A catechol / hydrophobic Janus nanosilica well wall stabilizer and a preparation method and application thereof

Abstract

The present application belongs to the technical field of wellbore stabilizing materials, and particularly relates to a catechol / hydrophobic Janus nanosilica wellbore stabilizer, a preparation method thereof and an application thereof. The preparation method of the wellbore stabilizer comprises: S1: preparing interface-coated nanosilica particles; S2: preparing a Janus nanosilica intermediate; and S3: preparing the catechol / hydrophobic Janus nanosilica wellbore stabilizer. The present application also provides the wellbore stabilizer prepared by the method and an application of the wellbore stabilizer in preparing a water-based drilling fluid. The catechol / hydrophobic Janus nanosilica wellbore stabilizer can realize the synergistic effect of "strong surface adsorption-dense plugging-hydrophobic modification" in the water-based drilling fluid, effectively plugs the micro-pores and cracks in the shale formation on one hand, and increases the hydrophobicity of the shale surface on the other hand, so as to significantly reduce the invasion amount of the drilling fluid filtrate, effectively blocks the water molecules, and is conducive to improving the wellbore stability of the water-sensitive shale and the shale formation with weakly developed faces.

Description

Technical Field

[0001] This invention belongs to the technical field of wellbore stabilizing materials, specifically relating to a catechol / hydrophobic Janus nano-silica wellbore stabilizer, its preparation method, and its application. More specifically, this invention relates to the preparation of Janus nano-silica particles with strong adsorption and hydrophobic functional surfaces. These particles can be used in water-based drilling fluids to slow the intrusion of drilling fluid filtrate along micropores, nanopore throats, microfractures, and weak bedding planes in shale formations, thereby improving the stability of shale wellbores. Background Technology

[0002] In oil and gas drilling, wellbore instability is one of the key engineering challenges restricting safe and efficient drilling in complex shale formations. Studies have shown that shale formations exhibit well-developed micro- and nano-scale fractures and pores, and a distinct bedding structure. Under the combined effects of bottomhole pressure differential, capillary force, and chemical potential difference, when water-based drilling fluids encounter complex shale formations, the drilling fluid filtrate easily enters the rock interior along micro- and nano-pore throats, micro-fractures, and bedding planes. This causes physicochemical effects such as clay mineral hydration and expansion, and weakening of weak bedding planes, thereby reducing the rock's mechanical strength and further increasing the risk of complex downhole accidents such as wellbore collapse, spalling, diameter reduction, and stuck pipe. Therefore, there is an urgent need to develop highly efficient treatment agents that combine plugging, inhibition, and filtrate control to improve the adaptability of water-based drilling fluids to complex shale formations and provide technical support for safe and efficient drilling of shale oil and gas.

[0003] To effectively seal micro- and nano-pores and cracks, numerous sealing agents have been developed in recent years, mainly including bituminous materials, nano-silica, polymer microspheres, graphene oxide sheets, and biomimetic wall-forming agents. Among these, nano-silica has advantages such as small particle size, large specific surface area, good temperature resistance, and ease of surface modification, making it suitable for sealing micro- and nano-pores in shale. However, the surface of ordinary nano-silica is mostly composed of hydrophilic silanol groups, which easily aggregate in water-based drilling fluids, and its adsorption capacity on shale surfaces is limited.

[0004] Biomimetic catechol materials, such as dopamine, polydopamine, tannic acid, and gallic acid, possess strong wet adhesion capabilities and can form hydrogen bonds, coordination, electrostatic, or multi-site adsorption interactions with hydroxyl groups, metal ion sites, and clay edge sites on mineral surfaces. These materials can adsorb and form films on shale surfaces. However, most catechol polymers have hydrophilic structures, limiting their ability to prevent water-based drilling fluid filtrate from penetrating the micropores of shale.

[0005] On the other hand, hydrophobic modified materials can increase the contact angle of shale surfaces and reduce the wetting and capillary self-adsorption of shale by aqueous filtrate. However, hydrophobic materials often suffer from poor dispersibility and insufficient adsorption capacity on shale surfaces.

[0006] Therefore, existing technologies still lack a highly efficient water-based drilling fluid treatment agent that can simultaneously achieve strong adsorption on shale surfaces and sealing of micro- and nano-pores. In particular, there is a lack of a Janus-type wellbore stabilizing material that spatially separates and integrates "strong adsorption function" and "hydrophobic function" onto the same nanoparticle. Summary of the Invention

[0007] To address the problems existing in the prior art, the present invention aims to provide a catechol / hydrophobic Janus nano silica wellbore stabilizer to improve the limited adsorption capacity of existing nano plugging agents on shale surfaces and the insufficient dispersion and retention capacity of hydrophobic plugging agents in water-based drilling fluid systems.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned wellbore stabilizer.

[0009] Another object of the present invention is to provide the application of the above-mentioned wellbore stabilizer in water-based drilling fluids to improve wellbore stability in shale formations.

[0010] The technical solution of the present invention is as follows:

[0011] A method for preparing a catechol / hydrophobic Janus nano-silica wellbore stabilizer includes the following steps:

[0012] S1: Preparation of interface-coated nano-silica particles

[0013] Nano-silica was added to deionized water and ultrasonically dispersed for 25-35 minutes. After adjusting the pH to 5.0-10.0, electrolyte was added and stirred until homogeneous. Then, surfactant was added and stirred until homogeneous to obtain nano-silica dispersion.

[0014] Then, the coating medium was melted and added to the nano-silica dispersion. The mixture was stirred, sheared or ultrasonically emulsified at 45~90℃ and 1000~1200rpm for 0.5~6 h. After emulsification, it was immediately cooled to 0~4℃ to obtain interface-coated nano-silica particles.

[0015] S2: Preparation of Janus nano-silica intermediate

[0016] Interface-coated nano silica particles were added to a hydrophobic modifier solution and reacted at 30-60°C for 1-24 h at a temperature 5°C or higher below the melting point of the coating medium. After washing and centrifugation, Janus nano silica intermediate was obtained.

[0017] S3: Preparation of Catechol / Hydrophobic Janus Nano-Silica Wellbore Stabilizer

[0018] Janus nano-silica intermediates were added to deionized water or buffer solution and stirred to disperse evenly. Catechol materials were then added to carry out the reaction. After the reaction was completed, the mixture was washed, centrifuged and dried to obtain a catechin / hydrophobic Janus nano-silica well wall stabilizer. The catechins were dopamine, dopamine hydrochloride, tannic acid, gallic acid, aldehydes containing catechol structures or catechin-modified polymers.

[0019] According to a preferred embodiment of the present invention, in step S1, the particle size of the nano-silica is 10~500nm; and the mass concentration of the nano-silica in deionized water is 0.1~10 wt%.

[0020] More preferably, the particle size of the nano-silica is 20~300nm; and the mass concentration of the nano-silica in deionized water is 0.5~3wt%.

[0021] According to a preferred embodiment of the present invention, in step S1, the pH adjustment is performed by adjusting the pH to 7.0-8.5 using one or more of hydrochloric acid, acetic acid, sodium hydroxide, potassium hydroxide, ammonia, Tris buffer, phosphate buffer, and carbonate / bicarbonate buffer.

[0022] According to a preferred embodiment of the present invention, in step S1, the electrolyte is one or more selected from NaCl, KCl, NH4Cl, CaCl2, MgCl2, Na2SO4, and K2SO4; the molar concentration of the electrolyte in deionized water is 1~300 mmol / L.

[0023] More preferably, the electrolyte is NaCl, KCl, or NH4Cl, and its molar concentration in deionized water is 10-50 mmol / L.

[0024] According to a preferred embodiment of the present invention, in step S1, the surfactant is one or more of a cationic surfactant, a nonionic surfactant, or an amphoteric surfactant; the mass ratio of the surfactant to nano-silica is (0.001~0.5):1; the stirring temperature needs to be at least 5°C higher than the melting point of the coating medium; and the stirring, shearing, or ultrasonic emulsification time is 1~3 hours.

[0025] The cationic surfactant is dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, bis(dodecyldimethylammonium bromide) or bis(hexadecyldimethylammonium bromide).

[0026] The nonionic surfactant is Tween 20, Tween 40, Tween 60, Tween 80, Span 20, Span 60, Span 80, polyoxyethylene ether surfactant, or polyether surfactant.

[0027] The amphoteric surfactant is dodecyl dimethyl betaine, cocamidopropyl betaine, or sulfobetaine-type surfactant.

[0028] More preferably, the surfactant is hexadecyltrimethylammonium bromide or bis(dodecyldimethylammonium bromide); the mass ratio of the surfactant to nano-silica is (0.005~0.05):1.

[0029] According to a preferred embodiment of the present invention, in step S1, the coating medium is one or more of paraffin wax, microcrystalline wax, beeswax, low-melting-point polyethylene wax, and low-melting-point Fischer-Tropsch wax; the mass ratio of nano-silica to the coating medium is 1:(2~50). This coating medium forms a molten wax phase when its melting point is above its melting point, and forms a solidified wax phase after cooling, which can be removed by organic solvents.

[0030] More preferably, the coating medium is paraffin or microcrystalline wax with a melting point of 40~80℃; the mass ratio of the nano-silica to the coating medium is 1:(5~20).

[0031] According to a preferred embodiment of the present invention, in step S1, the cooling is performed by rapidly cooling using an ice bath, a cold water bath, or a temperature-controlled method.

[0032] According to a preferred embodiment of the present invention, in step S2, the hydrophobic modifier is one or more of long-chain alkyltrialkoxysilane, fluoroalkyltrialkoxysilane, or silane coupling agents containing hydrophobic segments.

[0033] The mass ratio of the hydrophobic modifier to the interface-coated nano-silica particles is (0.05~5):1;

[0034] The hydrophobic modifier solution has a mass concentration of 0.5~10 mg / mL and is prepared by adding the hydrophobic modifier to an ethanol aqueous solution and pre-hydrolyzing it at 20~45℃ for 10~60 min.

[0035] The reaction temperature is 35~50℃ and more than 5℃ below the melting point of the coating medium, and the reaction time is 2~12h.

[0036] More preferably, the hydrophobic modifier is one or more of octyltrialkoxysilane, dodecyltriethoxysilane, dodecyltrialkoxysilane, hexadecyltrialkoxysilane, octadecyltrialkoxysilane, fluoroalkyltrimethoxysilane, and fluoroalkyltriethoxysilane.

[0037] The mass ratio of the hydrophobic modifier to the interface-coated nano-silica particles is (0.2~2):1;

[0038] The hydrophobic modifier solution has a mass concentration of 2~10 mg / mL and is prepared by adding the hydrophobic modifier to an ethanol aqueous solution, adjusting the pH of the solution to 4.0~6.0 with acetic acid, glacial acetic acid or dilute acetic acid, and pre-hydrolyzing at 25~35℃ for 20~40 min.

[0039] According to a preferred embodiment of the present invention, in step S2, the washing and centrifugation process is as follows: first, the particles are washed 3 to 6 times with an organic solvent to remove the coating medium; then, they are washed 3 to 6 times with alternating ethanol and water to remove unreacted hydrophobic modifiers and residual solvents; after each washing, the particles are collected by centrifugation at 6000 to 12000 rpm for 8 to 20 minutes.

[0040] The organic solvent may be one or more of n-hexane, cyclohexane, petroleum ether, toluene, and dichloromethane.

[0041] According to a preferred embodiment of the present invention, in step S3, the buffer solution is Tris-HCl buffer, carbonate buffer, or phosphate buffer.

[0042] According to a preferred embodiment of the present invention, in step S3, when the catechol is dopamine or dopamine hydrochloride, the dispersion concentration of Janus nano silica intermediate is 0.5~20 mg / mL, and the concentration of dopamine or dopamine hydrochloride is 0.1~5 mg / mL.

[0043] The reaction is carried out by stirring in the presence of air or oxygen for 1 to 4 hours. By controlling the dopamine concentration and reaction time, the polydopamine layer is preferentially deposited on the hydrophilic surface that retains the silanol groups, while avoiding excessive deposition that would completely cover the hydrophobic surface.

[0044] According to a preferred embodiment of the present invention, in step S3, when the catechin is tannic acid or gallic acid, the dispersion concentration of Janus nano silica intermediate is 0.5~20 mg / mL, and the concentration of tannic acid or gallic acid is 0.1~5 mg / mL.

[0045] The reaction is as follows: after adding tannic acid or gallic acid, a metal ion compound is added, and the pH is adjusted to 4.0~7.0 before the deposition reaction is carried out for 1~30 min; wherein, the molar ratio of tannic acid or gallic acid to the metal ion compound is 1:(0.05~2); wherein, the metal ion compound is FeCl3, Fe(NO3)3, AlCl3, Al(NO3)3 or ZrOCl2.

[0046] According to a preferred embodiment of the present invention, in step S3, when the catechin is a catechin-modified polymer, the dispersion concentration of the Janus nano silica intermediate is 0.5~20 mg / mL;

[0047] The reaction is as follows: after the Janus nano silica intermediate is evenly dispersed, aminosilane is first added, the pH is adjusted to 4.5-6.5, and the reaction is stirred at 25-45℃ for 2-12 h. After washing with ethanol 3-6 times and centrifuging, the aminated Janus nano silica intermediate is obtained. Then, the aminated Janus nano silica intermediate is dispersed in an ethanol aqueous solution, 3,4-dihydroxybenzaldehyde is added, the pH is adjusted to 6.5-8.5, and the reaction is stirred at 25-45℃ for 2-12 h.

[0048] The aminosilane is γ-aminopropyltriethoxysilane or γ-aminopropyltrimethoxysilane; the mass ratio of aminosilane to Janus nano silica intermediate is (0.1~0.5):1, and the mass ratio of 1,3,4-dihydroxybenzaldehyde to aminated Janus nano silica intermediate is (0.05~0.2):1.

[0049] According to a preferred embodiment of the present invention, in step S3, the washing, centrifugation, and drying processes are as follows:

[0050] Wash 3-6 times with deionized water, ethanol or ethanol-water solution, then centrifuge at 8000-12000 rpm for 8-20 min; finally dry at 40-80℃ for 6-24 h.

[0051] A catechin / hydrophobic Janus nano-silica wellbore stabilizer is prepared according to the above method.

[0052] According to a preferred embodiment of the present invention, the catechol / hydrophobic Janus nano silica well wall stabilizer uses nano silica as an inorganic core and has an asymmetric interface structure on both sides of the inorganic core surface: one side is a catechol hydrophilic strong adsorption functional layer, and the other side is a silane hydrophobic functional layer.

[0053] The application of the above-mentioned catechin / hydrophobic Janus nano silica wellbore stabilizer in the preparation of water-based drilling fluids.

[0054] The technical features of this invention are as follows:

[0055] 1) The catechol hydrophilic strong adsorption functional layer in the catechol / hydrophobic Janus nano silica wellbore stabilizer provided by this invention can undergo hydrogen bonding, coordination, electrostatic adsorption, or multi-point adhesion with clay minerals, quartz, feldspar, carbonates, iron oxides, organic matter, etc. on the surface of shale, enabling nano silica particles to stably remain on the surface of shale, weak bedding planes, and micro-fracture walls. The silane hydrophobic functional layer can reduce the hydrophilicity of the shale surface, increase the contact angle between shale and water, and weaken the capillary self-priming and continuous penetration ability of water-based drilling fluid filtrate.

[0056] 2) In step S1 of the present invention, by adjusting the pH of the aqueous phase and adding electrolytes and surfactants, the nano-silica is made to have moderate wettability suitable for adsorption at the water-molten wax phase interface. Subsequent coating medium and stirring, shearing or ultrasonic emulsification treatment can make the nano-silica dispersion form a Pickering emulsion. The nano-silica particles are adsorbed and arranged at the water-molten wax phase interface, with a part of the surface exposed to the aqueous phase and the other part of the surface embedded in the molten wax phase. Finally, an interface-coated nano-silica particle with one side covered by the coating medium and the other side exposed to the aqueous phase is obtained, which provides a structural basis for the subsequent selective hydrophobic modification of the exposed surface.

[0057] 3) In step S2 of this invention, the hydrophobic modifier is hydrolyzed to generate silanol groups, which then undergo a condensation reaction with the silanol groups on the surface of nano-silica to form Si–O–Si covalent bonds on the surface of nano-silica, thereby introducing alkyl, fluoroalkyl, or other hydrophobic segments. The main reaction can be represented as: SiO2–OH + R–Si(OR')3 → SiO2–O–Si(R)(OR')2 + R'OH; further condensation forms SiO2–O–Si–R type hydrophobic hemispheres, where R is a C8~C18 long-chain alkyl, fluoroalkyl, or organic group containing hydrophobic segments.

[0058] 4) In step S3 of the present invention, when the catechol is dopamine or dopamine hydrochloride, it can be oxidized and self-polymerized in a buffer system with pH=7.5~9.0 to form a polydopamine layer. Then, the polydopamine layer is fixed on the surface of silica through hydrogen bonding, electrostatic interaction and multi-point adsorption.

[0059] When catechins are tannic acid or gallic acid, they can form a metal-polyphenol coordination network with metal ions and be deposited on the surface of silica.

[0060] When catechol is used as a modified polymer, alkoxysilane is hydrolyzed to generate silanol groups, which then undergo a condensation reaction with the silanol groups on the originally shielded hemispherical surface of silica to form Si–O–Si covalent bonds, thereby fixing the aminosilane layer onto the silica surface. Subsequently, the aldehyde groups in aldehyde compounds containing catechol structures undergo a Schiff base reaction with the amino groups in the aminosilane layer, fixing the catechol groups onto the nano-silica surface.

[0061] The beneficial effects of this invention are as follows:

[0062] 1. In this invention, the hydrophilic adsorption functional layer of catechin and the hydrophobic functional layer of silane are spatially separated but integrated on the same nano-silica particle, so that the material has a typical Janus asymmetric structure, and a catechin / hydrophobic Janus nano-silica well wall stabilizer is prepared.

[0063] 2. The catechol / hydrophobic Janus nano silica well wall stabilizer of this invention contains hydrophilic groups such as catechol, dopamine, polydopamine or polycatechol modified polymer, which can form multi-point adsorption on the surface of shale minerals, thereby improving the material's retention ability on shale microcracks and weak bedding surfaces.

[0064] 3. The silane hydrophobic functional groups in the catechol / hydrophobic Janus nano silica wellbore stabilizer of this invention can improve the hydrophobicity of the shale surface, reduce the wetting and capillary self-adsorption of water-based drilling fluid filtrate on shale, thereby slowing down the intrusion of filtrate.

[0065] 4. After the catechol / hydrophobic Janus nano silica wellbore stabilizer of this invention enters the micropores or microcracks of shale, the rigid core of nano silica seals the pores and cracks, the catechol surface strongly adsorbs shale through the hydrophilic adsorption functional layer of catechol, and the hydrophobic functional surface slows down the intrusion of water molecules through the silane hydrophobic functional layer, thereby achieving the purpose of synergistic stabilization of the wellbore.

[0066] 5. The catechol / hydrophobic Janus nano silica wellbore stabilizer of this invention can achieve a synergistic effect of "strong surface adsorption - sealing and plugging - hydrophobic modification" in water-based drilling fluids. After water-based drilling fluid containing this wellbore stabilizer enters the micropores and fractures of shale, it effectively seals the micropores and fractures on the one hand, and increases the hydrophobicity of the shale surface on the other hand. This can significantly reduce the amount of drilling fluid filtrate intrusion, effectively slow down the entry of water molecules, and help improve the wellbore stability of water-sensitive shale and shale formations with weak surfaces. Attached Figure Description

[0067] Figure 1 The Fourier transform infrared spectra of the polydopamine / dodecyl Janus nano silica well wall stabilizer prepared in Example 1 and the original nano silica are shown.

[0068] Figure 2 The results are experimental evaluations of the pressure transmission effect of the catechol / hydrophobic Janus nano-silica wellbore stabilizers prepared in Examples 1-3 in shale. Detailed Implementation

[0069] The present invention will be further illustrated below with specific embodiments, but is not limited thereto. Unless otherwise specified, the experimental methods described in the embodiments are conventional methods; the reagents and materials used are commercially available unless otherwise specified.

[0070] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0071] Example 1

[0072] A method for preparing a catechol / hydrophobic Janus nano-silica wellbore stabilizer includes the following steps:

[0073] S1: Preparation of interface-coated nano-silica particles

[0074] Accurately weigh 1.0 g of nano-silica with an average particle size of 80 nm, add it to 100 mL of deionized water, and sonicate for 30 min. Adjust the pH to 8.0 with ammonia water, add 0.12 g of NaCl, stir to dissolve it completely, and then add 0.02 g of hexadecyltrimethylammonium bromide (CTAB) as a wetting regulator. Continue stirring and mixing for 30 min to allow CTAB to adsorb onto the surface of nano-silica and adjust its interfacial wettability, thus obtaining a nano-silica dispersion.

[0075] 10 g of paraffin wax (melting point 62~65℃) was heated to 80℃ and melted. It was then added to a nano-silica dispersion and stirred and emulsified at 80℃ and 1200 rpm for 2 hours to form a water-wax Pickering emulsion. After emulsification, the mixture was immediately placed in an ice-water bath to cool it, which allowed the molten paraffin wax to solidify rapidly and the nano-silica particles to be partially embedded in the paraffin phase, thus obtaining interface-coated nano-silica particles.

[0076] S2: Preparation of Janus nano-silica intermediate

[0077] Take 0.8 g of dodecyltriethoxysilane and add it to an ethanol-water solution (ethanol to water volume ratio of 90:10). Adjust the pH to 5.0 with a small amount of glacial acetic acid and pre-hydrolyze at 25℃ for 30 min to obtain a dodecyltriethoxysilane solution.

[0078] 1g of interface-coated nano silica particles were added to a dodecyltriethoxysilane solution and reacted at 50℃ for 10h to allow the exposed silica hemispheres to undergo a hydrophobic silanization reaction. After the reaction, the particles were washed 5 times with n-hexane to remove paraffin, and then washed 3 times alternately with ethanol and deionized water. Finally, the particles were centrifuged at 9000rpm for 10min to obtain Janus nano silica intermediate with a dodecyl hydrophobic layer on one side and silanol groups on the other side.

[0079] S3: Preparation of Catechol / Hydrophobic Janus Nano-Silica Wellbore Stabilizer

[0080] Janus nano-silica intermediates were dispersed in 10 mmol / L Tris-HCl buffer at pH 8.5 to a concentration of 5 mg / mL. Dopamine hydrochloride was then added to a concentration of 1.0 mg / mL. The mixture was stirred for 2 h in the presence of air or oxygen. After the reaction, the mixture was centrifuged at 10,000 rpm for 10 min, then washed alternately with ethanol and deionized water until the supernatant was colorless and transparent. Finally, it was vacuum dried at 60 °C for 12 h to obtain a polydopamine / dodecyl Janus nano-silica wellbore stabilizer, denoted as PDA−SiO2−C. 12 .

[0081] The PDA surface of the polydopamine / dodecyl Janus nano-silica wellbore stabilizer prepared in this embodiment is a strong adsorption surface of shale, C 12 The alkyl surface is hydrophobic, and its Fourier transform infrared spectrum is shown below. Figure 1 As shown.

[0082] Depend on Figure 1 It can be seen that the product of Example 1 successfully introduced alkyl functional groups and polydopamine functional groups, indicating that the polydopamine / dodecyl Janus nano silica well wall stabilizer was successfully prepared.

[0083] Example 2

[0084] A method for preparing a catechol / hydrophobic Janus nano-silica wellbore stabilizer includes the following steps:

[0085] S1: Preparation of interface-coated nano-silica particles

[0086] Accurately weigh 1.0 g of nano-silica with an average particle size of 80 nm, add it to 100 mL of deionized water, and sonicate for 30 min. Adjust the pH to 8.0 with ammonia water, add 0.12 g of NaCl, stir to dissolve it completely, and then add 0.02 g of hexadecyltrimethylammonium bromide (CTAB) as a wetting regulator. Continue stirring and mixing for 30 min to allow CTAB to adsorb onto the surface of nano-silica and adjust its interfacial wettability, thus obtaining a nano-silica dispersion.

[0087] 10 g of paraffin wax (melting point 62~65℃) was heated to 80℃ and melted. It was then added to a nano-silica dispersion and stirred and emulsified at 80℃ and 1200 rpm for 2 hours to form a water-wax Pickering emulsion. After emulsification, the mixture was immediately placed in an ice-water bath to cool it, which allowed the molten paraffin wax to solidify rapidly and the nano-silica particles to be partially embedded in the paraffin phase, thus obtaining interface-coated nano-silica particles.

[0088] S2: Preparation of Janus nano-silica intermediate

[0089] Take 0.8 g of dodecyltriethoxysilane and add it to an ethanol-water solution (ethanol to water volume ratio of 90:10). Adjust the pH to 5.0 with a small amount of glacial acetic acid and pre-hydrolyze at 25℃ for 30 min to obtain a dodecyltriethoxysilane solution.

[0090] 1g of interface-coated nano silica particles were added to a dodecyltriethoxysilane solution and reacted at 50℃ for 10h to allow the exposed silica hemispheres to undergo a hydrophobic silanization reaction. After the reaction, the particles were washed 5 times with n-hexane to remove paraffin, and then washed 3 times alternately with ethanol and deionized water. Finally, the particles were centrifuged at 9000rpm for 10min to obtain Janus nano silica intermediate with a dodecyl hydrophobic layer on one side and silanol groups on the other side.

[0091] S3: Preparation of Catechol / Hydrophobic Janus Nano-Silica Wellbore Stabilizer

[0092] Janus nano-silica intermediates were dispersed in deionized water to a concentration of 5 mg / mL. Tannic acid was then added to a concentration of 1.0 mg / mL. After adjusting the pH to 6.5, FeCl3 solution was added to allow the tannic acid to react with Fe... 3+ The molar ratio was 1:0.2. The deposition reaction was carried out with stirring at 25°C for 10 min. After the reaction, the mixture was first centrifuged at 10000 rpm for 10 min, and then washed four times alternately with ethanol and deionized water to remove unbound tannic acid and Fe. 3+ Finally, it was vacuum dried at 50℃ for 12 h to obtain tannic acid-Fe 3+ / Dodecyl Janus nano silica wellbore stabilizer, denoted as TA-Fe−SiO2−C 12 .

[0093] The tannic acid-Fe prepared in this embodiment 3+ / Dodecyl Janus nano-silica wellbore stabilizer uses tannic acid to provide strong polyphenol adsorption groups, which can form hydrogen bonds and coordination with hydroxyl groups and Fe / Al / Ca sites on the surface of shale minerals; C 12 The alkyl hemispheres provide hydrophobic and water-blocking properties. Compared to the dopamine route, this embodiment has the advantage of lower raw material costs.

[0094] Example 3

[0095] A method for preparing a catechol / hydrophobic Janus nano-silica wellbore stabilizer includes the following steps:

[0096] S1: Preparation of interface-coated nano-silica particles

[0097] Accurately weigh 1.0 g of nano-silica with an average particle size of 80 nm, add it to 100 mL of deionized water, and sonicate for 30 min. Adjust the pH to 8.0 with ammonia water, add 0.12 g of NaCl, stir to dissolve it completely, and then add 0.02 g of hexadecyltrimethylammonium bromide (CTAB) as a wetting regulator. Continue stirring and mixing for 30 min to allow CTAB to adsorb onto the surface of nano-silica and adjust its interfacial wettability, thus obtaining a nano-silica dispersion.

[0098] 10 g of paraffin wax (melting point 62~65℃) was heated to 80℃ and melted. It was then added to a nano-silica dispersion and stirred and emulsified at 80℃ and 1200 rpm for 2 hours to form a water-wax Pickering emulsion. After emulsification, the mixture was immediately placed in an ice-water bath to cool it, which allowed the molten paraffin wax to solidify rapidly and the nano-silica particles to be partially embedded in the paraffin phase, thus obtaining interface-coated nano-silica particles.

[0099] S2: Preparation of Janus nano-silica intermediate

[0100] Take 0.8 g of dodecyltriethoxysilane and add it to an ethanol-water solution (ethanol to water volume ratio of 90:10). Adjust the pH to 5.0 with a small amount of glacial acetic acid and pre-hydrolyze at 25℃ for 30 min to obtain a dodecyltriethoxysilane solution.

[0101] 1g of interface-coated nano silica particles were added to a dodecyltriethoxysilane solution and reacted at 50℃ for 10h to allow the exposed silica hemispheres to undergo a hydrophobic silanization reaction. After the reaction, the particles were washed 5 times with n-hexane to remove paraffin, and then washed 3 times alternately with ethanol and deionized water. Finally, the particles were centrifuged at 9000rpm for 10min to obtain Janus nano silica intermediate with a dodecyl hydrophobic layer on one side and silanol groups on the other side.

[0102] S3: Preparation of Catechol / Hydrophobic Janus Nano-Silica Wellbore Stabilizer

[0103] 1.0 g of Janus nano-silica intermediate was dispersed in 200 mL of ethanol-water solution (ethanol to water volume ratio 90:10). After ultrasonic dispersion for 20 min, 0.20 g of γ-aminopropyltriethoxysilane was added, and the pH was adjusted to 5.5 with glacial acetic acid. The mixture was stirred at 35 °C for 6 h to allow the γ-aminopropyltriethoxysilane to hydrolyze and condense with the silanol groups of silica on the originally shielded hemispherical surface, forming a surface aminosilane layer. After the reaction, the mixture was washed three times with ethanol, and the aminated Janus nano-silica intermediate was collected by centrifugation. Subsequently, the aminated Janus nano-silica intermediate was redispersed in 200 mL of ethanol-water solution (ethanol to water volume ratio 90:10), and 0.10 g of 3,4-dihydroxybenzaldehyde was added. The pH was adjusted to 7.5 with ammonia, and the mixture was stirred at 35 °C for another 6 h. h, the aldehyde group in 3,4-dihydroxybenzaldehyde undergoes a Schiff base reaction with the surface amino group, thereby fixing the dihydroxyphenyl group containing the catechol structure onto the originally shielded hemispherical surface; after the reaction, it is washed 5 times alternately with ethanol and deionized water, centrifuged at 10000 rpm for 10 min, and finally vacuum dried at 50℃ for 12 h to obtain catechol aldehyde / KH550 bridged modified-dodecyl Janus nano silica well wall stabilizer.

[0104] Example 4

[0105] Add 0.3% low-viscosity polyanionic cellulose and 0.2% xanthan gum to 4% bentonite-based slurry, and stir at high speed for 30 minutes to fully disperse the components and obtain drilling fluid-based slurry.

[0106] Then, Janus nano silica wellbore stabilizer prepared in Example 1, Example 2 or Example 3 was added to the drilling fluid base slurry at a mass percentage of 1%, and the mixture was stirred and dispersed at high speed for 30 min to obtain water-based drilling fluid containing Janus nano silica wellbore stabilizer, which were respectively designated as experimental groups 1 to 3.

[0107] Meanwhile, drilling fluid-based slurry without wellbore stabilizer and slurry with 1.0% ordinary nano silica were used as control groups 1 and 2, respectively. The specific groupings are shown in Table 1.

[0108] Table 1

[0109]

[0110] Experimental Example 1

[0111] Contact angle test: Shale cores from the same stratum were cut into circular pieces with a diameter of 25 mm and a thickness of 5 mm. The surface of the shale was polished sequentially with 400-grit, 800-grit, and 1200-grit sandpaper, and the surface dust was cleaned with anhydrous ethanol. The shale pieces were dried in a 60℃ oven for 12 h and then cooled to room temperature before use.

[0112] Nano silica and Janus nano silica well wall stabilizer prepared in Examples 1-3 were added to deionized water at a mass percentage of 1% to obtain nano silica dispersion and product dispersion of Examples 1-3.

[0113] The mudstone and shale flakes were then immersed in deionized water, 1% nano-silica dispersion, 1% dispersion of the product from Example 1, 1% dispersion of the product from Example 2, and 1% dispersion of the product from Example 3, respectively, and allowed to stand for 4 hours. After treatment, they were naturally dried at 40°C for 4 hours, and the contact angle of the surface was tested. Subsequently, the surface was quickly rinsed with a small amount of deionized water, and after natural drying at 40°C for 4 hours, the surface contact angle was tested again. Static water contact angle tests were performed using a contact angle meter. The volume of deionized water droplets was 2 μL, and three different locations were selected for testing for each sample. The average value was taken, and the test results are shown in Table 2 below.

[0114] Table 2

[0115]

[0116] As shown in Table 2, the contact angle of the shale surface decreased after treatment with the nano-silica dispersion, indicating that its hydrophilic surface easily enhances the wettability of the shale surface. After treatment with the Janus nano-silica wellbore stabilizer prepared in Examples 1-3 of this invention, the contact angle of the shale surface increased from 20.5° after deionized water treatment to approximately 55°, and remained above 50° even after rinsing with deionized water. This demonstrates that the product of this invention possesses both strong adsorption capacity and hydrophobic capacity on the shale surface.

[0117] Experimental Example 2

[0118] Pressure transmission test: Cores of mudstone and shale from the same stratum were processed into core sections with a diameter of 25 mm and a length of 5 mm. The end faces of the cores were smoothed with 800-grit sandpaper, and the sides were sealed with heat-shrink sleeves, leaving only the axial flow channel. The cores were placed in the pressure transmission test device, and a confining pressure of 5 MPa was applied. The upstream pressure was set to a constant pressure of 2 MPa, and the downstream initial pressure was 1 MPa. The test solution used in the experiment was the same as in Test Example 1. The test results are as follows. Figure 2 As shown in Table 3.

[0119] Table 3

[0120]

[0121] Depend on Figure 2 As shown in Table 3, compared with deionized water, the nano-silica dispersion can reduce the pressure transmission rate of shale to a certain extent, but the reduction is limited (the pressure transmission time increases by about 167%). In contrast, the Janus nano-silica wellbore stabilizer dispersions prepared in Examples 1-3 of this invention achieved pressure transmission times of 1511.63, 1301.83, and 1619.72 minutes, respectively, representing increases of over 900% compared to deionized water (Example 3 showed the best increase at 1159%). This indicates that the product of this invention has a far superior sealing effect on shale than ordinary silica dispersions (performance improvement of approximately 3.8-4.7 times), effectively sealing the nanopore throats and micro-fractures of shale and slowing the transmission of water-based drilling fluid filtrate into the shale.

[0122] Experimental Example 3

[0123] Rheological and filtration performance evaluation of drilling fluids: Drilling fluids prepared in Example 4, including control group 1-2 and experimental group 1-3, were tested according to the national standard GB / T 16783.1-2025 "Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids". A six-speed rotational viscometer was used to read the values ​​at 600 r / min and 300 r / min, and the apparent viscosity AV, plastic viscosity PV, and dynamic shear force YP were calculated. The API filtration loss was measured using a medium-pressure filtration meter at a test pressure of 0.69 MPa for 30 min. The test results are shown in Table 4.

[0124] Table 4

[0125]

[0126] As shown in Table 4, the apparent viscosity, plastic viscosity, and dynamic shear stress of the drilling fluid only increased moderately after adding the Janus nano-silica wellbore stabilizer prepared in Examples 1-3 of this invention, indicating that its effect on the rheological properties of the drilling fluid is controllable. Compared with the base mud, the API filtration loss of the drilling fluid decreased from 18.6 mL to 7.6 mL (product average) after adding the Janus nano-silica wellbore stabilizer prepared in Examples 1-3 of this invention, a reduction of approximately 59.1%. This indicates that the product of this invention can improve the compactness of the mud cake and has a good filtration loss reduction effect.

[0127] Experiment Example 4

[0128] Shale rolling recovery rate test: Shale cuttings from the same formation were tested according to the industry standard SY / T5613-2016 "Test Method for Physicochemical Properties of Shale in Drilling Fluid". The test solutions were the drilling fluids prepared in control groups 1-2 and experimental groups 1-3 in Example 4. The test results are shown in Table 5 below.

[0129] Table 5

[0130]

[0131] As shown in Table 5, the rolling recovery rate of shale in the base slurry without wellbore stabilizer was 80.6%, indicating that the shale has a certain degree of hydration dispersibility. The rolling recovery rate increased slightly to 82.8% after adding nano-silica. However, the rolling recovery rates of shale after adding the Janus nano-silica wellbore stabilizer prepared in Examples 1-3 of this invention were 94.3%, 91.0%, and 93.5%, respectively, which were significantly higher than the results of control groups 1 and 2. This indicates that the product of this invention can reduce the hydration dispersion of shale and improve the integrity of shale fragments through strong adsorption and hydrophobic effects.

[0132] In summary, the catechol / hydrophobic Janus nano-silica wellbore stabilizer of this invention can be adsorbed onto the surface of shale through its strong adsorption groups on one side and its hydrophobic groups facing outwards on the other, significantly improving the hydrophobicity of the shale surface, reducing the pressure transmission rate of shale, and improving the wellbore stability of shale. Compared with ordinary hydrophilic nano-silica, the material of this invention has both spatially independent strong adsorption groups and hydrophobic groups, which can form a synergistic effect of "strong adsorption-nano-blocking-hydrophobicity" in the micropores, microcracks, or weak bedding planes of shale, thereby improving the wellbore stability of water-based drilling fluids.

[0133] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Furthermore, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. In addition, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, they should also be considered as the content disclosed by the present invention.

Claims

1. A method for preparing a catechin / hydrophobic Janus nano-silica wellbore stabilizer, characterized in that, The steps include the following: S1: Preparation of interface-coated nano-silica particles Nano-silica was added to deionized water and ultrasonically dispersed for 25-35 minutes. After adjusting the pH to 5.0-10.0, electrolyte was added and stirred until homogeneous. Then, surfactant was added and stirred until homogeneous to obtain nano-silica dispersion. The coating medium was then melted and added to the nano-silica dispersion. The mixture was stirred, sheared, or ultrasonically emulsified at 45–90 °C and 1000–1200 rpm for 0.5–6 h. After emulsification, the mixture was immediately cooled to 0–4 °C to obtain interface-coated nano-silica particles. The coating medium was one or more of paraffin wax, microcrystalline wax, beeswax, low-melting-point polyethylene wax, and low-melting-point Fischer-Tropsch wax. S2: Preparation of Janus nano-silica intermediate Interface-coated nano silica particles were added to a hydrophobic modifier solution and reacted at 30-60°C for 1-24 h at a temperature 5°C or higher below the melting point of the coating medium. After washing and centrifugation, Janus nano silica intermediate was obtained. The hydrophobic modifier is one or more of octyltrialkoxysilane, dodecyltrialkoxysilane, hexadecyltrialkoxysilane, octadecyltrialkoxysilane, fluoroalkyltrimethoxysilane, and fluoroalkyltriethoxysilane. S3: Preparation of Catechol / Hydrophobic Janus Nano-Silica Wellbore Stabilizer Janus nano-silica intermediates were added to deionized water or buffer solution and stirred to disperse evenly. First, aminosilane was added to adjust the pH to 4.5–6.5, and the reaction was carried out at 25–45°C for 2–12 h with stirring. The mixture was washed 3–6 times with ethanol and centrifuged to obtain aminated Janus nano-silica intermediates. Then, the aminated Janus nano-silica intermediates were dispersed in an ethanol-water solution, and 3,4-dihydroxybenzaldehyde was added to adjust the pH to 6.5–8.

5. The reaction was carried out at 25–45°C for 2–12 h with stirring. After the reaction was completed, the mixture was washed, centrifuged, and dried to obtain a catechol / hydrophobic Janus nano-silica well wall stabilizer. The dispersion concentration of Janus nano silica intermediate is 0.5~20 mg / mL; the aminosilane is γ-aminopropyltriethoxysilane or γ-aminopropyltrimethoxysilane; the mass ratio of aminosilane to Janus nano silica intermediate is (0.1~0.5): the mass ratio of 1,3,4-dihydroxybenzaldehyde to aminated Janus nano silica intermediate is (0.05~0.2):

1.

2. The preparation method of the catechin / hydrophobic Janus nano-silica wellbore stabilizer as described in claim 1, characterized in that, In step S1, the particle size of the nano-silica is 10~500nm; The mass concentration of the nano-silica in deionized water is 0.1~10 wt%; The pH adjustment is achieved by adjusting the pH to 7.0-8.5 using one or more of the following: hydrochloric acid, acetic acid, sodium hydroxide, potassium hydroxide, ammonia, Tris buffer, phosphate buffer, and carbonate / bicarbonate buffer. The electrolyte is one or more of NaCl, KCl, NH4Cl, CaCl2, MgCl2, Na2SO4, and K2SO4; The molar concentration of the electrolyte in deionized water is 1~300 mmol / L; The surfactant is one or more of cationic surfactants, nonionic surfactants, or amphoteric surfactants; wherein the cationic surfactant is dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, bis(dodecyldimethylammonium bromide) or bis(hexadecyldimethylammonium bromide); the amphoteric surfactant is dodecyldimethyl betaine, cocamidopropyl betaine, or sulfobetaine-type surfactant; and the nonionic surfactant is Tween 20, Tween 40, Tween 60, Tween 80, Span 20, Span 60, or Span 80. The mass ratio of the surfactant to nano-silica is (0.001~0.5):1; The stirring, shearing, or ultrasonic emulsification time is 1-3 hours. The coating medium is paraffin or microcrystalline wax with a melting point of 40~80℃; The mass ratio of the nano-silica to the coating medium is 1:(2~50).

3. The preparation method of the catechin / hydrophobic Janus nano-silica well wall stabilizer as described in claim 2, characterized in that, The particle size of the nano-silica is 20~300nm; The mass concentration of the nano-silica in deionized water is 0.5~3wt%; The electrolyte is NaCl, KCl or NH4Cl, and its molar concentration in deionized water is 10~50 mmol / L; The surfactant is hexadecyltrimethylammonium bromide or didodecyldimethylammonium bromide; The mass ratio of the surfactant to nano-silica is (0.005~0.05):1; The mass ratio of the nano-silica to the coating medium is 1:(5~20).

4. The preparation method of the catechin / hydrophobic Janus nano-silica wellbore stabilizer as described in claim 1, characterized in that, In step S2, the mass ratio of the hydrophobic modifier to the interface-coated nano-silica particles is (0.05~5):1; The hydrophobic modifier solution has a mass concentration of 0.5~10 mg / mL and is prepared by adding the hydrophobic modifier to an ethanol aqueous solution and pre-hydrolyzing it at 20~45℃ for 10~60 min. The reaction temperature is 35~50℃ and more than 5℃ below the melting point of the coating medium, and the reaction time is 2~12h.

5. The preparation method of the catechin / hydrophobic Janus nano-silica wellbore stabilizer as described in claim 4, characterized in that, The hydrophobic modifier is dodecyltriethoxysilane; The mass ratio of the hydrophobic modifier to the interface-coated nano-silica particles is (0.2~2):1; The hydrophobic modifier solution has a mass concentration of 2~10 mg / mL and is prepared by adding the hydrophobic modifier to an ethanol aqueous solution, adjusting the pH of the solution to 4.0~6.0 with acetic acid, glacial acetic acid or dilute acetic acid, and pre-hydrolyzing at 25~35℃ for 20~40 min.

6. A catechin / hydrophobic Janus nano-silica wellbore stabilizer, characterized in that, It is prepared according to the method described in any one of claims 1 to 5; the catechol / hydrophobic Janus nano silica well wall stabilizer uses nano silica as an inorganic core and has an asymmetric interface structure on both sides of the inorganic core surface: one side is a catechol hydrophilic strong adsorption functional layer and the other side is a silane hydrophobic functional layer.

7. The application of the catechin / hydrophobic Janus nano silica wellbore stabilizer according to claim 6 in the preparation of water-based drilling fluids.

Images