A double-shell high-thermal-conductivity phase-change heat storage microcapsule for ultra-deep drilling fluid and a preparation method and application thereof

Abstract

The present application relates to a kind of double-shell high-thermal-conductivity phase change heat storage microcapsules for ultra-deep drilling fluid and its preparation method and application, belong to the drilling fluid chemistry field of petroleum industry.The present application respectively with two high-melting-point phase change materials and two eutectic compounds of phase change material as core material, by twice the coating of outer shell, a kind of double-shell high-thermal-conductivity phase change heat storage microcapsules for ultra-deep drilling fluid is prepared, the material has high phase change temperature, phase change temperature is between 173.3-230.7 DEG C, phase change enthalpy is as high as 211.4J / g, when in phase change temperature range, a large number of heat will be absorbed, play the role of " phase change latent heat", the material is applied to drilling fluid can significantly reduce the temperature of drilling fluid, improve the tolerance of drilling fluid to high temperature formation.

Description

Technical Field

[0001] This invention relates to a double-shell high thermal conductivity phase change thermal storage microcapsule for ultra-deep drilling fluid, its preparation method and application, belonging to the field of drilling fluid chemistry in the petroleum industry. Background Technology

[0002] my country is rich in deep and ultra-deep oil and gas resources, with a total resource volume of 671 × 10⁻⁶. 8 Of the newly discovered reserves in the past decade, deep and ultra-deep oil and gas resources account for more than 50%, and their efficient development is of great significance to ensuring national energy security. In the drilling process of deep and ultra-deep formations, drilling fluid plays a crucial role, serving as a core technology for carrying cuttings, stabilizing the wellbore, and protecting the reservoir. However, deep and ultra-deep wells face harsh conditions at the bottom of the well, even at extremely high temperatures. The high-temperature stability of drilling fluids under these conditions presents a significant challenge, and improper control can easily lead to complex safety accidents such as wellbore instability and stuck pipe, seriously affecting the safety of drilling operations. Effectively reducing the circulating temperature of drilling fluids at the bottom of ultra-deep wells and improving their tolerance to high-temperature and even ultra-high-temperature formations is crucial. Currently, some progress has been made in drilling fluid cooling methods both domestically and internationally. Drilling fluid cooling technology can reduce the temperature of drilling fluids, thereby reducing the impact of high temperatures on drilling fluid performance. The main methods for cooling drilling fluids include: drilling fluid surface cooling systems, heat-insulated drilling tools, and chemical cooling materials for drilling fluids.

[0003] Currently, the most researched chemical cooling materials for drilling fluids are phase change materials (PCMs). PCMs typically absorb a large amount of heat within their phase change temperature range, thereby lowering the ambient temperature. Solid-liquid phase change materials (SCMs) have high latent heat of phase change and are therefore a focus of research. However, SCMs change from solid to liquid at their phase change temperature, which can severely affect the rheological properties of drilling fluids. When the temperature drops below their freezing point, these PCMs solidify and precipitate from the system, forming large clumps, which is very dangerous for drilling operations. Furthermore, current PCMs typically have low thermal conductivity, which hinders their rapid heat absorption. Encapsulating PCMs with high thermal conductivity materials to form microcapsules—with the PCM as the core and a high thermal conductivity shell (such as an inorganic shell)—can significantly improve the applicability of SCMs in drilling fluids.

[0004] Patent document CN117701255A discloses a phase change microcapsule for drilling fluid cooling, with silica as the outer coating layer and two inorganic salts as the phase change core material. The phase change temperature reaches 236℃, and the latent heat of phase change is 192 J / g. Although its performance is excellent, its thermal conductivity is unknown. Patent document CN115491183A discloses a method for preparing high-temperature and high-pressure resistant microspheres for active cooling of drilling fluids. This material has a phase change temperature of less than 150℃ and a latent heat of 236.1 J / g. Although the latent heat value is high, it cannot be effectively applied to cooling drilling fluids in ultra-high temperature formations. Patent document CN113249097A discloses a polyacrylate phase change microcapsule and its preparation method. The melting point is less than 40℃, and the phase change enthalpy is less than 180 J / g. The phase change temperature is too low. Furthermore, the use of polymer-coated phase change materials in this microcapsule results in low thermal conductivity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, especially the problems of low phase change temperature and low thermal conductivity of existing phase change materials, this invention provides a double-shell high thermal conductivity phase change thermal storage microcapsule for ultra-deep drilling fluids, its preparation method, and its application.

[0006] This invention prepares a double-shell high thermal conductivity phase change heat storage microcapsule using a two-step encapsulation method. This material has a high phase change temperature (173.3-235.1℃). When within the phase change temperature range, it absorbs a large amount of heat, playing the role of "latent heat of phase change." At the same time, it has excellent thermal conductivity with a high thermal conductivity coefficient. Applying this material to drilling fluid can significantly reduce the drilling fluid's tolerance to high-temperature formations. When the drilling fluid circulates to the high-temperature well section (phase change temperature of the phase change microcapsule), it absorbs a large amount of heat transferred from the high-temperature formation to the drilling fluid, preventing the drilling fluid temperature from rising sharply. This avoids drilling fluid system failure and wellbore instability, which is crucial for safe and efficient drilling.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] A method for preparing double-shell high thermal conductivity phase change thermal storage microcapsules for ultra-deep drilling fluids includes the following steps:

[0009] (1) First outer shell covering

[0010] a. Preparation of phase change microcapsule material 1

[0011] Phase change material 1, polyvinylpyrrolidone, and emulsifier 1 were sequentially added to deionized water to obtain a supersaturated solution of phase change material 1. The supersaturated solution of phase change material 1 was heated and stirred in a water bath to obtain an aqueous phase. Emulsifier 2 was added to cyclohexane and stirred at high speed to obtain an oil phase.

[0012] The aqueous phase was poured into the oil phase for emulsification. After emulsification, the mixture was heated and stirred in a water bath. Then, a mixture of tetraethyl silicate and γ-aminopropyltriethoxysilane was added dropwise. After the reaction was completed, the reaction sample was centrifuged and washed to obtain phase change microcapsule material 1.

[0013] b. Preparation of phase change microcapsule material 2

[0014] Replace phase change material 1 with phase change material 2, and then prepare phase change microcapsule material 2 according to the method in step a;

[0015] c. Preparation of phase change microcapsule material 3

[0016] Phase change material 1 and phase change material 2 are mixed and heated to make the two phase change materials miscible together to obtain eutectic phase change material 3. Phase change material 1 is replaced with eutectic phase change material 3, and then phase change microcapsule material 3 is prepared according to the method in step a.

[0017] (2) Secondary outer shell coating:

[0018] Phase change microcapsule material 1, phase change microcapsule material 2, and phase change microcapsule material 3 are mixed to obtain mixed phase change microcapsules, which serve as primary capsule particles. Emulsifier 3 and mixed phase change microcapsules are added sequentially to deionized water, followed by the addition of calcium chloride aqueous solution. The mixture is continuously stirred to form a stable emulsion. The emulsion is heated and stirred in a water bath, and sodium carbonate aqueous solution is added dropwise while continuously and slowly stirred. The mixture is then filtered to obtain secondary encapsulated phase change material. After washing and drying at room temperature, a double-shell high thermal conductivity phase change heat storage microcapsule is obtained.

[0019] According to a preferred embodiment of the present invention, in step a, the phase change material 1 is galactitol and the emulsifier 1 is Tween 80.

[0020] According to a preferred embodiment of the present invention, in step a, the mass ratio of phase change material 1, polyvinylpyrrolidone, and emulsifier 1 is (3-4.5):(0.01-0.03):(0.05-0.2), the mass ratio of phase change material 1 to deionized water is (3-4.5):(10-15), the heating temperature is 40-60℃, and the heating and stirring time is 20 min.

[0021] According to a preferred embodiment of the present invention, in step a, the mass-to-volume ratio of emulsifier 2 to cyclohexane is (0.3-0.8):(50-75), in g / mL.

[0022] According to a preferred embodiment of the present invention, in step a, the high-speed stirring speed is 800-1500 r / min, and the stirring time is 10-30 min.

[0023] According to a preferred embodiment of the present invention, in step a, the aqueous phase is poured into the oil phase and emulsified at 3000 r / min for 10 min under shear emulsifier.

[0024] According to a preferred embodiment of the present invention, in step a, the water bath heating temperature is 40-60℃, the stirring speed is 400-600 r / min, and the stirring is continued for 10 min.

[0025] According to a preferred embodiment of the present invention, in step a, the mass ratio of the aqueous phase to the oil phase is (10-20):(40-55), and the volume ratio of tetraethyl silicate to γ-aminopropyltriethoxysilane in the mixture of tetraethyl silicate and γ-aminopropyltriethoxysilane is 1:0.5-0.8.

[0026] According to a preferred embodiment of the present invention, in step a, the mass-to-volume ratio of the emulsion after emulsification to the mixture of tetraethyl silicate and γ-aminopropyltriethoxysilane is (70-80):(7-9), unit, g / mL, the reaction time is 10-15 h, and the mixture is washed three times with cyclohexane.

[0027] According to a preferred embodiment of the present invention, in step b, the phase change material 2 is inositol.

[0028] According to a preferred embodiment of the present invention, in step c, the mass ratio of phase change material 1 and phase change material 2 is 1.0-2.0:1, the heating temperature is 200-220℃, and the heating time is 8-15 min.

[0029] According to a preferred embodiment of the present invention, in step (2), the mass ratio of phase change microcapsule material 1, phase change microcapsule material 2, and phase change microcapsule material 3 is 1:1:1, the emulsifier 3 is sodium dodecylbenzenesulfonate, and the mass ratio of emulsifier 3, mixed phase change microcapsules, and deionized water is (0.8-1.5):(20-40):100.

[0030] According to a preferred embodiment of the present invention, in step (2), the mass fraction of the calcium chloride aqueous solution is 15-25%, the volume ratio of the calcium chloride aqueous solution to the deionized water is (35-50):100, and after adding the calcium chloride aqueous solution, the mixture is continuously stirred at 1000 r / min for 60 min to form a stable emulsion.

[0031] According to a preferred embodiment of the present invention, in step (2), the emulsion water bath heating and stirring temperature is 35-45℃, and the stirring speed is 40-60r / min.

[0032] According to a preferred embodiment of the present invention, in step (2), the mass fraction of the sodium carbonate aqueous solution is 15-25%, the volume ratio of the amount of sodium carbonate aqueous solution added to the volume of deionized water is (40-60):100, and after adding the sodium carbonate aqueous solution, the mixture is slowly stirred for 4 hours.

[0033] This invention uses two high-melting-point phase change materials and a eutectic compound of the two phase change materials as core materials, and prepares a double-shell high thermal conductivity phase change thermal storage microcapsule for ultra-deep drilling fluid by coating it with two outer shells.

[0034] A double-shell high thermal conductivity phase change thermal storage microcapsule for ultra-deep drilling fluid was prepared using the above method.

[0035] The above-mentioned application of double-shell high thermal conductivity phase change thermal storage microcapsules for ultra-deep drilling fluids is used in oil industry drilling operations. It is suitable for cooling ultra-deep well drilling fluids. When the bottom hole temperature is within the phase change temperature range of the phase change thermal storage microcapsules, it absorbs a large amount of heat from the formation and reduces the temperature of the circulating drilling fluid. The amount of phase change thermal storage microcapsules added is 4%-8% of the weight of the drilling fluid.

[0036] The beneficial effects of the present invention through the above technical solution are as follows:

[0037] 1. This invention prepares a double-shell high thermal conductivity phase change heat storage microcapsule for drilling fluid using a two-step coating method. The material has a high phase change temperature, ranging from 173.3 to 235.1°C, and a phase change enthalpy as high as 211.4 J / g. When within the phase change temperature range, it absorbs a large amount of heat, playing the role of "latent heat of phase change". Applying this material to drilling fluid can significantly reduce the temperature of the drilling fluid and improve the drilling fluid's tolerance to high-temperature formations.

[0038] 2. The drilling fluid double-shell high thermal conductivity phase change thermal storage microcapsules of the present invention have excellent thermal conductivity, with a thermal conductivity coefficient reaching 2.14 W·m. -1 ·K -1 When applied to drilling fluids, the material can rapidly transfer the heat from the formation to the drilling fluid to the phase change microcapsules and undergo rapid heat absorption when it is at its phase change temperature.

[0039] 3. The drilling fluid double-shell high thermal conductivity phase change heat storage microcapsules of the present invention have excellent temperature resistance. After aging at 220℃ for 16 hours, the high temperature leakage rate of the phase change microcapsules is only 2.25%. Detailed Implementation

[0040] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, a detailed description of specific embodiments of the present invention is provided below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0041] Example 1

[0042] The preparation method of double-shell high thermal conductivity phase change thermal storage microcapsules for ultra-deep drilling fluids includes the following steps:

[0043] (1) First outer shell covering

[0044] a. Preparation of phase change microcapsule materials

[0045] Weigh 12g of deionized water, add 3.5g of phase change material 1 (galactitol), 0.015g of polyvinylpyrrolidone, and 0.15g of Tween 80 to prepare a supersaturated solution of phase change material 1 (at room temperature). Heat and stir in a water bath at 50℃ for 20min to promote the dissolution of phase change material 1, obtaining an aqueous phase. Measure 60mL of cyclohexane into a beaker, add 0.6g of Span 80, and stir at high speed for 20min to obtain an oil phase. Pour the aqueous phase into the oil phase and shear emulsion. The mixture was emulsified at 3000 r / min for 10 min under the presence of a catalyst to obtain a stable W / O emulsion. The emulsion was then heated in a water bath at 50°C with stirring at 500 r / min for 10 min. Subsequently, 8 mL of tetraethyl silicate and γ-aminopropyltriethoxysilane were measured at a volume ratio of 3:1 and added dropwise to the emulsion using a constant pressure funnel. The reaction was continued for 12 h. Finally, the reaction sample was centrifuged and washed three times with cyclohexane to obtain phase change microcapsules 1.

[0046] b. Preparation of phase change microcapsule material 2

[0047] Replace phase change material 1 with phase change material 2 (inositol), and then prepare phase change microcapsule material 2 according to the method in step a;

[0048] c. Preparation of phase change microcapsule material 3

[0049] Weigh 4g of phase change material 1 (galactitol) and phase change material 2 (inositol) in a mass ratio of 1.5:1 and place them in a small crucible. Heat at 210℃ for 10min to allow the two phase change materials to mix together and obtain eutectic phase change material 3. Then, prepare phase change microcapsule material 3 according to the method in step a.

[0050] (2) Secondary outer shell coating:

[0051] 100 mL of deionized water was added to a three-necked flask, followed by the addition of 1.0 g of sodium dodecylbenzenesulfonate. 30 g of phase change microcapsules (phase change microcapsules 1, 2, and 3, in a mass ratio of 1:1:1) were then added sequentially as primary capsule particles. Using a constant-pressure funnel, 45 mL of a 20% (mass fraction) calcium chloride aqueous solution was added dropwise to the system, and the mixture was continuously stirred at 1000 rpm for 60 min to form a stable emulsion. Finally, the three-necked flask was transferred to a water bath and heated to 40 °C. While stirring at 50 rpm, 30 mL of a 20% (mass fraction) sodium carbonate aqueous solution was added dropwise to the system using a constant-pressure funnel, and the mixture was continuously and slowly stirred for 4 h. The resulting product was filtered to obtain the secondary-encapsulated phase change material. The collected product was washed several times with ethanol and deionized water, and then dried at room temperature to obtain the double-shell high thermal conductivity phase change heat storage microcapsules.

[0052] Example 2

[0053] The preparation method of double-shell high thermal conductivity phase change thermal storage microcapsules for ultra-deep drilling fluids includes the following steps:

[0054] (1) First outer shell covering

[0055] a. Preparation of phase change microcapsule materials

[0056] Weigh 12g of deionized water, add 3.5g of phase change material 1 (galactitol), 0.015g of polyvinylpyrrolidone, and 0.15g of Tween 80 to prepare a supersaturated solution of phase change material 1 (at room temperature). Heat and stir in a water bath at 50℃ for 20min to promote the dissolution of phase change material 1, obtaining the aqueous phase. Measure 60mL of cyclohexane into a beaker, add 0.6g of Span 80, and stir at high speed for 20min to obtain the oil phase. The aqueous phase was poured into the oil phase and emulsified at 3000 r / min for 10 min under shear emulsifier to obtain a stable W / O emulsion. The emulsion was heated in a water bath at 50°C and stirred at 500 r / min for 10 min. Then, 8 mL of tetraethyl silicate and γ-aminopropyltriethoxysilane were weighed at a volume ratio of 3:1 and added dropwise to the emulsion using a constant pressure funnel. The reaction was continued for 12 h. Finally, the reaction sample was centrifuged and washed three times with cyclohexane to obtain phase change microcapsules 1.

[0057] b. Preparation of phase change microcapsule material 2

[0058] Replace phase change material 1 with phase change material 2 (inositol), and then prepare phase change microcapsule material 2 according to the method in step a;

[0059] c. Preparation of phase change microcapsule material 3

[0060] Weigh 4g of phase change material 1 (galactitol) and phase change material 2 (inositol) in a 1:1 mass ratio and place them in a small crucible. Heat at 210℃ for 10min to mix the two phase change materials together to obtain eutectic phase change material 3. Then prepare phase change microcapsule material 3 according to the method in step a.

[0061] (2) Secondary outer shell coating:

[0062] 100 mL of deionized water was added to a three-necked flask, followed by the addition of 1.0 g of sodium dodecylbenzenesulfonate 3, and 30 g of phase change microcapsules (phase change microcapsules 1, 2, and 3 in a 1:1:1 mass ratio) as primary capsule particles. Additionally, 45 mL of a 20% (mass fraction) calcium chloride aqueous solution was added dropwise to the system using a constant-pressure funnel, and the mixture was continuously stirred at 1000 rpm for 60 min to form a stable emulsion. Finally, the three-necked flask was transferred to a water bath and heated to 40 °C. The stirring speed was set to 50 rpm, and 30 mL of a 20% (mass fraction) sodium carbonate aqueous solution was added dropwise to the system using a constant-pressure funnel, with continuous slow stirring for 4 h. The mixture was then filtered to obtain the secondary encapsulated phase change material. The collected product was washed several times with ethanol and deionized water, and then dried at room temperature to obtain the double-shell high thermal conductivity phase change heat storage microcapsules.

[0063] Example 3

[0064] The preparation method of double-shell high thermal conductivity phase change thermal storage microcapsules for ultra-deep drilling fluids includes the following steps:

[0065] (1) First outer shell covering

[0066] a. Preparation of phase change microcapsule materials

[0067] Weigh 12g of deionized water, add 3.5g of phase change material 1 (galactitol), 0.015g of polyvinylpyrrolidone, and 0.15g of Tween 80 to prepare a supersaturated solution of phase change material 1 (at room temperature). Heat and stir in a water bath at 50℃ for 20min to promote the dissolution of phase change material 1, obtaining the aqueous phase. Measure 60mL of cyclohexane into a beaker, add 0.6g of Span 80, and stir at high speed for 20min to obtain the oil phase. The aqueous phase was poured into the oil phase and emulsified at 3000 r / min for 10 min under shear emulsifier to obtain a stable W / O emulsion. The emulsion was heated in a water bath at 50°C and stirred at 500 r / min for 10 min. Then, 8 mL of tetraethyl silicate and γ-aminopropyltriethoxysilane were weighed at a volume ratio of 3:1 and added dropwise to the emulsion using a constant pressure funnel. The reaction was continued for 12 h. Finally, the reaction sample was centrifuged and washed three times with cyclohexane to obtain phase change microcapsules 1.

[0068] b. Preparation of phase change microcapsule material 2

[0069] Replace phase change material 1 with phase change material 2 (inositol), and then prepare phase change microcapsule material 2 according to the method in step a;

[0070] c. Preparation of phase change microcapsule material 3

[0071] Weigh 4g of phase change material 1 (galactitol) and phase change material 2 (inositol) in a mass ratio of 2:1 and place them in a small crucible. Heat at 210℃ for 10min to mix the two phase change materials together to obtain eutectic phase change material 3. Then prepare phase change microcapsule material 3 according to the method in step a.

[0072] (2) Secondary outer shell coating:

[0073] 100 mL of deionized water was added to a three-necked flask, followed by the addition of 1.0 g of sodium dodecylbenzenesulfonate 3, and 30 g of phase change microcapsules (phase change microcapsules 1, 2, and 3 in a 1:1:1 mass ratio) as primary capsule particles. Additionally, 45 mL of a 20% (mass fraction) calcium chloride aqueous solution was added dropwise to the system using a constant-pressure funnel, and the mixture was continuously stirred at 1000 rpm for 60 min to form a stable emulsion. Finally, the three-necked flask was transferred to a water bath and heated to 40 °C. The stirring speed was set to 50 rpm, and 30 mL of a 20% (mass fraction) sodium carbonate aqueous solution was added dropwise to the system using a constant-pressure funnel, with continuous slow stirring for 4 h. The mixture was then filtered to obtain the secondary encapsulated phase change material. The collected product was washed several times with ethanol and deionized water, and then dried at room temperature to obtain the double-shell high thermal conductivity phase change heat storage microcapsules.

[0074] Example 4

[0075] The preparation method of double-shell high thermal conductivity phase change thermal storage microcapsules for ultra-deep drilling fluids includes the following steps:

[0076] (1) First outer shell covering

[0077] a. Preparation of phase change microcapsule materials

[0078] Weigh 12g of deionized water, add 3.5g of phase change material 1 (galactitol), 0.015g of polyvinylpyrrolidone, and 0.15g of Tween 80 to prepare a supersaturated solution of phase change material 1 (at room temperature). Heat and stir in a water bath at 50℃ for 20min to promote the dissolution of phase change material 1, obtaining the aqueous phase. Measure 60mL of cyclohexane into a beaker, add 0.6g of Span 80, and stir at high speed for 20min to obtain the oil phase. The aqueous phase was poured into the oil phase and emulsified at 3000 r / min for 10 min under shear emulsifier to obtain a stable W / O emulsion. The emulsion was heated in a water bath at 50°C and stirred at 500 r / min for 10 min. Then, 8 mL of tetraethyl silicate and γ-aminopropyltriethoxysilane were weighed at a volume ratio of 3:1 and added dropwise to the emulsion using a constant pressure funnel. The reaction was continued for 12 h. Finally, the reaction sample was centrifuged and washed three times with cyclohexane to obtain phase change microcapsules 1.

[0079] b. Preparation of phase change microcapsule material 2

[0080] Replace phase change material 1 with phase change material 2 (inositol), and then prepare phase change microcapsule material 2 according to the method in step a;

[0081] c. Preparation of phase change microcapsule material 3

[0082] Weigh 4g of phase change material 1 (galactitol) and phase change material 2 (inositol) in a mass ratio of 2:1 and place them in a small crucible. Heat at 210℃ for 10min to mix the two phase change materials together to obtain eutectic phase change material 3. Then prepare phase change microcapsule material 3 according to the method in step a.

[0083] (2) Secondary outer shell coating:

[0084] 100 mL of deionized water was added to a three-necked flask, followed by the addition of 1.0 g of sodium dodecylbenzenesulfonate 3, and 20 g of phase change microcapsules 1, 2, and 3 (in a mass ratio of 1:1:1) as primary capsule particles. Additionally, 45 mL of a 20% (mass fraction) calcium chloride aqueous solution was added dropwise to the system using a constant-pressure funnel, and the mixture was continuously stirred at 1000 rpm for 60 min to form a stable emulsion. Finally, the three-necked flask was transferred to a water bath and heated to 40 °C. The stirring speed was set to 50 rpm, and 30 mL of a 20% (mass fraction) sodium carbonate aqueous solution was added dropwise to the system using a constant-pressure funnel, with continuous slow stirring for 4 h. The mixture was then filtered to obtain the secondary encapsulated phase change material. The collected product was washed several times with ethanol and deionized water, and then dried at room temperature to obtain the double-shell high thermal conductivity phase change heat storage microcapsules.

[0085] Example 5

[0086] The preparation method of double-shell high thermal conductivity phase change thermal storage microcapsules for ultra-deep drilling fluids includes the following steps:

[0087] (1) First outer shell covering

[0088] a. Preparation of phase change microcapsule materials

[0089] Weigh 12g of deionized water, add 3.5g of phase change material 1 (galactitol), 0.015g of polyvinylpyrrolidone, and 0.15g of Tween 80 to prepare a supersaturated solution of phase change material 1 (at room temperature). Heat and stir in a water bath at 50℃ for 20min to promote the dissolution of phase change material 1, obtaining the aqueous phase. Measure 60mL of cyclohexane into a beaker, add 0.6g of Span 80, and stir at high speed for 20min to obtain the oil phase. The aqueous phase was poured into the oil phase and emulsified at 3000 r / min for 10 min under shear emulsifier to obtain a stable W / O emulsion. The emulsion was heated in a water bath at 50°C and stirred at 500 r / min for 10 min. Then, 8 mL of tetraethyl silicate and γ-aminopropyltriethoxysilane were weighed at a volume ratio of 3:1 and added dropwise to the emulsion using a constant pressure funnel. The reaction was continued for 12 h. Finally, the reaction sample was centrifuged and washed three times with cyclohexane to obtain phase change microcapsules 1.

[0090] b. Preparation of phase change microcapsule material 2

[0091] Replace phase change material 1 with phase change material 2 (inositol), and then prepare phase change microcapsule material 2 according to the method in step a;

[0092] c. Preparation of phase change microcapsule material 3

[0093] Weigh 4g of phase change material 1 (galactitol) and phase change material 2 (inositol) in a mass ratio of 2:1 and place them in a small crucible. Heat at 210℃ for 10min to mix the two phase change materials together to obtain eutectic phase change material 3. Then prepare phase change microcapsule material 3 according to the method in step a.

[0094] (2) Secondary outer shell coating:

[0095] 100 mL of deionized water was added to a three-necked flask, followed by the addition of 1.0 g of sodium dodecylbenzenesulfonate 3, and 40 g of phase change microcapsules 1, 2, and 3 (in a mass ratio of 1:1:1) as primary capsule particles. Additionally, 45 mL of a 20% (mass fraction) calcium chloride aqueous solution was added dropwise to the system using a constant-pressure funnel, and the mixture was continuously stirred at 1000 rpm for 60 min to form a stable emulsion. Finally, the three-necked flask was transferred to a water bath and heated to 40 °C. The stirring speed was set to 50 rpm, and 30 mL of a 20% (mass fraction) sodium carbonate aqueous solution was added dropwise to the system using a constant-pressure funnel, with continuous slow stirring for 4 h. The mixture was then filtered to obtain the secondary encapsulated phase change material. The collected product was washed several times with ethanol and deionized water, and then dried at room temperature to obtain the double-shell high thermal conductivity phase change heat storage microcapsules.

[0096] Example 6

[0097] The preparation method of double-shell high thermal conductivity phase change thermal storage microcapsules for ultra-deep drilling fluids includes the following steps:

[0098] (1) First outer shell covering

[0099] a. Preparation of phase change microcapsule materials

[0100] Weigh 12g of deionized water, add 3.5g of phase change material 1 (galactitol), 0.015g of polyvinylpyrrolidone, and 0.15g of Tween 80 to prepare a supersaturated solution of phase change material 1 (at room temperature). Heat and stir in a water bath at 50℃ for 20min to promote the dissolution of phase change material 1, obtaining the aqueous phase. Measure 60mL of cyclohexane into a beaker, add 0.6g of Span 80, and stir at high speed for 20min to obtain the oil phase. The aqueous phase was poured into the oil phase and emulsified at 3000 r / min for 10 min under shear emulsifier to obtain a stable W / O emulsion. The emulsion was heated in a water bath at 50°C and stirred at 500 r / min for 10 min. Subsequently, 6 mL of tetraethyl silicate and 1 mL of γ-aminopropyltriethoxysilane were added dropwise to the emulsion using a constant pressure funnel, and the reaction was continued for 12 h. Finally, the reaction sample was centrifuged and washed three times with cyclohexane to obtain phase change microcapsules 1.

[0101] b. Preparation of phase change microcapsule material 2

[0102] Replace phase change material 1 with phase change material 2 (inositol), and then prepare phase change microcapsule material 2 according to the method in step a;

[0103] c. Preparation of phase change microcapsule material 3

[0104] Weigh 4g of phase change material 1 (galactitol) and phase change material 2 (inositol) in a mass ratio of 2:1 and place them in a small crucible. Heat at 210℃ for 10min to mix the two phase change materials together to obtain eutectic phase change material 3. Then prepare phase change microcapsule material 3 according to the method in step a.

[0105] (2) Secondary outer shell coating:

[0106] 100 mL of deionized water was added to a three-necked flask, followed by the addition of 1.0 g of sodium dodecylbenzenesulfonate 3, and 30 g of phase change microcapsules (phase change microcapsules 1, 2, and 3 in a 1:1:1 mass ratio) as primary capsule particles. Additionally, 45 mL of a 20% (mass fraction) calcium chloride aqueous solution was added dropwise to the system using a constant-pressure funnel, and the mixture was continuously stirred at 1000 rpm for 60 min to form a stable emulsion. Finally, the three-necked flask was transferred to a water bath and heated to 40 °C. The stirring speed was set to 50 rpm, and 30 mL of a 20% (mass fraction) sodium carbonate aqueous solution was added dropwise to the system using a constant-pressure funnel, with continuous slow stirring for 4 h. The mixture was then filtered to obtain the secondary encapsulated phase change material. The collected product was washed several times with ethanol and deionized water, and then dried at room temperature to obtain the double-shell high thermal conductivity phase change heat storage microcapsules.

[0107] Comparative Example 1

[0108] The preparation method is the same as described in Example 1, except that:

[0109] Step (2) did not include phase change microcapsules 1.

[0110] Comparative Example 2

[0111] The preparation method is the same as described in Example 1, except that:

[0112] Step (2) did not include phase change microcapsules 2.

[0113] Comparative Example 3

[0114] The preparation method is the same as described in Example 1, except that:

[0115] Step (2) did not include phase change microcapsules 3.

[0116] Comparative Example 4

[0117] The preparation method is the same as described in Example 1, except that:

[0118] Step (2): 30g of phase change microcapsules 1, 2 and 3 in a mass ratio of 1:1:1 are mixed together without secondary shell coating.

[0119] Comparative Example 5

[0120] The preparation method is the same as described in Example 1, except that:

[0121] In step c, 4g of phase change material 1 (galactitol) and phase change material 2 (inositol) were weighed and mixed directly at a mass ratio of 1.5:1. The two phase change materials were not subjected to high-temperature miscibility. Eutectic phase change material 3 was obtained, and then phase change microcapsule material 3 was prepared according to the method in step a.

[0122] Experimental Example

[0123] The high thermal conductivity double-shell phase change thermal storage microcapsules prepared in the examples and comparative examples were evaluated as follows: phase change temperature and latent heat of phase change analysis, thermal conductivity, high temperature leakage rate, and particle size distribution.

[0124] (1) Phase transition temperature and latent heat of phase transition analysis

[0125] In engineering applications, the selection of phase change materials is based on two principles: suitable phase change temperature and latent heat of phase change. In ultra-deep drilling, suitable phase change materials have a significant impact on effectively reducing the temperature of the circulating drilling fluid at the bottom of the well. Therefore, this section measures the phase change temperature and enthalpy of the samples in each embodiment and comparative example. The specific operation method is as follows: the phase change temperature and enthalpy of the cooling materials in each embodiment and comparative example are measured using a German Netzsch DSC214 differential scanning calorimeter. The test conditions are: temperature range 40℃-300℃, heating rate 5K·min⁻¹, nitrogen as the protective gas, and gas flow rate 20.0mL·min⁻¹. The experimental results are shown in Table 1.

[0126] Table 1. Phase transition temperature and latent heat of phase transition

[0127]

[0128] Table 1 shows the phase transition temperature and enthalpy of each example and comparative sample. As shown in Table 1, Example 1 exhibits the optimal phase transition temperature range and enthalpy, with a phase transition temperature between 173.3 and 230.7 °C and a high enthalpy of 211.4 J / g. Comparative Examples 1, 2, and 3, without the addition of phase transition microcapsules 1, 2, and 3 respectively, significantly affect both the phase transition temperature and latent heat of phase transition, resulting in two distinct temperature ranges and a significant decrease in enthalpy. Comparative Example 4, without secondary shell coating, does not significantly affect the phase transition temperature, but its enthalpy decreases. In Comparative Example 5, during the preparation of phase transition microcapsule material 3, the two phase transition materials were not subjected to high-temperature miscibility, and no eutectic compound was formed. Therefore, the final phase transition material exhibits two discontinuous phase transition temperature stages.

[0129] (2) Thermal conductivity measurement

[0130] 100g of each of the examples and comparative samples were selected, and the thermal conductivity of each example and comparative sample was measured using a HotDisk thermal conductivity meter. The results are shown in Table 2.

[0131] Table 2. Results of thermal conductivity measurement of phase change thermal storage microcapsules

[0132]

[0133] The thermal conductivity results of each embodiment and comparative sample are shown in Table 2. Table 2 shows that Example 1 has the highest thermal conductivity. In Example 6, the reduced amount of KH550 weakened the hydrolytic performance of tetraethyl silicate, affecting the encapsulation of the primary phase change microcapsules and resulting in a lower thermal conductivity compared to Example 1. In Comparative Examples 1, 2, and 3, the absence of phase change microcapsules 1, 2, and 3 significantly affected the overall thermal conductivity of the material, resulting in a significant decrease in thermal conductivity. In Comparative Example 4, the lack of secondary shell encapsulation weakened the overall thermal conductivity of the material. This is because the secondary encapsulation of inorganic calcium carbonate can effectively improve the thermal conductivity of the phase change thermal storage microcapsule material. In Comparative Example 5, the phase change microcapsules 3 were not subjected to high-temperature miscibility during preparation, which did not affect the overall thermal conductivity of the material.

[0134] (3) High-temperature leakage rate measurement

[0135] The two phase change materials selected in this invention are galactitol and inositol, which are two typical solid-liquid phase change thermal storage materials. When phase change materials are applied to drilling fluids, the transition from solid to liquid state within their phase change temperature range can severely affect the rheological stability of the drilling fluid at high temperatures. This invention reduces the impact of the phase change on the rheological properties of the drilling fluid by coating the phase change materials with an external shell.

[0136] The main operating steps of the high-temperature leakage rate experiment are as follows: Add 12g of the example or comparative sample to 400mL, stir at low speed for 20min, and the sample is fully dispersed in the aqueous phase to obtain an aqueous solution of the example or comparative sample with a mass fraction of 3%. After preparation, add each sample solution to an aging tank and age at 220℃ for 16h. After aging, centrifuge the solid phase in the solution and dry it at 80℃ to constant weight, and record its mass as M. Calculate the high-temperature leakage rate using the formula (1.1). The experimental results are as follows.

[0137] As shown in Table 3.

[0138]

[0139] In the formula: R is the high-temperature leakage rate, %;

[0140] M is the mass of the sample after centrifugation and drying, in grams.

[0141] Table 3. High-temperature leakage rate results of phase change thermal storage microcapsules

[0142] sample High-temperature leakage rate (%) sample High-temperature leakage rate (%) Example 1 2.25 Comparative Example 1 2.38 Example 2 2.14 Comparative Example 2 2.21 Example 3 2.34 Comparative Example 3 2.14 Example 4 2.10 Comparative Example 4 10.56 Example 5 2.76 Comparative Example 5 2.23 Example 6 3.12

[0143] The high-temperature leakage rate experimental results of each embodiment and comparative sample are shown in Table 3. As can be seen from Table 3, the omission of phase change microcapsules 1, 2, and 3 in Comparative Examples 1, 2, and 3, respectively, has a certain impact on the high-temperature leakage rate of the phase change thermal storage microcapsules, but the overall impact is small. The operation in Comparative Example 4 affected the coverage of the primary shell and the secondary shell, thus having a significant impact on the high-temperature leakage rate of the final prepared phase change thermal storage microcapsules. In Comparative Example 5, the phase change microcapsule 3 was not subjected to high-temperature miscibility during preparation, which has a certain impact on the high-temperature leakage rate of the phase change thermal storage microcapsules, but the overall impact is small.

[0144] (4) Particle size distribution test

[0145] The selected example is a sample solution prepared with a mass fraction of 3%, stirred for 20 min, ultrasonically dispersed for 20 min, and the particle size distribution of each sample was measured using a Malvern 3000 particle size analyzer. Then, the above materials were placed in an aging tank and aged at 220℃ for 16 h, and the particle size was tested again. The experimental results are shown in Table 4.

[0146] Table 4 Particle size distribution of phase change thermal storage microcapsules

[0147]

[0148]

[0149] The particle size distribution of the various embodiments and comparative samples in water is shown in Table 4. As can be seen from Table 4, Comparative Example 4 does not undergo secondary shell coating, therefore the particle size is reduced. Compared to Example 1, the particle size changes in the other embodiments and comparative examples are not significant, indicating that the factors in these examples have a negligible impact on the final particle size of the phase change thermal storage microcapsules.

[0150] Based on the comprehensive evaluation of the above four experiments, it is concluded that the sample of Example 1 has the best "thermal conductivity", "temperature resistance", "high latent heat" and "low leakage", and its overall performance is excellent.

Claims

1. A method for preparing double-shell high-thermal-conductivity phase change heat storage microcapsules for ultra-deep drilling fluids, comprising the following steps: (1) First external shell coating a. Preparation of phase change microcapsule material 1 Phase change material 1, polyvinylpyrrolidone, and emulsifier 1 are sequentially added to deionized water to obtain a supersaturated solution of phase change material 1, which is heated and stirred in a water bath to obtain an aqueous phase; emulsifier 2 is added to cyclohexane and stirred at high speed to obtain an oil phase; phase change material 1 is galactitol, emulsifier 1 is Tween 80, and the mass ratio of phase change material 1, polyvinylpyrrolidone, and emulsifier 1 is (3-4.5):(0.01-0.03):(0.05-0.2), the mass ratio of phase change material 1 to deionized water is (3-4.5):(10-15), the heating temperature is 40-60°C, and the heating and stirring time is 20 min; The aqueous phase is poured into the oil phase for emulsification, and then heated and stirred in a water bath, after which a mixture of tetraethyl silicate and γ-aminopropyl triethoxysilane is added dropwise, the reaction sample is centrifuged and washed after the reaction is completed to obtain phase change microcapsule material 1; b. Preparation of phase change microcapsule material 2 Phase change material 1 is replaced by phase change material 2, and then phase change microcapsule material 2 is prepared according to the method in step a, and phase change material 2 is inositol; c. Preparation of phase change microcapsule material 3 Phase change material 1 and phase change material 2 are mixed and heated to make the two phase change materials miscible together to obtain eutectic phase change material 3, phase change material 1 is replaced by eutectic phase change material 3, and then phase change microcapsule material 3 is prepared according to the method in step a; the mass ratio of phase change material 1 and phase change material 2 mixed is 1.0-2.0:1, the heating temperature is 200-220°C, and the heating time is 8-15 min; (2) Secondary external shell coating: Phase change microcapsule material 1, phase change microcapsule material 2, and phase change microcapsule material 3 are mixed to obtain mixed phase change microcapsules as primary capsule particles, emulsifier 3 and mixed phase change microcapsules are sequentially added to deionized water, and then calcium chloride aqueous solution is added dropwise, continuously stirred to form a stable emulsion, the emulsion is heated and stirred in a water bath, sodium carbonate aqueous solution is added dropwise, and continuous slow stirring is performed, and the secondary coated phase change material is obtained by suction filtration, washed, and dried at room temperature to obtain double-shell high-thermal-conductivity phase change heat storage microcapsules.

2. The production method according to claim 1, characterized by, In step a, the mass-volume ratio of emulsifier 2 to cyclohexane is (0.3-0.8):(50-75), unit g / mL.

3. The preparation method according to claim 1, characterized in that, In step a, the high-speed stirring speed is 800-1500 r / min, and the stirring time is 10-30 min; the aqueous phase is poured into the oil phase and emulsified at 3000 r / min for 10 min under shearing of the emulsifier, the water bath heating temperature is 40-60°C, the stirring speed is 400-600 r / min, and the continuous stirring time is 10 min.

4. The method of claim 1, wherein, In step a, the mass ratio of the water phase to the oil phase is (10-20):(40-55), the volume ratio of tetraethyl silicate to gamma-aminopropyl triethoxysilane in the mixture of tetraethyl silicate and gamma-aminopropyl triethoxysilane is 1:0.5-0.8, the mass to volume ratio of the emulsion after emulsification to the mixture of tetraethyl silicate and gamma-aminopropyl triethoxysilane is (70-80):(7-9), unit, g / mL, the reaction time is 10-15 h, and cyclohexane is used for washing three times.

5. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the phase change microcapsule material 1, the phase change microcapsule material 2 and the phase change microcapsule material 3 is 1:1:1, the emulsifier 3 is sodium dodecyl benzene sulfonate, the mass ratio of the emulsifier 3, the mixed phase change microcapsule and deionized water is (0.8-1.5):(20-40):100, the mass fraction of the calcium chloride aqueous solution is 15-25%, the volume ratio of the added amount of the calcium chloride aqueous solution to deionized water is (35-50):100, after the calcium chloride aqueous solution is added, continuous stirring is carried out at a speed of 1000 r / min for 60 min to form a stable emulsion.

6. The method of claim 1, wherein, In step (2), the emulsion is heated and stirred in a water bath at a temperature of 35-45 DEG C, the stirring speed is 40-60 r / min, the mass fraction of the sodium carbonate aqueous solution is 15-25%, the volume ratio of the added amount of the sodium carbonate aqueous solution to deionized water is (40-60):100, after the sodium carbonate aqueous solution is added, slow stirring is carried out for 4 h. 7.A double-shell high-thermal-conductivity phase change heat storage microcapsule for ultra-deep drilling fluid, which is prepared by any one of the methods in claims 1-6. 8.The application of the double-shell high-thermal-conductivity phase change heat storage microcapsule for ultra-deep drilling fluid in claim 7, which is used in drilling operations in the petroleum industry and is suitable for cooling the drilling fluid in ultra-deep wells, absorbs a large amount of heat from the formation when the bottom hole temperature is within the phase change temperature range of the phase change heat storage microcapsule, reduces the temperature of the circulating drilling fluid, and the added amount of the phase change heat storage microcapsule is 4%-8% of the weight of the drilling fluid.

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