Pre-crosslinking gel profile control water plugging agent and preparation method thereof

Abstract

This invention discloses a pre-crosslinked gel profile control and water shut-off agent and its preparation method, relating to the field of oil and gas field development technology. The pre-crosslinked gel profile control and water shut-off agent is prepared by free radical polymerization of a main monomer, an active monomer, an allyl polyethylene glycol monomer, a sulfonate monomer, and inorganic nanoparticles under the action of an initiator and a crosslinking agent, followed by drying and pulverization. The main monomer is at least one of an acrylamide monomer and acrylic acid, and the active monomer is prepared by reacting amino acid reactants and methyl vinyl sulfone. The pre-crosslinked gel profile control and water shut-off agent prepared by this invention exhibits good profile control and water shut-off effects. In heterogeneous cores with a permeability difference of approximately 7, the sealing rate of high-permeability layers can reach 98%, while having virtually no impact on low-permeability layers. Simultaneously, the sealing layer formed within the high-permeability layer also possesses high compressive strength, reaching a maximum of 52.4 MPa / m.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, specifically to a pre-crosslinked gel profile control and water shut-off agent and its preparation method. Background Technology

[0002] For major oilfields in China, the increasing water content in produced fluids is leading to a gradual decline in oil production efficiency. This is mainly due to long-term waterflooding and the inherent heterogeneity of the reservoirs. In the later stages of production, dominant channels form in the reservoir, through which most of the injected water is discharged, making it difficult to develop low-permeability reservoirs. Therefore, my country began researching water shut-off and profile control technologies in the 1950s.

[0003] Currently, most profile control agents are gel-type profile control agents. For example, Chinese patent CN114380942A discloses a temperature-resistant and salt-resistant polyacrylamide nanosphere and its preparation method. It copolymerizes anionic monomers, cationic monomers, nonionic monomers, temperature-resistant and salt-resistant monomers, hydrophobic monomers and acrylamide monomers, and the final product has good temperature and salt resistance properties.

[0004] Chinese patent CN106883357A discloses a pre-crosslinked gel slow-swelling microsphere profile control agent, its preparation method and uses. It utilizes a reaction of polyacrylic acid grafted prepolymer, acrylamide monomer, hydrophobic monomer, salt-resistant monomer, temperature-resistant thickening monomer, and modified kaolin to finally obtain a profile control agent with good temperature and salt resistance as well as thickening properties.

[0005] However, one major drawback of gel-based pre-crosslinked gel profile control and water shut-off agents is the potential for them to fail to effectively plug the water. During waterflooding, the pressure is typically high, reaching tens of megapascals. Currently available profile control agents have relatively low strength. Therefore, oilfields often need to inject large amounts of these agents to form a thicker profile control and plugging layer to withstand the high waterflooding pressure. However, injecting too much profile control agent not only increases costs but also risks migrating to deeper formations, potentially plugging reservoirs that wouldn't otherwise require plugging, leading to a decrease in overall oil recovery. Summary of the Invention

[0006] In view of the above technical problems, the purpose of this invention is to address the deficiencies of the prior art by providing a pre-crosslinked gel profile control and water shut-off agent and its preparation method, which can not only shut off and control water in the high-permeability layer of heterogeneous reservoirs, but also form a water shut-off layer with high strength.

[0007] The present invention adopts the following technical solution: a method for preparing a pre-crosslinked gel profile control and water-blocking agent, using a main monomer, an active monomer, an allyl polyethylene glycol monomer, a sulfonate monomer, and inorganic nanoparticles in a mass ratio of 10:0.1~0.5:0.5~2:0.5~1:0.1~0.3 as raw materials, and performing free radical polymerization under the action of an initiator and a crosslinking agent, followed by drying and pulverizing to obtain the agent; wherein, the molecular weight of the allyl polyethylene glycol monomer does not exceed 1500, and the main monomer is at least one of an acrylamide monomer and acrylic acid; the preparation method of the active monomer is as follows: an amino acid reactant is taken and dissolved, and under alkaline conditions, methyl vinyl sulfone is added to react. After the reaction is completed, the active monomer is obtained by separation and purification. The amino acid reactant is a compound containing one double bond, at least one primary amine, and at least one carboxyl group, and the molar ratio of the amino acid reactant to the methyl vinyl sulfone is 1:1~1.1.

[0008] The preparation method of this pre-crosslinked gel profile control and water-blocking agent is the same as that of conventional pre-crosslinked gels. All monomers, initiators, and crosslinking agents are added to water, and polymerization is carried out under deoxygenated conditions at the initiation temperature of the initiator. During the preparation process, the total concentration of each monomer in the water is approximately 20-30 wt%. This is a conventional preparation method in this field.

[0009] In one embodiment of the present invention, the amino acid reactant is one of vinylglycine, allylglycine, and S-allyl-L-cysteine; the solvent for preparing the active monomer is a mixture of methanol and water with a volume ratio of 0.2~0.4:1. The vinylglycine used is also known as 2-amino-4-pentenoic acid, which contains both optically active and racemic molecules, both of which can be used in the present invention; allylglycine also has different optical rotations, but both can be used in the present invention; S-allyl-L-cysteine, also known as allicin, is a garlic extract.

[0010] One embodiment of the present invention is that the acrylamide monomer is at least one selected from acrylamide, methacrylamide, and N,N-dimethylacrylamide; and the sulfonate monomer is sodium p-styrenesulfonate.

[0011] Furthermore, the main monomer is composed of a mixture of acrylamide, acrylic acid, and N,N-dimethylacrylamide in a mass ratio of 1:0.5~0.8:0.1~0.3; or, the main monomer is composed of a mixture of acrylamide and N,N-dimethylacrylamide in a mass ratio of 1:0.2~0.5. In this invention, because the amount of acrylamide monomers added is relatively increased, the composition of acrylamide monomers has a significant impact on the performance of the final pre-crosslinked gel profile control and water-blocking agent. After extensive testing, the inventors found that both formulations exhibit superior performance.

[0012] One embodiment of the present invention is that the molecular weight of the allyl polyethylene glycol monomer is 400-800.

[0013] In one embodiment of the present invention, the initiator is one of a redox initiator, a persulfate initiator, and a water-soluble azo initiator, and the amount of the initiator added is 0.3% to 1.0% of the total mass of the monomer; the crosslinking agent is N,N-methylenebisacrylamide, and the amount added is 0.2% to 1.0% of the total mass of the monomer. These are common initiators and crosslinking agents in the art.

[0014] One embodiment of the present invention involves preparing the crosslinking agent by the following method: 1 mole of ethylene glycol diglycidyl ether is dissolved in a solvent, and 2-2.4 parts of N-allyl methylamine are added dropwise at 20-60°C under alkaline catalysis conditions, and the reaction is continued for 1-5 hours. After the reaction, low-boiling substances are removed by vacuum distillation to obtain the agent. The solvent is one or two of water, ethanol, and isopropanol, and the catalyst is triethylamine. The amount of crosslinking agent added is 0.2%-1.0% of the total mass of the monomer. The crosslinking agent prepared by this method is more effective than conventional N,N-methylenebisacrylamide due to the presence of multiple hydroxyl groups. Furthermore, because its linking group is an amide group, it is more stable than tetraethylene glycol dimethacrylate with a similar structure and can maintain stability for a longer period. The solvent in this reaction process can be ethanol, a mixed solution of ethanol and water (e.g., ethanol and water in a volume ratio of 1:0.5-2), isopropanol, etc. The purpose of the solvent is to promote the dissolution of the two reactants without participating in the reaction; those skilled in the art can set the solvent according to the actual situation. Since N-allyl methylamine has relatively low basicity, an appropriate amount of catalyst needs to be added. The amount of catalyst added is 1% to 5% of the molar amount of ethylene glycol diglycidyl ether.

[0015] In one embodiment of the present invention, the inorganic nanoparticles are one of nano-silica or bentonite. The main function of the inorganic nanoparticles is to increase the strength of the gel.

[0016] Furthermore, the inorganic nanoparticles are grafted with a silane coupling agent containing double bonds, wherein the silane coupling agent containing double bonds is KH570. For KH570-modified nano-silica, in practical applications, it can be prepared by reacting KH570 and nano-silica in a mixed solution of ethanol / water. This preparation method is conventional in the art, or commercially available products can be directly purchased. In the art, there are two methods for adding inorganic nanoparticles to gels: one is simple physical mixing, i.e., directly adding inorganic nanoparticles to the gel; the other is chemical grafting, i.e., grafting gel particles and inorganic nanoparticles through a chemical reaction. Both methods have their advantages and can be applied according to specific circumstances.

[0017] Another object of the present invention is to disclose a pre-crosslinked gel profile control and water-blocking agent, prepared by any of the methods described above.

[0018] The beneficial effects of this invention are as follows: The pre-crosslinked gel profile control and water shut-off agent prepared by this invention has a good profile control and water shut-off effect. In heterogeneous cores with a permeability difference of about 7, the sealing rate of high-permeability layers can reach 98%, while having virtually no effect on low-permeability layers. At the same time, the sealing layer formed in the high-permeability layer also has a high compressive strength, reaching up to 52.4 MPa / m. Therefore, after using the pre-crosslinked gel profile control and water shut-off agent of this invention to shut off water in heterogeneous reservoirs, the high strength of the formed sealing layer makes it difficult to be breached during subsequent high-pressure water drive processes. Detailed Implementation

[0019] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail with reference to the embodiments, but this should not be construed as limiting the scope of implementation of the present invention.

[0020] In the following embodiments, unless otherwise specified, the number of parts refers to parts by weight.

[0021] In the following embodiments, unless otherwise specified, the operations described are conventional operations in the art.

[0022] Unless otherwise specified, the pharmaceutical agents used in the following examples are conventional commercial products.

[0023] Example 1: Take 5.4 parts of acrylamide, 3.5 parts of acrylic acid, 1.1 parts of N,N-dimethylacrylamide, 0.3 parts of active monomer, 1.2 parts of allyl polyethylene glycol monomer (APEG-700), 0.8 parts of sodium p-styrene sulfonate, and 0.2 parts of nano silica, dissolve them in water, purge with nitrogen for 30 min to remove oxygen, then add 0.06 g of potassium persulfate / sodium bisulfite initiator and 0.1 g of initiator in a mass ratio of 1:1, react at 30°C for 2 h, after which dry and pulverize to obtain the pre-crosslinked gel profile control and water-blocking agent.

[0024] The preparation method of the active monomer is as follows: a mixed solvent of methanol and water with a volume ratio of 0.3:1 is prepared, 16.1 parts of S-allyl-L-cysteine ​​are added, the pH of the solution is adjusted to 9.5, the temperature is raised to 60℃, and 11.1 parts of methyl vinyl sulfone are added dropwise. After the addition is completed, the reaction is continued for 1.5 h. After the reaction is completed, ethyl acetate is added for extraction three times, the aqueous phase is collected, and the solvent is removed to obtain the active monomer.

[0025] The preparation method of the crosslinking agent is as follows: Take 17.4 parts of ethylene glycol diglycidyl ether and 0.1 parts of triethylamine and add them to a mixed solution of ethanol and water with a volume ratio of 1:1. Stir to dissolve, adjust the temperature to 40℃, add 2.3 parts of N-allyl methylamine dropwise to the above reaction solution, and continue to react for 3 hours. After the reaction is completed, remove the low-boiling substances by vacuum distillation to obtain the crosslinking agent.

[0026] Example 2: Take 7.4 parts of acrylamide, 2.6 parts of N,N-dimethylacrylamide, 0.4 parts of active monomer, 0.8 parts of allyl polyethylene glycol monomer (APEG-700), 0.6 parts of sodium p-styrene sulfonate, and 0.2 parts of nano silica, dissolve them in water, purge with nitrogen for 30 min to remove oxygen, then add 0.06 g of potassium persulfate / sodium bisulfite initiator (mass ratio 1:1) and 0.1 g of N,N-methylenebisacrylamide, react at 30°C for 2 h, and after the reaction is complete, dry and pulverize to obtain the final product.

[0027] The preparation method of the active monomer is as follows: prepare a mixed solvent of methanol and water with a volume ratio of 0.3:1, add 10.1 parts of L-vinylglycine, adjust the pH of the solution to 9.5, heat to 60℃, add 11.1 parts of methyl vinyl sulfone dropwise, and continue the reaction for 1 hour after the addition is complete. After the reaction is completed, add ethyl acetate for extraction 3 times, take the aqueous phase, and remove the solvent to obtain the active monomer.

[0028] Example 3: The difference between this example and Example 1 is that the nano-silica is KH570 modified nano-silica, and all other aspects are the same.

[0029] Example 4: The difference between this example and Example 1 is that the raw materials for preparing the pre-crosslinked gel profile control and water-blocking agent are: 8.2 parts acrylamide, 1.8 parts acrylic acid, 0.4 parts active monomer, 1.5 parts allyl polyethylene glycol monomer (APEG-1000), 0.6 parts sodium p-styrene sulfonate, and 0.25 parts nano silica. All other components are the same.

[0030] Comparative Example 1: The difference between this example and Example 1 is that the crosslinking agent is replaced with tetraethylene glycol dimethacrylate, and all other aspects are the same.

[0031] Comparative Example 2: The difference between this comparative example and Example 1 is that no active monomer was added, but all other aspects are the same.

[0032] Comparative Example 3: The difference between this comparative example and Example 1 is that the active monomer is replaced with S-allyl-L-cysteine, and all other aspects are the same.

[0033] To further illustrate the effect of the pre-crosslinked gel profile control and water-blocking agent prepared in the embodiments of the present invention, its performance was tested using specific methods below.

[0034] 1. Expansion performance test Take the pre-crosslinked gel profile control agents prepared in Examples 1-5 and Comparative Examples 1-2, add 100 times the mass of water to the pre-crosslinked gel profile control agents and place them in vials. Place them in an oven at 150°C and record their maximum expansion ratio, the time taken to reach the maximum expansion ratio, and the final state after 50 days. The final results are shown in Table 1.

[0035] Table 1. Results of Expansion Ratio Test

[0036] As can be seen from the above, the pre-crosslinked gel profile control agent prepared in the embodiments of the present invention can withstand high temperatures and maintain the gel state for a long time, meeting the actual needs of profile control and water shut-off agents. Among them, in Comparative Examples 2 and 3, due to the partial degradation of the particles, the expansion ratio was significantly reduced after 50 days.

[0037] 2. Blocking and profile adjustment test Take the pre-crosslinked gel profile control and water plugging agent from Examples 1-4 above, add water to prepare a profile control and plugging solution with a mass concentration of 2%, and then test it according to the following method.

[0038] Cores with permeabilities of approximately 300 mD (low permeability) and 2000 mD (high permeability) were taken and connected in parallel. After saturating the cores with water, 0.5 PV of the aforementioned profile control and plugging fluid was injected. The cores were then kept at 80℃ for 48 hours. After the incubation period, the permeability of the two parallel cores was measured. Following the permeability measurement, simulated formation water (salt content 8000 mg / L) was injected into the initially high-permeability core at a rate of 1 mL / min until a sudden drop in injection pressure occurred. The highest pressure was recorded, and the breakthrough pressure gradient was calculated. The breakthrough pressure gradient was calculated as: η = P / L, where η represents the breakthrough pressure gradient (MPa / m), P represents the highest pressure (MPa), and L represents the core length (m). The final results are shown in Table 2.

[0039] Table 2. Results of the plugging and profile adjustment test

[0040] As shown in Table 2, the pre-crosslinked gel profile control and water shut-off agent prepared in the embodiments of this invention can achieve a maximum plugging rate of 98% for high-permeability cores with a permeability difference of 6-7, while having little impact on the permeability of low-permeability cores. This indicates that the pre-crosslinked gel profile control and water shut-off agent prepared in the embodiments of this invention can be well applied to profile control and water shut-off in heterogeneous reservoirs, enabling subsequent waterflooding to expand the swept area and thereby increase the recovery rate.

[0041] Meanwhile, it can be seen that the pre-crosslinked gel profile control and water shut-off agent prepared in the embodiments of the present invention has a high breakthrough pressure gradient. Therefore, after it is injected into the reservoir, it can withstand the subsequent high water drive pressure relatively easily.

[0042] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a pre-crosslinked gel profile control and water-blocking agent, characterized in that, Using a mass ratio of 10:0.1~0.5:0.5~2:0.5~1:0.1~0.3 as raw materials, a main monomer, an active monomer, an allyl polyethylene glycol monomer, a sulfonate monomer, and inorganic nanoparticles are subjected to free radical polymerization under the action of an initiator and a crosslinking agent, followed by drying and pulverization to obtain the active monomer. The allyl polyethylene glycol monomer has a molecular weight not exceeding 1500, and the main monomer is at least one of an acrylamide monomer and acrylic acid. The preparation method of the active monomer is as follows: an amino acid reactant is taken and dissolved, and methyl vinyl sulfone is added under alkaline conditions to react. After the reaction is completed, the active monomer is obtained by separation and purification. The amino acid reactant is a compound containing one double bond, at least one primary amine, and at least one carboxyl group, and the molar ratio of the amino acid reactant to the methyl vinyl sulfone is 1:1~1.

1. The crosslinking agent is N,N-methylenebisacrylamide, or the preparation method of the crosslinking agent includes the following steps: dissolving 1 mole of ethylene glycol diglycidyl ether in a solvent, adding 2-2.4 parts of N-allyl methylamine dropwise at 20-60°C under alkaline catalyst conditions and continuing the reaction for 1-5 hours; after the reaction is completed, removing low-boiling substances by vacuum distillation to obtain the crosslinking agent; the solvent is one or two of water, ethanol, and isopropanol, and the catalyst is triethylamine; the amount of crosslinking agent added is 0.2%-1.0% of the total mass of the monomer.

2. The method according to claim 1, characterized in that, The amino acid reactant is one of vinylglycine, allylglycine, and S-allyl-L-cysteine; the solvent for preparing the active monomer is a mixture of methanol and water with a volume ratio of 0.2 to 0.4:

1.

3. The method according to claim 1, characterized in that, The acrylamide monomer is at least one of acrylamide, methacrylamide, and N,N-dimethylacrylamide; the sulfonate monomer is sodium p-styrenesulfonate.

4. The method according to claim 3, characterized in that, The main monomer is composed of a mixture of acrylamide, acrylic acid, and N,N-dimethylacrylamide in a mass ratio of 1:0.5~0.8:0.1~0.

3.

5. The method according to claim 1, characterized in that, The molecular weight of the allyl polyethylene glycol monomer is 400-800.

6. The method according to claim 1, characterized in that, The initiator is one of redox initiators, persulfate initiators, and water-soluble azo initiators, and the amount of the initiator added is 0.3% to 1.0% of the total mass of the monomers; the amount of the crosslinking agent added is 0.2% to 1.0% of the total mass of the monomers.

7. The method according to claim 1, characterized in that, The inorganic nanoparticles are either nano-silica or bentonite.

8. The method according to claim 7, characterized in that, The inorganic nanoparticles are grafted with a silane coupling agent containing double bonds, and the silane coupling agent containing double bonds is KH570.

9. A pre-crosslinked gel profile control and water-blocking agent, prepared by the method described in any one of claims 1 to 8.

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