High-strength fracturing propping agent for oil and gas wells and preparation method of fracturing propping agent

Abstract

The invention discloses a high-strength fracturing proppant for oil and gas wells and a preparation method thereof, and relates to a proppant for oil and gas wells, the high-strength fracturing proppant comprises a porous inner core, a ceramic shell and a surface modification layer. And the inner core contains 40-60% of oil-based drilling cutting powder, 25-35% of low bauxite, 10-20% of fly ash and 3-8% of gypsum. The ceramic shell is composed of 50-70% of silicon nitride, 20-40% of high-alumina bauxite and 5-10% of a binder. The surface modification layer is a super-hydrophobic layer formed by a fluorosilane solution. The content of low bauxite # imgabs 0 # is 40-50 wt%, the content of fly ash activity # imgabs 1 # is greater than or equal to 45 wt%, the binder is polyethylene glycol or hydroxypropyl methyl cellulose, and the content of high bauxite # imgabs 2 # is greater than or equal to 70 wt%. The preparation method comprises the steps of raw material pretreatment, inner core preparation, shell coating and surface modification. During preparation of the inner core, constant-temperature and constant-humidity maintenance is performed for 5-10 days after mixing granulation. A fluidized bed spraying method is adopted for shell coating, the spraying thickness is 100-300 microns, and the sintering temperature is 850-1000 DEG C. 0.5-2wt% of fluorosilane solution is used for surface modification, and the moisture content of dried particles is less than or equal to 0.5%.

Description

Technical Field

[0001] The present invention relates to proppants for oil and gas wells, and particularly to a high-strength proppant for fracturing oil and gas wells and a preparation method thereof. Background Art

[0002] In oil and gas well fracturing operations, proppants need to have high strength, low density, and corrosion resistance to ensure long-term conductivity. In the prior art, the sintering method usually uses high-grade bauxite ( ), which is sintered at 1200 - 1350 °C to form a mullite-corundum phase structure (such as CN115232613B "A Proppant and a Method for Preparing a Proppant Using Oil Sludge Generated from Oil and Gas Field Exploitation"). Although it can achieve high strength (compressive strength ≥ 80 MPa), the raw material cost is high and the density is relatively large (> 2.2 g / cm³), which limits its application in deep wells; the non-sintering method uses industrial solid wastes (such as fly ash and desulfurized gypsum) to form through a cementation reaction (such as CN102061159B "A High-Density and High-Strength Proppant for Oil and Gas Wells and a Preparation Method Thereof"), but the compressive strength is generally lower than 40 MPa, and the curing period is up to more than 14 days; the film coating method uses resin or silane coating to improve the surface performance, but the resin film has poor heat resistance (< 150 °C) and is prone to failure in high-temperature wells, while the acid solubility of the traditional silane coating is still higher than 5%.

[0003] In the above technologies, the existing processes are difficult to simultaneously meet the requirements of high strength, low density, high solid waste content, and corrosion resistance. Specifically, it is manifested as follows: (1) The dependence on high-grade bauxite leads to high costs and low utilization rate of solid wastes (< 30%); (2) The non-sintering method has insufficient strength and a long curing period; (3) The contradiction between high energy consumption of high-temperature sintering (> 1200 °C) and poor heat resistance of resin film coating; (4) The traditional silane coating cannot solve the attenuation of conductivity caused by acid corrosion. Therefore, there is an urgent need to develop a proppant solution that takes into account solid waste resource utilization, low-temperature preparation, high strength and low density, and ultra-high corrosion resistance. Summary of the Invention

[0004] Aiming at the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a high-strength proppant for oil and gas wells and a preparation method thereof to solve one or more problems in the prior art.

[0005] To achieve the above purpose, the technical solution of the present invention is as follows: A high-strength proppant for oil and gas wells, comprising (a) A porous inner core, which is composed of the following raw materials by mass percentage: 40 - 60% of oil-based drill cuttings powder, 25 - 35% of low-grade bauxite, 10 - 20% of fly ash, and 3 - 8% of gypsum.

[0006] (b) A ceramic outer shell coated on the inner core, the ceramic outer shell being composed of 50-70% silicon nitride, 20-40% high-aluminum bauxite, and 5-10% binder.

[0007] (c) A surface modification layer, a superhydrophobic layer formed by a fluorosilane solution on the surface of the ceramic outer shell.

[0008] Further, the content of the low-aluminum bauxite is 40-50 wt%, and the activity of the fly ash content ≥ 45 wt%.

[0009] Further, the binder is polyethylene glycol or hydroxypropyl methylcellulose.

[0010] Further, the content of the high-aluminum bauxite content ≥ 70 wt%.

[0011] To make the technical effect complete, the present invention prepares a second set of technical solutions, which are: A preparation method of a high-strength fracturing proppant for oil and gas wells, comprising the following steps: (1) Raw material pretreatment: Ball-mill the oil-based drill cuttings residue to 150-250 mesh and dry it at 80-120 °C for 1-3 h. Crush the low-aluminum bauxite to a particle size ≤ 100 mesh.

[0012] (2) Inner core preparation: Mix and granulate the oil-based drill cuttings powder, low-aluminum bauxite, fly ash, and gypsum, and cure them at a constant temperature and humidity for 5-10 days, and the curing conditions are a temperature of 20-30 °C and a relative humidity ≥ 90%.

[0013] (3) Outer shell coating: Spray the composite slurry of silicon nitride, high-aluminum bauxite, and binder onto the surface of the inner core by the fluidized bed spraying method, and sinter it at 850-1000 °C for 1-4 h, and the heating rate ≤ 5 °C / min.

[0014] (4) Surface modification: Immerse the sintered particles in a fluorosilane solution with a concentration of 0.5-2 wt% and treat them at 40-80 °C for 0.5-2 h to form a superhydrophobic layer.

[0015] Further, it is characterized in that: in step (2), the particle size of the granulated particles is 20-40 mesh.

[0016] Further, it is characterized in that: in step (3), the spraying thickness of the composite slurry is 100-300 μm.

[0017] Further, it is characterized in that: in step (4), the fluorosilane solution is a mixed solution of perfluorooctyltriethoxysilane and hydrogen peroxide, and the mixing volume ratio is 1:1-1:3.

[0018] Further, it is characterized in that: in the mixed solution of perfluorooctyltriethoxysilane and hydrogen peroxide, the concentration of hydrogen peroxide is 3-5 wt%.

[0019] Further, it is characterized in that: in step (4), the surface-modified proppant is dried at 60-80 °C for 0.5-1 h, and the water content of the dried particles is ≤0.5%.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) Through the multi-solid waste synergistic ratio of oil-based drill cuttings powder (40-60%), low-aluminum bauxite (25-35%), fly ash (10-20%) and gypsum (3-8%), combined with constant temperature and humidity curing (20-30 °C / RH≥90%, 5-10 days), the balance of the inner core porosity and strength is achieved. This combination utilizes the activity of oil-based drill cuttings, the cementitious properties of fly ash and the excitation effect of gypsum to generate an intertwined structure of C-S-H gel and ettringite, enabling the compressive strength of the non-fired inner core to exceed 50 MPa, while the density is reduced to 1.6-1.8 g / cm³, overcoming the contradiction of low strength in the traditional non-fired method and high density in the sintering method.

[0021] (2) Through the low-temperature sintering (850-1000 °C) of the composite shell of silicon nitride (50-70%) and high-aluminum bauxite (20-40%), combined with the fluidized bed spraying process (spraying thickness 100-300 μm), a "high-strength shell-lightweight inner core" gradient structure is formed. The low-temperature reaction sintering characteristics of silicon nitride avoid the high temperature (>1200 °C) required for traditional corundum phase sintering. The compressive strength of the shell reaches 100-120 MPa, while the overall density is maintained at 1.8-2.0 g / cm³, meeting the requirements of high strength and low density for proppants in deep fracturing.

[0022] (3) Through the surface modification of the mixed solution of perfluorooctyltriethoxysilane and hydrogen peroxide (volume ratio 1:1-1:3, hydrogen peroxide concentration 3-5 wt%), combined with low-temperature treatment (40-80 °C / 0.5-2 h), a chemically bonded superhydrophobic layer (contact angle >150°) is constructed on the surface of the ceramic shell. Hydrogen peroxide oxidizes and activates the hydroxyl groups on the surface of the shell, enhancing the grafting density of fluorosilane, reducing the acid solubility from 5% of the traditional resin coating to below 0.5%, and avoiding the microcrack defects caused by high-temperature coating.

[0023] (4) Through the pretreatment of oil-based drill cuttings residue (oil removal rate ≥95% / calcination at 300-400 °C) and the raw material adaptation design of low-aluminum bauxite ( 40-50%), matching fly ash (activity ≥45%), achieving performance stability when the solid waste content is greater than 60%. This combination removes organic interference through deoiling and calcination, and uses the aluminum-silicon ratio of low-bauxite to adjust the composition of the gel phase, so that the performance fluctuation range of solid waste-based proppants (compression resistance ±5%) is lower than the ±10% allowed by the industry standard (SY / T5108-2014). BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the production process flow of a method for preparing a high-strength fracturing proppant for oil and gas wells in an exemplary description of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and exemplary descriptions. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no technical substantive significance. Any structural modification, change in proportional relationship or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical content disclosed by the present invention.

[0026] Application Overview In the field of oil and gas well fracturing proppants, the existing technology mainly prepares corundum-mullite phase proppants by high-temperature sintering of bauxite, or uses a non-sintering gelling process to consolidate industrial solid waste to achieve low-cost production. The high-temperature sintering method relies on high-grade bauxite ( ≥70%) forms a dense corundum phase above 1200℃. Although the strength meets the standard, the raw material cost is high and the density is too large (>2.2g / cm³), which is difficult to adapt to the needs of deep oil and gas extraction; the non-burning method uses cement, gypsum and other cementing materials to consolidate oil-based drill cuttings or fly ash and other solid wastes. Although the density is reduced (<1.8g / cm³), the strength of the gel is insufficient (<40MPa) and a maintenance cycle of more than 14 days is required, which seriously restricts production efficiency. In addition, although the conventional resin coating process can improve the corrosion resistance of the proppant surface, the coating layer is easy to decompose and fail at high temperature (>150℃), and the acid solubility is still higher than 5%, and the long-term conductivity is difficult to guarantee. These conventional schemes generally have problems such as high energy consumption, low solid waste utilization rate (<30%), and difficulty in balancing comprehensive performance, which restricts the application of fracturing proppants in complex formation environments.

[0027] Comprehensive description Raw material pretreatment The oil-based drill cuttings residue needs to be crushed to a particle size of 150 - 250 mesh by a ball mill (such as QM-3SP04 planetary ball mill), and then dried in an oven at 80 - 120 °C for 1 - 3 hours until the moisture content ≤ 1%. The low-aluminum bauxite ( with a content of 40 - 50 wt%) is crushed to a particle size ≤ 100 mesh by a jaw crusher (such as PE-150×250 type). Fly ash (active content ≥ 45 wt%) and gypsum (purity ≥ 95%) do not require pretreatment and are directly weighed in proportion.

[0028] Inner core preparation Put the pretreated oil-based drill cuttings powder (40 - 60 wt%), low-aluminum bauxite (25 - 35 wt%), fly ash (10 - 20 wt%) and gypsum (3 - 8 wt%) into a double-shaft mixer (such as SJ-300 type), and mix at a speed of 800 - 1000 r / min for 10 - 30 minutes to ensure the uniformity of the materials. Then add 10 - 15 wt% of water and granulate through a granulator (such as ZL-200 type disk granulator, speed 200 - 400 r / min), controlling the particle size of the granules to be 20 - 40 mesh. The granulated particles are transferred to a constant temperature and humidity box (such as HWS-250 type) and cured for 5 - 10 days under the conditions of a temperature of 20 - 30 °C and a relative humidity ≥ 90% to generate a porous inner core mainly composed of an interwoven structure of C-S-H gel and ettringite.

[0029] Outer shell coating After mixing silicon nitride powder (purity ≥ 99%, particle size ≤ 10 μm, accounting for 50 - 70 wt%) and high-aluminum bauxite ( content ≥ 70 wt%, particle size ≤ 100 mesh, accounting for 20 - 40 wt%), add a binder (polyethylene glycol or hydroxypropyl methylcellulose, accounting for 5 - 10 wt%) and prepare a slurry with a solid content of 40 - 60% (viscosity 100 - 500 mPa•s, measured by NDJ-8S rotary viscometer) with deionized water. Use a fluidized bed spraying device (such as FLP-200 type, fluidizing gas is nitrogen, flow rate 0.5 - 1.5 m³ / h) to evenly spray the slurry onto the surface of the inner core to form a pre-coating with a thickness of 100 - 300 μm. The sprayed particles are placed in a muffle furnace (such as SX2-12-16 type), heated to 850 - 1000 °C at a rate ≤ 5 °C / min, held for 1 - 4 hours, and then cooled to below 200 °C at a rate ≤ 3 °C / min and naturally cooled to room temperature to form a dense silicon nitride-corundum phase composite ceramic outer shell.

[0030] Surface modification Immerse the sintered particles in a 0.5 - 2 wt% fluorosilane solution (prepared by mixing perfluorooctyltriethoxysilane and 3 - 5 wt% hydrogen peroxide in a volume ratio of 1:1 - 1:3), and treat them in a constant temperature water bath at 40 - 80 °C for 0.5 - 2 hours. After taking them out, place them in a drying oven at 60 - 80 °C and dry for 0.5 - 1 hour until the moisture content ≤ 0.5%, and finally form a chemically bonded superhydrophobic layer on the surface of the ceramic shell (contact angle > 150°, verified by a JC2000D contact angle measuring instrument).

[0031] Basis for key parameters: The lower limit of the curing time (5 days) is verified by XRD and SEM. When it is shorter than 5 days, the hydration products are not completely formed and the compressive strength < 40 MPa; when the curing exceeds 10 days, the strength gain < 5%, so 5 - 10 days are selected.

[0032] The lower limit of the sintering temperature (850 °C) is based on the starting temperature of the solid-phase reaction between silicon nitride and (DSC test result). When the temperature is lower than this value, the density of the ceramic layer decreases significantly (porosity > 15%).

[0033] Optional alternative: Fly ash can be replaced by slag powder (activity index ≥ 95%), and gypsum can be replaced by sulfoaluminate cement (accounting for 3 - 5 wt%). It is necessary to synchronously adjust the curing humidity to ≥ 95%.

[0034] Fluidized bed spraying can be replaced by centrifugal spray granulation (such as LPG - 200 type, rotation speed 1000 - 1500 r / min, atomization pressure 0.2 - 0.5 MPa), and the coating thickness error needs to be controlled within ±10 μm.

[0035] Equipment adaptability: If a non-fluidized bed spraying equipment (such as electrostatic spraying) is used, a dispersant (such as sodium hexametaphosphate, 0.1 - 0.5 wt%) needs to be added additionally to improve the fluidity of the slurry.

[0036] To verify the actual influence of key parameters (oil-based drill cuttings powder ratio, sintering temperature, fluorosilane concentration) on the performance of the proppant, the following control experiments are designed, and the test methods are based on GB / T 17671 - 2021 (compressive strength), **SY / T 5108 - 2014 (acid solubility) and ISO 13503 - 5 (permeability): Compressive strength: Place the proppant particles in a fracturing simulation device with a closing pressure of 52 MPa, and record the crushing rate; Acid solubility: Immerse in a 12% HCl solution for 2 hours, and measure the mass loss rate; Permeability: Simulate the formation environment through a flow-through cell, and measure the product of the permeability of the proppant layer and the fracture width.

[0037] Table 1. Experimental data comparison table

[0038] Note: Parameters marked with * are beyond the preset range; Comprehensive score = compressive strength × 40% + (100-acid solubility × 10) × 30% + conductivity × 30%; The performance of the conventional groups (1-5) was better than that of the variable groups (6-9) in all aspects: for example, the compressive strength of group 3 (108.71MPa) was significantly higher than that of group 6 (85.47MPa), and the acid solubility (0.29%) was much lower than that of group 9 (0.78%); Nonlinear relationship verification: The highest score appeared in group 3 (55% cuttings ratio + 950℃ + 1.5wt% fluorosilane), not in the endpoint group (group 4 or group 2); The blank control group (Group 10) had the worst performance: the conductivity of the traditional sintering method was only 62.37μm²•cm, and the acid solubility was as high as 5.20%.

[0039] Experimental conclusion The preset parameter range (oil-based drill cuttings 40-60%, sintering temperature 850-1000℃, fluorosilane 0.5-2wt%) has significant technical significance through experimental verification: Parameter collaborative optimization: Group 3 (55% / 950℃ / 1.5%) has the best comprehensive performance, proving that the preset range covers the best process window; Boundary failure verification: Exceeding the range (such as 35% of drill cuttings in group 6 and 820°C sintering temperature in group 8) leads to a cliff-like drop in performance; Disadvantages of existing technology: The compressive strength (68.92 MPa) of the traditional sintering method (Group 10) is only 63.4% of that of Group 3.

[0040] Performance trend analysis based on experimental results 1. Oil-based cuttings ratio (40-60%) and gel structure formation Molecular mechanism: Residues in oil-based drill cuttings and Under the alkaline activation of gypsum, the active The reaction generates CSH gel ( ) and ettringite ( When the cuttings ratio is less than 40% (e.g., group 6, 35%), the activity Insufficient amounts of calcium aluminate lead to a decrease in the amount of calcium aluminate produced, an increase in the porosity of the gel (SEM shows pore size > 5 μm), and a significant decrease in the compressive strength (85.47 MPa). When the ratio is higher than 60% (such as group 7, 65%), the excess and Proportion imbalance (Al / Si > 1), forming amorphous aluminosilicate instead of crystal structure, increasing the brittleness of the gel (fracture toughness < 1.5 MPa•m¹ / ²).

[0041] Optimal range verification: In Group 3 (55%), Al / Si ≈ 0.9, the volume fraction of C-S-H and ettringite reaches 75% (XRD quantitative analysis), the porosity of the gel < 10%, and the compressive strength is 108.71 MPa.

[0042] 2. Sintering temperature (850 - 1000 °C) and ceramic grain boundary strengthening Molecular mechanism: Silicon nitride ( ), and high-alumina bauxite ( ) generate Si-Al-O-N (β-SiAlON) phase through solid-state reaction at 850 - 1000 °C. Its grain boundary energy (γ_gb ≈ 1.2 J / m²) is lower than that of pure (γ_gb ≈ 2.5 J / m²), promoting grain refinement (average grain size < 1 μm, observed by TEM). When the temperature is lower than 850 °C (such as Group 8, 820 °C), the reaction is incomplete, and residual free forms weak grain boundaries (EDS shows Al enrichment at the grain boundaries), and the compressive strength drops to 78.29 MPa; when the temperature is higher than 1000 °C (such as Group 9, 1050 °C), the β-SiAlON phase decomposes into and corundum ( ), and microcracks are generated at the grain boundaries (SEM shows crack density > 5 cracks / μm²), and the flow conductivity drops to 79.14 μm²•cm.

[0043] Optimal temperature verification: In Group 3 (950 °C), the proportion of β-SiAlON phase > 80% (Rietveld refinement), the grain size is uniform (0.5 - 1.2 μm), and the compressive strength is 108.71 MPa.

[0044] 3. Concentration of fluorosilane (0.5 - 2 wt%) and chemical bonding of superhydrophobic surface Molecular mechanism: Perfluorooctyltriethoxysilane (FAS) is oxidized by hydrogen peroxide ( ), and its ethoxy group ( ) is hydrolyzed into silanol (-Si-OH), which forms Si-O-Si covalent bonds with the hydroxyl groups (-OH) on the surface of the ceramic shell through dehydration condensation (FTIR shows Characteristic peak). When the concentration is lower than 0.5% (e.g., Group 1, 0.5%), the silane coverage rate < 50% (XPS semi-quantitative), there are unreacted -OH residues on the surface (contact angle < 130°), and the acid solubility increases to 0.48%; when the concentration is higher than 2% (e.g., Group 4, 2.0%), the stacking of excessive silane molecules leads to multi-layer physical adsorption (AFM shows a film thickness > 50 nm), and internal stress causes film cracking (crack density > 3 per 100 μm²), and the acid solubility rebounds to 0.41%.

[0045] Optimal concentration verification: For Group 3 (1.5%), the monolayer coverage rate of silane > 90% (contact angle > 150°), the film thickness ≈ 15 nm (measured by ellipsometer), and the acid solubility is 0.29%.

[0046] Nonlinear correlation of comprehensive performance In the experimental data, Group 3 (55% / 950 °C / 1.5%) has the highest comprehensive score (95.62), but it is not the extreme value of the parameters. The reasons are as follows: Interface matching between the gel phase and the ceramic phase: The difference in the thermal expansion coefficients between the inner core gel (thermal expansion coefficient ≈ ) and the ceramic shell ( ) needs to relieve the interface stress through gradient sintering (heating rate ≤ 5 °C / min). Excessive deviation from the optimal parameters will lead to interface peeling (e.g., for Group 4, 60% / 1000 °C, the interface peeling area > 10%).

[0047] Balance between chemical bonding and physical adsorption: When the concentration of fluorosilane is too high, the physical adsorption layer hinders the formation of covalent bonds, while when the concentration is too low, the coverage rate is insufficient. The 1.5% concentration in Group 3 achieves the best balance between the bonding density and the film integrity.

[0048] Conclusion The pre-defined parameter ranges (drill cuttings 40 - 60%, sintering 850 - 1000 °C, fluorosilane 0.5 - 2 wt%) correspond to the following optimization mechanisms at the molecular level: The Al / Si stoichiometric ratio controls the composition of the gel phase; The β-SiAlON grain boundary phase inhibits crack propagation; The covalent bonding of the silane monolayer ensures superhydrophobicity.

[0049] The experimental data verifies the scientific necessity of these ranges. Going beyond the ranges will cause molecular structure defects and lead to a significant deterioration in performance.

[0050] Exemplary illustration Example 1

[0051] Preparation method: Raw material pretreatment: The oil-based drill cuttings residues were crushed to 200 mesh by a planetary ball mill, and then dried in an oven at 100 °C for 2 hours, with the moisture content reduced to 0.8%; Low-aluminum bauxite ( content 45 wt%) was crushed to 80 mesh by a jaw crusher; Fly ash (active content 48 wt%) and gypsum (purity 96%) were directly weighed and set aside.

[0052] Preparation of the inner core: Weigh 50% of the oil-based drill cuttings powder, 30% of low-aluminum bauxite, 15% of fly ash, and 5% of gypsum by mass percentage; Put them into a double-shaft mixer and mix at 900 r / min for 20 minutes, add 12 wt% of water, and granulate through a disk granulator (rotation speed 300 r / min) to obtain 25-mesh granules; Place the granules in a constant temperature and humidity box (temperature 25 °C, relative humidity 92%) for 7 days.

[0053] Coating of the outer shell: Weigh 60% of silicon nitride (purity 99.5%, particle size 5 μm), 35% of high-aluminum bauxite ( content 72 wt%, particle size 80 mesh), and 5% of polyethylene glycol (molecular weight 4000); Add deionized water to prepare a slurry with a solid content of 50% (viscosity 300 mPa•s), and spray it onto the surface of the inner core through a fluidized bed spraying device (nitrogen flow rate 1.0 m³ / h) to form a 200-μm pre-coating; Heat it in a muffle furnace from room temperature to 950 °C at a rate of 3 °C / min, hold for 2 hours, and then cool it to 180 °C at a rate of 2 °C / min and let it cool naturally.

[0054] Surface modification: Immerse the sintered particles in a 1.5 wt% fluorosilane solution (perfluorooctyltriethoxysilane and 4 wt% hydrogen peroxide mixed at a volume ratio of 1:2), and treat them at 60 °C for 1 hour; Take them out and dry them in a drying oven at 70 °C for 0.8 hours, with the moisture content of 0.4%.

[0055] Example 2

[0056] All environmental parameters and constants in this example are the same as those in Example 1, except that: the proportion of oil-based drill cuttings is 40%, the sintering temperature is 850 °C, and the concentration of fluorosilane is 0.5%.

[0057] Example 3

[0058] All environmental parameters and constants in this example are the same as those in Example 1, except that: the proportion of oil-based drill cuttings is 55%, the sintering temperature is 950 °C, and the concentration of fluorosilane is 1.5%.

[0059] Example 4

[0060] All environmental parameters and constants in this example are the same as those in Example 1, except that: the proportion of oil-based drill cuttings is 60%, the sintering temperature is 1000 °C, and the concentration of fluorosilane is 2.0%.

[0061] Example 5

[0062] All environmental parameters and constants in this example are the same as those in Example 1, except that: the proportion of oil-based drill cuttings is 45%, the sintering temperature is 920 °C, and the concentration of fluorosilane is 0.8%.

[0063] Example 6

[0064] All environmental parameters and constants in this example are the same as those in Example 1, except that: the proportion of oil-based drill cuttings is 35% (*), the sintering temperature is 900 °C, and the concentration of fluorosilane is 1.0%.

[0065] Example 7

[0066] All environmental parameters and constants in this example are the same as those in Example 1, except that: the proportion of oil-based drill cuttings is 65% (*), the sintering temperature is 900 °C, and the concentration of fluorosilane is 1.0%.

[0067] Example 8

[0068] All environmental parameters and constants in this example are the same as those in Example 1, except that: the proportion of oil-based drill cuttings is 50%, the sintering temperature is 820 °C (*), and the concentration of fluorosilane is 1.0%.

[0069] Example 9

[0070] All environmental parameters and constants in this example are the same as those in Example 1, except that: the proportion of oil-based drill cuttings is 50%, the sintering temperature is 1050 °C (*), and the concentration of fluorosilane is 1.0%.

[0071] Example 10

[0072] All environmental parameters and constants in this example are the same as those in Example 1, except that: the traditional sintering process is adopted (the proportion of oil-based drill cuttings is 0%, the sintering temperature is 1200 °C, and no fluorosilane treatment is carried out).

[0073] Specific working process After the oil-based drill cuttings residue is pretreated by ball milling and drying, it is mixed and granulated with crushed low-aluminum bauxite, fly ash and gypsum to obtain porous core particles. Subsequently, silicon nitride, high-aluminum bauxite and a binder are mixed to form a composite slurry, which is uniformly coated on the surface of the core by the fluidized bed spraying method and sintered at high temperature to form a strong ceramic shell. The sintered ceramic particles are immersed in a fluorosilane solution for surface treatment to form a superhydrophobic surface modification layer. The whole process realizes the transformation from waste oil-based drill cuttings to high-strength fracturing proppants. Each step is closely connected. Through processes such as pretreatment, granulation, coating and sintering, and surface modification, high-performance fracturing proppants suitable for oil and gas wells are finally prepared.

[0074] The various technical features described in the above exemplary description can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the various technical features in the above exemplary description are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

Claims

1. A high-strength fracturing proppant for oil and gas wells, characterized in that: Comprising (a)A porous inner core, composed of raw materials in the following mass percentages: 40 - 60% oil-based drill cuttings powder, 25 - 35% low-aluminum bauxite, 10 - 20% fly ash, 3 - 8% gypsum; (b)A ceramic outer shell coated on the outer surface of the inner core, the ceramic outer shell being composed of 50 - 70% silicon nitride, 20 - 40% high-aluminum bauxite and 5 - 10% binder; (c)A surface modification layer, a super-hydrophobic layer formed by a fluorosilane solution on the surface of the ceramic outer shell.

2. The high-strength fracturing proppant for oil and gas wells according to claim 1, wherein: The content of the low-aluminum bauxite is 40-50 wt%, and the activity content of the fly ash is ≥45 wt%.

3. The high-strength fracturing proppant for oil and gas wells according to claim 1, wherein: The binder is polyethylene glycol or hydroxypropyl methylcellulose.

4. The high-strength fracturing proppant for oil and gas wells according to claim 1, characterized in that: The content of the bauxite is ≥ 70 wt%.

5. A preparation method of a high-strength fracturing proppant for oil and gas wells, based on any one of claims 1-4, characterized in that, Including the following steps: (1)Raw material pretreatment: Ball-mill the oil-based drill cuttings residue to 150 - 250 mesh and dry it at 80 - 120°C for 1 - 3 h; Crush the low-aluminum bauxite to a particle size of ≤100 mesh; (2)Inner core preparation: Mix and granulate the oil-based drill cuttings powder, low-aluminum bauxite, fly ash, and gypsum, and cure it under constant temperature and humidity for 5 - 10 days, with the curing conditions being a temperature of 20 - 30°C and a relative humidity of ≥90%; (3)Outer shell coating: Spray the composite slurry of silicon nitride, high-aluminum bauxite and binder onto the surface of the inner core by the fluidized bed spraying method, and sinter it at 850 - 1000°C for 1 - 4 h, with a heating rate of ≤5°C / min; (4)Surface modification: Immerse the sintered particles in a fluorosilane solution with a concentration of 0.5 - 2 wt%, and treat them at 40 - 80°C for 0.5 - 2 h to form a super-hydrophobic layer.

6. The preparation method of a high-strength fracturing proppant for oil and gas wells according to claim 5, characterized in that: In step (2), the particle size of the granulated particles is 20 - 40 mesh.

7. The preparation method of a high-strength fracturing proppant for oil and gas wells according to claim 5, characterized in that: In step (3), the spraying thickness of the composite slurry is 100 - 300 μm.

8. The preparation method of a high-strength fracturing proppant for oil and gas wells according to claim 5, characterized in that: In step (4), the fluorosilane solution is a mixed solution of perfluorooctyltriethoxysilane and hydrogen peroxide, and the mixing volume ratio is 1:1 - 1:

3.

9. The preparation method of a high-strength fracturing proppant for oil and gas wells according to claim 8, wherein: In the mixed solution of perfluorooctyltriethoxysilane and hydrogen peroxide, the concentration of hydrogen peroxide is 3 - 5 wt%.

10. The preparation method of a high-strength fracturing proppant for oil and gas wells according to claim 5, characterized in that: In step (4), the supported agent after surface modification is dried at 60 - 80°C for 0.5 - 1 h, and the moisture content of the dried particles is ≤0.5%.

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