Preparation method and application of inner rigid and outer flexible core-shell structure nano zinc oxide plugging agent for marine drilling fluid

Abstract

The present application relates to a kind of marine drilling fluid with the preparation method and application of inner rigid outer soft core-shell structure nano zinc oxide blocking agent, the present application is polymerized by acrylamide, 2-acrylamide-2-methylpropane sulfonic acid and grafted on the surface of modified nano zinc oxide, and the micro-morphology is formed for the core-shell structure zinc oxide blocking agent of inner rigid outer soft;With the rigid plugging of nanometer material and the flexible plugging of the deformation filling of high molecular polymer, soft and hard combination, high efficient plugging shale micro-nanopore, further maintain wellbore stability, while effectively inhibit the secondary generation of hydrate, improve the safety and efficiency of deepwater drilling, preparation method is simple, raw material is cheap and easy to obtain, high efficiency and environmental protection;And good compatibility with drilling fluid.Effective plugging of micro-nanopore in deepwater formation can prevent drilling fluid filtrate from invading the formation, reduce reservoir hydration dispersion and improve the safety of deepwater drilling and production process.

Description

Technical Field

[0001] This invention relates to a method for preparing and applying a core-shell structured nano zinc oxide plugging agent with an inner rigid and outer flexible structure for marine drilling fluids, belonging to the field of deep-water oil and gas development. Background Technology

[0002] In recent years, the majority of major global oil and gas discoveries (approximately 50%) have originated in deep-sea areas. Deep-sea oil and gas exploration and development has become a core focus and research frontier for the petroleum industry.

[0003] In deepwater drilling, the requirements for drilling fluid treatment agents are becoming increasingly stringent. This is primarily due to the complex environment of deepwater formations, where pressure, temperature, and other conditions have a greater impact on drilling fluid performance. Therefore, drilling fluids need to possess higher stability to ensure drilling efficiency and safety. Maintaining wellbore stability is crucial during drilling operations. The main cause of wellbore instability is the infiltration of drilling fluid filtrate, which leads to formation water absorption and expansion, reduced strength, and ultimately, wellbore collapse. This is particularly common in expansive formations such as shale. To prevent filtrate intrusion and ensure wellbore stability, effective strategies are needed to seal the porosity of shale formations. The low permeability, microporosity, and microfracture characteristics of shale formations result in pore sizes primarily in the 5-30 nm range, placing high demands on the selection of sealing materials. Sealing materials with appropriate particle sizes must be chosen, capable of penetrating the micropores and microfractures of shale to effectively seal the pores, prevent further intrusion of drilling fluid filtrate, and maintain wellbore stability.

[0004] In recent years, the application of nanotechnology in drilling has led to the rapid development of the oil exploration industry. Researchers have conducted in-depth studies on the use of nanomaterials in drilling fluids and have found that these materials can effectively seal the micropores in finely fractured formations such as shale and mudstone, significantly reducing shale permeability and pressure transmission, thereby enhancing the formation's bearing capacity and improving wellbore stability. Applying nanoparticles to drilling fluids offers advantages such as reducing formation damage, enhancing rheology, and maintaining wellbore stability. However, the silanol groups on the surface of nanoparticles are prone to polymerization, making them difficult to disperse in drilling fluids and thus failing to achieve the ideal nano-size effect, consequently reducing the overall performance of the drilling fluid. To address the problem of nanoparticle aggregation, researchers have chemically modified them to improve their dispersibility in drilling fluids. Experimental results show that using these chemically modified nanoparticles as drilling fluid additives can significantly reduce filtration loss and play a positive role in protecting oil and gas reservoirs. Therefore, in-depth research on the development and mechanism of action of plugging agents for deepwater drilling fluids has significant practical application value for the oil exploration industry.

[0005] In deep-water environments, the formation is undercompacted and contains large sections of soft mudstone and shale with numerous nanopores. Furthermore, the high pressure and low temperature of deep water make secondary hydrate formation highly susceptible. To ensure safe and efficient drilling operations, large amounts of hydrate thermodynamic inhibitors need to be added, resulting in high costs and severe environmental pollution. Additionally, existing chemically modified nanoparticles are unsuitable for deep-water, high-pressure, and low-temperature environments, limiting their application.

[0006] Currently, there are no reports of targeted products in publicly available literature, both domestically and internationally. Therefore, it is of particular importance to develop a nano-plugging agent for deepwater drilling fluids that can seal nanopores and inhibit hydrate formation. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing and applying a core-shell structured nano zinc oxide plugging agent with an inner rigid and outer flexible structure for marine drilling fluids.

[0008] The core-shell structured nano zinc oxide plugging agent of this invention can effectively seal micro- and nano-scale pores in deep water formations, prevent drilling fluid filtrate from further invading the formation, and effectively inhibit hydrate formation. This is beneficial for protecting wellbore stability during deep water drilling, reducing reservoir hydration dispersion, and improving the safety of deep water drilling and production processes.

[0009] The technical solution of the present invention is as follows:

[0010] A method for preparing a core-shell structured nano-zinc oxide plugging agent with an inner rigid and outer flexible structure for marine drilling fluids includes the following steps:

[0011] Acrylamide aqueous solution, 2-acrylamido-2-methylpropanesulfonic acid solution and KH570 modified nano zinc oxide solution were mixed evenly; under a protective atmosphere and stirring conditions, an initiator aqueous solution was added dropwise; after stirring and reaction under a protective atmosphere, the mixture was washed, dried and pulverized to obtain a modified nano zinc oxide core-shell structure plugging agent for marine drilling fluids.

[0012] According to a preferred embodiment of the present invention, the mass concentration of the acrylamide aqueous solution is 6-15%.

[0013] According to a preferred embodiment of the present invention, the mass concentration of the 2-acrylamido-2-methylpropanesulfonic acid solution is 20-26%, and the solvent is water.

[0014] According to a preferred embodiment of the present invention, the mass concentration of the KH570 modified nano zinc oxide solution is 15-25%, and the solvent is water.

[0015] According to a preferred embodiment of the present invention, the molar ratio of acrylamide to 2-acrylamido-2-methylpropanesulfonic acid is (1-3):1.

[0016] Most preferably, the molar ratio of acrylamide to 2-acrylamido-2-methylpropanesulfonic acid is 1:1.

[0017] According to a preferred embodiment of the present invention, the molar ratio of acrylamide to KH570 modified nano zinc oxide is 1:(1-6).

[0018] More preferably, the molar ratio of acrylamide to KH570 modified nano zinc oxide is 1:(2-4).

[0019] According to a preferred embodiment of the present invention, the mixing is carried out under stirring conditions, with a stirring rate of 200-300 rpm, a stirring time of 10-20 minutes, and a mixing temperature of 15-25°C.

[0020] According to a preferred embodiment of the present invention, the protective atmosphere is nitrogen.

[0021] According to a preferred embodiment of the present invention, the mass concentration of the initiator aqueous solution is 0.9%-1.5%; the initiator is ammonium persulfate.

[0022] According to a preferred embodiment of the present invention, the mass of the initiator is 0.5%-1% of the total mass of acrylamide, dimethyl diallyl ammonium chloride, and KH570 nano zinc oxide.

[0023] More preferably, the initiator is 0.5%-0.8% of the total mass of acrylamide, dimethyl diallyl ammonium chloride, and KH570 nano zinc oxide.

[0024] According to a preferred embodiment of the present invention, the initiator aqueous solution is added at a rate of one drop every 2-4 seconds.

[0025] According to a preferred embodiment of the present invention, after the initiator is added dropwise, the stirring reaction temperature is 65-85°C, the stirring speed is 20-35 rpm, and the stirring reaction time is 6 hours.

[0026] According to a preferred embodiment of the present invention, the washing is performed using ethanol; the drying temperature is 65-85°C.

[0027] This invention uses acrylamide and 2-acrylamide-2-methylpropanesulfonic acid polymerized and grafted onto the surface of modified nano zinc oxide to form a core-shell structure zinc oxide blocker with a microstructure that is rigid inside and flexible outside, with modified nano zinc oxide as the core and a polymer shell covering the outside.

[0028] A nano zinc oxide plugging agent with an inner rigid and outer flexible core-shell structure for marine drilling fluids is prepared by the above method.

[0029] The above-mentioned marine drilling fluid uses a core-shell structured nano zinc oxide plugging agent with an inner rigid and outer flexible structure. As a plugging agent, it is applied to deep-water reservoir drilling to seal micro- and nano-sized pores in the formation and inhibit the formation of natural gas hydrates. The addition amount is 1-5g / 300-600mL.

[0030] The technical features and beneficial effects of this invention are as follows:

[0031] 1. This invention uses acrylamide and 2-acrylamide-2-methylpropanesulfonic acid polymerized and grafted onto the surface of modified nano-zinc oxide to form a core-shell structure zinc oxide plugging agent with a rigid inner and flexible outer microstructure. By combining the rigid plugging of nanomaterials with the flexible plugging of polymer deformation, it effectively plugs the micro- and nano-pores of shale, thereby maintaining wellbore stability. At the same time, it effectively inhibits the secondary formation of hydrates, improves the safety and efficiency of deepwater drilling, and the preparation method is simple, the raw materials are inexpensive and readily available, and it is highly efficient and environmentally friendly. In addition, it has good compatibility with drilling fluids.

[0032] 2. Acrylamide molecular chains can flexibly fill and adapt to different shapes and sizes of microcracks or pores, providing a flexible and enhanced sealing effect. 2-Acrylamido-2-methylpropanesulfonic acid (AMPS) can enhance the polymer's temperature and salt resistance. At the same time, AMPS contains sulfonic acid groups and hydroxyl groups, which increases the polymer's thermal stability, and stronger CS and CN bonds also improve temperature resistance. The cations of dimethyl diallyl ammonium chloride (DMDAAC) will be adsorbed on the clay surface through electrostatic interaction, and some will enter the interlayer, replacing the interlayer cations, thereby expelling interlayer water molecules. The positive charge provided by DMDAAC can form a strong charge adsorption with the negatively charged clay minerals in shale, enhancing the polymer's sealing and inhibition effects. The specific ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and modified nano zinc oxide in this invention gives the resulting sealing agent both a complete shell and better flexibility to the polymer shell, forming a core-shell structure zinc oxide sealing agent with a rigid inner layer and a flexible outer layer, which has a stronger micron-level sealing ability. Attached Figure Description

[0033] Figure 1 The infrared spectrum of the nano-blocking agent prepared in Example 1.

[0034] Figure 2 Thermogravimetric analysis (TGA) diagram of the nano-blocking agent prepared in Example 1.

[0035] Figure 3 The particle size distribution diagram is for the nano-blocking agent prepared in Example 1. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0037] Furthermore, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods; and unless otherwise specified, the reagents, materials and equipment are all commercially available.

[0038] Example 1

[0039] The preparation method of the core-shell structured nano zinc oxide plugging agent with an inner rigid and outer flexible structure for marine drilling fluids is as follows:

[0040] (1) Mix 4.6g (0.065mol) acrylamide with 50g pure water at 25℃ and stir for 15 minutes at a stirring rate of 200r / min to obtain an acrylamide aqueous solution;

[0041] (2) Add 13.40 g (0.065 mol) of 2-acrylamido-2-methylpropanesulfonic acid to the acrylamide aqueous solution obtained in step (1), and stir for 15 minutes at a stirring rate of 200 r / min and a temperature of 25 °C to obtain a mixed solution of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid.

[0042] (3) Mix 12g (0.147mol) of KH570 modified nano zinc oxide with 60g of pure water at 25℃ and stir for 15 minutes at a stirring rate of 200r / min to obtain KH570 modified nano zinc oxide aqueous solution.

[0043] (4) Add the mixed solution of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid and the KH570 modified nano zinc oxide aqueous solution to a 250mL three-necked flask and mix well. Place the flask in a constant temperature water bath and continuously purge nitrogen gas for 15 minutes at a temperature of 65℃ and a speed of 30rpm to remove the air in the flask while continuing to stir.

[0044] (5) Weigh 0.09 g of ammonium persulfate initiator and dissolve it in 10 mL of pure water to obtain 10 mL of ammonium persulfate initiator aqueous solution. Under stirring and nitrogen protection, add the initiator aqueous solution dropwise to a three-necked flask at a rate of 3 drops per second. After the addition is complete, continue to react for 6 hours under stirring at a rate of 30 r / min, a temperature of 65 °C, and nitrogen. After the reaction is complete, wash with anhydrous ethanol, dry in an electric thermostatic drying oven at 60 °C for 24 h, and pulverize to obtain a core-shell structured nano zinc oxide sealing agent with an inner rigid and outer flexible core.

[0045] The inner-rigid, outer-flexible core-shell structured nano-zinc oxide plugging agent prepared in this embodiment was subjected to infrared spectroscopy using an IRTracer-100 infrared spectrometer, and the KBr pellet method was used for sample preparation. (See attached image.) Figure 1 .

[0046] from Figure 1 It can be seen that 3433cm-1 A stretching vibration peak of amino-NH2 appears nearby, at 1602 cm⁻¹. -1 An absorption peak of 1363 cm⁻¹ appears near the carbonyl group (-C=O) of the amide group. -1 It is the characteristic peak of the carbon-carbon double bond -C=C, at 1190 cm⁻¹. -1 It is the antisymmetric stretching vibration peak of the sulfonic acid group -SO3H, at 1043 cm⁻¹. -1 The peak represents the symmetric stretching vibration of the sulfonic acid group. Infrared spectroscopy analysis indicates that the product contains characteristic functional groups of various monomers designed in the molecular structure, suggesting that each monomer participated in the polymerization reaction and the target product was successfully synthesized.

[0047] The thermogravimetric / differential thermal analysis (TGA) was used to study the core-shell structured zinc oxide nanoparticles with an inner rigid and outer flexible core-shell structure prepared in this embodiment. Figure 2 As shown, in the first stage (40-310℃), the product slowly loses 9.8% of its weight. Because the copolymer contains a large number of hydrophilic amide groups, the weight loss mainly comes from intermolecular and intramolecular water. In the second stage (310-490℃), the product begins to decompose, the carbon-carbon backbone breaks, and the functional groups on the KH570 modified nano-zinc oxide also degrade, resulting in a weight loss of 33.2%. In the third stage (490-800℃), the polymer chains continue to carbonize and break. At the final temperature of 800℃, the product still retains 37% of its mass. In summary, the functional groups contained in the nano-plugging agent for surface deep-water drilling fluids exhibit good thermal stability.

[0048] The particle size of the core-shell structured zinc oxide nanoparticle plugging agent with an inner rigid and outer flexible structure prepared in this embodiment was analyzed using a nanoparticle size potentiometer. Figure 3 As shown, the nanoparticles have a relatively concentrated particle size distribution, and the curve is peak-shaped, with a distribution range of 200-300 nm and an average particle size of 240 nm.

[0049] Example 2

[0050] The preparation method of the core-shell structured nano zinc oxide plugging agent with an inner rigid and outer flexible structure for marine drilling fluids is as follows:

[0051] (1) Mix 6.11g (0.086mol) acrylamide with 50g pure water at 25℃ and stir for 15 minutes at a stirring rate of 200r / min to obtain an acrylamide aqueous solution.

[0052] (2) Add 11.89 g (0.057 mol) of 2-acrylamido-2-methylpropanesulfonic acid to the acrylamide aqueous solution obtained in step (1), and stir for 15 minutes at a stirring rate of 200 r / min and a temperature of 25 °C to obtain a mixed solution of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid.

[0053] (3) Mix 12g (0.147mol) of KH570 modified nano zinc oxide with 60g of pure water at 25℃ and stir for 15 minutes at a stirring rate of 200r / min to obtain KH570 modified nano zinc oxide aqueous solution.

[0054] (4) Add the mixed solution of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid and the aqueous solution of KH570 modified nano zinc oxide to a 250mL three-necked flask and mix well. Place the flask in a constant temperature water bath and continuously purge nitrogen gas for 15 minutes at a temperature of 85℃ and a speed of 30rpm to remove the air in the flask while continuing to stir.

[0055] (5) Weigh 0.12 g of ammonium persulfate initiator and dissolve it in 10 mL of pure water to obtain 10 mL of ammonium persulfate initiator aqueous solution. Under stirring and nitrogen protection, add the initiator aqueous solution dropwise to a three-necked flask at a rate of 3 drops per second. After the addition is complete, continue to react for 6 hours under stirring at a rate of 30 r / min, a temperature of 85 °C, and nitrogen. After the reaction is complete, wash with anhydrous ethanol, dry in an electric thermostatic drying oven at 60 °C for 24 h, and pulverize to obtain a core-shell structured nano zinc oxide sealing agent with an inner rigid and outer flexible core.

[0056] Example 3

[0057] The preparation method of the core-shell structured nano zinc oxide plugging agent with an inner rigid and outer flexible structure for marine drilling fluids is as follows:

[0058] (1) Mix 7.32g (0.103mol) acrylamide with 50g pure water at 25℃ and stir for 15 minutes at a stirring rate of 200r / min to obtain an acrylamide aqueous solution.

[0059] (2) Add 10.68 g (0.052 mol) of 2-acrylamido-2-methylpropanesulfonic acid to the acrylamide aqueous solution obtained in step (1), and stir for 15 minutes at a stirring rate of 200 r / min and a temperature of 25 °C to obtain a mixed solution of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid.

[0060] (3) Mix 12g (0.147mol) of KH570 modified nano zinc oxide with 60g of pure water at 25℃ and stir for 15 minutes at a stirring rate of 200r / min to obtain KH570 modified nano zinc oxide aqueous solution.

[0061] (4) Add the mixed solution of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid and the aqueous solution of KH570 modified nano zinc oxide to a 250mL three-necked flask and mix well. Place the flask in a constant temperature water bath and continuously purge nitrogen gas for 15 minutes at a temperature of 75℃ and a speed of 30rpm to remove the air in the flask while continuing to stir.

[0062] (5) Weigh 0.12 g of ammonium persulfate initiator and dissolve it in 10 mL of pure water to obtain 10 mL of ammonium persulfate initiator aqueous solution. Under stirring and nitrogen protection, add the initiator aqueous solution dropwise to a three-necked flask at a rate of 3 drops per second. After the addition is complete, continue to react for 6 hours under stirring at a rate of 30 r / min, a temperature of 75 °C, and nitrogen. After the reaction is complete, wash with anhydrous ethanol and dry in an electric thermostatic drying oven at 60 °C for 24 h. After pulverization, obtain a core-shell structured nano zinc oxide sealing agent with an inner rigid and outer flexible core.

[0063] Comparative Example 1

[0064] A method for preparing a nano-blocking agent is carried out according to Example 1, except that:

[0065] The reaction temperature was 85°C, and the other steps and conditions were the same as in Example 1.

[0066] Comparative Example 2

[0067] A method for preparing a nano-blocking agent is carried out according to Example 1, except that:

[0068] The amount of acrylamide used was 6.11 g (0.086 mol), the amount of 2-acrylamido-2-methylpropanesulfonic acid used was 11.89 g (0.057 mol), the amount of ammonium persulfate used was 0.15 g, and the other steps and conditions were the same as in Example 1.

[0069] Comparative Example 3

[0070] A method for preparing a nano-blocking agent is carried out according to Example 1, except that:

[0071] The amount of acrylamide used was 7.32 g (0.103 mol), the amount of 2-acrylamido-2-methylpropanesulfonic acid used was 10.68 g (0.052 mol), the amount of ammonium persulfate used was 0.15 g, the reaction temperature was 85 °C, and other steps and conditions were the same as in Example 1.

[0072] Experimental Example

[0073] 1. Rheological filtration experiment:

[0074] Preparation of base slurry: 400 mL of distilled water, 0.6 g of sodium carbonate, and 20 g of bentonite for drilling fluid test slurry preparation were mixed at high speed for 20 min on a high-speed mixer and then cured in a sealed environment at 25℃±1℃ for 24 h.

[0075] Example and comparative sample preparation: Take 6 400mL base slurries, add 2g of the example or comparative sample to each, and stir for 20min at 7000r / min.

[0076] Aging of the sample samples in the examples and comparative examples: The sample slurry was placed in a high-temperature roller heating furnace and aged at 180°C for 16 hours. After aging, it was taken out and cooled, and stirred at 7000 r / min for 20 minutes.

[0077] Referring to the national standard GB / T 29170-2012 "Laboratory Testing of Drilling Fluids for Petroleum and Natural Gas Industry", the rheological parameters of the base slurry of the examples or comparative samples, as well as the filtration loss at room temperature and pressure and the filtration loss under high temperature and pressure after aging, were measured. The experimental results are shown in Table 1.

[0078] Table 1. Rheological filtration tests of the slurry in the examples and comparative samples.

[0079]

[0080]

[0081] As shown in Table 1, the apparent viscosity (AV) and plastic viscosity (PV) of the base slurry added to the examples or comparative examples increased before aging, while the filtration loss under normal temperature and pressure decreased significantly. After aging at 180℃, the apparent viscosity (AV) and plastic viscosity (PV) of the base slurry added to the examples or comparative examples remained basically unchanged, while the filtration loss under high temperature and pressure decreased significantly. Among them, the FL of the base slurry added to Example 1 before and after aging... API The values ​​were 11.2 mL and 58 mL, respectively. Comparing Example 1 with Examples 2 and 3 and Comparative Examples 2 and 3, it can be found that with the increase of the amount of 2-acrylamido-2-methylpropanesulfonic acid, the increase of sulfonic acid groups can increase the rigidity of the polymer chain, making it form a more effective blocking structure; the sulfonic acid groups have good high-temperature resistance, which can further improve the blocking performance of the product under high-temperature environments. Comparing Example 1 with Comparative Example 1, it can be found that the present invention, by changing a suitable reaction temperature, can further improve the blocking ability of the product and reduce filtration loss.

[0082] 2. Evaluation experiment on the inhibition of hydrate formation:

[0083] Turn on the gas pipeline and methane cylinder, and use the gas pressurization device to increase the pressure to 20MPa. Prepare a 0.5% nano-blocking agent aqueous solution and pure water and place them in the reactor. Start the vacuum pump and evacuate for 15 minutes to reduce the pressure inside the reactor to -0.09MPa. Inject 14MPa of pressure into the reactor and start temperature control and stirring to ensure that the pressure inside the reactor is maintained at 14MPa when the temperature starts to drop at a uniform rate.

[0084] A data acquisition system was used to record data in real time, including liquid temperature, gas temperature, pressure, and stirring torque. The experimental results are shown in Table 2.

[0085] Table 2 Hydrate Formation Inhibition Test

[0086]

[0087] As can be seen from Table 2, compared with pure water, adding 0.5% of Example 1 can extend the time for large-scale hydrate formation from 3.80h to 5.95h and reduce the large-scale formation temperature from 11.10℃ to 4.61℃, indicating that Example 1 has good hydrate formation inhibition performance.

[0088] 3. Microporous membrane filtration loss experiment:

[0089] Microporous membranes with nanoscale pores were used to simulate the pore size of deep-water formations. The filtration loss of samples was measured at room temperature and pressure using microporous membranes with different pore sizes. The results are shown in Table 3.

[0090] Table 3 Microporous membrane filtration loss experiment

[0091]

[0092] As shown in Table 3, compared with pure water, Example 1 can effectively block nanoscale pores of different sizes, thereby significantly reducing the filtration loss of the microporous membrane, indicating that Example 1 has good blocking ability.

[0093] 4. Medium-pressure sand bed sealing test:

[0094] The micro- and nano-sized pores in the formation under different environments were simulated using 160-180 mesh sand, and the sealing performance of the samples was tested. The results are shown in Table 4.

[0095] Table 4 shows the sealing experiment of medium-pressure sand bed.

[0096]

[0097] As shown in Table 4, all the base slurry after hot rolling was lost, while the penetration depth of the base slurry after hot rolling + 0.5% of Example 1 in the sand bed was 5.1 cm, indicating that Example 1 has a good sealing ability.

[0098] Comparative Example 4

[0099] A method for preparing a nano-blocking agent is carried out according to Example 1, except that:

[0100] The amount of ammonium persulfate used was 0.12 g, the reaction temperature was 75 °C, and other steps and conditions were the same as in Example 1. The filtration loss at room temperature and pressure was 21.2 mL.

[0101] Comparative Example 5

[0102] A method for preparing a nano-blocking agent is carried out according to Example 1, except that:

[0103] The amount of ammonium persulfate used was 0.15 g, the reaction temperature was 85 °C, and other steps and conditions were the same as in Example 1. The filtration loss at room temperature and pressure was 19.6 mL.

Claims

1. A method for preparing a core-shell structured nano-zinc oxide plugging agent with an inner rigid and outer flexible structure for marine drilling fluids, wherein the plugging agent is applied to deep-water reservoir drilling to seal micro- and nano-scale pores in the formation and simultaneously inhibit the formation of natural gas hydrates, comprising the following steps: Acrylamide aqueous solution, 2-acrylamido-2-methylpropanesulfonic acid solution and KH570 modified nano zinc oxide solution were mixed evenly; under a protective atmosphere and stirring conditions, an initiator aqueous solution was added dropwise; after stirring under a protective atmosphere, the mixture was washed, dried and pulverized. Acrylamide and 2-acrylamido-2-methylpropanesulfonic acid polymerized and grafted onto the surface of modified nano zinc oxide to form a core-shell structure zinc oxide plugging agent with a microstructure of internal rigidity and external flexibility, thus obtaining a modified nano zinc oxide core-shell structure plugging agent for marine drilling fluid. The molar ratio of acrylamide to 2-acrylamido-2-methylpropanesulfonic acid was (1-3):

1. The mass concentration of the KH570 modified nano zinc oxide solution is 15-25%, and the solvent is water; The molar ratio of acrylamide to KH570 modified nano zinc oxide is 1:(1-6); mixing is carried out under stirring conditions, with a stirring rate of 200-300 rpm, a stirring time of 10-20 minutes, and a mixing temperature of 15-25℃; the protective atmosphere is nitrogen.

2. The preparation method according to claim 1, characterized in that, The mass concentration of acrylamide aqueous solution is 6-15%.

3. The preparation method according to claim 1, characterized in that, The mass concentration of the 2-acrylamido-2-methylpropanesulfonic acid solution is 20-26%, and the solvent is water.

4. The preparation method according to claim 1, characterized in that, The mass concentration of the initiator aqueous solution is 0.9%-1.5%; the initiator is ammonium persulfate, and the mass of the initiator is 0.5%-1% of the total mass of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and KH570 nano zinc oxide. The dropping rate of the initiator aqueous solution is one drop every 2-4 seconds. After the initiator is added, the stirring reaction temperature is 65-85℃, the stirring speed is 20-35 rpm, the stirring reaction time is 6 hours, and washing is performed with ethanol. The drying temperature is 65-85℃.

5. A nano zinc oxide plugging agent with an inner rigid and outer flexible core-shell structure for marine drilling fluids, prepared by the method described in any one of claims 1-4.

6. The application of the core-shell structured nano zinc oxide plugging agent with an inner rigid and outer flexible core for marine drilling fluid as described in claim 5, used as a plugging agent in deep-water reservoir drilling to seal micro- and nano-scale pores in the formation and inhibit the formation of natural gas hydrates, with an addition amount of 1-5g / 300-600mL.

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