A seawater-based polymer-coated self-suspending proppant, its preparation method and application

Abstract

The present invention provides a seawater-based polymer-coated self-suspending proppant and its preparation method and application, which belong to the technical field of oilfield fracturing and exploitation. The proppant of the present invention is prepared from the following raw materials: proppant, silane coupling agent γ-methacryloyloxypropyltrimethoxysilane, acrylamide, hydrophobic monomer hexadecyldimethylallyl ammonium chloride, twin-tailed betaine monomer, sodium styrene sulfonate, initiator, and solvent. The self-suspending proppant of the present invention and non-ionic surfactant are compounded and used in fracturing fluid. On the one hand, the polymer on the surface of the proppant of the present invention has good salt resistance and dissolves after encountering seawater, thereby increasing its viscosity; on the other hand, the surfactant and the dissolved polymer coating produce a synergistic effect to achieve a viscosity-increasing effect. The same sand suspension effect as the viscosity-increasing effect of normal fracturing fluid is produced to meet the requirements of low-permeability seawater fracturing.

Description

Technical Field

[0001] This invention belongs to the field of oilfield fracturing technology, specifically relating to a seawater-based polymer-coated self-suspending proppant, its preparation method, and its application. Background Technology

[0002] As onshore oilfield development expands and recoverable reserves dwindle, research has increasingly shifted to offshore oilfields. Hydraulic fracturing, a key reservoir stimulation technology, has been widely used in the development of low-permeability oil and gas. Its main mechanism involves injecting fracturing fluid into the reservoir using a surface high-pressure pump at a rate exceeding the reservoir's absorption capacity. This creates artificial fractures in the wellbore under high pressure. Propane-laden fluid is then injected into these fractures to support them, forming several highly conductive channels for oil and gas migration, thereby increasing production and injection.

[0003] Proppants are key materials in hydraulic fracturing operations. They support fracturing fractures, preventing them from closing due to stress release, thus maintaining unobstructed oil and gas channels, improving conductivity, and increasing recovery rates. Current research indicates that the selection and performance of proppants directly affect the fracturing effect and economic benefits in offshore oilfield fracturing operations. Commonly used proppants in oilfields include artificial ceramic aggregates and quartz sand. While these are low-cost, they tend to settle easily in offshore fracturing operations, making it difficult to reach the distal fracture ends and provide effective support. To improve the suspension performance of proppants and enable them to migrate deep into formation fractures, self-suspension proppants with low settling velocity and good support effect have been developed. Self-suspension proppants consist of a polymer coating on the proppant surface. This coating rapidly disperses and swells in water, forming a polymer solution of a certain viscosity that effectively suspends the proppant. However, self-suspension proppant systems primarily use freshwater for preparation, which faces the following problems in offshore fracturing engineering applications: First, using freshwater leads to high development costs; second, although seawater can save water resources and reduce costs, seawater has high salinity and is rich in sodium. + K + Ca 2+ Mg 2+ High concentrations of metal ions can trigger conformational changes in the polymer coating layer, causing the polymer chain segments to curl up by compressing the electric double layer, reducing its performance, resulting in poor self-suspension ability, and failing to meet the requirements of offshore fracturing.

[0004] Chinese patent document CN 109423271 A discloses a bulk-expanding magnetic self-suspending proppant and its preparation method. The proppant is a silane coupling agent-modified magnetic proppant aggregate grafted with an aqueous bulk-expanding polymer material. The method includes: spraying a silane coupling agent solution onto the surface of the proppant aggregate, causing a first reaction to obtain the coupling agent-modified magnetic proppant aggregate; and spraying an emulsion of the aqueous bulk-expanding polymer material onto the silane coupling agent-modified magnetic proppant aggregate, causing a second reaction to obtain the bulk-expanding magnetic self-suspending proppant. The magnetic self-suspending proppant of this invention has good self-suspending function and good magnetic induction. However, the salt resistance of the proppant obtained by this invention needs improvement and cannot meet the requirements of offshore fracturing.

[0005] Therefore, for offshore low-permeability oil fields, it is urgent to develop new proppants that not only have excellent suspension properties but also meet higher salt tolerance requirements, thereby overcoming the shortcomings of existing technologies. This is of great significance for the efficient development of offshore low-permeability oil fields. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a seawater-based polymer-coated self-suspending proppant, its preparation method, and its applications. This invention first coats the proppant surface with a polymer layer. The polymer coating layer consists of a silane coupling agent KH570, acrylamide (AM), and a hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride (C). 16 This invention utilizes a self-suspending proppant and a nonionic surfactant in combination for use in fracturing fluids. On one hand, the polymer on the proppant surface exhibits good salt resistance, dissolving upon contact with seawater and increasing its viscosity. On the other hand, the surfactant synergistically interacts with the dissolved polymer coating, resulting in a thickening effect. Similar to the thickening effect of normal fracturing fluids, it produces a sand-suspending effect, meeting the requirements of low-permeability fracturing in seawater.

[0007] The technical solutions of the present invention are as follows:

[0008] This invention provides a seawater-based polymer-coated self-suspending proppant, prepared from the following raw materials: proppant, silane coupling agent γ-methacryloyloxypropyltrimethoxysilane (KH570), acrylamide (AM), and hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride (C 16 DMAAC), DSDAP (dimethyl betaine monomer), sodium styrene sulfonate (SSS), initiator, solvent.

[0009] According to a preferred embodiment of the present invention, the preparation method of diglycinate monomer (DSDAP) includes the following steps:

[0010] (1) Dissolve (2-bromomethyl)dimethylamine, sodium methanesulfonate and potassium carbonate in N,N-dimethylformamide (DMF), heat and reflux the reaction, and then post-process to obtain 3-(dimethylamino)propane-1-sulfonate (SDAP).

[0011] (2) Dissolve 3-(dimethylamino)propane-1-sulfonate (SDAP) in anhydrous ethanol, add anhydrous ethanol solution of 1,4-dichloro-2-butene (DB) dropwise, heat and reflux the reaction, and then post-process to obtain twin betaine monomer (DSDAP).

[0012] Preferably, in step (1), the mass ratio of (2-bromomethyl)dimethylamine, sodium methanesulfonate, and potassium carbonate is 1:1.0-1.6:2, and more preferably 1:1.03:2.

[0013] Preferably, in step (1), the mass ratio of (2-bromomethyl)dimethylamine to the volume ratio of DMF is 1:1-10 g / mL, and more preferably 1:2.2 g / mL.

[0014] Preferably, in step (1), the reflux reaction temperature is 60-80℃ and the reaction time is 6-12h, preferably 80℃ and 8h. The reflux reaction is carried out under stirring conditions.

[0015] Preferably, in step (1), the post-treatment method includes the following steps: the reaction solution is cooled to room temperature, DMF is removed by vacuum distillation, the viscous residue after vacuum distillation is dissolved in ethanol, heated to 50°C and stirred for 5-10 min, deionized water is added, the mixture is shaken and allowed to stand for separation, and the aqueous phase is discarded; the organic phase is dried with anhydrous sodium sulfate, filtered and then rotary evaporated; then it is added to a silica gel column, the eluent is a mixture of ethyl acetate and methanol, wherein the volume ratio of ethyl acetate to methanol is 9:1, the target fraction is collected, the solvent is removed by rotary evaporation to obtain a white solid, which is 3-(dimethylamino)propane-1-sulfonate.

[0016] Preferably, in step (2), the mass ratio of 3-(dimethylamino)propane-1-sulfonate (SDAP) to 1,4-dichloro-2-butene (DB) is 1.7-3.1:1.0, and more preferably 2.6:1.0.

[0017] Preferably, in step (2), the mass ratio of 3-(dimethylamino)propane-1-sulfonate (SDAP) to the volume ratio of anhydrous ethanol is 0.5-2 g / mL.

[0018] Preferably, in step (2), the mass concentration of the anhydrous ethanol solution of 1,4-dichloro-2-butene (DB) is 0.1-1 g / mL; the dropping rate of the anhydrous ethanol solution of 1,4-dichloro-2-butene (DB) is 1-5 drops per second; and the dropping of the anhydrous ethanol solution of 1,4-dichloro-2-butene (DB) is carried out under stirring and at 40-70°C.

[0019] Preferably, in step (2), the reflux reaction temperature is 40-70℃ and the reaction time is 12-20h, preferably 65℃ and 18h. The reflux reaction is carried out under stirring conditions.

[0020] Preferably, in step (2), the post-processing method includes the following steps: the reaction solution is distilled under reduced pressure, the obtained product is dissolved in acetone, cooled and crystallized, washed with acetone, filtered, and dried to obtain the twin betaine monomer (DSDAP).

[0021] According to a preferred embodiment of the present invention, the diglycinate monomer (DSDAP) has the structure shown in Formula I:

[0022] According to a preferred embodiment of the present invention, the proppant is selected from quartz sand or ceramsite.

[0023] According to a preferred embodiment of the present invention, the initiator includes a chain extender, an oxidant, a reducing agent, and an initiation catalyst.

[0024] Preferably, the chain extender is an aqueous solution of a polyamine, wherein the polyamine is tetramethylethylenediamine or dimethylethylenediamine, preferably tetramethylethylenediamine. The mass concentration of the chain extender is 0.02-0.16%, preferably 0.08%.

[0025] Preferably, the oxidant is an aqueous solution of potassium persulfate, and the reducing agent is an aqueous solution of sodium bisulfite. The mass concentration of both the aqueous solution of potassium persulfate and the aqueous solution of sodium bisulfite is 0.005-0.009%, preferably 0.007%.

[0026] Preferably, the initiating catalyst is an aqueous solution of ferric chloride, and the mass concentration of the aqueous solution of ferric chloride is 0.0005-0.00225%, preferably 0.00125%.

[0027] According to a preferred embodiment of the present invention, the solvent is distilled water.

[0028] According to a preferred embodiment of the present invention, acrylamide (AM) and the hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride (C) are used. 16 The mass ratio of DMAAC, dimethicone monomer (DSDAP), and sodium styrene sulfonate (SSS) is 5-6:0.3-0.5:4-5:1, preferably 5.8:0.33:4.19:1.

[0029] According to a preferred embodiment of the present invention, the mass ratio of the proppant, the silane coupling agent γ-methacryloyloxypropyltrimethoxysilane (KH570), and the acrylamide (AM) is 100-500:1:0.5-4, preferably 100:1:0.64.

[0030] According to a preferred embodiment of the present invention, acrylamide (AM) and the hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride (C) are used. 16 The total mass percentage of DMAAC, disaccharide betaine monomer (DSDAP), and sodium styrene sulfonate (SSS) to the solvent is 15%-30%, preferably 25%.

[0031] According to a preferred embodiment of the present invention, the mass ratio of initiator to acrylamide (AM) is 1:0.1-0.5, preferably 1:0.128.

[0032] According to a preferred embodiment of the present invention, the particle size of the seawater-based polymer-coated self-suspending proppant is 550 μm-600 μm; the structural schematic is shown below:

[0033]

[0034] The preparation method of the above-mentioned seawater-based polymer-coated self-suspending proppant includes the following steps:

[0035] (1) The proppant was washed with distilled water and organic solvent in sequence to remove organic and inorganic impurities on the surface of the proppant and dried; silane coupling agent γ-methacryloyloxypropyltrimethoxysilane (KH570) was added, soaked, and dried to obtain the pretreated proppant;

[0036] (2) Acrylamide (AM), hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride (C 16 DMAAC, DSDAP (dimethyl betaine monomer), and SSS (sodium styrene sulfonate) are dissolved in a solvent, and the pH of the system is adjusted. A pretreated proppant is added, and the mixture is fully dispersed. An initiator is added dropwise, and the mixture undergoes copolymerization. The resulting product is then dried, pulverized, and sieved to obtain a seawater-based polymer-coated self-suspending proppant.

[0037] According to a preferred embodiment of the present invention, in step (1), the organic solvent is selected from at least one of ethanol, acetone or petroleum ether.

[0038] According to a preferred embodiment of the present invention, in step (1), the soaking time is 3-8 hours, preferably 6 hours; the soaking temperature is 50-60°C, preferably 50°C; and the soaking is carried out under stirring conditions.

[0039] According to a preferred embodiment of the present invention, in step (2), the pH value of the system is adjusted to 7 using an aqueous sodium hydroxide solution with a mass concentration of 15%-30%.

[0040] According to a preferred embodiment of the present invention, in step (2), the initiator is added at a rate of 1-2 drops per second; the addition is carried out under stirring, protective gas protection, and at a temperature of 35-40°C. The protective gas is nitrogen or argon.

[0041] According to a preferred embodiment of the present invention, in step (2), the copolymerization reaction temperature is 35-40°C and the reaction time is 4-6 hours, preferably 35°C and 6 hours. The copolymerization reaction is carried out under stirring and a protective gas atmosphere. The protective gas is nitrogen or argon.

[0042] The above-mentioned seawater-based polymer-coated self-suspending proppant is applied to hydraulic fracturing in offshore low-permeability oil fields or high-salt, low-permeability oil fields.

[0043] According to a preferred embodiment of the present invention, the application method includes the steps of: fully dispersing a seawater-based polymer-coated self-suspending proppant and a nonionic surfactant in seawater or highly mineralized water to obtain a proppant-carrying fluid for use in hydraulic fracturing of low-permeability offshore oilfields or high-salt, low-permeability offshore oilfields.

[0044] Preferably, the nonionic surfactant is fatty alcohol polyoxyethylene ether AEO-3 or Span-80, with fatty alcohol polyoxyethylene ether AEO-3 being the most preferred.

[0045] Preferably, the mass ratio of the seawater-based polymer-coated self-suspending proppant to the nonionic surfactant is 40-60:1, and more preferably 50:1.

[0046] Preferably, the mass ratio of the seawater-based polymer-coated self-suspending proppant to the volume of seawater or highly mineralized water in the sand-carrying solution is 0.01-1 g / mL, and more preferably 0.15 g / mL.

[0047] Preferably, the mineralization of seawater is 35,000 mg / L; the mineralization of highly mineralized water is greater than 35,000 mg / L and less than or equal to 200,000 mg / L.

[0048] The technical features and beneficial effects of this invention are as follows:

[0049] (1) The self-suspended proppant of the present invention is used for hydraulic fracturing. It can achieve the goal of eliminating the need to add thickeners required for the preparation of proppant-carrying fluid in conventional fracturing processes. The polymer coating layer on the surface of the proppant dissolves in water or seawater. The proppant-carrying fluid after the polymer dissolves in water or seawater has viscoelasticity, increased fluid density, and increased viscosity, thereby promoting the deep migration of proppant, reducing the use of fracturing fluid chemicals such as slickwater, simplifying the fracturing process, and reducing fracturing costs.

[0050] (2) The polymer-coated self-suspending proppant provided by this invention has good salt resistance. This is attributed to the introduction of a molecular structure that imparts salt resistance into the proppant. On the one hand, the introduction of the hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride increases the hydrophobic groups on the polymer chain, enhances the hydrophobic association, and constructs supramolecular aggregates. These hydrophobic long chains intertwine to form a spatial network structure. This network structure has a stronger ability to encapsulate or adsorb water molecules, and the hydrodynamic volume of the polymer increases, resulting in increased viscosity. On the other hand, the twin-betaine monomer DSDAP contains a certain number of cationic and anionic groups. Its special molecular structure gives it a certain anti-polyelectrolyte effect. As the mineralization in the aqueous solution continues to increase, the mutual attraction between positive and negative ions will be shielded by salt ions, thereby enhancing the interaction between solvents, making the molecular structure more extended, and giving the polymer higher viscosity in seawater, exhibiting salt thickening properties. In addition, the sulfonic acid group has a strong hydration effect, which can resist the destructive effect of salt ions and increase the rigidity of the polymer chain.

[0051] (3) The polymer coating layer in the proppant of the present invention has active groups such as sulfonic acid group and quaternary ammonium cationic group after the micelles formed in seawater or water are broken, and contains nonionic surfactant. The broken liquid can reduce the interfacial tension and improve the oil displacement efficiency of the reservoir through the action of multiple active groups.

[0052] (4) The polymer-coated self-suspending proppant of this invention breaks through the traditional reliance on freshwater and significantly improves the suspension and transport capacity of the proppant by utilizing the excellent ionic environment of seawater, thereby reducing the consumption of freshwater for fracturing and providing a green solution with both economic and environmental benefits for the development of offshore low-permeability oil and gas resources.

[0053] (5) This invention introduces a new initiation system for the synthesis of polymer-coated self-suspending proppant. Based on the conventional redox initiation system, a highly efficient chain extender and initiation catalyst are introduced to form a highly efficient initiation system, significantly promoting the redox reaction rate, increasing free radical activity, and achieving high-efficiency initiation with low dosage. Compared with the conventional redox initiation system, the polymer-coated self-suspending proppant synthesized by this system results in higher viscosity and stronger suspension capacity of the sand-carrying liquid.

[0054] (6) The polymer-coated self-suspending proppant of this invention is compounded with a nonionic surfactant during use, and the two have a synergistic effect. When the amount of nonionic surfactant is small, the hydrophilic chain of the surfactant encapsulates the hydrophobic chain of the polymer, which breaks down the hydrophobic association between molecules and reduces the viscosity of the system. As the surfactant concentration is further increased, the hydrophobic chains of the surfactant and the hydrophobic chains of the polymer form mixed micelles. The mixed micelles encapsulate the hydrophobic segments on different molecular chains in the same micelle, which acts as a bridge. The polymer coating layer forms a large composite network structure through the bridging points, and the viscosity increases. When the surfactant concentration is too high, entanglement occurs between the micelles, the network structure continues to expand, and the viscosity increases accordingly. The self-suspending proppant is not easy to settle, so it can be transported to the far end of the crack to provide effective support. Attached Figure Description

[0055] Figure 1 This is a synthetic route diagram for the twin-betaine monomer (DSDAP) of the present invention;

[0056] Figure 2 This is a synthetic route diagram of the polymer-coated self-suspending proppant of the present invention;

[0057] Figure 3 The infrared spectrum of the pretreated proppant prepared in Example 1 of this invention;

[0058] Figure 4 The infrared spectrum is shown for the polymer-coated self-suspending support prepared in Example 1 of this invention. Detailed Implementation

[0059] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Example 1

[0060] A method for preparing a seawater-based polymer-coated self-suspending proppant:

[0061] 1. Synthesis of DSDAP, the monomer of twin-tailed betaine, via the following route: Figure 1 shown

[0062] (1) Dissolve 13.8 g of (2-bromomethyl)dimethylamine in 30 mL of DMF, then add 14.2 g of sodium methanesulfonate and 27.6 g of potassium carbonate, and stir until dissolved. Heat to 80 °C and reflux for 8 h. After the reaction is complete, cool to room temperature, remove DMF by vacuum distillation, dissolve the viscous residue after vacuum distillation in 20 mL of ethanol, heat to 50 °C and stir for 5 min, add 40 mL of deionized water, transfer to a separatory funnel, shake and allow to stand for separation, discard the aqueous phase. Dry the organic phase with anhydrous sodium sulfate, filter and then rotary evaporate. Then add the sample to a silica gel column (eluent: ethyl acetate / methanol volume ratio = 9:1), and collect the target fraction. Remove the solvent by rotary evaporation to obtain a white solid, which is 3-(dimethylamino)propane-1-sulfonate.

[0063] (2) Weigh 16.5 g of 3-(dimethylamino)propane-1-sulfonate (SDAP) and dissolve it in 30 mL of anhydrous ethanol. Then add it to a three-necked flask equipped with a thermometer, stirrer, and reflux condenser. Heat the flask to 65 °C. Dissolve 6.25 g of 1,4-dichloro-2-butene (DB) in 30 mL of anhydrous ethanol and place it in a constant pressure dropping funnel. Add the solution dropwise to the three-necked flask under stirring. The dropping rate of the anhydrous ethanol solution of 1,4-dichloro-2-butene (DB) is 2 drops per second. Heat the flask to reflux at 65 °C and stir for 18 h. After the reaction is complete, distill off the unreacted monomer and anhydrous ethanol under reduced pressure. Dissolve the product after reduced pressure distillation in 120 mL of acetone and then cool it in a refrigerator to crystallize. Wash the synthesized product three times with acetone, then filter it. Finally, dry the product in a vacuum drying oven to constant weight to obtain the twin-betaine monomer DSDAP.

[0064] 2. Synthesis of polymer-coated self-suspending proppant, the route is as follows: Figure 2 shown

[0065] (1) Wash the quartz sand (20-40 mesh) proppant several times with distilled water, ethanol and acetone in sequence to remove impurities on the surface of the quartz sand, and dry it; weigh 4 kg of quartz sand and add 40 g of silane coupling agent (KH570), soak and stir at 50 °C for 6 h, filter, and vacuum dry to obtain the pretreated proppant.

[0066] The infrared spectrum of the pretreated proppant is as follows: Figure 3 In the spectral curve of the pretreated proppant, 2840–2980 cm⁻¹ -1 The nearby peaks are characteristic of methyl and methylene groups, at 1781 cm⁻¹. -1 The peak at 960 cm⁻¹ represents the C=O vibrational peak in the coupling agent. -1 The absorption peak is due to the bending vibration of Si-OH, at 800 cm⁻¹. -1 The left and right sides are symmetrical contraction vibration peaks of Si-O-Si bonds; at 2300 cm⁻¹-1 The presence of a C=C characteristic peak indicates that the silane coupling agent has formed a chemical bond with the hydroxyl groups on the surface of the quartz sand, and the coupling agent has been successfully grafted onto the surface of the proppant.

[0067] (2) Weigh 25.60g of acrylamide (AM) and 1.48g of the hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride (C 16 DMAAC, 18.50g of dimethyl betaine monomer (DSDAP), and 4.42g of heat-resistant and salt-resistant sodium styrene sulfonate monomer (SSS) were added to 200g of distilled water and stirred thoroughly at 600r / min until completely dissolved. The pH of the system was adjusted to 7 with a 15% NaOH aqueous solution. The resulting solution was then added to a three-necked flask, and N2 was bubbled through the flask for 30min to remove oxygen from the system, thus obtaining the surface coating solution.

[0068] (3) Add the pretreated proppant to the surface coating liquid, disperse it fully, heat it to 35°C, and stir continuously. The reaction is always under N2 protection. Under stirring conditions, every 10 minutes, add the following solutions in sequence to the three-necked flask: a 0.08% tetramethylethylenediamine aqueous solution (0.04 g of tetramethylethylenediamine), a 0.007% potassium persulfate aqueous solution (0.0035 g of potassium persulfate), a 0.007% sodium bisulfite aqueous solution (0.0035 g of sodium bisulfite), and a 0.00125% ferric chloride aqueous solution (0.000625 g of ferric chloride). The dropping rate is 1 drop per second. After copolymerization and stirring at 35℃ for 6 hours, the polymer was removed, cut into small pieces, dried in an 80℃ drying oven to constant weight, then pulverized and sieved to obtain a polymer-coated self-suspending proppant with a particle size of 580μm.

[0069] Polymer-coated self-suspending proppant such as Figure 4 As shown. 3444 cm -1 and 1665 cm -1 There are two absorption peaks at 1588 cm⁻¹, corresponding to the stretching vibration absorption peaks of NH and C=O in acrylamide, respectively; -1 and 1450 cm -1 The characteristic absorption peaks at this location correspond to the absorption peaks of the two C=C stretching vibrations in the aromatic ring framework structure, combined with the 810 cm⁻¹ peaks. -1 The presence of an aromatic ring in the polymer molecule indicates the presence of a sodium p-styrene sulfonate aromatic ring structure; 1330 cm⁻¹ -1 The peak at 982 cm⁻¹ is the stretching vibration peak of -N-CH₃. -1The characteristic absorption peak of the quaternary ammonium salt group is at 731 cm⁻¹. -1 The peak at this point represents the rocking vibration of a long-chain alkyl group, indicating that the hydrophobic monomer C... 16 DMAAC has also been successfully introduced into polymer molecular chains; 2928.84 cm -1 1650.00 cm -1 The peak at 1190 cm⁻¹ is related to the -CH₂- and -CH₃ groups on the DSDAP monomer of betaine. -1 The peak at 1040 cm⁻¹ represents the stretching vibration of the S=O group on the sulfonic acid group. -1 The peak at this point represents the stretching vibration peak of SO on the sulfonic acid group. The above results indicate that the polymer has the characteristic absorption peak of the DSDAP functional group of the twin-tailed betaine monomer.

[0070] The above-mentioned seawater-based polymer-coated self-suspending proppant is applied to hydraulic fracturing in low-permeability offshore oilfields. The application method includes the following steps:

[0071] Add 100 mL of simulated seawater (mineralization of 35000 mg / L) or highly mineralized water (mineralization of 200000 mg / L) to the container, turn on the stirrer, add 15 g of polymer-coated self-suspending proppant and 0.3 g of nonionic surfactant fatty alcohol polyoxyethylene ether AEO-3, and mix thoroughly to obtain a sand-carrying solution with a sand ratio of 15%. Example 2

[0072] A method for preparing a seawater-based polymer-coated self-suspending proppant is described in Example 1, except that the amount of diglycinate betaine monomer (DSDAP) added in the synthesis of the polymer-coated self-suspending proppant is 19.5 g. Other steps and conditions are the same as in Example 1.

[0073] The application method of the above-mentioned seawater-based polymer-coated self-suspending proppant is the same as in Example 1. Example 3

[0074] A method for preparing a seawater-based polymer-coated self-suspending proppant, as described in Example 1, differs only in that, in the synthesis of the polymer-coated self-suspending proppant, the hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride (C... 16 The amount of DMAAC added was 1.8g. Other steps and conditions were the same as in Example 1.

[0075] The application method of the above-mentioned seawater-based polymer-coated self-suspending proppant is the same as in Example 1. Example 4

[0076] A method for preparing a seawater-based polymer-coated self-suspending proppant is described in Example 1, except that the mass of the quartz sand is 6 kg. Other steps and conditions are the same as in Example 1.

[0077] The application method of the above-mentioned seawater-based polymer-coated self-suspending proppant is the same as in Example 1. Example 5

[0078] A method for preparing a seawater-based polymer-coated self-suspending support is described in Example 1, except that the amount of silane coupling agent KH570 added is 8g. Other steps and conditions are the same as in Example 1.

[0079] The application method of the above-mentioned seawater-based polymer-coated self-suspending proppant is the same as in Example 1. Example 6

[0080] A method for preparing a seawater-based polymer-coated self-suspending proppant is the same as in Example 1.

[0081] The application of the above-mentioned seawater-based polymer-coated self-suspending proppant is as described in Example 1, except that the nonionic surfactant is Span-80. Other steps and conditions are the same as in Example 1.

[0082] The application method of the above-mentioned seawater-based polymer-coated self-suspending proppant is the same as in Example 1. Example 7

[0083] A method for preparing a seawater-based polymer-coated self-suspending proppant is the same as in Example 1.

[0084] The application of the above-mentioned seawater-based polymer-coated self-suspending support is as described in Example 1, except that the amount of nonionic surfactant fatty alcohol polyoxyethylene ether AEO-3 added is 0.25g. Other steps and conditions are the same as in Example 1.

[0085] The application method of the above-mentioned seawater-based polymer-coated self-suspending proppant is the same as in Example 1. Example 8

[0086] A method for preparing a seawater-based polymer-coated self-suspending proppant is described in Example 1, except that the mass concentration of the ferric chloride aqueous solution is 0.002% (wherein the mass of ferric chloride is 0.001g). Other steps and conditions are the same as in Example 1.

[0087] The application method of the above-mentioned seawater-based polymer-coated self-suspending proppant is the same as in Example 1. Comparative Example 1

[0088] A method for preparing a proppant is described in Example 1, except that the dimethicone monomer (DSDAP) is replaced with N,N-dimethyl(methacryloyloxyethyl)aminopropanesulfonic acid inner salt (DMAPS). Other steps and conditions are the same as in Example 1.

[0089] The application method of the above-mentioned proppant is the same as that in Example 1. Comparative Example 2

[0090] A method for preparing a proppant, as described in Example 1, differs only in that the hydrophobic monomer hexadecyldimethylallylammonium chloride (C16H2O) is not added. 16 (DMAAC). Other steps and conditions are the same as in Example 1.

[0091] The application method of the above-mentioned proppant is the same as that in Example 1. Comparative Example 3

[0092] A method for preparing a proppant is described in Example 1, except that no disaccharide betaine monomer (DSDAP) is added. Other steps and conditions are the same as in Example 1.

[0093] The application method of the above-mentioned proppant is the same as that in Example 1. Comparative Example 4

[0094] A method for preparing a proppant is the same as in Example 1.

[0095] The application of the above-mentioned proppant is as described in Example 1, except that the nonionic surfactant fatty alcohol polyoxyethylene ether AEO-3 is not added. Other steps and conditions are the same as in Example 1.

[0096] The application method of the above-mentioned proppant is the same as that in Example 1. Comparative Example 5

[0097] A method for preparing a proppant is described in Example 1, except that only potassium persulfate and sodium bisulfite are added to the initiation system, omitting tetramethylethylenediamine and ferric chloride. Other steps and conditions are the same as in Example 1.

[0098] The application method of the above-mentioned proppant is the same as that in Example 1. Comparative Example 6

[0099] A proppant, wherein the proppant is a single piece of quartz sand (20-40 mesh).

[0100] The application method of the above-mentioned proppant is the same as that in Example 1.

[0101] Experimental Example 1

[0102] Suspension performance test. This experiment was used to test the suspension ability of the proppant prepared in the examples and comparative examples. The test method is as follows:

[0103] Take the sand-carrying solution (the mineralization of the simulated seawater used is 35000 mg / L) from Examples 1-8 and Comparative Examples 1-6 respectively, mix them evenly, and pour them into a 10 mL graduated cylinder. Let them stand at 25℃ or 90℃, observe the dispersion state of the proppant in the seawater, and record the time required for the proppant to completely settle, which is the suspension time. The test results are shown in Table 1.

[0104] Take the sand-carrying solution (the mineralization degree of the high-mineralized water used is 200000 mg / L) of the well-mixed Examples 1-8 and Comparative Examples 1-6 and pour it into a 10 mL graduated cylinder. Let it stand at 25°C and observe the dispersion state of the proppant in seawater. Record the time required for the proppant to completely settle, which is the suspension time. The test results are shown in Table 2.

[0105] Table 1. Record of suspension time of sand-carrying fluid prepared in simulated seawater.

[0106]

[0107] Table 2. Suspension time record of sand-carrying solution prepared with high-mineralized water with a mineralization of 200,000 mg / L.

[0108]

[0109] Experimental Example 2

[0110] Thickening ability test. This experiment was used to test the thickening ability of the proppants prepared in the examples and comparative examples. The test method is as follows:

[0111] Take the sand-carrying solution from Examples 1-8 and Comparative Examples 1-6, which are mixed evenly (the salinity of the simulated seawater used is 35000 mg / L), filter the sand-carrying solution to remove the proppant, and test the viscosity of the filtrate at 25℃ and 90℃ using a six-speed rotational viscometer. The experimental results are shown in Table 3.

[0112] Table 3 Viscosity data for different proppants

[0113]

[0114] Experimental Example 3

[0115] Interfacial tension test of the breaking solution. This experiment was used to test the interfacial tension of the proppant prepared in the examples and comparative examples. The test method is as follows:

[0116] (1) Take 50 mL of the sand-carrying liquid (the mineralization of the simulated seawater used is 35000 mg / L) that is mixed evenly in Examples 1-8 and Comparative Examples 1-6, add 0.005 g of potassium persulfate as a breaker, set the breaker temperature to 90℃, and the breaker time to 2 h. After the breaker is completed, take out the breaker liquid for later use.

[0117] (2) The interfacial tension of the broken adhesive solution at 60℃ was tested using a TX-500C interfacial tension meter. The experimental results are shown in Table 4.

[0118] Table 4. Interfacial tension of different breaker solutions

[0119]

[0120] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An application of a seawater-based polymer-coated self-suspending proppant, characterized in that, It is applied to hydraulic fracturing in offshore low-permeability oilfields or high-salinity low-permeability oilfields; the application method includes the following steps: fully dispersing a seawater-based polymer-coated self-suspending proppant and a nonionic surfactant in seawater or highly saline water to obtain a proppant-carrying fluid, which is then applied to hydraulic fracturing in offshore low-permeability oilfields or high-salinity low-permeability oilfields; the nonionic surfactant is fatty alcohol polyoxyethylene ether AEO-3 or Span-80; The seawater-based polymer-coated self-suspending proppant is prepared from the following raw materials: proppant, silane coupling agent γ-methacryloyloxypropyltrimethoxysilane, acrylamide, hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride, betaine monomer, sodium styrene sulfonate, initiator, and solvent. The preparation method of betaine monomer includes the following steps: (1) Dissolve (2-bromomethyl)dimethylamine, sodium methanesulfonate and potassium carbonate in N,N-dimethylformamide, heat and reflux the reaction, and then post-process to obtain 3-(dimethylamino)propane-1-sulfonate; (2) Dissolve 3-(dimethylamino)propane-1-sulfonate in anhydrous ethanol, add anhydrous ethanol solution of 1,4-dichloro-2-butene dropwise, heat and reflux the reaction, and then obtain the twin-betaine monomer after post-treatment. The initiator includes a chain extender, an oxidant, a reducing agent, and an initiation catalyst; the chain extender is an aqueous solution of a polyamine, which is tetramethylethylenediamine or dimethylethylenediamine; the oxidant is an aqueous solution of potassium persulfate; the reducing agent is an aqueous solution of sodium bisulfite; and the initiation catalyst is an aqueous solution of ferric chloride. The mass ratio of acrylamide, hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride, betaine monomer, and sodium styrene sulfonate is 5-6:0.3-0.5:4-5:1; the mass ratio of proppant, silane coupling agent γ-methacryloyloxypropyltrimethoxysilane, and acrylamide is 100-500:1:0.5-4; and the mass ratio of initiator to acrylamide is 1:0.1-0.

5.

2. The application of the seawater-based polymer-coated self-suspending proppant according to claim 1, characterized in that, The preparation method of betaine monomer includes one or more of the following conditions: i. In step (1), the mass ratio of (2-bromomethyl)dimethylamine, sodium methanesulfonate, and potassium carbonate is 1:1.0-1.6:2; ii. In step (1), the mass ratio of (2-bromomethyl)dimethylamine to the volume ratio of N,N-dimethylformamide is 1:1-10 g / mL; iii. In step (1), the reflux reaction temperature is 60-80℃ and the reaction time is 6-12h. The reflux reaction is carried out under stirring conditions. iv. In step (2), the mass ratio of 3-(dimethylamino)propane-1-sulfonate to 1,4-dichloro-2-butene is 1.7-3.1:1.0; v. In step (2), the mass ratio of 3-(dimethylamino)propane-1-sulfonate to the volume ratio of anhydrous ethanol is 0.5-2 g / mL; vi. In step (2), the mass concentration of the anhydrous ethanol solution of 1,4-dichloro-2-butene is 0.1-1 g / mL; the dropping rate of the anhydrous ethanol solution of 1,4-dichloro-2-butene is 1-5 drops per second; the dropping of the anhydrous ethanol solution of 1,4-dichloro-2-butene is carried out under stirring and at 40-70°C. vii. In step (2), the reflux reaction temperature is 40-70℃ and the reaction time is 12-20h. The reflux reaction is carried out under stirring conditions.

3. The application of the seawater-based polymer-coated self-suspending proppant according to claim 1, characterized in that, Includes one or more of the following conditions: i. The proppant is selected from quartz sand or ceramsite; ii. The solvent is distilled water.

4. The application of the seawater-based polymer-coated self-suspending proppant according to claim 1, characterized in that, The mass concentration of the chain extender is 0.02-0.16%; the mass concentrations of potassium persulfate aqueous solution and sodium bisulfite aqueous solution are both 0.005-0.009%; and the mass concentration of ferric chloride aqueous solution is 0.0005-0.00225%.

5. The application of the seawater-based polymer-coated self-suspending proppant according to claim 1, characterized in that, The total mass percentage of acrylamide, hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride, twin betaine monomer, and sodium styrene sulfonate to the solvent is 15%-30%.

6. The application of the seawater-based polymer-coated self-suspending proppant according to claim 1, characterized in that, The preparation method of seawater-based polymer-coated self-suspending proppant includes the following steps: (1) The proppant was washed with distilled water and organic solvent in sequence to remove organic and inorganic impurities on the surface of the proppant and dried; γ-methacryloxypropyltrimethoxysilane, a silane coupling agent, was added, soaked, and dried to obtain the pretreated proppant; (2) Acrylamide, hydrophobic monomer hexadecyl dimethyl allyl ammonium chloride, twin betaine monomer and sodium styrene sulfonate are dissolved in a solvent and the pH value of the system is adjusted; a pretreated proppant is added, fully dispersed, an initiator is added dropwise, and after copolymerization, the seawater-based polymer-coated self-suspending proppant is obtained by drying, crushing and sieving.

7. The application of the seawater-based polymer-coated self-suspending proppant according to claim 6, characterized in that, Includes one or more of the following conditions: i. In step (1), the organic solvent is selected from at least one of ethanol, acetone or petroleum ether; ii. In step (1), the soaking time is 3-8 hours; the soaking temperature is 50-60℃; and the soaking is carried out under stirring conditions. iii. In step (2), the pH of the system is adjusted to 7 using a sodium hydroxide aqueous solution with a mass concentration of 15%-30%; iv. In step (2), the initiator is added at a rate of 1-2 drops per second; the addition is carried out under stirring, protective gas protection, and at 35-40°C; the protective gas is nitrogen or argon. v. In step (2), the copolymerization reaction temperature is 35-40℃ and the reaction time is 4-6h; the copolymerization reaction is carried out under stirring and protective gas protection; the protective gas is nitrogen or argon.

8. The application of the seawater-based polymer-coated self-suspending proppant according to claim 1, characterized in that, Includes one or more of the following conditions: i. The mass ratio of seawater-based polymer-coated self-suspending proppant and nonionic surfactant is 40-60:1; ii. In the sand-carrying solution, the mass ratio of the seawater-based polymer-coated self-suspending proppant to the volume ratio of seawater or highly mineralized water is 0.01-1 g / mL; iii. The mineralization of seawater is 35,000 mg / L; the mineralization of highly mineralized water is greater than 35,000 mg / L and less than or equal to 200,000 mg / L.

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