Recyclable phase change microcapsule for drilling fluid and preparation method thereof

Abstract

The embodiment of the invention provides a recyclable phase-change microcapsule for drilling fluid and a preparation method thereof, and relates to the technical field of petrochemical engineering, the phase-change microcapsule comprises a phase-change material core, and an impermeable layer, a magnetic layer and an anti-wear layer which sequentially coat the surface of the phase-change material core. The phase change microcapsule is high in stability and recoverability and low in use cost.

Description

Technical Field

[0001] The present application relates to the field of petrochemical industry, and in particular to a recyclable phase-change microcapsule for drilling fluid and a preparation method thereof. Background Art

[0002] Drilling fluid plays an indispensable role in the exploration and development of oil and gas. In order to meet drilling needs, by adding phase change materials to the drilling fluid, the stability and performance of the drilling fluid can be effectively improved through the latent heat storage and release characteristics of the phase change materials during the phase change process.

[0003] However, if phase change materials are directly added to drilling fluid, they may react adversely with the chemical components in the drilling fluid, affecting its thermal stability, and causing changes in the rheological properties of the drilling fluid, affecting the dynamic characteristics of the downhole fluid. Therefore, microencapsulation technology has become a key strategy to optimize the performance of phase change materials and expand their application in drilling fluids.

[0004] Phase-change microcapsules are currently widely used in petroleum engineering applications such as drilling, cementing, and hydrate development. However, existing technologies still have many limitations. Most phase-change microcapsules exhibit poor stability in high-temperature drilling fluids and are non-recyclable, making them difficult to separate from the drilling fluid after use and resulting in high costs. Summary of the Invention

[0005] The embodiments of the present application provide a recyclable phase-change microcapsule for drilling fluid and a preparation method thereof, so as to improve the stability and recyclability of the phase-change microcapsule and reduce the cost of use.

[0006] In a first aspect, the present invention provides a recyclable phase-change microcapsule for drilling fluid, comprising:

[0007] A phase change material core and an anti-permeability layer, a magnetic layer and an anti-wear layer are sequentially coated on the surface of the phase change material core.

[0008] In some embodiments, the phase change material comprises one or more of sodium nitrate-potassium nitrate eutectic salt, sodium chloride-potassium chloride eutectic salt, or potassium chloride-zinc chloride eutectic salt; and / or,

[0009] The anti-seepage layer comprises an anti-seepage material, and the anti-seepage material comprises silicon carbide and / or boron nitride; and / or,

[0010] The magnetic layer includes a magnetic material, and the magnetic material includes Modified carbon nanotubes and / or Modifying carbon nanotubes; and / or,

[0011] The anti-wear layer includes an anti-wear material, and the anti-wear material includes one or more of silicon boride, boron carbide, aluminum oxide or titanium dioxide.

[0012] In some embodiments, the phase-change microcapsules have a particle size of 60 μm to 80 μm.

[0013] In a second aspect, the present invention provides a method for preparing recyclable phase-change microcapsules for drilling fluid, comprising:

[0014] The phase change material and the cationic surfactant aqueous solution are mixed and emulsified to obtain a phase change material emulsion; the anti-seepage material and the anionic surfactant aqueous solution are mixed and dispersed to obtain an anti-seepage material suspension; the magnetic material and the cationic surfactant aqueous solution are mixed and dispersed to obtain a magnetic material suspension; the anti-wear material and the anionic surfactant aqueous solution are mixed and dispersed to obtain an anti-wear material suspension;

[0015] Adding the anti-seepage material suspension dropwise into the phase change material emulsion, and depositing the anti-seepage material on the surface of the phase change material through electrostatic adsorption to form a microcapsule suspension coated with an anti-seepage layer;

[0016] Adding the magnetic material suspension dropwise to the microcapsule suspension coating the anti-seepage layer, and depositing the magnetic material outside the anti-seepage layer by electrostatic adsorption to form a microcapsule suspension coating the magnetic layer;

[0017] Adding the anti-wear material suspension dropwise to the microcapsule suspension coating the magnetic layer, and depositing the anti-wear material outside the magnetic layer through electrostatic adsorption to form a microcapsule suspension coating the anti-wear layer;

[0018] The suspension of the microcapsules coated with the anti-wear layer is solidified to obtain recyclable phase-change microcapsules for drilling fluid.

[0019] In some embodiments, the cationic surfactant comprises polyethyleneimine and / or a quaternary ammonium salt; and / or,

[0020] The anionic surfactant includes one or more of sodium lauryl sulfate, polystyrene sulfonate or Span 80.

[0021] In some embodiments, the mass ratio of the anti-seepage material to the phase change material is 1:(2-3); and / or,

[0022] The mass ratio of the magnetic material to the anti-seepage material is (1-3):2; and / or,

[0023] The mass ratio of the anti-wear material to the magnetic material is (1-3):1.

[0024] In some embodiments, when preparing the phase change material emulsion, the concentration of the cationic surfactant aqueous solution is 1 wt%-10 wt%; and / or,

[0025] When preparing the anti-seepage material suspension, the concentration of the anionic surfactant aqueous solution is 1wt%-5wt%; and / or,

[0026] When preparing the magnetic material suspension, the mass concentration of the cationic surfactant aqueous solution is 1wt%-5wt%; and / or,

[0027] When preparing the anti-wear material suspension, the concentration of the anionic surfactant aqueous solution is 1wt%-3wt%.

[0028] In some embodiments, when preparing the phase change material emulsion, the volume ratio of the mass of the phase change material to the cationic surfactant aqueous solution is 1:0.05-1; and / or,

[0029] When preparing the anti-seepage material suspension, the volume ratio of the mass of the anti-seepage material to the aqueous solution of anionic surfactant is 1:0.01-0.1; and / or,

[0030] When preparing the magnetic material suspension, the volume ratio of the mass of the magnetic material to the cationic surfactant aqueous solution is 1:0.01-0.1; and / or,

[0031] When preparing the anti-wear material suspension, the volume ratio of the mass of the anti-wear material to the anionic surfactant aqueous solution is 1:0.01-0.1.

[0032] In some embodiments, when depositing the anti-seepage material on the surface of the phase change material, the electrostatic adsorption method is to stir at 600 rpm to 1000 rpm at 40° C. to 70° C. for 0.5 h to 5 h;

[0033] When depositing the magnetic material outside the anti-seepage layer, the electrostatic adsorption method is to stir at 400 rpm to 600 rpm at 40° C. to 70° C. for 1 h to 1.5 h;

[0034] When the anti-wear material is deposited outside the magnetic layer, the electrostatic adsorption method is to stir at 400-1000 r / min at 40° C.-70° C. for 1 h-1.5 h.

[0035] In some embodiments, the curing treatment is an alkali treatment or a heat treatment;

[0036] The alkali treatment comprises: adding an alkaline aqueous solution to the suspension of the microcapsules coated with the anti-wear layer, standing at room temperature for 1 hour to 3 hours, and then separating, washing and drying to obtain the phase change microcapsules; and / or,

[0037] The heat treatment comprises: separating, washing and drying the microcapsule suspension coated with the anti-wear layer, and then placing it at a temperature of 100° C. to 150° C. for 2 h to 4 h to obtain the phase change microcapsules. DETAILED DESCRIPTION

[0038] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application are clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0039] In the embodiments of the present application, words such as "first" and "second" are used to distinguish between identical or similar items with substantially the same functions and effects, and do not limit their order. Those skilled in the art will understand that words such as "first" and "second" do not limit the quantity or execution order, and words such as "first" and "second" do not necessarily mean different.

[0040] It should be noted that in the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described in this application as "exemplary" or "for example" should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0041] Drilling fluid plays an indispensable role in the exploration and development of oil and gas. To ensure the stability of drilling fluid during use, phase change materials can be added to the drilling fluid. The characteristics of phase change materials in storing and releasing latent heat to regulate the temperature of the system (i.e., absorbing heat when the temperature rises and releasing heat when the temperature drops) can effectively improve the stability of the drilling fluid, especially the high-temperature stability, thereby ensuring the progress of drilling operations.

[0042] However, directly adding phase change materials to the drilling fluid system may face many challenges. For example, phase change materials may react adversely with the chemical components of the drilling fluid, affecting its thermal stability, phase change behavior and long-term cyclic performance. In addition, some phase change materials may cause changes in the rheological properties of the drilling fluid during the phase change process, affecting the downhole fluid dynamics. Therefore, microencapsulation technology has become a key strategy for optimizing the performance of phase change materials and expanding their applications in drilling fluids. By rationally designing the microcapsule shell material, not only can the structural stability of the phase change material be improved to avoid degradation or failure due to changes in external conditions, but its dispersibility in the drilling fluid can also be enhanced to ensure the uniformity and long-term stability of the system. In addition, microencapsulated phase change materials can achieve controllable heat release and improve thermal cycling performance, showing good application prospects in high-temperature drilling fluid temperature control, hydrate inhibition, and oil well cement slurry hydration thermal regulation.

[0043] Phase change materials can be divided into organic phase change materials and inorganic phase change materials. Organic phase change materials include paraffin, fatty acids, and their derivatives. They have good chemical stability and strong compatibility, but they have problems such as poor thermal conductivity and low thermal stability, making them unsuitable for high-temperature drilling fluid systems. Inorganic phase change materials include nitrates, chlorides, and their eutectic systems. They have advantages such as high heat storage density, good thermal conductivity, and high temperature resistance, making them more suitable for energy storage applications in high-temperature environments. However, they are prone to sedimentation in fluid systems and have a high degree of supercooling. Therefore, they need to be encapsulated using microencapsulation technology to improve dispersion stability and prevent leakage of the phase change material.

[0044] Phase-change microcapsules are currently widely used in oil drilling, cementing, and hydrate development, but existing technologies still have many limitations. Most phase-change microcapsules are non-recyclable and difficult to separate from drilling fluid after use, forcing them to be disposed of as waste. This leads to high costs and increased environmental pollution. Furthermore, when the phase-change material liquefies, the microcapsules are prone to leakage, resulting in poor stability.

[0045] In response to the above problems, the embodiments of the present application provide a recyclable phase change microcapsule for drilling fluid and a preparation method thereof. By constructing a multi-layer microcapsule structure, the stability of the phase change microcapsule in a high-temperature drilling environment is improved, and the drilling fluid temperature can be effectively regulated. At the same time, efficient separation is achieved through magnetic recovery, thereby improving recyclability. It is suitable for temperature regulation applications of drilling fluid systems in high-temperature and high-pressure wells and complex drilling conditions.

[0046] In a first aspect, an embodiment of the present application provides a recyclable phase-change microcapsule for drilling fluid, wherein the phase-change microcapsule comprises a phase-change material core and an anti-seepage layer, a magnetic layer and an anti-wear layer sequentially coated on the surface of the phase-change material core.

[0047] In some embodiments, the phase change material is one or more of sodium nitrate-potassium nitrate eutectic salt, sodium chloride-potassium chloride eutectic salt, or potassium chloride-zinc chloride eutectic salt.

[0048] In some embodiments, the barrier layer comprises a barrier material comprising silicon carbide and / or boron nitride.

[0049] In some embodiments, the magnetic layer includes a magnetic material including Modified carbon nanotubes and / or Modified carbon nanotubes.

[0050] In some embodiments, the anti-wear layer comprises an anti-wear material, and the anti-wear material comprises one or more of silicon boride, boron carbide, aluminum oxide, or titanium dioxide.

[0051] The phase-change microcapsules provided in the embodiments of the present application can have good magnetic response capabilities through the design of the magnetic layer, so that the phase-change microcapsules can be efficiently recovered in complex fluid environments; by constructing an anti-seepage layer between the phase-change material and the magnetic layer, the leakage of the phase-change material can be effectively prevented, the encapsulation rate can be improved, and the high-temperature resistance can be enhanced; at the same time, the corrosion of the magnetic layer by the phase-change material is prevented, the loss of the magnetic material is avoided, and the microcapsules maintain stable magnetic response capabilities during long-term use; by constructing an anti-wear layer outside the magnetic layer, the shear resistance of the microcapsules can be improved, so that they can maintain structural integrity in complex fluid environments such as high-temperature drilling fluids.

[0052] The magnetic material in the embodiment of the present application is Modified carbon nanotubes or Modified carbon nanotubes, combined with The magnetic properties of carbon nanotubes and the high thermal conductivity of carbon nanotubes provide good chemical stability and mechanical strength in high temperature environments. The microcapsules are endowed with magnetic responsiveness, allowing them to be recovered under the influence of an external magnetic field. The high thermal conductivity of carbon nanotubes improves the microcapsules' heat transfer efficiency and enhances their shear resistance. Therefore, the microcapsules provided in the embodiments of the present application can meet the requirements of high-temperature drilling environments.

[0053] The embodiments of the present application use high-temperature stable inorganic materials as the anti-seepage layer and the anti-wear layer, further improving the heat resistance and thermal conductivity of the microcapsules, enabling them to exhibit better performance in applications such as high-temperature drilling fluid temperature control, hydrate inhibition, and cementing hydration heat regulation. At the same time, combined with the magnetic recovery design, the recycling rate of the microcapsules is improved and the cost of use is reduced.

[0054] In some embodiments, the phase-change microcapsules have a particle size of 60 μm to 80 μm. For example, the particle size of the phase-change microcapsules can be 60 μm, 65 μm, 70 μm, or 80 μm. When the particle size of the phase-change microcapsules is within this range, the microcapsules are of moderate size, which can further enhance their performance. When the particle size of the phase-change microcapsules is within the range of 60 μm to 80 μm, the microcapsules are of moderate size, which helps improve their dispersion stability, thermal response efficiency, and recovery efficiency in the drilling fluid, thereby further enhancing the overall performance of the phase-change microcapsules. When the particle size of the phase-change microcapsules is too large (e.g., exceeding 100 μm), the microcapsules' sedimentation rate in the drilling fluid increases, making uniform distribution difficult. Furthermore, the heat transfer rate decreases, resulting in delayed thermal response and affecting temperature control. Furthermore, due to their large size, they may have difficulty passing through the sieves commonly used in drilling fluid systems, causing blockage and separation difficulties, impacting field efficiency. When the particle size is too small (such as less than 10μm), although the dispersibility is enhanced, the mechanical strength and thermal stability of the microcapsule shell decrease, and it is easy to break in a high temperature and high shear environment, causing the phase change material to leak, reducing the service life and safety.

[0055] In a second aspect, the present invention provides a method for preparing recyclable phase-change microcapsules for drilling fluid, comprising the following steps:

[0056] (1) The phase change material and the cationic surfactant aqueous solution are mixed and fully emulsified to obtain a phase change material emulsion.

[0057] (2) The anti-seepage material and the aqueous solution of anionic surfactant are fully mixed and dispersed to obtain an anti-seepage material suspension; the anti-seepage material suspension is added dropwise to the phase change material emulsion, and the anti-seepage material is deposited on the surface of the phase change material through electrostatic adsorption to obtain a suspension of microcapsules coated with an anti-seepage layer.

[0058] (3) The magnetic material and the cationic surfactant aqueous solution are fully mixed and dispersed to obtain a magnetic material suspension; the magnetic material suspension is dropped into the suspension of the microcapsules coated with the anti-seepage layer, and the magnetic material is deposited outside the microcapsule anti-seepage layer by electrostatic adsorption, thereby obtaining a suspension of microcapsules coated with the magnetic layer.

[0059] (4) The anti-wear material and the aqueous solution of anionic surfactant are fully mixed and dispersed to obtain an anti-wear material suspension; the anti-wear material suspension is added dropwise to the suspension of microcapsules coated with the magnetic layer, and the anti-wear material is deposited outside the magnetic layer of the microcapsules through electrostatic adsorption to obtain a suspension of microcapsules coated with the anti-wear layer.

[0060] (5) The suspension of microcapsules coated with the anti-wear layer is solidified to obtain phase change microcapsules for drilling fluid that can be recycled and reused.

[0061] The preparation method of recyclable phase change microcapsules for drilling fluid provided in the embodiment of the present application is based on a eutectic salt inorganic phase change material as the core, and a multi-layer microcapsule structure is constructed by gradually depositing an anti-seepage layer, a magnetic layer and an anti-wear layer. First, the phase change material is dispersed in a cationic surfactant solution to form an emulsion system, so that it is stably suspended. Subsequently, an anionic surfactant solution containing an anti-seepage material is added to the emulsion system, and an anti-seepage layer is deposited on the surface of the phase change material by electrostatic interaction to form a first layer of coating structure. Then, a cationic surfactant solution containing a magnetic material is introduced into the obtained microcapsule system coated with the anti-seepage layer, and the magnetic material is deposited outside the anti-seepage layer by electrostatic adsorption to form a magnetic layer. Subsequently, an anionic surfactant solution containing an anti-wear material is further added to deposit the anti-wear material outside the magnetic layer to form an outer protective shell. Finally, the obtained microcapsules are cured to obtain recyclable phase change microcapsules.

[0062] The embodiment of the present application constructs an anti-seepage layer, a magnetic layer and an anti-wear layer layer by layer through an electrostatic deposition method, which can effectively improve the sealing, mechanical stability, high temperature and chemical stability, and magnetic recovery ability of the microcapsules. The anti-seepage layer can effectively prevent the leakage of the phase change material, improve the encapsulation rate, and enhance the high temperature resistance; at the same time, it prevents the corrosion of the magnetic layer by the phase change material, avoids the loss of the magnetic material, and enables the microcapsules to maintain a stable magnetic response ability during long-term use. The magnetic layer gives the microcapsules good magnetic response ability, so that they can be efficiently recovered in complex fluid environments. The anti-wear layer improves the shear resistance of the microcapsules, so that they can maintain structural integrity in complex fluid environments such as high-temperature drilling fluids. The combined effect of the various layers of the embodiment of the present application improves the adaptability of the phase change microcapsules in high-temperature drilling fluid systems, and has good stability and chemical stability under high temperature environments, high magnetic recovery efficiency, high mechanical stability and mechanical strength, and good thermal conductivity.

[0063] The embodiment of the present application adopts an electrostatic deposition method to replace the traditional precipitation method or polymerization method, so that materials of different layers are deposited layer by layer by relying on electrostatic interactions, which can accurately control the shell thickness and structural uniformity, improve the uniformity, bonding strength, integrity and stability of the shell, avoid the interface detachment between the wall material and the phase change material, and ensure the long-term stability of the microcapsules in high temperature, high pressure and strong shear environment.

[0064] In some embodiments, the cationic surfactant in step (1) and step (3) comprises polyethyleneimine and / or a quaternary ammonium salt.

[0065] In some embodiments, the anionic surfactant in step (2) and step (4) includes one or more of sodium lauryl sulfate, polystyrene sulfonate, or Span 80.

[0066] In some embodiments, the concentration of the cationic surfactant aqueous solution in step (1) is 1 wt%-10 wt%, for example, 1 wt%, 3 wt%, 5 wt%, 7 wt%, or 10 wt%.

[0067] In some embodiments, in step (1), the ratio of the mass of the phase change material to the volume of the cationic surfactant aqueous solution is 1:(0.05-1), for example, 1:0.05, 1:0.15, 1:0.3, 1:0.5, 1:0.7, or 1:1. The unit of the mass of the phase change material is gram (g), and the unit of the volume of the cationic surfactant aqueous solution is milliliter (ml).

[0068] In some embodiments, in step (1), the emulsification conditions are as follows: stirring at 1000 r / min to 1500 r / min and 60°C to 65°C for 20 min to 40 min to uniformly disperse the phase change material, followed by ultrasonic treatment at 40 kHz for 20 min to 40 min. The above emulsification conditions can improve the stability of the emulsified system and prevent aggregation or sedimentation of the microcapsule core layer material.

[0069] In some embodiments, the concentration of the aqueous anionic surfactant solution in step (2) is 1 wt% to 5 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0070] In some embodiments, in step (2), the ratio of the mass of the anti-seepage material to the volume of the anionic surfactant aqueous solution is 1:(0.01-0.1), for example, 1:0.01, 1:0.03, 1:0.05, 1:0.07, or 1:0.1. The unit of the mass of the anti-seepage material is gram (g), and the unit of the volume of the anionic surfactant aqueous solution is milliliter (ml).

[0071] In some embodiments, in step (2), the mass ratio of the anti-seepage material to the phase change material is 1:(2-3), for example, 1:2, 1:2.5, or 1:3.

[0072] In some embodiments, in step (2), the conditions for fully mixing and dispersing the anti-seepage material and the aqueous solution of anionic surfactant are as follows: stirring at 1000-1500 r / min for 20-40 min, followed by ultrasonic treatment at 40 kHz for 10-30 min.

[0073] In some embodiments, in step (2), the electrostatic adsorption conditions are as follows: stirring at 600 rpm to 1000 rpm at 40°C to 70°C for 0.5 to 5 hours. During the deposition process, the resulting suspension is slowly added to the microcapsule system and continuously stirred under stirring conditions to allow the anti-seepage material to be uniformly adsorbed onto the surface of the phase change material.

[0074] In some embodiments, in step (2), the anti-seepage material suspension is added dropwise to the phase change material emulsion at a stirring rate of 30 mL / min to 45 mL / min at a stirring rate of 600 r / min to 1000 r / min to ensure uniform deposition of the anti-seepage layer and prevent particle agglomeration. The anti-seepage material suspension is added dropwise to the phase change material emulsion to form a first layer of coating structure on the surface of the phase change material through electrostatic adsorption. During the addition process, a constant stirring rate is maintained to promote uniform deposition of the anti-seepage material and prevent agglomeration.

[0075] In some embodiments, in step (3), the concentration of the cationic surfactant aqueous solution is 1 wt%-5 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0076] In some embodiments, the mass ratio of the magnetic material in step (3) to the barrier material in step (2) is (1-3):2, for example, 1:2, 1.5:2, 2:2, 2.5:2, or 3:2. Controlling the mass ratio of the magnetic material to the barrier material within the above range can improve the uniform coating of the magnetic layer and enhance the magnetic recovery performance of the microcapsules.

[0077] In some embodiments, in step (3), the ratio of the mass of the magnetic material to the volume of the cationic surfactant aqueous solution is 1:(0.01-0.1), for example, 1:0.01, 1:0.03, 1:0.05, 1:0.07, 1:0.1. The unit of the mass of the magnetic material is gram (g), and the unit of the volume of the cationic surfactant aqueous solution is milliliter (ml).

[0078] In some embodiments, in step (3), the magnetic material and the cationic surfactant aqueous solution are fully mixed and dispersed under the following conditions: stirring at 1000-1500 r / min for 20-40 min, followed by 40 kHz ultrasonic treatment for 10-30 min.

[0079] In some embodiments, in step (3), the electrostatic adsorption conditions are as follows: stirring at 600-1000 r / min and 40-70° C. for 1-1.5 h. The above conditions can ensure uniform distribution of the magnetic layer and avoid agglomeration or sedimentation of the magnetic material.

[0080] In some embodiments, in step (3), the magnetic material suspension is added dropwise to the suspension of the microcapsules coated with the anti-seepage layer at a rate of 30 mL / min to 45 mL / min under a stirring rate of 600 r / min to 1000 r / min. During the addition process, the system is kept uniformly stirred and the concentration of the added magnetic material is controlled to ensure uniform deposition of the magnetic layer. The magnetic material solution is gradually added dropwise to the resulting microcapsule system coated with the anti-seepage layer, so that the magnetic material forms a second coating structure on the surface of the anti-seepage layer through electrostatic adsorption.

[0081] In some embodiments, in step (4), the ratio of the mass of the anti-wear material to the volume of the anionic surfactant aqueous solution is 1:(0.01-0.1), for example, 1:0.01, 1:0.03, 1:0.05, 1:0.07, 1:0.1. The unit of the mass of the anti-wear material is gram (g), and the unit of the volume of the anionic surfactant aqueous solution is milliliter (ml).

[0082] In some embodiments, in step (4), the concentration of the aqueous anionic surfactant solution is 1-3 wt %, for example, 1 wt %, 2 wt %, or 3 wt %.

[0083] In some embodiments, the mass ratio of the anti-wear material in step (4) to the magnetic material in step (3) is (1-3):1. For example, 1:1, 1:2, 1:3. The above mass ratio can improve the coating uniformity of the anti-wear layer.

[0084] In some embodiments, in step (4), the anti-wear material and the aqueous anionic surfactant solution are fully mixed and dispersed under the following conditions: stirring at 1000-1500 r / min for 20-40 min, followed by 40 kHz ultrasonic treatment for 10-30 min.

[0085] In some embodiments, in step (4), the electrostatic adsorption conditions are as follows: stirring at 600-1000 r / min and 40-70°C for 1-1.5 h. The above conditions can ensure the uniform distribution of the anti-wear layer and avoid agglomeration or sedimentation of the anti-wear material, thereby ensuring the uniformity and stability of the anti-wear layer.

[0086] In some embodiments, in step (4), the anti-wear material suspension is added dropwise to the suspension of the microcapsules coated with the magnetic layer at a stirring rate of 10 to 45 mL / min under a stirring rate of 600 r / min to 1000 r / min. During the addition process, the system is kept uniformly stirred, and the concentration of the anti-wear material is controlled to ensure uniform deposition of the anti-wear layer. The anti-wear material solution is gradually added dropwise to the suspension of the microcapsules coated with the magnetic layer, so that the anti-wear material is uniformly deposited on the surface of the magnetic layer to form an outer protective shell.

[0087] In some embodiments, in step (5), the curing treatment method is alkali treatment or heat treatment.

[0088] The alkali treatment method is as follows: add 0.5~1.0 mol / L alkaline aqueous solution (for example, NaOH aqueous solution) to the suspension of microcapsules coated with the anti-wear layer, and let it stand at room temperature for 1-3 hours to promote the cross-linking and curing of the shell layer, thereby improving the high temperature resistance and anti-swelling ability of the microcapsules, and then obtain recyclable and reusable phase change microcapsules for drilling fluid through separation, washing and drying; wherein the mass ratio of the suspension of microcapsules coated with the anti-wear layer to the alkaline aqueous solution is 1: (5-10).

[0089] The heat treatment method is as follows: the suspension of microcapsules coated with the anti-wear layer is separated, washed, and dried, and then subjected to a temperature of 100-150°C for 2-4 hours to improve the mechanical strength, heat resistance, and crack resistance of the shell layer, thereby obtaining phase-change microcapsules for recycling and reuse in drilling fluid. The resulting multilayer coated microcapsules are then cured to enhance the mechanical strength and chemical stability of the shell layer.

[0090] The curing method affects the final structural stability of the microcapsules. The washing, separation, and drying steps described above are used to remove undeposited surfactant and free ions. The microcapsules are separated by centrifugation or filtration and washed with deionized water. The microcapsules are separated using a centrifugal speed of 3000-5000 rpm and then dried at 50-80°C for 6-12 hours.

[0091] The recyclable phase change microcapsules for drilling fluid provided by the present application are described in detail below through specific examples.

[0092] Example 1

[0093] (1) Sodium nitrate-potassium nitrate eutectic salt and polyethyleneimine aqueous solution with a mass volume ratio of 1:0.15 were mixed and stirred at 1200 r / min and 60°C for 30 min to uniformly disperse the sodium nitrate-potassium nitrate eutectic salt. The mixture was then ultrasonically treated at 40 kHz for 30 min to fully emulsify the mixture and obtain a phase change material emulsion.

[0094] (2) Silicon carbide (the mass ratio of silicon carbide to sodium nitrate-potassium nitrate eutectic salt is 1:2) and sodium dodecyl sulfate aqueous solution with a mass-to-volume ratio of 1:0.05 were stirred at 1200 r / min for 30 min, and then ultrasonically treated at 40 kHz for 20 min to fully mix and disperse to obtain an anti-seepage material suspension.

[0095] The anti-seepage material suspension was added dropwise to the phase change material emulsion, and stirred at 800 r / min and 60°C for 2.5 h. The anti-seepage material was deposited on the surface of the phase change material by electrostatic adsorption to obtain a suspension of microcapsules coated with an anti-seepage layer;

[0096] (3) The mass volume ratio is 1:0.05 Modified carbon nanotubes ( The modified carbon nanotubes and silicon carbide (mass ratio of 2:2) and polyethyleneimine aqueous solution were stirred at 1200 r / min for 30 min, followed by 40 kHz ultrasonic treatment for 20 min to fully mix and disperse to obtain a magnetic material suspension.

[0097] The magnetic material suspension was added dropwise to the suspension of the microcapsules coated with the anti-seepage layer, and stirred at 600 r / min at 55°C for 1 hour. The magnetic material was deposited outside the microcapsule anti-seepage layer by electrostatic adsorption to obtain a suspension of microcapsules coated with the magnetic layer.

[0098] (4) Silicon boride (silicon boride and The modified carbon nanotubes (with a mass ratio of 2:1) and the sodium dodecyl sulfate aqueous solution were stirred at 1200 r / min for 30 min, and then ultrasonically treated at 40 kHz for 20 min to fully mix and disperse to obtain an anti-wear material suspension.

[0099] The anti-wear material suspension is added dropwise to the suspension of microcapsules coated with the magnetic layer, and stirred at 600 r / min at 55°C for 1 hour to allow electrostatic adsorption to deposit the anti-wear material on the outside of the microcapsule magnetic layer, thereby obtaining a suspension of microcapsules coated with the anti-wear layer.

[0100] (5) The suspension of microcapsules coated with the anti-wear layer is separated, washed, dried, and then placed at 120°C for 3 hours for solidification to obtain recyclable phase change microcapsules for drilling fluid.

[0101] Example 2

[0102] The preparation method of the phase change microcapsules for recyclable drilling fluid in Example 2 is the same as that in Example 1, except that the sodium nitrate-potassium nitrate eutectic salt is replaced by sodium chloride-potassium chloride eutectic salt, polyethyleneimine is replaced by quaternary ammonium salt, silicon carbide is replaced by boron nitride, sodium lauryl sulfate is replaced by polystyrene sulfonate, and Modified carbon nanotubes replaced with The carbon nanotubes were modified, and silicon boride was replaced with boron carbide. Meanwhile, the ratio of the anti-seepage material to the phase change material was changed to 1:3, the mass ratio of the magnetic material to the anti-seepage material was changed to 3:2, and the mass ratio of the anti-wear material to the magnetic material was changed to 3:1.

[0103] Example 3

[0104] The preparation method of the recyclable drilling fluid phase-change microcapsules in Example 3 is the same as that in Example 1, except that the sodium nitrate-potassium nitrate eutectic salt is replaced with a potassium chloride-zinc chloride eutectic salt, sodium lauryl sulfate is replaced with Span 80, and silicon boride is replaced with aluminum oxide. Furthermore, the mass ratio of the magnetic material to the anti-seepage material is changed to 1:2, and the mass ratio of the anti-wear material to the magnetic material is changed to 1:1.

[0105] Example 4

[0106] The preparation method of the recyclable and reusable phase change microcapsules for drilling fluid in Example 4 is the same as that in Example 1, except that the volume ratio of the mass of the phase change material to the cationic surfactant aqueous solution is 1:1; the volume ratio of the mass of the anti-seepage material to the anionic surfactant aqueous solution is 1:0.1; the volume ratio of the mass of the magnetic material to the cationic surfactant aqueous solution is 1:0.1; and the volume ratio of the mass of the anti-wear material to the anionic surfactant aqueous solution is 1:0.1.

[0107] Example 5

[0108] The preparation method of the recyclable and reusable phase change microcapsules for drilling fluid in Example 5 is the same as that in Example 1, except that the volume ratio of the mass of the phase change material to the cationic surfactant aqueous solution is 1:0.05; the volume ratio of the mass of the anti-seepage material to the anionic surfactant aqueous solution is 1:0.01; the volume ratio of the mass of the magnetic material to the cationic surfactant aqueous solution is 1:00.1; and the volume ratio of the mass of the anti-wear material to the anionic surfactant aqueous solution is 1:00.1.

[0109] Example 6

[0110] The method for preparing recyclable phase-change microcapsules for drilling fluid in Example 6 is the same as that in Example 1, except that the heat treatment in step 5 is replaced with an alkaline treatment. The alkaline treatment comprises dropwise adding an alkaline aqueous solution to the suspension of microcapsules coated with the anti-wear layer, allowing the suspension to stand at room temperature for 2 hours, and then separating, washing, and drying to obtain the phase-change microcapsules.

[0111] Example 7

[0112] The preparation method of the recyclable and reusable phase change microcapsules for drilling fluid in Example 7 is the same as that in Example 1, except that the mixture is stirred at 600 r / min and 40°C for 0.5 h, and the anti-seepage material is deposited on the surface of the phase change material by electrostatic adsorption; the mixture is stirred at 400 r / min and 40°C for 1 h, and the magnetic material is deposited outside the anti-seepage layer of the microcapsule by electrostatic adsorption; the mixture is stirred at 400 r / min and 40°C for 1 h, and the anti-wear material is deposited outside the magnetic layer of the microcapsule by electrostatic adsorption.

[0113] Example 8

[0114] The preparation method of the recyclable and reusable phase change microcapsules for drilling fluid in Example 8 is the same as that in Example 1, except that the mixture is stirred at 1000 r / min and 70°C for 5 h, and the anti-seepage material is deposited on the surface of the phase change material by electrostatic adsorption, and the mixture is stirred at 600 r / min and 70°C for 1.5 h, and the magnetic material is deposited outside the anti-seepage layer of the microcapsule by electrostatic adsorption, and the anti-wear material is deposited outside the magnetic layer of the microcapsule by electrostatic adsorption.

[0115] Comparative Example 1

[0116] The preparation method of the recyclable phase change microcapsules for drilling fluid in Comparative Example 1 is similar to that of Example 1, except that the anti-seepage layer is not included.

[0117] Comparative Example 2

[0118] The preparation method of the recyclable and reusable phase change microcapsules for drilling fluid in Comparative Example 2 is similar to that of Example 1, except that the magnetic layer is not included.

[0119] Comparative Example 3

[0120] The preparation method of the recyclable and reusable phase change microcapsules for drilling fluid in Comparative Example 3 is similar to that of Example 1, except that the anti-wear layer is not included.

[0121] Test example

[0122] 1. Recyclability test

[0123] To evaluate the magnetic recoverability of phase-change microcapsules in drilling fluid, the microcapsules prepared in the above examples and comparative examples were added to a field-formulated drilling fluid at a 3% mass fraction. The suspension was stirred at 6000 rpm for 30 minutes using a high-speed shear disperser to prepare a uniformly dispersed suspension of magnetic microcapsules. The mixture was then transferred to a transparent plastic container equipped with an adjustable electromagnet. The electromagnet generated a magnetic field strength of approximately 0.4 T, and the magnetic field was switched on and off, with the direction of the field controlled by current flow and polarity. The electromagnetic field was applied for 10 minutes, causing the magnetic microcapsules to rapidly aggregate toward the container wall. Drilling fluid samples from the aggregated areas were then collected using a pipette, dried, and weighed. The recovery rate of the magnetic microcapsules was calculated based on the ratio of the recovered mass to the initial mass added to evaluate their magnetic responsiveness and repeatable recovery in the drilling fluid system. This method enables targeted recovery and improves microcapsule recovery efficiency.

[0124] 2. Encapsulation efficiency test

[0125] In order to determine the encapsulation efficiency of phase change microcapsules, UV-visible spectrophotometry was used for quantitative analysis. First, an appropriate amount of microcapsule core material was prepared into a solution. A full-band scan was performed in the range of 190–400 nm using a UV-visible spectrophotometer, and its absorption spectrum curve was plotted to determine the maximum absorption wavelength of the core material in the UV region. Subsequently, a series of core material standard concentration gradient solutions were prepared using this wavelength as the detection point, and their absorbance was measured and a concentration-absorbance standard curve was established to obtain a linear regression equation. The dried microcapsule sample was then added to an ethanol solvent and ultrasonically treated for 30 minutes to fully break the wall and release the core material. After centrifugation or filtration to remove the solid residue, the supernatant was taken to measure the absorbance and substituted into the standard curve to calculate the actual content of the core material. The encapsulation efficiency was calculated by combining the total mass of the microcapsules and the theoretical addition amount according to formula (1). All samples were measured in parallel three times, and the average value was taken to ensure data accuracy and repeatability.

[0126] Encapsulation rate (%) = Actual core material mass / Theoretical added mass × 100% (1)

[0127] 3. Thermal stability test

[0128] To evaluate the structural thermal stability of phase-change microcapsules in high-temperature drilling fluid environments, the prepared microcapsules were added to a field-formulated drilling fluid at a mass fraction of 3%. The suspension was stirred at 6000 rpm for 30 minutes using a high-speed shear disperser to form a uniformly dispersed microcapsule drilling fluid suspension. This suspension was placed in a sealed aging tank and placed in a hot rolling oven at 220°C for 96 hours. After cooling to room temperature, a sample of the hot-rolled drilling fluid was collected and its absorbance was measured. The core material concentration in the sample was calculated by applying the absorbance to a standard curve based on core material concentration versus absorbance. The microcapsule breakage rate was calculated based on the ratio of the core material concentration in the sample to the theoretical core material content in the microcapsules. This was used to evaluate the structural thermal stability of the microcapsules at 220°C for 96 hours. A lower breakage rate indicates a more stable microcapsule structure and better heat resistance.

[0129] The test results are shown in the following table:

[0130]

[0131] It can be seen from the above table that, compared with Comparative Example 2, the recyclability of the prepared phase change microcapsules is greatly increased after the magnetic layer is added.

[0132] Furthermore, compared with Comparative Examples 1-3, the encapsulation efficiency and thermal stability of the prepared phase-change microcapsules including the multi-layer structure are greatly increased due to the interaction between the layers.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A recyclable phase change microcapsule for drilling fluid, characterized in that: include: A phase change material core and an anti-permeability layer, a magnetic layer and an anti-wear layer are sequentially coated on the surface of the phase change material core.

2. The phase change microcapsule according to claim 1, characterized in that The phase change material comprises one or more of sodium nitrate-potassium nitrate eutectic salt, sodium chloride-potassium chloride eutectic salt or potassium chloride-zinc chloride eutectic salt; and / or, The anti-seepage layer comprises an anti-seepage material, and the anti-seepage material comprises silicon carbide and / or boron nitride; and / or, The magnetic layer includes a magnetic material, and the magnetic material includes Modified carbon nanotubes and / or Modifying carbon nanotubes; and / or, The anti-wear layer includes an anti-wear material, and the anti-wear material includes one or more of silicon boride, boron carbide, aluminum oxide or titanium dioxide.

3. The phase-change microcapsule according to claim 1, characterized in that: The particle size of the phase-change microcapsules is 60 μm-80 μm.

4. A method for preparing recyclable phase-change microcapsules for drilling fluid, characterized in that: include: mixing a phase change material and an aqueous solution of a cationic surfactant and performing an emulsification treatment to obtain a phase change material emulsion; Mixing and dispersing an anti-seepage material and an anionic surfactant aqueous solution to obtain an anti-seepage material suspension; mixing and dispersing a magnetic material and a cationic surfactant aqueous solution to obtain a magnetic material suspension; mixing and dispersing an anti-wear material and an anionic surfactant aqueous solution to obtain an anti-wear material suspension; Adding the anti-seepage material suspension dropwise into the phase change material emulsion, and depositing the anti-seepage material on the surface of the phase change material through electrostatic adsorption to form a microcapsule suspension coated with an anti-seepage layer; Adding the magnetic material suspension dropwise to the microcapsule suspension coating the anti-seepage layer, and depositing the magnetic material outside the anti-seepage layer by electrostatic adsorption to form a microcapsule suspension coating the magnetic layer; Adding the anti-wear material suspension dropwise to the microcapsule suspension coating the magnetic layer, and depositing the anti-wear material outside the magnetic layer through electrostatic adsorption to form a microcapsule suspension coating the anti-wear layer; The suspension of the microcapsules coated with the anti-wear layer is solidified to obtain recyclable phase-change microcapsules for drilling fluid.

5. The preparation method according to claim 4, characterized in that The cationic surfactant includes polyethyleneimine and / or quaternary ammonium salt; and / or, The anionic surfactant includes one or more of sodium lauryl sulfate, polystyrene sulfonate or Span 80.

6. The preparation method according to claim 4, characterized in that The mass ratio of the anti-seepage material to the phase change material is 1:(2-3); and / or, The mass ratio of the magnetic material to the anti-seepage material is (1-3):2; and / or, The mass ratio of the anti-wear material to the magnetic material is (1-3):

1.

7. The preparation method according to any one of claims 4 to 6, characterized in that When preparing the phase change material emulsion, the concentration of the cationic surfactant aqueous solution is 1wt%-10wt%; and / or, When preparing the anti-seepage material suspension, the concentration of the anionic surfactant aqueous solution is 1wt%-5wt%; and / or, When preparing the magnetic material suspension, the mass concentration of the cationic surfactant aqueous solution is 1wt%-5wt%; and / or, When preparing the anti-wear material suspension, the concentration of the anionic surfactant aqueous solution is 1wt%-3wt%.

8. The preparation method according to any one of claims 4 to 6, characterized in that When preparing the phase change material emulsion, the volume ratio of the phase change material mass to the cationic surfactant aqueous solution is 1:0.05-1; and / or, When preparing the anti-seepage material suspension, the volume ratio of the mass of the anti-seepage material to the aqueous solution of anionic surfactant is 1:0.01-0.1; and / or, When preparing the magnetic material suspension, the volume ratio of the mass of the magnetic material to the cationic surfactant aqueous solution is 1:0.01-0.1; and / or, When preparing the anti-wear material suspension, the volume ratio of the mass of the anti-wear material to the anionic surfactant aqueous solution is 1:0.01-0.

1.

9. The preparation method according to any one of claims 4 to 6, characterized in that: When depositing the anti-seepage material on the surface of the phase change material, the electrostatic adsorption method is to stir at 600 rpm to 1000 rpm at 40° C. to 70° C. for 0.5 h to 5 h; When depositing the magnetic material outside the anti-seepage layer, the electrostatic adsorption method is to stir at 400 rpm to 600 rpm at 40° C. to 70° C. for 1 h to 1.5 h; When the anti-wear material is deposited outside the magnetic layer, the electrostatic adsorption method is to stir at 400-1000 r / min at 40° C.-70° C. for 1 h-1.5 h.

10. The preparation method according to any one of claims 4 to 6, characterized in that: The curing treatment is alkali treatment or heat treatment; The alkali treatment comprises: adding an alkaline aqueous solution to the suspension of the microcapsules coated with the anti-wear layer, standing at room temperature for 1 hour to 3 hours, and then separating, washing and drying to obtain the phase change microcapsules; and / or, The heat treatment comprises: separating, washing and drying the microcapsule suspension coated with the anti-wear layer, and then placing it at a temperature of 100° C. to 150° C. for 2 h to 4 h to obtain the phase change microcapsules.

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