An intelligent nano-osmotic oil displacement agent based on natural macromolecules and a preparation method thereof

Abstract

The application discloses a kind of intelligent nano imbibition oil displacement agent based on natural macromolecule, including core and shell, core is composed of modified multifunctional natural macromolecule nanoparticle and ultra-low interfacial tension surfactant, shell is formed by interpenetrating crosslinking of soluble natural macromolecule and polyacrylamide.The starch-PAM interpenetrating network shell is outside, the modified starch core (size is about 100nm) and ultra-low interfacial tension surfactant are inside, and the nanoscale size makes the product be able to be uniformly dispersed in water without precipitation, the modified starch core has obvious temperature response, smaller size is conducive to the particle more easily enter into smaller pore channel to expand swept area, and hydrophobicity is conducive to the core dispersion in crude oil, so that the crude oil adhered on the pore wall is stripped, and is more easily displaced.

Description

Technical Field

[0001] This invention relates to the field of nano-permeation displacement agent technology, specifically to a smart nano-permeation displacement agent based on natural polymers and its preparation method. Background Technology

[0002] In recent years, people's understanding of oil reservoirs has evolved from trapped reservoirs to continuous reservoirs, which are rock formations with a network of interconnected micron- or even nano-sized pores. These pores serve as both oil and gas migration channels and storage spaces, and have high exploitation value. As a result, nano-enhanced oil recovery has gradually become a hot topic in recent years.

[0003] Most existing nano-displacement oil displacement agents consist of a combination of surfactants and inorganic nanomaterials. The mechanism of action involves the surfactants promoting the entry of inorganic nanomaterials into the pores. The nanomaterials then ① adsorb onto the oil-water interface, improving emulsion stability; ② adsorb onto the rock surface, altering its wettability; and ③ accumulate in large pores, forming a sealing effect, thereby enhancing the energy supply to oil-bearing formations. Compared to traditional surfactant-based oil displacement agents, nano-permeability oil displacement agents have a more advanced mechanism of action and are more suitable for low-permeability reservoirs, showing great development potential.

[0004] However, the surfactants in nano-displacement agents are easily depleted and their performance is affected by external environmental factors such as temperature, pH and salinity, resulting in problems such as ① reduced emulsion stability, ② weakened ability of nanomaterials to enter pores, and ③ premature accumulation of nanomaterials in the near-wellbore zone, leading to blockage. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the aforementioned background technology by providing a smart nano-absorption oil displacement agent based on natural polymers that provides oil displacement efficiency, as well as its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A smart nano-absorption oil displacement agent based on natural polymers includes a core and a shell. The core is composed of modified multifunctional natural polymer nanoparticles and an ultra-low interfacial tension surfactant, while the shell is formed by interpenetrating crosslinking of soluble natural polymers and polyacrylamide.

[0007] The present invention also provides a method for preparing the above-mentioned nano-permeation displacement agent, comprising the following steps: a. Choose natural polymers as the base material; b. Modify the substrate material; make the natural polymer amphiphilic by grafting hydrophilic and hydrophobic groups; c. Select small molecule surfactants with ultra-low interfacial tension; d. A core-shell structured nano-permeation displacement agent product was prepared by W / O / W emulsion polymerization.

[0008] Compared with the prior art, the beneficial effects of the present invention are: The invention consists of an outer starch-PAM interpenetrating network shell and an inner modified starch core (approximately 100 nm in size) and an ultra-low interfacial tension surfactant. The nanoscale size allows the product to be uniformly dispersed in water without precipitation. The modified starch core exhibits significant temperature responsiveness, and its smaller size facilitates the entry of particles into smaller pores, thereby expanding the sweep area. Furthermore, its hydrophobicity helps the core disperse in crude oil, causing the crude oil adhering to the pore walls to peel off and be more easily displaced. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a schematic diagram of the structure (a) and mechanism of action (b) of the intelligent nano-permeation oil displacement agent of the present invention; Figure 2 This is a schematic diagram of the starch-PAM shell (a), core-shell structure (b), modified starch core (c), and temperature sensitivity of the starch core (d) of the product of this invention. Figure 3 This describes the variation of the water dispersibility of the product of this invention with concentration. Figure 4 This invention provides a starch core-stabilized oil-in-water emulsion. Figure 5 The surface and interfacial tension of the core in this invention varies with concentration; Figure 6 This represents the change in percolation recovery rate before and after drug application. Detailed Implementation

[0010] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0011] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0012] Secondly, the present invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0013] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0014] A smart nano-absorption oil displacement agent based on natural polymers includes a core and a shell. The core is composed of modified multifunctional natural polymer nanoparticles and an ultra-low interfacial tension surfactant, while the shell is formed by interpenetrating crosslinking of soluble natural polymers and polyacrylamide.

[0015] Its structure is as follows Figure 1 As shown in (a), its outer shell is an interpenetrating cross-linked structure of soluble natural polymers and polyacrylamide, which functions to regulate the release of internal oil displacement agents, prolong the effective action time, increase the viscosity of the aqueous phase, improve the oil-water flow rate ratio, and expand the sweep range. Its core is composed of amphiphilic multifunctional modified natural polymer particles and ultra-low interfacial tension surfactants, which function to stabilize the oil-water interface to form microemulsions, reduce the oil-water interfacial tension, improve crude oil fluidity, and respond positively to environmental changes, including changing size and hydrophilicity / hydrophobicity to improve oil displacement efficiency.

[0016] Its mechanism of action is as follows Figure 1 As shown in (b), when the nano-oil displacement agent is injected into the formation with water flow, the soluble natural polymer shell begins to slowly dissolve, and the internal oil displacement polymer is released.

[0017] A method for preparing a smart nano-absorption oil displacement agent based on natural polymers includes the following steps: a. Choose natural polymers as the base material; natural polymers such as starch and cellulose are chosen as base materials because they are abundant, widely available, and inexpensive to obtain; their molecular chains contain a large number of hydroxyl groups, making them easy to modify; they have strong hydrophilicity, which can act as a thickener for the aqueous phase; in addition, they are non-toxic, harmless, and environmentally friendly, making them a high-quality base material. b. Modify the substrate material; by grafting hydrophilic and hydrophobic groups, natural polymers acquire amphiphilicity, enabling them to adsorb at the oil-water interface, reduce the interfacial tension, and form different types of emulsions. Compared to small molecule surfactants, natural polymers have a larger specific surface area and greater adsorption energy at the oil-water interface, resulting in more stable emulsions. Furthermore, by grafting functional groups, environmental responsiveness (including temperature, pH, and magnetism) can be achieved. In addition, some oil reservoirs have high temperature and high salt characteristics; by grafting temperature- and salt-resistant groups, the product can maintain long-term effectiveness in harsh environments. c. Select small molecule surfactants with ultra-low interfacial tension; to facilitate the diffusion of nanoparticles into the pores. d. A core-shell structured nano-permeation displacement agent product is prepared by W / O / W emulsion polymerization. Most nano-displacement agents cannot achieve intelligent displacement regulation. After injection into the formation, they exhibit a gradient concentration distribution, with high concentration near the wellbore and low concentration far from the wellbore. This results in some agent being wasted near the wellbore and premature blockage, increasing injection resistance, while insufficient agent dosage leads to low oil displacement efficiency far from the wellbore. The soluble shell can effectively reduce the accumulation of oil displacement agent near the wellbore and carry more agent to the far well, thereby expanding the sweep range and improving displacement efficiency.

[0018] Specifically, the preparation examples are as follows: 1. Preparation of modified starch ester Modified starch esters were prepared using a one-pot method. Acid-hydrolyzed waxy corn starch was dispersed in a mixture of dimethylformamide and pyridine (volume ratio 2:1), activated for 1 h in a 75 °C water bath with stirring, then a certain amount of PNIPAM was added, and the reaction was carried out for 2 h. The temperature was then lowered to 40 °C, and long-chain acyl chlorides were added. The temperature was then raised to 75 °C, and the reaction was carried out for 2 h to obtain a mixture containing composite starch esters.

[0019] 2. Preparation of W / O emulsion A W / O emulsion was formed by mixing starch composite ester mixture as the aqueous phase and cyclohexane and oil-soluble initiator as the oil phase at a volume ratio of 5:5 and stirring at high speed.

[0020] 3. Preparation of W / O / W emulsions A certain amount of Fe3O4 was added to a mixed dispersion of soluble amylose, ethanol, and water under stirring. Due to electrostatic adsorption, the starch and Fe3O4 formed a complex. Acrylamide monomer, a crosslinking agent, and an O / W emulsifier were then added to the dispersion. This mixture was used as the outer phase of a multiphase emulsion, and the W / O emulsion as the inner phase. Through high-speed stirring, a W / O / W multiphase emulsion was finally formed.

[0021] 4. Preparation of core-shell structured oil displacement agent particles by W / O / W emulsion emulsion polymerization The polymerization was carried out under a nitrogen atmosphere and with condensate, at a reaction temperature of 65°C, and with stirring for 4 hours. The final product was a dispersion of oil displacement agent particles with a core-shell structure.

[0022] Experimental results 1. Core-shell structure and temperature resistance of the product The penetrant particles have a distinct core-shell structure (such as...) Figure 2 (b) shows an external starch-PAM interpenetrating network shell with an average size of 507 nm, and an internal modified starch core (approximately 100 nm in size) and an ultra-low interfacial tension surfactant. The nanoscale size allows the product to be uniformly dispersed in water without precipitation, such as... Figure 3 As shown. The thermosensitive properties of the modified starch core are demonstrated by testing the particle size change at different temperatures, such as... Figure 2 As shown in (d), the modified starch core exhibits a significant temperature response. At room temperature, the particle size of the modified starch core is approximately 130 nm, slightly higher than the value obtained from the electron microscopy images. This is because the PNIPAM chains in the particles are in a relaxed state at this temperature, making the particles relatively hydrophilic and exhibiting slight swelling when dispersed in water. At 30-35℃, the size decreases sharply to about 50 nm, indicating that the modified starch core undergoes an inversion within this temperature range. The PNIPAM chains begin to fold as the temperature increases, and the modified starch core changes from hydrophilic to hydrophobic. This change is advantageous, as the smaller size allows the particles to more easily enter smaller pores, thereby increasing the sweep area. The hydrophobicity, on the other hand, facilitates the dispersion of the core in crude oil, causing the crude oil adhering to the pore walls to peel off and be more easily displaced.

[0023] 2. Product water dispersibility The figure shows the condition of aqueous dispersions of the product at different concentrations after one week of storage, with no precipitation occurring. This indicates that the product has good water dispersibility, which is beneficial for the product to enter micro- and nano-sized pores.

[0024] 3. Relevant performance tests of the product core A. Emulsifying properties of starch nuclei After adding a certain amount of modified starch core, a stable W / O emulsion was formed. This indicates that the starch core has acquired amphiphilic properties through chemical grafting and can be adsorbed at the oil-water interface to form an emulsion, which is beneficial to the formation of the next W / O / W emulsion.

[0025] B. Interfacial tension of the nucleus Adding surfactants with ultra-low interfacial tension facilitates the entry of oil-displacing particles into the pores. The table below shows the interfacial tension test results for the core:

[0026] The addition of surfactants gives the core a good ability to reduce interfacial tension.

[0027] C. Temperature resistance of the nucleus The temperature resistance of the core was observed by testing the contact angle and interfacial tension of the core at different aging temperatures and times. The results are shown in the table below:

[0028] The core exhibits good temperature resistance; even at an aging temperature of 150°C for 10 days, the contact angle and interfacial tension did not change significantly, indicating that the core has good stability.

[0029] D. Salt tolerance of the nucleus The salt tolerance of the core was tested, and the results showed that the core has good salt tolerance. Even with a mineralization of up to 100,000 mg / L, the interfacial tension did not change significantly.

[0030]

[0031] 4. Extractive oil recovery rate The displacement ability of the product was understood by testing the change in harvest rate before and after pesticide application using displacement experiments. The results are as follows: Figure 6 As shown, after adding 0.3% of the product, the displacement efficiency increased from the original 15% to 32%, indicating that the product has a good oil displacement effect.

[0032] Although the present invention has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, as long as there is no structural conflict, the features in the disclosed embodiments can be combined with each other in any manner. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A smart nano-absorption oil displacement agent based on natural polymers, characterized in that, It includes a core and a shell. The core is composed of modified multifunctional natural polymer nanoparticles and an ultra-low interfacial tension surfactant, and the shell is composed of soluble natural polymers and polyacrylamide interpenetrating crosslinked together.

2. A method for preparing a smart nano-absorption oil displacement agent based on natural polymers, characterized in that, Includes the following steps, Choose natural polymers as the base material; Modify the substrate material; make the natural polymer amphiphilic by grafting hydrophilic and hydrophobic groups; Select small molecule surfactants with ultra-low interfacial tension; A core-shell structured nano-permeation displacement agent product was prepared by W / O / W emulsion polymerization.

3. The intelligent nano-absorption oil displacement agent based on natural polymers according to claim 2, characterized in that, The natural polymer material is corn starch, and the ultra-low interfacial tension small molecule surfactant is a mixture of dimethylformamide and pyridine, mixed at a volume ratio of 2:

1. The hydrophilic and hydrophobic groups are N-isopropylacrylamide (PNIPAM) and long-chain acyl chloride (PA).

4. The preparation method of the intelligent nano-absorption oil displacement agent based on natural polymers according to claim 3, characterized in that, A W / O emulsion was formed by mixing starch composite ester mixture as the aqueous phase and cyclohexane and oil-soluble initiator as the oil phase at a volume ratio of 5:5 and stirring at high speed.

5. The preparation method of a smart nano-absorption oil displacement agent based on natural polymers according to claim 4, characterized in that, A certain amount of Fe3O4 was added to a mixed dispersion of soluble amylose, ethanol, and water under stirring conditions. Due to electrostatic adsorption, starch and Fe3O4 formed a complex. Acrylamide monomer, crosslinking agent, and O / W type emulsifier were then added to the dispersion. This mixture was used as the outer phase of a multiphase emulsion, and the W / O emulsion was used as the inner phase. Through high-speed stirring, a W / O / W multiphase emulsion was finally formed.

6. The preparation method of a smart nano-absorption oil displacement agent based on natural polymers according to claim 5, characterized in that, W / O / W multiphase emulsion polymerization was carried out under a nitrogen atmosphere and with condensate, with the reaction temperature set at 65°C and the stirring time at 4 hours. The final product was a dispersion of oil displacement agent particles with a core-shell structure.

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