Anti-230 ℃ high-salt high-density water-based drilling fluid and preparation method and application thereof

Abstract

The application provides an anti-230 DEG C high-salt high-density water-based drilling fluid and a preparation method and application thereof. The drilling fluid comprises the following raw material components in mass fraction: 100 parts of water, 1-3 parts of sodium-based bentonite, 1-2 parts of salt-resistant soil, 0.3-0.7 parts of an alkaline regulator, 0.1-0.4 parts of an oxygen remover, 2-4 parts of a high-temperature-resistant salt-resistant micro-crosslinking hydrophobic association zwitterionic fluid loss additive A, 2-4 parts of a high-temperature-resistant salt-resistant inorganic / organic hybrid zwitterionic fluid loss additive B, 2-3 parts of superfine calcium carbonate, 3-5 parts of a high-temperature-resistant high-salt rigid-flexible complementary plugging agent, 1-3 parts of a lubricant and 50-200 parts of a weighting agent. The drilling fluid has excellent rheological property, filtration wall building property, plugging property, sedimentation stability, inhibition of shale hydration and expansion, and maintenance of well wall stability and lubricity, and has the characteristics of high-temperature resistance, high-salt resistance and high density, thereby providing technical support for deep well and ultra-deep well drilling.

Description

Technical Field

[0001] This invention relates to a water-based drilling fluid resistant to 230℃, high salt content, and high density, as well as its preparation method and application, belonging to the field of drilling fluid technology. Background Technology

[0002] Deep and ultra-deep wells are key areas for oil and gas exploration and development in my country. The safe and efficient development of deep oil and gas resources is of great significance to ensuring my country's energy security. However, deep or ultra-deep wells have high bottom-hole temperatures (up to 220℃~260℃) and high pressures, and often contain large sections of gypsum and salt layers. Drilling fluids are prone to failure in high-temperature, high-salt environments, easily leading to complex downhole accidents such as wellbore instability, stuck pipe, and blowouts, causing significant economic losses and severely restricting the development of deep oil and gas resources.

[0003] Although oil-based drilling fluids exhibit strong temperature and salt resistance and good lubrication, they are costly, cause severe environmental pollution, and are difficult to recycle. Existing high-temperature and salt-resistant, high-density water-based drilling fluids are mostly polymer or polysulfonate drilling fluids. For example, Chinese patent document CN115820228 A discloses a high-temperature, high-density water-based drilling fluid with a density of 2.2 g / cm³. 3 It has a temperature resistance of up to 200℃, a salt resistance of up to 15%, and a potassium resistance of up to 7%. Chinese patent document CN107118750A discloses a high-density drilling fluid resistant to high-temperature saturated brine, with a density of 2.30 g / cm³. 3 It can withstand temperatures up to 200℃ and salt saturation. Chinese patent document CN 116083061A discloses a high-density, low-solids water-based drilling fluid that can withstand temperatures up to 220℃, but has a density of only 1.5 g / cm³. 3 Furthermore, it does not mention salt resistance. Chinese patent document CN 112574725 A discloses a high-temperature resistant polymer drilling fluid with a density of 2.4 g / cm³. 3 It can withstand temperatures up to 230℃, but only resists 7% potassium chloride. The drilling fluid described in the aforementioned patent literature cannot simultaneously possess the properties of high density, high temperature resistance, and high salt resistance.

[0004] Therefore, researching a drilling fluid that simultaneously possesses high density, high temperature resistance, and high salt resistance is of great significance for the safe and efficient development of deep oil and gas resources. Summary of the Invention

[0005] To address the shortcomings of existing high-temperature and high-salt-resistant high-density drilling fluids, this invention provides a 230℃-resistant, high-salt-resistant, high-density water-based drilling fluid, its preparation method, and its applications. The drilling fluid of this invention exhibits excellent rheological properties, filtration and wall-building properties, plugging properties, settling stability, inhibition of shale hydration and expansion, and maintenance of wellbore stability and lubrication. It also possesses high-temperature resistance, high-salt resistance, and high-density characteristics, providing technical support for deep and ultra-deep well drilling.

[0006] The technical solution of the present invention is as follows:

[0007] A water-based drilling fluid resistant to 230℃, high salt content, and high density comprises the following raw materials in parts by weight: 100 parts water, 1-3 parts sodium-based bentonite, 1-2 parts salt-resistant clay, 0.3-0.7 parts alkaline regulator, 0.1-0.4 parts oxygen scavenger, 2-4 parts high-temperature and salt-resistant micro-crosslinked hydrophobic associated zwitterionic filtration reducer A, 2-4 parts high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration reducer B, 2-3 parts ultrafine calcium carbonate, 3-5 parts high-temperature and high-salt-resistant rigid-flexible plugging agent, 1-3 parts lubricant, and 50-200 parts weighting agent.

[0008] According to a preferred embodiment of the present invention, the 230℃-resistant, high-salt, high-density water-based drilling fluid comprises the following raw material components in parts by weight: 100 parts water, 2 parts sodium-based bentonite, 2 parts salt-resistant clay, 0.7 parts alkaline regulator, 0.4 parts oxygen scavenger, 4 parts high-temperature and salt-resistant micro-crosslinked hydrophobic associated zwitterionic filtration reducer A, 4 parts high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration reducer B, 2 parts ultrafine calcium carbonate, 5 parts high-temperature and high-salt-resistant rigid-flexible sealing agent, 3 parts lubricant, and 60-200 parts weighting agent.

[0009] According to a preferred embodiment of the present invention, the alkaline regulator is one or a combination of two or more of sodium hydroxide, sodium carbonate, or sodium bicarbonate; the pH value of the drilling fluid is adjusted to 8-10 using the alkaline regulator.

[0010] According to a preferred embodiment of the present invention, the total mass of sodium-based bentonite and salt-resistant clay in the drilling fluid is 2-4 wt% of the mass of water.

[0011] According to a preferred embodiment of the present invention, the oxygen scavenger is one of sodium sulfite, sodium bisulfite, or maleic anhydride.

[0012] According to a preferred embodiment of the present invention, the average particle size of the ultrafine calcium carbonate is 10-30 nm.

[0013] According to a preferred embodiment of the present invention, the lubricant is RH-3.

[0014] According to a preferred embodiment of the present invention, the weighting agent is 300-mesh barite powder.

[0015] According to a preferred embodiment of the present invention, the preparation method of the high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration loss reducing agent A includes the following steps:

[0016] 2-Acrylamido-2-methylpropanesulfonic acid was dissolved in deionized water and the pH was adjusted to 7. Sodium dodecyl sulfate and styrene were added and fully sheared and emulsified. N,N-dimethylacrylamide and acryloyloxyethyl dimethylbenzylammonium chloride were added and fully dispersed. Potassium persulfate initiator and N,N-dimethylenebisacrylamide crosslinking agent were added. After reaction, the mixture was washed, dried and pulverized to obtain high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration loss reducer A.

[0017] Preferably, the mass ratio of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acryloyloxyethyl dimethylbenzylammonium chloride, and styrene is 15-25:5-15:5-10:5-10.

[0018] Preferably, the mass ratio of deionized water to total monomers is 100:25-35. The total mass of the monomers is the total mass of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acryloyloxyethyl dimethylbenzylammonium chloride, and styrene.

[0019] Preferably, the pH value is adjusted to 7 using a NaOH aqueous solution with a concentration of 30wt%-50wt%.

[0020] Preferably, the mass ratio of sodium dodecyl sulfonate to the total monomer is 0.3-0.8:25-35.

[0021] Preferably, the shear emulsification time is 20-30 min, the shear emulsification rate is 200-400 rpm, and the shear emulsification temperature is room temperature.

[0022] Preferably, the mass ratio of potassium persulfate to total monomers is 0.10-0.20:25-35.

[0023] Preferably, the mass ratio of N,N-dimethylenebisacrylamide to the total monomer is 0.02-0.08:25-35.

[0024] Preferably, the reaction temperature is 60-70℃, the reaction time is 4-6h, and the reaction is carried out in a nitrogen atmosphere.

[0025] According to a preferred embodiment of the present invention, the preparation method of the high-temperature resistant and salt-tolerant inorganic / organic hybrid zwitterionic filtration loss reducing agent B includes the following steps:

[0026] (1) Mix the nano-silica ethanol dispersion and KH570 dispersion evenly, adjust the pH to 7, react, and then filter, wash and dry to obtain KH570 modified nano-silica;

[0027] (2) Dissolve 2-acrylamido-2-methylpropanesulfonic acid in deionized water and adjust the pH to 7; add N,N-dimethylacrylamide (DMAA), KH570 modified nano silica, and 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt and disperse them evenly; add potassium persulfate initiator, react, and then wash, dry and pulverize to obtain high temperature resistant and salt resistant inorganic / organic hybrid zwitterionic filtration loss reducer B.

[0028] Preferably, in step (1), the mass ratio of nano-silica to ethanol in the nano-silica ethanol dispersion is 15-25:100; the particle size of the nano-silica is 20-80 nm.

[0029] Preferably, in step (1), the mass ratio of KH570 to solvent in the KH570 dispersion is 1-3:100; the solvent is a mixed solution of water and ethanol, and the mass ratio of water to ethanol in the mixed solution is 1:9-10; the mass ratio of KH570 to nano silica is 1:10-15.

[0030] Preferably, in step (1), triethylamine is used to adjust the pH to 7.

[0031] Preferably, in step (1), the reaction temperature is 60-90℃ and the reaction time is 4-8h.

[0032] Preferably, in step (2), the mass ratio of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, KH570 modified nano silica, and the inner salt of 1-(3-sulfopropyl)-2-vinylpyridine hydroxide is 20-30:10-20:5-10:5-10.

[0033] Preferably, in step (2), the mass ratio of 2-acrylamido-2-methylpropanesulfonic acid to deionized water is 1-20:100.

[0034] Preferably, in step (2), the pH value is adjusted to 7 using a NaOH aqueous solution with a concentration of 30wt%-50wt%.

[0035] Preferably, in step (2), the mass of potassium persulfate is 0.1-0.5% of the total mass of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, KH570 modified nano silica, and 1-(3-sulfopropyl)-2-vinylpyridine hydroxide internal salt.

[0036] Preferably, in step (2), the reaction temperature is 60-85℃, the reaction time is 4-6 hours, and the reaction is carried out in a nitrogen atmosphere.

[0037] Preferably, in step (2), the average particle size of the high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B is 30nm-150nm, and more preferably 50nm-100nm.

[0038] According to the present invention, the high-temperature resistant and high-salt-resistant sealing agent with a combination of rigidity and flexibility is prepared according to the method in patent document CN115160513A. Preferably, the preparation method includes the following steps:

[0039] 1) Disperse 2-acrylamide-2-methylpropanesulfonic acid thoroughly in water, adjust the pH to 7-8, then add sodium dodecylbenzenesulfonate and stir until fully dispersed; add KH570 modified nano silica and disperse thoroughly to obtain solution a;

[0040] 2) Mix styrene and divinylbenzene thoroughly, and wash away the polymerization inhibitor with NaOH solution to obtain solution b;

[0041] 3) Under high-speed stirring, add solution b dropwise to solution a, then add RAFT reagent N,N'-diethyldithiocarbamate (BDC), mix thoroughly; add potassium persulfate initiator, and react at 70°C for 6 hours under nitrogen atmosphere to obtain the final product.

[0042] A further preferred method for preparing a high-temperature resistant, high-salt resistant, rigid-flexible sealing agent includes the following steps:

[0043] 1) Weigh 5g of 2-acrylamide-2-methylpropanesulfonic acid and add it to a flask containing 130g of water. Stir until fully dispersed, adjust the pH to 7-8, then add 0.3g of sodium dodecylbenzenesulfonate and stir until fully dispersed; add 1g of KH570 modified nano silica, stir for 10 minutes and then sonicate for 30 minutes to obtain solution a;

[0044] 2) Weigh 15g of styrene and 2g of divinylbenzene, stir until fully mixed, and then wash away the polymerization inhibitor with NaOH solution to obtain solution b;

[0045] 3) Under high-speed stirring, add solution b dropwise to solution a, then add 0.01g of RAFT reagent N,N'-diethyldithiocarbamate (BDC) and stir for 30 minutes; add the liquid to a flask, stir, and deoxygenate with nitrogen for 30 minutes; heat to 70℃, add 0.15g of initiator potassium persulfate, and react with nitrogen for 6 hours; after the reaction is complete, keep stirring, stop heating, and wait for the temperature to drop to 30-40℃ before pouring the contents out of the flask to obtain the product.

[0046] The preparation method of the above-mentioned 230℃-resistant, high-salt, high-density water-based drilling fluid includes the following steps: At a stirring speed of 2000-4000 rpm, sodium-based bentonite, salt-resistant clay, and an alkaline regulator are added sequentially to water, stirred for 2-4 hours, and then allowed to stand at room temperature for 20-30 hours to obtain the base slurry; at a stirring speed of 2000-4000 rpm, an oxygen scavenger is added, and stirred for 1-5 minutes; a high-temperature-resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration reducer A is added, and the stirring speed is adjusted to 8000-12000 rpm for 10-20 minutes; at 8000-12000 rpm... At a stirring speed of 0 rpm, add high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B and stir for 10-20 minutes; at a stirring speed of 8000-12000 rpm, add ultrafine calcium carbonate and stir for 5-10 minutes; at a stirring speed of 8000-12000 rpm, add a high-temperature and salt-resistant rigid-flexible plugging agent and stir for 5-10 minutes; at a stirring speed of 8000-12000 rpm, add a lubricant and stir for 10-20 minutes; finally, add a weighting agent and mix thoroughly to obtain a 230℃-resistant, high-salt-resistant, high-density water-based drilling fluid.

[0047] The above-mentioned water-based drilling fluid, which is resistant to 230℃, high salt content, and high density, is used in deep or ultra-deep well drilling.

[0048] The technical features and beneficial effects of this invention are as follows:

[0049] 1. Bentonite has excellent mud-forming ability, which can increase the viscosity and shear strength of drilling fluid, enabling it to carry and suspend rock cuttings and clean the bottom of the well. However, excessive use of bentonite can lead to excessively high drilling fluid viscosity, and even gelation after high-temperature aging. Salt-resistant clay has a lower mud-forming rate than bentonite, but stronger resistance to temperature and salt. Salt-resistant clay not only has a smaller viscosity-increasing effect but also enhances the filtration and wall-building properties of drilling fluid, reducing filtration loss. A 1:1 mixture of bentonite and salt-resistant clay provides the drilling fluid with a certain viscosity and shear strength while effectively controlling filtration loss. To avoid high-temperature gelation, the total clay content in this invention is controlled to within 4%.

[0050] 2. The micro-crosslinked structure of the high-temperature and salt-resistant, salt-tolerant, micro-crosslinked, hydrophobic, and zwitterionic filtration reducer A enhances the rigidity of the molecular chains. The three-dimensional network structure allows the molecular chains to fully extend in high-salt environments, resulting in excellent temperature and salt resistance. The hydrophobic association of the benzene ring promotes crosslinking of polymer molecules through hydrogen bonds, forming a three-dimensional physical crosslinked network, strengthening the micro-crosslinked three-dimensional network structure, further enhancing the polymer's rigidity, allowing the molecular chains to extend further in high-salt environments, and further improving the polymer's salt resistance. During the preparation of the high-temperature and salt-resistant, salt-tolerant, micro-crosslinked, hydrophobic, and zwitterionic filtration reducer A, after adding the emulsifier SDS and styrene, shear emulsification is required to ensure the formation of a stable oil-in-water emulsion, which is beneficial for smooth and uniform polymerization. The benzene ring has significant steric hindrance; if the mass proportions of acryloyloxyethyl dimethyl benzyl ammonium chloride and styrene in the monomers are too high, it will lead to a decrease in the degree of polymerization and a decline in performance. The amount of crosslinking agent needs to be strictly controlled. Too much crosslinking agent will result in a polymer molecular weight that is too large, causing excessively high drilling fluid viscosity. In the preparation process of the filtration loss reducer A of the present invention, the selection and amount of the reactive monomers, as well as the type and amount of the crosslinking agent, will affect the performance of the obtained filtration loss reducer, and thus affect the performance of the drilling fluid; if the above conditions are not suitable, the performance of both the filtration loss reducer and the drilling fluid will be reduced.

[0051] 3. Unlike conventional cationic and anionic monomers such as dimethyldiallylammonium chloride and 2-acrylamido-2-methylpropanesulfonic acid, the inner salt of betaine monomer 1-(3-sulfopropyl)-2-vinylpyridine hydroxide possesses quaternary ammonium cations, a rigid pyridine ring, and sulfonate groups, thus exhibiting excellent adsorption properties, temperature and salt resistance. Modified nano-silica possesses excellent adsorption, high-temperature resistance, and plugging capabilities, effectively filling the water loss channels inside the mud cake and reducing filtration loss. The quaternary ammonium cations form a strong electrostatic force with the clay, and the Si-OH of the modified nano-silica undergoes a condensation reaction with the Si-OH on the clay surface. These two strong chemical adsorption processes allow the polymer to be tightly adsorbed onto the clay surface at high temperatures, increasing the amount of polymer adsorbed on the clay. In the preparation of high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B, the KH570 modified nano-silica and the 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt exhibit significant steric hindrance. If their mass proportion in the monomer is too high, it will lead to a decrease in the degree of polymerization and a reduction in the performance of the filtration loss reducer. During the preparation of filtration loss reducer B in this invention, the selection and dosage of raw materials will affect the performance of the resulting filtration loss reducer, and consequently, the performance of the drilling fluid; if the above conditions are unsuitable, the performance of both the filtration loss reducer and the drilling fluid will decrease.

[0052] 4. The filtration loss reducer B of this invention has a stronger adsorption effect than filtration loss reducer A, and filtration loss reducer B tightly adsorbs and encapsulates the clay. Filtration loss reducer A is distributed on the outside of filtration loss reducer B and clay, protecting the inner layer of filtration loss reducer B and clay structure from high-temperature damage through its network structure and excellent temperature resistance. The sulfonic acid groups have strong hydration properties, which can increase the thickness of the hydration film on the clay surface and increase the repulsive force of the hydration film, thereby effectively preventing the agglomeration of clay particles under high temperature and high salt conditions, maintaining clay dispersion, maintaining a reasonable particle size distribution in the drilling fluid, and forming a dense filter cake, thus achieving excellent filtration loss reduction effect.

[0053] 5. In this invention, ultrafine calcium carbonate, as a high-temperature resistant solid plugging agent, can improve mud cake quality and reduce filtration loss. However, its viscosity-increasing effect is significant, and the dosage needs to be reasonably controlled according to the viscosity of the drilling fluid. The high-temperature resistant, high-salt, rigid-flexible plugging agent is an emulsion plugging agent. Under pressure differential, this plugging agent can reduce drilling fluid filtration loss, fill and deposit around the wellbore, forming an effective pressure-bearing plugging layer, preventing pressure transmission and filtrate intrusion. Furthermore, the emulsion can play a certain role in viscosity reduction. Using an alkaline regulator to adjust the pH of the system to the range of 8-10 is beneficial for the treatment agent to fully exert its performance. The oxygen scavenger can remove dissolved oxygen in the water, preventing the filtration loss reducer from being oxidized and becoming ineffective. The lubricant gives the drilling fluid good lubricity, reduces drilling friction, improves drilling efficiency, and also has a viscosity-reducing effect. The weighting agent increases the drilling fluid density to balance formation pressure.

[0054] 6. This invention rationally regulates the rheological and filtration properties of drilling fluids by controlling the amounts of clay, filtration reducer, and plugging agent. The raw material composition of this invention is integrated, with each ingredient exhibiting synergistic effects. This combined action gives the drilling fluid of this invention the characteristics of high temperature resistance, high salt tolerance, and high density. The drilling fluid exhibits excellent rheological properties, filtration wall-building properties, plugging properties, inhibition properties, settling stability, and lubricity. The drilling fluid of this invention can withstand temperatures up to 230℃, resist salt to saturation, resist calcium up to 5%, and resist potassium up to 10%, overcoming the technical challenges of existing drilling fluids failing under high density, high temperature, and high salt conditions, providing technical support for deep and ultra-deep well drilling. This invention does not use sulfonated materials such as sulfonated asphalt or sulfonated lignite resin, meeting environmental protection requirements in sensitive areas. The selection of raw material types and the ratio between raw materials are particularly important; choosing other similar raw materials or having an inappropriate ratio between raw materials will lead to a decline in the performance of the drilling fluid. Detailed Implementation

[0055] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0056] Unless otherwise specified, all materials used in the embodiments are commercially available.

[0057] Preparation Example 1

[0058] Preparation of high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration loss reducer A1 (all parts below are by weight):

[0059] Add 100 parts of deionized water and 8 parts of 2-acrylamido-2-methylpropanesulfonic acid to a clean three-necked flask and stir until homogeneous. Adjust the pH of the system to 7 by adding 40 wt% NaOH aqueous solution and stir for 5 min. Add 0.5 parts of sodium dodecyl sulfate and 5 parts of styrene to the three-necked flask and shear emulsify at 300 rpm for 20 min. Add 15 parts of N,N-dimethylacrylamide and 5 parts of acryloyloxyethyl dimethylbenzylammonium chloride and stir thoroughly for 5 min to ensure complete dispersion of the monomers. Purge the reaction system with nitrogen to remove oxygen. Heat the system to the set temperature in a 65°C water bath, add 0.2 parts of potassium persulfate and 0.08 parts of N,N-dimethylenebisacrylamide, and react under a nitrogen atmosphere for 4 h to obtain a polymer gel. Wash the gel twice with acetone, dry it at 100°C, and pulverize it to obtain the micro-crosslinked hydrophobic associated zwitterionic filtration loss reducer A1.

[0060] Preparation Example 2

[0061] Preparation of high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B1 (all parts below are by weight):

[0062] Add 25 parts of KH570 dispersion (wherein the mass ratio of nano-silica to ethanol is 20:100; the particle size of nano-silica is 50 nm) to 50 parts of nano-silica ethanol dispersion (wherein the mass ratio of KH570 to solvent is 3:100; the solvent is a mixed solution of water and ethanol, where the mass ratio of water to ethanol in the mixed solution is 1:10). After mixing thoroughly, adjust the pH of the system to 7 with triethylamine; heat to 80℃ and react for 4 h; after the reaction is complete, filter, wash, and dry to obtain KH570 modified nano-silica. Add 100 parts of deionized water to a clean three-necked flask, dissolve 15 parts of 2-acrylamido-2-methylpropanesulfonic acid in deionized water, and adjust the pH of the system to 7 with 40 wt% NaOH aqueous solution. Add 25 parts DMAA, 5 parts KH570 modified nano silica, and 5 parts 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt, and stir thoroughly to dissolve the monomer. Heat the system to 65°C, purge with nitrogen to remove oxygen from the flask, add 0.15 parts potassium persulfate initiator, and react in a nitrogen atmosphere for 4 hours to obtain a polymer gel. Wash the gel with acetone, dry, and pulverize to obtain high-temperature resistant and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B1 with an average particle size of 85 nm.

[0063] Preparation Example 3

[0064] Preparation of high-temperature and high-salt resistant, rigid-flexible sealing agent C1:

[0065] 1) Weigh 5g of 2-acrylamide-2-methylpropanesulfonic acid, add it to a flask containing 130g of water, stir until fully dispersed, adjust the pH to 7-8, then add 0.3g of sodium dodecylbenzenesulfonate, and stir until fully dispersed;

[0066] 2) Add 1g of KH570 modified nano silica to the liquid in step 1), stir for 10 minutes and then sonicate for 30 minutes to obtain solution a;

[0067] 3) Weigh 15g of styrene and 2g of divinylbenzene, stir until fully mixed, and then wash away the polymerization inhibitor with NaOH solution to obtain solution b;

[0068] 4) While stirring at high speed, add solution b dropwise to solution a, then add 0.01g of RAFT reagent N,N'-diethyldithiocarbamate (BDC) and keep stirring for 30 minutes.

[0069] 5) Add the liquid from step 4) to the flask, keep stirring, and deoxygenate with nitrogen for 30 minutes;

[0070] 6) Heat to 70℃, add 0.15g of potassium persulfate initiator, and react with nitrogen gas for 6 hours;

[0071] 7) After the reaction is complete, keep stirring and stop heating. After the temperature drops to 30-40℃, pour the contents out of the flask. The result is the high-temperature resistant, high-salt resistant, rigid-flexible sealing agent C1.

[0072] Example 1

[0073] Preparation of water-based drilling fluid:

[0074] Take 300g of tap water and disperse 6g of sodium-based bentonite, 6g of salt-resistant clay, 0.9g of Na2CO3, and 1.2g of NaOH in the water sequentially at 3000rpm. Stir continuously for 2 hours and allow to stand at room temperature for 24 hours to obtain the base slurry. Slowly add 1.2g of sodium sulfite to the pre-hydrated base slurry at 3000rpm and stir for 3 minutes. Slowly add 12g of high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration loss reducer A1 and stir at 10000rpm for 20 minutes. Slowly add 12g of high-temperature resistant, salt-resistant, inorganic / organic hybrid zwitterionic filtration loss reducer B1 at 10000rpm and stir for 20 minutes. Add 6g of ultrafine calcium carbonate (average particle size 20nm) at 10000rpm and stir for 10 minutes. Add 15g of high-temperature resistant, high-salt, rigid-flexible sealing agent C1 at 10000rpm and stir for 10 minutes. Add 9g of lubricant RH-3 at 10000rpm and stir for 10 minutes. Finally, add 331g of barite powder (300 mesh) to adjust the drilling fluid density to 1.6g / cm³. 3 Stir for 20 minutes to obtain drilling fluid.

[0075] Example 2

[0076] The water-based drilling fluid was prepared as described in Example 1, except that 180g of barite powder (300 mesh) was added to adjust the density of the drilling fluid to 1.4g / cm³. 3 Other steps and conditions are the same as in Example 1.

[0077] Example 3

[0078] Water-based drilling fluid was prepared as described in Example 1, except that 450g of barite powder (300 mesh) was added to adjust the density of the drilling fluid to 1.8g / cm³. 3 Other steps and conditions are the same as in Example 1.

[0079] Example 4

[0080] Water-based drilling fluid was prepared as described in Example 1, except that 580g of barite powder (300 mesh) was added to adjust the drilling fluid density to 2.0g / cm³. 3 Other steps and conditions are the same as in Example 1.

[0081] Example 5

[0082] Water-based drilling fluid was prepared as described in Example 1, except that 8g of sodium-based bentonite and 4g of salt-resistant clay were added; other steps and conditions were the same as in Example 1.

[0083] Example 6

[0084] Water-based drilling fluid was prepared as described in Example 1, except that 9g of high-temperature and salt-resistant micro-crosslinked hydrophobic associated zwitterionic filtration reducer A1 and 9g of high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration reducer B1 were added; other steps and conditions were the same as in Example 1.

[0085] Example 7

[0086] Water-based drilling fluid was prepared as described in Example 1, except that 12g of high-temperature and high-salt resistant, rigid-flexible plugging agent C1 was added; other steps and conditions were the same as in Example 1.

[0087] Example 8

[0088] Water-based drilling fluid was prepared as described in Example 1, except that 9g of ultrafine calcium carbonate was added; other steps and conditions were the same as in Example 1.

[0089] Example 9

[0090] The high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration loss reducer was prepared as described in Preparation Example 1, except that: the amount of N,N-dimethylacrylamide was 20 parts, the amount of 2-acrylamido-2-methylpropanesulfonic acid was 5 parts, the amount of acryloyloxyethyl dimethylbenzylammonium chloride was 10 parts, and the amount of styrene was 10 parts; other steps and conditions were the same as in Preparation Example 1; the resulting polymer was denoted as A2.

[0091] Water-based drilling fluid was prepared as described in Example 1, except that the high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration loss reducer A1 was replaced with A2; other steps and conditions were the same as in Example 1.

[0092] Example 10

[0093] The high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B was prepared as described in Preparation Example 2, except that the amount of 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt was 10 parts; other steps and conditions were the same as in Preparation Example 2; the resulting filtration loss reducer was designated as B2.

[0094] Prepare a water-based drilling fluid resistant to 230℃, high salt, and high density as described in Example 1, except that the high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B1 is replaced with B2; other steps and conditions are the same as in Example 1.

[0095] Example 11

[0096] The high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B was prepared as described in Preparation Example 2, except that: the amount of N,N-dimethylacrylamide was 20 parts, the amount of 2-acrylamido-2-methylpropanesulfonic acid was 10 parts, and the amount of KH570 modified nano silica was 10 parts; other steps and conditions were the same as in Preparation Example 2; the resulting filtration loss reducer was designated as B3.

[0097] Prepare a water-based drilling fluid resistant to 230℃, high salt, and high density as described in Example 1, except that the high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B1 is replaced with B3; other steps and conditions are the same as in Example 1.

[0098] Comparative Example 1

[0099] Water-based drilling fluid was prepared as described in Example 1, except that salt-resistant soil was not added; other steps and conditions were the same as in Example 1.

[0100] Comparative Example 2

[0101] Water-based drilling fluid was prepared as described in Example 1, except that the high-temperature and salt-resistant micro-crosslinked hydrophobic associative zwitterionic filtration reducer A1 was replaced with sulfonate copolymer DSP-1, and the high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration reducer B1 was replaced with sulfonate copolymer DSP-2; other steps and conditions were the same as in Example 1.

[0102] Comparative Example 3

[0103] The high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration loss reducer was prepared as described in Preparation Example 1, except that 0.5 parts of N,N-dimethylenebisacrylamide were added; other steps and conditions were the same as in Preparation Example 1; the resulting polymer was denoted as DA1.

[0104] Water-based drilling fluid was prepared as described in Example 1, except that the high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration reducer A1 was replaced with DA1; other steps and conditions were the same as in Example 1.

[0105] Comparative Example 4

[0106] The preparation of the high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer is as described in Preparation Example 2, except that: no 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt monomer is added; other steps and conditions are the same as in Preparation Example 2; the resulting filtration loss reducer is denoted as DB1.

[0107] Prepare a water-based drilling fluid resistant to 230℃, high salt, and high density as described in Example 1, except that the high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B1 is replaced with DB1; other steps and conditions are the same as in Example 1.

[0108] Comparative Example 5

[0109] The preparation of the high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration loss reducer is as described in Preparation Example 1, except that styrene is not added; other steps and conditions are the same as in Preparation Example 1; the resulting polymer is denoted as DA2.

[0110] Water-based drilling fluid was prepared as described in Example 1, except that the high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration reducer A1 was replaced with DA2; other steps and conditions were the same as in Example 1.

[0111] Comparative Example 6

[0112] The preparation of the high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration loss reducer is as described in Preparation Example 1, except that: acryloyloxyethyl dimethyl benzyl ammonium chloride is not added; other steps and conditions are the same as in Preparation Example 1; the resulting polymer is denoted as DA3.

[0113] Water-based drilling fluid was prepared as described in Example 1, except that the high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration reducer A1 was replaced with DA3; other steps and conditions were the same as in Example 1.

[0114] Comparative Example 7

[0115] The high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration loss reducer was prepared as described in Preparation Example 1, except that: acryloyloxyethyl dimethyl benzyl ammonium chloride was replaced with acryloyloxyethyl trimethyl ammonium chloride; other steps and conditions were the same as in Preparation Example 1; the resulting polymer was denoted as DA4.

[0116] Water-based drilling fluid was prepared as described in Example 1, except that the high-temperature resistant, salt-resistant, micro-crosslinked, hydrophobic, zwitterionic filtration reducer A1 was replaced with DA4; other steps and conditions were the same as in Example 1.

[0117] Comparative Example 8

[0118] The preparation of the high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer is as described in Preparation Example 2, except that KH570 modified nano-silica is not added; other steps and conditions are the same as in Preparation Example 2; the resulting filtration loss reducer is denoted as DB2.

[0119] Prepare a water-based drilling fluid resistant to 230℃, high salt, and high density as described in Example 1, except that the high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B1 is replaced with DB2; other steps and conditions are the same as in Example 1.

[0120] Comparative Example 9

[0121] Water-based drilling fluid was prepared as described in Example 1, except that the high-temperature and high-salt resistant, rigid-flexible plugging agent C1 was replaced with nano-polyester NP-1; other steps and conditions were the same as in Example 1.

[0122] Experimental Example 1

[0123] During the drilling of deep and ultra-deep wells, large sections of gypsum-salt layers are often encountered, Na + The dissolution of inorganic cations can easily lead to the failure of drilling fluid performance; therefore, drilling fluids need to possess excellent temperature and salt resistance. NaCl was added to the drilling fluids prepared in the examples and comparative examples, and stirred for 20 minutes to achieve a NaCl mass content of 15%, resulting in salt-containing drilling fluids. The salt-containing drilling fluids prepared in Examples 1 and 5-11 were named F1-F8, and the salt-containing drilling fluids prepared in Comparative Examples 1-9 were named DF1-DF9. The above drilling fluids were respectively placed in stainless steel high-temperature aging tanks and aged at 230°C for 16 hours. The apparent viscosity AV (mPa·s), plastic viscosity PV (mPa·s), dynamic shear force YP (mPa·s), and API filtration loss FL of the aged drilling fluids were tested according to GB / T16783.1-2014 Petroleum and Natural Gas Industry Drilling Fluid Field Testing - Part 1 Water-based Drilling Fluids. API and the filtration loss FL at high temperature and high pressure of 220℃×3.5MPa HTHP The results are shown in Table 1.

[0124] Table 1. Performance of drilling fluid at 230℃ and 15% NaCl

[0125]

[0126] The test results show that the drilling fluid of this invention has a viscosity of 1.6 g / cm³. 3 Under 15% high-salt conditions, the API filtration loss after aging at 230℃ for 16 hours was only 0.4 mL, and the high-temperature, high-pressure filtration loss was only 15.4 mL, with viscosity and shear stress within a reasonable range. This indicates that the drilling fluid of this invention is resistant to temperatures up to 230℃ and salts up to 15%, exhibiting good rheological and filtration performance under high-density conditions. Salt-resistant clay has a low slurry-forming rate and a small thickening effect, but its temperature and salt resistance is stronger than bentonite. Reducing the amount of salt-resistant clay will increase the viscosity and filtration loss of the drilling fluid. However, its cost is high, and its dosage should be controlled within 2%. Appropriately reducing the total amount of filtration loss reducers A and B in the drilling fluid reduces the viscosity and increases the filtration loss, but it remains at a low level. Ultrafine calcium carbonate can achieve a good plugging effect, but its thickening effect is strong; the maximum addition in this drilling fluid should not exceed 3%. The high-temperature and high-salt resistant, rigid-flexible plugging agent C1 is an emulsion with certain viscosity and filtration loss reduction effects, and is low in cost.

[0127] The DF3 test results show that if the crosslinking degree of the high-temperature and salt-resistant micro-crosslinked hydrophobic associative zwitterionic filtration reducer is too high, it will lead to excessive viscosity of the drilling fluid, which is not conducive to field construction. The DF4 test results show that after removing the key monomer 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt of the high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration reducer B1, the temperature and salt resistance of filtration reducer B decreased significantly, ultimately leading to a decrease in drilling fluid viscosity and shear stress, and an increase in filtration loss.

[0128] By appropriately increasing the proportion of styrene and acryloyloxyethyl dimethyl benzyl ammonium chloride in the high-temperature and salt-resistant micro-crosslinked hydrophobic associative zwitterionic filtration loss reducer A1, the rigidity and hydrophobic association effect of the polymer are enhanced, allowing the polymer to fully extend in a high-salt environment, thereby improving the polymer's temperature and salt resistance. If styrene and acryloyloxyethyl dimethyl benzyl ammonium chloride are removed, or if acryloyloxyethyl dimethyl benzyl ammonium chloride is replaced with acryloyloxyethyl trimethyl ammonium chloride, the polymer loses its rigidity and hydrophobic association effect, its temperature and salt resistance weakens, and the filtration loss increases.

[0129] By appropriately increasing the proportion of 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt in the high-temperature and salt-resistant inorganic / organic hybrid zwitterionic filtration loss reducer B1, the polymer's temperature and salt resistance are improved. The 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt itself is a rigid amphoteric cyclic monomer, enhancing the polymer's high-temperature hydrolytic stability. Furthermore, the cations increase the polymer's adsorption on the clay surface, while the anions increase the repulsion of the clay hydration film, dispersing the clay into fine particles and reducing drilling fluid filtration loss. Appropriately increasing the proportion of modified nano-silica can increase the polymer's adsorption on clay, enhancing its rigidity and plugging ability, thereby improving the performance of filtration loss reducer B and reducing drilling fluid filtration loss.

[0130] Nano-polyester NP-1 has insufficient temperature resistance and will undergo thermal degradation and performance failure at 230℃, resulting in increased drilling fluid filtration loss. In contrast, the high-temperature and high-salt resistant, rigid-flexible plugging agent C1 has a temperature resistance of up to 240℃, reaches salt saturation, is stable at high temperatures, and can adapt to the size and shape of water loss channels in the mud cake, thus exhibiting excellent plugging performance and reducing filtration loss.

[0131] Experimental Example 2

[0132] Deep formations have high pressure, requiring drilling fluids with increased density to balance this pressure. However, adding excessive weighting materials can lead to excessively high drilling fluid viscosity, hindering normal drilling. Therefore, drilling fluids must possess excellent rheological and filtration properties even at high densities. NaCl was added to the drilling fluids prepared using the methods in Examples 1-4 and stirred for 20 minutes to achieve a NaCl content of 15% by mass, resulting in saline drilling fluids. These saline drilling fluids were subsequently named F... 10F9, F 11 F 12 The high-density salt-containing drilling fluid was placed in a stainless steel high-temperature aging tank and aged at 230°C for 16 hours. The apparent viscosity AV (mPa·s), plastic viscosity PV (mPa·s), dynamic shear force YP (mPa·s), and API filtration loss FL of the aged drilling fluid were tested according to GB / T16783.1-2014 Petroleum and Natural Gas Industry Drilling Fluid Field Testing - Part 1 Water-based Drilling Fluids. API and the filtration loss FL at high temperature and high pressure of 220℃×3.5MPa HTHP The results are shown in Table 2.

[0133] Table 2. Performance of drilling fluid at different densities

[0134]

[0135] Increasing the amount of barite will increase the viscosity of the drilling fluid and worsen its filtration and wall-building properties. If the amount of drilling fluid treatment agent and barite addition are not coordinated, the increased weight will result in excessively high drilling fluid viscosity or increased filtration loss. As the density increases from 1.4 g / cm³... 3 Increased to 2.0 g / cm³ 3 The drilling fluid's AV increased from 73 mPa·s to 156 mPa·s, PV increased from 59 mPa·s to 96 mPa·s, and YP increased from 14 Pa to 60 Pa, with all rheological parameters remaining within a reasonable range. API Increase from 0.2 mL to 0.8 mL, FL HTHP The fluid loss remained low even as the volume increased from 12.8 mL to 23.0 mL. This indicates that the drilling fluid of the present invention has a reasonable ratio of various treatment agents, and that the core treatment agents such as the fluid loss reducer and the plugging agent have excellent performance, enabling the drilling fluid to have reasonable rheological parameters and a low level of fluid loss under high temperature, high salinity, and high density conditions.

[0136] Experimental Example 3

[0137] Drilling fluids need to have excellent resistance to K. + Ca 2+ and the properties of composite salts.

[0138] To the drilling fluid prepared by the method in Example 1, KCl (mass concentration in the drilling fluid is 10%), CaCl2 (mass concentration in the drilling fluid is 5%), KCl and NaCl (mass concentration of KCl is 7% and mass concentration of NaCl is 7%), and CaCl2 and NaCl (mass concentration of CaCl2 is 3% and mass concentration of NaCl is 7%) were added respectively, and stirred for 20 minutes to obtain high-density salt-containing drilling fluid F. 13 F 14 F 15F 16 High-density, salt-containing drilling fluid was placed in a stainless steel high-temperature aging tank and aged at 230°C for 16 hours. The apparent viscosity AV (mPa·s), plastic viscosity PV (mPa·s), dynamic shear force YP (mPa·s), and API filtration loss FL of the aged drilling fluid were tested according to GB / T16783.1-2014 Petroleum and Natural Gas Industry Drilling Fluid Field Testing - Part 1 Water-based Drilling Fluids. API and the filtration loss FL at high temperature and high pressure of 220℃×3.5MPa HTHP Evaluation of drilling fluid resistance to K + Ca 2+ The properties of the composite salt were studied, and the results are shown in Table 3.

[0139] Table 3. Drilling fluid resistance to K + Ca 2+ and properties of composite salts

[0140]

[0141]

[0142] At a density of 1.6 g / cm³ 3 FL drilling fluid aged at 230℃ under 10% KCl conditions API 0.8 mL, FL HTHP The value was 19.0 mL. Furthermore, under conditions of 7% KCl and 7% NaCl, FL... HTHP The value was 17.8 mL. This indicates that the drilling fluid can effectively resist K. + Na + and K + Complex salt pollution. According to the Schützel-Hardy rule, Ca... 2+ Its ability to coagulate clay is far stronger than that of K. + and Na + If the drilling fluid is resistant to Ca 2 + Insufficient performance will cause clay to lose the repulsive force of the hydration film and precipitate. High temperatures will cause flocculation in the drilling fluid, increasing its viscosity and shear stress, leading to a dramatic increase in filtration loss and performance failure. The high-density drilling fluid of this invention did not exhibit flocculation phenomena with increased viscosity and shear stress under conditions of 230℃ and 5% CaCl2, and its rheological parameters remained within a reasonable range. Drilling fluid F 14 FL aged at 230℃ API 1.6 mL, FL HTHP The filtrate loss was 23.8 mL, indicating a low level of filtration loss. Furthermore, under conditions of 3% CaCl2 and 7% NaCl, FL... HTHP The volume was 21.8 mL. This indicates that the drilling fluid can effectively resist Ca. 2+ Na + and Ca 2+Complex salt contamination. The filtration loss reducing agent of this invention uses sulfonate groups with good temperature and salt resistance, instead of using Ca. 2+ The sensitive carboxylic acid group ensures that the drilling fluid has excellent resistance to K. + Anti-Ca 2+ ability.

[0143] Test Example 4

[0144] Deep drilling often encounters highly permeable layers, which can easily lead to complex situations such as wellbore instability. Drilling fluids need to have excellent plugging properties to prevent pressure transmission and filtrate from entering the formation, thereby maintaining wellbore stability.

[0145] The drilling fluid F1-F prepared in the above experimental example 16 DF1-DF9 are placed in a stainless steel high-temperature aging tank and aged at 230℃ for 16 hours. After aging, they are removed and ready for use. 300cm of [unclear text - possibly a type of filling material] is then placed in the clean, transparent glass filling tube of the FA.BX type medium-pressure sand bed plugging instrument. 3 After spreading and compacting 80-mesh quartz sand, add 150cm of [unclear text - possibly a typo, should be "80-mesh quartz sand"]. 3 The depth of the aged drilling fluid penetrating the sand bed was tested for 30 minutes at room temperature and 0.69±0.03MPa. The results are shown in Table 4.

[0146] Table 4. Sand Bed Plugging Experiment

[0147]

[0148]

[0149] Drilling fluid F1-F 16 The penetration depth into the sand bed within 30 minutes was less than 1.0 cm, indicating that the present invention has excellent plugging performance against high-temperature and high-density drilling fluid at 230℃. The rigid-flexible plugging agent C1 has a soft polymer shell with high elasticity and toughness, which can adapt to the size and shape of the mud cake and sand bed pores. It can not only fill the water loss channels inside the mud cake to form a dense and tough mud cake to reduce filtrate loss, but also fill and deposit around the well wall to form an effective pressure-bearing plugging layer, prevent pressure transmission and filtrate intrusion, and maintain well wall stability.

[0150] A combination of rigid and flexible plugging agent C1, ultrafine calcium carbonate, barite, and clay forms a reasonable particle size distribution. Under pressure differential, the dense accumulation of solid particles such as clay forms a thin and tough mud cake, preventing filtrate from invading the sand bed. If the performance of the filtrate reducer and plugging agent is insufficient, the clay will agglomerate and grow larger under high temperature and high salinity conditions, resulting in a poor particle size distribution of the drilling fluid. The mud cake formed will be loose and thin, unable to form a tight sealing layer, making it easier for the drilling fluid to invade the sand bed.

[0151] Experimental Example 5

[0152] Settling stability is a critical performance characteristic of high-density drilling fluids. Poor settling stability can lead to increased material settling and potentially stuck pipe. Insufficient density at the top can also cause well kicks, blowouts, and other complex accidents, prolonging the drilling cycle and increasing costs. Therefore, high-density drilling fluids should possess excellent settling stability. The drilling fluid F9-F in the test example... 12 The samples were aged at 230℃ for 0, 16, 32, and 48 hours, respectively. After aging, the samples were cooled to room temperature, stirred at 12,000 rpm for 20 minutes, and allowed to stand for 2 hours. The density of the upper and lower layers and the density difference were measured using a densitometer. The results are shown in Table 5.

[0153] Table 5 Evaluation of Drilling Fluid Settling Stability

[0154]

[0155]

[0156] Drilling fluid F9-F 12 The density difference between the upper and lower layers after 48 hours of high-temperature aging was less than 0.3 g / cm³. 3 This demonstrates that the drilling fluid of the present invention has excellent settling stability at high density, which can effectively prevent complex downhole accidents such as stuck pipe and well kick.

[0157] Experimental Example 6

[0158] The drilling fluid should possess good inhibitory properties to prevent the hydration and swelling of shale. Take 50g of 6-10 mesh reddish-brown shale, dry it to constant weight, and record the weight as m1 (g). Add it to the drilling fluid F prepared in the test example. 13 The drilling fluid was hot-rolled at 200℃ for 16 hours. After hot rolling, the drilling fluid was passed through a 40-mesh sieve. The remaining cuttings were dried to constant weight at 105℃, and the weight was recorded as m2 (g). The rolling recovery rate R was calculated using the following formula:

[0159]

[0160] Table 6 Evaluation of Drilling Fluid Inhibition Performance

[0161] formula Experimental conditions Residue mass (g) Rolling recovery rate (%) Deionized water + 50g rock chips 200℃×16h 7.8 15.6％ <![CDATA[F 13 +50g rock chips]]> 200℃×16h 49.2 98.4％

[0162] The rolling recovery rate of deionized water is only 15.6%, while that of drilling fluid F 13 The rolling recovery rate is 98.4%, indicating that the drilling fluid of the present invention has strong inhibition properties and can effectively inhibit the hydration and expansion of mudstone and shale during the drilling process, thus maintaining wellbore stability.

[0163] Experimental Example 7

[0164] Drilling fluids used in deep and ultra-deep wells should possess excellent lubricity. Good lubricity reduces drill string wear, extends their service life, prevents stuck pipe and drill string breakage, and ensures drilling safety and efficiency. Drilling fluid F9-F was tested using an EP-R type ultimate pressure lubrication tester. 12 The lubrication coefficient is calculated using the following steps: Before each test, calibrate the lubricator with deionized water, adjust the speed to 60 rpm and the torque to 16.95 N·m, and run it for 5 minutes to obtain the deionized water reading. Then replace the deionized water with the drilling fluid to be tested and obtain the drilling fluid reading. The lubrication coefficient is calculated using the following formula:

[0165]

[0166] Table 7 Evaluation of Drilling Fluid Lubricating Performance

[0167] Drilling fluid Lubrication coefficient <![CDATA[F9]]> 0.135 <![CDATA[F 10 ]]> 0.159 <![CDATA[F 11 ]]> 0.173 <![CDATA[F 12 ]]> 0.196

[0168] Because barite is abrasive, an increase in barite content leads to increased friction between the drilling fluid and the drill string. Therefore, as density increases, the lubricity of the drilling fluid decreases. Drilling fluid F9-F 12 The lubrication coefficients are all less than 0.20, indicating that the drilling fluid of the present invention has good lubricity, which can reduce drill bit wear and prevent complex accidents such as stuck drill bit and drill bit breakage during drilling.

[0169] In summary, the drilling fluid of this invention has a temperature resistance of up to 230℃, a NaCl resistance of up to 15%, and effectively resists K. + Ca 2+ K + and Na + Complex salt, Na + and Ca 2+ The contamination of composite salts exhibits good rheological properties, filtration and wall-building properties, plugging properties, settling stability, inhibition of shale hydration and expansion, and maintenance of wellbore stability and lubrication under high density, meeting the drilling needs of deep and ultra-deep wells.

[0170] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0171] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0172] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A high density water base drilling fluid resistant to 230°C, high salt, characterized in that, The raw material composition comprises the following quality parts: 100 parts of water, 1-3 parts of sodium bentonite, 1-2 parts of salt-resistant soil, 0-3-0.7 parts of alkaline regulator, 0.1-0.4 parts of oxygen scavenger, 2-4 parts of high-temperature-resistant salt-resistant micro-crosslinking hydrophobic association zwitterionic fluid loss additive A, 2-4 parts of high-temperature-resistant salt-resistant inorganic / organic hybrid zwitterionic fluid loss additive B, 2-3 parts of superfine calcium carbonate, 3-5 parts of high-temperature-resistant high-salt rigid-flexible plugging agent, 1-3 parts of lubricant and 50-200 parts of weighting agent; The preparation method of the high-temperature-resistant salt-resistant micro-crosslinking hydrophobic association zwitterionic fluid loss additive A comprises the following steps: 2-acrylamido-2-methylpropane sulfonic acid is dissolved in deionized water, and the pH value is adjusted to 7; sodium dodecyl sulfate and styrene are added, and emulsified by shearing; N,N-dimethyl acrylamide and acryloyloxyethyl dimethyl benzyl ammonium chloride are added and dispersed; potassium persulfate initiator and N,N-dimethylene bisacrylamide crosslinking agent are added, reacted, and then washed, dried and crushed to obtain the high-temperature-resistant salt-resistant micro-crosslinking hydrophobic association zwitterionic fluid loss additive A; The preparation method of the high-temperature-resistant salt-resistant inorganic / organic hybrid zwitterionic fluid loss additive B comprises the following steps: (1) The nano-silica ethanol dispersion liquid and the KH570 dispersion liquid are uniformly mixed, the pH is adjusted to 7, and then filtered, washed and dried to obtain the KH570 modified nano-silica; (2) 2-acrylamido-2-methylpropane sulfonic acid is dissolved in deionized water, and the pH is adjusted to 7; N,N-dimethyl acrylamide (DMAA), KH570 modified nano-silica and 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt are added and uniformly dispersed; potassium persulfate initiator is added, reacted, and then washed, dried and crushed to obtain the high-temperature-resistant salt-resistant inorganic / organic hybrid zwitterionic fluid loss additive B; The preparation method of the high-temperature-resistant high-salt rigid-flexible plugging agent comprises the following steps: 1) 2-acrylamido-2-methylpropane sulfonic acid is dispersed in water, the pH is adjusted to 7-8, and then sodium dodecylbenzenesulfonate is added and stirred until dispersed; KH570 modified nano-silica is added and dispersed to obtain solution a; 2) Styrene and divinylbenzene are mixed, and the polymerization inhibitor is washed away with NaOH solution to obtain solution b; 3) Under high-speed stirring, solution b is added dropwise into solution a, and then RAFT reagent N,N'-diethyl dithiocarbamic acid benzyl ester (BDC) is added and mixed uniformly; initiator potassium persulfate is added, and the reaction is carried out at 70°C for 6 hours in a nitrogen atmosphere.

2. The high density water base drilling fluid resistant to high salt at 230 °C according to claim 1, characterized in that, The anti-230 DEG C high-salt-resistant high-density water-based drilling fluid comprises the following raw material components in mass fraction: 100 parts of water, 2 parts of sodium-based bentonite, 2 parts of salt-resistant soil, 0.7 parts of alkaline regulator, 0.4 parts of oxygen scavenger, 4 parts of high-temperature-resistant salt-resistant micro-crosslinking hydrophobic association zwitterionic fluid loss additive A, 4 parts of high-temperature-resistant salt-resistant inorganic / organic hybrid zwitterionic fluid loss additive B, 2 parts of superfine calcium carbonate, 5 parts of high-temperature-resistant high-salt rigid-flexible combined plugging agent, 3 parts of lubricant and 60-200 parts of weighting agent.

3. The high density water base drilling fluid resistant to high salt at 230 °C of claim 1, wherein, One or more of the following conditions are included: i. The alkaline regulator is one or a combination of two or more of sodium hydroxide, sodium carbonate or sodium bicarbonate; the pH value of the drilling fluid is adjusted to 8-10 using the alkaline regulator; ii. In the drilling fluid, the total mass of sodium-based bentonite and salt-resistant soil is 2-4 wt% of the mass of water; iii. The oxygen scavenger is one of sodium sulfite, sodium bisulfite or maleic anhydride; iv. The average particle size of the superfine calcium carbonate is 10-30 nm; v. The lubricant is RH-3; vi. The weighting agent is 300-mesh barite powder.

4. The high density water base drilling fluid of claim 1, wherein the high density water base drilling fluid is resistant to high salt at 230 °C. In the preparation method of the high-temperature-resistant salt-resistant micro-crosslinking hydrophobic association zwitterionic fluid loss additive A, one or more of the following conditions are included: i. The mass ratio of N,N-dimethyl acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acryloyloxyethyl dimethyl benzyl ammonium chloride and styrene is 15-25:5-15:5-10:5-10; ii. The total mass ratio of deionized water to monomers is 100:25-35; iii. The pH value is adjusted to 7 using a NaOH aqueous solution with a concentration of 30 wt%-50 wt%; iv. The total mass ratio of sodium dodecyl sulfonate to monomers is 0.3-0.8:25-35; v. The shear emulsification time is 20-30 min, the shear emulsification rate is 200-400 rpm, and the shear emulsification temperature is room temperature; vi. The total mass ratio of potassium persulfate to monomers is 0.10-0.20:25-35; vii. The total mass ratio of N,N-dimethylene bisacrylamide to monomers is 0.02-0.08:25-35; viii. The reaction temperature is 60-70 DEG C, the reaction time is 4-6 h, and the reaction is carried out in a nitrogen atmosphere.

5. The high density water base drilling fluid of claim 1, wherein the high density water base drilling fluid is resistant to high salt at 230 °C. In the preparation method of the high-temperature-resistant salt-resistant inorganic / organic hybrid zwitterionic fluid loss additive B, one or more of the following conditions are included: i. In step (1), the mass ratio of nano-silicon dioxide to ethanol in the nano-silicon dioxide ethanol dispersion liquid is 15-25:100; the particle size of the nano-silicon dioxide is 20-60 nm; ii. In step (1), the mass ratio of KH570 to solvent in the KH570 dispersion liquid is 1-3:100; the solvent is a mixed solution of water and ethanol, the mass ratio of water to ethanol in the mixed solution is 1:9-10; the mass ratio of KH570 to nano-silicon dioxide is 1:10-15; iii. In step (1), triethylamine is used to adjust the pH to 7; iv. In step (1), the reaction temperature is 60-90 DEG C, and the reaction time is 4-8 h; v. In step (2), the mass ratio of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, KH570 modified nano-silica, and 1-(3-sulfopropyl)-2-vinylpyridinium hydroxide inner salt is 20-30:10-20:5-10:5-10; vi. In step (2), the mass ratio of 2-acrylamido-2-methylpropanesulfonic acid and deionized water is 1-20:100; vii. In step (2), the pH value is adjusted to 7 using a NaOH aqueous solution with a concentration of 30 wt%-50 wt%; viii. In step (2), the mass of potassium persulfate is 0.1-0.5% of the total mass of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, KH570 modified nano-silica, and 1-(3-sulfopropyl)-2-vinylpyridinium hydroxide inner salt; ix. In step (2), the reaction temperature is 60-85°C, and the reaction time is 4-6 hours, and the reaction is carried out in a nitrogen atmosphere; x. In step (2), the average particle size of the high-temperature-resistant and salt-resistant inorganic / organic hybrid zwitterionic fluid loss additive B is 30 nm-150 nm.

6. The method for preparing the 230°C high-salt-resistant high-density water-based drilling fluid according to any one of claims 1-5, comprising the steps of: adding sodium-based bentonite, salt-resistant soil, and alkaline adjusting agent into water in sequence under a stirring speed of 2000-4000 rpm, and stirring for 2-4 hours and then maintaining at room temperature for 20-30 hours to obtain a base slurry; adding an oxygen scavenger under a stirring speed of 2000-4000 rpm and stirring for 1-5 minutes; adding the high-temperature-resistant and salt-resistant micro-crosslinked hydrophobic association zwitterionic fluid loss additive A and adjusting the stirring speed to 8000-12000 rpm and stirring for 10-20 minutes; adding the high-temperature-resistant and salt-resistant inorganic / organic hybrid zwitterionic fluid loss additive B under a stirring speed of 8000-12000 rpm and stirring for 10-20 minutes; adding ultra-fine calcium carbonate under a stirring speed of 8000-12000 rpm and stirring for 5-10 minutes; adding the high-temperature-resistant and high-salt-resistant rigid-flexible joint plugging agent under a stirring speed of 8000-12000 rpm and stirring for 5-10 minutes; adding the lubricant under a stirring speed of 8000-12000 rpm and stirring for 10-20 minutes; and finally adding the weighting agent and thoroughly mixing to obtain the 230°C high-salt-resistant high-density water-based drilling fluid.

7. The application of the 230°C high-salt-resistant high-density water-based drilling fluid according to any one of claims 1-5, which is applied to deep well or ultra-deep well drilling.

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