High-strength self-degrading gel encapsulant and method for producing the same.

Abstract

This document provides a high-strength, self-degrading gel chelating agent and a method for producing the same. [Solution] A primary diamine compound and an unsaturated glycidyl compound having a molar ratio of 1:3 to 4.1 are added to a solvent and dissolved. Then, at 20 to 35°C, the primary diamine compound solution is added dropwise in the presence of a catalyst and a polymerization inhibitor to produce a multi-armed crosslinking agent by reaction with the unsaturated glycidyl compound. Next, an acrylamide monomer, an acid monomer, a rigid monomer, and a 2-methacryloyloxyethyl phosphorylcholine monomer are polymerized under the action of the multi-armed crosslinking agent and an initiator. After the reaction is complete, the material is pulverized, dried, and granulated to obtain a high-strength self-degrading gel chelating agent. The high-strength self-degrading gel chelating agent produced by the present invention not only has high strength but also self-degradability, and has a high recovery rate of permeability in the storage layer after decomposition, with little impact on the storage layer.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and specifically to a high-strength self-decomposable gel temporary plugging agent and a method for manufacturing the same.

Background Art

[0002] Staged hydraulic fracturing is one of the methods in the hydraulic fracturing construction of horizontal wells. By performing staged and multiple hydraulic fracturing operations on a horizontal well, the aim is to improve the effective utilization status of the oil layer in a low-permeability reservoir. During staged hydraulic fracturing construction, it is necessary to temporarily seal the artificially fractured zones that have already been hydraulically fractured to avoid the inflow of hydraulic fracturing fluid into the artificial fractures.

[0003] Conventional temporary plugging methods usually include mechanical plugging and chemical plugging. In mechanical plugging, it is necessary to introduce mechanical plugging tools such as bridge plugs and packers into the wellbore, which requires multiple pipe string lifting and lowering operations, thus significantly increasing the construction cost. Also, after the completion of hydraulic fracturing construction, it is necessary to dissolve and grind bridge plugs and packers, etc., which takes a relatively long time and also poses a risk of pipe string blockage by sand. Chemical plugging usually realizes temporary plugging by injecting a temporary plugging agent to form a sealing zone in the fracture. Conventional temporary plugging agents are usually degradable polymers such as polyglycolic acid, polylactic acid, and degradable polyacrylamide. Although polyglycolic acid and polylactic acid-based temporary plugging agents have good decomposition effects, their manufacturing costs are extremely high. Degradable polyacrylamide-based temporary plugging agents are a new type of temporary plugging agent that has attracted attention in recent years. Polyethylene glycol diacrylate is used as a crosslinking agent, but this crosslinking agent decomposes rapidly under high-temperature conditions, and accordingly, the temporary plugging agent particles decompose, thereby restoring the permeability of the fracture.

[0004] Conventional biodegradable polyacrylamide gel particles struggle to balance strength and biodegradability. While using polyethylene glycol diacrylate as a crosslinking agent can impart self-degradability to the gel particles, the resulting gel particles have low strength. Simultaneously, temporary chelating agents using polyethylene glycol diacrylate as a crosslinking agent have poor heat resistance and decompose rapidly in environments above 80°C, making it difficult to meet actual usage requirements. [Overview of the project]

[0005] In view of the above technical challenges, the object of the present invention is to provide a high-strength self-degrading gel chelating agent and a method for producing the same, in order to overcome the shortcomings of the prior art.

[0006] The present invention employs the following technical solution: A method for producing a high-strength self-degrading gel chelating agent comprising the following steps: A primary diamine compound and an unsaturated glycidyl compound having a molar ratio of 1:3 to 4.1 are each added to a solvent and dissolved. Then, at 20 to 35°C, in the presence of a catalyst and a polymerization inhibitor, the primary diamine compound solution is added dropwise to the unsaturated glycidyl compound solution to carry out the reaction. After the reaction is complete, low-boiling point substances are removed by vacuum distillation to obtain a multi-armed crosslinking agent (multi-branched crosslinking agent). The unsaturated glycidyl compound is one of glycidyl acrylate and glycidyl methacrylate, and the primary diamine compound is one of propanediamine, 1,3-diamino-2-propanol, and butanediamine.

[0007] Acrylamide monomer, acid monomer, rigid monomer, and 2-methacryloyloxyethyl phosphorylcholine monomer are taken and polymerized under the action of an initiator and a multi-armed crosslinking agent. After polymerization, the product is obtained by pulverization, drying, and granulation.

[0008] In this invention, a multi-armed crosslinking agent is first produced. This multi-armed crosslinking agent is generated by the reaction of an epoxy group in an unsaturated glycidyl compound with an amino group in a primary diamine compound. As is well known to those skilled in the art, 1 mole of primary amino groups can react with 2 moles of epoxy groups, and this reaction can be carried out at room temperature, with a fast reaction rate and extremely high reaction yield. A multi-armed crosslinking agent usually refers to a crosslinking agent having three or more active functional groups. In this invention, 1 mole of 1,3-diamino-2-propanol can react with up to 4 moles of an unsaturated glycidyl compound. The temperature should not be excessively high during this reaction process. If the temperature is too high, the amino group of the primary diamine compound will cause side reactions such as Michael addition and amine transesterification with the double bond of the unsaturated glycidyl compound. Also, if the polymerization inhibitor is deactivated, the unsaturated glycidyl compound will undergo self-polymerization, reducing the crosslinking effect of the final product and adversely affecting the performance of the temporary chelating agent.

[0009] Generally, short-chain primary diamine compounds are more effective. In particular, the inventors found that ethylenediamine was relatively less effective. This is presumed to be because the distance between the two amino groups of ethylenediamine is short, and after glycidyl methacrylate is grafted onto the primary amino group to form a secondary amine, steric hindrance makes it difficult to form a multi-armed crosslinking agent. Furthermore, other similar amino acids, such as lysine and ornithine, are also relatively less effective. This is thought to be because the carboxyl group exhibits electron-withdrawing properties towards the α-amino group, reducing the nucleophilicity of the amino group. In addition, other existing similar materials, such as melamine, mainly have a cyclic structure, resulting in significant steric hindrance and relatively low effectiveness.

[0010] Compared to conventional polyethylene glycol diacrylate crosslinking agents, the multi-armed crosslinking agent of the present invention has high strength because it does not have flexible molecular chains and its molecular chains are relatively short. On the other hand, because the crosslinking agent is a multi-armed crosslinking agent, its crosslinking density is high, which not only improves the water absorption ratio of the temporary chelating agent particles but also further improves the mechanical strength of the temporary chelating agent particles. As a result, the self-degrading acrylamide-based temporary chelating agent of the present invention has higher strength than conventional general-purpose temporary chelating agents.

[0011] In the above-mentioned temporary chelating agent, acrylamide monomer is the main monomer of the temporary chelating agent, and acidic monomers modify the temporary chelating agent and improve its performance. Rigid monomers are mainly used to increase the strength of the gel particles, and 2-methacryloyloxyethyl phosphorylcholine monomer not only increases the water absorption ratio of the temporary chelating agent particles but also further reduces the effect of inorganic salts on the gel particles.

[0012] Grinding, drying, and granulation are all standard operations in this field. Because the manufactured gel blocks are relatively large, they are first cut and ground into smaller fragments, and then the smaller fragments of the gel block are dried. The drying temperature can be set to 60°C, 70°C, 80°C, etc., and vacuum drying and forced-air drying can also be performed. After drying, the gel is crushed and granulated using a grinder. The particle size of the gel particles can be set based on the actual crack width of the storage layer, for example, by passing them through sieves of 50 mesh, 30 mesh, 20 mesh, etc., or by compounding gel particles of multiple different mesh sizes.

[0013] In one embodiment of the present invention, when producing the multi-armed crosslinking agent, the catalyst is tetrabutylammonium bromide, added in an amount of 1-1.5% of the total mass of the primary diamine compound and the unsaturated glycidyl compound, the polymerization inhibitor is p-methoxyphenol, added in an amount of 50-100 ppm, the solvent is DMF, and the reaction time is 15-25 hours. The reaction between the amino group and the epoxy group is relatively fast and proceeds rapidly even under low temperature conditions, but in order to completely react and produce a tertiary amine, it is necessary to extend the reaction time.

[0014] In one embodiment of the present invention, the primary diamine compound is 1,3-diamino-2-propanol. Compared to conventional primary diamine compounds, 1,3-diamino-2-propanol is more effective because it has a hydroxyl group.

[0015] In one embodiment of the present invention, the mass ratio of the acrylamide monomer, the acidic monomer, the rigid monomer, and the 2-methacryloyloxyethyl phosphorylcholine monomer is 10:3 to 8:0.5 to 2:0.1 to 0.3.

[0016] In one embodiment of the present invention, the acrylamide monomer is one of acrylamide and methacrylamide, the acidic monomer is at least one of acrylic acid, sodium acrylate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-styrenesulfonate, and the rigid monomer is one of N-vinylpyrrolidone and N-vinylimidazole. Here, with respect to the acidic monomer, carboxylic acid monomers such as acrylic acid and sodium acrylate can improve the water absorption ratio of the temporary chelating agent particles, and sulfonic acid monomers such as sodium 2-acrylamido-2-methylpropanesulfonate and sodium p-styrenesulfonate can further improve the heat resistance and salt resistance of the gel particles.

[0017] Furthermore, the acidic monomer is a mixture of acrylic acid and sodium 2-acrylamido-2-methylpropanesulfonate in a mass ratio of 1:2, and the rigid monomer is N-vinylimidazole. When such an acidic monomer and rigid monomer are combined with the aforementioned acrylamide monomer and 2-methacryloyloxyethyl phosphorylcholine monomer, the overall performance of the chelating agent particles produced is optimized.

[0018] In one embodiment of the present invention, the initiator is one of a persulfate-based initiator, a persulfate / sodium bisulfite-based initiator, or a water-soluble azo-based initiator, the amount of the initiator added is 0.1 to 0.8% of the total mass of the total monomers, and the amount of the multi-armed crosslinking agent added is 0.1 to 0.5% of the total mass of the total monomers.

[0019] In one embodiment of the present invention, the polymerization is one of either aqueous solution radical polymerization or reversed-phase emulsion polymerization. Both aqueous solution radical polymerization and reversed-phase emulsion polymerization are common methods in the art. Aqueous solution radical polymerization involves adding all monomers, initiators, and crosslinking agents to water as the solvent and reacting them under starting temperature conditions. Reverse-phase emulsion polymerization is a polymerization method in which oil is the continuous phase and the aqueous phase is the dispersed phase. In this embodiment, since all monomers have good water solubility and water-soluble materials are selected for the crosslinking agent and initiator, reversed-phase emulsion polymerization can be carried out. In reversed-phase emulsion polymerization, white oil or diesel fuel can be selected as the oil. Aqueous solution radical polymerization and reversed-phase emulsion polymerization each have their advantages. Aqueous solution radical polymerization has relatively simple reaction conditions, low cost, and is environmentally friendly because the solvent is water. Reverse-phase emulsion polymerization has a fast reaction rate and relatively good performance, but is expensive. Those skilled in the art can select an appropriate polymerization method according to the actual situation.

[0020] Another object of the present invention is to provide a high-strength self-degrading gel chelating agent that can be produced by any of the methods described above.

[0021] The beneficial effects of the present invention are as follows. The high-strength self-degrading gel temporary plugging agent manufactured according to the present invention not only has high strength but also has self-degrading properties, and after decomposition, the permeability recovery rate of the reservoir layer is high, and the influence on the reservoir layer is small.

Embodiments for Carrying out the Invention

[0022] To more clearly understand the technical features, objectives, and beneficial effects of the present invention, the technical solution of the present invention will be described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of the present invention.

[0023] In the following embodiments, unless otherwise specified, all the methods used are common operating methods in the relevant field.

[0024] In the following embodiments, unless otherwise specified, all the reagents used are common commercially available products.

[0025] In the following embodiments, unless otherwise specified, all "parts" used mean parts by mass.

[0026] In the following embodiments, unless otherwise specified, "dropping" means adding one solution to another solution at a rate of 2 drops / second or less.

[0027] Example 1 9.0 parts of 1,3-diamino-2-propanol and 57.5 parts of glycidyl methacrylate were respectively added to DMF and dissolved. 0.7 part of tetrabutylammonium bromide was added to the 1,3-diamino-2-propanol solution, and p-methoxyphenol was added as a polymerization inhibitor to the glycidyl methacrylate solution to make the concentration of p-methoxyphenol 80 ppm. Under the conditions of 35°C and continuous stirring, the 1,3-diamino-2-propanol solution was dropped into the glycidyl methacrylate solution, and after the dropping was completed, the reaction was carried out for 16 hours. After the reaction was completed, low-boiling substances were removed by vacuum distillation to obtain a multi-arm cross-linking agent.

[0028] 10 parts of acrylamide, 1.5 parts of acrylic acid, 3 parts of sodium 2-acrylamido-2-methylpropanesulfonate, 1 part of N-vinylimidazole, and 0.2 part of 2-methacryloyloxyethyl phosphorylcholine were added to water and dissolved. After maintaining the concentration of all monomers at 25 wt% and performing deoxygenation treatment by bubbling nitrogen gas, 0.30 part of ammonium persulfate / sodium bisulfite initiator with a mass ratio of 1:1 and 0.36 part of a multi-arm crosslinking agent were added, and the reaction was carried out at 35 °C for 2 hours. After the reaction was completed, the gel block was cut, dried, crushed, and passed through a 50-mesh sieve to obtain the product.

[0029] Example 2 The difference between this example and Example 1 is that 9.0 parts of 1,3-diamino-2-propanol were replaced with 8.8 parts of 1,4-butanediamine, and the rest were the same.

[0030] Example 3 The difference between this example and Example 1 is that the addition amount of glycidyl methacrylate was adjusted to 44.0 parts and the addition amount of the multi-arm crosslinking agent was adjusted to 0.45 parts, and the rest were the same.

[0031] <00​​​​​​​​​​​​​​The only difference between this example and Example 1 is that the amount of N-vinylimidazole added was adjusted to 1.5 parts and the amount of 2-methacryloyloxyethyl phosphorylcholine added to 0.15 parts; everything else is the same.

[0034] Comparative Example 1 The only difference from Example 1 is that the multi-armed crosslinking agent was replaced with polyethylene glycol dimethacrylate with a molecular weight of 1000; everything else is the same.

[0035] Comparative Example 2 The only difference from Example 1 is that the multi-arm crosslinking agent was replaced with ethylene glycol dimethacrylate; everything else is the same.

[0036] Comparative Example 3 The difference from Example 1 is that in the gel particle manufacturing process, 0.39 parts of glycidyl methacrylate was added to water together with acrylamide, acrylic acid, sodium 2-acrylamido-2-methylpropanesulfonate, N-vinylimidazole, and 2-methacryloyloxyethyl phosphorylcholine and dissolved. Then, 0.06 parts of 1,3-diamino-2-propanol was added to the above solution along with the initiator as a crosslinking agent and the reaction was carried out. Everything else is the same.

[0037] Comparative Example 4 The only difference from Example 1 is that in the manufacturing process of the multi-armed crosslinking agent, 9.0 parts of 1,3-diamino-2-propanol were replaced with 13.2 parts of ornithine; everything else is the same.

[0038] Comparative Example 5 The only difference from Example 1 is that in the manufacturing process of the multi-arm crosslinking agent, 9.0 parts of 1,3-diamino-2-propanol were replaced with 6.0 parts of ethylenediamine; everything else is the same.

[0039] Comparative Example 6 The only difference from Example 1 is that in the manufacturing process of the multi-arm crosslinking agent, 9.0 parts of 1,3-diamino-2-propanol were replaced with 12.6 parts of melamine; everything else is the same.

[0040] To further illustrate the effects of the embodiments of the present invention, tests were conducted using the following specific methods.

[0041] 1. Swelling and decomposition Appropriate amounts of the temporary chelating agents prepared in Examples 1-6 and Comparative Examples 1-6 were taken and placed in vials. Then, a sufficient amount of saline solution (19,500 mg / L sodium chloride, 500 mg / L calcium chloride) was added, and the vials were sealed. These were placed in an oven at 100°C, the maximum swelling ratio was recorded, and then the temperature conditions were maintained, with observations made every 10 hours, and the time until complete decomposition was recorded.

[0042] Simultaneously, after the temporary chelating agent had completely decomposed, the vial was incubated for a further 10 hours, and then the decomposition rate was measured using the following method. After cooling the decomposed vial, it was centrifuged for 10 minutes under conditions of 5000 r / min. After centrifugation, the solid phase was collected, dried under reduced pressure at 60°C, and the mass of the solid phase was weighed. The decomposition rate was calculated using the following formula: η = (m1 - m2) / m1. In the formula, η represents the decomposition rate, m1 represents the mass of the dried temporary chelating agent used before swelling, and m2 represents the mass of the solid phase.

[0043] The final results are shown in Table 1.

[0044] JPEG0007879544000001.jpg134170

[0045] As is clear from Table 1, the temporary chelating agent according to the embodiments of the present invention has high water absorption and swelling performance under high salt conditions. At the same time, this temporary chelating agent has good temperature resistance and can exist stably for a certain period of time under relatively high temperature conditions. Referring to Examples 1 and 3, it can be seen that the decomposition time of the temporary chelating agent can be controlled by adjusting the amount of multi-armed crosslinking agent added. Referring to Comparative Example 1, it can be seen that when conventional polyethylene glycol dimethacrylate is used as a crosslinking agent, its heat resistance is poor and it decomposes easily under high temperature conditions. Referring to Comparative Examples 2 and 4, it can be seen that crosslinking agents with relatively short chain lengths have relatively low swelling ratios. Referring to Comparative Example 3, it can be seen that when a multi-armed crosslinking agent is produced by pre-reacting 1,3-diamino-2-propanol with glycidyl methacrylate, the effect is far superior to the method using 1,3-diamino-2-propanol as the crosslinking agent. Referring to Comparative Example 5, the effect is low when ethylenediamine is used. This is because the distance between the two amino groups in ethylenediamine is short, and after glycidyl methacrylate is grafted onto the primary amino group to form a secondary amine, steric hindrance makes it difficult to form a multi-armed crosslinking agent. Referring to Comparative Example 6, it can be seen that the effect is relatively low when melamine is used.

[0046] 2. Substitution Test The temporary chelating agents prepared in Examples 1-6 and Comparative Examples 1-6 were collected, and water was added to prepare a 5 wt% temporary chelating agent solution. An artificial rock core with a crack width of 5 mm was collected, and quartz sand of a certain particle size was added to the crack to prepare a test rock core with a water permeability of approximately 3000 mD. After loading the test rock core into a rock core holder, it was connected to a displacement device, and under conditions of 90°C, brine (19500 mg / L sodium chloride, 500 mg / L calcium chloride) was first injected at a rate of 0.2 mL / min and held until the displacement pressure reached equilibrium. Next, 1 PV of temporary chelating agent solution was injected, and then the temperature was maintained for 10 hours. After the temperature was maintained, water flooding with brine was performed again at a rate of 0.2 mL / min, and the pressure P at the point when the pressure dropped sharply during the water flooding process (pressure dropped by 10% or more) was recorded, and the breakthrough pressure gradient was calculated using the following formula: G = P / L. In the formula, G represents the breakthrough pressure gradient (MPa / m), and L represents the length of the sand-filled pipe (m).

[0047] The sand-filled tube was then kept warm for another 20 days, after which brine was injected at a rate of 0.2 mL / min and held until the displacement pressure reached equilibrium. The water osmotic rate k2 was measured, and the osmotic rate recovery rate was calculated using the following formula: η = k2 / k1 × 100%. In the formula, η represents the osmotic rate recovery rate, k1 represents the water osmotic rate before displacement, and k2 represents the water osmotic rate after gel crushing.

[0048] The final test results are shown in Table 2.

[0049] JPEG0007879544000002.jpg125170

[0050] As is clear from Table 2, the temporary chelating agent produced by the embodiment of the present invention has a high breakthrough pressure gradient, reaching a maximum of 23 MPa / m or more. At the same time, after automatic decomposition and gel pulverization, it has little effect on the permeability of the storage layer, the permeability recovery rate reaches a maximum of 97% or more, and the damage to the storage layer is small. Referring to Comparative Example 1, it can be seen that when a conventional decomposable crosslinking agent is used, the strength is relatively low. Referring to Comparative Examples 2 and 5, it can be seen that when short-chain ethylene glycol dimethacrylate or ethylenediamine is used as a crosslinking agent, the strength is high, but the permeability recovery rate is relatively low. Referring to Comparative Example 3, it can be seen that after changing the order of addition of the materials, the strength of the product decreases sharply. Referring to Comparative Example 4, it can be seen that when an amino acid having two primary amino groups is used as a raw material for a multi-armed crosslinking agent, the effect is relatively low. Referring to Comparative Example 6, it can be seen that when melamine is used as a raw material for a multi-armed crosslinking agent, both the strength and permeability recovery rate are poor.

[0051] The above are merely preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that a person skilled in the art can easily conceive of within the scope of the art disclosed in the embodiments of the present invention should be included within the scope of protection of the present invention. Accordingly, the scope of protection of the present invention shall be based on the claims.

Claims

1. A method for producing a high-strength self-degrading gel chelating agent, The process involves adding a primary diamine compound and an unsaturated glycidyl compound in a molar ratio of 1:3 to 4.1 to a solvent and dissolving them, then reacting the primary diamine compound solution dropwise into the unsaturated glycidyl compound solution at 20 to 35°C in the presence of a catalyst and polymerization inhibitor, and after the reaction is complete, removing low-boiling point substances by vacuum distillation to obtain a multi-armed crosslinking agent, wherein the unsaturated glycidyl compound is one of glycidyl acrylate and glycidyl methacrylate, and the primary diamine compound is one of propanediamine, 1,3-diamino-2-propanol and butanediamine. A method for producing a high-strength self-degrading gel chelating agent, comprising the steps of taking an acrylamide monomer, an acid monomer, a rigid monomer which is one of N-vinylpyrrolidone and N-vinylimidazole, and a 2-methacryloyloxyethyl phosphorylcholine monomer, polymerizing them under the action of an initiator and a multi-armed crosslinking agent, and then grinding, drying, and granulating the polymerized material, wherein the mass ratio of the acrylamide monomer, the acid monomer, the rigid monomer, and the 2-methacryloyloxyethyl phosphorylcholine monomer is 10:3 to 8:0.5 to 2:0.1 to 0.3, the amount of the initiator added is 0.1 to 0.8% of the total mass of all monomers, and the amount of the multi-armed crosslinking agent added is 0.1 to 0.5% of the total mass of all monomers.

2. A method for producing a high-strength self-degrading gel chelating agent according to claim 1, characterized in that, in the production of the multi-armed crosslinking agent, the catalyst is tetrabutylammonium bromide, the amount added is 1 to 1.5% of the total mass of the primary diamine compound and the unsaturated glycidyl compound, the polymerization inhibitor is p-methoxyphenol, the concentration in the unsaturated glycidyl compound solution is 50 to 100 ppm, the solvent is DMF, and the reaction time is 15 to 25 hours.

3. A method for producing a high-strength self-degrading gel chelating agent according to claim 1, characterized in that the primary diamine compound is 1,3-diamino-2-propanol.

4. The method for producing a high-strength self-degrading gel chelating agent according to claim 1, wherein the acidic monomer is at least one of acrylic acid, sodium acrylate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-styrenesulfonate.

5. The method for producing a high-strength self-degrading gel chelating agent according to claim 1, characterized in that the acidic monomer is a mixture of acrylic acid and sodium 2-acrylamido-2-methylpropanesulfonate in a mass ratio of 1:2, and the rigid monomer is N-vinylimidazole.

6. The method for producing a high-strength self-degrading gel chelating agent according to claim 1, characterized in that the polymerization is one of aqueous solution radical polymerization or reverse-phase emulsion polymerization.

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