Deep flooding density controllable multi-stage expansion pre-crosslinked gel particles and preparation method thereof

Abstract

The present invention provides a multi-stage expansion pre-crosslinked gel particle with controllable density for deep flooding and a preparation method thereof, belonging to the field of oilfield chemical technology. The gel particles comprise: monomers (acrylamide, triphenylethyl phenol polyoxyethylene ether methacrylate), hydroquinone / hexamethylenetetramine at a molar ratio of 1:1, polyethylene glycol diacrylate, a modified inorganic lightweight additive, and a toughening agent. The toughening agent improves the strength of the pre-crosslinked gel particles and controls the amount of the modified inorganic lightweight additive to achieve controllable density of the gel particles. The structure of the triphenylethyl phenol polyoxyethylene ether methacrylate delays the initial water absorption and expansion process of the gel particles. The network structure formed by the hydroquinone / hexamethylenetetramine and polyethylene glycol diacrylate imparts multi-stage expansion characteristics to the gel particles under different temperature conditions, thereby resolving the problems of gel particles settling and expanding too quickly during fracture prevention, resulting in weak sealing strength and short migration distance.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield chemistry, and in particular relates to a multi-stage expansion pre-crosslinked gel particle with controllable density for deep flooding and a preparation method thereof. Background Art

[0002] As reservoir waterflooding reaches its mid- to late-stages, "high fluid and water production" is a common problem. To effectively seal high-permeability zones and improve waterflooding efficiency, researchers have combined "injection," "blocking," and "adjustment" to develop deep-seated flooding technology. The core of this technology is to inject selective plugging agents deep into the high-permeability zones to seal them, thereby redirecting the flow of subsequently injected water, improving the sweep efficiency of the waterflood and ultimately increasing overall recovery.

[0003] Currently, commonly used deep-seated profile adjustment and displacement agents include weak polymer gels, colloidal dispersion gels, pre-crosslinked gel particles, clay flocculation systems, and foams. Both weak polymer gels and colloidal dispersion gels are underground crosslinked gels with good injectability and low cost, but are significantly affected by formation conditions and have relatively weak temperature and salinity resistance. Clay flocculation systems utilize the formation of polymer floccules after hydration of bentonite, creating a mechanical plug. While this plugging strength is high, the system suffers from poor injectability and strict requirements for on-site equipment. Foam systems are less damaging to the formation, but their effectiveness is short and they exhibit severe gravity separation. Pre-crosslinked gel particles, as surface-forming gels, offer high gel strength, excellent temperature and salinity resistance, and have proven effective in oilfields such as the Bohai, Shengli, and Dagang oilfields. However, in practical applications, the pre-crosslinked gel particles often experience excessive initial expansion and settling, resulting in the expansion plugging process before reaching the target. This results in reduced plugging efficiency and insignificant improvement in the water absorption profile. Summary of the Invention

[0004] In order to solve the above problems, one object of the present invention is to provide a density-controlled multi-stage expansion pre-crosslinked gel particle for deep flooding, which has good slow swelling performance, high strength and controllable density, meeting the needs of deep flooding.

[0005] To achieve the above objectives, the technical solutions of the present invention are as follows:

[0006] A density-controlled multi-stage expansion pre-crosslinked gel particle for deep flooding, comprising the following components in percentage by mass:

[0007] Monomers, including:

[0008] Acrylamide, 20% to 25%;

[0009] Triphenylethylphenol polyoxyethylene ether methacrylate, 2% to 6%;

[0010] Hydroquinone / hexamethylenetetramine at a molar ratio of 1:1, 0.6%-1% of the monomer mass;

[0011] Polyethylene glycol diacrylate, 0.6%-1% by weight of monomer;

[0012] Initiator, 0.05%-0.1% of monomer mass;

[0013] Modified inorganic lightweight additives, 10%-25%;

[0014] Toughener, 5-15%;

[0015] The polymerization degree of polystyrene in the triphenethylphenol polyoxyethylene ether methacrylate is between 10 and 40.

[0016] As a specific embodiment of the present invention, the toughening agent is sodium bentonite.

[0017] As a specific embodiment of the present invention, the initiator is a persulfate / bisulfite redox initiation system or azobisisobutylamidine hydrochloride.

[0018] As a specific embodiment of the present invention, the modified inorganic lightweight additive is γ-(methacryloyloxy)propyltrimethoxysilane modified carboxylated hollow glass microspheres.

[0019] Furthermore, the synthesis method of the γ-(methacryloyloxy)propyltrimethoxysilane modified carboxylated hollow glass microspheres is as follows:

[0020] (1) Hollow glass microspheres and γ-(methacryloyloxy)propyltrimethoxysilane were uniformly dispersed in toluene by ultrasound, and then the solution was placed in an oil bath at 80-90°C under stirring and nitrogen protection for 8-10 hours.

[0021] (2) After the reaction is completed, the mixture is cooled to room temperature and the modified hollow glass microbeads are filtered out using a microporous filter membrane; the modified hollow glass microbeads are repeatedly washed with anhydrous ethanol and filtered out to clean the toluene and unreacted γ-(methacryloyloxy)propyltrimethoxysilane on the surface of the modified hollow glass microbeads.

[0022] (3) The obtained product is dried to obtain γ-(methacryloyloxy)propyltrimethoxysilane modified carboxylated hollow glass microspheres.

[0023] Another object of the present invention is to provide a method for preparing the above-mentioned density-controllable multi-stage expansion pre-crosslinked gel particles for deep flooding, comprising the following steps:

[0024] (1) completely dissolving or dispersing acrylamide, triphenylethylphenol polyoxyethylene ether methacrylate, hydroquinone, hexamethylenetetramine, polyethylene glycol diacrylate, modified inorganic lightweight additive, and toughening agent in deionized water;

[0025] (2) slowly adding the initiator to the system, passing nitrogen to remove dissolved oxygen in the system, and then placing the system in a water bath at a temperature of 45-60°C for 2-4 hours to obtain a pre-crosslinked gel;

[0026] (3) Granulating, drying, and crushing the obtained gel to obtain density-controllable multi-stage expanded pre-crosslinked gel particles.

[0027] Beneficial effects:

[0028] (1) The pre-crosslinked gel particles of the present invention have good heat resistance, which can reach 120°C, and salt resistance can reach 20×10 4 mg / L.

[0029] (2) The pre-crosslinked gel particles of the present invention have better strength and elasticity. The intercalated structure formed by the cross-linking of the monomers into the layered structure of sodium bentonite and the hydrogen bonding between the hollow glass microspheres and the layer of sodium bentonite can greatly enhance the strength and thermal stability of the pre-crosslinked gel particles.

[0030] (3) On the one hand, triphenylethylphenol polyoxyethylene ether methacrylate is introduced to delay the hydrolysis of the pre-crosslinked gel particle structure; on the other hand, polyethylene glycol diacrylate is used as an unstable crosslinker to delay the initial expansion rate of the pre-crosslinked gel particles and achieve multi-stage expansion characteristics by decomposing the unstable crosslinker structure.

[0031] (4) The pre-crosslinked gel particles of the present invention have simple production and on-site use processes, strong operability, and can adjust density according to reservoir requirements, thus having broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a physical picture of different pre-crosslinked gel particle samples swelling after absorbing water;

[0033] Figure 2 is the expansion performance curve of different pre-cross-linked gel particle samples;

[0034] Figure 3 is a graph showing the expansion performance of the pre-crosslinked gel particle sample of Example 3 at different temperatures;

[0035] Figure 4 This is a strength test curve of different pre-crosslinked gel particle samples under high temperature and high mineralization conditions;

[0036] Figure 5This is a curve chart showing the effect of hollow glass microsphere modification on the strength of pre-crosslinked gel particles. DETAILED DESCRIPTION

[0037] The specific implementation methods of the present invention will be clearly and completely described below with reference to examples. Obviously, the examples described are only part of the embodiments of the present invention, rather than all the embodiments.

[0038] (1) Preparation of gel particles

[0039] The hollow glass microspheres modified with γ-(methacryloyloxy)propyltrimethoxysilane and carboxylated in the following examples and comparative examples have a median particle size of 75 μm and a bulk density of 0.62 g / cm 3 , which is modified by the following method:

[0040] (1) 50 g of hollow glass microspheres and 50 g of γ-(methacryloyloxy)propyltrimethoxysilane were uniformly dispersed in a three-necked flask containing 300 ml of toluene by ultrasound. The flask was then placed in an oil bath at 90 °C for 8 h under magnetic stirring and nitrogen protection.

[0041] (2) After the reaction is completed, the mixture is cooled to room temperature and filtered out using a microporous filter membrane. The modified hollow glass microbeads are repeatedly washed with anhydrous ethanol and filtered out to remove toluene and unreacted γ-(methacryloyloxy)propyltrimethoxysilane from the surface of the modified hollow glass microbeads.

[0042] (3) The obtained product was placed in an oven at 80°C and dried for 24 h to obtain γ-(methacryloyloxy)propyltrimethoxysilane-modified carboxylated hollow glass microspheres.

[0043] The triphenyl phenol polyoxyethylene ether methacrylate in the following examples and comparative examples was obtained from Zhangjiagang Renda Chemical Co., Ltd., and its degree of polymerization was 20.

[0044] Comparative Example 1

[0045] (1) Completely dissolve or disperse 19.2 g of acrylamide, 16 g of γ-(methacryloyloxy)propyltrimethoxysilane-modified carboxylated hollow glass microspheres, 4 g of sodium bentonite, and 0.35 g of hydroquinone / hexamethylenetetramine (molar ratio 1:1) in 39 mL of deionized water. Ultrasonic stirring was performed for 3 h to allow the sodium bentonite to fully hydrate and swell.

[0046] (2) Prepare a 1% mass concentration of azobisisobutylamidine hydrochloride mother solution, take 1.4 mL and slowly add it to the system, pass nitrogen for 30 minutes to remove dissolved oxygen in the system, and then place the system in a water bath at a temperature of 55°C for 4 hours to obtain a pre-crosslinked gel;

[0047] (3) The obtained gel is granulated, dried, and crushed to obtain pre-crosslinked gel particles, which are recorded as Sample 1.

[0048] Example 1

[0049] (1) Completely dissolve or disperse 16 g of acrylamide, 3.2 g of triphenylethylphenol polyoxyethylene ether methacrylate, 16 g of γ-(methacryloyloxy)propyltrimethoxysilane-modified carboxylated hollow glass microspheres, 4 g of sodium bentonite, 0.16 g of hydroquinone / hexamethylenetetramine (molar ratio 1:1), and 0.19 g of polyethylene glycol diacrylate in 39 mL of deionized water. Ultrasonic stirring was performed for 3 h to allow the sodium bentonite to fully hydrate and swell.

[0050] (2) Prepare a 1% mass concentration of azobisisobutylamidine hydrochloride mother solution, take 1.4 mL and slowly add it to the system, pass nitrogen for 30 minutes to remove dissolved oxygen in the system, and then place the system in a water bath at a temperature of 55°C for 4 hours to obtain a pre-crosslinked gel;

[0051] (3) The obtained gel is granulated, dried, and crushed to obtain pre-crosslinked gel particles, which are recorded as Sample 2.

[0052] Example 2

[0053] (1) Completely dissolve or disperse 16 g of acrylamide, 3.2 g of triphenylethylphenol polyoxyethylene ether methacrylate, 13.5 g of γ-(methacryloyloxy)propyltrimethoxysilane-modified carboxylated hollow glass microspheres, 5.6 g of sodium bentonite, 0.16 g of hydroquinone / hexamethylenetetramine (molar ratio 1:1), and 0.19 g of polyethylene glycol diacrylate in 40 mL of deionized water. Ultrasonic stirring was performed for 3 h to allow the sodium bentonite to fully hydrate and swell.

[0054] (2) Prepare a 1% mass concentration of azobisisobutylamidine hydrochloride mother solution, take 1.4 mL and slowly add it to the system, pass nitrogen for 30 minutes to remove dissolved oxygen in the system, and then place the system in a water bath at a temperature of 55°C for 4 hours to obtain a pre-crosslinked gel;

[0055] (3) The obtained gel is granulated, dried, and crushed to obtain pre-crosslinked gel particles, which are recorded as Sample 3.

[0056] Comparative Example 2

[0057] (1) Completely dissolve or disperse 16 g acrylamide, 3.2 g triphenylethylphenol polyoxyethylene ether methacrylate, 13.5 g hollow glass microspheres, 5.6 g sodium bentonite, 0.16 g hydroquinone / hexamethylenetetramine (molar ratio 1:1), and 0.19 g polyethylene glycol diacrylate in 40 mL of deionized water. Ultrasonic stirring was performed for 3 h to allow the sodium bentonite to fully hydrate and swell.

[0058] (2) Prepare a 1% mass concentration of azobisisobutylamidine hydrochloride mother solution, take 1.4 mL and slowly add it to the system, pass nitrogen for 30 minutes to remove dissolved oxygen in the system, and then place the system in a water bath at a temperature of 55°C for 4 hours to obtain a pre-crosslinked gel;

[0059] (3) The obtained gel was granulated, dried, and crushed to obtain pre-crosslinked gel particles, which were recorded as Sample 4.

[0060] (2) Performance test

[0061] The mineralization degree is 20×10 4 mg / L NaCl simulated formation water is ready for use.

[0062] 1. Sample density test

[0063] 5 g of samples from Comparative Example 1, Example 1, and Example 2 were weighed respectively, and their initial densities were tested using the drainage method. The results showed that the initial densities of Sample 1, Sample 2, and Sample 3 were 0.94 g / cm 3 , 1.03g / cm 3 and 2.01g / cm 3 The results show that the density of the samples can be changed by adjusting the content of modified inorganic lightweight additives, toughening agents, hydrophobic monomers and crosslinking agents. The three samples were placed in deionized water (density 1g / cm 3 ) and then expanded in a 60°C oven for 24 hours. The three pre-crosslinked gel particles were in the following states in water: Figure 1 The results show that the pre-cross-linked gel with a density similar to that of the suspending liquid can maintain good suspension after swelling with water. Under different reservoir conditions, the density of the pre-cross-linked gel particles can be adjusted according to the displacement position and the density of the injection fluid to control its sedimentation rate, thereby improving the displacement effect.

[0064] 2. Hydration expansion test

[0065] 5g of each of the three samples of Example 1, Example 2, and Comparative Example 1 were placed in simulated formation water and aged in ovens at different temperatures. The expansion ratios of the different samples at different times were measured. The expansion ratios of Sample 1, Sample 2, and Sample 3 at 90°C change as shown in the following table. Figure 2 The expansion multiple of Sample 3 at 60℃, 90℃ and 120℃ changes as shown in the figure. Figure 3 shown.

[0066] from Figure 2 It can be seen that Samples 2 and 3, after adding the hydrophobic monomer and unstable crosslinker, exhibit lower expansion rates in the initial expansion compared to Sample 1. On the one hand, the hydrophobic monomer reduces the water absorption rate of the pre-crosslinked gel particles during the initial expansion; on the other hand, with the decomposition of the unstable crosslinker, the pre-crosslinked gel particles can achieve a larger expansion multiple in the later stages, meeting the requirements of deep reservoir profile adjustment and flooding. Comparing Samples 2 and 3, it can be seen that the content of sodium bentonite and modified inorganic lightweight additives not only affects density but also has a certain impact on the expansion multiple.

[0067] from Figure 3 It can be seen that the expansion ratio of the pre-crosslinked gel particles increases with increasing temperature. On the one hand, the higher the temperature, the more intense the thermal motion of water molecules, and the faster they enter the three-dimensional network structure of the gel; on the other hand, high temperature accelerates the decomposition rate of the unstable crosslinking agent in the pre-crosslinked gel particles, resulting in an increase in the expansion ratio. The experimental results show that at 120°C and a mineralization degree of 20×10 4 mg / L, the pre-crosslinked gel particles still have good swelling properties and can meet the reagent requirements of different reservoir flooding operations.

[0068] 3. Strength test

[0069] Three different samples were taken, placed in simulated formation water, and aged in a 90°C oven. The strength of the pre-crosslinked gel particles at different aging times was tested using the steering pressure method (TGU). The test results are shown in Figure 2. Figure 4 shown.

[0070] from Figure 4 It can be seen that the strength of all samples shows a trend of first increasing and then decreasing. Comparing Sample 1 and Sample 2, when the hydrophobic monomer and unstable cross-linking agent are added, the strength of the pre-cross-linked gel particles increases. After aging, the strength of Sample 1 is lower than the initial value, indicating that its stability is poor. Sample 2 and Sample 3 still maintain good strength after aging, indicating that the addition of hydrophobic monomers and unstable cross-linking agents can enhance the strength and stability of the pre-cross-linked gel particles. Figure 2 and Figure 3 It can be seen that increasing the content of sodium bentonite can increase the density of pre-crosslinked gel particles while enhancing their stability and strength, but will affect their expansibility to a certain extent.

[0071] from Figure 5 It can be seen that the strength of all samples decreases to some extent with increasing aging time, and the strength of Sample 4 decreases rapidly after 30 days. When the aging time reaches 100 days, the strength of Sample 4 is much lower than that of Sample 3. In the embodiments of the present invention, the molecular structure is designed so that the modified inorganic lightweight additive participates in the gelation reaction in the form of chemical bonds, effectively enhancing the long-term stability of the pre-crosslinked gel particles.

[0072] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art will appreciate that these embodiments are intended to illustrate the present invention only and are not to be construed as limiting the scope of the present invention. Further improvements may be made without departing from the principles of the present invention, and such improvements are intended to fall within the scope of protection of the present invention.

Claims

1. A density-controllable multi-stage expansion pre-crosslinked gel particle for deep flooding, characterized in that: Calculated by mass percentage, including: Monomers, including: acrylamide, 20%~25%, triphenyl phenol polyoxyethylene ether methacrylate, 2%~6%; Hydroquinone / hexamethylenetetramine at a molar ratio of 1:1, 0.6%-1% of the monomer mass; Polyethylene glycol diacrylate, 0.6%-1% by weight of monomer; Initiator, 0.05%-0.1% of monomer mass; γ-(methacryloyloxy)propyltrimethoxysilane modified hollow glass microspheres, 10%-25%; Sodium bentonite, 5-15%; The polymerization degree of polyoxyethylene in triphenethylphenol polyoxyethylene ether methacrylate is between 10 and 40.

2. The density-controllable multi-stage expansion pre-crosslinked gel particles for deep flooding according to claim 1, characterized in that: The initiator is a persulfate / bisulfite redox initiation system or azobisisobutylamidine hydrochloride.

3. The density-controllable multi-stage expansion pre-crosslinked gel particles for deep flooding according to claim 1, characterized in that: The γ-(methacryloyloxy)propyltrimethoxysilane-modified hollow glass microspheres are prepared by a method comprising the following steps: (1) Hollow glass microspheres and γ-(methacryloyloxy)propyltrimethoxysilane were uniformly dispersed in toluene by ultrasound, and then the solution was placed in an oil bath at 80-90°C under stirring and nitrogen protection for 8-10 hours; (2) After the reaction is completed, the mixture is cooled to room temperature and the modified hollow glass microspheres are filtered out using a microporous filter membrane; the modified hollow glass microspheres are repeatedly washed with anhydrous ethanol and filtered out; (3) The obtained product is dried to obtain γ-(methacryloyloxy)propyltrimethoxysilane modified hollow glass microspheres.

4. A method for preparing density-controlled multi-stage expansion pre-crosslinked gel particles for deep flooding, for preparing the density-controlled multi-stage expansion pre-crosslinked gel particles for deep flooding according to any one of claims 1 to 3, characterized in that: The steps include: (1) Completely dissolving or dispersing acrylamide, triphenylethylphenol polyoxyethylene ether methacrylate, hydroquinone / hexamethylenetetramine, polyethylene glycol diacrylate, a modified inorganic lightweight additive, and a toughening agent in deionized water, wherein the modified inorganic lightweight additive is hollow glass microspheres modified with γ-(methacryloyloxy)propyltrimethoxysilane, and the toughening agent is sodium bentonite; (2) Slowly add the initiator to the system, pass nitrogen to remove the dissolved oxygen in the system, and then place the system in a water bath at a temperature of 45-60°C for 2-4 hours to obtain a pre-crosslinked gel; (3) The obtained gel is granulated, dried, and crushed to obtain density-controllable multi-stage expanded pre-cross-linked gel particles.

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