A method for identifying structure of fractured-vug type reservoir based on Fluent

Abstract

The present application relates to a kind of based on the structure identification method of fracture-cave type oil reservoir of Fluent, comprising the following steps: constructing three-dimensional fracture-cave type oil reservoir mechanism model as measured model;The grid file is obtained by grid division to measured model;Grid file is imported into Fluent software, and transient calculation is carried out;With the upper end of wellbore as speed entrance, mixed speed is 0.1 m / s, and the volume fraction of water is 1;Pressure-velocity coupling solution algorithm is set, and the pressure data of speed entrance is output once every time step;The required water injection time is calculated, time step is set, and the total water injection amount or water injection time is reached to end calculation, and the speed of entrance is returned to 0, and recalculation is carried out;Select standard initialization calculation;Judge whether convergence, if convergence, then continue to calculate and obtain the time required to reach convergence;After calculation, the pressure drop and pressure drop derivative double logarithm diagram of measured model in the shut-in stage is drawn.It can help to identify fracture-cave structure type, guide fracture-cave type oil reservoir water injection oil displacement development well selection.

Description

A Fluent-based method for identifying fractured-vuggy reservoir structures Technical Field

[0001] This invention relates to the field of reservoir identification, and more particularly to a Fluent-based method for identifying fracture-vuggy reservoir structures. Background Technology

[0002] Carbonate reservoirs account for more than half of the world's total oil and gas resources, most of which are fracture-vuggy reservoirs. In my country, these reservoirs are mainly distributed in the Tarim Basin. Large cavities in fracture-vuggy reservoirs are the main reservoir spaces for oil and gas resources, while fractures are the main seepage channels. These reservoirs are characterized by strong heterogeneity, complex spatial relationships between fracture-vuggy reservoirs, dispersed distribution, and irregular morphology. Internal fluid flow is also complex and unpredictable, leading to significant development challenges.

[0003] In the early stages of production, fractured-vuggy reservoirs rely on natural energy for extraction. However, as production time increases, natural energy gradually decreases, leading to a rapid decline in production and low recovery rates. Water injection is a crucial development method to improve recovery rates. This involves injecting water into the reservoir through production wells, followed by well shut-in. During shut-in, gravity differentiation facilitates oil-water exchange, increasing formation pressure. Once sufficient oil and water have been exchanged, production resumes. Multiple rounds of water injection gradually increase crude oil recovery. However, injected water easily breaches and forms dominant channels, limiting the water drive's reach and gradually diminishing the effectiveness of water injection. Furthermore, the development results of water injection vary depending on the fractured-vuggy unit structure.

[0004] Currently, researchers have conducted numerous physical simulation experiments to delineate fracture-cavity units. However, due to incomplete geological data and difficulties in characterizing fracture-cavity structures and understanding reserves, these experiments cannot accurately reflect the impact of fracture-cavity spatial relationships on water injection for oil replacement, making it impossible to select water injection wells suitable for this technology, thus resulting in economic losses. Therefore, it is necessary to propose a simulation method for accurately identifying fracture-cavity structures to understand the flow patterns of fluids within fracture-cavity reservoirs and the mechanism of water injection for oil replacement. Summary of the Invention

[0005] This invention addresses the current inability to accurately understand the impact of fracture-cavity spatial relationships on water injection for oil replacement, thus hindering the selection of water injection wells with the necessary technology and resulting in economic losses. It provides a Fluent-based method for identifying fracture-cavity reservoir structures to solve this problem. The Fluent software visualizes the water injection process in single wells within fracture-cavity reservoirs, enriching the study of the water injection mechanism. Based on the characteristics of the plotted pressure drop curves, the structural types of fractures and cavities can be identified during actual water injection for oil replacement, thereby guiding well selection for water injection development in fracture-cavity reservoirs and improving production efficiency.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] A Fluent-based method for identifying fractured-vuggy reservoir structures includes the following steps:

[0008] S1. Construct a three-dimensional fractured-vuggy reservoir mechanism model with a wellbore using the Design Modeler software on the Ansys Workbench platform, and save the mechanism model as the model to be tested;

[0009] S2. Mesh software is used to generate a mesh for the model under test. Boundary layer meshes are added through Insert-Inflation settings. Different fluid domains and boundaries are named and saved as mesh files.

[0010] S3. Import the mesh file into Fluent software, select double precision, check the mesh, then select the pressure-based solver for transient calculation, select laminar and multiphase flow models, set the fluid domain and related parameters, and set the fluid material and properties of the model to be tested. The fluid includes crude oil, water, and gas.

[0011] S4. The upper end of the well shaft is the velocity inlet, the mixing velocity is 0.1 m / s, and the water volume fraction is 1.

[0012] S5. Set the pressure-velocity coupled solution algorithm and set the residual of the continuity equation to 0.0001. Create a monitoring surface in the mesh file and set it to output the pressure data at the velocity inlet once every time step. Select standard initialization calculation and set the animation surface for real-time monitoring.

[0013] S6. Calculate the required water injection time according to the following formula, set the time step size, number of time steps, and maximum number of iterations. The calculation ends when the total water injection volume or injection time is reached. Then, change the inlet velocity to 0, restart the calculation, and enter the well shut-in phase.

[0014]

[0015] In the formula, Q is the total water injection volume (m³). 3 v is the injection velocity (m / s), and r is the wellbore radius (m).

[0016] S7. Determine if convergence has occurred. If convergence has occurred, continue to calculate the time required to reach convergence. If convergence has not occurred, appropriately reduce the relaxation factor or modify the pressure-velocity coupling algorithm and recalculate.

[0017] S8. After the calculation is completed, CFD-Post post-processing is used to view the dynamic changes of the oil-water interface during the water injection and shut-in stages. Based on the inlet pressure data output by Fluent, a double logarithmic plot of the pressure drop and pressure drop derivative of the model under test during the shut-in stage is plotted.

[0018] Preferably, in step S3, the crack in the slit is set as a porous medium region, and then the porosity of the porous medium region and the viscous resistance coefficients in the x, y, and z directions are input, wherein the viscous resistance coefficients are the reciprocal of the permeability of the porous medium.

[0019] Preferably, when checking the mesh quality in step S3, the average element quality is required to be greater than 0.8; the skewness is less than 0.9; the aspect ratio is less than 5; and the boundary layer is less than 10. If any one of these conditions is not met, the process returns to step S2 to re-mesh.

[0020] Preferably, in step S6, the pressure-velocity coupling algorithm is the SIMPLE method, and the spatial discretization methods are as follows: gradient is the least squares unit, pressure is PRESTO!, density, momentum, and energy are second-order upwind schemes, volume fraction is geometric reconstruction, and the transient formula is a first-order implicit formula.

[0021] Preferably, in step S6, the initial input pressure for standard initialization is the bottom hole pressure before water injection, and the volume fraction of water and gas is 0. If the reservoir contains gas before water injection, a marked region should be created in advance through Cell Registers-New-Region, and the region should be initialized in conjunction with Patch, setting the volume fraction of gas in the region to 1.

[0022] Preferably, when setting the animation surface in step S6, first in

[0023] In Results-Graphics-Contour, set up a contour plot of the oil or water phase volume fraction. Then, add the contour plot in Solution-Calculation activities-Solution Animations, input the update frequency, and set the oil or water volume fraction to be updated every N time steps to monitor the changes in the oil-water interface in real time.

[0024] Preferably, after obtaining the double logarithmic plot of pressure drop and pressure drop derivative of the model under test during the shut-in stage, the model under test is modified to obtain double logarithmic plots of pressure drop and pressure drop derivative of various fractured-vuggy reservoir mechanism models during the shut-in stage.

[0025] In actual production, while injecting water to replace oil in the oil well, the characteristics of the water injection pressure drop curve of the oil well are tested, and compared with the double logarithmic plots of pressure drop and pressure drop derivative of various fractured-vuggy reservoir mechanism models at the shut-in stage to determine the fractured-vuggy unit type corresponding to the oil well, so as to select a suitable oil well for water injection to replace oil.

[0026] The beneficial technical effects of the present invention are as follows:

[0027] (I) A three-dimensional fractured-vuggy reservoir mechanism model was constructed. The model was then meshed, and the mesh file was imported into Fluent software for testing. Using the inlet pressure data output by Fluent, a double logarithmic plot of the pressure drop and its derivative was plotted during the well shut-in phase. In actual production, when water injection is performed on oil wells, the characteristics of the oil well's pressure drop curve can be compared with the double logarithmic plot of the pressure drop and its derivative in the model. This allows for the identification of fractured-vuggy structures suitable for water injection, determination of fractured-vuggy unit types, and guidance for well selection in water injection development of fractured-vuggy reservoirs, thereby improving production efficiency.

[0028] (ii) Add a contour plot in Solution-Calculation activities-Solution Animations and enter the update frequency. You can visually see the changes in the volume fraction of the oil or water phase during the calculation process.

[0029] (iii) While injecting water to replace oil in the oil well, test the characteristics of the water injection pressure drop curve of the oil well. Compare it with the double logarithmic plot of pressure drop and pressure drop derivative of various fractured and vulcan reservoir mechanism models measured in this scheme during the shut-in stage. This can easily determine the fractured and vulcan unit type corresponding to the oil well, so as to select a suitable oil well for water injection to replace oil. Attached Figure Description

[0030] Figure 1 shows a schematic diagram of the structure of the fractured-vuggy reservoir structure identification method based on Fluent in an embodiment of the present invention;

[0031] Figure 2 shows a schematic diagram of the single-slit hole model in an embodiment of the present invention;

[0032] Figure 3 shows a schematic diagram of the structure of the double-slit hole model in an embodiment of the present invention.

[0033] Marked in the attached diagram:

[0034] 1-Cave; 2-Fissure; 3-Entrance. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the following detailed description of a Fluent-based fractured-vuggy reservoir structure identification method proposed by this invention, in conjunction with the accompanying drawings and specific embodiments, will provide further clarity. The advantages and features of this invention will become clearer from the following description. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, used only to facilitate and clearly illustrate the purpose of the embodiments of this invention. Please refer to the accompanying drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0036] Example

[0037] The technical solution of a Fluent-based fractured-vuggy reservoir structure identification method of the present invention will be described in detail below with reference to Figure 1 and specific embodiments.

[0038] As shown in Figure 1, a Fluent-based method for identifying fractured-vuggy reservoir structures in this embodiment includes the following steps:

[0039] S1. Construct a three-dimensional fractured-vuggy reservoir mechanism model with a wellbore using the Design Modeler software on the Ansys Workbench platform, and save the mechanism model as the model to be tested.

[0040] In this step, when constructing the mechanism model, different fracture-cavity structures should be constructed according to the actual situation, such as single cavity, single-crack cavity, double-crack cavity, and triple-crack cavity. Furthermore, the two cases of wells inside and outside the cavity should also be considered. In the constructed mechanism model, the cavity 1 can be represented by a cylinder or cube with the interior filled, while the crack 2 is represented by a slender cylinder or cuboid. The well shaft is connected to the crack 2 or the cavity 1.

[0041] S2. Mesh software is used to generate a mesh for the model under test. Boundary layer meshes are added through Insert-Inflation settings. Different fluid domains and boundaries are named and saved as mesh files.

[0042] In addition, when performing mesh generation, it is necessary to modify the size of the mesh cells according to the size of the model to be tested and to refine the mesh.

[0043] S3. Import the mesh file into Fluent software, select double precision, check the mesh, then select the pressure-based solver for transient calculation, select laminar and multiphase flow models, set the fluid domain and related parameters, and set the fluid material and properties of the model under test. The fluids include crude oil, water, and gas.

[0044] In this step, based on the problem addressed by this solution, the VOF model from the laminar flow model and multiphase flow model is selected. To perform calculations and tests on the oil-water interface distribution, the VOF model should be selected with three phases (oil, water, and gas), and the Implicit Body Force option should be activated. Continuous surface tension and wall adhesion are selected from the surface tension model, and the surface tension coefficients between oil and water, gas and oil, and gas and water are input as 0.045 N / m, 0.04 N / m, and 0.072 N / m, respectively.

[0045] The aforementioned VOF model is primarily applicable to unsteady multiphase flow models, capable of simulating immiscible fluid flows. Furthermore, all fluids share a common set of momentum equations, tracking the volume fraction of each phase in each computational unit across the entire flow domain. Let the volume fraction of phase j be α. j , with α j This represents the ratio of the volume of phase j in a unit cell to the total volume of the unit cell. The sum of the volume fractions of all phases in the entire watershed is 1, i.e.

[0046]

[0047] For phase j, the mass conservation equation is:

[0048]

[0049] In the formula, m ij This refers to the mass transfer that occurs from phase i to phase j.

[0050] In this embodiment, the fluid material in the model consists of three phases: crude oil, water, and gas. Both water and crude oil are set as compressible liquids. Specifically: gas is an ideal gas (Fluent has a preset `ideal_gas`, whose default properties can be used directly); water is liquid water from the Fluent material database, with the input reference pressure being the original formation pressure of 2.3 × 10⁷ Pa and the reference density of 998.2 kg / m³. 3 The reference bulk modulus is the reciprocal of the compressibility coefficient, 4.5 × 10⁻⁶. 10 Pa, density index is 1; the properties of crude oil are modified from those of water, and the input reference pressure is set to 2.3 × 10⁻⁶. 7 Pa, with a reference density of 800 kg / m³ 3 The reference bulk modulus is 2.7 × 10⁻⁶.9 Pa, density index is 1.

[0051] In the model of the fractured-vuggy structure, there are two fluid domains. The fluid flow in the fractured-vuggy reservoir is coupled flow, while the flow in fracture 2 is seepage, which can be considered a porous medium region. The flow in cavern 1 is free flow, approximating pipe flow. This invention uses the Brinkman equation to achieve a unified characterization of seepage and free flow in fractured-vuggy reservoirs:

[0052]

[0053] In the formula, ρ is the fluid density, μ is the fluid viscosity, u is the fluid velocity vector, and ρg is the gravity term. For porosity, K -1 This is the permeability tensor, which depends on the medium type. For free-flow regions, When K = ∞, for porous media regions... K represents the regional porosity, and K represents the regional permeability. -1 It is called the viscous resistance coefficient.

[0054] S4. With the upper end of the well shaft as the velocity inlet 3, the mixing velocity is 0.1 m / s, and the water volume fraction is 1.

[0055] S5. Set the pressure-velocity coupled solution algorithm and set the residual of the continuity equation to 0.0001. Create a monitoring surface in the mesh file and set it to output the pressure data at velocity inlet 3 once every time step. Select standard initialization calculation and set the animation surface for real-time monitoring.

[0056] In this embodiment, the pressure-velocity coupling algorithm is set to the SIMPLE method, and the spatial discretization methods are as follows: the gradient is the least squares unit, the pressure is PRESTO!, the density, momentum, and energy are second-order upwind schemes, the volume fraction is geometric reconstruction, and the transient formula is a first-order implicit formula.

[0057] Fluent's default convergence criterion is that, except for energy, the residual values ​​of all equations must be less than 0.001, and the residual value of energy must be less than 1e-6. In general, the default criterion is sufficient; setting the residual value of the continuity equation to 0.0001 here is for stringent requirements and to improve computational accuracy.

[0058] After setting up the animation plane in this embodiment, the volume fraction contour plot of oil or water can be updated every N time steps. In practice, first set the volume fraction contour plot of oil or water phase in Results-Graphics-Contour. This is where we set which phase in the entire model we want to monitor for volume fraction changes. Then, add the contour plot in Solution-Calculation activities-Solution Animations, and input the update frequency. This allows you to visually observe the changes in the volume fraction of oil or water phase during the calculation process. Additionally, setting Autosave to save the calculation process every N time steps facilitates viewing the contour plots and animations at the selected time points during post-processing.

[0059] S6. Calculate the required water injection time according to the following formula, set the time step size, number of time steps, and maximum number of iterations. The calculation ends when the total water injection volume or injection time is reached. Then, change the inlet 3 velocity to 0, restart the calculation, and enter the well shut-in phase.

[0060]

[0061] In the formula, Q is the total water injection volume (m³). 3 v is the injection velocity (m / s), and r is the wellbore radius (m).

[0062] When setting the time step size, if the time step method is Fixed, the time step size and number of steps are set according to the required time. The initial step size is set to 0.0001, and the step size is increased appropriately after the calculation converges. If the time step method is Variable, the step size is automatically adjusted according to the convergence.

[0063] S7. Determine if convergence has occurred. If convergence has occurred, continue to calculate the time required to reach convergence. If convergence has not occurred, appropriately reduce the relaxation factor or modify the pressure-velocity coupling algorithm and recalculate.

[0064] S8. After the calculation is completed, CFD-Post post-processing is used to view the dynamic changes of the oil-water interface during the water injection and shut-in stages. Based on the inlet 3 pressure data output by Fluent, a double logarithmic plot of the pressure drop and pressure drop derivative of the model under test during the shut-in stage is plotted.

[0065] After convergence is confirmed, the time required for water injection is continuously calculated. Then, the velocity at inlet 3 is changed to 0 to simulate the shut-in phase. The operation of outputting the pressure at inlet 3 every time step still exists, so the output shows the pressure data at inlet 3 over all simulation time periods. Ultimately, the analysis focuses on the pressure during the shut-in phase.

[0066] Specifically, in step S3, since the fluid flow pattern in crack 2 is Darcy flow, crack 2 is set as a porous medium region. Then, the porosity of the porous medium region and the viscous resistance coefficients in the x, y, and z directions are input. The viscous resistance coefficients are the reciprocal of the permeability of the porous medium region, i.e., crack 2.

[0067] Specifically, when checking mesh quality in step S3, it is necessary to ensure that the average element quality is greater than 0.8; the skewness is less than 0.9; the aspect ratio is less than 5; and the boundary layer is less than 10. If any of these conditions are not met, return to step S2 to re-mesh. If the mesh is incorrect or of poor quality, it may cause non-convergence at the beginning or middle of subsequent calculations.

[0068] Specifically, in step S6, the initial input pressure for standard initialization is the bottom hole pressure before water injection, and the volume fraction of water and gas is 0. If the reservoir contains gas before water injection, a marked region should be created in advance through Cell Registers-New-Region, and the region should be initialized in conjunction with Patch, setting the volume fraction of gas in the region to 1.

[0069] After obtaining the double logarithmic plots of pressure drop and pressure drop derivative of the model under test during the shut-in stage, the model under test was modified to obtain double logarithmic plots of pressure drop and pressure drop derivative of various fractured-vuggy reservoir mechanism models during the shut-in stage.

[0070] In actual production, while injecting water to replace oil in oil wells, the characteristics of the water injection pressure drop curve of the oil wells are tested. By comparing the double logarithmic plots of pressure drop and pressure drop derivative of the above-mentioned various fractured-vuggy reservoir mechanism models during the shut-in stage with the double logarithmic plots during the actual water injection process, the type of fractured-vuggy unit corresponding to the oil well can be determined, thereby selecting a suitable oil well for water injection to replace oil.

[0071] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for identifying fractured-vuggy reservoir structures based on Fluent, characterized in that, Includes the following steps: S1. Construct a three-dimensional fractured-vuggy reservoir mechanism model with a wellbore using the Design Modeler software on the Ansys Workbench platform, and save the mechanism model as the model to be tested; S2. Use Mesh software to mesh the model to be tested, add boundary layer meshes through Insert-Inflation settings, name different fluid domains and boundaries, and save as mesh files; S3. Import the mesh file into Fluent software, select double precision, check the mesh, and then select the pressure-based solver for transient calculations. Select laminar and multiphase flow models, set the fluid domain and related parameters, and set the fluid material and properties of the model under test. The fluid includes crude oil, water, and gas; both water and crude oil are set as compressible liquids, where: gas is an ideal gas, directly using its default properties; water is liquid water from the Fluent material database, and the input reference pressure is the original formation pressure of 2.3 × 10⁷ Pa, and the reference density is 998.2 kg / m³. 3 The reference bulk modulus is the reciprocal of the compressibility coefficient, 4.5 × 10⁻⁶. 10 Pa, density index is 1; the properties of crude oil are modified from those of water, and the input reference pressure is set to 2.3 × 10⁻⁶. 7 Pa, with a reference density of 800 kg / m³ 3 The reference bulk modulus is 2.7 × 10⁻⁶. 9 Pa, density index is 1; in the fractured-vuggy structure model, there are two fluid domains: the fluid flow in the fractured-vuggy reservoir is coupled flow, and the flow in the fractures is seepage, which can be set as a porous medium region; the flow in the caverns is free flow, approximating pipe flow; using the Brinkman equation, a unified characterization of seepage and free flow in the fractured-vuggy reservoir is achieved: In the formula, For fluid density, Let ρ be the fluid viscosity, u be the fluid velocity vector, and ρg be the gravity term. For porosity, K -1 For the permeability tensor, which depends on the medium type, for free-flowing regions, =1, K=∞, for porous media regions K represents the regional porosity, and K represents the regional permeability. -1 This is called the viscous resistance coefficient; S4. Using the upper end of the wellbore as the velocity inlet, the mixing velocity is 0.1 m / s, and the water volume fraction is 1; S5. Set the pressure-velocity coupled solution algorithm, and set the residual of the continuity equation to 0.0001. Create a monitoring surface in the mesh file, and set it to output the pressure data at the velocity inlet once every time step; select standard initialization calculation, and set the animation surface for real-time monitoring; S6. Calculate the required water injection time according to the following formula, set the step size, number of time steps, and maximum number of iterations. When the total water injection volume or water injection time is reached, end the calculation, change the inlet velocity to 0, restart the calculation, and enter the well shut-in stage. In the formula, Q is the total water injection volume, in cubic meters (m³). 3 v is the injection velocity in m / s, and r is the wellbore radius in m. S7. Determine if convergence has occurred. If convergence is confirmed, continue calculating the time required to reach convergence. If convergence fails, appropriately reduce the relaxation factor or modify the pressure-velocity coupling algorithm and recalculate. S8. After calculation, use CFD-Post post-processing to view the dynamic changes of the oil-water interface during the water injection and shut-in stages. Based on the inlet pressure data output by Fluent, plot a double logarithmic graph of the pressure drop and pressure drop derivative of the model under test during the shut-in stage.

2. The Fluent-based method for identifying fractured-vuggy reservoir structures as described in claim 1, characterized in that, In step S3, the crack in the slit is set as a porous medium region, and then the porosity of the porous medium region and the viscous resistance coefficients in the x, y, and z directions are input. The viscous resistance coefficients are the reciprocal of the permeability of the porous medium.

3. The Fluent-based method for identifying fractured-vuggy reservoir structures as described in claim 1, characterized in that, When checking the mesh quality in step S3, the average element quality must be greater than 0.8; the skewness must be less than 0.9; the aspect ratio must be less than 5; and the boundary layer must be less than 10. If any of these conditions are not met, return to step S2 to re-mesh.

4. The Fluent-based method for identifying fractured-vuggy reservoir structures as described in claim 1, characterized in that, In step S6, the SIMPLE method is chosen as the pressure-velocity coupling algorithm for solving the problem. The spatial discretization methods for each item are as follows: the gradient is a least squares unit, the pressure is PRESTO!, the density, momentum, and energy are second-order upwind schemes, the volume fraction is geometric reconstruction, and the transient formula is a first-order implicit formula.

5. The Fluent-based method for identifying fractured-vuggy reservoir structures as described in claim 1, characterized in that, In step S6, the initial input pressure for standard initialization is the bottom hole pressure before water injection, and the volume fraction of water and gas is 0. If the reservoir contains gas before water injection, a marked region should be created in advance through Cell Registers-New-Region, and the region should be initialized in conjunction with Patch, setting the volume fraction of gas in the region to 1.

6. The Fluent-based method for identifying fractured-vuggy reservoir structures as described in claim 1, characterized in that, When setting up the animation plane in step S6, first set the contour plot of the oil or water phase volume fraction in Results-Graphics-Contour, then add the contour plot in Solution-Calculation activities-Solution Animations, input the update frequency, and set the oil or water volume fraction to be updated every N time steps to monitor the change of the oil-water interface in real time.

7. The Fluent-based method for identifying fractured-vuggy reservoir structures as described in claim 1, characterized in that, After obtaining the double logarithmic plot of pressure drop and pressure drop derivative of the test model during the shut-in stage, the test model is modified to obtain double logarithmic plots of pressure drop and pressure drop derivative of various fractured-vuggy reservoir mechanism models during the shut-in stage. During actual production, the water injection pressure drop curve characteristics of the oil well are tested while water is injected to replace oil, and compared with the double logarithmic plots of pressure drop and pressure drop derivative of the above-mentioned various fractured-vuggy reservoir mechanism models during the shut-in stage to determine the fractured-vuggy unit type corresponding to the oil well, so as to select a suitable oil well for water injection to replace oil.

Images