Emulsifier for ultrahigh-temperature-resistant oil-based drilling fluid, preparation method of emulsifier and oil-based drilling fluid

Abstract

The invention provides an emulsifier for an ultrahigh-temperature-resistant oil-based drilling fluid, a preparation method of the emulsifier and the oil-based drilling fluid. The emulsifier for the ultrahigh-temperature-resistant oil-based drilling fluid is prepared from a polymerization product of surface-modified nano silicon dioxide, styrene, maleic anhydride and unsaturated fatty acid and a solvent, wherein the surface modified nano silicon dioxide is modified by adopting a silane coupling agent containing a C = C bond. The invention also provides a preparation method of the emulsifier and an oil-based drilling fluid prepared from the emulsifier. The polymerization product in the emulsifier contains a large amount of silicon hydroxyl as an active end of the emulsifier, can be firmly adsorbed on an oil-water phase interface in a multi-point adsorption manner according to a Pickering emulsion principle to play a role in stabilizing the emulsion, and can keep the long-acting stability of the water-in-oil emulsion in an ultrahigh-temperature environment of 220-240 DEG C; the problem of instability of the oil-based drilling fluid in an ultra-high-temperature environment is effectively solved, and a technical guarantee is provided for drilling in a myriameter deep field.

Description

Technical Field

[0001] This invention relates to the field of oil-based drilling fluid technology for petroleum drilling, specifically to an emulsifier for ultra-high temperature resistant oil-based drilling fluid, its preparation method, and the oil-based drilling fluid. Background Technology

[0002] In drilling operations, compared to conventional shallow and medium-depth drilling, drilling to depths of 10,000 meters encounters increasingly complex geological conditions, with prominent challenges such as bottom-hole temperatures exceeding 240°C, high pressure, and high salinity, posing significant challenges to drilling fluid technology. Oil-based drilling fluids are widely used in high-temperature deep well drilling due to their excellent thermal stability, inhibition properties, and reservoir protection capabilities. However, existing oil-based drilling fluid systems generally have a temperature resistance of around 220°C, which is insufficient to meet the requirements of drilling to depths of 10,000 meters.

[0003] The key component of oil-based drilling fluid systems is the emulsifier. Existing high-temperature resistant oil-based drilling fluid emulsifiers are generally fatty acid amides, fatty acid imidazoline, and fatty acid alcohol amines. However, at temperatures exceeding 220°C, these commonly exhibit problems such as desorption at the oil-water interface and high-temperature hydrolysis, leading to system instability. This results in reduced demulsification voltage, uncontrolled rheology, oil-water stratification, and even solid phase sedimentation, posing significant risks to deep-ground drilling. Therefore, developing superior emulsifiers for oil-based drilling fluids to improve their stability in ultra-high-temperature environments is a crucial and urgent issue that needs to be addressed. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the purpose of this invention is to provide an emulsifier for ultra-high temperature oil-based drilling fluid, its preparation method, and an oil-based drilling fluid. This emulsifier for ultra-high temperature oil-based drilling fluid can maintain the long-term stability of water-in-oil emulsions under extreme high temperature environments (220-260℃).

[0005] The present invention first provides an emulsifier for oil-based drilling fluid with resistance to ultra-high temperature, wherein the emulsifier for oil-based drilling fluid with resistance to ultra-high temperature is composed of surface-modified nano-silica, styrene, maleic anhydride, polymer products of unsaturated fatty acids and solvent;

[0006] The surface-modified nano-silica is modified by using a silane coupling agent containing C=C bonds. The molar ratio of the nano-silica to the silane coupling agent containing C=C bonds is 1:0.05-1:1. The molar amount of the nano-silica is expressed as the molar amount of silicon.

[0007] The molar ratio of nano-silica, styrene, maleic anhydride, and unsaturated fatty acid is 1:0.01-1.5:0.1-2:0.1-1, wherein the molar amount of nano-silica is expressed as the molar amount of silicon.

[0008] The mass ratio of the polymer product to the solvent is 1:0.1-1:3.

[0009] In the above-mentioned emulsifier for ultra-high temperature oil-based drilling fluid, preferably, the particle size of the nano silica (unmodified nano silica) is 30-300 nm.

[0010] In the above-mentioned emulsifiers for ultra-high temperature oil-based drilling fluids, preferably, the silane coupling agent containing C=C bonds is selected from one or more combinations of γ-methacryloyloxypropyltrimethoxysilane (KH-570), methacryloyloxysilane coupling agent (Z-6030), vinyltrimethoxysilane, and vinyltriethoxysilane.

[0011] In the above-mentioned emulsifiers for ultra-high temperature oil-based drilling fluids, preferably, the unsaturated fatty acids are selected from one or more combinations of oleic acid, linoleic acid, tall oleic acid, palmitic acid and 9-hexadecenoic acid.

[0012] In the above-mentioned emulsifiers for ultra-high temperature oil-based drilling fluids, preferably, the solvent is selected from one or more combinations of triethylene glycol monobutyl ether, diethylene glycol monobutyl ether, n-octanol, isooctanol, and ethylene glycol.

[0013] In the above-mentioned emulsifier for ultra-high temperature oil-based drilling fluid, preferably, the molar ratio of the nano-silica to the silane coupling agent containing C=C bonds is 1:0.1-1:0.7, more preferably 1:0.2-1:0.5.

[0014] In the above-mentioned emulsifier for ultra-high temperature oil-based drilling fluid, preferably, the molar ratio of nano-silica, styrene, maleic anhydride, and unsaturated fatty acids is 1:0.03-0.1:0.3-1.5:0.2-0.8, more preferably 1:0.05-0.07:0.5-1:0.3-0.5.

[0015] In the above-mentioned emulsifier for ultra-high temperature oil-based drilling fluid, preferably, the mass ratio of the polymer product to the solvent is 1:0.3-1:1.5, more preferably 1:0.5-1:1.

[0016] This invention also provides a method for preparing the above-mentioned emulsifier for ultra-high temperature oil-based drilling fluid, comprising the following steps:

[0017] S101: Add nano-silica to an alcohol-water mixed solvent and disperse it ultrasonically. Add a silane coupling agent containing C=C bonds and raise the temperature to 40-80℃ to react, and obtain a dispersion system of the first reaction product.

[0018] S102: Add styrene, maleic anhydride and unsaturated fatty acid to the dispersion system of the first reaction product, stir under nitrogen gas, heat to 50-100℃, add initiator, carry out polymerization reaction, and then filter out the alcohol-water mixed solvent to obtain the polymerization product.

[0019] S103: Dissolve the polymer product in a solvent, heat and stir until uniformly mixed to obtain the emulsifier for ultra-high temperature oil-based drilling fluid.

[0020] In the above method, preferably, in step S101, the volume ratio of alcohol to water in the alcohol-water mixed solvent is 9:1-1:9, more preferably 7:3-3:7, and even more preferably 6:4-4:6. Wherein, the alcohol is preferably anhydrous ethanol, and the water is preferably distilled water.

[0021] In the above method, preferably, in step S102, the molar ratio of the nano-silica to the initiator is 1:0.01-1:0.08, more preferably 1:0.02-1:0.06, and even more preferably 1:0.03-1:0.05, wherein the molar amount of the nano-silica is expressed as the molar amount of silicon.

[0022] According to a specific embodiment of the present invention, preferably, the method for preparing the emulsifier for ultra-high temperature oil-based drilling fluid may include the following steps:

[0023] (1) Add an appropriate amount of nano-silica (e.g., 2g of nano-silica to 100mL of alcohol / water mixed solvent) to an alcohol / water mixed solvent and disperse it ultrasonically (e.g., for 30 minutes), wherein the alcohol / water mixed solvent is a mixture of anhydrous ethanol and distilled water, and the volume ratio of alcohol to water is 9:1-1:9, preferably 7:3-3:7, more preferably 6:4-4:6; add a silane coupling agent containing C=C bonds dropwise to the reaction vessel and mix evenly, wherein the molar ratio of nano-silica to silane coupling agent containing C=C bonds is 1:0.05-1:1 (the molar amount of nano-silica is based on the molar amount of silicon), preferably 1:0.1-1:0.7, more preferably 1:0.2-1:0.5, raise the temperature to 40-80℃ and react for 1-5 hours to obtain a dispersion system of the first reaction product.

[0024] (2) Add styrene, maleic anhydride, and unsaturated fatty acids to the dispersion system of the first reaction product. The molar ratio of silicon dioxide, styrene, maleic anhydride, and unsaturated fatty acids is 1:0.01-1.5:0.1-2:0.1-1 (the molar amount of nano-silica is based on the molar amount of silicon), preferably 1:0.03-0.1:0.3-1.5:0.2-0.8, more preferably 1:0.05-0.07:0.5-1:0.3-0.5. Under nitrogen purging, stir (the stirring speed can be controlled as needed, for example, controlled at 100 r / min), heat to 50-100℃, and maintain for an appropriate time (the maintenance time can be adjusted as needed). The time for adding the initiator should be controlled, for example, 30 minutes. Add an appropriate amount of distilled aqueous solution of the initiator (the amount of which can be controlled as needed, for example, 10 mL). The molar ratio of the nano-silica to the initiator is 1:0.01-1:0.08 (the molar amount of the nano-silica is based on the molar amount of silicon), preferably 1:0.02-1:0.06, more preferably 1:0.03-1:0.05. The addition time can be controlled as needed (for example, around 30 minutes). The initiator is azobisisobutyronitrile or potassium persulfate, etc. Increase the stirring speed (for example, to 200 r / min), keep warm for 3-5 hours, then filter out the alcohol / water mixed solvent to obtain the polymerization product.

[0025] (3) Dissolve the above-mentioned polymer product in a solvent, and control the mass ratio of polymer product to solvent to be 1:0.1-1:3, preferably 1:0.3-1:1.5, more preferably 1:0.5-1:1. Heat to 70°C and stir (stirring speed can be controlled as needed, for example, controlled to 200 r / min) until the mixture is uniform, and discharge directly (discharge while hot) to obtain the emulsifier for ultra-high temperature oil-based drilling fluid.

[0026] The present invention also provides an oil-based drilling fluid containing the above-mentioned emulsifier for ultra-high temperature resistant oil-based drilling fluids, wherein the amount of the emulsifier added is 1%-4%. The oil phase used can be a commonly used oil phase in drilling fluids, such as diesel oil or white oil.

[0027] The technical solution of the present invention has the following beneficial technical effects:

[0028] The emulsifier for ultra-high temperature oil-based drilling fluid provided by this invention is a product obtained by copolymerizing nano-silica with styrene, maleic anhydride, and unsaturated fatty acids after modification with a C=C bond silane coupling agent. This nanocomposite polymer contains a large number of silanol groups provided by silica as active ends of the emulsifier. It can be firmly adsorbed at the oil-water interface through multi-point adsorption via the Pickering emulsion principle to play a role in stabilizing the emulsion. It can maintain the long-term stability of water-in-oil emulsions in ultra-high temperature environments of 220-240℃, effectively solving the problem of instability of oil-based drilling fluids in ultra-high temperature environments, and providing technical support for drilling at depths of 10,000 meters. Detailed Implementation

[0029] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0030] Unless otherwise stated, all chemical reagents used in the following examples are commercially available. Specifically, nano-silica (particle size 50-100nm) was purchased from Nanjing Baoket New Materials Co., Ltd., oleic acid and tall oleic acid were purchased from Jining Hongming Chemical Reagent Co., Ltd., and styrene, maleic anhydride, silane coupling agent KH570, vinyltrimethoxysilane, anhydrous ethanol, triethylene glycol monobutyl ether, and diethylene glycol monobutyl ether were all purchased from Saen Chemical Technology (Shanghai) Co., Ltd.

[0031] Example 1

[0032] This embodiment provides an emulsifier for ultra-high temperature oil-based drilling fluids, and its preparation method is as follows:

[0033] 2g of nano-silica (particle size 50-100nm) was added to 100mL of alcohol / water mixed solvent (anhydrous ethanol and distilled water volume ratio of 6:4) and ultrasonically dispersed for 30 minutes; then vinyltrimethoxysilane was added and mixed evenly, wherein the molar ratio of nano-silica to vinyltrimethoxysilane was 1:0.2, and the molar amount of nano-silica was expressed as the molar amount of silicon; the temperature was raised to 50℃ and reacted for 3 hours to obtain the dispersion system of the first reaction product.

[0034] Styrene, maleic anhydride, and oleic acid were added to the dispersion system of the first reaction product. The molar ratio of nano-silica to styrene, maleic anhydride, and oleic acid was 1:0.05:0.5:0.5, where the molar amount of nano-silica was expressed as the molar amount of silicon. Under nitrogen purging, the mixture was stirred at 100 rpm and heated to 70°C, which was maintained for 30 minutes. A total of 10 mL of distilled potassium persulfate aqueous solution was prepared and added dropwise to the reaction system, wherein the molar ratio of nano-silica to potassium persulfate was 1:0.05:0.5. 0.03, the molar amount of the nano-silica is calculated as the molar amount of silicon, and the dropping time is controlled at about 30 minutes; after the dropping is completed, the stirring speed is increased to 200 r / min, the temperature is maintained for 3 hours, the alcohol / water mixed solvent is filtered off, the obtained polymerization product is dissolved in triethylene glycol monobutyl ether, the mass ratio of polymerization product to solvent is controlled at 1:0.5, the temperature is raised to 70℃ and stirred at 200 r / min until the mixture is uniform, and then the material is discharged while hot, thus obtaining the emulsifier HTEM-1 for ultra-high temperature oil-based drilling fluid.

[0035] Example 2

[0036] This embodiment provides an emulsifier for ultra-high temperature oil-based drilling fluids, and its preparation method is as follows:

[0037] 2g of nano-silica (particle size 50-100nm) was added to 100mL of alcohol / water mixed solvent (anhydrous ethanol and distilled water volume ratio of 6:4) and ultrasonically dispersed for 30 minutes; then vinyltrimethoxysilane was added and mixed evenly, wherein the molar ratio of nano-silica to vinyltrimethoxysilane was 1:0.5, and the molar amount of nano-silica was calculated as the molar amount of silicon; the temperature was raised to 50℃ and reacted for 3 hours to obtain the dispersion system of the first reaction product.

[0038] Styrene, maleic anhydride, and oleic acid were added to the dispersion system of the first reaction product. The molar ratio of nano-silica to styrene, maleic anhydride, and oleic acid was 1:0.05:0.5:0.5, where the molar amount of nano-silica was expressed as the molar amount of silicon. Under nitrogen purging, the mixture was stirred at 100 r / min and heated to 70°C, which was maintained for 30 minutes. A total of 10 mL of distilled potassium persulfate aqueous solution was prepared and added dropwise to the reaction system, wherein the molar ratio of nano-silica to potassium persulfate was 1:0.05:0.5. The molar amount of the nano-silica is calculated based on the molar amount of silicon, and the dropping time is controlled at about 30 minutes. After the dropping is completed, the stirring speed is increased to 200 r / min, and the temperature is maintained for 3 hours. The alcohol / water mixed solvent is filtered out, and the obtained polymerization product is dissolved in triethylene glycol monobutyl ether. The mass ratio of the polymerization product to the solvent is controlled at 1:0.5. After heating to 70°C, the mixture is stirred at 200 r / min until it is uniformly mixed. Then, the product is discharged while hot to obtain the emulsifier HTEM-2 for ultra-high temperature oil-based drilling fluid.

[0039] Example 3

[0040] This embodiment provides an emulsifier for ultra-high temperature oil-based drilling fluids, and its preparation method is as follows:

[0041] 2g of nano-silica (particle size 50-100nm) was added to 100mL of alcohol / water mixed solvent (anhydrous ethanol and distilled water volume ratio of 6:4) and ultrasonically dispersed for 30 minutes; then KH570 was added and mixed evenly, wherein the molar ratio of nano-silica to vinyltrimethoxysilane was 1:0.2, and the molar amount of nano-silica was expressed as the molar amount of silicon; the temperature was raised to 50℃ and reacted for 3 hours to obtain the dispersion system of the first reaction product.

[0042] Styrene, maleic anhydride, and oleic acid were added to the dispersion system of the first reaction product. The molar ratio of nano-silica to styrene, maleic anhydride, and oleic acid was 1:0.05:0.5:0.5, where the molar amount of nano-silica was expressed as the molar amount of silicon. Under nitrogen purging, the mixture was stirred at 100 rpm and heated to 70°C, which was maintained for 30 minutes. A total of 10 mL of distilled potassium persulfate aqueous solution was prepared and added dropwise to the reaction system, wherein the molar ratio of nano-silica to potassium persulfate was... The molar amount of silica is calculated as the molar amount of silicon, and the dropping time is controlled at about 30 minutes. After the dropping is completed, the stirring speed is increased to 200 r / min, and the temperature is maintained for 3 hours. The alcohol / water mixed solvent is filtered off, and the obtained polymerization product is dissolved in triethylene glycol monobutyl ether. The mass ratio of polymerization product to solvent is controlled at 1:0.5. After heating to 70°C, the mixture is stirred at 200 r / min until it is uniformly mixed. Then, the product is discharged while hot to obtain HTEM-3, an emulsifier for oil-based drilling fluid resistant to ultra-high temperature.

[0043] Example 4

[0044] This embodiment provides an emulsifier for ultra-high temperature oil-based drilling fluids, and its preparation method is as follows:

[0045] 2g of nano-silica (particle size 50-100nm) was added to 100mL of alcohol / water mixed solvent (anhydrous ethanol and distilled water volume ratio of 6:4) and ultrasonically dispersed for 30 minutes; then vinyltrimethoxysilane was added and mixed evenly, wherein the molar ratio of nano-silica to vinyltrimethoxysilane was 1:0.2, and the molar amount of nano-silica was expressed as the molar amount of silicon; the temperature was raised to 50℃ and reacted for 3 hours to obtain the dispersion system of the first reaction product.

[0046] Styrene, maleic anhydride, and tallowic acid were added to the dispersion system of the first reaction product. The molar ratio of nano-silica to styrene, maleic anhydride, and tallowic acid was 1:0.05:0.5:0.5, where the molar amount of nano-silica was expressed as the molar amount of silicon. Under nitrogen purging, the mixture was stirred at 100 rpm and heated to 70°C, which was maintained for 30 minutes. A total of 10 mL of distilled potassium persulfate aqueous solution was prepared and added dropwise to the reaction system. The molar amounts of nano-silica and potassium persulfate were... The ratio is 1:0.03, the molar amount of the nano-silica is based on the molar amount of silicon, and the dropping time is controlled at about 30 minutes. After the dropping is completed, the stirring speed is increased to 200 r / min, the temperature is maintained for 3 hours, the alcohol / water mixed solvent is filtered off, the obtained polymerization product is dissolved in triethylene glycol monobutyl ether, the mass ratio of polymerization product to solvent is controlled at 1:0.5, the temperature is raised to 70℃ and stirred at 200 r / min until the mixture is uniform, and then the material is discharged while hot to obtain the emulsifier HTEM-4 for ultra-high temperature oil-based drilling fluid.

[0047] Example 5

[0048] This embodiment provides an emulsifier for ultra-high temperature oil-based drilling fluids, and its preparation method is as follows:

[0049] 2g of nano-silica (particle size 50-100nm) was added to 100mL of alcohol / water mixed solvent (anhydrous ethanol and distilled water volume ratio of 6:4) and ultrasonically dispersed for 30 minutes; then KH570 was added and mixed evenly, wherein the molar ratio of nano-silica to vinyltrimethoxysilane was 1:0.3, and the molar amount of nano-silica was expressed as the molar amount of silicon; the temperature was raised to 50℃ and reacted for 3 hours to obtain the dispersion system of the first reaction product.

[0050] Styrene, maleic anhydride, and tallowic acid were added to the dispersion system of the first reaction product. The molar ratio of nano-silica to styrene, maleic anhydride, and tallowic acid was 1:0.07:0.6:0.5, where the molar amount of nano-silica was expressed as the molar amount of silicon. Under nitrogen purging, the mixture was stirred at 100 rpm and heated to 70°C, which was maintained for 30 minutes. A total of 10 mL of distilled potassium persulfate aqueous solution was prepared and added dropwise to the reaction system, wherein the molar amounts of nano-silica and potassium persulfate were... The ratio is 1:0.03, the molar amount of the nano-silica is based on the molar amount of silicon, and the dropping time is controlled at about 30 minutes. After the dropping is completed, the stirring speed is increased to 200 r / min, the temperature is maintained for 3 hours, the alcohol / water mixed solvent is filtered off, the obtained polymerization product is dissolved in triethylene glycol monobutyl ether, the mass ratio of polymerization product to solvent is controlled at 1:0.5, the temperature is raised to 70℃ and stirred at 200 r / min until the mixture is uniform, and then the material is discharged while hot to obtain the emulsifier HTEM-5 for ultra-high temperature oil-based drilling fluid.

[0051] Example 6

[0052] This embodiment provides an emulsifier for ultra-high temperature oil-based drilling fluids, and its preparation method is as follows:

[0053] 2g of nano-silica (particle size 50-100nm) was added to 100mL of alcohol / water mixed solvent (anhydrous ethanol and distilled water volume ratio of 6:4) and ultrasonically dispersed for 30 minutes; then vinyltrimethoxysilane was added and mixed evenly, wherein the molar ratio of nano-silica to vinyltrimethoxysilane was 1:0.2, and the molar amount of nano-silica was expressed as the molar amount of silicon; the temperature was raised to 80℃ and reacted for 1 hour to obtain the dispersion system of the first reaction product.

[0054] Styrene, maleic anhydride, and oleic acid were added to the dispersion system of the first reaction product. The molar ratio of nano-silica to styrene, maleic anhydride, and oleic acid was 1:0.05:0.5:0.5, and the molar amount of nano-silica was calculated based on the molar amount of silicon. Under nitrogen purging, the mixture was heated to 60°C with a stirring speed of 100 r / min and maintained for 30 minutes. Prepare 10 mL of a distilled aqueous solution of potassium persulfate and add it dropwise to the reaction system. The molar ratio of nano-silica to potassium persulfate is 1:0.03, and the molar amount of nano-silica is based on the molar amount of silicon. The dropwise addition time is controlled at about 30 minutes. After the dropwise addition is completed, increase the stirring speed to 200 r / min, keep it at the temperature for 5 hours, filter out the alcohol / water mixed solvent, dissolve the obtained polymerization product in triethylene glycol monobutyl ether, control the mass ratio of polymerization product to solvent to be 1:0.5, heat to 70℃, stir at 200 r / min until uniformly mixed, and then discharge the material while hot to obtain HTEM-6, an emulsifier for oil-based drilling fluid with resistance to ultra-high temperature.

[0055] Comparative Example 1

[0056] This comparative example provides an emulsifier for oil-based drilling fluids, the preparation method of which is as follows:

[0057] The preparation method of Comparative Example 1 differs from that of Example 1 except that no silane coupling agent is added, resulting in the preparation of DHTEM-1, an emulsifier for oil-based drilling fluids.

[0058] Test Example 1

[0059] This test example uses the oil-based drilling fluid emulsifiers provided in Examples 1-6 and Comparative Example 1, as well as the commonly used high-temperature resistant oil-based drilling fluid emulsifier oleic acid diethanolamide (purchased from Jiangsu Haian Petrochemical Plant), in an oil-in-water system to test the oil-water interfacial tension. The oil-based drilling fluid emulsifiers were dispersed in No. 3 white oil to prepare oil-based drilling fluid emulsifier / oil solutions of different concentrations. The effect of each emulsifier on the oil-water interfacial tension was then evaluated using the ring method.

[0060] The specific experimental steps for evaluating the ring method are as follows: Using a Sigma 700 automatic surface tension meter (ring method, circular platinum ring), the test temperature is set to 30℃. The equilibrium surface tension of the aqueous solution, white oil solution, and oil / water equilibrium system are measured at this temperature. Before each measurement, the system to be tested is preheated to the set temperature, added to the measurement cell, and then allowed to stand for 10 minutes to reach equilibrium.

[0061] The effects of emulsifiers in oil-based drilling fluids on the magnitude of oil-water interfacial tension are shown in Table 1.

[0062] Table 1

[0063]

[0064] The results showed that Examples 1-6 and oleic acid diethanolamide could significantly reduce the oil-water interfacial tension. Among the examples, the HTEM-2 emulsifier for ultra-high temperature oil-based drilling fluid provided in Example 2 had the lowest efficiency in reducing interfacial tension. This was because the amount of silane coupling agent used during silica modification was relatively large, resulting in fewer exposed silanol groups on the silica surface and a lower adsorption amount at the oil-water interface, thus weakening its ability to reduce interfacial tension. In Comparative Example 1, the nano-silica was not modified and did not participate in the polymerization reaction; the emulsifier molecular chain lacked silanol groups as active groups, resulting in poor ability to reduce oil-water interfacial tension. Overall, the ability of Examples 1, 3, 4, 5, and 6 to reduce oil-water interfacial tension was close to that of oleic acid diethanolamide, indicating that these oil-based drilling fluid emulsifiers have good ability to stabilize water-in-oil emulsions.

[0065] Test Example 2

[0066] This test example uses the oil-based drilling fluid emulsifiers provided in Examples 1-6 and Comparative Example 1, as well as the commonly used high-temperature resistant emulsifier for oil-based drilling fluids, oleic acid diethanolamide (purchased from Jiangsu Haian Petrochemical Plant), in an oil-in-water system to evaluate emulsification efficiency. The oil-based drilling fluid emulsifier was dispersed into the oil-based drilling fluid base fluid (base fluid formulation: 240 mL diesel + 2% organic clay + 60 mL 20% CaCl2 solution; the amount of organic clay added is based on the total volume of diesel and CaCl2 solution, 2% means 2g organic clay added per 100 mL), stirred at 11000 rpm for 30 minutes, aged at 240℃ for 16 hours, stirred at 11000 rpm for 10 minutes, and allowed to stand for 24 hours. The oil content separated from the emulsion was observed, and the corresponding emulsification rate R was calculated.

[0067] R = V_milk / V_total

[0068] R represents the emulsion emulsification efficiency, %; V_emulsion represents the volume of the emulsion layer, mL; V_total represents the total volume of the oil-water emulsion system, in mL.

[0069] The results of emulsification efficiency of different oil-based drilling fluids using emulsifiers are shown in Table 2.

[0070] Table 2

[0071]

[0072] The results showed that the emulsification efficiency gradually increased with the increase of the concentration of each emulsifier. Compared with oleic acid diethanolamide, the emulsifiers for ultra-high temperature oil-based drilling fluids provided in Examples 1-6 have a significant advantage in emulsification efficiency. This is because the emulsifiers for ultra-high temperature oil-based drilling fluids provided in the embodiments of the present invention achieve multi-point adsorption at the oil-water interface through the silanol groups on the surface of nano-silica, exhibiting the characteristics of Pickering emulsions. Their adsorption strength is much higher than that of traditional surfactants such as fatty acid amides and fatty acid alcohol amines, and they can still effectively adsorb at the oil-water interface and maintain emulsion stability at high temperatures. Comparative Example 1 did not have an emulsifying effect, resulting in an emulsification rate of 0.

[0073] Test Example 3

[0074] In this test example, the oil-based drilling fluid emulsifiers provided in Examples 1-6 and Comparative Example 1, as well as the commonly used high-temperature resistant emulsifier for oil-based drilling fluids, oleic acid diethanolamide (purchased from Jiangsu Haian Petrochemical Plant), were used in a water-in-oil system for demulsification voltage testing. The oil-based drilling fluid emulsifier was dispersed into the oil-based drilling fluid base fluid (base fluid formulation: 240 mL diesel + 2% organic clay + 60 mL 20% CaCl2 solution), stirred at 11000 rpm for 30 minutes, aged at 260℃ for 16 hours, and then stirred at 11000 rpm for 10 minutes before the emulsion demulsification voltage was tested using a Fann 23D demulsification voltage tester. The results of the influence of different oil-based drilling fluid emulsifiers on the emulsion demulsification voltage are shown in Table 3.

[0075] Table 3

[0076]

[0077] The results showed that demulsification gradually increased with increasing emulsifier concentration. At the same concentration, the demulsification voltage of the emulsions formulated with the emulsifiers for ultra-high temperature oil-based drilling fluids provided in Examples 1-6 was much higher than that of oleic acid diethanolamide, which is more conducive to the formation of stable water-in-oil emulsions under extreme high temperature environments, ensuring the temperature stability of oil-based drilling fluids. In this test example, the emulsion system formulated with the emulsifier for oil-based drilling fluids provided in Comparative Example 1 showed oil-water stratification immediately after high-temperature stirring following aging, and could not form a stable water-in-oil emulsion; therefore, demulsification voltage testing was not performed.

[0078] Test Example 4

[0079] This test case evaluates the effects of the oil-based drilling fluid emulsifiers and the commonly used high-temperature resistant emulsifier oleic acid diethanolamide provided in Examples 1-6 and Comparative Example 1 on the interfacial tension of the oil-water interface under high temperature and high pressure. 3% (based on the mass of white oil as 100%) of the oil-based drilling fluid emulsifier was dispersed in No. 3 white oil to prepare an oil solution. The effects of each emulsifier on the oil-water interfacial tension were then tested under controlled temperature conditions using a TECLIS Tracker high-temperature and high-pressure interfacial tension / rheometer. During the test, water was placed in a quartz dish, and a bent needle was inserted into the water to squeeze out 0.2 μL of the emulsifier oil solution. The pressure was maintained at 600 psi. The results of the effects of the oil-based drilling fluid emulsifier on the magnitude of the oil-water interfacial tension at different temperatures are shown in Table 4.

[0080] Table 4

[0081]

[0082] The results show that the interfacial tension of the blank oil-water interface gradually decreases with increasing temperature. Interfacial tension arises from the downward direction of the net intermolecular attraction on the interfacial molecules, thus causing the interface to tend to contract. Besides the inherent properties of the substances themselves, temperature is also a significant factor affecting the interfacial tension between the two phases. At high temperatures, intermolecular attraction weakens with increased molecular thermal motion, reducing the energy required for molecules within the phase to reach the interface, which macroscopically manifests as a decrease in interfacial tension. The oleic acid diethanolamide and emulsifiers for ultra-high temperature oil-based drilling fluids provided in Examples 1-6 can both reduce the interfacial tension of the oil-water interface at 30°C, but the interfacial tension gradually increases with increasing temperature. This is because, with increasing temperature, the thermal motion of the emulsifier molecules increases, causing them to gradually desorb from the oil-water interface, ultimately weakening the emulsion stabilizing effect. Compared to oleic acid diethanolamide, the emulsifiers for ultra-high temperature oil-based drilling fluids provided in Examples 1-6 exhibit better interfacial tension stability at high temperatures, which is more conducive to maintaining the high-temperature stability of oil-based drilling fluids. The emulsifier for the oil-based drilling fluid provided in Comparative Example 1 has almost no effect on the oil-water interfacial tension at different temperatures.

[0083] In summary, the modified nano-silica composite polymer provided by this invention can be used as an ultra-high temperature resistant emulsifier in oil-based drilling fluid systems, effectively improving the emulsification stability of oil-based drilling fluids, with a temperature resistance of up to 240℃.

[0084] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An emulsifier for ultra-high temperature oil-based drilling fluids, wherein, The emulsifier for ultra-high temperature oil-based drilling fluid is composed of surface-modified nano-silica, styrene, maleic anhydride, polymers of unsaturated fatty acids, and solvents. The surface-modified nano-silica is modified by using a silane coupling agent containing C=C bonds. The molar ratio of the nano-silica to the silane coupling agent containing C=C bonds is 1:0.05-1:

1. The molar amount of the nano-silica is expressed as the molar amount of silicon. The molar ratio of nano-silica, styrene, maleic anhydride, and unsaturated fatty acid is 1:0.01-1.5:0.1-2:0.1-1, wherein the molar amount of nano-silica is expressed as the molar amount of silicon. The mass ratio of the polymer product to the solvent is 1:0.1-1:

3.

2. The emulsifier for ultra-high temperature oil-based drilling fluid according to claim 1, wherein, The particle size of the nano-silica is 30-300 nm.

3. The emulsifier for ultra-high temperature oil-based drilling fluid according to claim 1, wherein, The silane coupling agent containing C=C bonds is selected from one or more combinations of γ-methacryloxypropyltrimethoxysilane, methacryloxysilane coupling agent, vinyltrimethoxysilane, and vinyltriethoxysilane.

4. The emulsifier for ultra-high temperature oil-based drilling fluid according to claim 1, wherein, The unsaturated fatty acids are selected from one or more combinations of oleic acid, linoleic acid, tall oleic acid, palmitoleic acid, and 9-hexadecenoic acid.

5. The emulsifier for ultra-high temperature oil-based drilling fluid according to claim 1, wherein, The solvent is selected from one or more of triethylene glycol monobutyl ether, diethylene glycol monobutyl ether, n-octanol, isooctanol and ethylene glycol.

6. The emulsifier for ultra-high temperature oil-based drilling fluid according to claim 1, wherein, The molar ratio of the nano-silica to the silane coupling agent containing C=C bonds is 1:0.1-1:0.

7.

7. The emulsifier for ultra-high temperature oil-based drilling fluid according to claim 1, wherein, The molar ratio of nano-silica, styrene, maleic anhydride, and unsaturated fatty acids is 1:0.03-0.1:0.3-1.5:0.2-0.

8.

8. The emulsifier for ultra-high temperature oil-based drilling fluid according to claim 1, wherein, The mass ratio of the polymer product to the solvent is 1:0.3 to 1:1.

5.

9. The method for preparing the emulsifier for ultra-high temperature oil-based drilling fluid according to any one of claims 1-8, wherein, Includes the following steps: S101: Add nano-silica to an alcohol-water mixed solvent and disperse it ultrasonically. Add a silane coupling agent containing C=C bonds and raise the temperature to 40-80℃ to react, and obtain a dispersion system of the first reaction product. S102: Add styrene, maleic anhydride and unsaturated fatty acid to the dispersion system of the first reaction product, stir under nitrogen gas, heat to 50-100℃, add initiator, carry out polymerization reaction, and then filter out the alcohol-water mixed solvent to obtain the polymerization product. S103: Dissolve the polymer product in a solvent, heat and stir until uniformly mixed to obtain the emulsifier for ultra-high temperature oil-based drilling fluid.

10. The method according to claim 9, wherein, In S101, the volume ratio of alcohol to water is 9:1 to 1:

9.

11. The method according to claim 9, wherein, In step S102, the molar ratio of the nano-silica to the initiator is 1:0.01-1:0.08, wherein the molar amount of the nano-silica is expressed as the molar amount of silicon.

12. An oil-based drilling fluid comprising the ultra-high temperature resistant oil-based drilling fluid emulsifier according to any one of claims 1-8, wherein, The amount of emulsifier added is 1%-4%.

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