A high-strength fracturing proppant for oil and gas wells and its preparation method

Abstract

This invention discloses a high-strength fracturing proppant for oil and gas wells and its preparation method. The proppant comprises a porous core, a ceramic shell, and a surface-modified layer. The core contains 40-60% oil-based drill cuttings powder, 25-35% low-alumina bauxite, 10-20% fly ash, and 3-8% gypsum. The ceramic shell is composed of 50-70% silicon nitride, 20-40% high-alumina bauxite, and 5-10% binder. The surface-modified layer is a superhydrophobic layer formed by a fluorosilane solution. The low-alumina bauxite content is 40-50 wt%, the fly ash active content is ≥45 wt%, the binder is polyethylene glycol or hydroxypropyl methylcellulose, and the high-alumina bauxite content is ≥70 wt%. The preparation method includes raw material pretreatment, core preparation, shell coating, and surface modification. During core preparation, the mixture is granulated and then cured at a constant temperature and humidity for 5-10 days. The outer shell is coated using a fluidized bed spraying method, with a coating thickness of 100-300 μm and a sintering temperature of 850-1000℃. Surface modification is performed using a 0.5-2 wt% fluorosilane solution, and the moisture content of the particles after drying is ≤0.5%.

Description

Technical Field

[0001] This invention relates to proppant for oil and gas wells, and more particularly to a high-strength fracturing proppant for oil and gas wells and its preparation method. Background Technology

[0002] In oil and gas well fracturing operations, proppants need to possess high strength, low density, and corrosion resistance to ensure long-term conductivity. In existing technologies, sintering methods typically use high-grade bauxite (… Sintering at 1200-1350℃ with ≥70wt% of the material to form a mullite-corundum phase structure (e.g., CN115232613B "A fracturing proppant and a method for preparing fracturing proppant using oil sludge generated from oil and gas field extraction") can achieve high strength (compressive strength ≥80MPa), but the raw material cost is high and the density is relatively high (>2.2g / cm³), which limits its application in deep wells. The non-sintering method uses industrial solid waste (such as fly ash and desulfurized gypsum) to form through a gelation reaction (e.g., CN102061159B "A high-density, high-strength oil and gas well fracturing proppant and its preparation method"), but the compressive strength is generally lower than 40MPa, and the curing period is as long as 14 days or more. The coating method uses resin or silane coatings to improve surface properties, but resin coatings have poor temperature resistance (<150℃) and are prone to failure in high-temperature wells, while the acid solubility of traditional silane coatings is still higher than 5%.

[0003] Among the aforementioned technologies, existing processes struggle to simultaneously meet the requirements of high strength, low density, high solid waste content, and corrosion resistance. Specifically, this manifests in the following ways: (1) dependence on high-grade bauxite leads to high costs and low solid waste utilization (<30%); (2) the non-fired method results in insufficient strength and a long curing cycle; (3) the contradiction between high energy consumption (>1200℃) in high-temperature sintering and poor temperature resistance of resin coating; and (4) traditional silane coatings cannot solve the problem of reduced conductivity caused by acid corrosion. Therefore, there is an urgent need to develop a fracturing proppant solution that balances solid waste resource utilization, low-temperature preparation, high strength and low density, and ultra-corrosion resistance. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a high-strength fracturing proppant for oil and gas wells and its preparation method, so as to solve one or more problems in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A high-strength fracturing proppant for oil and gas wells, comprising

[0007] (a) Porous inner core, composed of the following raw materials in weight percentage: 40-60% oil-based drill cuttings powder, 25-35% low-alumina bauxite, 10-20% fly ash, and 3-8% gypsum.

[0008] (b) A ceramic shell covering the inner core, the ceramic shell being made of 50-70% silicon nitride, 20-40% high alumina bauxite and 5-10% binder sintered at 850-1000°C.

[0009] (c) Surface modification layer, a superhydrophobic layer formed on the surface of the ceramic shell by a 0.5-2 wt% fluorosilane solution. The fluorosilane solution is a mixture of perfluorooctyltriethoxysilane and hydrogen peroxide.

[0010] Furthermore, the low-alumina bauxite The content is 40-50 wt%, and the activity of fly ash is... Content ≥45wt%.

[0011] Furthermore, the adhesive is polyethylene glycol or hydroxypropyl methylcellulose.

[0012] Furthermore, the high-alumina bauxite Content ≥70wt%.

[0013] To ensure the completeness of the technical effect, this invention provides a second technical solution: a method for preparing a high-strength fracturing proppant for oil and gas wells, comprising the following steps:

[0014] (1) Raw material pretreatment: The oil-based drill cutting residue is ball-milled to 150-250 mesh and dried at 80-120℃ for 1-3 hours. Low-alumina bauxite is crushed to a particle size ≤100 mesh.

[0015] (2) Core preparation: Mix oil-based drill cuttings powder, low-alumina bauxite, fly ash and gypsum into granules, and cure at constant temperature and humidity for 5-10 days. The curing conditions are temperature 20-30℃ and relative humidity ≥90%.

[0016] (3) Outer shell coating: A composite slurry of silicon nitride, high alumina bauxite and binder is sprayed onto the inner core surface using a fluidized bed spraying method and sintered at 850-1000℃ for 1-4h with a heating rate ≤5℃ / min.

[0017] (4) Surface modification: The sintered particles are immersed in a 0.5-2wt% fluorosilane solution and treated at 40-80℃ for 0.5-2h to form a superhydrophobic layer.

[0018] Furthermore, the feature is that in step (2), the particle size of the granulated particles is 20-40 mesh.

[0019] Furthermore, the feature is that in step (3), the coating thickness of the composite slurry is 100-300μm.

[0020] Furthermore, the feature is that in step (4), the fluorosilane solution is a mixture of perfluorooctyltriethoxysilane and hydrogen peroxide, with a mixing volume ratio of 1:1 to 1:3.

[0021] Furthermore, the characteristic is that the concentration of hydrogen peroxide in the mixture of perfluorooctyltriethoxysilane and hydrogen peroxide is 3-5 wt%.

[0022] Furthermore, its characteristic is that in step (4), the surface-modified proppant is dried at 60-80℃ for 0.5-1h, and the moisture content of the particles after drying is ≤0.5%.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0024] (I) By using a synergistic blend of multiple solid wastes—oil-based drill cuttings powder (40-60%), low-alumina bauxite (25-35%), fly ash (10-20%), and gypsum (3-8%)—combined with constant temperature and humidity curing (20-30℃ / RH≥90%, 5-10 days), a balance between core porosity and strength is achieved. This combination utilizes the... / The active, cementing properties of fly ash and the activating effect of gypsum generate a CSH gel and ettringite interwoven structure, which makes the compressive strength of the non-fired core exceed 50MPa, while the density is reduced to 1.6-1.8g / cm³, overcoming the contradiction of low strength in traditional non-fired methods and high density in sintering methods.

[0025] (II) A gradient structure of "high-strength outer shell - lightweight inner core" is formed by low-temperature sintering (850-1000℃) of a composite shell of silicon nitride (50-70%) and high-alumina bauxite (20-40%), combined with fluidized bed spraying (100-300μm spraying thickness). The low-temperature reaction sintering characteristics of silicon nitride avoid the high temperature (>1200℃) required by traditional corundum phase sintering. The compressive strength of the outer shell reaches 100-120MPa, while the overall density is maintained at 1.8-2.0g / cm³, meeting the requirements of high strength and low density proppant for deep fracturing.

[0026] (III) Surface modification with a mixture of perfluorooctyltriethoxysilane and hydrogen peroxide (volume ratio 1:1-1:3, hydrogen peroxide concentration 3-5wt%), combined with low-temperature treatment (40-80℃ / 0.5-2h), constructs a chemically bonded superhydrophobic layer (contact angle >150°) on the ceramic shell surface. Hydrogen peroxide oxidizes and activates the hydroxyl groups on the shell surface, enhancing the grafting density of fluorosilanes, reducing acid solubility from 5% in traditional resin coatings to below 0.5%, and avoiding microcrack defects caused by high-temperature coatings.

[0027] (iv) Pretreatment of oil-based drill cuttings residue (oil removal rate ≥95% / calcination at 300-400℃) with low-alumina bauxite ( The raw material compatibility design (40-50%) is matched with fly ash (active) With a gelling activity of ≥45%, performance stability is achieved at solid waste content >60%. This combination removes organic interference through deoiling and calcination, and adjusts the composition of the gelling phase using the aluminum-silicon ratio of low-alumina bauxite, so that the performance fluctuation range (compressive strength ±5%) of the solid waste-based proppant is lower than the ±10% allowed by the industry standard (SY / T5108-2014). Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the production process of a method for preparing a high-strength fracturing proppant for oil and gas wells, as illustrated in the exemplary description of this invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and exemplary descriptions. It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0030] Application Overview

[0031] In the field of oil and gas well fracturing proppant, existing technologies mainly involve preparing corundum-mullite phase proppants through high-temperature sintering of bauxite, or using a non-sintering cementation process to solidify industrial solid waste to achieve low-cost production. The high-temperature sintering method relies on high-grade bauxite (… While proppant with a content of ≥70% forms a dense corundum phase above 1200℃, achieving the required strength, its high raw material cost and excessive density (>2.2g / cm³) make it unsuitable for deep oil and gas extraction. The non-burning method, which uses cement, gypsum, and other cementing materials to solidify oil-based drill cuttings or fly ash, reduces density (<1.8g / cm³), but the cementitious strength is insufficient (<40MPa) and requires a curing period of over 14 days, severely limiting production efficiency. Furthermore, while conventional resin coating processes improve the surface corrosion resistance of proppant, the coating layer is prone to decomposition and failure at high temperatures (>150℃), and its acid solubility remains above 5%, making long-term conductivity difficult to guarantee. These conventional solutions generally suffer from high energy consumption, low solid waste utilization (<30%), and difficulty in achieving comprehensive performance, thus restricting the application of fracturing proppant in complex formation environments.

[0032] Comprehensive explanation

[0033] Raw material pretreatment

[0034] Oil-based drill cuttings residue needs to be pulverized to 150-250 mesh using a ball mill (e.g., a QM-3SP04 planetary ball mill), and then dried in an oven at 80-120℃ for 1-3 hours until the moisture content is ≤1%. Low-alumina bauxite ( (Content 40-50wt%) is crushed to a particle size ≤100 mesh using a jaw crusher (such as PE-150×250 type). Fly ash (active) For products with a content ≥45wt% and gypsum (purity ≥95%), no pretreatment is required; weigh directly according to the proportion.

[0035] Core preparation

[0036] Pretreated oil-based drill cuttings powder (40-60 wt%), low-alumina bauxite (25-35 wt%), fly ash (10-20 wt%), and gypsum (3-8 wt%) are added to a twin-shaft mixer (such as the SJ-300 type) and mixed at 800-1000 r / min for 10-30 minutes to ensure uniform material composition. Then, 10-15 wt% water is added, and the mixture is granulated using a granulator (such as the ZL-200 type disc granulator, 200-400 r / min) to control the particle size to 20-40 mesh. The granulated particles are then transferred to a constant temperature and humidity chamber (such as the HWS-250 type) and cured for 5-10 days at 20-30℃ and relative humidity ≥90% to generate a porous core mainly composed of CSH gel and ettringite interwoven structures.

[0037] outer shell

[0038] Silicon nitride powder (purity ≥99%, particle size ≤10μm, percentage 50-70wt%) and high-alumina bauxite ( After mixing (content ≥70wt%, particle size ≤100 mesh, accounting for 20-40wt%), a binder (polyethylene glycol or hydroxypropyl methylcellulose, accounting for 5-10wt%) is added, and a slurry with a solid content of 40-60% is prepared with deionized water (viscosity 100-500 mPa•s, measured by an NDJ-8S rotational viscometer). The slurry is uniformly sprayed onto the inner core surface using a fluidized bed spraying device (such as the FLP-200 type, with nitrogen as the fluidizing gas and a flow rate of 0.5-1.5 m³ / h) to form a pre-coating layer with a thickness of 100-300 μm. The sprayed particles are then placed in a muffle furnace (such as the SX2-12-16 type) and heated to 850-1000℃ at a rate ≤5℃ / min, held at that temperature for 1-4 hours, and then cooled to below 200℃ at a rate ≤3℃ / min, and allowed to cool naturally to room temperature to form a dense silicon nitride-corundum phase composite ceramic shell.

[0039] Surface modification

[0040] The sintered particles were immersed in a 0.5-2 wt% fluorosilane solution (prepared by mixing perfluorooctyltriethoxysilane and 3-5 wt% hydrogen peroxide at a volume ratio of 1:1-1:3) and treated in a constant temperature water bath at 40-80℃ for 0.5-2 hours. After removal, they were placed in a drying oven at 60-80℃ and dried for 0.5-1 hour until the moisture content was ≤0.5%, ultimately forming a chemically bonded superhydrophobic layer on the surface of the ceramic shell (contact angle >150°, verified by a JC2000D contact angle measuring instrument).

[0041] Key parameters are based on:

[0042] The minimum curing time (5 days) was verified by XRD and SEM. When the curing time was less than 5 days, the hydration products were not fully generated and the compressive strength was <40MPa. After curing for more than 10 days, the strength gain was <5%. Therefore, 5-10 days was selected.

[0043] The lower limit of the sintering temperature (850℃) is based on silicon nitride and The solid-state reaction initiation temperature (DSC test results) is below which the density of the ceramic layer decreases significantly (porosity > 15%).

[0044] Alternative options:

[0045] Fly ash can be replaced with slag powder (activity index ≥95%), and gypsum can be replaced with sulfoaluminate cement (accounting for 3-5wt%). The curing humidity needs to be adjusted to ≥95% simultaneously.

[0046] Fluidized bed spraying can be replaced by centrifugal spray granulation (such as LPG-200 type, rotation speed 1000-1500r / min, atomization pressure 0.2-0.5MPa), and the coating thickness error needs to be controlled within ±10μm.

[0047] Equipment compatibility:

[0048] If non-fluidized bed spraying equipment (such as electrostatic spraying) is used, an additional dispersant (such as sodium hexametaphosphate, 0.1-0.5 wt%) needs to be added to improve the slurry fluidity.

[0049] To verify the actual impact of key parameters (proportion of oil-based drill cuttings powder, sintering temperature, and concentration of fluorosilane) on proppant performance, the following control experiment was designed. The test methods were based on GB / T17671-2021 (compressive strength), **SY / T5108-2014 (acid solubility), and ISO13503-5 (fluid conductivity) standards:

[0050] Compressive strength: The proppant particles were placed in a fracturing simulation device with a closing pressure of 52 MPa, and the breakage rate was recorded;

[0051] Acid solubility: The mass loss rate was determined after soaking in 12% HCl solution for 2 hours.

[0052] Diversion capacity: The permeability of the proppant layer and the product of the fracture width are measured by simulating the formation environment through a diversion chamber.

[0053] Table 1. Comparison of Experimental Data

[0054]

[0055] Note: Parameters marked with * are outside the preset range; Overall score = compressive strength × 40% + (100 - acid solubility × 10) × 30% + conductivity × 30%;

[0056] The conventional groups (1-5) outperformed 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%).

[0057] Nonlinear relationship verification: The highest score appeared in group 3 (55% drill cuttings ratio + 950℃ + 1.5wt% fluorosilane), rather than the endpoint group (group 4 or group 2).

[0058] The blank control group (group 10) had the worst performance: the conductivity of the traditional sintering method was only 62.37 μm²•cm, and the acid solubility was as high as 5.20%.

[0059] Experimental conclusions

[0060] The preset parameter range (40-60% oil-based drill cuttings, sintering temperature 850-1000℃, 0.5-2wt% fluorosilane) has been experimentally verified to have significant technical implications.

[0061] Parameter co-optimization: Group 3 (55% / 950℃ / 1.5%) showed the best overall performance, proving that the preset range covers the optimal process window;

[0062] Boundary failure verification: Exceeding the range (e.g., 35% drill cuttings ratio in group 6, 820℃ sintering temperature in group 8) leads to a precipitous drop in performance;

[0063] Disadvantages of existing technology: The compressive strength (68.92MPa) of the traditional sintering method (Group 10) is only 63.4% of that of Group 3.

[0064] Performance trend analysis based on experimental results

[0065] 1. The proportion of oil-based drill cuttings (40-60%) and the formation of cementitious structure.

[0066] Molecular mechanism: Residual in oil-based drill cuttings and Under alkaline activation of gypsum, it reacts with the active substances in fly ash. The reaction produces CSH gel (CaO• • ) and ettringite (3CaO• • • When the proportion of drill cuttings is below 40% (e.g., group 6, 35%), activity... Insufficient ettringite formation leads to reduced aggregate porosity, increased gel porosity (SEM showed pore size > 5 μm), and a significant decrease in compressive strength (85.47 MPa). When the proportion exceeds 60% (e.g., group 7, 65%), excessive ettringite... and An imbalance in the ratio (Al / Si > 1) leads to the formation of amorphous aluminosilicates with an amorphous structure, increasing the brittleness of the gel (fracture toughness < 1). ).

[0067] Optimal range verification: Group 3 (55%) has Al / Si≈0.9, CSH and ettringite volume ratio reaches 75% (XRD quantitative analysis), gel porosity <10%, and compressive strength 108.71MPa.

[0068] 2. Sintering temperature (850-1000℃) and ceramic grain boundary strengthening

[0069] Molecular mechanism: Silicon nitride ( ) and high-alumina bauxite ( The Si-Al-ON (β-SiAlON) phase is generated through a solid-state reaction at 850-1000℃, and its grain boundary energy (γ_gb≈1.2J / m²) is lower than that of pure SiAlON. (γ_gb≈2.5J / m²), promoting grain refinement (average grain size <1μm, TEM observation). At temperatures below 850℃ (e.g., group 8, 820℃), the reaction is incomplete, leaving residual free... Weak grain boundaries form (EDS shows Al enrichment at the grain boundaries), reducing the compressive strength to 78.29 MPa; at temperatures above 1000℃ (e.g., group 9, 1050℃), the β-SiAlON phase decomposes into... Corundum ( Microcracks were generated at the grain boundaries (SEM showed a crack density of >5 cracks / μm²), and the conductivity decreased to 79.14 μm²•cm.

[0070] Optimal temperature verification: Group 3 (950℃) has a β-SiAlON phase ratio of >80% (Rietveld refinement), uniform grain size (0.5-1.2μm), and compressive strength of 108.71MPa.

[0071] 3. Fluorosilane concentration (0.5-2wt%) and chemical bonding with superhydrophobic surfaces

[0072] Molecular mechanism: Perfluorooctyltriethoxysilane (FAS) in hydrogen peroxide (… Under oxidation, its ethoxy group ( Hydrolyzed into silanol (-Si-OH), it forms Si-O-Si covalent bonds with hydroxyl groups (-OH) on the ceramic shell surface through dehydration condensation (FTIR display). Characteristic peaks). When the concentration is below 0.5% (e.g., Group 1, 0.5%), the silane coverage is <50% (XPS semi-quantitative), unreacted -OH residues remain on the surface (contact angle <130°), and the acid solubility increases to 0.48%; when the concentration is above 2% (e.g., Group 4, 2.0%), excessive silane molecule accumulation leads to multilayer physical adsorption (AFM shows film thickness >50nm), internal stress induces film cracking (crack density >3 lines / 100μm²), and the acid solubility rebounds to 0.41%.

[0073] Optimal concentration verification: Group 3 (1.5%) had a silane monolayer coverage of >90% (contact angle >150°), film thickness ≈15nm (ellipsometry measurement), and acid solubility of 0.29%.

[0074] Nonlinear correlation of overall performance

[0075] Group 3 (55% / 950℃ / 1.5%) had the highest overall score (95.62) in the experimental data, but it was not an extreme value of the parameter. The reason is:

[0076] Interface matching between the cementitious phase and the ceramic phase: inner core cement (thermal expansion coefficient ≈ ) and ceramic shell (≈ The difference in thermal expansion coefficients needs to be alleviated by gradient sintering (heating rate ≤ 5℃ / min). Excessive deviation from the optimal parameters will lead to interface peeling (e.g., Group 4, 60% / 1000℃ interface peeling area > 10%).

[0077] 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 is insufficient. The 1.5% concentration in group 3 achieves the best balance between bonding density and film integrity.

[0078] in conclusion

[0079] The predefined parameter range (40-60% drill cuttings, 850-1000℃ sintering, 0.5-2wt% fluorosilane) corresponds to the following optimization mechanism at the molecular level:

[0080] The Al / Si stoichiometric ratio controls the composition of the gel phase;

[0081] β-SiAlON grain boundary phases inhibit crack propagation;

[0082] Silane monolayer covalent bonding ensures superhydrophobicity.

[0083] Experimental data validated the scientific necessity of these ranges; exceeding these ranges would trigger molecular structural defects, leading to significant performance degradation.

[0084] Exemplary Description

[0085] Example 1

[0086] Preparation method:

[0087] Raw material pretreatment:

[0088] The oil-based drill cuttings residue was pulverized to 200 mesh using a planetary ball mill, and then dried in an oven at 100°C for 2 hours until the moisture content dropped to 0.8%.

[0089] Low-alumina bauxite ( (Content 45wt%) was crushed to 80 mesh using a jaw crusher;

[0090] fly ash (active) Weigh directly the 48wt% content and gypsum (96% purity) for later use.

[0091] Core fabrication:

[0092] Weigh out the following by weight percentage: 50% oil-based drill cuttings powder, 30% low-alumina bauxite, 15% fly ash, and 5% gypsum.

[0093] Mix the mixture in a twin-shaft mixer at 900 r / min for 20 minutes, add 12 wt% water, and granulate it through a disc granulator (300 r / min) to obtain 25 mesh particles.

[0094] The particles were placed in a constant temperature and humidity chamber (temperature 25℃, relative humidity 92%) for 7 days.

[0095] Outer shell covering:

[0096] Weigh out 60% silicon nitride (purity 99.5%, particle size 5μm) and high-alumina bauxite ( Content 72wt%, particle size 80 mesh) 35%, polyethylene glycol (molecular weight 4000) 5%;

[0097] Add deionized water to prepare a slurry with a solid content of 50% (viscosity 300 mPa•s), and spray it onto the inner core surface through a fluidized bed spraying device (nitrogen flow rate 1.0 m³ / h) to form a 200 μm pre-coating layer;

[0098] The temperature was increased to 950°C in a muffle furnace at a rate of 3°C / min and held for 2 hours. Then the temperature was decreased to 180°C at a rate of 2°C / min and allowed to cool naturally.

[0099] Surface modification:

[0100] The sintered particles were immersed in a 1.5wt% fluorosilane solution (perfluorooctyltriethoxysilane and 4wt% hydrogen peroxide were mixed at a volume ratio of 1:2) and treated at 60℃ for 1 hour.

[0101] After being removed, it was dried in a drying oven at 70℃ for 0.8 hours, with a moisture content of 0.4%.

[0102] Example 2

[0103] This embodiment is identical to Embodiment 1 in all environmental parameters and constants, except that: the proportion of oil-based drill cuttings is 40%, the sintering temperature is 850℃, and the concentration of fluorosilane is 0.5%.

[0104] Example 3

[0105] This embodiment is identical to Embodiment 1 in all environmental parameters and constants, except that: the proportion of oil-based drill cuttings is 55%, the sintering temperature is 950℃, and the concentration of fluorosilane is 1.5%.

[0106] Example 4

[0107] This embodiment is identical to Embodiment 1 in all environmental parameters and constants, except that: the proportion of oil-based drill cuttings is 60%, the sintering temperature is 1000℃, and the concentration of fluorosilane is 2.0%.

[0108] Example 5

[0109] This embodiment is identical to Embodiment 1 in all environmental parameters and constants, except that: the proportion of oil-based drill cuttings is 45%, the sintering temperature is 920℃, and the concentration of fluorosilane is 0.8%.

[0110] Example 6

[0111] This embodiment is identical to Embodiment 1 in all environmental parameters and constants, except that: the proportion of oil-based drill cuttings is 35% (*), the sintering temperature is 900℃, and the concentration of fluorosilane is 1.0%.

[0112] Example 7

[0113] This embodiment is identical to Embodiment 1 in all environmental parameters and constants, except that: the proportion of oil-based drill cuttings is 65% (*), the sintering temperature is 900℃, and the concentration of fluorosilane is 1.0%.

[0114] Example 8

[0115] This embodiment is identical to Embodiment 1 in all environmental parameters and constants, except that: the proportion of oil-based drill cuttings is 50%, the sintering temperature is 820℃ (*), and the concentration of fluorosilane is 1.0%.

[0116] Example 9

[0117] This embodiment is identical to Embodiment 1 in all environmental parameters and constants, except that: the proportion of oil-based drill cuttings is 50%, the sintering temperature is 1050℃ (*), and the concentration of fluorosilane is 1.0%.

[0118] Example 10

[0119] This embodiment is identical to Embodiment 1 in all environmental parameters and constants, except that it uses a traditional sintering process (0% oil-based drill cuttings, sintering temperature 1200℃, and no fluorosilane treatment).

[0120] Specific work process

[0121] Oil-based drill cuttings residue is pretreated by ball milling and drying, then mixed with crushed low-alumina bauxite, fly ash, and gypsum and granulated to obtain porous core particles. Subsequently, silicon nitride, high-alumina bauxite, and a binder are mixed to form a composite slurry, which is then uniformly coated onto the core surface using a fluidized bed spraying method. High-temperature sintering forms a robust ceramic shell. The sintered ceramic particles are then immersed in a fluorosilane solution for surface treatment, forming a superhydrophobic surface-modified layer. This entire process transforms waste oil-based drill cuttings into a high-strength fracturing proppant. The steps are closely integrated, and through pretreatment, granulation, coating sintering, and surface modification, a high-performance fracturing proppant suitable for oil and gas wells is ultimately produced.

[0122] The technical features described above can be combined in any way. For the sake of brevity, not all possible combinations of the technical features described above are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A high-strength fracturing proppant for oil and gas wells, characterized in that: include (a) A porous core, composed of the following raw materials by weight percentage: 40-60% oil-based drill cuttings powder, 25-35% low-alumina bauxite, 10-20% fly ash, and 3-8% gypsum; (b) A ceramic shell covering the inner core, the ceramic shell being made of 50-70% silicon nitride, 20-40% high-alumina bauxite and 5-10% binder sintered at 850-1000°C; (c) Surface modification layer, a superhydrophobic layer formed on the surface of the ceramic shell by a fluorosilane solution with a concentration of 0.5-2wt%; wherein the fluorosilane solution is a mixture of perfluorooctyltriethoxysilane and hydrogen peroxide.

2. The high-strength fracturing proppant for oil and gas wells as described in claim 1, characterized in that: The low-alumina bauxite The content is 40-50 wt%, and the activity of fly ash is... Content ≥45wt%.

3. The high-strength fracturing proppant for oil and gas wells as described in claim 1, characterized in that: The adhesive is polyethylene glycol or hydroxypropyl methylcellulose.

4. The high-strength fracturing proppant for oil and gas wells as described in claim 1, characterized in that: The high-alumina bauxite Content ≥70wt%.

5. A method for preparing a high-strength fracturing proppant for oil and gas wells, based on the fracturing proppant according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Raw material pretreatment: ball mill the oil-based drill cutting residue to 150-250 mesh and dry it at 80-120℃ for 1-3 hours; crush the low-alumina bauxite to a particle size ≤100 mesh; (2) Core preparation: Mix oil-based drill cuttings powder, low-alumina bauxite, fly ash and gypsum into granules, and cure at a constant temperature and humidity for 5-10 days. The curing conditions are temperature 20-30℃ and relative humidity ≥90%. (3) Outer shell coating: A composite slurry of silicon nitride, high alumina bauxite and binder is sprayed onto the inner core surface using a fluidized bed spraying method and sintered at 850-1000℃ for 1-4h with a heating rate ≤5℃ / min; (4) Surface modification: The sintered particles are immersed in a 0.5-2wt% fluorosilane solution and treated at 40-80℃ for 0.5-2h to form a superhydrophobic layer.

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

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

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

3.

9. The method for preparing a high-strength fracturing proppant for oil and gas wells as described in claim 8, characterized in that: The hydrogen peroxide concentration in the mixture of perfluorooctyltriethoxysilane and hydrogen peroxide is 3-5 wt%.

10. The method for preparing a high-strength fracturing proppant for oil and gas wells as described in claim 5, characterized in that: In step (4), the surface-modified proppant is dried at 60-80℃ for 0.5-1h, and the moisture content of the dried particles is ≤0.5%.

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