A nano plugging agent for drilling fluid and a preparation method thereof

Abstract

The application discloses a kind of nanometer plugging agent for drilling fluid and preparation method thereof, belong to plugging agent technical field, nanometer plugging agent for drilling fluid, this nanometer plugging agent is prepared by core layer plugging agent and shell layer plugging agent reaction, core layer plugging agent is prepared by nanometer silicon dioxide, gamma-methacryloxypropyl trimethoxysilane and first portion of vinyl phosphonic acid, with secondary plugging capacity;Shell layer plugging agent is prepared by second portion of vinyl phosphonic acid, styrene and 2-dodecane olefin-1-yl succinic anhydride, with flexible characteristics.Nanometer plugging agent has rigid support and flexible deformation capacity, significantly improve the high temperature stability and compressive strength of plugging layer.Enhance the chemical bonding force of plugging agent and rock;The hydrolysable methoxy retained in core layer provides secondary plugging function, prolongs the effective period of plugging.A kind of preparation method of nanometer plugging agent for drilling fluid, it is used for preparing nanometer plugging agent for drilling fluid.

Description

Technical Field

[0001] This invention belongs to the field of plugging agent technology, specifically relating to a nano plugging agent for drilling fluid and its preparation method. Background Technology

[0002] In shale oil and gas drilling, water-based drilling fluids offer significant advantages in terms of environmental protection, leak prevention and plugging, and cost. However, the wellbore's inherent fracturing, water absorption, and high risk of instability severely limit the application of water-based drilling fluids. Wellbore stabilization technology, primarily using micro- and nano-sealing materials, is a crucial solution to the problem of wellbore instability.

[0003] As one of the core treatment agents for water-based drilling fluids, plugging agents are divided into traditional micron plugging agents and nano-micron plugging agents. When plugging agents are added to drilling fluids, they seal the pores and prevent the filtrate from entering the formation through physical and chemical means, thus avoiding uneven stress distribution caused by hydration repulsion and other effects that could lead to wellbore instability.

[0004] Microfractures in formations are mostly nano- and micro-sized pores, and nano-plugging agents have initially achieved the sealing of these pores. However, some plugging agents fail at high temperatures, and the sealing layer formed by conventional plugging agents is prone to collapse and lacks secondary sealing capability. Conventional plugging agents (1–10 μm) have poor size matching with the pores (20–1000 nm) of shale and mudstone. Rigid nanoparticles lack deformation characteristics and have poor geometric adaptability to rock pores and fractures, resulting in a sealing efficiency of approximately 60%–70%, which requires further improvement.

[0005] Therefore, further improvements to existing technologies are needed. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a nano-plugging agent for drilling fluid and its preparation method, with the aim of solving at least one of the above problems.

[0007] This invention achieves its technical objective through the following technical solutions:

[0008] A nano-plugging agent for drilling fluids, which is prepared by reacting a core plugging agent and a shell plugging agent;

[0009] The core layer blocking agent is prepared by reacting nano-silica, silane coupling agent and first vinylphosphonic acid (VPA);

[0010] The shell plugging agent was prepared by reacting a second portion of vinylphosphonic acid (VPA), styrene (St) and 2-dodecen-1-ylsuccinic anhydride;

[0011] The shell plugging agent encapsulates the core plugging agent.

[0012] This invention also provides a method for preparing a nano-plugging agent for drilling fluids, which includes the following steps:

[0013] Step 1: Preparation of core layer nano-blocking agent;

[0014] Step 2: Shell plugging agent coats core plugging agent;

[0015] Step 3: After purification and drying, a core-shell structured nano-blocking agent is obtained.

[0016] Compared with the prior art, the present invention has at least the following advantages:

[0017] This invention utilizes a core-shell structure design, resulting in a nano-plugging agent with an initial plugging rate exceeding 90% and a secondary plugging rate still above 82%, significantly outperforming traditional plugging agents and comparative examples. This demonstrates superior initial plugging capability and sustained plugging effect at high temperatures. The hydrolyzable methoxy groups retained in the core structure can further hydrolyze and condense at high temperatures, forming a stable Si-O-Si three-dimensional cross-linked network, achieving intelligent secondary plugging and effectively solving the problem of conventional plugging agents easily failing at high temperatures. The shell layer possesses flexible deformation capabilities, better adapting to the geometry of nano- and micro-sized pores in the formation, improving the compactness and compressive strength of the plugging layer, and preventing its collapse. The nano-plugging agent used can significantly reduce the permeability of artificial rock cores. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the reaction principle of γ-methacryloxypropyltrimethoxysilane undergoing hydrolysis to replace one methoxy group in this invention.

[0019] Figure 2 This is a schematic diagram illustrating the reaction principle of silanol condensation between γ-(methacryloyloxy)propylhydroxydimethoxysilane and silanol-activated nano-silica according to the present invention.

[0020] Figure 3 This is a schematic diagram illustrating the reaction principle of the copolymerization of γ-(methacryloyloxy)propyldimethylsiloxysilane with the first vinylphosphonic acid radical in this invention.

[0021] Figure 4 This is a schematic diagram of the reaction principle of 2-dodecen-1-ylsuccinic anhydride ring opening in this invention;

[0022] Figure 5 This is a schematic diagram of the reaction principle of the shell polymer in this invention. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] All chemical reagents used in this invention are of analytical grade and purchased from commercially available products.

[0025] like Figures 1 to 5 As shown, the present invention provides a nano-plugging agent for drilling fluid, which is prepared by reacting a core plugging agent and a shell plugging agent;

[0026] The core layer nano-sealing agent is prepared by reacting nano-silica (SiO2), silane coupling agent, and the first vinylphosphonic acid (CH2=CH-PO(OH)2). For example, γ-methacryloxypropyltrimethoxysilane (CH2=C(CH3)COO(CH2)3Si(OCH3)3) is used as the silane coupling agent. Nano-SiO2 is used as the framework, grafted with γ-methacryloxypropyltrimethoxysilane (KH-570), and copolymerized with the first vinylphosphonic acid. The methoxy group (-OCH3) retained after partial hydrolysis of KH-570 is the key to "intelligence". It is stable when the shell is intact. Once the shell is worn and exposed to the downhole water environment, it can undergo further hydrolysis and condensation, and the silanol group -SiOH dehydrates and condenses to form a stable Si-O-Si three-dimensional cross-linked network structure.

[0027] The shell nano-blocking agent was prepared by reacting a second portion of vinylphosphonic acid CH2=CH-PO(OH)2, styrene C6H5CH=CH2, and 2-dodecen-1-ylsuccinic anhydride CH3(CH2)8CH=CHCH2-CH(OC(=O)CH2C(=O)) (DDSA);

[0028] The shell plugging agent encapsulates the core plugging agent.

[0029] Preferably, in the preparation of the nano-blocking agent, the molar ratios of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part vinylphosphonic acid, the second part vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled at (1–1.3):(1.3–1.8):(1.1–1.7):(3.5–5.5):(3.5–5.5). This molar ratio will be referred to as the predetermined molar ratio in the following text. It should be noted that the first part vinylphosphonic acid refers to the vinylphosphonic acid used in the preparation of the core layer nano-blocking agent, and the second part vinylphosphonic acid refers to the vinylphosphonic acid used in the preparation of the shell layer nano-blocking agent.

[0030] A method for preparing a nano-plugging agent for drilling fluid, comprising the following steps:

[0031] Step 1: Preparation of the core-layer nano-blocking agent; First, the surface silanol groups of nano-silica (SiO2) are activated, including high-temperature calcination to remove organic matter, alkaline treatment to enhance the surface hydroxyl density, and washing with ethanol to avoid gelation, resulting in an activated silanol ≡Si-OH surface. Subsequently, γ-methacryloyloxypropyltrimethoxysilane (KH-570) is partially hydrolyzed (low temperature, weak acid catalysis, precise water metering), mainly generating a monohydroxy silane intermediate retaining double bonds and two methoxy groups. This intermediate is then grafted with activated SiO2 via a silanol condensation reaction to form modified nanoparticles with polymerizable olefin bonds on the surface. Finally, the modified nanoparticles are free-radical copolymerized with the first vinylphosphonic acid under the action of an initiator (e.g., benzoyl peroxide BPO) to form the final cross-linked polymer network, i.e., the core-layer nano-blocking agent. This core layer retains unhydrolyzed methoxy groups (-OCH3);

[0032] Step 2: The shell-layer blocking agent encapsulates the core-layer blocking agent; 2-dodecen-1-ylsuccinic anhydride (DDSA) is hydrolyzed and ring-opened to obtain 3-carboxy-5-pentadecanenoic acid; a shell monomer mixture is composed of 3-carboxy-5-pentadecanenoic acid, a second portion of vinylphosphonic acid, and styrene. The core-layer nano-blocking agent prepared in Step 1 is uniformly dispersed and then added to the shell monomer mixture, allowing the monomers to be fully adsorbed onto the core surface. Under inert gas protection, a free radical copolymerization reaction is initiated by an initiator (e.g., benzoyl peroxide BPO). The shell layer is physically adsorbed and molecular chains entangled on the core surface, forming a stable core-shell structure.

[0033] Step 3: After purification and drying, a core-shell structured nano-blocking agent is obtained.

[0034] Furthermore, silanol-activated silica is prepared using the following steps:

[0035] Step A1: Calcine nano-silica (SiO2) powder (particle size in the range of 10-150 nanometers) in a muffle furnace at a temperature of 300°C for at least 2 hours to remove organic matter and activate surface hydroxyl groups; then cool to room temperature and store in a vacuum drying oven for later use.

[0036] Step A2: Weigh an appropriate amount of calcined nano-silica and disperse it in a sodium hydroxide solution. The molar concentration of the sodium hydroxide solution (NaOH) is 0.1 mol / L. The solid-liquid ratio of nano-silica to sodium hydroxide solution is 1:10. Ultrasonic treatment (power 600W, 40kHz, 30min). Stir at 80℃ for 20min and react for 2-4 hours to ensure the activation of silanol groups on the surface of nano-silica SiO2.

[0037] Step A3: After activating the silanol groups on the surface of nano-silica (SiO2), the activated silica is washed with ethanol to remove inorganic salts. Ethanol has a certain effect on Na+. + OH - Plasma has high solubility, effectively eluting sodium salts and avoiding gelation caused by water washing; the weakly polar environment of ethanol maintains the stability of activated silanol groups, preventing hydroxyl condensation caused by water washing; and provides a compatible organic medium environment for subsequent hydrophobic modification (such as silane coupling agent grafting). The silanol-activated silica is then separated by centrifugation (e.g., 3000 rpm, 10 minutes) and decantation, and dried in a vacuum drying oven at 60–80 °C for at least 12 hours until constant weight. ≡Si-OH represents silanol-activated nano-silica, and ≡ indicates the bonding of three oxygen atoms.

[0038] Furthermore, the hydrolysis of γ-methacryloxypropyltrimethoxysilane CH2=C(CH3)COO(CH2)3Si(OCH3)3 converts -Si(OCH3)3 into active -Si-OH, ultimately forming a silanol condensate containing a Si-O-Si crosslinked structure, while retaining the polymerizable olefin double bond;

[0039] Hydrolysis reaction that replaces a methoxy group -OCH3:

[0040] CH2=C(CH3)COO(CH2)3Si(OCH3)3+H2O→CH2=C(CH3)COO(CH2)3Si(OH)(OCH3)2+CH3OH

[0041] or

[0042] CH2=C(CH3)COO(CH2)3Si(OCH3)3+H2O→HO-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2+CH3OH

[0043] It should be noted that the hydrolysis reaction that replaces one methoxy group -OCH3 has a reaction rate of K1. γ-Methacryloxypropyltrimethoxysilane CH2=C(CH3)COO(CH2)3Si(OCH3)3 hydrolyzes to generate γ-(methacryloyloxy)propylhydroxydimethoxysilane CH2=C(CH3)COO(CH2)3Si(OH)(OCH3)2.

[0044] Hydrolysis reaction that replaces two methoxy groups -OCH3:

[0045] CH2=C(CH3)COO(CH2)3Si(OH)(OCH3)2+H2O→CH2=C(CH3)COO(CH2)3Si(OH)2(OCH3)+CH3OH

[0046] It should be noted that the hydrolysis reaction that replaces the two methoxy groups -OCH3 has a reaction rate of K2; γ-methacryloxypropyltrimethoxysilane CH2=C(CH3)COO(CH2)3Si(OCH3)3 hydrolyzes to generate γ-(methacryloxy)propyldihydroxymethoxysilane CH2=C(CH3)COO(CH2)3Si(OH)2(OCH3).

[0047] Hydrolysis reaction of three methoxy groups -OCH3:

[0048] CH2=C(CH3)COO(CH2)3Si(OH)2(OCH3)+H2O→CH2=C(CH3)COO(CH2)3Si(OH)3+CH3OH

[0049] It should be noted that the hydrolysis reaction of replacing the three methoxy groups (-OCH3) has a reaction rate of K3; γ-methacryloyloxypropyltrimethoxysilane (CH2=C(CH3)COO(CH2)3Si(OCH3)3) hydrolyzes to γ-(methacryloyloxy)propyltrihydroxysilane (CH2=C(CH3)COO(CH2)3Si(OH)3). Due to the low electronegativity of silicon atoms, after the first methoxy group hydrolyzes, the electron cloud density of silicon atoms decreases, increasing the difficulty of subsequent hydrolysis; therefore, K1 > K2 > K3.

[0050] A mixed solution with γ-(methacryloyloxy)propylhydroxydimethoxysilane CH2=C(CH3)COO(CH2)3Si(OCH3)3 as the main product was obtained by hydrolysis of γ-methacryloyloxypropyltrimethoxysilane CH2=C(CH3)COO(CH2)3Si(OH)(OCH3)2. The solution was prepared by the following steps:

[0051] Step B1: Dissolve γ-methacryloxypropyltrimethoxysilane in a dry, nonpolar, inert organic solvent (e.g., toluene, xylene, and n-hexane). The purpose is to provide a reaction medium, reduce the water concentration, slow the reaction rate, and facilitate control. Nonpolar solvents help reduce the condensation of silanol groups.

[0052] Step B2: During hydrolysis, a weak acid catalyst is used, such as acetic acid (CH3COOH) or very low concentrations of hydrochloric acid (HCl, e.g., 0.01-0.05 mol / L). Strong acids (such as concentrated sulfuric acid, high-concentration hydrochloric acid) or strong bases (such as NaOH) should be avoided, as these will accelerate all hydrolysis steps, making them difficult to control. The amount of weak acid catalyst used is 0.5%-2% of the molar amount of γ-methacryloyloxypropyltrimethoxysilane.

[0053] Step B3: Use water with a strictly stoichiometric ratio, aiming for 1.0–1.2 molar equivalents (relative to the target number of methoxy groups hydrolyzed, i.e., 1). Slowly add water dropwise to a vigorously stirred, low-temperature solvent mixture containing the silane and catalyst. Alternatively, slowly add water dropwise to a solvent containing a precisely measured amount of water. Use deionized water to avoid interference from impurities. A solvent dried with molecular sieves can be used, followed by a precisely measured amount of water. Limiting the water molecule concentration is key to inhibiting the hydrolysis of the second and third methoxy groups. A low water content ensures that after the water molecules react with the first methoxy group to form a monohydroxysilane, the remaining water molecules in the system are insufficient to effectively attack the remaining two methoxy groups (or the generated silanol groups).

[0054] Step B4: Control the reaction temperature between 0°C and 10°C. Low temperatures significantly reduce the reaction rate of all hydrolysis steps, providing a longer reaction window for precise control (e.g., dropwise addition, monitoring). Low temperatures also help suppress the self-condensation of the generated silanol groups (-SiOH). The reaction time needs to be strictly controlled and optimized according to specific conditions (catalyst concentration, temperature, stirring efficiency). Typically, at low temperatures, after dropwise addition, continuous stirring is required for a period of time (e.g., 30 minutes to 2 hours) to ensure that the first methoxy group reacts substantially completely; then, immerse the reaction flask in an ice-salt bath (-10°C to -20°C) or a cooling bath at a lower temperature to rapidly cool the reaction mixture to near 0°C or lower. This minimizes molecular thermal motion and slows down any residual hydrolysis or condensation reaction rates.

[0055] Step B5: Under continuous vigorous stirring and maintaining a low temperature (0°C to 5°C), slowly add a pre-cooled weakly alkaline aqueous solution. Saturated sodium bicarbonate (NaHCO3) aqueous solution is preferred, as its alkalinity is sufficient to neutralize weak acids (such as acetic acid), and the generated CO2 bubbles aid stirring without causing strong exothermic reactions or side reactions. Add until the system pH is close to neutral (monitor with precise pH paper; target pH 6-8). Dilute ammonia (NH4OH, 1-2%) is a secondary option; however, the addition rate and amount need to be carefully controlled to avoid localized over-alkalinity and exothermic reactions. Add until neutral as well. Avoid using strong bases (such as NaOH, KOH aqueous solutions), as this may lead to silanolate formation, accelerated condensation, or trigger acrylate double bond reactions. The purpose is to completely neutralize any residual acidic catalyst, terminate its catalytic activity, and prevent it from continuing to catalyze silanol condensation or further hydrolysis in subsequent steps.

[0056] Step B6: Transfer the reaction mixture to a separatory funnel; during the first wash, add pre-cooled deionized water (0-5°C), approximately 1 / 3 to 1 / 2 the volume of the organic phase. Gently but thoroughly agitate (avoid vigorous shaking to prevent emulsification), allow to stand and separate into layers, and quickly remove the lower aqueous phase; repeat this cold water washing step 2-3 times;

[0057] Step B7: Combine the washed organic phases (upper layer) and add sufficient high-efficiency desiccant. Anhydrous sodium sulfate (Na2SO4) is commonly used due to its strong water absorption capacity. Sufficient amount is required (observe that the particles no longer clump together). Stir and dry at 0°C to 5°C (in an ice bath) for 15-30 minutes. This thoroughly removes any trace amounts of dissolved water from the organic phase to prevent condensation during subsequent concentration or storage.

[0058] Step B8: Rapidly filter to remove the desiccant under low-temperature conditions (e.g., in a cold room or on an ice bath). Immediately transfer the filtrate (the organic solution containing the product) to a pre-dried, cooled receiving bottle filled with an inert gas (N2 or Ar) to isolate it from air (oxygen and moisture) and prevent oxidation and moisture absorption.

[0059] Furthermore, a mixed solution of γ-(methacryloyloxy)propylhydroxydimethoxysilane CH2=C(CH3)COO(CH2)3Si(OH)(OCH3)2 obtained by hydrolysis was reacted with silanol-activated nano-silica (≡Si-OH) under nitrogen protection and at 80°C to generate γ-(methacryloyloxy)propyldimethylsiloxysilane ≡Si-O-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2, as shown in the following reaction:

[0060] ≡Si-OH+HO-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2→

[0061] ≡Si-O-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2+H2O

[0062] It should be noted that the catalyst acetic acid, based on the weight percentage of SiO2, is 0.05–0.1 wt%. The reaction time is controlled within 8–10 hours. The stirring rate is 300–400 rpm (mechanical stirring) to prevent nanoparticle sedimentation and ensure uniform mass transfer. Nitrogen protection is used, with N2 introduced before the reaction (30 min) to remove oxygen / water; a positive pressure N2 flow rate (0.5 L / min) is maintained; and air moisture is blocked (O2 < 1 ppm, H2O < 5 ppm). Centrifugation (10000 rpm × 20 min) is used to remove physically adsorbed silanes; toluene / ethanol is used for three alternating washes to break hydrogen bond adsorption with ethanol; vacuum drying at 60℃ for 12 h is used to prevent residual water from initiating subsequent condensation.

[0063] Furthermore, under benzoyl peroxide (BPO) initiation and at 80°C, the main reaction between γ-(methacryloyloxy)propyldimethylsiloxysilane ≡Si-O-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2 and the first vinylphosphonic acid CH2=CH-PO(OH)2 is free radical copolymerization, forming a core-layer nanoblocking agent (core-layer copolymer). This forms an alternating / random copolymer containing siloxane and phosphonic acid side groups. The free radical copolymerization reaction is as follows:

[0064] ≡Si-O-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2+CH2=CH-PO(OH)2→

[0065] ≡Si-O-Si(OCH3)2(CH2)3OOC-[CH2-C(CH3)] n -[CH2-CH(PO(OH)2)] m

[0066] It includes the following steps:

[0067] Step S1: The prepared γ-(methacryloyloxy)propyldimethylsiloxysilane ≡Si-O-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2 and the first portion of vinylphosphonic acid CH2=CH-PO(OH)2 are mixed in a solvent. During the mixing process, the mixture is treated with an ultrasonic dispersion device (600W power, 40kHz, 30min) for 1-1.5 hours to ensure that the γ-(methacryloyloxy)propyldimethylsiloxysilane ≡Si-O-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2 and the first portion of vinylphosphonic acid CH2=CH-PO(OH)2 are uniformly dispersed in the solvent; wherein, ethanol is used as the solvent and benzoyl peroxide (BPO) is used as the initiator. Benzoyl peroxide (BPO) solution is added to the mixed solution, and stirring is continued to ensure that the initiator is uniformly dispersed;

[0068] Step S2: Transfer the solution obtained in Step S1 to a magnetic stirrer. Set the stirring speed to 200 rpm and the stirring time to 1 hour. Place the mixed reactants in an oil bath or water bath and slowly heat to 80°C, ensuring uniform temperature. During the heating process, continue stirring to prevent localized overheating. Maintain the reaction temperature at 80°C with continuous stirring. The reaction time is divided into 2–3 hours, 3–5 hours, and 6–8 hours. By controlling the reaction time, the diameter of the core-layer nano-blocking agent can be controlled. Figure 3 As shown, n and m are positive integers, and n and m represent the degree of polymerization. In the polymer chain, the positional relationship between γ-(methacryloyloxy)propyldimethylsiloxysilane and the first vinylphosphonic acid is alternating and random.

[0069] Step S3: Cool the reaction mixture. Once the reaction has reached the desired extent, stop heating and cool the reaction mixture to room temperature; rapid cooling via an ice-water bath can be used to terminate the reaction. Add an appropriate amount of terminating agent (such as ethanol) to the cooled reaction mixture to ensure complete cessation of the reaction.

[0070] Furthermore, 2-dodecen-1-ylsuccinic anhydride CH3(CH2)8CH=CHCH2-CH(OC(=O)CH2C(=O)) is hydrolyzed to open the ring and generate 3-carboxy-5-pentadecanenoic acid CH3(CH2)8CH=CHCH2-CH(COOH)CH2COOH, which is prepared by the following method:

[0071] Weigh 1 g of 2-dodecen-1-ylsuccinic anhydride (DDSA) and dissolve it in 5 mL of tetrahydrofuran (THF). Disperse the solution in 20 mL of deionized water and stir at 25 °C for 15 min. Then, raise the temperature to 40-50 °C and react for 2-4 hours, monitoring the reaction until the starting material spot disappears using thin-layer chromatography. After the reaction is complete, remove most of the THF by rotary evaporation. Extract the residue with diethyl ether, dry the organic phase with anhydrous sodium sulfate, filter, and concentrate to obtain 3-carboxy-5-pentadecanenoic acid, a white or off-white solid, which can be used for the next polymerization step without further purification.

[0072] Furthermore, under benzoyl peroxide (BPO) initiation and at 80°C, the primary reaction of the second vinylphosphonic acid (CH2=CH-PO(OH)2), styrene (C6H5CH=CH2), and 3-carboxy-5-pentadecanoic acid (CH3(CH2)8CH=CHCH2-CH(COOH)CH2COOH) is free radical copolymerization, forming a shell nano-blocking agent. In the shell monomer, the second vinylphosphonic acid provides a reactant with Ca... 2+ The coordination ability of plasma; styrene provides hydrophobicity and segment rigidity; 3-carboxy-5-pentadecanoic acid provides carboxyl crosslinking sites and flexible segments; a core-layer nano-blocking agent is added during the preparation of the shell-layer nano-blocking agent, and the shell-layer blocking agent encapsulates the core-layer blocking agent to generate the nano-blocking agent, which includes the following steps:

[0073] Step SS1: Mix the second portion of vinylphosphonic acid (CH2=CH-PO(OH)2), styrene (C6H5CH=CH2), and 3-carboxy-5-pentadecanenoic acid (CH3(CH2)8CH=CHCH2-CH(COOH)CH2COOH) into a solvent. During mixing, treat the mixture with an ultrasonic dispersion device (600W, 40kHz, 30min) for 1–1.5 hours to ensure uniform dispersion of the second portion of vinylphosphonic acid (CH2=CH-PO(OH)2), styrene (C6H5CH=CH2), and 3-carboxy-5-pentadecanenoic acid (CH3(CH2)8CH=CHCH2-CH(COOH)CH2COOH) in the solvent; wherein, ethanol is used as the solvent and benzoyl peroxide (BPO) is used as the initiator. Add benzoyl peroxide (BPO) solution to the mixed solution and continue stirring to ensure uniform dispersion of the initiator;

[0074] Following step S3 (SS2), the core-layer nano-blocking agent (i.e., core-layer copolymer) prepared in step S3 is dispersed in anhydrous ethanol and ultrasonically treated (600W, 30 minutes) to ensure uniform dispersion of the core-layer particles and prevent agglomeration. The shell-layer monomer mixture is slowly added to the above core-layer dispersion. Ultrasonic treatment continues for 1 hour to allow the shell-layer monomers to fully adsorb onto the core-layer surface. The polymerization reaction is initiated by adding initiator BPO (molar ratio of 1% of the total shell-layer monomers), and the mixture is heated to 80°C under N2 protection and mechanically stirred (300 rpm) for 6–8 hours.

[0075] Step SS3: After the reaction is complete, cool to room temperature and add ethanol to terminate the reaction. Centrifuge (10000 rpm, 20 minutes), wash three times with ethanol to remove unreacted monomers and homopolymers. Vacuum dry at 60℃ for 12 hours to obtain core-shell structured nano-blocking agents; the average particle size of the core-shell structured nano-blocking agents is 50-500 nm. Example

[0076] This embodiment provides a nano-plugging agent for drilling fluid, which is prepared by reacting a core plugging agent and a shell plugging agent;

[0077] The core-layer blocking agent was prepared by reacting nano-silica, γ-methacryloxypropyltrimethoxysilane, and a first-component vinylphosphonic acid. The nano-silica (SiO2) underwent surface silanol activation treatment, including high-temperature calcination to remove organic matter, alkaline treatment to enhance the surface hydroxyl density, and ethanol washing to prevent gelation and obtain an activated ≡Si-OH surface. γ-methacryloxypropyltrimethoxysilane CH2=C(CH3)COO(CH2)3Si(OCH3)3 was hydrolyzed to obtain CH2=C(CH3)COO(CH2)3Si(OH)(OCH3)2 as the main product. γ-(methacryloyloxy)propylhydroxydimethoxysilane CH2=C(CH3)COO(CH2)3Si(OH)(OCH3)2 undergoes silanol condensation with silanol-activated nano-silica (≡Si-OH) under nitrogen protection and at 80°C to generate γ-(methacryloyloxy)propyldimethylsiloxysilane ≡Si-O-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2; under benzoyl peroxide (BPO) initiation and at 80°C, the main reaction between γ-(methacryloyloxy)propyldimethylsiloxysilane ≡Si-O-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2 and the first vinylphosphonic acid CH2=CH-PO(OH)2 is self- A core-layer nano-blocking agent is formed by free radical copolymerization. The silanol-activated silica is prepared using steps A1 to A3. γ-methacryloyloxypropyltrimethoxysilane CH2=C(CH3)COO(CH2)3Si(OCH3)3 is hydrolyzed to obtain CH2=C(CH3)COO(CH2)3Si(OH)(OCH3)2 as the main product, which is prepared using steps B1 to B8. γ-(methacryloyloxy)propyldimethylsiloxysilane ≡Si-O-Si(OCH3)2(CH2)3OOC-C(CH3)=CH2 undergoes free radical copolymerization with the first vinylphosphonic acid CH2=CH-PO(OH)2. The core-layer nano-blocking agent is prepared using steps S1 to S3.

[0078] The shell-sealing agent was prepared by reacting a second portion of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride. 2-Dodecen-1-ylsuccinic anhydride CH3(CH2)8CH=CHCH2-CH(OC(=O)CH2C(=O)) was hydrolyzed to open the ring, generating 3-carboxy-5-pentadecanoic acid CH3(CH2)8CH=CHCH2-CH(COOH)CH2COOH. Under benzoyl peroxide (BPO) initiation and at 80°C, the second portion of vinylphosphonic acid CH2=CH-PO(OH)2, styrene C6H5CH=CH2, and 3-carboxy-5-pentadecanoic acid CH3(CH2)8CH=CHCH2-CH(COOH)CH2COOH underwent free radical copolymerization to form the shell-sealing nano-sealing agent.

[0079] The nano-blocking agent is a core-layer blocking agent encapsulated by a shell-layer blocking agent. The core-layer nano-blocking agent is added during the preparation of the shell-layer nano-blocking agent to generate the nano-blocking agent. It is prepared by steps SS1 to SS3.

[0080] In the preparation of the nano-blocking agent, the molar ratio of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part vinylphosphonic acid, the second part vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride is controlled at 1:1.5:1.3:4.1:4.1:4.1. Example

[0081] The difference between this embodiment and Embodiment 1 is that the raw material ratio has been adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled in a molar ratio of 1:0.5:1.3:4.1:4.1:4.1. Example

[0082] The difference between this embodiment and Embodiment 1 is that the raw material ratio has been adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled in a molar ratio of 1:2:1.3:4.1:4.1:4.1. Example

[0083] The difference between this embodiment and Embodiment 1 is that the raw material ratio has been adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled in a molar ratio of 1:1.5:0.5:4.1:4.1:4.1. Example

[0084] The difference between this embodiment and Embodiment 1 is that the raw material ratio has been adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled in a molar ratio of 1:1.5:2:4.1:4.1:4.1. Example

[0085] The difference between this embodiment and Embodiment 1 is that the raw material ratio has been adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled in a molar ratio of 1:1.5:1.3:2:4.1:4.1. Example

[0086] The difference between this embodiment and Embodiment 1 is that the raw material ratio has been adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled in a molar ratio of 1:1.5:1.3:5:4.1:4.1. Example

[0087] The difference between this embodiment and Embodiment 1 is that the raw material ratio has been adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled in a molar ratio of 1:1.5:1.3:4.1:2:4.1. Example

[0088] The difference between this embodiment and Embodiment 1 is that the raw material ratio has been adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled in a molar ratio of 1:1.5:1.3:4.1:5:4.1. Example

[0089] The difference between this embodiment and Embodiment 1 is that the raw material ratio has been adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled at a molar ratio of 1:1.5:1.3:4.1:4.1:2. Example

[0090] The difference between this embodiment and Embodiment 1 is that the raw material ratio has been adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride are controlled at a molar ratio of 1:1.5:1.3:4.1:4.1:5.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is that the core layer plugging agent used is only silicon dioxide, which is silicon dioxide that has not been activated by silanol groups;

[0093] The raw materials and their proportions were adjusted: during the preparation of the nano-blocking agent, the amounts of silica, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride were controlled in a molar ratio of 1:4.1:4.1:4.1.

[0094] Comparative Example 2

[0095] The difference between this comparative example and Example 1 is that the nano-blocking agent consists only of the core layer blocking agent;

[0096] The raw materials and their proportions were adjusted: during the preparation of the nano-blocking agent, the molar ratio of nano-silica, γ-methacryloyloxypropyltrimethoxysilane and the first batch of vinylphosphonic acid was controlled at 1:1.5:1.3.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 1 is that the nano-blocking agent consists only of a shell-type blocking agent.

[0099] The raw materials and their proportions were adjusted: during the preparation of the nano-blocking agent, the amount of vinylphosphonic acid, styrene and 2-dodecen-1-ylsuccinic anhydride used in the second part was controlled at a molar ratio of 4.1:4.1:4.1.

[0100] Comparative Example 4

[0101] The difference between this comparative example and Example 1 is that the raw material ratio was adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride were controlled at a molar ratio of 1:1.5:1.3:1:1:1.

[0102] Comparative Example 5

[0103] The difference between this comparative example and Example 1 is that the raw material ratio was adjusted: during the preparation of the nano-blocking agent, the amounts of nano-silica, γ-methacryloyloxypropyltrimethoxysilane, the first part of vinylphosphonic acid, the second part of vinylphosphonic acid, styrene, and 2-dodecen-1-ylsuccinic anhydride were controlled at a molar ratio of 1:1.5:1.3:2:2:2.

[0104] Test Example 1

[0105] A performance test for a nano-plugging agent for drilling fluid is conducted using an artificial core to simulate the nano- and micro-pore structure of the formation. The average flow rate of the drilling fluid system in the artificial core is measured, and the permeability is calculated using Darcy's formula. The changes in the permeability of the artificial core before and after the addition of the nano-plugging agent are compared to evaluate the plugging effect of the agent. The permeability of the artificial core is K = Qμl / (AΔP).

[0106] The initial plugging rate is (initial permeability - permeability after initial plugging) / initial permeability × 100%.

[0107] The second sealing rate is (initial permeability - permeability after second sealing) / initial permeability × 100%. It should be noted that heating the artificial rock core (e.g., to 230℃ or 235℃, depending on the specific scenario) disrupts the surface structure of the nano-sealing agent. This primarily refers to breaking the bond between the nano-sealing agent and the artificial rock core (which is rock in the actual application). Taking Example 1 as an example, by disrupting the bond between the shell sealing agent and the artificial rock core (e.g., the shell sealing agent collapses at high temperatures), it loses its initial sealing ability; the core sealing agent then performs the second sealing on the artificial rock core. The first artificial rock core permeability refers to the permeability measured after adding the nano-sealing agent; the second artificial rock core permeability refers to the permeability measured after disrupting the surface structure of the nano-sealing agent.

[0108] The permeability of the artificial core without any sealing material refers to the permeability without the addition of nano-sealing agent, as in Example 1.

[0109] Table 1. Permeability Performance Test

[0110]

[0111] Results Analysis and Conclusions

[0112] As can be seen from the data in Table 1, Example 1 (preferred ratio) exhibits the best plugging performance, with a first plugging rate as high as 90.2% and a second plugging rate of 82.3%, indicating that it has excellent initial plugging ability and secondary plugging ability at high temperature. The core plugging agent provides rigid support and high temperature stability, while the shell provides flexible adaptation and chemical bonding force. The synergistic effect of the two significantly improves the durability of the plugging layer.

[0113] In Examples 2 to 5 and 7 to 11, the first plugging rate of some formulations (such as Examples 6, 8, and 10) decreased significantly (53.7% to 61.9%), indicating that insufficient or excessive shell monomer ratio will affect the plugging effect. The second plugging rate of Examples 6, 8, and 10 also decreased significantly (48.8% to 50.1%), further demonstrating that the coordination of the shell and core ratio is crucial to maintaining the plugging capability at high temperatures.

[0114] In Comparative Example 1 (using only silica as the core plugging agent), although there was a certain initial plugging rate (87.8%), there was absolutely no secondary plugging capability. Comparative Examples 2 (using only the core plugging agent) and 3 (using only the shell plugging agent) could not achieve secondary plugging, verifying the necessity of the core-shell dual structure. In Comparative Examples 4 and 5 (with unbalanced proportions), the plugging rates were significantly lower than those in Example 1, indicating that a reasonable material ratio is the key to achieving efficient plugging.

[0115] The second component of vinylphosphonic acid and 3-carboxy-5-pentadecanoic acid in the shell layer provides coordination ability with formation ions, enhancing the binding force between the plugging agent and the rock; styrene provides hydrophobicity and segment rigidity, effectively inhibiting filtrate intrusion. The methoxy groups retained in the core layer undergo hydrolysis and condensation at high temperature to form a Si-O-Si three-dimensional network structure, achieving secondary plugging and significantly extending the effective period of plugging.

[0116] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and utility model concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A nano plugging agent for drilling fluid, which is prepared by the reaction of a core layer plugging agent and a shell layer plugging agent, characterized in that, The core layer blocking agent is prepared from nano-silica, silane coupling agent and the first portion of vinyl phosphonic acid; the shell layer blocking agent is prepared from the second portion of vinyl phosphonic acid, styrene and 2-dodecylene-1-yl succinic anhydride; The shell layer blocking agent wraps the core layer blocking agent; The silane coupling agent is selected from γ-methacryloxypropyl trimethoxysilane; In the preparation of the nano-blocking agent, the usage amount of nano-silica, γ-methacryloxypropyl trimethoxysilane, the first portion of vinyl phosphonic acid, the second portion of vinyl phosphonic acid, styrene and 2-dodecylene-1-yl succinic anhydride is controlled in the molar ratio of (1-1.3):(1.3-1.8):(1.1-1.7):(3.5-5.5):(3.5-5.5):(3.5-5.5).

2. The nano-plugging agent for drilling fluid according to claim 1, characterized in that, The average particle size of the nano-blocking agent with core-shell structure is 50-500 nm.

3. A method for preparing a nano plugging agent for drilling fluid, which is used for preparing the nano plugging agent for drilling fluid according to claim 1 or 2, characterized in that, It comprises the following steps : Step one, preparation of core layer nano-blocking agent; Step two, the shell layer blocking agent wraps the core layer blocking agent; Step three, purification and drying to obtain the nano-blocking agent with core-shell structure.

4. The method of claim 3, wherein the nano-sealing agent is prepared by the steps of: (a) mixing the nano-sealing agent with the drilling fluid; (b) adding the nano-sealing agent to the drilling fluid; and (c) mixing the nano-sealing agent with the drilling fluid. In step one, first, the surface silicon hydroxyl of nano-silica is activated, including high temperature calcination, to obtain an activated silicon hydroxyl surface; then, γ-methacryloxypropyl trimethoxysilane (KH-570) is partially hydrolyzed and grafted with activated SiO2 through silanol condensation reaction to form modified nanoparticles with polymerizable olefin bond on the surface; finally, the modified nanoparticles and the first portion of vinyl phosphonic acid are subjected to free radical copolymerization under the action of an initiator to form the core layer nano-blocking agent.

5. The method of claim 3, wherein the nano-sealing agent is prepared by the steps of: (a) mixing the nano-sealing agent with the drilling fluid; (b) adding the nano-sealing agent to the drilling fluid; and (c) mixing the nano-sealing agent with the drilling fluid. In step two, 2-dodecylene-1-yl succinic anhydride is hydrolyzed to obtain 3-carboxy-5-pentadecenoic acid; a shell monomer mixture is composed of 3-carboxy-5-pentadecenoic acid, the second portion of vinyl phosphonic acid and styrene; after the core layer nano-blocking agent prepared in step one is uniformly dispersed, the shell monomer mixture is added to allow the monomers to be fully adsorbed on the surface of the core layer; under the protection of inert gas, the shell layer blocking agent wraps the core layer blocking agent through free radical copolymerization reaction initiated by an initiator.

6. The method of claim 4, wherein the nano-sealing agent is prepared by the steps of: (a) mixing the nano-sealing agent with the drilling fluid; (b) adding the nano-sealing agent to the drilling fluid; and (c) mixing the nano-sealing agent with the drilling fluid. In step one, γ-methacryloxypropyl trimethoxysilane is hydrolyzed to obtain a mixed solution containing γ-(methacryloxy) propyl hydroxydimethoxysilane.

7. The method of claim 6, wherein the nano-sealing agent is prepared by the steps of: (a) mixing the nano-sealing agent with the drilling fluid; (b) adding the nano-sealing agent to the drilling fluid; and (c) mixing the nano-sealing agent with the drilling fluid. In step one, the γ-(methacryloxy) propyl hydroxydimethoxysilane mixed solution obtained by hydrolysis is used to perform silanol condensation with silicon hydroxyl activated nano-silica under the protection of nitrogen and at 80°C to generate γ-(methacryloxy) propyl dimethylsiloxy silane.

8. A method for preparing a nano-plugging agent for drilling fluid as described in claim 3 or 5, characterized in that, In step two, 2-dodecylene-1-yl succinic anhydride is hydrolyzed to generate 3-carboxy-5-pentadecenoic acid.

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