Fluorine-containing polymer wetting reversal agent suitable for shale reservoir protection as well as preparation method and application of fluorine-containing polymer wetting reversal agent

Abstract

The invention provides a fluorine-containing polymer wetting reversal agent suitable for shale reservoir protection as well as a preparation method and application of the fluorine-containing polymer wetting reversal agent. The preparation method of the reverse wetting agent comprises the following steps: adding ethylamine, triethylamine and deionized water into a reaction flask, and adding perfluorooctanoyl chloride into the system for reaction; after the reaction is completed, potassium hydroxide and 2-chloroethanol are continuously added for reaction; and after the reaction is completed, obtaining the N-ethyl-N-hydroxyethyl perfluorooctanamide. Adding nanoparticles, a silane coupling agent and ammonia water into the dispersant solution, and carrying out a modification reaction to obtain a modified nanoparticle solution; and adjusting the pH value of the obtained modified nanoparticle solution to 5-9, adding N-ethyl-N-hydroxyethyl perfluorooctanamide, introducing nitrogen to remove oxygen, adding an initiator, and carrying out thermal initiation polymerization reaction to obtain the composite material. The wetting reversal agent disclosed by the invention has excellent wetting reversal performance and a certain filtration reduction effect, and provides innovative thinking for development of a high-performance water-based drilling fluid technology.

Description

Technical Field

[0001] The invention relates to a fluorine-containing polymer wettability reversal agent suitable for shale reservoir protection, a preparation method and application thereof, and belongs to the technical field of oilfield chemistry for oil and gas resource reservoir reconstruction. Background Art

[0002] In recent years, with the updating and iteration of exploration theories, technologies and equipment, the exploration and development of oil and gas resources has further expanded to complex oil and gas such as deep / ultra-deep layers, deepwater / ultra-deepwater and unconventional oil and gas. Unconventional oil and gas with huge reserves has become the most important successor to oil and gas resources after the end of the "easy oil era". Unconventional oil and gas fields - shale oil and gas are very rich in my country, with proven reserves of 9368.35×10 8 t, far greater than the world's proven reserves of crude oil, ranking second in the world. However, shale reservoirs have small natural fractures and pore throat radii, rich clay minerals, and obvious capillary self-imbibition. When foreign fluids invade, they lead to weakening of the mechanical properties of the fracture surface, hydration and detachment of water-sensitive clay minerals, and accelerated closure of natural / artificial fractures, which induces liquid phase closure and other fatal reservoir damages, which are important reasons that restrict the efficient development of shale oil and gas production. Drilling fluid plays a key role in the exploitation of shale gas resources. However, when drilling with water-based drilling fluid in shale formations, water contacts with clay-rich shale, causing hydration and expansion, which can easily induce solid phase clogging damage and liquid phase closure damage. A high-quality drilling fluid system can greatly reduce the potential physical and chemical damage to shale gas reservoirs. The complexity and variability of shale reservoirs make changes in their wettability one of the key factors restricting development efficiency. Therefore, considering changing wettability and optimizing the water-based drilling fluid system used in water-sensitive shale formations has become a research hotspot worldwide.

[0003] The wettability of reservoir rocks plays a decisive role in controlling the distribution of fluids in rock pores. By changing the surface energy or surface morphology of rocks and then adjusting the surface wettability of rocks, it is an effective technical approach to reduce the liquid phase invasion of drilling and completion fluids, relieve the damage of liquid phase closure, improve the micro-micro-nano pore throat seepage channels, and improve reservoir protection. Commonly used wettability reversal agents include silicon-based and fluorine-based surfactants or their polymer solutions. Silicon-based wettability reversal agents have good dispersibility and strong adsorption in formations, but their ability to transform the wettability of formations is limited, and they are suitable for formations with high permeability. The fluorine atom radius in fluorinated polymers is extremely small, and the bond energy of CF bonds is extremely large, which makes fluorinated polymers have extremely low surface energy. Their hydrophobic properties are much higher than those of silicon-based wettability reversal agents, which can transform the core surface from hydrophilic to hydrophobic, achieve wettability reversal, and prevent water lock damage, providing an effective idea for improving the high-performance drilling fluid for shale oil and gas.

[0004] Chinese patent document CN110982009A discloses a fluorinated polymer microemulsion wettability reversal agent and its preparation method, which can significantly change the wettability of the reservoir. The wettability reversal agent is composed of acrylic monomers, emulsifiers, initiators, fluorocarbon surfactants, ethanol, and water, and is used to transform the reservoir. The reaction conditions are mild and the process is safe. The wettability reversal agent has a simple preparation process and has good compatibility with other water-soluble systems, and can change the reservoir from water wettability to hydrophobicity. Chinese patent document CN115820226A prepares a wetting reversal agent by using fatty acid, organic amine, quaternary ammonium salt reagent and diluent in a mass volume ratio of 1.8-2.2g:0.8-1.2g:0.8-1.2g:0.2-0.4mL. The wetting reversal agent forms an effective adsorption effect with the surface of the weighting material, changes the hydrophilicity of the surface of the weighting material, increases the compatibility of the weighting material with the oil-based drilling fluid system, and after being evenly mixed with diesel, barite is added without obvious sedimentation, thereby solving the sedimentation stability problem of the weighting material in the system. Chinese patent document CN115895629A provides a wettability reversal agent with a double-phobic sulfonated carbon nanotube / modified graphene oxide pressure-reducing and injection-increasing effect, which is made of modified graphene oxide, silane coupling agent, sulfonated carbon nanotube, fluorine-containing monomer, and organic solvent, and can change the reservoir from hydrophilic to lipophilic, thereby weakening the adverse effects of the liquid lock effect, helping to improve the injection capacity of the hydrophilic oil layer of the reservoir, and achieving the purpose of pressure reduction and injection. Chinese patent document CN112961662A provides a wettability reversal agent, a wettability reversal fluid, and a pressure-driven water injection method. The wettability reversal agent is composed of anionic surfactants, nanoparticles, cationic polymers, and water, and is used to change the wettability of the pore throat rock surface, and then pump water into the fracture network to displace crude oil. The injected water can easily displace the movement of crude oil, thereby improving the recovery rate of crude oil.

[0005] In view of the problem of liquid phase trap damage in water-sensitive shale reservoirs, it is proposed to add a wetting reversal agent to the drilling fluid to reduce the degree of water lock damage, which provides ideas for the drilling and completion fluid technology to protect low-permeability and ultra-low-permeability reservoirs. However, the wetting reversal agent currently used in drilling fluids can only make the water phase contact angle reach a maximum of more than 110°, but not more than 135°. The performance of the drilling fluid can only meet the basic requirements of rock carrying and inhibiting hydration expansion, but the reservoir protection effect is not very ideal, the permeability recovery value of the reservoir core is low, and the complex structural characteristics of the shale reservoir are not fully considered. Therefore, improving the wetting reversal effect of drilling fluids is of great significance for the efficient development of shale gas, relieving my country's energy pressure, ensuring energy security and optimizing energy structure. Summary of the invention

[0006] In view of the shortcomings of the prior art, especially the poor dispersibility and poor wetting change ability of the wettability reversal agent for the existing water-based drilling fluid, the present invention provides a fluorine-containing polymer wettability reversal agent suitable for shale reservoir protection and its preparation method and application. The wettability reversal agent of the present invention has excellent wettability reversal performance without affecting the rheology of the drilling fluid system, and has a certain filtration loss reduction effect, providing innovative thinking for the development of high-performance water-based drilling fluid technology, thereby supporting the safe, efficient and economical drilling of unconventional oil and gas resources.

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

[0008] A method for preparing a fluorinated polymer wettability reversal agent suitable for shale reservoir protection comprises the following steps:

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

[0010] Ethylamine, triethylamine and deionized water are added to a reaction bottle, and then perfluorooctanoyl chloride is added to the system to react; after the reaction is completed, potassium hydroxide and 2-chloroethanol are added to react; after the reaction is completed, N-ethyl-N-hydroxyethyl perfluorooctanoyl amide is obtained;

[0011] (2) Preparation of fluorinated polymer wettability reversal agents

[0012] Nanoparticles, silane coupling agent and ammonia water are added to a dispersant solution, and after being uniformly dispersed by ultrasonication, a mixed solution is obtained, and 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, the N-ethyl-N-hydroxyethyl perfluorooctylamide prepared in step (1) is added, and after nitrogen is passed to deoxygenate, an initiator is added to initiate a thermal polymerization reaction to obtain a fluorine-containing polymer wettability reversal agent suitable for shale reservoir protection.

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

[0014] According to the 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 1:0.1-0.4, and more preferably 1:0.2-0.3.

[0015] Preferably, according to the present invention, the perfluorooctanoyl chloride in step (1) is added dropwise to the system at a temperature of 20 to 40° C., more preferably 25 to 35° C.; and the dropping speed is 2 to 3 drops / s.

[0016] Preferably, according to the present invention, the temperature for adding perfluorooctanoyl chloride to react in step (1) is 55-65° C., and the reaction time is 3-7 h.

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

[0018] According to the 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] Preferably, in step (1), the temperature for adding potassium hydroxide and 2-chloroethanol to react is 70-80° C., and the reaction time is 20-30 h.

[0020] Preferably, in step (1), after the potassium hydroxide and 2-chloroethanol are added to complete the reaction, a post-treatment 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, and the obtained solid is washed with distilled water for 2 to 3 times, and dried at 80°C for 12 hours to obtain N-ethyl-N-hydroxyethyl perfluorooctaneamide.

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

[0022]

[0023] Preferably, according to the present invention, the dispersant solution in step (2) 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 (PVA); the mass ratio of the dispersant to water is 1:1 to 3, and more preferably 1:1 to 2; the weight average molecular weight of the polyvinyl alcohol (PVA) is 10,000 to 200,000.

[0024] Preferably according to the present invention, the nanoparticles in step (2) are silicon dioxide nanoparticles and / or silicon nanoparticles; and the particle size of the nanoparticles is 30 to 100 nm.

[0025] Preferably, according to 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-glycidyloxypropyltrimethoxysilane (KH-560), and γ-mercaptopropyltriethoxysilane (KH-580).

[0026] Preferably according to the present invention, the mass fraction of NH3 in the aqueous ammonia in step (2) is 25-28%.

[0027] Preferably, according to the present invention, the mass ratio of the nanoparticles, the silane coupling agent and the ammonia water in step (2) is 1 to 7:1 to 6:1.

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

[0029] Preferably, according to 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] Preferably, according to the present invention, in step (2), a 20-30% by mass NaOH aqueous solution is used to adjust the pH of the modified nanoparticle solution to 5-9.

[0031] Preferably according to the present invention, the ratio of the mass of the N-ethyl-N-hydroxyethyl perfluorooctaneamide in step (2) to the total mass of the nanoparticles, the silane coupling agent and the ammonia water is 0.15 to 0.3:1.

[0032] Preferably, according to 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 ratio of the mass of the initiator to the total mass of the nanoparticles, the silane coupling agent, and the ammonia water is 0.03 to 0.05:1.

[0033] Preferably according to 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 6-9h, more preferably 7-8h; the stirring speed during the polymerization reaction is 300-600rpm, more preferably 400-500rpm.

[0034] A fluorine-containing polymer wettability reversal agent suitable for shale reservoir protection is prepared by adopting the above preparation method.

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

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

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

[0038] 2. The wettability reversal agent of the present invention introduces an organosilicon functional group with super-hydrophobic properties into the molecular structure of a conventional fluorine-containing wettability reversal agent, and utilizes the synergistic effect of organofluorine and silicon to adsorb, deform, and accumulate on the rock surface to form a dense hydrophobic film, thereby achieving wettability reversal, reducing the migration resistance of the fluid 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 wettability reversal agent prepared by the present invention in a specific proportion has the function of inhibiting the hydration and dispersion of shale and drill cuttings after high temperature (180°C) aging, and also has the functions of reducing filtration loss, improving flow pattern and the like.

[0040] 4. The preparation method of the present invention has mild conditions, readily available raw materials, easy control of reaction conditions, and a safe reaction process. The preparation can be completed under general chemical conditions without the need for complex equipment and harsh reaction conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the infrared spectrum of N-ethyl-N-hydroxyethyl perfluorooctaneamide prepared in Example 1.

[0042] Figure 2 This is the NMR spectrum of N-ethyl-N-hydroxyethyl perfluorooctaneamide prepared in Example 1.

[0043] Figure 3 This is a contact angle test diagram of the core piece after treatment in Example 1. DETAILED DESCRIPTION

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

[0045] The molecular weight of the polyvinyl alcohol used in the examples is 30,000 to 50,000; the particle size of the silicon dioxide nanoparticles used is 40 to 60 nm.

[0046] Example 1

[0047] A method for preparing a fluorinated polymer wettability reversal agent suitable for shale reservoir protection comprises the following steps:

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

[0049] (1.1) 10 g of ethylamine, 10 g of triethylamine and 20 g of deionized water were added to a three-necked flask equipped with a condensation reflux device and a mechanical stirrer. At 35°C, 4.5 g of perfluorooctanoyl chloride was dripped into the flask at a rate of 2 drops / s using a constant pressure dropping funnel. After the addition was completed, the oil bath was heated to 60°C and reacted at 60°C for 4 hours to obtain a mixed solution.

[0050] (1.2) Add 1 g potassium hydroxide and 3 g 2-chloroethanol to the mixed solution obtained in the above step (1.1), heat to 75° C., and react at 75° C. for 24 h. After the reaction, cool the reaction mixture naturally to room temperature, add 50 g distilled water, and then centrifuge. Wash the solid obtained by centrifugation 3 times with distilled water, and dry the solid at 80° C. for 12 h to obtain N-ethyl-N-hydroxyethyl perfluorooctaneamide.

[0051] (2) Preparation of fluorinated polymer wettability reversal agents

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

[0053] (2.2) slowly adding (1 drop / s) a 25% by mass NaOH aqueous solution to the modified nano-silica solution obtained in the above step (2.1) under stirring conditions to adjust the pH value of the monomer solution to 8, and then adding 2.4 g of N-ethyl-N-hydroxyethyl perfluorooctaneamide prepared in step (1.2) to obtain a mixed reaction solution;

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

[0055] Example 2

[0056] A method for preparing a fluorinated polymer wettability reversal agent suitable for shale reservoir protection comprises the following steps:

[0057] (1.1) 10 g of ethylamine, 10 g of triethylamine and 20 g of deionized water were added to a three-necked flask equipped with a condensation reflux device and a mechanical stirrer. At 35°C, 4.5 g of perfluorooctanoyl chloride was dripped into the flask at a rate of 2 drops / s using a constant pressure dropping funnel. After the addition was completed, the oil bath was heated to 60°C and reacted at 60°C for 4 hours to obtain a mixed solution.

[0058] (1.2) Add 1 g potassium hydroxide and 3 g 2-chloroethanol to the mixed solution obtained in the above step (1.1), heat to 75° C., and react at 75° C. for 24 h. After the reaction, cool the reaction mixture naturally to room temperature, add 50 g distilled water, and then centrifuge. Wash the solid obtained by centrifugation 3 times with distilled water, and dry the solid at 80° C. for 12 h to obtain N-ethyl-N-hydroxyethyl perfluorooctaneamide.

[0059] (2) Preparation of fluorinated polymer wettability reversal agents

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

[0061] (2.2) slowly adding (1 drop / s) a 25% by mass NaOH aqueous solution to the modified nano-silica solution obtained in the above step (2.1) under stirring conditions to adjust the pH value of the monomer solution to 8, and then adding 2.4 g of N-ethyl-N-hydroxyethyl perfluorooctaneamide prepared in step (1.2) to obtain a mixed reaction solution;

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

[0063] Example 3

[0064] A method for preparing a fluorinated polymer wettability reversal agent suitable for shale reservoir protection comprises the following steps:

[0065] (1.1) 10 g of ethylamine, 10 g of triethylamine and 20 g of deionized water were added to a three-necked flask equipped with a condensation reflux device and a mechanical stirrer. At 35°C, 4.5 g of perfluorooctanoyl chloride was dripped into the flask at a rate of 2 drops / s using a constant pressure dropping funnel. After the addition was completed, the oil bath was heated to 60°C and reacted at 60°C for 4 hours to obtain a mixed solution.

[0066] (1.2) Add 1 g potassium hydroxide and 3 g 2-chloroethanol to the mixed solution obtained in the above step (1.1), heat to 75° C., and react at 75° C. for 24 h. After the reaction, cool the reaction mixture naturally to room temperature, add 50 g distilled water, and then centrifuge. Wash the solid obtained by centrifugation 3 times with distilled water, and dry the solid at 80° C. for 12 h to obtain N-ethyl-N-hydroxyethyl perfluorooctaneamide.

[0067] (2) Preparation of fluorinated polymer wettability reversal agents

[0068] (2.1) 15 g of anhydrous ethanol and 30 g of deionized water were weighed and placed in a beaker to prepare a dispersant solution. Then, 5 g of silica nanoparticles, 3 g of KH-570, and 1 g of ammonia water were added to the beaker. The mixture was ultrasonically treated in a water bath at room temperature for 30 min. The resulting mixed solution was added to a three-necked flask equipped with a condensation reflux device and a mechanical stirrer. The mixture was reacted in an oil bath at 70°C and 450 rpm for 6 h to obtain a modified nano-silica solution.

[0069] (2.2) slowly adding (1 drop / s) a 25% by mass NaOH aqueous solution to the modified nano-silica solution obtained in the above step (2.1) under stirring conditions to adjust the pH value of the monomer solution to 8, and then adding 2.4 g of N-ethyl-N-hydroxyethyl perfluorooctaneamide prepared in step (1.2) to obtain a mixed reaction solution;

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

[0071] Example 4

[0072] A method for preparing a fluorinated polymer wettability reversal agent suitable for shale reservoir protection comprises the following steps:

[0073] (1.1) 10 g of ethylamine, 10 g of triethylamine and 20 g of deionized water were added to a three-necked flask equipped with a condensation reflux device and a mechanical stirrer. At 35°C, 5 g of perfluorooctanoyl chloride was dripped into the flask at a rate of 2 drops / s using a constant pressure dropping funnel. After the addition was completed, the oil bath was heated to 60°C and reacted at 60°C for 4 hours to obtain a mixed solution.

[0074] (1.2) Add 1 g potassium hydroxide and 3 g 2-chloroethanol to the mixed solution obtained in the above step (1.1), heat to 75° C., and react at 75° C. for 24 h. After the reaction, cool the reaction mixture naturally to room temperature, add 50 g distilled water, and then centrifuge. Wash the solid obtained by centrifugation 3 times with distilled water, and dry the solid at 80° C. for 12 h to obtain N-ethyl-N-hydroxyethyl perfluorooctaneamide.

[0075] (2) Preparation of fluorinated polymer wettability reversal agents

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

[0077] (2.2) slowly adding (1 drop / s) a 25% by mass NaOH aqueous solution to the modified nano-silica solution obtained in the above step (2.1) under stirring conditions to adjust the pH value of the monomer solution to 8, and then adding 1.75 g of N-ethyl-N-hydroxyethyl perfluorooctaneamide prepared in step (1.2) to obtain a mixed reaction solution A;

[0078] (2.3) The mixed reaction liquid A obtained in the above step (2.2) was deoxygenated for 30 minutes under nitrogen protection, then heated to 80°C, 0.4 g of initiator azobisisobutyronitrile was added, and polymerization was carried out at 80°C and a stirring rate of 500 rpm for 8 hours. After the reaction was completed, it was cooled to room temperature to obtain a fluorine-containing polymer wettability reversal agent suitable for shale reservoir protection.

[0079] Example 5

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

[0081] Example 6

[0082] A method for preparing a fluorinated polymer wettability reversal agent suitable for shale reservoir protection is as described in Example 1, except that in step (2.2), a 25% by mass NaOH aqueous solution is used to adjust the pH value 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 fluorinated polymer wettability 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 fluorinated polymer wettability reversal agent suitable for shale reservoir protection is as described in Example 1, except that an equal mass of ammonium persulfate is used instead of azobisisobutyronitrile in step (2.3), and other conditions and component ratios are the same as in Example 1.

[0087] Comparative Example 1

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

[0089] Comparative Example 2

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

[0091] Comparative Example 3

[0092] A method for preparing a fluorinated polymer wettability 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 0 g.

[0093] Comparative Example 4

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

[0095] Comparative Example 5

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

[0097] Comparative Example 6

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

[0099] Comparative Example 7

[0100] Comparative Example 7 is commercially available drilling fluid surfactant OP-10, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0101] Test example

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

[0103] A method for detecting a fluoropolymer wettability reversal agent suitable for shale reservoir protection comprises 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, interrupt at least twice to scrape off the adherent matter on the cup wall, and then seal and 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 wettability reversal agent prepared in the embodiment and the comparative example, respectively, and stir at room temperature at a speed of 6000 r / min for 20 min;

[0106] (I) Contact angle test

[0107] The fluorinated polymer wettability reversal agent synthesized in the examples and comparative examples was prepared into a 2.0 wt.% aqueous solution, and the natural core was cut into 0.5 cm thick slices and immersed in the wettability reversal agent solution, taken out after 24 hours, and dried at 105° C. for 4 hours. On the measuring instrument, a micropipette was used to drop a drop of liquid on the surface of the core treated with different wettability reversal agents, and then the measurement software was used to magnify the morphology of the drop on the rock surface, and after making it clear, it was photographed, and the size of the wetting angle was measured by the software. The same shooting and measurement were repeated three times, and the average value was taken to obtain the contact angle value. The contact angle measurement data is 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 can be seen from Table 1 above, by comparing the performance test data of the embodiment and the comparative example, when the core is not treated, the core surface shows strong water wettability, and the contact angle with water is 27.1°. At the same use concentration, the wettability reversal agent of the fluorine-containing polymer prepared in Example 1 has the best effect of 149.7°. In Example 2, due to the increase in the content of nano-silica, the number of hydrophobic chain grafts is insufficient, the steric hindrance effect is reduced, and the interaction between the silane coupling agent and the nano-silica is hindered. In Example 3 and Example 4, the amount of KH570 and N-ethyl-N-hydroxyethyl perfluorooctylamide was reduced respectively, resulting in a weakening of the dehydration reaction of the modifier and a reduction in the adsorption of the fluorine-containing polymer on the surface of the modified silica. In Example 6, the pH value of the solution is 6, and the hydrolysis rate of fluoride at this pH value is relatively fast, resulting in a reduction in the number of hydrophobic groups. In Example 5 and Example 8, polyvinyl alcohol of equal mass is used instead of anhydrous ethanol, and ammonium persulfate is used instead of azobisisobutyronitrile, respectively, resulting in a low effective conversion rate of modified nano-silica, resulting in reduced performance of the wettability reversal agent. In Comparative Example 1, the amount of fluoropolymer N-ethyl-N-hydroxyethyl perfluorooctaneamide is increased. Excessive fluoropolymer segments may hinder the contact between water molecules and the surface of nano-silica, thereby weakening the realization of wettability reversal. Comparative Example 2 does not contain KH570 silane coupling agent, and lacks the hydrophobic organic chain introduced by KH570 on its surface by bonding. The silanol group (Si-OH) at the hydroxyl end of KH570 itself cannot be connected to the surface hydroxyl of nano-silica to form a stable silicon-oxygen bond, thereby weakening the chemical bonding between the particle and the polymer. Comparative Example 3 does not contain the initiator azobisisobutyronitrile, and cannot initiate a chemical reaction on the surface of silica through free radical polymerization, which hinders its substitution reaction with the hydroxyl (-OH) on the surface of SiO2, making it difficult to form a layer of hydrophobic polymer film, and inhibiting the hydrophilic to hydrophobic transformation of the surface of nano-silica. In Comparative Example 4, KH550 is directly used to replace the KH570 of the present invention. The amino group of KH550 easily forms hydrogen bonds with water molecules, resulting in the hydrophobic effect and the stability of the wetting reversal agent being inferior to KH570. In Comparative Example 5, calcium oxide nanoparticles are directly used to replace silica nanoparticles. Calcium oxide nanoparticles easily react with water in water to form calcium hydroxide (Ca(OH)2), resulting in nanoparticle agglomeration and difficulty in controlling their surface properties, making the modification effect not as good as that of silica nanoparticles. In Comparative Example 6, an equal amount of polytrifluorochloroethylene (PCTFE) was directly used to replace the fluorinated compound N-ethyl-N-hydroxyethyl perfluorooctaneamide. The compatibility between polytrifluorochloroethylene and nano-silicon dioxide was poor, resulting in stratification of the modified material during preparation and use, resulting in a decrease in wetting reversal. In Comparative Example 7, the domestic surfactant OP-10 was used, but no obvious wetting reversal effect was seen, and its wetting reversal ability was significantly reduced compared with Example 1.In summary, the fluorinated polymer wettability reversal agent of the present invention can effectively reduce the liquid phase invasion of drilling and completion fluids, eliminate the damage of liquid-solid phase closure, and improve the micro-micro-nano pore throat seepage channel by changing the surface free energy of the rock and then adjusting the surface wettability of the rock, which is of great value for improving the protection performance of the reservoir.

[0111] (II) Capillary self-priming test

[0112] An untreated hard neutral glass spotting capillary with an inner diameter of 0.5 mm and a tube length of 100 mm was used to measure the wetting reversal agents of the embodiments and comparative examples with different mass fractions. The capillary was vertically inserted into the solution, the self-imbibition height of the solution in the capillary was recorded, and the reduction rate of the capillary self-imbibition liquid level height was calculated. Clear water was used as the control group. The capillary data are shown in Table 2.

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

[0114]

[0115]

[0116] As shown in Table 2 above, the performance test data of the embodiment and the comparative example are compared. The fluorinated polymer wettability reversal agent prepared in Example 1 is aggregated on the rock surface in large quantities by introducing fluoroalkyl groups and self-configuring to form a hydrophobic surface, the hydrophobic performance is enhanced, the capillary resistance is reduced, and the liquid level at the top of the capillary changes from a concave liquid surface to a convex liquid surface, thereby reversing the reservoir wettability, and the capillary self-absorption liquid level height can be reduced from 49mm to 6mm, and the capillary self-absorption liquid level height reduction rate is 87.8%, and the wetting effect is the best. In Example 2, due to the increase in the content of nano-silicon dioxide, the aggregation or accumulation phenomenon between particles is increased, resulting in the hydrophobic group being wrapped inside the particle or at the interface between adjacent particles, and cannot be exposed on the particle surface. In Example 3 and Example 4, the amount of KH570 and N-ethyl-N-hydroxyethyl perfluorooctylamide was reduced respectively, and the adsorption sites on the surface of nano-silicon dioxide were excessive, resulting in uneven adsorption sites of silane coupling agents and fluorinated groups on their surface, reducing the hydrophobic effect. The pH value of the solution in Example 6 is 6, and the surface charge of the nano-silica is not strong enough, resulting in incomplete adsorption of the silane coupling agent, thereby affecting the hydrophobicity. In Example 5 and Example 8, polyvinyl alcohol of equal mass is used instead of anhydrous ethanol, and ammonium persulfate is used instead of azobisisobutyronitrile, which cannot effectively react with the hydrophobic substances on the surface of the nano-silica, thereby affecting the reaction rate, the hydrophobic modification effect and the final surface morphology. In Comparative Example 1, the amount of fluoropolymer N-ethyl-N-hydroxyethyl perfluorooctaneamide is increased. Under the influence of strong acid or strong base environment, too much fluoropolymer will react or degrade, which reduces the wetting reversal effect. Comparative Example 2 does not contain KH570 silane coupling agent, and the chemical bonding between the silica nanoparticles and the fluoropolymer is reduced, resulting in a decrease in adhesion, and it is difficult to form a tight hydrophobic film on the rock surface. Comparative Example 3 does not contain the initiator azobisisobutyronitrile, which causes the nanoparticles to agglomerate or settle. The poor dispersibility leads to a larger particle size, which reduces the wetting performance of the wetting reversal agent and the dispersion performance in the base slurry. In Comparative Example 4, KH550 is used instead of KH570 of the present invention. Since KH550 contains hydrophilic groups, it is impossible to use methoxy groups to replace some hydrogen atoms, which prevents it from tending to form hydrophobic bonds. In Comparative Example 5, calcium oxide nanoparticles are used instead of silica nanoparticles. The calcium oxide nanoparticles have been hydrolyzed with water, which greatly reduces the wetting reversal effect of the wetting reversal agent in the base slurry. In Comparative Example 6, an equal amount of polytrifluorochloroethylene (PCTFE) is used to replace the fluorinated compound N-ethyl-N-hydroxyethyl perfluorooctaneamide. Polytrifluorochloroethylene does not contain hydroxyl groups, and forms a strong interfacial tension when in contact with water, resulting in poor wetting reversal performance. In Comparative Example 7, domestic surfactant OP-10 was used, and the capillary self-imbibition liquid level was comparable to that of the untreated capillary self-imbibition liquid level. The reduction rate of the capillary self-imbibition height showed a sharp downward trend compared with Example 1.It can be seen that the wettability of the core can be changed from hydrophilic to hydrophobic by reducing the capillary imbibition liquid level and increasing the capillary imbibition reduction rate.

[0117] (III) Evaluation of API rheological properties of drilling fluid

[0118] 400 mL of drilling fluid samples were taken respectively, aged at 180 °C, and stirred at 4000 r / min for 20 min at room temperature. The apparent viscosity (AV, mPa.s), plastic viscosity (PV, mPa.s), dynamic shear force (YP, Pa), API filtration loss (FL) of the drilling fluids were measured according to GB / T16783.1 2006. API , mL), and the evaluation data are shown in Table 3.

[0119] Table 3 API rheological properties of base slurry containing example lubricants

[0120]

[0121] As can be seen from the data in Table 3, by comparing the performance test data of the embodiment and the comparative example, the wettability reversal agent developed in Example 1 of the present invention has an increasing trend for the apparent viscosity (AV, mPa·s) and plastic viscosity (PV, mPa·s) of the drilling fluid base slurry, and the API filtration loss can be reduced to 9.8mL. In Example 2, due to the increase in the content of nano-silica, the surface modification is uneven, resulting in weak hydrophobicity in some areas. In Example 3 and Example 4, the dosage of KH570 and N-ethyl-N-hydroxyethyl perfluorooctylamide was reduced respectively, and the surface of the modified silica lost part of its hydrophobicity, resulting in a decrease in its dispersibility, and it could not effectively form a stable colloidal structure with the drilling fluid base slurry. In Example 6, the pH value of the solution is 6, and the surface charge of silica changes, affecting the adsorption effect of the silane coupling agent. In Example 5 and Example 8, polyvinyl alcohol of equal mass is used instead of anhydrous ethanol, and ammonium persulfate is used instead of azobisisobutyronitrile, resulting in a low effective conversion rate of modified nano-silica, uneven dispersion, and stratification and coagulation. The increase in the amount of fluoropolymer in Comparative Example 1, the excessive fluoropolymer will make the drilling fluid too dense, resulting in a decrease in the stability and fluidity of the drilling fluid, and flocculation and precipitation are prone to occur, thereby causing filter cake formation and clogging. Comparative Examples 2 and 3 do not contain KH570 silane coupling agent and initiator azobisisobutyronitrile, respectively, and nano-silicon dioxide is more easily integrated into the drilling fluid system, the wetting reversal performance fails, and the flow resistance of the drilling fluid is reduced, resulting in an increase in filtration loss. In Comparative Examples 4 and 5, KH550 is directly used instead of the KH570 of the present invention, and calcium oxide nanoparticles are used instead of silicon dioxide nanoparticles. The viscosity of the drilling fluid base slurry decreases slightly, but does not affect the overall performance of the drilling fluid, and the performance such as filtration loss and density is basically unchanged. In Comparative Example 6, an equal amount of polytrifluorochloroethylene (PCTFE) is directly used to replace the fluorinated compound N-ethyl-N-hydroxyethyl perfluorooctylamide. The molecular chain of polytrifluorochloroethylene is relatively long and rigid, which limits its fluidity and interaction in the liquid, making the viscosity relatively high and the filtration loss large. In Comparative Example 7, the surfactant OP-10 is used, which has little effect on the rheological properties of the drilling fluid base slurry. It can be seen that the wettability reversal agent of the present invention has almost no effect on the rheological properties of the drilling fluid base slurry, and can maximize the apparent viscosity and plastic viscosity, and has a certain filtration loss reduction effect.

[0122] In summary, the fluorinated polymer wettability reversal agent for shale reservoir protection developed in the present invention can greatly reduce the solid-phase interfacial tension, change the wettability of the reservoir from superhydrophilicity to superhydrophobicity, and be dispersed in the drilling fluid base slurry with micro-nano particle size, so as to change its own capillary force from resistance to power, effectively inhibit the fluid sensitive damage and liquid lock effect caused by the entry of foreign fluid into the water-sensitive shale reservoir, reduce the probability of pore throat blockage, increase the dominant channel for fluid flow, solve the technical problem of insufficient wettability reversal performance of the existing water-based drilling fluid wettability reversal agent, and have little effect on the rheology of the drilling fluid, thereby promoting the further development of water-based drilling fluid technology for shale reservoir protection.

Claims

1. A method for preparing a fluorinated polymer wettability reversal agent suitable for shale reservoir protection, comprising the following steps: (1) Synthesis of N-ethyl-N-hydroxyethyl perfluorooctaneamide Ethylamine, triethylamine and deionized water are added to a reaction bottle, and then perfluorooctanoyl chloride is added to the system to react; after the reaction is completed, potassium hydroxide and 2-chloroethanol are added to react; after the reaction is completed, N-ethyl-N-hydroxyethyl perfluorooctanoyl amide is obtained; (2) Preparation of fluorinated polymer wettability reversal agents Nanoparticles, silane coupling agent and ammonia water are added to a dispersant solution, and after being uniformly dispersed by ultrasonication, a mixed solution is obtained, and 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, the N-ethyl-N-hydroxyethyl perfluorooctylamide prepared in step (1) is added, and after nitrogen is passed to deoxygenate, an initiator is added to initiate a thermal polymerization reaction to obtain a fluorine-containing polymer wettability reversal agent suitable for shale reservoir protection.

2. The method for preparing the fluorinated polymer wettability reversal agent suitable for shale reservoir protection according to claim 1, characterized in that: The mass ratio of ethylamine to triethylamine in step (1) is 1-2:1, preferably 1:1; the mass ratio of deionized water to triethylamine is 1-3:1; the mass ratio of the total mass of ethylamine and triethylamine to the mass of perfluorooctanoyl chloride is 1:0.1-0.4, preferably 1:0.2-0.

3.

3. The method for preparing the fluorinated polymer wettability reversal agent suitable for shale reservoir protection according to claim 1, characterized in that: The perfluorooctanoyl chloride described in step (1) is added dropwise to the system at a temperature of 20 to 40° C., preferably 25 to 35° C.; the dropping speed is 2 to 3 drops / s; the temperature for adding perfluorooctanoyl chloride to react is 55 to 65° C., and the reaction time is 3 to 7 hours.

4. The method for preparing the fluorinated polymer wettability 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 to 6:1, preferably 2 to 4.5:1; 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, preferably 0.1-0.2:

1.

5. The method for preparing the fluorinated polymer wettability reversal agent suitable for shale reservoir protection according to claim 1, characterized in that: In step (1), the temperature for adding potassium hydroxide and 2-chloroethanol to react is 70 to 80° C., and the reaction time is 20 to 30 hours; In step (1), after potassium hydroxide and 2-chloroethanol are added to complete the reaction, a post-treatment step is further included, which is specifically as follows: the obtained reaction mixture is naturally cooled to room temperature, distilled water is added, and the mass ratio of the added distilled water to the reaction mixture is 0.5 to 2:1, centrifuged, and the obtained solid is washed with distilled water for 2 to 3 times, and dried at 80° C. for 12 hours to obtain N-ethyl-N-hydroxyethyl perfluorooctaneamide.

6. The method for preparing the fluorinated polymer wettability reversal agent suitable for shale reservoir protection according to claim 1, characterized in that: 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; the mass ratio of the dispersant to water is 1:1 to 3, preferably 1:1 to 2; the weight average molecular weight of the polyvinyl alcohol is 10,000 to 200,000; The nanoparticles are silicon dioxide nanoparticles and / or silicon nanoparticles; the particle size of the nanoparticles is 30 to 100 nm; The silane coupling agent is one or a combination of two or more of γ-(methacryloyloxy)propyltrimethoxysilane, γ-glycidyloxypropyltrimethoxysilane, and γ-mercaptopropyltriethoxysilane; The mass fraction of NH3 in the ammonia water is 25-28%; The mass ratio of the nanoparticles, the silane coupling agent and the ammonia water is 1-7:1-6:

1.

7. The method for preparing the fluorinated polymer wettability reversal agent suitable for shale reservoir protection according to claim 1, characterized in that: The total mass fraction of the nanoparticles, silane coupling agent and ammonia water in the mixed solution in step (2) is 10-40%, preferably 15-30%; the temperature of the modification reaction is 50-80° C.; the time of the modification reaction is 4-7 hours; In step (2), a NaOH aqueous solution with a mass fraction of 20 to 30% is used to adjust the pH of the modified nanoparticle solution to 5 to 9.

8. The method for preparing the fluorinated polymer wettability reversal agent suitable for shale reservoir protection according to claim 1, characterized in that: The ratio of the mass of the N-ethyl-N-hydroxyethyl perfluorooctaneamide in step (2) to the total mass of the nanoparticles, the silane coupling agent and the ammonia water is 0.15 to 0.3:1; The initiator is one or a combination of two or more of azobisisobutyronitrile, ammonium persulfate, and benzoyl peroxide; the ratio of the mass of the initiator to the total mass of the nanoparticles, the silane coupling agent, and the ammonia water is 0.03 to 0.05:1; The polymerization reaction temperature is 60-90° C., preferably 70-80° C.; the polymerization reaction time is 6-9 hours, preferably 7-8 hours; the stirring speed during the polymerization reaction is 300-600 rpm, preferably 400-500 rpm.

9. A fluorinated polymer wettability reversal agent suitable for shale reservoir protection, characterized in that: The preparation method according to claim 1 is used for preparation.

10. Use of the fluorinated polymer wettability reversal agent suitable for shale reservoir protection according to claim 1 in water-based drilling fluid, characterized in that: The content of the fluorine-containing polymer wettability reversal agent suitable for shale reservoir protection in the drilling fluid is 1.5-2 wt %.

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