Temperature-resistant and salt-resistant nano cross-linking agent, preparation method and polymer gel

Abstract

The invention discloses a temperature-resistant and salt-resistant nano cross-linking agent, a preparation method and polymer gel, and the preparation method comprises the following steps: step 1, sufficiently and uniformly stirring a coupling agent and nano particles in a solvent to obtain a mixture; carrying out ultrasonic treatment on the mixture and then fully reacting to obtain modified nanoparticles; and 2, fully mixing the modified nano-particles obtained in the step 1 with a reaction monomer, fully reacting, washing, and drying to obtain the required nano cross-linking agent, the nano cross-linking agent obtained by the invention can improve the stability of polymer gel in a high-temperature environment; the salt tolerance of the polymer gel can be improved, so that the polymer gel still keeps good rheological property and structural integrity under high salinity; the method can be used for high-temperature and high-salt oil reservoirs, effectively regulate and control dominant channels of the oil reservoirs, improve the heterogeneity of oil layers, improve the sweep efficiency of low-permeability areas, improve the oil recovery efficiency of the oil reservoirs and achieve water control and oil increase of the oil reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield exploitation, and particularly relates to a temperature-resistant and salt-resistant nano-crosslinking agent, a preparation method thereof, and a polymer gel. Background Art

[0002] Water flooding is an economical and effective technique aimed at maintaining the driving force of an oilfield to achieve sustainable oil production. However, with the continuous increase in high water cut, excessive water production has a significant impact on the economic life of production wells. The main reason for excessive water production is the spatial difference in fluid flow performance, which is usually caused by the heterogeneity of the reservoir. Due to a large amount of oil in the reservoir not being swept, severe vertical and horizontal heterogeneity has become a severe challenge for reservoir engineers. To address the problem of excessive water production, various comprehensive remedial strategies have been adopted, among which profile control and water plugging are one of the most common techniques. In recent years, polymer gel systems have been widely used in water flooding to effectively control water production. This technique involves injecting a polymer gel system into the formation to change the fluid flow direction, restrict the flow of water in the swept zone or water channeling channels, and drive the water to the unswept oil area, thereby improving the recovery rate of residual oil.

[0003] Currently, one of the most widely used polymer gel systems is the system crosslinked by acrylamide copolymer and inorganic metal ions (such as chromium, aluminum, zirconium). However, these polymer gel systems are prone to losing their hydrated state and having a short gel time under high-temperature conditions, which limits their application in oil reservoirs with temperatures above 80°C. Summary of the Invention

[0004] The present invention provides a temperature-resistant and salt-resistant nano-crosslinking agent, a preparation method thereof, and a polymer gel for the problems existing in the prior art.

[0005] The technical solution adopted by the present invention is: a preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent, comprising the following steps:

[0006] Step 1: Thoroughly stir a coupling agent and nanoparticles in a solvent to obtain a mixture; after ultrasonic treatment of the mixture, fully react to obtain modified nanoparticles;

[0007] Step 2: Thoroughly mix the modified nanoparticles obtained in Step 1 with a reaction monomer, and after full reaction, wash and dry to obtain the required nano-crosslinking agent;

[0008] Wherein the reaction monomer is one of an amine monomer and a phenolic resin monomer;

[0009] The mass ratio of the modified nanoparticles to the reaction monomer is 2:3.

[0010] Further, the coupling agent in the step 1 is one of trimethoxyvinylsilane, γ-aminopropyltriethoxysilane, and γ-glycidoxypropyltrimethoxysilane; the hydroxyl density on the surface of the nanoparticle is ≥5OH / nm 2 , the particle size is 20 - 100 nm, and the specific surface area is ≥200 m 2 / g.

[0011] Further, the ultrasonic treatment is gradient ultrasonic treatment, and the specific ultrasonic regime is as follows:

[0012] Ultrasonic for 15 min under the condition of 40 kHz, then ultrasonic for 10 min under the condition of 60 kHz, and finally ultrasonic for 5 min under the condition of 80 kHz.

[0013] Further, a dispersant is added to the mixture after ultrasonic treatment in the step 1, and the addition amount of the dispersant is 0.1 - 0.5 wt.% of the mass of the nanoparticles.

[0014] Further, the amine monomer is one of polyethyleneimine, polyetheramine, polypropyleneamine, N,N'-methylenebisacrylamide, and hexamethylenetetramine; the phenolic resin monomer is one of phenol-formaldehyde, phenol-glutaraldehyde, hydroquinone-formaldehyde, hydroquinone-glutaraldehyde, resorcinol-formaldehyde, and resorcinol-glutaraldehyde.

[0015] Further, the reaction temperature in the step 1 is 95 °C, and the reaction time is 6 hours; the reaction temperature in the step 2 is 90 °C, and the reaction time is 4 hours.

[0016] Further, the drying in the step 2 adopts vacuum gradient drying,

[0017] First, dry for 2 hours under the condition of 50 °C, then dry for 3 hours under the condition of 80 °C, and finally dry for 5 hours under the condition of 110 °C;

[0018] After drying, pulverize and then classify to obtain the nano-crosslinker with the required particle size.

[0019] A temperature-resistant and salt-resistant nano-crosslinker.

[0020] A temperature-resistant and salt-resistant polymer gel, which is obtained by crosslinking reaction of the nano-crosslinker and a polymer; the addition amount of the nano-crosslinker is 0.1 - 0.4 wt.% of the mass of the polymer, and the polymer is one of partially hydrolyzed polyacrylamide and its derivatives.

[0021] Further, the polymer gel has a three-dimensional network structure, and the range of its network pore size a is 20 nm ≤ a ≤ 50 nm.

[0022] The beneficial effects of the present invention are:

[0023] (1) The nano-crosslinker obtained in the present invention can improve the stability of polymer gels in high-temperature environments (70 - 140 °C); and can improve the salt tolerance of polymer gels, enabling them to still maintain good rheological properties and structural integrity at high salinity (150,000 - 280,000 mg / L);

[0024] (2) The nano-crosslinker obtained in the present invention can be used in high-temperature and high-salinity oil reservoirs, effectively regulating the preferential flow channels of the reservoir, improving the reservoir heterogeneity, increasing the sweep efficiency in low-permeability areas, enhancing the oil recovery rate of the reservoir, and achieving water control and oil repulsion in the reservoir;

[0025] (3) The nano-crosslinker obtained in the present invention can effectively improve the water retention capacity of polymer gels, reducing dehydration phenomena in high-temperature and high-salt environments;

[0026] (4) The preparation process of the nano-crosslinker obtained in the present invention is green and pollution-free, can be directly injected with oilfield formation water, has obvious energy-saving and emission-reduction effects, and reduces the negative impact on the environment. Description of the Drawings

[0027] Figure 1 It is the infrared spectrum diagram of the nano-crosslinker obtained in Example 5 of the present invention and the nano-particle SiO2 used in this example.

[0028] Figure 2 It is the AFM morphology (a) and height distribution (b) of the nano-crosslinker obtained in Example 5 of the present invention.

[0029] Figure 3 It is the SEM morphology diagram of the nano-crosslinker obtained in Example 5 of the present invention.

[0030] Figure 4 It is the SEM diagram of the polymer gel obtained by using the nano-crosslinker obtained in Example 5 of the present invention and the traditional organic crosslinked gel, and a and b are the results at different magnification levels.

[0031] Figure 5 It is the AFM diagram of the polymer gel obtained by using the nano-crosslinker obtained in Example 5 of the present invention and the traditional organic crosslinked gel, where a is the result of Example 5 and b is the result of the traditional organic crosslinked gel system.

[0032] Figure 6 It is the schematic diagram of the TG / DTG test result curve of the polymer gel obtained by using the nano-crosslinker obtained in Example 5 of the present invention. Detailed Embodiments

[0033] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0034] A preparation method of a temperature-resistant and salt-resistant nano crosslinking agent, comprising the following steps:

[0035] Step 1: Thoroughly stir a coupling agent and nanoparticles in a solvent to obtain a mixture; after ultrasonic treatment of the mixture, transfer it to a sealed reaction vessel and react at a constant temperature of 95 °C for 6 hours to obtain modified nanoparticles; the solvent is an alcohol solvent, which can be one or both of ethanol or glycerol; the mass ratio of the coupling agent, nanoparticles, alcohol solvent, and reaction monomer is 1:2:2:3.

[0036] The coupling agent is one of trimethoxyvinylsilane, γ-aminopropyltriethoxysilane, and γ-glycidoxypropyltrimethoxysilane; the hydroxyl density on the surface of the nanoparticles is ≥5OH / nm 2 with a particle size of 20 - 100 nm and a specific surface area of ≥200 m 2 / g, which can be one of silicon dioxide, iron tetroxide, carbon nanotubes, carbon dots, and graphite oxide, or other nanoparticles meeting the above conditions.

[0037] The ultrasonic treatment is gradient ultrasonic, and the specific ultrasonic regime is as follows:

[0038] Ultrasonic at 40 kHz for 15 min, then ultrasonic at 60 kHz for 10 min, and finally ultrasonic at 80 kHz for 5 min. Gradient ultrasonic breaks the aggregates of nanoparticles step by step through mechanical vibrations at different frequencies (SEM verifies that the aggregation rate <5%), and the dispersion efficiency is 40% higher than that of conventional single-frequency ultrasonic. After ultrasonic dispersion, add 0.1 - 0.5 wt% of sodium dodecyl sulfate as a dispersant to enhance the stability and reaction uniformity of the nanoparticles.

[0039] Step 2: Thoroughly mix the modified nanoparticles obtained in Step 1 with the reaction monomer. After sufficient reaction, wash alternately with hot ethanol and deionized water. The hot ethanol is 60 ± 2 °C and is used to dissolve the unreacted monomer, and the deionized water is used to remove ionic impurities. After drying, the required nano crosslinking agent can be obtained. The reaction temperature is 90 °C and the reaction time is 4 hours.

[0040] Drying is carried out by vacuum gradient drying. First, dry at 50 °C for 2 hours, then dry at 80 °C for 3 hours, and finally dry at 110 °C for 5 hours;

[0041] After drying, crush and then classify to obtain a nano crosslinking agent with a particle size meeting the requirements.

[0042] The crushing adopts an ultrafine crushing process, and the classification adopts air classification. It can increase the specific surface area of the powder (380 m 2 / g) and improve the dispersion efficiency of the crosslinking agent in the polymer solution.

[0043] The reaction monomer is one of amine monomers and phenolic resin monomers.

[0044] The amine monomer molecule chain contains at least 3 primary amino groups or secondary amino groups, and the molecular weight ranges from 200 to 5000 Da to ensure efficient reaction with the surface groups of the modified nanoparticles. The amine monomer is one of polyethyleneimine, polyetheramine, polypropyleneamine, N,N'-methylenebisacrylamide, and hexamethylenetetramine. The phenolic resin monomer is one of phenol-formaldehyde, phenol-glutaraldehyde, hydroquinone-formaldehyde, hydroquinone-glutaraldehyde, resorcinol-formaldehyde, and resorcinol-glutaraldehyde, and the molar ratio of its aldehyde group to phenolic hydroxyl group is 1.5:1 to 2:1.

[0045] Both Step 1 and Step 2 adopt a nitrogen protection system built into a closed reactor and a programmed temperature control process, so that the reaction degree reaches more than 92%, and the stability of the reaction product is increased by 15% compared with the traditional direct high-temperature reaction.

[0046] After obtaining the nano crosslinking agent, crosslinking the crosslinking agent with the polymer can obtain the required polymer gel system. The polymer is one of partially hydrolyzed polyacrylamide and its derivatives.

[0047] The specific process is as follows:

[0048] Take 100 ml of formation water in a beaker, set the stirring speed of the formation water to 400 - 600 revolutions per minute, weigh 0.15 g - 1 g (0.15% - 1%) of polymer powder, and slowly add it to the formation water to prepare a polymer solution, with a stirring time of 4 - 6 hours. The formation water salinity is 150000 - 280000 mg / L.

[0049] Add 0.1 g - 0.4 g (0.1% - 0.4%) of nano crosslinking agent to the polymer solution and stir it slowly to dissolve, then place it on a stirrer and stir for 15 min to fully mix.

[0050] After preparing the nano composite crosslinked polymer gel system, place it in an oven set at 70 - 140 °C for aging to obtain the required polymer gel system.

[0051] The obtained polymer gel system uses three-stage gradient ultrasound and sodium dodecyl sulfate dispersant to ensure uniform dispersion of the nanoparticles and full exposure of the surface hydroxyl groups, and then reacts with a coupling agent, an amine or a phenolic resin monomer under nitrogen protection at 95 °C for 6 hours, providing high-density reaction sites. The crosslinking point density is 3 - 5 times that of traditional organic crosslinking agents (quantitatively analyzed by AFM), and the high crosslinking density restricts the thermal movement of polymer chains (AFM shows that the crosslinking point spacing ≤ 20 nm).

[0052] The temperature of the closed reactor is programmed to ensure that the hydrolysis and polycondensation of the coupling agent and the grafting of the monomer are completed in stages, avoiding local overreaction (SEM shows that the CV value of the pore size distribution is <10%), and the vacuum gradient drying maintains the integrity of the hydrogen bond network with a network pore size of ≤50 nm (statistical analysis by SEM), and the dense cross-linked network reduces the salt ion penetration path.

[0053] The nano-composite cross-linked polymer gel system maintains long-term stability, with less than 10% dehydration in 3 months and less than 20% dehydration in 6 months, and can effectively improve the oil recovery rate in oilfield profile control and flooding. The application method is applicable to high-temperature and high-salt oil reservoirs.

[0054] Example 1

[0055] A preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent, comprising the following steps:

[0056] Step 1: Add 5 g of γ-aminopropyltriethoxysilane and 10 g of glycerol to a beaker, stir well to form a homogeneous mixture. Then add 10 g of nano-ferroferric oxide, and ultrasonically treat for 30 minutes. Add 0.1 wt.% of sodium dodecyl sulfate as a dispersant to ensure its uniform dispersion. Transfer the mixture to a closed reactor and place it in a constant temperature reaction at 95 °C for 6 hours to obtain modified nano-ferroferric oxide particles.

[0057] Step 2: Mix the modified nano-ferroferric oxide particles with 15 g of polyetheramine evenly, and heat in a closed reactor at 90 °C for 4 hours. Take the reaction product and place it in a high-temperature resistant glass sand core filtration device, add a preheated ethanol solution (60 ± 2 °C), with a solid-liquid ratio of 1:10 (g / mL), and filter under a circulating water vacuum pump. Repeat the washing 3 times, stirring for 5 minutes each time (magnetic stirrer speed 400 rpm) and pour it into the ethanol solution. Then, use deionized water at 50 °C for alternating washing, with a solid-liquid ratio of 1:15 (g / mL), and use a pulsed washing method (filtration for 10 s → pause for 5 s → filtration for 10 s) to cycle 5 times, with a total time of 8 minutes. Transfer the filter cake to a vacuum drying oven at 90 °C for drying, and use an air flow pulverizer combined with air flow classification to grind it into powder to obtain nano-crosslinking agent 1.

[0058] Example 2

[0059] A preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent, comprising the following steps:

[0060] Step 1: Add 5 g of γ-glycidoxypropyltrimethoxysilane and 10 g of glycerol to a beaker, stir well to form a homogeneous mixture. Then add 10 g of carbon nanotubes, and ultrasonically treat for 30 minutes. Add 0.2 wt.% of sodium dodecyl sulfate as a dispersant to ensure its uniform dispersion. Transfer the mixture to a closed reactor and place it in a constant temperature reaction at 95 °C for 6 hours to obtain modified carbon nanotubes.

[0061] Step 2: Mix the modified carbon nanotubes evenly with 15 g of polyacrylamide, and heat them in a sealed reactor at 90 °C for 4 hours. Take the reaction product and place it in a high-temperature resistant glass sand core filtration device. Add a preheated ethanol solution (60 ± 2 °C) with a solid-liquid ratio of 1:10 (g / mL), and filter it under a circulating water vacuum pump. Repeat the washing 3 times, stirring for 5 minutes each time (magnetic stirrer speed 400 rpm). Pour it into the ethanol solution, and then use deionized water at 50 °C for alternating washing with a solid-liquid ratio of 1:15 (g / mL). Adopt the pulse washing method (filtration for 10 s → pause for 5 s → filtration for 10 s) and cycle 5 times, with a total time of 8 minutes. Transfer the filter cake to a vacuum drying oven at 90 °C for drying, and use an air flow pulverizer combined with air flow classification to grind it into powder to obtain nano-crosslinking agent 2.

[0062] Example 3

[0063] A preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent, comprising the following steps:

[0064] Step 1: Add 5 g of trimethoxyvinylsilane and 10 g of glycerol to a beaker, and stir well to form a homogeneous mixture. Then add 10 g of nano-silica, and perform ultrasonic treatment for 30 minutes. Add 0.3 wt.% of sodium dodecyl sulfate as a dispersant to ensure its uniform dispersion. Transfer the mixture to a sealed reactor and place it in a constant temperature reaction at 95 °C for 6 hours to obtain modified nano-silica.

[0065] Step 2: Mix the modified nano-silica evenly with 15 g of N,N'-methylenebisacrylamide, and heat them in a sealed reactor at 90 °C for 4 hours. Take the reaction product and place it in a high-temperature resistant glass sand core filtration device. Add a preheated ethanol solution (60 ± 2 °C) with a solid-liquid ratio of 1:10 (g / mL), and filter it under a circulating water vacuum pump. Repeat the washing 3 times, stirring for 5 minutes each time (magnetic stirrer speed 400 rpm). Pour it into the ethanol solution, and then use deionized water at 50 °C for alternating washing with a solid-liquid ratio of 1:15 (g / mL). Adopt the pulse washing method (filtration for 10 s → pause for 5 s → filtration for 10 s) and cycle 5 times, with a total time of 8 minutes. Transfer the filter cake to a vacuum drying oven at 90 °C for drying, and use an air flow pulverizer combined with air flow classification to grind it into powder to obtain nano-crosslinking agent 3.

[0066] Example 4

[0067] A preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent, comprising the following steps:

[0068] Step 1: Add 5 g of γ-aminopropyltriethoxysilane and 10 g of glycerol into a beaker, and stir well to form a homogeneous mixture. Then add 10 g of hydrophilic nano-graphite oxide, and ultrasonically treat for 30 minutes. Add 0.4 wt.% of sodium dodecyl sulfate as a dispersant to ensure its uniform dispersion. Transfer this mixture to a closed reactor and place it in a constant temperature of 95 °C for reaction for 6 hours to obtain modified nano-graphite oxide.

[0069] Step 2: Mix the modified nano-graphite oxide with 15 g of hydroquinone-glutaraldehyde evenly, and heat in a closed reactor at 90 °C for 4 hours. Take the reaction product and place it in a high-temperature resistant glass sand core filtering device. Add a preheated ethanol solution (60 ± 2 °C) with a solid-liquid ratio of 1:10 (g / mL), and filter under a circulating water vacuum pump. Repeat the washing 3 times, stirring for 5 minutes each time (magnetic stirrer speed 400 rpm) and pour it into the ethanol solution. Then use deionized water at 50 °C for alternative washing with a solid-liquid ratio of 1:15 (g / mL), and adopt the pulse washing method (filtration for 10 s → pause for 5 s → filtration for 10 s) for 5 cycles, with a total time of 8 minutes. Transfer the filter cake to a vacuum drying oven at 90 °C for drying, and grind it into powder using a jet mill combined with air classification to obtain nano-crosslinker 4.

[0070] Example 5

[0071] A preparation method of a temperature-resistant and salt-resistant nano-crosslinker, comprising the following steps:

[0072] Step 1: Add 5 g of trimethoxyvinylsilane and 10 g of glycerol into a beaker, and stir well to form a homogeneous mixture. Then add 10 g of nano-silica, and ultrasonically treat for 30 minutes. The ultrasonic process is as follows: ultrasonic for 15 min under the condition of 40 kHz, then ultrasonic for 10 min under the condition of 60 kHz, and finally ultrasonic for 5 min under the condition of 80 kHz.

[0073] After ultrasonic treatment, add 0.5 wt.% of sodium dodecyl sulfate as a dispersant to ensure its uniform dispersion. Transfer this mixture to a closed reactor and place it in a constant temperature of 95 °C for reaction for 6 hours to obtain nano-silica.

[0074] Step 2: Mix the modified nano-graphite oxide evenly with 15 g of hydroquinone-glutaraldehyde, and heat it in a sealed reactor at 90 °C for 4 hours. Take the reaction product and place it in a high-temperature resistant glass sand core filtration device. Add a preheated ethanol solution (60 ± 2 °C) with a solid-liquid ratio of 1:10 (g / mL), and filter it under a circulating water vacuum pump. Repeat the washing 3 times, stirring for 5 minutes each time (magnetic stirrer speed 400 rpm), pour it into the ethanol solution, and then use deionized water at 50 °C for alternating washing with a solid-liquid ratio of 1:15 (g / mL). Use the pulse washing method (filtration for 10 s → pause for 5 s → filtration for 10 s) and cycle 5 times, with a total time of 8 minutes. Transfer the filter cake to a vacuum drying oven for drying, and use an air flow pulverizer combined with air flow classification to grind it into powder to obtain nano-crosslinking agent 5. The drying regime is as follows: Drying is carried out using vacuum gradient drying. First, dry it at 50 °C for 2 hours, then at 80 °C for 3 hours, and finally at 110 °C for 5 hours.

[0075] Example 6

[0076] A preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent, comprising the following steps:

[0077] Step 1: Add 5 g of trimethoxyvinylsilane and 10 g of ethanol to a beaker, stir well to form a homogeneous mixture. Then add 10 g of nano-carbon dots, and perform ultrasonic treatment for 30 minutes. Add 0.4 wt.% of sodium dodecyl sulfate as a dispersant to ensure its uniform dispersion. Transfer the mixture to a sealed reactor and place it in a constant temperature reaction at 95 °C for 6 hours to obtain modified nano-carbon dots.

[0078] Step 2: Mix the modified nano-carbon dots evenly with 15 g of hexamethylenetetramine, and heat it in a sealed reactor at 90 °C for 4 hours. Take the reaction product and place it in a high-temperature resistant glass sand core filtration device. Add a preheated ethanol solution (60 ± 2 °C) with a solid-liquid ratio of 1:10 (g / mL), and filter it under a circulating water vacuum pump. Repeat the washing 3 times, stirring for 5 minutes each time (magnetic stirrer speed 400 rpm), pour it into the ethanol solution, and then use deionized water at 50 °C for alternating washing with a solid-liquid ratio of 1:15 (g / mL). Use the pulse washing method (filtration for 10 s → pause for 5 s → filtration for 10 s) and cycle 5 times, with a total time of 8 minutes. Transfer the filter cake to a 90 °C vacuum drying oven for drying, and use an air flow pulverizer combined with air flow classification to grind it into powder to obtain nano-crosslinking agent 6.

[0079] Example 7

[0080] A preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent, comprising the following steps:

[0081] Step 1: Add 5 g of γ-aminopropyltriethoxysilane and 10 g of glycerol into a beaker, stir well to form a homogeneous mixture. Then add 10 g of carbon nanotubes and ultrasonically treat for 30 minutes. Add 0.35 wt.% of sodium dodecyl sulfate as a dispersant to ensure its uniform dispersion. Transfer this mixture to a sealed reactor and place it in a constant temperature of 95 °C for reaction for 6 hours to obtain modified carbon nanotubes.

[0082] Step 2: Mix the modified carbon nanotubes evenly with 15 g of phenol-formaldehyde and heat in a sealed reactor at 90 °C for 4 hours. Take the reaction product and place it in a high-temperature resistant glass sand core filtration device. Add a preheated ethanol solution (60 ± 2 °C) with a solid-liquid ratio of 1:10 (g / mL), and filter under a circulating water vacuum pump. Repeat the washing 3 times, stirring for 5 minutes each time (magnetic stirrer speed 400 rpm), pour it into the ethanol solution, then use deionized water at 50 °C for alternating washing with a solid-liquid ratio of 1:15 (g / mL), and use the pulse washing method (filtration for 10 s → pause for 5 s → filtration for 10 s) to cycle 5 times, with a total time of 8 minutes. Transfer the filter cake to a vacuum drying oven at 90 °C for drying, and use an air flow crusher combined with air classification to grind it into powder to obtain nano-crosslinking agent 7.

[0083] Example 8

[0084] A preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent, comprising the following steps:

[0085] Step 1: Add 5 g of γ-glycidoxypropyltrimethoxysilane and 10 g of glycerol into a beaker, stir well to form a homogeneous mixture. Then add 10 g of nano-silica and ultrasonically treat for 30 minutes. Add 0.25 wt.% of sodium dodecyl sulfate as a dispersant to ensure its uniform dispersion. Transfer this mixture to a sealed reactor and place it in a constant temperature of 95 °C for reaction for 6 hours to obtain modified nano-silica.

[0086] Step 2: Mix the modified nano-silica evenly with 15 g of phenol-formaldehyde and heat in a sealed reactor at 90 °C for 4 hours. Take the reaction product and place it in a high-temperature resistant glass sand core filtration device. Add a preheated ethanol solution (60 ± 2 °C) with a solid-liquid ratio of 1:10 (g / mL), and filter under a circulating water vacuum pump. Repeat the washing 3 times, stirring for 5 minutes each time (magnetic stirrer speed 400 rpm), pour it into the ethanol solution, then use deionized water at 50 °C for alternating washing with a solid-liquid ratio of 1:15 (g / mL), and use the pulse washing method (filtration for 10 s → pause for 5 s → filtration for 10 s) to cycle 5 times, with a total time of 8 minutes. Transfer the filter cake to a vacuum drying oven at 90 °C for drying, and use an air flow crusher combined with air classification to grind it into powder to obtain nano-crosslinking agent 8.

[0087] Example 9

[0088] A preparation method of a temperature-resistant and salt-resistant nano crosslinking agent, comprising the following steps:

[0089] Step 1: Add 5 g of γ-glycidoxypropyltrimethoxysilane and 10 g of glycerol into a beaker, and stir well to form a homogeneous mixture. Then add 10 g of nano-ferroferric oxide, and ultrasonically treat for 30 minutes. Add 0.35 wt.% of sodium dodecyl sulfate as a dispersant to ensure its uniform dispersion. Transfer the mixture to a closed reactor, and place it in a constant temperature reaction at 95 °C for 6 hours to obtain modified nano-ferroferric oxide.

[0090] Step 2: Mix the modified nano-ferroferric oxide with 15 g of polyetheramine evenly, and heat in a closed reactor at 90 °C for 4 hours. Take the reaction product and place it in a high-temperature resistant glass sand core filtration device. Add a preheated ethanol solution (60 ± 2 °C), with a solid-liquid ratio of 1:10 (g / mL). Filter under a circulating water vacuum pump, repeat the washing 3 times, stir for 5 minutes each time (magnetic stirrer speed 400 rpm), pour it into the ethanol solution, and then use deionized water at 50 °C for alternate washing, with a solid-liquid ratio of 1:15 (g / mL). Use the pulse washing method (filtration for 10 s → pause for 5 s → filtration for 10 s) to cycle 5 times, with a total time of 8 minutes. Transfer the filter cake to a vacuum drying oven at 90 °C for drying, and use a jet mill combined with air classification to grind it into powder to obtain nano crosslinking agent 9.

[0091] The nano-silica and the nano crosslinking agent prepared in Example 5 were characterized by infrared infrared spectroscopy and Fourier transform spectroscopy, as Figure 1 shown. It can be seen from the figure that the ATR-FTIR spectrum of the nano crosslinking agent shows a relatively wide absorption peak in the range of 3000 - 3500 cm -1 These peaks are caused by the -OH groups of SiO2, the -OH groups and -NH groups on the hyperbranched backbone monomer carboxylic acid. There is a strong and wide absorption peak at about 2925 cm -1 indicating the presence of asymmetric stretching vibration of CH2 within the molecule. In addition, the peak at 1411 cm -1 is related to carbon-oxygen stretching vibration, while the peak at 1582 cm -1 is related to nitrogen-hydrogen bending vibration. The peak at 1367 cm -1 is the multiple stretching vibration of -NH-, and the peak near 1100 cm -1 is the Si-O stretching vibration, indicating that the silane coupling agent has been successfully grafted onto the surface of nano-SiO2. These infrared analysis results confirm that the nano-silica crosslinking agent contains a PEI structure, indicating successful synthesis.

[0092] The AFM characterization of the nano-silica crosslinking agent obtained in Example 5 was carried out, and the results are as Figure 2As shown, a is the AFM morphology and b is the height distribution map. It can be seen from the figure that the thickness of the SiO2 layer is about 2 nm. In contrast, the thickness of the nano-silica crosslinker layer increases to about 4.3 nm. This increase indicates that PEI is successfully attached to the surface of the nano-SiO2 substrate.

[0093] The SEM of the nano-silica crosslinker obtained in Example 5 was characterized as Figure 3 shown. The microstructures of the silane coupling agent-modified nano-SiO2 and the nano-silica crosslinker are as Figure 3 shown in a of Figure 3 and b of

[0094] Take 100 ml of formation water in a beaker, set the stirring speed of the formation water to 500 revolutions per minute, weigh 0.5 g of polyacrylamide / 2-acrylamido-2-methylpropanesulfonic acid sodium powder, and slowly add it to the formation water to prepare a polymer solution, with a stirring time of 5 hours. The formation water salinity is 200,000 mg / L.

[0095] Add 0.3 g of the nano-crosslinker to the polymer solution and stir it slowly to dissolve, then place it on a stirrer and stir for 15 min to fully mix.

[0096] Place it in an oven set at 100 °C for aging to obtain a polymer gel system.

[0097] The nano-crosslinker obtained in Example 5 and the traditional phenolic crosslinker were respectively crosslinked with polyacrylamide / 2-acrylamido-2-methylpropanesulfonic acid sodium to form a gel system according to the above method, and its SEM image is as Figure 4 shown. It can be seen from the figure that the traditional organic crosslinked gel system initially has a good network structure. However, after 12 days of aging, this structure is damaged, resulting in obvious dehydration in the gel system, as Figure 4 shown in a of Figure 4 while the gel system formed by the crosslinker obtained in Example 5 of the present invention has long-term stability, as

[0098] shown in b of Figure 5 It can be seen from the figure that even after 90 days of aging, the microstructure of the enhanced gel system hardly changes, effectively maintaining its hydrated state, indicating that the nano-crosslinker introduces additional crosslinking points, thus enhancing the network structure. The enhancing effect of the nano-crosslinker on the long-term stability of the polymer gel. Figure 5(a) shows that the traditional organic crosslinked gel system presents an irregular and uneven network structure. The irregularity of this structure indicates that instability and dehydration are likely to occur under pressure. Figure 5 (b) shows the nano - composite crosslinked polymer gel system. The nano - crosslinker promotes a denser and more ordered gel network structure by providing more crosslinking sites. The resulting gel exhibits stronger stability and significantly reduces the sensitivity to dehydration.

[0099] The nano - crosslinker obtained in Example 5 of the present invention is used. According to the above - mentioned method, the polymer type, concentration, crosslinker type, salinity, and temperature are replaced to obtain a series of polymer gel systems. The performance of the polymer gel systems is tested, and the results are shown in Table 2.

[0100] Table 1 is the Sydansk gel strength code.

[0101] Table 1. Standard table of gel strength codes

[0102]

[0103]

[0104] Table 2. Test results of the long - term stability of the obtained gel system

[0105]

[0106]

[0107] It can be seen from Table 2 that the nano - crosslinker obtained in the examples of the present invention can significantly improve the long - term stability of the gel under high - temperature and high - salt conditions. For example, in Experiment 3 (140 °C, 280,000 mg / L) when using the nano - crosslinker, it still maintains Grade H strength (dehydration rate is only 7%) after 6 months. In Experiment 7 (140 °C, 280,000 mg / L) under the action of the nano - crosslinker, the gel strength is always Grade I (rigid gel). The 6 - month dehydration rate of the gel system added with the nano - crosslinker is generally less than 20%.

[0108] Under the same conditions, the gel strength of the traditional crosslinker drops rapidly. For example, in Experiment 4 (140 °C, 280,000 mg / L) when using the phenolic aldehyde crosslinker, the strength drops to Grade D (dehydration rate 48%) after 6 months. The phenolic aldehyde crosslinked system in Experiment 12 (low - concentration polymer) only remains Grade A strength (dehydration rate 58%) after 6 months. Therefore, the nano - crosslinker has stronger adaptability to extreme conditions, while the performance of the traditional crosslinker drops sharply when the salinity > 150,000 mg / L or the temperature > 90 °C.

[0109] The TG / DTG test results of the polymer gel system obtained in Example 5 of the present invention are as Figure 6As shown, it can be seen from the figure that the thermal degradation of the polymer gel sample can be divided into three different stages. Initially, from 40°C to 100°C, the first stage involves the evaporation of free water within the sample. Subsequently, the second stage occurs between 100°C and 180°C, which is characterized by the release and volatilization of bound water in the gel, a key process that affects the gel stability through dehydration. In the final stage, between 180°C and 600°C, it marks the decomposition of covalent bonds within the gel structure.

[0110] The present invention uses three-stage gradient ultrasound and sodium dodecyl sulfate dispersant to ensure the uniform dispersion of nanoparticles and the full exposure of surface hydroxyl groups. Then, it reacts with coupling agents, amine or phenolic resin monomers under nitrogen protection at 95°C for 6 hours, providing high-density reaction sites. The crosslinking point density is 3 to 5 times that of traditional organic crosslinking agents (quantitatively analyzed by AFM). The high crosslinking density restricts the thermal movement of polymer chains (AFM shows that the crosslinking point spacing ≤ 20 nm). After the stage is completed, local overreaction is avoided (SEM shows that the CV value of pore size distribution < 10%). Vacuum gradient drying maintains the integrity of the hydrogen bond network with a network pore size of 20 nm to 50 nm (statistically analyzed by SEM), and the dense crosslinking network reduces the salt ion penetration path. The obtained nano-composite crosslinked polymer gel system maintains long-term stability, with less than 10% dehydration in 3 months and less than 20% dehydration in 6 months, and can effectively improve the oil recovery rate in oilfield profile control and flooding. The polymer gel is suitable for high-temperature and high-salinity oil reservoirs.

[0111] The nano-composite crosslinked polymer gel system formed by the nano-crosslinking agent provided by the present invention and partially hydrolyzed polyacrylamide and its derivative polymers has ideal injection ability and has a good effect on profile control and flooding in high-temperature and high-salinity oil reservoirs. The nanoparticles used in the nano-crosslinking agent are inorganic materials with a high specific surface area and good chemical stability, and their surfaces are rich in hydroxyl groups. The amino or hydroxymethyl groups in the nano-crosslinking agent react with the active groups on the polymer chain to form covalent bonds. This chemical crosslinking enables a three-dimensional network structure to be formed between polymer chains, enhancing the strength and stability of the gel. The high specific surface area and nano-scale size of the nanoparticles also enable them to interact with polymer chains through physical adsorption, further enhancing the structural stability of the gel. The polymer chains gradually form a dense three-dimensional network structure under the action of the nano-crosslinking agent. This network structure can effectively capture water molecules in the solution to form a stable gel state.

[0112] The present invention prepares a nano-crosslinking agent through addition and substitution reactions among coupling agents, nanoparticles, amine monomers or phenolic resin monomers. The nano-crosslinking agent can be directly used for injection with polymers using produced water (sewage) from oilfields, and can remain stable for a long time in high-temperature and high-salinity reservoir environments, so as to achieve the purpose of expanding the water flooding sweep efficiency, inhibiting the tongue advance phenomenon, and further improving the heterogeneity of high-temperature and high-salinity reservoirs. The present invention can not only promote the development of the theory of enhanced oil recovery in high-temperature and high-salinity reservoirs, but also provide important technical and method support for the efficient development of water flooding in high-temperature and high-salinity reservoirs.

Claims

1. A preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent, characterized in that It includes the following steps: Step 1: Stir the coupling agent and nanoparticles evenly in a solvent to obtain a mixture; after ultrasonic treatment of the mixture, react fully to obtain modified nanoparticles; Step 2: Mix the modified nanoparticles obtained in Step 1 with the reaction monomer fully, after full reaction, wash and dry to obtain the required nano-crosslinker; Wherein the reaction monomer is one of amine monomers and phenolic resin monomers; The mass ratio of the modified nanoparticles to the reaction monomer is 2:

3.

2. The preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent according to claim 1, characterized in that The coupling agent described in step 1 is one of trimethoxyvinylsilane, γ-aminopropyltriethoxysilane, and γ-glycidoxypropyltrimethoxysilane; the hydroxyl density on the surface of the nanoparticles is ≥5OH / nm 2 , the particle size is 20 - 100 nm, and the specific surface area is ≥200 m 2 / g.

3. The preparation method of a temperature-resistant and salt-resistant nano crosslinking agent according to claim 1, characterized in that, The ultrasonic treatment is gradient ultrasonic, and the specific ultrasonic regime is as follows: Ultrasonic for 15 min under the condition of 40 kHz, then ultrasonic for 10 min under the condition of 60 kHz, and finally ultrasonic for 5 min under the condition of 80 kHz.

4. The preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent according to claim 3, characterized in that, A dispersant is added to the mixture after ultrasonic treatment in Step 1, and the addition amount of the dispersant is 0.1-0.5 wt.% of the mass of the nanoparticles.

5. The preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent according to claim 1, wherein, The amine monomer is one of polyethyleneimine, polyetheramine, polypropyleneamine, N,N'-methylenebisacrylamide, hexamethylenetetramine; the phenolic resin monomer is one of phenol-formaldehyde, phenol-glutaraldehyde, hydroquinone-formaldehyde, hydroquinone-glutaraldehyde, resorcinol-formaldehyde, resorcinol-glutaraldehyde.

6. The preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent according to claim 1, characterized in that, The reaction temperature in Step 1 is 95 °C and the reaction time is 6 hours; the reaction temperature in Step 2 is 90 °C and the reaction time is 4 hours.

7. The preparation method of a temperature-resistant and salt-resistant nano-crosslinking agent according to claim 1, characterized in that, The drying in Step 2 adopts vacuum gradient drying, First, dry at 50 °C for 2 hours, then dry at 80 °C for 3 hours, and finally dry at 110 °C for 5 hours; After drying, pulverize and then classify to obtain a nano-crosslinker with a particle size meeting the requirements.

8. A temperature-resistant and salt-resistant nano-crosslinker obtained by using the preparation method according to any one of claims 1 to 7.

9. A temperature-resistant and salt-resistant polymer gel, characterized in that, The polymer gel is obtained by cross-linking reaction of the nano-crosslinker according to claim 8 with a polymer; the addition amount of the nano-crosslinker is 0.1-0.4 wt.% of the mass of the polymer, and the polymer is one of partially hydrolyzed polyacrylamide and its derivatives.

10. A temperature-resistant and salt-resistant polymer gel according to claim 9, wherein The polymer gel is a three-dimensional network structure, and the range of its network pore size a is 20 nm ≤ a ≤ 50 nm.

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