CO2 pollution resistant high-density water-based drilling fluid and preparation method thereof

Abstract

The invention relates to the technical field of oil field drilling fluids, and discloses a CO2 pollution resistant high-density water-based drilling fluid and a preparation method thereof, the drilling fluid comprises the following raw materials by weight: 0.1-0.5 part of bentonite; 0.2 to 0.4 part of an alkalinity regulator; 1.0 to 1.5 parts of an amino inhibitor; 5.0 to 8.0 parts of a lubricating foam inhibitor; 1.0 to 1.5 parts of a complexing stabilizer; 1.0 to 2.0 parts of a polymer filtrate reducer; 0.5 to 1.0 part of a coating agent; 1.0 to 3.0 parts of a glue protecting agent; 3.0 to 6.0 parts of a plugging filtrate reducer; 1.0 to 3.0 parts of an inhibiting and lubricating agent; 1.0 to 3.0 parts of a divalent ion stabilizer; 5.0 to 7.0 parts of potassium chloride; 10 to 15.0 parts of sodium chloride; 1.0 to 3.0 parts of calcium chloride; and 1.0 to 3.0 parts of zinc chloride. The drilling fluid system thought of a traditional bentonite tackifying suspension drilling fluid is jumped out, the drilling fluid system with the ultralow bentonite content is adopted, and damage of HCO3 <-> / CO3 < 2-> to the drilling fluid system is greatly and fundamentally reduced; and moreover, a multi-component strong inhibition technology of compounding high-salinity brine and an amino inhibitor is adopted, so that the anti-pollution capacity of the drilling fluid system is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of oilfield drilling fluid technology in petroleum exploration and development, specifically to a high-density water-based drilling fluid resistant to CO2 pollution and its preparation method. Background Technology

[0002] Drilling fluid is the circulating flushing medium used in the drilling process, and can be divided into water-based drilling fluid, oil-based drilling fluid, and gas drilling fluid. Among them, water-based drilling fluid is the most widely used type of drilling fluid due to its low cost and wide availability of materials. However, in actual drilling applications, water-based drilling fluid is easily contaminated by acidic gas CO2.

[0003] Drilling fluids contaminated with CO2 often exhibit decreased pH, increased viscosity, and in severe cases, loss of fluidity, increased filtration loss, decreased density, and thick, loose mud cake. Furthermore, the properties of CO2-contaminated drilling fluids are difficult to restore, typically requiring mud replacement for treatment. This significantly impacts on-site drilling operations and causes substantial economic losses to drilling operations.

[0004] To combat CO2 pollution, engineers have implemented various measures over the past two decades. For example, early methods involved adding CaCl2 to treat contaminated drilling fluids. However, due to limitations in early colloid-protecting technologies, the addition of calcium chloride easily led to pH imbalances in the drilling fluid. While it could remove calcium promptly, filtration loss was prone to becoming uncontrollable. Later, CaO was added for calcium removal. However, the addition of CaO caused some treatment agents with poor calcium resistance in the drilling fluid to become ineffective, and poor control of calcium ion content could lead to calcium contamination. Furthermore, calcium ions are rapidly depleted when exposed to CO2 pollution, and their preventative capabilities are limited. These methods are primarily based on treating contaminated drilling fluids, with very little research specifically addressing the prevention of CO2 pollution in drilling fluids.

[0005] In recent years, researchers have gradually shifted their focus from treating CO2 pollution to preventing it. For example, Zhang Kun, Huang Ping, and others, in their work "High-Density Water-Based Drilling Fluid CO2 Pollution Prevention Technology," employed "solid phase capacity limit expansion technology," using composite electrolytes and diluent HTX to increase the solid phase capacity limit of the drilling fluid system. This improved the drilling fluid's resistance to pollution and, to some extent, curbed CO2 pollution. Liu Xiang, Luo Yufeng, and others, in their work "Test Methods and Treatment Technology for CO2 Pollution in Drilling Fluids," used a potassium-lime sulfonated coarse dispersion drilling fluid system to prevent CO2 pollution. This drilling fluid system exhibits strong inhibition and resistance to acid gas pollution, but its overall pollution resistance remains limited.

[0006] For example, invention patent CN114292632A discloses a carbon dioxide complexing agent for drilling fluid, its preparation method, and its application. This technology uses an amidoguanidine complex as a CO2 absorbent, absorbing CO2 at the bottom of the well and releasing it at the surface, thus achieving a certain degree of CO2 prevention. However, this technology suffers from problems such as high production costs and rapid consumption due to easy adsorption by drill cuttings.

[0007] For example, invention patent CN117487529A discloses a low-solids emulsion-type high-calcium brine-based drilling fluid system. This patent uses treatment agents such as strong calcium-resistant filtration loss reducers, strong calcium-resistant plugging agents, and strong calcium-resistant coating agents. Strong calcium-resistant treatment agents are not only costly but also have complex synthesis processes. Furthermore, they limit the application of conventional treatment agents, hindering the widespread application of the entire system. Summary of the Invention

[0008] To address the problems and shortcomings of the existing technologies, this invention proposes a high-temperature, high-density drilling fluid that is resistant to high CO2 pollution, has a simple processing technology, and is cost-controllable, as well as its preparation method.

[0009] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0010] This invention provides a high-temperature, high-density drilling fluid resistant to CO2 pollution, characterized in that, based on 100 parts by mass of water added, the drilling fluid further comprises:

[0011] Bentonite: 0.1–0.5 parts;

[0012] Alkalinity adjuster: 0.2–0.4 parts;

[0013] Amine inhibitor: 1.0–1.5 parts;

[0014] Lubricating defoamer: 5.0–8.0 parts;

[0015] Divalent ion stabilizer: 1.0–3.0 parts;

[0016] Complexing stabilizer: 1.0–1.5 parts;

[0017] Polymer filtration loss reducer: 1.0–2.0 parts;

[0018] Coating agent: 0.5–1.0 parts;

[0019] Protective agent: 1.0–3.0 parts;

[0020] Blocking and filtration reduction agent: 3.0–6.0 parts;

[0021] Inhibiting lubricant: 1.0–3.0 parts;

[0022] Potassium chloride: 5-7.0 parts

[0023] Sodium chloride: 10-15.0 parts;

[0024] Calcium chloride: 1.0–3.0 parts;

[0025] Zinc chloride: 1.0 to 3.0 parts.

[0026] In a preferred embodiment of the present invention, the content of the alkalinity regulator is 0.3 parts;

[0027] In a preferred embodiment of the present invention, the content of the amino inhibitor is 1.0 part;

[0028] In a preferred embodiment of the present invention, the content of the lubricating defoamer is 7.0 parts;

[0029] In a preferred embodiment of the present invention, the content of the divalent ion stabilizer is 2.0 parts;

[0030] In a preferred embodiment of the present invention, the content of the complexing stabilizer is 1.2 parts;

[0031] In a preferred embodiment of the present invention, the content of the polymer filtration loss reducing agent is 1.5 parts;

[0032] In a preferred embodiment of the present invention, the content of the adhesive is 2.0 parts;

[0033] In a preferred embodiment of the present invention, the content of the sealing and filtration loss reducing agent is 4.0 parts;

[0034] In a preferred embodiment of the present invention, the content of the inhibitory lubricant is 2.0 parts;

[0035] In a preferred embodiment of the present invention, the potassium chloride content is 7.0 parts;

[0036] In a preferred embodiment of the present invention, the sodium chloride content is 12.0 parts;

[0037] In a preferred embodiment of the present invention, the content of calcium chloride is 2.0 parts;

[0038] In a preferred embodiment of the present invention, the content of zinc chloride is 2.0 parts.

[0039] In a preferred embodiment of the present invention, the amount of bentonite added in the above-mentioned drilling fluid system is determined according to the required density of the drilling fluid. Preferably, when the required density of the drilling fluid is 1.5 g / cm³... 3When preparing drilling fluid, the amount of bentonite added is 0.5 parts; when the required drilling fluid density is 1.8 g / cm³... 3 When preparing drilling fluid, the amount of bentonite added is 0.8 parts; when the required drilling fluid density is 2.0 g / cm³... 3 When preparing drilling fluid, the amount of bentonite added is 0.1 parts.

[0040] In a preferred embodiment of the present invention, the amount of coating agent added in the above-described drilling fluid system is determined according to the required density of the drilling fluid. Preferably, when the required density of the drilling fluid is 1.5 g / cm³... 3 When preparing drilling fluid, the amount of coating agent added is 1.0 part; when the required drilling fluid density is 1.8 g / cm³ 3 When preparing drilling fluid, the amount of coating agent added is 0.8 parts; when the required drilling fluid density is 2.0 g / cm³. 3 When preparing drilling fluid, the amount of coating agent added is 0.5 parts.

[0041] As a preferred embodiment of the present invention, the alkalinity regulator is usually a common alkaline substance such as sodium hydroxide or potassium hydroxide used to adjust the pH of drilling fluid, and commercially available finished products can be purchased.

[0042] As a preferred embodiment of the present invention, the amino group inhibitor is typically selected from amino cationic polyethylene glycol, which mainly plays an inhibitory role.

[0043] In a preferred embodiment of the present invention, the lubricating defoamer is a compound of 10# white oil and polydimethyl silicone oil in a 5:1 ratio. The lubricating defoamer primarily functions as a lubricant and defoamer in drilling fluid, allowing CO2 gas that has invaded the drilling fluid to quickly slip out, especially at the surface, where it can rapidly desorb from the drilling fluid, thereby reducing damage to the drilling fluid's properties.

[0044] As a preferred embodiment of the present invention, the divalent ion stabilizer is prepared by mixing diethanol monoisopropanolamine and dimethylimidazole in a ratio of 5:3 at 60°C, stirring at 3000 rpm for 1 hour, and then cooling to room temperature.

[0045] The stabilizer formed by diethanol monoisopropanolamine and dimethylimidazole can form a semi-stable complex structure with calcium and zinc ions in the drilling fluid. Due to the large presence of hydroxyl groups in diethanol monoisopropanol, the water solubility of this semi-stable complex remains unaffected, while the interaction between divalent ions and the polymer is significantly weakened. This significantly enhances the polymer's filtration reduction effect against divalent ions without compromising its inhibitory properties. Furthermore, because it forms a semi-stable complex, when the drilling fluid encounters CO2 or H2S gas intrusion, the divalent ions such as calcium and zinc can quickly react with CO32-. 2- Calcium carbonate (zinc) precipitate is formed. Hydrogen sulfide gas can rapidly form zinc sulfide precipitate with zinc ions, thereby releasing diethanol monoisopropanolamine and dimethylimidazole.

[0046] In a preferred embodiment of the present invention, the complexing stabilizer is one or both of ferric citrate or ferric hydroxycitrate, and commercially available finished products are readily available. In the drilling fluid, the complexing stabilizer adsorbs onto the clay end face, increasing the hydration film thickness of the clay particles; on the other hand, it complexes with the polymers in the drilling fluid, preventing the polymer treatment agent from curling under high mineralization and high pollution conditions, thereby stabilizing the filtration loss.

[0047] As a preferred embodiment of the present invention, the polymer filtration reducer is MYK-1, a drilling fluid filtration reducer sodium allyl sulfonate copolymer, which plays a role in reducing filtration loss in drilling fluid and controlling the filtration loss of the drilling fluid system.

[0048] As a preferred embodiment of the present invention, the coating agent is NMI-4, a plant-based adhesive modified with a coating inhibitor for drilling fluid, which mainly plays a coating inhibition role in drilling fluid.

[0049] As a preferred embodiment of the present invention, the protective agent is mainly composed of two types: sulfonated phenolic resin and lignite resin, in a 1:1 ratio, and mainly plays the role of protecting the core and reducing filtration loss in drilling fluid.

[0050] As a preferred embodiment of the present invention, the plugging and filtration loss reducing agent is mainly composed of two substances in a 1:1 ratio: sulfonated asphalt powder FT-1A and drilling fluid anti-high temperature filtration loss reducing agent modified natural resin composite JNJS-220. In drilling fluid, it mainly plays the role of plugging and reducing filtration loss.

[0051] As a preferred embodiment of the present invention, the inhibitory lubricant is PGCS-1, a solid polymeric alcohol for drilling fluids, which has both inhibitory and lubricating effects in drilling fluids. Commercially available finished products are readily available.

[0052] As a preferred embodiment of the present invention, the potassium chloride, sodium chloride, calcium chloride, and zinc chloride can be commercially available finished products. These components provide potassium ions, sodium ions, calcium ions, and zinc ions in the drilling fluid, thereby contributing to the mineralization of the drilling fluid.

[0053] In another aspect, the present invention provides a method for preparing the above-mentioned high-density water-based drilling fluid resistant to CO2 pollution, the method comprising the following steps and procedures:

[0054] Step S1. Weigh out the following ingredients according to the specified ratio: bentonite, alkalinity regulator, amine inhibitor, lubricant and defoaming agent, divalent ion stabilizer, complexing stabilizer, polymer filtration loss reducer, coating agent, protective agent, plugging filtration loss reducer, inhibitory lubricant, potassium chloride, sodium chloride, calcium chloride, and zinc chloride.

[0055] Step S2. First, fully hydrate the weighed bentonite for 24 hours to form a prehydrated bentonite slurry; then add 100 parts of clean water to the drilling fluid tank, and then add the prehydrated bentonite slurry to the drilling fluid tank and stir to mix evenly.

[0056] Step S3. Add alkalinity regulator, protective agent, coating agent, polymer filtration loss reducer, complexing stabilizer, blocking filtration loss reducer, lubricant inhibitor, lubricant defoamer and other treatment agents to the solution formed in step S2, and stir thoroughly to form a glue solution;

[0057] Step S4. First, add a divalent ion stabilizer to the adhesive solution formed in step S3, stir and mix evenly, then add sodium chloride, potassium chloride, calcium chloride and amine inhibitor, stir and mix evenly again to form an adhesive solution;

[0058] Step S5. Add barium sulfate (barite) as a weighting agent to the adhesive solution obtained in step S4, and adjust the density of the adhesive solution to the required density (1.1~2.3 g / cm³). 3 Ultimately, a high-density water-based drilling fluid resistant to CO2 pollution was obtained.

[0059] As a preferred embodiment of the present invention, the specific preparation process and the order of addition of each component in step S3 are as follows:

[0060] First, add the alkalinity adjuster to the solution formed in step S2 and stir continuously for 10-30 minutes until the mixture is homogeneous.

[0061] Then add the protective agent and continue stirring for 10-30 minutes until well mixed;

[0062] Next, add the polymer filtration reducer and continue stirring for 10-30 minutes until the mixture is homogeneous;

[0063] Add the complexing stabilizer and stir continuously for 10-30 minutes until well mixed;

[0064] Add the filtration reduction and sealing agent and stir continuously for 10-30 minutes until well mixed;

[0065] Add the lubricant and continue stirring for 10-30 minutes until well mixed;

[0066] Finally, add the lubricating and defoaming agent and continue stirring for 10-30 minutes until well mixed.

[0067] After adding the above raw material components, continue stirring the resulting adhesive solution for 12 hours.

[0068] As a preferred embodiment of the present invention, the specific preparation process and the order of addition of each component in step S4 are as follows:

[0069] First, add a divalent ion stabilizer to the adhesive solution formed in step S3 and stir continuously for 10-20 minutes until it is evenly mixed.

[0070] Then add sodium chloride and continue stirring for 10-20 minutes until well mixed;

[0071] Next, add potassium chloride and continue stirring for 10-20 minutes until well mixed;

[0072] Add calcium chloride and stir continuously for 10-20 minutes until well mixed;

[0073] Add zinc chloride and stir continuously for 10-20 minutes until well mixed;

[0074] Finally, add the amino inhibitor and continue stirring for 10-30 minutes until well mixed.

[0075] As a preferred embodiment of the present invention, in step S5, barite is added while stirring to adjust the prepared drilling fluid to the required density, and stirring is continued for 6 hours to finally obtain the high-density water-based drilling fluid resistant to CO2 pollution of the present invention.

[0076] As a preferred embodiment of the present invention, in the process of preparing the above-mentioned drilling fluid, the stirring and mixing rate is 100-500 rpm, and the on-site slurry preparation uses a weighted pump for circulating shearing to ensure uniform mixing.

[0077] The beneficial effects of this invention are:

[0078] 1. This invention innovatively employs a "multi-component composite strong inhibition technology of compounded high-mineralization brine + amine inhibitor." By using a multi-component compounded high-mineralization brine of "potassium chloride + sodium chloride + calcium chloride + zinc chloride" and an amine inhibitor for synergistic strong inhibition, especially since the inhibitory effect of divalent ions is significantly higher than that of conventional monovalent ions, this technology ensures that when the soil phase (including formation intrusion) of the drilling fluid is contaminated by CO2, it will not be affected by HCO3-. - / CO32- The presence of CO2 disperses the CO2, fundamentally eliminating its destructive effects and significantly enhancing the drilling fluid system's resistance to contamination. Simultaneously, because high-concentration brine significantly reduces the solubility of CO2 gas in the drilling fluid, most of the CO2 gas that enters the drilling fluid exists in a free form, preventing it from entering the drilling fluid as ions. Upon reaching the surface, it can quickly degas, thus significantly reducing the impact of CO2 on the drilling fluid itself.

[0079] 2. Because the essence of CO2 pollution is usually HCO3 entering the drilling fluid. - / CO3 2- Bentonite reacts with clay particles in the drilling fluid, causing them to disperse and then aggregate, thus disrupting the drilling fluid. This invention creatively departs from the traditional "bentonite-enhanced suspension drilling fluid" approach, employing "ultra-low-bentonite-free drilling fluid technology." This utilizes a drilling fluid system with ultra-low bentonite content, significantly reducing HCO3 content. - / CO3 2- It does not damage the drilling fluid system. Furthermore, compared to traditional water-based drilling fluid systems, the CO2-resistant drilling fluid of this invention has advantages such as simple and widely available raw materials, easy preparation and production operations, convenient on-site maintenance, and ease of large-scale production and application.

[0080] 3. This invention employs a "low-viscosity, high-lubricity, long-lasting slippage and foam suppression technology." This technology reduces the apparent adhesive-plastic viscosity of the drilling fluid and appropriately increases its structural viscosity, thereby enhancing the lubrication and foam suppression properties of the -10# oil combined with foam-suppressing silicone oil. This allows CO2 gas that has infiltrated the drilling fluid to quickly slip out, especially at the surface, where it can rapidly desorb from the drilling fluid, thus reducing damage to the drilling fluid's properties.

[0081] 4. This invention employs divalent ion stabilization technology. Diethanol monoisopropanolamine and dimethylimidazole can form semi-stable complex structures with calcium and zinc ions. Due to the abundant presence of hydroxyl groups in diethanol monoisopropanol, the water solubility of this semi-stable complex remains unaffected, while the interaction between the divalent ions and the polymer is significantly weakened. This significantly enhances the polymer's filtration-reducing effect against divalent ions, without compromising its inhibitory properties. Because a semi-stable complex is formed, when the system encounters CO2 or H2S gas intrusion, the calcium and zinc divalent ions can rapidly react with CO32-. 2- Calcium carbonate (zinc) precipitate is formed. Hydrogen sulfide gas can rapidly react with zinc ions to form zinc sulfide precipitate, thereby releasing diethanolamine and dimethylimidazole. The system only needs to be replenished according to the consumption of zinc and calcium ions. The generated micro- and nano-sized precipitates also provide excellent sealing in the drilling fluid.

[0082] 5. This invention innovatively incorporates a complexing stabilizer, ferric citrate or ferric hydroxycitrate, or a combination of both, into the drilling fluid system. Ferric citrate strongly adsorbs onto the end faces of clay particles in the drilling fluid, forming a thick hydration film on the surface of the colloidal particles. This prevents the aggregation of clay particles and solid particles such as barite, thus stabilizing the rheological properties of the drilling fluid. Furthermore, due to the complexation of trivalent iron ions with the polymer, the curvature of the polymer in the drilling fluid is significantly reduced under high temperatures, contaminated conditions, and high mineralization, greatly improving the polymer's anti-fouling ability. This, in turn, stabilizes the filtration loss of the drilling fluid system. Detailed Implementation

[0083] To enable those skilled in the art to better understand the technical solutions of this invention, several specific embodiments will be used to further illustrate the technical solutions for achieving the objectives of this invention. It should be noted that the technical solutions claimed by this invention include, but are not limited to, the following embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort should fall within the scope of protection of this invention.

[0084] Example 1

[0085] This embodiment discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0086] 0.1 parts bentonite; 0.3 parts alkalinity regulator; 1.0 part amine inhibitor; 7.0 parts lubricant and defoamer; 1.2 parts polymer complexing stabilizer; 1.5 parts polymer filtration loss reducer; 0.5 parts coating agent; 2.0 parts adhesive; 2.0 parts plugging and filtration loss reducer; 2.0 parts inhibitory lubricant; 2.0 parts divalent ion stabilizer; 7.0 parts potassium chloride; 12.0 parts sodium chloride; 2.0 parts calcium chloride; 2.0 parts zinc chloride.

[0087] A method for preparing a high-density water-based drilling fluid system resistant to CO2 pollution, used to prepare the aforementioned high-density water-based drilling fluid resistant to CO2 pollution, the method comprising the following steps:

[0088] (1) First, the bentonite is pre-hydrated and fully hydrated for 24 hours to form bentonite slurry. Then, 100 parts of clean water are added to the drilling fluid tank, and finally the bentonite slurry is added to the clean water.

[0089] (2) Using a drilling fluid pump, add the following to the above solution in sequence: alkalinity regulator (stirring continuously for 20 minutes), protective agent (stirring continuously for 20 minutes), coating agent (stirring continuously for 20 minutes), polymer filtration reducer (stirring continuously for 20 minutes), polymer complexing stabilizer (stirring continuously for 20 minutes), plugging filtration reducer (stirring continuously for 20 minutes), lubricant inhibitor (stirring continuously for 20 minutes), and lubricant defoamer (stirring continuously for 20 minutes); after the addition of the chemicals, continue stirring for 12 hours to finally form a gel solution.

[0090] (3) Add divalent ion stabilizer to the above adhesive solution and stir continuously for 10 minutes, add sodium chloride and stir continuously for 15 minutes, add potassium chloride and stir continuously for 15 minutes, add calcium chloride and stir continuously for 15 minutes, add zinc chloride and stir continuously for 15 minutes, add amino inhibitor and stir continuously for 15 minutes, and stir until uniform.

[0091] (4) Add barite to the above adhesive solution and adjust the density to the required 2.0 g / cm³. 3 This forms a weighted drilling fluid, thus obtaining the CO2-resistant high-temperature, high-density water-based drilling fluid system.

[0092] In the embodiments described in this invention, all the stirring is done by electric stirring, and the stirring speed is 100-500 rpm.

[0093] Example 2

[0094] This embodiment discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0095] 0.1 parts bentonite; 0.3 parts alkalinity regulator; 1.0 part amine inhibitor; 7.0 parts lubricant and defoamer; 1.0 part polymer complexing stabilizer; 1.5 parts polymer filtration loss reducer; 0.5 parts coating agent; 2.0 parts adhesive protectant; 2.0 parts plugging and filtration loss reducer; 2.0 parts lubricant inhibitor; 2.0 parts divalent ion stabilizer; 7.0 parts potassium chloride; 12.0 parts sodium chloride; 3.0 parts calcium chloride; 2.0 parts zinc chloride.

[0096] A method for preparing a high-density water-based drilling fluid system resistant to CO2 pollution, used to prepare the aforementioned high-density water-based drilling fluid resistant to CO2 pollution, includes the following steps:

[0097] (1) First, the bentonite is pre-hydrated and fully hydrated for 24 hours to form bentonite slurry. Then, 100 parts of clean water are added to the drilling fluid tank, and finally the bentonite slurry is added to the clean water.

[0098] (2) Using a drilling fluid pump, add the following to the above solution in sequence: alkalinity regulator (stirring continuously for 20 minutes), protective agent (stirring continuously for 20 minutes), coating agent (stirring continuously for 20 minutes), polymer filtration reducer (stirring continuously for 20 minutes), polymer complexing stabilizer (stirring continuously for 20 minutes), plugging filtration reducer (stirring continuously for 20 minutes), lubricant inhibitor (stirring continuously for 20 minutes), and lubricant defoamer (stirring continuously for 20 minutes); after the addition of the chemicals, continue stirring for 12 hours until a gel is formed.

[0099] (3) Add divalent ion stabilizer to the above adhesive solution and stir continuously for 10 minutes; add sodium chloride and stir continuously for 15 minutes; add potassium chloride and stir continuously for 15 minutes; add calcium chloride and stir continuously for 15 minutes; add zinc chloride and stir continuously for 15 minutes; add amino inhibitor and stir continuously for 15 minutes; stir and mix evenly.

[0100] (4) Finally, add barite to the above adhesive solution and adjust the density to the required 2.0 g / cm³. 3 This forms a weighted drilling fluid, thus obtaining the CO2-resistant high-temperature, high-density water-based drilling fluid system.

[0101] In the embodiments described in this invention, all the stirring is done by electric stirring, and the stirring speed is 100-500 rpm.

[0102] Example 3

[0103] This embodiment discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0104] 0.1 parts bentonite, 0.3 parts alkalinity regulator, 1.0 part amine inhibitor, 7.0 parts lubricant and defoamer, 1.5 parts polymer complexing stabilizer, 1.5 parts polymer filtration loss reducer, 0.5 parts coating agent, 2.0 parts protective agent, 2.0 parts blocking filtration loss reducer, 2.0 parts inhibitory lubricant, 2.0 parts divalent ion stabilizer, 7.0 parts potassium chloride, 12.0 parts sodium chloride, 3.0 parts calcium chloride, and 2.0 parts zinc chloride.

[0105] A method for preparing a high-density water-based drilling fluid system resistant to CO2 pollution, used to prepare the aforementioned high-density water-based drilling fluid resistant to CO2 pollution, includes the following steps:

[0106] (1) First, the bentonite is pre-hydrated and fully hydrated for 24 hours to form bentonite slurry. Then, 100 parts of clean water are added to the drilling fluid tank, and finally the bentonite slurry is added to the clean water.

[0107] (2) Using a drilling fluid pump, add the following to the above slurry in sequence: alkalinity adjuster (stirring continuously for 20 minutes), protective agent (stirring continuously for 20 minutes), coating agent (stirring continuously for 20 minutes), polymer filtration reducer (stirring continuously for 20 minutes), polymer complexing stabilizer (stirring continuously for 20 minutes), plugging filtration reducer (stirring continuously for 20 minutes), lubricant inhibitor (stirring continuously for 20 minutes), and lubricant defoamer (stirring continuously for 20 minutes); after adding the chemicals, continue stirring for 12 hours to form a gel.

[0108] (3) Add divalent ion stabilizer to the above adhesive solution and stir continuously for 10 minutes, add sodium chloride and stir continuously for 15 minutes, add potassium chloride and stir continuously for 15 minutes, add calcium chloride and stir continuously for 15 minutes, add zinc chloride and stir continuously for 15 minutes, add amino inhibitor and stir continuously for 15 minutes; stir evenly.

[0109] (4) Finally, add barite to the above adhesive solution and adjust the density to the required 2.0 g / cm³. 3 This forms a weighted drilling fluid, resulting in a high-temperature, high-density water-based drilling fluid system resistant to CO2 pollution.

[0110] Example 4

[0111] This embodiment discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0112] 0.3 parts bentonite, 0.3 parts alkalinity regulator, 1.0 part amine inhibitor, 7.0 parts lubricant and defoamer, 1.2 parts polymer complexing stabilizer, 1.5 parts polymer filtration loss reducer, 0.5 parts coating agent, 2.0 parts adhesive protectant, 2.0 parts plugging and filtration loss reducer, 2.0 parts inhibitory lubricant, 2.0 parts divalent ion stabilizer, 7.0 parts potassium chloride, 12.0 parts sodium chloride, 2.0 parts calcium chloride, and 2.0 parts zinc chloride.

[0113] The method and steps for preparing the CO2-resistant high-density water-based drilling fluid in this embodiment can be referred to in Examples 1-3, and will not be elaborated here. The final drilling fluid density is 2.0 g / cm³. 3 .

[0114] Example 5

[0115] This embodiment discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0116] 0.4 parts bentonite, 0.3 parts alkalinity regulator, 1.0 part amine inhibitor, 7.0 parts lubricant and defoamer, 1.2 parts polymer complexing stabilizer, 1.5 parts polymer filtration loss reducer, 0.5 parts coating agent, 2.0 parts protective agent, 2.0 parts blocking filtration loss reducer, 2.0 parts inhibitory lubricant, 2.0 parts divalent ion stabilizer, 7.0 parts potassium chloride, 12.0 parts sodium chloride, 2.0 parts calcium chloride, and 2.0 parts zinc chloride.

[0117] The method and steps for preparing the CO2-resistant high-density water-based drilling fluid in this embodiment can be referred to in Examples 1-3, and will not be elaborated here. The final drilling fluid density is 2.0 g / cm³. 3 .

[0118] Comparative Example 1

[0119] Comparative Example 1 discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0120] 3 parts bentonite, 0.3 parts alkalinity regulator, 1.0 part amine inhibitor, 7.0 parts lubricant and defoamer, 1.2 parts polymer complexing stabilizer, 1.5 parts polymer filtration loss reducer, 0.5 parts coating agent, 2.0 parts adhesive protectant, 2.0 parts plugging and filtration loss reducer, 2.0 parts inhibitory lubricant, 2.0 parts divalent ion stabilizer, 7.0 parts potassium chloride, 12.0 parts sodium chloride, 2.0 parts calcium chloride, and 2.0 parts zinc chloride.

[0121] The method and steps for preparing the CO2-resistant high-density water-based drilling fluid in Comparative Example 1 can be referred to in Examples 1-3, and will not be elaborated here. The final drilling fluid density was 2.0 g / cm³. 3 .

[0122] Comparative Example 2

[0123] Comparative Example 2 discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0124] 0.1 parts bentonite, 0.3 parts alkalinity regulator, 1.0 part amine inhibitor, 7.0 parts lubricant and defoamer, 1.0 part polymer complex stabilizer, 1.5 parts polymer filtration loss reducer, 0.5 parts coating agent, 2.0 parts protective agent, 2.0 parts blocking filtration loss reducer, 2.0 parts inhibitory lubricant, 2.0 parts divalent ion stabilizer, 3.0 parts potassium chloride, 4.0 parts sodium chloride, 1 part calcium chloride, and 1.0 part zinc chloride.

[0125] The method and steps for preparing the CO2-resistant high-density water-based drilling fluid in Comparative Example 2 can be referred to in Examples 1-3, and will not be elaborated here. The final drilling fluid density was 2.0 g / cm³. 3 .

[0126] Comparative Example 3

[0127] Comparative Example 3 discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0128] 0.1 parts bentonite, 0.3 parts alkalinity regulator, 1.0 part amine inhibitor, 1.2 parts polymer complexing stabilizer, 1.5 parts polymer filtration loss reducer, 0.5 parts coating agent, 2.0 parts protective agent, 2.0 parts plugging filtration loss reducer, 2.0 parts inhibitory lubricant, 2.0 parts divalent ion stabilizer, 7.0 parts potassium chloride, 12.0 parts sodium chloride, 2.0 parts calcium chloride, and 2.0 parts zinc chloride.

[0129] Similarly, the method and steps for preparing the CO2-resistant high-density water-based drilling fluid in Comparative Example 3 can be referred to in Examples 1-3, and will not be elaborated here. The final drilling fluid density is 2.0 g / cm³. 3 .

[0130] Comparative Example 4

[0131] Comparative Example 4 discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0132] 0.1 parts bentonite, 0.3 parts alkalinity regulator, 7.0 parts lubricant and defoamer, 1.2 parts polymer complexing stabilizer, 1.5 parts polymer filtration loss reducer, 0.5 parts coating agent, 2.0 parts protective agent, 2.0 parts blocking filtration loss reducer, 2.0 parts inhibitory lubricant, 7.0 parts potassium chloride, 12.0 parts sodium chloride, 2.0 parts divalent ion stabilizer, 2.0 parts calcium chloride, and 2.0 parts zinc chloride.

[0133] Similarly, the method and steps for preparing the CO2-resistant high-density water-based drilling fluid in Comparative Example 4 can be referred to in Examples 1-3, and will not be elaborated further here. The final drilling fluid density is 2.0 g / cm³. 3 .

[0134] Comparative Example 5

[0135] Comparative Example 5 discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0136] 0.1 parts bentonite, 0.3 parts alkalinity regulator, 1.0 part amine inhibitor, 7.0 parts lubricant and defoamer, 1.5 parts polymer filtration loss reducer, 0.5 parts coating agent, 2.0 parts protective agent, 2.0 parts plugging and filtration loss reducer, 2.0 parts inhibitory lubricant, 2.0 parts divalent ion stabilizer, 7.0 parts potassium chloride, 12.0 parts sodium chloride, 2.0 parts calcium chloride, and 2.0 parts zinc chloride.

[0137] Similarly, the method and steps for preparing the CO2-resistant high-density water-based drilling fluid in Comparative Example 5 can be referred to in Examples 1-3, and will not be elaborated here. The final drilling fluid density is 2.0 g / cm³. 3 .

[0138] Comparative Example 6

[0139] Comparative Example 6 discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0140] 0.1 parts bentonite, 0.3 parts alkalinity regulator, 1.0 part amine inhibitor, 7.0 parts lubricant and defoamer, 1.0 part polymer complexing stabilizer, 1.5 parts polymer filtration loss reducer, 0.5 parts coating agent, 2.0 parts adhesive protectant, 2.0 parts plugging and filtration loss reducer, 2.0 parts inhibitory lubricant, 2.0 parts divalent ion stabilizer, 7.0 parts potassium chloride, and 12.0 parts sodium chloride.

[0141] Similarly, the method and steps for preparing the CO2-resistant high-density water-based drilling fluid in Comparative Example 6 can be referred to in Examples 1-3, and will not be elaborated further here. The final drilling fluid density is 2.0 g / cm³. 3 .

[0142] Comparative Example 7

[0143] Comparative Example 7 discloses a high-density water-based drilling fluid resistant to CO2 pollution, comprising the following raw materials in parts by weight:

[0144] 0.1 parts bentonite, 0.3 parts alkalinity regulator, 1.0 part amine inhibitor, 7.0 parts lubricant and defoamer, 1.0 part polymer complexing stabilizer, 1.5 parts polymer filtration loss reducer, 0.5 parts coating agent, 2.0 parts adhesive protectant, 2.0 parts plugging and filtration loss reducer, 2.0 parts inhibitory lubricant, 7.0 parts potassium chloride, 12.0 parts sodium chloride, 1.0 part calcium chloride, and 2.0 parts zinc chloride.

[0145] Similarly, the method and steps for preparing the CO2-resistant high-density water-based drilling fluid in Comparative Example 7 can be referred to in Examples 1-3, and will not be elaborated further here. The final drilling fluid density is 2.0 g / cm³. 3 .

[0146] Comparative Example 8

[0147] Comparative Example 8 discloses a potassium-lime sulfonated coarse dispersion drilling fluid system, comprising the following raw materials in the following proportions:

[0148] 2.0 parts bentonite; 0.3 parts caustic soda; 4.0 parts high-temperature salt-resistant treatment agent SMP-3; 4.0 parts RSTF; 7.0 parts potassium chloride; 1.5 parts quicklime.

[0149] The preparation method of the above-mentioned potassium-lime sulfonated coarse dispersion drilling fluid system includes the following steps:

[0150] (1) First, the bentonite is pre-hydrated and fully hydrated for 24 hours to form bentonite slurry. Then, 100 parts of clean water are added to the drilling fluid tank, and finally the bentonite slurry is added to the clean water.

[0151] (2) Using a drilling fluid pump, add the following to the above slurry in sequence: caustic soda and stir for 20 minutes, add SMP-3 and stir for 20 minutes, and add RSTF and stir for 20 minutes to form a gel.

[0152] (3) Add potassium chloride to the above adhesive solution in sequence and stir continuously for 15 minutes, then add quicklime and stir continuously for 15 minutes until the mixture is uniform;

[0153] (4) Add barite to the above adhesive solution and adjust the density to the required 2.0 g / cm³. 3 This forms a weighted drilling fluid, resulting in a potassium-lime sulfonated coarse dispersion drilling fluid system.

[0154] In the embodiments described in this invention, all the above stirring is electric stirring, and the stirring speed is 100-500 revolutions.

[0155] Comparative Example 9

[0156] Comparative Example 9 discloses a conventional polysulfonated water-based drilling fluid system comprising the following raw materials in the following proportions:

[0157] 2.0 parts bentonite; 0.3 parts sodium hydroxide alkalinity regulator; 2.0 parts polymer filtration loss reducer MYK-1; 0.5 parts coating agent KPAM; 2.0 parts protective agent sulfonated lignite resin SPNH; 2.0 parts sulfonated phenolic resin SMP-3.

[0158] The preparation method of the above-mentioned conventional polysulfonated water-based drilling fluid system includes the following steps:

[0159] (1) First, the bentonite is pre-hydrated and fully hydrated for 24 hours to form bentonite slurry. Then, 100 parts of clean water are added to the drilling fluid tank, and finally the bentonite slurry is added to the clean water.

[0160] (2) Using a drilling fluid pump, add the following to the above slurry in sequence: alkalinity regulator and stir for 20 minutes, coating agent and stir for 20 minutes, polymer filtration loss reducer and stir for 20 minutes, adhesive protectant and stir for 20 minutes, and sulfonated phenolic resin and stir for 20 minutes to form an adhesive.

[0161] (3) Finally, add barite to the above adhesive solution and adjust the density to the required 2.0 g / cm³.3 This forms a weighted drilling fluid, thus obtaining the conventional polysulfonate water-based drilling fluid system.

[0162] In the embodiments described in this invention, all the above stirring is electric stirring, and the stirring speed is 100-500 revolutions.

[0163] Performance Evaluation

[0164] The performance of the products prepared in Examples 1-5 and Comparative Examples 1-9 was evaluated as follows:

[0165] 1. Basic performance test

[0166] Take 400 mL of each of the drilling fluids prepared in Examples 1-5 and Comparative Examples 1-9 above, heat-roll them in a roller furnace at 180°C for 16 hours, cool them to room temperature, stir them at high speed in a drilling fluid cup for 30 minutes, and then test their rheological properties, API filtration loss, HTHP filtration loss, and other properties after aging according to the method specified in GB / T16783.1-2014 Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry Part 1: Water-based Drilling Fluids.

[0167] 2. Evaluation of anti-pollution performance

[0168] The drilling fluids prepared in Examples 1-5 and Comparative Examples 1-9 were used as samples. Three 400ml portions of drilling fluid were taken from each example and comparative example. 4.0g, 8.0g, and 12.0g of dry ice were quickly added to the three portions of drilling fluid from each example and comparative example, respectively. The drilling fluids were placed in a sealed aging tank and hot-rolled at 180°C for 16 hours. After cooling to room temperature and releasing residual gas, the fluids were stirred at high speed in a drilling fluid cup for 30 minutes. The rheological properties, API filtration loss, and HTHP filtration loss after aging were tested according to the methods specified in GB / T16783.1-2014 Petroleum and Natural Gas Industry Drilling Fluid Field Testing Part 1: Water-based Drilling Fluids.

[0169] 3. Inhibition evaluation

[0170] Take 400 ml of each of the drilling fluids prepared in Examples 1-5 and Comparative Examples 1-9, and then add 50 g of 5-10 mesh rock cuttings to each drilling fluid. Roll the mixture at 180°C for 16 hours. Measure the rolling recovery rate of the comparative examples and examples.

[0171] 4. Test Results

[0172] The specific test results are shown in Table 1 below.

[0173] Table 1. Comparison of drilling fluid performance between examples and comparative examples.

[0174]

[0175]

[0176]

[0177] As can be seen from the rheological properties and filtration loss effects of different embodiments and comparative examples, the CO2-resistant high-density water-based drilling fluid system prepared by this invention has the following specific characteristics:

[0178] (1) The high-density water-based drilling fluid systems with CO2 pollution resistance prepared in Examples 1-5 exhibit good performance. After aging at 180℃, they have moderate viscosity, low filtration loss, and strong inhibition properties. They can not only meet the drilling requirements of salt-gypsum layers, but also have strong adaptability to mudstone and shale formations, and their temperature resistance can reach 180℃.

[0179] (2) A comparison of Examples 1-3 shows that increasing the calcium ion concentration significantly improves the overall system's resistance to CO2 pollution. However, increasing the calcium ion concentration reduces the overall viscosity of the system, necessitating increases in both the polymeric stabilizer and the divalent ion stabilizer. Therefore, the dosage of each treatment agent must be within a reasonable range. In fact, the addition of the divalent ion stabilizer aims to reduce the destructive effect of divalent ions on colloidal particles and polymers. Conversely, the polymeric stabilizer enhances the polymer's resistance to divalent ion pollution through complexation and other mechanisms.

[0180] (3) A comparison of Examples 1-5 and Comparative Example 1 shows that although the bentonite content further reduces the filtration loss and increases the viscosity-shear ratio of the entire system, it significantly reduces the system's resistance to contamination. After encountering CO2 contamination, the viscosity-shear ratio of the drilling fluid increases significantly, especially the structural viscosity. Analysis suggests that the low bentonite content in the drilling fluid system lowers the "reactive point" of the system with CO2, thereby improving the overall resistance to contamination. Furthermore, a comparison of Examples 1-5 also shows that as the bentonite content increases, the system's resistance to CO2 contamination does not decrease significantly, further demonstrating that the system has a certain "clay capacity."

[0181] (4) Comparison of Examples 1-5 and Comparative Example 2 shows that the viscosity of the comparative example does not change significantly with the decrease in salt concentration, but the filtration loss decreases. After encountering CO2 contamination, the filtration loss of the system does not change significantly, but the viscosity increases significantly. After encountering contamination, the density of the system decreases, and residual bubbles are visible. This indicates that the addition of salt mainly affects the viscosity during the anti-contamination process of the system. It is believed that, on the one hand, the decrease in salt concentration leads to an increase in the viscosity of the CO2-contaminated drilling fluid, thereby affecting the removal of CO2. On the other hand, the decrease in salt concentration increases the solubility of CO2 in the slurry, resulting in an increase in residual CO2, which further damages the performance of the drilling fluid. Therefore, conversely, the examples show that, because high-concentration brine significantly reduces the solubility of CO2 gas in the drilling fluid, most of the CO2 gas that enters the drilling fluid exists in a free form and does not enter the drilling fluid in the form of ions, allowing for rapid degassing upon reaching the surface. This also significantly reduces the impact of CO2 on the drilling fluid itself.

[0182] (5) A comparison of Examples 1-5 and Comparative Example 3 shows that the plastic viscosity of the drilling fluid system without lubricant and defoamer increases significantly after high-speed agitation and degassing upon opening the tank. Simultaneously, the density of the contaminated system is lower than that of Examples 1-5, and a greater number of microbubbles are visible in the sample. Therefore, the addition of lubricant and defoamer helps CO2 gas that has invaded the drilling fluid to quickly slide out of the drilling fluid, especially at the surface, where it can quickly desorb from the drilling fluid, thereby reducing damage to the drilling fluid's properties.

[0183] (6) A comparison of Examples 1-5 and Comparative Example 4 shows that the basic properties of the sample without the addition of an amine inhibitor are not significantly different from those of the examples in terms of rheology and filtration performance. However, the rolling recovery rate of the system is reduced, and the inhibition is significantly reduced. After encountering CO2 pollution, the viscosity increases more significantly than in the examples, and the filtration loss is also higher. Therefore, the addition of an amine inhibitor is very helpful in improving the system's resistance to CO2 pollution and plays an indispensable role.

[0184] (7) Comparison of Examples 1-5 and Comparative Example 5 shows that, after high-temperature aging, the rheological properties and filtration loss of the sample without polymeric stabilizer exhibit a decrease in viscosity and an increase in filtration loss to some extent, but overall the performance changes are not significant. However, data comparison after exposure to CO2 pollution shows that the viscosity of the sample without high-temperature stabilizer increased significantly after exposure to CO2 pollution, and the filtration loss increased substantially. This indicates that under CO2 pollution conditions, the addition of polymeric stabilizer has a very significant effect on improving the stability of the entire system and is indispensable for improving anti-pollution performance. Analysis suggests that polymeric complex stabilizer can strongly adsorb onto the end face of clay particles in drilling fluid, forming a thick hydration film on the surface of the colloidal particles in the drilling fluid, thereby preventing the aggregation of clay particles and the aggregation of clay particles with solid particles such as barite, thus stabilizing the rheological properties of the drilling fluid. On the other hand, due to the complexation of trivalent iron ions with the polymer, the curvature of the polymer in the drilling fluid is significantly reduced under high temperature, contaminated conditions, and high salinity, greatly improving the polymer's anti-fouling ability. This stabilizes the filtration loss of the drilling fluid system.

[0185] (8) A comparison of Examples 1-5 and Comparative Example 6 shows that the filtration loss of the system itself is significantly reduced without the addition of divalent ions. However, after contamination, the viscosity and filtration loss increase rapidly, indicating that the divalent ion stabilizer plays an indispensable role in the system's anti-contamination ability. Analysis suggests that this is mainly because divalent ions react with CO2 after encountering CO2 contamination. The system lacking divalent ions not only has reduced inhibitory properties but also lacks substances that react with CO2.

[0186] (9) Comparison of Examples 1-5 and Comparative Example 7 shows that without the addition of divalent ion stabilizers, the rheological properties of the comparative example samples did not change significantly after high-temperature aging, but the filtration loss increased. Comparison of data after CO2 contamination shows that initially, the viscosity and filtration loss of the system did not increase significantly after CO2 contamination, but both increased significantly after further contamination. This indicates that the addition of divalent ion stabilizers plays a crucial role in the stability of the system itself. Especially in the data from uncontaminated slurry, it can be seen that divalent ion stabilizers can effectively reduce the destructive effect of divalent ions on the system. The system's performance deteriorated after contamination, indicating that although divalent ions can improve the system's inhibition and anti-contamination ability under normal conditions, their effect is ineffective under high-contamination conditions.

[0187] (10) A comparison of Examples 1-5 with Comparative Examples 8 and 9 shows that, compared with conventional polysulfonated drilling fluids, the potassium-lime sulfonated coarse dispersion drilling fluid system exhibits similar rheological properties after high-temperature aging. However, the rolling recovery rate of the examples is significantly higher than that of the comparative examples, and the filtration loss of the two comparative examples is lower than that of the examples. However, after the drilling fluid system is contaminated with CO2, the rheological properties and filtration loss of the examples are very stable. In contrast, in Comparative Example 6, the performance is significantly damaged after CO2 addition exceeds 8g, with a significant increase in viscosity and filtration loss. In Comparative Example 7, the performance begins to deteriorate after CO2 contamination, and the system performance is significantly damaged after CO2 addition reaches 8g, eventually exhibiting a tofu-like consistency. These phenomena indicate that the CO2-resistant high-density water-based drilling fluid system prepared by this invention has a significantly superior anti-contamination ability compared to conventional systems, with an anti-contamination ability at least 2-3 times that of conventional drilling fluid systems.

[0188] (11) The rolling recovery rates of Examples 1-5 and Comparative Examples 2, 4, 6, 8, and 9 show that the inhibition effects of the examples are all very high, significantly better than conventional potassium lime polysulfonate drilling fluid and polysulfonate drilling fluid. In actual field applications, the higher the inhibition effect, the better the wellbore stability.

[0189] Finally, the above experimental results demonstrate that the components in the high-density CO2-resistant water-based drilling fluid system formula prepared by this invention work synergistically with each other. The absence of a certain component or the replacement of that component with a commonly used component in this field will not achieve the CO2-resistant effect of the drilling fluid system prepared by the formula of this invention.

[0190] The above description is merely a preferred embodiment of the present invention and is not intended to hinder the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A high-density water-based drilling fluid resistant to CO2 pollution, characterized in that, Based on 100 parts by weight of water added, it also includes: Bentonite: 0.1~0.5 parts; Alkalinity adjuster: 0.2~0.4 parts; Amine inhibitor: 1.0~1.5 parts; Lubricating defoamer: 5.0~8.0 parts; Divalent ion stabilizer: 1.0~3.0 parts; Complexation stabilizer: 1.0~1.5 parts; Polymer filtration loss reducer: 1.0~2.0 parts; Coating agent: 0.5~1.0 parts; Protective agent: 1.0~3.0 parts; Blocking and filtration loss reducing agent: 3.0~6.0 parts; Inhibiting lubricant: 1.0~3.0 parts; Potassium chloride: 5.0~7.0 parts, Sodium chloride: 10.0~15.0 parts; Calcium chloride: 1.0~3.0 parts; Zinc chloride: 1.0~3.0 parts.

2. The high-density water-based drilling fluid resistant to CO2 pollution according to claim 1, characterized in that, The drilling fluid is composed of the following raw materials in parts by weight: Alkalinity adjuster: 0.3 parts; Amine inhibitor: 1.0 part; Lubricating defoamer: 7.0 parts; Divalent ion stabilizer: 2.0 parts; Complexation stabilizer: 1.2 parts; Polymer filtration loss reducer: 1.5 parts; Adhesive protectant: 2.0 parts; Blocking and filtration loss reducing agent: 4.0 parts; Lubricant inhibitor: 2.0 parts; Potassium chloride: 7.0 parts; Sodium chloride: 12.0 parts; Calcium chloride: 2.0 parts; Zinc chloride: 2.0 parts.

3. The high-density water-based drilling fluid resistant to CO2 pollution according to claim 1, characterized in that, Drilling fluid with a density of 1.5 g / cm³ contains 0.5 parts bentonite; drilling fluid with a density of 1.8 g / cm³ contains 0.8 parts bentonite; drilling fluid with a density of 2.0 g / cm³ contains 0.1 parts bentonite.

4. The high-density water-based drilling fluid resistant to CO2 pollution according to claim 1, characterized in that, The coating agent content of drilling fluid with a density of 1.5 g / cm³ is 1.0 part; the coating agent content of drilling fluid with a density of 1.8 g / cm³ is 0.8 parts; and the coating agent content of drilling fluid with a density of 2.0 g / cm³ is 0.5 parts.

5. A method for preparing a high-density water-based drilling fluid resistant to CO2 pollution, wherein the preparation method is used to produce the drilling fluid according to any one of claims 1-4, characterized in that, Includes the following steps: Step S1. Weigh the following ingredients according to the specified ratio: bentonite, alkalinity regulator, amine inhibitor, lubricant and defoaming agent, divalent ion stabilizer, complexing stabilizer, polymer filtration loss reducer, coating agent, protective agent, plugging and filtration loss reducer, inhibitory lubricant, potassium chloride, sodium chloride, calcium chloride, and zinc chloride. Step S2. Add 100 parts of clean water to the drilling fluid tank, then add bentonite to the drilling fluid tank and mix thoroughly. Step S3. Add alkalinity regulator, protective agent, coating agent, polymer filtration loss reducer, complexing stabilizer, blocking filtration loss reducer, lubricant inhibitor, and antifoaming agent to the solution in step S2 in sequence, and stir thoroughly to form a glue solution. Step S4. First, add the divalent ion stabilizer to the above adhesive solution, stir and mix evenly, then add sodium chloride, potassium chloride, calcium chloride and amine inhibitor in sequence, and then stir and mix evenly. Step S5. Add barite to the adhesive obtained in step S4 to adjust the density of the adhesive to the required density, and finally obtain a high-density water-based drilling fluid resistant to CO2 pollution.

6. The method for preparing a high-density water-based drilling fluid resistant to CO2 pollution according to claim 5, characterized in that, In step S2, the weighed bentonite is first fully hydrated for 24 hours to form a prehydrated bentonite slurry; then 100 parts of clean water are added to the drilling fluid tank, and the prehydrated bentonite slurry is added to the drilling fluid tank and stirred and mixed evenly.

7. The method for preparing a high-density water-based drilling fluid resistant to CO2 pollution according to claim 5, characterized in that, In step S3, after each ingredient is added, continue stirring for 10-30 minutes until the mixture is uniform before adding the next ingredient; after all ingredients have been added, continue stirring for 12 hours.

8. The method for preparing a high-density water-based drilling fluid resistant to CO2 pollution according to claim 5, characterized in that, In step S4, after each ingredient is added, stir continuously for 10-20 minutes until the mixture is uniform, and then add the next ingredient; finally, add the amino inhibitor and stir continuously for 10-30 minutes.

9. The method for preparing a high-density water-based drilling fluid resistant to CO2 pollution according to claim 5, characterized in that, In step S5, barite is added while stirring to adjust the adhesive solution to the required density, and stirring is continued for 6 hours until the mixture is uniform, ultimately forming a high-density water-based drilling fluid resistant to CO2 pollution.

10. The method for preparing a high-density water-based drilling fluid resistant to CO2 pollution according to claim 5, characterized in that, During the preparation of drilling fluid, the stirring and mixing rate is 100-500 rpm.

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