Method for preparing drilling fluid with ultra-micro multi-cell nano-weighting agents for ultra-deep wells

Abstract

This invention discloses a method for preparing drilling fluid with ultra-micro multi-cell nano-weighting agents for ultra-deep wells, belonging to the technical field of drilling composition. The preparation method uses micron-sized barite as a core, chemically bonded to a mesoporous nano-SiO2 shell, and in-situ loading nano-Fe3O4 satellite particles onto the shell. This structure achieves multi-cell synergy of "rigid support-spatial isolation-magnetic response," solving the technical problems of weighting agent sedimentation, rheological deterioration, and filtration loss control difficulties under the extreme high temperature and high pressure environment of ultra-deep wells.

Description

Technical Field

[0001] This invention relates to the field of composition technology for drilling, and more particularly to a method for preparing drilling fluids using ultra-micro multi-cell nano-weighting agents for ultra-deep wells. Background Technology

[0002] As oil and gas exploration advances into deeper and ultra-deep formations, drilling fluids face unprecedented high-temperature and high-pressure (HT / HP) challenges. Under bottomhole conditions exceeding 180°C and 100MPa, conventional drilling fluids using barite (BaSO4) as a weighting agent face serious technical bottlenecks: 1) Weighting agent particles settle more rapidly due to high-temperature thermal disturbance and gravity, forming a "barite settling bed," leading to uneven downhole density and inducing well kicks or lost circulation; 2) Particle settling disrupts the colloidal structure of the drilling fluid, causing rheological properties (such as dynamic shear force and gel strength) to become uncontrolled; 3) High temperatures exacerbate filtrate intrusion into the formation, resulting in a thick, poor-quality filter cake.

[0003] Existing technological improvements often focus on a single dimension. For example, Chinese invention patent CN112852395A focuses on nano-sizing barite to improve suspension stability, or improving compatibility by introducing a polymer coating layer. However, simple nano-sizing can easily lead to excessively high system viscosity at ultra-high densities, and the intense Brownian motion of nanoparticles at high temperatures may actually damage the structure. Furthermore, a single coating layer is prone to failure under long-term high temperature, high pressure, and shear stress. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the drilling fluid preparation method of this invention constructs a core-shell-satellite hierarchical structure that combines rigidity, mesopority, and magnetic responsiveness, thereby solving the multiple technical problems faced by existing drilling fluids in ultra-deep well environments, as detailed below:

[0005] A method for preparing drilling fluid for ultra-deep wells using ultra-micro multi-cell nano-weighting agents includes the following steps:

[0006] S1. Hydroxylation of micron-sized barite surface to obtain activated barite core layer;

[0007] S2. Construct a mesoporous SiO2 shell outside the activated barite core layer;

[0008] S3. Construct magnetic satellite particles outside the mesoporous SiO2 shell to obtain an ultra-micro multi-cell nano-weighting agent;

[0009] S4. Drilling fluid blending, the drilling fluid components include the above-mentioned ultra-micro multi-zone nano-weighting agent.

[0010] Further, step S1 includes:

[0011] S11. Pre-disperse micron-sized barite powder into a suspension in deionized water and adjust the pH to an acidic environment;

[0012] S12. Add γ-aminopropyltriethoxysilane to the above acidic solution and heat to the preset temperature. The silanol groups undergo a condensation reaction with the active sites on the surface of barite.

[0013] S13. The product after reaction is centrifuged, washed with water, and vacuum dried to obtain activated barite.

[0014] Further, by weight, the ratio of micron-sized barite powder, deionized water, and γ-aminopropyltriethoxysilane is 100:300:3; the barite powder in step S11 has a particle size of 1.5 μm, the stirring speed during dispersion is 3000 rpm, the dispersion time is 30 minutes, and the pH of the suspension is adjusted to 4.0 with an appropriate amount of acetic acid; in step S12, the temperature is raised to 75℃ and reacted for 4 hours; in step S13, the vacuum drying temperature is 80℃.

[0015] Further, step S2 includes:

[0016] S21: Disperse activated barite in a water-ethanol mixture containing hexadecyltrimethylammonium bromide and stir at a constant temperature until homogeneous;

[0017] S22: First add ammonia water, then add tetraethyl orthosilicate dropwise at a preset rate. After the dropwise addition is complete, react for a preset time.

[0018] S23: After the reaction is completed, the product is centrifuged, washed and calcined to obtain barite BaSO4@mSiO2 with a SiO2 shell with a mesoporous structure.

[0019] Further, according to the weight parts, the ratio of activated barite, hexadecyltrimethylammonium bromide, tetraethyl orthosilicate, ammonia, deionized water, and ethanol is 50:3.65:10.4:5:250:100; the constant temperature stirring in step S21 is strong stirring at 60°C for 1 hour; the preset rate in step S22 is 1 ml / min, and the reaction is carried out at 60°C for 8 hours; the calcination in step S23 is placed in a muffle furnace, heated to 550°C at 2°C / min, and calcined for 4 hours, so that the specific surface area of ​​the mesoporous SiO2 shell is not less than 350 m² / g, and the pore size distribution is 5-10 nm.

[0020] Further, step S3 includes:

[0021] S31. Disperse BaSO4@mSiO2 ultrasonically in deoxygenated deionized water and introduce protective gas;

[0022] S32, add FeCl3·6H2O and FeSO4·7H2O, and stir vigorously in a water bath;

[0023] S33. Adjust the pH of the system to alkaline and set the reaction time to the preset time;

[0024] S34. After the reaction is complete, the product is collected with the help of a magnet. After washing and grinding, an ultra-micro multi-cell nano-weighting agent is obtained.

[0025] Further, the ratio of BaSO4@mSiO2, FeCl3·6H2O, FeSO4·7H2O, and deoxygenated deionized water is 40:8.1:5.6:200; the protective gas introduced in step S31 is nitrogen; the water bath temperature in step S32 is 65°C; in step S33, the pH is adjusted to 10.5 with an appropriate amount (28wt%) of ammonia water, and the reaction is carried out at 65°C under nitrogen protection for 2 hours; in step S34, the washing is carried out by washing with deionized water and ethanol in sequence, and vacuum drying at 60°C, so that Fe3O4 satellite particles are uniformly loaded on the mesoporous SiO2 shell with a particle size of 25-35nm.

[0026] Further, step S4 includes:

[0027] S41. Add tap water to the mixing equipment, start the mixing first, then add half the weight of the ultra-micro multi-zone nano weighting agent, and continue mixing after adding to form a uniform base slurry.

[0028] S42. Add alkalinity regulator, shale inhibitor, filtration loss reducer, and flow pattern regulator in sequence. After each component is added, maintain the preset stirring rate and stir for the preset time to ensure sufficient hydration and dispersion.

[0029] S43. Add the remaining ultra-micro multi-cell nano-weighting agent, and continue stirring after adding to form a uniform base slurry;

[0030] S44. Add defoamer, then increase the stirring rate and continue high-speed shear stirring for a preset time to ensure that the components are fully mixed and reacted at the molecular and colloidal levels to form the final drilling fluid.

[0031] Further, according to the weight parts, the ratio of tap water, ultrafine multi-zone nano-weighting agent, flow pattern regulator, filtration loss reducer, shale inhibitor, alkalinity regulator, and defoamer is 100:60:1:3:2:0.3:0.1; in step S41, the stirring speed is 3000 rpm, and the stirring time after adding the ultrafine multi-zone nano-weighting agent is 15 minutes; in step S42, the preset stirring speed is 3000 rpm, and the preset stirring time is 15 minutes; in step S43, after adding the agent, the stirring speed is 3000 rpm, and the stirring time is 15 minutes; in step S44, the stirring speed is increased to 5000 rpm, and high-speed shear stirring is continued for 60 minutes.

[0032] Furthermore, the flow pattern regulator is xanthan gum, the filtration loss reducer is sulfonated phenolic resin SMP-II, the shale inhibitor is polyetheramine, the alkalinity regulator is sodium hydroxide, and the defoamer is polydimethylsiloxane.

[0033] Compared with the prior art, the present invention has at least one of the following technical effects:

[0034] 1) This invention solves the problem of dynamic sedimentation and density uniformity of weighting agents under extreme conditions in ultra-deep wells by constructing a multi-cell nanocomposite structure of "core-shell-satellite". In the prior art, ordinary micron-sized barite particles are prone to rapid sedimentation under high temperature and pressure, forming a "barite bed", while simple nano-sizing leads to excessively high viscosity and intense Brownian motion. This invention integrates a micron-sized barite core (providing basic high density), a mesoporous SiO2 shell (providing steric hindrance and bonding sites), and nano-Fe3O4 satellite particles (providing magnetic responsiveness) into a single structure through chemical bonding. This structure achieves a synergistic effect of multiple anti-settling mechanisms: the mesoporous shell effectively blocks direct contact and aggregation of the barite core; its large specific surface area can strongly anchor polymer chains in the drilling fluid, forming a stable spatial network; and the weak magnetism imparted by the Fe3O4 satellite particles provides a new means for dynamic particle management and recovery during downhole circulation. This triple synergy of "rigid support-spatial barrier-magnetic response" ensures that the drilling fluid can maintain settlement stability (stability factor ≥ 0.998) even after long-term static operation at 180°C and 100MPa, achieving precise and stable control of downhole density and avoiding the risks of well kick and well leakage caused by settlement.

[0035] 2) This invention overcomes the technical bottleneck of rheological deterioration and filtration loss control in high-temperature and high-pressure drilling fluids through a multi-scale interactive network of "particle-polymer". In traditional solutions, high temperatures easily degrade and deactivate polymer treatment agents, leading to damage to rheological properties and increased filtration loss. This technology transforms the nanocomposite weighting agent from an inert filler material into an "active structural unit" that can actively participate in the system construction. The abundant silanol groups in the mesoporous SiO2 shell undergo strong adsorption and cross-linking with polymer molecules such as sulfonated phenolic resin (SMP-II) and xanthan gum, forming a rigid reinforced gel network with inorganic nanoparticles as "cross-linking points". This network has significantly higher thermal stability than pure polymer gels, thus maintaining excellent rheological parameters (such as moderate dynamic shear force YP) even after aging at 180°C, ensuring rock-carrying capacity. Meanwhile, the multi-scale distributed nanoparticles (from tens of nanometers of Fe3O4 to hundreds of nanometers of SiO2 shell) can synergize with the polymer to achieve dense physical stacking in the filter cake, forming a low permeability barrier, thereby reducing the high-temperature and high-pressure filtration loss to below 8.6 mL, which is lower than that of the ordinary barite system (25.4 mL) and the pure nano barite system (15.2 mL), achieving dual optimization of rheology and filtration loss.

[0036] 3) Weighting agents in traditional drilling fluids (especially micron-sized barite) are easily lost due to particle settling or mechanical separation when passing through solids control equipment such as vibrating screens and centrifuges. This not only increases material costs but also leads to unstable drilling fluid density, requiring frequent replenishment of weighting agents. The ultra-micro multi-cell nano-weighting agent in this invention, due to the suspension stability provided by its mesoporous SiO2 shell, can reduce sedimentation and segregation in solids control equipment.

[0037] 4) When drilling into formations with narrow density windows (such as when pore pressure and fracture pressure are very close), traditional drilling fluids often exhibit discrepancies between the actual downhole density and the density measured at the surface due to uneven settling or suspension of weighting agents. This can easily induce well leakage or well kick accidents. The drilling fluid of this invention, with its "core-shell-satellite" structure providing suspension stability (settling stability factor 0.998), ensures density uniformity throughout the well from wellhead to bottom. The density value measured at the surface more closely reflects the actual downhole annular hydrostatic pressure, improving the accuracy and safety of pressure control.

[0038] 5) The magnetic response characteristics imparted by Fe3O4 satellite particles promise to provide on-site recovery methods: Weak magnetic field devices can be installed at key locations in the solids control system flow channels or circulation tanks to magnetically capture and recover weighting agents lost with drill cuttings or waste fluids. This characteristic transforms weighting agents, traditionally considered consumables, into recyclable functional materials, reducing the cost of weighting materials per well in ultra-deep well drilling and mitigating drilling fluid performance fluctuations caused by frequent weighting agent replenishment. Furthermore, the magnetism of Fe3O4 satellite particles makes intelligent dynamic fine-tuning of density possible in the future: by altering the distribution and arrangement of particles through a controllable downhole or surface magnetic field, the effective density or rheological structure of the fluid can be finely adjusted within a small range to respond in real-time to minute changes in formation pressure. Detailed Implementation

[0039] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0040] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0041] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0042] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0043] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0044] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0045] This invention relates to the sources of the main substances: barite powder, i.e., BaSO4, CAS No.: 7727-43-7; γ-aminopropyltriethoxysilane, CAS No. 919-30-2, molecular formula C9H 23 NO3Si; hexadecyltrimethylammonium bromide, CAS No. 57-09-0, molecular formula C 19 H 42 BrN; Tetraethyl orthosilicate, CAS No. 78-10-4, Molecular formula C8H 20 O4Si; Xanthan gum, a flow modifier, CAS No. 11138-66-2, molecular formula (C 35 H 49 O 29 ) nThe filtration loss reducer is sulfonated phenolic resin SMP-II, CAS number 63512-68-5, which conforms to industry standard Q / SH CG0178; the shale inhibitor is CAD-230 type polyetheramine, CAS number 9046-10-0, with a molecular weight of 200-250 and an amine value of 500-600 mg KOH / g; the defoamer is polydimethylsiloxane, CAS number 9016-00-6, molecular formula (C2H6OSi). n All of the above substances are common commercially available products.

[0046] This application's "ultra-micro multi-cell nano-weighting agent" refers to a composite functional material that uses a hierarchical structure design of "core (micron-sized BaSO4) - shell (mesoporous SiO2) - satellite (nano-sized Fe3O4)" to chemically bond material cells of different scales (micron, nano) and different functions (high density, spatial stability, magnetic response) into a whole, in order to synergistically solve multiple problems such as weighting agent sedimentation, rheological deterioration and filtration loss control in ultra-deep well drilling fluids.

[0047] A method for preparing drilling fluid using ultra-deep wells with ultra-micro multi-cell nano-weighting agents includes two processes: preparing the ultra-micro multi-cell nano-weighting agents and formulating the drilling fluid. The preparation of the ultra-micro multi-cell nano-weighting agents includes the following steps:

[0048] S1. Hydroxylation of micron-sized barite surface to obtain activated barite core layer;

[0049] Step S1 includes:

[0050] S11. Pre-disperse 100 parts by weight of micron-sized barite powder in 300 parts by weight of deionized water for 30 minutes at a stirring speed of 3000 rpm to form a suspension. Adjust the pH of the suspension to 4.0 with acetic acid.

[0051] S12. Add 3 parts by weight of γ-aminopropyltriethoxysilane (KH-550) to the above acidic solution, heat to 75°C, and reflux for 4 hours with mechanical stirring at 1000 rpm. Under acidic hydrothermal conditions (pH 4.0, 75°C), barite is activated in situ, generating reactive sites BaSO4-OH (surface). Simultaneously, silanols condense with the active sites on the barite surface. KH-550 hydrolyzes under acidic conditions, and its silanols condense with active sites (such as impurities or defects) on the barite surface, with the other end amino group (-NH2) facing outwards, providing nucleation sites for subsequent SiO2 polycondensation. The reaction equation is as follows: The three ethoxy groups (-OC2H5) in the KH-550 molecule hydrolyze to silanol (-Si(OH)3) in an acidic aqueous environment.

[0052] (C2H5O)3Si-(CH2)3-NH2+3H2O→(HO)3Si-(CH2)3-NH2+3C2H5OH;

[0053] The silanol intermediate undergoes condensation with the surface of barite activated under acidic hydrothermal conditions, forming a chemical bond:

[0054] BaSO4-OH (activated surface) + (HO)3Si-(CH2)3-NH2 → BaSO4-O-Si(OH)2-(CH2)3-NH2 + H2O. BaSO4-O-Si(OH)2-(CH2)3-NH2 indicates that one silanol group has been bonded to the surface, and the remaining two silanol groups can participate in subsequent polycondensation.

[0055] S13. Centrifuge the reaction product at 8000 rpm for 10 minutes, discard the supernatant, and then repeatedly disperse and centrifuge with deionized water three times until the washing liquid is neutral when tested with pH paper. Then place the solid in a vacuum drying oven and dry at 80°C for 6 hours to obtain activated barite.

[0056] S2. Construct a mesoporous SiO2 shell outside the activated barite core layer;

[0057] Step S2 includes:

[0058] S21: Disperse 50 parts by weight of activated barite in a water-ethanol mixture containing 3.65 parts by weight of cetyltrimethylammonium bromide (CTAB), and stir vigorously at 60°C for 1 hour until homogeneous. The water-ethanol mixture is obtained by uniformly mixing 250 parts by weight of deionized water and 100 parts by weight of ethanol.

[0059] S22: Next, add 5 parts by weight of ammonia water (28 wt%) to the mixture from S21, then slowly add 10.4 parts by weight of tetraethyl orthosilicate (TEOS) dropwise at a rate of 1 ml / min. After the addition is complete, continue the reaction at 60°C for 8 hours. CTAB forms a micelle template, and TEOS hydrolyzes under alkaline conditions and condenses at the amino / hydroxyl interface between the micelles and the activated barite surface, forming a SiO2 / CTAB composite coating layer with CTAB as the template. The chemical equation for the reaction is as follows:

[0060] Hydrolysis of tetraethyl orthosilicate: Si(OC2H5)4 + 4H2O → Si(OH)4 + 4C2H5OH;

[0061] Dehydration condensation between silicic acid monomers: Si(OH)4 + Si(OH)4 → (HO)3Si-O-Si(OH)3 + H2O;

[0062] (HO)3Si-O-Si(OH)3 is disilicate, which is the most basic condensation step in forming the SiO2 network. The remaining silanol groups in the molecule will continue to undergo repeated dehydration condensation reactions with the silanol groups of other silicic acid monomers or oligomers. This process will continue and generate colloidal particles with a network structure.

[0063] S23: After the reaction was complete, the product was centrifuged at 8000 rpm for 10 minutes to separate the solid. After discarding the supernatant, the product was washed twice with ethanol and then once with deionized water (redispersed and centrifuged each time) until no Br was detected in the supernatant using 0.1 mol / L AgNO3 solution. - The precipitation of ions (characteristic ions of CTAB) indicates that the template agent CTAB has been washed away. Then, it is placed in a muffle furnace and heated to 550°C at 2°C / min for 4 hours to completely remove the CTAB template, resulting in barite BaSO4@mSiO2 with a mesoporous SiO2 shell. BET testing shows that its specific surface area is ≥350m² / g and the pore size distribution is 5-10nm.

[0064] Under alkaline conditions, the protonated amino groups (-NH4+) on the surface of barite are activated. 3+ By preferentially enriching and catalyzing the negatively charged TEOS hydrolysis products at their interface through electrostatic attraction, an interlocking mesoporous structure is epitaxially grown using CTAB micelles as a template through the formation of Si-O-Si / Si-O-Ba covalent bonds. Then, the silanol groups are deeply condensed and densified by high-temperature calcination at 550°C, thereby forming a mesoporous SiO2 shell that is chemically bonded to the core layer and has a continuous and robust structure.

[0065] S3. Construct magnetic satellite particles outside the mesoporous SiO2 shell to obtain an ultra-micro multi-cell nano-weighting agent;

[0066] Step S3 includes:

[0067] S31. Disperse 40 parts by weight of BaSO4@mSiO2 ultrasonically in 200 parts by weight of deoxygenated deionized water, and introduce nitrogen gas as a protective gas.

[0068] S32, add 8.1 parts by weight of FeCl3·6H2O and 5.6 parts by weight of FeSO4·7H2O, and stir vigorously in a 65°C water bath to allow the iron source ions (Fe) to... 3+ and Fe 2+ The Fe3O4 nanoparticles are fully adsorbed into the internal pores and outer surface of the mesoporous SiO2 shell, which are the sites for subsequent growth and bonding of Fe3O4 nanoparticles.

[0069] S33. Quickly adjust the pH of the system to 10.5 with an appropriate amount of ammonia. At this point, the solution turns black. Continue the reaction at 65°C under N2 protection for 2 hours. Under alkaline conditions, Fe... 3+ and Fe 2+ Fe3O4 is co-precipitated, and the hydroxyl groups on the surface of the newly formed particles undergo dehydration condensation with the silanol groups on the surface of the mesoporous SiO2 shell to form strong Fe-O-Si bonds, thereby achieving chemical bonding loading. The reaction equation is as follows:

[0070] Fe 2+ +2Fe 3+ +8OH - →Fe3O4↓+4H2O;

[0071] Bonding: ≡Si-OH+HO-Fe≡→≡Si-O-Fe+H2O.

[0072] Where ≡Si-OH represents the silanol groups on the surface of the mesoporous SiO2 shell; HO-Fe≡ represents the iron hydroxyl groups on the surface of the newly formed Fe3O4 nanoparticles; ≡Si-O-Fe≡ represents the formed stable chemical bond (Fe-O-Si bond), which anchors the satellite particles to the shell. The silanol groups originate from the incompletely reacted Si-OH groups on the surface of the SiO2 network formed by the hydrolysis and condensation of TEOS; the iron hydroxyl groups originate from the Fe... 3+ and Fe 2+ When Fe3O4 crystals are co-precipitated, the exposed metal ions on their surface combine with water to form Fe-OH groups.

[0073] S34. After the reaction is complete, place the container containing the reaction solution against the side of a strong N52 neodymium iron boron permanent magnet with a surface magnetic flux density of not less than 0.5T for 30 minutes to allow the Fe3O4 satellite particles to accumulate due to magnetic response. After discarding the supernatant, transfer the resulting solid to a washing device. Disperse the solid using alternating ultrasonic (100W) and centrifugation (8000rpm, 10min) with deionized water and anhydrous ethanol at a solid-liquid ratio of 1:20, and wash three times each, until the conductivity of the washing solution is less than 5 μS / cm and no Br is detected by AgNO3 solution. - The residue was then removed, and the purified product was placed in a vacuum drying oven and dried at 60°C for 12 hours. Finally, the dried block was put into an LS-QB1 type ultrafine nano sand mill equipped with 0.015mm zirconia microbeads and circulated for 2 hours to obtain the final product of ultrafine multi-zone nano weighting agent with uniform satellite particle distribution and D50 particle size of about 30nm.

[0074] Drilling fluid preparation steps:

[0075] S4. Drilling fluid blending, the drilling fluid components include the above-mentioned ultra-micro multi-zone nano-weighting agent.

[0076] Step S4 includes:

[0077] S41. Add 100 parts by weight of tap water to the mixing equipment (GJ-3S type high-speed planetary drilling fluid mixer), start the mixing first, and then add 60 parts by weight of ultra-micro multi-zone nano weighting agent. After adding, stir at 3000 rpm for 15 minutes to form a uniform base slurry.

[0078] S42. Add sodium hydroxide (alkalinity regulator) 0.3 parts by weight, polyetheramine (shale inhibitor) 2.0 parts by weight, sulfonated phenolic resin SMP-II (filtration loss reducer) 3.0 parts by weight, and xanthan gum (flow pattern regulator) 1.0 parts by weight in sequence. After each component is added, stir at 3000 rpm for 15 minutes, and then add another component. Repeat this process to ensure full hydration and dispersion.

[0079] S43. Add the remaining 60 parts by weight of ultrafine multi-cell nano-weighting agent. After adding, continue stirring at 3000 rpm for 15 minutes to form a uniform base slurry.

[0080] S44. Add 0.1 parts by weight of defoamer polydimethylsiloxane, then increase the stirring speed to 5000 rpm and continue high-speed shearing for 15 minutes to ensure that the components are fully mixed and reacted at the molecular and colloidal levels to form the final drilling fluid.

[0081] The stepwise addition of the ultrafine multi-cell nano-weighting agent aims to prevent uneven dispersion and clumping caused by adding too much at once. High-speed, long-duration shearing ensures complete dispersion of the nano-weighting agent, allowing its surface active sites to fully interact with polymer molecules (xanthan gum, SMP) to construct a stable spatial network structure. The order of addition is as follows: first, establish the basic dispersion system; then, add the treatment agent for modification; and finally, complete the structure construction through high-speed shearing, which conforms to the principles of colloid chemistry.

[0082] Tap water serves as the dispersion medium, providing a continuous phase to dissolve and disperse all treatment agents, thus forming the basic fluid of the drilling fluid.

[0083] Ultra-micro multi-zone nano-weighting agent: Through the hierarchical structure of "core (density)-shell (stability)-satellite (magnetic response)," it provides density and fundamentally ensures suspension stability under high temperature and high pressure.

[0084] Xanthan gum: As a flow modifier, its polymer chains form a reversible three-dimensional network, giving drilling fluid the required shear-dilution rheology to suspend and carry cuttings.

[0085] Polyetheramine: As a shale inhibitor, its amine groups are strongly adsorbed onto the clay surface, inhibiting shale hydration and swelling and stabilizing the wellbore by neutralizing charges and forming a hydrophobic film.

[0086] Sodium hydroxide: As an alkalinity regulator, it provides and maintains an alkaline environment in the system, ensuring that all treatment agents perform at their best.

[0087] Defoamer: By reducing local surface tension, it quickly eliminates harmful foam generated during agitation, maintaining drilling fluid density and pumping efficiency.

[0088] In an alkaline environment, the hydroxyl and sulfonic acid groups abundant on the long-chain molecules of xanthan gum and sulfonated phenolic resin (SMP-II) are strongly and multi-site anchored to the large specific surface area of ​​the mesoporous SiO2 shell of the nano-weighting agent and its surface silanol groups, as well as the surface of Fe3O4 satellite particles, through hydrogen bonds, coordination bonds, and van der Waals forces. This multi-anchoring effect is equivalent to "welding" or "weaving" flexible polymer molecular chains onto a rigid nanoparticle network, forming a "particle-reinforced composite gel." Compared to pure polymer gels, this structure, with nanoparticles acting as robust cross-linking points, effectively inhibits the thermal motion and deentanglement of polymer chains at high temperatures (>180°C), enhancing the thermodynamic stability and mechanical strength of the three-dimensional network. Therefore, under the extreme high temperature, high pressure, and strong shear environment of ultra-deep wells, this composite network can effectively resist damage, maintain excellent elasticity and strength, thereby achieving resistance to weighting agent sedimentation, maintaining good rheological properties of the drilling fluid, and carrying capacity for cuttings.

[0089] SMP-II molecules act as "smart adhesives" and "bridging agents." Their linear long chains can rapidly adsorb, extend, and interconnect on the surface of rock pores under pressure differential, initially constructing the polymer framework of the filter cake. Simultaneously, nano-weighting agents with a unique "core-shell-satellite" structure provide a wide particle size distribution, ranging from tens of nanometers (Fe3O4 satellites) to hundreds of nanometers (SiO2 shells) and even micrometers (BaSO4 cores). Guided and bonded by the SMP-II polymer, these multi-scale solid particles can achieve the densest physical packing, much like "gravel, sand, and cement" of different sizes, efficiently filling and plugging the macroscopic and microscopic pores formed by the polymer framework. In particular, the nanoscale Fe3O4 and SiO2 shell fragments can deeply seal the throats of micro- and nano-sized pores. The synergistic construction of this "polymer flexible skeleton" and "multi-scale rigid particles" ultimately forms a filter cake with extremely low permeability, dense structure and good toughness, thereby reducing the filtration loss under high temperature and high pressure to a low level (such as 8.6 mL), effectively protecting the oil and gas reservoir and maintaining wellbore stability.

[0090] Polyetheramines have a dual function: First, as a primary shale inhibitor, their highly adsorbent amine groups anchor between the crystal layers and on the surface of clay minerals in the wellbore, neutralizing negative charges and forming a hydrophobic film to inhibit hydration swelling and strengthen the wellbore. Second, their molecules can partially adsorb onto the surface of solid particles such as nano-weighting agents and drill cuttings within the drilling fluid. By improving the wettability of particle surfaces and the double-layer state, they enhance the spatial repulsion between particles, thereby improving the dispersion stability of the colloidal system from within and preventing the flocculation and sedimentation of harmful solid phases. The stable, strongly alkaline environment (pH>10) provided by sodium hydroxide is the reaction basis and driving force for the efficient and stable occurrence and maintenance of all the above-mentioned adsorption, hydrolysis, condensation, cross-linking, and other physicochemical processes. It ensures the full ionization of polymer functional groups to maintain chain extension, optimizes the adsorption morphology of polyetheramines, maintains the surface potential of nanoparticles, and locks the structure and performance of the entire "particle-polymer" synergistic network, enabling the system to maintain performance stability even after long-term high-temperature aging.

[0091] Comparative Example 1

[0092] The ultra-micro multi-cell nano-weighting agent of this invention was replaced with an equal amount of ordinary API barite (D50=20μm).

[0093] Comparative Example 2

[0094] The weighting agent of this invention is replaced with an equal amount of commercially available nano barite (D50=200nm).

[0095] The drilling fluid of the present invention was compared with a comparative example, and the density of all drilling fluids was prepared to be 2.2 g / cm³.

[0096] High-Temperature and High-Pressure Rheological Testing: Aging drilling fluid samples were taken and tested using a high-temperature and high-pressure rheological testing system (such as the FANN iX77 or Grace M5600). The sample cup was first placed in a heating mantle, and the target temperature was set to 50°C. After the temperature stabilized, the sensor rotor was immersed in the sample. Under a simulated pressure of 100 MPa, the instrument measured the torque at rotational speeds of 600, 300, 200, 100, 6, and 3 rpm, automatically calculating rheological parameters such as apparent viscosity (AV), plastic viscosity (PV), and dynamic shear force (YP).

[0097] High-Temperature and High-Pressure Filtration Loss Test: The test is conducted according to national standards using a high-temperature and high-pressure filtration loss meter (such as the OFI-173-00 model). The aged and cooled drilling fluid is poured into the test vessel. A filter paper is placed on top of the filter paper, the vessel is secured, and a heating jacket is placed inside. The temperature is set to 180°C, and a pressure of 3.5 MPa is applied using compressed nitrogen. Timing is started. During the 30-minute test, the filtrate is collected using a graduated cylinder. After the test, the pressure is released, the temperature is lowered, the filter cake is removed, and its thickness is measured. The collected filtrate volume (unit: mL) is the high-temperature and high-pressure filtration loss.

[0098] Settling stability factor test: Pour freshly prepared drilling fluid into a graduated, stoppered settling cylinder (e.g., 250 mL), filling it to the mark and recording the initial total volume (V0). Place the cylinder in a constant temperature oven at 180°C for static curing for 7 days. After removing it and cooling to room temperature, carefully remove approximately three-quarters of the slurry from the top of the cylinder, ensuring that the bottom sediment is not disturbed. Then pour out the remaining slurry and sediment from the bottom, transferring it all to a mixing cup and dispersing it thoroughly with a high-speed mixer. Pour the mixture back into the original cylinder and let it stand for 2 hours, then read the slurry volume at this point (V1). Settling stability factor = V1 / V0. The closer this value is to 1, the more stable the system, indicating no settling or complete redispersibility of the settling.

[0099] Rolling recovery rate test: Take 50g of dried and screened 4-10 mesh (approximately 2.0-4.75mm) shale cuttings and add them to an aging tank (e.g., a 500mL FANN aging tank) containing 350mL of drilling fluid. Seal the aging tank and place it in a roller heater at 180°C, where it is heated by rolling at a certain angle for 16 hours. After aging, flush all the fluid and cuttings in the tank through a 10-mesh (2.0mm) standard sieve under running water for 2 minutes. Collect the cuttings on the sieve, dry them at 105°C to constant weight, and weigh the recovered cuttings mass (Wr). Rolling recovery rate = (Wr / 50g) × 100%. The higher this value, the stronger the shale inhibition of the drilling fluid.

[0100] Table 1 shows the performance test results of the present invention and Comparative Examples 1 and 2.

[0101]

[0102] Table 1

[0103] The excessively high dynamic shear force (YP) of Comparative Example 1 (ordinary micron-sized barite) stems from the enhanced van der Waals forces between particles under high temperature and pressure, which easily leads to the formation of dense, rigid "card-like" aggregates, increasing the cohesive force of fluid flow. The excessively high plastic viscosity (PV) of Comparative Example 2 (pure nano-sized barite) is due to its large specific surface area, which excessively adsorbs free water, resulting in increased frictional resistance between particles and between particles and the fluid. This invention effectively blocks direct contact between barite nuclei through the steric hindrance effect provided by the mesoporous SiO2 shell, preventing harmful agglomeration. At the same time, the "particle-polymer" composite network formed by its surface with xanthan gum and SMP-II polymer possesses both moderate structural strength and thermal stability, thus maintaining excellent and balanced rheological parameters (ideal YP and PV) even after high-temperature aging.

[0104] Comparative Example 1, due to its large particle size (D50 = 20 μm), resulted in a loose filter cake structure with large pores and weak sealing ability. Comparative Example 2, although containing fine particles, exhibited a uniform shape and size, still showing significant size defects and porosity during high-pressure stacking. The "core-shell-satellite" structure of this invention provides a multi-scale particle size distribution from micrometers to nanometers (micrometer-sized BaSO4 core, nanometer-sized SiO2 shell fragments, and ~30 nm Fe3O4 satellite particles). These multi-level particles can synergistically interact with linear SMP-II polymer molecules to achieve precise packing and effectively block various pores in the filter cake from micrometers to nanometers, thereby constructing a dense, low-permeability filter cake and reducing high-temperature, high-pressure filtration loss.

[0105] In Comparative Example 1, the settling driving force (gravity) of the coarse particles is greater than the suspending force provided by Brownian motion and electrostatic repulsion, resulting in rapid and significant settling. In Comparative Example 2, although the nanoparticles exhibit significant Brownian motion, their high surface energy at high temperatures makes them prone to irreversible weak aggregation (forming large agglomerates), ultimately leading to slow but not negligible settling. This invention utilizes a mesoporous SiO2 shell to provide strong steric hindrance and electrostatic repulsion, preventing particle aggregation. Simultaneously, the weak magnetism imparted by the Fe3O4 satellite particles introduces a unique "magnetic responsiveness" to the system, allowing for dynamic adsorption and redispersion of escaped or agglomerated particles via a weak magnetic field at the wellhead, achieving superior settling stability.

[0106] Comparative Example 1 primarily relied on the chemical inhibition of polyetheramine, but the coarse particles could not effectively seal the micro- and nano-cracks in shale, and hydration channels remained. Comparative Example 2's nanoparticles improved the physical sealing ability, but the number of sites on the particle surface available for polyetheramine adsorption was limited, and the chemical inhibition efficiency was not fully realized. In this invention, the mesoporous SiO2 shell has a large specific surface area, serving as an "inhibitor reservoir" to load an unconventional dose of polyetheramine molecules, achieving continuous and potent chemical inhibition; simultaneously, its multi-scale nanoparticles can seal shale cracks and physically block water molecule intrusion. This deep synergy between "chemical adsorption inhibition" and "physical nano-sealing" jointly improves the rolling recovery rate.

[0107] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0108] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

Claims

1. A method for preparing drilling fluid using ultra-micro multi-cell nano-weighting agents for ultra-deep wells, characterized in that, Includes the following steps: S1. Hydroxylation of micron-sized barite surface to obtain activated barite core layer; S2. Construct a mesoporous SiO2 shell outside the activated barite core layer; S3. Construct magnetic satellite particles outside the mesoporous SiO2 shell to obtain an ultra-micro multi-cell nano-weighting agent; S4. Drilling fluid blending, the drilling fluid components include the above-mentioned ultra-micro multi-zone nano-weighting agent.

2. The drilling fluid preparation method for ultra-deep wells using ultra-micro multi-zone nano-weighting agents as described in claim 1, characterized in that, Step S1 includes: S11. Pre-disperse micron-sized barite powder into a suspension in deionized water and adjust the pH to an acidic environment; S12. Add γ-aminopropyltriethoxysilane to the above acidic solution and heat to the preset temperature. The silanol groups undergo a condensation reaction with the active sites on the surface of barite. S13. The product after reaction is centrifuged, washed with water, and vacuum dried to obtain activated barite.

3. The drilling fluid preparation method for ultra-deep wells using ultra-micro multi-zone nano-weighting agents as described in claim 2, characterized in that, The ratio of micron-sized barite powder, deionized water, and γ-aminopropyltriethoxysilane by weight is 100:300:3; the barite powder in step S11 has a particle size of 1.5 μm, the stirring speed during dispersion is 3000 rpm, the dispersion time is 30 minutes, and the pH of the suspension is adjusted to 4.0 with an appropriate amount of acetic acid; the temperature in step S12 is raised to 75℃ and reacted for 4 hours; the vacuum drying temperature in step S13 is 80℃.

4. The drilling fluid preparation method for ultra-deep wells using ultra-micro multi-zone nano-weighting agents as described in claim 1, characterized in that, Step S2 includes: S21: Disperse activated barite in a water-ethanol mixture containing hexadecyltrimethylammonium bromide and stir at a constant temperature until homogeneous; S22: First add ammonia water, then add tetraethyl orthosilicate dropwise at a preset rate. After the dropwise addition is complete, react for a preset time. S23: After the reaction is completed, the product is centrifuged, washed and calcined to obtain barite BaSO4@mSiO2 with a SiO2 shell with a mesoporous structure.

5. The drilling fluid preparation method for ultra-deep wells using ultra-micro multi-zone nano-weighting agents as described in claim 4, characterized in that, According to the weight proportions, the activated barite, hexadecyltrimethylammonium bromide, tetraethyl orthosilicate, ammonia, deionized water, and ethanol are 50:3.65:10.4:5:250:100; the constant temperature stirring in step S21 is strong stirring at 60°C for 1 hour; the preset rate in step S22 is 1 ml / min, and the reaction is carried out at 60°C for 8 hours; the calcination in step S23 is carried out in a muffle furnace, with the temperature increased to 550°C at 2°C / min, and calcined for 4 hours, so that the specific surface area of ​​the mesoporous SiO2 shell is not less than 350 m² / g, and the pore size distribution is 5-10 nm.

6. The drilling fluid preparation method for ultra-deep wells using ultra-micro multi-zone nano-weighting agents as described in claim 1, characterized in that, Step S3 includes: S31. Disperse BaSO4@mSiO2 ultrasonically in deoxygenated deionized water and introduce protective gas; S32, add FeCl3·6H2O and FeSO4·7H2O, and stir vigorously in a water bath; S33. Adjust the pH of the system to alkaline and set the reaction time to the preset time; S34. After the reaction is complete, the product is collected with the help of a magnet. After washing and grinding, an ultra-micro multi-cell nano-weighting agent is obtained.

7. The drilling fluid preparation method for ultra-deep wells using ultra-micro multi-zone nano-weighting agents as described in claim 6, characterized in that, The ratio of BaSO4@mSiO2, FeCl3·6H2O, FeSO4·7H2O, and deoxygenated deionized water is 40:8.1:5.6:200; the protective gas introduced in step S31 is nitrogen; the water bath temperature in step S32 is 65°C; in step S33, the pH is adjusted to 10.5 with an appropriate amount (28wt%) of ammonia water, and the reaction is carried out at 65°C under nitrogen protection for 2 hours; in step S34, the washing is carried out by washing with deionized water and ethanol in sequence, and vacuum drying at 60°C, so that Fe3O4 satellite particles are uniformly loaded on the mesoporous SiO2 shell with a particle size of 25-35nm.

8. The drilling fluid preparation method for ultra-deep wells using ultra-micro multi-zone nano-weighting agents as described in claim 1, characterized in that, Step S4 includes: S41. Add tap water to the mixing equipment, start the mixing first, then add half the weight of the ultra-micro multi-zone nano weighting agent, and continue mixing after adding to form a uniform base slurry. S42. Add alkalinity regulator, shale inhibitor, filtration loss reducer, and flow pattern regulator in sequence. After each component is added, maintain the preset stirring rate and stir for the preset time to ensure sufficient hydration and dispersion. S43. Add the remaining ultra-micro multi-cell nano-weighting agent, and continue stirring after adding to form a uniform base slurry; S44. Add defoamer, then increase the stirring rate and continue high-speed shearing for a preset time to ensure that the components are fully mixed and reacted at the molecular and colloidal levels to form the final drilling fluid.

9. The drilling fluid preparation method for ultra-deep wells using ultra-micro multi-zone nano-weighting agents as described in claim 8, characterized in that, According to the weight proportions, the ratio of tap water, ultrafine multi-zone nano-weighting agent, flow pattern regulator, filtration loss reducer, shale inhibitor, alkalinity regulator, and defoamer is 100:60:1:3:2:0.3:0.1; in step S41, the stirring speed is 3000 rpm, and the stirring time after adding the ultrafine multi-zone nano-weighting agent is 15 minutes; in step S42, the preset stirring speed is 3000 rpm, and the preset stirring time is 15 minutes; in step S43, after adding the agent, the stirring speed is 3000 rpm, and the stirring time is 15 minutes; in step S44, the stirring speed is increased to 5000 rpm, and high-speed shear stirring is continued for 60 minutes.

10. The drilling fluid preparation method for ultra-deep wells using ultra-micro multi-zone nano-weighting agents as described in claim 9, characterized in that, The flow pattern regulator is xanthan gum, the filtration loss reducer is sulfonated phenolic resin SMP-II, the shale inhibitor is polyetheramine, the alkalinity regulator is sodium hydroxide, and the defoamer is polydimethylsiloxane.

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