A method for making microscopic visual lithography model

Abstract

The present invention discloses a method for making a microscopic visualized photolithography model and its experimental process. The complete pore throat size and distribution characteristics of the rock sample are obtained by high-pressure mercury injection and nuclear magnetic resonance and other technologies, and the corresponding pore space is extracted from the cast thin slice in combination with the difference in pore-skeleton color value (i.e., RGB value). At the same time, the isolated pore spaces are connected by the watershed method to form a complete pore throat network structure, and the corresponding distribution function is obtained by fitting the pore throat radius distribution curve, and a random number that obeys the distribution is generated and assigned by a computer. Finally, the obtained pore throat network structure is etched on tin foil through photolithography mask imaging, and after post-processing, the side of the carrier glass with the pore throat network structure is bonded to the cover glass to form the final visualized glass photolithography model. The model making process of the present invention is simple, and the structure matches the actual rock sample, with strong repeatability, and can meet the requirements of microscopic experiments under reservoir conditions.

Description

Technical Field

[0001] The present invention relates to the technical field, and in particular to a method for making a microscopic visualized photolithography model and an experimental process thereof. Background Art

[0002] Microscopic visualization technology can intuitively observe the distribution, flow and occurrence characteristics of single-phase and multi-phase fluids in porous media, and reveal the flow mechanism of fluids in pore throat space, which is of great significance to improving oil recovery and achieving full utilization of resources. However, the basis for achieving all this is to make a microscopic model that matches the pore throat space of the underground reservoir. At present, the existing microscopic visualization models are mainly divided into: real core model, sand filling micromodel and etching model.

[0003] The real core model is made by grinding the full-diameter rock sample into a thin slice, clamping it with glass, and then bonding the model slice with rubber. Application No. 201910198918.4 announced a real sandstone high-temperature and high-pressure microscopic visualization model. The model preferably uses an optical glass that is resistant to high pressure and high temperature and has high light transmittance to make a real sandstone microscopic visualization model. However, the model has a long production cycle, a limited service life, cannot be reused, and has high process requirements. When the seal between the glasses is poor, it is very likely that a true "core" false seepage will occur. The sand-filled microscopic model uses quartz sand particles tightly bonded to a glass sheet and embedded in a specific transparent rubber sleeve. However, the pore structure of the model is quite different from the actual rock sample, the human factor is large, and the model is disposable and cannot be reused. The etching model uses a pore mask and a roar mask to etch the substrate to form an etched substrate, and finally the etched substrate is bonded to the cover to form a microscopic visualization model. The invention patent application with application number 202210226097.2 discloses a three-dimensional microscopic visualization glass etching model and its preparation method. The method adopts dry etching to image and etch the pore network structure on the protective glue through a photolithography mask, and then use a developer to make the pore network structure pattern on the protective glue visible; etch the pore pattern of the pore network structure, and then further etch the carrier glass so that the pores of the pore network structure are deepened to the required depth to form a pore network structure etching model; bond the side of the carrier glass with the pore network structure to the cover glass to form a visualized glass etching model. However, the model manufacturing process is complicated, and the design of the pore network structure of the model mainly comes from the casting thin film image processing. This method is difficult to accurately extract the throat and its size, especially for unconventional reservoirs such as dense sandstone with small throats.

[0004] In order to make the pore structure characteristics of the experimental model similar to the actual pore structure characteristics of the reservoir, and to achieve the purpose of simple and fast manufacturing process and reusable model, a microscopic visualization model and its preparation method are urgently needed to further meet people's needs for microscopic experimental research on the basis of previous physical models. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for making a microscopic visualized photolithography model and its experimental process. The pore throat network structure of the model is similar to that of the actual rock sample, the production method is simple, and the model is reusable.

[0006] The present invention adopts the following technical solutions:

[0007] A method for making a microscopic visual lithography model comprises the following steps:

[0008] S1. Select a cylindrical rock sample with a length of 7 to 10 cm, wash it with oil and dry it, measure the porosity φ and permeability k of the rock sample, and then cut the rock sample into three sections;

[0009] S2. Size and distribution of pores and throats of rock samples: High-pressure mercury injection test was performed on the rock samples of Section I. The throat radius and its distribution of the rock samples were obtained based on the high-pressure mercury injection test. The rock samples of Section II were saturated with water and the nuclear magnetic resonance T was measured under the fully saturated water state. 2 Spectrum curve, combining high-pressure mercury injection and nuclear magnetic resonance test results to obtain the complete pore and throat distribution of rock samples;

[0010] S3. Extracting pore space in rock samples: Performing cast thin section experiments on rock samples from Section III, dividing the cast thin section images into different units, collecting cast thin section images of each unit, and extracting the pore space distribution of the rock sample from the image after noise reduction and contrast processing, combined with the difference in pore-skeleton RGB values, and numbering each pore;

[0011] S4. Pore throat space connectivity division: Based on the extracted pore throat space image, the watershed algorithm is used to connect each pore space and number each throat;

[0012] S5, pore and throat size assignment: according to the obtained complete pore and throat distribution curve, the distribution function corresponding to the pore and throat radius is obtained by fitting the distribution curve, and a random number obeying the distribution function is generated by a computer, and the generated random number is assigned to the corresponding pore and throat according to the pore and throat number;

[0013] S6. Model making: The pore-throat network structure obtained in step S5 is etched on tin foil through a photolithography mask, and then the tin foil is glued to a glass slide. The pores and throats are observed and cleaned with the help of a microscope to ensure that each pore and throat is interconnected. Finally, the side of the slide glass with the pore-throat network structure is bonded to the cover glass to form a visualized glass photolithography model.

[0014] The beneficial effects of the present invention are:

[0015] The present invention first obtains the complete throat and pore size and distribution characteristics of the rock sample through high-pressure mercury injection and nuclear magnetic resonance and other technologies, and uses relevant software to extract the corresponding pore space from the cast thin section in combination with the difference in pore-skeleton color value (i.e., RGB value). On this basis, the isolated pore space is connected using the watershed algorithm to form a complete pore throat network structure. On this basis, the corresponding distribution function is obtained by fitting the pore and throat radius distribution curve, and a random number that obeys the distribution is generated by a computer, and randomly assigned according to the pore and throat number. Finally, the obtained pore throat network structure is etched on tin foil through photolithography mask imaging, and after post-processing, the side of the carrier glass with the pore throat network structure is bonded to the cover glass to form the final visualized glass photolithography model.

[0016] The invention has a simple manufacturing process, and the obtained pore throat network structure matches the actual rock sample, so that the simulation result can better reflect the actual underground seepage situation. The model has good light transmittance, low cost, short manufacturing cycle, and the model can be reused, which is convenient for designing different comparative experiments. In addition, the model can withstand microscopic displacement experiments under reservoir conditions and meet the requirements of most current microscopic seepage experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

[0018] Figure 1 This is a schematic diagram of the distribution of the high-pressure mercury injection throat of the present invention;

[0019] Figure 2 This is a schematic diagram of the nuclear magnetic resonance pore throat distribution of the present invention;

[0020] Figure 3 This is a schematic diagram of the pore and throat sizes and their distribution obtained based on high-pressure mercury injection and nuclear magnetic resonance in the present invention;

[0021] Figure 4 It is a schematic diagram of the casting thin slice of the present invention;

[0022] Figure 5A schematic diagram of the pore space extracted from the casting thin slice of the present invention;

[0023] Figure 6 It is a schematic diagram of the pore-throat connectivity relationship based on the watershed algorithm of the present invention;

[0024] Figure 7 This is a schematic diagram of the experimental results of water-displacing oil on the photolithography model produced by the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment 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.

[0026] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure shall have the usual meanings understood by persons with ordinary skills in the field to which the present disclosure belongs. The words "include" or "comprise" and the like used in the present disclosure mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0027] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0028] like Figures 1 to 5 As shown, a method for making a microscopic visualized lithography model and its experimental process include the following steps:

[0029] S1. Select a cylindrical rock sample with a length of 7 to 10 cm, wash it with oil and dry it, measure the porosity (φ) and permeability (k) of the rock sample, and then cut the rock sample into three sections;

[0030] S2. Size and distribution of pores and throats of rock samples: According to the provisions of the mercury injection method in the national standard GB / T 29171-2012 "Determination of capillary pressure curve of rock", the first section of rock samples (length 2-3 cm) were subjected to high-pressure mercury injection test. The throat radius and its distribution of rock samples were obtained based on the high-pressure mercury injection experiment ( Figure 1 ), and for the rock sample saturated with water in the second section, the nuclear magnetic resonance T in the fully saturated water state is measured according to the requirements of the industry standard SY / T 6490-2014 "Laboratory Measurement Specifications for Nuclear Magnetic Resonance Parameters of Rock Samples" 2 Spectrum curve ( Figure 2), and the complete pore and throat distribution of rock samples was obtained by combining high-pressure mercury injection and nuclear magnetic resonance test results ( Figure 3 );

[0031] S21, according to nuclear magnetic resonance T 2 The functional relationship between relaxation time and pore size (Formula 1) is used to calculate the relaxation rate using Formulas (2) to (4) (where the shape factor is 2, and the high-pressure mercury injection data mainly regards the throat as a long cylinder), and the NMR T 2 The spectrum curve is converted into a pore throat distribution curve ( Figure 2 );

[0032]

[0033] In the formula, ρ 2 is the surface relaxation rate, μm / ms; F s is the pore shape factor (2 for long cylinder and 3 for sphere); R NMR is the pore throat radius after NMR conversion, μm; φ NMR is the porosity obtained by NMR, %; T 2gm is the geometric mean of the relaxation time, ms; T 2i is the relaxation time corresponding to the i-th pore throat; φ i is the porosity corresponding to the pore throat of the i-th level, %;

[0034] S22, processing the obtained high-pressure mercury injection throat distribution curve and nuclear magnetic resonance pore throat distribution curve into standard distribution curves according to formula (5), and plotting them in the same coordinate system;

[0035]

[0036] Where r is the pore throat radius, μm; for high-pressure mercury injection and nuclear magnetic resonance, v is the volume of mercury per unit mass of sample and for nuclear magnetic resonance, T 2 Cumulative pore volume from small to large, cm 3 ;

[0037] S23. Subtract the throat differential distribution curve obtained by high-pressure mercury injection from the standardized NMR pore throat differential distribution curve to obtain the differential distribution curve representing the pore portion. Multiply the differential distribution curve of the pore portion by the ratio of the shape factors of the spherical pore and the tubular pore (3 / 2) to obtain the differential distribution curve of the pore portion below the spherical pore.

[0038] S3. Extraction of pore space in rock samples: Cast thin sections were conducted on the rock samples of Section III. Cast thin sections of rock samples were made according to the industry standard SY / T5368-2000 "Rock Thin Section Identification" ( Figure 4), the casting thin section image is divided into different units, and the casting thin section images of each unit are collected. After noise reduction and contrast processing, the pore space distribution of the rock sample is extracted from the image in combination with the difference in pore-skeleton color value (i.e., RGB value) ( Figure 5 ), and number each pore;

[0039] S4. Pore throat space connectivity division: Based on the extracted pore throat space image, the watershed algorithm is used to connect each pore space and number each throat ( Figure 6 );

[0040] S5, pore and throat size assignment: according to the obtained complete pore and throat distribution curve, the distribution function corresponding to the pore and throat radius is obtained by fitting the distribution curve, and a random number obeying the distribution function is generated by a computer, and the generated random number is assigned to the corresponding pore and throat according to the pore and throat number;

[0041] S6, model making: the pore-throat network structure obtained in step S5 is etched on tin foil through a photolithography mask, and then the tin foil is glued to a glass slide, and the excess residual glue in the pores and throats is observed and removed under a microscope to ensure that each pore and throat is connected to each other, and finally the side of the glass slide with the pore-throat network structure is bonded to the cover glass to form a visualized glass photolithography model;

[0042] The microscopic visualization photolithography model of the present invention can be used to quantitatively study the migration law of oil and water phases in the pore throat space, the law of remaining oil occurrence, and the optimization of tertiary oil recovery technology, etc., which are related to the microscopic seepage mechanism of the reservoir. This embodiment takes the microscopic visualization water flooding experiment of high temperature and high pressure rock as an example ( Figure 7 ). The experimental device includes a seepage simulation system, a micro displacement and metering system connected to the seepage simulation system, and an image acquisition and analysis system. The experimental principle is to use the microscopic visualization photolithography model to conduct a water-to-oil experiment, and to record, organize and analyze the oil displacement process in the form of images through a microscope and a data collector to study the oil displacement characteristics at different stages.

[0043] The steps of the water-displacing oil experiment of the microscopic visualization photolithography model include: vacuuming the rock sample - saturating the experimental water - displacing the water with oil to establish bound water saturation - water-displacing oil experiment - ending the experiment, that is, placing the microscopic visualization photolithography model in a visualization high-temperature and high-pressure autoclave, first vacuuming the microscopic visualization photolithography model to saturate the experimental water, then displacing the water with oil at a certain flow rate to establish a bound water state, and finally conducting a water-displacing oil experiment, using a stereo microscope to observe the occurrence characteristics of oil and water and the distribution characteristics of residual oil in the water-displacing oil process, and at the same time collecting microscopic images of a fixed area under the saturated water state, bound water state and residual oil state, and obtaining the microscopic displacement efficiency of the rock sample through image statistics.

[0044] The specific steps are as follows:

[0045] S1. Vacuuming the microscopic visualized photolithography model: Fix the microscopic visualized photolithography model rock sample model in a visualized high-temperature autoclave, and use a vacuum pump to evacuate the microscopic model;

[0046] S2. Saturation of experimental water in microscopic visualization lithography model: injecting simulated water into the microscopic visualization lithography model, observing the filling of the injected water in the microscopic visualization lithography model using a stereo microscope, and counting the saturation in the microscopic visualization lithography model;

[0047] S3. Establishing irreducible water saturation by oil-driven water: Slowly pressurize the microscopic visualization photolithography model to drive oil and drain water to the irreducible water state, use a stereo microscope and a high-speed camera to capture the oil-water seepage law and the oil-water occurrence state in the irreducible water state in real time during the oil-driven water process, and statistically obtain the irreducible water saturation of the rock sample in the microscopic visualization photolithography model;

[0048] S4. Water-displacing oil experiment: Carry out water-displacing oil experiment on the microscopic visualized photolithography model, observe the oil-water seepage law in the water-displacing oil process, take real-time images of the oil-water distribution in the water-displacing oil process, obtain statistics on the oil-water saturation under the corresponding state, and calculate the microscopic oil displacement efficiency until the residual oil state;

[0049] S5. End the experiment.

[0050] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for making a microscopic visual lithography model, It is characterized in that The following steps are involved: S1. Select a cylindrical rock sample with a length of 7 to 10 cm, wash it with oil and dry it, measure the porosity φ and permeability k of the rock sample, and then cut the rock sample into three sections; S2. Size and distribution of pores and throats of rock samples: High-pressure mercury injection test was performed on the rock samples of Section I. The throat radius and its distribution of the rock samples were obtained based on the high-pressure mercury injection test. The rock samples of Section II were saturated with water and the nuclear magnetic resonance T was measured under the fully saturated water state. 2 Spectrum curve, combining high-pressure mercury injection and nuclear magnetic resonance test results to obtain the complete pore and throat distribution of rock samples; S3. Extracting pore space in rock samples: Performing cast thin section experiments on rock samples from Section III, dividing the cast thin section images into different units, collecting cast thin section images of each unit, and extracting the pore space distribution of the rock sample from the image after noise reduction and contrast processing, combined with the difference in pore-skeleton RGB values, and numbering each pore; S4. Pore throat space connectivity division: Based on the extracted pore throat space image, the watershed algorithm is used to connect each pore space and number each throat; S5, pore and throat size assignment: according to the obtained complete pore and throat distribution curve, the distribution function corresponding to the pore and throat radius is obtained by fitting the distribution curve, and a random number obeying the distribution function is generated by a computer, and the generated random number is assigned to the corresponding pore and throat according to the pore and throat number; S6. Model making: The pore-throat network structure obtained in step S5 is etched on tin foil through a photolithography mask, and then the tin foil is glued to a glass slide. The pores and throats are observed and cleaned with the help of a microscope to ensure that each pore and throat is interconnected. Finally, the side of the slide glass with the pore-throat network structure is bonded to the cover glass to form a visualized glass photolithography model.

2. A method for making a microscopic visualized lithography model according to claim 1, It is characterized in that In step S2, the step of obtaining the complete pore and throat distribution of the rock sample by integrating the high-pressure mercury injection and nuclear magnetic resonance test results includes the following steps: S21. Based on the functional relationship between the nuclear magnetic resonance T2 relaxation time and the pore size, the relaxation rate is calculated using formulas (2) to (4), where the shape factor is 2. The high-pressure mercury injection data mainly regards the throat as a long cylinder, and the nuclear magnetic resonance T2 spectrum curve is converted into a pore throat distribution curve; Where ρ2 is the surface relaxation rate, μm / ms; Fs is the pore shape factor, where the Fs value of the long cylinder is 2 and the Fs value of the sphere is 3; R NMR is the pore throat radius after NMR conversion, μm; φ NMR is the porosity obtained by NMR, %; T 2gm is the geometric mean of the relaxation time, ms; T 2i is the relaxation time corresponding to the i-th pore throat; φ i is the porosity corresponding to the pore throat of the i-th level, %; S22, processing the obtained high-pressure mercury injection throat distribution curve and nuclear magnetic resonance pore throat distribution curve into standard distribution curves according to formula (5), and plotting them in the same coordinate system; Where r is the pore throat radius, μm; for high-pressure mercury injection and nuclear magnetic resonance, v is the volume of mercury per unit mass of sample and for nuclear magnetic resonance, T 2 Cumulative pore volume from small to large, cm 3 ; S23. Subtract the throat differential distribution curve obtained by high-pressure mercury injection from the standardized NMR pore throat differential distribution curve to obtain the differential distribution curve representing the pore portion, and multiply the differential distribution curve of the pore portion by the ratio of the shape factors of spherical pores and tubular pores to obtain the differential distribution curve of the pore portion below the spherical pores; wherein the ratio of the shape factors of spherical pores and tubular pores is 3 / 2.

3. A method for making a microscopic visualized lithography model according to claim 1, It is characterized in that The capillary pressure test of rock samples was carried out according to the mercury injection method in the national standard GB / T 29171-2012 “Determination of capillary pressure curve of rock”.

4. A method for making a microscopic visualized lithography model according to claim 1, It is characterized in that Nuclear magnetic resonance experiments are carried out on rock samples according to the industry standard SY / T 6490-2014 "Laboratory Measurement Specifications for Nuclear Magnetic Resonance Parameters of Rock Samples".

5. A method for making a microscopic visualized lithography model according to claim 1, It is characterized in that Cast thin sections of rock samples are made according to the industry standard SY / T 5368-2000 "Identification of Rock Thin Sections".

6. A method for making a microscopic visualized lithography model according to claim 1, It is characterized in that, In step S1, the length of section I is 2-3 cm, the length of section II is 4-5 cm, and the length of section III is 1-2 cm.

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