Ultrahigh-temperature high-density water-based drilling fluid and preparation method thereof

Abstract

The invention provides an ultrahigh-temperature high-density water-based drilling fluid and a preparation method thereof, and relates to the technical field of oilfield chemistry. The ultrahigh-temperature high-density water-based drilling fluid provided by the invention comprises the following components in parts by mass: 100 parts of water, 1.0-2.0 parts of a high-temperature suspending agent, 0.5-2.0 parts of an alkaline pH regulator, 1.0-4.0 parts of a high-temperature-resistant polymer tackifying filtrate reducer, 1.0-3.0 parts of a high-temperature-resistant viscosity reducer, 2.0-4.0 parts of an anti-collapse blocking agent, 10-20 parts of a high-temperature stabilizer and a weighting agent, the weight part of the weighting agent is based on the condition that the density of the drilling fluid is 2.1-2.5 g / cm < 3 >. The density of the drilling fluid provided by the invention can reach 2.5 g / cm < 3 >, the temperature resistance can reach 250 DEG C, and the drilling fluid is stable in rheological property, excellent in water loss wall-building performance, good in long-time sedimentation stability and strong in anti-pollution capacity under the conditions of ultrahigh temperature and high density, and is favorably applied to complex stratums such as deep wells, ultra-deep wells, salt-gypsum layers and the like.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemistry in petroleum drilling engineering, and in particular to an ultra-high temperature and high density water-based drilling fluid and a preparation method thereof. Background Art

[0002] In recent years, with the continuous deepening of oil and gas exploration and development in the world, oil and gas production has gradually shifted from shallow formations to deep and ultra-deep formations. During the drilling process in deep formations, as the well depth continues to increase, the bottom hole temperature is also getting higher and higher, which puts higher requirements on the various properties of drilling fluids in high temperature environments. Under the conditions of deep ultra-high temperature and high pressure formations, drilling fluids generally have problems such as poor rheology, large high temperature and high pressure filtration, poor sedimentation stability, and weak anti-pollution ability, which easily lead to frequent complex situations underground. Summary of the invention

[0003] In view of this, the object of the present invention is to provide an ultra-high temperature and high density water-based drilling fluid and a preparation method thereof. The ultra-high temperature and high density water-based drilling fluid provided by the present invention has good rheology, strong suspension stability, low high temperature and high pressure filtration loss and strong anti-pollution ability.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides an ultra-high temperature and high density water-based drilling fluid, comprising the following components in parts by weight:

[0006] 100 parts of water, 1.0-2.0 parts of high-temperature suspending agent, 0.5-2.0 parts of alkaline pH adjusting agent, 1.0-4.0 parts of high-temperature resistant polymer viscosity increasing and filtration reducing agent, 1.0-3.0 parts of high-temperature resistant viscosity reducing agent, 2.0-4.0 parts of anti-collapse plugging agent, 10-20 parts of high-temperature stabilizer, and weighting agent; the mass fraction of the weighting agent is such that the density of the ultra-high temperature and high-density water-based drilling fluid is 2.1-2.5 g / cm 3 shall prevail;

[0007] The high temperature resistant polymer viscosity increasing and fluid loss reducing agent is obtained by polymerization of monomers, wherein the monomers include acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentenesulfonate;

[0008] The high temperature resistant viscosity reducing agent is a tannin graft copolymer, which is obtained by modifying tannic acid with formaldehyde, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and sodium styrenesulfonate;

[0009] The anti-collapse plugging agent is polymer modified asphalt, and the polymer modified asphalt is obtained by modifying natural asphalt with hydrogenated styrene-butadiene block copolymer and sulfonating it.

[0010] Preferably, the high-temperature suspending agent is aluminum magnesium silicate and / or lithium magnesium silicate, and the particle sizes of aluminum magnesium silicate and lithium magnesium silicate are both nanometer level.

[0011] Preferably, the preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent comprises the following steps:

[0012] Mixing water, acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentenesulfonate to obtain a mixed solution; the pH value of the mixed solution is 7;

[0013] The mixed solution is mixed with an initiator to carry out polymerization reaction to obtain a gel product;

[0014] The gel product is washed and dried in sequence to obtain the high temperature resistant polymer viscosity increasing and fluid loss reducing agent.

[0015] Preferably, the mass ratio of water, acrylamide, 2-acrylamide-2-methylpropane sulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentene sulfonate is 200:(10-20):(15-30):(10-20):(5-10):(5-10); the polymerization reaction temperature is 60-65°C and the reaction time is 3-5h.

[0016] Preferably, the preparation method of the high temperature resistant viscosity reducing agent comprises the following steps:

[0017] Mixing water, tannic acid and formaldehyde solution, and subjecting the obtained mixed solution to polycondensation reaction to obtain a polycondensation product; the pH value of the mixed solution is 8;

[0018] The polycondensation product is mixed with acrylic acid, 2-acrylamide-2-methylpropane sulfonic acid, sodium styrene sulfonate and an initiator to carry out a polymerization reaction to obtain a polymerization product;

[0019] The polymerized product is washed and dried in sequence to obtain the high temperature resistant viscosity reducing agent.

[0020] Preferably, the mass fraction of the formaldehyde solution is 37%, and the mass ratio of the water, tannic acid, formaldehyde solution, acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid and sodium styrene sulfonate is 200:(50-80):(8-15):(5-10):(10-25):(5-10); the temperature of the polycondensation reaction is 60-70°C, and the time is 1-2h; the temperature of the polymerization reaction is 60-70°C, and the time is 2-3h.

[0021] Preferably, the method for preparing the anti-collapse plugging agent comprises the following steps:

[0022] mixing an organic solvent, natural asphalt and a hydrogenated styrene-butadiene block copolymer to obtain a mixture;

[0023] The mixture is mixed with oleum to carry out a sulfonation reaction to obtain a sulfonated product;

[0024] After the pH value of the sulfonated product is adjusted to 9, the organic solvent is removed and the product is dried in sequence to obtain the anti-collapse plugging agent.

[0025] Preferably, the mass ratio of the organic solvent, natural asphalt, hydrogenated styrene-butadiene block copolymer and fuming sulfuric acid is (50-70):(10-20):(0.5-3):(5-10); the temperature of the sulfonation reaction is 60-70°C and the time is 2-3h.

[0026] Preferably, the high temperature stabilizer is one or more of sodium formate, potassium formate and cesium formate; the weighting agent is spherical manganese tetraoxide powder; and the alkaline pH regulator is one or more of sodium hydroxide, sodium carbonate and magnesium hydroxide.

[0027] The present invention provides a method for preparing the ultra-high temperature and high density water-based drilling fluid described in the above technical solution, comprising the following steps:

[0028] The ultra-high temperature and high density water-based drilling fluid is obtained by mixing water, a high temperature suspending agent, an alkaline pH adjusting agent, a high temperature resistant polymer viscosity increasing and filtration reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer and a weighting agent.

[0029] The invention provides an ultra-high temperature and high density water-based drilling fluid, comprising the following components in parts by weight: 100 parts of water, 1.0-2.0 parts of high temperature suspending agent, 0.5-2.0 parts of alkaline pH adjusting agent, 1.0-4.0 parts of high temperature resistant polymer viscosity increasing and filtration reducing agent, 1.0-3.0 parts of high temperature resistant viscosity reducing agent, 2.0-4.0 parts of anti-collapse plugging agent, 10-20 parts of high temperature stabilizer, and weighting agent; the weighting agent is in such a quantity that the density of the ultra-high temperature and high density water-based drilling fluid is 2.1-2.5 g / cm 3The high temperature resistant polymer viscosity increasing and fluid loss reducing agent is obtained by polymerization of monomers, and the monomers include acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentene sulfonate; the high temperature resistant viscosity reducing agent is a tannin graft copolymer, and the tannin graft copolymer is obtained by modifying tannic acid with formaldehyde, acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid and sodium styrene sulfonate; the anti-collapse plugging agent is a polymer modified asphalt, and the polymer modified asphalt is natural asphalt modified with hydrogenated styrene-butadiene block copolymer and sulfonated. The present invention uses the high temperature resistant polymer viscosity increasing and fluid loss reducing agent, the high temperature resistant viscosity reducing agent and the anti-collapse plugging agent as the core treating agent, and cooperates with a high temperature suspending agent, a high temperature stabilizer, a weighting agent and an alkaline pH adjusting agent. The density of the obtained water-based drilling fluid reaches 2.5g / cm 3 , temperature resistance reaches 250°C, rheological properties are stable under ultra-high temperature and high density conditions, water loss and wall building performance is excellent under high temperature, long-term sedimentation stability performance is good, and anti-pollution ability is strong, which is conducive to application in deep wells, ultra-deep wells and complex formations such as salt-gypsum layers; in addition, the ultra-high temperature and high-density water-based drilling fluid provided by the present invention has the characteristics of small amount of treatment agent added, convenient on-site configuration, etc., and is easy to apply on-site. DETAILED DESCRIPTION

[0030] The present invention provides an ultra-high temperature and high density water-based drilling fluid, comprising the following components in parts by weight:

[0031] 100 parts of water, 1.0-2.0 parts of high-temperature suspending agent, 0.5-2.0 parts of alkaline pH adjusting agent, 1.0-4.0 parts of high-temperature resistant polymer viscosity increasing and filtration reducing agent, 1.0-3.0 parts of high-temperature resistant viscosity reducing agent, 2.0-4.0 parts of anti-collapse plugging agent, 10-20 parts of high-temperature stabilizer, and weighting agent; the mass fraction of the weighting agent is such that the density of the ultra-high temperature and high-density water-based drilling fluid is 2.1-2.5 g / cm 3 shall prevail;

[0032] The high temperature resistant polymer viscosity increasing and fluid loss reducing agent is obtained by polymerization of monomers, wherein the monomers include acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentenesulfonate;

[0033] The high temperature resistant viscosity reducing agent is a tannin graft copolymer, which is obtained by modifying tannic acid with formaldehyde, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and sodium styrenesulfonate;

[0034] The anti-collapse plugging agent is polymer modified asphalt, and the polymer modified asphalt is obtained by modifying natural asphalt with hydrogenated styrene-butadiene block copolymer and sulfonating it.

[0035] In the present invention, unless otherwise specified, the raw materials involved are commercially available products well known in the art.

[0036] The ultra-high temperature and high density water-based drilling fluid provided by the present invention comprises 100 parts of water by weight. In the present invention, the water is preferably fresh water or sea water.

[0037] Based on the mass fraction of the water, the ultra-high temperature and high density water-based drilling fluid provided by the present invention includes 1.0 to 2.0 parts of a high temperature suspension agent, which may be 1.0, 1.2, 1.5, 1.8 or 2.0 parts. In the present invention, the high temperature suspension agent is preferably magnesium aluminum silicate and / or magnesium lithium silicate, and the particle size of the magnesium aluminum silicate and magnesium lithium silicate is preferably nanometer level, and further preferably 100 to 1000 nm; when the high temperature suspension agent is magnesium aluminum silicate and magnesium lithium silicate, the mass ratio of the magnesium aluminum silicate and magnesium lithium silicate is preferably (30 to 70): (30 to 70), and specifically may be 30:70, 50:50, 60:40 or 70:30. In the present invention, nanometer-level magnesium aluminum silicate and magnesium lithium silicate have extremely strong gelation and suspension ability in the water system, which can effectively improve the suspension stability, dispersibility and thixotropy of the particles under high temperature conditions, and have the characteristics of being less affected by temperature and having good suspension stability.

[0038] Based on the mass fraction of the water, the ultra-high temperature and high density water-based drilling fluid provided by the present invention includes 0.5 to 2.0 parts of an alkaline pH regulator, which can be 0.5, 1.0, 1.2, 1.5 or 1.8 parts. In the present invention, the alkaline pH regulator is preferably one or more of sodium hydroxide, sodium carbonate and magnesium hydroxide. When the alkaline pH regulator is sodium hydroxide, sodium carbonate and magnesium hydroxide, the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is preferably (20 to 50): (30 to 40): (20 to 40), and can specifically be 20:40:40, 35:35:30, 40:30:30 or 50:30:20. In the present invention, the sodium hydroxide and sodium carbonate mainly provide a certain alkaline environment for the drilling fluid system, so that each treatment agent can play its role in an alkaline environment; magnesium hydroxide can still maintain a good alkaline environment under high temperature conditions to ensure the stability of the drilling fluid under high temperature conditions.

[0039] Based on the mass fraction of the water, the ultra-high temperature and high density water-based drilling fluid provided by the present invention includes 1.0 to 4.0 parts of a high temperature resistant polymer viscosity increasing and fluid loss reducing agent, which can be 1.0, 2.0, 2.5, 3.0, 3.5 or 4.0 parts. In the present invention, the high temperature resistant polymer viscosity increasing and fluid loss reducing agent is obtained by polymerization of monomers, and the monomers include acrylamide (AM), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), diallyldimethylammonium chloride (DADMAC), 1-vinyl-2-pyrrolidone (NVP) and sodium (2-acryloyloxy)isopentene sulfonate (AOIAS). In the present invention, the preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent preferably includes the following steps:

[0040] Mixing water, acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentenesulfonate to obtain a mixed solution; the pH value of the mixed solution is 7;

[0041] The mixed solution is mixed with an initiator to carry out polymerization reaction to obtain a gel product;

[0042] The gel product is washed and dried in sequence to obtain the high temperature resistant polymer viscosity increasing and fluid loss reducing agent.

[0043] In the present invention, the mass ratio of the water, acrylamide, 2-acrylamide-2-methylpropane sulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentene sulfonate is preferably 200:(10-20):(15-30):(10-20):(5-10):(5-10), specifically 200:12:20:10:5:5, 200:18:25:13:10:8 or 200:15:30:15:7:8; the water is preferably distilled water. In the present invention, the method for mixing the water, acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloxy)isopentenesulfonate is preferably as follows: water is added to a reaction container, acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloxy)isopentenesulfonate are slowly added under stirring conditions, and after fully dissolving, the pH value of the system is adjusted to 7 with a NaOH solution to obtain the mixed solution. In the present invention, the mass fraction of the NaOH solution is preferably 10%.

[0044] In the present invention, the initiator is preferably azobisisobutyramidine hydrochloride (AIBA), and the mass of the initiator is preferably 0.5% of the total mass of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentenesulfonate (i.e., the total mass of monomers). In the present invention, the polymerization temperature is preferably 60-65°C, more preferably 60°C, the time is preferably 3-5h, more preferably 4h; the polymerization reaction is preferably carried out in a nitrogen atmosphere. The present invention preferably passes nitrogen, then heats the mixed solution to 60-65°C, adds the initiator thereto, carries out the polymerization reaction, and obtains a gel-like product.

[0045] In the present invention, the washing is preferably performed by washing with ethanol and then filtering; the drying is preferably performed by vacuum drying. After the drying, it is also preferably pulverized to obtain the high temperature resistant polymer viscosity increasing and fluid loss reducing agent in powder form.

[0046] In the present invention, the high temperature resistant viscosity increasing fluid loss reducer is a multi-polymer, which contains a variety of functional monomers. The introduction of AM, AMPS and AOIAS monomers provides strong adsorption groups such as amide groups and sulfonic acid groups for the molecular chain, which is conducive to the adsorption of polymer macromolecules on the high temperature suspension agent particles to form a grid structure, prevent the high temperature suspension agent from agglomerating and flocculating, maintain its dispersibility and colloidal properties, and help to form a dense mud cake, which plays a role in maintaining the stability of the system and reducing fluid loss. At the same time, the difficult to degrade high temperature resistant monomer NVP is introduced into the molecular chain, and the five-membered heterocyclic ring on its unit has a large steric hindrance, which effectively improves the rigidity of the molecular chain; combined with the temperature resistant sulfonic acid groups on the AMPS and AOIAS monomers, the steric hindrance effect of the large volume group and the rigidity of the cyclic group are utilized to make the synthesized molecular chain configuration difficult to change, effectively improving the thermal stability and salt resistance of the fluid loss reducer. At the same time, DADMAC and NVP monomers are connected to the main chain of the molecular chain through high-energy CC bonds and CN bonds. The higher the bond energy, the more stable it is, and it is not easy to break and decompose with the main chain at high temperature, further improving the thermal stability of the polymer molecules. In addition, there are a variety of adsorption groups in the molecular chain, which can absorb a large number of water molecules and increase the viscosity of the drilling fluid, thus having a certain viscosity-increasing effect.

[0047] Based on the mass fraction of the water, the ultra-high temperature and high density water-based drilling fluid provided by the present invention includes 1.0 to 3.0 parts of a high temperature resistant viscosity reducer, which can be 1.0, 1.5, 2.0, 2.5 or 3.0 parts. In the present invention, the high temperature resistant viscosity reducer is a tannin graft copolymer, which is obtained by modifying tannic acid with formaldehyde, acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and sodium styrene sulfonate (SSS). In the present invention, the preparation method of the high temperature resistant viscosity reducer preferably includes the following steps:

[0048] Mixing water, tannic acid and formaldehyde solution, and subjecting the obtained mixed solution to polycondensation reaction to obtain a polycondensation product; the pH value of the mixed solution is 8;

[0049] The polycondensation product is mixed with acrylic acid, 2-acrylamide-2-methylpropane sulfonic acid, sodium styrene sulfonate and an initiator to carry out a polymerization reaction to obtain a polymerization product;

[0050] The polymerized product is washed and dried in sequence to obtain the high temperature resistant viscosity reducing agent.

[0051] In the present invention, the mass fraction of the formaldehyde solution is preferably 37%, the formaldehyde solution is specifically a formaldehyde aqueous solution, the mass ratio of the water, tannic acid, formaldehyde solution, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, sodium styrene sulfonate and initiator is preferably 200:(50-80):(8-15):(5-10):(10-25):(5-10):(0.3-0.5), specifically 200:65:10:10:20:5:0.4, 200:55:8:8:15:10:0.3 or 200:70:12:10:15:10:0.4; the water is preferably distilled water. In the present invention, the method of mixing the water, tannic acid and formaldehyde solution is preferably: water, tannic acid and formaldehyde solution are added to a reaction container in sequence, and the pH value is adjusted to 8 with a NaOH solution to obtain the mixed solution. In the present invention, the temperature of the polycondensation reaction is preferably 60-70°C, more preferably 65°C, and the time is preferably 1-2h, more preferably 1.5h; after the polycondensation reaction, no post-treatment is required and the next step of reaction can be directly carried out.

[0052] In the present invention, the initiator is preferably ammonium persulfate and sodium bisulfite, and the mass ratio of the ammonium persulfate and sodium bisulfite is preferably 1:1. In the present invention, the method of mixing the polycondensation product with acrylic acid, 2-acrylamide-2-methylpropane sulfonic acid, sodium styrene sulfonate and the initiator is preferably: acrylic acid, 2-acrylamide-2-methylpropane sulfonic acid and sodium styrene sulfonate are added to the polycondensation product in sequence, and stirred evenly; then nitrogen is introduced and the initiator is added. In the present invention, the temperature of the polymerization reaction is preferably 60 to 70°C, more preferably 60°C, and the time is preferably 2 to 3h, more preferably 2.5h. After the polymerization reaction is completed, it is cooled to room temperature to obtain a viscous liquid copolymer, i.e., the polymerization product.

[0053] In the present invention, the reagent used for washing is preferably anhydrous ethanol; the drying is preferably oven drying; and after drying, the agent is preferably crushed to obtain the high temperature resistant viscosity reducing agent in powder form.

[0054] In the present invention, tannic acid is a natural material with excellent viscosity reducing performance, with fewer ether bonds in its structural formula and strong temperature resistance. It forms macromolecules after polycondensation, which improves the rigidity of the viscosity reducer. The polycondensation product undergoes graft copolymerization with organic monomers, and rigid groups such as sulfonic acid groups and benzene rings are introduced into the tannic acid molecules, so that the temperature resistance of the molecular chain is further improved, and it is not easy to degrade under high temperature conditions; by introducing AMPS monomers, the amide groups are connected to the macromolecules, which improves the adsorption and water solubility of the viscosity reducer. The modified tannic acid molecules synthesized finally have a large number of adsorption groups and hydration groups such as hydroxyl groups, amide groups, and carboxyl groups, so that it can be effectively adsorbed on the clay surface, enhance the hydration film thickness and electrostatic repulsion on the surface of clay particles, make the clay particles in a good dispersed state, reduce the grid structure formed between clays, and thus achieve the viscosity reducing effect. When it is added to high-density drilling fluid, the adsorption groups can also be adsorbed on the surface of the weighting agent in large quantities, reduce the friction between solid phase particles, and thus improve the rheology of high-density drilling fluid.

[0055] Based on the mass fraction of the water, the ultra-high temperature and high density water-based drilling fluid provided by the present invention includes 2.0 to 4.0 parts of an anti-collapse plugging agent, which may be 2.0, 3.0, 3.5 or 4.0 parts. In the present invention, the anti-collapse plugging agent is a polymer-modified asphalt, which is obtained by modifying and sulfonating natural asphalt with hydrogenated styrene-butadiene block copolymer (SEBS). In the present invention, the preparation method of the anti-collapse plugging agent preferably includes the following steps:

[0056] mixing an organic solvent, natural asphalt and a hydrogenated styrene-butadiene block copolymer to obtain a mixture;

[0057] The mixture is mixed with oleum to carry out a sulfonation reaction to obtain a sulfonated product;

[0058] After the pH value of the sulfonated product is adjusted to 9, the organic solvent is removed and the product is dried in sequence to obtain the anti-collapse plugging agent.

[0059] In the present invention, the organic solvent is preferably kerosene, and the natural asphalt is preferably high-temperature asphalt powder with a softening point of ≥250°C; the mass ratio of the organic solvent, natural asphalt, hydrogenated styrene-butadiene block copolymer and fuming sulfuric acid is preferably (50-70):(10-20):(0.5-3):(5-10), and specifically can be 60:10:1:8, 55:18:2:10 or 70:18:1.5:10. In the present invention, the method for mixing the organic solvent, natural asphalt and hydrogenated styrene-butadiene block copolymer is preferably: adding an organic solvent to a reaction vessel, slowly adding natural asphalt and hydrogenated styrene-butadiene block copolymer thereto under stirring, heating to 120°C to completely dissolve the hydrogenated styrene-butadiene block copolymer, and obtaining the mixture.

[0060] In the present invention, the mixture is preferably cooled and then fuming sulfuric acid is added to carry out a sulfonation reaction. In the present invention, the temperature of the sulfonation reaction is preferably 60 to 70° C., more preferably 60° C., and the time is preferably 2 to 3 hours, more preferably 2.5 hours. After the sulfonation reaction, no post-treatment is required and subsequent operations can be directly carried out.

[0061] The present invention preferably uses 10wt% NaOH solution to adjust the pH value of the sulfonated product to 9. In the present invention, the method of removing the organic solvent is preferably distillation; the drying is preferably drying; and after the drying, the product is preferably crushed to obtain the anti-collapse plugging agent in powder form.

[0062] In the present invention, SEBS polymer is introduced into the natural asphalt, and the product has polymer characteristics and better elasticity and toughness; at the same time, the introduction of the polymer increases the sulfonated substance, and the added polymer can be connected with the asphalt particles through the grid structure, and the interaction between them promotes the dispersion of the asphalt particles to form a dense asphalt layer, which is conducive to the formation of a thin and dense mud cake; sulfonic acid groups are introduced into the modified asphalt through fuming sulfuric acid, so that its high temperature resistance is improved; at the same time, the modified sulfonated asphalt is adsorbed on the surface of clay particles in large quantities through the sulfonic acid group, which improves the electronegativity of the clay particles, is conducive to the dispersion of the clay particles in the drilling fluid, and thus reduces the filtration loss.

[0063] Based on the mass fraction of the water, the ultra-high temperature and high density water-based drilling fluid provided by the present invention includes 10 to 20 parts of a high temperature stabilizer, which can be 10, 15 or 20 parts. In the present invention, the high temperature stabilizer is preferably one or more of sodium formate, potassium formate and cesium formate. When the high temperature stabilizer is sodium formate, potassium formate and cesium formate, the mass ratio of the sodium formate, potassium formate and cesium formate is preferably (20 to 40): (35 to 60): (20 to 30), and can specifically be 20:60:20, 30:45:25, 30:50:20, 30:40:30 or 35:35:30. In the present invention, the free formate ions in the alkali metal formates such as sodium formate, potassium formate and cesium formate are antioxidants that can quickly remove hydroxyl radicals and provide a strong protective effect against the oxidative degradation of heat-sensitive substances such as water-soluble polymers at high temperatures. In aqueous solution, alkali metal formates, especially cesium formate, can change the structure of surrounding water molecules, making the properties of water similar to those of ice, making dissolved polymer molecules more orderly, tough and stable at high temperatures, thereby improving the polymer's high temperature stability. In addition, formates also have excellent inhibitory effects, and have a stronger compression effect on the double electric layer of shale clay, making the attraction of the clay layer far greater than the repulsion of the double electric layer, thereby effectively inhibiting the hydration expansion of shale and stabilizing the well wall.

[0064] Based on the mass fraction of the water, the ultra-high temperature and high density water-based drilling fluid provided by the present invention includes a weighting agent; the mass fraction of the weighting agent is such that the density of the ultra-high temperature and high density water-based drilling fluid is 2.1 to 2.5 g / cm 3 The density may be 2.1, 2.2, 2.3, 2.4 or 2.5 g / cm 3 In the present invention, the weighting agent is preferably spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is preferably 4.8 g / cm 3 , the particle size is preferably 0.5 to 5 μm. In the present invention, the average particle size of the spherical manganese tetraoxide powder is much lower than that of barite, and the sedimentation rate is low; and the density is high, and the solid content required to be weighted to the same density is lower than that of barite, and it has better suspension in ultra-high temperature and high-density drilling fluid and is not easy to settle; its spherical structure is stable and the particle surface charge is high. Compared with barite and iron ore powder, the surface hydrophilicity in the drilling fluid system is stronger, and the particle stability is better. In addition, the particles of manganese tetraoxide powder are spherical, which can convert the sliding friction between particles into rolling friction. It has lower friction and torque than the drilling fluid weighted by conventional barite and iron ore powder, and effectively reduces the internal friction of the drilling fluid flow.

[0065] The ultra-high temperature and high density water-based drilling fluid provided by the present invention has a wide range of density and temperature applications, and the density can reach 2.5g / cm 3 , the temperature resistance can reach 250℃, and it has good rheological properties, strong suspension stability, low high temperature and high pressure filtration loss and strong anti-pollution ability under ultra-high temperature and high density, and has excellent performance.

[0066] The present invention provides a method for preparing the ultra-high temperature and high density water-based drilling fluid described in the above technical solution, comprising the following steps:

[0067] The ultra-high temperature and high density water-based drilling fluid is obtained by mixing water, a high temperature suspending agent, an alkaline pH adjusting agent, a high temperature resistant polymer viscosity increasing and filtration reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer and a weighting agent.

[0068] The present invention has no special requirements for the mixing method, and the components can be evenly mixed by a conventional mixing method. The ultra-high temperature and high density water-based drilling fluid provided by the present invention is convenient to configure on site and easy to apply on site.

[0069] In order to further illustrate the present invention, the ultra-high temperature and high density water-based drilling fluid and the preparation method thereof provided by the present invention are described in detail below in conjunction with examples, but they should not be construed as limiting the scope of protection of the present invention.

[0070] In each example, hydrogenated styrene-butadiene block copolymer (SEBS) was purchased from Sinopec Baling Petrochemical Co., Ltd., model number YH-502T.

[0071] Example 1

[0072] An ultra-high temperature and high density water-based drilling fluid, comprising: water, a high temperature suspending agent, a pH regulator, a high temperature resistant polymer viscosity increasing and fluid loss reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer, and a weighting agent, and the mass fractions of each component are as follows:

[0073] Water: 100 parts,

[0074] High temperature suspension agent: 1.2 parts,

[0075] pH adjuster: 1.2 parts,

[0076] High temperature resistant polymer viscosity increasing and fluid loss reducing agent: 2.5 parts,

[0077] High temperature resistance viscosity reducer: 1.5 parts,

[0078] Anti-collapse plugging agent: 2 parts,

[0079] High temperature stabilizer: 15 parts,

[0080] Weighting agent: adjust the system density to 2.3g / cm 3 .

[0081] in,

[0082] The water is fresh water.

[0083] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate (the particle sizes of aluminum magnesium silicate and lithium magnesium silicate are 100-1000nm), and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 1:1.

[0084] The pH regulator is a compound of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 35:35:30.

[0085] The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent is as follows:

[0086] Add distilled water to a four-necked flask, slowly add acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), diallyldimethylammonium chloride (DADMAC), 1-vinyl-2-pyrrolidone (NVP), and sodium (2-acryloyloxy)isopentenesulfonate (AOIAS) under stirring, fully dissolve, then adjust the pH of the system to 7 with 10% NaOH solution, pass nitrogen for 30 minutes, heat to 60°C, add 0.5% of the total weight of the monomer initiator azobisisobutyramidine hydrochloride (AIBA), and react 4h to obtain a gel product, which is cooled to room temperature, washed with ethanol and filtered, then placed in a vacuum drying oven for drying and crushed. The powdery product finally obtained is a high temperature resistant polymer viscosity increasing and filtration reducer; the mass ratio of distilled water, acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), diallyldimethylammonium chloride (DADMAC), 1-vinyl-2-pyrrolidone (NVP) and sodium (2-acryloyloxy)isopentenesulfonate (AOIAS) is 200:12:20:10:5:5.

[0087] The preparation method of the high temperature resistant viscosity reducing agent is as follows:

[0088] Add distilled water, tannic acid, and formaldehyde solution (37 wt % formaldehyde aqueous solution) into a four-necked round-bottom flask, adjust the pH to 8 with NaOH solution, heat to 65° C. and react for 1.5 hours to carry out polycondensation reaction, continue to add acrylic acid (AA), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and sodium styrene sulfonate (SSS) to the above solution in sequence, stir evenly, introduce N2, add initiator (ammonium persulfate: sodium bisulfite = 1:1), and carry out polymerization reaction at 60° C. for 3 hours. After the reaction is completed, cool to room temperature to obtain a viscous liquid copolymer, and wash with anhydrous ethanol, dry and crush to obtain the desired viscosity reducer; the mass ratio of the distilled water, tannic acid, formaldehyde solution, acrylic acid (AA), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), sodium styrene sulfonate (SSS) and initiator is 200:65:10:10:20:5:0.4.

[0089] The preparation method of the anti-collapse plugging agent is as follows:

[0090] Add kerosene to a three-necked flask, then slowly add natural asphalt (softening point ≥ 250°C) and hydrogenated styrene-butadiene block copolymer (SEBS) under stirring, heat to 120°C to completely dissolve the SEBS, add oleum after the mixture is cooled, heat to 60°C to react for 2.5 hours, use 10% NaOH solution to adjust the pH of the system to 9, evaporate the solvent, dry and crush the modified product in an oven, and finally obtain polymer modified asphalt powder; the mass ratio of the kerosene, natural asphalt, hydrogenated styrene-butadiene block copolymer (SEBS) and oleum is 60:10:1:8.

[0091] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 30:50:20.

[0092] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 ; Particle size is 0.5~5μm.

[0093] The density of the ultra-high temperature and high density water-based drilling fluid system is 2.3 g / cm 3 The hot rolling temperature of the drilling fluid system is 230℃.

[0094] Example 2

[0095] An ultra-high temperature and high density water-based drilling fluid, comprising: water, a high temperature suspending agent, a pH regulator, a high temperature resistant polymer viscosity increasing and fluid loss reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer, and a weighting agent, and the mass fractions of each component are as follows:

[0096] Water: 100 parts,

[0097] High temperature suspension agent: 2.0 parts,

[0098] pH adjuster: 1.8 parts,

[0099] High temperature resistant polymer viscosity increasing and fluid loss reducing agent: 3.5 parts,

[0100] High temperature resistance viscosity reducer: 2.5 parts,

[0101] Anti-collapse plugging agent: 3 parts,

[0102] High temperature stabilizer: 10 parts,

[0103] Weighting agent: adjust the system density to 2.3g / cm 3 .

[0104] in,

[0105] The water is sea water.

[0106] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate, and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 70:30.

[0107] The pH regulator is a compound of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 40:30:30.

[0108] The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent is as follows:

[0109] Add distilled water to a four-necked flask, slowly add acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), diallyldimethylammonium chloride (DADMAC), 1-vinyl-2-pyrrolidone (NVP), and sodium (2-acryloyloxy)isopentenesulfonate (AOIAS) under stirring, fully dissolve, then adjust the system pH to 7 with 10% NaOH solution, pass nitrogen for 30 minutes, heat to 65°C, add 0.5% of the total weight of the monomer initiator azobisisobutyramidine hydrochloride (AIBA), and react 5h to obtain a gel product, which is cooled to room temperature, washed with ethanol and filtered, then placed in a vacuum drying oven for drying and crushing, and the powdery product finally obtained is a high temperature resistant polymer viscosity increasing and filtration reducer; the mass ratio of distilled water, acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), diallyldimethylammonium chloride (DADMAC), 1-vinyl-2-pyrrolidone (NVP) and sodium (2-acryloyloxy)isopentenesulfonate (AOIAS) is 200:18:25:13:10:8.

[0110] The preparation method of the high temperature resistant viscosity reducing agent is as follows:

[0111] Add distilled water, tannic acid, and formaldehyde solution (37 wt % formaldehyde aqueous solution) into a four-necked round-bottom flask, adjust the pH to 8 with NaOH solution, heat to 65° C. and react for 1.5 h to carry out polycondensation reaction, continue to add acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and sodium styrene sulfonate (SSS) to the above solution in sequence, stir evenly, introduce N2, add initiator (ammonium persulfate: sodium bisulfite = 1:1), and carry out polymerization reaction at 60° C. for 3 h. After the reaction is completed, cool to room temperature to obtain a viscous liquid copolymer, wash with anhydrous ethanol, and dry and crush. The mass ratio of the distilled water, tannic acid, formaldehyde solution, AA, AMPS, SSS and initiator is 200:55:8:8:15:10:0.3.

[0112] The preparation method of the anti-collapse plugging agent is as follows:

[0113] Add kerosene to a three-necked flask, and then slowly add natural asphalt (softening point ≥ 250°C) and hydrogenated styrene-butadiene block copolymer (SEBS) under stirring, heat to 120°C to completely dissolve the SEBS, add oleum after the mixture is cooled, heat to 60°C to react for 2h, use 10% NaOH solution to adjust the pH of the system to 9, evaporate the solvent, dry and crush the modified product in an oven, and finally obtain polymer modified asphalt powder; the mass ratio of the kerosene, natural asphalt, SEBS and oleum is 55:18:2:10.

[0114] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 20:60:20.

[0115] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 , particle size is 0.5~5μm.

[0116] The drilling fluid system density is 2.3 g / cm 3 The hot rolling temperature of the drilling fluid system is 230℃.

[0117] Example 3

[0118] An ultra-high temperature and high density water-based drilling fluid, comprising: water, a high temperature suspending agent, a pH regulator, a high temperature resistant polymer viscosity increasing and fluid loss reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer, and a weighting agent, and the mass fractions of each component are as follows:

[0119] Water: 100 parts,

[0120] High temperature suspension agent: 1.5 parts,

[0121] pH adjuster: 1.2 parts,

[0122] High temperature resistant polymer viscosity increasing and fluid loss reducing agent: 3.0 parts,

[0123] High temperature resistance viscosity reducer: 2.0 parts,

[0124] Anti-collapse plugging agent: 4.0 parts,

[0125] High temperature stabilizer: 20 parts,

[0126] Weighting agent: adjust the system density to 2.3g / cm 3 .

[0127] in,

[0128] The water is fresh water.

[0129] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate, and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 60:40.

[0130] The pH regulator is a compound of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 40:30:30.

[0131] The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent is as follows:

[0132] Add distilled water to a four-necked flask, slowly add acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), diallyldimethylammonium chloride (DADMAC), 1-vinyl-2-pyrrolidone (NVP), and sodium (2-acryloyloxy)isopentenesulfonate (AOIAS) under stirring, fully dissolve, then adjust the pH of the system to 7 with 10% NaOH solution, pass nitrogen for 30 minutes, heat to 60°C, add 0.5% of the total weight of the monomer initiator azobisisobutyramidine hydrochloride (AIBA), and react 4h to obtain a gel product, which is cooled to room temperature, washed with ethanol and filtered, then placed in a vacuum drying oven for drying and crushing, and the powdery product finally obtained is a high temperature resistant polymer viscosity increasing and filtration reducer; the mass ratio of distilled water, acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), diallyldimethylammonium chloride (DADMAC), 1-vinyl-2-pyrrolidone (NVP) and (2-acryloyloxy) sodium isopentene sulfonate (AOIAS) is 200:15:30:15:7:8.

[0133] The preparation method of the high temperature resistant viscosity reducing agent is as follows:

[0134] Add distilled water, tannic acid, and formaldehyde solution (37 wt % formaldehyde aqueous solution) into a four-necked round-bottom flask, adjust the pH to 8 with NaOH solution, heat to 65° C. and react for 1.5 h to carry out polycondensation reaction, continue to add acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and sodium styrene sulfonate (SSS) to the above solution in sequence, stir evenly, introduce N2, add initiator (ammonium persulfate: sodium bisulfite = 1:1), and carry out polymerization reaction at 60° C. for 2.5 h. After the reaction is completed, cool to room temperature to obtain a viscous liquid copolymer, wash with anhydrous ethanol, and dry and crush. The mass ratio of the distilled water, tannic acid, formaldehyde solution, AA, AMPS, SSS and initiator is 200:70:12:10:15:10:0.4.

[0135] The preparation method of the anti-collapse plugging agent is as follows:

[0136] Add kerosene to a three-necked flask, and then slowly add natural asphalt (softening point ≥ 250°C) and hydrogenated styrene-butadiene block copolymer (SEBS) under stirring, heat to 120°C to completely dissolve the SEBS, add oleum after the mixture is cooled, heat to 60°C to react for 2h, use 10% NaOH solution to adjust the pH of the system to 9, evaporate the solvent, dry and crush the modified product in an oven, and finally obtain polymer modified asphalt powder; the mass ratio of the kerosene, natural asphalt, SEBS and oleum is 70:18:1.5:10.

[0137] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 30:45:25.

[0138] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 , particle size is 0.5~5μm.

[0139] The drilling fluid system density is 2.3 g / cm 3 The hot rolling temperature of the drilling fluid system is 230℃.

[0140] Example 4

[0141] An ultra-high temperature and high density water-based drilling fluid, comprising: water, a high temperature suspending agent, a pH regulator, a high temperature resistant polymer viscosity increasing and fluid loss reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer, and a weighting agent, and the mass fractions of each component are as follows:

[0142] Water: 100 parts,

[0143] High temperature suspension agent: 1.8 parts,

[0144] pH adjuster: 1.5 parts,

[0145] High temperature resistant polymer viscosity increasing and fluid loss reducing agent: 2.0 parts,

[0146] High temperature resistance viscosity reducer: 2.0 parts,

[0147] Anti-collapse plugging agent: 3.0 parts,

[0148] High temperature stabilizer: 20 parts,

[0149] Weighting agent: adjust the system density to 2.1g / cm 3 .

[0150] in,

[0151] The water is fresh water.

[0152] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate, and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 50:50.

[0153] The pH regulator is a mixture of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 20:40:40;

[0154] The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent used in this example is the same as that in Example 3.

[0155] The preparation method of the high temperature resistant viscosity reducing agent used in this example is the same as that in Example 3.

[0156] The preparation method of the anti-collapse plugging agent used in this example is the same as that in Example 3.

[0157] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 30:45:25.

[0158] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 , particle size is 0.5~5μm.

[0159] The drilling fluid system density is 2.1 g / cm 3 The hot rolling temperature of the drilling fluid system is 230℃.

[0160] Example 5

[0161] An ultra-high temperature and high density water-based drilling fluid, comprising: water, a high temperature suspending agent, a pH regulator, a high temperature resistant polymer viscosity increasing and fluid loss reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer, and a weighting agent, and the mass fractions of each component are as follows:

[0162] Water: 100 parts,

[0163] High temperature suspension agent: 1.2 parts,

[0164] pH adjuster: 1.5 parts,

[0165] High temperature resistant polymer viscosity increasing and fluid loss reducing agent: 3.0 parts,

[0166] High temperature resistance viscosity reducer: 3.0 parts,

[0167] Anti-collapse plugging agent: 3.0 parts,

[0168] High temperature stabilizer: 20.0 parts,

[0169] Weighting agent: adjust the system density to 2.5g / cm 3 .

[0170] in,

[0171] The water is fresh water.

[0172] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate, and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 30:70.

[0173] The pH regulator is a compound of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 40:30:30;

[0174] The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent used in this example is the same as that in Example 3.

[0175] The preparation method of the high temperature resistant viscosity reducing agent used in this example is the same as that in Example 3.

[0176] The preparation method of the anti-collapse plugging agent used in this example is the same as that in Example 3.

[0177] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 30:40:30.

[0178] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 , particle size is 0.5~5μm.

[0179] The drilling fluid system density is 2.5 g / cm 3 The hot rolling temperature of the drilling fluid system is 230℃.

[0180] Example 6

[0181] An ultra-high temperature and high density water-based drilling fluid, comprising: water, a high temperature suspending agent, a pH regulator, a high temperature resistant polymer viscosity increasing and fluid loss reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer, and a weighting agent, and the mass fractions of each component are as follows:

[0182] Water: 100 parts,

[0183] High temperature suspension agent: 1.5 parts,

[0184] pH adjuster: 1.2 parts,

[0185] High temperature resistant polymer viscosity increasing and fluid loss reducing agent: 2.0 parts,

[0186] High temperature resistance viscosity reducer: 2.0 parts,

[0187] Anti-collapse plugging agent: 3.0 parts,

[0188] High temperature stabilizer: 20 parts,

[0189] Weighting agent: adjust the system density to 2.3g / cm 3 .

[0190] in,

[0191] The water is fresh water.

[0192] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate, and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 50:50.

[0193] The pH regulator is a mixture of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 50:30:20;

[0194] The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent used in this example is the same as that in Example 3.

[0195] The preparation method of the high temperature resistant viscosity reducing agent used in this example is the same as that in Example 3.

[0196] The preparation method of the anti-collapse plugging agent used in this example is the same as that in Example 3.

[0197] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 20:60:20.

[0198] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 , particle size is 0.5~5μm.

[0199] The drilling fluid system density is 2.3 g / cm 3 The hot rolling temperature of the drilling fluid system is 210℃.

[0200] Example 7

[0201] An ultra-high temperature and high density water-based drilling fluid, comprising: water, a high temperature suspending agent, a pH regulator, a high temperature resistant polymer viscosity increasing and fluid loss reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer, and a weighting agent, and the mass fractions of each component are as follows:

[0202] Water: 100 parts,

[0203] High temperature suspension agent: 1.8 parts,

[0204] pH adjuster: 1.5 parts,

[0205] High temperature resistant polymer viscosity increasing and fluid loss reducing agent: 4.0 parts,

[0206] High temperature resistance viscosity reducer: 2.5 parts,

[0207] Anti-collapse plugging agent: 3.5 parts,

[0208] High temperature stabilizer: 20 parts,

[0209] Weighting agent: adjust the system density to 2.3g / cm 3 .

[0210] in,

[0211] The water is fresh water.

[0212] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate, and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 50:50.

[0213] The pH regulator is a compound of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 40:30:30.

[0214] The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent used in this example is the same as that in Example 3.

[0215] The preparation method of the high temperature resistant viscosity reducing agent used in this example is the same as that in Example 3.

[0216] The preparation method of the anti-collapse plugging agent used in this example is the same as that in Example 3.

[0217] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 30:40:30.

[0218] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 , particle size is 0.5~5μm.

[0219] The drilling fluid system density is 2.3 g / cm 3 The hot rolling temperature of the drilling fluid system is 250℃.

[0220] Example 8

[0221] An ultra-high temperature and high density water-based drilling fluid, comprising: water, a high temperature suspending agent, a pH regulator, a high temperature resistant polymer viscosity increasing and fluid loss reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer, and a weighting agent, and the mass fractions of each component are as follows:

[0222] Water: 100 parts,

[0223] High temperature suspension agent: 1.2 parts,

[0224] pH adjuster: 1.5 parts,

[0225] High temperature resistant polymer viscosity increasing and fluid loss reducing agent: 4.0 parts,

[0226] High temperature resistance viscosity reducer: 3.0 parts,

[0227] Anti-collapse plugging agent: 4.0 parts,

[0228] High temperature stabilizer: 20 parts,

[0229] Weighting agent: adjust the system density to 2.5g / cm 3 .

[0230] in,

[0231] The water is fresh water.

[0232] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate, and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 50:50.

[0233] The pH regulator is a mixture of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 35:35:30;

[0234] The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent used in this example is the same as that in Example 3.

[0235] The preparation method of the high temperature resistant viscosity reducing agent used in this example is the same as that in Example 3.

[0236] The preparation method of the anti-collapse plugging agent used in this example is the same as that in Example 3.

[0237] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 30:40:30.

[0238] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 , particle size is 0.5~5μm.

[0239] The drilling fluid system density is 2.5 g / cm 3 The hot rolling temperature of the drilling fluid system is 250℃.

[0240] Comparative Example 1

[0241] An ultra-high temperature and high density water-based drilling fluid, comprising: water, high temperature suspending agent, pH regulator, fluid loss reducer, high temperature resistant viscosity reducer, anti-collapse plugging agent, high temperature stabilizer, weighting agent, the mass fractions of each component are as follows:

[0242] Water: 100 parts,

[0243] High temperature suspension agent: 1.8 parts,

[0244] pH adjuster: 1.5 parts,

[0245] Fluid loss reducer: 4.0 parts,

[0246] High temperature resistance viscosity reducer: 2.5 parts,

[0247] Anti-collapse plugging agent: 3.5 parts,

[0248] High temperature stabilizer: 20 parts,

[0249] Weighting agent: adjust the system density to 2.3g / cm 3 .

[0250] in,

[0251] The water is fresh water.

[0252] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate, and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 50:50.

[0253] The pH regulator is a compound of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 40:30:30.

[0254] The fluid loss reducer used in this comparative example is sulfonated lignite resin SPNH.

[0255] The preparation method of the high temperature resistant viscosity reducing agent used in this comparative example is the same as that in Example 3.

[0256] The preparation method of the anti-collapse plugging agent used in this comparative example is the same as that in Example 3.

[0257] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 30:40:30.

[0258] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 , particle size is 0.5~5μm.

[0259] The drilling fluid system density is 2.3 g / cm 3 The hot rolling temperature of the drilling fluid system is 250℃.

[0260] Comparative Example 2

[0261] An ultra-high temperature and high density water-based drilling fluid, comprising: water, high temperature suspending agent, pH regulator, high temperature resistant polymer viscosity increasing and fluid loss reducing agent, viscosity reducing agent, anti-collapse plugging agent, high temperature stabilizer, and weighting agent, and the mass fractions of each component are as follows:

[0262] Water: 100 parts,

[0263] High temperature suspension agent: 1.8 parts,

[0264] pH adjuster: 1.5 parts,

[0265] High temperature resistant polymer fluid loss reducer: 4.0 parts,

[0266] Viscosity reducer: 2.5 parts,

[0267] Anti-collapse plugging agent: 3.5 parts,

[0268] High temperature stabilizer: 20 parts,

[0269] Weighting agent: adjust the system density to 2.3g / cm 3 .

[0270] in,

[0271] The water is fresh water.

[0272] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate, and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 50:50.

[0273] The pH regulator is a compound of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 40:30:30.

[0274] The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent used in this comparative example is the same as that in Example 3.

[0275] The viscosity reducer used in this comparative example is sulfonated tannin SMT.

[0276] The preparation method of the anti-collapse plugging agent used in this comparative example is the same as that in Example 3.

[0277] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 30:40:30.

[0278] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 , particle size is 0.5~5μm.

[0279] The drilling fluid system density is 2.3 g / cm 3 The hot rolling temperature of the drilling fluid system is 250℃.

[0280] Comparative Example 3

[0281] An ultra-high temperature and high density water-based drilling fluid, comprising: water, a high temperature suspending agent, a pH regulator, a high temperature resistant polymer viscosity increasing and fluid loss reducing agent, a high temperature resistant viscosity reducing agent, a high temperature stabilizer, and a weighting agent, and the mass fractions of each component are as follows:

[0282] Water: 100 parts,

[0283] High temperature suspension agent: 1.8 parts,

[0284] pH adjuster: 1.5 parts,

[0285] High temperature resistant polymer fluid loss reducer: 4.0 parts,

[0286] High temperature resistance viscosity reducer: 2.5 parts,

[0287] Anti-collapse plugging agent: 0 parts,

[0288] High temperature stabilizer: 20 parts,

[0289] Weighting agent: adjust the system density to 2.3g / cm 3 .

[0290] in,

[0291] The water is fresh water.

[0292] The high temperature suspending agent is a compound of aluminum magnesium silicate and lithium magnesium silicate, and the mass ratio of aluminum magnesium silicate to lithium magnesium silicate is 50:50.

[0293] The pH regulator is a compound of sodium hydroxide, sodium carbonate and magnesium hydroxide, and the mass ratio of sodium hydroxide, sodium carbonate and magnesium hydroxide is 40:30:30.

[0294] The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent used in this comparative example is the same as that in Example 3.

[0295] The preparation method of the high temperature resistant viscosity reducing agent used in this comparative example is the same as that in Example 3.

[0296] The high temperature stabilizer is a compound of sodium formate, potassium formate and cesium formate, and the mass ratio of sodium formate, potassium formate and cesium formate is 30:40:30.

[0297] The weighting agent is spherical manganese tetraoxide powder, and the density of the spherical manganese tetraoxide powder is 4.8g / cm 3 , particle size is 0.5~5μm.

[0298] The drilling fluid system density is 2.3 g / cm 3 The hot rolling temperature of the drilling fluid system is 250℃.

[0299] The performance tests were performed on the drilling fluids obtained in the embodiments and comparative examples:

[0300] (1) Basic performance test

[0301] According to GB / T 16783.1-2012 "Field Test of Drilling Fluids in the Petroleum and Natural Gas Industry Part 1: Water-Based Drilling Fluids", the rheological properties, filtration properties, etc. of the drilling fluids of Examples 1 to 8 and Comparative Examples 1 to 3 were evaluated, and the experimental results are shown in Table 1 (the aging time (i.e., hot rolling time) in Table 1 is 16 hours).

[0302] Table 1 Basic properties of ultra-high temperature and high density water-based drilling fluid

[0303] Drilling Fluid ρ T AV PV YP Φ6 / Φ3 API HTHP Example 1 2.3 230 51 40 11 8 / 7 2.6 11.8 Example 2 2.3 230 45 37 8 7 / 6 2.1 10.6 Example 3 2.3 230 47 38 9 7 / 6 2.3 11.2 Example 4 2.1 230 38 31 7 6 / 5 2.5 9.8 Example 5 2.5 230 67 55 12 9 / 8 2.2 12.2 Example 6 2.3 210 48 39 9 7 / 6 2.0 10.8 Example 7 2.3 250 44 36 8 7 / 5 2.7 13.8 Example 8 2.5 250 68 55 13 9 / 8 2.8 13.6 Comparative Example 1 2.3 250 32 30 2 2 / 1 6.8 32.6 Comparative Example 2 2.3 250 89 68 21 17 / 15 5.3 28.8 Comparative Example 3 2.3 250 34 32 2 2 / 1.5 8.2 37.2

[0304] It can be seen from Examples 1, 2, 3, 4, and 5 that at 230°C, the 3 In the density range, the rheological properties and filtration performance of the ultra-high temperature and high density water-based drilling fluid system are good, indicating that the comprehensive performance of the system is good at high density. It can be seen from Examples 3, 6, and 7 that 2.3 g / cm 3 density, in the temperature range of 210-250°C, the rheological properties and filtration loss of the system fluctuate slightly, indicating that the system has good stability under ultra-high temperature conditions and is suitable for ultra-high temperature well applications; as can be seen from Example 8, the system has good stability under ultra-high temperature conditions and 250°C and 2.5 g / cm 3 It still has good rheological and fluid loss reduction performance under the conditions; it can be seen from Example 7 and Comparative Example 1 that the stability of the system after hot rolling at 250°C after adding sulfonated lignite resin is significantly reduced, degradation occurs, the viscosity and shearing are significantly reduced, and the high-temperature and high-pressure fluid loss is significantly increased, indicating that the fluid loss reducer of the present invention can withstand a temperature of 250°C and has a better fluid loss reduction effect and a certain viscosity-increasing effect under ultra-high temperature conditions. It can be seen from Example 7 and Comparative Example 2 that the system adds ungrafted and modified sulfonated tannin, and the viscosity and shearing force increase significantly after hot rolling, and the high-temperature and high-pressure fluid loss increases significantly, which is not conducive to the circulation of drilling fluid and the stability of the wellbore under ultra-high temperature conditions; it can be seen from Example 7 and Comparative Example 3 that the system does not add anti-collapse plugging agent, and the stability becomes worse after hot rolling, the viscosity and shearing decrease, and the fluid loss increases significantly, indicating that the anti-collapse plugging agent of the present invention has excellent fluid loss reduction and plugging effect under ultra-high temperature conditions, which is conducive to the high-temperature rheological stability and water loss wall building performance of the system. It can be seen from the results of Example 7 and Comparative Examples 1, 2, and 3 that the best drilling fluid performance can be achieved according to the formula provided by the present invention.

[0305] (2) High temperature static sedimentation stability test

[0306] The static sedimentation stability test is a method for evaluating the sedimentation tendency of drilling fluid under static conditions in the wellbore. The drilling fluids prepared in Examples 1 to 8 and Comparative Examples 1 to 3 are placed in a constant temperature drying oven and left to stand at a specified temperature at high temperature (vertically placed). After standing for a period of time, they are taken out vertically and naturally cooled. The liquids in the upper and lower layers of the drilling fluid are respectively taken for density testing to measure the density ρ of the upper part of the drilling fluid column. top and the density ρ at the bottom bottom And calculate the static settlement factor SF of the drilling fluid. The calculation formula of SF is as follows:

[0307]

[0308] When SF is 0.5, it means that no static sedimentation occurs; when SF is greater than 0.52, it means that the static sedimentation stability is poor. The sedimentation stability of the drilling fluids of Examples 1 to 8 and Comparative Examples 1 to 3 at different temperatures for 1 day, 3 days, 5 days, etc. was evaluated indoors, and the experimental results are shown in Table 2.

[0309] Table 2 Evaluation of sedimentation stability of ultra-high temperature and high density water-based drilling fluid

[0310]

[0311]

[0312] It can be seen from Table 2 that after the drilling fluids of Examples 1 to 8 were left standing at high temperatures for different times, the sedimentation factors were all less than 0.52, while the sedimentation factors of the drilling fluids of Comparative Examples 1 to 3 exceeded 0.52, indicating that the ultra-high temperature and high density system of the present invention has good high temperature standing sedimentation stability and can meet the requirements for ultra-high temperature and high pressure formation drilling.

[0313] (3) Anti-pollution performance test

[0314] Taking Example 3 as an example, the anti-pollution performance of the ultra-high temperature and high density water-based drilling fluid of the present invention was evaluated to study the ability of the system to be affected by foreign pollutants. The results are shown in Table 3 (the aging time in Table 3 is 16 hours).

[0315] Table 3 Evaluation of anti-pollution ability of ultra-high temperature and high density water-based drilling fluid

[0316] pollute Temperature,℃ AV PV YP Φ6 / Φ3 API HTHP blank 230 47 38 9 7 / 6 2.3 11.2 5% NaCl 230 49 39 10 8 / 7 2.4 11.6 10% NaCl 230 45 37 8 7 / 6 3.1 14.8 5% simulated drill cuttings 230 52 43 9 8 / 6 2.3 12.2 10% simulated drill cuttings 230 58 47 11 11 / 9 2.9 13.8 <![CDATA[1.5%CaSO4]]> 230 47 39 8 7 / 6 2.6 11.4 <![CDATA[3.0%CaSO4]]> 230 44 37 7 6 / 5 3.5 14.0

[0317] Note: 5% NaCl in Table 3 means adding 5wt% NaCl into the drilling fluid, and the rest are similar.

[0318] It can be seen from Table 3 that after being contaminated by NaCl, simulated cuttings, and CaSO4, the rheological properties of the system changed slightly after aging at 230℃ for 16h, and the high-temperature and high-pressure filtration loss increased slightly, but was still within 20mL, and the performance was basically stable. The results show that the ultra-high temperature and high-density water-based drilling fluid has good anti-pollution performance at high temperature.

[0319] Note: The meanings of the parameters in Tables 1 to 3 are as follows:

[0320] T: drilling fluid aging temperature, °C;

[0321] ρ: drilling fluid density, g / cm 3 ;

[0322] AV: drilling fluid apparent viscosity, mPa·s;

[0323] PV: drilling fluid plastic viscosity, mPa·s;

[0324] YP: dynamic shear force of drilling fluid, Pa;

[0325] Φ6: 6-speed rotary viscometer 6-turn reading, dimensionless;

[0326] Φ3: 3-turn reading of a six-speed rotary viscometer, dimensionless;

[0327] API: medium-pressure water loss of drilling fluid (0.7MPa, room temperature, 30min), mL;

[0328] HTHP: high temperature and high pressure water loss of drilling fluid (3.5MPa, T, 30min), mL;

[0329] SF: drilling fluid sedimentation factor, dimensionless.

[0330] The eight groups of embodiments of the ultra-high temperature and high density water-based drilling fluid of the present invention are prepared at different densities (2.1-2.5 g / cm 3 ) and after aging at different temperatures (210-250°C): the system viscosity and shear force are moderate, API filtration loss and high-temperature and high-pressure water loss are low; the long-term high-temperature sedimentation stability is good, which effectively improves the high-temperature suspension stability of the system; the anti-pollution performance is strong, and it is suitable for drilling construction in deep wells, ultra-deep wells, and complex formations such as salt-gypsum layers.

[0331] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. An ultra-high temperature and high density water-based drilling fluid, characterized in that: The composition includes the following components in parts by weight: 100 parts of water, 1.0-2.0 parts of high-temperature suspending agent, 0.5-2.0 parts of alkaline pH adjusting agent, 1.0-4.0 parts of high-temperature resistant polymer viscosity increasing and filtration reducing agent, 1.0-3.0 parts of high-temperature resistant viscosity reducing agent, 2.0-4.0 parts of anti-collapse plugging agent, 10-20 parts of high-temperature stabilizer, and weighting agent; the mass fraction of the weighting agent is such that the density of the ultra-high temperature and high-density water-based drilling fluid is 2.1-2.5 g / cm 3 shall prevail; The high temperature resistant polymer viscosity increasing and fluid loss reducing agent is obtained by polymerization of monomers, wherein the monomers include acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentenesulfonate; The high temperature resistant viscosity reducing agent is a tannin graft copolymer, which is obtained by modifying tannic acid with formaldehyde, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and sodium styrenesulfonate; The anti-collapse plugging agent is polymer modified asphalt, and the polymer modified asphalt is obtained by modifying natural asphalt with hydrogenated styrene-butadiene block copolymer and sulfonating it.

2. The ultra-high temperature and high density water-based drilling fluid according to claim 1, characterized in that: The high temperature suspending agent is aluminum magnesium silicate and / or lithium magnesium silicate, and the particle sizes of aluminum magnesium silicate and lithium magnesium silicate are both nanometer level.

3. The ultra-high temperature and high density water-based drilling fluid according to claim 1, characterized in that: The preparation method of the high temperature resistant polymer viscosity increasing and fluid loss reducing agent comprises the following steps: Mixing water, acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentenesulfonate to obtain a mixed solution; the pH value of the mixed solution is 7; The mixed solution is mixed with an initiator to carry out polymerization reaction to obtain a gel product; The gel product is washed and dried in sequence to obtain the high temperature resistant polymer viscosity increasing and fluid loss reducing agent.

4. The ultra-high temperature and high density water-based drilling fluid according to claim 3, characterized in that: The mass ratio of water, acrylamide, 2-acrylamide-2-methylpropane sulfonic acid, diallyldimethylammonium chloride, 1-vinyl-2-pyrrolidone and sodium (2-acryloyloxy)isopentene sulfonate is 200:(10-20):(15-30):(10-20):(5-10):(5-10); the polymerization reaction temperature is 60-65°C and the reaction time is 3-5h.

5. The ultra-high temperature and high density water-based drilling fluid according to claim 1, characterized in that: The preparation method of the high temperature resistant viscosity reducing agent comprises the following steps: Mixing water, tannic acid and formaldehyde solution, and subjecting the obtained mixed solution to polycondensation reaction to obtain a polycondensation product; the pH value of the mixed solution is 8; The polycondensation product is mixed with acrylic acid, 2-acrylamide-2-methylpropane sulfonic acid, sodium styrene sulfonate and an initiator to carry out a polymerization reaction to obtain a polymerization product; The polymerized product is washed and dried in sequence to obtain the high temperature resistant viscosity reducing agent.

6. The ultra-high temperature and high density water-based drilling fluid according to claim 5, characterized in that: The mass fraction of the formaldehyde solution is 37%, and the mass ratio of the water, tannic acid, formaldehyde solution, acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid and sodium styrene sulfonate is 200:(50-80):(8-15):(5-10):(10-25):(5-10); the temperature of the polycondensation reaction is 60-70°C, and the time is 1-2h; the temperature of the polymerization reaction is 60-70°C, and the time is 2-3h.

7. The ultra-high temperature and high density water-based drilling fluid according to claim 1, characterized in that: The preparation method of the anti-collapse plugging agent comprises the following steps: mixing an organic solvent, natural asphalt and a hydrogenated styrene-butadiene block copolymer to obtain a mixture; The mixture is mixed with fuming sulfuric acid to carry out a sulfonation reaction to obtain a sulfonated product; After the pH value of the sulfonated product is adjusted to 9, the organic solvent is removed and the product is dried in sequence to obtain the anti-collapse plugging agent.

8. The ultra-high temperature and high density water-based drilling fluid according to claim 7, characterized in that: The mass ratio of the organic solvent, natural asphalt, hydrogenated styrene-butadiene block copolymer and fuming sulfuric acid is (50-70):(10-20):(0.5-3):(5-10); the temperature of the sulfonation reaction is 60-70°C and the time is 2-3h.

9. The ultra-high temperature and high density water-based drilling fluid according to claim 1, characterized in that: The high temperature stabilizer is one or more of sodium formate, potassium formate and cesium formate; the weighting agent is spherical manganese tetraoxide micropowder; and the alkaline pH regulator is one or more of sodium hydroxide, sodium carbonate and magnesium hydroxide.

10. The method for preparing the ultra-high temperature and high density water-based drilling fluid according to any one of claims 1 to 9, characterized in that: The following steps are involved: The ultra-high temperature and high density water-based drilling fluid is obtained by mixing water, a high temperature suspending agent, an alkaline pH adjusting agent, a high temperature resistant polymer viscosity increasing and filtration reducing agent, a high temperature resistant viscosity reducing agent, an anti-collapse plugging agent, a high temperature stabilizer and a weighting agent.

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