Nanoscale plugging agent for oil field drilling fluid and preparation method thereof

Abstract

The invention discloses a nanoscale plugging agent for oil field drilling fluid, which is prepared from the following raw materials: a water phase, an oil phase and an initiator solution, and the weight ratio of the water phase to the oil phase is (40-60): (40-60). According to the plugging agent for the drilling fluid, the reaction monomers of the acrylamide, the acrylic acid, the 2-acrylamide-2-methylpropanesulfonic acid and the N, N-methylene bisacrylamide are combined, so that the prepared plugging agent for the drilling fluid has a relatively good plugging effect in mortar, and can still maintain a good plugging effect in a high-temperature and high-salt environment. And white oil with the mark numbers of 3 #, 5 # and 10 # is adopted as an oil phase, and the formed microemulsion type plugging agent emulsion has the nano-scale particle size, is suitable for nano-scale gaps of shale, and has the advantages of good plugging effect and stable effect. Meanwhile, the emulsifier combination of Tween 80 and peregal O-25 is adopted, so that the formed plugging agent polymer is nanoscale and can be used for plugging pores of the shale, reducing water loss and preventing borehole diameter shrinkage caused by hydration of the shale.

Description

Technical Field

[0001] The invention relates to C09K, and to the field of additives in drilling compositions, and in particular to a nanometer-level plugging agent for oilfield drilling fluid and a preparation method thereof. Background Art

[0002] With the growing demand for energy, an important means to solve the energy problem is to develop new energy. Shale gas, dense sandstone, and coalbed methane are all unconventional energy sources, among which shale gas exploitation is an important direction for the development of new energy. However, shale itself has the characteristics of small pore throat and low permeability, which makes it impossible to form a dense mud cake on the inner wall of the wellbore during drilling, resulting in increased filtration loss, and mud shale is easy to absorb water and swell, thus limiting the development of shale gas. Mud shale has a special fracture pore structure and belongs to an ultra-low porosity and low permeability reservoir. The matrix pores are not developed, mainly capillary pores. The existing technology mostly uses oil-based drilling fluid, but the cost of use is high, and there are disadvantages of polluting the environment and polluting the reservoir. Water-based drilling fluid is easy to hydrate mud shale and cause downhole accidents. In addition, the commonly used plugging agents in water-based drilling fluids are mostly micron-level, and most of the pores in shale are nanometer-level. The size of the pores and the plugging agent does not match, and the plugging effect is not good. Therefore, it is very important to develop a nano-level drilling fluid plugging agent and avoid pollution problems.

[0003] Chinese invention patent CN117186850A discloses a double-repellent nano plugging agent for drilling fluid and its preparation method and application. The surface of nano calcium carbonate is modified by silane coupling agent. The obtained double-repellent nano plugging agent can enrich fluorine element mainly in the shell layer, while reducing the amount of fluorine monomer, the original performance of organic fluorine polymer can be maintained, and an excellent hydrophobic polymer surface can be obtained. At the same time, the amount of fluorine silicon raw material can be reduced. However, nano calcium carbonate is easy to agglomerate during use, resulting in particle enlargement and failure to achieve plugging effect. Chinese invention patent CN110591674B discloses a plugging agent for drilling fluid and its preparation method. The plugging agent uses modified water-based acrylic resin as the middle layer, silicon dioxide as the core inside, and emulsified white oil as the shell outside, which solves the problem that conventional plugging materials have strong hydrophilicity, large particle size, and unsatisfactory plugging effect on shale micro-fracture formations. However, silicon dioxide is also easy to agglomerate, resulting in particle enlargement, and can only achieve micron-level gap plugging, which is unsatisfactory for nano-level gap plugging. Summary of the invention

[0004] In order to develop a nano-scale plugging agent for drilling fluid and avoid pollution problems, the first aspect of the present invention provides a nano-scale plugging agent for oilfield drilling fluid, the preparation raw materials include an aqueous phase, an oil phase and an initiator solution, the aqueous phase includes, by weight: 50-70 parts of reaction monomers, 5-15 parts of emulsifier I, 0.1-1 parts of molecular regulators, 0.1-0.5 parts of initiators, 0.01-0.1 parts of chelating agents, 1-10 parts of alkaline regulators, and 100 parts of deionized water.

[0005] As a preferred embodiment, the weight ratio of the water phase to the oil phase is (40-60): (40-60).

[0006] As a preferred embodiment, the weight ratio of the water phase, the oil phase and the initiator solution is (40-60): (40-60): (5-6).

[0007] As a preferred embodiment, the reactive monomer is selected from at least one of methyl methacrylate, hydroxyethyl methacrylate, 2-acrylamide-2-methylpropanesulfonic acid, methyl acrylate, butyl acrylate, acrylic acid, acrylamide, and polyethylene glycol diacrylate.

[0008] As a preferred embodiment, the reaction monomers include acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N,N-methylenebisacrylamide in a weight ratio of (40-50):(5-15):(1-10):(0.1-0.3).

[0009] As a preferred embodiment, the reaction monomers include acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N,N-methylenebisacrylamide in a weight ratio of (43-48): (8-13): (3-8): (0.15-0.2).

[0010] As a preferred embodiment, the reactive monomers include acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N,N-methylenebisacrylamide in a weight ratio of 45:10:5:0.15.

[0011] The inventors found in the experiment that the combination of acrylamide, acrylic acid, 2-acrylamide-2-methylpropane sulfonic acid and N,N-methylenebisacrylamide as reaction monomers, the prepared plugging agent for drilling fluid has better plugging effect in mortar, and can still maintain good plugging effect in high temperature and high salt environment. The possible reason is guessed that: N,N-methylenebisacrylamide has excellent high temperature resistance, and the polymer molecular chain formed by cooperating with acrylamide has higher strength. Compared with polyethylene glycol diacrylate, it is not easy to have molecular chain breakage in high temperature environment, which affects the water loss effect. In addition, the introduced 2-acrylamide-2-methylpropane sulfonic acid contains sulfonic acid groups, which has higher solubility in high salt environment, avoiding the precipitation of polymer in high salt environment, causing unstable problems and affecting the sand bed closure filtration loss. At the same time, the polymer obtained by the combination of acrylamide, acrylic acid, 2-acrylamide-2-methylpropane sulfonic acid and N,N-methylenebisacrylamide has better hydrophilicity, and the polymer particles will swell when absorbing water, plugging the larger gaps, further improving the plugging effect of the plugging agent.

[0012] As a preferred embodiment, the oil phase comprises white oil and emulsifier II, and the weight ratio of the white oil to the emulsifier II is (80-95): (20-30).

[0013] As a preferred embodiment, the weight ratio of the white oil to the emulsifier II is (85-95):(25-30).

[0014] As a preferred embodiment, the weight ratio of the white oil to the emulsifier II is 90:28.

[0015] As a preferred embodiment, the white oil is selected from at least one of 3# white oil, 5# white oil, 7# white oil and 10# white oil.

[0016] As a preferred embodiment, the white oil is selected from at least one of 3# white oil, 5# white oil and 10# white oil.

[0017] The inventors found in the experimental process that the particle size of the microemulsion plugging agent emulsion formed by using white oils labeled 3#, 5#, and 10# as the oil phase is nanometer-level, which is suitable for nano-level voids in shale, has a better plugging effect, and the effect is stable. It is speculated that the possible reason is that the viscosity of the white oils labeled 3#, 5#, and 10# is appropriate, which can make the small droplets containing polymers evenly dispersed in the oil phase. When the viscosity exceeds the preferred range, it will cause the small droplets to be difficult to disperse evenly, the water phase is easy to aggregate, and the particle size increases sharply, resulting in a decrease in the stability of the plugging agent microemulsion, which is no longer suitable for nano plugging.

[0018] As a preferred embodiment, the emulsifier I and the emulsifier II are both selected from anionic surfactants, nonionic surfactants or a combination of both.

[0019] As a preferred embodiment, the emulsifier I and the emulsifier II are both selected from at least one of Span 80, Tween 80, sodium fatty acid, potassium disproportionated rosin acid, OP-10, and Peregal O-25.

[0020] As a preferred embodiment, the emulsifier I comprises a combination of Tween 80 and Parfait O-25, and the weight ratio of the Tween 80 and Parfait O-25 is (4-8): (1-3).

[0021] As a preferred embodiment, the weight ratio of Tween 80 to Piperidin O-25 is (5-7): (1.5-2.5).

[0022] As a preferred embodiment, the weight ratio of Tween 80 to Paroxysmal O-25 is 6:2.

[0023] During the experiment, the inventors found that the combination of Tween 80 and Pingpingjia O-25 as an emulsifier can form a nanoscale polymer microemulsion, which can block the pores of mudstone, reduce water loss, and prevent the shrinkage of the wellbore caused by the hydration of mudstone. The possible reason is guessed to be: the combination of Tween 80 and Pingpingjia O-25 as an emulsifier can make the polymer evenly dispersed in each small droplet, ensuring the nanoscale distribution of the droplet particle size, so that it can enter the tiny gaps for plugging. The applicant further found that when Tween 80 and Pingpingjia O-25 are used in a weight ratio of 6:2, the microemulsion formed has a higher stability, which exceeds the preferred weight ratio range, and the particle size of the formed microemulsion is too large to achieve nano-plugging. It may even cause the microemulsion to break and stratify, and the water phase to coalesce, resulting in the inability to achieve the plugging effect.

[0024] As a preferred embodiment, the emulsifier II is Span 80.

[0025] As a preferred embodiment, the molecular regulator is selected from at least one of tert-dodecyl mercaptan, diisopropyl xanthate disulfide, mercaptoethanol and thioglycolic acid.

[0026] As a preferred embodiment, the initiator is selected from at least one of potassium persulfate, ammonium persulfate, sodium sulfite, sodium bisulfite, formaldehyde sodium bisulfite, hydrogen peroxide, benzoyl peroxide, and p-menthane hydroperoxide.

[0027] As a preferred embodiment, the mass concentration of the initiator solution is 1-5wt%, and more preferably, the mass concentration of the initiator solution is 3wt%.

[0028] As a preferred embodiment, the chelating agent is EDTA-sodium.

[0029] As a preferred embodiment, the alkaline regulator includes but is not limited to sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia water, etc.

[0030] The second aspect of the present invention provides a method for preparing a nano-scale plugging agent for oilfield drilling fluid, comprising the following steps:

[0031] S1: Add the reaction monomer and chelating agent into the reactor, add deionized water, add the alkaline regulator, stir and dissolve, add the emulsifier I and the molecular regulator, continue to stir evenly, add the initiator, continue to stir for 20-40 minutes, and prepare the aqueous phase for use;

[0032] S2: Prepare the oil phase: Mix the white oil and emulsifier II and stir evenly to prepare the oil phase for use;

[0033] S3 prepares an initiator solution;

[0034] S4: Slowly add the water phase to the oil phase, start stirring, continue to introduce inert gas, start water bath stirring, stir for 20-40 minutes, then dropwise add the initiator solution while stirring, continue stirring for 50-90 minutes, and the reaction is complete.

[0035] As a preferred embodiment, the water bath temperature is 30-40°C.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The nanometer-scale plugging agent for oilfield drilling fluid of the present invention adopts a reaction monomer combination of acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N,N-methylenebisacrylamide. The plugging agent for drilling fluid prepared by the present invention has a better plugging effect in mortar and can still maintain a good plugging effect in a high temperature and high salt environment.

[0038] (2) The nano-scale plugging agent for oilfield drilling fluid of the present invention adopts white oils with the numbers 3#, 5#, and 10# as the oil phase, and the particle size of the microemulsion plugging agent emulsion formed is of nanometer level, which is suitable for nano-scale voids in shale and has better and more stable plugging effect.

[0039] (3) The nanometer-scale plugging agent for oilfield drilling fluid of the present invention adopts an emulsifier combination of Tween 80 and Parpenta O-25. The plugging agent polymer formed is nanometer-scale and can plug the pores of shale, reduce water loss, and prevent the shrinkage of the wellbore caused by hydration of shale.

[0040] (4) The nanometer-scale plugging agent for oilfield drilling fluid of the present invention is a nanometer-scale emulsion plugging agent, which not only avoids the problem of inapplicability of water-based plugging agents in terms of size, but also reduces the problem of environmental pollution and reservoir pollution caused by oil-based plugging agents.

[0041] (5) The nano-scale plugging agent for oilfield drilling fluid of the present invention can be evenly dispersed in each small droplet, ensuring that the particle size distribution is at the nanometer level. At the same time, the polymer is resistant to high temperature and salt, ensuring that the performance of the drilling fluid system remains unchanged during deep well and brine mud slurry, and the plugging effect is sustained and effective. The API filtration loss, sand bed sealing filtration loss, brine mud API filtration loss, high temperature and high pressure filtration loss are relatively high, basically meeting the current needs of deep well drilling in oil fields. DETAILED DESCRIPTION

[0042] Example 1

[0043] A nanometer plugging agent for oilfield drilling fluid, the preparation raw materials of which include water phase, oil phase and initiator solution, the weight ratio of which is 174.8:118:5.

[0044] The aqueous phase comprises, by weight: 60.15 parts of reaction monomers, 8 parts of emulsifier I, 0.4 parts of molecular regulator, 0.2 parts of initiator, 0.05 parts of chelating agent, 6 parts of alkaline regulator, and 100 parts of deionized water.

[0045] The reactive monomers include acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N,N-methylenebisacrylamide in a weight ratio of 45:10:5:0.15.

[0046] The emulsifier I comprises a combination of Tween 80 and Parfait O-25, with a weight ratio of 6:2.

[0047] The molecular regulator is tert-dodecyl mercaptan, the initiator is ammonium persulfate, the chelating agent is EDTA-2 sodium, and the alkaline regulator is sodium hydroxide.

[0048] The oil phase includes white oil and emulsifier II, and the weight ratio of the white oil to the emulsifier II is 90:28.

[0049] The white oil is 10# white oil, and the emulsifier II is Span 80.

[0050] 10# white oil was purchased from Daqing Refinery, and Pingpingjia O-25 was purchased from Jiangsu Hai'an Petrochemical Plant.

[0051] The initiator solution is a sodium bisulfite aqueous solution with a mass concentration of 3 wt %.

[0052] A method for preparing a nanometer-scale plugging agent for oilfield drilling fluid comprises the following steps:

[0053] S1: Add the reaction monomer and chelating agent into the reactor, add deionized water, add the alkaline regulator, stir and dissolve, add the emulsifier I and the molecular regulator, continue to stir evenly, add the initiator, continue to stir for 30 minutes, and prepare the aqueous phase for use;

[0054] S2: Prepare the oil phase: Mix the white oil and emulsifier II and stir evenly to prepare the oil phase for use;

[0055] S3 prepares an initiator solution;

[0056] S4: Slowly add the water phase to the oil phase, start stirring at 800r / min, continue to introduce nitrogen, start stirring in a water bath, stir for 30 minutes, then dropwise add the initiator solution while stirring, and continue stirring for 60 minutes before the reaction is complete.

[0057] The water bath temperature was 35°C.

[0058] Example 2

[0059] A nanometer-scale plugging agent for oilfield drilling fluid and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that 2-acrylamide-2-methylpropane sulfonic acid is replaced by polyethylene glycol diacrylate, which is purchased from Jinan Kaichuang Chemical Co., Ltd.

[0060] Example 3

[0061] A nanometer-scale plugging agent for oilfield drilling fluid and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the reactive monomer is 55.15 parts by weight, and the reactive monomer comprises a combination of acrylamide, acrylic acid and N,N-methylenebisacrylamide in a weight ratio of 45:10:0.15.

[0062] Example 4

[0063] A nanometer-scale plugging agent for oilfield drilling fluid and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the aqueous phase comprises, by weight: 50.15 parts of a reaction monomer, 8 parts of an emulsifier I, 0.4 parts of a molecular regulator, 0.2 parts of an initiator, 0.05 parts of a chelating agent, 0 parts of an alkaline regulator, and 100 parts of deionized water.

[0064] The reactive monomers include acrylamide, 2-acrylamide-2-methylpropanesulfonic acid and N,N-methylenebisacrylamide in a weight ratio of 45:5:0.15.

[0065] Example 5

[0066] A nanometer-scale plugging agent for oilfield drilling fluid and a preparation method thereof, the specific implementation manner is the same as that of Example 1, except that the preparation raw materials include a water phase, an oil phase and an initiator solution, and the weight ratio is 174.8:106:5.

[0067] The emulsifier I comprises a combination of Tween 80 and OP-10 in a weight ratio of 6:2. OP-10 was purchased from Xingtai Xinlanxing Technology Co., Ltd.

[0068] The weight ratio of the white oil to the emulsifier II is 90:16.

[0069] Test results: As the temperature rises, the solution breaks, the oil and water separate, the water phase coalesces, and the experiment fails. This means that when the amount of Span 80 added is less than 20%, a stable microemulsion cannot be formed.

[0070] Example 6

[0071] A nanometer-scale plugging agent for oilfield drilling fluid and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the preparation raw materials include a water phase and an oil phase in a weight ratio of 166.8:106.

[0072] The aqueous phase comprises, by weight: 60.15 parts of reaction monomers, 0 parts of emulsifier I, 0.4 parts of molecular regulator, 0.2 parts of initiator, 0.05 parts of chelating agent, 6 parts of alkaline regulator, and 100 parts of deionized water.

[0073] The weight ratio of the white oil to the emulsifier II is 90:16.

[0074] Test results: The plugging agent solution was not translucent, but a semi-milky solution. After 2 hours of storage, the oil and water separated and a layered state appeared. This shows that when the HLB value is too low, it is not conducive to the formation of microemulsion.

[0075] Example 7

[0076] A nanometer-scale plugging agent for oilfield drilling fluid and a preparation method thereof, the specific implementation manner is the same as that of Example 1, except that the preparation raw materials include a water phase, an oil phase and an initiator solution, and the weight ratio is 172.8:112:5.

[0077] The aqueous phase comprises, by weight: 60.15 parts of reaction monomers, 4 parts of emulsifier I, 0.4 parts of molecular regulator, 0.2 parts of initiator, 0.05 parts of chelating agent, 6 parts of alkaline regulator, and 100 parts of deionized water.

[0078] The emulsifier I is Tween 80.

[0079] The weight ratio of the white oil to the emulsifier II is 90:22.

[0080] Test results: After the reaction, the median particle size was measured using a laser particle size distribution analyzer. 50 It is 1.6 μm, which means that when the emulsifier is reduced, the stirring speed can be increased to form a stable emulsion, but the emulsion particle size is too large and is not nanoscale.

[0081] Performance Testing

[0082] 1. pH value detection: The sample solutions of Examples 1-4 were measured using precision pH test paper.

[0083] 2. API filtration loss: The test is performed in accordance with the provisions of 7.2 of GB / T 16783.1-2014.

[0084] 3. Sand bed closed filtration loss: Use a high-temperature and high-pressure filtration meter with openings at both ends of the cup body as a test instrument, install and fix the bottom of the slurry cup with a filter screen and the valve stem, and close the bottom valve stem. Add 100g of quartz sand with a particle size between 0.15mm and 0.25mm to the slurry cup, and shake the drilling fluid cup to make the quartz sand flat on the bottom of the cup. Take 400mL of base slurry and add 16mL of the sample solution of Examples 1-4, stir at high speed for 20min, and slowly and evenly add the sample slurry after adding and stirring (if foaming occurs after stirring, a small amount of defoaming agent can be added to defoam) into the slurry cup along the cup wall (do not let the base slurry directly impact the quartz sand at the bottom of the cup, so as to avoid uneven sand layer thickness and affect the test accuracy), install and fix the slurry cup top cover and valve stem, and close the top valve stem. Put the slurry cup into the heating sleeve, connect the adjustable pressure source to the top valve stem, and lock it in the appropriate position. Adjust the pressure source to 0.45MPa, open the top valve stem, adjust the pressure to 0.7MPa, open the bottom valve stem 1 / 4 turn and start timing, maintain the pressure of 0.7MPa, collect the filtrate for 30min, which is the closed filtration loss (no need to calibrate to 45.8cm 3 filtration area).

[0085] 4. API filtration loss of brine mud: brine mud is a mud prepared to contain 4% sodium chloride, and the test method is carried out according to the provisions of 7.2 of GB / T 16783.1-2014.

[0086] 5.120℃ high temperature and high pressure filtration loss: Test according to the relevant provisions of 7.3 of GB / T 16783.1-2014.

[0087] 6. Median particle size: Use a laser particle size distribution analyzer with a measuring range of 0.01μm to 1000μm to measure the median particle size of the sample according to the measurement steps of the instrument.

[0088] The qualified technical requirements are shown in Table 1 and the test results are shown in Table 2.

[0089] Table 1

[0090] project index pH 7.0～10.0 API filtration loss, mL ≤10 Sand bed sealing filtration loss, mL ≤35 API filtration loss of brine slurry, mL ≤12 120℃ high temperature and high pressure filtration loss, mL ≤30 Median particle size, nm ≤800

[0091] Table 2

[0092]

[0093]

[0094] The test results show that polyethylene glycol diacrylate and N,N-methylenebisacrylamide can react well with monomers as crosslinking agents, and the products after the reaction have good plugging effects at room temperature. However, polyethylene glycol diacrylate is not heat-resistant. At 120°C, it will decompose due to heat, resulting in the disconnection of the molecular chain, which cannot effectively reduce water loss and greatly reduces the plugging effect. AMPS has a good salt resistance effect because of the sulfonic acid group in its molecular structure. Experiments have shown that the API filtration loss of the brine slurry without adding AMPS (Example 3) is higher than that of the other samples, indicating that the addition of AMPS has a good salt resistance effect. At the same time, in the sand bed sealing filtration loss experiment, it was found that the plugging effect of Example 4 without adding acrylic acid was poor due to the slightly larger pores in the sand bed, and the plugging effects of the other three samples were relatively low and close, indicating that the hydrophilic group of the molecule is stronger after adding acrylic acid, and the particle water absorption and expansion effect is better, and the slightly larger pores can be plugged through volume expansion.

Claims

1. A nanometer-scale plugging agent for oilfield drilling fluid, characterized in that: The raw materials include water phase, oil phase and initiator solution. The water phase includes, by weight: 50-70 parts of reaction monomer, 5-15 parts of emulsifier I, 0.1-1 parts of molecular regulator, 0.1-0.5 parts of initiator, 0.01-0.1 parts of chelating agent, 1-10 parts of alkaline regulator and 100 parts of deionized water.

2. The nanometer-scale plugging agent for oilfield drilling fluid according to claim 1, characterized in that: The weight ratio of the water phase to the oil phase is (40-60): (40-60).

3. The nanoscale plugging agent for oilfield drilling fluid according to claim 2, characterized in that: The reactive monomer is selected from at least one of methyl methacrylate, hydroxyethyl methacrylate, 2-acrylamide-2-methylpropanesulfonic acid, methyl acrylate, butyl acrylate, acrylic acid, acrylamide, and polyethylene glycol diacrylate.

4. The nanoscale plugging agent for oilfield drilling fluid according to claim 3, characterized in that: The reactive monomers include acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N,N-methylenebisacrylamide in a weight ratio of (40-50):(5-15):(1-10):(0.1-0.3).

5. The nanoscale plugging agent for oilfield drilling fluid according to claim 2, characterized in that: The oil phase comprises white oil and emulsifier II, and the weight ratio of the white oil to the emulsifier II is (80-95):(20-30).

6. The nanometer-scale plugging agent for oilfield drilling fluid according to claim 5, characterized in that: The white oil is selected from at least one of 3# white oil, 5# white oil, 7# white oil and 10# white oil.

7. The nanometer-scale plugging agent for oilfield drilling fluid according to claim 5, characterized in that: The emulsifier I and emulsifier II are both selected from anionic surfactants, nonionic surfactants or a combination of both.

8. The nanometer-scale plugging agent for oilfield drilling fluid according to claim 5, characterized in that: The emulsifier I and emulsifier II are both selected from at least one of Span 80, Tween 80, sodium fatty acid, potassium disproportionate rosin acid, OP-10, and Peregal O-25.

9. The nanoscale plugging agent for oilfield drilling fluid according to claim 2, characterized in that: The molecular regulator is selected from at least one of tert-dodecyl mercaptan, diisopropyl xanthate disulfide, mercaptoethanol and thioglycolic acid.

10. A method for preparing the nanoscale plugging agent for oilfield drilling fluid according to any one of claims 2 to 9, characterized in that: The following steps are involved: S1: Add the reaction monomer and chelating agent into the reactor, add deionized water, add the alkaline regulator, stir and dissolve, add the emulsifier I and the molecular regulator, continue to stir evenly, add the initiator, continue to stir for 20-40 minutes, and prepare the aqueous phase for use; S2 is configured with oil phase; S3 prepares an initiator solution; S4: Slowly add the water phase to the oil phase, start stirring, continue to introduce inert gas, start water bath stirring, stir for 20-40 minutes, then dropwise add the initiator solution while stirring, continue stirring for 50-90 minutes, and the reaction is complete.

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