Pre-crosslinked gel profile control water shutoff agent and preparation method thereof

Abstract

The invention discloses a pre-crosslinked gel profile control water plugging agent and a preparation method thereof, and relates to the technical field of oil-gas field development. The pre-crosslinked gel profile control and water plugging agent is prepared by taking a main monomer, an active monomer, an allyl polyethylene glycol monomer, a sulfonate monomer and inorganic nanoparticles as raw materials, carrying out free radical polymerization under the action of an initiator and a crosslinking agent, and then drying and crushing, the main monomer is at least one of an acrylamide monomer and acrylic acid, and the active monomer is prepared from an amino acid reactant and methyl vinyl sulfone. The prepared pre-crosslinked gel profile control and water plugging agent has good profile control and water plugging effects, the plugging rate of a high-permeability layer can reach 98% in a heterogeneous rock core with the permeability grade difference being about 7, and a low-permeability layer is basically not affected; and meanwhile, the plugging layer formed in the high-permeability layer also has relatively high compressive strength, and the highest compressive strength can reach 22.4 MPa / m.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and in particular to a pre-crosslinked gel profile control and water plugging agent and a preparation method thereof. Background Art

[0002] Currently, major oilfields in China are experiencing increasing water content in produced fluids, leading to a gradual decline in oil recovery efficiency. This is primarily due to long-term water flooding and the heterogeneity of the reservoirs themselves. In the later stages of production, dominant channels form within the reservoir, through which most injected water is discharged, making the development of low-permeability reservoirs difficult. To address this, my country began researching water plugging 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 heat-resistant and salt-resistant polyacrylamide nanosphere and its preparation method. The nanosphere copolymerizes anionic monomers, cationic monomers, nonionic monomers, heat-resistant and salt-resistant monomers, hydrophobic monomers and acrylamide monomers. The final product has good heat and salt resistance.

[0004] Chinese patent CN106883357A discloses a pre-crosslinked gel slow-swelling microsphere profile control agent, its preparation method and use. The profile control agent is prepared by reacting a polyacrylic acid grafted prepolymer, an acrylamide monomer, a hydrophobic monomer, a salt-resistant monomer, a temperature-resistant viscosity-increasing monomer, and modified kaolin. The resulting profile control agent has good temperature and salt resistance and viscosity-increasing properties.

[0005] However, one of the pain points of pre-crosslinked gel-based profile control and water plugging agents is the potential for them to "fail to plug." During water flooding, water pressures are typically high, reaching tens of MPa. Common profile control agents currently available have relatively low strength. Therefore, when using these agents in oil fields, large quantities of them are typically injected to form a thicker profile control and plugging layer to withstand the higher water flooding pressures. However, injecting too much profile control agent not only increases costs but also risks it migrating deeper into the formation, plugging reservoirs that don't need to be plugged, resulting in a decrease in overall oil recovery. Summary of the Invention

[0006] In view of the above technical problems, the purpose of the present invention is to address the defects of the existing technology and provide a pre-crosslinked gel profile control and water plugging agent and its preparation method, which can not only block water and adjust the high permeability layer of heterogeneous reservoirs, but also form a water plugging layer with higher strength.

[0007] The present invention adopts the following technical scheme: a method for preparing a pre-crosslinked gel profile control and water plugging agent, comprising: 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, subjecting them to free radical polymerization under the action of an initiator and a crosslinking agent, and then drying and crushing the raw materials; 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; and the preparation method of the active monomer is as follows: taking an amino acid reactant and dissolving it, adding methyl vinyl sulfone under alkaline conditions to react, and after the reaction, separating and purifying to obtain the active monomer, wherein the amino acid reactant is a compound containing a 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 for this pre-crosslinked gel profile control and water plugging agent is the same as that for conventional pre-crosslinked gels. All monomers, initiators, and crosslinkers are added to water, and polymerization is carried out by heating the water to the initiator's initiation temperature under deoxygenated conditions. During the preparation process, the total concentration of the monomers in the water is approximately 20-30 wt%. This is a conventional preparation method in the art.

[0009] One embodiment of the present invention is that the amino acid reactant is one of vinylglycine, allylglycine, and S-allyl-L-cysteine; the solvent used in preparing the active monomer is a mixture of methanol and water in a volume ratio of 0.2 to 0.4:1. The vinylglycine used, also known as 2-amino-4-pentenoic acid, 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 alliin, is a garlic extract.

[0010] In one embodiment of the present invention, the acrylamide monomer is at least one of 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 the present invention, since the amount of acrylamide monomer added is relatively large, the composition of the acrylamide monomer has a significant impact on the performance of the final pre-cross-linked gel profile control and water plugging agent. After extensive testing, the inventors found that these two formulations have superior performance.

[0012] In one embodiment of the present invention, 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 monomer weight; the crosslinker is N,N-methylenebisacrylamide, and the amount added is 0.2% to 1.0% of the total monomer weight. These are common initiators and crosslinkers in the art.

[0014] One embodiment of the present invention provides a crosslinking agent prepared by the following method: dissolving 1 mole of ethylene glycol diglycidyl ether in a solvent, adding 2 to 2.4 parts of N-allylmethylamine dropwise at 20 to 60°C in the presence of an alkaline catalyst, and continuing the reaction for 1 to 5 hours. After completion of the reaction, the crosslinking agent is removed 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% to 1.0% of the total weight of the monomers. The crosslinking agent prepared by this method is more effective than conventional N,N-methylenebisacrylamide due to its multiple alcoholic hydroxyl groups. Furthermore, its amide linking group is more stable than tetraethylene glycol dimethacrylate of a similar structure, maintaining stability for a long time. The solvent used in the reaction can be ethanol, a mixed solution of ethanol and water (e.g., a volume ratio of ethanol to water of 1:0.5 to 2), isopropanol, etc. The purpose of the solvent is to dissolve the two reactants and not participate in the reaction. Those skilled in the art can select the appropriate solvent based on actual conditions. Since the alkalinity of N-allylmethylamine is relatively low, 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 selected from nano-silicon dioxide and 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. In actual use, the KH570-modified nanosilica can be prepared by reacting KH570 and nanosilica in a mixed solution of ethanol / water. This preparation method is conventional in the art, and a mature commercial product can also be directly purchased. In the art, there are two methods for adding inorganic nanoparticles to gels: simple physical mixing, which directly adds the inorganic nanoparticles to the gel; and chemical grafting, which grafts the gel particles and the inorganic nanoparticles via a chemical reaction. Each method has its 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 plugging agent prepared by any of the above methods.

[0018] The beneficial effects of the present invention are as follows: the pre-crosslinked gel profile control and water plugging agent prepared by the present invention has a good profile control and water plugging effect. In a heterogeneous core with a permeability difference of about 7, the plugging rate of the high permeability layer can reach 98%, and there is basically no effect on the low permeability layer; at the same time, the plugging layer formed in the high permeability layer also has a high compressive strength, which can reach up to 52.4 MPa / m; therefore, after the pre-crosslinked gel profile control and water plugging agent of the present invention is used to plug water in a heterogeneous reservoir, the formed plugging layer has a high strength, making it difficult to be broken through in the subsequent high-pressure water flooding process. DETAILED DESCRIPTION

[0019] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is described in detail below in conjunction with the embodiments, but it should not be understood as limiting the scope of implementation of the present invention.

[0020] In the following examples, unless otherwise specified, the parts are by mass.

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

[0022] In the following examples, unless otherwise specified, the drugs used 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, add water to dissolve, and after nitrogen is passed through for deoxygenation for 30 minutes, add 0.06 g of potassium persulfate / sodium bisulfite initiator and 0.1 g of initiator with a mass ratio of 1:1, and react at 30°C for 2 hours. After the reaction is completed, dry and crush it to obtain a pre-crosslinked gel profile control and water plugging 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 ​​is added, the pH of the solution is adjusted to 9.5, the temperature is raised to 60° C., 11.1 parts of methyl vinyl sulfone is added dropwise, and after the addition is complete, the reaction is continued for 1.5 hours. 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 cross-linking agent is as follows: 17.4 parts of ethylene glycol diglycidyl ether and 0.1 parts of triethylamine are added to a mixed solution of ethanol and water in a volume ratio of 1:1, stirred to dissolve, the temperature is adjusted to 40°C, 2.3 parts of N-allylmethylamine are added dropwise to the above reaction solution, and the reaction is continued for 3 hours. After the reaction is completed, low-boiling substances are removed by distillation under reduced pressure to obtain the cross-linking 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, add water to dissolve, and after nitrogen is passed through for deoxygenation for 30 minutes, add 0.06 g of potassium persulfate / sodium bisulfite initiator with a mass ratio of 1:1 and 0.1 g of N,N-methylenebisacrylamide, and react at 30°C for 2 hours. After the reaction is completed, dry and crush to obtain the product.

[0027] 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, 10.1 parts of L-vinylglycine is added, the pH of the solution is adjusted to 9.5, the temperature is raised to 60°C, 11.1 parts of methyl vinyl sulfone is added dropwise, and after the addition is completed, the reaction is continued for 1 hour. After the reaction is completed, ethyl acetate is added for extraction three times, the aqueous phase is taken, and the solvent is removed to obtain the active monomer.

[0028] Example 3: This example differs from Example 1 in that the nano-silica is nano-silica modified with KH570, and the rest are the same.

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

[0030] Comparative Example 1: This embodiment differs from Example 1 in that the cross-linking agent is replaced with tetraethylene glycol dimethacrylate, and the rest are the same.

[0031] Comparative Example 2: This comparative example differs from Example 1 in that no active monomer is added, and the rest are the same.

[0032] Comparative Example 3: This comparative example differs from Example 1 in that the active monomer is replaced with S-allyl-L-cysteine, and the rest are the same.

[0033] In order to further illustrate the effect of the pre-crosslinked gel profile control and water plugging agent prepared in the embodiment of the present invention, the performance thereof is tested using a specific method as follows.

[0034] 1. Expansion performance test The pre-crosslinked gel profile control agents prepared in Examples 1 to 5 and Comparative Examples 1 to 2 were added with water 100 times the mass of the pre-crosslinked gel profile control agent and placed in a vial. The vial was then placed in an oven at 150° C. The maximum expansion ratio, the time taken to reach the maximum expansion ratio, and the final state after 50 days were recorded. The final results are shown in Table 1.

[0035] Table 1 Expansion multiple test results

[0036] As can be seen from the above, the pre-crosslinked gel profile control agent prepared in the present embodiment can withstand high temperatures and maintain a gel state for a long time, meeting the practical requirements of a profile control and water plugging agent. In Comparative Examples 2 and 3, the expansion multiples were significantly reduced after 50 days due to partial degradation of the particles.

[0037] 2. Plugging and profile control test The pre-crosslinked gel profile control and water plugging agents of Examples 1 to 4 were prepared with water to prepare a profile control and plugging fluid with a mass concentration of 2%, which was then tested according to the following method.

[0038] Cores with permeabilities of approximately 300 mD (low permeability) and 2000 mD (high permeability) were connected in parallel. After saturating the cores with water, 0.5 PV of the aforementioned profile control and plugging fluid was injected. After injection, the cores were held at 80°C for 48 hours. After the holding period, the permeabilities of the two parallel cores were measured. After the permeability measurements were completed, simulated formation water (salinity content of 8000 mg / L) was injected into the initially high permeability core at a rate of 1 mL / min until the injection pressure dropped sharply. The peak 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 peak pressure (MPa); and L represents the core length (m). The final results are shown in Table 2.

[0039] Table 2 Plugging and profile control test results

[0040] As shown in Table 2, the pre-crosslinked gel profile control and water plugging agent prepared in this embodiment of the present invention achieves a plugging rate of up to 98% in cores with a permeability gradient of 6-7 for high-permeability cores, while having minimal impact on the permeability of low-permeability cores. This demonstrates that the pre-crosslinked gel profile control and water plugging agent prepared in this embodiment of the present invention is well suited for profile control and water plugging in heterogeneous reservoirs, enabling subsequent water flooding to expand the affected area and thereby increase recovery.

[0041] It can also be seen that the pre-cross-linked gel profile control and water plugging agent prepared in the embodiment of the present invention has a high breakthrough pressure gradient. Therefore, after being injected into the reservoir, it can more easily withstand the subsequent high water flooding pressure.

[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 changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a pre-crosslinked gel profile control and water plugging agent, characterized in that: The method comprises the following steps: 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, subjecting the raw materials to free radical polymerization under the action of an initiator and a cross-linking agent, and then drying and crushing the raw materials; 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; and preparing the active monomer as follows: taking an amino acid reactant and dissolving it, adding methyl vinyl sulfone under alkaline conditions to react, and separating and purifying the active monomer after the reaction is completed, wherein the amino acid reactant is a compound containing a 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.

2. The method according to claim 1, characterized in that The amino acid reactant is one of vinylglycine, allylglycine, and S-allyl-L-cysteine; and the solvent used in the preparation of the active monomer is a mixture of methanol and water in 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; and 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, wherein 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 a redox initiator, a persulfate initiator and a water-soluble azo initiator, and the added amount of the initiator is 0.3% to 1.0% of the total weight of the monomer; the cross-linking agent is N,N-methylenebisacrylamide, and the added amount is 0.2% to 1.0% of the total weight of the monomer.

7. The method according to claim 1, characterized in that The crosslinking agent is prepared by the following method: taking 1 mole part of ethylene glycol diglycidyl ether in a solvent and dissolving it, adding 2 to 2.4 parts of N-allylmethylamine dropwise at 20 to 60° C. and in the presence of an alkaline catalyst, and continuing the reaction for 1 to 5 hours. After the reaction is completed, removing low-boiling substances by reduced pressure distillation to obtain the crosslinking agent; the solvent is one or two of water, ethanol, and isopropanol; the catalyst is triethylamine; and the amount of the crosslinking agent added is 0.2% to 1.0% of the total weight of the monomer.

8. The method according to claim 1, characterized in that The inorganic nanoparticles are one of nano silicon dioxide and bentonite.

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

10. A pre-crosslinked gel profile control and water plugging agent, prepared by the method according to any one of claims 1 to 9.

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