High-density ultralow-viscosity synthetic base drilling fluid

Abstract

The invention relates to the technical field of oil field chemistry of oil and gas drilling engineering, in particular to a high-density ultralow-viscosity synthetic base drilling fluid. The synthetic base drilling fluid is prepared from the following raw materials in parts by mass: a component a and a component b, the component a is prepared from the following components in parts by volume: 80 to 90 parts of oil phase and 10 to 20 parts of water phase; and the component b is composed of an emulsifier, a viscosity-reducing and shear-improving agent, an alkalinity regulator, organic soil, a filtrate reducer, a lubricant and barite. When the density of the synthetic base drilling fluid reaches 2.4 g / cm < 3 >, the plastic viscosity of the synthetic base drilling fluid can still be controlled within 40 mPa.s, the synthetic base drilling fluid shows excellent fluidity, and excellent borehole cleaning, shale inhibition, plugging and friction and resistance reduction performance are considered.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas drilling engineering and oilfield chemistry, and particularly to a high-density and ultra-low-viscosity synthetic-based drilling fluid. Background Art

[0002] With the increasingly in-depth exploration and development of unconventional oil and gas resources (such as shale gas, tight gas, deep oil and gas, etc.), drilling engineering faces many technical challenges such as increased well depth, complex wellbore trajectories, high formation temperatures, high-pressure conditions, and poor formation stability, which put forward higher requirements for the comprehensive performance of the drilling fluid system. Modern drilling fluids not only need to have excellent rheological properties, inhibition properties, cuttings carrying capacity, wellbore stability, and lubrication performance, but also need to take into account multiple comprehensive properties such as environmental protection.

[0003] Due to its excellent lubrication performance, inhibition performance, electrical stability, wellbore stability, and low environmental toxicity, synthetic-based drilling fluids have gradually become an important non-aqueous system to replace traditional oil-based drilling fluids. However, when the density of the drilling fluid is increased to more than 2.2 g / cm³, the viscosity of the existing synthetic-based drilling fluids increases significantly, resulting in a series of technical problems: such as an increase in the circulation resistance of the drilling fluid, a significant increase in pump pressure and energy consumption; a decrease in the cuttings return efficiency, making it difficult to clean the wellbore; weighting agents are prone to settling, resulting in unstable density and increasing the well control risk; in areas where lost circulation is sensitive or the formation pressure-bearing capacity is low, high-viscosity systems are prone to cause serious lost circulation and wellbore instability.

[0004] Therefore, to effectively address the above problems, there is an urgent need to develop an innovative synthetic-based drilling fluid system with both high density and ultra-low viscosity properties to ensure the efficiency and safety of drilling operations in complex well sections, especially the applicability in special working conditions such as high temperature and high pressure, high lost circulation risk, and long horizontal sections. Summary of the Invention

[0005] In view of this, the present invention provides a high-density and ultra-low-viscosity synthetic-based drilling fluid.

[0006] To achieve the above object, the present invention provides the following solutions: The present invention provides a synthetic-based drilling fluid, comprising component a and component b; By volume fraction, the component a is composed of 80 - 90 parts of an oil phase and 10 - 20 parts of a water phase; The component b is composed of an emulsifier, a viscosity reducer and gel strength enhancer, an alkalinity regulator, organophilic clay, a filtration reducer, a lubricant, and barite; In every 100 mL of component a, there are 6.0 - 8.0 g of emulsifier, 0.5 - 1.5 g of viscosity reducer and thixotropic agent, 2.0 - 3.0 g of alkalinity regulator, 1.0 - 2.0 g of organophilic clay, 3.0 - 4.0 g of filtrate reducer, 0.5 - 1.5 g of lubricant and barite; among them, the mass of barite is not limited, and it is added until the density of the synthetic-based drilling fluid reaches 2.0 - 2.4 g / cm 3 up to.

[0007] In a preferred embodiment of the present invention, by volume, the oil phase is composed of 65 - 75 parts of linear α-olefin, 10 - 15 parts of low molecular fatty acid ester, 3 - 5 parts of low molecular synthetic ether and 7 - 20 parts of co-solvent; The linear α-olefin is at least one of C10 α-olefin, C11 α-olefin, and C12 α-olefin; the linear α-olefin is the main body of the continuous phase of the synthetic-based drilling fluid, with low viscosity, good lubricity, and easy miscibility with other organic compounds; its non-polar structure can provide excellent high-temperature stability and ensure that the system viscosity remains low under higher density conditions.

[0008] The low molecular fatty acid ester is at least one of ethyl acetate, methyl propionate, and methyl valerate; the low molecular fatty acid ester can assist in reducing the overall viscosity, enhancing the oil phase dispersion ability, and improving environmental protection; due to the certain polarity of the ester group, it can partially dissolve or emulsify polar components and form a stable mixed system with α-olefin, reducing the surface tension.

[0009] The low molecular synthetic ether is at least one of butyl ether, isopropyl ether, and methyl tert-butyl ether; the viscosity and fluidity are further optimized through the low molecular synthetic ether, and it has a certain affinity for both the hydrocarbon phase and the polar phase, assisting in maintaining the system compatibility and stability.

[0010] The co-solvent is at least one of trimethylpentane, 2,2,4-trimethylpentane, and 3,3-dimethylnonane. The co-solvent can adjust the viscosity and polarity of the oil phase within a wide temperature range, avoiding the layering or precipitation of oil phase components; its branched-chain structure can reduce the crystallization tendency and ensure that different oil phase components remain single-phase and homogeneous under high temperature, high pressure, and long-term storage conditions.

[0011] In a preferred embodiment of the present invention, the aqueous phase is an aqueous calcium chloride solution with a mass fraction of 25% - 35%. Calcium salts have strong inhibition, can inhibit the hydration swelling of formation clay, and protect the wellbore stability; it plays the role of the internal phase in the emulsion system and promotes the formation of a stable W / O emulsion.

[0012] In a preferred embodiment of the present invention, the preparation method of the emulsifier includes the following steps: Add diamine to erucic acid and carry out reaction 1 to obtain product A; Add erucic acid, tetralin, and an initiator to rosin in a molten state and carry out Reaction 2 to obtain Product B; Add monoethanolamine to polyisobutylene succinic anhydride and carry out Reaction 3 to obtain Product C; Mix the above-mentioned Product A, Product B, and Product C evenly to obtain the emulsifier.

[0013] In a preferred embodiment of the present invention, when preparing Product A, the mass ratio of erucic acid to diamine is 160-200:20-25; the specific process of Reaction 1 is to first stir and react at 120-140 °C for 10-30 min, and then heat up to 160-180 °C and keep warm for 4-6 hours; When preparing Product B, the mass ratio of rosin to erucic acid and tetralin is 90-120:60-80:45-60; the specific process of Reaction 2 is to react at 180-200 °C for 2-3 hours; the initiator is diisopropylbenzene peroxide; When preparing Product C, the mass ratio of polyisobutylene succinic anhydride to monoethanolamine is 80-100:10-12; the specific process of Reaction 3 is to react at 140-160 °C for 18-24 h; In some specific embodiments of the present invention, the preparation method of the emulsifier includes the following steps: Step 1: First, preheat 160-200 parts by mass of erucic acid to 100-120 °C, and remove oxygen, trace moisture, and low-boiling impurities by passing nitrogen under stirring; then heat up to 120-140 °C, slowly dropwise add 20-25 parts by mass of diamine, stir for 10-30 min, continue to heat up to 160-180 °C, and maintain for 4-6 hours, during which the generated water is removed in real time through a water separator; after the reaction is completed, cool to 90 °C, filter to remove insoluble substances, and obtain Product A.

[0014] Step 2: First, heat 90-120 parts by mass of rosin to 130-150 °C to make it molten, and stir for 10-30 min to facilitate the escape of bubbles and the volatilization of trace moisture; at the same time, preheat 60-80 parts by mass of erucic acid to 100-120 °C and carry out nitrogen purging to remove residual moisture or low-boiling impurities; then, while stirring, slowly add erucic acid and 45-60 parts by mass of the solvent tetralin to the molten rosin, and then add 1%-1.5% of diisopropylbenzene peroxide based on the total mass of unsaturated monomers as the initiator. Under nitrogen protection, continue to heat up to 180-200 °C, and control the reaction time to 2-3 hours; after the reaction is completed, cool down to 130-150 °C, and remove the solvent by vacuum distillation to obtain Product B.

[0015] Step 3: First, preheat 80 - 100 parts by mass of polyisobutenyl succinic anhydride at 100 - 120 °C and stir. Subsequently, slowly dropwise add 10 - 12 parts by mass of monoethanolamine, raise the temperature to 140 - 160 °C, and continuously stir for 18 - 24 h. During this period, remove the generated water in real time through a water separator; after the reaction ends, cool to 80 °C, filter to remove insolubles, and obtain product C.

[0016] Step 4: The final product obtained by uniformly mixing product A, product B, and product C is the ternary composite emulsifier.

[0017] In a preferred embodiment of the present invention, the diamine is one of ethylenediamine, propylenediamine, and butylenediamine; The mass ratio of product A, product B, and product C is 40 - 50∶20 - 30∶20 - 40. Product A can firmly adsorb on the oil - water interface under high - temperature / high - salt environments, form a relatively low interfacial tension and inhibit the agglomeration of the water phase, strengthening the emulsification stability against temperature and salt. Product B contains a rosin ring structure and a fatty acid long chain, and improves the molecular weight and degree of branching through free - radical copolymerization, forming a relatively hard and flexible film structure at the oil - water interface of the W / O emulsion, enhancing shear resistance and impact resistance, and at the same time playing a role in plugging and inhibiting fluid loss on the wellbore surface. Product C, relying on the polyisobutene long chain and amino function, achieves excellent wetting and dispersion of solid weighting materials, reduces the agglomeration tendency under high - density conditions, and thus maintains a relatively low plastic viscosity. Overall, the ternary composite emulsifier plays a complementary effect in aspects such as interfacial adsorption, dispersion modification, and network structure regulation, effectively preventing the demulsification of the emulsion and significantly improving the suspension stability and low - viscosity rheological properties of barite in the synthetic - based environment.

[0018] In a preferred embodiment of the present invention, the preparation method of the viscosity - reducing and yield - stress - increasing agent includes the following steps: Heat 120 - 150 parts by mass of erucic acid to 110 - 130 °C, and purge water and low - boiling impurities with nitrogen; then, raise the temperature to 240 - 260 °C, add 3 - 5 parts by mass of activated clay, and stir and react for 4 - 6 hours; after the reaction ends, cool to 120 - 140 °C, add 15 - 25 parts by mass of diethanolamine under stirring, and raise the temperature to 160 - 180 °C, react for 2 - 4 hours, and filter after cooling to obtain the viscosity - reducing and yield - stress - increasing agent.

[0019] The viscosity - reducing and yield - stress - increasing agent contains long - chain fatty acid amides and various polar groups. The former has excellent "dispersion - swelling" performance in the oil phase, can break or reduce the agglomeration between particles in the synthetic - based drilling fluid, improve the sliding between particles, and thus reduce the plastic viscosity; the latter can form a weak flocculation network in the low - shear zone, increase the strength of the colloidal structure, raise the yield stress, and improve the carrying capacity of cuttings or weighting agents.

[0020] In a preferred embodiment of the present invention, by mass parts, the alkalinity regulator is composed of 60 - 80 parts of calcium oxide and 20 - 40 parts of magnesium oxide. Alkaline oxides form hydroxides after contacting with water or absorbing acidic components, effectively regulating the pH value, maintaining the alkaline environment of the system, stabilizing the colloid structure and emulsion system, and inhibiting the intrusion of acidic gases.

[0021] In a preferred embodiment of the present invention, by mass parts, the organoclay consists of 20 - 30 parts of BENTONE ® 38, 20 - 30 parts of BENTONE ® 42 and 40 - 60 parts of BENTONE ® 150. The BENTONE ® 38, BENTONE ® 42, BENTONE ® 150 is sourced from Elementis; organically modified bentonite has a lamellar structure and polar groups, which, acting together with emulsifiers and viscosity reducers / thixotropic agents, can form a stable network structure, providing wellbore suspension and shear thickening characteristics, maintaining the suspension of drill cuttings at low shear rates; and not significantly increasing the viscosity at high shear rates.

[0022] In a preferred embodiment of the present invention, by mass parts, the filtrate reducer is composed of 30 - 40 parts of organic lignite, 30 - 40 parts of humic acid amide, and 20 - 40 parts of polymethyl methacrylate microspheres. Organic lignite / humic acid amide can form a flexible and dense film on the wellbore wall, and polymethyl methacrylate microspheres improve the quality of the filter cake through particle embedding, synergistically reducing pore channels and reducing the filtration of the liquid phase into the formation.

[0023] In a preferred embodiment of the present invention, by mass parts, the lubricant is composed of 10 - 20 parts of boron nitride, 30 - 40 parts of graphite, 20 - 30 parts of polyetheretherketone micropowder, and 20 - 30 parts of polytetrafluoroethylene micropowder. In high-density synthetic-based drilling fluids, the layered lattices of boron nitride and graphite can form a strong solid lubricating film on the wellbore wall and the surface of the drill string, withstanding high temperatures and pressures and significantly reducing metal-metal contact; polyetheretherketone micropowder has excellent wear resistance and toughness, can disperse impact loads and reduce micro-etching; polytetrafluoroethylene provides a continuous sliding layer with an extremely low coefficient of friction, significantly inhibiting torque and stick-slip vibration. The four, in synergy with low-viscosity synthetic-based oil, fill the voids and dry areas in the high-density particle environment, prevent the destruction of the oil film and strengthen lubrication protection, ensuring that the contact interface between the drill string and the wellbore wall always maintains a low-friction and wear-resistant working state. Through the multiple lubrication mechanism of "solid-liquid coexistence", this compound system can still achieve excellent friction and wear reduction performance under high contents of barite and complex well conditions.

[0024] The present invention does not particularly limit the preparation method of the synthetic-based drilling fluid, and any preparation method of the synthetic-based drilling fluid well-known to those skilled in the art can be adopted.

[0025] Focusing on the two core requirements of high density and ultra-low viscosity, the present invention has carried out collaborative design and innovation in each key link of the synthetic-based drilling fluid. First, the main oil phase is compounded with multiple components such as linear α-olefins, low molecular weight fatty acid esters, low molecular weight synthetic ethers, and isoparaffins to obtain low viscosity and stable compatibility in high-temperature and high-pressure environments, significantly reducing the viscosity soaring caused by the large introduction of weighting agents. Secondly, based on the internal phase of calcium chloride aqueous solution, a ternary composite emulsifier is combined: the erucic acid-diamine amide product (Product A) has strong anti-shear and anti-demulsification capabilities for both brine and high temperature; the erucic acid-abietic acid copolymer (Product B) forms a tough viscoelastic film on the wellbore and particle surfaces, inhibiting filtration loss and enhancing wellbore stability; the polyisobutylene succinic anhydride-amine derivative (Product C) has good wetting and dispersion properties for solid-phase particles such as barite, ensuring low viscosity and uniform dispersion under high solid content conditions. To balance the flow and carrying functions at high density, a viscosity reducer and yield point enhancer are also introduced, which can not only change the microscopic colloid structure, reduce the plastic viscosity, but also form a weak flocculation network to increase the yield value, which is crucial for preventing cuttings and weighting particles from settling. At the same time, the solid lubricant, with its layered or polymer characteristics, constructs a persistent "solid-liquid synergistic lubricating film" on the downhole shear contact surface and the rock surface, not only reducing friction and torque, but also effectively slowing down the abrasion under the background of high solid content. Through the synergistic effect of this multi-component system, the present invention still maintains excellent rheological properties and stable suspension in the high-density range of 2.0 - 2.4 g / cm³, significantly reducing the risks of lost circulation and wellbore collapse; and the synthetic-based oil (i.e., the oil phase) used has low toxicity and biodegradability, meeting the green requirements for environmentally sensitive sea areas and unconventional oil and gas development. Overall, it provides a comprehensive solution in aspects such as reducing viscosity energy consumption, strengthening wellbore stability, reducing friction and wear, and ensuring environmental protection and safety for complex working conditions such as deep wells, ultra-deep wells, high-risk lost circulation zones, and long horizontal sections.

[0026] The present invention discloses the following technical effects: The synthetic-based drilling fluid of the present invention can still control the plastic viscosity within 40 mPa·s when the density reaches 2.4 g / cm 3 ³, demonstrating excellent fluidity, and at the same time taking into account excellent hole cleaning, shale inhibition, plugging, and friction and drag reduction performances, providing a safe, efficient, environmentally friendly drilling fluid solution for harsh working conditions such as deep wells, ultra-deep wells, and complex wellbore trajectories. Specific Embodiments

[0027] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0030] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are merely exemplary.

[0031] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0032] The technical solutions described in the present invention are all conventional solutions in the art unless otherwise specified. The reagents or raw materials used, unless otherwise specified, are all purchased from commercial channels or have been publicly disclosed.

[0033] The organic lignite used in the embodiments of the present invention is from Becken Energy (Chengdu) Co., Ltd.

[0034] The technical solutions provided by the present invention will be described in detail below in conjunction with the embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0035] Example 1: This example provides a high-density ultra-low viscosity synthetic-based drilling fluid, which consists of component a and component b; By volume, component a consists of 80 parts of oil phase and 20 parts of water phase; Component b consists of an emulsifier, a viscosity reducer and gel strength enhancer, an alkalinity regulator, organoclay, a filtration loss reducer, a lubricant, and barite. The addition amount of component b in component a is specifically as follows: In every 100 mL of component a, there are 6.0 g of emulsifier, 0.5 g of viscosity reducer and gel strength enhancer, 2.0 g of alkalinity regulator, 1.0 g of organoclay, 3.0 g of filtration loss reducer, and 0.5 g of lubricant; the mass of barite is not limited, and it is weighted until the required density is reached.

[0036] Among them: By volume fraction, the oil phase consists of 65 parts of linear α-olefin (C10 α-olefin), 10 parts of low molecular weight fatty acid ester (ethyl acetate), 5 parts of low molecular weight synthetic ether (butyl ether), and 20 parts of co-solvent (trimethylpentane). The aqueous phase is a calcium chloride aqueous solution with a mass fraction of 25%.

[0037] The emulsifier is a ternary composite emulsifier, and the preparation method of the emulsifier is as follows: Step 1: Preheat 160 parts by mass of erucic acid to 100 °C, and purge with nitrogen to remove oxygen, trace moisture, and low-boiling impurities under stirring; then raise the temperature to 120 °C, slowly dropwise add 20 parts by mass of ethylenediamine, stir for 10 min, then continue to raise the temperature to 160 °C and maintain for 4 hours, during which the generated water is removed in real time through a water separator; after the reaction ends, cool to 90 °C, and filter to remove insoluble substances to obtain product A.

[0038] Step 2: Heat 90 parts by mass of rosin to 130 °C to melt it, and stir for 10 min to facilitate the escape of bubbles and the volatilization of trace moisture; at the same time, preheat 60 parts by mass of erucic acid to 100 °C and conduct nitrogen purging to remove residual moisture or low-boiling impurities; then, while stirring, slowly add erucic acid and 45 parts by mass of the solvent tetralin to the molten rosin, and then add 1% by mass of dicumyl peroxide based on the total unsaturated monomer (rosin + erucic acid) as an initiator. Under nitrogen protection, continue to raise the temperature to 180 °C and control the reaction time to 2 hours; after the reaction ends, cool to 130 °C, and remove the solvent by vacuum distillation to obtain product B.

[0039] Step 3: First, preheat 80 parts by mass of polyisobutylene succinic anhydride at 100 °C and stir, then slowly dropwise add 10 parts by mass of monoethanolamine, raise the temperature to 140 °C, and continuously stir for 18 h, during which the generated water is removed in real time through a water separator; after the reaction ends, cool to 80 °C, and filter to remove insoluble substances to obtain product C.

[0040] Step 4: By mass fraction, mix 40 parts of product A, 20 parts of product B, and 40 parts of product C evenly, and the final product obtained is the ternary composite emulsifier.

[0041] The preparation method of the viscosity reducer and gel strength enhancer is as follows: First, heat 120 parts by mass of erucic acid to 110 °C, and purge water and low-boiling impurities with nitrogen; then, raise the temperature to 240 °C, add 3 parts by mass of activated clay as a catalyst, and stir and react for 4 hours; after the reaction ends, cool down to 120 °C, slowly add 15 parts by mass of diethanolamine under stirring, raise the temperature to 160 °C, react for 2 hours, cool to 60 °C, and the filtered product is the viscosity reducer and gel strength enhancer.

[0042] By mass, the alkalinity regulator consists of 60 parts of calcium oxide and 40 parts of magnesium oxide.

[0043] By mass, the organoclay consists of 20 parts of BENTONE ® 38, 20 parts of BENTONE ® 42 and 60 parts of BENTONE ® 150.

[0044] By mass, the filtration reducer consists of 30 parts of organic lignite, 30 parts of humic acid amide, and 40 parts of polymethyl methacrylate microspheres.

[0045] By mass, the lubricant consists of 10 parts of boron nitride, 30 parts of graphite, 30 parts of polyether ether ketone micropowder, and 30 parts of polytetrafluoroethylene micropowder.

[0046] In this example, the density of the drilling fluid is 2.0 g / cm 3 , and the hot rolling temperature of the drilling fluid is 120 °C.

[0047] Example 2: This example provides a high-density and ultra-low-viscosity synthetic-based drilling fluid, which consists of component a and component b; By volume, component a consists of 90 parts of the oil phase and 10 parts of the water phase; Component b consists of an emulsifier, a viscosity reducer and gel strength enhancer, an alkalinity regulator, an organoclay, a filtration reducer, a lubricant, and barite; The addition amount of component b in component a is as follows: In every 100 mL of component a, there are 8.0 g of emulsifier, 1.5 g of viscosity reducer and gel strength enhancer, 3.0 g of alkalinity regulator, 2.0 g of organoclay, 4.0 g of filtration reducer, and 1.5 g of lubricant; the mass of barite is not limited and is weighted to the required density.

[0048] Among them: By volume, the oil phase consists of 75 parts of linear α-olefin (C11 α-olefin), 15 parts of low molecular fatty acid ester (methyl propionate), 3 parts of low molecular synthetic ether (isopropyl ether), and 7 parts of co-solvent (2,2,4-trimethylpentane); The aqueous phase is an aqueous calcium chloride solution with a mass fraction of 35%.

[0049] The emulsifier is a ternary composite emulsifier, and the preparation method of the emulsifier is as follows: Step 1: First, preheat 200 parts by mass of erucic acid to 120 °C, and pass nitrogen to remove oxygen, trace moisture and low-boiling impurities under stirring; then raise the temperature to 140 °C, slowly dropwise add 25 parts by mass of propylenediamine, stir for 30 min, continue to raise the temperature to 180 °C, and maintain for 6 hours. During this period, remove the generated water in real time through a water separator; after the reaction is completed, cool to 90 °C, filter to remove insoluble substances to obtain product A.

[0050] Step 2: First, heat 120 parts by mass of rosin to 150 °C to melt it, and stir for 30 min to facilitate the escape of bubbles and the volatilization of trace moisture; at the same time, preheat 80 parts by mass of erucic acid to 120 °C and conduct nitrogen purging to remove residual moisture or low-boiling impurities; then, while stirring, slowly add erucic acid and 60 parts by mass of the solvent tetralin to the molten rosin, and then add 1.5% of diisopropylbenzene peroxide based on the total mass of unsaturated monomers as an initiator. Under nitrogen protection, continue to raise the temperature to 200 °C, and control the reaction time to 3 hours; after the reaction is completed, cool to 150 °C, and remove the solvent by vacuum distillation to obtain product B.

[0051] Step 3: First, preheat 100 parts by mass of polyisobutylene succinic anhydride at 120 °C and stir, then slowly dropwise add 12 parts by mass of monoethanolamine, raise the temperature to 160 °C, and continuously stir for 24 h. During this period, remove the generated water in real time through a water separator; after the reaction is completed, cool to 80 °C, filter to remove insoluble substances to obtain product C.

[0052] Step 4: The final product obtained by uniformly mixing 50 parts of product A, 30 parts of product B, and 20 parts of product C by mass is the ternary composite emulsifier.

[0053] The preparation method of the viscosity reducer and thixotropic agent is as follows: First, heat 150 parts by mass of erucic acid to 130 °C, and conduct nitrogen purging to remove water and low-boiling impurities; then, raise the temperature to 260 °C, add 5 parts by mass of activated clay as a catalyst, and stir and react for 6 hours; after the reaction is completed, cool to 140 °C, slowly add 25 parts by mass of diethanolamine under stirring, and raise the temperature to 180 °C, react for 4 hours, cool to 60 °C, and the filtered product is the viscosity reducer and thixotropic agent.

[0054] By mass, the alkalinity regulator is composed of 80 parts of calcium oxide and 20 parts of magnesium oxide.

[0055] By mass, the organoclay consists of 30 parts of BENTONE ®38, 30 parts of BENTONE ® 42 and 40 parts of BENTONE ® It consists of 150.

[0056] By mass fraction, the filtration reducer consists of 40 parts of organic lignite, 40 parts of humic acid amide and 20 parts of polymethyl methacrylate microspheres.

[0057] By mass fraction, the lubricant consists of 20 parts of boron nitride, 40 parts of graphite, 20 parts of polyetheretherketone fine powder and 20 parts of polytetrafluoroethylene fine powder.

[0058] In this embodiment, the density of the drilling fluid is 2.2 g / cm 3 , and the thermal rolling temperature of the drilling fluid is 140 °C.

[0059] Example 3: This embodiment provides a high-density ultra-low-viscosity synthetic-based drilling fluid, which consists of component a and component b; By volume fraction, component a consists of 85 parts of oil phase and 15 parts of water phase; Component b consists of an emulsifier, a viscosity reducer and thixotropic agent, an alkalinity regulator, organophilic clay, a filtration reducer, a lubricant and barite; The addition amount of component b in component a is specifically as follows: In every 100 mL of component a, there are 7.0 g of emulsifier, 1.0 g of viscosity reducer and thixotropic agent, 2.5 g of alkalinity regulator, 1.5 g of organophilic clay, 3.5 g of filtration reducer, 1.0 g of lubricant; the mass of barite is not limited, and it is weighted to the required density.

[0060] Among them: By volume fraction, the oil phase consists of 70 parts of linear α-olefin (C12 α-olefin), 12.5 parts of low molecular weight fatty acid ester (methyl valerate), 4 parts of low molecular weight synthetic ether (methyl tert-butyl ether) and 13.5 parts of co-solvent (3,3-dimethylnonane); The water phase is an aqueous calcium chloride solution with a mass fraction of 30%.

[0061] The emulsifier is a ternary composite emulsifier, and the preparation method of the emulsifier is as follows: Step 1: First, preheat 180 parts by mass of erucic acid to 110 °C, and purge oxygen, trace moisture and low-boiling impurities by passing nitrogen under stirring conditions; then raise the temperature to 130 °C, slowly drop 22.5 parts by mass of butanediamine, stir for 20 min, then continue to raise the temperature to 170 °C and maintain for 5 hours, and during this period, remove the generated water in real time through a water separator; after the reaction ends, cool to 90 °C and filter to remove insoluble substances to obtain product A.

[0062] Step 2: First, heat 110 parts by mass of rosin to 140 °C to melt it, and stir for 20 min to facilitate the escape of bubbles and the volatilization of trace moisture; meanwhile, preheat 70 parts by mass of erucic acid to 110 °C and conduct nitrogen purging to remove residual moisture or low-boiling impurities; then, while stirring, slowly add erucic acid and 52.5 parts by mass of the solvent tetralin to the molten rosin, and subsequently add 1.25% of diisopropylbenzene peroxide based on the total mass of unsaturated monomers as an initiator. Under nitrogen protection, continue to heat up to 190 °C and control the reaction time to 2.5 hours; after the reaction is completed, cool down to 140 °C, and remove the solvent by vacuum distillation to obtain product B.

[0063] Step 3: First, preheat 90 parts by mass of polyisobutylene succinic anhydride at 110 °C and stir, then slowly dropwise add 11 parts by mass of monoethanolamine, heat up to 150 °C, and continuously stir for 21 h. During this period, remove the generated water in real time through a water separator; after the reaction is completed, cool down to 80 °C, filter to remove insoluble substances to obtain product C.

[0064] Step 4: By mass, mix 45 parts of product A, 25 parts of product B, and 30 parts of product C evenly, and the resulting final product is the ternary composite emulsifier.

[0065] The preparation method of the viscosity-reducing and gel-strengthening agent is as follows: First, heat 135 parts by mass of erucic acid to 120 °C, and conduct nitrogen purging to remove water and low-boiling impurities; then, heat up to 250 °C, add 4 parts by mass of activated clay as a catalyst, and stir and react for 5 hours; after the reaction is completed, cool down to 130 °C, slowly add 20 parts by mass of diethanolamine while stirring, and heat up to 170 °C, react for 3 hours, cool down to 60 °C, and the filtered product is the viscosity-reducing and gel-strengthening agent.

[0066] By mass, the alkalinity regulator consists of 70 parts of calcium oxide and 30 parts of magnesium oxide.

[0067] By mass, the organoclay consists of 25 parts of BENTONE ® 38, 25 parts of BENTONE ® 42 and 50 parts of BENTONE ® 150.

[0068] By mass, the filtrate reducer consists of 35 parts of organic lignite, 35 parts of humic acid amide, and 30 parts of polymethyl methacrylate microspheres.

[0069] By mass, the lubricant consists of 15 parts of boron nitride, 35 parts of graphite, 25 parts of polyetheretherketone micropowder, and 25 parts of polytetrafluoroethylene micropowder.

[0070] In this example, the density of the drilling fluid is 2.3 g / cm 3, the thermal rolling temperature of the drilling fluid is 160 °C.

[0071] Example 4: This example provides a high-density ultra-low-viscosity synthetic-based drilling fluid, which consists of component a and component b; By volume, component a consists of 88 parts of oil phase and 12 parts of water phase; Component b consists of an emulsifier, a viscosity reducer and gel strength enhancer, an alkalinity regulator, organophilic clay, a filtration reducer, a lubricant and barite; The addition amounts of component b in component a are specifically as follows: In every 100 mL of component a, there are 8 g of emulsifier, 0.8 g of viscosity reducer and gel strength enhancer, 2.4 g of alkalinity regulator, 1.5 g of organophilic clay, 3.0 g of filtration reducer, 1.0 g of lubricant; the mass of barite is not limited, and it is weighted to the required density.

[0072] Among them: By volume, the oil phase consists of 70 parts of linear α-olefin, 10 parts of low molecular weight fatty acid ester, 5 parts of low molecular weight synthetic ether and 15 parts of co-solvent; among them, the linear α-olefin is a mixture of C10 α-olefin, C11 α-olefin and C12 α-olefin with a mass ratio of 40:40:20; the low molecular weight fatty acid ester is a mixture of ethyl acetate, methyl propionate and methyl valerate with a mass ratio of 30:40:30; the low molecular weight synthetic ether is a mixture of butyl ether, isopropyl ether and methyl tert-butyl ether with a mass ratio of 35:40:25; the co-solvent is a mixture of trimethylpentane, 2,2,4-trimethylpentane and 3,3-dimethylnonane with a mass ratio of 25:45:30.

[0073] The water phase is an aqueous calcium chloride solution with a mass fraction of 26%.

[0074] The emulsifier is a ternary composite emulsifier, and the preparation method of the emulsifier is as follows: Step 1: First, preheat 170 parts by mass of erucic acid to 105 °C, and remove oxygen, trace moisture and low-boiling impurities by passing nitrogen under stirring conditions; then raise the temperature to 125 °C, slowly dropwise add 22 parts by mass of propylenediamine, stir for 25 min, continue to raise the temperature to 165 °C, and maintain for 5.5 hours, during which the generated water is removed in real time through a water separator; after the reaction is completed, cool to 90 °C, and filter to remove insoluble substances to obtain product A.

[0075] Step 2: First, heat 100 parts by mass of rosin to 145 °C to melt it, and stir for 18 min to facilitate the escape of bubbles and the volatilization of trace moisture. At the same time, preheat 65 parts by mass of erucic acid to 108 °C and conduct nitrogen purging to remove residual moisture or low-boiling impurities. Then, while the rosin is in a molten state, slowly add erucic acid and 50 parts by mass of the solvent tetralin with stirring, and then add 1.1% of diisopropylbenzene peroxide based on the total mass of unsaturated monomers as an initiator. Under nitrogen protection, continue to heat up to 185 °C, and control the reaction time to be 2.2 hours. After the reaction is completed, cool down to 135 °C, and remove the solvent by vacuum distillation to obtain Product B.

[0076] Step 3: First, preheat 85 parts by mass of polyisobutylene succinic anhydride at 110 °C and stir, then slowly dropwise add 11 parts by mass of monoethanolamine, heat up to 155 °C, and continuously stir for 22 h. During this period, remove the generated water in real time through a water separator. After the reaction is completed, cool down to 80 °C, filter to remove insoluble substances to obtain Product C.

[0077] Step 4: By mass, mix 50 parts of Product A, 20 parts of Product B, and 30 parts of Product C evenly, and the resulting final product is the ternary composite emulsifier.

[0078] The preparation method of the viscosity reducing and rheology increasing agent is as follows: First, heat 130 parts by mass of erucic acid to 115 °C, and conduct nitrogen purging to remove water and low-boiling impurities. Then, heat up to 245 °C, add 4 parts by mass of activated clay as a catalyst, and stir and react for 4.5 hours. After the reaction is completed, cool down to 126 °C, slowly add 18 parts by mass of diethanolamine with stirring, and heat up to 175 °C, react for 3 hours, cool down to 60 °C, and the filtered product is the viscosity reducing and rheology increasing agent.

[0079] By mass, the alkalinity regulator consists of 75 parts of calcium oxide and 25 parts of magnesium oxide.

[0080] By mass, the organoclay consists of 25 parts of BENTONE ® 38, 30 parts of BENTONE ® 42 and 45 parts of BENTONE ® 150.

[0081] By mass, the filtrate reducer consists of 40 parts of organic lignite, 40 parts of humic acid amide, and 20 parts of polymethyl methacrylate microspheres.

[0082] By mass, the lubricant consists of 20 parts of boron nitride, 30 parts of graphite, 20 parts of polyetheretherketone micropowder, and 30 parts of polytetrafluoroethylene micropowder.

[0083] In this example, the density of the drilling fluid is 2.4 g / cm 3, the thermal rolling temperature of the drilling fluid is 180 °C.

[0084] The drilling fluid prepared in the above embodiment was tested for rheological properties, electrical stability properties, plugging and filtration reduction properties, inhibition properties, and lubrication properties with reference to GB / T 29170-2012 "Petroleum and natural gas industries - Drilling fluids - Laboratory testing", GBT 16783.2-2012 "Petroleum and natural gas industries - Drilling fluids - Field testing - Part 2: Oil-based drilling fluids", and SY / T 6094-1994 "Evaluation procedure for lubricants used in drilling fluids". The results are shown in Tables 1, 2, and 3.

[0085] Table 1 Rheological and electrical stability properties of drilling fluid , Table 2 Plugging and filtration reduction properties of drilling fluid , Table 3 Inhibition and lubrication properties of drilling fluid , It can be seen from Tables 1-3 that in the high-density range of 2.0~2.4 g / cm 3 , the synthetic-based drilling fluid of the present invention exhibits excellent temperature resistance characteristics and fluidity. The plastic viscosity is stably lower than 40 mPa·s, achieving the balance between high density and ultra-low viscosity; at the same time, the dynamic shear force remains above 6 Pa, which can effectively suspend the weighting agent and carry cuttings. The demulsification voltage of the formed water-in-oil emulsion exceeds 1200 V; the plugging and filtration reduction properties are good, and the HTHP, sand-packed, and PPT filtration losses do not exceed 4.0 mL, and the mud cake-based oil filtration loss is extremely low, showing high density and low permeability, and effectively plugging the formation. In the test of the tolerance limit of inferior solids, the increase in apparent viscosity after 10% contamination with sodium bentonite does not exceed 10%, indicating its strong anti-pollution ability, and the shale rolling recovery rate is higher than 99%, and the clay linear expansion rate is 0, indicating significant inhibition effect. In the friction reduction test, both the extreme pressure friction coefficient and the four-ball friction coefficient are lower than 0.05, and the wear scar diameter does not exceed 0.05 mm 2 , demonstrating excellent lubrication and protection performance, meeting the construction requirements of harsh working conditions such as deep wells, ultra-deep wells, and complex wellbores.

[0086] Note: ρ: Density of drilling fluid, g / cm 3 ; T: Aging temperature of drilling fluid, °C; AV: Apparent viscosity of drilling fluid, mPa·s; PV: Plastic viscosity of drilling fluid, mPa·s; YP: Dynamic shear force of drilling fluid, Pa; Φ6: The reading of the six-speed rotational viscometer at 6 r / min, dimensionless; Φ3: The reading of the six-speed rotational viscometer at 3 r / min, dimensionless; ES: Demulsification voltage, V; HTHP: High temperature and high pressure fluid loss of drilling fluid (3.5 MPa, T, 30 min), mL; O HTHP : Oil-based fluid loss of HTHP mud cake (3.5 MPa, room temperature, 30 min), mL; FL: Sand-packed fluid loss of drilling fluid (3.5 MPa, T, 60 - 80 mesh sand, 30 min), mL; PPT: Permeation fluid loss of drilling fluid (6.9 MPa, T, 30 min), mL; O PPT : Oil-based fluid loss of PPT mud cake (6.9 MPa, room temperature, 30 min), mL; I1: Apparent viscosity increase rate after contamination with 5% sodium bentonite, %; I2: Apparent viscosity increase rate after contamination with 10% sodium bentonite, %; θ: Shale rolling recovery rate, %; γ: Linear expansion rate of clay, %; EP: Extreme pressure friction coefficient, dimensionless; CF: Four-ball friction coefficient (147 N, 120 rpm, 30 min), dimensionless; MA: Four-ball wear scar diameter, mm 2 。

[0087] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A high-density ultra-low viscosity synthetic-based drilling fluid, characterized in that, It includes component a and component b; By volume fraction, component a consists of 80 - 90 parts of oil phase and 10 - 20 parts of water phase; Component b consists of an emulsifier, a viscosity reducer and thixotropic agent, an alkalinity regulator, organoclay, a filtrate reducer, a lubricant and barite; In every 100 mL of component a, there are 6.0 - 8.0 g of emulsifier, 0.5 - 1.5 g of viscosity reducer and gel strength enhancer, 2.0 - 3.0 g of alkalinity regulator, 1.0 - 2.0 g of organophilic clay, 3.0 - 4.0 g of filtration loss reducer, 0.5 - 1.5 g of lubricant and barite; wherein, the mass of barite is not limited, and it is added until the density of the synthetic-based drilling fluid reaches 2.0 - 2.4 g / cm 3 up to.

2. The high-density ultra-low-viscosity synthetic-based drilling fluid according to claim 1, wherein By volume fraction, the oil phase consists of 65 - 75 parts of linear α-olefin, 10 - 15 parts of low molecular fatty acid ester, 3 - 5 parts of low molecular synthetic ether and 7 - 20 parts of cosolvent; The linear α-olefin is at least one of C10 α-olefin, C11 α-olefin, C12 α-olefin; The low molecular fatty acid ester is at least one of ethyl acetate, methyl propionate, methyl valerate; The low molecular synthetic ether is at least one of butyl ether, isopropyl ether, methyl tert-butyl ether; The cosolvent is at least one of trimethylpentane, 2,2,4-trimethylpentane, 3,3-dimethylnonane; 3. The high-density ultra-low-viscosity synthetic-based drilling fluid according to claim 1, wherein The water phase is an aqueous calcium chloride solution with a mass fraction of 25% - 35%; 4. The high-density ultra-low viscosity synthetic-based drilling fluid according to claim 1, wherein The preparation method of the emulsifier includes the following steps: Add a diamine to erucic acid for reaction 1 to obtain product A; Add erucic acid, tetralin and an initiator to molten rosin for reaction 2 to obtain product B; Add monoethanolamine to polyisobutylene succinic anhydride for reaction 3 to obtain product C; Mix product A, product B and product C evenly to obtain the emulsifier.

5. The high-density ultra-low viscosity synthetic-based drilling fluid according to claim 4, characterized in that, The diamine is one of ethylenediamine, propylenediamine, butylenediamine; When preparing product A, the mass ratio of erucic acid to diamine is 160 - 200∶20 - 25; The specific reaction 1 is to first stir and react at 120 - 140 °C for 10 - 30 min, and then heat up to 160 - 180 °C for heat preservation for 4 - 6 hours; When preparing product B, the mass ratio of rosin to erucic acid and tetralin is 90 - 120∶60 - 80∶45 - 60; The specific reaction 2 is to react at 180 - 200 °C for 2 - 3 hours; The initiator is diisopropylbenzene peroxide; When preparing product C, the mass ratio of polyisobutylene succinic anhydride to monoethanolamine is 80 - 100∶10 - 12; The specific reaction 3 is to react at 140 - 160 °C for 18 - 24 h; The mass ratio of product A, product B and product C is 40 - 50∶20 - 30∶20 - 40.

6. The high-density ultra-low viscosity synthetic-based drilling fluid according to claim 1, characterized in that, The preparation method of the viscosity reducer and thixotropic agent includes the following steps: Heat 120 - 150 parts by mass of erucic acid to 110 - 130 °C, and purge with nitrogen to remove water and low-boiling impurities; Then, heat up to 240 - 260 °C, add 3 - 5 parts by mass of activated clay, and stir and react for 4 - 6 hours; After the reaction is completed, cool down to 120 - 140 °C, add 15 - 25 parts by mass of diethanolamine under stirring, and heat up to 160 - 180 °C, react for 2 - 4 hours, and filter after cooling to obtain the viscosity reducer and thixotropic agent.

7. The high-density ultra-low viscosity synthetic-based drilling fluid according to claim 1, wherein By mass fraction, the alkalinity regulator consists of 60 - 80 parts of calcium oxide and 20 - 40 parts of magnesium oxide.

8. The high-density ultra-low viscosity synthetic-based drilling fluid according to claim 1, characterized in that, By mass parts, the organic clay consists of 20 to 30 parts of BENTONE ® 38, 20 to 30 parts of BENTONE ® 42 and 40 to 60 parts of BENTONE ® 150.

9. The high-density ultra-low viscosity synthetic-based drilling fluid according to claim 1, wherein, By mass fraction, the filtrate reducer consists of 30 - 40 parts of organic lignite, 30 - 40 parts of humic acid amide and 20 - 40 parts of polymethyl methacrylate microspheres.

10. The high-density ultra-low viscosity synthetic-based drilling fluid according to claim 1, characterized in that, By mass parts, the lubricant is composed of 10 to 20 parts of boron nitride, 30 to 40 parts of graphite, 20 to 30 parts of polyetheretherketone micropowder, and 20 to 30 parts of polytetrafluoroethylene micropowder.