no long chain and no unsaturated bonds, which reduces the degree of densification relative to KH570, thereby reducing the relative density and increasing the crushing rate. Silicone oil molecules have long chains but no unsaturated bonds, resulting in the relative density and crushing rate of the ceramsite proppant being in the middle. It can be seen that when the external conditions are the same and the instantaneous sintering aid is an organic matter, the sample performance is mainly affected by whether the instantaneous sintering aid molecules have long chains and unsaturated bonds.

[0121] Examples 14 to 15 control a single variable: the amount of instantaneous sintering aid is 3%, the pressure of the first pressurized treatment is 500 MPa, the temperature is 110°C, and the pressure of the second pressurized treatment is 500 MPa, which remain unchanged; what is changed is that the instantaneous sintering aids are silicic acid and hexyl orthosilicate, respectively; by hydrolysis, silicic acid obtains SiO2 and H2O, and during the sintering process, SiO2 is distributed around the grains (i.e., at the grain boundaries) to fill the gaps, and the generated H2O can be effectively volatilized at a temperature greater than 100°C, and the two effects jointly promote densification; the examples illustrate the effect of changing the type of instantaneous sintering aid on the density (evaluated by relative density) and crushing rate of ceramsite proppant.

[0122] Embodiment 14

[0123] 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.

[0124] Embodiment 15

[0125] The difference between this embodiment and embodiment 3 is that the instantaneous sintering agent is hexyl orthosilicate. The performance results of the obtained samples are shown in Table 5.

[0126] Table 5 Performance results of samples of Examples 14 to 15

[0127] Example Relative density Crushing rate (%) 14 0.98 2 15 0.99 1

[0128] It can be seen from Examples 14 to 15 that when the instantaneous sintering aid is silicic acid or hexyl orthosilicate, the hydrolysis product SiO2 occupies the position of the pores at the grain boundaries, fills the gaps, and promotes densification, thereby obtaining a fracturing proppant with a relative density of up to 0.99, and the breakage rate is only 1%.

[0129] Examples 16 to 18 control a single variable: the amount of instantaneous sintering agent is 3%, the pressure of the first pressurized treatment is 500 MPa, the temperature is 110°C, and the pressure of the second pressurized treatment is 500 MPa, which remain unchanged; what is changed is: the instantaneous sintering agents are ammonia water, urea, and NaOH, respectively; the volatilization of ammonia water and urea is utilized to promote densification; NaOH and SiO2 grains can generate an adhesive, and the generated H2O can be effectively volatilized at a temperature greater than 100°C, and the two effects jointly promote grain densification; the examples illustrate the effect of changing the type of instantaneous sintering agent on the density (evaluated by relative density) and crushing rate of the ceramsite proppant.

[0130] Example 16

[0131] The difference between this embodiment and embodiment 3 is that the instantaneous sintering agent is ammonia water. The performance results of the obtained samples are shown in Table 6.

[0132] Embodiment 17

[0133] The difference between this embodiment and embodiment 3 is that the instantaneous burning aid is urea. The performance results of the obtained samples are shown in Table 6.

[0134] Embodiment 18

[0135] The difference between this embodiment and embodiment 3 is that the instantaneous sintering agent is NaOH. The performance results of the obtained samples are shown in Table 6.

[0136] Table 6 Performance results of samples of Examples 16 to 18

[0137] Example Relative density Crushing rate (%) 16 0.97 3 17 0.97 3 18 0.98 2

[0138] It can be seen from Examples 16 to 18 that when the instantaneous sintering aid is ammonia water or urea, the generated NH3 and H2O can be effectively volatilized at a temperature greater than 100°C, thereby 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 a temperature greater than 100°C. These two effects jointly promote grain densification.

[0139] Comparative Examples 1-18

[0140] The raw material prepared in Comparative Examples 1-18 is 1000 g of SiO2 powder with a particle size of 1 μm, and the pressure of the first pressurization treatment is 300 MPa, the time of the first pressurization treatment is 40 min, the pressure of the second pressurization treatment is 500 MPa, and the temperature of the second pressurization treatment is 20°C.

[0141] The remaining conditions and properties of the prepared silica fracturing proppant are shown in Table 7 below:

[0142] Table 7 Condition variables and performance results of comparative examples 1-18

[0143]

[0144] It can be seen from Table 7 above that when the raw material used for fracturing proppant is only SiO2 powder, even if the preparation method is the same as that of the present application, that is, two-stage pressure treatment (such as Example 5-10 and Comparative Example 5-10), and the same mass and type of instantaneous combustion aid are used (such as Example 1-4, 11-18 and Comparative Example 1-4, 11-18), the performance parameters of relative density and crushing rate of silica fracturing proppant obtained by Comparative Example 1-18 are worse than those of Example 1-18 of the present application.

[0145] The SiO2-Al2O3 mullite phase fracturing proppant of the present application has better quality in relative density and crushing rate than ordinary silica fracturing proppant, and can play a role in application environments with higher requirements. Specifically, since the preparation raw materials of the present application also include Al2O3 powder, and the SiO2 powder is subjected to the self-generated pressure of the instantaneous sintering agent, low-temperature auxiliary sintering and solvent heat (water) under the first pressurization treatment, after pressure maintenance and heat preservation, the densified SiO2-Al2O3 mullite phase can be initially obtained; then, in the second stage of pressurization, the whole densification process is completed by low-temperature sintering. Thus, at 90-120°C, a SiO2-Al2O3 mullite phase fracturing proppant with excellent mechanical properties, low crushing rate, stable physical and chemical properties, and chemical corrosion resistance is obtained, so that the SiO2-Al2O3 mullite phase fracturing proppant is suitable for harsh working conditions such as complex formations and changeable environments.

[0146] From the above description, it can be seen that the above embodiment of the present invention achieves the following technical effects: the instant sintering aid is mixed with the raw material, and the mixture is first pre-pressurized to make the air pressure in the sintering chamber higher than the external air pressure. The instant sintering aid in the sintering chamber forms a mullite phase with high mechanical properties with the raw material under high pressure and low temperature, and densifies the ceramsite grains. Then the air pressure in the low-temperature sintering device is made consistent with the outside world, and the fracturing proppant is further pressurized to densify, so that a relatively dense ceramsite fracturing proppant can be obtained at a lower temperature, thereby effectively reducing the crushing rate of the ceramsite fracturing proppant. Among them, the low-temperature sintering device can provide constant pressure and constant temperature at the same time, providing external conditions for the sintering process, and the volatility and adhesiveness of the instant sintering aid can provide material conditions for the densification process, so that the silicon dioxide grains reach a densification degree at a lower temperature, the relative density is greater than 0.90, and the crushing rate is less than 10%.

[0147] The technical solution of the present application does not require a high-temperature process, effectively reduces the sintering temperature of the ceramsite proppant, and when the sintering temperature is lower than two-thirds of the melting point of the sintered material, a dense ceramsite proppant with low breakage rate, high strength and good mechanical properties can be obtained. The technical solution of the present application as a whole has the advantages of simple synthesis, easy implementation, low sintering temperature, and energy saving, which is conducive to promotion in the field of oil and gas industry fracturing and has broad application prospects.

[0148] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a ceramsite fracturing proppant having a SiO2-Al2O3 mullite phase at low temperature, characterized in that: The method comprises: placing a mixture of SiO2, Al2O3 and an instantaneous sintering aid in a low-temperature sintering device; The pressure relief port of the pressure shaft is in a closed state, and the pressure shaft is used to perform a first pressurization treatment on the sintering chamber, wherein during the first pressurization treatment process, the gas pressure in the sintering chamber is controlled to be higher than the gas pressure outside the sintering chamber, so as to obtain a first pressurization treatment product; The pressure relief port is opened, the air pressure inside the sintering chamber is adjusted to be consistent with the air pressure outside the sintering chamber, and the product of the first pressure treatment is subjected to a second pressure treatment by 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; The instant sintering aid is selected from the following: water, siloxane, silicic acid, hexyl orthosilicate and alkali; The mass of the instantaneous sintering aid accounts for 1-4% of the sum of the masses of the SiO2, the Al2O3 and the instantaneous sintering aid.

2. The method according to claim 1, characterized in that The particle sizes of the SiO2 and the Al2O3 are independently ≤10 μm; Preferably, the molar ratio of the SiO2 to the Al2O3 is 1:2-5.

3. The method according to any one of claims 1 to 2, characterized in that: Before performing the first pressurization treatment and the second pressurization treatment, the temperature in the sintering chamber is pre-heated to a temperature required for the first pressurization treatment or the second pressurization treatment by a heat supply device.

4. The method according to claim 3, characterized in that The pressure of the first pressurization treatment is 100-500 MPa; Preferably, the first pressurization treatment time is 2-4h; Preferably, the pressure of the second pressurization treatment is 100-500 MPa; Preferably, the second pressurization treatment is performed for 1-4 hours.

5. The method according to claim 1, characterized in that The low temperature sintering device comprises: A pressure shaft (3), a sintering chamber (5), an upper end surface (6) and a lower end surface (7); The pressure shaft (3) is arranged on a side of the upper end surface (6) close to the lower end surface (7); The sintering chamber (5) is arranged on a side of the lower end surface (7) close to the upper end surface (6); The pressure shaft (3) is hollow and can be inserted into the sintering chamber (5) and perform piston movement in the vertical direction; A pressure relief port (4) is provided on the side wall of the pressure shaft (3) and communicates with a gas channel outlet (13) at one end of the pressure shaft close to the sintering chamber (5), thereby forming a gas channel (11).

6. The method according to claim 5, characterized in that The sintering chamber (5) is provided with a plurality of sintering tanks (10) for containing sintering raw materials; A plurality of sintering tank pressure shafts (12) are arranged at one end of the pressure shaft (3) close to the sintering chamber (5), and 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; Preferably, 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 independently 100-800 μm.

7. The method according to claim 5, characterized in that The low-temperature sintering device further comprises a press (1); The press (1) comprises an upper press and a lower press, wherein the upper press is in detachable contact with a side of the upper end surface (6) away from the lower end surface (7), and the lower press is in detachable contact with a side of the lower end surface (7) away from the upper end surface (6).

8. The method according to claim 5, characterized in that The low-temperature sintering device further comprises a heat supply device (2); The heat supply device (2) is sleeved on the outer periphery of the sintering chamber (5) and is used to provide heat for the sintering chamber (5); Preferably, the heating device (2) further comprises a temperature display element, and the temperature display element is selected from a thermometer, a sensor or a temperature digital display.

9. The method according to any one of claims 5 to 8, characterized in that: The gas channel (11) is a single hollow structure arranged inside the pressure shaft (3), and the projection of the gas channel (11) in the longitudinal direction cannot fall into the sintering tank (10), and the projection of the gas channel (11) in the horizontal direction does not overlap with the sintering tank (10); Preferably, the gas channel (11) is cylindrical, and the diameters of the gas channel outlet (13) and the pressure relief port (4) are less than 100 μm; Preferably, the upper end surface (6) and the lower end surface (7) are connected via a screw (8).

10. The method according to claim 9, characterized in that The low-temperature sintering device also includes an inner end surface (9), and there are two inner end surfaces (9), one of which is arranged between the side of the upper end surface (6) close to the lower end surface (7) and the pressure shaft (3), and the other of which is arranged between the side of the lower end surface (7) close to the upper end surface (6) and the sintering chamber (5).

11. The method according to claim 9, characterized in that The pressure relief port (4) has two states of on and off, and the on and off control of the pressure relief port (4) is achieved through the connection relationship between the nut and the thread inside the pressure relief port (4) or the buckle arranged outside the pressure relief port (4).

12. A ceramsite fracturing proppant having a SiO2-Al2O3 mullite phase obtained by the method according to any one of claims 1 to 11, characterized in that: The relative density of the ceramsite fracturing proppant is greater than 90%; Preferably, under the SY / T5108-2014 proppant performance test method for hydraulic fracturing and gravel packing operations, the breakage rate of the ceramsite fracturing proppant is less than 10%.

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