Preparation method of drag reducer for high-salt-resistance fracturing fluid

Abstract

The invention relates to the technical field of oilfield exploitation, and discloses a preparation method of a drag reducer for a high-salt-resistance fracturing fluid. According to the preparation method, methacrylamide, acrylic acid, N-allyl imidazole, naphthyl modified sulfo modified morpholine derivatives and quaternary ammonium salt modified triazinyl pyrrolidone are polymerized in water, washed and dried, and the drag reducer for the high-salt-resistance fracturing fluid is obtained. The sulfonate radical enhances the solubility of the polymer, and enables the molecular chain skeleton of the polymer to carry more negative charges, so that the molecular chain is not easy to curl, and the salt resistance and shear resistance are improved; a hydrophobic association structure formed by introducing a long carbon chain and naphthyl on a polymer molecular chain is beneficial to association among molecules under the action of external salt, so that the salt-resistant and shear-resistant effects are enhanced; a steric effect generated by a pyrrole group, a morpholine group and a triazine group can limit hydrolysis of a primary amide group of a main chain, so that the salt resistance is improved; the quaternary ammonium salt group can increase the rigidity of a molecular chain, so that the anti-shearing performance is improved.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield exploitation, and in particular to a method for preparing a drag reducer for a high-salt-resistance fracturing fluid. Background Art

[0002] With the continuous deepening of oil and gas exploration and development in my country, the development of shale reservoirs has gradually developed from medium and shallow layers to deep layers. Slickwater fracturing technology is the main technical means to achieve efficient development of shale reservoirs. Fracturing fluid, as the "blood" of fracturing, determines the success or failure of fracturing construction. The construction characteristics of slickwater fracturing fluid, "large liquid volume and high displacement", will cause the fracturing fluid to produce greater friction resistance in the wellbore. In order to overcome the high friction resistance of the wellbore and effectively reduce the pumping cost, drag reducers with high drag reduction efficiency at low concentrations are widely used as the core additives of slickwater. Drag reducers can significantly improve the fluidity of fracturing fluid, reduce friction resistance, and thus increase the recovery rate of shale gas. The drag reducers currently used are mostly acrylamide copolymers, which have achieved good indoor evaluation and field application results, but there are still two outstanding problems. The first is the salt resistance of fracturing fluid drag reducers. The amount of fracturing construction in shale gas reservoirs is large, and a large amount of fracturing fluid will flow back to the ground. However, the flowback fluid is in contact with the formation for a long time and often contains a high degree of mineralization. Therefore, the development of polymer drag reducers with high mineralization resistance can effectively reduce the consumption of fresh water resources. The second is the shear resistance of drag reducers. Under the high shear rate of the fluid in the shale gas fracturing operation column, the polymer chain segments of ordinary drag reducers are easy to break, which reduces the relative molecular weight and the drag reduction performance. In the document "Preparation and Performance Evaluation of Drag Reducers for Shale Gas Horizontal Well Fracturing", a new type of drag reducer was prepared by using polyacrylamide as the main raw material, supplemented by polyvinyl alcohol and phosphate as additives. It has excellent temperature and pressure resistance and good environmental adaptability, but its salt resistance and shear resistance need to be improved. Summary of the invention

[0003] 1. Technical issues to be resolved In order to solve the problems in the prior art, the present invention provides a method for preparing a drag reducer for high salt resistance fracturing fluid. The drag reducer prepared by the present invention improves the salt resistance and shear resistance while ensuring a good drag reduction effect.

[0004] (II) Technical solution To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a drag reducer for a high salt resistance fracturing fluid, the preparation method comprising the following steps: (1) Add 9-13 g of sodium bisulfite and deionized water into a flask, heat while stirring until the sodium bisulfite is dissolved, raise the temperature to 65-72° C., dropwise add 5-7 g of 1,2-epoxy-9-decene, raise the temperature to 80-86° C. and keep the temperature to react for 2-5 hours. After the reaction is completed, cool the reaction solution in an ice water bath, filter the crystals precipitated after cooling, and recrystallize to obtain sodium olefin sulfonate; (2) Add 11-17 g of sodium olefin sulfonate, 10-15 g of 2-(4-chlorophenyl)morpholine, and 0.02-0.03 g of sodium hydride catalyst to tetrahydrofuran solvent, stir and mix, raise the temperature to the reaction temperature, and react for 3-4 hours. After the reaction is completed, filter, wash, and dry to obtain a sulfonic acid group-modified morpholine derivative; (3) Add 15-18 g of the sulfonic acid modified morpholine derivative and 8-10 g of ethyl[(naphthalene-2-yl)methyl]amine to a flask, then add 0.3-0.7 g of hydrochloric acid solution as a catalyst, add 24-32 g of formaldehyde solution dropwise while stirring, control the temperature at 18-24° C., continue stirring to react, and after the reaction is completed, allow to stand for crystallization, filter and wash to obtain a naphthyl-modified sulfonic acid modified morpholine derivative; (4) Add N-vinyl pyrrolidone, paraformaldehyde and hydroquinone reducing agent into a flask, introduce nitrogen for 35-45 minutes to remove oxygen, raise the temperature to 88-94°C, add melamine, raise the temperature to 135-145°C to react for 5-8 hours, and after the reaction is completed, wash and dry to obtain triazine pyrrolidone; (5) Add 6-8 g of triazine pyrrolidone and 7-14 g of methacryloyloxyethyl trimethyl ammonium chloride to a methanol solvent, stir to dissolve, then add 0.01-0.03 g of a catalyst, react at 25-30° C. for 2.5-3.5 h, filter, wash and dry after the reaction to obtain quaternary ammonium salt-modified triazine pyrrolidone; (6) Add 45-50 g of methacrylamide, 20-28 g of acrylic acid, 10-14 g of N-allylimidazole, 3-7 g of naphthyl-modified sulfonic acid-modified morpholine derivative, and 4-6 g of quaternary ammonium salt-modified triazine pyrrolidone to deionized water, stir and mix, introduce nitrogen for 30-50 min to remove oxygen, add 0.01-0.05 g of initiator, react at 42-50° C. to form a gel block polymer, cut the gel block into granules, wash with anhydrous ethanol, and dry at 100-105° C. to obtain a drag reducer for high salt resistance fracturing fluid.

[0005] Preferably, the dripping time of 1,2-epoxy-9-decene in step (1) is 45-60 min.

[0006] Preferably, the reaction temperature in step (2) is 30-40°C.

[0007] Preferably, in step (3), the mass fraction of the hydrochloric acid solution is 5%-9%, and the mass fraction of the formaldehyde solution is 35%-38%.

[0008] Preferably, the reaction time in step (3) is 1.5-2 h.

[0009] Preferably, in step (4), the mass ratio of N-vinyl pyrrolidone, paraformaldehyde, hydroquinone and melamine is 1.05-1.15:1:0.01-0.03:0.8-0.85.

[0010] Preferably, the catalyst in step (5) is sodium ethoxide.

[0011] Preferably, the initiator in step (6) is azobisisobutyramidine hydrochloride.

[0012] Preferably, the reaction time in step (6) is 5-10 hours.

[0013] 3. Beneficial technical effects The invention obtains a drag reducer for a high salt-resistant fracturing fluid by polymerizing methacrylamide, acrylic acid, N-allylimidazole, naphthyl-modified sulfonic acid-modified morpholine derivatives and quaternary ammonium salt-modified triazine pyrrolidone in water, followed by washing and drying.

[0014] The epoxy group in 1,2-epoxy-9-decene undergoes a ring-opening addition reaction with sodium bisulfite to obtain sodium olefin sulfonate and introduce hydroxyl groups and long carbon chains. The hydroxyl group in sodium olefin sulfonate undergoes a substitution reaction with the chlorine in 2-(4-chlorophenyl)morpholine to obtain sulfonic acid group-modified morpholine derivatives. The sulfonic acid group-modified morpholine derivatives undergo an amine methylation reaction with ethyl [(naphthalene-2-yl)methyl]amine and formaldehyde to obtain naphthyl-modified sulfonic acid group-modified morpholine derivatives. N-vinyl pyrrolidone, polyformaldehyde and the amino group in melamine undergo a Mannich reaction to obtain triazine pyrrolidone and introduce secondary amines. The secondary amine in triazine pyrrolidone undergoes a Michael addition reaction with the olefin group in methacryloyloxyethyl trimethylammonium chloride to obtain quaternary ammonium salt-modified triazine pyrrolidone.

[0015] Sulfonic acid groups have high solubility in polar solvents, thereby enhancing the solubility of polymers in fracturing fluids, and the introduction of sulfonic acid groups can allow the polymer molecular chain skeleton to carry more negative charges and have a larger hydrodynamic volume, so that the polymer molecular chain is not easy to curl, thereby improving the salt resistance and shear resistance of the drag reducer; hydrophobic long carbon chains and naphthyl hydrophobic groups are introduced into the polymer molecular chain to form a hydrophobic association structure, which is more conducive to intermolecular association under the action of added salt to form a network supramolecular structure, thereby enhancing the salt resistance and shear resistance of the drag reducer; the steric hindrance effect produced by the introduction of non-benzene ring structures of pyrrole groups, morpholine groups and triazine groups can limit the hydrolysis of the main chain primary amide groups, thereby improving the salt resistance of the drag reducer; after the quaternary ammonium salt group is introduced into the polyacrylamide molecular chain, the rigidity of the molecular chain can be increased, making the molecular chain less likely to deform and break when subjected to shear force, thereby improving the shear resistance of the drag reducer. DETAILED DESCRIPTION Example 1

[0016] (1) Add 9 g of sodium bisulfite and deionized water into a flask, heat while stirring until the sodium bisulfite is dissolved, raise the temperature to 65° C., dropwise add 5 g of 1,2-epoxy-9-decene, raise the temperature to 80° C. and keep the temperature to react for 2 h. After the reaction is completed, cool the reaction solution in an ice water bath, filter the crystals precipitated after cooling, and recrystallize to obtain sodium olefin sulfonate; (2) Add 11 g of sodium olefin sulfonate, 10 g of 2-(4-chlorophenyl)morpholine, and 0.02 g of sodium hydride catalyst to tetrahydrofuran solvent, stir and mix, raise the temperature to 30° C. and react for 3 h. After the reaction is completed, filter, wash and dry to obtain a sulfonic acid group-modified morpholine derivative; (3) Add 15 g of sulfonic acid modified morpholine derivative and 8 g of ethyl [(naphthalene-2-yl)methyl] amine to a flask, then add 0.3 g of 5% by mass hydrochloric acid solution as a catalyst, add 24 g of 35% by mass formaldehyde solution dropwise while stirring, control the temperature at 18°C, continue stirring and react for 1.5 hours, and after the reaction is completed, allow to stand for crystallization, filter and wash to obtain a naphthyl modified sulfonic acid modified morpholine derivative; (4) Add N-vinyl pyrrolidone, paraformaldehyde, and hydroquinone reducing agent into a flask, introduce nitrogen for 35 minutes to remove oxygen, heat to 88°C, add melamine, wherein the mass ratio of N-vinyl pyrrolidone, paraformaldehyde, hydroquinone, and melamine is 1.05:1:0.01:0.8, heat to 135°C, react for 5 hours, and after the reaction is completed, wash and dry to obtain triazine pyrrolidone; (5) Add 6 g of triazine pyrrolidone and 7 g of methacryloyloxyethyl trimethyl ammonium chloride to a methanol solvent, stir to dissolve, then add 0.01 g of sodium ethoxide catalyst, and react at 25° C. for 2.5 h. After the reaction is completed, filter, wash and dry to obtain quaternary ammonium salt-modified triazine pyrrolidone; (6) Add 45 g of methacrylamide, 20 g of acrylic acid, 10 g of N-allylimidazole, 3 g of naphthyl-modified sulfonic acid-modified morpholine derivative, and 4 g of quaternary ammonium salt-modified triazine pyrrolidone to deionized water, stir and mix, introduce nitrogen for 30 min to remove oxygen, add 0.01 g of azobisisobutylamidine hydrochloride initiator, react at 42 °C for 5 h to form a gel block polymer, cut the gel block into granules, wash with anhydrous ethanol and dry at 100 °C to obtain a drag reducer for high salt resistance fracturing fluid. Example 2

[0017] (1) Add 13 g of sodium bisulfite and deionized water into a flask, heat while stirring until the sodium bisulfite is dissolved, raise the temperature to 72° C., dropwise add 7 g of 1,2-epoxy-9-decene, raise the temperature to 86° C. and keep the temperature to react for 5 h. After the reaction is completed, cool the reaction solution in an ice water bath, filter the crystals precipitated after cooling, and recrystallize to obtain sodium olefin sulfonate; (2) Add 17 g of sodium olefin sulfonate, 15 g of 2-(4-chlorophenyl)morpholine, and 0.03 g of sodium hydride catalyst to tetrahydrofuran solvent, stir and mix, heat to 40° C. and react for 4 h. After the reaction is completed, filter, wash and dry to obtain a sulfonic acid group-modified morpholine derivative; (3) Add 18 g of sulfonic acid modified morpholine derivative, 10 g of ethyl [(naphthalene-2-yl) methyl] amine, and then add 0.7 g of 9% hydrochloric acid solution as a catalyst into a flask, add 32 g of 38% formaldehyde solution dropwise while stirring, control the temperature at 24°C, continue stirring and react for 2 h, and after the reaction is completed, allow to crystallize, filter and wash to obtain a naphthyl modified sulfonic acid modified morpholine derivative; (4) Add N-vinyl pyrrolidone, paraformaldehyde, and hydroquinone reducing agent into a flask, introduce nitrogen for 45 minutes to remove oxygen, heat to 94°C, add melamine, wherein the mass ratio of N-vinyl pyrrolidone, paraformaldehyde, hydroquinone, and melamine is 1.15:1:0.03:0.85, heat to 145°C, react for 8 hours, and after the reaction is completed, wash and dry to obtain triazine pyrrolidone; (5) Add 8 g of triazine pyrrolidone and 14 g of methacryloyloxyethyl trimethyl ammonium chloride to a methanol solvent, stir to dissolve, then add 0.03 g of sodium ethoxide catalyst, and react at 30° C. for 3.5 h. After the reaction is completed, filter, wash and dry to obtain quaternary ammonium salt-modified triazine pyrrolidone; (6) Add 50 g of methacrylamide, 28 g of acrylic acid, 14 g of N-allylimidazole, 7 g of naphthyl-modified sulfonic acid-modified morpholine derivative, and 6 g of quaternary ammonium salt-modified triazine pyrrolidone to deionized water, stir and mix, introduce nitrogen for 50 min to remove oxygen, add 0.05 g of azobisisobutylamidine hydrochloride initiator, react at 50 °C for 10 h until a gel-like polymer is obtained, cut the gel into granules, wash with anhydrous ethanol, and dry at 105 °C to obtain a drag reducer for high salt-resistant fracturing fluid. Example 3

[0018] (1) Add 11 g of sodium bisulfite and deionized water into a flask, heat while stirring until the sodium bisulfite is dissolved, raise the temperature to 68.5° C., dropwise add 6 g of 1,2-epoxy-9-decene, raise the temperature to 83° C. and keep the temperature to react for 3.5 h. After the reaction is completed, cool the reaction solution in an ice water bath, filter the crystals precipitated after cooling, and recrystallize to obtain sodium olefin sulfonate; (2) Add 14 g of sodium olefin sulfonate, 12.5 g of 2-(4-chlorophenyl)morpholine, and 0.025 g of sodium hydride catalyst to tetrahydrofuran solvent, stir and mix, raise the temperature to 35° C. and react for 3.5 h. After the reaction is completed, filter, wash and dry to obtain a sulfonic acid group-modified morpholine derivative; (3) Add 16.5 g of sulfonic acid modified morpholine derivative and 9 g of ethyl [(naphthalene-2-yl)methyl] amine to a flask, then add 0.5 g of 7% hydrochloric acid solution as a catalyst, add 28 g of 36.5% formaldehyde solution dropwise while stirring, control the temperature at 21°C, continue stirring and react for 1.8 h, and after the reaction is completed, allow to stand for crystallization, filter and wash to obtain a naphthyl modified sulfonic acid modified morpholine derivative; (4) Add N-vinyl pyrrolidone, paraformaldehyde, and hydroquinone reducing agent into a flask, introduce nitrogen for 40 minutes to remove oxygen, heat to 91°C, add melamine, wherein the mass ratio of N-vinyl pyrrolidone, paraformaldehyde, hydroquinone, and melamine is 1.1:1:0.02:0.82, heat to 140°C, react for 6.5 hours, and after the reaction is completed, wash and dry to obtain triazine pyrrolidone; (5) Add 7 g of triazine pyrrolidone and 10.5 g of methacryloyloxyethyl trimethyl ammonium chloride to a methanol solvent, stir to dissolve, then add 0.02 g of sodium ethoxide catalyst, and react at 28 °C for 3 h. After the reaction is completed, filter, wash and dry to obtain quaternary ammonium salt modified triazine pyrrolidone; (6) Add 47.5 g of methacrylamide, 24 g of acrylic acid, 12 g of N-allylimidazole, 5 g of naphthyl-modified sulfonic acid-modified morpholine derivative, and 5 g of quaternary ammonium salt-modified triazine pyrrolidone to deionized water, stir and mix, introduce nitrogen for 40 min to remove oxygen, add 0.03 g of azobisisobutylamidine hydrochloride initiator, react at 46 °C for 7.5 h until a gel-like polymer is obtained, cut the gel into granules, wash with anhydrous ethanol, and dry at 102 °C to obtain a drag reducer for highly salt-resistant fracturing fluid. Example 4

[0019] (1) Add 9 g of sodium bisulfite and deionized water into a flask, heat while stirring until the sodium bisulfite is dissolved, raise the temperature to 65° C., dropwise add 5 g of 1,2-epoxy-9-decene, raise the temperature to 80° C. and keep the temperature to react for 2 h. After the reaction is completed, cool the reaction solution in an ice water bath, filter the crystals precipitated after cooling, and recrystallize to obtain sodium olefin sulfonate; (2) Add 11 g of sodium olefin sulfonate, 10 g of 2-(4-chlorophenyl)morpholine, and 0.02 g of sodium hydride catalyst to tetrahydrofuran solvent, stir and mix, raise the temperature to 30° C. and react for 3 h. After the reaction is completed, filter, wash and dry to obtain a sulfonic acid group-modified morpholine derivative; (3) Add 18 g of sulfonic acid modified morpholine derivative, 10 g of ethyl [(naphthalene-2-yl) methyl] amine, and then add 0.7 g of 9% hydrochloric acid solution as a catalyst into a flask, add 32 g of 38% formaldehyde solution dropwise while stirring, control the temperature at 24°C, continue stirring and react for 2 h, and after the reaction is completed, allow to crystallize, filter and wash to obtain a naphthyl modified sulfonic acid modified morpholine derivative; (4) Add N-vinyl pyrrolidone, paraformaldehyde, and hydroquinone reducing agent into a flask, introduce nitrogen for 45 minutes to remove oxygen, heat to 94°C, add melamine, wherein the mass ratio of N-vinyl pyrrolidone, paraformaldehyde, hydroquinone, and melamine is 1.15:1:0.03:0.85, heat to 145°C, react for 8 hours, and after the reaction is completed, wash and dry to obtain triazine pyrrolidone; (5) Add 7 g of triazine pyrrolidone and 10.5 g of methacryloyloxyethyl trimethyl ammonium chloride to a methanol solvent, stir to dissolve, then add 0.02 g of sodium ethoxide catalyst, and react at 28 °C for 3 h. After the reaction is completed, filter, wash and dry to obtain quaternary ammonium salt modified triazine pyrrolidone; (6) Add 47.5 g of methacrylamide, 24 g of acrylic acid, 12 g of N-allylimidazole, 5 g of naphthyl-modified sulfonic acid-modified morpholine derivative, and 5 g of quaternary ammonium salt-modified triazine pyrrolidone to deionized water, stir and mix, introduce nitrogen for 40 min to remove oxygen, add 0.03 g of azobisisobutylamidine hydrochloride initiator, react at 46 °C for 7.5 h until a gel-like polymer is obtained, cut the gel into granules, wash with anhydrous ethanol, and dry at 102 °C to obtain a drag reducer for highly salt-resistant fracturing fluid. Example 5

[0020] (1) Add 13 g of sodium bisulfite and deionized water into a flask, heat while stirring until the sodium bisulfite is dissolved, raise the temperature to 72° C., dropwise add 7 g of 1,2-epoxy-9-decene, raise the temperature to 86° C. and keep the temperature to react for 5 h. After the reaction is completed, cool the reaction solution in an ice water bath, filter the crystals precipitated after cooling, and recrystallize to obtain sodium olefin sulfonate; (2) Add 17 g of sodium olefin sulfonate, 15 g of 2-(4-chlorophenyl)morpholine, and 0.03 g of sodium hydride catalyst to tetrahydrofuran solvent, stir and mix, heat to 40° C. and react for 4 h. After the reaction is completed, filter, wash and dry to obtain a sulfonic acid group-modified morpholine derivative; (3) Add 16.5 g of sulfonic acid modified morpholine derivative and 9 g of ethyl [(naphthalene-2-yl)methyl] amine to a flask, then add 0.5 g of 7% hydrochloric acid solution as a catalyst, add 28 g of 36.5% formaldehyde solution dropwise while stirring, control the temperature at 21°C, continue stirring and react for 1.8 h, and after the reaction is completed, allow to stand for crystallization, filter and wash to obtain a naphthyl modified sulfonic acid modified morpholine derivative; (4) Add N-vinyl pyrrolidone, paraformaldehyde, and hydroquinone reducing agent into a flask, introduce nitrogen for 40 minutes to remove oxygen, heat to 91°C, add melamine, wherein the mass ratio of N-vinyl pyrrolidone, paraformaldehyde, hydroquinone, and melamine is 1.1:1:0.02:0.82, heat to 140°C, react for 6.5 hours, and after the reaction is completed, wash and dry to obtain triazine pyrrolidone; (5) Add 6 g of triazine pyrrolidone and 7 g of methacryloyloxyethyl trimethyl ammonium chloride to a methanol solvent, stir to dissolve, then add 0.01 g of sodium ethoxide catalyst, and react at 25° C. for 2.5 h. After the reaction is completed, filter, wash and dry to obtain quaternary ammonium salt-modified triazine pyrrolidone; (6) Add 45 g of methacrylamide, 20 g of acrylic acid, 10 g of N-allylimidazole, 3 g of naphthyl-modified sulfonic acid-modified morpholine derivative, and 4 g of quaternary ammonium salt-modified triazine pyrrolidone to deionized water, stir and mix, introduce nitrogen for 30 min to remove oxygen, add 0.01 g of azobisisobutylamidine hydrochloride initiator, react at 42 °C for 5 h to form a gel block polymer, cut the gel block into granules, wash with anhydrous ethanol and dry at 100 °C to obtain a drag reducer for high salt resistance fracturing fluid.

[0021] Comparative Example 1 The difference between this comparative example and Example 1 is that step (6) does not contain a naphthyl-modified sulfonic acid-modified morpholine derivative.

[0022] Comparative Example 2 The difference between this comparative example and Example 1 is that step (6) does not contain quaternary ammonium salt-modified triazine pyrrolidone.

[0023] The drag reducer solution for high salt resistance fracturing fluid with a mass fraction of 0.2% was prepared with distilled water, and then the drag reduction performance of the drag reducer solution was measured using an SLSY pipeline friction tester. The pipeline diameter was 8 mm and the experimental flow rate was 2 L·s -1 , the experimental temperature is 25°C. The test results are shown in Table 1.

[0024] Table 1: Drag reduction performance test.

[0025] project Drag reduction rate (%) Example 1 87.4 Example 2 85.6 Example 3 84.8 Example 4 86.2 Example 5 85.0 Comparative Example 1 72.4 Comparative Example 2 75.5 It can be seen from Table 1 that the drag reducers of Examples 1-5 of the present invention can effectively reduce the friction resistance between the fracturing fluid and the pipe wall, compared with the drag reducers of Comparative Examples 1-2, and have better drag reduction effects.

[0026] A drag reducer solution with a mass fraction of 0.2% for high salt resistance fracturing fluid was prepared with distilled water, and then the apparent viscosity of the drag reducer solution at different shear times was measured using a DSR-1 dynamic shear rheometer. The shear rate was 170s -1 , the experimental temperature is 25°C. The test results are shown in Table 2.

[0027] Table 2: Shear resistance test.

[0028]

[0029] As shown in Table 2, the drag reducers of Examples 1-5 of the present invention are better than those of Comparative Examples 1-2 at 170s. -1 Under the shear rate condition, it can still maintain a high viscosity value after a certain shear time, and has good shear resistance, which can ensure that it can still maintain a high viscosity value under large-displacement pumping conditions on site.

[0030] The drag reducer solution for high salt resistance fracturing fluid with a mass fraction of 0.2% was prepared using sodium chloride solutions with different mineralization degrees, and then the apparent viscosity of the drag reducer solution was measured using a NDJ-79 rotational viscometer. The experimental temperature was 25°C. The test results are shown in Table 3.

[0031] Table 3: Salt resistance test.

[0032]

[0033] It can be seen from Table 3 that the drag reducers of Examples 1-5 of the present invention can still maintain a higher viscosity value in an aqueous solution with a certain salinity, compared with the drag reducers of Comparative Examples 1-2, and have good salt resistance.

[0034] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a drag reducer for a high salt resistance fracturing fluid, characterized in that: The preparation method comprises the following steps: (1) Add 9-13 g of sodium bisulfite and deionized water into a flask, heat while stirring until the sodium bisulfite is dissolved, raise the temperature to 65-72° C., dropwise add 5-7 g of 1,2-epoxy-9-decene, raise the temperature to 80-86° C. and keep the temperature to react for 2-5 hours. After the reaction is completed, cool the reaction solution in an ice water bath, filter the crystals precipitated after cooling, and recrystallize to obtain sodium olefin sulfonate; (2) Add 11-17 g of sodium olefin sulfonate, 10-15 g of 2-(4-chlorophenyl)morpholine, and 0.02-0.03 g of sodium hydride catalyst to tetrahydrofuran solvent, stir and mix, raise the temperature to the reaction temperature, and react for 3-4 hours. After the reaction is completed, filter, wash, and dry to obtain a sulfonic acid group-modified morpholine derivative; (3) Add 15-18 g of the sulfonic acid modified morpholine derivative and 8-10 g of ethyl[(naphthalene-2-yl)methyl]amine to a flask, then add 0.3-0.7 g of hydrochloric acid solution as a catalyst, add 24-32 g of formaldehyde solution dropwise while stirring, control the temperature at 18-24° C., continue stirring to react, and after the reaction is completed, allow to stand for crystallization, filter and wash to obtain a naphthyl-modified sulfonic acid modified morpholine derivative; (4) Add N-vinyl pyrrolidone, paraformaldehyde and hydroquinone reducing agent into a flask, introduce nitrogen for 35-45 minutes to remove oxygen, raise the temperature to 88-94°C, add melamine, raise the temperature to 135-145°C to react for 5-8 hours, and after the reaction is completed, wash and dry to obtain triazine pyrrolidone; (5) Add 6-8 g of triazine pyrrolidone and 7-14 g of methacryloyloxyethyl trimethyl ammonium chloride to a methanol solvent, stir to dissolve, then add 0.01-0.03 g of a catalyst, react at 25-30° C. for 2.5-3.5 h, filter, wash and dry after the reaction to obtain quaternary ammonium salt-modified triazine pyrrolidone; (6) Add 45-50 g of methacrylamide, 20-28 g of acrylic acid, 10-14 g of N-allylimidazole, 3-7 g of naphthyl-modified sulfonic acid-modified morpholine derivative, and 4-6 g of quaternary ammonium salt-modified triazine pyrrolidone to deionized water, stir and mix, introduce nitrogen for 30-50 min to remove oxygen, add 0.01-0.05 g of initiator, react at 42-50° C. to form a gel block polymer, cut the gel block into granules, wash with anhydrous ethanol, and dry at 100-105° C. to obtain a drag reducer for high salt resistance fracturing fluid.

2. The method for preparing the drag reducer for high salt resistance fracturing fluid according to claim 1, characterized in that: The dripping time of 1,2-epoxy-9-decene in the step (1) is 45-60 minutes.

3. The method for preparing the drag reducer for high salt resistance fracturing fluid according to claim 1, characterized in that: The reaction temperature in step (2) is 30-40°C.

4. The method for preparing the drag reducer for high salt resistance fracturing fluid according to claim 1, characterized in that: In step (3), the mass fraction of the hydrochloric acid solution is 5%-9%, and the mass fraction of the formaldehyde solution is 35%-38%.

5. The method for preparing the drag reducer for high salt resistance fracturing fluid according to claim 1, characterized in that: The reaction time in step (3) is 1.5-2h.

6. The method for preparing a drag reducer for high salt resistance fracturing fluid according to claim 1, characterized in that: In the step (4), the mass ratio of N-vinyl pyrrolidone, paraformaldehyde, hydroquinone and melamine is 1.05-1.15:1:0.01-0.03:0.8-0.

85.

7. The method for preparing a drag reducer for high salt resistance fracturing fluid according to claim 1, characterized in that: The catalyst in step (5) is sodium ethoxide.

8. The method for preparing a drag reducer for high salt resistance fracturing fluid according to claim 1, characterized in that: The initiator in step (6) is azobisisobutyramidine hydrochloride.

9. The method for preparing a drag reducer for high salt resistance fracturing fluid according to claim 1, characterized in that: The reaction time in step (6) is 5-10 hours.

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