High-temperature-resistant high-performance oil-based drilling fluid and preparation method and application thereof

Abstract

This invention discloses a high-temperature resistant, high-performance oil-based drilling fluid, its preparation method, and its application, belonging to the field of oil and gas drilling engineering. The drilling fluid includes a dedicated emulsifier combination and a filtration loss reducer. The emulsifier combination employs a primary and secondary emulsifier combination derived from a homologous framework. While ensuring oil phase compatibility, it can undergo a secondary reaction under high downhole temperatures (≥220℃), converting destructive thermal shock into chemical energy that strengthens the interfacial film, achieving self-reinforcement and long-term stability of the emulsifier system under extreme conditions. The core-shell structured filtration loss reducer achieves "dual-use (oil and water)" and "filtration loss reduction without viscosity increase" through ingenious molecular design, while significantly reducing toxicity and reservoir damage. The drilling fluid system using the above-mentioned emulsifier combination and filtration loss reducer significantly outperforms commercially available high-performance material systems in terms of demulsification voltage, high-temperature and high-pressure filtration loss control, and viscosity stability, and maintains good performance even after long-term aging, fully meeting the requirements of field operations.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling engineering, specifically to a high-temperature resistant, high-performance oil-based drilling fluid, its preparation method, and its application. Background Technology

[0002] As global oil and gas exploration and development moves towards deeper, ultra-deep, and complex formations, drilling fluid systems face increasingly severe high-temperature, high-pressure (HPHT) challenges. Conventional oil-based drilling fluids exhibit significant performance degradation or even failure in downhole environments exceeding 200°C, primarily due to the following limitations: High-temperature rheological runaway: Conventional organic clay cutting agents and emulsifiers are prone to structural degradation at sustained high temperatures, leading to a sharp decrease in drilling fluid viscosity and shear force, loss of suspension and cuttings carrying capacity, and a reduction in demulsification voltage, resulting in the collapse of the emulsion system.

[0003] Poor high-temperature emulsification stability: Existing commercial emulsifiers have insufficient thermal stability at temperatures of 240℃ and above, and are prone to molecular chain breakage or functional group deactivation, resulting in rapid decay of the oil-water interface film strength, decreased electrical stability of the system, and a surge in filtration loss.

[0004] The contradiction between the environmental friendliness and effectiveness of filtration loss reducers: Traditional high-temperature and high-pressure wells rely on asphalt, oxidized asphalt, or lignite resin-based plugging materials. While these materials have a certain effect on reducing filtration loss, they also have problems such as high toxicity and the potential to cause irreversible damage to the reservoir (clogging pore throats). At the same time, conventional polymer filtration loss reducers have poor dispersibility in oil-based systems and are prone to dissolving and thickening in water-based systems, especially in freshwater bentonite-based slurries where the viscosity effect is extremely severe, affecting flow control performance.

[0005] Therefore, developing a drilling fluid system that can maintain excellent electrical stability, rheological properties, and low filtration loss after long-term aging at 240℃, and that is environmentally friendly and does not damage the reservoir, has become an urgent need for the industry. Summary of the Invention

[0006] To address the technical challenges in drilling ultra-deep and high-temperature, high-pressure wells, this invention provides an emulsifier combination with a homologous framework and a low-toxicity polymer latex filtration reducer applicable to both oil-based and water-based drilling fluids.

[0007] This invention provides an emulsifier combination for drilling fluids, comprising a primary emulsifier and a secondary emulsifier; wherein the primary emulsifier is tall oil fatty acid diethanolamide as shown in Formula 1: Formula 1: RCON(CH2CH2OH)2; The co-emulsifier is tall oil fatty acid polyoxyethylene ester as shown in Formula 2: Formula 2: RCOO(CH2CH2O) n H; In Formulas 1 and 2, R is a mixed alkyl chain of C18-C20 derived from tall oil, wherein the mixed alkyl chain includes hydrocarbon groups derived from oleic acid, linoleic acid, and rosin acid, and, n = 2~6 or 3~5 or 4; The weight ratio of the primary emulsifier to the secondary emulsifier is 1:1 to 4:1 or 1:1 to 2:1.

[0008] Furthermore, the primary emulsifier is prepared by the following method: Tall oil fatty acids were mixed with an excess of diethanolamine and heated to 170±5°C under a continuous nitrogen flow. The temperature was maintained and the mixture was stirred and refluxed for 3 hours. After the reaction was completed, the product was cooled to below 80°C to obtain the main emulsifier.

[0009] Furthermore, the co-emulsifier is prepared by the following method: Tall oil fatty acids were mixed with an alkaline catalyst and heated to 115±5℃ under negative pressure for stirring and dehydration. The air in the reaction system was replaced with high-purity nitrogen, and the temperature was raised to 155±5℃. Ethylene oxide was slowly introduced while maintaining the reaction pressure at 0.25~0.35MPa. The temperature was maintained and the mixture was stirred for 1 hour to ripen the reaction. The weight ratio of ethylene oxide to tall oil fatty acids was n:1. After the reaction, the temperature was lowered to 80~90℃, and the catalyst was neutralized with acid. The product was subjected to depressurized volatilization for 1 hour while maintaining the temperature and negative pressure. After filtration, a clear liquid phase was obtained, which is the co-emulsifier.

[0010] In the emulsifier combination provided by this invention, both the primary emulsifier and the co-emulsifier are derived from tall oil fatty acids as a common raw material skeleton, possessing homologous chemical structures. This homology ensures their close arrangement and synergistic adsorption at the oil-water interface, forming a denser and stronger composite interfacial film. More importantly, this combination can undergo further esterification or cross-linking reactions under downhole high-temperature (≥200℃) conditions. This process consumes a portion of the bottomhole thermal energy, thereby converting some of the destructive "thermal shock" into "chemical reaction energy" that enhances the stability of the interfacial film, greatly delaying the thermal decomposition failure process of the emulsifier molecules themselves. To achieve the above-mentioned beneficial effects, this invention has specifically designed the emulsifier molecules: the co-emulsifier uses a lower ethylene oxide addition number (n≈4) to retain highly reactive terminal hydroxyl groups and ensure oil phase compatibility; the primary emulsifier uses a moderately excessive amount of amine (molar ratio 1:1.3) to provide abundant reaction site reserves. When the two come into contact at high temperatures, the amine and hydroxyl groups can undergo a highly efficient condensation reaction.

[0011] Another aspect of the present invention provides a filtration loss reducer for drilling fluids, wherein the filtration loss reducer is a polymer latex having a core-shell structure, wherein: The core is a styrene-acrylate copolymer with a glass transition temperature of not less than 120°C; The shell is a modified acrylate copolymer containing amide and sulfonic acid groups; The weight ratio of the core to the shell is 2:1 to 2.5:1; And / or, the styrene-acrylate copolymer has a structure as shown in Formula 3: Formula 3: -CH2-CH(Ph)-CH2-C(CH3)(COOCH3)-CH2-CH(COO(CH2)3CH3)-CH2-CH(Ph-CH=CH-CH2-Ph)-CH2-CH(COOCH3)-; And / or, the modified acrylate copolymer has a structure as shown in Formula 4: Formula 4: -CH2-CH(CONH2)-CH2-CH(CONH-C(CH3)2-CH2-SO3H)-CH2-CH(COOCH2CH2OH)-CH2-C(CH3)(COOCH3)-CH2-CH(CONH2)-.

[0012] Furthermore, the core is mainly prepared from the following components in weight fractions: 50-60 parts styrene, 30-40 parts methyl methacrylate, 5-10 parts butyl acrylate, and 0.5-15 parts divinylbenzene; And / or, the shell is mainly prepared from the following components in parts by weight: Acrylamide 15-20 parts, 2-acrylamido-2-methylpropanesulfonic acid 10-15 parts, hydroxyethyl acrylate 10-15 parts and methyl methacrylate 5-10 parts.

[0013] Furthermore, the filtration loss reducing agent is prepared by the following method: Styrene, methyl methacrylate, butyl acrylate and divinylbenzene are mixed and continuously sheared and stirred at high temperature under the action of 3-5 parts of preemulsifier to form a core layer preemulsion; the core layer preemulsion is heated to 80-85°C under nitrogen, 0.5-1 parts of initiator are added, and the reaction is carried out for 2-3.5 hours; the temperature is maintained and the mixture is allowed to mature for another hour to obtain a core layer latex solution. Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, hydroxyethyl acrylate, and methyl methacrylate are mixed and continuously sheared and stirred at high temperature under the action of 3-5 parts of preemulsifier to form a shell preemulsion; the shell preemulsion and initiator are added to the core latex at 80-85°C and reacted for 1.5-2.5 hours; the temperature is maintained and the mixture is allowed to mature for another 1.5 hours to obtain a polymer latex with a core-shell structure. The polymer latex solution is cooled to below 40°C, the pH is adjusted to 7.0~8.0, filtered and dried to obtain the filtration loss reducer. And / or, the filtration loss reducing agent is prepared by the following method: Styrene, methyl methacrylate, butyl acrylate, and divinylbenzene are mixed and continuously sheared and stirred at high temperature for 30 minutes under the action of 3-5 parts of preemulsifier to form a core layer preemulsion. 5-20% of the core layer preemulsion is taken, heated to 80-85°C, and 0.1-0.4 parts of initiator are added. The reaction is carried out for 20-30 minutes to obtain a seed emulsion. While keeping the temperature constant, the remaining core layer preemulsion and 0.15-0.4 parts of initiator are added to the seed emulsion under stirring. The addition time is 2-3 hours. After the addition is completed, the temperature is maintained and the mixture is allowed to mature for another hour to obtain a core layer latex.

[0014] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, hydroxyethyl acrylate, and methyl methacrylate are mixed and continuously sheared and stirred at high temperature for 30 minutes under the action of 3-5 parts of preemulsifier to form a shell preemulsion. The shell preemulsion and 0.15-0.4 parts of initiator are slowly added dropwise to the core latex at 80-85°C for 1.5-2.5 hours. After the addition is completed, the temperature is maintained and the mixture is allowed to mature for another 1.5 hours to obtain a polymer latex with a core-shell structure. The polymer latex solution is cooled to below 40°C, the pH is adjusted to 7.0~8.0, filtered and dried to obtain the filtration loss reducer.

[0015] Furthermore, the preemulsifier comprises sodium dodecyl sulfate and octylphenol polyoxyethylene ether-10; the initiator is potassium persulfate.

[0016] In this invention, by adding pre-emulsions of core and shell monomers in a stepwise manner, the polymerization reaction is ensured to first form high-Tg core latex particles. Subsequently, the shell monomers polymerize and coat the surface of the core particles, thus forming a clear core-shell structure. Simultaneous addition of the initiator is crucial for controlling the reaction's stability, avoiding explosive polymerization, and obtaining uniform particle size. Acrylamide in the shell provides adsorption groups (amide groups), AMPS provides strong hydration groups (sulfonic acid groups) to enhance particle stability, and hydroxyethyl acrylate provides further modification sites. This design gives the shell both hydrophilic and oleophilic properties, forming the basis for achieving "dual-effect" oil-water applications. The synthesis process uses water as a medium and does not use toxic organic solvents. The selected monomers have significantly lower toxicity than traditional asphalt or sulfonated asphalt products, laying the foundation for the low-toxicity characteristics of subsequent products.

[0017] A third aspect of the present invention provides a high-temperature resistant, high-performance oil-based drilling fluid, comprising two or more of an oil phase, a wetting agent, a cutting agent, an organically modified bentonite, and a pH adjuster, and further comprising the above-mentioned emulsifier combination and a filtration loss reducer; And / or, the drilling fluid may further include an aqueous phase.

[0018] Further, it includes the following components in parts by weight: 90-95 parts oil phase, 3-6 parts of the above-mentioned emulsifier combination, 0.5-1.5 parts wetting agent, 1-3 parts shearing agent, 3-6 parts of the above-mentioned filtration loss reducer, 2-4 parts organic modified bentonite, 2-3 parts pH adjuster, and 5-10 parts aqueous phase. And / or, the oil phase is selected from at least one of white oil, diesel oil, and Saraline 185V; And / or, the wetting agent is a phosphate ester wetting agent; And / or, the cutting agent is organically modified lithium saponite; And / or, the pH adjuster is calcium oxide; And / or, the aqueous phase is a 20-25 wt% aqueous solution of calcium chloride.

[0019] The fourth aspect of the present invention provides the application of the above-mentioned emulsifier combination and filtration loss reducer in the preparation of high-temperature resistant drilling fluid, wherein the high temperature is not lower than 200°C, 220°C, or 240°C.

[0020] The technical effects of this invention are as follows: This invention discloses an emulsifier combination for drilling fluids and a filtration loss reducer for drilling fluids, as well as a drilling fluid comprising the above-mentioned emulsifier combination and filtration loss reducer. The emulsifier combination provided by this invention adopts a primary and secondary emulsifier combination derived from a homologous framework. Through synergistic design of the molecular structures of the two components: on the one hand, controlling the polyoxyethylene ester to have a low ethylene oxide addition number, so as to retain the highly reactive terminal hydroxyl groups and ensure oil phase compatibility; on the other hand, controlling the diethanolamide to have a moderate excess of amine, providing abundant reaction site reserves. At the same time, taking advantage of its characteristic of undergoing secondary reactions under high-temperature (≥200℃) downhole environment, the hydroxyl and amine groups between the two types of molecules can undergo efficient esterification, amidation and other condensation reactions. This process not only consumes bottomhole thermal energy, but also generates surface-active oligomers with larger molecular weight and stronger interfacial anchoring ability in situ, thereby converting the destructive thermal shock into chemical energy to strengthen the interfacial film, realizing the self-reinforcement and long-term stability of the emulsifier system under extreme conditions. The mechanism of "thermosetting film" that converts some of the destructive thermal energy into the chemical energy of a stable system is not revealed by existing technology, resulting in an unexpected technical effect that the demulsification voltage is still greater than 2000V after extreme aging.

[0021] The filtration loss reducer provided by this invention achieves "dual-use in oil and water" and "filtration loss reduction without viscosity increase" through ingenious molecular design, breaking through the barrier that traditional materials cannot simultaneously achieve the desired performance in two systems. Traditional latex-type filtration loss reducers have significant limitations; in oil-based drilling fluids, their hydrophilicity leads to viscosity increase and demulsification, or their hydrophobic segments prevent sufficient dispersion and film formation in water-based drilling fluid systems. Simultaneously, its low toxicity and low reservoir damage achieve top-tier engineering performance while meeting the most stringent reservoir protection and environmental requirements.

[0022] The drilling fluid system using the above-mentioned emulsifier combination and filtration loss reducer is significantly superior to the currently commonly used high-performance imported material system in terms of demulsification voltage, high-temperature and high-pressure filtration loss control and viscosity stability. Moreover, it maintains good performance after long-term aging, fully meets the requirements of field operations, and is suitable for promotion and application. Attached Figure Description

[0023] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, and these illustrative examples are not intended to limit the embodiments. The term "illustrative" as used herein means "serving as an example, embodiment, or illustration." Any embodiment illustrated herein as "illustrative" is not necessarily to be construed as superior to or better than other embodiments.

[0024] Figure 1 The image shows the DSC curve of the polymer latex filtration loss reducer described in Example 4. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprising of," etc., will be understood to include the stated elements or components, and does not exclude other elements or other components.

[0026] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art will understand that the present invention can still be practiced even without certain specific details. In some embodiments, materials, elements, methods, and means well known to those skilled in the art are not described in detail in order to highlight the spirit of the invention.

[0027] Unless otherwise specified, the raw materials and equipment used in the following examples can be purchased commercially.

[0028] Example 1: Preparation of the primary emulsifier The primary emulsifier was prepared using the following method: In a four-necked flask equipped with a water separator, thermometer, and nitrogen protection device, 152 g (0.5 mol) of tall oil fatty acid (acid value 195 mg KOH / g) and 68.3 g (0.65 mol) of diethanolamine were added sequentially. Under continuous nitrogen protection, the reaction mixture was heated to 170 ± 5 °C and stirred under reflux for 3 h. Water generated during the reaction was separated and measured in real time using a water separator. After the reaction was completed, the product was cooled to below 80 °C to obtain an amber-colored viscous liquid, which was the main emulsifier.

[0029] The primary emulsifier is a mixture, the main component of which is tall oil fatty acid diethanolamide as shown in Formula 1: Formula 1: RCON(CH2CH2OH)2; R mainly originates from the mixed alkyl chains of tall oil fatty acids; the main components and mass percentages of this primary emulsifier are as follows: (1) Oleic acid diethanolamide, which is prepared by condensation of oleic acid and diethanolamine in tall oil fatty acids, with a mass ratio of 45% to 55%, and the structural formula is CH3(CH2)7CH=CH(CH2)7CON(CH2CH2OH)2; (2) Linoleic acid diethanolamide, which is prepared by condensation of linoleic acid and diethanolamine in tall oil fatty acids, with a mass ratio of 30% to 40%, and the structural formula is CH3(CH2)4CH=CHCH2CH=CH(CH2)7CON(CH2CH2OH)2; (3) Stearic acid diethanolamide, which is prepared by condensation of stearic acid and diethanolamine in tall oil fatty acids, accounting for 5% to 15% by mass, and has the structural formula CH3(CH2). 16 -CON(CH2-CH2-OH)2; (4) A small amount of saturated acid amides and unreacted amines, with a total mass percentage not exceeding 10%.

[0030] The obtained primary emulsifier was tested and found to have an acid value of 8.2 mg KOH / g and an amine value of 160.5 mg KOH / g.

[0031] Example 2: Preparation of co-emulsifier The co-emulsifier was prepared using the following method: S1: Dehydration pretreatment: Add 280.0g (1mol) of tall oil fatty acid and 1.8g of solid potassium hydroxide to a high-pressure reactor, seal it, evacuate to -0.09MPa, heat to 115±5℃ and stir to dehydrate for 30 minutes.

[0032] S2: System replacement: High-purity nitrogen is used to pressurize and depressurize the reactor three times to completely replace the air in the reaction system.

[0033] S3: Ethoxylation reaction: The material temperature is raised to 155±5℃, and then 176.2g (4.0mol) of ethylene oxide is slowly introduced. By precisely controlling the introduction rate and the cooling system, the reaction pressure is maintained at 0.25~0.35MPa, and the temperature is kept constant within the set range.

[0034] S4: Maturation and Neutralization: After the ethylene oxide is added, continue stirring and maturing at 155°C for 1 hour. Then cool to 80°C and add 1.5g of 85% phosphoric acid aqueous solution to neutralize the catalyst.

[0035] S5: Post-treatment: The product is subjected to vacuum de-evaporation at 80~90℃ and -0.095MPa for 1 hour, followed by filtration to obtain a clear product, which is a light yellow oily liquid at room temperature (25℃), and is the co-emulsifier.

[0036] The co-emulsifier is a mixture, and its main component is tall oil fatty acid polyoxyethylene ester as shown in Formula 2: Formula 2: RCOO(CH2CH2O)4H; Where R is a mixed alkyl chain derived from tall oil, and the average EO addition number of the main component is n=4; the main components and mass percentages of this co-emulsifier are as follows: (1) Oleic acid polyoxypropylene (4) ester, which is prepared by the addition of oleic acid in tall oil fatty acid with 4 molar equivalent of propylene oxide via potassium hydroxide catalysis, with a mass ratio of 45% to 55%, and the structural formula is: CH3(CH2)7CH=CH(CH2)7COOCH(CH3)CH2OCH(CH3)CH2OCH(CH3)CH2OCH(CH3)CH2OCH(CH3)CH2OH; (2) Linoleic acid polyoxypropylene (4) ester, which is prepared by the addition of linoleic acid in tall oil fatty acid with 4 molar equivalents of propylene oxide via potassium hydroxide catalysis, with a mass ratio of 30% to 40%, and the structural formula is: CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOCH(CH3)CH2OCH(CH3)CH2OCH(CH3)CH2OCH(CH3)CH2OH; (3) Stearic acid polyoxypropylene (4) ester, which is prepared by the addition reaction of stearic acid in tall oil fatty acid with 4 molar equivalents of propylene oxide via potassium hydroxide catalysis, with a mass ratio of 5% to 15%, and the structural formula is: CH3(CH2). 16 COOCH(CH3)CH2OCH(CH3)CH2OCH(CH3)CH2OCH(CH3)CH2OH; (4) A small amount of saturated fatty acid polyoxypropylene esters such as palmitic acid polyoxypropylene (4) ester and myristic acid polyoxypropylene (4) ester, and trace amounts of unreacted propylene oxide self-polymerization products and free fatty acids, with a total mass percentage not exceeding 10%.

[0037] The obtained co-emulsifier was tested and found to have an acid value of 2.3 mg KOH / g and a hydroxyl value of 159.8 mg KOH / g.

[0038] Example 3: High-Temperature Reaction Verification and Performance Characterization of Emulsifier Combinations The primary emulsifier was prepared using the following method: The primary emulsifier prepared in Example 1 and the secondary emulsifier prepared in Example 2 were mixed in a mass ratio of 1:1 and stirred evenly to obtain a high-temperature reactive emulsifier combination.

[0039] To verify the reaction behavior of the obtained emulsifier combination in a high-temperature downhole environment, a simulated aging experiment was conducted. The emulsifier combination sample was placed in a sealed high-pressure reactor and heated to 220±5℃ under a nitrogen atmosphere for static thermal aging at 0 hours, 24 hours, and 72 hours. Key chemical indicators of the samples were monitored before and after high-temperature aging. Simultaneously, emulsification stability tests were performed on the emulsifier combination samples before and after aging, determining the time required for 10% oil-water separation in a 200℃ system of 10% calcium chloride aqueous solution and white oil. The results are shown in Table 1.

[0040] Table 1. Detection results of emulsifier combinations before and after aging.

[0041] Monitoring data shows that during the 220℃ high-temperature aging process, the acid value, amine value, and hydroxyl value of the emulsifier combination sample exhibited a synchronous and regular decreasing trend. This directly confirms that the designed-expected intermolecular condensation reaction (mainly esterification and amidation) did indeed occur between the excess amine groups (-NH-, -OH) in the main emulsifier molecule and the high density of terminal hydroxyl groups (-OH) in the co-emulsifier molecule. This chemical reaction process actively consumes the thermal energy within the system, transforming the destructive thermal shock into a driving force for the formation of new chemical bonds.

[0042] Oil-water separation experiments showed that after high-temperature aging, cross-linking reactions occurred between molecules, resulting in the in-situ formation of a surface-active associated structure with stronger interfacial anchoring ability and spatial stability. This significantly enhanced the strength and durability of the emulsion film, achieving a performance transformation from "withstanding thermal shock" to "self-reinforcing through thermal energy." This characteristic enables it to greatly delay its own thermal decomposition failure process and provide long-lasting and stable emulsification performance in extreme high-temperature environments (≥200℃) downhole.

[0043] Example 4: Preparation of polymer latex filtration loss reducer The components used in the preparation of the filtration loss reducing agent in this embodiment are as follows: (1) Core layer monomer mixture (total 100.5 parts) Styrene: 60 parts; Methyl methacrylate: 30 parts; Butyl acrylate: 10 parts; Crosslinking agent (divinylbenzene): 0.5 parts; (2) Shell monomer mixture (45 parts in total) Acrylamide: 20 parts; 2-Acrylamido-2-methylpropanesulfonic acid: 10 parts; Hydroxyethyl acrylate: 10 parts; Methyl methacrylate: 5 parts; (3) Reaction system Deionized water: 250 parts; Composite emulsifier (a mixture of sodium dodecyl sulfate and octylphenol polyoxyethylene ether-10): 5 parts; Initiator (potassium persulfate): 0.5 parts (dissolved in an appropriate amount of water); pH adjuster (sodium hydroxide solution): used to adjust the pH of the system to 7.0~8.0.

[0044] The filtration loss reducer was prepared using the following method: S1: Preparation of pre-emulsion Dissolve the entire amount of the composite emulsifier in approximately two-thirds of the volume of deionized water to prepare an emulsifier aqueous solution. Slowly add the core monomer mixture and the shell monomer mixture separately to two equal portions of the above emulsifier aqueous solution while stirring, and continuously stir at high speed for 30 minutes to form core pre-emulsion and shell pre-emulsion, respectively, for later use.

[0045] S2: Seed emulsion and core layer polymerization Add the remaining deionized water and approximately one-tenth of the core layer preemulsion to a four-necked flask equipped with a stirrer, condenser, thermometer, and constant-pressure dropping funnel. Under nitrogen protection, heat to 80-85°C, add approximately one-third of the initiator solution, and react for 20-30 minutes to form a pale blue seed emulsion. While stirring, slowly add the remaining core layer preemulsion through the constant-pressure dropping funnel, simultaneously adding the other half of the remaining initiator solution. Control the dropping time to be completed within 2-3 hours, maintaining a constant reaction temperature. After the core layer monomer is completely added, continue to cure at 85°C for 1 hour to ensure complete polymerization of the core layer monomer, obtaining a core layer latex solution.

[0046] S3: Shell aggregation Stabilize the reaction system temperature at 80-85℃, and slowly add the shell pre-emulsion and the remaining initiator solution dropwise to the core latex obtained in S2, controlling the dropwise addition time to be completed within 1.5-2.5 hours. After the shell monomer is completely added, maintain the temperature at 85℃ for 1.5 hours to ensure complete polymerization of the shell monomer.

[0047] S4: Post-processing After the reaction is complete, the system is cooled to below 40°C, and the pH of the emulsion is adjusted to 7.0~8.0 with sodium hydroxide solution. After filtration, a slightly bluish, semi-transparent core-shell polymer with a solid content of about 30%~35% is obtained. After spray drying, a white or light yellow powder is obtained, which is the finished product of the filtration loss reducer.

[0048] The obtained filtration loss reducer was tested and found to have a pH value of 7.0–8.0, a viscosity of <100 mPa·s (25°C, Brookfield viscometer), and an average particle size of 80–150 nm (measured by a laser particle size analyzer). The core component of the obtained filtration loss reducer is a styrene-acrylate copolymer with a structure as shown in Formula 3. Formula 3: -CH2-CH(Ph)-CH2-C(CH3)(COOCH3)-CH2-CH(COO(CH2)3CH3)-CH2-CH(Ph-CH=CH-CH2-Ph)-CH2-CH(COOCH3)-; The shell is composed of a modified acrylate copolymer and has a structure as shown in Formula 4: Formula 4: -CH2-CH(CONH2)-CH2-CH(CONH-C(CH3)2-CH2-SO3H)-CH2-CH(COOCH2CH2OH)-CH2-C(CH3)(COOCH3)-CH2-CH(CONH2)-.

[0049] The obtained filtration loss reducer was verified by differential scanning calorimetry (DSC). Figure 1 As shown, the DSC curves reveal two distinct glass transition temperatures (Tg). The first Tg occurs in the 120–130°C range, corresponding to the high Tg core polymer (styrene-acrylate copolymer); the second Tg occurs in the 40–60°C range, corresponding to the low Tg shell polymer (modified acrylate copolymer). This directly confirms the successful construction of the core-shell structure.

[0050] Example 5: Verification of the dual-system universality of polymer latex filtration loss reducer Oil-based system (density 2.0): Take 225 mL of 0# diesel oil, add 7.5 g of organic bentonite, 7.5 g of primary emulsifier (talc fatty acid diethanolamide), 4.5 g of secondary emulsifier (talc fatty acid polyoxyethylene ester), 2.5 g of phosphate ester wetting agent, and 9 g of polymer latex. After aging at 240℃, the HTHP filtration loss is only 3.8 mL.

[0051] Water-based system (4% bentonite slurry): Take 400 mL of distilled water, add 16 g of bentonite for drilling fluid, let it stand for 24 hours, and then add 6 g of polymer latex.

[0052] Comparative sample: A commonly used high-temperature resistant polymer filtration loss reducer (Chevron Phillips Driscal D) was used instead of the polymer latex, and the rest was the same as the water-based system. The mixture was stirred at 11000 r / min for 20 min.

[0053] The water-based system, the control sample, and the 4% bentonite-based slurry were aged at 180°C for 16 hours. The changes in API filtration rate and apparent viscosity of each group were measured, and the results are shown in Table 2.

[0054] Table 2. Test results of drilling fluid before and after aging with different filtration loss reducers.

[0055] Table 2 shows that the API filtration loss of the water-based system was significantly reduced compared to the base slurry, with a reduction of 81%, while the apparent viscosity only increased slightly from 22 mPa·s to 23 mPa·s (an increase of 4.5%), perfectly achieving "reduced filtration loss without increased viscosity," thus resolving the long-standing technical contradiction of water-based drilling fluids. The comparative sample showed a 70% reduction in API filtration loss compared to the base slurry, also achieving a good filtration loss reduction effect, but its apparent viscosity increased sharply from 22 mPa·s to 65 mPa·s (an increase of 195.5%). This excessive increase in viscosity is detrimental to the rheological control of the drilling fluid.

[0056] Therefore, the polymer latex filtration loss reducer provided by the present invention can achieve excellent filtration loss reduction effects in both oil-based and water-based systems, and can realize the universality of a filtration loss reducer in both oil-based and water-based systems.

[0057] Example 6: Preparation and Performance Testing of Oil-Based Drilling Fluid System Oil-based drilling fluids were prepared according to the following system: 95 parts white oil, 3 parts main emulsifier (talc fatty acid diethanolamide), 1.5 parts co-emulsifier (talc fatty acid polyoxyethylene ester), 1 part phosphate ester wetting agent, 4 parts polymer latex filtration loss reducer, 3 parts organic clay, 2 parts cutting agent (organolithium saponite), 2.5 parts calcium oxide, and 5 parts 25% CaCl2 brine (oil-water ratio 95:5) are mixed and weighed to a density of 1.45 g / cm³ to obtain the oil-based drilling fluid.

[0058] The prepared oil-based drilling fluid (density adjustable range 1.2~2.2 g / cm³) was subjected to hot rolling aging at 240℃ for 7 days, and its core performance was tested. Its biotoxicity was determined according to GB 15193.3-2014 "National Food Safety Standard: Acute Oral Toxicity Test". The test results are shown in Table 3.

[0059] Table 3. Core performance of the oil-based drilling fluid of the present invention after high-temperature aging

[0060] The results show that the performance of the oil-based drilling fluid provided by this invention is significantly superior to that of existing high-performance oil-based drilling fluids. Specifically, the demulsification voltage averages 2150V and reaches a maximum of 2280V, indicating that the interfacial film formed by the homologous emulsifier combination provided by this invention is exceptionally stable at high temperatures. Rheological testing shows that before aging, AV = 40 mPa·s, PV = 27 mPa·s, YP = 26 lb / 100 sq.ft; after aging, AV = 38 mPa·s, PV = 26 mPa·s, YP = 24 lb / 100 sq.ft, with minimal changes before and after aging, indicating excellent temperature resistance of the synergistic network structure of the cutting agent and organic soil. Biotoxicity testing results show that the LC50 of the oil-based drilling fluid of this invention is greater than 100,000 mg / L, which, according to the acute toxicity classification standard of GA57-93 "Classification, Classification and Name Numbering of Highly Toxic Substances", belongs to the practically non-toxic level. Therefore, the oil-based drilling fluid provided by this invention exhibits significantly improved performance and is safe and non-toxic, demonstrating clear advantages.

[0061] Example 7: Comparison of Material Properties in Oil-Based Drilling Fluid Systems The oil-based drilling fluid prepared in Example 6 was used as system A, and a control drilling fluid was prepared as system B according to the following system: 95 parts white oil, 3 parts main emulsifier (EnvaMul® 1699), 1.5 parts co-emulsifier (EnvaMul® 1767), 1 part phosphate ester wetting agent, 4 parts high-temperature filtration loss reducer (asphalt), 3 parts organic clay, 2 parts cutting agent (polyamide), 2.5 parts calcium oxide, 5 parts 25% CaCl2 brine (oil-water ratio 95:5), weighted to a density of 1.45 g / cm³.

[0062] Both systems were subjected to hot rolling aging at 240℃. Rheology, demulsification voltage, and high-temperature, high-pressure filtration loss at 240℃ and 500psi were tested at 16h, 72h, and 168h, respectively, according to GB / T 16783.1 and GB / T16783.2, before and after rolling at 65℃. The test results are shown in Table 4.

[0063] Table 4. Performance changes of two oil-based drilling fluid systems during high-temperature aging.

[0064] The results show that the oil-based drilling fluid system provided by this invention is significantly superior to the currently commonly used high-performance imported material system in terms of demulsification voltage, high-temperature and high-pressure filtration loss control and viscosity stability. Moreover, it maintains good performance after long-term aging and fully meets the requirements of field operations.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An emulsifier composition for drilling fluids, characterized in that, It includes a primary emulsifier and a secondary emulsifier; wherein the primary emulsifier is tall oil fatty acid diethanolamide as shown in Formula 1: Formula 1: RCON(CH2CH2OH)2; The co-emulsifier is tall oil fatty acid polyoxyethylene ester as shown in Formula 2: Formula 2: RCOO(CH2CH2O) n H; In Formulas 1 and 2, R is a mixed alkyl chain of C18-C20 derived from tall oil, wherein the mixed alkyl chain includes hydrocarbon groups derived from oleic acid, linoleic acid, and rosin acid, and, n = 2~6 or 3~5 or 4; The weight ratio of the primary emulsifier to the secondary emulsifier is 1:1 to 4:1 or 1:1 to 2:

1.

2. The emulsifier combination according to claim 1, characterized in that, The primary emulsifier is prepared by the following method: Tall oil fatty acids were mixed with an excess of diethanolamine and heated to 170±5°C under a continuous nitrogen flow. The temperature was maintained and the mixture was stirred and refluxed for 3 hours. After the reaction was completed, the product was cooled to below 80°C to obtain the main emulsifier.

3. The emulsifier combination according to claim 1, characterized in that, The co-emulsifier is prepared by the following method: Tall oil fatty acids were mixed with an alkaline catalyst and heated to 115±5℃ under negative pressure for stirring and dehydration. The air in the reaction system was replaced with high-purity nitrogen, and the temperature was raised to 155±5℃. Ethylene oxide was slowly introduced while maintaining the reaction pressure at 0.25~0.35MPa. The temperature was maintained and the mixture was stirred for 1 hour to ripen the reaction. The weight ratio of ethylene oxide to tall oil fatty acids was n:

1. After the reaction, the temperature was lowered to 80~90℃, and the catalyst was neutralized with acid. The product was subjected to depressurized volatilization for 1 hour while maintaining the temperature and negative pressure. After filtration, a clear liquid phase was obtained, which is the co-emulsifier.

4. A fluid loss reducer for drilling fluids, characterized in that, The filtration loss reducer is a polymer latex with a core-shell structure, wherein: The core is a styrene-acrylate copolymer with a glass transition temperature of not less than 120°C; The shell is a modified acrylate copolymer containing amide and sulfonic acid groups; The weight ratio of the core to the shell is 2:1 to 2.5:1; And / or, the styrene-acrylate copolymer has a structure as shown in Formula 3: Formula 3: -CH2-CH(Ph)-CH2-C(CH3)(COOCH3)-CH2-CH(COO(CH2)3CH3)-CH2-CH(Ph-CH=CH-CH2-Ph)-CH2-CH(COOCH3)-; And / or, the modified acrylate copolymer has a structure as shown in Formula 4: Formula 4: -CH2-CH(CONH2)-CH2-CH(CONH-C(CH3)2-CH2-SO3H)-CH2-CH(COOCH2CH2OH)-CH2-C(CH3)(COOCH3)-CH2-CH(CONH2)-.

5. The filtration loss reducing agent according to claim 4, characterized in that, The core is mainly prepared from the following components in weight fractions: 50-60 parts styrene, 30-40 parts methyl methacrylate, 5-10 parts butyl acrylate, and 0.5-15 parts divinylbenzene; And / or, the shell is mainly prepared from the following components in parts by weight: Acrylamide 15-20 parts, 2-acrylamido-2-methylpropanesulfonic acid 10-15 parts, hydroxyethyl acrylate 10-15 parts and methyl methacrylate 5-10 parts.

6. The filtration loss reducing agent according to claim 5, characterized in that, The filtration loss reducer is prepared by the following method: Styrene, methyl methacrylate, butyl acrylate and divinylbenzene are mixed and continuously sheared and stirred at high temperature under the action of 3-5 parts of preemulsifier to form a core layer preemulsion; the core layer preemulsion is heated to 80-85°C under nitrogen, 0.5-1 parts of initiator are added, and the reaction is carried out for 2-3.5 hours; the temperature is maintained and the mixture is allowed to mature for another hour to obtain a core layer latex solution. Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, hydroxyethyl acrylate, and methyl methacrylate are mixed and continuously sheared and stirred at high temperature under the action of 3-5 parts of preemulsifier to form a shell preemulsion; the shell preemulsion and initiator are added to the core latex at 80-85°C and reacted for 1.5-2.5 hours; the temperature is maintained and the mixture is allowed to mature for another 1.5 hours to obtain a polymer latex with a core-shell structure. The polymer latex solution is cooled to below 40°C, the pH is adjusted to 7.0~8.0, filtered and dried to obtain the filtration loss reducer. And / or, the filtration loss reducing agent is prepared by the following method: Styrene, methyl methacrylate, butyl acrylate, and divinylbenzene are mixed and continuously sheared and stirred at high temperature for 30 minutes under the action of 3-5 parts of preemulsifier to form a core layer preemulsion. 5-20% of the core layer preemulsion is taken, heated to 80-85°C, and 0.1-0.4 parts of initiator are added. The reaction is carried out for 20-30 minutes to obtain a seed emulsion. While maintaining a constant temperature, the remaining core layer preemulsion and 0.15-0.4 parts of initiator are added to the seed emulsion under stirring. The addition time is 2-3 hours. After the addition is completed, the temperature is maintained and the mixture is allowed to mature for another hour to obtain a core layer latex. Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, hydroxyethyl acrylate, and methyl methacrylate are mixed and continuously sheared and stirred at high temperature for 30 minutes under the action of 3-5 parts of preemulsifier to form a shell preemulsion. The shell preemulsion and 0.15-0.4 parts of initiator are slowly added dropwise to the core latex at 80-85°C for 1.5-2.5 hours. After the addition is completed, the temperature is maintained and the mixture is allowed to mature for another 1.5 hours to obtain a polymer latex with a core-shell structure. The polymer latex solution is cooled to below 40°C, the pH is adjusted to 7.0~8.0, filtered and dried to obtain the filtration loss reducer.

7. The filtration loss reducing agent according to claim 6, characterized in that, The preemulsifier includes sodium dodecyl sulfate and octylphenol polyoxyethylene ether-10; the initiator is potassium persulfate.

8. A high-temperature resistant, high-performance oil-based drilling fluid, comprising two or more of an oil phase, a wetting agent, a cutting agent, organically modified bentonite, and a pH adjuster, characterized in that, It also includes the emulsifier combination according to any one of claims 1 to 3 and the filtration loss reducer according to any one of claims 4 to 7; And / or, the drilling fluid may further include an aqueous phase.

9. The drilling fluid according to claim 8, characterized in that, The product comprises the following components in parts by weight: 90-95 parts of oil phase, 3-6 parts of emulsifier combination according to any one of claims 1-3, 0.5-1.5 parts of wetting agent, 1-3 parts of shearing agent, 3-6 parts of filtration loss reducer according to any one of claims 4-7, 2-4 parts of organic modified bentonite, 2-3 parts of pH adjuster, and 5-10 parts of aqueous phase; And / or, the oil phase is selected from at least one of white oil, diesel oil, and Saraline 185V; And / or, the wetting agent is a phosphate ester wetting agent; And / or, the cutting agent is organically modified lithium saponite; And / or, the pH adjuster is calcium oxide; And / or, the aqueous phase is a 20-25 wt% aqueous solution of calcium chloride.

10. The application of the emulsifier combination of any one of claims 1 to 3 and the filtration loss reducer of any one of claims 4 to 7 in the preparation of high-temperature resistant drilling fluid, wherein the high temperature is not lower than 200°C, 220°C, or 240°C.

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