A numerical simulation method for fractured oil and gas reservoirs

Abstract

A numerical simulation method for fractured oil and gas reservoirs relates to the technical field of oil and gas development, and mainly comprises the following steps: establishing a dual medium model of an oil and gas reservoir, including a dual medium model with a fixed grid and a dual medium model with a non-fixed grid; based on the type of the dual medium model, converting the dual medium model into an equivalent single medium model; calculating the overall elastic energy of the reservoir in the equivalent single medium model, and obtaining the single medium model of the oil and gas reservoir; the present invention converts the complex dual medium model into a corresponding single medium model, which can effectively improve the calculation efficiency for reservoir simulation and reduce the calculation cost, and is suitable for large-scale reservoir simulation or fast solution optimization. Compared with the conventional method of converting dual medium to single medium, the present invention combines the principle of physical seepage process, takes into account practical factors such as the change of grid size after conversion and the actual flow area of ​​the fluid, so that the final conversion result is more accurate.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas development, in particular to a numerical simulation method for fractured oil and gas reservoirs. Background Art

[0002] Fractured oil and gas reservoirs are an important area of ​​global oil and gas resource development, with significant strategic position and economic benefits. However, the strong heterogeneity, multi-scale characteristics and dynamic evolution behavior of fractured reservoirs lead to common challenges such as rapid water breakthrough and low recovery rate during development. Therefore, how to realize the complex flow mechanism of fractured gas reservoirs and optimize the development strategy through numerical simulation technology is the core issue for achieving efficient resource development.

[0003] The importance of fractured reservoirs stems from their unique seepage mechanism and the limitations of traditional models. The fracture system dominates high-speed seepage at the millimeter-micrometer scale, and the permeability can reach tens of thousands of times that of the matrix, while the matrix system relies on nanoscale pores to slowly release fluids. The two form a coupling mechanism of "matrix fluid supply-fracture diversion" through dynamic exchange.

[0004] The most widely used method for numerical simulation of fractured reservoirs is the dual medium model, which divides the reservoir into two interacting matrix systems and fracture systems. The matrix system usually has low permeability and high porosity and is responsible for storing fluids. The fracture system has high permeability and low porosity and is mainly responsible for the flow of fluids. The fluid exchange between the matrix and the fractures is described by a transfer function (such as the shape factor), which is often used in cases where the fracture distribution is relatively uniform and the matrix-fracture interaction is significant.

[0005] When there are significant differences between the two media in the reservoir, and the reservoir is composed of a high-porosity, low-permeability matrix (storage fluid) and low-porosity, high-permeability fractures (dominant flow), a dual-media model is required. During the development process, the fluid in the matrix needs to slowly replenish the fractures through imbibition, diffusion, etc., which affects the production capacity dynamics. In this case, a dual-media model is required, such as coalbed methane and shale gas. When the difference in permeability between the matrix and fractures is small, or when isolated fractures or fracture networks are not developed in the reservoir, there is no need to distinguish between media.

[0006] In numerical simulation of oil and gas reservoirs, dual media can accurately characterize the differences and coupling effects of matrix-fracture systems and distinguish between reservoir and flow functions. Dual media models are widely used because of their accurate depiction of complex reservoir dynamics.

[0007] However, the dual-medium model is a model with overly idealized geometric assumptions (such as the Warren-Root model). The model is highly dependent on the shape factor, which needs to be obtained indirectly through experiments or historical matching. The coupling parameters between the matrix and the fracture are also difficult to determine. In addition, during the historical matching process, the matrix porosity, fracture permeability, shape factor and other parameters are coupled with each other, and multiple solutions are prone to occur during historical matching, resulting in inaccurate development prediction results.

[0008] At the same time, in the numerical calculation process, the number of dual variables and equations doubles, and the strong coupling between the matrix and the fracture often requires implicit joint solution, which further increases the computational burden. The calculation cost is high and time-consuming, and it is difficult to adapt to the gradually applied large models. Summary of the invention

[0009] In view of this, the main purpose of the present invention is to provide a numerical simulation method for fractured oil and gas reservoirs, which realizes efficient and accurate simulation of fractured reservoirs by converting a dual medium model into a single medium model.

[0010] The technical solution of the present invention is a method for numerical simulation of fractured oil and gas reservoirs, comprising the following steps:

[0011] Step S1: establishing a dual medium model of an oil and gas reservoir, including a dual medium model with a fixed grid and a dual medium model with a non-fixed grid;

[0012] Step S2: based on the type of the dual medium model, converting the dual medium model into an equivalent single medium model;

[0013] Step S3: Calculate the overall elastic energy of the reservoir in the equivalent single medium model to obtain the single medium model of the oil and gas reservoir.

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

[0015] 1. The present invention converts the computationally complex dual medium model into a corresponding single medium model, which can effectively improve the computational efficiency of reservoir simulation and reduce the computational cost, and is suitable for large-scale reservoir simulation or rapid solution optimization.

[0016] 2. The number of parameters in the simulation process is greatly reduced, which reduces the multi-solution of parameters in the fitting process and makes data preparation more convenient. At the same time, the parameter sensitivity is reduced, and the historical fitting process is more efficient.

[0017] 3. On the basis of unchanged reserves and based on the principle of equivalent seepage, the present invention converts the dual medium model (including the dual-porosity dual-permeability model and the dual-porosity single-permeability model) into a single medium model. The entire method and process have strict physical seepage meanings. The converted single medium model has a flow effect similar to that of the dual medium model, and at the same time greatly improves the calculation efficiency.

[0018] 4. In the process of reducing the dual medium to an equivalent single continuous medium, the initial reserves and seepage process of the reservoir are approximately equal, so that the simulation effect of the single medium is basically consistent with that of the dual medium, ensuring the accuracy of the conversion.

[0019] 5. Compared with the conventional method of converting dual media to single media, the present invention combines the principles of physical seepage process, based on the principle of constant flow rate and velocity, and takes into account practical factors such as the change in grid size after conversion and the actual flow area of ​​the fluid, so that the final conversion result is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments.

[0021] Figure 1 is a gas-water distribution diagram of the dual medium model in Example 1 of the present invention;

[0022] Figure 2 is a gas-water distribution diagram of the single medium model in Example 1 of the present invention;

[0023] Figure 3 This is a comparison chart of water breakthrough time and recovery rate of the dual medium model and the single medium model in Example 1 of the present invention;

[0024] Figure 4 A comparison diagram of formation pressure changes of the dual medium model and the single medium model in Example 1 of the present invention;

[0025] Figure 5 This is a comparison chart of the calculation time of the dual medium model and the single medium model in Example 2 of the present invention;

[0026] Figure 6 This is a comparison diagram of the water production fitting effects of the dual medium model and the single medium model in Example 2 of the present invention;

[0027] Figure 7 This is the gas-water distribution diagram of the single-weight medium model after 5 years of production in Example 2 of the present invention;

[0028] Figure 8 This is the gas-water distribution diagram of the dual medium model after 5 years of production in Example 2 of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below in conjunction with the embodiments and drawings.

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] A numerical simulation method for fractured oil and gas reservoirs comprises the following steps:

[0032] Step S1: establishing a dual medium model of an oil and gas reservoir, including a dual medium model with a fixed grid and a dual medium model with a non-fixed grid.

[0033] Based on the prior art in this field, it is known that the dual medium model can be divided into a fixed grid model and a non-fixed grid model, wherein the fixed grid model is a model in which the grid is refined, and the overall model has been perfectly established, and its size does not change; while for the non-fixed grid model, its internal grid has not been refined after the model is established, and the basic data such as the grid parameters inside the model can also be set or adjusted accordingly as needed. Therefore, it is necessary to consider the cases of fixed grid and non-fixed grid separately during the conversion.

[0034] In addition to the feature of whether the grid is fixed or not, the dual-medium model can also be divided into a double-porosity single-permeability model and a double-porosity double-permeability model according to the grid permeability type. Both the double-porosity single-permeability model and the double-porosity double-permeability model correspond to the same grid model. The difference between the two is that the double-porosity single-permeability model only considers the flow of fluid in the fracture system, while the double-porosity double-permeability model considers the flow of the fracture system and the matrix system at the same time. It can be seen that the grid parameters, matrix, and fractures involved in the double-porosity single-permeability model and the double-porosity double-permeability model are basically the same.

[0035] Step S2: based on the type of the dual medium model, converting the dual medium model into an equivalent single medium model;

[0036] From the above classification, we can know that the dual medium model can include fixed grid and non-fixed grid models, dual porosity and single permeability models, and dual porosity and dual permeability models. Therefore, the conversion process of the dual medium model to the single medium model needs to be divided into the following four cases for consideration:

[0037] First, in order to ensure the stability of the model, no matter which of the four cases the conversion process is, the overall size of the model needs to be kept unchanged. Therefore, the net-to-gross ratio of the model is set equal to 1, so that the total reserves of the model before and after the conversion remain unchanged, and the porosity before and after the conversion remains unchanged. At this time, the relationship shown in formula (18) is obtained:

[0038] (18);

[0039] In formula (18), Φ f is the porosity of the fractures in the dual medium model before conversion; Φ m is the porosity of the matrix in the dual medium model before conversion; Φ The porosity of the single medium model obtained by converting the dual medium model;

[0040] Then calculate the equivalent permeability of the single medium model, and adjust the grid size of the dual medium model to obtain the grid of the equivalent single medium model. Since the grid size does not change in the fixed grid dual medium model, it is necessary to calculate the equivalent permeability of the single medium model after conversion for the dual medium model with a non-fixed grid, and adjust the grid size at the same time. For the dual medium model with a fixed grid, only the permeability is calculated. The specific steps are as follows:

[0041] The grid of the dual medium model can be determined by the dimensions in the three directions of the X-axis, Y-axis, and Z-axis. For the dual medium model with double porosity and single permeability and a non-fixed grid, the permeability of the converted single medium model is shown in equations (1) to (3):

[0042] (1);

[0043] (2);

[0044] (3);

[0045] For the dual-porosity and dual-permeability dual-medium model with non-fixed grids, the permeability of the converted single-medium model is shown in equations (4) to (6):

[0046] (4);

[0047] (5);

[0048] (6);

[0049] In formulas (1) to (6), K x The X-direction permeability of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model, in mD; K y The permeability in the Y direction of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model, in mD; K z The permeability in the Z direction of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model, in mD; kx The X-direction permeability of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model, in mD; k y The permeability in the Y direction of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model, in mD; k z The permeability in the Z direction of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model, in mD; Φ f is the porosity of the fractures in the dual medium model before conversion; Φ m is the porosity of the matrix in the dual medium model before conversion; k fx is the permeability of the fracture system in the X direction in the dual-medium model (including dual-porosity and dual-permeability and dual-porosity and single-permeability), in mD; k fy , is the permeability of the fracture system in the Y direction in the dual-medium model (including dual-porosity and dual-permeability and dual-porosity and single-permeability), in mD; k fz , is the permeability of the fracture system in the Z direction in the dual-medium model (including dual-porosity and dual-permeability and dual-porosity and single-permeability), in mD; k mx , the X-direction permeability of the matrix in the dual medium model, in mD; k my , the Y-direction permeability of the matrix in the dual medium model, in mD; k mz , the Z-direction permeability of the matrix in the dual medium model, in mD;

[0050] For the dual-porosity and single-permeability dual-medium model with non-fixed grids and the dual-porosity and double-permeability dual-medium model with non-fixed grids, the grids before and after the conversion will change. When calculating, the size of the grid on a certain axis can be determined first, and then the size in other directions can be calculated based on the determined size. Here, the grid on the Z axis of the converted single-medium model is determined by the fluid density in the model, as shown in formula (7):

[0051] (7);

[0052] In formula (7), D z’ The grid size in the Z direction of the single medium model obtained by converting the dual medium model, in m; ρ is the density of oil or gas, in kg / m 3 ; g is the acceleration due to gravity, take 9.8m / s 2 ;

[0053] At the same time, no matter whether the type of the dual medium model before conversion is dual porosity and single permeability or dual porosity and dual permeability, the size in other directions can be calculated based on the determined size. Therefore, both types of dual medium models can use formula (7) to calculate the vertical grid size of the single medium model after conversion. In addition, D z’ The value needs to be no greater than the thickness of a single interlayer.

[0054] The grid sizes in other directions of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model with non-fixed grids are shown in equations (8) and (9):

[0055] (8);

[0056] (9);

[0057] The grid sizes in other directions of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model with non-fixed grids are shown in equations (10) and (11):

[0058] (10);

[0059] (11);

[0060] In formulas (8) to (11), Φ The porosity of the single medium model obtained by converting the dual medium model; D dx’ The X-direction grid size of the single medium model obtained by converting the double-porosity and single-permeability dual medium model, in m; D dy’ The Y-direction grid size of the single medium model obtained by converting the double-porosity and single-permeability dual medium model, in m; D sx’ The X-direction grid size of the single medium model obtained by converting the double-porosity and double-permeability dual medium model, in m; D sy’ The Y-direction grid size of the single medium model obtained by converting the double-porosity and double-permeability dual medium model, in m; D x is the grid size in the X direction of the dual medium model, in m; D y is the Y-direction grid size of the dual medium model, in m; D z is the grid size in the Z direction of the dual medium model, in m;

[0061] For the dual-porosity and single-permeability dual-medium model with a fixed grid, the grid is a fine grid. The geological model has been established and cannot be changed after the grid is divided. The dimensions of the grid on the XYZ three axes are fixed and cannot be modified. The dimensions of the three axes are usually set equal. Therefore, only the change in permeability is calculated during the conversion. The permeability of the single-medium model obtained by conversion is shown in Equations (12) to (14):

[0062] (12);

[0063] (13);

[0064] (14);

[0065] For the dual-porosity and dual-permeability dual-medium model with a fixed grid, the permeability of the converted single-medium model is shown in Equations (15) to (17):

[0066] (15);

[0067] (16);

[0068] (17);

[0069] In formulas (12) to (17), K dx The X-direction permeability of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model with fixed grids, in mD; K dy The Y-direction permeability of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model with fixed grids, in mD; K dz The Z-direction permeability of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model with fixed grids, in mD; k dx The X-direction permeability of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model with fixed grids, in mD; k dy The X-direction permeability of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model with fixed grids, in mD; k dz It is the X-direction permeability of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model with a fixed grid, in mD.

[0070] Based on the above formulas, the relevant parameters of the converted single medium model can be calculated, thereby converting the dual medium model into an equivalent single medium model.

[0071] Step S3: Calculate the overall elastic energy of the reservoir in the equivalent single medium model to obtain the single medium model of the oil and gas reservoir.

[0072] After the dual medium models of different types and grid fixation mentioned above are converted into equivalent single medium models, the elastic energy of the reservoir needs to be calculated. The calculation method is mainly as follows: on the premise that the overall compressibility of the rock remains unchanged before and after the conversion, the reservoir conductivity coefficient is fitted, and the rock energy-related method in the prior art is used to correct the rock conductivity to obtain the elastic energy distribution corresponding to each equivalent single medium model, so as to determine the single medium model of the oil and gas reservoir obtained after the conversion for subsequent research.

[0073] Example 1: Taking a gas reservoir modeling as an example, a dual-porosity and dual-permeability dual-medium model is first established, and the model parameters are as follows:

[0074] Model size: 3000m×3000m×5m;

[0075] Grid size: DX=DY=10m in the plane and DZ=1m in the vertical direction; the total number of grids is 900,000;

[0076] Water body size: underground pore volume of natural gas 3.15×10 6 m³; the volume of water is 3.15×10 7 m³, water body multiple is 10 times, and water body multiples in the east, west, south and north are all 2.5 times;

[0077] Reserve size: 6.96×10 8 m³;

[0078] The matrix permeability is 0.1mD, and the fracture permeability is 50mD;

[0079] Matrix porosity 5%, fracture porosity 2%;

[0080] Then, it is converted into a single medium model according to the above method. The parameters of the single medium model are as follows:

[0081] Convert to single density medium model, porosity 0.07, permeability 36mD.

[0082] The calculation size of the vertical grid is about 1.2m. The vertical grid of the original dual-medium model is 1m, which is a refined grid. Therefore, the vertical grid can be no larger than 1.2m, and 1m is specifically selected.

[0083] The grid size in the X and Y directions is 20 m.

[0084] The gas-water distribution of the model before and after the conversion is as follows: Figure 1 , Figure 2 As shown in the figure, the water breakthrough time and recovery rate are compared. Figure 3 As shown in Figure 4 As shown by Figure 1 , 2 It can be seen that the gas-water distribution of the model before and after the conversion is basically the same. Figure 3 It can be seen that the water breakthrough time and recovery rate of the two models are basically the same. Figure 4 It is proved that the pressure changes of the two models are basically consistent. Therefore, the simulation results of the single medium model after conversion and the dual medium model before conversion can be basically consistent, which proves the accuracy of the conversion using the method of the present invention.

[0085] Example 2: Actual data was used for simulation. The relevant data were as follows: a gas reservoir with an east-west length of 31 km, a north-south width of 4 km, a reservoir thickness of 300 m, and well-developed gas reservoir fractures. Considering that its permeability was between 0.001 and 895 mD, the matrix permeability was relatively small (0.001-0.05 mD, an average of 0.018 mD), and the average fracture permeability was 74.5 mD, a dual-porosity and single-permeability model was adopted.

[0086] The total number of grid blocks in the system is: 629×83×102×2=10650228, and the number of grid blocks in the dual-medium model is 10650228.

[0087] The gas reservoir pressure is between 106-117MPa, with an average pressure of 116MPa. The gas reservoir porosity is mainly between 3% and 8%, with an average porosity of 5.12%, of which the average matrix porosity is 4.95% and the average fracture porosity is 1.65%.

[0088] Convert it to a single medium for calculation. The calculation time of the two models before and after the conversion is compared. Figure 5 As shown in Figure 2, the water production fitting effect is as follows: Figure 6 As shown, the gas-water distribution diagrams of the single medium model and the dual medium model after 5 years of production are as follows: Figure 7 , Figure 8 As shown by Figure 5 It can be seen that the blue curve is the dual medium model, and the red curve is the single medium model. The calculation time of the single medium model in Example 2 is about one third of that of the dual medium model, indicating that the calculation of the single medium model after conversion requires less time and has higher calculation efficiency than the dual medium model. Figure 6 This is a comparison of the fitting effects of the two models, proving that the fitting results of the single-medium model and the dual-medium model are basically consistent. Figure 7 and Figure 8The gas-water distribution diagram of the single medium model and the dual medium model after 5 years of production, from which it can be seen that the gas-water distribution of the two models is basically the same. It can be seen that the method of converting the dual medium model into the single medium model in the present invention to implement numerical simulation can improve the calculation efficiency as much as possible on the basis of ensuring the simulation effect.

[0089] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A numerical simulation method for fractured oil and gas reservoirs, characterized in that: The following steps are involved: Step S1: establishing a dual medium model of an oil and gas reservoir, including a dual medium model with a fixed grid and a dual medium model with a non-fixed grid, and the types of the dual medium model include dual porosity and single permeability and dual porosity and dual permeability; Step S2: based on the type of the dual medium model, converting the dual medium model into an equivalent single medium model; Step S3: calculating the overall elastic energy of the reservoir in the equivalent single medium model to obtain the single medium model of the oil and gas reservoir; The process of converting the dual medium model into an equivalent single medium model in step S2 includes the following steps: On the basis of keeping the overall size of the model fixed, the net-to-gross ratio is determined to be equal to 1, and based on the type of the dual-medium model, the permeability of the dual-medium model is converted and calculated to be equivalent to the permeability of the single-medium model, and depending on the grid division of the dual-medium model, the grid size of the dual-medium model with a non-fixed grid is adjusted, and the grid of the dual-medium model with a non-fixed grid is re-divided into a single-medium model grid to obtain the equivalent single-medium model after conversion; Among them, for the dual-porosity and single-permeability dual-medium model with non-fixed grids, the permeability of the converted single-medium model is shown in equations (1) to (3): （1）； （2）； （3）； For the dual-porosity and dual-permeability dual-medium model with non-fixed grids, the permeability of the converted single-medium model is shown in equations (4) to (6): （4）； （5）； （6）； In formulas (1) to (6), K x The X-direction permeability of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model, in mD; K y The permeability in the Y direction of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model, in mD; K z The permeability in the Z direction of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model, in mD; k x The X-direction permeability of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model, in mD; k y The permeability in the Y direction of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model, in mD; k z The permeability in the Z direction of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model, in mD; Φ f is the porosity of the fractures in the dual medium model before conversion; Φ m is the porosity of the matrix in the dual medium model before conversion; k fx is the X-direction permeability of the fracture system in the dual medium model, in mD; k fy , is the permeability of the fracture system in the Y direction in the dual medium model, in mD; k fz , is the permeability of the fracture system in the dual medium model in the Z direction, in mD; k mx , the X-direction permeability of the matrix in the dual medium model, in mD; k my , the Y-direction permeability of the matrix in the dual medium model, in mD; k mz , the Z-direction permeability of the matrix in the dual medium model, in mD; For the dual-porosity and single-permeability dual-medium model with non-fixed grids and the dual-porosity and double-permeability dual-medium model with non-fixed grids, the vertical grid size of the converted single-medium model is shown in formula (7): （7）； In formula (7), D z’ The grid size in the Z direction of the single medium model obtained by converting the dual medium model, in m; ρ is the density of oil or gas, in kg / m 3 ; g is the acceleration due to gravity, take 9.8m / s 2 ; The grid sizes in other directions of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model with non-fixed grids are shown in equations (8) and (9): （8）； （9）； The grid sizes in other directions of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model with non-fixed grids are shown in equations (10) and (11): （10）； （11）； In formulas (8) to (11), Φ The porosity of the single medium model obtained by converting the dual medium model; D dx’ The X-direction grid size of the single medium model obtained by converting the double-porosity and single-permeability dual medium model, in m; D dy’ The Y-direction grid size of the single medium model obtained by converting the double-porosity and single-permeability dual medium model, in m; D sx’ The X-direction grid size of the single medium model obtained by converting the double-porosity and double-permeability dual medium model, in m; D sy’ The Y-direction grid size of the single medium model obtained by converting the double-porosity and double-permeability dual medium model, in m; D x is the grid size in the X direction of the dual medium model, in m; D y is the Y-direction grid size of the dual medium model, in m; D z is the grid size in the Z direction of the dual medium model, in m; For the dual-porosity and single-permeability dual-medium model with a fixed grid, the permeability of the converted single-medium model is shown in equations (12) to (14): （12）； （13）； （14）； For the dual-porosity and dual-permeability dual-medium model with a fixed grid, the permeability of the converted single-medium model is shown in Equations (15) to (17): （15）； （16）； （17）； In formulas (12) to (17), K dx The X-direction permeability of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model with fixed grids, in mD; K dy The Y-direction permeability of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model with fixed grids, in mD; K dz The Z-direction permeability of the single medium model obtained by converting the dual-porosity and single-permeability dual medium model with fixed grids, in mD; k dx The X-direction permeability of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model with fixed grids, in mD; k dy The X-direction permeability of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model with fixed grids, in mD; k dz It is the X-direction permeability of the single medium model obtained by converting the dual-porosity and dual-permeability dual medium model with a fixed grid, in mD.

2. A method for numerical simulation of fractured oil and gas reservoirs according to claim 1, characterized in that: The grid size in the Z direction of the single medium model obtained by converting the dual medium model with a non-fixed grid D z’ The value is not greater than the thickness of a single interlayer.

3. The method for numerical simulation of fractured oil and gas reservoirs according to claim 1, characterized in that: The calculation method of the elastic energy of the entire reservoir in the equivalent single medium model is: on the premise that the overall compressibility of the rock remains unchanged before and after the conversion, the reservoir conductivity coefficient is fitted and the rock conductivity is corrected and calculated.

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