Ultra-low density micro-nano proppant for unconventional reservoir fracturing and preparation method of ultra-low density micro-nano proppant

Abstract

The invention relates to the technical field of oil and gas field fracturing, and particularly discloses an ultra-low density micro-nano proppant for unconventional reservoir fracturing and a preparation method of the ultra-low density micro-nano proppant. The proppant is prepared by emulsifying a mixture containing 30-60 wt% of a vinyl monomer, 10-25 wt% of an acrylate monomer and 25-50 wt% of unsaturated resin into micro-nano-scale liquid drops through a compound emulsifier system, and then curing the micro-nano-scale liquid drops. The preparation method comprises the following steps: mixing a resin composition with an emulsifier to form a uniform oil phase, and dispersing the uniform oil phase in a water phase under high-speed shearing to form a micro-nano emulsion; and then complete solidification of the liquid drops is realized under a mild condition through a redox solidification system. The proppant provided by the invention has ultra-low density and micro-nano-scale particle size, can effectively enter and support an ultra-far-end complex micro-nano-scale fracture network in an unconventional reservoir, and greatly improves the oil and gas recovery rate. The structure is complete under the closing pressure of 60 MPa, and the crack flow conductivity can be remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of proppants, in particular to an ultra-low density micro-nano proppant for unconventional reservoir fracturing and a preparation method thereof. BACKGROUND

[0002] The exploitation of oil and gas usually requires the use of hydraulic fracturing technology, and proppants are the key materials for fracturing operations. Proppants, also known as oil fracturing proppants, are used in the exploitation of deep oil and gas wells. After fracturing treatment of high closure pressure and low permeability deposits, the oil and gas bearing rock layers are cracked, and the oil and gas collects from the channels formed by the cracks. At this time, fluid is injected into the rock base to exceed the pressure of the formation breaking strength, causing the rock layers around the wellbore to crack and form a channel with high conductivity. To maintain the cracks formed after fracturing and ensure smooth passage of oil and gas products, a mixture of proppants and fracturing fluid is pumped into the well bottom at high pressure and high speed, filling the rock cracks in the formation, and forming a good flow channel using the compressive strength of the proppants to support the cracks from closing due to stress release, thereby maintaining high conductivity and allowing oil and gas to flow freely, increasing production.

[0003] In the prior art, the preparation method of self-suspending proppants for clear water fracturing, with publication number CN120795896A, changes the solid ceramic particles to a porous reinforced structure, introduces a self-repairing function, uses a bio-based polymer to replace traditional surfactants, improves environmental friendliness, and introduces nano deposition and microwave technology.

[0004] However, the particle size of solid ceramic particles is large, and they cannot penetrate deep into the complex fracture network with fracturing fluid, thereby failing to support the fracture network at the farthest end and failing to provide complete support. SUMMARY

[0005] The purpose of the present application is to provide an ultra-low density micro-nano proppant for unconventional reservoir fracturing and a preparation method thereof, to solve the technical problem of the large particle size of solid ceramic particles, which cannot penetrate deep into the complex fracture network with fracturing fluid, thereby failing to support the fracture network at the farthest end and failing to provide complete support, and to achieve the purpose of having an ultra-low density (bulk density 0.95-1.15 g / cm³) and a micro-nano particle size (particle size mainly distributed in 1-100 microns), being able to effectively enter and support the complex micro-nano scale fracture network at the farthest end in unconventional reservoirs, and greatly improving oil and gas recovery.

[0006] To achieve the above purpose, the present application adopts the following technical solutions: An ultra-low density micro-nano proppant for unconventional reservoir fracturing, comprising a resin composition with the following mass percentage components, which is emulsified and cured to obtain: vinyl monomer 30-60 wt%, acrylate monomer 10-25 wt%, unsaturated resin 25-50 wt%; The support agent has a bulk density of 0.95-1.15 g / cm³, a median particle size D50 of 1-50 microns, and can maintain structural integrity under a closed pressure of 60 MPa.

[0007] As a preferred scheme of the present application, the resin composition further comprises functional nanofillers accounting for 5-30% of the total mass of the resin composition. The functional nanofillers are one or more of nanosilica, nanoalumina, carbon nanotubes, and nanomontmorillonite.

[0008] As a preferred scheme of the present application, the vinyl monomer is selected from one or more of alpha-methylstyrene, vinylpyrrolidone, vinyl versatate, and trimethylolpropane triacrylate.

[0009] As a preferred scheme of the present application, the acrylate monomer is selected from one or more of isobornyl acrylate, stearyl acrylate, ethoxylated bisphenol A dimethacrylate, tripropylene glycol diacrylate (TPGDA), and polyurethane acrylate. The unsaturated resin is a vinyl ester resin or a furan resin.

[0010] Another object of the present application is to provide a preparation method of an ultra-low-density micro-nano support agent for unconventional reservoir fracturing, comprising an ultra-low-density micro-nano support agent for unconventional reservoir fracturing as described above. The method comprises the following steps: Step (1) preparation of an oil phase: uniformly mix a vinyl monomer, an acrylate monomer, an unsaturated resin, a curing agent, optional functional nanofillers, and an emulsifier to form a homogeneous oil phase mixture; Step (2) pre-emulsification: slowly add the oil phase mixture obtained in step (1) to part of the water phase under low-speed stirring to form a coarse emulsion; Step (3) high-pressure homogenization emulsification: pass the coarse emulsion obtained in step (2) through a high-pressure homogenizer, and cycle homogenization 2-5 times under a pressure of 50-150 MPa to form a micro-nano emulsion with concentrated particle size distribution; Step (4) curing and forming: add a promoter to the micro-nano emulsion obtained in step (3), and perform an oxidation-reduction curing reaction at a low temperature of 20-50°C to form cured micro-nano spherical particles; Step (5) post-treatment: after the reaction is completed, perform centrifugal separation, washing, and spray drying to obtain the ultra-low-density micro-nano support agent product.

[0011] As a preferred scheme of the present application, the emulsifier in step (1) is a compound system of Span (Span-80), Tween (Tween-80) and fatty alcohol polyoxyethylene ether (AEO-9), the total addition amount is 2-8wt% of the total mass of the oil phase, and the mass ratio of Span, Tween and AEO-9 is (2-4):(1-2):1.

[0012] As a preferred scheme of the present application, the curing agent in step (4) is one or more of cumene hydroperoxide, tert-butyl peroxybenzoate, di(2-ethylhexyl) peroxydicarbonate and azobis isopropyl cyanide, the addition amount is 0.5-3% of the total mass of the resin composition; the accelerator is one or more of N,N-dimethyl-p-toluidine, manganese isooctanoate and mercaptan compounds (such as dodecyl mercaptan), the addition amount is 0.2-1% of the total mass of the resin composition.

[0013] As a preferred scheme of the present application, the curing reaction in step (4) is carried out in an ultrasonic oscillation environment to promote the decomposition of the curing agent and the generation of free radicals, and to ensure the uniformity of the curing inside and outside the micro-nanoparticles.

[0014] The beneficial effects of the present application are: 1. By selecting specific resin and monomer combination, and using Span-Tween-AEO compound emulsifier and high-pressure homogenization technology, the scale production of micro-nano spherical particles with good monodispersity is successfully realized. The innovative low-temperature oxidation-reduction curing system combined with ultrasonic auxiliary technology ensures the uniformity and integrity of the micron-sized droplets curing. The obtained product has ultra-low density and small particle size, and can penetrate into the end of the complex fracture network with fracturing fluid, and effectively support the micro-nano cracks. At the same time, the temperature resistance and surface properties can be flexibly adjusted through formula design, which meets the harsh requirements of different geological conditions, and provides strong technical support for the efficient development of unconventional oil and gas resources. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0016] Embodiment 1: An ultra-low density micro-nano proppant for unconventional reservoir fracturing is prepared by emulsifying and curing a resin composition comprising the following mass percentage components: vinyl monomer 30-60wt%, acrylic ester monomer 10-25wt%, and unsaturated resin 25-50wt%.

[0017] The support agent has a bulk density of 0.95-1.15 g / cm3, a median particle size D50 of 1-50 microns, and can maintain structural integrity under a closed pressure of 60 MPa.

[0018] The resin composition further comprises functional nanofillers in an amount of 5-30% of the total mass of the resin composition. The functional nanofillers are one or more of nanosilica, nanoalumina, carbon nanotubes, and nanomontmorillonite.

[0019] The vinyl monomer is one or more of alpha-methylstyrene, vinylpyrrolidone, vinyl versatate, and trimethylolpropane triacrylate.

[0020] The acrylate monomer is one or more of isobornyl acrylate, stearyl acrylate, ethoxylated bisphenol A dimethacrylate, and tripropylene glycol diacrylate (TPGDA); and the unsaturated resin is a vinyl ester resin or a furan resin.

[0021] Embodiment 2: A method for preparing an ultra-low-density micro-nano support agent for fracturing of unconventional reservoirs, comprising the ultra-low-density micro-nano support agent for fracturing of unconventional reservoirs as described above. The method comprises the following steps: Step (1): preparing an oil phase, wherein the oil phase is prepared by mixing the vinyl monomer, the acrylate monomer, the unsaturated resin, the curing agent, the optional functional nanofillers, and the emulsifier.

[0022] The emulsifier is a complex system of Span-80, Tween-80, and fatty alcohol polyoxyethylene ether (AEO-9), and the total amount of the emulsifier is 2-8 wt% of the total mass of the oil phase, and the mass ratio of Span, Tween, and AEO-9 is (2-4):(1-2):1.

[0023] Step (2): pre-emulsification, wherein the oil phase mixture obtained in step (1) is slowly added to part of the water phase under low-speed stirring to form a coarse emulsion. Step (3): high-pressure homogenization emulsification, wherein the coarse emulsion obtained in step (2) is subjected to 2-5 cycles of homogenization under a pressure of 50-150 MPa by using a high-pressure homogenizer to form a micro-nano emulsion with concentrated particle size distribution. Step (4): curing and forming, wherein the micro-nano emulsion obtained in step (3) is added with a promoter, and an oxidation-reduction curing reaction is performed at a low temperature of 20-50°C to form cured micro-nano spherical particles.

[0024] The curing agent is one or more of cumene hydroperoxide, tert-butyl peroxybenzoate, di(2-ethylhexyl) peroxydicarbonate, and azobisdimethylvaleronitrile, and the addition amount is 0.5-3% of the total mass of the resin composition; the accelerator is one or more of N,N-dimethyl-p-toluidine, manganese isooctoate, and a thiol compound, and the addition amount is 0.2-1% of the total mass of the resin composition.

[0025] In the present embodiment, the thiol compound is, but is not limited to, dodecyl mercaptan.

[0026] In the present embodiment, the curing reaction is carried out in an ultrasonic oscillation environment to promote the decomposition of the curing agent and the generation of free radicals, and to ensure uniform curing inside and outside the micro-nanoparticles.

[0027] Step (5) post-treatment: after the reaction is completed, centrifugal separation, washing, and spray drying are performed to obtain the ultra-low-density micro-nano proppant product.

[0028] As shown above: by selecting a specific combination of resin and monomer, and using a Span-Tween-AEO compound emulsifier and high-pressure homogenization technology, the large-scale production of micro-nano-sized, well-dispersed spherical particles is successfully achieved. The innovative low-temperature oxidation-reduction curing system combined with ultrasonic auxiliary technology ensures the uniformity and integrity of the micron-sized droplet curing. The obtained product has ultra-low density and small particle size, and can penetrate deep into the end of the complex fracture network with the fracturing fluid, effectively supporting the micro-nano cracks. At the same time, the temperature resistance and surface properties can be flexibly adjusted through formula design, meeting the harsh requirements of different geological conditions, and providing strong technical support for the efficient development of unconventional oil and gas resources.

[0029] Example 3, a formula of an ultra-low-density micro-nano proppant for fracturing of unconventional reservoirs: Resin composition: 40 parts of vinyl ester resin (DERAKANE MOMENTUM 411-350), 45 parts of alpha-methylstyrene, and 15 parts of isobornyl acrylate.

[0030] Functional nanofiller: oil-wet treated nanosilica, accounting for 10% of the total mass of the resin composition.

[0031] Emulsifier: Span-80 (3 parts), Tween-80 (1.5 parts), and AEO-9 (1 part), totaling 5.5 parts.

[0032] Curing agent: tert-butyl peroxybenzoate (TBPB), accounting for 1.5% of the total mass of the resin composition.

[0033] Aqueous phase: deionized water (oil phase to water phase mass ratio of 1:3), containing 0.5% of magnesium chloride as an electrolyte.

[0034] Promoter: N,N-dimethyl-p-toluidine, 0.5% of the total mass of the resin composition.

[0035] Preparation method: Preparation of oil phase: Mix the vinyl ester resin, alpha-methyl styrene, isobornyl acrylate, nano-silica, emulsifier and tert-butyl peroxybenzoate, and mechanically stir for 1 hour to form a uniform transparent oil phase.

[0036] Pre-emulsification: Slowly add the oil phase to half the amount of water phase under stirring at 300 rpm to form a milky white coarse emulsion.

[0037] High-pressure homogenization emulsification: Introduce the coarse emulsion into a high-pressure homogenizer, and cycle homogenization 3 times at a pressure of 100 MPa to obtain a semi-transparent, blueish micro-nano emulsion.

[0038] Curing and molding: Add the remaining water phase to the emulsion to dilute the concentration, add N,N-dimethyl-p-toluidine under stirring in a 25°C water bath, and apply ultrasonic wave assisted reaction at a frequency of 40 kHz for 6 hours.

[0039] Post-processing: After the reaction is completed, use a high-speed centrifuge to separate the solid particles at 8000 rpm, wash them with ethanol and deionized water three times, and finally dry them through a spray dryer (inlet temperature 150°C) to obtain a free-flowing white micro-nano powder.

[0040] Product performance test: Bulk density: 1.02 g / cm³ (according to SY / T5108-2014) Particle size distribution (laser particle size analyzer): D10: 2.1 μm, D50: 18.5 μm, D90: 65.3 μm.

[0041] Micro-morphology (SEM): The particles are regular spherical and smooth in surface.

[0042] Pressure resistance: Fill the proppant into a specially designed mold, and maintain the pressure at 60 MPa for 30 minutes. After pressure relief, observe through SEM, and most of the particles remain intact without large-scale crushing.

[0043] Flow conductivity contribution: Mix with conventional 40-70 mesh ceramic particles at a mass ratio of 1:9, and test at 50 MPa. The flow conductivity of the mixed proppant is about 15% higher than that of pure ceramic particles, which proves that it effectively fills the small gaps between the ceramic particles and improves the overall propping efficiency.

[0044] Example 4: Preparation of high temperature resistant micro-nano proppant This example aims to prepare a micro-nano proppant suitable for higher temperature reservoirs (about 120°C).

[0045] Formulation: Resin composition: furan resin 35 parts, VeoVa10 50 parts, TPGDA 15 parts.

[0046] Functional nanofiller: nano-alumina, accounting for 15% of the total mass of the resin composition.

[0047] Emulsifier: Span-80 (2.5 parts), Tween-80 (1 part), AEO-9 (0.8 parts).

[0048] Curing agent: di (2-ethylhexyl) peroxide (EHP), accounting for 2% of the total mass of the resin composition.

[0049] Aqueous phase: deionized water (oil phase: aqueous phase = 1:4).

[0050] Promoter: manganese isooctoate, accounting for 0.8% of the total mass of the resin composition.

[0051] Preparation method: the preparation steps are the same as in Example 1, the high-pressure homogenization pressure is adjusted to 80 MPa, the curing temperature is 35°C, and no ultrasonic assistance is used. Product performance test: Bulk density: 1.08 g / cm³.

[0052] Particle size distribution: D50: 8.7 μm.

[0053] Temperature aging test: after aging in 2% KCl solution at 120°C for 7 days, the particle morphology is stable, and the glass transition temperature (Tg) is increased from 105°C before aging to 112°C, indicating that the crosslinked network is further strengthened at high temperature, and has excellent long-term temperature resistance.

[0054] Example 5: Surface-active micro-nano proppant with adjustable surface activity This embodiment introduces special monomers and promoters to give the proppant the property of adjustable surface activity.

[0055] Formulation: Resin composition: vinyl ester resin 38 parts, trimethylolpropane triacrylate 20 parts, stearyl acrylate 30 parts, vinyl pyrrolidone 12 parts.

[0056] Emulsifier: Span-80 (3.2 parts), Tween-80 (1.8 parts), AEO-9 (1.2 parts).

[0057] Curing agent: azobis isodecanitrile (ABVN), accounting for 1.8% of the total mass of the resin composition.

[0058] Aqueous phase: deionized water (oil phase: aqueous phase = 1:2.5).

[0059] Promoter: dodecyl mercaptan, 0.6% of the total mass of the resin composition.

[0060] Dodecyl mercaptan has both chain transfer agent and promoter functions, and can impart hydrophobicity to the surface of the particles.

[0061] Preparation method: The preparation steps are the same as those in Example 1, the high-pressure homogenization pressure is 120 MPa, the curing temperature is 40°C, and ultrasonic assistance is used.

[0062] Product performance test: Bulk density: 0.98 g / cm³.

[0063] Particle size distribution: D50: 25.1 μm.

[0064] Surface wettability: the contact angle with water is 145°, showing superhydrophobic properties. This property makes it easier to disperse in the oil phase and strongly adsorbed on the surface of oil-wet reservoir rocks, greatly reducing the risk of particle migration caused by water flow, especially suitable for strong oil-wet shale reservoirs.

[0065] In summary: by selecting specific resin and monomer combination, and using Span-Tween-AEO compound emulsifier and high-pressure homogenization technology, the large-scale preparation of micro-nano spherical particles with good monodispersity is successfully realized. The innovative low-temperature redox curing system combined with ultrasonic assistance technology ensures the uniformity and integrity of the micron-sized droplets. The product has ultra-low density and small particle size, and can penetrate deep into the complex fracture network with fracturing fluid, effectively supporting micro-nano cracks. At the same time, the temperature resistance and surface properties can be flexibly adjusted through formula design to meet the harsh requirements of different geological conditions, providing strong technical support for the efficient development of unconventional oil and gas resources.

[0066] Example 6: Comparison of excellent suspension and migration performance brought by ultra-low density This example aims to prove the significant advantages of the proppant of the present application in suspension and fracture migration ability through comparative experiments.

[0067] Test samples: (1) The product of the present application: the proppant prepared in Example 3 (bulk density 1.02 g / cm³, D50: 18.5 μm).

[0068] (2) Comparative Example A: commercially available 100-mesh fine powder ceramic (main component is alumina, bulk density: 1.70 g / cm³, D50: 150 μm).

[0069] (3) Comparative Example B: nano-silica powder (oil-wet treated, D50: 800 nm).

[0070] Static suspension stability test: Method: Disperse three kinds of samples in the same linear gel fracturing fluid (concentration 0.3%) at a concentration of 1wt%, pour into a graduated sedimentation column, observe and record the sedimentation situation.

[0071] Results: (1) Comparative example A (fine powder ceramic): rapidly settled to the bottom within 10 minutes, the supernatant became clear, and the sedimentation rate was > 50 cm / min.

[0072] (2) Comparative example B (nano-silica): a stable colloid was formed initially, but obvious aggregation and sedimentation occurred after 30 minutes, forming a loose sediment layer, with poor stability and easy agglomeration.

[0073] (3) Product of the application: after 2 hours of standing, the system remained uniformly milky white without obvious sedimentation interface. After 24 hours, only a slight clear layer appeared, and the sedimentation volume was less than 10% of the total volume. The calculated static sedimentation rate was < 0.1 cm / min.

[0074] Microcrack migration and propping experiment: Method: Mix the three samples with the fracturing fluid, and under the same pumping pressure, displace through a transparent microfluidic chip with a 10-50 μm artificial microcrack network, and observe the migration and placement behavior.

[0075] Results: Comparative example A (fine powder ceramic): almost all were blocked at the entrance of the main channel and could not enter the microcracks, forming a filter cake at the entrance.

[0076] Comparative example B (nano-silica): although it could enter the microcracks, due to strong Brownian motion and van der Waals forces, a large number of particles were adsorbed on the crack wall, forming a thick adsorption layer, rather than forming effective support in the middle of the crack.

[0077] Product of the application: under the synergistic effect of ultra-low density and suitable particle size, it smoothly enters and fills the entire microcrack network with the fracturing fluid. After pump stop, the particles are uniformly distributed in the cracks, forming effective support points.

[0078] Conclusion: The ultra-low density micro-nano proppant of the application combines the small size of inorganic nano materials and the low density advantage of organic polymer materials, achieving long-term stable suspension and efficient and deep migration and placement in the micro-nano crack network, solving the industry problem that traditional materials cannot enter or cannot effectively support after entering.

[0079] Example 7: verification of the large-scale improvement effect on microcrack conductivity This example quantifies the contribution of the proppant of the present application to the conductivity of microfractures through core flow experiments to verify the technical effect of "nearly 100 times higher".

[0080] Test samples: Experimental group: The proppant prepared in Example 3 was laid in a 50 μm wide artificial fracture at a laying concentration of 5 kg / m².

[0081] Blank control group: A 50 μm artificial fracture of the same specification without any proppant laid.

[0082] Test method: The gas phase conductivity of the experimental group and the blank control group was tested respectively under 2 MPa confining pressure and 10 MPa closure pressure using nitrogen as the medium (according to the microfracture test method revised on the basis of API RP61 standard).

[0083] Test results: Blank control group conductivity: The conductivity of the fracture is extremely low due to the almost complete closure of the fracture under closure pressure, and the measured value is about 0.5 mD·cm.

[0084] Experimental group conductivity: The proppant of the present application provides uniform and stable support points in the fracture, so that the fracture remains an effective flow channel even under closure pressure, and the measured value is about 48 mD·cm.

[0085] Effect comparison: Conductivity improvement multiple = experimental group conductivity / blank control group conductivity ≈ 48 / 0.5 = 96 times.

[0086] Conclusion: The experimental data powerfully prove that the ultra-low density micro-nano proppant of the present application can create and maintain extremely high flow channels for micro-nano fractures that originally have no conductivity, and the conductivity is improved by nearly 100 times, which has revolutionary significance for unlocking the huge microfracture resources in unconventional reservoirs.

[0087] Example 8: Comparison of long-term conductivity retention with rigid nanomaterials This example demonstrates the performance advantage of the proppant of the present application under long-term stress.

[0088] Test samples: Product of the present application: Product of Example 3.

[0089] Comparative Example C: High-strength rigid ceramic nanoparticles (D50: 2 μm).

[0090] Test method: The two samples were laid in microfractures at the same concentration, and the change of their conductivity with time (120 hours) was continuously tested under 40 MPa closure pressure.

[0091] Test results: Comparative Example C (rigid ceramic nanoparticles): The initial flow conductivity is high (35 mD·cm), but due to its high rigidity and brittleness, some particles are broken under long-term high pressure, producing small fragments to block the flow channel, and the flow conductivity decreases by more than 60% after 120 hours.

[0092] The product of the application: thanks to the toughness and elasticity of the resin-based material, it will deform slightly under high pressure rather than break, and can better adapt to the changes in the fracture surface and redistribute stress. The initial flow conductivity is 30 mD·cm, and the flow conductivity remains stable during the 120-hour test, with a decay rate of less than 5%.

[0093] Conclusion: The proppant of the application not only has excellent initial flow conductivity, but also has excellent retention rate of flow conductivity under long-term formation stress due to its toughness and elasticity, avoiding the problem of rapid decline of flow conductivity caused by the breakage of rigid nanoparticles, and having a longer effective production cycle.

[0094] In summary: through Examples 6, 7 and 8, setting reasonable comparative examples (fine powder ceramic, nano silicon dioxide and rigid ceramic nanoparticles), and introducing static suspension, microscopic migration observation, large-scale flow conductivity improvement quantification, long-term flow conductivity retention and other experiments, the outstanding advantages of the ultra-low density micro-nano proppant in terms of suspension migration and large-scale improvement and maintenance of micro-fracture flow conductivity are systematically and powerfully proved.

[0095] Each device selected in the application is a general standard part or a part known to those skilled in the art, and its structure and principle can be known by those skilled in the art through a technical manual or through a conventional experimental method.

[0096] In the description of the embodiments of the application, unless otherwise explicitly specified and limited, the terms "mounting", "connection" and "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0097] Based on the above ideal embodiments according to the application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the application. The technical scope of the application is not limited to the contents in the specification, and the technical scope must be determined according to the scope of claims.

Claims

1. An ultra-low density micro / nano proppant for unconventional reservoir fracturing, characterized in that, A resin composition comprising the following components in weight percentages is obtained by emulsification and curing: Vinyl monomers 30-60 wt%, acrylate monomers 10-25 wt%, unsaturated resins 25-50 wt%; The proppant has a bulk density of 0.95-1.15 g / cm³, a median particle size D50 of 1-50 micrometers, and can maintain structural integrity under a closure pressure of 60 MPa.

2. The ultra-low density micro / nano proppant for unconventional reservoir fracturing as described in claim 1, characterized in that, The resin composition also contains 5-30% by weight of functional nanofillers; The functional nanofiller is one or more of nano-silica, nano-alumina, carbon nanotubes, and nano-montmorillonite.

3. The ultra-low density micro / nano proppant for unconventional reservoir fracturing as described in claim 2, characterized in that, The vinyl monomer is selected from one or more of α-methylstyrene, vinylpyrrolidone, vinyl tert-carbonate, and trimethylolpropane triacrylate.

4. The ultra-low density micro / nano proppant for unconventional reservoir fracturing as described in claim 3, characterized in that, The acrylate monomer is selected from one or more of isobornyl acrylate, octadecyl acrylate, bisphenol A dimethacrylate, tripropylene glycol diacrylate (TPGDA), and polyurethane acrylate. The unsaturated resin is a vinyl ester resin or a furan resin.

5. A method for preparing an ultra-low density micro / nano proppant for unconventional reservoir fracturing, characterized in that, Including an ultra-low density micro / nano proppant for unconventional reservoir fracturing as described in any one of claims 1-4; It includes the following steps: Step (1) Preparation of oil phase: Mix vinyl monomer, acrylate monomer, unsaturated resin, curing agent, optional functional nanofiller and emulsifier evenly to form a homogeneous oil phase mixture; Step (2) Pre-emulsification: The oil phase mixture obtained in step (1) is slowly added to a portion of the aqueous phase under low-speed stirring to form a crude emulsion; Step (3) High-pressure homogenization emulsification: The crude emulsion obtained in step (2) is passed through a high-pressure homogenizer and homogenized 2-5 times under a pressure of 50-150 MPa to form a micro-nano-scale emulsion with a concentrated particle size distribution. Step (4) Curing and molding: Add an accelerator to the micro-nano emulsion obtained in step (3) and carry out an oxidation-reduction curing reaction at a low temperature of 20-50℃ to form cured micro-nano spherical particles; Step (5) Post-processing: After the reaction is completed, the product is obtained by centrifugation, washing and spray drying to obtain the ultra-low density micro-nano proppant product.

6. The method for preparing an ultra-low density micro / nano proppant for unconventional reservoir fracturing as described in claim 5, characterized in that, The emulsifier mentioned in step (1) is a compound system of Span, Tween and fatty alcohol polyoxyethylene ether (AEO-9), the total amount of which is added is 2-8 wt% of the total mass of the oil phase, and the mass ratio of Span, Tween and AEO-9 is (2-4):(1-2):

1.

7. The method for preparing an ultra-low density micro / nano proppant for unconventional reservoir fracturing as described in claim 6, characterized in that, The curing agent mentioned in step (4) is one or more of cumene hydroperoxide, tert-butyl peroxide, dicarbonate peroxide, and azobisisobutyronitrile, and its addition amount is 0.5-3% of the total mass of the resin composition; the accelerator is one or more of N,N-dimethyl-p-toluidine, manganese isooctanoate, and thiols, and its addition amount is 0.2-1% of the total mass of the resin composition.

8. The method for preparing an ultra-low density micro / nano proppant for unconventional reservoir fracturing as described in claim 7, characterized in that, The curing reaction in step (4) is carried out in an ultrasonic oscillation environment to promote the decomposition of the curing agent and the generation of free radicals, so as to ensure uniform curing inside and outside the micro-nano particles.