A method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation, the organic-inorganic composite drilling fluid plugging agent and its application.

Abstract

This invention provides a method for preparing an organic-inorganic composite drilling fluid plugging agent based on phase separation control, the organic-inorganic composite drilling fluid plugging agent, and its application, belonging to the technical field of drilling fluid treatment agents. The method includes the following steps: modifying nano-silica with a silane coupling agent to obtain surface-modified nano-silica; adding an emulsifier, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and a protective agent to water, adjusting the pH to 6.8-7.5, adding the surface-modified nano-silica, and pre-dispersing by ultrasonic and mechanical stirring to obtain an aqueous phase; mixing styrene, an interface-stabilizing monomer, and a crosslinking agent divinylbenzene to obtain an oil phase; adding the obtained oil phase dropwise to the obtained aqueous phase to form an O / W type emulsion; adding an initiator to the obtained emulsion to carry out the reaction, and obtaining the plugging agent. The plugging agent of this invention can maintain a good dispersion state and inhibit particle agglomeration, exhibiting excellent plugging ability.

Description

Technical Field

[0001] This invention relates to a method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation, the organic-inorganic composite drilling fluid plugging agent and its application, belonging to the field of drilling fluid treatment agent technology. Background Technology

[0002] During the drilling and completion of oil and gas wells, microfractures and nano- and micron-sized pores in the formation around the wellbore can easily lead to the intrusion of drilling fluid filtrate, causing wellbore instability. To reduce filtrate loss, plugging agents are often added to water-based drilling fluids. Existing plugging agent material systems include inorganic particles, organic solids, polymers, and nanocomposite materials.

[0003] In recent years, combining nanoparticles with polymers to achieve both rigid support and flexible adaptation has become a research hotspot. For example, Chinese patent document CN120988215A discloses a method for combining nanoparticles with polymers. Yan Zhu (Master's thesis, Southwest Petroleum University, 2016) further studied the preparation of silica nanoparticles modified with hydrophilic polymers (such as polyacrylamide and polyAMPS), obtaining hybrid particles with certain dispersion stability. However, under high temperature (>150℃) and high mineralization conditions such as deep wells and ultra-deep wells, the structural stability of nanoparticles still faces challenges when relying solely on the grafting or coating of linear polymer chains on the surface of nanoparticles: polymer chains are prone to segment movement or degradation at high temperatures, resulting in incomplete coating layers, re-exposure and aggregation of nanoparticles, and a decrease in the density of the sealing layer.

[0004] To enhance structural rigidity, existing technologies have attempted to introduce rigid monomers or crosslinking agents into the system. However, these technologies often involve core-shell coating of inorganic cores / organic shells or simple blending after polymerization. Under high-temperature aging conditions above 150°C and high-shear conditions, traditional core-shell structures are prone to shell rupture, interfacial peeling, or particle re-agglomeration due to the significant differences in thermal expansion and mechanical response between the inorganic and organic phases. This results in a loose sealing layer and increased filtration loss.

[0005] Therefore, the urgent problem to be solved is to achieve controllable spatial reconstruction of the organic and inorganic phases during polymerization, constructing a stable heterogeneous composite structure that differs from traditional core-shell coating and simple blending systems. Specifically, it is necessary to induce controlled phase separation and interfacial rearrangement between the organic and inorganic phases through the coordinated control of the initial dispersion state of the inorganic phase, the introduction rhythm of hydrophobic monomers, and the timing of polymerization / crosslinking fixation. This results in structural units that combine rigid support with flexible adaptation, solving the problems of easy interfacial peeling, particle agglomeration, and loose sealing layer in traditional systems after high-temperature aging. To this end, this invention is proposed. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing organic-inorganic composite drilling fluid plugging agents based on phase separation regulation, the organic-inorganic composite drilling fluid plugging agent itself, and its applications. The core inventiveness of this invention lies in the synergistic regulation of the phase separation path using specific pre-dispersion, rate-limited dripping, and in-situ polymerization steps. This constructs a stable heterogeneous composite structure that differs from traditional core-shell coating, simple physical mixing, and pre-emulsification followed by inorganic phase addition routes. In this heterogeneous composite structure, the inorganic reinforcing phase is stably distributed as discrete reinforcing units within the organic polymer network and / or at the interface. Even after aging at 150°C, it maintains good dispersion and inhibits particle agglomeration, thereby enhancing the material's ability to plug microcracks and micro / nano-scale pore throats.

[0007] The technical solution of the present invention is as follows: A method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation includes the following steps: (1) Surface-modified nano-silica was obtained by modifying nano-silica with silane coupling agent; (2) Add the emulsifier to the water and stir evenly. Then add acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone and protective agent to obtain a mixture. Adjust the pH of the mixture to 6.8-7.5 and add the surface-modified nano silica obtained in step (1). Then pre-disperse the mixture by ultrasonic and mechanical stirring to make the surface-modified nano silica form a stable initial dispersion state in the water to obtain an aqueous phase. (3) Styrene, interfacial stabilizing monomer and crosslinking agent divinylbenzene are mixed to obtain an oil phase; under nitrogen protection and stirring conditions, the obtained oil phase is added dropwise to the aqueous phase obtained in step (2) to form an O / W type emulsion; (4) Under nitrogen protection and stirring conditions, an initiator is added to the O / W type emulsion obtained in step (3) to carry out the reaction; after the reaction is completed, the reaction is terminated, centrifuged, washed and dried to obtain an organic-inorganic composite drilling fluid plugging agent.

[0008] According to a preferred embodiment of the present invention, the silane coupling agent in step (1) is γ-methacryloyloxypropyltrimethoxysilane (KH570); the particle size of the nano silica is 20-50 nm; and the mass ratio of the silane coupling agent to the nano silica is 0.2-0.3:1.

[0009] According to a preferred embodiment of the present invention, the surface-modified nano-silica in step (1) is prepared by the following method: nano-silica is added to ethanol and ultrasonically dispersed to form a uniform suspension; a silane coupling agent is added to the suspension, the pH of the system is adjusted to 4-5, and the reaction is carried out; after the reaction is completed, the surface-modified nano-silica is obtained by centrifugation, washing, and drying.

[0010] Preferably, in the preparation of surface-modified nano-silica, the volume ratio of ethanol to the mass ratio of nano-silica is 40-60 mL: 1 g.

[0011] Preferably, in the preparation of surface-modified nano-silica, the pH of the system is adjusted to 4-5 using glacial acetic acid or an aqueous solution of 0.1 mol / L HCl.

[0012] Preferably, in the preparation of surface-modified nano-silica, the reaction temperature is 65-75℃ and the reaction time is 2-4h.

[0013] Preferably, in the preparation of surface-modified nano-silica, the washing is performed by washing with ethanol 2-4 times, and the drying is performed by vacuum drying at 50-60°C for 10-15 hours.

[0014] According to a preferred embodiment of the present invention, the emulsifier in step (2) is an anionic surfactant and / or a nonionic surfactant; more preferably, the emulsifier is one or a combination of two or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, Tween 80, OP-10, and fatty alcohol polyoxyethylene ether; the mass ratio of the emulsifier to acrylamide is 0.1-2:2-4.

[0015] According to a preferred embodiment of the present invention, the mass ratio of acrylamide to 2-acrylamido-2-methylpropanesulfonic acid in step (2) is 2-4:1-3.

[0016] According to a preferred embodiment of the present invention, the mass ratio of N-vinylpyrrolidone to acrylamide in step (2) is 0.1-0.3:1.

[0017] According to a preferred embodiment of the present invention, the protective agent in step (2) is polyvinyl alcohol and / or polyvinylpyrrolidone, and the mass ratio of the protective agent to acrylamide is 0.05-0.5:2-4; more preferably, the number average molecular weight M of the polyvinyl alcohol is... n The value is 30,000-70,000; the polyvinylpyrrolidone is PVP K30 or PVP K60.

[0018] According to a preferred embodiment of the present invention, in step (2), the pH is adjusted to 6.8-7.5 using a NaOH aqueous solution with a concentration of 0.1 mol / L.

[0019] According to a preferred embodiment of the present invention, the mass ratio of acrylamide to surface-modified nano-silica in step (2) is 2-4:1-2; more preferably 3-3.5:1.5-1.8.

[0020] According to a preferred embodiment of the present invention, the total mass concentration of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, protective agent, emulsifier and surface-modified nano silica in the aqueous phase in step (2) is 1-5 wt%.

[0021] According to a preferred embodiment of the present invention, the ultrasonic power in step (2) is 200-400W and the ultrasonic time is 10-20min; the mechanical stirring speed is 600-1000r / min and the mechanical stirring time is 20-40min.

[0022] According to a preferred embodiment of the present invention, the mass ratio of styrene to surface-modified nano-silica in step (3) is 10-20:1-2.5; more preferably 15-18:1.5-1.8.

[0023] According to a preferred embodiment of the present invention, the interfacial stabilizing monomer in step (3) is hydroxyethyl methacrylate and / or glycidyl methacrylate, and the mass ratio of the interfacial stabilizing monomer to styrene is 0.05-0.15:1. The interfacial stabilizing monomer of the present invention contains unsaturated double bonds that can participate in free radical polymerization and contains polar functional groups such as hydroxyl and epoxy groups. During the polymerization process, the interfacial stabilizing monomer can participate in the copolymerization reaction of styrene, divinylbenzene and hydrophilic monomers. At the same time, it can improve the interfacial compatibility between hydrophilic polymerization segments, hydrophobic polymerization segments and surface-modified nano silica through polar interaction, hydrogen bonding or interfacial entanglement, thereby helping to improve the stability of the organic-inorganic composite interface during emulsion polymerization.

[0024] According to a preferred embodiment of the present invention, the mass of the crosslinking agent divinylbenzene in step (3) is 3-8% of the mass of styrene.

[0025] According to a preferred embodiment of the present invention, the stirring speed in step (3) is 8000-15000 rpm; the droplet acceleration rate of the oil phase is 0.5-2.0 mL / min; under high-speed stirring conditions, a stable O / W type emulsion is formed, wherein the droplet size in the O / W type emulsion is controlled at 40-200 nm.

[0026] According to a preferred embodiment of the present invention, the initiator in step (4) is a redox initiator, the oxidant is ammonium persulfate, the reductant is sodium bisulfite, and the mass ratio of oxidant to reductant in the redox initiator is 1:1; the mass of the initiator is 1-2% of the total mass of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, styrene, interfacial stabilizing monomer and crosslinking agent divinylbenzene; the initiator is added dropwise to the system in the form of an initiator aqueous solution at a dropping rate of 0.3-1.0 mL / min, and the concentration of the initiator aqueous solution is 0.01-0.05 g / mL.

[0027] According to a preferred embodiment of the present invention, the initiator in step (4) is added to the system under stirring conditions at a temperature of 55-70°C and a rotation speed of 600-900 rpm.

[0028] According to a preferred embodiment of the present invention, the reaction temperature in step (4) is 55-70°C, the reaction time is 4-6 hours, and the stirring speed during the reaction is 600-900 rpm.

[0029] According to a preferred embodiment of the present invention, the termination step in step (4) is: adding a terminator to the obtained reaction solution to terminate the polymerization reaction, wherein the terminator is hydroquinone, and the amount of the terminator added is 0.05-0.3% of the total mass of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, styrene, interfacial stabilizing monomer and crosslinking agent divinylbenzene.

[0030] According to a preferred embodiment of the present invention, the washing in step (4) is washing with deionized water 2-4 times, and the drying is vacuum drying at 50-60°C for 12-24 hours.

[0031] This invention provides an organic-inorganic composite drilling fluid plugging agent, which is prepared by the above method.

[0032] According to the present invention, the above-mentioned organic-inorganic composite drilling fluid plugging agent is used in water-based drilling fluids, wherein the mass fraction of the organic-inorganic composite drilling fluid plugging agent in the water-based drilling fluid is 0.5-2.0%.

[0033] The pre-dispersion in step (2), the rate-limited drop addition in step (3), and the in-situ polymerization / crosslinking fixation in step (4) of this invention are carried out in sequence, which together are used to induce and lock the controlled phase separation process of the organic phase and the inorganic phase, thereby constructing a stable heterogeneous composite structure. Although the steps are presented in the form of process, their technical contribution is actually reflected in the final structural innovation, that is, the designable construction of the spatial distribution state of the organic / inorganic phase is achieved through phase separation control, rather than simply the optimization of operating conditions.

[0034] In this invention, "phase separation" is not simply a system instability phenomenon, but a controlled spatial differentiation and interface reconstruction process driven by the differences in polarity, interfacial energy, and polymerization rate between the hydrophilic polymerizing component, the hydrophobic crosslinking component, and the surface-modified nano-silica during emulsion polymerization and crosslinking fixation. This process forms a heterogeneous reinforced structure. Specifically, the nano-silica modified with a silane coupling agent serves as an inorganic reinforcing phase, which is embedded, anchored, or enriched in the organic polymer network and interfacial region formed by copolymerization of acrylamide / AMPS / styrene / divinylbenzene, etc., in the form of discrete reinforcing units. It also forms a stable interfacial connection through polymerizable groups on the surface participating in polymerization or interfacial entanglement. This structure is different from the complete core-shell encapsulation structure with silica as the core and polymer as the shell, and also different from the random agglomeration structure formed by dry powder post-mixing. Traditional core-shell structures typically feature inorganic particles as the core, with a polymer forming a relatively continuous coating layer on its outer surface. In contrast, in this invention, surface-modified nano-silica is embedded, anchored, or enriched within the organic polymer network and interfacial regions as discrete reinforcing units. The two are connected through polymerization by polymerizable groups, interfacial entanglement, or polar interactions, forming a stable interfacial connection. Therefore, the structure obtained in this invention is a stable heterogeneous composite structure formed through phase separation control, rather than a core-shell particle with a single inorganic core and a continuous organic shell.

[0035] Furthermore, the pre-dispersion in step (2), the rate-limited droplet addition and droplet size control in step (3), and the in-situ polymerization / crosslinking fixation in step (4) are not independent of each other, but jointly determine the final spatial structure and interface configuration of the composite particles. Among them, pre-dispersion determines the initial distribution basis of the inorganic reinforcing phase, rate-limited droplet addition determines the local enrichment of the hydrophobic phase and the interface migration path, and in-situ polymerization / crosslinking fixation locks the heterogeneous composite structure formed during the phase separation evolution process. The synergistic effect of the three results in the construction of a stable heterogeneous composite structure that is different from the existing core-shell coating and simple post-mixing methods. This is the fundamental reason why the plugging agent of the present invention achieves excellent high-temperature plugging performance. Therefore, the way the process steps are described in the present invention is only the implementation path. Its inventive point should be attributed to the special structure constructed by this path and its high-temperature stable dispersion characteristics.

[0036] The technical features and beneficial effects of this invention are as follows:

[0037] 1. This invention enhances the interfacial compatibility and bonding stability between the inorganic reinforcing phase and the organic component by surface modification of nano-silica. The invention employs a silane coupling agent with polymerizable groups to modify the surface of nano-silica, introducing unsaturated groups capable of participating in polymerization reactions onto the surface of the inorganic particles. This improves the compatibility between the inorganic and organic phases, reduces the tendency of nanoparticles to aggregate in the system, and provides a foundation for the inorganic reinforcing phase to participate in phase separation and reconstruction, forming stable interfacial connections and heterogeneous composite structures.

[0038] 2. This invention, through continuous control of "pre-dispersion-rate-limited dropping-in-situ polymerization / crosslinking fixation," can induce controlled phase separation between the organic and inorganic phases, and further construct a stable heterogeneous composite structure that differs from random aggregation, simple post-mixing, and mere surface coating. The core contribution of this invention lies in the structural innovation itself: the inorganic reinforcing phase no longer exists merely as a filler, but is embedded in the organic network as a structural support node and interface reinforcement unit, thereby significantly improving the compactness, structural stability, and high-temperature pressure resistance of the sealing layer.

[0039] 3. This invention, through in-situ polymerization and cross-linking fixation, can promptly lock in the organic-inorganic heterogeneous structure formed during phase separation, preventing interface detachment, particle re-agglomeration, or structural collapse during subsequent aging. TEM comparison before and after aging further illustrates that the obtained product maintains a good discrete distribution state after aging at 150℃ / 16h, without obvious large-scale agglomeration, indicating that this special structure can ensure that the material remains dispersed and is not prone to agglomeration under high-temperature conditions.

[0040] 4. The plugging agent obtained by this invention combines the flexible adaptability of the organic phase with the rigid support of the inorganic phase, thus meeting the multi-scale plugging requirements under complex pore structure conditions. Through the synergistic design of acrylamide, AMPS, styrene, divinylbenzene, and surface-modified nano-silica, this invention enables the resulting plugging agent to not only improve the compactness and stability of the plugging layer but also adapt to complex reservoir channel conditions such as microfractures, micron-sized pores, and nano-sized pore throats, making it suitable for high-temperature water-based drilling fluid plugging applications.

[0041] 5. This invention, by introducing a protective agent and an interface-stabilizing monomer, synergistically ensures the efficient construction and ultimate stability of a special heterogeneous composite structure. During the pre-dispersion and polymerization processes, the protective agent adsorbs at the interface, effectively preventing the unstable aggregation of droplets during controlled phase separation and providing steric protection for the dispersion of the inorganic reinforcing phase. Meanwhile, the interface-stabilizing monomer, possessing both polar groups and polymerizable double bonds, acts as a "molecular bridge" between the hydrophilic polymeric segments, the hydrophobic oil phase, and the modified silica. This not only strengthens the polar interactions and interfacial entanglement between the inorganic phase and the organic polymer network but also firmly locks in the favorable interfacial configuration formed during phase separation, thereby completely overcoming the defect of traditional composite materials being prone to interfacial delamination under high-temperature shear.

[0042] 6. The product obtained by this invention is in powder form, which is convenient for storage, transportation, and on-site use, and has good application convenience. After the polymerization reaction is completed, the powdered composite plugging agent is obtained through termination, centrifugation, washing, and drying. This product form is beneficial for on-site management and engineering applications, and can be directly added to water-based drilling fluid systems, facilitating widespread use.

[0043] 7. While achieving the construction of stable heterogeneous composite structures, this invention adopts an aqueous system and a free radical polymerization route. The key conditions are clearly defined and have good repeatability. While ensuring the controllable formation of the structure, it also takes into account the needs of laboratory implementation, subsequent scale-up production and field application. Attached Figure Description

[0044] Figure 1 The infrared spectrum of the organic-inorganic composite drilling fluid plugging agent and nano-silica prepared in Example 1.

[0045] Figure 2 A photograph of the organic-inorganic composite drilling fluid plugging agent prepared in Example 1.

[0046] Figure 3 The images show the TEM morphology of the organic-inorganic composite drilling fluid plugging agent prepared in Example 1 before aging at different scales, with the magnification decreasing sequentially from (a) to (d).

[0047] Figure 4 The images show the TEM morphology of the organic-inorganic composite drilling fluid plugging agent prepared in Example 1 after aging at different scales, with the magnification decreasing sequentially from (a) to (d).

[0048] Figure 5 Electronic image (a) and EDS composite color distribution map (b) of the organic-inorganic composite drilling fluid plugging agent prepared in Example 1.

[0049] Figure 6 The elemental distribution of Si, O, S, and Na in the organic-inorganic composite drilling fluid plugging agent prepared in Example 1 is shown in the diagram.

[0050] Figure 7 The image shows the EDS spectrum of the organic-inorganic composite drilling fluid plugging agent prepared in Example 1. Detailed Implementation

[0051] The following embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Experimental conditions and operating methods not described in detail in the embodiments can all be implemented using conventional techniques in the art.

[0052] Unless otherwise specified, the experimental methods described in the examples are conventional methods; the reagents and materials used are commercially available unless otherwise specified.

[0053] Example 1 A method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation includes the following steps:

[0054] (1) 2.00 g of nano silica (particle size 30-40 nm) was added to 100 mL of ethanol and ultrasonically dispersed for 20 min under ultrasonic power of 250 W to form a uniform suspension. 0.50 g of γ-methacryloyloxypropyltrimethoxysilane (KH570) was added to the system and the pH was adjusted to 4.5 with glacial acetic acid. The mixture was stirred at 70 °C for 3 h. After the reaction was completed, the mixture was centrifuged and the precipitate was washed three times with ethanol. The washed precipitate was then vacuum dried at 60 °C for 12 h to obtain surface-modified nano silica.

[0055] (2) Add 300 mL of deionized water to a four-necked flask, add 0.30 g of sodium dodecyl sulfate (SDS), stir well, and then add 3.00 g of acrylamide, 2.00 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.60 g of N-vinylpyrrolidone and 0.30 g of polyvinyl alcohol (number average molecular weight M) as a protective agent. n The solution was stirred at a stirring rate of 600 r / min until completely dissolved (50000). The pH of the system was adjusted to 7.0 using a 0.1 mol / L NaOH aqueous solution, and nitrogen gas was introduced for 15 min to remove dissolved oxygen from the system.

[0056] (3) Add 1.5g of surface-modified nano silica obtained in step (1) to the system obtained in step (2), and ultrasonically disperse it for 15min under the conditions of ultrasonic power of 300W and frequency of 25kHz. Then, continue stirring for 30min under the condition of mechanical stirring rate of 800r / min to make the inorganic nanoparticles uniformly dispersed in the system and obtain an aqueous phase.

[0057] (4) Mix 15.00g styrene, 1.5g hydroxyethyl methacrylate, and 0.75g divinylbenzene evenly as the oil phase. Under high-speed stirring (12000rpm), slowly add the oil phase to the aqueous phase obtained in step (3) at a dropping rate of 1mL / min to form a stable O / W type emulsion.

[0058] (5) Heat the reaction system to 60°C, and under nitrogen protection and stirring at 700 r / min, add an aqueous initiator solution (prepared by dissolving 0.15 g ammonium persulfate and 0.15 g sodium bisulfite in 10 mL deionized water) at a dropping rate of 0.5 mL / min. After the addition is complete, react at 60°C and stirring at 700 r / min for 5 h.

[0059] (6) After the reaction is completed, add 0.02g hydroquinone to terminate the reaction and cool naturally to room temperature; centrifuge the reaction solution, wash the obtained precipitate with deionized water 3 times, and vacuum dry the washed precipitate at 50℃ for 18h to obtain the organic-inorganic composite drilling fluid plugging agent based on phase separation control.

[0060] Example 2 A method for preparing an organic-inorganic composite drilling fluid plugging agent based on phase separation regulation includes the following steps:

[0061] (1) Same as step (1) in Example 1.

[0062] (2) Add 300 mL of deionized water to a four-necked flask, add 0.30 g of sodium dodecyl sulfate (SDS), stir well, and then add 3.50 g of acrylamide, 2.50 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.70 g of N-vinylpyrrolidone and 0.35 g of the protective agent polyvinyl alcohol (number average molecular weight M). n The solution was stirred at a stirring rate of 600 r / min until completely dissolved (50000). The pH of the system was adjusted to 7.0 using a 0.1 mol / L NaOH aqueous solution, and nitrogen gas was introduced for 15 min to remove dissolved oxygen from the system.

[0063] (3) Add 1.8g of surface-modified nano silica obtained in step (1) to the system obtained in step (2), and ultrasonically disperse it for 15min under the conditions of ultrasonic power of 300W and frequency of 25kHz. Then, continue stirring for 30min under the condition of mechanical stirring rate of 800r / min to make the inorganic nanoparticles uniformly dispersed in the system and obtain an aqueous phase.

[0064] (4) Mix 18.00g styrene, 1.80g hydroxyethyl methacrylate, and 0.75g divinylbenzene evenly as the oil phase. Under high-speed stirring (12000rpm), slowly add the oil phase to the aqueous phase obtained in step (3) at a dropping rate of 1mL / min to form a stable O / W type emulsion.

[0065] (5) Heat the reaction system to 60°C, and under nitrogen protection and stirring at 700 r / min, add an aqueous initiator solution (prepared by dissolving 0.15 g ammonium persulfate and 0.15 g sodium bisulfite in 10 mL deionized water) at a dropping rate of 0.5 mL / min. After the addition is complete, react at 60°C and stirring at 700 r / min for 5 h.

[0066] (6) After the reaction is completed, add 0.02g hydroquinone to terminate the reaction and cool naturally to room temperature; centrifuge the reaction solution, wash the obtained precipitate with deionized water 3 times, and vacuum dry the washed precipitate at 50℃ for 18h to obtain the organic-inorganic composite drilling fluid plugging agent based on phase separation control.

[0067] Example 3 A method for preparing an organic-inorganic composite drilling fluid plugging agent based on phase separation regulation is described in Example 1, except that the protective agent in step (2) is PVP K30.

[0068] Example 4 A method for preparing an organic-inorganic composite drilling fluid plugging agent based on phase separation regulation is described in Example 1, except that the interfacial stabilizing monomer in step (4) is glycidyl methacrylate.

[0069] Comparative Example 1 A method for preparing a drilling fluid plugging agent is as described in Example 1, except that: surface-modified nano-silica is not added, that is, steps (1) and (3) are not performed, while the remaining steps and conditions remain the same.

[0070] Comparative Example 2 A method for preparing a drilling fluid plugging agent is described in Example 1, except that: in step (4), the crosslinking agent divinylbenzene is not added, while the remaining steps and conditions remain the same.

[0071] Comparative Example 3 A method for preparing a drilling fluid plugging agent is as described in Example 1, except that step (1) is omitted, and nano-silica is directly added in step (3), while the remaining steps and conditions remain the same.

[0072] Comparative Example 4 A method for preparing a drilling fluid plugging agent is described in Example 1, except that acrylamide is not added in step (2), while the remaining steps and conditions remain the same.

[0073] Comparative Example 5 A method for preparing a drilling fluid plugging agent includes the following steps:

[0074] (1) Same as step (1) in Example 1.

[0075] (2) Add 300 mL of deionized water to a four-necked flask, add 0.30 g of sodium dodecyl sulfate (SDS), stir well, and then add 3.00 g of acrylamide, 2.00 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.60 g of N-vinylpyrrolidone and 0.30 g of the protective agent polyvinyl alcohol (number average molecular weight M). nThe solution was stirred at a stirring rate of 600 r / min until completely dissolved (50000). The pH of the system was adjusted to 7.0 using a 0.1 mol / L NaOH aqueous solution, and nitrogen gas was introduced for 15 min to remove dissolved oxygen from the system, resulting in an aqueous phase.

[0076] (3) Mix 15.00g styrene, 1.50g hydroxyethyl methacrylate, and 0.75g divinylbenzene evenly as the oil phase. Under high-speed stirring (speed of 12000rpm), slowly add the oil phase to the aqueous phase obtained in step (2) at a dropping rate of 1mL / min to form an O / W type monomer emulsion.

[0077] (4) Add 1.50g of the surface-modified nano silica obtained in step (1) to the O / W type monomer emulsion obtained in step (3), and stir for 30min at a mechanical stirring rate of 800r / min to disperse the surface-modified nano silica in the formed monomer emulsion.

[0078] (5) Same as step (5) in Example 1.

[0079] (6) Same as step (6) in Example 1.

[0080] In this comparative example, acrylamide, AMPS, styrene, and divinylbenzene were first mixed to form an emulsion, and then surface-modified nano-silica was added and polymerization continued. The difference from Example 1 is that in Example 1, surface-modified nano-silica was first added to the aqueous phase and subjected to ultrasonic and mechanical pre-dispersion before being added to the oil phase; while in this comparative example, surface-modified nano-silica was added after the aqueous and oil phases formed an O / W type monomer emulsion.

[0081] Comparative Example 6 A method for preparing a drilling fluid plugging agent includes the following steps:

[0082] (1) Same as step (1) in Example 1.

[0083] (2) Add 300 mL of deionized water to a four-necked flask, add 0.30 g of sodium dodecyl sulfate (SDS), stir well, and then add 3.00 g of acrylamide, 2.00 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.60 g of N-vinylpyrrolidone and 0.30 g of polyvinyl alcohol (number average molecular weight M) as a protective agent. n The solution was stirred at a stirring rate of 600 r / min until completely dissolved (50000). The pH of the system was adjusted to 7.0 using a 0.1 mol / L NaOH aqueous solution, and nitrogen gas was introduced for 15 min to remove dissolved oxygen from the system.

[0084] (3) Add 1.50g of the surface-modified nano silica obtained in step (1) directly to the system obtained in step (2), stir for 5min under mechanical stirring at 600r / min, without ultrasonic dispersion or mechanical pre-dispersion treatment at 800r / min for 30min, to obtain the aqueous phase.

[0085] (4) Mix 15.00g styrene, 1.5g hydroxyethyl methacrylate, and 0.75g divinylbenzene evenly as the oil phase. Under high-speed stirring (12000rpm), slowly add the oil phase to the aqueous phase obtained in step (3) at a dropping rate of 1mL / min to form a stable O / W type emulsion.

[0086] (5) Same as step (5) in Example 1.

[0087] (6) Same as step (6) in Example 1.

[0088] This comparative example does not perform ultrasonic pre-dispersion of the surface-modified nano-silica. Instead, it directly mixes with the aqueous and oil phase components and then emulsifies and polymerizes. The difference from Example 1 is that in Example 1, after the surface-modified nano-silica is added to the aqueous phase, it is pre-dispersed by ultrasonication at 300W for 15 minutes and mechanical stirring at 800r / min for 30 minutes. However, this comparative example omits the pre-dispersion step and only mechanically stirs for a short time to homogenize before emulsifying and polymerizing the oil phase.

[0089] Comparative Example 7 A method for preparing a drilling fluid plugging agent includes the following steps:

[0090] (1) Same as step (1) in Example 1.

[0091] (2) Add 300 mL of deionized water to a four-necked flask, add 0.30 g of sodium dodecyl sulfate (SDS) as an emulsifier, and then add 3.00 g of acrylamide, 2.00 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.60 g of N-vinylpyrrolidone and 0.30 g of polyvinyl alcohol (number average molecular weight M) as a protective agent. n The solution was stirred at a stirring rate of 600 r / min until completely dissolved (50000). The pH of the system was adjusted to 7.0 using a 0.1 mol / L NaOH aqueous solution, and nitrogen gas was introduced for 15 min to remove dissolved oxygen from the system, resulting in an aqueous phase.

[0092] (3) Mix 15.00g styrene, 1.5g interfacial stabilizer hydroxyethyl methacrylate and 0.75g divinylbenzene evenly as the oil phase. Add the oil phase to the aqueous phase obtained in step (2) at once. Shear for 15min under high-speed stirring at 12000rpm to form an O / W type monomer emulsion.

[0093] (4) Add 1.50g of the surface-modified nano silica obtained in step (1) to the O / W type monomer emulsion obtained in step (3), and stir for 30min at a mechanical stirring rate of 800r / min to disperse the surface-modified nano silica in the formed monomer emulsion.

[0094] (5) Same as step (5) in Example 1.

[0095] (6) Same as step (6) in Example 1.

[0096] This comparative example replicates the publicly available route of a composite plugging agent: first, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, styrene, crosslinking agent, and emulsifier are formed into a monomer emulsion, and then surface-modified nano-silica is added to the resulting emulsion and a polymerization reaction is carried out. The difference from Example 1 is that Example 1 uses the route of "pre-dispersing surface-modified nano-silica in the aqueous phase - rate-limited drop addition to the oil phase - in-situ polymerization / crosslinking fixation"; while this comparative example uses the conventional route of "first shearing the aqueous phase and oil phase to form a monomer emulsion - then adding surface-modified nano-silica - then polymerization".

[0097] Comparative Example 8 A method for preparing a drilling fluid plugging agent is described in Example 1, except that N-vinylpyrrolidone is not added in step (2).

[0098] Comparative Example 9 A method for preparing a drilling fluid plugging agent is described in Example 1, except that no protective agent is added in step (2).

[0099] Comparative Example 10 A method for preparing a drilling fluid plugging agent is described in Example 1, except that an interface stabilizing monomer is not added in step (4).

[0100] Experimental Example 1 The rheological properties, filtration loss at room temperature and pressure, and filtration loss at high temperature and pressure of the plugging agents prepared in the examples and comparative examples were tested in drilling fluid-based slurries. The specific methods are as follows: Preparation of drilling fluid-based slurry: Add 4.00g of sodium bentonite to 96.00g of deionized water, stir at high speed of 8000rpm for 20min, and then hydrate in a sealed container for 24h to obtain the drilling fluid-based slurry. Preparation of test slurry: Add the plugging agent to the base slurry at a dosage of 1.0 wt% of the base slurry mass, and stir at high speed at 8000 rpm for 20 minutes to fully disperse the plugging agent and obtain the test slurry.

[0101] The tests were conducted according to the national standard GB / T 16783.1-2014 "Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids". Before aging, the rheological properties and filtration loss at room temperature and pressure were directly tested. After aging, the samples were placed in a high-temperature roller furnace and hot-rolled at 180°C for 16 hours. After cooling to room temperature, the samples were stirred at high speed for 5 minutes, and then the rheological properties and filtration loss at high temperature and pressure were tested. The filtration loss at room temperature and pressure was measured using an API filtration loss meter at room temperature, 0.69 MPa, and 30 minutes. The filtration loss at high temperature and pressure was measured using a high-temperature and high-pressure filtration loss meter at 180°C, 3.5 MPa, and 30 minutes.

[0102] Table 1. Rheological filtration test results of the slurries containing the plugging agents of the examples and comparative examples.

[0103] As shown in Table 1, adding 1% of the example sample to the base slurry significantly reduced both the filtration loss at room temperature and pressure and the filtration loss at high temperature and pressure. Specifically, the filtration loss at room temperature and pressure before aging in Example 1 decreased from 23.6 mL to 8.4 mL, and the filtration loss at high temperature and pressure after hot rolling aging at 180℃ for 16 h decreased from 40.0 mL to 24.6 mL, indicating that the organic-inorganic composite plugging agent obtained in this invention can effectively improve the filtration loss control performance of water-based drilling fluids.

[0104] Comparative Example 1 did not introduce surface-modified nano-silica, Comparative Example 2 did not introduce a divinylbenzene crosslinking structure, and Comparative Example 3 used unmodified nano-silica. The high-temperature and high-pressure filtration losses of the above comparative examples after hot rolling aging at 180℃ for 16h were 58.4 mL, 64.8 mL, and 52.3 mL, respectively, all higher than those of Example 1 and also higher than the base slurry. This result indicates that under high-temperature aging conditions, systems lacking modified inorganic reinforcing phases, crosslinking structures, or effective interface modification are unlikely to form stable and effective blocking structures. Furthermore, some composite particles with poor structural stability may affect the compactness of the base slurry filter cake, leading to increased high-temperature and high-pressure filtration losses.

[0105] Comparative Example 4 (without acrylamide), Comparative Example 8 (without N-vinylpyrrolidone), Comparative Example 9 (without a protective agent), and Comparative Example 10 (without an interface-stabilizing monomer) had high-temperature and high-pressure filtration losses of 33.8 mL, 34.2 mL, 36.5 mL, and 36.1 mL, respectively, all higher than that of Example 1. This indicates that hydrophilic polymerizable monomers, heat-resistant functional monomers, protective agents, and interface-stabilizing monomers all have a certain influence on the filtration loss control performance of the composite plugging agent.

[0106] Further comparison of Comparative Examples 5, 6, and 7 reveals that, under similar raw material compositions, altering the order of addition of surface-modified nano-silica, omitting sufficient pre-dispersion treatment, or adopting a method of first forming a monomer emulsion and then adding the inorganic phase all decrease the filtration loss control performance of the resulting composite plugging agent. Specifically, the high-temperature and high-pressure filtration loss of Comparative Examples 5, 6, and 7 is higher than that of Example 1. This result indicates that the pre-dispersion state of the surface-modified nano-silica, the method of introducing the oil phase, and the subsequent in-situ polymerization / crosslinking fixation process affect the distribution state and interfacial stability of the organic and inorganic phases in the composite system, and are important factors in obtaining better high-temperature plugging performance.

[0107] Experimental Example 2 The sealing performance of the plugging agents prepared in the examples and comparative examples was evaluated by using a medium-pressure sand bed to simulate a formation with micron-sized pores. The sand bed plugging experiment was conducted at room temperature (25±2℃) and the sand bed was filled with 20-40 mesh quartz sand (bed height 30mm).

[0108] Preparation of drilling fluid-based slurry: Add 4.00g of sodium bentonite to 96.00g of deionized water, stir at high speed of 8000rpm for 20min, and then hydrate in a sealed container for 24h to obtain the drilling fluid-based slurry.

[0109] Preparation of test slurry: Add the plugging agent to the base slurry at a dosage of 1.0 wt% of the base slurry mass, and stir at high speed at 8000 rpm for 20 minutes to fully disperse the plugging agent and obtain the test slurry.

[0110] After being hot-rolled at 180℃ for 16 hours and cooled to room temperature, the test slurry was stirred at high speed for 5 minutes at 8000 rpm. A plugging experiment was then conducted by filling a sand bed under a pressure difference of 0.69 MPa. After the experiment, the sand bed was disassembled, and the penetration depth of the drilling fluid in the sand bed was measured. To highlight the effects of interface modification, acrylamide assisted action, and the order of addition / pre-dispersion on the plugging effect of micron-sized pores, Table 2 only selects representative samples for comparison in medium-pressure sand bed plugging experiments.

[0111] Table 2. Medium-Pressure Sand Bed Plugging Experiment

[0112] Table 2 shows that, under the same hot rolling aging conditions, the penetration depth of Example 1 in the sand bed was significantly lower than that of the comparative examples, indicating that it has a better sealing effect on micron-sized pores. In particular, Comparative Examples 5, 6, and 7 further demonstrate that, with similar raw material compositions, the order of addition of modified nano-silica, the pre-dispersion step, and the rate-limited dropwise addition of the oil phase directly affect the deposition, bridging, and sealing layer formation process of the sealing components in the sand bed, reflecting differences in the microstructure of the composite system corresponding to different formation paths. This difference in microstructure further leads to different deposition, bridging, and sealing layer formation capabilities of the sealing components in the sand bed. These results indicate that the technical effect of this invention depends not only on the raw material composition but also on the distribution state of the organic / inorganic phase and the control of the phase separation path during polymerization.

[0113] Experimental Example 3 The sealing performance of the plugging agents prepared in the examples and comparative examples was tested under simulated deep dense shale or microfractured formation conditions.

[0114] Preparation of drilling fluid-based slurry: Add 4.00g of sodium bentonite to 96.00g of deionized water, stir at high speed of 8000rpm for 20min, and then hydrate in a sealed container for 24h to obtain the drilling fluid-based slurry.

[0115] Preparation of test slurry: Add the plugging agent to the base slurry at a dosage of 1.0 wt% of the base slurry mass, and stir at high speed at 8000 rpm for 20 minutes to fully disperse the plugging agent and obtain the test slurry.

[0116] Before testing, the initial permeability K1 of the core was determined using deionized water. Then, the core was displaced with the prepared test slurry at 150℃ and a pressure difference of 3.5MPa. After the flow rate reached a stable level, the permeability K2 after plugging was determined using deionized water in the same direction. The plugging efficiency was calculated according to the plugging rate η=(K1-K2) / K1×100%.

[0117] Table 3 Core plugging efficiency of different plugging agents

[0118] Table 3 shows that the organic-inorganic composite plugging agent prepared in this invention can effectively reduce the permeability of dense cores. When the plugging agent dosage is 1%, under the conditions of 150℃ and 3.5MPa pressure difference, Example 1 shows the best plugging effect. The plugging efficiency of Comparative Example 4 is lower than that of Example 1, indicating that although AM is a commonly used water-soluble monomer, in the phase separation control system defined in this invention, its main role is to participate in the formation of organic network and assist in stabilizing the spatial distribution of organic / inorganic phases. The plugging efficiencies of Comparative Examples 5 and 6 decreased to 70.09% and 66.67%, respectively, indicating that changing the order of addition of modified nano-silica or canceling the pre-dispersion step will weaken the effective deposition and pressure-bearing capacity of the composite plugging agent in dense pore throats. The core plugging efficiency of Comparative Example 7 was 63.89%, lower than that of Example 1, indicating that compared with the existing publicly disclosed composite plugging agent preparation routes, the phase separation path, interface construction sequence, and process control method defined in this application are more conducive to improving the effective deposition and pressure-bearing capacity of the plugging agent in dense pore throats. This result further shows that, under the premise of similar raw material composition, the order of introduction of the modified inorganic reinforcing phase, the rate-limited addition of the oil phase, and the pre-dispersion treatment not only affect the effective deposition and pressure-bearing capacity of the composite plugging agent in dense pore throats, but also affect the final distribution state of the organic / inorganic phase in the composite system; this difference in distribution state is one of the important reasons why the plugging rate of Example 1 reached 86.79%, while that of Comparative Examples 5-7 was only 63.89%-70.09%.

[0119] It is important to emphasize that the phase separation control in this invention is not an irreplaceable general process step, but a necessary condition for forming the target composite structure. Without the pre-dispersion step, the inorganic phase will be difficult to establish a stable initial distribution; if the oil phase is added uncontrolled, it will be difficult to form gradual interface migration and local enrichment; without timely in-situ polymerization / crosslinking fixation, the favorable structure formed by phase separation will be difficult to lock in in time and will easily transform into random agglomeration or interface peeling in subsequent processes. The results of Comparative Examples 5, 6, and 7 show that, under the condition that the raw material composition is basically similar, changing only the phase separation formation path will lead to an increase in filtration loss, an increase in penetration depth, and a decrease in blockage rate, indicating that phase separation control is not an auxiliary factor for performance improvement, but a necessary prerequisite for achieving the target structure and technical effect.

[0120] As shown in Tables 1, 2, and 3, the absence of modified inorganic reinforcing phase, crosslinking agent, or interface modification, or changes in the introduction order and pre-dispersion method of modified SiO2, all lead to a decrease in the high-temperature filtration control capability and plugging performance of the plugging agent. Especially under the premise of similar raw material composition, simply changing the addition order of modified SiO2, eliminating the pre-dispersion step, or adopting a conventional emulsion organization method results in a significant increase in high-temperature and high-pressure filtration loss, an increase in sand bed intrusion depth, and a decrease in core plugging rate. This result indicates that the technical effect of this application is not a linear improvement resulting from the simple parallel addition of individual components, but rather stems from the synergistic regulation of the organic / inorganic phase separation path, spatial distribution state, and structural fixation process during polymerization by the pre-dispersion of the surface-modified inorganic reinforcing phase, the rate-limited droplet addition of the oil phase, and the polymerization / crosslinking timing control. This invention achieves the designable construction of stable heterogeneous composite structures of organic and inorganic phases through phase separation regulation, obtaining stable heterogeneous composite structures that are difficult to form using traditional core-shell coating or simple post-mixing methods. This stable heterogeneous composite structure is an important structural basis for improving its high-temperature filtration control capability, reducing sand bed intrusion depth, and increasing core plugging rate.

[0121] Test Example 4 The organic-inorganic composite plugging agent prepared in Example 1 was subjected to Fourier transform infrared spectroscopy (FT-IR) to characterize its molecular structure and organic-inorganic composite composition. The test results are as follows: Figure 1 As shown.

[0122] Depend on Figure 1 (Comparison of infrared spectra of unmodified inorganic silica and the sealing agent of this invention) It can be seen that the unmodified inorganic silica has a lower infrared spectrum at 3418.1 cm⁻¹. -1 A broad and strong absorption peak is present nearby, attributed to the stretching vibration of free hydroxyl groups (-OH) on its surface. However, in the blocking agent of Example 1, the intensity of this hydroxyl absorption peak is significantly reduced and overlaps with the NH stretching vibration of the amide groups in the polymer, indicating that a large number of hydroxyl groups on the surface of the inorganic particles have participated in the interfacial reaction. Meanwhile, at 2800-2900 cm⁻¹... -1 A new stretching vibration peak of the organic chain segment CH appeared in the interval; at 1600.8 cm⁻¹. -1 A distinct absorption peak appeared nearby, attributed to the overlap between the characteristic vibration of the amide group and the C=C vibration of the benzene ring skeleton in styrene; at 1114.4 cm⁻¹ -1 and 1023.1cm -1 The presence of a very strong and broad absorption peak at 698.7 cm⁻¹ is a result of the combined superposition of the asymmetric stretching vibration of the inorganic nano-silica Si-O-Si framework and the characteristic absorption of the sulfonic acid group (-SO₃H) in 2-acrylamido-2-methylpropanesulfonic acid; furthermore, a peak is observed at 698.7 cm⁻¹. -1 A distinct out-of-plane bending vibrational peak of the monosubstituted benzene ring was observed at the location.

[0123] The significant changes and co-occurrence of the aforementioned characteristic peaks indicate that organic components such as styrene, acrylamide, and AMPS have participated in the polymerization and successfully combined with the inorganic reinforcing phase to form a composite system, proving that the sample has strong interfacial interaction characteristics of organic-inorganic composites.

[0124] Experimental Example 5 The organic-inorganic composite plugging agent prepared in Example 1 was characterized by transmission electron microscopy (TEM). Two samples were submitted for this experiment: Sample 1 corresponds to the sample before aging, and Sample 2 corresponds to the sample after aging at 150℃ for 16h. Figure 3 and Figure 4 TEM testing was used to observe the morphology of samples at different scales, including 50 nm, 100 nm, 200 nm, and 500 nm, to compare the distribution and stability of the composite structure obtained by phase separation regulation before and after aging.

[0125] Depend on Figure 3 It is evident that the pre-aging sample exhibits relatively clear composite particle boundary features at high resolution scales such as 50 nm, and shows a good discrete distribution at scales of 100 nm, 200 nm and 500 nm. This indicates that the system obtained through "pre-dispersion-rate-limited drop-in-in-situ polymerization / cross-linking fixation" is not a simple physical mixture or obvious agglomeration structure, but rather forms a heterogeneous composite morphology with a certain degree of stability.

[0126] Depend on Figure 4 As can be seen, after aging at 150℃ for 16h, the samples maintained good particle dispersion at different scales, without obvious large-area melting and agglomeration, nor significant continuous blocky unstable aggregation. This indicates that the heterogeneous composite structure constructed by phase separation regulation still has good structural retention under aging conditions at 150℃, which is beneficial for inhibiting particle re-agglomeration and maintaining the dispersion stability of the material. The comparison before and after TEM aging shows that the phase separation regulation described in this invention is not a general process optimization, but a key path to form the target heterogeneous composite structure and ensure its high-temperature stability.

[0127] TEM morphology revealed that the sample did not exhibit a large number of regular mononuclear-continuous shell-like particles, but rather a well-dispersed composite distribution. Even after aging at 150℃ for 16 hours, no significant large-scale agglomeration or unstable aggregation resulting from shell rupture was observed. This result differs from the failure mode of traditional core-shell structures, which are prone to shell rupture and interface delamination at high temperatures, further supporting the view that the product obtained in this application is a stable heterogeneous composite structure formed by phase separation regulation.

[0128] It should be noted that the TEM test was mainly used to characterize the microstructure retention characteristics of the samples under aging conditions of 150℃ / 16h; Tables 1 and 2 were mainly used to evaluate the filtration control capability and sand bed plugging performance of the samples under hot rolling aging conditions of 180℃ / 16h; Table 3 was used to evaluate the core dynamic plugging effect of the samples under 150℃ and 3.5MPa conditions. The above results, from the three aspects of microstructure retention, macroscopic filtration control, and dynamic plugging performance, jointly demonstrate the effectiveness of the phase separation regulation structure of the present invention.

[0129] Experimental Example 6 The elemental surface distribution and energy dispersive spectroscopy (EDS) analysis of the organic-inorganic composite plugging agent prepared in Example 1 were performed. The test results are shown in the figure. Figure 5 , Figure 6 , Figure 7 And Table 4. EDS testing is used to further distinguish the spatial coexistence of inorganic reinforcing phase and organic polymer network related elements, and to help determine whether the sample belongs to a traditional inorganic core / continuous organic shell coating structure.

[0130] Table 4. Elemental composition analysis of EDS sample from Example 1.

[0131] Table 4 shows that the elemental signals of O, Na, Si, and S in the sample are all quite significant. Si and O mainly correspond to the inorganic reinforcing phase of nano-silica and its Si-O-Si framework, while S mainly corresponds to the sulfonic acid groups in the AMPS structure. Na mainly originates from the sodium salt component introduced during AMPS neutralization or pH adjustment. The simultaneous presence of these elements indicates that the obtained product indeed contains both an inorganic silica reinforcing phase and a sulfonic acid-containing organic polymer network, further confirming that it is an organic-inorganic composite system.

[0132] Depend on Figure 5 and Figure 6 It is evident that Si and O elements exhibit a relatively dispersed enrichment distribution within the observation area, rather than a single large-particle core concentration. S element also shows a continuous or diffuse distribution within the observation area, indicating that the AMPS-containing organic polymeric component and the silica inorganic reinforcing phase coexist at the microscale and form a spatially interwoven distribution. Combined with... Figure 7 The co-occurrence of peaks for elements such as Si, O, S, and Na in the energy spectrum further illustrates that the inorganic reinforcing phase and the organic polymer network are not simply mechanically mixed and completely separated, but rather form a composite structure with interfacial relationships during the polymerization process.

[0133] It should be noted that the EDS elemental distribution results are mainly used to demonstrate the coexistence and spatial distribution characteristics of the inorganic phase and the sulfonic acid-containing organic phase within the same observation area; they do not, in themselves, prove a complete core-shell structure. On the contrary, considering both the elemental distribution and the morphological results before and after TEM aging, the sample does not exhibit the typical core-shell particle characteristics of silica as a single core and polymer as a continuous outer shell, but rather conforms more closely to the stable heterogeneous composite structure formed through "pre-dispersion-rate-limited dropping-in-situ polymerization / crosslinking fixation" described in this application. In this structure, the inorganic reinforcing phase is embedded, anchored, or enriched within the organic polymer network and / or the interface region in the form of discrete reinforcing units, thus providing a structural basis for maintaining good dispersion and excellent plugging performance even after high-temperature aging.

[0134] In summary, the technical effect of this invention does not stem from general process optimization, but rather from the stable heterogeneous composite structure formed by phase separation control. It is precisely because this structure can maintain dispersion, inhibit aggregation, and preserve interfacial connectivity even at high temperatures that the resulting plugging agent exhibits superior high-temperature filtration control and plugging performance.

Claims

1. A method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation, characterized in that, The steps include the following: (1) Surface-modified nano-silica is obtained by modifying nano-silica with a silane coupling agent; the silane coupling agent is γ-methacryloxypropyltrimethoxysilane, and the mass ratio of the silane coupling agent to nano-silica is 0.2-0.3:

1. (2) Add the emulsifier to water, stir evenly, then add acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone and a protective agent to obtain a mixture; adjust the pH of the obtained mixture to 6.8-7.5, then add the surface-modified nano silica obtained in step (1), and pre-disperse it by ultrasonic and mechanical stirring in sequence to obtain an aqueous phase; the emulsifier is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, Tween 80, OP-10 and fatty alcohol polyoxyethylene ether. The combination of the following: the emulsifier and acrylamide have a mass ratio of 0.1-2:2-4; the acrylamide and 2-acrylamido-2-methylpropanesulfonic acid have a mass ratio of 2-4:1-3; the N-vinylpyrrolidone and acrylamide have a mass ratio of 0.1-0.3:1; the protective agent is polyvinyl alcohol and / or polyvinylpyrrolidone, and the protective agent and acrylamide have a mass ratio of 0.05-0.5:2-4; the acrylamide and surface-modified nano-silica have a mass ratio of 2-4:1-2. (3) Styrene, interfacial stabilizer monomer and crosslinking agent divinylbenzene are mixed to obtain an oil phase; under nitrogen protection and stirring conditions, the obtained oil phase is added dropwise to the aqueous phase obtained in step (2) to form an O / W type emulsion; the mass ratio of styrene to surface-modified nano silica is 10-20:1-2.5; the interfacial stabilizer monomer is hydroxyethyl methacrylate and / or glycidyl methacrylate, and the mass ratio of the interfacial stabilizer monomer to styrene is 0.05-0.15:1; the mass of the crosslinking agent divinylbenzene is 3-8% of the mass of styrene; (4) Under nitrogen protection and stirring conditions, an initiator is added to the O / W type emulsion obtained in step (3) to carry out the reaction; after the reaction is completed, the reaction is terminated, centrifuged, washed and dried to obtain an organic-inorganic composite drilling fluid plugging agent based on phase separation control; the initiator is a redox initiator, the oxidant is ammonium persulfate and the reducing agent is sodium bisulfite, and the mass ratio of oxidant to reducing agent in the redox initiator is 1:1; the mass of the initiator is 1-2% of the total mass of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, styrene, interface stabilizing monomer and crosslinking agent divinylbenzene.

2. The method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation according to claim 1, characterized in that, The nano-silica in step (1) has a particle size of 20-50 nm; the surface-modified nano-silica is prepared by the following method: nano-silica is added to ethanol and ultrasonically dispersed to form a uniform suspension; A silane coupling agent was added to the suspension, the pH of the system was adjusted to 4-5, and the reaction was carried out. After the reaction was completed, the surface-modified nano-silica was obtained by centrifugation, washing, and drying.

3. The method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation according to claim 2, characterized in that, In the preparation of surface-modified nano-silica, the volume ratio of ethanol to the mass of nano-silica is 40-60 mL: 1 g; the pH of the system is adjusted to 4-5 using glacial acetic acid or a 0.1 mol / L HCl aqueous solution; the reaction temperature is 65-75℃, and the reaction time is 2-4 h; the washing is performed by washing with ethanol 2-4 times, and the drying is performed by vacuum drying at 50-60℃ for 10-15 h.

4. The method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation according to claim 1, characterized in that, The number-average molecular weight M of the polyvinyl alcohol mentioned in step (2) n The value is 30,000-70,000; the polyvinylpyrrolidone is PVP K30 or PVP K60. In step (2), the pH is adjusted to 6.8-7.5 using a 0.1 mol / L NaOH aqueous solution; The mass ratio of acrylamide to surface-modified nano-silica is 3-3.5:1.5-1.

8.

5. The method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation according to claim 1, characterized in that, The total mass concentration of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, protective agent, emulsifier, and surface-modified nano-silica in the aqueous phase in step (2) is 1-5 wt%. The ultrasonic power is 200-400W, and the ultrasonic time is 10-20min; the mechanical stirring speed is 600-1000r / min, and the mechanical stirring time is 20-40min.

6. The method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation according to claim 1, characterized in that, The mass ratio of styrene to surface-modified nano-silica in step (3) is 15-18:1.5-1.8; The stirring speed is 8000-15000 rpm; the drop rate of the oil phase is 0.5-2.0 mL / min.

7. The method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation according to claim 1, characterized in that, In step (4), the initiator is added to the system dropwise in the form of an initiator aqueous solution at a drop rate of 0.3-1.0 mL / min and the concentration of the initiator aqueous solution is 1-5 wt%. The initiator is added to the system under stirring conditions at a temperature of 55-70℃ and a speed of 600-900 rpm.

8. The method for preparing organic-inorganic composite drilling fluid plugging agent based on phase separation regulation according to claim 1, characterized in that, The reaction temperature in step (4) is 55-70℃, the reaction time is 4-6h, and the stirring speed during the reaction is 600-900rpm; The termination step is as follows: adding a terminator to the obtained reaction solution to terminate the polymerization reaction. The terminator is hydroquinone, and the amount of the terminator added is 0.05-0.3% of the total mass of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, styrene, interface stabilizing monomer and crosslinking agent divinylbenzene. The washing process involves washing with deionized water 2-4 times, and the drying process involves vacuum drying at 50-60℃ for 12-24 hours.

9. An organic-inorganic composite drilling fluid plugging agent, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. The application of the organic-inorganic composite drilling fluid plugging agent according to claim 9 in water-based drilling fluid, characterized in that, The mass fraction of organic-inorganic composite drilling fluid plugging agent in water-based drilling fluid is 0.5-2.0%.

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