Self-healing gel plugging agent for fractured formation and preparation method and application thereof

Abstract

The application provides a self-healing gel plugging agent for fractured formation and a preparation method and application thereof, and belongs to the technical field of plugging agent preparation. The preparation method of the self-healing gel plugging agent comprises the following steps: under stirring, polyvinyl alcohol is dissolved in deionized water to form a uniform solution, then acrylamide, 3-acrylamidophenylboronic acid, polyethyleneimine and diethylaminoethyl methacrylate are sequentially added to obtain a mixed solution; an initiator is added to the obtained mixed solution, mixed uniformly, and reacted to obtain a self-healing gel; and the obtained self-healing gel is dried and crushed to obtain the self-healing gel plugging agent for fractured formation. The self-healing gel plugging agent has excellent deformation adaptability, damage healing ability, shear thinning resistance, crack retention performance and mechanical properties, and breaks through the limitation that traditional gels are unstable and prone to failure in dynamic cracks.

Description

Technical Field

[0001] This invention relates to a self-healing gel plugging agent for fractured formations, its preparation method and application, belonging to the field of plugging agent preparation technology. Background Technology

[0002] As oil and gas exploration and development continue to advance into deeper and more complex formations, the geological environment faced by drilling operations is becoming increasingly complex. Against this backdrop, drilling fluid loss caused by formation pressure depletion and the development of natural fractures is becoming increasingly prominent. Well leakage, a complex downhole situation where drilling fluid is lost in large quantities into the formation, is one of the key factors restricting drilling efficiency, safety, and economic benefits. Well leakage is particularly common in complex formations, such as fractured formations, formations with well-developed pores, formations with low pore pressure, and loose or poorly cemented formations. These formations have complex geological conditions, often composed of rock types such as limestone, dolomite, sandstone, and shale. The size, shape, and distribution of fractures or pores are uneven, making it difficult for conventional one-time plugging materials to function stably and reliably over a long period.

[0003] To address different types of drilling fluid loss, Chinese and foreign scholars have developed a series of plugging materials, such as bridge plug plugging materials, high fluid loss plugging materials, and water / oil absorbent polymer plugging materials. Conventional plugging materials mainly rely on physical filling or a one-time chemical reaction. Although they can cope with some static or regular fractures, they generally have limitations: First, the plugging effect is highly dependent on the fracture size matching and the initial molding quality; second, they have poor adaptability to irregular and dynamically changing fractures, and the materials are easily washed away or fail; third, they lack effective self-healing capabilities. Once secondary damage occurs due to stress changes or operational disturbances after plugging, they lose their plugging function, leading to repeated losses. For example, Chinese patent document CN120590929A discloses a plugging agent suitable for severely lost formations. This plugging agent comprises the following raw materials in the following mass fractions: 30%-40% skeleton particles, 20%-30% smart responsive binder, 15%-25% impact-resistant reinforcing component, 5%-10% functional additives, 1%-3% dispersant, and the balance being water. The skeleton particles are a mixture of coarse-grained walnut shells and medium-grained calcium carbonate, the smart responsive binder is a mixture of thermosensitive resin and pH-responsive hydrogel, and the impact-resistant reinforcing component is a mixture of nano-silica and chopped glass fibers. However, this plugging agent has the following limitations: its smart response mechanism strictly relies on both temperature and pH triggering. When the formation temperature or pH does not meet the requirements, the response delay may cause failure, limiting its adaptability. Furthermore, once the plugging structure is damaged under crack disturbance, it is difficult to achieve structural self-repair, and can only achieve limited compensation through re-accumulation or re-triggering, resulting in insufficient durability. Chinese patent document CN117736705A discloses a self-healing resin-based leak-sealing agent for drilling. This agent comprises the following raw materials in parts by weight: 70-80 parts polyurethane precursor, 4-8 parts curing agent, 5-10 parts self-healing additive, 2-4 parts antioxidant, 0.3-0.9 parts toughening agent, and 5-10 parts filler. The polyurethane precursor is a combination of isocyanate compounds and polyols. The curing agent is a combination of two or more of dimethylamine, trimethylamine, ethylenediamine, isophorone diamine, and N,N,N',N'-tetramethylethylenediamine. However, the healing process of this leak-sealing agent mainly relies on the chemical reaction and curing process of the polyurethane system, belonging to an irreversible or weakly reversible reactive healing mechanism. Moreover, this type of system has high requirements for temperature and proportion, and after forming a rigid structure in the crack, its adaptability to changes in crack morphology decreases.

[0004] Therefore, for areas with complex geological structures and widespread leakage channels, there is an urgent need to develop a plugging gel that can autonomously restore its integrity after repeated damage inside the fractures. This is to meet the actual working conditions of changing leakage channels in fractured formations in complex geological areas, solve well leakage and well collapse problems during drilling and completion, and shorten the drilling cycle. Summary of the Invention

[0005] To address the shortcomings of existing technologies, particularly the insufficient self-healing ability, poor stability, and complex processing of existing plugging materials in complex fractured formations, this invention provides a self-healing gel plugging agent for fractured formations, its preparation method, and its application. The plugging agent of this invention is a self-healing plugging agent based on dynamic borate-amine bonds and multiple physical interactions (hydrogen bonds, ionic interactions). This invention uses dynamic borate ester bonds formed by polyvinyl alcohol (PVA) and 3-acrylamidophenylboronic acid (3-APBA) as the main crosslinking network, introduces multiple ionic interactions through free radical copolymerization of acrylamide (AM) and diethylaminoethyl methacrylate (DMAEMA), and utilizes hydrogen bonds formed by acrylamide (AM), polyvinyl alcohol (PVA), and polyethyleneimine (PEI) to assist crosslinking, constructing a multi-crosslinking system that enables the gel to possess self-healing capabilities, achieving long-term, stable, and adaptive plugging in complex fractured environments.

[0006] The technical solution of the present invention is as follows: A method for preparing a self-healing gel plugging agent for fractured formations includes the following steps: Under stirring conditions, polyvinyl alcohol (PVA) was dissolved in deionized water to form a homogeneous solution. Then, acrylamide (AM), 3-acrylamidophenylboronic acid (3-APBA), polyethyleneimine (PEI), and diethylaminoethyl methacrylate (DEAEMA) were added sequentially to obtain a mixed solution. An initiator was added to the obtained mixed solution, and the mixture was stirred evenly to carry out the reaction and obtain a self-healing gel. The obtained self-healing gel was dried and pulverized to obtain a self-healing gel plugging agent for fractured formations.

[0007] According to a preferred embodiment of the present invention, the number average molecular weight of the polyvinyl alcohol (PVA) is 13,000-23,000; and the mass ratio of the polyvinyl alcohol (PVA) to deionized water is 1:2-5.

[0008] According to a preferred embodiment of the present invention, the number-average molecular weight of the polyethyleneimine (PEI) is 1500-2000.

[0009] According to a preferred embodiment of the present invention, the mass ratio of polyvinyl alcohol (PVA), acrylamide (AM), 3-acrylamidophenylboronic acid (3-APBA), polyethyleneimine (PEI) to diethylaminoethyl methacrylate (DEAEMA) is (14-16):(14-16):1:(0.6-1):(0.8-1.5), and more preferably 15:15:1:0.85:1; only when the ratio of PVA, AM and 3-APBA meets this range can the phenylboronic acid groups be uniformly distributed in the copolymer backbone, thereby forming a continuous and stable dynamic borate amine bond network with the added PEI.

[0010] According to a preferred embodiment of the present invention, the initiator is a redox initiator, wherein the oxidant is ammonium persulfate (APS) and the reducing agent is sodium bisulfite (SBS), and the mass ratio of the oxidant to the reducing agent is 1:1; the mass of the initiator is 0.5%-1.5% of the total mass of polyvinyl alcohol (PVA), acrylamide (AM), 3-acrylamidophenylboronic acid (3-APBA), polyethyleneimine (PEI) and diethylaminoethyl methacrylate (DEAEMA), more preferably 1%.

[0011] According to a preferred embodiment of the present invention, the reaction time is 0.5-2 hours.

[0012] According to a preferred embodiment of the present invention, the drying is performed at 55-65°C for 40-50 hours.

[0013] The present invention also provides a self-healing gel plugging agent for fractured formations, which is prepared by the above-described preparation method.

[0014] According to the present invention, the above-described self-healing gel plugging agent for fractured formations is used in water-based drilling fluids.

[0015] In this invention, room temperature has a commonly known meaning, referring to 25±5℃.

[0016] The technical features and beneficial effects of this invention are as follows: 1. The core innovation of the self-healing gel sealing agent of this invention lies in constructing a reversible cross-linking system with dynamic borate-amine bonds as the main cross-linking network and multiple physical interactions as auxiliary components, formed between 3-acrylamidophenylboronic acid (3-APBA) and polyethyleneimine (PEI). The reversible breaking and recombination characteristics of borate-amine bonds enable the gel to have self-repair capabilities. After being damaged by external forces, it can spontaneously recombine to achieve structural self-repair, effectively coping with dynamic crack propagation or construction damage, and significantly improving durability. This invention introduces multiple physical interactions (ionic interactions, hydrogen bonds) as an auxiliary cross-linking mechanism to form multiple reversible networks with borate-amine bonds. Ionic interactions and hydrogen bonds enhance the mechanical stability and interfacial adhesion of the sealing agent. The synergistic effect of these multiple factors gives the gel excellent deformation adaptability, damage healing ability, shear dilution resistance, crack retention performance, and mechanical properties, breaking through the limitations of traditional gels in sealing dynamic cracks, which are unstable and prone to failure.

[0017] 2. When the plugging agent of this invention is applied to fractured formations in complex structural areas, its "isolation-type plugging" mechanism allows the material to fully fill irregular fracture spaces and form adaptive plugs with certain strength and adhesion within the fractures, effectively blocking drilling fluid leakage channels. Simultaneously, its self-healing properties can cope with dynamic changes or secondary damage to fractures, significantly improving the success rate of primary plugging and long-term plugging stability, reducing the risk of repeated leakage, and providing new material support for the management of severe leakage.

[0018] 3. The plugging agent of the present invention exhibits good physicochemical stability in high temperature, high salinity and complex fluid environments, has adjustable gelation time, temperature resistance and anti-dilution ability, good compatibility with existing drilling fluid systems, does not affect rheological and filtration performance, and meets the requirements of field processes.

[0019] 4. This invention uses a polymerization method to prepare the gel in an aqueous phase. The raw materials are readily available, the synthesis process is mild, and the conditions are controllable. Currently, self-healing gel plugging materials based on borate-amine bonds designed for complex fracture characteristics have not been systematically reported in the field of well drilling plugging both domestically and internationally, demonstrating distinct regional adaptability and technological novelty.

[0020] 5. The plugging agent of the present invention is particularly suitable for blocks with complex structures, developed fractures, and variable geostress. It can effectively cope with multiple complex working conditions such as dynamic fracture propagation and wellbore instability, and realize the integrated function of "plugging leakage and stabilizing wellbore". It provides key technical support for safe and efficient drilling in deep and complex formations, and has important engineering application value and promotion prospects. Attached Figure Description

[0021] Figure 1 A photograph of the self-healing gel prepared in Example 1.

[0022] Figure 2 The infrared spectrum of the self-healing gel sealant prepared in Example 1.

[0023] Figure 3 Photos of the self-healing gel sealant prepared in Example 1 before and after stretching after hot rolling healing at 120°C (a) and (b).

[0024] Figure 4 Photos of the self-healing gel sealant prepared in Example 1 before and after stretching after hot rolling healing at 150°C (a) and (b).

[0025] Figure 5 Photos of the self-healing gel sealant prepared in Example 1 before and after stretching after hot rolling healing at 180°C (a) and (b).

[0026] Figure 6Photos of the self-healing gel sealant prepared in Example 1 before and after stretching after hot rolling healing at 205°C (a) and (b). Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0028] The polyvinyl alcohol (PVA) used in the examples has a number average molecular weight of 20,000; the polyethyleneimine (PEI) has a number average molecular weight of 1,800.

[0029] Example 1 A method for preparing a self-healing gel plugging agent for fractured formations includes the following steps: 12.65g of polyvinyl alcohol (PVA) powder was added to 30g of deionized water and stirred at 90℃ until the PVA was completely dissolved. After naturally cooling to room temperature, a transparent and homogeneous PVA solution was formed. Acrylamide (AM), 3-acrylamidophenylboronic acid (3-APBA), polyethyleneimine (PEI), and diethylaminoethyl methacrylate (DEAEMA) were added sequentially to the obtained PVA solution to obtain a mixed solution containing PVA, AM, 3-APBA, PEI, and DEAEMA. The mass ratio of A is 15:15:1:0.85:1; a redox initiator (the oxidant in the redox initiator is ammonium persulfate, the reducing agent is sodium bisulfite, and the mass ratio of oxidant to reducing agent is 1:1) is added to the obtained mixed solution. The mass of the redox initiator is 1% of the total mass of PVA, AM, 3-APBA, PEI, and DEAEMA. The mixture is reacted at room temperature for 1 hour to obtain a self-healing gel; the obtained self-healing gel is dried at 60°C for 48 hours, pulverized, and then a self-healing gel plugging agent for fractured formations is obtained.

[0030] The actual photograph of the healing gel obtained in this embodiment is shown below. Figure 1 As shown.

[0031] The infrared spectrum of the self-healing gel sealing agent obtained in this embodiment is as follows: Figure 2 As shown, 3442.1cm -1 The broad and strong absorption peak at 2823.6 cm⁻¹ is attributed to the stretching vibrations of OH and NH bonds, proving the presence of hydroxyl and amide / amine groups in polyvinyl alcohol (PVA), acrylamide (AM), and polyethyleneimine (PEI), which are the basis for the formation of hydrogen bond networks; -1 The absorption peak at 2050.0 cm⁻¹ corresponds to the stretching vibration of the CH bond, and to the alkyl structure in the polymer backbone and the side chain of diethylaminoethyl methacrylate (DEAEMA); -1The nearby weak peak is related to the structure of 3-acrylamidophenylboronic acid (3-APBA); 1593.7 cm⁻¹ -1 The strong peak at 1384.7 cm⁻¹ corresponds simultaneously to the stretching vibration of the C=O double bond in the amide I band and the stretching vibration of the dynamic borate amine bond (BN), indicating that 3-acrylamidophenylboronic acid (3-APBA) reacts with PEI to form a reversible covalent crosslinked network; -1 and 1353.0cm -1 The absorption peak at 1272.0 cm⁻¹ is attributed to the bending vibration of the CH bond. -1 and 1080.2cm -1 The strong peaks at 1630-1680 cm⁻¹ correspond to the stretching vibrations of the CO and CN bonds, respectively; furthermore, the peaks at 1630-1680 cm⁻¹ correspond to the stretching vibrations of the CO and CN bonds, respectively. -1 No characteristic absorption peaks of olefin C=C double bonds were observed in the range, indicating that the vinyl monomers have fully participated in the copolymerization reaction; the stretching and bending vibrations of many corresponding functional groups in the infrared spectrum prove that a multi-linked network with dynamic borate amine bonds as the core and synergistic hydrogen bonds and ionic interactions has been successfully constructed.

[0032] Example 2 A method for preparing a self-healing gel plugging agent for fractured formations is described in Example 1, except that: the mass of polyvinyl alcohol (PVA) powder is 8.43 g, and the mass ratio of PVA, AM, 3-APBA, PEI, and DEAEMA is 15:15:1:0.85:1.

[0033] Example 3 A method for preparing a self-healing gel plugging agent for fractured formations is described in Example 1, except that: the mass of polyvinyl alcohol (PVA) powder is 7.03 g, and the mass ratio of PVA, AM, 3-APBA, PEI, and DEAEMA is 15:15:1:0.85:1.

[0034] Example 4 A method for preparing a self-healing gel plugging agent for fractured formations is described in Example 1, except that the mass ratio of PVA, AM, 3-APBA, PEI, and DEAEMA is 15:15:1:0.6:1.

[0035] Example 5 A method for preparing a self-healing gel plugging agent for fractured formations is described in Example 1, except that the mass ratio of PVA, AM, 3-APBA, PEI, and DEAEMA is 15:15:1:1:1.

[0036] Example 6 A method for preparing a self-healing gel plugging agent for fractured formations is described in Example 1, except that the mass ratio of PVA, AM, 3-APBA, PEI, and DEAEMA is 15:15:1:0.85:0.8.

[0037] Example 7 A method for preparing a self-healing gel plugging agent for fractured formations is described in Example 1, except that the mass ratio of PVA, AM, 3-APBA, PEI, and DEAEMA is 15:15:1:1:1.5.

[0038] Comparative Example 1 A method for preparing a self-healing gel plugging agent for fractured formations is as described in Example 1, except that diethylaminoethyl methacrylate (DEAEMA) is not added.

[0039] Comparative Example 2 A method for preparing a self-healing gel plugging agent for fractured formations is described in Example 1, except that polyvinyl alcohol (PVA) is not added.

[0040] Comparative Example 3 A method for preparing a self-healing gel plugging agent for fractured formations is described in Example 1, except that 3-acrylamidophenylboronic acid (3-APBA) is replaced with phenylboronic acid.

[0041] Comparative Example 4 A method for preparing a self-healing gel plugging agent for fractured formations is as described in Example 1, except that acrylamide (AM) is not added.

[0042] Comparative Example 5 A method for preparing a self-healing gel plugging agent for fractured formations is as described in Example 1, except that polyethyleneimine (PEI) is not added.

[0043] Experimental Example 1 High-temperature stability performance evaluation To evaluate the temperature resistance of the self-healing gel plugging agent prepared in Example 1 at different temperatures, a BGRL-2 roller heating furnace was used to simulate a high-temperature drilling environment to test its stability. The prepared self-healing gel plugging agent was mixed with water at a mass ratio of 1:1.6, and then hot-rolled at 120℃, 150℃, 180℃, and 205℃ for 16.5 hours. Changes in the plugging agent were then observed, and the results are as follows: Figure 3 , 4 As shown in Figures 5 and 6.

[0044] Photos showing the sealant added to water and cured at 120℃, before and after stretching, are shown below. Figure 3As shown, after absorbing water, the sealant particles merge into a whole, with no gaps between them, exhibiting the properties of an integral gel, which can be lifted and stretched by hand.

[0045] Photos showing the sealant added to water and cured at 150℃, before and after stretching, are shown below. Figure 4 As shown, after absorbing water, the sealant particles merge into a whole, with no gaps between them, exhibiting the properties of an integral gel, which can be lifted and stretched by hand.

[0046] Photos showing the sealant added to water and cured at 180℃, before and after stretching, are shown below. Figure 5 As shown, after absorbing water, the sealant particles merge into a whole, with no gaps between them, exhibiting the properties of an integral gel, which can be lifted and stretched by hand.

[0047] Photos showing the sealant added to water and cured at 205℃, before and after stretching, are shown below. Figure 6 As shown, after absorbing water, the sealant particles merge into a whole, with no gaps between them, exhibiting the properties of an integral gel, which can be lifted and stretched by hand.

[0048] In summary, the self-healing gel plugging agent of this invention possesses excellent temperature stability, maintaining the reversible structure of the dynamic cross-linked network under high-temperature conditions, thereby ensuring its continuous plugging and self-healing effects in high-temperature fractured formations. Within a certain range, the healing performance of the gel enhances with increasing temperature. The activity of functional groups on the polymer molecular chains increases with increasing temperature, and the interaction of the cross-linked network structure intensifies; therefore, the healing performance of the self-healing gel plugging agent increases with increasing temperature.

[0049] Experimental Example 2 The self-healing gel sealants prepared in the examples and comparative examples were evaluated for their self-healing and sealant performance.

[0050] (1) Self-healing effect test To evaluate the healing performance of the self-healing gel sealant of the present invention, the self-healing gel sealants prepared in the examples and comparative examples were placed in two identical cuboid molds with a length of 2 cm, a width of 1 cm, and a height of 3 cm, respectively. Deionized water was added (the mass ratio of the self-healing gel sealant to water was 1:1.6), and contact pressure was slowly applied. Then, the molds were left to stand at 150°C for 4 hours to allow them to heal into complete gel blocks. After the gels cooled to room temperature, two strip-shaped samples were obtained, and the height of the samples was taken as the initial length L0 (in cm). One sample was subjected to a tensile test using a WDW-20 electronic universal testing machine at room temperature. The tensile rate was set to 60.0 mm / min. Both ends of the sample were fixed in the clamps, and the sample was stretched until it broke at room temperature. The fracture length L1 (in cm) was recorded. Another sample was dried (at 60℃ for 48 hours) and pulverized to obtain gel particles with a particle size of 10-40 mesh. These gel particles were then re-packed into a rectangular mold of the same size (2 cm long, 1 cm wide, 3 cm high), deionized water was added (the mass ratio of gel particles to water was 1:1.6), and slow pressure was applied. The mold was then left to stand at 150℃ for 4 hours to allow it to heal into a single gel. Using the same WDW-20 testing machine, the tensile rate was set to 60.0 mm / min. Both ends of the gel sample were fixed in the clamps, and the sample was stretched until it broke at room temperature. The fracture length L2 (in cm) was recorded. The elongation σ and healing rate θ of the self-healing gel sealant are calculated using the following formulas: σ = L1 / L0 × 100%; θ = L2 / L1 × 100%.

[0051] The evaluation method for self-healing performance and the test results of tensile strength and healing rate of the sealing agents prepared in each embodiment and comparative example are shown in Table 1 and Table 2, respectively.

[0052] (2) Static leak-stopping pressure-bearing capacity test Preparation of drilling fluid-based slurry: Add 14g of bentonite and 0.7g of anhydrous sodium carbonate to 350mL of water, stir thoroughly at 6000r / min for 20min, and then hydrate for 24h to obtain drilling fluid-based slurry; Five parts by mass of the plugging agent particles were dispersed in 100 parts by mass of the drilling fluid-based slurry to obtain a drilling fluid-based slurry containing the plugging agent particles. The drilling fluid-based slurry containing the plugging agent particles was added to a high-temperature and high-pressure dynamic and static leakage tester. At 150°C, the drilling fluid-based slurry containing the plugging agent particles passed through a leak-proof fracture model with a fracture width of 0.1 mm. The plugging agent particles were pressed and healed under pressure. When the outlet leakage slowly decreased to a constant value, it was considered that the plugging agent particles had sealed the fracture. When the plugging agent particles had fully healed at 150°C until the outlet leakage was 0, the pressure of the plugging tester was slowly increased until leakage occurred. The pressure corresponding to this point is the plugging pressure strength τ1. The test results of the plugging agents prepared in each embodiment and comparative example are shown in Table 2.

[0053] (3) Dynamic test of leak-proof pressure resistance during drilling Preparation of drilling fluid-based slurry: Add 14g of bentonite and 0.7g of anhydrous sodium carbonate to 350mL of water, stir thoroughly at 6000r / min for 20min, and then hydrate for 24h to obtain drilling fluid-based slurry; Five parts by weight of plugging agent particles were dispersed in 100 parts by weight of drilling fluid base slurry to obtain drilling fluid base slurry containing plugging agent particles. The drilling fluid base slurry containing plugging agent particles was injected into a high-temperature and high-pressure dynamic and static leakage meter. Under constant temperature conditions of 150°C, the base slurry was passed through a plugging fracture model with a fracture width of 3 mm. The plugging agent particles healed through pressure accumulation and compaction. When the outlet leakage slowly decreased to a constant value, it was considered that the self-healing plugging agent particles had sealed the fracture. After the plugging agent particles stabilized at 150°C for 30 minutes, the pressure of the plugging meter was slowly increased, and the critical pressure at which significant leakage of the drilling fluid recurred was recorded. This critical pressure was the plugging pressure bearing strength τ2 of the plugging agent particles. The test results of the plugging agents prepared in each embodiment and comparative example are shown in Table 2.

[0054] Table 1 Evaluation Methods for Healing and Leak-Plugging Performance

[0055] Table 2. Test results of the plugging agents prepared in the examples and comparative examples.

[0056] As shown in Table 2, the self-healing sealing gels prepared in Examples 1-3 of this invention all exhibit excellent pressure resistance and healing ability, with a "superior" rating for healing and sealing performance. This indicates that the self-healing gel system constructed in this invention can achieve stable and efficient sealing in high-temperature and high-pressure crack environments. Examples 4-7 further verified the synergistic effect of each component by finely adjusting the ratio of PEI to DEAEMA. The performance of Examples 4 and 5 decreased compared to Example 1, indicating that PEI, as a key crosslinking agent for forming dynamic borate-amine bonds, requires a moderate amount; too little PEI results in insufficient crosslinking points, reducing network strength and healing efficiency; too much PEI may limit network dynamism. The performance of Examples 6 and 7 demonstrates the importance of the ionic interactions provided by DEAEMA in enhancing the mechanical properties of the gel, and its amount also needs to be optimized to obtain the best overall performance.

[0057] In Comparative Example 1, the absence of diethylaminoethyl methacrylate (DEAEMA) limited ionic interactions in the gel system, resulting in significantly reduced healing rate, tensile properties, and compressive strength. This demonstrates the crucial role of ionic interactions in enhancing gel performance. In Comparative Example 2, the absence of polyvinyl alcohol led to significantly lower healing rate and compressive strength compared to the examples, exhibiting the worst self-healing performance. In Comparative Example 3, phenylboronic acid was used instead of 3-acrylamidophenylboronic acid (3-APBA), weakening the formation efficiency of dynamic borate-amine bonds. Its compressive strength and healing performance decreased compared to the examples, further demonstrating that the dynamic borate-amine bonds formed by 3-acrylamidophenylboronic acid (3-APBA) and polyethyleneimine (PEI) form the core network for the mechanical strength and self-repairing properties of the self-healing gel of this invention. In Comparative Example 4, the absence of acrylamide (AM) resulted in the loss of the long polyacrylamide chains constituting the main polymer backbone of the gel, leading to a sharp decline in various properties. This illustrates the fundamental role of AM as the polymer backbone in providing basic mechanical strength and a complete network structure. In Comparative Example 5, no polyethyleneimine (PEI) was added, resulting in weakened hydrogen bonding and ionic interactions. However, its healing rate and pressure resistance were significantly lower than those of the Example, indicating that polyethyleneimine (PEI), as a component that enhances hydrogen bonding and ionic interactions, plays a crucial role in constructing a stable gel structure.

[0058] As can be seen from the comparative examples and embodiments, the dynamic borate amine bonds and multiple physical interactions synergistically support each other in the gel system of the present invention: the borate amine bonds endow the material with excellent strength and reversible reconstruction ability, while ionic interactions and hydrogen bonds further enhance the toughness and healing efficiency of the gel. The multiple dynamic cross-linked structure jointly constructed by these factors is the key to achieving the gel's high pressure resistance, high healing ability and stable leak-sealing performance.

[0059] In summary, the self-healing plugging gel for fractured formations in complex structural zones provided by this invention, relying on dynamic borate-amine bonds and multiple physical interactions, possesses excellent self-healing properties and mechanical stability, and can effectively achieve long-term and stable sealing of complex fractures.

Claims

1. A method for preparing a self-healing gel plugging agent for fractured formations, characterized in that, The steps include the following: Under stirring conditions, polyvinyl alcohol is dissolved in deionized water to form a homogeneous solution. Then, acrylamide, 3-acrylamidophenylboronic acid, polyethyleneimine, and diethylaminoethyl methacrylate are added sequentially to obtain a mixed solution. An initiator is added to the obtained mixed solution, and the mixture is stirred evenly to carry out the reaction and obtain a self-healing gel. The obtained self-healing gel is dried and pulverized to obtain a self-healing gel plugging agent for fractured formations. The mass ratio of polyvinyl alcohol, acrylamide, 3-acrylamidophenylboronic acid, polyethyleneimine, and diethylaminoethyl methacrylate is (14-16):(14-16):1:(0.6-1):(0.8-1.5). The initiator is a redox initiator, wherein the oxidant is ammonium persulfate and the reducing agent is sodium bisulfite; the mass of the initiator is 0.5%-1.5% of the total mass of polyvinyl alcohol, acrylamide, 3-acrylamidophenylboronic acid, polyethyleneimine and diethylaminoethyl methacrylate.

2. The method for preparing the self-healing gel plugging agent for fractured formations according to claim 1, characterized in that, The number average molecular weight of the polyvinyl alcohol is 13,000-23,000; the mass ratio of the polyvinyl alcohol to deionized water is 1:2-5.

3. The method for preparing the self-healing gel plugging agent for fractured formations according to claim 1, characterized in that, The number-average molecular weight of the polyethyleneimine is 1500-2000.

4. The method for preparing the self-healing gel plugging agent for fractured formations according to claim 1, characterized in that, The mass ratio of polyvinyl alcohol, acrylamide, 3-acrylamidophenylboronic acid, polyethyleneimine and diethylaminoethyl methacrylate is 15:15:1:0.85:

1.

5. The method for preparing the self-healing gel plugging agent for fractured formations according to claim 1, characterized in that, The mass ratio of oxidant to reductant in the redox initiator is 1:1; the mass of the initiator is 1% of the total mass of polyvinyl alcohol, acrylamide, 3-acrylamidophenylboronic acid, polyethyleneimine and diethylaminoethyl methacrylate.

6. The method for preparing the self-healing gel plugging agent for fractured formations according to claim 1, characterized in that, The reaction time is 0.5-2 hours.

7. The method for preparing the self-healing gel plugging agent for fractured formations according to claim 1, characterized in that, The drying process involves drying at 55-65℃ for 40-50 hours.

8. A self-healing gel plugging agent for fractured formations, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. The application of the self-healing gel plugging agent for fractured formations as described in claim 8 in water-based drilling fluids.

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