Preparation method of fracturing fluid thickening agent for oil field

Abstract

The invention belongs to the technical field of preparation of thickening agents, and particularly relates to a preparation method of a fracturing fluid thickening agent for an oil field. The preparation method comprises the following steps: (1) preparing an ethanol solution of N-dodecyl acrylamide; (2) preparing a water phase; (3) removing oxygen; (4) initiating; and (5) post-treatment. According to the preparation method of the fracturing fluid thickening agent for the oil field, acrylamide is used as a main monomer, and functional monomers of N, N-dimethyl-N-acrylamide propyl-N-propane sulfonic acid inner salt, 4-acryloyl morpholine and N-dodecyl acrylamide are introduced; carrying out free radical copolymerization reaction through a potassium peroxodisulfate / sodium hydrogen sulfite redox initiation system; and the obtained product has stable performance and is especially suitable for oil-gas well fracturing operation under high-temperature, high-salt and medium-low shear working conditions.

Description

Technical Field

[0001] This invention belongs to the field of thickener preparation technology, specifically relating to a method for preparing a thickener for fracturing fluid used in oil fields. Background Technology

[0002] Fracturing, also known as hydraulic fracturing, is a method used in oil production to create fractures in the reservoir. In oilfield development, fracturing has become a crucial element in increasing oil production due to its ability to modify reservoir properties, increase the flow area of ​​formation fluids, reduce resistance, and improve well productivity. Its application is becoming increasingly widespread in major oilfields. The fracturing fluid used in fracturing operations is a heterogeneous and unstable chemical system formed by various additives in specific proportions. It typically consists of thickeners, dispersants, anti-swelling agents, bactericides, and other functional additives.

[0003] Patent CN201911025482.5 discloses an emulsion polymer for fracturing and its preparation method. The fracturing emulsion polymer in this patent application can achieve both thickening and drag reduction effects, but its shear viscosity in 600 mg / L brine (6000 salinity) is only 30-40 mPa·s, and its drag reduction rate is only 70-74%. Its thickening and drag reduction performance under high salinity conditions needs to be further improved.

[0004] Common thickeners on the domestic and international markets mainly include natural polymers, biopolymers, and synthetic polymers. Compared with natural polymers, synthetic polymers have better temperature and shear resistance, stronger thickening ability, better suspension and debinding properties, and are less susceptible to bacteria, exhibiting superior performance in all aspects. Domestic and international synthetic polymer thickeners mainly include acrylamide polymers, ethylene polymers, and cross-linked polymers. Among them, acrylamide polymer thickeners have become the mainstream product due to their excellent performance; however, they still have problems such as slow dissolution, poor salt resistance, and poor temperature resistance.

[0005] Therefore, it is necessary to explore a new type of thickener for fracturing fluid used in oil fields. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a thickener for oilfield fracturing fluid. This preparation method offers high operational control, and the prepared thickener exhibits excellent temperature resistance, salt resistance, and shear resistance.

[0007] The preparation method of the oilfield fracturing fluid thickener of the present invention comprises the following steps: (1) Add N-dodecylacrylamide to ethanol and sonicate until the solid is completely dissolved. Then, rotary evaporate. Stop rotary evaporation when the recovered ethanol mass reaches 30% of the initial ethanol mass. The remaining solution is the ethanol solution of N-dodecylacrylamide. (2) Preparation of aqueous phase Add water for dissolving in the reaction vessel, then add acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt and 4-acryloylmorpholine in sequence and stir for 30-33 min until completely dissolved. Then add the ethanol solution of N-dodecylacrylamide prepared in step (1) and continue stirring for 5-7 min. Add water to make up the volume, add sodium hydroxide to adjust the pH of the reaction system to 7.8-8.2, and finally add disodium ethylenediaminetetraacetate and stir for 5-7 min to prepare an aqueous phase. (3) Deoxygenation In a water bath at 22-25℃, nitrogen gas is continuously passed through the aqueous phase prepared in step (2) at a flow rate of 0.3 L / min for 30-35 min to remove oxygen. Then the flow rate is reduced to 0.05 L / min to maintain a slight positive pressure nitrogen protection and the mixture is stirred until the reaction is complete. (4) Trigger Under stirring, a 5% potassium persulfate aqueous solution was first added to the reaction system of step (3) within 15-18s, stirred for 1min, and then a 5% NaHSO3 aqueous solution was added to the reaction system within 15-18s. The reaction was carried out at 22-25℃ for 6h, and then the temperature was raised to 43-45℃ to continue the reaction for 2h to obtain a gel. (5) Post-processing The gel prepared in step (4) is cut into small pieces, then soaked in deionized water, and finally vacuum dried and pulverized to prepare a fracturing fluid thickener for oil fields. Wherein: the sum of the molar percentages of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, and N-dodecylacrylamide in step (1) is 100%, acrylamide accounts for 82-84 mol%, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt accounts for 10-11 mol%, 4-acryloylmorpholine accounts for 5.4-6.3 mol%, and N-dodecylacrylamide accounts for 0.5-0.7 mol.

[0008] In step (1), the mass ratio of N-dodecylacrylamide to ethanol is 1:10.

[0009] In step (1), the ultrasonic dissolution temperature during ultrasonic treatment is 39-42℃, the ultrasonic dissolution time is 17-20min, the ultrasonic power is 300W, and the ultrasonic frequency is 40KHz.

[0010] In step (1), the rotary evaporation temperature is 40℃ and the rotary evaporation vacuum degree is -0.09MPa.

[0011] In step (2), the stirring temperature is 22-25℃ and the stirring speed is 200-300r / min.

[0012] In step (2), the concentration of sodium hydroxide is 1 mol / L.

[0013] The purpose of adding disodium ethylenediaminetetraacetate in step (2) is to chelate trace amounts of Ca. 2+ Mg 2+ Fe 2+ To prevent metal ions from inducing free radical deactivation and affecting subsequent cross-linking reactions, the added mass accounts for 0.025% of the final total mass of the aqueous phase.

[0014] In step (2), the total mass of the water used for dissolving and the water used for volume adjustment is 100%, of which the water used for dissolving accounts for 79% and the water used for volume adjustment accounts for 21%.

[0015] The total mass of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, and N-dodecylacrylamide in step (2) accounts for 20% of the total mass of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, water for dissolution, water for volume adjustment, and N-dodecylacrylamide in step (1).

[0016] In step (3), the stirring speed is 200-300 r / min.

[0017] In step (4), based on the mass of acrylamide in step (2), 0.32 wt% of potassium persulfate and 0.32 wt% of sodium bisulfite are added respectively, all on a dry mass basis.

[0018] In step (5), the deionized water is changed every 8 hours during soaking, for a total of 5-7 times.

[0019] In step (5), the vacuum drying temperature is 40℃, the vacuum drying time is 24h, and the powder is pulverized through an 80-mesh sieve.

[0020] Compared with the prior art, the present invention has the following advantages: (1) The preparation method of the oilfield fracturing fluid thickener of the present invention uses acrylamide as the main monomer and introduces functional monomers N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine and N-dodecylacrylamide, and carries out free radical copolymerization reaction through potassium persulfate / sodium bisulfite redox initiation system. Among them, the N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, as an amphoteric monomer, can effectively suppress the negative impact of salt effect on solution viscosity through the "anti-polyelectrolyte effect" by its intramolecular opposite charge centers, especially avoiding the precipitation problem caused by divalent calcium and magnesium ions; the rigid morpholine ring structure of the 4-acryloylmorpholine side chain can significantly enhance the rigidity of the polymer backbone, reduce the thermal motion and conformational coiling of the molecular chain at high temperatures, thereby improving the product's temperature resistance; and N-dodecylacrylamide, as a hydrophobic monomer, can form a dynamic and reversible three-dimensional physical cross-linked network in aqueous solution through intermolecular hydrophobic association of its long alkyl chain. This network structure endows the product with good thickening ability and unique shear resistance. The synergistic effect of the above four monomers makes the final thickener have good solubility, high temperature resistance, salt resistance, high thickening and shear resistance. (2) The preparation method of the oilfield fracturing fluid thickener of the present invention effectively integrates the characteristics of each functional monomer into the same polymer molecular chain through free radical copolymerization. The rigid side ring of 4-acryloylmorpholine and the large side group of N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt together construct the rigid skeleton of the polymer, which greatly enhances the thermal stability of the material and makes it less prone to chemical degradation or physical conformation collapse in high temperature environment. The presence of N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt enables the polymer solution to maintain or even increase its apparent viscosity in a high salinity environment. The introduction of N-dodecylacrylamide is due to its hydrophobic association properties, which can form a huge dynamic physical cross-linked network in water, thereby providing high initial viscosity; the network structure will temporarily dissociate when subjected to high-speed shear, and can quickly reassociate once the shearing effect is eliminated, thus exhibiting excellent shear resistance. (3) The preparation method of the oilfield fracturing fluid thickener of the present invention has clear process parameters, strong controllability of operation, and is easy to achieve large-scale preparation. The resulting product has stable performance and is particularly suitable for oil and gas well fracturing operations under high temperature, high salt and medium-low shear conditions. Detailed Implementation

[0021] Example 1 The preparation method of the oilfield fracturing fluid thickener described in Example 1 consists of the following steps: (1) Add N-dodecylacrylamide to ethanol and sonicate until the solid is completely dissolved. Then, rotary evaporate. Stop rotary evaporation when the recovered ethanol mass reaches 30% of the initial ethanol mass. The remaining solution is the ethanol solution of N-dodecylacrylamide. (2) Preparation of aqueous phase Add dissolving water to the reaction vessel, then add acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt and 4-acryloylmorpholine in sequence and stir for 31 min until completely dissolved. Then add the ethanol solution of N-dodecylacrylamide prepared in step (1) and continue stirring for 6 min. Add water to make up the volume, add sodium hydroxide to adjust the pH of the reaction system to 8.0, and finally add disodium ethylenediaminetetraacetate and stir for 6 min to prepare an aqueous phase. (3) Deoxygenation In a 23°C water bath environment, nitrogen gas was continuously passed through the aqueous phase prepared in step (2) at a flow rate of 0.3 L / min for 33 min to remove oxygen. Then the flow rate was reduced to 0.05 L / min to maintain a slight positive pressure nitrogen protection, and stirring was maintained until the reaction was completed. (4) Trigger Under stirring, a 5% potassium persulfate aqueous solution was first added to the reaction system of step (3) within 16s, stirred for 1min, and then a 5% NaHSO3 aqueous solution was added to the reaction system within 16s. The reaction was carried out at 23℃ for 6h, and then the temperature was raised to 44℃ to continue the reaction for 2h to prepare a gel. (5) Post-processing The gel prepared in step (4) is cut into small pieces, then soaked in deionized water, and finally vacuum dried and pulverized to prepare a fracturing fluid thickener for oil fields. Wherein: the sum of the molar percentages of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, and N-dodecylacrylamide in step (2) is 100%, acrylamide accounts for 83 mol%, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt accounts for 10.5 mol%, 4-acryloylmorpholine accounts for 6 mol%, and N-dodecylacrylamide accounts for 0.5 mol.

[0022] In step (1), the mass ratio of N-dodecylacrylamide to ethanol is 1:10.

[0023] In step (1), the ultrasonic dissolution temperature during ultrasonic treatment is 41℃, the ultrasonic dissolution time is 18min, the ultrasonic power is 300W, and the ultrasonic frequency is 40KHz.

[0024] In step (1), the rotary evaporation temperature is 40℃ and the rotary evaporation vacuum degree is -0.09MPa.

[0025] In step (2), the stirring temperature is 23℃ and the stirring speed is 250r / min.

[0026] In step (2), the concentration of sodium hydroxide is 1 mol / L.

[0027] The purpose of adding disodium ethylenediaminetetraacetate in step (2) is to chelate trace amounts of Ca. 2+ Mg 2+ Fe 2+ To prevent metal ions from inducing free radical deactivation and affecting subsequent cross-linking reactions, the added mass accounts for 0.025% of the final total mass of the aqueous phase.

[0028] In step (2), the total mass of the water used for dissolving and the water used for volume adjustment is 100%, of which the water used for dissolving accounts for 79% and the water used for volume adjustment accounts for 21%.

[0029] The total mass of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, and N-dodecylacrylamide in step (2) accounts for 20% of the total mass of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, water for dissolution, water for volume adjustment, and N-dodecylacrylamide in step (1).

[0030] In step (3), the stirring speed is 250 r / min.

[0031] In step (4), based on the mass of acrylamide in step (2), 0.32 wt% of potassium persulfate and 0.32 wt% of sodium bisulfite are added respectively, all on a dry mass basis.

[0032] In step (5), the deionized water is changed every 8 hours during soaking, for a total of 6 times.

[0033] In step (5), the vacuum drying temperature is 40℃, the vacuum drying time is 24h, and the powder is pulverized through an 80-mesh sieve.

[0034] Example 2 The preparation method of the oilfield fracturing fluid thickener described in Example 2 consists of the following steps: (1) Add N-dodecylacrylamide to ethanol and sonicate until the solid is completely dissolved. Then, rotary evaporate. Stop rotary evaporation when the recovered ethanol mass reaches 30% of the initial ethanol mass. The remaining solution is the ethanol solution of N-dodecylacrylamide. (2) Preparation of aqueous phase Add dissolving water to the reaction vessel, then add acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt and 4-acryloylmorpholine in sequence and stir for 33 min until completely dissolved. Then add the ethanol solution of N-dodecylacrylamide prepared in step (1) and continue stirring for 5 min. Add water to make up the volume, add sodium hydroxide to adjust the pH of the reaction system to 8.2, and finally add disodium ethylenediaminetetraacetate and stir for 7 min to prepare an aqueous phase. (3) Deoxygenation In a water bath at 22°C, nitrogen gas was continuously passed through the aqueous phase prepared in step (2) at a flow rate of 0.3 L / min for 35 min to remove oxygen. Then the flow rate was reduced to 0.05 L / min to maintain a slight positive pressure nitrogen protection and the mixture was stirred until the reaction was completed. (4) Trigger Under stirring, a 5% potassium persulfate aqueous solution was first added to the reaction system of step (3) within 18s, stirred for 1min, and then a 5% NaHSO3 aqueous solution was added to the reaction system within 18s. The reaction was first carried out at 22℃ for 6h, and then the temperature was raised to 43℃ to continue the reaction for 2h to prepare a gel. (5) Post-processing The gel prepared in step (4) is cut into small pieces, then soaked in deionized water, and finally vacuum dried and pulverized to prepare a fracturing fluid thickener for oil fields. in: In step (2), the sum of the molar percentages of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, and N-dodecylacrylamide in step (1) is 100%, with acrylamide accounting for 82 mol%, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt accounting for 11 mol%, 4-acryloylmorpholine accounting for 6.3 mol%, and N-dodecylacrylamide accounting for 0.7 mol.

[0035] In step (1), the mass ratio of N-dodecylacrylamide to ethanol is 1:10.

[0036] In step (1), the ultrasonic dissolution temperature during ultrasonic treatment is 39℃, the ultrasonic dissolution time is 20min, the ultrasonic power is 300W, and the ultrasonic frequency is 40KHz.

[0037] In step (1), the rotary evaporation temperature is 40℃ and the rotary evaporation vacuum degree is -0.09MPa.

[0038] In step (2), the stirring temperature is 22℃ and the stirring speed is 300r / min.

[0039] In step (2), the concentration of sodium hydroxide is 1 mol / L.

[0040] The purpose of adding disodium ethylenediaminetetraacetate in step (2) is to chelate trace amounts of Ca. 2+ Mg 2+ Fe 2+ To prevent metal ions from inducing free radical deactivation and affecting subsequent cross-linking reactions, the added mass accounts for 0.025% of the final total mass of the aqueous phase.

[0041] In step (2), the total mass of the water used for dissolving and the water used for volume adjustment is 100%, of which the water used for dissolving accounts for 79% and the water used for volume adjustment accounts for 21%.

[0042] The total mass of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, and N-dodecylacrylamide in step (2) accounts for 20% of the total mass of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, water for dissolution, water for volume adjustment, and N-dodecylacrylamide in step (1).

[0043] In step (3), the stirring speed is 300 r / min.

[0044] In step (4), based on the dry mass of acrylamide in step (2), 0.32 wt% of potassium persulfate and 0.32 wt% of sodium bisulfite are added respectively, all based on dry mass.

[0045] In step (5), the deionized water is changed every 8 hours during soaking, for a total of 7 times.

[0046] In step (5), the vacuum drying temperature is 40℃, the vacuum drying time is 24h, and the powder is pulverized through an 80-mesh sieve.

[0047] Example 3 The preparation method of the oilfield fracturing fluid thickener described in Example 3 consists of the following steps: (1) Add N-dodecylacrylamide to ethanol and sonicate until the solid is completely dissolved. Then, rotary evaporate. Stop rotary evaporation when the recovered ethanol mass reaches 30% of the initial ethanol mass. The remaining solution is the ethanol solution of N-dodecylacrylamide. (2) Preparation of aqueous phase Add dissolving water to the reaction vessel, then add acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt and 4-acryloylmorpholine in sequence and stir for 30 min until completely dissolved. Then add the ethanol solution of N-dodecylacrylamide prepared in step (1) and continue stirring for 7 min. Add water to make up the volume, add sodium hydroxide to adjust the pH of the reaction system to 7.8, and finally add disodium ethylenediaminetetraacetate and stir for 5 min to prepare an aqueous phase. (3) Deoxygenation In a 25°C water bath environment, nitrogen gas was continuously passed through the aqueous phase prepared in step (2) at a flow rate of 0.3 L / min for 30 min to remove oxygen. Then the flow rate was reduced to 0.05 L / min to maintain a slight positive pressure nitrogen protection and the mixture was stirred until the reaction was completed. (4) Trigger Under stirring, a 5% potassium persulfate aqueous solution was first added to the reaction system of step (3) within 15s, stirred for 1min, and then a 5% NaHSO3 aqueous solution was added to the reaction system within 15s. The reaction was carried out at 25℃ for 6h, and then the temperature was raised to 45℃ to continue the reaction for 2h to prepare a gel. (5) Post-processing The gel prepared in step (4) is cut into small pieces, then soaked in deionized water, and finally vacuum dried and pulverized to prepare a fracturing fluid thickener for oil fields. Wherein: the sum of the molar percentages of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, and N-dodecylacrylamide in step (2) is 100%, acrylamide accounts for 84 mol%, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt accounts for 10 mol%, 4-acryloylmorpholine accounts for 5.4 mol%, and N-dodecylacrylamide accounts for 0.6 mol.

[0048] In step (1), the mass ratio of N-dodecylacrylamide to ethanol is 1:10.

[0049] In step (1), the ultrasonic dissolution temperature during ultrasonic treatment is 42℃, the ultrasonic dissolution time is 17min, the ultrasonic power is 300W, and the ultrasonic frequency is 40KHz.

[0050] In step (1), the rotary evaporation temperature is 40℃ and the rotary evaporation vacuum degree is -0.09MPa.

[0051] In step (2), the stirring temperature is 25℃ and the stirring speed is 200r / min.

[0052] In step (2), the concentration of sodium hydroxide is 1 mol / L.

[0053] The purpose of adding disodium ethylenediaminetetraacetate in step (2) is to chelate trace amounts of Ca. 2+ Mg 2+ Fe 2+ To prevent metal ions from inducing free radical deactivation and affecting subsequent cross-linking reactions, the added mass accounts for 0.025% of the final total mass of the aqueous phase.

[0054] In step (2), the total mass of the water used for dissolving and the water used for volume adjustment is 100%, of which the water used for dissolving accounts for 79% and the water used for volume adjustment accounts for 21%.

[0055] The total mass of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, and N-dodecylacrylamide in step (2) accounts for 20% of the total mass of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, water for dissolution, water for volume adjustment, and N-dodecylacrylamide in step (1).

[0056] In step (3), the stirring speed is 200 r / min.

[0057] In step (4), based on the mass of acrylamide in step (2), 0.32 wt% of potassium persulfate and 0.32 wt% of sodium bisulfite are added respectively, all on a dry mass basis.

[0058] In step (5), the deionized water is changed every 8 hours during soaking, for a total of 5 times.

[0059] In step (5), the vacuum drying temperature is 40℃, the vacuum drying time is 24h, and the powder is pulverized through an 80-mesh sieve.

[0060] Comparative Example 1 The preparation method of the oilfield fracturing fluid thickener described in Comparative Example 1 is the same as that in Example 1. The only difference is that in step (2), when preparing the aqueous phase, the monomer N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt is not added.

[0061] The sum of the molar percentages of acrylamide, 4-acryloylmorpholine, and N-dodecylacrylamide in step (1) is 100%, with acrylamide accounting for 93.5 mol, 4-acryloylmorpholine accounting for 6 mol, and N-dodecylacrylamide accounting for 0.5 mol.

[0062] Comparative Example 2 The preparation method of the oilfield fracturing fluid thickener described in Comparative Example 2 is the same as that in Example 1, except that in step (2), the monomer 4-acryloylmorpholine is not added when preparing the aqueous phase. In step (2), the sum of the molar percentages of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, and N-dodecylacrylamide in step (1) is 100%, with acrylamide accounting for 89 mol%, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt accounting for 10.5 mol%, and N-dodecylacrylamide accounting for 0.5 mol%.

[0063] Comparative Example 3 The preparation method of the oilfield fracturing fluid thickener described in Comparative Example 3 is the same as that in Example 1, except that step (1) is omitted and an ethanol solution of N-dodecylacrylamide is not added in step (2). In step (2), the sum of the molar percentages of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, and 4-acryloylmorpholine is 100%, with acrylamide accounting for 83.5 mol%, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt accounting for 10.5 mol%, and 4-acryloylmorpholine accounting for 6 mol%.

[0064] The oilfield fracturing fluid thickeners prepared in Examples 1-3 and Comparative Examples 1-3 were formulated into a 0.5 wt% solution and subjected to a 180 s incubation period at 25°C. -1 The apparent viscosity was tested; the results are shown in Table 1.

[0065] Table 1 Apparent viscosity at room temperature

[0066] As shown in Table 1, the oilfield fracturing fluid thickeners prepared in Examples 1-3 of this application have a better viscosity-enhancing effect compared with Comparative Examples 1-3.

[0067] The oilfield fracturing fluid thickeners prepared in Examples 1-3 and Comparative Examples 1-3 were formulated into 0.5 wt% solutions, and their performance at 120°C for 180 seconds was tested. -1 and 150℃, 180s -1 The apparent viscosity was measured; the results are shown in Table 2.

[0068] Table 2 Apparent viscosity at high temperature

[0069] As shown in Table 2, the oilfield fracturing fluid thickeners prepared in Examples 1-3 of this application still have good viscosity at high temperatures compared with Comparative Examples 1-3, proving that they have good temperature resistance.

[0070] The oilfield fracturing fluid thickeners prepared in Examples 1-3 and Comparative Examples 1-3 were formulated into 0.5 wt% solutions, and subjected to fracturing fluid thickeners at 25°C for 180 seconds. -1 After shearing for 2.5 hours, the apparent viscosity was tested; the results are shown in Table 3.

[0071] Table 3 180s -1 Apparent viscosity after 2.5 hours of shearing

[0072] As shown in Table 3, the oilfield fracturing fluid thickeners prepared in Examples 1-3 of this application have better shear resistance than comparative examples 1-3.

[0073] The oilfield fracturing fluid thickeners prepared in Examples 1-3 and Comparative Examples 1-3 were formulated into a 0.5 wt% solution. NaCl was added until the NaCl concentration in the system was 1.0 g / L. The solution was then incubated at 25°C for 180 seconds. -1 The apparent viscosity was tested; the results are shown in Table 4.

[0074] Table 4 Salt resistance test results

[0075] As shown in Table 4, the oilfield fracturing fluid thickeners prepared in Examples 1-3 of this application have better salt resistance than comparative examples 1-3.

[0076] The oilfield fracturing fluid thickeners prepared in Examples 1-3 and Comparative Examples 1-3 were prepared into a 0.5 wt% aqueous solution, stirred until completely dissolved, allowed to stand to defoam, and zirconium citrate crosslinking agent was added to the base fluid at a rate of 0.4% based on the mass of the base fluid. The crosslinking reaction was carried out at 90°C for 2 hours using a stirrer at a speed of 400 r / min. The gel strength of the formed gel was tested, and the results are shown in Table 5.

[0077] Ammonium persulfate was added to the formed gel at a concentration of 0.03 wt%. The gel was broken up at 90°C for 8 hours. The broken gel was then cooled to 25°C and subjected to further treatment at 25°C for 180 seconds. -1 The apparent viscosity of the gelling liquid was tested under the specified conditions, and the results are shown in Table 5.

[0078] Centrifuge 50 mL of the fracturing fluid at 3000 r / min for 35 min, pour off the supernatant, wash the fracturing container with water and pour it back into the centrifuge tube, centrifuge at 3000 r / min for 35 min, pour off the supernatant again, place the centrifuge tube in an oven to dry to constant weight, and divide the mass of the residue by the amount of fracturing fluid used to obtain the fracturing fluid residue content. The results are shown in Table 5.

[0079] Table 5. Application Effects of Thickeners for Fracturing Fluids in Oilfields

[0080] Compared with comparative examples 1-3, the oilfield fracturing fluid thickeners prepared in Examples 1-3 of this invention can crosslink well, form gels with high strength, and break down quickly with low residue content after breaking down, which proves that they cause less damage to the formation.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a thickener for fracturing fluid used in oilfields, characterized in that: It consists of the following steps: (1) Add N-dodecylacrylamide to ethanol and sonicate until the solid is completely dissolved. Then, rotary evaporate. Stop rotary evaporation when the recovered ethanol mass reaches 30% of the initial ethanol mass. The remaining solution is the ethanol solution of N-dodecylacrylamide. (2) Preparation of aqueous phase Add water for dissolving in the reaction vessel, then add acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt and 4-acryloylmorpholine in sequence and stir for 30-33 min until completely dissolved. Then add the ethanol solution of N-dodecylacrylamide prepared in step (1) and continue stirring for 5-7 min. Add water to make up the volume, add sodium hydroxide to adjust the pH of the reaction system to 7.8-8.2, and finally add disodium ethylenediaminetetraacetate and stir for 5-7 min to prepare an aqueous phase. (3) Deoxygenation In a water bath at 22-25℃, nitrogen gas is continuously passed through the aqueous phase prepared in step (2) at a flow rate of 0.3 L / min for 30-35 min to remove oxygen. Then the flow rate is reduced to 0.05 L / min to maintain a slight positive pressure nitrogen protection and the mixture is stirred until the reaction is complete. (4) Trigger Under stirring, a 5% potassium persulfate aqueous solution was first added to the reaction system of step (3) within 15-18s, stirred for 1min, and then a 5% NaHSO3 aqueous solution was added to the reaction system within 15-18s. The reaction was carried out at 22-25℃ for 6h, and then the temperature was raised to 43-45℃ to continue the reaction for 2h to obtain a gel. (5) Post-processing The gel prepared in step (4) is cut into small pieces, then soaked in deionized water, and finally vacuum dried and pulverized to prepare a thickener for fracturing fluid in oil fields. Wherein: the sum of the molar percentages of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, and N-dodecylacrylamide in step (1) is 100%, acrylamide accounts for 82-84 mol%, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt accounts for 10-11 mol%, 4-acryloylmorpholine accounts for 5.4-6.3 mol%, and N-dodecylacrylamide accounts for 0.5-0.7 mol.

2. The method for preparing the oilfield fracturing fluid thickener according to claim 1, characterized in that: In step (1), the mass ratio of N-dodecylacrylamide to ethanol is 1:10; The ultrasonic dissolution temperature during the ultrasonic treatment in step (1) is 39-42℃, the ultrasonic dissolution time is 17-20min, the ultrasonic power is 300W, and the ultrasonic frequency is 40KHz. In step (1), the rotary evaporation temperature is 40℃ and the rotary evaporation vacuum degree is -0.09MPa.

3. The method for preparing the oilfield fracturing fluid thickener according to claim 1, characterized in that: In step (2), the stirring temperature is 22-25℃ and the stirring speed is 200-300 r / min; In step (2), the concentration of sodium hydroxide is 1 mol / L.

4. The method for preparing the oilfield fracturing fluid thickener according to claim 1, characterized in that: In step (2), the mass of disodium ethylenediaminetetraacetate added accounts for 0.025% of the final total mass of the aqueous phase; In step (2), the total mass of the water used for dissolving and the water used for volume adjustment is 100%, of which the water used for dissolving accounts for 79% and the water used for volume adjustment accounts for 21%.

5. The method for preparing the oilfield fracturing fluid thickener according to claim 1, characterized in that: The total mass of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, and N-dodecylacrylamide in step (2) accounts for 20% of the total mass of acrylamide, N,N-dimethyl-N-acrylamidopropyl-N-propanesulfonic acid inner salt, 4-acryloylmorpholine, water for dissolution, water for volume adjustment, and N-dodecylacrylamide in step (1).

6. The method for preparing the oilfield fracturing fluid thickener according to claim 1, characterized in that: In step (3), the stirring speed is 200-300 r / min.

7. The method for preparing the oilfield fracturing fluid thickener according to claim 1, characterized in that: In step (4), based on the mass of acrylamide in step (2), 0.32 wt% of potassium persulfate and 0.32 wt% of sodium bisulfite are added respectively, all on a dry mass basis.

8. The method for preparing the oilfield fracturing fluid thickener according to claim 1, characterized in that: In step (5), the deionized water is changed every 8 hours during soaking, for a total of 5-7 times.

9. The method for preparing the oilfield fracturing fluid thickener according to claim 1, characterized in that: In step (5), the vacuum drying temperature is 40℃, the vacuum drying time is 24h, and the powder is pulverized through an 80-mesh sieve.

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