Ultralow-density ceramsite sand as well as preparation method and application thereof

Abstract

The invention relates to the field of petroleum fracturing propping agents, in particular to ultra-low-density ceramsite sand as well as a preparation method and application thereof. The ultralow-density ceramsite sand is prepared from the following raw materials in percentage by mass: 3-6% of zircon sand, 4-8% of metal silicon powder, 1-3% of silicon nitride powder, 5-10% of an open-pore inorganic additive, 0-25% of high-alumina fly ash and the balance of high-alumina bauxite, the opening inorganic auxiliary agent is at least one of shell powder, limestone sand and marble sand. The ultra-low-density ceramsite sand provided by the invention is used as a petroleum proppant, the 9% crushing grade of the ultra-low-density ceramsite sand can reach 10K (the crushing rate at 69MPa is generally less than or equal to 9%), and the ultra-low-density ceramsite sand can meet the fracturing operation requirements of deep oil and gas reservoirs.

Description

Technical Field

[0001] The present invention relates to the field of petroleum fracturing proppants, in particular to ultra-low density ceramsite sand, a preparation method and application thereof. Background Art

[0002] Hydraulic fracturing is currently the primary technology for extracting coalbed methane, shale gas, and oil. The specific method of hydraulic fracturing is as follows: a section of a borehole with exposed bedrock is selected and sealed at both ends with packers. A fracturing fluid containing proppants is then injected into the borehole and pressurized until the borehole wall fractures. The proppant, along with the fracturing fluid, fills and propels the cracks. After depressurization, the fracturing fluid flows back, leaving the proppant in the cracks to maintain their open state, increasing the permeability of the oil and gas well and, consequently, the recovery rate. Therefore, the performance of the proppant plays a significant role in increasing the yield of oil and gas wells.

[0003] The development of deep-penetration oil and gas wells requires the use of large quantities of low-density, high-strength proppants. Conventional quartz sand proppants are suitable for fracturing oil and gas reservoirs with low formation closure pressures, but cannot meet the requirements of deep-penetration oil and gas well fracturing operations. Sintered ceramsite proppants, with their advantages of excellent sphericity, corrosion resistance, high temperature resistance, high pressure resistance, and low production costs, have gradually replaced quartz sand proppants and are suitable for fracturing medium-deep oil and gas reservoirs with medium to high formation closure pressures.

[0004] As the exploitation of low- and medium-permeability oil and gas wells gradually reaches saturation, the exploitation of deep-permeability oil and gas wells will gradually become a major trend in the future. This will lead to an increasing demand for sintered ceramsite proppants for use at high formation closure pressures. However, the 9% crushing grade of sintered ceramsite proppants currently used in deep oil and gas reservoir fracturing operations is at the 7.5K level. For example, domestically produced sintered ceramsite proppants with a mesh size of 20-40 (850 / 425µm) have a crushing rate of ≤9% at 52MPa (7500psi), while at 69MPa (1000psi) the crushing rate is generally greater than 12%. There is an urgent need for a ceramsite sand proppant with an ultra-low density and a high 9% crushing grade. Summary of the Invention

[0005] In order to solve the problem that the existing sintered ceramsite proppant has a low crushing grade of 9% and cannot meet the requirements of deep oil and gas reservoir fracturing operations, the present invention provides an ultra-low density ceramsite sand, a preparation method and an application.

[0006] The ultra-low density ceramsite sand provided by the present invention is achieved through the following technical solutions: An ultra-low-density ceramsite sand is made from the following raw materials in percentage by mass: 3-6% of zircon sand, 4-8% of metallic silicon powder, 1-3% of silicon nitride powder, 5-10% of an open-pore inorganic additive, 0-25% of high-alumina fly ash, and the balance is high-alumina bauxite; the open-pore inorganic additive is at least one of shell powder, limestone sand, and marble sand.

[0007] Further preferably, the ultra-low density ceramsite sand is made of the following raw materials in the following mass percentages: 4-5% zircon sand, 6-8% metallic silicon powder, 1.5-2% silicon nitride powder, 7-8.5% open-pore inorganic additives, 10-20% high-alumina fly ash, and the balance is high-alumina bauxite; the open-pore inorganic additives are composed of shell powder and marble sand in a mass ratio of 1:(1-2).

[0008] The ultra-low density ceramsite sand provided in the present invention is used as a petroleum proppant, and its crushing grade can reach 10K at 9% (the crushing rate at 69 MPa is generally ≤9%), which can meet the needs of deep oil and gas reservoir fracturing operations.

[0009] Preferably, the chemical composition of the high-alumina bauxite is as follows by weight: Al2O3 content is 70-90%, SiO2 content is 5-15%, CaO content is less than 0.8%, Fe2O3 content is less than 3.0%, and other inevitable impurities.

[0010] Further preferably, the high-alumina bauxite is at least one of special-grade high-alumina bauxite, first-grade high-alumina bauxite, and second-grade high-alumina bauxite.

[0011] Preferably, the chemical composition of the high-alumina fly ash is as follows by weight: Al2O3 content of 37% to 50%, SiO2 content of 30% to 40%, Fe2O3 content of 5% to 10%, and other inevitable impurities.

[0012] Preferably, the shell powder is a carbon-enhanced shell powder raw material, which is composed of 80-90 parts of shell powder raw material and 10-20 parts of nanocarbon; the nanocarbon is at least one of coke, carbon powder, and graphite with a particle size of ≤2000 mesh.

[0013] The thermal calcination of organic matter in the carbon-enhanced shell powder raw material will produce water vapor and amorphous carbon, which helps to improve the open porosity of the ceramsite sand and reduce the density of the ceramsite sand. The amorphous carbon and the supplementary nanocarbon will first react with the metal silicon powder to form silicon carbide at a calcination temperature of ≥450℃. Then, when the calcination temperature is ≥1200℃, the silicon dioxide will react with the remaining amorphous carbon and nanocarbon to form silicon carbide and carbon monoxide. In addition, silicon nitride powder will form silicon oxynitride silicon ceramics with silicon dioxide at ≥1400℃, improving the seismic resistance and high temperature resistance of the ceramsite sand. The nitrogen produced by the pyrolysis of urea will react with the metal silicon powder to produce silicon nitride. The silicon carbide and silicon nitride formed by calcination can effectively improve the ceramsite sand's resistance to crushing pressure, high temperature resistance, high pressure resistance, and corrosion resistance.

[0014] The present invention provides a method for preparing ultra-low density ceramsite sand, which is achieved through the following technical solutions: A method for preparing ultra-low density ceramsite sand comprises the following steps: Step 1: ball milling zircon sand, metallic silicon powder, silicon nitride powder, open-pore inorganic additive, high-aluminum fly ash, and high-aluminum bauxite to obtain ultrafine zircon sand, ultrafine metallic silicon powder, ultrafine silicon nitride powder, ultrafine open-pore inorganic additive, ultrafine high-aluminum fly ash, and ultrafine high-aluminum bauxite with a particle size of ≤18µm; Step 2: weighing ultrafine zircon sand, ultrafine metallic silicon powder, ultrafine silicon nitride powder, ultrafine open-pore inorganic additive, ultrafine high-alumina fly ash, and ultrafine high-alumina bauxite according to a ratio, and mixing them evenly to obtain a prefabricated mixture; Step 3: The prefabricated mixture is air-fed to a pelletizer to produce ceramsite green pellets with a moisture content of 8-10%; Step 4: The ceramsite green pellets are screened to obtain semi-finished ceramsite of required specifications; Step 5: The semi-finished ceramsite is calcined and cooled to obtain ultra-low density ceramsite sand.

[0015] The preparation method of the present invention is relatively simple, has low operational difficulty, and is easy to implement large-scale production.

[0016] Preferably, in step three, the prefabricated mixture is air-fed to a granulator, and a 1-3 wt% pore-opening aqueous solution in a towerless water supply is added to the granulator through an atomizing water spray system, wherein the pore-opening aqueous solution contains 1-3 wt% urea, and the granulator is rotated for 1-2 hours to obtain ceramsite green granules with a water content of 8-10%.

[0017] The thermal decomposition of urea in the semi-finished ceramsite produces nitrogen and amorphous carbon, which is conducive to the reaction to produce more silicon carbide and silicon nitride, and improve the ceramsite sand's resistance to crushing pressure, high temperature resistance, high pressure resistance, and corrosion resistance.

[0018] Preferably, in the step five, the semi-finished ceramsite is calcined: first, the temperature is increased to 300-350°C at 5-20°C / min and kept warm for 40-60min, then the temperature is increased to 1300-1450°C at 20-30°C / min and kept warm for 50-100min, then the temperature is decreased to 1100-1200°C at 5-10°C / min and kept warm for 60-90min, and finally the temperature is decreased to 300-400°C at 3-6°C / min, and the ultra-low density ceramsite sand is obtained by naturally cooling the furnace to room temperature.

[0019] It should be noted that when the nitrogen is consumed, the stability of silicon nitride at a temperature of ≥1200°C deviates, so the temperature is reduced to 1100-1200°C and kept warm for 60-90 minutes to ensure the stability of the formed silicon nitride. The ultra-low density ceramsite sand after calcination treatment in the present invention can generate relatively more silicon carbide, effectively improving the ceramsite sand's resistance to crushing pressure, high temperature resistance, high pressure resistance, and corrosion resistance.

[0020] The ultra-low density ceramsite sand provided by the present invention is used as a petroleum proppant and is suitable for deep oil and gas reservoir fracturing operations with a formation closure pressure of 52-69 MPa, especially for deep oil and gas reservoir fracturing operations with a formation closure pressure of 69 MPa. The ultra-low density ceramsite sand has a 9% crushing grade of up to 10K, a crushing rate of generally ≤9% at 69 MPa (1000 psi), a roundness of 0.9, a sphericity of 0.9, and a bulk density of ≤1.50 g / cm 3 , which can meet the needs of deep oil and gas reservoir fracturing operations.

[0021] In summary, the present invention has the following advantages: 1. The ultra-low density ceramsite sand provided in the present invention is used as a petroleum proppant, and its crushing grade can reach 10K at 9% (the crushing rate at 69 MPa is generally ≤9%), which can meet the needs of deep oil and gas reservoir fracturing operations.

[0022] 2. The preparation method of the present invention is relatively simple, has low operational difficulty, and is easy to implement large-scale production.

[0023] 3. The preparation method of the present invention further improves the crushing pressure resistance, high temperature resistance, high pressure resistance and corrosion resistance of ceramsite sand by regulating the calcination treatment temperature.

[0024] 4. The raw material cost of the ceramsite sand in the present invention is relatively low, which is conducive to industrialized batch production. DETAILED DESCRIPTION

[0025] In order to further understand the creativity and technical advancement of the present invention, the preferred embodiments of the present invention are discussed in detail below in conjunction with examples and comparative examples.

[0026] Example: An ultra-low density ceramsite sand is made of the following raw materials in percentage by mass: 3-6% zircon sand, 4-8% metallic silicon powder, 1-3% silicon nitride powder, 5-10% open-pore inorganic additive, 0-25% high-alumina fly ash, and the balance is high-alumina bauxite.

[0027] The chemical composition of high-alumina bauxite is as follows by weight: Al2O3 content is 70-90%, SiO2 content is 5-15%, CaO content is less than 0.8%, Fe2O3 content is less than 3.0%, and other inevitable impurities.

[0028] Preferably, the high-alumina bauxite is at least one of super-grade high-alumina bauxite, first-grade high-alumina bauxite, and second-grade A high-alumina bauxite. Further preferably, the high-alumina bauxite is first-grade high-alumina bauxite.

[0029] The chemical composition of high-alumina fly ash is as follows by weight: Al2O3 content is 37% to 50%, SiO2 content is 30% to 40%, Fe2O3 content is 5% to 10%, and other inevitable impurities.

[0030] The pore-forming inorganic additive is at least one of shell powder, limestone sand, and marble sand. Preferably, the pore-forming inorganic additive is composed of shell powder and marble sand in a mass ratio of 1:(1-2).

[0031] Further preferably, the shell powder is a carbon-enhanced shell powder raw material, which is composed of 80-90 parts of shell powder raw material and 10-20 parts of nanocarbon. The nanocarbon is at least one of coke, carbon powder, and graphite with a particle size of ≤2000 mesh. Preferably, the nanocarbon is natural flake graphite with a particle size of ≤2000 mesh.

[0032] The optimized design scheme of ultra-low density ceramsite sand is as follows. The ultra-low density ceramsite sand is made of the following raw materials in the following mass percentages: 4-5% zircon sand, 6-8% metallic silicon powder, 1.5-2% silicon nitride powder, 7-8.5% open-pore inorganic additives, 10-20% high-alumina fly ash, and the balance is high-alumina bauxite.

[0033] A method for preparing ultra-low density ceramsite sand comprises the following steps: Step 1: ball milling zircon sand, metallic silicon powder, silicon nitride powder, open-pore inorganic additive, high-aluminum fly ash, and high-aluminum bauxite to obtain ultrafine zircon sand, ultrafine metallic silicon powder, ultrafine silicon nitride powder, ultrafine open-pore inorganic additive, ultrafine high-aluminum fly ash, and ultrafine high-aluminum bauxite with a particle size of ≤18µm; Step 2: weighing ultrafine zircon sand, ultrafine metallic silicon powder, ultrafine silicon nitride powder, ultrafine open-pore inorganic additive, ultrafine high-alumina fly ash, and ultrafine high-alumina bauxite according to a ratio, and mixing them evenly to obtain a prefabricated mixture; Step 3: The prefabricated mixture is air-fed to a granulator, and a 1-3 wt% pore-opening aqueous solution in a towerless water supply device is added to the granulator through an atomizing water spray system. The pore-opening aqueous solution contains 1-3 wt% urea. The granulator rotates for 1-2 hours to obtain ceramsite green granules with a water content of 8-10%. Step 4: The ceramsite green pellets are screened to obtain semi-finished ceramsite of required specifications; Step 5: calcining the semi-finished ceramsite: first, heating to 300-350°C at 5-20°C / min and holding for 40-60min, then heating to 1300-1450°C at 20-30°C / min and holding for 50-100min, then cooling to 1100-1200°C at 5-10°C / min and holding for 60-90min, and finally cooling to 300-400°C at 3-6°C / min. The furnace is opened and naturally cooled to room temperature to obtain ultra-low density ceramsite sand. The obtained ultra-low density ceramsite sand can be used as a petroleum proppant. The crushing grade can reach 10K at 9%, the crushing rate at 69MPa (1000psi) is generally ≤9%, the roundness is 0.9, the sphericity is 0.9, and the bulk density is ≤1.50g / cm 3 , which can meet the needs of deep oil and gas reservoir fracturing operations.

[0034] Example 1: Ultra-low density ceramsite sand is made from 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhancing shell powder raw meal, 4% limestone sand, and 80% premium high-alumina bauxite. The carbon-enhancing shell powder raw meal is composed of 90 parts shell powder raw meal and 10 parts 2000 mesh natural flake graphite.

[0035] Zircon sand, 325 mesh zircon powder, zircon content 65%, Shijiazhuang Chen Gaoxin Material Technology Co., Ltd.

[0036] Metallic silicon powder, 2000 mesh, brand SF70, Qinghe Chaotai Metal Materials Co., Ltd.

[0037] Silicon nitride powder, 3000 mesh, brand SF90, Qinghe Chaotai Metal Materials Co., Ltd.

[0038] Shell powder raw material, average particle size 800μm, Lingshou County Yongzhuo New Material Technology Co., Ltd.

[0039] Natural flake graphite, 1000 mesh, Qingdao Tianshengda Graphite Co., Ltd.

[0040] Limestone, Lingshou County Huixin Mining Processing Plant, commissioned processing to obtain 325 mesh limestone powder.

[0041] Special grade high alumina bauxite, Hebei Mingzhe Mineral Products Co., Ltd., Al2O3 content is 85.7%, SiO2 content is 4.7%, CaO content is 0.61%, Fe2O3 content is 2.07%, and other inevitable impurities.

[0042] A method for preparing ultra-low density ceramsite sand comprises the following steps: Step 1: ball-milling zircon sand, metallic silicon powder, silicon nitride powder, carbon-enhanced shell powder raw material, limestone sand, and high-alumina bauxite to obtain ultrafine zircon sand, ultrafine metallic silicon powder, ultrafine silicon nitride powder, ultrafine limestone sand, ultrafine carbon-enhanced shell powder raw material, and ultrafine special-grade high-alumina bauxite with a particle size of ≤18µm; Step 2: weighing ultrafine zircon sand, ultrafine metallic silicon powder, ultrafine silicon nitride powder, ultrafine limestone sand, ultrafine carbon-enhanced shell powder raw material, and ultrafine special high-alumina bauxite according to a ratio, and mixing them evenly to obtain a prefabricated mixture; Step 3: The prefabricated mixture is air-fed to a granulator, and a 2.0 wt% urea aqueous solution in a towerless water supply is added to the granulator through an atomizing water spray system. The granulator rotates for 100 minutes to obtain ceramsite green granules, and the content of the ceramsite green granules is measured to be 8.8%; Step 4: The ceramsite green pellets are screened to obtain 20 / 40 mesh semi-finished ceramsite; Step 5: calcining the semi-finished ceramsite: first, heating to 300°C at 10°C / min and keeping warm for 60min, then heating to 1400°C at 30°C / min and keeping warm for 60min, then cooling to 1150°C at 10°C / min and keeping warm for 80min, and finally cooling to 400°C at 3°C / min, opening the furnace and naturally cooling to room temperature to obtain ultra-low density ceramsite sand.

[0043] The difference between Example 2 and Example 1 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 5% high-alumina fly ash (Gongyi Fuquan Refractory Co., Ltd.), and 75% special-grade high-alumina bauxite.

[0044] The chemical composition of high-alumina fly ash is as follows by weight: Al2O3 content is 43.6%, SiO2 content is 40.5%, Fe2O3 content is 6.8%, and other inevitable impurities.

[0045] The difference in the preparation method of ultra-low density ceramsite sand is: Step 1: ball-milling zircon sand, metallic silicon powder, silicon nitride powder, carbon-enhanced shell powder raw meal, limestone sand, high-aluminum fly ash, and super-grade high-aluminum bauxite to obtain ultrafine zircon sand, ultrafine metallic silicon powder, ultrafine silicon nitride powder, ultrafine limestone sand, ultrafine carbon-enhanced shell powder raw meal, ultrafine high-aluminum fly ash, and ultrafine super-grade high-aluminum bauxite with a particle size of ≤18µm; Step 2: weigh ultrafine zircon sand, ultrafine metallic silicon powder, ultrafine silicon nitride powder, ultrafine limestone sand, ultrafine carbon-enhanced shell powder raw material, ultrafine high-aluminum fly ash, and ultrafine special high-aluminum bauxite according to the ratio, mix them evenly to obtain a prefabricated mixture, and the remaining steps are the same.

[0046] The difference between Example 3 and Example 2 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 10% high-alumina fly ash, and 70% special-grade high-alumina bauxite.

[0047] The difference between Example 4 and Example 2 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 65% special-grade high-aluminum bauxite.

[0048] The difference between Example 5 and Example 2 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 20% high-aluminum fly ash, and 60% special-grade high-aluminum bauxite.

[0049] The difference between Comparative Example 1 and Example 1 is that the ceramsite sand is made of 4% carbon-enhanced shell powder raw material, 4% marble sand, and 92% super-high-alumina bauxite. The difference in the preparation method of the ceramsite sand is that: Step 1, the carbon-enhanced shell powder raw material, limestone sand, and super-high-alumina bauxite are respectively ball-milled to obtain ultrafine limestone sand, ultrafine carbon-enhanced shell powder raw material, and ultrafine super-high-alumina bauxite with a particle size of ≤18µm; Step 2, the ultrafine limestone sand, ultrafine carbon-enhanced shell powder raw material, and ultrafine super-high-alumina bauxite are weighed according to a ratio and evenly mixed to obtain a prefabricated mixture. The remaining steps are the same.

[0050] Comparative Example 2 differs from Example 1 in that the ceramsite sand is made from 3% zircon sand, 4% carbon-enhancing shell powder raw material, 4% marble sand, and 80% premium high-alumina bauxite. The preparation method of the ceramsite sand differs in that: Step 1: zircon sand, carbon-enhancing shell powder raw material, limestone sand, and high-alumina bauxite are ball-milled to obtain ultrafine zircon sand, ultrafine limestone sand, ultrafine carbon-enhancing shell powder raw material, and ultrafine premium high-alumina bauxite with a particle size of ≤18µm; Step 2: Ultrafine zircon sand, ultrafine limestone sand, ultrafine carbon-enhancing shell powder raw material, and ultrafine premium high-alumina bauxite are weighed according to a proportion and uniformly mixed to obtain a prefabricated mixture. The remaining steps are the same.

[0051] The difference between Comparative Example 3 and Example 1 is that the ceramsite sand is made of 7% metallic silicon powder, 4% carbon-enhancing shell powder raw material, 4% marble sand, and 80% super-grade high-alumina bauxite. The difference in the preparation method of the ceramsite sand is that: Step 1, the metallic silicon powder, the carbon-enhancing shell powder raw material, the limestone sand, and the high-alumina bauxite are respectively ball-milled to obtain ultrafine metallic silicon powder, ultrafine limestone sand, ultrafine carbon-enhancing shell powder raw material, and ultrafine super-grade high-alumina bauxite with a particle size of ≤18µm; Step 2, the ultrafine metallic silicon powder, ultrafine limestone sand, ultrafine carbon-enhancing shell powder raw material, and ultrafine super-grade high-alumina bauxite are weighed according to a ratio and mixed evenly to obtain a prefabricated mixture. The remaining steps are the same.

[0052] The difference between Comparative Example 4 and Example 1 is that the ceramsite sand is made of 2% silicon nitride powder, 4% carbon-enhancing shell powder raw material, 4% marble sand, and 80% super-high-alumina bauxite. The difference in the preparation method of the ceramsite sand is that: Step 1, silicon nitride powder, carbon-enhancing shell powder raw material, limestone sand, and high-alumina bauxite are respectively ball-milled to obtain ultrafine silicon nitride powder, ultrafine limestone sand, ultrafine carbon-enhancing shell powder raw material, and ultrafine super-high-alumina bauxite with a particle size of ≤18µm; Step 2, ultrafine silicon nitride powder, ultrafine limestone sand, ultrafine carbon-enhancing shell powder raw material, and ultrafine super-high-alumina bauxite are weighed according to a ratio and mixed evenly to obtain a prefabricated mixture, and the remaining steps are the same.

[0053] The difference between Comparative Example 5 and Example 2 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 25% high-aluminum fly ash, and 55% special-grade high-aluminum bauxite.

[0054] Performance testing: The industry standard SY / T5108-2014 "Proppant Performance Test Method for Hydraulic Fracturing and Gravel Packing Operations" is adopted to measure seven major aspects including sphericity, acid solubility, turbidity, bulk density, crushing rate and ignition loss.

[0055] Table 1: Performance test parameters of ceramsite sand in Examples 1-5 and Comparative Examples 1-5 Combining Examples 1-5 and Comparative Examples 1-4 with Table 1, it can be seen that the synergistic use of zircon sand, metallic silicon powder, and silicon oxynitride powder can achieve an excellent anti-crushing pressure enhancement effect. The prepared ceramsite sand has a 9% crushing grade of up to 10K, which can meet the requirements of deep oil and gas reservoir fracturing operations.

[0056] Combining Examples 1-5 and Comparative Example 5 with Table 1, it can be seen that as the amount of high-alumina fly ash added increases, that is, the alumina content in the ceramsite sand decreases, the crushing pressure of the prepared ceramsite sand decreases. When the amount of high-alumina fly ash added exceeds 20%, the crushing pressure of the ceramsite sand decreases significantly. Therefore, it is appropriate to control the amount of high-alumina fly ash added to 0-20%. Preferably, the amount of high-alumina fly ash added is controlled to 15±1%, ensuring that the ceramsite sand can achieve a crushing grade of 10K at 9%, while reducing the production cost of the ceramsite sand.

[0057] The difference between Example 6 and Example 4 is that the special-grade high-alumina bauxite is replaced by the first-grade high-alumina bauxite (Hebei Mingzhe Mineral Products Co., Ltd., Al2O3 content is 81.2%, SiO2 content is 5.1%, CaO content is 0.69%, Fe2O3 content is 2.15%, and other inevitable impurities).

[0058] The difference between Example 7 and Example 4 is that the special grade high-alumina bauxite is replaced by the second grade A high-alumina bauxite (Hebei Mingzhe Mineral Products Co., Ltd., Al2O3 content is 76.3%, SiO2 content is 5.3%, CaO content is 0.73%, Fe2O3 content is 2.32%, and other inevitable impurities).

[0059] The difference between Example 8 and Example 4 is that 65% of the special-grade high-alumina bauxite is replaced by 25% of the special-grade high-alumina bauxite and 40% of the second-grade high-alumina bauxite.

[0060] The difference between Comparative Example 6 and Example 4 is that the special high-alumina bauxite is replaced by secondary high-alumina bauxite (Hebei Mingzhe Mineral Products Co., Ltd., with an Al2O3 content of 65.1%, a SiO2 content of 5.5%, a CaO content of 0.78%, a Fe2O3 content of 2.63%, and other inevitable impurities).

[0061] Table 2: Performance test parameters of ceramsite sand in Example 4, Examples 6-8 and Comparative Example 6 Combining Example 4, Examples 6-8 and Comparative Example 6 with Table 2, it can be seen that the alumina content in the ceramsite sand has a significant effect on the crushing pressure resistance of the ceramsite sand. By selecting special high-alumina bauxite, first-grade high-alumina bauxite, and second-grade high-alumina bauxite with higher alumina content, the ceramsite sand prepared can have a crushing grade of 9% up to 10K.

[0062] The difference between Example 9 and Example 4 is that the ultra-low density expanded clay sand is made of 4% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 64% special-grade high-aluminum bauxite.

[0063] The difference between Example 10 and Example 4 is that the ultra-low density expanded clay sand is made of 5% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 63% special-grade high-aluminum bauxite.

[0064] The difference between Example 11 and Example 4 is that the ultra-low density expanded clay sand is made of 6% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 62% special-grade high-aluminum bauxite.

[0065] The difference between Comparative Example 7 and Example 4 is that the ultra-low density expanded clay sand is made of 0% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 68% special-grade high-aluminum bauxite.

[0066] The difference between Comparative Example 8 and Example 4 is that the ultra-low density expanded clay sand is made of 1% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 67% special-grade high-aluminum bauxite.

[0067] Table 3: Performance test parameters of ceramsite sand in Example 4, Examples 9-11 and Comparative Examples 7-8 From Example 4, Examples 9-11, and Comparative Examples 7-8, and Table 3, it can be seen that the addition of zircon sand introduces zirconium oxide into the ceramsite sand, and the C-phase zirconia is transformed into a stable T-phase zirconia at above 1000°C and in the presence of the stabilizer CaO. Under the action of external stress, the T-phase zirconia can undergo a stress-induced phase transition, absorb the external stress energy, increase the crack propagation resistance, and effectively improve the crushing performance of the ceramsite sand at 69 MPa.

[0068] The difference between Example 12 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 4% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 68% special-grade high-aluminum bauxite.

[0069] The difference between Example 13 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 5% metallic silicon powder, 2% silicon nitride powder, 4% carburized shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 67% special-grade high-aluminum bauxite.

[0070] The difference between Example 14 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 6% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-alumina fly ash, and 66% special-grade high-alumina bauxite.

[0071] The difference between Example 15 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 8% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 64% special-grade high-aluminum bauxite.

[0072] The difference between Comparative Example 9 and Example 4 is that the ultra-low density ceramsite sand is made of 3% zircon sand, 0% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 72% special high-aluminum bauxite. The difference between Comparative Example 10 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 2% metallic silicon powder, 2% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 70% special-grade high-aluminum bauxite.

[0073] Table 4: Performance test parameters of ceramsite sand in Example 4, Examples 12-15 and Comparative Examples 9-10 As can be seen from Example 4, Examples 12-15, and Comparative Examples 9-10, along with Table 4, metallic silicon powder reacts with nitrogen and carbon monoxide at high temperatures to form silicon nitride and silicon carbide, which improve the crushing performance of ceramsite sand at 69 MPa. Controlling the addition of metallic silicon powder to 4-8% significantly improves the crushing resistance of ceramsite sand. Preferably, the addition of metallic silicon powder is 6-7%.

[0074] The difference between Example 16 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 1% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 66% special-grade high-aluminum bauxite.

[0075] The difference between Example 17 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 1.5% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-alumina fly ash, and 65.5% special-grade high-alumina bauxite.

[0076] The difference between Example 18 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2.5% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-alumina fly ash, and 64.5% special-grade high-alumina bauxite.

[0077] The difference between Example 19 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 3% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 64% special-grade high-aluminum bauxite.

[0078] The difference between Comparative Example 11 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 0% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 67% special-grade high-aluminum bauxite.

[0079] The difference between Comparative Example 12 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 0.5% silicon nitride powder, 4% carbon-enhanced shell powder raw material, 4% limestone sand, 15% high-aluminum fly ash, and 66.5% special-grade high-aluminum bauxite.

[0080] Table 5: Performance test parameters of ceramsite sand in Example 4, Examples 16-19 and Comparative Examples 11-12 Combining Example 4, Examples 12-15, and Comparative Example 9 with Table 5, it can be seen that the addition of metallic silicon powder can improve the anti-crushing performance of ceramsite sand. Combining Comparative Example 10, it can be seen that controlling the addition amount of metallic silicon powder to 1-3% can impart good anti-crushing performance to ceramsite sand, and the crushing grade can reach 10K at 9%. Preferably, the addition amount of metallic silicon powder is 2.0-2.5%.

[0081] The difference between Example 20 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 2.5% carbon-enhanced shell powder raw material, 2.5% limestone sand, 15% high-alumina fly ash, and 68% special-grade high-alumina bauxite.

[0082] The difference between Example 21 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 5% carbon-enhanced shell powder raw material, 5% limestone sand, 15% high-aluminum fly ash, and 63% special-grade high-aluminum bauxite.

[0083] The difference between Example 22 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 8% carbon-enhanced shell powder raw material, 15% high-alumina fly ash, and 65% special-grade high-alumina bauxite.

[0084] The difference between Example 23 and Example 4 is that the ultra-low density expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 4% shell powder raw material, 4% limestone sand, 15% high-alumina fly ash, and 65% special-grade high-alumina bauxite.

[0085] The difference between Example 24 and Example 4 is that the ultra-low density expanded clay sand is made of 5% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 6% carbon-enhanced shell powder raw material, 3% limestone sand, 10% high-alumina fly ash, and 67% special-grade high-alumina bauxite.

[0086] The difference between Comparative Example 13 and Example 4 is that the expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 2% carbon-enhancing shell powder raw material, 2% limestone sand, 15% high-alumina fly ash, and 69% special-grade high-alumina bauxite.

[0087] The difference between Comparative Example 14 and Example 4 is that the expanded clay sand is made of 3% zircon sand, 7% metallic silicon powder, 2% silicon nitride powder, 6% carbon-enhancing shell powder raw material, 6% limestone sand, 15% high-aluminum fly ash, and 58% special-grade high-aluminum bauxite.

[0088] The difference between Comparative Example 15 and Example 4 is that the difference in the preparation method of ceramsite sand is that: in step five, the semi-finished ceramsite is calcined: first, the temperature is increased to 300°C at 10°C / min and kept warm for 60 minutes, then the temperature is increased to 1400°C at 30°C / min and kept warm for 140 minutes, and then the temperature is cooled to 600°C at 10°C / min by air cooling, and the furnace is opened and naturally cooled to room temperature to obtain low-density ceramsite sand.

[0089] Table 6: Performance test parameters of ceramsite sand in Example 4, Examples 20-24 and Comparative Examples 13-15 Combining Example 4, Examples 20-21 and Comparative Examples 13-14 with Table 6, it can be seen that the addition amount of the pore-forming inorganic additive is controlled at 5-10%, which can ensure the anti-crushing performance of the ceramsite sand and give it a lower density, thereby facilitating deep oil and gas reservoir fracturing operations.

[0090] From Example 4 and Example 23 and Table 6, it can be seen that the comprehensive performance of the ceramsite sand prepared from the carbon-enhanced shell powder raw material is better than that of the ceramsite sand prepared from the shell powder raw material. Adding an appropriate amount of ultrafine carbon is beneficial to the ceramsite sand to generate more silicon carbide, which is beneficial to improving the comprehensive performance of the ceramsite sand.

[0091] From Example 4 and Comparative Example 15 and Table 6, it can be seen that the 9% crushing grade of the ceramsite sand in Comparative Example 15 is 7.5K, while the 9% crushing grade of the ceramsite sand prepared by the calcining method provided in the present invention can reach 10K. Therefore, the ceramsite sand prepared by the calcining method of the present invention has relatively good anti-crushing performance.

[0092] In summary, the ultra-low density ceramsite sand provided in the present invention can be used as a petroleum proppant to meet the requirements of deep oil and gas reservoir fracturing operations. The crushing grade can reach 10K at 9%, the crushing rate is generally ≤9% at 69MPa (1000psi), the roundness is 0.9, the sphericity is 0.9, and the bulk density is ≤1.50g / cm 3 , acid solubility <5.0%.

[0093] It should be noted that this specific embodiment is merely an explanation of the technical solution of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. An ultra-low density ceramsite sand, characterized by: The ultra-low density ceramsite sand is made of the following raw materials in percentage by mass: 3-6% zircon sand, 4-8% metallic silicon powder, 1-3% silicon nitride powder, 5-10% open-pore inorganic additive, 0-25% high-alumina fly ash, and the balance is high-alumina bauxite; the open-pore inorganic additive is at least one of shell powder, limestone sand, and marble sand.

2. The ultra-low density ceramsite sand according to claim 1, characterized in that: The chemical composition of the high-alumina bauxite is as follows by weight: Al2O3 content is 70-90%, SiO2 content is 5-15%, CaO content is less than 0.8%, Fe2O3 content is less than 3.0%, and other inevitable impurities.

3. The ultra-low density ceramsite sand according to claim 2, characterized in that: The high-alumina bauxite is at least one of special-grade high-alumina bauxite, first-grade high-alumina bauxite, and second-grade high-alumina bauxite.

4. The ultra-low density ceramsite sand according to claim 2, characterized in that: The chemical composition of the high-alumina fly ash is as follows by weight: Al2O3 content is 37% to 50%, SiO2 content is 30% to 40%, Fe2O3 content is 5% to 10%, and other inevitable impurities.

5. The ultra-low density ceramsite sand according to claim 4, characterized in that: The ultra-low density ceramsite sand is made of the following raw materials in percentage by mass: 4-5% zircon sand, 6-8% metallic silicon powder, 1.5-2% silicon nitride powder, 7-8.5% open-pore inorganic additive, 10-20% high-alumina fly ash, and the balance is high-alumina bauxite; the open-pore inorganic additive is composed of shell powder and marble sand in a mass ratio of 1:(1-2).

6. The ultra-low density ceramsite sand according to claim 5, characterized in that: The shell powder is a carbon-enhanced shell powder raw material, which is composed of 80-90 parts of shell powder raw material and 10-20 parts of nano-carbon; the nano-carbon is at least one of coke, carbon powder, and graphite with a particle size of ≤2000 mesh.

7. A method for preparing the ultra-low density ceramsite sand according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: ball milling zircon sand, metallic silicon powder, silicon nitride powder, open-pore inorganic additive, high-aluminum fly ash, and high-aluminum bauxite to obtain ultrafine zircon sand, ultrafine metallic silicon powder, ultrafine silicon nitride powder, ultrafine open-pore inorganic additive, ultrafine high-aluminum fly ash, and ultrafine high-aluminum bauxite with a particle size of ≤18µm; Step 2: weighing ultrafine zircon sand, ultrafine metallic silicon powder, ultrafine silicon nitride powder, ultrafine open-pore inorganic additive, ultrafine high-alumina fly ash, and ultrafine high-alumina bauxite according to a ratio, and mixing them evenly to obtain a prefabricated mixture; Step 3: The prefabricated mixture is air-fed to a pelletizer to produce ceramsite green pellets with a moisture content of 8-10%; Step 4: The ceramsite green pellets are screened to obtain semi-finished ceramsite of required specifications; Step 5: The semi-finished ceramsite is calcined and cooled to obtain ultra-low density ceramsite sand.

8. The method for preparing ultra-low density ceramsite sand according to claim 7, wherein: In the step three, the prefabricated mixture is air-fed to a granulator, and a 1-3 wt% pore-opening aqueous solution in a towerless water supply device is added to the granulator through an atomizing water spray system, wherein the pore-opening aqueous solution contains 1-3 wt% urea, and the granulator is rotated for 1-2 hours to obtain ceramsite green granules with a water content of 8-10%.

9. The method for preparing ultra-low density ceramsite sand according to claim 7, wherein: In the step 5, the semi-finished ceramsite is calcined: first, the temperature is increased to 300-350°C at 5-20°C / min and kept warm for 40-60min, then the temperature is increased to 1300-1450°C at 20-30°C / min and kept warm for 50-100min, then the temperature is decreased to 1100-1200°C at 5-10°C / min and kept warm for 60-90min, and finally the temperature is decreased to 300-400°C at 3-6°C / min, and the furnace is opened and naturally cooled to room temperature to obtain ultra-low density ceramsite sand.

10. Use of the ultra-low density ceramsite sand according to any one of claims 1 to 6 as a petroleum proppant, characterized in that: Suitable for fracturing operations in deep oil and gas reservoirs with formation closure pressure of 52-69MPa.

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