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

Abstract

The invention relates to a pressure-difference-resistant equal-density spherical temporary plugging agent which is of a core-shell composite structure with a core material and a shell layer, hollow glass microspheres serve as the core material and are dispersed in polyvinyl acetal, and the polyvinyl acetal is prepared from the following raw materials in parts by mass: 28-35 parts of polyvinyl alcohol 1 with the polymerization degree of 1500-2000, 12-16 parts of polyvinyl alcohol 2 with the polymerization degree of 3000-4000 and 0.5-1 part of aryl group monoaldehyde. 0.2-0.3 part 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 ratio of the mass of the hollow glass microspheres to the total mass of the polyvinyl alcohol is 100: (35-50); the particle size of the temporary plugging agent is 8-30 mm. The density of the spherical temporary plugging agent is continuously adjustable in a range of 0.95-1.05 g / cm < 3 >, and the density difference is lt; and 0.03 g / cm < 3 >. The temporary plugging agent provided by the invention has the characteristics of slow dissolution in water, adhesion, spontaneous aggregation, bridging and plugging, and automatic adhesion loss and plugging removal in water dissolution.

Description

Technical Field

[0001] The invention belongs to the technical field of temporary plugging for oil and gas exploration and exploitation fracturing, and particularly relates to a pressure difference resistant equal density spherical temporary plugging agent and a preparation method thereof. Background Art

[0002] Horizontal well ball-dropping temporary fracturing involves injecting temporary plugging agents into high-permeability blastholes for a period of time, increasing the perforation blasthole opening rate and forcing the fracturing fluid to divert to low-permeability zones, thereby promoting the development of fractures in low-permeability areas. After fracturing, the plugging can be self-unplugged by the dissolution or hydrolysis of the water-based fracturing fluid. It is an important technical means of increasing production in unconventional oil and gas reservoirs. Horizontal well ball-dropping temporary fracturing requires the spherical temporary plugging agent to have a sufficiently high plugging efficiency. The plugging efficiency of a spherical temporary plugging agent is closely related to its pressure resistance difference and density difference. Spherical temporary plugging agents with a density greater than that of the fracturing fluid tend to sink and become dead balls that are difficult for the fracturing fluid to transport to the high-permeability blastholes, affecting their plugging efficiency. Floating temporary plugging agents with a density less than that of the fracturing fluid are relatively effective, but their plugging efficiency is still lower than that of suspended, isopycnic temporary plugging agents with a density close to that of the fracturing fluid. If the pressure differential resistance (plugging strength) of a spherical temporary plugging ball is insufficient, even if it can be transported by the fracturing fluid to the high-permeability blasthole, it will quickly deform and fail under the high pressure differential generated by fracturing, thus affecting its plugging efficiency. Temporary plugging materials with high pressure differential resistance and water solubility or hydrolysis typically have a density significantly higher than that of water-based fracturing fluid. Currently, there is a lack of water-soluble temporary plugging materials with a density close to that of fracturing fluid or lower than that of water and sufficient temporary plugging strength for fracturing. The current market for water-soluble spherical temporary plugging agents has a suboptimal plugging effect in oil and gas field fracturing operations, partly due to their higher density than water-based fracturing fluids and insufficient plugging strength.

[0003] CN106047323A discloses a water-soluble temporary plugging agent made from bone glue, modified starch, and hydroxypropyl guar gum. It can withstand high pressures but is not heat-resistant, requiring only temperatures 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, and carbon fibers, but the agent has a low degradation rate and requires high temperatures and pressures to completely break down into tiny particles that can move with the water flow. CN118703184A discloses a temporary plugging particle for oil and gas field fracturing. The particle is spherical and comprises a spherical ceramic aggregate and a temporary plugging agent coating applied to the spherical ceramic aggregate. The temporary plugging agent coating is composed, based on 100 parts by weight, of the following raw materials: 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 temporary plugging particles. CN118206969A discloses a temporary plugging ball for fracturing. The ball has a core-shell structure. The inner core is a spherical structure formed by mixing and granulating a two-component temporary plugging material, comprising polypropylene and / or polyethylene. The outer shell is made of polyurethane rubber and polyvinyl alcohol. The temporary plugging agents in the above patents have a relatively high density and are prone to sinking to become dead balls that are difficult to be transported by the fracturing fluid to the high-permeability boreholes, thereby affecting the plugging efficiency.

[0004] CN118460192A discloses a low-density water-soluble room-temperature temporary plugging agent for coal mine hydraulic fracturing, which is made from sodium acrylate, acrylamide, and polyvinyl alcohol paraffin. The density of the temporary plugging agent obtained by testing is 0.92 g / cm 3 At the same temperature, the density of water is 0.9971 g / cm 3On the one hand, too low a density is not conducive to the plugging effect. On the other hand, the temporary plugging agent of this patent has a breakage rate of over 10% under relatively high pressure, which limits the plugging strength. CN116462797A discloses a polymer copolymer temporary plugging agent obtained by copolymerizing acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, methyl acrylate, and a cross-linking agent. The density can be adjusted by controlling the raw materials and the ratio. CN115850573A discloses a similar polymer-based temporary plugging agent obtained by copolymerizing acrylamide, methyl acrylate, a cross-linking agent, an initiator, etc. This type of polymer material temporary plugging agent can obtain a spherical temporary plugging agent of appropriate density by regulating the type and ratio of monomers, but it is difficult to balance the requirements of strength and degradability. If the plugging ability is to be improved, the amount of cross-linking agent used needs to be increased, which will reduce the degradation performance. In other words, the temporary plugging agent of this patent cannot balance strength and degradability. The ideal temporary plugging agent basically does not degrade in the initial injection stage and can be rapidly degraded after the plugging is completed. Moreover, this type of pure polymer temporary plugging agent is difficult to completely remove from the bottom layer, which causes great damage to the formation and may reduce the permeability of the formation, and is not green and environmentally friendly.

[0005] CN115838589A discloses a granular temporary plugging agent for fracturing diversion, prepared using polyvinyl alcohol, an aldehyde crosslinker, and a catalyst. The agent is prepared by mixing polyvinyl alcohol, a dialdehyde crosslinker, and a latent acid catalyst, and then subjecting the mixture to a freeze-thaw cycle to produce a gel. However, the strength of this temporary plugging agent is determined by using the crystallized regions formed by the polyvinyl alcohol during the freeze-thaw process as physical crosslinking points. These physical crosslinking points rapidly lose their effectiveness at high temperatures. Even if the dialdehyde forms low-density chemical crosslinks, even if the agent does not degrade at high temperatures, it will rapidly lose strength and deform, even breaking into pieces, due to the loss of physical crosslinking points. Therefore, its plugging ability is limited in high-temperature environments.

[0006] Therefore, a new fracturing fluid with a density close to that of the fracturing fluid (density difference ≤ 0.03 g / cm 3 The spherical temporary plugging agent has important practical significance and use value. It has high pressure resistance difference, can be used in high temperature environment, has appropriate degradation time, and will not cause damage to the formation after degradation. Summary of the Invention

[0007] In order to make up for the deficiencies of the above-mentioned prior art, the present invention provides a kind of water-based fracturing fluid with a density close to that of the water-based fracturing fluid (density difference <0.03g / cm 3 ), a spherical temporary plugging agent with good suspension, high temporary plugging strength, self-unblocking ability, and environmentally friendly properties, and a preparation method thereof. Specifically, the present invention provides the following technical solutions to achieve the above-mentioned objectives: A pressure differential-resistant, isodense spherical temporary plugging agent comprises hollow glass microspheres as a core material dispersed in polyvinyl acetal. The polyvinyl acetal is prepared by raw materials including 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 part by mass of an aromatic monoaldehyde, 0.2-0.3 parts by mass of an aromatic polyaldehyde, 0.7-1.3 parts by mass of an inorganic base, and 3-5 parts by mass of an organic acid. The ratio of the mass of the hollow glass microspheres to the total mass of the 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 the polyvinyl alcohol is the sum of the masses of the polyvinyl alcohol 1 and the polyvinyl alcohol 2.

[0008] The present invention uses aromatic aldehydes for acetalization because of their high boiling points. Since the subsequent injection molding stage is carried out at a high temperature above 220°C, it is necessary to select aldehydes with a boiling point higher than 220°C.

[0009] The density of the pressure difference resistant equal density spherical temporary plugging agent is 0.95-1.05g / cm 3 Adjustable within the range, preferably 0.97-1.03g / cm 3 Adjustable within the range, more preferably 0.98-1.02g / cm 3 range, such as 0.99 g / cm 3 , 1.00 g / cm 3 , 1.01g / cm 3 Furthermore, the differential pressure resistant spherical temporary plugging agent of the present invention has a differential pressure resistance of ≥60 MPa at 90°C for 120 minutes. Furthermore, the spherical temporary plugging agent of the present invention exhibits suitable degradation properties. It does not degrade in the initial stage of use, maintaining excellent plugging performance. After a certain period of time, the degradation rate accelerates, allowing it to be completely discharged from the formation without affecting the formation permeability.

[0010] Furthermore, the aromatic monoaldehyde is selected from at least one of benzaldehyde, 1-naphthaldehyde, 2-naphthaldehyde, 9-anthracenealdehyde, and salicylaldehyde; the aromatic polyaldehyde is selected from at least one of 2,6-naphthalene dicarboxaldehyde, 2,3-naphthalene dicarboxaldehyde, 2,6-dialdehyde-1,5-dihydroxynaphthalene, terephthalaldehyde, 3,4',5-trialdehyde-1,1-biphenyl, tetraaldehyde tetraphenylethylene, 3,3',5,5'-tetraaldehyde biphenyl, tetrakis(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.

[0011] Furthermore, the polyaldehyde is a compound of a dialdehyde and an aldehyde with a functionality of 3 or more in a mass ratio of 4-6:1, the dialdehyde is selected from at least one of 2,6-naphthalene dicarboxaldehyde, 2,3-naphthalene dicarboxaldehyde, 2,6-dialdehyde-1,5-dihydroxynaphthalene, and terephthalaldehyde, and the aldehyde with a functionality of 3 or more is selected from 3,4',5-trialdehyde-1,1-biphenyl, tetraaldehyde tetraphenylethylene, 3,3',5,5'-tetraaldehyde biphenyl, tetrakis(4-aldehydephenyl)methane, and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl.

[0012] In the preparation of cross-linked polyvinyl acetal, a combination of the aforementioned dialdehyde and an aldehyde with a functionality of 3 or greater can ensure that the cross-linked polyvinyl acetal in the shell has both mechanical strength and suitable degradability. Preferably, the aromatic polyaldehyde is a combination of the dialdehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 4-6:1.

[0013] The second object of the present invention is to provide a method for preparing the above-mentioned pressure difference resistant isodensity spherical temporary plugging agent, comprising the following steps: (S1) immersing the hollow glass microspheres in an alcohol aqueous solution of an aldehyde silane coupling agent, heating to fully react, removing, washing, and drying to obtain aldehyde surface-modified hollow glass microspheres; (S2) The aldehyde surface-modified hollow glass microspheres, polyvinyl alcohol 1, aromatic monoaldehyde, and inorganic base are uniformly mixed, put into an injection molding machine, 60-80% of an organic acid is added, and the mixture is kept warm at 210-230°C for 5-7 hours. The temperature is maintained, polyvinyl alcohol 2, aromatic polyaldehyde, and the remaining organic acid are added, and the mixture is kept warm for 3-5 hours to complete mixing, plasticization, and homogenization. The mixture is injected into a spherical mold, cooled, and opened to obtain the product.

[0014] The alcoholysis degree of the polyvinyl alcohol used in the present invention is ≥90%, preferably ≥95%.

[0015] Furthermore, 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 / cm 3 , closed hollow glass microspheres with a compressive strength of 40-70 MPa; the aldehyde 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 silane coupling agent in the alcohol aqueous solution is 4-7wt%, the volume concentration of alcohol in the alcohol aqueous solution is 60-80%, and the alcohol is at least one of methanol, ethanol, and isopropanol; heating for sufficient reaction is to react at 40-60°C for 6-10h; washing is 3-5 times of alcohol washing.

[0016] After treating the hollow glass microspheres with an aldehyde-based silane coupling agent, the surfaces of the microspheres are modified with aldehyde groups. In the subsequent acetalization reaction of polyvinyl alcohol (PVA), the aldehyde groups on the surface of the hollow glass microspheres also participate in the reaction, forming a chemical bond between the hollow glass microspheres and the PVA shell, improving compatibility and enhancing the performance of the core-shell spherical temporary plugging agent. A combination of aromatic monoaldehydes (such as benzaldehyde) and polyaldehydes (such as alkane dialdehydes and aromatic polyaldehydes) optimizes the shell structure through staged crosslinking. The aromatic monoaldehyde preferentially reacts with PVA 1 to form a preliminary crosslinked network. The polyaldehyde is subsequently introduced, primarily to enhance the crosslink density on the outer surface. This results in a porous inner layer of the spherical temporary plugging agent, reducing its density and facilitating degradation. The increased crosslink density in the outer layer provides sufficient plugging strength and pressure differential resistance, and also demonstrates excellent plugging strength even at high temperatures. The existing technology mostly uses a single aldehyde and polyvinyl alcohol for polycondensation, which has a single cross-linking structure and is difficult to balance mechanical strength and degradability. The present invention adopts a two-stage process. First, polyvinyl alcohol 1 with a lower degree of polymerization is polycondensed with an aromatic monoaldehyde. During the polycondensation process, the added inorganic base and organic acid catalyst react to produce gas, forming a porous polyvinyl alcohol acetal with a certain pore structure; then polyvinyl alcohol 2 with a high degree of polymerization and a polyaldehyde are added to form a polyvinyl alcohol acetal with a higher cross-linking density in the outer layer, thereby improving the blocking strength of the spherical temporary plugging agent. This specific high cross-linking shell structure makes the spherical temporary plugging agent of the present invention basically non-degradable in the initial stage of input, and has excellent blocking ability at high temperature. As the high cross-linking shell degrades, the degradation rate in the later stage is rapidly accelerated. It can be quickly dissolved in hot water, does not require acidic deblocking, is green and environmentally friendly, and will not cause damage to the formation permeability.

[0017] In particular, when polyaldehydes are added, the combination of dialdehydes and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl produces a product that not only exhibits both strength and degradation capabilities but also 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.

[0018] The present invention can conveniently adjust the density of the spherical temporary plugging agent to 0.95~1.05g / cm by adjusting the relative ratio of hollow glass microspheres and polyvinyl alcohol. 3 Continuously adjustable, close to fracturing fluids of different densities, density difference <0.03g / cm 3 The temporary plugging agent provided by the present invention has the characteristics of slowly dissolving in water, forming stickiness, spontaneously agglomerating and bridging to block, and dissolving in abundant water to lose stickiness and unblock. The degradation rate is basically no degradation in the early stage, and the degradation rate is accelerated in the later stage. It can meet the plugging requirements and can also be quickly discharged from the formation without damaging the formation permeability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a physical picture of the spherical temporary plugging agents of Example 1 and Comparative Example 6.

[0020] Figure 2 These are photos of the distribution states of the spherical temporary plugging agents of Example 1 and Comparative Example 6 in the fracturing fluid. DETAILED DESCRIPTION

[0021] The present invention is further described below with reference to examples, but the scope of protection of the present invention is not limited to the examples. The alcoholysis degree of the polyvinyl alcohol used in the present invention is above 90%. Example 1

[0022] (S1) hollow glass microspheres (density 0.61 g / cm 3 ) were immersed in an ethanol aqueous solution with a concentration of 5 wt% of 4-(trimethoxymethylsilyl)butyraldehyde (the volume ratio of ethanol to water was 8:2), heated to 50°C under stirring for 10 h, taken out, washed three times with anhydrous ethanol, and vacuum-dried to obtain aldehyde-surface-modified hollow glass microspheres; (S2) 100 parts by mass of aldehyde surface-modified hollow glass microspheres, 32 parts by mass of polyvinyl alcohol with a degree of polymerization of 2000, 0.83 parts by mass of 1-naphthaldehyde, and 1 part by mass of sodium bicarbonate are mixed evenly, put into an injection molding machine, 3 parts by mass of p-toluenesulfonic acid are added, and the mixture is kept warm at 220°C for 7 hours. While maintaining the temperature, 15 parts by mass of polyvinyl alcohol with a degree of polymerization of 3500, 0.26 parts by mass of polyaldehyde (a mixture of 2,6-naphthalenedicarboxaldehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 5:1), and 1 part by mass of p-toluenesulfonic acid are added, and the mixture is kept warm for 4 hours to complete the mixing, plasticizing, and homogenization. The mixture is injected into a spherical mold, and the mold is cooled and opened to obtain the product, which is a spherical temporary plugging agent with a diameter of about 20 mm. Example 2

[0023] (S1) hollow glass microspheres (density 0.55 g / cm 3 ) were immersed in an ethanol aqueous solution with a concentration of 4 wt% of 4-(triethoxymethylsilane)butyraldehyde (the volume ratio of ethanol to water was 8:2), heated to 50°C under stirring for 10 h, taken out, washed three times with anhydrous ethanol, and vacuum-dried to obtain aldehyde-surface-modified hollow glass microspheres; (S2) 100 parts by mass of aldehyde surface-modified hollow glass microspheres, 35 parts by mass of polyvinyl alcohol with a degree of polymerization of 2000, 1.1 parts by mass of 1-naphthaldehyde, and 1.2 parts by mass of sodium bicarbonate are mixed evenly, put into an injection molding machine, 3.2 parts by mass of p-toluenesulfonic acid are added, and the mixture is kept warm at 220°C for 7 hours. While maintaining the temperature, 18 parts by mass of polyvinyl alcohol with a degree of polymerization of 4000, 0.3 parts by mass of polyaldehyde (a mixture of 2,6-naphthalenedicarboxaldehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 6:1), and 1 part by mass of p-toluenesulfonic acid are added, and the mixture is kept warm for 4 hours to complete the mixing, plasticizing, and homogenization, and the mixture is injected into a spherical mold. The mold is cooled and opened to obtain the product, which is a spherical temporary plugging agent with a diameter of about 20 mm. Example 3

[0024] (S1) hollow glass microspheres (density 0.64 g / cm 3 ) were immersed in an ethanol aqueous solution with a concentration of 5 wt% of 4-(trimethoxymethylsilyl)butyraldehyde (the volume ratio of ethanol to water was 8:2), heated to 50°C under stirring for 10 h, taken out, washed three times with anhydrous ethanol, and vacuum-dried to obtain aldehyde-surface-modified hollow glass microspheres; (S2) 100 parts by mass of aldehyde surface-modified hollow glass microspheres, 28 parts by mass of polyvinyl alcohol with a degree of polymerization of 2000, 0.7 parts by mass of 1-naphthaldehyde, and 0.8 parts by mass of sodium bicarbonate are mixed evenly, put into an injection molding machine, 2.5 parts by mass of p-toluenesulfonic acid are added, and the mixture is kept warm at 220°C for 7 hours. While maintaining the temperature, 12 parts by mass of polyvinyl alcohol with a degree of polymerization of 4000, 0.22 parts by mass of polyaldehyde (a mixture of 2,3-naphthalenedicarboxaldehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 4:1), and 0.7 parts by mass of p-toluenesulfonic acid are added, and the mixture is kept warm for 4 hours to complete the mixing, plasticizing, and homogenization. The mixture is injected into a spherical mold, cooled, and opened to obtain a product, which is a spherical temporary plugging agent with a diameter of about 20 mm. Example 4

[0025] Other conditions were the same as those in Example 1, except that step (S2) was modified to: 100 parts by mass of aldehyde-surface-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 a polyaldehyde (a mixture of 2,6-naphthalenedicarboxaldehyde and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl in a mass ratio of 5:1), and 1 part by mass of sodium bicarbonate were mixed uniformly, placed in an injection molding machine, 4 parts by mass of p-toluenesulfonic acid were added, and the mixture was kept at 220°C for 10 hours to complete mixing, plasticization, and homogenization. The mixture was then injected into a spherical mold, cooled, and opened to obtain a spherical temporary plugging agent with a diameter of approximately 20 mm. That is, compared to Example 1, step S2 of Example 4 was a one-stage acetalization reaction, while Example 1 was a two-stage acetalization reaction. Example 5

[0026] Other conditions are the same as those in Example 1, except that in step (S2), 0.26 parts by mass of the polyaldehyde is a mixture of 2,6-naphthalenedicarboxaldehyde and 3,3',5,5'-tetraaldehydebiphenyl in a mass ratio of 5:1. Example 6

[0027] Other conditions are the same as those in Example 1, except that in step (S2), all of the 0.26 parts by mass of the polyaldehyde are 2,6-naphthalene dicarboxaldehyde. Example 7

[0028] Other conditions were the same as those in Example 1, except that in step (S2), all of the 0.26 parts by mass of the polyaldehyde were 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl.

[0029] Comparative Example 1 Other conditions were the same as those in Example 1, except that step (S1) was eliminated and hollow glass microspheres that had not been treated with an aldehyde-based silane coupling agent were used in step (S2).

[0030] Comparative Example 2 Other conditions were the same as those in Example 1, except that in step (S2), 15 parts by mass of polyvinyl alcohol with a degree of polymerization of 3500 was replaced by an equal amount of polyvinyl alcohol with a degree of polymerization of 2000. That is, the degree of polymerization of all polyvinyl alcohols was 2000.

[0031] Comparative Example 3 Other conditions were the same as those in Example 1, except that in step (S2), 32 parts by mass of polyvinyl alcohol with a degree of polymerization of 2000 was replaced by an equal amount of polyvinyl alcohol with a degree of polymerization of 3500. That is, the degree of polymerization of all polyvinyl alcohols was 3500.

[0032] Comparative Example 4 Other conditions are the same as those in Example 1, except that sodium bicarbonate is not added in step (S2).

[0033] Comparative Example 5 Other conditions were the same as those in Example 1, except that step (S1) was eliminated and in step (S2), 0.26 parts by mass of the polyaldehyde was replaced by 0.5 parts by mass of 1-naphthaldehyde.

[0034] Comparative Example 6 A commercial blasthole temporary plugging agent with a density of 1.09g / cm 3 .

[0035] Figure 1 These are physical pictures of the spherical temporary plugging agents of Example 1 (left) and Comparative Example 6 (right).

[0036] Figure 2The distribution of the spherical temporary plugging agents from Example 1 and Comparative Example 6 in a simulated fracturing fluid at 60°C is shown. The left image shows the result immediately after addition of the simulated fracturing fluid, and the right image shows the result 4 hours after addition. The simulated fracturing fluid formulation consists of: 0.15wt% water-soluble polyethylene oxide, 0.5wt% NaCl, 0.1wt% KCl, 0.6wt% cetyltrimethylammonium chloride, 0.1wt% drainage aid CF-5D, 5wt% spherical temporary plugging agent, and the balance water. As can be seen, the spherical temporary plugging agent from Example 1 remains stably suspended in the 60°C simulated fracturing fluid, while the commercial spherical temporary plugging agent from Comparative Example 6 sinks and fails to effectively seal the fluid.

[0037] Application Examples The spherical temporary plugging agents prepared in the above examples and comparative examples were subjected to performance tests, and the results are shown in Table 1 below.

[0038] The plugging strength and 120h solubility are tested in accordance with the petroleum and natural gas industry standard (SY / T 7811-2024). The plugging strength test temperature is 90°C, and the effective plugging time is ≥120min.

[0039] In the temporary plugging rate and permeability recovery rate tests, the permeability of the simulated core was 5200-5400×10 -3 μm 2 The length of the crack is 7-8 cm, the diameter is 2.5±0.1 cm, the test temperature is 90°C, and the fracturing fluid is injected into the simulated core (fracturing fluid formula: 0.15wt% water-soluble polyethylene oxide, 0.5wt% NaCl, 0.1wt% KCl, 0.6wt% hexadecyltrimethylammonium chloride, 0.1wt% drainage agent CF-5D, 5wt% spherical temporary plugging agent, and the balance is water). The permeability before and after plugging is tested, and the temporary plugging rate is calculated; then the formation water is used for flushing, and the permeability recovery rate is calculated.

[0040] During the solubility test, the mass of the hollow glass microspheres was not considered, and only the mass loss rate of the polyvinyl acetal at 90°C was calculated.

[0041]

[0042] It can be seen from the data in Table 1 that the density of the spherical temporary plugging agent prepared by the present invention can be adjusted to 0.97-1.03 g / cm by adjusting the amount of hollow glass microspheres and polyvinyl alcohol, as well as the density of the hollow microspheres themselves. 3The invention can adjust the spherical temporary plugging agent within a certain range, so as to facilitate the use of fracturing fluids with different densities. In the preparation of the spherical temporary plugging agent, two polyvinyl alcohols with different polymerization degrees are used, and the acetalization reaction of aromatic monoaldehyde and aromatic polyaldehyde at different stages is used to prepare polyvinyl acetal to coat the hollow glass microspheres. The inner layer of the polyvinyl acetal produces a porous polyvinyl acetal sponge structure due to the gas generated by inorganic alkali and acid; the outer layer is formed by the subsequent addition of polyvinyl alcohol and polyaldehyde to produce a high cross-linking density shell, which has high compressive strength and will not deform due to pressure difference and thus fail to seal. While improving the sealing strength, it will not affect the degradability, has a high permeability recovery rate, and will not cause damage to the formation. It is a temporary plugging agent that is green and friendly to the formation environment.

Claims

1. A pressure differential resistant and isodense spherical temporary plugging agent, characterized in that: Hollow glass microspheres are dispersed in polyvinyl acetal. The raw materials for preparing the polyvinyl acetal include 28-35 parts by mass of polyvinyl alcohol 1 with a polymerization degree of 1500-2000, 12-16 parts by mass of polyvinyl alcohol 2 with a polymerization degree of 3000-4000, 0.5-1 part by mass of aromatic monoaldehyde, 0.2-0.3 part 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 ratio of the mass of the hollow glass microspheres to the total mass of the polyvinyl alcohol is 100:40-55. The particle size of the pressure difference resistant isodensity spherical temporary plugging agent is 8-30 mm.

2. The pressure difference resistant and isodense spherical temporary plugging agent according to claim 1, characterized in that: The density of the spherical temporary plugging agent is 0.95-1.05g / cm 3 Adjustable within the range; 90℃, 120min pressure difference ≥60Mpa.

3. The pressure difference resistant and isodense spherical temporary plugging agent according to claim 1, characterized in that: The aromatic monoaldehyde is at least one selected from benzaldehyde, 1-naphthaldehyde, 2-naphthaldehyde, 9-anthracenealdehyde, and salicylaldehyde.

4. The pressure difference resistant and isodense spherical temporary plugging agent according to claim 1, characterized in that: The aromatic polyaldehyde is selected from at least one of 2,6-naphthalene dicarboxaldehyde, 2,3-naphthalene dicarboxaldehyde, 2,6-dialdehyde-1,5-dihydroxynaphthalene, terephthalaldehyde, 3,4',5-trialdehyde-1,1-biphenyl, tetraaldehyde tetraphenylethylene, 3,3',5,5'-tetraaldehyde biphenyl, tetrakis(4-aldehydephenyl)methane, and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl.

5. The pressure difference resistant and isodense spherical temporary plugging agent according to claim 1, characterized in that: 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.

6. The pressure difference resistant and 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 more in a mass ratio of 4-6:1, the dialdehyde is selected from at least one of 2,6-naphthalene dicarboxaldehyde, 2,3-naphthalene dicarboxaldehyde, 2,6-dialdehyde-1,5-dihydroxynaphthalene, and terephthalaldehyde, and the aldehyde with a functionality of 3 or more is selected from 3,4',5-trialdehyde-1,1-biphenyl, tetraaldehyde tetraphenylethylene, 3,3',5,5'-tetraaldehyde biphenyl, tetrakis(4-aldehydephenyl)methane, and 3,3',5,5'-tetraaldehyde-4,4'-dihydroxybiphenyl.

7. The pressure difference resistant and 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.

8. The method for preparing the pressure difference resistant and isodense spherical temporary plugging agent according to any one of claims 1 to 7, characterized in that: The following steps are involved: (S1) immersing the hollow glass microspheres in an alcohol aqueous solution of an aldehyde silane coupling agent, heating to fully react, removing, washing, and drying to obtain aldehyde-surface-modified hollow glass microspheres; (S2) The aldehyde surface-modified hollow glass microspheres, polyvinyl alcohol 1, aromatic monoaldehyde, and inorganic base are uniformly mixed, put into an injection molding machine, 60-80% of an organic acid is added, and the mixture is kept warm at 210-230°C for 5-7 hours. The temperature is maintained, polyvinyl alcohol 2, aromatic polyaldehyde, and the remaining organic acid are added, and the mixture is kept warm for 3-5 hours to complete mixing, plasticization, and homogenization. The mixture is injected into a spherical mold, cooled, and opened to obtain the product.

9. The preparation method according to claim 8, 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 / cm 3 , closed hollow glass microspheres with compressive strength of 40-70MPa.

10. The preparation method according to claim 8, wherein in step (S1), the aldehyde 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 silane coupling agent in the alcohol aqueous solution is 4-7wt%, the volume concentration of the alcohol in the alcohol aqueous solution is 60-80%, and the alcohol is at least one of methanol, ethanol, and isopropanol; heating for sufficient reaction is reacting at 40-60° C. for 6-10 hours; and washing is washing with alcohol 3-5 times.

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