A method for making a wettability-regulating capillary model of a shale oil reservoir

Abstract

This invention relates to the field of shale oil and gas reservoir research technology, specifically to a method for fabricating a capillary model for studying the wetting regulation of shale oil reservoirs. The method includes the following steps: mask fabrication, glass slide cleaning, chromium-coated topcoat spraying, pre-baking (hardening), exposure, development, hardening, chromium layer etching, glass slide etching, topcoat and chromium removal, thermal bonding, and wettability modification. By preparing capillaries with micron-nanometer diameters and modifying their wettability, capillary models with an aspect ratio of approximately 1:2, etching precision of 500 nm, and maximum pressure resistance of 10 MPa can be fabricated. Combined with a microfluidic image acquisition module and pressure acquisition module, the fluid flow patterns within the non-uniform wetting micropores of the reservoir can be visualized for research.

Description

Technical Field

[0001] This invention relates to the field of shale oil and gas reservoir research technology, specifically to a method for constructing a capillary model for studying the wetting regulation of shale oil reservoirs. Background Technology

[0002] Currently, shale oil extraction primarily relies on large-scale volumetric fracturing, which extends the natural fracture network through hydraulic fracturing and utilizes fracture percolation for extraction. This involves percolating water from the fractures into the matrix pores, displacing oil within the fractures, and then using water injection or fracturing fluid backflow to bring the crude oil to the bottom of the production well. However, shale oil and gas reservoirs are characterized by low porosity, low permeability, and non-uniform wetting, making conventional capillary models inapplicable for studying fluid flow patterns. Currently, there is a lack of research on the microscopic pore structure characteristics of reservoirs and their fluid flow patterns.

[0003] Due to limitations in pore size, conventional experimental methods struggle to visually represent the flow behavior of crude oil within micro- and nano-scale channels. Furthermore, most oil and gas flow theories established using conventional experimental methods are based on the assumption of a continuous medium, making them only applicable in the early stages of conventional oil and gas reservoir development. For unconventional oil and gas reservoirs with significant microscale effects and for older, high-water-cut reservoirs with significant oil-water interface interactions, conventional experimental methods are insufficient to provide insights into the internal flow patterns within oil and gas flow channels.

[0004] Fluids flowing in micro- and nano-scale spaces are generally referred to as microfluidics, and the related technologies for displacing and controlling microfluidics under low Reynolds number or laminar flow conditions in micro- and nano-scale channels are called microfluidics. Microfluidics can manipulate fluids in micrometer-scale spaces, miniaturizing the basic functions of biological and chemical laboratories onto a model of a few square centimeters. The model that carries this function is called a microfluidic model. Microfluidic models can evaluate the seepage behavior of crude oil and chemical liquids under capillary action.

[0005] Chinese patent application CN201610953629.7 discloses a method for preparing a microscopic, visualized etching low-permeability model. The process includes the following steps: 1. glass slide washing; 2. glass slide baking; 3. spin coating; 4. pre-baking; 5. exposure; 6. development; 7. hardening; 8. wax sealing; 9. acid etching; 10. wax and resist removal. By using two layers of primer and etching adhesive respectively during the spin coating process, closely adhering them to the glass slide to be processed, and then setting specific process parameters based on the characteristics of the mixed adhesives, a microscopic, visualized etching model can be obtained. The maximum precision of the resulting etching marks can reach 1.2 μm, and the resulting marks are V-shaped with uniform width and appropriate depth, which can well simulate the porosity of real formations and better meet the needs of laboratory analysis.

[0006] Chinese patent application CN201210496465.1 discloses a fabrication process for a microscopic oil displacement model used in laboratory simulations of low-permeability reservoirs and research on oil displacement processes in oilfield chemical and acid fracturing. The technical solution is as follows: A glass substrate is polished, cleaned, and dried, then baked on a baking sheet. A layer of tackifier is spin-coated onto the glass substrate, and the substrate is baked on the baking sheet to form a nanofilm. A layer of photoresist is then spin-coated onto the glass substrate and baked on the baking sheet. The reservoir image is converted to a black and white image, imported into photolithography software, and the glass substrate is exposed and developed in a developing solution, cleaned, dried, and baked on the baking sheet. Paraffin wax is used to seal the areas of the glass substrate other than the exposed areas, and the substrate is etched in an etching solution. After cleaning, the substrate is boiled in sulfuric acid and hydrogen peroxide, then cleaned and dried. The glass substrate and mica sheet are tightly bonded together and sintered in a muffle furnace. Finally, the inlet and outlet channels are polished, and a capillary tube is inserted into the channels to create a microscopic oil displacement model for studying the oil displacement process.

[0007] Chinese patent application CN201610022125.3 discloses a micron-scale capillary bundle model and its fabrication method for qualitative analysis of capillary action in porous media, as well as an experimental device for qualitative analysis of capillary action in porous media. Based on the Hagen-Poiseuille law, this invention simulates the seepage of fluid in the pores of oil reservoir rocks as seepage in a set of micron-scale capillary bundles with the same or different inner diameters. A micron-scale capillary bundle model was designed accordingly, and combined with an image acquisition system, it enables qualitative analysis and intuitive observation of capillary action in porous media, solving the problem that existing core physical models cannot qualitatively characterize and intuitively observe the flow process of oil displacement agents. The fabrication method of this micron-scale capillary bundle model involves tightly fastening a prepared master plate to a substrate, then etching the capillary bundles from the master plate onto the substrate using ultraviolet light irradiation. A etching solution is then immersed in the area etched with the capillary bundles, and through chemical etching, several parallel capillaries of equal or unequal diameters are obtained, ultimately yielding the model.

[0008] However, the above methods cannot solve the problems of shale layers. Shale is composed of mudstone and sandstone, and kerogen in mudstone is a source rock. Therefore, shale is a self-generated and self-storing type of oil and gas reservoir. This also leads to the heterogeneous wetting of shale reservoirs. Some parts are water-wetted, and some parts are oil-wetted. In recent years, capillary model research has increased. However, most of the capillary models currently involved are in the millimeter-micrometer range in diameter, which cannot meet the characteristics of low porosity and low permeability of shale. Commonly used etching models include glass slides and silicon wafers. Glass slides are strongly water-wetted and cannot simulate shale reservoirs. Silicon wafers are oleophilic wetted, but they are fragile and expensive.

[0009] Furthermore, existing millimeter-micron level capillary etching is uneven, and the flow channels cannot accurately reflect the flow state of fluid within pores of a certain size. Moreover, when existing technologies are used to etch nanochannels, the unevenness of the etching and the tendency for the channels to become severely blocked can easily lead to deviations when studying dynamic processes.

[0010] Therefore, it is essential to develop a method for constructing a capillary model of wetting regulation in shale oil reservoirs that can solve the above-mentioned technical problems. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing a wetting-controlled capillary model for studying the flow patterns of shale oil reservoirs. Two nanometer- to micrometer-diameter capillary regions are etched onto a substrate, namely a hydrophilic region and a wetting-modification region. The substrate is a glass slide with good light transmittance and high bonding strength. The two regions can be used separately or in parallel. Therefore, this invention can simulate the fluid flow patterns in hydrophilic sandstone fractures and weakly oleophilic matrix fractures individually, or it can simulate the fluid flow patterns in heterogeneously wetted shale in parallel using the two regions.

[0012] The purpose of this invention is to etch nano- to micron-scale capillaries with diameters between 500 nm and 10 μm, aspect ratios of 1:2, and inlet / outlet grooves with a diameter of 100 μm. Furthermore, a wetting modifier is used to wet the capillaries in the wetting-modified regions.

[0013] This invention is achieved through the following technical solutions:

[0014] Unless otherwise specified, all ratios mentioned below are volume ratios.

[0015] A method for constructing a capillary model for wetting regulation in shale oil reservoirs includes the following steps:

[0016] Step 1, Mask fabrication: Use a laser to etch a capillary model onto a film; or etch the capillary onto a chromium plate or thin rock section using photosensitive etching to obtain the capillary model.

[0017] Step 2: Clean the substrate;

[0018] Step 3, Chromium Spraying and Coating: Spray a layer of chromium onto the substrate to obtain a chromium layer, and then evenly apply photoresist to obtain a photoresist layer;

[0019] Step 4, Pre-baking (hardening): Place the substrate from Step 3 on a baking machine for baking;

[0020] Step 5, Exposure and Development: The capillary model on the mask is transferred to the photoresist layer of the substrate through exposure and development, thus revealing the photolithographic capillary model;

[0021] Step 6, Hardening: Use a photoresist baking machine to stabilize the softened and expanded photoresist after development of the substrate;

[0022] Step 7, Chromium layer etching: Using cerium ammonium nitrate, the capillary model is transferred to the chromium layer;

[0023] Step 8, Substrate Etching: Use BOE etchant to perform wet etching on the substrate;

[0024] Step 9, Removal of Photoresist and Chromium: The photoresist layer and chromium layer are removed by developing and etching the chromium layer respectively to obtain the etched substrate;

[0025] Step 10, Thermal Bonding: The etched substrate and cover plate are stacked in a muffle furnace, heated by programmed temperature rise, and finally annealed.

[0026] Step 11, Wetting Modification: Inject Piranha solution into the capillary model of the etched substrate and dry it. Then inject a wetting modifier to obtain the wetting-controlled capillary model.

[0027] The wetting-regulating capillary model is divided into a hydrophilic region and a wetting-modifying region. The two regions are connected by grooves.

[0028] The wetting control capillary model also includes three pairs of inlets and outlets, with the hydrophilic region and the wetting modification region connected by grooves in the relatively large-diameter flow channel.

[0029] Preferably, the inner diameter of the capillary in step 1 is between 500 nm and 10 μm, and the width-to-depth ratio is 1:2.

[0030] Preferably, the diameter of the groove connecting the capillary inlet and outlet in step 1 is 100 μm.

[0031] Preferably, the substrate in step 2 is a rigid material with good light transmittance.

[0032] Preferably, the rigid material with good light transmittance is a substrate.

[0033] More preferably, the substrate in step 2 is made of ultra-clear glass. Ultra-clear glass, as the etching substrate, has high pressure resistance and a light transmittance of 91.5%, meeting the requirements for visualization and pressure resistance. In addition to SiO2, its composition also includes Al2O3, Fe2O3, CaO, MgO, Na2O, etc., resulting in good substrate etching performance.

[0034] Preferably, the cleaning process in step 2 is as follows: first, clean with anhydrous ethanol and acetone, then ultrasonically clean with deionized water for 20-40 minutes, remove and dry; then soak the substrate in Piranha solution, remove and clean with deionized water, dry, and set aside.

[0035] More preferably, the cleaning process in step 2 is to first clean with anhydrous ethanol and acetone, then ultrasonically clean with deionized water for 30 minutes, remove and dry; then soak the substrate in Piranha solution for 1 hour, remove and clean with deionized water, blow dry with nitrogen, repeat three times and store for later use.

[0036] More preferably, the Piranha solution in step 2 is prepared by mixing 98% H2SO4 and 30% H2O2 in a volume ratio of 7:3. This invention uses a hot Piranha solution to hydroxylate the glass surface.

[0037] Preferably, in step 3, a chromium layer is sprayed onto the substrate using a magnetron sputtering machine to obtain a chromium layer.

[0038] Preferably, the thickness of the chromium layer in step 3 is 100 nm.

[0039] Preferably, after obtaining the chromium layer in step 3, the substrate is cleaned with anhydrous ethanol and acetone.

[0040] Preferably, a spin coater is used to apply the photoresist in step 3.

[0041] Preferably, the photoresist is applied in step 3 using a KW-4A spin coater.

[0042] Preferably, in step 3, the photoresist used is AR-P 3100 positive photoresist.

[0043] Preferably, the specific process for applying photoresist in step 3 is as follows: applying the photoresist at a rotation speed of 4000 rpm for 30 seconds, resulting in a photoresist thickness of 10 μm. This allows for the etching of nanoscale lines.

[0044] Preferably, the glue baking machine mentioned in steps 4 and 6 is a KWH-350 glue baking machine.

[0045] Preferably, in step 4, the substrate from step 3 is baked on a 90°C baking machine for 1 hour to ensure sufficient adhesion of the photoresist.

[0046] Preferably, in step 5, an URE-2000 lithography machine is used for exposure, and AR 300-26 developer is used for development.

[0047] Preferably, in step 5, UV preheating is performed for 30 minutes, followed by vertical UV irradiation. This causes the photoresist to undergo a cross-linking reaction, transferring the model from the mask onto the photoresist layer. The exposure time is 2 minutes. Development is performed using AR 300-26 developer. The substrate is immersed in the developer for 2 minutes, then rinsed with deionized water. This step is repeated twice. The photolithographic capillary model is then revealed.

[0048] Preferably, in step 6, the substrate is placed on a KWH-350 photoresist baking machine and baked at 150°C for 2 hours. This allows the softened and expanded photoresist to solidify and adhere well to the glass substrate.

[0049] In step 7, chromium is etched using a cerium ammonium nitrate solution. The cerium ammonium nitrate solution has virtually no etching effect on the AR-P 3100 photoresist and is non-toxic and harmless.

[0050] Preferably, after step 7, a wax sealing process is required to protect the uncoated substrate surface.

[0051] Preferably, the BOE corrosion solution in step 8 is a mixed aqueous solution of HF and NH4F.

[0052] More preferably, the BOE corrosion solution is a mixture of 49% HF aqueous solution and 40% NH4F aqueous solution in different proportions.

[0053] More preferably, the BOE corrosion solution is a mixture of 49% HF aqueous solution and 40% NH4F aqueous solution in a mass ratio of 1:3.

[0054] More preferably, the etching time for wet etching in step 8 is 20s to 60s.

[0055] Preferably, after removing the photoresist layer and chromium layer in step 9, step 2 is repeated to increase the number of hydroxyl groups on the glass surface, which facilitates bonding.

[0056] More preferably, in step 9, a dewaxing step is required, in which the wax on the substrate surface is scraped off with a blade.

[0057] Preferably, in step 10, a polished graphite plate is placed on top of the etched substrate and the cover plate, and a stainless steel block is placed on the upper graphite plate and placed in a muffle furnace for programmed heating. The temperature is eventually raised to 20-50°C above the glass annealing point, and then programmed cooling annealing is performed.

[0058] More preferably, in step 10, a polished graphite plate is placed on top of the etched substrate and the cover plate, and a stainless steel block is placed on the upper graphite plate and placed in a muffle furnace for programmed heating. The hydrogen bonds on the interface are converted into silicon-oxygen bonds. Finally, the temperature is raised to 20-50°C above the annealing point of ultra-white glass (547°C) and maintained for a period of time. Then, a programmed cooling annealing process is performed to allow the atoms between the two surfaces to react with each other and form chemical bonds, thereby bonding the etched substrate and the cover plate.

[0059] More preferably, after step 10, if the experimental pressure reaches 5 MPa or higher, a matching microfluidic chip fixture needs to be added.

[0060] Preferably, in step 11, the capillary model of the etched substrate is injected with Piranha solution and dried, and this process is repeated three times to give the capillary more hydroxyl active groups, which facilitates wettability modification. Then, a wetting modifier is injected to change the strongly hydrophilic channel into a weakly oleophilic or neutral channel, thus obtaining the wetting-controlled capillary model.

[0061] Preferably, the wetting modifier in step 11 includes at least one of a surfactant and a nanomolecular film.

[0062] More preferably, the surfactant includes at least one of sodium dodecylbenzenesulfonate and sodium salt of fatty alcohol polyoxyethylene ether sulfate.

[0063] More preferably, the nanomolecular membrane is prepared from dimethyl carbonate and N,N,N',N'-tetramethylethylenediamine.

[0064] In step 11, different degrees of wettability changes can be obtained by altering the concentration of the wetting modifier. This changes the substrate wettability from water-wetting to neutral or oil-wetting, facilitating the simulation of heterogeneous wetting of shale formations.

[0065] More preferably, before step 11, the wetting angle of the prepared wetting modifier needs to be measured. The etched substrate is cleaned and dried according to step 1, then immersed in the wetting modifier for 24 hours to allow the wetting modifier to fully adsorb onto the glass surface, followed by ventilation and drying. The angle of a water droplet on the etched substrate is measured using a wetting angle meter. This allows for obtaining different wetting modification angles corresponding to different concentrations, facilitating subsequent changes in wetting properties to achieve the desired specific wetting characteristics.

[0066] The beneficial effects of this invention are:

[0067] This invention provides a method for preparing a wetting-controlled capillary model for studying the flow patterns of shale oil reservoirs. This method can create micron-nanoscale flow channels. Thermal bonding is used between the substrate and the cover plate, resulting in excellent pressure resistance. Furthermore, the etching depth has been optimized compared to wet etching. This model is primarily used to study the flow patterns of shale oil reservoirs. First, the size of fractures after formation fracturing is measured, and capillaries of corresponding sizes are etched. The model on the mask is etched onto photoresist using ultraviolet light irradiation. Then, a second etching process using a chromium etching solution is performed to transfer the model to the chromium layer. Finally, the model is transferred to the substrate using wet etching. This method overcomes the problem of uneven etching between nanon and micron levels, resulting in more precise and uniform flow channels. Adding a chromium layer during etching allows for a clearer and more uniform transfer of the model from the master plate to the substrate. Wet etching is used for the glass slides; wet etching is a mature method, and the etching rate and depth can be controlled by changing the solution concentration.

[0068] The capillary model fabricated in this invention is divided into two blocks, each containing several capillary channels of varying diameters. The biggest difference between the two blocks lies in their wettability; they can be used separately or in parallel. Its advantages are: firstly, reduced cost; and secondly, simulation of fluid flow patterns in hydrophilic, oleophilic, and non-uniformly wetted capillaries. Furthermore, the etching effect and precision meet requirements, the fabrication is relatively simple, and it solves the problem of studying the influence of wettability on fluid flow patterns.

[0069] In this invention, Piranha solution is used to imbue the capillary surface with hydroxyl active groups, thereby forming a hydrophilic wall. The wetting modifier has both hydrophilic and lipophilic groups, and therefore can be adsorbed onto the capillary wall, resulting in a change in wettability. Furthermore, ammonium fluoride can decompose into hydrofluoric acid and ammonia, thus serving as a buffer for the reaction between hydrofluoric acid and silicon dioxide, controlling the etching rate of the glass and achieving nano- to micron-level channel etching. In addition, this invention involves evaporating the glass surface to leave a suitable water molecule film (hydration layer), then bonding the etched substrate and cover plate face-to-face, and heating them in a muffle furnace for high-temperature annealing. This allows for thermal bonding of the two surfaces (dehydration condensation of the hydration layer), improving pressure resistance. Attached Figure Description

[0070] Figure 1 This is a flowchart illustrating the preparation process of the capillary model for wetting regulation according to the present invention.

[0071] Figure 2 This is a schematic diagram of the capillary model for micron-nano-scale wetting regulation of the present invention;

[0072] Among them, 1. Ultra-white glass, 2. Wetting-modified region injection port, 3. Main injection port, 4. Injection end connecting groove, 5. Hydrophilic region injection port, 6. Hydrophilic region capillary, 7. Hydrophilic region outlet, 8. Main injection port, 9. Outlet connecting groove, 10. Wetting-modified region outlet, 11. Wetting-modified region capillary.

[0073] Figure 3 This is a schematic diagram of the notch structure;

[0074] Figure 4 A schematic diagram of water flow in the capillary of the wetting-modified region;

[0075] Figure 5 This is a schematic diagram showing the contact angles of the glass slide before and after wetting modification with ZY-1.

[0076] Figure 6 This is a schematic diagram showing the contact angles of the glass slide before and after MD-S wetting modification. Detailed Implementation

[0077] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as a result. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0078] This invention provides a method for preparing a wetting-controlled capillary model for studying the flow characteristics of shale oil reservoirs. The model is divided into a hydrophilic region and a wetting-modified region, connected by grooves. The wetting-controlled capillary model also includes three pairs of inlets and outlets, with the hydrophilic and wetting-modified regions connected by grooves in relatively large-diameter flow channels. The process involves the following steps: mask fabrication, slide cleaning, chromium sputtering, slide cleaning, resist coating, pre-baking (hardening), exposure, development, hardening, chromium layer etching, slide etching, resist and chromium removal, thermal bonding, and wetting modification. Nano- to micron-scale capillaries with diameters between 500 nm and 10 μm, an aspect ratio of 1:2, and inlet / outlet grooves with a diameter of 100 μm are etched onto an ultra-white glass substrate. A wetting modifier is then used to modify the wetting of the capillaries in the wetting-modified region.

[0079] Unless otherwise specified, all chemicals mentioned below can be purchased through conventional methods.

[0080] Unless otherwise specified, all ratios mentioned below are volume ratios.

[0081] Reference Figure 1 The flowchart shown illustrates the preparation of a micron-nanoscale wetting-regulating capillary model for studying the flow characteristics of shale oil reservoirs, comprising the following steps:

[0082] Step 1, Mask fabrication: Use a laser to etch a capillary model on the film with an inner diameter between 500nm and 10μm and a width-to-depth ratio of 1:2; the diameter of the groove connecting the capillary inlet and outlet is 100μm.

[0083] Step 2: Cleaning the ultra-white glass slide: Using the ultra-white glass slide as the substrate, first clean it in anhydrous ethanol and acetone for 15 minutes each, then ultrasonically clean it with deionized water for 30 minutes, remove it, and dry it. Next, hydroxylate the glass surface in a Piranha solution (V(98% H2SO4):V(30% H2O2) = 7:3) at 60℃ for 1 hour. After soaking, remove the glass slide, clean it thoroughly with plenty of deionized water, and then dry it with nitrogen. Repeat this process three times before storing it for later use. The model must be kept clean to prevent contamination.

[0084] Step 3, Chromium Sputtering and Coating: A 100nm thick chromium layer is sputtered onto the glass slide using a magnetron sputtering machine. Then, the substrate is cleaned with anhydrous ethanol and acetone for 15 minutes to enhance the adhesion between the photoresist and the substrate. Finally, the substrate is removed and dried, and after natural cooling, the photoresist is coated. Using a KW-4A photoresist coater, the vacuum button is pressed first, and the glass slide is adsorbed onto the rotating stage by external vacuum pressure. The rotation speed is adjusted to 4000 rpm. AR-P 3100 positive photoresist is evenly applied using a dropper and held for 30 seconds, resulting in a 10μm photoresist layer.

[0085] Step 4, Pre-baking (hardening): Place the glass slide obtained in Step 3 on a KWH-350 photoresist baking machine, maintain the temperature at 90℃, and bake for 1 hour. This ensures full adhesion of the photoresist, prevents poor exposure, and avoids photoresist dripping during development. After baking, allow it to cool in the dark.

[0086] Step 5, Exposure and Development: The glass slide obtained in Step 4 is exposed using a URE-2000 lithography machine. UV preheating is performed for 30 minutes, then the pump is turned on, and the glass slide is adsorbed onto the stage using vacuum pressure. Then, vertical UV irradiation is applied, causing the photoresist to undergo a cross-linking reaction, transferring the capillary model from the photomask to the photoresist layer on the glass slide. The exposure time is 2 minutes. Development is performed using AR 300-26 developer. The glass slide is immersed in the developer for 2 minutes, then rinsed with deionized water. This step is repeated twice. The photolithographic capillary model is then revealed.

[0087] Step 6, Hardening: Place the glass slide on a KWH-350 photoresist baking machine, maintain the temperature at 150℃, and bake for 2 hours. This allows the softened and expanded photoresist to solidify and adhere well to the glass substrate.

[0088] Step 7, Chromium layer etching: Immerse the substrate in a 10wt% cerium ammonium nitrate solution for 2 minutes, and transfer the capillary model to the chromium layer. AR-P 3100 positive photoresist is insoluble in cerium ammonium nitrate solution.

[0089] Step 8, Glass Slide Etching: First, perform a wax sealing treatment to protect the uncoated glass surface. Then, use BOE etchant (a mixture of 49% HF aqueous solution and 40% NH4F aqueous solution in a 1:3 volume ratio) to wet-etch the glass slide for 40 seconds. The smaller the channel diameter, the shorter the etching time; conversely, the larger the diameter, the longer the etching time.

[0090] Step 9: Dewaxing, Resin Removal, and Chromium Removal: Use a blade to scrape off the wax from the glass slide surface. Then, use development and chromium etching methods to remove the photoresist and chromium layers. Repeat step 2 to increase the number of hydroxyl groups on the glass surface, facilitating bonding. The etched microfluidic model needs to be examined under a microscope to ensure it meets the etching channel requirements. If it does not, repeat steps 1-8 until the substrate meets the requirements, obtaining the etched glass substrate.

[0091] Step 10, Thermal Bonding: Place a polished graphite plate on top of the glass-etched substrate and the cover plate, respectively, and then press a stainless steel block into the muffle furnace. Perform programmed heating (heating rate 1℃ / min), converting the hydrogen bonds at the interface into silicon-oxygen bonds. Finally, heat to 50℃ above the ultra-white glass annealing point of 547℃ and maintain for 3 hours, then perform programmed cooling (cooling rate 2℃ / min) annealing treatment, allowing the atoms between the two surfaces to react and form chemical bonds, thus bonding the substrate and cover plate.

[0092] Step 11, Wettability Modification: Inject Piranha solution into the capillary model of the wetting-modified region and dry it, repeating this process three times. This results in the capillary having more hydroxyl active groups, facilitating wetting modification. Finally, inject a laboratory-made wetting modifier MD-S or ZY-1 (a mixed solution of 0.5 wt% dodecyltrimethylammonium chloride and 1 wt% ethanol), with the concentration controlled between 500 mg / L and 6000 mg / L, which can achieve a shift in the wetting angle from 40° to 120°. Then, place the glass slide in an oven at 80°C to dry the chip, changing the wettability of the glass slide from hydrophilic to neutral or oleophilic.

[0093] The preparation process of wetting modifier MD-S is as follows:

[0094] (1) Synthesis of ionic liquids

[0095] First, add an appropriate amount of N-methylimidazole to a three-necked flask, add a certain amount of acetonitrile as a solvent, remove oxygen with nitrogen, raise the reaction temperature to 40°C, add excess bromoethane, react for 16 hours, and then distill off the excess bromoethane and solvent under reduced pressure for purification and later use.

[0096] (2) Synthesis of molecular film agents

[0097] An appropriate amount of N,N,N',N'-tetramethylethylenediamine was added to a reaction vessel. An ionic liquid was used as both catalyst and solvent, with the amount of ionic liquid added being 50% of the mass of N,N,N',N'-tetramethylethylenediamine. DMC was added at a molar ratio of 1:5 (N,N,N',N'-tetramethylethylenediamine: dimethyl carbonate DMC). The reaction was carried out at 140°C for 12 hours. Unreacted dimethyl carbonate was distilled off under reduced pressure, and the resulting product was dried to obtain CO3. 2- Quaternary ammonium salts.

[0098] (3) Transformation

[0099] The monomethyl carbonate quaternary ammonium salt obtained in step (2) was slowly added to an equal volume of 3 mol / L hydrochloric acid solution under stirring, and a large number of bubbles were released. After acid washing, the mixture was transferred to a separatory funnel, allowed to stand and separate phases, and the aqueous phase was separated. The pH value of the aqueous phase was 1-2. The oil phase was washed three times with an equal volume of 0.6 mol / L NaOH solution until it was weakly alkaline. After standing and separating phases, the aqueous phase was separated. After the transformation was completed, the water was distilled off under reduced pressure to obtain Cl. - Quaternary ammonium salts are the wetting modifiers MD-S.

[0100] Using the above method, capillary models with inner diameters between 500 nm and 10 μm and wettability modification can be etched.

[0101] like Figure 2 As shown, a wetting-controlled capillary model for studying the flow characteristics of shale oil reservoirs was etched using the above method. In the figure, 1 is ultra-clear glass, 2 is the injection port of the wetting-modified zone, 3 is the main injection port, 4 is the injection end connecting groove, 5 is the injection port of the hydrophilic zone, 6 is the capillary of the hydrophilic zone, 7 is the production outlet of the hydrophilic zone, 8 is the main production outlet, 9 is the production end connecting groove, 10 is the production outlet of the wetting-modified zone, and 11 is the capillary of the wetting-modified zone.

[0102] When using the hydrophilic zone (simulating underground shale rock fractures) alone or the wetting-modified zone (simulating matrix fractures), it is necessary to install dead plugs on the main injection port 3 and the main extraction port 8.

[0103] When simulating the overall non-uniform wetting of the shale layer, it is necessary to install dead plugs on the other four ports besides the main injection port 3 and the main production outlet 8.

[0104] Figure 2 In the model, the line connecting the main injection port 3 and the main extraction port 8 divides the capillary model into a hydrophilic region and a wetting-modified region. The region of capillary 6 containing the hydrophilic region is the hydrophilic region, and the region of capillary 11 containing the wetting-modified region is the wetting-modified region, i.e., the oleophilic region.

[0105] like Figure 3 As shown, the etched flow channel end face is a semi-circular notch with a width-to-depth ratio of 1:2.

[0106] like Figure 4 The diagram shows the flow of water in the capillary of the wetting and modified region, which becomes a forward-convex shape.

[0107] like Figure 5 and Figure 6The figures show the contact angle test results before and after modifying the glass sheet with ZY-1 or MD-S in step 11. Before modification, the wetting angle of the ultra-clear glass was 24.19°, indicating hydrophilicity. After modification with ZY-1, the wetting angle became 111.29°; after modification with MD-S, the wetting angle became 107.51°, both indicating oleophilicity. Adjusting the concentration of the wetting modifier can alter the wetting angle after modification.

[0108] The nano- to micron-scale models prepared by this invention can withstand pressures of over 5 MPa.

[0109] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A method for constructing a capillary model for studying the wetting regulation of shale oil reservoirs, characterized in that, Includes the following steps: Step 1, Mask fabrication: Use a laser to etch a capillary model onto a film; or etch the capillary onto a chromium plate or thin rock section using photosensitive etching to obtain the capillary model. Step 2: Clean the substrate; Step 3, Chromium Spraying and Coating: Spray a layer of chromium onto the substrate to obtain a chromium layer, and then evenly apply photoresist to obtain a photoresist layer; Step 4, Pre-baking: Place the substrate from Step 3 on a baking machine for baking; Step 5, Exposure and Development: The capillary model on the mask is transferred to the photoresist layer of the substrate through exposure and development, thus revealing the photolithographic capillary model; Step 6, Hardening: Use a photoresist baking machine to stabilize the softened and expanded photoresist after development of the substrate; Step 7, Chromium layer etching: Using cerium ammonium nitrate, the capillary model is transferred to the chromium layer; Step 8, Substrate Etching: Use BOE etchant to perform wet etching on the substrate; Step 9, Removal of Photoresist and Chromium: The photoresist layer and chromium layer are removed by developing and etching the chromium layer respectively to obtain the etched substrate; Step 10, Thermal Bonding: The etched substrate and cover plate are stacked in a muffle furnace, heated by programmed temperature rise, and finally annealed. Step 11, Wetting Modification: Inject Piranha solution into the capillary model of the etched substrate and dry it. Then inject a wetting modifier to obtain the wetting-controlled capillary model.

2. The manufacturing method according to claim 1, characterized in that, The wetting-regulating capillary model is divided into a hydrophilic region and a wetting-modification region.

3. The manufacturing method according to claim 1, characterized in that, The capillary inner diameter mentioned in step 1 is between 500nm and 10μm, and the width-to-depth ratio is 1:

2.

4. The manufacturing method according to claim 1, characterized in that, The substrate used in step 2 is glass.

5. The manufacturing method according to claim 1, characterized in that, The cleaning process described in step 2 is as follows: first, clean with anhydrous ethanol and acetone respectively, then ultrasonically clean with deionized water for 20-40 minutes, remove and dry; then soak the substrate in Piranha solution, remove and clean with deionized water, dry and set aside.

6. The manufacturing method according to claim 1, characterized in that, In step 3, the photoresist was applied using a KW-4A spin coater. The photoresist used was AR-P 3100 positive photoresist. The specific process for applying the photoresist was as follows: the photoresist was applied at a speed of 4000 rpm, and the photoresist thickness was 10 μm.

7. The manufacturing method according to claim 1, characterized in that, The glue baking machine mentioned in steps 4 and 6 is a KWH-350 glue baking machine.

8. The manufacturing method according to claim 1, characterized in that, In step 5, an URE-2000 lithography machine is used for exposure, and AR 300-26 developer is used for development.

9. The manufacturing method according to claim 1, characterized in that, The BOE corrosion solution mentioned in step 8 is a mixed aqueous solution of HF and NH4F.

10. The manufacturing method according to claim 1, characterized in that, In step 10, a polished graphite plate is placed on top of the etched substrate and the cover plate, and a stainless steel block is placed on the upper graphite plate. The plate is then placed in a muffle furnace for programmed heating, which eventually raises the temperature to 20-50°C above the glass annealing point. Finally, programmed cooling annealing is performed.

11. The manufacturing method according to claim 1, characterized in that, The wetting modifier mentioned in step 11 includes at least one of surfactant and nanomolecular film.

12. The manufacturing method according to claim 11, characterized in that, The surfactant includes at least one of sodium dodecylbenzenesulfonate and sodium salt of fatty alcohol polyoxyethylene ether sulfate.

13. The manufacturing method according to claim 11, characterized in that, The nanomolecular membrane was prepared from dimethyl carbonate and N,N,N',N'-tetramethylethylenediamine.

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