Encapsulated proppant as well as preparation process and application thereof

Abstract

The invention relates to the technical field of oil and gas field exploitation, discloses a rubber-coated proppant as well as a preparation process and application thereof, and aims to overcome the defects that an existing quartz sand proppant is insufficient in strength and easy to break and does not have an inorganic salt scale resistance function. The encapsulation proppant is composed of a quartz sand matrix and a covering film, wherein the covering film is formed by compounding bisphenol A epoxy resin, a latent curing agent, an organic silane coupling agent, an anti-scaling functional monomer and long-chain alkyl modified polysiloxane. According to the preparation method, gradient cooling and step-by-step feeding processes are adopted, and chemical bonding of the coupling agent to the matrix, covalent immobilization of the anti-scaling monomer in a resin network and surface enrichment of the hydrophobic agent are realized by accurately controlling the adding sequence of different components in a specific temperature interval. The proppant particles prepared by the invention have low breakage rate, high inorganic salt scale inhibition rate and hydrophobic surface, and the acid solubility and turbidity index of the proppant particles are also improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field exploitation, and in particular to a coated proppant and a preparation process and application thereof. BACKGROUND

[0002] In the stimulation operation of oil and gas fields, hydraulic fracturing is a core technology. The technology forms an artificial fracture with high conductivity in the reservoir by injecting high-pressure fracturing fluid into the formation. In order to keep the fracture open under closure pressure, it is necessary to fill the fracture with solid particulate material called proppant. Quartz sand is one of the most widely used proppant materials due to its abundant reserves and low price.

[0003] However, ordinary quartz sand proppant has inherent performance defects. Especially in the high closure pressure environment of deep or ultra-deep wells, the compressive strength of quartz sand is insufficient, and the particles are prone to breakage. The fine powder produced after breaking can be transported with the fluid, blocking the seepage channels in the fracture, causing the conductivity of the fracture to drop sharply, and seriously affecting the production effect and stable production period of the oil and gas well.

[0004] In order to improve the mechanical properties of quartz sand, the prior art usually adopts the method of coating a layer of resin film on the surface of quartz sand to make coated quartz sand. Although this coating treatment improves the anti-breaking capacity of the proppant to some extent, it still has several deep-seated technical problems. Most of the coating is only physically adhered to the quartz sand matrix, and the interfacial bonding force is weak. In the complex environment of high temperature and high pressure downhole and fluid scouring, the coating has the risk of falling off, thereby losing the protective effect. In addition, conventional coated proppants do not have functionality themselves. For the scaling ions commonly present in formation water, their surfaces cannot inhibit the crystallization and deposition of inorganic salt scale, and after long-term use, the scale layer will cover the surface of the proppant and block the pores, also causing loss of conductivity. At the same time, the surface of conventional coating materials is usually hydrophilic, which may cause water lock effect in the formation, hindering the effective flow of oil and gas. Therefore, developing a new type of proppant that can ensure high strength and integrate anti-scaling, improve surface wettability and other multiple functions is a technical problem to be solved in the field. SUMMARY

[0005] The technical problem to be solved by the present application is that the resin coating of the resin coated proppant in the prior art has insufficient stability in the complex downhole environment, and at the same time, in oil and gas wells with high salinity of formation water, inorganic salt scale is easily formed on the surface and between the pores of the proppant accumulation body, resulting in a decrease in fracture conductivity over time.

[0006] To solve the above technical problems, the present application provides a coated proppant and a preparation process and application thereof.

[0007] The first aspect of the present application provides a coated proppant prepared from the following raw materials by weight: quartz sand matrix: 92-95 parts; bisphenol A type epoxy resin: 3-5 parts; medium temperature latent curing agent: 1-3 parts; organosilane coupling agent: 0.1-0.5 parts; toughening and hydrophobic modifier: 0.2-0.8 parts; anti-fouling functional monomer: 0.2-1.0 parts; lubricant: 0.3-1.0 parts.

[0008] In a specific embodiment, the anti-fouling functional monomer is selected from at least one of taurine, p-aminobenzenesulfonic acid, aminotri-methylene phosphonic acid, and 2-aminoethyl phosphonic acid.

[0009] In a specific embodiment, the toughening and hydrophobic modifier is a long-chain alkyl modified polysiloxane.

[0010] In a specific embodiment, the particle size of the quartz sand matrix is 850 μm-425 μm, and the lubricant is calcium stearate.

[0011] The second aspect of the present application provides a preparation process of a coated proppant, which uses the coated proppant raw material of any one of the above aspects, and includes the following steps: Step S1: heating the quartz sand matrix for pretreatment at a first preset temperature of 180-220°C; Step S2: adding organosilane coupling agent to the pretreated quartz sand matrix for surface activation treatment at a second preset temperature of 150-170°C; Step S3: adding anti-fouling functional monomer and bisphenol A type epoxy resin to the activated quartz sand matrix for coating to form a functionalized inner layer film at a third preset temperature of 100-120°C; Step S4: adding toughening and hydrophobic modifier and medium temperature latent curing agent to the sand particles with the functionalized inner layer film for compounding at a fourth preset temperature of 85-95°C; Step S5: adding lubricant to the product after Step S4 for anti-adhesion treatment at a temperature lower than 70°C, and obtaining the coated proppant after cooling.

[0012] The third aspect of the present application provides an application of a coated proppant, which is the application of the coated proppant of any one of the above aspects to the hydraulic fracturing process of oil and gas exploitation, for supporting the fractured cracks and inhibiting the formation of inorganic salt scale of formation water on the surface and gaps of the proppant.

[0013] To sum up, the present application includes at least one of the following beneficial technical effects: 1. The present application improves the interface bonding stability of the coating by building chemical bonding between the inorganic matrix and the organic coating layer. In the preparation process, the organosilane coupling agent chemically reacts with the hydroxyl groups on the surface of quartz sand and the epoxy resin, forming a covalent bond connection instead of physical adsorption. This chemical connection improves the anti-peeling ability of the coating under high temperature, high pressure and water-based environment, thereby maintaining the structural integrity of the proppant particles and reducing the risk of fine particles caused by coating shedding.

[0014] 2. The present application enables the proppant to have long-acting and non-consumable anti-inorganic scale function. By using anti-scale functional monomers in the form of copolymerization, the functional groups such as sulfonic acid groups or phosphonic acid groups are permanently immobilized on the surface of the coating as part of the molecular skeleton after the epoxy resin is cured. This structure ensures that the anti-scale function will not be lost or degraded due to long-term flushing of the formation fluid, and can continuously inhibit the crystallization and deposition of calcium and magnesium ions in the formation water on the surface of the proppant and in the pores of the accumulation body.

[0015] 3. The present application realizes the synergy of multiple properties through the combination of component compounding and programmed process, and ensures the consistency of product properties. The introduction of toughening and hydrophobic modifier improves the anti-crushing ability of the coating while its hydrophobicity provides a physical barrier for salt scale inhibition. The step-by-step and gradient temperature control preparation process provides conditions for the reaction or dispersion of each component at a specific temperature range, ensuring that the predetermined structure from the interface chemical layer to the functionalized inner layer and then to the composite outer layer is formed, and guaranteeing the repeatability of each performance index of the final product. DETAILED DESCRIPTION

[0016] The present application will be further described in detail below in combination with examples, comparative examples and test examples.

[0017] The sources and specifications of the main raw materials and reagents used in the following examples and comparative examples are as follows. The reagents not specifically mentioned are commercially available analytical pure or higher grade products.

[0018] Bisphenol A type epoxy resin: CAS No. 25085-99-8.

[0019] Medium temperature latent curing agent: Dicyandiamide; CAS No. 461-58-5.

[0020] Organosilane coupling agent: (3-Glycidyloxypropyl) trimethoxysilane; CAS No. 2530-83-8.

[0021] Toughening and hydrophobic modifier: Hydroxyl-terminated long-chain alkyl-modified polydimethylsiloxane.

[0022] Antifouling functional monomer (Taurine): CAS No. 107-35-7; analytical pure, purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0023] Antifouling functional monomer (2-Aminoethylphosphonic acid): CAS No. 2041-14-7.

[0024] Antifouling functional monomer (Aminotris (methylenephosphonic acid)): CAS No. 6419-19-8.

[0025] Lubricant (Calcium stearate): CAS No. 1592-23-0.

[0026] Calcium chloride: CAS No. 10043-52-4; analytical pure.

[0027] Sodium bicarbonate: CAS No. 144-55-8; analytical pure.

[0028] Ethylene diamine tetraacetic acid: CAS No. 60-00-4; analytical pure.

[0029] Hydrochloric acid: CAS No. 7647-01-0.

[0030] Hydrofluoric acid: CAS No. 7664-39-3.

[0031] The toughening and hydrophobic modifier in the embodiments of the present application, i.e. hydroxyl-terminated long-chain alkyl-modified polydimethylsiloxane, can be prepared by the following steps: Raw material preparation: Raw material A: α, ω-dihydroxypolymethylhydrogenosiloxane. It is a random copolymer of polydimethylsiloxane and methylhydrogenosiloxane chain segments, and the two ends of the polymer chain are hydroxyl groups. Its structure contains silicon-hydrogen bonds (Si-H) for subsequent grafting reactions.

[0032] Raw material B: long-chain α-olefin, such as 1-hexadecene (CAS: 629-73-2) or 1-octadecene (CAS: 112-88-9). The length of the alkyl chain determines the hydrophobic properties of the final product.

[0033] Catalyst: Karstedt's catalyst or isopropanol solution of chloroplatinic acid (H2PtCl6).

[0034] Preparation process steps: Step (1), into a reaction vessel equipped with mechanical stirring, thermometer and reflux condenser, 100 parts by weight of raw material A (α, ω-dihydroxypolydimethylhydrosiloxane) and 200 parts by weight of toluene as solvent were added, and the stirring was started to mix them uniformly.

[0035] Step (2), the temperature in the reaction vessel was raised to 75°C, and a catalyst solution in isopropyl alcohol was slowly added dropwise through a dropping funnel, which was 10 ppm of the total mass of the reactants.

[0036] Step (3), 30-40 parts by weight of raw material B (long-chain α-olefin) was started to be added at a constant rate. The dropping speed was controlled so that the temperature in the reaction vessel did not exceed 90°C. After the addition was completed, the reaction was continued at this temperature for 4-6 hours.

[0037] Step (4), the progress of the reaction was monitored by Fourier transform infrared spectroscopy (FTIR) until the characteristic absorption peak of Si-H bond in raw material A near 2160 cm -1 disappeared, indicating that the hydrosilylation reaction was basically completed.

[0038] Step (5), after the reaction was completed, the temperature was raised to 120°C, and the solvent toluene and a small amount of unreacted long-chain α-olefin were removed by vacuum distillation.

[0039] Step (6), the product was cooled to room temperature to obtain a colorless or light yellow viscous liquid, which was the target product of hydroxyl-terminated long-chain alkyl-modified polydimethylsiloxane. The product randomly distributed long-chain alkyl side groups on the polymer backbone, and hydroxyl (-OH) functional groups were retained at both ends of the chain.

[0040] Examples 1-3: Example 1: This example provides a coated proppant.

[0041] Components: Prepared from the following raw materials by weight: Quartz sand matrix (particle size 850 μm-425 μm): 93.5 parts; Bisphenol A type epoxy resin: 4.0 parts; Medium temperature latent curing agent: 2.0 parts; Organic silane coupling agent: 0.3 parts; Toughening and hydrophobic modifier (long-chain alkyl-modified polysiloxane): 0.5 parts; Antifouling functional monomer (taurine): 0.4 parts; Lubricant (calcium stearate): 0.3 parts.

[0042] Preparation process: Including the following steps: Step S1, put 93.5 parts of quartz sand matrix into the mixer, and pre-treat at 200℃; Step S2, reduce the temperature to 160℃, and add 0.3 parts of organosilane coupling agent for surface activation treatment; Step S3, reduce the temperature to 110℃, and sequentially add 0.4 parts of taurine and 4.0 parts of bisphenol A type epoxy resin for coating to form a functionalized inner layer film; Step S4, reduce the temperature to 90℃, and sequentially add 0.5 parts of long-chain alkyl modified polysiloxane and 2.0 parts of medium-temperature latent curing agent for compounding; Step S5, reduce the temperature to 65℃, and add 0.3 parts of calcium stearate for anti-adhesion treatment, and sieve after cooling to obtain the coated proppant finished product.

[0043] Example 2: The present embodiment provides a coated proppant.

[0044] Components: Prepared from the following raw materials by weight parts: Quartz sand matrix (particle size 850μm-425μm): 94.5 parts; Bisphenol A type epoxy resin: 3.0 parts; Medium-temperature latent curing agent: 1.0 parts; Organosilane coupling agent: 0.1 parts; Toughening and hydrophobic modifier (long-chain alkyl modified polysiloxane): 0.2 parts; Anti-fouling functional monomer (2-aminoethyl phosphonic acid): 0.8 parts; Lubricant (calcium stearate): 0.4 parts.

[0045] Preparation process: Including the following steps: Step S1, put 94.5 parts of quartz sand matrix into the mixer, and pre-treat at 180℃; Step S2, reduce the temperature to 150℃, and add 0.1 parts of organosilane coupling agent for surface activation treatment; Step S3, reduce the temperature to 100℃, and sequentially add 0.8 parts of 2-aminoethyl phosphonic acid and 3.0 parts of bisphenol A type epoxy resin for coating to form a functionalized inner layer film; Step S4, reduce the temperature to 85℃, and sequentially add 0.2 parts of long-chain alkyl modified polysiloxane and 1.0 parts of medium-temperature latent curing agent for compounding; Step S5, reduce the temperature to 60℃, and add 0.4 parts of calcium stearate for anti-adhesion treatment, and sieve after cooling to obtain the coated proppant finished product.

[0046] Example 3 The present embodiment provides a coated proppant.

[0047] Components: Prepared from the following raw materials by weight: Quartz sand matrix (particle size 850 μm-425 μm): 92.0 parts; Bisphenol A type epoxy resin: 5.0 parts; Medium temperature latent curing agent: 3.0 parts; Organic silane coupling agent: 0.5 parts; Toughening and hydrophobic modifier (long-chain alkyl modified polysiloxane): 0.8 parts; Antifouling functional monomer (aminotri-methylene phosphonic acid): 1.0 parts; Lubricant (calcium stearate): 0.7 parts.

[0048] Preparation process: Comprising the following steps: Step S1, 92.0 parts of quartz sand matrix is put into a mixer, and pre-processed by heating to 220°C; Step S2, the temperature is lowered to 170°C, and 0.5 parts of organic silane coupling agent is added for surface activation treatment; Step S3, the temperature is lowered to 120°C, and 1.0 parts of aminotri-methylene phosphonic acid and 5.0 parts of bisphenol A type epoxy resin are sequentially added, and coated to form a functional inner layer film; Step S4, the temperature is lowered to 95°C, and 0.8 parts of long-chain alkyl modified polysiloxane and 3.0 parts of medium temperature latent curing agent are sequentially added, and compounded; Step S5, the temperature is lowered to 68°C, and 0.7 parts of calcium stearate is added for anti-blocking treatment, and after cooling, sieved to obtain the coated proppant finished product.

[0049] Comparative Examples 1-3: Comparative Example 1: Compared with Example 1, the difference lies in that no organic silane coupling agent and antifouling functional monomer (taurine) are used in the raw material components; accordingly, in the preparation process, the step S2 of adding organic silane coupling agent is omitted, and no antifouling functional monomer is added in step S3. The rest of the component ratio and process parameters are the same as those of Example 1.

[0050] Comparative Example 2: Compared with Example 1, the difference lies in that no antifouling functional monomer (taurine) is used in the raw material components, and no antifouling functional monomer is added in step S3 of the preparation process. The rest of the component ratio and process parameters are the same as those of Example 1.

[0051] Comparative Example 3: The difference compared with Example 1 is that no organosilane coupling agent is used in the raw material components, and the step S2 of adding the organosilane coupling agent is omitted in the preparation process. The rest of the component ratio and process parameters are the same as Example 1.

[0052] Comparative Example 4: The quartz sand raw sand from the same source, same batch, and same particle size (850 μm-425 μm) as used in Examples 1-3 is directly used without any coating treatment as a benchmark control sample.

[0053] Test Examples 1-3: Test Example 1: Comprehensive Performance Test The coated proppant samples prepared in Examples 1-3, Comparative Examples 1-3, and Comparative Example 4 (quartz sand raw sand) as a benchmark control sample are subjected to the following performance evaluations under the same test standards and environments.

[0054] Test Method: Anti-breaking rate test: The test procedure is carried out in accordance with the Petroleum and Natural Gas Industry Standard SY / T5108-2014. The quantitative sample is placed in a pressure chamber, and is kept under a closed pressure of 52 MPa and 69 MPa for 2 minutes, respectively. After pressure relief, the fine powder mass generated by breaking is collected and weighed, and the percentage of the initial total mass of the sample is calculated, which is the breaking rate.

[0055] Turbidity test: The test procedure is carried out in accordance with the Petroleum and Natural Gas Industry Standard SY / T5108-2014. The quantitative sample is added to deionized water, stirred under specified conditions, and then placed. The turbidity value (FTU) of the supernatant is measured using a turbidimeter.

[0056] Roundness and sphericity evaluation: The evaluation method refers to the chart method in the Petroleum and Natural Gas Industry Standard SY / T5108-2014. The sample particle morphology is compared with the standard chart under a microscope to obtain the evaluation value.

[0057] Acid solubility test: The test procedure is carried out in accordance with the Petroleum and Natural Gas Industry Standard SY / T5108-2014. The dried constant weight sample is placed in a mixed acid solution composed of 12% hydrochloric acid and 3% hydrofluoric acid, and is reacted at 75°C. After washing and drying the sample to constant weight, the percentage of mass loss is measured.

[0058] Experimental Data: Table 1: Comprehensive performance test results of each sample Summary based on test results: The test data of Table 1 shows that the key performance indicators of all the coated samples (Examples 1-3 and Comparative Examples 1-3) have systematically changed compared to the untreated quartz sand raw sand (Comparative Example 4). The data shows that the breakage rate at 52 MPa is reduced from 16.7% to below 10.0%; the turbidity is reduced from 130 FTU to below 30 FTU; the roundness and sphericity are both increased from 0.6 to 0.8; and the acid solubility is also reduced due to the presence of the resin layer. This series of data shows that the resin coating treatment of the quartz sand substrate can effectively improve the mechanical properties, surface finish and chemical stability of the particles.

[0059] Among all the coated samples, the samples of Examples 1-3 exhibit lower breakage rates compared to Comparative Example 1 and Comparative Example 3, which lack specific technical elements. The 52 MPa breakage rates of Examples 1-3 are all below 4.7%, while the breakage rates of Comparative Examples 1 and 3 are both above 9.0%. The difference in data is due to the chemical bonding between the organosilane coupling agent and the epoxy resin coating on the quartz sand substrate in the preparation process of the examples. This interface structure has higher stability under high pressure load, can effectively transfer and disperse stress, thereby reducing the probability of particle breakage.

[0060] In addition, in terms of acid solubility, the values of Examples 1-3 and Comparative Example 3 (all below 2.7%) are significantly lower than those of Comparative Example 1, Comparative Example 2 and the raw sand (all above 5.5%). This phenomenon indicates that after the anti-fouling functional monomer is chemically bonded into the resin network through the preparation process step S3, a dense structure layer with specific functional groups is formed in the inner layer of the coating. This structure layer not only provides anti-fouling function, but also enhances the ability of the entire coating to resist chemical attack by acidic fluids, ultimately resulting in lower acid solubility loss rates.

[0061] Test Example 2: Anti-inorganic salt scale performance test This test is used to quantitatively evaluate the inhibition ability of each proppant sample surface to the crystallization and precipitation of inorganic salts in water.

[0062] Experimental steps: Analytically pure calcium chloride and sodium bicarbonate were used to prepare a scale solution with deionized water as the solvent. The initial concentration of calcium ions (Ca 2+ ) in this solution was 800 mg / L, and the initial concentration of bicarbonate ions (HCO3 - ) was 1952 mg / L. This initial Ca 2 + concentration is denoted as C initial .

[0063] Take 8 clean 250 mL beakers. One of the beakers only adds 200 mL of the above scale-forming solution, without adding any solid sample, as a blank control group. The remaining 7 beakers add 200 mL of scale-forming solution and 20.0 g of samples of Examples 1-3 and Comparative Examples 1-4, respectively.

[0064] Put all 8 beakers in a constant temperature water bath device at 80°C, and stand for 24 hours to accelerate the formation of calcium carbonate scale.

[0065] After the reaction period, take all the beakers out of the water bath and cool to room temperature. Use a microporous filter membrane with a pore size of 0.45 μm to filter the liquid in each beaker to separate all solid particles (including the proppant sample and the generated precipitate).

[0066] Use the ethylenediaminetetraacetic acid (EDTA) standard solution titration method to accurately determine the remaining Ca 2+ concentration in each group of filtrate. The Ca 2+ concentration of the blank control group filtrate is recorded as C blank , and the Ca 2+ concentration of each sample group filtrate is recorded as C sample .

[0067] Calculate the scale inhibition rate of each sample according to the following formula: Scale inhibition rate (%) = [(C sample -C blank ) / (C initial -C blank )] x 100%; Experimental data: Table 2: Test results of each sample's resistance to inorganic salt scale Summary based on test results: The test data in Table 2 shows that the samples of Example 1-3 all exhibit a scale inhibition rate of more than 93%, while the scale inhibition rates of all comparative examples (Comparative Examples 1-4) are less than 7%. This result shows that the proppant prepared using the specific technical solution has a significantly quantified difference in the ability to inhibit the precipitation of inorganic salts in water compared to several reference technical solutions and substrates. This performance difference is a direct reflection of the different surface chemical functionalities of the samples.

[0068] The high scale inhibition rate of the samples of Examples 1-3 is due to the introduction of specific scale inhibition functional monomers in the film structure. In step S3 of the preparation process, the amino group of the monomer (such as taurine or amino phosphonic acid) contained in the monomer molecule undergoes ring-opening addition reaction with the epoxy group of the epoxy resin, allowing the monomer to be covalently bonded to the resin macromolecular network skeleton after cross-linking and curing. In this way, the sulfonic acid or phosphonic acid functional groups with the ability to inhibit crystal nucleation and growth are permanently immobilized on the surface of the proppant particles, effectively interfering with the crystallization process of scale-forming ions in the formation water.

[0069] Comparative Examples 1, 2 and 4 do not contain scale inhibition functional monomers in their components, so their surfaces do not have chemical functional groups that can inhibit the formation of salt scale, and their scale inhibition rate values are close to zero. Although Comparative Example 3 contains scale inhibition functional monomers in its raw material components, the low scale inhibition rate obtained is in clear contrast to the examples. This shows that simply physically mixing scale inhibition functional monomers without chemically bonding them to the resin main body through precise process steps to form stable and effective immobilization cannot achieve the expected scale inhibition technical effect.

[0070] Test Example 3: Hydrophobicity Test This test is used to quantitatively evaluate the water wetting performance of the surface of each proppant sample.

[0071] Experimental Steps: 2.0 g of dry samples of Examples 1-3 and Comparative Examples 1-4 were weighed separately. Each sample was placed in a tablet press mold and pressed at a pressure of 10 MPa for 1 minute to form a circular thin slice with a smooth surface for subsequent testing.

[0072] The prepared sample slice was placed horizontally on the sample stage of the static contact angle measuring instrument.

[0073] A microsyringe was used to accurately titrate a 5 μL drop of deionized water onto the center of the surface of the sample slice.

[0074] After the drop was stable on the sample surface, the side profile image of the drop was captured by the built-in camera of the instrument.

[0075] The analysis software provided with the instrument was used to calculate the angle between the edge of the drop and the surface of the sample slice, i.e. the static water contact angle, by the tangent method. To ensure the reliability of the data, each sample slice was measured 5 times at different positions, and the arithmetic mean was taken as the final result.

[0076] Experimental Data: Table 3: Test Results of Static Water Contact Angle of Each Sample Surface Sample No. Static water contact angle (°) Example 1 102.3 Example 2 105.1 Example 3 99.8 Comparative Example 1 75.8 Comparative Example 2 76.5 Comparative Example 3 74.2 Comparative Example 4 (quartz sand as received) 35.6 Summary Based on Test Results: The test data in Table 3 shows that the surface static water contact angle values of the samples of Examples 1-3 are all above 95°, while the contact angle values of all the comparative samples (Comparative Examples 1-4) are all below 80°. Among them, the contact angle of the quartz sand raw sand (Comparative Example 4) is the lowest, only 35.6°. This set of quantitative data directly reflects that the wettability of the surface of the samples prepared by different technical solutions is fundamentally different.

[0077] The significant increase of the surface contact angle of the sample of the example is a direct result of the introduction of the long-chain alkyl-modified polysiloxane in the film-forming component. In step S4 of the preparation process, this component is added to the epoxy resin system. Due to the low surface energy characteristics of the polysiloxane backbone and the repulsive effect of the non-polar long-chain alkyl group on its side chain, the molecule will migrate and accumulate to the film-air interface during the curing process of the resin. This process results in the outermost surface of the proppant particle being covered by low surface energy chemical groups during the final shaping process, thereby reducing the surface free energy of the solid, making the water droplets on its surface tend to shrink into a spherical shape to reduce the contact area, which macroscopically shows a high contact angle.

[0078] The samples of Comparative Examples 1-3 do not contain long-chain alkyl-modified polysiloxane in their formulations, and their surfaces mainly exhibit the chemical properties of the epoxy resin itself, showing a certain degree of hydrophilicity. The surface of the quartz sand raw sand of Comparative Example 4 is rich in hydrophilic hydroxyl groups, and therefore shows the lowest contact angle. The comparison of the data shows that by adding a specific hydrophobic modifier at a specific preparation stage, the surface wettability of the proppant particles can be effectively changed from hydrophilic to hydrophobic.

[0079] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. An encapsulated proppant, characterized in that, Prepared from the following raw materials by weight: quartz sand matrix 92-95 parts, bisphenol A type epoxy resin 3-5 parts, medium temperature latent curing agent 1-3 parts, organosilane coupling agent 0.1-0.5 parts, toughening and hydrophobic modifier 0.2-0.8 parts, anti-fouling functional monomer 0.2-1.0 parts, lubricant 0.3-1.0 parts.

2. An encapsulated proppant according to claim 1, wherein, The anti-fouling functional monomer is selected from at least one of taurine, p-aminobenzenesulfonic acid, aminotri-methylene phosphonic acid, and 2-aminoethyl phosphonic acid.

3. An encapsulated proppant according to claim 1, wherein, The toughening and hydrophobic modifier is long-chain alkyl modified polysiloxane.

4. The encapsulated proppant of claim 1, wherein, The particle size of the quartz sand matrix is 850 μm-425 μm, and the lubricant is calcium stearate.

5. A process for preparing the encapsulated proppant of any one of claims 1-4, characterized in that, The method comprises the following steps: S1, heating the quartz sand matrix at a first preset temperature for pretreatment; S2, adding organosilane coupling agent to the pretreated quartz sand matrix at a second preset temperature for surface activation treatment; S3, adding anti-fouling functional monomer and bisphenol A type epoxy resin to the activated quartz sand matrix at a third preset temperature for coating to form a functionalized inner layer coating; S4, adding toughening and hydrophobic modifier and medium temperature latent curing agent to the sand particles with the functionalized inner layer coating at a fourth preset temperature for compounding; S5, adding lubricant to S4 at a temperature lower than 70°C for anti-adhesion treatment, and obtaining the coated proppant after cooling.

6. The process of claim 5, wherein the resin is a thermoset resin. The first preset temperature is 180°C-220°C.

7. The process of claim 5, wherein the coating is applied by a process selected from the group consisting of: dip coating, spray coating, and electrostatic coating. The second preset temperature is 150°C-170°C.

8. The process of claim 5, wherein the encapsulated proppant is prepared by the process comprising: The third preset temperature is 100°C-120°C.

9. The preparation process of the overcoating support according to claim 5, characterized in that, The fourth preset temperature is 85°C-95°C.

10. Use of the coated proppant according to any one of claims 1 to 4 in the hydraulic fracturing process of oil and gas exploitation, for supporting the fractured cracks and inhibiting the formation of inorganic salt scale on the surface and gaps of the proppant.

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