Low-swelling, temperature-resistant and salt-resistant gel water plugging agent with thixotropic behavior and preparation method of low-swelling, temperature-resistant and salt-resistant gel water plugging agent

Abstract

The invention discloses a low-swelling temperature-resistant salt-resistant gel water shutoff agent with thixotropic behavior and a preparation method thereof, and belongs to the technical field of oilfield development. The gel water plugging agent is prepared from the following substances in parts by weight: 6.3 to 12.8 parts of acrylamide, 2.1 to 4.2 parts of acrylic acid, 2.1 to 4.2 parts of N-vinyl pyrrolidone, 6.9 to 15.7 parts of alumina sol, 1.2 to 3.6 parts of amylopectin, 0.5 to 1.05 parts of cross-linking agent, 0.0002 to 0.006 part of initiator and the balance of water, and the sum of the parts by weight of the substances is 100 parts. The preparation method comprises the following steps: dissolving acrylamide, acrylic acid and N-vinyl pyrrolidone in water, and adding alumina sol, a cross-linking agent and an initiator to obtain a reaction base solution; mixing the reaction base solution with the pre-gelatinized amylopectin solution to obtain a reaction solution; and injecting the reaction solution into the stratum for polymerization and cross-linking. The gel water shutoff agent is excellent in performance and low in cost, and has a wide market application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield development, and particularly relates to a temperature-resistant and salt-resistant gel water shutoff agent with thixotropy and low swelling property and a preparation method thereof. Background Art

[0002] Excessive water production is one of the main problems faced in the development of shale oil and gas. Excessive water will significantly reduce the productivity of oil wells, cause corrosion and scaling, and sometimes even lead to the shutdown of production wells. It has been proven that plugging high-permeability water leakage zones is an economical and effective method.

[0003] "An oil well water shutoff agent and an oil well water shutoff method" (CN102876305B), the oil well water shutoff agent includes: an anionic surfactant, a nonionic-anionic surfactant, C1-C8 fatty alcohols, heavy oil and water, and has the characteristics of strong resistance to high salinity water, strong temperature resistance, strong stability, low cost and no formation pollution. However, the water shutoff agent for large pore channels in oil reservoirs needs to have a certain strength. The components in this invention have relatively small molecular weights, and the strength of the product is limited, which will affect the plugging effect. Therefore, the application range is limited.

[0004] "A gel profile control agent for plugging channeling in waterflooded oil reservoirs in oilfields" (CN202311392830.9), uses partially hydrolyzed polyacrylamide as the main agent and organic chromium as the crosslinking agent to prepare a gel water shutoff agent for plugging channeling in oilfields. This gel water shutoff agent has a relatively high plugging strength. However, in the face of increasingly complex reservoir environments, such as temperature > 100 °C and salinity > 100,000, it is difficult to apply.

[0005] The present invention provides a low-swelling, temperature-resistant, salt-resistant in-situ gel water shutoff agent with thixotropy. This gel water shutoff agent is composed of two crosslinked networks, which can significantly improve the gel strength. And this gel water shutoff agent has a low swelling multiple and will not lose its mechanical properties and plugging strength due to swelling under high-temperature formation conditions. At the same time, considering that the initial viscosity of the water-based gel temporary plugging agent is low and it is prone to filtration when it has not crosslinked to form a solid gel in the formation, this gel water shutoff agent can exhibit a certain thixotropy when in liquid state, which can not only achieve a good pumping effect, but also increase its viscosity after being injected into the predetermined position, and can also reduce the filtration of the plugging agent to a certain extent. Summary of the Invention

[0006] The purpose of the present invention is to provide a temperature-resistant and salt-resistant gel water shutoff agent with thixotropic behavior, which has the advantages of controllable gelation time, good temperature and salt resistance, low swelling multiple, good injection performance, good anti-filtration performance and low price, and has broad market application prospects.

[0007] Another object of the present invention is also to provide a preparation method of the low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior. The principle of this method is reliable, the operation is simple, the raw materials are cheap and easy to obtain, the preparation process is controllable, and it is suitable for industrial promotion.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solutions.

[0009] The low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior is composed of the following substances in parts by weight: 6.3 - 12.8 parts of acrylamide, 2.1 - 4.2 parts of acrylic acid, 2.1 - 4.2 parts of N-vinylpyrrolidone, 6.9 - 15.7 parts of aluminum sol, 1.2 - 3.6 parts of branched starch, 0.5 - 1.05 parts of crosslinking agent, 0.0002 - 0.006 parts of initiator, and the balance is water. The sum of the parts by weight of the above substances is 100 parts.

[0010] Further, the crosslinking agent is N,N'-methylenebisacrylamide or divinylbenzene.

[0011] Further, the initiator is one or more of dicumyl peroxide, tert-butyl peroxybenzoate, and tert-butyl hydroperoxide.

[0012] Further, the mass ratio of acrylamide, acrylic acid, and N-vinylpyrrolidone is 3:1:1.

[0013] Further, the mass concentration of the aluminum sol is 30%.

[0014] Further, the branched starch is corn branched starch.

[0015] The preparation method of the low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior successively includes the following steps: First, weigh a certain mass of branched starch and disperse it in deionized water. After stirring and mixing evenly at room temperature, place it in a constant temperature environment of 90 °C for pregelatinization for 30 min to obtain a pregelatinized starch solution; Second, take a certain mass of acrylamide, acrylic acid, and N-vinylpyrrolidone and dissolve them in an appropriate amount of water, where the mass ratio of acrylamide, acrylic acid, and N-vinylpyrrolidone is 3:1:1. Then add aluminum sol, crosslinking agent, and initiator to obtain a reaction base liquid; Third, mix the reaction base liquid with the pregelatinized starch solution, and make up the balance of water. After stirring and mixing evenly, obtain a temperature- and salt-resistant gel plugging agent reaction solution; Fourth, inject the temperature- and salt-resistant gel plugging agent reaction solution into a formation environment with a temperature of 100 - 150 °C for in-situ polymerization crosslinking to obtain a low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior.

[0016] Further, the stirring rate is 200 - 300 r / min.

[0017] Further, when the temperature is 100 - 150 °C and the salinity is 10×10 4 ~25×10 4 mg / L, the gel plugging agent can be stable for 30 days without degradation.

[0018] The gel plugging agent of the present invention is formed by a chemical cross - linked network constructed by acrylamide, acrylic acid and N - vinylpyrrolidone and a physical cross - linked network constructed by aluminum sol and starch. At the beginning, the aluminum sol interacts with acrylic acid and starch to form a physical cross - linked structure. As the temperature rises, acrylamide, acrylic acid and N - vinylpyrrolidone form a chemical cross - linked network under the action of an initiator and a cross - linker. The chemical cross - linked network grows and penetrates each other in the physical network, and finally forms a uniformly distributed double cross - linked network structure, which can significantly improve the strength of the gel.

[0019] The gel plugging agent has a low swelling ratio and will not lose its mechanical properties and plugging strength due to swelling under high - temperature formation conditions. At the same time, the gel plugging agent can show a certain thixotropy when in liquid state, achieving a good pumping effect. When injected into a predetermined position, its viscosity increases, which can reduce the filtration loss of the plugging agent.

[0020] The reaction process of the gel plugging agent is as follows:

[0021] Compared with the prior art, the beneficial effects of the present invention are: (1) The initiator used in the gel plugging agent system of the present invention is a high - temperature initiator, which needs to have strong initiation activity under higher temperature conditions, so that the system can be applicable to in - situ gel formation in high - temperature reservoirs; (2) After introducing aluminum sol into the gel plugging agent of the present invention, it can further interact with the polymer network, increasing the complexity of the network structure and improving the mechanical properties of the gel; (3) Under the action of starch and Al, the gel plugging agent of the present invention can show a certain thixotropy in the liquid state, which can reduce the filtration loss while ensuring effective migration; (4) The gel plugging agent of the present invention has a low swelling ratio, and even under high - temperature conditions, it can ensure that its plugging performance will not be lost over time; (5) The gel plugging agent of the present invention has excellent temperature and salt tolerance performance, and can be stable for more than 30 days under the conditions of temperature 100 - 150 °C and salinity 10×10 4 ~25×10 4 mg / L. Description of the Drawings

[0022] Figure 1 It is the swelling curve of the gel plugging agent at different salinities.

[0023] Figure 2 is the viscosity curve of the gel plugging agent at different shear rates. Detailed Embodiments

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] During actual use, the system components can be appropriately adjusted according to well conditions, well types, formation water quality conditions, etc.

[0026] I. Preparation of a Low-Swelling Temperature- and Salt-Resistant Gel Plugging Agent with Thixotropic Behavior

[0027] Example 1 Weigh 1.2 g of corn amylopectin and dissolve it in 20 g of water, and place it in a constant temperature environment at 90 °C for pre-gelatinization for 30 min to obtain a pre-gelatinized solution. Take 6.3 g of acrylamide, 2.1 g of acrylic acid and 2.1 g of N-vinylpyrrolidone and add them to 20 g of water, and stir evenly at a stirring speed of 300 r / min to obtain a monomer solution. Take 0.6 g of N,N'-methylenebisacrylamide, 15.6 g of aluminum sol and 0.0002 g of tert-butyl peroxybenzoate and add them to the monomer solution, and continuously stir for 10 min. Then mix this solution with the pre-gelatinized starch solution, and add deionized water to make the total mass of the system 100 g, and continuously stir for 10 min. React at 130 °C for 56 min and then cure.

[0028] Place the gel plugging agent at 130 °C, 10 × 10 4 mg / L for 30 days of aging, and the gel will not degrade and can still maintain its original state.

[0029] Example 2 Weigh 1.8 g of corn amylopectin and dissolve it in 20 g of water, and place it in a constant temperature environment at 90 °C for pre-gelatinization for 30 min to obtain a pre-gelatinized solution. Take 8.1 g of acrylamide, 2.7 g of acrylic acid and 2.7 g of N-vinylpyrrolidone and add them to 20 g of water, and stir evenly at a stirring speed of 300 r / min to obtain a monomer solution. Take 0.8 g of divinylbenzene, 13.2 g of aluminum sol and 0.0002 g of tert-butyl hydroperoxide and add them to the monomer solution, and continuously stir for 10 min. Then mix this solution with the pre-gelatinized starch solution, and add deionized water to make the total mass of the system 100 g, and continuously stir for 10 min. React at 110 °C for 70 min and then cure.

[0030] The gel plugging agent does not degrade after aging for 30 days under the conditions of 110 °C and 15×10 4 mg / L and can still maintain its original state.

[0031] Example 3 Weigh 2.4 g of corn amylopectin, dissolve it in 20 g of water, and place it in a constant temperature environment of 90 °C for pregelatinization for 30 min to obtain a pregelatinized solution. Take 12.6 g of acrylamide, 4.2 g of acrylic acid, and 4.2 g of N-vinylpyrrolidone, add them to 20 g of water, stir evenly at a stirring speed of 300 r / min to obtain a monomer solution. Take 0.9 g of divinylbenzene, 8.3 g of aluminum sol, and 0.0006 g of tert-butyl peroxybenzoate and add them to the monomer solution, and continue stirring for 10 min. Then mix this solution with the pregelatinized starch solution, and add deionized water to make the total mass of the system 100 g, and continue stirring for 10 min. Cure after reacting in an environment of 150 °C for 21 min.

[0032] The gel plugging agent does not degrade after aging for 30 days under the conditions of 150 °C and 20×10 4 mg / L and can still maintain its original state.

[0033] Example 4 Weigh 3.2 g of corn amylopectin, dissolve it in 20 g of water, and place it in a constant temperature environment of 90 °C for pregelatinization for 30 min to obtain a pregelatinized solution. Take 10.5 g of acrylamide, 3.5 g of acrylic acid, and 3.5 g of N-vinylpyrrolidone, add them to 20 g of water, stir evenly at a stirring speed of 300 r / min to obtain a monomer solution. Take 0.7 g of N,N-methylenebisacrylamide, 10.6 g of aluminum sol, and 0.003 g of diisopropyl peroxide and add them to the monomer solution, and continue stirring for 10 min. Then mix this solution with the pregelatinized starch solution, and add deionized water to make the total mass of the system 100 g, and continue stirring for 10 min. Cure after reacting in an environment of 130 °C for 19 min.

[0034] The gel plugging agent does not degrade after aging for 30 days under the conditions of 130 °C and 25×10 4 mg / L and can still maintain its original state.

[0035] II. Performance test of the low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior Comparative Example 1 Replace the crosslinking agent in Example 1 with polyethylene glycol diacrylate, and keep other components, dosages, and reaction conditions the same as in Example 1. Age in a simulated formation environment with a temperature of 130 °C and a salinity of 22×10 4 mg / L for 30 days. The mass retention rate of the plugging agent is 5%, and it loses its plugging performance.

[0036] Comparative Example 2 Replace the aluminum sol in Example 2 with nano-clay. The other components, dosages, and reaction conditions are the same as those in Example 2, and the gel strength obtained is significantly reduced.

[0037] 1. Plugging performance test: Taking the water plugging agent formulas of Examples 1 - 4 as the research objects, denoted as 1# - 4# respectively, their plugging abilities were investigated. The core used in the experiment was a shale core, and standard cores were prepared by wire cutting. The experimental steps were as follows: First, place the shale core in the holder, set the confining pressure to be always 2.0 MPa higher than the injection pressure, and inject the thixotropic low-swelling temperature- and salt-resistant gel water plugging agent into the core at a displacement rate of 0.5 mL / min. After liquid flowed out at the outlet end, stop the injection. Then, react and cure to form a plug at 130°C, and inject water for displacement at a rate of 0.5 mL / min, record the change trend of the displacement pressure. The breakthrough pressure was when the pressure dropped suddenly, and the displacement pressure after plugging is shown in Table 1.

[0038]

[0039] The results show that: compared with the water plugging agent added with conventional nano materials, this gel water plugging agent has a higher plugging strength and can be applied to oil reservoirs with higher plugging strength requirements.

[0040] 2. Swelling performance test Taking Example 1 as the research object, the prepared gel water plugging agent was placed in salinity solutions of 10×10 4 mg / L, 15×10 4 mg / L, 20×10 4 mg / L, and 25×10 4 mg / L respectively, and then aged at 130°C for 30 d. At regular intervals, take out the gel water plugging agent and test and record its swelling multiple at different aging times. The results are as Figure 1 shown.

[0041] It can be seen from Figure 1 that the swelling multiple of this gel water plugging agent first increases and then gradually stabilizes with the increase of aging time, and the swelling multiple of the gel water plugging decreases gradually with the decrease of salinity, but its maximum swelling multiple does not exceed 6 times, indicating that this gel water plugging agent can maintain its mechanical and plugging properties in high-temperature and high-salinity reservoirs for a long time.

[0042] 3. Rheological property analysis Taking Example 4 as the research object, use a rheometer to measure the viscosity of the reaction solution at a shear rate of 0.01 - 1000 s -1 . The results are as Figure 2 shown.

[0043] It can be seen from Figure 2 that as the shear rate increases, the viscosity of the reaction liquid decreases rapidly, the fluidity increases, which is beneficial to the transportation of the liquid gel in pipelines and fractures, indicating that the gel water plugging agent has good pumping performance when it is in liquid state. After reaching the predetermined position, the viscosity of the liquid gel increases, so that the filtration loss can be effectively reduced.

[0044] As mentioned above, only the preferred specific embodiments of the present invention are described, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior, which is composed of the following substances in parts by weight: 6.3 - 12.8 parts of acrylamide, 2.1 - 4.2 parts of acrylic acid, 2.1 - 4.2 parts of N - vinylpyrrolidone, 6.9 - 15.7 parts of aluminum sol, 1.2 - 3.6 parts of branched starch, 0.5 - 1.05 parts of cross - linker, 0.0002 - 0.006 parts of initiator, with the balance being water, and the sum of the weight parts of the above substances being 100 parts.

2. The thixotropic low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior as described in claim 1, wherein The cross - linker is N,N - methylenebisacrylamide or divinylbenzene.

3. The thixotropic low-swelling temperature- and salt-resistant gel water plugging agent according to claim 1, characterized in that, The initiator is one or more of di - isopropylbenzene peroxide, tert - butyl peroxybenzoate, and tert - butyl hydroperoxide.

4. The thixotropic low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior as claimed in claim 1, wherein The mass ratio of acrylamide, acrylic acid, and N - vinylpyrrolidone is 3:1:

1.

5. The thixotropic low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior as claimed in claim 1, characterized in that, The mass concentration of the aluminum sol is 30%.

6. The thixotropic low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior as claimed in claim 1, characterized in that, The branched starch is corn branched starch.

7. The preparation method of the low-swelling temperature- and salt-resistant gel plugging agent with thixotropic behavior according to claim 1, 2, 3, 4, 5 or 6, successively It includes the following steps: First, weigh a certain mass of branched starch and disperse it in deionized water. After stirring and mixing evenly at room temperature, place it in a constant - temperature environment of 90 °C for pre - gelatinization for 30 min to obtain a pre - gelatinized starch solution. Second, take a certain mass of acrylamide, acrylic acid, and N - vinylpyrrolidone and dissolve them in an appropriate amount of water, and then add aluminum sol, cross - linker, and initiator to obtain a reaction base liquid. Third, mix the reaction base liquid with the pre - gelatinized starch solution, and make up the remaining amount of water. After stirring and mixing evenly, obtain a reaction solution of the temperature - resistant and salt - resistant gel plugging agent. Fourth, inject the reaction solution of the temperature - resistant and salt - resistant gel plugging agent into a formation environment with a temperature of 100 - 150 °C for in - situ polymerization cross - linking to obtain a temperature - resistant and salt - resistant gel plugging agent with thixotropic behavior and low swelling property.

8. The method according to claim 7, wherein The stirring rate is 200 - 300 r / min.

9. The method according to claim 7, wherein When the temperature is 100~150 °C and the salinity is 10×10 4 ~25×10 4 mg / L, the gel plugging agent can be stable for 30 days without degradation.

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