Pressure-resistant differential density spherical temporary plugging agent and preparation method thereof

Abstract

The present application relates to a kind of pressure difference resistant equal density spherical temporary plugging agent, it is the core-shell composite structure of core material plus shell layer, hollow glass microsphere is dispersed in polyvinyl acetal as core material, the preparation raw material of polyvinyl acetal includes 28-35 mass parts polyvinyl alcohol 1 of degree of polymerization 1500-2000, 12-16 mass parts polyvinyl alcohol 2 of degree of polymerization 3000-4000, 0.5-1 mass parts aromatic monobasic aldehyde, 0.2-0.3 mass parts aromatic polyaldehyde, 0.7-1.3 mass parts inorganic base, 3-5 mass parts organic acid;The ratio of the total mass of hollow glass microsphere and polyvinyl alcohol is 100:35-50;Temporary plugging agent particle size is 8-30mm.The density of spherical temporary plugging agent provided by the present application is continuously adjustable between 0.95~1.05g / cm 3 , and the density difference is less than 0.03g / cm 3 . Temporary plugging agent provided by the present application has the characteristics of slow water-soluble viscosity spontaneous aggregation bridging plugging, and water-soluble viscosity loss plugging.

Description

Technical Field

[0001] This invention belongs to the field of temporary plugging technology for fracturing in oil and gas exploration and development, specifically relating to a pressure differential resistant isodense spherical temporary plugging agent and its preparation method. Background Technology

[0002] Horizontal well ball-type temporary plugging fracturing involves deploying spherical plugging agents to temporarily seal high-permeability perforations for a period of time, increasing the perforation opening rate, forcing the fracturing fluid to redirect towards low-permeability layers, and promoting good fracture development in low-permeability areas. After fracturing, the plugging agent can self-unblock under the dissolution or hydrolysis of water-based fracturing fluid, making it an important technique for enhancing production in unconventional oil and gas reservoirs. Horizontal well ball-type temporary plugging fracturing requires the spherical plugging agent to have sufficiently high plugging efficiency. The plugging efficiency of the spherical plugging agent is closely related to its pressure difference and density difference. Spherical plugging agents with a density greater than the fracturing fluid tend to sink, becoming dead balls that are difficult to be transported to high-permeability perforations by the fracturing fluid, thus affecting plugging efficiency. Floating spherical plugging agents with a density less than the fracturing fluid are relatively better, but their plugging efficiency is still lower than that of suspended isodense spherical plugging agents with a density close to that of the fracturing fluid. If the pressure differential resistance (plugging strength) of spherical temporary plugging balls is not high enough, even if they can be transported to high-permeability boreholes by fracturing fluid, they will quickly deform and fail under the high pressure differential generated by fracturing, thus affecting plugging efficiency. Temporary plugging materials with high pressure differential resistance and that are water-soluble or hydrolyzable typically have a density significantly higher than that of water-based fracturing fluids. Currently, water-soluble temporary plugging materials with densities close to or less than water and sufficiently high fracturing temporary plugging strength are still lacking. The unsatisfactory plugging effect of currently available water-soluble spherical temporary plugging agents in oil and gas field fracturing operations is partly related to their higher density than water-based fracturing fluids or insufficient plugging strength.

[0003] CN106047323A discloses a water-soluble temporary plugging agent, the raw materials of which are bone glue, modified starch, and hydroxypropyl guar gum. It can withstand high pressure but is not heat-resistant and can only be used at around 100°C. CN109762544A discloses a high-temperature resistant temporary plugging agent, comprising a semi-aromatic amide polymer, additives, and fillers. The fillers include hollow glass microspheres, glass fibers, carbon fibers, etc., but the degradation rate is not high, and high temperature and pressure conditions are required to completely break it down into tiny particles that move with the water flow. CN118703184A discloses a temporary plugging particle for fracturing in oil and gas fields. The particle is spherical and comprises spherical ceramic aggregate and a temporary plugging agent coating covering the spherical ceramic aggregate. The total weight of the temporary plugging agent coating, calculated as 100 parts, consists of the following raw materials in parts by weight: 4-15 parts acrylamide, 0.5-3 parts polypropylene fiber, 1-1.5 parts dispersant, 1.5-4 parts reinforcing agent, 0.5-1.0 parts curing agent, and the balance being water. The temporary plugging particles include 6 / 12 mesh, 12 / 20 mesh, 20 / 40 mesh, 30 / 50 mesh, and / or 40 / 70 mesh particles. CN118206969A discloses a fracturing temporary plugging ball with a core-shell structure. The inner core is a spherical structure formed by granulation of a two-component temporary plugging material, including polypropylene and / or polyethylene temporary plugging materials. The outer shell is made of polyurethane rubber and polyvinyl alcohol. The temporary plugging agents in the aforementioned patents have relatively high densities, making them prone to settling and becoming dead balls that are difficult to be transported by fracturing fluid to high-permeability boreholes, thus affecting plugging efficiency.

[0004] CN118460192A discloses a low-density, water-soluble, room-temperature temporary plugging agent for hydraulic fracturing in coal mines, which is prepared from sodium acrylate, acrylamide, and polyvinyl alcohol paraffin. The density of the tested temporary plugging agent is 0.92 g / cm³. 3 At the same temperature, the density of water is 0.9971 g / cm³. 3On the one hand, too low a density is not conducive to the sealing effect; on the other hand, the temporary plugging agent of this patent has a breakage rate of over 10% under high pressure, limiting the sealing strength. CN116462797A discloses a polymer copolymer temporary plugging agent, which is obtained by copolymerizing acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, methyl acrylate, and a crosslinking agent. The density can be adjusted by controlling the raw materials and ratios. CN115850573A discloses a similar polymer-based temporary plugging agent, which is prepared by copolymerizing acrylamide, methyl acrylate, a crosslinking agent, an initiator, etc. Such polymer material temporary plugging agents can obtain spherical temporary plugging agents with suitable densities by controlling the types and ratios of monomers, but it is difficult to simultaneously meet the requirements of strength and degradability. If the sealing ability is to be improved, the amount of crosslinking agent used needs to be increased, which will reduce the degradation performance. That is, the temporary plugging agent of this patent cannot balance strength and degradability. An ideal temporary plugging agent does not degrade much in the initial stage of injection, but can degrade rapidly after sealing is completed. Moreover, these pure polymeric temporary plugging agents are difficult to completely remove from the bottom layer, causing significant damage to the formation and potentially reducing formation permeability, making them less environmentally friendly.

[0005] CN115838589A discloses a particulate temporary plugging agent for fracturing diversion prepared using polyvinyl alcohol, an aldehyde crosslinking agent, and a catalyst. This agent is obtained by mixing polyvinyl alcohol, a dialdehyde crosslinking agent, and a potential acid catalyst, followed by a freeze-thaw cycle to produce a gel. However, the strength of this temporary plugging agent relies on the crystalline regions formed by polyvinyl alcohol during the freeze-thaw process as physical crosslinking points. At high temperatures, these physical crosslinking points rapidly fail. Even if dialdehyde substances form low-density chemical crosslinks, without degradation at high temperatures, the disappearance of physical crosslinking points will cause a rapid loss of strength and deformation, even breaking into fragments. Therefore, its plugging ability is limited in high-temperature environments.

[0006] Therefore, it is necessary to develop a fluid with a density close to that of fracturing fluid (density difference ≤ 0.03 g / cm³). 3 Spherical temporary plugging agents with high pressure differential resistance, suitable for use in high-temperature environments, and with appropriate degradation time that do not damage the formation after degradation have significant practical significance and application value. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention provides a solution with a density close to that of water-based fracturing fluid (density difference <0.03 g / cm³). 3 This invention discloses a spherical temporary plugging agent with good suspension properties, high temporary plugging strength, self-dissolving ability, and environmental friendliness, as well as its preparation method. Specifically, the invention provides the following technical solutions to achieve the above objectives:

[0008] A pressure differential resistant isodense spherical temporary plugging agent is comprising hollow glass microspheres as the core material dispersed in polyvinyl acetal. The raw materials for preparing the polyvinyl acetal include 28-35 parts by mass of polyvinyl alcohol 1 with a degree of polymerization of 1500-2000, 12-16 parts by mass of polyvinyl alcohol 2 with a degree of polymerization of 3000-4000, 0.5-1 parts by mass of aryl monoaldehyde, 0.2-0.3 parts by mass of aromatic polyaldehyde, 0.7-1.3 parts by mass of inorganic base, and 3-5 parts by mass of organic acid. The mass ratio of the hollow glass microspheres to the total mass of polyvinyl alcohol is 100:40-55. The particle size of the pressure differential resistant isodense spherical temporary plugging agent is 8-30 mm. The total mass of polyvinyl alcohol is the sum of the masses of polyvinyl alcohol 1 and polyvinyl alcohol 2.

[0009] This invention uses aromatic aldehydes for acetalization because of their high boiling point. Since the subsequent injection molding stage is carried out at temperatures above 220°C, aldehydes with boiling points higher than 220°C are necessary.

[0010] The density of the pressure differential resistant isodense spherical temporary plugging agent is 0.95-1.05 g / cm³. 3 Adjustable within a range, preferably 0.97-1.03 g / cm³. 3 Adjustable within a range, more preferably 0.98-1.02 g / cm³ 3 Within a range, for example, 0.99 g / cm³ 3 1.00 g / cm 3 1.01 g / cm 3 Furthermore, the pressure differential resistant isodense spherical temporary plugging agent of the present invention exhibits a pressure differential resistance value ≥60 MPa at 90°C for 120 minutes. Moreover, the spherical temporary plugging agent of the present invention possesses suitable degradation properties; it does not degrade in the initial stage of use, maintaining excellent plugging performance. After a certain period, the degradation rate accelerates, allowing it to be completely discharged from the formation without affecting formation permeability.

[0011] Furthermore, the aromatic monoaldehyde is selected from at least one of benzaldehyde, 1-naphthaldehyde, 2-naphthaldehyde, 9-anthraaldehyde, and salicylaldehyde; the aromatic polyaldehyde is selected from at least one of 2,6-naphthyldicarboxaldehyde, 2,3-naphthyldicarboxaldehyde, 2,6-dialdehyde-1,5-dihydroxynaphthalene, terephthalaldehyde, 3,4',5-trialdehyde-1,1-biphenyl, tetraaldehyde tetraphenylethylene, 3,3',5,5'-tetraaldehyde-biphenyl, tetra(4-aldehydephenyl)methane, and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl; the inorganic base is selected from at least one of sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate; and the organic acid is selected from at least one of p-toluenesulfonic acid and chloroacetic acid.

[0012] Further, the polyaldehyde is a compound of a dialdehyde and an aldehyde with a functionality of 3 or higher in a mass ratio of 4-6:1. The dialdehyde is selected from at least one of 2,6-naphthalenedicarboxyl, 2,3-naphthalenedicarboxyl, 2,6-dialdehyde-1,5-dihydroxynaphthalene, and terephthalaldehyde. The aldehyde with a functionality of 3 or higher is selected from 3,4',5-trialdehyde-1,1-biphenyl, tetraaldehyde-tetraphenylene, 3,3',5,5'-tetraaldehyde-biphenyl, tetra(4-aldehyde-phenyl)methane, and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl.

[0013] In the preparation of cross-linked polyvinyl acetal, selecting the above-mentioned dialdehyde and aldehyde with a functionality of 3 or higher can give the cross-linked polyvinyl acetal shell both mechanical strength and suitable degradability. Preferably, the aromatic polyaldehyde is a compound of a dialdehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 4-6:1.

[0014] The second objective of this invention is to provide a method for preparing the above-mentioned pressure differential resistant isodense spherical temporary plugging agent, comprising the following steps:

[0015] (S1) Hollow glass microspheres are immersed in an alcohol-water solution of aldehyde-based silane coupling agent, heated to react completely, removed, washed, and dried to obtain aldehyde-based surface-modified hollow glass microspheres;

[0016] (S2) The aldehyde-modified hollow glass microspheres, polyvinyl alcohol 1, aromatic monoaldehyde, and inorganic alkali are mixed evenly and put into an injection molding machine. 60-80% organic acid is added and the mixture is kept at 210-230℃ for 5-7 hours. While maintaining the temperature, polyvinyl alcohol 2, aromatic polyaldehyde, and the remaining organic acid are added. The mixture is kept at the temperature for another 3-5 hours to complete the mixing, plasticizing, and homogenization. The mixture is then injected into a spherical mold, cooled, and the mold is opened to obtain the product.

[0017] The degree of alcoholysis of the polyvinyl alcohol used in this invention is ≥90%, preferably ≥95%.

[0018] Further, in step (S1), the hollow glass microspheres have a particle size of 20-80 μm and a true density of 0.55-0.65 g / cm³. 3 The product consists of sealed hollow glass microspheres with a compressive strength of 40-70 MPa; the aldehyde-based silane coupling agent is selected from at least one of 4-(trimethoxymethylsilane)butyraldehyde, 4-(triethoxymethylsilane)butyraldehyde, and 4-(tripropoxymethylsilane)butyraldehyde; the concentration of the aldehyde-based silane coupling agent in the alcohol-water solution is 4-7 wt%, and the volume concentration of the alcohol in the alcohol-water solution is 60-80%, with the alcohol being at least one of methanol, ethanol, and isopropanol; the reaction is carried out at 40-60℃ for 6-10 hours; and the washing is performed 3-5 times with alcohol.

[0019] After treating hollow glass microspheres with an aldehyde-based silane coupling agent, the surface of the hollow glass microspheres is modified with aldehyde groups. In the subsequent polyvinyl alcohol acetal reaction, the aldehyde groups on the surface of the hollow glass microspheres also participate in the reaction, resulting in chemical bonding between the hollow glass microspheres and the shell layer of polyvinyl alcohol acetal. This improves affinity and is more conducive to the performance of the core-shell structured spherical plugging agent. The combination of aryl monoaldehydes (such as benzaldehyde) and polyaldehydes (such as alkane dialdehydes and aromatic polyaldehydes) optimizes the shell structure through staged crosslinking. The aryl monoaldehyde preferentially reacts with polyvinyl alcohol 1 to form a preliminary crosslinking network; the polyaldehydes are then introduced, mainly to enhance the crosslinking density on the outer side. This results in the inner layer of the polyvinyl alcohol acetal in the obtained spherical plugging agent tending to be porous polyvinyl alcohol acetal, reducing the density of the spherical plugging agent and facilitating degradation; the increased crosslinking density of the outer layer provides sufficient plugging strength and pressure differential resistance, and also maintains good plugging strength at high temperatures. Existing technologies often employ single aldehydes and polyvinyl alcohol for polycondensation, resulting in a simple cross-linking structure that makes it difficult to balance mechanical strength and degradability. This invention utilizes a two-stage process. First, polyvinyl alcohol 1 with a lower degree of polymerization and an aromatic monoaldehyde undergo polycondensation. During this process, an inorganic base and organic acid catalyst react, generating gas and forming a porous polyvinyl alcohol acetal with a specific pore structure. Then, polyvinyl alcohol 2 with a higher degree of polymerization and a polyaldehyde are added, forming a polyvinyl alcohol acetal with an even higher cross-linking density on the outer layer, thus improving the sealing strength of the spherical temporary plugging agent. This specific high-crosslinking shell structure ensures that the spherical temporary plugging agent of this invention is essentially non-degradable in the initial stage of application and exhibits excellent sealing ability at high temperatures. As the highly cross-linked shell degrades, the degradation rate accelerates rapidly in the later stages, allowing it to dissolve quickly in hot water without the need for acidic deblocking. This environmentally friendly process avoids damaging formation permeability.

[0020] Especially when polyaldehydes are added, the combination of dialdehydes and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl results in a product that, in addition to strength and degradation ability, significantly improves its blocking ability at high temperatures. This is likely due to the effect of the hydroxyl groups on 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl.

[0021] This invention allows for convenient adjustment of the density of the spherical temporary plugging agent to between 0.95 and 1.05 g / cm³ by adjusting the relative ratio of hollow glass microspheres and polyvinyl alcohol. 3 The density is continuously adjustable, similar to fracturing fluids of different densities, with a density difference of <0.03 g / cm³. 3 The temporary plugging agent provided by this invention has the characteristics of slow dissolution and adhesion upon contact with water, spontaneous aggregation and bridging, and dissolution and deadlocking in abundant water. Its degradation rate is minimal initially, but accelerates later. It can meet the plugging requirements and can also be quickly discharged from the formation without damaging formation permeability. Attached Figure Description

[0022] Figure 1 These are physical images of the spherical temporary plugging agents of Example 1 and Comparative Example 6.

[0023] Figure 2 These are photographs showing the distribution of the spherical temporary plugging agents in fracturing fluid in Examples 1 and 6. Detailed Implementation

[0024] The present invention will be further illustrated below with reference to examples, but the scope of protection of the present invention is not limited to the scope of the embodiments. The degree of alcoholysis of the polyvinyl alcohol used in the present invention is above 90%. Example 1

[0025] (S1) Hollow glass microspheres (density 0.61 g / cm³) 3 The 4-(trimethoxymethylsilane)butyraldehyde was immersed in an ethanol aqueous solution with a concentration of 5wt% (ethanol to water volume ratio of 8:2), and the mixture was heated to 50℃ and reacted for 10h under stirring. The mixture was then removed, washed three times with anhydrous ethanol, and dried under vacuum to obtain aldehyde-modified hollow glass microspheres.

[0026] (S2) Mix 100 parts by weight of aldehyde-modified hollow glass microspheres, 32 parts by weight of polyvinyl alcohol with a degree of polymerization of 2000, 0.83 parts by weight of 1-naphthaldehyde, and 1 part by weight of sodium bicarbonate evenly, put the mixture into an injection molding machine, add 3 parts by weight of p-benzenesulfonic acid, keep it at 220℃ for 7 hours, maintain the temperature, add 15 parts by weight of polyvinyl alcohol with a degree of polymerization of 3500, 0.26 parts by weight of poly(2,6-naphthyldicarboxaldehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 5:1), and 1 part by weight of p-benzenesulfonic acid, continue to keep it at the temperature for 4 hours to complete the mixing, plasticizing and homogenization, inject into a spherical mold, cool and open the mold to obtain the product, which is a spherical temporary plugging agent with a diameter of about 20 mm. Example 2

[0027] (S1) Hollow glass microspheres (density 0.55 g / cm³) 3 The 4-(triethoxymethylsilane)butyraldehyde was immersed in an ethanol aqueous solution with a concentration of 4wt% (ethanol and water volume ratio of 8:2), and the mixture was heated to 50℃ and reacted for 10h under stirring. The mixture was then removed, washed three times with anhydrous ethanol, and dried under vacuum to obtain aldehyde-modified hollow glass microspheres.

[0028] (S2) Mix 100 parts by weight of aldehyde-modified hollow glass microspheres, 35 parts by weight of polyvinyl alcohol with a degree of polymerization of 2000, 1.1 parts by weight of 1-naphthaldehyde, and 1.2 parts by weight of sodium bicarbonate evenly, put the mixture into an injection molding machine, add 3.2 parts by weight of p-benzenesulfonic acid, keep the mixture at 220℃ for 7 hours, maintain the temperature, add 18 parts by weight of polyvinyl alcohol with a degree of polymerization of 4000, 0.3 parts by weight of poly(2,6-naphthaldehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 6:1), and 1 part by weight of p-benzenesulfonic acid, continue to keep the mixture at 220℃ for 4 hours to complete the mixing, plasticizing and homogenization, inject the mixture into a spherical mold, cool and open the mold to obtain the product, which is a spherical temporary plugging agent with a diameter of about 20 mm. Example 3

[0029] (S1) Hollow glass microspheres (density 0.64 g / cm³) 3 The 4-(trimethoxymethylsilane)butyraldehyde was immersed in an ethanol aqueous solution with a concentration of 5wt% (ethanol to water volume ratio of 8:2), and the mixture was heated to 50℃ and reacted for 10h under stirring. The mixture was then removed, washed three times with anhydrous ethanol, and dried under vacuum to obtain aldehyde-modified hollow glass microspheres.

[0030] (S2) Mix 100 parts by weight of aldehyde-modified hollow glass microspheres, 28 parts by weight of polyvinyl alcohol with a degree of polymerization of 2000, 0.7 parts by weight of 1-naphthaldehyde, and 0.8 parts by weight of sodium bicarbonate evenly, put the mixture into an injection molding machine, add 2.5 parts by weight of p-benzenesulfonic acid, keep it at 220℃ for 7 hours, maintain the temperature, add 12 parts by weight of polyvinyl alcohol with a degree of polymerization of 4000, 0.22 parts by weight of poly(2,3-naphthaldehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 4:1), and 0.7 parts by weight of p-benzenesulfonic acid, continue to keep it at the temperature for 4 hours to complete the mixing, plasticizing and homogenization, inject into a spherical mold, cool and open the mold to obtain the product, which is a spherical temporary plugging agent with a diameter of about 20 mm. Example 4

[0031] The other conditions are the same as in Example 1, except that step (S2) is changed to: 100 parts by mass of aldehyde-modified hollow glass microspheres, 32 parts by mass of polyvinyl alcohol with a degree of polymerization of 2000, 15 parts by mass of polyvinyl alcohol with a degree of polymerization of 3500, 0.83 parts by mass of 1-naphthaldehyde, 0.26 parts by mass of polyaldehyde (a mixture of 2,6-naphthyldicarboxaldehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 5:1), and 1 part by mass of sodium bicarbonate are mixed evenly, put into an injection molding machine, add 4 parts by mass of p-benzenesulfonic acid, and keep at 220°C for 10 hours to complete the mixing, plasticizing and homogenization. The mixture is then injected into a spherical mold, cooled and opened to obtain the product, which is a spherical temporary plugging agent with a diameter of about 20 mm. That is, compared with Example 1, step S2 of Example 4 is a one-stage acetal reaction, while that of Example 1 is divided into two stages. Example 5

[0032] The other conditions are the same as in Example 1, except that in step (S2), 0.26 parts by mass of the polyaldehyde is a mixture of 2,6-naphthalenedicarboxyl and 3,3',5,5'-tetraaldehyde biphenyl in a mass ratio of 5:1. Example 6

[0033] The other conditions are the same as in Example 1, except that in step (S2), all 0.26 parts by mass of the polyaldehyde are 2,6-naphthalenedicarboxylate. Example 7

[0034] The other conditions are the same as in Example 1, except that in step (S2), all 0.26 parts by mass of the polyaldehyde are 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl.

[0035] Comparative Example 1

[0036] The other conditions are the same as in Example 1, except that step (S1) is omitted and hollow glass microspheres that have not been treated with aldehyde silane coupling agent are used in step (S2).

[0037] Comparative Example 2

[0038] The other conditions are the same as in Example 1, except that in step (S2), 15 parts by mass of polyvinyl alcohol with a degree of polymerization of 3500 are replaced with an equal mass of polyvinyl alcohol with a degree of polymerization of 2000. That is, all polyvinyl alcohol has a degree of polymerization of 2000.

[0039] Comparative Example 3

[0040] The other conditions are the same as in Example 1, except that in step (S2), 32 parts by mass of polyvinyl alcohol with a degree of polymerization of 2000 are replaced with an equal mass of polyvinyl alcohol with a degree of polymerization of 3500. That is, all polyvinyl alcohol has a degree of polymerization of 3500.

[0041] Comparative Example 4

[0042] The other conditions are the same as in Example 1, except that sodium bicarbonate is not added in step (S2).

[0043] Comparative Example 5

[0044] The other conditions are the same as in Example 1, except that step (S1) is omitted and in step (S2), 0.26 parts by mass of polyaldehyde is replaced with 0.5 parts by mass of 1-naphthaldehyde.

[0045] Comparative Example 6

[0046] A commercially available spherical temporary plugging agent for blasting boreholes, with a density of 1.09 g / cm³. 3 .

[0047] Figure 1 These are physical images of the spherical temporary plugging agents of Example 1 (left) and Comparative Example 6 (right).

[0048] Figure 2 The figures show the distribution of the spherical temporary plugging agents from Example 1 and Comparative Example 6 in simulated fracturing fluid at 60°C. The left figure shows the distribution immediately after addition to the simulated fracturing fluid, and the right figure shows the distribution after 4 hours. The simulated fracturing fluid formulation is: 0.15 wt% water-soluble polyethylene oxide, 0.5 wt% NaCl, 0.1 wt% KCl, 0.6 wt% hexadecyltrimethylammonium chloride, 0.1 wt% pumping aid CF-5D, 5 wt% spherical temporary plugging agent, and the balance being water. It can be seen that the spherical temporary plugging agent from Example 1 can be stably suspended in the simulated fracturing fluid at 60°C, while the commercial spherical temporary plugging agent from Comparative Example 6 sinks and cannot effectively plug the fracturing fluid.

[0049] Application examples

[0050] The spherical temporary plugging agents prepared in the above embodiments and comparative examples were subjected to performance tests, and the results are shown in Table 1 below.

[0051] The plugging strength and 120-hour solubility were tested in accordance with the oil and gas industry standard (SY / T 7811-2024). The plugging strength test temperature was 90℃, and the plugging strength was ≥120 min with an effective plugging time.

[0052] In the tests of temporary plugging rate and permeability recovery rate, the permeability of the simulated core was 5200-5400×10⁻⁶. -3 μm 2 The fracture was 7-8 cm long and 2.5 ± 0.1 cm in diameter. The test temperature was 90℃. Fracturing fluid was injected into the simulated core (fracturing fluid formula: 0.15 wt% water-soluble polyethylene oxide, 0.5 wt% NaCl, 0.1 wt% KCl, 0.6 wt% hexadecyltrimethylammonium chloride, 0.1 wt% drainage aid CF-5D, 5 wt% spherical temporary plugging agent, balance water). The permeability before and after plugging was tested, and the temporary plugging rate was calculated. Then, formation water was used to flush the core, and the permeability recovery rate was calculated.

[0053] In the solubility test, the mass of the glass hollow microspheres is not considered, and only the mass loss rate of polyvinyl acetal at 90°C is calculated.

[0054]

[0055] As can be seen from the data in Table 1, the density of the spherical temporary plugging agent prepared by this invention can be adjusted to be between 0.97 and 1.03 g / cm³ by regulating the amounts of hollow glass microspheres and polyvinyl alcohol, as well as the density of the hollow microspheres themselves. 3The formula allows for adjustment within a certain range, facilitating the use of fracturing fluids of different densities. In the preparation of this spherical temporary plugging agent, two types of polyvinyl alcohol with different degrees of polymerization are used, along with aromatic mono-aldehydes at different stages. The acetalization reaction of the aromatic poly-aldehydes yields polyvinyl alcohol acetals that encapsulate hollow glass microspheres. The inner layer of the polyvinyl alcohol acetal exhibits a porous polyvinyl alcohol acetal sponge structure due to the gas generated by inorganic alkali and acid. The outer layer, through the subsequent addition of polyvinyl alcohol and poly-aldehydes, forms a high-crosslink density shell, resulting in high compressive strength. This prevents deformation due to pressure differentials, thus avoiding plugging failure. While improving plugging strength, it does not affect degradability, exhibits high permeability recovery, and does not damage the formation. Therefore, it is a green and environmentally friendly temporary plugging agent.

Claims

1. A pressure differential resistant, isodense spherical temporary plugging agent, characterized in that, Hollow glass microspheres are dispersed in polyvinyl acetal. The raw materials for preparing polyvinyl acetal include 28-35 parts by mass of polyvinyl alcohol 1 with a degree of polymerization of 1500-2000, 12-16 parts by mass of polyvinyl alcohol 2 with a degree of polymerization of 3000-4000, 0.5-1 parts by mass of aryl monoaldehyde, 0.2-0.3 parts by mass of aromatic polyaldehyde, 0.7-1.3 parts by mass of inorganic base, and 3-5 parts by mass of organic acid. The mass ratio of hollow glass microspheres to the total mass of polyvinyl alcohol is 100:40-55. The particle size of the pressure differential resistant isodense spherical temporary plugging agent is 8-30 mm. The aromatic monoaldehyde is selected from at least one of benzaldehyde, 1-naphthaldehyde, 2-naphthaldehyde, 9-anthraaldehyde, and salicylaldehyde; the aromatic polyaldehyde is selected from at least one of 2,6-naphthyldicarboxaldehyde, 2,3-naphthyldicarboxaldehyde, 2,6-dialdehyde-1,5-dihydroxynaphthalene, terephthalaldehyde, 3,4',5-trialdehyde-1,1-biphenyl, tetraaldehyde tetraphenylethylene, 3,3',5,5'-tetraaldehyde-biphenyl, tetra(4-aldehydephenyl)methane, and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl; the inorganic base is selected from at least one of sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate; the organic acid is selected from at least one of p-toluenesulfonic acid and chloroacetic acid. The preparation method of the pressure differential resistant isodense spherical temporary plugging agent includes the following steps: (S1) Hollow glass microspheres are immersed in an alcohol-water solution of aldehyde-based silane coupling agent, heated to react completely, removed, washed, and dried to obtain aldehyde-based surface-modified hollow glass microspheres; (S2) The aldehyde-modified hollow glass microspheres, polyvinyl alcohol 1, aromatic monoaldehyde, and inorganic alkali are mixed evenly and put into an injection molding machine. 60-80% organic acid is added and the mixture is kept at 210-230℃ for 5-7 hours. While maintaining the temperature, polyvinyl alcohol 2, aromatic polyaldehyde, and the remaining organic acid are added. The mixture is kept at the temperature for another 3-5 hours to complete the mixing, plasticizing, and homogenization. The mixture is then injected into a spherical mold, cooled, and the mold is opened to obtain the product.

2. The pressure differential resistant isodense spherical temporary plugging agent according to claim 1, characterized in that, The density of the spherical temporary plugging agent is between 0.95 and 1.05 g / cm³. 3 Adjustable within the range; withstands a pressure difference of ≥60 MPa at 90℃ for 120 minutes.

3. The pressure differential resistant isodense spherical temporary plugging agent according to claim 1, characterized in that, The aromatic polyaldehyde is a compound of a dialdehyde and an aldehyde with a functionality of 3 or higher in a mass ratio of 4-6:

1. The dialdehyde is selected from at least one of 2,6-naphthalenedicarboxyl, 2,3-naphthalenedicarboxyl, 2,6-dialdehyde-1,5-dihydroxynaphthalene, and terephthalaldehyde. The aldehyde with a functionality of 3 or higher is selected from 3,4',5-trialdehyde-1,1-biphenyl, tetraaldehyde-tetraphenylene, 3,3',5,5'-tetraaldehyde-biphenyl, tetra(4-aldehyde-phenyl)methane, and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl.

4. The pressure differential resistant isodense spherical temporary plugging agent according to claim 1, characterized in that, The polyaldehyde is a compound of alkane dialdehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 4-6:

1.

5. The pressure differential resistant, isodense spherical temporary plugging agent according to claim 1, wherein in step (S1), the hollow glass microspheres have a particle size of 20-80 μm and a true density of 0.55-0.65 g / cm³. 3 Closed hollow glass microspheres with a compressive strength of 40-70 MPa.

6. The pressure differential resistant isodense spherical temporary plugging agent according to claim 1, in step (S1), the aldehyde-based silane coupling agent is selected from at least one of 4-(trimethoxymethylsilane)butyraldehyde, 4-(triethoxymethylsilane)butyraldehyde, and 4-(tripropoxymethylsilane)butyraldehyde; the concentration of the aldehyde-based silane coupling agent in the alcohol-water solution is 4-7 wt%, the volume concentration of the alcohol in the alcohol-water solution is 60-80%, and the alcohol is at least one of methanol, ethanol, and isopropanol; the heating reaction is carried out at 40-60℃ for 6-10 h; and the washing is performed by alcohol washing 3-5 times.

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