Experimental device and method for testing physical property evolution law of fluid in porous medium

Abstract

The invention discloses an experimental device and method for testing the physical property evolution law of fluid in a porous medium, and belongs to the technical field of oil-gas field development simulation experimental devices. The device comprises a rock core fixing device and an altimeter, the rock core fixing device comprises a transparent rubber cylinder used for containing a rock core and a transparent pressure-resistant cylinder body located outside the rubber cylinder, and the altimeter is located outside the rubber cylinder and used for detecting gas-oil interface changes in the rock core. A traditional hollow cavity design is abandoned, a real porous medium core is integrated into a high-temperature and high-pressure visual cavity, and oil-gas interface evolution characteristics in the porous medium are quantified through height change of an altimeter. Seamless fusion is carried out on the two traditional independent fields of large-volume fluid phase state research and real porous medium seepage research, and the evolution law of the fluid phase state in the porous medium under the real oil reservoir condition can be obtained.

Description

Technical Field

[0001] This invention relates to the technical field of simulation experimental devices for oil and gas field development, specifically to an experimental device and method for testing the evolution law of fluid properties in porous media. Background Technology

[0002] Oil and gas exploration and development, especially of deep and unconventional oil and gas resources, faces enormous challenges. One of the core issues is accurately understanding and predicting the phase behavior and property changes of formation fluids under high temperature and pressure conditions. Traditional PVT (Polymer Transformation Test) apparatus has long been a crucial tool for acquiring this data. It simulates reservoir conditions (temperature and pressure environment) by placing formation fluid samples in a hollow, temperature- and pressure-controlled chamber. During the test, a mechanical agitator at the bottom of the PVT chamber mixes the fluids uniformly, allowing them to quickly reach phase equilibrium, thus obtaining the subsurface fluid to be tested. However, the test involves external human intervention, which differs significantly from the actual situation in reservoir gas injection development where injected gas forms a mixed fluid through diffusion and dissolution mechanisms. In actual reservoirs, there is no intense agitation between injected gas and crude oil, and they cannot achieve phase equilibrium in a very short time, which is completely different from the PVT testing process. Furthermore, this "large-volume" fluid experiment has certain limitations: it ignores the changes in fluid properties caused by the flow of fluids in real porous media and microporous networks. The main issue is that the small pore throat scale in reservoirs (pore sizes can be as small as nanometers) leads to capillary pressure, interfacial adsorption, and pore confinement effects that can significantly alter the phase equilibrium of the fluid. Simultaneously, the physicochemical reactions between the fluid and the rock cause changes in the fluid properties within the reservoir. Therefore, fluid properties (density, viscosity, coefficient of expansion, dissolved gas-oil ratio, etc.) measured using PVT equipment have certain biases and cannot accurately reflect the fluid property parameters in porous media. To accurately measure the evolution of crude oil properties in porous media in the future, it is urgent to develop new equipment for precise testing. Summary of the Invention

[0003] To address the aforementioned issues, this invention provides an experimental apparatus and method for testing the evolution of fluid properties in porous media. The experimental apparatus integrates a real porous media core into a high-temperature, high-pressure visualization cavity. By measuring the height changes of an altimeter, the evolution characteristics of the oil-gas interface in the porous media are quantified. This seamlessly integrates the traditionally independent fields of "large-volume fluid phase state research" and "real porous media seepage research," enabling the acquisition of the evolution laws of fluid phase state in porous media under real oil reservoir conditions.

[0004] To achieve the above objectives, the specific solution of the present invention is as follows: An experimental apparatus for testing the evolution of fluid properties in porous media includes: Core fixing device, including: Vertically arranged transparent rubber tubes are used to hold rock cores; A transparent pressure-resistant cylinder coaxially sleeved around and spaced apart from the rubber tube; Two first covers are symmetrically arranged at both ends of the cylinder. The first cover is a stepped ring. The two first covers are connected by a tie rod, so that the step in the middle of the stepped ring presses against the end face of the cylinder. A tapered sleeve is arranged coaxially with the first cover body. Its side wall is a conical curved surface. Its lower end extends into the rubber tube and presses the rubber tube tightly against the inner wall of the first cover body, thereby forming a sealed cavity between the cylinder and the rubber tube, called the confining cavity. The second cover is threadedly connected to the first cover. The second cover is also a stepped ring. The step in the middle abuts against the upper end of the tapered sleeve, and a sealing ring is provided on the contact surface of the two. The second cover is used to push the tapered sleeve to move axially along the first cover, thereby pressing the rubber tube against the inner wall of the first cover. The plug is threaded to the second cover body. One end of the plug passes through the tapered sleeve and abuts against the end face of the core, thereby positioning the core and preventing it from moving in the rubber sleeve. At the same time, the plug is provided with a fluid channel for transmitting fluid to the core. A sealing mechanism is used to seal the gap between the second cover and the plug; The altimeter is located outside the cylinder and is used to detect changes in the gas-oil interface in the core. A rotating base is used to drive the core fixing device to rotate circumferentially around the cylinder body; A confining pressure pump connected to the confining pressure chamber; An injection and production device connected to a fluid channel is used to inject fluid into and remove fluid from the core.

[0005] In one specific embodiment of the present invention, the height measuring instrument includes: Supports extending axially along the cylinder body; A high-definition camera, arranged radially along the core and capable of sliding along the support axis, is used to observe the gas-oil interface in the core. A high-precision rangefinder fixed to a high-definition camera is used to measure the distance the high-definition camera slides along the axis of the support. A high-definition display device electrically connected to a high-definition camera and a high-precision rangefinder.

[0006] In one specific embodiment of the present invention, the sealing mechanism includes: The inner wall of the second cover contains a smooth hole section and a first threaded section, wherein the inner diameter of the smooth hole section is larger than the inner diameter of the first threaded section. The smooth rod section and the second threaded section are located on the outer wall of the plug sidewall, wherein the outer diameter of the smooth rod section is larger than the outer diameter of the second threaded section, and the first threaded section and the second threaded section are threadedly connected. The first retaining ring is located between the optical rod section and the optical aperture section and is slidably connected to both; A sealing ring located between the smooth rod section and the smooth hole section and abutting the end of the first retaining ring away from the first threaded section; A pressure ring that is threadedly connected to the second cover to push the sealing ring to expand radially; Furthermore, it also includes a second retaining ring located between the pressure ring and the sealing ring, which is situated between the smooth rod section and the smooth hole section.

[0007] As a specific embodiment of the present invention, the injection and production equipment includes a production device and an injection device. The production device includes a back pressure valve for controlling the inlet pressure of the back pressure valve when discharging fluid. The injection device includes an injection pump and an intermediate tank connected in sequence, wherein the intermediate tank stores test fluid.

[0008] In one specific embodiment of the present invention, the cylindrical body is made of sapphire glass.

[0009] As a specific embodiment of the present invention, the rotating base is provided with a platform with six degrees of freedom, and the cylinder is fixed on the platform, thus enabling the simulation of reservoir fluid properties at different formation dip angles.

[0010] Another object of the present invention is to provide a method of using the above-described device.

[0011] A method for testing the evolution of fluid properties in porous media, using the above-mentioned experimental apparatus, includes the following steps: S1. After drying the core, install it into the experimental apparatus, heat it to the target temperature, and then evacuate it to obtain a clean porous media system. S2. The degassed crude oil and natural gas from the oilfield are blended under target temperature and pressure conditions to obtain blended formation crude oil; S3. Test the evolution of oil and gas contact in the core, including: S31. Maintain the core temperature at the target temperature and inject a visible fluid into the confining pressure chamber so that the confining pressure is higher than the core pressure during the test. S32. Inject reservoir testing gas into the core to replace the entire system and increase the core pressure to the target pressure. During this process, continue to inject visual fluid into the confining pressure chamber to maintain the confining pressure higher than the core pressure. S33. Inject the compounded formation crude oil into the core from the bottom. During the injection process, the upper part of the core is vented to maintain the core pressure at the target pressure until the oil and gas interface in the core reaches the target height. S34. Close the core inlet and outlet valves, let it stand, and observe the evolution of the gas-oil interface through the visualization window. Record the pressure change data caused by the test gas merging into the crude oil through the pressure sensor at the top of the system. S35. After the predetermined settling time, inject an inert gas (such as Ar) to slowly discharge the crude oil in the core into the sampler in segments and test its physical properties. S36. Based on the recorded pressure data, analyze the characteristics of reservoir pressure changes after gas injection to guide on-site pressure prediction in the oilfield and lay the foundation for predicting reservoir pressure changes during gas injection development; determine the expansion coefficient of crude oil based on the evolution law of the oil-gas interface; test the properties of crude oil in each section and compare the evolution law of crude oil composition and properties after gas injection.

[0012] In one specific embodiment of the present invention, the reservoir test gas is the injection gas used in the reservoir gas injection development process, such as CO2, N2, etc.

[0013] In one specific embodiment of the present invention, the visualized fluid is clear water or white oil. When making a specific selection, it is required that the fluid does not vaporize under the simulated reservoir temperature and pressure conditions.

[0014] Compared with existing technologies, this invention abandons the traditional hollow cavity design and integrates a real porous media core into a high-temperature, high-pressure visualization cavity. By quantifying the evolution characteristics of the oil-gas interface in the porous media through changes in altitude using an altimeter, it seamlessly integrates the traditionally independent fields of "large-volume fluid phase state research" and "real porous media seepage research." This allows for the acquisition of the evolution laws of fluid phase state in porous media under real reservoir conditions. Its main advantages are as follows: (1) Physical reproducibility: This experimental setup can highly reproduce the complex three-dimensional pore structure, pore connectivity, rock anisotropy, and fluid-rock interface adsorption and wettability in real reservoir porous media. It fully considers the diffusion and dissolution process of injected gas-crude oil and the reaction law of injected gas-rock minerals under reservoir environment conditions, so that the experimental results of fluid property testing in oil reservoirs can more accurately reflect the evolution law of fluid property under formation conditions, rather than the idealized large-volume fluid behavior.

[0015] (2) Existing technologies all characterize the expansion coefficient of crude oil by measuring changes in crude oil level. In this invention, after using real rock samples, it is impossible to obtain the level. However, this invention can determine the movement of the gas-oil interface through visualization technology, and then obtain the expansion coefficient. This provides a method for measuring the expansion coefficient of crude oil in rock samples. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of a specific embodiment of the experimental apparatus of the present invention; Figure 2 yes Figure 1 A schematic diagram of the core fixing device in the apparatus shown; Figure 3 yes Figure 2A magnified view of a portion of the image; Figure 4 yes Figure 3 A magnified view of a portion of the image; The diagram shows: core fixing device 100, height gauge 200, rotating base 300, confining pressure pump 400, valve 700, core 800, rubber sleeve 110, cylinder 120, confining pressure cavity 121, first cover 130, pull rod 131, tapered sleeve 140, second cover 150, plug 160, sealing mechanism 170, support column 210, high-definition camera 220, high-precision rangefinder 230, display 240, back pressure valve 510, sampler 520, injection pump 610, intermediate tank 620, smooth section 171, first threaded section 172, smooth rod section 173, second threaded section 174, first retaining ring 175, sealing ring 176, pressure ring 177, second retaining ring 178, confining pressure channel 1211, and fluid channel 161. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0018] Please refer to Figure 1This invention illustrates an experimental apparatus for testing the evolution of fluid properties in porous media. The apparatus comprises a core fixing device 100, a height gauge 200, a rotating base 300, a confining pressure pump 400, and injection / production equipment. The core fixing device 100 includes a rubber sleeve 110, a cylinder 120, a first cover 130, a tie rod 131, a tapered sleeve 140, a second cover 150, a plug 160, and a sealing mechanism 170. The rubber sleeve 110 is vertically arranged to hold the core 800. The rubber sleeve 110 is made of transparent material, facilitating observation of the oil-gas interface in the core through a high-definition camera 220. The cylinder body 120 is made of sapphire, a transparent and pressure-resistant material, allowing light to pass through. The cylinder body 120 is coaxially fitted around the rubber sleeve 110 and spaced a certain distance apart, facilitating the formation of a confining pressure cavity 121. There are two first cover bodies 130, which are stepped rings symmetrically arranged at both ends of the cylinder body 120. The two first cover bodies 130 are connected by a pull rod 131, causing the step in the middle of the stepped ring to press against the end face of the cylinder body 120, thereby sealing the gap between the first cover body 130 and the cylinder body 120. To enhance the sealing performance, a sealing ring (such as a rubber ring) can be placed on the sealing surface. Furthermore, if leakage occurs during the experiment, the pressure of the two first cover bodies 130 on the cylinder body 120 can be adjusted using the pull rod 131, thereby improving the sealing effect. The tapered sleeve 140 is coaxially arranged with the first cover 130. Its annular outer wall is a conical surface, and its lower end extends into the rubber sleeve 110, pressing the rubber sleeve 110 tightly against the inner wall of the first cover 130. Thus, a sealed cavity, called the confining pressure cavity 131, is formed between the cylinder 120 and the rubber sleeve 110. Pushing the tapered sleeve 140 downwards allows the rubber sleeve 110 to be used as a sealing material, enhancing the sealing ability of the confining pressure cavity 121. The first cover 130 is provided with a confining pressure channel 1211 that communicates with the confining pressure cavity 121. The confining pressure pump 400 is connected to the confining pressure channel 1211 and is used to inject fluid to control the confining pressure of the core. The second cover 150 is also a stepped ring, threadedly connected to the first cover 130, with its central step abutting against the tapered sleeve. The upper end of 140 is used to push the tapered sleeve 140 to move axially along the first cover 130, thereby pressing the rubber tube 110 against the inner wall of the first cover 130 to seal the confining cavity 121. In addition, a sealing ring is also provided on the contact surface between the second cover 150 and the tapered sleeve 140. The plug 160 is threadedly connected to the second cover 150, and one end of it passes through the tapered sleeve 140 and abuts against the end face of the core, thereby positioning the core and preventing it from moving in the rubber tube 110. At the same time, the plug 160 is provided with a fluid channel 161 for transmitting fluid to the core. The sealing mechanism 170 is used to seal the gap between the second cover 150 and the plug 160 to prevent the fluid in the rubber tube 110 from leaking along the gap.An altimeter 200, located outside the cylinder 120, is used to detect changes in the gas-oil interface in the core. It includes a support column 210, a high-definition camera 220, a high-precision rangefinder 230, and a display 240. The support column 210 extends axially along the cylinder 120. The high-definition camera 220 is arranged radially along the core to observe the gas-oil interface and can slide axially along the support column 210 to ensure it faces the gas-oil interface. The high-precision rangefinder 230 is fixed to the high-definition camera 220 and measures the distance the camera slides axially along the support column 210. The display 240... 40 is electrically connected to the high-definition camera 220 and the high-precision rangefinder 230; the rotating base 300 is used to drive the core fixing device 100 to rotate circumferentially around the cylinder 120; the injection and production equipment includes a production device and an injection device, wherein the production device includes a back pressure valve 510 and a sampler 520, the back pressure valve 510 is used to control the inlet pressure of the back pressure valve when discharging fluid, the injection device includes an injection pump 610 and an intermediate tank 620 connected in sequence, the intermediate tank 620 stores the test fluid, and at the same time, valves 700 are provided on the pipelines connecting the injection device and the production device to the fluid channel to isolate the two.

[0019] In this invention, the sealing mechanism 170 includes a smooth hole section 171, a first threaded section 172, a smooth rod section 173, a second threaded section 174, a first retaining ring 175, a sealing ring 176, a pressure ring 177, and a second retaining ring 178. The smooth hole section 171 and the first threaded section 172 are located on the inner wall of the second cover 150, and the inner diameter of the smooth hole section 171 is larger than the inner diameter of the first threaded section 172. The smooth rod section 173 and the second threaded section 174 are located on the outer wall of the side wall of the plug 160 (wherein the outer diameter of the smooth rod section 173 is larger than the outer diameter of the second threaded section 174, and the first threaded section 172 is threadedly connected to the second threaded section 174). The first retaining ring 175 is located between the smooth rod section 173 and the smooth hole section. The sealing ring 176 is located between the smooth rod section 173 and the smooth hole section 171 and abuts against the first retaining ring 175 at the end opposite to the first threaded section 172. The pressure ring 177 is threadedly connected to the second cover 150 to push the sealing ring 176 to expand radially. The second retaining ring 178 is located between the pressure ring 177 and the sealing ring 176 and between the smooth rod section 173 and the smooth hole section 171. The first retaining ring 175 can prevent the sealing ring 176 from contacting and being damaged or not sealing properly with the first threaded section 172 or the second threaded section 174. The second retaining ring 178 can reduce the sliding friction of the pressure ring 177 on the sealing ring 176 during rotation, reducing its risk of damage.

[0020] In addition, the experimental apparatus of the present invention is also equipped with a pressure sensor 300 for measuring the pressure in the upper fluid channel.

[0021] In some embodiments, the altimeter 200 can convert a small distance change into a larger displacement change by multiplying it by a magnification factor through the principle of multiplication, thereby enabling better observation of the evolution of the gas-oil interface height in the core over time.

[0022] In some embodiments, the rotating base is provided with a platform having six degrees of freedom, on which the cylinder is fixed, thus enabling the simulation of reservoir fluid properties at different formation dip angles.

[0023] In some embodiments, the core fixing device 100 may also be equipped with heating equipment and temperature sensors to control the core temperature. Alternatively, the device may be placed in a constant temperature chamber to control the core temperature, thereby simulating formation temperature conditions.

[0024] A method of using the above-mentioned experimental apparatus includes the following steps: S1. After drying the core, install it in the experimental apparatus, heat it to the target temperature (reservoir temperature), and then evacuate it to obtain a clean porous media system. The specific steps include the following: S11. The core samples obtained from the oilfield are cut, cleaned, and dried. The processed core samples or core assemblies (multiple core samples) are placed in the core fixing device, and then the entire experimental setup is connected, such as... Figure 1 As shown; S12. Place the experimental apparatus in a temperature control chamber and heat it to the preset reservoir temperature. S13. Use a vacuum pump to evacuate the core for 6 to 12 hours to remove residual gas and air, ensuring a clean porous media system (core). S2. The degassed crude oil and natural gas from the oilfield are blended under target temperature and pressure conditions to obtain blended formation crude oil. This process includes the following steps: S21. Perform oil-water separation, filtration, and impurity removal operations on the degassed crude oil retrieved from the oilfield. S22. Natural gas is compounded according to the composition of oilfield produced gas, or produced natural gas is obtained on-site; S23. The crude oil processed in S21 is mixed with compounded natural gas (or the natural gas retrieved) under reservoir pressure and temperature conditions, according to the reservoir dissolved gas-oil ratio, so that the natural gas is completely dissolved in the crude oil, thereby forming formation crude oil (underground crude oil). The compounded formation crude oil here is crude oil with saturated dissolved gas under reservoir pressure. S3. Test the evolution of oil and gas contact in the core, including: S31. Maintain the core temperature at the target temperature and inject a visual fluid (when the target temperature is below 100℃, the visual fluid is clear water; when the target temperature is above 100℃, the visual fluid is white oil) into the confining pressure chamber to make the confining pressure 3MPa higher than the core pressure. S32. Inject reservoir test gas (CO2 as an example) into the core to replace the entire system and increase the core pressure to the target pressure (reservoir pressure). During this process, continue to inject the visible fluid into the confining pressure chamber to maintain the confining pressure 3MPa higher than the core pressure. After the reservoir pressure is established, turn off the top injection pump and set the top back pressure valve pressure to the reservoir test pressure to maintain the reservoir pressure stability during subsequent crude oil injection. S33. Maintain the pressure of the top back pressure valve at the test reservoir pressure. Slowly inject the compounded formation crude oil into the core from the bottom injection pump to the bottom injection port of the core fixing device. During the injection process, the pressure in the core is kept constant at the test pressure by the top back pressure valve of the test system. As the injection of crude oil increases the pressure in the core, the top back pressure valve controls the balance. When the liquid level reaches the expected liquid level (1 / 2 of the total length of the core), the injection is stopped. S34. Close the core inlet and outlet valves, let the system stand still, observe the gas-oil interface evolution process in real time through the visualization window, and record the pressure change data caused by the test gas merging into the crude oil through the pressure sensor at the top of the system. The injected gas comes into contact with the crude oil, undergoing diffusion and dissolution to maintain continuous contact between the gas and oil phases, and is then allowed to stand. During this period, an altimeter system is used to test the migration of the oil-gas interface, thereby calculating the real-time liquid-gas interface change pattern in the porous medium. S35. After the predetermined settling time, inject inert gas (Ar), open the injection port at the bottom of the core, and slowly discharge the crude oil after the test gas has acted on it into the sampler in segments to test its physical properties (density, viscosity, dissolved gas-oil ratio).

[0025] Because the diffusion and dissolution of test gas in crude oil within porous media occurs from top to bottom, the dissolved gas content varies at different locations, with higher content at the top and lower content at the bottom. This results in different crude oil properties at different parts of the core, a phenomenon closely matching the diffusion process of injected gas during on-site gas injection development in oilfields. To more accurately analyze the evolution of crude oil properties at different locations in the reservoir, it is necessary to extract crude oil from different locations after the injection of gas and test its properties separately, providing more precise experimental data.

[0026] S36. Based on the recorded pressure data, analyze the characteristics of reservoir pressure changes after gas injection to guide on-site pressure prediction in the oilfield and lay the foundation for predicting reservoir pressure changes during gas injection development; determine the expansion coefficient of crude oil based on the evolution law of the oil-gas interface, test the properties of crude oil in each section, and compare the evolution law of crude oil composition and properties after gas injection. Viscosity: The viscosity of each section of crude oil was tested using a rheometer; Density: The density of each section of crude oil was tested using a density meter; Component analysis: Gas chromatography-mass spectrometry (GC-MS) was used to analyze the concentrations of all components of crude oil and different hydrocarbon fractions. Dissolved gas-oil ratio: The gas-oil ratio of each section of crude oil was tested using an oil-gas separator; Expansion Coefficient: Calculated based on changes in altimeter position. When crude oil in the core interacts with injected test gas, its volume expands, causing the gas-liquid interface to rise. Because the rise is relatively small, it is difficult to observe. Using an altimeter amplifies the height change and displays it on a monitor, allowing for clear measurement of the gas-liquid interface height change. This enables the calculation of the dynamic expansion coefficient at different times (the height of the gas-liquid interface after the gas interaction divided by the original liquid level), providing crucial reference for oilfield operations.

[0027] The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included within the protection scope of the present invention.

Claims

1. An experimental apparatus for testing the evolution of fluid properties in porous media, characterized in that, include: Core fixing device, including: Vertically arranged transparent rubber tubes are used to hold rock cores; A transparent pressure-resistant cylinder coaxially sleeved outside the rubber sleeve and spaced apart from it; Two first covers symmetrically arranged at both ends of the cylinder are stepped rings. The two first covers are connected by a tie rod, so that the step in the middle of the stepped ring presses against the end face of the cylinder. A tapered sleeve is arranged coaxially with the first cover body. Its sidewall is a conical curved surface, and its lower end extends into the rubber tube and presses the rubber tube tightly against the inner wall of the first cover body, thereby forming a sealed cavity between the tube body and the rubber tube, called the confining pressure cavity. The second cover, which is threadedly connected to the first cover, is a stepped ring. The middle step abuts against the upper end of the tapered sleeve, and a sealing ring is provided on the contact surface between the two. The second cover is used to push the tapered sleeve to move axially along the first cover, thereby pressing the rubber tube against the inner wall of the first cover. The plug, which is threaded to the second cover, has one end passing through the tapered sleeve and abutting against the end face of the rock core. The plug has a fluid channel for transmitting fluid to the rock core. A sealing mechanism for sealing the gap between the second cover and the plug; An altimeter, located outside the cylinder, is used to detect changes in the gas-oil interface within the rock core. A rotating base is used to drive the core fixing device to rotate circumferentially around the cylinder body. A confining pressure pump connected to the confining pressure chamber; The fluid channel is connected to an injection and extraction device for injecting fluid into the core and extracting fluid from the core.

2. The experimental apparatus for testing the evolution of fluid properties in porous media according to claim 1, characterized in that, The altimeter includes: A support extending axially along the cylinder body; A high-definition camera, arranged radially along the core and capable of sliding along the axis of the support, is used to observe the gas-oil interface in the core. A high-precision rangefinder fixed to the high-definition camera is used to measure the distance the high-definition camera slides along the axis of the support column; A high-definition display device electrically connected to the high-definition camera and the high-precision rangefinder.

3. The experimental apparatus for testing the evolution of fluid properties in porous media according to claim 1, characterized in that, The sealing mechanism includes: The second cover body has a perforated section and a threaded section on its inner wall, wherein the inner diameter of the perforated section is larger than the inner diameter of the threaded section. The smooth rod section and the second threaded section are located on the outer wall of the plug sidewall, wherein the outer diameter of the smooth rod section is larger than the outer diameter of the second threaded section, and the first threaded section and the second threaded section are threadedly connected. A first retaining ring located between the optical rod segment and the optical aperture segment and slidably connected to both; A sealing ring located between the optical rod section and the optical hole section and abutting against the end of the first retaining ring opposite to the first threaded section; A pressure ring that is threaded to the second cover to push the sealing ring to expand radially.

4. The experimental apparatus for testing the evolution of fluid properties in porous media according to claim 3, characterized in that, It also includes a second retaining ring located between the pressure ring and the sealing ring, which is located between the optical rod section and the optical hole section.

5. The experimental apparatus for testing the evolution of fluid properties in porous media according to claim 1, characterized in that, The injection and production equipment includes a production device and an injection device. The production device includes a back pressure valve for controlling the inlet pressure of the back pressure valve when discharging fluid. The injection device includes an injection pump and an intermediate tank connected in sequence, wherein the intermediate tank stores test fluid.

6. The experimental apparatus for testing the evolution of fluid properties in porous media according to claim 1, characterized in that, The cylinder is made of sapphire glass.

7. The experimental apparatus for testing the evolution of fluid properties in porous media according to claim 1, characterized in that, The rotating base is equipped with a platform with six degrees of freedom, and the cylinder is fixed on the platform.

8. A testing method for an experimental apparatus for testing the evolution law of fluid properties in porous media, comprising the experimental apparatus for testing the evolution law of fluid properties in porous media as described in claim 1, characterized in that, Includes the following steps: S1. After drying the core, install it into the experimental apparatus, heat it to the target temperature, and then evacuate it to obtain a clean porous media system. S2. The degassed crude oil and natural gas from the oilfield are blended under target temperature and pressure conditions to obtain blended formation crude oil; S3. Test the evolution of oil and gas contact in the core, including: S31. Maintain the core temperature at the target temperature and inject a visible fluid into the confining pressure chamber so that the confining pressure is higher than the core pressure during the test. S32. Inject reservoir testing gas into the core to replace the entire system and increase the core pressure to the target pressure. During this process, continue to inject visual fluid into the confining pressure chamber to maintain the confining pressure higher than the core pressure. S33. Inject the compounded formation crude oil into the core from the bottom. During the injection process, the upper part of the core is vented to maintain the core pressure at the target pressure until the oil and gas interface in the core reaches the target height. S34. Close the core inlet and outlet valves, let it stand, and observe the evolution of the gas-oil interface through the visualization window. Record the pressure change data caused by the test gas merging into the crude oil through the pressure sensor at the top of the system. S35. After the predetermined settling time, inert gas is injected, and the crude oil in the core is slowly discharged into the sampler in segments to test its physical properties. S36. Based on the recorded pressure data, analyze the characteristics of reservoir pressure changes after gas injection to guide on-site pressure prediction in the oilfield and lay the foundation for predicting reservoir pressure changes during gas injection development; determine the expansion coefficient of crude oil based on the evolution law of the oil-gas interface; test the properties of crude oil in each section and compare the evolution law of crude oil composition and properties after gas injection.

9. The testing method of the experimental apparatus for testing the evolution law of fluid properties in porous media according to claim 8, wherein the oil reservoir test gas is the injection gas during the oil reservoir gas injection development process.

10. The testing method of the experimental apparatus for testing the evolution law of fluid properties in porous media according to claim 8, wherein the visualized fluid is clear water or white oil.

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