A thermally reversible hydrogel, its preparation method, and its application in temporary plugging of oil and gas pipelines.

Abstract

This invention relates to a thermally reversible hydrogel, its preparation method, and its application in the temporary plugging of oil and gas pipelines. It pertains to the field of temporary plugging technology for thermal operations in oil and gas pipelines. The thermally reversible hydrogel provided by this invention is obtained by non-covalent crosslinking of a functional polymer containing uracil groups and a small-molecule crosslinking agent such as melamine through triple hydrogen bonding. Compared to existing thermally reversible hydrogels, the thermally reversible hydrogel based on triple hydrogen bonding formed by the above-mentioned specific raw materials has a faster thermal response rate and can achieve a rapid sol-gel transition at a certain temperature. Utilizing the thermally reversible property of the hydrogel, it effectively solves the problems of reduced strength after injection into pipelines and difficulty in complete gel breaking of existing hydrogels. Furthermore, when this thermally reversible hydrogel is applied to the temporary plugging of oil and gas pipelines, it is injected into the pipeline in solution form for gel formation and sealing, followed by unblocking with hot water, effectively ensuring the safety of thermal operations and subsequent pipeline operation.

Description

Technical Field

[0001] This invention relates to the field of temporary plugging technology in thermal operations of oil and gas pipelines, and particularly to a thermally reversible hydrogel, its preparation method, and its application in temporary plugging of oil and gas pipelines. Background Technology

[0002] Oil and gas pipelines are a safe, efficient, and inexpensive means of transporting oil and gas. With the increasing extraction of oil and gas, there is a growing demand for upgrading and retrofitting oil and gas pipelines. Furthermore, corrosion and stress often lead to damage to oil and gas pipelines, necessitating repair and renovation to avoid significant economic losses. Current pipeline repair and retrofitting methods typically involve cutting old pipe sections using cold cutting during shutdowns, installing plugs inside the pipeline, sealing the pipe, and then welding. To facilitate plug removal, matching flanges are added to the newly installed pipe section. This entire process is inefficient, difficult to remove plugs, and results in prolonged downtime and substantial economic losses.

[0003] Replacing cold cutting with hot cutting significantly improves construction efficiency and avoids economic losses from prolonged downtime. The hot cutting process requires sealing the pipe section to isolate oil and gas, ensuring the safety of the hot work. Hydrogels are polymeric materials composed of a three-dimensional cross-linked network structure and a solvent filling the network. They possess high water content, adjustable mechanical properties, and morphological transformation under varying environmental stimuli such as temperature and pH, making them suitable for pipeline plugging. Existing technology discloses a chemically cross-linked hydrogel for pipeline plugging that ensures the safety of hot work. However, chemically cross-linked hydrogels are subjected to significant shear stress during pipeline injection, reducing their strength and hindering effective plugging. Furthermore, complete disintegration of chemically cross-linked hydrogels is difficult, and residual gel particles may clog valves or instruments within the pipeline, posing a significant challenge to pipeline safety. Summary of the Invention

[0004] To address the above problems, this invention provides a thermally reversible hydrogel, its preparation method, and its application in the temporary plugging of oil and gas pipelines.

[0005] In a first aspect, the present invention provides a thermally reversible hydrogel, which is obtained by non-covalent crosslinking of a functional polymer containing uracil groups and a small molecule crosslinking agent;

[0006] The general chemical structure of the functional polymer containing the uracil group is shown in formula (I);

[0007] Formula (I): R represents a functional polymer chain;

[0008] The small molecule crosslinking agent includes at least one of melamine, 2,6-diaminopurine, and 2,6-diaminopyridine.

[0009] Furthermore, the small molecule crosslinking agent is melamine.

[0010] Furthermore, the method for preparing the functional polymer containing uracil groups includes the following steps:

[0011] The polyamino polymer, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, orotic acid, and N-hydroxysuccinimide were dissolved in the first solvent, the pH was adjusted to 2-9, and the reaction was carried out at 25-75°C for 12-48 hours to obtain an aqueous polymer solution.

[0012] The polymer aqueous solution was dialyzed using a dialysis device with a molecular weight cutoff of 3000-5000 Daltons to obtain the functional polymer containing uracil groups.

[0013] The polyamino polymer includes at least one of chitosan and polyethyleneimine.

[0014] Furthermore, the weight ratio of the functional polymer containing the uracil group to the small molecule crosslinking agent is (0.1-10):(0.1-10).

[0015] Secondly, the present invention provides a method for preparing the thermally reversible hydrogel according to any one of the first aspects, the preparation method comprising the following steps:

[0016] A functional polymer containing uracil groups was obtained;

[0017] The functional polymer containing uracil groups is dissolved in a second solvent and heated and stirred to obtain a hot solution of the functional polymer.

[0018] A small molecule crosslinking agent is added to the hot solution of the functional polymer and stirred to dissolve, thereby obtaining a pregel solution;

[0019] The pregel solution is cooled to obtain the thermally reversible hydrogel.

[0020] Furthermore, the heating and stirring temperature is 65–95°C; the second solvent includes water.

[0021] Further, by weight percentage, the content of the functional polymer containing uracil groups in the hot solution of the functional polymer is 0.1% to 10%; by weight percentage, the content of small molecule crosslinking agent in the pregel solution is 0.1% to 10%.

[0022] Thirdly, the present invention provides the application of the thermally reversible hydrogel described in any one of the first aspects, and / or the thermally reversible hydrogel prepared by the preparation method described in any one of the second aspects, in the temporary plugging of oil and gas pipelines.

[0023] Furthermore, when applying the thermally reversible hydrogel to temporarily plug oil and gas pipelines, the following steps are included:

[0024] The thermally reversible hydrogel was heated to obtain a thermally reversible hydrogel solution;

[0025] The thermally reversible hydrogel solution is injected into the pipe in the area to be sealed after cooling treatment to complete the sealing.

[0026] After the heating operation is completed, hot water is injected into the pipe to unblock it, thus completing the unblocking process.

[0027] Furthermore, during sealing, the thermally reversible hydrogel solution can be replaced with the pre-formed adhesive solution; the temperature of the thermally reversible hydrogel solution and the pre-formed adhesive solution is 40-70°C, and the temperature of the pipe in the area to be sealed is -10-20°C;

[0028] When unblocking, the temperature of the hot water should be between 50℃ and 90℃.

[0029] The technical solutions provided in the embodiments of the present invention have at least the following advantages compared with the prior art:

[0030] 1) This invention provides a thermally reversible hydrogel, which is obtained by non-covalent cross-linking of a functional polymer containing uracil groups and a small molecule cross-linking agent such as melamine through triple hydrogen bonding. Compared with existing thermally reversible hydrogels, the thermally reversible hydrogel based on triple hydrogen bonding formed by the above-mentioned specific raw materials has a faster thermal response rate, can quickly break down and unblock, and can achieve a rapid sol-gel transition at a certain temperature. Utilizing the thermally reversible property of the hydrogel, it can effectively solve the problems of reduced strength after existing hydrogels are injected into pipelines and the difficulty in completely breaking down the gel.

[0031] 2) The present invention utilizes non-covalent bonds (triple hydrogen bonding) to construct thermally reversible hydrogel materials. The preparation process is simple. In the application of temporary plugging of oil and gas pipelines, the solution is injected into the pipeline to form a gel for sealing. Hot water is then used to unblock the blockage. This effectively avoids the problems of reduced gel strength and difficulty in completely breaking down the gel and unblocking the blockage that occur when the hydrogel is directly injected into the pipeline, thus ensuring the safety of thermal operations and subsequent pipeline operation. Attached Figure Description

[0032] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic flowchart illustrating a method for preparing a thermally reversible hydrogel according to an embodiment of the present invention.

[0035] Figure 2 This is a schematic diagram of the thermal reversibility of the chitosan-based thermally reversible hydrogel provided in an embodiment of the present invention.

[0036] Figure 3 The rheological curve of the chitosan thermally reversible hydrogel provided in the embodiment of the present invention is shown in the strain scan diagram.

[0037] Figure 4 Temperature scanning rheological curve of chitosan-based thermally reversible hydrogel provided in an embodiment of the present invention.

[0038] Figure 5 This is a schematic diagram of the thermal reversibility of the polyethyleneimine-based thermally reversible hydrogel provided in an embodiment of the present invention.

[0039] Figure 6 Temperature scanning rheological curve of the polyethyleneimine-based thermally reversible hydrogel provided in the embodiments of the present invention.

[0040] Figure 7 This diagram illustrates the process of simulating the unblocking of a pipe using a chitosan-based thermally reversible hydrogel in this invention.

[0041] Figure 8 This is a schematic diagram illustrating the application of thermally reversible hydrogel in the thermal operation of oil and gas pipelines for sealing and unblocking.

[0042] Figure 9 This is a temperature-scanning rheological curve of the chemically cross-linked hydrogel in this invention.

[0043] Figure 10 This is a temperature-scanning rheological curve of the quadruple hydrogen-bonded hydrogel in this invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0046] In a first aspect, the present invention provides a thermally reversible hydrogel, which is obtained by non-covalent crosslinking of a functional polymer containing uracil groups and a small molecule crosslinking agent;

[0047] The general chemical structure of the functional polymer containing the uracil group is shown in formula (I);

[0048] Formula (I): R represents a functional polymer chain;

[0049] The small molecule crosslinking agent includes at least one of melamine, 2,6-diaminopurine, and 2,6-diaminopyridine.

[0050] This invention provides a thermally reversible hydrogel, which is obtained by non-covalent cross-linking of a functional polymer containing uracil groups and a small-molecule cross-linking agent such as melamine through triple hydrogen bonding. Compared with existing thermally reversible hydrogels, the thermally reversible hydrogel based on triple hydrogen bonding formed by the above-mentioned specific raw materials has a faster thermal response rate, can quickly break down and unblock, and can achieve a rapid sol-gel transition at a certain temperature. Utilizing the thermally reversible property of the hydrogel, it can effectively solve the problems of reduced strength after existing hydrogels are injected into pipes and the difficulty in completely breaking down the gel.

[0051] Furthermore, compared to existing chemically cross-linked hydrogels, this invention utilizes a functional polymer containing uracil groups and a small-molecule cross-linking agent such as melamine to achieve non-covalent cross-linking through triple hydrogen bonding. This self-assembly forms an extended and entangled three-dimensional network structure, fixing solvent molecules within the network structure. This results in a dispersion system that is intermediate between solid and liquid, thus forming a thermally reversible hydrogel with triple hydrogen bonding. Due to the weak intermolecular hydrogen bonding interactions, this thermally reversible hydrogel is easier to control than chemically cross-linked hydrogels, exhibiting different states at different temperature ranges and responding more readily. This effectively solves the problems of reduced strength after injection into channels and difficulty in complete gel breaking in existing hydrogels.

[0052] In one embodiment of this application, the small molecule crosslinking agent is melamine.

[0053] In this application, melamine is preferably used as a small molecule crosslinking agent.

[0054] As one embodiment of this application, the method for preparing the functional polymer containing uracil groups includes the following process:

[0055] The polyamino polymer, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, orotic acid, and N-hydroxysuccinimide were dissolved in the first solvent, the pH was adjusted to 2-9, and the reaction was carried out at 25-75°C for 12-48 hours to obtain an aqueous polymer solution.

[0056] The polymer aqueous solution was dialyzed using a dialysis device with a molecular weight cutoff of 3000-5000 Daltons to obtain the functional polymer containing uracil groups.

[0057] The polyamino polymer includes at least one of chitosan and polyethyleneimine.

[0058] In some specific embodiments, the preparation method of the functional polymer containing uracil groups may specifically include the following processes:

[0059] (1) Dissolve the polyamino polymer, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, orotic acid, and N-hydroxysuccinimide in water, adjust the pH to 2-9, and react at 25-75°C for 12-48 hours to obtain an aqueous polymer solution.

[0060] (2) The polymer aqueous solution obtained in step (1) was dialyzed for three days using a dialysis bag with a molecular weight cutoff of 3,000 to 5,000 Daltons, with the water changed every 12 hours. After dialysis, the modified functional polymer (i.e., the functional polymer containing uracil groups) was obtained.

[0061] As one embodiment of this application, the weight ratio of the functional polymer containing uracil groups to the small molecule crosslinking agent is (0.1-10):(0.1-10).

[0062] In this invention, controlling the weight ratio of the functional polymer containing uracil groups to the small molecule crosslinking agent to be (0.1–10):(0.1–10) ensures the formation of a thermally reversible hydrogel with suitable strength. If the weight ratio of the functional polymer containing uracil groups to the small molecule crosslinking agent is too large (i.e., the amount of the functional polymer containing uracil groups is relatively excessive) or too small (i.e., the amount of the functional polymer containing uracil groups is relatively insufficient), the resulting thermally reversible hydrogel will have excessive strength, hindering the subsequent unblocking process or making it difficult to form a thermally reversible hydrogel.

[0063] Secondly, based on a general inventive concept, the present invention provides a method for preparing the thermally reversible hydrogel described in any of the first aspects, such as... Figure 1As shown, the preparation method includes the following steps:

[0064] A functional polymer containing uracil groups was obtained;

[0065] The functional polymer containing uracil groups is dissolved in a second solvent and heated and stirred to obtain a hot solution of the functional polymer.

[0066] A small molecule crosslinking agent is added to the hot solution of the functional polymer and stirred to dissolve, thereby obtaining a pregel solution;

[0067] The pregel solution is cooled to obtain the thermally reversible hydrogel.

[0068] The thermally reversible hydrogel synthesized by this invention has a simple preparation process, uses readily available raw materials, and has good economic benefits.

[0069] In some specific embodiments, the preparation method of the above-mentioned thermally reversible hydrogel may specifically include the following processes:

[0070] (1) Dissolve the polyamino polymer, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, orotic acid, and N-hydroxysuccinimide in water, adjust the pH to 2-9, and react at 25-65°C for 12-48 hours to obtain an aqueous polymer solution; preferably, the pH is 2-5, the reaction temperature is 25-45°C, and the reaction time is 18-24 hours.

[0071] (2) Dialyze the polymer aqueous solution obtained in step (1) using a dialysis bag with a molecular weight cutoff of 3000-5000 Daltons for three days, changing the water every 12 hours. After dialysis, a functional polymer containing uracil groups is obtained.

[0072] (3) Add the functional polymer containing uracil groups obtained in step (2) to water and stir at 65-95°C until the functional polymer containing uracil groups is completely dissolved to form a functional polymer hot solution, wherein the content of the functional polymer is 0.1%-10%; preferably, the heating temperature is 70-90°C and the content of the functional polymer is 1%-5%.

[0073] (4) Add a small molecule crosslinking agent such as melamine to the hot solution of the functional polymer obtained in step (3), stir until completely dissolved, and obtain a pre-gel solution, wherein the content of the small molecule crosslinking agent such as melamine is 0.1% to 10%; preferably, the content of melamine is 0.5% to 5%.

[0074] (5) After cooling the pregel solution obtained in step (4), a thermally reversible hydrogel is formed; after heating again, the thermally reversible hydrogel is transformed into a solution.

[0075] In some specific embodiments, the heating and stirring temperature is 65–95°C; the second solvent includes water.

[0076] In some specific embodiments, the content of the functional polymer containing uracil groups in the hot solution of the functional polymer is 0.1% to 10% by weight; and the content of the small molecule crosslinking agent in the pregel solution is 0.1% to 10% by weight.

[0077] Thirdly, based on the same inventive concept, the present invention provides the application of the thermally reversible hydrogel described in any one of the first aspects, and / or the thermally reversible hydrogel prepared by the preparation method described in any one of the second aspects, in the temporary plugging of oil and gas pipelines.

[0078] The thermally reversible hydrogel provided by this invention possesses excellent mechanical properties and can effectively seal pipes. Furthermore, this thermally reversible hydrogel is cross-linked based on hydrogen bonding; these hydrogen bonds can break and regenerate under certain conditions, making the hydrogel more responsive and simplifying the unblocking process after pipe sealing.

[0079] As one embodiment of this application, when applying the thermally reversible hydrogel to temporarily plug oil and gas pipelines, the following steps are included:

[0080] The thermally reversible hydrogel was heated to obtain a thermally reversible hydrogel solution;

[0081] The thermally reversible hydrogel solution is injected into the pipe in the area to be sealed after cooling treatment to complete the sealing.

[0082] After the heating operation is completed, hot water is injected into the pipe to unblock it, thus completing the unblocking process.

[0083] In some specific embodiments, when the thermally reversible hydrogel is applied to temporarily plug oil and gas pipelines, the following process may be included:

[0084] (1) Determine the amount of sealing material according to the length of the pipe to be sealed, and prepare a pre-formed adhesive solution or thermally reversible hydrogel at 40-70°C in advance; preferably, the temperature of the pre-formed adhesive solution is 45-50°C.

[0085] (2) Cool the area of ​​the pipeline to be blocked. Cooling measures include cold water cooling, dry ice cooling, liquid nitrogen cooling, etc.

[0086] (3) When the temperature inside the pipe in the area to be sealed drops to -10 to 20°C, inject the pre-formed gel solution into the pipe, or heat the thermally reversible hydrogel before injecting; preferably, the temperature inside the pipe drops to -5 to 10°C.

[0087] (4) The pre-formed adhesive solution gradually forms an adhesive after the temperature decreases in the area of ​​the pipeline to be sealed, thereby achieving effective sealing in the pipeline;

[0088] (5) After the hot work is completed, 50℃~90℃ produced water or hot water is injected into the pipeline to unblock it. Under the stimulation of temperature, the hydrogel completely dissolves, thereby completing the unblocking of the pipeline; preferably, the temperature of the produced water or hot water is 70~80℃.

[0089] This invention utilizes the thermal reversibility of triple hydrogen-bonded hydrogels. A heated pre-gel solution or a heated thermally reversible hydrogel is injected into a pipeline. As the temperature of the pre-gel solution or thermally reversible hydrogel solution decreases, it gels within the pipeline, thus sealing the pipe. This effectively avoids the situation where direct injection of hydrogel into the pipeline results in strong shear, leading to reduced strength or even failure to seal the pipeline. The effective sealing of the hydrogel within the pipeline isolates oil and gas, ensuring the safety of the thermal operation. After the thermal operation is completed, introducing hot water into the pipeline completely dissolves any remaining hydrogel, preventing incompletely dissolved gel particles from clogging pipeline valves or instruments, and ensuring the safe operation of the pipeline in the future.

[0090] In some specific embodiments, during sealing, the thermally reversible hydrogel solution can be replaced with the pre-formed gel solution; the temperature of the thermally reversible hydrogel solution and the pre-formed gel solution is 40-70°C, and the temperature of the pipe in the area to be sealed is -10-20°C;

[0091] When unblocking, the temperature of the hot water should be between 50℃ and 90℃.

[0092] It should be noted that, unless otherwise specified, the raw material compounds involved in this invention, such as thermally reversible hydrogels, can be directly used as commercially available products or can be prepared in-house according to existing preparation processes. At the same time, unless otherwise specified, the preparation process steps and application methods of thermally reversible hydrogels involved in this invention can be carried out in accordance with existing technologies, and will not be described in detail in this application.

[0093] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0094] Example 1

[0095] This example provides a thermally reversible hydrogel (specifically a chitosan-based thermally reversible hydrogel), the preparation method of which includes the following steps:

[0096] Chitosan (purchased from Shanghai Maclean Biochemical Technology Co., Ltd., hereinafter the same; degree of deacetylation ≥95%; viscosity 100-200 mPa·s), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, orotic acid, and N-hydroxysuccinimide were dissolved in water, and the pH was adjusted to 3-4. The mixture was reacted at 45°C for 24 hours. The polymer aqueous solution was dialyzed for three days using a dialysis bag with a molecular weight cutoff of 3000 Daltons, with the water changed every 12 hours. After dialysis, modified functional chitosan (i.e., functional polymer containing uracil groups) was obtained. The modified functional chitosan was added to water, stirred at 85°C, and the pH was adjusted to 3-4 to completely dissolve it, resulting in a 2% functional chitosan solution. Melamine was added to the solution and completely dissolved, with a melamine concentration of 1%, resulting in a pregel solution. The pregel solution was cooled to form a thermally reversible hydrogel.

[0097] The thermal reversibility diagram of the chitosan-based thermally reversible hydrogel obtained in this example is shown below. Figure 2 As shown. Simultaneously, the strength of this thermally reversible hydrogel was tested using a rheometer, as shown. Figure 3 As shown, the strain range of 0.1%-100% indicates a viscous viscoelastic region, suggesting that the strength of this thermally reversible hydrogel is approximately 40 Pa (storal modulus G'). The rheological properties of this thermally reversible hydrogel were tested at 25–70 °C, as shown... Figure 4 As shown, the gel breaking temperature of this hydrogel is approximately 46℃.

[0098] Example 2

[0099] This example provides a thermally reversible hydrogel (specifically a polyethyleneimine-based thermally reversible hydrogel), the preparation method of which includes the following steps:

[0100] Polyethyleneimine (purchased from Shanghai Maclean Biochemical Technology Co., Ltd., molecular weight 10000), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, orotic acid, and N-hydroxysuccinimide were dissolved in water, and the pH was adjusted to 5-6. The reaction was carried out at 45℃ for 24 hours. The molecular weight of the polyethyleneimine used was 70000. After the reaction was completed, the mixture was dialyzed for three days using a dialysis bag with a molecular weight cutoff of 5000 Daltons, with the water changed every 12 hours. After dialysis, modified functional polyethyleneimine (i.e., a functional polymer containing uracil groups) was obtained. The modified functional polyethyleneimine was added to water and stirred at 80℃ until it was completely dissolved, resulting in a 1% functional polyethyleneimine solution. Melamine was added to the solution and dissolved completely, with a melamine concentration of 0.8%, resulting in a pregel solution. The pregel solution was cooled to form a thermally reversible hydrogel.

[0101] A schematic diagram of the thermal reversibility of the polyethyleneimine-based thermally reversible hydrogel obtained in this example is shown below. Figure 5As shown. Furthermore, the rheological properties of this hydrogel were tested at 25–70 °C, such as... Figure 6 As shown, the breaking temperature of this thermally reversible hydrogel is approximately 61°C.

[0102] Example 3

[0103] This example applies the chitosan-based thermally reversible hydrogel obtained in Example 1 to the temporary plugging of oil and gas pipelines, specifically including the following process:

[0104] A 50mm diameter pipe was used to simulate the application of chitosan-based thermally reversible hydrogel in temporary pipe plugging. The amount of hydrogel to be used was determined based on the area to be plugged, and a chitosan-based pre-gel solution was prepared. A cryogenic jacket was used to encase the pipe area to be plugged. Liquid carbon dioxide was injected into the cryogenic jacket and cooled to form dry ice inside. When the temperature inside the pipe dropped to approximately 0℃, the pre-gel solution was injected through the injection hole or the damaged area. The initial temperature of the pre-gel solution should be maintained at approximately 45℃. The injection flow rate was controlled to allow the pre-gel solution to gradually gel and plug the pipe. Based on the rheological breaking temperature of the chitosan-based thermally reversible hydrogel, the unblocking process was simulated using 75℃ hot water. Figure 7 As shown. When the hydrogel was used to seal a 300mm diameter pipe with a diameter of 50mm, it took 21 minutes for the thermally reversible hydrogel to completely break down and unblock the pipe. The complete unblocking process was as follows. Figure 7 As shown. The process of using thermally reversible hydrogels for sealing and unblocking in thermal operations of oil and gas pipelines is as follows. Figure 8 As shown.

[0105] Example 4

[0106] This example applies the polyethyleneimine-based thermally reversible hydrogel obtained in Example 2 to the temporary plugging of oil and gas pipelines, specifically including the following process:

[0107] The application of polyethyleneimine-based thermally reversible hydrogel in temporary pipe plugging was simulated using a 50mm diameter pipe. The amount of hydrogel to be used was determined based on the area to be plugged, and a polyethyleneimine pre-gel solution was prepared. A cryogenic jacket was used to encase the pipe area to be plugged, and liquid carbon dioxide was injected into the jacket and cooled to form dry ice inside. When the pipe temperature dropped to approximately 0℃, the pre-gel solution was injected through the injection port or the damaged area. The initial temperature of the pre-gel solution should be maintained at approximately 45℃. The injection flow rate was controlled to allow the pre-gel solution to gradually gel and seal the pipe. Based on the rheological breaking temperature of the polyethyleneimine-based thermally reversible hydrogel, the unblocking process was simulated using 80℃ hot water. When the hydrogel was used to plug 300mm of a 50mm diameter pipe, it took 26 minutes for the thermally reversible hydrogel to completely break down and unblock the pipe.

[0108] Comparative Example 1

[0109] This example provides a chemically cross-linked hydrogel, the preparation method of which includes the following process: using acrylamide (4.15g) and acrylic acid (0.85g) as monomers, N,N'-methylenebisacrylamide (0.05g) as a cross-linking agent, and ammonium persulfate (0.005g) as an initiator, 95mL of water is added, and the chemically cross-linked hydrogel is formed after polymerization for 5 hours under a water bath at 70°C.

[0110] The rheological curve of the chemically cross-linked hydrogel obtained in this example under temperature scanning is as follows: Figure 9 As shown, chemically cross-linked hydrogels are less affected by temperature, making it difficult to achieve a complete gel breaking process. Furthermore, based on Example 3, the aforementioned chemically cross-linked hydrogel was used to replace the chitosan-based thermally reversible hydrogel in the temporary plugging of oil and gas pipelines. This hydrogel can be directly injected into the pipeline for sealing, but the chemically cross-linked hydrogel is difficult to completely break down through temperature stimulation or other methods.

[0111] Comparative Example 2

[0112] This example provides a thermally reversible hydrogel with fourfold hydrogen bond crosslinking. The preparation method includes the following steps: 4.5 g of 2-amino-4-hydroxy-6-methylpyrimidine is added to 100 mL of dimethyl sulfoxide and completely dissolved in a water bath at 170 °C. 5.5 g of isocyanate methacrylate is added to the above solution, and the mixture is stirred continuously for 2 hours. 200 mL of acetone is added to wash out a white solid, which is the fourfold hydrogen bond monomer. 0.9 g of the fourfold hydrogen bond monomer and 4 g of acrylamide are dissolved in dimethyl sulfoxide, and then 0.005 g of azobisisobutyronitrile is added. Polymerization is carried out in a water bath at 70 °C for 5 hours. Adding 200 mL of isopropanol precipitates the fourfold hydrogen bond polymer. 1 g of the fourfold hydrogen bond polymer is added to 50 mL of water and dissolved in a water bath at 85 °C. After cooling, a thermally reversible hydrogel with fourfold hydrogen bond crosslinking is formed.

[0113] The preparation method of the quadruple hydrogen-bonded crosslinked thermally reversible hydrogel obtained in this example is relatively complex, involving multiple steps, which is not conducive to industrial application. Furthermore, the rheological curve of the quadruple hydrogen-bonded crosslinked thermally reversible hydrogel under temperature scanning is as follows: Figure 10 As shown, the rheological breaking temperature of the quadruple hydrogen-bonded hydrogel is relatively high, around 80°C. Based on Example 3, replacing the chitosan-based thermally reversible hydrogel with the aforementioned quadruple hydrogen-bonded crosslinked hydrogel for temporary plugging of oil and gas pipelines requires a higher breaking temperature environment during pipeline unblocking, which is not conducive to practical engineering applications.

[0114] In summary, this invention provides a thermally reversible hydrogel, its preparation method, and its application in the temporary plugging of oil and gas pipelines. This thermally reversible hydrogel is obtained by non-covalent cross-linking of a functional polymer containing uracil groups and a small-molecule cross-linking agent such as melamine through triple hydrogen bonding. Compared to existing thermally reversible hydrogels, the thermally reversible hydrogel based on triple hydrogen bonding formed by the aforementioned specific raw materials exhibits a faster thermal response rate and can achieve a rapid sol-gel transition at a certain temperature. Utilizing the thermally reversible property of the hydrogel effectively solves the problems of reduced strength after injection into pipelines and difficulty in complete gel breaking of existing hydrogels. Furthermore, when this thermally reversible hydrogel is applied to the temporary plugging of oil and gas pipelines, it is injected into the pipeline in solution form for gel formation and sealing, followed by unblocking with hot water, effectively ensuring the safety of thermal operations and subsequent pipeline operation.

[0115] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0116] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A thermoreversible hydrogel, characterized in that, The thermoreversible hydrogel is obtained by non-covalent bond crosslinking of a functional polymer containing a uracil group and a small molecule crosslinking agent; The chemical structure general formula of the functional polymer containing a uracil group is shown as formula (I); Formula (I): ; R is a functional polymer chain; The small molecule crosslinking agent is melamine; The preparation method of the functional polymer containing a uracil group comprises the following processes: A polyamino polymer, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, orotic acid, and N-hydroxysuccinimide are dissolved in a first solvent, the pH value is adjusted to 2-9, and the reaction is carried out at 25-75 DEG C for 12-48 hours to obtain a polymer aqueous solution; The polymer aqueous solution is dialyzed by using a dialysis device with a molecular weight cut-off of 3000-5000 daltons to obtain the functional polymer containing a uracil group; The polyamino polymer includes at least one of chitosan and polyethyleneimine.

2. The thermoreversible hydrogel according to claim 1, characterized in that, The weight ratio of the functional polymer containing a uracil group to the small molecule crosslinking agent is (0.1-10):(0.1-10).

3. A method for preparing a thermoreversible hydrogel according to any one of claims 1 to 2, characterized in that, The preparation method comprises the following steps: The functional polymer containing a uracil group is obtained; The functional polymer containing a uracil group is dissolved in a second solvent for heating and stirring to obtain a functional polymer hot solution; The small molecule crosslinking agent is added to the functional polymer hot solution for stirring and dissolving to obtain a pre-gel solution; The pre-gel solution is cooled to obtain the thermoreversible hydrogel.

4. The method for preparing a thermoreversible hydrogel according to claim 3, characterized in that, The temperature of the heating and stirring is 65-95 DEG C; and the second solvent includes water.

5. The method for preparing a thermoreversible hydrogel according to claim 4, characterized in that, The content of the functional polymer containing a uracil group in the functional polymer hot solution is 0.1%-10% by weight; and the content of the small molecule crosslinking agent in the pre-gel solution is 0.1%-10% by weight.

6. The thermoreversible hydrogel prepared by the preparation method of any one of claims 3-5 is applied in oil and gas pipeline temporary plugging.

7. Use according to claim 6, characterized in that, The thermoreversible hydrogel is applied in oil and gas pipeline temporary plugging, which comprises the following steps: The thermoreversible hydrogel is heated to obtain a thermoreversible hydrogel solution; The thermoreversible hydrogel solution is injected into the pipeline of the region to be plugged after temperature reduction treatment to complete plugging; After the hot work is completed, hot water is injected into the pipeline to complete unplugging.

8. Use according to claim 7, characterized in that, During plugging, the thermoreversible hydrogel solution can be replaced by the pre-gel solution; the temperature of the thermoreversible hydrogel solution and the pre-gel solution is 40-70 DEG C, and the temperature of the pipeline of the region to be plugged is -10-20 DEG C; During unplugging, the temperature of the hot water is 50 DEG C-90 DEG C.

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