A high-temperature resistant, high-density, solid-phase-free completion fluid viscosity enhancer and its preparation method and application

Abstract

The present invention provides a high-temperature resistant and high-density solid-free completion fluid thickener and its preparation method and application. The present invention first prepares a zwitterionic monomer 3-(dimethyl(4-vinylbenzyl)amino)butanesulfonate using 4-vinylbenzyl chloride, dimethylamine and 1,4-butane sultone as raw materials, and then reacts the zwitterionic monomer with an amide monomer, a hydrophilic monomer and a cationic monomer through aqueous solution free radical polymerization or emulsion polymerization to obtain a high-temperature resistant and high-density solid-free completion fluid thickener. The thickener of the present invention has good solubility and thickening effect in high-density divalent inorganic salt water. The thickener of the present invention can resist high temperatures of 200°C and has excellent temperature resistance. It overcomes the shortcomings of the existing solid-free completion fluid thickeners with insufficient high-temperature stability. At the same time, the monomers of the synthetic thickener of the present invention are all hydrophilic materials and contain zwitterions, which are easily dissolved in high-density salt water.

Description

Technical Field

[0001] The invention relates to a high-temperature resistant, high-density, solid-phase-free completion fluid viscosity enhancer, a preparation method and application thereof, and belongs to the field of oilfield chemistry in the petroleum industry. Background Art

[0002] As my country's oil and gas exploration and development progresses into deep and ultra-deep formations, high-temperature, high-pressure, and complex formations continue to increase. The underground drilling environment is becoming increasingly harsh, and development is becoming increasingly difficult. This poses severe challenges to the performance of completion fluid treatment agents. Completion fluids balance formation pressure, purify the wellbore, stabilize the wellbore wall, control filtration and leakage, and maintain stable in-well properties. They require specialized properties such as excellent temperature and salt resistance, corrosion resistance, environmental friendliness, and low cost. However, in deep and ultra-deep oil and gas reservoirs, submicron clay particles in completion fluids can easily invade reservoir pores and microfractures, blocking oil and gas pathways, significantly reducing reservoir permeability, and damaging the reservoir. To meet the demands for rapid, high-quality drilling and reservoir protection in deep and ultra-deep wells, zero- and low-solids completion fluids have been widely researched and applied.

[0003] Zero-solids / low-solids completion fluid systems increase system density through soluble salts and viscosity through high-molecular-weight polymers, resulting in improved cuttings carrying and suspension capabilities. Compared to traditional clay-containing completion fluid systems, they offer reduced static shear force and flow resistance, effectively increasing drilling speed and shortening drilling cycles while also protecting oil and gas reservoirs. Solids-free or low-solids completion fluid systems contain little or no clay, necessitating the use of high-temperature polymer viscosifiers to address the problem of cuttings carryover and suspension during drilling. High-molecular-weight, highly hydrophilic materials such as xanthan gum, carboxymethyl cellulose, and modified starch are commonly added to completion fluids to enhance viscosity. However, these polymer viscosifiers are susceptible to degradation and failure at high temperatures, and their operating temperature should not exceed 150°C. In recent years, domestic and foreign scholars have found that the use of organic salts such as potassium formate has a certain synergistic temperature resistance effect on polymer viscosifiers, with a temperature resistance of up to 180°C. However, the cost of high-density organic salt completion fluids is too high to meet the conditions for large-scale use and promotion of solid-free water-based completion fluids.

[0004] Chinese patent document CN104650827A discloses a temperature-resistant, slightly cross-linked viscosity enhancer and a high-temperature, solid-free, water-based drilling fluid. This invention utilizes olefin sulfonic acid, olefin amide, and olefin benzene to produce a slightly cross-linked copolymer that maintains excellent viscosity-enhancing properties after aging in saturated brine at 180°C, surpassing imported products. However, high-density divalent brine completion fluids contain relatively low levels of free water, and the introduction of hydrophobic side chains hinders their solubility, making them unsuitable for high-density divalent brine completion fluids.

[0005] Chinese patent document CN114214049A discloses a method for preparing a solid-free viscosifying workover fluid for ultra-deep, ultra-high-temperature oil and gas wells. By adding an ultra-high-temperature polymer crosslinker, an ultra-high-temperature polymer stabilizer, and an ultra-high-temperature heat stabilizer to brine, the viscosifier can be used at a temperature of up to 200°C. This workover fluid meets the requirement for maintaining the stability of the viscosifying agent in high-temperature, solid-free brine, but the brine used has a density of only 1.1 to 1.3 g / cm 3 , and it is a monovalent sodium salt, which does not meet the conditions for use of high-density completion fluid.

[0006] In summary, the existing high-temperature, high-density, solid-free completion fluid thickeners have the following disadvantages: (1) insufficient high-temperature resistance. The polymer easily degrades and fails under high-temperature conditions, which cannot meet the requirements of high-temperature drilling in deep formations. (2) The high-density completion fluid brine has a low free water content. The synthetic polymer is difficult to fully dissolve or even cannot dissolve in the high-density brine, and cannot produce a thickening effect. Therefore, it is urgent to develop a high-temperature, high-density, solid-free completion fluid thickener. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the present invention provides a high-temperature resistant and high-density solid-free completion fluid thickener and its preparation method and application. The present invention uses an amide monomer with good hydrophilic properties as the main monomer, prepares a zwitterionic monomer 3-(dimethyl(4-vinylbenzyl)amino)butanesulfonate with good temperature and salt resistance, polymerizes it with strongly hydrophilic acrylic acid and other monomers using the principle of free radical polymerization, and prepares a zwitterionic polymer thickener with good solubility and thickening effect in high-density divalent inorganic salt water. The thickener of the present invention can withstand high temperatures of 200°C and has excellent temperature resistance, overcoming the shortcomings of the existing thickeners for solid-free completion fluids that have insufficient high-temperature stability. At the same time, the monomers of the synthetic thickener of the present invention are all hydrophilic materials and contain zwitterions, which are easily soluble in high-density salt water.

[0008] The technical solutions of the present invention are as follows:

[0009] A method for preparing a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer comprises the following steps:

[0010] (1) Preparation of zwitterionic monomers

[0011] 4-vinylbenzyl chloride and a dimethylamine aqueous solution are added to ethanol, stirred evenly, and then subjected to a first reaction to obtain N,N-dimethyl-4-vinylbenzylamine; N,N-dimethyl-4-vinylbenzylamine and 1,4-butane sultone are added to acetonitrile, stirred evenly, and then subjected to a second reaction to obtain a zwitterionic monomer 3-(dimethyl(4-vinylbenzyl)amino)butane sulfonate;

[0012] (2) Preparation of aqueous solution

[0013] Add amide monomer, hydrophilic monomer, cationic monomer and zwitterionic monomer to water, adjust the pH of the system to 7-8, add chain transfer agent, stir evenly to obtain an aqueous phase solution;

[0014] (3) Preparation of high-temperature resistant, high-density, solid-free completion fluid viscosifier

[0015] An initiator is added to the aqueous solution to carry out aqueous solution free radical polymerization; or the aqueous solution is added to the oil solution, and then an initiator is added to carry out emulsion polymerization to obtain a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer.

[0016] Preferably, according to the present invention, the mass fraction of the dimethylamine aqueous solution in step (1) is 70% and the density is 0.9 g / mL; and the molar ratio of dimethylamine to 4-vinylbenzyl chloride is 1.2-1.5:1.

[0017] According to the preferred embodiment of the present invention, the ratio of the mass of 4-vinylbenzyl chloride to the volume of ethanol in step (1) is 1 g:5-10 mL.

[0018] According to the preferred embodiment of the present invention, the temperature of the first reaction in step (1) is 40-60° C., the time of the first reaction is 20-30 h; and the first reaction is carried out under a nitrogen atmosphere.

[0019] According to the preferred embodiment of the present invention, in step (1), after the first reaction is completed, a post-treatment step is further included, specifically as follows: the obtained reaction solution is subjected to rotary evaporation to remove the solvent, and the obtained crude product is purified by column chromatography using petroleum ether as an eluent to obtain N,N-dimethyl-4-vinylbenzylamine.

[0020] According to the preferred embodiment of the present invention, the molar ratio of 1,4-butanesultone to N,N-dimethyl-4-vinylbenzylamine in step (1) is 0.8-1:1.

[0021] According to the preferred embodiment of the present invention, the ratio of the mass of N,N-dimethyl-4-vinylbenzylamine to the volume of acetonitrile in step (1) is 1 g:20-40 mL.

[0022] According to the preferred embodiment of the present invention, the temperature of the second reaction in step (1) is 40-60° C., the time of the second reaction is 40-60 h; and the second reaction is carried out under a nitrogen atmosphere.

[0023] According to a preferred embodiment of the present invention, after the second reaction in step (1) is completed, a post-treatment step is included, specifically as follows: filtering the obtained reaction solution, and drying the filtered solid at 40-45° C. for 10-12 hours.

[0024] The reaction scheme of 3-(dimethyl(4-vinylbenzyl)amino)butanesulfonate of the present invention is as follows:

[0025]

[0026] According to the preferred embodiment of the present invention, the amide monomer in step (2) is one or a combination of two or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N,N-dimethylacrylamide; and the mass ratio of the amide monomer to water is 0.1-0.2:1.

[0027] According to the preferred embodiment of the present invention, the hydrophilic monomer in step (2) is one of acrylic acid, methacrylic acid, and methenyl butenedioic acid; and the mass ratio of the hydrophilic monomer to the amide monomer is 0.5-1:1.

[0028] Preferably, according to the present invention, the cationic monomer in step (2) is dimethyldiallylammonium chloride; and the mass ratio of the cationic monomer to the amide monomer is 0.3-0.75:1.

[0029] According to the preferred embodiment of the present invention, the mass ratio of the zwitterionic monomer to the amide monomer in step (2) is 0.25-0.5:1.

[0030] Preferably, according to the present invention, in step (2), a sodium hydroxide solution with a mass fraction of 20-40% is used to adjust the pH of the system.

[0031] According to the preferred embodiment of the present invention, the chain transfer agent in step (2) is dodecanethiol, isopropanol or acetone; the mass of the chain transfer agent is 0.5-1% of the total mass of the amide monomer, the hydrophilic monomer, the cationic monomer and the zwitterionic monomer.

[0032] According to the preferred embodiment of the present invention, the initiators in step (3) are potassium persulfate, ammonium persulfate, or a combination of one of potassium persulfate and ammonium persulfate with sodium bisulfite; the mass of the initiators is 0.05-0.5% of the total mass of the amide monomer, the hydrophilic monomer, the cationic monomer and the zwitterionic monomer.

[0033] Preferably, according to the present invention, the temperature of the aqueous solution free radical polymerization reaction in step (3) is 55-65° C., the time of the aqueous solution free radical polymerization reaction is 5-6 hours; and the aqueous solution free radical polymerization reaction is carried out under a nitrogen atmosphere.

[0034] Preferably, according to the present invention, the oil phase solution in step (3) is prepared by the following method: adding an emulsifier to white oil and stirring evenly; the emulsifier is Span80 or Span65, and the mass ratio of the emulsifier to the white oil is 1:70-80.

[0035] Preferably, according to the present invention, the mass ratio of the white oil in the oil phase solution to the water in the aqueous phase solution in step (3) is 2-4:1; after the aqueous phase solution is added to the oil phase solution, it is sheared at 5000-6000 r / min for 10-20 min to obtain an emulsion.

[0036] Preferably, according to the present invention, the temperature of the emulsion polymerization reaction in step (3) is 55-65° C., the time of the emulsion polymerization reaction is 5-6 hours, and the emulsion polymerization reaction is carried out under a nitrogen atmosphere.

[0037] Preferably, according to the present invention, after the aqueous solution free radical polymerization reaction or emulsion polymerization reaction is completed in step (3), a post-treatment step is further included, specifically as follows: the reaction liquid is filtered, washed, and dried to obtain a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer; the washing is performed by washing with ethanol 3-5 times; and the drying is performed at 75-80°C for 8-10 hours.

[0038] The present invention also provides a high-temperature resistant, high-density, solid-phase-free completion fluid viscosity enhancer, which is prepared by the above method.

[0039] According to the present invention, the above-mentioned viscosity enhancer for high-temperature resistant and high-density solid-free completion fluid is used in a solid-free / low-solid completion fluid.

[0040] The technical features and beneficial effects of the present invention are as follows:

[0041] 1. The present invention first prepares a zwitterionic monomer 3-(dimethyl(4-vinylbenzyl)amino)butane sulfonate with good temperature and salt resistance, and then polymerizes it with monomers such as strongly hydrophilic acrylic acid to obtain a zwitterionic polymer thickener with good solubility and thickening effect in high-density inorganic brine. The strong hydrophilic group in the polymer enhances the solubility of the polymer molecular chain. At the same time, the zwitterion has a good anti-polyelectrolyte effect, which enables the polymer molecular chain to stretch in high-concentration brine to form a spatial structure, thereby enhancing the flow resistance of the brine solution and increasing the viscosity. The thickener of the present invention is suitable for high formation temperatures. The high formation temperature and brine environment in deep wells and ultra-deep wells cause the polymer molecular chain to break and degrade easily, and the hydrophilic groups such as amide groups hydrolyze faster, causing the polymer molecules to lose their function. The thickener developed by the present invention can stably exist in 200°C deep high-temperature brine, and its performance remains good and is not easily degraded. It can meet the performance requirements of solid-phase completion fluids in deep high-temperature formations.

[0042] 2. The viscosity enhancer of the present invention is suitable for high-density brine. Solid-free completion fluids are weighted with soluble salts. In high-density brine, firstly, the free water content is low, making it difficult for polymers to dissolve. Secondly, the presence of the polyelectrolyte effect causes the polymer molecular chains to curl up, making it difficult to form a complex spatial conformation to function. The viscosity enhancer of the present invention can solve the problems of low free water content in high-density completion fluid brine, making it difficult for polymers to dissolve. Moreover, under high temperature conditions, polymer degradation and failure lead to a significant decrease in completion fluid viscosity. The density of brine used for the viscosity enhancer of the present invention can reach 1.5-1.7 g / cm 3 , the temperature resistance can reach 200℃, which makes up for the shortcomings of existing high-temperature resistant, high-density, solid-free completion fluid viscosity enhancers.

[0043] 3. The viscosity enhancer of the present invention is suitable for deep and ultra-deep oil and gas drilling, meets the performance requirements of solid-free completion fluid in high-temperature and high-pressure formations, and plays a certain supporting role in the protection of deep, high-temperature and high-pressure oil and gas reservoirs. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to specific examples, but is not limited thereto.

[0045] The raw materials used in the examples are all conventional raw materials and can be obtained commercially; the methods described are all based on existing technologies unless otherwise specified.

[0046] Example 1

[0047] A method for preparing a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer comprises the following steps:

[0048] (1) Preparation of zwitterionic monomers:

[0049] 30.5 g of 4-vinylbenzyl chloride and 20 mL of a 70% by mass dimethylamine solution were added to 200 mL of anhydrous ethanol and stirred uniformly. The mixed solution was transferred to a three-necked flask, heated to 50°C, and nitrogen was introduced. The mixture was stirred and reacted for 24 hours. After the reaction was completed, the resulting reaction solution was evaporated to remove the solvent. The crude product was purified by column chromatography using petroleum ether as the eluent, and the solvent was evaporated to obtain N,N-dimethyl-4-vinylbenzylamine as a light yellow transparent oil. 3.22 g of N,N-dimethyl-4-vinylbenzylamine and 2.72 g of 1,4-butane sultone were dissolved in 100 mL of acetonitrile, nitrogen was introduced, and the mixture was reacted at 50°C for 48 hours. After the reaction was completed, the resulting reaction solution was filtered, and the filtered solid was dried at 40°C for 10 hours to obtain the zwitterionic monomer 3-(dimethyl(4-vinylbenzyl)amino)butane sulfonate, which was ground into powder and stored at 2-4°C.

[0050] (2) Preparation of high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer

[0051] 12 g of amide monomer, 8 g of hydrophilic monomer, 6 g of cationic monomer and 4 g of the zwitterionic monomer prepared in step (1) were added to 80 g of deionized water in sequence. After all monomers were completely dissolved, a 30% by mass NaOH solution was used to adjust the pH of the system to 7, 0.2 g of chain transfer agent dodecanethiol was added, and the mixture was stirred for 10 min using a magnetic stirrer. The resulting solution was transferred to a three-necked flask; the solution was heated to 55° C. using a water bath heating method, and 0.03 g of initiator was added thereto. The mixture was reacted under a nitrogen environment for 5 h, with a stirring speed of 300 r / min during the reaction; after the reaction was completed, the resulting reaction solution was filtered, and the filtered solid was washed with ethanol three times, dried at 75° C. for 10 h, and crushed to obtain a high-temperature resistant, high-density, solid-free completion fluid thickener;

[0052] Among them, the amide monomer is a combination of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid, and the mass ratio of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid is 2:1; the hydrophilic monomer is acrylic acid; the cationic monomer is dimethyldiallylammonium chloride, and the initiator is potassium persulfate.

[0053] Example 2

[0054] A method for preparing a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer comprises the following steps:

[0055] (1) The preparation of zwitterionic monomer is the same as step (1) of Example 1.

[0056] (2) Preparation of high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer

[0057] 10 g of amide monomer, 8 g of hydrophilic monomer, 6 g of cationic monomer and 4 g of the zwitterionic monomer prepared in step (1) were added to 80 g of deionized water in sequence. After all monomers were completely dissolved, a 30% by mass NaOH solution was used to adjust the pH of the system to 7, 0.2 g of chain transfer agent dodecanethiol was added, and the mixture was stirred for 10 min using a magnetic stirrer. The resulting solution was transferred to a three-necked flask; the solution was heated to 60° C. using a water bath heating method, and 0.03 g of initiator was added thereto. The mixture was reacted under a nitrogen environment for 5 h, with a stirring speed of 300 r / min during the reaction; after the reaction was completed, the resulting reaction solution was filtered, and the filtered solid was washed with ethanol three times, dried at 75° C. for 10 h, and crushed to obtain a high-temperature resistant, high-density, solid-free completion fluid thickener;

[0058] Among them, the amide monomer is a combination of N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid, and the mass ratio of N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid is 1:1; the hydrophilic monomer is methacrylic acid; the cationic monomer is dimethyldiallylammonium chloride; and the initiator is a combination of ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.

[0059] Example 3

[0060] A method for preparing a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer comprises the following steps:

[0061] (1) The preparation of zwitterionic monomer is the same as step (1) of Example 1.

[0062] (2) Preparation of high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer

[0063] 9 g of amide monomer, 6 g of hydrophilic monomer, 5 g of cationic monomer and 4 g of the zwitterionic monomer prepared in step (1) were added to 80 g of deionized water in sequence. After all monomers were completely dissolved, a 30% by mass NaOH solution was used to adjust the pH of the system to 7, 0.2 g of chain transfer agent dodecanethiol was added, and the mixture was stirred for 10 min using a magnetic stirrer. The resulting solution was transferred to a three-necked flask; the solution was heated to 65° C. using a water bath heating method, and 0.03 g of initiator was added thereto. The mixture was reacted under a nitrogen environment for 5 h, with a stirring speed of 300 r / min during the reaction; after the reaction was completed, the resulting reaction solution was filtered, and the filtered solid was washed three times with ethanol, dried at 75° C. for 10 h, and crushed to obtain a high-temperature resistant, high-density, solid-free completion fluid thickener;

[0064] The amide monomer is acrylamide; the hydrophilic monomer is methenyl butylated acid; the cationic monomer is dimethyl diallyl ammonium chloride; and the initiator is potassium persulfate.

[0065] Example 4

[0066] A method for preparing a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer comprises the following steps:

[0067] (1) The preparation of zwitterionic monomer is the same as step (1) of Example 1.

[0068] (2) Preparation of high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer

[0069] Preparation of aqueous solution: To 50 g of deionized water, 9 g of amide monomer, 6 g of hydrophilic monomer, 5 g of cationic monomer, and 4 g of zwitterionic monomer were added in sequence. After all monomers were completely dissolved, the pH of the system was adjusted to 7 with a 30% by mass NaOH solution. 0.2 g of chain transfer agent dodecanethiol was added, and the mixture was stirred with a magnetic stirrer for 10 min to obtain an aqueous solution.

[0070] Preparation of oil phase solution: Add 150g white oil and 2g Span80 to a beaker and stir well to obtain an oil phase solution;

[0071] The aqueous solution was added to the oil phase solution and sheared at 6000 r / min for 10 minutes using an emulsifying shearing machine. The emulsified emulsion was transferred to a three-necked flask. The flask was heated to 65° C. using a water bath heating method, and 0.03 g of initiator was added thereto. The mixture was reacted under a nitrogen atmosphere for 5 hours with a stirring speed of 300 r / min. After the reaction was completed, the reaction liquid was filtered, and the filtered solid was washed three times with ethanol, dried at 80° C. for 8 hours, and crushed to obtain a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer.

[0072] The amide monomer is acrylamide; the hydrophilic monomer is methenyl butylated acid; the cationic monomer is dimethyl diallyl ammonium chloride; and the initiator is potassium persulfate.

[0073] Comparative Example 1

[0074] A method for preparing a solid-free completion fluid viscosifier is as described in Example 1, except that no zwitterionic monomer is added.

[0075] Comparative Example 2

[0076] A method for preparing a solid-free completion fluid viscosifier is as described in Example 1, except that no cationic monomer is added.

[0077] Comparative Example 3

[0078] Use imported polymer thickener HE300.

[0079] Comparative Example 4

[0080] Uses bio-based polymer xanthan gum.

[0081] Comparative Example 5

[0082] A method for preparing a solid-free completion fluid viscosifier is as described in Example 1, except that no hydrophilic monomer is added.

[0083] Comparative Example 6

[0084] A method for preparing a tackifier for solid-free completion fluid is as described in Example 1, except that the mass of the amide monomer is 20 g.

[0085] Test example

[0086] The following performance evaluations were performed on the tackifiers prepared in the Examples and Comparative Examples:

[0087] (1) Test of viscosity increasing effect of thickener in brine with different densities

[0088] The prepared tackifier was tested for rheological parameters (apparent viscosity, plastic viscosity, dynamic shear force) according to the American Petroleum Institute (API) standard (API RP 13B-1, 2009). The density of the prepared tackifier was 1.29 g / cm 3 Calcium chloride solution, 1.56 g / cm 3 A solution of calcium bromide salt with a density of 1.7 g / cm 3 Calcium chloride / calcium bromide composite brine was added with the viscosifiers prepared in the Examples and Comparative Examples, with the mass fraction of the viscosifiers in the base fluids of different densities being 1%. The apparent viscosity, plastic viscosity, and dynamic shear force of the viscosifiers in the base fluids of different densities were then tested. The experimental results are shown in Tables 1-3.

[0089] Table 1 Density is 1.29 g / cm 3 Performance of viscosity enhancer in calcium chloride solution

[0090]

[0091]

[0092] From Table 1, we can see that at a density of 1.29 g / cm 3In calcium chloride solution, under the same mass addition, the performance of the zwitterionic thickener prepared by the present invention is better than that of the imported thickener HE300, and the thickening effect is stable, and the apparent viscosity AV can reach more than 50mPa·s. At the same time, it can be found by comparative example 1 that the role of zwitterionic monomers in high-concentration salt water is irreplaceable. The introduction of zwitterions in polymers can effectively weaken the influence of polyelectrolytes, so that polymer molecules can still stretch in high-concentration salt water, increase the water phase flow resistance, and play a role in thickening. It can be seen from comparative example 2 that removing the cationic monomer diallyldimethylammonium chloride in the polymer has a certain effect on the polymer thickening performance, and the solution viscosity decreases significantly, indicating that the presence of cationic monomers enhances the salt resistance of the polymer. In comparative example 5, the hydrophilic monomer is removed to form a polymer long chain spatial configuration that is simpler than the embodiment, and the thickening effect is reduced. Comparative example 6 increases the content of amide monomers. Since the amide monomer activity is higher, the polymer molecules are linked longer, and the thickening effect is better in salt water. The biopolymer xanthan gum, due to its polysaccharide structure, dissolves well in saline. In saline, its molecular chains form super-coalesced aggregates, resulting in excellent viscosity-increasing properties that exceed the measurement range. Therefore, at room temperature, the biopolymer xanthan gum exhibits the best viscosity-increasing properties.

[0093] Table 2 density is 1.56g / cm 3 Performance of viscosity enhancer in calcium bromide solution

[0094]

[0095]

[0096] At a density of 1.56 g / cm 3 When the same mass fraction of thickener is added to the calcium bromide solution, due to the reduction of free water and the strong polyelectrolyte effect, the synthetic thickeners in Comparative Examples 1 and 3 are more difficult to dissolve when added, and the time for the synthetic polymer dry powder to be completely dissolved is greatly extended. The zwitterionic polymer used in the present invention has good solubility in high-density saline and is easy to dissolve completely in high-density divalent saline. When the same polymer addition amount is added, compared with low-density saline, the solution flow in high-density saline is more difficult due to the lower free water content, and the result is an increase in the viscosity of the system; at the same time, Example 4 adopts the emulsion polymerization method, and the resulting synthetic polymer has a higher degree of polymerization and a longer molecular chain, and its performance in saline is close to that of free radical polymerization in water. It can be seen from Comparative Example 3 that the performance of the polymer thickener synthesized by the present invention is 1.56g / cm 3 The performance of the thickening polymer in calcium bromide brine was superior to that of imported thickeners. For the same reason, the effect of xanthan gum was best in the room temperature test.

[0097] Table 3 density is 1.70g / cm 3Performance of viscosity enhancers in composite brine

[0098]

[0099] In calcium chloride / calcium bromide composite brine, the zwitterionic polymers of the present invention exhibited excellent viscosity-increasing effects, with the Examples all outperforming the imported thickener HE300. Furthermore, in high-density composite brine, the zwitterionic polymers of the present invention exhibited excellent solubility, with no insoluble particles appearing. However, in Comparative Examples 1, 3, and 5, insoluble colloidal particles appeared during the addition process. The strong charge in the high-density brine inhibited the ionization of ions on the polymer chains, making it difficult for the polymer chains to unwind, forcing them to curl up and precipitate. The Examples demonstrate that the zwitterionic polymer thickeners of the present invention exhibit excellent viscosity-increasing effects.

[0100] (2) Tackifier temperature resistance test

[0101] The preparation density is 1.7g / cm 3 Calcium chloride / calcium bromide composite brine was added with 1% by mass of thickeners prepared in different embodiments and comparative examples. After aging at different temperatures, the changes in apparent viscosity, plastic viscosity, and dynamic shear force of the brine solutions containing the thickeners in different embodiments and comparative examples were tested. The experimental results are shown in Tables 4 to 6.

[0102] Table 4 Thickener at 1.70 g / cm 3 Performance changes before and after aging at 150℃ in composite brine

[0103]

[0104] After aging at 150°C for 16 hours, the tackifiers in each example exhibited excellent temperature resistance, with the tackifying performance remaining largely unchanged at 150°C. Furthermore, as the temperature increased, the polymer chains became more soluble in water, transitioning from a curled state to an extended state in the solution, increasing the solution's flow resistance. The tackifying effect after aging at 150°C was significantly better than before. The results show that both the example and comparative example HE300 did not fail at 150°C, maintaining excellent tackifying performance. Comparative Example 1 exhibited poor solubility before aging, with virtually no tackifying effect. After aging, the polymer's solubility in salt water increased, the polymer chains expanded somewhat, and the viscosity increased slightly. Comparative Example 4 demonstrates that, unlike the synergistic heat-resistance effect of organic salt water, the biopolymer xanthan gum exhibited poor heat-resistance in inorganic salt water, completely failing after aging at 150°C. Comparative Example 6 demonstrates that the addition of amide monomers significantly decreased the viscosity of the tackifier after aging at 150°C, due to the susceptibility of amide groups to hydrolysis at high temperatures.

[0105] Table 5 Thickener at 1.70 g / cm 3Performance changes after aging at 180℃ in composite brine

[0106]

[0107] After aging at 180°C for 16 hours, except for the biopolymer xanthan gum, which completely failed, the other comparative examples began to experience a loss of viscosity-enhancing properties. Comparative Example 1, due to the polyelectrolyte effect, was unable to dissolve and stretch well in high-density salt water, resulting in poor viscosity-enhancing properties. As can be seen from Comparative Example 2, the cationic monomer not only enhances the solubility of the polymer molecules but also has a certain impact on their temperature resistance. The zwitterions used in the present invention contain temperature-resistant sulfonates, which are not easily degraded and lost under high-temperature conditions. At the same time, the zwitterions have good solubility in high-density salt water, and the molecular chains easily stretch in salt water, providing a good viscosity-enhancing effect. Even under 180°C high-temperature conditions, the present invention still maintains good viscosity-enhancing properties.

[0108] Table 6 Thickener at 1.70 g / cm 3 Performance changes after aging at 200℃ in composite brine

[0109]

[0110]

[0111] After aging at 200°C for 16 hours, the comparative polymer chain degraded due to molecular chain breakage, completely losing its effectiveness. However, the polymer of the present invention features a high-energy -CC- backbone structure, and the monomers used contain temperature-resistant sulfonate groups, which enhance the polymer's heat resistance. While the viscosity of the example decreased slightly at 200°C, it still maintained good overall performance.

[0112] (3) Determination of viscosity-enhancing performance of viscosifiers in completion fluid systems

[0113] Configuration 1.7g / cm 3 The calcium bromide completion fluid system was used to determine the effect of a viscosity enhancer (1% by mass) in the system. The system was then aged at 200°C. After aging, the apparent viscosity, plastic viscosity, and dynamic shear force of the completion fluid system were determined.

[0114] Completion fluid system formula: 1.7g / cm 3 Calcium bromide brine 350mL + monoethanolamine 10mL + calcium carbonate (2μm) 10.0g + calcium carbonate (5μm) + calcium carbonate (12μm) 10.0g + magnesium oxide 5.0g + silicone defoamer 2.0g + sodium thiosulfate 2.0g.

[0115] The experimental results are shown in Table 7 below.

[0116] Table 7 Thickener at 1.70 g / cm3 Viscosity-increasing properties of calcium bromide in brine system

[0117]

[0118] In the system, the high-density completion fluid inherently has a low viscosity due to the absence of solid clay. However, the addition of a viscosifier significantly increases the apparent viscosity. Comparative Example 1 lacks zwitterions, and even though all the reactive monomers are hydrophilic, it exhibits poor solubility and viscosifying properties in high-density divalent brine. The zwitterionic polymer of the present invention exhibits excellent viscosifying properties in the high-density completion fluid system and maintains a strong viscosifying effect even after aging at 200°C for 16 hours. Compared to imported viscosifiers, the present invention exhibits superior salt-resistant viscosifying properties.

[0119] Based on the above experimental results, the zwitterionic polymer thickener of the present invention possesses significant advantages. First, it has excellent solubility. In high-density brine, the thickener of the present invention utilizes a combination of strongly hydrophilic functional groups and zwitterions to minimize the effects of polyelectrolytes, allowing the polymer molecular chains to fully expand and dissolve in the high-density completion fluid brine, exerting a thickening effect. Second, it is suitable for high formation temperatures. The thickener developed by the present invention can be stable at high temperatures of 200°C, maintaining excellent performance and resisting degradation, meeting the performance requirements of solid-free completion fluids in deep, high-temperature formations.

Claims

1. A method for preparing a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer, comprising the following steps: (1) Preparation of zwitterionic monomers 4-vinylbenzyl chloride and a dimethylamine aqueous solution are added to ethanol, stirred evenly, and then subjected to a first reaction to obtain N,N-dimethyl-4-vinylbenzylamine; N,N-dimethyl-4-vinylbenzylamine and 1,4-butane sultone are added to acetonitrile, stirred evenly, and then subjected to a second reaction to obtain a zwitterionic monomer 3-(dimethyl(4-vinylbenzyl)amino)butane sulfonate; (2) Preparation of aqueous solution Adding an amide monomer, a hydrophilic monomer, a cationic monomer, and a zwitterionic monomer to water, adjusting the pH of the system to 7-8, adding a chain transfer agent, and stirring uniformly to obtain an aqueous phase solution; the amide monomer is one or a combination of two or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N,N-dimethylacrylamide; the hydrophilic monomer is one of acrylic acid, methacrylic acid, and methenyl butenedioic acid; the mass ratio of the hydrophilic monomer to the amide monomer is 0.5-1:1; the cationic monomer is dimethyl diallyl ammonium chloride; the mass ratio of the cationic monomer to the amide monomer is 0.3-0.75:1; and the mass ratio of the zwitterionic monomer to the amide monomer is 0.25-0.5:1; (3) Preparation of high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer An initiator is added to the aqueous solution to carry out aqueous solution free radical polymerization; or the aqueous solution is added to the oil solution, and then an initiator is added to carry out emulsion polymerization to obtain a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer.

2. The method for preparing the high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer according to claim 1, characterized in that: The mass fraction of the dimethylamine aqueous solution in step (1) is 70%; the molar ratio of dimethylamine to 4-vinylbenzyl chloride is 1.2-1.5:1; the mass ratio of 4-vinylbenzyl chloride to ethanol is 1 g:5-10 mL; The temperature of the first reaction is 40-60° C., the time of the first reaction is 20-30 hours; the first reaction is carried out under a nitrogen atmosphere; After the first reaction is completed, a post-processing step is further included, specifically as follows: the obtained reaction solution is subjected to rotary evaporation to remove the solvent, and the obtained crude product is purified by column chromatography using petroleum ether as an eluent to obtain N,N-dimethyl-4-vinylbenzylamine.

3. The method for preparing the high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer according to claim 1, characterized in that: The molar ratio of 1,4-butane sultone to N,N-dimethyl-4-vinylbenzylamine in step (1) is 0.8-1:1; the mass ratio of N,N-dimethyl-4-vinylbenzylamine to the volume of acetonitrile is 1 g:20-40 mL; The temperature of the second reaction is 40-60° C., and the time of the second reaction is 40-60 h; the second reaction is carried out under a nitrogen atmosphere; After the second reaction is completed, a post-processing step is included, specifically as follows: the obtained reaction solution is filtered, and the filtered solid is dried at 40-45° C. for 10-12 hours.

4. The method for preparing the high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer according to claim 1, characterized in that: The mass ratio of the amide monomer to water in step (2) is 0.1-0.2:

1.

5. The method for preparing the high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer according to claim 1, characterized in that: In step (2), a sodium hydroxide solution having a mass fraction of 20-40% is used to adjust the pH of the system; The chain transfer agent is dodecanethiol, isopropanol or acetone; the mass of the chain transfer agent is 0.5-1% of the total mass of the amide monomer, the hydrophilic monomer, the cationic monomer and the zwitterionic monomer.

6. The method for preparing the high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer according to claim 1, characterized in that: The initiators in step (3) are potassium persulfate, ammonium persulfate, or a combination of one of potassium persulfate and ammonium persulfate and sodium bisulfite; the mass of the initiators is 0.05-0.5% of the total mass of the amide monomer, the hydrophilic monomer, the cationic monomer, and the zwitterionic monomer; The temperature of the aqueous solution free radical polymerization reaction is 55-65° C., the time of the aqueous solution free radical polymerization reaction is 5-6 hours, and the aqueous solution free radical polymerization reaction is carried out under a nitrogen atmosphere.

7. The method for preparing the high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer according to claim 1, characterized in that: The oil phase solution in step (3) is prepared by the following method: adding an emulsifier to white oil and stirring uniformly to obtain the obtained product; the emulsifier is Span80 or Span65, and the mass ratio of the emulsifier to the white oil is 1:70-80; the mass ratio of the white oil in the oil phase solution to the water in the aqueous phase solution is 2-4:1; After the aqueous phase solution is added to the oil phase solution, shearing is carried out at 5000-6000 r / min for 10-20 minutes to obtain an emulsion; The emulsion polymerization reaction temperature is 55-65° C., the emulsion polymerization reaction time is 5-6 hours, and the emulsion polymerization reaction is carried out under a nitrogen atmosphere; After the aqueous solution free radical polymerization reaction or emulsion polymerization reaction is completed, a post-processing step is further included, specifically as follows: filtering the reaction liquid, washing, and drying to obtain a high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer; the washing is performed by washing with ethanol 3-5 times; and the drying is performed at 75-80° C. for 8-10 hours.

8. A high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer, characterized in that: The preparation method according to claim 1 is used for preparation.

9. Use of the high-temperature resistant, high-density, solid-free completion fluid viscosity enhancer according to claim 8 in a solid-free or low-solid completion fluid.

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