Hematite coated organic alcohol phase change microcapsule for drilling fluid and preparation method and application thereof

Abstract

The application provides a hematite coated organic alcohol phase change microcapsule for drilling fluid and a preparation method and application thereof, and belongs to the field of drilling fluid chemistry in the petroleum industry. The preparation method comprises the following steps: (1) adding a phase change core material into a silane coupling agent solution and performing reaction; after standing, settling, washing and drying, a modified phase change core material is obtained; (2) dissolving hematite precursors in deionized water, adding a surfactant A and uniformly stirring to obtain a shell material precursor solution; (3) adding the modified phase change core material obtained in the step (1) and urea into deionized water, adding a surfactant B and uniformly stirring to obtain a suspension; adding the shell material precursor solution obtained in the step (2) into the suspension and performing reaction; after the reaction is completed, cooling, aging, centrifugation, washing and drying are performed to obtain the hematite coated organic alcohol phase change microcapsule. The phase change microcapsule can be used for delaying the temperature rise of drilling fluid in high-temperature deep wells, ultra-deep wells and geothermal wells.

Description

Technical Field

[0001] This invention relates to a hematite-coated organic alcohol phase change microcapsule for drilling fluid, its preparation method and application, belonging to the field of drilling fluid chemistry in the petroleum industry. Background Technology

[0002] As oil and gas exploration and development moves into deeper and ultra-deep formations, the challenges of high-temperature and high-pressure (HPHT) drilling operations are becoming increasingly severe. In deep shale gas reservoirs and geothermal wells, bottom hole temperatures often exceed 150°C, and can even reach over 200°C. This sustained high-temperature environment not only easily causes water-based drilling fluid system failures and exacerbates wellbore instability risks, but also causes irreversible thermal damage to the electronic components of precision instruments such as logging-while-drilling (LWD) and rotary steerable drilling (RSS), leading to tool failures, increased non-productive time, and significantly higher operating costs.

[0003] To address the issue of high downhole temperatures, traditional methods such as surface cooling devices or increasing drilling fluid circulation are largely passive heat dissipation methods. These are inefficient, have limited effectiveness in deep formations, and require significant equipment investment, making them unsuitable for meeting the cooling demands of ultra-deep oil and gas exploration and development. Phase change materials (PCMs), as latent heat storage materials, can undergo a phase transition at a specific temperature (phase transition temperature), achieving efficient energy storage and release through changes in intermolecular forces. This enables efficient and intelligent active temperature control, making PCM-based temperature regulation an effective approach to solving thermal management problems in high-temperature environments. However, directly applying PCMs to drilling fluids presents challenges such as easy leakage, low thermal conductivity, and poor thermal stability. Furthermore, it suffers from poor compatibility with drilling fluids and the potential disruption of the drilling fluid density system due to density mismatch.

[0004] Microencapsulation technology is an effective means to overcome the above-mentioned shortcomings, but existing phase change microcapsules have two major bottlenecks. First, there is a compatibility issue between the shell material density and high-density drilling fluid systems. Current research mainly focuses on silica (density approximately 2.2 g / cm³). 3 ) or low-density polymers (density typically less than 1.5 g / cm³) 3 For example, Chinese patent document CN120137602A discloses a drilling fluid cooling composite shell phase change microcapsule with paraffin and fatty acids as the core material and polyacrylic acid, polyurethane, and silica as the shell material. When this type of microcapsule is introduced into a high-density drilling fluid system, the shell material density is much lower than that of barite (density 4.2-4.5 g / cm³). 3Conventional weighting agents, such as those used in drilling fluids, can easily cause particle flotation, uneven solid phase distribution, or complicated formulation control, thus affecting the rheological and density stability of the drilling fluid. Secondly, there is a contradiction between latent heat value and dosage. Existing phase change microcapsule systems have limited latent heat values ​​for their core materials (mostly paraffin or fatty acids), resulting in relatively limited latent heat values ​​per unit mass (usually below 200 J / g), leading to insufficient thermal control capacity per unit volume. To achieve effective downhole temperature control, the dosage of microcapsules in the drilling fluid system needs to be increased, thereby significantly increasing the solid volume fraction. This not only places higher demands on the control of drilling fluid rheological properties and rock-carrying capacity but also increases material costs and construction complexity, limiting its engineering applications.

[0005] The hematite (Fe2O3) weighting material commonly used in drilling fluids has a high density (5.0-5.3 g / cm³). 3 While hematite is chemically stable and possesses good suspension and weighting properties, its function is limited, lacking temperature control capabilities. Therefore, if high-density inorganic materials like hematite can be constructed into phase-change microcapsule shells and combined with core materials possessing high latent heat and high melting points, it is hoped that a "dual-effect" material combining thermal management and weighting / compatibility advantages can be obtained. This invention is proposed for this purpose. Summary of the Invention

[0006] To address the shortcomings of existing technologies, particularly the low density of phase change microcapsule shells, insufficient compatibility with high-density drilling fluid solid systems, and the difficulty of forming a stable and dense shell layer on the surface of organic alcohol core materials using traditional coating methods, this invention provides a hematite-coated organic alcohol phase change microcapsule for drilling fluids, its preparation method, and its application. This invention employs a composite coating technology combining silane coupling agent surface modification with in-situ deposition of urea for uniform precipitation. This achieves uniform nucleation, continuous growth, and stable coating of a high-density iron oxide shell layer on the surface of the organic alcohol core material, thereby obtaining hematite-coated organic alcohol phase change microcapsules suitable for drilling fluid thermal management.

[0007] The technical solution of the present invention is as follows: A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluids includes the following steps: (1) The phase change core material is added to the silane coupling agent solution and reacted; after standing sedimentation, washing and drying, the modified phase change core material is obtained; (2) Dissolve the hematite precursor in deionized water, add surfactant A, stir evenly to obtain shell material precursor solution; (3) Add the modified phase change core material and urea obtained in step (1) to deionized water, add surfactant B, stir evenly to obtain a suspension; add the shell material precursor solution obtained in step (2) to the above suspension for reaction; after the reaction is completed, cool, age, centrifuge, wash and dry to obtain drilling fluid hematite-coated organic alcohol phase change microcapsules.

[0008] According to a preferred embodiment of the present invention, the phase change core material in step (1) is one or more of erythritol, D-mannitol and D-galactitol.

[0009] According to a preferred embodiment of the present invention, the silane coupling agent in step (1) is N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KH-792); the mass of the silane coupling agent is 3-8% of the mass of the phase change core material, more preferably 5%; the silane coupling agent solution is obtained by dissolving the silane coupling agent in anhydrous ethanol, and the concentration of the silane coupling agent solution is 0.001-0.01 g / mL.

[0010] According to a preferred embodiment of the present invention, the temperature of the reaction in step (1) is room temperature, and the reaction time is 1.5-3h.

[0011] According to a preferred embodiment of the present invention, the settling time in step (1) is 1-2 hours, after which the supernatant is removed to obtain the lower precipitate; the washing is to wash the lower precipitate obtained by settling with anhydrous ethanol 2-4 times; the drying is to dry at 40-50°C for 6-8 hours.

[0012] According to a preferred embodiment of the present invention, the hematite precursor in step (2) is a water-soluble ferric ion metal salt, or a mixture of a water-soluble ferric ion metal salt and a water-soluble ferrous ion metal salt, wherein the molar ratio of the water-soluble ferric ion metal salt to the water-soluble ferrous ion metal salt in the mixture is 19-20:1; the water-soluble ferric ion metal salt is at least one of FeCl3·6H2O and Fe(NO3)3·9H2O, and the water-soluble ferrous ion metal salt is FeSO4·7H2O.

[0013] According to a preferred embodiment of the present invention, the concentration of the shell precursor in the shell precursor solution in step (2) is 0.2-0.9 mol / L.

[0014] According to a preferred embodiment of the present invention, the surfactant A in step (2) is sodium dodecyl sulfate (SDS) or sodium dodecylbenzene sulfonate (SDBS).

[0015] According to a preferred embodiment of the present invention, the mass ratio of the modified phase change core material to the volume of deionized water in step (3) is 0.03-0.08 g: 1 mL.

[0016] According to a preferred embodiment of the present invention, the molar ratio of urea to iron in the shell precursor in step (3) is 3-4:1.

[0017] According to a preferred embodiment of the present invention, the surfactant B in step (3) is the same as the surfactant A in step (2); the mass of the surfactant B is 0.5-1.5% of the mass of the modified phase change core material.

[0018] According to a preferred embodiment of the present invention, the mass of hematite precursor in the shell precursor solution in step (3), converted to the mass of Fe2O3, is such that the mass ratio of Fe2O3 to the modified phase change core material is 1:1-4, more preferably 1:2; the mass of surfactant A in the shell precursor solution is 1.5-2.5% of the mass of the modified phase change core material.

[0019] According to a preferred embodiment of the present invention, the temperature of the reaction in step (3) is 75-95°C; the reaction time is 4-6 hours; and the temperature is increased to the reaction temperature at a heating rate of 2-3°C / min.

[0020] According to a preferred embodiment of the present invention, the cooling in step (3) is natural cooling to room temperature; the aging is stirring and aging at room temperature for 1-2 hours; the centrifugation is centrifuging at 5000-6000 rpm for 5-10 minutes; the washing is centrifuging and washing with deionized water and anhydrous ethanol 2-3 times each; and the drying is drying at 40-50°C to constant weight.

[0021] This invention provides a hematite-coated organic alcohol phase change microcapsule for drilling fluid, which is prepared using the above-described preparation method.

[0022] According to the present invention, the above-mentioned drilling fluid uses hematite-coated organic alcohol phase change microcapsules in water-based drilling fluids.

[0023] The technical features and beneficial effects of this invention are as follows: The core of this invention lies in the successful construction of composite microcapsules using a composite coating technology combining surface modification pretreatment and in-situ deposition. These microcapsules utilize high-density hematite (Fe2O3) as the shell material and a high latent heat phase change material as the core material. This method effectively improves the interfacial bonding strength between the hematite shell and the core material, ensuring the density and integrity of the shell. The resulting microcapsules not only possess high latent heat of phase change and a controllable phase change temperature, but also exhibit high density, endowing them with excellent pressure resistance, salt resistance, and thermal cycling stability. They can be used simultaneously as a highly efficient drilling fluid weighting agent and a reliable temperature regulator. Compared with existing phase change microcapsules, this invention has the following advantages:

[0024] 1. Synergistic effect of shell density and function: This invention uses hematite as the shell layer to replace the traditional low-density silica or polymer shell layer, which increases the overall density of the microcapsule, significantly improves its compatibility with the high-density drilling fluid solid system, reduces the risk of low-density phase change microcapsules floating and stratifying in drilling fluid, and enables it to be used as a drilling fluid thermal management agent and auxiliary weighting material.

[0025] 2. Improved coating process and structural stability: The interfacial bonding between the organic alcohol core and the inorganic shell is enhanced by surface modification with silane coupling agent. Then, the iron ions are slowly hydrolyzed and uniformly deposited on the core surface by uniform precipitation of urea. This avoids local oversaturation, particle agglomeration and uneven shell caused by direct addition of strong alkali, forming a more complete and dense iron oxide shell layer, which improves pressure resistance, salt resistance and thermal cycling stability.

[0026] 3. Adjustable core material temperature range and latent heat advantage: Erythritol, D-mannitol and D-galactitol have high phase transition temperatures and high latent heat, which can cover a downhole temperature range of about 110-190℃. By selecting different core materials, thermal buffer zones can be customized for different well depths, geothermal gradients and downhole instrument temperature windows, and significant temperature control effects can be achieved with low addition amounts.

[0027] 4. Simplicity and economy of preparation method: The present invention adopts an aqueous in-situ deposition process, which has a simple preparation process, mild reaction conditions, no need for complicated equipment, avoids the safety risks and high cost problems caused by high temperature and high pressure synthesis, and has good industrial application prospects. Attached Figure Description

[0028] Figure 1 SEM image of the hematite-coated organic alcohol phase change microcapsules for drilling fluid prepared in Example 1.

[0029] Figure 2 The temperature-time curves of different drilling fluid samples in Experiment Example 3 are shown. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments, but is not limited thereto.

[0031] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0032] In the embodiments, all phase change core materials used were dried at a temperature of 60°C for 4 hours, and then ground for later use.

[0033] Example 1 A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluids includes the following steps: (1) Add 0.5g of silane coupling agent KH-792 to 100mL of anhydrous ethanol and sonicate for 5 minutes to obtain a silane coupling agent solution; add 10g of dried erythritol powder to the above silane coupling agent solution and stir magnetically at room temperature for 2 hours; let the obtained reaction solution stand for 1 hour to settle and discard the supernatant; wash the lower precipitate obtained by standing for 3 times with anhydrous ethanol, transfer the washed wet powder to a petri dish, and dry at 40℃ for 6 hours to obtain the modified phase change core material; (2) Dissolve 16.1g FeCl3·6H2O and 0.86g FeSO4·7H2O in 150mL of deionized water, add 0.2g of surfactant sodium dodecyl sulfate (SDS), stir well to obtain shell material precursor solution; the mass of 16.1g FeCl3·6H2O and 0.86g FeSO4·7H2O converted to Fe2O3 is 5g; (3) Add 10g of the modified phase change core material obtained in step (1) and 12.8g of urea to 200mL of deionized water, add 0.1g of surfactant sodium dodecyl sulfate (SDS), stir evenly to obtain a suspension; add the shell material precursor solution obtained in step (2) to the above suspension, heat to 85℃ at a heating rate of 2℃ / min, and then react at 85℃ for 4h; after the reaction is completed, cool the obtained reaction solution to room temperature naturally, stir and age at room temperature for 1h; then centrifuge at 6000rpm for 10min, wash the precipitate obtained by centrifugation twice with deionized water, then wash twice with anhydrous ethanol, and finally dry the washed precipitate at 45℃ to constant weight to obtain drilling fluid hematite-coated organic alcohol phase change microcapsules.

[0034] Figure 1 This is a SEM image of the hematite-coated organic alcohol phase change microcapsules for drilling fluid prepared in this embodiment. Figure 1 It can be seen that the obtained microcapsules have an overall spherical or ellipsoidal particle morphology, and the particle surface is relatively rough, indicating that the iron oxide shell or iron oxide particles have been deposited on the surface of the phase change core material to form a coating structure.

[0035] Example 2 A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid is described in Example 1, except that in step (1), the phase change core material is replaced by D-mannitol instead of erythritol.

[0036] Example 3 A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid is described in Example 1, except that in step (1), the phase change core material is replaced by D-galactitol instead of erythritol.

[0037] Example 4 A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid is described in Example 1, except that the amount of urea added in step (3) is 11.3g.

[0038] Example 5 A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid is described in Example 1, except that the amount of urea added in step (3) is 15g.

[0039] Example 6 A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid is described in Example 1, except that the reaction temperature in step (3) is 75°C.

[0040] Example 7 A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid is described in Example 1, except that the reaction temperature in step (3) is 95°C.

[0041] Example 8 A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid is as described in Example 1, except that: in step (2), 8.05g of FeCl3·6H2O and 0.43g of FeSO4·7H2O are added, and the mass ratio of Fe2O3 to the modified phase change core material is 1:4 based on the conversion to Fe2O3; in step (3), the mass of urea added is 6.4g.

[0042] Example 9 A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid is as described in Example 1, except that: in step (2), 32.2g of FeCl3·6H2O and 1.72g of FeSO4·7H2O are added, and the mass ratio of Fe2O3 to the modified phase change core material is 1:1; in step (3), the mass of urea added is 25.6g.

[0043] Comparative Example 1 A method for preparing phase change microcapsules for drilling fluid is described in Example 1, except that in step (1), the phase change core material is replaced by paraffin (phase change temperature about 55°C) instead of erythritol.

[0044] Comparative Example 2 A method for preparing phase change microcapsules for drilling fluid is described in Example 1, except that step (1) is omitted and 10g of erythritol, the phase change core material, is directly added in step (3).

[0045] Comparative Example 3 A method for preparing phase change microcapsules for drilling fluids includes the following steps: Erythritol was coated with melamine resin as the shell material, and polymer-shell phase change microcapsules were prepared by conventional in-situ polymerization. The specific preparation method was as follows: 1.5 g of melamine and 3.0 g of 37% formaldehyde solution were added to 30 mL of deionized water, the pH was adjusted to 8.5 with triethanolamine, and the mixture was stirred at 70 °C for 30 min to obtain a melamine resin prepolymer solution; separately, 10 g of dried erythritol powder was added to 200 mL of an aqueous solution containing 0.2 g of sodium dodecyl sulfate, and the mixture was stirred at high speed... The mixture was stirred and dispersed for 20 min to obtain a core material suspension. Then, the obtained melamine resin prepolymer solution was added dropwise to the core material suspension at a dropping rate of 2 drops / s. The pH of the system was adjusted to 5.5 using a 5% (w / w) dilute hydrochloric acid aqueous solution, and the mixture was stirred and reacted at 70 °C for 3 h. After the reaction was completed, the reaction solution was naturally cooled to room temperature, centrifuged, and the precipitate obtained by centrifugation was washed with deionized water and then dried at 45 °C to constant weight to obtain polymer shell phase change microcapsules with melamine resin shells coated with erythritol.

[0046] The density of the microcapsules obtained in this comparative example is approximately 1.4 g / cm³. 3 When added at 5 wt% to drilling fluid-based slurry, it tends to float easily and exhibits poor dispersion stability. After high-temperature and high-pressure aging, the polymer shell material softens and deforms, resulting in insufficient pressure resistance and sealing performance. This comparative example highlights the compatibility advantages of high-density inorganic shells based on hematite in drilling fluid systems.

[0047] Comparative Example 4 A phase change material for drilling fluids is erythritol.

[0048] Comparative Example 5 A method for preparing phase change microcapsules for drilling fluid is described in Example 1, except that: in step (1), the silane coupling agent KH-792 is replaced with γ-methacryloyloxypropyltrimethoxysilane (KH-570); KH-570 does not contain amino groups, and its coordination or hydrogen bonding with iron ions and iron oxide shell precursors is weaker than that of KH-792, making it difficult to effectively induce iron species to uniformly nucleate and continuously deposit on the surface of the organic alcohol core material, resulting in poor shell density and integrity.

[0049] Experimental Example 1 The phase change microcapsules prepared in the examples and comparative examples were tested for average particle size, phase change temperature, latent heat of phase change, encapsulation rate, density and leakage rate.

[0050] The phase transition temperature (°C) and latent heat of phase transition (J / g) of the phase change microcapsules were calculated using differential scanning calorimetry (DSC, TA Instruments Q2000 instrument, heating rate 10°C / min, nitrogen atmosphere). The encapsulation rate (%) was calculated using the latent heat value method. The formula for calculating the encapsulation rate is as follows: Coverage rate (%) = ΔHm 微胶囊 / ΔHm 芯材 ×100%; Wherein, ΔHm 微胶囊 The latent heat of phase change of phase change microcapsules during DSC heating is expressed in J / g; ΔHm 芯材 The latent heat of phase change of pure phase change core material under the same test conditions is expressed in J / g; each sample was tested in parallel three times, and the average value was taken as the final result.

[0051] The average particle size (μm) of phase change microcapsules was determined using a laser particle size analyzer (such as Malvern Mastersizer 3000). During the test, 0.02 g of phase change microcapsule sample was weighed and added to 100 mL of 0.1% sodium dodecyl sulfate aqueous solution. The solution was ultrasonically dispersed for 2 min to obtain the dispersion to be tested. The dispersion to be tested was added to the sample cell of the laser particle size analyzer, and the light shading rate was controlled within the range of 5%-15%. After circulating dispersion for 1 min, the test was started. The volume average particle size D50 was used as the average particle size of the phase change microcapsules. Each sample was tested in parallel 3 times, and the average value was taken.

[0052] The overall density of phase change microcapsules was determined using the liquid displacement specific gravity bottle method. The specific steps were as follows: the sample was vacuum dried to constant weight at 45℃, and a certain mass of the dried phase change microcapsule sample was weighed; the mass of the empty specific gravity bottle (m1), the mass of the specific gravity bottle filled with displacement liquid (m2), the mass of the specific gravity bottle after adding the sample (m3), and the mass of the specific gravity bottle after adding the sample and replenishing with displacement liquid (m4) were recorded; using n-hexane as the displacement liquid, its density ρ0 was measured at 25℃. Each sample was tested in triplicate, and the average value was taken; the density of the phase change microcapsules was calculated using the following formula: ρ=(m3–m1)ρ0 / [(m2-m1)-(m4-m3)].

[0053] Pressure resistance and leakage rate testing: Phase change microcapsules were placed in a high-temperature and high-pressure aging tank and allowed to stand for 4 hours at a pressure of 50 MPa and a temperature of 200 °C for high-temperature and high-pressure treatment. After cooling, the core material leakage rate was calculated using the solvent extraction-weighing method. The specific steps were as follows: 1 g of the phase change microcapsule sample after high-temperature and high-pressure treatment was weighed and added to 50 mL of an extractant matched with the core material. The mixture was magnetically stirred at 25 °C for 30 min to fully extract the core material that had leaked to the outside of the microcapsules. For samples with erythritol, D-mannitol, or D-galactitol as the core material, a water / ethanol mixed solvent (9:1 volume ratio of ethanol to water) was used as the extractant; for comparative samples with paraffin as the core material, n-hexane was used as the extractant. After extraction, the extract was centrifuged and collected. The extract was then concentrated by rotary evaporation and vacuum dried to constant weight to obtain the mass m of the leaked core material. A Theoretical mass of core material m B The value is calculated from the mass and encapsulation rate of the phase change microcapsules, i.e., m. B =m0 × Encapsulation rate, where m0 is the mass of the phase change microcapsules used in the test; the core material leakage rate is calculated using the following formula: Leakage rate (%) = m A / m B ×100%; Where, m A The mass of the leaked core material obtained from extraction is expressed in g and m. B Let g represent the theoretical core material mass.

[0054] The results are shown in Table 1.

[0055] Table 1. Average particle size, phase transition temperature, latent heat value, encapsulation efficiency, density, and leakage rate of phase change microcapsules.

[0056] As shown in Table 1, the phase change microcapsules prepared in Examples 1-3 have a particle size concentrated in the range of 15.2-16.8 μm, an encapsulation rate of 84-88%, and an overall density of 3.71-3.95 g / cm³. 3 The leakage rate was 1.4-2.3%, indicating a low overall leakage level. The type of core material determines the phase transition temperature. When the core material was changed from erythritol to D-mannitol and D-galactitol, the phase transition temperature increased from 118.5℃ to 167.2℃ and 181.5℃, respectively, achieving coverage of different downhole temperature zones.

[0057] The shell-to-core mass ratio is a key factor in balancing heat storage capacity and sealing performance. Comparing Examples 1 and 8-9, it can be seen that with a shell-to-core ratio of 1:4, the shell layer is insufficient, resulting in low coverage and increased leakage rate, and the latent heat of phase change is not effectively maintained. With a shell-to-core ratio of 1:1, the shell layer is too thick; although the leakage rate is low, the proportion of inorganic shell layer increases, the effective core material content decreases, and the latent heat drops to approximately 200 J / g, significantly reducing the heat storage efficiency. The approximately 1:2 shell-to-core mass ratio used in Example 1 achieves a good balance between latent heat, coverage, density, and leakage rate. Comparing Examples 1 and 4-5, it can be seen that when the amount of urea added is low, the iron ion hydrolysis deposition rate is slow, the iron oxide shell layer grows insufficiently, the shell layer is thin and lacks density, resulting in a reduced coverage rate of the obtained microcapsules to 75% and an overall density of 3.29 g / cm³. 3 The leakage rate increased, and the latent heat of phase change was lower than in Example 1. When a large amount of urea was added, the alkalinity of the system increased rapidly, the iron ion hydrolysis and deposition rate was too high, and iron oxide particles tended to self-aggregate in the solution rather than being uniformly deposited on the surface of the core material. The resulting microcapsules had a coverage rate of 80% and an overall density of 3.56 g / cm³. 3 The latent heat of phase change in Example 1 was still lower than that in Example 1, and the leakage rate remained relatively high. In contrast, the amount of urea added in Example 1 resulted in a more uniform and dense iron oxide shell, with a coverage rate of 85%, thus achieving a better balance between latent heat of phase change, coverage rate, and leakage rate. Comparing Examples 1 and Examples 6-7, it can be seen that urea decomposition and shell growth were slower at 75°C, with a coverage rate of 78% and an overall density of 3.41 g / cm³. 3 The leakage rate is relatively high; at 95℃, the shell grows rapidly, with some areas exhibiting excessive shell thickness, which may cause slight dissolution or agglomeration of the core material. The coverage rate is 82%, and the overall density is 3.71 g / cm³. 3 The latent heat is reduced; 85℃ is the preferred temperature for achieving a good balance between coverage, latent heat and leakage rate.

[0058] Compared with the comparative examples, the material system of this invention simultaneously possesses three key characteristics: high-temperature core material, high-density inorganic shell, and interface modification. Comparative Example 1 shows that low-temperature paraffin core material cannot meet the high-temperature conditions of deep wells; Comparative Example 2 shows that the lack of surface modification leads to shell defects and decreased cycle stability; Comparative Example 3 shows that low-density polymer shell is difficult to match with the drilling fluid solid phase system; Comparative Example 4 shows that uncoated core material cannot stably perform phase change function in drilling fluid; In Comparative Example 5, after replacing KH-792 with amino-free KH-570, the ability of iron species to induce nucleation and continuous deposition on the core material surface is weakened, the shell density decreases, resulting in a decrease in coating rate and an increase in leakage rate, indicating that amino-containing silane coupling agents play an important role in improving the shell-core interface bonding and coating stability.

[0059] Experimental Example 2 The effects of phase change microcapsules on the rheological and filtration properties of drilling fluid after aging were investigated to verify the compatibility of phase change microcapsules with the drilling fluid system and to evaluate their impact on the rheological properties, filtration properties and dispersion stability of drilling fluid after high-temperature aging.

[0060] Preparation of base slurry: Add 4 parts by weight of sodium bentonite and 0.2 parts by weight of anhydrous sodium carbonate to 100 parts by weight of deionized water, stir at 10,000 rpm for 30 minutes in a high-speed mixer, and then seal at room temperature for 24 hours to obtain base slurry.

[0061] Preparation of drilling fluid samples: The phase change microcapsules prepared in Examples 1-3 and Comparative Example 3 were added to the base slurry at an addition amount of 5 wt% based on the total mass of the final drilling fluid sample, that is, 5 parts by weight of phase change microcapsules were added to every 95 parts by weight of base slurry. The mixture was stirred at 6000 rpm for 30 minutes to obtain the drilling fluid sample. At the same time, a base slurry without microcapsules was set up as a blank control.

[0062] Aging treatment: The above drilling fluid samples were loaded into a high-temperature and high-pressure aging tank and placed in a roller heating furnace for hot rolling aging at 200°C and 3.5MPa for 16 hours to simulate the high-temperature environment downhole.

[0063] Performance testing: After aging, the material was cooled to room temperature, and the apparent viscosity (AV), plastic viscosity (PV), and dynamic shear force (YP) were measured using a six-speed rotational viscometer according to the American Petroleum Institute (API) standard (API RP 13B-1, 2009); the filtration loss (FL) at room temperature under medium pressure was measured using an API filtration loss meter; the experimental results are shown in Table 2.

[0064] The sedimentation rate is calculated based on the density difference between the upper and lower layers of the sample after settling, and is used to characterize the dispersion stability of the drilling fluid sample. The specific steps are as follows: After the aged drilling fluid sample is thoroughly stirred, it is transferred to a graduated measuring cylinder and settling at 25°C for 24 hours; after settling, equal volumes of drilling fluid samples from the upper and lower layers are taken, and the density ρ of the upper layer is measured using a drilling fluid density meter. 上 and lower layer density ρ 下 Simultaneously, the initial density ρ of the homogeneous drilling fluid before settling was measured. 初 The settlement rate is calculated using the following formula:

[0065] Settlement rate (%) = (ρ 下 -ρ 上 ) / ρ 初 ×100%;

[0066] Each sample was tested in parallel three times, and the average value was taken.

[0067] Table 2. Effects of phase change microcapsules on rheological and filtration properties of drilling fluid after aging.

[0068] As shown in Table 2, after adding the microcapsules prepared in Examples 1-3, the AV, PV, and YP of the drilling fluid only increased slightly, with a small overall change, indicating that the microcapsules of the present invention did not significantly damage the colloidal structure of the drilling fluid after high-temperature aging. The API filtration loss decreased from 16.5 mL to 13.8-14.2 mL, indicating that the dense inorganic shell particles can participate in the densification of the mud cake and improve filtration performance. The sedimentation rate of the samples in Examples 1-3 was all below 2.5%, with no obvious sedimentation or floating, indicating that under the combined effect of particle size control, surface modification, and high overall density, the microcapsules have good dispersion stability in the base slurry. In contrast, Comparative Example 3, due to its low polymer shell density and insufficient temperature resistance, exhibited poor dispersion stability and performance after aging. The above results demonstrate that the hematite-coated organic alcohol phase change microcapsules prepared in this invention have excellent compatibility with the drilling fluid system. After high-temperature aging, it can maintain good rheological stability of drilling fluid, significantly reduce filtration loss, and has no sedimentation or floating, fully meeting the requirements of high-temperature deep well drilling fluid for additives.

[0069] Experimental Example 3 The study on the temperature control performance of phase change microcapsules or phase change materials is used to evaluate the active temperature control capability of microcapsules or phase change materials under heated conditions, and to analyze the influence of shell integrity and core material phase change characteristics on temperature control performance.

[0070] Preparation of base slurry: Add 4 parts by weight of sodium bentonite and 0.2 parts by weight of anhydrous sodium carbonate to 100 parts by weight of deionized water, stir at 10,000 rpm for 30 minutes in a high-speed mixer, and then seal at room temperature for 24 hours to obtain base slurry.

[0071] Preparation of drilling fluid samples: The phase change microcapsules prepared in Examples 1-3 and Comparative Example 2, as well as the phase change material in Comparative Example 4, were added to the base slurry at an addition rate of 5 wt% based on the total mass of the final drilling fluid sample, i.e., 5 parts by weight of phase change microcapsules or phase change material were added to every 95 parts by weight of base slurry. The mixture was stirred at 6000 rpm for 30 minutes to obtain the drilling fluid sample. At the same time, a base slurry without microcapsules was set up as a blank control.

[0072] Test procedure: The drilling fluid sample was placed in a high-pressure aging tank and then placed in a programmable temperature-controlled oven to heat from room temperature to 190°C. A thermocouple was inserted to record the center temperature of the drilling fluid in real time, with data recorded every 5 minutes, and a temperature-time curve was plotted.

[0073] Data processing: Calculate the temperature difference (temperature drop, ΔT, °C) between the temperature riser and the base slurry at 190 °C. A schematic diagram of the temperature rise curve is shown below. Figure 2 As shown, the key data is summarized in Table 3.

[0074] Table 3 Summary of temperature control performance data for phase change microcapsules

[0075] Combination Figure 2 As shown in Table 3, the drilling fluid temperature rise curves with the addition of microcapsules from Examples 1-3 are generally below the base fluid curve, indicating that the microcapsules absorb heat and delay the temperature rise of the drilling fluid during the phase transition. The temperature drop in Example 1 was 12.5℃, while in Examples 2 and 3 it was 9.8℃ and 8.5℃, respectively.

[0076] The temperature control effect is closely related to the phase transition temperature and latent heat of the core material. Erythritol undergoes a phase transition earlier and provides a continuous thermal buffering effect throughout the heating process; D-mannitol and D-galactitol have higher phase transition temperatures and are more suitable for thermal buffering in higher well temperature ranges. Comparative Example 2 suffered from shell defects due to lack of surface modification, resulting in partial core material leakage and a significant decrease in temperature control effect; Comparative Example 4 was not coated, and the core material was difficult to disperse stably in the drilling fluid after melting, thus failing to form an effective thermal buffer. The above results demonstrate that the hematite-coated organic alcohol phase transition microcapsules prepared in this invention can effectively slow down the drilling fluid heating rate, and the temperature control range of the microcapsules can be customized by selecting different core materials to meet the drilling fluid thermal management needs under different well depths and geothermal gradient conditions.

Claims

1. A method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid, characterized in that, The steps include the following: (1) The phase change core material is added to a silane coupling agent solution and reacted; after settling, washing, and drying, a modified phase change core material is obtained; the phase change core material is one or more of erythritol, D-mannitol, and D-galactitol; the silane coupling agent is N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; the mass of the silane coupling agent is 3-8% of the mass of the phase change core material; (2) Dissolve the hematite precursor in deionized water, add surfactant A, and stir until homogeneous to obtain a shell material precursor solution; the hematite precursor is a water-soluble ferric ion metal salt, or a mixture of a water-soluble ferric ion metal salt and a water-soluble ferrous ion metal salt, wherein the molar ratio of the water-soluble ferric ion metal salt to the water-soluble ferrous ion metal salt in the mixture is 19-20:1; the surfactant A is sodium dodecyl sulfate or sodium dodecylbenzene sulfonate; (3) Add the modified phase change core material and urea obtained in step (1) to deionized water, add surfactant B, stir evenly to obtain a suspension; add the shell material precursor solution obtained in step (2) to the above suspension for reaction; after the reaction is completed, cool, age, centrifuge, wash and dry to obtain drilling fluid hematite-coated organic alcohol phase change microcapsules; the molar ratio of urea to iron in the shell material precursor is 3-4:1; the surfactant B is the same as the surfactant A in step (2), and the mass of surfactant B is 0.5-1.5% of the modified phase change core material; the mass of hematite precursor in the shell material precursor solution is converted to the mass of Fe2O3, and the mass ratio of Fe2O3 to modified phase change core material is 1:1-4; the mass of surfactant A in the shell material precursor solution is 1.5-2.5% of the modified phase change core material; the reaction temperature is 75-95℃; the reaction time is 4-6h.

2. The method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid according to claim 1, characterized in that, The mass of the silane coupling agent in step (1) is 5% of the mass of the phase change core material; the silane coupling agent solution is obtained by dissolving the silane coupling agent in anhydrous ethanol, and the concentration of the silane coupling agent solution is 0.001-0.01 g / mL.

3. The method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid according to claim 1, characterized in that, The reaction temperature in step (1) is room temperature, the reaction time is 1.5-3h; the settling time is 1-2h, after which the supernatant is removed to obtain the lower precipitate; the washing is to wash the lower precipitate obtained by settling with anhydrous ethanol 2-4 times; the drying is to dry at 40-50℃ for 6-8h.

4. The method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid according to claim 1, characterized in that, The water-soluble ferric ion metal salt mentioned in step (2) is at least one of FeCl3·6H2O and Fe(NO3)3·9H2O, and the water-soluble ferrous ion metal salt is FeSO4·7H2O; the concentration of the shell material precursor in the shell material precursor solution is 0.2-0.9 mol / L.

5. The method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid according to claim 1, characterized in that, The mass ratio of the modified phase change core material to the volume of deionized water in step (3) is 0.03-0.08 g: 1 mL.

6. The method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid according to claim 1, characterized in that, The mass of hematite precursor in the shell precursor solution in step (3) is converted into the mass of Fe2O3, and the mass ratio of Fe2O3 to modified phase change core material is 1:

2.

7. The method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid according to claim 1, characterized in that, In step (3), the temperature is increased to the reaction temperature at a rate of 2-3℃ / min; the cooling is natural cooling to room temperature.

8. The method for preparing hematite-coated organic alcohol phase change microcapsules for drilling fluid according to claim 1, characterized in that, The aging process in step (3) involves stirring and aging at room temperature for 1-2 hours; the centrifugation process involves centrifuging at 5000-6000 rpm for 5-10 minutes; the washing process involves centrifuging and washing with deionized water and anhydrous ethanol 2-3 times each; and the drying process involves drying at 40-50℃ to constant weight.

9. A type of hematite-coated organic alcohol phase change microcapsule for drilling fluid, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the hematite-coated organic alcohol phase change microcapsules for drilling fluid as described in claim 9 in water-based drilling fluids.

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