Oleophobic agents for improving wellbore stability, their preparation and application, and drilling fluids

Abstract

This invention provides an oleophobic agent for improving wellbore stability, its preparation and application, and a drilling fluid. The oleophobic agent has a core-shell structure, comprising a core structure, a polymer film coating the outer surface of the core structure, and modified inorganic nanoparticles adsorbed onto the polymer film to form the shell structure; or it comprises a core structure and modified inorganic nanoparticles for forming the shell structure, wherein the modified inorganic nanoparticles are adsorbed onto the core structure via electrostatic attraction using a positively charged surfactant; wherein the core structure is selected from particles with a size ranging from submicron to micron. This oleophobic agent possesses a core-shell structure and a dual-level roughness of nano-submicron to micron, which can modify the wettability of rock surfaces to superoleophobic, thereby stabilizing the wellbore by inhibiting the absorption of oil phases into the rock.

Description

Technical Field

[0001] This invention relates to an oleophobic agent for improving wellbore stability, its preparation and application, and drilling fluid, belonging to the field of petrochemical technology. Background Technology

[0002] The development of existing shallow and medium-grade, high-grade, conventional oil and gas resources has generally entered its later stages. To ensure subsequent oil and gas supply and continuously increase reserves, the development of oil and gas resources is gradually shifting from shallow and medium-grade reservoirs to deep and ultra-deep reservoirs, and the types of oil and gas resources are also shifting from conventional to unconventional. Deep and ultra-deep oil and gas reservoirs, as well as unconventional oil and gas reservoirs, have harsh geological environments, characterized by high temperatures, high salinity, and high formation water sensitivity. Simultaneously, to achieve efficient and large-scale development of unconventional oil and gas, horizontal well technology is increasingly widely used, placing extremely stringent requirements on the lubricity and temperature resistance of drilling fluids. Currently, oil-based drilling fluids exhibit good performance in terms of temperature resistance, lubrication, and salt resistance, and can initially meet the above-mentioned resource development needs, becoming the main type of drilling fluid for deep, ultra-deep, and unconventional oil and gas development.

[0003] However, wellbore instability still occurs in recent years with the application of oil-based drilling fluids. Accidents such as stuck pipe and burial of the drilling guide due to blockage and wellbore collapse can occur, sometimes even leading to wellbore abandonment, significantly delaying construction and causing substantial economic losses. Analysis shows that the main cause of wellbore instability is the infiltration of oil phase into the wellbore rock, where it undergoes physicochemical reactions with rock components, leading to a decrease in rock mechanical stability. Numerous capillary fractures in the rock provide pathways for oil phase intrusion. Under the positive pressure of drilling fluid and formation fluids, and driven by capillary forces, a large amount of oil phase intrudes into the rock. On the one hand, oil phase intrusion increases the pore pressure within the rock, inducing pore expansion and damaging the internal rock structure. On the other hand, the organic matter in the rock swells or even dissolves under oil phase immersion, also causing internal changes and reducing rock mechanical stability. Currently, the drilling fluid industry has reached a consensus that the key to improving wellbore stability with oil-based drilling fluids lies in reducing the amount of oil phase intrusion into the rock.

[0004] In the drilling fluid field, filtration loss reducers and plugging agents are commonly used to prevent oil phase from seeping into the rock. However, due to poor matching between particle size and porosity and microfractures, the application effect is not satisfactory, so there is an urgent need to develop new products.

[0005] Oil phases penetrate into the rock through capillary action within the rock. The driving forces promoting oil phase absorption in this process are primarily the pressure difference between the drilling fluid and formation fluids, as well as capillary forces. With increasing awareness of reservoir protection, underbalanced drilling is being used more frequently. In this case, the drilling fluid column pressure is essentially the same as the formation fluid pressure, and the main force driving oil phase absorption into the rock is capillary force. The direction of capillary force is determined by the wettability of the rock surface. When the rock is oleophilic, the capillary force points towards the depths of the pores, promoting oil phase absorption; when the rock surface is oleophobic, the direction of the capillary force reverses, becoming a resistance to oil phase absorption and effectively inhibiting oil phase intrusion into the rock.

[0006] Chinese patent CN 114085551 A discloses a type of wellbore-enhancing, dual-hydrophobic, soil-free oil-based drilling fluid containing a silica composite treatment agent. This silica composite treatment agent contains supramolecular materials, modified silica nanoparticles, and Janus particles of silica. Based on dual-hydrophobic theory and supramolecular chemistry, this technology can effectively solve problems encountered in drilling unconventional and complex oil and gas reservoirs, such as wellbore collapse, lost circulation, unclean wellbore, and oil and gas reservoir damage. The key treatment agent relied upon by this technology is modified nano-silica, which, by adjusting rock wettability, inhibits oil phase absorption and improves wellbore stability. Making the rock interface oleophobic, increasing rock surface roughness, and reducing its surface energy are two essential measures. However, the modified nano-silica disclosed in this technology can only construct single-level nano-roughness on the rock surface, with limited effect on improving rock surface roughness, thus affecting the oleophobic modification and reducing the effectiveness of the oleophobic agent in inhibiting oil phase absorption and improving wellbore stability.

[0007] Therefore, providing a novel oleophobic agent for improving wellbore stability, as well as its preparation, application, and drilling fluid, has become a pressing technical problem to be solved in this field. Summary of the Invention

[0008] To address the limited effectiveness of existing dual-hydrophobic nanomaterials in improving rock surface roughness in oil-based drilling fluids, which can easily lead to wellbore collapse, this invention aims to provide an oleophobic agent for improving wellbore stability. The oleophobic agent provided by this invention possesses a core-shell structure and a dual-level roughness from nanometer to submicron to micrometer, modifying the wettability of rock surfaces to superoleophobic properties. By inhibiting the absorption of oil phases into the wellbore / rock, it stabilizes the wellbore, thereby improving its mechanical stability. Furthermore, this oleophobic agent can adsorb and form a film on the rock surface, increasing rock cohesion through bonding, thus enhancing the rock's resistance to external damage and effectively improving wellbore stability.

[0009] Another object of the present invention is to provide a method for preparing the above-described oleophobic agent for improving wellbore stability.

[0010] Another object of the present invention is to provide a drilling fluid comprising the above-described oleophobic agent for improving wellbore stability.

[0011] Another object of the present invention is to provide the application of the above-described oleophobic agents for improving wellbore stability or the above-described drilling fluids in the development of deep, ultra-deep, or unconventional oil and gas formations.

[0012] To achieve the above objectives, on the one hand, the present invention provides an oleophobic agent for improving wellbore stability, wherein the oleophobic agent for improving wellbore stability has a core-shell structure, comprising a core structure, a polymer film coating the outer surface of the core structure, and modified inorganic particulate nanomaterials adsorbed on the polymer film for forming a shell structure;

[0013] Alternatively, it may include a core structure and modified inorganic particulate nanomaterials for forming a shell structure, wherein the modified inorganic particulate nanomaterials are adsorbed onto the core structure by electrostatic attraction via a positively charged surfactant.

[0014] The core structure is selected from particles with sizes ranging from submicron (100nm-1μm) to micron.

[0015] In this invention, the modified inorganic particulate nanomaterial carries a negative charge, and a positively charged surfactant is adsorbed onto the core structure. The positively charged surfactant adsorbs the modified inorganic particulate nanomaterial through electrostatic attraction to form a core-shell structure.

[0016] As a specific embodiment of the oleophobic agent described above in this invention, the core-shell structure includes a core structure and modified inorganic particulate nanomaterials for forming the shell structure. Both the core structure and the modified inorganic particulate nanomaterials contain silane groups, and the core structure and the modified inorganic particulate nanomaterials are assembled to form the core-shell structure through a silane hydrolysis-condensation reaction.

[0017] In one specific embodiment of the oleophobic agent described above in this invention, the size of the core structure is 100nm-10μm.

[0018] As a specific embodiment of the oleophobic agent described above in this invention, the core structure is an inorganic particle or an organic particle; wherein the inorganic particle includes silicon dioxide, calcium carbonate or titanium dioxide, etc., and the organic particle includes polystyrene, polymethyl methacrylate or polyacrylate, etc.

[0019] As a specific embodiment of the oleophobic agent described above in this invention, the core structure includes polystyrene with silane groups on its surface, polymethacrylate with silane groups on its surface, or polyacrylate with silane groups on its surface.

[0020] In some preferred embodiments of the oleophobic agent described above in this invention, the core structure is selected from polystyrene, poly(meth)acrylate, silica, and calcium carbonate; more preferably, it is polystyrene. In a specific embodiment of the oleophobic agent described above in this invention, the size of the modified inorganic particulate nanomaterial is 10 nm-100 nm.

[0021] In this invention, the modifier used to modify inorganic particulate nanomaterials is a low surface energy substance such as fluorinated siloxane.

[0022] As a specific embodiment of the oleophobic agent described above in this invention, the modified inorganic particulate nanomaterial includes inorganic particulate nanomaterials modified with fluorinated siloxane.

[0023] As a specific embodiment of the oleophobic agent described above in this invention, the fluorinated siloxane includes fluorinated hydrocarbon siloxanes and / or fluorinated polyether siloxanes, etc.

[0024] In some preferred embodiments of the oleophobic agent described above in this invention, the fluorinated siloxane is a fluorinated hydrocarbon-based siloxane. In some embodiments of this invention, the fluorinated hydrocarbon-based siloxane may be, for example, perfluorooctyltriethoxysilane, and the fluorinated polyether siloxane may be a hexacarbon perfluoropolyether siloxane.

[0025] As a specific embodiment of the oleophobic agent described above in this invention, the inorganic particulate nanomaterials include nano-silica and / or nano-titanium dioxide, etc.

[0026] In some preferred embodiments of the oleophobic agent described above in this invention, the inorganic particulate nanomaterial is nano-silica.

[0027] As a specific embodiment of the oleophobic agent described above in this invention, the polymer film includes polydopamine film, etc.

[0028] In one specific embodiment of the oleophobic agent described above in this invention, the positively charged surfactant includes quaternary ammonium salt surfactants, pyridine halides, or alkyl imidazoline surfactants. In some embodiments of this invention, the quaternary ammonium salt surfactant may be, for example, dodecyltrimethylammonium bromide.

[0029] As a specific embodiment of the oleophobic agent described above in this invention, the shape of the oleophobic agent includes any shape such as spherical, ellipsoidal, raspberry-shaped, or strip-shaped.

[0030] On the other hand, the present invention also provides a method for preparing the above-described oleophobic agent for improving wellbore stability, wherein the preparation method includes:

[0031] (1) Add the monomer raw material corresponding to the polymer membrane to the buffer solution or add the positively charged surfactant to the water and dissolve it;

[0032] (2) Add submicron to micron particles to the solution obtained in step (1) and sonicate them. Then place them at room temperature and under stirring for a period of time to allow the monomer raw material to polymerize on the surface of the submicron to micron particles to form a polymer film or to allow the positively charged surfactant to adsorb on the surface of the submicron to micron particles.

[0033] (3) Add the modified inorganic nanoparticles to the solution obtained in step (2) and sonicate it. Then heat it under stirring to allow the modified inorganic nanoparticles to adsorb onto the polymer film to obtain the oleophobic agent.

[0034] Preferably, the mass ratio of the monomer raw material, submicron to micron-sized particles, and modified inorganic nanomaterials corresponding to the polymer film is 3-4:10-20:7-10;

[0035] Alternatively, under stirring conditions, the modified inorganic nanoparticles are adsorbed onto the submicron to micron-sized particles by a positively charged surfactant to obtain the oleophobic agent.

[0036] Preferably, the mass ratio of the positively charged surfactant, submicron to micron-sized particles, and modified inorganic nanomaterials is 1-2:10-20:7-10;

[0037] Alternatively, the solution obtained in step (2) can be added to an alcohol solvent, and then tetraethoxysilane (TEOS) and ammonia can be added in sequence to adjust the pH value to 9-11 and carry out a condensation reaction under stirring conditions; after the condensation reaction is completed, a modifier can be added to carry out a modification reaction, and the oleophobic agent can be obtained after the modification reaction is completed.

[0038] Preferably, the mass ratio of the monomer raw material or positively charged surfactant, submicron to micron-sized particles, tetraethoxysilane and modifier corresponding to the polymer film is 3-4 or 1-2:10-20:9.4-28.2:20-30.

[0039] As a specific embodiment of the preparation method described above in this invention, in step (1), the pH value of the buffer solution is 7-10, preferably 8.5;

[0040] More preferably, the buffer solution comprises a tris(hydroxymethyl)aminomethane hydrochloride solution.

[0041] As a specific embodiment of the preparation method described above in this invention, in step (2), the ultrasonic treatment time is 10-15 min.

[0042] As a specific embodiment of the preparation method described above in this invention, in step (2), the stirring speed is 100-400 r / min.

[0043] In a specific embodiment of the preparation method described above in this invention, the placement time in step (2) is 24 hours.

[0044] In a specific embodiment of the preparation method described above in this invention, the ultrasonic treatment time in step (3) is 10-15 min.

[0045] As a specific embodiment of the preparation method described above in this invention, in step (3), the stirring speed is 100-400 r / min.

[0046] As a specific embodiment of the preparation method described above in this invention, in step (3), the temperature is raised to 40-60°C and maintained for 4-6 hours.

[0047] As a specific embodiment of the preparation method described above in this invention, in step (3), the temperature of the condensation reaction is 50-70°C and the time is 6-8h.

[0048] As a specific embodiment of the preparation method described above in this invention, in step (3), the temperature of the modification reaction is 60-70℃ and the time is 2-4h.

[0049] As a specific embodiment of the preparation method described above in this invention, in step (3), the alcohol solvent may be an alcohol organic solvent such as ethanol.

[0050] As a specific embodiment of the preparation method described above in this invention, in step (3), the preparation method of the modified inorganic particulate nanomaterial includes:

[0051] (a) Adding inorganic particulate nanomaterials to an organic solvent and subjecting them to ultrasonic treatment;

[0052] (b) Add a pH adjuster to the solution obtained in step (a) and mix well to adjust the pH of the system to 4-6 or 10-11;

[0053] (c) Add the modifier to the solution obtained in step (b) and react at 50-60℃ for 5-10 h under stirring conditions; wherein the mass ratio of the modifier to the inorganic particulate nanomaterial is 1-2:15-30.

[0054] (d) Dry the solution obtained after the reaction in step (c), and grind the solid phase obtained after drying to obtain the modified inorganic particulate nanomaterial.

[0055] In a specific embodiment of the preparation method described above in this invention, in step (a), the organic solvent includes ethanol.

[0056] In a specific embodiment of the preparation method described above in this invention, in step (a), the ultrasonic treatment time is 10-15 min.

[0057] In one specific embodiment of the preparation method described above in this invention, in step (b), the pH adjuster includes ammonia or acetic acid.

[0058] In a specific embodiment of the preparation method described above in this invention, in step (c), the stirring speed is 100-400 r / min.

[0059] In a specific embodiment of the preparation method described above in this invention, in step (d), the drying is performed by drying in an oven at 105°C for 6 hours.

[0060] As a specific embodiment of the preparation method described above in this invention, when the core structure and the modified inorganic particulate nanomaterials are assembled to form a core-shell structure through a silane hydrolysis-condensation reaction, the preparation method includes:

[0061] 1) Add vinyl monomers, silane reagents containing double bonds and initiators to water, and prepare submicron to micron-sized particles with silane groups on the surface through polymerization reaction;

[0062] 2) Add the solution obtained in step 1) to an alcohol solvent, then add tetraethoxysilane and ammonia in sequence, adjust the pH value to 9-11, and carry out a condensation reaction under stirring conditions; after the condensation reaction is completed, add a modifier to carry out a modification reaction, and after the modification reaction is completed, the oleophobic agent is obtained.

[0063] Preferably, the mass ratio of vinyl monomer, silane reagent containing double bond, TEOS and modifier is 10-15:1-3:9.4-28.2:20-30.

[0064] In step 1) of the present invention, the order of addition of the vinyl monomer, the silane reagent containing double bonds and the initiator will not have a substantial impact on the performance of the oleophobic agent. The order of addition of the three can be reasonably adjusted according to the actual needs of on-site operation.

[0065] In a specific embodiment of the preparation method described above in this invention, in step 1), the vinyl monomer includes styrene, methacrylate, or acrylate.

[0066] As a specific embodiment of the preparation method described above in this invention, in step 1), the silane reagent containing double bonds includes one or a combination of several of the following: methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, and vinyltris(b-methoxyethoxy)silane.

[0067] As a specific embodiment of the preparation method described above in this invention, in step 1), the initiator includes one or a combination of several of azobisisobutyronitrile, potassium persulfate, and ammonium persulfate.

[0068] As a specific embodiment of the preparation method described above in this invention, in step 1), the polymerization reaction temperature is 50-70℃ and the time is 6-10h.

[0069] In step 2) of the present invention, under alkaline conditions, tetraethoxysilane hydrolyzes both the silane groups on the surface of submicron to micron-sized particles with silane groups to generate silanol groups. The silanol groups further undergo condensation, causing tetraethoxysilane to be deposited on the surface of the particles to form nano-silica. After the condensation reaction is completed, a modifier is added to modify the nano-silica. After the modification is completed, the oleophobic agent is obtained.

[0070] In a specific embodiment of the preparation method described above in this invention, in step 2), the temperature of the condensation reaction is 50-70°C and the time is 6-8 hours.

[0071] In a specific embodiment of the preparation method described above in this invention, in step 2), the temperature of the modification reaction is 60-70°C and the time is 2-4 hours.

[0072] In a specific embodiment of the preparation method described above in this invention, in step 2), the alcohol solvent may be an alcohol organic solvent such as ethanol.

[0073] As some preferred embodiments of the preparation method described above in this invention, the method for preparing the oleophobic agent for improving wellbore stability specifically includes:

[0074] Preparation of nuclear structures:

[0075] Add 3-4g of dopamine to 100mL of buffer solution with a pH of 7-10 and stir until dissolved;

[0076] Add 10-20g of submicron to micron-sized particles to the solution obtained in the previous step and sonicate for 10-30 minutes.

[0077] At a stirring speed of 100-400 r / min and placed at room temperature for 24 h, dopamine polymerizes on the surface of submicron to micron-sized particles to form a polymer film.

[0078] Assembly of core-shell structure:

[0079] Add 7-10g of the modified inorganic particulate nanomaterial to the solution obtained in the previous step, and sonicate for 10-15 minutes; wherein, the preparation method of the modified inorganic particulate nanomaterial specifically includes:

[0080] (a) Add 15-30g of inorganic particulate nanomaterials to 80g of ethanol and sonicate for 10-15min.

[0081] (b) Add pH adjuster to the solution obtained in step (a) and stir at low speed until homogeneous to adjust the pH of the system to 4-6 or 10-11;

[0082] (c) Add 1-2g of modifier to the solution obtained in step (b), adjust the stirring speed to 100-400r / min, and react at 50-60℃ for 5-10h;

[0083] (d) Place the reaction solution obtained in step (c) in an oven at 105°C and dry for 6 hours. After drying, the solid phase is lightly ground to obtain the modified inorganic particulate nanomaterial. Dry and store for later use.

[0084] At a stirring speed of 100-400 r / min, the temperature is increased to 40-60℃ and maintained for 4-6 h to allow the modified inorganic particulate nanomaterials to be adsorbed onto the polymer film. The resulting product is then centrifuged and rinsed with deionized water in sequence, repeated three times. After that, the product is dried (in an oven at 105℃ for 4 h), and then the dried product is subjected to solid-phase grinding to obtain the oleophobic agent.

[0085] As some preferred embodiments of the preparation method described above in this invention, the method for preparing the oleophobic agent for improving wellbore stability specifically includes:

[0086] Preparation of nuclear structures:

[0087] Add 1-2g of positively charged surfactant to 100mL of deionized water and stir until dissolved;

[0088] Add 10-20g of submicron to micron-sized particles to the solution obtained in the previous step and sonicate for 10-30 minutes.

[0089] The particles are placed at room temperature for 2-4 hours with a stirring speed of 100-400 r / min to allow the positively charged surfactant to adsorb onto the submicron to micron-sized particles.

[0090] Assembly of core-shell structure:

[0091] Add 7-10g of the modified inorganic particulate nanomaterial to the solution obtained in the previous step, and sonicate for 10-15 minutes; wherein, the preparation method of the modified inorganic particulate nanomaterial specifically includes:

[0092] (a) Add 15-30g of inorganic particulate nanomaterials to 100mL of ethanol and sonicate for 10-15min.

[0093] (b) Add pH adjuster to the solution obtained in step (a) and stir at low speed until homogeneous to adjust the pH of the system to 4-6 or 10-11;

[0094] (c) Add 1-2g of modifier to the solution obtained in step (b), adjust the stirring speed to 100-400r / min, and react at 50-60℃ for 5-10h;

[0095] (d) Place the reaction solution obtained in step (c) in an oven at 105°C and dry for 6 hours. After drying, the solid phase is lightly ground to obtain the modified inorganic particulate nanomaterial. Dry and store for later use.

[0096] At a stirring speed of 100-400 r / min, the modified inorganic particulate nanomaterials are adsorbed onto the submicron to micron-sized particles by electrostatic attraction via a positively charged surfactant to form a core-shell structure. The resulting product is then centrifuged and washed with deionized water in sequence, repeated three times. After that, the product is dried (in an oven at 105°C for 4 hours), and then the dried product is subjected to solid-phase grinding to obtain the oleophobic agent.

[0097] As some preferred embodiments of the preparation method described above in this invention, the method for preparing the oleophobic agent for improving wellbore stability specifically includes:

[0098] Preparation of nuclear structures:

[0099] Add 3-4g of dopamine to 100mL of buffer solution with a pH of 7-10 and stir until dissolved;

[0100] Add 10-20g of submicron to micron-sized particles to the solution obtained in the previous step and sonicate for 10-30 minutes.

[0101] At a stirring speed of 100-400 r / min and placed at room temperature for 24 h, dopamine polymerizes on the surface of submicron to micron-sized particles to form a polymer film.

[0102] Assembly of core-shell structure:

[0103] Add 600-900g of an alcohol solvent, such as ethanol, to the solution obtained in the preparation process of the core structure, then add 9.4-28.2g of TEOS, and then add ammonia dropwise using a separatory funnel to adjust the pH to 9-11. React at 200r / min and 50-70℃ for 6-8h to allow TEOS to condense and form nano-silica, i.e., inorganic particulate nanomaterials.

[0104] Add 20-30g of a modifier, such as perfluorooctyltriethoxysilane, dropwise to the solution obtained in the previous step using a separatory funnel, and continue the reaction at 60℃ for 2-4 hours to modify the inorganic particulate nanomaterials. After the modification reaction is complete, the product is centrifuged and rinsed with deionized water, and the process is repeated three times. Then, it is dried in an oven (at 105℃ for 4 hours). After drying, the product is subjected to solid-phase grinding to obtain the oleophobic agent.

[0105] As some preferred embodiments of the preparation method described above in this invention, the method for preparing the oleophobic agent for improving wellbore stability specifically includes:

[0106] Preparation of nuclear structures:

[0107] Add 1-2g of positively charged surfactant to 100mL of deionized water and stir until dissolved;

[0108] Add 10-20g of submicron to micron-sized particles to the solution obtained in the previous step and sonicate for 10-30 minutes.

[0109] The particles were stirred at 100-400 r / min and left at room temperature for 2-h to allow the positively charged surfactant to adsorb onto the submicron to micron-sized particles.

[0110] Assembly of core-shell structure:

[0111] Add 600-900g of an alcohol solvent, such as ethanol, to the solution obtained in the preparation process of the core structure, then add 9.4-28.2g of TEOS, and then add ammonia dropwise using a separatory funnel to adjust the pH to 9-11. React at 200r / min and 50-70℃ for 6-8h to allow TEOS to condense and form nano-silica, i.e., inorganic particulate nanomaterials.

[0112] Add 20-30g of a modifier, such as perfluorooctyltriethoxysilane, dropwise to the solution obtained in the previous step using a separatory funnel, and continue the reaction at 60℃ for 2-4 hours to modify the inorganic particulate nanomaterials. After the modification reaction is complete, the product is centrifuged and rinsed with deionized water, and the process is repeated three times. Then, it is dried in an oven (at 105℃ for 4 hours). After drying, the product is subjected to solid-phase grinding to obtain the oleophobic agent.

[0113] As some preferred embodiments of the preparation method described above in this invention, when the core structure and the modified inorganic particulate nanomaterials are assembled to form a core-shell structure through a silane hydrolysis-condensation reaction, the preparation method of the oleophobic agent for improving wellbore stability specifically includes:

[0114] 1) Add 0.1-0.3g of initiator, 10-15g of vinyl monomer and 1-3g of silane reagent containing double bond to 100mL of deionized water, remove oxygen with nitrogen for 30min, and react at 50-70℃ for 6-10h.

[0115] 2) Add 600-900g of ethanol to the solution obtained in step 1), and then add 9.4-28.2g of TEOS. Then, using a separatory funnel, add 50-100mL of ammonia dropwise to adjust the pH of the system to 9-11. React at 200r / min and 50-70℃ for 6-8h to allow TEOS to condense and form nano-silica, i.e., inorganic particulate nanomaterials.

[0116] 3) Using a separatory funnel, add 20-30g of modifier dropwise and continue the reaction at 60℃ for 2-4 hours to modify the inorganic particulate nanomaterials. After the modification reaction is complete, centrifuge and rinse with deionized water in sequence, repeating the process three times. Then dry the product (in an oven at 105℃ for 4 hours) and then perform solid-phase grinding on the dried product to obtain the oleophobic agent.

[0117] In another aspect, the present invention also provides a drilling fluid comprising the above-described oleophobic agent for improving wellbore stability.

[0118] As a specific embodiment of the drilling fluid described above in this invention, the drilling fluid is an oil-based drilling fluid or a water-based drilling fluid.

[0119] Furthermore, the present invention also provides the application of the above-mentioned oleophobic agents for improving wellbore stability or the above-mentioned drilling fluids in the development of deep, ultra-deep, or unconventional oil and gas formations.

[0120] In field application, alcohol is first added to the oleophobic agent at a mass ratio of 5:1-20, where the alcohol may include ethanol, methanol, or isopropanol, with ethanol being preferred. The mixture is then ultrasonically treated for 10-15 minutes. Finally, the resulting dispersion is added to the oil-based drilling fluid through a shear funnel. As the oil-based drilling fluid circulates into the wellbore, the oleophobic agent spontaneously adsorbs onto the well wall under the influence of surface energy, forming an oleophobic film. This oleophobic modification effectively inhibits the absorption of oil phase into the rock.

[0121] In summary, compared with the prior art, the beneficial technical effects achieved by the oleophobic agent for improving wellbore stability provided by this invention include:

[0122] (1) The oleophobic agent provided by the present invention can change the wettability of the rock surface from oleophilic to superoleophobic. The contact angle of diesel on the rock surface after modification is as high as 150° or more. This can improve the mechanical stability of the wellbore by inhibiting the absorption of oil phase into the rock.

[0123] (2) The oleophobic agent provided by the present invention can be quickly adsorbed on the rock surface to form a film, and improve the cohesion of the rock through cementation, thereby enhancing the rock's ability to resist external damage and effectively improving the stability of the well wall;

[0124] (3) The oleophobic agent provided by the present invention can construct a micro-nano (nano-submicron to micron) dual-level roughness on the rock surface, which has a more significant effect on improving the oleophobicity of the rock and inhibiting the absorption of oil phase;

[0125] (4) In preparing the oleophobic agent, dopamine is polymerized on the surface of submicron to micron particles to form a film, and the modified inorganic nanoparticles are further adsorbed onto the film surface to construct a core-shell bi-level roughness structure; or the modified inorganic nanoparticles are connected to the core structure by a positively charged surfactant to construct a core-shell bi-level roughness structure; or the core structure and the modified inorganic nanoparticles are assembled into a core-shell structure through a silane hydrolysis condensation reaction.

[0126] (5) The surface of the oleophobic agent provided by the present invention is coated with a large amount of modified inorganic particulate nanomaterials, which makes the oleophobic agent have excellent high temperature resistance. Thermogravimetric experiments have shown that its temperature resistance can reach up to 300℃.

[0127] (6) This product can also be used to improve the wellbore stability of water-based drilling fluids. Attached Figure Description

[0128] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0129] Figure 1 This is an electron microscope image of the oleophobic agent provided in Example 1 of the present invention.

[0130] Figure 2 The thermogravimetric curve of the oleophobic agent provided in Example 1 of the present invention. Detailed Implementation

[0131] It should be noted that the term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0132] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0133] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0134] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0135] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0136] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the appendices and embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0137] Example 1

[0138] This embodiment provides an oleophobic agent, which is prepared by a method including the following specific steps:

[0139] (1) Add 4g of dopamine to 100mL of a tris(hydroxymethyl)aminomethane hydrochloride solution with a pH of 8.5 and stir until dissolved;

[0140] (2) Add 10g of polystyrene (median particle size 1μm) to the solution obtained in the previous step and sonicate for 15min;

[0141] (3) The solution obtained in the previous step was placed at room temperature for 24 hours with a stirring speed of 200 r / min to allow dopamine to polymerize on the polystyrene surface to form a polydopamine film.

[0142] (4) Add 900g of ethanol to the solution obtained in the previous step, then add 18.8g of TEOS, and then add 100mL of ammonia water dropwise using a separatory funnel to adjust the pH of the system to 9-11. React at 200r / min and 60℃ for 6h to allow TEOS to condense and form nano-silica, i.e. inorganic particle nanomaterials.

[0143] (5) Add 20g of perfluorooctyltriethoxysilane dropwise to the solution obtained in the previous step using a separatory funnel, and continue to react at 60°C for 2h to modify the inorganic particulate nanomaterials with the modifier. After the modification reaction is completed, the product is centrifuged and rinsed with deionized water, and the process is repeated three times. Then, it is dried in an oven at 105°C for 4h. After drying, the product is ground in a solid phase to obtain the oleophobic agent.

[0144] The electron microscope image of the oleophobic agent obtained in this embodiment is as follows: Figure 1 As shown, from Figure 1 As can be seen, the oleophobic agent has a raspberry-like core-shell structure, with multiple nano-sized particles embedded on the surface of the micron-sized ellipsoidal core structure.

[0145] The thermogravimetric curve of the oleophobic agent obtained in this embodiment is shown in the figure below. Figure 2 As shown, from Figure 2 As can be seen, the oleophobic agent can withstand temperatures up to 300℃, proving that it has excellent high-temperature resistance.

[0146] Example 2

[0147] This embodiment provides an oleophobic agent, which differs from Example 1 only in that: perfluorooctyltriethoxysilane in step (5) is replaced with hexacarbon perfluoropolyether siloxane.

[0148] Example 3

[0149] This embodiment provides an oleophobic agent, which is prepared by a method including the following specific steps:

[0150] (1) Add 1g of dodecyltrimethylammonium bromide to 100g of deionized water and stir until dissolved;

[0151] (2) Add 10g of polystyrene (median particle size 1μm) to the solution obtained in the previous step and sonicate for 15min;

[0152] (3) The solution obtained in the previous step was placed at room temperature for 2 hours with a stirring speed of 200 r / min to allow dodecyltrimethylammonium bromide to be adsorbed on the polystyrene surface;

[0153] (4) Add 900g of ethanol to the solution obtained in the previous step, then add 18.8g of TEOS, and then use a separatory funnel to add 100mL of ammonia dropwise to adjust the pH of the system to 9-11. Maintain the solution at 200r / min and 60℃.

[0154] The reaction was carried out for 6 hours to allow TEOS to condense and form nano-silica, i.e., inorganic particulate nanomaterials.

[0155] (5) Add 20g of perfluorooctyltriethoxysilane dropwise to the solution obtained in the previous step using a separatory funnel, and continue to react at 60°C for 2h to modify the inorganic particulate nanomaterials with the modifier. After the modification reaction is completed, the product is centrifuged and rinsed with deionized water, and the process is repeated three times. Then, it is dried in an oven at 105°C for 4h. After drying, the product is ground in a solid phase to obtain the oleophobic agent.

[0156] Example 4

[0157] This embodiment provides an oleophobic agent, which differs from Example 1 only in that the polystyrene in step (2) is replaced with ultrafine calcium carbonate with a particle size of 1 μm.

[0158] Example 5

[0159] This embodiment provides an oleophobic agent, which differs from Example 1 only in that the amount of perfluorooctyltriethoxysilane in step (5) is adjusted from 20g to 10g, and the reaction time is extended from 2h to 4h.

[0160] Example 6

[0161] This embodiment provides an oleophobic agent, which differs from Example 1 only in that the amount of dopamine in step (1) is adjusted from 4g to 3g, and the pH value of the tris(hydroxymethyl)aminomethane hydrochloride solution is adjusted from 8.5 to 10.

[0162] Example 7

[0163] This embodiment provides an oleophobic agent, which differs from Example 1 only in that: the amount of TEOS in step (4) is adjusted from 18.8g to 9.4g, the reaction temperature is adjusted from 60℃ to 50℃, and the reaction time is adjusted from 6h to 8h.

[0164] Example 8

[0165] This embodiment provides an oleophobic agent, which is prepared by a method including the following specific steps:

[0166] I. Preparation of modified nano-silica:

[0167] (a) Add 20g of nano-silica (median particle size 30nm) to 80g of ethanol and sonicate for 15min;

[0168] (b) Add ammonia to the solution obtained in step (a) and stir at low speed until homogeneous to adjust the pH of the system to 10;

[0169] (c) Add 2g of perfluorooctyltriethoxysilane to the solution obtained in step (b), adjust the stirring speed to 100r / min, and react at 60℃ for 8h;

[0170] (d) The reaction solution obtained in step (c) was dried in an oven at 105°C for 6 hours. After drying, the solid phase was lightly ground and then dried and stored for later use.

[0171] II. Preparation of nuclear structure:

[0172] (a) Add 4g of dopamine to 100mL of a tris(hydroxymethyl)aminomethane hydrochloride solution with a pH of 8.5 and stir until dissolved;

[0173] (b) Add 10g of polystyrene (median particle size 1μm) to the solution obtained in the previous step and sonicate for 15min;

[0174] (c) The mixture was placed at room temperature for 24 hours with a stirring speed of 200 r / min to allow dopamine to polymerize on the surface of submicron-sized materials and adsorb into a polymer film.

[0175] III. Core-shell structure assembly:

[0176] (a) Add 10g of the modified nano-silica prepared in step I to the final solution obtained in step II and sonicate for 15min;

[0177] (b) At a stirring speed of 100 r / min-400 r / min, the temperature was increased to 60 °C and the reaction was carried out for 6 h to allow the modified nano-silica to be adsorbed onto the polymer film;

[0178] (c) After the reaction is complete, the product is centrifuged and rinsed with deionized water. This process is repeated three times. Then, the product is dried in an oven at 105°C for 4 hours. Finally, the dried product is subjected to solid-phase grinding to obtain the oleophobic agent.

[0179] Example 9

[0180] This embodiment provides an oleophobic agent, which is prepared by a method including the following specific steps:

[0181] (1) Add 0.1g of azobisisobutyronitrile, 10g of styrene and 2g of methacryloyloxypropyltrimethoxysilane to 100mL of deionized water, remove oxygen with nitrogen for 30min, and react at 60℃ for 8h.

[0182] (2) Add 900g of ethanol to the solution obtained in the previous step, then add 18.8g of TEOS, and then add 100mL of ammonia water dropwise using a separatory funnel to adjust the pH of the system to 9-11. React at 200r / min and 60℃ for 6h to allow TEOS to condense and form nano-silica, i.e. inorganic particle nanomaterials.

[0183] (3) Using a separatory funnel, 20g of perfluorooctyltriethoxysilane was added dropwise to the solution obtained in the previous step, and the reaction was continued at 60℃ for 2h to modify the inorganic particulate nanomaterials with the modifier. After the modification reaction was completed, the product was centrifuged and rinsed with deionized water, and the process was repeated three times. Then, it was dried in an oven at 105℃ for 4h. After drying, the product was subjected to solid-phase grinding to obtain the oleophobic agent.

[0184] Comparative Example 1

[0185] This comparative example provides an oleophobic agent, which is prepared by a method including the following specific steps:

[0186] (1) Add 4g of dopamine to 100mL of a tris(hydroxymethyl)aminomethane hydrochloride solution with a pH of 8.5 and stir until dissolved;

[0187] (2) Add 10g of polystyrene (median particle size 1μm) to the solution obtained in the previous step and sonicate for 15min;

[0188] (3) The solution obtained in the previous step was placed at room temperature for 24 hours with a stirring speed of 200 r / min to allow dopamine to polymerize on the polystyrene surface to form a polydopamine film.

[0189] (4) Add 900g of ethanol to the solution obtained in the previous step, then add 18.8g of TEOS, and then add 100mL of ammonia water dropwise using a separatory funnel to adjust the pH of the system to 9-11. React at 200r / min and 60℃ for 6h to allow TEOS to condense and form nano-silica, i.e. inorganic particle nanomaterials.

[0190] (5) After the reaction is complete, the product is centrifuged and rinsed with deionized water. This process is repeated three times. Then, the product is dried in an oven at 105°C for 4 hours. After drying, the product is ground in a solid phase to obtain the oleophobic agent.

[0191] Comparative Example 2

[0192] This comparative example provides an oleophobic agent, which is prepared by a method including the following specific steps:

[0193] (1) Add 4g of dopamine to 100mL of a tris(hydroxymethyl)aminomethane hydrochloride solution with a pH of 8.5 and stir until dissolved;

[0194] (2) Add 10g of polystyrene (median particle size 1μm) to the solution obtained in the previous step and sonicate for 15min;

[0195] (3) The solution obtained in the previous step was placed at room temperature for 24 hours with a stirring speed of 200 r / min to allow dopamine to polymerize on the polystyrene surface to form a polydopamine film.

[0196] (4) Add 900g of ethanol to the solution obtained in the previous step, and then add 100mL of ammonia water dropwise using a separatory funnel to adjust the pH of the system to 9-11. Then add 20g of perfluorooctyltriethoxysilane dropwise using a separatory funnel. React at 60℃ for 2h. After the reaction is complete, the product is centrifuged and washed with deionized water. This process is repeated three times. Then, the product is dried in an oven at 105℃ for 4h. After drying, the product is ground in a solid phase to obtain the oleophobic agent.

[0197] Comparative Example 3

[0198] This comparative example provides an oleophobic agent, which is prepared by a method including the following specific steps:

[0199] (1) Take 18.8g of TEOS and add it to a mixture of 900g of ethanol and 100g of deionized water. Then, use a separatory funnel to add 100mL of ammonia water dropwise to adjust the pH of the system to 9-11. React at 200r / min and 60℃ for 6h.

[0200] (2) Then, 20g of perfluorooctyltriethoxysilane was added dropwise using a separatory funnel, and the reaction was continued at 60℃ for 2h. After the reaction was completed, the product was centrifuged and rinsed with deionized water. This process was repeated three times. Then, the product was dried in an oven at 105℃ for 4h. After drying, the product was ground in a solid phase to obtain the oleophobic agent.

[0201] Comparative Example 4

[0202] This comparative example provides an oleophobic agent, which is prepared by a method including the following specific steps:

[0203] (1) Add 10g of polystyrene (median particle size 1μm) to a tris(hydroxymethyl)aminomethane hydrochloride solution with pH 8.5 and sonicate for 15min;

[0204] (2) Add 900g of ethanol to the solution obtained in the previous step, then add 18.8g of TEOS, and then add 100mL of ammonia water dropwise using a separatory funnel to adjust the pH of the system to 9-11. React at 200r / min and 60℃ for 6h.

[0205] (3) Then, 20g of perfluorooctyltriethoxysilane was added dropwise using a separatory funnel, and the reaction was continued at 60℃ for 2h. After the reaction was completed, the product was centrifuged and rinsed with deionized water. This process was repeated three times. Then, the product was dried in an oven at 105℃ for 4h. After drying, the product was ground in a solid phase to obtain the oleophobic agent.

[0206] Test Example 1

[0207] This test example evaluates the oleophobic properties of the oleophobic agents provided in Examples 1-9 and Comparative Examples 1-4, specifically including:

[0208] Take shale outcrops from Longmaxi, Sichuan, and process them into circular thin slices with a diameter of about 4 centimeters;

[0209] The oleophobic agents provided in Examples 1-9 and Comparative Examples 1-4 were diluted 20 times with ethanol, and the circular thin films were immersed in them and kept for 10 minutes, and then removed and dried.

[0210] The contact angles of diesel fuel on the circular sheet after adsorption of the oleophobic agent and on the original circular sheet were then measured using a contact angle meter. The test results are shown in Table 1.

[0211] Test Example 2

[0212] This test example examines the oleophobic agents provided in Examples 1-9 and Comparative Examples 1-4 to test their effectiveness in inhibiting capillary permeation. Specifically, the tests include:

[0213] The oleophobic agents provided in Examples 1-9 and Comparative Examples 1-4 were diluted 10 times with ethanol.

[0214] Take a glass capillary tube with an inner diameter of 0.1 mm and immerse it in an oleophobic solution diluted 10 times. Keep it for 10 minutes and then take it out and dry it.

[0215] The dried glass capillary tube and the original glass capillary tube were then inserted into beakers containing diesel fuel. After 4 hours, the adsorption height of the oil phase in the glass capillary tube compared to the external oil phase surface was observed. The experimental results are shown in Table 1.

[0216] Test Example 3

[0217] This test example evaluates the uniaxial compressive strength of the oleophobic agents provided in Examples 1-9 and Comparative Examples 1-4, specifically including:

[0218] The Longmaxi shale outcrop was taken and processed into a cylindrical core column with a size of 25 (diameter) × 50 (length) mm;

[0219] Take 1g of the oleophobic agent provided in Examples 1-9 and Comparative Examples 1-4, and add it to 2mL of ethanol. After wetting the oleophobic agent with ethanol, add 97.2g of diesel oil. Soak the core column in the diesel oil containing 1wt% oleophobic agent obtained above, and soak it in an oven at 150℃ for 72h.

[0220] After removal, the uniaxial compressive strength of the core column after soaking and the original core column were tested in accordance with the requirements of GB / T 23561.7-2009 "Methods for Determination of Physical and Mechanical Properties of Coal and Rock Part 7: Method for Determination of Uniaxial Compressive Strength and Calculation of Softening Coefficient".

[0221] In addition, for comparison, the cylindrical core column in this test case was also immersed in pure white oil and then in an oven at 150°C for 72 hours;

[0222] After removal, the uniaxial compressive strength of the core sample after soaking in pure white oil was tested in accordance with the requirements of GB / T 23561.7-2009 "Methods for Determination of Physical and Mechanical Properties of Coal and Rock Part 7: Method for Determination of Uniaxial Compressive Strength and Calculation of Softening Coefficient".

[0223] To ensure testing accuracy, four core columns were immersed in diesel or pure white oil containing 1 wt% oleophobic agent in each group. The average uniaxial stress value of the four core columns was taken as the uniaxial compressive strength test result. The test results are shown in Table 1.

[0224] Table 1. Data on the effects of oleophobic agents on improving the oleophobicity of core surfaces, inhibiting oil phase absorption, and enhancing wellbore mechanical stability.

[0225] category Oil phase contact angle / ° Capillary absorption height / mm Uniaxial compressive strength / MPa Original rock core 9 / 195.7 primitive capillary / 25 / Core samples soaked in pure white oil / / 149.7 Example 1 157 -29 201.1 Example 2 144 -25 197.4 Example 3 135 -23 187.2 Example 4 142 -24 195.3 Example 5 147 -25 197.5 Example 6 142 -25 194.5 Example 7 141 -23 192.7 Example 8 143 -25 190.4 Example 9 144 -27 191.9 Comparative Example 1 16 24 152.4 Comparative Example 2 2 28 145.8 Comparative Example 3 54 19 157.9 Comparative Example 4 31 22 156.7

[0226] As shown in Table 1, the rock surfaces modified with the oleophobic agents prepared in Examples 1-9 exhibit oleophobic properties. In particular, after modifying the rock with the oleophobic agent prepared in Example 1, the contact angle of diesel fuel on the rock surface is as high as 157°, and the rock surface exhibits a superoleophobic state. In contrast, the contact angle of diesel fuel on the original core surface is only 9°. The comparison shows that the oleophobic agent provided by the embodiments of the present invention has a good modification effect.

[0227] Regarding the suppression of oil phase absorption, as shown in Table 1, when the unmodified glass capillary, i.e. the original glass capillary, is inserted into diesel fuel, diesel fuel is absorbed into the glass capillary under the action of capillary force due to the oleophilic nature of the glass capillary itself. After stabilization, the oil phase liquid level inside the glass capillary (higher than the external liquid level) is 25 mm. However, after modifying the glass capillary with the oleophobic agent prepared in Examples 1-9, the glass capillary is in an oleophobic state, and the capillary force suppresses the absorption of the oil phase into its interior. Therefore, the oil phase liquid level inside the glass capillary is lower than the external oil phase liquid level. In particular, after the glass capillary is modified with the oleophobic agent obtained in Example 1, the absorption height of the glass capillary reaches -29 mm.

[0228] The effect of the oleophobic agent on improving wellbore stability was further characterized by testing the rock compressive strength. Table 1 shows that the original core had a uniaxial compressive strength of 195.7 MPa. After aging in white oil, its uniaxial compressive strength decreased to 149.7 MPa, a reduction of 23.5%. The rock modified with the oleophobic agents prepared in Examples 1-9 of this invention showed a significantly reduced decrease in compressive strength after aging in white oil. In fact, after modifying the rock with the oleophobic agents prepared in Examples 1, 2, or 5, the rock's compressive strength was even higher than that of the original core. This indicates that the oleophobic agent provided in this invention can improve the cohesiveness of rock particles through adsorption film formation and cementation, thereby increasing the compressive strength.

[0229] Furthermore, in Comparative Example 1, when preparing the oleophobic agent, no fluorosilane with reduced surface energy, namely perfluorooctyltriethoxysilane, was grafted onto the surface of the nano-silica. Although this oleophobic agent could construct micro-nano dual-level roughness at the rock interface, its surface energy was still higher than that of the oil phase, thus failing to achieve oleophobicity. In Comparative Example 2, although the low-surface-energy perfluorooctyltriethoxysilane was introduced during the synthesis of the oleophobic agent, TEOS was not added, resulting in the absence of nano-silica formation, i.e., no nanoparticles were introduced. In this case, the oleophobic agent could not construct oleophobicity at the rock interface after adsorption on the rock surface. Because it has nano-roughness, it does not have an oleophobic modification effect; in Comparative Example 3, only a modified nano-oleophobic agent was synthesized. This material can only construct a single-level nano-roughness, and its effect on improving the roughness of the rock surface is limited, so the oleophobic effect is limited; in Comparative Example 4, dopamine was not added, so the nano-silica generated by the hydrolysis and condensation of TEOS could not be effectively adsorbed onto the surface of styrene particles, so it was difficult to construct a stable micro-nano composite structure. Therefore, this oleophobic agent could not establish a micro-nano dual-level roughness at the rock interface, so the oleophobic effect of this oleophobic agent was also limited.

[0230] In summary, compared with the prior art, the beneficial technical effects achieved by the oleophobic agent for improving wellbore stability provided in the embodiments of the present invention include:

[0231] (1) The oleophobic agent provided in the embodiments of the present invention can change the wettability of the rock surface from oleophilic to superoleophobic. The contact angle of diesel on the rock surface after modification is as high as 150° or more. This can improve the mechanical stability of the wellbore by inhibiting the absorption of oil phase into the rock.

[0232] (2) The oleophobic agent provided in the embodiments of the present invention can be quickly adsorbed on the rock surface to form a film, and improve the cohesion of the rock through cementation, thereby enhancing the rock's ability to resist external damage and effectively improving the stability of the well wall;

[0233] (3) The oleophobic agent provided in the embodiments of the present invention can construct a micro-nano (nano-submicron to micron) dual-level roughness on the rock surface, which has a more significant effect on improving the oleophobicity of rocks and inhibiting the absorption of oil phases;

[0234] (4) When preparing the oleophobic agent, dopamine is polymerized on the surface of submicron to micron particles to form a film, and the modified inorganic nanoparticles are further adsorbed onto the film surface to construct a core-shell structure with dual roughness; or the modified inorganic nanoparticles are connected to the core structure by a positively charged surfactant to construct a core-shell structure with dual roughness.

[0235] (5) The surface of the oleophobic agent provided in the embodiments of the present invention is coated with a large amount of modified inorganic particulate nanomaterials, which makes the oleophobic agent have excellent high temperature resistance. Thermogravimetric experiments have shown that its temperature resistance can reach up to 300℃.

[0236] (6) This product can also be used to improve the wellbore stability of water-based drilling fluids.

[0237] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical inventions, and technical inventions in this invention can be freely combined and used.

Claims

1. An oleophobic agent for improving the stability of a well wall, characterized by, The oleophobic agent used to improve wellbore stability has a core-shell structure, which includes a core structure, a polymer film coating the outer surface of the core structure, and modified inorganic nanoparticles adsorbed on the polymer film to form the shell structure; wherein, the polymer film includes a polydopamine film; Alternatively, it may include a core structure and modified inorganic particulate nanomaterials for forming a shell structure, wherein the modified inorganic particulate nanomaterials are adsorbed onto the core structure by electrostatic attraction via a positively charged surfactant. The core structure is selected from particles with a size ranging from submicron to micron. The modified inorganic particulate nanomaterials include inorganic particulate nanomaterials modified with fluorinated siloxanes.

2. The oleophobic agent according to claim 1, characterized in that, The core-shell structure includes a core structure and modified inorganic particulate nanomaterials for forming the shell structure, wherein both the core structure and the modified inorganic particulate nanomaterials contain silane groups, and the core structure and the modified inorganic particulate nanomaterials are assembled to form the core-shell structure through a silane hydrolysis-condensation reaction.

3. The agent according to claim 1 or 2, characterized in that, The size of the core structure is 100nm-10μm.

4. The agent of claim 1, wherein The core structure is an inorganic particle or an organic particle; wherein the inorganic particle includes silicon dioxide, calcium carbonate or titanium dioxide, and the organic particle includes polystyrene, polymethyl methacrylate or polyacrylate.

5. The oleophobic agent according to claim 2, characterized in that, The core structure includes polystyrene with silane groups on its surface, polymethacrylate with silane groups on its surface, or polyacrylate with silane groups on its surface.

6. The oleophobe according to claim 1 or 2, characterized in that, The modified inorganic particulate nanomaterials have a size of 10nm-100nm.

7. The oleophobe according to claim 1, wherein The fluorinated siloxanes include fluorinated hydrocarbon siloxanes and / or fluorinated polyether siloxanes.

8. The oleophobe according to claim 1, wherein The inorganic particulate nanomaterials include nano-silica and / or nano-titanium dioxide.

9. The oleophobe according to claim 1, wherein The positively charged surfactants include quaternary ammonium salt surfactants, pyridine halides, or alkyl imidazoline surfactants.

10. The oleophobe according to claim 1 or 2, characterized in that, The oleophobic agent may be spherical, ellipsoidal, raspberry-shaped, or strip-shaped.

11. The method of preparing an oleophobe for improving wellbore stability according to any one of claims 1 to 10, characterized in that, The preparation method includes: (1) Add the monomer raw material corresponding to the polymer membrane to the buffer solution or add the positively charged surfactant to the water and dissolve it; (2) Add submicron to micron particles to the solution obtained in step (1) and sonicate them. Then place them at room temperature and under stirring for a period of time so that the monomer raw material polymerizes on the surface of the submicron to micron particles to form a polymer film or so that the positively charged surfactant is adsorbed on the surface of the submicron to micron particles. (3) Add the modified inorganic nanoparticles to the solution obtained in step (2) and sonicate it. Then heat it under stirring to allow the modified inorganic nanoparticles to adsorb onto the polymer film to obtain the oleophobic agent. Alternatively, under stirring conditions, the modified inorganic nanoparticles are adsorbed onto the submicron to micron-sized particles by a positively charged surfactant to obtain the oleophobic agent. Alternatively, the solution obtained in step (2) can be added to an alcohol solvent, and then tetraethoxysilane and ammonia can be added in sequence to adjust the pH value to 9-11 and carry out a condensation reaction under stirring conditions; after the condensation reaction is completed, a modifier is added to carry out a modification reaction, and the oleophobic agent is obtained after the modification reaction is completed.

12. The method of claim 11, wherein, In step (1), the pH value of the buffer solution is 7-10.

13. The method of claim 12, wherein, The pH value of the buffer solution is 8.

5.

14. The method of any one of claims 11-13, wherein, The buffer solution comprises a trihydroxymethylaminomethane hydrochloride solution.

15. The preparation method according to claim 11, characterized in that, In step (3), the temperature is raised to 40-60℃ and maintained for 4-6 h.

16. The preparation method according to claim 11, characterized in that, In step (3), the condensation reaction is carried out at a temperature of 50-70°C for 6-8 hours.

17. The preparation method according to claim 11, characterized in that, In step (3), the temperature of the modification reaction is 60-70℃ and the time is 2-4h.

18. The preparation method according to claim 11, characterized in that, The mass ratio of the monomer raw material, submicron to micron-sized particles and modified inorganic nanomaterials corresponding to the polymer film is 3-4:10-20:7-10.

19. The preparation method according to claim 11, characterized in that, The mass ratio of positively charged surfactants, submicron to micron-sized particles, and modified inorganic nanomaterials is 1-2:10-20:7-10.

20. The preparation method according to claim 11, characterized in that, The mass ratio of the monomer raw material or positively charged surfactant, submicron to micron particles, tetraethoxysilane and modifier corresponding to the polymer film is 3-4 or 1-2:10-20:9.4-28.2:20-30.

21. The preparation method according to any one of claims 11-13, 15-20, characterized in that, The preparation method of the modified inorganic particulate nanomaterial includes: (a) Adding inorganic particulate nanomaterials to an organic solvent and subjecting them to ultrasonic treatment; (b) Add a pH adjuster to the solution obtained in step (a) and mix well to adjust the pH of the system to 4-6 or 10-11; (c) Add the modifier to the solution obtained in step (b) and react at 50-60℃ for 5-10 h under stirring conditions, wherein the mass ratio of the modifier to the inorganic particulate nanomaterial is 1-2:15-30; (d) Dry the solution obtained after the reaction in step (c), and grind the solid phase obtained after drying to obtain the modified inorganic particulate nanomaterial.

22. The preparation method according to claim 11, characterized in that, When the core structure and modified inorganic particulate nanomaterials are assembled into a core-shell structure via a silane hydrolysis-condensation reaction, the preparation method includes: 1) Add vinyl monomers, silane reagents containing double bonds and initiators to water, and prepare submicron to micron-sized particles with silane groups on the surface through polymerization reaction; 2) Add the solution obtained in step 1) to an alcohol solvent, then add tetraethoxysilane and ammonia in sequence, adjust the pH value to 9-11, and carry out a condensation reaction under stirring conditions; after the condensation reaction is completed, add a modifier to carry out a modification reaction, and after the modification reaction is completed, the oleophobic agent is obtained.

23. The preparation method according to claim 22, characterized in that, The mass ratio of vinyl monomer, double-bonded silane reagent, TEOS and modifier is 10-15:1-3:9.4-28.2:20-30.

24. The preparation method according to claim 22, characterized in that, In step 1), the silane reagent containing double bonds includes one or a combination of several of methacryloyloxypropyltrimethoxysilane, vinyltrimethoxysilane, and vinyltris(b-methoxyethoxy)silane.

25. The preparation method according to claim 22, characterized in that, The initiator includes one or a combination of several of azobisisobutyronitrile, potassium persulfate, and ammonium persulfate.

26. The preparation method according to claim 22, characterized in that, The vinyl monomers include styrene, methacrylates, or acrylates.

27. The preparation method according to claim 22, characterized in that, In step 1), the polymerization reaction is carried out at a temperature of 50-70°C for 6-10 hours.

28. The preparation method according to claim 22, characterized in that, In step 2), the condensation reaction is carried out at a temperature of 50-70°C for 6-8 hours.

29. The preparation method according to claim 22, characterized in that, In step 2), the temperature of the modification reaction is 60-70℃ and the time is 2-4h.

30. A drilling fluid comprising an oil-repellent agent for improving wellbore stability as described in any one of claims 1-10.

31. The drilling fluid according to claim 30, characterized in that, The drilling fluid is either oil-based or water-based.

32. The application of the oleophobic agent for improving wellbore stability as described in any one of claims 1-10 or the drilling fluid as described in claim 30 or 31 in the development of deep, ultra-deep or unconventional oil and gas.

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