Drilling fluid as well as preparation method and application thereof

Abstract

The invention discloses a drilling fluid and a preparation method and application thereof, and the drilling fluid comprises the following raw materials by weight: 60-95 parts of base oil, 5-40 parts of a saline solution, 2-8 parts of an emulsifier, 1-3 parts of a wetting agent, 1-5 parts of calcium oxide, 1-5 parts of organic soil, 2-8 parts of a filtrate reducer, and 0-500 parts of a weighting material. The preparation method of the drilling fluid comprises the following steps: (1) uniformly mixing the base oil and the emulsifier, then adding the wetting agent, the saline solution and the calcium oxide, and continuously and uniformly mixing; (2) adding organic soil and a filtrate reducer into the solution obtained in the step (1), and uniformly mixing; and (3) adding a weighting material into the material flow obtained in the step (3) to adjust the material flow to the required density, and uniformly mixing to obtain the drilling fluid. The drilling fluid provided by the invention has the advantages of high density, low viscosity, excellent temperature resistance and the like.

Description

Technical Field

[0001] This invention belongs to the field of drilling fluid technology, specifically relating to an oil-based drilling fluid, its preparation method, and its application. Background Technology

[0002] Oil-based drilling fluids are widely used as an important tool for drilling ultra-deep wells, offshore wells, highly deviated directional wells, horizontal wells, and water-sensitive complex formations, as well as for reservoir protection, due to their advantages such as high-temperature resistance, resistance to salt and calcium intrusion, good wellbore stability, good lubricity, and minimal damage to oil and gas reservoirs. With the continuous expansion of oil and gas exploration and development areas, oil drilling is gradually extending from shallow to deep formations, from inland to remote areas, and to blocks with complex formations. Drilling operations in these areas encounter high-pressure oil and gas layers, gypsum mudstone, and brine layers. During drilling operations, creep in soft mudstone and gypsum mudstone layers can easily occur, leading to complex downhole accidents such as blowouts, leaks, wellbore instability, obstruction during tripping, and stuck pipe. To address these challenges, high-density oil-based drilling fluids are required. However, as the density of the drilling fluid increases, the amount of weighting agent also increases, leading to a sharp rise in the apparent viscosity and plastic viscosity of the drilling fluid. This causes problems such as increased pump pressure, difficulty in wellbore cleaning, and can result in complex downhole conditions like lost circulation, blowouts, and well collapse, severely impacting field operations. The article "Research and Application of Oil-Based Drilling Fluid Viscosity Reducers for Deep Shale Gas Reservoirs," published by Liang Wenli et al. in *Natural Gas Exploration and Development*, Vol. 43, No. 1, reports that in the Pingqiao and Jiangdong blocks of the Fuling shale gas reservoir, the density of the oil-based drilling fluid reached as high as 1.90 g / cm³. 3 At that time, due to the increase in density and solid content, the fluidity of oil-based drilling fluid deteriorates, circulation pressure loss is high, and pump pressure is high, reaching up to 28MPa. High pump pressure will affect mechanical power and energy consumption is large.

[0003] To address these issues, it is necessary to improve the rheological properties of high-density drilling fluids. As a result, many domestic and international oil companies and oil fields have invested heavily in developing low-viscosity, high-density oil-based drilling fluid systems.

[0004] Patent CN111269701A relates to a high-density, ultra-low viscosity oil-based drilling fluid, the composition and weight percentages of which are as follows: The oil-based drilling fluid consists of a water-in-oil base fluid, a primary emulsifier, a secondary emulsifier, a filtration reducer, an alkalinity regulator, organic clay, a wetting agent, and a weighting agent; per 100 mL of the water-in-oil base fluid, the amounts of the remaining components are: 0-2 parts organic clay, 0.3-3 parts primary emulsifier, 0.5-3 parts secondary emulsifier, 0.5-2 parts wetting agent, 1-4 parts alkalinity regulator, 4-8 parts filtration reducer, and the amount of weighting agent is adjusted according to the density; wherein, the water-in-oil base fluid is composed of base oil and brine in a volume ratio of 70:30-95:5. This oil-based drilling fluid has ultra-low viscosity and excellent settling stability, which helps reduce the operational risks of drilling long horizontal sections of shale gas wells; this drilling fluid can effectively resolve the contradictory relationship between viscosity and settling stability.

[0005] Patent CN105733530A provides a low-viscosity, high-shear, high-density oil-based drilling fluid formulation, prepared from the following raw materials by weight percentage: 30-80% base oil, 10-30% CaCl2 brine, 3-6% composite emulsifier G326#HEM, 2-5% filtration reducer G328, 1-5% calcium hydroxide, 0.5-1% viscosifier G336#VIS, 1.5-5% shear enhancer G322#MOD, with the remainder being barite. This invention solves the problem of excessively thick high-density oil-based drilling fluids caused by a significant increase in viscosity when increasing shear strength. It exhibits high dynamic shear strength and low plastic viscosity, with good rheological properties, making it suitable for the sand-carrying capacity requirements of oil-based drilling fluids in horizontal sections of shale gas wells.

[0006] Patent CN111057527A relates to the field of high-density oil-based drilling fluids, and more specifically to a high-density oil-based drilling fluid suitable for high-pressure shale gas formations and its preparation method. The high-density oil-based drilling fluid of this invention comprises the following raw materials in parts by weight: 80-90 parts base oil, 2-4 parts primary emulsifier, 0.5-3 parts secondary emulsifier, 1-2 parts organic bentonite, 2-3 parts alkalinity adjuster, 3-5 parts filtration loss reducer, 10-20 parts calcium chloride aqueous solution with a mass fraction of 25-35%, and a weighting agent. The primary emulsifier is composed of higher fatty acid esters diethylenetriamine, maleic polyamide, and polyoxyethylene ether, and the secondary emulsifier is sodium dodecylbenzene sulfonate. The oil-based drilling system of this invention, with diesel or white oil as the continuous phase, exhibits good emulsification, high demulsification voltage, low water loss under high temperature and pressure, strong inhibition, and good fluidity even with high solids content.

[0007] The aforementioned reports disclosed the preparation and application methods of different types of high-density, low-viscosity oil-based drilling fluids, all of which achieved beneficial technical results. However, the reports mainly aimed to reduce the viscosity of drilling fluids by adjusting the types of weighting materials, viscosifiers, and shearing agents. Summary of the Invention

[0008] Currently, when using high-density oil-based drilling fluids, the amount of weighting agent required increases with the increase in fluid density, leading to a sharp increase in both apparent and plastic viscosity. This results in problems such as increased pump pressure and difficulties in wellbore cleaning. Current methods primarily aim to reduce drilling fluid viscosity by adjusting the type of weighting materials, viscosity improvers, and shearing agents. However, the applicant discovered during their research that the oil phase, comprising 70wt%–95wt% of the drilling fluid's liquid phase, plays a crucial role in the rheological properties of oil-based drilling fluids, a concept not addressed in existing technologies. Currently, the oil phase in oil-based drilling fluids mainly uses diesel oil and light white oil. Due to their complex composition, containing hydrocarbons of various molecular weights and structures, they have low flash points, high volatility, and relatively high viscosity, resulting in high viscosity oil-based drilling fluids. This application is based on the above findings. By adjusting the structure and molecular weight of the oil phase and matching a suitable emulsifier, it solves the problems of high viscosity of conventional high-density oil-based drilling fluids causing increased pump pressure and difficulty in wellbore cleaning.

[0009] To address the shortcomings of existing technologies, this invention provides a drilling fluid, its preparation method, and its application. The drilling fluid is a low-viscosity, high-density oil-based drilling fluid with a maximum density of 2.5 g / cm³. 3 It has an apparent viscosity of no more than 50 mPa·s, a temperature resistance of no less than 180℃, and advantages such as high density, low viscosity, and excellent temperature resistance.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0011] The first aspect of the present invention provides a drilling fluid, wherein the drilling fluid raw materials, based on parts by weight, include: 60-95 parts base oil, 5-40 parts brine solution, 2-8 parts emulsifier, 1-3 parts wetting agent, 1-5 parts calcium oxide, 1-5 parts organic clay, 2-8 parts filtration loss reducer, and 0-500 parts weighting material, preferably 100-500 parts.

[0012] Furthermore, as some preferred embodiments, the base oil includes hydrocarbons with 12-20 (preferably 12-14) carbon atoms, wherein the content of alkanes is not less than 99% and the content of isoparaffins is not less than 90%.

[0013] Furthermore, as some preferred embodiments, the molecular weight of the base oil is 170 to 280.

[0014] Furthermore, as some preferred embodiments, the pour point of the base oil is not higher than -50°C (preferably not higher than -55°C), the flash point is not lower than 85°C (preferably not lower than 90°C), the aromatic content is not greater than 10 mg / kg, and the kinematic viscosity (40°C) is not greater than 2.0 cst.

[0015] Furthermore, as some preferred embodiments, the base oil has a distillation range of 200–300°C, preferably 210–290°C, and even more preferably 210–235°C.

[0016] Furthermore, as some preferred embodiments, the base oil can be a fraction obtained by cutting Fischer-Tropsch synthetic oil after hydroisomerization, wherein the initial boiling point of the fraction is 200-210°C and the final boiling point is 235-300°C; the Fischer-Tropsch synthetic oil contains not less than 90 wt% alkanes (preferably not less than 95 wt%).

[0017] Furthermore, as some preferred embodiments, the catalyst used in the hydroisomerization reaction is a bifunctional catalyst for hydroisomerization. It can be a commercially available product or prepared according to methods disclosed in the art. For example, at least one of the catalysts FIW-12U, FIW-12D, and FIW-20 developed by Sinopec (Dalian) Petrochemical Research Institute Co., Ltd. can be selected.

[0018] Furthermore, as some preferred embodiments, the hydroisomerization reaction conditions are generally as follows: reaction temperature of 280–340°C, reaction pressure of 3–10 MPa, hydrogen-to-oil volume ratio of 300:1–500:1, and volume hourly space velocity of 0.8–1 h⁻¹. -1 .

[0019] Furthermore, as some preferred embodiments, the base oil has a narrow molecular weight distribution range and lower viscosity compared to conventional drilling fluid base oils. The viscosity of the oil-based drilling fluid formulated with it is significantly reduced, which is beneficial for obtaining low-viscosity, high-density oil-based drilling fluid.

[0020] Furthermore, as some preferred embodiments, the emulsifier has a structural formula of any one of the structural formulas shown in formula (1), formula (2), formula (3), and formula (4);

[0021]

[0022]

[0023] Wherein, X represents a halogen, which can be at least one of iodine, bromine, and chlorine. X at different positions in the same structural formula can be the same or different.

[0024] R represents a hydrocarbon group having 2 to 35 carbon atoms, preferably a hydrocarbon group having 12 to 24 carbon atoms; the hydrocarbon group may be selected from at least one of alkyl, aryl, and cycloalkyl groups;

[0025] R1 and R2 represent alkyl groups having 1 to 3 carbon atoms, preferably methyl groups;

[0026] R3 represents a hydrocarbon group having 1 to 35 carbon atoms, preferably a hydrocarbon group having 12 to 24 carbon atoms; the hydrocarbon group may be selected from at least one of alkyl, alkenyl, alkynyl, aryl, and cycloalkyl groups;

[0027] M is one or more monovalent metals, specifically one or more group IA metals, preferably sodium and / or potassium, more preferably sodium; L is one or more divalent metals, selected from magnesium, calcium, copper, ferrous iron; Z is one or more trivalent metals, selected from iron, aluminum; Y is one or more tetravalent metals, selected from titanium, zirconium.

[0028] Furthermore, as some preferred embodiments, the wetting agent is one or more of dodecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and dodecylenediol polyoxyethylene ether.

[0029] Furthermore, as some preferred embodiments, the salt solution is one or more of calcium chloride solution, potassium chloride solution, and potassium formate solution, and the concentration of the salt solution is 10wt% to 30wt%.

[0030] Furthermore, as some preferred embodiments, the filtration loss reducing agent is one or more of organic lignite, oxidized asphalt, humic acid amide, and sulfonated asphalt.

[0031] Furthermore, as some preferred embodiments, the weighting material is one or more of barite and manganese ore powder, and the barite can be any of ordinary barite or micronized barite.

[0032] Furthermore, as some preferred embodiments, the drilling fluid density is 1.5–2.5 g / cm³. 3 The apparent viscosity is 20–50 mPa·s.

[0033] Furthermore, as some preferred embodiments, the drilling fluid has a temperature resistance of 180°C to 250°C.

[0034] This invention also provides a method for preparing drilling fluid, comprising the following steps:

[0035] (1) Mix the base oil and emulsifier evenly, then add the wetting agent, brine solution and calcium oxide and continue to mix evenly;

[0036] (2) Add organic soil and filtration loss reducer to the solution obtained in step (1) and mix well;

[0037] (3) Add weighting material to the material flow obtained in step (3) to adjust to the required density, and mix evenly to obtain drilling fluid.

[0038] Furthermore, as some preferred embodiments, in the above-mentioned drilling fluid preparation method, the mixing in steps (1), (2) and (3) can be carried out by stirring, such as stirring at high speed at 8000 to 12000 r / min for 10 to 20 min.

[0039] Furthermore, as some preferred embodiments, the amounts of base oil, emulsifier, wetting agent, brine solution, calcium oxide, organoclay, filtration loss reducer, and weighting material, based on parts by weight, are as follows: 60-95 parts base oil, 5-40 parts brine solution, 2-8 parts emulsifier, 1-3 parts wetting agent, 1-5 parts calcium oxide, 1-5 parts organoclay, 2-8 parts filtration loss reducer, and 0-500 parts weighting material, preferably 100-500 parts.

[0040] Furthermore, as some preferred embodiments, the base oil in step (1) includes hydrocarbons with 12-20 (preferably 12-14) carbon atoms, wherein the content of alkanes is not less than 99% and the content of isoparaffins is not less than 90%.

[0041] Furthermore, as some preferred embodiments, the molecular weight of the base oil in step (1) is 170 to 280.

[0042] Furthermore, as some preferred embodiments, the pour point of the base oil in step (1) is not higher than -50°C (preferably not higher than -55°C), the flash point is not lower than 85°C (preferably not lower than 90°C), the aromatic content is not greater than 10 mg / kg, and the kinematic viscosity (40°C) is not greater than 2.0 cst.

[0043] Furthermore, as some preferred embodiments, the base oil in step (1) has a distillation range of 200-300°C, preferably 210-290°C, and even more preferably 210-235°C.

[0044] Furthermore, as some preferred embodiments, the base oil in step (1) can be a fraction obtained by cutting Fischer-Tropsch synthetic oil after hydroisomerization reaction, wherein the initial boiling point of the fraction is 200-210°C and the final boiling point is 235-300°C; the Fischer-Tropsch synthetic oil contains not less than 90 wt% alkanes (preferably not less than 95 wt%).

[0045] Furthermore, as some preferred embodiments, the catalyst used in the hydroisomerization reaction is a bifunctional catalyst for hydroisomerization. It can be a commercially available product or prepared according to methods disclosed in the art. For example, at least one of the catalysts FIW-12U, FIW-12D, and FIW-20 developed by Sinopec (Dalian) Petrochemical Research Institute Co., Ltd. can be selected.

[0046] Furthermore, as some preferred embodiments, the hydroisomerization reaction conditions are generally as follows: reaction temperature of 280–330°C, reaction pressure of 3–6 MPa, hydrogen-to-oil volume ratio of 300:1–500:1, and volume hourly space velocity of 0.8–1 h⁻¹. -1 .

[0047] Furthermore, as some preferred embodiments, the emulsifier described in step (1) has a structural formula of any one of the structural formulas shown in formula (1), formula (2), formula (3), and formula (4);

[0048]

[0049]

[0050] Wherein, X represents a halogen, which can be at least one of iodine, bromine, and chlorine. X at different positions in the same structural formula can be the same or different.

[0051] R represents a hydrocarbon group having 2 to 35 carbon atoms, preferably a hydrocarbon group having 12 to 24 carbon atoms; the hydrocarbon group may be selected from at least one of alkyl, aryl, and cycloalkyl groups;

[0052] R1 and R2 represent alkyl groups having 1 to 3 carbon atoms, preferably methyl groups;

[0053] R3 represents a hydrocarbon group having 1 to 35 carbon atoms, preferably a hydrocarbon group having 12 to 24 carbon atoms; the hydrocarbon group may be selected from at least one of alkyl, alkenyl, alkynyl, aryl, and cycloalkyl groups;

[0054] M is one or more monovalent metals, specifically one or more group IA metals, preferably sodium and / or potassium, more preferably sodium; L is one or more divalent metals, selected from magnesium, calcium, copper, ferrous iron; Z is one or more trivalent metals, selected from iron, aluminum; Y is one or more tetravalent metals, selected from titanium, zirconium.

[0055] Furthermore, as some preferred embodiments, the wetting agent mentioned in step (1) is one or more of dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and dodecylenediol polyoxyethylene ether.

[0056] Furthermore, as some preferred embodiments, the salt solution in step (1) is one or more of calcium chloride solution, potassium chloride solution, and potassium formate solution, and the concentration of the salt solution is 10wt% to 30wt%.

[0057] Furthermore, as some preferred embodiments, the filtration loss reducing agent mentioned in step (2) is one or more of organic lignite, oxidized asphalt, humic acid amide, and sulfonated asphalt.

[0058] Furthermore, as some preferred embodiments, the weighting material mentioned in step (3) is one or more of barite and manganese ore powder, and the barite can be any of ordinary barite or micronized barite.

[0059] A third aspect of the present invention also provides the use of the drilling fluid in the drilling process.

[0060] Compared with the prior art, the drilling fluid and its preparation method provided by the present invention have the following beneficial effects:

[0061] 1. Currently, when using high-density oil-based drilling fluids, the amount of weighting agent increases with the increase in fluid density, leading to a sharp increase in both apparent and plastic viscosity. This results in problems such as increased pump pressure and difficulties in wellbore cleaning. The current approach primarily aims to reduce drilling fluid viscosity by adjusting the type of weighting materials, viscosifiers, and shearing agents. However, during the applicant's research, it was discovered that the oil phase, comprising 70wt% to 95wt% of the drilling fluid's liquid phase, plays a crucial role in the rheological properties of oil-based drilling fluids. This is not addressed in existing technologies. Currently, the oil phase in oil-based drilling fluids mainly uses diesel oil and light white oil. Due to their complex composition, containing hydrocarbons of various molecular weights and structures, they have low flash points, high volatility, and relatively high viscosity, resulting in high viscosity oil-based drilling fluids. This application is based on the above findings. By adjusting the structure and molecular weight of the oil phase and matching a suitable emulsifier, it solves the problems of high viscosity of conventional high-density oil-based drilling fluids causing increased pump pressure and difficulty in wellbore cleaning.

[0062] 2. The base oil provided by this invention has the characteristics of low kinematic viscosity and good viscosity-temperature performance under the same flash point conditions. However, due to its relatively simple structure, it contains almost no cyclic hydrocarbons and heteroatoms such as sulfur and nitrogen, resulting in weak polarity and insufficient binding ability with existing processing agents. When formulated with conventional emulsifiers to produce oil-based drilling fluids, it suffers from problems such as poor emulsification stability, low dynamic shear force, and insufficient suspension capacity. Therefore, the base oil provided by this invention is compounded with an emulsifier containing phosphonic acid groups to improve its emulsification stability and dynamic shear force. Through the comprehensive regulation of the above methods, a low-viscosity, high-density oil-based drilling fluid is prepared, which has the characteristics of low viscosity, high flash point, and excellent temperature resistance, especially with a density of 2.0 g / cm³. 3 Above (highest value 2.5g / cm) 3 This high-density drilling fluid exhibits significantly improved rheological properties, addressing issues such as high viscosity and poor anti-fouling ability in conventional high-density oil-based drilling fluids. Detailed Implementation

[0063] The following specific embodiments further describe the low-viscosity, high-density oil-based drilling fluid, its preparation method, and its application according to the present invention, but these do not constitute a limitation on the present invention.

[0064] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprising" shall be understood to include the stated elements or components without excluding other elements or other components.

[0065] In this paper, the reflux reaction is carried out by heating to a reflux temperature that is not higher than the boiling point of the solvent used in the reaction.

[0066] In this document, all numeric values ​​of parameters (e.g., quantity or condition) should be understood to be modified by the term “about” in all cases, regardless of whether “about” actually appears before the numeric value.

[0067] The base oil of this invention can be obtained by the following preparation method:

[0068] In the presence of hydrogen, Fischer-Tropsch synthetic oil was contacted with FIW-20 isomerization dewaxing catalyst to undergo a hydroisomerization reaction. The reaction conditions were as follows: reaction temperature 320℃, reaction pressure 8 MPa, hydrogen-to-oil volume ratio 300:1, and volume hourly space velocity 1.0 h⁻¹. -1 The properties of the Fischer-Tropsch synthetic oil feedstock are as follows: density (20℃) is 813.4 kg / m³. 3 The distillation range is 276–576℃, and the viscosity (40℃) is 0.955 L / mm. 2 ·s -1 The sulfur content is 1.0 μg / g, the nitrogen content is 1.2 μg / g, and the alkane content is 98.1 wt%.

[0069] Following hydroisomerization, a distillation fraction with a boiling range of 210-235℃ was obtained as the base oil. This fraction contained 91.05 wt% isoparaffins and had the following properties: density (20℃) 759.2 kg / m³. 3 The sulfur content is 0 μg·g -1 The nitrogen content is 0 μg·g -1 It has a pour point of -60℃, a flash point of 92℃, and an aromatic hydrocarbon content of 9mg / kg; its kinematic viscosity (40℃) is 1.199cst.

[0070] The preparation method of the emulsifier of the present invention includes the following steps:

[0071] (1) Mix phosphorous acid and organic solvent evenly, adjust the pH of the system to no more than 7, and then introduce diallylamine to react;

[0072] (2) Slowly introduce aldehydes into the reaction stream obtained in step (1) to carry out a reflux reaction;

[0073] (3) Adjust the pH value of the reaction stream obtained in step (2) to 6-8 and continue to reflux the reaction. The solid phase obtained by separating the reaction product is dried to obtain solid material.

[0074] (4) The solid material obtained in step (3), the halogenated hydrocarbon and the first solvent are mixed and reacted. The material obtained after the reaction is washed and dried to obtain the solid material.

[0075] (5) Add the solid material, catalyst and second solvent obtained in step (4) to the reactor, and then introduce hydrogen halide gas. After the reaction is completed, dry the material to obtain material A.

[0076] (6) Under the reaction conditions, material A, the third solvent and the tertiary amine are mixed and reacted. After the reaction, the mixture is dried by rotary evaporation to obtain a phosphonic acid-based gemini surfactant.

[0077] In the above method for preparing emulsifier, the mass ratio of phosphorous acid to organic solvent in step (1) is 1:0.5 to 15, preferably 1:0.5 to 8.

[0078] In the above method for preparing emulsifier, the organic solvent in step (1) is preferably an alcohol with 1-12 carbon atoms, an ester with 2-12 carbon atoms, or an ether ketone with 2-12 carbon atoms, and more preferably one or more of methanol, ethanol, butanol, ethyl acetate, butyl acetate, isoamyl acetate, diethyl ether, butyl ether, acetone, and methyl ethyl ketone.

[0079] In the above method for preparing the emulsifier, the pH value of the system in step (1) is adjusted to 1 to 6.8, more preferably the pH value of the system is adjusted to 1 to 4, and even more preferably the pH value of the system is adjusted to 1 to 3.

[0080] In the above method for preparing emulsifier, step (1) involves adding an acid to adjust the pH value of the system. The acid is an inorganic acid and / or an organic acid, specifically selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, glacial acetic acid, carbonic acid, hydrofluoric acid, citric acid, malic acid, tartaric acid, succinic acid, etc.

[0081] In the above method for preparing the emulsifier, diallylamine is introduced in step (1) by slow addition, such as by dripping. More specifically, the dripping rate can be controlled between 10 mL / h and 200 mL / h. The temperature at which diallylamine is introduced is -20 to 10°C, preferably -10 to 5°C.

[0082] In the above method for preparing emulsifier, the molar ratio of diallylamine to phosphorous acid in step (1) is 1:1 to 2, preferably 1:1 to 1.5.

[0083] In the above method for preparing the emulsifier, the aldehyde in step (2) is at least one of formaldehyde, dioxymethylene, trioxymethylene, and paraoxymethylene, preferably formaldehyde. The aldehyde is introduced in liquid form. For example, when formaldehyde is used, it can be added directly in liquid form; when dioxymethylene, trioxymethylene, or paraoxymethylene is used, it can be dissolved in an organic solvent first and then added in liquid form. The organic solvent used can be one or more of alcohols, esters, ethers, and ketones. Furthermore, the number of carbon atoms of the alcohol, ester, ether, or ketone can be 1 to 12, specifically selected from one or more of methanol, ethanol, butanol, ethyl acetate, butyl acetate, isoamyl acetate, diethyl ether, butyl ether, acetone, and methyl ethyl ketone.

[0084] In the above method for preparing emulsifier, the aldehyde can be introduced slowly in step (2) by dripping. Furthermore, the dripping rate can generally be controlled within the range of 10 mL / h to 200 mL / h.

[0085] In the above method for preparing emulsifier, the molar ratio of aldehyde to diallylamine in step (2) is 1 to 2:1, preferably 1 to 1.5:1.

[0086] In the above method for preparing emulsifier, the reaction temperature in step (3) is 0 to 90°C, preferably 20 to 40°C; the reaction time is 0.5 to 6 hours, preferably 1 to 3 hours.

[0087] In the above method for preparing emulsifier, in step (3), an alkaline substance is added to adjust the pH value of the reaction stream obtained in step (2). The alkaline substance can be an inorganic base and / or an alkaline inorganic salt. The metal element in the inorganic base and / or alkaline inorganic salt is selected from one or more of monovalent, divalent, trivalent, and tetravalent metals. More specifically, it can be selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, magnesium hydroxide, magnesium carbonate, calcium carbonate, calcium hydroxide, iron hydroxide, copper hydroxide, titanium hydroxide, zirconium hydroxide, etc., preferably sodium hydroxide and potassium hydroxide.

[0088] In the above method for preparing the emulsifier, the separation mentioned in step (3) is solid-liquid separation. The solid-liquid separation can be achieved by any means that can separate the solid and liquid phases. The selection of the separation means is a basic skill of those skilled in the art, and can be reasonably selected according to the actual situation. Specifically, one or more of the following methods can be used: filtration separation, centrifugation separation, etc. The separated liquid phase can be recycled back to step (1) for continued use, and the reaction can continue after supplementing other raw materials.

[0089] In the above method for preparing emulsifier, the drying temperature in step (3) is 60-120℃ and the drying time is 6-12h.

[0090] In the above method for preparing the emulsifier, the halogenated hydrocarbon in step (4) is a monohalogenated hydrocarbon; it can be at least one of chlorinated hydrocarbons, bromine hydrocarbons, and iodocarbons; the halogenated hydrocarbon is a hydrocarbon group with 2 to 35 carbon atoms, preferably a hydrocarbon group with 12 to 24 carbon atoms; the hydrocarbon group can be at least one of alkyl, aryl, and cycloalkyl; more specifically, the halogenated hydrocarbon is one or more of bromododecane, bromotridecane, bromotetradecane, bromopentadecanane, bromohexadecane, bromoheptadecane, bromooctadecane, iodododecane, iodotridecane, iodotetradecane, iodopentadecanane, iodohexadecane, iodoheptadecane, iodooctadecane, chlorododecane, chlorotridecane, chlorotetradecane, chloropentadecanane, chlorohexadecane, chloroheptadecane, and chlorooctadecane.

[0091] In the above method for preparing the emulsifier, the first solvent in step (4) is water and / or an organic solvent, and the organic solvent is one or more of methanol, ethanol, butanol, methyl acetate, ethyl acetate, diethyl ether, butyl ether, acetone, chloroform, dichloromethane, toluene, cyclohexane, petroleum ether, hexane, and pentane.

[0092] In the above method for preparing emulsifier, the molar ratio of haloalkanes to diallylamine in step (4) is 0.5 to 1.2:1, preferably 0.8 to 1.1:1.

[0093] In the above method for preparing emulsifiers, the reaction temperature in steps (4) and (5) is 20 to 80°C.

[0094] In the above method for preparing emulsifier, the second solvent in step (5) is one or more of glacial acetic acid and trifluoroacetic acid.

[0095] In the above method for preparing the emulsifier, the hydrogen halide in step (5) is one or more of hydrogen iodide, hydrogen bromide, and hydrogen chloride. The molar ratio of the hydrogen halide introduced in step (5) to diallylamine is 1.8 to 2.2:1, preferably 1.9 to 2.1:1.

[0096] In the above method for preparing emulsifier, the catalyst in step (5) is aluminum trichloride.

[0097] In the above method for preparing the emulsifier, the third solvent in step (6) can be one or more of water, methanol, ethanol, butanol, methyl acetate, ethyl acetate, diethyl ether, butyl ether, acetone, chloroform, dichloromethane, toluene, cyclohexane, petroleum ether, hexane, and pentane.

[0098] In the above method for preparing emulsifier, the reaction temperature in step (6) is 20-80℃.

[0099] In the above method for preparing the emulsifier, the molar ratio of the tertiary amine to diallylamine in step (6) is 1.8 to 2.2:1, preferably 1.9 to 2.1:1. The tertiary amine can be dimethyl tertiary amine, diethyl tertiary amine, or dipropyl tertiary amine, and the chain length of the carbon chain in the tertiary amine is 1 to 35.

[0100] In the above method for preparing the emulsifier, the tertiary amine in step (6) is a dimethyl tertiary amine. The chain length of the carbon chain of the dimethyl tertiary amine is 12-24, and it can be selected from one or more of N,N-dimethyldodecylamine, N,N-dimethyltridecylamine, N,N-dimethyltetradecylamine, N,N-dimethylpentadecanylamine, N,N-dimethylhexadecylamine, N,N-dimethylheptadecylamine, N,N-dimethyloctadecylamine, N,N-dimethylnonadecanylamine, N,N-dimethyleicosylamine, N,N-dimethyltimosylamine, N,N-dimethyltimosylamine, N,N-dimethyltimosylamine, and N,N-dimethyltimosylamine.

[0101] Example 1

[0102] Preparation of emulsifier A

[0103] 5.7 g of phosphorous acid and 7 mL of anhydrous ethanol were added to a reaction vessel, followed by 2 mL of concentrated sulfuric acid (98 wt%) to adjust the pH to 1. The reaction vessel was then placed in an ice-water bath, and 8.6 mL of diallylamine was added dropwise through a constant dropping funnel over a period of 45 min. After the addition was complete, the temperature was raised to reflux temperature, and the reaction was continued for 2 h. Subsequently, a mixture of 12.6 g of paraformaldehyde and 7 mL of anhydrous ethanol was added dropwise through a constant dropping funnel over a period of 20 min, followed by reflux reaction for 3 h. Then, 5.6 g of NaOH was added to the system to adjust the pH to 7, and the reaction was carried out at 20 °C for 1 h. After further centrifugation, the resulting solid phase was dried at 80 °C for 10 h to obtain the intermediate product.

[0104] The intermediate product and 17.4 g of bromododecane were then added sequentially to a mixed solution of 60 g toluene and 10 g water. The mixture was heated to 80 °C and reacted for 2 h. After rotary evaporation, a solid powder was obtained, which was then washed several times with acetone, filtered, and dried to obtain a solid material. The solid material and 0.5 g of aluminum trichloride were added to 60 g of glacial acetic acid, and 17 g of hydrogen iodide was introduced. The mixture was reacted at 50 °C for 3 h. After the reaction was complete, the mixture was dried by rotary evaporation to obtain material A. Material A and 28.4 g of N,N-dimethyldodecylamine were added to 70 g of toluene and 30 g of butanol. The mixture was reacted at 60 °C for 3 h and dried by rotary evaporation to obtain emulsifier A (purity 92.5%).

[0105] Example 2

[0106] Preparation of emulsifier B

[0107] 15g of phosphorous acid and 14mL of anhydrous ethanol were added sequentially to a reaction vessel. Then, 6mL of concentrated sulfuric acid (98wt%) was added to adjust the pH to 1. The reaction vessel was then placed in an ice-water bath, and 8.6mL of diallylamine was added dropwise through a constant-drop funnel, completing the addition over 45 minutes. After the addition was complete, the mixture was refluxed for 3 hours. Subsequently, a mixture of 15g of trioxymethylene and 14mL of anhydrous ethanol was added dropwise through a constant-drop funnel, completing the addition over 40 minutes. After the addition was complete, the mixture was refluxed for 4 hours. 11.5g of KOH was added to adjust the pH to 7, and the reaction was carried out at 20℃ for 3 hours. After further centrifugation, the resulting solid phase was dried at 90℃ for 10 hours to obtain the intermediate product.

[0108] The intermediate product and 22.8 g of iodododecane were then added sequentially to a mixed solution of 90 g of cyclohexane and 15 g of ethanol. The mixture was heated to 60 °C and reacted for 3 h. After rotary evaporation, a solid powder was obtained, which was then washed several times with acetone, filtered, and dried to obtain a solid material. The solid material, 0.6 g of aluminum trichloride, and 11.9 g of hydrogen bromide were added to 80 g of glacial acetic acid, and the mixture was reacted at 60 °C for 3 h. After the reaction was complete, the mixture was dried by rotary evaporation to obtain material A. Material A, 35.5 g of N,N-dimethyltetradecylamine, and 100 g of petroleum ether and 20 g of ethanol were added to a mixture and reacted at 50 °C for 3 h. After rotary evaporation, emulsifier B was obtained (purity 92.7%).

[0109] Example 3

[0110] 144g of base oil and 8g of emulsifier A were stirred until homogeneous to obtain a mixture. Then, 2g of dodecyltrimethylammonium bromide, 24g of 25wt% calcium chloride solution, and 2g of calcium oxide were added to the mixture and stirred until homogeneous. Next, 8g of organocarb, 3g of oxidized asphalt, and 2g of humic acid amide filtration reducer were added and stirred at high speed until homogeneous. Finally, barite was added to adjust the density to 2.0g / cm³. 3 After stirring and mixing evenly, drilling fluid is obtained.

[0111] Example 4

[0112] 112g of base oil and 10g of emulsifier A were stirred until homogeneous to obtain a mixture. Then, 2g of cetyltrimethylammonium bromide, 2g of dodecyltrimethylammonium bromide, a mixed salt solution of 72g of calcium chloride (20wt%) and potassium chloride (10wt%), and 8g of calcium oxide were added to the mixture and stirred until homogeneous. Next, 6g of organic clay, 3g of organic lignite, and 5g of sulfonated asphalt filtration reducer were added and stirred at high speed until homogeneous. Finally, barite was added to adjust the density to 2.0g / cm³. 3 After stirring and mixing evenly, drilling fluid is obtained.

[0113] Example 5

[0114] 144g of base oil and 15g of emulsifier B were stirred evenly to obtain a mixture. Then, 4g of cetyltrimethylammonium bromide, 2g of dodecaacetylenide diol polyoxyethylene ether, 24g of a mixed salt solution of calcium chloride (10wt%) and potassium formate (20wt%), and 5g of calcium oxide were added to the mixture and stirred evenly. Next, 6g of organic clay, 3g of organic lignite, 5g of sulfonated asphalt filtration reducer, and 2g of humic acid amide filtration reducer were added and stirred at high speed until evenly mixed. Finally, 100g of micronized barite and an appropriate amount of barite were added to adjust the density to 2.2g / cm³. 3 After stirring and mixing evenly, drilling fluid is obtained.

[0115] Example 6

[0116] 144g of base oil and 15g of emulsifier B were stirred evenly to obtain a mixture. Then, 4g of hexadecyltrimethylammonium bromide, 2g of dodecaacetylenide diol polyoxyethylene ether, 24g of a salt solution containing 10wt% calcium chloride and 30wt% potassium formate, and 5g of calcium oxide were added to the mixture and stirred evenly. Next, 6g of organic clay, 3g of organic lignite, 5g of sulfonated asphalt filtration reducer, and 2g of humic acid amide filtration reducer were added and stirred at high speed until evenly mixed. Finally, 100g of micronized barite and an appropriate amount of manganese ore powder were added to adjust the density to 2.5g / cm³. 3 After stirring and mixing evenly, drilling fluid is obtained.

[0117] Comparative Example 1

[0118] It is basically the same as Example 3, except that the base oil used is No. 3 light white oil.

[0119] Comparative Example 2

[0120] It is basically the same as Example 3, except that the emulsifier used is tall oil fatty acid amide.

[0121] Comparative Example 3

[0122] It is basically the same as Example 4, except that the base oil used is No. 3 light white oil and the emulsifier used is tall oil fatty acid amide.

[0123] Drilling fluid performance evaluation test:

[0124] The test method was as follows: Drilling fluids prepared in Examples 3-6 and Comparative Examples 1-3 were placed in an aging tank and heated at 180°C for 16 hours. Rheological properties and emulsion stability were measured at 65°C. The test results are shown in Table 1. The rheological properties were measured using a ZNN-D6 six-speed rotational viscometer, and the emulsion stability was measured using a DWY-2 drilling fluid electrical stability tester.

[0125] As can be seen from the performance test results in Table 1, after high-temperature aging at 180℃ for 16 hours, the drilling fluid prepared using base oil in Example 3, compared with Comparative Example 1, exhibits lower apparent viscosity AV and plastic viscosity. Compared with Comparative Example 2, the drilling fluid prepared using emulsifier A in Example 3 has a higher demulsification voltage. Compared with Comparative Example 3, the drilling fluid prepared using base oil and emulsifier A in Example 4 has lower apparent viscosity AV and plastic viscosity, and a higher demulsification voltage.

[0126] The drilling fluid density was 2.0 g / cm³ in Examples 3 and 4. 3 Increased to 2.20 g / cm³ in Example 5. 3 And 2.50 g / cm in Example 6 3 At this point, its apparent viscosity AV and plastic viscosity PV increase only slightly with increasing density, and the viscosity remains at a low level. This indicates that the oil-based drilling fluid provided by this invention has better rheological properties, which helps to solve problems such as increased pump pressure and difficulty in wellbore cleaning caused by the high viscosity of conventional high-density oil-based drilling fluids.

[0127] Table 1. Rheological property evaluation results of oil-based drilling fluid (hot rolling at 180℃ for 16 hours)

[0128]

Claims

1. A drilling fluid, wherein the raw materials for the drilling fluid include, based on parts by weight: The composition includes 60-95 parts base oil, 5-40 parts brine solution, 2-8 parts emulsifier, 1-3 parts wetting agent, 1-5 parts calcium oxide, 1-5 parts organic clay, 2-8 parts filtration loss reducer, and 0-500 parts weighting material, preferably 100-500 parts.

2. The drilling fluid according to claim 1, wherein, The base oil contains hydrocarbons with 12-20 carbon atoms (preferably 12-14), of which the content of alkanes is not less than 99% and the content of isoparaffins is not less than 90%.

3. The drilling fluid according to claim 1, wherein, The molecular weight of the base oil is 170–280.

4. The drilling fluid according to claim 1, wherein, The base oil has a pour point not higher than -50℃ (preferably not higher than -55℃), a flash point not lower than 85℃ (preferably not lower than 90℃), an aromatic content not greater than 10mg / kg, and a kinematic viscosity (40℃) not greater than 2.0cst.

5. The drilling fluid according to claim 1, wherein, The base oil has a distillation range of 200–300°C, preferably 210–290°C, and more preferably 210–235°C.

6. The drilling fluid according to claim 1, wherein, The base oil is a fraction obtained by cutting Fischer-Tropsch synthetic oil after hydroisomerization reaction. The initial boiling point of the fraction is 200-210℃, and the final boiling point is 235-300℃. The Fischer-Tropsch synthetic oil contains not less than 90 wt% alkanes (preferably not less than 95 wt%).

7. The drilling fluid according to claim 1, wherein, The emulsifier has a structural formula of any one of the structural formulas shown in formula (1), formula (2), formula (3), and formula (4); Equation (1) Equation (2) Equation (3) Equation (4) Wherein, X represents a halogen, which can be at least one of iodine, bromine, and chlorine. X at different positions in the same structural formula can be the same or different. R represents a hydrocarbon group having 2 to 35 carbon atoms, preferably a hydrocarbon group having 12 to 24 carbon atoms; the hydrocarbon group may be selected from at least one of alkyl, aryl, and cycloalkyl groups; R1 and R2 represent alkyl groups having 1 to 3 carbon atoms, preferably methyl groups; R3 represents a hydrocarbon group having 1 to 35 carbon atoms, preferably a hydrocarbon group having 12 to 24 carbon atoms; the hydrocarbon group may be selected from at least one of alkyl, alkenyl, alkynyl, aryl, and cycloalkyl groups; M is one or more monovalent metals, specifically one or more group IA metals, preferably sodium and / or potassium, more preferably sodium; L is one or more divalent metals, selected from magnesium, calcium, copper, ferrous iron; Z is one or more trivalent metals, selected from iron, aluminum; Y is one or more tetravalent metals, selected from titanium, zirconium.

8. The drilling fluid according to claim 1, wherein, The wetting agent is one or more of dodecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and dodecylenediol polyoxyethylene ether.

9. The drilling fluid according to claim 1, wherein, The saline solution is one or more of calcium chloride solution, potassium chloride solution, and potassium formate solution, and the concentration of the saline solution is 10wt% to 30wt%.

10. The drilling fluid according to claim 1, wherein, The filtration loss reducer is one or more of organic lignite, oxidized asphalt, humic acid amide, and sulfonated asphalt.

11. The drilling fluid according to claim 1, wherein, The weighting material is one or more of barite and manganese ore powder. The barite can be any of ordinary barite or micronized barite.

12. The drilling fluid according to claim 1, wherein, The density of the drilling fluid is 1.5–2.5 g / cm³. 3 The apparent viscosity is 20–50 mPa·s.

13. The drilling fluid according to claim 1, wherein, The drilling fluid has a temperature resistance of 180℃~250℃.

14. A method for preparing the drilling fluid according to any one of claims 1-13, comprising the following steps: (1) Mix the base oil and emulsifier evenly, then add the wetting agent, brine solution and calcium oxide and continue to mix evenly; (2) Add organic soil and filtration loss reducer to the solution obtained in step (1) and mix well; (3) Add weighting material to the material flow obtained in step (3) to adjust to the required density, and mix evenly to obtain drilling fluid.

15. Use of the drilling fluid according to any one of claims 1-13 in the drilling process.

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