Temperature-resistant and compression-resistant temporary plugging agent as well as preparation method and application thereof

Abstract

The invention relates to the field of oilfield chemical industry. The invention relates to a temporary plugging agent, in particular to a temperature-resistant and compression-resistant temporary plugging agent and a preparation method and application thereof. The temperature-resistant and compression-resistant temporary plugging agent is prepared from the following raw material components in parts by weight: 60 to 80 parts of graphene modified polyimide; 5-10 parts of calcium carbonate nanofibers of which the surfaces are assembled with amphiphilic block copolymers; 0.1-2 parts of an auxiliary agent; wherein the graphene modified polyimide is prepared by taking biphenyl tetracarboxylic dianhydride, ethidene diamine and maleic anhydride as polymerization reaction raw materials, and adding graphene to carry out in-situ polymerization modification; the amphiphilic block copolymer assembled on the surface of the calcium carbonate nanofiber is polystyrene-b-polyacrylic acid. The temperature-resistant and compression-resistant temporary plugging agent provided by the invention has excellent high temperature resistance, compression resistance and plugging capacity, can be quickly hydrolyzed and crushed after temporary plugging is finished, can realize quick plugging removal, and is suitable for a high-temperature and high-pressure mining environment with the formation temperature (use environment) of 241-270 DEG C and the formation pressure of 100 Mpa or above.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical engineering. More specifically, it relates to a temperature- and pressure-resistant temporary plugging agent, its preparation method, and its application. Background Technology

[0002] Traditional high-permeability oil and gas reservoirs are facing increasing resource depletion and challenges in maintaining stable production due to long-term large-scale exploitation. Meanwhile, low-permeability oil and gas reservoirs with abundant reserves face significant technical challenges in their economically effective development due to poor reservoir properties and low natural productivity. Against this backdrop, fracturing technology, as a key means to enhance oil and gas well production and water injection well injection, plays an irreplaceable role in improving reservoir utilization and oil and gas recovery rates.

[0003] In fracturing technology, temporary plugging agents are core materials for achieving precise reservoir stimulation and fracture network expansion. By temporarily plugging already opened fractures, they redirect fracturing fluid towards insufficiently stimulated areas, thereby forming a complex fracture network and significantly increasing the stimulated volume. As oil and gas exploration and development gradually moves towards deeper and ultra-deep formations, downhole temperature and pressure conditions are becoming increasingly extreme, with some formation temperatures reaching over 240°C, even approaching 300°C, and the pressure environment becoming more demanding. Furthermore, the differences in geological conditions among various oil and gas reservoirs place diverse demands on the performance of temporary plugging agents, necessitating the development of temporary plugging agent systems capable of adapting to complex high-temperature and high-pressure environments to meet application needs under different operating conditions.

[0004] Currently, various temporary plugging agents have been reported, but their temperature and pressure resistance still falls short of the requirements for deep oil and gas reservoir stimulation. For example, the water-soluble temporary plugging agent (composed of bone glue, modified starch, etc.) disclosed in CN106047323A has an operating temperature below 100℃; the acid fracturing temporary plugging agent (resin, ceresin, inorganic salts, etc.) involved in CN102604627A has a maximum applicable temperature of about 100℃ and a plugging strength greater than 50MPa, but its high-temperature adaptability is still insufficient; the water-soluble temporary plugging agent (plant starch, polymers, etc.) described in CN103409121A also has an operating temperature below 120℃. Therefore, existing temporary plugging agent technologies are mostly concentrated in medium- and low-temperature formations, facing risks such as performance degradation and plugging failure under high-temperature and high-pressure environments.

[0005] Polyimide, a high-performance polymer with an imide ring structure in its main chain, is hailed as the "pinnacle of polymer materials" due to its excellent thermal stability, mechanical strength, and chemical inertness. In recent years, researchers have attempted to use it in the development of temporary plugging agents to improve its temperature and pressure resistance. For example, CN 117304894A discloses a high-temperature resistant temporary plugging agent based on thermoplastic polyimide and polyamide, which can operate stably at 250–270℃ and has a pressure resistance of up to 100 MPa, demonstrating good degradability and adaptability to high temperature and pressure. However, the pressure resistance of this temporary plugging agent under further ultra-high temperature conditions (such as above 270℃) remains insufficient, making it difficult to meet the higher performance requirements of materials under current extreme working conditions.

[0006] Therefore, developing a high-performance temporary plugging agent that can withstand ultra-high temperatures above 270℃ and a pressure resistance of no less than 100MPa has become a key technological requirement for promoting the effective development of deep and ultra-deep oil and gas resources, and also has important engineering application value and practical significance. Summary of the Invention

[0007] Based on the above-mentioned deficiencies, the first objective of this invention is to provide a temperature- and pressure-resistant temporary plugging agent. This temperature- and pressure-resistant temporary plugging agent possesses both excellent high-temperature resistance and pressure resistance, making it suitable for fracturing operations with formation temperatures of 241-270℃ and ground pressures exceeding 100 MPa.

[0008] The second objective of this invention is to provide a method for preparing the temperature-resistant and pressure-resistant temporary plugging agent as described above.

[0009] A third objective of this invention is to provide an application of the temperature-resistant and pressure-resistant temporary plugging agent described above in oil and gas extraction or geothermal extraction.

[0010] To achieve the first objective mentioned above, the present invention adopts the following technical solution: This invention discloses a temperature-resistant and pressure-resistant temporary plugging agent, which comprises the following raw material components by weight: 60-80 parts of graphene-modified polyimide; 5-10 parts of calcium carbonate nanofibers with amphiphilic block copolymers assembled on their surface; 0.1-2 parts of auxiliary agent; The graphene-modified polyimide is prepared by in-situ polymerization modification using biphenyl tetracarboxylic dianhydride, ethylenediamine and maleic anhydride as polymerization raw materials and adding graphene. The amphiphilic block copolymer assembled on the surface of calcium carbonate nanofibers is polystyrene-b-polyacrylic acid.

[0011] Furthermore, the graphene-modified polyimide is prepared according to the following steps: Biphenyltetracarboxylic dianhydride, ethylenediamine, and maleic anhydride were dissolved in dimethyl sulfoxide at room temperature. Then, graphene was added, and the reaction system was heated to 50-90°C for reflux reaction. After filtration and drying, graphene-modified polyimide powder was obtained.

[0012] The polyimide matrix resin powder of this invention is prepared using biphenyl dianhydride as the aromatic dianhydride monomer, ethylenediamine as the diamine monomer, and maleic anhydride as the end-capping agent. Biphenyl dianhydride contains an aryl benzene ring structure, resulting in polyimide with higher thermal stability compared to polyimide without an aryl benzene ring. The polyimide prepared by this invention has a melting point above 300°C, a weight-average molecular weight of 10,000-25,000, preferably a melting point of 300-325°C, exhibiting excellent thermal stability. Simultaneously, this invention disperses graphene powder into the polyimide resin matrix through in-situ polymerization. This method ensures sufficient contact between graphene and the monomers during polymerization, achieving nanoscale uniform dispersion within the resin matrix, which is impossible to achieve with simple physical blending (addition). Furthermore, this invention disperses graphene powder into the polyimide resin matrix through an in-situ polymerization process. The polar groups (such as hydroxyl and carboxyl groups) on the surface of graphene can form stable hydrogen bonds with the polar groups on the polyimide molecular chain, resulting in good interfacial compatibility and structural stability. Furthermore, graphene can effectively scavenge free radicals and inhibit the thermal oxidative degradation of the resin matrix. Based on the robust interfacial effect constructed through in-situ polymerization, graphene significantly enhances the heat resistance and high-temperature dimensional stability of the matrix resin.

[0013] Furthermore, the amount of graphene added is 0.8-2 wt% of the mass of biphenyltetracarboxylic dianhydride; for example, the amount of graphene added is 0.8 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt% of the mass of biphenyltetracarboxylic dianhydride, etc.

[0014] Furthermore, the molar ratio of biphenyltetracarboxylic dianhydride, ethylenediamine, and maleic anhydride is 1:1.1:0.1.

[0015] Furthermore, the calcium carbonate nanofibers with amphiphilic block copolymers assembled on their surface are prepared according to the following steps: Calcium carbonate nanofibers were dispersed in ethanol, a coupling agent was added, and the mixture was stirred at 25-60℃ for 1-2 hours to obtain surface-modified calcium carbonate nanofibers. Then, the amphiphilic block copolymer polystyrene-b-polyacrylic acid was added, and the mixture was stirred for another 1-2 hours to obtain the final product.

[0016] The calcium carbonate nanofibers of this invention are grafted with a coupling agent (e.g., KH570) to reduce the surface energy of the calcium carbonate nanofibers, changing the surface from hydrophilic to hydrophobic. Furthermore, this invention creatively utilizes the amphiphilic block copolymer polystyrene-b-polyacrylic acid to self-assemble on the surface of the surface-modified calcium carbonate nanofibers, resulting in calcium carbonate nanofibers with an amphiphilic block copolymer assembled on their surface. One end of the amphiphilic block copolymer polystyrene-b-polyacrylic acid is connected to the calcium carbonate nanofiber, and the other end is connected to polyimide; specifically, the lipophilic end of the polystyrene-b-polyacrylic acid first self-assembles on the surface of the surface-modified calcium carbonate nanofiber, and then the hydrophilic end of the polystyrene-b-polyacrylic acid connects to the polar groups of the polyimide, making the connection between the calcium carbonate nanofiber and the matrix resin polyimide more compact, improving the stability of the temporary plugging agent, and enabling it to withstand high temperatures in high-temperature environments. This directional assembly and interfacial bonding mode based on a specific chemical structure is difficult to achieve with ordinary block copolymers or other amphiphilic block copolymers. In particular, the rigid aromatic ring structure of polystyrene segments and polyimide molecular chains can produce a π-π stacking effect, while polyacrylic acid segments have ionization and swelling properties in acidic environments. The synergistic effect of the two not only significantly enhances the interfacial bonding strength between the fiber and the matrix, but also improves the overall stability of the temporary plugging agent under high temperature and high pressure.

[0017] The calcium carbonate nanofibers of this invention can be prepared by methods in the prior art, particularly by electrospinning. The calcium carbonate used in this invention is in nanofiber form, unlike the granular calcium carbonate powder used in the prior art. In this invention, the nanofiber-like calcium carbonate is more uniformly dispersed in polyimide through a coupling agent (e.g., KH570) and the amphiphilic block polymer polystyrene-b-polyacrylic acid, and the bond with the polyimide is tighter. Compared to granular calcium carbonate, the nanofiber-like calcium carbonate, due to its longer fiber length, enhances the strength of the resin through its bridging effect, thus improving the compressive strength of the temporary plugging agent. Moreover, during deblocking under acidic conditions, the uniformly dispersed nanofiber-like calcium carbonate, due to its larger specific surface area and longer fiber length, reacts more readily with acid, generating more voids after the reaction, accelerating the hydrolysis and breakup of the polyimide, and increasing the deblocking speed.

[0018] Furthermore, the calcium carbonate nanofibers have a length of 40-60 μm and a diameter of 80-150 nm; The polystyrene-b-polyacrylic acid fragment has a molecular weight of 13,000-17,000 g / mol and a molecular weight of 1,200-2,000 g / mol. The coupling agent is KH570.

[0019] Furthermore, the mass ratio of the calcium carbonate nanofibers, coupling agent, and polystyrene-b-polyacrylic acid is 10:1-3:1-3.

[0020] Furthermore, the additives include lubricants, and the additives do not contain antioxidants.

[0021] Furthermore, the lubricant is selected from one or more of polyethylene wax, polyamide wax, hydrogenated castor oil, and paraffin wax.

[0022] To achieve the second objective mentioned above, the present invention adopts the following technical solution: This invention discloses a method for preparing the temperature-resistant and pressure-resistant temporary plugging agent as described above, comprising the following steps: The graphene-modified polyimide, calcium carbonate nanofibers with amphiphilic block copolymers assembled on their surface, and additives are mixed according to the formula. The mixture is then extruded through a twin-screw extruder, pelletized, dried, and cryogenically pulverized to obtain a temperature-resistant and pressure-resistant temporary plugging agent with a particle size of 0.075-2.0 mm.

[0023] In this invention, the twin-screw extruder is used for extrusion, pelletizing, and drying, all of which are conventional operating methods in the prior art and will not be described in detail here. Preferably, the temperature for extrusion is 330-370℃.

[0024] Furthermore, the cryogenic pulverization is carried out in a cryogenic pulverizer and cooled by liquid nitrogen, with the cryogenic pulverization temperature ≤ -50℃.

[0025] To achieve the third objective mentioned above, the present invention adopts the following technical solution: This invention discloses the application of the temperature-resistant and pressure-resistant temporary plugging agent described above in oil and gas extraction or geothermal extraction. The temperature-resistant and pressure-resistant temporary plugging agent is suitable for extraction environments with formation temperatures of 241-270℃ and formation pressures of 100MPa or higher.

[0026] The beneficial effects of this invention are as follows: The temperature-resistant and pressure-resistant temporary plugging agent disclosed in this invention has both excellent high-temperature resistance and pressure resistance, and can be used in high-temperature and high-pressure environments of 241-270℃ and above 100Mpa; at the same time, it can be rapidly hydrolyzed and broken down after the temporary plugging ends, so as to achieve rapid unblocking.

[0027] The polyimide matrix resin powder of this invention uses aromatic dianhydride biphenyltetracarboxylic dianhydride as the dianhydride monomer. The resulting polyimide exhibits higher thermal stability compared to polyimides without aryl benzene rings. Furthermore, this invention disperses graphene powder into the polyimide resin matrix through in-situ polymerization, preventing oxidation of the resin matrix and significantly improving the heat resistance of the matrix resin. The calcium carbonate nanofibers of this invention are grafted with a coupling agent (e.g., KH570) and linked to the polyimide resin matrix via an amphiphilic block polymer, polystyrene-b-polyacrylic acid, thereby enhancing stability and enabling them to withstand high temperatures in high-temperature environments. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0030] Example 1 This example provides a method for preparing a temporary plugging agent, including the following steps: Step (1): Biphenyltetracarboxylic dianhydride, ethylenediamine, and maleic anhydride in a molar ratio of 1:1.1:0.1 are dissolved in dimethyl sulfoxide at room temperature. Then, graphene is added, and the reaction system is heated to 70°C and refluxed to obtain graphene-modified polyimide. After filtration and drying, graphene-modified polyimide powder is obtained. The amount of graphene added is 1% of the mass of biphenyltetracarboxylic dianhydride. Step (2): Prepare calcium carbonate nanofibers, KH570, and polystyrene-b-polyacrylic acid in a mass ratio of 10:2:2; disperse calcium carbonate nanofibers with a fiber length of 50 μm and a diameter of 90 nm in ethanol, add coupling agent KH570, and stir at 30 °C for 2 h to obtain surface-modified calcium carbonate nanofibers; then add amphiphilic block copolymer polystyrene-b-polyacrylic acid (the molecular weight of polystyrene fragment in polystyrene-b-polyacrylic acid is 15000 g / mol, and the molecular weight of polyacrylic acid fragment is 1600 g / mol), and continue stirring for 2 h; obtain calcium carbonate nanofibers with amphiphilic block copolymer assembled on the surface; Step (3): By weight, 80 parts of graphene-modified polyimide powder obtained in step (1), 10 parts of calcium carbonate nanofibers with amphiphilic block copolymers on the surface obtained in step (2) and 1 part of lubricant polyethylene wax are mixed and extruded through a twin-screw extruder (extrusion temperature is 350℃), and then pelletized and dried to obtain extruded granules. Step (4) involves cryogenically grinding the extruded particles from step (3) at -50°C in a cryogenic pulverizer to obtain a temporary blockage agent with a particle size of 0.075 mm to 2.0 mm.

[0031] Example 2 This example provides a method for preparing a temporary plugging agent, including the following steps: Step (1): Biphenyltetracarboxylic dianhydride, ethylenediamine, and maleic anhydride in a molar ratio of 1:1.1:0.1 are dissolved in dimethyl sulfoxide at room temperature. Then, graphene is added, and the reaction system is heated to 70°C and refluxed to obtain graphene-modified polyimide. After filtration and drying, graphene-modified polyimide powder is obtained. The amount of graphene added is 1% of the mass of biphenyltetracarboxylic dianhydride. Step (2): Prepare calcium carbonate nanofibers, KH570, and polystyrene-b-polyacrylic acid in a mass ratio of 10:2:2; disperse calcium carbonate nanofibers with a fiber length of 50 μm and a diameter of 90 nm in ethanol, add coupling agent KH570, and stir at 40 °C for 2 h to obtain surface-modified calcium carbonate nanofibers; then add amphiphilic block copolymer polystyrene-b-polyacrylic acid (the molecular weight of polystyrene fragment in polystyrene-b-polyacrylic acid is 15000 g / mol, and the molecular weight of polyacrylic acid fragment is 1400 g / mol), and continue stirring for 2 h; obtain calcium carbonate nanofibers with amphiphilic block copolymer assembled on the surface; Step (3): By weight, 60 parts of graphene-modified polyimide powder obtained in step (1), 10 parts of calcium carbonate nanofibers with amphiphilic block copolymers on the surface obtained in step (2) and 1 part of lubricant polyethylene wax are mixed; the mixture is extruded through a twin-screw extruder (extrusion temperature is 340℃), granulated and dried to obtain extruded granules. Step (4) involves cryogenically grinding the extruded particles from step (3) at -50°C in a cryogenic pulverizer to obtain a temporary blockage agent with a particle size of 0.075 mm to 2.0 mm.

[0032] Example 3 This example provides a method for preparing a temporary plugging agent, including the following steps: Step (1): Biphenyltetracarboxylic dianhydride, ethylenediamine, and maleic anhydride in a molar ratio of 1:1.1:0.1 are dissolved in dimethyl sulfoxide at room temperature. Then, graphene is added, and the reaction system is heated to 70°C and refluxed to obtain graphene-modified polyimide. After filtration and drying, graphene-modified polyimide powder is obtained. The amount of graphene added is 1% of the mass of biphenyltetracarboxylic dianhydride. Step (2): Prepare calcium carbonate nanofibers, KH570, and polystyrene-b-polyacrylic acid in a mass ratio of 10:2:2; disperse calcium carbonate nanofibers with a fiber length of 50 μm and a diameter of 90 nm in ethanol, add coupling agent KH570, and stir at 50 °C for 2 h to obtain surface-modified calcium carbonate nanofibers; then add amphiphilic block copolymer polystyrene-b-polyacrylic acid (the molecular weight of polystyrene fragment in polystyrene-b-polyacrylic acid is 13000 g / mol, and the molecular weight of polyacrylic acid fragment is 1700 g / mol), and continue stirring for 2 h; obtain calcium carbonate nanofibers with amphiphilic block copolymer assembled on the surface; Step (3): By weight, 80 parts of graphene-modified polyimide powder obtained in step (1), 5 parts of calcium carbonate nanofibers with amphiphilic block copolymers on the surface obtained in step (2) and 1 part of lubricant polyethylene wax are mixed; the mixture is extruded through a twin-screw extruder (extrusion temperature is 360℃), granulated and dried to obtain extruded granules. Step (4) involves cryogenically grinding the extruded particles from step (3) at -50°C in a cryogenic pulverizer to obtain a temporary blockage agent with a particle size of 0.075 mm to 2.0 mm.

[0033] Example 4 This example provides a method for preparing a temporary plugging agent, including the following steps: Step (1): Biphenyltetracarboxylic dianhydride, ethylenediamine, and maleic anhydride in a molar ratio of 1:1.1:0.1 are dissolved in dimethyl sulfoxide at room temperature. Then, graphene is added, and the reaction system is heated to 70°C and refluxed to obtain graphene-modified polyimide. After filtration and drying, graphene-modified polyimide powder is obtained. The amount of graphene added is 1% of the mass of biphenyltetracarboxylic dianhydride. Step (2): Prepare calcium carbonate nanofibers, KH570, and polystyrene-b-polyacrylic acid in a mass ratio of 10:2:2; disperse calcium carbonate nanofibers with a fiber length of 50 μm and a diameter of 90 nm in ethanol, add coupling agent KH570, and stir at 60 °C for 2 h to obtain surface-modified calcium carbonate nanofibers; then add amphiphilic block copolymer polystyrene-b-polyacrylic acid (the molecular weight of polystyrene fragment in polystyrene-b-polyacrylic acid is 15000 g / mol, and the molecular weight of polyacrylic acid fragment is 1600 g / mol), and continue stirring for 2 h; obtain calcium carbonate nanofibers with amphiphilic block copolymer assembled on the surface; Step (3): 75 parts by weight of graphene-modified polyimide powder obtained in step (1), 7 parts by weight of calcium carbonate nanofibers with amphiphilic block copolymers on the surface obtained in step (2) and 1 part by weight of lubricant polyethylene wax are mixed; the mixture is extruded through a twin-screw extruder (extrusion temperature is 370℃), granulated and dried to obtain extruded granules. Step (4) involves cryogenically grinding the extruded particles from step (3) at -50°C in a cryogenic pulverizer to obtain a temporary blockage agent with a particle size of 0.075 mm to 2.0 mm.

[0034] Example 5 This example provides a method for preparing a temporary plugging agent, including the following steps: Step (1): Biphenyltetracarboxylic dianhydride, ethylenediamine, and maleic anhydride in a molar ratio of 1:1.1:0.1 are dissolved in dimethyl sulfoxide at room temperature. Then, graphene is added, and the reaction system is heated to 70°C and refluxed to obtain graphene-modified polyimide. After filtration and drying, graphene-modified polyimide powder is obtained. The amount of graphene added is 1% of the mass of biphenyltetracarboxylic dianhydride. Step (2): Prepare calcium carbonate nanofibers, KH570, and polystyrene-b-polyacrylic acid in a mass ratio of 10:2:2; disperse calcium carbonate nanofibers with a fiber length of 50 μm and a diameter of 90 nm in ethanol, add coupling agent KH570, and stir at 50 °C for 2 h to obtain surface-modified calcium carbonate nanofibers; then add amphiphilic block copolymer polystyrene-b-polyacrylic acid (the molecular weight of polystyrene fragment in polystyrene-b-polyacrylic acid is 13000 g / mol, and the molecular weight of polyacrylic acid fragment is 2000 g / mol), and continue stirring for 2 h; obtain calcium carbonate nanofibers with amphiphilic block copolymer assembled on the surface; Step (3): By weight, 60 parts of graphene-modified polyimide powder obtained in step (1), 9 parts of calcium carbonate nanofibers with amphiphilic block copolymers on the surface obtained in step (2) and 1 part of lubricant polyethylene wax are mixed; the mixture is extruded through a twin-screw extruder (extrusion temperature is 350℃), granulated and dried to obtain extruded granules. Step (4) involves cryogenically grinding the extruded particles from step (3) at -50°C in a cryogenic pulverizer to obtain a temporary blockage agent with a particle size of 0.075 mm to 2.0 mm.

[0035] Example 6 This example provides a method for preparing a temporary plugging agent, including the following steps: Step (1): Biphenyltetracarboxylic dianhydride, ethylenediamine, and maleic anhydride in a molar ratio of 1:1.1:0.1 are dissolved in dimethyl sulfoxide at room temperature. Then, graphene is added, and the reaction system is heated to 70°C and refluxed to obtain graphene-modified polyimide. After filtration and drying, graphene-modified polyimide powder is obtained. The amount of graphene added is 1% of the mass of biphenyltetracarboxylic dianhydride. Step (2): Prepare calcium carbonate nanofibers, KH570, and polystyrene-b-polyacrylic acid in a mass ratio of 10:2:2; disperse calcium carbonate nanofibers with a fiber length of 50 μm and a diameter of 90 nm in ethanol, add coupling agent KH570, and stir at room temperature (40 °C) for 2 h to obtain surface-modified calcium carbonate nanofibers; then add amphiphilic block copolymer polystyrene-b-polyacrylic acid (the molecular weight of polystyrene fragment in polystyrene-b-polyacrylic acid is 13800 g / mol, and the molecular weight of polyacrylic acid fragment is 1800 g / mol), and continue stirring for 2 h; obtain calcium carbonate nanofibers with amphiphilic block copolymer assembled on the surface; Step (3): By weight, 65 parts of graphene-modified polyimide powder obtained in step (1), 6 parts of calcium carbonate nanofibers with amphiphilic block copolymers on the surface obtained in step (2) and 1 part of lubricant polyethylene wax are mixed; the mixture is extruded through a twin-screw extruder (extrusion temperature is 365℃), granulated and dried to obtain extruded granules. Step (4) involves cryogenically grinding the extruded particles from step (3) at -50°C in a cryogenic pulverizer to obtain a temporary blockage agent with a particle size of 0.075 mm to 2.0 mm.

[0036] Example 7 This example provides a method for preparing a temporary plugging agent. The preparation method is the same as in Example 1, except that in step (1), the amount of graphene added is adjusted to 0.5% of the mass of biphenyltetracarboxylic dianhydride. The remaining steps and parameters are exactly the same as in Example 1.

[0037] Example 8 This example provides a method for preparing a temporary plugging agent. The preparation method is the same as in Example 3, except that in step (3), the 5 parts of calcium carbonate nanofibers with PS-b-PAA assembled on the surface are adjusted to 10 parts. The remaining steps and parameters are exactly the same as in Example 3.

[0038] Comparative Example 1 This example provides a method for preparing a temporary plugging agent, including the following steps: By weight, 70 parts of polyimide powder (excluding aryl benzene ring structure), 6 parts of calcium carbonate powder with a particle size of 50μm, 1 part of lubricant polyethylene wax and 1 part of antioxidant DNP are mixed, extruded by a twin-screw extruder, pelletized and dried to obtain extruded granules; the extruded granules are then cryogenically pulverized at -50℃ in a cryogenic pulverizer to obtain a temporary plugging agent with a particle size of 0.075mm-2.0mm.

[0039] Comparative Example 2 The preparation method is the same as in Example 1, except that in step (1), the rigid monomer biphenyl tetracarboxylic dianhydride is replaced with an equimolar amount of the flexible monomer adipic acid, which is then polymerized with ethylenediamine to prepare polyimide.

[0040] Comparative Example 3 The preparation method is the same as in Example 1, except that in step (2), the coupling agent KH570 is replaced with an equal mass of titanate coupling agent NDZ-201.

[0041] Comparative Example 4 The preparation method is the same as in Example 1, except that graphene is not added in step (1). In step (3), graphene powder equivalent to 1% of the mass of biphenyl dianhydride is directly physically blended with other components such as polyimide powder and then extruded.

[0042] Performance testing Temporary plugging agent particles with a particle size of 0.075-2.0 mm obtained after extrusion processing and cryogenic pulverization of Examples 1-6 and Comparative Example 1 were heat-treated for 120 hours in hot water at 250℃ (saturated vapor pressure 3.9-4 MPa), 260℃ (saturated vapor pressure 4.5-4.7 MPa), and 270℃ (saturated vapor pressure 5.3-5.5 MPa). The particles were then removed and their mass loss rate and compressive strength were tested. The test results are shown in Table 1.

[0043] Table 1

[0044] It is evident that Examples 1-6 of the present invention can withstand high-temperature environments of 250°C, 260°C, and 270°C. Therefore, the temporary plugging agent composition of the present invention can be used at 241-270°C. Comparative Examples 1-4 exhibit significant mass loss in the temperature range of 250°C to 270°C, and are not suitable for high-temperature use.

[0045] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A temperature- and pressure-resistant temporary plugging agent, characterized in that, By weight, it includes the following raw material components: 60-80 parts of graphene-modified polyimide; 5-10 parts of calcium carbonate nanofibers with amphiphilic block copolymers assembled on their surface; 0.1-2 parts of auxiliary agent; The graphene-modified polyimide is prepared by in-situ polymerization modification using biphenyl tetracarboxylic dianhydride, ethylenediamine and maleic anhydride as polymerization raw materials and adding graphene. The amphiphilic block copolymer assembled on the surface of calcium carbonate nanofibers is polystyrene-b-polyacrylic acid.

2. The temperature-resistant and pressure-resistant temporary plugging agent according to claim 1, characterized in that, The graphene-modified polyimide was prepared according to the following steps: Biphenyltetracarboxylic dianhydride, ethylenediamine, and maleic anhydride were dissolved in dimethyl sulfoxide at room temperature. Then, graphene was added, and the reaction system was heated to 50-90°C for reflux reaction. After filtration and drying, graphene-modified polyimide powder was obtained.

3. The temperature-resistant and pressure-resistant temporary plugging agent according to claim 2, characterized in that, The amount of graphene added is 0.8-2 wt% of the mass of biphenyltetracarboxylic dianhydride.

4. The temperature-resistant and pressure-resistant temporary plugging agent according to claim 2, characterized in that, The molar ratio of biphenyltetracarboxylic dianhydride, ethylenediamine, and maleic anhydride is 1:1.1:0.

1.

5. The temperature-resistant and pressure-resistant temporary plugging agent according to claim 1, characterized in that, The calcium carbonate nanofibers with amphiphilic block copolymers assembled on their surfaces were prepared according to the following steps: Calcium carbonate nanofibers were dispersed in ethanol, a coupling agent was added, and the mixture was stirred at 25-60℃ for 1-2 hours to obtain surface-modified calcium carbonate nanofibers. Then, the amphiphilic block copolymer polystyrene-b-polyacrylic acid was added, and the mixture was stirred for another 1-2 hours to obtain the final product.

6. The temperature-resistant and pressure-resistant temporary plugging agent according to claim 5, characterized in that, The calcium carbonate nanofibers have a length of 40-60 μm and a diameter of 80-150 nm. The polystyrene-b-polyacrylic acid fragment has a molecular weight of 13,000-17,000 g / mol and a molecular weight of 1,200-2,000 g / mol. The coupling agent is KH570.

7. The temperature-resistant and pressure-resistant temporary plugging agent according to claim 5, characterized in that, The mass ratio of the calcium carbonate nanofibers, coupling agent, and polystyrene-b-polyacrylic acid is 10:1-3:1-3.

8. The temperature-resistant and pressure-resistant temporary plugging agent according to claim 1, characterized in that, The additives include lubricants, and the additives do not contain antioxidants; Preferably, the lubricant is selected from one or more of polyethylene wax, polyamide wax, hydrogenated castor oil, and paraffin wax.

9. The method for preparing the temperature-resistant and pressure-resistant temporary plugging agent according to any one of claims 1-8, characterized in that, Includes the following steps: The graphene-modified polyimide, calcium carbonate nanofibers with amphiphilic block copolymers assembled on their surface, and additives are mixed according to the formula. The mixture is then extruded through a twin-screw extruder, pelletized, dried, and cryogenically pulverized to obtain a temperature-resistant and pressure-resistant temporary plugging agent with a particle size of 0.075-2.0 mm.

10. The application of the temperature-resistant and pressure-resistant temporary plugging agent according to any one of claims 1-8 in oil and gas extraction or geothermal extraction, characterized in that, The temperature-resistant and pressure-resistant temporary plugging agent is suitable for mining environments with formation temperatures of 241-270℃ and formation pressures of over 100 MPa.

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