A nano-plugging fluid loss reducer and its preparation method and application

Abstract

The present invention proposes a nano-plugging fluid loss control agent comprising a polytannic acid grafted hyperbranched polymer. The polytannic acid grafted hyperbranched polymer comprises a hyperbranched polymer formed by the polycondensation reaction of polyethylene polyamine and acrylic acid monomers, which is then reacted with tannic acid in the presence of an oxidant to form a polytannic acid grafted hyperbranched polymer. The nano-plugging fluid loss control agent has a particle size of 90 to 150 nm. By utilizing the ultrahigh surface activity of nanoparticles, combined with the hyperbranched polymer's properties of easy solubility, low viscosity, strong dispersion, and high number of end groups and high activity, the agent exhibits a core-shell structure, strong dispersibility, low viscosity, and excellent flexibility. The hyperbranched polymer fluid loss control agent utilizes its strong bonding strength to microfracture end faces to seal shale pore throats, maximizing film-forming plugging capacity and fluid loss reduction performance, improving plugging efficiency, enhancing the density and strength of the mud cake, reducing drilling fluid loss, and enhancing wellbore stability in microfracture formations.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling fluids, and in particular relates to a nano plugging fluid loss reducer and a preparation method and application thereof. Background Art

[0002] The difficulty in shale mining lies primarily in its nanoscale pore size. Currently, commonly used plugging agents are relatively large in particle size, making them ineffective against the nanopores and microfractures of shale. This directly increases drilling fluid loss during shale mining, leading to a series of problems such as wellbore instability during drilling. The small size of nano-plugging materials makes them suitable for use as plugging agents in drilling fluids, but existing nano-plugging agents, such as nano-silica, are prone to agglomeration and lack of plugging layer stability.

[0003] Therefore, there is an urgent need for a plugging and fluid loss reducer with nano-scale, strong dispersibility, low viscosity and good flexibility. Summary of the Invention

[0004] In order to solve the above problems in the prior art, the present invention is proposed.

[0005] In a first aspect, the present invention provides a nano-plugging fluid loss control agent, which includes a polytannic acid grafted hyperbranched polymer; the polytannic acid grafted hyperbranched polymer includes a hyperbranched polymer generated by a condensation reaction between polyethylene polyamine and an acrylic monomer, and a polytannic acid grafted hyperbranched polymer formed by a tannic acid under the action of an oxidant; the particle size of the nano-plugging fluid loss control agent is 90 to 150 nm.

[0006] It should be noted that hyperbranched polymers are soluble branched polymers with a three-dimensional structure. Their structure exhibits certain defects. Unlike perfect dendritic macromolecules, they require highly symmetrical molecules and a complete and standardized structure. This results in very low synthesis yields, which greatly limits their industrialization. Hyperbranched polymers not only inherit most of the excellent properties of dendritic macromolecules, possessing a large number of active end groups, low viscosity and high solubility, but also have simple synthesis methods and low production difficulty. In addition, the dispersion characteristics of hyperbranched polymers are similar to those of colloidal particles. Their "core-shell" structure can exist stably in water as a single-molecule dispersion, with strong dispersibility and molecular size controllable to several nanometers. Therefore, their advantages are mainly reflected in size and stability.

[0007] Tannic acid (TA), a polyphenolic compound derived from natural plants, is rich in benzene rings and phenolic hydroxyl groups. It oxidizes in air to form a quinone-like structure, which then undergoes Michael addition or Schiff base reactions with amino groups in hyperbranched polymers. Simultaneously, it polymerizes, forming nanoparticles through π-π interactions, stacking, and deposition of benzene rings. The resulting polytannic acid (PTA) nanoparticles are grafted with hyperbranched polymers and used as plugging and fluid loss additives. The grafted hyperbranched polymers can alleviate the agglomeration of the PTA nanoparticles and improve their dispersibility and stability. The abundant amino and catechol hydroxyl groups on the polytannic acid form strong, multi-site adhesion interactions with clay molecules, effectively inhibiting clay hydration, swelling, and dispersion. The stacked benzene ring structure is hydrophobic, hindering water from entering the clay layer. Furthermore, the nanoparticle structure acts as a physical plugging agent.

[0008] As a specific embodiment of the present invention, the polyethylene polyamine is any one or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine.

[0009] As a specific embodiment of the present invention, the acrylic monomer is any one or more of acrylic acid, methyl acrylate, and ethyl acrylate.

[0010] As a specific embodiment of the present invention, the molar ratio of the polyethylene polyamine to the acrylic monomer is 1:(2-5); and / or,

[0011] The mass ratio of the tannic acid to the hyperbranched polymer is 1:(5-10).

[0012] As a specific embodiment of the present invention, the oxidant is ammonium persulfate ((NH4)2S2O8 or sodium periodate (NaIO4);

[0013] The mass ratio of the oxidant to tannic acid is (0.05-0.1):1.

[0014] In a second aspect, the present invention provides a method for preparing the nano-plugging fluid loss additive, comprising the following steps:

[0015] S1: Polycondensation reaction of polyethylene polyamine and acrylic monomers to synthesize hyperbranched polymers;

[0016] S2: dissolving the hyperbranched polymer and tannic acid obtained in step S1 in a solvent respectively, and performing an addition reaction under the action of an oxidant to obtain a tannic acid-grafted hyperbranched polymer.

[0017] As a specific embodiment of the present invention, step S1 further includes the following steps:

[0018] S11: Under a nitrogen atmosphere, reacting polyethylene polyamine and methyl acrylate in a first solvent to generate an intermediate;

[0019] S12: Under vacuum conditions, subjecting the intermediate obtained in step S11 to polymerization in a second solvent to obtain a hyperbranched polymer.

[0020] As a specific embodiment of the present invention, in step S11, the first solvent is tetrahydrofuran; the tetrahydrofuran solution of polyethylene polyamine and the tetrahydrofuran solution of acrylic acid monomer are mixed and reacted, the concentration of polyethylene polyamine in the tetrahydrofuran solution of polyethylene polyamine is 0.02-0.2 g / mL; the concentration of acrylic acid monomer in the tetrahydrofuran solution of acrylic acid monomer is 0.05-0.2 g / mL; the molar ratio of polyethylene polyamine to acrylic acid monomer is 1:(2-5); preferably, the mixing temperature of polyethylene polyamine and methyl acrylate in the first solvent is 0-10°C; and the reaction temperature is 20-40°C.

[0021] Preferably, step S11 comprises: placing the reaction vessel in an ice-water bath for cooling, introducing nitrogen, and dropwise adding a tetrahydrofuran solution containing an acrylic acid monomer into the reaction vessel, controlling the dropwise addition time to be 0.5 to 2 hours. After the dropwise addition is completed, continuing the reaction at 25 to 35° C. for 4 to 8 hours to generate an intermediate; placing the intermediate on a rotary evaporator, setting the reduced vacuum degree to 500 to 1000 Pa, and drying at 30 to 50° C. for 4 to 7 hours to remove unreacted monomers and other solvents.

[0022] As a specific embodiment of the present invention, in step S12, the second solvent is methanol, the intermediate concentration is 0.05-0.2 g / mL; the vacuum degree is 500-1000 Pa, the polymerization reaction temperature is 90-130° C., and the polymerization reaction time is 8-16 h.

[0023] As a specific embodiment of the present invention, the step S12 further comprises cooling the mixture to 25-35° C. after the polymerization reaction is completed to obtain a hyperbranched polymer.

[0024] As a specific embodiment of the present invention, step S2 further includes the following steps:

[0025] S21: dissolving tannic acid and a hyperbranched polymer in a third solvent, respectively, to obtain a mixture of a tannic acid solution and a hyperbranched polymer solution;

[0026] S22: dissolving the oxidant in an acid-base buffer solution to obtain an oxidant solution;

[0027] S23: adding the mixture of the tannic acid solution and the hyperbranched polymer solution obtained in step S21 to the oxidant solution obtained in step S22 to carry out an addition reaction, and obtaining a polytannic acid grafted hyperbranched polymer through sedimentation, centrifugal separation, and drying.

[0028] As a specific embodiment of the present invention, in step S21, the third solvent is ethanol; the mass ratio of tannic acid to hyperbranched polymer is 1:(5-10); the concentration of tannic acid solution is 0.005-0.05 g / ml; the concentration of hyperbranched polymer solution is 0.01-0.1 g / ml;

[0029] In the step S22, the oxidant is ammonium persulfate ((NH4)2S2O8) or sodium periodate (NaIO4);

[0030] The acid-base buffer is a Tris-HCl buffer; the pH value of the acid-base buffer is 7 to 9; the solubility of the oxidant in the buffer is 0.002 to 0.01 g / mL;

[0031] In step S23, the mass ratio of the oxidant to tannic acid is (0.05-0.1):1; the addition reaction temperature is 25-40° C., and the addition reaction time is 2-4 hours.

[0032] The above raw materials in the present invention can be prepared in-house or purchased commercially, and the present invention is not particularly limited thereto.

[0033] In a third aspect, the present invention provides an application of the nano-plugging fluid loss reducer in the field of drilling fluid.

[0034] As a specific embodiment of the present invention, the mass fraction of the nano plugging fluid loss reducer in the drilling fluid is 0.5%-2%.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The nano plugging and fluid loss reducer of the present invention is prepared by Michael reaction and amidation reaction between polyethylene polyamine and acrylic monomer to obtain hyperbranched polymers containing amino groups of different generations; the generated hyperbranched polymers containing amino groups undergo Michael addition or Schiff base reaction with tannic acid and simultaneously self-polymerize to form nanoparticles through π-π interaction, stacking, and deposition of benzene rings; the hyperbranched polymers are grafted onto the formed polytannic acid (PTA) nanoparticles, and the resulting nanoparticles are used as a plugging and fluid loss reducer for drilling fluids.

[0037] 2. The nano-plugging fluid loss reducer of the present invention has particles rich in catechol hydroxyl groups from tannic acid and amino groups from branched polyamines, which can form multi-site, strong adhesion effects with clay molecules, and can have a strong connection force on the end faces of micro-fractures in the formation, thereby sealing the pore throats of mudstone. The stacked structure of polytannic acid benzene rings is hydrophobic, which can prevent water molecules from entering the clay layer and reduce fluid loss. The nanoparticle structure can play a physical plugging role. The composition and structural characteristics of the above nano-plugging fluid loss reducer for drilling fluid are conducive to maintaining the stability of mudstone.

[0038] 3. The present invention utilizes the natural plant polyphenol compound tannic acid (TA) grafted with a hyperbranched polymer to prepare a nanometer plugging and filtration reducer for drilling fluid. The obtained particles are low in toxicity, environmentally friendly, degradable, environmentally friendly, and green. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to specific examples, but they do not constitute any limitation to the present invention.

[0040] In each embodiment of the present invention, the specific information of the reagents used is as follows:

[0041] Diethylenetriamine was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0042] Triethylenetetramine was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0043] Tetraethylenepentamine was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0044] Pentaethylenehexamine was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0045] Acrylic acid, analytical grade, was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0046] Methyl acrylate, analytical grade, was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0047] Ethyl acrylate, analytical grade, was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0048] Tannic acid was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0049] Tetrahydrofuran, analytical grade, was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0050] Tris-HCl buffer was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0051] Example 1

[0052] This embodiment provides a nano-plugging fluid loss additive and a preparation method thereof, the specific details of which are as follows:

[0053] S1: Weigh 3.7g of triethylenetetramine and mix with 100mL of tetrahydrofuran and place in a reaction vessel. Then weigh 5.4g of acrylic acid, dissolve it in 50mL of tetrahydrofuran and place it in a constant pressure dropping funnel. Place the reaction vessel in an ice-water bath, control the temperature to 5°C, pass nitrogen and add the tetrahydrofuran solution containing acrylic acid to the reaction vessel dropwise within 0.5h. After the addition is complete, raise the temperature to 30°C and react for 4h. After the reaction is completed, filter and obtain the intermediate; the intermediate is vacuum-dried at a temperature of 40°C and a vacuum degree of 500Pa for 5h to remove unreacted monomers and other solvents.

[0054] S2: 5.0 g of the intermediate obtained in step S1 was dissolved in 100 ml of methanol in a flask. The temperature was raised to 110° C. under a vacuum degree of 500 Pa, and vacuum rotary polymerization was performed for 8 h. The mixture was then cooled to 30° C. to obtain a hyperbranched polymer.

[0055] S3: Dissolve 0.5 g of tannic acid in 50 ml of ethanol and 3.0 g of the hyperbranched polymer obtained in step S2 in 100 ml of ethanol to obtain a mixture of a tannic acid solution and a hyperbranched polymer solution; dissolve 0.05 g of an oxidizing agent, ammonium persulfate ((NH4)2S2O8), in 10 ml of Tris-HCl buffer, the pH value of the buffer being 8, to obtain an oxidizing agent solution; mix the tannic acid solution and the hyperbranched polymer solution, then add the oxidizing agent solution, stir, react at 25°C for 2 h, settle overnight, centrifuge, and dry to obtain a polytannic acid grafted hyperbranched polymer.

[0056] Example 2

[0057] This embodiment provides a nano-plugging fluid loss additive and a preparation method thereof, the specific details of which are as follows:

[0058] S1: Weigh 4.7g of tetraethylenepentamine and mix with 100mL of tetrahydrofuran and place in a reaction vessel. Then weigh 10.8g of acrylic acid and dissolve it in 100mL of tetrahydrofuran and place in a constant pressure dropping funnel. Place the reaction vessel in an ice-water bath, control the temperature to 0°C, pass nitrogen and add the tetrahydrofuran solution containing acrylic acid to the reaction vessel dropwise. The addition is completed within 1.0h. After the addition is completed, raise the temperature to 25°C and react for 6h. After the reaction is completed, filter and obtain the intermediate; the intermediate is vacuum-dried at a temperature of 50°C and a vacuum degree of 700Pa for 7h to remove unreacted monomers and other solvents.

[0059] S2: 5.0 g of the intermediate obtained in step S1 was dissolved in 100 ml of methanol in a flask. The temperature was raised to 90° C. under a vacuum degree of 700 Pa, and vacuum rotary polymerization was performed for 12 h. The mixture was then cooled to 25° C. to obtain a hyperbranched polymer.

[0060] S3: Dissolve 0.5 g of tannic acid in 50 ml of ethanol and 2.5 g of the hyperbranched polymer obtained in step S2 in 100 ml of ethanol to obtain a mixture of a tannic acid solution and a hyperbranched polymer solution; dissolve 0.025 g of an oxidizing agent, sodium periodate (NaIO4), in 10 ml of a Tris-HCl buffer solution having a pH of 9 to obtain an oxidizing agent solution; mix the prepared tannic acid solution and the hyperbranched polymer solution, add the oxidizing agent solution, stir, react at 30°C for 3 h, allow to settle overnight, centrifuge, and dry to obtain a polytannic acid grafted hyperbranched polymer.

[0061] Example 3

[0062] This embodiment provides a nano-plugging fluid loss additive and a preparation method thereof, the specific details of which are as follows:

[0063] S1: Weigh 2.6g of diethylenetriamine and mix with 100mL of tetrahydrofuran and place in a reaction vessel. Then weigh 12.5g of ethyl acrylate and dissolve it in 100mL of tetrahydrofuran and place in a constant pressure dropping funnel. Place the reaction vessel in an ice-water bath, control the temperature to 10°C, pass nitrogen and add the tetrahydrofuran solution containing acrylic acid to the reaction vessel dropwise. The addition is completed within 2.0h. After the addition is completed, raise the temperature to 35°C and react for 8h. After the reaction is completed, filter and obtain the intermediate; the intermediate is vacuum-dried at a temperature of 30°C and a vacuum degree of 1000Pa for 7h to remove unreacted monomers and other solvents.

[0064] S2: 5.0 g of the intermediate obtained in step S1 was dissolved in 100 ml of methanol in a flask. The temperature was raised to 130° C. under a vacuum degree of 1000 Pa, and vacuum rotary polymerization was performed for 16 h. The polymer was then cooled to 35° C. to obtain a hyperbranched polymer.

[0065] S3: Dissolve 0.5 g of tannic acid in 50 ml of ethanol and 4.5 g of the hyperbranched polymer obtained in step S2 in 100 ml of ethanol to obtain a mixture of a tannic acid solution and a hyperbranched polymer solution; dissolve 0.05 g of an oxidizing agent, ammonium persulfate ((NH4)2S2O8), in 10 ml of a Tris-HCl buffer solution having a pH of 7 to obtain an oxidizing agent solution; mix the tannic acid solution and the hyperbranched polymer solution, then add the oxidizing agent solution, stir, react at 40°C for 4 h, allow to settle overnight, centrifuge, and dry to obtain a polytannic acid grafted hyperbranched polymer.

[0066] Example 4

[0067] This embodiment provides a nano-plugging fluid loss additive and a preparation method thereof, the specific details of which are as follows:

[0068] S1: Weigh 5.8g of pentaethylenehexamine and mix with 100mL of tetrahydrofuran and place in a reaction vessel. Weigh 10.0g of ethyl acrylate and dissolve it in 100mL of tetrahydrofuran and place in a constant pressure dropping funnel. Place the reaction vessel in an ice-water bath, control the temperature to 5°C, pass nitrogen and add the tetrahydrofuran solution containing acrylic acid to the reaction vessel dropwise within 1.5h. After the addition is complete, raise the temperature to 25°C and react for 5h. After the reaction is completed, filter and obtain the intermediate; the intermediate is vacuum-dried at 50°C and a vacuum degree of 900Pa for 5h to remove unreacted monomers and other solvents.

[0069] S2: 5.0 g of the intermediate obtained in step S1 was dissolved in 100 ml of methanol in a flask. The temperature was raised to 100° C. under a vacuum degree of 1000 Pa, and vacuum rotary polymerization was performed for 10 h. The mixture was then cooled to 30° C. to obtain a hyperbranched polymer.

[0070] S3: Dissolve 0.5 g of tannic acid in 50 ml of ethanol and 5.0 g of the hyperbranched polymer obtained in step S2 in 100 ml of ethanol; dissolve 0.04 g of the oxidant sodium periodate (NaIO4) in 10 ml of Tris-HCl buffer, the buffer having a pH of 8, to obtain an oxidant solution; mix the tannic acid solution and the hyperbranched polymer solution, add the oxidant solution, stir, react at 25°C for 3 h, allow to settle overnight, centrifuge, and dry to obtain a polytannic acid grafted hyperbranched polymer.

[0071] Example 5

[0072] This embodiment provides a nano-plugging fluid loss additive and a preparation method thereof, the specific details of which are as follows:

[0073] S1: Weigh 3.7g of triethylenetetramine and mix with 100mL of tetrahydrofuran and place in a reaction vessel. Weigh 4.3g of methyl acrylate and dissolve it in 50mL of tetrahydrofuran and place in a constant pressure dropping funnel. Place the reaction vessel in an ice-water bath, control the temperature to 7°C, pass nitrogen and add the tetrahydrofuran solution containing acrylic acid to the reaction vessel dropwise within 2.0h. After the addition is complete, raise the temperature to 35°C and react for 6h. After the reaction is completed, filter and obtain the intermediate; the intermediate is vacuum-dried at a temperature of 30°C and a vacuum degree of 800Pa for 7h to remove unreacted monomers and other solvents.

[0074] S2: 5.0 g of the intermediate obtained in step S1 was dissolved in 100 ml of methanol in a flask. The temperature was raised to 90° C. under a vacuum degree of 800 Pa, and vacuum rotary polymerization was performed for 8 h. The mixture was then cooled to 35° C. to obtain a hyperbranched polymer.

[0075] S3: Dissolve 0.5 g of tannic acid in 50 ml of ethanol and 4.0 g of the hyperbranched polymer obtained in step S2 in 100 ml of ethanol; dissolve 0.03 g of the oxidant ammonium persulfate ((NH4)2S2O8) in 10 ml of Tris-HCl buffer, the buffer having a pH of 9, to obtain an oxidant solution; mix the tannic acid solution and the hyperbranched polymer solution, add the oxidant solution, stir, react at 40°C for 4 h, allow to settle overnight, centrifuge, and dry to obtain a polytannic acid grafted hyperbranched polymer.

[0076] Comparative Example 1

[0077] This comparative example provides a nano-plugging fluid loss additive and a preparation method thereof, the specific details of which are as follows:

[0078] The 3.7 g of triethylenetetramine and 5.4 g of acrylic acid in step S1 of Example 1 were replaced with 7.3 g of triethylenetetramine and 3.6 g of acrylic acid, i.e., the molar ratio of triethylenetetramine to acrylic acid was 1:1, and other conditions remained unchanged to prepare a nano plugging fluid loss additive.

[0079] Comparative Example 2

[0080] This comparative example provides a nano-plugging fluid loss additive and a preparation method thereof, the specific details of which are as follows:

[0081] The polymerization temperature of the intermediate of 100° C. in step S2 of Example 1 was replaced with 150° C., that is, the polymerization temperature of the intermediate was 150° C., and other conditions remained unchanged, to prepare a nano plugging fluid loss additive.

[0082] Comparative Example 3

[0083] This comparative example provides a nano-plugging fluid loss additive and a preparation method thereof, the specific details of which are as follows:

[0084] The 3.0 g of hyperbranched polymer in step S3 of Example 1 was replaced with 7.5 g of hyperbranched polymer, that is, the mass ratio of tannic acid to hyperbranched polymer was 1:15, and other conditions remained unchanged to prepare a nano plugging fluid loss additive.

[0085] Test Example 1

[0086] The particle sizes of the nano plugging agents for drilling fluids of Examples 1 to 5 and Comparative Examples 1 to 3 were measured using a nano laser particle size analyzer. The results are shown in Table 1.

[0087] Table 1 Particle size test results of drilling fluid nano plugging agent

[0088] Test sample Particle size / nm Example 1 102-126 Example 2 90-115 Example 3 95-133 Example 4 110-145 Example 5 130-150 Comparative Example 1 97-122 Comparative Example 2 312-353 Comparative Example 3 242-278

[0089] As can be seen from the data in Table 1, the nano-plugging fluid loss additive particles produced in Examples 1-5 are small, all below 150 nm. Comparative Example 1 produces smaller particles; Comparative Example 2 increases the intermediate polymerization temperature, intensifying the polymerization reaction and producing larger particles; and Comparative Example 3 increases the amount of hyperbranched polymer, increasing the viscosity of the reaction solution and failing to utilize dispersion, resulting in the product being easily agglomerated.

[0090] Test Example 2

[0091] Plugging Performance Evaluation: Referring to GB16783.1-2014, "Field Testing of Drilling Fluids in the Petroleum and Natural Gas Industry, Part 1: Water-Based Drilling Fluids," the viscosity, fluid loss reduction, and plugging performance of the nano-plugging agents used in Examples 1-5 and Comparative Examples 1-3 were evaluated in a 6wt% bentonite-based slurry. Plugging fluid loss was measured using an OFITE plugging filter meter under test conditions of 150°C, 21 MPa, and a filter disc model 170-55 with a pore size of 3μm and a permeability of 400mD. The test sample consisted of 2wt% of the nano-plugging agent added to a 6wt% bentonite-based slurry.

[0092] The preparation method of 6wt% bentonite-based slurry (hereinafter referred to as 6%-based slurry) is as follows: 0.8g sodium carbonate, 0.8g sodium hydroxide and 24g sodium clay are added to 400mL fresh water, stirred at 10000rpm / min for 20min, and hydrated at room temperature for 24h.

[0093] The test results are shown in Table 2 below.

[0094] Table 2 Performance evaluation results of drilling fluid nano plugging agents

[0095]

[0096]

[0097] As can be seen from the data in Table 2, adding 2 wt% of Examples 1 to 5 to the 6% base slurry increases viscosity and significantly reduces fluid loss. Furthermore, after aging at 150°C for 16 hours, the slurry still exhibits good fluid loss reduction and plugging effects.

[0098] In Comparative Example 1, due to the reduced content of acrylic acid monomers, the viscosity of the generated hyperbranched polymer is low, resulting in unsatisfactory viscosity, fluid loss reduction and plugging effects of the product nano-plugging fluid loss reducer.

[0099] In Comparative Example 2, increasing the polymerization temperature of the intermediate causes the polymerization reaction of the hyperbranched polymer to intensify, the molecular weight to increase, and the viscosity to rise, which is not conducive to the grafting reaction. As a result, the generated nano plugging and fluid loss reducer has a high viscosity, but the molecular volume formed is large, which is not conducive to plugging and causes an increase in fluid loss.

[0100] In Comparative Example 3, the amount of hyperbranched polymer added was increased, the viscosity of the reaction solution increased, and tannic acid was not used for dispersion, and its surface grafting was not used to cause hyperbranched polymer, resulting in a decrease in the viscosity of the generated nano-plugging fluid loss agent, a decrease in plugging ability, and an increase in fluid loss.

[0101] In summary, the nano-plugging and fluid loss reducing agent of the present invention utilizes the ultra-high surface activity of nanoparticles, combined with the characteristics of hyperbranched polymers such as easy solubility, low viscosity, strong dispersion, and multiple end groups and high activity, and has "core-shell structure, strong dispersibility, low viscosity and good flexibility"; the hyperbranched polymer fluid loss reducing and plugging agent of the present invention utilizes its strong connection force to the end faces of micro-fractures to achieve the plugging of shale pore throats, maximize the film-forming plugging ability and fluid loss reduction performance, improve the plugging efficiency, enhance the density and strength of the mud cake, reduce drilling fluid loss, and enhance the wellbore stability of micro-fracture formations.

[0102] Any numerical value mentioned in the present invention includes all values ​​that increase by one unit each time from the lowest value to the highest value if there is only a gap of two units between any minimum value and any maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, time, etc. is stated to be 50-90, it is meant in this specification to specifically list values ​​such as 51-89, 52-88... and 69-71 and 70-71. For non-integer values, it is appropriate to consider units of 0.1, 0.01, 0.001 or 0.0001. These are just some special examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed lowest value and the listed highest value are considered to have been disclosed.

[0103] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation of the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A nano plugging fluid loss additive, characterized in that: The nano plugging and fluid loss reducer comprises a tannic acid grafted hyperbranched polymer; the tannic acid grafted hyperbranched polymer comprises a hyperbranched polymer generated by a polycondensation reaction of polyethylene polyamine and acrylic monomers, and a polytannic acid grafted hyperbranched polymer formed by reacting tannic acid with an oxidant; The molar ratio of the polyethylene polyamine to the acrylic monomer is 1:(2-5); The mass ratio of the tannic acid to the hyperbranched polymer is 1:(5-10); The acrylic monomer is any one or more of acrylic acid, methyl acrylate, and ethyl acrylate; The particle size of the nano plugging fluid loss reducer is 90-150 nm.

2. The nano plugging fluid loss agent according to claim 1, characterized in that: The polyethylene polyamine is any one or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine.

3. The nano plugging fluid loss agent according to claim 1 or 2, characterized in that: The oxidant is ammonium persulfate ((NH4)2S2O8) and / or sodium periodate (NaIO4); The mass ratio of the oxidant to tannic acid is (0.05-0.1):

1.

4. A method for preparing the nano plugging fluid loss additive according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: Synthesis of hyperbranched polymers by polycondensation of polyethylene polyamine and acrylic monomers; S2: dissolving the hyperbranched polymer and tannic acid obtained in step S1 in a solvent respectively, and performing an addition reaction under the action of an oxidant to obtain a tannic acid-grafted hyperbranched polymer.

5. The preparation method according to claim 4, characterized in that The step S1 further comprises the following steps: S11: Under a nitrogen atmosphere, polyethylene polyamine and methyl acrylate are mixed and reacted in a first solvent to generate an intermediate; S12: Under vacuum conditions, subjecting the intermediate obtained in step S11 to polymerization in a second solvent to obtain a hyperbranched polymer.

6. The preparation method according to claim 5, characterized in that In step S11, the first solvent is tetrahydrofuran; the tetrahydrofuran solution of polyethylene polyamine and the tetrahydrofuran solution of acrylic acid monomer are mixed and reacted, the concentration of polyethylene polyamine in the tetrahydrofuran solution is 0.02 to 0.2 g / mL; the concentration of acrylic acid monomer in the tetrahydrofuran solution is 0.05 to 0.2 g / mL; And / or, the molar ratio of the polyethylene polyamine to the acrylic monomer is 1:(2-5).

7. The preparation method according to claim 6, characterized in that In the step S11, the mixing temperature of the polyethylene polyamine and methyl acrylate in the first solvent is 0-10°C; and the reaction temperature is 20-40°C.

8. The preparation method according to claim 5, characterized in that In step S12, the second solvent is methanol, the intermediate concentration is 0.05-0.2 g / mL; the vacuum degree is 500-1000 Pa, the polymerization temperature is 90-130° C., and the polymerization time is 8-16 h; And / or, the step S12 further comprises cooling the mixture to 25-35° C. after the polymerization reaction is completed to obtain a hyperbranched polymer.

9. The preparation method according to any one of claims 4 to 8, characterized in that The step S2 further comprises the following steps: S21: dissolving tannic acid and a hyperbranched polymer in a third solvent, respectively, to obtain a mixture of a tannic acid solution and a hyperbranched polymer solution; S22: dissolving the oxidant in an acid-base buffer solution to obtain an oxidant solution; S23: adding the mixture of the tannic acid solution and the hyperbranched polymer solution obtained in step S21 to the oxidant solution obtained in step S22 to carry out an addition reaction, and then subjecting the mixture to sedimentation, centrifugal separation, and drying to obtain a polytannic acid grafted hyperbranched polymer.

10. The preparation method according to claim 9, characterized in that In step S21, the third solvent is ethanol; the mass ratio of tannic acid to hyperbranched polymer is 1:(5-10); and / or the concentration of the tannic acid solution is 0.005-0.05 g / ml; the concentration of the hyperbranched polymer solution is 0.01-0.1 g / ml; and / or, in step S22, the oxidant is ammonium persulfate ((NH4)2S2O8) or sodium periodate (NaIO4); And / or, the acid-base buffer is Tris-HCl buffer; And / or, in step S23, the mass ratio of the oxidant to tannic acid is (0.05-0.1):1; the addition reaction temperature is 25-40° C., and the addition reaction time is 2-4 hours.

11. The preparation method according to claim 10, characterized in that: The pH value of the buffer solution is 7 to 9; And / or, the solubility of the oxidant in the acid-base buffer solution is 0.002-0.01 g / mL.

12. Use of the nano-plugging fluid loss agent according to any one of claims 1 to 3 or the nano-plugging fluid loss agent prepared by the preparation method according to any one of claims 4 to 11 in the field of drilling fluids.

13. The use according to claim 12, characterized in that The mass fraction of the nano plugging and fluid loss reducer in the drilling fluid is 0.5%-2%.

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