An expanded graphite multi-stage plugging material for high-temperature thick oil exploitation and a preparation method thereof

Abstract

This invention relates to the field of plugging materials technology, and discloses an expanded graphite multi-stage plugging material for high-temperature heavy oil extraction and its preparation method, comprising the following steps: selecting flake-shaped expandable graphite as a reserve raw material; mixing a composite alumina-zirconate high-temperature stabilizer with an amino-modified polyether silane coupling agent to obtain a composite modifier; immersing the reserve raw material in the composite modifier for modification treatment to obtain modified expandable graphite; subjecting the modified expandable graphite to high-temperature expansion treatment to obtain expanded graphite; crushing, sieving, and classifying the expanded graphite to obtain graded expanded graphite; and compounding the graded expanded graphite to obtain the expanded graphite multi-stage plugging material for high-temperature heavy oil extraction. The material obtained by this invention has excellent high-temperature performance, wet phase expansion retention rate, and multi-stage plugging performance.

Description

Technical Field

[0001] This invention relates to the field of sealing materials technology, and more specifically, to an expanded graphite multi-stage sealing material for high-temperature heavy oil extraction and its preparation method. Background Technology

[0002] In the field of oil and gas field development, heavy oil resources are abundant, but their high viscosity and poor fluidity usually require thermal recovery processes such as steam injection and steam drive for extraction. However, shallow heavy oil reservoirs (burial depth <1000 meters) face two major technical challenges in steam injection thermal recovery: First, the strong heterogeneity of the formation leads to severe steam channeling, with steam preferentially entering high-permeability layers or large channels, resulting in low steam sweep efficiency and crude oil recovery of less than 15%; second, conventional sealing agents are prone to degradation and failure in high-temperature (≥350℃) and high-salinity formation environments, resulting in short sealing effectiveness.

[0003] To address the problem of steam channeling, various plugging materials have been developed in existing technologies, mainly including gel-based, granular, and foam-based materials. Among them, polymer gel-based plugging materials have a certain plugging effect under medium and low temperature conditions, but in high-temperature (>150℃) steam environments, the gel structure is prone to hydrolysis and oxidative degradation, resulting in poor chemical stability and plugging failure, making it difficult to meet the exploitation requirements of high-temperature heavy oil reservoirs; rigid granular materials (such as resin particles and nutshell particles) have high plugging strength, but poor flexibility and limited transport capacity in porous media, easily accumulating in the near-wellbore zone, making it difficult to achieve deep formation plugging; foam-based materials have poor stability and are prone to defoaming under high temperature and high pressure environments, making it difficult to maintain the plugging effect for a long time.

[0004] Meanwhile, existing plugging materials generally suffer from a single plugging mode, typically relying solely on particle size matching for physical accumulation and plugging. They lack adaptability and multi-level plugging capabilities, resulting in unsatisfactory plugging effects on complex pores. Furthermore, it is difficult to balance the contradiction between transport performance and plugging strength. While small-particle materials can achieve deep transport, their plugging strength is weak, while large-particle materials have high plugging strength but poor transport ability, failing to achieve the ideal plugging effect of being able to inject and block effectively.

[0005] Expandable graphite, as a novel inorganic material, possesses certain expansion properties and high-temperature resistance, and has been attempted for use in the sealing field. However, existing expandable graphite technologies have significant limitations: the initial expansion temperature of traditional expandable graphite is mostly between 150-300℃, and it is prone to over-expansion or oxidative decomposition in high-temperature environments above 350℃, resulting in insufficient thermal stability; the expansion ratio of ordinary expanded graphite decreases significantly in wet-phase environments, affecting the sealing effect; in addition, existing technologies often use acidic intercalating agents such as concentrated sulfuric acid to treat expandable graphite, which not only easily corrodes mining equipment but also poses environmental hazards.

[0006] Therefore, it is of great practical significance to provide a product that is resistant to ultra-high temperatures, has strong wet phase expansion, is environmentally friendly, and has multi-stage sealing capabilities. Summary of the Invention

[0007] In view of this, the present invention proposes an expanded graphite multi-stage plugging material for high-temperature heavy oil extraction and its preparation method, aiming to solve at least one of the current background technical problems.

[0008] This invention proposes a method for preparing expanded graphite multi-stage plugging material for high-temperature heavy oil extraction, comprising the following steps:

[0009] Select expandable flake graphite as a backup raw material;

[0010] A composite modifier is obtained by mixing a composite alumina zirconate high-temperature stabilizer with an amino-modified polyether silane coupling agent.

[0011] The prepared raw material is immersed in the composite modifier for modification treatment to obtain modified expandable graphite;

[0012] The modified expandable graphite was subjected to high-temperature expansion treatment to obtain expanded graphite;

[0013] The expanded graphite is crushed, sieved, and classified to obtain graded expanded graphite.

[0014] The graded expanded graphite is compounded to obtain the expanded graphite multi-stage plugging material for high-temperature heavy oil extraction;

[0015] The composite alumina zirconate high-temperature stabilizer was prepared by a combination of sol-gel method and co-precipitation method.

[0016] Preferably, the carbon content of the flake-shaped expandable graphite is ≥99%, and the expansion ratio is 200-400 mL / g.

[0017] Preferably, the preparation method of the composite alumina-zirconate high-temperature stabilizer includes the following steps:

[0018] Aluminum nitrate and zirconium oxychloride were dissolved in water to prepare aqueous solutions of aluminum nitrate with a concentration of 0.8-1.2 mol / L and zirconium oxychloride with a concentration of 0.4-0.6 mol / L.

[0019] Citric acid was dissolved in anhydrous ethanol and ultrasonically dispersed to obtain a citric acid ethanol solution with a concentration of 0.05-0.08 mol / L.

[0020] The zirconium oxychloride aqueous solution, aluminum nitrate aqueous solution and citric acid ethanol solution were mixed and complexed. Then, the pH value was adjusted to 8.5-9.5 with sodium hydroxide aqueous solution with a concentration of 2 mol / L. After stirring at a stirring rate of 300-400 rpm for 1.5-2 hours, a mixed system containing white flocculent precipitate was obtained.

[0021] The mixed system containing the white flocculent precipitate was aged, then washed and dried. The dried precipitate was then calcined to obtain the composite alumina zirconate high-temperature stabilizer.

[0022] Preferably, the aging treatment specifically involves: placing the mixed system containing the white flocculent precipitate in a constant temperature water bath at 60°C and letting it stand for 24 hours; the drying conditions are: temperature of 80°C, vacuum degree of -0.08MPa, and time of 6 hours; the calcination treatment parameters are: calcination temperature of 600-700°C, time of 3-4 hours, and heating rate of 5°C / min.

[0023] Preferably, the preparation method of the amino-modified polyether silane coupling agent includes the following steps:

[0024] An epoxy silane and isopropanol are first mixed to obtain a first mixture;

[0025] Dibutyltin dilaurate was mixed with the first mixture, and then polyetheramine was added for a second mixing to obtain a second mixture;

[0026] The second mixture was purified by distillation to obtain the amino-modified polyether silane coupling agent.

[0027] Preferably, the temperature of the first mixing is 50°C and the time is 10 minutes;

[0028] The second mixing process is as follows: under conditions of 50-60℃ and a stirring rate of 200-250rpm, polyetheramine is added dropwise to the mixture of dibutyltin dilaurate and the first mixture at a dropping rate of 1-2mL / min. After the addition is complete, the temperature is raised to 70-80℃ until the epoxy value of the second mixture is ≤0.05mmol / g, at which point the second mixing process ends.

[0029] Preferably, the molar ratio of the epoxy silane, isopropanol, dibutyltin dilaurate and polyetheramine is 1:1.6-2.4:0.01-0.02:0.6-1.0, and the distillation parameters are: temperature of 60-70℃ and vacuum degree of -0.09MPa.

[0030] Preferably, the high-temperature expansion treatment is performed at a temperature of 850-1000℃ for 10-30 seconds.

[0031] The graded expanded graphite includes particles of a first size, particles of a second size, and particles of a third size; the particle size range of the first size particles is 20-40 mesh, the particle size range of the second size particles is 40-80 mesh, and the particle size range of the third size particles is 80-100 mesh; when compounded, the mass ratio of the first size particles, the second size particles, and the third size particles is 2-3:5-6:2.

[0032] Preferably, the mass concentration of the coupling agent in the composite modifier is 1.0-1.2%, and the mass concentration of the high-temperature stabilizer is 0.5-0.8%.

[0033] The present invention also provides an expanded graphite multi-stage plugging material for high-temperature heavy oil extraction, wherein the expanded graphite multi-stage plugging material is prepared by the preparation method described in the above technical solution.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] The expanded graphite multi-stage plugging material obtained by this invention for high-temperature heavy oil extraction exhibits excellent high-temperature performance, maintaining long-term stability in high-temperature environments of 350-450℃, thus solving the problem of easy degradation and failure of traditional plugging materials at high temperatures. Furthermore, it has a high wet phase expansion retention rate, maintaining good expansion effects even in high-salt formation environments, adapting to the actual wet environment requirements of formations. In addition, this invention achieves all-round plugging of pores with different pore sizes through a three-stage particle size compounding, overcoming the shortcomings of traditional materials' single plugging mode. Balancing migration and plugging strength, the material can migrate deep into the formation, and the plugging layer has high compressive strength, achieving both successful injection and effective plugging. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0037] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] This invention provides a method for preparing expanded graphite multi-stage plugging material for high-temperature heavy oil extraction, comprising the following steps:

[0042] Select expandable flake graphite as a backup raw material;

[0043] A composite modifier is obtained by mixing a composite alumina zirconate high-temperature stabilizer with an amino-modified polyether silane coupling agent.

[0044] The prepared raw material is immersed in the composite modifier for modification treatment to obtain modified expandable graphite;

[0045] The modified expandable graphite was subjected to high-temperature expansion treatment to obtain expanded graphite;

[0046] The expanded graphite is crushed, sieved, and classified to obtain graded expanded graphite.

[0047] The graded expanded graphite is compounded to obtain the expanded graphite multi-stage plugging material for high-temperature heavy oil extraction;

[0048] The composite alumina zirconate high-temperature stabilizer was prepared by a combination of sol-gel method and co-precipitation method.

[0049] The first step in the preparation method of the expanded graphite multi-stage sealing material of the present invention is: selecting flake-shaped expandable graphite as a backup raw material;

[0050] In this invention, the carbon content of the flake-shaped expandable graphite is preferably ≥99%, and the expansion ratio is preferably 200-400 mL / g.

[0051] This invention uses flake-like expandable graphite as the core matrix of the final material. Its layered structure can expand along the interlayer to form a worm-like structure at high temperatures, providing a physical basis for sealing. Specifically, expandable graphite with a carbon content ≥99% can reduce the impact of impurities on high-temperature stability and avoid the decomposition of impurities at high temperatures, which would lead to the destruction of the material structure. An expansion ratio of 200-400 mL / g ensures that the material forms sufficient volume expansion at high temperatures to meet the filling requirements of different pores. If the expansion ratio is lower than 200 mL / g, the sealing and filling effect is insufficient; if it is higher than 400 mL / g, it is prone to over-expansion, leading to particle fragmentation.

[0052] Subsequently, a composite alumina zirconate high-temperature stabilizer and an amino-modified polyether silane coupling agent were prepared. After preparation, the two were mixed to obtain a composite modifier.

[0053] In this invention, the preparation method of the composite alumina zirconate high-temperature stabilizer preferably includes the following steps:

[0054] Aluminum nitrate and zirconium oxychloride were dissolved in water to prepare aqueous solutions of aluminum nitrate with a concentration of 0.8-1.2 mol / L and zirconium oxychloride with a concentration of 0.4-0.6 mol / L.

[0055] Citric acid is dissolved in anhydrous ethanol and ultrasonically dispersed to obtain a citric acid ethanol solution with a concentration of 0.05-0.08 mol / L. The present invention does not impose special limitations on the ultrasonic dispersion parameters; parameters well known to those skilled in the art can be used.

[0056] The zirconium oxychloride aqueous solution and aluminum nitrate aqueous solution were mixed at a volume ratio of 1:1 and stirred evenly. Then, citric acid ethanol solution was added dropwise to the mixed solution of zirconium oxychloride aqueous solution and aluminum nitrate aqueous solution at a rate of 1-2 mL / min. The volume ratio of citric acid ethanol solution to aluminum nitrate aqueous solution was 24:1. After the addition was completed, the mixture was stirred for 30-60 minutes. Then, the pH value was adjusted to 8.5-9.5 with a 2 mol / L sodium hydroxide aqueous solution. After stirring at a stirring rate of 300-400 rpm for 1.5-2 hours, a mixed system containing white flocculent precipitate was obtained.

[0057] The mixture containing the white flocculent precipitate was placed in a constant temperature water bath at 60°C and left to stand for 24 hours for aging treatment. After washing with clean water, it was dried at 80°C and a vacuum of -0.08MPa for 6 hours. The precipitate obtained after drying was then calcined at a heating rate of 5°C / min. When the temperature reached 600-700°C, it was maintained at this temperature for calcination for 3-4 hours to obtain the composite alumina zirconate high-temperature stabilizer.

[0058] In the preparation of the composite alumina-zirconate high-temperature stabilizer of this invention, citric acid is added as a complexing agent to promote the uniform complexation of aluminum ions and zirconium ions, avoiding ion segregation during precipitation. Then, sodium hydroxide aqueous solution is used to adjust the pH value to 8.5-9.5 to ensure complete precipitation of aluminum ions and zirconium ions. Aging treatment makes the precipitate crystallize completely, improving the structural stability of the subsequent calcination product. Finally, calcination can form a stable composite alumina-zirconate crystal structure, ensuring the protective effect at high temperatures.

[0059] The composite alumina-zirconate high-temperature stabilizer specifically prepared by this invention can improve the high-temperature resistance of materials, form a dense oxide protective film in high-temperature environments above 350°C, inhibit the oxidative decomposition of expanded graphite, and solve the problem of easy failure of traditional expanded graphite at high temperatures; it forms chemical bonds with the surface of expanded graphite, enhances the stability of particle structure, and avoids excessive expansion or breakage at high temperatures.

[0060] In this invention, the preparation method of the amino-modified polyether silane coupling agent preferably includes the following steps:

[0061] An epoxy silane and isopropanol are first mixed to obtain a first mixture;

[0062] Dibutyltin dilaurate was mixed with the first mixture, and then polyetheramine was added for a second mixing to obtain a second mixture;

[0063] The second mixture was purified by distillation to obtain the amino-modified polyether silane coupling agent.

[0064] In this invention, the temperature of the first mixing is preferably 50°C, and the time is preferably 10 minutes;

[0065] The second mixing is preferably carried out by adding polyetheramine dropwise to the mixture of dibutyltin dilaurate and the first mixture at a temperature of 50-60℃ and a stirring rate of 200-250rpm at a dropping rate of 1-2mL / min. After the addition is completed, the temperature is raised to 70-80℃ until the epoxy value of the second mixture is ≤0.05mmol / g, at which point the second mixing is completed.

[0066] In this invention, the molar ratio of epoxy silane, isopropanol, dibutyltin dilaurate and polyetheramine is preferably 1:1.6-2.4:0.01-0.02:0.6-1.0, and the distillation parameters are preferably: temperature of 60-70℃ and vacuum degree of -0.09MPa.

[0067] In this invention, isopropanol is used as a solvent to promote the homogeneous reaction between epoxy silane and polyetheramine when preparing the amino-modified polyether silane coupling agent. Dibutyltin dilaurate is used as a catalyst to accelerate the ring-opening reaction between epoxy and amino groups. At the same time, controlling the dropping rate and reaction temperature of the polyetheramine can avoid uneven product structure caused by violent local reactions. Finally, unreacted raw materials and solvents are removed by distillation purification to improve the purity of the coupling agent and ensure the modification effect.

[0068] The silane coupling agent specifically prepared by this invention can improve the hydrophilicity and hydrophobicity of expanded graphite surface, enhance adhesion to the surface of formation rocks, improve the firmness of the sealing layer, and reduce sealing failure caused by formation water erosion; promote the uniform dispersion of high-temperature stabilizers on the graphite surface, avoid stabilizer agglomeration affecting the modification effect; and also improve the dispersibility of the material in a wet environment, solving the problem of decreased wet phase expansion ratio of ordinary expanded graphite.

[0069] The selected raw materials are completely immersed in the composite modifier and left to stand for 2-2.5 hours for modification. After that, they are dried to obtain modified expandable graphite.

[0070] The mass concentration of the amino-modified polyether silane coupling agent in the composite modifier is 1.0-1.2%, and the mass concentration of the composite alumina zirconate high-temperature stabilizer is 0.5-0.8%.

[0071] After the modification treatment is completed, the obtained modified expandable graphite is placed in a high temperature expansion treatment at 850-1000℃ for 10-30 seconds to obtain expanded graphite.

[0072] This invention specifies special parameters for the high-temperature expansion process, enabling controllable expansion. Expansion is insufficient below 850℃, while temperatures above 1000℃ easily lead to graphite oxidation. A heating rate ≥50℃ / second achieves instantaneous expansion, preventing premature loss of intercalated material due to slow heating and ensuring uniform expansion. Through high-temperature expansion, this invention causes the intercalated material in the graphite layers to decompose, generating gas that promotes interlayer separation, forming worm-like expanded graphite. Its loose, porous structure enhances the density and deformability of the sealing layer.

[0073] Then, the expanded graphite is crushed, sieved, and classified to obtain graded expanded graphite; the graded expanded graphite includes particles of a first size, particles of a second size, and particles of a third size; the particle size range of the first size particles is 20-40 mesh, the particle size range of the second size particles is 40-80 mesh, and the particle size range of the third size particles is 80-100 mesh.

[0074] This invention does not limit the crushing conditions; as long as the target particle size of the graded particles defined by this invention can be obtained, the particles can be sieved through 20-mesh, 40-mesh, 80-mesh, and 100-mesh standard sieves to obtain three grades of particles: 20-40 mesh, 40-80 mesh, and 80-100 mesh. These particles are suitable for the sealing requirements of large, medium, and micro pores, respectively, providing a particle size basis for multi-stage sealing.

[0075] Finally, the graded expanded graphite is compounded. During compounding, the mass ratio of the first-size particles, the second-size particles, and the third-size particles is 2-3:5-6:2. After compounding, the multi-stage expanded graphite plugging material for high-temperature heavy oil extraction is obtained.

[0076] This invention achieves a multi-stage plugging effect—large particle bridging, medium particle filling, and small particle sealing—through the synergistic effect of particles of different sizes, thus solving the technical problems of single-size material plugging mode and the contradiction between transport and strength.

[0077] The present invention also provides an expanded graphite multi-stage plugging material for high-temperature heavy oil extraction, wherein the expanded graphite multi-stage plugging material is prepared by the preparation method described in the above technical solution.

[0078] Example 1

[0079] (1) Raw material preparation: Select flake-shaped expandable graphite with a carbon content of 99.2% and an expansion ratio of 280mL / g as the backup raw material.

[0080] (2) Preparation of composite alumina zirconate high temperature stabilizer: Prepare 1.0 mol / L aluminum nitrate aqueous solution and 0.5 mol / L zirconium oxychloride aqueous solution, mix them evenly at a volume ratio of 1:1 to obtain a mixed solution; then prepare 0.06 mol / L citric acid ethanol solution, add the above mixed solution dropwise at a rate of 1.5 mL / min (volume ratio of citric acid ethanol solution to aluminum nitrate aqueous solution is 24:1), and stir for 45 minutes;

[0081] The pH was adjusted to 9.0 with a 2 mol / L sodium hydroxide aqueous solution, and the mixture was stirred at 350 rpm for 1.8 hours to obtain a white flocculent precipitate mixture. The mixture was then aged in a constant temperature water bath at 60℃ for 24 hours, washed with water, and vacuum dried at 80℃ and -0.08 MPa for 6 hours. Finally, the temperature was increased to 650℃ at 5℃ / min and calcined for 3.5 hours to obtain a composite alumina zirconate high-temperature stabilizer.

[0082] (3) Preparation of amino-modified polyether silane coupling agent: Weigh epoxy silane, isopropanol, dibutyltin dilaurate and polyether amine in a molar ratio of 1:2.0:0.015:0.8;

[0083] The epoxy silane was mixed with isopropanol at 50°C for 10 minutes to obtain the first mixture.

[0084] Then, dibutyltin dilaurate was added, and polyetheramine was added dropwise at 1.5 mL / min under conditions of 55 °C and 220 rpm. After the addition was completed, the temperature was raised to 75 °C, and the reaction was carried out until the epoxy value was 0.04 mmol / g. Then, the mixture was purified by vacuum distillation under conditions of 65 °C and -0.09 MPa to obtain the amino-modified polyether silane coupling agent.

[0085] (4) Preparation of composite modifier: Mix the above coupling agent with the high temperature stabilizer, and control the mass concentration of coupling agent to 1.1% and the mass concentration of high temperature stabilizer to 0.6%.

[0086] (5) Preparation of modified expandable graphite: The raw materials were completely immersed in the composite modifier and left to stand for 2.2 hours. After drying, the modified expandable graphite was obtained.

[0087] (6) High temperature expansion treatment: The modified expandable graphite was subjected to a high temperature expansion treatment at 900℃ for 20 seconds to obtain expanded graphite.

[0088] (7) Grading and compounding: After crushing the expanded graphite, it is sieved through a standard sieve to obtain 20-40 mesh (first particle size), 40-80 mesh (second particle size), and 80-100 mesh (third particle size) particles, which are compounded in a mass ratio of 2.5:5.5:2 to obtain expanded graphite multi-level sealing material.

[0089] Example 2

[0090] (1) Raw material preparation: Select flake-shaped expandable graphite with a carbon content of 99.5% and an expansion ratio of 320mL / g as the backup raw material.

[0091] (2) Preparation of composite aluminum zirconate high temperature stabilizer: Prepare 0.8 mol / L aluminum nitrate aqueous solution and 0.4 mol / L zirconium oxychloride aqueous solution, mix them evenly at a volume ratio of 1:1 to obtain a mixed solution; then prepare 0.05 mol / L citric acid ethanol solution, add the above mixed solution dropwise at a rate of 1.0 mL / min (volume ratio of citric acid ethanol solution to aluminum nitrate aqueous solution is 24:1), and stir for 30 minutes;

[0092] The pH was then adjusted to 8.5 using a 2 mol / L sodium hydroxide aqueous solution, and stirred at 300 rpm for 1.5 hours to obtain a white flocculent precipitate mixture. The white flocculent precipitate mixture was aged in a 60℃ constant temperature water bath for 24 hours, washed with water, and then vacuum dried at 80℃ and -0.08 MPa for 6 hours.

[0093] Finally, the temperature was increased to 600℃ at 5℃ / min and calcined for 4 hours to obtain the composite alumina zirconate high-temperature stabilizer.

[0094] (3) Preparation of amino-modified polyether silane coupling agent: Epoxy silane, isopropanol, dibutyltin dilaurate and polyether amine were weighed in a molar ratio of 1:1.6:0.01:0.6; the epoxy silane and isopropanol were mixed at 50℃ for 10 minutes to obtain the first mixture; then dibutyltin dilaurate was added, and polyether amine was added dropwise at 1.0 mL / min at 50℃ and 200 rpm. After the addition was completed, the temperature was raised to 70℃ and the reaction was carried out until the epoxy value was 0.03 mmol / g; the amino-modified polyether silane coupling agent was purified by vacuum distillation at 60℃ and -0.09 MPa.

[0095] (4) Preparation of composite modifier: Mix the above coupling agent with the high temperature stabilizer, and control the mass concentration of coupling agent to 1.0% and the mass concentration of high temperature stabilizer to 0.5%.

[0096] (5) Preparation of modified expandable graphite: The raw materials were completely immersed in the composite modifier and left to stand for 2.0 hours. After drying, the modified expandable graphite was obtained.

[0097] (6) High temperature expansion treatment: The modified expandable graphite was subjected to a high temperature expansion treatment at 850℃ for 30 seconds to obtain expanded graphite.

[0098] (7) Grading and compounding: After crushing the expanded graphite, it is sieved through a standard sieve to obtain 20-40 mesh (first particle size), 40-80 mesh (second particle size), and 80-100 mesh (third particle size) particles, which are compounded in a mass ratio of 2:5:2 to obtain expanded graphite multi-level sealing material.

[0099] Example 3

[0100] (1) Raw material preparation: Select flake-shaped expandable graphite with a carbon content of 99.8% and an expansion ratio of 380mL / g as the backup raw material.

[0101] (2) Preparation of composite aluminum zirconate high temperature stabilizer: Prepare 1.2 mol / L aluminum nitrate aqueous solution and 0.6 mol / L zirconium oxychloride aqueous solution, mix them evenly at a volume ratio of 1:1 to obtain a mixed solution; prepare 0.08 mol / L citric acid ethanol solution, add the above mixed solution dropwise at a rate of 2.0 mL / min (volume ratio of citric acid ethanol solution to aluminum nitrate aqueous solution is 24:1), and stir for 60 minutes;

[0102] The pH was then adjusted to 9.5 using a 2 mol / L sodium hydroxide aqueous solution, and the mixture was stirred at 400 rpm for 2.0 hours to obtain a white flocculent precipitate mixture. The mixture was then aged in a 60℃ constant temperature water bath for 24 hours, washed with water, and vacuum dried at 80℃ and -0.08 MPa for 6 hours. Finally, the temperature was increased to 700℃ at 5℃ / min and calcined for 3 hours to obtain a composite aluminazirconate high-temperature stabilizer.

[0103] (3) Preparation of amino-modified polyether silane coupling agent: Epoxy silane, isopropanol, dibutyltin dilaurate and polyether amine were weighed in a molar ratio of 1:2.4:0.02:1.0; the epoxy silane and isopropanol were mixed at 50°C for 10 minutes to obtain the first mixture; then dibutyltin dilaurate was added, and polyether amine was added dropwise at 2.0 mL / min at 60°C and 250 rpm. After the addition was completed, the temperature was raised to 80°C and the reaction was carried out until the epoxy value was 0.05 mmol / g; finally, the mixture was purified by vacuum distillation at 70°C and -0.09 MPa to obtain the amino-modified polyether silane coupling agent.

[0104] (4) Preparation of composite modifier: Mix the above coupling agent with the high temperature stabilizer, and control the mass concentration of coupling agent to 1.2% and the mass concentration of high temperature stabilizer to 0.8%.

[0105] (5) Preparation of modified expandable graphite: The raw materials were completely immersed in the composite modifier and left to stand for 2.5 hours. After drying, the modified expandable graphite was obtained.

[0106] (6) High temperature expansion treatment: The modified expandable graphite is subjected to a high temperature expansion treatment at 1000℃ for 10 seconds to obtain expanded graphite.

[0107] (7) Grading and compounding: After the expanded graphite is crushed, it is sieved through a standard sieve to obtain 20-40 mesh (first particle size), 40-80 mesh (second particle size), and 80-100 mesh (third particle size) particles, which are compounded in a mass ratio of 3:6:2 to obtain expanded graphite multi-level sealing material.

[0108] Performance testing

[0109] The expanded graphite multi-stage sealing materials obtained in Examples 1-3 were used as samples for the following performance tests.

[0110] (1) High temperature stability test

[0111] Testing equipment: high-temperature muffle furnace, electronic balance, X-ray diffractometer (XRD), scanning electron microscope (SEM).

[0112] Test procedure: Take 5g of each sample and place it in a ceramic crucible. Keep it at a constant temperature in a muffle furnace at 350℃, 400℃ and 450℃ for 180 days respectively. After taking it out and cooling it to room temperature, weigh the remaining mass of the sample and calculate the mass retention rate (mass retention rate = mass after high temperature / initial mass × 100%).

[0113] XRD analysis was used to analyze changes in the crystal structure of the samples, and SEM was used to observe whether there were any cracks or oxidation peeling on the surface morphology.

[0114] The test results are shown in Table 1.

[0115] Table 1. High Temperature Stability Test Results

[0116]

[0117] As shown in Table 1, the expanded graphite multi-level sealing material prepared by this invention retained a mass retention rate of ≥95.5% after standing for 180 days at a high temperature of 350-450℃. XRD analysis showed no significant change in crystal structure, and SEM observation showed that the surface was intact without oxidation and peeling. This indicates that the material obtained by this invention has excellent high-temperature stability and can work stably for a long time in high-temperature environments below 450℃, effectively solving the technical problems of easy degradation and oxidative decomposition of traditional sealing materials at high temperatures.

[0118] (2) Wet phase expansion ratio test

[0119] Testing equipment: constant temperature water bath, graduated cylinder, electronic balance, vacuum drying oven.

[0120] Test procedure: Prepare simulated formation brine (NaCl concentration 20000 mg / L, CaCl2 concentration 5000 mg / L, MgCl2 concentration 3000 mg / L), and keep it in a 60℃ constant temperature water bath; take 2g of each sample, vacuum dry to constant weight, and record the initial volume V0; immerse the sample in saturated brine, let it stand for 24 hours, and read the total volume V1 after the sample expands;

[0121] Calculate the wet phase expansion ratio (wet phase expansion ratio = V1 / initial mass, unit: mL / g), and at the same time test the expansion ratio under the dry environment as a control, calculate the wet phase expansion retention rate (wet phase expansion retention rate = wet phase expansion ratio / expansion ratio under the dry environment × 100%).

[0122] The test results are shown in Table 2.

[0123] Table 2 Results of Wet Phase Expansion Ratio Test

[0124]

[0125] As shown in Table 2, the wet phase expansion retention rate of the sealing materials obtained by this invention is ≥92.2%, and the wet phase expansion ratio can reach 295-355 mL / g. This indicates that the sealing materials obtained by this invention have excellent wet phase adaptability, improve dispersibility and expansion stability in saturated brine environments, solve the problem of decreased wet phase expansion ratio of ordinary expanded graphite, and ensure that the materials can still perform well in sealing and filling effects in actual formation wet environments.

[0126] (3) Multi-stage plugging performance test

[0127] Test equipment: high temperature and high pressure core flow test device, sand-filled pipe model (simulating large pores (pore diameter 200-300μm), medium pores (pore diameter 100-200μm), and micro pores (pore diameter 50-100μm) respectively), pressure sensor, and flow meter.

[0128] Test procedure: The sand-filled tube model was filled with quartz sand to prepare simulated rock cores with different pore sizes, and the simulated formation brine was saturated to measure the initial permeability K0; each sample was prepared into a suspension at a concentration of 0.5 g / mL, and injected into the sand-filled tube model at a rate of 0.5 mL / min using a high-pressure pump. The injection volume was twice the pore volume of the model.

[0129] The valve was closed and left to stand for 24 hours to allow the material to fully expand and seal. Then, simulated formation brine was injected at the same rate, and the permeability K1 after stabilization was recorded.

[0130] Calculate the plugging rate (plugging rate = (K0-K1) / K0×100%), and test the plugging effect of each sample in large, medium and micro pore models respectively.

[0131] The test results are shown in Table 3.

[0132] Table 3. Test Results of Multi-stage Blocking Performance

[0133]

[0134] As shown in Table 3, the material obtained by this invention achieves a blocking rate of ≥94.8% in large, medium, and micro pore models, demonstrating strong adaptability to different pore sizes. Based on this, it can be seen that the three-level particle size compound design of 20-40 mesh, 40-80 mesh, and 80-100 mesh in this invention realizes the synergistic effect of large particle bridging, medium particle filling, and small particle blocking, effectively solving the problems of single blocking mode and poor adaptability to complex pores in traditional materials, and meeting the multi-level blocking requirements of heterogeneous strata.

[0135] (4) Migration-blocking strength balance test

[0136] Test equipment: a dual-sand-filled pipe series model (the front section is a high-permeability sand-filled pipe (permeability 5000mD), simulating the near-wellbore zone; the rear section is a low-permeability sand-filled pipe (permeability 1000mD), simulating the deep formation), a high-temperature and high-pressure pump, a pressure sensor, and a tensile testing machine.

[0137] Test Procedure: Saturate simulated formation brine and measure the initial total permeability Ktotal of the tandem model (Ktotal = 0); inject sample suspension (concentration 0.5 g / mL), record pressure changes during injection, and determine whether the material can smoothly pass through the high-permeability sand-filled pipe in the front section and enter the low-permeability sand-filled pipe in the back section (migration capacity evaluation: if it can enter the back section, it is judged as qualified for migration); after standing for 24 hours, test the stable total permeability Ktotal of the tandem model and calculate the total plugging rate;

[0138] Disassemble the sand-filled pipe, remove the sealing layer, and test the compressive strength of the sealing layer (unit: MPa) using a tensile testing machine.

[0139] The test results are shown in Table 4.

[0140] Table 4. Results of the Migration-Plugging Strength Balance Test

[0141]

[0142] As shown in Table 4, the sealing materials obtained by this invention can all smoothly pass through the high-permeability sand-filled pipe in the front section and enter the low-permeability sand-filled pipe in the rear section, exhibiting good transport capacity. Furthermore, the total sealing rate is ≥94.2%, and the compressive strength of the sealing layer is ≥3.6 MPa. This indicates that the present invention, through reasonable particle size classification and compounding, successfully balances the material's transport performance and sealing strength, achieving the ideal effect of successful injection and effective sealing, and resolving the contradiction between transport and strength in traditional materials.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an expanded graphite multi-stage plugging material for high-temperature heavy oil extraction, characterized in that, Includes the following steps: Expandable, scaly graphite was used as a backup raw material. A composite modifier is obtained by mixing a composite alumina zirconate high-temperature stabilizer with an amino-modified polyether silane coupling agent. The prepared raw material is immersed in the composite modifier for modification treatment to obtain modified expandable graphite; The modified expandable graphite was subjected to high-temperature expansion treatment to obtain expanded graphite; The expanded graphite is crushed, sieved, and classified to obtain graded expanded graphite. The graded expanded graphite is compounded to obtain the expanded graphite multi-stage plugging material for high-temperature heavy oil extraction; The composite alumina zirconate high-temperature stabilizer was prepared by a combination of sol-gel method and co-precipitation method; The preparation method of the composite alumina-zirconate high-temperature stabilizer includes the following steps: Aluminum nitrate and zirconium oxychloride were dissolved in water to prepare aqueous solutions of aluminum nitrate with a concentration of 0.8-1.2 mol / L and zirconium oxychloride with a concentration of 0.4-0.6 mol / L. Citric acid was dissolved in anhydrous ethanol and ultrasonically dispersed to obtain a citric acid ethanol solution with a concentration of 0.05-0.08 mol / L. The zirconium oxychloride aqueous solution, aluminum nitrate aqueous solution and citric acid ethanol solution were mixed and complexed. Then, the pH value was adjusted to 8.5-9.5 with sodium hydroxide aqueous solution with a concentration of 2 mol / L. After stirring at a stirring rate of 300-400 rpm for 1.5-2 hours, a mixed system containing white flocculent precipitate was obtained. The mixed system containing the white flocculent precipitate was aged, then washed and dried. The dried precipitate was then calcined to obtain the composite alumina zirconate high-temperature stabilizer.

2. The method for preparing expanded graphite multi-stage plugging material for high-temperature heavy oil extraction according to claim 1, characterized in that, The carbon content of the flake-shaped expandable graphite is ≥99%, and the expansion ratio is 200-400 mL / g.

3. The method for preparing expanded graphite multi-stage plugging material for high-temperature heavy oil extraction according to claim 1, characterized in that, The aging treatment specifically involves placing the mixed system containing the white flocculent precipitate in a constant temperature water bath at 60°C and letting it stand for 24 hours; the drying conditions are: temperature of 80°C, vacuum degree of -0.08MPa, and time of 6 hours; the calcination treatment parameters are: calcination temperature of 600-700°C, time of 3-4 hours, and heating rate of 5°C / min.

4. The method for preparing expanded graphite multi-stage plugging material for high-temperature heavy oil extraction according to claim 1, characterized in that, The preparation method of the amino-modified polyether silane coupling agent includes the following steps: An epoxy silane and isopropanol are first mixed to obtain a first mixture; Dibutyltin dilaurate was mixed with the first mixture, and then polyetheramine was added for a second mixing to obtain a second mixture; The second mixture was purified by distillation to obtain the amino-modified polyether silane coupling agent.

5. The method for preparing expanded graphite multi-stage plugging material for high-temperature heavy oil extraction according to claim 4, characterized in that, The temperature of the first mixture is 50°C, and the time is 10 minutes; The second mixing process is as follows: under conditions of 50-60℃ and stirring speed of 200-250rpm, polyetheramine is added dropwise to the mixture of dibutyltin dilaurate and the first mixture at a dropping rate of 1-2mL / min. After the addition is completed, the temperature is raised to 70-80℃ until the epoxy value of the second mixture is ≤0.05mmol / g, at which point the second mixing process ends.

6. The method for preparing expanded graphite multi-stage plugging material for high-temperature heavy oil extraction according to claim 4, characterized in that, The molar ratio of the epoxy silane, isopropanol, dibutyltin dilaurate and polyetheramine is 1:1.6-2.4:0.01-0.02:0.6-1.0, and the distillation parameters are: temperature of 60-70℃ and vacuum degree of -0.09MPa.

7. The method for preparing expanded graphite multi-stage plugging material for high-temperature heavy oil extraction according to claim 1, characterized in that, The high-temperature expansion treatment is performed at a temperature of 850-1000℃ for 10-30 seconds. The graded expanded graphite includes particles of a first size, particles of a second size, and particles of a third size; the particle size range of the first size particles is 20-40 mesh, the particle size range of the second size particles is 40-80 mesh, and the particle size range of the third size particles is 80-100 mesh; when compounded, the mass ratio of the first size particles, the second size particles, and the third size particles is 2-3:5-6:

2.

8. The method for preparing expanded graphite multi-stage plugging material for high-temperature heavy oil extraction according to claim 1, characterized in that, The mass concentration of the coupling agent in the composite modifier is 1.0-1.2%, and the mass concentration of the high-temperature stabilizer is 0.5-0.8%.

9. An expanded graphite multi-stage plugging material for high-temperature heavy oil extraction, characterized in that, The expanded graphite multi-stage sealing material is prepared by the preparation method described in any one of claims 1-8.

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