Silica-polyurethane composite phase change microcapsules for water-based drilling fluids, and preparation method and application thereof

Abstract

The application relates to a kind of silica-polyurethane composite phase change microcapsules for water-based drilling fluid and a preparation method and application thereof, and belongs to the technical field of oilfield drilling fluid.The application successfully obtains a kind of phase change microcapsule with ternary nitrate / graphene composite phase change material as core material and silica-polyurethane composite material as shell material by sol-gel interface polymerization method.The phase change microcapsule of the application circulates to the bottom of well high-temperature stratum along with drilling fluid, when the temperature of system reaches its phase change temperature, the core material generates phase change endothermic behavior from solid to liquid, avoids the rapid rise of drilling fluid temperature, thereby improving the high-temperature stability of drilling fluid.When drilling fluid circulates into upper low-temperature stratum, microcapsule generates phase change exothermic behavior, realizes multiple cycle temperature control effect.

Description

Technical Field

[0001] This invention relates to a silica-polyurethane composite phase change microcapsule for water-based drilling fluids, its preparation method and application, belonging to the field of oilfield drilling fluid technology. Background Technology

[0002] In drilling operations, as well depth increases, formation temperature gradually rises, placing extremely high demands on the temperature resistance of drilling fluids. Insufficient temperature resistance of drilling fluids can easily lead to deterioration in the system's rheological properties, filtration efficiency, and settling stability, inducing complex downhole accidents and severely hindering drilling operations. Currently, researchers have conducted extensive studies on improving the high-temperature resistance of drilling fluids, including the use of high-temperature resistant bentonite, high-temperature treatment agents, and high-temperature stabilizers. However, these methods primarily rely on passive temperature resistance through chemical means, with limited research on how to actively reduce drilling fluid temperature or slow down the rate of temperature rise under high-temperature conditions at the bottom of the well using physical methods.

[0003] Phase change materials (PCMs) are latent heat storage materials with advantages such as large heat storage per unit volume, near-isothermal heat storage and release processes, and stable chemical properties. The relationship between temperature and energy changes during PCM phase change is as follows: in the solid stage or when the PCM completely transforms into a liquid stage, energy is stored or released through temperature increases or decreases, which is the sensible heat storage stage; during the phase change process, the temperature remains constant, and energy is stored or released through the phase change itself, which is the latent heat storage stage. Currently, research and application of PCMs in drilling fluids are still limited, indicating extremely high research value and promising prospects.

[0004] Microencapsulation of phase change materials can effectively prevent leakage of the internal phase change materials, and the micro-nano size distribution can be used with drilling fluid circulation through drilling fluid vibration sieve. After one cycle, it can be separated from the drilling fluid by special methods, cooled and restored, and then added back to the drilling fluid for the next cooling cycle.

[0005] However, the phase change capsules reported so far have the following shortcomings: 1) The mechanical properties of the wall material of the phase change microcapsule are poor, the thermal stability is low, and the thermal conductivity is poor in high-temperature environments; 2) There is a large difference between the phase change temperature and the bottom hole temperature during ultra-deep formation drilling, resulting in low latent heat of phase change; 3) The core material has a low thermal conductivity and a slow heat transfer rate, which affects the downhole heat exchange rate; 4) The phase change temperature is low and cannot be used for drilling fluid temperatures in high-temperature formations in deep / ultra-deep wells; 5) The phase change temperature is not adjustable and cannot meet the requirements of different formation temperatures.

[0006] For example, Chinese patent document CN110126385A discloses a multi-walled microcapsule of high-temperature, high-enthalpy phase change material and its preparation method. The shell structure comprises three layers: a volume expansion buffer layer, a corrosion-resistant layer, and a high-temperature resistant and strong layer. This three-layer structure of the microcapsule results in a low thermal conductivity and a slow heat transfer rate, which affects the downhole heat exchange rate.

[0007] Therefore, it is of great significance to develop a phase change microcapsule for drilling fluid that combines excellent mechanical properties, thermal stability, high thermal conductivity, and adjustable phase change temperature. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a silica-polyurethane composite phase change microcapsule for water-based drilling fluids, its preparation method, and its application.

[0009] The phase change microcapsules of this invention have a core-shell structure, with a ternary nitrate / graphene composite phase change material as the core and an outer layer coated with a silica-polyurethane composite material. The shell layer composed of silica-polyurethane composite material has a high coverage rate, excellent high-temperature stability, and high mechanical strength, ensuring that the phase change microcapsules will not rupture and release the core material at high temperatures. It can effectively resist the volume change and external stress influence during the phase change process of the core material. The ternary nitrate / graphene composite phase change material core has a high thermal conductivity, fast heat conduction, and can quickly and efficiently absorb and release heat. Moreover, the phase change temperature is adjustable, effectively improving the thermal conductivity of the material. The phase change microcapsules of this invention are a drilling fluid additive that can circulate during drilling, achieving efficient and precise temperature control without affecting the performance of the drilling fluid.

[0010] This invention is achieved through the following technical solution: A method for preparing silica-polyurethane composite phase change microcapsules for water-based drilling fluids includes the following steps: S1. Dissolve the ternary nitrate in deionized water, then add graphene and stir thoroughly to disperse it in the deionized water, forming solution A; S2. Thoroughly mix ethyl silicate, diisocyanate, emulsifier, and oil phase solution to form solution B; S3. Slowly add solution A to solution B, heat and stir thoroughly to form a stable water-in-oil emulsion; S4. Slowly add an initiator to the water-in-oil emulsion to initiate a sol-gel reaction and form a silica-polyurethane composite shell at the oil-water interface. S5. After the reaction is complete, the product is washed and dried to obtain silica-polyurethane composite phase change microcapsules for water-based drilling fluid.

[0011] According to a preferred embodiment of the present invention, in step S1, the ternary nitrate is a mixture of sodium nitrate, potassium nitrate, and sodium nitrite.

[0012] According to a preferred embodiment of the present invention, in step S1, the mass ratio of sodium nitrate, potassium nitrate and sodium nitrite is (1-8):(1-8):(1-5).

[0013] According to a preferred embodiment of the present invention, in step S1, the mass ratio of the ternary nitrate to graphene is (8-12):(1.5-4.5).

[0014] Most preferably, in step S1, the mass ratio of the ternary nitrate to graphene is 10:2.

[0015] According to a preferred embodiment of the present invention, in step S1, the total mass of the ternary nitrate and graphene is 30-60% of the mass of solution A.

[0016] That is, 100g of aqueous solution contains 30g-60g of ternary nitrate and graphene composite phase change material. Different mass ratios of ternary nitrate and graphene result in core materials with different phase change temperatures to match formations at different temperatures.

[0017] The mass ratio of ternary nitrate to graphene in this invention enables the prepared phase change microcapsules to have a high thermal conductivity, fast heat conduction, fast heat absorption, and high phase change enthalpy. The phase change temperature can be adjusted by adjusting the mass ratio of ternary nitrate to graphene.

[0018] According to a preferred embodiment of the present invention, in step S2, the diisocyanate is selected from one or a mixture of two or more of isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate.

[0019] According to a preferred embodiment of the present invention, in step S2, the mass ratio of the diisocyanate to ethyl silicate is 1:(0.25-3).

[0020] Most preferably, in step S2, the mass ratio of the diisocyanate to ethyl silicate is 1:0.5.

[0021] According to a preferred embodiment of the present invention, in step S2, the oil phase solution is selected from one or more of liquid paraffin, silicone oil, and white oil.

[0022] According to a preferred embodiment of the present invention, in step S2, the emulsifier is selected from one or a mixture of two or more of Tween-80, Span-80, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate.

[0023] More preferably, in step S2, the emulsifier is a mixture of Tween-80 and Span-80, and the mass ratio of Tween-80 to Span-80 is 1:(1.5-4).

[0024] According to a preferred embodiment of the present invention, in step S2, the mass of the emulsifier is 2%-15% of the mass of the oil phase solution. That is, 2g-15g of emulsifier is added to 100g of oil phase solution.

[0025] According to a preferred embodiment of the present invention, in step S2, the ratio of the total mass of the ethyl silicate and diisocyanate to the total mass of the ternary nitrate and graphene is (1-5):1.

[0026] Most preferably, in step S2, the ratio of the total mass of the ethyl silicate and diisocyanate to the total mass of the ternary nitrate and graphene is 1.5:1.

[0027] According to a preferred embodiment of the present invention, in step S2, the mass ratio of the ethyl silicate to the oil phase solution is (5-15):(40-100).

[0028] According to a preferred embodiment of the present invention, in step S3, solution A is added dropwise to solution B so that the mass ratio of deionized water in step S1 to oil phase solution in step S2 is 1:(1-6).

[0029] Most preferably, in step S3, solution A is added dropwise to solution B so that the mass ratio of deionized water in step S1 to oil phase solution in step S2 is 1:2.5.

[0030] According to a preferred embodiment of the present invention, in step S4, the initiator is selected from one or more of 3-aminopropyltriethoxysilane (APTES), ammonia water with a mass concentration of 25%-28%, and sodium hydroxide.

[0031] More preferably, in step S4, the initiator is a mixture of 3-aminopropyltriethoxysilane (APTES) and ammonia water with a mass concentration of 25%-28%, and the mass ratio of 3-aminopropyltriethoxysilane (APTES) to ammonia water with a mass concentration of 25%-28% is 1:(0.25-4).

[0032] According to a preferred embodiment of the present invention, in step S4, the mass of the initiator is 1%-5% of the mass of the oil phase solution in step S2. That is, 1g-5g of initiator is added to 100g of oil phase solution.

[0033] According to a preferred embodiment of the present invention, in steps S3 and S4, the reaction temperature is 40℃-90℃, the time is 4h-7h, and the reaction is carried out at a stirring speed of 200-1000r / min.

[0034] According to a preferred embodiment of the present invention, in step S5, the drying is performed at 40-50°C for 20-30 hours.

[0035] A silica-polyurethane composite phase change microcapsule for water-based drilling fluid is prepared by the above method.

[0036] According to a preferred embodiment of the present invention, the silica-polyurethane composite phase change microcapsules for water-based drilling fluid are white solid powders with an average particle size of 0.2-2 μm, a phase change temperature of 180-250 ℃, and a latent heat of phase change of 130-200 J / g.

[0037] The above-mentioned silica-polyurethane composite phase change microcapsules are used in water-based drilling fluids. Based on the total weight of the water-based drilling fluid as 100 wt%, the content of the silica-polyurethane composite phase change microcapsules is 3-10 wt%.

[0038] Technical features and effects of the present invention:

[0039] 1. This invention successfully prepared a high-temperature phase change microcapsule using a sol-gel interfacial polymerization method. The microcapsule has a ternary nitrate / graphene composite phase change material as its core and a silica-polyurethane composite material as its shell. The microcapsule circulates with the drilling fluid to the high-temperature formation at the bottom of the well. When the system temperature reaches its phase change temperature, the core material undergoes an endothermic phase change from solid to liquid, preventing a rapid rise in drilling fluid temperature and thus improving the high-temperature stability of the drilling fluid. When the drilling fluid circulates into the upper, lower-temperature formation, the microcapsule undergoes an exothermic phase change, achieving multiple-cycle temperature control.

[0040] 2. The phase change microcapsules of this invention have a core-shell structure, with a ternary nitrate / graphene composite phase change material as the core material and an outer layer coated with a silica-polyurethane composite material. Compared with traditional organic shell materials, the phase change microcapsules of this invention use an inorganic-organic composite material as the shell material (the shell layer is composed of silica-polyurethane composite material), which has a high coverage rate, excellent high-temperature stability and high mechanical strength. This prevents the microcapsules from rupturing and releasing the core material at high temperatures. It can effectively resist the volume change and external stress influence during the phase change process of the core material. It has good compatibility with commonly used drilling fluid treatment agents and will not significantly affect other properties of drilling fluid.

[0041] 3. The phase change microcapsule core material of the present invention has a high thermal conductivity and fast heat conduction, which can quickly and efficiently absorb and release heat, effectively improving the thermal conductivity of the material. It undergoes rapid heat absorption behavior at high temperatures, reaching the high-temperature formation. When the system temperature reaches its phase change temperature, the core material absorbs heat and undergoes a phase change from solid to liquid. The core material temperature remains unchanged during the phase change process, thereby achieving precise and efficient temperature control, effectively reducing the impact of high formation temperature on drilling fluid performance, slowing down the drilling fluid heating rate, and improving the high-temperature stability of drilling fluid.

[0042] 4. The phase change microcapsules of the present invention can change their phase change temperature by adjusting the mass ratio of ternary nitrate to graphene. The phase change temperature is 180-250 ℃, which expands its working temperature range and makes it suitable for formations with different temperatures. The addition of graphene, which is compounded with ternary nitrate to form a composite phase change core material, increases the phase change enthalpy value and the latent heat of phase change is 130-200 J / g.

[0043] 5. The phase change microcapsules of the present invention have a wide range of raw material sources, a relatively simple preparation method, require a small amount, have low cost, can be reused, and are easy to industrialize. Attached Figure Description

[0044] Figure 1 SEM image of silica-polyurethane composite phase change microcapsules C-1 for water-based drilling fluid prepared in Example 1;

[0045] Figure 2 This is a schematic diagram of the dynamic heating cycle system.

[0046] In the diagram, 1 is a temperature sensor, 2 is a liquid storage tank, 3 is a circulation pipeline, 4 is a heater, and 5 is a circulation pump. Detailed Implementation

[0047] The present invention will be further described below with reference to specific embodiments, but is not limited thereto. All materials used in the embodiments can be synthesized from conventional raw materials or are commercially available; unless otherwise specified, the methods described are prior art.

[0048] The FA367 used in the test examples is available from Henan Yuanchun Chemical Co., Ltd.; DSP-2 is available from Hebei Haizuan Oil & Chemical Co., Ltd.; SMP-2 is available from Jining Huakai Resin Co., Ltd.; SPNH is available from Shandong Zhengyang New Material Technology Co., Ltd.; and white oil is available from Jinan Xinjiarun New Material Co., Ltd.

[0049] Example 1

[0050] The preparation method of silica-polyurethane composite phase change microcapsules for water-based drilling fluids includes the following steps:

[0051] S1. Dissolve 3g sodium nitrate, 4g potassium nitrate, and 3g sodium nitrite in 20g deionized water, then add 1.5g graphene and stir thoroughly to disperse it, forming solution A; S2. Add 6g of ethyl silicate, 12g of isophorone diisocyanate, 1.5g of Tween-80, and 3.5g of Span-80 to 50g of liquid paraffin in sequence, and stir thoroughly to form solution B. S3. Slowly add solution A to solution B and stir at 500 rpm for 1 hour under a water bath heating condition at 70°C to form a stable water-in-oil emulsion; S4. Slowly add 2g of initiator to the water-in-oil emulsion. The initiator is obtained by thoroughly mixing 1g of APTES with 1g of ammonia water with a mass concentration of 28%. After the addition is complete, continue stirring at 500rpm for 5 hours under a water bath heating condition of 70℃ to allow it to react fully.

[0052] S5. After the reaction is complete, the product is washed and dried at 45°C for 24 hours to obtain silica-polyurethane composite phase change microcapsules for water-based drilling fluid, denoted as C-1.

[0053] The silica-polyurethane composite phase change microcapsules C-1 prepared in Example 1 were observed using a Hitachi SU5000 thermal field emission scanning electron microscope. The results are shown in the figure below. Figure 1 .from Figure 1 As can be seen, the prepared silica-polyurethane composite phase change microcapsules have a dense spherical core-shell structure with a particle size of 0.2-2 μm. Although there is agglomeration between the particles, it is still at the micro-nano level and has little impact on the drilling fluid system.

[0054] Example 2

[0055] The preparation method of silica-polyurethane composite phase change microcapsules for water-based drilling fluids includes the following steps:

[0056] S1. Add 1g sodium nitrate, 8g potassium nitrate, 1g sodium nitrite, and 2g graphene to 20g deionized water and stir thoroughly to dissolve and disperse them, forming solution A. S2. Add 6g of ethyl silicate, 12g of isophorone diisocyanate, 1.5g of Tween-80, and 3.5g of Span-80 to 50g of liquid paraffin in sequence, and stir thoroughly to form solution B. S3. Slowly add solution A to solution B and stir at 500 rpm for 1 hour under a water bath heating condition at 70°C to form a stable water-in-oil emulsion; S4. Slowly add 2g of initiator to the water-in-oil emulsion. The initiator is obtained by thoroughly mixing 1g of APTES with 1g of ammonia water with a mass concentration of 28%. After the addition is complete, continue stirring at 500rpm for 5 hours under a water bath heating condition of 70℃ to allow it to react fully.

[0057] S5. After the reaction is complete, the product is washed and dried at 45°C for 24 hours to obtain silica-polyurethane composite phase change microcapsules for water-based drilling fluid, denoted as C-2.

[0058] Example 3

[0059] The preparation method of silica-polyurethane composite phase change microcapsules for water-based drilling fluids includes the following steps:

[0060] S1. Add 3g sodium nitrate, 2g potassium nitrate, 5g sodium nitrite, and 3g graphene to 20g deionized water and stir thoroughly to dissolve and disperse them, forming solution A. S2. Add 6g of ethyl silicate, 12g of isophorone diisocyanate, 1.5g of Tween-80, and 3.5g of Span-80 to 50g of liquid paraffin in sequence, and stir thoroughly to form solution B. S3. Slowly add solution A to solution B and stir at 500 rpm for 1 hour under a water bath heating condition at 70°C to form a stable water-in-oil emulsion; S4. Slowly add 2g of initiator to the water-in-oil emulsion. The initiator is obtained by thoroughly mixing 1g of APTES with 1g of ammonia water with a mass concentration of 28%. After the addition is complete, continue stirring at 500rpm for 5 hours under a water bath heating condition of 70℃ to allow it to react fully.

[0061] S5. After the reaction is complete, the product is washed and dried at 45°C for 24 hours to obtain silica-polyurethane composite phase change microcapsules for water-based drilling fluid, denoted as C-3.

[0062] Example 4

[0063] The preparation method of silica-polyurethane composite phase change microcapsules for water-based drilling fluids includes the following steps:

[0064] S1. Add 8g sodium nitrate, 1g potassium nitrate, 1g sodium nitrite, and 4g graphene to 20g deionized water and stir thoroughly to dissolve and disperse them, forming solution A. S2. Add 6g of ethyl silicate, 12g of isophorone diisocyanate, 1.5g of Tween-80, and 3.5g of Span-80 to 50g of liquid paraffin in sequence, and stir thoroughly to form solution B. S3. Slowly add solution A to solution B and stir at 500 rpm for 1 hour under a water bath heating condition at 70°C to form a stable water-in-oil emulsion; S4. Slowly add 2g of initiator to the water-in-oil emulsion. The initiator is obtained by thoroughly mixing 1g of APTES with 1g of ammonia water with a mass concentration of 28%. After the addition is complete, continue stirring at 500rpm for 5 hours under a water bath heating condition of 70℃ to allow it to react fully.

[0065] S5. After the reaction is complete, the product is washed and dried at 45°C for 24 hours to obtain silica-polyurethane composite phase change microcapsules for water-based drilling fluid, denoted as C-4.

[0066] Example 5 The method described in the same way as in Example 1 differs in that: In step S2, the amount of ethyl silicate added was replaced with 9g, the amount of isophorone diisocyanate added was replaced with 9g, and the rest was carried out as in Example 1, to obtain silica-polyurethane composite phase change microcapsules for water-based drilling fluid, denoted as C-5.

[0067] Example 6

[0068] The method described in the same way as in Example 1 differs in that: In step S2, 12g of isophorone diisocyanate was replaced with 12g of hexamethylene diisocyanate, and the rest was carried out as in Example 1, to obtain silica-polyurethane composite phase change microcapsules for water-based drilling fluid, denoted as C-6.

[0069] Example 7

[0070] The method described in the same way as in Example 1 differs in that: In step S4, the initiator is replaced with a mixture of 1.5g APTES and 0.5g ammonia solution with a mass concentration of 28%, and the rest is carried out as in Example 1, to obtain silica-polyurethane composite phase change microcapsules for water-based drilling fluid, denoted as C-7.

[0071] Comparative Example 1 A method for preparing phase change microcapsules for water-based drilling fluids, as described in Example 1, differs in that: In step S1, no graphene was added, and the rest was carried out as in Example 1. The resulting phase change microcapsules were denoted as D-1.

[0072] Comparative Example 2 A method for preparing phase change microcapsules for water-based drilling fluids, as described in Example 1, differs in that: In step S1, the amount of graphene added was 0.5g, and the rest was carried out as in Example 1. The resulting phase change microcapsules were denoted as D-2.

[0073] Comparative Example 3 A method for preparing phase change microcapsules for water-based drilling fluids, as described in Example 1, differs in that: In step S1, the amount of graphene added was 6g, and the rest was carried out as in Example 1. The resulting phase change microcapsules were denoted as D-3.

[0074] Comparative Example 4 A method for preparing phase change microcapsules for water-based drilling fluids, as described in Example 1, differs in that: Step S1: Replace 3g sodium nitrate, 4g potassium nitrate, and 3g sodium nitrite with 10g sodium nitrate, and proceed as in Example 1. The resulting phase change microcapsules are denoted as D-4.

[0075] Comparative Example 5 A method for preparing phase change microcapsules for water-based drilling fluids, as described in Example 1, differs in that: Step S1: Replace 3g sodium nitrate, 4g potassium nitrate, and 3g sodium nitrite with 10g potassium nitrate, and proceed as in Example 1. The resulting phase change microcapsules are denoted as D-5.

[0076] Comparative Example 6 A method for preparing phase change microcapsules for water-based drilling fluids, as described in Example 1, differs in that: Step S1: Replace 3g sodium nitrate, 4g potassium nitrate, and 3g sodium nitrite with 10g sodium nitrite, and proceed as in Example 1. The resulting phase change microcapsules are denoted as D-6.

[0077] Comparative Example 7 A method for preparing phase change microcapsules for water-based drilling fluids, as described in Example 1, differs in that: In step S2, without adding ethyl silicate, the rest was carried out as in Example 1, and the resulting phase change microcapsules were designated as D-7.

[0078] Comparative Example 8 A method for preparing phase change microcapsules for water-based drilling fluids, as described in Example 1, differs in that: Step S2: Replace 6g of ethyl silicate with 30g of ethyl silicate, and proceed as in Example 1. The resulting phase change microcapsules are denoted as D-8.

[0079] Experimental Example 1

[0080] The mechanical strength of the phase change microcapsules prepared in Examples 1-7 and Comparative Examples 1-8 was tested using the Shanghai Baosheng TA.XTC microsphere strength tester. The test results are shown in Table 1.

[0081] Table 1. Breakage Mechanical Strength

[0082]

[0083] Table 1 shows that the phase change microcapsules prepared in Examples 1-7 and Comparative Examples 1-6 have high mechanical strength, indicating that the phase change microcapsules with silica-polyurethane composite material as shell material have excellent high-temperature stability and high mechanical strength. This prevents the microcapsules from rupturing and releasing the core material at high temperatures, effectively resisting volume changes and external stress during the phase change process of the core material. It can better prevent the core material from leaking out and affecting the drilling fluid in the downhole environment. However, the mechanical strength of the organic shell material prepared in Comparative Example 7 without the addition of ethyl silicate is greatly reduced, resulting in a decrease in the high-temperature stability of the phase change microcapsules. The mechanical strength of the organic shell material prepared in Comparative Example 8 with the addition of excessive ethyl silicate is also low. This is because excessive ethyl silicate will affect the mechanical properties of the inorganic-organic composite material as a shell material.

[0084] Experimental Example 2

[0085] Preparation of bentonite-based slurry: Add 16 g of sodium-based bentonite for drilling fluid to 400 mL of tap water, stir at 10000 r / min for 30 min, and let stand in a sealed container for 24 h to obtain 4% prehydrated bentonite-based slurry.

[0086] 12 g (i.e., 3% w / v) of the phase change microcapsules obtained in Examples 1-7 and Comparative Examples 1-8 were added to 400 mL of the bentonite-based slurry prepared above. After stirring at 6000 r / min for 20 min, the rheological properties and filtration properties of the slurry were tested at 65℃ using a viscometer. The test results are shown in Table 2.

[0087] Table 2

[0088]

[0089] As shown in Table 2, after adding the phase change microcapsules prepared in Examples 1-7 and Comparative Examples 1-8 to the bentonite-based slurry, the apparent viscosity, plastic viscosity, and dynamic shear force of Examples 1-7 and Comparative Examples 1-6 did not change significantly compared with the base slurry, indicating that they had little impact on the rheological properties of the bentonite-based slurry and could still maintain good fluidity. The phase change microcapsules and the bentonite-based slurry have good compatibility. The filtration loss of Examples 1-7 and Comparative Examples 1-6 was significantly lower than that of the base slurry and Comparative Examples 7-8, showing a certain effect on reducing filtration loss. This indicates that the microcapsule shell has good integrity and will not cause damage to the filter cake structure due to breakage or overflow. However, Comparative Example 7 did not add ethyl silicate, and Comparative Example 8 added too much ethyl silicate, which would reduce the integrity of the microcapsule shell and lead to an increase in filtration loss compared with the base slurry.

[0090] Experimental Example 3

[0091] The phase transition temperature and latent heat of phase transition of the phase change microcapsules prepared in Examples 1-7 and Comparative Examples 1-8 were tested using a DSC25-TA differential scanning calorimeter.

[0092] The particle size of the phase change microcapsules prepared in Examples 1-7 and Comparative Examples 1-8 was tested using the Omni multi-angle particle size and high-sensitivity Zeta potential analyzer from Brookhaven Instruments, Inc., USA. The test results are shown in Table 3.

[0093] Table 3

[0094]

[0095] As shown in Table 3, in Examples 1-4, the phase transition temperature of the phase change microcapsules can be changed by adjusting the mass ratio of the core material ternary nitrate to graphene. The phase transition temperature range is 180-250℃, which expands its working temperature range and allows it to be applied to drilling in formations with different temperatures.

[0096] Comparative Example 1, due to the absence of graphene in the core material, resulted in phase change microcapsules D-1 with significantly lower phase change enthalpy and thermal conductivity compared to the examples. With increasing graphene content, both the examples and the comparative examples showed an increasing trend in phase change enthalpy and thermal conductivity, enhancing the rate at which the phase change material absorbs heat. However, when the graphene content was excessively high (Comparative Example 3), the phase change enthalpy and thermal conductivity decreased compared to the examples. This is because the amount of graphene coated by the shell is limited; exceeding a certain amount prevents complete coating of graphene, leading to a decrease in phase change enthalpy and thermal conductivity.

[0097] The core material of Comparative Examples 4-6 was mononitrate, and the phase change enthalpy and thermal conductivity of the resulting phase change microcapsules were lower than those of the other examples, indicating that the ternary nitrate / graphene composite material used in this invention has a higher phase change enthalpy than the mononitrate material.

[0098] In summary, the phase change microcapsules prepared in the embodiments of the present invention have the advantages of high latent heat of phase change and small particle size, which can well meet the cooling requirements of high-temperature water-based drilling fluids.

[0099] Test Example 4

[0100] A dynamic heating circulation system (heating temperature ranging from -25℃ to 300℃) was used to simulate the working environment of drilling fluid circulation. The effects of adding phase change microcapsules prepared in Examples 1-7 and Comparative Examples 1-8 on the circulation temperature of high-temperature water-based drilling fluid were tested. A schematic diagram of the dynamic heating circulation system is shown below. Figure 2 As shown, the dynamic heating circulation system includes a heater 4 and a storage tank 2. A temperature sensor 1 is installed in the storage tank 2. The storage tank 2 is connected to a circulation pipeline 3. A circulation pump 5 is installed on the circulation pipeline 3. The heater 4 is installed outside the circulation pipeline 3.

[0101] The testing methods and high-temperature water-based drilling fluid formulations are as follows:

[0102] Test method: High-temperature water-based drilling fluid was heated and circulated using a dynamic heating circulation system until the circulating temperature of the drilling fluid reached the set temperature and stabilized. Then, 5% of the phase change microcapsules prepared in Examples 1-7 and Comparative Examples 1-8 were added to the drilling fluid, and the maximum decrease in circulating temperature was tested. The set circulating temperature corresponds to the phase change temperature of the phase change microcapsules. The test results are shown in Table 4.

[0103] Preparation of high-temperature water-based drilling fluid: Add 0.8g sodium carbonate, 0.8g sodium hydroxide, 1.2g FA367, 3.2g DSP-2, 12g SMP-2, 12g SPNH, 28g potassium chloride, and 12g white oil to 400mL of prehydrated bentonite-based slurry to prepare the drilling fluid. During the preparation of the drilling fluid, stir at 10000r / min for 20min after each material is added. After all materials are added, continue stirring for 60min to finally obtain the high-temperature water-based drilling fluid.

[0104] Table 4

[0105]

[0106] As can be seen from Table 4, the silica-polyurethane composite phase change microcapsules prepared in Examples 1-7 using ternary nitrate / graphene composite material as the core material have a significant cooling effect on high-temperature water-based drilling fluids at different temperatures. They can slow down the heating rate of the drilling fluid, increase the applicable formation temperature of the drilling fluid, and achieve the purpose of cooling the drilling tools.

[0107] In summary, the silica-polyurethane composite phase change microcapsules prepared in this invention can effectively regulate the temperature of high-temperature water-based drilling fluids at different temperatures. Adding phase change microcapsules with different core material ratios to water-based drilling fluids utilizes their ability to absorb heat and maintain relatively stable temperature during phase change, as well as the different phase change temperatures associated with different core material ratios. This achieves the goal of reducing the circulating temperature of the water-based drilling fluid within the wellbore at different formation temperatures, enhancing the performance of the drilling fluid under high-temperature environments, and cooling the drilling tools. Furthermore, the shell material is a silica-polyurethane composite shell, which significantly improves mechanical strength compared to traditional polyurethane shells.

[0108] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing silica-polyurethane composite phase change microcapsules for water-based drilling fluids, comprising the following steps: S1. Dissolve the ternary nitrate in deionized water, then add graphene and stir thoroughly to disperse it in the deionized water, forming solution A; the ternary nitrate is a mixture of sodium nitrate, potassium nitrate, and sodium nitrite, with a mass ratio of (1-8):(1-8):(1-5), and a mass ratio of the ternary nitrate to graphene of (8-12):(1.5-4.5), the total mass of the ternary nitrate and graphene being 30-60% of the mass of solution A; S2. Thoroughly mix ethyl silicate, diisocyanate, emulsifier and oil phase solution to form solution B; the total mass ratio of ethyl silicate and diisocyanate to the total mass of ternary nitrate and graphene is (1-5):1, and the mass ratio of ethyl silicate to oil phase solution is (5-15):(40-100). S3. Slowly add solution A to solution B, heat and stir thoroughly to form a stable water-in-oil emulsion; S4. Slowly add an initiator to the water-in-oil emulsion to initiate a sol-gel reaction and form a silica-polyurethane composite shell at the oil-water interface. S5. After the reaction is complete, the product is washed and dried to obtain silica-polyurethane composite phase change microcapsules for water-based drilling fluid.

2. The preparation method according to claim 1, characterized in that, In step S2, the diisocyanate is selected from one or more of isophorone diisocyanate, hexamethylene diisocyanate and dicyclohexylmethane diisocyanate, and the mass ratio of the diisocyanate to ethyl silicate is 1:(0.25-3).

3. The preparation method according to claim 1, characterized in that, In step S2, the oil phase solution is selected from one or more of liquid paraffin, silicone oil, and white oil, and the emulsifier is selected from one or more of Tween-80, Span-80, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate, and the mass of the emulsifier is 2%-15% of the mass of the oil phase solution.

4. The preparation method according to claim 1, characterized in that, In step S3, solution A is added dropwise to solution B so that the mass ratio of deionized water in step S1 to oil phase solution in step S2 is 1:(1-6).

5. The preparation method according to claim 1, characterized in that, In step S4, the initiator is a mixture of 3-aminopropyltriethoxysilane (APTES) and ammonia water with a mass concentration of 25%-28%, and the mass ratio of 3-aminopropyltriethoxysilane (APTES) to ammonia water with a mass concentration of 25%-28% is 1:(0.25-4). The mass of the initiator is 1%-5% of the mass of the oil phase solution in step S2.

6. The preparation method according to claim 1, characterized in that, In steps S3 and S4, the reaction temperature is 40℃-90℃, the time is 4h-7h, and the reaction is carried out at a stirring speed of 200-1000r / min. In step S5, the drying is carried out at 40-50℃ for 20-30 hours.

7. A silica-polyurethane composite variable microcapsule for water-based drilling fluid, characterized in that, It is prepared by the method described in any one of claims 1-6.

8. The application of the silica-polyurethane composite phase change microcapsules for water-based drilling fluid as described in claim 7 in water-based drilling fluid, characterized in that, Based on a total weight of 100 wt% of the water-based drilling fluid, the content of the silica-polyurethane composite phase change microcapsules is 3-10 wt%.

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