Modified silica nanoparticles plugging agent, preparation method and application thereof

Abstract

The application belongs to the technical field of oil and gas drilling, and particularly relates to a modified silica nanoparticle plugging agent and a preparation method and application thereof. The preparation raw materials of the plugging agent comprise 50 parts of acrylamide monomer, 5-15 parts of acrylic ester monomer, 2-20 parts of 1-propyl sulfonic acid-3-vinylimidazole inner salt, 0.06-0.8 parts of N,N-methylene bisacrylamide, 5-16 parts of emulsifier, 8-12 parts of composite silica nanoparticles, 0.1-0.6 parts of initiator and 100-144 parts of water. The plugging agent has multi-scale plugging capacity, excellent dispersion stability, temperature resistance and salt resistance, and the formed plugging layer has high pressure-bearing capacity.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas drilling technology, specifically relating to a modified silica nanoparticle plugging agent, its preparation method, and its application. Background Technology

[0002] Well collapse, lost circulation, and reservoir protection are the three major technical challenges hindering the smooth progress of drilling operations. For formations with well-developed bedding and fractures, especially shale formations, drilling fluids with strong sealing properties are required to prevent well collapse and lost circulation, and to reduce damage to reservoirs. These fluids must effectively seal bedding and fractures, preventing drilling fluid and its filtrate from entering the formation, thereby improving the formation's pressure-bearing capacity, stabilizing the wellbore, preventing lost circulation, and protecting the reservoir.

[0003] Shale has extremely low permeability and very small pore throat size. Traditional plugging agents typically have particle sizes between 0.1 and 500 μm, mainly suitable for plugging formation microfractures of 0.1-1 mm. However, shale formations generally have nano- and micron-sized microfractures with a wide width distribution. Therefore, the selected plugging particles need to have a sufficiently wide size distribution to form a good seal in shale. Conventional drilling fluid treatment agents can only form mud cakes in shale formations. Only nano-sized particles can effectively seal shale microfractures, prevent liquid phase intrusion into the formation, and maintain wellbore stability.

[0004] Nanoparticle plugging agents are commonly used functional materials in water-based drilling fluids to address wellbore instability caused by formation fracture hydration. However, commonly used inorganic nanoparticle plugging agents, due to their small size, often spontaneously form large particle aggregates before reaching the formation fractures, making it difficult to effectively plug micro-fractures and unpredictable in their plugging effect. Furthermore, inorganic nanoparticle plugging agents exhibit poor dispersibility in water-based drilling fluids, resulting in poor ability to plug nanoscale micro-cracks. For example, CN105801783A discloses a modified silica nanoparticle plugging agent, which is generated by polymerizing nano-silica particles with specific structural monomers after forming grafting sites through a coupling agent. The particle size is mainly distributed below 50 nm, making it difficult to effectively plug micro-fractures larger than 50 nm. CN201911317842.9 discloses a modified nano-silica plugging agent, which is modified by copolymerization of acrylic acid and polybutyl methacrylate emulsion to plug 0.1-1mm mudstone and shale cracks. However, the reaction process is difficult to control and the nano-silica plugging agent is prone to spontaneous aggregation during the reaction.

[0005] Therefore, the existing nano-sealing agents have problems such as severe nanoparticle aggregation, insufficient adaptability to multi-scale cracks, and poor pressure bearing capacity of the sealing layer, which have become technical problems that urgently need to be solved. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a modified silica nanoparticle plugging agent, its preparation method, and its application. This plugging agent possesses multi-scale plugging capability, excellent dispersion stability, temperature and salt resistance, and the resulting plugging layer exhibits strong pressure resistance.

[0007] On one hand, the present invention provides a modified composite silica nanoparticle plugging agent, the raw materials for which are prepared include: The composition comprises 50 parts of acrylamide monomers, 5-15 parts of acrylate monomers, 2-20 parts of 1-propylsulfonic acid-3-vinylimidazolium inner salt, 0.06-0.8 parts of N,N-methylenebisacrylamide, 5-16 parts of emulsifier, 8-12 parts of composite silica nanoparticles, 0.1-0.6 parts of initiator, and 100-144 parts of water; the composite silica nanoparticles are a mixture of 10-50 nm and 100-450 nm silica nanoparticles.

[0008] In some embodiments, the acrylamide monomer is at least one of acrylamide or methacrylamide.

[0009] In some embodiments, the acrylate monomer is at least one of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, or butyl methacrylate.

[0010] In some implementations, the weight ratio of 10-50 nm nano-silica particles to 100-450 nm nano-silica particles is 1-5:1.

[0011] In some embodiments, the emulsifier is a sorbitan fatty acid ester and / or a polyoxyethylene sorbitan fatty acid ester, preferably one or more of SPAN-60, SPAN-80, SPAN-85, TWEEN40, TWEEN60 or TWEEN80.

[0012] In some embodiments, the initiator is a water-soluble peroxide initiator, preferably one of potassium persulfate, ammonium persulfate, or hydrogen peroxide. Preferably, the amount of initiator used is 0.3-0.8% of the total mass of acrylamide monomers, acrylate monomers, and 1-propylsulfonic acid-3-vinylimidazolium inner salt monomers.

[0013] In some implementation schemes, water includes, but is not limited to, distilled water and deionized water.

[0014] On the other hand, the present invention provides a method for preparing the aforementioned modified composite silica nanoparticle plugging agent, comprising: Acrylamide monomers, acrylate monomers, 1-propylsulfonic acid-3-vinylimidazolium inner salt and N,N-methylenebisacrylamide were mixed with emulsifier and water and stirred, and then mixed with composite silica nanoparticles to obtain a mixed dispersion. An inert gas is introduced into the mixed dispersion, and then an initiator is added to initiate a polymerization reaction to obtain a modified composite silica nanoparticle plugging agent.

[0015] In some embodiments, the mixture with the emulsifier and water is stirred by mechanical stirring or ultrasonic dispersion, preferably ultrasonic dispersion. Preferably, the mechanical stirring speed is 500-800 rpm, the mechanical stirring time is 2-4 hours, the ultrasonic frequency is 20-40 kHz, and the ultrasonic time is 2-4 hours.

[0016] In some implementations, the mixing and stirring of the composite silica nanoparticles is carried out by mechanical stirring. Preferably, the mechanical stirring speed is 2000-5000 rpm and the time is 3-5 hours.

[0017] In some embodiments, the polymerization temperature is 50-90°C, preferably 70-80°C, and the polymerization time is 6-15 hours, preferably 8-12 hours.

[0018] The preparation method of the present invention involves Pickering emulsion polymerization of acrylamide monomers, acrylate monomers, and 1-propylsulfonic acid-3-vinylimidazolium inner salt monomer in the presence of crosslinking monomers. During the emulsion polymerization, silica nanoparticles with different particle size combinations are introduced to form modified composite silica nanoparticles with multi-scale plugging capabilities as plugging agents, which can simultaneously and effectively plug formation fractures of different levels.

[0019] On the other hand, the present invention provides the application of the aforementioned modified composite silica nanoparticle plugging agent in water-based drilling fluids.

[0020] In some implementations, the modified composite silica nanoparticle plugging agent is added to the drilling fluid at an amount of 3-5%.

[0021] Compared with the prior art, the sealing agent of the present invention has the following beneficial effects: (1) Multi-scale plugging capability: By combining silica nanoparticles with two particle size ranges of 10-50 nm and 100-450 nm, the particle size distribution effect can be utilized to simultaneously plug formation microfractures at the nanoscale and micrometer scale. Experimental results show that the filtration loss of the dual-particle-size plugging agent on filter membranes with different pore sizes from 0.01 μm to 0.5 μm is ≤5.4 mL, which is far superior to the single-particle-size combination.

[0022] (2) Excellent dispersion stability: The imidazole ring and sulfonic acid group of the introduced 1-propylsulfonic acid-3-vinylimidazolium inner salt monomer provide dual stabilizing effects of steric hindrance and electrostatic repulsion, effectively preventing the aggregation of nanoparticles and maintaining good dispersion in water-based drilling fluid.

[0023] (3) Temperature and salt resistance: The introduced 1-propylsulfonic acid-3-vinylimidazolium inner salt monomer has a rigid imidazolium ring structure and a sulfonic acid group with strong hydration ability, which gives the plugging agent excellent temperature resistance (150℃) and salt resistance.

[0024] (4) Strong pressure resistance of the sealing layer: Under high temperature and high pressure conditions of 150℃ and 3.5MPa, the sealing agent of the present invention can still maintain low filtration loss, indicating that the sealing layer has high pressure resistance. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1 50g of methacrylamide, 10g of methyl methacrylate, 4g of 1-propylsulfonic acid-3-vinylimidazolium inner salt, 0.3g of N,N-methylenebisacrylamide, and 10g of SPAN-60 were added to 100g of distilled water and emulsified by mechanical stirring (600rpm, 3h). Then, 8g of nano-silica (1.33g 100nm + 6.67g 20nm) was added and dispersed by stirring at 3000rpm for 4h. Nitrogen gas was introduced to raise the temperature to 65℃, and 0.4g of potassium persulfate was added dropwise. The mixture was reacted at 150rpm for 10h to obtain a modified composite silica nanoparticle blocking agent.

[0027] Example 2 50g of methacrylamide, 8g of butyl methacrylate, 10g of 1-propylsulfonic acid-3-vinylimidazolium inner salt, 0.5g of N,N-methylenebisacrylamide, and 10g of SPAN-60 were added to 100g of distilled water and ultrasonically emulsified (30 kHz, 3h). Then, 10g of nano-silica (1.67g 100 nm + 8.33g 20 nm) was added and stirred and dispersed at 4000 rpm for 4h. Nitrogen gas was introduced and the temperature was raised to 70℃, and 0.32g of potassium persulfate was added dropwise. The reaction was carried out for 12h to obtain a modified composite silica nanoparticle blocking agent.

[0028] Example 3 50g acrylamide, 10g ethyl acrylate, 8g 1-propylsulfonic acid-3-vinylimidazolium inner salt, 0.5g N,N-methylenebisacrylamide, and 12g TWEEN60 were added to 110g distilled water and ultrasonically emulsified (25 kHz, 3 h). Then, 9g of nano-silica (6.75g 30nm + 2.25g 200nm) was added and stirred and dispersed at 3500 rpm for 4 h. Nitrogen gas was introduced and the temperature was raised to 70℃, and 0.4g ammonium persulfate was added dropwise. The reaction was carried out for 10 h to obtain the modified composite silica nanoparticle sealing agent.

[0029] Example 4 50g of methacrylamide, 15g of butyl methacrylate, 15g of 1-propylsulfonic acid-3-vinylimidazolium inner salt, 0.8g of N,N-methylenebisacrylamide, and 16g of SPAN-80 were added to 144g of distilled water and emulsified by mechanical stirring (800 rpm, 2 h). Then, 12g of nano-silica (8g 10nm + 4g 450nm) was added and dispersed by stirring at 5000 rpm for 3 h. Nitrogen gas was introduced to raise the temperature to 90℃, and 0.6g of potassium persulfate was added dropwise. The reaction was carried out for 6 h to obtain the modified composite silica nanoparticle sealing agent.

[0030] Example 5 50g acrylamide, 5g methyl acrylate, 2g 1-propylsulfonic acid-3-vinylimidazolium inner salt, 0.06g N,N-methylenebisacrylamide, and 5.7g TWEEN40 were added to 85.5g distilled water and ultrasonically emulsified (20 kHz, 4 h). Then, 8g of nano-silica (4g 50nm + 4g 100nm) was added and stirred and dispersed at 2000 rpm for 5 h. Nitrogen gas was introduced and the temperature was raised to 50℃, and 0.17g hydrogen peroxide was added dropwise. The reaction was carried out for 15 h to obtain the modified composite silica nanoparticle sealing agent.

[0031] Example 6 50g of methacrylamide, 10g of methyl methacrylate, 2g of 1-propylsulfonic acid-3-vinylimidazolium inner salt, 0.3g of N,N-methylenebisacrylamide, and 10g of SPAN-60 were added to 100g of distilled water and emulsified by mechanical stirring (600rpm, 3h). Then, 8g of nano-silica (1.33g 100nm + 6.67g 20nm) was added and dispersed by stirring at 3000rpm for 4h. Nitrogen gas was introduced to raise the temperature to 65℃, and 0.4g of potassium persulfate was added dropwise. The mixture was reacted at 150rpm for 10h to obtain a modified composite silica nanoparticle blocking agent.

[0032] Example 7 50g of methacrylamide, 10g of butyl acrylate, 20g of 1-propylsulfonic acid-3-vinylimidazolium inner salt, 0.3g of N,N-methylenebisacrylamide, and 10g of SPAN-60 were added to 100g of distilled water and emulsified by mechanical stirring (600 rpm, 3 h). Then, 8g of composite nano-silica (1.33g 100nm + 6.67g 20nm) was added and dispersed by stirring at 3000 rpm for 4 h. Nitrogen gas was introduced to raise the temperature to 65℃, and 0.4g of potassium persulfate was added dropwise. The mixture was reacted at 150 rpm for 10 h to obtain the modified composite silica nanoparticle blocking agent.

[0033] Comparative Example 1 The difference from Example 1 is that nano-silica is removed, resulting in a sealing agent without modified composite silica nanoparticles.

[0034] Comparative Example 2 The difference from Example 1 is that the composite nano-silica is replaced with silica particles with a particle size of 20 nm to obtain the modified composite silica nanoparticle blocker.

[0035] Comparative Example 3 The difference from Example 1 is that the composite nano-silica is replaced with silica particles with a particle size of 100 nm to obtain the modified composite silica nanoparticle blocker.

[0036] Comparative Example 4 The difference from Example 1 is that 1-propylsulfonic acid-3-vinylimidazolium inner salt was not added, and the modified composite silica nanoparticle plugging agent was finally obtained.

[0037] Comparative Example 5 The difference from Example 1 is that 1-propylsulfonic acid-3-vinylimidazolium inner salt was replaced with an equal mass of sodium styrene sulfonate, and the modified composite silica nanoparticle plugging agent was finally obtained.

[0038] Comparative Example 6 The difference from Example 1 is that 1-propylsulfonic acid-3-vinylimidazolium inner salt was replaced with an equal mass of sodium methacrylate sulfonate, and the modified composite silica nanoparticle plugging agent was finally obtained.

[0039] Comparative Example 7 The difference from Example 1 is that 1-propylsulfonic acid-3-vinylimidazolium inner salt was replaced with an equal mass of sodium 4-vinylbenzenesulfonate, and the modified composite silica nanoparticle plugging agent was finally obtained.

[0040] Comparative Example 8 8 g of nano-silica (1.33 g 100 nm + 6.67 g 20 nm) was added to water and sonicated at 20 kHz for 2 h to obtain a suspension. Then, 50 g of methacrylamide, 10 g of methyl methacrylate, and 4 g of 1-propylsulfonic acid-3-vinylimidazolium inner salt were added to the suspension and stirred until homogeneous. The mixture was heated to 65 °C under nitrogen purging, and 0.3 g of N,N-methylenebisacrylamide and 0.4 g of potassium persulfate were added. The reaction was carried out at 150 rpm for 10 h to obtain a modified composite silica nanoparticle blocking agent.

[0041] The plugging agents prepared in the above examples and comparative examples were added to water-based drilling fluid slurries, and their dispersion stability, plugging performance, and temperature and salt resistance were tested, as follows: (1) Dispersion stability test Table 1. Dispersion stability test results

[0042] As shown in Table 1, the dual-particle-size gradation (Example 1) utilizes small particles to fill the gaps between large particles, inhibiting particle migration and collision, and its anti-agglomeration ability is significantly better than that of the single-particle-size system (Comparative Example 2). Insufficient zwitterionic monomer dosage (Example 6) leads to insufficient steric hindrance and slow flocculation, while excessive dosage (Example 7) causes bridging flocculation. The rigid steric hindrance of the imidazole ring and the strong hydration layer of the sulfonic acid group (Example 1) improve the stability of particle dispersion, which is better than that of conventional sulfonate monomers (Comparative Examples 5-7). The synthesis process of emulsification followed by polymerization (Example 1) ensures the formation of a core-shell structure, and its dispersion performance is significantly higher than that of the direct mixing process (Comparative Example 8). The lack of a rigid SiO2 framework (Comparative Example 1) directly results in the system being dominated by micron-sized particles.

[0043] (2) Blocking performance test Water-based drilling fluid slurry: 100 parts by weight of water, 4g of sodium bentonite, and 0.15g of sodium carbonate are mixed to obtain the slurry.

[0044] Plugging performance test: Polytetrafluoroethylene (PTFE) microporous filter membranes with pore sizes of 0.01μm, 0.1μm, 0.3μm, and 0.5μm were selected and cut to a diameter of 63.5mm (meeting the API standard filtration area of ​​3.5 square inches). A high-temperature, high-pressure filtration loss meter was used to measure the filtration loss for 30 minutes at 150℃ and 3.5MPa. Three tests were conducted for each group, and the average value was taken.

[0045] Table 2. Filtration loss test results of polytetrafluoroethylene (PTFE) microporous filter membrane at 150℃ and 3.5MPa

[0046] Table 2 shows that the dual-particle-size combination in Examples 1-5 yielded the best results, with the lowest filtration loss (≤5.4 mL) across all four pore sizes, demonstrating that the particle gradation of 5-50 nm and 100-500 nm can simultaneously block nanoscale and microscale pores. Comparative Example 2, with only small-sized nano-silica particles, showed very low filtration loss (5.2, 7.8 mL) in 0.01 μm and 0.1 μm pores, but a high filtration loss of 31.3 mL in 0.5 μm macropores. Comparative Example 3, with only large-sized nano-silica particles, showed very low filtration loss (8.9, 6.5 mL) in 0.3 μm and 0.5 μm macropores, but a high filtration loss of 24.6 mL in 0.01 μm pores. Comparative Example 1, without nano-SiO2, showed the worst blocking effect, with significantly higher filtration losses across all pore sizes than the sample containing nano-SiO2, indicating that physical blocking by nanoparticles is crucial.

[0047] Furthermore, in Examples 6-7, when the mass ratio of methacrylamide, methyl methacrylate, and 1-propylsulfonic acid-3-vinylimidazolium inner salt was not within the optimal range, the blocking effect was worse than that in Examples 1-5. In Comparative Example 4, the absence of 1-propylsulfonic acid-3-vinylimidazolium inner salt significantly reduced the blocking agent's effectiveness, indicating that the content of 1-propylsulfonic acid-3-vinylimidazolium inner salt has a significant impact on the blocking agent's performance. Meanwhile, Comparative Examples 5-7 attempted to replace 1-propylsulfonic acid-3-vinylimidazolium inner salt with other sulfonates, but without producing comparable results. Comparative Example 8 did not use an emulsifier and employed a suspension polymerization method; the blocking agent prepared by this method did not produce ideal results.

[0048] (3) Verification of temperature and salt resistance performance 20% NaCl brine-based slurry: Place the slurry under a high-speed stirrer and slowly add 20% sodium chloride in five batches, stirring and mixing to obtain 20% NaCl brine-based slurry.

[0049] 0.5% CaCl2 high-calcium slurry: Place the slurry under a high-speed stirrer and slowly add 10% CaCl2 solution until the CaCl2 concentration in the slurry reaches 0.5%. Stir and mix to obtain 0.5% CaCl2 high-calcium slurry.

[0050] Plugging performance test: A polytetrafluoroethylene (PTFE) microporous filter membrane with a pore size of 0.5 μm was selected and cut into pieces with a diameter of 63.5 mm (meeting the API standard filtration area of ​​3.5 square inches). A high-temperature, high-pressure filtration loss meter was used to measure the filtration loss for 30 minutes at 150℃ and 3.5 MPa. Three tests were conducted for each group, and the average value was taken.

[0051] Table 3. Filtration loss (mL) of 0.5μm filter membrane

[0052] As shown in Table 3, the plugging agents of Examples 1-7 of the present invention can stably control the filtration loss in the low range in all three base slurries, proving that their plugging layer has a strong resistance to salt / calcium ion erosion. The filtration loss of Comparative Example 3 in fresh water base slurry is only 6.5 mL, but the plugging performance is significantly reduced in 20% NaCl brine base slurry or 0.5% CaCl2 high calcium base slurry, which confirms that the dual particle size distribution and the synergistic effect of imidazole zwitterionic polymer can improve the plugging performance in high temperature and high salt environment. The lack of imidazole internal salt or its structural replacement in Comparative Examples 4-7 leads to insufficient salt adsorption capacity of the polymer itself, resulting in a filtration loss of more than 20 mL in general. Comparative Example 8 fails due to the accelerated desorption of the loose coating structure under the action of salt and calcium.

[0053] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified composite silica nanoparticle plugging agent, characterized in that, Its raw materials include: The composition includes 50 parts of acrylamide monomers, 5-15 parts of acrylate monomers, 2-20 parts of 1-propylsulfonic acid-3-vinylimidazolium inner salt, 0.06-0.8 parts of N,N-methylenebisacrylamide, 5-16 parts of emulsifier, 8-12 parts of composite silica nanoparticles, 0.1-0.6 parts of initiator, and 100-144 parts of water. The composite silica nanoparticles are a mixture of 10-50 nm silica nanoparticles and 100-450 nm silica nanoparticles.

2. The modified composite silica nanoparticle plugging agent according to claim 1, characterized in that, The acrylamide monomer is at least one of acrylamide or methacrylamide.

3. The modified composite silica nanoparticle plugging agent according to claim 1, characterized in that, The acrylate monomer is at least one of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, or butyl methacrylate.

4. The modified composite silica nanoparticle plugging agent according to claim 1, characterized in that, The weight ratio of the 10-50nm nano-silica particles to the 100-450nm nano-silica particles is 1-5:

1.

5. The modified composite silica nanoparticle plugging agent according to claim 1, characterized in that, The emulsifier is sorbitan fatty acid ester and / or polyoxyethylene sorbitan fatty acid ester, and the initiator is a water-soluble peroxide initiator.

6. The modified composite silica nanoparticle plugging agent according to claim 5, characterized in that, The emulsifier is one or more of SPAN-60, SPAN-80, SPAN-85, TWEEN40, TWEEN60 or TWEEN80, and the initiator is one of potassium persulfate, ammonium persulfate or hydrogen peroxide.

7. A method for preparing the modified composite silica nanoparticle plugging agent according to any one of claims 1-6, characterized in that, The preparation method includes: Acrylamide monomers, acrylate monomers, 1-propylsulfonic acid-3-vinylimidazolium inner salt and N,N-methylenebisacrylamide were mixed with emulsifier and water and stirred, and then mixed with composite silica nanoparticles to obtain a mixed dispersion. An inert gas is introduced into the mixed dispersion, and then an initiator is added to initiate a polymerization reaction to obtain the modified composite silica nanoparticle plugging agent.

8. The preparation method of the modified composite silica nanoparticle plugging agent according to claim 7, characterized in that, The polymerization reaction is carried out at a temperature of 50-90℃ for 6-15 hours.

9. The application of the modified composite silica nanoparticle plugging agent according to any one of claims 1-6 in water-based drilling fluids.

10. The application according to claim 9, characterized in that, The modified composite silica nanoparticle plugging agent is added to the drilling fluid at a rate of 3-5%.

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