A CO2 flooding simulation device and method for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures

Abstract

The present invention discloses a CO2 flooding simulation device and method for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures, which relates to the technical field of CCUS oil and gas field development. It solves the problem that dynamic fractures are not considered in related technologies of three-dimensional physical simulation methods. According to the on-site geological knowledge and dynamic development characteristics of ultra-low permeability reservoirs, the present invention designs a CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures. Compared with existing CO2 displacement experiments, the device can realize simulation research of dynamic fractures, and can control the properties, number and opening limit pressure of dynamic fractures; realize simulation development of three-dimensional multi-layer ultra-low permeability oil reservoirs containing dynamic fractures; realize direct verification of dynamic fracture parameters and production dynamic characteristics; support research on the influence of dynamic fracture properties, scale and state on oil displacement efficiency and storage volume during multi-layer joint injection, and combine with CT scanning method to achieve obvious advantages of visualization and verification.

Description

Technical Field

[0001] The present invention relates to the field of CCUS oil and gas fields, and in particular to a CO2 flooding simulation device and method for a multi-layer ultra-low permeability oil and gas reservoir containing dynamic fractures. Background Art

[0002] Ultra-low permeability reservoirs, with their low permeability, strong heterogeneity, and well-developed fractures, differ significantly from other geological reservoirs of CCUS. They exhibit distinct characteristics during CO2 injection and flooding. Research on dynamic fractures is crucial for understanding the flow patterns, distribution characteristics, and storage efficiency of CO2 in formations. These fractures, controlled by the current geostress field, continuously extend toward production wells as injection rates increase and bottomhole pressure rises, until they connect with the pressure fractures in production wells. These newly formed, effective fractures are referred to as dynamic fractures.

[0003] Dynamic fractures affect the design of the coordinated CO2 flooding scheme at the bottom surface: (1) There are almost no fractures in the early stage of gas injection, making it difficult to identify fractures and determine their parameters, which affects the early well network deployment and the formulation of gas injection technology policies. (2) The dynamic changes of fractures cause the migration of the dominant flow layer, increasing the heterogeneity of the oil layer. (3) The presence of dynamic fractures makes the oil layer production more complicated and reduces the degree of production. In short, CO2 has strong mobility, and the presence of dynamic fractures will profoundly affect the flow pattern and distribution characteristics of injected CO2. Understanding and studying the impact of dynamic fractures is an important prerequisite for optimizing engineering parameters and enhancing the effect of CO2 flooding.

[0004] Current research on dynamic fractures primarily involves numerical simulation and physical methods. Numerical simulation methods can investigate dynamic fractures in reservoirs on a three-dimensional scale by building virtual models. For example, a method for characterizing dynamic fractures in low-permeability reservoirs has been developed. However, due to the invisibility of the reservoir, the numerical simulation predictions cannot be directly verified. Therefore, experimental methods are needed to conduct direct and verifiable studies of the characteristics of dynamic fractures. Another example is a physical testing device for dynamic fractures in low-permeability reservoirs during water injection, which enables dynamic fracture genesis research based on one-dimensional core flow. Furthermore, a dynamic fracture identification method and device for a pore channel network model in displacement simulations can study the impact of dynamic fractures on development on a small, two-dimensional plane. However, these studies fail to directly investigate the impact of dynamic fractures on reservoir development on a three-dimensional scale. Furthermore, many technologies related to three-dimensional physical simulation methods, such as a three-dimensional physical simulation experimental device and a method for simulating tight oil reservoir development, as well as a three-dimensional physical simulation system for cyclic injection and production of gas storage, do not consider dynamic fractures. Summary of the Invention

[0005] CCUS carbon dioxide geological storage is a long-term process. Dynamic fractures are a crucial factor that cannot be ignored during gas injection and long-term storage. They have a significant impact on the design of gas injection parameters and pressure control levels. However, there is currently a lack of methods to directly study and verify dynamic fractures at the three-dimensional reservoir scale. This invention designs dynamic fracture simulation components, and designs the distribution direction, number, and activation pressure of dynamic fracture simulation components based on the parameters describing the fractures in oil and gas reservoir engineering. This is combined with the fabrication of an indoor ultra-low permeability three-dimensional physical model device and experimental methods to achieve a directly verifiable study of the influence of dynamic fractures.

[0006] A CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures, the device comprises two cap layers, n reservoir layers, n-1 interlayers, m dynamic fracture simulation devices, n flow control devices, n metering devices, and a flow injection pipeline; the reservoir layer is a physical model containing a dynamic fracture device or not containing a dynamic fracture device, and the interlayer is a physical model without dynamic fractures; an interlayer and a reservoir form a set of rectangular physical models of the same shape, the reservoir layers and interlayers are placed alternately up and down, the reservoir layer of each set of dynamic fracture physical models contains at least one dynamic fracture simulation component to form a dynamic fracture simulation device, and the left and right ends of the reservoir of each set of dynamic fracture simulation devices are respectively The same number of cylindrical holes as the number of dynamic fracture simulation components is drilled. The left end of the reservoir of each group of dynamic fracture simulation devices is connected to the control valve of the corresponding flow control device, and the right end of the reservoir of each group of dynamic fracture simulation devices is connected to the flow metering device. The dynamic fracture simulation components are pre-buried in a cylindrical groove reserved in the reservoir of each dynamic fracture simulation device. After pre-buried, the dynamic fracture simulation device is cast and fixed with a proportioned reservoir cement. Interlayers and reservoirs of the dynamic fracture simulation device are alternately placed to form a physical model group. A cap layer is used to form n layers of CO2 flooding buried simulation devices, which are composed of n reservoirs and n-1 interlayers, and the bottom and top are sealed respectively. Where n ≥ 2, m ≥ 1.

[0007] When the control valve of the flow control device connected to the left end of reservoir I of the first physical model is opened and the bottom control valve is closed, the displacement medium CO2 gas is injected into the fluid injection pipeline at a constant temperature of 20℃~100℃ and a displacement pressure of 2.5MPa~30MPa to carry out oil displacement, and the first metering device is opened to measure the displaced oil volume, outlet pressure and CO2 emission, and record the time and related data;

[0008] When the control valve of the flow control device of the second flow control device connected to the left end of the reservoir II of the second group of physical models is opened and the bottom control valve is closed, the left end control valve of the first group of physical models is closed and the bottom control valve is opened, the displacement medium CO2 gas is injected into the fluid injection pipeline at a constant temperature of 20℃~100℃ and a displacement pressure of 2.5MPa~30MPa, and oil displacement is carried out. The second metering device is opened to measure the displaced oil volume, outlet pressure and CO2 emission, and the time and related data are recorded;

[0009] Similarly, when the nth flow control device is connected to the nth reservoir of the nth group of physical models, the nth meter records the data of the nth group of physical models; when the control pressure of each group of physical models is consistent, the recorded data are the same-pressure driving experiment data of n reservoirs; when the control pressure of each group of physical models is inconsistent, the different pressure driving experiment data of the first, second, ..., n reservoirs are recorded in sequence.

[0010] Preferably, the cover layer is used to encapsulate the bottom and top of the physical simulation model, and the cover layer is made of acrylic board; after the completed cover layer is alternately placed with the reservoir layer and the interlayer, polyvinyl alcohol (PVA) adhesive is used on the outside for gluing and sealing; the reservoir layer is made of cement, gypsum, and quartz sand of 40-80 mesh, which are bonded in a certain mass ratio, wherein the mass ratio of reservoir I is 1:1:2, the mass ratio of reservoir II is 1:1:3, and the mass ratio of reservoir III is 1:1:4;

[0011] The interlayer is made of cement and gypsum in a bonding mass ratio of 1:1;

[0012] The dynamic fracture simulation device is configured to produce artificial high-permeability core columns according to required specifications. The artificial high-permeability core columns have a size range of φ2.5 cm to 10 cm and a length of 8 cm to 50 cm. Quartz sand of 1 mm to 2 mm is used, and the cement, gypsum, and quartz sand bonding mass ratio is 1:1:3. The solidified and cut artificial high-permeability core columns 4 are used to make dynamic fracture simulation components, which are then placed in the dynamic fracture simulation component grooves reserved in the reservoir, and then a mixture of cement and gypsum is poured and fixed. The cement and gypsum mass ratio is 1:1.

[0013] The flow control device is used to control the pressure of n reservoirs, and the pressure adjustment range is 2.5MPa to 30MPa.

[0014] Preferably, each group of physical models injects CO2 into the control valve of the flow control device, and the control valve is provided at the bottom and right side of the flow control device, and is opened in one direction alone when in use;

[0015] The metering device is a reservoir oil output metering device, a pressure metering device, or a CO2 emission metering device.

[0016] Preferably, the dynamic fracture simulation device is assembled by inserting a dynamic fracture simulation component into a dynamic fracture groove reserved in the reservoir; the dynamic fracture simulation component is composed of a filter plate 1, a sealing baffle 2, a spring component 3, an artificial high-permeability core column 4, a cementing and fixing glue 5, and a shell 6;

[0017] The artificial high permeability core column 4 is cylindrical, and a spring component 3 is installed at each end. The spring component 3 is placed into the artificial high permeability core column frame when the artificial high permeability core column is manufactured, and is welded and fixed at the outer connection between the spring component 3 and the artificial high permeability core column (4) at both ends, and the welded assembly is sleeved and fixed on the artificial high permeability core column 4 frame; the other ends of the two spring components 3 are sleeved with the sealing baffle 2 respectively, and are fixed by welded screw caps, and the sealing baffle 2 is located at the support point inside the shell 6; the prepared artificial high permeability core column 4 and the shell 6 are connected and sealed with a bonding adhesive 5; the two filter plates 1 are respectively fixedly assembled at the outer support points at both ends of the shell 6;

[0018] The spring length of the spring component is selected based on the deformation length when the spring is subjected to a preset pressure value.

[0019] Preferably, the working principle of the dynamic fracture simulation device is as follows: the dynamic fracture simulation device is pre-buried in a reserved groove when the reservoir is made. The dynamic fracture simulation reservoir contains dynamic fractures and the buried characteristics. When the pressure inside and outside the dynamic fracture simulation device is balanced, the spring is in its original state. According to Hooke's law, it can be known that:

[0020] F=-kx (1)

[0021]

[0022] In the above formula: k - spring coefficient;

[0023] X——stretched or compressed length, cm;

[0024] P——spring pressure, N / mm;

[0025] F——tensile force or compressive force on the spring, N;

[0026] δ——tensile or compressive amount, mm;

[0027] In its original state, the dynamic fracture simulation component is sealed. When a pressure differential exists across the spring and the pressure is greater than the calculated spring pressure P, the left sealing baffle moves to the right, the compression spring contracts to the right, and the left channel opens. Fluid passes through the artificial high-permeability core, simulating the injection of fluid into the fracture. Under the action of pressure, the right spring stretches to the right, the right sealing baffle moves to the right, and the right channel opens.

[0028] Preferably, the filter plate 1 is used to prevent reservoir cement and fluid impurities from entering the interior of the component; the sealing baffle 2 supports the spring component and moves under the action of pressure difference to simulate the opening and closing of the crack; the spring component 3 simulates the crack opening pressure; the artificial high-permeability core 4 simulates the dynamic fracture equivalent permeability medium; the bonding glue 5 fixes the artificial high-permeability core 4 and the shell and plays a sealing role at the same time; the shell 6 is poured to seal the core component to prevent the fluid from flowing from the edge of the core and prevent the formation of high-permeability channels at the edge.

[0029] The present invention provides a CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures, which solves the problem that relevant technologies of three-dimensional physical simulation methods do not consider dynamic fractures. According to the on-site geological knowledge and dynamic development characteristics of ultra-low permeability reservoirs, the present invention designs a CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures. Compared with existing CO2 displacement experiments, the device can realize simulation research on dynamic fractures, and can control the properties, number and opening limit pressure of dynamic fractures; realize simulation development of three-dimensional multi-layer ultra-low permeability oil reservoirs containing dynamic fractures; realize direct verification of dynamic fracture parameters and production dynamic characteristics; support research on the influence of dynamic fracture properties, scale and state on oil recovery efficiency and storage volume during multi-layer injection, and combine with CT scanning method to achieve obvious advantages of visualization and verification.

[0030] In another aspect, the present invention provides a CO2 flooding simulation method for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures, the method comprising a single reservoir flooding experimental method, a multi-reservoir flooding experimental method at the same pressure, a multi-reservoir flooding experimental method at different pressures, and a multi-reservoir dynamic fracture flooding experimental method.

[0031] The steps of the single reservoir flooding experiment are as follows:

[0032] Step 1: Prepare simulated formation water and crude oil for the experiment;

[0033] Step 2: Place the multi-layer physical device without dynamic cracks into the constant temperature system, connect the fluid injection pipeline, and heat the constant temperature box to 80°C;

[0034] Step 3: Saturate the formation water, sequentially saturating reservoirs I, II, ..., and n in the physical model group. First, close the inlet valves of reservoirs II, ..., and n, and use a constant flow displacement method to allow the saturated formation water to pass through reservoir I alone. The displacement is stopped at 20 PV. Then, saturate reservoirs II, ..., and n in sequence.

[0035] Step 4: Saturate the formation crude oil. To ensure full saturation, saturate reservoirs I, II, ..., and n in sequence. First, close the control valves in reservoirs II, ..., and n. Use a constant flow displacement method to allow saturated formation water to flow solely through reservoir I. Displace the saturated formation water until no more water is produced, and record the water output. Then, saturate reservoirs II, ..., and n in sequence, and record the water output.

[0036] Step 6: The displacement medium CO2 gas is kept at a constant temperature of 80°C and a displacement pressure of 13 MPa and injected into the gas well through the fluid injection pipeline;

[0037] Step 7: Close the bottom control valve of the first flow control device, open the right control valve to allow CO2 gas to enter the reservoir to displace oil, open the first metering device to measure the displaced oil volume, outlet pressure and CO2 emission, and record the time and related data;

[0038] Step 8: Close the right control valve of the first flow control device and open the bottom control valve; close the bottom control valve of the second flow control device and open the right control valve; allow CO2 gas to enter reservoir II to displace oil, open the second metering device, measure the displaced oil volume, outlet pressure, and CO2 emission, and record the time and related data;

[0039] Step 9: Close the right control valve of the first flow control device and open the bottom control valve. Close the right control valve of the second flow control device and open the bottom control valve. Close the bottom control valve of the third flow control device and open the right control valve to allow CO2 gas to enter reservoir III to displace oil. Open the third metering device to measure the displaced oil volume, outlet pressure, and CO2 emissions, and record the time and related data.

[0040] Similarly, close the right control valves of n-1 flow control devices in sequence and open the n-1 bottom control valves; open the right control valve of the nth flow control device to allow CO2 gas to enter reservoir n for oil displacement, open the nth metering device, measure the displaced oil volume, outlet pressure and CO2 emission, and record the time and related data.

[0041] Preferably, the device further includes a multi-reservoir flooding experiment with the same pressure, the steps of which are as follows:

[0042] Step 2-1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment;

[0043] Step 2-2: Place the multi-layer physical device without dynamic fractures in a constant temperature system, connect the fluid injection pipeline, and heat the constant temperature box to 80°C; inject gas into the steam well through the fluid injection pipeline, close the bottom control valve of the third flow control device, open the right control valve, and open the bottom and right control valves of the first and second flow control devices to allow CO2 gas to enter reservoirs I, II, and III. Use pressure regulators at the inlet ends of the first and second flow control devices to control the pressure to the same 13 MPa for oil displacement. Open the first, second, and third metering devices to measure the displaced oil volume, outlet pressure, and CO2 emission, and record the relevant data separately.

[0044] Preferably, the multi-reservoir different pressure flooding experimental method comprises the following steps:

[0045] Step 3-1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment;

[0046] Step 3-2: Place the multi-layer physical device without dynamic fractures in the constant temperature system, connect the fluid injection pipeline, heat the constant temperature box to 80°C; inject gas into the steam well through the fluid injection pipeline, close the bottom control valve of the third flow control device, open the right control valve, open the bottom and right control valves of the first and second flow control devices, and allow CO2 gas to enter reservoirs I, II, and III. Use pressure regulators at the inlet ends of the first and second flow control devices to control the pressure from reservoir I to reservoir III to 10MPa, 13MPa, and 16MPa, respectively, to carry out oil displacement. Open the first, second, and third metering devices to measure the amount of oil displaced, the outlet pressure, and the amount of CO2 discharged, and record the relevant data respectively.

[0047] Preferably, in one embodiment, the multi-reservoir dynamic fracture flooding experimental method comprises the following steps:

[0048] Step 4-1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment;

[0049] Step 4-2: Place the multi-layer physical device of dynamic fractures in a constant temperature system, connect the fluid injection pipeline, and heat the constant temperature box to 80°C. Inject gas into the steam well through the fluid injection pipeline. Close the bottom control valve of the third flow control device and open the right control valve. Open the bottom and right control valves of the first and second flow control devices to allow CO2 gas to enter reservoirs I, II, and III. Use a pressure regulator at the inlet of the flow control device to control the pressure to the same 13 MPa. Under this pressure, all fracture channels are opened and oil displacement is carried out. Open the first, second, and third metering devices to measure the amount of oil displaced, the outlet pressure, and the CO2 emission, and record the relevant data.

[0050] The present invention provides a CO2 flooding simulation device and method for a multi-layer ultra-low permeability oil and gas reservoir containing dynamic fractures, which solves the problem that the relevant technologies of the three-dimensional physical simulation method do not consider dynamic fractures. The present invention designs a CO2 flooding simulation device for a multi-layer ultra-low permeability oil and gas reservoir containing dynamic fractures based on the on-site geological knowledge and dynamic development characteristics of the ultra-low permeability reservoir. Compared with the existing CO2 displacement experiment, the device can realize the simulation research of dynamic fractures, and can control the properties, number and opening limit pressure of dynamic fractures; realize the simulation development of three-dimensional multi-layer ultra-low permeability oil reservoirs containing dynamic fractures; realize the direct verification of dynamic fracture parameters and production dynamic characteristics; support the study of the influence of dynamic fracture properties, scale and state on oil recovery efficiency and storage volume during multi-layer injection, and combine with the CT scanning method to achieve the obvious advantages of visualization and verification. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A schematic structural diagram of an embodiment of a CO2 flooding simulation device for a multi-layer ultra-low permeability oil and gas reservoir containing dynamic fractures;

[0052] Figure 2a-1 A dynamic fracture simulation component front view and left view of a CO2 flooding simulation device for a multi-layer ultra-low permeability oil and gas reservoir with dynamic fractures;

[0053] Figure 2a-2 A dynamic fracture simulation device for CO2 flooding in a multi-layer ultra-low permeability oil and gas reservoir with dynamic fractures. The shape diagram of the baffle and spring components of the dynamic fracture simulation component.

[0054] Figure 2a-3 A three-dimensional diagram of the spring component of the dynamic fracture simulation component of a CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs with dynamic fractures

[0055] Figure 2b A CO2 flooding simulation device for a multi-layer ultra-low permeability oil and gas reservoir containing dynamic fractures, schematic diagram of dynamic fractures and reservoir containing dynamic fractures;

[0056] Figure 3 A single-layer oil production efficiency diagram of a CO2 flooding simulation device for a multi-layer ultra-low permeability oil and gas reservoir with dynamic fractures;

[0057] Figure 4 A CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs with dynamic fractures shows the oil production efficiency of three layers with the same pressure and simultaneous injection and production;

[0058] Figure 5 A CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs with dynamic fractures shows the oil production efficiency of three layers with different pressures.

[0059] Figure 6 A CO2 flooding simulation device for a multi-layer ultra-low permeability oil and gas reservoir with dynamic fractures shows the injection and production efficiency diagram of three layers with the same pressure (including dynamic fractures);

[0060] Figure 7 A CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs with dynamic fractures, CO2 storage mass ratio diagram for different reservoir combinations and injection-production methods;

[0061] Figure 8 Schematic diagram of the structure of a CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs with dynamic fractures. DETAILED DESCRIPTION

[0062] Exemplary embodiments will be described in detail herein, examples of which are illustrated in the accompanying drawings. In the following description, when referring to the drawings, like numbers in different figures represent like or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all possible embodiments consistent with the present invention. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present invention, as detailed in the appended claims.

[0063] On the one hand, the present invention provides a CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures, such as Figure 8 As shown, the device includes 2 cap layers, n reservoir layers, n-1 interlayers, m dynamic fracture simulation devices, n flow control devices, n metering devices, and flow injection pipelines; the reservoir layer is a physical model containing or not containing a dynamic fracture device, and the interlayer is a physical model without dynamic fractures; an interlayer and a reservoir layer form a set of rectangular physical models of the same shape, and the reservoir layers and interlayers are placed alternately up and down. The reservoir layer of each group of dynamic fracture physical models contains at least one dynamic fracture simulation component to form a dynamic fracture simulation device, and the left and right ends of the reservoir layer of each group of dynamic fracture simulation devices are respectively drilled with the dynamic fracture simulation component. The same number of cylindrical holes are provided. The left end of the reservoir of each group of dynamic fracture simulation devices is connected to the control valve of the corresponding flow control device, and the right end of the reservoir of each group of dynamic fracture simulation devices is connected to the flow metering device. The dynamic fracture simulation component is pre-buried in a cylindrical groove reserved in the reservoir of each dynamic fracture simulation device. After pre-buried, the dynamic fracture simulation device is cast and fixed with a proportioned reservoir cement. Interlayers and reservoirs of the dynamic fracture simulation device are alternately placed to form a physical model group. The n reservoirs and n-1 interlayers are used as a cap layer to form n layers of CO2 flooding buried simulation devices, respectively sealing the bottom and top. Wherein, n ≥ 2, m ≥ 1.

[0064] When the control valve of the flow control device connected to the left end of reservoir I of the first physical model is opened and the bottom control valve is closed, the displacement medium CO2 gas is injected into the fluid injection pipeline at a constant temperature of 20℃~100℃ and a displacement pressure of 2.5MPa~30MPa to carry out oil displacement, and the first metering device is opened to measure the displaced oil volume, outlet pressure and CO2 emission, and record the time and related data;

[0065] When the control valve of the flow control device of the second flow control device connected to the left end of the reservoir II of the second group of physical models is opened and the bottom control valve is closed, the left end control valve of the first group of physical models is closed and the bottom control valve is opened, the displacement medium CO2 gas is injected into the fluid injection pipeline at a constant temperature of 20℃~100℃ and a displacement pressure of 2.5MPa~30MPa, and oil displacement is carried out. The second metering device is opened to measure the displaced oil volume, outlet pressure and CO2 emission, and the time and related data are recorded;

[0066] Similarly, when the nth flow control device is connected to the nth reservoir of the nth group of physical models, the nth meter records the data of the nth group of physical models; when the control pressure of each group of physical models is consistent, the recorded data are the same-pressure driving experiment data of n reservoirs; when the control pressure of each group of physical models is inconsistent, the different pressure driving experiment data of the first, second, ..., n reservoirs are recorded in sequence.

[0067] In one embodiment, the cover layer is used to encapsulate the bottom and top of the physical simulation model, and the cover layer is made of acrylic board; after the finished cover layer is alternately placed with the reservoir layer and the interlayer, polyvinyl alcohol (PVA) adhesive is used on the outside to glue and seal;

[0068] The reservoir is formed by cement, gypsum, and quartz sand of 40-80 meshes, which are cemented in a certain mass ratio, wherein the mass ratio of reservoir I is 1:1:2, the mass ratio of reservoir II is 1:1:3, and the mass ratio of reservoir III is 1:1:4;

[0069] The interlayer is made of cement and gypsum in a bonding mass ratio of 1:1;

[0070] The dynamic fracture simulation device is configured to produce artificial high-permeability core columns according to required specifications. The artificial high-permeability core columns have a size range of φ2.5 cm to 10 cm and a length of 8 cm to 50 cm. Quartz sand of 1 mm to 2 mm is used, and the cement, gypsum, and quartz sand bonding mass ratio is 1:1:3. The solidified and cut artificial high-permeability core columns 4 are used to make dynamic fracture simulation components, which are then placed in the dynamic fracture simulation component grooves reserved in the reservoir, and then a mixture of cement and gypsum is poured and fixed. The cement and gypsum mass ratio is 1:1.

[0071] Among them, the flow control device is used to control the pressure of n reservoirs, and the pressure adjustment range is 2.5MPa to 30MPa.

[0072] In one embodiment, each physical model injects CO2 into the control valve of the flow control device, and the control valve is provided at the bottom and right side of the flow control device, and is opened in one direction alone when in use;

[0073] The metering device is a reservoir oil output metering device, a pressure metering device, or a CO2 emission metering device.

[0074] In one embodiment, a dynamic fracture simulation device is assembled by inserting a dynamic fracture simulation component into a dynamic fracture groove reserved in a reservoir; the dynamic fracture simulation component comprises a filter plate 1, a sealing baffle 2, a spring component 3, an artificial high-permeability core column 4, a cementing adhesive 5, and a housing 6;

[0075] The artificial high permeability core column 4 is cylindrical, and a spring component 3 is installed at each end. The spring component 3 is placed into the artificial high permeability core column frame when the artificial high permeability core column is manufactured, and is welded and fixed at the outer connection between the spring component 3 and the artificial high permeability core column (4) at both ends, and the welded assembly is sleeved and fixed on the artificial high permeability core column 4 frame; the other ends of the two spring components 3 are sleeved with the sealing baffle 2 respectively, and are fixed by welded screw caps, and the sealing baffle 2 is located at the support point inside the shell 6; the prepared artificial high permeability core column 4 and the shell 6 are connected and sealed with a bonding adhesive 5; the two filter plates 1 are respectively fixedly assembled at the outer support points at both ends of the shell 6;

[0076] The spring length of the spring component is selected based on the deformation length when the spring is subjected to a preset pressure value.

[0077] It should be noted that the high permeability of artificial high permeability core columns refers to high permeability. In the oil industry, high permeability generally refers to more than 1000 millidarcy, 50-1000 millidarcy is medium permeability, and less than 50 millidarcy is low permeability.

[0078] In one embodiment, the working principle of the dynamic fracture simulation device is as follows: the dynamic fracture simulation device is pre-buried in a reserved groove during reservoir formation. The dynamic fracture simulation reservoir contains dynamic fractures and has the characteristics of burying. When the pressure inside and outside the dynamic fracture simulation device is balanced, the spring is in its original state. According to Hooke's law,

[0079] F=-kx (1)

[0080]

[0081] In the above formula: k - spring coefficient;

[0082] X——stretched or compressed length, cm;

[0083] P——spring pressure, N / mm;

[0084] F——tensile force or compressive force on the spring, N;

[0085] δ——tensile or compressive amount, mm;

[0086] In its original state, the dynamic fracture simulation component is sealed. When a pressure differential exists across the spring and the pressure is greater than the calculated spring pressure P, the left sealing baffle moves to the right, the compression spring contracts to the right, and the left channel opens. Fluid passes through the artificial high-permeability core, simulating the injection of fluid into the fracture. Under the action of pressure, the right spring stretches to the right, the right sealing baffle moves to the right, and the right channel opens.

[0087] In one embodiment, the filter plate 1 is used to prevent reservoir cement and fluid impurities from entering the interior of the component; the sealing baffle 2 supports the spring component and moves under the action of pressure difference to simulate the opening and closing of the crack; the spring component 3 simulates the crack opening pressure; the artificial high-permeability core 4 simulates the dynamic fracture equivalent permeability medium; the bonding glue 5 fixes the artificial high-permeability core 4 and the shell and also plays a sealing role; after the shell 6 is poured, it seals the core component to prevent the fluid from flowing from the edge of the core and prevent the formation of high-permeability channels at the edge.

[0088] The present invention provides a CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures, which solves the problem that relevant technologies of three-dimensional physical simulation methods do not consider dynamic fractures. According to the on-site geological knowledge and dynamic development characteristics of ultra-low permeability reservoirs, the present invention designs a CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures. Compared with existing CO2 displacement experiments, the device can realize simulation research on dynamic fractures, and can control the properties, number and opening limit pressure of dynamic fractures; realize simulation development of three-dimensional multi-layer ultra-low permeability oil reservoirs containing dynamic fractures; realize direct verification of dynamic fracture parameters and production dynamic characteristics; support research on the influence of dynamic fracture properties, scale and state on oil recovery efficiency and storage volume during multi-layer injection, and combine with CT scanning method to achieve obvious advantages of visualization and verification.

[0089] Another aspect of the present invention provides a method for simulating CO2 flooding in multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures, the method comprising a single reservoir flooding experimental method, a multi-reservoir flooding experimental method at the same pressure, a multi-reservoir flooding experimental method at different pressures, and a multi-reservoir dynamic fracture flooding experimental method.

[0090] The steps of the single reservoir flooding experiment are as follows:

[0091] Step 1: Prepare simulated formation water and crude oil for the experiment;

[0092] Step 2: Place the multi-layer physical device without dynamic cracks into the constant temperature system, connect the fluid injection pipeline, and heat the constant temperature box to 80°C;

[0093] Step 3: Saturate the formation water, sequentially saturating reservoirs I, II, ..., and n in the physical model group. First, close the inlet valves of reservoirs II, ..., and n, and use a constant flow displacement method to allow the saturated formation water to pass through reservoir I alone. The displacement is stopped at 20 PV. Then, saturate reservoirs II, ..., and n in sequence.

[0094] Step 4: Saturate the formation crude oil. To ensure full saturation, saturate reservoirs I, II, ..., and n in sequence. First, close the control valves in reservoirs II, ..., and n. Use a constant flow displacement method to allow saturated formation water to flow solely through reservoir I. Displace the saturated formation water until no more water is produced, and record the water output. Then, saturate reservoirs II, ..., and n in sequence, and record the water output.

[0095] Step 6: The displacement medium CO2 gas is kept at a constant temperature of 80°C and a displacement pressure of 13 MPa and injected into the gas well through the fluid injection pipeline;

[0096] Step 7: Close the bottom control valve of the first flow control device, open the right control valve to allow CO2 gas to enter the reservoir to displace oil, open the first metering device to measure the displaced oil volume, outlet pressure and CO2 emission, and record the time and related data;

[0097] Step 8: Close the right control valve of the first flow control device and open the bottom control valve; close the bottom control valve of the second flow control device and open the right control valve; allow CO2 gas to enter reservoir II to displace oil, open the second metering device, measure the displaced oil volume, outlet pressure, and CO2 emission, and record the time and related data;

[0098] Step 9: Close the right control valve of the first flow control device and open the bottom control valve. Close the right control valve of the second flow control device and open the bottom control valve. Close the bottom control valve of the third flow control device and open the right control valve to allow CO2 gas to enter reservoir III to displace oil. Open the third metering device to measure the displaced oil volume, outlet pressure, and CO2 emissions, and record the time and related data.

[0099] Similarly, close the right control valves of n-1 flow control devices in sequence and open the n-1 bottom control valves; open the right control valve of the nth flow control device to allow CO2 gas to enter reservoir n for oil displacement, open the nth metering device, measure the displaced oil volume, outlet pressure and CO2 emission, and record the time and related data.

[0100] In one embodiment, the apparatus further includes a multi-reservoir flooding experiment with the same pressure, the steps of which are as follows:

[0101] Step 2-1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment;

[0102] Step 2-2: Place the multi-layer physical device without dynamic fractures in a constant temperature system, connect the fluid injection pipeline, and heat the constant temperature box to 80°C; inject gas into the steam well through the fluid injection pipeline, close the bottom control valve of the third flow control device, open the right control valve, and open the bottom and right control valves of the first and second flow control devices to allow CO2 gas to enter reservoirs I, II, and III. Use pressure regulators at the inlet ends of the first and second flow control devices to control the pressure to the same 13 MPa for oil displacement. Open the first, second, and third metering devices to measure the displaced oil volume, outlet pressure, and CO2 emission, and record the relevant data separately.

[0103] In one embodiment, the multi-reservoir different pressure flooding experimental method comprises the following steps:

[0104] Step 3-1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment;

[0105] Step 3-2: Place the multi-layer physical device without dynamic fractures in the constant temperature system, connect the fluid injection pipeline, heat the constant temperature box to 80°C; inject gas into the steam well through the fluid injection pipeline, close the bottom control valve of the third flow control device, open the right control valve, open the bottom and right control valves of the first and second flow control devices, and allow CO2 gas to enter reservoirs I, II, and III. Use pressure regulators at the inlet ends of the first and second flow control devices to control the pressure from reservoir I to reservoir III to 10MPa, 13MPa, and 16MPa, respectively, to carry out oil displacement. Open the first, second, and third metering devices to measure the amount of oil displaced, the outlet pressure, and the amount of CO2 discharged, and record the relevant data respectively.

[0106] In one embodiment, the multi-reservoir dynamic fracture flooding experimental method comprises the following steps:

[0107] Step 4-1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment;

[0108] Step 4-2: Place the multi-layer physical device of dynamic fractures in a constant temperature system, connect the fluid injection pipeline, and heat the constant temperature box to 80°C. Inject gas into the steam well through the fluid injection pipeline. Close the bottom control valve of the third flow control device and open the right control valve. Open the bottom and right control valves of the first and second flow control devices to allow CO2 gas to enter reservoirs I, II, and III. Use a pressure regulator at the inlet of the flow control device to control the pressure to the same 13 MPa. Under this pressure, all fracture channels are opened and oil displacement is carried out. Open the first, second, and third metering devices to measure the amount of oil displaced, the outlet pressure, and the CO2 emission, and record the relevant data.

[0109] An embodiment of the present invention provides a CO2 flooding simulation method for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures, which solves the problem that relevant technologies of three-dimensional physical simulation methods do not consider dynamic fractures. According to the on-site geological understanding and dynamic development characteristics of ultra-low permeability reservoirs, the present invention designs a CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures. Compared with existing CO2 displacement experiments, it can realize the simulation study of dynamic fractures, and can realize the control of the properties, number and opening limit pressure of dynamic fractures; realize the simulation development of three-dimensional multi-layer ultra-low permeability oil reservoirs containing dynamic fractures; realize direct verification of dynamic fracture parameters and production dynamic characteristics; support the study of the influence of dynamic fracture properties, scale and state on oil recovery efficiency and storage volume during multi-layer injection, and combine with CT scanning method to achieve obvious advantages of visualization and verification.

[0110] Example 1

[0111] This paper designs a CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures. Based on CO2 flooding, this device simulates the recovery rate and storage volume of multi-layer (3-layer, 4-layer, 5-layer) oil and gas reservoirs under dynamic fracture conditions. This example uses the simulation experiment of three reservoirs as an example, and the details are as follows:

[0112] The dimensions of the model produced in the embodiment are 50*50*10 cm in length (L)*width (D)*height (H). Two sets of physical models are used in the embodiment, one set without dynamic cracks and one set with dynamic cracks.

[0113] The multi-layer CO2 flooding simulation device designed by the present invention is as follows: Figure 1 As shown, it mainly includes: 2 cap layers, 3 reservoir layers, 2 interlayers, 3 dynamic fracture devices, 3 flow control devices and 3 flow meter devices;

[0114] 1. Separately make cap layer, reservoir layer and interlayer to form a multi-reservoir physical model.

[0115] The reservoir is made of cement, gypsum, and quartz sand (40-80 mesh) in a certain mass ratio, with the mass ratio of reservoir I being 1:1:2, the mass ratio of reservoir II being 1:1:3, and the mass ratio of reservoir III being 1:1:4. Three cylindrical grooves of φ5×10cm are reserved, which can also be adjusted to other sizes as needed, ranging from φ5 to 10cm and 10 to 50cm in length. The size is 1-2cm larger than the entire dynamic fracture simulation device, so that there is space left for pouring after the subsequent device is placed. At the same time, three corresponding holes are drilled at both ends of the reservoir, with a hole diameter of 3 to 10cm. The holes are drilled to facilitate the placement of the flow metering device and the circulation control device. The cover layer is made of acrylic board, and the interlayer is made of cement and gypsum (cementation mass ratio of 1:1).

[0116] 2. Dynamic crack simulation device

[0117] The artificial high-permeability core column 4 is made of quartz sand (1-2 mm) with a cement, gypsum, and quartz sand bonding ratio of 1:1:3. After solidification and cutting, the artificial high-permeability core column is used to create a dynamic fracture simulation component, which is then installed into the dynamic fracture groove reserved in the reservoir. It is then cast and secured with a cement-gypsum mixture in a 1:1 cement-gypsum ratio. A spring with a 5 mm deformation requires 5 MPa of pressure, meaning the opening pressure is 5 MPa.

[0118] The dynamic crack simulation component shell 6 is a cylindrical hollow cylinder that can be disassembled into two identical half-fan-shaped cylinders. After being cured and cut into the required specifications, the artificial high-permeability core column 4 is installed in the dynamic crack simulation component. First, the artificial high-permeability core column 4 is coated with adhesive fixing glue around it and placed in the reserved position in one half of the fan-shaped cylinder of the shell. After the fixing glue is firmly adhered, the outer connection between the spring component 3 and the artificial high-permeability core column 4 is welded and fixed, and the sealing plate 2 is placed. The sealing plate 2 has a connection with the spring component 3 for fixing with a nut. When installing, just tighten the nut at the connection, and the sealing plate 2 is installed. After that, it should just be stuck in the inner supporting points at both ends of the shell 6 to form a sealed space inside. Finally, the filter plate 1 is installed on the corresponding outer supporting points of the shell 6, and the other half of the shell is merged with the part that has been completed. The other half of the artificial high-permeability core column 4 that is not coated with the bonding fixing glue is coated with the fixing glue, and the contact parts of the two half-fan-shaped columns are glued together with the fixing glue. After it is firmly glued, the dynamic fracture simulation component is assembled and placed in the dynamic fracture groove reserved in the reservoir. It is then cast and fixed with a mixture of cement and gypsum to complete the combination between the dynamic fracture simulation component and the reservoir to form a dynamic fracture simulation device.

[0119] 3. Reservoir settings with dynamic fractures

[0120] Three cylindrical grooves (with a size of φ5×10 cm) were reserved on the reservoir, and the dynamic fracture simulation device was installed. After the dynamic fracture simulation device was placed, cement with a reservoir proportion was used for pouring.

[0121] 4. Physical model assembly

[0122] After the completed cover layer, reservoir layer and interlayer are placed alternately, high-strength solidifying glue is used on the outside to glue and seal them.

[0123] 5. Dynamic crack simulation components such as Figure 2a-1 、 Figure 2a-2 、 Figure 2a-3 The structure assembly relationship is described as shown

[0124] The dynamic fracture simulation component consists of a filter plate 1, a sealing baffle 2, a spring component 3, an artificial high-permeability core 4, a cementing and fixing glue 5, and an outer shell 6. The two ends of the cylindrical artificial high-permeability core 4 are respectively equipped with n spring components 4. After the prepared core is placed in the outer shell, the spring components are fixedly embedded in the two ends of the core through a pre-welded combination sleeve of the spring components, and the combination sleeve is welded to the outer shell to fix it. The other ends of the two spring components are sleeved with the sealing baffle 2 and fixed by a welded screw cap. The prepared artificial high-permeability core 4 and the outer shell 6 are connected and sealed with a cementing and fixing glue 5. The two filter plates 1 are respectively assembled and fixed to the two ends of the dynamic fracture simulation component.

[0125] Table 1 Basic data of artificial high permeability core

[0126]

[0127] The specific steps of the simulation method are as follows:

[0128] 1. Single reservoir flooding experiment:

[0129] Step 1: Prepare simulated formation water and crude oil for the experiment;

[0130] Step 2: Place the multi-layer physical device without dynamic cracks into the constant temperature system, connect the pipelines, and heat the constant temperature box to 80°C;

[0131] Step 3: Saturate the formation water. To ensure full saturation, saturate reservoir I, reservoir II, and reservoir III in sequence.

[0132] First, close the inlet valves of reservoir II and reservoir III, adopt constant flow displacement mode, and allow saturated formation water to pass through reservoir I alone, and stop at 20PV. Then saturate reservoir II and reservoir III in turn.

[0133] Step 4: Saturate the formation crude oil. To ensure full saturation, saturate Reservoir I, Reservoir II, and Reservoir III in sequence. First, close the inlet valves to Reservoir II and Reservoir III. Use a constant flow displacement method to allow saturated formation water to flow solely through Reservoir I. Displace until no more water is produced, and record the water output. Then, saturate Reservoir II and Reservoir III in sequence, and record the water output.

[0134] Step 6: Keep the displacement medium CO2 gas at a constant temperature of 80℃ and a displacement pressure of 13MPa. Figure 1 The fluid is injected into the pipeline gas injection well;

[0135] Step 7: Close the bottom control valve at the first flow control device, open the right control valve, allow CO2 gas to enter reservoir I to displace oil, open the first metering device, measure the displaced oil volume, outlet pressure, and CO2 emission, and record the time and related data;

[0136] Step 8: Close the right control valve of the first flow control device and open the bottom control valve. Close the bottom control valve of the second flow control device and open the right control valve. Allow CO2 gas to enter reservoir II to displace oil. Open the second metering device to measure the displaced oil volume, outlet pressure, and CO2 discharge, and record the time and related data.

[0137] Step 9: Close the right control valve of the first flow control device and open the bottom control valve. Close the right control valve of the second flow control device and open the bottom control valve. Close the bottom control valve of the third flow control device and open the right control valve to allow CO2 gas to enter reservoir III to drive oil. Open the third metering device to measure the amount of oil displaced, outlet pressure and CO2 discharge, and record the time and related data. The experimental data and Figure 3 The single reservoir oil production efficiency diagram is shown as follows:

[0138] Table 2 Single reservoir oil production efficiency

[0139] Time (min) Reservoir I oil production efficiency Reservoir II oil production efficiency Reservoir III oil production efficiency 0 0 0 0 50 7.21 6.77 6.42 100 13.52 12.58 11.95 150 21.11 19.74 17.72 200 30.34 28.35 26.47 250 39.65 37.62 34.52 300 45.56 42.11 38.92 350 52.34 47.74 43.34 400 56.15 51.32 44.25 450 58.37 51.67 44.47 500 59.95 51.92 44.62

[0140] 2. Multi-reservoir flooding experiment with the same pressure:

[0141] Step 1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment;

[0142] Step 2: Gas Passage Figure 1The fluid was injected into the steam injection well of the pipeline. The bottom control valve of the third flow control device was closed and the right control valve was opened. The bottom and right control valves of the first and second flow control devices were opened to allow CO2 gas to enter reservoirs I, II and III. A pressure regulator was used at the inlet end to control the pressure to be the same at 13 MPa to drive oil. The first, second and third metering devices were opened to measure the amount of oil displaced, the outlet pressure and the amount of CO2 discharged, and record the relevant data. The experimental data and Figure 4 The oil production efficiency of three layers injected and produced simultaneously at the same pressure is shown.

[0143] Table 3 Oil production efficiency of three layers with the same pressure and simultaneous injection and production

[0144] min Reservoir I oil production efficiency Reservoir II oil production efficiency Reservoir III oil production efficiency 0 0 0 0 50 7.21 6.67 6.11 100 15.23 12.15 11.14 150 23.29 19.82 18.65 200 35.35 30.95 28.37 250 45.46 40.01 37.76 300 51.56 44.85 42.34 350 57.79 52.54 47.87 400 62.84 56.32 50.28 450 65.56 57.42 51.85 500 66.67 58.44 52.34

[0145] 3. Multi-reservoir flooding experiment with different pressures:

[0146] Step 1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment;

[0147] Step 2: Gas Passage Figure 1 The fluid was injected into the steam injection well of the pipeline. The bottom control valve of the third flow control device was closed and the right control valve was opened. The bottom and right control valves of the first and second flow control devices were opened to allow CO2 gas to enter reservoirs I, II and III. A pressure regulator was used at the inlet end to control the pressure from reservoir I to reservoir III to 10 MPa, 13 MPa and 16 MPa, respectively, to carry out oil displacement. The first, second and third metering devices were opened to measure the amount of oil displaced, the outlet pressure and the amount of CO2 discharged, and the relevant data were recorded. The experimental data and Figure 5 The oil production efficiency curve of three layers with different pressures is shown in the figure.

[0148] Table 4 Oil production efficiency of three layers with different pressures

[0149] min Reservoir I Reservoir II Reservoir III 0 0 0 0 50 7.11 6.61 6.10 100 15.54 14.12 13.83 150 23.65 21.82 21.0 200 35.55 32.91 32.34 250 45.45 43.22 41.77 300 51.13 48.84 47.38 350 57.22 53.32 51.82 400 62.14 58.54 56.21 450 64.57 60.03 57.98 500 65.81 60.28 58.31

[0150] 4. Multi-reservoir dynamic fracture flooding experiment:

[0151] Step 1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment III;

[0152] Step 2: Gas Passage Figure 1In the steam injection well of the liquid injection pipeline, close the third bottom control valve, open the right control valve, open the first, second bottom and right control valves, and allow CO2 gas to enter reservoir I, reservoir II, and reservoir III. The three reservoirs all contain dynamic fracture simulation devices. A pressure regulator is used at the inlet end, and the control pressure is the same, all 13 MPa. Under this pressure, all fracture channels are opened to carry out oil displacement. The first, second and third metering devices are opened to measure the displaced oil volume, outlet pressure and CO2 emission, and record the relevant data, as shown in Table 5. Figure 6 The injection and production efficiency curve of three layers with the same pressure (including dynamic fractures) is shown in the figure.

[0153] Table 5 Injection-production efficiency of three layers with the same pressure (including dynamic fractures)

[0154] min Reservoir I Reservoir II Reservoir III 0 0 0 0 50 7.21 6.63 6.21 100 16.32 12.52 11.32 150 25.55 21.81 18.22 200 33.43 30.01 28.44 250 41.0 38.60 37.86 300 47.24 43.85 42.46 350 54.54 50.56 47.88 400 57.56 53.54 50.21 450 58.84 54.44 51.45 500 59.64 54.43 51.35

[0155] 5. Comparison of CO2 storage mass ratios in different flooding experiments

[0156] Through pressure flooding experiments with four different reservoir combination injection and production methods, namely single reservoir injection and production, multi-reservoir injection and production at the same pressure, multi-reservoir injection and production at different pressures, and multi-reservoir injection and production at the same pressure (dynamic fracture), the CO2 injection rate at the inlet and the CO2 discharge rate at the outlet of each reservoir were recorded, the experimental data were recorded, and the difference between the two was calculated to obtain the CO2 storage mass ratio of each reservoir under the four different injection methods, as shown in Table 6. Figure 7 The CO2 storage mass ratio of different reservoir combination injection and production methods is shown in the figure.

[0157] Table 6 CO2 storage mass ratio in pressure flooding experiments using injection-production methods for different reservoir combinations

[0158]

[0159] An embodiment of the present invention provides a CO2 flooding simulation device for a multi-layer ultra-low permeability oil and gas reservoir containing dynamic fractures, which solves the problem that the relevant technologies of the three-dimensional physical simulation method do not consider dynamic fractures. The present invention designs a CO2 flooding simulation device for a multi-layer ultra-low permeability oil and gas reservoir containing dynamic fractures based on the on-site geological understanding and dynamic development characteristics of the ultra-low permeability reservoir. Compared with the existing CO2 displacement experiment, the device can realize the simulation study of dynamic fractures, and can control the properties, quantity and opening limit pressure of dynamic fractures; realize the simulation development of three-dimensional multi-layer ultra-low permeability oil reservoirs containing dynamic fractures; realize direct verification of dynamic fracture parameters and production dynamic characteristics; simulate the actual situation of CO2 injection and production at different reservoir pressures, and effectively improve the understanding of the actual recovery rate of multi-layer ultra-low permeability oil and gas reservoirs under CO2 flooding; simulate the actual situation of CO2 storage under different pressure combinations of multiple reservoirs, and play a quantitative role in studying the CO2 storage effect and storage mass ratio of multi-layer ultra-low permeability oil and gas reservoirs; support the study of the influence of dynamic fracture properties, scale and state on oil displacement efficiency and storage volume during multi-layer injection, and combine with CT scanning method to achieve obvious advantages of visualization and verification.

Claims

1. A CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures, characterized in that: The device includes two cap layers, n reservoir layers, n-1 interlayers, m dynamic fracture simulation devices, n flow control devices, n metering devices, and flow injection pipelines; the reservoir layer is a physical model containing a dynamic fracture device or not containing a dynamic fracture device, and the interlayer is a physical model without dynamic fractures; an interlayer and a reservoir layer form a group of rectangular physical models of the same shape, and the reservoir layers and interlayers are placed alternately up and down. The reservoir layer of each group of dynamic fracture physical models contains at least one dynamic fracture simulation component to form a dynamic fracture simulation device, and the left and right ends of the reservoir layer of each group of dynamic fracture simulation devices are respectively drilled with a dynamic fracture simulation component. The left end of the reservoir of each dynamic fracture simulation device is connected to the control valve of the corresponding flow control device, and the right end of the reservoir of each dynamic fracture simulation device is connected to the flow metering device; wherein, the dynamic fracture simulation component is pre-buried in a cylindrical groove reserved in the reservoir of each dynamic fracture simulation device, and after pre-buried, the dynamic fracture simulation device is cast and fixed with a proportioned reservoir cement, and the interlayer and the reservoir of the dynamic fracture simulation device are alternately placed to form a physical model group, and the cap layer is used to form n layers of CO2 flooding buried simulation devices with n reservoirs and n-1 interlayers to seal the bottom and top respectively; wherein n ≥ 2, m ≥ 1; When the control valve of the flow control device connected to the left end of reservoir I of the first physical model is opened and the bottom control valve is closed, the displacement medium CO2 gas is injected into the fluid injection pipeline at a constant temperature of 20℃~100℃ and a displacement pressure of 2.5MPa~30MPa to carry out oil displacement, and the first metering device is opened to measure the displaced oil volume, outlet pressure and CO2 emission, and record the time and related data; When the control valve of the flow control device of the second flow control device connected to the left end of the reservoir II of the second group of physical models is opened and the bottom control valve is closed, the left end control valve of the first group of physical models is closed and the bottom control valve is opened, the displacement medium CO2 gas is injected into the fluid injection pipeline at a constant temperature of 20℃~100℃ and a displacement pressure of 2.5MPa~30MPa, and oil displacement is carried out. The second metering device is opened to measure the displaced oil volume, outlet pressure and CO2 emission, and the time and related data are recorded; Similarly, when the nth flow control device is connected to the nth reservoir of the nth group of physical models, the nth meter records the data of the nth group of physical models; when the control pressure of each group of physical models is consistent, the recorded data are the same-pressure driving experiment data of n reservoirs; when the control pressure of each group of physical models is inconsistent, the different pressure driving experiment data of the first, second, ..., n reservoirs are recorded in sequence.

2. The CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures according to claim 1 is characterized in that: The cover layer is used to encapsulate the bottom and top of the physical simulation model. The cover layer is made of acrylic board. After the finished cover layer is alternately placed with the reservoir layer and the interlayer, polyvinyl alcohol (PVA) adhesive is used on the outside to glue and seal. The reservoir is formed by cement, gypsum, and quartz sand of 40-80 meshes, which are cemented in a certain mass ratio, wherein the mass ratio of reservoir I is 1:1:2, the mass ratio of reservoir II is 1:1:3, and the mass ratio of reservoir III is 1:1:4; The interlayer is made of cement and gypsum in a bonding mass ratio of 1:1; The dynamic fracture simulation device is configured to manufacture an artificial high-permeability core column according to required specifications. The artificial high-permeability core column has a size range of φ2.5 cm to 10 cm and a length of 8 cm to 50 cm. The artificial high-permeability core column is made of 1 mm to 2 mm quartz sand and has a cement, gypsum, and quartz sand bonding mass ratio of 1:1:

3. The artificial high-permeability core column (4) after solidification and cutting is used to manufacture a dynamic fracture simulation component and is placed in a dynamic fracture simulation component groove reserved in the reservoir, and then a mixture of cement and gypsum is poured and fixed; wherein the cement and gypsum mass ratio is 1:1; The flow control device is used to control the pressure of n reservoirs, and the pressure adjustment range is 2.5MPa to 30MPa.

3. The CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures according to claim 1 is characterized in that: Each group of physical models injects CO2 into the control valve of the flow control device. The control valve is set at the bottom and right side of the flow control device, and is opened in one direction separately when in use; The metering device is a reservoir oil output metering device, a pressure metering device, or a CO2 emission metering device.

4. The CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures according to claim 2, characterized in that: The dynamic fracture simulation device is assembled by inserting a dynamic fracture simulation component into a dynamic fracture groove reserved in a reservoir; the dynamic fracture simulation component is composed of a filter plate (1), a sealing baffle (2), a spring component (3), an artificial high-permeability core column (4), a cementing and fixing glue (5), and a shell (6); The artificial high permeability core column (4) is cylindrical, and is respectively provided with a spring component (3) at both ends. The spring component (3) is placed into the artificial high permeability core column frame when the artificial high permeability core column is manufactured, and is welded and fixed at the outer connection between the spring component (3) and the artificial high permeability core column (4) at both ends, and the welded assembly is sleeved and fixed on the artificial high permeability core column (4) frame; the other ends of the two spring components (3) are respectively sleeved with the sealing baffle (2), and are fixed by welded screw caps, and the sealing baffle (2) is located at the support point inside the shell (6); the prepared artificial high permeability core column (4) and the shell (6) are connected and sealed with a bonding adhesive (5); the two filter plates (1) are respectively fixedly assembled at the outer support points at both ends of the shell (6); The spring length of the spring member is selected based on the length of deformation when the spring is subjected to a preset pressure value.

5. The CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures according to claim 4 is characterized in that: The working principle of the dynamic fracture simulation device is as follows: the dynamic fracture simulation device is pre-buried in a reserved groove when the reservoir is made. The dynamic fracture simulation reservoir contains dynamic fractures and has the characteristics of burying. When the pressure inside and outside the dynamic fracture simulation device is balanced, the spring component is in its original state. According to Hooke's law, it can be known that: F=-kx (1) In the above formula: k - spring coefficient; X——stretched or compressed length, cm; P——spring pressure, N / mm; F——tensile force or compressive force on the spring, N; δ——tensile or compressive amount, mm; In its original state, the dynamic fracture simulation component is sealed. When a pressure differential exists across the spring and the pressure is greater than the calculated spring pressure P, the left sealing baffle moves to the right, the compression spring contracts to the right, and the left channel opens. Fluid passes through the artificial high-permeability core column, simulating the injection of fluid into the fracture. Under the action of pressure, the right spring stretches to the right, the right sealing baffle moves to the right, and the right channel opens.

6. The CO2 flooding simulation device for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures according to claim 4, characterized in that: The filter plate (1) is used to prevent reservoir cement and fluid impurities from entering the interior of the component; the sealing baffle (2) supports the spring component and moves under the action of pressure difference to simulate the opening and closing of the crack; the spring component (3) simulates the crack opening pressure; the artificial high-permeability core column (4) simulates the dynamic fracture equivalent permeability medium; the cementing glue (5) fixes the artificial high-permeability core column (4) and the shell and plays a sealing role at the same time; the shell (6) seals the core component after injection to prevent fluid from flowing from the edge of the core and prevent the formation of high-permeability channels at the edge.

7. A CO2 flooding simulation method for multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures, characterized in that: The method includes a single reservoir flooding test method, a multi-reservoir same pressure flooding test method, a multi-reservoir different pressure flooding test method and a multi-reservoir dynamic fracture flooding test method; The steps of the single reservoir flooding experimental method are as follows: Step 1: Prepare simulated formation water and crude oil for the experiment; Step 2: Place the multi-layer physical device without dynamic cracks into the constant temperature system, connect the fluid injection pipeline, and heat the constant temperature box to 80°C; Step 3: Saturate the formation water, and saturate reservoirs I, II, ..., and n in the physical model group in sequence. First, close the inlet valves of reservoirs II, ..., and n, and use a constant flow displacement method to allow the saturated formation water to pass through reservoir I alone. The displacement is cut off at 20 PV. Then saturate reservoirs II, ..., and n in sequence. Step 4: Saturate the formation crude oil. To ensure full saturation, saturate reservoir I, reservoir II, ..., reservoir n in sequence. First, close the inlet valves of the control valves of reservoir II, ..., reservoir n, and use a constant flow displacement method to allow the saturated formation water to pass through reservoir I alone. Displace until no water is produced, and record the water output. Saturate reservoir II, ..., reservoir n in sequence and record the water yield; Step 6: The displacement medium CO2 gas is kept at a constant temperature of 80°C and a displacement pressure of 13 MPa and injected into the gas well through the fluid injection pipeline; Step 7: Close the bottom control valve of the first flow control device, open the right control valve to allow CO2 gas to enter the reservoir to displace oil, open the first metering device to measure the displaced oil volume, outlet pressure and CO2 emission, and record the time and related data; Step 8: Close the right control valve of the first flow control device and open the bottom control valve; close the bottom control valve of the second flow control device and open the right control valve; allow CO2 gas to enter reservoir II to displace oil, open the second metering device, measure the displaced oil volume, outlet pressure, and CO2 emission, and record the time and related data; Step 9: Close the right control valve of the first flow control device and open the bottom control valve; close the right control valve of the second flow control device and open the bottom control valve; close the bottom control valve of the third flow control device and open the right control valve to allow CO2 gas to enter reservoir III to displace oil. Open the third metering device to measure the displaced oil volume, outlet pressure, and CO2 emission, and record the time and related data. Similarly, close the right control valves of n-1 flow control devices in sequence and open the n-1 bottom control valves; open the right control valve of the nth flow control device to allow CO2 gas to enter reservoir n for oil displacement, open the nth metering device, measure the displaced oil volume, outlet pressure and CO2 emission, and record the time and related data.

8. The method for simulating CO2 flooding in multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures according to claim 7, characterized in that: The multi-reservoir same pressure flooding experimental method comprises the following steps: Step 2-1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment; Step 2-2: Place the multi-layer physical device without dynamic fractures in a constant temperature system, connect the fluid injection pipeline, and heat the constant temperature box to 80°C; inject gas into the steam well through the fluid injection pipeline, close the bottom control valve of the third flow control device, open the right control valve, and open the bottom and right control valves of the first and second flow control devices to allow CO2 gas to enter reservoirs I, II, and III. Use pressure regulators at the inlet ends of the first and second flow control devices to control the pressure to the same 13 MPa for oil displacement. Open the first, second, and third metering devices to measure the displaced oil volume, outlet pressure, and CO2 emission, and record the relevant data separately.

9. The method for simulating CO2 flooding in multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures according to claim 7, characterized in that: The multi-reservoir different pressure flooding experimental method has the following steps: Step 3-1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment; Step 3-2: Place the multi-layer physical device without dynamic fractures in a constant temperature system, connect the fluid injection pipeline, and heat the constant temperature box to 80°C; inject gas into the steam well through the fluid injection pipeline, close the bottom control valve of the third flow control device, open the right control valve, and open the bottom and right control valves of the first and second flow control devices to allow CO2 gas to enter reservoirs I, II, and III. Use pressure regulators at the inlet ends of the first and second flow control devices to control the pressures from reservoirs I to III to 10 MPa, 13 MPa, and 16 MPa, respectively, to carry out oil displacement. Open the first, second, and third metering devices to measure the amount of oil displaced, the outlet pressure, and the amount of CO2 discharged, and record the relevant data.

10. The method for simulating CO2 flooding in multi-layer ultra-low permeability oil and gas reservoirs containing dynamic fractures according to claim 7, characterized in that: The multi-reservoir dynamic fracture flooding experimental method comprises the following steps: Step 4-1: Clean the physical model and re-saturate it with water and oil according to the single reservoir experiment; Step 4-2: Place the multi-layer physical device of dynamic fractures in a constant temperature system, connect the fluid injection pipeline, and heat the constant temperature box to 80°C. Inject gas into the steam well through the fluid injection pipeline. Close the bottom control valve of the third flow control device and open the right control valve. Open the bottom and right control valves of the first and second flow control devices to allow CO2 gas to enter reservoirs I, II, and III. Use a pressure valve regulator at the inlet of the flow control device to control the pressure to the same 13 MPa. At the same pressure, all fracture channels are opened to carry out oil displacement. Open the first, second, and third metering devices to measure the amount of oil displaced, the outlet pressure, and the amount of CO2 discharged, and record the relevant data.

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