Phase change microcapsule, preparation method thereof and water-based drilling fluid

Abstract

The application belongs to the technical field of drilling fluids, and provides a phase change microcapsule, a preparation method thereof, and a water-based drilling fluid.The phase change microcapsule comprises a capsule core and a capsule wall wrapping the capsule core; the capsule core comprises a phase change core material; the capsule wall comprises a wall material and a crosslinking agent connecting the wall material; and the crosslinking agent comprises one or more of pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, trimethylpropane trimethacrylate and N,N-methylene bisacrylamide.In the application, pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, trimethylpropane trimethacrylate and N,N-methylene bisacrylamide are used as the crosslinking agent, the polymerization density of the wall material in the phase change microcapsule is improved, and the leakage of the phase change microcapsule is avoided.Further, a reinforcing agent is introduced into the capsule wall of the phase change microcapsule, so that the strength and heat conduction performance of the capsule wall are improved.

Description

Technical Field

[0001] This invention relates to the field of drilling fluid technology, and in particular to a phase change microcapsule and its preparation method, as well as a water-based drilling fluid. Background Technology

[0002] Natural gas hydrates are cage-like compounds formed from natural gas and water under high pressure and low temperature. They have advantages such as abundant reserves, no pollution after combustion, and high energy density. The drilling and development of natural gas hydrates has become a hot topic and a frontier of technological innovation in the world's energy sector.

[0003] During drilling in natural gas hydrate formations, changes in formation stress and the mass and heat transfer effects brought about by drilling fluid intrusion into the formation cause natural gas hydrates to decompose, releasing large amounts of natural gas. This can lead to serious engineering problems and even marine geological disasters. The main manifestations are as follows: (1) Decomposition of formation hydrates can cause wellbore enlargement or wellbore collapse; (2) The decomposition of large amounts of hydrates can generate a large amount of gas, which may induce well blowouts and reduce the formation bearing capacity; (3) The gas generated by the decomposition of hydrates is very likely to regenerate hydrates in low-temperature drilling fluids, clogging pipelines and blowout preventers. Therefore, how to suppress the decomposition of hydrates during drilling in formations is one of the technical challenges facing the safe and efficient drilling and development of hydrates.

[0004] Currently, lowering the drilling fluid temperature is the most direct and effective way to inhibit hydrate decomposition. Existing natural gas hydrate drilling technologies typically use cooling equipment on the platform to physically cool the drilling fluid, but once it enters the wellbore, temperature changes become uncontrollable. Some countries have conducted natural gas hydrate core sampling or test production in marine and permafrost regions, using cooling equipment on the drilling platform to lower the drilling fluid temperature (usually below 4°C) to control hydrate decomposition, but wellbore collapses and core sampling failures due to hydrate decomposition have still occurred repeatedly.

[0005] The ideal way to cool down drilling fluid is through real-time temperature control throughout the entire process. When the temperature exceeds a certain critical value, the drilling fluid in the wellbore can be cooled in real time to prevent hydrate decomposition. The key lies in exploring temperature control materials suitable for natural gas hydrate drilling conditions. Phase change materials are highly efficient heat storage substances, with a large amount of energy stored and released during their phase transition process. They can be used to adjust and control the temperature of the surrounding environment and can be reused multiple times. However, they have the drawback of being prone to leakage in practical applications. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a phase change microcapsule, a method for preparing the same, and a water-based drilling fluid. The phase change microcapsule provided by this invention is less prone to leakage.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] The present invention provides a phase change microcapsule, comprising a core and a capsule wall enclosing the core;

[0009] The core material includes a phase change core material;

[0010] The capsule wall includes a wall material and a crosslinking agent that connects the wall material;

[0011] The crosslinking agent includes one or more of pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, trimethylpropane trimethacrylate, and N,N'-methylenebisacrylamide.

[0012] Preferably, the phase change core material includes one or more of n-tetradecane, n-octadecane, decanol, n-dodecanol, n-tetradecane, and n-hexadecane;

[0013] The wall material includes one or more of methyl methacrylate, propyl methacrylate, and butyl methacrylate.

[0014] Preferably, the mass ratio of the phase change core material to the wall material is 1:(1~5).

[0015] Preferably, the capsule wall further includes a reinforcing agent; the reinforcing agent includes one or more of silver, silver oxide, silicon, silicon oxide, cerium and cerium oxide; the mass ratio of the reinforcing agent to the wall material is 1:(10~100).

[0016] Preferably, the mass ratio of the crosslinking agent to the wall material is 1:(20~30).

[0017] This invention also provides a method for preparing the phase change microcapsules described in the above technical solution, comprising the following steps:

[0018] The phase change core material and the wall material are mixed to obtain the oil phase;

[0019] The emulsifier is dissolved in water to obtain an aqueous phase;

[0020] The oil phase and the water phase are mixed and emulsified to obtain an oil-in-water emulsion;

[0021] The oil-in-water emulsion, initiator, and crosslinking agent are mixed and subjected to a polymerization reaction to obtain the phase change microcapsules.

[0022] Preferably, the emulsifier includes one or more of sodium vinyl sulfonate, sodium methacrylate sulfonate, sodium dodecylbenzene sulfonate, Span-80, and Tween-80; the mass ratio of the emulsifier to the phase change core material is 1:(1~5).

[0023] Preferably, the mass ratio of the oil phase to the water phase is 1:(1~8); the emulsification is carried out under stirring conditions, the stirring speed is 2000~6000 r / min, and the time is 30~60 min.

[0024] Preferably, the initiator comprises azobisisobutyronitrile and / or potassium persulfate, and the mass ratio of the initiator to the wall material is 1:(20~30).

[0025] The polymerization reaction is carried out at a temperature of 70-80°C for 4-5 hours.

[0026] The present invention also provides a water-based drilling fluid comprising the following substances in parts by weight:

[0027] 100 parts water, 5-10 parts phase change microcapsules, 0.1-1 parts thickening and coating agent, 1-2 parts filtration loss reducer, 10-12 parts hydrate inhibitor, and 1-5 parts mudstone hydration inhibitor;

[0028] The phase change microcapsules are the phase change microcapsules described in the above technical solution or the phase change microcapsules prepared by the preparation method described in the above technical solution.

[0029] This invention provides a phase change microcapsule, comprising a core and a wall encapsulating the core; the core comprises a phase change core material; the wall comprises a wall material and a crosslinking agent connecting the wall material; the crosslinking agent comprises one or more of pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, trimethylpropane trimethacrylate, and N,N'-methylenebisacrylamide. This invention uses one or more of pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, trimethylpropane trimethacrylate, and N,N'-methylenebisacrylamide as a crosslinking agent, thereby improving the polymerization density of the wall material in the phase change microcapsule and preventing leakage of the phase change microcapsule.

[0030] Furthermore, the present invention uses one or more of the following as phase change core materials: n-tetradecane, n-octadecane, decanol, n-dodecyl alcohol, n-tetradecyl alcohol, and n-hexadecyl alcohol. By selecting different phase change core materials and adjusting their contents, the phase change temperature of the phase change microcapsules can be adjusted.

[0031] Furthermore, the present invention introduces a reinforcing agent into the capsule wall of the phase change microcapsule to improve the strength and thermal conductivity of the capsule wall.

[0032] This invention also provides a water-based drilling fluid comprising the following components by weight: 100 parts water, 5-10 parts phase change microcapsules, 0.1-1 parts thickening and coating agent, 1-2 parts filtration loss reducer, 10-12 parts hydrate inhibitor, and 1-5 parts mudstone hydration inhibitor; wherein the phase change microcapsules are those described in the above-mentioned technical solution or those prepared by the method described in the above-mentioned technical solution. The water-based drilling fluid of this invention can significantly reduce temperature and inhibit hydrate decomposition. Detailed Implementation

[0033] The present invention provides a phase change microcapsule, comprising a core and a capsule wall enclosing the core;

[0034] The core material includes a phase change core material;

[0035] The capsule wall includes a wall material and a crosslinking agent that connects the wall material;

[0036] The crosslinking agent includes one or more of pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, trimethylpropane trimethacrylate, and N,N'-methylenebisacrylamide.

[0037] Unless otherwise specified, all raw materials used in this invention are preferably commercially available products.

[0038] The phase change microcapsule provided by this invention includes a core; the core includes a phase change core material. In this invention, the phase change core material preferably includes one or more of n-tetradecane, n-octadecane, decanol, n-dodecanol, n-tetradecane, and n-hexadecane; more preferably, it includes one or more of n-tetradecane, dodecanol, hexadecane, and decanol; more preferably, it is a mixture of n-tetradecane, dodecanol-hexadecane, or dodecanol-decanol. In this invention, the mass ratio of dodecanol to hexadecane in the dodecanol-hexadecane mixture is preferably 8:2; the mass ratio of dodecanol to decanol in the dodecanol-decanol mixture is preferably 5:5.

[0039] The phase change microcapsule provided by the present invention includes a capsule wall encapsulating the capsule core; the capsule wall includes a wall material and a crosslinking agent connecting the wall material.

[0040] In this invention, the wall material preferably comprises one or more of methyl methacrylate, propyl methacrylate, and butyl methacrylate. In this invention, the mass ratio of the phase change core material to the wall material is preferably 1:(1~5), more preferably 1:(2~3).

[0041] In this invention, the crosslinking agent includes one or more of pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, trimethylpropane trimethacrylate, and N,N'-methylenebisacrylamide. In this invention, the mass ratio of the crosslinking agent to the wall material is preferably 1:(20-30), more preferably 1:(22-28), and even more preferably 1:(24-26).

[0042] In this invention, the capsule wall preferably further includes a reinforcing agent; the reinforcing agent preferably includes one or more of silver, silver oxide, silicon, silicon oxide, cerium, and cerium oxide. In this invention, the mass ratio of the reinforcing agent to the wall material is preferably 1:(10~100), more preferably 1:(20~80), and even more preferably 1:(40~60).

[0043] In this invention, the average particle size of the phase change microcapsules is preferably 2~200μm, and more preferably 5~30μm.

[0044] In this invention, the phase transition temperature of the phase change microcapsule is preferably 3~20℃.

[0045] This invention also provides a method for preparing the phase change microcapsules described in the above technical solution, comprising the following steps:

[0046] The phase change core material and the wall material are mixed to obtain the oil phase;

[0047] The emulsifier is dissolved in water to obtain an aqueous phase;

[0048] The oil phase and the water phase are mixed and emulsified to obtain an oil-in-water emulsion;

[0049] The oil-in-water emulsion, initiator, and crosslinking agent are mixed and subjected to a polymerization reaction to obtain the phase change microcapsules.

[0050] This invention mixes phase change core material and wall material to obtain an oil phase.

[0051] When the phase change core material is preferably a mixture of multiple substances, the mixing of the phase change core material and the wall material preferably includes: mixing the multiple phase change core materials first, and then mixing them with the wall material. In this invention, the mixing of the multiple phase change core materials is preferably performed by sequential stirring and ultrasonic dispersion. In this invention, the stirring speed is preferably 300~600 r / min, and the stirring time is preferably 30~60 min. In this invention, the subsequent mixing with the wall material is preferably performed under stirring conditions, the stirring speed is preferably 300~600 r / min, and the stirring time is preferably 30~60 min.

[0052] In this invention, when the capsule wall preferably also includes a reinforcing agent, the reinforcing agent is preferably mixed together with the phase change core material and the wall material. In this invention, the particle size of the reinforcing agent is preferably 20-100 nm.

[0053] This invention dissolves an emulsifier in water to obtain an aqueous phase.

[0054] In this invention, the emulsifier preferably includes one or more of sodium vinyl sulfonate (SVS), sodium methacrylate sulfonate (SMAS), sodium dodecylbenzene sulfonate (SDBS), Span-80, and Tween-80. In this invention, the mass ratio of the emulsifier to the phase change core material is preferably 1:(1~5), more preferably 1:(1.5~4.5), and even more preferably 1:(2~4). In this invention, the water is preferably deionized water.

[0055] After obtaining the oil phase and the aqueous phase, the present invention mixes the oil phase and the aqueous phase and emulsifies them to obtain an oil-in-water emulsion.

[0056] In this invention, the mass ratio of the oil phase to the water phase is preferably 1:(1~8), and more preferably 1:(3~6).

[0057] In this invention, the mixing of the oil phase and the water phase preferably includes: adding the oil phase dropwise to the water phase. In this invention, the mixing temperature of the oil phase and the water phase is preferably 65°C.

[0058] In this invention, the emulsification is carried out under stirring conditions, the stirring speed is preferably 2000~6000 r / min, more preferably 3000~5000 r / min; the stirring time is preferably 30~60 min.

[0059] After obtaining the oil-in-water emulsion, the present invention mixes the oil-in-water emulsion, initiator and crosslinking agent, and carries out a polymerization reaction to obtain the phase change microcapsules.

[0060] In this invention, the initiator preferably comprises azobisisobutyronitrile (AIBN) and / or potassium persulfate, more preferably a mixture of AIBN and potassium persulfate; in the mixture, the mass ratio of AIBN to potassium persulfate is preferably 1:(0.5~5), more preferably 1:(1~4), and even more preferably 1:(2~3). In this invention, the mass ratio of the initiator to the wall material is preferably 1:(20~30), more preferably 1:(22~28), and even more preferably 1:(24~26).

[0061] In this invention, the type and amount of crosslinking agent are the same as those in the above technical solution, and will not be repeated here.

[0062] In this invention, the polymerization reaction temperature is preferably 70-80°C, and the reaction time is preferably 4-5 hours. The polymerization reaction is preferably carried out under water bath heating, a protective atmosphere, and stirring. The protective atmosphere preferably includes one or more of nitrogen, argon, and helium, and more preferably nitrogen. The stirring speed is preferably 300-600 r / min, and more preferably 400-500 r / min.

[0063] Following the polymerization reaction, the present invention preferably further includes washing, purifying, and drying the system obtained from the polymerization reaction sequentially. In the present invention, the drying temperature is preferably 35°C, and the drying time is preferably 12 hours.

[0064] The present invention also provides a water-based drilling fluid comprising the following substances in parts by weight:

[0065] 100 parts water, 5-10 parts phase change microcapsules, 0.1-1 parts thickening and coating agent, 1-2 parts filtration loss reducer, 10-12 parts hydrate inhibitor, and 1-5 parts mudstone hydration inhibitor;

[0066] The phase change microcapsules are the phase change microcapsules described in the above technical solution or the phase change microcapsules prepared by the preparation method described in the above technical solution.

[0067] The water-based drilling fluid provided by this invention comprises 100 parts by weight of water.

[0068] The water-based drilling fluid provided by this invention comprises 5-10 parts by weight of phase change microcapsules, preferably 6-8 parts by weight. In this invention, the phase change microcapsules are the phase change microcapsules described in the above-described technical solution or the phase change microcapsules prepared by the preparation method described in the above-described technical solution.

[0069] The water-based drilling fluid provided by this invention includes 0.1 to 1 part by weight of a thickening and coating agent, preferably 0.2 to 0.8 parts by weight, and more preferably 0.4 to 0.6 parts by weight. In this invention, the thickening and coating agent preferably includes xanthan gum.

[0070] The water-based drilling fluid provided by this invention includes 1-2 parts by weight of a filtration loss reducer, preferably 1.2-1.8 parts by weight, and more preferably 1.4-1.6 parts by weight. In this invention, the filtration loss reducer preferably includes one or more of starch (CMS) and polyanionic cellulose, and more preferably a mixture of starch (CMS) and polyanionic cellulose; the mass ratio of starch (CMS) to polyanionic cellulose in the mixture is preferably 7:5.

[0071] The water-based drilling fluid provided by this invention comprises 10-12 parts by weight of a hydrate inhibitor, preferably 10.4-11.5 parts by weight. In this invention, the hydrate inhibitor preferably comprises one or more of sodium chloride and polyvinylpyrrolidone, more preferably a mixture of sodium chloride and polyvinylpyrrolidone hydrate inhibitors; the mass ratio of sodium chloride to polyvinylpyrrolidone in the hydrate inhibitor mixture is preferably 10:0.4.

[0072] The water-based drilling fluid provided by this invention includes 1-5 parts by weight of a mudstone hydration inhibitor, preferably 2-4 parts by weight. In this invention, the mudstone hydration inhibitor preferably includes polyamine.

[0073] The present invention does not specifically limit the preparation method of the water-based drilling fluid; any water-based drilling fluid preparation method known to those skilled in the art can be used.

[0074] The following detailed description, in conjunction with embodiments, illustrates the phase change microcapsules and their preparation method, as well as the water-based drilling fluid provided by this invention. However, these descriptions should not be construed as limiting the scope of protection of this invention.

[0075] Example 1

[0076] The preparation of a phase change microcapsule includes the following steps:

[0077] 30g of methyl methacrylate, 0.3g of nano-cerium oxide (particle size 20~100nm), and 30g of n-tetradecane were mixed and mechanically stirred at 400r / min for 30min to obtain an oil phase. 3.0g of SVS was added to 200mL of deionized water to obtain an aqueous phase. The oil phase was added dropwise to the aqueous phase in a 65℃ constant temperature water bath, and mechanically stirred at 3000r / min for 50min to form an oil-in-water emulsion. 1.2g of pentaerythritol tetraacrylate, 0.6g of azobisisobutyronitrile, and 0.6g of potassium persulfate were added to the oil-in-water emulsion. Under nitrogen protection, the mixture was placed in an 80℃ constant temperature water bath and mechanically stirred at 400r / min for 5h. After the reaction, the mixture was washed, filtered, and dried at 35℃ for 24h to obtain phase change microcapsule powder, labeled GX-1. The average particle size of the phase change microcapsules GX-1 was 30μm, and the phase change temperature was 3℃.

[0078] Example 2

[0079] The preparation of a phase change microcapsule includes the following steps:

[0080] 30g of methyl methacrylate, 0.3g of nano-silver (particle size 20-100nm), and 15g of core material (composed of dodecanol and hexadecyl alcohol in a mass ratio of 8:2) were mixed and mechanically stirred at 400r / min for 30min to obtain the oil phase; 3.0g... SDBS was added to 200 mL of deionized water to obtain an aqueous phase. The oil phase was added dropwise to the aqueous phase in a 65°C constant temperature water bath, and stirred at 3000 r / min for 50 min to form an oil / water emulsion. 1.2 g of ethylene glycol dimethacrylate, 0.6 g of azobisisobutyronitrile, and 0.6 g of potassium persulfate were added to the oil / water emulsion. Under nitrogen protection, the mixture was placed in an 80°C constant temperature water bath and mechanically stirred at 500 r / min for 5 h. After the reaction, the mixture was washed, purified, and dried for 24 hours to obtain phase change microcapsule powder, labeled GX-2. The average particle size of the phase change microcapsules GX-2 was 24 μm, and the phase change temperature was 16.5°C.

[0081] Example 3

[0082] The preparation of a phase change microcapsule includes the following steps:

[0083] 30g of methyl methacrylate and 30g of a mixture of dodecanol and decanol (in a mass ratio of 5:5) were mixed and mechanically stirred at 400 rpm for 30 min to obtain an oil phase. 2.0g of Span 80 and 1.0g of Tween 80 were added to 200mL of deionized water to obtain an aqueous phase. The oil phase was added dropwise to the aqueous phase in a 65℃ constant temperature water bath, and the mixture was stirred at 4800 rpm for 50 min to form an oil / water emulsion. 1.5g of pentaerythritol tetraacrylate and 1.5g of potassium persulfate were added to the oil / water emulsion, and the mixture was placed in an 80℃ constant temperature water bath under nitrogen protection and mechanically stirred at 600 rpm for 5 h. After the reaction, the mixture was washed, filtered, and dried at 35℃ for 24 h to obtain phase change microcapsule powder, labeled GX-3. The average particle size of the phase change microcapsules GX-3 was 5μm, and the phase change temperature was 10℃.

[0084] Application Example 1

[0085] A smart temperature-controlled water-based drilling fluid comprises the following components in parts by weight:

[0086] 100 parts water

[0087] Eight portions of phase change microcapsules (GX-1) prepared in Example 1 were prepared.

[0088] Tackifying and coating agent: 0.2 parts xanthan gum (XC),

[0089] Filtration loss reducer: Starch (CMS) 0.7 parts; Polyanionic cellulose (PAC-LV) 0.5 parts,

[0090] Hydrate inhibitor: 10 parts sodium chloride, 0.4 parts polyvinylpyrrolidone.

[0091] Mudstone hydration inhibitor: 2 parts polyamine (SDJA).

[0092] A smart temperature-controlled water-based drilling fluid was prepared.

[0093] Application Example 2

[0094] Water-based drilling fluid was prepared using the same method as in Application Example 1, except that "8 parts of phase change microcapsules (GX-1) prepared in Example 1" were replaced with "8 parts of phase change microcapsules (GX-2) prepared in Example 2".

[0095] A smart temperature-controlled water-based drilling fluid was prepared.

[0096] Application Example 3

[0097] Water-based drilling fluid was prepared using the same method as in Application Example 1, except that "8 parts of phase change microcapsules (GX-1) prepared in Example 1" were replaced with "8 parts of phase change microcapsules (GX-3) prepared in Example 3".

[0098] A smart temperature-controlled water-based drilling fluid was prepared.

[0099] Application Comparative Example 1

[0100] Water-based drilling fluid was prepared using the same method as in Application Example 1, except that "phase change microcapsules (GX-1) prepared in Example 1" was removed, i.e., no phase change microcapsules were added.

[0101] A water-based drilling fluid was prepared.

[0102] Application Comparative Example 2

[0103] Water-based drilling fluid was prepared using the same method as in Application Example 2, except that "phase change microcapsules (GX-2) prepared in Example 2" was removed, i.e., no phase change microcapsules were added.

[0104] A water-based drilling fluid was prepared.

[0105] Application Comparative Example 3

[0106] Water-based drilling fluid was prepared using the same method as in Application Example 3, except that "phase change microcapsules (GX-3) prepared in Example 3" was removed, i.e., no phase change microcapsules were added.

[0107] A water-based drilling fluid was prepared.

[0108] Application Comparative Example 4

[0109] Water-based drilling fluid was prepared using the same method as in Application Example 1, except that "8 parts of phase change microcapsules (GX-1) prepared in Example 1" were replaced with "4 parts of phase change microcapsules (GX-1) prepared in Example 1".

[0110] A water-based drilling fluid was prepared.

[0111] Application Comparative Example 5

[0112] Water-based drilling fluid was prepared using the same method as in Application Example 1, except that "8 parts of phase change microcapsules (GX-1) prepared in Example 1" was replaced with "16 parts of phase change microcapsules (GX-1) prepared in Example 1".

[0113] A water-based drilling fluid was prepared.

[0114] Test Example 1

[0115] Phase change temperature control performance test:

[0116] The temperatures of the intelligent temperature-controlled water-based drilling fluids prepared in Application Examples 1-3 and the water-based drilling fluids in Comparative Examples 1-5 were lowered to 2°C to simulate the initial temperature of low-temperature drilling fluids in marine natural gas hydrate drilling. Then, the intelligent temperature-controlled water-based drilling fluids prepared in Application Examples 1-3 (hereinafter referred to as Application Examples) and the water-based drilling fluids in Comparative Examples 1-5 (hereinafter referred to as Comparative Examples) were placed in a constant-temperature water bath at 30°C and heated simultaneously. The temperature changes of the Application Examples and Comparative Examples over time were recorded. When the temperature of the Application Examples rose to the phase change temperature of the phase change microcapsules in the Application Examples under water bath heating conditions, the core material inside the phase change microcapsules underwent a phase change, releasing cold energy, causing the temperature of the Application Examples to decrease or remain stable for a certain period of time. The maximum temperature difference between the Application Examples and the Comparative Examples without phase change microcapsules at the same time was the temperature decrease value. Specific results are shown in Table 1.

[0117] Additionally, it should be noted in this invention that the maximum temperature difference (temperature reduction value) is defined as follows: Under the same water bath heating conditions, the comparative example and the application example are heated simultaneously. In the comparative example without phase change material, the test solution temperature continuously rises; however, in the application example with phase change material, the test solution, due to the cold energy stored in the phase change material itself, undergoes a phase change reaction when the temperature rises to the phase change temperature, releasing the cold energy. This causes the test solution temperature to plateau, no longer rising rapidly. However, since the test solution is still in a 30°C water bath, the released cold energy cools the drilling fluid, and the temperature will eventually continue to rise. After releasing the cold energy, the test solution temperature will maintain a certain stable value, for example, 2.8°C at 7 minutes, while the comparative example, under the same conditions, is already 6°C at 7 minutes. Therefore, the maximum temperature reduction value is 6 - 2.8 = 3.2°C, which is the maximum temperature difference, also known as the temperature reduction value.

[0118] Table 1. Experimental Results of Drilling Fluid Temperature Control

[0119] Application Example 1 3.0 4.2 Application Example 2 16.5 4.8 Application Example 3 10.0 4.3 Application Comparative Example 1 none Phase change-free cooling effect Application Comparative Example 2 none Phase change-free cooling effect Application Comparative Example 3 none Phase change-free cooling effect Application Comparative Example 4 3.0 2.0 Application Comparative Example 5 3.0 7.3

[0120] Note: Comparative Examples 1-3 are drilling fluids without phase change microcapsules. The maximum temperature difference between the comparative examples 1-3 (blank drilling fluid) and the drilling fluid with phase change microcapsules within the same time period is used to represent the phase change temperature control effect of the drilling fluid. The larger the difference, the better the temperature control effect of the drilling fluid in the application example, indicating that it can effectively keep the drilling fluid at a low temperature.

[0121] The phase transition temperature is the critical temperature at which a phase transition occurs, and the decrease in temperature is equal to the maximum temperature difference.

[0122] The results showed that the drilling fluid temperature of Comparative Examples 1-3 without phase change microcapsules continued to rise to about 30℃, while the intelligent temperature-controlled water-based drilling fluid with phase change microcapsules underwent a phase change and released cold energy after the temperature rose to the phase change temperature, thus reducing the drilling fluid temperature. This kept the temperature of the intelligent temperature-controlled water-based drilling fluid basically constant for a period of time, and prevented it from heating up due to the water bath, thereby avoiding the decomposition of hydrates in the formation.

[0123] In Application Example 1, the phase change microcapsules began to exert their phase change temperature control effect when the temperature rose to 3℃, with a maximum temperature difference of 4.2℃ compared to the blank sample in Comparative Example 1. In Application Example 2, the phase change microcapsules began to exert their phase change temperature control effect when the temperature rose to 14.0℃, with a maximum temperature difference of 4.8℃ compared to the blank sample in Comparative Example 2. Furthermore, it is worth noting that because Application Example 2 used phase change microcapsules containing the reinforcing agent nano-silver, its thermal conductivity was improved. The time for the maximum temperature difference to appear in the comparative example was later than in the case of phase change microcapsules without nano-silver, and the overall temperature of the test solution remained near the phase change temperature of the phase change microcapsules for a longer period. In Application Example 3, the phase change microcapsules began to exert their phase change temperature control effect when the temperature rose to 9.0℃, with a maximum temperature difference of 4.3℃ compared to the blank sample in Comparative Example 3.

[0124] Therefore, during drilling operations in marine natural gas hydrate formations, when the drill string cuts and breaks rocks, and friction causes the drilling fluid temperature to rise, this temperature increase leads to hydrate decomposition. Drilling fluids incorporating phase change microcapsules can achieve intelligent temperature control through phase change cooling, preventing hydrate decomposition caused by temperature rise. This can solve problems such as wellbore collapse caused by hydrate decomposition, improving the safety and efficiency of drilling operations. The critical temperature for hydrate decomposition can be determined based on the actual drilling pressure conditions, allowing for the selection of microcapsule materials with suitable phase change temperatures.

[0125] In Comparative Example 4, the phase change microcapsule dosage was reduced, resulting in a decrease in the phase change cooling effect. In Comparative Example 5, the phase change microcapsule dosage was increased, leading to a more significant phase change temperature control effect, but also a more pronounced impact on the drilling fluid performance, causing an increase in viscosity.

[0126] Test Example 2

[0127] Wall material strength testing of phase change microcapsules

[0128] To simulate drilling conditions in marine natural gas hydrate formations, appropriate amounts of phase change microcapsules (GX-1 and GX-3) prepared in Examples 1 and 3 were weighed and dispersed in deionized water. The mixture was sheared and stirred at 8000 r / min for 30 min using a high-speed shear mill. After washing, filtering, and drying, the remaining mass was weighed. The loss of the phase change microcapsules after shearing, washing, and filtering was due to the loss of core material after breakage. Dividing this loss by the average encapsulation rate of the phase change microcapsules yielded the average loss rate. The average loss rates of the phase change microcapsules in Examples 1 and 3 are shown in Table 2.

[0129] Table 2. Test results of phase change microcapsule breakage rate

[0130] Average breakage rate 5% 9%

[0131] The results show that the addition of reinforcing nanomaterials can improve the strength of phase change microcapsules.

[0132] The amount of phase change microcapsules added in Comparative Example 4 was too low. Compared with Comparative Example 1, it could only reduce the temperature by 2.0℃, which could not play a significant role in cooling down and inhibiting hydrate decomposition in actual field operations.

[0133] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A water-based drilling fluid, characterized in that, The substances include the following parts by weight: 100 parts water, 5-10 parts phase change microcapsules, 0.1-1 parts thickening and coating agent, 1-2 parts filtration loss reducer, 10-12 parts hydrate inhibitor, and 1-5 parts mudstone hydration inhibitor; The phase change microcapsule includes a core and a capsule wall that encloses the core; The core material includes a phase change core material; The capsule wall includes a wall material and a crosslinking agent that connects the wall material; The crosslinking agent is pentaerythritol tetraacrylate or ethylene glycol dimethacrylate; The phase change core material is a mixture of dodecanol and decanol, wherein the mass ratio of dodecanol to decanol in the dodecanol-decanol mixture is 5:

5. The mass ratio of the crosslinking agent to the wall material is 1:(24~26); The wall material includes one or more of methyl methacrylate, propyl methacrylate, and butyl methacrylate; The mass ratio of the phase change core material to the wall material is 1:(1~5).

2. The water-based drilling fluid according to claim 1, characterized in that, The capsule wall also includes a reinforcing agent; the reinforcing agent includes one or more of silver, silver oxide, silicon, silicon oxide, cerium and cerium oxide; the mass ratio of the reinforcing agent to the wall material is 1:(10~100).

3. The water-based drilling fluid according to claim 1, characterized in that, The method for preparing the phase change microcapsules includes the following steps: The phase change core material and the wall material are mixed to obtain the oil phase; The emulsifier is dissolved in water to obtain an aqueous phase; The oil phase and the water phase are mixed and emulsified to obtain an oil-in-water emulsion; The oil-in-water emulsion, initiator, and crosslinking agent are mixed and subjected to a polymerization reaction to obtain the phase change microcapsules.

4. The water-based drilling fluid according to claim 3, characterized in that, The emulsifier includes one or more of sodium vinyl sulfonate, sodium methacrylate sulfonate, sodium dodecylbenzene sulfonate, Span-80, and Tween-80; the mass ratio of the emulsifier to the phase change core material is 1:(1~5).

5. The water-based drilling fluid according to claim 3, characterized in that, The mass ratio of the oil phase to the water phase is 1:(1~8); The emulsification is carried out under stirring conditions, with a stirring speed of 2000~6000 r / min and a stirring time of 30~60 min.

6. The water-based drilling fluid according to claim 3, characterized in that, The initiator includes azobisisobutyronitrile and / or potassium persulfate, and the mass ratio of the initiator to the wall material is 1:(20~30). The polymerization reaction is carried out at a temperature of 70-80°C for 4-5 hours.