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

Abstract

The application relates to the field of oil and gas field fracturing technology, and particularly discloses an ultra-low-density micro-nano proppant for unconventional reservoir fracturing and a preparation method thereof. The proppant is prepared from a mixture containing 30-60 wt% of a vinyl monomer, 10-25 wt% of an acrylic ester monomer and 25-50 wt% of an unsaturated resin, emulsified into micro-nano scale droplets through a compounded emulsifier system, and then solidified. The preparation method comprises the following steps: mixing the resin composition with the emulsifier to form a uniform oil phase, dispersing the oil phase into an aqueous phase under high-speed shearing to form a micro-nano emulsion; and then realizing complete solidification of the droplets under mild conditions through an oxidation-reduction solidification system. The proppant has ultra-low density and micro-nano scale particle size, can effectively enter and support a super-remote complex micro-nano scale fracture network in an unconventional reservoir, and greatly improves the oil and gas recovery rate. The proppant has a complete structure under a 60MPa closed pressure, and can significantly improve the fracture conductivity.

Description

An ultra-low density micro / nano proppant for unconventional reservoir fracturing and its preparation method Technical Field

[0001] This invention relates to the technical field of proppant, and more particularly to an ultra-low density micro / nano proppant for unconventional reservoir fracturing and its preparation method. Background Technology

[0002] Oil and gas extraction typically requires hydraulic fracturing technology, and proppant is a key material in fracturing operations. Also known as oil fracturing proppant, proppant is used in deep oil and gas well production. After fracturing in high-pressure, low-permeability deposits, the oil and gas-bearing rock formations are fractured, allowing oil and gas to flow through the channels created by the fractures. At this point, fluid is injected into the rock matrix at pressures exceeding the formation's fracturing strength, causing fractures to form around the wellbore and creating a highly conductive channel. To maintain the fractures created after fracturing and ensure the smooth flow of oil and gas products, a mixture of proppant and fracturing fluid is pumped into the wellbore at high pressure and speed using hydraulic fracturing. This mixture fills the rock fractures, utilizing the proppant's pressure resistance to create a good flow channel, preventing the fractures from closing due to stress release. This maintains high conductivity, ensuring smooth oil and gas flow and increasing production.

[0003] In the prior art, the preparation method of self-suspended proppant for water fracturing, disclosed in CN120795896A, changes the solid ceramsite to a porous reinforced structure, introduces self-healing function, uses bio-based polymers to replace traditional surfactants to improve environmental friendliness, and introduces nano-deposition and microwave technology.

[0004] However, solid ceramic granules have a large particle size and cannot penetrate deep into the end of the complex fracture network with the fracturing fluid, thus failing to support the end of the fracture network and providing complete support. Summary of the Invention

[0005] The purpose of this invention is to provide an ultra-low density micro / nano proppant for unconventional reservoir fracturing and its preparation method, in order to solve the technical problem that solid ceramic particles have a large particle size and cannot penetrate into the outermost part of the complex fracture network with the fracturing fluid, thus failing to support the outermost fracture network and achieve complete support. The invention achieves ultra-low density (volume density 0.95-1.15 g / cm³) and micro / nano-scale particle size (particle size mainly distributed in 1-100 micrometers), which can effectively enter and support the complex micro / nano-scale fracture network at the far end of unconventional reservoirs, thereby significantly improving oil and gas recovery.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An ultra-low density micro / nano proppant for unconventional reservoir fracturing is prepared by emulsification and curing of a resin composition comprising the following components in weight percentages:

[0008] Vinyl monomers 30-60 wt%, acrylate monomers 10-25 wt%, unsaturated resins 25-50 wt%;

[0009] 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.

[0010] As a preferred embodiment of the present invention, the resin composition further comprises 5-30% by weight of a functional nanofiller.

[0011] The functional nanofiller is one or more of nano-silica, nano-alumina, carbon nanotubes, and nano-montmorillonite.

[0012] As a preferred embodiment of the present invention, the vinyl monomer is selected from one or more of α-methylstyrene, vinylpyrrolidone, vinyl tert-carbonate, and trimethylolpropane triacrylate.

[0013] As a preferred embodiment of the present invention, the acrylate monomer is selected from one or more of isobornyl acrylate, octadecyl acrylate, bisphenol A dimethacrylate, tripropylene glycol diacrylate (TPGDA), and polyurethane acrylate.

[0014] The unsaturated resin is a vinyl ester resin or a furan resin.

[0015] Another object of the present invention is to provide a method for preparing an ultra-low density micro / nano proppant for unconventional reservoir fracturing, including an ultra-low density micro / nano proppant for unconventional reservoir fracturing as described above.

[0016] It includes the following steps:

[0017] 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;

[0018] 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;

[0019] 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.

[0020] 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;

[0021] 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.

[0022] As a preferred embodiment of the present invention, the emulsifier in step (1) is a compound system of Span-80, Tween-80 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.

[0023] As a preferred embodiment of the present invention, the curing agent in step (4) is one or more of cumene hydroperoxide, tert-butyl peroxide, di(2-ethylhexyl) percarbonate, 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 thiol compounds (such as dodecyl mercaptan), and its addition amount is 0.2-1% of the total mass of the resin composition.

[0024] As a preferred embodiment of the present invention, 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.

[0025] The beneficial effects of this invention are:

[0026] 1. By selecting specific resin and monomer combinations and employing a Span-Tween-AEO compound emulsifier and high-pressure homogenization technology, the large-scale preparation of micro / nano-sized, highly monodisperse spherical particles was successfully achieved. An innovative low-temperature redox curing system combined with ultrasonic-assisted technology ensured the uniformity and integrity of the solidification of micron-sized droplets. The resulting product has ultra-low density and tiny particle size, allowing it to penetrate deep into the ends of complex fracture networks with fracturing fluid, effectively supporting micro / nano fractures. Furthermore, its temperature resistance and surface properties can be flexibly controlled through formulation design to meet the stringent requirements of different geological conditions, providing strong technical support for the efficient development of unconventional oil and gas resources. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1:

[0029] An ultra-low density micro / nano proppant for unconventional reservoir fracturing is prepared by emulsification and curing of a resin composition comprising the following components in weight percentage: 30-60 wt% vinyl monomer, 10-25 wt% acrylate monomer, and 25-50 wt% unsaturated resin.

[0030] 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.

[0031] The resin composition also contains 5-30% functional nanofillers by weight.

[0032] The functional nanofiller is one or more of nano-silica, nano-alumina, carbon nanotubes, and nano-montmorillonite.

[0033] The vinyl monomer is selected from one or more of α-methylstyrene, vinylpyrrolidone, vinyl tert-carbonate, and trimethylolpropane triacrylate.

[0034] 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.

[0035] Example 2: A method for preparing an ultra-low density micro / nano proppant for unconventional reservoir fracturing, comprising the above-mentioned ultra-low density micro / nano proppant for unconventional reservoir fracturing;

[0036] It includes the following steps:

[0037] 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.

[0038] The emulsifier is a compound system of Span-80, Tween-80 and fatty alcohol polyoxyethylene ether (AEO-9), and its total addition amount 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.

[0039] 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;

[0040] 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 50-150MPa to form a micro-nano-scale emulsion with a concentrated particle size distribution.

[0041] 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.

[0042] The intermediate curing agent is one or more of cumene hydroperoxide, tert-butyl peroxide, di(2-ethylhexyl) percarbonate, 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.

[0043] In this embodiment, the thiol compound used is, but is not limited to, dodecyl thiol.

[0044] In this 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, ensuring uniform curing inside and outside the micro-nano particles.

[0045] Step (5) Post-processing: After the reaction is completed, the product is centrifuged, washed and spray-dried to obtain an ultra-low density micro-nano proppant product.

[0046] In summary, by selecting specific resin and monomer combinations and employing a Span-Tween-AEO compound emulsifier and high-pressure homogenization technology, the large-scale preparation of micro / nano-sized, highly monodisperse spherical particles was successfully achieved. The innovative low-temperature redox curing system combined with ultrasonic-assisted technology ensured the uniformity and integrity of the micron-sized droplet solidification. The resulting product has ultra-low density and tiny particle size, allowing it to penetrate deep into the ends of complex fracture networks with fracturing fluid, effectively supporting micro / nano fractures. Furthermore, its temperature resistance and surface properties can be flexibly controlled through formulation design to meet the stringent requirements of different geological conditions, providing strong technical support for the efficient development of unconventional oil and gas resources.

[0047] Example 3, a formulation of an ultra-low density micro / nano proppant for unconventional reservoir fracturing:

[0048] Resin composition: 40 parts vinyl ester resin (DERAKANE MOMENTUM 411-350), 45 parts α-methylstyrene, and 15 parts isobornyl acrylate.

[0049] Functional nanofiller: oleophilic treated nano-silica, accounting for 10% of the total mass of the resin composition.

[0050] Emulsifiers: Span-80 (3 parts), Tween-80 (1.5 parts), AEO-9 (1 part), total 5.5 parts.

[0051] Curing agent: tert-butyl peroxide (TBPB), accounting for 1.5% of the total mass of the resin composition.

[0052] Aqueous phase: deionized water (oil phase to water phase mass ratio of 1:3), containing 0.5% magnesium chloride as electrolyte.

[0053] Accelerator: N,N-dimethyl-p-toluidine, accounting for 0.5% of the total mass of the resin composition.

[0054] Preparation method:

[0055] Preparation of the oil phase: Mix vinyl ester resin, α-methylstyrene, isobornyl acrylate, nano silica, emulsifier and tert-butyl peroxide, and mechanically stir for 1 hour until a uniform and transparent oil phase is formed.

[0056] Pre-emulsification: While stirring at 300 rpm, slowly add the oil phase to half of the aqueous phase to form a milky white crude emulsion.

[0057] High-pressure homogenization emulsification: The crude emulsion is introduced into a high-pressure homogenizer and homogenized three times under a pressure of 100 MPa to obtain a translucent, bluish micro-nano emulsion.

[0058] Curing and molding: The remaining aqueous phase is added to the emulsion to dilute the concentration. N,N-dimethyl-p-toluidine is added while stirring in a 25°C water bath, and ultrasonic waves at a frequency of 40kHz are applied to assist the reaction for 6 hours.

[0059] Post-processing: After the reaction was completed, the solid particles were separated by centrifugation at 8000 rpm using a high-speed centrifuge. The particles were washed three times with ethanol and deionized water, and finally dried by spray dryer (inlet temperature 150℃) to obtain free-flowing white micro-nano powder.

[0060] Product performance testing:

[0061] Bulk density: 1.02 g / cm³ (according to SY / T5108-2014)

[0062] Particle size distribution (laser particle size analyzer): D10: 2.1μm, D50: 18.5μm, D90: 65.3μm.

[0063] Microscopic morphology (SEM): The particles are regular spherical with smooth surfaces.

[0064] Pressure resistance: The proppant was filled into a special mold and held under a closed pressure of 60 MPa for 30 minutes. After depressurization, SEM observation showed that the vast majority of particles remained intact, and no large-scale breakage occurred.

[0065] Contribution to flow conductivity: When mixed with conventional 40-70 mesh ceramsite at a mass ratio of 1:9, the flow conductivity of the mixed proppant was increased by about 15% compared with that of pure ceramsite at 50MPa, proving that it effectively filled the tiny gaps between the ceramsite particles and improved the overall proppant efficiency.

[0066] Example 4: Preparation of high-temperature resistant micro / nano proppant

[0067] This embodiment aims to prepare micro / nano proppant suitable for reservoirs at higher temperatures (around 120°C).

[0068] formula:

[0069] Resin composition: 35 parts furan resin, 50 parts ethylene tert-carbonate (VeoVa10), and 15 parts tripropylene glycol diacrylate (TPGDA).

[0070] Functional nanofiller: nano-alumina, accounting for 15% of the total mass of the resin composition.

[0071] Emulsifiers: Span-80 (2.5 parts), Tween-80 (1 part), AEO-9 (0.8 parts).

[0072] Curing agent: di(2-ethylhexyl) peroxide dicarbonate (EHP), accounting for 2% of the total mass of the resin composition.

[0073] Aqueous phase: Deionized water (oil phase: aqueous phase = 1:4).

[0074] Accelerator: Manganese isooctanoate, accounting for 0.8% of the total mass of the resin composition.

[0075] Preparation method: The preparation steps are the same as in Example 1, except that the high-pressure homogenization pressure is adjusted to 80 MPa, the curing temperature is 35℃, and ultrasonic assistance is not used. Product performance testing:

[0076] Bulk density: 1.08 g / cm³.

[0077] Particle size distribution: D50: 8.7 μm.

[0078] Temperature resistance aging test: After aging in 2% KCl solution at 120℃ for 7 days, the particle morphology is stable and the glass transition temperature (Tg) increases from 105℃ before aging to 112℃, indicating that its cross-linking network is further strengthened at high temperature and has excellent long-term temperature resistance.

[0079] Example 5: Micro / Nano Support with Adjustable Surface Activity This example introduces special monomers and promoters to endow the support with adjustable surface activity.

[0080] formula:

[0081] Resin composition: 38 parts vinyl ester resin, 20 parts trimethylolpropane triacrylate, 30 parts octadecyl acrylate, and 12 parts vinylpyrrolidone.

[0082] Emulsifiers: Span-80 (3.2 parts), Tween-80 (1.8 parts), AEO-9 (1.2 parts).

[0083] Curing agent: azobisisobutyronitrile (ABVN), accounting for 1.8% of the total mass of the resin composition.

[0084] Aqueous phase: Deionized water (oil phase: aqueous phase = 1:2.5).

[0085] Accelerator: Dodecyl mercaptan, accounting for 0.6% of the total mass of the resin composition.

[0086] Dodecyl mercaptan functions as both a chain transfer agent and a accelerator, and can impart hydrophobicity to the particle surface.

[0087] Preparation method:

[0088] The preparation steps are the same as in Example 1, with a high-pressure homogenization pressure of 120 MPa, a curing temperature of 40°C, and ultrasonic assistance.

[0089] Product performance testing:

[0090] Bulk density: 0.98 g / cm³.

[0091] Particle size distribution: D50: 25.1 μm.

[0092] Surface wettability: With a contact angle of 145° with water, it exhibits superhydrophobic properties. This property makes it easier to disperse in the oil phase and strongly adsorbs onto the surface of oil-wet reservoir rocks, greatly reducing the risk of particle migration caused by water flow, making it particularly suitable for highly oil-wet shale reservoirs.

[0093] In summary, by selecting specific resin and monomer combinations and employing a Span-Tween-AEO compound emulsifier and high-pressure homogenization technology, the large-scale preparation of micro / nano-sized, highly monodisperse spherical particles was successfully achieved. The innovative low-temperature redox curing system combined with ultrasonic-assisted technology ensured the uniformity and integrity of the micron-sized droplet solidification. The resulting product has ultra-low density and tiny particle size, allowing it to penetrate deep into the ends of complex fracture networks with fracturing fluid, effectively supporting micro / nano fractures. Furthermore, its temperature resistance and surface properties can be flexibly controlled through formulation design to meet the stringent requirements of different geological conditions, providing strong technical support for the efficient development of unconventional oil and gas resources.

[0094] Example 6: Comparison of superior suspension and transport properties resulting from ultra-low density

[0095] This embodiment aims to demonstrate, through comparative experiments, the significant advantages of the proppant of the present invention in terms of suspension and crack transport capabilities compared to other inorganic micro / nano materials.

[0096] Test sample:

[0097] (1) Product of the present invention: proppant prepared in Example 3 (bulk density 1.02 g / cm³, D50: 18.5 μm).

[0098] (2) Comparative Example A: Commercially available 100-mesh fine ceramsite (main component is bauxite, bulk density: 1.70 g / cm³, D50: 150 μm).

[0099] (3) Comparative Example B: Nano silica powder (oil-loving treatment, D50: 800nm).

[0100] Static suspension stability test:

[0101] Method: The three samples were dispersed at a concentration of 1 wt% in the same linear gel fracturing fluid (concentration 0.3%), poured into a graduated sedimentation column, and allowed to stand for observation and recording of sedimentation.

[0102] result:

[0103] (1) Comparative Example A (fine ceramsite): It settled rapidly to the bottom within 10 minutes, the supernatant became clear, and the settling rate was >50cm / min.

[0104] (2) Comparative Example B (nano silica): Initially, a stable colloid is formed, but after 30 minutes, obvious aggregation begins to appear, forming a loose precipitate layer with poor stability and easy agglomeration.

[0105] (3) Product of the present invention: After standing for 2 hours, the system still remains uniformly milky white with no obvious sedimentation interface. After 24 hours, only a slight clarification layer appears, and the sedimentation volume is less than 10% of the total volume. The static sedimentation rate is calculated to be <0.1cm / min.

[0106] Microcrack transport and support experiments:

[0107] Methods: Three samples were mixed with fracturing fluid and, under the same pumping pressure, displaced through a transparent microfluidic chip containing a 10-50 μm artificial microfracture network. Their migration and deployment behavior were observed.

[0108] result:

[0109] Comparative Example A (fine ceramsite): almost all of it was blocked at the entrance of the main channel and could not enter the micro-cracks, forming a filter cake at the entrance.

[0110] Comparative Example B (nano silica): Although it can enter microcracks, due to strong Brownian motion and van der Waals forces, a large number of particles are adsorbed on the crack walls, forming a thick adsorption layer, rather than forming effective support in the middle of the crack.

[0111] The product of this invention, through the synergistic effect of ultra-low density and suitable particle size, smoothly enters and fills the entire microfracture network with the fracturing fluid. After pump shutdown, the particles are uniformly distributed in the fractures, forming effective support points.

[0112] Conclusion: The ultra-low density micro / nano proppant of this invention combines the advantages of small size of inorganic nanomaterials and low density of organic polymer materials, achieving long-term stable suspension and efficient, deep transport and placement of micro / nano crack networks, solving the industry problem that traditional materials either cannot penetrate or cannot effectively support the cracks once they have penetrated.

[0113] Example 7: Verification of the significant improvement in the conductivity of microcracks

[0114] This embodiment uses core flow experiments to quantify the contribution of the proppant of the present invention to the conductivity of microfractures, in order to verify the technical effect of "nearly 100 times higher".

[0115] Test sample:

[0116] Experimental group: The proppant prepared in Example 3 was laid in an artificial crack with a width of 50 μm at a laying concentration of 5 kg / m².

[0117] Blank control group: 50μm artificial cracks of the same size without any proppant.

[0118] Test method:

[0119] Using nitrogen as the medium, the gas phase conductivity of the experimental group and the blank control group was tested under a confining pressure of 2 MPa and a closing pressure of 10 MPa, respectively (based on the microcrack test method revised according to APIRP61 standard).

[0120] Test results:

[0121] The conductivity of the blank control group is extremely low, with a measured value of about 0.5 mD·cm, because the crack is almost completely closed under the closing pressure.

[0122] Flow conduction capacity of the experimental group: The proppant of the present invention provides uniform and stable support points in the crack, so that the crack maintains an effective flow channel even under closure pressure, with a measured value of about 48 mD·cm.

[0123] Comparison of effects:

[0124] The improvement factor of flow capacity = flow capacity of experimental group / flow capacity of blank control group ≈ 48 / 0.5 = 96 times.

[0125] Conclusion: The experimental data strongly demonstrates that the ultra-low density micro / nano proppant of this invention can create and maintain extremely high flow channels for micro / nano fractures that originally had no flow capacity, with a flow capacity increase of nearly 100 times. This is of revolutionary significance for unlocking the huge microfracture resources in unconventional reservoirs.

[0126] Example 8: Comparison with rigid nanomaterials in maintaining long-term conductivity

[0127] This embodiment demonstrates the performance advantages of the proppant of the present invention under long-term stress.

[0128] Test sample:

[0129] Product of this invention: Product of Example 3.

[0130] Comparative Example C: High-strength rigid ceramic nanoparticles (D50: 2μm).

[0131] Test method:

[0132] Two samples were laid in microcracks at the same concentration, and their conductivity was continuously tested over time (120 hours) under a closure pressure of 40 MPa.

[0133] Test results:

[0134] Comparative Example C (rigid ceramic nanoparticles): The initial conductivity was high (35 mD·cm), but due to its high rigidity and brittleness, some particles broke under long-term high pressure, producing small fragments that blocked the flow channels. After 120 hours, the conductivity decreased by more than 60%.

[0135] The product of this invention benefits from the toughness and elasticity of the resin-based material, exhibiting slight deformation rather than breakage under high pressure. This allows it to better adapt to changes in the crack wall and redistribute stress. The initial conductivity is 30 mD·cm, and it remains stable with a decay rate of less than 5% during a 120-hour test.

[0136] Conclusion: The proppant of this invention not only has excellent initial conductivity, but its tough and elastic properties also ensure an excellent retention rate of conductivity under long-term formation stress, avoiding the problem of rapid decline in conductivity caused by the breakage of rigid nanoparticles, and has a longer effective production enhancement cycle.

[0137] In summary, through Examples 6, 7, and 8, reasonable comparative examples (fine ceramsite, nano-silica, and rigid ceramic nanoparticles) were set up, and experiments were introduced in multiple dimensions such as static suspension, microscopic transport observation, quantification of the significant improvement in conductivity, and long-term maintenance of conductivity. These experiments systematically and powerfully demonstrated the outstanding advantages of the ultra-low density micro / nano proppant described in this invention in terms of suspension transport and significantly improving and maintaining the conductivity of microcracks.

[0138] All the devices selected in this application are general standard parts or components known to those skilled in the art. Their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0139] In the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention based on the specific circumstances.

[0140] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the 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: 30-60 wt% vinyl monomer, 10-25 wt% acrylate monomer, and 25-50 wt% unsaturated resin; the bulk density of the support is 0.95-1.15 g / cm³. 3 The median particle size D50 is 1-50 micrometers, and it can maintain structural integrity under a closing pressure of 60 MPa; wherein, the vinyl monomer is selected from one or more of α-methylstyrene, vinylpyrrolidone, vinyl tert-carbonate, and trimethylolpropane triacrylate; 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 vinyl ester resin or furan resin.

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

3. A method for preparing an ultra-low density micro / nano proppant for unconventional reservoir fracturing, characterized in that, The invention includes an ultra-low density micro / nano proppant for unconventional reservoir fracturing as described in any one of claims 1-2; comprising the following steps: Step (1) preparing the oil phase: mixing vinyl monomer, acrylate monomer, unsaturated resin, curing agent, optional functional nanofiller and emulsifier uniformly to form a homogeneous oil phase mixture; Step (2) pre-emulsification: slowly adding the oil phase mixture obtained in step (1) to a portion of the aqueous phase under low-speed stirring to form a coarse emulsion; Step (3) high-pressure homogenization emulsification: passing the coarse emulsion obtained in step (2) through a high-pressure homogenizer and circulating homogenizing it 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: adding an accelerator to the micro / nano emulsion obtained in step (3) and performing an oxidation-reduction curing reaction at a low temperature of 20-50℃ to form cured micro / nano spherical particles; Step (5) post-treatment: after the reaction is completed, centrifuging, washing and spray drying are performed to obtain the ultra-low density micro / nano proppant product.

4. The method for preparing an ultra-low density micro / nano proppant for unconventional reservoir fracturing as described in claim 3, characterized in that, The emulsifier mentioned in step (1) is a compound system of Span, Tween and fatty alcohol polyoxyethylene ether, and its total addition amount is 2-8 wt% of the total mass of the oil phase, and the mass ratio of Span, Tween and fatty alcohol polyoxyethylene ether is (2-4):(1-2):

1.

5. The method for preparing an ultra-low density micro / nano proppant for unconventional reservoir fracturing as described in claim 4, characterized in that, The curing agent mentioned in step (4) is one or more of cumene hydroperoxide, tert-butyl 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 thiol compounds, and its addition amount is 0.2-1% of the total mass of the resin composition.

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 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.