Self-suspending proppant and preparation method thereof

Abstract

The invention discloses a self-suspending proppant and a preparation method thereof, and relates to the technical field of oil and gas field fracturing exploitation, the method comprises the following steps: S1, preparing modified core particles; step S2, preparing coated particles; and S3, preparing the self-suspending proppant. The self-suspending proppant prepared by introducing a silane coupling agent, a hydrophobic monomer and a sulfonic group-containing monomer and coating acrylamide polymer films with different functions in a double-layer manner mainly comprises modified inner core particles, an outer coating layer 1 and an outer coating layer 2, the self-suspension proppant has the advantages of being stable in structure, good in self-suspension capacity, high in shear resistance, capable of still keeping suspension after being washed for multiple times and the like.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field fracturing and exploitation, and in particular to a self-suspending proppant and a preparation method thereof. Background Art

[0002] Hydraulic fracturing is an important measure to increase the production and injection of oil and gas fields, and has achieved good results in the production increase and transformation of oil and gas reservoirs. Hydraulic fracturing mainly uses a ground high-pressure pump truck group to inject high-viscosity liquid into the well, forming high pressure at the bottom of the well. When the bottom hole pressure is greater than the fracture pressure of the formation, cracks are generated, and sand-carrying fluid with proppants is continuously injected. The cracks extend forward and are filled with proppants. After shutting down the well and returning the flow, the cracks are closed on the proppants, so that the cracks can be supported, thereby forming sand-filled cracks with high conductivity in the reservoir layer, and finally achieving the purpose of increasing production and injection. For this purpose, the proppant needs to be evenly distributed in the cracks to increase the effective contact area of ​​the cracks. The commonly used quartz sand or ceramic proppants are easy to settle in water and cannot be well brought into the cracks, and the expected effect of fracturing cannot be achieved. The improvement of proppants can beneficially improve the performance of fracturing fluid in hydraulic fracturing systems.

[0003] Patent document CN115141328A discloses "a self-suspending proppant and a preparation method thereof", comprising: mixing ceramsite with a surface treatment agent, and obtaining modified ceramsite after drying; modifying β-cyclodextrin with a modifier to obtain modified β-cyclodextrin; adding sodium acrylate, a sulfonic acid group-containing monomer, modified ceramsite, and modified β-cyclodextrin to deionized water for polymerization reaction to obtain ceramsite grafted modified anionic polymer; and polymerizing nonionic monomers, alcohol polymers, hydrophobic monomers, acrylic acid, ceramsite grafted modified anionic polymers, deionized water, a pH regulator, and an initiator to obtain a self-suspending proppant.

[0004] Patent document CN114437707A discloses a "self-suspending proppant and its preparation method", which includes aggregate, a low-density high-strength coating layer and a hydrophobic layer, wherein the low-density high-strength coating layer is coated on the surface of the aggregate, and the hydrophobic layer is coated on the surface of the low-density high-strength coating layer; the low-density high-strength coating layer is a lightweight porous structure, and self-suspension is achieved through high-strength lightweight porous coating and super hydrophobic properties.

[0005] Patent document CN104944840A discloses a "method for preparing self-suspended proppants for natural hydraulic fracturing construction". The method is to use 6-200 mesh particles as aggregate, add a binder solution to the aggregate, the binder solution accounts for 10-30% of the weight of the aggregate, and then add a water-soluble polymer material accounting for 0.1-5% of the weight of the aggregate. Stir evenly, dry and sieve.

[0006] Patent document CN105754580A discloses a "method for preparing low-friction self-suspending proppants for fracturing", which includes: taking 100g of proppant, slowly adding 1-3g of surface treatment agent and stirring rapidly until the surface treatment liquid is evenly distributed on the proppant surface, continuing to add 0.1-0.5g of thickener fine powder, and continuing to stir at high speed until uniform.

[0007] Patent document CN104946235A discloses a "method for preparing a self-suspending proppant and the proppant obtained therefrom", comprising: dispersing a water-soluble polymer material in an aggregate at 15-150°C; wherein the water-soluble polymer material is selected from a natural polymer, an artificially synthesized polymer or a semi-natural and semi-artificially synthesized polymer material, and the amount of the water-soluble polymer used is 0.1 to 15 wt% of the amount of the aggregate used.

[0008] Patent document CN104364343A discloses a "self-suspending proppant for hydraulic fracturing", wherein the modified proppant contains proppant particles and a hydrogel coating, wherein the hydrogel coating is applied to the surface of the proppant particles and localized on the surface to produce the modified proppant.

[0009] In the above disclosed prior art, the existing self-suspending proppants have problems such as difficulty in maintaining suspension after being sheared by the holes and easy to settle. Therefore, it is necessary to develop a self-suspending proppant with greatly improved mechanical shear resistance and able to maintain suspension after high-speed shearing of the holes. Summary of the invention

[0010] The purpose of the present invention is to provide a self-suspending proppant and a preparation method thereof. The self-suspending proppant prepared by the method mainly comprises modified core particles, an outer coating layer 1 and an outer coating layer 2; the self-suspending proppant has the advantages of stable structure, good self-suspending ability, strong shear resistance, and can still remain suspended after multiple washings. To achieve the above purpose, the present invention provides the following technical solutions:

[0011] The present invention provides a method for preparing a self-suspending proppant, the method comprising the following steps:

[0012] Step S1, preparation of modified core particles: washing the core particles, mixing with the surface treatment agent, heating and stirring for 4 to 6 hours, and drying to obtain modified core particles;

[0013] Step S2, preparation of coated particles: adding propylene monomer, sulfonic acid group-containing monomer, and hydrophobic monomer to water to modify the core particles, adjusting the pH to 6-7, the temperature to 20-40° C., introducing nitrogen to deoxygenate, and then sequentially adding an oxidant and a reducing agent, heating and stirring, and keeping the system warm to 50-70° C. for 4-6 hours, drying, and sieving to obtain coated particles;

[0014] Step S3, preparation of self-suspending proppant: add acrylamide copolymer, polyethylene polyamine, emulsifier, coated particles to alcohol, adjust the pH to 6-7, the temperature to 20-40°C, introduce nitrogen to deoxygenate, then add oxidant and reductant in sequence, heat, stir at a speed of 800-1000 r / min, stir for 0.5-1.5h after the system is heated to 50-70°C, dry, and sieve to obtain a self-suspending proppant.

[0015] Furthermore, the core particles are at least one of quartz sand or expanded clay; the surface treatment agent is at least one of trimethyl (1-methylvinyloxy) silane, vinyl trimethoxy silane, γ-methacryloxypropyl trimethoxy silane or methacryloxypropyl triethoxy silane.

[0016] Furthermore, the acrylic monomer is at least one of acrylic acid or acrylamide.

[0017] Furthermore, the acrylic monomer is a mixture of acrylic acid and acrylamide, wherein the weight ratio of acrylic acid to acrylamide is (2-4):1.

[0018] Furthermore, the sulfonic acid group-containing monomer is at least one of sodium 2-acrylamido-2-methylpropane sulfonate, sodium p-styrene sulfonate, sodium allyl sulfonate or sodium 3-prop-2-enoyloxypropane-1-sulfonate; and the hydrophobic monomer is at least one of hexadecyl dimethyl allyl ammonium chloride or octadecyl dimethyl allyl ammonium chloride.

[0019] Furthermore, the oxidizing agent is at least one of ammonium persulfate or sodium persulfate; and the reducing agent is at least one of sodium pyrosulfite or sodium bisulfite.

[0020] Furthermore, the acrylamide copolymer is one or more of acrylamide-dodecyl methacrylate-polyethylene glycol diacrylate copolymer, acrylamide-2-acrylamide-2methyl-propanesulfonic acid-polyethylene glycol diacrylate copolymer or acrylamide-3-acrylamidetrimethylammonium chloride-polyethylene glycol diacrylate copolymer.

[0021] Furthermore, the polyethylene polyamine is one or more of ethylenediamine, triethylenetetramine or tetraethylenepentamine; and the emulsifier is one or more of OP-10, Tween 80 or Span 80.

[0022] Furthermore, the alcohol is one or more of anhydrous methanol, anhydrous ethanol, anhydrous propanol or anhydrous isopropanol.

[0023] The present invention also provides a self-suspending proppant, which comprises, from the inside to the outside, modified core particles and outer coating layers 1 and 2; wherein:

[0024] The raw materials for preparing the modified core particles include: 5-10 wt% of a surface treatment agent and core particles;

[0025] The raw materials for preparing the outer coating layer 1 include: 1-5wt% of hydrophobic monomer, 12-16wt% of propylene monomer, 10-20wt% of sulfonic acid group-containing monomer, 0.03-0.05wt% of oxidant and 0.02-0.04wt% of reducing agent, and the balance is water;

[0026] The raw materials for preparing the outer coating layer 2 include: 10-18 wt% of acrylamide copolymer, 2-5 wt% of polyethylene polyamine, 0.04-0.1 wt% of emulsifier, and the balance is alcohol.

[0027] Technical effects and advantages of the present invention:

[0028] The present invention introduces silane coupling agents, hydrophobic monomers, and sulfonic acid group-containing monomers, and double-coats acrylamide polymer films with different functions to prepare a self-suspending proppant with good suspension effect and good shear resistance and flushing resistance. Due to the double-layer polymer film coating, when the outer polymer film fails after high-speed shearing through the hole, the inner polymer film can still play a role. At the same time, the presence of the inner hydrophobic group means that even after high-speed shearing, the cross-linking between molecules can be re-formed after the shear is reduced or eliminated, and mechanical degradation will not occur. The suspension state is always maintained, so that the proppant can reach the farther end of the crack. After high-speed shearing and multiple flushing, the self-suspending proppant prepared by the present invention still has uniform distribution of sand particles, is placed in a 90°C water bath, and has almost no sedimentation phenomenon after standing for 48 hours, and has excellent shear resistance and flushing resistance.

[0029] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a flow chart of a method for preparing a self-suspending proppant. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In order to solve the deficiencies of the prior art, the present invention discloses a method for preparing a self-suspending proppant. Figure 1 is a flow chart of a method for preparing a self-suspending proppant of the present invention, as shown in Figure 1 As shown, the method comprises the following steps:

[0033] Step S1, preparation of modified core particles: washing the core particles, mixing with the surface treatment agent, heating and stirring for 4 to 6 hours, and drying to obtain modified core particles;

[0034] Step S2, preparation of coated particles: adding propylene monomer, sulfonic acid group-containing monomer, and hydrophobic monomer to water to modify the core particles, adjusting the pH to 6-7, the temperature to 20-40° C., introducing nitrogen to deoxygenate, and then sequentially adding an oxidant and a reducing agent, heating, stirring, and keeping the system warm to 50-70° C. for 4-6 hours, drying, and sieving to obtain coated particles;

[0035] Step S3, preparation of self-suspending proppant: add acrylamide copolymer, polyethylene polyamine, emulsifier, coated particles to alcohol, adjust the pH to 6-7, heat, stir at a speed of 800-1000 r / min, stir for 0.5-1.5h after the system is heated to 50-70°C, dry, and sieve to obtain the self-suspending proppant.

[0036] In step S1 of the present invention, the core particles are at least one of quartz sand or ceramsite. The surface treatment agent is at least one of trimethyl (1-methylvinyloxy) silane, vinyl trimethoxy silane, γ-methacryloxypropyl trimethoxy silane, and methacryloxypropyl triethoxy silane.

[0037] In step S2 of the present invention, the acryl monomer is at least one of acrylic acid and acrylamide; preferably, the acryl monomer is a mixture of acrylic acid and acrylamide, wherein the weight ratio of acrylic acid to acrylamide is (2-4):1. The sulfonic acid group-containing monomer is at least one of sodium 2-acrylamido-2-methylpropane sulfonate, sodium p-styrene sulfonate, sodium allyl sulfonate, and sodium 3-prop-2-enoyloxypropane-1-sulfonate. The hydrophobic monomer is at least one of hexadecyl dimethyl allyl ammonium chloride and octadecyl dimethyl allyl ammonium chloride, the oxidant is at least one of ammonium persulfate and sodium persulfate; the reducing agent is at least one of sodium pyrosulfite and sodium bisulfite.

[0038] In step S3 of the present invention, the acrylamide copolymer is one or more of acrylamide-dodecyl methacrylate-polyethylene glycol diacrylate copolymer, acrylamide-2-acrylamide-2methyl-propanesulfonic acid-polyethylene glycol diacrylate copolymer, acrylamide-3-acrylamidetrimethylammonium chloride-polyethylene glycol diacrylate copolymer and the like; the polyethylene polyamine is one or more of ethylenediamine, triethylenetetramine, and tetraethylenepentamine; the emulsifier is one or more of OP-10, Tween 80, and Span 80; the alcohol is one or more of anhydrous methanol, anhydrous ethanol or anhydrous propanol, and anhydrous isopropanol.

[0039] Based on the above preparation method, the present invention also discloses a self-suspending proppant, which comprises, from the inside to the outside, modified core particles and outer coating layer 1 and outer coating layer 2; wherein,

[0040] The raw materials for preparing the modified core particles include: 5-10 wt% of a surface treatment agent and core particles;

[0041] The raw materials for preparing the outer coating layer 1 include: 1-5wt% of hydrophobic monomer, 12-16wt% of propylene monomer, 10-20wt% of sulfonic acid group-containing monomer, 0.03-0.05wt% of oxidant, 0.02-0.04wt% of reducing agent, and the balance is water;

[0042] The raw materials for preparing the outer coating layer 2 include: 10-18 wt% of acrylamide copolymer, 2-5 wt% of polyethylene polyamine, 0.04-0.1 wt% of emulsifier, and the balance is alcohol.

[0043] Example 1

[0044] Embodiment 1 of the present invention provides a self-suspending proppant, which comprises, by mass fraction:

[0045] The raw materials for preparing the modified core particles include: 10wt% of vinyltrimethoxysilane and 1000wt% of ceramsite;

[0046] The raw materials for preparing the outer coating layer 1 include: 3wt% hexadecyldimethylallylammonium chloride, 10wt% acrylic acid, 5wt% acrylamide, 10wt% 2-acrylamide-2-methylpropanesulfonic acid, 0.04wt% ammonium persulfate, 0.03wt% sodium bisulfite, and 72wt% water;

[0047] The raw materials for preparing the outer coating layer 2 include: 12 wt% of acrylamide-2-acrylamide-2-methyl-propanesulfonic acid-polyethylene glycol diacrylate copolymer, 3 wt% of triethylenetetramine, 0.06 wt% of Tween 80 emulsifier, and 85 wt% of ethanol.

[0048] Embodiment 1 of the present invention provides a method for preparing a self-suspending proppant, the method comprising the following steps:

[0049] Step S1, repeatedly washing 1000wt% ceramsite with deionized water, acetone and ethanol, then adding 10w% vinyltrimethoxysilane, stirring and heating for 5h, taking out, and drying to obtain modified core particles a;

[0050] Step S2, weighing 3wt% hexadecyldimethylallylammonium chloride, 10wt% acrylic acid, 5wt% acrylamide, 10wt% 2-acrylamide-2-methylpropanesulfonic acid, 72wt% water, and 800wt% modified core particles a, adding them into a three-necked flask, adjusting the pH to 6-7, introducing nitrogen to deoxygenate, and then sequentially adding 0.04wt% ammonium persulfate and 0.03wt% sodium bisulfite, the temperature was 20°C, heating and stirring, and after the system was heated to 50°C, it was kept warm for 5h, dried, and sieved to obtain coated particles a;

[0051] Step S3, measuring 12wt% of acrylamide-2-acrylamide-2methyl-propanesulfonic acid-polyethylene glycol diacrylate copolymer, 3wt% of triethylenetetramine, 0.06wt% of Tween 80 emulsifier, 85wt% of ethanol, 800wt% of coated particles a, adjusting the pH to 6-7, heating, stirring at a speed of 800r / min, stirring for 1.0h after the system is heated to 50°C, drying, and sieving to obtain a self-suspending proppant a.

[0052] Embodiment 2:

[0053] Embodiment 2 of the present invention provides a self-suspending proppant, which comprises, by mass fraction:

[0054] The raw materials for preparing the modified core particles include: 10wt% of gamma-methacryloxypropyltrimethoxysilane and 1000wt% of quartz sand;

[0055] The raw materials for preparing the outer coating layer 1 include: 3wt% octadecyldimethylallyl ammonium chloride, 12wt% acrylic acid, 4wt% acrylamide, 10wt% sodium p-styrene sulfonate, 0.04wt% ammonium persulfate, 0.03wt% sodium bisulfite, and 71wt% water;

[0056] The raw materials for preparing the outer coating layer 2 include: 12 wt % of acrylamide-3-acrylamidotrimethylammonium chloride-polyethylene glycol diacrylate copolymer, 3 wt % of ethylenediamine, 0.06 wt % of Tween 80 emulsifier, and 85 wt % of ethanol.

[0057] Embodiment 2 of the present invention provides a method for preparing a self-suspending proppant, the method comprising the following steps:

[0058] Step S1, repeatedly washing 1000wt% ceramsite with deionized water, acetone and ethanol, then adding 10wt% of γ-methacryloxypropyltrimethoxysilane, stirring and heating for 5h, taking out, and drying to obtain modified core particles b;

[0059] Step S2, measuring 3wt% of octadecyldimethylallylammonium chloride, 12wt% of acrylic acid, 4wt% of acrylamide, 10wt% of sodium p-styrene sulfonate, 71wt% of water, and 800wt% of modified core particles b, adding them into a three-necked flask, adjusting the pH to 6-7, introducing nitrogen to deoxygenate, and then sequentially adding 0.04wt% of ammonium persulfate and 0.03wt% of sodium bisulfite, the temperature was 30°C, heating and stirring, and after the system was heated to 60°C, it was kept warm for 5h, dried, and sieved to obtain coated particles b;

[0060] Step S3, measuring 12wt% of acrylamide-3-acrylamidotrimethylammonium chloride-polyethylene glycol diacrylate copolymer, 3wt% of ethylenediamine, 0.06wt% of Tween 80 emulsifier, 85wt% of ethanol, and 800% of coated particles b, adjusting the pH to 6-7, heating, stirring at a speed of 900r / min, stirring for 1.0h after the system is heated to 60°C, drying, and sieving to obtain a self-suspending proppant b.

[0061] Embodiment 3:

[0062] Embodiment 3 of the present invention provides a self-suspending proppant, which comprises, by mass fraction:

[0063] The raw materials for preparing the modified core particles include: 5wt% of vinyltrimethoxysilane, 5wt% of gamma-methacryloxypropyltrimethoxysilane, and 1000wt% of ceramsite;

[0064] The raw materials for preparing the outer coating layer 1 include: 1.5wt% hexadecyldimethylallyl ammonium chloride, 1.5wt% octadecyldimethylallyl ammonium chloride, 12wt% acrylic acid, 3wt% acrylamide, 5wt% 2-acrylamide-2-methylpropanesulfonic acid, 5wt% sodium p-styrenesulfonate, 0.04wt% ammonium persulfate, 0.03wt% sodium bisulfite, and 72wt% water;

[0065] The raw materials for preparing the outer coating layer 2 include: 12 wt % of acrylamide-lauryl methacrylate-polyethylene glycol diacrylate copolymer, 3 wt % of triethylenetetramine, 0.06 wt % of Tween 80 emulsifier, and 85 wt % of ethanol.

[0066] Embodiment 3 of the present invention provides a method for preparing a self-suspending proppant, the method comprising the following steps:

[0067] Step S1, repeatedly washing 1000wt% ceramsite with deionized water, acetone and ethanol, then adding 5wt% vinyltrimethoxysilane and 5wt% γ-methacryloxypropyltrimethoxysilane, stirring and heating for 5h, taking out, and drying to obtain modified core particles c.

[0068] Step S2, weighing 1wt% hexadecyldimethylallylammonium chloride, 1wt% octadecyldimethylallylammonium chloride, 12wt% acrylic acid, 3wt% acrylamide, 5wt% 2-acrylamide-2-methylpropanesulfonic acid, 5wt% sodium p-styrenesulfonate, 73wt% water, and 800wt% modified core particles c, adding them into a three-necked flask, adjusting the pH to 6-7, introducing nitrogen to deoxygenate, and then sequentially adding 0.04wt% ammonium persulfate and 0.03wt% sodium bisulfite, the temperature was 40°C, heating and stirring, and after the system was heated to 70°C, it was kept warm for 5h, dried, and sieved to obtain coated particles c;

[0069] Step S3, measuring 12wt% of acrylamide-dodecyl methacrylate-polyethylene glycol diacrylate copolymer, 3wt% of triethylenetetramine, 0.06wt% of Span 80 emulsifier, 85wt% of ethanol, and 800wt% of coated particles c, adjusting the pH to 6-7, heating, stirring at a speed of 1000r / min, stirring for 1.0h after the system is heated to 70°C, drying, and sieving to obtain a self-suspending proppant c;

[0070] Comparative Example 1:

[0071] Comparative Example 1 is substantially the same as Example 1, except that hexadecyldimethylallylammonium chloride is not added, and 3 wt % of water is added instead, i.e., 75 wt % of water in total.

[0072] Comparative Example 2:

[0073] Comparative Example 2 is substantially the same as Example 1, except that only the outer coating layer 1 solution is used for coating.

[0074] Comparative Example 3:

[0075] Comparative Example 3 is substantially the same as Example 1, except that only the outer coating layer 2 solution is used for coating.

[0076] Test Example 1:

[0077] Suspension ability test of Example 1-3: The self-suspending proppant prepared in Example 1-3 was tested for suspension ability under different stirring rates and flushing times. In the test, 50 mL of the self-suspending proppant was weighed and added to a beaker, and then water was added to 100 mL, placed in a high-speed stirrer and stirred at a certain rate for 1 min, then stopped stirring, placed in a 100 mL measuring cylinder, placed in a 90°C water bath, and left to stand for 48 hours to observe the distribution state of the self-suspending proppant in the measuring cylinder; 50 mL of the self-suspending proppant was weighed, water was added to 100 mL, stirred at the same stirring rate for 3 minutes, the self-suspending proppant was taken out, filtered, and water was added again to 100 mL. After repeating a certain number of times, it was placed in a 100 mL measuring cylinder, placed in a 90°C water bath, and left to stand for 48 hours to observe the distribution state of the self-suspending proppant in the measuring cylinder. The test results are shown in Table 1.

[0078] Table 1 Suspension ability test of self-suspending proppants prepared in Examples 1-3 at different stirring speeds and different flushing times

[0079]

[0080] It can be seen from the suspension ability tests of Examples 1-3 above that the self-suspending proppant prepared by the present invention has evenly distributed sand particles after high-speed shearing and multiple washings, and has almost no sedimentation after being placed in a 90° C. water bath and standing for 48 hours, showing good swelling, shear resistance and scouring resistance.

[0081] Test Example 2:

[0082] Suspension ability test of Example 1 and Comparative Examples 1-3: The self-suspending proppants prepared in Example 1 and Comparative Examples 1-3 were tested for suspension ability under different stirring rates and flushing times. In the test, 50 mL of the self-suspending proppants were weighed and added to a beaker, and then water was added to 100 mL, and the mixture was placed in a high-speed stirrer and stirred at a certain rate for 1 min, then the stirring was stopped, and the mixture was placed in a 100 mL measuring cylinder, placed in a 90°C water bath, and allowed to stand for 48 hours to observe the distribution state of the self-suspending proppants in the measuring cylinder; 50 mL of the self-suspending proppants were weighed, water was added to 100 mL, and the mixture was stirred at the same stirring rate for 3 minutes, the self-suspending proppants were taken out, filtered, and water was added to 100 mL again. After repeating the process for a certain number of times, the mixture was placed in a 100 mL measuring cylinder, placed in a 90°C water bath, and allowed to stand for 48 hours to observe the distribution state of the self-suspending proppants in the measuring cylinder. The test results are shown in Table 2.

[0083] Table 2 Suspension ability test of self-suspending proppants prepared in Example 1 and Comparative Examples 1-3 at different stirring speeds and different flushing times

[0084]

[0085]

[0086] From the suspension ability test of the above Example 1 and Comparative Examples 1-3, it can be seen that the self-suspending proppant prepared by the present invention, by introducing a silane coupling agent, a hydrophobic monomer, and a sulfonic acid group-containing monomer, is double-coated with a polymer film with different functions. After multiple high-speed shearing and washing, the sand particles are still evenly distributed, and are placed in a 90°C water bath, and there is almost no sedimentation after standing for 48 hours, showing good shear resistance and scouring resistance.

[0087] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a self-suspending proppant, characterized in that: The method comprises the following steps: Step S1, preparation of modified core particles: washing the core particles, mixing with the surface treatment agent, heating and stirring for 4 to 6 hours, and drying to obtain modified core particles; Step S2, preparation of coated particles: adding propylene monomer, sulfonic acid group-containing monomer, and hydrophobic monomer to water to modify the core particles, adjusting the pH to 6-7, the temperature to 20-40° C., introducing nitrogen to deoxygenate, and then sequentially adding an oxidant and a reducing agent, heating and stirring, and keeping the system warm to 50-70° C. for 4-6 hours, drying, and sieving to obtain coated particles; Step S3, preparation of self-suspending proppant: add acrylamide copolymer, polyethylene polyamine, emulsifier, coated particles to alcohol, adjust the pH to 6-7, the temperature to 20-40°C, introduce nitrogen to deoxygenate, then add oxidant and reductant in sequence, heat, stir at a speed of 800-1000 r / min, stir for 0.5-1.5h after the system is heated to 50-70°C, dry, and sieve to obtain a self-suspending proppant.

2. The method for preparing a self-suspending proppant according to claim 1, characterized in that: The core particles are at least one of quartz sand or ceramsite; the surface treatment agent is at least one of trimethyl (1-methylvinyloxy) silane, vinyl trimethoxy silane, γ-methacryloxypropyl trimethoxy silane or methacryloxypropyl triethoxy silane.

3. The method for preparing a self-suspending proppant according to claim 1 or 2, characterized in that: The acrylic monomer is at least one of acrylic acid or acrylamide.

4. The method for preparing a self-suspending proppant according to claim 3, characterized in that: The acrylic monomer is a mixture of acrylic acid and acrylamide, wherein the weight ratio of acrylic acid to acrylamide is (2-4):

1.

5. The method for preparing a self-suspending proppant according to claim 1, characterized in that: The sulfonic acid group-containing monomer is at least one of sodium 2-acrylamido-2-methylpropane sulfonate, sodium p-styrene sulfonate, sodium allyl sulfonate or sodium 3-prop-2-enoyloxypropane-1-sulfonate; and the hydrophobic monomer is at least one of hexadecyl dimethyl allyl ammonium chloride or octadecyl dimethyl allyl ammonium chloride.

6. The method for preparing a self-suspending proppant according to claim 1 or 5, characterized in that: The oxidizing agent is at least one of ammonium persulfate or sodium persulfate; the reducing agent is at least one of sodium pyrosulfite or sodium bisulfite.

7. The method for preparing a self-suspending proppant according to claim 1, characterized in that: The acrylamide copolymer is one or more of acrylamide-dodecyl methacrylate-polyethylene glycol diacrylate copolymer, acrylamide-2-acrylamide-2methyl-propanesulfonic acid-polyethylene glycol diacrylate copolymer or acrylamide-3-acrylamidetrimethylammonium chloride-polyethylene glycol diacrylate copolymer.

8. The method for preparing a self-suspending proppant according to claim 1, characterized in that: The polyethylene polyamine is one or more of ethylenediamine, triethylenetetramine or tetraethylenepentamine; the emulsifier is one or more of OP-10, Tween 80 or Span 80.

9. The method for preparing a self-suspending proppant according to claim 1, characterized in that: The alcohol is one or more of anhydrous methanol, anhydrous ethanol, anhydrous propanol or anhydrous isopropanol.

10. A self-suspending proppant prepared by the method according to any one of claims 1 to 9, characterized in that: The self-suspending proppant comprises, from the inside to the outside, modified core particles and outer coating layer 1 and outer coating layer 2; wherein, The raw materials for preparing the modified core particles include: 5-10 wt% of a surface treatment agent and core particles; The raw materials for preparing the outer coating layer 1 include: 1-5wt% of hydrophobic monomer, 12-16wt% of propylene monomer, 10-20wt% of sulfonic acid group-containing monomer, 0.03-0.05wt% of oxidant and 0.02-0.04wt% of reducing agent, and the balance is water; The raw materials for preparing the outer coating layer 2 include: 10-18 wt% of acrylamide copolymer, 2-5 wt% of polyethylene polyamine, 0.04-0.1 wt% of emulsifier, and the balance is alcohol.

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