Channeling sealing agent for carbon dioxide flooding and preparation method of channeling sealing agent

Abstract

The invention provides a channeling sealing agent for carbon dioxide flooding and a preparation method thereof, and relates to the technical field of oilfield development. The channeling sealing agent for carbon dioxide flooding comprises 8-15% of a reaction monomer, 1.5-2% of N-sulfonated chitosan, 0.5-1% of a cross-linking agent, 0.1-0.5% of an initiator and the balance of water, the reaction monomers comprise a first monomer and a second monomer 2-acrylamido-2-methylpropanesulfonic acid. The channeling sealing agent is low in viscosity under the normal-temperature non-gelling condition, easy to pump into a stratum, high in strength after gelling, good in temperature resistance, good in salt resistance and high in plugging property, and can be used for preventing and controlling carbon dioxide gas channeling in carbon dioxide flooding exploitation.

Description

Technical Field

[0001] The present application relates to the technical field of oilfield development, and particularly relates to a channeling plugging agent for carbon dioxide flooding and a preparation method thereof. Background Art

[0002] In the process of oilfield development, water flooding or carbon dioxide flooding technology is usually adopted for low-permeability reservoirs. Among them, carbon dioxide flooding technology has the advantages of good injection performance, wide application range, low flooding cost, and significant improvement in oil recovery. However, during the carbon dioxide flooding process, due to the influence of factors such as reservoir heterogeneity, mobility difference, and density difference, when carbon dioxide flows in the formation, the phenomena of viscous fingering and gravity segregation will cause the carbon dioxide to channel through high-permeability channels. Especially in artificial fracturing fractures, the channeling phenomenon is very serious. The gas channeling phenomenon will form an ineffective cycle of gas, resulting in a decrease in the sweep efficiency and the decline of the crude oil production degree, seriously affecting the development effect. Therefore, controlling and delaying carbon dioxide gas channeling in fractures is the most important problem faced in carbon dioxide flooding.

[0003] Plugging the channeling with a channeling plugging agent before injecting carbon dioxide is an effective way to improve carbon dioxide gas channeling. Currently, the commonly used channeling plugging agents are mainly inorganic particle type channeling plugging agents, gel type channeling plugging agents, etc. Among them, inorganic particle type plugging agents have the disadvantages of short action distance and great damage to the formation. With the increasing awareness of oil well formation protection, the use of this type of plugging agent is decreasing. Therefore, gel type channeling plugging agents are the main research direction. Among gel type channeling plugging agents, the most widely used is polymer gel type channeling plugging agents, which have good channeling plugging and water plugging effects, but have limited temperature resistance. Conventional polymer gel type channeling plugging agents can only be applied to medium and low temperature reservoirs of 60-120°C, have poor salt resistance, are easy to fail in high salinity reservoirs, and the permeability will decrease significantly after long-term use, ultimately leading to a reduction in production. For example, Patent CN104293330A discloses a CO2 gas flooding channeling plugging agent for high-temperature and low-permeability reservoirs. This channeling plugging agent is composed of acrylamide, modifier, emulsifier, initiator, N,N-methylenebisacrylamide, formaldehyde, retarder, and water. It has good stability at 126°C, cannot be applied to high-temperature reservoirs, and does not involve salt resistance.

[0004] Therefore, it is still an urgent problem to be solved in the art to provide a channeling plugging agent for carbon dioxide flooding with good channeling plugging effect, good temperature resistance, and good salt resistance. Summary of the Invention

[0005] The purpose of the present application is to provide a channeling plugging agent for carbon dioxide flooding and a preparation method thereof in view of the deficiencies of the prior art. This channeling plugging agent has good channeling plugging effect, good temperature resistance, good salt resistance, does not separate water for a long time, and can be used for a long time.

[0006] To achieve the above purpose, the technical solutions adopted in the present application are as follows: A plugging agent for carbon dioxide flooding, by mass percentage, comprises the following raw materials: 8-15% of reactive monomers, 1.5-2% of N-sulfonated chitosan, 0.5-1% of crosslinking agent, 0.1-0.5% of initiator, and the balance is water; Among them, the reactive monomers include a first monomer and a second monomer 2-acrylamido-2-methylpropanesulfonic acid.

[0007] Furthermore, the N-sulfonated chitosan is prepared by sulfonating chitosan with sodium 3-chloro-2-hydroxypropyl sulfonate; the molecular weight of the chitosan is 20 kDa - 50 kDa, the degree of deacetylation is 75 - 90%, and the sulfonation degree of the N-sulfonated chitosan is 0.33 - 0.48.

[0008] Furthermore, the N-sulfonated chitosan is prepared by the following method: Add chitosan to an acetic acid solution, stir, add a 45% sodium 3-chloro-2-hydroxypropyl sulfonate solution, raise the temperature for reaction to obtain a crude product; then add water to the crude product, adjust the pH to neutral, filter, wash, and dry to obtain N-sulfonated chitosan.

[0009] Optionally, the weight ratio of the chitosan to the sodium 3-chloro-2-hydroxypropyl sulfonate is 1:(1.5 - 2.2).

[0010] Optionally, the temperature for the temperature-raising reaction is 60 - 80 °C and the time is 3 - 4 h.

[0011] In this application, N-sulfonated chitosan is added to the plugging agent. Compared with chitosan, the addition of N-sulfonated chitosan can form a graft structure with acrylamide, etc., improve the gel strength, improve the plugging effect, enable it to maintain a relatively high gel strength for a long time at 160 °C, and improve the temperature resistance. However, it is found that the introduction of sulfonated chitosan leads to a decrease in its long-term storage stability, affecting the gelation strength and plugging performance of the plugging agent; in addition, it is also found that although the addition of N-sulfonated chitosan can improve the temperature resistance of the material, the molecular weight and degree of deacetylation of N-sulfonated chitosan need to be controlled. If the molecular weight is too high or too low, or the degree of deacetylation is too high or too low, it is easy to cause a decrease in the temperature and salt resistance of the plugging agent; in addition, the sulfonation degree of chitosan also affects the performance of the plugging agent. The higher the sulfonation degree, the more sulfonic groups, resulting in a decrease in salt resistance and poorer stability.

[0012] Furthermore, the first monomer is selected from at least one of acrylamide, methacrylamide, N-ethylacrylamide, N-methylmethacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, and N,N-diethylacrylamide.

[0013] Furthermore, the reaction monomer further comprises a third monomer N-(isobutoxy)methylacrylamide, and the molar ratio of the first monomer, the second monomer and the third monomer is 10:(3-3.5):(0-0.7), preferably 10:(3-3.5):(0.4-0.7).

[0014] In this application, a free-radical polymerizable monomer containing only acrylamide is used as the first monomer, and the second monomer 2-acrylamido-2-methylpropanesulfonic acid is used as the main monomer to react to prepare a polyacrylamide gel plugging agent. The presence of sulfonic acid groups in 2-acrylamido-2-methylpropanesulfonic acid improves the temperature resistance and salt tolerance of the material, and the plugging rate is above 85%. However, its temperature resistance is around 160°C and it cannot be applied to oil reservoir development at higher temperatures. It is found that introducing a certain amount of N-(isobutoxy)methylacrylamide into the reaction monomer helps to further improve the temperature resistance of the material, enabling it to withstand high temperatures of 200°C and not dehydrate for 2 months, and the plugging rate is increased to over 90%.

[0015] Furthermore, the crosslinking agent is glutaraldehyde and epichlorohydrin with a weight ratio of (88-95):(5-12).

[0016] Furthermore, the initiator is selected from organic or inorganic peroxides. Specifically, the initiator exemplarily includes but is not limited to at least one of potassium persulfate, sodium persulfate, ammonium persulfate, benzoyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, azobisisobutyronitrile, tert-butyl peroxypivalate, and cumene hydroperoxide.

[0017] Furthermore, the water is any one of fresh water, river water, and simulated formation water.

[0018] Although the above-mentioned plugging agent has good temperature resistance, salt resistance and plugging rate, its long-term storage stability needs to be improved. Therefore, in a further embodiment, a polyethylene glycol monomethyl ether grafted silicone oxygen polymer is further added to the plugging agent for carbon dioxide flooding, and the addition amount is 0-2.7%, preferably 2-2.7%. The addition of the polyethylene glycol monomethyl ether grafted silicone oxygen polymer can improve its storage stability, but attention needs to be paid to the grafting rate of polyethylene glycol monomethyl ether to avoid excessive grafting of polyethylene glycol, which may cause a decrease in temperature resistance and salt resistance.

[0019] Furthermore, the preparation method of the polyethylene glycol monomethyl ether grafted silicone oxygen polymer includes the following steps: Add polyethylene glycol monomethyl ether to a poly(diethoxysiloxane) ethanol solution for transesterification reaction. After the reaction, reduce the pressure to extract ethanol and then dry to obtain polyethylene glycol monomethyl ether.

[0020] Optionally, the molecular weight of the polyethylene glycol monomethyl ether is 200-800.

[0021] Optionally, the viscosity of the polydiethoxysiloxane ethanol solution is 4000-10000 cp (at 20-30 °C).

[0022] Optionally, the mass ratio of the polyethylene glycol monomethyl ether to the polydiethoxysiloxane is 1:(0.2-0.5).

[0023] Optionally, the temperature of the transesterification reaction is 60-70 °C, and the time is 2-4 h.

[0024] According to another aspect of the present application, a method for preparing a gas channeling plugging agent for carbon dioxide flooding is provided, including the following steps: Disperse the reaction monomers evenly in water, and add N-sulfonated chitosan, a crosslinking agent, an initiator, and a polyethylene glycol monomethyl ether grafted siloxane polymer and mix evenly to obtain the product.

[0025] Compared with the prior art, the present application has the following beneficial effects: 1. The present application provides a polyacrylamide gel-based gas channeling plugging agent for carbon dioxide flooding. This plugging agent has a low viscosity under the condition of not forming gel at normal temperature, is easy to pump into the formation, has high strength after forming gel, good temperature resistance, good salt resistance, and strong plugging property, and can be used to prevent and control carbon dioxide gas channeling in carbon dioxide flooding.

[0026] 2. A certain amount of N-sulfonated chitosan is added to the plugging agent of the present application, which can form a stable structure with acrylamide, etc., improve the gel strength, and enhance the plugging property; the plugging agent uses a free-radical polymerizable monomer containing acrylamide in a certain proportion as the main reaction monomer, and the addition of 2-acrylamido-2-methylpropanesulfonic acid and N-(isobutoxy)methylacrylamide helps to improve the temperature resistance and salt resistance of the plugging agent. Combined with N-sulfonated chitosan, it can withstand high temperatures of 160 °C.

[0027] 3. A certain amount of polyethylene glycol grafted siloxane polymer is also added to the plugging agent of the present application, which helps to improve the stability of the plugging agent and further enhance the temperature resistance, so that it maintains good gel performance and plugging property during long-term storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the infrared spectrum of N-sulfonated chitosan in the present application; in the figure, a represents unmodified chitosan, and b represents N-sulfonated chitosan; Figure 2 It is the infrared spectrum of the polyethylene glycol monomethyl ether grafted siloxane polymer in the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present application, but do not limit the present application in any way. The following content is merely an exemplary illustration of the scope claimed by the present application. Those skilled in the art can make various changes and modifications to the invention of the present application based on the disclosed content, and it should also fall within the scope claimed by the present application.

[0030] In the embodiments of the present application, various chemical reagents are obtained through conventional commercial channels unless otherwise specified. Among them, acrylamide was purchased from Shandong Yukang Chemical Co., Ltd., N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-(isobutoxy)methylacrylamide were purchased from Hubei Jusheng Technology Co., Ltd.; polydiethoxysiloxane was purchased from Hubei Yongkuo Technology Co., Ltd., and polyethylene glycol monomethyl ether was purchased from Hubei Jusheng Technology Co., Ltd.; sodium dichlorodihydroxypropyl sulfonate was purchased from Hubei Jusheng Technology Co., Ltd., and chitosan was purchased from Hubei Xinmingtai Chemical Co., Ltd. In the following specific embodiments, the initiator is potassium persulfate. It can be understood that replacing the initiator with other peroxide initiators can achieve the technical effects of the present application, and it does not constitute a limitation to the present application.

[0031] In the following specific embodiments, N-sulfonated chitosan is prepared by the following method: Add chitosan to an acetic acid solution, stir and swell, add a sodium dichlorodihydroxypropyl sulfonate solution, raise the temperature for reaction to obtain a crude product; then add water to the crude product, adjust the pH to neutral, filter, wash, and dry to obtain N-sulfonated chitosan; wherein, The molecular weight of chitosan is 20 kDa to 50 kDa, and the degree of deacetylation is 75 to 90%; In the present application, the sulfonation degree of sulfonated chitosan is mainly adjusted by controlling the ratio of the sulfonating agent sodium dichlorodihydroxypropyl sulfonate to chitosan. The present application limits the weight ratio of chitosan with a specific molecular weight and degree of deacetylation to sodium dichlorodihydroxypropyl sulfonate to be 1:(1.5 - 2.2), and N-sulfonated chitosan with a sulfonation degree in the range of 0.33 to 0.48 can be obtained. As long as the N-sulfonated chitosan that meets the above conditions can achieve the technical effects of the present application, such as improving the gelation strength of the plugging agent and enhancing the temperature and salt resistance; if N-sulfonated chitosan with a sulfonation degree lower than or higher than this range is to be obtained, the ratio of chitosan and sodium dichlorodihydroxypropyl sulfonate can be adjusted adaptively. Therefore, only the preparation methods of N-sulfonated chitosan with sulfonation degrees of 0.33 and 0.48 are exemplarily given in the following text. It can be understood that by adaptively adjusting the ratio of chitosan to sodium dichlorodihydroxypropyl sulfonate, N-sulfonated chitosan with the desired sulfonation degree can be obtained.

[0032] In the actual preparation process of N-sulfonated chitosan, sodium dichlorodihydroxypropyl sulfonate is added in the form of an aqueous solution, and the mass concentration of its aqueous solution is not particularly limited, generally greater than 5% is sufficient, preferably 30-50%; the temperature for the temperature-raising reaction is 60-80°C and the time is 3-4 h.

[0033] Specifically, N-sulfonated chitosan with a sulfonation degree of 0.33 is prepared by the following method: Add 1 part of chitosan (molecular weight 20 kDa, deacetylation degree 75%) to 20 parts of a 2% acetic acid solution by mass fraction, stir to fully swell, then add 6 parts of a 30% sodium dichlorodihydroxypropyl sulfonate solution by mass concentration (react at 60°C for 4 h, after the reaction, add water, adjust the pH to neutral, filter, wash, dialyze, and dry to obtain. Infrared characterization is carried out on N-sulfonated chitosan and chitosan, and the results are as Figure 1 shown. It can be seen that, relative to chitosan (curve a), N-sulfonated chitosan (curve b) shows characteristic peaks of S=O and O=S=O in the -SO3 -1 group near 1160 cm -1 and 1036 cm - . Thus, it can be seen that sulfonic acid groups are introduced into N-sulfonated chitosan.

[0034] N-sulfonated chitosan with a sulfonation degree of 0.48 is prepared by the following method: Add 1 part of chitosan (molecular weight 50 kDa, deacetylation degree 90%) to 20 parts of a 2% acetic acid solution by mass fraction, stir to fully swell, then add 4.8 parts of a 40% sodium dichlorodihydroxypropyl sulfonate solution by mass concentration, raise the temperature to 80°C and react for 4 h, after the reaction, add water, adjust the pH to neutral, filter, wash, dialyze, and dry to obtain.

[0035] N-sulfonated chitosan with a sulfonation degree of 0.51 is prepared by the following method: Add 1 part of chitosan (molecular weight 50 kDa, deacetylation degree 90%) to 20 parts of a 2% acetic acid solution by mass fraction, stir to fully swell, then add 5.5 parts of a 50% sodium dichlorodihydroxypropyl sulfonate solution by mass concentration, raise the temperature to 80°C and react for 4 h, after the reaction, add water, adjust the pH to neutral, filter, wash, dialyze, and dry to obtain.

[0036] The present application will be further described below by way of specific examples.

[0037] Example 1 This example provides a channel plugging agent for carbon dioxide flooding, which includes, by mass percentage: 8% reactive monomers: acrylamide and 2-acrylamido-2-methylpropanesulfonic acid with a molar ratio of 10:3; 1.5% N-sulfonated chitosan: degree of sulfonation is 0.33; 0.5% crosslinking agent: glutaraldehyde and epichlorohydrin with a mass ratio of 88:12; 0.1% potassium persulfate; The balance is water.

[0038] The preparation method of the channel plugging agent for carbon dioxide flooding includes the following steps: Disperse the reaction monomers evenly in water, add N-sulfonated chitosan, crosslinking agent, and initiator and mix evenly to obtain.

[0039] Example 2 This example provides a channel plugging agent for carbon dioxide flooding, by mass percentage, including: 15% reaction monomers: N-isopropylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid with a molar ratio of 10:3.5; 2% N-sulfonated chitosan: degree of sulfonation is 0.48; 1% crosslinking agent: glutaraldehyde and epichlorohydrin with a mass ratio of 95:5; 0.5% potassium persulfate; The balance is water.

[0040] The preparation method of the channel plugging agent for carbon dioxide flooding includes the following steps: Disperse the reaction monomers evenly in water, add N-sulfonated chitosan, crosslinking agent, and initiator and mix evenly to obtain.

[0041] Example 3 The difference from Example 2 is that the reaction monomers further contain N-(isobutoxy)methylacrylamide, and the molar ratio of N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-(isobutoxy)methylacrylamide is 10:3.5:0.4, and the rest are the same as Example 2.

[0042] Example 4 The difference from Example 2 is that the reaction monomers further contain N-(isobutoxy)methylacrylamide, and the molar ratio of N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-(isobutoxy)methylacrylamide is 10:3.5:0.7, and the rest are the same as Example 2.

[0043] Example 5 This example provides a channel plugging agent for carbon dioxide flooding, by mass percentage, including: 15% reaction monomers: N-isopropylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid with a molar ratio of 10:3.5; 2% N-sulfonated chitosan: degree of sulfonation is 0.48; 2% polyethylene glycol monomethyl ether grafted silicone polymer; 1% crosslinking agent: glutaraldehyde and epichlorohydrin with a mass ratio of 95:5; 0.5% initiator potassium persulfate; The balance is water.

[0044] Among them, the polyethylene glycol monomethyl ether grafted silicone polymer is prepared by the following method: Add 1 part of polyethylene glycol monomethyl ether (molecular weight 800) to 1 part of a 20% polyethylene diethoxysiloxane ethanol solution, carry out transesterification reaction at 60 °C for 4 h, and after the reaction, reduce the pressure and dry to obtain it. Infrared spectrum characterization is carried out on it, and the results are as Figure 2 [[ID=?]]shown. It can be seen that the stretching vibration peak of -CH2 of polyethylene glycol monomethyl ether is near 2880 cm -1 The stretching vibration peak of C-O-C appears near 1120 cm -1 The stretching vibration peak of Si-O-Si appears near 1076 cm -1 The stretching vibration peak of Si-O-C appears near 1142 cm -1 indicating that the polyethylene glycol monomethyl ether grafted silicone polymer is successfully prepared.

[0045] The preparation method of the above-mentioned gas channeling plugging agent for carbon dioxide flooding includes the following steps: Disperse the reaction monomers evenly in water, and add N-sulfonated chitosan, crosslinking agent, initiator, and polyethylene glycol monomethyl ether grafted silicone polymer and mix evenly to obtain it.

[0046] Example 6 This example provides a gas channeling plugging agent for carbon dioxide flooding, which includes, by mass percentage: 15% reaction monomers: N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-(isobutoxy)methylacrylamide with a molar ratio of 10:3.5:0.7; 2% N-sulfonated chitosan: degree of sulfonation is 0.48; 2.7% polyethylene glycol monomethyl ether grafted silicone polymer; 1% crosslinking agent: glutaraldehyde and epichlorohydrin with a mass ratio of 95:5; 0.5% initiator potassium persulfate; The balance is water.

[0047] Among them, the polyethylene glycol monomethyl ether grafted silicone polymer is prepared by the following method: It should be noted that there seems to be an unclear part in the original text where the number after "2880 cm" etc. is not clearly presented in the provided text. I've translated it as best as possible based on the existing content.Add 1 part of methoxypolyethylene glycol (with a molecular weight of 200) to 2.5 parts of a 20% ethanol solution of polydiethoxysiloxane, carry out transesterification reaction at 70 °C for 3 h, after the reaction, reduce the pressure, extract ethanol, and dry to obtain the product.

[0048] The preparation method of the plugging agent for carbon dioxide flooding includes the following steps: Disperse the reaction monomers evenly in water, add N-sulfonated chitosan, crosslinking agent, initiator, and methoxypolyethylene glycol grafted siloxane polymer and mix evenly to obtain the product.

[0049] Comparative Example 1 The difference from Example 2 is that the addition amount of N-sulfonated chitosan is 3%, and the rest is the same as Example 2.

[0050] Comparative Example 2 The difference from Example 2 is that N-sulfonated chitosan is replaced with an equal amount of chitosan, that is, chitosan is not modified, and the rest is the same as Example 2.

[0051] Comparative Example 3 The difference from Example 2 is that the sulfonation degree of N-sulfonated chitosan is 0.51, and the rest is the same as Example 2.

[0052] Comparative Example 4 The difference from Example 2 is that the molecular weight of chitosan in the preparation process of N-sulfonated chitosan is 70 kDa and the degree of deacetylation is 95%, and the rest is the same as Example 2.

[0053] Comparative Example 5 The difference from Example 3 is that the reaction monomers also contain N-(isobutoxy)methacrylamide, the molar ratio of N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid and N-(isobutoxy)methacrylamide is 10:3.5:1, and the rest is the same as Example 6.

[0054] Comparative Example 6 The difference from Example 5 is that the dosage of the ethanol solution of polydiethoxysiloxane is 4 parts, and the rest is the same as Example 8.

[0055] Test Example 1 Taking the lost circulation plugging agents prepared in the above-mentioned examples and comparative examples as samples, the initial viscosity at room temperature was measured using a Brookfield DV-III type rotational viscometer, and then placed in a beaker and placed in an incubator at 80 °C for gelation reaction. When the surface of the gel in the inverted beaker did not deform, gelation occurred, and the time at this point was recorded as the gelation time. Each sample was subjected to two parallel tests, and the relative error between the two test results did not exceed 10%. When the relative error exceeded 10%, the test was retested. The final gelation time was the average of the two results; and the viscosity and gelation strength after gelation were measured.

[0056] The results are shown in Table 1 below.

[0057] Table 1

[0058] The results showed that the initial viscosities of the lost circulation plugging agents provided in Examples 1 and 2 of the present application at room temperature were not greater than 10 mPa·s. Their viscosities were low, the injectability was strong, and the viscosity of the gel after gelation was high. Compared with the examples, the gelation time in Comparative Example 1 and Comparative Example 2 increased, the viscosity after gelation decreased, and the gelation strength also decreased.

[0059] Test Example 2 Simulation plugging test Acidic brine was injected into an artificial microfractured sandstone core through a constant pressure and constant speed pump at an injection rate of 1 mL / min. After the pressure was stabilized, the permeability of the core was measured. Artificial cores with a permeability k0 of 1-2 mD were selected as experimental objects; subsequently, the lost circulation plugging agents in the above-mentioned examples and comparative examples were injected into the cores. After reacting in a constant temperature oven at 90 °C for 8 h, the permeability k was measured, and the plugging rate was calculated according to (k0 - k) / k0 × 100%.

[0060] The results are shown in Table 2.

[0061] Table 2

[0062] The results showed that acrylamide and the like in the lost circulation plugging agents obtained in Examples 1 and 2 of the present application formed gels, which could be used in carbon dioxide gas injection wells to prevent and control carbon dioxide gas channeling, and the plugging rate reached more than 90%. The plugging rate of the lost circulation plugging agent obtained in Example 6 reached more than 99%, and the plugging effect was good.

[0063] Test Example 3 After the lost circulation plugging agents after gelation in Test Example 1 were placed at 160 °C and 200 °C for 7 d respectively, their dehydration rates A and dehydration rates B were measured to evaluate their heat resistance.

[0064] Replace the water in the examples and comparative examples with simulated brine with a salinity of 200,000 mg / L and a calcium and magnesium ion content of 10,000 mg / L to prepare the lost circulation plugging agent, and then place it at 80 °C for 7 days to test its dehydration rate C for evaluating its salt tolerance; After the lost circulation plugging agent gelled in Test Example 1 was placed at 80 °C for 2 months respectively, the dehydration rate D was tested.

[0065] The results are shown in Table 3 below.

[0066] Table 3

[0067] The results show that the lost circulation plugging agent provided by this application has high temperature resistance and salt tolerance, can withstand a temperature of up to 200 °C, and hardly dehydrates in 2 months, with good stability.

[0068] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, this application is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of this application should be within the protection scope of this application.

Claims

1. A plugging agent for carbon dioxide flooding, characterized in that, By mass percentage, it includes the following raw materials: 8-15% of reaction monomers, 1.5-2% of N-sulfonated chitosan, 0.5-1% of crosslinking agent, 0.1-0.5% of initiator, and the balance is water; Among them, the reaction monomers include a first monomer and a second monomer 2-acrylamido-2-methylpropanesulfonic acid; The crosslinking agent is glutaraldehyde and epichlorohydrin with a weight ratio of (88-95):(5-12); The initiator is selected from organic or inorganic peroxides; The first monomer is selected from at least one of acrylamide, methacrylamide, N-ethylacrylamide, N-methylmethacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, and N,N-diethylacrylamide.

2. The lost circulation plugging agent for carbon dioxide flooding according to claim 1, wherein The N-sulfonated chitosan is prepared by sulfonating chitosan with sodium 2,3-dichloro-1-propanesulfonate; the molecular weight of the chitosan is 20 kDa to 50 kDa, the degree of deacetylation is 75-90%, and the sulfonation degree of the N-sulfonated chitosan is 0.33-0.

48.

3. The lost circulation plugging agent for carbon dioxide flooding according to claim 1, characterized in that, The reaction monomers further include a third monomer N-(isobutoxy)methylacrylamide.

4. The plugging agent for carbon dioxide flooding according to claim 3, characterized in that, The reaction monomers include the first monomer, the second monomer, and the third monomer in a molar ratio of 10:(3-3.5):(0-0.7).

5. The lost circulation plugging agent for carbon dioxide flooding according to claim 4, wherein The reaction monomers include the first monomer, the second monomer, and the third monomer in a molar ratio of 10:(3-3.5):(0.4-0.7).

6. The lost circulation plugging agent for carbon dioxide flooding according to any one of claims 1-5, characterized in that, The gas channeling plugging agent for carbon dioxide flooding further contains 0-2.7% of polyethylene glycol monomethyl ether grafted silicone oxygen polymer.

7. The lost circulation plugging agent for carbon dioxide flooding according to claim 6, wherein The preparation method of the polyethylene glycol monomethyl ether grafted silicone oxygen polymer includes the following steps: Adding polyethylene glycol monomethyl ether to a polydiethoxysiloxane multimer solution for transesterification reaction. After the reaction, reduce the pressure to extract ethanol and then dry to obtain polyethylene glycol monomethyl ether grafted silicone oxygen polymer; The mass ratio of the polyethylene glycol monomethyl ether to the polydiethoxysiloxane multimer is 1:(0.2-0.5).

8. The preparation method of the channel plugging agent for carbon dioxide flooding according to any one of claims 1 to 7, characterized in that, It includes the following steps: By mass percentage, add 8-15% of reaction monomers to water and disperse evenly, then add 1.5-2% of N-sulfonated chitosan, 0.5-1% of crosslinking agent, 0.1-0.5% of initiator, and 0-2.7% of polyethylene glycol monomethyl ether grafted silicone oxygen polymer and mix evenly to obtain it.

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