A cross-linked polymer and a method for preparing and using the same

Abstract

The application relates to the technical field of water treatment, in particular to a composite material and a preparation method and application thereof. The cross-linked polymer comprises a sulfonic acid group structural unit, an acrylamide structural unit, a first cross-linking unit and a second cross-linking unit; wherein the first cross-linking unit is a second cross-linking unit is a C1-C 25 alkyl straight chain. The application optimizes a cross-linking system, uses a sulfonic acid group monomer and an acrylamide monomer as raw materials, and improves the viscosity retention rate of the cross-linked polymer at high temperature through secondary cross-linking, enhances the salt resistance (resistance to NaCl saturation and CaCl2 saturation), and has good shear force.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oilfield chemical technology, and particularly relates to a high-temperature-resistant cross-linked polymer for drilling fluid, a preparation method and application thereof. BACKGROUND

[0002] With the increase of world energy demand and the development of drilling technology, deep and ultra-deep oil and gas has become an important replacement energy source in the world. 60% of the world's new oil and gas reserves come from deep, while China still has a large amount of deep oil and gas to be explored and developed. Therefore, it is inevitable to search for oil and gas in the deep strata. The drilling depth in China has reached 9000 meters, the bottom hole temperature is 180-260℃, and there is a large section of salt and gypsum layer in most areas, which puts higher requirements on the performance of drilling fluid treatment agents.

[0003] The (low) solid-phase-free drilling fluid system has good carrying and suspending capacity of cuttings due to low solid content, and can also play a good lubricating and drag-reducing role, and has been widely used in oilfield drilling operations. In the drilling process, in order to maintain the rheological property of the drilling fluid system, a cross-linked polymer is usually added to increase the viscosity of the drilling fluid system. The cross-linked polymer is a kind of treatment agent with large dosage in drilling and completion fluid, which is usually high-molecular polymerization, characterized by long molecular chain and good water solubility. In addition to the viscosity-increasing effect, the cross-linked polymer often also serves as shale inhibitor (coating agent), fluid loss additive and flow pattern modifier, etc. Therefore, the use of cross-linked polymer is often beneficial to improving the rheological property of drilling fluid and stabilizing the well wall.

[0004] In the prior art, CN102127401A discloses a high-temperature-resistant cross-linked polymer for drilling fluid and a preparation method thereof, which is prepared by mixing starch, guar gum, alkaline hydroxide, epoxide and alcohol solvent in a certain proportion, and then through stirring, drying, crushing and other processes. The temperature resistance of the product in fresh water drilling fluid can reach 150℃, and the temperature resistance in seawater drilling fluid can reach 140℃. CN101955564A discloses a preparation method of a high-temperature-resistant and salt-resistant cross-linked polymer for drilling fluid, which is prepared by polymerization of 2-acrylamide-2-methylpropane sulfonic acid, acrylic acid and acrylamide as raw materials by aqueous solution polymerization. The cross-linked polymer has good stability at a formation temperature of 150℃, and still has a certain effect in a 10% salt water solution, and has strong salt resistance. CN114805680A discloses an environmentally friendly high-temperature-resistant and salt-resistant cross-linked polymer for water-based drilling fluid, a preparation method and application thereof. The water-soluble high-temperature-resistant polymer cross-linked polymer with a certain network structure is prepared by inverse emulsion polymerization, and the obtained cross-linked polymer has excellent viscosity-increasing performance for water-based drilling fluid at a high temperature of 180℃ and is non-toxic and easy to biodegrade.

[0005] It is evident that the temperature resistance of domestically produced high-temperature crosslinking polymer products is typically around 150–180℃, and this resistance is further reduced when the system has a high degree of mineralization (especially Ca). 2+ Concentration higher than 1.4 × 10 4 When the concentration of cross-linked polymers (mg / L) is low, molecular chain coiling and entanglement can occur, leading to product failure. Conventional aqueous solution polymerization methods have certain limitations. There is an urgent need in this field to develop a cross-linked polymer product that can maintain good performance under high temperature and high salt conditions. Summary of the Invention

[0006] Currently, existing technologies for improving the performance of crosslinked polymers primarily focus on the selection of monomer structures. However, the highest temperature resistance of current high-temperature crosslinked polymer products is only around 180°C, and their salt resistance is relatively poor, leaving room for further improvement in practical applications. This application discovers that by optimizing the crosslinking system, the thermal stability of the product can be enhanced while simultaneously improving its salt resistance.

[0007] Based on this, the specific technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a crosslinked polymer, the crosslinked polymer comprising a sulfonic acid structural unit, an acrylamide structural unit, a first crosslinking unit and a second crosslinking unit;

[0009] Wherein, the first crosslinking unit is The second crosslinking unit is C1 to C1. 25 Straight-chain alkyl groups.

[0010] This invention discovers that the synergy of the two crosslinking units can not only significantly enhance the crosslinking strength, but also strengthen the spatial network structure of the molecules and improve the product's thickening properties. At the same time, the carbon-carbon long chain structure can further enhance the thermal stability of the crosslinked polymer and effectively inhibit the shrinkage of molecular chains under high salt conditions, thereby improving the product's salt resistance.

[0011] Preferably, the second crosslinking unit is C6~C6. 10 When straight-chain alkyl groups are used, the salt resistance and temperature resistance can be further improved.

[0012] Preferably, the total mass ratio of the sulfonic acid structural unit and the acrylamide structural unit to the second crosslinking unit is 5000-10000:1-5.

[0013] The present invention further discovers that by controlling the amount of the second crosslinking unit, excessive crosslinking of the crosslinked polymer can be effectively avoided, thereby further improving product stability, water solubility and other properties.

[0014] As preferred, the sulfonic acid group structural unit is selected from one or more of 2-acrylamido-2-methylpropane sulfonic acid, 2-acrylamidododecane sulfonic acid, 2-acryloyloxy-2-methylpropane sulfonic acid, acryloyloxybutyl sulfonic acid, 2-acrylamidotetradecane sulfonic acid and N-methyldiallylpropane sulfonic acid.

[0015] As preferred, the acrylamide structural unit is selected from one or more of N-(3-dimethylaminopropyl)methacrylamide, N-(2-hydroxyethyl)-2-methyl-2-acrylamide, N-isopropylmethacrylamide and N-methylacrylamide and N-hydroxymethylacrylamide.

[0016] As preferred, the cross-linked polymer is selected from one of the following general structures:

[0017]

[0018] wherein n represents the number of carbon atoms, 1≤n≤25; and R is selected from H, -CH2CH2CH2N(CH3)2, -CH2CH2OH, -(CH3)2 or -CH2OH.

[0019] As preferred, the cross-linked polymer has a polymerization degree of 50000-500000.

[0020] As preferred, the content of the second cross-linking unit is 0.01-0.05wt% based on the total weight of the cross-linked polymer; the content of the sulfonic acid group structural unit is 30-60wt%; the content of the acrylamide structural unit is 40-80wt%; and the content of the first cross-linking unit is 0.01-0.05wt%.

[0021] In a second aspect, the application further provides a preparation method of the cross-linked polymer, comprising: using a sulfonic acid group monomer and an acrylamide monomer as raw materials, and preparing the cross-linked polymer through secondary cross-linking.

[0022] wherein the first cross-linking agent used in the first cross-linking is 1,4-divinylbenzene; and the second cross-linking agent used in the second cross-linking is one or more of dihaloalkanes.

[0023] The application finds that the use of 1,4-divinylbenzene with a rigid benzene ring structure for the preliminary cross-linking of a sulfonic acid group monomer and an acrylamide monomer, in combination with the secondary cross-linking of the secondary amine groups in the polymer through alkylation reaction of dihaloalkanes, can significantly improve the cross-linking strength, enhance the thermal stability of the cross-linked polymer, effectively inhibit the curling of the molecular chain under high salt conditions, and improve the salt resistance of the product.

[0024] In the present application, the cross-linked polymer is obtained by a reverse emulsion polymerization method, and the reaction process is uniform in heat dissipation and will not cause local overheating and polymerization.

[0025] As preferred, the dihaloalkane is selected from 1,2-dichloroethane, 1,2-dichloropropane, 1,3-dichloropropane, 1,2-dichlorobutane, 1,3-dichlorobutane, 1,4-dichlorobutane, 1,2-dichloropentane, 1,3-dichloropentane, 1,4-dichloropentane, 1,5-dichloropentane, 1,2-dichlorohexane, 1,3-dichlorohexane, 1,4-dichlorohexane, 1,5-dichlorohexane, 1,6-dichlorohexane, 1,2-dichloroheptane, 1,3-dichloroheptane, 1,4-dichloroheptane, 1,5-dichloroheptane, 1,6-dichloroheptane, 1,7-dichloroheptane, 1,2-dichlorooctane, 1,3-dichlorooctane, 1,4-dichlorooctane, 1,5-dichlorooctane, 1,6-dichlorooctane, 1,7-dichlorooctane, 1,8-dichlorooctane, 1,2-dichlorononane, 1,3-dichlorononane, 1,4-dichlorononane, 1,5-dichlorononane, 1,6-dichlorononane, 1,7-dichlorononane, 1,8-dichlorononane, 1,9-dichlorononane, 1,2-dichlorodecane, 1,3-dichlorodecane, 1,4-dichlorodecane, 1,5-dichlorodecane, 1,6-dichlorodecane, 1,7-dichlorodecane, 1,8-dichlorodecane, 1,9-dichlorodecane, 1,10-dichlorodecane; 1,2-diiodoethane, 1,2-diiodopropane, 1,3-diiodopropane, 1,2-diiodobutane, 1,3-diiodobutane, 1,4-diiodobutane, 1,2-diiodopentane, 1,3-diiodopentane, 1,4-diiodopentane, 1,5-diiodopentane, 1,2-diiodohexane, 1,3-diiodohexane, 1,4-diiodohexane, 1,

[0026] 5-diiodohexane, 1,6-diiodohexane, 1,2-diiodoheptane, 1,3-diiodoheptane, 1,

[0027] 4-diiodoheptane, 1,5-diiodoheptane, 1,6-diiodoheptane, 1,7-diiodoheptane, 1,

[0028] 2-diiodooctane, 1,3-diiodooctane, 1,4-diiodooctane, 1,5-diiodooctane, 1,

[0029] 6-diiodooctane, 1,7-diiodooctane, 1,8-diiodooctane, 1,2-diiodononane, 1,

[0030] 3-diiodononane, 1,4-diiodononane, 1,5-diiodononane, 1,6-diiodononane, 1,

[0031] 7-diiodononane, 1,8-diiodononane, 1,9-diiodononane, 1,2-diiododecane, 1,

[0032] 3-diiodoheptane, 1,4-diiodoheptane, 1,5-diiodoheptane, 1,6-diiodoheptane, 1,

[0033] 7-diiodoheptane, 1,2-diiodooctane, 1,3-diiodooctane, 1,4-diiodooctane, 1,

[0034] 2-dibromopropane, 1,2-dibromobutane, 1,3-dibromobutane, 1,2-dibromopentane, 1,

[0035] 3-dibromopentane, 1,4-dibromopentane, 1,2-dibromohexane, 1,3-dibromohexane, 1,

[0036] 4-dibromohexane, 1,5-dibromohexane, 1,6-dibromohexane, 1,2-dibromoheptane, 1,

[0037] 3-dibromoheptane, 1,4-dibromoheptane, 1,5-dibromoheptane, 1,6-dibromoheptane, 1,

[0038] 7-dibromoheptane, 1,2-dibromooctane, 1,3-dibromooctane, 1,4-dibromooctane, 1,

[0039] 5-dibromooctane, 1,6-dibromooctane, 1,7-dibromooctane, 1,8-dibromooctane, 1,

[0040] 2-dibromononane, 1,3-dibromononane, 1,4-dibromononane, 1,5-dibromononane, 1,

[0041] 6-dibromononane, 1,7-dibromononane, 1,8-dibromononane, 1,9-dibromononane, 1,

[0042] 2-dibromodecane, 1,3-dibromodecane, 1,4-dibromodecane, 1,5-dibromodecane, 1,

[0043] 6-dibromodecane, 1,7-dibromodecane, 1,8-dibromodecane, 1,9-dibromodecane, 1,

[0044] 6-dibromodecane, 1,7-dibromodecane, 1,8-dibromodecane, 1,9-dibromodecane, 1,

[0045] 10-dibromodecane; 1,2-difluoroethane, 1,2-difluoropropane, 1,3-difluoropropane, 1,

[0046] 2-difluorobutane, 1,3-difluorobutane, 1,4-difluorobutane, 1,2-difluoropentane, 1,

[0047] 3-difluoropentane, 1,4-difluoropentane, 1,5-difluoropentane, 1,2-difluorohexane, 1,

[0048] 3-difluorohexane, 1,4-difluorohexane, 1,5-difluorohexane, 1,6-difluorohexane, 1,

[0049] 2-difluoroheptane, 1,3-difluoroheptane, 1,4-difluoroheptane, 1,5-difluoroheptane, 1,

[0050] 6-difluoroheptane, 1,7-difluoroheptane, 1,2-difluorooctane, 1,3-difluorooctane, 1,

[0051] 4-difluorooctane, 1,5-difluorooctane, 1,6-difluorooctane, 1,7-difluorooctane, 1,

[0052] 8-difluorooctane, 1,2-difluorononane, 1,3-difluorononane, 1,4-difluorononane, 1,5- difluorononane, 1,6-difluorononane, 1,7-difluorononane, 1,8-difluorononane, 1,9- difluorononane, 1,2-difluorodecane, 1,3-difluorodecane, 1,4-difluorodecane, 1,5- difluorodecane, 1,6-difluorodecane, 1,7-difluorodecane, 1,8-difluorodecane, 1,9- difluorodecane, or 1,10-difluorodecane.

[0053] More preferably, the dihaloalkane is selected from 1,6 dibromohexane, 1,7- dibromoheptane, 1,8-dibromo octane, 1,9-dibromo nonane or 1,10-dibromo decane.

[0054] As a preference, the sulfonic acid group monomer is selected from one or more of 2-acrylamido-2-methylpropane sulfonic acid, 2-acrylamidododecane sulfonic acid, 2- acryloyloxy-2-methylpropane sulfonic acid, acryloyloxybutyl sulfonic acid, 2- acrylamidotetradecane sulfonic acid, and N-methyldiallylpropane sulfonic acid.

[0055] More preferably, the sulfonic acid group monomer is selected from 2-acrylamido-2- methylpropane sulfonic acid or 2-acrylamidododecane sulfonic acid.

[0056] The present application finds that when the molecular structure contains the above carbon-carbon long chain and sulfonic acid group, the thermal stability and water solubility of the crosslinked polymer can be further improved.

[0057] As a preference, the acrylamide monomer is a monomer having a secondary amine group; more preferably, the acrylamide monomer is selected from one or more of N-(3- dimethylaminopropyl) methacrylamide, N-(2-hydroxyethyl)-2-methyl-2-acrylamide, N- isopropyl methacrylamide, N-methyl acrylamide, and N-hydroxymethyl acrylamide.

[0058] The present application finds that the acrylamide monomer side chain contains a certain amount of methyl or hydroxyl, which helps to increase the steric hindrance of the polymer, thereby further improving the salt resistance.

[0059] As preferred, the amount of the second crosslinking agent is 0.01-0.05wt% of the total mass of the sulfonic acid monomer and the acrylamide monomer.

[0060] As preferred, the amount of the first crosslinking agent is 0.01-0.05wt% of the total mass of the sulfonic acid monomer and the acrylamide monomer.

[0061] As preferred, the mass ratio of the first crosslinking agent to the second crosslinking agent is (0.7-1.5):1.

[0062] As preferred, the mass ratio of the sulfonic acid monomer to the acrylamide monomer is 1-5:1-5.

[0063] As preferred, the preparation method of the crosslinked polymer comprises the following steps:

[0064] S1: mixing the sulfonic acid monomer, the acrylamide monomer and water to obtain an aqueous phase;

[0065] S2: adding a basic substance to the aqueous phase to adjust the pH of the aqueous phase to 7-8;

[0066] S3: mixing white oil, an emulsifier and the first crosslinking agent to obtain an oil phase;

[0067] S4: mixing the aqueous phase and the oil phase to obtain an emulsion;

[0068] S5: mixing the emulsion with an initiator under a nitrogen atmosphere and at a temperature of 30-80℃ to obtain a reaction liquid;

[0069] S6: mixing the reaction liquid with the second crosslinking agent to obtain a product, which is the crosslinked polymer.

[0070] As preferred, in the S1, the mass ratio of the total mass of the sulfonic acid monomer and the acrylamide monomer to the mass of the water is (0.5-1.5):1.

[0071] As preferred, in the S2, the basic substance can be an inorganic base and / or an alkaline inorganic salt, the metal element in the inorganic base and / or the alkaline inorganic salt is selected from one or more of monovalent, divalent, trivalent and tetravalent metals, and is further specifically selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, magnesium hydroxide, magnesium carbonate, calcium carbonate, calcium hydroxide, iron hydroxide, copper hydroxide, titanium hydroxide, zirconium hydroxide, etc., and preferably one or more of sodium hydroxide and potassium hydroxide.

[0072] As preferred, in the S3, the white oil is an industrial white oil; preferably the industrial white oil is selected from one or more of No. 3 industrial white oil, No. 5 industrial white oil, No. 7 industrial white oil, No. 10 industrial white oil, No. 15 industrial white oil, No. 20 industrial white oil, No. 22 industrial white oil, No. 26 industrial white oil, No. 32 industrial white oil, No. 48 industrial white oil and No. 64 industrial white oil.

[0073] More preferably, the mass ratio of the white oil to the water in S1 is (0.8-1.5):1.

[0074] As preferred, in the S3, the emulsifier is selected from one or more of op10, span80 and tween60.

[0075] More preferably, the emulsifier is a composite emulsifier of span80 and op10 with a mass ratio of (4-10):1; or,

[0076] the emulsifier is a composite emulsifier of span80 and tween60 with a mass ratio of (4-10):1.

[0077] Further preferably, the amount of the emulsifier is 2-10% of the total mass of the sulfonic monomer and the acrylamide monomer.

[0078] In the specific implementation, for the mixing operation mentioned above, those skilled in the art can make the mixing uniform based on the prior art and the conventional technical ability in the art.

[0079] As preferred, in the S4, the stirring rate is controlled at 150-400 rpm when the oil phase and the water phase are mixed.

[0080] As preferred, in the S5, the initiator is selected from a persulfate and / or an azo compound; the persulfate is selected from one or more of potassium persulfate, sodium persulfate and ammonium persulfate; the azo compound is selected from one or more of azobisisobutyronitrile, azobisisoheptyl nitrile, azobisisobutyramidine hydrochloride and azobisisobutylimidazoline hydrochloride.

[0081] More preferably, the amount of the initiator is 0.5-5‰ of the total mass of the sulfonic monomer and the acrylamide monomer.

[0082] As preferred, in the S5, the temperature of the reaction is 40-70℃.

[0083] As preferred, in the S5, the time of the reaction is 1-6h.

[0084] As preferred, in the S6, the time of the reaction is 0.5-2h.

[0085] In a third aspect, the present application provides use of the crosslinked polymer in a drilling fluid or a completion fluid.

[0086] In the present application, the crosslinked polymer can be used in oilfield polymers for viscosity increase, viscosity increase, drilling and completion, and in the fields of water treatment, papermaking industry, fiber industry, coating industry, water-absorbing materials, printing and dyeing auxiliaries, biological medicine, etc.

[0087] As a preferred, the crosslinked polymer is used as a viscosity increasing agent.

[0088] As a preferred, the crosslinked polymer is used as a viscosity increasing agent.

[0089] As a preferred, the crosslinked polymer is used as a viscosity increasing agent.

[0090] In a fourth aspect, the present application provides a drilling fluid containing the crosslinked polymer described above.

[0091] In a fifth aspect, the present application provides a completion fluid containing the crosslinked polymer described above.

[0092] Based on the above technical solution, the present application has the following advantages:

[0093] The present application can significantly improve the viscosity retention rate of the crosslinked polymer at high temperature by optimizing the crosslinking system, and can enhance the salt resistance (resistance to NaCl saturation, resistance to CaCl2 saturation), and also has good shear force. DETAILED DESCRIPTION

[0094] In order to make the purpose, technical scheme and advantages of the present application more clear, the technical scheme in the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0095] Unless otherwise specified, the various raw materials used in the examples are commercially available conventional raw materials, and the technical means used is conventional means known to those skilled in the art.

[0096] Example 1

[0097] The present embodiment provides a crosslinked polymer, the structural formula of which is as follows:

[0098]

[0099] The present embodiment further provides a preparation method of the crosslinked polymer described above, comprising the following steps:

[0100] Into a flask, 20 g of 2-acrylamido-2-methylpropanesulfonic acid, 20 g of N-(2- hydroxyethyl)-2-methyl-2-acrylamide, 70 g of water were added, and stirred well to obtain a water phase. Into the water phase, 3.9 g of NaOH was added to adjust the pH to 7. 65 g of 7 # Into a beaker, 0.66 g of Span80, 0.14 g of Tween60, 0.004 g of 1,4-divinylbenzene were added, and stirred well to obtain an oil phase. Then the oil phase was added into the flask to mix with the water phase, and stirred well for 30 min to obtain an emulsion. 0.04 g of potassium persulfate was completely dissolved in 10 g of water, and the emulsion was mixed with the potassium persulfate aqueous solution to react under the condition of nitrogen atmosphere and 40°C to obtain a reaction liquid. After 2 h of reaction, 0.004 g of 1,6 dibromohexane was added into the reaction liquid, and the reaction was continued for 2 h, and then the reaction was stopped. The obtained product was a crosslinked polymer.

[0101] Example 2

[0102] This example provides a crosslinked polymer, and the structural formula is as follows:

[0103]

[0104] This example further provides a preparation method of the crosslinked polymer, and the method comprises the following steps:

[0105] Into a flask, 10 g of 2-acrylamidododecane sulfonic acid, 20 g of methacrylamide, 40 g of water were added, and stirred well to obtain a water phase. Into the water phase, 1.76 g of KOH was added to adjust the pH to 7. 50 g of 7 # Into a beaker, 1.3 g of Span80, 0.2 g of Tween60, 0.009 g of 1,4-divinylbenzene were added, and stirred well to obtain an oil phase. Then the oil phase was added into the flask to mix with the water phase, and stirred well for 30 min to obtain an emulsion. 0.06 g of ammonium persulfate was completely dissolved in 10 g of water, and the emulsion was mixed with the ammonium persulfate aqueous solution to react under the condition of nitrogen atmosphere and 50°C to obtain a reaction liquid. After 3 h of reaction, 0.006 g of 1,6 dibromoheptane was added into the reaction liquid, and the reaction was continued for 0.5 h, and then the reaction was stopped. The obtained product was a crosslinked polymer.

[0106] Example 3

[0107] This example provides a crosslinked polymer, and the structural formula is as follows:

[0108]

[0109] The embodiment further provides a preparation method of the cross-linked polymer, comprising the following steps:

[0110] In a flask, 25 g of 2-acrylamidyl dodecyl sulfonic acid, 5 g of methacrylamide, 20 g of water are added, and the solution is fully stirred to be uniform to obtain an aqueous phase. 4.4 g of KOH is added to the aqueous phase, and the pH is adjusted to 7. 30 g of 7 # White oil is added to a beaker, 1.35 g of Span80, 0.15 g of Tween60, 0.015 g of 1,4-divinylbenzene are added, and the mixture is fully stirred to be uniform to obtain an oil phase. Then the oil phase is added to the flask, mixed with the aqueous phase, and fully stirred for 30 min to obtain an emulsion. 0.06 g of azobisdimethylamidinum hydrochloride is completely dissolved in 10 g of water, and the emulsion is mixed with the azobisdimethylamidinum hydrochloride aqueous solution under a nitrogen atmosphere at 60°C to obtain a reaction solution. After 6 h of reaction, 0.015 g of 1,6 dibromo octane is added to the reaction solution, and the reaction is continued for 2 h, and then the reaction is stopped. The obtained product is a cross-linked polymer.

[0111] Example 4

[0112] The embodiment provides a cross-linked polymer, which has the same structural formula as that of Example 1, and a preparation method thereof, comprising the following steps:

[0113] In a flask, 10 g of 2-acrylamidyl-2-methylpropanesulfonic acid, 30 g of N-(2-hydroxyethyl)-2-methyl-2-acrylamide, 90 g of water are added, and the solution is fully stirred to be uniform to obtain an aqueous phase. 1.95 g of NaOH is added to the aqueous phase, and the pH is adjusted to 7. 80 g of 7 # White oil is added to a beaker, 0.66 g of Span80, 0.14 g of Tween60, 0.003 g of 1,4-divinylbenzene are added, and the mixture is fully stirred to be uniform to obtain an oil phase. Then the oil phase is added to the flask, mixed with the aqueous phase, and fully stirred for 30 min to obtain an emulsion. 0.04 g of potassium persulfate is completely dissolved in 10 g of water, and the emulsion is mixed with the potassium persulfate aqueous solution under a nitrogen atmosphere at 50°C to obtain a reaction solution. After 1 h of reaction, 0.004 g of 1,6 dibromo hexane is added to the reaction solution, and the reaction is continued for 2 h, and then the reaction is stopped. The obtained product is a cross-linked polymer.

[0114] Example 5

[0115] The embodiment provides a cross-linked polymer, which has the same structural formula and preparation method as those of Example 1, and the only difference is that the mass ratio of the first cross-linking agent to the second cross-linking agent is 2:1.

[0116] Comparative Example 1

[0117] This comparative example provides a crosslinked polymer, the structural formula and preparation method of which are the same as those of Example 1, the only difference being that the first crosslinking agent is replaced by an equal amount of N,N-methylenebisacrylamide.

[0118] Comparative Example 2

[0119] This comparative example provides a crosslinked polymer, the structural formula and preparation method of which are the same as those of Example 1, the only difference being that the second crosslinking agent is replaced by an equal amount of the first crosslinking agent.

[0120] In order to further illustrate the technical effects of the present application, the effect tests of the above examples and comparative examples in actual application are also given.

[0121] Test Example

[0122] 1. Viscosity and temperature resistance test

[0123] Preparation of polymer solution: 3.5 g of the crosslinked polymer prepared in the examples and comparative examples was added to 350 mL of deionized water, and stirred at 8000 r / min for 20 min to obtain a polymer solution sample.

[0124] Performance test: The apparent viscosity of the polymer solution was determined at room temperature by a six-speed viscometer according to the method specified in the national standard GB / T 16783.1-2006. After the determination, the polymer solution was transferred to a high-temperature roller oven and aged at 180℃ for 16 h. After the aging was completed, the solution temperature was reduced to room temperature, and then the polymer solution was stirred at 8000 r / min for 20 min to determine the apparent viscosity of the aged polymer solution. The apparent viscosity data before and after aging are shown in Table 1.

[0125] Table 1. Viscosity and temperature resistance test results of polymers

[0126]

[0127] 2. Salt resistance test

[0128] Preparation of polymer saturated salt solution: Under stirring at room temperature, NaCl was continuously added to 350 mL of deionized water until the solution could no longer dissolve NaCl, and a saturated NaCl solution was obtained. 3.5 mL of the polymer sample was added to 350 mL of the saturated NaCl solution, and stirred at 8000 r / min for 20 min to obtain a polymer saturated NaCl solution. The preparation method of the polymer saturated CaCl2 solution is the same as that of the polymer saturated NaCl solution.

[0129] Performance test: The apparent viscosity of polymer solution was measured at room temperature by six-speed viscometer according to the method specified in GB / T 16783.1-2006. After the measurement, the polymer solution was transferred to a high-temperature roller oven and aged at 180℃ for 16h. After the aging, the apparent viscosity of the polymer solution after aging was measured after the solution temperature was reduced to room temperature and stirred at 8000r / min for 20min. The apparent viscosity data of the polymer saturated NaCl solution and the polymer saturated CaCl2 solution before and after aging are listed in Table 2 and Table 3, respectively.

[0130] Table 2 Polymer anti-NaCl performance test results

[0131]

[0132] Table 3 Polymer anti-CaCl2 performance test results

[0133]

[0134]

[0135] As can be seen from the data in Tables 1-3, the crosslinked polymer prepared in the present application has excellent tackifying, salt-resistant and gel strength-improving properties, and still has a high viscosity retention rate after aging at 180℃ for 16h. The polymer can maintain good tackifying properties in saturated salt solution, and the apparent viscosity of the solution after aging is much higher than that in the comparative examples. In addition, the shear force of the polymer aqueous solution remains at a high level before and after aging, indicating that the crosslinked polymer prepared in the present application has good proppant-carrying properties.

[0136] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A crosslinked polymer, characterized in that, The crosslinked polymer includes sulfonic acid structural units, acrylamide structural units, a first crosslinking unit, and a second crosslinking unit; Wherein, the first crosslinking unit is The second crosslinking unit is C6~C 25 Straight-chain alkyl groups; Based on the total weight of the crosslinked polymer, the content of the second crosslinking unit is 0.01wt%~0.05wt%; the content of the sulfonic acid structural unit is 30wt%~60wt%; the content of the acrylamide structural unit is 40wt%~80wt%; and the content of the first crosslinking unit is 0.01wt%~0.05wt%.

2. The crosslinked polymer according to claim 1, characterized in that, The second crosslinking unit is C6~C 10 Straight-chain alkyl groups.

3. The crosslinked polymer according to claim 1 or 2, characterized in that, The total mass ratio of the sulfonic acid structural unit and the acrylamide structural unit to the second crosslinking unit is 5000~10000:1~5.

4. The crosslinked polymer according to claim 1 or 2, characterized in that, The sulfonic acid structural unit comprises one or more of 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-dodecylsulfonic acid, 2-acryloyloxy-2-methylpropanesulfonic acid, acryloyloxy-butylsulfonic acid, 2-acrylamido-tetradecanesulfonic acid, and N-methyldiallylpropanesulfonic acid; and / or The acrylamide structural unit includes one or more of N-(3-dimethylaminopropyl)methacrylamide, N-(2-hydroxyethyl)-2-methyl-2-acrylamide, N-isopropylmethacrylamide, N-methylacrylamide, and N-hydroxymethylacrylamide.

5. The crosslinked polymer according to claim 3, characterized in that, The sulfonic acid structural unit comprises one or more of 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-dodecylsulfonic acid, 2-acryloyloxy-2-methylpropanesulfonic acid, acryloyloxy-butylsulfonic acid, 2-acrylamido-tetradecanesulfonic acid, and N-methyldiallylpropanesulfonic acid; and / or The acrylamide structural unit includes one or more of N-(3-dimethylaminopropyl)methacrylamide, N-(2-hydroxyethyl)-2-methyl-2-acrylamide, N-isopropylmethacrylamide, N-methylacrylamide, and N-hydroxymethylacrylamide.

6. The crosslinked polymer according to claim 1, characterized in that, The crosslinked polymer is selected from one of the following structures: （I）； (II); Wherein, n represents the number of carbon atoms, 6≤n≤25; and R is selected from -H, -CH2CH2CH2N(CH3)2, -CH2CH2OH, -(CH3)2 or -CH2OH.

7. The crosslinked polymer according to claim 6, characterized in that, The degree of polymerization of the cross-linked polymer is 50,000 to 500,000.

8. The method for preparing the crosslinked polymer according to any one of claims 1 to 7, characterized in that, The crosslinked polymer was prepared by using sulfonic acid monomers and acrylamide monomers as raw materials through a two-stage crosslinking process. The first crosslinking agent used in the primary crosslinking is 1,4-divinylbenzene; the second crosslinking agent used in the secondary crosslinking is a dihaloalkane.

9. The method for preparing the crosslinked polymer according to claim 8, characterized in that, The second crosslinking agent is selected from 1,6-dibromohexane, 1,7-dibromoheptane, 1,8-dibromooctane, 1,9-dibromononane, or 1,10-dibromodecane.

10. The method for preparing the crosslinked polymer according to claim 8, characterized in that, The sulfonic acid monomer is selected from one or more of 2-acrylamido-2-methylpropanesulfonic acid and 2-acrylamido-dodecyl sulfonic acid; and / or The acrylamide monomers are monomers with secondary amine groups.

11. The method for preparing the crosslinked polymer according to claim 10, characterized in that, The acrylamide monomer is selected from one or more of N-(3-dimethylaminopropyl)methacrylamide, N-(2-hydroxyethyl)-2-methyl-2-acrylamide, N-isopropylmethacrylamide, N-methylacrylamide, and N-hydroxymethylacrylamide.

12. The method for preparing the crosslinked polymer according to any one of claims 8 to 11, characterized in that, The mass ratio of the first crosslinking agent to the second crosslinking agent is (0.7~1.5):

1.

13. The method for preparing the crosslinked polymer according to any one of claims 8 to 11, characterized in that, The mass ratio of the sulfonic acid monomer to the acrylamide monomer is 1~5:1~5.

14. The method for preparing the crosslinked polymer according to any one of claims 8 to 11, characterized in that, include: S1: Sulfonic acid monomers, acrylamide monomers and water are mixed to obtain an aqueous phase; S2: Add an alkaline substance to the aqueous phase to adjust the pH of the aqueous phase to 7-8; S3: Mix white oil, emulsifier and first crosslinking agent to obtain oil phase; S4: Mix the aqueous phase and the oil phase to obtain an emulsion; S5: The emulsion is mixed with an initiator and reacted under a nitrogen atmosphere and at a temperature of 30°C to 80°C to obtain a reaction solution; S6: The reaction solution is mixed with the second crosslinking agent and reacted to obtain the crosslinked polymer.

15. The method for preparing the crosslinked polymer according to claim 14, characterized in that, In S1, the total mass ratio of the sulfonic acid monomer and the acrylamide monomer to the mass ratio of water is (0.5~1.5):

1.

16. The method for preparing the crosslinked polymer according to claim 14, characterized in that, In S3, the white oil is industrial white oil.

17. The method for preparing the crosslinked polymer according to claim 16, characterized in that, The industrial white oil is selected from one or more of the following: No. 3 industrial white oil, No. 5 industrial white oil, No. 7 industrial white oil, No. 10 industrial white oil, No. 15 industrial white oil, No. 20 industrial white oil, No. 22 industrial white oil, No. 26 industrial white oil, No. 32 industrial white oil, No. 48 industrial white oil, and No. 64 industrial white oil.

18. The method for preparing the crosslinked polymer according to claim 14, characterized in that, The mass ratio of the white oil to the water in S1 is (0.8~1.5):

1.

19. The method for preparing the crosslinked polymer according to claim 14, characterized in that, In S3, the emulsifier is selected from one or more of OP10, Span80, and Tween60.

20. The method for preparing the crosslinked polymer according to claim 19, characterized in that, The emulsifier is a composite emulsifier of span80 and op10 in a mass ratio of (4~10):1; or, the emulsifier is a composite emulsifier of span80 and tween60 in a mass ratio of (4~10):

1.

21. The method for preparing the crosslinked polymer according to claim 19, characterized in that, The amount of emulsifier used is 2wt% to 10wt% of the total mass of sulfonic acid monomers and acrylamide monomers.

22. The method for preparing the crosslinked polymer according to claim 14, characterized in that, In S5, the initiator is selected from persulfates and / or azo compounds; the persulfate is selected from one or more of potassium persulfate, sodium persulfate, and ammonium persulfate; the azo compound is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisobutyramidine hydrochloride, and azobisisobutyramidoline hydrochloride.

23. The method for preparing the crosslinked polymer according to claim 22, characterized in that, The amount of the initiator is 0.5 wt‰ to 5 wt‰ of the total mass of the sulfonic acid monomer and the acrylamide monomer.

24. The use of the crosslinked polymer according to any one of claims 1 to 7 or the crosslinked polymer prepared by any one of claims 8 to 23 in drilling fluid or completion fluid.

25. The application according to claim 24, characterized in that, The crosslinked polymer is used as a thickener.

26. The application according to claim 25, characterized in that, When used as a thickener, the crosslinked polymer is used in drilling or completion fluids at a concentration of 3 g / L to 30 g / L.

27. A drilling fluid, characterized in that, It contains the crosslinked polymer of any one of claims 1 to 7 or the crosslinked polymer prepared by any one of claims 8 to 23.

28. A completion fluid, characterized in that, It contains the crosslinked polymer of any one of claims 1 to 7 or the crosslinked polymer prepared by any one of claims 8 to 23.

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