pH-responsive magnetic nano-chemical oil displacement agent and preparation and application thereof

Abstract

This invention discloses a pH-responsive magnetic nano-chemical oil displacement agent containing intelligent microspheres. The intelligent microspheres comprise a core formed by nano-SiO2 and dodecyl phosphate monoester clusters, with polyacrylamide and Fe3O4 nanoparticles sequentially attached to the surface of the core, and a shell formed by cross-linking sodium methacrylate. This invention also discloses its preparation and application. The oil displacement agent provided by this invention has mild preparation conditions, low cost, and good oil displacement effect, making it suitable for large-scale production. It can reduce energy consumption during the extraction process, reduce emissions and pollution, and improve crude oil recovery, thus having significant practical implications.

Description

Technical Field

[0001] This invention relates to a pH-responsive magnetic nano-chemical oil displacement agent, its preparation, and its application. Background Technology

[0002] Many low-permeability oilfields in my country, modified through fracturing and acid fracturing, suffer from small porosity and low permeability. Waterflooding results in low oil washing efficiency and small swept volume, leading to high injection pressure and development difficulties. New technologies are needed to address these issues. More importantly, most of my country's older medium-to-high permeability oilfields developed through water injection have entered a high water-cut, high-recovery phase, with severely scattered remaining oil and gas. Improving the recovery rate of high water-cut oilfields and blocks through technological advancements is a pressing problem.

[0003] Nanofluid flooding is an emerging oil recovery technology. Its large specific surface area and surface energy significantly reduce the interfacial tension between water, oil, and solids, allowing the injected fluid to easily detach crude oil from the rock surface into small droplets during the scouring of pores, which are then displaced by the displacing fluid. In recent years, the research and development of environmentally responsive nanofluid flooding agents has become a hot topic in academia and industry. This is due to the unique and excellent performance and environmental responsiveness of these agents, which indicate their enormous potential applications.

[0004] However, to date, existing environmentally responsive nano-displacement agents face a series of technical bottlenecks, such as mediocre oil displacement effects, poor profile control capabilities, inability to expand the affected volume, high energy consumption, high cost, and low recovery rate in tertiary oil recovery. Therefore, the development of new intelligent nano-displacement agents is urgently needed. Summary of the Invention

[0005] To further enrich the selection of oil displacement agents and provide an oil displacement agent with better oil displacement effect, this invention is made. The pH-responsive magnetic nano-chemical oil displacement agent provided by this invention, after being injected into the formation, can control the flow direction, range, and contact time of the nanofluid through the addition of a magnetic field. Simultaneously, it adjusts the pH to disperse and emulsify crude oil, facilitating oil-water separation, achieving intelligent operation, and thereby improving displacement and recovery rates.

[0006] As one aspect of the present invention, a pH-responsive magnetic nanochemical oil displacement agent is disclosed, comprising intelligent microspheres, wherein the intelligent microspheres include: a core formed by nano-SiO2 and dodecyl phosphate monoester clusters, polyacrylamide and Fe3O4 nanoparticles sequentially attached to the surface of the core, and a shell formed by cross-linking sodium methacrylate.

[0007] In a specific embodiment, the smart microspheres are suspended in a 2.0%-2.1% sodium hydroxide aqueous solution.

[0008] In a specific embodiment, sodium methacrylate is crosslinked using N,N′-methylenebisacrylamide as the crosslinking agent.

[0009] In the intelligent microspheres, the mass ratio of the core (dodecyl phosphate monoester + nano SiO2), polyacrylamide, Fe3O4 nanoparticles, and shell (sodium methacrylate + N,N′-methylenebisacrylamide) is 3-9:0.4-2.0:0.5-2.5:0.5–1.8; preferably 5.6-9:0.5-2.0:0.6-2.5:0.5–1.8.

[0010] In a specific embodiment, the mass ratio of dodecyl phosphate monoester to nano-SiO2 in the core is (1:2)-(2:1); and the mass ratio of N,N′-methylenebisacrylamide to sodium methacrylate in the shell is (1:1)-(4:1).

[0011] As another aspect of the present invention, a method for preparing a pH-responsive magnetic nano-chemical oil displacement agent is provided, comprising:

[0012] (1) Add dodecyl phosphate monoester and nano SiO2 to sodium hydroxide aqueous solution and stir. The nano SiO2 and dodecyl phosphate monoester clusters form microspheres.

[0013] (2) Add polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1);

[0014] (3) Add Fe3O4 nanoparticles and stir. The Fe3O4 nanoparticles are further attached to the surface of the microspheres.

[0015] (4) Add N,N′-methylenebisacrylamide, mix thoroughly, then add sodium methacrylate and stir to obtain a pH-responsive magnetic nano-chemical oil displacement agent.

[0016] In a specific embodiment, the mass ratio of dodecyl phosphate monoester, nano-SiO2, polyacrylamide, Fe3O4 nanoparticles, N,N′-methylenebisacrylamide and sodium methacrylate is 1.0-4.0: 2.0-5.0: 0.4-2.0: 0.5-2.5: 0.3-1.2: 0.2-1.0.

[0017] As another aspect of the present invention, it relates to the application of the above-mentioned pH-responsive magnetic nano-chemical flooding agent in oilfield development.

[0018] The oil displacement agent provided by this invention has mild preparation conditions, low oil displacement cost and good effect, and is more suitable for large-scale production. It can reduce energy consumption in the extraction process, reduce emissions and pollution, and improve crude oil recovery rate, which has important practical significance. Detailed Implementation

[0019] The specific embodiments of the present invention are described below with reference to examples, but the present invention is not limited to the following examples.

[0020] In the following embodiments, the evaluation method for enhancing oil recovery by oil displacement agents adopts the existing evaluation method, specifically:

[0021] (1) After vacuuming the artificial rock core, saturate it with simulated formation water, take it out and wipe the surface water droplets with filter paper, weigh the wet weight of the rock core, calculate its pore volume, and finally immerse the rock core in simulated formation water for later use.

[0022] (2) Take out the pretreated core, record the basic parameters of the core, put it into the core holder, apply confining pressure, and set the experimental temperature to 75℃.

[0023] (3) Saturate the core with simulated formation water, record the injection volume, inlet and outlet pressures, etc. in real time, calculate the water phase permeability of the core, and then saturate the core with simulated oil until no more simulated oil flows out of the outlet. Record the oil and water volume and displacement pressure at the outlet in real time.

[0024] (4) Water drive: until no more oil flows out of the outlet, record the oil and water volumes at the outlet, and calculate the water drive recovery rate; Oil displacement agent drive: inject the prepared oil displacement agent-water dispersion system until no more oil flows out of the outlet, record the oil volume at the outlet in real time, and calculate the crude oil recovery rate that the oil displacement agent can improve.

[0025] Example 1:

[0026] The preparation method of the oil displacement agent in this embodiment is as follows:

[0027] (1) Add 4g of dodecyl phosphate monoester and 2g of 100nm nano SiO2 material to a prepared 100mL sodium hydroxide aqueous solution with a concentration of 2.0%, and stir for 3 hours using a magnetic stirrer. The nano SiO2 and dodecyl phosphate monoester clusters form microspheres (in this invention, they serve as the core of the final spherical product).

[0028] (2) Add 2g of polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1);

[0029] (3) Add 2.5g of 100nm Fe3O4 nanoparticles and stir at room temperature for 4 hours. The Fe3O4 nanoparticles are further attached to the surface of the microspheres.

[0030] (4) Add 1g of N,N′-methylenebisacrylamide (crosslinking agent), mix thoroughly, then add 0.5 sodium methacrylate, and stir at room temperature for 5 hours to obtain the oil displacement agent.

[0031] The inventors discovered that when N,N′-methylenebisacrylamide (crosslinking agent) and sodium methacrylate are added simultaneously, poly(N-isopropylacrylamide) and sodium methacrylate cannot be uniformly coated onto the surface of the microspheres, resulting in unsatisfactory oil displacement effect. Therefore, in the embodiments of this application, the inventors first add N,N′-methylenebisacrylamide (crosslinking agent) and mix it evenly, and then add sodium methacrylate to form a shell coating the surface of the microspheres.

[0032] In the artificial core displacement experiment conducted at the Engineering Technology Research Center Laboratory of Tongji University, the experiment was carried out in accordance with the petroleum and natural gas industry standard SY / T5336-2006 "Core Analysis Methods". 0.2g of oil displacement agent was mixed with 100mL of deionized water to form an oil displacement agent-water dispersion system. Then, a physical model displacement experiment was performed on the artificial core (core diameter 2.5cm, length 5.1cm, permeability 0.46μm). 2 First, water flooding was performed to a water cut of 95%, and the oil recovery rate was measured to be 53.2%. Then, 0.4 pV (pore volume) of the oil displacement agent-water dispersion system of this embodiment was injected, and water flooding was continued to a water cut of 98%, and the oil recovery rate was measured to be 66.3%. It was calculated that the oil displacement agent can increase the oil recovery rate by 13.1% on the basis of water flooding.

[0033] In the artificial core displacement experiment, the inventors divided the cross-section of the core into two parts. The oil displacement agent of this invention was applied to one part, and a magnetic field was applied. The results showed that the oil displacement agent only displaced the oil in its corresponding part, while the oil in the other part remained undisplaced. Therefore, it can be concluded that the oil displacement agent prepared in this embodiment can achieve directional oil displacement under magnetic action.

[0034] In the artificial core displacement experiment, the inventors used a 0.5% NaCl solution to simulate formation water and adjusted the pH of the simulated formation water to 8, 6, 5, 4, and 3 using 5% HCl and 5% NaOH solutions. They found that as the pH of the formation water decreased, the resistance coefficient of the oil displacement agent prepared in this embodiment decreased during injection into the core, but the residual resistance coefficient did not change significantly. When the injection pH decreased from 8 to 3, the resistance coefficient decreased by 95%, while the residual resistance coefficient only decreased by 17%. Analysis suggests that lowering the pH of the injected formation water can significantly improve the injection performance of the oil displacement agent prepared in this embodiment, exhibiting obvious pH responsiveness, while also achieving a good sealing effect.

[0035] Example 2:

[0036] The preparation method of the oil displacement agent in this embodiment is as follows:

[0037] (1) 4g of dodecyl phosphate monoester and 5g of 100nm nano SiO2 material were added to 100mL of 2.1% sodium hydroxide aqueous solution and stirred for 3 hours with a magnetic stirrer. The nano SiO2 and dodecyl phosphate monoester clusters formed microspheres (in this invention, they serve as the core of the final spherical product).

[0038] (2) Add 1g of polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1);

[0039] (3) Add 2g of 100nm Fe3O4 nanoparticles and stir at room temperature for 4 hours. The Fe3O4 nanoparticles are further attached to the surface of the microspheres.

[0040] (4) Add 1.0g N,N′-methylenebisacrylamide (crosslinking agent), mix thoroughly, then add 1.0g sodium methacrylate, and stir at room temperature for 5 hours to obtain the oil displacement agent.

[0041] In the artificial core displacement experiment conducted at the Engineering Technology Research Center Laboratory of Tongji University, the experiment was carried out in accordance with the petroleum and natural gas industry standard SY / T5336-2006 "Core Analysis Methods". 0.2g of oil displacement agent was mixed with 100mL of deionized water to form an oil displacement agent-water dispersion system. Then, a physical model displacement experiment was performed on the artificial core (core diameter 2.5cm, length 5.0cm, permeability 0.43μm). 2 First, water flooding was carried out to a water cut of 95%, and the crude oil recovery rate was measured to be 51.6%. Then, 0.4 pV (pore volume) of the oil displacement agent-water dispersion system of this embodiment was injected, and water flooding was continued to a water cut of 98%, and the crude oil recovery rate was measured to be 62.0%. It was calculated that the oil displacement agent can increase the crude oil recovery rate by 10.4% on the basis of water flooding.

[0042] Example 3:

[0043] The preparation method of the oil displacement agent in this embodiment is as follows:

[0044] (1) Add 4g of dodecyl phosphate monoester and 2g of 100nm nano SiO2 material to a prepared 100mL sodium hydroxide aqueous solution with a concentration of 2.0%, and stir for 3 hours using a magnetic stirrer. The nano SiO2 and dodecyl phosphate monoester clusters form microspheres (in this invention, they serve as the core of the final spherical product).

[0045] (2) Add 0.5g of polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1);

[0046] (3) Add 0.6g of 100nm Fe3O4 nanoparticles and stir at room temperature for 4 hours. The Fe3O4 nanoparticles are further attached to the surface of the microspheres.

[0047] (4) Add 0.3g N,N′-methylenebisacrylamide (crosslinking agent), mix thoroughly, then add 0.2g sodium methacrylate, and stir at room temperature for 5 hours to obtain the oil displacement agent.

[0048] In the artificial core displacement experiment at the Engineering Technology Research Center Laboratory of Tongji University, the experiment was conducted in accordance with the petroleum and natural gas industry standard SY / T5336-2006 "Core Analysis Methods". 0.2g of intelligent nano-chemical displacement agent was mixed with 100mL of deionized water to form an intelligent nano-chemical displacement agent-water dispersion system. Then, a physical model displacement experiment was conducted using an artificial core (core diameter 2.5cm, length 4.8cm, permeability 0.39μm). 2 First, water flooding was carried out to a water cut of 95%, and the crude oil recovery rate was measured to be 52.3%. Then, 0.4 pV (pore volume) of the oil displacement agent-water dispersion system of this embodiment was injected, and water flooding was continued to a water cut of 98%, and the crude oil recovery rate was measured to be 64.1%. It was calculated that the oil displacement agent can increase the crude oil recovery rate by 11.8% on the basis of water flooding.

[0049] Example 4:

[0050] The preparation method of the oil displacement agent in this embodiment is as follows:

[0051] (1) 1g of dodecyl phosphate monoester and 2g of 100nm nano SiO2 material were added to 100mL of 2.0% sodium hydroxide aqueous solution and stirred for 3 hours with a magnetic stirrer. The nano SiO2 and dodecyl phosphate monoester clusters formed microspheres (in this invention, they serve as the core of the final spherical product).

[0052] (2) Add 0.4g of polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1);

[0053] (3) Add 0.5g of 100nm Fe3O4 nanoparticles and stir at room temperature for 4 hours. The Fe3O4 nanoparticles are further attached to the surface of the microspheres.

[0054] (4) Add 0.3g N,N′-methylenebisacrylamide (crosslinking agent), mix thoroughly, then add 0.2g sodium methacrylate, and stir at room temperature for 5 hours to obtain the oil displacement agent.

[0055] In the artificial core displacement experiment conducted at the Engineering Technology Research Center Laboratory of Tongji University, the experiment was carried out in accordance with the petroleum and natural gas industry standard SY / T5336-2006 "Core Analysis Methods". 0.2g of oil displacement agent was mixed with 100mL of deionized water to form an oil displacement agent-water dispersion system. Then, a physical model displacement experiment was performed using an artificial core (core diameter 2.5cm, length 4.8cm, permeability 0.39μm). 2 First, water flooding was carried out to a water cut of 95%, and the crude oil recovery rate was measured to be 46.5%. Then, 0.4 pV (pore volume) of the oil displacement agent-water dispersion system of this embodiment was injected, and water flooding was continued to a water cut of 98%, and the crude oil recovery rate was measured to be 56.7%. It was calculated that the oil displacement agent can increase the crude oil recovery rate by 10.2% on the basis of water flooding.

[0056] Example 5:

[0057] The preparation method of the oil displacement agent in this embodiment is as follows:

[0058] (1) 1g of dodecyl phosphate monoester and 2g of 100nm nano SiO2 material were added to 100mL of 2.0% sodium hydroxide aqueous solution and stirred for 3 hours with a magnetic stirrer. The nano SiO2 and dodecyl phosphate monoester clusters formed microspheres (in this invention, they serve as the core of the final spherical product).

[0059] (2) Add 2g of polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1);

[0060] (3) Add 2.5g of 100nm Fe3O4 nanoparticles and stir at room temperature for 4 hours. The Fe3O4 nanoparticles are further attached to the surface of the microspheres.

[0061] (4) Add 1.2g N,N′-methylenebisacrylamide (crosslinking agent), mix thoroughly, then add 0.6g sodium methacrylate, stir at room temperature for 5 hours to obtain the oil displacement agent.

[0062] In the artificial core displacement experiment conducted at the Engineering Technology Research Center Laboratory of Tongji University, the experiment was carried out in accordance with the petroleum and natural gas industry standard SY / T5336-2006 "Core Analysis Methods". 0.2g of oil displacement agent was mixed with 100mL of deionized water to form an oil displacement agent-water dispersion system. Then, a physical model displacement experiment was performed using an artificial core (core diameter 2.5cm, length 4.8cm, permeability 0.39μm). 2First, water flooding was carried out to a water cut of 95%, and the crude oil recovery rate was measured to be 44.1%. Then, 0.4 pV (pore volume) of the oil displacement agent-water dispersion system of this embodiment was injected, and water flooding was continued to a water cut of 98%, and the crude oil recovery rate was measured to be 53.0%. It was calculated that the oil displacement agent can increase the crude oil recovery rate by 8.9% on the basis of water flooding.

[0063] Example 6:

[0064] The preparation method of the oil displacement agent in this embodiment is as follows:

[0065] (1) Add 4g of dodecyl phosphate monoester and 2g of 100nm nano SiO2 material to a prepared 100mL sodium hydroxide aqueous solution with a concentration of 2.0%, and stir for 3 hours using a magnetic stirrer. The nano SiO2 and dodecyl phosphate monoester clusters form microspheres (in this invention, they serve as the core of the final spherical product).

[0066] (2) Add 1g of polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1);

[0067] (3) Add 1g of 100nm Fe3O4 nanoparticles and stir at room temperature for 4 hours. The Fe3O4 nanoparticles are further attached to the surface of the microspheres.

[0068] (4) Add 0.8g N,N′-methylenebisacrylamide (crosslinking agent), mix thoroughly, then add 0.2g sodium methacrylate, and stir at room temperature for 5 hours to obtain the oil displacement agent.

[0069] In the artificial core displacement experiment conducted at the Engineering Technology Research Center Laboratory of Tongji University, the experiment was carried out in accordance with the petroleum and natural gas industry standard SY / T5336-2006 "Core Analysis Methods". 0.2g of oil displacement agent was mixed with 100mL of deionized water to form an oil displacement agent-water dispersion system. Then, a physical model displacement experiment was performed using an artificial core (core diameter 2.5cm, length 5.1cm, permeability 0.41μm). 2 First, water flooding was carried out to a water cut of 95%, and the crude oil recovery rate was measured to be 52.0%. Then, 0.4 pV (pore volume) of the oil displacement agent-water dispersion system of this embodiment was injected, and water flooding was continued to a water cut of 98%, and the crude oil recovery rate was measured to be 64.3%. It was calculated that the oil displacement agent can increase the crude oil recovery rate by 12.3% on the basis of water flooding.

[0070] Example 7:

[0071] The preparation method of the oil displacement agent in this embodiment is as follows:

[0072] (1) 3.6g of dodecyl phosphate monoester and 2g of 100nm nano SiO2 material were added to 100mL of 2.0% sodium hydroxide aqueous solution and stirred for 3 hours with a magnetic stirrer. The nano SiO2 and dodecyl phosphate monoester clusters formed microspheres (in this invention, they serve as the core of the final spherical product).

[0073] (2) Add 2g of polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1);

[0074] (3) Add 2.5g of 100nm Fe3O4 nanoparticles and stir at room temperature for 4 hours. The Fe3O4 nanoparticles are further attached to the surface of the microspheres.

[0075] (4) Add 1.2g N,N′-methylenebisacrylamide (crosslinking agent), mix thoroughly, then add 0.6g sodium methacrylate, stir at room temperature for 5 hours to obtain the oil displacement agent.

[0076] In the artificial core displacement experiment conducted at the Engineering Technology Research Center Laboratory of Tongji University, the experiment was carried out in accordance with the petroleum and natural gas industry standard SY / T5336-2006 "Core Analysis Methods". 0.2g of oil displacement agent was mixed with 100mL of deionized water to form an oil displacement agent-water dispersion system. Then, a physical model displacement experiment was performed using an artificial core (core diameter 2.5cm, length 5.5cm, permeability 0.43μm). 2 First, water flooding was carried out to a water cut of 95%, and the crude oil recovery rate was measured to be 51.5%. Then, 0.4 pV (pore volume) of the oil displacement agent-water dispersion system of this embodiment was injected, and water flooding was continued to a water cut of 98%, and the crude oil recovery rate was measured to be 64.5%. It was calculated that the oil displacement agent can increase the crude oil recovery rate by 13.0% on the basis of water flooding.

[0077] Example 8:

[0078] The preparation method of the oil displacement agent in this embodiment is as follows:

[0079] (1) 3.6g of dodecyl phosphate monoester and 5g of 100nm nano SiO2 material were added to 100mL of 2.0% sodium hydroxide aqueous solution and stirred for 3 hours with a magnetic stirrer. The nano SiO2 and dodecyl phosphate monoester clusters formed microspheres (in this invention, they serve as the core of the final spherical product).

[0080] (2) Add 2g of polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1);

[0081] (3) Add 2.5g of 100nm Fe3O4 nanoparticles and stir at room temperature for 4 hours. The Fe3O4 nanoparticles are further attached to the surface of the microspheres.

[0082] (4) Add 0.8g N,N′-methylenebisacrylamide (crosslinking agent), mix thoroughly, then add 0.2g sodium methacrylate, and stir at room temperature for 5 hours to obtain the oil displacement agent.

[0083] In the artificial core displacement experiment conducted at the Engineering Technology Research Center Laboratory of Tongji University, the experiment was carried out in accordance with the petroleum and natural gas industry standard SY / T5336-2006 "Core Analysis Methods". 0.2g of oil displacement agent was mixed with 100mL of deionized water to form an oil displacement agent-water dispersion system. Then, a physical model displacement experiment was performed on the artificial core (core diameter 2.5cm, length 5.3cm, permeability 0.38μm). 2 First, water flooding was carried out to a water cut of 95%, and the crude oil recovery rate was measured to be 48.3%. Then, 0.4 pV (pore volume) of the oil displacement agent-water dispersion system of this embodiment was injected, and water flooding was continued to a water cut of 98%, and the crude oil recovery rate was measured to be 60.1%. It was calculated that the oil displacement agent can increase the crude oil recovery rate by 11.7% on the basis of water flooding.

[0084] Example 9:

[0085] The preparation method of the oil displacement agent in this embodiment is as follows:

[0086] (1) 3.6g of dodecyl phosphate monoester and 5g of 100nm nano SiO2 material were added to 100mL of 2.0% sodium hydroxide aqueous solution and stirred for 3 hours with a magnetic stirrer. The nano SiO2 and dodecyl phosphate monoester clusters formed microspheres (in this invention, they serve as the core of the final spherical product).

[0087] (2) Add 1g of polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1);

[0088] (3) Add 1g of 100nm Fe3O4 nanoparticles and stir at room temperature for 4 hours. The Fe3O4 nanoparticles are further attached to the surface of the microspheres.

[0089] (4) Add 0.8g N,N′-methylenebisacrylamide (crosslinking agent), mix thoroughly, then add 0.2g sodium methacrylate, and stir at room temperature for 5 hours to obtain the oil displacement agent.

[0090] In the artificial core displacement experiment conducted at the Engineering Technology Research Center Laboratory of Tongji University, the experiment was carried out in accordance with the petroleum and natural gas industry standard SY / T5336-2006 "Core Analysis Methods". 0.2g of oil displacement agent was mixed with 100mL of deionized water to form an oil displacement agent-water dispersion system. Then, a physical model displacement experiment was performed using an artificial core (core diameter 2.5cm, length 5.0cm, permeability 0.41μm). 2 First, water flooding was carried out to a water cut of 95%, and the crude oil recovery rate was measured to be 46.2%. Then, 0.4 pV (pore volume) of the oil displacement agent-water dispersion system of this embodiment was injected, and water flooding was continued to a water cut of 98%, and the crude oil recovery rate was measured to be 56.9%. It was calculated that the oil displacement agent can increase the crude oil recovery rate by 10.7% on the basis of water flooding.

[0091] The comparison shows that, compared with water drive, the crude oil recovery rate of Examples 1-9 all achieved an increase of more than 8.9%, among which Examples 1 and 7 were more effective, and Example 1 was the most effective.

[0092] The intelligent microspheres contained in the oil displacement agents prepared in Examples 1-9 of this invention include: a core formed by nano-SiO2 and dodecyl phosphate monoester clusters, polyacrylamide and Fe3O4 nanoparticles sequentially attached to the surface of the core, and a shell formed by cross-linked sodium methacrylate.

[0093] In this process, N,N′-methylenebisacrylamide is used as the crosslinking agent for the crosslinking of sodium methacrylate.

[0094] In the intelligent microspheres, the mass ratio of the core (dodecyl phosphate monoester + nano SiO2), polyacrylamide, Fe3O4 nanoparticles, and shell (sodium methacrylate + N,N′-methylenebisacrylamide) is 3-9:0.4-2.0:0.5-2.5:0.5–1.8; preferably 5.6-9:0.5-2.0:0.6-2.5:0.5–1.8.

[0095] In a specific embodiment, the mass ratio of dodecyl phosphate monoester to nano-SiO2 in the core is (1:2)-(2:1); and the mass ratio of N,N′-methylenebisacrylamide to sodium methacrylate in the shell is (1:1)-(4:1).

Claims

1. A pH-responsive magnetic nano-chemical oil displacement agent, characterized in that, The product contains intelligent microspheres, which include: a core formed by nano-SiO2 and dodecyl phosphate monoester clusters, polyacrylamide and Fe3O4 nanoparticles sequentially attached to the surface of the core, and a shell formed by cross-linking sodium methacrylate.

2. The pH-responsive magnetic nano-chemical oil displacement agent according to claim 1, characterized in that, The smart microspheres are suspended in a 2.0%-2.1% sodium hydroxide aqueous solution.

3. The pH-responsive magnetic nano-chemical oil displacement agent according to claim 1, characterized in that, Sodium methacrylate is crosslinked using N,N′-methylenebisacrylamide as the crosslinking agent.

4. The pH-responsive magnetic nano-chemical oil displacement agent according to claim 3, characterized in that, In the intelligent microsphere, the mass ratio of the core, polyacrylamide, Fe3O4 nanoparticles, and shell is 3-9:0.4-2.0:0.5-2.5:0.5-1.

8.

5. The pH-responsive magnetic nano-chemical oil displacement agent according to claim 4, characterized in that, In the intelligent microsphere, the mass ratio of the core, polyacrylamide, Fe3O4 nanoparticles, and shell is 5.6-9:0.5-2.0:0.6-2.5:0.5-1.

8.

6. The pH-responsive magnetic nano-chemical oil displacement agent according to claim 5, characterized in that, In the core, the mass ratio of dodecyl phosphate monoester to nano-SiO2 is (1:2)-(2:1).

7. The pH-responsive magnetic nano-chemical oil displacement agent according to claim 5, characterized in that, In the outer shell, the mass ratio of N,N′-methylenebisacrylamide to sodium methacrylate is (1:1)-(4:1).

8. A method for preparing pH-responsive magnetic nano-chemical oil displacement agents, characterized in that, include: (1) Add dodecyl phosphate monoester and nano SiO2 to sodium hydroxide aqueous solution and stir. The nano SiO2 and dodecyl phosphate monoester clusters form microspheres. (2) Add polyacrylamide and stir to allow the polyacrylamide to adhere to the surface of the microspheres formed in step (1); (3) Add Fe3O4 nanoparticles and stir. The Fe3O4 nanoparticles are further attached to the surface of the microspheres. (4) Add N,N′-methylenebisacrylamide, mix thoroughly, then add sodium methacrylate and stir to obtain a pH-responsive magnetic nano-chemical oil displacement agent.

9. The method according to claim 8, characterized in that, The mass ratio of dodecyl phosphate monoester, nano-SiO2, polyacrylamide, Fe3O4 nanoparticles, N,N′-methylenebisacrylamide and sodium methacrylate is 1.0-4.0: 2.0-5.0: 0.4-2.0: 0.5-2.5: 0.3-1.2: 0.2-1.

0.

10. An oilfield development process, characterized in that, Use the pH-responsive magnetic nanochemical oil displacement agent according to any one of claims 1-7.