A polymer plugging agent suitable for oil-based drilling fluid, a preparation method and application thereof

Abstract

The application relates to the technical field of oil field chemistry, and discloses a polymer plugging agent suitable for oil-based drilling fluid, a preparation method and application of the polymer plugging agent, wherein the polymer plugging agent is composed of the following raw materials: graphene oxide, hexahydrate chloride and 2-amino terephthalic acid; the molar ratio of the hexahydrate chloride and the 2-amino terephthalic acid is 1:1-1.5; and the mass of the graphene oxide is 5-10% of the total mass of the hexahydrate chloride and the 2-amino terephthalic acid. When the plugging agent is prepared, the hexahydrate chloride and the 2-amino terephthalic acid are first dissolved in a solvent, then activated graphene oxide powder is added into the above mixed solution, and after uniform mixing, heat reaction is carried out at 150-160 DEG C for 6-8 hours; after the heat reaction is completed, the reacted product is subjected to solid-liquid separation and purification, and the plugging agent is obtained. The plugging agent overcomes the problem that particles lose nanometer size, and can effectively plug micro-nano cracks in shale formations and prevent drilling fluid from invading the formations.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to a polymer plugging agent suitable for oil-based drilling fluids, its preparation method, and its application. Background Technology

[0002] The increasingly complex geological conditions in the exploration and development of oil and gas have placed higher demands on the stability of the wellbore. During the drilling process, drilling fluid filtrate can easily enter the formation through tiny pores under pressure differential. The transmission of hydraulic pressure in the microfractures causes fracture induction and development, which leads to poor wellbore stability and, in severe cases, drilling accidents such as wellbore collapse.

[0003] Wellbore instability has been a major engineering problem that has plagued the drilling industry for many years, and remains largely unresolved. Wellbore instability can lead to a series of complex downhole conditions, including leakage, blowouts, collapses, stuck holes, and deviations. This, in turn, prolongs drilling cycles, increases drilling costs, reduces drilling speed, and severely impacts the economic benefits of oil and gas exploration and development. Statistics show that wellbore instability in deep formations accounts for approximately 35% of the time required to handle complex drilling conditions, and over 90% of wellbore instability occurs in shale formations, with hard and brittle shale formations accounting for about two-thirds of these. Wellbore stability is crucial for the efficient development of oil and gas resources, and strengthening the sealing of nanopores is one of the key measures to address wellbore instability. Because commonly used drilling fluid plugging agents have large particle sizes, they are insufficient to effectively seal nanopores in shale formations. Therefore, nanoscale plugging agents are needed. Currently, commonly used drilling fluid nano-plugging agents are mainly classified into organic nano-plugging agents, inorganic nano-plugging agents, and organic / inorganic nano-plugging agents. Existing inorganic nanoparticle plugging agents tend to agglomerate during use, leading to a sharp increase in particle size. Organic / inorganic nanoparticle plugging agents, due to hybridization processes during preparation, result in particles that lose their nanoscale size. Therefore, synthesizing a plugging agent with nanoscale dimensions would be an excellent option for sealing nanofissures in shale.

[0004] Metal-organic frameworks (MOFs) possess advantages such as high specific surface area, large porosity, and good thermal stability, making them a promising class of materials. Graphene oxide (GO) is a product obtained by oxidizing graphite. Although similar to graphene, GO contains a large number of oxygen-containing functional groups, such as carboxyl groups (COOH), hydroxyl groups (OH), and epoxy groups (COC). The addition of these oxygen-containing functional groups to hydrophobic polymer films can effectively overcome the hydrophobicity. Furthermore, the insertion of oxygen-containing groups between GO layers not only gives GO good chemical stability but also a large specific surface area, high porosity, and high adsorption capacity. Summary of the Invention

[0005] To address the problems and shortcomings of the existing technology, this invention specifically proposes a polymer plugging agent suitable for oil-based drilling fluids, its preparation method, and its application. To achieve the above-mentioned objectives, the technical solution of the present invention is as follows: Firstly, this invention discloses a polymer plugging agent suitable for oil-based drilling fluids, wherein the polymer plugging agent is composed of the following raw materials: graphene oxide, chloride hexahydrate, and 2-aminoterephthalic acid, wherein the molar ratio of chloride hexahydrate to 2-aminoterephthalic acid is 1:1-1.5, and the mass of graphene oxide is 5-10% of the total mass of chloride hexahydrate and 2-aminoterephthalic acid.

[0006] Furthermore, the hexahydrate chloride is any one of ferric chloride hexahydrate, cobalt chloride hexahydrate, and nickel chloride hexahydrate.

[0007] Based on the same inventive concept, another aspect of the present invention discloses a method for preparing a polymer plugging agent suitable for oil-based drilling fluids. The method for preparing the aforementioned plugging agent is characterized by comprising the following steps: Step S1. Take chloride hexahydrate and 2-aminoterephthalic acid according to the ratio, and then dissolve the two substances in a solvent. Stir continuously during the dissolution process until the solid is completely dissolved. Step S2. Add the activated graphene oxide powder to a mixed solution of chloride hexahydrate and 2-aminoterephthalic acid, mix evenly, and then heat-react at 150~160℃ for 6~8 hours. Step S3. After the thermal reaction is completed, cool down to room temperature, take the reaction product for solid-liquid separation and purification, and obtain the polymer blocking agent.

[0008] Further, in step S1, the solvent is N,N-dimethylformamide.

[0009] Furthermore, in step S3, the specific steps of solid-liquid separation and purification are as follows: After the product is heated and cooled to room temperature, solid-liquid separation is performed to obtain the solid phase. Then, it is washed multiple times with N,N-dimethylformamide and methanol. After washing, the solid phase is soaked in methanol for 24-30 hours. After soaking, it is dried at 60-70℃ to obtain the polymer blocking agent.

[0010] Furthermore, the preparation method further includes: Graphene oxide was placed in ultrapure water and ultrasonically dispersed, then dried in an oven to obtain activated graphene oxide.

[0011] Furthermore, the ultrasonic dispersion treatment time is 2-3 hours; the drying time is 12-16 hours, and the drying temperature is 60-70℃.

[0012] Furthermore, during ultrasonic dispersion, the mass ratio of graphite oxide to ultrapure water is 1:(1000-1125).

[0013] This invention also provides the application of the polymer plugging agent prepared by the above preparation method in the preparation of oil-based drilling fluids.

[0014] Another aspect of the present invention discloses an oil-based drilling fluid, comprising the following components by weight: 70-90 parts white oil: 0.5-1 part primary emulsifier; 1-3 parts co-emulsifier; 2-10 parts of filtration loss reducer; 2-5 parts organic soil; 0.6-6.5 parts quicklime; 10-30 parts of CaCl2 salt solution with a concentration of 20-25%; 0.5-2.1 parts wetting agent; 1-10 parts of the polymer plugging agent prepared by the method of the present invention.

[0015] Further, the white oil is No. 3 white oil; the primary emulsifier is any one of OME, HIEMUL, and HW Pmul-1; the secondary emulsifier is any one of OME-2, HICOAT, and HW Smul-1; the wetting agent is HW Wet-1; the filtration loss reducer is oxidized asphalt or HWTrol-101; and the organic clay is HW Gel-3.

[0016] This invention also provides the application of the above-mentioned oil-based drilling fluid in oil and gas reservoir drilling.

[0017] Furthermore, the application of the oil-based drilling fluid in oil and gas reservoir drilling includes the following steps: Step A. Prepare the sealing agent as described in claim 1 or 2; Step B. Prepare the oil-based drilling fluid as described in claim 10 or 11, ensuring uniform distribution of the plugging agent during the preparation process using a stirrer or circulating pump; Step C. Start the drilling fluid circulation system to circulate the drilling fluid in the wellbore, ensuring that the plugging agent in the drilling fluid is evenly distributed and reaches the lost circulation area.

[0018] The beneficial effects of this invention are: 1. The plugging agent of this invention can effectively seal micro- and nano-fractures in shale formations, effectively preventing drilling fluid from invading the formation, reducing damage to the formation, ensuring smooth drilling operations, and maintaining formation stability. Furthermore, at a dosage of 3 wt%, its plugging rate in shale can reach over 95%. Simultaneously, it exhibits good compatibility with oil-based drilling fluids, and its rheological properties and stability under reservoir conditions are better than conventional nano-plugging agents. It maintains good performance in complex underground environments, ensuring that the drilling fluid functions properly during circulation and cuttings carrying, thus improving drilling efficiency and quality and reducing downhole accidents. 2. This invention selects one of ferric chloride hexahydrate, cobalt chloride hexahydrate, and nickel chloride hexahydrate as the metal ion source, and 2-aminoterephthalic acid as the organic ligand. The aforementioned hexahydrate chlorides provide stable metal nodes, and the specific structure of 2-aminoterephthalic acid makes it an ideal organic ligand. This combination of raw materials allows for sufficient coordination between the metal ions and the organic ligand in subsequent reactions, forming a stable and ordered MOF framework. The high specific surface area and high porosity of MOFs provide a large number of adsorption sites and an efficient pore structure for the plugging agent, which helps it play a key role in the plugging of micro- and nano-fractures in shale formations.

[0019] 3. In this invention, chloride hexahydrate and 2-aminoterephthalic acid are dissolved in N,N-dimethylformamide to obtain the corresponding solutions. N,N-dimethylformamide, as an excellent solvent, not only uniformly disperses the raw materials but also provides a suitable chemical environment for the coordination reaction between metal ions and organic ligands in subsequent reactions, promoting the smooth progress of the reaction and ensuring the orderly growth of MOF structures.

[0020] 4. In this invention, the 2-aminoterephthalic acid solution is added dropwise to the chloride solution and mixed thoroughly. This process strictly controls the initial reaction conditions and the contact mode of the reactants. Under continuous stirring, the metal ions and organic ligands can fully contact and undergo coordination reactions, gradually constructing the framework structure of MOFs. This precisely controlled mixing reaction process helps to form structurally regular and stable MOFs, thereby improving the overall performance of the plugging agent.

[0021] 5. This invention involves ultrasonically dispersing and activating graphene oxide by placing it in ultrapure water for 2-3 hours and then drying it at 60℃-70℃ for 12-16 hours to obtain activated graphene oxide. This process not only achieves the transformation of graphene oxide into graphene oxide but also enables it to function better in subsequent reactions. Furthermore, the activated graphene oxide, when dispersed in a solvent, provides a good dispersion for its composite with metal-organic frameworks (MOFs).

[0022] 6. In this invention, the solvothermal reaction is carried out at a temperature of 150℃-160℃ for 6-8 hours. This specific reaction condition helps to further improve and stabilize the MOF structure. Under the high temperature and high pressure solvothermal environment, the crystal structure of MOFs can become more regular and internal defects can be reduced, thereby improving their physical and chemical properties. At the same time, this process also promotes the interaction between graphene oxide and MOFs, enabling them to better fuse and form a higher-performance organic-inorganic blocking agent.

[0023] 7. The separation and purification steps of this invention can further improve the quality of the organic-inorganic plugging agent. The product after the solvothermal reaction and cooling to room temperature undergoes solid-liquid separation. The solid phase is then washed multiple times with N,N-dimethylformamide and methanol, and then soaked in methanol for 24-30 hours. Finally, it is dried at 60-70°C to obtain the organic-inorganic plugging agent. This series of separation and purification steps effectively removes residual impurities and unreacted raw materials from the reaction process, improving the purity and quality of the plugging agent. Washing and soaking remove surface-adsorbed impurities, optimizing the surface properties of the plugging agent; the drying process makes the structure of the plugging agent more stable, ensuring that it can fully exert its excellent plugging performance in practical applications. Attached Figure Description

[0024] The foregoing and hereinafter detailed description of the invention becomes clearer when read in conjunction with the following drawings, in which: Figure 1 This is a particle size distribution diagram of the polymer plugging agent suitable for oil-based drilling fluid in Example 1 of the present invention; Figure 2 This is a particle size distribution diagram of the polymer plugging agent suitable for oil-based drilling fluid in Example 2 of the present invention; Figure 3 This is a particle size distribution diagram of the polymer plugging agent suitable for oil-based drilling fluid in Example 3 of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions of this invention, several specific embodiments will be used to further illustrate the technical solutions for achieving the objectives of this invention. It should be noted that the technical solutions claimed by this invention include, but are not limited to, the following embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort should fall within the scope of protection of this invention.

[0026] Example 1 This embodiment discloses a method for preparing a polymer plugging agent suitable for oil-based drilling fluids, the preparation method comprising the following steps: Weigh 15 mg of graphene oxide and measure 16 mL of ultrapure water. Mix the graphene oxide and ultrapure water, then perform ultrasonic dispersion treatment for 2.2 h and dry at 60 °C for 12 h to obtain activated graphene oxide. Next, 0.35 g of ferric chloride hexahydrate and 0.25 g of 2-aminoterephthalic acid were weighed and mixed with 10 mL of N,N-dimethylformamide until the solids were completely dissolved. Then, 0.03 g of activated graphene oxide powder was weighed and uniformly dispersed in the aforementioned solution. The mixture was then transferred to a polytetrafluoroethylene-lined stainless steel autoclave, sealed, and heated at 152 °C for 6 h. After cooling to 25 °C, the product was subjected to solid-liquid separation. The solid phase from the solid-liquid separation was collected and washed three times each with N,N-dimethylformamide and methanol. Finally, the washed sample was dried at 60 °C for 25 h to prepare the No. 1 plugging agent. The particle size distribution of the prepared No. 1 plugging agent is as follows: Figure 1 As shown.

[0027] Example 2 This embodiment provides a polymer plugging agent suitable for oil-based drilling fluids, the preparation method of which includes the following steps: Weigh 19 mg of graphene oxide and measure 20 mL of ultrapure water. Mix the graphene oxide and ultrapure water, then ultrasonically disperse for 2.8 h and dry at 68 °C for 15 h to obtain activated graphene oxide. Next, 0.48 g of cobalt chloride hexahydrate and 0.45 g of 2-aminoterephthalic acid were weighed and mixed with 18 mL of N,N-dimethylformamide until the solids were completely dissolved. Then, 0.07 g of activated graphene oxide powder was weighed and uniformly dispersed in the aforementioned solution. The mixture was then transferred to a PTFE-lined stainless steel autoclave, sealed, and heated at 158 ​​°C for 8 h. After cooling to 22 °C, the product was subjected to solid-liquid separation. The solid phase from the solid-liquid separation was collected and washed five times each with N,N-dimethylformamide and methanol. Finally, the washed sample was dried at 68 °C for 28 h to prepare the No. 2 plugging agent. The particle size distribution of the prepared No. 2 plugging agent is shown in the figure. Figure 2 As shown.

[0028] Example 3 This embodiment provides a polymer plugging agent suitable for oil-based drilling fluids, the preparation method of which includes the following steps: Weigh 16 mg of graphene oxide and measure 18 mL of ultrapure water. Mix the graphene oxide and ultrapure water, then ultrasonically disperse for 2.5 h and dry at 66 °C for 13 h to obtain activated graphene oxide. Next, 0.42 g of nickel chloride hexahydrate and 0.35 g of 2-aminoterephthalic acid were weighed and mixed with 15 mL of N,N-dimethylformamide until the solids were completely dissolved. Then, 0.05 g of activated graphene oxide powder was weighed and uniformly dispersed in the aforementioned solution. The mixture was then transferred to a PTFE-lined stainless steel autoclave, sealed, and heated at 155 °C for 7 h. After cooling to 28 °C, the product was subjected to solid-liquid separation. The solid phase from the solid-liquid separation was collected and washed four times each with N,N-dimethylformamide and methanol. Finally, the washed sample was dried at 66 °C for 26 h to prepare the No. 3 plugging agent. The particle size distribution of the prepared No. 3 plugging agent is shown in the figure. Figure 3 As shown.

[0029] Example 4 This embodiment provides a polymer plugging agent suitable for oil-based drilling fluids, the preparation method of which includes the following steps: Weigh 15 mg of graphene oxide and measure 15 mL of ultrapure water. Mix the graphene oxide and ultrapure water, disperse them by ultrasonication for 2 h, and dry them at 60 °C for 16 h to obtain activated graphene oxide.

[0030] Weigh 0.27 g of ferric chloride hexahydrate and 0.18 g of 2-aminoterephthalic acid, and mix the two substances with 8 mL of N,N-dimethylformamide until the solid is completely dissolved. Then weigh 0.0225 g of activated graphene oxide powder and uniformly disperse it in the above solution. Next, transfer the mixture to a polytetrafluoroethylene-lined stainless steel autoclave, seal it, and heat it at 150 °C for 8 h. After cooling to 25 °C, perform solid-liquid separation on the product, take the solid phase from the solid-liquid separation, and then wash it three times each with N,N-dimethylformamide and methanol. Finally, dry the washed sample at 70 °C for 24 h to prepare the No. 4 sealing agent.

[0031] Example 5 This embodiment provides a polymer plugging agent suitable for oil-based drilling fluids, the preparation method of which includes the following steps: Weigh 20 mg of graphene oxide and measure 20 mL of ultrapure water. Mix the graphene oxide and ultrapure water, disperse by ultrasonication for 2 h, and dry at 60 °C for 16 h to obtain activated graphene oxide.

[0032] Weigh 0.5 g of ferric chloride hexahydrate and 0.5 g of 2-aminoterephthalic acid, and mix the two substances with 15 mL of N,N-dimethylformamide until the solid is completely dissolved. Then weigh 0.1 g of activated graphene oxide powder and uniformly disperse it in the above solution. Next, transfer the mixture to a polytetrafluoroethylene-lined stainless steel autoclave, seal it, and heat it at 160 °C for 6 h. After cooling to 28 °C, perform solid-liquid separation on the product, take the solid phase from the solid-liquid separation, and then wash it three times each with N,N-dimethylformamide and methanol. Finally, dry the washed sample at 70 °C for 30 h to prepare the No. 5 sealing agent.

[0033] Example 6 This embodiment provides a drilling fluid, which is prepared as follows: (1) Preparation of base slurry: Weigh 1.80g of primary emulsifier HW Pmul-1, 4.50g of secondary emulsifier HWSmul-1, and 2.40g of wetting agent HW Wet-1 directly into a high-speed stirring cup; measure 240mL of No. 3 white oil into the high-speed stirring cup, place the high-speed stirring cup on a high-speed mixer, and stir at 12000rpm for 10min; weigh 9g of organo-soil HW Gel-3 using cellophane, and slowly add organo-soil HW Gel-3 into the high-speed stirring cup while stirring at high speed to prevent splashing, and stir at high speed for 10min; while stirring at high speed, measure 60mL of 25% CaCl2. Add the aqueous solution to the high-speed stirring cup to prevent splashing, and stir at high speed for 10 minutes; while stirring at high speed, slowly add 9g of quicklime HW-pH to the high-speed stirring cup, and stir at high speed for 10 minutes; while stirring at high speed, slowly add 24g of filtration agent HW Trol-101 ​​to the high-speed stirring cup, and stir for 10 minutes to prepare the base slurry.

[0034] (2) Preparation of drilling fluid: Based on the base slurry prepared above, 10g of the polymer plugging agent prepared in any of the above Examples 1-5 is slowly added to the high-stirring cup under high stirring conditions and stirred for 10min, during which the high-stirring cup is removed and the wall is scraped; under high stirring conditions, 10g of barite is slowly added to the high-stirring cup, the liquid density is adjusted, and stirring is continued for 30min, during which the high-stirring cup is removed and the wall is scraped again, and finally the drilling fluid is prepared.

[0035] Example 7 This embodiment provides a drilling fluid, which is prepared as follows: (1) Preparation of base slurry: Weigh 1.00g of primary emulsifier HW Pmul-1, 3.00g of auxiliary emulsifier HWSmul-1, and 2.10g of wetting agent HW Wet-1 directly into a high-speed stirring cup; measure 90mL of No. 3 white oil into the high-speed stirring cup, place the high-speed stirring cup on a high-speed stirrer, and stir at 12000rpm for 10min; weigh 5g of organo-soil HW Gel-3 using cellophane, and slowly add the organo-soil HW Gel-3 to the high-speed stirring cup while stirring at high speed to prevent splashing, and stir for 10min; while stirring at high speed, measure 30mL of 25% CaCl2 aqueous solution into the high-speed stirring cup while stirring at high speed to prevent splashing, and stir for 10min; while stirring at high speed, slowly add 6.5g of quicklime HW-pH to the high-speed stirring cup, and stir for 10min; while stirring at high speed, add 10g of filtrate HW... Trol-101 ​​was slowly added to a high-speed stirring cup and stirred for 10 minutes to prepare the base slurry.

[0036] (2) Preparation of drilling fluid Based on the base slurry prepared above, 40g of the polymer plugging agent prepared in any of the above Examples 1-5 is slowly added to the high-stirring cup under high stirring conditions and stirred for 10 minutes. During this period, the high-stirring cup is removed and the wall is scraped. Under high stirring conditions, 40g of barite is slowly added to the high-stirring cup to adjust the liquid density and continue stirring for 30 minutes. During this period, the high-stirring cup is removed and the wall is scraped again to finally obtain the drilling fluid.

[0037] Example 8 Based on the preparation method of Example 6, 14 portions of base slurry were first prepared, and the amounts of the 14 portions of base slurry were the same.

[0038] First, take out one portion of the base slurry and, under high-speed stirring (12000 rpm), slowly add the calculated amount of barite into the agitator and continue stirring for 30 minutes. During this time, remove the agitator and scrape the wall to finally prepare the corresponding No. 0 drilling fluid.

[0039] Further, take three portions of base slurry. Under high-speed stirring, add 2% of No. 1 plugging agent to one portion, 2% of No. 2 plugging agent to another portion, and 2% of No. 3 plugging agent to the remaining portion. After adding the plugging agents, stir for 10 minutes, scraping the walls of the stirrer during this time. Then, under high-speed stirring, slowly add the calculated amount of barite to each of the three solutions to adjust the density of the liquid to the design value. Continue stirring for 30 minutes, removing the stirrer and scraping the walls again during this time. Finally, the corresponding drilling fluids, namely Drilling Fluid No. 4, Drilling Fluid No. 5, and Drilling Fluid No. 6, are prepared.

[0040] Furthermore, take three portions of base slurry. Under high-speed stirring, add 3% of No. 1 plugging agent to one portion, 3% of No. 2 plugging agent to another portion, and 3% of No. 3 plugging agent to the remaining portion. After adding the plugging agents, stir for 10 minutes, scraping the walls of the stirrer during this time. Then, under high-speed stirring, slowly add the calculated amount of barite to each of the three solutions to adjust the density of the liquid to the design value. Continue stirring for 30 minutes, removing the stirrer and scraping the walls again during this time. Finally, the corresponding drilling fluids, namely Drilling Fluid No. 7, Drilling Fluid No. 8, and Drilling Fluid No. 9, are prepared.

[0041] Furthermore, three portions of the base slurry were taken. Under high-speed stirring, 4% of No. 1 plugging agent was added to one portion, 4% of No. 2 plugging agent was added to another portion, and 4% of No. 3 plugging agent was added to the remaining portion. After adding the plugging agents, the mixture was stirred for 10 minutes, during which time the walls of the agitator were scraped. Then, under high-speed stirring, the calculated amount of barite was slowly added to each of the three solutions to adjust the density of the liquid to the design value. The mixture was then stirred for another 30 minutes, during which time the agitator was removed and the walls were scraped again. Finally, the corresponding drilling fluids, namely Drilling Fluid No. 10, Drilling Fluid No. 11, and Drilling Fluid No. 12, were prepared.

[0042] Take the last remaining portion of base slurry, add the commonly used plugging material MB-1 (a rigid plugging material mainly composed of barium sulfate) under high-speed stirring, stir for 10 minutes, and scrape the wall of the stirrer during the process; then, under high-speed stirring, slowly add the calculated amount of barite to the solution to adjust the density of the liquid to the design value, and then continue stirring for 30 minutes, during which the stirrer is removed and the wall is scraped again, and finally the corresponding drilling fluid, namely drilling fluid No. 13, is obtained.

[0043] In this embodiment of the invention, the pH of the prepared oil-based drilling fluid is typically 8.5 to 11.5; and the density of the oil-based drilling fluid is typically 1.30 to 2.10 g / cm³. 3 .

[0044] To further illustrate the effects of the polymer plugging agent and oil-based drilling fluid prepared in this invention, the performance of 14 portions of oil-based drilling fluid prepared in this embodiment and the polymer plugging agent prepared in Examples 1-3 were tested below.

[0045] (1) Particle size test The particle size of the polymer blocking agents prepared in Examples 1-3 was measured using a BI-200SM laser scattering instrument manufactured by Brookhaven Instruments, Inc., USA. The particle size test results for the three examples are as follows: Figure 1 , Figure 2 , Figure 3As shown in the particle size diagram above, the polymer plugging agent prepared by the present invention has a particle size of nano-micron size, and is roughly distributed between 70-1470 nm. This particle size has a high degree of matching with the nano-micron level crack size in shale, and can effectively plug it.

[0046] (2) Artificial core sealing experiment Drilling fluids No. 0-12 prepared in Example 8 were used to test their sealing effect on artificial core samples. Details are as follows: Artificial cores were used to simulate nano- and micro-fractured formations. The average flow rate of the drilling fluid system in the artificial cores was measured. The permeability of the artificial cores before and after the addition of the polymer plugging agent was calculated using the Darcy formula: K = Qμl / (AΔP). The plugging rate of the polymer plugging agent on the artificial cores was then calculated. The test results are shown in Table 1 below.

[0047] Table 1 Test data on the sealing performance of artificial cores As shown in the table above, the polymer plugging agent prepared based on this invention, when used as a drilling fluid plugging agent, can effectively reduce mud cake permeability. Furthermore, when the amount of plugging agent added is 1%, the permeability of the mud cake decreases by 77.32%, 77.56%, and 77.80%, respectively. The plugging effect is better with increasing polymer plugging agent dosage, reaching its optimal effect at 3%, with plugging rates of 94.88%, 95.12%, and 94.88%, respectively. However, when the dosage exceeds 3%, the decrease in mud cake permeability becomes almost negligible. The polymer plugging agent of this invention has a particularly good plugging effect on low-permeability oil and gas reservoirs, and the plugging effect is best when the amount of polymer plugging agent added is 3%.

[0048] (3) Performance testing of oil-based drilling fluids Drilling fluids No. 0-3 and No. 13 prepared in Example 8 were hot-rolled at 150°C for 16 hours, and their rheological properties were measured. The results are shown in Table 2 below.

[0049] Table 2 Performance parameters of oil-based drilling fluids As shown in the table above, the drilling fluids formed by adding the plugging agents prepared in Examples 1, 2, and 3 to the base slurry exhibit excellent rheological properties, with viscosity and shear stress meeting the requirements of field drilling. Furthermore, as the amount of polymer plugging agent increases, the viscosity of the oil-based drilling fluid increases, but the change is not significant, and the shear stress remains stable, indicating that the plugging agent has good compatibility with the oil-based drilling fluid. The filtration loss of the drilling fluid decreases with increasing addition of the metal-organic framework-based graphene oxide polymer plugging agent, demonstrating excellent plugging performance. In addition, compared with the performance of oil-based drilling fluids using rigid plugging material MB-1 as a plugging agent, the performance of the oil-based drilling fluids from all examples is lower in terms of API and high-temperature, high-pressure filtration loss. Therefore, the oil-based drilling fluids formulated with the polymer plugging agent synthesized in this invention have better performance.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to hinder the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A polymer plugging agent suitable for oil-based drilling fluids, characterized in that, The sealing agent is composed of the following raw materials: graphene oxide, chloride hexahydrate and 2-aminoterephthalic acid, wherein the molar ratio of chloride hexahydrate and 2-aminoterephthalic acid is 1:1-1.5, and the mass of graphene oxide is 5-10% of the total mass of chloride hexahydrate and 2-aminoterephthalic acid.

2. The polymer plugging agent suitable for oil-based drilling fluids according to claim 1, characterized in that, The hexahydrate chloride is any one of ferric chloride hexahydrate, cobalt chloride hexahydrate, and nickel chloride hexahydrate.

3. A method for preparing a polymer plugging agent suitable for oil-based drilling fluids, the method being used to prepare the plugging agent according to any one of claims 1-2, characterized in that, Includes the following steps: Step S1. Take chloride hexahydrate and 2-aminoterephthalic acid according to the ratio, and then dissolve the two substances in a solvent. Stir continuously during the dissolution process until the solid is completely dissolved. Step S2. Add the activated graphene oxide powder to a mixed solution of chloride hexahydrate and 2-aminoterephthalic acid, mix evenly, and then heat-react at 150~160℃ for 6~8 hours. Step S3. After the thermal reaction is completed, cool down to room temperature, take the reaction product for solid-liquid separation and purification, and obtain the polymer blocking agent.

4. The method for preparing a polymer plugging agent suitable for oil-based drilling fluids according to claim 3, characterized in that, In step S1, the solvent is N,N-dimethylformamide.

5. A method for preparing a polymer plugging agent suitable for oil-based drilling fluids according to claim 3, characterized in that, In step S3, the specific steps of solid-liquid separation and purification are as follows: After the product is heated and cooled to room temperature, solid-liquid separation is performed to obtain the solid phase. Then, it is washed multiple times with N,N-dimethylformamide and methanol. After washing, the solid phase is soaked in methanol for 24-30 hours. After soaking, it is dried at 60-70℃ to obtain the polymer blocking agent.

6. A method for preparing a polymer plugging agent suitable for oil-based drilling fluids according to claim 3, characterized in that, The method further includes: Graphene oxide was placed in ultrapure water and ultrasonically dispersed, then dried in an oven to obtain activated graphene oxide.

7. A method for preparing a polymer plugging agent suitable for oil-based drilling fluids according to claim 6, characterized in that, The ultrasonic dispersion treatment takes 2-3 hours; the drying time is 12-16 hours, and the drying temperature is 60-70℃.

8. A method for preparing a polymer plugging agent suitable for oil-based drilling fluids according to claim 6, characterized in that, During ultrasonic dispersion, the mass ratio of graphite oxide to ultrapure water is 1:(1000-1125).

9. The application of a polymer plugging agent suitable for oil-based drilling fluids according to claim 1 or 2 in the preparation of oil-based drilling fluids.

10. An oil-based drilling fluid, characterized in that, By weight, it comprises the following components: 70-90 parts white oil: 0.5-1 part primary emulsifier; 1-3 parts co-emulsifier; 2-10 parts of filtration loss reducer; 2-5 parts organic soil; 0.6-6.5 parts quicklime; 10-30 parts of CaCl2 salt solution with a concentration of 20-25%; 0.5-2.1 parts wetting agent; 1-10 parts of the polymer plugging agent as described in claim 1 or 2.

11. The oil-based drilling fluid according to claim 10, characterized in that, The white oil is No. 3 white oil; the primary emulsifier is any one of OME, HIEMUL, and HW Pmul-1; the secondary emulsifier is any one of OME-2, HICOAT, and HWSmul-1; the wetting agent is HW Wet-1; the filtration loss reducer is oxidized asphalt or HWTrol-101; and the organic soil is HW Gel-3.

12. The application of the oil-based drilling fluid according to claim 10 or 11 in oil and gas reservoir drilling.

13. The application of the oil-based drilling fluid according to claim 12 in oil and gas reservoir drilling, characterized in that, Includes the following steps: Step A. Prepare the sealing agent as described in claim 1 or 2; Step B. Prepare the oil-based drilling fluid as described in claim 10 or 11, ensuring uniform distribution of the plugging agent during the preparation process using a stirrer or circulating pump; Step C. Start the drilling fluid circulation system to circulate the drilling fluid in the wellbore, ensuring that the plugging agent in the drilling fluid is evenly distributed and reaches the lost circulation area.

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