A channeling blocking agent for carbon dioxide flooding and preparation method thereof

Abstract

The present application provides a carbon dioxide flooding channeling blocking agent and a preparation method thereof, relating to the field of oilfield development technology. The carbon dioxide flooding channeling blocking agent comprises: 8-15% reactive monomers, 1.5-2% N-sulfonated chitosan, 0.5-1% cross-linking agent, 0.1-0.5% initiator, and the balance being water; the reactive monomers comprise a first monomer and a second monomer, 2-acrylamido-2-methylpropanesulfonic acid. The channeling blocking agent has low viscosity at room temperature before gelling, making it easy to pump into the formation. After gelling, it has high strength, good temperature resistance, excellent salt resistance, and strong plugging properties. It can be used to prevent and control carbon dioxide gas channeling during carbon dioxide flooding production.

Description

Technical Field

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

[0002] During oilfield development, low-permeability reservoirs are typically developed using water flooding or CO2 flooding technologies. CO2 flooding offers advantages such as excellent injection performance, wide applicability, low recovery costs, and significant enhanced oil recovery. However, due to reservoir heterogeneity, differential mobility, and density, CO2 flow in the formation can cause viscous fingering and gravity differentiation, leading to channeling through high-permeability channels. This channeling is particularly severe within artificially fractured fractures. This gas channeling leads to ineffective gas circulation, reduced sweep efficiency, decreased crude oil recovery, and severe impacts on development effectiveness. Therefore, controlling and delaying CO2 channeling within fractures is a key challenge facing CO2 flooding.

[0003] Applying sealing agents before CO2 injection is an effective way to mitigate CO2 gas channeling. Currently, commonly used sealing agents include inorganic particle-based sealing agents and gel-based sealing agents. Inorganic particle-based sealing agents have the disadvantages of a short effective range and significant formation damage. With increasing awareness of oil well formation protection, their use is declining, leading to the development of gel-based sealing agents as a major research focus. Polymer gel-based sealing agents are the most widely used of these gel-based sealing agents. While they offer excellent channeling and water blocking effects, they have limited temperature tolerance. Conventional polymer gel-based sealing agents are only suitable for medium- and low-temperature reservoirs with temperatures between 60 and 120°C. They have poor salt tolerance and are prone to failure in highly salinized reservoirs. Long-term use can significantly reduce permeability, ultimately leading to production losses. For example, patent CN104293330A discloses a CO2 gas drive sealing agent for high-temperature, low-permeability oil reservoirs. The sealing agent consists of acrylamide, a modifier, an emulsifier, an initiator, N,N-methylenebisacrylamide, formaldehyde, a retarder and water. It has good stability at 126°C, is not suitable for high-temperature oil reservoirs, and does not involve salt resistance.

[0004] Therefore, providing a carbon dioxide flooding channeling blocking agent with good channeling effect, good temperature resistance and good salt resistance is still an urgent problem to be solved in this field. Summary of the Invention

[0005] The purpose of this application is to address the deficiencies of the existing technology and provide a carbon dioxide flooding channeling blocking agent and a preparation method thereof. The channeling blocking agent has good channeling 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 objectives, the technical solutions adopted in this application are as follows:

[0007] A carbon dioxide flooding channeling blocking agent comprises the following raw materials, calculated by mass percentage: 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 being water;

[0008] Wherein, the reaction monomers include a first monomer and a second monomer 2-acrylamido-2-methylpropanesulfonic acid.

[0009] Furthermore, the N-sulfonated chitosan is prepared by sulfonating chitosan with sodium trichlorodihydroxypropyl sulfonate; the molecular weight of the chitosan is 20kDa to 50kDa, the degree of deacetylation is 75 to 90%, and the degree of sulfonation of the N-sulfonated chitosan is 0.33 to 0.48.

[0010] Furthermore, the N-sulfonated chitosan is prepared by the following method:

[0011] Chitosan is added to an acetic acid solution, stirred, and a sodium trichlorodihydroxypropyl sulfonate solution with a mass concentration of 45% is added, and the temperature is raised to react to obtain a crude product; then water is added to the crude product, the pH is adjusted to neutral, filtered, washed, and dried to obtain N-sulfonated chitosan.

[0012] Optionally, the weight ratio of chitosan to sodium trichlorodihydroxypropyl sulfonate is 1:(1.5-2.2).

[0013] Optionally, the temperature of the temperature-raising reaction is 60-80° C. and the time is 3-4 hours.

[0014] This application adds N-sulfonated chitosan to the channeling agent. Compared with chitosan, the addition of N-sulfonated chitosan can form a grafted structure with acrylamide and other materials, thereby increasing the gel strength and the plugging effect, enabling it to maintain a high gel strength for a long time at 160°C, and improving its temperature resistance. However, the study found that the introduction of sulfonated chitosan led to a decrease in its long-term storage stability, affecting the gel strength and plugging performance of the channeling agent. In addition, it was found that although the addition of N-sulfonated chitosan can improve the temperature resistance of the material, the molecular weight and deacetylation degree of N-sulfonated chitosan need to be controlled. Too high or too low a molecular weight, or too high or too low a deacetylation degree, can easily lead to a decrease in the temperature and salt resistance of the channeling agent. In addition, the sulfonation degree of chitosan also affects the performance of the channeling agent. The higher the sulfonation degree, the more sulfonated groups there are, resulting in a decrease in salt resistance and poor stability.

[0015] 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.

[0016] Furthermore, the reaction monomers further comprise a third monomer, N-(isobutyloxy)methyl acrylamide, 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).

[0017] This application uses a free radical polymerizable monomer containing only acrylamide as the first monomer, and the second monomer 2-acrylamido-2-methylpropanesulfonic acid as the main monomer to react and prepare a polyacrylamide gel-type channeling blocking agent. The presence of the sulfonic acid group in 2-acrylamido-2-methylpropanesulfonic acid improves the material's temperature resistance and salt tolerance, with a blocking rate of over 85%. However, its temperature resistance is around 160°C, making it unsuitable for oil reservoir development at higher temperatures. Research has found that introducing a certain amount of N-(isobutyloxy)methyl acrylamide into the reaction monomer can help further improve the material's temperature resistance, enabling it to withstand temperatures of 200°C and withstand temperatures for two months without dehydration, increasing the blocking rate to over 90%.

[0018] Furthermore, the cross-linking agent is glutaraldehyde and epichlorohydrin in a weight ratio of (88-95): (5-12).

[0019] Furthermore, the initiator is selected from organic or inorganic peroxides. Specifically, the initiator illustratively includes but is not limited to at least one of potassium persulfate, sodium persulfate, ammonium persulfate, benzoyl peroxide, di-tert-butyl peroxide, dodecyl peroxide, azobisisobutyronitrile, tert-butyl peroxyvalerate, and cumene hydroperoxide.

[0020] Furthermore, the water is any one of clean water, river water, and simulated formation water.

[0021] While the aforementioned channeling agents have good temperature and salt resistance and a high blocking efficiency, their long-term storage stability needs to be improved. Therefore, in a further embodiment, the carbon dioxide flooding channeling agent further includes a polyethylene glycol monomethyl ether grafted siloxane polymer in an amount of 0-2.7%, preferably 2-2.7%. The addition of polyethylene glycol monomethyl ether grafted siloxane polymer can improve its storage stability, but the grafting rate of polyethylene glycol monomethyl ether should be carefully considered to avoid excessive polyethylene glycol grafting, which can reduce temperature resistance and salt resistance.

[0022] Furthermore, the preparation method of the polyethylene glycol monomethyl ether grafted siloxane polymer comprises the following steps:

[0023] Polyethylene glycol monomethyl ether is added to polydiethoxysiloxane ethanol solution to carry out ester exchange reaction. After the reaction is completed, the pressure is reduced, the ethanol is extracted, and the solution is dried to obtain the product.

[0024] Optionally, the molecular weight of the polyethylene glycol monomethyl ether is 200-800.

[0025] Optionally, the viscosity of the polydiethoxysiloxane ethanol solution is 4000-10000 cp (at 20-30° C.).

[0026] Optionally, the mass ratio of the polyethylene glycol monomethyl ether to the polydiethoxysiloxane is 1:(0.2-0.5).

[0027] Optionally, the temperature of the transesterification reaction is 60-70° C., and the time is 2-4 hours.

[0028] According to another aspect of the present application, a method for preparing a carbon dioxide flooding channeling blocking agent is provided, comprising the following steps:

[0029] The reaction monomers are added into water and dispersed evenly, and N-sulfonated chitosan, a cross-linking agent, an initiator and polyethylene glycol monomethyl ether grafted siloxane polymer are added and mixed evenly to obtain the product.

[0030] Compared with the prior art, this application has the following beneficial effects:

[0031] 1. The present application provides a polyacrylamide gel-based carbon dioxide flooding sealing agent. The sealing agent has low viscosity at room temperature before gelling and is easy to pump into the formation. After gelling, it has high strength, good temperature resistance, good salt resistance, and strong sealing properties. It can be used to prevent and control carbon dioxide gas channeling in carbon dioxide flooding mining.

[0032] 2. A certain amount of N-sulfonated chitosan is added to the channeling sealant of the present application, which can form a stable structure with acrylamide, etc., improve the gel strength, and enhance the blocking performance; the channeling sealant uses a certain proportion of acrylamide-containing free radical polymerizable monomers as the main reactive monomers, and the addition of 2-acrylamido-2-methylpropanesulfonic acid and N-(isobutyloxy)methacrylamide helps to improve the temperature resistance and salt resistance of the channeling sealant. In combination with N-sulfonated chitosan, it can withstand high temperatures of 160°C.

[0033] 3. A certain amount of polyethylene glycol grafted siloxane polymer is also added to the channel sealing agent of the present application, which helps to improve the stability of the channel sealing agent and further improves the temperature resistance, so that it can maintain good gel performance and blocking properties during long-term storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the infrared spectrum of N-sulfonated chitosan of the present application; in the figure, a represents unmodified chitosan, and b represents N-sulfonated chitosan;

[0035] Figure 2 This is the infrared spectrum of the polyethylene glycol monomethyl ether grafted siloxane polymer of this application. DETAILED DESCRIPTION

[0036] The following non-limiting examples are provided to enable those skilled in the art to more fully understand the present application, but are not intended to limit the present application in any way. The following contents are merely illustrative of the scope of protection claimed in the present application. Those skilled in the art may make various changes and modifications to the invention of the present application based on the disclosed contents, and such changes and modifications shall also fall within the scope of protection claimed in the present application.

[0037] Unless otherwise specified, the various chemical reagents used in the examples of this application were obtained through conventional commercial channels. Among them, acrylamide was purchased from Shandong Yukang Chemical Co., Ltd., N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid and N-(isobutoxy)methacrylamide were purchased from Hubei Jusheng Technology Co., Ltd.; polydiethoxysiloxane was purchased from Hubei Yongkuo Technology Co., Ltd., polyethylene glycol monomethyl ether was purchased from Hubei Jusheng Technology Co., Ltd.; sodium trichlorodihydroxypropyl 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 the technical effect of the present application can be achieved by replacing the initiator with other peroxide initiators, which does not constitute a limitation on the present application.

[0038] In the following specific examples, N-sulfonated chitosan was prepared by the following method:

[0039] Chitosan is added to an acetic acid solution, stirred to swell, and a sodium trichlorodihydroxypropyl sulfonate solution is added, and the temperature is raised to react to obtain a crude product; water is then added to the crude product, the pH is adjusted to neutral, filtered, washed, and dried to obtain N-sulfonated chitosan; wherein,

[0040] The molecular weight of chitosan is 20kDa to 50kDa, and the degree of deacetylation is 75 to 90%;

[0041] The sulfonation degree of sulfonated chitosan in this application is mainly adjusted by controlling the ratio of the sulfonating agent sodium trichlorodihydroxypropyl sulfonate to chitosan. This application limits the weight ratio of chitosan with a specific molecular weight and deacetylation degree to sodium trichlorodihydroxypropyl sulfonate to 1: (1.5-2.2), and can obtain N-sulfonated chitosan with a sulfonation degree in the range of 0.33-0.48. As long as the N-sulfonated chitosan meets the above conditions, it can achieve the technical effect of this application, improve the gelling strength of the sealing agent, improve the temperature resistance and salt resistance, etc.; if you want to obtain N-sulfonated chitosan with a sulfonation degree lower or higher than this range, you can adaptively adjust the ratio of chitosan and sodium trichlorodihydroxypropyl sulfonate. Therefore, the following only exemplifies the preparation method of N-sulfonated chitosan with a sulfonation degree of 0.33 and 0.48. It can be understood that the N-sulfonated chitosan with the required sulfonation degree can be obtained by adaptively adjusting the chitosan and sodium trichlorodihydroxypropyl sulfonate.

[0042] In the actual preparation process of N-sulfonated chitosan, sodium trichlorodihydroxypropyl sulfonate is added in the form of an aqueous solution. The mass concentration of the aqueous solution is not particularly limited, and is generally greater than 5%, preferably 30-50%. The temperature of the temperature-raising reaction is 60-80°C and the time is 3-4 hours.

[0043] Specifically, N-sulfonated chitosan with a sulfonation degree of 0.33 was prepared by the following method:

[0044] 1 part of chitosan (molecular weight of 20kDa, degree of deacetylation of 75%) was added to 20 parts of 2% acetic acid solution by mass, stirred and fully swollen, and then 6 parts of 30% sodium trichlorodihydroxypropyl sulfonate solution by mass were added (heated to 60 ° C and reacted for 4 hours. After the reaction, water was added and the pH was adjusted to neutral. The mixture was filtered, washed, dialyzed and dried to obtain the product. The infrared characterization of N-sulfonated chitosan and chitosan was performed. The results are as follows: Figure 1 As shown in the figure, it can be seen that compared with chitosan (curve a), N-sulfonated chitosan (curve b) has a -1 、1036cm -1 -SO3 appears nearby - The characteristic peaks of S=O and O=S=O in the groups indicate that sulfonic acid groups have been introduced into N-sulfonated chitosan.

[0045] N-sulfonated chitosan with a sulfonation degree of 0.48 was prepared by the following method:

[0046] Add 1 part of chitosan (molecular weight of 50kDa, degree of deacetylation of 90%) to 20 parts of 2% acetic acid solution, stir to fully swell, then add 4.8 parts of 40% sodium trichlorodihydroxypropyl sulfonate solution, heat to 80°C and react for 4 hours. After the reaction is complete, add water and adjust the pH to neutral. Filter, wash, dialyze, and dry to obtain the product.

[0047] N-sulfonated chitosan with a sulfonation degree of 0.51 was prepared by the following method:

[0048] Add 1 part of chitosan (molecular weight of 50kDa, degree of deacetylation of 90%) to 20 parts of 2% acetic acid solution, stir to fully swell, then add 5.5 parts of 50% sodium trichlorodihydroxypropyl sulfonate solution, heat to 80°C and react for 4 hours. After the reaction is complete, add water and adjust the pH to neutral. Filter, wash, dialyze, and dry to obtain the product.

[0049] The present application will be further described below in the form of specific embodiments.

[0050] Example 1

[0051] This embodiment provides a carbon dioxide flooding anti-channeling agent, which comprises, by mass percentage:

[0052] 8% reactive monomers: acrylamide and 2-acrylamido-2-methylpropanesulfonic acid at a molar ratio of 10:3;

[0053] 1.5% N-sulfonated chitosan: degree of sulfonation is 0.33;

[0054] 0.5% cross-linking agent: glutaraldehyde and epichlorohydrin in a mass ratio of 88:12;

[0055] 0.1% potassium persulfate;

[0056] The balance is water.

[0057] The preparation method of the above-mentioned carbon dioxide flooding anti-channeling agent comprises the following steps:

[0058] The reaction monomer is added into water and dispersed evenly, and N-sulfonated chitosan, a cross-linking agent and an initiator are added and mixed evenly to obtain the product.

[0059] Example 2

[0060] This embodiment provides a carbon dioxide flooding anti-channeling agent, which comprises, by mass percentage:

[0061] 15% reactive monomers: N-isopropylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid in a molar ratio of 10:3.5;

[0062] 2% N-sulfonated chitosan: sulfonation degree is 0.48;

[0063] 1% cross-linking agent: glutaraldehyde and epichlorohydrin in a mass ratio of 95:5;

[0064] 0.5% potassium persulfate;

[0065] The balance is water.

[0066] The preparation method of the above-mentioned carbon dioxide flooding anti-channeling agent comprises the following steps:

[0067] The reaction monomer is added into water and dispersed evenly, and N-sulfonated chitosan, a cross-linking agent and an initiator are added and mixed evenly to obtain the product.

[0068] Example 3

[0069] The difference from Example 2 is that the reaction monomer further contains N-(isobutoxy)methacrylamide, and the molar ratio of N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid and N-(isobutoxy)methacrylamide is 10:3.5:0.4. The rest is the same as Example 2.

[0070] Example 4

[0071] The difference from Example 2 is that the reaction monomer further contains N-(isobutoxy)methacrylamide, and the molar ratio of N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid and N-(isobutoxy)methacrylamide is 10:3.5:0.7. The rest is the same as Example 2.

[0072] Example 5

[0073] This embodiment provides a carbon dioxide flooding anti-channeling agent, which comprises, by mass percentage:

[0074] 15% reactive monomers: N-isopropylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid in a molar ratio of 10:3.5;

[0075] 2% N-sulfonated chitosan: sulfonation degree is 0.48;

[0076] 2% polyethylene glycol monomethyl ether grafted silicone polymer;

[0077] 1% cross-linking agent: glutaraldehyde and epichlorohydrin in a mass ratio of 95:5;

[0078] 0.5% initiator potassium persulfate;

[0079] The balance is water.

[0080] Wherein, the polyethylene glycol monomethyl ether grafted siloxane polymer is prepared by the following method:

[0081] Add 1 part of polyethylene glycol monomethyl ether (molecular weight 800) to 1 part of polydiethoxysiloxane ethanol solution with a mass concentration of 20%, and carry out ester exchange reaction at 60℃ for 4 hours. After the reaction, reduce the pressure and dry to obtain the product. The infrared spectrum of the product is as follows. Figure 2 As shown, it can be seen that 2880cm -1 Nearby is the stretching vibration peak of the heavy -CH2 of polyethylene glycol monomethyl ether, 1120cm -1 The stretching vibration peak of COC appears near 1076 cm -1 The stretching vibration peak of Si-O-Si appears near 1142 cm -1 The stretching vibration peak of Si-OC appears nearby, indicating that the polyethylene glycol monomethyl ether grafted siloxane polymer was successfully prepared.

[0082] The preparation method of the above-mentioned carbon dioxide flooding anti-channeling agent comprises the following steps:

[0083] The reaction monomers are added into water and dispersed evenly, and N-sulfonated chitosan, a cross-linking agent, an initiator, and polyethylene glycol monomethyl ether grafted siloxane polymer are added and mixed evenly to obtain the product.

[0084] Example 6

[0085] This embodiment provides a carbon dioxide flooding anti-channeling agent, which comprises, by mass percentage:

[0086] 15% reactive monomers: N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-(isobutyloxy)methacrylamide in a molar ratio of 10:3.5:0.7;

[0087] 2% N-sulfonated chitosan: sulfonation degree is 0.48;

[0088] 2.7% polyethylene glycol monomethyl ether grafted siloxane polymer;

[0089] 1% cross-linking agent: glutaraldehyde and epichlorohydrin in a mass ratio of 95:5;

[0090] 0.5% initiator potassium persulfate;

[0091] The balance is water.

[0092] Wherein, the polyethylene glycol monomethyl ether grafted siloxane polymer is prepared by the following method:

[0093] Add 1 part of polyethylene glycol monomethyl ether (molecular weight 200) to 2.5 parts of 20% polydiethoxysiloxane ethanol solution, carry out ester exchange reaction at 70°C for 3 hours, reduce the pressure after the reaction, extract the ethanol, and dry to obtain the product.

[0094] The preparation method of the above-mentioned carbon dioxide flooding anti-channeling agent comprises the following steps:

[0095] The reaction monomers are added into water and dispersed evenly, and N-sulfonated chitosan, a cross-linking agent, an initiator, and polyethylene glycol monomethyl ether grafted siloxane polymer are added and mixed evenly to obtain the product.

[0096] Comparative Example 1

[0097] The difference from Example 2 is that the added amount of N-sulfonated chitosan is 3%, and the rest is the same as Example 2.

[0098] Comparative Example 2

[0099] The difference from Example 2 is that N-sulfonated chitosan is replaced by an equal amount of chitosan, that is, the chitosan is not modified. The rest is the same as Example 2.

[0100] Comparative Example 3

[0101] 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.

[0102] Comparative Example 4

[0103] 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%. The rest is the same as Example 2.

[0104] Comparative Example 5

[0105] The difference from Example 3 is that the reaction monomer further contains N-(isobutoxy)methacrylamide, and the molar ratio of N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid and N-(isobutoxy)methacrylamide is 10:3.5:1. The rest is the same as Example 6.

[0106] Comparative Example 6

[0107] The difference from Example 5 is that the amount of polydiethoxysiloxane ethanol solution used is 4 parts, and the rest is the same as Example 8.

[0108] Test Example 1

[0109] The sealants prepared in the above embodiments and comparative examples were used as samples, and the initial viscosity at room temperature was tested using a Brookfield DV-III rotational viscometer. The samples were then placed in a beaker and placed in a constant temperature box at 80°C for gelation reaction. When the beaker was turned over, the gel surface did not deform, which meant that gelation had occurred. The time at this point was recorded as the gelation time. Two parallel tests were performed for each sample, and the relative error of the two test results did not exceed 10%. If the relative error exceeded 10%, the sample was retested, and the final gelation time was the average of the two results. The viscosity and gelation strength after gelation were also tested.

[0110] The results are shown in Table 1 below.

[0111] Table 1

[0112]

[0113] The results show that the initial viscosity of the channeling sealants provided in Examples 1 and 2 of the present application at room temperature is no greater than 10 mPa·s, indicating low viscosity, strong injectability, and high viscosity of the gel after gelation. Compared to the examples, the gelation time in Comparative Examples 1 and 2 was increased, and the viscosity and strength of the gel after gelation were reduced.

[0114] Test Example 2

[0115] Simulated plugging test

[0116] Acidic brine was injected into the artificial micro-fractured sandstone core using a constant pressure and constant speed pump at an injection rate of 1 mL / min. After the pressure stabilized, the core permeability was tested, and artificial cores with a permeability k0 of 1-2 mD were selected as experimental objects. Subsequently, the sealing agents described in the above embodiments 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 as (k0-k) / k0×100%.

[0117] The results are shown in Table 2.

[0118] Table 2

[0119]

[0120] The results show that acrylamide and the like in the channeling blocking agents obtained in Examples 1 and 2 of the present application form a gel, which can be used in carbon dioxide gas drive wells to prevent and control carbon dioxide gas channeling, with a plugging rate of over 90%. The plugging rate of the channeling blocking agent obtained in Example 6 reaches over 99%, with a good plugging effect.

[0121] Test Example 3

[0122] The sealant of Test Example 1 was placed at 160°C and 200°C for 7 days, and its dehydration rate A and dehydration rate B were measured to evaluate its heat resistance.

[0123] The water in the Examples and Comparative Examples was replaced with a mineralization of 200,000 mg / L and a calcium and magnesium ion content of 10,000 mg / L of simulated brine to prepare a channeling agent, which was then placed at 80°C for 7d to test its dehydration rate C for evaluating its salt resistance;

[0124] The gelled sealant of Test Example 1 was placed at 80° C. for 2 months, and the dehydration rate D was measured.

[0125] The results are shown in Table 3 below.

[0126] Table 3

[0127]

[0128] The results show that the sealing agent provided in this application has high temperature resistance and salt resistance, can withstand temperatures up to 200°C, and hardly dehydrates in 2 months, with good stability.

[0129] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, this application is not limited to the above-described embodiments. Any improvements and modifications made by those skilled in the art based on the disclosure of this application, without departing from the scope of this application, should be within the scope of protection of this application.

Claims

1. A carbon dioxide flooding anti-channeling agent, characterized in that: The raw materials include, by mass percentage, 8-15% of reaction monomer, 1.5-2% of N-sulfonated chitosan, 0.5-1% of cross-linking agent, 0.1-0.5% of initiator, and the balance of water; Wherein, the reaction monomers include a first monomer and a second monomer 2-acrylamido-2-methylpropanesulfonic acid; The cross-linking agent is glutaraldehyde and epichlorohydrin in a weight ratio of (88-95): (5-12); The initiator is selected from organic or inorganic peroxides; The first monomer is at least one selected from acrylamide, methacrylamide, N-ethylacrylamide, N-methylmethacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, and N,N-diethylacrylamide; The N-sulfonated chitosan is prepared by sulfonating chitosan with sodium trichlorodihydroxypropyl sulfonate; the molecular weight of the chitosan is 20kDa-50kDa, the deacetylation degree is 75-90%, and the sulfonation degree of the N-sulfonated chitosan is 0.33-0.

48.

2. The carbon dioxide flooding blocking agent according to claim 1, characterized in that The reactive monomers further include a third monomer, N-(isobutyloxy)methacrylamide.

3. The carbon dioxide flooding blocking agent according to claim 2, characterized in that: The reactive monomers include a first monomer, a second monomer, and a third monomer in a molar ratio of 10:(3-3.5):(0-0.7).

4. The carbon dioxide flooding blocking agent according to claim 3, characterized in that: The reactive monomers include a first monomer, a second monomer, and a third monomer in a molar ratio of 10:(3-3.5):(0.4-0.7).

5. The carbon dioxide flooding channeling blocking agent according to any one of claims 1 to 4, characterized in that: The carbon dioxide flooding anti-channeling agent further comprises 0-2.7% of polyethylene glycol monomethyl ether grafted siloxane polymer.

6. The carbon dioxide flooding blocking agent according to claim 5, characterized in that: The preparation method of the polyethylene glycol monomethyl ether grafted siloxane polymer comprises the following steps: Polyethylene glycol monomethyl ether is added to polydiethoxysiloxane ethanol solution to carry out ester exchange reaction, and after the reaction is completed, the pressure is reduced, the ethanol is extracted, and the solution is dried to obtain the product; The mass ratio of the polyethylene glycol monomethyl ether to the polydiethoxysiloxane is 1:(0.2-0.5).

7. The method for preparing the carbon dioxide flooding channeling blocking agent according to any one of claims 1 to 6, characterized in that: The following steps are involved: Calculated by mass percentage, 8-15% of the reaction monomers are added into water and dispersed evenly, and then 1.5-2% of N-sulfonated chitosan, 0.5-1% of a cross-linking agent, 0.1-0.5% of an initiator and 0-2.7% of a polyethylene glycol monomethyl ether grafted siloxane polymer are added and mixed evenly to obtain the product.

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