A water-soluble temporary plugging agent for oil well fracturing and its preparation method

Abstract

This invention relates to the field of temporary plugging agents, and discloses a water-soluble temporary plugging agent for oil well fracturing and its preparation method. The water-soluble temporary plugging agent prepared by this invention uses sodium lignosulfonate / graphene oxide as a core, then coats the core surface with a polyacrylic acid-polyacrylamide copolymer to form a first shell, and then coats the first shell surface with acrylate-modified chitosan to form a second shell. This temporary plugging agent, when applied to oil well fracturing, not only exhibits excellent plugging performance, dissolving performance, and shear resistance, but also improves the transport capacity of the temporary plugging agent during the oil well fracturing process.

Description

Technical Field

[0001] This invention relates to the field of temporary plugging agents, specifically to a water-soluble temporary plugging agent for oil well fracturing and its preparation method. Background Technology

[0002] Hydraulic fracturing is one of the core technologies for enhancing oil and gas field production. It involves injecting high-pressure fluid into the formation to form a fracture network and improve reservoir permeability. In multi-layered or heterogeneous reservoirs, temporary plugging technology is needed to achieve directional propagation of fractures or repeated fracturing in order to balance the stimulation effect. As a key material, temporary plugging agent needs to achieve precise control of temporary plugging and unplugging under specific conditions. Traditional temporary plugging agents (such as inert particles, fibers or chemically cross-linked gels) have the following limitations: (1) Insoluble residues: Quartz sand, polymer gels, etc., can easily cause reservoir damage and reduce conductivity; (2) Incomplete unplugging: It is necessary to backflow or acid unplugging, which increases the operating cost and complexity.

[0003] Water-soluble temporary plugging agents have emerged, with their core advantages being self-degradability, controllability, and environmental friendliness. These advantages make water-soluble temporary plugging agents consistent with the trend of green oil and gas field development. However, the most commonly used acrylamide polymer-based water-based temporary plugging agents currently have some problems during use: (1) the water absorption and expansion rate is too fast during use, resulting in expansion before reaching the target location, which leads to a low plugging rate; (2) they lack sufficient stability and strength, making them prone to structural damage and membrane collapse. Therefore, in order to address the problems of existing water-soluble temporary plugging agents, researchers need to develop a water-soluble temporary plugging agent with excellent strength, water solubility, and high plugging rate to meet the needs of practical applications. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a water-soluble temporary plugging agent for oil well fracturing and its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for preparing a water-soluble temporary plugging agent for oil well fracturing includes the following steps:

[0007] Step S1: Mix 10g acrylic acid, 3-3.2g sodium hydroxide and 50mL water until homogeneous, and react in an ice-water bath until the neutralization degree of the acrylic acid aqueous solution is 60%-70%. Then add 9-9.5g acrylamide, 0.18-0.21g aluminum nitrate and 0.15-0.17g potassium persulfate and stir until homogeneous. Then add 0.5-1g sodium lignosulfonate / graphene oxide (LSC / GO) and ultrasonically mix for 20min. Then stir and react at 60-80℃ for 5-7h. Filter and dry to obtain LSC / GO@PAA-PAM particles (polyacrylic acid-polyacrylamide copolymer coated LSC / GO particles).

[0008] Step S2: Stir 10g of LSC / GO@PAA-PAM particles in 200mL of ethanol until homogeneous, heat to 80℃, add 0.1-0.5g of acrylate-modified chitosan and stir for 30min, then add 0.015-0.02g of potassium persulfate and 0.02-0.03g of aluminum nitrate, maintain the temperature and stir for 24h, filter, wash and dry to obtain water-soluble temporary plugging agent for oil well fracturing.

[0009] Further, the sodium lignosulfonate / graphene oxide is prepared by the following steps:

[0010] Step A1: Mix sodium lignosulfonate (LSC), sodium hydroxide and water, add N-methyl-4-nitrobenzylamine, heat to 85°C, add 36wt% formaldehyde aqueous solution, reflux for 5 hours, add 1mol / L hydrochloric acid solution dropwise until no precipitate forms, filter, wash, dry, grind, filter again, wash and dry to obtain sodium nitrated lignosulfonate;

[0011] Further, in step A1, the ratio of sodium lignosulfonate, sodium hydroxide, water, N-methyl-4-nitrobenzylamine, and formaldehyde aqueous solution is 10g:0.5-0.6g:50mL:2.8-3.5g:4-5mL;

[0012] Step A2: Mix sodium nitrated lignin sulfonate, reduced iron powder, methanol and water evenly, heat to 80°C, add ammonium chloride and reflux for 5-7 hours, filter, wash and dry to obtain sodium ammoniated lignin sulfonate.

[0013] Furthermore, in step A2, the ratio of sodium nitrate lignosulfonate, reduced iron powder, methanol, water, and ammonium chloride is 5g:1.5-3.5g:20mL:10mL:1-2g.

[0014] Step A3: Sonicate 5g of graphene oxide in 200mL of water for 1-2 hours, collect the upper dispersion, filter, and dry to obtain pretreated graphene oxide; disperse the pretreated graphene oxide evenly in a mixture of ethanol and water (ethanol to water volume ratio of 1:3), add 30wt% potassium hydroxide aqueous solution to adjust the pH of the system to 8.5, add amination sodium lignosulfonate, sonicate in a water bath for 30 minutes, react under nitrogen at 75-85℃ for 5-7 hours, then add allylamine to maintain the temperature for 6 hours, filter, wash, and dry to obtain sodium lignosulfonate / graphene oxide (LSC / GO).

[0015] Furthermore, in step A3, the ratio of pretreated graphene oxide, ethanol, water, aminated sodium lignosulfonate, and allylamine in the sodium lignosulfonate / graphene oxide process is 1g:20mL:60mL:1-2g:0.3-0.6g.

[0016] Further, the acrylate-modified chitosan is prepared by the following steps:

[0017] Step B1: Mix 3-chloro-1-propanol, dichloromethane and triethylamine, stir in an ice-water bath for 30 min, add acryloyl chloride dichloromethane solution and stir for 1-2 h, then heat to 30-40℃ and react for 12 h, wash, rotary evaporate, column chromatography for purification, and rotary evaporate a second time to obtain acrylate derivatives.

[0018] Further, in step B1, the ratio of the amounts of 3-chloro-1-propanol, dichloromethane, triethylamine, and acryloyl chloride dichloromethane solution is 0.01-0.03 mol: 50 mL: 1-3 g: 20 mL;

[0019] Furthermore, in step B1, the acryloyl chloride dichloromethane solution is prepared by mixing and stirring acryloyl chloride and dichloromethane at a volume ratio of 0.01-0.03 mol: 20 mL;

[0020] Step B2: Soak 5g of chitosan in 30mL of 3wt% glacial acetic acid for 30min, then wash with anhydrous ethanol until neutral, dry, and collect the pretreated chitosan; mix the pretreated chitosan with 1-allyl-3-methylimidazolium chloride ionic liquid, stir in an oil bath at 80℃ for 1.5-2.5h, then add 1,2-epoxydodecane, maintain the temperature and stir for 8-10h, add an ethanol / acetone mixture (ethanol and acetone volume ratio of 1:1) and stir for 10min, filter, wash, and dry to obtain hydrophobically modified chitosan;

[0021] Further, in step B2, the ratio of pretreated chitosan, 1-allyl-3-methylimidazolium chloride ionic liquid, 1,2-epoxydodecane and ethanol / acetone mixture is 1g:10-20g:2-3g:100mL.

[0022] Step B3: Mix hydrophobically modified chitosan, sodium hydroxide and tetrahydrofuran, purge with nitrogen and heat and stir until reflux, then add acrylate derivative, reflux under heating and stirring for 14-18 hours, wash with ether, wash with water and dry to obtain acrylate-modified chitosan.

[0023] Furthermore, in step B3, the ratio of hydrophobically modified chitosan, sodium hydroxide, tetrahydrofuran, and acrylate derivative is 2g:2.5-3.5g:50mL:0.5-1.5g.

[0024] The present invention also discloses a water-soluble temporary plugging agent for oil well fracturing prepared by the aforementioned preparation method.

[0025] The beneficial effects of this invention are:

[0026] The water-soluble temporary plugging agent prepared in this invention uses sodium lignosulfonate / graphene oxide as the core, then coats the core layer with polyacrylic acid-polyacrylamide copolymer to form a first shell layer, and then coats the first shell layer with acrylate-modified chitosan to form a second shell layer. When applied to oil well fracturing, this temporary plugging agent not only has excellent plugging performance, dissolving performance, and shear resistance, but also improves the transport capacity of the temporary plugging agent during the oil well fracturing process.

[0027] In this invention, the water-soluble temporary plugging agent contains a core layer of sodium lignosulfonate / graphene oxide that is chemically bonded to the first shell layer of polyacrylic acid-polyacrylamide copolymer. The graphene oxide and the benzene ring structure in the sodium lignosulfonate work synergistically to form a stable structure, which improves the strength of the temporary plugging agent and ensures good shear strength before reaching the target location. Furthermore, the sodium lignosulfonate absorbs water and swells after water molecules enter the agent, working synergistically with the polyacrylic acid-polyacrylamide copolymer in the shell structure to increase the expansion ratio and sealing effect of the temporary plugging agent. The first shell is made of acrylate-modified chitosan, which is based on small-molecule chitosan. A small amount of hydrophobic alkyl long chains and acrylate structures are introduced on its surface through chemical grafting. The acrylate structure can cross-link with the first shell to achieve coating, while the hydrophobic long chains can delay the water absorption and swelling of the temporary plugging agent in the initial stage by using their hydrophobic effect. After the hydrophobic layer is hydrolyzed, water molecules can enter the interior through the pores on the surface of the temporary plugging agent and absorb water and swell by using the hydrophilic groups inside. By introducing hydrophobic structures on the surface of the temporary plugging agent, the migration ability of the temporary plugging agent in the formation is improved. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1: Sodium lignosulfonate / graphene oxide was prepared by the following steps:

[0030] Step A1: Mix 10g sodium lignosulfonate, 0.5g sodium hydroxide and 50mL water, add 2.8g N-methyl-4-nitrobenzylamine, heat to 85℃, add 4mL of 36wt% formaldehyde aqueous solution, reflux for 5h, add 1mol / L hydrochloric acid solution dropwise until no precipitate forms, filter, wash, dry, grind, filter again, wash and dry to obtain sodium nitrated lignosulfonate;

[0031] Step A2: Mix 5g sodium nitrated lignin sulfonate, 1.5g reduced iron powder, 20mL methanol and 10mL water evenly, heat to 80℃, add 1g ammonium chloride and reflux for 5 hours, filter, wash and dry to obtain sodium nitrated lignin sulfonate.

[0032] Step A3: Ultrasonically treat 5g of graphene oxide in 200mL of water for 1h, collect the upper dispersion, filter, and dry to obtain pretreated graphene oxide; disperse 1g of pretreated graphene oxide evenly in a mixture of 20mL of ethanol and 60mL of water (volume ratio of ethanol to water is 1:3), add 30wt% potassium hydroxide aqueous solution to adjust the pH of the system to 8.5, add 1g of aminated sodium lignin sulfonate, ultrasonically treat in a water bath for 30min, react at 75℃ under nitrogen for 5h, then add 0.3g of allylamine to maintain the temperature and react for 6h, filter, wash, and dry to obtain sodium lignin sulfonate / graphene oxide.

[0033] Acrylate-modified chitosan is prepared by the following steps:

[0034] Step B1: Mix 0.01 mol 3-chloro-1-propanol, 50 mL dichloromethane, and 1 g triethylamine, stir in an ice-water bath for 30 min, add 20 mL acryloyl chloride dichloromethane solution and stir for 1 h, then heat to 30 °C and react for 12 h. Wash, rotary evaporate, column chromatography for purification, and rotary evaporate a second time to obtain the acrylate derivative. The acryloyl chloride dichloromethane solution is prepared by mixing acryloyl chloride and dichloromethane in a volume ratio of 0.01 mol: 20 mL and stirring.

[0035] Step B2: Soak 5g of chitosan in 30mL of 3wt% glacial acetic acid for 30min, then wash with anhydrous ethanol until neutral, dry, and collect the pretreated chitosan; mix 1g of pretreated chitosan and 10g of 1-allyl-3-methylimidazolium chloride ionic liquid, stir in an oil bath at 80℃ for 1.5h, then add 2g of 1,2-epoxydodecane, maintain the temperature and stir for 8h, add 100mL of ethanol / acetone mixture (ethanol and acetone volume ratio of 1:1) and stir for 10min, filter, wash, and dry to obtain hydrophobic modified chitosan;

[0036] Step B3: Mix 2g of hydrophobically modified chitosan, 2.5g of sodium hydroxide and 50mL of tetrahydrofuran, purge with nitrogen and heat and stir until refluxed, then add 0.5g of acrylate derivative, reflux under heating and stirring for 14h, wash with ether, wash with water and dry to obtain acrylate-modified chitosan.

[0037] Example 2: Sodium lignosulfonate / graphene oxide was prepared by the following steps:

[0038] Step A1: Mix 10g sodium lignosulfonate, 0.55g sodium hydroxide and 50mL water, add 3.1g N-methyl-4-nitrobenzylamine, heat to 85℃, add 4.5mL of 36wt% formaldehyde aqueous solution, reflux for 5h, add 1mol / L hydrochloric acid solution dropwise until no precipitate forms, filter, wash, dry, grind, filter again, wash and dry to obtain sodium nitrated lignosulfonate;

[0039] Step A2: Mix 5g sodium nitrated lignin sulfonate, 2.5g reduced iron powder, 20mL methanol and 10mL water evenly, heat to 80℃, add 1.5g ammonium chloride and reflux for 6 hours, filter, wash and dry to obtain sodium nitrated lignin sulfonate.

[0040] Step A3: Ultrasonically treat 5g of graphene oxide in 200mL of water for 1.5h, collect the upper dispersion, filter, and dry to obtain pretreated graphene oxide; disperse 1g of pretreated graphene oxide evenly in a mixture of 20mL of ethanol and 60mL of water (volume ratio of ethanol to water is 1:3), add 30wt% potassium hydroxide aqueous solution to adjust the pH of the system to 8.5, add 1.5g of aminated sodium lignin sulfonate, ultrasonically treat in a water bath for 30min, react at 80℃ under nitrogen for 6h, then add 0.45g of allylamine to maintain the temperature and react for 6h, filter, wash, and dry to obtain sodium lignin sulfonate / graphene oxide.

[0041] Acrylate-modified chitosan is prepared by the following steps:

[0042] Step B1: Mix 0.02 mol 3-chloro-1-propanol, 50 mL dichloromethane, and 2 g triethylamine, stir in an ice-water bath for 30 min, add 20 mL acryloyl chloride dichloromethane solution and stir for 1.5 h, then heat to 35 °C and react for 12 h. Wash, rotary evaporate, column chromatography for purification, and rotary evaporate a second time to obtain the acrylate derivative. The acryloyl chloride dichloromethane solution is prepared by mixing acryloyl chloride and dichloromethane in a volume ratio of 0.02 mol: 20 mL and stirring.

[0043] Step B2: Soak 5g of chitosan in 30mL of 3wt% glacial acetic acid for 30min, then wash with anhydrous ethanol until neutral, dry, and collect the pretreated chitosan; mix 1g of pretreated chitosan and 15g of 1-allyl-3-methylimidazolium chloride ionic liquid, stir in an oil bath at 80℃ for 2h, then add 2.5g of 1,2-epoxydodecane, maintain the temperature and stir for 9h, add 100mL of ethanol / acetone mixture (ethanol and acetone volume ratio of 1:1) and stir for 10min, filter, wash, and dry to obtain hydrophobic modified chitosan;

[0044] Step B3: Mix 2g of hydrophobically modified chitosan, 3g of sodium hydroxide and 50mL of tetrahydrofuran, purge with nitrogen and heat and stir until refluxed, then add 1g of acrylate derivative, reflux under heating and stirring for 16h, wash with ether, wash with water and dry to obtain acrylate-modified chitosan.

[0045] Example 3: Sodium lignosulfonate / graphene oxide was prepared by the following steps:

[0046] Step A1: Mix 10g sodium lignosulfonate, 0.6g sodium hydroxide and 50mL water, add 3.5g N-methyl-4-nitrobenzylamine, heat to 85℃, add 5mL of 36wt% formaldehyde aqueous solution, reflux for 5h, add 1mol / L hydrochloric acid solution until no precipitate forms, filter, wash, dry, grind, filter again, wash and dry to obtain sodium nitrated lignosulfonate;

[0047] Step A2: Mix 5g sodium nitrated lignin sulfonate, 3.5g reduced iron powder, 20mL methanol and 10mL water evenly, heat to 80℃, add 2g ammonium chloride and reflux for 7h, filter, wash and dry to obtain sodium nitrated lignin sulfonate.

[0048] Step A3: Ultrasonically treat 5g of graphene oxide in 200mL of water for 2h, collect the upper dispersion, filter, and dry to obtain pretreated graphene oxide; disperse 1g of pretreated graphene oxide evenly in a mixture of 20mL of ethanol and 60mL of water (ethanol to water volume ratio of 1:3), add 30wt% potassium hydroxide aqueous solution to adjust the pH of the system to 8.5, add 2g of aminated sodium lignin sulfonate, ultrasonically treat in a water bath for 30min, react at nitrogen and 85℃ for 7h, then add 0.6g of allylamine to maintain the temperature and react for 6h, filter, wash, and dry to obtain sodium lignin sulfonate / graphene oxide.

[0049] Acrylate-modified chitosan is prepared by the following steps:

[0050] Step B1: Mix 0.03 mol 3-chloro-1-propanol, 50 mL dichloromethane, and 3 g triethylamine, stir in an ice-water bath for 30 min, add 20 mL acryloyl chloride dichloromethane solution and stir for 2 h, then heat to 40 °C and react for 12 h. Wash, rotary evaporate, column chromatography for purification, and rotary evaporate a second time to obtain the acrylate derivative. The acryloyl chloride dichloromethane solution is prepared by mixing acryloyl chloride and dichloromethane in a volume ratio of 0.03 mol: 20 mL and stirring.

[0051] Step B2: Soak 5g of chitosan in 30mL of 3wt% glacial acetic acid for 30min, then wash with anhydrous ethanol until neutral, dry, and collect the pretreated chitosan; mix 1g of pretreated chitosan and 20g of 1-allyl-3-methylimidazolium chloride ionic liquid, stir in an oil bath at 80℃ for 2.5h, then add 3g of 1,2-epoxydodecane, maintain the temperature and stir for 10h, add 100mL of ethanol / acetone mixture (ethanol and acetone volume ratio of 1:1) and stir for 10min, filter, wash, and dry to obtain hydrophobic modified chitosan;

[0052] Step B3: Mix 2g of hydrophobically modified chitosan, 3.5g of sodium hydroxide and 50mL of tetrahydrofuran, purge with nitrogen and heat and stir until refluxed, then add 1.5g of acrylate derivative, reflux under heating and stirring for 18h, wash with ether, wash with water and dry to obtain acrylate-modified chitosan.

[0053] Example 4: A method for preparing a water-soluble temporary plugging agent for oil well fracturing includes the following steps:

[0054] Step S1: Mix 10g acrylic acid, 3g sodium hydroxide and 50mL water evenly and react in an ice-water bath until the neutralization degree of the acrylic acid aqueous solution is 60%. Then add 9g acrylamide, 0.18g aluminum nitrate and 0.15g potassium persulfate and stir evenly. Then add 0.5g sodium lignosulfonate / graphene oxide prepared in Example 1 and ultrasonically mix and stir for 20min. Then stir and react at 60℃ for 5h. Filter and dry to obtain LSC / GO@PAA-PAM particles.

[0055] Step S2: Stir 10g of LSC / GO@PAA-PAM particles in 200mL of ethanol until homogeneous, heat to 80℃, add 0.1g of acrylate-modified chitosan prepared in Example 1 and stir for 30min, then add 0.015g of potassium persulfate and 0.02g of aluminum nitrate, maintain the temperature and stir for 24h, filter, wash and dry to obtain water-soluble temporary plugging agent for oil well fracturing.

[0056] Example 5: A method for preparing a water-soluble temporary plugging agent for oil well fracturing includes the following steps:

[0057] Step S1: Mix 10g acrylic acid, 3.1g sodium hydroxide and 50mL water evenly and react in an ice-water bath until the neutralization degree of the acrylic acid aqueous solution is 65%. Then add 9.3g acrylamide, 0.2g aluminum nitrate and 0.16g potassium persulfate and stir evenly. Then add 0.75g sodium lignosulfonate / graphene oxide prepared in Example 2 and ultrasonically mix and stir for 20min. Then stir and react at 70℃ for 6h. Filter and dry to obtain LSC / GO@PAA-PAM particles.

[0058] Step S2: Stir 10g of LSC / GO@PAA-PAM particles in 200mL of ethanol until homogeneous, heat to 80℃, add 0.3g of acrylate-modified chitosan prepared in Example 2 and stir for 30min, then add 0.017g of potassium persulfate and 0.025g of aluminum nitrate, maintain the temperature and stir for 24h, filter, wash and dry to obtain water-soluble temporary plugging agent for oil well fracturing.

[0059] Example 6: A method for preparing a water-soluble temporary plugging agent for oil well fracturing includes the following steps:

[0060] Step S1: Mix 10g acrylic acid, 3.2g sodium hydroxide and 50mL water until homogeneous, and react in an ice-water bath until the neutralization degree of the acrylic acid aqueous solution is 70%. Then add 9.5g acrylamide, 0.21g aluminum nitrate and 0.17g potassium persulfate and stir until homogeneous. Then add 1g of sodium lignosulfonate / graphene oxide prepared in Example 3 and ultrasonically mix and stir for 20min. Then stir and react at 80℃ for 7h. Filter and dry to obtain LSC / GO@PAA-PAM particles.

[0061] Step S2: Stir 10g of LSC / GO@PAA-PAM particles in 200mL of ethanol until homogeneous, heat to 80℃, add 0.5g of acrylate-modified chitosan prepared in Example 3 and stir for 30min, then add 0.02g of potassium persulfate and 0.03g of aluminum nitrate, maintain the temperature and stir for 24h, filter, wash and dry to obtain water-soluble temporary plugging agent for oil well fracturing.

[0062] Comparative Example 1: This comparative example is a water-soluble temporary plugging agent. The difference between this example and Example 6 is that graphene oxide is used instead of sodium lignosulfonate / graphene oxide prepared in Example 3. All other aspects are the same.

[0063] Comparative Example 2: This comparative example is a water-soluble temporary plugging agent. The difference between this example and Example 6 is that sodium lignosulfonate is used instead of the sodium lignosulfonate / graphene oxide prepared in Example 3. All other aspects are the same.

[0064] Comparative Example 3: This comparative example is a water-soluble temporary plugging agent, which is the LSC / GO@PAA-PAM particles prepared in Example 6, and all other aspects are the same.

[0065] The performance of the water-soluble temporary plugging agents prepared in Examples 4-6 and Comparative Examples 1-3 was tested:

[0066] Dissolution performance test: The dissolution time of the test samples in simulated formation water (total salinity of 7000 mg / L) at 80℃ and fracturing fluid containing 0.5 wt% guar gum was tested. The test results are shown in Table 1.

[0067] Shear strength test: In simulated formation water (total salinity of 7000 mg / L), the material was fully expanded at 20℃ for 350 min. After the expansion ratio remained basically unchanged, the shear strength was measured using a bulk-expanded particle shear tester. The test results are shown in Table 1.

[0068] Plugging rate performance test: The test was conducted in accordance with the testing method for plugging rate in patent number CN115197364A;

[0069] Expansion performance test: The sample was added to simulated formation water (total salinity of 7000 mg / L) and allowed to fully absorb water and expand at 20°C. The sample was periodically removed and dried with filter paper. The expansion ratio of the temporary plugging agent was measured at room temperature. The test results are shown in Table 2.

[0070]

[0071] As can be seen from Table 1, the water-soluble temporary plugging agent prepared by this invention has excellent solubility, shear strength and high plugging rate.

[0072]

[0073] As can be seen from Table 2, after the expansion performance test, the expansion ratio of the water-soluble temporary plugging agent prepared in this invention is relatively small in the early stage, and gradually increases with the extension of time. This indicates that the hydrophobic components on the surface of the temporary plugging agent can delay the entry of water molecules into the interior in the early stage, thereby improving its migration ability in the formation.

[0074] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the scope defined by the inventive concept, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a water-soluble temporary plugging agent for oil well fracturing, characterized in that, Preparation includes the following steps: Step S1: Mix 10g acrylic acid, 3-3.2g sodium hydroxide and 50mL water until homogeneous, and react in an ice-water bath until the neutralization degree of the acrylic acid aqueous solution is 60%-70%. Then add 9-9.5g acrylamide, 0.18-0.21g aluminum nitrate and 0.15-0.17g potassium persulfate and stir until homogeneous. Then add 0.5-1g sodium lignosulfonate / graphene oxide and ultrasonically mix and stir for 20min. Then stir and react at 60-80℃ for 5-7h. Filter and dry to obtain LSC / GO@PAA-PAM particles. Step S2: Stir 10g of LSC / GO@PAA-PAM particles in 200mL of ethanol until homogeneous, heat to 80℃, add 0.1-0.5g of acrylate-modified chitosan and stir for 30min, then add 0.015-0.02g of potassium persulfate and 0.02-0.03g of aluminum nitrate, maintain the temperature and stir for 24h, filter, wash and dry to obtain water-soluble temporary plugging agent for oil well fracturing; The sodium lignosulfonate / graphene oxide is prepared by the following steps: Step A1: Mix sodium lignosulfonate, sodium hydroxide and water, add N-methyl-4-nitrobenzylamine, heat to 85°C, add 36wt% formaldehyde aqueous solution, reflux for 5 hours, add 1mol / L hydrochloric acid solution until no precipitate is formed, filter, wash, dry, grind, filter again, wash and dry to obtain sodium nitrated lignosulfonate. Step A2: Mix sodium nitrated lignin sulfonate, reduced iron powder, methanol and water evenly, heat to 80°C, add ammonium chloride and reflux for 5-7 hours, filter, wash and dry to obtain sodium ammoniated lignin sulfonate. Step A3: Ultrasonically treat 5g of graphene oxide in 200mL of water for 1-2 hours, collect the upper dispersion, filter, and dry to obtain pretreated graphene oxide; disperse the pretreated graphene oxide evenly in a mixture of ethanol and water, add 30wt% potassium hydroxide aqueous solution to adjust the pH of the system to 8.5, add amination sodium lignosulfonate, ultrasonicate in a water bath for 30 minutes, react under nitrogen at 75-85℃ for 5-7 hours, then add allylamine to maintain the temperature and react for 6 hours, filter, wash, and dry to obtain sodium lignosulfonate / graphene oxide; The acrylate-modified chitosan is prepared by the following steps: Step B1: Mix 3-chloro-1-propanol, dichloromethane and triethylamine, stir in an ice-water bath for 30 min, add acryloyl chloride dichloromethane solution and stir for 1-2 h, then heat to 30-40℃ and react for 12 h, wash, rotary evaporate, column chromatography for purification, and rotary evaporate a second time to obtain acrylate derivatives. Step B2: Soak 5g of chitosan in 30mL of 3wt% glacial acetic acid for 30min, then wash with anhydrous ethanol until neutral, dry, and collect the pretreated chitosan; mix the pretreated chitosan with 1-allyl-3-methylimidazolium chloride ionic liquid, stir in an oil bath at 80℃ for 1.5-2.5h, then add 1,2-epoxydodecane, maintain the temperature and stir for 8-10h, add ethanol / acetone mixture and stir for 10min, filter, wash and dry to obtain hydrophobic modified chitosan; Step B3: Mix hydrophobically modified chitosan, sodium hydroxide and tetrahydrofuran, purge with nitrogen and heat and stir until reflux, then add acrylate derivative, reflux under heating and stirring for 14-18 hours, wash with ether, wash with water and dry to obtain acrylate-modified chitosan.

2. The method for preparing a water-soluble temporary plugging agent for oil well fracturing according to claim 1, characterized in that, In step A1, the ratio of sodium lignosulfonate, sodium hydroxide, water, N-methyl-4-nitrobenzylamine, and formaldehyde aqueous solution is 10g:0.5-0.6g:50mL:2.8-3.5g:4-5mL.

3. The method for preparing a water-soluble temporary plugging agent for oil well fracturing according to claim 1, characterized in that, In step A2, the ratio of sodium nitrate lignosulfonate, reduced iron powder, methanol, water and ammonium chloride is 5g:1.5-3.5g:20mL:10mL:1-2g.

4. The method for preparing a water-soluble temporary plugging agent for oil well fracturing according to claim 1, characterized in that, In step A3, the ratio of pretreated graphene oxide, ethanol, water, aminated sodium lignosulfonate, and allylamine in the sodium lignosulfonate / graphene oxide process is 1g:20mL:60mL:1-2g:0.3-0.6g.

5. The method for preparing a water-soluble temporary plugging agent for oil well fracturing according to claim 1, characterized in that, In step B1, the ratio of 3-chloro-1-propanol, dichloromethane, triethylamine, and acryloyl chloride dichloromethane solution is 0.01-0.03 mol: 50 mL: 1-3 g: 20 mL. The acryloyl chloride dichloromethane solution is prepared by mixing and stirring acryloyl chloride and dichloromethane in a ratio of 0.01-0.03 mol: 20 mL.

6. The method for preparing a water-soluble temporary plugging agent for oil well fracturing according to claim 1, characterized in that, In step B2, the ratio of pretreated chitosan, 1-allyl-3-methylimidazolium chloride ionic liquid, 1,2-epoxydodecane, and ethanol / acetone mixture is 1g:10-20g:2-3g:100mL.

7. The method for preparing a water-soluble temporary plugging agent for oil well fracturing according to claim 1, characterized in that, In step B3, the ratio of hydrophobically modified chitosan, sodium hydroxide, tetrahydrofuran, and acrylate derivative is 2g:2.5-3.5g:50mL:0.5-1.5g.

8. A water-soluble temporary plugging agent for oil well fracturing, characterized in that, The water-soluble temporary plugging agent for oil well fracturing is prepared according to any one of claims 1-7.

Images