High-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells and its preparation method

Abstract

The invention discloses a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells and a preparation method thereof. The raw material components and weight contents are as follows: water: 1000 parts; sodium bentonite: 30-40 parts; cationic polymer coating agent: 2-4 parts; temperature-resistant and calcium-resistant polymer fluid loss reducer: 10-20 parts; clay surface hydration inhibitor: 3-5 parts; sulfonated phenolic resin: 20-30 parts; sulfonated lignite resin: 20-30 parts; low-fluorescence cationic asphalt powder: 30-50 parts; biolubricant: 20-40 parts; solid polyol: 15-25 parts; ultrafine calcium carbonate: 30-50 parts; micro-nano strong plugging agent: 5-15 parts; amphiphilic plugging agent: 10-15 parts; barite: 330-400 parts; and the pH value is adjusted to 9-10. The drilling fluid of the present invention can withstand high temperatures above 200°C, has strong salt and calcium resistance, and can resist calcium chloride pollution by 5%. It can reduce the comprehensive damage of filtrate to easily collapsed formations, improve the pressure bearing capacity of the formation, and meet the requirements of drilling construction.

Description

Technical Field

[0001] The present invention relates to a drilling fluid for ultra-deep well operations, in particular to a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells; the present invention also relates to a preparation method of the high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells, belonging to the technical field of drilling fluids. Background Art

[0002] In recent years, domestic oil and gas resource development efforts have continued to increase, with oil and gas exploration expanding from shallow to medium-deep layers and shifting from traditional conventional oil and gas extraction to unconventional oil and gas development. Deep well and unconventional oil and gas face complex formation conditions, including extreme factors such as high temperature, high pressure, high calcium content, and high salinity, placing even more stringent requirements on drilling fluid performance. Controlling the fluid loss performance of drilling fluids during deep well drilling is a key indicator for evaluating the quality of drilling fluid systems. Fluid loss reducers, as one of the core materials of drilling fluid treatment agents, combine with clay particles through adsorption and hydration to form a low-permeability and dense mud cake near the wellbore wall, effectively preventing the aqueous phase of the drilling fluid from entering the formation. The temperature and calcium resistance of fluid loss reducers are key to ensuring the stable performance of water-based drilling fluids in calcium-containing formations during high-temperature deep well drilling. Maintaining the temperature stability, good rheological properties, and reasonable high-temperature and high-pressure fluid loss rates of drilling fluids in ultra-deep well environments has always been a challenge in drilling fluid technology.

[0003] Currently, there are many types of temperature-resistant fluid loss control agents in China. Based on their composition, they can be divided into three categories: natural polymers, synthetic polymers, and organic / inorganic composites. Natural polymers have significant limitations in their heat resistance, which can be improved through modification. Synthetic polymer fluid loss control agents have become a research hotspot in recent years due to their advantages, including good molecular chain thermal stability, highly controllable molecular structure, a wide variety of functional monomers from a wide range of sources, and relatively simple synthesis processes. Inorganic / organic composites are materials prepared by blending and copolymerizing inorganic materials with polymers. The inorganic materials can act as fillers or interact with the polymer monomers to significantly improve the overall material performance. Composite fluid loss control agents mainly include silica / polymer and graphene / polymer. These fluid loss control agents have achieved significant fluid loss reduction effects in deep wells, especially ultra-deep wells exceeding 5,000 meters, and have been widely used. However, they still have limitations in calcium tolerance in ultra-deep wells. The main problem is that under the influence of high temperatures and high calcium concentrations, the fluid loss control agent molecules curl, significantly reducing their fluid loss reduction effectiveness and reducing their calcium tolerance. Therefore, the development of temperature-resistant and calcium-resistant water-based drilling fluids for ultra-deep well operations has become a hot topic to solve problems such as the failure of filtration agents under high temperature and high calcium conditions during ultra-deep well drilling.

[0004] Chinese invention patent publication number CN 102250595B discloses a drilling fluid for active shale drilling. Its components, by weight, are as follows: 2-6% bentonite, 0.2-0.5% coating inhibitor, 0.2-1.0% flow pattern modifier, 0.2-0.5% high-temperature polymer fluid loss reducer, 4-7% potassium chloride, 1-3% polyol, 0.5-1.0% polyamine inhibitor, 0.5-1.0% anti-balling and fast-drilling agent, and 45-85% water. This drilling fluid can prevent wellbore instability, drill cuttings dispersion, drill bit balling, and mudstone adhesion and agglomeration in active shale. However, it cannot be used in the high-temperature environments of ultra-deep wells exceeding 5,000 meters.

[0005] Based on the above reasons, a high-temperature and calcium-resistant water-based drilling fluid loss reducer with a hyperbranched structure has been developed, and a high-temperature and calcium-resistant water-based drilling fluid system suitable for ultra-deep wells has been formed with this treatment agent as the core. This is the key to solving a series of problems such as the failure of the loss reducer under high-temperature and high-calcium conditions during ultra-deep well drilling operations. Summary of the Invention

[0006] The primary purpose of the present invention is to overcome the problems existing in the prior art and provide a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells. Under the high-temperature and high-pressure environment of ultra-deep wells with temperatures exceeding 200°C and depths exceeding 5,000 meters, the drilling fluid has strong salt and calcium resistance and an anti-calcium chloride pollution resistance of 5%. This can reduce the comprehensive damage caused by filtrate to easily collapsed formations, improve the pressure bearing capacity of the formation, and meet the requirements of drilling construction.

[0007] To solve the above technical problems, the present invention provides a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells, whose raw material components and weight contents are as follows: water: 1000 parts; sodium bentonite: 30-40 parts; cationic polymer coating agent: 2-4 parts; temperature-resistant and calcium-resistant polymer fluid loss reducer: 10-20 parts; clay surface hydration inhibitor: 3-5 parts; sulfonated phenolic resin: 20-30 parts; sulfonated lignite resin: 20-30 parts; low-fluorescence cationic asphalt powder: 30-50 parts; biolubricant: 20-40 parts; solid polyol: 15-25 parts; ultrafine calcium carbonate: 30-50 parts; micro-nano strong plugging agent NANOFSEAL: 5-15 parts; amphiphilic plugging agent: 10-15 parts; barite: 330-400 parts; and the pH value is adjusted to 9-10 with NaOH.

[0008] Furthermore, the raw material components and weight contents are as follows: water: 1000 parts; sodium bentonite: 30 parts; cationic polymer coating agent: 2 parts; temperature-resistant and calcium-resistant polymer fluid loss reducer: 10 parts; clay surface hydration inhibitor: 3 parts; sulfonated phenolic resin: 20 parts; sulfonated lignite resin: 20 parts; low-fluorescence cationic asphalt powder: 30 parts; biolubricant: 20 parts; solid polyol: 15 parts; ultrafine calcium carbonate: 30 parts; micro-nano strong plugging agent NANOFSEAL: 5 parts; amphiphilic plugging agent: 10 parts; barite: 330 parts; and the pH value is adjusted to 9 with NaOH.

[0009] Furthermore, the raw material components and weight contents are as follows: water: 1000 parts; sodium bentonite: 35 parts; cationic polymer coating agent: 3 parts; temperature-resistant and calcium-resistant polymer fluid loss reducer: 15 parts; clay surface hydration inhibitor: 4 parts; sulfonated phenolic resin: 25 parts; sulfonated lignite resin: 25 parts; low-fluorescence cationic asphalt powder: 40 parts; biolubricant: 30 parts; solid polyol: 20 parts; ultrafine calcium carbonate: 40 parts; micro-nano strong plugging agent NANOFSEAL: 10 parts; amphiphilic plugging agent: 12 parts; barite: 360 parts; and the pH value is adjusted to 9.5 with NaOH.

[0010] Furthermore, the raw material components and weight contents are as follows: water: 1000 parts; sodium bentonite: 40 parts; cationic polymer coating agent: 4 parts; temperature-resistant and calcium-resistant polymer fluid loss reducer: 20 parts; clay surface hydration inhibitor: 5 parts; sulfonated phenolic resin: 30 parts; sulfonated lignite resin: 30 parts; low-fluorescence cationic asphalt powder: 50 parts; biolubricant: 40 parts; solid polyol: 25 parts; ultrafine calcium carbonate: 50 parts; micro-nano strong plugging agent NANOFSEAL: 15 parts; amphiphilic plugging agent: 15 parts; barite: 400 parts; and the pH value is adjusted to 10 with NaOH.

[0011] Another object of the present invention is to overcome the problems existing in the prior art and provide a method for preparing a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells. The prepared drilling fluid has strong salt and calcium resistance and an anti-calcium pollution capacity of 5% under the high-temperature and high-pressure environment of ultra-deep wells with temperatures exceeding 200°C and depths exceeding 5,000 meters. This can reduce the comprehensive damage caused by filtrate to easily collapsed formations, improve the pressure bearing capacity of the formation, and meet the requirements of drilling construction.

[0012] In order to solve the above technical problems, the present invention provides a method for preparing a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells, which comprises the following steps in sequence:

[0013] A1. First, 1000 parts of water and 30-40 parts of sodium bentonite were mixed, stirred at a stirring speed of 2000-4000 rpm for 30-60 minutes, then stirred at a stirring speed of 6000-10000 rpm for 30-40 minutes, and cured at room temperature for 24 hours to form a mixture 1;

[0014] A2. Slowly and evenly add 2 to 4 parts of cationic polymer coating agent to mixture 1 at a stirring speed of 6000 to 10000 rpm, stir evenly, then add 10 to 20 parts of temperature-resistant and calcium-resistant polymer fluid loss reducer and 3 to 5 parts of clay surface hydration inhibitor, and evenly add 20 to 30 parts of sulfonated phenolic resin and 20 to 30 parts of sulfonated lignite resin while stirring; then evenly add 30 to 50 parts of low-fluorescence cationic asphalt powder while stirring, stir evenly, add 20 to 40 parts of biolubricant, stir evenly, add 15 to 25 parts of solid polyol, stir evenly, add 5 to 15 parts of micro-nano strong plugging agent NANOFSEAL, stir evenly, add 10 to 20 parts of amphiphilic plugging agent and 30 to 50 parts of ultrafine calcium carbonate, and form mixture 2;

[0015] A3, adjusting the pH value of the mixture 2 to 9-10 with NaOH to form a mixture 3;

[0016] A4. Add 330-400 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry.

[0017] Furthermore, a method for preparing a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells comprises the following steps in sequence:

[0018] A1. First, 1000 parts of water and 30 parts of sodium bentonite were mixed, stirred at a stirring speed of 2000 rpm for 30 minutes, then stirred at a stirring speed of 6000 rpm for 30 minutes, and cured at room temperature for 24 hours to form a mixture 1;

[0019] A2. At a stirring speed of 6000 rpm, 2 parts of cationic polymer coating agent were slowly and evenly added to mixture 1. After stirring, 10 parts of temperature-resistant and calcium-resistant polymer fluid loss reducer and 3 parts of clay surface hydration inhibitor were added. 20 parts of sulfonated phenolic resin and 20 parts of sulfonated lignite resin were evenly added while stirring. Then, 30 parts of low-fluorescence cationic asphalt powder were evenly added while stirring. After stirring, 20 parts of biolubricant were added. After stirring, 15 parts of solid polyol were added. After stirring, 5 parts of micro-nano strong plugging agent NANOFSEAL were added. After stirring, 10 parts of amphiphilic plugging agent and 30 parts of ultrafine calcium carbonate were added to form mixture 2.

[0020] A3, adjusting the pH value of mixture 2 to 9 with NaOH to form mixture 3;

[0021] A4. Add 330 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry.

[0022] Furthermore, a method for preparing a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells comprises the following steps in sequence:

[0023] A1. First, 1000 parts of water and 35 parts of sodium bentonite were mixed, stirred at a stirring speed of 3000 rpm for 45 minutes, then stirred at a stirring speed of 8000 rpm for 35 minutes, and cured at room temperature for 24 hours to form a mixture 1;

[0024] A2. At a stirring speed of 8000 rpm, 3 parts of cationic polymer coating agent were slowly and evenly added to mixture 1. After stirring, 15 parts of temperature-resistant and calcium-resistant polymer fluid loss reducer and 4 parts of clay surface hydration inhibitor were added. 25 parts of sulfonated phenolic resin and 25 parts of sulfonated lignite resin were evenly added while stirring. Then, 40 parts of low-fluorescence cationic asphalt powder were evenly added while stirring. After stirring, 30 parts of biolubricant were added. After stirring, 20 parts of solid polyol were added. After stirring, 10 parts of micro-nano strong plugging agent NANOFSEAL were added. After stirring, 12 parts of amphiphilic plugging agent and 40 parts of ultrafine calcium carbonate were added to form mixture 2.

[0025] A3, adjusting the pH value of mixture 2 to 9.5 with NaOH to form mixture 3;

[0026] A4. Add 360 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry.

[0027] Furthermore, a method for preparing a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells comprises the following steps in sequence:

[0028] A1. First, 1000 parts of water and 40 parts of sodium bentonite were mixed, stirred at a stirring speed of 4000 rpm for 60 minutes, then stirred at a stirring speed of 10000 rpm for 40 minutes, and cured at room temperature for 24 hours to form a mixture 1;

[0029] A2. At a stirring speed of 10,000 rpm, 4 parts of a cationic polymer coating agent were slowly and evenly added to the mixture 1. After stirring, 20 parts of a temperature-resistant and calcium-resistant polymer fluid loss reducer and 5 parts of a clay surface hydration inhibitor were added. 30 parts of a sulfonated phenolic resin and 30 parts of a sulfonated lignite resin were evenly added while stirring. 50 parts of a low-fluorescence cationic asphalt powder were then evenly added while stirring. 40 parts of a biolubricant were added after stirring. 25 parts of a solid polyol were added after stirring. 15 parts of a micro-nano strong plugging agent NANOFSEAL were added after stirring. 20 parts of an amphiphilic plugging agent and 50 parts of ultrafine calcium carbonate were added after stirring to form a mixture 2.

[0030] A3, adjusting the pH value of mixture 2 to 10 with NaOH to form mixture 3;

[0031] A4. Add 400 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry.

[0032] Furthermore, the structural formula of the temperature-resistant and calcium-resistant polymer fluid loss reducer is shown below:

[0033]

[0034] Furthermore, the preparation of the temperature-resistant and calcium-resistant polymer fluid loss reducer comprises the following steps in sequence:

[0035] S1. Add 10 parts by weight of deionized water to the reactor, add 3-8 parts by weight of triallyl phosphate while stirring, adjust the pH value of the system to 10-12 with sodium hydroxide solution, and maintain the temperature at 30±3°C;

[0036] S2, filling the reactor with nitrogen for 30 minutes to remove oxygen from the reactor, and then continuing to fill the reactor with nitrogen during the reaction process;

[0037] S3, dissolving dibenzoyl peroxide in 5 times the mass of water to form a solution as a primary polymerization initiator;

[0038] S4, adding 0.1-0.3 parts by weight of a primary polymerization initiator into the reactor, maintaining the system temperature at 30±3°C, and conducting a primary polymerization reaction for 0.5 hours;

[0039] S5. Sodium persulfite and ammonium persulfate are mixed in a mass ratio of 1:1 and then dissolved in 5 times the mass of water as a secondary polymerization initiator;

[0040] S6, adding 0.5-1 parts by weight of a secondary polymerization initiator to the reactor, and then adding 5-15 parts by weight of dimethyldiallylammonium chloride, and continuing the reaction for 0.5 hours to carry out a secondary polymerization reaction;

[0041] S7, dissolving 10-20 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 20-30 parts by weight of acrylamide, 15-35 parts by weight of styrene and 5-15 parts by weight of sodium methacryloylsulfonate powder monomer in water equal to the total mass of the powder, and stirring uniformly;

[0042] S8, adding the solution obtained in step S7 to the reactor, controlling the reaction temperature in the reactor at 30±3°C, and performing three polymerization reactions for 2 hours;

[0043] S9, adding 1 part by weight of chain transfer agent trichloroethylene to the reactor and continuing the reaction for 4 hours;

[0044] S10, stop supplying nitrogen to the reactor, blow air into the reactor, add 1 part by weight of ferric chloride as a polymerization inhibitor to the reactor, react for 0.5 hours, and perform product end-capping;

[0045] S11. Dry the product in the reactor at 100° C. and crush it to obtain a powder of a temperature-resistant and calcium-resistant polymer fluid loss reducer.

[0046] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. The present invention uses barite as a weighting agent to make the mixture reach the density required by the design, and finally form a suspension-type drilling fluid. The advantages of the ultra-deep well salt-resistant, calcium-resistant and high-temperature-resistant drilling fluid formed are reflected in the following points: (1) When constructing in complex formations in deep well environments, the combination of high-temperature inhibitor cationic polymer coating agent and clay surface hydration inhibitor can greatly improve the overall inhibition of the drilling fluid, effectively prevent the hydration and dispersion of shale, and synergistically improve the stability of the well wall; (2) The temperature-resistant and calcium-resistant polymer filtration reducer can significantly reduce the high-temperature and high-pressure filtration loss of the drilling fluid. After addition, the drilling fluid does not increase viscosity, and has little effect on the rheological properties of the drilling fluid. After a long period of high temperature, the high-temperature and high-pressure filtration loss remains relatively stable and within a low range. The drilling fluid filter cake formed is thin and dense, thereby reducing the effect of the filtrate on the easy The comprehensive damage of collapsed formations, the temperature-resistant and calcium-resistant polymer filtration reducer used can not only improve the filtration reduction performance, but also has a good salt and calcium resistance, which can significantly improve the anti-pollution ability of the drilling fluid system; (3) The combined effect of the micro-nano strong plugging agent NANOFSEAL, the amphiphilic plugging agent and the low-fluorescence cationic asphalt powder makes the formed drilling fluid filter cake thin, tough and dense, and the drilling fluid has a stronger wall protection effect. It can not only effectively block the micro cracks in the easily collapsed mud shale formation, but also improve the formation pressure bearing capacity and delay the occurrence of complex downhole failures caused by the instability of the well wall caused by the filtrate entering the formation; (4) The addition of biolubricant greatly improves the lubricity of the drilling fluid and meets the needs of lubrication and anti-sticking. The comprehensive synergistic effect of the above points can greatly reduce the high-temperature and high-pressure filtration loss in deep well environments, and the various performance indicators of the drilling fluid are stable, which can improve the well wall stability of the ultra-deep well mud shale formation that is prone to collapse, and provide a good technical guarantee for the safe and efficient construction of ultra-deep wells. Therefore, compared with existing traditional deep well drilling fluids, the drilling fluid of the present invention has stable rheological properties under high temperature conditions, strong inhibitory properties, good water loss and wall building properties, stable high-temperature and high-pressure filtration loss control, strong and reliable sealing ability, strong resistance to salt invasion and calcium invasion, and more stable drilling fluid system performance.

[0047] 2. The uniqueness of the temperature-resistant and calcium-resistant fluid loss reducer prepared by the present invention is that triallyl phosphate is polymerized under the action of dibenzoyl peroxide to form a core, and is reacted with dimethyldiallyl ammonium chloride as a secondary polymerization reaction under the conditions of initiator sodium sulfite and ammonium persulfate. Finally, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, and methyl propylene sulfonic acid of styrene are added in sequence to carry out three polymerization reactions. Monoolefin derivatives are end-capped and a certain molecular chain is appropriately extended to obtain a hyperbranched structure. The carbon-carbon bond used in the core of this structure is branched, which is more stable than using carbon-oxygen bond, carbon-nitrogen bond, etc., so that the molecular core has good temperature resistance, so that the final product has good temperature resistance; because it has a hyperbranched structure, the outside contains a large amount of hydrophilic groups, so it has good solubility, is not easy to agglomerate, is more convenient to use, and can also play a significant effect at low temperatures.

[0048] 3. Compared with other types of high-temperature resistant drilling fluids currently available, the drilling fluid of the present invention has the following advantages: 1) The core treatment agent used in the drilling fluid system is a temperature-resistant and calcium-resistant filtration reducer, which can improve the drilling fluid system's resistance to calcium and salt pollution, and the temperature resistance of a single agent reaches 230°C; 2) The preparation method adopts a three-step polymerization method, which has mild and controllable reaction conditions and a fast reaction speed, and is suitable for industrial application and promotion.

[0049] 4. The temperature-resistant and calcium-resistant fluid loss reducer of the present invention is resistant to high temperature, salt, and calcium and does not increase viscosity. The synthesized product contains carboxyl, sulfonic acid, amide, amino, and ester groups, so that it can be well adsorbed on the surface of clay. The cyclic structure can enhance the rigidity of the molecule and enhance the high temperature resistance of the product. Due to its hyperbranched structure and the presence of carboxyl, sulfonic acid, amide, cyclic, and amino groups, the product has very good salt and calcium resistance, so that it can still have good fluid loss reduction performance in a high-salt and high-calcium environment.

[0050] 5. The use of inorganic micro-nano plugging agents and amphiphilic plugging agents in the prepared drilling fluid system can improve the drilling fluid's ability to plug micro-cracks in the formation under pressure. Among the two plugging materials, the inorganic micro-nano is a rigid plugging agent, and the amphiphilic is a fiber-flexible plugging agent. The combination of the two can synergistically improve the plugging efficiency; the composite calcium carbonate particles selected as bridging particles can significantly improve the quality of the filter cake, and the material is widely available and inexpensive. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The accompanying drawings are only provided for reference and illustration and are not intended to limit the present invention.

[0052] Figure 1 is the equation for a primary polymerization reaction in the preparation process of the fluid loss reducer of the present invention;

[0053] Figure 2 is the equation for the secondary polymerization reaction in the preparation process of the fluid loss reducer of the present invention;

[0054] Figure 3 is the equation for the tertiary polymerization reaction in the preparation process of the fluid loss reducer of the present invention;

[0055] Figure 4 is the reaction equation of the terminal free radical of the tertiary polymerization product and the chain transfer agent in the present invention;

[0056] Figure 5 is the reaction equation between the end group of the product and the polymerization inhibitor in the present invention;

[0057] Figure 6 is the structural formula of the temperature-resistant and calcium-resistant polymer fluid loss reducer of the present invention;

[0058] Figure 7 This is a graph showing the experimental data of the plugging and pressure bearing performance of the drilling fluid of the present invention. DETAILED DESCRIPTION

[0059] In the following description of the present invention, the term "parts" refers to "parts by weight" unless otherwise specified. In the process of preparing the temperature-resistant and calcium-resistant polymer fluid loss reducer, "deionized water" is used unless otherwise specified. Tap water can be used in the preparation of the drilling fluid.

[0060] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to specific illustrations.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0062] Example 1

[0063] The preparation of the temperature-resistant and calcium-resistant polymer fluid loss reducer of the present invention comprises the following steps in sequence:

[0064] S1. Add 10 parts by weight of deionized water to the reactor, add 3 parts by weight of triallyl phosphate while stirring, adjust the pH value of the system to 10 with sodium hydroxide solution, and maintain the temperature at 27°C;

[0065] S2, filling the reactor with nitrogen for 30 minutes to remove oxygen from the reactor, and then continuing to fill the reactor with nitrogen during the reaction process;

[0066] S3, dissolving dibenzoyl peroxide in 5 times the mass of water to form a solution as a primary polymerization initiator or catalyst;

[0067] S4, add 0.1 parts by weight of a primary polymerization initiator into the reactor, and maintain the system temperature at 27°C, and carry out a polymerization reaction for 0.5 hours. The process is as follows: Figure 1 As shown;

[0068] S5. Sodium persulfite and ammonium persulfate are mixed in a mass ratio of 1:1 and then dissolved in 5 times the mass of water as a secondary polymerization initiator;

[0069] S6, add 0.5 parts by weight of secondary polymerization initiator to the reactor, add 5 parts by weight of dimethyldiallyl ammonium chloride, and continue the reaction for 0.5 hours to carry out secondary polymerization reaction. The process is as follows: Figure 2 As shown;

[0070] S7, 10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 20 parts by weight of acrylamide, 15 parts by weight of styrene and 5 parts by weight of sodium methacrylic acid sulfonate powder monomer are dissolved in water equal to the total mass of the powder and stirred evenly;

[0071] S8, the solution obtained in step S7 is added to the reactor, the reaction temperature in the reactor is controlled at 27 ° C, and the polymerization reaction is carried out three times for 2 hours. The process is as follows Figure 3 As shown;

[0072] S9, add 1 part by weight of chain transfer agent trichloroethylene into the reactor and continue the reaction for 4 hours to control the molecular weight of the reaction. The reaction formula of the terminal free radical of the tertiary polymerization product and the chain transfer agent is as follows: Figure 4 shown.

[0073] S10, stop supplying nitrogen to the reactor, blow air into the reactor, and add 1 part by weight of ferric chloride as polymerization inhibitor to the reactor, react for 0.5 hours, and perform product end-capping. The reaction formula of the product end group and the polymerization inhibitor is as follows: Figure 5 shown.

[0074] S11, drying the product in the reactor at 100°C, and crushing it to obtain a powder of a temperature-resistant and calcium-resistant polymer fluid loss reducer. The final product structure is as follows: Figure 6 shown.

[0075] Example 2

[0076] The preparation of the temperature-resistant and calcium-resistant polymer fluid loss reducer of the present invention comprises the following steps in sequence:

[0077] S1. Add 10 parts by weight of deionized water to the reactor, add 6 parts by weight of triallyl phosphate while stirring, adjust the pH value of the system to 11 with sodium hydroxide solution, and maintain the temperature at 30°C;

[0078] S2, filling the reactor with nitrogen for 30 minutes to remove oxygen from the reactor, and then continuing to fill the reactor with nitrogen during the reaction process;

[0079] S3, dissolving dibenzoyl peroxide in 5 times the mass of water to form a solution as a primary polymerization initiator;

[0080] S4, adding 0.2 parts by weight of a primary polymerization initiator into the reactor, maintaining the system temperature at 30° C., and conducting a primary polymerization reaction for 0.5 hours;

[0081] S5. Sodium persulfite and ammonium persulfate are mixed in a mass ratio of 1:1 and then dissolved in 5 times the mass of water as a secondary polymerization initiator;

[0082] S6, adding 0.8 parts by weight of a secondary polymerization initiator to the reactor, and then adding 10 parts by weight of dimethyldiallylammonium chloride, and continuing the reaction for 0.5 hours to carry out a secondary polymerization reaction;

[0083] S7, 15 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 25 parts by weight of acrylamide, 25 parts by weight of styrene and 10 parts by weight of sodium methacrylic acid sulfonate powder monomer are dissolved in water equal to the total mass of the powder and stirred evenly;

[0084] S8, adding the solution obtained in step S7 to the reactor, controlling the reaction temperature in the reactor at 30° C., and performing three polymerization reactions for 2 hours;

[0085] S9. Add 1 part by weight of trichloroethylene, a chain transfer agent, to the reactor and continue the reaction for 4 hours to control the molecular weight of the reaction. The terminal free radicals of the tertiary polymerization product react with the chain transfer agent.

[0086] S10, stop supplying nitrogen to the reactor, blow air into the reactor, and add 1 part by weight of ferric chloride as a polymerization inhibitor into the reactor, react for 0.5 hours, cap the product, and react the product end groups with the polymerization inhibitor.

[0087] S11. Dry the product in the reactor at 100° C. and crush it to obtain a powder of a temperature-resistant and calcium-resistant polymer fluid loss reducer.

[0088] Example 3

[0089] The preparation of the temperature-resistant and calcium-resistant polymer fluid loss reducer of the present invention comprises the following steps in sequence:

[0090] S1. Add 10 parts by weight of deionized water to the reactor, add 8 parts by weight of triallyl phosphate while stirring, adjust the pH value of the system to 12 with sodium hydroxide solution, and maintain the temperature at 33°C;

[0091] S2, filling the reactor with nitrogen for 30 minutes to remove oxygen from the reactor, and then continuing to fill the reactor with nitrogen during the reaction process;

[0092] S3, dissolving dibenzoyl peroxide in 5 times the mass of water to form a solution as a primary polymerization initiator;

[0093] S4, adding 0.3 parts by weight of a primary polymerization initiator into the reactor, maintaining the system temperature at 33° C., and conducting a primary polymerization reaction for 0.5 hours;

[0094] S5. Sodium persulfite and ammonium persulfate are mixed in a mass ratio of 1:1 and then dissolved in 5 times the mass of water as a secondary polymerization initiator;

[0095] S6, adding 1 part by weight of a secondary polymerization initiator to the reactor, and then adding 15 parts by weight of dimethyldiallylammonium chloride, and continuing the reaction for 0.5 hours to carry out a secondary polymerization reaction;

[0096] S7, 20 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 30 parts by weight of acrylamide, 35 parts by weight of styrene and 15 parts by weight of sodium methacrylic acid sulfonate powder monomer are dissolved in water equal to the total mass of the powder and stirred evenly;

[0097] S8, adding the solution obtained in step S7 to the reactor, controlling the reaction temperature in the reactor at 33° C., and performing three polymerization reactions for 2 hours;

[0098] S9. Add 1 part by weight of trichloroethylene, a chain transfer agent, to the reactor and continue the reaction for 4 hours to control the molecular weight of the reaction. The terminal free radicals of the tertiary polymerization product react with the chain transfer agent.

[0099] S10, stop supplying nitrogen to the reactor, blow air into the reactor, and add 1 part by weight of ferric chloride as a polymerization inhibitor into the reactor, react for 0.5 hours, cap the product, and react the product end groups with the polymerization inhibitor.

[0100] S11. Dry the product in the reactor at 100° C. and crush it to obtain a powder of a temperature-resistant and calcium-resistant polymer fluid loss reducer.

[0101] The performance of the high temperature and calcium resistant polymer fluid loss reducer of the present invention was compared and evaluated:

[0102] 1. Freshwater slurry performance evaluation

[0103] Freshwater base slurry: Take 350mL of distilled water, add 14.0g of sodium bentonite and 0.2g of anhydrous sodium carbonate, stir at high speed for 20min, and seal and cure at 25±1℃ for 24h to obtain freshwater base slurry.

[0104] Add 3.5g of the sample to the freshwater-based slurry and stir at high speed for 20 minutes. Place the slurry in an aging tank and tumble at a constant temperature (140°C, 180°C, 220°C) for 16 hours. Remove from the aging tank, cool to room temperature, and stir at high speed for 5 minutes. Then, test the fluid loss and apparent viscosity at the corresponding temperature at 25±1°C according to the requirements of GB / T 16783.1-2014.

[0105] Traditional commonly used modified PAC, ternary polymer fluid loss additive and lignite resin were used as comparative examples. The modified PAC used was a product of Chongqing Lihong Fine Chemical Co., Ltd., and the ternary polymer fluid loss additive and lignite resin were products of Chengdu Dedao Petroleum Technology Co., Ltd.

[0106] The comparison of the filtration loss of each sample in fresh water slurry is shown in Table 1:

[0107] Table 1

[0108]

[0109] The apparent viscosity comparison of each sample in fresh water slurry is shown in Table 2:

[0110] Table 2

[0111]

[0112]

[0113] As can be seen from Tables 1 and 2, in freshwater-based slurries, at the same dosage, the temperature-resistant and calcium-resistant polymer fluid loss additive used in the present invention outperformed the modified PAC, ternary polymer fluid loss additive, and lignite resin at 140°C, 180°C, and 220°C. At 220°C, the high-temperature, high-pressure water loss was only 15.6-18.6 ml, demonstrating excellent temperature resistance. Both the modified PAC and lignite resin had low viscosities at 220°C, but had little fluid loss reduction effect. However, the temperature-resistant and calcium-resistant polymer fluid loss additive used in the present invention exhibited low viscosity at both low and high temperatures, with minimal change, indicating a minimal impact on slurry properties.

[0114] 2. Performance evaluation of 5% calcium slurry

[0115] Take 350 mL of distilled water, add 14 g of standard evaluation soil, 14 g of sodium bentonite and 0.2 g of anhydrous sodium carbonate in sequence, stir at high speed for 20 min, and cure at 25±1°C for 24 h to obtain base slurry.

[0116] Take the base slurry, add 7g of sample under stirring conditions, add 5% calcium chloride, stir at high speed for 20 minutes, transfer to an aging tank and roll at a constant temperature (140℃, 180℃, 220℃) for 16 hours, take out the aging tank, cool to room temperature, stir at high speed for 5 minutes, and measure the high-temperature and high-pressure filtration loss and apparent viscosity at the corresponding temperature at 25±1℃ according to the provisions of GB / T16783.1-2014.

[0117] Still taking the traditional commonly used modified PAC, ternary polymer fluid loss additive and lignite resin as comparative examples, the comparison of fluid loss of each sample in 5% calcium slurry is shown in Table 3:

[0118] Table 3

[0119]

[0120] The apparent viscosity comparison of each sample in 5% calcium slurry is shown in Table 4:

[0121] Table 4

[0122]

[0123]

[0124] As can be seen from the test results in Tables 3 and 4, the modified PAC and lignite resin have poor calcium salt resistance at both low and high temperatures, and both exhibit total fluid loss at high temperatures. The ternary polymer fluid loss reducer has certain calcium resistance at low temperatures, but at high temperatures, its water loss reaches 128 ml, and its fluid loss reduction effect is greatly weakened. Its high temperature and calcium resistance is poor, and its viscosity is relatively high, which has a significant impact on the viscosity of the drilling fluid. The temperature-resistant and calcium-resistant polymer fluid loss reducer used in the present invention, when aged at 220°C and with a calcium content of 5%, has a high-temperature and high-pressure fluid loss of only 24.4-26.4 mL, showing good calcium salt resistance. Furthermore, its drilling fluid viscosity is relatively low, and the viscosity does not change much with temperature, indicating that the treatment agent has little effect on the viscosity of the drilling fluid.

[0125] As can be seen from Tables 1, 2, 3, and 4, the temperature-resistant and calcium-resistant polymer fluid loss reducer used in the present invention not only has a good fluid loss reduction effect in fresh water slurry, but also has a good fluid loss reduction effect when the calcium chloride content reaches 5% and the temperature is 220°C, showing good temperature and calcium resistance. In the process of preparing drilling fluid, it dissolves quickly and does not easily agglomerate, making it more convenient to use. It has little effect on the viscosity of the drilling fluid, and the viscosity does not change much when the temperature changes, so it can be better applied in the field.

[0126] Example 4

[0127] The method for preparing high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells of the present invention comprises the following steps in sequence:

[0128] A1. First, 1000 parts of water and 30 parts of sodium bentonite were mixed, stirred at a stirring speed of 2000 rpm for 30 minutes, then stirred at a stirring speed of 6000 rpm for 30 minutes, and cured at room temperature for 24 hours to form a mixture 1;

[0129] A2. At a stirring speed of 6000 rpm, 2 parts of cationic polymer coating agents were slowly and evenly added to mixture 1. After stirring, 10 parts of the temperature-resistant and calcium-resistant polymer fluid loss reducer prepared in Example 1 and 3 parts of clay surface hydration inhibitor were added. 20 parts of sulfonated phenolic resin and 20 parts of sulfonated lignite resin were evenly added while stirring. 30 parts of low-fluorescence cationic asphalt powder were then evenly added while stirring. 20 parts of biolubricant were added after stirring. 15 parts of solid polyol were added after stirring. 5 parts of micro-nano strong plugging agent NANOFSEAL were added after stirring. 10 parts of amphiphilic plugging agent and 30 parts of ultrafine calcium carbonate were added after stirring to form mixture 2.

[0130] A3, adjusting the pH value of mixture 2 to 9 with NaOH to form mixture 3;

[0131] A4. Add 330 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry.

[0132] Example 5

[0133] The method for preparing high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells of the present invention comprises the following steps in sequence:

[0134] A1. First, 1000 parts of water and 35 parts of sodium bentonite were mixed, stirred at a stirring speed of 3000 rpm for 45 minutes, then stirred at a stirring speed of 8000 rpm for 35 minutes, and cured at room temperature for 24 hours to form a mixture 1;

[0135] A2. At a stirring speed of 8000 rpm, 3 parts of cationic polymer coating agents were slowly and evenly added to mixture 1. After stirring, 15 parts of the temperature-resistant and calcium-resistant polymer fluid loss reducer prepared in Example 2 and 4 parts of clay surface hydration inhibitor were added. 25 parts of sulfonated phenolic resin and 25 parts of sulfonated lignite resin were evenly added while stirring. 40 parts of low-fluorescence cationic asphalt powder were then evenly added while stirring. 30 parts of biolubricant were added after stirring. 20 parts of solid polyol were added after stirring. 10 parts of micro-nano strong plugging agent NANOFSEAL were added after stirring. 12 parts of amphiphilic plugging agent and 40 parts of ultrafine calcium carbonate were added after stirring to form mixture 2.

[0136] A3, adjusting the pH value of mixture 2 to 9.5 with NaOH to form mixture 3;

[0137] A4. Add 360 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry.

[0138] Example 6

[0139] The method for preparing high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells of the present invention comprises the following steps in sequence:

[0140] A1. First, 1000 parts of water and 40 parts of sodium bentonite were mixed, stirred at a stirring speed of 4000 rpm for 60 minutes, then stirred at a stirring speed of 10000 rpm for 40 minutes, and cured at room temperature for 24 hours to form a mixture 1;

[0141] A2. At a stirring speed of 10000 rpm, 4 parts of cationic polymer coating agents were slowly and evenly added to mixture 1. After stirring, 20 parts of the temperature-resistant and calcium-resistant polymer fluid loss reducer prepared in Example 3 and 5 parts of clay surface hydration inhibitor were added. 30 parts of sulfonated phenolic resin and 30 parts of sulfonated lignite resin were evenly added while stirring. Then, 50 parts of low-fluorescence cationic asphalt powder were evenly added while stirring. After stirring, 40 parts of biolubricant were added. After stirring, 25 parts of solid polyol were added. After stirring, 15 parts of micro-nano strong plugging agent NANOFSEAL were added. After stirring, 20 parts of amphiphilic plugging agent and 50 parts of ultrafine calcium carbonate were added to form mixture 2.

[0142] A3, adjusting the pH value of mixture 2 to 10 with NaOH to form mixture 3;

[0143] A4. Add 400 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry.

[0144] 3. Drilling fluid filtration performance test

[0145] The comparative example does not contain the temperature-resistant and calcium-resistant polymer fluid loss reducer, and the rest is the same as the water-based drilling fluid base slurry in Example 5. The comparative example is used in all tests unless otherwise specified.

[0146] The drilling fluid base slurries of the comparative slurry example and Examples 4 to 6 were poured into an aging tank, heated at 200°C for 16 hours, cooled, and stirred at high speed for 20 minutes. The rheological properties were measured using a six-speed rotary viscometer, and the medium-pressure fluid loss and high-temperature and high-pressure fluid loss were measured. The test results are shown in Table 5:

[0147] Table 5

[0148]

[0149] As shown in Table 5, the room-temperature medium-pressure fluid loss of the base slurry comparison example was 3.8 mL, while that of Examples 4 to 6 was 3.2 mL, 2.4 mL, and 2.4 mL, respectively. Examples 4 to 6 demonstrated significant fluid loss reduction at room temperature. After hot rolling, the medium-pressure fluid loss of the base slurry comparison example was 4.4 mL, while that of Examples 4 to 6 was 3.6 mL, 3.0 mL, and 3.0 mL, respectively. The high-temperature, high-pressure fluid loss of the base slurry comparison example after aging was 18.6 mL, while that of Examples 4 to 6 was 12.4 mL, 9.6 mL, and 9.4 mL, respectively. The high-temperature, high-pressure fluid loss reduction effect was significant. The water loss at high temperature and high pressure in Examples 5 and 6 was less than 10 mL.

[0150] The drilling fluids of Examples 4 to 6 were hot-rolled for 16 hours at different temperatures, and then subjected to medium-pressure fluid loss tests and high-temperature and high-pressure fluid loss tests under a pressure difference of 3.5 MPa to evaluate the high-temperature stability of the prepared drilling fluid systems. The results are shown in Table 6:

[0151] Table 6

[0152]

[0153] As shown in Table 6, after the temperature-resistant and calcium-resistant drilling fluids in Examples 4 to 6 were heated at different temperatures, the high-temperature and high-pressure fluid loss of the systems increased slightly with increasing temperature. However, the high-temperature and high-pressure fluid loss was controlled within a relatively low range. The difference between Examples 5 and 6 was not significant, both being less than 10 mL. This indicates that Example 5 met the requirements for high-temperature and high-pressure fluid loss control.

[0154] 4. Rheological properties test

[0155] The rheological properties of the base slurry without the addition of the temperature-resistant and calcium-resistant fluid loss reducer and the high-temperature calcium-resistant drilling fluid in the embodiment were tested before and after hot rolling. The test results are shown in Table 7:

[0156] Table 7

[0157]

[0158] As can be seen from Table 7, the viscosity and rheological properties of the drilling fluid before and after aging do not change much. The drilling fluid system has good temperature stability. There is no barite sedimentation before and after aging, indicating that the suspension performance is good, indicating that the rheological properties of this system are good.

[0159] 5. Inhibition performance test

[0160] The inhibitory properties of the present drilling fluids were evaluated by comparing the base slurry comparison sample with the high-temperature calcium-resistant drilling fluids described in the examples using expansion rate tests and rock chip recovery rate tests. Bentonite was used as the core powder for the expansion rate test. The recovery rate test used core powder from the Funing Formation in Jiangsu Province, which has a high mudstone content (large rock blocks crushed and passed through a 40-mesh sieve), with a particle size of 30 to 40 mesh. The test results are shown in Table 8.

[0161] Table 8

[0162] Experimental group Linear expansion rate / % Drill cuttings recovery rate / % clear water 89.51 49.6 base slurry 3.47 94.5 Drilling fluid of Example 4 2.30 95.6 Drilling fluid of Example 5 2.16 96.1 Drilling fluid of Example 6 2.16 96.4

[0163] The expansion of cores in hot-rolled base slurry was tested and compared with that in clean water. The cores exhibited a higher expansion in clean water, with an 8-hour expansion rate of 89.51%. However, the addition of a heat-resistant and calcium-resistant fluid loss reducer significantly improved the 8-hour expansion rate and 16-hour cuttings recovery rate. This demonstrates that the heat-resistant and calcium-resistant drilling fluid significantly enhances its dispersion suppression.

[0164] 6. Sodium and calcium resistance test

[0165] NaCl in different mass fractions was quantitatively weighed and added to the temperature-resistant and calcium-resistant freshwater drilling fluid system of Example 5, and the mixture was fully stirred and then cured in a sealed container for 24 hours.

[0166] The temperature-resistant and calcium-resistant freshwater drilling fluid system and the temperature-resistant and calcium-resistant brine drilling fluid system were stirred at high speed for 5 minutes, then placed in a high-temperature aging tank and heated at 200°C for 16 hours. The filtration loss of the drilling fluid was measured using a normal temperature medium pressure filter loss meter and a high temperature and high pressure filter loss meter. The results are shown in Table 9:

[0167] Table 9

[0168]

[0169] Analyzing the data in Table 9, different proportions of salt were added to the temperature-resistant and calcium-resistant drilling fluid in increasing order, and the drilling fluid performance after hot rolling was tested. When the salt content reached a maximum of 20%, the rheology and filtration loss of the drilling fluid changed very little, indicating that the system has good resistance to salt pollution.

[0170] Calcium chloride with different mass fractions was quantitatively weighed and added into the high temperature and calcium resistant water-based drilling fluid system, fully stirred and then cured in a sealed container for 24 hours.

[0171] The temperature-resistant and calcium-resistant freshwater drilling fluid system and the temperature-resistant and calcium-resistant brine drilling fluid system were stirred at high speed for 5 minutes, then placed in a high-temperature aging tank and heated at 200°C for 16 hours. The filtration loss of the drilling fluid was measured using a normal temperature medium pressure filter loss meter and a high temperature and high pressure filter loss meter. The results are shown in Table 10:

[0172] Table 10

[0173]

[0174]

[0175] Analyzing the data in the above table, different proportions of calcium chloride were added to the temperature-resistant and calcium-resistant drilling fluid from small to large, and the drilling fluid performance after hot rolling was tested. When the calcium chloride content reached a maximum of 5%, the rheology and filtration loss of the drilling fluid changed very little within a small range, and still maintained good rheology and low filtration loss, indicating that the system has good resistance to calcium pollution.

[0176] 7. Plugging performance test

[0177] A 400mD sand disk was selected for pressure sealing evaluation test. The comparative base slurry and the drilling fluid of Example 5 were subjected to sand disk sealing pressure bearing test to evaluate the sealing pressure bearing capacity. The experiment was conducted at a temperature of 200°C, and the pressure was gradually increased from 7MPa, 10MPa, 15MPa, 20MPa, 25MPa to 30MPa. The sand disk filtration loss of the drilling fluid under different pressure conditions was analyzed to evaluate the sealing pressure bearing performance of the 400mD sand disk. The results are shown in Table 11 and Table 12. Figure 7 shown.

[0178] Table 11

[0179]

[0180]

[0181] Note: Permeate loss = 2 × 30min filtration loss. From the experimental data in Table 11 and Figure 7 Experimental curve analysis shows that at 7 MPa, the osmotic fluid loss of the Example 2 base slurry was 15.2 mL, and the osmotic fluid loss of the Example 2 drilling fluid was 11.2 mL, with average permeation rates of 0.04 mL / min and 0.04 mL / min, respectively. At 30 MPa, the average permeation rates were 0.04 mL / min and 0.02 mL / min, respectively, indicating that the Example 5 drilling fluid significantly outperformed the Example 5 base slurry in its pressure-bearing and sealing properties on the sand tray.

[0182] 8. Comparison of performance indicators with traditional polysulfone drilling fluid

[0183] The drilling fluid of Example 5 and a conventional polysulfone drilling fluid were subjected to performance index tests, and the test method was in accordance with the book "Modern Mud Experimental Technology" published by the Petroleum University Press in 1999.

[0184] Table 12

[0185]

[0186] Table 12 shows that the temperature-resistant and calcium-resistant drilling fluid of Example 5 exhibits comparable rheological properties to conventional polysulfone drilling fluid at the same density. The temperature-resistant and calcium-resistant drilling fluid is superior to polysulfone drilling fluid in controlling fluid loss at medium and high-temperature and high-pressure conditions. The conventional polysulfone drilling fluid comprises: 1000 parts water; 35 parts sodium bentonite; 4 parts sodium hydroxide; 3 parts cationic polymer coating agent; 20 parts high-temperature sulfonate copolymer fluid loss reducer; 4 parts surface hydration inhibitor; 40 parts low-fluorescence cationic asphalt powder; 40 parts sulfonated phenolic resin; 40 parts sulfonated lignite resin; 30 parts biolubricant; 20 parts solid polyol; 25 parts composite calcium carbonate; 10 parts micro-nano strong plugging agent; 10 parts amphiphilic plugging agent; and 700 parts barite.

[0187] The above experiments show that the drilling fluid of the present invention has a temperature resistance exceeding 200°C, a calcium chloride resistance of 5%wt, a salt resistance of 20%wt, and a water loss of less than 10mL at 200°C, reducing the overall damage caused by filtrate to easily collapsed formations, improving the pressure bearing capacity of the formation, and meeting the requirements of drilling operations. At high temperatures, it exhibits excellent rheological properties, fluid loss reduction, inhibition, lubricity, and plugging and pressure bearing capacity, meeting the requirements of safe drilling in deep wells under high-temperature conditions and improving the efficiency of deep well development.

[0188] The manufacturers and performance requirements of the raw materials used in the present invention are as follows:

[0189]

[0190]

[0191] The above description is only a preferred embodiment of the present invention, which shows and describes the basic principles, main features and advantages of the present invention, but does not limit the scope of patent protection of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. In addition to the above embodiments, the present invention may have other implementation modes without departing from the spirit and scope of the present invention. The present invention may also have various changes and improvements, and all technical solutions formed by equivalent replacement or equivalent transformation fall within the scope of protection required by the present invention. The scope of protection required by the present invention is defined by the attached claims and their equivalents. Technical features not described in the present invention can be achieved by or using existing technologies, and will not be described here.

Claims

1. A high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells, characterized in that: The raw material components and weight contents are as follows: water: 1000 parts; sodium bentonite: 30-40 parts; cationic polymer coating agent: 2-4 parts; temperature-resistant and calcium-resistant polymer fluid loss reducer: 10-20 parts; clay surface hydration inhibitor: 3-5 parts; sulfonated phenolic resin: 20-30 parts; sulfonated lignite resin: 20-30 parts; low-fluorescence cationic asphalt powder: 30-50 parts; biolubricant: 20-40 parts; solid polyol: 15-25 parts; ultrafine calcium carbonate: 30-50 parts; micro-nano strong plugging agent NANOFSEAL: 5-15 parts; amphiphilic plugging agent: 10-15 parts; barite: 330-400 parts; NaOH is used to adjust the pH value to 9-10; The structural formula of the temperature-resistant and calcium-resistant polymer fluid loss reducer is shown below:

2. The high temperature and calcium resistant water-based drilling fluid for ultra-deep shale wells according to claim 1 is characterized in that: The raw material components and weight contents are as follows: water: 1000 parts; sodium bentonite: 30 parts; cationic polymer coating agent: 2 parts; temperature-resistant and calcium-resistant polymer fluid loss reducer: 10 parts; clay surface hydration inhibitor: 3 parts; sulfonated phenolic resin: 20 parts; sulfonated lignite resin: 20 parts; low-fluorescence cationic asphalt powder: 30 parts; biolubricant: 20 parts; solid polyol: 15 parts; ultrafine calcium carbonate: 30 parts; micro-nano strong plugging agent NANOFSEAL: 5 parts; amphiphilic plugging agent: 10 parts; barite: 330 parts; and the pH value is adjusted to 9 with NaOH.

3. The high temperature and calcium resistant water-based drilling fluid for ultra-deep shale wells according to claim 1 is characterized in that: The raw material components and weight contents are as follows: water: 1000 parts; sodium bentonite: 35 parts; cationic polymer coating agent: 3 parts; temperature-resistant and calcium-resistant polymer fluid loss reducer: 15 parts; clay surface hydration inhibitor: 4 parts; sulfonated phenolic resin: 25 parts; sulfonated lignite resin: 25 parts; low-fluorescence cationic asphalt powder: 40 parts; biolubricant: 30 parts; solid polyol: 20 parts; ultrafine calcium carbonate: 40 parts; micro-nano strong plugging agent NANOFSEAL: 10 parts; amphiphilic plugging agent: 12 parts; Barite: 360 parts; pH adjusted to 9.5 with NaOH.

4. The high temperature and calcium resistant water-based drilling fluid for ultra-deep shale wells according to claim 1, characterized in that: The raw material components and weight contents are as follows: water: 1000 parts; sodium bentonite: 40 parts; cationic polymer coating agent: 4 parts; temperature-resistant and calcium-resistant polymer fluid loss reducer: 20 parts; clay surface hydration inhibitor: 5 parts; sulfonated phenolic resin: 30 parts; sulfonated lignite resin: 30 parts; low-fluorescence cationic asphalt powder: 50 parts; biolubricant: 40 parts; solid polyol: 25 parts; ultrafine calcium carbonate: 50 parts; micro-nano strong plugging agent NANOFSEAL: 15 parts; amphiphilic plugging agent: 15 parts; barite: 400 parts; and the pH value is adjusted to 10 with NaOH.

5. A method for preparing a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells, characterized in that: The following steps are included in sequence: A1. First, 1000 parts of water and 30-40 parts of sodium bentonite were mixed, stirred at a stirring speed of 2000-4000 rpm for 30-60 minutes, then stirred at a stirring speed of 6000-10000 rpm for 30-40 minutes, and cured at room temperature for 24 hours to form a mixture 1; A2. Slowly and evenly add 2 to 4 parts of cationic polymer coating agent to mixture 1 at a stirring speed of 6000 to 10000 rpm, stir evenly, then add 10 to 20 parts of temperature-resistant and calcium-resistant polymer fluid loss reducer and 3 to 5 parts of clay surface hydration inhibitor, evenly add 20 to 30 parts of sulfonated phenolic resin and 20 to 30 parts of sulfonated lignite resin while stirring, then evenly add 30 to 50 parts of low-fluorescence cationic asphalt powder while stirring, stir evenly, add 20 to 40 parts of biolubricant, stir evenly, add 15 to 25 parts of solid polyol, stir evenly, add 5 to 15 parts of micro-nano strong plugging agent NANOFSEAL, stir evenly, add 10 to 20 parts of amphiphilic plugging agent and 30 to 50 parts of ultrafine calcium carbonate, to form mixture 2; A3, adjusting the pH value of the mixture 2 to 9-10 with NaOH to form a mixture 3; A4. Add 330-400 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry; The structural formula of the temperature-resistant and calcium-resistant polymer fluid loss reducer is shown below:

6. The method for preparing high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells according to claim 5, characterized in that: The following steps are included in sequence: A1. First, 1000 parts of water and 30 parts of sodium bentonite were mixed, stirred at a stirring speed of 2000 rpm for 30 minutes, then stirred at a stirring speed of 6000 rpm for 30 minutes, and cured at room temperature for 24 hours to form a mixture 1; A2. At a stirring speed of 6000 rpm, 2 parts of cationic polymer coating agent were slowly and evenly added to mixture 1. After stirring, 10 parts of temperature-resistant and calcium-resistant polymer fluid loss reducer and 3 parts of clay surface hydration inhibitor were added. 20 parts of sulfonated phenolic resin and 20 parts of sulfonated lignite resin were evenly added while stirring. Then, 30 parts of low-fluorescence cationic asphalt powder were evenly added while stirring. After stirring, 20 parts of biolubricant were added. After stirring, 15 parts of solid polyol were added. After stirring, 5 parts of micro-nano strong plugging agent NANOFSEAL were added. After stirring, 10 parts of amphiphilic plugging agent and 30 parts of ultrafine calcium carbonate were added to form mixture 2. A3, adjusting the pH value of mixture 2 to 9 with NaOH to form mixture 3; A4. Add 330 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry.

7. The method for preparing high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells according to claim 5, characterized in that: The following steps are included in sequence: A1. First, 1000 parts of water and 35 parts of sodium bentonite were mixed, stirred at a stirring speed of 3000 rpm for 45 minutes, then stirred at a stirring speed of 8000 rpm for 35 minutes, and cured at room temperature for 24 hours to form a mixture 1; A2. At a stirring speed of 8000 rpm, 3 parts of cationic polymer coating agent were slowly and evenly added to mixture 1. After stirring, 15 parts of temperature-resistant and calcium-resistant polymer fluid loss reducer and 4 parts of clay surface hydration inhibitor were added. 25 parts of sulfonated phenolic resin and 25 parts of sulfonated lignite resin were evenly added while stirring. Then, 40 parts of low-fluorescence cationic asphalt powder were evenly added while stirring. After stirring, 30 parts of biolubricant were added. After stirring, 20 parts of solid polyol were added. After stirring, 10 parts of micro-nano strong plugging agent NANOFSEAL were added. After stirring, 12 parts of amphiphilic plugging agent and 40 parts of ultrafine calcium carbonate were added to form mixture 2. A3, adjusting the pH value of mixture 2 to 9.5 with NaOH to form mixture 3; A4. Add 360 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry.

8. The method for preparing high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells according to claim 5, characterized in that: The following steps are included in sequence: A1. First, 1000 parts of water and 40 parts of sodium bentonite were mixed, stirred at a stirring speed of 4000 rpm for 60 minutes, then stirred at a stirring speed of 10000 rpm for 40 minutes, and cured at room temperature for 24 hours to form a mixture 1; A2. At a stirring speed of 10,000 rpm, 4 parts of a cationic polymer coating agent were slowly and evenly added to the mixture 1. After stirring, 20 parts of a temperature-resistant and calcium-resistant polymer fluid loss reducer and 5 parts of a clay surface hydration inhibitor were added. 30 parts of a sulfonated phenolic resin and 30 parts of a sulfonated lignite resin were evenly added while stirring. 50 parts of a low-fluorescence cationic asphalt powder were then evenly added while stirring. 40 parts of a biolubricant were added after stirring. 25 parts of a solid polyol were added after stirring. 15 parts of a micro-nano strong plugging agent NANOFSEAL were added after stirring. 20 parts of an amphiphilic plugging agent and 50 parts of ultrafine calcium carbonate were added after stirring to form a mixture 2. A3, adjusting the pH value of mixture 2 to 10 with NaOH to form mixture 3; A4. Add 400 parts of barite to mixture 3 and stir evenly to prepare a water-based drilling fluid slurry.

9. The method for preparing a high-temperature and calcium-resistant water-based drilling fluid for ultra-deep shale wells according to any one of claims 5 to 8, characterized in that: The preparation of the temperature-resistant and calcium-resistant polymer fluid loss reducer comprises the following steps in sequence: S1. Add 10 parts by weight of deionized water to the reactor, add 3-8 parts by weight of triallyl phosphate while stirring, adjust the pH value of the system to 10-12 with sodium hydroxide solution, and maintain the temperature at 30±3°C; S2, filling the reactor with nitrogen for 30 minutes to remove oxygen from the reactor, and then continuing to fill the reactor with nitrogen during the reaction process; S3, dissolving dibenzoyl peroxide in 5 times the mass of water to form a solution as a primary polymerization initiator; S4, adding 0.1-0.3 parts by weight of a primary polymerization initiator into the reactor, maintaining the system temperature at 30±3°C, and conducting a primary polymerization reaction for 0.5 hours; S5. Sodium persulfite and ammonium persulfate are mixed in a mass ratio of 1:1 and then dissolved in 5 times the mass of water as a secondary polymerization initiator; S6, adding 0.5-1 parts by weight of a secondary polymerization initiator to the reactor, and then adding 5-15 parts by weight of dimethyldiallylammonium chloride, and continuing the reaction for 0.5 hours to carry out a secondary polymerization reaction; S7, dissolving 10-20 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 20-30 parts by weight of acrylamide, 15-35 parts by weight of styrene and 5-15 parts by weight of sodium methacryloylsulfonate powder monomer in water equal to the total mass of the powder, and stirring uniformly; S8, adding the solution obtained in step S7 to the reactor, controlling the reaction temperature in the reactor at 30±3°C, and performing three polymerization reactions for 2 hours; S9, adding 1 part by weight of chain transfer agent trichloroethylene to the reactor and continuing the reaction for 4 hours; S10, stop supplying nitrogen to the reactor, blow air into the reactor, add 1 part by weight of ferric chloride as a polymerization inhibitor to the reactor, react for 0.5 hours, and perform product end-capping; S11. Dry the product in the reactor at 100° C. and crush it to obtain a powder of a temperature-resistant and calcium-resistant polymer fluid loss reducer.

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