A thermal association type scale inhibitor, an alkaline scale inhibition polymer fracturing fluid system and a preparation method thereof

Abstract

The application discloses a thermal association type scale inhibitor, a basic scale inhibition polymer fracturing fluid system and a preparation method thereof, and a molecular structural formula of the thermal association type scale inhibitor is as follows: wherein x=92-98, y=1-3, z=1-5, and the molar ratio of p to q is 3:2; the -COO- / -SO3- / -PO4- / -NH2 groups in the thermal association type scale inhibitor can have a good chelation effect on divalent ions such as calcium and magnesium in water, can be adsorbed on the surface of calcium carbonate crystals, change the crystal form, cause lattice distortion, and in addition, the hydrophobic groups in the molecular structure can make the molecular chains of the scale inhibitor fully stretch in water, so that the -COO- / -SO3- / -PO4- / -NH2 groups are more exposed outside, the attraction between strong carbonate and divalent ions such as calcium and magnesium is inhibited, the adsorption capacity of the scale inhibitor on the surface of scale microcrystals is enhanced, the crystal form of scale is distorted or dispersed, and the scale inhibition effect of the scale inhibitor is further improved.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development, specifically relating to a thermo-associated scale inhibitor, an alkaline scale inhibitor polymer fracturing fluid system, and its preparation method. Background Technology

[0002] As oilfield development deepens, reservoir geological characteristics become increasingly complex. Some oilfield reservoirs have low permeability, contain boron and zirconium ions, and contain large amounts of calcium carbonate with formation water of the sodium bicarbonate type. For these reservoirs, the following problems arise during development: First, these reservoirs require fracturing to achieve industrial oil flow; however, conventional guar gum fracturing fluid systems often result in incomplete fracturing and gum return, clogging the reservoir and severely impacting production. For fracturing these reservoirs, polymer-based fracturing fluid systems are necessary. Second, most polymer-based fracturing fluid systems are currently neutral or acidic, and their fracturing fluids are often weakly acidic, dissolving calcium carbonate in the formation and producing calcium carbonate (Ca). 2+ Ca 2+ HCO3 in formation water - Or CO3 2- Ions can form calcium carbonate precipitates, which can cause blockages in the near-wellbore area or perforation during the flowback process, affecting production.

[0003] Early commonly used scale inhibitors included inorganic polyphosphates, organic polyphosphates, polycarboxylic acids, and copolymers. However, with increasing environmental awareness, phosphorus-based formulations faced restrictions and were phased out. Under these circumstances, low-phosphorus and phosphorus-free green scale inhibitors became the mainstream. Environmentally friendly green scale inhibitors mainly include phosphorus-containing water-soluble polymers, alkyl epoxy carboxylates, polyaspartic acid derivatives, and polyepoxysuccinic acid derivatives. However, these scale inhibitors are primarily used to inhibit the formation of inorganic precipitates such as calcium carbonate or the deposition of inorganic salts like calcium carbonate on equipment or pipe walls. Literature reports that scale inhibitors can chelate several thousand milligrams per liter of calcium ions at relatively low dosages, achieving a scale inhibition rate of over 90%. The scale inhibition rate test involved adding HCO3. - With Ca 2+ The molar concentrations are in a 1:2 ratio, but the actual HCO3 in the reservoir formation water... - The content is far beyond this proportion, and the reservoir temperature is high, which will have a significant impact on the scale inhibition efficiency of the scale inhibitor. Therefore, scale inhibitors used on the market to inhibit scaling in water treatment equipment, heat exchange equipment, and pipelines are not suitable for reservoirs where the formation water is sodium bicarbonate water and the reservoir contains a large amount of calcium carbonate. They cannot effectively solve the problem of calcium carbonate precipitation or calcium spheres forming in such reservoirs after fracturing. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a thermo-associated scale inhibitor, an alkaline scale inhibitor polymer fracturing fluid system, and a method for preparing the same, thereby solving the problems of incomplete fracturing fluid gel breaking, reservoir blockage due to return of gel, and the formation of calcium carbonate precipitates or calcium carbonate balls in the reservoir that block the near-wellbore zone and perforation holes, thus improving the reservoir fracturing effect and significantly increasing post-fracturing production.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention discloses a thermo-associated scale inhibitor, the molecular structure of which is as follows:

[0007]

[0008] Where x = 92 to 98, y = 1 to 3, z = 1 to 5, and the molar ratio of p to q is 3:2.

[0009] This invention also discloses a method for preparing the above-mentioned thermo-associated scale inhibitor, the specific steps of which are as follows:

[0010] (1) Synthesis of thermosensitive oligomers

[0011] Weigh N,N-dimethylacrylamide and diacetone acrylamide as monomers, add deionized water, and after the monomers dissolve in the aqueous solution, transfer the monomer aqueous solution to a three-necked flask equipped with a stirring rod and placed in a constant temperature water bath. After passing N2 through, add K2S2O8 / Na2SO3 and mercaptoethylamine hydrochloride, and allow the polymerization reaction to occur for 7-9 hours. After the reaction is completed, add the reactants dropwise to acetone with constant stirring, filter the precipitate, and freeze-dry at low temperature to obtain a white solid, which is the thermosensitive oligomer containing terminal amino groups, denoted as P(DMA-co-DAAM).

[0012] (2) Synthesis of multi-component copolymers

[0013] Weigh out deionized water, add maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, sodium allyl polyoxyethylene propylene sulfonate, nonionic surfactant FS, disodium ethylenediaminetetraacetate, urea, sodium carbonate and sodium formate and stir thoroughly. Adjust the pH of the system to 7-8, control the temperature at 0-5℃, add a composite initiator and perform adiabatic polymerization for 5-8 hours to obtain a colloid. Then, the colloid is cut, swollen, purified, dried, pulverized and sieved to obtain a white low molecular weight polymer, which is a multi-component copolymer, denoted as P(MA / AMPS / APES).

[0014] (3) Synthesis of thermo-associated scale inhibitors

[0015] The thermosensitive oligomer and the multi-component copolymer were dissolved in deionized water to prepare a polymer solution. The polymer solution was transferred to a three-necked flask with a stir bar, and the pH of the polymer solution was adjusted to 7-8. EDC / NHS was added and the mixture was heated in a water bath at 20-40℃ for 12-24 hours. The reactants were then removed, thoroughly washed with anhydrous ethanol, cut into small pieces, soaked in anhydrous ethanol, and dried to obtain a thermo-associated scale inhibitor, denoted as P(MA / AMPS / APES)-gP(DMA-co-DAAM).

[0016] Preferably, in step (1), K2S2O8 / Na2SO3 is composed of K2S2O8 and Na2SO3, with a mass ratio of K2S2O8:Na2SO3 = 2:1; the amount of K2S2O8 / Na2SO3 added is 0.3 wt% of the mass of N,N-dimethylacrylamide and diacetone acrylamide; and the molar ratio of N,N-dimethylacrylamide and diacetone acrylamide is 60:40.

[0017] Preferably, in step (2), the mass ratio of maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, and sodium allyl polyoxyethylene propylene sulfonate is 75:20:5; the nonionic surfactant FS accounts for 0.1-0.5% of the total monomer mass; sodium ethylenediaminetetraacetate (EDTA) accounts for 0.001-0.01% of the total monomer mass; urea accounts for 1-3% of the total monomer mass; sodium formate accounts for 0.001-0.01% of the total monomer mass; sodium carbonate accounts for 0.001-0.05% of the total monomer mass; and the composite initiator is composed of ferrous ammonium sulfate and sodium bisulfite in a mass ratio of 1:5, with the amount of composite initiator accounting for 0.005-0.02% of the total monomer mass.

[0018] Preferably, in step (3), the total mass concentration of the thermosensitive oligomer and the multi-component copolymer in the polymer solution is 1.5-3%, and the molar ratio of the thermosensitive oligomer to the multi-component copolymer is (1-4):1;

[0019] The EDC / NHS is composed of EDC and NHS, wherein the molar ratio of EDC to NHS is 1:1, and the molar ratio of EDC to temperature-sensitive oligomer is 10⁻⁵:1.

[0020] This invention also discloses an alkaline scale-inhibiting polymer fracturing fluid system, comprising the following raw materials in the indicated mass percentages:

[0021] Thickener 0.03%–1.5%, pH adjuster 0.01%–0.04%, scale inhibitor 0.05%–0.3%, clay stabilizer 0.1%–0.3%, drainage aid 0.1%–0.3%, demulsifier 0.1%–0.3%, and degumming agent 0.002%–0.15%;

[0022] The scale inhibitor is a thermo-associated scale inhibitor, and its molecular structure is as follows:

[0023]

[0024] Where x = 92 to 98, y = 1 to 3, and z = 1 to 5.

[0025] Specifically, the thickener is one of modified polyacrylamide and its derivatives.

[0026] Preferably, the thickener is a powdered anti-salt associating polymer thickener GAF-KY or an emulsion-state anti-salt associating polymer GAF-TE.

[0027] Specifically, the pH adjuster is one or more of sodium hydroxide, sodium bicarbonate, and sodium carbonate.

[0028] Specifically, the clay stabilizer is one or more of potassium chloride, ammonium chloride, choline chloride, and quaternary ammonium salt organic clay stabilizers.

[0029] Specifically, the discharge aid is a fluorocarbon surfactant, GAF-6.

[0030] Specifically, the demulsifier is a polyether-based demulsifier, GAF-7.

[0031] Specifically, the de-gluing agent is one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0032] This invention also discloses a method for preparing an alkaline scale-inhibiting polymer fracturing fluid system, the specific steps of which are as follows:

[0033] Weigh each raw material, measure the water for preparing the solution and pour it into a beaker. While stirring, first add the thickener and stir. Then add the pH adjuster, scale inhibitor, clay stabilizer, drainage aid, demulsifier and breaker. Continue stirring to prepare the alkaline scale inhibitor polymer fracturing fluid system.

[0034] The thickener is a powdered polymer thickener.

[0035] This invention also discloses a method for preparing an alkaline scale-inhibiting polymer fracturing fluid system, the specific steps of which are as follows:

[0036] Weigh each raw material, measure the water for preparing the solution and pour it into a beaker. While stirring, add the thickener, pH adjuster, scale inhibitor, clay stabilizer, drainage aid, demulsifier and breaker, and stir to prepare the alkaline scale inhibitor polymer fracturing fluid system.

[0037] The thickener is an emulsion polymer thickener.

[0038] The beneficial effects of this invention are as follows:

[0039] 1. The -COO- / -SO3- / PO4- / -NH2 groups in the thermotropic associative scale inhibitor of this invention can effectively chelate divalent ions such as calcium and magnesium in water. Simultaneously, they can adsorb onto the surface of calcium carbonate crystals, altering the crystal morphology and causing lattice distortion. Furthermore, the hydrophobic groups in the molecular structure allow the scale inhibitor's molecular chains to fully extend in the water, exposing more of the -COO- / -SO3- / PO4- / -NH2 groups. This inhibits the attraction between strong carbonate ions and divalent ions such as calcium and magnesium, enhancing their adsorption capacity on the microcrystalline surface of scale, causing scale crystal distortion or dispersion, and further improving the scale inhibition effect. The introduction of tunable temperature-sensitive hydrophobic components into the thermotropic associative scale inhibitor allows for the design of suitable thermotropic associative scale inhibitors based on reservoir temperature, achieving adjustable scale inhibition performance.

[0040] Thermotropic scale inhibitors have no effect on the viscosity and dissolution time of anti-salt associative polymer thickeners, and will not affect the proppant carrying capacity, temperature resistance, and shear resistance of fracturing fluids, thus enabling the fracturing fluid system to meet the performance requirements of water-based fracturing fluids.

[0041] 2. This invention utilizes a polymer fracturing fluid system to avoid cross-linking reactions with boron and zirconium ions in the formation, thus solving the problems of incomplete fracturing and re-entrapment that occur after fracturing with a guar gum system. The addition of an alkaline pH adjuster adjusts the pH of the liquid system to alkalinity, increasing the pH of the fracturing fluid and reducing its dissolving effect on calcium carbonate in the reservoir, thereby reducing the amount of calcium ions dissolved. The addition of a thermotropic associative scale inhibitor prevents calcium ions dissolved from the fracturing fluid from reacting with HCO3- in the formation water. - and CO3 2- Ionic reactions produce calcium carbonate precipitate. The addition of clay stabilizers, drainage aids, and demulsifiers is to ensure that the fracturing fluid system meets performance requirements such as anti-swelling rate, interfacial tension, demulsification rate, and gel breaking performance.

[0042] 3. The fracturing fluid system of this invention does not exhibit cross-linking upon contact with boron and zirconium ions, thus completely breaking down the gel, with a kinematic viscosity of less than 5 mm². 2 / s; Add more than 1000 mg / L Ca to 0.1%–0.3% thermotropic associative scale inhibitors. 2+ When mixed with a NaHCO3 solution of 5000 mg / L or higher, the scale inhibition rate is greater than 80% at a reservoir temperature of 90℃. The system can solve the problem of re-gelation and formation of calcium carbonate balls in reservoirs containing boron, zirconium ions, and high calcium carbonate content with sodium bicarbonate water type after decompression, which leads to reservoir blockage.

[0043] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Specific Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] This invention discloses a thermo-associated scale inhibitor, the molecular structure of which is as follows:

[0046]

[0047] Where x = 92 to 98, y = 1 to 3, z = 1 to 5, and the molar ratio of p to q is 3:2.

[0048] The specific steps for preparing the above-mentioned thermo-associated scale inhibitor are as follows:

[0049] (1) Synthesis of thermosensitive oligomers

[0050] Weigh N,N-dimethylacrylamide and diacetone acrylamide as monomers, add deionized water, and after the monomers dissolve in the aqueous solution, transfer the monomer aqueous solution to a three-necked flask equipped with a stirring rod and placed in a constant temperature water bath. After passing N2 through, add K2S2O8 / Na2SO3 and mercaptoethylamine hydrochloride, and allow the polymerization reaction to occur for 7-9 hours. After the reaction is completed, add the reactants dropwise to acetone with constant stirring, filter the precipitate, and freeze-dry at low temperature to obtain a white solid, which is the thermosensitive oligomer containing terminal amino groups, denoted as P(DMA-co-DAAM).

[0051] Preferably, in step (1), K2S2O8 / Na2SO3 is composed of K2S2O8 and Na2SO3, with a mass ratio of K2S2O8:Na2SO3 = 2:1; the amount of K2S2O8 / Na2SO3 added is 0.3 wt% of the mass of N,N-dimethylacrylamide and diacetone acrylamide; and the molar ratio of N,N-dimethylacrylamide and diacetone acrylamide is 60:40.

[0052] (2) Synthesis of multi-component copolymers

[0053] Weigh out deionized water, add maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, sodium allyl polyoxyethylene propylene sulfonate, nonionic surfactant FS, disodium ethylenediaminetetraacetate, urea, sodium carbonate and sodium formate and stir thoroughly. Adjust the pH of the system to 7-8, control the temperature at 0-5℃, add a composite initiator and perform adiabatic polymerization for 5-8 hours to obtain a colloid. Then, the colloid is cut, swollen, purified, dried, pulverized and sieved to obtain a white low molecular weight polymer, which is a multi-component copolymer, denoted as P(MA / AMPS / APES).

[0054] Preferably, in step (2), the mass ratio of maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, and sodium allyl polyoxyethylene propylene sulfonate is 75:20:5; the nonionic surfactant FS accounts for 0.1-0.5% of the total monomer mass; sodium ethylenediaminetetraacetate (EDTA) accounts for 0.001-0.01% of the total monomer mass; urea accounts for 1-3% of the total monomer mass; sodium formate accounts for 0.001-0.01% of the total monomer mass; sodium carbonate accounts for 0.001-0.05% of the total monomer mass; and the composite initiator is composed of ferrous ammonium sulfate and sodium bisulfite in a mass ratio of 1:5, with the amount of composite initiator accounting for 0.005-0.02% of the total monomer mass.

[0055] (3) Synthesis of thermo-associated scale inhibitors

[0056] The thermosensitive oligomer and the multi-component copolymer were dissolved in deionized water to prepare a polymer solution. The polymer solution was transferred to a three-necked flask with a stir bar, and the pH of the polymer solution was adjusted to 7-8. EDC / NHS was added and the mixture was heated in a water bath at 20-40℃ for 12-24 hours. The reactants were then removed, thoroughly washed with anhydrous ethanol, cut into small pieces, soaked in anhydrous ethanol, and dried to obtain a thermo-associated scale inhibitor, denoted as P(MA / AMPS / APES)-gP(DMA-co-DAAM).

[0057] Preferably, in step (3), the total mass concentration of the thermosensitive oligomer and the multi-component copolymer in the polymer solution is 1.5-3%, and the molar ratio of the thermosensitive oligomer to the multi-component copolymer is (1-4):1; the EDC / NHS is composed of EDC and NHS, wherein the molar ratio of EDC to NHS is 1:1, and the molar ratio of EDC to the thermosensitive oligomer is 10-5:1.

[0058] This invention also discloses an alkaline scale-inhibiting polymer fracturing fluid system, comprising the following raw materials in the indicated mass percentages:

[0059] Thickener 0.03%–1.5%, pH adjuster 0.01%–0.04%, scale inhibitor 0.05%–0.3%, clay stabilizer 0.1%–0.3%, drainage aid 0.1%–0.3%, demulsifier 0.1%–0.3%, and degumming agent 0.002%–0.15%;

[0060] The scale inhibitor is a thermo-associated scale inhibitor, and its molecular structure is as follows:

[0061]

[0062] Where x = 92 to 98, y = 1 to 3, and z = 1 to 5.

[0063] Specifically, the thickener is one of modified polyacrylamide and its derivatives. Preferably, the thickener is a powdered salt-associated polymer thickener GAF-KY or an emulsion salt-associated polymer GAF-TE.

[0064] Specifically, the pH adjuster is one or more of sodium hydroxide, sodium bicarbonate, and sodium carbonate.

[0065] Specifically, the clay stabilizer is one or more of potassium chloride, ammonium chloride, choline chloride, and quaternary ammonium salt organic clay stabilizers.

[0066] Specifically, the discharge aid is a fluorocarbon surfactant, GAF-6.

[0067] Specifically, the demulsifier is a polyether-based demulsifier, GAF-7.

[0068] Specifically, the de-gluing agent is one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0069] This invention also discloses a method for preparing an alkaline scale-inhibiting polymer fracturing fluid system, the specific steps of which are as follows:

[0070] Weigh each raw material, measure the water for preparing the solution and pour it into a beaker. While stirring, first add the thickener and stir. Then add the pH adjuster, scale inhibitor, clay stabilizer, drainage aid, demulsifier and breaker. Continue stirring to prepare the alkaline scale inhibitor polymer fracturing fluid system.

[0071] The thickener is a powdered polymer thickener.

[0072] This invention also discloses a method for preparing an alkaline scale-inhibiting polymer fracturing fluid system, the specific steps of which are as follows:

[0073] Weigh each raw material, measure the water for preparing the solution and pour it into a beaker. While stirring, add the thickener, pH adjuster, scale inhibitor, clay stabilizer, drainage aid, demulsifier and breaker, and stir to prepare the alkaline scale inhibitor polymer fracturing fluid system.

[0074] The thickener is an emulsion polymer thickener.

[0075] The following specific embodiments further illustrate the present invention:

[0076] Example 1

[0077] Preparation method of thermo-associated scale inhibitor:

[0078] (1) Synthesis of thermosensitive oligomer P(DMA-co-DAAM)

[0079] Accurately weigh 7.86 g of N,N-dimethylacrylamide (DMA) and 12.14 g of diacetone acrylamide (DAAM), and dissolve them in 100 mL of deionized water to prepare a 20% monomer mass fraction aqueous solution. After the monomers dissolve in the aqueous solution, transfer the monomer aqueous solution to a three-necked flask equipped with a stir bar and placed in a 30°C constant temperature water bath. After purging with N2 for 30 min, add 0.3 wt% K2S2O8 / Na2SO3 (K2S2O8:Na2SO3 = 2:1 by mass ratio based on total monomer mass) and 0.056 g of mercaptoethylamine hydrochloride (AET·HCl). Stir at 100 rpm and allow the polymerization reaction to proceed for 8 h. After the reaction is complete, add the reactants dropwise to a large amount of acetone under constant stirring. Filter to remove the precipitate, and freeze-dry at low temperature to obtain a white solid, which is the thermosensitive oligomer containing terminal amino groups, denoted as P(DMA-co-DAAM). The reaction formula for this step is as follows:

[0080]

[0081] Where p / q = 3:2 (molar ratio).

[0082] (2) Synthesis of multi-component copolymer P(MA / AMPS / APES)

[0083] Accurately weigh 1000g of deionized water, and sequentially add 225g of maleic anhydride, 60g of 2-acrylamide-2-methylpropanesulfonic acid, 15g of sodium allyl polyoxyethylene propylene sulfonate (HPEG-2400), 0.9g of nonionic surfactant FS (C12-C13, EO=4-6), 0.03g of disodium ethylenediaminetetraacetate, 4.5g of urea, 0.015g of sodium carbonate, and 0.03g of sodium formate. Stir thoroughly, adjust the pH of the system to 7-8 with sodium hydroxide, and control the temperature at 0-5℃. Add 0.009g of ferrous ammonium sulfate and 0.045g of sodium bisulfite for adiabatic polymerization for 7h (5-8h is also acceptable). Then, the colloid is sheared, swollen, purified (preferably by adding ethanol or acetone), dried, pulverized, and sieved to obtain a white low molecular weight polymer, which is the multi-component copolymer, denoted as P(MA / AMPS / APES). The reaction formula for this step is as follows:

[0084]

[0085] The mass ratio x:y:z is 92-98:1-3:1-5.

[0086] (3) Synthesis of thermo-associated scale inhibitor P(MA / AMPS / APES)-gP(DMA-co-DAAM)

[0087] Dissolve the terminal amine-terminated thermosensitive oligomer P(DMA-co-DAAM) and the multi-component copolymer P(MA / AMPS / APES) in deionized water to prepare a polymer solution with a total mass concentration of 1.5-3%. After the two are uniformly dissolved, transfer them to a three-necked flask equipped with a stirrer. Adjust the pH of the polymer solution to 7-8, add the specified amount of EDC / NHS (EDC:NHS = 1:1 (mol:mol), the molar ratio of EDC to the terminal amine-terminated branched polymer is 10-5:1), and react in a water bath at 20-40℃ for 12-24 hours. Remove the reactants, wash them thoroughly with anhydrous ethanol, cut them into small pieces, soak them in anhydrous ethanol for 24 hours, and dry them in a constant temperature oven at 45℃ until constant weight to obtain a thermotropically associative scale inhibitor, namely P(MA / AMPS / APES)-gP(DMA-co-DAAM). The reaction formula for this step is as follows:

[0088]

[0089] Example 2

[0090] Based on the thermotropic associative scale inhibitor synthesized in Example 1, and using powdered salt-resistant associative polymer thickener GAF-KY (produced by Sichuan Guangya Polymer Chemical Co., Ltd.) as the thickener and NaOH as the pH adjuster, the viscosity of the fracturing fluid system after the addition of the scale inhibitor (hereinafter referred to as fracturing fluid viscosity) was tested according to the formulation in Table 1. 0.03% ammonium persulfate was added, and the mixture was broken up at 90°C. After breaking up, the viscosity and pH value of the broken-up fluid were tested using a Pinwitz viscometer.

[0091] Note: Low-concentration polymer fracturing fluid systems were tested using a Pinwitz viscometer, while high-concentration polymer fracturing fluid systems were tested using a six-speed rotational viscometer for 170 seconds. -1 Viscosity at shear rate.

[0092] Table 1 Performance of different alkaline scale-inhibiting polymer fracturing fluid systems

[0093]

[0094] The fracturing fluid system preparation method in Example 2 (for powdered polymer thickener) is as follows: Measure 500ml of water into a 1L beaker, adjust the stirrer speed to 500 rpm, weigh the corresponding thickener and other additives according to the formula, first add the thickener, stir for 3 minutes, then add the pH adjuster, thermo-associated scale inhibitor, clay stabilizer, drainage aid, demulsifier, and breaker, and continue stirring for 2 minutes to prepare the alkaline scale inhibitor polymer fracturing fluid system;

[0095] As shown in Table 1, the scale inhibitor added to the powder-based fracturing fluid system did not significantly change the viscosity of the fracturing fluid system, and the fracturing fluid system was able to break down normally, indicating that the scale inhibitor had no effect on the performance of the fracturing fluid system. At the same time, the addition of NaOH had no effect on the viscosity of the fracturing fluid system or the breaking down of the gel. As the amount of NaOH added increased, the pH value of the breaking solution increased, and the pH value of the breaking solution could be adjusted by adjusting the amount of NaOH added.

[0096] Example 3

[0097] Based on the thermotropic associative scale inhibitor and thickener selected in Example 1, the emulsion-state salt-resistant associative polymer GAF-TE (produced by Sichuan Guangya Polymer Chemical Co., Ltd.) was used, and NaOH was used as the pH adjuster, according to the formulation in Table 2. The viscosity of the fracturing fluid system after the addition of the scale inhibitor (hereinafter referred to as fracturing fluid viscosity) was tested. 0.03% ammonium persulfate was added, and the mixture was broken up at 90°C. After breaking up, the viscosity and pH value of the broken fluid were tested using a Pinwitz viscometer.

[0098] Note: Low-concentration polymer fracturing fluid systems were tested using a Pinwitz viscometer, while high-concentration polymer fracturing fluid systems were tested using a six-speed rotational viscometer for 170 seconds. -1 Viscosity at shear rate.

[0099] Table 2 Performance of different alkaline scale-inhibiting polymer fracturing fluid systems

[0100]

[0101]

[0102] The specific steps for preparing the fracturing fluid system in Example 3 (for emulsion polymer thickener) are as follows: Measure 500ml of water into a 1L beaker, adjust the stirrer speed to 500 rpm, weigh the corresponding thickener and other additives according to the formula, and add the thickener, pH adjuster, thermo-associated scale inhibitor, clay stabilizer, drainage aid, demulsifier, and breaker. Stir for 1 minute to prepare the alkaline scale inhibitor polymer fracturing fluid system.

[0103] As shown in Table 2, the viscosity of the fracturing fluid system remained essentially unchanged after adding scale inhibitors to the emulsion-type fracturing fluid system, and the fracturing fluid system was able to break down normally, indicating that the scale inhibitors had no effect on the performance of the fracturing fluid system. At the same time, the addition of NaOH had no effect on the viscosity and breaking down of the fracturing fluid system. As the amount of NaOH added increased, the pH value of the breaking solution increased, and the pH value of the breaking solution could be adjusted by adjusting the amount of NaOH added.

[0104] Comparative Example 1

[0105] Based on the thermotropic associative scale inhibitor synthesized in Example 1, a 2775 mg / L CaCl2 solution was prepared. Different concentrations of thermotropic associative scale inhibitor, sodium polyepoxysuccinate scale inhibitor, and polyaspartic acid scale inhibitor were added according to the concentrations in Table 3. Then, it was mixed with a 5000 mg / L NaHCO3 aqueous solution at a ratio of 1:1. The solution was placed in a 90°C constant temperature oven and allowed to stand for 8 hours. The scale inhibition rate was then tested, and the specific results are shown in Table 3.

[0106] Table 3 Comparison of Scale Inhibition Rate

[0107]

[0108]

[0109] The comparative test results show that under the conditions of 2775 mg / L CaCl2, 5000 mg / L NaHCO3 and 90℃, the scale inhibition rates of polyepoxysuccinate sodium and polyaspartic acid scale inhibitors are low, while the scale inhibition rate of the thermo-associated scale inhibitor is greater than 80%, which is significantly higher than the other two scale inhibitors.

[0110] Comparative Example 2

[0111] Based on the thermotropic associative scale inhibitor synthesized in Example 1, a 4000 mg / L CaCl2 solution was prepared. Different concentrations of thermotropic associative scale inhibitor, sodium polyepoxysuccinate scale inhibitor, and polyaspartic acid scale inhibitor were added according to the concentrations in Table 4. Then, it was mixed with a 7000 mg / L NaHCO3 aqueous solution at a ratio of 1:1. The solution was placed in a 100°C constant temperature oven and allowed to stand for 8 hours. The scale inhibition rate was then tested, and the specific results are shown in Table 4.

[0112] Table 4 Comparison of Scale Inhibition Rate

[0113]

[0114] The comparative test results show that under conditions of 4000 mg / L CaCl2, 7000 mg / L NaHCO3 and 100℃, the scale inhibition rates of polyepoxysuccinate sodium and polyaspartic acid scale inhibitors further decreased, while the scale inhibition rate of the thermo-associated scale inhibitor could still be maintained above 80%, indicating that the scale inhibitor has good resistance to high calcium, high bicarbonate and high temperature.

[0115] Comparative Example 3

[0116] Guar gum system: A base solution of 0.4% guar gum + 0.01% NaOH was prepared using tap water.

[0117] Emulsion-type fracturing fluid system: The base fluid consists of 1.0% thickener GAF-TE + 0.2% quaternary ammonium salt organic clay stabilizer + 0.2% fluorocarbon surfactant + 0.3% polyether demulsifier + 0.1% thermotropic associative scale inhibitor. The preparation method is shown in Example 3.

[0118] Take 60g of rock sample from well Ma28 and mix it evenly with 300ml of guar gum system and emulsion fracturing fluid system respectively. Let it stand at room temperature for 24h. Test the viscosity of guar gum base fluid and emulsion fracturing fluid system and observe whether gelation occurs.

[0119] Table 5 Comparison of Viscosity and Gelation Phenomenon

[0120]

[0121] Comparative tests show that cross-linking occurs when guar gum-based fluid is mixed with boron-zirconium ions from the Ma 28 well core and left to stand; emulsion-type fracturing fluid systems do not exhibit cross-linking or thickening.

[0122] It should be noted that:

[0123] In this embodiment, the viscosity of the fracturing fluid system and the viscosity of the breaker fluid were tested in accordance with "GB / T 10247-2008 Viscosity Measurement Method";

[0124] In this embodiment, the soluble calcium ion content and the scale inhibitor test method are based on "GB / T 16632-2019 Determination of scale inhibition performance of water treatment agents - calcium carbonate deposition method".

[0125] In the alkaline scale inhibitor polymer fracturing fluid system of the present invention, various raw materials can be selected according to actual conditions, and are not limited to those mentioned in the examples. Specifically, the thickener can be one of modified polyacrylamide and its derivatives, including powdered polymer thickener and emulsion polymer thickener. Preferably, the thickener is powdered anti-salt associating polymer thickener GAF-KY (purchased from Sichuan Guangya Polymer Chemical Co., Ltd.) or emulsion anti-salt associating polymer GAF-TE (purchased from Sichuan Guangya Polymer Chemical Co., Ltd.).

[0126] In the alkaline scale inhibitor fracturing fluid system of this invention, the pH adjuster can be one or more of sodium hydroxide, sodium bicarbonate, and sodium carbonate.

[0127] The clay stabilizer in the alkaline scale inhibitor polymer fracturing fluid system of this invention can be one or more of potassium chloride, ammonium chloride, choline chloride, and quaternary ammonium salt organic clay stabilizers.

[0128] The drainage aid in the alkaline scale inhibitor polymer fracturing fluid system of this invention can be any fluorocarbon surfactant GAF-6 (purchased from Sichuan Guangya Polymer Chemical Co., Ltd.).

[0129] The demulsifier in the alkaline scale inhibitor polymer fracturing fluid system of this invention can be any polyether demulsifier GAF-7 (purchased from Sichuan Guangya Polymer Chemical Co., Ltd.).

[0130] The breaker in the alkaline scale inhibitor polymer fracturing fluid system of this invention can be one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0131] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A thermotropic associative scale inhibitor, the molecular structural formula of which is as follows: in, x = 92–98, y = 1–3, z = 1–5, and the molar ratio of p to q is 3:

2.

2. A method for preparing the thermo-associated scale inhibitor as described in claim 1, comprising the following specific steps: (1) Synthesis of thermosensitive oligomers Weigh N,N-dimethylacrylamide and diacetone acrylamide as monomers, add deionized water, and after the monomers dissolve in the aqueous solution, transfer the monomer aqueous solution to a three-necked flask equipped with a stirring rod and placed in a constant temperature water bath. After passing N2 through, add K2S2O8 / Na2SO3 and mercaptoethylamine hydrochloride, and allow the polymerization reaction to occur for 7-9 hours. After the reaction is completed, add the reactants dropwise to acetone with constant stirring, filter the precipitate, and freeze-dry at low temperature to obtain a white solid, which is the thermosensitive oligomer containing terminal amino groups, denoted as P(DMA-co-DAAM). (2) Synthesis of multi-component copolymers Weigh out deionized water, add maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, sodium allyl polyoxyethylene propylene sulfonate, nonionic surfactant FS, disodium ethylenediaminetetraacetate, urea, sodium carbonate and sodium formate and stir thoroughly. Adjust the pH of the system to 7-8, control the temperature at 0-5℃, add a composite initiator and perform adiabatic polymerization for 5-8 hours to obtain a colloid. Then, the colloid is cut, swollen, purified, dried, pulverized and sieved to obtain a white low molecular weight polymer, which is a multi-component copolymer, denoted as P(MA / AMPS / APES). (3) Synthesis of thermo-associated scale inhibitors The thermosensitive oligomer and the multi-component copolymer were dissolved in deionized water to prepare a polymer solution. The polymer solution was transferred to a three-necked flask with a stir bar, and the pH of the polymer solution was adjusted to 7-8. EDC / NHS was added and the mixture was heated in a water bath at 20-40℃ for 12-24 hours. The reactants were then removed, thoroughly washed with anhydrous ethanol, cut into small pieces, soaked in anhydrous ethanol, and dried to obtain a thermo-associated scale inhibitor, denoted as P(MA / AMPS / APES)-gP(DMA-co-DAAM).

3. The method for preparing a thermo-associated scale inhibitor according to claim 2, wherein, In step (1), K2S2O8 / Na2SO3 is composed of K2S2O8 and Na2SO3, with a mass ratio of K2S2O8:Na2SO3 = 2:1; the amount of K2S2O8 / Na2SO3 added is 0.3wt% of the mass of N,N-dimethylacrylamide and diacetone acrylamide; the molar ratio of N,N-dimethylacrylamide and diacetone acrylamide is 60:

40.

4. The method for preparing a thermo-associated scale inhibitor according to claim 2, wherein, In step (2), the mass ratio of maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, and sodium allyl polyoxyethylene propylene sulfonate is 75:20:

5. The nonionic surfactant FS accounts for 0.1-0.5% of the total monomer mass, sodium ethylenediaminetetraacetate (EDTA) accounts for 0.001-0.01% of the total monomer mass, urea accounts for 1-3% of the total monomer mass, sodium formate accounts for 0.001-0.01% of the total monomer mass, sodium carbonate accounts for 0.001-0.05% of the total monomer mass, and the composite initiator is composed of ferrous ammonium sulfate and sodium bisulfite in a mass ratio of 1:

5. The amount of composite initiator accounts for 0.005-0.02% of the total monomer mass.

5. The method for preparing a thermo-associated scale inhibitor according to claim 2, wherein, In step (3), the total mass concentration of the thermosensitive oligomer and the multi-component copolymer in the polymer solution is 1.5-3%, and the molar ratio of the thermosensitive oligomer to the multi-component copolymer is (1-4):1; The EDC / NHS is composed of EDC and NHS, wherein the molar ratio of EDC to NHS is 1:1, and the molar ratio of EDC to temperature-sensitive oligomer is 10⁻⁵:

1.

6. An alkaline scale-inhibiting polymer fracturing fluid system, comprising the following raw materials in the indicated mass percentages: Thickener 0.03%–1.5%, pH adjuster 0.01%–0.04%, scale inhibitor 0.05%–0.3%, clay stabilizer 0.1%–0.3%, drainage aid 0.1%–0.3%, demulsifier 0.1%–0.3%, and degumming agent 0.002%–0.15%; in, The scale inhibitor is a thermo-associated scale inhibitor, and its molecular structure is as follows: Where x = 92 to 98, y = 1 to 3, and z = 1 to 5.

7. The alkaline scale-inhibiting polymer fracturing fluid system according to claim 6, wherein, The thickener is one of modified polyacrylamide and its derivatives.

8. The alkaline scale-inhibiting polymer fracturing fluid system according to claim 7, wherein, The thickener is a powdered anti-salt associating polymer thickener GAF-KY or an emulsion-state anti-salt associating polymer GAF-TE.

9. The alkaline scale-inhibiting polymer fracturing fluid system according to claim 6, wherein, The pH adjuster is one or more of sodium hydroxide, sodium bicarbonate, and sodium carbonate.

10. The alkaline scale-inhibiting polymer fracturing fluid system according to claim 6, wherein, The clay stabilizer is one or more of potassium chloride, ammonium chloride, choline chloride, and quaternary ammonium salt organic clay stabilizers.

11. The alkaline scale-inhibiting polymer fracturing fluid system according to claim 6, wherein, The drainage aid is a fluorocarbon surfactant, GAF-6.

12. The alkaline scale-inhibiting polymer fracturing fluid system according to claim 6, wherein, The demulsifier is a polyether-based demulsifier, GAF-7.

13. The alkaline scale-inhibiting polymer fracturing fluid system according to claim 6, wherein, The de-icing agent is one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

14. A method for preparing the alkaline scale-inhibiting polymer fracturing fluid system according to any one of claims 6-13, comprising the following specific steps: Weigh each raw material, measure the water for preparing the solution and pour it into a beaker. While stirring, first add the thickener and stir. Then add the pH adjuster, scale inhibitor, clay stabilizer, drainage aid, demulsifier and breaker. Continue stirring to prepare the alkaline scale inhibitor polymer fracturing fluid system. in, The thickener is a powdered polymer thickener.

15. A method for preparing the alkaline scale-inhibiting polymer fracturing fluid system according to any one of claims 6-13, comprising the following specific steps: Weigh each raw material, measure the water for preparing the solution and pour it into a beaker. While stirring, add the thickener, pH adjuster, scale inhibitor, clay stabilizer, drainage aid, demulsifier and breaker, and stir to prepare the alkaline scale inhibitor polymer fracturing fluid system. in, The thickener is an emulsion polymer thickener.

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