High-temperature-resistant gel plugging agent as well as preparation method and application thereof

Abstract

The invention relates to a high-temperature-resistant gel plugging agent as well as a preparation method and application thereof, and belongs to the technical field of drilling fluid plugging. The high-temperature-resistant gel plugging agent is prepared from the following raw materials in percentage by mass: 4 to 6 percent of modified temperature-resistant starch, 4 to 6 percent of acrylamide, 1 to 3 percent of temperature-resistant monomer, 0.1 to 0.8 percent of retarder, 0.03 to 0.1 percent of cross-linking agent, 0.01 to 0.05 percent of initiator and the balance of water. The gel plugging agent disclosed by the invention enters a stratum in a continuous phase form, barrier-free migration and sufficient pore crack filling are realized by virtue of low viscosity of a gel initial solution, and then under the action of a stratum temperature, a gel mother solution completes a free radical cross-linking reaction, conversion from a liquid phase to a solid phase is realized, and gel is embedded into a rock surface after being cured, so that cracks are plugged. The gel provided by the invention has the advantages of good temperature resistance and high gelling strength, and can realize high-pressure-bearing plugging of multi-scale cracks.

Description

Technical Field

[0001] This invention relates to a high-temperature resistant gel plugging agent, its preparation method and application, belonging to the field of drilling fluid plugging technology. Background Technology

[0002] Encountering fractured formations is a common geological phenomenon during oil and gas exploration. Besides naturally formed fractures, induced fractures may also occur during drilling operations. Furthermore, when the high-temperature wellbore comes into contact with drilling fluids at different temperatures, differences in thermal stress can trigger cooling-induced fractures. The presence of these fractures significantly increases the risk of drilling fluid loss, causing not only direct economic losses but also potentially leading to serious problems such as wellbore instability, and even complex downhole conditions like well kicks or lost circulation, posing a major challenge to the safe and efficient development of oilfields. As shallow oil and gas resources gradually deplete and exploration continues to advance into deeper formations, formation temperatures rise continuously with depth, placing increasingly stringent requirements on the high-temperature resistance of drilling fluids.

[0003] To effectively address well leakage problems, researchers have developed various plugging materials for different leakage types. Among them, loss control materials, as a key technology for controlling cyclic leakage and inhibiting fracture propagation, have been widely used. Traditional loss control materials, such as fine nutshells, calcium carbonate, and fibrous materials, mainly form a sealing layer in the leakage channel through a bridging-stabilization mechanism. However, their practical application has significant limitations: this mechanism has extremely strict requirements on the particle size distribution of the material, which must be highly matched with the size of the leakage channel. It is difficult to form an effective three-dimensional bridging structure, resulting in insufficient pressure-bearing capacity and poor stability of the sealing layer, making it prone to repeated leakage.

[0004] Hydrogels, as viscoelastic materials with a three-dimensional cross-linked network structure, have demonstrated significant application value in operations such as plugging, fracturing, and enhanced oil recovery due to their excellent sealing performance and good compatibility with various loss channels. By injecting various novel gel plugging agents, such as in-situ cross-linked plugging gels, self-healing gels, shape memory gels, and pre-formed gel particles, into the lost formation, efficient sealing of complex loss channels such as fractures and caverns can be achieved. However, existing gel plugging materials suffer from insufficient performance stability under high-temperature environments. Although a series of improvement measures have made some progress, the temperature resistance of current hydrogel materials generally still struggles to break through the technical bottleneck of 150℃, hindering their widespread application in deep, high-temperature drilling environments.

[0005] Starch, as a natural polymer material, possesses both good biodegradability and renewability. Its abundant surface hydroxyl groups facilitate the cross-linking formation of hydrogel networks. Starch gel systems, due to their high mechanical strength, have achieved practical results in oilfield leak sealing applications. Since the temperature resistance of natural starch is limited by the poor thermal stability of its molecular chains, it is often modified through structural optimization methods such as increasing molecular weight, introducing heteroatom groups, and rigid side groups to significantly improve its stability and leak sealing performance under high-temperature environments. Furthermore, the low viscosity of modified starch solutions allows the initial gel solution to easily enter pores and fractures, forming in situ gels under high formation temperatures and thus sealing leakage channels. The development of high-temperature resistant starch-based grafted gel leak sealing materials shows potential application value in the field of high-temperature reservoir leak sealing.

[0006] Therefore, the current gel plugging agents still have limitations such as insufficient temperature resistance and low plugging pressure, which are not conducive to the promotion and application of deep lost circulation wells. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a high-temperature resistant gel plugging agent, its preparation method, and its application. The gel plugging agent of this invention enters the formation in a continuous phase. Utilizing the low viscosity of the initial gel solution, it achieves unimpeded migration and thorough filling of pores and fractures. Then, under the influence of formation temperature, the gel mother liquor undergoes a free radical cross-linking reaction, transforming from a liquid phase to a solid phase. After solidification, the gel embeds itself on the rock surface, thereby sealing the fractures. The gel of this invention has the advantages of good temperature resistance and high gel strength, enabling high-pressure sealing of multi-scale fractures.

[0008] The technical solution of the present invention is as follows: A high-temperature resistant gel sealant, comprising the following raw materials in weight percentages: 4-6% modified heat-resistant starch, 4-6% acrylamide, 1-3% heat-resistant monomer, 0.1-0.8% retarder, 0.03-0.1% crosslinking agent, 0.01-0.05% initiator, and the balance being water.

[0009] According to a preferred embodiment of the present invention, the high-temperature resistant gel sealing agent comprises the following raw materials in weight percentages: 5% modified heat-resistant starch, 5% acrylamide, 2% heat-resistant monomer, 0.4% retarder, 0.07% crosslinking agent, 0.03% initiator, and the balance being water.

[0010] According to a preferred embodiment of the present invention, the modified thermo-resistant starch is modified thermo-resistant starch DFD.

[0011] According to a preferred embodiment of the present invention, the thermoresistant monomer is one or more combinations of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), vinylpyrrolidone (NVP), and maleic anhydride (MA).

[0012] According to a preferred embodiment of the present invention, the retarder is sodium p-styrene sulfonate (SSS).

[0013] According to a preferred embodiment of the present invention, the crosslinking agent is one or a combination of two of N,N'-methylenebisacrylamide (MBA) and polyethylene glycol diacrylate (PEGDA).

[0014] According to a preferred embodiment of the present invention, the initiator is potassium persulfate (KPS) or ammonium persulfate (KPA).

[0015] The preparation method of the above-mentioned high-temperature resistant gel sealing agent includes the following steps: According to the formula, the modified heat-resistant starch is added to the water while stirring. After it is fully dissolved, acrylamide, heat-resistant monomer and retarder are added. Stir at 300~500 r / min for 10~20 min. Then, crosslinking agent and initiator are added. Nitrogen gas is introduced while stirring until fully dissolved to obtain a gel solution. After sealing the gel solution, it is reacted at 60~90℃ to form a gel, thus obtaining a high-temperature resistant gel sealing agent.

[0016] According to the present invention, the above-mentioned high-temperature resistant gel plugging agent is applied to in-situ gel plugging in formations.

[0017] More specifically, the high-temperature resistant gel plugging agent is prepared into a solution and directly injected into the lost layer. Under the high temperature conditions of the formation, an in-situ cross-linking reaction is triggered to form a high-strength plugging gel.

[0018] According to a preferred embodiment of the present invention, the in-situ gelation and plugging temperature is no higher than 170°C, making it suitable for leakage control in deep, high-temperature formations. This plugging agent, through a "low-temperature pumping-high-temperature triggering" mechanism, ensures that the gel solution fully enters the leakage channel and precisely gels at the target location, thus avoiding premature solidification near the wellbore and effectively sealing deep fractures.

[0019] Beneficial effects: 1. The high-temperature resistant gel sealing agent provided by this invention comprises modified heat-resistant starch, acrylamide monomer, heat-resistant monomer, retarder, crosslinking agent, and initiator. The heat-resistant monomer (such as AMPS, NVP, etc.) forms a stable crosslinking network with the starch molecular chain through sulfonic acid groups or rigid ring structures, significantly improving the thermal stability and mechanical strength of the gel. For example, the sulfonic acid groups in 2-acrylamido-2-methylpropanesulfonic acid (AMPS) can enhance the temperature resistance and salt resistance of the molecular chain, while the rigid pyrrolidone ring of vinylpyrrolidone (NVP) inhibits the thermal motion of the molecular chain at high temperatures. The crosslinking agent (such as MBA, PEGDA) forms covalent crosslinking points through crosslinking copolymerization reactions with each monomer, constructing a high-temperature resistant three-dimensional network structure.

[0020] 2. The high-temperature resistant gel sealing agent provided by this invention is a modified starch grafted gel material. Compared with traditional starch gel, through the synergistic compounding of modified starch matrix and functional monomers, and the introduction of multiple cross-linking mechanisms (covalent bond and hydrogen bond), the sealing agent combines the environmental friendliness of natural materials and the high performance of functional monomers, and its temperature resistance exceeds 170℃.

[0021] 3. The high-temperature resistant gel plugging agent provided by this invention innovatively incorporates a retarder (sodium p-styrene sulfonate). Through the steric hindrance effect of its unique benzene ring structure and the electronegativity of the sulfonic acid groups, it effectively slows down the free radical cross-linking rate, achieving precise control of the gelation time (adjustable within a range of 10-110 minutes for a dosage of 0-0.8%). This design ensures that the gel solution can fully penetrate deep fractures while avoiding wellbore blockage caused by premature gelation.

[0022] 4. The high-temperature resistant gel plugging agent provided by this invention is easy to apply in the field. Simply pump the pre-prepared solution into the lost circulation zone, and it will automatically gel based on the formation temperature (≥70℃). After gelation, it can effectively seal multi-scale fractures and maintain long-term stability at high temperatures. Compared to plugging agents that need to be added while drilling, this solution is more suitable for remedial operations in well sections where losses have already occurred, especially in deep, high-temperature formations with fractured losses. Attached Figure Description

[0023] Figure 1 The infrared absorption spectrum of the high-temperature resistant gel plugging agent prepared in Example 1 is shown.

[0024] Figure 2 Thermogravimetric analysis (TGA) diagram of the high-temperature resistant gel sealing agent prepared in Example 1.

[0025] Figure 3 The temperature resistance of the high-temperature resistant gel sealant prepared in Example 1 at different temperatures.

[0026] Figure 4 The performance of the high-temperature resistant gel sealing agents prepared in Comparative Examples 1-4 at 170°C was measured.

[0027] Figure 5 The stress-strain curves are for the high-temperature resistant gel plugging agents prepared in Example 1 and Comparative Example 1.

[0028] Figure 6 The sealing effect of the high-temperature resistant gel plugging agent prepared in Example 1 on multi-scale parallel cracks is shown.

[0029] Figure 7 The sealing effect of the high-temperature resistant gel sealant prepared in Example 1 on a wedge-shaped crack with an inlet of 3 mm and an outlet of 1 mm after aging at 170°C for 16 hours is shown. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but is not limited thereto. All raw materials used in the embodiments are conventional and commercially available; unless otherwise specified, the methods described are existing technologies.

[0031] Example 1 A high-temperature resistant gel sealant comprises the following raw materials in weight percentages: 5% modified heat-resistant starch DFD, 5% acrylamide, 2% 2-acrylamide-2-methylpropanesulfonic acid, 0.4% sodium p-styrenesulfonate, 0.07% N,N'-methylenebisacrylamide, 0.03% potassium persulfate, and the balance being water.

[0032] The preparation method of the above-mentioned high-temperature resistant gel sealing agent includes the following steps: According to the formula, the modified heat-resistant starch DFD was added to the water while stirring. After it was fully dissolved, acrylamide, 2-acrylamide-2-methylpropanesulfonic acid and sodium p-styrenesulfonate were added. The mixture was stirred at 500 r / min for 15 min. Then, N,N'-methylenebisacrylamide and potassium persulfate were added while stirring with nitrogen gas until it was fully dissolved to obtain a gel solution. The gel solution was sealed and placed in a 70℃ water bath to react and form a gel, thus obtaining a high-temperature resistant gel sealant.

[0033] Example 2 A high-temperature resistant gel sealant comprises the following raw materials in weight percentages: 6% modified heat-resistant starch DFD, 4% acrylamide, 3% vinylpyrrolidone, 0.1% sodium p-styrene sulfonate, 0.03% N,N'-methylenebisacrylamide, 0.05% ammonium persulfate, and the balance being water.

[0034] Example 3 A high-temperature resistant gel sealant comprises the following raw materials in weight percentages: 4% modified heat-resistant starch DFD, 6% acrylamide, 1% maleic anhydride, 0.5% sodium p-styrene sulfonate, 0.1% N,N'-methylenebisacrylamide, 0.01% potassium persulfate, and the balance being water.

[0035] Comparative Example 1 A gel sealing agent comprising the following raw materials in weight percentages: 5% modified heat-resistant starch DFD, 5% acrylamide, 0.3-1% N,N'-methylenebisacrylamide, 0.03% potassium persulfate, and the balance being water.

[0036] The specific preparation method is the same as in Example 1.

[0037] Compared to Example 1, this comparative example does not contain temperature-resistant monomers and retarders, and the amount of crosslinking agent is different. The 0.3~1% of N,N'-methylenebisacrylamide refers to the amount of N,N'-methylenebisacrylamide used being 0.03%, 0.05%, 0.07%, and 0.1%, respectively.

[0038] Comparative Example 2 A gel sealing agent comprising the following raw materials in weight percentages: 5% modified heat-resistant starch DFD, 5% acrylamide, 0.07% N,N'-methylenebisacrylamide, 0.01-0.05% potassium persulfate, and the balance being water.

[0039] The specific preparation method is the same as in Example 1.

[0040] Compared to Example 1, this comparative example does not contain anti-temperature monomers and retarders, and the amount of initiator is different. The 0.01~0.05% of potassium persulfate refers to the amount of potassium persulfate used being 0.01%, 0.02%, 0.03%, 0.04%, and 0.05%, respectively.

[0041] Comparative Example 3 A gel sealing agent comprising the following raw materials in weight percentages: 5% modified heat-resistant starch DFD, 5% acrylamide, 1-3% 2-acrylamide-2-methylpropanesulfonic acid, 0.07% N,N'-methylenebisacrylamide, 0.03% potassium persulfate, and the balance being water.

[0042] The specific preparation method is the same as in Example 1.

[0043] Compared to Example 1, this comparative example does not contain a retarder, and the amount of temperature-resistant monomer is different. The 1-3% of 2-acrylamide-2-methylpropanesulfonic acid refers to the amount of 2-acrylamide-2-methylpropanesulfonic acid used being 1%, 2%, and 3%, respectively.

[0044] Comparative Example 4 A gel sealing agent comprising the following raw materials in weight percentages: 5% modified heat-resistant starch DFD, 5% acrylamide, 2% 2-acrylamide-2-methylpropanesulfonic acid, 0-0.8% sodium p-styrenesulfonate, 0.07% N,N'-methylenebisacrylamide, 0.03% potassium persulfate, and the balance being water.

[0045] The specific preparation method is the same as in Example 1.

[0046] Compared to Example 1, the amount of retarder used in this comparative example is different. The 0~0.8% of sodium styrene sulfonate refers to the amount of sodium styrene sulfonate used being 0%, 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.7%, and 0.8%, respectively.

[0047] Test case 1. Infrared analysis Infrared spectroscopy analysis was performed on the high-temperature resistant gel sealing agent prepared in Example 1. The infrared absorption spectrum is shown below. Figure 1 As shown.

[0048] The specific method is as follows: take the high-temperature resistant gel sealing agent prepared in Example 1 and dry potassium bromide powder, grind them until fully mixed, compress them into tablets, and use an IRTArcer-100 infrared spectrometer to measure the infrared spectrum in the wavenumber range of 4000~400.

[0049] Depend on Figure 1 It can be seen that the peak is located at 3346cm. −1 The absorption peak is assigned to the stretching vibration of the hydroxyl group. The absorption peak is located at 2915 cm⁻¹. -1 This is attributed to the stretching vibration of the CH bond. 1678cm −1 The stretching vibration of the C=O double bond in the amide group is observed at 1546 cm⁻¹. Furthermore, at 1546 cm⁻¹... −1 The position corresponds to the NH bond in the amide (CO-NH), and the benzene ring peak is 1449 cm⁻¹. −1 This is an indicator signal of the benzene ring, indicating that SSS was successfully integrated into the gel structure while undergoing delayed crosslinking; the peak value is 1032 cm⁻¹. −1 and 629 cm −1 The tensile vibration assigned to the sulfonic acid group SO3 indicates that the reactants in the reaction system reacted successfully, and the high-temperature resistant gel plugging agent was successfully synthesized.

[0050] 2. Thermogravimetric analysis Thermogravimetric analysis was performed on the high-temperature resistant gel sealing agent prepared in Example 1. The thermogravimetric analysis results are shown in the figure below. Figure 2 As shown.

[0051] The specific method is as follows: The high-temperature resistant gel sealing agent prepared in Example 1 is thoroughly dried to remove moisture and then pulverized into fine powder. The pulverized gel sample is subjected to thermogravimetric analysis using a TGA2 thermogravimetric analyzer manufactured by METTLER TOLEDO, Switzerland. The experiment is carried out under nitrogen protection, and the heating rate is set to 20 ℃ / min. The weight change of the sample is recorded during the heating process.

[0052] Depend on Figure 2 It can be seen that the high-temperature resistant gel plugging agent prepared in Example 1 loses about 10% of its mass when heated from room temperature to 130°C, mainly due to the removal of adsorbed water and low molecular weight volatiles; the decomposition rate reaches its highest at 254°C, corresponding to the thermal decomposition of amide groups; after exceeding 400°C, the main chain skeleton undergoes rapid degradation, and the residual mass decreases sharply, indicating that the high-temperature resistant gel plugging agent provided by the present invention has excellent thermal stability.

[0053] 3. Evaluation of gelling performance The gelation time and strength grade of the gel were determined by the Syndansk visual inspection method strength code, and then the gelation performance of the gel sealing agents of Example 1 and Comparative Examples 1-4 was evaluated. The gelation strength of the gel sealing agents of Comparative Examples 1-4 changed over time as shown in Tables 1-4.

[0054] The specific method is as follows: Place the prepared initial gel solution in a 70℃ oven and take it out every ten minutes to observe the gelation state.

[0055] As shown in Tables 1-4, the gel strength of the system increases and the gelation time decreases with the increase of the concentrations of the thermosetting monomer, crosslinking agent, and initiator. This is mainly because the increased concentration of each substance in the system leads to more sites of action for the crosslinking agent and a significant increase in the concentration of free radicals, thereby increasing the reaction rate. Furthermore, the addition of a retarder controls the gelation time, which is attributed to the retarder's resistance to polymerization.

[0056] 4. Evaluation of temperature resistance The high-temperature aging test was used to evaluate the temperature resistance of the high-temperature resistant gel sealing agents prepared in Example 1, Comparative Example 1 (0.07% by mass of N,N'-methylenebisacrylamide), Comparative Example 2 (0.05% by mass of potassium persulfate), Comparative Example 3 (3% by mass of 2-acrylamide-2-methylpropanesulfonic acid), and Comparative Example 4 (0.8% by mass of sodium styrene sulfonate). The results are as follows: Figure 3 , Figure 4 As shown.

[0057] The specific method is as follows: the high-temperature resistant gel sealing agents prepared in Example 1 and Comparative Examples 1 to 4 are aged at 70℃, 120℃, 150℃, 170℃ and 180℃ for 16 hours respectively, and the gel state is observed.

[0058] Depend on Figure 3 It can be seen that the high-temperature resistant gel plugging agent prepared in Example 1 can remain stable at 170°C. When the aging temperature is increased to 180°C, the gel network begins to break and a typical "tongue-out" H-level gel phenomenon appears, indicating that the structural stability is destroyed after exceeding its thermal decomposition threshold.

[0059] Depend on Figure 4 It can be seen that Comparative Examples 1 and 2, which do not contain thermo-resistant monomers, cannot maintain structural stability at 170℃. Comparative Example 3, which adds thermo-resistant monomers, can maintain gel structural stability. Comparative Example 4 shows that sodium styrene sulfonate has little impact on the thermo-resistant properties of the gel while achieving gel time control.

[0060] 5. Stress-strain curve The mechanical properties of the high-temperature resistant gel sealing agents prepared in Example 1 and Comparative Example 1 (N,N'-methylenebisacrylamide, mass percentage 0.07%) were tested using a universal testing machine under tensile stress. The stress-strain curves are shown below. Figure 5 As shown.

[0061] The specific method is as follows: The high-temperature resistant gel sealing agent prepared in Example 1 and Comparative Example 1 is made into a standard dumbbell shape with a total length of 75 mm and a cross-sectional area of ​​15 mm². 2 The test was conducted using a computer-controlled electronic universal testing machine. During the test, the dumbbell-shaped high-temperature resistant gel sealant prepared in Example 1 was fixed at both ends to the upper and lower clamps of the testing machine. The clamps were stretched upwards at a rate of 10 mm / s, and the tensile force and tensile displacement data were recorded simultaneously, and stress-strain curves were plotted. The greater the stress at which the gel breaks, the higher the tensile strength of the gel sealant.

[0062] Depend on Figure 5 As can be seen, compared with Comparative Example 1, Example 1 exhibits significantly enhanced tensile strength and elongation, with a maximum elongation of 203% and a peak stress of 92.54 kPa. This improvement is mainly attributed to the formation of ionic bonds between polymer chains by the sulfonic acid groups in AMPS and SSS, which enhances intermolecular forces and crosslinking density; at the same time, the hydrogen bonding of AMPS / SSS increases chain segment entanglement, achieving a more compact three-dimensional network structure, thereby significantly improving the tensile strength and extensibility of the gel.

[0063] 6. Multi-scale sealing performance The plugging capability of the high-temperature resistant gel plugging agent prepared in Example 1 in fractured lost circulation formations was evaluated using a high-temperature and high-pressure plugging and displacement device. The results of parallel fracture experiments are as follows: Figure 6 As shown, the experimental results of the wedge-shaped crack Figure 7 As shown.

[0064] The specific method is as follows: a multi-scale steel crack module is applied, with a crack diameter of 38 mm, a length of 300 mm, and the cracks are penetrating. The crack widths are 1 mm, 2 mm, and 3 mm, with parallel cracks and wedge-shaped cracks with an inlet of 3 mm and an outlet of 1 mm, which are used to simulate the depth of the formation cracks. The crack surface is roughened.

[0065] The gel solution prepared in Example 1 was then added to the working fluid vessel, and the long fracture plugging evaluation experimental device was assembled. A confining pressure of 10 MPa was applied to the long fracture module using a confining pressure pump to simulate the closure pressure of a downhole fracture. A deionized water pump was used to drive the piston inside the vessel, pushing the gel plugging working fluid into the long fracture. After injection, the drilling fluid outlet valve at the fracture outlet was closed to prevent the plugging working fluid from flowing out. The long fracture module was heated using a heating device to simulate the high-temperature environment of downhole gel crosslinking. The breakthrough pressure after gelation at 70°C was studied for parallel fractures, and the breakthrough pressure after aging at 170°C for 16 hours was studied for wedge-shaped fractures. After the gel crosslinked within the long fracture, the outlet valve was opened, and water was injected into the fracture at a flow rate of 4 mL / min to initiate gel breakthrough. The pressure inside the vessel was collected in real time using a computer until the plugging layer completely failed.

[0066] Depend on Figure 6 , 7 It can be seen that within the crack width range of 1mm, 2mm, and 3mm, the breakthrough pressure decreases as the crack width increases. The breakthrough pressure of the high-temperature resistant gel plugging agent prepared in Example 1 under wide crack conditions can reach approximately 3MPa. After high-temperature aging, the breakthrough pressure of a 3mm × 1mm wedge-shaped crack can still reach 3.86 MPa at 170℃. The gel displacement experiment shows that the high-temperature resistant gel plugging agent provided by this invention has high sealing pressure and high temperature resistance.

[0067] 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 them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-temperature resistant gel sealing agent, characterized in that, The high-temperature resistant gel sealing agent comprises the following raw materials in the following mass percentages: 4-6% modified heat-resistant starch, 4-6% acrylamide, 1-3% heat-resistant monomer, 0.1-0.8% retarder, 0.03-0.1% crosslinking agent, 0.01-0.05% initiator, and the balance being water.

2. The high-temperature resistant gel sealing agent as described in claim 1, characterized in that, The high-temperature resistant gel sealing agent comprises the following raw materials in the following weight percentages: 5% modified heat-resistant starch, 5% acrylamide, 2% heat-resistant monomer, 0.4% retarder, 0.07% crosslinking agent, 0.03% initiator, and the balance being water.

3. The high-temperature resistant gel sealing agent as described in claim 1, characterized in that, The modified thermo-resistant starch is modified thermo-resistant starch DFD.

4. The high-temperature resistant gel sealing agent as described in claim 1, characterized in that, The thermoresistant monomer is one or more combinations of 2-acrylamide-2-methylpropanesulfonic acid, vinylpyrrolidone, and styrene.

5. The high-temperature resistant gel sealing agent as described in claim 1, characterized in that, The retarder is sodium p-styrene sulfonate.

6. The high-temperature resistant gel sealing agent as described in claim 1, characterized in that, The crosslinking agent is one or a combination of two of N,N'-methylenebisacrylamide and polyethylene glycol diacrylate.

7. The high-temperature resistant gel sealing agent as described in claim 1, characterized in that, The initiator is potassium persulfate (KPS) or ammonium persulfate.

8. The method for preparing the high-temperature resistant gel sealing agent according to claim 1, characterized in that, The steps include the following: According to the formula, the modified heat-resistant starch is added to the water while stirring. After it is fully dissolved, acrylamide, heat-resistant monomer and retarder are added. Stir at 300~500 r / min for 10~20 min. Then, crosslinking agent and initiator are added. Nitrogen gas is introduced while stirring until fully dissolved to obtain a gel solution. After sealing the gel solution, it is reacted at 60~90℃ to form a gel, thus obtaining a high-temperature resistant gel sealing agent.

9. The application of the high-temperature resistant gel sealing agent according to any one of claims 1 to 7, characterized in that, It is used for in-situ gelation and plugging of leaks in formations.

10. The application as described in claim 9, characterized in that, After the high-temperature resistant gel plugging agent is prepared into a solution, it is directly injected into the lost layer. Under the high temperature conditions of the formation, an in-situ cross-linking reaction is triggered to form a high-strength plugging gel.

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