Carbon nanotube grafted polymer nanoplugging agent, preparation method thereof and drilling fluid prepared from the agent

Abstract

The application provides a carbon nanotube grafted polymer nano plugging agent, a preparation method thereof and a prepared drilling fluid, and the preparation method comprises the following steps: S1, reacting acrylic acid and amino functionalized multi-walled carbon nanotubes in a mass ratio of 1:0.1-0.2 to generate acrylic acid modified carbon nanotubes; and S2, performing a copolymerization reaction on acrylamide, the acrylic acid modified carbon nanotubes and octadecyl dimethyl allyl ammonium chloride in a mass ratio of 25:0.2-0.8:1.2-2.0 to obtain the carbon nanotube grafted polymer nano plugging agent. The carbon nanotube grafted polymer nano plugging agent comprises an amide group, a quaternary ammonium salt structure and an amino group, enhances the micro-nano plugging capacity of the plugging agent, enhances the inhibition capacity of the plugging agent to the hydration expansion and dispersion of formation mud shale, and has good temperature resistance, salt resistance and dispersion stability.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemicals in the petroleum industry, specifically relating to a carbon nanotube-grafted polymer nano-plugging agent, its preparation method, and the drilling fluid prepared therefrom. Background Technology

[0002] Shale gas is a clean and efficient new energy resource, but its shale reservoirs are prone to hydration. To effectively address wellbore instability induced by shale hydration expansion and dispersion, plugging agents are needed. Shale reservoirs typically exhibit low porosity (<10%), and these pores are mostly nanoscale. Existing drilling fluid plugging agents mainly include bituminous, paraffinic, polyol-based, and mineral materials. These plugging agents cannot achieve particle sizes below the micrometer level, making them ineffective for sealing formations with micropores and microfractures, especially mudstone and shale formations. Therefore, developing nanoscale plugging agents is crucial in shale gas drilling.

[0003] Carbon nanotubes (CNTs) possess excellent rheological, mechanical, and thermal properties, making them suitable as plugging agents in water-based drilling fluids to control reservoir filtration. However, CNTs are prone to coiling and aggregation, and the high-temperature, high-salinity environment of shale reservoirs further exacerbates this aggregation tendency. Therefore, the poor stability of CNT-based nanocolloid solutions limits their application in oil and gas fields. Adding surfactants and stabilizers, such as polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyacrylic acid, and nonionic surfactants, can improve the stability of CNTs in saline environments. However, the interaction between these chemicals and CNTs is relatively weak, making it difficult to achieve long-term stability of CNTs under high-temperature and high-salinity conditions.

[0004] Some existing technologies organically combine multi-walled carbon nanotubes (MWCNTs) with polymers, improving the plugging and dispersibility of MWCNTs. For example, CN109825263A discloses a nano-plugging agent for water-based drilling fluids, its preparation method, and drilling fluid, achieving uniform dispersion at the nanoscale in the drilling fluid with good plugging effect, effectively sealing micro and nano-sized pores in shale well walls. However, currently, there are few types of nano-plugging agents, and none possess both good shale inhibition properties.

[0005] Therefore, there is an urgent need to invent a carbon nanotube-grafted polymer nanoplugging agent that maintains good dispersion stability under high temperature and high salinity conditions, so as to meet the inhibition, plugging and environmental protection requirements of water-based drilling fluids during shale reservoir drilling. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a carbon nanotube-grafted polymer nano-plugging agent, its preparation method, and the drilling fluid prepared therefrom, so as to improve the dispersion stability of the nano-plugging agent under high temperature and high salinity environments, and to achieve shale inhibition and micro / nanopore plugging.

[0007] To achieve the above objectives, the present invention provides a method for preparing a carbon nanotube-grafted polymer nano-blocking agent, comprising the following steps:

[0008] S1: React acrylic acid with amino-functionalized multi-walled carbon nanotubes to generate acrylic acid-modified carbon nanotubes; wherein the mass ratio of acrylic acid to amino-functionalized multi-walled carbon nanotubes is 1:0.1-0.2.

[0009] S2: Acrylamide, the acrylic acid-modified carbon nanotubes, and octadecyl dimethyl allyl ammonium chloride are copolymerized to obtain the carbon nanotube grafted polymer nano-blocking agent; wherein the mass ratio of acrylamide, the acrylic acid-modified carbon nanotubes, and octadecyl dimethyl allyl ammonium chloride is 25:0.2-0.8:1.2-2.0, preferably 25:0.3-0.6:1.4-1.8.

[0010] This invention uses a chemical method to graft amino-functionalized multi-walled carbon nanotubes onto polymer molecules, resulting in a nano-plugging agent that exhibits good dispersion stability, salt resistance, shale inhibition, and plugging properties in drilling fluids.

[0011] The preparation of the carbon nanotube grafted polymer nanoblocking agent of the present invention is carried out in two steps. The first step is to react acrylic acid with amino-functionalized multi-walled carbon nanotubes (CNT-NH2) to generate acrylic acid-modified carbon nanotubes (CNT-AA). The second step is to synthesize the grafted carbon nanotube polymer (CNT-HPAM) by using acrylamide, acrylic acid-modified carbon nanotubes (CNT-AA) and octadecyl dimethyl allyl ammonium chloride as polymerizing monomers via aqueous solution monomer copolymerization.

[0012] The reactive synthesis route of acrylic acid modified carbon nanotubes (CNT-AA) in S1 of this invention is as follows:

[0013]

[0014] The reaction synthesis route of the carbon nanotube-grafted polymer nanoblocking agent (CNT-HPAM) in S2 of this invention is as follows:

[0015]

[0016] According to a specific embodiment of the present invention, preferably, step S1 of the preparation method of the above-mentioned carbon nanotube grafted polymer nanoblocking agent includes the following steps:

[0017] (1) Amino-functionalized multi-walled carbon nanotubes (CNT-NH2) and sodium dodecyl sulfate (SDS) were added to N,N-dimethylformamide (DMF) and ultrasonically dispersed to obtain carbon nanotube solution A;

[0018] (2) Add acrylic acid and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) to N,N-dimethylformamide (DMF), add hydrochloric acid dropwise to adjust the pH of the solution to 4-6, stir thoroughly to dissolve, and obtain acrylic acid solution B;

[0019] (3) The carbon nanotube solution A and the acrylic acid solution B are mixed and reacted to obtain a solid product, which is then filtered and washed to obtain the acrylic acid modified carbon nanotubes (CNT-AA).

[0020] According to a specific embodiment of the present invention, preferably, in S1, the mass ratio of amino-functionalized multi-walled carbon nanotubes, acrylic acid, sodium dodecyl sulfate, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 0.1-0.2:1:0.1-0.4:0.05-0.1.

[0021] According to a specific embodiment of the present invention, preferably, the reaction temperature of step (3) is 0-5℃ and the reaction time is 8-10h.

[0022] According to a specific embodiment of the present invention, preferably, the dissolution process in step (2) is carried out at 0-5°C.

[0023] According to a specific embodiment of the present invention, preferably, the reagent used for washing in step (3) is ethanol.

[0024] According to a specific embodiment of the present invention, preferably, step S2 of the preparation method of the carbon nanotube-grafted polymer nano-blocking agent includes the following steps:

[0025] (4) Acrylamide (AM), the acrylic acid-modified carbon nanotubes (CNT-AA), and octadecyl dimethyl allyl ammonium chloride (C 18 DMAAC was dissolved in water, its pH was adjusted to 8-10, nitrogen gas was introduced and ultrasonic dispersion was performed to obtain a dispersion.

[0026] (5) Add an initiator to the dispersion, continue to purge with nitrogen and stir until the solution viscosity increases; then stop stirring and purge with nitrogen, and continue the reaction to obtain a reaction solution;

[0027] (6) The reaction solution is heated and an alkaline solution is added to carry out a hydrolysis reaction to obtain a gel product. After washing and drying, the carbon nanotube grafted polymer nanoblocking agent (CNT-HPAM) is obtained.

[0028] According to a specific embodiment of the present invention, preferably, in S2, the initiator is a mixture of potassium persulfate (K2S2O8) and sodium bisulfite (NaHSO3).

[0029] According to a specific embodiment of the present invention, preferably, in S2, the mass ratio of potassium persulfate, sodium bisulfite and acrylamide is 0.03-0.06:0.06-0.1:25.

[0030] According to a specific embodiment of the present invention, preferably, the reaction time in step (5) is 4-6 hours.

[0031] According to a specific embodiment of the present invention, preferably, in step (6), the reaction solution is heated to 70-90°C and the hydrolysis reaction time is 4-6 hours.

[0032] According to a specific embodiment of the present invention, preferably, in step (6), the alkaline solution is sodium hydroxide and / or sodium carbonate.

[0033] According to a specific embodiment of the present invention, preferably, in step (6), the washing reagent is acetone.

[0034] According to a specific embodiment of the present invention, preferably, in step (6), the drying conditions are: drying at 60-80℃ for 10-15 hours.

[0035] The present invention also provides a carbon nanotube-grafted polymer nanoblocking agent, which is obtained by the above-mentioned preparation method of carbon nanotube-grafted polymer nanoblocking agent.

[0036] According to a specific embodiment of the present invention, preferably, the particle size distribution of the carbon nanotube-grafted polymer nanoblocking agent is between 16-451 nm.

[0037] The nano-blocking agent in this invention has a wider particle size distribution, ranging from 16-451 nm, which can block pores of more sizes in shale formations.

[0038] The present invention also provides a water-based drilling fluid containing the above-mentioned carbon nanotube grafted polymer nano-plugging agent.

[0039] Preferably, in the above-mentioned water-based drilling fluid, the raw materials of the water-based drilling fluid, by mass percentage (based on the total mass of the drilling fluid), include: 0.5-3% of the carbon nanotube grafted polymer nano-plugging agent, 0.5-1.5% of bentonite, 0.5-1.5% of the thickener, 1.0-2.0% of the filtration loss reducer, 0.5-1.5% of the pH adjuster, 2.0-4.0% of the lubricant, and the balance being water.

[0040] Preferably, the raw materials of the aforementioned water-based drilling fluid also include a weighting agent, and the density of the water-based drilling fluid with added weighting agent is 1.2-2.0 g / cm³. 3 .

[0041] When the carbon nanotube-grafted polymer nano-plugging agent of this invention is combined with drilling fluid chemical products such as water, bentonite, thickeners, filtration reducers, pH adjusters, lubricants, and weighting agents to form a water-based drilling fluid, it exhibits excellent plugging ability, good compatibility, strong inhibition, and is non-toxic and harmless, meeting environmental protection requirements. This invention investigated the compatibility of the nano-plugging agent with other drilling fluid materials, and the resulting water-based drilling fluid demonstrated excellent performance and good plugging effect.

[0042] The technical solution provided by this invention has the following beneficial effects:

[0043] Compared to commercially available amino-functionalized multi-walled carbon nanotubes and ordinary fiber plugging agents, the carbon nanotube-grafted polymer nanoplugging agent of this invention contains amide groups, quaternary ammonium salt structures, and amino groups. This enhances the micro / nano plugging capability of the agent while simultaneously strengthening its ability to inhibit hydration swelling and dispersion in formation mudstone and shale, and also exhibits good temperature and salt resistance and dispersion stability. In some specific embodiments, the nanoplugging agent of this invention can remain stable for 28 days in saturated brine and simulated formation water environments at 120°C. Attached Figure Description

[0044] Figure 1 Infrared spectra of the three nanomaterials CNT-NH2, CNT-AA-1, and CNT-HPAM-1 in Example 1 were obtained.

[0045] Figure 2 The changes in zeta potential of the CNT-HPAM-2 material in Example 2 after it was added to three solutions: deionized water, saturated brine, and simulated formation water. Detailed Implementation

[0046] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0047] Example 1

[0048] This embodiment provides a carbon nanotube-grafted polymer nanoblocking agent, the preparation method of which is as follows:

[0049] (1) Measure 40 ml of DMF solvent, add 0.1 g CNT-NH2 and 0.4 g SDS, stir and ultrasonically disperse for 2 h to obtain solution A; (2) Measure 20 ml of DMF solvent, add 1.0 g acrylic acid and 0.1 g EDC·HCl, add 1 M dilute hydrochloric acid to adjust the pH of the solution to 4, stir in an ice-water bath at 0-5℃ for 3 h to fully dissolve it to obtain solution B; (3) Mix the above solutions A and B, stir in an ice-water bath at 0-5℃ for 10 h, filter, wash several times with anhydrous ethanol, dry to obtain acrylic acid modified carbon nanotubes CNT-AA-1; (4) In a three-necked flask, add 25.0 g AM, 0.2 g CNT-AA-1 and 1.2 g C 18 DMAAC was completely dissolved in 100ml of deionized water. An appropriate amount of Na2CO3 was added to adjust the pH of the solution to 8. Nitrogen gas was introduced, and the solution was stirred at 40℃ and ultrasonically dispersed for 2h. (5) 0.06g K2S2O8 and 0.1g NaHSO3 were added, and nitrogen gas was introduced and stirred until the viscosity of the solution increased significantly. Stirring was stopped, nitrogen gas was stopped, and the reaction continued for 6h. (6) The temperature was raised to 85℃, and a mixture of NaOH and Na2CO3 was used for hydrolysis for 4h to obtain a black gel product. The product was granulated and washed repeatedly with acetone until a black solid precipitated. After drying at 70℃ for 12h, carbon nanotube grafted polymer nano-blocking agent CNT-HPAM-1 was obtained.

[0050] Example 2

[0051] This embodiment provides a carbon nanotube-grafted polymer nanoblocking agent, the preparation method of which is as follows:

[0052] (1) Measure 40 ml of DMF solvent, add 0.1 g CNT-NH2 and 0.2 g SDS, stir and ultrasonically disperse for 2 h to obtain solution A; (2) Measure 20 ml of DMF solvent, add 1.0 g acrylic acid and 0.07 g EDC·HCl, add 1 M dilute hydrochloric acid to adjust the pH of the solution to 5, stir in an ice-water bath at 0-5℃ for 3 h to fully dissolve it to obtain solution B; (3) Mix the above solution A and solution B, stir in an ice-water bath at 0-5℃ for 10 h, filter, wash several times with anhydrous ethanol, and dry to obtain acrylic acid modified carbon nanotubes CNT-AA-2; (4) In a three-necked flask, add 25.0 g AM, 0.5 g CNT-AA-2 and 1.6 g C 18DMAAC was completely dissolved in 100ml of deionized water. An appropriate amount of Na2CO3 was added to adjust the pH of the solution to 9. Nitrogen gas was passed through, and the solution was stirred at 40℃ and ultrasonically dispersed for 2h. (5) 0.04g K2S2O8 and 0.08g NaHSO3 were added, and nitrogen gas was passed through and stirred until the viscosity of the solution increased significantly. Stirring was stopped, nitrogen gas was stopped, and the reaction continued for 6h. (6) The temperature was raised to 85℃, and a mixture of NaOH and Na2CO3 was used for hydrolysis for 4h to obtain a black gel product. The product was granulated and washed repeatedly with acetone until a black solid precipitated. After drying at 70℃ for 12h, carbon nanotube grafted polymer nano-blocking agent CNT-HPAM-2 was obtained.

[0053] Example 3

[0054] This embodiment provides a carbon nanotube-grafted polymer nanoblocking agent, the preparation method of which is as follows:

[0055] (1) Measure 40 ml of DMF solvent, add 0.1 g CNT-NH2 and 0.1 g SDS, stir and ultrasonically disperse for 2 h to obtain solution A; (2) Measure 20 ml of DMF solvent, add 1.0 g acrylic acid and 0.05 g EDC·HCl, add 1 M dilute hydrochloric acid to adjust the pH of the solution to 6, stir in an ice-water bath at 0-5℃ for 3 h to fully dissolve it to obtain solution B; (3) Mix the above solutions A and B, stir in an ice-water bath at 0-5℃ for 10 h, filter, wash repeatedly with anhydrous ethanol, and dry to obtain acrylic acid modified carbon nanotubes CNT-AA-3; (4) In a three-necked flask, add 25.0 g AM, 0.8 g CNT-AA-3 and 2.0 g C 18 DMAAC was completely dissolved in 100ml of deionized water. An appropriate amount of Na2CO3 was added to adjust the pH of the solution to 10. Nitrogen gas was introduced, and the solution was stirred at 40℃ and ultrasonically dispersed for 2h. (5) 0.03g K2S2O8 and 0.06g NaHSO3 were added, and nitrogen gas was introduced and stirred until the viscosity of the solution increased significantly. Stirring was stopped, nitrogen gas was stopped, and the reaction continued for 4h. (6) The temperature was raised to 70℃, and a mixture of NaOH and Na2CO3 was used for hydrolysis for 4h to obtain a black gel product. The product was granulated and washed repeatedly with acetone until a black solid precipitated. After drying at 70℃ for 12h, carbon nanotube grafted polymer nano-blocking agent CNT-HPAM-3 was obtained.

[0056] Example 4

[0057] This embodiment provides a carbon nanotube-grafted polymer nanoblocking agent, the preparation method of which is as follows:

[0058] (1) Measure 40 ml of DMF solvent, add 0.2 g CNT-NH2 and 0.1 g SDS, stir and ultrasonically disperse for 2 h to obtain solution A; (2) Measure 20 ml of DMF solvent, add 1.0 g acrylic acid and 0.05 g EDC·HCl, add 1 M dilute hydrochloric acid to adjust the pH of the solution to 4, stir in an ice-water bath at 0-5℃ for 3 h to fully dissolve it to obtain solution B; (3) Mix the above solution A and solution B, stir in an ice-water bath at 0-5℃ for 10 h, filter, wash repeatedly with anhydrous ethanol, and dry to obtain acrylic acid modified carbon nanotubes CNT-AA-4; (4) In a three-necked flask, add 25.0 g AM, 0.2 g CNT-AA-4 and 1.2 g C 18 DMAAC was completely dissolved in 100ml of deionized water. An appropriate amount of Na2CO3 was added to adjust the pH of the solution to 8. Nitrogen gas was introduced, and the solution was stirred at 40℃ and ultrasonically dispersed for 2h. (5) 0.03g K2S2O8 and 0.06g NaHSO3 were added, and nitrogen gas was introduced and stirred until the viscosity of the solution increased significantly. Stirring was stopped, nitrogen gas was stopped, and the reaction continued for 6h. (6) The temperature was raised to 90℃, and a mixture of NaOH and Na2CO3 was used for hydrolysis for 6h to obtain a black gel product. The product was granulated and washed repeatedly with acetone until a black solid precipitated. After drying at 70℃ for 12h, carbon nanotube grafted polymer nano-blocking agent CNT-HPAM-4 was obtained.

[0059] Example 5

[0060] This embodiment provides a carbon nanotube-grafted polymer nanoblocking agent, the preparation method of which is as follows:

[0061] (1) Measure 40 ml of DMF solvent, add 0.2 g CNT-NH2 and 0.2 g SDS, stir and ultrasonically disperse for 2 h to obtain solution A; (2) Measure 20 ml of DMF solvent, add 1.0 g acrylic acid and 0.07 g EDC·HCl, add 1 M dilute hydrochloric acid to adjust the pH of the solution to 5, stir in an ice-water bath at 0-5℃ for 3 h to fully dissolve it to obtain solution B; (3) Mix the above solution A and solution B, stir in an ice-water bath at 0-5℃ for 10 h, filter, wash several times with anhydrous ethanol, and dry to obtain acrylic acid modified carbon nanotubes CNT-AA-5; (4) In a three-necked flask, add 25.0 g AM, 0.5 g CNT-AA-5 and 1.6 g C 18DMAAC was completely dissolved in 100ml of deionized water. An appropriate amount of Na2CO3 was added to adjust the pH of the solution to 9. Nitrogen gas was introduced, and the solution was stirred at 40℃ and ultrasonically dispersed for 2h. (5) 0.04g K2S2O8 and 0.08g NaHSO3 were added, and nitrogen gas was introduced and stirred until the viscosity of the solution increased significantly. Stirring was stopped, nitrogen gas was stopped, and the reaction continued for 4h. (6) The temperature was raised to 70℃, and a mixture of NaOH and Na2CO3 was used for hydrolysis for 6h to obtain a black gel product. The product was granulated and washed repeatedly with acetone until a black solid precipitated. After drying at 70℃ for 12h, carbon nanotube grafted polymer nano-blocking agent CNT-HPAM-5 was obtained.

[0062] Example 6

[0063] This embodiment provides a carbon nanotube-grafted polymer nanoblocking agent, the preparation method of which is as follows:

[0064] (1) Measure 40 ml of DMF solvent, add 0.2 g CNT-NH2 and 0.4 g SDS, stir and ultrasonically disperse for 2 h to obtain solution A; (2) Measure 20 ml of DMF solvent, add 1.0 g acrylic acid and 0.1 g EDC·HCl, add 1 M dilute hydrochloric acid to adjust the pH of the solution to 6, stir in an ice-water bath at 0-5℃ for 3 h to fully dissolve it to obtain solution B; (3) Mix the above solutions A and B, stir in an ice-water bath at 0-5℃ for 10 h, filter, wash several times with anhydrous ethanol, and dry to obtain acrylic acid modified carbon nanotubes CNT-AA-6; (4) In a three-necked flask, add 25.0 g AM, 0.8 g CNT-AA-6 and 2.0 g C 18 DMAAC was completely dissolved in 100ml of deionized water. An appropriate amount of Na2CO3 was added to adjust the pH of the solution to 10. Nitrogen gas was introduced, and the solution was stirred at 40℃ and ultrasonically dispersed for 2h. (5) 0.06g K2S2O8 and 0.1g NaHSO3 were added, and nitrogen gas was introduced and stirred until the viscosity of the solution increased significantly. Stirring was stopped, nitrogen gas was stopped, and the reaction continued for 4h. (6) The temperature was raised to 85℃, and a mixture of NaOH and Na2CO3 was used for hydrolysis for 6h to obtain a black gel product. The product was granulated and washed repeatedly with acetone until a black solid precipitated. After drying at 70℃ for 12h, carbon nanotube grafted polymer nano-blocking agent CNT-HPAM-6 was obtained.

[0065] Example 7

[0066] This embodiment provides a water-based drilling fluid. By mass percentage, the raw materials of this water-based drilling fluid are: 0.5% of the nano-plugging agent CNT-HPAM-1 from Example 1, 0.5% bentonite, 1.5% viscosifier, 2% filtration reducer, 1% pH adjuster, 2% lubricant, an appropriate amount of weighting agent (for adjusting the density of the water-based drilling fluid), and the balance being water. The density of the water-based drilling fluid in this embodiment is 1.7 g / cm³. 3 .

[0067] The preparation method of this water-based drilling fluid is as follows:

[0068] Add bentonite to water and stir at 2500 rpm for 3 hours to fully hydrate the bentonite; then add thickener, filtration reducer, pH adjuster, lubricant, and nano-sealant CNT-HPAM-1. Finally, add weighting agent to adjust the drilling fluid density. After mixing evenly, water-based drilling fluid C1 is obtained.

[0069] Example 8

[0070] This embodiment provides a water-based drilling fluid. By mass percentage, the raw materials of the water-based drilling fluid are: 2% of the nano-plugging agent CNT-HPAM-1 from Example 1, 1% bentonite, 1% thickener, 1.5% filtration reducer, 1% pH adjuster, 2% lubricant, an appropriate amount of weighting agent (for adjusting the density of the water-based drilling fluid), and the balance being water.

[0071] The density and preparation method of the water-based drilling fluid in this embodiment are the same as those in Example 7. This water-based drilling fluid is designated as C2.

[0072] Example 9

[0073] This embodiment provides a water-based drilling fluid, which, by mass percentage, consists of: 3% of the nano-plugging agent CNT-HPAM-1 from Example 1, 1.5% bentonite, 0.5% thickener, 1.5% filtration reducer, 1% pH adjuster, 2% lubricant, an appropriate amount of weighting agent (for adjusting the density of the water-based drilling fluid), and the balance being water.

[0074] The density and preparation method of the water-based drilling fluid in this embodiment are the same as those in Example 7. This water-based drilling fluid is designated as C3.

[0075] Example 10

[0076] This embodiment provides a water-based drilling fluid, which is the same as that in Example 8, except that the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-1 is replaced with the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-2 prepared in Example 2. This water-based drilling fluid is designated as B1.

[0077] Example 11

[0078] This embodiment provides a water-based drilling fluid, which is the same as that in Example 8, except that the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-1 is replaced with the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-3 prepared in Example 3. This water-based drilling fluid is designated as B2.

[0079] Example 12

[0080] This embodiment provides a water-based drilling fluid, which is the same as that in Example 8, except that the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-1 is replaced with the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-5 prepared in Example 5. This water-based drilling fluid is designated as B3.

[0081] Comparative Example 1

[0082] This comparative example provides a water-based drilling fluid that is identical to that of Example 8, except that the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-1 is replaced with the common plugging agent ultrafine calcium carbonate. This water-based drilling fluid is designated as D1.

[0083] Comparative Example 2

[0084] This comparative example provides a water-based drilling fluid that is identical to that of Example 8, except that the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-1 is replaced with commercially available amino-functionalized multi-walled carbon nanotubes. This water-based drilling fluid is designated D2.

[0085] Comparative Example 3

[0086] This comparative example provides a water-based drilling fluid that is identical to that of Example 8, except that the carbon nanotube-grafted polymer nano-plugging agent CNT-HPAM-1 is not added. This water-based drilling fluid is designated as D3.

[0087] Comparative Example 4

[0088] This comparative example provides a water-based drilling fluid that is identical to that of Example 8, except that the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-1 in this comparative example is replaced with the acrylic acid-modified carbon nanotube CNT-AA-1 of Example 1. This water-based drilling fluid is designated as D4.

[0089] Comparative Example 5

[0090] This comparative example provides a water-based drilling fluid that is identical to that of Example 8, except that the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-1 is replaced with a mixture of amino-functionalized multi-walled carbon nanotubes and polyacrylamide at a mass ratio of 0.1:25. This water-based drilling fluid is designated as D5.

[0091] Comparative Example 6

[0092] This comparative example provides a water-based drilling fluid that is identical to that of Example 8, except that the carbon nanotube-grafted polymer nanoplugging agent CNT-HPAM-1 is replaced with a common shale inhibitor RF-9. This water-based drilling fluid is designated D6.

[0093] Experimental Example 1: Particle Size Test

[0094] The six carbon nanotube-grafted polymer nanoblocking agents prepared in Examples 1-6, the acrylic acid-modified carbon nanotube CNT-AA-2 prepared in Example 2, and the raw material CNT-NH2 were added to pure water at a dosage of 1 wt%. The mixtures were then allowed to stand at 120°C. The particle size distribution of the different nanomaterials in pure water was tested using a particle size analyzer over 60 days. The results are shown in Table 1.

[0095] Table 1. Particle size distribution of various nanomaterials after standing at 120℃ for 60 days.

[0096]

[0097]

[0098] As shown in Table 1, the minimum particle size of CNT-HPAM-1, CNT-HPAM-2, CNT-HPAM-3, CNT-HPAM-4, CNT-HPAM-5, CNT-HPAM-6, CNT-NH2, and CNT-AA-2 materials varies little, while the average particle size changes by 5.67%, 5.25%, 5.54%, 4.78%, 6.11%, 5.67%, 6.42%, 58.3%, and 18.5% over 60 days, respectively. This indicates that the carbon nanotube-grafted polymer nano-blocking agent has good high-temperature stability.

[0099] Experimental Example 2: Infrared Spectroscopic Structural Characterization

[0100] This experiment characterized the infrared spectral structure of the three nanomaterials CNT-NH2, CNT-AA-1, and CNT-HPAM-1 from Example 1. The results are as follows: Figure 1 As shown.

[0101] from Figure 1 It can be seen that the infrared spectrum of CNT-NH2 is located at 3060 cm⁻¹. -1and 2947cm -1 The two characteristic absorption peaks are the stretching vibration peaks of NH, 1700-1500 cm⁻¹. -1 The characteristic absorption peak at 1009 cm⁻¹ is the in-plane bending vibration peak of NH₃. -1 The characteristic absorption peaks around the left and right are the shear-angle vibration peaks of NH, at 1072 cm⁻¹. -1 The characteristic absorption peaks on the left and right sides are the stretching vibration peaks of CN, 910-650 cm⁻¹. -1 The characteristic absorption peak at that location is the out-of-plane bending vibration peak of NH.

[0102] In the infrared spectrum of CNT-AA-1, at 3424 cm⁻¹ -1 The characteristic absorption peak at 1662 cm⁻¹ is the stretching vibration peak of NH₃. -1 The characteristic absorption peak at 1433 cm⁻¹ is the stretching vibration peak of C=O. -1 The characteristic absorption peak at 978 cm⁻¹ is the stretching vibration peak of CN. -1 The absorption peak at 910-650 cm⁻¹ is a characteristic peak of monosubstituted olefins. -1 The characteristic absorption peak at this location is the out-of-plane bending vibration peak of NH. Additionally, C=C is located at 1680-1620 cm⁻¹. -1 The stretching vibration peak of C=O is relatively weak, so it may be covered by the stretching vibration peak of C=O.

[0103] In the infrared spectrum of CNT-HPAM-1, at 3325 cm⁻¹ -1 and 3192cm -1 The two characteristic absorption peaks are the stretching vibration peaks of NH, at 2939 cm⁻¹. -1 The characteristic absorption peak at 1672 cm⁻¹ is the stretching vibration peak of CH in ammonium salt. -1 The characteristic absorption peak at 1560 cm⁻¹ is the stretching vibration peak of the C=O group in the amide group. -1 The characteristic absorption peak at 1410 cm⁻¹ is the surface bending vibration peak of NH₃. -1 and 1314cm -1 The two characteristic absorption peaks are the stretching vibration peaks of CN in the amide group, at 1192 cm⁻¹. -1 and 1124cm -1 The two characteristic absorption peaks are the stretching vibration peaks of CN in ammonium salt, 789 cm⁻¹. -1 and 663cm -1 The characteristic absorption peaks at both locations are out-of-plane bending vibration peaks of NH.

[0104] Therefore, infrared spectral analysis confirms that the present invention successfully synthesized acrylic acid-modified carbon nanotubes (CNT-AA) and carbon nanotube-grafted polymer nanoblocking agents (CNT-HPAM).

[0105] Experiment Example 3 Salt Tolerance Test

[0106] Zeta potential is an important indicator for characterizing the stability of colloidal dispersions. In this experiment, the salt resistance of the CNT-HPAM-2 material in Example 2 was evaluated using zeta potential analysis.

[0107] CNT-HPAM-2 material was added to three solutions—deionized water, saturated brine, and simulated formation water—at a concentration of 1 wt%. The mixture was thoroughly stirred and allowed to stand for 28 days. The zeta potential changes in each solution over those 28 days were then measured. The results are as follows: Figure 2 As shown.

[0108] according to Figure 2 It is known that the carbon nanotube-grafted polymer nanoblocking agent CNT-HPAM-2 has excellent stability and salt resistance.

[0109] Experiment Example 4: Blocking Performance Test

[0110] Based on Experiment 3, this experiment further evaluates the plugging performance of water-based drilling fluids in Examples 7-12 and Comparative Examples 1-3.

[0111] Drilling fluids were prepared according to Examples 7-12 and Comparative Examples 1-3, with each water-based drilling fluid having a density of 1.7 g / cm³. 3 The aging temperature was 120℃, and the aging time was 24 hours. After aging, the viscosity, dynamic shear force, and high-temperature high-pressure filtration loss of the water-based drilling fluid were tested, and the results are shown in Table 2.

[0112] Table 2. Sealing performance of water-based drilling fluids

[0113]

[0114]

[0115] As shown in Table 2, the water-based drilling fluid maintained good rheological properties after aging at 120℃. Compared with drilling fluids containing ordinary plugging agent ultrafine calcium carbonate (D1), amino-functionalized multi-walled carbon nanotubes (D2), no plugging agent (D3), acrylic acid modified carbon nanotubes (D4), a mixture of amino-functionalized multi-walled carbon nanotubes and polyacrylamide (D5), and ordinary shale inhibitor RF-9 (D6), the drilling fluid containing carbon nanotube grafted polymer nano-plugging agent CNT-HPAM (C1-C3, B1-B3) showed a significant reduction in filtration loss. Among them, the filtration loss of B1 was as low as 2.1 mL, which indicates that the nano-plugging agent improved the plugging performance of the water-based drilling fluid.

Claims

1. A method for preparing a carbon nanotube-grafted polymer nano-blocking agent, comprising the following steps: S1: Acrylic acid is reacted with amino-functionalized multi-walled carbon nanotubes to generate acrylic acid-modified carbon nanotubes; wherein, The mass ratio of acrylic acid to amino-functionalized multi-walled carbon nanotubes is 1:0.1-0.2; S2: Acrylamide, the acrylic acid-modified carbon nanotubes, and octadecyl dimethyl allyl ammonium chloride are copolymerized to obtain the carbon nanotube grafted polymer nano-blocking agent; wherein the mass ratio of acrylamide, the acrylic acid-modified carbon nanotubes, and octadecyl dimethyl allyl ammonium chloride is 25:0.2-0.8:1.2-2.

0.

2. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 1, wherein, S1 includes the following steps: (1) Add amino-functionalized multi-walled carbon nanotubes and sodium dodecyl sulfate to N,N-dimethylformamide and disperse by ultrasonication to obtain carbon nanotube solution A; (2) Add acrylic acid and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride to N,N-dimethylformamide, add hydrochloric acid dropwise to adjust the pH of the solution to 4-6, stir thoroughly to dissolve, and obtain acrylic acid solution B; (3) The carbon nanotube solution A and the acrylic acid solution B are mixed and reacted to obtain a solid product, which is then filtered and washed to obtain the acrylic acid modified carbon nanotube.

3. The method for preparing the carbon nanotube-grafted polymer nano-blocking agent according to claim 2, wherein, The mass ratio of amino-functionalized multi-walled carbon nanotubes, acrylic acid, sodium dodecyl sulfate, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 0.1-0.2:1:0.1-0.4:0.05-0.

1.

4. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 2, wherein, The reaction temperature in step (3) is 0-5℃ and the reaction time is 8-10h.

5. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 2, wherein, The dissolution process in step (2) is carried out at 0-5℃.

6. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 2, wherein, The reagent used for washing in step (3) is ethanol.

7. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 1, wherein, S2 includes the following steps: (4) Dissolve acrylamide, the acrylic acid-modified carbon nanotubes, and octadecyl dimethyl allyl ammonium chloride in water, adjust the pH value to 8-10, introduce nitrogen gas and ultrasonically disperse to obtain a dispersion; (5) Add an initiator to the dispersion, continue to purge with nitrogen and stir until the solution viscosity increases; then stop stirring and purge with nitrogen, and continue the reaction to obtain a reaction solution; (6) Heat the reaction solution, add alkaline solution to carry out hydrolysis reaction, obtain gel product, wash and dry to obtain the carbon nanotube grafted polymer nano-blocking agent.

8. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 7, wherein, The initiator is a mixture of potassium persulfate and sodium bisulfite.

9. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 8, wherein, The mass ratio of potassium persulfate, sodium bisulfite and acrylamide is 0.03-0.06:0.06-0.1:

25.

10. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 7, wherein, The reaction continues for 4-6 hours in step (5).

11. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 7, wherein, In step (6), the reaction solution is heated to 70-90℃ and the hydrolysis reaction takes 4-6 hours.

12. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 7, wherein, In step (6), the alkaline solution is sodium hydroxide and / or sodium carbonate.

13. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 7, wherein, In step (6), the washing reagent is acetone.

14. The method for preparing the carbon nanotube-grafted polymer nanoblocking agent according to claim 7, wherein, In step (6), the drying conditions are: drying at 60-80℃ for 10-15 hours.

15. A carbon nanotube-grafted polymer nanoblocking agent, which is obtained by the preparation method of the carbon nanotube-grafted polymer nanoblocking agent according to any one of claims 1-14.

16. The carbon nanotube-grafted polymer nanoblocking agent according to claim 15, wherein, The carbon nanotube-grafted polymer nanoblocking agent has a particle size distribution between 16 and 451 nm.

17. A water-based drilling fluid containing the carbon nanotube-grafted polymer nano-plugging agent as described in claim 15 or 16.

18. The water-based drilling fluid according to claim 17, wherein, By mass percentage, the raw materials of the water-based drilling fluid include: 0.5-3% of the carbon nanotube grafted polymer nano-plugging agent, 0.5-1.5% of bentonite, 0.5-1.5% of the thickener, 1.0-2.0% of the filtration loss reducer, 0.5-1.5% of the pH adjuster, 2.0-4.0% of the lubricant, and the balance being water.

19. The water-based drilling fluid according to claim 18, wherein, The raw materials for water-based drilling fluids also include weighting agents; water-based drilling fluids with added weighting agents have a density of 1.2-2.0 g / cm³. 3 .

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