A plugging anti-collapse agent, a plugging anti-collapse water-based drilling fluid and a preparation method thereof

Abstract

The application discloses a plugging anti-collapse agent and a water-based drilling fluid prepared from the plugging anti-collapse agent. The plugging anti-collapse agent is obtained by compounding oxidized pitch and a composite material. The composite material is obtained by compounding a polymer and modified nanometer carbon dots, wherein the polymer is formed by polymerization of an acrylamide compound, N-vinylpyrrolidone and a diallyl ammonium chloride compound, and the structure of the polymer is shown in the specification. The novel plugging anti-collapse agent prepared by the application solves the problem of poor temperature resistance of the plugging anti-collapse agent and has good temperature resistance and plugging performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil drilling fluid, and specifically relates to a novel plugging and anti-collapse agent and a plugging and anti-collapse type water-based drilling fluid and a preparation method thereof, which are mainly used in the preparation and preparation of drilling fluid in oil drilling. Background Art

[0002] With the acceleration of shale oil and gas exploration and development, and the expansion of oil exploration and development into deeper formations and offshore, the number of complex, deep, ultra-deep, and specialized wells has increased. Drilling in complex formations is prone to wellbore instability issues such as lost circulation, collapse, borehole shrinkage, and severe slurrying. These issues, including borehole shrinkage and collapse in shale, fractured coal seams, and high-salt formations, can cause these issues, impacting drilling efficiency and cementing quality, and even causing pipe sticking, seriously impacting the exploration and development process.

[0003] Plugging utilizes solid particles to bridge and plug pores and microcracks to reduce or even isolate the filtration loss pathways of the drilling fluid, preventing the wellbore drilling fluid pressure from invading and transmitting through the filtrate into the near-wellbore formation. According to the bridge plugging theory, plugging particles (materials) can directly block filtration loss pathways in solid-free drilling fluids through bridging and filling. However, in more cases, in solid-phase drilling fluids, plugging particles primarily achieve a tight seal of filtration loss pathways through a filling effect. Therefore, drilling fluid plugging and anti-collapse agents are key to improving anti-collapse performance and wellbore stability.

[0004] Existing plugging and anti-collapse agents primarily consist of modified asphalt, emulsified paraffin, polymer alcohols, organoaluminum compounds, and silicates. However, the anti-collapse effectiveness of asphalt treatment agents is significantly affected by the softening point of their raw material asphalt. Their effective operating temperature is near this softening point, making it difficult to effectively plug microcracks in formations across a wide temperature range. Asphalt treatment agents are made from petroleum asphalt and natural asphalt. The softening point of petroleum asphalt generally ranges from 40-100°C, and the softening point of natural asphalt in Xinjiang, my country, is only 90-140°C. This makes it difficult to effectively plug microcracks in deep, high-temperature formations, especially those with temperatures above 160°C and complex formations. Furthermore, asphaltene, the primary component of asphalt treatment agents, fluoresces, which can affect fluorescence logging and gas logging to a certain extent.

[0005] Silicate treatment agents, such as sodium silicate, potassium silicate, and methyl silicate, can form nanoparticles of varying sizes—ions, colloids, and macromolecules—in water. Through adsorption, diffusion, and chemical precipitation, they form a protective film on the rock surface, sealing microfractures. Once in the formation, silicate ions further react with calcium and magnesium ions to form calcium-magnesium silicate precipitates. Simultaneously, silanol groups condense with aluminum alcohol groups in formation minerals, bonding them together and improving the overall cementing capacity of the formation, ultimately sealing the wellbore. However, silicate treatment agents have high pH requirements for drilling fluids, often above 11. Due to the limited availability of compatible treatment agents, the rheological properties of drilling fluids are difficult to control, limiting their application.

[0006] Polyols, also known as polyether polyols, are nonionic, low-molecular-weight polymers. These include polyethylene glycol, polypropylene glycol, polyglycerol, polyethylene glycol, and ethylene glycol / propylene glycol copolymers. They are readily soluble in water below their cloud point. However, above this temperature, the polyols precipitate from the water and undergo phase separation, forming a turbid, emulsified liquid. Under the influence of hydroxyl adsorption and differential pressure, these droplets adhere to the wellbore wall or squeeze into microcracks and pore throats in the shale, sealing these microcracks and pore throats and forming a hydrophobic film on the wellbore surface, preventing free water in the drilling fluid from entering the shale. Polyols also exhibit good compatibility with conventional drilling fluid treatment agents. They are biodegradable, have low or no toxicity, and are environmentally friendly. Their low fluorescence facilitates the identification and discovery of oil and gas reservoirs. However, due to their cloud point, the effective temperature range of polyol treatment agents is limited. Effectively improving the anti-collapse properties of drilling fluids requires a cloud point temperature comparable to the bottomhole circulation temperature. Moreover, the polyol treating agent is a non-ionic surfactant, which often causes the drilling fluid to foam.

[0007] In recent years, shale gas exploration and development has accelerated. However, shale gas development is hampered by its small pore throats, low permeability, and the fact that most pores consist of microscopic capillary pores, which are prone to hydration and cause wellbore collapse. Addressing shale gas sealing and permeability issues has become a key issue in current shale gas drilling fluid technology research. Conventional drilling fluid additives have a particle size range of 0.1-100 μm, far larger than the average pore throat size of shale, making it difficult to effectively seal pores and microfractures in shale. Nanomaterials exhibit unique volume effects, interfacial effects, and quantum tunneling, making them more compatible with shale formation pore throats than conventional drilling fluids. Nanosilica is the most widely researched and applied, but it suffers from poor dispersibility and severe agglomeration, making it difficult to form nanoscale plugs. Graphene oxide, rich in oxygen-containing functional groups, can form a film-like barrier during plugging, resulting in a more thorough and effective plugging effect. However, graphene-based materials are not resistant to high temperatures and have poor dispersibility in water-based systems. Summary of the Invention

[0008] Based on the above background, the present invention provides a new plugging and anti-collapse agent. Using the plugging and anti-collapse agent as the core treatment agent, a high-temperature resistant and high-density plugging and anti-collapse water-based drilling fluid system is developed. The system can effectively solve complex situations encountered during the drilling process, such as lost circulation, blowout, and stuck pipe, and provide a research basis for on-site application in the field of oil drilling fluid technology.

[0009] In a first aspect, the present invention provides a plugging and anti-collapse agent, characterized in that the plugging and anti-collapse agent is prepared by mixing oxidized asphalt and a composite material at a mass ratio of 1:(1-2.2) at the softening point temperature of the oxidized asphalt.

[0010] The composite material is obtained by compounding a polymer formed by polymerizing acrylamide compounds, N-vinyl pyrrolidone and diallyl ammonium chloride compounds with modified nano carbon dots.

[0011] The structure of the polymer is shown in Formula I:

[0012]

[0013] x, y and z represent the proportion of polymer monomers, x+y+z=1, x is selected from 40-98.5%, y is selected from 0.5-3%, and z is selected from 1-15%.

[0014] Wherein, R1 and R2 are the same or different and are independently selected from -H, C 1-5 Straight chain / branched alkyl, wherein the H in the alkyl may be substituted by a sulfonic acid group; R3 and R4 are the same or different and are independently selected from -H, C 1-3 Straight chain / branched chain alkyl.

[0015] In a preferred embodiment of the present invention, R1 and R2 are independently selected from -H, -CH3, -CH2CH3, R3 and R4 are independently selected from -H and -CH3.

[0016] In a specific embodiment of the present invention, the structure of the polymer is as follows:

[0017]

[0018] m, n, p and q represent the proportion of polymer monomers, m+n+p+q=1, m is selected from 30-78.5%, n is selected from 10-20%, p is selected from 0.5-3%, and q is selected from 1-15%.

[0019] In the composite material, the mass proportion of the modified nano-carbon dots is 0.2-1.0%; preferably, the mass proportion of the modified nano-carbon dots is 0.5-1.0%.

[0020] The modified nano-carbon dots of the present invention are obtained by the following preparation method: dispersing the nano-carbon dots in an ethanol solution, adding a silane coupling agent, heating and refluxing at 60-75° C. for 4-5 hours, removing the solvent, and drying to obtain the modified nano-carbon dots.

[0021] The silane coupling agent is selected from one or a combination of two or more of γ-methacryloxypropyltrimethoxysilane (KH570), vinyltrimethoxysilane (KH-171), and vinyltri(b-methoxyethoxy)silane (KH-172). Those skilled in the art can make conventional adjustments to the amount of the silane coupling agent based on actual conditions.

[0022] The synthesis method of the nano-carbon dots used in the present invention refers to the document "Zhai Yuechen. Preparation and application of fluorescent composite materials based on carbon dots [D]. University of Chinese Academy of Sciences (Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences), 2020." (DOI: 10.27522 / d.cnki.gkcgs.2020.000005), which is synthesized using urea and citric acid using a microwave reaction method.

[0023] The oxidized asphalt of the present invention can be purchased through commercial channels or prepared by oneself. The preparation method of the oxidized asphalt comprises: softening the asphalt, adding potassium permanganate solution, heating and refluxing the asphalt, recovering the asphalt, and drying to obtain the oxidized asphalt.

[0024] In a second aspect, the present invention provides a method for preparing a plugging and anti-collapse agent, comprising the following steps:

[0025] (1) using a silane coupling agent to modify the nanocarbon dots to obtain modified nanocarbon dots;

[0026] (2) mixing acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinyl pyrrolidone, methyldiallylammonium chloride, and modified nanocarbon dots, adding an initiator to carry out polymerization reaction, and obtaining a composite material;

[0027] (3) heating the asphalt to the softening point and adding potassium permanganate solution for oxidation to obtain oxidized asphalt;

[0028] (4) The oxidized asphalt is heated to 100-120° C., and the composite material is added in a mass ratio of 1:(1-2.2), mixed, cooled and solidified, and crushed to obtain a plugging and anti-collapse agent.

[0029] Preferably, the silane coupling agent in step (1) is selected from one or a combination of two or more of γ-methacryloxypropyltrimethoxysilane (KH570), vinyltrimethoxysilane (KH-171), and vinyltri(b-methoxyethoxy)silane (KH-172). In a specific embodiment of the present invention, the silane coupling agent is KH570. The present invention does not limit the amount of the silane coupling agent used, and technicians can adjust it.

[0030] Preferably, the molar mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinyl pyrrolidone, and dimethyldiallylammonium chloride in step (2) is (30-78.5): (10-20): (0.5-3): (1-15). The amount of modified nano-carbon dots added accounts for 0.2-1.0% of the mass of the composite material.

[0031] Preferably, the initiator in step (2) is selected from one or a combination of ammonium persulfate and sodium bisulfite. In a specific embodiment of the present invention, the initiator is a combination of ammonium persulfate and sodium bisulfite. Those skilled in the art can adjust the amount of the initiator according to actual needs.

[0032] In a specific embodiment of the present invention, the plugging and anti-collapse agent is prepared by the following method:

[0033] (1) Dispersing the nanocarbon dots in an ethanol solution, adding KH570, and adding acetic acid to adjust the pH of the dispersion to a weak acidic state, heating under reflux at 70-75°C for 4-5 hours, removing the solvent, and drying to obtain modified nanocarbon dots;

[0034] (2) 2-Acrylamido-2-methylpropanesulfonic acid was weighed in proportion and dissolved in water, and NaOH of the same molar mass was added, followed by acrylamide, N-vinyl pyrrolidone, dimethyldiallylammonium chloride, and modified nano-carbon dots. An initiator was added under nitrogen protection to react, and the product was washed with ethanol and dried to obtain a composite material;

[0035] (3) heating the asphalt to the softening point, adding potassium permanganate solution under stirring, boiling and refluxing for 40-60 minutes, recovering the asphalt, and drying to obtain oxidized asphalt;

[0036] (4) heating the oxidized asphalt to 100-120° C., adding the composite material in a mass ratio of oxidized asphalt to composite material of 1:(1-2.2), mixing, cooling and solidifying, and crushing to obtain a plugging and anti-collapse agent.

[0037] In a third aspect, the present invention provides a use of a plugging and anti-collapse agent in the preparation of a water-based drilling fluid.

[0038] In a fourth aspect, the present invention provides a plugging and anti-collapse type water-based drilling fluid, characterized in that the drilling fluid includes a plugging and anti-collapse agent and a base slurry, wherein the weight percentage of the plugging and anti-collapse agent is 4.0-6.0%, and the base slurry includes the following components in weight percentage: clay 1.0-2.0%, coating agent 0.4-0.6%, filtration reducer 4-6%, viscosity reducer 1.8-2.2%, soda ash (Na2CO3) 0.2-0.3%, acid-base regulator 0.3-0.4%, weighting agent 0-60%, and the rest is water.

[0039] The above “weight percentages %” all represent the percentage of each component in the total weight of the water-based drilling fluid.

[0040] The clay is selected from at least one of sodium bentonite, calcium bentonite, and calcium sodium bentonite; in a specific embodiment of the present invention, the clay is sodium bentonite.

[0041] The coating agent is a zwitterionic polymer coating agent, specifically selected from one or a combination of two or more of acrylamide, acrylic acid, sodium allyl sulfonate, dimethyldiallylammonium chloride, and a multipolymer of 2-acrylamide-2-methylpropanesulfonic acid. In a specific embodiment of the present invention, the coating agent is FA-367.

[0042] The fluid loss control agent is selected from at least one of a sulfonated fluid loss control agent and a polymer fluid loss control agent, wherein the sulfonated fluid loss control agent is selected from one or a combination of two or more of sulfonated phenolic resin, lignite resin, sulfonated lignite, and sulfonated tannin; and the polymer fluid loss control agent is selected from at least one of a multi-polymer of acrylamide, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid, such as Dristemp, DSP-1, or DSP-2.

[0043] The viscosity reducer is selected from at least one of a sulfonated viscosity reducer and a synthetic polymer viscosity reducer, wherein the synthetic polymer viscosity reducer is selected from one or a combination of two or more of a multi-component copolymer of acrylamide, sodium allyl sulfonate, 2-acrylamide-2-methylpropanesulfonic acid, and dimethyldiallylammonium chloride. In a specific embodiment of the present invention, the viscosity reducer is Polythin or XY-27.

[0044] The acid-base regulator used in the present invention is NaOH or KOH.

[0045] The weighting agent is selected from at least one of calcium carbonate, barite, and hematite. Preferably, the weighting agent is barite A and / or barite B, the particle size of barite A is 50-70 μm, and the particle size of barite B is 1-1.2 μm.

[0046] In a preferred embodiment of the present invention, the drilling fluid comprises the following components by mass fraction: 4-5.5% plugging and anti-collapse agent, 1-2% sodium bentonite, 0.2% Na2CO3, 0.3% NaOH, 1.6-1.8% Polythin, 0.4-0.6% FA-367, 0.5-1% Dristemp or DSP-1 or DSP-2, 1-2% sulfonated phenolic resin, 2-4% lignite resin, 0.2-0.4% XY-27, 50-60% barite A and barite B, and the balance is water.

[0047] In a fifth aspect, the present invention provides a method for preparing a plugging and anti-collapse water-based drilling fluid, comprising the following steps:

[0048] (1) mixing water, clay, and soda ash, and performing static hydration to obtain a prehydrated raw material;

[0049] (2) Stirring the prehydrated raw materials, and sequentially adding a fluid loss reducer, a viscosity reducer, a coating agent, a plugging and anti-collapse agent, and an acid-base regulator, and continuing to stir, adding a weighting agent and stirring, thereby obtaining a drilling fluid.

[0050] The water-based drilling fluid prepared by the method provided by the present invention has a pH of 8-9 and a density of 1.7-2.0 g / cm 3 , high temperature resistance is 220℃.

[0051] The novel plugging and anti-collapse agent provided by the present invention has the following technical advantages:

[0052] (1) The present invention selects monomers of acrylamide, diacrylamido dimethylpropane sulfonic acid, N-vinyl pyrrolidone, dimethyldipropylene ammonium chloride, and modified nanocarbon dots, synthesizes a composite material by aqueous solution polymerization, and then compounding the composite material with oxidized asphalt to prepare a novel plugging and anti-collapse agent. The modified nanocarbon dots have good stability, low toxicity, a wide range of raw material sources, and a simple preparation method. The double bond structure in the modified nanocarbon dots allows the nanocarbon dots to participate in the polymerization reaction, polymerize in the polymer chain, and fill in the bridged grid structure, thereby improving the plugging effect of the plugging and anti-collapse agent.

[0053] (2) The composite material used in the present invention for preparing the plugging and anti-collapse agent has strong molecular chain rigidity, and the five-membered ring structure and nano-carbon dots formed by the polymerization of pyrrolidone and diallyl ammonium chloride can enhance the temperature resistance of the material, so that the water-based drilling fluid system prepared with the novel plugging and anti-collapse agent as the core has excellent temperature resistance. After hot rolling aging, the system has good sedimentation stability and rheological properties, has a low high-temperature and high-pressure filtration loss, and has excellent plugging performance and good protection performance for water-sensitive formations. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 TEM image of carbon nanodots.

[0055] Figure 2 Infrared spectrum of carbon nanodots. DETAILED DESCRIPTION

[0056] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0057] Preparation of carbon nanodots

[0058] 3g of citric acid and 6g of urea were dissolved in 20mL of deionized water and stirred until the citric acid and urea were completely dissolved to form a colorless and transparent solution. The solution was then placed in a 650W microwave oven and deeply heated for 5 minutes. During the heating process, the solution gradually changed from a colorless and transparent state to brown, and finally a dark brown solid was obtained. Finally, the dark brown solid was redissolved in 20mL of deionized water and stirred to fully dissolve it. After centrifugal purification, an aqueous solution of carbon dots was obtained, which was freeze-dried to obtain nanocarbon dots. Figure 1 This is a TEM image of the nano-carbon dots prepared in the present invention. From the image, we can see that the particle size of the nano-carbon dots is in the range of 5-10 nm. Figure 2 This is an infrared spectrum of the nano-carbon dots prepared by the present invention.

[0059] Preparation of plugging and anti-collapse agent

[0060] Preparation Example 1

[0061] S1 Modification of Nanocarbon Dots: Place 2g of nanocarbon dots in a beaker, add 92-100mL of ethanol and 0-8mL of deionized water, and ultrasonically disperse the nanocarbon dots in an ultrasonic bath for 15 minutes. Add a certain amount of KH570 to a round-bottom flask, adjust the pH to a weakly acidic state by adding half a drop of acetic acid, and pour the nanocarbon dot dispersion into the round-bottom flask. Heat and reflux at 75°C with stirring for 4 hours. After the reaction, remove the solvent using a rotary evaporator, dissolve the nanocarbon dots in deionized water, and freeze-dry to obtain the modified nanocarbon dots.

[0062] Preparation of the S2 composite material: 33g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) monomer was weighed and dissolved in deionized water, then stirred on a magnetic stirrer to dissolve. Sodium hydroxide solid was weighed using an analytical balance in a 1:1 molar ratio and added to the solution. After complete dissolution, the pH was adjusted with 20 mol / L sodium hydroxide solution. Then, 39.616g of acrylamide (AM), 1.770g of N-vinylpyrrolidone (NVP), 17.164g of dimethyldiallylammonium chloride (DMDAAC), and 0.458g of modified nanocarbon dots were added. The mixture was stirred on a magnetic stirrer for 20 minutes. After complete dissolution, the reaction apparatus was connected and the solution was poured into a three-necked flask. Stirred under nitrogen for 20 minutes. After reaching the desired temperature, 0.31g of (NH4)2S2O8 and 0.143g of NaHSO3 as initiators were added, and the reaction continued under nitrogen. After the reaction was completed, the mixture was cooled to room temperature, the colloid in the flask was taken out, and washed several times with anhydrous ethanol to remove unreacted monomers. Finally, the precipitate was vacuum dried at 65° C. and dried to granulate to obtain a composite material.

[0063] Preparation of S3 Oxidized Asphalt: Add asphalt powder (softening point 120°C) to a three-necked flask. Add potassium permanganate solution with magnetic stirring. Heat to boiling and reflux for 40 minutes until the potassium permanganate solution dissipates, stopping the reaction. At this point, a large amount of asphalt will float on the surface of the liquid, while manganese dioxide will sink to the bottom. Pour the mixture into a beaker, add water, and pour the upper solid layer into a Büchner funnel. Filter with suction (be careful not to pour in the lower layer of manganese dioxide), dry, and pulverize to obtain oxidized asphalt powder.

[0064] Preparation of S4 plugging and anti-collapse agent: Take oxidized asphalt in a beaker, heat and stir at a temperature of 100-120℃ until the asphalt begins to soften, slowly add the composite material at a mass ratio of 1:1, stir for 3-5 hours, mix thoroughly, cool to room temperature to solidify, and crush to obtain the plugging and anti-collapse agent.

[0065] Preparation Example 2

[0066] The raw materials and preparation method are the same as those in Preparation Example 1, except that modified carbon nanodots are not required, and the composite material prepared in step S2 does not contain modified carbon nanodots. The monomers for the composite material are acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and dimethyldiallylammonium chloride. The method for preparing the oxidized asphalt and the anti-collapse agent by compounding is the same as in Preparation Example 1.

[0067] Preparation Example 3

[0068] The raw materials and preparation method are the same as those in Preparation Example 1, except that the composite material prepared in step S2 does not contain N-vinyl pyrrolidone, and the polymerization monomers of the composite material are acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, dimethyldiallylammonium chloride, and nano-modified carbon dots. The oxidized asphalt and the method for obtaining the plugging anti-sloughing agent by compounding are the same as those in Preparation Example 1.

[0069] Preparation Example 4

[0070] The raw materials and preparation method are the same as those in Preparation Example 1, except that the composite material prepared in step S2 does not contain dimethyldiallylammonium chloride, and the polymerization monomers of the composite material are acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinyl pyrrolidone, and nano-modified carbon dots. The oxidized asphalt and the method for obtaining the plugging anti-sloughing agent by compounding are the same as those in Preparation Example 1.

[0071] Performance test of plugging anti-sloughing agent

[0072] Test purpose: To detect the performance of the plugging anti-sloughing agents prepared in Preparation Examples 1-4 of the application and the commercially available sulfonated asphalt FT-1.

[0073] Test method: The plugging anti-sloughing agents 1-4 prepared in the application and the commercially available sulfonated asphalt FT-1 are respectively added to 4wt% base slurry (16g of bentonite is added to 400mL of distilled water, and the mixture is stirred at room temperature for 24h to prepare the base slurry), to prepare drilling fluids with sample concentrations of 0.5wt%, 1.0wt%, 1.5wt%, and 2wt%; using a sand bed plugging instrument, the invasion depth of the drilling fluids into 40-60 mesh and 60-80 mesh sand beds is respectively measured at room temperature and a pressure of 0.7MPa. The specific test results are shown in the following table.

[0074] Table 1: Invasion depth data of sand bed

[0075]

[0076]

[0077] As can be seen from the data in the table above, the plugging and anti-collapse agent prepared by the present invention has better plugging ability than the commercially available sulfonated asphalt FT-1. When the content of both is 2%, the penetration depth of the plugging and anti-collapse agent prepared by the present invention into a 40-60 mesh sand bed is 8.0 cm, while the penetration depth of FT-1 is 9.6 cm. Moreover, when the modified nano-carbon dots are not introduced in Preparation Example 2, its plugging performance is poor, and its plugging performance is worse than that of the commercially available sulfonated asphalt FT-1. The ternary plugging and anti-collapse agents prepared by Preparation Examples 3 and 4 also have good plugging and anti-collapse performance, which is better than sulfonated asphalt FT-1, but slightly worse than the plugging and anti-collapse agent obtained in Preparation Example 1. The plugging and anti-collapse agent prepared by the present invention has excellent plugging effect on both 40-60 mesh and 60-80 mesh sand beds, further demonstrating that the plugging and anti-collapse agent of the present invention has a significant plugging effect and can adapt to pores of different sizes. As the amount of plugging and anti-collapse agent added increases, the penetration depth of the sand bed is lower and the plugging effect is better.

[0078] Preparation of plugging and anti-collapse drilling fluid

[0079] Example 1

[0080] The components of the drilling fluid are as follows in percentage by weight: 4% plugging and anti-collapse agent (Preparation Example 1) + 1% sodium bentonite + 0.2% Na2CO3 + 0.3% NaOH + 1.6% Polythin + 0.4% FA-367 + 1% Dristemp + 1% sulfonated phenolic resin + 2% lignite resin + 0.2% XY-27 + 50% barite A and barite B, and the rest is water; wherein the weight ratio of barite A to barite B is 7:3.

[0081] S1: Water, sodium bentonite and Na2CO3 are added to a slurry cup in sequence, and stirred for 10 minutes using a low-speed stirrer in the slurry cup; then stirred for 10 minutes using a high-speed stirrer, and then statically hydrated for 16-24 hours. After hydration for 16 hours, a prehydrated raw material is obtained;

[0082] S2: The pre-hydrated raw materials were taken out and placed in a low-speed stirrer for stirring. Polythin, FA-367, Dristemp, sulfonated phenolic resin, lignite resin, plugging and anti-collapse agent, XY-27 and NaOH were added in sequence and stirred for 10 minutes under the low-speed stirrer. Barite A and barite B were then added and stirred to obtain the drilling fluid.

[0083] Example 2

[0084] The preparation method of the drilling fluid is the same as that of Example 1, except that the components of the drilling fluid are different. The components of the drilling fluid provided in this example are as follows in terms of percentage by weight: 6% of the plugging and anti-sloughing agent (Preparation Example 1) + 2% of the sodium-based bentonite + 0.2% of Na2CO3+ 0.3% of NaOH + 1.8% of Polythin + 0.6% of FA-367 + 1% of DSP-1 + 1% of the sulfonated phenolic resin + 4% of the lignite resin + 0.4% of XY-27 + 58% of barite A and barite B, and the rest is water; wherein the weight ratio of barite A to barite B is 7:3.

[0085] Example 3

[0086] The preparation method of the drilling fluid is the same as that of Example 1, except that the components of the drilling fluid are different. The components of the drilling fluid provided in this example are as follows in terms of percentage by weight: 5% of the plugging and anti-sloughing agent (Preparation Example 1) + 1.5% of the sodium-based bentonite + 0.2% of Na2CO3+ 0.3% of NaOH + 1.5% of Polythin + 0.5% of FA-367 + 0.7% of DSP-1 + 1% of the sulfonated phenolic resin + 4% of the lignite resin + 0.4% of XY-27 + 50% of barite A and barite B, and the rest is water; wherein the weight ratio of barite A to barite B is 7:3.

[0087] Example 4

[0088] The preparation method of the drilling fluid is the same as that of Example 1, except that the components of the drilling fluid are different. The components of the drilling fluid provided in this example are as follows in terms of percentage by weight: 5% of the plugging and anti-sloughing agent (Preparation Example 1) + 1.7% of the sodium-based bentonite + 0.2% of Na2CO3+ 0.3% of NaOH + 1.6% of Polythin + 0.5% of FA-367 + 0.7% of DSP-2 + 1% of the sulfonated phenolic resin + 4% of the lignite resin + 0.4% of XY-27 + 54% of barite A and barite B, and the rest is water; wherein the weight ratio of barite A to barite B is 7:3.

[0089] Example 5

[0090] The preparation method of the drilling fluid is the same as that of Example 1, except that the components of the drilling fluid are different. The components of the drilling fluid provided in this example are as follows in terms of percentage by weight: 5.5% of the plugging and anti-sloughing agent (Preparation Example 1) + 1.8% of the sodium-based bentonite + 0.2% of Na2CO3+ 0.3% of NaOH + 1.6% of Polythin + 0.5% of FA-367 + 0.8% of DSP-1 + 1% of the sulfonated phenolic resin + 4% of the lignite resin + 0.4% of XY-27 + 56% of barite A and barite B, and the rest is water; wherein the weight ratio of barite A to barite B is 7:3.

[0091] Comparative Example 1

[0092] The preparation method of the drilling fluid is the same as that in Example 1, except that the components of the drilling fluid, the components of the drilling fluid provided in the present example are as follows in percentage by weight: 4% of commercially available sulfonated asphalt FT-1 + 1% of sodium-based bentonite + 0.2% of Na2CO3 + 0.3% of NaOH + 1.6% of Polythin + 0.4% of FA-367 + 1% of Dristemp + 1% of sulfonated phenolic resin + 2% of lignite resin + 0.2% of XY-27 + 50% of barite A and barite B, and the rest is water; wherein the weight ratio of barite A and barite B is 7:3.

[0093] Performance test of the plugging and anti-sloughing water-based drilling fluid

[0094] Test purpose: to test the performance of the drilling fluid prepared in Examples 1-5 of the present application, specifically including apparent viscosity (AV), plastic viscosity (PV), dynamic shear force (YP), static shear force (Gel), medium-pressure filtration loss at room temperature (FL API ), high-temperature and high-pressure filtration loss (FL HTHP );

[0095] Test method:

[0096] The method and conditions for determining the rheological properties of the drilling fluid are as follows:

[0097] (1) GB / T 16783.1 2006 national standard drilling fluid field test is used;

[0098] (2) The rheological property test temperature of the drilling fluid is 30℃;

[0099] (3) High-temperature 220℃ aging for 16h, high-temperature and high-pressure filtration loss determination temperature 180℃, pressure difference 3.5MPa. The test results are shown in the following table.

[0100] Table 2 Performance of the plugging and anti-sloughing water-based drilling fluid

[0101]

[0102]

[0103] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A plugging and anti-collapse agent, characterized in that: The plugging and anti-collapse agent is prepared by mixing oxidized asphalt and a composite material at a mass ratio of 1:(1-2.2) at a temperature equal to the softening point of the oxidized asphalt; the composite material is prepared by the following preparation method: (1) modifying nano-carbon dots using a silane coupling agent to obtain modified nano-carbon dots; (2) mixing acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinyl pyrrolidone, dimethyldiallylammonium chloride, and the modified nano-carbon dots, adding an initiator to carry out a polymerization reaction, and obtaining the composite material; The silane coupling agent is selected from one or a combination of two or more of γ-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, and vinyltri(b-methoxyethoxy)silane; In the step (2), the molar ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinyl pyrrolidone, and dimethyldiallylammonium chloride is (30-78.5): (10-20): (0.5-3): (1-15).

2. The plugging and anti-collapse agent according to claim 1, characterized in that: In the composite material, the mass proportion of modified nano-carbon dots is 0.2-1.0%; the modified nano-carbon dots are obtained by the following preparation method: dispersing the nano-carbon dots in an ethanol solution, adding a silane coupling agent, heating and refluxing at 60-75°C for 4-5 hours, removing the solvent, and drying to obtain the modified nano-carbon dots.

3. A method for preparing the plugging and anti-collapse agent according to claim 1, comprising the following steps: (1) using a silane coupling agent to modify the nanocarbon dots to obtain modified nanocarbon dots; (2) mixing acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinyl pyrrolidone, dimethyldiallylammonium chloride, and modified nanocarbon dots, adding an initiator to carry out polymerization reaction, and obtaining a composite material; (3) heating the asphalt to the softening point and adding potassium permanganate solution for oxidation to obtain oxidized asphalt; (4) The oxidized asphalt is heated to 100-120° C., and the composite material is added in a mass ratio of 1:(1-2.2), mixed, cooled and solidified, and crushed to obtain a plugging and anti-collapse agent.

4. The preparation method according to claim 3, characterized in that In the step (2), the molar ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinyl pyrrolidone and dimethyldiallylammonium chloride is (30-78.5): (10-20): (0.5-3): (1-15), and the amount of modified nano-carbon dots added accounts for 0.2-1.0% of the mass of the composite material.

5. The preparation method according to claim 4, characterized in that The plugging and anti-collapse agent is prepared by the following method: (1) Dispersing the nanocarbon dots in an ethanol solution, adding KH570, and adding acetic acid to adjust the pH of the dispersion to a weak acidic state, heating under reflux at 70-75°C for 4-5 hours, removing the solvent, and drying to obtain modified nanocarbon dots; (2) 2-Acrylamido-2-methylpropanesulfonic acid was weighed in proportion and dissolved in water, and an equal molar amount of NaOH was added, followed by acrylamide, N-vinyl pyrrolidone, dimethyldiallylammonium chloride, and modified nano-carbon dots. An initiator was added under nitrogen protection to react, and the product was washed with ethanol and dried to obtain a composite material; (3) heating the asphalt to the softening point, adding potassium permanganate solution under stirring, boiling and refluxing for 40-60 minutes, recovering the asphalt, and drying to obtain oxidized asphalt; (4) heating the oxidized asphalt to 100-120° C., adding the composite material in a mass ratio of oxidized asphalt to composite material of 1:(1-2.2), mixing, cooling and solidifying, and crushing to obtain a plugging and anti-collapse agent.

6. Use of the plugging and anti-collapse agent according to any one of claims 1 to 2 in the preparation of water-based drilling fluid.

7. A plugging and anti-collapse water-based drilling fluid, characterized in that: The drilling fluid comprises the plugging and anti-collapse agent and base slurry according to any one of claims 1-2, wherein the weight percentage of the plugging and anti-collapse agent is 4.0-6.0%, and the base slurry comprises the following components in weight percentage: 1.0-2.0% clay, 0.4-0.6% coating agent, 4-6% fluid loss reducer, 1.8-2.2% viscosity reducer, 0.2-0.3% soda ash (Na2CO3), 0.3-0.4% acid-base regulator, 0-60% weighting agent, and the rest is water.

8. A method for preparing the plugging and anti-collapse water-based drilling fluid according to claim 7, comprising the following steps: (1) mixing water, clay, and soda ash, and performing static hydration to obtain a prehydrated raw material; (2) Stirring the prehydrated raw materials, and sequentially adding a fluid loss reducer, a viscosity reducer, a coating agent, a plugging and anti-collapse agent, and an acid-base regulator, and continuing to stir, adding a weighting agent and stirring, thereby obtaining a drilling fluid.

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