A method for fabricating a porous-fracture medium model and visualizing spontaneous imbibition experiments

Abstract

The present invention discloses a method for making a porous-fracture medium model and a spontaneous imbibition visualization experiment, and belongs to the technical field of porous-fracture medium multiphase seepage analysis. The present invention uses inductively coupled plasma etching to obtain a silicon wafer mold containing a porous-fracture medium geometric pattern. After the mold is turned over, ultraviolet ozone is used to perform surface modification on the mold obtained by the mold turning over to obtain a porous-fracture medium model. When the porous-fracture medium model is used to perform a spontaneous imbibition experiment, the porous-fracture medium model is first saturated with a non-wetting fluid, and then a quantitative volume of a wetting fluid is dripped to realize a spontaneous imbibition process in the porous-fracture medium model. The spontaneous imbibition process can be observed and imaged in real time using a camera. Compared with the traditional indoor core spontaneous imbibition experiment, the present invention can realize low-cost, real-time dynamic observation of the spontaneous imbibition process in the porous-fracture medium, and quickly obtain a large amount of reliable spontaneous imbibition experimental data.

Description

Technical Field

[0001] The invention relates to the technical field of multiphase seepage analysis of porous-fracture media, and in particular to a method for making a porous-fracture medium model and a spontaneous imbibition visualization experiment. Background Art

[0002] Spontaneous imbibition in porous-fracture media involves many important natural processes and engineering problems, such as the rise of groundwater in soil and the extraction of underground oil and natural gas. Correctly understanding the influence of factors such as pores, fracture structure, wettability and boundary conditions on spontaneous imbibition will help reveal and understand the physical mechanism behind the spontaneous imbibition phenomenon and provide a reference for improving the degree of oil and gas recovery. Traditional spontaneous imbibition experiments are mainly based on indoor core experiments. These experimental results provide an important reference for people to understand the laws of spontaneous imbibition. However, due to the limitations of model preparation methods and experimental techniques, these experiments mainly use pure porous media models or porous-fracture media models containing only single fractures. These models are not sufficient to explore the influence of factors such as fracture network structure on spontaneous imbibition.

[0003] In addition, affected by factors such as core physical properties, core size and shape, the traditional indoor core spontaneous imbibition experiment time cycle is often long, ranging from a few hours to dozens of days, and sometimes even up to several months, which seriously limits the acquisition of a large amount of reliable data from spontaneous imbibition experiments. Moreover, traditional indoor core experiments are mainly based on mass method, volume method and nuclear magnetic resonance method. Among them, the mass method and volume method mainly obtain the imbibition mass by direct weighing and liquid level conversion, and cannot dynamically observe the imbibition process in real time; the nuclear magnetic resonance method is a non-invasive method for measuring the distribution and content of liquid inside the core. Although the nuclear magnetic resonance method can monitor the spontaneous imbibition process in real time, it is very expensive and complicated to operate. Summary of the invention

[0004] In view of the above shortcomings of the prior art, the present invention provides a pore-fracture medium model preparation and spontaneous imbibition visualization experimental method, which can dynamically monitor the spontaneous imbibition process in real time and quickly obtain a large amount of reliable spontaneous imbibition experimental data, and is simple to operate and low in cost.

[0005] To achieve the above purpose, the specific technical solutions of the present invention are as follows:

[0006] A method for making a visualized spontaneous imbibition pore-fracture medium model comprises the following steps:

[0007] (1) Design a pore-fracture medium model containing a fracture network structure and use inductively coupled plasma etching to obtain a silicon wafer mold containing a pore-fracture medium geometric pattern;

[0008] (2) Re-molding the mold;

[0009] (3) The mold obtained by molding in step (2) and the glass slide coated with optical glue are surface modified by using ultraviolet ozone to assemble a pore-fracture medium model.

[0010] The pore-fracture medium model is saturated with a non-wetting fluid, and a quantitative volume of the wetting fluid is dripped into the inlet of the pore-fracture medium model to realize a spontaneous imbibition process in the pore-fracture medium model.

[0011] Furthermore, in step (1), the pore-fracture medium model containing the fracture network needs to be representative, and the size, matrix and fracture network structure characteristics of the pore-fracture medium geometric model are determined before design; the fracture network structure includes a real pore-fracture network structure and a simulated pore-fracture network structure; wherein the simulated pore-fracture network structure includes but is not limited to an orthogonal fracture network structure, a discrete fracture network structure or a tree-like bifurcated network structure.

[0012] Furthermore, the simulated pore-fracture network structure is constructed by directly cutting on the matrix to realize the design of the pore-fracture medium geometric model containing the fracture network structure; the generation and cutting of the matrix can be completed in MATLAB and then exported to AutoCAD, or the matrix can be generated in MATLAB first, and then the fracture network structure can be added through AutoCAD.

[0013] Furthermore, in step (1), the method for calculating the time required for the inductively coupled plasma etching is: using a step profiler and an ellipsometer to respectively measure the total etching depth and the remaining glue thickness per unit time to calculate an accurate etching rate, and calculating the required etching time based on the etching rate.

[0014] Furthermore, in step (2), the molding process is performed by using polydimethylsiloxane (PDMS) and optical glue respectively.

[0015] Furthermore, the optical glue has a light transmittance of ≥95%, a viscosity of 20-300 cps, a refractive index of 1.46-1.56 after curing, and an elastic modulus of 20,000-300,000 psi.

[0016] Furthermore, the optical glue is Nolan chemical glue (NOA81).

[0017] Furthermore, the specific operation of the mold remodeling process is: pour the vacuumed PDMS liquid into a culture dish containing a silicon wafer mold, heat it at 80°C for 2 hours, then cut off the solidified PDMS and save it for later use; use plasma to clean the PDMS mold, then add optical glue to its surface, evenly coat it, and then cure it by ultraviolet light, peel off the solidified optical glue layer, and obtain an optical glue mold containing a pore-crack medium geometric pattern.

[0018] Furthermore, in step (3), the time of the modification treatment is determined according to the fluid pair used, the target contact angle and the standing time, and the relationship between the modification time, the target contact angle and the standing time is determined by a calibration experiment; the specific operation of the calibration experiment is: adding 1 to 2 drops of optical glue on the cover glass, using a glue spreader to spread it evenly, and then curing it by ultraviolet light to obtain an optical glue substrate; placing the optical glue substrate in an ultraviolet ozone cleaning machine for cleaning, placing the cleaned optical glue substrate in a transparent box with an upper opening, immersing the box with a fluid phase with a smaller density, and then dropping the fluid phase with a larger density onto the optical glue substrate, and after the shape of the three-phase contact angle is stable, promptly measuring the contact angle with a contact angle meter; or taking a picture with a camera, and measuring the contact angle using AutoCAD software and ImageJ software to obtain the relationship between the three-phase contact angle and the modification time and the standing time.

[0019] Furthermore, in step (3), during the surface modification treatment, a mask plate is made of silica glass, so that the pattern portion of the optical glue mold surface to be treated is transparent, and the remaining portion is blocked, so that the optical glue mold is still sticky after modification, which is convenient for subsequent drilling and assembly.

[0020] The present invention also provides a method for visualizing spontaneous imbibition in the pore-fracture medium, comprising the following steps:

[0021] S1, installing the pore-fracture medium model on the microfluidic stage below the camera;

[0022] S2, saturating the pore-fracture medium model with a non-wetting fluid, using a syringe pump and a micro-injector to accurately control the volume of the wetting fluid, and then dripping a quantitative volume of the wetting fluid into the inlet of the pore-fracture medium model to achieve a spontaneous imbibition process in the pore-fracture medium model;

[0023] S3, collecting experimental images of spontaneous imbibition in the pore-fracture medium model in real time through a camera to achieve visualization;

[0024] S4. The relationship between the degree of spontaneous imbibition and time is statistically analyzed through image post-processing, and the influence of wetting fluid volume and fracture network structure on spontaneous imbibition is analyzed.

[0025] Furthermore, in step S2, the specific operation of saturating the pore-fracture medium model with a non-wetting fluid is: using a micro-injector with a pipeline and a joint to absorb a certain amount of non-wetting fluid, and then slowly injecting it from one end of the pore-fracture medium model at a lower speed, and stopping the injection when the non-wetting fluid appears at the other end of the pore-fracture medium model.

[0026] Furthermore, in step S2, the specific operation of quantitative volume measurement of the wetting fluid is as follows: using a micro-injector with a pipeline to pre-absorb the vacuumed wetting fluid, exhausting the air in the micro-injector and the pipeline by repeatedly sucking in slowly and quickly, and then aspirating the corresponding volume of the wetting fluid; installing the micro-injector on the syringe pump, inputting the diameter and volume of the micro-injector, setting the injection volume and time, placing the pipeline outlet close to the inlet of the pore-fracture medium model, starting the syringe pump, and dripping a certain amount of wetting fluid onto the pore-fracture medium model to realize a spontaneous imbibition process in the pore-fracture medium model.

[0027] Furthermore, a blue light source is installed under the stage, and the non-wetting fluid and the wetting fluid are dyed before use, so as to ensure the imaging effect and capture the characteristics of angular flow and thin film flow under strong wetting conditions.

[0028] Furthermore, in step S3, the experimental image acquisition should be carried out simultaneously with the start of the injection pump, or the image acquisition can be started in advance to capture the complete spontaneous imbibition experimental process in the porous-fracture medium.

[0029] Furthermore, in step S4, the spontaneous imbibition extraction degree R f The calculation method is:

[0030] ;

[0031] In the formula, R f is a dimensionless quantity, S i is the saturation of the non-wetting phase at the initial moment, S f is the saturation of the non-wetting phase at the current moment.

[0032] Furthermore, the non-wetting phase saturation at the initial moment and the non-wetting phase saturation at the current moment are determined by counting the pixel space occupied by the non-wetting phase at the initial moment and the current moment, and the calculation method is:

[0033] ;

[0034] Where n total is the total number of pixels, n i and n fis the number of pixels occupied by the non-wetting phase at the initial and current moments; h is the thickness of the pore-fracture medium model, h1 is the spatial height occupied by the non-wetting phase, and when there is corner flow and film flow, h1 is calculated using the Lambert-Beer law.

[0035] Compared with the prior art, the present invention is beneficial in that:

[0036] 1. The present invention can not only produce a pore-fracture medium model containing a single fracture, but also quickly and conveniently construct a pore-fracture medium model containing a fracture network with different target contact angles within a strong wetting range.

[0037] 2. Compared with the spontaneous imbibition time of traditional indoor cores, which is several hours to dozens of days, the spontaneous imbibition time in the present invention is between a few seconds and a few minutes, which can quickly obtain a large amount of reliable spontaneous imbibition experimental data.

[0038] 3. The present invention can monitor the spontaneous imbibition process in real time and dynamically, and is simple to operate and low in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flow chart of the method of the present invention;

[0040] Figure 2 The matrix model designed for Example 1 and the pore-fracture medium model containing an orthogonal fracture network;

[0041] Figure 3 The size distribution of matrix throats in the pore-fracture medium model with an orthogonal fracture network structure designed for Example 1;

[0042] Figure 4 The relationship between the contact angle of water-air-NOA81 substrate and the exposure time and the standing time in Example 1;

[0043] Figure 5 The relationship between the degree of spontaneous water-air imbibition extraction and time obtained by post-treatment in Example 1. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] The present invention provides a method for preparing a spontaneous imbibition visualized pore-fracture medium model, comprising the following steps:

[0046] (1) Design a pore-fracture medium model containing a fracture network structure and use inductively coupled plasma etching to obtain a silicon wafer mold containing a pore-fracture medium geometric pattern;

[0047] (2) Re-molding the mold;

[0048] (3) The mold obtained by molding in step 2 and the glass slide coated with optical glue are surface modified by using ultraviolet ozone to assemble a pore-fracture medium model.

[0049] The pore-fracture medium model is saturated with a non-wetting fluid, and a quantitative volume of the wetting fluid is dripped into the inlet of the pore-fracture medium model to realize a spontaneous imbibition process in the pore-fracture medium model.

[0050] The present invention also provides a method for visualizing spontaneous imbibition in the pore-fracture medium model, comprising the following steps:

[0051] S1, installing the pore-fracture medium model on the microfluidic stage below the camera;

[0052] S2, saturating the pore-fracture medium model with a non-wetting fluid, dripping a quantitative volume of the wetting fluid into the inlet of the pore-fracture medium model, and realizing a spontaneous imbibition process in the pore-fracture medium model;

[0053] S3, collecting experimental images of spontaneous imbibition in the pore-fracture medium model in real time through a camera to achieve visualization;

[0054] S4. The relationship between the degree of spontaneous imbibition and time is statistically analyzed through image post-processing, and the influence of wetting fluid volume and fracture network structure on spontaneous imbibition is analyzed.

[0055] In a specific embodiment, in step S4, the spontaneous imbibition extraction degree R f The calculation method is:

[0056] ;

[0057] In the formula, R f is a dimensionless quantity, S i is the saturation of the non-wetting phase at the initial moment, S f is the saturation of the non-wetting phase at the current moment.

[0058] The non-wetting phase saturation at the initial moment and the non-wetting phase saturation at the current moment are determined by counting the pixel space occupied by the non-wetting phase at the initial moment and the current moment, and the calculation method is:

[0059] ;

[0060] Where ntotal is the total number of pixels, n i and n f is the number of pixels occupied by the non-wetting phase at the initial and current moments; h is the thickness of the pore-fracture medium model, h1 is the spatial height occupied by the non-wetting phase, and when there is corner flow and film flow, h1 is calculated using the Lambert-Beer law.

[0061] Example 1

[0062] A pore-fracture medium model, the preparation method steps are as follows:

[0063] Step 1: designing a pore-fracture medium model containing a fracture network structure, and obtaining a silicon wafer mold containing a pore-fracture medium geometric pattern by using an inductively coupled plasma etching technique;

[0064] Referring to the commonly used model specifications and characteristics in microfluidic experiments, the size of the pore-fracture medium model in this embodiment is set to 25.2 mm × 8.4 mm and the thickness is 40 μm; a cylindrical shape is used to represent solid particles, and the solid particles and the gaps between them constitute the entire matrix, the matrix porosity is 0.48, and the pore volume is 4.06 μL. At the same time, considering that the commonly used fracture network models mainly include orthogonal fracture network models, discrete fracture network models, and tree-like bifurcation network models, this embodiment combines the classic Warren-Root dual medium model and selects a representative orthogonal fracture network structure to simulate fractures. The fracture network structure in this embodiment is composed of two horizontal fractures and five vertical fractures, and the fracture openings are set to 30, 60, 120, 180 and 240 μm, respectively, and the corresponding fracture volume proportions are 0.03, 0.05, 0.10, 0.15 and 0.19, respectively.

[0065] A two-dimensional array of circular particles is generated in MATLAB according to the model size. These particles are arranged in an equilateral triangle lattice structure, containing 121 columns and 36 rows. These circular particles have the following characteristics:

[0066] (1) The distance between adjacent circle centers is 240 μm, and the reference radius is 90 μm;

[0067] (2) The circular radius fluctuates within the range of ±20% of the reference radius, introducing a certain degree of heterogeneity;

[0068] (3) The radius of the circle satisfies random uniform distribution.

[0069] The center coordinates and radius generated by MATLAB are saved as SCR scripts and loaded in AutoCAD; after successful loading, the position of the fracture is determined according to the model size and the selected fracture network structure, the outline of the fracture network structure is added to the image using the straight line command, and the matrix is ​​cut using the trim command to form a two-dimensional pore-fracture medium geometric model containing a fracture network structure. The matrix model designed in this embodiment and the pore-fracture medium model containing an orthogonal fracture network are shown in FIG. Figure 2 As shown in the figure, the left end is the model inlet and the right end is the model outlet; the size distribution of matrix throats in the pore-fracture medium model with an orthogonal fracture network structure is shown in Figure 3 As shown, the average throat radius of the matrix is ​​60 μm.

[0070] After the pore-fracture medium model containing the fracture network is designed, the mask is printed and the mold is made using the inductively coupled plasma etching technology. When the silicon wafer mold is obtained using the inductively coupled plasma etching technology, AZ6130 positive photoresist is first coated on the cleaned silicon wafer mold, and the spin coating speed is set to 4000 rpm for 30 s to obtain a photoresist layer with a thickness of about 3.5 μm; after coating, it is soft-baked on a 100℃ hot plate for 90 s to evaporate the solvent and enhance the adhesion of the photoresist; the silicon wafer coated with the photoresist is exposed to ultraviolet light using the mask corresponding to the pore-fracture medium model, and the exposure time is set to 20 s; after exposure, the developer is used for development for 60 s, and the mold is rinsed with deionized water and blown dry with nitrogen after development; in order to improve the etching accuracy, a layer of metal chromium is plated on the photoresist to form a mask.

[0071] After photolithography, the geometric pattern is presented on the silicon substrate through the photoresist, and the exposed silicon surface is etched by etching equipment; in order to accurately control the etching depth, the initial etching is carried out for 5 minutes, and then the etching depth is measured by a step meter, and the remaining photoresist thickness is measured by an ellipsometer to calculate the accurate etching rate, and the remaining etching time is calculated based on this rate. For example, after 5 minutes of initial etching, the etching depth of the silicon wafer is measured to be 6 μm, and the remaining photoresist thickness is 3.2 μm, then the etching rate of the silicon wafer is 1.2 μm / min, and the etching rate of the photoresist is 0.06 μm / min. According to this calculated rate, it theoretically takes 33.33 minutes to reach a depth of 40 μm; in order to ensure the accuracy of etching, the segmented etching method can be used, that is, the etching depth is checked every certain period of time (for example: 10 minutes), and when approaching the target depth, the etching rate is reduced to achieve more accurate depth control;

[0072] In order to improve the etching process and protect the sidewalls, it is necessary to intermittently introduce passivation gas during the downward etching process to prevent the etching gas from damaging the sidewalls, thereby ensuring that the pattern is etched downward as a whole; after the etching is completed, the silicon wafer needs to be de-gum treated by soaking the silicon wafer in an acetone solution to dissolve the glue; then, the silicon wafer is taken out and soaked in clean ethanol or isopropanol for a certain period of time to further clean the surface. Finally, the silicon wafer with geometric patterns is taken out and rinsed with deionized water and blown clean to ensure that the surface is clean and dry.

[0073] Step 2: Use PDMS and Nolan Chemical Glue (NOA81) to perform mold remodeling respectively;

[0074] The specific operation of the mold remodeling process is as follows: 32 g PDMS and 3.2 g curing agent (SYLGARD TM 184 Silicone Elastomer Curing Agent), stir thoroughly with a clean glass rod, then put it into a vacuum pump to evacuate, and then pour it into a culture dish containing a silicon wafer mold and let it stand; when there are no bubbles in the culture dish, place the culture dish on a hot plate for heating and curing; the heating temperature is set to 80℃ and the time is set to 2 h; then use a cutting knife to cut off the cured PDMS to obtain a PDMS mold, and save it for later use;

[0075] The PDMS mold was placed in a plasma cleaner for 30 seconds, and then 3 drops of NOA81 were added to the surface of the PDMS mold, and NOA81 was evenly spread on the PDMS mold; at the same time, 10 drops of NOA81 were added to a clean glass slide, and then placed on a glue spreader, and the speed of the glue spreader was set to 0.90 thousand revolutions per minute, and the glue spreader time was set to 20 seconds; the glue spreader was started to evenly spread NOA81 on the glass slide; when NOA81 was evenly spread on the PDMS mold without bubbles, the PDMS mold spread with NOA81 and the glass slide coated with NOA81 were placed in a UV curing instrument for curing, and the curing time was 36 seconds; after the curing was completed, the NOA81 coating was gently peeled off from the PDMS mold with tweezers to obtain a NOA81 mold;

[0076] Step 3, placing the NOA81 mold obtained in step 2 and the glass slide coated with NOA81 into a UV ozone cleaning machine for surface wettability modification, to obtain a pore-fracture medium model with a fracture network structure having target wettability;

[0077] The UV-ozone modification time of the NOA81 mold is determined according to the fluid pair used and the target contact angle and the standing time. The relationship among the modification time, the target contact angle and the standing time is determined by a calibration experiment. In this embodiment, water and air are used as the fluid pair. The specific operation of the calibration experiment is as follows: First, 2 drops of NOA81 are added to a plurality of clean cover slips, and a glue spreader is used to evenly spread the NOA81 on the cover slips, and then the cover slips coated with NOA81 are placed in a UV curing box for curing to obtain a plurality of NOA81 substrates; then, the UV-ozone cleaning time is set, and the NOA81 substrates are cleaned for 0, 1, 3, 5, 10, 20, and 30 minutes respectively. After cleaning, the NOA81 substrates are immediately placed in a transparent box with an upper opening, and the volume of water is controlled by a micro-injector. Approximately 4 μL of dyed deionized water was dropped onto the NOA81 substrate, and the three-phase contact angle morphology was photographed with a camera. The specific contact angle value was measured in ImageJ software. After the initial measurement, the measurement was performed every half an hour until the wettability of the modified NOA81 substrate was basically restored to that before cleaning, so as to obtain the following values: Figure 4 The relationship between the contact angle and the UV-ozone cleaning time and the standing time is shown.

[0078] The target contact angle in this embodiment is 30 o , it is more appropriate to select the UV-ozone modification time of 30 minutes and let it stand for 5 hours after modification. Put the NOA81 mold and the glass slide coated with NOA81 into the UV-ozone cleaning equipment and take them out after exposure for 30 minutes; when the NOA81 mold is put into the UV-ozone cleaning machine for cleaning, use silica glass to make the mask plate, let the pattern part of the NOA81 mold surface to be processed be transparent, and block the rest, so that the NOA81 mold is still sticky after modification, which is convenient for subsequent assembly. Use a 0.6 mm puncher to punch holes at the designed inlet and outlet of the pore-fracture medium model, and assemble the punched NOA81 mold and the glass slide coated with NOA81 together. After assembly, use AB glue to stick the B-20-32 base to the inlet and outlet of the pore-fracture medium model; let the pore-fracture medium model stand for 5 hours and use it when the contact angle of the pore-fracture medium model stabilizes to around 30°.

[0079] Step 4: Install the pore-fracture medium model on the microfluidic stage below the camera;

[0080] Use a clamp to fix the pore-fracture medium model to the stage, and ensure that the image of the pore-fracture medium model successfully appears in the industrial camera. This embodiment does not consider the effect of gravity on spontaneous imbibition, so it is necessary to ensure that the pore-fracture medium model is placed horizontally. After the pore-fracture medium model is installed, use a circular level bubble to check. If the bubble is centered, it can be considered that the pore-fracture medium model has been placed horizontally; if the bubble is not centered, reinstall the pore-fracture medium model until the bubble in the circular level bubble is centered.

[0081] In addition, before installing the pore-fracture medium model, the experimental water needs to be prepared in advance. The specific operation is as follows: 99.6 g of deionized water and 0.4 g of carmine are weighed with an electronic balance, and then carmine is poured into the deionized water, stirred evenly with a glass rod, and then vacuumed. After vacuuming, it is sealed with plastic wrap for later use. For strong wetting conditions, in order to capture and subsequently quantify the effects of corner flow and film flow on spontaneous imbibition, the proportion of carmine cannot exceed 5‰ when using carmine for dyeing.

[0082] Step 5, saturating the pore-fracture medium model with a non-wetting fluid, using a syringe pump and a micro-injector to accurately control the volume of the wetting fluid, and dripping a certain amount of the wetting fluid into the inlet of the pore-fracture medium model to achieve a spontaneous imbibition process in the pore-fracture medium model;

[0083] Prepare 50 μL micro-injectors I and II with tubing (1 / 32 PEEK tube) and connectors (1 / 32 integrated connector) in advance. Use injector I to inject 10 times the volume of air into the pore-fracture medium model from one end of the pore-fracture medium model to clean the pore-fracture medium model and fill the pore-fracture medium model with air; use injector II to draw 50 μL of dyed deionized water, install injector II on the syringe pump, input the injector diameter (1.1064 mm) and volume (50 μL), set the injection flow rate to 10 μL / min and the injection volume to 10 μL, and drop the corresponding volume of water to the inlet of the pore-fracture medium model to cause spontaneous infiltration in the pore-fracture medium model.

[0084] During the experiment, the volume of the wetting fluid should be strictly controlled and the interference of air should be eliminated. If air is found in the injector or pipeline when using injector II to absorb deionized water, the air can be exhausted by multiple slow suction and fast exhaust to ensure that there is no air in the injector and pipeline to ensure the smooth progress of the experiment.

[0085] Step 6: Using an industrial camera to collect experimental images of spontaneous imbibition in the pore-fracture medium model to achieve visualization;

[0086] Considering the contact angle of 30 oIt is a strong imbibition, and corner flow and thin film flow may occur. For better imaging, a 20 cm × 10 cm blue light source is installed under the stage. When acquiring images, the industrial camera (Alvium1800U-2040C) is started in advance to acquire images at a higher acquisition frequency (FPS=40) to fully monitor the spontaneous imbibition experimental process in the pore-fracture medium model.

[0087] Step 7: Statistically analyze the relationship between the degree of spontaneous imbibition and time through image post-processing, and analyze the influence of factors such as wetting fluid volume and fracture network structure on spontaneous imbibition.

[0088] The collected spontaneous imbibition experiment images were renumbered in sequence using MATLAB software. The recovery degree at different times was calculated based on the MATLAB program. The relationship between the recovery degree and the first power of time or the recovery degree and the square root of time was plotted to further analyze the effects of the fracture network structure and the volume of wetting fluid on spontaneous imbibition. Figure 5 This is the relationship between the recovery degree and time when the fracture network opening is 240 μm and the volume of the wetting fluid added is 10 μL.

[0089] Example 2

[0090] In this embodiment, the pore-fracture medium model prepared in Example 1 is used for a water-silicone oil spontaneous imbibition visualization experiment, and the steps are as follows:

[0091] Step 1: Install the pore-fracture medium model on the stage below the camera, clamp it with a clamp, and use a round level bubble to confirm whether the pore-fracture medium model is level.

[0092] Step 2: Use microinjector I to draw 50 μL of silicone oil with a viscosity of 10 mPa, and connect it to the outlet of the pore-fracture medium model through a pipeline; install the microinjector on the syringe pump II, input the volume (50 μL) and diameter (1.1064 mm) of the microinjector, set the injection flow rate to 0.5 μL / min, and the injection volume to 20 μL; start the syringe pump to slowly inject silicone oil (non-wetting fluid) into the pore-fracture medium model, and stop the injection when the pore-fracture medium model is saturated and silicone oil appears at the inlet section of the pore-fracture medium model.

[0093] Step 3. Use microinjector II to draw 50 μL of dyed deionized water, install the microinjector on syringe pump I, input the volume (50 μL) and diameter (1.1064 mm) of the microinjector, set the injection flow rate to 20 μL / min, and the injection volume to 5 μL; start the syringe pump, and drip a certain amount of water (wetting fluid) into the inlet of the pore-fracture medium model to generate spontaneous water-silicone oil infiltration in the pore-fracture medium model.

[0094] Step 4: Add dyed deionized water drops in front of the entrance of the pore-fracture medium model, turn on the 20 cm × 10 cm blue light source, start the industrial camera Alvium1800U-2040C, and collect images at an acquisition frequency of FPS=50 to achieve visual observation of spontaneous imbibition in the pore-fracture medium model.

[0095] Step 5: Post-process the collected images to obtain the relationship between the degree of spontaneous imbibition and time.

[0096] The above specific embodiments describe the implementation of the present invention in detail, but the present invention is not limited to the specific details in the above embodiments. Within the scope of the claims and technical concept of the present invention, the technical solution of the present invention can be modified and changed in many simple ways, and these simple modifications all belong to the protection scope of the present invention.

Claims

1. A method for conducting a spontaneous imbibition visualization experiment using a pore-fracture medium model, characterized in that: The following steps are involved: S1. Design a pore-fracture medium model containing a fracture network structure, and use inductively coupled plasma etching to obtain a silicon wafer mold containing a pore-fracture medium geometric pattern; The pore-fracture medium model containing a fracture network structure is designed by first determining the size, matrix and fracture network structure characteristics of the pore-fracture medium geometric model before designing, wherein the fracture network structure includes a real pore-fracture network structure and a simulated pore-fracture network structure; wherein the simulated pore-fracture network structure includes an orthogonal fracture network structure, a discrete fracture network structure and a tree-like bifurcated network structure; S2, using PDMS to perform mold remodeling on the silicon wafer mold to obtain a PDMS mold, and using NOA81 to perform mold remodeling on the PDMS mold to obtain a NOA81 mold; S3, using ultraviolet ozone to perform surface modification treatment on the NOA81 mold obtained by the mold turning in step S2 and the glass slide coated with NOA81, and assemble to obtain a pore-fracture medium model; the time of the modification treatment is determined according to the fluid pair used, the target contact angle and the standing time, and the relationship between the modification time, the target contact angle and the standing time is determined by a calibration experiment; the specific operation of the calibration experiment is: dripping NOA81 on the cover glass, using a glue spreader to spread it evenly, and then curing it by ultraviolet light irradiation to obtain a NOA81 substrate; using ultraviolet ozone to clean the NOA81 substrate, placing the cleaned NOA81 substrate in a transparent box, immersing the box with a fluid phase with a smaller density, and then dripping the fluid phase with a larger density onto the NOA81 substrate, and after the shape of the three-phase contact angle is stable, promptly measuring the contact angle with a contact angle meter; or after taking pictures, measuring the contact angle by software to obtain the relationship between the three-phase contact angle and the modification time and the standing time; Wherein, the target contact angle is 30 o The UV-ozone modification time was selected as 30 minutes, and the pore-fracture medium model was left to stand for 5 hours until the contact angle stabilized to 30 o Use when nearby; S4, installing the pore-fracture medium model on the microfluidic stage below the camera; S5, saturating the pore-fracture medium model with a non-wetting fluid, dripping a quantitative volume of the wetting fluid into the inlet of the pore-fracture medium model, and realizing a spontaneous imbibition process in the pore-fracture medium model; S6. Using a camera to collect experimental images of spontaneous imbibition in the pore-fracture medium model in real time to achieve visualization; S7. The relationship between the degree of spontaneous imbibition and time is statistically analyzed through image post-processing, and the influence of wetting fluid volume and fracture network structure on spontaneous imbibition is analyzed.

2. The method for spontaneous imbibition visualization experiment according to claim 1, characterized in that: In step S1, the simulated pore-fracture network structure is constructed by directly cutting on the matrix to realize the design of the pore-fracture medium geometric model containing the fracture network structure; cylinders are used to represent solid particles, and the solid particles and the gaps between them constitute the entire matrix; the generation and cutting of the matrix are completed in MATLAB and then exported to AutoCAD, or the matrix is ​​generated in MATLAB and then the fracture network structure is added through AutoCAD.

3. The method for spontaneous imbibition visualization experiment according to claim 1, characterized in that: In step S5, the specific operation of saturating the pore-fracture medium model with a non-wetting fluid is: using a micro-injector with a pipeline and a joint to absorb a certain amount of non-wetting fluid, and then slowly injecting it from one end of the pore-fracture medium model at a lower speed, and stopping the injection when the non-wetting fluid appears at the other end of the pore-fracture medium model.

4. The method for spontaneous imbibition visualization experiment according to claim 1, characterized in that: In step S5, the specific operation of the wetting fluid volume quantification is: use a micro-injector with a pipeline to pre-absorb the vacuum-evacuated wetting fluid, exhaust the air in the micro-injector and the pipeline by repeatedly slow suction and fast discharge, and then absorb the corresponding volume of wetting fluid; install the micro-injector on the injection pump, input the diameter and volume of the micro-injector, set the injection volume and time, place the pipeline outlet close to the inlet of the pore-fracture medium model, start the injection pump, and drip a certain amount of wetting fluid onto the pore-fracture medium model to realize the spontaneous imbibition process in the pore-fracture medium model.

5. The method for spontaneous imbibition visualization experiment according to claim 1, characterized in that: A blue light source is installed under the stage, and the non-wetting fluid and the wetting fluid are dyed before use.

6. The method for spontaneous imbibition visualization experiment according to claim 1, characterized in that: In step S7, the spontaneous imbibition extraction degree R f The calculation method is: ； In the formula, R f is a dimensionless quantity, S i is the saturation of the non-wetting phase at the initial moment, S f is the saturation of the non-wetting phase at the current moment.

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