A water-in-oil based drilling fluid and a method of preparing the same

Abstract

The application discloses a water-in-oil drilling fluid and a preparation method thereof. The water-in-oil drilling fluid comprises the following components in mass fraction: an emulsifier, 0.5-5%; organic soil, 1-3%; cationic modified high-softening-point asphalt particles, 1-5%; and an oil-water base fluid, 87-95%. The cationic modified high-softening-point asphalt particles comprise base asphalt and a modifier, and the modifier is obtained by activating silica with an activator. The water-in-oil drilling fluid can solve the problem that asphalt particles are difficult to disperse in the drilling fluid, has good plugging and filtration loss reduction effects, and improves the rock carrying capacity of the drilling fluid.

Description

Technical Field

[0001] This invention relates to the field of oil drilling and extraction technology, specifically to an oil-in-water based drilling fluid and its preparation method. Background Technology

[0002] As oil and gas exploration progresses to deeper formations, the chances of encountering high-temperature, high-pressure formations increase. This places higher demands on drilling fluid systems. Compared to water-based drilling fluids, oil-based drilling fluids offer advantages such as stronger anti-fouling capabilities, better lubrication, stronger inhibition properties, better wellbore stability, maximum protection of oil and gas reservoirs, and ease of maintenance. The superior high-temperature stability and inhibition properties of oil-based drilling fluids make them particularly advantageous when drilling complex wells, especially high-temperature deep wells and water-sensitive formations. They can effectively protect water-sensitive oil and gas reservoirs and increase oil and gas production.

[0003] Oil-based drilling fluids refer to drilling fluids with oil as the continuous phase, and are divided into all-oil-based drilling fluids and water-in-oil emulsion drilling fluids. All-oil-based drilling fluids typically contain less than 5% water. Water-in-oil emulsion drilling fluids consist of oil, water, emulsifiers, filtration reducers, activity balancers, etc., with a water content typically between 5% and 30%. However, water-in-oil drilling fluids resistant to temperatures above 180℃ generally have a water content of 5%-10%, rarely exceeding 15%. Increased water content increases the dynamic shear force of the system, improves rheological properties, and enhances the ability to carry cuttings. However, it decreases thermal and electrical stability. CN1660958A discloses a synthetic-based drilling fluid that, although maintaining good rheological and electrical stability after aging at 150℃ for 16 hours, has a maximum water content of 25%. Performance at higher temperatures and with higher water contents has not been reported.

[0004] While oil-based drilling fluids offer numerous advantages, the availability of suitable high-temperature treatment agents has become a limiting factor in their development, particularly for use in high-temperature, deep wells. Filtration reducers in these agents primarily control the filtration loss and stability of the drilling fluid system. To address this high-temperature, high-pressure environment, a type of oil-soluble polymer particle filtration reducer with good solubility in oil-based drilling fluids and strong high-temperature resistance has been developed abroad. During the filtration reduction process, these polymer particles form a thin, easily deformable mud cake on the outside, while internally they seal formation pores. Although this method achieves good filtration reduction, it is expensive.

[0005] Compared to specialty polymers, bituminous products are inexpensive and widely available, making them an indispensable agent in modern drilling engineering both domestically and internationally. They offer excellent comprehensive benefits, including anti-collapse, lubrication, reduced filtration loss, and high-temperature stability. However, bituminous products with a typical softening point may soften excessively or even flow, failing to meet the high-temperature requirements of deep well operations.

[0006] High softening point asphalt refers to asphalt with a softening point above 100℃, especially above 120℃. Due to its excellent high-temperature resistance, high softening point asphalt has a wide range of applications. It can be used in drilling operations in deep oil and gas fields as an important component of drilling fluid, playing a role in sealing, preventing collapse, stabilizing the wellbore, and reducing fluid loss under high-temperature conditions.

[0007] However, when high softening point asphalt particles are used in drilling fluid systems, especially in oil-in-water drilling fluid systems with high water content, they can cause problems such as easy aggregation and difficulty in dispersion, which affects the overall performance of the drilling fluid. Summary of the Invention

[0008] To address the problems of easy agglomeration, reduced suspension capacity, and poor high-temperature resistance of asphalt particles in the application of asphalt particles in water-in-oil drilling fluids, the present invention provides a water-in-oil drilling fluid and its preparation method, which can effectively solve the problem of difficult dispersion of asphalt particles in drilling fluid, achieve good sealing and filtration loss reduction effects, and improve the rock-carrying capacity of drilling fluid.

[0009] The first aspect of this invention provides an oil-in-water based drilling fluid, comprising, by mass fraction, the following components:

[0010]

[0011] The cationic modified high softening point asphalt particles include base asphalt and a modifier, wherein the modifier is obtained by activating silica with an activator.

[0012] Furthermore, the preparation method of the activator includes: firstly, synthesizing cyclic monomers from nitrile monomers under the action of a catalyst; then, subjecting the cyclic monomers to ring-opening polymerization to form a polymer of the cyclic monomers; finally, hydrolyzing the polymer of the cyclic monomers under acidic conditions to obtain the activator. Specifically:

[0013] (a) Add nitrile monomers and catalysts to a reactor, heat to 90-120°C, then add amino alcohol monomers, and react for 30-60 h to obtain cyclic monomers;

[0014] (b) The cyclic monomers, initiators and nitrile monomers obtained in step (a) are mixed and reacted at 100-160℃ for 30-90 min. Then, a methanol solution of KOH is added at -10℃ to 10℃ and stirred for 8-24 h. The solvent is removed, the residual polymer is dissolved in chloroform, precipitated and purified, and dried to obtain the polymer of the cyclic monomers.

[0015] (c) Dissolve the polymer of the cyclic monomer obtained in step (b) in hot water, heat under reflux, add hydrochloric acid solution, react for 24-72 h, remove the solvent, redissolve the residual polymer in hot water, add NaOH solution until the pH of the solution is 9-10, precipitate, centrifuge, remove the supernatant, repeat 2-3 times, dry, and obtain the activator.

[0016] Further, in step (a), the nitrile monomer is preferably ultra-dry acetonitrile and / or propionitrile. The catalyst is zinc acetate dihydrate. The volume-to-mass ratio of the nitrile monomer to the catalyst is 10-20:1 mL / g. The amino alcohol monomer is preferably one or more of 2-aminoethanol and 3-amino-1-propanol. The volume ratio of the nitrile monomer to the amino alcohol monomer is 1:1-1:3.

[0017] Further, in step (b), the initiator is a sulfonate cationic initiator, preferably one or more of methyl p-toluenesulfonate (MeOTs), ethyl trifluoromethanesulfonate, and 3-butynyl p-toluenesulfonate. In step (b), the nitrile monomer is preferably ultra-dry acetonitrile and / or propionitrile. The nitrile monomers in step (b) and step (a) may be the same or different. The volume ratio of the initiator to the cyclic monomer is 0.01-0.1:1; the volume ratio of the cyclic monomer to the nitrile monomer is 1:1-1:3.

[0018] Furthermore, in step (b), the cyclic monomer, initiator, and nitrile monomer are mixed and reacted in a microwave reactor.

[0019] Further, in step (b), the concentration of KOH in the methanol solution of KOH is 0.8-1.2 mol / L. The amount of KOH methanol solution added is 1 / 10-1 / 40 of the volume of the cyclic monomer.

[0020] Furthermore, in step (b), the stirring is carried out at 20-30°C, preferably at room temperature.

[0021] Further, in step (b), the solvent removal can be performed by rotary evaporation. The precipitation purification can be carried out in n-hexane. The drying conditions are: drying under vacuum at 30-50°C for 24-72 hours.

[0022] Further, in step (c), the temperature of the hot water is 40-80℃. The reflux temperature is 80-120℃, and the reflux time is 10-30 min. The mass concentration of the hydrochloric acid solution is 30%-38%. The mass ratio of the amount of hydrochloric acid solution added to the amount of cyclic monomer polymer added is 1-20:1. The solvent removal can be performed by rotary evaporation. The drying conditions are: vacuum drying at 50-70℃ for 24-72 h.

[0023] Furthermore, the average particle size of the cationic modified high softening point asphalt particles is 60-100 mesh.

[0024] Furthermore, the base asphalt has a softening point of 80-180℃ and is preferably at least one of oxidized asphalt, solvent-degreased asphalt, and natural asphalt.

[0025] Furthermore, based on the weight of the cationic modified high softening point asphalt particles, the content of the modifier is 1%-10%, and the content of the base asphalt is 90%-99%.

[0026] Furthermore, the particle size of the silica is 5μm-50μm.

[0027] Furthermore, the emulsifier is a long-chain fatty amide series surfactant, preferably at least one of lauroyl diethanolamine, oleamide, oleyl diethanolamine and cocoyl diethanolamine.

[0028] Furthermore, the oil-water base liquid comprises, by volume ratio, an oil phase: a water phase of 90:10 to 60:40;

[0029] Furthermore, in the oil-water base liquid, the oil phase is at least one of diesel oil, biodiesel, white oil, or vegetable oil, preferably white oil; the aqueous phase is a calcium chloride aqueous solution with a mass concentration of 10%-30%.

[0030] Furthermore, the oil-in-water based drilling fluid also includes a weighting agent. The amount of weighting agent added is sufficient to achieve a drilling fluid density of 1.50-2.10 g / cm³. 3 The weighting agent is barite and / or limestone.

[0031] A second aspect of this invention provides a method for preparing a water-in-oil based drilling fluid, comprising the following steps:

[0032] (1) Preparation of cationic modified high softening point asphalt particles;

[0033] (2) The cationic modified high softening point asphalt particles are mixed with emulsifier, organic soil and oil-water base fluid to obtain water-in-oil drilling fluid.

[0034] Further, in step (2), the preferred order of adding each component is to add an emulsifier to the oil-water base fluid, stir for the first time, add organic soil, stir for the second time, add cationic modified high softening point asphalt particles, stir for the third time, and obtain an oil-in-water base drilling fluid.

[0035] Furthermore, if it is necessary to adjust the density of the water-in-oil drilling fluid, a weighting agent is added in step (2).

[0036] Furthermore, in step (2), the first stirring time is 10-30 minutes, the second stirring time is 5-10 minutes, and the third stirring time is 20-40 minutes.

[0037] Furthermore, the method for preparing cationic modified high softening point asphalt particles in step (1) includes:

[0038] (I) Preparation of modifiers;

[0039] (II) The base asphalt is dissolved in an organic solvent, and then the modifier obtained in step (I) is added. The reaction is carried out under stirring to obtain cationic modified high softening point asphalt.

[0040] Further, in step (I), the method for preparing the modifier includes:

[0041] (i) Mix silica, epoxy silane coupling agent and ethanol, heat to reflux, centrifuge the resulting suspension, ultrasonically disperse the precipitate with ethanol, remove the supernatant, wash and dry to obtain the intermediate product.

[0042] (ii) Dissolve the activator in ethanol, add the intermediate product obtained in step (i), heat under reflux, centrifuge the resulting suspension, disperse the precipitate with water by ultrasonication, remove the supernatant, wash, and dry to obtain the modifier.

[0043] Further, in step (i), the epoxy silane coupling agent is 3-glycidyl etheroxypropylmethyldiethoxysilane (GPTMS). The mass-to-volume ratio of silica to epoxy silane coupling agent is 1:1-3 g / mL; silica, epoxy silane coupling agent and ethanol are mixed, wherein the volume ratio of epoxy silane coupling agent to ethanol is 1:1-5.

[0044] In steps (i) and (ii), the temperature of the heating reflux is 80-120°C, and the heating reflux time is 12-36h.

[0045] Further, in step (i), the centrifugation speed is 5000-15000 rpm, and the centrifugation time is 10-30 min. The ultrasonic dispersion frequency is 20 kHz-60 kHz, and the ultrasonic dispersion time is 5-20 min. The drying temperature is 50-80℃, and the drying time is 5-20 h.

[0046] Furthermore, the ethanol used in steps (i) and (ii) is anhydrous ethanol.

[0047] Further, in step (ii), the amount of activator added is 1-20% based on the mass of ethanol. The amount of intermediate product added is 1-30% based on the mass of ethanol. The mass ratio of activator to intermediate product added is 1:1-2.

[0048] Further, in step (ii), the centrifugation speed is 5000-15000 rpm, and the centrifugation time is 10-30 min. The ultrasonic dispersion frequency is 20 kHz-60 kHz, and the ultrasonic dispersion time is 5-20 min. The stirring reflux time is 12-36 h. The drying temperature is 50-80℃, and the drying time is 5-20 h.

[0049] Further, in step (II), the organic solvent is selected from one or more of chloroform, dichloromethane, toluene, tetrahydrofuran, and carbon tetrachloride. The mass ratio of the organic solvent to the base asphalt is 1-20:1.

[0050] Further, in step (II), the stirring speed is 80–2000 rpm. The reaction conditions are: reaction temperature 50–100℃, reaction time 2–10 h.

[0051] Further, in step (II), after the reaction is completed, the mixture is frozen and pulverized to obtain cationic modified high softening point asphalt particles with the required particle size.

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] (1) The cationic modified high softening point asphalt particles of the present invention use a specific modifier, namely micron-sized SiO2 treated with a special structure activator. The amine groups contained therein undergo a grafting reaction with asphalt, which solves the problem that micron-sized SiO2 is easy to agglomerate in asphalt and difficult to disperse. In addition, the addition of SiO2 treated with a special structure activator to asphalt can effectively increase the softening point of asphalt. The resulting modified asphalt has high temperature resistance and strong activity, and can continue to play a role at high temperatures when applied to drilling fluid.

[0054] (2) The cationic modified high softening point asphalt particles of the present invention have cationic groups grafted on their surface, which have strong surface activity and are easier to disperse evenly and stably in drilling fluid. This solves the problem that asphalt-based treatment agents are difficult to disperse stably in water-based or oil-based drilling fluids with high water content. Moreover, the surface of the cationic modified high softening point asphalt particles is positively charged, while the rock strata of the well wall are usually negatively charged. Therefore, they are more firmly bonded to the well wall and can better play the role of sealing and reducing filtration loss. Detailed Implementation

[0055] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0056] Example 1

[0057] Preparation of Modifier I

[0058] 31.2 mL of ultra-dry acetonitrile and 2.62 g of zinc acetate dihydrate were added to a 250 mL three-necked flask and heated to 105 °C. After reflux of the acetonitrile, 62.5 mL of 2-aminoethanol was slowly added dropwise using a constant-pressure dropping funnel. The reaction was allowed to proceed for 40.5 h, and after impurity removal, a cyclic monomer was obtained. 23.5 mL of the above cyclic monomer, 0.38 mL of methyl toluenesulfonate (MeOTs), and 38.5 mL of ultra-dry acetonitrile were mixed and reacted in a microwave reactor at 140 °C for 50 min. Then, 0.75 mL of a 1 mol / L KOH methanol solution was added at 0 °C, and the mixture was stirred at room temperature for 12 h to terminate the polymerization. The solvent was removed by rotary evaporation, and the residual polymer was dissolved in chloroform and purified by precipitation three times in n-hexane. The polymer was then dried under vacuum at 40 °C for 48 h to obtain the polymer containing the cyclic monomer. 22.5 g of the above-mentioned cyclic monomer polymer was dissolved in hot water at 60 °C, heated under reflux at 115 °C for 15 min, and then added to 300 g of 37% hydrochloric acid. The reaction was allowed to proceed for 36 h. The solvent was removed by rotary evaporation, and the residual solid was redissolved in hot water at 60 °C. NaOH solution was added to neutralize the solution to pH 9. The precipitate was centrifuged, and the supernatant was discarded. This process was repeated three times. The precipitate was then dried under vacuum at 65 °C for 48 h to obtain the activator.

[0059] Take 20g of SiO2 (particle size 10μm), 40mL of GPTMS, and 160mL of ethanol, add them to a 500mL flask, and reflux the mixture at 100℃ for 24h. Then, centrifuge the suspension at 11000rpm for 25min and remove the supernatant; sonicate with 120mL of ethanol for 20min at a frequency of 20kHz, remove the supernatant, repeat the washing three times, and place the product in a 60℃ oven for 12h to obtain an intermediate product. Take 22g of the activator prepared above, dissolve it in 200g of ethanol, and then add 27.5g of the intermediate product prepared above, and stir and reflux at 105℃ for 24h. Then, centrifuge the suspension at 11000rpm for 25min and remove the supernatant; sonicate with deionized water for 20min at a frequency of 20kHz, remove the supernatant, repeat the washing three times, and place the product in a 60℃ oven for 12h to obtain modifier I.

[0060] Example 2

[0061] Preparation of Modifier II

[0062] 46.5 mL of ultra-dry propionitrile and 4.25 g of zinc acetate dihydrate were added to a 250 mL three-necked flask and heated to 115 °C. After reflux of the propionitrile, 72 mL of 3-amino-1-propanol was slowly added dropwise using a constant-pressure dropping funnel. The reaction was allowed to proceed for 54.5 h, and after impurity removal, a cyclic monomer was obtained. 28.2 mL of the above cyclic monomer, 0.62 mL of 3-butynyl p-toluenesulfonate, and 49.6 mL of ultra-dry acetonitrile were mixed and reacted in a microwave reactor at 150 °C for 60 min. Then, 1.2 mL of a 1 mol / L KOH methanol solution was added at 2 °C, and the mixture was stirred at room temperature for 20 h to terminate the polymerization. The solvent was removed by rotary evaporation, and the residual polymer was dissolved in chloroform and purified by precipitation three times in n-hexane. The polymer was then dried under vacuum at 45 °C for 52 h to obtain the polymer containing the cyclic monomer. 27.4 g of the above-mentioned cyclic monomer polymer was dissolved in hot water at 70 °C, heated under reflux at 110 °C for 20 min, and then added to 250 g of 36% hydrochloric acid. The reaction was allowed to proceed for 48 h. The solvent was removed by rotary evaporation, and the residual solid was redissolved in hot water at 70 °C. NaOH solution was added to neutralize the solution to pH 9.5. The precipitate was centrifuged, and the supernatant was discarded. This process was repeated three times. The precipitate was then dried under vacuum at 65 °C for 52 h to obtain the activator.

[0063] 25 g of SiO2 (particle size 20 μm), 70 mL of LPTMS, and 185 mL of ethanol were added to a 500 mL flask, and the mixture was stirred and refluxed at 95 °C for 30 h. The suspension was then centrifuged at 14000 rpm for 20 min, and the supernatant was removed. The mixture was then ultrasonically dispersed in 150 mL of ethanol for 18 min at a frequency of 40 kHz, and the supernatant was removed. The washing was repeated three times, and the product was placed in a 65 °C oven for 20 h to obtain an intermediate product. 28.6 g of the activator prepared above was dissolved in 265 g of ethanol, and then 37.8 g of the intermediate product prepared above was added. The mixture was stirred and refluxed at 110 °C for 20 h. The suspension was then centrifuged at 14000 rpm for 25 min, and the supernatant was removed. The mixture was then ultrasonically dispersed in deionized water for 20 min at a frequency of 20 kHz, and the supernatant was removed. The washing was repeated three times, and the product was placed in a 65 °C oven for 16 h to obtain modifier II.

[0064] Example 3

[0065] 100g of solvent-decomposed asphalt with a softening point of 118.5℃ was placed in 240g of chloroform and dissolved completely. Modifier I prepared above was then added, and the mixture was stirred mechanically at 1000 rpm at 85℃ for 4 hours. After the reaction, excess organic solvent was removed by rotary evaporation, and the mixture was frozen at -25℃ for 4 hours. It was then pulverized for 50 seconds using a universal pulverizer and sieved to obtain cationic modified high softening point asphalt particles with an average particle size of 80 mesh. These cationic modified high softening point asphalt particles contained 5.2 wt% of modifier I.

[0066] Take No. 5 white oil and calcium chloride aqueous solution (concentration 20wt%), prepare base fluid according to oil-water volume ratio (80:20), add 2.5wt% oleic acid amide, stir at room temperature for 10min, add 1.2wt% organic clay, stir for 5min, add the above-prepared cationic modified high softening point asphalt particles accounting for 4.8wt% of the total drilling fluid, continue stirring for 20min, add weighting agent barite, adjust the drilling fluid density to the required value, and obtain stable oil-in-water drilling fluid.

[0067] Example 4

[0068] 100g of solvent-desorbed asphalt with a softening point of 126.4℃ was placed in 200g of tetrahydrofuran, and the modifier II prepared above was added after complete dissolution. The mixture was stirred mechanically at 1500 rpm at 75℃ for 8 hours. After the reaction was completed, excess organic solvent was removed by rotary evaporation, and the mixture was frozen at -30℃ for 4.5 hours. Then, it was pulverized for 45 seconds using a universal pulverizer and sieved to obtain cationic modified high softening point asphalt particles with an average particle size of 100 mesh. These cationic modified high softening point asphalt particles contained 5.8wt% modifier II.

[0069] Take No. 5 white oil and calcium chloride aqueous solution (concentration 30wt%), prepare base fluid according to oil-water volume ratio (70:30), add 2.0wt% lauroyl diethanolamine, stir at room temperature for 15min, add 1.0wt% organic soil, stir for 5min, add 3.6wt% of the above-prepared cationic modified asphalt particles accounting for the total drilling fluid volume and continue stirring for 30min, add weighting agent barite, adjust the drilling fluid density to the required value, and obtain stable oil-in-water drilling fluid.

[0070] Example 5

[0071] 100g of oxidized asphalt with a softening point of 132.5℃ was placed in 390g of chloroform and fully dissolved. Modifier I prepared above was added and stirred using a mechanical stirrer at 800 rpm. The mixture was stirred and reacted at 65℃ for 6.5h. After the reaction was completed, excess organic solvent was removed by rotary evaporation. The mixture was then frozen at -30℃ for 6 hours and then pulverized for 30s using a universal pulverizer. The pulverized asphalt particles with an average particle size of 80 mesh were obtained. These cationic modified high softening point asphalt particles contained 6.4wt% of modifier I.

[0072] Take No. 5 white oil and calcium chloride aqueous solution (concentration 25wt%), prepare base fluid according to oil-water volume ratio (75:25), add 1.6wt% lauroyl diethanolamine, stir at room temperature for 15min, add 1.4wt% organic soil, stir for 10min, add 4.5wt% of the above-prepared cationic modified asphalt particles, continue stirring for 40min, add weighting agent barite, adjust the drilling fluid density to the required value, and obtain stable oil-in-water drilling fluid.

[0073] Example 6

[0074] 100g of oxidized asphalt with a softening point of 152.4℃ was placed in 540g of chloroform and fully dissolved. Modifier II prepared above was added and stirred using a mechanical stirrer at 1200rpm. The mixture was stirred and reacted at 70℃ for 6h. After the reaction was completed, excess organic solvent was removed by rotary evaporation. The mixture was then frozen at -35℃ for 7h and then pulverized for 40s using a universal pulverizer. The pulverized asphalt particles with an average particle size of 100 mesh were obtained. These cationic modified high softening point asphalt particles contained 6.0wt% of modifier II.

[0075] Take No. 3 white oil and calcium chloride aqueous solution (concentration 20wt%), prepare base fluid according to oil-water volume ratio (65:35), add 2.2wt% oleic acid amide, stir at room temperature for 15min, add 2.5wt% organic soil, stir for 5min, add 4.0wt% of the above-prepared cationic modified asphalt particles, continue stirring for 30min, add weighting agent limestone, adjust the drilling fluid density to the required value, and obtain stable oil-in-water drilling fluid.

[0076] Comparative Example 1

[0077] 100g of oxidized asphalt with a softening point of 132.5℃ was frozen at -30℃ for 6 hours, then crushed for 30s using a universal pulverizer, and sieved to obtain modified asphalt particles for drilling fluid with an average particle size of 80 mesh.

[0078] Take No. 5 white oil and calcium chloride aqueous solution (concentration 25wt%), prepare base fluid according to oil-water volume ratio (75:25), add 1.6wt% lauroyl diethanolamine, stir at room temperature for 15min, add 1.4wt% organic soil, stir for 10min, add the above-prepared modified asphalt particles accounting for 4.5wt% of the total drilling fluid, continue stirring for 40min, add weighting agent barite, adjust the drilling fluid density to the required value, and obtain stable oil-in-water drilling fluid.

[0079] Comparative Example 2

[0080] 20 g of SiO2 (particle size 10 μm), 40 mL of GPTMS, and 160 mL of ethanol were added to a 500 mL flask, and the mixture was stirred and refluxed at 100 °C for 24 h. The suspension was then centrifuged at 11000 rpm for 25 min, and the supernatant was removed. The mixture was then ultrasonically dispersed with 120 mL of ethanol for 20 min at a frequency of 20 kHz. The supernatant was removed, and the washing was repeated three times. The product was then placed in a 60 °C oven for 12 h to obtain modifier III.

[0081] 100g of oxidized asphalt with a softening point of 132.5℃ was placed in 390g of chloroform and fully dissolved. Modifier III prepared above was added and stirred using a mechanical stirrer at 800 rpm. After stirring at 65℃ for 6.5h, excess organic solvent could be removed by rotary evaporation. The mixture was then frozen at -30℃ for 6h and then pulverized for 30s using a universal pulverizer. The pulverized asphalt particles with an average particle size of 80 mesh were obtained. These modified asphalt particles contained 6.4wt% of modifier III.

[0082] Take No. 5 white oil and calcium chloride aqueous solution (concentration 25wt%), prepare base fluid according to oil-water volume ratio (75:25), add 1.6wt% lauroyl diethanolamine, stir at room temperature for 15min, add 1.4wt% organic soil, stir for 10min, add 4.5wt% of the above-prepared cationic modified asphalt particles, continue stirring for 40min, add weighting agent barite, adjust the drilling fluid density to the required value, and obtain stable oil-in-water drilling fluid.

[0083] Table 1. Physicochemical parameters of cationic modified high softening point asphalt particles and comparative modified asphalt particles in each embodiment.

[0084]

[0085] Table 2. Performance of water-in-oil drilling fluids obtained from various examples and comparative examples.

[0086] <![CDATA[ρ / g.cm -3 ]]> AV / mPa.s PV / mPa.s YP / Pa YP / PV <![CDATA[FL HTHP / mL]]> ES / V Example 3 1.7 44.2 31.5 14.8 0.47 6.0 1620 Example 4 1.8 43.5 30.4 14.0 0.46 6.5 1680 Example 5 1.6 44.0 33.6 16.2 0.48 5.7 1700 Example 6 1.7 45.2 29.5 13.9 0.47 5.2 1750 Comparative Example 1 1.6 43.4 28.8 8.6 0.30 57.4 1320 Comparative Example 2 1.6 44.2 30.2 11.5 0.38 38.6 1430

[0087] Note: In Table 2, the hot rolling conditions are: time 16 hours, temperature 180℃;

[0088] The rheological test temperature is 60℃;

[0089] High-temperature and high-pressure filtration loss measurement conditions: 180℃, 3.5MPa;

[0090] Where: AV: apparent viscosity,

[0091] PV: Plastic viscosity

[0092] YP: Dynamic shear force

[0093] YP / PV: Dynamic Plasticity Ratio

[0094] FL HTHP High temperature and high pressure filtration loss

[0095] ES: Demulsification voltage.

Claims

1. A water-in-oil based drilling fluid, characterized by: By mass fraction, comprising the following components: Emulsifier 0.5-5%; Organic soil 1-3%; Cationic modified high softening point asphalt particles 1-5%; Oil-water based liquid 87-95%; The cationic modified high softening point asphalt particles comprise base asphalt and a modifier, and the modifier is obtained by activating silica with an activator; The activator is prepared by the following method: (a) adding a nitrile monomer and a catalyst into a reactor, heating to 90-120℃, then adding an amino alcohol monomer, and reacting for 30-60h to obtain a cyclic monomer; (b) mixing the cyclic monomer obtained in step (a), an initiator and a nitrile monomer, and reacting at 100-160℃ for 30-90min, then adding a KOH methanol solution at -10-10℃, stirring for 8-24h, removing the solvent, dissolving the residual polymer in chloroform, precipitating and purifying, and drying to obtain a polymer of the cyclic monomer; (c) dissolving the polymer of the cyclic monomer obtained in step (b) in hot water, heating to reflux, adding a hydrochloric acid solution, and reacting for 24-72h, removing the solvent, re-dissolving the residual polymer in hot water, adding a NaOH solution until the solution pH is 9-10, centrifuging the precipitate, removing the supernatant, repeating 2-3 times, and drying to obtain the activator.

2. The water-in-oil based drilling fluid of claim 1, wherein: In step (a), the nitrile monomer is super-dry acetonitrile and / or propionitrile; the catalyst is zinc acetate dihydrate; the volume-mass ratio of the nitrile monomer to the catalyst is 10-20:1 mL / g; the amino alcohol monomer is one or more of 2-aminoethanol and 3-amino-1-propanol; and the volume ratio of the nitrile monomer to the amino alcohol monomer is 1:1-3.

3. The water-in-oil based drilling fluid of claim 1, wherein: In step (b), the initiator is a sulfonate cationic initiator; in step (b), the nitrile monomer is super-dry acetonitrile and / or propionitrile; the volume ratio of the initiator to the cyclic monomer is 0.01-0.1:1; the volume ratio of the cyclic monomer to the nitrile monomer is 1:1-3; in step (b), the concentration of KOH in the KOH methanol solution is 0.8-1.2 mol / L; and the amount of the KOH methanol solution added is 1 / 10-1 / 40 of the volume of the cyclic monomer.

4. The water-in-oil based drilling fluid of claim 3, wherein: In step (b), the initiator is one or more of methyl p-toluenesulfonate, ethyl trifluoromethanesulfonate and 3-butynyl p-toluenesulfonate.

5. The water-in-oil based drilling fluid of claim 1, wherein: In step (c), the temperature of the hot water is 40-80℃; the temperature of the heating to reflux is 80-120℃, and the heating to reflux time is 10-30min; the mass concentration of the hydrochloric acid solution is 30%-38%; and the mass ratio of the amount of the hydrochloric acid solution added to the amount of the cyclic monomer polymer added is 1-20:

1.

6. The water-in-oil based drilling fluid of claim 1, wherein: The base asphalt is asphalt with a softening point of 80-180℃.

7. The water-in-oil based drilling fluid of claim 1, wherein: The base asphalt is at least one of oxidized asphalt, solvent deoiled asphalt and natural asphalt.

8. The water-in-oil based drilling fluid of claim 1, wherein: The content of the modifier is 1%-10% and the content of the base asphalt is 90%-99% by weight of the cationic modified high softening point asphalt particles.

9. The water-in-oil based drilling fluid of claim 1, wherein: The particle size of the silica is 5-50μm.

10. The water-in-oil based drilling fluid of claim 1, wherein: The emulsifier is a long-chain fatty amide-based surfactant.

11. The water-in-oil based drilling fluid of claim 10, wherein: The emulsifier is at least one of lauryl diethanolamide, oleic acid amide, oleoyl diethanolamide and cocoyl diethanolamide.

12. A method of preparing a water-in-oil based drilling fluid according to any one of claims 1 to 11, characterized in that: The method comprises the following steps: (1) preparing cationic modified high softening point asphalt particles; (2) mixing the cationic modified high softening point asphalt particles with an emulsifier, an organic clay and an oil-water base fluid to obtain a water-in-oil base drilling fluid.

13. The method of claim 12, wherein: The method for preparing the cationic modified high softening point asphalt particles in step (1) comprises: (I) preparing a modifier; (II) dissolving a base asphalt in an organic solvent, adding the modifier obtained in step (I) and stirring to react, to obtain the cationic modified high softening point asphalt.

14. The method of claim 13, wherein: In step (I), the method for preparing the modifier comprises: (i) mixing silica, an epoxy silane coupling agent and ethanol, heating and refluxing, centrifuging the obtained suspension, ultrasonic dispersing the precipitate with ethanol, removing the supernatant, washing and drying to obtain an intermediate product; (ii) dissolving an activating agent in ethanol, adding the intermediate product obtained in step (i), heating and refluxing, centrifuging the obtained suspension, ultrasonic dispersing the precipitate with water, removing the supernatant, washing and drying to obtain the modifier.

15. The method of claim 14, wherein: In step (i), the epoxy silane coupling agent is 3-glycidyloxypropylmethyldiethoxysilane; the mass-volume ratio of the silica to the epoxy silane coupling agent is 1:1-3 g / mL; the silica, the epoxy silane coupling agent and the ethanol are mixed, wherein the volume ratio of the epoxy silane coupling agent to the ethanol is 1:1-5; And / or, in step (i), the centrifuging is performed at a speed of 5000-15000 rpm for 10-30 min; the ultrasonic dispersing is performed at a frequency of 20 kHz-60 kHz for 5-20 min; the drying is performed at a temperature of 50-80℃ for 5-20 h.

16. The method of claim 14, wherein: In step (ii), the activating agent is added in an amount of 1-20% based on the mass of the ethanol; the intermediate product is added in an amount of 1-30% based on the mass of the ethanol; the mass ratio of the activating agent to the intermediate product is 1:1-2; And / or, in step (ii), the centrifuging is performed at a speed of 5000-15000 rpm for 10-30 min; the ultrasonic dispersing is performed at a frequency of 20 kHz-60 kHz for 5-20 min; the stirring and refluxing is performed for 12-36 h; the drying is performed at a temperature of 50-80℃ for 5-20 h.

17. The method of claim 13, wherein: In step (II), the organic solvent is selected from one or more of chloroform, dichloromethane, toluene, tetrahydrofuran and carbon tetrachloride; the mass ratio of the organic solvent to the base asphalt is 1-20:1; And / or, in step (II), the stirring is performed at a speed of 80-2000 rpm; the reaction is performed at a temperature of 50-100℃ for 2-10 h.

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