Device and method for preparing silicon dioxide fracturing propping agent at room temperature and product

Abstract

The invention provides a device and a method for preparing a silicon dioxide fracturing propping agent at room temperature and a product. The low-temperature sintering device comprises a pressure shaft, a sintering chamber, an upper end face and a lower end face, the pressure shaft is arranged on the side, close to the lower end face, of the upper end face. The sintering chamber is arranged on the side, close to the upper end face, of the lower end face. The pressure shaft is hollow and can be inserted into the sintering chamber and perform piston motion in the vertical direction; a pressure relief opening is formed in the side wall of the pressure shaft and communicated with a gas channel outlet in the end, close to the sintering chamber, of the pressure shaft, and a gas channel is formed. By utilizing the device, the sintering temperature of the silicon dioxide fracturing propping agent can be effectively reduced, the densified silicon dioxide fracturing propping agent with low breakage rate, high strength and good mechanical property is obtained, and the device has the advantages of simplicity in synthesis, low sintering temperature and energy conservation, is favorable for being popularized in the field of industrial fracturing of petroleum and natural gas, and has wide application prospects. Wide application prospects are realized.

Description

Technical Field

[0001] The present invention relates to the field of fracturing materials for petroleum and natural gas industries, and in particular to a device, method and product for preparing a silica fracturing proppant at room temperature. 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. How to solve the problem of high sintering temperature of ceramsite fracturing proppant, that is, how to reduce the sintering temperature of ceramsite fracturing proppant, is a key issue that needs to be solved urgently. Summary of the invention

[0005] The main purpose of the present invention is to provide a device, method and product for preparing silica fracturing proppants at room temperature, so as to solve the problem that silica fracturing proppants cannot be prepared by low-temperature sintering technology in the prior art.

[0006] In order to achieve the above-mentioned purpose, according to the first aspect of the present invention, there is provided a low-temperature sintering device for preparing silica fracturing proppant at room temperature, the low-temperature sintering device comprising: 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; the sintering chamber is arranged on the side of the lower end face close to the upper end face; the pressure shaft is hollow and 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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 does not 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.

[0011] 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.

[0012] 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.

[0013] In order to achieve the above-mentioned object, according to a second aspect of the present invention, there is provided a method for preparing a silica fracturing proppant at room temperature, the preparation method comprising: placing a mixture of SiO2 and an instantaneous sintering aid in the above-mentioned low-temperature sintering device; subjecting the low-temperature sintering device to a first pressure treatment, wherein during the first pressure treatment, the gas pressure in the low-temperature sintering device is controlled to be higher than the gas pressure outside the low-temperature sintering device, so as to obtain a first pressure treatment product; adjusting the gas pressure in the low-temperature sintering device to be consistent with the gas pressure outside the low-temperature sintering device, subjecting the first pressure treatment product to a second pressure treatment, so as to obtain a silica fracturing proppant; the temperature of the first pressure treatment and / or the second pressure treatment is 20-120°C, and the temperature of the first pressure treatment is higher than the temperature of the second pressure treatment; the instantaneous sintering aid is selected from one of the following: water, siloxane, silicic acid, hexyl orthosilicate and alkali; preferably, the mass of the instantaneous sintering aid accounts for 1-4% of the sum of the masses of silica and the instantaneous sintering aid.

[0014] Furthermore, the particle size of SiO2 is ≤10 μm.

[0015] Furthermore, before the first pressurization treatment and the second pressurization treatment, the temperature in the low temperature sintering device is preheated to a temperature required for the first pressurization treatment or the second pressurization treatment.

[0016] Further, the pressure of the first pressurization treatment is 100-500 MPa; preferably, the time of the first pressurization treatment is 10-40 min; preferably, the pressure of the second pressurization treatment is 100-500 MPa; preferably, the time of the second pressurization treatment is 30-70 min.

[0017] In order to achieve the above object, according to the third aspect of the present invention, there is provided a silica fracturing proppant obtained by the above method, wherein the relative density of the silica 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 silica fracturing proppant is less than 10%.

[0018] By applying the technical solution of the present invention, the low-temperature sintering device of the present application can adjust the gas pressure state in the sintering chamber for sintering more conveniently by setting a pressure relief port and a gas channel on the pressure shaft, thereby realizing the sintering preparation of silica fracturing proppants at a lower temperature. The sintering temperature of the silica fracturing proppants is effectively reduced, and silica fracturing proppants of qualified quality are obtained. The sintering preparation using the low-temperature sintering device of the present application 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

[0019] 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:

[0020] Figure 1 A front view of a low temperature sintering device according to the present invention is shown;

[0021] Figure 2 A horizontal cross-sectional view of a sintering chamber of a low-temperature sintering device of the present invention is shown;

[0022] Figure 3 A side view showing a pressure shaft of a low temperature sintering device of the present invention;

[0023] Figure 4 The SEM image of the SiO2 fracturing proppant obtained in Example 3 of the present invention is shown;

[0024] Figure 5 The XRD diagram of the SiO2 fracturing proppant obtained in Example 3 of the present invention is shown;

[0025] The above drawings include the following reference numerals:

[0026] 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

[0027] 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.

[0028] As mentioned in the background technology, the prior art still uses a high-temperature sintering method, and the sintering temperature is usually between 900°C and 1300°C, which results in an overly high sintering temperature, high production costs, and limits the scope of application of ceramsite proppants, restricts the further development of hydraulic fracturing, and is difficult to meet existing oil and gas production requirements and energy needs. Because the prior art 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, and 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.

[0029] 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 silica fracturing proppants, and the sintering temperature is still higher than 300°C, and it is impossible to obtain dense ceramic materials at room temperature (20°C); in addition, the raw material types of the existing cold sintering technology and the silica 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 silica fracturing proppants.

[0030] Beneficial Effects

[0031] 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 provides a method and product for preparing silica fracturing proppants at room temperature. The present invention uses a self-made low-temperature sintering device, assisted by an instant sintering aid, to achieve densification through the sintering process, and obtain a cylindrical SiO2 fracturing proppant at room temperature.

[0032] 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 SiO2 densification process at room temperature, thereby obtaining a fracturing proppant with low breakage rate, good mechanical properties and high strength.

[0033] 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 SiO2 grains reach a densified degree at room temperature, with a relative density greater than 0.90, and a crushing rate of less than 10% under the SY / T5108-2014 proppant performance test method for hydraulic fracturing and gravel filling operations.

[0034] The present invention does not require a high temperature process, effectively reduces the sintering temperature of the silica proppant, and achieves a dense, quality-qualified silica proppant when the sintering temperature is lower than two-thirds of the melting point of the sintered material. The present invention 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.

[0035] It should be noted that when the device of the present application performs silica fracturing and sintering, the temperature of the second pressure treatment can be a temperature lower than two-thirds of the melting point of the sintering material. In consideration of energy conservation and practical application of materials, the temperature of the second pressure treatment is preferably 20-120°C, preferably 20-80°C, preferably 20-50°C, more preferably room temperature, and further preferably room temperature is 20°C.

[0036] In a first typical embodiment of the present application, a low temperature sintering device for preparing silica fracturing proppant at room temperature is provided, such as Figure 1 As shown, the low-temperature sintering device 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; 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 arranged 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.

[0037] 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 silica fracturing proppant at a relatively low temperature (at least a temperature lower than two-thirds of the melting point of the sintering material). By creating a different air pressure in the sintering chamber 5 from that in the outside world, a higher air 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 silica proppant, and can obtain silica proppant of qualified quality, reducing the production cost of the silica proppant and the difficulty of expanding production.

[0038] Since fracturing proppants are mostly prepared as three-dimensional products to withstand greater pressure, and in order to further 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 needs.

[0039] In order to further keep the pressure acting on each sintering groove 10 uniform, and thus make the structure of the prepared 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.

[0040] In order to further obtain a columnar fracturing proppant, and to obtain a fracturing proppant with low breakage rate, high strength and good mechanical properties, 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.

[0041] In order to provide a relatively stable pressure during the sintering process of preparing the fracturing proppant, in a preferred embodiment, the low-temperature sintering device further includes a press 1. And in order to allow the fracturing proppant to form a more dense and uniform structure, in a preferred embodiment, 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, 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.

[0042] Since heat is required during the sintering process and maintained at a certain temperature, 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 for 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.

[0043] In order to be able to observe the temperature inside the sintering chamber 5 more timely 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.

[0044] In order to further 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, it is best that the gas channel does 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 shape that can complete the gas circulation inside the sintering groove 5 and the outside is suitable for 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 100μm.

[0045] 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 lead screw 8 .

[0046] 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.

[0047] In order to further facilitate the adjustment of the internal air pressure of the sintering tank 5, the pressure relief port 4 is controlled to have 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 set on the outside of the pressure relief port 4.

[0048] In a second typical embodiment of the present application, a method for preparing a silica fracturing proppant at room temperature is provided, the method comprising: placing a mixture of SiO2 and a transient sintering aid in the above-mentioned low-temperature sintering device; performing a first pressure treatment on the low-temperature sintering device, wherein, during the first pressure treatment, the gas pressure in the low-temperature sintering device is controlled to be higher than the gas pressure outside the low-temperature sintering device to obtain a first pressure treatment product; adjusting the gas pressure in the low-temperature sintering device to be consistent with the gas pressure outside the low-temperature sintering device, performing a second pressure treatment on the first pressure treatment product to obtain a silica fracturing proppant; the temperature of the first pressure treatment and / or the second pressure treatment is 20-120°C, and the temperature of the first pressure treatment is higher than the temperature of the second pressure treatment.

[0049] 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 SiO2 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 10-40min. 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.

[0050] 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 SiO2 powder. The sintering tank pressure shaft then transmits the pressure to the SiO2 powder in the corresponding sintering tank of the sintering chamber. The sintering tank pressure shaft needs to contact the SiO2 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 the SiO2 fracturing proppant.

[0051] 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.

[0052] 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.

[0053] The present application mixes an instantaneous sintering aid with SiO2, and first pre-pressurizes the mixture so that the air pressure in the low-temperature sintering device is higher than the external air pressure, and the instantaneous sintering aid in the low-temperature sintering device boils under high pressure and low temperature, while forming 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 by volatilization or bonding, and will not cause any contamination by impurities. After pre-pressurization, the air is released to make the air pressure in the low-temperature sintering device consistent with the external environment, and further mechanical force is applied to densify the initial fracturing proppant, so that a relatively dense silica fracturing proppant can be obtained at a lower temperature. Among them, any low-temperature sintering device that can pre-pressurize the mixture of sintering raw materials and instantaneous sintering aid and then release the air, and further apply mechanical force, is suitable for the present application. In a preferred embodiment, the present application utilizes Figure 1-3 The low temperature sintering device shown is used to prepare silica fracturing proppants. Preferably, the temperature of the first pressure treatment is 90-120° C., more preferably 110° C. Preferably, the temperature of the second pressure treatment is room temperature (20° C.).

[0054] 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 SiO2 densification process at room temperature, thereby obtaining a fracturing proppant with low breakage rate, good mechanical properties and high strength.

[0055] In a preferred embodiment, the instantaneous sintering aid includes: 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 silicon dioxide 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. In a preferred embodiment, the low-temperature sintering device includes a cylindrical groove for holding the mixture.

[0056] Among them, the performance of silica fracturing proppants 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 silica fracturing proppants made from siloxanes without long chains and unsaturated bonds (such as A171) is relatively general. The relative density and crushing rate performance of silica fracturing proppants made from siloxanes with long chains but no unsaturated bonds (such as silicone oil) are in the middle.

[0057] Silicic acid and silicic acid derivatives can generate SiO2 and H2O due to hydrolysis. The newly generated SiO2 and H2O can volatilize and improve the density of the silica fracturing proppant while filling the gaps during the sintering process.

[0058] 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.

[0059] In order to make the generated silica fracturing proppant more compact, in a preferred embodiment, the particle size of SiO2 is ≤10μm, or SiO2 powder material with a particle size of ≤10μm can be made through ball milling. Among them, the microscopic powder structure of silica can form sharp grains during the sintering process, and the grains can achieve the effect of reducing porosity and densification through grain boundary diffusion and grain boundary migration.

[0060] In order to more efficiently sinter to obtain silica 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 and the second pressure treatment, and the preheating heating rate is 10°C / min.

[0061] In order to complete sintering more efficiently, in a preferred embodiment, the pressure of the first pressurization treatment is 100-500MPa, more preferably 100-300MPa; preferably, the time of the first pressurization treatment is 10-40min, more preferably 30-40min; the pressure of the second pressurization treatment is 100-500MPa, more preferably 300-500MPa; preferably, the time of the second pressurization treatment is 30-70min, more preferably 70min.

[0062] In a third typical embodiment of the present application, a silica fracturing proppant obtained by the above method is provided, wherein the relative density of the silica 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 silica fracturing proppant is less than 10%. The above preparation method can obtain a silica fracturing proppant with better performance, i.e., higher density, at a lower temperature.

[0063] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0064] Example 1

[0065] The sintering process is completed by using the low temperature sintering device of the present application. Figures 1 to 3 shown.

[0066] 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.

[0067] 1000 g of SiO2 powder with a particle size of 1 μm was weighed, 10 g of 1% water was added, and the two were fully mixed to obtain a mixture, and then the mixture was evenly placed in each sintering tank 10 of the sintering chamber 5.

[0068] Close the pressure relief port 4, start the press machine 1, adjust the pressure shaft 3 to apply a pressure of 300 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 40 minutes, 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 the temperature in the sintering chamber 5 naturally drops to 20°C.

[0069] 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, and maintain the pressure and temperature (20°C) for 60 minutes. 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.

[0070] Example 2

[0071] The difference between this embodiment and embodiment 1 is that the amount of water used is 2%. The performance results of the obtained samples are shown in Table 1.

[0072] Example 3

[0073] The difference between this embodiment and embodiment 1 is that the amount of water used is 3%. The performance results of the obtained samples are shown in Table 1.

[0074] Example 4

[0075] The difference between this embodiment and embodiment 1 is that the amount of water used is 4%. The performance results of the obtained samples are shown in Table 1.

[0076] Table 1 Performance results of samples of Examples 1 to 4

[0077] Example Relative density Crushing rate (%) 1 0.86 15 2 0.89 11 3 0.92 8 4 0.92 8

[0078] 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.

[0079] The crushing rate is tested by using the SY / T5108-2014 proppant performance test method for hydraulic fracturing and gravel filling operations.

[0080] From Examples 1 to 4, it can be seen that increasing the amount of water can increase the relative density of SiO2 fracturing proppant, indicating that its compactness is improved. The increased compactness reduces the crushing rate, indicating that the mechanical properties are effectively improved. 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 when the first process pressure is maintained at 300MPa, the temperature is 110℃, and the second process pressure is 500MPa, when the instantaneous sintering agent is water, its optimal amount is 3% (Example 3), and its microscopic morphology is as follows Figure 4 As shown, the composition is Figure 5 As shown. Figure 4It 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 5 It can be seen that the sample obtained in Example 3 is a crystalline SiO2 phase, and when the diffraction angle is around 27°, it presents an obvious sharp diffraction peak, indicating a high degree of crystallinity, which helps to improve the mechanical properties of the sample.

[0081] Examples 3, 5 to 7 are single variable controls: water is used as the instantaneous sintering aid, and its dosage is 3%. The first process pressure is 300 MPa, and the second process pressure is 500 MPa, which remain unchanged; what is changed is the temperature of the first pressurized treatment, which is 90°C, 100°C, 110°C, and 120°C, respectively; the examples illustrate the effect of changing the temperature on the compactness (evaluated by relative density) and the crushing rate of the SiO2 fracturing proppant.

[0082] Example 5

[0083] 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.

[0084] Example 6

[0085] 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.

[0086] Example 7

[0087] 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.

[0088] Table 2 Performance results of samples of Examples 3, 5 to 7

[0089] Example Relative density Crushing rate (%) 3 0.92 8 5 0.88 12 6 0.90 9 7 0.92 8

[0090] From Examples 3, 5 to 7, it can be seen that increasing the temperature can increase the relative density of SiO2 fracturing proppant, indicating that its compactness is improved. 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 3%, the first process pressure is 300MPa, and the second process pressure is 500MPa.

[0091] Examples 3, 8 to 10 are single variable controls: water is used as the instantaneous sintering aid in an amount of 3%, the first process pressure is 300 MPa, the temperature is 110°C, and the second process pressure is 500 MPa, which remain unchanged; what is changed is: the second process pressure holding time is 40 min, 50 min, 60 min, and 70 min; the examples illustrate the effect of changing the second process pressure holding time on the compactness (evaluated by relative density) and crushing rate of SiO2 fracturing proppant.

[0092] Example 8

[0093] The difference between this embodiment and embodiment 3 is that the pressure holding time of the second process is 40 minutes. The performance results of the obtained samples are shown in Table 3.

[0094] Example 9

[0095] The difference between this embodiment and embodiment 3 is that the pressure holding time of the second process is 50 minutes. The performance results of the obtained samples are shown in Table 3.

[0096] Example 10

[0097] The difference between this embodiment and embodiment 3 is that the pressure holding time of the second process is 70 minutes. The performance results of the obtained samples are shown in Table 3.

[0098] Table 3 Performance results of samples of Examples 3, 8 to 10

[0099] Example Relative density Crushing rate (%) 3 0.92 8 8 0.89 11 9 0.91 9 10 0.92 8

[0100] From Examples 3, 8 to 10, it can be seen that extending the second process pressure holding time can increase the relative density of the SiO2 fracturing proppant, indicating that its compactness has been improved. The increased compactness reduces the crushing rate, indicating that the mechanical properties have been effectively improved; when the second process pressure holding time is extended to 70 minutes, the result is the same as that obtained at 60 minutes, so there is no need to blindly extend the second process pressure holding time. From the results, it can be seen that when the water dosage is 3%, the temperature is 110°C, the first process pressure is 300MPa, and the second process pressure is 500MPa, it is better to extend the second process pressure holding time to 70 minutes.

[0101] Examples 11 to 13 control a single variable: the amount of instantaneous sintering aid is 3%, the pressure of the first process is 300 MPa, the temperature is 110°C, and the pressure of the second process is 500 MPa, which remain unchanged; what is changed is that the instantaneous sintering aid 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, siloxane can combine with the surface of SiO2 powder and undergo a condensation reaction. The generated H2O can be effectively volatilized, and the condensation product remains on the surface of SiO2 powder to have a bonding effect. These two effects jointly promote the densification of SiO2 grains. The examples illustrate the effect of changing the type of instantaneous sintering aid on the density (evaluated by relative density) and crushing rate of SiO2 fracturing proppant.

[0102] Embodiment 11

[0103] 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.

[0104] 1000 g of SiO2 powder with a particle size of 1 μm was weighed, 30 g of 3% KH570 was added, and the two were fully mixed to obtain a mixture, and then the mixture was evenly placed in each sintering tank 10 of the sintering chamber 5.

[0105] Close the pressure relief port 4, start the press machine 1, adjust the pressure shaft 3 to apply a pressure of 300 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 40 minutes, 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 the temperature in the sintering chamber 5 naturally drops to 20°C.

[0106] 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, and maintain the pressure and temperature (20°C) for 60 minutes. 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 4.

[0107] Example 12

[0108] The difference between this embodiment and embodiment 11 is that the instantaneous sintering aid is A171. The performance results of the obtained samples are shown in Table 4.

[0109] Embodiment 13

[0110] The difference between this embodiment and embodiment 11 is that the instantaneous sintering aid is silicone oil. The performance results of the obtained samples are shown in Table 4.

[0111] Table 4 Performance results of samples of Examples 11 to 13

[0112] Example Relative density Crushing rate (%) 11 0.96 5 12 0.93 7 13 0.95 6

[0113] 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 SiO2 fracturing proppant are different due to the different molecular structures of different types of siloxanes; specifically, the KH570 molecule has a long chain and an unsaturated bond. The long chain can avoid the influence of the steric hindrance effect on the densification, and the unsaturated bond helps 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 bond, 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, and the relative density and crushing rate of the obtained SiO2 fracturing proppant are in the middle. It can be seen that low-temperature sintering is mainly affected by whether the instantaneous sintering aid molecules have long chains and unsaturated bonds under the same external conditions and when the instantaneous sintering aid is an organic matter.

[0114] Examples 14 to 15 control a single variable: the amount of instantaneous sintering aid is 3%, the pressure of the first process is 300 MPa, the temperature is 110°C, and the pressure of the second process 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, SiO2 is newly generated during the sintering process and can be distributed around the grains (i.e., at the grain boundaries), playing a role in filling the gaps, and the generated H2O can be effectively volatilized at a temperature greater than 100°C, and the two effects jointly promote the densification of SiO2 grains; the examples illustrate the effect of changing the type of instantaneous sintering aid on the density (evaluated by relative density) and crushing rate of SiO2 fracturing proppant.

[0115] Embodiment 14

[0116] The difference between this embodiment and embodiment 11 is that the instantaneous sintering aid is silicic acid. The performance results of the obtained samples are shown in Table 5.

[0117] Embodiment 15

[0118] The difference between this embodiment and embodiment 11 is that the instantaneous sintering aid is hexyl orthosilicate. The performance results of the obtained samples are shown in Table 5.

[0119] Table 5 Performance results of samples of Examples 14 to 15

[0120]

[0121]

[0122] 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. The hydrolysis product SiO2 and the SiO2 grains are the same component. Therefore, a fracturing proppant with a relative density of up to 0.99 can be obtained, and the breakage rate is only 2%.

[0123] Examples 16 to 18 control a single variable: the amount of instantaneous sintering agent is 3%, the pressure of the first process is 300 MPa, the temperature is 110°C, and the pressure of the second process is 500 MPa, which remain unchanged; what is changed is: the instantaneous sintering agent uses ammonia water, urea, and alkali (NaOH is used as an example); the volatilization effect of ammonia water and urea is used to promote densification; the alkali is used to generate an adhesive with SiO2 grains, and the generated H2O can be effectively volatilized at a temperature greater than 100°C, and the two effects jointly promote the densification of SiO2 grains; the examples illustrate the effect of changing the type of instantaneous sintering agent on the density (evaluated by relative density) and crushing rate of SiO2 fracturing proppant.

[0124] Example 16

[0125] The difference between this embodiment and embodiment 11 is that the instantaneous sintering agent is ammonia water. The performance results of the obtained samples are shown in Table 6.

[0126] Embodiment 17

[0127] The difference between this embodiment and embodiment 11 is that the instantaneous burning aid is urea. The performance results of the obtained samples are shown in Table 6.

[0128] Embodiment 18

[0129] The difference between this embodiment and embodiment 11 is that the instantaneous sintering agent is NaOH. The performance results of the obtained samples are shown in Table 6.

[0130] Table 6 Performance results of samples of Examples 16 to 18

[0131] Example Relative density Crushing rate (%) 16 0.93 7 17 0.93 7 18 0.97 4

[0132] 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 the densification of SiO2 grains. 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 the densification of SiO2 grains.

[0133] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: the present application uses low-temperature sintering equipment and instant sintering aids to allow silica fracturing proppants to achieve densification during the sintering process, and cylindrical silica fracturing proppants can be obtained at a relatively low temperature. Among them, the low-temperature sintering equipment provides 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 silica grains reach a densification degree at a relatively low temperature, with a relative density greater than 0.90, and under the SY / T5108-2014 proppant performance test method for hydraulic fracturing and gravel filling operations, the crushing rate is less than 10%.

[0134] The technical solution of the present application does not require a high-temperature process, effectively reduces the sintering temperature of the silica fracturing proppant, and when the sintering temperature is lower than two-thirds of the melting point of the sintered material, a dense, quality-qualified silica fracturing proppant 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 fracturing in the oil and gas industry and has broad application prospects.

[0135] 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 low temperature sintering device for preparing silica fracturing proppant at room temperature, 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).

2. The low temperature sintering device according to claim 1, 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.

3. The low temperature sintering device according to claim 1, 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).

4. The low temperature sintering device according to claim 1, 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.

5. The low temperature sintering device according to any one of claims 1 to 4, 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 does not fall in 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).

6. The low temperature sintering device according to claim 5, 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).

7. The low temperature sintering device according to claim 5, 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).

8. A method for preparing a silica fracturing proppant at room temperature, characterized in that: The method comprises: Placing a mixture of SiO2 and an instantaneous sintering aid in a low-temperature sintering device as described in any one of claims 1 to 7; Performing a first pressurization treatment on the low-temperature sintering device, wherein during the first pressurization treatment, the gas pressure inside the low-temperature sintering device is controlled to be higher than the gas pressure outside the low-temperature sintering device, to obtain a first pressurization treatment product; adjusting the gas pressure inside the low-temperature sintering device to be consistent with the gas pressure outside the low-temperature sintering device, and performing a second pressure treatment on the product of the first pressure treatment to obtain the silica fracturing proppant; The temperature of the first pressurization treatment and / or the second pressurization treatment is 20-120° 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 instant sintering aid accounts for 1-4% of the sum of the mass of the silicon dioxide and the instant sintering aid.

9. The method according to claim 8, characterized in that The particle size of the SiO2 is ≤10 μm.

10. The method according to claim 8, characterized in that Before performing the first pressurization treatment and the second pressurization treatment, the temperature in the low-temperature sintering device is pre-heated to a temperature required for the first pressurization treatment or the second pressurization treatment.

11. The method according to claim 10, characterized in that The pressure of the first pressurization treatment is 100-500 MPa; Preferably, the first pressurization treatment time is 10-40 minutes; Preferably, the pressure of the second pressurization treatment is 100-500 MPa; Preferably, the second pressurization treatment is performed for 30-70 minutes.

12. A silica fracturing proppant obtained by the method according to any one of claims 8 to 11, characterized in that: The relative density of the silica 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 silica fracturing proppant is less than 10%.

Images