Visualization experimental device and method for CO2 gravity-instability diffusion under porous media conditions

Abstract

The present invention discloses a device and method for visualizing the gravitationally unstable diffusion of CO2 in porous media. The device comprises a Hele-Shaw autoclave, an injection and pressure control module, a temperature control module, and an image acquisition and processing module. The injection and pressure control module comprises a displacement pump, a formation water intermediate container, a CO2 intermediate container, and a pressurizing liquid intermediate container, the displacement pump being connected to the formation water intermediate container, the CO2 intermediate container, and the pressurizing liquid intermediate container, respectively, and the formation water intermediate container, the CO2 intermediate container, and the pressurizing liquid intermediate container are all connected to the Hele-Shaw autoclave. The image acquisition and processing module comprises an image acquisition unit, an LED surface light source, and a controller, the controller being connected to the image acquisition unit. The present invention enables observation of the convective diffusion process of CO2 in formation water and the gravitational instability during the diffusion process under formation temperature, pressure, and gravity conditions, allowing intuitive study of the convective diffusion mechanism of CO2 in formations.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon sequestration experiments and CO2 flooding experiments, and specifically relates to a visualization experimental device and method for CO2 gravity-unstable diffusion under porous media conditions. Background Art

[0002] CO2 is the most important greenhouse gas that causes the global warming effect. Injecting CO2 into formations is the primary method for CO2 storage to achieve carbon neutrality.

[0003] Currently, bottom-water ridge intrusion is a major challenge facing the development of strong bottom-water reservoirs in my country. Because CO2 has a lower density than formation water, injecting CO2 from the top of the reservoir displaces the water phase downward, thereby achieving the goal of water cone formation. However, CO2 dissolving in formation water increases its density, and gravity-induced natural convection is a key factor influencing the effectiveness of CO2 water cone formation. Furthermore, the formation water containing dissolved CO2 settles to the bottom of the reservoir, inhibiting its escape and facilitating its long-term storage. Therefore, studying the convective instability and dissolution kinetics of CO2 in formation water under porous media conditions is of research value and practical significance.

[0004] Currently, the main experimental setup for visualizing gravity-induced natural convection is the Hele-Shaw model. This type of setup is a visual flat plate model, but it is generally not a model of porous media. For example, Lu Guohuan (2017, Master's thesis, Dalian University of Technology) conducted a visualization experiment on high-pressure CO2 dissolution convection using a thin-layer space model. However, gravity convection is significantly affected by the pore structure of the reservoir, making it difficult to simulate the convection and diffusion properties of CO2 in porous media using a cavity model.

[0005] Existing Hele-Shaw porous media models used to study gravitational instabilities are generally atmospheric or low-pressure devices. Common examples include glass bead-filled models and etched glass models. For example, Saffman and Taylor (1958, DOI: 10.1098 / rspa.1958.0085) first designed a sand-filled Hele-Shaw model to simulate unstable seepage. Fan Yinting (2018, Master's thesis, Dalian University of Technology) conducted experiments on convection and diffusion induced by CO2 dissolution using the Hele-Shaw model at ambient temperature and pressure. Mahmoodpour et al. (2019, DOI:10.1103 / PhysRevApplied.12.034016) designed a high-pressure Hele-Shaw model to study the convective diffusion of CO2 solutions, but their device's upper pressure limit was only 3.69 MPa (535.3 psi). Meanwhile, Guo Xingxue's (2019, DOI:10.13673 / j.cnki.cn37-1359 / te.2019.03.013) high-temperature, high-pressure experimental device was limited to 8 MPa. Pressure significantly affects the diffusion rate and solubility of CO2, making low-pressure models difficult to simulate the dissolution and diffusion properties of CO2 in formation conditions.

[0006] Due to the difficulty and time required to conduct experiments under reservoir conditions, few experiments have examined the convective dissolution of CO2 in geological reservoirs. Simulated fluids, such as two miscible fluids, are often used to replace the CO2-brine system. For example, Wooding et al. (2006) used potassium permanganate as a solute to replace CO2 to study convective fingering; Ennis-King et al. (2005) used an 80% glycerol and water mixture (to increase viscosity) as a mother liquor, creating gravitational instability by increasing salinity and observing the growth and coarsening of the fingering; Tsai et al. (2013) used water and propylene glycol to replace CO2 and brine, studying the effect of a sloped boundary on convection in the Hele-Shaw model. They obtained similar scaling relationships and suggested that a sloped boundary increases the dissolution rate of CO2 in brine; Slim et al. (2013) studied the convective diffusion of potassium permanganate in water in the Hele-Shaw model, identifying six different mechanisms as a function of Reynolds number Ra and horizontal diffusion time. There are two types of fluid model systems: the classic Rayleigh-Darcy convective system and the analogue-fluid model. However, in these simulations, the two phases of fluid are completely mixed, and the viscosity and diffusion of the mixed solution strongly depend on the concentration difference between the solutions. The fluid properties of the CO2-water system are influenced by factors such as the CO2 diffusion coefficient and concentration, making it often difficult to simulate the convective dissolution of CO2.

[0007] In summary, these existing devices are difficult to use for CO2 convection diffusion experiments based on gravity instability.

[0008] Therefore, there is a particular need for a method that can visually observe the convection diffusion process of CO2 in formation water and the gravitational instability during the diffusion process under formation temperature, pressure and gravity conditions, so as to study the convection diffusion mechanism of CO2 in the formation. Summary of the Invention

[0009] The purpose of the present invention is to provide a visualization experimental device and method for the gravity-unstable diffusion of CO2 under porous media conditions, which can realize the intuitive observation of the convective diffusion process of CO2 in formation water and the gravitational instability during the diffusion process under the conditions of formation temperature, pressure and gravity, and is used to study the convective diffusion mechanism of CO2 in the formation.

[0010] To achieve the above-mentioned object, the present invention provides a visualization experimental device for gravitationally unstable diffusion of CO2 under porous media conditions, comprising: a Hele-Shaw autoclave, an injection and pressure control module, a temperature control module, and an image acquisition and processing module; the injection and pressure control module comprises a displacement pump, a formation water intermediate container, a CO2 intermediate container, and a pressurizing liquid intermediate container, the displacement pump being connected to the formation water intermediate container, the CO2 intermediate container, and the pressurizing liquid intermediate container, respectively, and the formation water intermediate container, the CO2 intermediate container, and the pressurizing liquid intermediate container being all connected to the Hele-Shaw autoclave, wherein the simulated formation temperature in the Hele-Shaw autoclave reaches 150°C and the simulated formation pressure reaches 100 MPa; the temperature control module comprises a first heating and insulation jacket, a second heating and insulation jacket, a first temperature detection unit, a second temperature detection unit, and a temperature control unit, the temperature control unit being connected to the first heating and insulation jacket, the second heating and insulation jacket, the first temperature detection unit, and the second temperature detection unit, respectively; the image acquisition and processing module comprises an image acquisition unit, an LED surface light source, and a controller, and the controller being connected to the image acquisition unit.

[0011] Optionally, the displacement pump is respectively connected to the inlet of the formation water intermediate container, the inlet of the CO2 intermediate container and the inlet of the pressurized liquid intermediate container; the outlet of the formation water intermediate container and the outlet of the CO2 intermediate container are both connected to the top model inlet of the Hele-Shaw autoclave; the outlet of the pressurized liquid intermediate container is connected to the bottom ring pressure inlet of the Hele-Shaw autoclave.

[0012] Optionally, the bottom annular pressure inlet of the Hele-Shaw autoclave is also connected to a vacuum pump; the top annular pressure outlet of the Hele-Shaw autoclave is provided with a vent valve; and the bottom mold outlet of the Hele-Shaw autoclave is respectively connected to a back pressure valve and a vacuum pump.

[0013] Optionally, the first heating and insulation sleeve is wrapped around the outside of the Hele-Shaw autoclave, and the first temperature detection unit is arranged inside the first heating and insulation sleeve; the second heating and insulation sleeve is wrapped around the outside of the CO2 intermediate container, and the second temperature detection unit is arranged inside the second heating and insulation sleeve, and the temperature control unit receives temperature information from the first temperature detection unit and the second temperature detection unit, and controls the heating conditions of the first heating and insulation and or the second heating and insulation according to the temperature information.

[0014] Optionally, the LED surface light source is located behind the Hele-Shaw autoclave, and the image acquisition unit is located in front of the Hele-Shaw autoclave, collecting the light image of the LED surface light source transmitted on the front side of the Hele-Shaw autoclave, and transmitting the light image to the controller for the controller to analyze the light image and obtain the relationship between the CO2 concentration distribution and time change.

[0015] Optionally, the Hele-Shaw autoclave includes a front cover, a rear cover, an autoclave outer wall and a Hele-Shaw model, one end of the autoclave outer wall is connected to the front cover, the other end is connected to the rear cover, and the inner side wall of the autoclave outer wall is connected to the Hele-Shaw model.

[0016] Optionally, a first window groove is provided on the front cover, and the front cover plate fixes the front sapphire window in the window groove of the front cover; a second window groove is provided on the rear cover, and the rear cover plate fixes the rear sapphire window in the window groove of the rear cover; an annular protrusion is provided on the inner side of the outer wall of the autoclave, and the Hele-Shaw model is fixed on the annular protrusion on the outer wall of the autoclave through a model fixing plate.

[0017] Optionally, the Hele-Shaw model is a rectangular glass porous medium model, and the Hele-Shaw model is provided with an upper inlet and a lower outlet.

[0018] Optionally, the annular protrusion divides the internal annular pressure cavity of the autoclave into a front cavity and a rear cavity, a first through hole is provided at the bottom of the front cavity, and the first through hole is connected to the bottom annular pressure outlet of the autoclave, and a second through hole is provided at the bottom of the rear cavity, and the second through hole is connected to the top annular pressure outlet of the autoclave; a third through hole is provided on the annular protrusion, and the third through hole is respectively connected to the upper inlet of the Hele-Shaw model and the top model inlet of the Hele-Shaw autoclave; a fourth through hole is provided on the annular protrusion, and the fourth through hole is respectively connected to the lower outlet of the Hele-Shaw model and the bottom model outlet of the Hele-Shaw autoclave.

[0019] Optionally, a thin layer space is provided inside the Hele-Shaw model, the lower part of the thin layer space is a high permeability seepage channel, the high permeability seepage channel is connected to the lower outlet of the Hele-Shaw model, the upper part of the high permeability seepage channel is connected to the porous medium area, the upper part of the porous medium area is connected to the thin layer cavity, and the thin layer cavity is connected to the upper inlet of the Hele-Shaw model.

[0020] The present invention also provides a method for visualizing the gravitationally unstable diffusion of CO2 in porous media, and the method comprises:

[0021] Step 1: Close all valves, open the vacuum valve at the bottom annular pressure inlet of the Hele-Shaw autoclave and the vacuum valve at the bottom mold outlet three-way valve, use a vacuum pump to extract the air from the internal annular pressure chamber of the Hele-Shaw autoclave and the Hele-Shaw mold. After reaching the preset vacuum degree, continue vacuuming for the preset period of time and close the vacuum valve.

[0022] Step 2: Open the annular pressure inlet valve at the bottom of the Hele-Shaw autoclave, the three-way valve at the top mold inlet of the Hele-Shaw autoclave, and the inlet and outlet valves of the boosting liquid intermediate container and the formation water intermediate container. Use a displacement pump to inject the boosting liquid from the boosting liquid intermediate container into the internal annular pressure cavity of the Hele-Shaw autoclave at a first preset pressure. Also, inject the formation water containing the CO2 concentration indicator from the formation water intermediate container into the Hele-Shaw mold at a constant pressure until the internal annular pressure cavity of the Hele-Shaw autoclave and the Hele-Shaw mold are both filled with liquid and the injection pressure reaches and stabilizes at the first preset pressure. Use a back-pressure pump to increase the control pressure of the back-pressure valve to the first preset pressure. Open the outlet valve of the three-way valve at the bottom mold outlet of the Hele-Shaw autoclave to allow the formation water to fill the back-pressure valve.

[0023] Step 3: Turn on the temperature control module and heat the Hele-Shaw autoclave and the CO2 intermediate container to the preset temperature. During the temperature increase process, use the displacement pump and back pressure valve to maintain the annular pressure of the Hele-Shaw autoclave and the pressure inside the Hele-Shaw model stable at the first preset pressure.

[0024] Step 4: After both temperature and pressure have stabilized, gradually increase the displacement pump pressure to synchronize the annular pressure of the Hele-Shaw autoclave and the pressure within the Hele-Shaw model until the pressure reaches the second preset pressure. Close the top outlet valves of the formation water intermediate container and the pressurizing fluid intermediate container. Open the bottom inlet valve of the CO2 intermediate container and use the displacement pump in constant pressure mode to pressurize the CO2 in the CO2 intermediate container to the second preset pressure.

[0025] Step 5: After the CO2 pressure stabilizes, open the top outlet valves of the CO2 intermediate container and the boosting fluid intermediate container. Maintaining the back pressure at the second preset pressure, use a displacement pump to inject CO2 into the Hele-Shaw model at a constant flow rate. The CO2 fills the thin-layer cavity while simultaneously discharging formation water from the Hele-Shaw model through the back-pressure valve until the gas-liquid interface overlaps the interface between the thin-layer cavity and the porous medium region.

[0026] Step 6: Maintaining the CO2 pressure at a second preset pressure, the image acquisition unit begins capturing images of CO2 convection and diffusion in the porous medium. By monitoring the temporal changes in the CO2 concentration distribution in formation water under porous medium conditions, the gravity-induced unstable permeability and gravity convection and diffusion of CO2 in the porous medium are studied.

[0027] The beneficial effects of the present invention are as follows: the visualization experimental device for the gravity-unstable diffusion of CO2 under porous media conditions of the present invention introduces formation water in a formation water intermediate container and CO2 in a CO2 intermediate container into a Hele-Shaw autoclave, simulates the pressure in the formation by introducing the medium in the pressurized liquid intermediate container into the Hele-Shaw autoclave, simulates the temperature of the formation by a temperature control module, and collects and analyzes the diffusion image of CO2 in the simulated formation by an image processing unit, thereby realizing the observation of the convective diffusion process of CO2 in formation water and the gravity instability in the diffusion process under the conditions of formation temperature, pressure and gravity, and can intuitively study the convective diffusion mechanism of CO2 in the formation, which has practical significance for studying the oil displacement and storage mechanism of CO2 in high-water-content oil reservoirs.

[0028] The present invention has other features and advantages that will be apparent from or will be described in detail in the accompanying drawings and the following specific examples incorporated herein, which together serve to explain the specific principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0030] Figure 1 A connection structure diagram of a visualization experimental device for CO2 gravity-unstable diffusion under porous media conditions according to one embodiment of the present invention is shown.

[0031] Figure 2 A cross-sectional view of a Hele-Shaw autoclave for gravity-unstable diffusion of CO2 under porous media conditions according to one embodiment of the present invention is shown.

[0032] Figure 3 A cross-sectional view of a Hele-Shaw model for gravity-instability diffusion of CO2 in porous media according to one embodiment of the present invention is shown.

[0033] Figure 4 A flowchart of the experimental process of a visualization experimental device for CO2 gravity-unstable diffusion under porous media conditions according to one embodiment of the present invention is shown.

[0034] Description of main reference numerals:

[0035] 1. Front cover; 2. Front sapphire window; 3. Front cover plate; 4. Hele-Shaw model; 5. Model fixing plate; 6. Outer wall of autoclave; 7. Rear cover plate; 8. Rear sapphire window; 9. Rear cover; 11. Displacement pump; 12. Formation water intermediate container; 13. CO2 intermediate container; 14. Pressurized liquid intermediate container; 15. Hele-Shaw autoclave; 16. Base; 17. Temperature control module; 18. Image acquisition unit; 19. LED surface light source; 20. Back pressure valve; 21. Back pressure pump; 22. Vacuum pump; 23. Controller; 41. Thin layer space; 42. High permeability seepage channel; 43. Porous medium area; 44. Thin layer cavity. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Instead, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0037] According to the present invention, a visualization experimental device for gravitationally unstable diffusion of CO2 under porous media conditions is provided, comprising: a Hele-Shaw autoclave, an injection and pressure control module, a temperature control module, and an image acquisition and processing module; the injection and pressure control module comprises a displacement pump, a formation water intermediate container, a CO2 intermediate container, and a pressurized liquid intermediate container, the displacement pump being connected to the formation water intermediate container, the CO2 intermediate container, and the pressurized liquid intermediate container, respectively, and the formation water intermediate container, the CO2 intermediate container, and the pressurized liquid intermediate container being all connected to the Hele-Shaw autoclave, wherein the simulated formation temperature in the Hele-Shaw autoclave reaches 150° C. and the simulated formation pressure reaches 100 MPa; the temperature control module comprises a first heating and insulation jacket, a second heating and insulation jacket, a first temperature detection unit, a second temperature detection unit, and a temperature control unit, and the temperature control unit is connected to the first heating and insulation jacket, the second heating and insulation jacket, the first temperature detection unit, and the second temperature detection unit, respectively; the image acquisition and processing module comprises an image acquisition unit, an LED surface light source, and a controller, and the controller is connected to the image acquisition unit.

[0038] Specifically, the injection and pressure control system consists of a displacement pump, a formation water intermediate container, a CO2 intermediate container, a pressurized fluid intermediate container, and a back-pressure valve. The Hele-Shaw autoclave, consisting of a Hele-Shaw model and the autoclave's outer wall, simulates the actual formation environment. The formation water intermediate container holds experimental formation water, containing a dissolved CO2 concentration indicator. The CO2 intermediate container holds experimental CO2 gas. The pressurized fluid intermediate container holds pressurized fluid. The formation water in the formation water intermediate container and the CO2 in the CO2 intermediate container are introduced into a Hele-Shaw autoclave to simulate the diffusion of CO2 in the formation water. The pressurized fluid in the pressurized fluid intermediate container is introduced into the Hele-Shaw autoclave to simulate formation pressure, capable of simulating formation temperatures up to 150°C and pressures up to 100 MPa. The temperature control unit simultaneously monitors and controls temperature changes within the Hele-Shaw autoclave and the CO2 intermediate container to simulate formation temperature. The image acquisition and processing module captures and analyzes images of the CO2 diffusion in the formation water.

[0039] According to an exemplary embodiment, a visualization experimental device for gravitationally unstable diffusion of CO2 under porous media conditions introduces formation water in a formation water intermediate container and CO2 in a CO2 intermediate container into a Hele-Shaw autoclave, simulates the pressure in the formation by introducing the medium in the pressurized liquid intermediate container into the Hele-Shaw autoclave, simulates the temperature of the formation by a temperature control module, and collects and analyzes the diffusion image of CO2 in the simulated formation by an image processing unit, so as to realize observation of the convective diffusion process of CO2 in formation water and the gravitational instability during the diffusion process under the conditions of formation temperature, pressure and gravity, and intuitively study the convective diffusion mechanism of CO2 in the formation, which has practical significance for studying the oil displacement and storage mechanism of CO2 in high-water-content oil reservoirs.

[0040] As an optional solution, the displacement pump is connected to the inlet of the formation water intermediate container, the inlet of the CO2 intermediate container and the inlet of the pressurized liquid intermediate container respectively; the outlet of the formation water intermediate container and the outlet of the CO2 intermediate container are both connected to the top model inlet of the Hele-Shaw autoclave; and the outlet of the pressurized liquid intermediate container is connected to the bottom ring pressure inlet of the Hele-Shaw autoclave.

[0041] Specifically, the displacement pump is connected via metal pipelines to the inlet valves of the formation water intermediate container, the inlet valve of the CO2 intermediate container, and the inlet valve of the pressurized fluid intermediate container. The inlet valve of the formation water intermediate container and the outlet valve of the CO2 intermediate container are each connected via metal pipelines to the three-way valve at the top mold inlet of the Hele-Shaw autoclave. The outlet valve of the pressurized fluid intermediate container is also connected via metal pipelines to one end of the three-way valve at the annular pressure inlet of the bottom of the Hele-Shaw autoclave.

[0042] As an option, the bottom annular pressure inlet of the Hele-Shaw autoclave is also connected to a vacuum pump; the top annular pressure outlet of the Hele-Shaw autoclave is provided with a vent valve; the bottom mold outlet of the Hele-Shaw autoclave is connected to a back pressure valve and a vacuum pump respectively.

[0043] Specifically, the other end of the three-way valve at the annular pressure inlet of the Hele-Shaw autoclave is connected to a vacuum pump. A vent valve is installed at the annular pressure outlet of the Hele-Shaw autoclave. The three-way valve at the bottom mold outlet of the Hele-Shaw autoclave is connected to the inlet of the back-pressure valve and the vacuum pump via a metal pipeline. The pressure control port of the back-pressure valve is connected to the back-pressure pump.

[0044] As an optional solution, the first heating and insulation sleeve is wrapped around the outside of the Hele-Shaw autoclave, and the first temperature detection unit is arranged in the first heating and insulation sleeve; the second heating and insulation sleeve is wrapped around the outside of the CO2 intermediate container, and the second temperature detection unit is arranged in the second heating and insulation sleeve. The temperature control unit receives temperature information from the first temperature detection unit and the second temperature detection unit, and controls the heating conditions of the first heating and insulation or the second heating and insulation according to the temperature information.

[0045] Specifically, the temperature control system includes a first heating and insulation jacket, a first temperature detection unit, a second heating and insulation jacket, a second temperature detection unit, and a temperature control unit. The first heating and insulation jacket is wrapped around the exterior of the Hele-Shaw autoclave, and the first temperature detection unit is placed within the first heating and insulation jacket. The first heating and insulation jacket and the first temperature detection unit are connected to the temperature control unit via electrical wires. The CO2 intermediate container has an independent second heating and insulation jacket and a second temperature detection unit outside, which are connected to the temperature control unit via electrical wires. The temperature control unit is capable of simultaneously detecting and controlling temperature changes within the Hele-Shaw autoclave and the CO2 intermediate container.

[0046] As an optional solution, the LED surface light source is located behind the Hele-Shaw autoclave, and the image acquisition unit is located in front of the Hele-Shaw autoclave. It collects the light image of the LED surface light source transmitted on the front side of the Hele-Shaw autoclave and transmits the light image to the controller for the controller to analyze the light image and obtain the relationship between the CO2 concentration distribution and time change.

[0047] Specifically, the image acquisition unit is located in front of the Hele-Shaw autoclave, and the LED surface light source is located behind the Hele-Shaw autoclave. Light emitted by the LED surface light source can enter and pass through the sapphire window of the Hele-Shaw autoclave and be captured by the image acquisition unit. The image acquisition unit transmits the acquired image to the controller, which analyzes the image to obtain the relationship between the CO2 concentration distribution and time.

[0048] As an optional solution, the Hele-Shaw autoclave includes a front cover, a rear cover, an autoclave outer wall and a Hele-Shaw mold, one end of the autoclave outer wall is connected to the front cover, the other end is connected to the rear cover, and the inner side wall of the autoclave outer wall is connected to the Hele-Shaw mold.

[0049] Specifically, the front of the Hele-Shaw autoclave is a cylindrical stainless steel front cover, which is connected to the outer wall of the autoclave by screws. The front cover is embedded in the outer wall of the autoclave and contacts the outer wall of the autoclave through an O-ring to achieve the sealing of the autoclave. The rear of the Hele-Shaw autoclave is a cylindrical stainless steel rear cover, which is connected to the outer wall of the autoclave by screws. The rear cover is embedded in the outer wall of the autoclave and contacts the outer wall of the autoclave through an O-ring to achieve the sealing of the autoclave. The outer wall of the autoclave is a Hastelloy annular cylinder. There is an inward annular protrusion on the inner side of the outer wall of the autoclave, and the Hele-Shaw model is set on the annular protrusion.

[0050] As an optional solution, a first window groove is provided on the front cover, and the front cover plate fixes the front sapphire window in the window groove of the front cover; a second window groove is provided on the rear cover, and the rear cover plate fixes the rear sapphire window in the window groove of the rear cover; an annular protrusion is provided on the inner side of the outer wall of the autoclave, and the Hele-Shaw model is fixed to the annular protrusion on the outer wall of the autoclave through a model fixing pressure plate.

[0051] Specifically, there is a through-window slot in the middle of the front cover. The front sapphire window is a transparent cylindrical sapphire glass embedded in the window slot of the front cover. The front cover plate is a Hastelloy ring cover, which is fixed to the front cover via screws with sealing gaskets, and the front sapphire window is fixed in the front cover. Both sides of the front sapphire window are in contact with the front cover and the front cover plate via rubber gaskets to achieve sealing of the autoclave and prevent the sapphire window from breaking due to uneven force. There is a through-window slot in the middle of the back cover. The rear sapphire window is a transparent cylindrical sapphire glass embedded in the window slot of the back cover. The rear cover plate is a Hastelloy ring cover, which is fixed to the back cover via screws with sealing gaskets, and the rear sapphire window is fixed in the back cover. Both sides of the rear sapphire window are in contact with the back cover and rear cover plate through rubber gaskets to achieve the sealing of the autoclave and prevent the sapphire window from breaking due to uneven force.

[0052] The Hele-Shaw phantom is a rectangular glass porous medium phantom. It is secured to an annular protrusion on the inner side of the autoclave's outer wall using four phantom fixing plates. Each platen is secured to the annular protrusion on the inner side of the autoclave's outer wall with two screws. Each platen has a set screw with a rubber gasket embedded in it to contact the Hele-Shaw phantom. The Hele-Shaw phantom can be tightened by rotating the set screw.

[0053] As an alternative, the Hele-Shaw model is a rectangular glass porous medium model with an upper inlet and a lower outlet.

[0054] As an optional solution, the annular protrusion divides the internal annular pressure cavity of the autoclave into a front cavity and a rear cavity. A first through hole is provided at the bottom of the front cavity, which is connected to the bottom annular pressure outlet of the autoclave. A second through hole is provided at the bottom of the rear cavity, which is connected to the top annular pressure outlet of the autoclave. A third through hole is provided on the annular protrusion, which is respectively connected to the upper inlet of the Hele-Shaw model and the top model inlet of the Hele-Shaw autoclave. A fourth through hole is provided on the annular protrusion, which is respectively connected to the lower outlet of the Hele-Shaw model and the bottom model outlet of the Hele-Shaw autoclave.

[0055] Specifically, the annular protrusion on the outer wall of the autoclave divides the annular pressure cavity inside the autoclave into two connected cavities, the front and the rear. The bottom of the front cavity has a through hole penetrating the outer wall of the autoclave, which is connected to the annular pressure outlet at the bottom of the autoclave.

[0056] A through-hole is formed within the internal protrusion of the autoclave's outer wall, connecting the upper inlet of the Hele-Shaw model with the top model inlet of the autoclave. An O-ring seals the upper inlet of the Hele-Shaw model and the through-hole in the internal protrusion of the autoclave's outer wall, preventing the Hele-Shaw model from rupturing due to uneven force. A through-hole is formed within the internal protrusion of the autoclave's outer wall, connecting the lower outlet of the Hele-Shaw model with the bottom model outlet of the autoclave. An O-ring seals the lower outlet of the Hele-Shaw model and the through-hole in the internal protrusion of the autoclave's outer wall, preventing the Hele-Shaw model from rupturing due to uneven force. A through-hole is formed at the top of the rear cavity, extending through the outer wall of the autoclave and connecting to the top annular pressure outlet of the autoclave.

[0057] In one example, a Hele-Shaw autoclave has a base on the bottom that secures the autoclave to prevent it from rolling while leaving the lines running out of the bottom of the autoclave.

[0058] As an optional solution, a thin layer space is provided inside the Hele-Shaw model, the lower part of the thin layer space is a high permeability seepage channel, the high permeability seepage channel is connected to the lower outlet of the Hele-Shaw model, the upper part of the high permeability seepage channel is connected to the porous medium area, the upper part of the porous medium area is connected to the thin layer cavity, and the thin layer cavity is connected to the upper inlet of the Hele-Shaw model.

[0059] Specifically, the Hele-Shaw model has a rectangular thin space inside, and the thickness of the thin space is preferably 10 to 1000 μm. The lower part of the thin space is a high permeability seepage channel grid area, and the width of the high permeability seepage channel is preferably 1 / 20 to 1 / 5 of the height of the thin space, and the permeability of the high permeability seepage channel is preferably 1×10 -3μm 2 ~1×10 4 μm 2 . The high permeability seepage channel is connected to the lower outlet of the Hele-Shaw model. The upper part of the high permeability seepage channel area is connected to the porous medium area, preferably, it can be an etched porous medium model or a quartz sand filling model. The upper part of the porous medium area is connected to the thin layer cavity, and the width of the thin layer cavity is preferably 1 / 10 to 1 / 5 of the height of the thin layer space. The thin layer cavity is connected to the upper inlet of the Hele-Shaw model. The permeability of the thin layer cavity can be calculated by the following formula: K=D 2 / 12, K is the permeability of the thin layer space; D is the thickness of the thin layer space.

[0060] In one example, a visualization experimental device for the gravitational instability diffusion of CO2 in porous media is applicable to porous media with various porosity and permeability parameters, and applicable microscopic seepage models include a glass etching model and a sand filling model.

[0061] In one example, a CO2 concentration indicator is a multi-component acidic pH indicator. When the ground temperature remains constant, its color changes with the CO2 concentration. Depending on the experimental temperature, CO2 concentration indicators are typically mixtures of pH-sensitive dyes, such as methyl orange-bromocresol green and methyl red-bromothymol blue. The color of the methyl orange-bromocresol green indicator changes with CO2 concentration, changing from cyan to green, yellow, orange, and orange-red as the concentration increases.

[0062] The present invention also provides a method for visualizing the gravitationally unstable diffusion of CO2 in porous media, and the method comprises:

[0063] Step 1: Close all valves, open the vacuum valve at the bottom annular pressure inlet of the Hele-Shaw autoclave and the vacuum valve at the bottom mold outlet three-way valve, use a vacuum pump to extract the air from the internal annular pressure chamber of the Hele-Shaw autoclave and the Hele-Shaw mold. After reaching the preset vacuum degree, continue vacuuming for the preset period of time and close the vacuum valve.

[0064] Step 2: Open the annular pressure inlet valve at the bottom of the Hele-Shaw autoclave, the three-way valve at the top mold inlet of the Hele-Shaw autoclave, and the inlet and outlet valves of the boosting liquid intermediate container and the formation water intermediate container. Use a displacement pump to inject the boosting liquid from the boosting liquid intermediate container into the internal annular pressure cavity of the Hele-Shaw autoclave at a first preset pressure. Also, inject the formation water containing the CO2 concentration indicator from the formation water intermediate container into the Hele-Shaw mold at a constant pressure until the internal annular pressure cavity of the Hele-Shaw autoclave and the Hele-Shaw mold are both filled with liquid and the injection pressure reaches and stabilizes at the first preset pressure. Use a back-pressure pump to increase the control pressure of the back-pressure valve to the first preset pressure. Open the outlet valve of the three-way valve at the bottom mold outlet of the Hele-Shaw autoclave to allow the formation water to fill the back-pressure valve.

[0065] Step 3: Turn on the temperature control module and heat the Hele-Shaw autoclave and the CO2 intermediate container to the preset temperature. During the temperature increase process, use the displacement pump and back pressure valve to maintain the annular pressure of the Hele-Shaw autoclave and the pressure inside the Hele-Shaw model stable at the first preset pressure.

[0066] Step 4: After both temperature and pressure have stabilized, gradually increase the displacement pump pressure to synchronize the annular pressure of the Hele-Shaw autoclave and the pressure within the Hele-Shaw model until the pressure reaches the second preset pressure. Close the top outlet valves of the formation water intermediate container and the pressurizing fluid intermediate container. Open the bottom inlet valve of the CO2 intermediate container and use the displacement pump in constant pressure mode to pressurize the CO2 in the CO2 intermediate container to the second preset pressure.

[0067] Step 5: After the CO2 pressure stabilizes, open the top outlet valves of the CO2 intermediate container and the boosting fluid intermediate container. Maintaining the back pressure at the second preset pressure, use a displacement pump to inject CO2 into the Hele-Shaw model at a constant flow rate. The CO2 fills the thin-layer cavity while simultaneously discharging formation water from the Hele-Shaw model through the back-pressure valve until the gas-liquid interface overlaps the interface between the thin-layer cavity and the porous medium region.

[0068] Step 6: Maintaining the CO2 pressure at a second preset pressure, the image acquisition unit begins capturing images of CO2 convection and diffusion in the porous medium. By monitoring the temporal changes in the CO2 concentration distribution in formation water under porous medium conditions, the gravity-induced unstable permeability and gravity convection and diffusion of CO2 in the porous medium are studied.

[0069] The visualization experimental method using the experimental device for the unstable diffusion of CO2 under porous media conditions mentioned above includes the following technical solutions:

[0070] 1) Install the Hele-Shaw phantom into the Hele-Shaw autoclave, connect the Hele-Shaw autoclave to the experimental process, open the image acquisition and processing system, and adjust parameters such as brightness, field of view, and focal length to make the image of the Hele-Shaw phantom clear.

[0071] 2) Close all valves and open the vacuum valve at the annular pressure inlet of the Hele-Shaw autoclave and the vacuum valve at the three-way valve at the bottom mold outlet. Use a vacuum pump to evacuate the air from the annular pressure chamber of the Hele-Shaw autoclave and the Hele-Shaw mold. Once the required vacuum level is reached, continue vacuuming for one hour, then close the vacuum valves to stop the vacuuming process.

[0072] 3) Open the annular pressure inlet valve at the bottom of the Hele-Shaw autoclave, the three-way valve at the top mold inlet of the Hele-Shaw autoclave, and the inlet and outlet valves of the boosting liquid intermediate container and the formation water intermediate container. Simultaneously, using a displacement pump, inject the boosting liquid from the boosting liquid intermediate container into the internal annular pressure cavity of the Hele-Shaw autoclave at a constant pressure at a low pressure. Simultaneously, inject the formation water containing the CO2 concentration indicator from the formation water intermediate container into the Hele-Shaw mold at a constant pressure. Depending on the experimental requirements, the injection pressure is preferably 0.1-1 MPa. Continue until the internal annular pressure cavity of the Hele-Shaw autoclave and the Hele-Shaw mold are both filled with liquid and the injection pressure reaches and stabilizes at the aforementioned low pressure. Use a back-pressure pump to increase the control pressure of the back-pressure valve to the aforementioned low pressure. Open the outlet valve of the three-way valve at the bottom mold outlet to allow the formation water to fill the back-pressure valve.

[0073] 4) Turn on the temperature control system and heat up the Hele-Shaw autoclave and the CO2 intermediate container simultaneously. During the temperature increase, use a displacement pump and a back pressure valve to keep the annular pressure of the Hele-Shaw autoclave and the pressure inside the Hele-Shaw model stable at the lower pressure described in the step.

[0074] 5) After the temperature and pressure have stabilized, gradually increase the displacement pump pressure to increase the annular pressure of the Hele-Shaw autoclave and the pressure within the Hele-Shaw model simultaneously until the pressure reaches the required diffusion pressure. Close the top outlet valves of the formation water intermediate container and the pressurizing fluid intermediate container. Open the bottom inlet valve of the CO2 intermediate container and use the displacement pump in constant pressure mode to pressurize the CO2 in the CO2 intermediate container to the experimental pressure.

[0075] 6) After the CO2 pressure reaches a stable level, open the top outlet valves of the CO2 intermediate container and the booster fluid intermediate container. Maintaining the back pressure constant, use a displacement pump to inject CO2 into the Hele-Shaw model at a constant flow rate. The CO2 fills the thin layer cavity while simultaneously discharging the formation water in the Hele-Shaw model through the back pressure valve until the gas-liquid interface coincides with the interface between the thin layer cavity and the porous medium region.

[0076] 7) Maintaining a stable CO2 pressure, begin collecting images of CO2 convection and diffusion in the porous medium. By monitoring the time-dependent distribution of CO2 concentration in formation water under porous medium conditions, the gravity-induced instability permeability and gravity-induced convection and diffusion of CO2 in the porous medium can be studied.

[0077] Example:

[0078] Figure 1 A connection structure diagram of a visualization experimental device for CO2 gravity-unstable diffusion under porous media conditions according to one embodiment of the present invention is shown. Figure 2 A cross-sectional view of a Hele-Shaw autoclave for gravity-unstable diffusion of CO2 under porous media conditions according to one embodiment of the present invention is shown. Figure 3 A cross-sectional view of a Hele-Shaw model for gravity-instability diffusion of CO2 in porous media according to one embodiment of the present invention is shown. Figure 4 A flowchart of the experimental process of a visualization experimental device for CO2 gravity-unstable diffusion under porous media conditions according to one embodiment of the present invention is shown.

[0079] Combine Figure 1 、 Figure 2 and Figure 3As shown, the visualization experimental device for the gravitational instability diffusion of CO2 under porous media conditions includes: a Hele-Shaw autoclave 15, an injection and pressure control module, a temperature control module 17 and an image acquisition and processing module; the injection and pressure control module includes a displacement pump 11, a formation water intermediate container 12, a CO2 intermediate container 13 and a pressurized liquid intermediate container 14, the displacement pump 11 is connected to the formation water intermediate container 12, the CO2 intermediate container 13 and the pressurized liquid intermediate container 14 respectively, the formation water intermediate container 12, the CO2 intermediate container 13 and the pressurized liquid intermediate container 14 are all connected to the Hele-Shaw autoclave 15, an injection and pressure control module, a temperature control module 17 and an image acquisition and processing module; the injection and pressure control module includes a displacement pump 11, a formation water intermediate container 12, a CO2 intermediate container 13 and a pressurized liquid intermediate container 14 w autoclave 15, wherein the simulated formation temperature in the Hele-Shaw autoclave 15 reaches 150°C and the simulated formation pressure reaches 100 MPa; the temperature control module 17 includes a first heating and insulation jacket, a second heating and insulation jacket, a first temperature detection unit, a second temperature detection unit and a temperature control unit, and the temperature control unit is respectively connected to the first heating and insulation jacket, the second heating and insulation jacket, the first temperature detection unit and the second temperature detection unit; the image acquisition and processing module includes an image acquisition unit 18, an LED surface light source 19 and a controller 23, and the controller 23 is connected to the image acquisition unit 18.

[0080] Among them, the displacement pump 11 is respectively connected to the inlet of the formation water intermediate container 12, the inlet of the CO2 intermediate container 13 and the inlet of the pressurized liquid intermediate container 14; the outlet of the formation water intermediate container 12 and the outlet of the CO2 intermediate container 13 are both connected to the top model inlet of the Hele-Shaw autoclave 15; the outlet of the pressurized liquid intermediate container 14 is connected to the bottom ring pressure inlet of the Hele-Shaw autoclave 15.

[0081] The bottom annular pressure inlet of the Hele-Shaw autoclave 15 is also connected to a vacuum pump 22. The top annular pressure outlet of the Hele-Shaw autoclave 15 is equipped with a vent valve. The bottom mold outlet of the Hele-Shaw autoclave 15 is connected to a back-pressure valve 20 and a vacuum pump 22, respectively. The pressure control port of the back-pressure valve 20 is connected to a back-pressure pump 21.

[0082] Among them, the first heating and insulation cover is wrapped around the outside of the Hele-Shaw autoclave 15, and the first temperature detection unit is arranged in the first heating and insulation cover; the second heating and insulation cover is wrapped around the outside of the CO2 intermediate container 13, and the second temperature detection unit is arranged in the second heating and insulation cover. The temperature control unit receives the temperature information of the first temperature detection unit and the second temperature detection unit, and controls the heating conditions of the first heating and insulation or the second heating and insulation according to the temperature information.

[0083] The LED surface light source 19 is located behind the Hele-Shaw autoclave 15, and the image acquisition unit 18 is located in front of the Hele-Shaw autoclave 15. It collects the light image transmitted by the LED surface light source 19 on the front side of the Hele-Shaw autoclave 15 and transmits the light image to the controller 23 for the controller 23 to analyze the light image and obtain the relationship between the CO2 concentration distribution and time change.

[0084] Among them, the Hele-Shaw autoclave 15 includes a front cover 1, a rear cover 9, an autoclave outer wall 6 and a Hele-Shaw model 4. One end of the autoclave outer wall 6 is connected to the front cover 1, and the other end is connected to the rear cover 9. The inner side wall of the autoclave outer wall 6 is connected to the Hele-Shaw model 4.

[0085] Among them, a first window groove is provided on the front cover 1, and the front cover plate 3 fixes the front sapphire window 2 in the window groove of the front cover 1; a second window groove is provided on the rear cover 9, and the rear cover plate 7 fixes the rear sapphire window 8 in the window groove of the rear cover 9; an annular protrusion is provided on the inner side of the outer wall 6 of the autoclave, and the Hele-Shaw model 4 is fixed on the annular protrusion of the outer wall 6 of the autoclave through the model fixing pressure plate 5.

[0086] The Hele-Shaw model 4 is a rectangular glass porous medium model, and an upper inlet and a lower outlet are provided on the Hele-Shaw model 4.

[0087] Among them, the annular protrusion divides the internal annular pressure cavity of the autoclave into a front cavity and a rear cavity. A first through hole is provided at the bottom of the front cavity, which is connected to the bottom annular pressure outlet of the autoclave. A second through hole is provided at the bottom of the rear cavity, which is connected to the top annular pressure outlet of the autoclave; a third through hole is provided on the annular protrusion, which is respectively connected to the upper inlet of the Hele-Shaw model 4 and the top model inlet of the Hele-Shaw autoclave 15; a fourth through hole is provided on the annular protrusion, which is respectively connected to the lower outlet of the Hele-Shaw model 4 and the bottom model outlet of the Hele-Shaw autoclave 15.

[0088] Among them, a thin layer space 41 is provided inside the Hele-Shaw model 4, the lower part of the thin layer space 41 is a high permeability seepage channel 42, the high permeability seepage channel 42 is connected to the lower outlet of the Hele-Shaw model 4, the upper part of the high permeability seepage channel 42 is connected to the porous medium area 43, the upper part of the porous medium area 43 is connected to the thin layer cavity 44, and the thin layer cavity 44 is connected to the upper inlet of the Hele-Shaw model 4.

[0089] like Figure 4As shown in FIG, the steps for conducting a visualization experiment of porous media convection using a visualization experimental device for CO2 gravity-instability diffusion under porous media conditions include:

[0090] Step 1: Close all valves, open the vacuum valve at the bottom annular pressure inlet of the Hele-Shaw autoclave and the vacuum valve at the bottom mold outlet three-way valve, use a vacuum pump to extract the air from the internal annular pressure chamber of the Hele-Shaw autoclave and the Hele-Shaw mold. After reaching the preset vacuum degree, continue vacuuming for the preset period of time and close the vacuum valve.

[0091] Step 2: Open the annular pressure inlet valve at the bottom of the Hele-Shaw autoclave, the three-way valve at the top mold inlet of the Hele-Shaw autoclave, and the inlet and outlet valves of the boosting liquid intermediate container and the formation water intermediate container. Use a displacement pump to inject the boosting liquid from the boosting liquid intermediate container into the internal annular pressure cavity of the Hele-Shaw autoclave at a first preset pressure. Also, inject the formation water containing the CO2 concentration indicator from the formation water intermediate container into the Hele-Shaw mold at a constant pressure until the internal annular pressure cavity of the Hele-Shaw autoclave and the Hele-Shaw mold are both filled with liquid and the injection pressure reaches and stabilizes at the first preset pressure. Use a back-pressure pump to increase the control pressure of the back-pressure valve to the first preset pressure. Open the outlet valve of the three-way valve at the bottom mold outlet of the Hele-Shaw autoclave to allow the formation water to fill the back-pressure valve.

[0092] Step 3: Turn on the temperature control module and simultaneously raise the temperature of the Hele-Shaw autoclave and the CO2 intermediate container to a preset temperature of 110°C. During this temperature increase, a displacement pump and back-pressure valve are used to maintain the annular pressure of the Hele-Shaw autoclave and the pressure within the Hele-Shaw model at a first preset pressure of 1 MPa. This first preset pressure should be higher than the saturated vapor pressure to prevent liquid vaporization. In this example, the saturated vapor pressure of formation water at the preset temperature of 110°C is 0.1432 MPa.

[0093] Step 4: After both temperature and pressure have stabilized, gradually increase the displacement pump pressure to synchronize the annular pressure of the Hele-Shaw autoclave and the pressure within the Hele-Shaw model until the pressure reaches the second preset pressure. Close the top outlet valves of the formation water intermediate container and the pressurizing fluid intermediate container. Open the bottom inlet valve of the CO2 intermediate container and use the displacement pump in constant pressure mode to pressurize the CO2 in the CO2 intermediate container to the second preset pressure of 50 MPa.

[0094] Step 5: After the CO2 pressure stabilizes, open the top outlet valves of the CO2 intermediate container and the boosting fluid intermediate container. Maintaining the back pressure at the second preset pressure, use a displacement pump to inject CO2 into the Hele-Shaw model at a constant flow rate. The CO2 fills the thin-layer cavity while simultaneously discharging formation water from the Hele-Shaw model through the back-pressure valve until the gas-liquid interface overlaps the interface between the thin-layer cavity and the porous medium region.

[0095] Step 6: Maintaining the CO2 pressure at a second preset pressure, the image acquisition unit begins capturing images of CO2 convection and diffusion in the porous medium. By monitoring the temporal changes in the CO2 concentration distribution in formation water under porous medium conditions, the gravity-induced unstable permeability and gravity convection and diffusion of CO2 in the porous medium are studied.

[0096] The Tahe strong bottom water reservoir was used as the research object. The experimental conditions were the target reservoir conditions, with a reservoir temperature of 110°C and a reservoir pressure of 50 MPa. A visualization experiment on the diffusion of CO2 into formation water was conducted under the temperature and formation pressure conditions of the Tahe strong bottom water reservoir. The experimental steps are as follows:

[0097] (1) Install the Hele-Shaw model into the Hele-Shaw autoclave, connect the Hele-Shaw autoclave to the experimental process, turn on the image acquisition and processing system, and adjust parameters such as brightness, field of view, and focal length to make the image of the Hele-Shaw model clear.

[0098] (2) Close all valves and open the vacuum valve at the bottom annular pressure inlet of the Hele-Shaw autoclave and the vacuum valve at the bottom mold outlet three-way valve. Use a vacuum pump to evacuate the air in the internal annular pressure chamber of the Hele-Shaw autoclave and the air in the Hele-Shaw mold. After reaching the required vacuum level, continue vacuuming for one hour, then close the vacuum valve and stop vacuuming.

[0099] (3) Open the bottom annular pressure inlet valve of the Hele-Shaw autoclave, the top model inlet three-way valve of the Hele-Shaw autoclave, the inlet and outlet valves of the boosting liquid intermediate container and the formation water intermediate container, and use a displacement pump to inject the boosting liquid in the boosting liquid intermediate container into the internal annular pressure cavity of the Hele-Shaw autoclave at a lower pressure at a constant pressure, and inject the formation water containing the CO2 concentration indicator in the formation water intermediate container into the Hele-Shaw model at a constant pressure. According to the experimental requirements, the injection pressure is preferably 0.1-1MPa. Until the internal annular pressure cavity of the Hele-Shaw autoclave and the Hele-Shaw model are filled with liquid, and the injection pressure reaches and stabilizes at the lower pressure of 1MPa. Use a back pressure pump to increase the control pressure of the back pressure valve to the lower pressure, open the outlet valve of the bottom model outlet three-way valve, and allow the formation water to fill the back pressure valve.

[0100] (4) Turn on the temperature control system and simultaneously raise the temperature of the Hele-Shaw autoclave and the CO2 intermediate container to 110°C. During the temperature increase, use a displacement pump and a back pressure valve to maintain the annular pressure of the Hele-Shaw autoclave and the pressure inside the Hele-Shaw model at the lower pressure of 1 MPa as described in the previous step.

[0101] (5) After the temperature and pressure have stabilized, gradually increase the displacement pump pressure to increase the annular pressure of the Hele-Shaw autoclave and the pressure inside the Hele-Shaw model simultaneously until the pressure reaches 50 MPa, the pressure required for the diffusion experiment. Close the top outlet valves of the formation water intermediate container and the pressurized liquid intermediate container. Open the bottom inlet valve of the CO2 intermediate container and use the displacement pump in constant pressure mode to pressurize the CO2 in the CO2 intermediate container to the experimental pressure of 50 MPa.

[0102] (6) After the CO2 pressure reaches 50 MPa and stabilizes, open the top outlet valves of the CO2 intermediate container and the pressurized liquid intermediate container. Maintaining the back pressure at 50 MPa, use a displacement pump to inject CO2 into the Hele-Shaw model in a constant flow mode. CO2 fills the thin layer cavity, and at the same time, the formation water in the Hele-Shaw model is discharged from the back pressure valve until the gas-liquid interface coincides with the interface between the thin layer cavity and the porous medium area.

[0103] (7) Maintaining a stable CO2 pressure of 50 MPa, begin collecting images of CO2 convection and diffusion in the porous medium. By monitoring the time-dependent changes in the concentration distribution of CO2 in formation water under porous medium conditions, the gravity-induced unstable permeability and gravity convection diffusion of CO2 in the porous medium are studied.

[0104] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A visualization experimental device for CO2 gravity-instability diffusion under porous media conditions, characterized by: include: Hele-Shaw autoclave, injection and pressure control module, temperature control module and image acquisition and processing module; The injection and pressure control module includes a displacement pump, a formation water intermediate container, a CO2 intermediate container, and a pressurized liquid intermediate container. The displacement pump is connected to the formation water intermediate container, the CO2 intermediate container, and the pressurized liquid intermediate container, respectively. The formation water intermediate container, the CO2 intermediate container, and the pressurized liquid intermediate container are all connected to the Hele-Shaw autoclave, wherein the simulated formation temperature in the Hele-Shaw autoclave reaches 150°C and the simulated formation pressure reaches 100 MPa; The temperature control module includes a first heating and heat preservation sleeve, a second heating and heat preservation sleeve, a first temperature detection unit, a second temperature detection unit and a temperature control unit, and the temperature control unit is connected to the first heating and heat preservation sleeve, the second heating and heat preservation sleeve, the first temperature detection unit and the second temperature detection unit respectively; The image acquisition and processing module includes an image acquisition unit, an LED surface light source and a controller, and the controller is connected to the image acquisition unit; The Hele-Shaw autoclave comprises a front cover, a rear cover, an outer wall of the autoclave and a Hele-Shaw mold, one end of the outer wall of the autoclave is connected to the front cover, the other end is connected to the rear cover, and the inner side wall of the outer wall of the autoclave is connected to the Hele-Shaw mold; The front cover is provided with a first window groove, and the front cover plate fixes the front sapphire window in the window groove of the front cover; the rear cover is provided with a second window groove, and the rear cover plate fixes the rear sapphire window in the window groove of the rear cover; An annular protrusion is provided on the inner side of the outer wall of the autoclave, and the Hele-Shaw model is fixed on the annular protrusion on the outer wall of the autoclave through a model fixing plate; The Hele-Shaw model is a rectangular glass porous medium model, and the Hele-Shaw model is provided with an upper inlet and a lower outlet; The annular protrusion divides the internal annular pressure cavity of the autoclave into a front cavity and a rear cavity. A first through hole is provided at the bottom of the front cavity, which is connected to the bottom annular pressure outlet of the autoclave. A second through hole is provided at the bottom of the rear cavity, which is connected to the top annular pressure outlet of the autoclave. A third through hole is provided on the annular protrusion, which is respectively connected to the upper inlet of the Hele-Shaw model and the top model inlet of the Hele-Shaw autoclave. A fourth through hole is provided on the annular protrusion, which is respectively connected to the lower outlet of the Hele-Shaw model and the bottom model outlet of the Hele-Shaw autoclave.

2. The visualization experimental device for CO2 gravity-induced unstable diffusion under porous media conditions according to claim 1 is characterized in that: The displacement pump is respectively connected to the inlet of the formation water intermediate container, the inlet of the CO2 intermediate container and the inlet of the pressurized liquid intermediate container; the outlet of the formation water intermediate container and the outlet of the CO2 intermediate container are both connected to the top model inlet of the Hele-Shaw autoclave; the outlet of the pressurized liquid intermediate container is connected to the bottom annular pressure inlet of the Hele-Shaw autoclave; the bottom annular pressure inlet of the Hele-Shaw autoclave is also connected to a vacuum pump; the top annular pressure outlet of the Hele-Shaw autoclave is provided with a vent valve; the bottom model outlet of the Hele-Shaw autoclave is respectively connected to a back pressure valve and a vacuum pump.

3. The visualization experimental device for CO2 gravity-instability diffusion under porous media conditions according to claim 1 is characterized in that: The first heating and insulation sleeve is wrapped around the outside of the Hele-Shaw autoclave, and the first temperature detection unit is arranged in the first heating and insulation sleeve; the second heating and insulation sleeve is wrapped around the outside of the CO2 intermediate container, and the second temperature detection unit is arranged in the second heating and insulation sleeve. The temperature control unit receives temperature information of the first temperature detection unit and the second temperature detection unit, and controls the heating conditions of the first heating and insulation or the second heating and insulation according to the temperature information.

4. The visualization experimental device for CO2 gravity-induced unstable diffusion under porous media conditions according to claim 1 is characterized in that: The LED surface light source is located behind the Hele-Shaw autoclave, and the image acquisition unit is located in front of the Hele-Shaw autoclave. It collects the light image of the LED surface light source transmitted on the front side of the Hele-Shaw autoclave and transmits the light image to the controller for the controller to analyze the light image and obtain the relationship between the CO2 concentration distribution and time change.

5. The visualization experimental device for CO2 gravity-induced unstable diffusion under porous media conditions according to claim 1 is characterized in that: A thin layer space is provided inside the Hele-Shaw model, the lower part of the thin layer space is a high permeability seepage channel, the high permeability seepage channel is connected to the lower outlet of the Hele-Shaw model, the upper part of the high permeability seepage channel is connected to the porous medium area, the upper part of the porous medium area is connected to the thin layer cavity, and the thin layer cavity is connected to the upper inlet of the Hele-Shaw model.

6. A method for visualizing the gravitationally unstable diffusion of CO2 in porous media, using the apparatus for visualizing the gravitationally unstable diffusion of CO2 in porous media according to claims 1-5, characterized in that: include: Step 1: Close all valves, open the vacuum valve at the bottom annular pressure inlet of the Hele-Shaw autoclave and the vacuum valve at the bottom mold outlet three-way valve, use a vacuum pump to evacuate the air in the internal annular pressure chamber of the Hele-Shaw autoclave and the Hele-Shaw mold. After reaching the preset vacuum degree, continue the vacuuming for the preset period of time, and then close the vacuum valve; Step 2: Open the bottom annular pressure inlet valve of the Hele-Shaw autoclave, the top model inlet three-way valve of the Hele-Shaw autoclave, the inlet and outlet valves of the boosting liquid intermediate container and the formation water intermediate container, use a displacement pump to constantly inject the boosting liquid in the boosting liquid intermediate container into the internal annular pressure cavity of the Hele-Shaw autoclave at a first preset pressure, and constantly inject the formation water containing the CO2 concentration indicator in the formation water intermediate container into the Hele-Shaw model until the internal annular pressure cavity of the Hele-Shaw autoclave and the Hele-Shaw model are filled with liquid, and the injection pressure reaches and stabilizes at the first preset pressure, use a back pressure pump to increase the control pressure of the back pressure valve to the first preset pressure, open the outlet valve of the bottom model outlet three-way valve of the Hele-Shaw autoclave, and allow the formation water to fill the back pressure valve; Step 3: Turn on the temperature control module and heat the Hele-Shaw autoclave and the CO2 intermediate container to the preset temperature at the same time. During the heating process, use the displacement pump and back pressure valve to keep the annular pressure of the Hele-Shaw autoclave and the pressure inside the Hele-Shaw model stable at the first preset pressure; Step 4: After the temperature and pressure have stabilized, gradually increase the pressure of the displacement pump so that the annular pressure of the Hele-Shaw autoclave and the pressure in the Hele-Shaw model increase synchronously until the pressure reaches the second preset pressure. Close the top outlet valves of the formation water intermediate container and the pressurized liquid intermediate container, open the bottom inlet valve of the CO2 intermediate container, and use the displacement pump in a constant pressure mode to pressurize the CO2 in the CO2 intermediate container to the second preset pressure. Step 5: After the CO2 pressure reaches a stable state, the top outlet valves of the CO2 intermediate container and the pressurized liquid intermediate container are opened, and the back pressure is maintained at the second preset pressure. The CO2 is injected into the Hele-Shaw model using a displacement pump in a constant flow mode. The CO2 fills the thin layer cavity, and the formation water in the Hele-Shaw model is discharged from the back pressure valve until the gas-liquid interface coincides with the interface between the thin layer cavity and the porous medium area. Step 6: Keep the CO2 pressure stable at the second preset pressure, and start collecting images of CO2 convection and diffusion in the porous medium through the image acquisition unit. By monitoring the change of CO2 concentration distribution in formation water under porous medium conditions over time, the gravity unstable permeability and gravity convection diffusion of CO2 in the porous medium are studied.

Images