Thickening agent, salt-resistant and high-temperature-resistant fracturing fluid prepared by using thickening agent as well as preparation method and application of salt-resistant and high-temperature-resistant fracturing fluid

Abstract

The invention discloses a thickening agent, a salt-resistant and high-temperature-resistant fracturing fluid prepared by using the thickening agent as well as a preparation method and application of the salt-resistant and high-temperature-resistant fracturing fluid, and belongs to the technical field of oil and gas development. The problems that in the current oil and gas reservoir exploitation process, the flow-back fluid utilization rate is low, and a thickening agent and fracturing fluid prepared from the thickening agent are high in thickening cost, poor in efficiency, insufficient in temperature resistance and salt resistance and the like are solved. The amphoteric polyacrylamide copolymer is synthesized by using acrylamide, diacetone acrylamide and alkyl sulfobetaine, the copolymer is used as a thickening agent and can be used for preparing the fracturing fluid together with the fracturing flow-back fluid containing high salt, and the fracturing fluid which is high in consistency, resistant to high temperature and salt and high in viscosity can be obtained under the low concentration of the obtained fracturing fluid. And better rheological property and sand-carrying effect are achieved. In addition, an anti-swelling agent can be added into the fracturing fluid to prevent clay from swelling. Meanwhile, an auxiliary surfactant can be added into the fracturing fluid, so that the dissolving speed of the fracturing fluid is adjusted, and the surface tension is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas development, and in particular relates to a thickener, a salt-resistant and high-temperature-resistant fracturing fluid prepared by using the thickener, and a preparation method and application thereof. Background Art

[0002] Low-permeability formations around the world are rich in oil and gas resources, but their natural productivity is low, necessitating fracturing to boost well production. The application of fracturing fluid technology to exploit oil and gas reservoirs can increase production. Fracturing involves injecting slick water or a thickened, viscoelastic fluid with proppant into the formation to increase permeability and thereby boost oil and gas production.

[0003] In areas with scarce water resources, the contradiction between the scale of exploration and development and water extraction indicators is prominent; the volume of fracturing flowback fluid has increased sharply, putting great pressure on environmental protection, and the main characteristic of the flowback fluid is that it contains water with high mineralization and high salinity. In addition, most existing fracturing fluids use thickeners such as guar gum and polyacrylamide, which have poor drag reduction and thickening effects. This results in low viscosity and difficulty in carrying sand. It is necessary to add a higher concentration of polymer to thicken the fracturing fluid, or add a cross-linking agent for cross-linking to meet the viscosity requirements of fracturing fluid construction. This is costly, and the reuse rate of fracturing flowback fluid has been below 25% for a long time. Therefore, there is an urgent need to develop a thickener and a fracturing fluid formed with the thickener. The fracturing fluid can be mixed with fracturing flowback fluid and the thickener, has good drag reduction and thickening properties, and meets the requirements of unconventional tight oil and gas for pressure fluid.

[0004] Commonly used fracturing fluids are based on plant guar polysaccharides or their modified products, which contain high levels of residue. The amount of residue left after fracturing fluid debonding directly impacts the effectiveness of fracturing. Residues can clog fractures, reduce support zone permeability and formation matrix permeability, causing irreversible damage and severely impacting oil and gas production. Furthermore, fracturing fluids based on the small molecule association and aggregation of viscoelastic surfactants offer the advantages of being residue-free and minimally damaging to formations. Furthermore, fracturing fluids formulated with viscoelastic surfactants are simple to apply on-site, requiring no extensive equipment, crosslinkers, breakers, or other additives. However, the relatively high dosage and high cost of these fluids limit their application in oil and gas reservoirs.

[0005] Polymer fracturing fluids, such as conventional polyacrylamide fracturing fluids, are generally not salt-tolerant. Modified polyacrylamide copolymers can provide salt tolerance. Chinese invention patent CN118909182A discloses the preparation and application of a nitrogen-oxide zwitterion-functionalized polyacrylamide for compounding high-mineralization fracturing fluid flowback fluids. The polyacrylamide copolymer is obtained by copolymerizing amine oxide monomers with acrylic acid and acrylamide. However, the operating temperature of the copolymer is 90°C, which limits its scope of application. Other similar technologies have also failed to effectively solve problems such as thickening efficiency, high-temperature adaptability, rheological properties, and sand-carrying effect when preparing the flowback fluid.

[0006] In summary, there is an urgent need to develop a fracturing fluid system that can be formulated using high-salt fracturing flowback fluid, has good high-temperature adaptability, good rheological and sand-carrying effects, high thickening efficiency, and good drag reduction and thickening properties, so as to solve the technical problems of low utilization rate of fracturing flowback fluid, high thickening cost and poor efficiency, and insufficient temperature and salt resistance in the existing technology. Summary of the Invention

[0007] In order to solve the above problems existing in the prior art, the present invention provides a thickener, a salt-resistant and high-temperature-resistant fracturing fluid prepared using the thickener, and a preparation method and application thereof.

[0008] The purpose of the present invention is achieved through the following technical solutions: One of the objectives of the present invention is to provide a thickener, the chemical composition of which is a polyacrylamide copolymer containing a sulfonate betaine amphoteric group. The raw materials for preparing the polyacrylamide copolymer include, by mole percentage, 60-80% acrylamide, 20-40% diacetone acrylamide, and 0.5-3% alkyl sulfonate betaine, wherein the alkyl chain of the alkyl sulfonate betaine contains 12-22 carbon atoms.

[0009] It is further defined that the raw materials for preparing the polyacrylamide copolymer include, by mole percentage, 65-75% acrylamide, 25-35% diacetone acrylamide, and 1.0-2.0% alkyl sulfonate betaine, wherein the alkyl chain of the alkyl sulfonate betaine contains 14-18 carbon atoms.

[0010] It is further defined that the structural formula of the polyacrylamide copolymer is: , Wherein, x, y, and z represent the degree of polymerization of the acrylamide group, diacetone acrylamide group, and alkylsulfonate betaine amphoteric group, x:y:z=60-80:20-40:0.5-3, n=12-16, and the alkylsulfonate betaine amphoteric group contains 12-22 carbon atoms.

[0011] It is further defined that the structural formula of the polyacrylamide copolymer is: , Wherein, x, y, and z represent the degree of polymerization of the acrylamide group, diacetone acrylamide group, and alkylsulfonate betaine amphoteric group, x:y:z=65-75:25-35:1.0-2.0, n=12-16, and the alkyl chain of the alkylsulfonate betaine amphoteric group contains 14-18 carbon atoms.

[0012] It is further defined that the molecular weight of the polyacrylamide copolymer is 500,000-10,000,000.

[0013] The second object of the present invention is to provide a method for preparing the alkyl sulfonate betaine in the above-mentioned thickener, which comprises: (1) reacting equimolar sodium methyl taurate and alkyl halide in an alcohol solvent at 50-70°C under base catalysis and inert gas protection; (2) reacting the product of step (1) with 3-chloropropylene in an alcohol-water solution to obtain alkylsulfonate betaine. It is further defined that the alkyl halide in (1) is an alkyl chloride having 12 to 22 carbon atoms or an alkyl bromide having 12 to 22 carbon atoms; the base is a small molecule amine substance or an inorganic base; and the alcohol solvent is ethanol or isopropanol.

[0014] A third object of the present invention is to provide a method for preparing the above-mentioned thickener, which comprises dissolving acrylamide, diacetone acrylamide and alkyl sulfonate betaine in deionized water to prepare a 20-30 wt% solution, reacting at a certain temperature, purifying by solvent precipitation method and drying.

[0015] It is further defined that the reaction temperature is 40-50°C and the reaction time is 4-8 hours.

[0016] A fourth object of the present invention is to provide a salt-resistant and high-temperature-resistant fracturing fluid prepared using the above-mentioned thickener, wherein the fracturing fluid comprises the above-mentioned thickener and fracturing flowback fluid.

[0017] It is further defined that the fracturing fluid further comprises an auxiliary surfactant and / or an anti-swelling agent.

[0018] It is further defined that the auxiliary surfactant is one or more of anionic surfactants, cationic surfactants, nonionic surfactants and alcohol solvents.

[0019] It is further defined that the anionic surfactant is an alkyl sulfonate or sulfate, the cationic surfactant is an alkyl quaternary ammonium salt, the nonionic surfactant is one or more of alkyl fatty alcohol polyoxyethylene ether, alkyl glycoside and alkyl amide, and the alcohol solvent is one or more of methanol, ethanol, isopropanol, ethylene glycol and propylene glycol. It is further limited that the amount of alcohol solvent used is ≤1%.

[0020] A fifth object of the present invention is a method for preparing the salt-resistant and high-temperature-resistant fracturing fluid, which comprises mixing a thickener and fracturing flowback fluid and stirring them uniformly.

[0021] A sixth object of the present invention is a method for preparing the salt-resistant and high-temperature-resistant fracturing fluid, which comprises mixing a thickener, a fracturing flowback fluid, and an auxiliary surfactant and / or an anti-swelling agent, and stirring them uniformly.

[0022] A seventh object of the present invention is to provide an application of the above-mentioned salt-resistant and high-temperature resistant fracturing fluid, specifically, the fracturing fluid is used in oil and gas field fracturing.

[0023] The beneficial effects of the present invention are: (1) The present invention provides a thickener, which is an amphoteric polyacrylamide copolymer synthesized from acrylamide, diacetone acrylamide and alkyl sulfonic acid betaine. The amphoteric polyacrylamide copolymer can be prepared together with a fracturing flowback fluid containing high salt to form a fracturing fluid. The obtained fracturing fluid is not only salt-resistant and high-temperature-resistant, but also has a higher consistency at a lower concentration and has better rheological properties and sand-carrying effect.

[0024] (2) The thickener component of the fracturing fluid provided by the present invention is a polyacrylamide copolymer containing sulfonic acid betaine amphoteric groups. This is an amphoteric polymer that can significantly increase the viscosity of the fracturing fluid and has better compatibility with various ions. Therefore, compared with fracturing fluids prepared using traditional surfactants, the fracturing fluid provided by the present invention can achieve higher consistency and viscoelasticity at lower concentrations, and obtain better rheological properties and sand-carrying effects. In addition, the present invention can also add an anti-swelling agent to the fracturing fluid to prevent clay swelling. At the same time, the present invention can also adjust the dissolution rate of the fracturing fluid and reduce the surface tension by adding an auxiliary surfactant to the fracturing fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the viscosity test results of fracturing fluids prepared with different types and salinities of brines at 30°C; Figure 2 Viscosity test results of fracturing fluid without brine and fracturing fluid prepared with different types of 100 g / L salinity brine at 180°C, (a) without brine, (b) NaCl, (c) MgCl2, (d) CaCl2. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0027] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0028] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it constitute a separate or selective embodiment that is mutually exclusive of other embodiments.

[0029] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are conventional in the art and can be obtained commercially by those skilled in the art unless otherwise specified.

[0030] Example 1 1. Synthesis of Hexadecyl Sulfobetaine Monomer The synthetic route of hexadecyl sulfobetaine monomer is as follows:

[0031] (1) Synthesis of sodium hexadecyl methyl taurate (NMSC-16) In a 250 mL three-necked flask, 50 mmol of sodium methyltaurine (NMS, 64-66% aqueous solution), 50 mmol of hexadecane bromide, and 50 mmol of triethylamine were added to 80 mL of anhydrous ethanol and refluxed at 50-70°C for 12 h. The reaction system was then cooled to 25°C and filtered. The filtered material was washed with acetone and recrystallized from an ethanol-water mixed solvent to obtain white flaky crystals, which were then dried in a vacuum oven at 50°C for 12 h to obtain sodium hexadecyl methyltaurine (NMSC-16). (2) Synthesis of hexadecyl sulfobetaine monomer (ANMSC-16) In a 250 mL three-necked flask, 30 mmol of NMSC-16 and 35 mmol of 3-chloropropene were added to 100 mL of a solution consisting of anhydrous ethanol and water (v:v = 1:1). After reacting at 55°C for 24 h, the reaction solution was cooled to 25°C and filtered. The filtrate was evaporated and the evaporated material was recrystallized from anhydrous ethanol to obtain a brown needle-like product, namely hexadecylsulfobetaine monomer (ANMSC-16), which was dried in a vacuum oven at 50°C for 12 h. 2. Preparation of amphoteric polyacrylamide copolymer Acrylamide (69.3 mmol), diacetone acrylamide (29.7 mmol), and AMSC-16 (1 mmol) were dissolved in deionized water to prepare a 25 wt% solution. The solution was then transferred to a 100 mL three-necked flask. Nitrogen was then bubbled through the solution for 20 minutes to deoxygenate it. The initiator, 2,2-azobis(2-methylpropylimidamide) dihydrochloride (AIBA), was added at a concentration of 0.05% of the total weight of acrylamide, diacetone acrylamide, and AMSC-16. The reaction was incubated at 45°C for 5 hours. After completion of the reaction, a clear solution was obtained. The polymer was then purified by ethanol precipitation to obtain an amphoteric polyacrylamide copolymer, which was then dried and ground into a fine powder.

[0032] Example 2 Preparation of fracturing fluid: A fracturing fluid was prepared using brine with a certain salinity to simulate fracturing flowback water. The preparation process was as follows: the amphoteric polyacrylamide copolymer of Example 1 was dissolved in 10 g / L NaCl brine with a salinity of 0.7 wt % under stirring. The amphoteric polyacrylamide copolymer was then dissolved in 10 g / L NaCl brine with a salinity of 0.7 wt % based on the NaCl brine. The mixture was then stirred to obtain a fracturing fluid.

[0033] Example 3 The difference between this embodiment and embodiment 2 is that the concentration of NaCl brine in this embodiment is 50 g / L, and the steps and process parameters are the same as those in embodiment 2.

[0034] Example 4 The difference between this embodiment and embodiment 2 is that the concentration of NaCl brine in this embodiment is 100 g / L, and the steps and process parameters are the same as those in embodiment 2.

[0035] Example 5 The difference between this embodiment and embodiment 2 is that the type of brine in this embodiment is MgCl2, and the steps and process parameters are the same as those in embodiment 2.

[0036] Example 6 The difference between this embodiment and embodiment 5 is that the concentration of MgCl2 brine in this embodiment is 50g / L, and the steps and process parameters are the same as those in embodiment 2.

[0037] Example 7 The difference between this embodiment and embodiment 5 is that the concentration of MgCl2 brine in this embodiment is 100 g / L, and the steps and process parameters are the same as those in embodiment 2.

[0038] Example 8 The difference between this embodiment and embodiment 2 is that the type of brine in this embodiment is CaCl2, and the steps and process parameters are the same as those in embodiment 2.

[0039] Example 9 The difference between this embodiment and embodiment 8 is that the concentration of CaCl2 brine in this embodiment is 50g / L, and the steps and process parameters are the same as those in embodiment 8.

[0040] Example 10 The difference between this embodiment and embodiment 8 is that the concentration of CaCl2 brine in this embodiment is 100 g / L, and the steps and process parameters are the same as those in embodiment 8.

[0041] Effect Examples (1) On an Anton Paar MRC302 rheometer, at 100 s -1 The viscosity of the fracturing fluids of Examples 2-10 was tested at a shear rate of 30°C. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that when simulations were conducted under different flowback salinity conditions, the viscosity of the amphoteric polyacrylamide copolymer increased with increasing salt concentration. Compared to conventional polyacrylamide, which exhibits a decrease in viscosity due to the presence of divalent ions at high salinity, the amphoteric polyacrylamide copolymer of the present invention exhibits higher viscosity in solutions containing divalent ions. This further demonstrates that the fracturing fluid of the present invention can achieve high viscosity at low concentrations, demonstrating excellent integrated drag reduction and thickening properties.

[0042] (2) On the Anton Paar MRC302 rheometer, at 100s -1 The viscosity of the fracturing fluids of Examples 4, 7 and 10 was tested at a shear rate of 180°C, and the fracturing fluids prepared without adding inorganic salts were used as a comparison. The results are as follows: Figure 2 As shown. Figure 2 As can be seen, at 180°C and a high salinity of 100 g / L in different brine systems (NaCl, MgCl₂, and CaCl₂), the viscosity of the fracturing fluid changes very little. The viscosities of fracturing fluids prepared using MgCl₂ and CaCl₂ brines are similar to those prepared without brine, both meeting the viscosity requirements for fracturing fluid application. This demonstrates that the fracturing fluid of the present invention has strong tolerance to high-salinity environments and good high-temperature stability.

[0043] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A thickener, characterized in that The chemical composition of the thickener is a polyacrylamide copolymer containing sulfonic acid betaine amphoteric groups; The raw materials for preparing the polyacrylamide copolymer include, by mole percentage, 60-80% acrylamide, 20-40% diacetone acrylamide, and 0.5-3% alkyl sulfonic acid betaine; The alkyl chain of the alkyl sulfobetaine contains 12 to 22 carbon atoms.

2. The thickener according to claim 1, characterized in that The raw materials for preparing the polyacrylamide copolymer include, by mole percentage, 65-75% acrylamide, 25-35% diacetone acrylamide, and 1.0-2.0% alkyl sulfonic acid betaine; The alkyl chain of the alkyl sulfobetaine contains 14 to 18 carbon atoms.

3. The thickener according to claim 1, characterized in that The molecular weight of polyacrylamide copolymer is 500,000-10 million.

4. A method for preparing alkyl sulfobetaine in a thickener according to any one of claims 1 to 3, the method comprising: (1) Under base catalysis and inert gas protection, equimolar sodium methyl taurate and alkyl halide are placed in an alcohol solvent and reacted at 50-70°C; (2) reacting the product of step (1) with 3-chloropropylene in a mixed solution of alcohol and water to obtain alkylsulfonate betaine.

5. The preparation method according to claim 4, characterized in that (1) The alkyl halide is a chloroalkane having 12 to 22 carbon atoms or a bromoalkane having 12 to 22 carbon atoms; the base is a small molecule amine substance or an inorganic base, and the alcohol solvent is ethanol or isopropanol.

6. A method for preparing the thickener according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: dissolving acrylamide, diacetone acrylamide and alkyl sulfonate betaine in deionized water to prepare a 20-30 wt% solution, reacting the solution at a certain temperature, purifying the solution by a solvent precipitation method and drying the solution.

7. A salt-resistant and high-temperature resistant fracturing fluid prepared using the thickener according to any one of claims 1 to 3, characterized in that: The fracturing fluid includes a thickener and fracturing flowback fluid.

8. The salt-resistant and high-temperature resistant fracturing fluid according to claim 7, characterized in that: The fracturing fluid also includes an auxiliary surfactant and / or an anti-swelling agent.

9. A method for preparing the salt-resistant and high-temperature-resistant fracturing fluid according to claim 7, characterized in that: The preparation method comprises the following steps: mixing a thickener and fracturing flowback fluid, and stirring the mixture evenly.

10. Use of the salt-resistant and high-temperature resistant fracturing fluid according to any one of claims 7 to 8, characterized in that: The fracturing fluid is used in fracturing of oil and gas fields.

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