Preparation method of salt-resistant polyacrylamide aqueous suspension thickening agent for water-based fracturing fluid

Abstract

The invention belongs to the technical field of oil and gas well fracturing chemical additives, and relates to a preparation method of a salt-resistant polyacrylamide aqueous suspension thickening agent for a water-based fracturing fluid, a monomer AM, a salt-resistant monomer and acrylic acid are subjected to a redox-azo composite initiation system to prepare a ternary polymerization salt-resistant polyacrylamide product, and the ternary polymerization salt-resistant polyacrylamide product is used as a thickening agent for the salt-resistant polyacrylamide aqueous suspension thickening agent for the water-based fracturing fluid. The preparation method comprises the following steps: preparing one or two of anhydrous calcium chloride, sodium chloride and calcium sulfate into saline water, uniformly stirring for later use, grinding ternary polymerization salt-resistant polyacrylamide into 60-mesh fine powder, adding the fine powder into the saline water, uniformly stirring, adding a stabilizer, stirring, keeping the temperature at normal temperature of 25 DEG C, discharging, and bottling. The salt-resistant polymer is prepared into a water-phase suspension, so that the salt resistance of the thickening agent is improved; the capital can be saved by more than 300,000 through single-well fracturing; the fracturing fluid still has high viscosity under the condition of hypersalinity, the use effect is greatly improved, the use amount of the polymer is reduced, and the use cost of the fracturing fluid is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical additives for oil and gas well fracturing, and in particular relates to a method for preparing a salt-resistant polyacrylamide aqueous suspension thickener for water-based fracturing fluid. Background Art

[0002] In the process of oil and gas field development, due to different oil and gas storage conditions, especially tight oil and gas reservoirs, the initial production is limited or even no oil is produced. At this time, the oil and gas wells can have certain mining value after fracturing transformation. According to the reservoir range and reservoir depth, the most commonly used water-based gel fracturing fluid in China is currently water-based gel fracturing fluid. Since polyacrylamide is the main raw material of fracturing fluid thickener, and has the advantages of low friction, high viscoelasticity, strong sand carrying capacity, fast backflow, and no damage to the formation, it has been promoted and applied. At present, the polyacrylamide emulsion commonly used in fracturing fluid thickener has the characteristics of fast dissolution and on-site ready-to-use, but the maximum solid content of the emulsion is only 30%, and the molecular weight and viscosity of the emulsion are both low. It is difficult to synthesize ultra-high molecular performance emulsion using conventional emulsion synthesis methods.

[0003] In recent years, there have been many patents on the use of ultra-high molecular weight salt-resistant polyacrylamide ground into fine powder and suspended in white oil to make suspension emulsions. This method can increase the solid content to 40%, with high molecular weight and high viscosity. However, a large amount of white oil and surfactants are used. With the increase in international oil prices, the cost of single-well fracturing of fracturing fluids using this method as a thickener has increased significantly. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a salt-resistant polyacrylamide aqueous suspension thickener for water-based fracturing fluid, using a salt-resistant polymer to prepare an aqueous suspension, thereby improving the salt resistance of the thickener and reducing production costs.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing a salt-resistant polyacrylamide aqueous suspension thickener for a water-based fracturing fluid, comprising the following steps:

[0006] (1) Preparation of salt-resistant polymers:

[0007] The redox-azo composite initiator system is used, the monomer AM, the salt-resistant monomer, and the acrylic acid are mixed into a certain concentration according to a certain ratio, and then sodium hydroxide is added to adjust the pH value of the solution to 7.5-8.0, and urea accounting for 0.1wt%-0.5wt% of the reaction system is added, and the temperature is adjusted to 0-5°C and then placed in a Dewar flask, and high-purity nitrogen is blown in, and EDTA accounting for 0.003wt%-0.005wt% of the reaction system, sodium formate accounting for 0.05wt%-0.2wt% of the chain transfer agent in the reaction system, and sodium formate accounting for 0.01wt% of the reaction system are added. -0.02wt% of azo salt, 10ppm of tert-butyl hydroperoxide in the reaction system, 50ppm of reducing agent ammonium ferrous sulfate in the reaction system, the initiation temperature is 0-5°C, the reaction is performed for 4-6 hours, when the polymerization temperature rises to a certain temperature and no longer rises, the colloid is taken out for granulation, and a homemade heat stabilizer accounting for 0.5-1% of the colloid mass is added, and it is hydrolyzed in a constant temperature water bath at 80-90°C for 1.5-2 hours, then taken out, and cut into 2-3mm particle sizes, and dried at 65°C to obtain a ternary copolymer salt-resistant polyacrylamide product;

[0008] (2) Preparation of polymer aqueous suspension thickener:

[0009] Take one or two of anhydrous calcium chloride, sodium chloride, and calcium sulfate to make 1000g of 40wt% brine, stir evenly and set aside, take 55g-68g of ternary copolymer salt-resistant polyacrylamide and grind it into 60 mesh fine powder, add it to the brine and stir evenly, add 1-2g of stabilizer, continue stirring for 10min, and discharge and bottle after the temperature remains at room temperature 25℃.

[0010] Furthermore, the salt-resistant monomer in step (1) is one or both of 2-acrylamido-2-dimethylpropanesulfonic acid and sodium allyl sulfonate.

[0011] Furthermore, in step (1), the amount of monomer AM added accounts for 15wt%-18wt% of the reaction system, the amount of salt-resistant monomer added accounts for 2wt%-4wt% of the reaction system, and the amount of acrylic acid added accounts for 3wt%-8wt% of the reaction system.

[0012] Furthermore, the azo salt in step (1) is one or a mixture of two of azobisisobutyronitrile, azo V044, and azobisnitrile valeric acid.

[0013] Furthermore, the homemade heat stabilizer in step (1) is a mixture of thiourea and anhydrous ammonium sulfite, and thiourea and anhydrous ammonium sulfite are mixed in a mass ratio of 1:5.

[0014] Furthermore, in step (2), the stabilizer is one of polyethylene glycol, polyvinyl alcohol and polypyrrolidone; the preparation of the salt water needs to meet the solubility requirements, and on the premise of meeting the solubility requirements, one or two of the three salts are selected for preparation.

[0015] The present invention grinds polyacrylamide into 60 mesh fine powder and disperses it in a saturated aqueous solution containing 40% calcium chloride. Since the density of the saturated calcium chloride solution is close to that of the polyacrylamide, both of which are more than 1.3, it is beneficial to the suspension of the polyacrylamide. However, polyacrylamide particles gather due to electrostatic attraction during the suspension process. Therefore, a small amount of dispersion stabilizer is added to form an aqueous suspension. The suspension is prepared on-site and is cheaper than an oil-phase suspension. The cost of single-well fracturing is saved by more than 300,000 (taking the use of 100 cubic meters of thickener for a single well as an example). The dissolution speed is faster than that of the oil-phase suspension. Therefore, it is not necessary to grind the polyacrylamide to more than 100 meshes to prevent the polymer molecular chain from being further damaged and degraded.

[0016] The addition of salt causes the rapidly diffusing salt ions to react with water molecules to form hydrates. Due to the small ion state and the large number of water molecules combined, the bond energy of the hydrated ions formed is greater than the hydrogen bond energy between the polymer and the water molecules, making it impossible for the polymer to form hydrogen bonds with water and thus unable to dissolve the polymer. Since calcium ions have a smaller radius than sodium ions and a larger number of charges, calcium ions are added to obtain the maximum entropy of the aqueous solution. High-salt formations are generally dominated by calcium and magnesium ions, because most of the earth's formations are mainly calcium. 35-40% polymer powder is added to the saturated high-calcium aqueous solution, and diluted with 4% water during fracturing. The calcium ion content is 1.7g / L, which will not increase the impact on the formation. Therefore, this aqueous suspension can be used for fracturing in areas containing high-salt formations, such as the Northwest Oilfield.

[0017] The present invention has the following beneficial effects:

[0018] (1) The method of the present invention uses a salt-resistant polymer to prepare an aqueous suspension, thereby improving the salt resistance of the thickener.

[0019] (2) The method of the present invention effectively solves the high cost problem of conventional oil phase suspension emulsions, and the cost savings for single well fracturing can reach more than 300,000 yuan.

[0020] (3) The method of the present invention can still have a high viscosity under high salinity conditions, greatly improving the use effect, reducing the amount of polymer used, and reducing the cost of using the fracturing fluid. DETAILED DESCRIPTION

[0021] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the protection scope of the present invention is not limited to these embodiments. Any changes or equivalent substitutions that do not deviate from the concept of the present invention are included in the protection scope of the present invention.

[0022] Experimental drugs: acrylamide crystals (refined), AMPS (high purity), sodium allyl sulfonate (high purity), acrylic acid (ice crystal grade), sodium hydroxide (bin-chemical), sodium formate (analytical grade), urea, azobis(ethylbutyronitrile) (analytical grade), azobis(acetonitrile) valeric acid (analytical grade), azo salt V44 (analytical grade), tert-butyl hydroperoxide (analytical grade), ammonium ferrous sulfate (analytical grade), EDTA (analytical grade), calcium chloride (anhydrous), sodium chloride, calcium sulfate, stabilizer.

[0023] The reaction system of the present invention is a mixture of monomer AM, salt-resistant monomer and acrylic acid, mixed with pure water in a certain proportion to form a certain concentration, and sodium hydroxide is added to adjust the pH value to 7.5-8.0.

[0024] The self-made heat stabilizer described in the present invention is a mixture of thiourea and anhydrous ammonium sulfite, and the thiourea and the anhydrous ammonium sulfite are mixed in a mass ratio of 1:5.

[0025] Example 1: Preparation of suspension thickener A

[0026] (1) Preparation method of salt-resistant polyacrylamide

[0027] a) Add 742g of pure water to a wide-mouth bottle, add 160g of acrylamide crystals, stir and dissolve evenly, add 40g of acrylic acid, add 30g of AMPS again, stir and dissolve evenly, add 28g of granular sodium hydroxide to adjust the pH value to 7.5, and cool at the same time. The temperature should not exceed 15°C. After uniform dissolution, add 3g of urea, stir and cool to 0-5°C, transfer to a Dewar flask, deoxygenate with high-purity nitrogen ≧99.99% or more for 10min, add 0.03g of disodium EDTA, deoxygenate for 20min, add 0.05g of sodium formate, azobisisobutyronitrile and azobiscyanovaleric acid 0.01g, continue to deoxygenate for 20min, add 1mL of initiator tert-butyl hydroperoxide (concentration 1%), deoxygenate for 2min, add 5mL of reducing agent ammonium ferrous sulfate (concentration 1%), continue to pass nitrogen until the solution becomes viscous, then seal and react for 4-6 hours.

[0028] b) After the solution temperature reaches the highest value and cools down naturally for 2 hours, take out the colloid from the Dewar flask and granulate it into particles with a diameter of about 3-8 mm. Take out 100 g of the granulated colloid particles, put them into a beaker, add 1.0 g of homemade heat stabilizer, stir evenly, put them into a constant temperature water bath at 80°C and heat for 4 hours, then take them out for secondary granulation, dry them at 65°C for 2 hours, take them out, grind them and sieve them through 18-80 mesh to obtain the finished salt-resistant polymer.

[0029] (2) Preparation method of polymer aqueous suspension thickener

[0030] Take anhydrous calcium chloride to prepare 1000g of brine with a weight ratio of 40%, stir evenly and set aside. Take a part of the salt-resistant polymer obtained in step (1) and grind it into 60 mesh fine powder, take 68g of the fine powder and add it to the brine and stir evenly, add 2g of stabilizer polypyrrolidone again, continue stirring for 10 minutes, and after the temperature is maintained at room temperature of 25°C, discharge the material and bottle it.

[0031] (3) Performance evaluation

[0032] a) Performance evaluation of salt-resistant polyacrylamide: The molecular weight was tested according to the Sinopec enterprise standard Q / SH10201572-2017 method; the simulated brine mineralization was changed to 80000 mg / L (where the calcium and magnesium ion content was greater than 2000 mg / L). The testing temperature was changed to 80°C.

[0033] The evaluation results are: molecular weight 22.25 million, simulated water viscosity 7.0-7.5mPa.s, water insoluble matter 0.1%, and dissolution rate less than 60min.

[0034] b) Performance evaluation of polymer suspension thickener: The solid content and thickening time of the suspension are evaluated according to the enterprise standard Q / SFY 1001-2018. In addition, the suspension stability is evaluated according to the on-site requirements, and uniform dispersion is required within 24 hours.

[0035] The evaluation results are: solid content>35.5%, thickening time 5-10 seconds, suspension for more than 24 hours without generating flocs and lumps, good fluidity, and uniform dispersion.

[0036] Example 2: Preparation of suspension thickener B

[0037] (1) Preparation method of salt-resistant polyacrylamide

[0038] a) Add 690g pure water to a wide-mouth bottle, add 150g acrylamide crystals, stir and dissolve evenly, add 80g acrylic acid, add 30g AMPS again, stir and dissolve evenly, add 50g granular sodium hydroxide to adjust the pH value to 7.5, and cool at the same time. The temperature should not exceed 15°C. After dissolution, add 2g urea, stir and cool to 0-5°C, transfer to a Dewar flask, deoxygenate with high-purity nitrogen ≧99.99% or more for 10min, add 0.03g disodium EDTA, deoxygenate for 20min, add 0.1g sodium formate and 0.02g azobisisobutyronitrile, continue to deoxygenate for 20min, add 1mL of initiator tert-butyl hydroperoxide (concentration 1%), deoxygenate for 2min, add 5mL of reducing agent ammonium ferrous sulfate (concentration 1%), continue to pass nitrogen until the solution becomes viscous, then seal the bottle and react for 4-6 hours.

[0039] b) After the solution temperature reaches the highest value and cools down naturally for 2 hours, take out the colloid from the Dewar flask and granulate it into particles with a diameter of about 3-8 mm. Take out 100 g of the granulated colloid particles, put them into a beaker, add 0.5 g of homemade heat stabilizer, stir evenly, put them into a constant temperature water bath at 85°C and heat for 4 hours, then take them out for secondary granulation, dry them at 65°C for 2 hours, take them out, grind and sieve them through 18-80 mesh to obtain the finished product.

[0040] (2) Preparation method of polymer aqueous suspension thickener

[0041] Take anhydrous calcium chloride and calcium sulfate to prepare 1000g of brine with a weight ratio of 40%, stir evenly and set aside. Take a part of the salt-resistant polymer obtained in step (1) and grind it into 60 mesh fine powder, take 60g of the fine powder and add it to the brine and stir evenly, add 1g of stabilizer polyvinyl alcohol again, continue stirring for 10 minutes, and after the temperature is maintained at room temperature of 25°C, discharge the material and bottle it.

[0042] (3) Performance evaluation

[0043] a) Performance evaluation of salt-resistant polyacrylamide: The molecular weight was tested according to the Sinopec enterprise standard Q / SH1020 1572-2017 method; the simulated brine mineralization was changed to 80000 mg / L (where the calcium and magnesium ion content was greater than 2000 mg / L). The testing temperature was changed to 80°C.

[0044] The evaluation results are: molecular weight 23.5 million, simulated water viscosity 8.0-8.5mPa.s, water insoluble matter 0.12%, and dissolution rate less than 60min.

[0045] b) Performance evaluation of polymer suspension thickener: The solid content and thickening time of the suspension are evaluated according to the enterprise standard Q / SFY 1001-2018. In addition, the suspension and suspension stability are added according to the site requirements.

[0046] The evaluation results are: solid content>35.5%, thickening time 5-10 seconds, no floccules are generated after suspension for more than 24 hours, poor fluidity, and precipitation at the bottom.

[0047] Example 3: Preparation of suspension thickener C

[0048] (1) Preparation method of salt-resistant polyacrylamide

[0049] a) Add 710g pure water to a wide-mouth bottle, add 180g acrylamide crystals, stir and dissolve evenly, add 40g acrylic acid, add 40g AMPS again, stir and dissolve evenly, add 30g granular sodium hydroxide to adjust the pH value to 7.5, and cool at the same time. The temperature should not exceed 15°C. After dissolution, add 5g urea, stir and cool to 0-5°C, transfer to a Dewar flask, deoxygenate with high-purity nitrogen ≧99.99% or more for 10min, add 0.03g disodium EDTA, deoxygenate for 20min, add 0.2g sodium formate and 0.02g azo V044, continue to deoxygenate for 20min, add 1mL of initiator tert-butyl hydroperoxide (concentration 1%), deoxygenate for 2min, add 5mL of reducing agent ammonium ferrous sulfate (concentration 1%), continue to pass nitrogen until the solution becomes viscous, then seal the bottle and react for 4-6 hours.

[0050] b) After the solution temperature reaches the highest value and cools down naturally for 2 hours, take out the colloid from the Dewar flask and granulate it into particles with a diameter of about 3-8 mm. Take out 100 g of the granulated colloid particles, put them into a beaker, add 0.8 g of homemade heat stabilizer, stir evenly, put them into a constant temperature water bath at 90°C and heat for 4 hours, then take them out for secondary granulation, dry them at 65°C for 2 hours, take them out, grind and sieve them through 18-80 mesh to obtain the finished product.

[0051] (2) Preparation method of polymer aqueous suspension thickener

[0052] Take anhydrous calcium chloride and sodium chloride to prepare a 40% brine by weight, stir evenly and set aside. Take a portion of the salt-resistant polymer obtained in step (1) and grind it into 60 mesh fine powder. Take 55g of the fine powder and add it to the brine and stir evenly. Add 1g of stabilizer polyethylene glycol again and continue stirring for 10 minutes. After the temperature is maintained at room temperature of 25°C, discharge the material and bottle it.

[0053] (3) Performance evaluation

[0054] a) Performance evaluation of salt-resistant polyacrylamide: The molecular weight was tested according to the Sinopec enterprise standard Q / SH1020 1572-2017 method; the simulated brine mineralization was changed to 80000 mg / L (where the calcium and magnesium ion content was greater than 2000 mg / L). The testing temperature was changed to 80°C.

[0055] The evaluation results are: molecular weight 23 million, simulated water viscosity 10.0-9.8mPa.s, water insoluble matter 0.08%, and dissolution rate less than 60min.

[0056] b) Performance evaluation of polymer suspension thickener: The solid content and thickening time of the suspension are evaluated according to the enterprise standard Q / SFY 1001-2018. In addition, the suspension and suspension stability are added according to the site requirements.

[0057] The evaluation results are: solid content>35.5%, thickening time 5-10 seconds, no floccules generated after suspension for more than 24 hours, good fluidity and uniform dispersion.

[0058] Example 4: Preparation of suspension thickener D

[0059] (1) Preparation method of salt-resistant polyacrylamide

[0060] a) Add 726g of pure water to a wide-mouth bottle, add 180g of acrylamide crystals, stir and dissolve evenly, add 30g of acrylic acid, add 40g of AMPS again, stir and dissolve evenly, add 24g of granular sodium hydroxide to adjust the pH value to 7.5, and cool at the same time. The temperature should not exceed 15°C. After dissolution, add 1g of urea, stir and cool to 0-5°C, transfer to a Dewar flask, deoxygenate with high-purity nitrogen ≧99.99% or more for 10min, add 0.03g of disodium EDTA, deoxygenate for 20min, add 0.05g of sodium formate, azo V044 and 0.01g of azobisnitrile valeric acid, continue to deoxygenate for 20min, add 1mL of initiator tert-butyl hydroperoxide (concentration 1%), deoxygenate for 2min, add 5mL of reducing agent ammonium ferrous sulfate (concentration 1%), continue to pass nitrogen until the solution becomes viscous, then seal and react for 4-6 hours.

[0061] b) After the solution temperature reaches the highest value and cools down naturally for 2 hours, take out the colloid from the Dewar flask and granulate it into particles with a diameter of about 3-8 mm. Take out 100 g of the granulated colloid particles, put them into a beaker, add 1.0 g of homemade heat stabilizer, stir evenly, put them into a constant temperature water bath at 80°C and heat for 4 hours, then take them out for secondary granulation, dry them at 65°C for 2 hours, take them out, grind and sieve them through 18-80 mesh to obtain the finished product.

[0062] (2) Preparation method of polymer aqueous suspension thickener

[0063] Take anhydrous calcium chloride and sodium chloride to prepare 1000g of brine with a weight ratio of 40%, stir evenly and set aside. Take a part of the salt-resistant polymer obtained in step (1) and grind it into 60 mesh fine powder, take 65g of the fine powder and add it to the brine and stir evenly, add 1.5g of stabilizer polypyrrolidone again, continue stirring for 10 minutes, and after the temperature is maintained at room temperature of 25°C, discharge the material and bottle it.

[0064] (3) Performance evaluation

[0065] a) Performance evaluation of salt-resistant polyacrylamide: The molecular weight was tested according to the Sinopec enterprise standard Q / SH1020 1572-2017 method; the simulated brine mineralization was changed to 80000 mg / L (where the calcium and magnesium ion content was greater than 2000 mg / L). The testing temperature was changed to 80°C.

[0066] The evaluation results are: molecular weight 21.1 million, simulated water viscosity 9.8-9.5mPa.s, water insoluble matter 0.10%, and dissolution rate less than 60min.

[0067] b) Performance evaluation of polymer suspension thickener: The solid content and thickening time of the suspension are evaluated according to the enterprise standard Q / SFY 1001-2018. In addition, the suspension and suspension stability are added according to the site requirements.

[0068] The evaluation results are: solid content>35.5%, thickening time 5-10 seconds, no floccules generated after suspension for more than 24 hours, uniform dispersion, and good fluidity.

[0069] Example 5: Preparation of suspension thickener E

[0070] (1) Preparation method of salt-resistant polyacrylamide

[0071] a) Add 726g of pure water to a wide-mouth bottle, add 190g of acrylamide crystals, stir and dissolve evenly, add 30g of acrylic acid, add 20g of AMPS again, stir and dissolve evenly, add 34g of granular sodium hydroxide to adjust the pH value to 8.0, and cool at the same time. The temperature should not exceed 15°C. After dissolution, add 4g of urea, stir and cool to 0-5°C, transfer to a Dewar flask, deoxygenate with high-purity nitrogen ≧99.99% or more for 10min, add 0.03g of disodium EDTA, deoxygenate for 20min, add 0.15g of sodium formate and 0.02g of azobisnitrile valeric acid, continue to deoxygenate for 20min, add 1.5mL of initiator tert-butyl hydroperoxide (concentration 1%), add 5mL of reducing agent ferrous ammonium sulfate (concentration 1%) after deoxygenation for 2min, continue to pass nitrogen until the solution becomes viscous, then seal the bottle and react for 4-6 hours.

[0072] b) After the solution temperature reaches the highest value and cools down naturally for 2 hours, take out the colloid from the Dewar flask and granulate it into particles with a diameter of about 3-8 mm. Take out 100 g of the granulated colloid particles, put them into a beaker, add 1.0 g of homemade heat stabilizer, stir evenly, put them into a constant temperature water bath at 85°C and heat for 4 hours, then take them out for secondary granulation, dry them at 65°C for 2 hours, take them out, grind them and sieve them through 18-80 mesh to obtain the finished product.

[0073] (2) Preparation method of polymer aqueous suspension thickener

[0074] Take anhydrous calcium chloride to prepare 1000g of brine with a weight ratio of 40%, stir evenly and set aside. Take a part of the salt-resistant polymer prepared in step (1) and grind it into 60 mesh fine powder, take 60g of the fine powder and add it to the brine and stir evenly, add 2g of stabilizer polyvinyl alcohol again, continue stirring for 10 minutes, and after the temperature is maintained at room temperature of 25°C, discharge the material and bottle it.

[0075] (3) Performance evaluation

[0076] a) Performance evaluation of salt-resistant polyacrylamide: The molecular weight was tested according to the Sinopec enterprise standard Q / SH1020 1572-2017 method; the simulated brine mineralization was changed to 80000 mg / L (where the calcium and magnesium ion content was greater than 2000 mg / L). The testing temperature was changed to 80°C.

[0077] The evaluation results are: molecular weight 20.2 million, simulated water viscosity 9.0-8.9 mPa.s, water insoluble matter 0.08%, and dissolution rate less than 60 min.

[0078] b) Performance evaluation of polymer suspension thickener: The solid content and thickening time of the suspension are evaluated according to the enterprise standard Q / SFY 1001-2018. In addition, the suspension and suspension stability are added according to the site requirements.

[0079] The evaluation results are: solid content>35.5%, thickening time 5-10 seconds, no floccules generated after suspension for more than 24 hours, good fluidity and uniform dispersion.

[0080] Example 6: Preparation of suspension thickener F

[0081] (1) Preparation method of salt-resistant polyacrylamide

[0082] a) Add 726g of pure water to a wide-mouth bottle, add 180g of acrylamide crystals, stir and dissolve evenly, add 30g of acrylic acid, add 40g of AMPS again, stir and dissolve evenly, add 24g of granular sodium hydroxide to adjust the pH value to 7.5, and cool at the same time. The temperature should not exceed 15°C. After dissolution, add 4g of urea, stir and cool to 0-5°C, transfer to a Dewar flask, deoxygenate with high-purity nitrogen ≧99.99% or more for 10min, add 0.03g of disodium EDTA, deoxygenate for 20min, add 2.0g of sodium formate and 0.01g of azobisisobutyronitrile, continue to deoxygenate for 20min, add 1mL of initiator tert-butyl hydroperoxide (concentration 1%), deoxygenate for 2min, add 5mL of reducing agent ammonium ferrous sulfate (concentration 1%), continue to pass nitrogen until the solution becomes viscous, then seal the bottle and react for 4-6 hours.

[0083] b) After the solution temperature reaches the highest value and cools down naturally for 2 hours, take out the colloid from the Dewar flask and granulate it into particles with a diameter of about 3-8 mm. Take out 100 g of the granulated colloid particles, put them into a beaker, add 1.0 g of homemade heat stabilizer, stir evenly, put them into a constant temperature water bath at 80°C and heat for 4 hours, then take them out for secondary granulation, dry them at 65°C for 2 hours, take them out, grind and sieve them through 18-80 mesh to obtain the finished product.

[0084] (2) Preparation method of polymer aqueous suspension thickener

[0085] Take anhydrous calcium chloride and calcium sulfate to prepare 1000g of brine with a weight ratio of 40%, stir evenly and set aside. Take a part of the salt-resistant polymer obtained in step (1) and grind it into 60 mesh fine powder, take 68g of the fine powder and add it to the brine and stir evenly, add 1g of stabilizer polyethylene glycol again, continue stirring for 10 minutes, and after the temperature is maintained at room temperature of 25°C, discharge the material and bottle it.

[0086] (3) Performance evaluation

[0087] a) Performance evaluation of salt-resistant polyacrylamide: The molecular weight was tested according to the Sinopec enterprise standard Q / SH1020 1572-2017 method; the simulated brine mineralization was changed to 80000 mg / L (where the calcium and magnesium ion content was greater than 2000 mg / L). The testing temperature was changed to 80°C.

[0088] The evaluation results are: molecular weight 18.1 million, simulated water viscosity 6.5-6.8mPa.s, water insoluble matter 0.08%, and dissolution rate less than 60min.

[0089] b) Performance evaluation of polymer suspension thickener: The solid content and thickening time of the suspension are evaluated according to the enterprise standard Q / SFY 1001-2018. In addition, the suspension and suspension stability are added according to the site requirements.

[0090] The evaluation results are: solid content>35.5%, thickening time 5-10 seconds, no floccules generated after suspension for more than 24 hours, good fluidity and uniform dispersion.

[0091] The present invention is not limited to the above-mentioned implementation modes, and anyone should be aware of the structural changes made under the enlightenment of the present invention, and all those having the same or similar technical solutions as the present invention fall within the protection scope of the present invention.

[0092] The techniques, shapes, and structural parts not described in detail in the present invention are all well-known techniques.

Claims

1. A method for preparing a salt-resistant polyacrylamide aqueous suspension thickener for water-based fracturing fluid, characterized in that: The following steps are involved: (1) Preparation of salt-resistant polymers: The redox-azo composite initiator system is used, the monomer AM, the salt-resistant monomer and the acrylic acid are mixed into a certain concentration according to a certain ratio, and then sodium hydroxide is added to adjust the pH value of the solution to 7.5-8.0, and 0.1wt%-0.5wt% of urea is added to the reaction system, and the temperature is adjusted to 0-5°C, and then the mixture is placed in a Dewar flask, and high-purity nitrogen is blown in, and 0.003wt%-0.005wt% of EDTA is added to the reaction system, 0.005wt%-0.02wt% of the chain transfer agent sodium formate is added to the reaction system, and 0.001wt% of the reaction system is added. wt%-0.002wt% of azo salt, 10ppm of tert-butyl hydroperoxide in the reaction system, 50ppm of reducing agent ammonium ferrous sulfate in the reaction system, the initiation temperature is 0-5°C, the reaction is performed for 4-6 hours, when the polymerization temperature rises to a certain temperature and no longer rises, the colloid is taken out for granulation, and a homemade heat stabilizer accounting for 0.5-1% of the colloid mass is added, and it is hydrolyzed in a constant temperature water bath at 80-90°C for 4 hours, then taken out, and then cut into 2-3mm particle sizes, and dried at 65°C to obtain a ternary copolymer salt-resistant polyacrylamide product; (2) Preparation of polymer aqueous suspension thickener: Take one or two of anhydrous calcium chloride, sodium chloride, and calcium sulfate to make 1000g of 40wt% brine, stir evenly and set aside, take 55g-68g of ternary copolymer salt-resistant polyacrylamide and grind it into 60 mesh fine powder, add it to the brine and stir evenly, add 1-2g of stabilizer, continue stirring for 10min, and discharge and bottle after the temperature remains at room temperature 25℃.

2. The method for preparing the salt-resistant polyacrylamide aqueous suspension thickener for water-based fracturing fluid according to claim 1, characterized in that: In the step (1), the salt-resistant monomer is one or both of 2-acrylamide-2-methylpropane sulfonic acid and sodium allyl sulfonate.

3. The method for preparing the salt-resistant polyacrylamide aqueous suspension thickener for water-based fracturing fluid according to claim 1, characterized in that: In the step (1), the amount of monomer AM added accounts for 15wt%-18wt% of the reaction system, the amount of salt-resistant monomer added accounts for 2wt%-4wt% of the reaction system, and the amount of acrylic acid added accounts for 3wt%-8wt% of the reaction system.

4. The method for preparing the salt-resistant polyacrylamide aqueous suspension thickener for water-based fracturing fluid according to claim 1, characterized in that: The azo salt in step (1) is one or a mixture of two of azobisisobutyronitrile, azo V044, and azobisnitrile valeric acid.

5. The method for preparing the salt-resistant polyacrylamide aqueous suspension thickener for water-based fracturing fluid according to claim 1, characterized in that: The self-made heat stabilizer in step (1) is a mixture of thiourea and anhydrous ammonium sulfite, wherein thiourea and anhydrous ammonium sulfite are mixed in a mass ratio of 1:

5.

6. The method for preparing the salt-resistant polyacrylamide aqueous suspension thickener for water-based fracturing fluid according to claim 1, characterized in that: The stabilizer in step (2) is one of polyethylene glycol, polyvinyl alcohol and polypyrrolidone.