A fluorine-containing polymer wetting reversal agent suitable for shale reservoir protection, and a preparation method and application thereof

Abstract

The application provides a fluorine-containing polymer wetting reversal agent suitable for shale reservoir protection and a preparation method and application thereof. The preparation method of the wetting reversal agent comprises the following steps: adding ethylamine, triethylamine and deionized water into a reaction bottle, adding perfluorooctanoyl chloride into the system, and performing reaction; after the reaction is completed, continuously adding potassium hydroxide and 2-chloroethanol, and performing reaction; after the reaction is completed, N-ethyl-N-hydroxyethyl perfluorooctanoyl amide is obtained; nanometer particles, a silane coupling agent and ammonia water are added into a dispersant solution, a modification reaction is performed, and a modified nanometer particle solution is obtained; after the pH of the obtained modified nanometer particle solution is adjusted to 5-9, N-ethyl-N-hydroxyethyl perfluorooctanoyl amide is added, nitrogen is blown to remove oxygen, an initiator is added, and a thermal initiation polymerization reaction is performed. The wetting reversal agent has excellent wetting reversal performance and has a certain filtrate reduction effect, and provides innovative thinking for the development of high-performance water-based drilling fluid technology.

Description

Technical Field

[0001] This invention relates to a fluoropolymer wetting reversal agent suitable for shale reservoir protection, its preparation method and application, belonging to the field of oilfield chemical technology for oil and gas resource reservoir stimulation. Background Technology

[0002] In recent years, with the upgrading of exploration theories, technologies, and equipment, oil and gas resource exploration and development has further expanded into complex oil and gas formations such as deep / ultra-deep, deep / ultra-deep water, and unconventional formations. Unconventional oil and gas, with its enormous reserves, has become the most important successor to the "oil-dominated era." Unconventional oil and gas fields—shale oil and gas—are extremely rich in my country, with proven reserves reaching 9368.35 × 10⁻⁶. 8 Shale gas reserves, exceeding the world's proven crude oil reserves, rank second globally. However, shale reservoirs are characterized by small natural fractures and pore throat radii, abundant clay minerals, and pronounced capillary self-absorption. When exposed to external fluids, these intrusions lead to fatal reservoir damage, including weakened fracture surface mechanical properties, hydration and detachment of water-sensitive clay minerals causing blockage, and accelerated closure of natural / artificial fractures inducing liquid phase trapping. This is a major factor limiting the efficient development of shale oil and gas production. Drilling fluids play a crucial role in shale gas resource extraction; however, when using water-based drilling fluids in shale formations, the contact between water and clay-rich shale causes hydration and expansion, easily inducing solid phase blockage and liquid phase trapping damage. A high-quality drilling fluid system can significantly reduce the potential physicochemical damage to shale gas reservoirs. The complexity and variability of shale reservoirs make changes in wettability a key factor restricting development efficiency. Therefore, considering how to change wettability and optimize the water-based drilling fluid system used in water-sensitive mudstone and shale formations has become a research hotspot worldwide.

[0003] The wettability of reservoir rocks plays a decisive role in controlling the fluid distribution within the rock pores. Adjusting the surface wettability by modifying the surface energy or morphology of the rock is an effective technical approach to reduce fluid phase intrusion in drilling and completion fluids, eliminate fluid phase trapping damage, improve micro- and nano-pore throat seepage channels, and enhance reservoir protection. Commonly used wetting reversal agents include silicon-based and fluorine-based surfactants or their polymer solutions. Silicon-based wetting reversal agents have good dispersibility and strong adsorption in formations, but their ability to change formation wettability is limited, making them suitable for formations with high permeability. Fluoropolymers, with their extremely small fluorine atomic radii and extremely high CF bond energies, possess very low surface energy. Their hydrophobic properties are far superior to silicon-based wetting reversal agents, changing the core surface from hydrophilic to hydrophobic, achieving wettability reversal, preventing water-locking damage, and providing an effective approach to improving high-performance drilling fluids for shale oil and gas.

[0004] Chinese patent document CN110982009A discloses a fluoropolymer microemulsion wetting reversal agent capable of significantly altering reservoir wettability and its preparation method. This wetting reversal agent is composed of acrylic monomers, emulsifiers, initiators, fluorocarbon surfactants, ethanol, and water, and is used for reservoir modification. The reaction conditions are mild and the process is safe. The preparation process of this wetting reversal agent is simple, and it exhibits good compatibility with other water-soluble systems, enabling the reservoir to change from water-wettable to hydrophobic. Chinese patent document CN115820226A describes the preparation of a wetting reversal agent by using fatty acids, organic amines, quaternary ammonium salt reagents, and diluents in a mass-to-volume ratio of 1.8–2.2 g: 0.8–1.2 g: 0.8–1.2 g: 0.2–0.4 mL. The wetting reversal agent forms an effective adsorption effect on the surface of the weighting material, changes the hydrophilicity of the weighting material surface, and increases the compatibility of the weighting material with the oil-based drilling fluid system. After being mixed evenly with diesel oil and then barite is added, no significant sedimentation occurs, thus solving the sedimentation stability problem of the weighting material in the system. Chinese patent document CN115895629A discloses a wetting reversal agent with a dual-repellent sulfonated carbon nanotube / modified graphene oxide depressurization and injection enhancement effect. It is composed of modified graphene oxide, a silane coupling agent, sulfonated carbon nanotubes, a fluorinated monomer, and an organic solvent. This agent can change the reservoir's hydrophilic-oleophilic nature to dual-repellent, thereby mitigating the adverse effects of liquid lock-in and improving the injection capacity of the hydrophilic oil layer in the reservoir, achieving the goal of depressurization and injection enhancement. Chinese patent document CN112961662A discloses a wetting reversal agent, a wetting reversal fluid, and a pressure-driven water injection method. This wetting reversal agent is composed of anionic surfactants, nanoparticles, cationic polymers, and water. It is used to change the wettability of the pore throat rock surface, and then water is pumped into the fracture network to displace crude oil. The injected water can more easily displace the crude oil, thereby improving the crude oil recovery rate.

[0005] To address the problem of water-sensitive shale reservoir liquid phase trapping damage, this paper proposes adding wetting reversal agents to drilling fluids to mitigate water-locking damage, providing a new approach for drilling and completion fluid technology to protect low-permeability and ultra-low-permeability reservoirs. Currently, wetting reversal agents used in drilling fluids can only achieve a water phase contact angle of at most 110°, but not exceeding 135°. The drilling fluid performance only meets the basic requirements of carrying rock and inhibiting hydration swelling, but the reservoir protection effect is not ideal, with low core permeability recovery values, and the complex structural characteristics of shale reservoirs are not fully considered. Therefore, improving the wetting reversal effect of drilling fluids is of great significance for the efficient development of shale gas, alleviating my country's energy pressure, ensuring energy security, and optimizing the energy structure. Summary of the Invention

[0006] To address the shortcomings of existing technologies, particularly the poor dispersibility and limited wetting reversal capabilities of current water-based drilling fluid wetting reversal agents, this invention provides a fluoropolymer wetting reversal agent suitable for shale reservoir protection, along with its preparation method and application. This wetting reversal agent exhibits excellent wetting reversal performance without affecting the rheological properties of the drilling fluid system, and also has a certain effect on reducing filtration loss. It provides innovative thinking for the development of high-performance water-based drilling fluid technology, thereby supporting safe, efficient, and economical drilling in unconventional oil and gas resources.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection includes the following steps:

[0009] (1) Synthesis of N-ethyl-N-hydroxyethyl perfluorooctamide

[0010] Ethylamine, triethylamine, and deionized water were added to a reaction flask, followed by the addition of perfluorooctanoyl chloride to the system for further reaction. After the reaction was complete, potassium hydroxide and 2-chloroethanol were added to continue the reaction. After the reaction was complete, N-ethyl-N-hydroxyethylperfluorooctanoamide was obtained.

[0011] (2) Preparation of fluoropolymer wetting reversal agent

[0012] Nanoparticles, silane coupling agent, and ammonia were added to a dispersant solution and ultrasonically dispersed to obtain a mixed solution. Then, a modification reaction was carried out to obtain a modified nanoparticle solution. After adjusting the pH of the obtained modified nanoparticle solution to 5-9, N-ethyl-N-hydroxyethyl perfluorooctamide prepared in step (1) was added. After purging with nitrogen to remove oxygen, an initiator was added, and a thermally initiated polymerization reaction was carried out to obtain a fluoropolymer wetting reversal agent suitable for shale reservoir protection.

[0013] According to a preferred embodiment of the present invention, the mass ratio of ethylamine to triethylamine in step (1) is 1 to 2:1, more preferably 1:1; and the mass ratio of deionized water to triethylamine is 1 to 3:1.

[0014] According to a preferred embodiment of the present invention, the ratio of the total mass of ethylamine and triethylamine to the mass of perfluorooctanoyl chloride in step (1) is 1:0.1 to 0.4, and more preferably 1:0.2 to 0.3.

[0015] According to a preferred embodiment of the present invention, the perfluorooctanoic acid chloride added to the system in step (1) is added at a temperature of 20–40°C, more preferably 25–35°C, and the dropping rate is 2–3 drops / s.

[0016] According to a preferred embodiment of the present invention, the reaction temperature for adding perfluorooctanoyl chloride in step (1) is 55-65°C, and the reaction time is 3-7 hours.

[0017] According to a preferred embodiment of the present invention, the mass ratio of 2-chloroethanol to potassium hydroxide in step (1) is 1.5 to 6:1, and more preferably 2 to 4.5:1.

[0018] According to a preferred embodiment of the present invention, the ratio of the total mass of potassium hydroxide and 2-chloroethanol to the total mass of ethylamine and triethylamine in step (1) is 0.05 to 0.25:1, and more preferably 0.1 to 0.2:1.

[0019] According to a preferred embodiment of the present invention, in step (1), the reaction temperature for adding potassium hydroxide and 2-chloroethanol is 70-80°C, and the reaction time is 20-30 h.

[0020] According to a preferred embodiment of the present invention, in step (1), after the reaction of adding potassium hydroxide and 2-chloroethanol is completed, a post-processing step is further included, specifically as follows: the obtained reaction mixture is naturally cooled to room temperature, distilled water is added, the mass ratio of the added distilled water to the reaction mixture is 0.5 to 2:1, centrifuged, the obtained solid is washed with distilled water 2 to 3 times, and dried at 80°C for 12 hours to obtain N-ethyl-N-hydroxyethyl perfluorooctamide.

[0021] According to the present invention, the molecular structure of N-ethyl-N-hydroxyethyl perfluorooctamide obtained in step (1) is shown in Formula I below:

[0022]

[0023] According to a preferred embodiment of the present invention, the dispersant solution in step (2) is obtained by dissolving a dispersant in water, wherein the dispersant is one or a combination of two or more of anhydrous ethanol, glycerol, and polyvinyl alcohol (PVA); the mass ratio of the dispersant to water is 1:1 to 3, more preferably 1:1 to 2; and the weight average molecular weight of the polyvinyl alcohol (PVA) is 10,000 to 200,000.

[0024] According to a preferred embodiment of the present invention, the nanoparticles in step (2) are silica nanoparticles and / or silicon nanoparticles; the particle size of the nanoparticles is 30 to 100 nm.

[0025] According to a preferred embodiment of the present invention, the silane coupling agent in step (2) is one or a combination of two or more of γ-(methacryloyloxy)propyltrimethoxysilane (KH-570), γ-glycidoxypropyltrimethoxysilane (KH-560), and γ-mercaptopropyltriethoxysilane (KH-580).

[0026] According to a preferred embodiment of the present invention, the mass fraction of NH3 in the ammonia water in step (2) is 25-28%.

[0027] According to a preferred embodiment of the present invention, the mass ratio of the nanoparticles, silane coupling agent and ammonia in step (2) is 1-7:1-6:1.

[0028] According to a preferred embodiment of the present invention, the total mass fraction of nanoparticles, silane coupling agent and ammonia in the mixed solution in step (2) is 10-40%, more preferably 15-30%.

[0029] According to a preferred embodiment of the present invention, the temperature of the modification reaction in step (2) is 50-80°C; and the time of the modification reaction is 4-7 hours.

[0030] According to a preferred embodiment of the present invention, in step (2), the pH of the modified nanoparticle solution is adjusted to 5-9 using a NaOH aqueous solution with a mass fraction of 20-30%.

[0031] According to a preferred embodiment of the present invention, the mass ratio of N-ethyl-N-hydroxyethyl perfluorooctamide in step (2) to the total mass of nanoparticles, silane coupling agent and ammonia is 0.15 to 0.3:1.

[0032] According to a preferred embodiment of the present invention, the initiator in step (2) is one or a combination of two or more of azobisisobutyronitrile, ammonium persulfate, and benzoyl peroxide; the mass ratio of the initiator to the total mass of the nanoparticles, silane coupling agent, and ammonia is 0.03 to 0.05:1.

[0033] According to a preferred embodiment of the present invention, the temperature of the polymerization reaction in step (2) is 60-90°C, more preferably 70-80°C; the time of the polymerization reaction is 6-9 hours, more preferably 7-8 hours; and the stirring speed during the polymerization reaction is 300-600 rpm, more preferably 400-500 rpm.

[0034] A fluoropolymer wetting reversal agent suitable for shale reservoir protection is prepared using the above-described preparation method.

[0035] According to the present invention, the above-mentioned fluoropolymer wetting reversal agent suitable for shale reservoir protection is used in water-based drilling fluid; preferably, the content of the fluoropolymer wetting reversal agent suitable for shale reservoir protection in the drilling fluid is 1.5 to 2 wt%.

[0036] The technical features and beneficial effects of this invention are as follows:

[0037] 1. The wetting reversal agent of the present invention has good dispersibility in solution and uniform particle distribution. It can significantly reduce the surface tension of the liquid phase, prevent the self-absorption of rock capillaries, and increase the contact angle between the liquid phase and the rock surface, thereby changing the rock surface from water wetting to hydrophobic properties.

[0038] 2. The wetting reversal agent of the present invention introduces an organosilicon functional group with superhydrophobic properties into the molecular structure of conventional fluorinated wetting reversal agents. By utilizing the synergistic effect of organofluorine and silicon, it adsorbs, deforms, and accumulates on the rock surface to form a dense hydrophobic film, thereby achieving wetting reversal, reducing the migration resistance of fluids in the reservoir, preventing the liquid and solid phases in the drilling fluid from invading the formation, and effectively protecting the reservoir.

[0039] 3. The wetting reversal agent developed by the present invention in a specific ratio, after being aged at high temperature (180°C), has the effect of inhibiting the hydration and dispersion of mudstone and drill cuttings, and also has the effects of reducing filtration loss and improving flow pattern.

[0040] 4. The preparation method of the present invention is mild, the raw materials are readily available, the reaction conditions are easy to control, the reaction process is safe, and the preparation can be completed under general chemical conditions without the need for complex equipment and harsh reaction conditions. Attached Figure Description

[0041] Figure 1 The infrared spectrum of N-ethyl-N-hydroxyethyl perfluorooctamide prepared in Example 1 is shown.

[0042] Figure 2 The NMR spectrum of N-ethyl-N-hydroxyethyl perfluorooctamide prepared in Example 1 is shown.

[0043] Figure 3 This is a contact angle test diagram of the core slice after processing in Example 1. Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited thereto.

[0045] The polyvinyl alcohol used in the examples has a molecular weight of 30,000 to 50,000; the silica nanoparticles used have a particle size of 40 to 60 nm.

[0046] Example 1

[0047] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection includes the following steps:

[0048] (1) Synthesis of N-ethyl-N-hydroxyethyl perfluorooctamide

[0049] (1.1) Add 10g of ethylamine, 10g of triethylamine and 20g of deionized water to a three-necked flask equipped with a reflux condenser and a mechanical stirrer. At 35°C, add 4.5g of perfluorooctanoyl chloride dropwise at a rate of 2 drops / s using a constant pressure dropping funnel. After the addition is complete, heat the oil bath to 60°C and react at 60°C for 4 hours to obtain a mixed solution.

[0050] (1.2) Add 1g of potassium hydroxide and 3g of 2-chloroethanol to the mixed solution obtained in step (1.1) above, heat to 75℃, and react at 75℃ for 24h. After the reaction is completed, cool the resulting reaction mixture to room temperature naturally, add 50g of distilled water, centrifuge, wash the centrifuged solid three times with distilled water, and dry the solid at 80℃ for 12h to obtain N-ethyl-N-hydroxyethyl perfluorooctanoamide.

[0051] (2) Preparation of fluoropolymer wetting reversal agent

[0052] (2.1) Weigh 15g of anhydrous ethanol and 30g of deionized water into a beaker to prepare a dispersant solution. Then add 5g of silica nanoparticles, 4g of KH-570 and 1g of ammonia into the beaker. Sonicate in a water bath at room temperature for 30min. Add the resulting mixed solution into a three-necked flask equipped with a reflux condenser and a mechanical stirrer. React in an oil bath at 70℃ and 450rpm for 6h to obtain a modified nano silica solution.

[0053] (2.2) Add 25% NaOH aqueous solution (1 drop / s) to the modified nano silica solution obtained in step (2.1) under stirring to adjust the pH of the monomer solution to 8, and then add 2.4g of N-ethyl-N-hydroxyethyl perfluorooctamide prepared in step (1.2) to obtain a mixed reaction solution.

[0054] (2.3) The mixed reaction solution obtained in step (2.2) was deoxygenated for 30 min under nitrogen protection, then heated to 80°C, and 0.4 g of initiator azobisisobutyronitrile was added. The polymerization reaction was carried out at 80°C and a stirring rate of 500 rpm for 8 h. After the reaction was completed, it was cooled to room temperature to obtain a fluoropolymer wetting reversal agent suitable for shale reservoir protection.

[0055] Example 2

[0056] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection includes the following steps:

[0057] (1.1) Add 10g of ethylamine, 10g of triethylamine and 20g of deionized water to a three-necked flask equipped with a reflux condenser and a mechanical stirrer. At 35°C, add 4.5g of perfluorooctanoyl chloride dropwise at a rate of 2 drops / s using a constant pressure dropping funnel. After the addition is complete, heat the oil bath to 60°C and react at 60°C for 4 hours to obtain a mixed solution.

[0058] (1.2) Add 1g of potassium hydroxide and 3g of 2-chloroethanol to the mixed solution obtained in step (1.1) above, heat to 75℃, and react at 75℃ for 24h. After the reaction is completed, cool the resulting reaction mixture to room temperature naturally, add 50g of distilled water, centrifuge, wash the centrifuged solid three times with distilled water, and dry the solid at 80℃ for 12h to obtain N-ethyl-N-hydroxyethyl perfluorooctamide.

[0059] (2) Preparation of fluoropolymer wetting reversal agent

[0060] (2.1) Weigh 15g of anhydrous ethanol and 30g of deionized water into a beaker to prepare a dispersant solution. Then add 6g of silica nanoparticles, 4g of KH-570 and 1g of ammonia into the beaker. Sonicate in a water bath at room temperature for 30min. Add the mixed solution to a three-necked flask equipped with a reflux condenser and a mechanical stirrer. React in an oil bath at 70℃ and 450rpm for 6h to obtain a modified nano silica solution.

[0061] (2.2) Add 25% NaOH aqueous solution (1 drop / s) to the modified nano silica solution obtained in step (2.1) under stirring to adjust the pH of the monomer solution to 8, and then add 2.4g of N-ethyl-N-hydroxyethyl perfluorooctamide prepared in step (1.2) to obtain a mixed reaction solution.

[0062] (2.3) The mixed reaction solution obtained in step (2.2) was deoxygenated for 30 min under nitrogen protection, then heated to 80°C, and 0.4 g of initiator azobisisobutyronitrile was added. The polymerization reaction was carried out at 80°C and a stirring rate of 500 rpm for 8 h. After the reaction was completed, it was cooled to room temperature to obtain a fluoropolymer wetting reversal agent suitable for shale reservoir protection.

[0063] Example 3

[0064] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection includes the following steps:

[0065] (1.1) Add 10g of ethylamine, 10g of triethylamine and 20g of deionized water to a three-necked flask equipped with a reflux condenser and a mechanical stirrer. At 35°C, add 4.5g of perfluorooctanoyl chloride dropwise at a rate of 2 drops / s using a constant pressure dropping funnel. After the addition is complete, heat the oil bath to 60°C and react at 60°C for 4 hours to obtain a mixed solution.

[0066] (1.2) Add 1g of potassium hydroxide and 3g of 2-chloroethanol to the mixed solution obtained in step (1.1) above, heat to 75℃, and react at 75℃ for 24h. After the reaction is completed, cool the resulting reaction mixture to room temperature naturally, add 50g of distilled water, centrifuge, wash the centrifuged solid three times with distilled water, and dry the solid at 80℃ for 12h to obtain N-ethyl-N-hydroxyethyl perfluorooctanoamide.

[0067] (2) Preparation of fluoropolymer wetting reversal agent

[0068] (2.1) Weigh 15g of anhydrous ethanol and 30g of deionized water into a beaker to prepare a dispersant solution. Then add 5g of silica nanoparticles, 3g of KH-570 and 1g of ammonia into the beaker. Sonicate in a water bath at room temperature for 30min. Add the resulting mixed solution into a three-necked flask equipped with a reflux condenser and a mechanical stirrer. React in an oil bath at 70℃ and 450rpm for 6h to obtain a modified nano silica solution.

[0069] (2.2) Add 25% NaOH aqueous solution (1 drop / s) to the modified nano silica solution obtained in step (2.1) under stirring to adjust the pH of the monomer solution to 8, and then add 2.4g of N-ethyl-N-hydroxyethyl perfluorooctamide prepared in step (1.2) to obtain a mixed reaction solution.

[0070] (2.3) The mixed reaction solution obtained in step (2.2) was deoxygenated for 30 min under nitrogen protection, then heated to 80°C, and 0.4 g of initiator azobisisobutyronitrile was added. The polymerization reaction was carried out at 80°C and a stirring rate of 500 rpm for 8 h. After the reaction was completed, it was cooled to room temperature to obtain a fluoropolymer wetting reversal agent suitable for shale reservoir protection.

[0071] Example 4

[0072] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection includes the following steps:

[0073] (1.1) Add 10g of ethylamine, 10g of triethylamine and 20g of deionized water to a three-necked flask equipped with a reflux condenser and a mechanical stirrer. At 35°C, add 5g of perfluorooctanoic acid chloride dropwise at a rate of 2 drops / s using a constant pressure dropping funnel. After the addition is complete, heat the oil bath to 60°C and react at 60°C for 4 hours to obtain a mixed solution.

[0074] (1.2) Add 1g of potassium hydroxide and 3g of 2-chloroethanol to the mixed solution obtained in step (1.1) above, heat to 75℃, and react at 75℃ for 24h. After the reaction is completed, cool the resulting reaction mixture to room temperature naturally, add 50g of distilled water, centrifuge, wash the centrifuged solid three times with distilled water, and dry the solid at 80℃ for 12h to obtain N-ethyl-N-hydroxyethyl perfluorooctanoamide.

[0075] (2) Preparation of fluoropolymer wetting reversal agent

[0076] (2.1) Weigh 15g of anhydrous ethanol and 30g of deionized water into a beaker to prepare a dispersant solution. Then add 5g of silica nanoparticles, 4g of KH-570 and 1g of ammonia into the beaker. Sonicate in a water bath at room temperature for 30min. Add the mixed solution to a three-necked flask equipped with a reflux condenser and a mechanical stirrer. React in an oil bath at 70℃ and 450rpm for 6h to obtain a modified nano silica solution.

[0077] (2.2) Add 25% NaOH aqueous solution (1 drop / s) to the modified nano silica solution obtained in step (2.1) under stirring to adjust the pH of the monomer solution to 8, and then add 1.75g ​​of N-ethyl-N-hydroxyethyl perfluorooctamide prepared in step (1.2) to obtain mixed reaction solution A;

[0078] (2.3) The mixed reaction solution A obtained in step (2.2) above was deoxygenated for 30 min under nitrogen protection, then heated to 80°C, and 0.4 g of initiator azobisisobutyronitrile was added. The polymerization reaction was carried out at 80°C and a stirring rate of 500 rpm for 8 h. After the reaction was completed, it was cooled to room temperature, which is a fluoropolymer wetting reversal agent suitable for shale reservoir protection.

[0079] Example 5

[0080] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection is as described in Example 1, except that: in step (2.1), an equal mass of polyvinyl alcohol is used instead of anhydrous ethanol, and other conditions and component ratios are the same as in Example 1.

[0081] Example 6

[0082] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection is as described in Example 1, except that: in step (2.2), a 25% NaOH aqueous solution is used to adjust the pH of the monomer solution to 6, and other conditions and component ratios are the same as in Example 1.

[0083] Example 7

[0084] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection is as described in Example 1, except that the polymerization reaction temperature in step (2.3) is 75°C, and other conditions and component ratios are the same as in Example 1.

[0085] Example 8

[0086] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection is as described in Example 1, except that: in step (2.3), an equal mass of ammonium persulfate is used instead of azobisisobutyronitrile, and other conditions and component ratios are the same as in Example 1.

[0087] Comparative Example 1

[0088] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection is as described in Example 1, except that the amount of N-ethyl-N-hydroxyethyl perfluorooctamide added in step (1.1) is 4g.

[0089] Comparative Example 2

[0090] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection is described in Example 1, except that the amount of KH-570 added in step (2.1) is 0g.

[0091] Comparative Example 3

[0092] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection is as described in Example 1, except that the amount of azobisisobutyronitrile added in step (2.3) is 0g.

[0093] Comparative Example 4

[0094] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection is as described in Example 1, except that in step (2.1), KH-550 of equal mass is used instead of KH-570, and other conditions and component ratios are the same as in Example 1.

[0095] Comparative Example 5

[0096] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection is as described in Example 1, except that: in step (2.1), calcium oxide nanoparticles of equal mass are used instead of silica nanoparticles, and other conditions and component ratios are the same as in Example 1.

[0097] Comparative Example 6

[0098] A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection is as described in Example 1, except that: in step (2.2), an equal mass of polytrifluorochloroethylene (PCTFE) is used instead of the fluorinated compound N-ethyl-N-hydroxyethyl perfluorooctamide, and other conditions and component ratios are the same as in Example 1.

[0099] Comparative Example 7

[0100] Comparative Example 7 was OP-10, a commercially available surfactant for drilling fluids, purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0101] Test case

[0102] The various embodiments and comparative examples were tested according to the following methods.

[0103] A detection method for fluoropolymer wetting reversal agents suitable for shale reservoir protection includes the following steps:

[0104] Preparation of 4% bentonite-based slurry: Add 16g bentonite and 0.6g anhydrous sodium carbonate to 400mL distilled water, stir thoroughly at 8000rpm for 20min at room temperature, interrupting at least twice to scrape off the adhering material on the cup wall, and then seal and let stand at 25℃±1℃ for 24h for hydration.

[0105] Drilling fluid sample preparation: Take 400 mL of 4% bentonite-based slurry, add 8 g (2%) of the wetting reversal agent prepared in the examples and comparative examples respectively, and stir at 6000 r / min for 20 min at room temperature;

[0106] (a) Contact Angle Test

[0107] The fluoropolymer wetting reversal agents synthesized in the examples and comparative examples were prepared as 2.0 wt.% aqueous solutions. Natural rock cores were cut into 0.5 cm thick slices and immersed in the wetting reversal agent solution. After 24 hours, the slices were removed and dried at 105°C for 4 hours. Using a micropipette, droplets were placed onto the surface of the rock cores treated with different wetting reversal agents. The droplet morphology on the rock surface was magnified using measurement software to ensure clarity, and then photographed. The wetting angle was measured using software. This process was repeated three times, and the average value was taken to obtain the contact angle value. The contact angle measurement data are shown in Table 1.

[0108] Table 1. Contact angle data after wetting reversal agent treatment.

[0109] test sample Contact angle (water, °) Unprocessed 27.1 Example 1 149.7 Example 2 134.4 Example 3 132.7 Example 4 131.3 Example 5 133.7 Example 6 129.5 Example 7 131.8 Example 8 134.9 Comparative Example 1 94 Comparative Example 2 72.3 Comparative Example 3 86.4 Comparative Example 4 105.4 Comparative Example 5 108.9 Comparative Example 6 78 Comparative Example 7 36.8

[0110] As shown in Table 1 above, comparing the performance test data of the examples and comparative examples, the core surface exhibited strong water wettability without core treatment, with a contact angle of 27.1° with water. At the same concentration, the fluoropolymer wetting reversal agent prepared in Example 1 showed the best effect at 149.7°. In Example 2, the increased content of nano-silica resulted in a deficiency in the number of hydrophobic links, reducing the steric hindrance effect and hindering the interaction between the silane coupling agent and nano-silica. In Examples 3 and 4, the amounts of KH570 and N-ethyl-N-hydroxyethyl perfluorooctamide were reduced, leading to a weakened dehydration reaction of the modifier and a decrease in the adsorption of the fluoropolymer on the modified silica surface. In Example 6, the solution pH was 6, at which the hydrolysis rate of fluoride was faster, resulting in a reduction in the number of hydrophobic groups. In Examples 5 and 8, equal masses of polyvinyl alcohol were used instead of anhydrous ethanol, and ammonium persulfate was used instead of azobisisobutyronitrile, resulting in low effective conversion rates of the modified nano-silica and reduced performance of the wetting reversal agent. Comparative Example 1 increased the amount of the fluoropolymer N-ethyl-N-hydroxyethyl perfluorooctamide; excessive fluoropolymer segments may hinder the contact between water molecules and the nano-silica surface, thus weakening the wetting reversal. Comparative Example 2 lacked the KH570 silane coupling agent, thus missing the hydrophobic organic chains introduced by KH570 through bonding to its surface. The silanol groups (Si-OH) at the hydroxyl ends of KH570 could not connect with the surface hydroxyl groups of the nano-silica to form stable silicon-oxygen bonds, thereby weakening the chemical bond between the particles and the polymer. Comparative Example 3, lacking the initiator azobisisobutyronitrile (AIB), could not initiate a chemical reaction on the silica surface via free radical polymerization, hindering its substitution reaction with the hydroxyl groups (-OH) on the SiO2 surface. This made it difficult to form a hydrophobic polymer film and suppressed the hydrophilic-to-hydrophobic transition of the nano-silica surface. Comparative Example 4 directly used KH550 instead of the KH570 of this invention. The amino groups of KH550 easily form hydrogen bonds with water molecules, resulting in inferior hydrophobic effects and wetting reversal agent stability compared to KH570. Comparative Example 5 directly used calcium oxide nanoparticles instead of silica nanoparticles. Calcium oxide nanoparticles easily react with water to form calcium hydroxide (Ca(OH)2), causing nanoparticle aggregation and making it difficult to control their surface properties, resulting in a less effective modification than silica nanoparticles. In Comparative Example 6, an equal amount of polychlorotrifluoroethylene (PCTFE) was used to replace the fluorinated compound N-ethyl-N-hydroxyethyl perfluorooctamide. Poor compatibility between PCTFE and nano-silica led to delamination of the modified material during preparation and use, resulting in a decrease in wetting reversal. In Comparative Example 7, the domestically produced surfactant OP-10 was used, but no significant wetting reversal effect was observed; its wetting reversal ability was significantly lower than that of Example 1.In summary, the fluoropolymer wetting reversal agent of the present invention can effectively reduce the liquid phase invasion of drilling and completion fluids, relieve liquid-solid phase trap damage, and improve the seepage channels of micro-micro-nano pore throats by changing the free energy of the rock surface, thereby adjusting the wettability of the rock surface. It is of great value for improving the protection performance of reservoirs.

[0111] (II) Capillary self-priming test

[0112] Using untreated hard neutral glass spotting capillaries with an inner diameter of 0.5 mm and a length of 100 mm, wetting reversal agents of different mass fractions were prepared for the examples and comparative examples. The capillaries were vertically inserted into the solution, and the self-absorption height of the solution in the capillary was recorded. The self-absorption liquid level reduction rate of the capillary was calculated. Water was used as a control group. The capillary data are shown in Table 2.

[0113] Table 2. Capillary data after treatment with wetting reversal agent.

[0114]

[0115]

[0116] As shown in Table 2 above, comparing the performance test data of the examples and comparative examples, the fluoropolymer wetting reversal agent prepared in Example 1, by introducing a large number of fluoroalkyl groups that aggregate on the rock surface and self-configure to form a hydrophobic surface, enhances hydrophobicity and reduces capillary resistance, causing the liquid surface at the capillary tip to change from a concave liquid surface to a convex liquid surface, thereby reversing the reservoir wettability. It can reduce the capillary self-absorption liquid surface height from 49 mm to 6 mm, with a reduction rate of 87.8%, achieving the best wetting effect. In Example 2, due to the increased content of nano-silica, the aggregation or accumulation between particles increased, causing the hydrophobic groups to be wrapped inside the particles or at the interface between adjacent particles, unable to be exposed on the particle surface. In Examples 3 and 4, the dosages of KH570 and N-ethyl-N-hydroxyethyl perfluorooctamide were reduced, resulting in an excess of adsorption sites on the nano-silica surface. This led to uneven adsorption sites of the silane coupling agent and fluorinated groups on its surface, reducing the hydrophobic effect. In Example 6, the solution had a pH of 6, resulting in insufficient surface charge on the nano-silica, leading to incomplete adsorption of the silane coupling agent and thus affecting hydrophobicity. In Examples 5 and 8, equal masses of polyvinyl alcohol were used instead of anhydrous ethanol, and ammonium persulfate was used instead of azobisisobutyronitrile, respectively. These methods failed to effectively react with the hydrophobic substances on the nano-silica surface, thus affecting the reaction rate, hydrophobic modification effect, and final surface morphology. In Comparative Example 1, the amount of the fluoropolymer N-ethyl-N-hydroxyethyl perfluorooctamide was increased. However, under the influence of strong acid or strong alkali environments, excessive fluoropolymers can react or degrade, thereby reducing the wetting reversal effect. Comparative Example 2 did not contain KH570 silane coupling agent, resulting in reduced chemical bonding between the silica nanoparticles and the fluoropolymer, leading to decreased adhesion and difficulty in forming a tight hydrophobic film on the rock surface. Comparative Example 3 lacks the initiator azobisisobutyronitrile, leading to nanoparticle aggregation or sedimentation, poor dispersibility, and larger particle size, thus reducing the wetting performance and dispersion performance of the wetting reversal agent in the base slurry. Comparative Example 4 uses KH550 instead of KH570 of this invention. Because KH550 contains hydrophilic groups, it cannot utilize methoxy groups to replace some hydrogen atoms, preventing the formation of hydrophobic bonds. Comparative Example 5 uses calcium oxide nanoparticles instead of silica nanoparticles. Calcium oxide nanoparticles have already hydrolyzed with water, significantly reducing the wetting reversal effect of the wetting reversal agent in the base slurry. Comparative Example 6 uses an equal amount of polychlorotrifluoroethylene (PCTFE) instead of the fluorinated compound N-ethyl-N-hydroxyethyl perfluorooctamide. PCTFE lacks hydroxyl groups, forming strong interfacial tension upon contact with water, resulting in poor wetting reversal performance. In Comparative Example 7, the domestically produced surfactant OP-10 was used. The capillary self-absorption liquid level was comparable to that of the untreated capillary self-absorption liquid level. The capillary self-absorption height reduction rate showed a sharp downward trend compared with Example 1.Therefore, it can be seen that by reducing the height of the capillary self-absorption liquid level and increasing the capillary self-absorption reduction rate, the wettability of the core can be changed from hydrophilic to hydrophobic.

[0117] (III) Evaluation of API Rheological Properties of Drilling Fluids

[0118] Take 400 mL of drilling fluid samples, age them at 180℃, and then stir them at 4000 r / min for 20 min at room temperature. Determine the apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s), dynamic shear force (YP, Pa), and API filtration loss (FL) of the drilling fluids according to GB / T16783.1 2006. API The evaluation data (mL) are shown in Table 3.

[0119] Table 3. API rheological property data of the lubricant base paste containing the examples.

[0120]

[0121] As can be seen from the data in Table 3, comparing the performance test data of the examples and comparative examples, the wetting reversal agent developed in Example 1 of this invention showed a trend of increasing the apparent viscosity (AV, mPa·s) and plastic viscosity (PV, mPa·s) of the drilling fluid-based slurry, and the API filtration loss could be reduced to 9.8 mL. In Example 2, due to the increased content of nano-silica, the surface modification was uneven, resulting in weaker hydrophobicity in some areas. In Examples 3 and 4, the dosage of KH570 and N-ethyl-N-hydroxyethyl perfluorooctamide were reduced, respectively, causing the modified silica to lose some hydrophobicity, resulting in decreased dispersibility and inability to effectively form a stable colloidal structure with the drilling fluid-based slurry. In Example 6, the pH value of the solution was 6, which changed the surface charge of silica, affecting the adsorption effect of the silane coupling agent. In Examples 5 and 8, equal masses of polyvinyl alcohol were used to replace anhydrous ethanol, and ammonium persulfate was used to replace azobisisobutyronitrile, respectively, resulting in low effective conversion rate of modified nano-silica, uneven dispersion, and stratification and aggregation. In Comparative Example 1, the increased amount of fluoropolymer made the drilling fluid too thick, leading to decreased stability and fluidity, and increased flocculation and sedimentation, resulting in filter cake formation and blockage. Comparative Examples 2 and 3, which did not contain KH570 silane coupling agent and the initiator azobisisobutyronitrile (AIBN), allowed nano-silica to integrate more easily into the drilling fluid system, causing the wetting reversal performance to fail and reducing the flow resistance of the drilling fluid, thus increasing filtration loss. In Comparative Examples 4 and 5, KH550 was used directly instead of KH570 of this invention, and calcium oxide nanoparticles were used instead of silica nanoparticles, respectively. The viscosity of the drilling fluid base slurry decreased slightly, but this did not affect the overall performance of the drilling fluid; filtration loss and density remained essentially unchanged. In Comparative Example 6, an equal amount of polychlorotrifluoroethylene (PCTFE) was used instead of the fluorinated compound N-ethyl-N-hydroxyethyl perfluorooctamide. The long and rigid molecular chains of PCTFE restrict its flowability and interactions in the liquid, resulting in relatively high viscosity and significant filtration loss. In Comparative Example 7, surfactant OP-10 was used, which had minimal impact on the rheological properties of the drilling fluid-based slurry. Therefore, it can be concluded that the wetting reversal agent of this invention has almost no effect on the rheological properties of the drilling fluid-based slurry, but can maximize the increase in apparent viscosity and plastic viscosity, and has a certain effect on reducing filtration loss.

[0122] In summary, the fluoropolymer wetting reversal agent for shale reservoir protection developed in this invention can significantly reduce the solid-phase interfacial tension, reverse the wettability of the reservoir from superhydrophilic to superhydrophobic, and disperse in the drilling fluid-based slurry with micro-nano particle sizes. It transforms its capillary force from resistance to driving force, effectively suppressing fluid-sensitive damage and liquid-locking effects caused by the entry of external fluids into water-sensitive shale reservoirs, reducing the probability of pore throat blockage, increasing the advantageous channels for fluid flow, and solving the technical problem of insufficient wetting reversal performance of existing water-based drilling fluid wetting reversal agents. Furthermore, it has minimal impact on the rheological properties of the drilling fluid, thus promoting the further development of water-based drilling fluid technology for shale reservoir protection.

Claims

1. A method for preparing a fluoropolymer wetting reversal agent suitable for shale reservoir protection, comprising the following steps: (1) Synthesis of N-ethyl-N-hydroxyethyl perfluorooctamide Ethylamine, triethylamine, and deionized water were added to a reaction flask, followed by the addition of perfluorooctanoyl chloride to the system for further reaction. After the reaction was complete, potassium hydroxide and 2-chloroethanol were added to continue the reaction. After the reaction was complete, N-ethyl-N-hydroxyethylperfluorooctanoamide was obtained. (2) Preparation of fluoropolymer wetting reversal agent Nanoparticles, silane coupling agent and ammonia water are added to a dispersant solution and ultrasonically dispersed to obtain a mixed solution. Then, a modification reaction is carried out to obtain a modified nanoparticle solution. After adjusting the pH of the obtained modified nanoparticle solution to 5-9, N-ethyl-N-hydroxyethyl perfluorooctamide prepared in step (1) is added. After purging with nitrogen to remove oxygen, an initiator is added, and a thermally initiated polymerization reaction is carried out to obtain a fluoropolymer wetting reversal agent suitable for shale reservoir protection. The dispersant solution is obtained by dissolving a dispersant in water, and the dispersant is one or a combination of two or more of anhydrous ethanol, glycerol, and polyvinyl alcohol; the nanoparticles are silica nanoparticles and / or silicon nanoparticles; the silane coupling agent is one or a combination of two or more of γ-(methacryloyloxy)propyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-mercaptopropyltriethoxysilane; the mass ratio of the nanoparticles, silane coupling agent, and ammonia is 1~7:1~6:1; the mass ratio of N-ethyl-N-hydroxyethyl perfluorooctamide to the total mass of the nanoparticles, silane coupling agent, and ammonia is 0.15~0.3:

1.

2. The method for preparing the fluoropolymer wetting reversal agent suitable for shale reservoir protection according to claim 1, characterized in that, In step (1), the mass ratio of ethylamine to triethylamine is 1~2:1; the mass ratio of deionized water to triethylamine is 1~3:1; and the mass ratio of the total mass of ethylamine and triethylamine to the mass of perfluorooctanoyl chloride is 1:0.1~0.

4.

3. The method for preparing the fluoropolymer wetting reversal agent suitable for shale reservoir protection according to claim 1, characterized in that, In step (1), perfluorooctanoic acid chloride is added to the system at a temperature of 20-40°C and a dropping rate of 2-3 drops / s. The reaction temperature for adding perfluorooctanoic acid chloride is 55-65°C, and the reaction time is 3-7 hours.

4. The method for preparing the fluoropolymer wetting reversal agent suitable for shale reservoir protection according to claim 1, characterized in that, The mass ratio of 2-chloroethanol to potassium hydroxide in step (1) is 1.5~6:1; The ratio of the total mass of potassium hydroxide and 2-chloroethanol to the total mass of ethylamine and triethylamine is 0.05~0.25:

1.

5. The method for preparing the fluoropolymer wetting reversal agent suitable for shale reservoir protection according to claim 1, characterized in that, In step (1), potassium hydroxide and 2-chloroethanol are added and reacted at a temperature of 70~80℃ for 20~30h. In step (1), after the reaction with potassium hydroxide and 2-chloroethanol is completed, a post-processing step is also included, as follows: the obtained reaction mixture is naturally cooled to room temperature, distilled water is added, the mass ratio of the added distilled water to the reaction mixture is 0.5~2:1, centrifuged, the obtained solid is washed with distilled water 2~3 times, and dried at 80℃ for 12h to obtain N-ethyl-N-hydroxyethyl perfluorooctamide.

6. The method for preparing the fluoropolymer wetting reversal agent suitable for shale reservoir protection according to claim 1, characterized in that, In step (2), the mass ratio of the dispersant to water is 1:1 to 3; the weight-average molecular weight of the polyvinyl alcohol is 10,000 to 200,000; the particle size of the nanoparticles is 30 to 100 nm; and the mass fraction of NH3 in the ammonia water is 25 to 28%.

7. The method for preparing the fluoropolymer wetting reversal agent suitable for shale reservoir protection according to claim 1, characterized in that, In step (2), the total mass fraction of nanoparticles, silane coupling agent, and ammonia in the mixed solution is 10-40%; the temperature of the modification reaction is 50-80℃; and the time of the modification reaction is 4-7h. In step (2), the pH of the modified nanoparticle solution is adjusted to 5-9 using a NaOH aqueous solution with a mass fraction of 20-30%.

8. The method for preparing the fluoropolymer wetting reversal agent suitable for shale reservoir protection according to claim 1, characterized in that, The initiator mentioned in step (2) is one or a combination of two or more of azobisisobutyronitrile, ammonium persulfate, and benzoyl peroxide; the mass ratio of the initiator to the total mass of nanoparticles, silane coupling agent, and ammonia is 0.03~0.05:1; The polymerization reaction temperature is 60~90℃; the polymerization reaction time is 6~9h; and the stirring speed during the polymerization reaction is 300~600rpm.

9. A fluoropolymer wetting reversal agent suitable for shale reservoir protection, characterized in that, It was prepared using the preparation method described in claim 1.

10. The application of the fluoropolymer wetting reversal agent for shale reservoir protection as described in claim 1 in water-based drilling fluids, characterized in that, The drilling fluid contains 1.5 to 2 wt% of a fluoropolymer wetting reversal agent suitable for shale reservoir protection.

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